Integrated photon-pair sources are crucial for scalable photonic quantum systems. Thin-film lithium niobate is a promising platform for on-chip photon-pair generation through spontaneous parametric down-conversion (SPDC). However, the device implementation faces practical challenges. Periodically poled lithium niobate (PPLN), despite enabling flexible quasi-phase matching, suffers from poor fabrication reliability and device repeatability, while conventional modal phase matching (MPM) methods yield limited efficiencies due to inadequate mode overlaps. Here, we introduce a layer-poled lithium niobate (LPLN) nanophotonic waveguide for efficient photon-pair generation. It leverages layer-wise polarity inversion through electrical poling to break spatial symmetry and significantly enhance nonlinear interactions for MPM, achieving a notable normalized second-harmonic generation (SHG) conversion efficiency of 4615% W⁻¹cm⁻². Through a cascaded SHG and SPDC process, we demonstrate photon-pair generation with a normalized brightness of 3.1 × 10⁶ Hz nm⁻¹ mW⁻² in a 3.3 mm long LPLN waveguide, surpassing existing on-chip sources under similar operating configurations. Crucially, our LPLN waveguides offer enhanced fabrication reliability and reduced sensitivity to geometric variations and temperature fluctuations compared to PPLN devices. We expect LPLN to become a promising solution for on-chip nonlinear wavelength conversion and non-classical light generation, with immediate applications in quantum communication, networking, and on-chip photonic quantum information processing.

Silicon carbide (SiC) is emerging rapidly in novel photonic applications thanks to its unique photonic properties facilitated by the advances of nanotechnologies such as nanofabrication and nanofilm transfer. This review paper will start with the introduction of exceptional optical properties of silicon carbide. Then, a key structure, i.e., silicon carbide on insulator stack (SiCOI), is discussed which lays solid fundament for tight light confinement and strong light-SiC interaction in high quality factor and low volume optical cavities. As examples, microring resonator, microdisk and photonic crystal cavities are summarized in terms of quality (Q) factor, volume and polytypes. A main challenge for SiC photonic application is complementary metal-oxide-semiconductor (CMOS) compatibility and low-loss material growth. The state-of-the-art SiC with different polytypes and growth methods are reviewed and a roadmap for the loss reduction is predicted for photonic applications. Combining the fact that SiC possesses many different color centers with the SiCOI platform, SiC is also deemed to be a very competitive platform for future quantum photonic integrated circuit applications. Its perspectives and potential impacts are included at the end of this review paper.

Anisotropic metameterials (AM) provide a new avenue for a next-generation silicon platform to design ultra-compact, densely integrated optical components, thus functional devices based on AM are drawing increasing attention recently. Here, we propose a novel efficient polarization beam splitter (PBS) with high polarization extinction ratio based on AM. An ultra-compact coupling region of 2.5 × 14 µm² is achieved by tailoring the AM structures, which can efficiently suppress the TE mode coupling, and enhance the TM mode coupling in the directional couplers simultaneously. The insertion loss is simulated to be as low as 20 dB and wide operational bandwidth of >80 nm.

We report four-wave mixing with different polarization and spatial modes in a single 4H-silicon carbide photonic device. Our device shows great potential to perform high-dimensional multiplexing for optical communication and high-dimensional entanglement in quantum networks. We use a polarization-insensitive grating coupler and a multimode microring resonator that supports three polarization and spatial mode resonances. Finally, we show the polarization dependence of the third-order nonlinearity of 4H-silicon carbide. The measured nonlinear refractive index of the light polarized along the extraordinary axis, which is n_2,TM = (13.1 ± 0.7) × 10⁻¹⁹ m²/W, is twice as large as that of the light polarized along the ordinary plane, n_2,TE = (7.0 ± 0.3) × 10⁻¹⁹ m²/W, indicating that the extraordinary polarization is more efficient for nonlinear experiments in the 4H-silicon carbide integrated platforms as compared to the ordinary polarization.

The polarization beam splitter is a key component for polarization manipulation in photonic integrated circuits, but it is challenging to design for low-refractive-index optical materials, due to the low birefringence of the waveguides. We propose what we believe is a novel compact vertical-dual-slot waveguide-based coupling scheme for silicon carbide, enabling efficient low-birefringence polarization splitting by extensively modulating the transverse-magnetic mode distribution. We numerically and experimentally demonstrate the device in the 4H-silicon-carbide-on-insulator integrated platform, with a small footprint of 2 . 2 μm × 15 μm . The device, easy to fabricate via a single lithography process as other components on the chip, exhibits low insertion loss of < 0.71 dB and < 0.51 dB for the transverse-electric and transverse-magnetic polarized light, respectively, and polarization extinction ratio of > 13 dB , over 80 nm wavelength range.

We propose the realization of exceptional points (EP) at bound states in the continuum (BIC), with two coupled strips, made of an electron‐beam resist and patterned on the thin film photonic integrated platform, which makes possible etchless photonics integrated circuits (PIC). The loss rate of the EP can be significantly decreased through merging the BIC peaks in the dual‐BIC scheme. The orthogonality of the eigenvectors is retrieved for evaluating the Hermitian orthogonal eigenvectors and the non‐Hermitian EP features. We also find that engineering the dimension of the dual‐BIC scheme enables a transition between the coalesced eigenvectors in the EP and the orthogonal eigenvectors in the Hermitian system. This work is of great significance for the exploration on BIC‐based directional coupling with ultralow‐loss phase matching conditions, special coupling conditions of EPs and BICs with coupled quasi‐BIC systems, dynamical EP encircling, and EP topology, in PICs.