Hongqiao Wen

A time- and wavelength-division multiplexing sensor network with ultra-weak fiber Bragg gratings

A time- and wavelength-division multiplexing sensor network based on ultra-weak fiber Bragg gratings (FBGs) was proposed. The low insertion loss and the high multiplexing capability of the proposed sensor network were investigated through both theoretical analysis and experimental study. The demodulation system, which consists of two semiconductor optical amplifiers and one high-speed charge-coupled device module, was constructed to interrogate 2000 serial ultra-weak FBGs with peak reflectivity ranging from -47 dB to -51 dB and a spatial resolution of 2 m along an optical fiber. The distinct advantages of the proposed sensor network make it an excellent candidate for the large-scale sensing network.

Reflectivity measurement of weak fiber Bragg grating (FBG)

One method based on the end-face reflection as a reference was used to measure weak grating reflectivity of 0.01%–1%. For measuring ultra-weak grating reflectivity, the grating group with an identical wavelength was used. By using anhydrous alcohol and deionized water as the reflecting medium, the singlepulse FBG reflectivity of a highly doped-Ge photosensitive fiber was calculated to be about 0.747% and 0.739%, respectively; and the single-pulse FBG reflectivity of ordinary SMF fiber was about 0.016% and 0.015%, respectively. The consistent results by the two different reflecting media showed that the end-face reflection method on the grating group was feasible.

Interrogation system for a sensor array with 1310-nm band ultra-weak fiber Bragg gratings

Abstract. An interrogation system for the time-division multiplexed sensor array based on 1310-nm band ultra-weak fiber Bragg gratings (FBGs) was proposed in this study. Power spectral density was introduced to budget the optical power and evaluate the interrogation capability of the proposed system. The proposed system consists of one tunable laser and two semiconductor optical amplifiers, where the former scans the wavelength, and the latter modulates the light and separates the reflected pulses from different FBGs through delayed switching. Up to 1000 serial FBGs, with a peak reflectivity of −40 to −45  dB and a spatial resolution of 5 m along an optical fiber, were interrogated to demonstrate the feasibility of the interrogation system.

Distributed acoustic sensing system based on continuous wide-band ultra-weak fiber Bragg grating array

A distributed acoustic sensing system (DAS) with low-coherence ASE and Michelson interferometer based on continuous width-band ultra-weak fiber Bragg grating (UW-FBG) array is proposed and experimentally demonstrated. The experimental result shows that the proposed system has better performance in detecting acoustic waves than the conventional hydrophone.

Dual-fiber-Bragg gratings accelerometer for the detection of geosound caused by debris flow

Abstract. The cantilever-beam accelerometer based on dual-fiber-Bragg gratings (FBGs) is proposed to detect the geosound caused by debris flow. The structure and working principle of the accelerometer are demonstrated. Dual FBGs are introduced to improve the sensitivity and frequency response of the accelerometer. By using a bend insensitive optical fiber and ultrathin coating, the sensitivity and serial multiplexing performance of the sensor are improved remarkably. Experimental results show that the accelerometer, with a sensitivity of 900  pm/g and the natural frequency of 280 Hz, can effectively detect the geosound caused by debris flow.

Distributed acoustic sensing system using an identical weak fiber Bragg grating array

We propose and experimentally demonstrate a distributed acoustic sensing system using an identical weak fiber Bragg grating array. Phase, frequency and location information of vibration can be demodulated by using a path-match interferometry method. 3×3 coupler demodulation technique is employed to eliminate signal fading in interferometer. Experiments on detecting acoustic wave generated by PZT show that the system is capable of measuring vibrations of up to 1000 Hz over 1.6 km with 2.5m spatial resolution.

An Interrogation System Based on Two Semiconductor Optical Amplifiers for Weak Fiber Bragg Gratings

An interrogation system based on two semiconductor optical amplifiers for weak fiber Bragg gratings(FBGs) was proposed in this study. The first Semiconductor Optical Amplifier (SOA) was used to modulate the light and the second SOA separated the signal through delayed switching. The proposed system has lower insertion loss and higher spatial resolution, and can interrogate time-division and wavelength-division multiplexed FBG array. Up to 50 FBGs, with a reflectivity of 0.2% and a spatial resolution of 5m along the optical fiber, were distinguished to demonstrate the interrogation system.