To make a device small-sized by using two optical heterodyne detection having a stable frequency interval without using a high frequency oscillator.
Light emitted by LDs 1a and 1b is multiplexed and demultiplexed by a directional coupler 3a; and one of the output light becomes the output of an optical transmitter and the other one is inputted to a directional coupler 3b. Only one of the two demultiplexed output light passes through a delay line 7 and is outputted to optical detectors 4a and 4b and a phase comparator 5 makes phase comparison and outputs phase difference information. The output signal of the phase comparator 5 is inputted to a feedback circuit 6 to extract only phase difference information of low frequency and the information is sent as feedback information to a drive circuit 2, which corrects oscillation wavelength under the control of temperature or/and the drive current so that the frequency interval between the LDs 1a and 1b becomes equal to a desirable high angular frequency.
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FUKUSHIMA SEIJI
ONO TETSUICHIRO
MATSUOKA YUTAKA
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