Abstract: A Mach-Zehnder optical modulator includes: a Mach-Zehnder interferometer that includes first and second arms formed on a silicon substrate, and a controller that controls bias current of the first and second arms. The controller controls the bias current of the first and second arms respectively to be a first offset value. The controller repeatedly executes a current adjustment process to increase the bias current of the first arm until a gradient of a phase shift amount of the first arm with respect to the bias current of the first arm reaches a target value. The controller controls the bias current of the second arm to be a second offset value that is smaller than the first offset value. The controller repeatedly performs the current adjustment process to increase the bias current of the first arm until a phase difference of the Mach-Zehnder interferometer reaches a target phase difference.

Abstract: A Mach-Zehnder optical modulator includes: a Mach-Zehnder interferometer that includes first and second arms formed on a silicon substrate, and a controller that controls bias current of the first and second arms. The controller controls the bias current of the first and second arms respectively to be a first offset value. The controller repeatedly executes a current adjustment process to increase the bias current of the first arm until a gradient of a phase shift amount of the first arm with respect to the bias current of the first arm reaches a target value. The controller controls the bias current of the second arm to be a second offset value that is smaller than the first offset value. The controller repeatedly performs the current adjustment process to increase the bias current of the first arm until a phase difference of the Mach-Zehnder interferometer reaches a target phase difference.

Abstract: An optical transmitter includes an optical modulator that includes a first phase shifter for a most significant bit, a second phase shifter for a least significant bit, and a third phase shifter for fine adjustment, the first phase shifter, the second phase shifter, and the third phase shifter are disposed along an optical waveguide, and a drive circuit that includes a first driver that drives the first phase shifter, a second driver that drives the second phase shifter, and a third driver that drives the third phase shifter, wherein a drive polarity of the third driver is adjustable in a positive direction and a negative direction, and the third phase shifter adjusts an amount of phase change of the optical modulator in a positive direction or a negative direction based on a drive voltage inputted from the third driver.

Abstract: A laser diode control circuit includes, a control signal supply circuit that supplies a control signal including a direct current component and an alternating current component to a laser diode, an optical output signal acquisition circuit that acquires an optical output signal indicating an optical output of the laser diode according to the control signal, a phase determination circuit that determines whether a phase of the alternating current component included in the optical output signal is the same as the phase of the alternating current component included in the control signal, and a control signal determination circuit that determines to decrease the direct current component of the control signal when it is determined that the phase of the alternating current component included in the optical output signal is not the same as the phase of the alternating current component included in the control signal.

Abstract: An optical transmitter includes an optical modulator that includes a first phase shifter for a most significant bit, a second phase shifter for a least significant bit, and a third phase shifter for fine adjustment, the first phase shifter, the second phase shifter, and the third phase shifter are disposed along an optical waveguide, and a drive circuit that includes a first driver that drives the first phase shifter, a second driver that drives the second phase shifter, and a third driver that drives the third phase shifter, wherein a drive polarity of the third driver is adjustable in a positive direction and a negative direction, and the third phase shifter adjusts an amount of phase change of the optical modulator in a positive direction or a negative direction based on a drive voltage inputted from the third driver.