Abstract: A light source device has a continous wave (CW) light source for emitting first direct current (DC) light, a level converter for converting optical electric power of the first DC light into second DC light and outputting the second DC light, and a mixer for mixing an optical main signal having a constant extinction ratio with the second DC light.

Abstract: A preamplifier circuit, a clock switching circuit, and an optical receiver are provided that include a preamplifier that controls a bandwidth for conducting amplification on an input signal by varying a feedback resistance according to a control signal; a control signal generating part that determines the band of the output signal of the preamplifier to generate the control signal; and a correction signal generating part that generates a correction signal for correcting the control signal; wherein the correction signal corrects the control signal to adjust the feedback resistance. Accordingly, even when the number of rises and falls of an optical input signal in a given time period is less than a predetermined number range, the control signal may be properly generated to successfully conduct band control.

Abstract: A light source device has a CW light source for emitting first DC light, a level converter for converting optical electric power of the first DC light into second DC light and outputting the second DC light, and a mixer for mixing an optical main signal having a constant extinction ratio with the second DC light.

Abstract: A preamplifier circuit, a clock switching circuit, and an optical receiver are provided that include a preamplifier that controls a bandwidth for conducting amplification on an input signal by varying a feedback resistance according to a control signal; a control signal generating part that determines the band of the output signal of the preamplifier to generate the control signal; and a correction signal generating part that generates a correction signal for correcting the control signal; wherein the correction signal corrects the control signal to adjust the feedback resistance. Accordingly, even when the number of rises and falls of an optical input signal in a given time period is less than a predetermined number range, the control signal may be properly generated to successfully conduct band control.

Abstract: In an equalizing amplifier that equalizes an electric signal obtained from a light signal received via an optical transmission path, an AGC circuit generates first and second signals from the electric signal by referring to a threshold voltage. The first and second signals are complementary signals. An offset compensation circuit generates a first difference signal based on a difference between the first and second signals, compares the first difference signal with a first reference signal, and outputs, as the threshold voltage, a resultant error signal to the AGC circuit. The threshold voltage is varied so that it is located in the center of an amplitude of the electric signal whereby an offset of the AGC circuit can be compensated for.