The problem of tracking small changes in the output wavelength of laser diodes is addressed using a dual slab waveguide interferometer fabricated from silicon oxynitride. Waveguide mode dispersion differences between the waveguide modes provide a mechanism for identifying input wavelength shifts that are measured as shifts in the output far-field diffraction image. At visible wavelengths the device can transduce input wavelength changes into phase responses with a sensitivity of +0.9 rad/nm. The lower threshold limit of detection for laser output frequency shifts, is 2.2 GHz or 6 pm at a center wavelength of 635 nm. The TE and TM sensitivities to wavelength are approximately equivalent in the device described.
Cross, G. H., & Strachan, E. E. (2002). Diode laser wavelength tracking using an integrated dual slab waveguide interferometer. IEEE Photonics Technology Letters, 14(7), 950–952. https://doi.org/10.1109/LPT.2002.1012395