A compact scalable phase modulator with zero static power consumption for visible integrated photonics

Optical modulators in the visible regime have far-reaching applications from biophotonics to quantum science. Implementations of such optical phase modulators on a complementary metal-oxide-semiconductor (CMOS) compatible platform have been mainly limited to utilization of the thermo-optic effect, liquid crystal technology, as well as piezo-optomechanical effects. Despite excellent performance, the demonstrations using the thermo-optic effect and liquid crystal technology both suffer from limited modulation speed. Moreover, the demonstrations utilizing piezo-optomechanical effects, require very large footprints due to a weak modulation efficiency. Here, we report the demonstration of the first highly scalable compact CMOS-compatible phase modulator in the visible regime based on altering the refractive index of an indium-tin oxide capacitive stack over a Si${_3}$N${_4}$ waveguide through the charge accumulation effect. The implemented modulator achieves a two orders-of-magnitude larger bandwidth compared to thermo-optic and liquid crystal based counterparts and close to 3 orders-of-magnitude higher modulation efficiency with about two orders-of-magnitude smaller footprint compared to piezo-optomechanical modulators. The 50 ${\mu}$m long phase modulator achieves a modulation efficiency, V$_{\pi}$L, of 0.06 V$.$cm at a zero static power consumption and a 31 MHz bandwidth at 637.9 nm.