Micron-scale, efficient, and robust phase modulators at visible wavelengths

Optical phase modulators are essential to large-scale integrated photonic systems at visible wavelengths, promising for many emerging applications. However, current technologies require large device footprints and either high power consumption or high drive voltage, limiting the number of active elements in a visible integrated photonic circuit. Here, we demonstrate visible silicon-nitride thermo-optical phase modulators based on adiabatic micro-ring resonators that offer at least a one-order-of-magnitude reduction in both device footprint and power consumption compared to waveguide phase modulators. Designed to operate in the strongly over-coupled regime, the micro-resonators provide 2 pi phase modulation with minimal amplitude variations, corresponding to less than 1 dB device insertion losses. By delocalizing the resonant mode, the adiabatic micro-rings also exhibit substantially improved robustness against fabrication variations.