Research On RF Signal Transmission Technology Based On High Nonlinear Tolerance Of Few Mode Fiber

Optical fibers are used as an important medium for transmitting RF signals because of their low loss,large bandwidth,low weight,and immunity to electromagnetic interference.Analog optical links play an important role in many applications of microwave photons because they can achieve high gain,low noise figure and large spurious-free dynamic range at the same time.Improving the received optical power of photodetectors is improving the performance of analog optical link systems.At present,lasers with high emission power have been manufactured.In contrast,the power handling capability of optical fibers is one order of magnitude lower.Stimulated Brillouin scattering results in strong backscattering,while reducing the gain and SNR;Kerr nonlinearity causes intermodulation distortion,limiting the link to SFDR improved,so the main obstacle to improving the performance of analog optical links is the fiber itself.We study the theoretical analysis and experimental verification of fiber optic that improve the gain of analog optical links.Based on the discussion of SBS threshold characteristics,three methods for improving the performance of analog optical links are proposed.The corresponding experimental platform was built to analyze the performance indexes of SBS thr-eshold,link gain and SFDR.The experimental results are in line with theoretical expectations,and the feasibility of our method is also proved.Finally,the numerical calculation is based on SBS slow.The light effect compensates for the dispersion between the modes.The specific work of this paper includes the following three parts:Firstly,on the basis of introducing analog optical link source,modulator and photodetector,pointed out that high optical power transmission is the requirement of these devices,and improving the detection optical power of the link is to improve the link gain.The LP mode in the fiber is solved,the mode is proved,and the formula of the inter-mode dispersion is deduced.The mode coupling and the inter-mode dispersion are considered to select the LP01 and LP11 in the MDM experimental system.The fiber collimator and SLM-based mode excitation were introduced to prepare for the subsequent experiments.Secondly,based on the detailed discussion of the stimulated Brillouin scattering principle,threshold characteristics,especially the SBS threshold influencing factors,it is proposed to replace the single-mode fiber with the small-mode fiber.The mode LP11 is transmitted to improve the link gain and SFDR,and the SBS threshold test platform and the link performance test platform are tested.The results show that the SBS thresholds of the single-mode link and the two mode-links are 8dBm,12dBm and 17dBm,the SBS threshold and transmitted optical power of the mode-link link are improved and the third-order intermodulation distortion is suppressed,thereby improving the link gain and SFDR.The SFDR of the two mode-links are respectively compared to the single-mode link.The high 1.4dB and 3.4dB prove the feasibility of our proposed method.Thirdly,on the basis of discussing the influence of mode on the SBS thr-eshold in the MDM system,an analog optical link based on the MDM system is proposed to further improve the link performance and build an experimental platform.The results show that it is related to the small-mode LP11 link.Compared,the SBS threshold of the MDM link is 2dB higher and the transmitted optical power is 1dB higher,so the link gain is larger and the third-order intermodulation distortion is further suppressed.The SFDR of the MDM link is increased to 90dB.Finally,we numerically calculate the inter-mode dispersion compensation using the SBS slow light effect and explain the results.