This PDF file contains the front matter associated with SPIE Proceedings Volume 9655, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

In this investigation, we propose a multi-channel optical sensor to be used for precision industry to measure small gaps of a target or motion errors of a moving stage. The sensor consists of optical fiber components such as a CWDM and fiber probes for compactness, reliability and easy use. The operating principle of the sensor is based on the spectrally-resolved interferometry, where the spectral interferogram using a broadband light source is detected by a spectrometer. Each channel possesses its own spectrum as a result of spectral filtering of a CWDM and measures the distance independently. This optical sensor does not need any mechanical or electrical moving parts it can realize real-time measurements. In this presentation, we show the operating principle of the multi-channel optical gap sensor, its optical configuration and the experimental results.

We introduce a new prototype instrument for measuring the 2D spatially resolved distribution of spectral reflectance based on new spectral imaging technique. The instrument captures digital spectral images of a test sample using a pulsed LED-based monochromatic source and a scientific grade CCD array and special data acquisition algorithm is used to extract the useful image data corresponding to the target application. In earlier version of this instrument, we used a commercial CCD camera with 8-bit ADC without any cooling stages which has many drawbacks. In this work, we have modified our setup by introducing a new scientific grade CCD; deep-cooled interline transfer sensor with 16-bit ADC and electronic shutter. With this new instrument we could achieve a higher accuracy, higher spatially resolved measurements, higher dynamic range, mush better sensitivity and lower uncertainty and we could avoid many sources of errors in the old setup. With one wavelength scan, one can get the full reflectance data of the sample under test which saves a lot of time in comparison with conventional methods. This new instrument is promising with a potential of applications in the field of optical material testing.

Fiber laser has the advantages of ultra-narrow linewidth, low phase and intensity noise, which is beneficial for ultra-high-resolution strain sensing. This paper presents a novel demodulation technique for sub-nanostrain-resolution static strain measurement based on two distributed feedback fiber lasers (DFB FLs). A commercial PZT-tunable laser is used to interrogate the DFB FLs and get the periodic frequency-difference characteristics (two linear chrip signals) by swept beat-frequency principle. Two polarization controllers are used for adjusting the polarization direction of DFB FLs. And one of the two DFB FLs is used for temperature compensation and eliminating the frequency shift influence of the commercial laser. Static strain is demodulated by calculating the difference of the direct current (DC) components of the two swept beat-frequency signals. A static-strain resolution of 0.88 nε is obtained in the laboratory test.

A double closed-loop resonant micro optic gyro (RMOG) employing a hybrid digital phase modulation technique is demonstrated, showing encouraging progress. In this hybrid modulation scheme, the width of one stair of the stair-like digital serrodyne wave is optimized according to the rise time of the digital-to-analogue converter to obtain the maximum sideband suppression. Based on the optimum parameters of the hybrid modulation scheme, a typical bias stability of 0.05/s in 1 hr is demonstrated in an RMOG with a silica waveguide ring resonator having a ring length of 7.9 cm. This is the best long-term performance which has ever been reported in an RMOG to our knowledge.

Here, we demonstrated a polarimetric fiber vibration sensor based on a polarization-diversity loop structure (PDLS) by using polarization-maintaining photonic crystal fiber (PM-PCF). The PDLS is composed of a polarization beam splitter, PM-PCF, and polarization controllers, forming a Sagnac birefringence interferometer (SBI) that has periodic interference spectra. When static strain is applied to PM-PCF used as a sensor head, spectral shift is observed in the output interference spectrum of the SBI of the sensor. If a monochromatic light source such as a laser diode is introduced into the SBI, the output optical power of the SBI is determined by its wavelength-dependent transmittance. If the wavelength of the light source is properly located at a spectral region where the transmittance of the SBI linearly varies, therefore, the magnitude of strain applied to PM-PCF can be found by observing the output voltage variation of a photodetector connected to the output port of the SBI. To investigate the vibration response of the proposed sensor with respect to various types of vibration, vibration diverse in the amplitude and frequency was applied to 8-cm-long PM-PCF by using a cylindrical piezoelectric transducer or a metal cantilever. First, vibration characteristics were examined for single frequency vibration in a range of 1−3000 Hz. Then, the sensor response to naturally damped vibration was explored. It was experimentally observed that the cut-off frequency was ~1900 Hz in the frequency response, and the peak value of the sensor output signal increased with the amount of impulse for naturally damped vibration.

A fiber-optic Doppler velocimeter based on a dual-polarization fiber grating laser is demonstrated. The fiber grating laser produces two orthogonally polarized laser outputs with their frequency difference proportional to the intra-cavity birefringence. When the laser outputs are reflected from a moving targets, the laser frequencies will be shifted due to the Doppler effect. It shows that the frequency difference between the beat note of the laser outputs and the beat note of the reflected lasers is proportional to the velocity. The proposed fiber-optic Doppler velocimeter shows a high sensitivity of 0.64 MHz/m/s and is capable of measurement of wide range of velocity.

We reported an optical fiber based temperature sensor with mK-order resolution, wide temperature range and excellent long term stability. The sensor composes of a fiber Bragg grating (FBG) as the sensing element, an HCN gas cell for absolute frequency reference. A distributed feedback diode laser with current modulation is used as the light source. To overcome the frequency-sweep nonlinearity of the laser, an auxiliary Fabry-Perot interferometer with free spectrum range of 10 MHz is employed. A cross-correlation algorithm is employed to calculate the center frequency difference between the FBG and the gas cell. With the proposed configuration, a temperature resolution of 0.41 mK was demonstrated in experiment. To the best knowledge, this is the first time that an mK order temperature resolution has been achieved by optical fiber sensor.

Fabricating microstructures into the cladding of fiber Bragg grating, the FBG sensors will have wider applications in magnetic field measurement or gas sensing. In present paper, we regulate the physical feature of FBG by ablating single or cross spiral micro-trench with femtosecond laser. The influences of different processing parameters on M-FBG (microstructured FBG) have been investigated. The waveform variations and its controlling method have been discussed. It is shown that, the central wavelength shift enlarged with increasing of the laser energy, or decreasing of scanning speed. Finally, a cross spiral type M-FBG magnetic field probe and a temperature probe are also demonstrated.

We reported a few high-sensitivity optical strain sensors based on different types of in-fiber FPIs with air bubble cavities those were fabricated by use of a commercial fusion splicer. The cavity length and the shape of air bubbles were investigated to enhance its tensile strain sensitivity. A FPI based on a spherical air bubble was demonstrated by splicing together two sections of standard single-mode fibers, and the spherical air bubble was reshaped into an elliptical air bubble by mean of repeating arc discharge, so the strain sensitivity of the FPI based on an elliptical air bubble was enhanced to 6.0 pm⁄με owe to the decrease of the air cavity length. Moreover, a unique FPI based on a rectangular air bubble was demonstrated by use of an improved technique for splicing two sections of standard single mode fibers together and tapering the splicing joint. The sensitivity of the rectangular-bubble-based strain sensor was enhanced to be up to 43.0 pm/με and is the highest strain sensitivity among the in-fiber FPI-based strain sensors with air bubble cavities reported so far. The reason for this is that the rectangular air bubble has a sharply taper and a thin wall with a thickness of about 1 μm. Moreover, those strain sensors above have a very low temperature sensitivity of about 2.0 pm/oC. Thus, the temperature-induced strain measurement error is less than 0.046 με/oC.

A method of simultaneous evaluation for two branches of a multi-functional integrated optic chip (MFIOC) with a dual channel system is proposed. The difference between the two branches of the MFIOC can be tested simultaneously with a high precision. In the system, the chip is used as a 1×2 splitter and its two branches are combined by a 2×2 coupler. The characteristic peaks of the two branches are distinguished by selecting proper length of the extended fibers which connected to each polarization-maintaining (PM) pigtails. Temperature responses of the two branches of the MFIOC are experimented. Results show that the dual channel system can simultaneously measure the characteristics of the two branches of MFIOC with resolution of over -85 dB and dynamic range of 85dB.

An optimized phase generated carrier (PGC) demodulation algorithm is proposed for signal demodulation of interferometer. Similar to the traditional PGC algorithm, this optimized algorithm also need to adopt differential cross multiply (DCM), divides the two signals which processed by differential cross-multiplying could get the square of the tangent function of the output phase, output phase can be obtained by the corresponding calculation. The output of the optimization algorithm has no related items of modulated amplitude (C value) and interference signal AC amplitude (B value), therefor the demodulation error caused by C value and B value fluctuation could be suppressed.

A modified fiber-optic Sagnac interferometer with a stable π/2 phase bias is demonstrated for the demodulation of diaphragm-based acoustic sensors. The phase bias is obtained by introducing a nonreciprocal frequency shift between the counter-propagating waves. The system is passive and without complicated servo-control for phase stabilization. Interrogated by the proposed demodulation system, a 100 nm-thick graphite diaphragm-based acoustic sensor demonstrated a minimum detectable pressure level of ~ 450 μPa/Hz^1/2 at the frequency of 5 kHz and the output signal stability is less than 0.35 dB over an 8-hour period.

In this paper, a single layered passive photo sensor based on perylene/graphene composite is proposed, which is deposited in comb type silver electrodes separated as 50 μm spacing. To increase an electrical conductivity of the proposed sensor, perylene and graphene are blended. Photo sensing layer (120nm thick) and Silver electrodes (50 μm width, 350 nm thick) are deposited on poly(ethylene terephthalate) (PET) substrate through electro-hydrodynamic (EHD) system. The proposed photo sensor detects a terminal resistance inversely varied by an incident light in the range between 78 GΩ in dark and 25 GΩ at light intensity of 400lux. The device response is maximum at 465 nm ~ 535 nm wavelength range at blue light. The device exhibited bendability up to 4mm diameter for 1000 endurance cycles. The surface morphology analysis is carried out with FE-SEM and microscope.

We propose a stretchable photo sensor fabricated on uniform ridged polydimethylsiloxane PDMS substrate through electro-hydrodynamic (EHD) technique. An active layer, perylene/graphene composite thin film (67nm) is sandwiched between top and bottom ITO electrodes. The electrical conductivity of the perylene is enhanced by blending with graphene. The photo sensor changes the terminal resistance from 108MΩ to 87MΩ against light intensity of 0~400lux, respectively. To verify a stretchability, the proposed photo sensor under mechanical strain of 25% is normally worked, and it is stretchable up to 50% strain, maximally. A mechanical bendability test is carried out by folding the device for 1000 endurance cycles, while there is no change in the electrical behavior.

We proposed and experimentally demonstrated four kinds of high-sensitivity gas pressure sensors based on in-fiber devices, including a sub-micron silica diaphragm-based fiber-tip, a polymer-capped Fabry-Perot interferometer, an inflated long period fiber grating and a twin core fiber-based Mach-Zehnder interferometer, which have sensitivities of 1036, 1130, 1680, 9600 pm/MPa, respectively.

We propose and demonstrate experimentally a non-contact optical fiber displacement sensor based on bidirectional modulation of a Mach-Zehnder electro-optical modulator (MZ-EOM), which consists mainly of a tunable laser, MZEOM, optical collimator, specular object, and photodetector. The relationship between the free spectral range (FSR) and the displacement variation for the proposed scheme is given. The FSR is determined by the dip frequencies with the transfer function of the bidirectional modulation of an MZ-EOM and depends on the travel time. As a result, the FSRs according to the displacement variation are presented via both simulation and experiments. The experimental results for the several displacements using micro-stage and piezo-stack in the frequency range of 100 MHz to 300 MHz show a good agreement with the theoretical analysis. The measured sensitivities for the proposed scheme by using the FSR and the dip frequency shift show 437 kHz/mm and 1203 kHz/mm, respectively.

A novel hybrid polarization-maintaining (PM) air-core photonic bandgap fiber (PBF) ring resonator is demonstrated by using a conventional PM fiber coupler formed by splicing a section of air-core PBF into the resonator. The coupling loss between the PM air-core PBF and the conventional solid-core PM fiber is reduced down to ∼1.8 dB per junction. With the countermeasures proposed to reduce the backscattering induced noise, a bias stability of approximately 0.007 °/s was observed over a 1 hour timeframe, which is the best result reported to date, to the best of our knowledge, for RFOGs equipped with a hybrid air-core PBF ring resonator.

The vibration sensors with high sensitivity and wide frequency range have a large application demand for in the engineering project. Combining with the advantages of optical fiber sensor monitoring technique, in the paper, a kind of optical fiber Fabry-Perot (F-P) vibration sensor has been designed based on the differential-type structure of the double V-shaped cantilever a optical fiber F-P cavity. Through two different differential vibration of the cantilever beam, change the F-P cavity length, the realization of the vibration signal of large frequency range measurement the differential-type optical fiber F-P vibration sensor with large frequency range.

The topology image of an atomic force microscope is obtained by picking up a controlled output of a force-feedback loop that is proportional to the height of a sample under the assumption that no dynamics in a z-axis actuator exist. However, the dynamic effects such as hysteresis and creep in a PZT driving z-axis actuator cannot be ignored. To solve this problem, a strain-gage sensor is used as an additional sensor, which enables measurement of the absolute displacement of a z-axis PZT nano scanner. The advantage of using an additional sensor is experimentally provided and validated in topology images.

A fiber-optic epoxy cure monitoring technique for efficient wind turbine blade manufacturing and monitoring is presented. To optimize manufacturing cycle, fiber-optic sensors are embedded in composite materials of wind turbine blades. The reflection spectra of the sensors indicate the onset of gelification and the completion of epoxy curing. After manufacturing process, the same sensors are utilized for in-field condition monitoring. Because of residual stresses and strain gradients from the curing process, the embedded sensors may experience distortions in reflection spectra, resulting in measurement errors. We applied a Gaussian curve-fitting algorithm to the distorted spectra, which substantially improved the measurement accuracy.

A novel and compact fiber-probe pressure sensor was demonstrated based on micro Fabry-Perot interferometer (FPI). The device was fabricated by splicing both ends of a short section simplified hollow-core photonic crystal fiber (SHCPCF) with single mode fibers (SMFs), and then a micro channel was drilled by femtosecond laser micromachining in the SHC-PCF to significantly enhance the pressure sensitivity. The pressure sensing characteristics based on micro-FPI have been investigated by measuring the signals through the demodulation of phase since the external signal imposing on the interferometer will induce the phase change of interference signal. Then a FBG was cascaded to demodulate the signal. A micro FPI demonstrates a maximum pressure sensitivity of 32 dB/MPa, while a low temperature cross-sensitivity of 0.27 KPa/°C. Hence it may have potential for pressure applications in harsh environment.

A hybrid fiber-optic sensor system which combines fiber Bragg grating (FBG) sensors and a Michelson interferometer is suggested for condition monitoring uses of large scale wind turbine blades. The system uses single broadband light source to address both sensors, which simplifies the optical setup and enhances the cost-effectiveness of condition monitoring system. An athermal-packaged FBG is used to supply quasi-coherent light for the Michelson interferometer demodulation. For the feasibility test, different profiles of test strain, temperature and vibration have been applied to test structures, and successfully reconstructed with the proposed sensor system.

This paper describes a novel tactile sensor using a hetero-core fiber optic sensor for detecting particular tactile information of surface texture and hardness. The hetero-core fiber optic sensor consists of two single-mode fibers with different core diameters, which can detect soft bending on a sensor portion, moreover being tolerant to several environmental fluctuation such as corrosion, temperature fluctuation and electromagnetic interference. The hetero-core fiber optic tactile sensor was designed in order to detect contact force by means of the hetero-core fiber optic sensor implanted in three-point bending structure. Force property of the tactile sensor was experimentally confirmed to be highly-sensitive in reaction to force given in the range of 0.01 - 5.0 N. Therefore, it was observed that the tactile sensor could detect minute level change of surface texture in the height of 0.01 mm with the spatial accuracy within 0.10 mm. In addition, the degree of hardness and the other physical property of viscoelasticity could be detected by pushing the tactile sensor on materials. As a result, it was successfully performed that the proposed tactile sensor could detect various kinds of tactile information with high sensitivity.

A miniaturized device for colorimetry is presented that utilizes a LED array for illumination and a compact spectrometer for detection. It can be battery-powered, operated locally as a stand-alone device, or connected via wi-fi to the internet. It has potentials to be remotely operated by means of a tablet or a smartphone. In practice, it consists of a low-cost hardware configuration that is adaptable via software to the user’s most varied requests, as a spectroscopic platform appropriate for a variety of applications. The hardware and software modules can be designed with different performances, complexities and costs, with the aim of making the colorimeter a device for Internet-of-Things use. It will be suitable for a selected range of consumer applications, as well as for targeted industrial, environmental, and food applications.

We present a new approach to characterize dispersion of group birefringence in a long polarization-maintaining fiber (PMF). Two sinusoidal optical signals are respectively launched into fast and slow axes of a PMF under test. Wavelength dependent group-delay difference between two sinusoidal optical signals induced by group birefringence in the PMF is measured using a Kerr phase-interrogator, and dispersion of group birefringence is characterized from the group-delay difference. Measurements of wavelength dependent group birefringence and group birefringence dispersion for a 459.4-m Panda PMF are experimentally demonstrated.

This work presents a study on sensing capabilities of stacks of nano-films deposited on a single-mode optical fiber end-faces. The stacks consist of periodically interchanging thin-film layers of materials characterized by different refractive indices (RI). The number of layers is relatively small to encourage light-analyte interactions. Two different deposition techniques are considered, i.e., radio frequency plasma enhanced chemical vapor deposition (RF PECVD) and physical vapor deposition by reactive magnetron sputtering (RMS). The former technique allows to deposit stacks consisting of silicon nitride nano-films, and the latter is well suited for aluminum and titanium oxides alternating layers. The structures are tested for external RI and temperature measurements.

Top down imaging is used to extract the contact angle, θ, of drops on surfaces greatly relaxing the requirements and limits demanded by side imaging. The method is compared between two standard lateral measurement techniques (the tangent method and the height/diameter method) for the hydrophilic contact angle of a droplet of water (20 drops of 2 μl each) on borosilicate slide: θ= (52 ± 7)° and (52 ± 6)°, respectively, and (53 ± 8)°, for the proposed method, agreeing within experimental error. This technique can be applied on multiple contact angle measurements, depression, between electronic components and on concave surfaces. The top down method has the potential to revolutionize diagnostics by making contact angle measurements ubiquitous and accessible to low cost imaging.

The feasibility of optically detecting air and water bubbles flowing through the oil is presented. By scanning wavelengths it is possible to add functionalities by implementing a spectroscopy based chemical detection that can directly lead to chemical detection and imaging and/or chemical species tomography of flowing fluids. In this article, a halogen lamp (175 - 1000 W and centered at 1.2 mm) and an IR-array camera (8-12 μm, 31 x 32 pixels and 10 fps) is used to observe the three-phase flow involving oil, air and water.

We present multipoint vibration sensing using fiber Bragg gratings and optical frequency domain refrectometry (OFDR). In OFDR based method, the maximum number of arrayed sensor can be few thousands and the measurement time is determined by wavelength scanning rate of a light source. In our sensor system, a laser diode is used as a wavelength scanning light source. Lasing wavelength of a laser diode can be modulated by changing its injection current. The injection current can be precisely modulated at high frequency up to 100 kHz using a laser-diode controller and wavelength scanning can be then easily achieved with a laser diode.

The performance of an optical time-domain sensing technique, employing the slope of Brillouin dynamic gratings in polarization-maintaining fibers, can be significantly enhanced using Golay complementary sequences. The strain sensitivity of the reflectivity of a coded probe primarily depends on the detuning between the orthogonally polarized pumps, which generated the grating. The system broadband sensitivity for a 256 bit unipolar probe code was demonstrated to be 50nε/√Hz at a sampling rate of 2MHz, which to the best of our knowledge is a record sensitivity for Brillouin dynamic sensing. We report the measurement of 10kHz strain vibrations (which is the bandwidth limit of the vibration source) with a spatial resolution of 2cm. Owing to the system high sensitivity and spatial resolution, it has the potential to be used in distributed ultrasonic detection applications.

This paper presents a novel fiber flowmeter based on distributed feedback fiber laser (DFB-FL). The DFB-FL is encapsulated in a PU tube which is put in the center of the flow pipe. When the flow speed changes, the flow induced pressure turbulence on the surface of the PU tube will change correspondingly. This pressure fluctuation is demodulated using phase-generated-carrier (PGC) method. The test result shows that the sensitivity of the fiber laser flowmeter is about 8×10^-3 pm/(m³/h). A resolution of 1.25×10^-4 m³/h is achieved.

Intensity modulation technique is an attractive interrogation method for fiber-optic ultrasonic sensors using fiber Bragg gratings (FBGs), in which FBG modulates the intensity of reflected (or transmitted) narrowband light with a wavelength tuned to the slope of the FBG reflection (or transmission) spectrum curve if the vibration or acoustic wave is applied to the FBG and the intensity detection enables the direct observation of their waveforms. In this paper, principles of the intensity-based FBG ultrasonic sensors and their applications to vibration and underwater acoustic wave sensors are presented.

A new, simple signal processing, low-cost technique for the fabrication of a portable oxygen sensor based on time-resolved fluorescence is described. The sensing film uses the oxygen sensing dye platinum meso-tetra (pentfluorophenyl) porphyrin (PtTFPP) embedded in a polymer matrix. The experimental results reveal that the PtTFPP-doped oxygen sensor has a sensitivity of 2.2 in the 0-100% range. A preparation procedure for coating the photodiodes with the oxygen sensor film that produces repetitive and reliable sensing devices is proposed. The developed time-resolved optical oxygen sensor is portable, low-cost, has simple signal processing, and lacks optical filter elements. It is a cost-effective alternative to traditional electrochemical-based oxygen sensors and provides a platform for other optical based sensors.

The development of an evanescent wave optical fibre (EWOF) sensor modified with an organic-inorganic hybrid nanoporous thin film for alcohol vapor detection was demonstrated. The optical fibre with a core diameter of 200 μm was bent into U-shape probe optic fibre to enhance the penetation depth of light transferred into the evanescent filed. The bended region of the fibre was modified with a multilayered thin film of poly(allyamine hydrochloride) and silica nanoparticels, (PAH/SiO2)n, by a layer-by-layer (LbL) film deposition technique, followed by infusion of tetrakis(4- sulfophenyl)porphine, TPPS. The mesoporous film structure showed high sensitivity and selectivity to methanol by the aid of the TPPS infused inside the film. The optical sensor response was reversible and reproducible over many times of exposures to analytes, which was caused by the change in refractive index (RI) of the film.

Phase separation process of poly (N-isopropylacrylamide) (PNIPAM) aqueous solution was investigated by tapered optical fiber technique in this work. The optical transmission spectra revealed the transition of molecular conformation and aggregation of molecular chains in the course of phase separation and identified the lower critical solution temperatures (LCST) in a simple and clear way. It was found that upon heating PNIPAM chains changed from expanded coils to collapsed globules and then aggregated. It offers a new characterization technique for studying phase separation of polymer solutions or blends, and could provide abundant information of the interaction between two different macromolecules, revealing the internal mechanism of the interaction.

Using a smartphone-based portable spectrofluorimeter, measurement of metal ion concentration in water is reported. A UV LED (λ_ex ~ 370 nm), which is powered by the internal source of the smartphone was implemented to function as the excitation source. The emission peak of the UV LED overlaps well with the absorption peak of the Zn²⁺-responsive molecular probe 6-(1,4,8,11-cyclam-1-yl)ethyl-1,2,3-triazol-4-yl)2-ethyl-naphthalimide fluoro-ionophore (λ_abs ~ 358 nm). The fluorescence emission of this dye at λ_em ~ 458 nm is enhanced upon coordination of Zn²⁺. A customized Android application digitally processes the image from a nano-imprinted polymer diffraction grating and analyses the spectral changes. Zn²⁺ concentration in water samples were measured with a detection limit of δ ~ 5 μM.

We investigated various types of optical fiber sensor based on novel structure of photonic crystal fibers (PCFs) including Ge-doped ring defect PCF and Suspended ring core PCF. Furthermore, a new type of fiber named C-type fiber is utilized as a fiberized sensor unit in/outlet. This configuration enabled to package the entire sensor unit in fiber form as well as could overcome prior limitations in PCF-based optical sensors such as too small holes for efficient measurand entry and sophisticated fabrication processes. The experiment and simulation results proved that the designed sensor can improve both sensitivity and response time compare to conventional PCF based sensors.

A novel hydrogen sensor based on Pd/Ni co-sputtered coating on micro fiber Bragg grating (MFBG) is proposed and experimentally demonstrated. The microfiber is stretched uniformly and the Bragg grating is directly inscribed on the microfiber without hydrogen loading using 193 nm ArF excimer laser and a phase mask. Palladium and nickel coatings are co-sputtered on the micro fiber Bragg grating for hydrogen sensing. The MFBG hydrogen sensors are characterized concerning their response to the hydrogen, ambient temperature and ambient refractive index, respectively. The performance of the proposed MFBG hydrogen sensor is obviously enhanced, especially when compared to standard FBG hydrogen sensors.

An interferometric microfluidic sensor is proposed by perpendicularly coupling light into/out from a glass capillary with a pair of collimators. Light trapped in the wall of a capillary with inner and outer radius of 245μm and 413.5μm travels along different paths and interferes at the output, resulting in a multiple modes interferometer. By successively injecting salt solutions with different concentrations into the capillary air hole, red shift happens in the interferometric spectra with a sensitivity of 42.75nm/RIU. Such a sensing head offers potentials in identifying solutions in real time, especially for those not transparent for light.

In this paper, the multi-point hydrogen detection system using the hetero-core optical fiber hydrogen tip sensor based on surface plasmon resonance (SPR) and Pseudorandom Noise code correlation reflectometry (PNCR) has been proposed. This method makes use of the correlation between a launched pseudorandom noise code signal and its reflection, can obtain a high signal to noise ration. We demonstrated the 4 sensors characteristics to 4% hydrogen. It was observed from experimental results that all sensors induced a response time of 15 s for 4% hydrogen for the 25-nm Au / 60-nm Ta₂O₅ / 5-nm Pd multi-layers film. In addition, all sensors were detected the hydrogen concentration with sufficient sensitivities.

In this study, we measured the optical characteristics of pesticides by terahertz time-domain spectroscopy. Pesticide samples were prepared as pellets that were mixed with polyethylene powder and placed in the center of the path of a terahertz electromagnetic (EM) wave in the spectroscopy system. The absorbance of each sample showed obvious differences in absorption peaks. From this result, we showed that these pesticide products had resonance modes in the terahertz range, and this method can be used to make a sensor that is able to measure low concentrations of pesticides in farm produce.

This paper reports a new silica fiber-tip Fabry-Perot interferometer with thin film and large surface area characteristic for high pressure and vacuum degree detection simultaneously, which is fabricated by etching a flat fiber tip into concave surface firstly, with subsequent arc jointing the concave fiber into a inline Fabry-Perot cavity, then drawing one surface of the F-P cavity into several micrometers scale by arc discharge and finally etching the surface into sub-micrometer scale integrally. As the silica fiber-tip Fabry-Perot interferometer film thickness could be tailored very thinly by HF acid solution, plus the surface area of thin film could be expanded during the chemical etching process, the variation of the bubble cavity length is very sensitive to the inner/outer pressure difference of the fiber-tip Fabry-Perot interferometer. Experimental result shows an high sensitivity of 780nm/MPa is feasible. Such configuration has the advantages of lowcost, ease of fabrication and compact size, which make it a promising candidate for pressure and vacuum measurement.

A layer-by-layer (LbL) approach was used for the deposition of coatings with a nano-meter thickness onto a multimode optical fibre that was bent into a U-shape with the aim of demonstrating a fibre-optic ammonia sensor. The film was composed of alternate layers of tetrakis(4-sulfophenyl)porphine, TSPP, and poly(diallyldimethylammonium chloride), PDDA, deposited using the LbL electrostatic self-assembly process. Exposure of the assembled film to ammonia induced a change in its absorption spectrum, which could be observed in the transmission spectrum of the coated U-shaped optical fibre. The sensor showed a linear sensitivity (77.7 mV/ppm) to ammonia in the concentration range 1–100 ppm.

Fabrication process of thin boron-doped nanocrystalline diamond (B-NCD) microelectrode on fused silica single mode optical fiber has been investigated. The B-NCD films were deposited on the fibers using Microwave Plasma Assisted Chemical Vapor Deposition (MW PA CVD) at glass substrate temperature of 475 ºC. We have obtained homogenous, continuous and polycrystalline surface morphology with the mean grain size in the range of 100-250 nm and high sp³ content in B-NCD films. The films deposited on glass reference samples exhibit high refractive index (n≈2.05 at λ=550 nm) and low extinction coefficient. Furthermore, cyclic voltammograms (CV) were recorded to determine the electrochemical window and reaction reversibility at the B-NCD fibre-based electrode. Cyclic voltammetry (CV) measurements in aqueous media consisting of 5mM K3[Fe(CN)6] in 0.1M Na2SO4 demonstrated a width of the electrochemical window up to 2.5 V and relatively fast kinetics expressed by a redox peak splitting below 500 mV. Moreover, thanks to high-n B-NCD overlay, the coated fibers can be also used for enhancing sensitivity of long-period gratings (LPGs) induced in the fibers. The LPG is capable for measuring variations in refractive index of surrounding liquid by tracing shift in resonance appearing in transmitted spectrum. Possible combined CV and LPG-based measurements are discussed in this work.

Graphene is a promising material for vapor sensor applications because of its potential to be functionalized for specific chemical gases. In this work, we present a graphene gas sensor that uses single-stranded DNA (ssDNA) molecules as its sensing agent. We investigate the characteristics of graphene field effect transistors (FETs) coated with different ssDNAs. The sensitivity and recovery rate for a specific gas are modified according to the differences in the DNA molecules’ Guanine (G) and Cytosine (C) content. ssDNA-functionalized devices show a higher recovery rate compared to bare graphene devices. Pattern analysis of a 2-by-2 sensor array composed of graphene devices functionalized with different-sequence ssDNA enables identification of NH₃, NO₂, CO, SO₂ using Principle Component Analysis (PCA).

Arrays of partially selective chemical sensors have been the focus of extensive research over the past decades because of their potential for widespread application in ambient air monitoring, health and safety, and biomedical diagnostics. Especially, vapor sensor arrays based on functionalized nanomaterials have shown great promise with their high sensitivity by dimensionality and outstanding electronic properties. Here, we introduce experiments where individual vapors and mixtures of them are examined by different chemical sensor arrays. The collected data from those sensor arrays are further analyzed by a principal component analysis (PCA) and targeted vapors are recognized based on prepared database.

We present and demonstrate a novel single fiber optical tweezers which can trap and launch (clean) a target polystyrene (PS) microsphere (diameter~10μm) with independent control by using two wavelengths beams: 980nm and 1480nm. We employ 980nm laser beam to trap the target PS microsphere by molding the fiber tip into a special tapered-shape; and we employ 1480nm laser beam to launch the trapped PS microsphere with a certain velocity by using the thermophoresis force generated from the thermal effect due to the high absorption of the 1480nm laser beams in water. When the launching force is smaller than the trapping force, the PS microsphere will be trapped near the fiber tip, and the launching force will blow away other PS microspheres in the workspace realizing the cleaning function; When the launching force is larger than the trapping force, the trapped PS microsphere will be launched away from the fiber tip with a certain velocity and towards a certain direction, realizing the launching function. This PS microsphere launching and cleaning functions expanded new features of single fiber optical tweezers, providing for the possibility of more practical applications in the micro manipulation research fields.

We propose and demonstrate a mode division multiplexing single fiber optical tweezers. By using this tweezers, one can trap a yeast cell and then launch it away from the fiber tip with a certain speed to a certain position without moving the optical fiber in a single fiber optical trapping apparatus. We excite both LP₀₁ and LP₁₁ mode beams in a same normal communication fiber core to generate the optical launching force and trapping force by molding the fiber tip into a special tapered-tip shape. A yeast cell of 6μm diameter is trapped and then being launched away. We construct the optical trapping and launching potential wells by controlling the power of two mode beams. This micro particle directional launching function expands new features of fiber optical tweezers based on the normal communication fiber, providing for the possibility of more practical applications in the biomedical research fields.

A feasibility study on using polymer fiber Bragg sensors (PFBG) for providing force feedback to minimally invasive surgical devices is carried out. For this purpose a 3 mm long PFBG is fabricated and characterized for strain and temperature sensitivities. The PFBG sensor is then integrated onto a commercial laparoscopic clip applicator which is used as a proof of concept device. The force characterization of the clip applicator is carried out, with a replica setup which simulates the clip forming process of the device. An original clip is then formed without and with synthetic tissue samples of different hardness. The replica device force profile and original clip forming force profile follows the same pattern and thus the calibration data can be used to calculate the original force exerting on the tissues which can help in optimizing the clip formation process or can be used for providing force feedback capability to the device.

A high sensitivity biosensor based on graphene coated silica fiber taper interferometer is presented. Thank to the combination of graphene coating and the optical fiber taper interferometer structure, the biosensor demonstrates improved DNA concentration sensitivity of 0.4 nm/log M and good linearity, yielding the lower detection limit of 10 pM. This high sensitivity and biocompatibility enable the biosensor in precision in-situ DNA detection, even in ultra-diluted DNA solution. Based on our work, the graphene coating could convert the concentration information of target molecular to the RI variation, and further to light signals by the taper.

The terahertz is an electromagnetic wave with non-ionization and low average power; therefore it is thought not to be hazardous to biological tissues. The terahertz waves can excite the vibration mode and rotation mode of macromolecules, and both amplitude and phase information of samples which are detected can be gotten and contrasted. Compared with visible and infrared light, it also has the advantage of low scattering and that the surface character and depth pattern of samples can be acquired at the same time, which makes it possible to measure tissues in vivo without any damage in the field of biomedicine. In this article, THz transmission and reflection spectra of liquid and solid samples are tested and analyzed based on THz-TDS (Terahertz time Domain Spectra system), including glucose solution and different kinds of biological tissue slices, etc. The optical parameter relations of different samples are acquired. Spectrum results are contrasted and discussed for two kinds THz systems. The results show that THz spectra of different samples are differentiable, and they can be described quantitatively.

We report development of a new kind of micro-optical waveguide based on liquid core in a V-groove glass and air cladding and a similar finite element method was constructed to investigate the guiding properties such as mode distribution and modal birefringence. Through the detailed modeling, we investigate the role of each parameter such as, refractive index of core and diameter of core of V-groove structure. This work demonstrates numerically and experimentally high birefringence in this optical waveguide and different aspects of the fiber properties related to the fundamental mode and fiber birefringence are revealed. As a result, wave-guide with large birefringence is identified for opening angle of 40 degree and refractive index of 1.472.

In this report, we present a new type of non-contact detection method for glucose molecule using nano antenna array based bio sensing chip that operates at terahertz frequency range (0.5 – 2.5 THz). Localized and hugely enhanced transmitted terahertz field by nano antenna array in the sensing chip induced enhancement of absorption coefficient of glucose molecule that enables us to detect even very small volume of molecules. Nano antenna based terahertz sensing chip can be expected to offer accurate identification of glucose level as a non-invasive and painless sensing tool with high sensitivity.

Accurate in situ monitoring of bacterial transport is important for increased understanding and improvement of bioremediation processes where microorganisms convert toxic compounds to more benign compounds. Bioremediation methods have become the preferred mechanism for the rehabilitation of hard to reach contaminated environments. In this study, we have used fluorescence spectroscopy to monitor the movement of fluorescently labelled bacteria (Rhodococcus erythropolis and Pseudomonas putida) within a bench-top column filled with a porous medium. In situ fluorescence measurements made using a fibre optic based instrument (‘optrode’) were compared to ex situ measurements made using a plate reader. In situ monitoring using this fibre optic based instrument is a promising alternative to ex situ measurements as the initial flow of bacteria is reliably observed. However, a greater understanding of the effect of the porous medium on fluorescence measurements is required to develop an accurate calibration for bacterial concentration based in situ measurements.

An evanescent-wave optical fibre sensor modified with tetrakis(4-sulfophenyl)porphine (TSPP) and poly(allylamine hydrochloride) (PAH) bilayers using an layer-by-layer (LbL) approach was tested to measure the gas emitted from human skin. Optical intensity changes at different wavelengths in the transmission spectrum of the porphyrin-based film were induced by the human skin gas and measured as sensor response. Influence of relative humidity, which can be a major interference to sensor response, was significantly different when compared to the influence of skin emanations. Responses of the current optical sensor system could be considered as composite sensor array, where different optical wavelengths act as channels that have selective response to specific volatile compounds. Data obtained from the sensor system was analyzed through principal component analysis (PCA). This approach enabled to distinguish skin odors of different people and their altered physiological conditions after alcohol consumption.

Fluorescence microscopy is an indispensable imaging tool in modern biomedical research. Holography is well-known to have many interesting and useful imaging capabilities. But the requirement of coherent illumination has all but precluded holography as a means for fluorescence imaging, which is inherently incoherent. Recent developments in digital holography, however, including self-interference incoherent digital holography (SIDH), provide highly effective and versatile capabilities for 3D holographic imaging with incoherent light, that can remove the barrier between fluorescence and holography. Recent progress in holographic fluorescence microscopy is presented.

The magnitude of the force generated during orthodontic mechanics anchored in mini-implant in a maxilla model was analyzed. Data was collected during the insertion of the mini-implant and at the moment of applying forces to the structure of the maxilla and dentition. To obtain quantitative results, the Fibre Bragg Gratings (FBG) were inserted in an elastomeric material reproducing a maxilla model. It was observed levels of forces of approximately 3,78N next to the root of first premolar by the insertion of the mini-implant and different levels of the force to different orthodontic mechanics applied on the dental system.

We propose a one-shot dual-dimension microscope which captures 2D/3D information simultaneously based on light field microscopy. By locating a beam splitter into a relayed light field microscopy system, the simultaneous capture of both 2D and 3D information is possible. Two digital cameras are synchronized and simultaneously capture 2D and 3D information, respectively. We also discuss about the way to present 2D and 3D information together efficiently, and the way to develop the 3D depth image quality with the high resolution 2D image information.

Eye is an optical system composed briefly of cornea, lens, and retina. Ophthalmologists can diagnose status of patient’s eye from information provided by optical sensors or images as well as from history taking or physical examinations. Recently, we developed a prototype of optical coherence tomography (OCT) image guided femtosecond laser cataract surgery system. The system combined a swept-source OCT and a femtosecond (fs) laser and afford the 2D and 3D structure information to increase the efficiency and safety of the cataract procedure. The OCT imaging range was extended to achieve the 3D image from the cornea to lens posterior. A prototype of OCT image guided fs laser cataract surgery system. The surgeons can plan the laser illumination range for the nuclear division and segmentation, and monitor the whole cataract surgery procedure using the real time OCT. The surgery system was demonstrated with an extracted pig eye and in vivo rabbit eye to verify the system performance and stability.

Surface Plasmon Resonance has been one of the corner stone of label free biosensing for decades with a wide range of architectures, including fiber based SPR. Here we present the work we have achieved, using SPR scattering as an alternative approach for fiber based sensors, using rough metallic coating enabling to turn an intrinsically non radiative process into a radiative one. Although the use of rough metallic coating induces some inherent limitations, the architectural advantages and higher efficiency in some application such as Metal Enhanced Fluorescence as well as ways forward to overcome these limitation will be presented.

Using the nanostructures supported by surface plasmon polaritons (SPPs) has been a great issue in optical sensing applications. Especially, a focused spot of SPPs, which is often called a near-field hot spot, has been numerously researched due to its high compactness beyond the diffraction limit and strong field enhancement applicable to nanoparticle sensing and tweezing. In this presentation, a novel design method for arbitrary tuning of the location of near-field hot spot controlled by the polarization of incident light is proposed. The array of nanoslit with spatially different tilted angle distribution is used for polarization-sensitive phase profile of excited SPPs.

Damping noise reduction by optical radiation pressure has been proved to be a feasible scheme. We established quantum opto-mechanical coupling model by a twin core fiber in order to damp noise reduction by the optimal design of mechanical structure. By using a vibration modes related modulation frequency of the two laser beams irradiation from each core of the twin-core fiber at different positions along the micro-cantilever, we have investigated the two laser beams dependence of photothermal mode cooling.

A novel twin-core fiber connector has been made by using two pieces of gradient refractive index (GRIN) lenses. The coupling loss of this connector is analyzed and several impact factors, such as lens length, focusing length of the specific matching conditions are discussed. Those factors that cause more transverse displacement have much greater coupling loss sensitivity, and the system tolerance is also considered to evaluate the practicability and the fabrication technologies.

A novel optical fiber coupler was proposed and fabricated for coupling each core of a twin-core fiber (TCF) with a single-core fiber (SCF) core simultaneously and accessing independently both cores of the TCF. The coupler is mainly composed of two sides polished SCF and a side polished TCF. Each optical field launched from the TCF could be coupled into the side polished SCF. The coupler has a simple structure and less cross-talk between the two cores.

We propose a novel optical tweezers for particle trapping with a double-wedged shape tip in the end of a twin-core fiber by polish technique. The polishing setup and procedure are described in detail and the grinding angle θ has a relationship with the angle β between the convergent beams for trapping particles. By calculating, the optimal angle parameter θ and β depend on the surrounding background refractive index.

We investigated experimentally liquid crystal (LC) filled photonic crystal fiber’s temperature responses at different temperature ranging from 30 to 80°C. Experimental evidences presented that the LC’s clearing point temperature was 58°C, which is consistent with the theoretical given value. The bandgap transmission was found to have opposite temperature responses lower and higher than the LC’s clearing point temperature owing to its phase transition property. A high bandgap tuning sensitivity of 105 nm/°C was achieved around LC’s clearing point temperature.

We experimentally demonstrate a novel all-fiber Sagnac loop hybrid interferometer (SLHI) based on a highlybirefringent photonic crystal fiber with two asymmetric cores. Two cores exhibit unique birefringence properties and the light launched into them propagates with negligible coupling. Fast Fourier transform analysis of the transmission spectrum shows six frequency peaks in the spatial domain due to multiple interferences comprising the intra-core and inter-core mode interferences characterized by the four-beam interference model. The device response is investigated under the application of torsion, strain and temperature by measuring the phase-shift responses of three fiber interferences in the SLHI. The device application in simultaneous multi-parameter measurement is also discussed.

We propose a tunable optical switching based on thermo-optic nonlinear effect in an electro-microtube ring resonator (EMRR) made by a capillary embedded with a heating wire. The significant modes shift in the EMRR for nonlinear switching are attributed to a huge joule heat generated by the heating wire, leading to the resonant wavelength shifts over 0.9nm when using 250mA current. In our viewpoints, with such a significant performance, the EMRR may be practically applied to switching, optical filter, sensing and optical network process.

A self-powered smartphone-based field-portable “dual” spectrometer has been developed for both absorption and fluorescence measurements. The smartphone’s existing flash LED has sufficient optical irradiance to undertake absorption measurements within a 3D-printed case containing a low cost nano-imprinted polymer diffraction grating. A UV (λ_ex ~ 370 nm) and VIS (λ_ex ~ 450 nm) LED are wired into the circuit of the flash LED to provide an excitation source for fluorescence measurements. Using a customized app on the smartphone, measurements of absorption and fluorescence spectra are demonstrated using pH-sensitive and Zn²⁺-responsive probes. Detection over a 300 nm span with 0.42 nm/pixel spectral resolution is demonstrated. Despite the low cost and small size of the portable spectrometer, the results compare well with bench top instruments.

We present a novel method for converting channel plasmon polariton (CPP) waves in a waveguide into free-space optical waves. A grating decoupler in the CPP waveguide is designed by using grating equation. The CPP interacts with the grating decoupler and is re-radiated into the air. The effective index in the grating equation can be obtained by examining the dispersion characteristics of CPPs. In addition, a design strategy for efficient out-coupling is discussed. This works are believed to offer appropriate functionality for lab-on-a-chip sensing applications.

We propose a scheme to extend dynamic range of a Fabry-Perot (FP) resonator-based refractive index sensor while maintaining the sensitivity. We considered an intensiometric refractive index sensor using an FP resonator in a plasmonic waveguide which is formed by mode selective mirrors. Then, we demonstrated that the intensity degeneracy is a cause of small dynamic range. Lastly, we found that mode dependent transmission characteristics of the FP resonator and 180-degree phase shift across FP resonances can be exploited for extension of dynamic range.

This paper focus on the strain characteristic of the fiber-optic flexural disk accelerometer based on the multilayer sensing fiber coils. The strain state is analyzed in theory, and by using the simulation software, we built the simulation model and obtain the strain distribution of the multilayer sensing fiber coils in different bonding position of the flexural disk. The strain theoretical model agrees well with the strain distribution obtained by the simulation model. According to the results, a flexural disk accelerometer is produced. Experiment results show that the phase sensitivity is 6814rad/g, which is equivalent to the acceleration sensitivity of 15ng/Hz^1/2.

We have developed a novel single-shot optical tomography and profilometry that is able to measure the tomograms and surface profiles of a sample in realtime with long measurable range. The system comprises of an optical frequency comb interferometry and a diffraction grating. The grating plays as a spatial phase modulator (SPM), so that the realtime interference images can be achieved by a CCD camera. Owing to the diffraction lights by the SPM, the axial zooming operation of the proposed system can be realized. The zooming range of the proposed system depends on how many diffraction orders are generated by the SPM. Measurements of a reference Gauge-block step-height sample at different diffraction orders are performed to evaluate the proposed system.

A modified algorithm for tracking laser Doppler vibrometer (TLDV) is introduced to measure the vibration of rotating objects. The proposed algorithm unlike the old algorithm for TLDV can be used when the speed of the object to be tracked varies continuously or alternating in a small range. The proposed algorithm is to use encoder only as a position sensor. The position from the encoder is used to calculate the driving signals to the galvanometers. To verify the proposed method, experimental modal analysis of the circular plate in stationary and rotating cases are made.

Fiber optic smart structures have been developed over several decades by the recent fiber optic sensor technology. Optical intensity-based sensors, which use LD or LEDs, can be suitable for the monitor system to be simple and cost effective. In this paper, a novel fiber optic smart structure with human-like perception has been demonstrated by using intensity-based hetero-core optical fiber sensors system with the CMOS detector. The optical intensity from the hetero-core optical fiber bend sensor is obtained as luminance spots indicated by the optical power distributions. A number of optical intensity spots are simultaneously readout by taking a picture of luminance pattern. To recognize the state of fiber optic smart structure with the hetero-core optical fibers, the template matching process is employed with Sum of Absolute Differences (SAD). A fiber optic smart glove having five optic fiber nerves have been employed to monitor hand postures. Three kinds of hand postures have been recognized by means of the template matching process. A body posture monitoring has also been developed by placing the wearable hetero-core optical fiber bend sensors on the body segments. In order for the CMOS system to be a human brain-like, the luminescent spots in the obtained picture were arranged to make the pattern corresponding to the position of body segments. As a result, it was successfully demonstrated that the proposed fiber optic smart structure could recognize eight kinds of body postures. The developed system will give a capability of human brain-like processing to the existing fiber optic smart structures.

We suggest a linear polarization sensor, which has been developed for the Shack-Hartmann wave-front sensor. Our system is classified into three parts. First, polarization filter using wire-grid-plate structure selects only one polarized wave between two linear orthogonal polarization states. Second, graded index layer refracts the wave passed and gives the wave-front distortion. Third, a lens array, one part of the Shack-Hartmann wave-front sensor, focuses the wave on focal plane. We can detect linear polarization state through measuring displacement of the spot centroid. This study on polarization sensor can offer help on vector field sensing, which is crucial to obtain a complete description of light in nanoscale device.

We present linear and non linear optical applications of solid and hollow silica microresonators. Hollow microresonators or microbubble resonators combine the unique properties of whispering gallery mode resonators (WGMR) with the intrinsic capability of integrated microfluidics. Microbubbles were filled with water and aqueous solutions of ethanol in order to test the refractive index sensing capabilities of such resonators. We also tested the potential of microbubbles as nonlinear enhancement platform of both the filling material (Rhodamine 6G and Fluorescein) and the glass bubble.

We propose and design a high-birefringence two-core photonic crystal fiber for simultaneous measurement of pressure and temperature. One core is centered, while the other is off-center. Both cores are made non-circular by properly modifying the sizes of some air-holes surrounding them. This introduces geometric modal birefringence to the fiber. When a broadband light launches into the centered core and transmits for a few centimeters, the output spectrum is sinusoid-like due to the intermodal coupling of the supermodes guided by the two cores. For x-polarized input light, we find it has a pressure sensitivity of 21.7 pm/MPa and a temperature sensitivity of 11.6 pm/C; for y-polarized input light, we find it has a pressure sensitivity of 18.0 pm/MPa and a temperature sensitivity of 10.7 pm/C. Hence, simultaneous measurement of pressure and temperature can be achieved by using a matrix method.

To perform distributed strain and temperature measurement, we have recently developed simplified Brillouin optical correlation-domain reflectometry (S-BOCDR), in which the light Fresnel-reflected at the ends of the fiber under test (FUT) is used as a reference light. Here, we implement S-BOCDR using a plastic optical fiber (POF) as an FUT, which provides the following advantages over S-BOCDR using a standard silica single-mode fiber (SMF): (1) the beat signal of the Stokes light and the Fresnel-reflected light that is obtained at the interface between the POF and the SMF (the pigtail of an optical circulator) can be stabilized, and (2) the effect of the 0th correlation peak can be easily and effectively suppressed by exploiting a so-called Brillouin frequency shift-hopping phenomenon. We then experimentally demonstrate a distributed measurement and detect a 0.46-m-long heated POF section.

To obtain the strain sensing for the high sensitivity PCF (Photonic Crystal Fibers), the high refractive index mixture is infiltrated into the air hole of the PCF. In this paper, we propose to adjust the infiltrated length of the air hole in order to make the loss maximum. The goal is to realize the PCF sensor with high sensitive strain. The experimental results show that the strain sensitivity is about 4.36 pm / μ ε when the infiltrated length is 30mm and the refractive index of the liquid is 1.5. The experimental results are consistent with the simulation ones. This kind of device can apply to the ultrasensitive strain sensing.

In this study, we successfully generated the large bandwidth of supercontinuum spectra through hollow fibers filled with DNA. Also, by observing that spectra bandwidth was the widest in the order of the hollow core fiber filled with DNA modified by copper ion, the hollow core fiber with only DNA, and the bulk hollow core fiber, we demonstrated that DNA material modified with copper ions can further enhance the spectral bandwidth of supercontinuum. As a result, we anticipate that the SCG as a broadband light source can be used in analytical methods to demonstrate a wide range of biological and environmental questions.

Recently the “lab-on-fiber” technology has been rapidly developed and demonstrated in several interdisciplinary application fields. It expressed as multifunctional photonic devices and components arising from the integration onto optical fibers of different materials at micro and nano-scale with suitable physical, chemical and biological properties. In this paper, a briefly introduction about the concept of “lab-in/on-fiber” has been given. Then, we concentrate to discuss in-fiber waveguides integration technology which provides an infrastructure for “lab-in/on-fiber”. Finally, we give several examples to show each unique experimental lab-in/on-fiber in different application fields and to demonstrate how it is possible to exploit the micro laboratories platforms.

A novel fiber-optic magnetic field sensor is proposed by embedding a heterodyning fiber laser into an epoxy resin bonded magnetostrictive composite material with Terfenol-D particles doped. The magnetic field induced strain in the magnetostrictive composite material is converted to transversal stress by a structure which is applied to the fiber laser to produce beat note frequency changes for measurement. The response of the proposed sensor is measured, which shows a quite good directivity with a sensitivity of 10.5 Hz/μT to magnetic field and a large measurable range up to about 0.3 T.

Ytterbium-doped silica optical fibers were fabricated using a modified chemical vapor deposition process with chelate precursor. The typical core diameters of the preforms made by the chelate doping method are 5.79mm, and the useful length of the preforms is about 900mm, twice the length of the preforms by the solution doping method. The Ytterbium-doped fiber with octagonal inner cladding shape drawn in a double clad configuration has a background loss of 15dB/km at 1200nm. The Ytterbium ion concentration in the fiber core is up to 0.709wt% and a slope efficiency of 81.9% can be generated when pumped with 915nm laser.

In this paper, we analyzed the mode field distributions of the seven-core fiber consisting of a central core and six symmetrically surrounding single mode cores in a common cladding by the finite element method (FEM). The excitation characteristics in the splicing process between the seven-core fibers were numerically investigated. The efficiency of the fundamental mode excited by the incident light was studied by calculating the excitation coefficients in two cases, in which a lateral offset and a rotation offset are introduced between the two fiber ends, respectively. The results show that the excitation coefficient of the fundamental mode decreases from 1.0 to 0.1816 when the lateral offset increases from 0 to 9 μm. Similarly, when the rotation offset increases gradually from 0º to 10º, the excitation coefficient of the fundamental mode in the six surrounding cores gradually and synchronously decreases from 1.0 to 0.1779, while that of the central core is always constant.

We propose and demonstrate a highly sensitive micro-fluidic temperature sensor based on a two-core photonic crystal fiber (TCPCF). TCPCF has two cores of small asymmetry in sizes that serves as two arms in the inline Mach-Zehnder interferometer (MZI). Using manual gluing and subsequent infiltration technique, the cladding air holes near one core are selectively filled with polymer of high thermo-optic coefficient, which makes its core-mode effective index sensitive to temperature variation and induces large thermo-optic mismatch between the two cores. A high sensitivity of 1.595 nm/ ^oC is achieved in our experiment, which is almost 200 times improved from that of the sensor device before polymer infiltration process.

Two highly sensitive ammonia sensors, formed by depositing coatings composed of titanium dioxide (TiO₂) onto the cladding of an optical fibre sensing platform, are evaluated. A long period grating (LPG) of period 111 μm was fabricated in the core of an optical fibre so that the LPG operates at or near the phase matching turning point (PMTP). The first coating that was investigated was composed of TiO₂ nanoparticles deposited by liquid phase deposition. The sensor showed high sensitivity and allowed low concentrations of ammonia in water (0.01 ppm) to be detected with a response time of less than 60 sec. The second coating was composed of TiO₂ with subsequent layers of poly (allyamine hydrochloride) (PAH), and SiO₂ nanospheres infused with a sensitive element composed of porphine. The ammonia adsorption to the porphine compound led to the changes in the LPG’s transmission spectrum and allowed 0.1 ppm of ammonia in water to be detected with a response time of less than 60 sec.

We developed strain and temperature sensors based on multimode interference in perfluorinated graded-index (GI) plastic optical fibers, and investigate their sensing performance at 1300 nm. At room temperature, we achieve ultra-high sensitivities of strain and temperature of –112 pm/με and +49.8 nm/°C/m, the absolute value of which are approximately 7.2 and over 1800 times as large as those in silica GI multimode fibers, respectively. We also find that the temperature sensitivity is drastically enhanced with increasing temperature toward ~80 °C, where phase transition of core polymer partially occurs.

Sensing the nanometric displacement of a micro-/nano-fiber induced by optical forces is a key technology to study optical forces and optical momentum. When the gap between a micro-/nano-fiber and glass substrate becomes down to micrometer scale or less, a white light interference was observed. The gap changes when optical force arising from the propagating pump light along the micro-/nano-fiber causes a transversal nanometric displacement of a micro-/nanofiber, resulting in movement of the interferometric fringes. Therefore this movement of the interferometric fringes can be used to sense the nanometric displacement of the micro-/nano-fiber induced by optical forces. Experimental results show that the resolutions of this method can reach 7.27nm/pixel for tilted angle 0.8^o between the micro-/nano-fiber and substrate. It is concluded that the white light interferometry method is suitable for measuring the weak optical force.

In this study, we fabricated the ultra-thin fiber-optic dosimeter (UTFOD) for high energy photon beam therapy dosimetry. The UTFOD has high spatial resolution due to the relatively small volume compared to conventional dosimeters therefore the UTFOD can measure depth doses precisely in build-up regions of therapeutic radiation beams. For 10 MV photon beams, we measured the scintillation signal generated from the UTFOD according to monitor units (MUs) and dose rates of the clinical linear accelerator (CLINAC). Also, we measured percentage depth doses (PDDs) at different depths of solid water phantoms using the UTFOD and the GAFCHROMIC^® EBT films, and the results were compared with those using the Monte Carlo N-Particle eXtended (MCNPX) code.

A second harmonic 400-nm femtosecond pulse laser has demonstrated efficient hole drilling for a fiber optic spectroscopic measurement. A pulse train of 1 kHz with a pulse width of 350 fs was irradiated during approximately 1 s onto an optical fiber to make a through hole that penetrates whole fiber core and works to be a sample cell for a spectroscopic measurement. The spectroscopic measurement is shown using dye of rhodamine 6G. Even with a pico-liter cell volume of a through hole, the absorption spectrum is appeared in the visible range centered at 530 nm depending on the dye concentration. Discussions have also been made on the optimum arrangement of the through hole to obtain sufficient performance of spectroscopic measurements.

We demonstrate a self Q-switched Bismuth-doped germanosilicate fiber laser operating at 1463 nm. It is experimentally shown that stable Q-switched pulses with a temporal width of ~ 1.8 μs can be obtained from a simple, all-fiberized Fabry-Perot type cavity without using a saturable absorber at a repetition rate of ~65 kHz with a pump power of ~260 mW. The tuning capability of the temporal characteristics of the output pulses is also investigated. The possible physical mechanism is discussed.

We realize a microdroplet-etched fiber Fabry-Perot resonator. Strong polarization discrimination is achieved due to the asymmetric fiber cross section in the cavity, which should be useful for improving the measurement precision in the refractive index (RI) sensing application. The measured RI sensitivities are ~133.8 nm/RI-unit for the x polarization and 117.1 nm/RI-unit for the y polarizations, respectively. Simultaneously, the temperature effect can be eliminated by monitoring the peak difference of the two polarizations, which have the similar temperature coefficient but different RI responses.

The radiation resistance effect of two superfluorescent fiber sources using Er-doped photonic crystal fiber is studied under 500 Gy gamma-ray irradiation. One is trimmed into a quasi-Gaussian spectrum by a filter and the other is not trimmed. The results show that the SFS with spectrum trimming has a smaller radiation induced attenuation and a higher mean wavelength stability (2.616 dB and 24.803 ppm) than that of the SFS without spectrum trimming (3.187 dB and 611.766 ppm). Therefore, this method has practical use for improving radiation resistance in space environment.

We demonstrate an all-solid photonic bandgap fiber modal interferometer by concatenating two tapers separated with a middle section of the fiber. Unlike the conventional devices, our structure has a lower effective index in the core and a higher effective index in the cladding, which produce novel sensing characteristics. The measured sensing sensitivities are ~63pm/°C for temperarure and ~1.74nm/N for the axial stress, respectively.

An ultra-broad band single-polarization single-mode photonic crystal fiberis investigated based on zero order Surface Plasmon Polariton (SPP) mode by using the full vector finite element method. Highly wavelength-dependent transmission is obtained because of the bonding zero-order SPP mode stimulated over the interface of gold/liquid. With a filled refractive index (RI) of 1.52, the polarization extinction is higher than 30dB/cm among a large bandwidth of 360 nm in the second communication window. Meanwhile, the linear relationship between the resonant wavelength of the bonding zero-order SPP mode and the RI value of the filled liquid, make it a good candidate for liquid RI sensor with high linearity and sensitivity.

We investigate the spectral characteristics of Brillouin scattering in micro-scaled silica fibers with diameter of ~2μm. A multiple-peak structure in contrast to the conventional counterparts is observed. The measured temperature and strain sensitivities are ~0.8MHz/°C and ~0.05MHz/με, respectively, corresponding to a fiber diameter of 2.01μm. A comparison with the conventional single-mode fiber is made in our manuscript.

Sapphire based optical fibers provide an attractive basis for ultra-high temperature stable optical sensor elements. Fiber Bragg gratings can be inscribed in such fibers by means of femtosecond-laser pulses with a wavelength of 400 nm in combination with a two-beam phase mask interferometer. We have investigated crystalline optical fibers as well as structured sapphire-derived all glass optical fibers with aluminum content in the core of up to 50 mol%. The reflection properties, the index modulation and the attenuation effects will be discussed. Results concerning the temperature and strain sensitivity for use as sensor elements at high temperatures will be presented.

Regeneration of long period gratings (LPGs) in hydrogen-loaded, boron-codoped germanosilicate fibre is studied. The regenerated LPGs survive temperatures exceeding T > 950 °C. High temperature stability and stable spectra of these gratings were studied under different annealing temperatures. Regeneration was faster at higher temperatures, and occurred within 75 minutes in the region of 850 °C to 950 °C. These regenerated LPGs also exhibit ultra-low strain sensitivity.

A gap fiber Bragg grating (g-FBG) is fabricated by cutting a uniform FBG in the middle to introduce a small air gap between the two sections. Numerical and experimental investigations show that the g-FBG has the characteristics of both a phase shifted FBG and a Fizeau interferometer. The influence of the air-gap shift longitudinally or transversely with respect to the fiber central axis and temperature to g-FBG's spectrums are investigated with numerical simulation and experiments, and the mathematic models are made. Based on g-FBG's different sensitivity to gap width and temperature, a micro-gap and temperature simultaneous measurement sensor was demonstrated. And a g-FBG based tunable fiber ring laser with a narrow line-width is demonstrated.

In this paper, an abnormal grating evolution was recorded during microfiber Bragg grating (mFBG) inscription under 193nm excimer laser. Within 20 minutes exposing, a Type IIa FBG could be obtained with above 20dB strength in 8.5 μm microfiber. This regenerated mFBG had good survival ability against high temperature up to 800 °C. Moreover, the strain response of the regenerated grating was enlarged by the microfiber structure. Thus, highly sensitive strain sensor with considerable temperature resistance could be obtained, which had potential applications in gas/oil and aerospace territory.

Fiber Bragg gratings (FBGs) in gold-coated SMF have been successfully inscribed with NIR femtosecond laser and a phase mask for high temperature sensing application. The spectrums of FBGs inscribed by femtosecond laser are broader and asymmetrical with flat-toped profile which degrades the accuracy of FBGs interrogation with common peak detection techniques. A smart interrogation algorithm based on pattern matching (PMSIA) is reported in this paper. In this algorithm, an adjustable fitting spectrum template was proposed which enables the ability to suit for various spectrum patterns was proposed. The results of simulation and experiment demonstrate the noise immunity and threshold reliability of PMSIA. Less than 7pm interrogation error PMSIA was obtained even if the spectrum changes greatly in the very large sensing temperature range (up to 700°C).

The beat frequency dependence of the sensitivity for a Faraday-rotation based heterodyning fiber laser magnetic field sensor is studied, which shows that lower beat frequency results in higher sensitivity. By lowering the beat frequency to 2 MHz, the maximum sensitivity of about 43 Hz/μT to magnetic field has been achieved for a heterodyning fiber laser inscribed on an Erbium doped fiber. It also shows that the beat frequency is dependent on the polarization of the 980 nm pump. Therefore, dynamical tuning of the sensitivity optically has also been demonstrated by tuning the polarization of the 980 nm pump.

The noise performance of the beat note generated by a dual-polarization fiber grating laser is very critical for sensing applications. To reduce the noise of the beat note, external optical feedback is employed with a fiber Bragg grating as a reflector. It then shows that a longer feedback time results in larger noise reduction. With a 50 m single mode fiber as the delay line, more than 20 dB phase noise reduction has been achieved for a dual-polarization fiber grating laser which shows a phase noise of -92 dBc/Hz @ 10 kHz offset with external optical feedback applied.

A novel Bragg fiber grating (FBG) in an embedded-core hollow optical fiber (ECHOF) has been proposed and experimentally demonstrated. The high-quality FBG fabricated with phase-mask technique by using 248 nm ultraviolet laser, has a resonant wavelength of ~943.1 nm and a dip of ~24.2 dB. Subsequently, the dependences of the resonant peak on the temperature and the axial strain were studied. Experimental results show that the temperature and axial stain sensitivity are 6.5 pm/°С and 1.1 pm/με, respectively. In addition, a 0.03 nm shift of the transmission dip can be obtained when the polarization state changes from X polarization to Y polarization.

Large scale distributed sensor networks based on fiber Bragg gratings (FBGs) can find a wide range of uses. However, when identical FBGs are connected in series, the crosstalk will occur because of multiple reflections among the FBGs. In this article, theoretical simulations were done on the crosstalk in an array with FBG peak reflectivity of -35dB. An array consisting of identical weak FBGs with peak reflectivities ranging from -33dB to -37dB and a spatial resolution of 2.5m was prepared in-line on a fiber draw tower. The testing results of the FBG array are in close agreement with the theoretical simulations and ghost gratings can be observed on the reflection spectrum of the FBG array.

A Michelson interferometer is fabricated on silica planar waveguide by using the one-step technology based on 157nm mask laser micromachining. The fabrication time for one device is ~10s. Experimental results show that such an interferometer has an excellent fringe contrast of >20dB. Its temperature and refractive index (RI) responses are tested by observing the wavelength shift of the interferometric fringes, which shows linear characteristics with a thermo-coefficient of ~9.5pm/°C and a RI-coefficient of ~36.7nm/RIU, respectively. The fabrication technology may pave a new way for direct writing of planar silica waveguide devices for sensing applications with high efficiency and quality.

The plasmonics is expected to be a potential candidate of future sensing technologies, such as single-molecular detections and surface-enhanced Raman scattering, because of concentrated and enhanced electric fields at a sharp edge of a metallic nanostructure. In particular, breaking symmetry of a plasmonic structure results in anisotropic angular optical responses and allows a broad tunability of surface plasmons. In this study, we suggest a structure of asymmetric double metal caps on a dielectric nanosphere in order to increase the asymmetry of component structures and to improve the tunability of a plasmonic sensor.

A Long period grating (LPG) with a period of 111 μm was fabricated in the highly birefringent (Hi-Bi) optical fibre with the aim of developing a sensor for chirality measurements. The LPG sensor was exposed to different concentrations of glucose D(+) and fructose D(-) in water, which have similar structures but exhibit opposite optical rotations, i.e. chirality. The behaviour of the resonance bands of the submodes corresponding to the two orthogonal polarization states was different depending on the chirality of the compound, thus allowing discrimination between two compounds.

The use of bacteriorhodopsin (Br) coatings to create photosensitive optical fibre long period gratings (LPGs) is described. The response of the coated LPGs both sustained and pulsed illumination at a wavelength of 532 nm is monitored. The results show a clear response to the illumination and full recovery of the optical properties of the coating. This technique could allow the use of LPG for typifying photosensitive compounds and to develop optically controlled chemical sensors.

We propose a novel system for a two-dimensional (2-D) single-shot tomography and profilometry that can be realized by installing a Virtually Imaged Phased Array (VIPA) into a 2-D interferometer with a CCD. The VIPA simultaneously outputs incoherent optical frequency combs (OFC) whose teeth interval, such as free-spectral range (FSR), are scanned as a function of its output angle when the low-coherent light source is incident into the VIPA. Thus, the single-shot imaging can be realized with the FSR scanned Fourier-domain OFC interference monitored by the CCD. In other words, the fast imaging without mechanical moving part can be operated by the proposed OFC interferometry. And VIPA can use all of incident light. So this system enables to realize a high energy efficient interference measurement.

FSR of the output light of the VIPA is nonlinear with respect to the sweep direction. So we simulated the characteristics of the VIPA. As a result, we knew linearity optimal output angle depend on reflective index of the VIPA. And the VIPA can change the measurement range on the CCD by the number. In other word, the VIPA can zoom in and out no mechanical part. We will present the operation principle with its confirmed results in terms of both simulation and experiment.

Highly precise fiber optic strain and temperature measurements using chirped long period fiber grating (CLPG) are proposed and demonstrated, in which cascaded CLPGs (C-CLPGs) are employed as the sensing element and a Fourier transform technique is applied for the interrogation scheme. In this technique, strain and/or temperature-induced wavelength shift is determined precisely from the cross-correlation or cross-spectrum between the original and shifted channeled spectrum. In the experiment, C-CLPGs are fabricated by UV-irradiation technique, and strain and temperature characteristics are investigated. The highly precise measurements are confirmed by comparing with the results of the peak tracking method.

We demonstrate an accelerometer based on a dual-frequency DBR fiber laser with a resolution of 6 μg/Hz^1/2 at 1 kHz. The accelerometer is implemented by mounting a 250-milligram proof mass onto the laser cavity and converting the vibration into change in beat frequency between the two orthogonal polarization lasing modes. Experimental result shows that the sensitivity reaches 1.7 MHz/g at 1 kHz with a working bandwidth over 1 kHz. The high resolution is also a result of the noise level as low as 10 Hz/Hz^1/2 due to the compensation between the two lasing modes. The present accelerometer with extremely high resolution and light weight is promising for geophysical applications.

The successful regeneration of fibre Bragg gratings (FBGs) inscribed in an inline fibre etalon is demonstrated. The etalon is formed by UV-micromaching of the fibre end-face to form a cylindrical hole, the fibre is then fusion spliced to seal the cavity. Such a fibre device has excellent potential for the simultaneous measurement of ultra-high temperatures and strain.

The current study describes metal ion sensing with double crossover DNAs (DX₁ and DX₂), artificially designed as a platform of doping. The sample for sensing is prepared by a facile annealing method to grow the DXs lattice on a silicon/silicon oxide. Adding and incubating metal ion solution with the sensor substrate into the micro-tube lead the optical property change. Photoluminescence (PL) is employed for detecting the concentration of metal ion in the specimen. We investigated PL emission for sensor application with the divalent copper. In the range from 400 to 650 nm, the PL features of samples provide significantly different peak positions with excitation and emission detection. Metal ions contribute to modify the optical characteristics of DX with structural and functional change, which results from the intercalation of them into hydrogen bonding positioned at the center of double helix. The PL intensity is decreased gradually after doping copper ion in the DX tile on the substrate.

A temperature fiber sensor with nanostructured cladding composed ted by titanium dioxide (TiO2) nanoparticles was demonstrated. The nanoparticles self-assembled onto a side polished optical fiber (SPF). The enhancement of interaction between the propagating light and the TiO2 nanoparticles (TN) can be obtained via strong evanescent field of the SPF. The strong light–TN interaction gives rise to temperature sensing with a optical power variation of ~4dB in SPF experimentally for an environment temperature ranging from -7.8°C to 77.6°C. The novel temperature sensor shows a sensitivity of ~0.044 dB/°C. The TN-based fiber-optic temperature sensor is facile to manufactured, compatible with fiber-optic interconnections and high potential in photonics applications.

Graphene is a promising material for its exceptional electrical and mechanical properties. Starting with the initial demonstration of isolating a single graphene sheet from graphite, much progress has been made in realizing graphene based devices for diverse applications. Here, we introduce an experiment in which the electrical properties of graphene are modified by coating different-sequence single-stranded deoxyribonucleic acid (ssDNA) molecules. We fabricated a graphene-field effect transistor (FET) by transferring CVD graphene on copper foil onto a Si/SiO2 wafer. A passivation layer opened up windows on the surface of the graphene to enable interaction with liquid buffers. ssDNA molecules with different base sequences were coated onto the active graphene channels. We observed a variation in the Dirac voltage of the ssDNA-coated graphene FETs according to the ssDNA base sequences. Electrical control of the graphene FET is obtained via gating effect of the deposited ssDNAs. We conduct a systematic study of this ssDNAinduced gating effect with different base sequences, concentrations, and lengths of molecules, leading to extraction of characteristic parameters of the graphene FET accordingly.

Mechanoluminescence (ML), the emission of light from certain crystals induced by mechanical stress, is being considered for structural health monitoring (SHM), potentially offering passive and real-time distributed detection systems. We measured the mechanoluminescent radiance of ZnS:Mn, a crystal with a relatively strong ML emission, embedded in a matrix of transparent polyurethane under different loading and fracture. This data is invaluable for the design and performance evaluation of ML sensor systems.

Monitoring the hazardous and noxious substances (HNS) is a very important issue for mitigating the influence of catastrophic accidents in ocean and coastal areas. However, research on the HNS sensor is just in the beginning stage. In this study, we proposed a new HNS sensor using a printed ITO layer. We carried out a series of experiments of detecting the NH₄OH and seawater solution to investigate the feasibility as a HNS sensor. The resistance of ITO layer dropped abruptly when it soaked into the solutions. The resistance change (δR) was linearly correlated with the NH₄OH concentration of the solution, also it can be classified into two states; one is the transition stage, the other is the stabilized stage. The former is considered to be caused by the large capacitance of the electrical double layer (EDL) on the ITO surface. Also, the ITO layer showed considerable chemical stability within our experimental condition. In this paper, we have investigated the feasibility of printed ITO layer as a sensitive and cheap HNS sensor.

In this invited talk, we will present the advances in research and development activities of optical reflectometry in our laboratory. The performance of phase-sensitive coherent OTDR, which is developed for distributed vibration measurement, is reported with the results of field tests. The performance of time-gated digital OFDR, which is developed for optical access network diagnostics, is also reported. We will also discuss how to increase the frequency sweep span of the linearly-swept optical source, a very important part for improving the performance of optical reflectometry.

A multi optical path generator based on a tunable long Fabry-Perot optical fiber cavity is proposed and demonstrated. It would be used in an optical fiber sensing system which could multiplex a number of fiber sensors with different gauge lengths. Using this optical path generator, we can get a sequence of light beams with different optical paths, which will be coupled to the fiber sensor array in the sensing system. The multi optical path lengths generated by the device are analyzed and discussed. And the relative intensity of the corresponding light beam is calculated. The multiplexing capability caused by the optical path generator is discussed and the experimental results are confirmed this. The system can be used in strain or deformation sensing for smart structure health monitoring.

In traditional OFDR systems, the backscattered profile of a sensing fiber is inefficiently duplicated to the negative band of spectrum. In this work, we present a new OFDR design and algorithm that remove this redundancy and make use of negative beat frequencies. In contrary to conventional OFDR designs, it facilitates efficient use of the available system bandwidth and enables distributed sensing with the maximum allowable interrogation update-rate for a given fiber length. To enable the reconstruction of negative beat frequencies an I/Q type receiver is used. In this receiver, both the in-phase (I) and quadrature (Q) components of the backscatter field are detected. Following detection, both components are digitally combined to produce a complex backscatter signal. Accordingly, due to its asymmetric nature, the produced spectrum will not be corrupted by the appearance of negative beat-frequencies. Here, via a comprehensive computer simulation, we show that in contrast to conventional OFDR systems, I/Q OFDR can be operated at maximum interrogation update-rate for a given fiber length. In addition, we experimentally demonstrate, for the first time, the ability of I/Q OFDR to utilize negative beat-frequencies for long-range distributed sensing.

We propose a high-resolution optical time domain reflectometry (OTDR) based on an all-fiber supercontinuum source. The source simply consists of a laser with moderate power and a section of fiber which has a zero dispersion wavelength near the laser’s central wavelength. Spectrum and time domain properties of the source are investigated, showing that the source has great capability in nonlinear optics, such as correlation OTDR. We analyze one of the key factors limiting the operational range of such an OTDR, i.e., sampling time. Finally, we experimentally demonstrate a correlation OTDR with 25km sensing range and 5.3cm spatial resolution, as a verification of theoretical analysis.

A bus line network based on white light fiber-optic Mach-Zehnder interferometer is introduced by consideration of multiplexing capacity and coupler tailoring. The network topology which consists of N rungs sensing elements linked by N-1 couplers has been contrasted with three cases. The optimization formula has been used to couple more sensors, and Zoom-FFT has been used to analyze spectrum. After using these two methods, the multiplexing capability of the structure is enhanced evidently and a unambiguous spectrum is acquired.

We have proposed a Brillouin optical correlation domain reflectometry (BOCDR) with lock-in detection scheme. The weak and noisy spontaneous Brillouin signal is output from the electrical spectrum analyzer as an analog signal, and detected synchronously and amplified using a lock-in amplifier. By further introducing phase modulation into the system to suppress the background optical noise, and using large frequency modulation amplitude with appropriate filtering, the performance of the system is enhanced. A 4cm spatial resolution is experimented over 100m measurement range.

With the growing demand for monitoring length and channel number of the fully distributed optical fiber sensors (DOFSs), the amount of sensing data is increasing rapidly, and there will be a heavy pressure for the massive data storage and transmission. In this paper, two lossless compression algorithms of Lempel-Ziv-Welch (LZW) and Huffman are comparatively studied to effectively compress the huge amount of data of typical DOFSs, e.g. Φ -OTDR, POTDR, and BOTDA systems. The comparison results show that the LZW based on dictionary has a better performance in the consuming time and compression ratio for the DOFS data.

Temperature dependence of birefringence in various types of polarization-maintaining fibers (PMF’s) is rigorously investigated by the spectral analysis of Brillouin dynamic grating (BDG). PANDA, Bowtie, and PM photonic crystal fibers are tested in the temperature range of -30 to 150 ºC, where nonlinear temperature dependence is quantified for each fiber to an accuracy of ±7.6 × 10-8. It is observed that the amount of deviation from the linearity varies according to the structural parameters of the PMF’s and the existence of acrylate jacket. Experimental confirmation of the validity of the BDG-based birefringence measurement is also presented in comparison to the periodic lateral force method.

We developed a novel optical coherent domain reflectometer (OCDR) technique with large measurement range by using of dual frequency modulation. The probe and local oscillator beams are frequency modulated independently, and the sensing position can be adjusted digitally via the time delay between the driving signals for the two modulators. Meanwhile, the frequency tuning spans of the two paths are different to enable heterodyne detection. In the demonstrational experiments, a spatial resolution of 3.9 m over a range of 24.6 km fiber was achieved with 35 MHz tunable range of the modulator, and the spatial resolution keeps a constant over the whole measurement range.

We propose and experimentally demonstrate the feasibility of a highly efficient FBG-based quasi-distributed sensing system employing dual-wavelength cyclic pulse coding. Significant improvement in the measurement range, resolution and TDM multiplexing capabilities can be achieved, as well as crosstalk reduction with respect to a single wavelength TDM-based FBG interrogation scheme. The mechanism of noise reduction by quasi-periodic cyclic coding is experimentally demonstrated, pointing out significant improvement in accuracy with respect to dual-wavelength single pulse TDM-based FBG interrogation. The proposed technique can also enhance the sensing range of hybrid fiber optic sensor systems in which continuous monitoring of distributed and discrete points are simultaneously measured over the same sensing fiber.

Steel corrosion in concrete leads to severe destructions of the civil engineering structures. The detecting of the early corrosion is especially essential for steel-based structures. This paper summarized a series research works on optical fibre corrosion sensors, based on Fe(C)-coated Fibre Bragg Grating (FBG) and Fe-coated optical fibre polarizer. Three types of optical fibre sensors are presented. Type 1 and type 2, Fe-C coated FBG sensor and Fe coated etched FBG sensor, are both based on Fe(C)-coated FBG. The volume expansion and the RI variation of the coating lead to the FBG central wavelength shift respectively. By monitoring the wavelength shift, the corrosion status is evaluated and monitored. Type 3, Fe-coated optical fibre polarizer, is fabricated by side-polishing a single mode optical fibre and depositing a Fe-film on the polished side-face. The birefringence characteristics of the sensor will be reduced after being corroded, which is used for the corrosion status indicating. The fabrication processes of the three types of sensors are introduced. By investigating the experimental results of corrosion test in NaCl solution, the performance of the sensors are discussed. The experimental results show that the proposed sensors are proved to be sensible of early corrosion.

Fiber-optic ultrasonic sensing systems have been developed for structural health monitoring of composite structures by introduction of phase-shifted fiber Bragg gratings (PS-FBGs). The systems can achieve the compatibility of high sensitivity and broadband performance. First, PS-FBG balanced sensing system was developed and succeeded in detection of small acoustic emission signals of composite laminates. Next, erbium fiber ring laser sensing system with inbuilt PS-FBG was developed. This system has high robustness due to its self-adjustment function for environmental disturbances and achieved much higher sensitivity and ultra-broadband respondency than piezoelectric ceramic sensors. These systems have large potential to realize the ultrasonic SHM.

Phase-( Φ -) and Polarization- sensitive (P-) Optical-Time-Domain Reflectometries (OTDRs) are both representative optical fiber fence technologies, which have promising applications in long or ultra-long perimeter security with precise location ability. However, the challenge is that they are liable to be interfered by environmental influences due to their high sensitivity feature. Real human intrusions are always buried in the environmental noises and interferences, which lead to poor detection results. Thus it is proposed in this paper to extract human intrusion signals and separate the complicated noisy backgrounds by using a multi-scale Wavelet decomposition method. Practical test results prove its effectiveness.

An epoxy cure monitoring system has been constructed by combining fiber grating sensors and Fresnel reflection monitoring. The sensors measure strain and refractive index variations during the curing process, indicating the onset of gelification, the progress, and the end of curing. We used a wavelength-swept laser source to address both types of sensors. The signals from different sensors could be easily separated, resulting in simple optical setup and increased efficiency. The fiber grating sensors are demodulated by a spectrometer. The output fluctuation in the Fresnel reflection was compensated by referencing it with the tapped output of light source.

We demonstrated an ultrasensitive temperature sensor based on a unique fiber Fabry-Perot interferometer (FPI). The FPI was created by means of splicing a mercury-filled silica tube with a single-mode fiber (SMF). The FPI had an air cavity, which was formed by the end face of the SMF and that of the mercury column. Experimental results showed that the FPI had an ultrahigh temperature-sensitivity of up to -41 nm/°C, which was about one order of magnitude higher than those of the reported FPI-based fiber tip sensors. Such a FPI temperature sensor is expected to have potential applications for highly-sensitive ambient temperature sensing.

We measured the Brillouin frequency in fiber taper and identified the shift of the Brillouin frequency when strain and temperature changed. As taper diameter decreases, strain coefficient for Brillouin frequency decreases down to 0.0488 MHz/με while temperature coefficient is maintained.

The FBG sensor has globally been commercialized in various fields that is actively applied in Korea as well. Especially it is widely used as a structural monitoring sensor in civil engineering and construction structures due to its advantages including electrical stability, chemical stability and multiplexing. This report aims to introduce safety inspection of the FBG sensor in respect of radioactivity which has been applied to a silo structure for radioactive waste disposal as an example.

The design and performance analysis of a new sensor is introduced which is on board a small unmanned aerial vehicle (UAV) for coastal water remote sensing. The top level requirements of sensor are to have at least 4cm spatial resolution at 500m operating height, and 4° field of view (FOV) and 100 signal-to-noise ratio (SNR) value at 660nm. We determined the design requirements that its entrance pupil diameter is 70mm, and F-ratio is 5.0 as an optical design requirement. The three-mirror system is designed including aspheric primary and secondary mirrors, which optical performance are 1/15 λRMS wavefront error and 0.75 MTF value at 660nm. Considering the manufacturing and assembling phase, we performed the sensitivity, tolerance, and stray-light analysis. From these analysis we confirmed this optical system, which is having 4cm spatial resolution at 500m operating height, will be applied with remote sensing researches.

Whole optic fiber weighing technique and its device of belt conveyor are developed and put into application. Four FBG stress cells support a frame in a belt conveying line. In each cell, two FBG strain gauges are respectively installed at the stretching and compressing places to get the effects of sensitivity enhancement and temperature compensation. The weighing signals are from both FBG wavelength shift of loading cells and fiber belt speed meter. By means of integral algorithm, the weighing result is obtained. Actual coal weighing test shows that the accuracy of this weighing device is under 0.5%.

Multiphase flow measurements play a crucial role in monitoring productions processes in many industries. To guarantee the safety of processes involving multiphase flows, it is important to detect changes in the flow conditions before they can cause damage, often in fractions of seconds. Here we demonstrate how the scattering pattern of a laser beam passing a two-phase flow under an oblique angle to the flow direction can be used to detect derivations from the desired flow conditions in microseconds. Applying machine-learning techniques to signals obtained from three photo-detectors we achieve a compact, versatile, low-cost sensor design for safety applications.