Clock-Data-Recovery-Based Delta-Sigma Modulation over Multi-Mode Fiber under Axis-Misalignment Condition

We evaluate higher-order modal noises excited by the misalignment in the fiber connection as jitter and phase noise under multi-mode optical fiber transmission. A clock data recovery at the receiver side will recover the quality of the delta-sigma modulation-based clock signal, even with a large displacement of the core axis.

I. Introduction

An optical fiber communication system is mandatory to provide network and Internet services. Typically, this fiber communication is based on a single-mode optical fiber (SMF) link because the high capacity of the communication is highly demanded. Even in data center communication, which requires low-cost solutions, the SMF is used for 10 Gb/s or higher data rates up to 400 Gb/s. Particularly in short-reach communication less than 100 or 200 m in the data center, a multi-mode optical fiber (MMF) is also used for the cost-effective solution and its insensitivity to the fiber bending losses as compared to the SMF [1]. However, the MMF has a limitation in the data rate due to the modal dispersion. The modal dispersion is caused by the different group velocities of the higher-order spatial modes, which are even excited at the center of the fiber core (restricted mode launch condition).