Researchers at Georgia Institute of Technology (Georgia Tech) have integrated a microheater and a microring resonator onto a silicon carbide (SiC) chip, creating a photonic integrated chip that can be thermally tuned by applying an electric signal. The approach could one day be used to create a range of reconfigurable devices such as phase-shifters and tunable optical couplers needed for networking applications and quantum information processing. SiC has defects that can be optically controlled and manipulated as qubits, making it an attractive material for quantum computing and communication applications. It is biocompatible and can operate at wavelengths from the visible to infrared. The new work builds on the researchers’ previous development of a platform called crystalline SiC-on-insulator, a technology that enables wafer-level manufacturing of SiC devices. To create a SiC-based photonic integrated chip, the researchers needed to tune the chip’s optical properties so that the single chip-based structure could be used to provide different functions. Making use of the thermo-optics effect, the researchers modified the material’s optical properties by changing its temperature. The team fabricated tiny ring-shaped optical cavities — microring resonators — using the crystalline SiC-on-insulator technology. In each resonator, light at resonance wavelengths built up strength through constructive interference while traveling around the ring. The resonator could then be used to control the amplitude and phase of the light in a waveguide coupled to the resonator. To create a tunable resonator with a high degree of control, the researchers fabricated electric heaters on top of the microrings. When an electric current was applied to the integrated microheater, it locally increased the temperature of the SiC microring and changed its resonant wavelengths — a result of the thermo-optic effect. Researchers created the first thermally tunable optical switch using a silicon carbide-on-insulator platform. The schematic image shows their concept for a quantum photonic integrated circuit chip that includes circular microring resonators and microheaters. The inset shows the temperature and electric field distributions at the cross-section of a microring resonator heated by a microheater. Courtesy of Ali Adibi, Georgia Institute of Technology. The researchers tested the performance of the integrated microring resonators and microheaters by applying different levels of electrical power and then measuring the optical transmission of the waveguide coupled to the microring resonator. The results showed that it is possible to achieve high-quality resonators with low-power thermal tunability using a device that can be manufactured using semiconductor foundry processes. “Combined with other unique features of our crystalline SiC-on-insulator platform, these high-quality devices have the basic requirements for enabling new chip-scale devices that operate in a wide range of wavelengths,” professor Ali Adibi, who led the research, said. “This chip-scale tunability is essential for performing quantum operations necessary for quantum computing and communication. In addition, because of the biocompatibility of SiC, it could be very useful for in vivo biosensing.” The researchers are now working to build elements with the crystalline SiC-on-insulator platform for quantum photonic integrated circuits, including on-chip pump lasers, single photon sources, and single photon detectors that could be used with the tunable microring resonator to create a fully functional chip for advanced optical quantum computing. The research was published in Optics Letters, a publication of OSA, The Optical Society (https://doi.org/10.1364/OL.44.004941).