Infinera Corporation
REDUCTION OF PDL PENALTY USING TRANSMIT SIGNAL PROCESSING ON SUB-CARRIER MULTIPLEXED SIGNALS

Abstract:

Consistent with the present disclosure, a transmitter is provided that include a modulator and a laser. The modulator is driven based on outputs from a digital signal processor (DSP), such that the modulator outputs a modulated optical signal including a plurality of subcarriers. Each subcarrier includes an x pol component and a y pol component, but certain subcarriers may have an effective x pol and y pol rotations compared to other subcarriers. The amount of rotation may be determined by a polarization rotation circuit that supplies inputs to the DSP (alternatively the polarization rotation circuit may be part of the DSP). Accordingly, regardless of the orientation of PDL in an optical link, certain subcarriers may have lower overall Q (a parameter related to the signal-to-noise ratio (SNR)) while others may have a higher Q, such that the average Q over all the subcarriers in a modulated optical signal is higher than if each subcarrier has the same x pol and y pol orientations. In one example, a PDL penalty (reduction in Q due to the PDL, for example) may be reduced by 0.5 dB and, in other examples, the PDL penalty may be reduced by 1.0 dB. Overall improved SNR for the modulated optical signal including a plurality of subcarriers may also be achieved.