Showing papers on "Diffraction grating published in 2020"
TL;DR: This work investigates what may be regarded as the ultimate level of miniaturization for a spectrometer, in which it consists solely of a detector array, and demonstrates the use of the chip to reconstruct the spectrum of an unknown light source impinging upon it.
Abstract: Spectroscopy is a cornerstone in the field of optics. Conventional spectrometers generally require two elements. The first provides wavelength selectivity, for example, diffraction grating or Michelson interferometer. The second is a detector (or detector array). Many applications would benefit from very small and lightweight spectrometers. This motivates us to investigate what may be regarded as an ultimate level of miniaturization for a spectrometer, in which it consists solely of a detector array. We demonstrate a chip containing 24 pixels, each comprising a silicon nanowire (Si NW) array photodetector formed above a planar photodetector. The NWs are structurally colored, enabling us to engineer the responsivity spectra of all photodetectors in the chip. Each pixel thus combines wavelength selectivity and photodetection functions. We demonstrate the use of our chip to reconstruct the spectrum of an unknown light source impinging upon it. This is achieved by an algorithm that takes as its inputs the measured photocurrents from the pixels and a library of their responsivity spectra.
71 citations
TL;DR: The femtosecond (fs) laser fabrication of biomimetic omnidirectional iridescent metallic surfaces exhibiting efficient diffraction for practically any angle of light incidence was reported in this article.
Abstract: We report the femtosecond (fs) laser fabrication of biomimetic omnidirectional iridescent metallic surfaces exhibiting efficient diffraction for practically any angle of light incidence. Such diffractive behavior is realized by means of mul-ti-directional low-spatial-frequency, laser-induced periodic surface structures (LSFL) formed upon exploiting the cylindrical symmetry of a cylindrical vector (CV) fs field. We particularly demonstrate that the multi-directional gratings formed on stainless steel surface by a radially polarized fs beam, could mimic the omnidirectional structural coloration properties found in some natural species. Accordingly, the fabricated grating structures can spatially disperse the incident light into individual wavelength with high efficiency, exhibiting structural iridescence at all viewing angles. Analytical calculations using the grating equation reproduced the characteristic variation of the vivid colors observed as a function of incident angle. We envisage that our results will significantly contribute to the development of new photonic and light sensing devices.
54 citations
TL;DR: A unique feature of proposed structure is the synergetic combination of high transparency, tunability, high Q-factor of the resonances and superior magneto-optical response that is two orders higher in magnitude than in the non-structured smooth iron-garnet film.
Abstract: We provide the experimental research on a novel type of all-dielectric magnetic structure designed to achieve an enhanced magneto-optical response. 1D grating fabricated via etching of bismuth substituted iron garnet film supports the excitation of optical guided modes, which are highly sensitive to the external magnetic field. A unique feature of proposed structure is the synergetic combination of high transparency, tunability, high Q-factor of the resonances and superior magneto-optical response that is two orders higher in magnitude than in the non-structured smooth iron-garnet film. The considered all-dielectric magnetic garnet structures have great potential in various fields including the magneto-optical modulation of light, biosensing and magnetometry.
41 citations
TL;DR: A facile grating fabrication method using a biosourced lyotropic LC formed by cellulose nanocrystals (CNCs), a material extracted from plants, is reported, which can be broadly applied to various grating materials and opens up a new area of optical materials from lyotropicLCs.
Abstract: Diffraction gratings are important for modern optical components, such as optical multiplexers and signal processors. Although liquid crystal (LC) gratings based on thermotropic LCs have been extensively explored, they often require expensive molecules and complicated manufacturing processes. Lyotropic LCs, which can be broadly obtained from both synthetic and natural sources, have not yet been applied in optical gratings. Herein, a facile grating fabrication method using a biosourced lyotropic LC formed by cellulose nanocrystals (CNCs), a material extracted from plants, is reported. Hydrogel sheets with vertically aligned uniform periodic structures are obtained by fixing the highly oriented chiral nematic LC of CNCs in polymer networks under the cooperative effects of gravity on phase separation and a magnetic field on LC orientation. The hydrogel generates up to sixth-order diffraction spots and shows linear polarization selectivity, with tunable grating periodicity controlled through LC concentration regulation. This synthesis strategy can be broadly applied to various grating materials and opens up a new area of optical materials from lyotropic LCs.
34 citations
TL;DR: Using 3D-finite-difference time-domain simulations, this study reveals that devices with high coupling efficiencies are distributed over a wide region of the design space with varied back-reflections, while still maintaining minimum feature sizes larger than 100 nm and even 130 nm.
Abstract: We present perfectly vertical grating couplers for the 220 nm silicon-on-insulator platform incorporating subwavelength metamaterials to increase the minimum feature sizes and achieve broadband low back-reflection. Our study reveals that devices with high coupling efficiencies are distributed over a wide region of the design space with varied back-reflections, while still maintaining minimum feature sizes larger than 100 nm and even 130 nm. Using 3D-finite-difference time-domain simulations, we demonstrate devices with broadband low back-reflection of less than −20dB over more than 100 nm bandwidth centered around the C-band. Coupling efficiencies of 72% and 67% are achieved for minimum feature sizes of 106 nm and 130 nm, respectively. These gratings are also more fabrication tolerant compared to similar designs not using metamaterials.
31 citations
TL;DR: In this paper, a review of the substantial literature concerning photonic jet and photonic hook phenomena is presented, and the guidelines of jets' efficient manipulation, through the variation of both the shape and spatial period of diffraction grating rulings, are considered.
Abstract: The study of accelerating Airy-family beams has made significant progress, not only in terms of numerical and experimental investigations, but also in conjunction with many potential applications. However, the curvature of such beams (and hence their acceleration) is usually greater than the wavelength. Relatively recently, a new type of localized wave beams with subwavelength curvature, called photonic hooks, was discovered. This paper briefly reviews the substantial literature concerning photonic jet and photonic hook phenomena, based on the photonic jet principle. Meanwhile, the photonic jet ensemble can be produced by optical wave diffraction at 2D phase diffraction gratings. The guidelines of jets’ efficient manipulation, through the variation of both the shape and spatial period of diffraction grating rulings, are considered. Amazingly, the mesoscale dielectric Janus particle, with broken shape or refractive index symmetry, is used to generate the curved photonic jet—a photonic hook—emerging from its shadow-side surface. Using the photonic hook, the resolution of optical scanning systems can be improved to develop optomechanical tweezers for moving nanoparticles, cells, bacteria and viruses along curved paths and around transparent obstacles. These unique properties of photonic jets and hooks combine to afford important applications for low-loss waveguiding, subdiffraction-resolution nanopatterning and nanolithography.
23 citations
TL;DR: In this paper, the authors present the design methodology and experimental characterization of compact out-of-plane focusing grating couplers for integration with magnetoresistive random access memory technology.
Abstract: We present the design methodology and experimental characterization of compact out-of-plane focusing grating couplers for integration with magnetoresistive random access memory technology. Focusing grating couplers have recently found attention as layer-couplers for photonic-electronic integration. The components we demonstrate are designed for a wavelength of 1550 nm, fabricated in a standard 220 nm SOI photonic platform and optimized given the fabrication restrictions for standard 193-nm UV lithography. For the first time, we extend the design based on the phase matching condition to a two-dimensional (2-D) grating design with two optical input ports. We further present the experimental characterization of the focusing behaviour by spatially probing the emitted beam with a tapered-and-lensed fiber and demonstrate the polarization controlling capabilities of the 2-D FGCs.
22 citations
TL;DR: In this paper, the mechanism of excitation of high-k Bloch-like Plasmon Polariton (BPPs) modes with ultrasmall modal volume using a meta-grating was investigated.
Abstract: Hyperbolic metamaterials (HMMs) represent a novel class of fascinating anisotropic plasmonic materials, supporting highly confined propagating plasmon polaritons in addition to surface plasmon polaritons. However, it is very challenging to tailor and excite these modes at optical frequencies by prism coupling because of the intrinsic difficulties in engineering non-traditional optical properties with artificial nanostructures and the unavailability of high refractive index prisms for matching the momentum between the incident light and the guided modes. Here, we report the mechanism of excitation of high-k Bloch-like Plasmon Polariton (BPPs) modes with ultrasmall modal volume using a meta-grating, which is a combined structure of a metallic diffraction grating and a type II HMM. We show how a 1D plasmonic grating without any mode in the infrared spectral range, if coupled to a HMM supporting high-k modes, can efficiently enable the excitation of these modes via coupling to far-field radiation. Our theoretical predictions are confirmed by reflection measurements as a function of angle of incidence and excitation wavelength. We introduce design principles to achieve a full control of high-k modes in meta-gratings, thus enabling a better understanding of light-matter interaction in this type of hybrid meta-structures. The proposed spectral response engineering is expected to find potential applications in bio-chemical sensors, integrated optics and optical sub-wavelength imaging.
22 citations
TL;DR: In this article, a vibration-assisted fly cutting (VAFC) is proposed to fabricate two-level iridescent structures with high accuracy in a single step, which involves the lowfrequency vibration of the workpiece in the vertical direction during the feed in the horizontal direction and the high-speed rotation of the diamond cutting tool.
22 citations
TL;DR: In this article, the authors proposed a waveguide-to-fiber coupling scheme based on micro-fabricated free-form optical reflectors, which can be versatilely adapted for coupling between photonic chips, fibers, and free-space surface-incident devices.
Abstract: Coupling of light between different photonic devices, for example on-chip waveguides, fibers, and free-space optical elements, is an essential function enabling integrated optical systems. Efficient optical coupling demands matching the optical mode profiles and effective indices between two devices, and often changing propagation direction of the light. To date, such coupling is pre-dominantly accomplished via direct butt coupling of two devices, or meticulously optimized diffraction gratings. In this article, we present a new coupling scheme based on microfabricated free-form optical reflectors. The free-form reflector simultaneously achieves the functions of light beam re-directing and shaping (for mode matching), and can be versatilely adapted for coupling between photonic chips, fibers, and free-space surface-incident devices. We show that this technology uniquely fulfills all key performance requirements for optical interfaces with exceptionally low coupling loss (0.2–0.3 dB per coupler), large bandwidth (over half an octave), high density (large 2-D coupler arrays), polarization diversity, and superior alignment tolerance commensurate with passive alignment techniques. Preliminary experimental validation demonstrates waveguide-to-fiber coupling with a low insertion loss (IL) of 0.9 dB. We foresee that the technology will become a promising solution to the chip-level photonic interconnection and packaging challenges plaguing integrated photonics.
22 citations
TL;DR: Bio-inspired chiral nematic cellulose films with periodic surface grating structures exhibit optically programmable photonic–photonic coupling.
Abstract: Photonic crystals based on plasmonic or dielectric periodic structures have attracted considerable interest owing to their capabilities to control light-matter interactions with tailored precision. By using a nanocellulose derived chiral liquid crystal as a building block, here we demonstrate a bio-inspired dual photonic structure that contains the combination of microscopic periodic 1D surface grating and nanoscopic helical organization, giving rise to programmable colour mixing and polarization rotation. We show that a variation in the photonic band-gap in the bulk matrix leads to simultaneous control over the reflection and diffraction of light with controllable iridescence.
20 Jul 2020
TL;DR: In this paper, the mechanism of excitation of high-index Bloch plasmon polariton modes with sub-diffraction spatial confinement using a meta-grating, which is a combined structure of a metallic diffraction grating and a type II HMM, was investigated.
Abstract: Hyperbolic metamaterials (HMMs) are anisotropic optical materials supporting highly confined propagating electromagnetic modes. However, it is challenging to tailor and excite these modes at optical frequencies by prism coupling because of the unavailability of high refractive index prisms for matching the momentum between the incident light and the guided modes. Here, we report on the mechanism of excitation of high-index Bloch plasmon polariton modes with sub-diffraction spatial confinement using a meta-grating, which is a combined structure of a metallic diffraction grating and a type II HMM. We show how a one-dimensional plasmonic grating without any mode in the infrared spectral range, if coupled to an HMM supporting high-index modes, can efficiently enable the excitation of these modes via coupling to far-field radiation. Our theoretical predictions are confirmed by experimental reflection measurements as a function of angle of incidence and excitation wavelength. We introduce design principles to achieve a full control of high-index modes in meta-gratings, thus enabling a better understanding of light–matter interaction in this type of hybrid structure. The exploitation of the spectral response of these modes can find applications in bio-chemical sensing, integrated optics, and optical sub-wavelength imaging.
TL;DR: In this paper, a shearing interferometry module for digital holographic microscopy is proposed, which enables the selection of shearing distance based on the spatial density of the sample, without losing spatial frequency content due to overlapping of the complex wave fronts in the spatial frequency domain.
Abstract: We introduce a new shearing interferometry module for digital holographic microscopy, in which the off-axis angle, which defines the interference fringe frequency, is not coupled to the shearing distance, as is the case in most shearing interferometers. Thus, it enables the selection of shearing distance based on the spatial density of the sample, without losing spatial frequency content due to overlapping of the complex wave fronts in the spatial frequency domain. Our module is based on a 4f imaging unit and a diffraction grating, in which the hologram is generated from two mutually coherent, partially overlapping sample beams, with adjustable shearing distance, as defined by the position of the grating, but with a constant off-axis angle, as defined by the grating period. The module is simple, easy to align, and presents a nearly common-path geometry. By placing this module as an add-on unit at the exit port of an inverted microscope, quantitative phase imaging can easily be performed. The system is characterized by a 2.5 nm temporal stability and a 3.4 nm spatial stability, without using anti-vibration techniques. We provide quantitative phase imaging experiments of silica beads with different shearing distances, red blood cell fluctuations, and cancer cells flowing in a micro-channel, which demonstrate the capability and versatility of our approach in different imaging scenarios.
TL;DR: In this article, a magneto-optical trap (MOT) of alkaline-earth atoms using a nanofabricated diffraction grating chip was demonstrated. But the trap lifetime was only ∼1 s.
Abstract: We demonstrate a compact magneto-optical trap (MOT) of alkaline-earth atoms using a nanofabricated diffraction grating chip. A single input laser beam, resonant with the broad 1S0 → 1P1 transition of strontium, forms the MOT in combination with three diffracted beams from the grating chip and a magnetic field produced by permanent magnets. A differential pumping tube limits the effect of the heated, effusive source on the background pressure in the trapping region. The system has a total volume of around 2.4 l. With our setup, we have trapped up to 5 × 106 88Sr atoms at a temperature of ∼6 mK, and with a trap lifetime of ∼1 s. Our results will aid the effort to miniaturize quantum technologies based on alkaline-earth atoms.
TL;DR: A novel, scalable nanofabrication method for creating off-axis holographic gratings that demonstrate near ideal diffraction efficiencies for binary, sinusoidal, and blazed grating groove profiles.
Abstract: In a transmission electron microscope, electrons are described by matter-waves with wavelengths five orders of magnitude smaller than optical electromagnetic waves. Analogous to optical holography, electron wavefronts can be shaped using nanoscale holographic gratings. Here we demonstrate a novel, scalable nanofabrication method for creating off-axis holographic gratings that demonstrate near ideal diffraction efficiencies for binary, sinusoidal, and blazed grating groove profiles. We show that this method can produce up to 50 µm diameter area gratings that diffract up to 68% of the transmitted electron wave into a desired diffraction order with less than 7% into any other order. Additionally, we find that the amount of inelastically scattered electrons from the material gratings remaining in the coherent diffraction orders from the gratings is negligible in the far field.
TL;DR: Bragg diffraction of the antibiotic ciprofloxacin and the dye molecule phthalocyanine is demonstrated and an equal-amplitude splitting and maximum momentum transfer are achieved, paving the way for efficient, large-momentum beam splitters and mirrors for hot and complex molecules.
Abstract: We demonstrate Bragg diffraction of the antibiotic ciprofloxacin and the dye molecule phthalocyanine at a thick optical grating. The observed patterns show a single dominant diffraction order with the expected dependence on the incidence angle as well as oscillating population transfer between the undiffracted and diffracted beams. We achieve an equal-amplitude splitting of 14ℏk (photon momenta) and maximum momentum transfer of 18ℏk. This paves the way for efficient, large-momentum beam splitters and mirrors for hot and complex molecules.
TL;DR: In this article, a force measurement method based on polydimethylsiloxane (PDMS) grating is introduced, which is precise, low-cost, and easy to follow.
Abstract: With the rapid development of flexible materials, various high-performance biocompatible flexible sensors have been proposed for specific measurement applications. Among these materials, polydimethylsiloxane (PDMS) is one of the most popular polymers by curing the mixture of pre-polymer (base) and cross-linker (curing agent). In this paper, a force measurement method based on PDMS grating is introduced. The PDMS grating is cast from a commercial master grating, which is precise, low-cost, and easy to follow. The elastic modulus can be controlled by the curing temperature and the mixing ratio. The PDMS grating is tested using a tension testing machine. As the stretching force increases, the grating line-spacing simultaneously increases and the diffraction light spot shifts. By capturing the light spot shift using a camera, the relationship between light spot position and stretching force is established and evaluated. Experimental results show that the linearity (R2) of the proposed method is better than 0.998, adding that the sensitivity is ~0.5–0.7N/mm and the accuracy is up to 0.05N.
TL;DR: In this paper, the Vernier effect between two thermally tunable micro-ring resonators was used to achieve a tuning range of 154nm and a maximum average output power on the order of 10 mW at 2.63μm, with a peak power of 100 mW.
Abstract: We report two tunable diode laser configurations emitting around 2.6 μm, where the gain is provided by a high-gain GaSb-based reflective semiconductor optical amplifier. The lasers are driven in pulsed mode at 20 °C, with a pulse width of 1 μs and 10% duty cycle to minimize heating effects. To demonstrate the broad tuning and high output power capability of the gain chip, an external cavity diode laser configuration based on using a ruled diffraction grating in a Littrow configuration is demonstrated. The laser shows a wide tuning range of 154 nm and a maximum average output power on the order of 10 mW at 2.63 μm, corresponding to a peak power of 100 mW. For a more compact and robust integrated configuration, we consider an extended-cavity laser design where the feedback is provided by a silicon photonics chip acting as a reflector. In particular, the integrated tuning mechanism is based on utilizing the Vernier effect between two thermally tunable micro-ring resonators. In this case, a tuning range of around 70 nm is demonstrated in a compact architecture, with an average power of 1 mW, corresponding to a peak power of 10 mW.
TL;DR: In this paper, a two-layer five-port diffraction grating with operation in transmission was designed and the accurate grating vector parameters were optimized using rigorous coupled-wave analysis (RCWA).
Abstract: In this paper, we report a two-layer five-port diffraction grating by a polarization-independent design under normal incidence. To be different from conventional five-port gratings, initially, we design a novel two-layer grating with operation in transmission. Next, we firstly design a polarization-independent grating with five-port splitting output. On the one hand, the accurate grating vector parameters are optimized using rigorous coupled-wave analysis (RCWA) approach. On the other hand, the inherent coupling mechanism happened in the grating region can be well explained by employing simplified modal method (SMM). More importantly, all reported conventional five-port beam splitter gratings were designed based on polarization dependent. Although they could obtain high diffraction efficiency for TE or TM polarization, it requires more complicated and time-consuming fabrication processes in practical grating applications. Thus, this work can open up a possible thought for designing polarization-independent multi-port beam splitter diffraction gratings.
TL;DR: A reflective two-dimensional metal-dielectric grating based on cylindrical hole nano arrays with excellent polarization-independent high diffraction efficiency and a potential candidate as planar grating rulers for high precision multi-axis displacement measurement is proposed.
Abstract: In this paper, we propose a reflective two-dimensional (2D) metal-dielectric grating based on cylindrical hole nano arrays with excellent polarization-independent high diffraction efficiency. The effects of the geometrical parameters on the polarization characteristic and diffraction efficiency are studied. Optimized results show that the (-1, 0) order diffraction efficiency of transverse electric (TE) and transverse magnetic (TM) polarizations under Littrow mounting is 98.31% and 98.05% at 780 nm incident wavelength, and the diffraction efficiency equilibrium is 99.74%, which is a significant improvement over the previously reported 2D gratings. The high efficiency in both TE and TM polarizations makes it a potential candidate as planar grating rulers for high precision multi-axis displacement measurement. Moreover, the cylindrical hole-based structure performs well in manufacturing tolerances, which provides the possibility for practical applications.
TL;DR: In this article, an optimized method for the inverse design of guided-mode resonance (GMR) filters using one-and two-dimensional (1D and 2D) grating structures was proposed.
Abstract: We propose an optimized method for the inverse design of guided-mode resonance (GMR) filters using one- and two-dimensional (1D and 2D) grating structures. This work for 2D state is based on developing the effective permittivity of 1D grating structures along three orthogonal axes to predict the physical dimensions of the structure, for the first time to our knowledge. Also, we compare three optimization methods to reach the optimized conditions based on the characteristics of multilayer structures. Both the transfer matrix method and rigorous coupled-wave analysis are used to simulate and show the reflection and transmission of the proposed 2D GMR filters. The results show that insensitivity to polarization, the best accuracy in resonance location design, and a high quality factor can be achieved for both the rectangular and cylindrical structures as the ideal 2D GMR filters. Also, the effect of each layer thickness on the resonance location and the full width at half-maximum is illustrated. Finally, we investigate three different reasons for decreasing the FWHM of the output reflection of the GMR filters.
TL;DR: The study reveals that paramecium has self-helical forward motion characteristics, or more specifically, 77% clockwise and 23% anti-clockwise rotation when moving forward.
Abstract: This study presents a polarization grating based diffraction phase microscopy (PG-DPM) and its application in bio-imaging. Compared with traditional diffraction phase microscopy (DPM) of which the fringe contrast is sample-dependent, the fringe contrast of PG-DPM is adjustable by changing the polarization of the illumination beam. Moreover, PG-DPM has been applied to real-time phase imaging of live paramecia for the first time. The study reveals that paramecium has self-helical forward motion characteristics, or more specifically, 77% clockwise and 23% anti-clockwise rotation when moving forward. We can envisage that PG-DPM will be applied to many different fields.
TL;DR: A smart diffraction grating immunosensor based on antigen-responsive hydrogel with enhanced analyte-induced volume changes is developed for highly selective and sensitive detection of human immunoglobulins.
Abstract: A smart diffraction grating immunosensor based on antigen-responsive hydrogel with enhanced analyte-induced volume changes is developed for highly selective and sensitive detection of human immunog...
TL;DR: In this paper, a compound metallic grating (a periodic metallic structure with more than one slit in each period) is proposed for anomalous reflection, which has an unprecedented near-to-unitary efficiency of 99.9%.
Abstract: Metagrating is a new concept for wavefront manipulation that, unlike phase gradient metasurfaces, does not suffer from low efficiency and also has a less complicated fabrication process. In this paper, a compound metallic grating (a periodic metallic structure with more than one slit in each period) is proposed for anomalous reflection. We propose an analytical method for analyzing the electromagnetic response of this grating. Closed-form and analytical expressions are presented for the reflection coefficients of zeroth diffracted order and also higher diffracted orders. The proposed method is verified against full-wave simulations and the results are in excellent agreement. Thanks to the geometrical asymmetry of compound metallic grating, it can be used for designing anomalous reflection at the normal incidence. Given analytical expressions for reflection coefficients, we design a perfect anomalous reflector for a TM polarized plane wave via transferring all the incident power to ( − 1) diffraction order . The structure designed in this study has an unprecedented near-to-unitary efficiency of 99.9%. Finally, a multi-element compound metallic grating is proposed for reflecting the normal incidence to angles of below 30°, which is a challenging accomplishment. This excellent performance of compound metallic grating shows its high potential for microwave and terahertz wavefront manipulation applications.
TL;DR: In this article, a far-field grating interferometer with a tailored 2D-design is proposed to estimate small-angle scattering information with spatial resolution in a single shot through the inclusion of a circular diffraction grating.
Abstract: Within neutron imaging, different methods have been developed with the aim to go beyond the conventional contrast modalities, such as grating interferometry. Existing grating interferometers are sensitive to scattering in a single direction only, and thus investigations of anisotropic scattering structures imply the need for a circular scan of either the sample or the gratings. Here we propose an approach that allows assessment of anisotropic scattering in a single acquisition mode and to broaden the range of the investigation with respect to the probed correlation lengths. This is achieved by a far-field grating interferometer with a tailored 2D-design. The combination of a directional neutron dark-field imaging approach with a scan of the sample to detector distance yields to the characterization of the local 2D real-space correlation functions of a strongly oriented sample analogous to conventional small-angle scattering. Our results usher in quantitative and spatially resolved investigations of anisotropic and strongly oriented systems beyond current capabilities. Acquiring orientation-resolved neutron images currently requires the sample or system to be rotated, precluding single-shot measurement. Here, the authors achieve small-angle scattering information with spatial resolution in a single shot through the inclusion of a circular diffraction grating.
TL;DR: In this paper, an electrically controlled polariton laser was demonstrated in a compact, easy-to-fabricate and integrable configuration, based on a semiconductor waveguide.
Abstract: Exciton-polaritons are mixed light-matter particles offering a versatile solid state platform to study many-body physical effects. In this work we demonstrate an electrically controlled polariton laser, in a compact, easy-to-fabricate and integrable configuration, based on a semiconductor waveguide. Interestingly, we show that polariton lasing can be achieved in a system without a global minimum in the polariton energy-momentum dispersion. The surface cavity modes for the laser emission are obtained by adding couples of specifically designed diffraction gratings on top of the planar waveguide, forming an in-plane Fabry-Perot cavity. It is thanks to the waveguide geometry, that we can apply a transverse electric field in order to finely tune the laser energy and quality factor of the cavity modes. Remarkably, we exploit the system sensitivity to the applied electric field to achieve an electrically controlled population of coherent polaritons. The precise control that can be reached with the manipulation of the grating properties and of the electric field provides strong advantages to this device in terms of miniaturization and integrability, two main features for the future development of coherent sources from polaritonic technologies.
TL;DR: A novel technique to modulate the spatial phase profile of a propagating light beam by means of liquid crystals, electro-optically addressed by indium-tin oxide (ITO) grating microstructures, is proposed and experimentally demonstrated.
Abstract: There is an increasing need to control light phase with tailored precision via simple means in both fundamental science and industry. One of the best candidates to achieve this goal are electro-optical materials. In this work, a novel technique to modulate the spatial phase profile of a propagating light beam by means of liquid crystals (LC), electro-optically addressed by indium-tin oxide (ITO) grating microstructures, is proposed and experimentally demonstrated. A planar LC cell is assembled between two perpendicularly placed ITO gratings based on microstructured electrodes. By properly selecting only four voltage sources, we modulate the LC-induced phase profile such that non-diffractive Bessel beams, laser stretching, beam steering, and 2D tunable diffraction gratings are generated. In such a way, the proposed LC-tunable component performs as an all-in-one device with unprecedented characteristics and multiple functionalities. The operation voltages are very low and the aperture is large. Moreover, the device operates with a very simple voltage control scheme and it is lightweight and compact. Apart from the demonstrated functionalities, the proposed technique could open further venues of research in optical phase spatial modulation formats based on electro-optical materials.
TL;DR: This paper proposes a design for a reconfigurable MEMS-based reflection grating consisting of multiple subwavelength reflectors which are driven by 5-bit, high-throw electrostatic actuators which can steer the angle of the terahertz waves in a range of up to ± 56.4∘.
Abstract: With an increasing number of applications of terahertz systems in industrial fields and communications, terahertz beamforming and beam steering techniques are required for high-speed, large-area scanning. As a promising means for beam steering, micro-electro-mechanical system (MEMS)-based reflection gratings have been successfully implemented for terahertz beam control. So far, the diffraction grating efficiency is relatively low due to the limited vertical displacement range of the reflectors. In this paper, we propose a design for a reconfigurable MEMS-based reflection grating consisting of multiple subwavelength reflectors which are driven by 5-bit, high-throw electrostatic actuators. We vary the number of the reflectors per grating period and configure the throw of individual reflectors so that the reflection grating is shaped as a blazed grating to steer the terahertz beam with maximum diffraction grating efficiency. Furthermore, we provide a mathematical model for calculating the radiation pattern of the terahertz wave reflected by general reflection gratings consisting of subwavelength reflectors. The calculated and simulated radiation patterns of the designed grating show that we can steer the angle of the terahertz waves in a range of up to ± 56.4 ∘ with a maximum sidelobe level of −10 dB at frequencies from 0.3 THz to 1 THz.
TL;DR: In this article, a method to detect the topological charges (TCs) for vortex beams by using gradually changing-period spiral spoke grating (GCPSSG) is designed and experimentally demonstrated.
Abstract: A method to detect of the topological charges (TCs) for vortex beams by using gradually changing-period spiral spoke grating (GCPSSG) is designed and experimentally demonstrated. The value of TC can be measured due to the fact that the diffraction spot will appear a bright high intensity when the TC is equal to the diffractive grating spoke number, and otherwise the central intensity remains doughnut-like structure. Meanwhile, the rotated direction of the twist fringes is opposite with the grating, therefore the sign of TC can be distinguished. Moreover, in addition to discussing the light beam illuminates the geometric center of the grating, the beam misalignment condition is also considered. In this case, the magnitude and sign of TC can be simultaneously determined by the number and orientation of the bright spots, respectively. The detection of TCs up to ± 160 is realized with this scheme. The experimental results indicate that this scheme is robust and effective because the GCPSSG shows good tolerance to environment vibration and beam misalignment for the TC diagnostics, which is anticipated to be useful for optical communication.