Comments, with reply, on 'Performance of coherent optical receivers' by J.R. Barry and E.A. Lee

The commenter shows how nonzero extinction ratios affect the performance of an otherwise ideal on-off keyed (OOK) communication system. In their reply, J.R. Barry and E.A. Lee point out that by using these results, experimenters will be able to state accurately what fraction of their sensitivity deviation from the ideal quantum limit is due to the nonzero extinction ratio. The ideal ten-photon quantum limit for OOK measures the number of photons per bit required by an ideal system-including the transmitter and channel, and not just the detector-to achieve a BER of 10/sup -9/. Barry and Lee agree with the commenter that it is not a useful benchmark for detectors alone; it is, however, a useful benchmark for the entire system.<
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