Research On A Novel Mode Division (De) Multiplexer And Optical Transmission

With the continuous expansion of the scale,capacity and traffic of optical fiber communication network,the optical transmission capacity of single-mode optical fiber has reached 100 TB/s,approaching the Shannon limit,which will pose an unprecedented major challenge to the optical communication network.Therefore,it is urgent to find a new high-speed and high-capacity optical fiber transmission technology,which will also be the key to the development of optical communication network in the future.In this context,in order to solve the transmission bottleneck in the current optical communication network,mode division multiplexing technology has once again become the focus of attention.In short-range mode division multiplexing system,mode channel crosstalk will lead to the complexity,power consumption and cost of multi input and multi output digital signal processing methods at the receiver,which will increase sharply with the increase of the number of modes.Therefore,this thesis proposes a new mode division multiplexer and demultiplexer without multiple input and multiple output digital signal processing.In addition,for the mode division multiplexing transmission,a mode division multiplexing experimental transmission system is built by using the characteristics of few mode fiber,that is,the quasi single-mode experimental transmission system based on few mode fiber.The main innovations are as follows:A novel mode division（de）multiplexer with low loss and low crosstalk based on elliptical core transmission channel is proposed for the multiple input multiple output free（MIMO-FREE）applications in this thesis,which is called the MIMO-FREE-（DE）MUX.The elliptical core with a large effective refractive index difference(the effective refractive index difference between LP01 and LP11a is greater than 3.92×10^-3)between modes is proposed as the mode transmission channel to effectively reduce mode crosstalk and improve the mode extinction ratio of the MIMO-FREE-（DE）MUX.Meanwhile,the degeneracy of LP11a and LP11b is broken,and the mode maintaining function is achieved.In order to effectively reduce the transmission loss and splicing loss in the optical communication system,the elliptical core is made of the pure silica.In the C-band,the intrinsic loss of our proposed elliptical core transmission channel is less than 0.162 d B/km,which can realize the（de）multiplexing of LP01,LP11a and LP11b modes in the MIMO-FREE application scenario.In this thesis,the performance of the MIMO-FREE-（DE）MUX is studied using beam propagation method and finite element method.The refractive index distribution characteristics of transmission channel,the variation relationship of intrinsic loss with different incident wavelengths,the transmission characteristics of coupling efficiency with the transmission distance,and the variation relationship of mode coupling efficiency and mode extinction ratio with different incident wavelengths are studied.In the 1520 nm-1600 nm band,the coupling efficiency of three modes in the MIMO-FREE-（DE）MUX is better than-2.26 d B,and the extinction ratio is better than 39.93 d B.In C-band,the coupling efficiency of the three modes in the MIMO-FREE-（DE）MUX is better than-0.58 d B,and the extinction ratio is better than 41.18 d B,which is 19.98 d B higher than that in the previous reference.This new mode division（de）multiplexer can improve the transmission capacity of optical communication system,reduce loss and crosstalk,reduce the cost of optical communication system,obtain high performance indexes such as high coupling efficiency and high extinction ratio,and other characteristics are also better than the parameters in the previous reference.A quasi single-mode transmission system based on few mode fiber is proposed.In the quasi single-mode transmission system based on few mode fiber,firstly,the constellation diagram of X polarization state after transmission of 0.46 km and 19.27 km is analyzed when the input optical power is-4 d Bm,-16 d Bm and-20 d Bm,respectively.Then,the variation of EVM,Q-factor and BER with input optical power after signal transmission are analyzed.Finally,it is proved that the quasi single-mode transmission system based on few mode fiber can be applied to optical transmission.