Abstract
To use coherent heterodyne system configurations effectively and to take full advantage of the potential sensitivity improvement over direct detection systems, it is essential to develop low-noise heterodyne-receiver frontends. So far, such development has proved difficult (especially for gigabit-per-second applications) because of the parasitics of typical photodiodes. The best results so far with bandwidths of ≥2 GHz have used inductive tuning1 to obtain typical noise spectral densities of 2,3 for frontends with one photodiode. In many systems, the influence of relative intensity noise (RIN) on the local oscillator laser can be important.4 The requirements to the RIN level can be significantly eased using a balanced- (two-photodiode) receiver frontend, but this frontend tends to increase the influence of photodiode parasitics and requires careful coupling of the photodiodes. We have developed a design, usable for gigabit-per-second applications, which simultaneously gives a high common-mode rejection owing to the balancing and the lowest level of the noise spectral density reported so far.
© 1991 Optical Society of America
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