Surface plasmon resonance detections based on phase changes have demonstrated superior sensitivities over the intensity, spectral and angular methods due to the singularity effect (abrupt change of phase value) observed at resonance. The Goos–Hänchen effect, a higher first order derivative of the phase, can be observable as a lateral displacement of the reflected wave at total internal reflection and magnified by the surface plasmons. The GH sensitivity can be further improved through the addition of a phase change material nanolayer beneath the gold. Vanadium dioxide (VO2) belongs to the family of phase change materials that exhibit reversible insulator-metal behavior when heated above 68℃. Adding a thin layer of VO2 below the metal proved to theoretically enhance the sensitivity of a conventional gold-based surface plasmon biosensor (up to 28 times of improvement in comparison with the bare gold configuration).
We report on fluorescence enhancement using a suspended core photonic crystal fiber (PCF) as an optofluidic platform. By employing metallic nanoparticles and an organic spacer, we achieved a thirty-fold signal enhancement of Cy5 dye at picomolar concentrations. The combination of fluorescence enhancement and PCF offers robustness, ease of use, and high sensitivity. This comprehensive study explores fluorescence enhancement using PCF, highlighting the significant enhancement achieved through metallic nanoparticles and organic spacers associated by the long length of light-analyte interactions offered by the PCF. These findings might contribute to the development of highly sensitive optical fiber-platforms for biomedical applications.
Surface enhanced Raman scattering (SERS) is a powerful biosensing technique allowing direct detection of target molecules thanks to their vibrational fingerprint Raman spectra. SERS is usually performed on nano roughened plamonic planar substrates/colloidal nanoparticles. However, the irregularities of plasmonic nanostructures lead to measurement reliability limitations. We have recently demonstrated that SERS-probes based on opto-fluidic photonic crystal fiber (PCF) composed of a silica-core surrounded by large air channels are remarkable sensing platforms leading to tremendous SERS sensitivity and excellent measurement reliability (98% in reproducibility and 95% in repeatability). However, a major limitation occurs when looking for highly reliable and easy-to-use biosensing platform. Actual SERS biosensors (planar substrate or fiber probe) require their alignment under a microscope, which could restrict on-field practical use. Here, we address this issue by developing a tapered opto-fluidic PCF allowing excellent reliability, efficient and easy coupling through a Plug-&-Play type modality. This novel type of SERS probe realized by reducing the fiber diameter, which increases the SERS sensitivity while enabling efficient light coupling to the Raman spectrometer with a relative standard deviation (RSD) of only 3.5% in reproducibility and 3.84% in repeatability. We demonstrate this easy Plug-&-Play type coupling based on a simple bare fiber connector, with a RSD of 4.5% in reproducibility measurements (i.e. removing and reconnecting the fiber SERS-probe to the Raman spectrometer without any additional alignment). We envision that this easy-to-use platform can be translated to - clinically viable SERS probes for liquid biopsy.
Surface enhanced Raman spectroscopy (SERS) allows sensitive detection of analytes, thanks to their vibrational Raman spectra. Planar SERS substrates often lack the reliability in measurement due to larger variations in signal intensity contributed by irregularities in nanostructures. In this context, photonic crystal fibers (PCFs) that combine excellent light guiding properties and the possibility to incorporate nanostructures and liquid or gas analytes into their axially aligned air holes, offer tremendous promise as an opto-fluidic SERS platform. Such sensors possess the enormous signal enhancement inherent to SERS and the flexibility of optical fibers. In addition, PCFs offer improved reproducibility, repeatability and sensitivity in measurement compared to planar substrates, due to the larger volume of interaction between the guided light and the analyte, and to highly reliable light couplings into the fiber core. Here, we present a novel design of PCF called ring core fiber (RCF), which is specifically engineered to further increase the interaction area in order to improve the sensitivity and reliability of the sensor. Preliminary experimental results showed that sensitivity of SERS sensing is improved by 115% compared to the best SuC-PCFs. Ongoing numerical simulations indicate that by further optimizing the dimensions of the ring, sensitivity could be improved by at least one order of magnitude with RCF. We envision that this new design with increased sensitivity and measurement reliability could be the next major step towards a clinically viable liquid biopsy fiber probe.
The paper deals with the determination of group and phase birefringence of an experimental highly birefringent (Hi-Bi) optical fiber across a wide wavelength span ranging from 1200 nm to 1700 nm. Several approaches for birefringence determination are used and the results are discussed. For the investigation, a set of two plane polarizers, a broadband light source, and an optical spectrum analyzer are used. The front face of the Hi-Bi fiber is illuminated by a linearly polarized light from a broadband light source and the end face of the fiber is connected to a fiber plane polarizer. At the output of the fiber plane polarizer, a typical spectrum – an interference pattern consisting of a quasi-periodic distribution of maxima and minima is measured by an optical spectrum analyzer. From the positions of subsequent minima of the interference pattern measured by the optical spectrum analyzer, the group birefringence dispersion is determined. The mean value obtained is in good agreement with that calculated from a differential group delay. The phase birefringence dispersion is determined by finding the appropriate dispersion functions representing the phase birefringence by fitting the measured spectrum to a calculated one, as the character of the spectrum depends on the phase birefringence.
Fiber lasers are a great source for tunable lasers due to the wide and relatively flat gain spectra of rare earth transitions in a glassy host (as compared to crystals). Thulium (Tm)-doped fibers, in particular, offer an extremely wide tunability of up to 330 nm in the 2μm wavelength region in a dual gain module configuration1. More recently, new concepts have emerged, which allow the synchronized emission of two or even more wavelengths2. These sources are particularly useful for nonlinear frequency conversion via four-wave mixing (FWM) or difference frequency generation (DFG). We will present a very versatile fiber-integrated approach based on Fiber-Bragg-Grating (FBG) arrays implemented in a theta-shaped cavity. The Tm-doped fiber source emits typical average powers of 0.5W and is tunable from 1931nm to 2040nm. The emission linewidth follows the spectral characteristic of the FBG and is typically 30GHz in our case. This concept allows a constant wavelength-independent repetition rate as well as a synchronous emission of two or even three independently tunable wavelengths. The tuning is performed purely electronically by optical gating, and in addition the pulse duration can be tuned between 4ns and 25ns. The switching speed is very fast and was measured to be less than 10μs. These experiments will be contrasted with a different approach based on a VLMA fiber associated to a set of two volume Bragg gratings (VBG), one of them being angle-tunable. This concept allows pulsed (Q-switched) as well as CW operation and features a continuous and wider tunability of up to 144nm especially and also the dual wavelength mode. The output power was > 4.5W in CW mode and pulse peak power of 12kW have been obtained in the Q-switched mode with pulse durations of 25ns.
We experimentally demonstrated a temperature sensor by selectively infiltrating refractive index liquid (RIL) in the central air hole of a twin-core photonic crystal fiber (PCF). The selective liquid infiltration was realized by putting the PCF in the bulk liquid with its central air hole open for liquid infiltration using capillary effect. The rest of the air holes were covered by UV glue. The three-dimensional stage was used to translate the PCF, and a tapered SMF was used to transfer the UV glue to cover the air holes under the microscope. After UV glue was solidified by exposing the fiber end under the UV light, the PCF end was dipped into the RIL to fill the central air hole by capillary effect. Due to the large thermos-optic coefficient of the RIL, the RIL filled air channel would act as a liquid core whose core modes would be highly dependent on the ambient temperature. The core modes of the RIL filled core would be phase matched to the fundamental mode of the two solid cores. Therefore, the phase matching wavelengths for the mode coupling among the two solid cores of PCF and the liquid core were highly temperature sensitive. The resonant dips in the transmission spectrum were measured to estimate the temperature sensitivity. The experiment used a commercially available twin core PCF, and blocked all but the central airhole at one of the ends facets by UV glue (NOA81, Norland), the remaining open holes are infiltrated over a length of 10 cm by capillary force with fluid (Cargille Laboratories Inc. index-matching fluid, series A) that possesses a refractive index of 1.46 at 589.3nm, 25°C, and the thermal coefficient is – 0.000389 RIU/°C, which is around 10 times of that coefficient of silica. Any temperature induced changes will have an influence on the propagation properties because of the highly temperature response of the refractive index of the fluid. With a fiber cleaver, a 1.8 cm long PCF was then cut from the longer length of the partially liquid filled twin core PCF and then fusion spliced with SMFs at both ends to observe its transmission spectrum when the sample is heated. When the temperature increase to around 54°C, the liquid RI drops quickly to match that of silica, and a three parallel waveguide structure is formed, in which the central liquid waveguide have the same index value with the two solid core. Because of the small separation between adjacent waveguides, a strong mode-field overlap occurs, which leads to a significant enhancement of the coupling coefficient, therefore, light energy can be easily transferred between two solid cores and the liquid rod in a short coupling length. Thus, the transmission spectrum of the device contain two sets of interference fringe pattern, the large spectrum envelope originated from the interference between the three eigenmodes generated by three-parallel waveguide structure based on the mode coupling theory, and fine interference fringes generated by the interference between the higher order modes in one core. By tracking the dip wavelength shift of the large spectrum envelope, the sensor exhibited a high temperature sensitivity of up to 37.011 nm/°C within the temperature range from 53.8°C to 55°C due to the satisfaction of phase match condition, and maintain a high sensitivity of 19.681 nm/°C from 55°C to 58.2°C, which is benefit from the high thermal optic coefficient of the selectively filled liquid in the twin core PCF.
An optical fiber sensor consisting of short sample of experimental Hi-Bi optical fiber integrated between two single mode (SM) optical fibers is proposed and experimentally demonstrated. The experimental fiber consists of core with diameter equals 8.5 μm and the two side Stress Applied Part (SAP) of diameter 25 μm. The SAPs are made of Al-Ladoped silica. The birefringence of the fiber is 3.19·10-4. We measured spectral distribution of intensity at the output of the SM fiber as function of the analyzer's adjustment angle and the suitable position of the analyzer was determined. Then we applied the bodies with weights up to 100 g on the fiber for two significant positions of SAPs: SAPs were next to each other and above each other. Evaluation of the measurements were done by the peak-to-peak amplitude of optical power difference (in dB) of two measurement for which we determine the applied force (weight). The sensitivities were determined to be 0.081 dB/g for SAPs next to each other and 0.037 dB/g for second position of SAPs, respectively. From the results it follows that the sensor could be used not only for determination of lateral force but also for determination of applied force position.
Over the last few years, there has been an increasing demand for medium-grade gyroscopes to fill the gap (in terms of cost and performance) between MEMS and current optical devices. There has also been a longstanding quest for a compact high-grade gyroscope to reduce the size of current inertial navigation units and make them available for most carriers (extending their time of GPS-free autonomous navigation). In this paper, we will describe two approaches we are following towards these goals, with support from the European Space Agency: the solid-state ring laser gyroscope and the resonant hollow-core fiber optic gyroscope.
One of the most peculiar characteristics of the insulator-to-metal transition (MIT) in vanadium dioxide (VO2) material is its broadband response, manifested by drastic electrical and dielectric properties changes between the insulator and metallic states on a very large frequency spectrum. We are presenting the characterization of the MIT in VO2 films over a wide range of the electromagnetic spectrum (75-110GHz, 0.1-1.4THz) and illustrate the materials’ capabilities for manipulating the electromagnetic radiation in the millimeter-waves and THz domains. We demonstrate the possibility of realizing tunable THz devices by introducing this phase transition material as localized patterns in the structure of THz planar metamaterials. We designed, simulated and fabricated tunable VO2-based THz metamaterials devices which show significant variations in their THz transmission under the effect of thermal stimuli but also by applying an electrical voltage across the devices.
We study the effect of hydrogen gas diffusion in silica optical fibers on Brillouin and Rayleigh scatterings. By modeling hydrogen diffusion kinetics as a function of temperature and pressure and by measuring simultaneously Rayleigh and Brillouin scattering on G652 single-mode fiber samples during H2 desorption (previously exposed to 175 bars H2 at 80°C), we have demonstrated experimentally that acoustic velocity increases linearly with H2 concentration with a ratio of about (4.8 m/s) / (%mol H2).
In this paper, we report the fabrication and characterization of a new concept of optical fibers whose cladding is composed of palladium particles embedded into the silica glass cladding. Since conventional fiber processes are not suitable for such realizations, we developed an original process based on powder technology to prepare our specific preforms. Step, graded index and photonic crystal optical fibers with original shapes were realized. The use of high purity powders as raw materials combined to a specific preforms heat treatment allowed the fabrication of resistant and long length metal-cladding optical fibers. Microstructured Pd-SiO2 composite cladding optical fibers with single-mode behavior and optical losses lower than 2 dB/m at 1530 nm were characterized. Hydrogen-induced attenuation sensitivity of these fibers at the 1245 nm wavelength was demonstrated after long H2 exposure. Dehydrogenation kinetics calculations and experiments were studied.
We report on SiO2-Al2O3-La2O3 glasses – with and without Yb2O3 – suitable for nonlinear and fiber laser applications. We also present successful supercontinuum generation and fiber laser operation around 1060 nm in step-index fibers. We have optimized the glass compositions in terms of thermal and optical requirements for both a high La2O3 (24 mol%) and Yb2O3(6 mol%) concentration. The aluminum concentration was adjusted to about 21 mol% Al2O3 to increase the solubility of lanthanum and ytterbium in the glass beyond possible MCVD based techniques. The glasses have been characterized by dilatometrical methods to find transition temperatures from 860 to 880°C and thermal expansion coefficients between 4.1 and 7.0 × 10-6 K-1. Structured step index fibers with a SiO2-Al2O3-La2O3 core and silica cladding have been realized showing a fiber loss minimum of about 500 dB/km at 1200 nm wavelength. The chromatic dispersion could be adjusted to shift the zero dispersion wavelength (ZDW) close to the pump wavelength of 1550 nm in a supercontinuum generation setup. First fiber laser experiments show an efficiency of about 41 % with a remarkably reduced photodarkening compared to MCVD based fibers.
We report on recent developments on fabrication and optical guidance of Kagome-lattice hollow-core photonic crystal
fiber (HC-PCF). These include the design and fabrication of a hypocycloid-shaped core Kagome HC-PCF that combines
a record optical attenuation with a baseline exhibiting ~180 dB/km over a transmission bandwidth larger than 200 THz.
These results are corroborated with theoretical simulations which show that both the core-shape and the cladding ring
number play role in inhibited coupling, inducing core-mode confinement for the fundamental transmission band. We also
show that the inhibited coupling is weaker for the first higher-order transmission band by theoretically and
experimentally comparing Kagome HC-PCF with a single anti-resonant ring hollow-core fiber.
We report about preparation technique and characterization of structured fibers composed of HMO core glasses and
silica cladding. Two processes as material preparation techniques have been developed based on glasses prepared by
melting of SAL (e.g. 70SiO2-20Al2O3-10La2O3) glasses and the reactive powder sintering (REPUSIL) method. The
melted glasses have been characterized by dilatometrical methods to find Tg values of 827-875°C and expansion
coefficients between 4.3 and 7.0×10-6 K-1. The latter is one order of magnitude higher than the expansion coefficient of
pure silica glass. Structured fibers (SAL core, silica cladding) were fabricated following the Rod-in-Tube (RIT) and
Granulate-in-Tube (GIT) process. The HMO glasses were chosen due du their high lanthanum content and the expected
high nonlinearity, suitable for nonlinear applications (e.g. supercontinuum sources).
The partial substitution of lanthanum by other rare earth elements (e.g. Ytterbium) allows the preparation of fibers with
extremely high rare earth concentration up to 5 mol% Yb2O3. The concentration of alumina in the HMO glasses as
"solubilizer" for lanthanide was adjusted to about 20 mol%. So we overcame the concentration limits of rare earth
doping of MCVD (maximum ca. 2 mol% RE2O3). Nevertheless, the investigated HMO glasses show their limits by
integration in structured silica based fibers: Optical losses are typically in the dB/m range, best value of this work is
about 600 dB/km.
The mechanical stability of fibers is influenced by mechanical strain caused by the high thermal expansion of the core
material and the lower network bonding stability of the HMO glasses, but partially compensated by the silica cladding.
Chalcogenide or heavy metal oxide glasses are well known for their good transparency in the mid-infrared (MIR)
domain as well as their high nonlinear refractive index (n2) tens to hundreds times higher than that of silica. We have
investigated the nonlinear frequency conversion processes, based upon either stimulated Raman scattering (SRS) or
soliton fission and soliton self-frequency shift (SSFS) in fibres made up with such highly nonlinear infrared transmitting
glasses. First, SRS has been investigated in a chalcogenide As2S3 step index fibre. In the single pass configuration, under
quasi continuous wave 1550 nm pumping, Raman cascade up to the forth Stokes order has been obtained in a 3 m long
piece of fibre. The possibility to build a Raman laser thanks to
in-fibre written Bragg gratings has also been investigated.
A 5 dB Bragg grating has been written successfully in the core. Then, nonlinear frequency conversion in ultra-short pulse
regime has been studied in a heavy metal oxide (lead-bismuth-gallium ternary system) glass photonic crystal fibre.
Broadband radiation, from 800 nm up to 2.8 μm, has been obtained by pumping an 8 cm long piece of fibre at 1600 nm
in sub-picosecond pulsed regime. The nonlinear frequency conversion process was assessed by numerical modelling
taking into account the actual fibre cross-section as well as the measured linear and nonlinear parameters and was found
to be due to soliton fission and Raman-induced SSFS.
Optical fiber sources have experienced a massive growth over the past ten years principally due to the compactness,
robustness and good spatial quality of such systems. Fiber sources now cover a large spectrum from visible to near
infrared helped on this point by the development of microstructured fibers (MOFs). A particular class of MOFs also
called hollow-core photonic crystal fibers (HC-PCFs) offers to get rid of silica's absorption thanks to band gap guidance
and therefore to extend transmission range of silica fibers. We propose here two all-fiber architectures based on HCPCFs
in view to generate mid infrared wavelengths by amplification of spontaneous Raman scattering (SRS) in gaseous
medium. We report on design, fabrication and characterization of two kinds of HC-PCF matching the architecture needs.
In the last ten years, the development of air-silica microstructured fibers has opened an exciting route to study new type
of optical waveguides, leading to a wide range of applications. Now, the possibility offer by this photonic technology to
incorporate original materials and mix different fabrication processes give a promising way to adapt the optical designs
and extend the applications in a large area from UV to mid IR.
The delivery or generation of high power in optical fibre requires the increase of the core size to increase the threshold of
nonlinear effects and the damage threshold. However the bend loss strongly limits the increase of the effective area
(Aeff). All-solid photonic bandgap fibres are attractive for the delivery of power since they can be made singlemode
whatever the core diameter is. Moreover the silica core can be doped with rare-earth ions. A Bragg fibre is a bandgap
fibre composed of a low index core surrounded by N concentric layers of high and low index. We have fabricated Large
Mode Area Bragg fibres by the MCVD process. These Bragg fibres present a ratio Aeff/λ2 close to 500. A first Bragg
fibre, defined by N = 3 and an index contrast between the cladding layers Δn = 0.01, exhibits a measured critical bend
radius Rc close to 16 cm (bend loss equal to 3 dB/m). Increasing the index contrast Δn leads to a tighter field
confinement. The field distribution of the guided mode strongly decays in the periodic cladding and is thus less sensitive
to bending. We propose here the design of an improved Bragg fibre with a very large index contrast Δn = 0.035 which
leads to a dramatic reduction of the bend loss. The critical bend radius was measured to be lower than 3 cm. This fibre is
less bend sensitive than an equivalent solid core fibre, either a step-index fibre or a photonic crystal fibre.
Photonic bandgap fibers have already proved their huge potential for guiding light in air over kilometric lengths.
Nowadays, solid-core bandgap fibers draw considerable attention due to their unusual properties. For instance, the
bandgap effect may lead to very large mode area operation, management of the chromatic dispersion curve, spectral
filtering or bend loss reduction, all features that could enhance fiber laser performances. Recent results about the design,
fabrication and characterization of large mode area solid-core bandgap fibers are presented. Prospects of further
development of bandgap fiber lasers are discussed.
Bandpass filters based on π-phase-shifted long-period fiber grating have been theoretically analyzed and experimentally fabricated by the electric-arc technique. Calculations and numerical simulations, based on coupled mode theory associated with the F-matrix method, have shown that the isolation of lateral rejected bands is maximum when the total length of the grating is optimised and the π-phase-shift inserted when the transmission at the desired resonance wavelength is -6.9dB. Two π-phase-shifts are introduced at optimised positions to obtain a large bandwidth of the badpass filter. We have fabricated the first bandpass filters that have lateral rejected bands isolation higher than 20 dB and bandpass filters with very large flat-top bandwidths (FWHM =19.5 nm) around 1538 nm peak, the fabricated filters are characterized by a very low insertion loss (<0.5 dB).
We have used a CO2 laser as a heating source to fabricate a single-mode fiber couplers. The process consists of fusing and stretching two standard single model fibers initially maintained in lateral contact. We have fabricated 3 dB couplers at 1500 nm with insertion loss < 0.5dB. We also have fabricated multiplexers such as a 100% coupler at 1310 nm and at 1550 nm. The channel isolation of these components are > 30dB with a bandwidth of 30 nm at -30dB. Finally, a coupler with a long constant waist have been fabricated.
We have fabricated Long Period Grating filters in two Dual Concentric Core Fibers by an electric arc discharge technique. The gratings have induced coupling between the fundamental modes of the two cores. We have obtained filter with rejected band around 1220 nm and 1559 nm respectively, characterized by insertion loss lower than 0.5 dB. We also have investigated the inteest of using this fiber to implement a highly selective Mach-Zehnder interferometer with a 2.4 nm inter-fringe. Despite the high Ge-doping of the used fiber, thermal characterizations show a temperature sensitivity of the transmitted spectrum similar to that of the same grating written in a standard Single Mode Fiber.
A simple method of fabricating long-period fiber gratings, by performing an electric discharge to optical fiber, is presented. Standard single mode fiber is used without hydrogen loading. Grating filters present competitive characteristics, very low insertion loss and high dynamic rejections. We have performed high temperature characterizations of realized gratings in the range 30 - 1200 degree(s)C. Resonance wavelength shifts behavior and grating stability at several annealing cycles have been investigated. The temperature sensitivity are in good agreement with recent published works. Irreversible evolution of the peak shifts is to be emphasized.
We present the fabrication of long period fiber grating, in non-hydrogenated standard telecommunication fiber, using an electric discharge. We have obtained a gratin with low insertion loss, dynamic rejection of 37.5dB at 1530 nm and bandwidth of 16.3nm at -3 dB. The performances are competitive compared to literature. We have demonstrated the flexibility of the process by fabricating band pass and compact concatenated filters.
We have fabricated Long Period Fiber Gratings (LPFG), using non-hydrogenated standard single-mode fiber (SMF28TM), with an electric arc discharge, issued from a commercial splicer. We have obtained gratings with low insertion loss and isolation of 37.5 dB at 1530 nm. The bandwidth at -3 dB (FWHM) is evaluated to be 16 nm. Evolution of the spectral responses (peaks isolation, bandwidth) are explored. We have performed temperature characterization of the realized gratings between 0 degrees C and 750 degrees C. The gratings exhibit a robust and stable behavior to temperature annealing. We showed a spectral shift of the resonance peaks with temperature, these evolutions are worthy of note. We have studied and experimented phase-shift filters. The filters performances are competitive compared to literature. These characterizations provide a set of phenomena to help explanation of the inscription mechanism of the gratings. The fabrication is simple, it does not require to hydrogenate the fiber. The control of the filter parameters makes it possible to produce any filter profile. We have demonstrated the simplicity and flexibility of the process.
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