Laser & Optoelectronics Progress, Volume. 59, Issue 23, 2300002(2022)
Research Progress of φ-OTDR Noise Reduction Processing
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![φ-OTDR sensing system based on few-mode fiber space division multiplexing[30]](/Images/icon/loading.gif){kind=icon}
Fig. 7. φ-OTDR sensing system based on few-mode fiber space division multiplexing[30]
Table 1. Classification and definition of various main noises
View tableTable 1. Classification and definition of various main noises
Classification Cause of noise Whether it is the main component of system noise Coherent noise RBS caused by phase length or cancellation of pulse light detected at different positions of optical fiber yes Polarization noise when the polarization state of the pulse light is orthogonal, the interference light intensity disappears completely yes Common mode noise caused by frequency drift of laser source or environmental change along the optical fiber no Light source noise caused by unsatisfactory bandwidth of light source or insufficient extinction ratio no
Table 2. Typical coherent fading suppression techniques
View tableTable 2. Typical coherent fading suppression techniques
Ref. Suppress result Advantage Disadvantage Room of improvement ［ 15 ］compared with the amplitude extraction method, SNR is increased by 11 dB it is easy to obtain the spatial information of vibration points by using the virtual peak discrimination method only the false alarm is eliminated, and high fidelity signal reconstruction is not fundamentally realized strengthen the screening of discriminant points to achieve correct virtual peak reconstruction ［ 19 ］SNR is up to 26 dB, and the spatial resolution is close to 5 m system has low complexity and low cost the accuracy of time control gate circuit is not ideal can be combined with high-speed camera ［ 20 ］SNR increased by 7.1 dB, measurement time halved frequency drift compensation by spectrum extraction spatial resolution of the system is not ideal introduction of less mode fiber for light wave transmission ［ 30 ］phase error caused by interference fading is completely eliminated system structure is simple by combining space division multiplexing and few mode fiber transmission distance is low, and the uneven scattering points of the optical fiber are not considered consider combining multimode fiber with frequency division multiplexing technology
Table 3. Typical polarization fading suppression techniques
View tableTable 3. Typical polarization fading suppression techniques
Ref. Suppress result Advantage Disadvantage Room of improvement ［ 32 ］SNR increased by 15 dB polarization dependence of signal intensity using Rayleigh interference structure of the experimental system is complex，and the demodulation signal processing formula is complex introducing polarization multiplexing technology based on orthogonal polarization switching ［ 34 ］polarization fading can be effectively eliminated in sensitive areas combining PMF with SOP for noise reduction interference caused by SOP small circle rotation is not completely eliminated reduce the angle and number of SOP rotations ［ 35 ］insensitive to polarization effect sensor with dual polarization multiplexing polarization diversity sensing structure is not considered introducing time division multiplexing technology into the structure with polarization diversity
Table 4. Typical common mode noise suppression techniques
View tableTable 4. Typical common mode noise suppression techniques
Ref. Suppress result Advantage Disadvantage Room of improvement ［ 38 ］avoid the effect of too many pulses on common mode noise applying the DCM to common mode rejection poor spatial resolution and can not be applied to long-distance sensing can combine radiosonde technology with frequency division multiplexing ［ 39 ］strong signal acquisition capability and low noise signal transmission using Mini-DAS module influence of seabed pressure on the pressure along the optical fiber is not considered for seabed inspection, the entire optical fiber shall be coated with compressive materials
Table 5. Comparison of various types of noise
View tableTable 5. Comparison of various types of noise
Type Whether it is the main component of noise？ Advantage Disadvantage Future direction Coherent noise yes space division multiplexing technology based on few mode fiber coherence of various high-order modes or same order modes of space division multiplexing is too high combination of multi-core fiber and time division multiplexing technology Polarization noise yes technology of transforming single mode fiber into polarization maintaining fiber disturbance caused by different polarization states cannot be eliminated transformation of polarization maintaining fiber using polarization multiplexing technology Common mode noise no Mini-DAS module technology limited light wave signal transmission introducing frequency division multiplexing technology Light source noise no time delay interferometry amplified light source signal frequency is difficult to meet the requirements combining high-speed camera with ultra-low frequency drift light source
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Ke Li, Yandong Gong, Zhuo Zhang. Research Progress of φ-OTDR Noise Reduction Processing[J]. Laser & Optoelectronics Progress, 2022, 59(23): 2300002
Paper Information
Category: Reviews
Received: Oct. 9, 2021
Accepted: Nov. 10, 2021
Published Online: Oct. 11, 2022
The Author Email: Yandong Gong (eydgong@bistu.edu.cn)
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