Abstract

The potential for high-density wavelength division multiplexing and very high receiver sensitivity has stimulated research on coherent optical communication techniques [1]. One consideration in the design of coherent receivers is the inherent problem of noise generated by the local oscillator. It has been shown that the local oscillator excess intensity noise can be suppressed by using a dual-photodetector, balanced optical receiver [2]. Initial implementations of this circuit utilized discrete photodiodes and an optical fiber directional coupler [3]. Recently, improved performance has been achieved with integrated twin InGaAs p-i-n photodiodes [4]. In this paper, we report, for the first time, integration of a 3-dB directional coupler with two InGaAs p-i-n photodiodes in a balanced mixer configuration.

© 1989 Optical Society of America