Scan-Free KrF Laser Phase Tuning of Non-Hydrogen Loaded Planar Lightwave Circuit Interferometer Arrays

The large-scale deployment of planar lightwave circuits (PLCs) is becoming a reality, but high yield and precise phase control continues to pose challenges in mass production. We demonstrate a scan-free protocol employing a large emitting beam krypton fluoride excimer laser and no hydrogen loading to precisely tune the local refractive index of PLCs directly on the die’s measurement stage. Asymmetrical Mach-Zehnder interferometers are locally irradiated with an accumulated fluence greater than 180 kJ/cm2 without damage or increased loss, inducing reproducible wavelength shifts greater than 120 nm in the interferometer response, corresponding to refractive index shifts greater than 0.001. Accumulated fluence is the primary factor controlling the index change, while per-pulse fluence determines the speed of trimming, within limits determined by the damage onset. Aside from a 20% decrease following initial thermal treatment, the photo-induced changes are thermally stable. A small amount of photo-induced birefringence is observed, but shown to be manipulatable predictively. With potential for low-cost automated implementation, the proposed protocol offers a scalable solution to improve PLC chip deployability in areas including LiDAR and photonic computing.