Characterization and Equalization of Imperfect Optical Transceivers

Abstract

Transceiver imperfections become the primary source of impairment as baud rate and modulation order grow in advanced optical communications. Thus, transceiver imperfections, both linear and nonlinear, need to be appropriately characterized, measured, and compensated. This tutorial reviews the transceiver's linear and nonlinear imperfection modeling, characterization, measurement, and compensation technologies. Treatments for linear imperfections are relatively mature. The frequency transfer function can sufficiently describe the linear characteristics, and the adaptive finite impulse response filter compensates linear imperfections. The remaining task is to accurately measure the transfer function with limited resources. In the case of nonlinear imperfections, the situation is complex. Various nonlinear models and specifications are reviewed in this tutorial at first. Then methods to estimate nonlinear system performance based on device nonlinear characteristics are discussed. This is a quite challenging task because the nonlinear impairment does not only depend on the device nonlinear status, but also on the input signal characteristics, such as signal power, spectrum, and probability distribution function. Finally, various nonlinear compensation methods including transmitter side digital pre-distortion and receiver side digital equalization are reviewed.