Recently, a review entitled Silicon carbide for integrated photonics from XOI group led by Xin Ou in Shanghai Institute of Microsystem and Information Technology (SIMIT) has been published in Applied Physics Reviews. In this article, milestones and challenges in SiC-based integrated optics are comprehensively reviewed.

Photonic Integrated Circuits (PICs) are expected to solve two bottlenecks of transmission bandwidth and processing speed in information technology. However, traditional silicon photonics cannot realize all functions required by information society. As supplements, platforms such as LiNbO₃, Si₃N₄, etc. are explored. Particularly, SiC, benefited from its high refractive index, wide transparency window, high nonlinear coefficient, CMOS-compatibility, etc., is accepted as a promising platform for PICs.

In nonlinear optics, ultra-high Q (highest value 7.1×10⁶) SiC optical resonators, octave-spanning Kerr frequency microcombs and soliton Kerr frequency microcombs at cryogenic temperature have been successively demonstrated in recent three years. In electro-optics, a CMOS-driven microring-based electro-optical (EO) modulator operating at high optical density was demonstrated in 2022. SiC also received much attention in quantum optics. It can host single spin defect with bright emission and long spin coherence time. Coherent manipulation of single divacancy spin in 4H-SiC and efficient coupling of SiV to resonators (micro-pillars or PhCs) in 4H-SiCOI have been respectively realized. Furthermore, a cubic lattice site SiV (V2) generated by He⁺ implantation was successfully integrated into waveguide without deterioration of intrinsic spin-optical properties in 2022.

Obviously, SiC photonics is presently in a stage of blossoming growth with great opportunities but also challenges, especially preparation of high-quality SiCOI.

XOI group from SIMIT has carried out systematic research on SiCOI-based integrated photonics. In 2019, researchers fabricated 4-inch 4H-SiCOI of high uniformity for integrated optics by ion-cutting technology [Opt. Mater. 107, 109990 (2020)] and generated a room-temperature coherent controlled spin defect in the 4H-SiC by H⁺ implantation [npj Quantum Inf 6, 38 (2020)]. Subsequently, an SiC resonator was fabricated through femtosecond laser-assisted chemical-mechanical polishing (CMP) method and the optical quality factor was measured to be 7.1×10⁶, which is the highest value in SiC photonics so far [Light Sci Appl 10, 139 (2021)]. Owing to the ultrahigh-Q, broadband frequency conversion, cascaded Raman lasing and wide bandwidth Kerr frequency were achieved. In 2022, 4H-SiC photonic chip was integrated with InGaAs quantum dot (QD)-based single-photon sources (SPSs) by pick-and-place technique [Laser Photonics Rev. 2022, 2200172]. By designing bilayer vertical couplers and 1 × 2 multimode interferometers with a power splitting ratio of 50:50, generation and highly efficient routing of single-photon emission in the hybrid quantum photonic chip were realized. Recently, XOI group is aimed at the fabrication of 4H-SiCOI with low optical loss and promoting integrated nonlinear and quantum SiC photonics, especially wide bandwidth soliton frequency Kerr comb.

In combination with the advances in SiC nonlinear and quantum optics, a broader prospect for SiC integrated optics could be expected. The development of low-cost, wafer-scale and high quality 4H-SiCOI will push nonlinear and quantum optics, even SiC power and RF devices ahead.

Illustration of single crystal 4H-SiC and Kerr comb generation (image by Light: Science & Applications)