The ability to tune the wavelength of light emission on a silicon chip is important for scalable photonic networks, distributed photonic sensor networks, and next generation computer architectures. Here we demonstrate light emission in a chip-scale optomechanical device, with wide tunablity provided by a combination of radiation pressure and photothermal effects. To achieve this, we develop an optically active double-disk optomechanical system through implantation of erbium ions. We observe frequency tuning of photoluminescence in the telecommunications band with a wavelength range of 520 pm, green up-conversion lasing with a threshold of $340\pm 70\mu \mathrm{W}$, and optomechanical self-pulsing caused by the interplay of radiation pressure and thermal effects. These results provide a path towards widely tunable micron-scale lasers for photonic networks.

Strong acousto-optic interaction in high-index waveguides and cavities generally requires the releasing of the high-index core to avoid mechanical leakage into the underlying low-index substrate. This complicates fabrication, limits thermalization, reduces the mechanical robustness, and hinders large-area optomechanical devices on a single chip. Here, we overcome this limitation by employing vertical photonic-phononic engineering to drastically reduce mechanical leakage into the cladding by adding a pedestal with specific properties between the core and the cladding. We apply this concept to a silicon-based platform, due to the remarkable properties of silicon to enhance optomechanical interactions and the technological relevance of silicon devices in multiple applications. Specifically, the insertion of a thick silicon nitride layer between the silicon guiding core and the silica substrate contributes to reducing gigahertz-frequency phonon leakage while enabling large values of the Brillouin gain in an unreleased platform. We numerically obtain values of the Brillouin gain around $300(\mathrm{W\; m}{)}^{-1}$ for different configurations, which could be further increased by operation at cryogenic temperatures. These values should enable Brillouin-related phenomena in centimeter-scale waveguides or in more compact ring resonators. Our findings could pave the way toward large-area unreleased-cavity and waveguide optomechanics on silicon and other high-index photonic technologies.

Harnessing the quantum interference of the pair generation processes, infrared quantum spectroscopy, based on nonlinear interferometers with visible-infrared photon-pair sources, enables the extraction of the infrared optical properties of a sample through visible photon detection without the need for an infrared optical source or detector. We develop a theoretical framework for quantum Fourier-transform infrared (QFTIR) spectroscopy. The proposed Fourier analysis method, which fully utilizes the phase information in the interferogram, allows us to determine the complex transmittance and optical constants for a sample in a simple setup without the use of any dispersive optics for spectral selection. In the experimental demonstrations, the transmittance spectrum of a bandpass filter and the refractive index of silica glass are measured in the near-infrared region using QFTIR operated in a low gain regime; these results agree well with the independently measured spectrum using a conventional spectrometer and an value estimated from references. These demonstrations prove the validity and great potential of QFTIR spectroscopy.

Through the use of experimental and numerical techniques, we study coherent networks of plasmonic phase-correlated dipole domains that can spread coherent properties along ultralong distances. The phase-correlated domains occur in regions containing closely packed metallic nanoparticles with random positions, shapes, and sizes. We demonstrate that when such regions are periodically arranged, forming two-dimensional arrays, optical diffraction can coherently excite and align the plasmonic dipoles of the nanoparticles within each region, forming delocalized collective plasmon resonances associated with the in-phase coupling of the dipoles. We study the impact of the number of metallic nanoparticles in each region, determining the limit at which it becomes a phase-correlated dipole domain and establishes coherent interdomain coupling. Our results show how such a coupling can form coherent networks of packages of delocalized states with the same phase information. $\mathrm{Au}$ nanoislands with different packings, sizes, and shapes are considered as experimental models to explore phase-correlated dipole domains and interdomain coupling. The conditions in which the coherent interdomain coupling occurs via parallel or orthogonal hybridization of the Rayleigh anomaly with the delocalized plasmon resonances supported by the domains are explored. The outcomes offer alternative techniques for coherent transport of energy and information, in which phase-correlated dipole domains serve as units with large coherent spatial extension.

We present a theoretical study of the collective quasiparticle excitations responsible for the electromagnetic response of ultrathin plane-parallel homogeneous periodic single-wall carbon-nanotube arrays and weakly inhomogeneous single-wall carbon-nanotube films. We show that in addition to varying film composition, the collective response can be controlled by varying the film thickness. For single-type nanotube arrays, the real part of the dielectric response shows a broad negative refraction band near a quantum interband transition of the constituent nanotube, whereby the system behaves as a hyperbolic metamaterial at higher frequencies than those classical plasma oscillations have to offer. By decreasing nanotube diameters it is possible to push this negative refraction into the visible region, and using weakly inhomogeneous multitype nanotube films broadens its bandwidth.

The fields of cavity quantum electrodynamics and magnetism have recently merged into cavity spintronics, investigating a quasiparticle that emerges from the strong coupling between standing electromagnetic waves confined in a microwave cavity resonator and the quanta of spin waves, magnons. This phenomenon is now expected to be employed in a variety of devices for applications ranging from quantum communication to dark matter detection. To be successful, most of these applications require a vast control of the coupling strength, resulting in intensive efforts to understanding coupling by a variety of different approaches. Here, the electromagnetic properties of both resonator and magnetic samples are investigated to provide a comprehensive understanding of the coupling between these two systems. Because the coupling is a consequence of the excitation vector fields, which directly interact with magnetization dynamics, a highly accurate electromagnetic perturbation theory is employed that predicts the resonant hybrid mode frequencies for any field configuration within the cavity resonator. The coupling is shown to be strongly dependent not only on the excitation vector fields and sample’s magnetic properties but also on the sample’s shape. These findings are illustrated by applying the theoretical framework to two distinct experiments: a magnetic sphere placed in a three-dimensional resonator and a rectangular, magnetic prism placed in a two-dimensional resonator. The theory provides comprehensive understanding of the overall behavior of strongly coupled systems and it can be easily modified for a variety of other systems.

Electromagnetic scattering on subwavelength structures is attracting much attention owing to the broad range of possible applications where this phenomenon can be used. Fundamental limits of the scattering cross section, which are well understood in spherical geometries, are overlooked in cases of low-symmetry resonators. Here we revise the notion of superscattering and link this property with symmetry groups of scattering potentials. We demonstrate pathways to spectrally overlap several eigenmodes of a resonator in a way such that they interfere constructively and increase the scattering cross section. As a particular example, we demonstrate spectral overlapping of several electric and magnetic modes in a subwavelength ceramic resonator. The optimized structures have a dipolar scattering cross-section limit exceeding that for a sphere by up to a factor of 4. The revealed rules, which link symmetry groups with fundamental scattering limits, allow assessment of the designs and performance of subwavelength superscatterers, which can be used in label-free imaging, compact antennas, long-range radio-frequency identification, and many other fields.

The broken mirror symmetry in subwavelength photonic systems has manifested many interesting chiroptical effects, such as optical rotation and circular dichroism. When such systems are placed periodically in a lattice form, in addition to intrinsic chirality, extrinsic chirality also takes part, and the overall effect depends not only on the basis and lattice but also the excitation configuration. Here, we study planar chiral nanohole arrays in square lattice that support Bloch-like surface plasmon polaritons (SPPs) and clarify how the system geometry and the excitation contribute to circular dichroism. By using temporal coupled mode theory, the dissymmetry factor and the scattering matrix of the arrays are analytically formulated. Remarkably, we find the dissymmetry factor depends only on the coupling polarization angle and the in-coupling phase difference between the p- and s-polarizations. Furthermore, the upper limit of the dissymmetry factor at ±2 can be reached simply by orienting the lattice of the arrays for properly exciting the Bloch-like SPPs and at the same time making the basis mimic two orthogonal and relatively displaced dipoles, demonstrating the interplay between extrinsic and intrinsic chirality. The models have been verified by numerical simulations and experiments, yielding dissymmetry factors of 1.82 and 1.55, respectively, from the proposed dual slot system.

By independently engineering strain and composition, this work demonstrates and investigates direct-band-gap emission in the midinfrared range from ${\mathrm{Ge}}_{1\text{−}x}{\mathrm{Sn}}_x$ layers grown on silicon. We extend the room-temperature emission wavelength above approximately 4.0 µm upon postgrowth strain relaxation in layers with uniform Sn content of 17 at.%. The fundamental mechanisms governing the optical emission are discussed based on temperature-dependent photoluminescence, absorption measurements, and theoretical simulations. Regardless of strain and composition, these analyses confirm that single-peak emission is always observed in the probed temperature range of 4–300 K, ruling out defect- and impurity-related emission. Moreover, carrier losses into thermally activated nonradiative recombination channels are found to be greatly minimized as a result of strain relaxation. Absorption measurements validate the direct band-gap in strained and relaxed samples at energies closely matching photoluminescence data. These results highlight the strong potential of ${\mathrm{Ge}}_{1\text{−}x}{\mathrm{Sn}}_x$ semiconductors as versatile building blocks for scalable, compact, and silicon-compatible midinfrared photonics and quantum optoelectronics.

We demonstrate second-harmonic generation in a fiber-coupled periodically poled titanium in-diffused lithium niobate waveguide over the temperatures range from 292 to 4.4 K. We observe a reproducible shift in the phase-matched pump wavelength within the telecom band, which is at odds with the phase matching arising from existing models of the refractive indices in this temperature regime. We further investigate transient discontinuities while temperature cycling, which we attribute to the build-up and discharge of pyroelectric fields. Our results show that modifications of the Sellmeier coefficients for lithium niobate are required in the cryogenic temperature regime for our waveguides, but also establish titanium in-diffused waveguides in lithium niobate as a versatile nonlinear photonic integration platform compatible with cryogenic quantum technologies.

A valley photonic crystal is one type of photonic topological insulator, the realization of which needs only P-symmetry breaking. The domain wall between two valley-contrasting photonic crystals supports robust edge states, which can wrap around sharp corners without backscattering. Using the robust edge states, one can achieve pulse transmission. Here, using time-domain measurements in the microwave regime, we show distortionless pulse transmission in a sharply bended waveguide. An Ω-shaped waveguide with four 120° bends is constructed with the domain wall between two valley photonic crystal slabs. Experimental results show the progress of Gaussian pulse transmission without distortion, and the full width at half maximum of the output signal changes slightly in the Ω-shaped waveguide. By measuring the steady-state electric field distribution, we also confirm the confined edge states without out-of-plane radiation, which benefits from dispersion below the light line. Our work provides a way for high-fidelity optical pulse signal transmission and the development of high-performance optical elements, such as photonic circuits or optical delay lines.

A Bessel beam has the properties of propagation invariance and a self-healing effect, leading to a variety of interesting phenomena and applications. Recently, as a planar diffractive element with miniaturized size, metasurfaces are widely employed to manipulate light in the subwavelength region, including generating a Bessel beam. However, such a metasurface-generated Bessel beam allows output light with no tunable functions. Here, with the interplay of the geometric phase and the dynamic phase, we propose a method to generate and allow conversion from any orthogonal polarizations to independent Bessel beams with a single-layer dielectric metasurface. The simulation results indicate that the arbitrary conversion between different Bessel beams is related to the spin-dependent orbit motion caused by the tight-focusing effect, leading to the singularity of the spot. This physical mechanism is well studied and the theoretical model for revealing the dependence of different incident polarization on the conversion dynamics is presented. Our approach paves a way for efficient generation and multifunctional applications, ranging from high-numerical-aperture devices to compact nanophotonic platforms for spin-dependent structured beams.

We theoretically and experimentally demonstrate a thermally tunable anapole metasurface. By thermally changing the dielectric function, our studies unveil the tolerance of the nonradiating anapole source to the presence of dissipation losses in systems of all-dielectric meta-atoms. The so-called anapole state is an ac current distribution of electric and toroidal dipoles in such a relation that their exclusive destructive interference leads to the absence of far-field radiation. It has been shown to exist in variable dielectric configurations that involve assemblies of infinite dielectric rods, yet a systematic study of its tolerance to losses is still open. Here we examine two designs focusing on their tolerance to dissipation losses: one combining the toroidal mode of a peripheral four-cylinder system with the mixed toroidal mode of a single central cylinder of adjusted size, and another consisting of five rods in a regular pentagon arrangement. The first design exhibits a particularly enhanced toroidal dipole moment and high anapole precision. The second design exhibits anapole states with enhanced loss tolerance and, thus, it is the target of our experimental investigation. For the experiment, we use water-based rod metasurfaces designed for anapole operation in the microwave regime and we employ a characterization in a standard rectangular waveguide. The dielectric properties of water exhibit significant temperature dependence that allows for controlled permittivity and dissipation, leading to the dynamical modification of Mie resonances in meta-atoms. Thus, we experimentally prove the emergence of an anapole state and its tolerance to the losses in a well-controlled system; furthermore, we demonstrate and expose the potential of aqueous schemes for tunable electromagnetic applications.

We report a reduction in the linewidth and suppression of spectral diffusion of quantum emitters in hexagonal boron nitride supported on a conductive substrate. We observe a temperature-dependent reduction in the spectral emission linewidth for CVD-grown and exfoliated crystals on conductive ITO relative to those seen on silicon dioxide (${\mathrm{Si}\mathrm{O}}_2$) substrates. We show that the inhomogeneous linewidth can be suppressed by 45% as a result of using a conductive substrate. We investigate the zero-phonon line profile at temperatures ranging from 4 to 300 K and decompose the effects of thermal broadening and spectral diffusion at each temperature by Voigt fitting. The temperature dependence of homogeneous and inhomogeneous components of the broadening is discussed.

In the device-independent quantum-information approach, the implementation of a given task can be self-tested solely from the recorded statistics and without detailed models for the employed devices. Even though experimentally demanding, it provides appealing verification schemes for advanced quantum technologies that naturally fulfil the associated requirements. In this work, we experimentally study whether self-testing protocols can be adopted to certify the proper functioning of quantum devices built with modern space-division multiplexing optical fiber technology. Specifically, we consider the prepare-and-measure protocol of Farkas and Kaniewski [Phys. Rev. A 99, 032316 (2019)] for self-testing measurements corresponding to mutually unbiased bases (MUBs) in a dimension $d>2$. In our scheme, the state preparation and measurement stages are implemented using a multiarm interferometer built with multicore optical fibers and related components. Due to the high overlap of the interferometer’s optical modes achieved with this technology, we are able to reach the required visibilities for self-testing the implementation of two four-dimensional MUBs. We also quantify two operational quantities of the measurements: (i) the incompatibility robustness, connected to Bell violations, and (ii) the randomness extractable from the outcomes. Since MUBs lie at the core of several quantum-information protocols, our results are of practical interest for future quantum works relying on space-division multiplexing optical fibers.

High-density low-crosstalk waveguide superlattices can potentially help shrink the pitch of an optical phased array to half-wavelength, which may lead to superior beam characteristics. While a superlattice’s longitudinal coherence is exploited to create phase mismatch and reduce crosstalk, its transverse coherence is also modified and will inevitably disturb the beam forming of the optical phased array. Our theory shows that the transverse and longitudinal coherence can be balanced in a nontrivial superlattice such that superlattice-induced disturbance of the beam can be suppressed without compromising crosstalk. Large supercells less restrained by symmetry offer more degrees of freedom for finding a desirable superlattice structure. The supercell configuration order and structural modulation strength are crucial to balancing coherence and approaching the ideal characteristics of a half-wavelength pitch optical phased array. Experimental results show a high main-beam energy ratio, low sidelobe levels, and a wide angular scanning range. Such optical phased arrays may potentially open up further opportunities for light detection and ranging (LIDAR), wireless optical communications, and biomedical scanning imaging.

We propose lateral optical trapping of Rayleigh particles using tailored anisotropic and hyperbolic metasurfaces illuminated with a linearly polarized Gaussian beam. This platform permits optical traps to be engineered at the beam axis with a response governed by nonconservative and giant lateral recoil force coming from the directional excitation of confined surface plasmons during the light-scattering process. Compared to optical traps set over uniform metals, either in bulk or thin-layer configurations, the proposed traps are broadband in the sense that they can be set with beams oscillating at any frequency within a wide range in which the metasurface supports surface plasmons. Over that range, the metasurface dispersion evolves from an anisotropic elliptic to a hyperbolic regime going through a topological transition and enables optical traps with distinctive spatially asymmetric potential distribution, local potential barriers arising from the momentum imbalance of the excited plasmons, and an enhanced potential depth that permits stable trapping of nanoparticles using low-intensity laser beams. To investigate the performance of this platform, we develop a rigorous formalism based on Lorentz force within the Rayleigh approximation combined with anisotropic Green’s functions and calculate the trapping potential of nonconservative lateral forces using the Helmholtz decomposition method. Tailored anisotropic and hyperbolic metasurfaces, commonly implemented by nanostructuring thin metallic layers, permit to use low-intensity laser sources operating in the visible or infrared frequencies to trap and manipulate particles at the nanoscale, and may enable a wide range of applications in bioengineering, physics, and chemistry.