Tunable laser source with an integrated wavelength monitor and method of operating same

Abstract

A wavelength monitor is provided based on the transmission response of an optical filter. The monitor provides feedback to the laser enabling it to lock to any given wavelength within its tuning range. The invention is also a process for integrating the wavelength monitor directly on chip with a variety of tunable semiconductor lasers. The invention also comprises a method for controlling the wavelength of a tunable laser by using a wavelength monitor to measure the output light and provide feedback to a control system. The laser and wavelength monitor are integrated together on a single indium phosphide chip. The wavelength monitor comprises a filter with a wavelength dependent transmission function and a pair of detectors. One detector is illuminated with light that has passed through the filter and the other provides a reference to measure the input intensity. Taking the ratio of the filtered light level to the unfiltered light provides a wavelength dependent wavelength. The filter is designed such that the transmission function is monotonic and varies from a minimum at one extent of the laser's tuning range to a maximum at the other extent.