Abstract
In multigigabit-per-second optical coherent communication systems, the optical front-end amplifier is a crucial component, since it has to operate at a high intermediate frequency (IF)—at least twice the bit rate—over a large bandwidth and has to exhibit low noise. In many systems the influence of relative intensity noise (RIN) is important, particularly if the IF is dose to the relaxation frequency of the local-oscillator laser.1 Here, RIN is reduced by using a balanced-receiver front-end employing two photodiodes; this slightly increases the noise from the photodiode parasitics, and requires precise coupling to the photodiodes to achieve matching in phase and amplitude between the two balancing arms. Wide bandwidth and low noise is achieved by the use of a tuning network between the photodetectors and the first transistor, avoiding the f2 noise contribution, found in conventional receivers.2
© 1992 Optical Society of America
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