In this paper, in order to improve fabrication efficiency, a novel multimode open-cavity Mach-Zehnder interferometer (MOC-MZI) is proposed and completed based on joint-assistance of microfiber and multimode fibers (MMFs), through flame brush and arc-discharged core-offset splicing techniques, in which a sub-millimeter-long MMF is used as the expansion fiber. The light field distributions of MOC-MZI with different core diameters of MMF (denoted by dMMF) by beam propagation method were investigated, and the effective beam expansion range was quantified with respect to the length of MMF (denoted by LMMF). Moreover, the optimal offset value of the microfiber (denoted by α) with different waist diameters (denoted by d) was obtained by simulation. According to the simulation results, the maximum fringe visibility can reach 28.3 dB via the optimized LMMF (=600 μm) and microfiber (d=40 μm, α=30 μm). Additionally, the energy attenuation of MOC-MZI is studied with varied cavity length, and the possible intensity-sensitive cavity length is found. Multiple open-cavity structures with different dMMF from 0 to 105 μm were then experimentally prepared and compared. When dMMF=105 μm, a millimeter-length open-cavity MZI is obtained with the visibility of ~8-dB, and its temperature response was characterized in terms of wavelength and intensity.
In this paper, a novel fiber-optic liquid level sensor is proposed and experimentally completed through a cascaded multimode-single-mode-multimode (MSM) structure with the same length of 25 mm. Two typical in-line Mach-Zehnder interferometers (MZIs) are respectively formed in each MSM structure, but more cladding modes are excited in the second MZI. A multimode-interference-like fringe then is observed, due to the mismatched energy of two MZIs. The comprehensive tests are performed in terms of liquid (water) level and temperature. The experimental results show that obvious intensity variation is demonstrated in a continuous liquid level measurement, but with a slight wavelength drift (about ±0.522 nm). The liquid level sensitivity reaches 0.261 dB/mm in the range from 0 to 40 mm with the linearity of 0.98. Inversely, the temperature response exhibits a flat wavelength shift. The wavelength sensitivity is 43.27 pm/°C and the intensity change is merely 0.01 dB/°C In the range from 24 to 58 °C. So the calculated temperature crosstalk is about 0.04 mm/°C and the measured error is compressed within 0.02%. It is obvious that, owing to such low crosstalk, our senor has the potential in high discriminative simultaneous measurement of engineering application.
In this paper, an all-fiber novel fabricated Mach-Zehnder interferometer (MZI) based on refractive index (RI) sensor is presented and simulated. This RI sensor is composed of a single-mode fiber (SMF) with a core diameter of 9 μm and a multimode fiber (MMF) with a core diameter of 105 μm. The microgroove can be etched by femtosecond laser or ground by grinding machine technology. It greatly reduces the limitations of structure fabrication. The RI response of this sensor is obtained by beam propagation method. In the range of 1.33-1.334 RIU, the RI sensitivity is -10373 nm/RIU and the linearity is 99.98% by wavelength demodulation. The intensity demodulation shows a nonlinear trend, and the sensitivity increases with the increase of RI . The maximum RI sensitivity is -9614 dB/RIU, and the fitting is 98.69%. The structure has the advantages of simple manufacture, high sensitivity and good linearity. It is very suitable for the practical applications of RI sensing with high sensitivity.
KEYWORDS: Sensors, Cladding, Optical fibers, Temperature metrology, Single mode fibers, Interferometers, Temperature sensors, Light sources, Fiber optics sensors, Refractive index
This type of sensor is manufactured by using the KF-FBT type fusion taper machine to uniformly pull the same single mode optical fiber. Double tapered section cascade type singles mode fiber. When the signal light passes through the concatenation fiber cone, the cladding mode is excited after passing through the first stage cone region. After a certain distance transmission, the second stage cone region interferes with the core mode. The change of the waveform is seen from the spectrometer. When the two cones are bent by 90, the article explores a double-cone-section cascading sensor that is easy to operate and easy to perform multi-point measurements from both theory and experiment. The spectral peak-to-valley contrast of the interference fringe is more obvious, and it can serve as a sensor head to test the ambient temperature. The sensor has a temperature sensitivity of 60 pm/°C.
In-fiber modal interferometers have been widely used in the applications of biochemical sensing, mine safety and health monitoring of buildings. The temperature feature of sensors is one of the most important characteristics, but the studies are rarely reported under the condition of subzero temperature. In this paper, through core-mismatch fiber splicing method, three in-fiber Mach-Zehnder interferometers (MZIs) are fabricated based on single-mode fiber (SMF), erbium-doped fiber (EDF, with core diameter of 3.6 μm) and multimode fiber (MMF, with core diameter of 50 μm), respectively. Their interference patterns are investigated through beam propagation method and Fast Fourier Transform analysis. The comprehensive tests of temperature are then performed in the range from -40 to 0°C. The experimental results show that, in subzero temperature, the transmission spectrums of MZI sensors based on single mode fiber (SMF) and MMF are worsened in terms of fringe visibility and intensity. And the sensitivity of MMF-based structure is 68.8 pm/°C with a 12.3-dB deduction of fringe visibility. Comparatively, the EDF-based MZI presents ideal sensitivity due to negative gain-temperature feature. By calculation, the 124.7 pm/°C sensitivity is gained with the linearity of 0.9892. Moreover, 10-dB enhancement in intensity and over-20-dB fringe visibility are demonstrated, which indicates that the EDF-based sensor is potential and promising for the applications of cryogenic sensing.
In this paper, a novel fiber ring laser (FRL) is proposed and investigated based on modal interference. Through core-offset splicing technique, an in-fiber Mach-Zehnder interferometer (MZI) is fabricated based on thin-core fiber and single mode fibers. Its distribution of light filed is comprehensively analyzed by beam propagation method. The FRL is then setup, in which the fabricated MZI is used as a band-pass filter. The output of laser is controlled and optimized by accurately adjusting the state of polarization controller. The experimental results show that, the extinction ratio of lasing wavelength reaches 39.8 dB, and the line width is less than 0.1 nm. Moreover, the proposed FRL is applied in temperature sensing, and the tested sensitivity reaches 122.7 pm/°C with the linearity of 0.9982. In addition, by calculation, the amplitude noise and the spectrum resolution are 8.84×10-3 nm and 2.89×10-3 nm, respectively. Therefore the detection limit in this laser sensor is about 0.07°C, which is obviously higher than that in passive fiber optic sensor.
The stability of gain-clamped erbium-doped fiber amplifiers (EDFAs) may be affected by the parameter drift of active and passive devices. We propose a hybrid gain-control scheme to enhance the working stability, which consists of an optical dual-fiber-Bragg-grating (FBG)-based linear cavity and an electrical fuzzy-based controller. The principle of optical gain clamping is then depicted and a detailed design about dual-channel fuzzy controller is given. The experimental results show that, in the dual-FBG configuration, with 20.2-dB mean gain, the designed L-band EDFA simultaneously guarantees the ±0.1-dB stability (with 30-dB dynamic range) and the ∼0.4-dB flatness in the range of 1570 to 1610 nm. In addition, under the electrical feedback control, the flatness stability of gain spectrum reaches ±0.18 dB within 60 min and the mean gain stability is about ±0.34 dB within 10-h continuous operation.
In order to improve the measurement accuracy of the angle and signal processing speed of operation, this paper proposes a novel method of second harmonic measurement of multi-beam laser heterodyne for the angle, which based on the combination of Doppler effect and heterodyne technology, loaded the information of the angle to the frequency difference of second harmonic of the multi-beam laser heterodyne signal by frequency modulation of the oscillating mirror, which is in the light path. Heterodyne signal frequency can be obtained by fast Fourier transform, and can obtain values of the angle accurately after the multi-beam laser heterodyne signal demodulation. This novel method is used to simulate measurement for incident angle of standard mirror by Matlab, the obtained result shows that the relative measurement error of this method is just 0.5213%.
The gain flatness of an L-band erbium-doped fiber amplifier (EDFA) is still an open issue. We improve the conventional single-pass two-stage configuration by placing a fiber Bragg grating (FBG) with the center wavelength at 1529.4 nm. Then, a weak lasing resonance cavity is formed by this FBG and a fiber isolator, which is able to increase the pump conversion efficiency by reflecting the residual amplified spontaneous emission and compressing the raised gain around 1570 nm based on the gain-clamped effect. The experimental results show that by adopting the proposed scheme, the gain un-flatness of the L-band EDFA is controlled within ±0.4 dB in the range of 1570 to 1610 nm, and an ∼29 dB average gain is simultaneously maintained.
It is a challenge to get gain-stabilization and gain-flatness of erbium doped fiber amplifier (EDFA) in C-band, simultaneously. In this article, we establish a gain-clamped EDFA model based uniform fiber grating-pair and optimize the reflectivity of grating by the designed targets. The tradeoff between stabilization and flatness can be obtained when an ideal reflectivity is adopted. The numerical results show that the gain-stabilization is controlled in ±0.1dB and gain-flatness is less than ±1.41dB in the range from 1535nm to 1565nm.
Fiber grating-pair is one of the efficient methods for gain stabilization of erbium doped fiber amplifier (EDFA) but with a gain-reduction of signals, especially in C-band. In order to overcome it, in this article, we establish a configuration of EDFA based uniform fiber grating-pair and conduct a comprehensive study on gain stabilization by varying the reflectivity, center wavelength and 3dB bandwidth of grating, and by varying the channel number and pump power. The numerical results show that under the optimal parameters of grating the gain stabilization at 1550nm is ±0.044dB with high gain and large dynamic range.
This paper proposes a novel method of multi-beam laser heterodyne measurement for Young modulus. Based on Doppler effect and heterodyne technology, loaded the information of length variation to the frequency difference of the multi-beam laser heterodyne signal by the frequency modulation of the oscillating mirror, this method can obtain many values of length variation caused by mass variation after the multi-beam laser heterodyne signal demodulation simultaneously. Processing these values by weighted-average, it can obtain length variation accurately, and eventually obtain value of Young modulus of the sample by the calculation. This novel method is used to simulate measurement for Young modulus of wire under different mass by MATLAB, the obtained result shows that the relative measurement error of this method is just 0.3%.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.