Mr. Jian Fang Profile

Jian Fang

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Proceedings Article | 29 March 2023 Paper

A time-domain network for laser speech bandwidth extension

Jian Fang, Shenglai Zhen, Xin Chen, Shanjing Tao, Tao Lv, Benli Yu

Proceedings Volume 12594, 125940Q (2023) https://doi.org/10.1117/12.2671462

KEYWORDS: Education and training, Signal to noise ratio, Convolution, Phase reconstruction, Laser frequency, Image restoration, Performance modeling

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In the process of signal acquisition by laser microphones, the high frequency components of speech are missing due to nonadditive distortion. In this paper, we proposed an end-to-end speech bandwidth extension (BWE) approach to recover narrow-band speech acquired by laser microphones. Our preliminary research showed that speech enhancement algorithms based on log-magnitude spectrogram in the frequency domain could not achieve satisfactory performance for this task. Therefore, we designed a speech BWE model in time domain, this model was modified by Wave-U-Net structure, we introduced the time convolution module (TCM), the dilation of convolution is helpful to increase receptive field, improves speech long-range correlation, at the same time introduced the multi-resolution loss function (L_MSTFT) instead of the mean square error (MSE), the time-domain Wave-U-Net method avoided the decoupling of magnitude and phase in the frequency domain. The results showed that the signal-to-noise ratio (SNR) of speech was improved significantly compared with approach in the frequency domain, and obtained elaborate high-frequency components than frequency-domain convolutional recurrent network (CRN). We chose laser speech to test the model in an actual scene, which further verifies the practicability of the structure through the speech spectrum analysis, and had better performance and generalization ability than the original Wave-U-Net model.

Proceedings Article | 6 March 2023 Paper

Analysis of multi-beam interference in heterodyne detection system

Shanjing Tao, Shenglai Zhen, Jian Fang, Xin Chen, Benli Yu

Proceedings Volume 12553, 125530R (2023) https://doi.org/10.1117/12.2667728

KEYWORDS: Demodulation, Vibration, Stray light, Heterodyning, Laser beam diagnostics, Optical components, Laser Doppler velocimetry, Distortion, Vibrometry, Signal to noise ratio

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The Laser Doppler Vibrometry (LDV) system can measure parameters such as amplitude, velocity and acceleration of micro-vibrating objects. However, in the actual measurement process, in addition to the probe beam and the reference beam, as the surface roughness of the measured object increases and the diffuse reflectance decreases, the echo energy of the laser will decrease rapidly. This phenomenon can be extended to heterodyne detection systems. Due to the limitation of optical devices, the third beam (ie stray beam) caused by parasitic reflection is unavoidable. At the same time, the third beam has a certain intensity and phase distribution, which seriously affects signal demodulation of micro-vibrating objects. This paper analyzes the effects of multi-beam interference competition in heterodyne demodulation systems. Mathematical analysis shows that the interference competition depends on the signal amplitude, the interferometric light intensity ratio and the relative phase difference. Through mathematical derivation and simulation verification, the following conclusions can be drawn: when the relative phase difference is π rad, when the ratio of light intensity between the probe light and the stray light is controlled to tend to one, the simple harmonic motion with an amplitude of 1 nm is demodulated, and the amplitude can be observed to be nearly 200 times of the enhancement effect. For micro vibration with different amplitudes, the simulation shows that when the amplitude coefficient is π, the demodulation amplitude does not have amplification effect, and the amplitude coefficient is π can be used as the limit of demodulation amplitude amplification. This method has great application value in the high-sensitivity measurement direction of micro-vibrating objects.

Proceedings Article | 26 January 2021 Paper

Simulation and optical optimization of deep-sea hydrothermal velocity measurement system

Qianjing Xiong, Wenli Peng, Jian Fang, Benli Yu, Shenglai Zhen

Proceedings Volume 11767, 117670N (2021) https://doi.org/10.1117/12.2592357

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The deep-sea hydrothermal velocity measurement system based on laser Doppler is mainly used for in-situ accurate measurement of deep-sea hydrothermal velocity. Due to the high-pressure environment of the deep-sea hydrothermal area, the optical window of the measurement system will be deformed under pressure, attenuating the energy of the scattered light received by the system. The system selects sapphire as the compressive window material, uses finite element analysis to simulate the compressive deformation of the optical window at a sea depth of 4000 meters (40MPa), and fits the deformed optical window to the optical design software. The simulation result shows the deep-sea high pressure will reduce the energy utilization rate of the measurement system by 43%. Through the optimized design of the optical system, the laser intensity utilization rate has been increased by 52.2% to meet actual application requirements.

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