The broadband enhancement of single‑photon emission from nitrogen‐vacancy centers in nanodiamonds coupled to a planar multilayer metamaterial with hyperbolic dispersion is studied experimentally. The metamaterial is fabricated as an epitaxial metal/dielectric superlattice consisting of CMOS‐compatible ceramics: titanium nitride (TiN) and aluminum scandium nitride (AlxSc1‐xN). It is demonstrated that employing the metamaterial results in significant enhancement of collected single‑photon emission and reduction of the excited‐state lifetime. Our results could have an impact on future CMOS‐compatible integrated quantum sources.
Monocrystalline titanium dioxide (TiO2) micro‐spheres support two orthogonal magnetic dipole modes at terahertz (THz) frequencies due to strong dielectric anisotropy. For the first time, we experimentally detected the splitting of the first Mie mode in spheres of radii m through near‐field time‐domain THz spectroscopy. By fitting the Fano lineshape model to the experimentally obtained spectra of the electric field detected by the sub‐wavelength aperture probe, we found that the magnetic dipole resonances in TiO2 spheres have narrow linewidths of only tens of gigahertz. Anisotropic TiO2 micro‐resonators can be used to enhance the interplay of magnetic and electric dipole resonances in the emerging THz all‐dielectric metamaterial technology.
A novel approach to facilitate excitation and readout processes of isolated negatively charged nitrogen‐vacancy (NV) centers is proposed. The approach is based on the concept of all‐dielectric nanoantennas. It is shown that the all‐dielectric nanoantenna can significantly enhance both the emission rate and emission extraction efficiency of a photoluminescence signal from a single NV center in a diamond nanoparticle on a dielectric substrate. The proposed approach provides high directivity, large Purcell factor, and efficient beam steering, thus allowing an efficient far‐field initialization and readout of several NV centers separated by subwavelength distances.
The recent progress in integrated quantum optics has set the stage for the development of an integrated platform for quantum information processing with photons, with potential applications in quantum simulation. Among the different material platforms being investigated, direct‐bandgap semiconductors and particularly gallium arsenide (GaAs) offer the widest range of functionalities, including single‐ and entangled‐photon generation by radiative recombination, low‐loss routing, electro‐optic modulation and single‐photon detection. This paper reviews the recent progress in the development of the key building blocks for GaAs quantum photonics and the perspectives for their full integration in a fully‐functional and densely integrated quantum photonic circuit.
Wide‐angle, polarization‐independent structural reflective colors from both directions based on a one‐dimensional photonic crystal are demonstrated. Our device produces a distinct and saturated color with high angular tolerant performance up to ±70° for any polarization state of an incident light wave, which is highly desirable for a broad range of research areas. Moreover, the purity of the color and luminous intensity of the proposed device are improved as compared to conventional colorant‐based color filters and colloidal glasses. The present approach may have the potential to replace existing color filters and pigments and pave the way for various applications, including color displays and image sensor technologies.
Optical absorbers find uses in a wide array of applications across the electromagnetic spectrum, including photovoltaic and photochemical cells, photodetectors, optical filters, stealth technology, and thermal light sources. Recent efforts have sought to reduce the footprint of optical absorbers, conventionally based on graded structures or Fabry‐Perot‐type cavities, by using emerging concepts in plasmonics, metamaterials, and metasurfaces. Unfortunately, these new absorber designs require patterning on subwavelength length scales, and are therefore impractical for many large‐scale optical and optoelectronic devices. In this article, we summarize recent progress in the development of optical absorbers based on lossy films with thicknesses significantly smaller than the incident optical wavelength. These structures have a small footprint and require no nanoscale patterning. We outline the theoretical foundation of these absorbers based on “ultra‐thin‐film interference”, including the concepts of loss‐induced phase shifts and critical coupling, and then review several applications, including ultra‐thin color coatings, decorative photovoltaics, high‐efficiency photochemical cells, and infrared scene generators.
Monitoring the aquatic environment and the life of free‐floating organisms remains on the borderline of our technical capabilities. Therefore, our insights into aquatic habitats, such as, abundance and behavior of organisms are limited. In order to improve our understanding of aquatic life, we have developed a low‐cost inelastic hyperspectral lidar with unlimited focal depth and enough sensitivity and spatiotemporal resolution to detect and resolve position and behavior of individual submillimeter organisms. In this work, we demonstrate elastic as well as molecular ranging by using the water Raman band, and by observing fluorescence from chlorophyll and from dye‐tagged organisms. We present an aquatic laser‐diode‐based inelastic light detection and ranging (lidar) system with unprecedented sensitivity, spatiotemporal resolution and number of spectral bands. Our system offers new opportunities for quantitative in situ studies of aquatic organisms, and has the potential to considerably advance our understanding of biological life in aquatic systems.
Tailoring of electromagnetic spontaneous emission predicted by E. M. Purcell more than 50 years ago has undoubtedly proven to be one of the most important effects in the rich areas of quantum optics and nanophotonics. Although during the past decades the research in this field has been focused on electric dipole emission, the recent progress in nanofabrication and study of magnetic quantum emitters, such as rare‐earth ions, has stimulated the investigation of the magnetic side of spontaneous emission. Here, we review the state‐of‐the‐art advances in the field of spontaneous emission enhancement of magnetic dipole quantum emitters with the use of various nanophotonics systems. We provide the general theory describing the Purcell effect of magnetic emitters, overview realizations of specific nanophotonics structures allowing for the enhanced magnetic dipole spontaneous emission, and give an outlook on the challenges in this field, which remain open to future research.
A scheme for active temporal‐to‐spatial demultiplexing of single photons generated by a solid‐state source is introduced. The scheme scales quasi‐polynomially with photon number, providing a viable technological path for routing n photons in the one temporal stream from a single emitter to n different spatial modes. Active demultiplexing is demonstrated using a state‐of‐the‐art photon source—a quantum‐dot deterministically coupled to a micropillar cavity—and a custom‐built demultiplexer—a network of electro‐optically reconfigurable waveguides monolithically integrated in a lithium niobate chip. The measured demultiplexer performance can enable a six‐photon rate three orders of magnitude higher than the equivalent heralded SPDC source, providing a platform for intermediate quantum computation protocols.
We present a general theory of circular dichroism in planar chiral nanostructures with rotational symmetry. It is demonstrated, analytically, that the handedness of the incident field's polarization can control whether a nanostructure induces either absorption or scattering losses, even when the total optical loss (extinction) is polarization‐independent. We show that this effect is a consequence of modal interference so that strong circular dichroism in absorption and scattering can be engineered by combining Fano resonances with planar chiral nanoparticle clusters.
A semiconductor optical amplifier at 2.0‐µm wavelength is reported. This device is heterogeneously integrated by directly bonding an InP‐based active region to a silicon substrate. It is therefore compatible with low‐cost and high‐volume fabrication infrastructures, and can be efficiently coupled to other active and passive devices in a photonic integrated circuit. On‐chip gain larger than 13 dB is demonstrated at 20 °C, with a 3‐dB bandwidth of ∼75 nm centered at 2.01 µm. No saturation of the gain is observed for an on‐chip input power up to 0 dBm, and on‐chip gain is observed for temperatures up to at least 50 °C. This technology paves the way to chip‐level applications for optical communication, industrial or medical monitoring, and non‐linear optics.
In the development of microfluidic chips, conventional 2D processing technologies contribute to the manufacturing of basic microchannel networks. Nevertheless, in the pursuit of versatile microfluidic chips, flexible integration of multifunctional components within a tiny chip is still challenging because a chip containing micro‐channels is a non‐flat substrate. Recently, on‐chip laser processing (OCLP) technology has emerged as an appealing alternative to achieve chip functionalization through in situ fabrication of 3D microstructures. Here, the recent development of OCLP‐enabled multifunctional microfluidic chips, including several accessible photochemical/photophysical schemes, and photosensitive materials permiting OCLP, is reviewed. To demonstrate the capability of OCLP technology, a series of typical micro‐components fabricated using OCLP are introduced. The prospects and current challenges of this field are discussed.
Recently, the coexistence of a parity‐time (PT) symmetric laser and absorber has gained tremendous research attention. While PT‐symmetric lasers have been observed in microring resonators, the experimental demonstration of a PT‐symmetric stripe laser is still absent. Here, we experimentally study a PT‐symmetric laser absorber in a stripe waveguide. Using the concept of PT‐symmetry to exploit the light amplification and absorption, PT‐symmetric laser absorbers have been successfully obtained. In contrast to the single‐mode PT‐symmetric lasers, the PT‐symmetric stripe lasers have been experimentally confirmed by comparing the relative wavelength positions and mode spacing under different pumping conditions. When the waveguide is half‐pumped, the mode spacing is doubled and the lasing wavelengths shift to the center of every two initial lasing modes. All these observations are consistent with the theoretical predictions and well confirm the PT‐symmetry breaking.
We demonstrate a scheme incorporating dual‐coupled microresonators through which mode interactions are intentionally introduced and controlled for Kerr frequency comb (microcomb) generation in the normal‐dispersion region. Microcomb generation, repetition rate selection, and mode locking are achieved with coupled silicon nitride microrings controlled via an on‐chip microheater. The proposed scheme shows for the first time a reliable design strategy for normal‐dispersion microcombs and may make it possible to generate microcombs in an extended wavelength range (e.g. in the visible) where normal material dispersion is likely to dominate.
Optically levitated nanodiamonds with nitrogen‐vacancy centers promise a high‐quality hybrid spin‐optomechanical system. However, the trapped nanodiamond absorbs energy from laser beams and causes thermal damage in vacuum. It is proposed here to solve the problem by trapping a composite particle (a nanodiamond core coated with a less absorptive silica shell) at the center of strongly focused doughnut‐shaped laser beams. Systematical study on the trapping stability, heat absorption, and oscillation frequency concludes that the azimuthally polarized Gaussian beam and the linearly polarized Laguerre‐Gaussian beam LG03 are the optimal choices. With our proposal, particles with strong absorption coefficients can be trapped without obvious heating and, thus, the spin‐optomechanical system based on levitated nanodiamonds are made possible in high vacuum with the present experimental techniques.
A compact 64‐channel hybrid demultiplexer based on silicon‐on‐insulator nanowires is proposed and demonstrated experimentally to enable wavelength‐division‐multiplexing and mode‐division‐multiplexing simultaneously in order to realize an ultra‐large capacity on‐chip optical‐interconnect link. The present hybrid demultiplexer consists of a 4‐channel mode multiplexer constructed with cascaded asymmetrical directional‐couplers and two bi‐directional 17 × 17 arrayed‐waveguide gratings (AWGs) with 16 channels. Here each bi‐directional AWG is equivalent as two identical 1 × 16 AWGs. The measured excess loss and the crosstalk for the monolithically integrated 64‐channel hybrid demultiplexer are about ‐5 dB and ‐14 dB, respectively. Better performance can be achieved by minimizing the imperfections (particularly in AWGs) during the fabrication processes.
Following Mie theory, nanoparticles made of a high‐refractive‐index dielectric, such as silicon, exhibit a resonator‐like behavior and very rich resonance spectra. Which electric or magnetic particle mode is excited depends on the wavelength, the refractive‐index contrast relative to the environment, and the geometry of the nanoparticle itself. In addition, the spatial structure of the impinging light field plays a major role in the excitation of the nanoparticle resonances. Here, it is shown that, by tailoring the excitation field, individual multipole resonances can be selectively addressed while suppressing the excitation of other particle modes. This enables a detailed study of selected individual resonances without interference by the other modes.
A Luneburg lens is a fascinating gradient refractive index (GRIN) lens that can focus parallel light on a perfect point without aberration in geometrical optics. Constructing a three‐dimensional (3D) Luneburg lens at optical frequencies is a challenging task due to the difficulty of fabricating the desired GRIN materials. Here, we present the practical implementation of a 3D Luneburg lens at optical frequencies. Such a 3D Luneburg lens is designed with GRIN 3D simple cubic metamaterial structures, and fabricated with dielectric metamaterials by femtosecond laser direct writing in the commercial negative‐photoresist IP‐L. Simulated and experimental results exhibit an interesting 3D ideal focus for the infrared light. The protocol for developing the 3D Luneburg lens with ideal focus would prompt the potential applications in integrated light‐coupled devices and lab‐on‐chip integrated biological sensors based on infrared light.
Narrow‐linewidth lasers are key elements in optical metrology and spectroscopy. Spectral purity of these lasers determines accuracy of the measurements and quality of collected data. Solid state and fiber lasers are stabilized to relatively large and complex external optical cavities or narrow atomic and molecular transitions to improve their spectral purity. While this stabilization technique is rather generic, its complexity increases tremendously moving to longer wavelenghts, to the infrared (IR) range. Inherent increase of losses of optical materials at longer wavelengths hinders realization of compact, room temperature, high finesse IR cavities suitable for laser stabilization. In this paper, we report on demonstration of quantum cascade lasers stabilized to high‐Q crystalline mid‐IR microcavities. The lasers operating at room temperature in the 4.3‐4.6 μm region have a linewidth approaching 10 kHz and are promising for on‐chip mid‐IR and IR spectrometers.
