Partial Pre-Emphasis for Pluggable 400 G Short-Reach Coherent Systems

Abstract

Pre-emphasis filters are used to pre-compensate for the transmitter frequency response of coherent systems to mitigate receiver noise enhancement. This is particularly essential for low-cost, low-power coherent transceivers due to having an extremely bandlimited transmitter. However, the pre-emphasis filter also increases the signal peak-to-average power ratio (PAPR), thus posing a higher effective number of bits (ENoB) requirement for the arbitrary waveform generator (AWG). In this paper, we first numerically study the PAPR impact of partial pre-emphasis filters. We show that with partial pre-emphasis, an ENoB reduction from 5 to 4.5 bits is attainable at the same signal-to-noise ratio (SNR) out of the AWG. Next, we experimentally investigate the overall performance penalty of partial pre-emphasis in a 50 Gbaud 16QAM coherent system. A manageable Q factor penalty of around 0.5 dB is found for both single-polarization and dual-polarization systems with a 0.8 dB PAPR reduction.

Adaptive Pre/Post-Compensation of Cascade Filters in Coherent Optical Transponders

“…As shown in Equation 16, allows system to be more resilient to jitter for the PLL driving the DAC clocking. It is known that high-frequency components are more sensitive to jitter [52,53], therefore by reducing peaking, higher system SNR can be achieved.…”