Jianjun Chen

Due to out‐of‐plane diffraction channels or scattering channels of defects, on‐chip micro‐lasers always suffer from severe emission of free‐space photons. This severely hampers not only the development of ultra‐high Q and ultra‐dark on‐chip micro‐lasers but also the high‐density integration with other nanophotonic components. Herein, ultra‐dark on‐chip plasmonic lasers are experimentally realized in high‐quality Ag‐SiO ₂ nanodisk lattices. The out‐of‐plane diffraction channel is eliminated by using the first‐order‐feedback mechanism. The losses of the scattering channels are greatly decreased by fabricating high‐quality Ag‐SiO ₂ nanodisk lattices. As a result, an “ultra‐dark” plasmonic lattice laser with ultra‐high Q is realized at room temperature. Linewidths of as small as Δ λ _FWHM‐T ≈ 0.003 nm at visible wavelengths are deconvolution‐inferred, and the corresponding Q factor is as high as Q ≈ 2.1 × 10 ⁵ , which is approximately 75 times the largest Q factor in previous plasmonic lattice lasers. The in‐plane coupling efficiency of the on‐chip plasmonic lasers is approximately 99%, indicating that there is hardly any emission of free‐space laser photons. The ratio of laser emission in free space (∼1%) is approximately 20 times lower than that (≥20%) reported in previous works. Based on the “ultra‐dark” plasmonic lasers, the high‐density integration of multiple components and functions is demonstrated.

Metasurfaces have exhibited huge potential for manipulating fields of on‐chip light sources. It is known that the scattering properties of nano‐scatterers depend not only on the diverse incident directions of the excited in‐plane waveguide modes but also on the in‐plane orientations of nano‐scatterers. This greatly complicates the design of metasurfaces for freely manipulating fields of on‐chip light sources. Herein, we propose an identical‐scatterer scheme to make the scattering properties of each nano‐scatterer independent of the various in‐plane incident directions of on‐chip sources. Then, a self‐discretizing iterative computational holographic intelligent algorithm is developed to arrange identical nano‐scatterers to create vectorial metasurfaces for free manipulation of on‐chip sources. Experimentally, we demonstrate not only eight independent emission beams, each with its own emission direction and polarization state, exhibiting round and near‐diffraction‐limited profiles (divergence ≈ 1.0°) with high polarization purities (91%–99%), but also complex emission patterns with different emission directions and polarization states.

Symmetry breaking is commonly employed to optimize the functionalities of cavities, such as the single‐wavelength resonance, directional output, or high quality‐factor ( Q ). Due to the mutual influence and restriction of these performance metrics, it is a great challenge to realize high‐ Q multiple‐wavelength resonances with each wavelength's emission being directional and distinguished. Here, a non‐circular inner and circular outer (NICO) cavity is proposed, and dual‐wavelength resonant modes with different in‐plane emission directions for the two wavelengths are realized. More importantly, the Q of the two modes in the NICO cavity remains unchanged (100%) compared to the fully circular cavity. To gradually change the inner ellipse shape to the outer‐circle shape, only the coordinates (not the refractive index) are transformed. This transformation makes the cavity easy to fabricate in the experiment. Both the band‐gap confinement effect of the outer circle layers and the gradual change from the inner ellipse shape to the outer‐circle shape significantly halt the Q ‐spoiling phenomena. Solutions of increasing refractive index differences and further breaking symmetry are provided to improve the Q factors (as high as 10 ¹³ ) and narrow the emission divergence angles (by approximately twice), as well as increase the splitting wavelengths (by ≈6 times).

Metasurfaces have exhibited huge potential for manipulating fields of both free-space and on-chip light sources. To design a metasurface, a group of nano-scatterers should be firstly found and optimized and then be arranged. For on-chip integrated light sources, the scattering amplitudes, phases, and polarizations of nano-scatterers depend on not only incident directions of light but also in-plane orientations of nano-scatterers. This greatly increases the difficulty of designing metasurfaces for freely manipulating fields of on-chip light sources, such as achieving multiple emission directions (even with complex emission patterns) with fully independent polarization states. Herein, we propose to utilize an identity scheme, which employs identical nano-scatterers with only one incident angle, to eliminate the harmful influence of diverse incident directions of light and in-plane orientations of nano-scatterers on scattering properties of nano-scatterers. So, it is not needed any more to seek nano-scatterer groups for on-chip light sources. Then, a self-discretized iterative computational holographic intelligent algorithm is exploited to arrange these identical nano-scatterers to create vectorial metasurfaces, enabling free manipulation of on-chip light sources. Multiple (up to 8) collimated emission beams (divergence angles ≤ 1.4°) with fully independent polarization states of high purities are demonstrated. Moreover, complex emission patterns with different emission directions and different polarization states are also presented experimentally. This identity scheme and the intelligent algorithm provide new perspectives for designing metasurfaces, especially for freely manipulating on-chip sources.

Photon momentums and their control are important for carrying quantum information and increasing information capacities. It is a great challenge to freely control multiple momentums of single photons based on only phase‐dependent schemes in isotropic metasurfaces because exact manipulations of interference phases and precise alignments between quantum emitters and metasurfaces are involved. Here, an anisotropic metasurface, in which anisotropic rather than isotropic nanoscatterers are arranged anisotropically, is proposed to freely control multiple momentums of single photons. In the metasurfaces, the phase‐independent and phase‐dependent schemes are used to independently control spin angular momentums (SAMs) and linear momentums (LMs), respectively. The phase‐independent scheme allows robust alignment between quantum emitters and metasurfaces. The anisotropic design amends geometrical phases for oblique emissions, providing larger ranges (up to 53°) for tailoring LMs. In experiments, three‐channel single‐photon emissions with independent SAMs and LMs are demonstrated. The introduction of anisotropic nanoscatterers and anisotropic arrangements of nanoscatterers is a more general design method for metasurfaces, and it could provide more flexibility to freely and efficiently tailor single‐photon emissions.

Based on luminosity contributions, we develop a spectroscopic modelling method to derive atmospheric parameters of component stars in binary systems. The method is designed for those spectra of binaries which show double-lined features due to the radial velocities differences between the component stars. We first derive the orbital parameters and the stellar radii by solving the light and radial velocity curves. Then the luminosity contributions in different phases can be calculated. The synthesised double-lined spectra model is constructed by superposing theoretical single-star spectra according to the luminosity contributions. Finally, we derive the atmospheric parameters of each component star by the model fitting method. For multi-epoch double-lined spectra observed by the Large sky Area Multi-Object Spectroscopic Telescope (LAMOST) Medium Resolution Survey ($R \sim 7500$), our method gives robust results for detached eclipsing binary systems observed in different orbital phases. Furthermore, this method can also be applied to other spectroscopic data with different resolutions as long as the systems are detached eclipsing binaries with nearly spherical stars.

Due to nanometric hotspots in a metallic nanoantenna or phase sensitivities in a metasurface, precise placement of a quantum emitter is rigorously required to tailor single‐photon emission, which considerably increases alignment and fabrication difficulties. Here, a scalar‐superposition metasurface is proposed to achieve robust placement of a quantum emitter and meanwhile tailor the single‐photon emission to a desired polarization (e.g., linear, circular, or elliptical polarization). In this metasurface, the far‐field interference of the scattered fields from all unit nanostructures can be simplified as a scalar‐superposition process. As a result, the emission polarization state is insensitive to the phase or the position of the quantum emitter. The simualtion and experiment show that the placement accuracy of the quantum emitter relative to the center of the metasurface is released to about 3λ (wavelength), which is dozens of times greater than that in previous works. This high placement robustness together with the deflection effect of emission directions of the metasurfaces further enable to tailor the polarization of multiple single‐photon emission spots. The strategy of the scalar‐superposition metasurfaces with robust placement makes the nanostructure design and alignment easy, and it also might provide new possibilities for realizing multifunctional and novel quantum nanophotonic devices.

Optical phased array provides a promising platform for multi-beam steering in optical bands. Here, we propose and demonstrate an effective multi-beam steering scheme employing a phase-only spatial light modulator. The beam orientations and beam amplitudes are both programmable in our proposal. With Huygens-Fresnel simulation, the fidelity value of ~0.998 and ~0.999 are evaluated corresponding to the case of random beam orientations and random beam amplitude ratios, respectively. Furthermore, up to 101-beam steering is experimentally observed, which is much higher than existed reports.