A frequency reference photonic integrated circuit for WDM with low polarization dependence

Abstract
A photonic circuit implementing ten frequency reference filters for narrow-channel wavelength division multiplexing (WDM) has been fabricated. A diluted multiquantum-well waveguide structure is shown to yield a very low TE/TM polarization dependence of 1 AA, as well as improved absolute frequency control and reproducibility. A standard deviation in absolute filter wavelength of 3.33 AA is measured on a random set of devices from a 2-in wafer. The ten channels are evenly spaced by 7.2 AA. Such filters can be used to lock tunable lasers to a set of reference frequencies for WDM applications. The demonstrated diluted multiquantum-well waveguide structure with low birefringence and improved absolute wavelength control could potentially be used in other WDM integrated circuits requiring tight wavelength tolerance and polarization insensitivity.<>