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.
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.
The spatial coherence of organic light‐emitting diodes (OLEDs) is an important parameter that has gained little attention to date. Here, we present a method for making quantitative measurements of the spatial coherence of OLEDs using a Young's double‐slit experiment. The usefulness of the method is demonstrated by making measurements on a range of OLEDs with different emitters (iridium and europium complexes) and architectures (bottom and top emitting) and the fringe visibility is further manipulated by gratings embedded in external diffractive optical elements. Based on the experiments and simulation of the results, we quantitatively determine the spatial coherence lengths of several OLEDs and find them to be a few micrometers. A 60% increase in the spatial coherence length was observed when using a narrow bandwidth emitter and a metal‐coated grating.
We experimentally demonstrate an optically‐pumped III‐V/Si vertical‐cavity laser with lateral emission into a silicon waveguide. This on‐chip hybrid laser comprises a distributed Bragg reflector, a III‐V active layer, and a high‐contrast grating reflector, which simultaneously funnels light into the waveguide integrated with the laser. This laser has the advantages of long‐wavelength vertical‐cavity surface‐emitting lasers, such as low threshold and high side‐mode suppression ratio, while allowing integration with silicon photonic circuits, and is fabricated using CMOS compatible processes. It has the potential for ultrahigh‐speed operation beyond 100 Gbit/s and features a novel mechanism for transverse mode control.
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.
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.
High efficiency, broad bandwidth, and robust angular tolerance are key considerations in photonic device design. Here, a few‐layer, asymmetric light transmitting metasurface that simultaneously satisfies all the above requirements is reported. The metasurface consists of coupled metallic sheets. It has a measured transmission efficiency of 80%, extinction ratio of 13.8 dB around 1.5 μm, and a full width half maximum bandwidth of 1.7 μm. It is as thin as 290 nm, has good performance tolerance against the angle of incidence and constituent nano‐structure geometry variations. This work demonstrates a practical asymmetric light transmission device with optimal performance for large scale manufacturing.
Femtosecond laser machining has been widely used for fabricating arbitrary 2.5 dimensional (2.5D) structures. However, it suffers from the problems of low fabrication efficiency and high surface roughness when processing hard materials. To solve these problems, we propose a dry‐etching‐assisted femtosecond laser machining (DE‐FsLM) approach in this paper. The fabrication efficiency could be significantly improved for the formation of complicated 2.5D structures, as the power required for the laser modification of materials is lower than that required for laser ablation. Furthermore, the surface roughness defined by the root‐mean‐square improved by an order of magnitude because of the flat interfaces of laser‐modified regions and untreated areas as well as accurate control during the dry‐etching process. As the dry‐etching system is compatible with the IC fabrication process, the DE‐FsLM technology shows great potential for application in the device integration processing industry.
We reveal unusually strong polarization sensitivity of electric and magnetic dipole resonances of high‐index dielectric nanoparticles placed on a metallic film. By employing dark‐field spectroscopy, we observe the polarization‐controlled transformation from high‐Q magnetic‐dipole scattering to broadband suppression of scattering associated with the electric dipole mode, and show numerically that it is accompanied by a strong enhancement of the respective fields by the nanoparticle. Our experimental data for silicon nanospheres are in an excellent agreement with both analytical calculations based on Green's function approach and the full‐wave numerical simulations. Our findings further substantiate dielectric nanoparticles as strong candidates for many applications in enhanced sensing, spectroscopy and nonlinear processes at the nanoscale.
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.
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.
Red‐light photodetectors without filters are in urgent need for narrowband applications such as full‐color imaging and multi‐output visible light communication (VLC). However, their development is hindered by the lack of small‐band‐gap and narrowband response materials. Without wavelength filters, a new type of photodetector with a simple single‐layer architecture is developed, based on a stable small‐band‐gap squarylium dye and characterized by a detectivity peak at 680 nm and full width at half maximum of 80 nm. The device, which exhibits high stability in air and humid conditions, shows a significantly low dark current of ∼2 nA·cm−2 at −2 V and high specific detectivity of 3.2 × 1012 Jones. The response current ratio of the device to red, green, and blue lights with a luminous flux amplitude ratio of 3:6:1 (standard ratio for white light) is 100:12:1.1. These properties indicate that the squarylium dye red‐light photodetectors are promising for VLC and other narrowband optoelectronic applications.
This work proves the feasibility of a novel concept of differential absorption lidar based on the Scheimpflug principle. The range‐resolved atmospheric backscattering signal of a laser beam is retrieved by employing a tilted linear sensor with a Newtonian telescope, satisfying the Scheimpflug condition. Infinite focus depth is achieved despite employing a large optical aperture. The concept is demonstrated by measuring the range‐resolved atmospheric oxygen concentration with a tunable continuous‐wave narrow‐band laser diode emitting around 761 nm over a path of one kilometer during night time. Laser power requirements for daytime operation are also investigated and validated with single‐band atmospheric aerosol measurements by employing a broad‐band 3.2‐W laser diode. The results presented in this work show the potential of employing the continuous‐wave differential absorption lidar (CW‐DIAL) technique for remote profiling of atmospheric gases in daytime if high‐power narrow‐band continuous‐wave light sources were to be employed.
This article reviews the state of the art of ultrafast transient absorption microscopy, discusses current experimental concepts and highlights future challenges. The advantages of transient absorption microscopy over other micro‐spectroscopic techniques are its high optical resolution combined with high temporal resolution as well as its ability to study non‐fluorescent and weakly fluorescent molecular species and to probe excited‐state processes. In conventional transient absorption spectroscopy the spectroscopic information usually presents a spatial average over the focal spot of the typically weakly focused probe beam. Transient absorption microscopy, however, enables investigations of the excited state dynamics in individual microscopic areas of a sample. Hence, the technique does not only yield detailed morphological information based on a label‐free molecular contrast, but also gives insight into the ultrafast morphology‐dependent photoinduced processes in heterogeneous samples. Different variations of transient absorption microscopy have found a number of applications ranging from material sciences to biology, which are discussed in this review together with different setup modifications and approaches towards transient absorption spectroscopy with spatial resolution below the diffraction limit.
The design of micro‐optical resonator arrays are introduced and tailored towards refractive index sensing applications, building on the previously unexplored benefits of open dielectric stacks. The resonant coupling of identical hollow cavities present strong and narrow spectral resonance bands beyond that available with a single Fabry Perot interferometer. Femtosecond laser irradiation with selective chemical etching is applied to precisely fabricate stacked and waveguide‐coupled open resonators into fused silica, taking advantage of small 12 nm rms surface roughness made available by the self‐alignment of nanograting planes. Refractive index sensing of methanol‐water solutions confirm a very attractive sensing resolution of 6.5 × 10−5 RIU. Such high finesse optical elements open a new realm of optofluidic sensing and integrated optical circuit concepts for detecting minute changes in sample properties against a control solution that may find importance in chemical and biological sensors, telecom sensing networks, biomedical probes, and low‐cost health care products.
Traditional detour‐phase hologram is a powerful optical device for manipulating phase and amplitude of light, but it is usually not sensitive to the polarization of light. By introducing the light‐metasurface interaction mechanism to the traditional detour phase hologram, we design a novel plasmonic nano‐slits assisted polarization selective detour phase meta‐hologram, which has attractive advantages of polarization multiplexing ability, broadband response, and ultra‐compact size. The meta‐hologram relies on the dislocations of plasmonic slits to achieve arbitrary phase distributions, showing strong polarization selectivity to incident light due to the plasmonic response of deep‐subwavelength slits. To verify its polarization sensitive and broadband responses, we experimentally demonstrate two holographic patterns of an optical vortex and an Airy beam at p‐ and s‐polarized light with wavelengths of 532nm, 633nm and 780nm, respectively. Furthermore, we realize an application example of the meta‐hologram as a polarization multiplexed photonic device for multi‐channel optical angular momentum (OAM) generation and detection. Such meta‐holograms could find widespread applications in photonics, such as chip‐level beam shaping and high‐capacity OAM communication.
In this work, we report optomechanical coupling, resolved sidebands and phonon lasing in a solid‐core microbottle resonator fabricated on a single mode optical fiber. Mechanical modes with quality factors (Qm) as high as 1.57 × 104 and 1.45 × 104 were observed, respectively, at the mechanical frequencies and . The maximum Hz is close to the theoretical lower bound of 6 × 1012 Hz needed to overcome thermal decoherence for resolved‐sideband cooling of mechanical motion at room temperature, suggesting microbottle resonators as a possible platform for this endeavor. In addition to optomechanical effects, scatter‐induced mode splitting and ringing phenomena, which are typical for high‐quality optical resonances, were also observed in a microbottle resonator.
The terahertz (THz) radiation from InGaN/GaN dot‐in‐a‐wire nanostructures has been investigated. A submicrowatt THz signal is generated with just ten vertically stacked InGaN quantum dots (QDs) in each GaN nanowire. Based on the experimental results and analysis, a single quantum wire is expected to generate an output power as high as 10 pW, corresponding to 1 pW per dot. These structures are among the most efficient three‐dimensional quantum‐confined nanostructures for the THz emission. By applying a reverse bias along the wires in a light‐emitting device (LED) consisting of such nanostructures, the THz output power is increased more than fourfold. Based on THz and photoluminescence (PL) experiments, the mechanism for the THz emission is attributed to dipole radiation induced by internal electric fields and enhanced by external fields.
