Pump Linewidth Requirements for Processing Dispersion-Altered DQPSK Signals using FWM

TL;DR

This paper investigates pump linewidth requirements for four-wave mixing (FWM) processing of dispersion-altered DQPSK signals, revealing that higher baud rates demand sub-MHz linewidths to prevent OSNR penalties.

Contribution

It provides baudrate-dependent pump linewidth tolerances for FWM-based processing of dispersion-altered signals, highlighting the need for ultra-narrow linewidths at higher data rates.

Findings

10 Gbaud DQPSK signals are tolerant to pump linewidths.

28 and 56 Gbaud DQPSK signals require sub-MHz pump linewidths.

Pump linewidth constraints are critical for FWM-based optical processing at high data rates.

Abstract

We report on a potentially deleterious issue regarding the four-wave mixing based processing of dispersion-altered signals. We estimate the baudrate-dependent pump linewidth tolerances by calculating the extra optical signal to noise ratio (OSNR) penalty with respect to the propagation distance. We find that the issue is not important for 10 Gbaud differential quadrature phase shift keying (DQPSK) signals, though for 28 Gbaud (and 56 Gbaud) DQPSK signals we find that the pump linewidth requirements to implement FWM based optical signal processing needs to be in the sub-MHz range in order to avoid excessive OSNR penalties for the case of dispersion-altered signals. These results are pertinent for systems employing FWM, which could be all-optical wavelength converters for packet switching or mid-span spectral inversion techniques.