Coupling of Photon Emitters in Monolayer WS2 with a Photonic Waveguide Based on Bound States in the Continuum.

On-chip light sources are an essential component of scalable photonic integrated circuits (PICs), and coupling between light sources and waveguides has attracted a great deal of attention. Photonic waveguides based on bound states in the continuum (BICs) allow optical confinement in a low-refractive-index waveguide on a high-refractive-index substrate and thus can be employed for constructing PICs. In this work, we experimentally demonstrated that the photoluminescence (PL) from a monolayer of tungsten sulfide (WS2) could be coupled into a BIC waveguide on a lithium-niobate-on-insulator (LNOI) substrate. Using finite-difference time-domain simulations, we numerically obtained a coupling efficiency of ∼2.3% for an in-plane-oriented dipole and a near-zero loss at a wavelength of 620 nm. By breaking through the limits of 2D-material integration with conventional photonic architectures, our work offers a new perspective for light-matter coupling in monolithic PICs.

Synthesis of single-crystal low-loss LiB3O5 nanowire and its optical properties.

Optical-quality single-crystal LiB3O5 (LBO) nanowires are synthesized for the first time using a sol-gel method. The LBO nanowires possess diameters ranging from 200 to 800 nm and lengths of up to 200 µm, and exhibit excellent uniformity, smooth surfaces, and good mechanical properties. A typical propagating loss of 0.038 dB/µm at 532 nm is obtained for a 620 nm-diameter nanowire. This is a decrease of one order of magnitude compared with that of a ß-BaB2O4 (BBO) nanowire with similar diameter, which makes the LBO nanowire a promising candidate to construct miniaturized nonlinear photonic devices.