Abstract

We present an ultralow-noise balanced receiver module based on a three-stage high-impedance design using commercially available high- electron-mobility transfers (HEMT’s) (see Fig. 1). The first state, consisting of a monolithically integrated dual P-I-N diode,¹ a bond wire together with a thin microstrip line for serial-noise tuning,² and a transistor with a 10 kΩ bias resistor, is optimized for noise suppression. We have chosen serial tuning because of its broadband characteristics and its ease of implementation. A flat frequency response is achieved by implementing an equalizing circuit between stages 2 and 3 and a microwave matching circuit between the stages. A common problem of optical front ends is increased effective gain ripple from electrical reflections at the output. We solved this problem by two measures: (i) the gain is so high that a few decibels of attenuation at the output can be tolerated without noticeable signal-to-noise ratio degradation; and (ii) In contrast to Gimlett,³ we avoid an equalizing circuit at the output, which allows us to optimize the output match without causing the response to deteriorate. The entire circuit was designed with microwave simulation software.

© 1991 Optical Society of America