US Patent 7787781 Optical receiver reliably detectable loss-of-signal state

The present invention is to provide an optical receiver that prohibits the miss-detection of the recovery from the LOS (Loss-Of-Signal) state. The optical receiver includes an light-receiver device for converting an optical input signal to a photo-current, a pre-amplifier for converting this photo-current into a voltage signal, and a LOS detector to detect the LOS state based on the output from the pre-amplifier. The LOS detector includes a bottom hold that detects and keeps the bottom level of the output from the pre-amplifier and the comparator that sets the output thereof when the output from the bottom hold exceeds the threshold VTH(−).