[show abstract][hide abstract] ABSTRACT: A simple photonic approach to generate ultrawideband (UWB) pulse signals utilizing a gain-switched semiconductor laser with optical feedback is proposed and demonstrated. The RF spectrum of the generated chaotic UWB signals has a -10 dB bandwidth of 9 GHz and central frequency of 6.6 GHz (fractional bandwidth of 155%), which is consistent with the Federal Communications Commission indoor mask. The central frequency and -10 dB bandwidth can be tuned by adjusting the bias current and feedback strength of the semiconductor laser. After transmission through a 30 km single-mode fiber, the spectrum shape of the chaotic UWB signals is almost unaffected by the chromatic dispersion of the fiber.
[show abstract][hide abstract] ABSTRACT: We propose a new wavelength-division-multiplexing method for extrinsic fiber Fabry-Perot interferometric (EFPI) sensing in a polarized low-coherence interferometer configuration. In the proposed method, multiple LED sources are used with different center wavelengths, and each LED is used by a specific sensing channel, and therefore the spatial frequency of the low-coherence interferogram of each channel can be separated. A bandpass filter is used to extract the low-coherence interferogram of each EFPI channel, and thus the cavity length of each EFPI channel can be identified through demultiplexing. We successfully demonstrate the simultaneous demodulation of EFPI sensors with same nominal cavity length while maintaining high measurement precision.
[show abstract][hide abstract] ABSTRACT: A demodulation algorithm based on the birefringence dispersion characteristics for a polarized low-coherence interferometer is proposed. With the birefringence dispersion parameter taken into account, the mathematical model of the polarized low-coherence interference fringes is established and used to extract phase shift information between the measured coherence envelope center and the zero-order fringe, which eliminates the interferometric 2π ambiguity of locating the zero-order fringe. A pressure measurement experiment using an optical fiber Fabry-Perot pressure sensor was carried out to verify the effectiveness of the proposed algorithm. The experiment result showed that the demodulation precision was 0.077 kPa in the range of 210 kPa, which was improved by 23 times compared to the traditional envelope detection method.
[show abstract][hide abstract] ABSTRACT: We present a simple and effective method to compensate the optical frequency tuning nonlinearity of a tunable laser source (TLS) in a long range optical frequency-domain reflectometry (OFDR) by using the deskew filter, where a frequency tuning nonlinear phase obtained from an auxiliary interferometer is used to compensate the nonlinearity effect on the beating signals generated from a main OFDR interferometer. The method can be applied to the entire spatial domain of the OFDR signals at once with a high computational efficiency. With our proposed method we experimentally demonstrated a factor of 93 times improvement in spatial resolution by comparing the results of an OFDR system with and without nonlinearity compensation. In particular we achieved a measurement range of 80 km and a spatial resolution of 20 cm and 1.6 m at distances of 10 km and 80 km, respectively with a short signal processing time of less than 1 s for 5 × 10<sup>6</sup> data points. The improved performance of the OFDR with a high spatial resolution, a long measurement range and a short process time will lead to practical applications in the real-time monitoring, test and measurement of fiber optical communication networks and sensing systems.
[show abstract][hide abstract] ABSTRACT: A demodulation algorithm based on absolute phase recovery of a selected monochromatic frequency is proposed for optical fiber Fabry-Perot pressure sensing system. The algorithm uses Fourier transform to get the relative phase and intercept of the unwrapped phase-frequency linear fit curve to identify its interference-order, which are then used to recover the absolute phase. A simplified mathematical model of the polarized low-coherence interference fringes was established to illustrate the principle of the proposed algorithm. Phase unwrapping and the selection of monochromatic frequency were discussed in detail. Pressure measurement experiment was carried out to verify the effectiveness of the proposed algorithm. Results showed that the demodulation precision by our algorithm could reach up to 0.15kPa, which has been improved by 13 times comparing with phase slope based algorithm.
[show abstract][hide abstract] ABSTRACT: The up to date progress of fiber sensing technologies in Tianjin University are proposed in this paper. Fiber-optic temperature
sensor based on the interference of selective higher-order modes in circular optical fiber is developed. Parallel demodulation
for extrinsic Fabry-Perot interferometer (EFPI) and fiber Bragg grating (FBG) sensors is realized based on white light interference.
Gas concentration detection is realized based on intra-cavity fiber laser spectroscopy. Polarization maintaining fiber (PMF)
is used for distributed position or displacement sensing. Based on the before work and results, we gained National Basic Research
Program of China on optical fiber sensing technology and will develop further investigation in this area.
KeywordsFiber sensing–high temperature–parallel demodulation–gas detection–distributed sensing
[show abstract][hide abstract] ABSTRACT: A simple equation for peak wavelength detection of fiber Bragg grating
(FBG) with three spectral data is proposed, which has almost the same
order of computing load as the conventional maximum search algorithm and
uncertainty as the least-squares fit algorithm. The factors effecting
performance of the new technique was investigated by simulation. For FBG
with spectral bandwidth 0.2 nm, simulation results show that sample
resolution lying between 0.07 and 0.16 nm have small measure standard
deviation, which is less than 1 pm for SNR greater than 20.75 dB.
Experiments were carried out with FBG and interrogator based on InGaAs
linear array, and the results verified the effectiveness of the new
[show abstract][hide abstract] ABSTRACT: Detection of pollution, inflammable, explosive gases such as methane,
acetylene, carbon monoxide and so on is very important for many areas,
such as environmental, mining and petrochemical industry. Intra-cavity
gas absorption sensing technique (ICGAST) based on Erbium-doped fiber
ring laser (EDFRL) is one of novel methods for trace gas with higher
precision. It has attracted considerable attention, and many research
institutes focus on it. Instrumentation and optimization of ICGAST was
reported in this paper. The system consists of five parts, which are
variable gain module, intelligent frequency-selection module, gas cell,
DAQ module and computer respectively. Variable gain module and
intelligent frequency-selection module are combined to establish the
intra-cavity of the ring laser. Gas cell is used as gas sensor. DAQ
module is used to realize data acquisition synchronously. And gas
demodulation is finished in the computer finally. The system was
optimized by adjusting the sequence of the components. Take experimental
simulation as an example, the absorptance of gas was increased five
times after optimization, and the sensitivity enhancement factor can
reach more than twenty. By using Fabry-Perot (F-P) etalon, the
absorption wavelength of the detected gas can be obtained, with error
less than 20 pm. The spectra of the detected gas can be swept
continuously to obtain several absorption lines in one loop. The
coefficient of variation (CV) was used to show the repeatability of gas
concentration detection. And results of CV value can be less than 0.014.
[show abstract][hide abstract] ABSTRACT: In this paper, a novel method based on simulated annealing algorithm
(SAA) was described for polarization errors suppression in distributed
perturbation sensor based on dual Mach-Zehnder interferometer(DMZI). It
was shown both theoretically and experimentally that the inaccuracy
(+/-100m) of the position of the perturbation is caused by
polarization-induced phase errors. By applying high speed polarization
controller based on SAA, the polarization-induced phase errors were
suppressed and the accuracy of the position of the perturbation is up
[show abstract][hide abstract] ABSTRACT: Through laser ablation process, a diaphragm with mesa structure is fabricated successfully in silicon wafer with Nd:YAG laser machining system. Then the silicon diaphragm is used to make optical fiber Fabry-Perot pressure sensor. The pressure sensing experiment showed the sensor had a good linear response with sensitivity 10.6 nm/kPa at the range 40–240 kPa.
Optical Communications and Networks (ICOCN 2010), 9th International Conference on; 11/2010
[show abstract][hide abstract] ABSTRACT: A polarization-mode dispersion (PMD) measurement system using a pair of polarization-state generators (PSGs) is demonstrated. Based on the saturation characteristics of magneto-optic rotators, the PSG can be digitally controlled, ensuring high-speed and highly repeatable generation of five distinct polarization states. Thus, the PSG can make full use of the advantage of the Mueller matrix method of PMD measurement. The experimental result shows that the system has good measurement repeatability and potential for field testing.
Chinese Optics Letters 06/2010; 8(7):639-641. · 0.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: The article was based on the technology and principle of DWDM, which was widely used in optical fiber communication systems, and made use of filter curve and technology of WDM into multichannel dynamic measurements. The technology of the investigation was based on the passive demodulation technologies. The samling rate of the real-time high-speed mutilchannel fiber Bragg grating monitoring system can reach 200KHz, which can both meet the needs of static and dynamic measurement and achieve the monitoring in dynamic environment. In order to adapt the requirement of static and dynamic measurement, increasing the sampling and transmission speed of the fiber grating demodulation is needed. In this article, the wavelength demodulation range of the system is about 0.7 nm, the precision can be 10~17 pm, and transmission interface is based on the USB 2.0, which speed is fast enough for the use of our monitoring system.
[show abstract][hide abstract] ABSTRACT: Detection of pollution gas is important in environmental and pollution monitoring, which can be used widely in mining and petrochemical industry. Fiber optical spectrum absorption (FOSA) at near-IR wavelength is widely used in gas detection due to its essential advantages. It has attracted considerable attention, and there are several types and methods in FOSA. Wavelength modulation technique (WMT) is one of them, which will improve the gas detection sensitivity dramatically. This technique can be realized by detecting the intensity of the second-harmonic component signal. Intra-cavity laser spectroscopy (ICLS) is another alternative technique for high sensitivity absorption measurement. With an absorber directly placed within the laser cavity, a short absorption cell can be transformed into a high sensitivity system. But the practical sensitivity is obviously less than the theoretical value. The authors did some works in these fields and have obtained some remarkable progress. With broad reflectors instead of FBG as mirror of the cavity and wavelength sweep technique (WST), several absorption spectra of detected gas can be collected. And the detection sensitivity can be enhanced sharply by averaging the results of each spectrum, with acetylene sensitivity less than 100 ppm . When ICLS is used combined with WST and WMT, the detection sensitivity of acetylene can be enhanced further. The sensitivity is less than 75 ppm. By using FBGs as wavelength references, the absorption wavelength of the detected gas is obtained, which can be used to realize gas recognition. The system is capable of accessing into fiber intelligent sensing network.
[show abstract][hide abstract] ABSTRACT: We describe a new algorithm in a cost effective polarization division multiplexing (PDM) system. Without modifying the existing transmitter, receiver electronics, or softwares, we use a special optical scheme to demultiplex the signal multiplexed and improve it with a conjugated gradient algorithm. We experimentally resume the polarization state with a deviation under 5% and the power loss less than 20 dB which proves the feasibility of the polarization control algorithm in the new polarization multiplexing system.
Chinese Optics Letters 10/2008; 6(11):812-814. · 0.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: A novel hand vein recognition algorithm is developed based on multi-resolution wavelet analysis. The texture feature of hand vein can be extracted by three-level wavelet decomposition. Furthermore, K-nearest neighbor (KNN) with support vector machines (SVM) and minimum distance classifier (MDC) are employed for feature matching. Finally, the experiments are respectively performed in identification and verification modes using Tianjin University (TJU) hand vein image database constructed by our group. The results show the feasibility and effectiveness of the proposed method.
Chinese Optics Letters 08/2008; 6(9):657-660. · 0.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: The proper segmentation of the iris image determines the iris recognition accurate to a great extent. Most of the iris images are covered by upper or lower eyelids, thus it is essential to detect the eyelid boundary for improving the iris recognition accuracy furthermore. An eyelid detection method based on maximal connection path is presented in this paper. After the preprocessing of the iris image, the horizontal segmentation operator and image binarization are used to extract the eyelid edge information. The eyelids span the whole image in horizontal direction and the average of vertical gradients is larger in the area with eyelid boundary, therefore, the horizontal distance of the connection area with eyelid boundary should be the longest one in the edge image. In use of this feature, the candidate edge points of eyelid boundary are detected. Eventually, the eyelid boundaries are modeled with the parabola curves. The algorithm performance is tested in CASIA Iris Database, and experiment results show that about 0.117 second at speed and 88.9% at precision are reached for the upper eyelid detection, and about 0.078 second at speed and 98.5% at precision for the lower eyelid detection. In comparison with Daugman's method, this algorithm enhances the detection speed largely and shows good accuracy.
[show abstract][hide abstract] ABSTRACT: We derive a generalized expression based on a three-dimensional (3-D)
model to fully describe the dependence of the nonreciprocity in a fiber
coil caused by temperature gradient along the axial, radial, and
circumferential directions respectively. We use the finite element
analysis method to numerically solve the partial differential equations
describing heat transfer in the fiber coil and obtain the rate and
angular errors induced by the thermal transient effect with a better
accuracy. We show that the 3-D model can describe the thermal transient
effects induced by both the symmetrical and asymmetrical temperature
gradients, which is not possible using the traditional two-dimensional
model. Finally, we validate the ability of the 3-D model for predicting
the thermal transient behavior in the fiber coil by comparing numerical
and experimental results. The 3-D model proves useful for the
development of a testing system capable of characterizing symmetrical
and asymmetrical temperature transient effects in the fiber gyro coil.