Abstract: Apparatus for optical communications, the apparatus being adapted for mounting on a circuit pack and including, as a single, self-contained module, circuitry comprising at least one of an optical receiver for converting a received optical signal into a received electrical signal and an optical transmitter for converting an electrical transmission signal into an optical transmission signal, at least one electrical connector for conveying at least one of said received electrical signal and said electrical transmission signal, and at least one optical connector for conveying at least one of said received optical signal and said optical transmission signal. The circuitry further comprises at least an optical detector for detecting said received optical signal based on a decision level, and the receiver includes at least one decision block having a selectively variable decision level.