Research Of A Highly Integrated CWDM4 Single Fiber Bi-directional Transmission Module

With the arrival of 5G era,the construction of data center is driving into the fast lane,and the optical fiber interconnection technology is also upgrading,from multi-mode optical fiber parallel transmission to CWDM4 single fiber bidirectional transmission,and the integration requirements of optical fiber transmission module are put forward.In this paper,a high integrated CWDM4 single fiber bidirectional transmission module is studied,which can be integrated into the optical fiber transceiver module of QSFP structure.Three interleaver series parallel structures are used as CWDM4 multiplexing/demultiplexing,and the stabilized coupler and MMI-MZ-MMI coupler are used in the interleaver to reduce the crosstalk.Three kinds of Interleaver using directional coupler,stabilized coupler and MMI-MZ-MMI coupler were designed and manufactured,and good device performance was obtained.In the optimal performance band,for Interleaver using directional coupler,insertion loss was less than 3.22 d B,crosstalk lower than-12.6d B,0.5d B bandwidth greater than 1.645THz;For interleaver with stabilized coupler,insertion loss is less than 4.4d B,crosstalk lower than-16.1d B,0.5d B bandwidth greater than 2.808THz;For interleaver using MMI-MZ-MMI coupler,insertion loss is less than 3.45 d B,crosstalk is less than-23.8d B,and the 0.5d B bandwidth is greater than 2.117 THz.The test results prove that the Interleaver using MMI-MZ-MMI coupler has better crosstalk characteristics and process tolerance than the Interleaver of the other two couplers,and the results are in line with expectations.A single-sided input/output three-port optical circulator is designed.In the optical circulator,a reflective lens is used to fold the optical path to achieve single-sided input/output,and to achieve miniaturization of optical components to be combined with wavelength division multiplexing/demultiplexing.The mixed integration of multiplexing chips reduces the size of the CWDM4 single-fiber bidirectional transmission module.This design solution breaks the current situation that single-fiber bidirectional transmission requires an external independent optical circulator for QSFP modules.