Patent ID: 6559997
Filing Date: 2003-05-06
Classification: H04B

Abstract:
An optical transmitter, for coupling to communication devices though a optical divider/coupler, having a source outputting a drive current, a light-emitting element, for outputting optical signal to an optical fiber coupled to at least one of the communication devices, that is driven by the drive current for generating an optical output signal and, a modulator controlling the supply and cutoff of the drive current to the light-emitting element, comprising:a detecting circuit that detects a source voltage; a control circuit that stops, if the detected source voltage is lower than a predetermined voltage, the supply of the drive current to the light-emitting element; a photodiode that converts part of an optical output signal of the light-emitting element into an electrical signal; an automatic power control circuit that outputs, in response to the electrical signal from the photodiode, a control signal for making an optical power of the optical output signal constant; a switch circuit that transmits the control signal outputted from the automatic power control circuit to the current source if the detected source voltage is over the predetermined voltage; and wherein the automatic power control circuit has a buffer circuit that performs level conversion of a light-on/off signal, a first peak hold circuit that holds a maximum output level of the buffer circuit, a second peak hold circuit that holds a maximum output level of the photodiode, and a comparator that makes a comparison between output levels of the first peak hold circuit and the second peak hold circuit.