Research On The EDFA/FRA Hybrid Optical Amplification In The Remote Optical Fiber Hydrophone System

In recent years,the researches on the optical fiber hydrophone system have focused more on making its distance longer and scale larger,which can bring in a huge optical attenuation that restricts the development of the optical fiber hydrophone system a lot.Hence,the optical amplification has become a key technology in the remote optical fiber hydrophone system.EDFA,which has been widely used,has the shortcomings of narrow gain bandwidth,high noise figure,and discrete amplification,while FRA has a relatively lower gain.In such a case,neither of them can meet the requirements of the remote optical fiber hydrophone system for a high gain,low noise figure amplifier.The EDFA/FRA hybrid optical amplifier has been widely applied to the high speed optical communication systems presently.In this dissertation,some workes have been done on the application of the EDFA/FRA hybrid optical amplifier to the remote optical fiber hydrophone system.In this dissertation,theoretical models of the downlink and uplink hybrid optical amplifiers based on the Raman power coupling model and the Giles model are built with thier gain and noise characteristics analyzed by numerical simulation and experimental research.SBS is easier to occur in the FRA part of the hybrid optical amplifier in contrast with the common single-mode fiber because of the gain,which will influence the hybrid optical amplifier a lot.In this dissertation,the threshold characteristic of SBS in the FRA is studied theoretically,and the effects of it on the gain and noise characteristics of the FRA are analyzed experimentally.Phase modulation is one of the effective ways to suppress SBS.In the dissertation,the physical mechanism is deeply analyzed,and a theoretical model on the suppression is put forward.The phase modulation method is adopted in the forward pumped FRA to enhance the gain saturation power resulting from SBS,and it is used to suppress SBS and reduce the phase noise in the remote optical hydrophone system as well.Apart from SBS,other noise sources can also influence the performance of hybrid optical amplifier,whose effects on the phase noise and the suppression methods are studied experimentally.The main innovation points and achievements of this dissertation are as follows,(1)The phase modulation method is adopted to enhance the gain saturation power in the forward pumped FRA,the theoretical model is demonstrated by experiments.As a result,the gain saturation power can be enhanced by 6.45 d B within the scope of the study(phase modulation index 0~3.189 and modulation frequency 0~100MHz).(2)The forward pumped FRA is used as a downlink optical amplifier for a 100 km one-way transmission fiber optical hydrophone system,the phase noise of which is as low as-103 dB/Hz1/2 by adopting the phase modulation.On basis of the discussion above,a 1ow-noise hybrid optical amplifier applied to the remote optical fiber hydrophone system with 100 km round-trip transmission is built,the phase noise of the system without bringing in the optical attenuation of the array is measured,which is-95.78 dB/Hz1/2@1kHz.