Patent ID: 7991299

Claim:
An optical transmitter that transmits a light signal, comprising: a light source, a Mach-Zehnder optical modulator, a modulator driver, an optical coupler, an eye monitor, and a driving voltage controller, wherein the Mach-Zehnder optical modulator modulates the light intensity of output light from the light source by use of a modulator driving signal, the modulator driver outputs the modulator driving signal according to an input data signal, the optical coupler splits modulated light from the Mach-Zehnder optical modulator, the eye monitor calculates the extinction ratio of the modulated light, and the driving voltage controller outputs, to the modulator driver, a control signal for setting the latest driving voltage, according to the calculated extinction ratio, wherein the eye monitor comprises: a light receiver that converts the modulated light into an electric signal; a clock reproducer that reproduces a clock signal from the electric signal; an analog-digital converter that converts the electric signal into a digital signal according to the clock signal; and an extinction ratio calculator that calculates the extinction ratio according to the digital signal.