Research On Utilizing Self-injected Locking Semiconductor Laser In ?—OTDR Vibration Sensing System

Distributed optical fiber vibration sensing technology based on phase-sensitive optical time-domain reflectometry(?-OTDR)has the advantages of simple structure,high positioning accuracy,long sensing distance,etc.,and has been applied in many fields.This sensing system requires a coherent light source with narrow linewidth and low frequency drift.Generally,such a high-performance light source is expensive.In this thesis,we used the self-injection locked DFB semiconductor laser as the light source of the ?-OTDR distributed fiber vibration sensing system,and related theoretical and experimental studies were carried out.Base on the coherent superposition of the scattered points,the effects of pulse width and laser frequency drift on the scattering intensity were calculated and analyzed.The self-injection locking of a DFB semiconductor laser was accomplished by using optical fiber and optical waveguide ring resonators.The linewidths of the self-injection locked DFB semiconductor laser were measured by the delayed self-heterodyne interferometer method.The linewidth of the laser was narrowed by 42,32 and 27 times respectively by using two fiber ring resonators with perimeters of 4 m and 63 cm,and an optical waveguide ring of 12.57 cm.The mode hopping phenomenon and the stabilizing time as locked upon the three ring resonators were measured.The stabilizing times were 20 s,65 s and 320 s,respectively,which indicated that the optical waveguide ring resonator could significantly suppress the generation of the mode hopping.A ?-OTDR distributed fiber vibration sensing system was built.Using a narrow-linewidth fiber laser and the self-injection locked DFB semiconductor laser as the light source,the vibration point was located at 1 km on a sensing fiber of 3.2 km.Comparison of the sensing effects demonstrated that as using the laser locked upon the waveguide ring,the position of vibration point measured is more stable and the signal-to-noise ratio is higher than using the laser locked upon the fiber ring,which indicates that using the optical waveguide ring resonator is more advantageous than the optical fiber ring resonator for locking the DFB semiconductor laser and using it in the vibration sensing system.The research of this thesis further reveals the feasibility of using the self-injection locked DFB semiconductor laser as the light source of the ?-OTDR distributed fiber vibration sensing system and has made a beneficial exploration for reducing the cost of the sensing system.