Demonstration of Record Sensitivities in Optically Pre-amplified Receivers by Combining PDM-QPSK and m-ary Pulse-Position Modulation
18 July 2011
a recently introduced high-sensitivity modulation format based on the combined use of polarization-division-multiplexed quadrature phase-shift keying (PDM-QPSK, or PQ) and m-ary pulse-position modulation (m-PPM). This novel modulation format, termed as PQ-mPPM, offers high receiver sensitivity in optically pre-amplified receivers. We study the sensitivity of the PQ-mPPM format both analytically and experimentally, and compare it to common modulation formats such as PDM-QPSK, m-PPM, differential phase-shift keying (DPSK), and polarization-switched QPSK. The bandwidth expansion factor of this format is also discussed. A record sensitivity of 3.5 photons per bit at BER=10-3 is experimentally demonstrated at 2.5 Gb/s with a novel pilot-assisted digital coherent-detection scheme, outperforming PDM-QPSK by about 3 dB.
