Optical Fiber Raman Temperature Research Articles

Distributed fiber Raman temperature measurement system based on cumulative average

Distributed optical fiber Raman temperature sensor (DTS) system is a set of measuring principle of Raman scattering light in optical fiber, based on the distributed temperature monitoring system, which uses Raman scattering light in optical fiber temperature and fiber strength state related principle for real-time monitoring of temperature. A set of 9 km optical fiber Raman temperature measurement system was designed, the Stokes and the anti-Stokes light was collected by data acquisition card, the temperature was accumulated and averaged at the computer terminal, and the weak signal was extracted from the system noise to increase its signal-to-noise ratio.With accumulative average of 16 000 times, the accuracy of temperature measurement can reach to ±2℃.

Field test of optical and electrical fire detectors in simulated fire scenes in a cable tunnel

This paper presents the testing results of three types of fire detectors: electrical heat sensing cable, optical fiber Raman temperature sensing detector, and optical fiber Bragg grating (FBG) temperature sensing detector, in two simulated fire scenes in a cable tunnel. In the small-scale fire with limited thermal radiation and no flame, the fire alarm only comes from the heat sensors which directly contact with the heat source. In the large-scale fire with about 5 °C/min temperature rising speed within a 3-m span, the fire alarm response time of the fiber Raman sensor and FBG sensors was about 30 seconds. The test results can be further used for formulating regulation for early fire detection in cable tunnels.

Spatial Resolution Improvement of Distributed Optical Fiber Raman Temperature Sensor System by Using Amplitude Modification Algorithm

Spatial resolution is an important parameter in distributed optical fiber Raman temperature sensor system (DOFRTS). In this paper, a 10 kilometers long DOFRTS with spatial resolution of about 6 meters is constructed. The spatial resolution is limited by electrical bandwidth of the photodetector circuit and the data acquisition part. The abrupt temperature changes along the fiber axis are treated as temporal pulse signals, and a linear amplitude coefficient modification algorithm is used to improve the spatial resolution. The experimental results show that the temperature amplitudes from 3 meters region to 6 meters can be modified accurately. Therefore, a DOFRTS of high spatial resolution but low system cost could be successfully constructed.

一种提高分布式光纤测温系统空间分辨率的线性修正算法

Because of deficient bandwidth,the space resolution of Distributed Optical Fiber Raman Temperature Sensor(DOFRTS) is low.When the sensing length of fiber is close to space resolution,there is no accurate temperature response.For solving the problems,a new linear algorithm is proposed.Firstly,the relationship between Raman ratio and temperature and the characteristics of frequency response are analyzed,and then a mathematical model is built up for this algorithm.A single-mode temperature sensor system for 10 km long is built up,some related experiments are carried out by using the algorithm.Experiment results are consistent with theoretical analysis,the temperature amplitudes of testing fiber from 3 meters to 6 meters are corrected.The temperature measurement accuracy reaches 1℃ and measuring time is 40 seconds.By applying this algorithm,the limit of bandwidth can be overcome effectively and the system cost is cut down obviously,at the same time,space resolution,temperature resolution and measuring time are optimized.

High-power EDFA applied in distributed optical fiber Raman temperature sensor system

In this paper, a high-power erbium-doped fiber amplifier (EDFA) for the temperature sensor system is theoretically designed and experimentally demonstrated. It consists of an erbium-doped fiber that is pumped bidirectionally with two 980-nm high-power laser diodes (LDs). At the EDFA input, an optical isolator (ISO) is used to ensure that the signal pulse transmits forward only. After that, a wavelength division multiplexer (WDM) is employed to combine the forward pump laser (980 nm) and incident optical pulse (1550 nm) into the erbium-doped fiber for direct amplification in the optical domain. At the EDFA output, another WDM couples the backward pump laser (980 nm) into the erbium-doped fiber and outputs the amplified optical pulse (1550 nm) with an ISO followed to isolate the backscattering light. According to this structure, we carried out the experiment in the condition as follows. For 980 nm pump LD, the operating current is 590 mA, and the setting temperature is 25°C. For EDFA, the length of erbium-doped fiber is 12.5 m, and the power of 1550 nm input signal is 1.5mW. As a result, the power of pump LD is 330mW, and the power uncertainty is 0.5%. The power of EDFA output at 1550 nm is 300mW, and the power uncertainty is ± 3mW.

Design of distributed Raman temperature sensing system based on single-mode optical fiber

The distributed optical fiber temperature sensor system based on Raman scattering has developed rapidly since it was invented in 1970s. The optical wavelengths used in most of the distributed temperature optical fiber sensor system based on the Raman scattering are around from 840 to 1330 nm, and the system operates with multimode optical fibers. However, this wavelength range is not suitable for long-distance transmission due to the high attenuation and dispersion of the transmission optical fiber. A novel distributed optical fiber Raman temperature sensor system based on standard single-mode optical fiber is proposed. The system employs the wavelength of 1550 nm as the probe light and the standard communication optical fiber as the sensing medium to increase the sensing distance. This system mainly includes three modules: the probe light transmitting module, the light magnifying and transmission module, and the signal acquisition module.