Multiple Beam Splitters Research Articles

Flat optics of nonuniform phase gradient metasurfaces

Flat optics of uniform phase gradient metasurfaces based on the generalized Snell’s law has been extensively studied. The optics of nonuniform phase gradient metasurfaces (NPGMs) is less clear. Here based on Huygens’ principle and finite-difference time-domain (FDTD) simulation, we explore the optical properties of NPGMs made of nanorods (meta-atoms), which can be tuned by modulation of propagation phase and geometric phase. It is found that the nonuniformity of phase gradient may lead to multichannel anomalous reflection/refraction. The multiple beam splitters with arbitrary intensity ratio can be achieved by using the amplitude/phase modulation. Based on our design principle, we can obtain different anomalous reflection patterns (with channels ±1, ±2, both ±1 and ±2, or no reflection at anomalous angle) by different arrangement of just two types of meta-atoms. In addition, we are able to achieve chiral anomalous reflections for designed NPGMs made of nanorods and L-shaped nanoparticles. Our formulism provides general design guidance for NPGMs and can be used to realize the beam splitting function with adjustable angle and intensity ratio.

A compact flexible sub-nanosecond framing photographic system.

A novel high-speed multi-frame photographic system is presented in this paper. The system demonstrates exceptional compactness and flexibility, requiring only the introduction of a cavity comprising multiple beam-splitters in the optical path to enable multi-frame imaging of sub-nanosecond events. The number and temporal delay of frames can be easily adjusted by adjusting the distance and angle between beam-splitters. These capabilities are demonstrated by observing the laser ablation process, highlighting the great potential for application in capturing ultrafast time-evolving events such as optical breakdown, the evolution of laser-produced plasmas, and the propagation of shock waves.

Reconfigurable and multiple beam steerable non-orthogonal-multiple-access system for optical wireless communication

The ability to reconfigure and adapt to different application scenarios plays an important role in future wireless communication systems. Here, a beam dividable and steerable optical wireless communication (OWC) system adopting a spatial light modulator (SLM) is presented. The reconfigurable multiple beam splitter as well as the adjustable splitting ratio are demonstrated. Experimental results show the proposed system can nearly evenly partition the input beam into up to five spots and can have the adjustable splitting ratio for the two-spot case. Combining non-orthogonal multiple access (NOMA) and wavelength division multiplexing (WDM), the proof-of-concept experimental demonstration shows the proposed system can provide 320.08 Gbit/s and 179.68 Gbit/s for the single-user scenario without beam steering and with steering of about 4°, respectively. Moreover, the data rates pairs of (92.20 Gbit/s, 119.17 Gbit/s) and (51.50 Gbit/s, 124.78 Gbit/s) can be achieved for the two-user scenario at different beam steering angles, respectively. The flexibility of data rate allocation for multiple users is also discussed. The OWC system under evaluation can satisfy the pre-forward error correction bit-error rate limit (pre-FEC BER = 3.8 × 10−3).

On-chip multiple beam splitting assisted by bound states in the continuum.

Usually, on-chip beam splitting can be achieved by manipulating the in-plane iso-frequency curves (IFCs) of the structure, where the confinement of light along the out-of-plane direction is governed by total internal reflection. In this Letter, without needing a high-index dielectric background material for total internal reflection, we achieve on-chip beam splitting in a linear-crossing metamaterial (LCMM) mimicked by a two-dimensional photonic crystal (PhC) slab where the vertical confinement is enabled by a bound state in the continuum (BIC) and totally beyond the light cone. Particularly, the light propagating inside the LCMM can be flexibly controlled by the rotation angle of the rectangular silicon pillars in the PhC slab. On-chip triple beam splitting can further be designed by combining two kinds of LCMM with opposite rotation angles. Such light beam splitting beyond the light cone originates from the combined manipulation of the BIC and the spatial dispersion of LCMMs. Our work promotes the development of optical devices in integrated optics, such as on-chip focusing, switching, and (de)multiplexing.

Controllable multiple beam splitting in Hermitian and non-Hermitian symmetric coupled waveguide systems

We investigate high-fidelity multiple beam splitting in Hermitian and non-Hermitian (NH) symmetric coupled waveguides (WGs) with one input and 2 N output WG channels. In Hermitian systems, we realize adiabatically light splitting in resonant case based on the stimulated Raman adiabatic passage and arbitrary proportion from the middle WG to outer WGs in propagation coefficients mismatch case using shortcuts to adiabaticity (STA) technique. In NH systems with even WGs being dissipative, the compact and robust beam splitting can be achieved by eliminating the non-adiabatic coupling via the NH STA method. We further verify the feasibility of our theoretical predictions by means of the beam propagation method. The suggested multiple beam splitters open new opportunities for the realization of on-chip high-bandwidth photonics with high fidelity in short distances.

Multimode N00N states in driven atomtronic circuits

We propose a method to generate multi-mode N00N states with arrays of ultracold atoms. Our protocol requires a strong relative offset among the wells and a drive of the interparticle interaction at a frequency resonant with the offsets. The proposal is demonstrated by a numerical and a Floquet analysis of the quantum dynamics of a ring-shaped atomtronics circuit made of M weakly coupled optical traps. We generate a hierarchy of energy scales down to very few low-energy states where N00N dynamics takes place, making multi-mode N00N states appear at nearly regular time intervals. The production of multi-mode N00N states can be probed by time-of-flight imaging. Such states may be used to build a multiple beam splitter.

Electromagnetically induced polarization grating

Based on electromagnetically induced transparency (EIT), we investigate an all-optical grating structure to realize polarization-dependent multiple beam splitting in the Raman-Nath limit. To optimize the grating performance, higher excited state [e.g., nS1/2 (n ≥ 6)] of ultracold 87Rb atoms is employed to construct a five-level Ξ-Λ system sharing one common populated ground state. A principal advantage of our proposed scheme is that the σ± components of a linearly polarized weak probe field can be decoupled and thus be independently diffracted with high efficiency in both one and two dimensions by exploiting different quasi-standing waves as the two strong coupling fields in the Ξ and Λ configurations. Such an all-optical polarization-sensitive operation could greatly enhance the tunability and capacity of all-optical multiplexing, interconnecting, and networking in free space for both classical and quantum applications.

Angularly symmetric splitting of a light beam upon reflection and refraction at an air-dielectric plane boundary.

Conditions for achieving equal and opposite angular deflections of a light beam by reflection and refraction at an air-dielectric boundary are determined. Such angularly symmetric beam splitting (ASBS) is possible only if the angle of incidence is >60° by exactly one third of the angle of refraction. This simple law, plus Snell's law, leads to several analytical results that clarify all aspects of this phenomenon. In particular, it is shown that the intensities of the two symmetrically deflected beams can be equalized by proper choice of the prism refractive index and the azimuth of incident linearly polarized light. ASBS enables a geometrically attractive layout of optical systems that employ multiple prism beam splitters.

Multiple beam splitting in elastic phononic crystal plates

This work presents an experimental evidence for triple beam splitting in an elastic plate with an embedded elastic phononic crystal (PC) prism and elaborates on its working mechanism. While there were reports on negative refraction and double beam splitting with PCs, no experimental evidence on the splitting of triple or more ultrasonic elastic beams through PCs has been shown yet. After the experimental results are presented in case of triple beam splitting, further analysis is carried out to explain how triple or more beams can be split depending on elastic PC prism angles.

Adiabatic evolution of light in an array of parallel curved optical waveguides

Adiabatic evolution of light in parallel curved optical waveguide array is investigated theoretically. This problem is shown to bear a close connection with the process of coherent population transfer in a ``bow-tie'' model in quantum physics. Under certain conditions on the geometry of the waveguides and the optical properties of the system complete light transfer between the outer waveguides is achieved. Special attention is paid to the case of three waveguides, which is analyzed using the solutions of the well-known bow-tie model. The analytic solution is used to design recipes for creating arbitrary superpositions of light intensity between the waveguides, with possible applications in achromatic optical multiple-beam splitters. For more than three waveguides complete light transfer between the outer waveguides and beam splitting is demonstrated numerically.

Planar achromatic multiple beam splitter by adiabatic light transfer

We introduce a novel achromatic and robust scheme for n-fold multiple beam splitting based on adiabatic light transfer in a planar geometry of coupled waveguides (WGs). The concept is experimentally verified for a one-to-three beam splitter by using a reconfigurable light-induced WG structure at two operating wavelengths. The demonstrated planar-type achromatic beam splitter opens new opportunities for the realization of ultra-high bandwidth on-chip photonic devices.

Multiple beam splitter using volumetric multiplexed Fresnel zone plates fabricated by ultrafast laser-writing

A simple approach to producing a 1×N beam splitter is demonstrated by fabricating a volumetric multiplex phase Fresnel zone plate in bulk transparent material. This comprised four layers of zone plates created in borosilicate glass by femtosecond laser direct-writing, each shifted laterally relative to the illumination axis, creating four separate beamlets. Since the power transmitted in each beamlet is proportional to the diffraction efficiency of the corresponding zone plate, the power ratios can be customized by adjusting the fabrication parameters of each layer. This approach demonstrates the potential of femtosecond laser direct-writing for the fabrication of complex optical elements in transparent media as components of integrated monolithic photonic devices.

Achromatic multiple beam splitting by adiabatic passage in optical waveguides

A variable achromatic optical beam splitter with one input and $N$ output waveguide channels is introduced. The physical mechanism of this multiple beam splitter is adiabatic passage of light between neighboring optical waveguides in a fashion reminiscent of the technique of stimulated Raman adiabatic passage in quantum physics. The input and output waveguides are coupled via a mediator waveguide and the ratios of the light intensities in the output channels are controlled by the couplings of the respective waveguides to the mediator waveguide. Due to its adiabatic nature the beam splitting efficiency is robust to variations in the experimental parameters.

A Simplified Cold Atom Source for 3-D MOT Loading

A simplified two-dimensional (2-D) magneto-optical trap (MOT) for loading atoms into a 3-D MOT is realized. Instead of utilizing multiple wave plates and beam splitters to cover a large cooling region, we deploy cooling beams with elliptical cross-section profiles to achieve a comparable cooling volume. This simplification reduces the cost and difficulty of alignment. The 3-D MOT achieves a loading rate of 2 × 108 atoms per second via this simplified 2-D MOT. Correlation between the loading rate and parameters of optical system is also determined.

Increased field of view through optical multiplexing

Traditional approaches to wide field of view (FoV) imager design usually lead to overly complex optics with high optical mass and/or pan-tilt mechanisms that incur significant mechanical/weight penalties, which limit their applications, especially on mobile platforms such as unmanned aerial vehicles (UAVs).We describe a compact wide FoV imager design based on superposition imaging that employs thin film shutters and multiple beamsplitters to reduce system weight and eliminate mechanical pointing. The performance of the superposition wide FoV imager is quantified using a simulation study and is experimentally demonstrated. Here, a threefold increase in the FoV relative to the narrow FoV imaging optics employed imager design is realized. The performance of a superposition wide FoV imager is analyzed relative to a traditional wide FoV imager and we find that it can offer comparable performance.

Compensation of beam walk-off in hollow metal waveguides

Hollow metal waveguides feature well collimated beams and small losses across air gaps. This enables introduction of multiple optical beam splitters, or taps, along the waveguide to multicast signals from a source to multiple receivers. The splitters need to be of sufficient thickness to provide mechanical integrity and ease of handling. As a result, passing through the thickness leads to a beam walk-off. Walk-off dependence on the splitter thickness and its effect on the system optical efficiency are investigated. Two methods to compensate the walk-off are described: by offsetting the outgoing waveguide, and by introducing an additional symmetric optical element to shift the beam back to the original optical path. Both methods have been shown to effectively mitigate the walk-off effects.

Design of a polarized head-mounted projection display using ferroelectric liquid-crystal-on-silicon microdisplays

It has been a common problem in optical see-through head-mounted displays that the displayed image lacks brightness and contrast compared with the direct view of a real-world scene. This problem is aggravated in head-mounted projection displays in which multiple beam splitting and low retroreflectance of a typical retroreflective projection screen yield low luminous transfer efficiency. To address this problem, we recently proposed a polarized head-mounted projection display (p-HMPD) design where the polarization states of the light are deliberately manipulated to maximize the luminous transfer efficiency. We report the design of a compact p-HMPD prototype system using a pair of high-resolution ferroelectric liquid-crystal-on-silicon (FLCOS) microdisplays. In addition to higher resolution, the FLCOS displays have much higher optical efficiency than a transmissive-type liquid crystal display (LCD) and help to further improve the overall light efficiency and image quality. We detail the design of a compact illumination unit for the FLCOS microdisplay, also commonly referred to as the light engine, and a projection lens, both of which are key parts of the p-HMPD system. The performances of the light engine and projection lens are analyzed in detail. Finally, we present the design of a compact p-HMPD prototype using the custom-designed light engine and projection optics.

Diffractive optical elements designed for highly precise far-field generation in the presence of artifacts typical for pixelated spatial light modulators

Diffractive optical elements (DOEs) realized by spatial light modulators (SLMs) often have features that distinguish them from most conventional, static DOEs: strong coupling between phase and amplitude modulation, a modulation versus steering parameter characteristic that may not be precisely known (and may vary with, e.g., temperature), and deadspace effects and interpixel cross talk. For an optimal function of the DOE, e.g. as a multiple-beam splitter, the DOE design must account for these artifacts. We present an iterative design method in which the optimal setting of each SLM pixel is carefully chosen by considering the SLM artifacts and the design targets. For instance, the deadspace-interpixel effects are modeled by dividing the pixel to be optimized, and its nearest neighbors, into a number of subareas, each with its unique response and far-field contribution. Besides the customary intensity control, the design targets can also include phase control of the optical field in one or more of the beams in the beam splitter. We show how this can be used to cancel a strong unwanted zeroth-order beam, which results from using a slightly incorrect modulation characteristic for the SLM, by purposely sending a beam in the same direction but with the opposite phase. All the designs have been implemented on the 256 x 256 central pixels of a reflective liquid crystal on silicon SLM with a selected input polarization state and a direction of transmission axis of the output polarizer such that for the available different pixel settings a phase modulation of ~2pi rad could be obtained, accompanied by an intensity modulation depth as high as >95%.

8.1: Invited Paper: Achieving Near-Correct Focus Cues in a 3D Display using Multiple Image Planes

Focus cues specify inappropriate 3d scene parameters in conventional displays because the light comes from a single surface, independent of the depth relations in the portrayed scene. We examine the efficacy of a stereo-display prototype designed to minimize these problems by using multiple image planes to present near-correct focus cues. Each eye's view is the sum of several images presented at different focal distances. Variation in focal distance is provided by either multiple beam splitters or by use of a switchable lens. The stimulus to accommodation is more consistent with the portrayed depth than with conventional displays. Compared to a normal, fixed-distance display, observers show improved stereoscopic performance in different psychophysical tasks including speed of fusing stereoscopic images. The multiple image-planes approach provides a practical solution for some shortcomings of conventional displays.

Multiple beam splitter for single photons

We propose a method using ``light storage'' and fractional stimulated Raman adiabatic passage (F-STIRAP) to get entangled multiple Fock states from a single photon. A light storage technique is used to store the quantum information of a single-photon pulse in atoms. F-STIRAP pulses then split the stored coherence, such that reading pulses retrieve the quantum information from this new coherence. Since each reading pulse only retrieves part of the total coherence, we can obtain entangled multiple Fock states with arbitrary relative amplitude. This method to create entanglement is versatile for obtaining frequency, time, and∕or spatial entanglement. Indeed, we obtain a multiple beam splitter with easily adjustable parameters.