Abstract: A demultiplex unit demultiplexes the optical output of a Mach-Zehnder optical modulator and inputs the demultiplexed optical output to a wavelength detection unit. The wavelength detection unit detects the wavelength deviations in the ascending or descending part of the optical signal and inputs the wavelength deviations to a detection unit. The detection unit detects the sign and magnitude of chirping in the magnitude of wavelength deviation and inputs the sign and magnitude of chirping to a driving voltage control unit. The driving voltage control unit compares the detected sign and amount of chirping with the target sign and magnitude of chirping, and a driving voltage generation circuit provides the Mach-Zehnder optical modulator with a suitable driving voltage.

Abstract: A demultiplex unit demultiplexes the optical output of a Mach-Zehnder optical modulator and inputs the demultiplexed optical output to a wavelength detection unit. The wavelength detection unit detects the wavelength deviations in the ascending or descending part of the optical signal and inputs the wavelength deviations to a detection unit. The detection unit detects the sign and magnitude of chirping in the magnitude of wavelength deviation and inputs the sign and magnitude of chirping to a driving voltage control unit. The driving voltage control unit compares the detected sign and amount of chirping with the target sign and magnitude of chirping, and a driving voltage generation circuit provides the Mach-Zehnder optical modulator with a suitable driving voltage.

Abstract: An optical transmitter is capable of constantly operating at an optimal operating point, even when a polarization angle varies, which is realized by an operation processing device controlling such that a predetermined range of an input-and-output characteristic of a modulator is scanned in order to obtain a bias voltage point that gives an optimal operation range, and an operation point controlling circuit controlling the operation range by a feedback control with the detected bias voltage point as a starting point.