Wavelength tracking of a remote WDM router in a passive optical network

We propose, analyze, and demonstrate a simple, robust method which enables a laser to track uncontrolled changes in a remotely located WDM device. As opposed to locking to a wavelength standard, our method locks the wavelength comb of a tunable DBR to a waveguide grating router (200-GHz channel spacing). We have demonstrated tracking at a 1 C/min temperature slew rate without requiring sacrificial channels, a pilot tone, or analog dithering circuitry. We discuss tradeoffs between step size, slew rate, measurement accuracy, and power penalty.