Patent ID: 7266309

Claim:
An apparatus for stabilizing a bias voltage for an external modulator used for pulse generation, comprising: optical dividing means for allowing an optical signal output from the external modulator, to which the bias voltage is to be applied, to branch off; optical/electrical converting means for converting the output optical signal branched by the optical dividing means into an electrical signal; multiplying means for multiplying the optical signal, output from the external modulator and applied through the optical/electrical converting means, by a drive clock signal applied to the external modulator; mean output measuring means for measuring a mean output value of products obtained by multiplication of an output signal of the external modulator and the clock signal; and control means for initializing an optimal bias ascertaining variable to be “0”, increasing a bias voltage by a unit value when the optimal bias ascertaining variable is “0” and the mean output value is “0”, changing the optimal bias ascertaining variable to be “1” when the optimal bias ascertaining variable is “0”, and the mean output value is not “0”, increasing or decreasing the bias voltage by the unit value depending on whether the mean output value is negative or positive when the optimal bias ascertaining variable is “1” and the mean output value is not “0”, and maintaining a present bias voltage as it is when the optimal bias ascertaining variable is “1” and the mean output value is “0”.