Large Bidirectional Refractive Index Change in Silicon‐rich Nitride via Visible Light Trimming

Abstract Phase‐sensitive integrated photonic devices are highly susceptible to minor manufacturing deviations, resulting in significant performance inconsistencies. This variability has limited the scalability and widespread adoption of these devices. Here, a major advancement is achieved through continuous‐wave (CW) visible light (405 and 520 nm) trimming of plasma‐enhanced chemical vapor deposition (PECVD) silicon‐rich nitride (SRN) waveguides. The demonstrated method achieves precise, bidirectional refractive index tuning with a single laser source in CMOS‐compatible SRN samples with refractive indices of 2.4 and 2.9 (measured at 1550 nm). By utilizing a cost‐effective setup for real‐time resonance tracking in micro‐ring resonators, the resonant wavelength shifts as fine as 10 pm are attained. Additionally, a record red shift of 49.1 nm and a substantial blue shift of 10.6 nm are demonstrated, corresponding to refractive index changes of approximately 0.11 and −2 × 10 ⁻² . The blue and red shifts are both conclusively attributed to thermal annealing. These results highlight SRN's exceptional capability for permanent optical tuning, establishing a foundation for stable, precisely controlled performance in phase‐sensitive integrated photonic devices.