LIGHT INTENSITY MODULATING APPARATUS

PROBLEM TO BE SOLVED: To obtain a drift in the modulation curve L with high accuracy by using a simple structure and to control to obtain the optimum bias voltage with high accuracy. SOLUTION: A light intensity modulating apparatus is equipped with an LN modulator 3 which modulates the intensity of a light signal S1 by using an inputted electric signal S2, outputs the resultant modulated light signal S3 to the outside and has a monitor PD3a to monitor the modulated signal S3; a DA converter 15 which outputs a bias voltage Vb of the electric signal S3; a synthesizer 17 which generates a pilot signal Va of a fundamental frequency fp; an adder 20 which superposes the bias voltage Vb and the pilot signal Va; a band pass filter 12; and a controller C which calculates the ratio of the second harmonic wave component 2fp to the fundamental frequency component fp, determines the drift in the modulation curve of the LN modulator 3 based on the calculation result and generates a bias voltage Vp to offset the drift. COPYRIGHT: (C)2004,JPO