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31.
YANG Ruimu;DONG Xiaopeng 《光子学报》2023,52(8):52-63
Fiber optic Extrinsic Fabry-Perot Interferometers （EFPI） are frequently utilized in many acoustic sensing scenarios due to their simple structure, ease of fabrication, high sensitivity, high phase consistency, and strong resistance to electromagnetic interference. However, the cavity length of the EFPI sensor is susceptible to environmental variables such as temperature and air pressure, and the drifting of the orthogonal working point caused by the change of cavity length will lead to signal fading and distortion. Nevertheless, several demodulation methods are less practical or even ineffective when dealing with small signals： Dual-wavelength method for Mach-Zehnder interferometer is inconvenient to apply to the EFPI demodulation; the Ellipse-Fitting Algorithm's （EFA） Lissajous figure will degenerate into a straight line for small signals, and there are also the disadvantages of poor real-time performance and slow demodulation speed; the second-order Differentiate-and-Cross-Multiply （DCM） operation has wide applicability, but the Direct Current （DC） term must be accurately removed, for small signals, the removal of DC term is difficult; the Bessel method has the same difficulties as DCM, and it can only demodulate single-frequency signals; The method of using tunable laser feedback to control the orthogonal working point has the drawback of high cost, and lasers with wavelength scanning function have high requirements for hardware reliability; Phase Generated Carrier （PGC） technology requires a complex carrier modulation system with a limited frequency response range, and the system is complex and large when PGC uses piezoelectric transducer to generate phase carriers. In contrast, intensity demodulation has the advantages of a linear transfer function, simple signal processing, high sensitivity and is suitable for the detection of high-speed and small signal. JIANG Yi et al. proposed a Symmetrical Demodulation Method （SDM） suitable for unstable cavity length and unknown cavity length, which constructs two equal interference phase differences between the three output signals by selecting specific three wavelengths, and then recovers the phase of the signal through mathematical operations. This method has the advantages of large dynamic range and simple operation, and it is more suitable for the detection of large signals. However, in the case of small signals, the SDM algorithm may lead to increased noise and error in the demodulation result.If the wavelength of the light source is 1 550 nm, the interference phase of EFPI changes 0~2π, corresponding to the cavity length variation range of 775 nm. When the cavity length change caused by vibration is less than 30.11 nm, that is, the radian value in the interference phase is less than 0.22 rad, the approximate error of ![]()
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32.
REN Qianyu;JIA Pinggang;QIAN Jiang;WANG Jun;LIU Wenyi;XIONG Jijun 《光子学报》2022,51(9):188-197
Fiber-optic Fabry-Pérot sensors have a wide range of applications, including aerospace, large-scale construction, oil collection, and many other fields. In many cases, dynamic parameters, such as dynamic pressure, vibration, acoustics, and ultrasonics are required to be measured. In order to measure these parameters, a variety of fiber-optic Fabry-Pérot sensors are produced. In some fields, the multi-cavity fiber-optic Fabry-Pérot sensor is inevitable for some advantages. For example, in the field of aerospace engine testing, dynamic pressure is a key parameter that often needs to be measured, and the micro-electro-mechanical system external Fabry-Pérot interferometer pressure sensors with multiple Fabry-Pérot cavities are often designed for aerospace engine pressure measurement due to their consistency and airtightness. Moreover, multi-cavity Fabry-Pérot sensors are good candidates for multi-parameter measurements. The different Fabry-Pérot cavities with different lengths are used to measure different parameters to achieve multi-parameter measurement. Therefore, multi-cavity Fabry-Pérot sensors are becoming increasingly important in engineering applications. However, extracting dynamic signals in multi-cavity Fabry-Pérot sensors is a challenge. In this paper, an improved passive three-wavelength phase demodulation technology based on a broadband light source is proposed for dynamic interrogation of the shortest cavity in a multi-cavity Fabry-Pérot sensor. According to the principle of low coherence interference, when the optical path difference introduced by the Fabry-Pérot interferometer is less than the coherent length received by the photodetectors, interference occurs. In contrast, when the optical path difference introduced by the Fabry-Pérot interferometers is longer than five times the coherence length, the interference phenomenon becomes insignificant and it can be considered that the interference disappears. Therefore, a flat-top amplified spontaneous emission light source and three broadband fiber filters were used to ensure the interference only occurs in the short cavity. The quadrature signals are obtained by three filtered optical signals with arbitrary cavity length using an improved phase calibration algorithm. The established signal calibration algorithm allows the demodulation technology for arbitrary short cavity lengths and arbitrary central wavelength. The demodulation technology can work without the direct-current voltages, so the demodulation system can reduce the fiber-optic disturbance noise. The arctangent algorithm is established to extract vibration signals by the quadrature signals. Compared with the previous phase calibration algorithm, the phase calibration algorithm proposed in the paper is more concise. The experimental system was consisted of a reflective bracket, a light source, a multi-cavity Fabry-Pérot interferometer, a fiber-optic coupler, three fiber filters, three photodiodes, an analog-to-digital conversion and a personal computer. The light from the light source passed through the fiber-optic coupler to the multi-cavity Fabry-Pérot interferometer. A multi-cavity Fabry-Pérot interferometer consists of a gradient-index lens and a 300-μm-thick double-polished quartz glass fixed on a piezoelectric transducer. The light reflected from the interferometer passed through the coupler and through the filters to the photodiodes. Three interferometric signals at each center wavelength were obtained using three photodiodes. The voltage signals were collected by analog-to-digital conversion and transmitted to a personal computer. The feasibility of the demodulation algorithm was verified by simulations and experiments. The experimental results show that the vibration signals with a frequency of 1 kHz and peak-to-peak amplitude of 2.6 µm is successfully extracted with different Fabry-Pérot cavity length, which proves that the three-wavelength demodulation algorithm can be used for optical fiber multi-cavity Fabry-Pérot sensor with arbitrary short cavity length. The demodulation speed is 500 kHz and the demodulation resolution is 0.25 nm. The demodulation technology makes it possible to extract dynamic signals in a multi-cavity Fabry-Pérot sensor. If the spectrometer is used at the same time, the dynamic signal measured by the short cavity and the static signal measured by the long cavity can be interrogated at the same time. This demodulation technology has the advantages of a compact system, low cost, fast speed and high robustness, illustrating its bright potential for multi-cavity Fabry-Pérot sensors. 相似文献
33.
光纤水听器是水声研究领域的关键技术,在实际应用中具有显著优势,广泛应用于AUV导航定位、资源勘探、海水警戒等场景.光纤水听器将声信号转化为光信号传播,在接收信号时就需要对光信号进行解调提取出声压信号.总结了几种常用的信号解调算法及关键技术,包括PGC解调法、3×3耦合器解调法和外差解调法;介绍了各种解调算法的基本原理和... 相似文献
34.
Multi-address coding (MAC) lidar is a novel lidar system recently developed by our laboratory. By applying a new combined technique of multi-address encoding, multiplexing and decoding, range resolution is effectively improved. In data processing, a signal enhancement method involving laser signal demodulation and wavelet de-noising in the downlink is proposed to improve the signal to noise ratio (SNR) of raw signal and the capability of remote application. In this paper, the working mechanism of MAC lidar is introduced and the implementation of encoding and decoding is also illustrated. We focus on the signal enhancement method and provide the mathematical model and analysis of an algorithm on the basis of the combined method of demodulation and wavelet de-noising. The experimental results and analysis demonstrate that the signal enhancement approach improves the SNR of raw data. Overall, compared with conventional lidar system, MAC lidar achieves a higher resolution and better de-noising performance in long-range detection. 相似文献
35.
对一种基于马赫-曾德尔和萨格纳克混合干涉仪原理的分布式光纤泄漏检测系统调制解调技术进行研究,对PGC解调技术进行理论分析。针对所选泄漏分布式光纤传感特点设计了PGC解调硬件电路,并对PGC解调电路进行了测试。实验中待测信号为0~50 kHz,载波频率为300 kHz,截止频率为50 kHz, 移相后与待测信号的相关系数达到0.95,谐波失真小于3%,泄漏源位置为7.865 km,泄漏检测定位系统绝对定位误差为235 m,相对定位误差为2.35%。本解调定位系统具有稳定性和抗干扰性。 相似文献
36.
干涉型光纤传感器相位生成载波技术研究与改进 总被引：3，自引：3，他引：0
对干涉型光纤传感器的相位生成载波解调技术进行了研究.对PGC算法进行了数学推导和仿真计算,对数字低通滤波器进行了详细分析,给出了其影响PGC解调性能的原因及数字滤波器的设计方法.讨论了传感器干涉光强对PGC算法输出结果的影响,提出了改进的PGC算法,该算法可以有效的实现自动增益控制,消除干涉光强漂移对解调的影响,并大大减小由干涉光强引入的系统噪音;还可以在有限阶数低通滤波器的情况下,极大的增加系统可解调的大信号幅度,提高系统动态范围12 dB以上. 相似文献
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