PHASE NOISE REDUCTION APPARATUS

摘要

PROBLEM TO BE SOLVED: To provide a phase noise reduction apparatus which does not use a change in light intensity for detecting phase noise and eliminates the need of a variable phase shifter which operates in the frequency band of a laser beam.

SOLUTION: The phase noise reduction apparatus includes: a delay line 3 for delaying one of outputs of a beam splitter 2 which splits the output of a semiconductor laser into two outputs; an RF-band oscillator 10 which is oscillated in the RF band; a light intensity modulator 4 which performs amplitude modulation on the other output of the beam splitter 2 using the output of the RF-band oscillator 10; an optical coupler 6 which adds or subtracts and outputs the output of the delay line 3 and an upper side band signal of the amplitude modulated signal; a balanced photodiode 7 which inputs the output of the optical coupler 6; a variable phase shifter 11 which changes the phase of an input signal in the oscillation frequency band of the RF-band oscillator 10; a mixer 8 which mixes the output of the balanced photodiode 7 and the results of phase-changing the output of the RF-band oscillator 10 through the variable phase shifter 11; and a low-pass filter 9 which selects a low frequency component in the output of the mixer. The phase of an optical oscillation signal of the semiconductor laser 1 is controlled.

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