High Tolerance to Coherent Crosstalk by Differential-Phase- Shift-Keying Modulation with Balanced Detection

The tolerance to in-band coherent crosstalk in differential- phase-shift-keying (DPSK) systems is investigated. It is found experimentally that DPSK with balanced detection offers ~6 dB higher tolerance to coherent crosstalk than on-off-keying (OOK) with similar signal pulse profile. The high crosstalk tolerance of DPSK can be explained by its 6-dB lowered peak signal power as compared to that in OOK for equal BER in OSNR- limited systems. The worst-case OSNR penalties resulting from -12 dB in-band crosstalk are measured to be ~5.6 dB and ~2. 2 dB for BER=10-9 and 6x10-5, respectively, in a DPSK system. The impact of signal coherence on crosstalk tolerance in a 10-Gb/s DPSK system adopting a standard Reed-Solomon FEC is also investigated. Index Terms— Coherent crosstalk, differential phase-shift keying, forward error correction.