Dual-Polarization DBR Fiber Lasers And Their Applications In Communication And Sensing

Fiber laser is an advanced optical active device and is also one of the most important devices in optical engineering field. It not only has many features of the traditional passive components of the fiber Bragg grating, in the sensing area, but also has the distinct advantages of narrow linewidth and high signal to noise ratio, etc., which can achieve more accurate sensing measurements. Moreover, some of the new sensing concepts and technologies based on fiber lasers have been realized and applied. In the communication field, fiber laser is also one of the key components in dense wavelength division multiplexing system (DWDM), optical time division multiplexing system (OTDM), the new microwave photonics field (ROF) and other second-generation all-optical network technology applications.This thesis research mainly focuses on dual-polarization DBR fiber lasers as well as their applications in sensing and communicating fields. In radio frequency domain, we use the orthogonal polarization beat frequency generated by the fiber laser as the sensor signal, which not only obtains higher accuracy and sensitivity than the passive sensors such as sensors based on fiber Bragg grating, but possesses of advantages such as more mature demodulation techniques and lower cost than the sensors based on traditional wavelength encoding methods. In the future, optical sensing and network will develop toward the direction of miniaturization, networking, multi-functional, systematic. Polarization based DBR fiber laser has the huge potential and a realistic prospect in the industry toward the development tendency of the sensing applications. In this paper, based on the National Natural Science Foundation Key Project (No.60736039):integrated, high-speed, multi-parameter, critical mass of new fiber-optic sensor network technology and its application, focusing on the key technology of fiber-optic sensor network, we successfully completed the development of high-performance dual-polarization fiber lasers, complete study of the fiber laser features and eventually combined with experimental research, we realized a number of innovative applications in sensing and communication field. Here are some important breakthroughs and brief overview of innovation points:1) For the first time we fabricated ultra-short cavity DBR fiber laser with only 1 mm laser caivity in erbium and ytterbium (Er/Yb) co-doped gain fiber. By masting the fabrication technology of DBR fiber laser, with optimizations and repeated attempts, we ultimately demonstrated the high performance DBR fiber laser with the length of only 8.4mm, physical cavity length of only 1mm. The theoretical calculated effective length of the～1mm laser cavity, principally ensures absolute stabile single longitudinal mode output of the DBR fiber laser which successfully solves the mode hopping problem in DBR fiber lasers. The lmm short cavity shows the compact overall structure. Thus to greatly improve the spatial resolution in sensing application is possible.2) A low pump pass loss ultra-short cavity DBR fiber laser was demonstrated in erbium-doped low-gain fiber. After mastering the short-cavity DBR fiber laser production technology, in response to the requirement of reduced pump absorption loss of a single sensor unit in future large-scale sensor network applications, and more compact structure, low absorption loss in single Er-doped fiber ultra-short DBR fiber laser was developed with total length of 8mm. After optimization of joints loss we achieve only 0.9dB single fiber laser-pumped absorption loss, which is lower compared with the loss in Er/Yb co-doped gain fiber based ultra-short cavity fiber laser, and this laser will significantly improve the multiplexing capability in large-scale networking.3) For the first time we successfully demonstrated a high temperature (500℃) environment resistant DBR fiber laser in the Er/Yb gain fiber. Through innovatively using of highly saturated fiber Bragg grating as the reflection grating in fiber laser, we achieved that the matched fiber Bragg gratings after annealing at high temperature still have sufficient stability reflectivity. The results showed very good high temperature stability, and in the entire range form room temperature to 500℃the laser maintained a very high output power and signal to noise ratio.4) We proposed for the first time beat frequency signal modulation technology by ultraviolet (UV) exposure method. In experiments, we successfully realized the trimming of beat frequency in the frequency domain to positive and negative direction with tuning range up to 700MHz. This technology is the key to achieve the critical network technologies in the frequency domain. On this basis, we firstly and successfully demonstrated a six-channel frequency division multiplexing DBR fiber laser ray.5) In sensing applications, to achieve a wide range of sensing applications, based on polarization heterodyning DBR fiber laser sensors, we realized the design and experiments of lateral pressure sensors, hydraulic sensors and micro-displacement sensor, and obtained a high sensor sensitivity and measurement accuracy.6) In communication applications, we for the first time successfully used a single-longitudinal mode dual-polarization DBR fiber laser to produce a tunable microwave (ROF) generator. The microwave signal generated by the signal generator can be toned by PZT with 0-55V voltage from 3.34GHz to 14.75GHz, and its structure is more compact than other ROF generator, with low cost.