DSP for Optical Transponders

Abstract

This chapter outlines the principles of the digital signal processing (digital signalprocessing (DSP)) used in modern optical transceivers. The historic developments that have led to the emergence of DSP being applied in optical transceivers is reviewed, including the high-speed complementary metal oxide semiconductor (complementary metal–oxide–semiconductor (CMOS)) analog to digital converters (analog-to-digital converter (ADC)) that have facilitated the creation of the application-specific integrated circuit (application-specific integrated circuit (ASIC)) which underpins digital coherent transceivers. Following on from this, the mathematics associated with finite impulse response (finite impulse response (FIR)) filters is reviewed, including the Wiener and least-squares design of FIR filters. The mathematics associated with the adaptive multiple-input-multiple-output (multiple-input multiple-output (MIMO)) filter employed in the receiver is also discussed, including derivation of the stochastic descent algorithm based on differentiation with respect to a complex vector. Subsequently, we provide an overview of DSP algorithms, before detailing both those required for equalization and synchronization. Following a summary of error correction used in a digital transceiver, we reflect on the current research trends and future opportunities for DSP in optical transceivers.