Jiageng Chen

Ultrahigh resolution optical fiber strain sensor using dual Pound–Drever–Hall feedback loops

We present an ultrahigh resolution optical fiber strain sensor with a broad frequency range from quasi-static to several hundred hertz. The sensor consists of a π-phase shifted fiber Bragg grating for strain sensing and a fiber Fabry-Perot interferometer as reference. The laser carrier and sideband are locked to the reference and sensing elements, respectively, via two individual feedback loops, in which the Pound-Drever-Hall technique is employed to generate the error signals. The sampling rate is up to 500 samples/s in the demonstrational experiments, only limited by the updating rate of the frequency counter. The strain resolution exhibits a 1/f characteristic in the bandwidth of 0.01-250 Hz, and is better than 0.01 nϵ at 10 Hz with a dynamic range up to 149 dB. Compared with the traditional static strain sensors, the proposed sensor shows a great improvement in both resolution and sensing bandwidth, and can be a powerful tool for geophysical applications.

Sub-Nano-Strain Multiplexed Fiber Optic Sensor Array for Quasi-Static Strain Measurement

This letter presents a high resolution multiplexed strain sensor for quasi-static strain measurement based on π-phase-shifted fiber Bragg gratings (π-PSFBGs). The sensor array is composed by four π-PSFBGs in parallel with different delay lines, and a time-division multiplexing scheme is proposed to interrogate the π-PSFBGs in turn. The Pound-Drever-Hall technique and the sideband interrogation method are employed to improve the resolution and the sampling rate. In the demonstrational experiment, three-channel quasi-static strain sensing is realized with a resolution better than 0.4 n and a sampling rate of 100 samples/s.

Multiplexed sub-nano resolution quasi-static strain sensor based on transient response of Fabry-Perot interferometers

We present a multiplexed quasi-static strain sensor with sub-nano resolution using fiber Fabry-Perot interferometers (FFPls). The FFPls are connected in ladder structure with cascaded couplers and delay fibers for multiplexing, and their transient response excited by laser pulses are acquired to distinguish the resonant frequencies of each FFPI. An electro-optical system based on acousto-optic modulator is employed to interrogate the sensor array. In the demonstrational experiment, 3-channel strain measurement with resolutions better than 0.2 nε/Hz½ in frequency band from 0.1 Hz to 100 Hz is realized.

Coherent Pound-Drever-Hall technique for high resolution fiber-optic strain sensor at very low light power

Pound-Drever-Hall (PDH) technique has been widely adopted for ultrahigh resolution fiber-optic sensors, but its performance degenerates seriously as the light power drops. To solve this problem, we developed a coherent PDH technique for weak optical signal detection, with which the signal-to-noise ratio (SNR) of demodulated PDH signal is dramatically improved. In the demonstrational experiments, a high resolution fiber-optic sensor using the proposed technique is realized, and nε-order strain resolution at a low light power down to −43 dBm is achieved, which is about 15 dB lower compared with classical PDH technique. The proposed coherent PDH technique has great potentials in longer distance and larger scale sensor networks.

High resolution optical fiber sensor for quasi-static strain measurement by strain-temperature discrimination

A high resolution quasi-static strain sensor based on a novel scheme for strain and temperature discrimination has been developed. Within 16000s measurement, resolutions of 0.025 με in strain and 0.0019 ° in temperature are achieved.

Time-domain multiplexed high resolution fiber optics strain sensor system based on temporal response of fiber Fabry-Perot interferometers

We developed a multiplexed strain sensor system with high resolution using fiber Fabry-Perot interferometers (FFPI) as sensing elements. The temporal responses of the FFPIs excited by rectangular laser pulses are used to obtain the strain applied on each FFPI. The FFPIs are connected by cascaded couplers and delay fiber rolls for the time-domain multiplexing. A compact optoelectronic system performing closed-loop cyclic interrogation is employed to improve the sensing resolution and the frequency response. In the demonstration experiment, 3-channel strain sensing with resolutions better than 0.1 nε and frequency response higher than 100 Hz is realized.

Ultrahigh Resolution Fiber Bragg Grating Sensors for Quasi-Static Crustal Deformation Measurement

Recently developed ultrahigh resolution optical fiber grating sensors provide powerful tools for crustal deformation monitoring thanks to their unique advantages such as high resolution, low cost, easy deployment, and capability of remote and multiplexed sensing. This paper reviews the development of several types of fiber-optic sensors with ultrahigh resolution in quasi-static domain, including a fiber Bragg grating sensor interrogated with a narrow-linewidth wavelength-sweeping laser, a fiber grating based Fabry–Perot interferometer sensor by using Pound–Drever–Hall technique, sensors interrogated with sideband interrogation method, and the realization of time division multiplexed ultrahigh resolution fiber sensors. The implementation of fiber grating sensors for in situ measurement of crustal deformation are also introduced.

0.1-nano-strain resolution fiber optic sensor for quasi-static strain measurement with 1 kS/s sampling rate

We present a newly developed high performance fiber optics sensor for quasi-static strain measurement. The sensor consists of a piece of π-phase shifted FBG for static strain sensing, and fiber Fabry-Perot interferometer for reference, interrogated by an improved sideband interrogation method with real-time feedback loops. Strain resolution of 0.12 nano-strain was achieved with sampling rate up to 1 kS/s in laboratory experiments. Compared with previous sensor systems, the proposed method shows great improvement in the sensing rate as well as the resolution.

Optical fiber temperature sensor with mK resolution and absolute frequency reference

We reported an optical fiber based temperature sensor with mK-order resolution, wide temperature range and excellent long term stability. The sensor composes of a fiber Bragg grating (FBG) as the sensing element, an HCN gas cell for absolute frequency reference. A distributed feedback diode laser with current modulation is used as the light source. To overcome the frequency-sweep nonlinearity of the laser, an auxiliary Fabry-Perot interferometer with free spectrum range of 10 MHz is employed. A cross-correlation algorithm is employed to calculate the center frequency difference between the FBG and the gas cell. With the proposed configuration, a temperature resolution of 0.41 mK was demonstrated in experiment. To the best knowledge, this is the first time that an mK order temperature resolution has been achieved by optical fiber sensor.