Implementation of Blind Carrier Phase Recovery for Coherent Fiber-Optical Receivers

Abstract

The use of higher-order modulation formats has been suggested as one way to increase the speed of fiber-optical systems. These formats are more sensitive to phase noise, which is why blind phase-search (BPS) has been suggested as one way to perform carrier recovery. In this thesis we demonstrate the feasibility of BPS by developing a hardware implementation and synthesizing it using a regular-Vt, 28nm standard cell library. The power consumption of the design, at a symbol rate of 40GBd, is found to be lower than 2.0 pJ/bit for 16QAM and lower than 3.1 pJ/bit for 64QAM. Higher symbol rates can also be used, without significantly affecting the energy/bit. Fixed-point aspects of the design are examined and we show that using 7 bits for 16QAM and 8 bits for 64QAM result in a penalty of less than 0.3 dB, compared to floating point. We also present a hardware-efficient method to approximately calculate the distance to the closest constellation point, without significantly affecting the bit-error rate (BER). Furthermore, the feasibility of joint processing of multiple channels sharing the same phase noise is evaluated and phase estimation is shown to consume approximately 5 times the power of the phase compensation.