Optically Preamplified 3 Gb/s DPSK Receiver with 80 Photons/bit Sensitivity

Abstract

Differential phase shift keying (DPSK) is a sensitive signaling format offering improved sensitivity over on/off keying (OOK) and a much simpler receiver than homodyne phase shift keying (PSK). Most DPSK experiments to date have used heterodyne detection although the equivalence in sensitivity between optically preamplified and heterodyne DPSK is known.[1] Direct detection DPSK, in which the received signal is optically demodulated with a delay and multiply discriminator, has been reported previously but lacked an optical preamplifier. As a result, the sensitivity was ~30000 photons/bit. [2] In the current literature most activity involving optical preamplifiers at high rates has centered around OOK, for which sensitivity of 112 photons/bit at 10-9 bit error rate (BER) has been achieved at 10 Gb/s.[3] Although ideal DPSK offers a 6 dB peak power receiver sensitivity advantage over ideal OOK, to our knowledge the best reported multi-Gb/s DPSK experiment employed heterodyne detection and achieved a sensitivity of 209 photons/bit at 4 Gb/s. [4] Using optical preamplified and optically demodulated DPSK we achieved a record sensitivity of 80 photons/bit.