For electric servo system，this paper introduces Dense Wavelength Division (WDM) type single fiber bi-directional (SFBD) communication technology which is applied in multi-turn absolute rotary encoder motor position feedback strategy. The corresponding photoelectric conversion circuits and Non-Return-to-Zero (NRZ) coding data format are also presented. Through constructing experiment platform, the feasibility of the method is verified. The method in this paper can achieve bidirectional communication between the driver and motor encoder by only one single fiber. In the experimental system, the motor runs well, and achieve to improve the reliability and data communication system with lower cost.