Abstract
This investigation proposes a novel all-optical phase noise averager to reduce residual phase noise in the differential phase-shift keying (DPSK) transmission system with phase-preserving amplitude regenerators. The proposed phase noise averager is based on a phase-sensitive amplifier but does not require an extra phase-locking optical pump beam. It can increase the correlation between the phase noises of neighboring bits and greatly reduce the differential phase noise in the transmission system. Independently of the cascaded spans, analytical analysis demonstrates that, in the DPSK system with repeated averagers, the total differential phase noise will be less than that before the first averager. Theoretical analysis and numerical simulation are carried out and confirm the significant improvement of DPSK signals using the proposed novel phase noise averagers.
Highlights
In differential phase-shift keying (DPSK) format, an optical pulse appears in each bit slot with the binary data encoded as either a zero or π phase shift between adjacent bits
The most obvious advantage of the DPSK format with balanced detection over on-off keying (OOK) is that its optical signal-to-noise ratio (OSNR) required to reach a given bit-error ratio (BER) is approximately 3 dB lower [1]
This study proposes a novel all-optical phase-sensitive amplifier (PSA)-based phase noise averager (PNA) that does not require a complicated optical coherent pump beam with optical phase-locking
Summary
In differential phase-shift keying (DPSK) format, an optical pulse appears in each bit slot with the binary data encoded as either a zero or π phase shift between adjacent bits. Constraining PN by the stabilization of amplitude [10, 11], in-line regenerators for DPSK signals are needed to manage either AN or PN and to further expand the transmission distance. The reduction of AN is such that the nonlinear PN caused by the Gordon-Mollenauer effect will be reduced [20, 21] and the transmission distance will be extended These regenerators can constrain only some of the nonlinear PN and preserve the original linear PN. The proposed PNA can average the PN of one bit with that of its neighboring bit coherently and does not need an extra phase-locking pump beam These PNAs can effectively diminish differential PN and greatly extend the reach of DPSK signals. In amplitude-managed DPSK systems with repeated PNAs, the total differential PN is always less than that before the first averager and is irrelevant to the number of DPSK spans
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