Optical phase modulators are essential to large-scale integrated photonic systems at visible wavelengths and are promising for many emerging applications. However, current technologies require large device footprints and either high power consumption or high drive voltages, limiting the number of active elements in a visible-spectrum integrated photonic circuit. Here, we demonstrate visible-spectrum silicon nitride thermo-optic phase modulators based on adiabatic micro-ring resonators that offer at least a one-order-of-magnitude reduction in both the device footprint and power consumption compared with waveguide phase modulators. Designed to operate in the strongly over-coupled regime, the micro-resonators provide 1.6π phase modulation with minimal amplitude variations, corresponding to modulation losses as small as 0.61 dB. By delocalizing the resonant mode, the adiabatic micro-rings exhibit improved robustness against fabrication variations: compared with regular micro-rings, less than one-third of the power is needed to thermo-optically align the resonances of the adiabatic micro-rings across the chip to the laser frequency.

光相位调制器对于可见光波长的大规模集成光子系统至关重要，并且有望用于许多新兴应用。然而，当前技术需要较大的器件尺寸以及高功耗或高驱动电压，从而限制了可见光谱集成光子电路中有源元件的数量。在这里，我们展示了基于绝热微环谐振器的可见光谱氮化硅热光相位调制器，与波导相位调制器相比，它在器件占地面积和功耗方面至少降低了一个数量级。设计用于在强过耦合状态下工作，微谐振器提供 1.6π 相位调制，幅度变化最小，对应的调制损耗低至 0.61 dB。