Research On Polarization Diversity Heterodyne Balanced-receiver Of Optical Frequency Domain Reflectometry

Distributed optical fiber backscattering measurement technology has recently attracted the attention of the world with the maturity of production process and relative measurement technology, thanks to its unique analysis ability of distributed factors and outstanding distance distinguishing capacity. As an important method of detection and analysis, it can be widely used to detect the failure of optical fiber link, health condition of large objects such as bridges, dams, oil pipes and electrical line, as well as an alarm for the collapse of wells, tunnels and buildings.Optical Time Domain Reflectometry(OTDR) and Optical Frequency Domain Reflectometry(OFDR) are two representative and widely used technologies among all the distributed optical fiber backscattering measurement technologies.Since the beginning of 21 century, the rapid updates of demand and the continuous development of relative device and key technologies have largely promoted the development of OTDR and OFDR, as well as the evolution of the products. Compared to OTDR, OFDR has higher signal noise ratio/ spatial resolution and sensitivity, and can meet the more severe test demand modern time. In 2006, American company Luna Technologies launched the first OFDR product worldwide, which can support 3mm resolution with 2km range. The product was not widely used due to its high expense. China is still in shortage of our own OFDR technology and product, 100% of our OFDR device is imported.To adapt to the demand of the mentioned distributed measurement, we have to make improvement to the existing OFDR technology regarding to its performance. This thesis studies thus deeply into the theory and technology of OFDR, builds up OFDR system model design. Focusing on the problems existing in OFDR system as the light intensity noise, cross-modulation, polarization fading and there influence to the performance of the system, we did profound analysis, and stated balanced receiver, heterodyne detection, polarization diversity reception and other solutions, theoretically validated the design of OFDR system receiver. In this paper, a balanced mixed polarization diversity optical heterodyne receiver for OFDR system is designed and implemented. A detailed analysis is carried out on the analog front end of the balanced receiver involving the optical current amplification, broadband filtering, low-pass filtering and the coherent demodulation.In the end the OFDR system based on DFB laser is realized, and the measurement of a range of 2km with a resolution of 3mm is achieved.