| 摘要 |
PURPOSE:To attain stable operation by providing an optical frequency shifter provided separately from a local oscillating light source as a means shifting the frequency of a local oscillating light. CONSTITUTION:A single mode coupler 2 is provided as a means synthesizing a signal light and local oscillating light, and as a means shifting the frequency of the local oscillating light so as to make the detection output of a photodetector 3 substantially constant, a loop filter 4, a voltage source 5, an adder 6 and a voltage controlled oscillator 7 are provided. Moreover, as the shift means, an acoustic optical frequency shifter 1 is provided separately from a local oscillation light source. A beat signal detected by the photodetector 3 a DC signal depending on the phase difference when the frequency of the signal light and that of the local oscillating light are coincident. Thus, the steady-state phase error of the optical phase locked loop is changed by varying the bias by the voltage source 5. Thus, the signal lights from two different light sources are subject to stable phase locking. |
