Multichannel Single-Photon Emissions with On-Demand Momentums by Using Anisotropic Quantum Metasurfaces.

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.

Ultralow-Loss Phonon Polaritons in the Isotope-Enriched α-MoO3.

α-MoO3, a natural van der Waals (vdWs) material, has received wide attention in nano-optics for supporting highly confined anisotropic phonon polaritons (PhPs) from the mid-infrared to the terahertz region, which opens a new route for manipulating light at the nanoscale. However, its optical loss hinders light manipulation with high efficiency. This work demonstrates that the isotope-enriched Mo element enables ultralow-loss PhPs in the α-MoO3. Raman spectra reveal that the isotope-enriched Mo element in the α-MoO3 allows different optical phonon frequencies by efficiently altering the Reststrahlen band's dispersion. The Mo isotope-enriched α-MoO3 significantly reduces the PhPs' optical loss due to efficient optical coherence, which enhances the propagation length revealed by infrared nanoimaging. These findings suggest that the isotope-enriched α-MoO3 is a new feasible 2D material with an ultralow optical loss for possible high-performance integrated photonics and quantum optics devices.

Toward Microlasers with Artificial Structure Based on Single-Crystal Ultrathin Perovskite Films.

A perovskite microlaser is potentially valuable for integrated photonics due to its excellent properties. The artificial microlasers were mostly made on polycrystalline films. Though a perovskite single crystal has significantly improved properties in comparison with its polycrystalline counterpart, an artificial microlaser based on single-crystal perovskite has been much less explored due to the difficulty in producing an ultrathin-single-crystal (UTSC) film. Here we show a device processing based on a perovskite UTSC film, confirming the high performance of the UTSC device with a quality factor of 1250. The single-crystal device shows 4.5 times the quality factor and 8 times the radiation intensity in comparison with its polycrystalline counterpart. The experiment first proved that hybrid perovskite microlasers with a subwavelength fine structure can be processed by focused ion beams (FIB). In addition, a wavelength-tunable distributed feedback (DFB) laser is demonstrated, with a tuning range of ∼4.6 nm. The research provides an easily applicable approach for perovskite photonic devices with excellent performance.

High-sensitivity plasmonic sensor by narrowing Fano resonances in a tilted metallic nano-groove array.

Plasmonic sensors exhibit enormous potential in the areas of environmental monitoring, biomedical diagnostics, healthcare, food safety, security, and chemical reactions. However, the large bandwidths of surface-plasmon response spectra greatly reduce the sensitivities and detection limits of plasmonic sensors. Herein, we propose to tilt a metallic nano-groove array to reduce linewidths of Fano resonances, and the figure of merit (FOM) of a refractive index sensor is greatly increased. The Fano resonances stem from interference between narrow SPP resonant modes and a broad LSP mode in the metallic nano-groove array. When tilting the metallic nano-groove array, new Fano resonances emerge, greatly compressing the linewidth of Fano resonance of interest to ∼1.1 nm in the simulation. Experimentally, a narrow Fano resonance with a linewidth of Δλ≈2.5 nm is achieved, and a high-FOM (FOM ≈ 263) plasmonic sensor is demonstrated. This value of FOM is more than 4.7 times that (FOM ≤ 55) of Fano sensors based on SPP modes, and it is even approximately twice that (FOM ≈ 140) of the previous Fano sensor based on Wood's Anomaly.

Imaging and Controlling Photonic Modes in Perovskite Microcavities.

Perovskite microcavities have excellent photophysical properties for integrated optoelectronic devices, such as nanolasers. Imaging and controlling the photonic modes within the cavity are fundamentally important to understand and develop applications. Here, photoemission electron microscopy (PEEM) is used to image the photonic modes within optical microcavities with a nanometer-scale spatial resolution. From a CsPbBr3 microcavity, hybrid mode patterns are observed. Spatial frequency spectrum analysis on the patterns uncovers the characteristic cavity modes, which are modeled with transverse magnetic (TM) and transverse electric (TE) waves, and assigned to exciton-polariton modes. Based on this understanding, the light focus in a designed microcavity is imaged in real space and controlled by the light field polarization. The study confirms that the cavity modes in perovskites can be effectively observed by the PEEM technique under resonant excitation, which, in turn, promotes the design of optoelectronic devices based on perovskite microcavities.