An optimum weak optical signal receiver for intensity modulation/direct detection optical communication systems

Abstract

AbstractThis paper presents a detailed study of a binary optical direct detection optimum receiver for the use of optical space communication systems, where a long‐distance transmission makes optical received signals extremely week. At such a low‐power operation of the receiver, the quantum discreteness structure of the shot noise process is evident in the optical detector output.A statistical model for optical detection output is derived, considering this quantum discreteness, thermal noise at the receiver circuit system, dark current at optical detector, and random photomultiplication. Moreover, the optical detection system is considered as an ideal integration system, and optical detection output is expressed by using a time‐dependent sample value vector.A logarithmic likelihood function derived from this sample value vector on the basis of maximum likelihood testing is studied, and the optimum receiver structure for weak optical signals is clarified. That is, it is shown that, even under the existence of thermal noise and random photomultiplication, primary photon count plays an essential role in signal detection similar to that in the shot noise limited case and the primary photocount estimator‐maximum likelihood detection receiver is derived theoretically. Then the error rate performance is analyzed theoretically and compared with that of a conventional direct detection receiver. As a result, it is shown that by introducing a wide‐band optical detection system, a significant improvement in error rate performance is observed over conventional receivers.