Method for control of optical intensity and extinction ratio of laser modulation in an optical transmitter

摘要

Controlling the optical intensity and the extinction ratio of the modulation of a laser diode of an optical data transmitter comprising: current driver circuitry configured to supply a drive current to a laser diode wherein said current comprises a fixed component and a modulated component, said modulated component having a magnitude related to an input data stream. The monitor circuitry comprising a photodiode and a first transimpedance amplifier coupled to said photodiode, said monitor circuitry configured to provide an output signal related to an optical intensity of said laser diode. The system further comprising replica monitor circuitry comprising a replica capacitor with a replica capacitance and a second transimpedance amplifier configured to be substantially identical in construction to said first transimpedance amplifier, said second transimpedance amplifier coupled to said replica capacitor. The system further comprising replica capacitance control circuitry configured to control said replica capacitance of said replica capacitor to match a capacitance associated with said photodiode. The parallel replica signal path allows for the effects of gain and bandwidth on data to be taken into account. The probability density function (PDF) of the monitor signal may then be used to infer the extinction ratio. (Extinction ratio, or modulation depth, being the ratio of optical intensity for data 1 and data 0).