2022, 10(9) Column
Surface Optics and Plasmonics Optical Devices Fiber Optics and Optical Communications Quantum Optics Optical and Photonic Materials Nonlinear Optics Integrated Optics Ultrafast Optics Lasers and Laser Optics Imaging Systems, Microscopy, and Displays Silicon Photonics Next-generation Silicon Photonics Optical Metasurfaces: Fundamentals and Applications
Photonics Research 第10卷 第9期
Metasurfaces have powerful light field manipulation capabilities and have been researched and developed extensively in various fields. With an increasing demand for diverse functionalities, terahertz (THz) metasurfaces are also expanding their domain. In particular, integrating different functionalities into a single device is a compelling domain in metasurfaces. In this work, we demonstrate a functionally decoupled THz metasurface that can incorporate any two functions into one metasurface and switch dynamically through external excitation. This proposed metasurface is formed by the combination of split-ring resonators and phase change material vanadium dioxide (
). It operates in the single-ring resonant mode and double-ring resonant mode with varying in insulating and metallic states, respectively. More importantly, the phase modulation is independent in two operating modes, and both cover a 360° cross-polarized phase with efficient polarization conversion. This characteristic makes it obtain arbitrary independent phase information on the metasurface with different modes to switch dual functions dynamically. Here, we experimentally demonstrate the functions of a tunable focal length and large-angle focus deflection of a THz off-axis parabolic mirror to verify the dual-function switching characteristics of the functionally decoupled metasurface. The functionally decoupled metasurface developed in this work broadens the way for the research and application of multifunctional modulation devices in the THz band.
Optical orbital angular momentum multiplexing communication via inversely-designed multiphase plane light conversion
Multiplexing and demultiplexing of optical orbital angular momentum (OAM) are critical operations in mode-division multiplexing communications. Traditional Dammann gratings, spiral phase planes, and optical geometric transformations are regarded as convenient methods for OAM mode (de)multiplexing. However, crosstalk between the different modes and the difficulty of mode multiplexing greatly limit their application to mode-division multiplexing communications. Here, using a set of inversely-designed phase planes, we demonstrate an OAM (de)multiplexer based on multiphase plane light conversion that can enable perfect OAM multiplexing communication. The sorted patterns are Gaussian-like and can be coupled easily into single-mode fiber arrays. Inputs from the fiber array are turned into coaxial OAM modes after the phase planes. OAM mode crosstalk generated by the multiplexer is less than
, with insertion loss of less than 2.6 dB. OAM modes are sorted by the demultiplexer with mode crosstalk below , and the sorting results are coupled to the fiber array. OAM modes carrying 10 Gbit/s on–off keying signals were transmitted in a 5 km few-mode fiber. The measured bit-error-rate curves have power penalties of less than 10 dB. The proposed configuration is highly efficient and convenient and will be beneficial for potential applications in quantum information, information processing, and optical communications.
Polarization conversion using customized subwavelength laser-induced periodic surface structures on stainless steel
Stainless steel is a basic raw material used in many industries. It can be customized by generating laser-induced periodic surface structure (LIPSS) as subwavelength gratings. Here, we present the capabilities of an LIPSS on stainless steel to modify the polarization state of the reflected radiation at the IR band. These structures have been modeled using the finite element method and fabricated by femtosecond laser processing. The Stokes parameters have been obtained experimentally and a model for the shape has been used to fit the simulated Stokes values to the experimental data. The birefringence of the LIPSS is analyzed to explain how they modify the polarization state of the incoming light. We find the geometry of the subwavelength grating that makes it work as an optical retarder that transforms a linearly polarized light into a circularly polarized wave. In addition, the geometrical parameters of the LIPSS are tuned to selectively absorb one of the components of the incoming light, becoming a linear axial polarizer. Appropriately selecting the geometrical parameters and orientation of the fabricated LIPSS makes it possible to obtain an arbitrary pure polarization state when illuminated by a pure linearly polarized state oriented at an azimuth of 45°. The overall reflectance of these transformations reaches values close to 60% with respect to the incident intensity, which is the same reflectivity obtained for non-nanostructured stainless steel flat surfaces.
The interaction between magnetic quantum emitters and the local electromagnetic environment is a promising method to manipulate the spontaneous emission. However, it is severely limited by the weak interactions between the magnetic component of light and natural materials. Herein, we demonstrate that the special type of anapole states associated with the “onefold” electric toroidal dipole moment can be excited by efficient interaction between magnetic dipole emitters and silver oligomers. Based on magnetic anapole states, the radiative power is effectively suppressed with significant coupling between the emitter and the silver nonamer, physically providing an ideal playground for the study of non-radiative transitions. These findings not only introduce magnetic anapoles to plasmonics but also open a door for the development of new high-performance magnetic-dipole-based optoelectronic devices.
Single optical microfiber enabled tactile sensor for simultaneous temperature and pressure measurement
The ability to sense heat and touch is essential for healthcare, robotics, and human–machine interfaces. By taking advantage of the engineerable waveguiding properties, we design and fabricate a flexible optical microfiber sensor for simultaneous temperature and pressure measurement based on theoretical calculation. The sensor exhibits a high temperature sensitivity of 1.2 nm/°C by measuring the shift of a high-order mode cutoff wavelength in the short-wavelength range. In the case of pressure sensing, the sensor shows a sensitivity of 4.5% per kilopascal with a fast temporal frequency response of 1000 Hz owing to the strong evanescent wave guided outside the microfiber. The cross talk is negligible because the temperature and pressure signals are measured at different wavelengths based on different mechanisms. The properties of fast temporal response, high temperature, and pressure sensitivity enable the sensor for real-time skin temperature and wrist pulse measurements, which is critical to the accurate analysis of pulse waveforms. We believe the sensor will have great potential in wearable optical devices ranging from healthcare to humanoid robots.
We experimentally demonstrate a method for detection of entanglement via construction of entanglement witnesses from a limited fixed set of local measurements (
). Such a method does not require a priori knowledge about the form of the entanglement witnesses. It is suitable for a scenario where a full state tomography is not available, but the only resource is a limited set of . We demonstrate the method on pure two-qubit entangled states and mixed two-qubit entangled states, which emerge from photonic implementation of controllable quantum noisy channels. The states we select are motivated by realistic experimental conditions, and we confirm it works well for both cases. Furthermore, possible generalizations to higher-dimensional bipartite systems have been considered, which can potentially detect both decomposable and indecomposable entanglement witnesses. Our experimental results show perfect validity of the method, which indicates that even a limited set of local measurements can be used for quick entanglement detection and further provide a practical test bed for experiments with entanglement witnesses.
Recent moiré configurations provide a new platform for tunable and sensitive photonic responses, as their enhanced light–matter interactions originate from the relative displacement or rotation angle in a stacking bilayer or multilayer periodic array. However, previous findings are mostly focused on atomically thin condensed matter, with limitations on the fabrication of multilayer structures and the control of rotation angles. Structured microwave moiré configurations are still difficult to realize. Here, we design a novel moiré structure, which presents unprecedented capability in the manipulation of light–matter interactions. Based on the effective medium theory and
-parameter retrieval process, the rotation matrix is introduced into the dispersion relation to analyze the underlying physical mechanism, where the permittivity tensor transforms from a diagonal matrix to a fully populated one, whereas the permeability tensor evolves from a unit matrix to a diagonal one and finally becomes fully filled, so that the electromagnetic responses change drastically as a result of stacking and rotation. Besides, the experiment and simulation results reveal hybridization of eigenmodes, drastic manipulation of surface states, and magic angle properties by controlling the mutual rotation angles between two isolated layers. Here, not only a more precisely controllable bilayer hyperbolic metasurface is introduced to moiré physics, the findings also open up a new avenue to realize flat bands at arbitrary frequencies, which shows great potential in active engineering of surface waves and designing multifunctional plasmonic devices.
Integrated photonic circuits with quantum dots provide a promising route for scalable quantum chips with highly efficient photonic sources. However, unpolarized emission photons in general sacrifice half efficiency when coupling to the waveguide fundamental mode by a cross polarization technique for suppressing the excitation laser, while suspended waveguide photonics sources without polarization filters have poor scalability due to their mechanical fragility. Here, we propose a strategy for overcoming the challenge by coupling an elliptical Bragg resonator with waveguides on a solid-state base, featuring near-unity polarization efficiency and enabling on-chip pulsed resonant excitation without any polarization filters. We theoretically demonstrate that the proposed devices have outstanding performance of a single-photon source with 80% coupling efficiency into on-chip planar waveguides and an ultra-small extinction ratio of
, as well as robustness against quantum dot position deviation. Our design provides a promising method for scalable quantum chips with a filter-free high-efficiency single-photon source.
There are extensive studies to date on optical nonlinearities in microcavities at the near and mid-IR wavelengths. Pushing this research into the visible region is equally valuable. Here, we demonstrate a directly pumped, blue band Kerr frequency comb and stimulated Raman scattering (SRS) at 462 nm in a silica nanofiber-coupled whispering gallery microcavity system. Notably, due to the high optical intensities achieved, photodarkening is unavoidable and can quickly degrade the optical quality of both the coupling optical nanofiber and the microcavity, even at very low pump powers. Nonetheless, stable hyperparametric oscillation and SRS are demonstrated in the presence of photodarkening by taking advantage of in-situ thermal bleaching. This work highlights the challenges of silica-based, short wavelength nonlinear optics in high-quality, small mode volume devices and gives an effective method to overcome this apparent limitation, thus providing a baseline for optics research in the blue region for any optical devices fabricated from silica.
Bridging the gap between resonance and adiabaticity: a compact and highly tolerant vertical coupling structure
We present a compact, highly tolerant vertical coupling structure, which can be a generic design that bridges the gap between conventional resonant couplers and adiabatic couplers for heterogeneously integrated devices. We show insights on relaxing the coupler alignment tolerance and provide a detailed design methodology. By the use of a multisegmented inverse taper structure, our design allows a certain proportion of the odd supermode to be excited during the coupling process, which simultaneously facilitates high tolerance and compactness. With a total length of 87 μm, our coupler is almost threefold shorter than the state-of-the-art alignment-tolerant adiabatic couplers and outperforms them by demonstrating a more than 94% coupling efficiency (for
coupling loss) with misalignment tolerance, which, to our best knowledge, is a new record for III-V-on-silicon vertical couplers. Furthermore, our design has high tolerance to fabrication-induced structural deformation and ultrabroad bandwidth. These features make it particularly suitable for building densely integrated III-V-on-silicon photonic circuits with commercially available microtransfer printing assembly tools. The proposed design can be widely adopted in various integration platforms.
We experimentally demonstrate tunable non-Hermitian coupling in an atomic-vapor cell where atomic coherences in different optical channels are dissipatively coupled through atomic motion. Introducing a far-detuned light wall in the reservoir between the optical channels, we decorate the inter-channel coupling term so that it can be switched from dissipative to coherent. The tunable non-Hermiticity is then confirmed through measurements of the inter-channel light transport where the light-wall-induced phase shift is directly probed. Based on the tunable non-Hermiticity, we further discuss an exemplary scheme in which our setup can serve as a building block for the experimental study of exotic non-Hermitian criticality.
Self-consistent Maxwell–Bloch model for high-order harmonic generation in nanostructured semiconductors
In pursuit of efficient high-order harmonic conversion in semiconductor devices, modeling insights into the complex interplay among ultrafast microscopic electron–hole dynamics, nonlinear pulse propagation, and field confinement in nanostructured materials are urgently needed. Here, a self-consistent approach coupling semiconductor Bloch and Maxwell equations is applied to compute transmission and reflection high-order harmonic spectra for finite slab and sub-wavelength nanoparticle geometries. An increase in the generated high harmonics by several orders of magnitude is predicted for gallium arsenide nanoparticles with a size maximizing the magnetic dipole resonance. Serving as a conceptual and predictive tool for ultrafast spatiotemporal nonlinear optical responses of nanostructures with arbitrary geometry, our approach is anticipated to deliver new strategies for optimal harmonic manipulation in semiconductor metadevices.
Octave-spanning optical frequency comb (OFC) generation has achieved great breakthroughs and enabled significant applications in many fields, such as optical clocks and spectroscopy. Here, we demonstrate octave-spanning OFC generation with a repetition rate of tens of GHz via a four-wave mixing (FWM) effect seeded by a dual-mode microcavity laser for the first time, to our knowledge. A 120-m Brillouin nonlinear fiber loop is first utilized to generate wideband OFCs using the FWM effect. Subsequently, a time-domain optical pulse is shaped by appropriate optical filtering via fiber Bragg gratings. The high-repetition-rate pulse train is further boosted to 11 pJ through optimal optical amplification and dispersion compensation. Finally, an octave optical comb spanning from 1100 to 2200 nm is successfully realized through the self-phase modulation effect and dispersion wave generation in a commercial nonlinear optical fiber. Using dual-mode microcavity lasers with different mode intervals, we achieve frequency combs with octave bandwidths and repetition rates of 29–65 GHz, and demonstrate the dual-mode lasing microcavity laser as an ideal seeding light source for octave-spanning OFC generation.
Experimental demonstration of mode-matching and Sagnac effect in a millimeter-scale wedged resonator gyroscope
The highly efficient coupling of light from conventional optical components to optical mode volumes lies in the heart of chip-based micro-devices, which is determined by the mode-matching between propagation constants of fiber taper and the whispering-gallery-mode (WGM) of the resonator. Optical gyroscopes, typically realized as fiber-optic gyroscopes and ring-laser gyroscopes, have been the mainstay in diverse applications such as positioning and inertial sensing. Here, the mode-matching is theoretically analyzed and experimentally verified. We observe the Sagnac effect in a millimeter-scale wedged resonator gyroscope, which has attracted considerable attention and has been rapidly promoted in recent years. We demonstrate a bidirectional pump and probe scheme, which directly measures the frequency beat caused by the Sagnac effect. We establish the linear response between the detected beat frequency and the rotation velocity. The clockwise and counterclockwise rotation can also be distinguished according to the value of the frequency beat. The experimental results verify the feasibility of developing the gyroscope in a WGM resonator system and pave the way for future development.
1T-polytype tantalum disulfide (
), an emerging strongly correlated material, features a narrow bandgap of 0.2 eV, bridging the gap between zero-bandgap graphene and large-bandgap 2D nonlinear optical (NLO) materials. Combined with its intense light absorption, high carrier concentration, and high mobility, shows considerable potential for applications in broadband optoelectronic devices. However, its NLO characteristics and related applications have rarely been explored. Here, nanosheets are prepared by chemical vapor deposition. The ultrafast carrier dynamics in the 400–1100 nm range and broadband NLO performance in the 515–2500 nm range are systematically studied using femtosecond lasers. An obvious saturable absorption phenomenon is observed in the visible to IR range. The nonlinear absorption coefficient is measured to be under 1030 nm, which is larger than that of other typical 2D saturable absorber (SA) materials (graphene, black phosphorus, and ) under similar experimental conditions. Based on these findings, using as a new SA, passively Q-switched laser operations are successfully performed at 1.06, 1.34, and 1.94 μm. The results highlight the promise of for broadband optical modulators and provide a potential candidate material system for mid-IR nonlinear optical applications.
Boosting electroluminescence performance of all solution processed InP based quantum dot light emitting diodes using bilayered inorganic hole injection layers
The development of high-performance InP-based quantum dot light-emitting diodes (QLEDs) has become the current trend in ecofriendly display and lighting technology. However, compared with Cd-based QLEDs that have already been devoted to industry, the efficiency and stability of InP-based QLEDs still face great challenges. In this work, colloidal
and Mg-doped nanocrystals were used to prepare a bilayered hole injection layer (HIL) to replace the classical polystyrene sulfonate (PEDOT:PSS) HIL to construct high-performance InP-based QLEDs. Compared with QLEDs with a single HIL of PEDOT:PSS, the bilayered HIL enables the external quantum efficiencies of the QLEDs to increase from 7.6% to 11.2%, and the lifetime (time that the device brightness decreases to 95% of its initial value) under a high brightness of to prolong about 7 times. The improved performance of QLEDs is attributed to the bilayered HIL reducing the mismatched potential barrier of hole injection, narrows the potential barrier difference of indium tin oxide (ITO)/hole transport layer interface to promote carrier balance injection, and realizes high-efficiency radiative recombination. The experimental results indicate that the use of bilayered HILs with p-type might be an efficient method for fabricating high-performance InP-based QLEDs.
Generation of single solitons tunable from 3 to 3.8
μm in cascaded Er3+-doped and Dy3+-doped fluoride fiber amplifiers
High-power tunable femtosecond mid-infrared (MIR) pulses are of great interest for many scientific and industrial applications. Here we demonstrate a compact fluoride-fiber-based system that generates single solitons tunable from 3 to 3.8 μm. The system is composed of an Er:ZBLAN fiber oscillator and amplifier followed by a fusion-spliced Dy:ZBLAN fiber amplifier. The Er:ZBLAN fiber amplifier acts as a power booster as well as a frequency shifter to generate Raman solitons up to 3 μm. The Dy:ZBLAN fiber amplifier transfers the energy from the residual 2.8 μm radiation into the Raman solitons using an in-band pumping scheme, and further extends the wavelength up to 3.8 μm. Common residual pump radiation and secondary solitons accompanying the soliton self-frequency shift (SSFS) are recycled to amplify Raman solitons, consequently displaying a higher output power and pulse energy, a wider shifting range, and an excellent spectral purity. Stable 252 fs pulses at 3.8 μm with a record average power of 1.6 W and a pulse energy of 23 nJ are generated. This work provides an effective way to develop high-power widely tunable ultrafast single-soliton MIR laser sources, and this method can facilitate the design of other SSFS-based laser systems for single-soliton generation.
Nitrogen vacancy diamonds have emerged as sensitive solid-state magnetic field sensors capable of producing diffraction limited and sub-diffraction field images. Here, for the first time, to our knowledge, we extend those measurements to high-speed imaging, which can be readily applied to analyze currents and magnetic field dynamics in circuits on a microscopic scale. To overcome detector acquisition rate limitations, we designed an optical streaking nitrogen vacancy microscope to acquire two-dimensional spatiotemporal kymograms. We demonstrate magnetic field wave imaging with micro-scale spatial extent and
temporal resolution. In validating this system, we detected magnetic fields down to 10 μT for 40 Hz magnetic fields using single-shot imaging and captured the spatial transit of an electromagnetic needle at streak rates as high as 110 μm/ms. This design has the capability to be readily extended to full 3D video acquisition by utilizing compressed sensing techniques and a potential for further improvement of spatial resolution, acquisition speed, and sensitivity. The device opens opportunities to many potential applications where transient magnetic events can be isolated to a single spatial axis, such as acquiring spatially propagating action potentials for brain imaging and remotely interrogating integrated circuits.
Single-pixel imaging (SPI) can capture 2D images of the target with only a nonpixelated detector, showing promising application potential in nonvisible spectral imaging, low-photon imaging, lidar, and other extreme imaging fields. However, the imaging mechanism of traditional SPI makes it difficult to achieve high imaging speed, which is a primary barrier for its widespread application. To address this issue, in this work, we propose and demonstrate a novel high-speed 2D and 3D imaging scheme based on traditional SPI, termed time-resolved single-pixel imaging (TRSPI). Previous SPI works mainly utilize correlation between a stable target and iterative illumination masks to reconstruct a single image. In TRSPI, by further exploiting correlation information between a dynamic scene and every static mask, we can reconstruct a series of time-varying images of the dynamic scene, given the dynamic scene is repetitive or reproducible. Experimentally, we conducted 2D and 3D imaging on a rotating chopper with a speed of 4800 revolutions per minute (rpm), and imaging speeds up to 2,000,000 fps. It is believed that this technology not only opens up a novel application direction for SPI, but also will provide a powerful solution for high-speed imaging.
A light-trapping-structure vertical Ge photodetector (PD) is demonstrated. In the scheme, a 3 μm radius Ge mesa is fabricated to constrain the optical signal in the circular absorption area. Benefiting from the light-trapping structure, the trade-off between bandwidth and responsivity can be relaxed, and high opto-electrical bandwidth and high responsivity are achieved simultaneously. The measured 3 dB bandwidth of the proposed PD is around 67 GHz, and the responsivity is around 1.05 A/W at wavelengths between 1520 and 1560 nm. At 1580 nm, the responsivity is still over 0.78 A/W. A low dark current of 6.4 nA is also achieved at
bias voltage. Based on this PD, a clear eye diagram of 100 GBaud four-level pulse amplitude modulation (PAM-4) is obtained. With the aid of digital signal processing, 240 Gb/s PAM-4 signal back-to-back transmission is achieved with a bit error ratio of . After 1 km and 2 km fiber transmission, the highest bit rates are 230 and 220 Gb/s, respectively.
As a quantum resource, quantum coherence plays an important role in modern physics. Many coherence measures and their relations with entanglement have been proposed, and the dynamics of entanglement has been experimentally studied. However, the knowledge of general results for coherence dynamics in open systems is limited. Here we propose a coherence factorization law that describes the evolution of coherence passing through any noisy channels characterized by genuinely incoherent operations. We use photons to implement the quantum operations and experimentally verify the law for qubits and qutrits. Our work is a step toward understanding of the evolution of coherence when the system interacts with the environment, and will boost the study of more general laws of coherence.
Directional radiation enhancement of nanowire quantum dots based on line-array plasmonic antenna coupling
The integration of a single III-V semiconductor quantum dot with a plasmonic nanoantenna as a means toward efficient single-photon sources (SPEs) is limited due to its weak, wide-angle emission, and low emission rate. These limitations can be overcome by designing a unique linear array of plasmonic antenna structures coupled to nanowire-based quantum dot (NWQD) emitters. A linear array of a coupled device composed of multiple plasmonic antennas at an optimum distance from the quantum dot emitter can be designed to enhance the directionality and the spontaneous emission rate of an integrated single-photon emitter. Finite element modeling has been used to design these compact structures with high quantum efficiencies and directionality of single-photon emission while retaining the advantages of NWQDs. The Purcell enhancement factor of these structures approaches 66.1 and 145.8, respectively. Compared to a single NWQD of the same diameter, the fluorescence was enhanced by 1054 and 2916 times. The predicted collection efficiencies approach 85% (numerical aperture,
) and 80% ( ), respectively. Unlike single-photon emitters based on bulky conventional optics, this is a unique nanophotonic single-emission photon source based on a line-array configuration that uses a surface plasmon-enhanced design with minimum dissipation. The designs presented in this work will facilitate the development of SPEs with potential integration with semiconductor optoelectronics.
Mapping magnetic fields from different materials and structures can provide a powerful means for broad applications of activity probe and feature analysis. Here, we present a high-sensitivity and wide-bandwidth fiber-based quantum magnetometer at the scale of a few hundred micrometers. We propose a fiber-coupled diamond magnetometer. Tracking a pulsed optically detected magnetic resonance spectrum allows a magnetic field sensitivity of
and a bandwidth of 2.6 kHz. Additionally, with an approach of coating the diamond surface with silver reflective film, both the fluorescence collection and excitation efficiency are significantly enhanced, and the sensitivity and bandwidth are expected to be further improved to and 4.1 kHz, respectively. Finally, this fiber-based quantum magnetometer is applied as a probe to successfully map the magnetic field induced by the current-carrying copper-wire mesh. Such a stable and compact magnetometer can provide a powerful tool in many areas of physical, chemical, and biological researches.
General strategy for ultrabroadband and wide-angle absorbers via multidimensional design of functional motifs
Developing wide-angle, polarization-independent, and effective electromagnetic absorbers that endow devices with versatile characteristics in solar, terahertz, and microwave regimes is highly desired, yet it is still facing a theoretical challenge. Herein, a general and straightforward strategy is proposed to surmount the impedance mismatching in the ultrabroadband and wide-angle absorber design. A vertical atom sticking on
horizontal meta-atoms with conductive film is proposed as the functional motif, exhibiting the strong ohmic dissipation along both vertical and horizontal directions. Assisted by the intelligent optimization strategy, the structure dimension, location, and film distribution are designed to maintain absorbing performance under different incident angles. As a demonstration, an absorber was designed and proved in both simulation and experiment. Significantly, the over 10 dB absorption from 5 to 34 GHz is achieved in the range of 0° to 70° for both TE and TM, and even 3 to 40 GHz from 60° to 70° for the TE wave. Meanwhile, the proposed multidimensional design of functional motifs can be attached with optical transparency function at will. That is to say, our effort provides an effective scheme for expanding matching area and may also be made in optical, infrared, and terahertz regimes.
Aqueous solutions cannot be detected using transmissive terahertz metamaterials because water strongly absorbs terahertz waves. Transmissive terahertz metamaterials are easier to integrate terahertz emitters and receivers into single and compact devices than reflective terahertz metamaterials. The detection of aqueous solutions using transmissive terahertz metamaterials is a big challenge. This work fabricates a transmissive terahertz metamaterial using a folding metamaterial comprising split-ring resonators (SRRs) with nano-profiles with a high aspect ratio of 41.4. The folding metamaterial has a small transmittance of
at its resonance frequency, large transmittance contrast of approximately with respect to the transmittance of its substrate, large refractive index sensitivity of 647 GHz/RIU, and large quality factor of 37. This result arises from the nano-profiles of the SRRs. The nano-profiles increase the surface areas of the SRRs, increasing their surface currents and enhancing the electromagnetic resonance of the folding metamaterial. The folding metamaterial detects a 188-μm-thick rabbit-blood layer that is deposited on it, which cannot be detected by using a common metamaterial. This result reveals that folding metamaterials have potential in detecting the products of live microorganisms with geometrical sizes up to several hundreds of micrometers, such as hydrogen gas, hydrocarbons, and antibodies.
While the uncertainty principle for linear position and linear momentum, and more recently for angular position and angular momentum, is well established, its radial equivalent has so far eluded researchers. Here we exploit the logarithmic radial position,
, and hyperbolic momentum, , to formulate a rigorous uncertainty principle for the radial degree of freedom of transverse light modes. We show that the product of their uncertainties is bounded by Planck’s constant, , and identify a set of radial intelligent states that satisfy the equality. We illustrate the radial uncertainty principle for a variety of intelligent states, by preparing transverse light modes with suitable radial profiles. We use eigenmode projection to measure the corresponding hyperbolic momenta, confirming the minimum uncertainty bound. Optical systems are most naturally described in terms of cylindrical coordinates, and our radial uncertainty relation provides the missing piece in characterizing optical quantum measurements, providing a new platform for the fundamental tests and applications of quantum optics.
Ultrasensitive and high-speed AlGaN/AlN solar-blind ultraviolet photodetector: a full-channel-self-depleted phototransistor by a virtual photogate
High sensitivity, high solar rejection ratio, and fast response are essential characteristics for most practical applications of solar-blind ultraviolet (UV) detectors. These features, however, usually require a complex device structure, complicated process, and high operating voltage. Herein, a simply structured n-AlGaN/AlN phototransistor with a self-depleted full channel is reported. The self-depletion of the highly conductive n-AlGaN channel is achieved by exploiting the strong polarization-induced electric field therein to act as a virtual photogate. The resulting two-terminal detectors with interdigital Ohmic electrodes exhibit an ultrahigh gain of
, an ultrafast response speed with rise/decay times of 537.5 ps/3.1 μs, and an ultrahigh Johnson and shot noise (flicker noise) limited specific detectivity of ( ) Jones at 20-V bias. Also, a very low dark current of the order of and a photo-to-dark current ratio of above are obtained, due to the complete depletion of the channel layer and the high optical gain. The proposed planar phototransistor combines fabrication simplicity and performance advantages, and thus is promising in a variety of UV detection applications.
Low-threshold and narrow-emission random lasing in a self-assembly TiN nanoparticle-doped carbon quantum dot/DCM nanowire composite
The random lasing in quantum dot systems is in anticipation for widespread applications in biomedical therapy and image recognition, especially in random laser devices with high brightness and high monochromaticity. Herein, low-threshold, narrowband emission, and stable random lasing is realized in carbon quantum dot (CQD)/DCM nanowire composite-doped TiN nanoparticles, which are fabricated by the mixture of carbon quantum dots and self-assembly DCM dye molecules. The Förster resonance energy transfer process results in a high luminescence efficiency for the composite of carbon dots and DCM nanowires, allowing significant random lasing actions to emerge in CQD/DCM composite as TiN particles are doped that greatly enhance the emission efficiency through the plasmon resonance and random scattering. Thus, sharp and low-threshold random lasing is finally realized and even strong single-mode lasing occurs under higher pumping energy in the TiN-doped CQD/DCM composite. This work provides a promising way in high monochromaticity random laser applications.
Micro-endoscopes are widely used for detecting and visualizing hard-to-reach areas of the human body and for
in vivo observation of animals. A micro-endoscope that can realize 3D imaging at the camera framerate could benefit various clinical and biological applications. In this work, we report the development of a compact light-field micro-endoscope (LFME) that can obtain snapshot 3D fluorescence imaging, by jointly using a single-mode fiber bundle and a small-size light-field configuration. To demonstrate the real imaging performance of our method, we put a resolution chart in different positions and capture the z-stack images successively for reconstruction, achieving 333-μm-diameter field of view, 24 μm optimal depth of field, and up to 3.91 μm spatial resolution near the focal plane. We also test our method on a human skin tissue section and HeLa cells. Our LFME prototype provides epi-fluorescence imaging ability with a relatively small (2-mm-diameter) imaging probe, making it suitable for in vivo detection of brain activity and gastrointestinal diseases of animals.
The kinetics of photoinduced changes, namely, photobleaching and photodarkening in sputtered ternary
thin films, was studied. The study of time evolution of the absorption coefficient upon room-temperature near-bandgap irradiation revealed several types of photoinduced effects. The as-deposited films exhibited a fast photodarkening followed by a dominative photobleaching process. Annealed thin films were found to undergo photodarkening only. The local structure studied by Raman scattering spectroscopy showed significant structural changes upon thermal annealing, which are presumably responsible for a transition from the photobleaching observed in as-deposited and reversible photodarkening in annealed thin films. Moreover, a transient photodarkening process was observed in both as-deposited and annealed thin films. The influence of the initial film thickness and laser optical intensity on the kinetics of photoinduced changes is discussed.
Silicon photonics for high-capacity data communicationsDownload：1196次
In recent years, optical modulators, photodetectors, (de)multiplexers, and heterogeneously integrated lasers based on silicon optical platforms have been verified. The performance of some devices even surpasses the traditional III-V and photonic integrated circuit (PIC) platforms, laying the foundation for large-scale photonic integration. Silicon photonic technology can overcome the limitations of traditional transceiver technology in high-speed transmission networks to support faster interconnection between data centers. In this article, we will review recent progress for silicon PICs. The first part gives an overview of recent achievements in silicon PICs. The second part introduces the silicon photonic building blocks, including low-loss waveguides, passive devices, modulators, photodetectors, heterogeneously integrated lasers, and so on. In the third part, the recent progress on high-capacity silicon photonic transceivers is discussed. In the fourth part, we give a review of high-capacity silicon photonic networks on chip.
Spin splitting of light originates from the interplay between the polarization and spatial degrees of freedom as a fundamental constituent of the emerging spin photonics, providing a prominent pathway for manipulating photon spin and developing exceptional photonic devices. However, previously relevant devices were mainly designed for routing monotonous spin splitting of light. Here, we realize an oscillatory spin splitting of light via metasurface with two channel Pancharatnam–Berry phases. For the incidence of a linearly polarized light, the concomitant phases arising from opposite spin states transition within pathways of the metasurface induce lateral spin splitting of light with alternately changed transport direction during beam guiding. We demonstrate the invariance of this phenomenon with an analogous gauge transformation. This work provides a new insight on steering the photon spin and is expected to explore a novel guiding mechanism of relativistic spinning particles, as well as applications of optical trapping and chirality sorting.
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