| 摘要 |
PURPOSE: To execute adjustment by modulating an input bias signal having a pilot signal, detecting a modulator output part corresponding to the pilot signal, detecting non-linear relation between the detected pilot signal and the modulator output part and permitting a DC bias level to have more linear relation. CONSTITUTION: A low frequency pilot signal having a prescribed deviation is supplied to the electric modulating signal input(26) of a Mach-Zehnder electrooptical modulator(18) together with an electric input signal. A bias voltage VB selected for biasing the modulator(18) to a linear point(Vπ/2) is also supplied to the signal input(26). The optical output of the modulator(18) is detected and the sizes of the positive and the negative deviations of the output signal corresponding to the positive and negative deviations of the pilot signal are mutually compared. When the modulator(18) is linearly biased to a desired value, the deviation has the same correlative relation as the deviation of the pilot signal.
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