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This paper presents a quasi-distributed Fabry-Perot fiber optic temperature sensor array using Optical Time Domain Reflectometry (OTDR) technique. The F-P sensor was made by two face to face single-mode optical fibers and their surfaces have been polished. Due to the low reflectivity of the fiber surfaces, the sensor was described as low Fresnel FPI. The working principle was analyzed using two-beam...
Wavelength sweep technique (WST) is introduced into intra-cavity fiber laser (ICFL) for low concentration gas detection. The limitation induced by noise can be eliminated using this method, and the performance of the system is improved. The sensitivity of the system is reduced to less than 300 ppm. With WST, sweeping characteristic of the ICFL can be described according to known gas absorption spectra.
Wavelength modulation technique (WMT) and wavelength sweep technique (WST) are introduced into intra-cavity absorption gas sensors (ICAGS) for low concentration gas detection. The optimized parameters of the system maximizing the signal-to-noise ratio (SNR) are found. Calibration of acetylene concentration and gas recognition are both realized.
A room-temperature broadly tunable mid-infrared difference frequency laser source for highly sensitive trace gas detection has been developed recently in our laboratory. The mid-infrared laser system is based on quasi-phase-matched (QPM) difference frequency generation (DFG) in a multi-grating, temperature-controlled periodically poled LiNbO3 (PPLN) crystal and employs two near-infrared diode lasers...
We report about fiber Bragg gratings (FBGs) inscribed in a small-core Ge-doped photonic crystal fibers with a UV laser and a Talbot interferometer. We systematically investigated the responses of such FBGs to temperature, strain, bending, and transverse-loading. The Bragg wavelength of the FBGs shifts toward longer wavelengths with increasing temperature, tensile strain, and transverse-loading. The...
External optical feedback effects due to reflection, Rayleigh backscattering and coherent Rayleigh backscattering in DFB fiber laser sensor system has been investigated. If the feedback intensity exceeds critical amount, excess noise would be induced in the demodulator. The maximum tolerable intensity back-reflection coefficient Rc and backscattering coefficient Sc into a fiber distributed feedback...
We propose a novel nonlinear mirror structure that can increase the optical signal-to-noise ratio of a distributed fiber Raman temperature sensor. The nonlinear mirror is constructed by a four-port 3 dB coupler, which links two sensing optical fibers. The two sensing fibers make a bunch, and sense the same circumstance. When the quasi-continuous wave optical light is injected, the 3 dB coupler forms...
In this letter, we propose a novel structure of the pure macro-bending sensor based on the tilted fiber Bragg grating (TFBG). The TFBG located in the half circle with the different diameters is bent at a constant angle with respect to the tilted grating planes. With the variations of the curvature, the core-mode resonance is unchanged and the transmission power of cladding modes detected by the photodiodes...
A method to interrogate fibre Bragg grating vibration sensor by narrow line width light is demonstrated; the interrogation scheme takes advantage of the intensity modulation of narrow spectral bandwidth light, such as distributed feedback laser, when a reflection or transmission spectrum curve of an FBG moves due to the strain which applied on the sensor. The sensor's response to acceleration frequency...
Microwave heterodyne detection can be used to measure the temperature and strain distribution along a fiber with high accuracy in a Brillouin optical time domain reflectometry (BOTDR) system. This method involves simultaneous measurement of Brillouin scattering and Rayleigh scattering in fiber, and scanning of Brillouin spectrum to obtain the desired information. This paper has presented a simultaneous...
The Amplification Effect on SBS and Rayleigh Scattering in the backward pumped G652 Fibers Raman Amplifier have been researched, pumped by the tunable power 1427.2nm fiber Raman laser and signal source is a tunable narrow spectral bandwidth (<;10MHz) ECL. The Rayleigh scattering lines are amplified by fiber Raman amplifier, and Stokes stimulated Brillouin scattering lines are amplified by fiber...
There is a simple distributed optical fiber sensing system which is used to monitor vibration signal, having an additional sub-loop coupled with main ring by a 3dB coupler. This paper compares three outputting interfered beams, each of them traveling in the sub-ring 0, 1, 2 times separately. Using the simultaneous equations produced by those three outputs, it finds the relation between the interference...
We present a landslide monitoring application using a high-resolution distributed fiber optic stress sensor. The sensor is used to monitor the intra-stress distribution and variations in landslide bodies, and can be used for the early warning of the occurrence of the landslides. The principle of distributed fiber optic stress sensing and the intra-stress monitoring method for landslides were described...
We propose a laser sensing system based on beat frequency demodulation. The sensor uses a single-longitudinal-mode distributed Bragg reflector (DBR) fiber laser as sensing element. This laser sensor has great multiplexing capability due to its wide free spectral range. Wavelength-Division-Multiplex (WDM) and Frequency-Division-Multiplex (FDM) techniques were studied. The sensing system has high sensitivity...
This paper presents the fundamental technique of PGC (phase generated carrier) and its realization on Compact RIO (Compact Reconfigurable Input and Output) which adopts real-time and FPGA (Field Programmable Grate Array) techniques. Improvement of the PGC technique is also introduced by using peak-to-peak value detection method to reduce the influence of variation of the light intensity. A four-element...
Aiming at some security problem in railway running and the application condition of existing technology, this paper studies some issues of using fiber optic sensing technology in railway security monitoring. Through field experiment measuring the strain of the rail and analyzing the experiment data, the method of diagnosing the health condition of rail and wheel is investigated and the application...
High-speed and wide-band LiNbO3 waveguide electro-optic intensity modulator has drawn great attention in the field of optical fiber communication and sensor. This paper reports the research results on the measurement of frequency shift characteristics of Mach-Zehnder electro-optic intensity modulator. Two measurement methods of frequency shift characteristics for high and low frequency modulations...
We demonstrate stable single-mode CW operation of a DFB ring laser based on Er3+ doped photonics crystal fibre. The incorporation of a ring cavity allows one single mode to lase and also suppresses the unwanted effect of self-pulsing.
We describe a distributed feedback fiber laser (DFB FL) sensor system with ultra-high resolution. The sensor is made by writing distributed feedback structures into a high gain active fiber, and the system employs an unbalanced Michelson interferometer to translate laser wavelength shifts induced by weak measurands into phase shifts. A digital phase generated carrier demodulation scheme is introduced...
An optical MEMS pressure sensor with a mesa membrane is presented. The operating principle of the MEMS pressure sensor is expatiated by the Fabry-Perot (F-P) interference and the relation between deflection and pressure is analyzed. Both the mechanical model of the mesa structure diaphragm and the signal averaging effect is validated by simulation, which declares that the mesa structure diaphragm...
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