FREQUENCY MODULATOR FOR SEMICONDUCTOR LASER

摘要

PURPOSE:To apply FM modulation with a high modulation efficiency to a radiated light whose spectrum width is narrowered by feeding back an instantaneous phase control signal proportional to the variation of an instantaneous frequency of a laser by FM modulation to an external mirror in an opposite phase so as to modulate the instantaneous phase of the returned light to the laser. CONSTITUTION:A frequency controller 2 applies the frequency control of a laser drive current FM-modulated by the radiated light from the semiconductor laser 1. A liquid crystal reflection type modulator 25 modulates the radiated light from the semiconductor laser based on a modulation reference signal (c) from a modulator drive oscillator 29 generating a modulation reference signal of a low frequency and feeds back the result to the semiconductor laser 1. An output (g) of an automatic phase controller 3 control the central phase of the radiated light based on the modulation reference signal and the radiated light from the semiconductor laser 1 and an output (i) of the instantaneous phase control circuit 4 generating an instantaneous phase control signal nearly in opposite phase to the detected FM modulation component are added at an adder 32, the sum is fed to a piezoelectric conversion element 26 to drive a modulator 25 in the optical axis direction, which is integrated with the element 26.