A light detector measures optical power of light incident thereon. Using a beam steering device that is rotatable about two orthogonal axes, wavelength components of different channels are scanned onto the light detector in accordance with programmable parameters. The programmable parameters specify the light detector to which the wavelength components are directed, the order the wavelength components are monitored by the light detector, and the time duration over which each of the wavelength components is monitored by the light detector.