Improved OSSB modulation with FBG-based acousto-optic tunable filter and Return-to-Zero pulse transmission

摘要

An improved OSSB modulation scheme is proposed in this paper. The improvements are realized by three aspects. Firstly, the fiber Bragg grating based acousto-optic tunable filter (FBG-AOTF) is introduced to tune the Optical Carrier-to-Sideband Ratio (OCSR). Secondly, the Return-to-Zero (RZ) pulse is chosen as the data transmitting pulse. In the end, the OSSB signal with optimized OCSR is separated, and only the optical carrier is modulated by the data. When the transmission distance is within 360 km, the receiving sensitivity of the link in the improved scheme is relatively stable in the range of (- 23.6 dBm, - 24.1 dBm) with the increase of the distance. While for the original OSSB modulation, under the same condition, the receiving sensitivity is only about - 20.0 dBm when the fiber length is 200 km. Not only the OCSR of the OSSB can be optimized, but also the problem of time shift of code edges caused by the fiber dispersion can be eliminated. As a result, both the performance and the stability of the OSSB system can be upgraded in the improved scheme. Two complete simulation systems are built by using the characteristic of the experimentally made FBG-AOTF. And the increased receiving sensitivity of 2.6 dB in the improved scheme further verifies the conclusion.