2. State Key Laboratory of Safety and Control for Chemicals, SINOPEC Research Institute of Safety Engineering, Qingdao, Shandong 266000, China
Overview: Optical fiber sensing system depends closely on the quality of the laser source employed, because laser parameters such as the power stability, linewidth and phase noise, have a great impact on the performance of the fiber sensing system in such parameters as the maximum measuring distance, precision, sensitivity and noise characteristics which finds tremendous applications to areas to name a few; distributed oil pipeline monitoring, high resolution sensing, low noise microwave generation, optical atomic clocks, optical precision metrology, high resolution spectroscopy, microwave photonics and laser radars etc. In order to improve the measurement range, noise characteristics, sensitivity and precision of optical fiber sensing system, we need to obtain a narrow linewidth laser light source with a longer coherent length (characterized by laser linewidth), phase noise (characterizing laser frequency stability) and low intensity noise (characterizing laser power stability). In the light of all this, a great deal of attention over the years has been witnessed in academia and industry in regards to the related high-quality laser source employed for fiber sensing system to name a few; long distance super high resolution distributed oil pipeline monitoring system whose predominant distributed optical fiber sensing technology such as OFDR (optical frequency domain reflectometry) technique is greatly dependent of the laser source linewidth for better sensitivity, range and other key factors to its applications, in optical fiber hydrophone system the linewidth of the laser source employed very much determines the system noise and minimum measurable signal of the system, the use of FBG (fiber Bragg grating) to build up a sensor network operating under the technique of either spectral analysis or tunable filter matching method for demodulation purposes greatly depends on high stable power of the laser source employed for simultaneous demodulation of multiple FBG in a sensor network due to its insertion loss and bandwidth. In this article, a brief review on the development trend of the laser source for fiber sensing is presented which firstly emphasizes on narrow linewidth lasers followed by tunable laser and lastly white laser source. Finally, the main limiting factors and kernel technology of laser source for the optical fiber sensing are summarized. In order to achieve high performance of optical fiber sensing, the availability of the ideal ultra-narrow-linewidth and ultra-stable laser, which could be tuned at a desired wavelength span and tuning rate, will be definitely one of the main research directions of the future optical fiber sensing.