Zaixuan Zhang

Acoustic vibration sensor based on nonadiabatic tapered fibers

A simple and low-cost vibration sensor based on single-mode nonadiabatic fiber tapers is proposed and demonstrated. The environmental vibrations can be detected by demodulating the transmission loss of the nonadiabatic fiber taper. Theoretical simulations show that the transmission loss is related to the microbending of the fiber taper induced by vibrations. Unlike interferometric sensors, this vibration sensor does not need any feedback loop to control the quadrature point to obtain a stable performance. In addition, it has no requirement for the coherence of the light source and is insensitive to temperature changes. Experimental results show that this sensing system has a wide frequency response range from a few hertz to tens of kilohertz with the maximal signal to noise ratio up to 73 dB.

Compact micro-displacement sensor with high sensitivity based on a long-period fiber grating with an air-cavity

We proposed and experimentally demonstrated a compact micro-displacement sensor with high sensitivity based on a long-period fiber grating (LPG) with an air-cavity. The sensor head is obtained by composing an air-cavity with the ends of a LPG and a single mode fiber (SMF). The wavelength shift of the LPG has a linear relationship with the length of the air gap which agrees well with the theoretical analysis. The experimental results show that the sensitivity is ~0.22 nm/µm within the micro-displacement range of 0 to 140 µm.

Simple Fresnel Reflection-Based Optical Fiber Sensor for Multipoint Refractive Index Measurement Using an AWG

A simple Fresnel reflection-based optical fiber refractometer for simultaneous multipoint measurement based on an arrayed-waveguide grating (AWG) is proposed. The AWG is used as a demultiplexing unit and different channel fibers of the AWG work as different sensor heads. Every channel light divided by the AWG is marked with a different central wavelength, and its reflection from its fiber-solution interface is used to measure the RI of the inserted solution. By using the AWG unit, a simple and compact structure sensor for multipoint sensing is achieved. Experiment results show that the sensor works well and the average sensitivity is ~ 01.9 dB/RIU for refractive indices, in the range of 1.33-1.42.

Optimum design of 6-km LD-distributed optical fiber Raman photon sensor (DOFRPS) system

In the 6km DOFRPS system, the 1550nm LD is excited photon source. The spontaneous Raman scattering photon are carriers of temperature signal and the Rayleigh scattering photon are carriers of strain and pressure signal. On the 6km optical fiber, the 3000 point temperature, strain and pressure are measured on time and the position of measured local domain have been determined by OTDR technique. The optimum design of 6km LD DOFRPS system and the configuration of the system are discussed in the paper.

Optimum design of 30-km long-distance distributed optical fiber Raman temperature sensor system

A 30km long distance distributed optical fiber Raman temperature sensor (DOFRTS) system has been made, it use new measuring temperature principle of optical fiber amplified anti-Stokes Raman spontaneous scattering. In the system, 1550nm erbium-doped optical fiber laser, a highness speed data acquisition card and signal processing technique are used. By using these technique, the problem of weak signal detection is resolved and signal to noise ratio is increased. All components of system are put into an intellectualized constant temperature box and work in constant temperature condition. Stability and environment adaptability are improved. By appraisal, performance of the system is listed as follows: length of single mode fiber: 31km, temperature rang:0-100°C (can be expanded), temperature measuring uncertainty:±2°C, temperature resolution:0.1°C, measurement time:432s, spatial resolution :3m.

Research of distributed optical fiber Raman gain amplifier

The operation principle of distributed optical fiber Raman gain amplifier has been discussed. The amplification phenomena have been observed in the 1410-nm wavelength range pumped by the 1320-nm solid laser using 23-km single-mode GI optical fiber. The Raman gain is depending on optical fiber interaction length . The optical fiber effective interaction lengths are 15.5 km and 10.5 km when pump pulse peak power are 50W and 30W. The relation between the gain of Raman amplifier and pump power at different effective interaction length of optical fiber is discussed. The Raman gain of optical fiber is 0.62x10-15 m/W during 50W pump power and the effective interaction area of optical fiber is 30 micrometers 2. The effective interaction area of optical fiber is 41.4 micrometers 2 during the pump power is 30W.

Application research of distributed optical fiber temperature sensor in power system

Principles and application of distributed optical fiber temperature sensor (DTS) are introduced. Applications of DTS in power system in Shanghai World Expo project and Shanghai Caojing thermal power plant are studied as examples. Problems and solutions are researched. Test results of the two examples engineering project are listed.

Amplification effect on SBS and Rayleigh scattering in the backward pumped distributed fiber Raman amplifier

The amplification effect on stimulated Brillouin scattering (SBS) and Rayleigh scattering in the backward pumped G652 fiber Raman amplifier (FRA) is studied. The pump source is a 1427.2-nm fiber Raman laser whose power is tunable between 0-1200 mW, and the signal source is a tunable narrow spectral bandwidth (l10 MHz) external cavity laser (ECL). The Rayleigh scattering lines are amplified by the FRA and Stokes SBS lines are amplified by the FRA and the fiber Brillouin amplifier. The total gain of SBS lines is the production of the gain of Raman amplifier and that of Brillouin amplifier. In experiment, the SBS gain is about 42 dB and the saturation gain of 25-km G652 backward FRA is about 25 dB, so the gain of fiber Brillouin amplifier is about 17 dB.

Experimental study of Raman amplification on stimulated Brillouin scattering in the G652 fibers at 1520nm

The forward and backward cascaded stimulated Brillouin scattering(SBS) in the backward pumped S band distributed G652 fiber Raman amplifier have been researched, pumped by the tunable power at 1428nm fiber Raman laser and signal source is a tunable power external cavity laser (ECL) with narrow spectral bandwidth (<100MHz). The threshold power of backward Stokes the first and second stimulated Brillouin scattering SB1- and SB2- in the backward pumped S band distributed fiber Raman amplifier is 5mW and 67.6mW, respectively. The Stokes stimulated Brillouin scattering lines is amplified by fiber Raman amplifier and fiber Brillouin amplifier. The total GA is production of the gain of Raman GR and the gain of Brillouin amplifier GB. GA=GR×GB. In experimental work, the saturation gain of SB1- and SB2- is about 50dB and 65dB respectively and the saturation gain of 25km G652 backward FRA is about 25dB, so the gain of backward fiber Brillouin amplifier SB1- and SB2- are about 25dB and 40dB, respectively. The forward SBS does not obey the common theory that only weakening backward-SBS lines existed, according to conservation of energy and momentum and wave vector selected rule. Because the wave-guide characters weaken the wave vector rule, but the forward transmit sound wave-guide forward Brillouin scattering lines are generated and amplified in S band G652 FRA. The stimulated threshold power of the forward first Stokes SBS (SB1- ) in the backward pumped FRA is 6.6mW. In experimental work, the saturation gain of SB1- is about 49dB and the saturation gain of 25km G652 backward FRA is about 10dB, so the gain of SB1- in the forward fiber Brillouin amplifier is about 39dB.

Forward cascaded stimulated Brillouin scattering (SBS) in an S-band distributed G652 fiber Raman amplifier

The cascaded forward stimulated Brillouin scattering (SBS) in the S band distributed G652 fiber Raman amplifier forward pumped and backward pumped by the tunable power fiber laser and signal source is a tunable narrow spectral bandwidth(<100MHz)ECL have been studied. Forward SBS does not obey the common theory, that only weaken backward-SBS lines existed, according to conservation of energy and momentum and wave vector selected rule. Because the wave-guide character weaken the wave vector rule. The forward transmit sound wave-guide Brillouin scattering lines are generated and amplified in FRA. Forward SBS that is amplified phenomena of transmit sound wave Brillouin scattering in the FRA, during pump power is larger than the threshold value of SBS in a S band G652 FRA. The 2 orders Stokes forward Brillouin lines are present during forward pump power of FRA is 920mW, the pump power of BP line is 7.7dBm and the FRA gain is 15.05dB, the power of first order Brillouin lines is smaller than the second Brillouin scattering line. When pump power is further increased, cascaded SBS lines and comb profile are observed. The even order SBS lines is stronger than odd order SBS lines, The odd order SBS lines are named Brillouin- Rayleigh scattering lines.