Guangyao Yang

Long-Range Distributed Vibration Sensing Based on Phase Extraction From Phase-Sensitive OTDR

Distributed fiber-optic vibration sensors based on phase-sensitive optical timedomain reflectometry (Φ-OTDR) have found many applications in various fields. In this paper, we analyze the phase noise of Φ-OTDR, which is the main limiting factor of the measurement range. We found that the laser phase noise and phase extraction error caused by the intensity noise in photodetection contribute to the total phase noise. By introducing a series of auxiliary weak reflection points along the fiber, we develop a phase-noise-compensated Φ-OTDR and realize a long-range distributed vibration sensing based on the phase extraction. Furthermore, a statistical analysis was proposed to maintain the vibration measurement sensitivity along the whole fiber. In the experiment, vibrations at 30 km were measured with a linear response, which confirmed the validity of our proposed system.

Sub-THz-range linearly chirped signals characterized using linear optical sampling technique to enable sub-millimeter resolution for optical sensing applications

Pulse compression technique is a particularly competitive method that enables both high spatial resolution and dynamic range in coherent radar and distributed fiber sensing systems. Up to now, the frequency bandwidths of most pulse compression techniques are restricted to tens of GHz. In this paper, we propose an all-optic sub-THz-range linearly chirped optical source and a large-bandwidth detection system to characterize it. Taking advantage of the chromatic dispersion effect, ultrashort optical pulses are stretched to be ~10 ns linearly chirped pulses with sub-THz range, which yields a large time-bandwidth product of 4500, a high compression ratio of 4167 and a chirp rate of 45 GHz/ns. The generated waveform is characterized with high precision thanks to the large detection bandwidth of linear optical sampling technique. A spatial resolution of 120 μm and an extinction ratio of 20.4 dB is demonstrated by using this technique, which paves the way for ultra-high spatial resolution and long range sensing applications such as LIDAR and optical reflectometry.

Strain Dynamic Range Enlargement of Slope-Assisted BOTDA by Using Brillouin Phase-Gain Ratio

A novel technique to enlarge the dynamic range of strain measurement for slope-assisted Brillouin optical time domain analysis (SA-BOTDA) is proposed by introducing a new parameter called Brillouin phase-gain ratio, which combines Brillouin phase shift and Brillouin gain. With the new technique, the dynamic range of strain measurement can be enlarged, and the pump-power-dependency problem mitigated. In the experiment, a 100-MHz frequency span of linear slope is demonstrated with a 25-ns pump pulse, which is 3.3 times of that in conventional SA-BOTDA, and a dynamic strain with a large amplitude of about 1000

Increasing the frequency response of direct-detection phase-sensitive OTDR by using frequency division multiplexing

\mu \varepsilon

Dynamic Strain Sensing by using Phase-Gain Ratio in Slope-Assisted Brillouin Optical Time Domain Analysis

is successfully measured.

Fiber-optic distributed acoustic sensors (DAS) and applications in railway perimeter security

The frequency division multiplexing (FDM) technique is firstly introduced into a direct-detection phase-sensitive OTDR to improve the distributed fiber acoustic sensing performance by using a frequency step sweeping laser source and a dual probe pulse scheme. By using FDM technique, a 40 kHz sampling rate to vibration is realized with a 10 km measurement range, which implies the tradeoff between the frequency response and the measurement range is broken. In experiment, a 6 kHz vibration is successfully measured.

Brillouin gain spectrum shape manipulation for enlarging measurement range of dynamic strain using slope-assisted BOTDA

We introduce the phase-gain ratio into slope-assisted BOTDA to enhance the performance of dynamic strain measurement. A linear slope is achieved with a doubled dynamic range of strain measurement, and the pump-power-dependency is also suppressed.

Distributed Fiber-Optic Vibration Sensing Based on Phase Extraction From Optical Reflectometry

The paper introduces the DAS system based on advanced phase-sensitive optical time domain reflectometry (φ-OTDR) with fading noise suppressed. Besides, the DAS system based on time-gated digital optical frequency domain reflectometry (TGD-OFDR) and its improved systems are introduced. The application of DAS in railway perimeter security is introduced at the end of the paper.

A low-cost, system-on-chip for Optical Time Domain Reflectometry (OTDR)

We propose a novel method to improve the performance of slope-assisted BOTDA by manipulating the shape of Brillouin gain spectrum. By using this method, we enlarge the measurement range of dynamic strain to 2.4 times comparing with conventional methods.

Polarization fading elimination in phase-extracted OTDR for distributed fiber-optic vibration sensing

Distributed fiber-optic vibration sensing based on phase extraction from optical reflectometry is discussed in this paper. The principles on the phase extraction from coherent phase-sensitive optical time-domain reflectometry and time-gated digital optical frequency-domain reflectometry are introduced, and the experimental results of distributed vibration measurements based on the two techniques are demonstrated. To have a better understanding on the performance of the techniques, the phase extraction noise in the phase extraction process is analyzed. To solve the problem of existing measurement dead zones, the influence of Rayleigh fading phenomenon is investigated, and a solution of using statistical analysis to overcome this drawback is introduced and experimentally verified. With these improvements, long-range nondead-zone distributed vibration sensing techniques with linear response to external vibration signals based on phase extraction from optical reflectometry are realized.