[Show abstract][Hide abstract] ABSTRACT: An improved positioning algorithm for dual Mach–Zehnder interferometry (DMZI) disturbance sensing system is proposed. We employ zero-crossing method, which can be computed easily to extract the disturbance signal segment with maximum zero-crossing rate. Meanwhile, we use general cross correlation based on Wiener filtering and subtraction weighting function (WG-GCC) to estimate the time delay of the extracted signal, which is robust to the correlated noise. Finally, we experimentally demonstrate that the proposed positioning algorithm can greatly improve the positioning accuracy with positioning error of ±20 m. Compared with the traditional positioning algorithm, the positioning error has been reduced by an order of magnitude. This algorithm has a promising potential in real-time fence perimeter applications.
[Show abstract][Hide abstract] ABSTRACT: This letter investigates a simultaneous detection method of mixed gases concentration based on overlapped spectra separation with software lock-In demodulation technique (SLIDT). Based on the additivity of the gases absorption lines, the spectra separation method of mixed gases was proposed theoretically and experimentally. The SLIDT instead of the hardware lock-in amplifier technique is introduced into the system, with structure simplification and cost reduction. The overlapped spectra of CO and CO2 mixed gases near 1582 nm were obtained based on SLIDT with the optimized modulation parameters. Using the sum of first, second, and third derivatives of Lorentzian function with the optimized fitting coefficients, the respective spectra of mixed gases with 4% CO and 6% CO2 were separated successfully with fitting errors of 2.401 and 2.470 mV. The relationship between different CO and CO2 concentrations and amplitudes of the separated second harmonics is linear with the linear correlation coefficients of 0.99828 and 0.99715.
[Show abstract][Hide abstract] ABSTRACT: We propose a novel fiber-optic Fabry–Perot interferometric (FFPI) temperature sensor based on differential pressure resulting from thermal expansion of sealed air. A thin silicon diaphragm is sandwiched between two micro-circular cavity-structured Pyrex plates to construct a FP and an air cavity. The thermal expansion of sealed air induces differential pressure variation between cavities and thus the deformation of thin diaphragm, which transfers temperature change into cavity length shift of FP interferometer. Theory analysis results indicate that the temperature-sensitivity can be designed flexibly by choosing the parameters of radius and thickness of silicon diaphragm, and the differential pressure between two cavities. Experimental results demonstrate that the temperature sensitivity of 6.07 nm/°C is achieved with the resolution of 0.10°C under the range of −50°C to 100°C, and the response time is around 1.3 s with temperature change from 28°C to 100°C.
[Show abstract][Hide abstract] ABSTRACT: We propose an ultraprecise resonance wavelength determination algorithm for optofluidic sensing applications, which can be expected to overcome the defect that the quality factor of the capillary resonator is deteriorated by the severe absorption in water. A parameter proportional to sinusoidal value of electrical field phase shift before and after the interaction with the capillary is constructed to determine the resonance wavelength of the optofluidic capillary. It is numerically demonstrated that this algorithm can narrow the full-width at half-maximum (FWHM) of resonance peak down to ~5% of the FWHM of transmission spectrum, which makes an ultraprecise peak determination feasible. Besides, this algorithm can reduce the FWHM of resonance peak to at least one quarter of FWHM of transmission spectrum in a rather wide region spans from undercoupling to overcoupling, and can be widely used in whisper-gallery mode-based sensor to improve the sensing precision conveniently.
[Show abstract][Hide abstract] ABSTRACT: We present a distributed optical-fiber magnetic-field sensor based on magnetostriction using the Rayleigh backscattering spectra (RBS) shift in optical frequency-domain reflectometry (OFDR). The magnetostrictive Fe-Co-V alloy thin films are attached to a 51-m single-mode fiber (SMF). We detect the strain coupled to the SMF caused by the magnetic field using the RBS shift. We measure the range of the magnetic field to be from 0 to 143.3 mT. The minimum measurable magnetic intensity variation is 12.9 mT when the spatial resolution is 4 cm, and it can be improved to 5.3 mT by deteriorating the spatial resolution to 14 cm. (C) 2015 The Japan Society of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: Based on the research of the traditional empirical mode decomposition (EMD) method, we proposed a modified EMD algorithm for the detected signal processing in tunable diode laser absorption spectroscopy. The modified EMD algorithm introduced Savitzky-Golay filtering and cross-correlation operation into the traditional EMD algorithm and reconstructed the signal by using the cross-correlation coefficients effectively. Based on the modified EMD algorithm in theory, the second harmonic component analysis was simulated by comparing with some other filtering algorithms. The experiments system was performed for carbon monoxide (CO) concentration detection. Comparing the sensing performances without and with using EMD-FCR and other filtered methods, the experimental results show that the signal-to-noise ratio of the system was significantly improved from 7.32 to 14.31 dB by EMD-FCR corresponding to one absorption line of CO at 1567.32 nm, leading to the minimum detection limit of 2 ppm. The accuracy and stability of the system are both improved by proposing the modified EMD algorithm.
[Show abstract][Hide abstract] ABSTRACT: We propose and simulate an on-chip mid-IR frequency comb generator based on the four-wave mixing (FWM) effect in a coupled silicon microring resonator. The resonator is formed by suspended ridge waveguides that are designed to have low group-velocity dispersion. A continuous-wave pump laser coupled into the resonator excites other longitudinal modes of the resonator through FWM-based parametric oscillations. In comparison with the device based on a single-ring resonator, we numerically demonstrate that the pump threshold can be dramatically reduced by introducing an auxiliary ring resonator to compensate the phase mismatch between the pump and the generated comb components. The proposed frequency comb generator has a low pump threshold of ~40 mW and a high efficiency of ~25% at the pump power of 100 mW.
[Show abstract][Hide abstract] ABSTRACT: We demonstrated a simple and batch-producible fiber-optic sensor based on hybrid Fabry–Pérot (FP) configuration for simultaneous pressure and temperature sensing. The proposed sensor head chips are batch fabricated by double-sided anodic bonding of a through-holes-array-structured glass wafer and two silicon wafers. The silicon–glass–silicon sandwich bonding structure constructs two serially connected low-finesse FP cavities naturally. The first cavity (FP1) is a silicon cavity and utilizes the refractive indices temperature dependence of silicon to achieve temperature sensing. The second cavity (FP2) is a vacuum cavity and employs a thin silicon diaphragm as a pressure sensing element. The reflection spectra exhibit hybrid interference fringes with different frequencies produced by silicon and vacuum cavity, and the temperature and pressure are simultaneously measured. Experiment results demonstrate that the pressure sensitivity of FP2 is 12.82 nm/kPa with a high linear pressure response over the range of 10–250 kPa, and the temperature sensitivity of FP1 is 142.02 nm/°C under the range of –20 °C–70 °C.
[Show abstract][Hide abstract] ABSTRACT: We present a method for improving the spatial resolution and the amplitude by an optimized deskew filter in long-range optical frequency-domain reflectometry (OFDR). In a previous deskew-filter method, as the nonlinear phase estimated from an auxiliary interferometer is used to compensate for the nonlinearity effect in the beating signals generated from a main OFDR interferometer, the spatial resolution and amplitude of the reflection peak in a long range (i.e., 80 km) are deteriorated by a residual nonlinearity effect due to the estimation inaccuracy of the nonlinear phase. In the proposed optimized deskew-filter method, the estimation accuracy of the nonlinear phase is improved by the higher orders of Taylor expansion and the high accuracy of the estimation of the time delay in the auxiliary interferometer using a cepstrum. We experimentally demonstrate that the amplitude of a reflection peak at 80 km increases by 20.5 dB and that the spatial resolution is up to 80 cm, which is about 187 times enhancement when compared with that of the same OFDR trace without nonlinearity compensation.
[Show abstract][Hide abstract] ABSTRACT: Defocusing distance plays a key role in laser cleaning result and can be either positive or negative, depending on the focus position relative to the sample surface. In this paper, we investigate the effect of the defocusing distance on the cleaning efficiency of oxidized brass surface. The oxide layer from the surface of a brass ring was processed with a three dimensional (3-D) dynamically focused laser galvanometer scanning system. The relationship between removal efficiency of the oxide layer and the defocusing distance was analyzed. The sample surface topography, element content before and after the laser cleaning were analyzed by a scanning electron microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDS), the surface quality after laser cleaning was analyzed by a Atomic Force Microscope (AFM), the chemical constituents of the oxide layer on the sample surface after being processed with different defocusing distances were examined by x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The results show that the ratios of Cu/O and Zn/O reach the maximum of 53.2 and 27.78 respectively when the defocusing distance is +0.5 mm. The laser pulses will lose the ability to remove the oxide layer from the substrate surface when the defocusing distance is larger than ±2 mm.
Optics and Lasers in Engineering 08/2014; 59:11–18. DOI:10.1016/j.optlaseng.2014.02.010 · 2.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The sensitivity enhancement at multiple wavelengths is investigated for fiber intra-cavity gas detection. Dynamic gain control and cascaded gas cells are used to enhance the laser absorption. The minimum detectable acetylene concentration is 9.4 ppm.
Fiber-Based Technologies and Applications; 06/2014
[Show abstract][Hide abstract] ABSTRACT: We present a method to realize temperature variation measurement in the cryogenic environment (e.g., at 76 K) using Rayleigh backscattering spectra (RBS) shift in standard single mode optical fiber by optical frequency-domain reflectometry. By analyzing the relationship of effective sensing segment size of fiber (or sensing spatial resolution), minimal measurable temperature variation, and temperature response of RBS shift, we found minimal measurable temperature variation in the cryogenic environment can be improved by increasing effective sensing segment size. Our experiments show that at a relatively high temperature (e.g., above 195 K), minimal measurable temperature variation is 0.21 K with an effective sensing segment size of 8 cm. When the temperature is very low (e.g., at 76 K), minimal measurable temperature variation can still maintain 0.34 K by simply increasing the effective sensing segment size of fiber to 48 cm.
[Show abstract][Hide abstract] ABSTRACT: We propose a direct and nondestructive self-referenced residual pressure measurement method for MEMS chip of fiber-optic pressure sensor. In the proposed method, two multimode fibers are placed at the center and the edge position of the sealed cavity. With scanning external pressure, two groups of cavity lengths data are obtained by using polarization low-coherence interference demodulator. The intersection point of their linear fitting curves indicates that the diaphragm is in flat condition and residual pressure is determined by the external pressure at this point. We successfully demonstrated the effectiveness of the residual pressure measurement method with measure error 0.049 kPa.
[Show abstract][Hide abstract] ABSTRACT: We present a high precision and fast speed demodulation method for a polarized low-coherence interferometer with location-dependent birefringence dispersion. Based on the characteristics of location-dependent birefringence dispersion and five-step phase-shifting technology, the method accurately retrieves the peak position of zero-fringe at the central wavelength, which avoids the fringe order ambiguity. The method processes data only in the spatial domain and reduces the computational load greatly. We successfully demonstrated the effectiveness of the proposed method in an optical fiber Fabry-Perot barometric pressure sensing experiment system. Measurement precision of 0.091 kPa was realized in the pressure range of 160 kPa, and computation time was improved by 10 times compared to the traditional phase-based method that requires Fourier transform operation.
[Show abstract][Hide abstract] ABSTRACT: In this study, a gas detection system based on intra-cavity absorption spectroscopy technique and L-band erbium-doped fiber ring laser is constructed. With a fiber Fabry-Perot tunable filter used for spectral scanning, the system can acquire multiple absorption lines of the detected gas. In order to improve the detection accuracy, reference wavelengths are introduced to calibrate the nonlinearity of the filter, and polynomial fitting is proposed to compensate the impact of temperature variation on gas absorption. When the system is applied to detect the concentration of CO2, the absolute error is less than 400 ppm, corresponding to a relative error under 0.52%. The monitoring error of absorption wavelength is no more than 30 pm. The system also has the ability to detect other gas species which have absorption lines in L-band. Crown Copyright
Sensors and Actuators B Chemical 03/2014; 193:356-362. DOI:10.1016/j.snb.2013.11.073 · 4.10 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigated the fiber Bragg grating (FBG) thermal response in space vacuum thermal environment. The FBGs were packaged with 6061-T6 aluminum. The liquid nitrogen immersion experiment results show that its wavelength shift standard deviation is 0.76 pm for 217 h. The combination effect of vacuum and cryogenic temperature was studied by thermal cycling process in space environment simulator. The FBG sensors show accuracy better than 2% full scale, and the hysteresis errors are below 1%. It proves that these metal packaged FBG sensors can survive and meet the requirement of space measurement.
The Review of scientific instruments 12/2013; 84(12):123107. DOI:10.1063/1.4842295 · 1.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Optical fiber sensor has great advantage for applications dealing with extreme environment. We developed a high precision optical pressure sensor for aviation industry. The optical pressure sensor is based on two-beam interference of microcavity and is fabricated with Micro-electromechanical systems (MEMS) and laser fusion technology. The cavity length variation resulting from external pressure is demodulated with spatial polarization low coherence interference unit and a high stable phase demodulation algorithm. The effect of light source output parameter is also investigated. We carried out research on optical fiber strain, temperature and acoustic vibration sensor for aerospace application. The optical fiber sensors for strain and temperature measurement are based on fiber Bragg grating(FBG).Both bare FBG and packaged FBG performances under cryogenic temperature and high vacuum are investigated. An eight-channel parallel FBG wavelength interrogator is developed. The optical fiber acoustic vibration sensor is based on two-beam interference of microcavity and use intensity demodulation method for high speed response. The mutiple-parameter and multiplepoint measurement instrument is successfully applied to status monitoring of water sublimator.
Proceedings of SPIE - The International Society for Optical Engineering 11/2013; DOI:10.1117/12.2037227 · 0.20 Impact Factor