Showing papers on "Beam splitter published in 2019"

Giant Enhancement of the Goos-Hänchen Shift Assisted by Quasibound States in the Continuum

Abstract: In optics, the two main mechanisms for enhancing the Goos-H\"anchen (GH) shift of a reflected light beam have a common shortcoming: The maximum shift is located exactly at the reflectance dip, which makes the reflected beam hard to detect. Here the authors tune the excitation of guided modes in a compound grating-waveguide structure, to realize quasibound states in the continuum (quasi-BICs) with ultrahigh $Q$-factors. Assisted by these quasi-BICs, the GH shift at the reflectance peak can be greatly enhanced. This giant GH shift with high reflectance can be used for $e.g.$ ultrasensitive sensors, wavelength-division (de)multiplexers, optical switches, and polarization beam splitters.

Exceptional points of any order in a single, lossy waveguide beam splitter by photon-number-resolved detection

Abstract: Exceptional points (EPs) are degeneracies of non-Hermitian operators where, in addition to the eigenvalues, the corresponding eigenmodes become degenerate. Classical and quantum photonic systems with EPs have attracted tremendous attention due to their unusual properties, topological features, and an enhanced sensitivity that depends on the order of the EP, i.e., the number of degenerate eigenmodes. Yet, experimentally engineering higher-order EPs in classical or quantum domains remain an open challenge due to the stringent symmetry constraints that are required for the coalescence of multiple eigenmodes. Here, we analytically show that the number-resolved dynamics of a single, lossy waveguide beam splitter, excited by N indistinguishable photons and post-selected to the N-photon subspace, will exhibit an EP of order N+1. By using the well-established mapping between a beam splitter Hamiltonian and the perfect state transfer model in the photon-number space, we analytically obtain the time evolution of a general N-photon state and numerically simulate the system’s evolution in the post-selected manifold. Our results pave the way toward realizing robust, arbitrary-order EPs on demand in a single device.

Dynamic modulation yields one-way beam splitting

Abstract: This paper demonstrates the realization of an extraordinary beam splitter, exhibiting one-way beam splitting amplification Such a dynamic beam splitter operates based on nonreciprocal and synchronized photonic transitions in obliquely illuminated space-time-modulated (STM) slabs which impart the coherent temporal frequency and spatial frequency shifts As a consequence of such unusual photonic transitions, a one-way beam splitting is exhibited by the STM slab Beam splitting is a vital operation for various communication systems, including circuit quantum electrodynamics, and signal-multiplexing and demultiplexing Despite that the beam splitting is conceptually a simple operation, the performance characteristics of beam splitters significantly influence the repeatability and accuracy of the entire system As of today, there has been no approach exhibiting a nonreciprocal beam splitting accompanied with transmission gain and an arbitrary splitting angle Here, we show that oblique illumination of a periodic and semicoherent dynamically-modulated slab results in coherent photonic transitions between the incident light beam and its counterpart space-time harmonic (STH) Such transitions introduce a unidirectional synchronization and momentum exchange between two STHs with same temporal frequencies but opposite spatial frequencies Such a beam splitting technique offers high isolation, transmission gain, and zero beam tilting, and is expected to drastically decrease the resource and isolation requirements in communication systems In addition to the analytical solution, we provide a closed-form solution for the electromagnetic fields in STM structures, and accordingly, investigate the properties of the wave isolation and amplification in subluminal, superluminal, and luminal ST modulations

Observation of enhanced optical spin Hall effect in a vertical hyperbolic metamaterial

Abstract: Hyperbolic metamaterials, horizontally stacked metal and dielectric multilayer, have recently been studied as a platform to observe optical spin Hall effect. However, the large optical spin Hall effect in the horizontal hyperbolic metamaterials accompanies extremely low transmission, which obstructs its practical applications. Reducing the sample thickness to augment the transmission causes diminishment of the shift. In this letter, we demonstrate that a vertical hyperbolic metamaterial can enhance the shift by several orders of magnitude in comparison to the shift of its horizontal counterpart. Under the same conditions of material combinations and total thickness, the shift enhancement, which is incident angle-dependent, can be higher than 800-fold when the incident angle is 5 degree, and 5000-fold when the incident angle is 1 degree. As a proof of concept, we fabricate a large-scale gold nano-grating by nanoimprint lithography and measure the helicity-dependent shift by Stokes polarimetry setup, which agrees well with the simulated result. The gigantic optical spin Hall effect in a vertical hyperbolic metamaterial will enable helicity-dependent control of optical devices including filters, sensors, switches and beam splitters.

High-efficiency anomalous splitter by acoustic meta-grating

Abstract: As an inversely designed artificial device, meta-surface usually means densely arranged meta-atoms with complex substructures. In acoustics, those meta-atoms are usually constructed by multifolded channels or multiconnected cavities of a deep subwavelength feature, which limits their implementation in pragmatic applications. We propose here a comprehensive concept of high-efficiency anomalous splitter based on an acoustic meta-grating. The beam splitter is designed by etching only two or four straight-walled grooves per period on a planar hard surface. Different from the recently reported reflectors or splitters, our device can split an incident wave into different desired directions with arbitrary power flow partition. In addition, because ultrathin substructures with thin walls and narrow channels are avoided in our design procedure, the proposed beam splitter can be used for waves with much shorter wavelength compared to the previous suggested systems. The design is established by rigorous formulas developed under the framework of the grating theory and a genetic optimization algorithm. Numerical simulation and experimental evidence are provided to discuss the involved physical mechanism and to give the proof of concept for the proposed high-efficiency anomalous acoustic splitter.

Hong-Ou-Mandel interferometry on a biphoton beat note

Abstract: Hong-Ou-Mandel interference, the fact that identical photons that arrive simultaneously on different input ports of a beam splitter bunch into a common output port, can be used to measure optical delays between different paths. It is generally assumed that great precision in the measurement requires that photons contain many frequencies, i.e., a large bandwidth. Here we challenge this “well-known” assumption and show that the use of two well-separated frequencies embedded in a quantum entangled state (discrete color entanglement) suffices to achieve great precision. We determine optimum working points using a Fisher Information analysis and demonstrate the experimental feasibility of this approach by detecting thermally-induced delays in an optical fiber. These results may significantly facilitate the use of quantum interference for quantum sensing, by avoiding some stringent conditions such as the requirement for large bandwidth signals.

Topological beam-splitting in photonic crystals

Abstract: We create a passive wave splitter, created purely by geometry, to engineer three-way beam splitting in electromagnetism in transverse electric and magnetic polarisation. We do so by considering arrangements of Indium Phosphide dielectric pillars in air, in particular we place several inclusions within a cell that is then extended periodically upon a square lattice. Hexagonal lattice structures are more commonly used in topological valleytronics but, as we discuss, three-way splitting is only possible using a square, or rectangular, lattice. To achieve splitting and transport around a sharp bend we use accidental, and not symmetry-induced, Dirac cones. Within each cell pillars are either arranged around a triangle or square; we demonstrate the mechanism of splitting and why it does not occur for one of the cases. The theory is developed and full scattering simulations demonstrate the effectiveness of the proposed designs.

Photon Bunching in a Rotating Reference Frame.

Abstract: Although quantum physics is well understood in inertial reference frames (flat spacetime), a current challenge is the search for experimental evidence of nontrivial or unexpected behavior of quantum systems in noninertial frames. Here, we present a novel test of quantum mechanics in a noninertial reference frame: we consider Hong-Ou-Mandel (HOM) interference on a rotating platform and study the effect of uniform rotation on the distinguishability of the photons. Both theory and experiments show that the rotational motion induces a relative delay in the photon arrival times at the exit beam splitter and that this delay is observed as a shift in the position of the HOM dip. This experiment can be extended to a full general relativistic test of quantum physics using satellites in Earth’s orbit and indicates a new route toward the use of photonic technologies for investigating quantum mechanics at the interface with relativity.

Wireless optical power transfer system by spatial wavelength division and distributed laser cavity resonance

Abstract: A novel wireless optical power transfer (WOPT) system using diverging angular dispersion and spatially distributed laser cavity resonance is proposed. In the transmitter, a diffraction grating spatially disperses the broadband light from a semiconductor optical amplifier. Receiving units spread across a wide field of view are embedded with retroreflecting beam splitters that reflect the incident beam back to the transmitter, thereby completing multiple resonant cavities. Retroreflectors enable a user-friendly alignment and tap power from the resonating cavity, supplying optical power. We demonstrate an automatic safety mechanism that instantly ceases the cavity resonance should any vulnerable organ break the transmitter–receiver line of sight. The results indicate that a single-channel WOPT system can provide a resonating average power of 17.2 mW (receiving power of 1.7 mW to the photodetector) over a distance of 1 m with a channel linewidth of 0.035 nm. For a proof-of-principle experiment, seven receiver units were successfully demonstrated to supply optical power. With careful retroreflector design and field-of-view optimization, the potential of our scheme can be further exploited toward commercial deployment.

Laser processing apparatus

Abstract: A laser beam applying unit of a laser processing apparatus for processing a wafer includes a laser oscillator for emitting a pulsed laser beam having a wavelength transmittable through the wafer, a beam condenser for converging the pulsed laser beam emitted from the laser oscillator onto the wafer held on a chuck table, a beam splitter assembly disposed between the laser oscillator and the beam condenser, for splitting the pulsed laser beam emitted from the laser oscillator to form at least two converged spots on the wafer that are spaced from each other in X-axis directions, and a mask assembly disposed between the laser oscillator and the beam condenser, for reducing the width of the converged spots on the wafer in Y-axis directions to keep the converged spots on the wafer within the width of the projected dicing lines on the wafer.

Acoustic Topological Transport and Refraction in a Kekulé Lattice

Abstract: Acoustic topological insulators can yield directional antennas for sound, enabling energy-efficient communication. This study explores using the interface-dependent spin Hall or valley Hall -like transport in a Kekul\'e lattice to generate directed beams: one, two in symmetric or antisymmetric fashion, or multiple beams. This topological refractive system could serve as an acoustic beam splitter, offering the advantages of stability, efficiency, and parity control.

Terahertz Dual-Polarization Beam Splitter Via an Anisotropic Matrix Metasurface

Abstract: A metasurface composed of multiple resonator arrangements with a certain phase distribution is capable of efficient wavefront manipulation. An anisotropic matrix metasurface consisting of asymmetric metal cross particles with a near-field coupling-induced achieves simultaneous distinctive dual-polarization anomalous reflections. Using polarization splitting, due to the anisotropic phase gradients of the matrix subunit, the x- and y- polarization components of the incident terahertz waves can be efficiently deflected with different deflection angles in a single plane or in orthogonal planes. Both simulated and experimental results show that the anisotropic matrix metasurface efficiently reflects the x- and y- polarization components of normal incident waves in different directions at 0.32–0.42 THz with a relative bandwidth of 27%, and the maximum deflection coefficient is measured to exceed 85%. The proposed anisotropic matrix metasurface is promising for applications in high-performance terahertz polarization beam splitters, spectral splitting, directional emitters, polarization-sensitive imaging, and polarization multiplexers.

Quantum Optics of Spin Waves through ac Stark Modulation.

Abstract: We bring the set of linear quantum operations, important for many fundamental studies in photonic systems, to the material domain of collective excitations known as spin waves. Using the ac Stark effect we realize quantum operations on single excitations and demonstrate a spin-wave analog of the Hong-Ou-Mandel effect, realized via a beam splitter implemented in the spin-wave domain. Our scheme equips atomic-ensemble-based quantum repeaters with quantum information processing capability and can be readily brought to other physical systems, such as doped crystals or room-temperature atomic ensembles.

Quantum coherent absorption of squeezed light

Abstract: We investigate coherent perfect absorption (CPA) in quantum optics, in particular when pairs of squeezed coherent states of light are superposed on an absorbing beam splitter. First, by employing quantum optical input–output relations, we derive the absorption coefficients for quantum coherence and for intensity, and reveal how these will differ for squeezed states. Second, we present the remarkable properties of a CPA gate: two identical but otherwise arbitrary incoming squeezed coherent states can be completely stripped of their coherence, producing a pure entangled squeezed vacuum state that with its finite intensity escapes from an otherwise perfect absorber. Importantly, this output state of light is not entangled with the absorbing beam splitter by which it was produced. Its loss-enabled functionality makes the CPA gate an interesting new tool for continuous-variable quantum state preparation.

Hong-Ou-Mandel interferometry on a biphoton beat note

Abstract: Hong-Ou-Mandel interference, the fact that identical photons that arrive simultaneously on different input ports of a beam splitter bunch into a common output port, can be used to measure optical delays between different paths. It is generally assumed that great precision in the measurement requires that photons contain many frequencies, i.e., a large bandwidth. Here we challenge this well-known assumption and show that the use of two well-separated frequencies embedded in a quantum entangled state (discrete color entanglement) suffices to achieve great precision. We determine optimum working points using a Fisher Information analysis and demonstrate the experimental feasibility of this approach by detecting thermally-induced delays in an optical fiber. These results may significantly facilitate the use of quantum interference for quantum sensing, by avoiding some stringent conditions such as the requirement for large bandwidth signals.

Coherent spin-wave processor of stored optical pulses

Abstract: A device being a pinnacle of development of an optical quantum memory should combine the capabilities of storage, inter-communication, and processing of stored information. In particular, the ability to capture a train of optical pulses, interfere them in an arbitrary way and finally, perform on-demand release could realize arbitrary optical computation. Here we demonstrate the operation of a coherent optical memory being able to store optical pulses in the form of collective spin-wave excitations in a two-dimensional wavevector space. During storage, we perform complex beamsplitter operations and demonstrate a variety of protocols implemented at the processing stage, including real-time controlled interference of a pair of spin-wave modes with 95% visibility. The highly multimode structure of the presented memory lends itself to enhancing classical optical telecommunication, as well as parallel processing of optical qubits at the single-photon level.

Thermally condensing photons into a coherently split state of light

Abstract: The quantum state of light plays a crucial role in a wide range of fields, from quantum information science to precision measurements. Whereas complex quantum states can be created for electrons in solid-state materials through mere cooling, optical manipulation and control builds on nonthermodynamic methods. Using an optical dye microcavity, we show that photon wave packets can be split through thermalization within a potential with two minima subject to tunnel coupling. At room temperature, photons condense into a quantum-coherent bifurcated ground state. Fringe signals upon recombination show the relative coherence between the two wells, demonstrating a working interferometer with the nonunitary thermodynamic beam splitter. Our energetically driven optical-state preparation method provides a route for exploring correlated and entangled optical many-body states.

Engineering Schr\"odinger cat states with a photonic even-parity detector

Abstract: When two equal photon-number states are combined on a balanced beam splitter, both output ports of the beam splitter contain only even numbers of photons. Consider the time-reversal of this interference phenomenon: the probability that a pair of photon-number-resolving detectors at the output ports of a beam splitter both detect the same number of photons depends on the overlap between the input state of the beam splitter and a state containing only even photon numbers. Here, we propose using this even-parity detection to engineer quantum states containing only even photon-number terms. As an example, we demonstrate the ability to prepare superpositions of two coherent states with opposite amplitudes, i.e. two-component Schr\"odinger cat states. Our scheme can prepare cat states of arbitrary size with nearly perfect fidelity. Moreover, we investigate engineering more complex even-parity states such as four-component cat states by iteratively applying our even-parity detector.

Entangled coherent states created by mixing squeezed vacuum and coherent light

Abstract: Entangled coherent states are a fundamentally interesting class of quantum states of light, with important implications in quantum information processing, for which robust schemes to generate them are required. Here, we show that entangled coherent states emerge, with high fidelity, when mixing coherent and squeezed vacuum states of light on a beam splitter. These maximally entangled states, where photons bunch at the exit of a beam splitter, are measured experimentally by Fock-state projections. Entanglement is examined theoretically using a Bell-type nonlocality test and compared with ideal entangled coherent states. We experimentally show nearly perfect similarity with entangled coherent states for an optimal ratio of coherent and squeezed vacuum light. In our scheme, entangled coherent states are generated deterministically with small amplitudes, which could be beneficial, for example, in deterministic distribution of entanglement over long distances.

Cylindrical vector beam generator using a two-element interferometer

Abstract: We realize a robust and compact cylindrical vector beam generator that consists of a simple two-element interferometer composed of a beam displacer and a cube beamsplitter. The interferometer operates on the higher-order Poincare sphere transforming a homogeneously polarized vortex into a cylindrical vector (CV) beam. We experimentally demonstrate the transformation of a single vortex beam into all the well-known CV beams and show the operations on the higher-order Poincare sphere according to the control parameters. Our method offers an alternative to the Pancharatnam-Berry phase optical elements and has the potential to be implemented as a monolithic device.

The origin of anticorrelation for photon bunching on a beam splitter

Abstract: The Copenhagen interpretation has been long-lasted, whose core concepts are in the Heisenberg's uncertainty principle and nonlocal correlation of EPR. The second-order anticorrelation on a beam splitter represents these phenomena where it cannot be achieved classically. Here, the anticorrelation of nonclassicality on a beam splitter is interpreted in a purely coherence manner. Unlike a common belief in a particle nature of photons, the anticorrelation roots in pure wave nature of coherence optics, where quantum superposition between two input fields plays a key role. This interpretation may intrigue a fundamental question of what nonclassicality should be and pave a road to coherence-based quantum information.

Dual-directional shearography based on a modified common-path configuration using spatial phase shift.

Abstract: This paper describes a dual-directional shearography system to address the issue of two-dimensional characterization of the surface strain. A common-path configuration coupled with an additional light path is used to provide the shearing in two directions. One of the three interfering beams is shared by both directional shearograms to improve the light efficiency and enhance the robustness of the system. The two directional shearograms are carried by different spatial carriers to distinguish one from the other. The spatial carrier is introduced by the single-aperture-lens Wollaston prism configuration. Rather than the conventional method in which the aperture is fixed at the front focal point of the imaging lens, a general case is considered by introducing a variable distance between the aperture and the imaging lens. The influence of the aperture-lens distance on the spatial carrier is then analyzed, which enables the separate control of the shearing amount and the spatial carrier. Two types of dual-directional shearography are presented to demonstrate the feasibility and the flexibility of the system. Type I is the simultaneous dual lateral shearography in orthogonal directions, and Type II is the simultaneous lateral and radial shearography. The spatial carrier introduced by the single-aperture-lens Wollaston prism configuration is discussed, and a configuration in which the Wollaston prism and the aperture are located at different sides of the lens is recommended for further shearography applications.

Integrated photonic tunable basic units using dual-drive directional couplers.

Abstract: Photonic integrated circuits based on waveguide meshes and multibeam interferometers call for large-scale integration of Tunable Basic Units (TBUs) that feature beam splitters and waveguides. This units are loaded with phase actuators to provide complex linear processing functionalities based on optical interference and can be reconfigured dynamically. Here, we propose and experimentally demonstrate, to the best of our knowledge, for the first time, a thermally actuated Dual-Drive Directional Coupler (DD-DC) design integrated on a silicon nitride platform. It operates both as a standalone optical component providing arbitrary optical beam splitting and common phase as well as a low loss and potentially low footprint TBU. Finally, we report the experimental demonstration of the first integrated triangular waveguide mesh arrangement using DD-DC based TBUs and provide an extended analysis of its performance and scalability.

Interference between quantum paths in coherent Kapitza─Dirac effect

Abstract: In the Kapitza-Dirac effect, atoms, molecules, or swift electrons are diffracted off a standing wave grating of the light intensity created by two counter-propagating laser fields. In ultrafast electron optics, such a coherent beam splitter offers interesting perspectives for ultrafast beam shaping. Here, we study, both analytically and numerically, the effect of the inclination angle between two laser fields on the diffraction of pulsed, low-energy electron beams. For sufficiently high light intensities, we observe a rich variety of complex diffraction patterns. These do not only reflect interferences between electrons scattered off intensity gratings that are formed by different vector components of the laser field. They may also result, for certain light intensities and electron velocities, from interferences between these ponderomotive scattering and direct light absorption and stimulated emission processes, usually forbidden for far-field light. Our findings may open up perspectives for the coherent manipulation and control of ultrafast electron beams by free-space light.

MEMS-in-the-lens architecture for a miniature high-NA laser scanning microscope

Abstract: Laser scanning microscopes can be miniaturized for in vivo imaging by substituting optical microelectromechanical system (MEMS) devices in place of larger components. The emergence of multifunctional active optical devices can support further miniaturization beyond direct component replacement because those active devices enable diffraction-limited performance using simpler optical system designs. In this paper, we propose a catadioptric microscope objective lens that features an integrated MEMS device for performing biaxial scanning, axial focus adjustment, and control of spherical aberration. The MEMS-in-the-lens architecture incorporates a reflective MEMS scanner between a low-numerical-aperture back lens group and an aplanatic hyperhemisphere front refractive element to support high-numerical-aperture imaging. We implemented this new optical system using a recently developed hybrid polymer/silicon MEMS three-dimensional scan mirror that features an annular aperture that allows it to be coaxially aligned within the objective lens without the need for a beam splitter. The optical performance of the active catadioptric system is simulated and imaging of hard targets and human cheek cells is demonstrated with a confocal microscope that is based on the new objective lens design. Microscopes that generate images by laser scanning could be miniaturized using microelectromechanical systems (MEMS) to replace the larger components currently required, allowing more-effective imaging of small structures in laboratory animals and humans. Researchers in the USA led by David Dickensheets at Montana State University, developed the new concept using simulation studies and experiments to examine human cheek cells. The process uses a recently developed MEMS mirror to both scan and focus the laser beam. The mirror is part of a catadioptric lens, meaning one that builds its images using both the reflection and the refraction of light. This allows light to be gathered across a wide range of angles—technically described as a high numerical aperture—to generate the images. The system’s advantages are likely to allow improved diagnosis of medical conditions, including cancer.

Polarization- and wavelength-agnostic nanophotonic beam splitter

Abstract: High-performance optical beam splitters are of fundamental importance for the development of advanced silicon photonics integrated circuits. However, due to the high refractive index contrast of silicon-on-insulator platforms, state-of-the-art nanophotonic splitters are hampered by trade-offs in bandwidth, polarization dependence and sensitivity to fabrication errors. Here, we present a new strategy that exploits modal engineering in slotted waveguides to overcome these limitations, enabling ultra-broadband polarization-insensitive optical power splitters with relaxed fabrication tolerances. The proposed splitter design relies on a single-mode slot waveguide that is gradually transformed into two strip waveguides by a symmetric taper, yielding equal power splitting. Based on this concept, we experimentally demonstrate −3 ± 0.5 dB polarization-independent transmission for an unprecedented 390 nm bandwidth (1260–1650 nm), even in the presence of waveguide width deviations as large as ±25 nm.