Patent ID: 8666256

Claim:
An optical receiving apparatus comprising: an optoelectrical converting circuit which receives an optical signal and optoelectrically converts the optical signal to reproduce an error-correcting-code-added electric signal; a pre-stage synchronizing word detecting circuit which detects a synchronizing word included in said error-correcting-code-added electric signal; a decoder which performs an error correcting process on the error-correcting-code-added electric signal from which the synchronizing word has been detected, to reproduce a frame-added electric signal; a post-stage frame synchronization detecting circuit which determines whether or not the first number of successive synchronizing words whose bit errors are equal to or smaller than a first allowable value, among synchronizing words included in said frame-added electric signal, has reached a first prescribed number, in a predetermined number of frames subsequent to a frame in which said synchronizing word has been detected; and a receiver frame synchronization display output circuit which decides that frame synchronization of said optical signal has been established if said first number of successive synchronizing words has reached said first prescribed number.