US Patent 7313326 Method to inject pilot tone into microcontroller-supervised DWDM transmitters

The power of a digital signal such as an optical data stream is set via digital-to-analog converter having a reference input for connection to a DC reference signal. The pilot tone is injected into the reference input of the digital-to-analog converter. In the place of a dual amplitude control (modulation current and pilot tone), the disclosed arrangement only requires a single control, thereby reducing cost, power consumption, microcontroller input/output activity, area occupation (PCB real estate) and failure rate.