Abstract

Direct detection of FSK signals (DDFSK), using a baseband optical receiver and a tunable Fabry-Perot interferometer (FPI) for channel selection and optical frequency discrimination, has been proposed as a practical alternative to coherent techniques for polarization-insensitive FSK demodulation [1]. DDFSK also lends itself naturally to the use of optical preamplifiers since the FPI also serves as a narrow band optical filter to suppress spontaneous emission. We report the first use of an optical amplifier in a DDFSK system and show that a high-gain erbium-doped fiber amplifier can simultaneously improve the sensitivities of more than 10 receivers by 20 dB, to better than -40 dBm. We also assess the implications for multi-optical-channel systems as well as the trade-offs between receiver sensitivity and distribution capacity. A receiver sensitivity with the ASK equivalent of 171 photons/bit was achieved, the best reported to date for an erbium fiber preamplifier.

© 1990 Optical Society of America