Integrated photonics is fast evolving. Investigators are now exploring the shorter—visible—wavelength range to develop a wide variety of emerging applications. These include chip-scale light detection and ranging (LIDAR), augmented/virtual/mixed reality (AR/VR/MR) goggles, holographic displays, quantum information processing chips, and implantable optogenetic probes in the brain. The one device critical to all these applications in the visible range is an optical phase modulator, which controls the phase of a light wave, similar to how the phase of radio waves is modulated in wireless computer networks.
Researchers can build an on-chip optical switch with a phase modulator that channels light into different waveguide ports. With an extensive network of these optical switches, researchers could create sophisticated integrated optical systems that control light propagating on a tiny chip or light emission from the chip. But these devices in the visible range are tough to make. There are no materials that are transparent enough in the visible spectrum while also providing large tunability, either through thermo-optical or electro-optical effects.
Now, the researchers have developed a way based on micro-ring resonators to dramatically reduce the size and the power consumption of a visible-spectrum phase modulator, from one millimeter to 10 microns, and from tens of milliwatts for π phase tuning to below one milliwatt.