Integrated multi-wavelength interferometer using waveguide holograms for nanometer precision sensing

We present a tri-wavelength integrated photonic interferometer for nanometer-resolution displacement sensing in semiconductor metrology. The device integrates large-area waveguide hologram couplers optimized for 635 nm, 780 nm, and 850 nm to illuminate and receive light from a reflective target, forming a Mach–Zehnder interferometer. A novel design method enables scalable intensity control, achieving an average focusing efficiency of −12.8 dB , the highest reported for tri-wavelength couplers, to our knowledge. Interferometric operation was verified at 633 nm and 775 nm. Displacement measurements were demonstrated down to 16 nm, currently limited by the resolution of the external translation stages. Picometer-scale resolution is feasible using commercially available signal processing systems. These results demonstrate a path toward compact, solid-state, high-resolution optical metrology systems.