Multiport Beam Splitters Research Articles

Polarization-independent two-dimensional dielectric grating for 3 × 3 beam splitter

Conventional multi-port beam splitters with spot arrays, while being key components in diversiform optical systems, show polarization sensitivity and insufficient uniformity. Here, we proposed a polarization-independent high-efficiency 3 × 3 beam splitter based on the two-dimensional(2D) cylindrical dielectric grating (CDG), which could redistribute the incident light into nine beams with equal power. The proposed grating consists of a double-layer dielectric cylinder on the substrate of fused silica. The parameters of grating structure and fabrication tolerance are calculated by using rigorous coupled wave analysis (RCWA) and simulated annealing algorithm. The numerical results show that nine diffraction orders ((0, 0), (±1, 0), (0, ±1), (±1, ±1)) have average diffraction efficiencies of 10.12 % with uniformity of 2.8 % and mean polarization-independent loss (PDL) of 0.076 dB for TE and TM polarization. This work can open a new and positive way for researching the 2D multi-spot beam splitter and has promising applications in the field of three-dimensional(3D) imaging and reconstruction, microscopy techniques, material processing, etc.

Plus-shaped dielectric grating for seven-channel transmission

A new seven-channel transmission grating with plus-shaped array under normal incidence is proposed and discussed in this paper. Through the simulated annealing (SA) algorithm and rigorous coupled-wave analysis (RCWA), the novel microstructure can split the incident energy into 0-th/±1-st/±2-nd/±3-rd orders evenly. The influence of incident angle, period, incident wavelength, and other parameters on the diffraction efficiency are also analyzed in this paper. For transverse magnetic (TM) polarization, the range of period is 3062–3246 nm and the bandwidth of incident angle and wavelength is 1.96° and 32.3 nm, respectively. It can be concluded that the TM-polarized light of the designed grating has a good performance in incident bandwidth and fabrication tolerance. In addition, the efficiency of transverse electric (TE) polarization has the satisfactory uniformity of 2.40%. Therefore, the proposed grating has a certain significance for the research of multi-port beam splitter, especially for the seven-channel polarization-independent beam splitter.

Metasurface‐Based Free‐Space Multi‐Port Beam Splitter with Arbitrary Power Ratio

AbstractA beam splitter (BS) is one of the most critical building blocks in optical systems. Despite various attempts of flat‐type BSs to miniaturize the conventional cube BS reported, it remains a challenge to realize an ultrathin optical BS with multi‐port output, non‐uniform splitting ratio, and steerable outgoing directions. Herein, a free‐space optical multi‐port beam splitter (MPBS) based on a polarization‐independent all‐dielectric metasurface is demonstrated. By applying an optimized phase‐pattern paradigm via a gradient‐descent‐based iterative algorithm to amorphous silicon (α‐Si) metasurfaces, a variety of MPBS samples with arbitrarily predetermined output port number (2–7), power ratio, and spatial distribution of output beams are prepared. The experimental results reveal that the fabricated MPBSs can achieve high total splitting efficiency (TSE, above 74.7%) and beam‐splitting fidelity (similarity, above 78.4%) within the bandwidth of 100 nm (1500–1600 nm). Such proposed MPBS can provide fabulous flexibility for optical integrated system and diverse applications.

Generating Greenberger-Horne-Zeilinger states using multiport splitters

Symmetric multiport splitters are versatile tools in optical quantum information processing. They can be used for studying multiparticle scattering, for studying distinguishability and mixedness, and also for the generation of multipartite entangled quantum states. Here, we show that $N$-photon $N$-mode Greenberger-Horne-Zeilinger (GHZ) states can be generated using symmetric multiport beam splitters. Varying the input states' internal degrees of freedom and postselecting onto certain photon-number distributions allows the probabilistic generation of GHZ states with arbitrary photon numbers. We present two schemes, one for odd and one for even numbers of photons, to generate GHZ states using symmetric multiport splitters and compare them to a strategy utilizing a $2N$-port network as well as the standard postselection method.

Certification of a non-projective qudit measurement using multiport beamsplitters

The most common form of measurement in quantum mechanics projects a wavefunction onto orthogonal states that correspond to definite outcomes. However, generalized quantum measurements that do not fully project quantum states are possible and have an important role in quantum information tasks. Unfortunately, it is difficult to certify that an experiment harvests the advantages made possible by generalized measurements, especially beyond the simplest two-level qubit system. Here we show that multiport beamsplitters allow for the robust realization of high-quality generalized measurements in higher-dimensional systems with more than two levels. Using multicore optical fibre technology, we implement a seven-outcome generalized measurement in a four-dimensional Hilbert space with a fidelity of 99.7%. We present a practical quantum communication task and demonstrate a success rate that cannot be simulated in any conceivable quantum protocol based on standard projective measurements on quantum messages of the same dimension. Our approach, which is compatible with modern photonic platforms, showcases an avenue for faithful and high-quality implementation of genuinely non-projective quantum measurements beyond qubit systems. Generalized measurements that do not correspond to conventional basis projections of the quantum wavefunction are a part of several important protocols in quantum information. These measurements can be certifiably performed on higher-dimensional systems using optical fibre technology.

Bend-free multiarm interferometers on optical chips

Multiarm interferometers can enhance measurement precision and provide multiparameter capability to the measurement. Their realisation requires multiport beam splitters, which has been a long-standing challenge in free-space and integrated optics. Here, we propose a new type of multiport interferometers suitable for implementation on optical chips. Their prospective advantages over the standard directional-coupler architectures: an arbitrary number of arms, planar architecture and two orders of magnitude reduction in footprint, are achieved by the layout based exclusively on the finite modulated photonic lattices. The inverse design of photonic lattices is facilitated by restricting the light propagation to periodic patterns. The corresponding interferometer model predicts the maximum \(1/\sqrt{N}\) sensitivity scaling with the number of arms N. While the presented design solutions are ubiquitous to all implementations, the advantages are discussed in both the low and high refractive-index contrast platforms. Finally, we provide an outlook on the possibilities for the interferometer applications in distributed classical and quantum measurements.

Maximizing quantum discord from interference in multi-port fiber beamsplitters

Fourth-order interference is an information processing primitive for photonic quantum technologies, as it forms the basis of photonic controlled-logic gates, entangling measurements, and can be used to produce quantum correlations. Here, using classical weak coherent states as inputs, we study fourth-order interference in 4 × 4 multi-port beam splitters built within multi-core optical fibers, and show that quantum correlations, in the form of geometric quantum discord, can be controlled and maximized by adjusting the intensity ratio between the two inputs. Though these states are separable, they maximize the geometric discord in some instances, and can be a resource for protocols such as remote state preparation. This should contribute to the exploitation of quantum correlations in future telecommunication networks, in particular in those that exploit spatially structured fibers.

Enhancement of amplitude-squared squeezing of light with the SU(3) multiport beam splitters

We study the effect of a tritter, a linear optical circuit of three beam splitters following SU(3) unitary group transformations having three inputs and three output ports, on the ‘Amplitude-Squared Squeezing (ASS)’. We study the variation of ASS with different parameters of the tritter and find that there are a number of conditions where ASS is enhanced at the output of the tritter when we inject light beam exhibiting ASS at one of the input port and light beams in coherent state at another two input ports of the tritter.

Multi-core fiber integrated multi-port beam splitters for quantum information processing

Multi-port beam splitters are cornerstone devices for high-dimensional quantum information tasks, which can outperform the two-dimensional ones. Nonetheless, the fabrication of such devices has proven to be challenging with progress only recently achieved with the advent of integrated photonics. Here, we report on the production of high-quality N × N (with N = 4 , 7 ) multi-port beam splitters based on a new scheme for manipulating multi-core optical fibers. By exploring their compatibility with optical fiber components, we create four-dimensional quantum systems and implement the measurement-device-independent random number generation task with a programmable four-arm interferometer operating at a 2 MHz repetition rate. Due to the high visibilities observed, we surpass the one-bit limit of binary protocols and attain 1.23 bits of certified private randomness per experimental round. Our result demonstrates that fast switching, low loss, and high optical quality for high-dimensional quantum information can be simultaneously achieved with multi-core fiber technology.

Polarization-Independent Two-Layer Grating With Five-Port Splitting Output Under Normal Incidence

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.

Entanglement condition for W type multimode states and schemes for experimental realization

We derive a class of inequality relations, using both the sum uncertainty relations of su(2) algebra operators and the Schrodinger–Robertson uncertainty relation of partially transposed su(1,1) algebra operators, to detect the three-mode entanglement of non-Gaussian states of electromagnetic field. These operators are quadratic in mode creation and annihilation operators. The inseparability condition obtained using su(2) algebra operators is shown to guarantee the violation of Schrodinger–Robertson uncertainty relation of partially transposed su(1,1) algebra operators. The obtained inseparability condition incorporates all the required bipartite entanglement conditions to detect the W type three-mode entangled states and hence it is shown to be a necessary condition for W type three-mode entangled states. A general form for a family of such inseparability conditions is provided. The results derived for three-mode systems are generalized to multimode systems. Experimental schemes using symmetric multiport beam splitters and multi-Λ EIT system are proposed to test the violation of multimode separability condition.

Entanglement indicators for quantum optical fields: three-mode multiport beamsplitters EPR interference experiments

We generalize a new approach to entanglement conditions for light of undefined photons numbers given in Żukowski et al (2017 Phys. Rev. A 95 042113) for polarization correlations to a broader family of interferometric phenomena. Integrated optics allows one to perform experiments based upon multiport beamsplitters. To observe entanglement effects one can use multi-mode parametric down-conversion emissions. When the structure of the Hamiltonian governing the emissions has (infinitely) many equivalent Schmidt decompositions into modes (beams), one can have perfect EPR-like correlations of numbers of photons emitted into ‘conjugate modes’ which can be monitored at spatially separated detection stations. We provide entanglement conditions for experiments involving three modes on each side, and three-input-three-output multiport beamsplitters, and show their violations by bright squeezed vacuum states. We show that a condition expressed in terms of averages of observed rates is a much better entanglement indicator than a related one for the usual intensity variables. Thus, the rates seem to emerge as a powerful concept in quantum optics, especially for fields of undefined intensities.

基于光子数测量的量子信道物理安全检测

理想的单光子源和高性能的单光子探测器是制约量子密钥分配系统中的密钥安全和码率的两个关键因素。弱相干脉冲作为单光子源，为保证安全性，平均光子数必须少而限制了码率的提高。本文介绍了超导边沿传感器单光子探测器，提出了多端口分束器与多APD结合可用于量子密钥分配系统中检测弱相干脉冲中的光子数。对窃听者的攻击策略进行分析的基础上，基于光子数的检测，指出在保证安全性的前提条件下可以提高弱相干脉冲中的平均光子数，进而提高系统的量子密钥成码率。 The ideal single photon source and high performance single photon detectors are two key factors that restrict the key security and bit rate in quantum key distribution system. As a single photon source, the weak coherent pulse must contain fewer average photon number for the sake of security, thus the quantum bit rate cannot be raised to a high level. Superconducting transition edge sensor for single photon detection has been introduced. It is proposed that multi-port beam splitter combined with many APDs can be used to detect the photon number in weak coherent pulse in quantum key distribution system. The attack tactics of eavesdropper is analyzed, and based on photon number detection, it is proposed that the average photon number in weak coherent pulse can be improved, thus the quantum key bit rate can be improved.

Ultra‐broadband nanophotonic beamsplitter using an anisotropic sub‐wavelength metamaterial

AbstractNanophotonic beamsplitters are fundamental building blocks in integrated optics, with applications ranging from high speed telecom receivers to biological sensors and quantum splitters. While high‐performance multiport beamsplitters have been demonstrated in several material platforms using multimode interference couplers, their operation bandwidth remains fundamentally limited. Here, we leverage the inherent anisotropy and dispersion of a sub‐wavelength structured photonic metamaterial to demonstrate ultra‐broadband integrated beamsplitting. Our device, which is three times more compact than its conventional counterpart, can achieve high‐performance operation over an unprecedented 500 nm design bandwidth exceeding all optical communication bands combined, and making it one of the most broadband silicon photonics components reported to date. Our demonstration paves the way toward nanophotonic waveguide components with ultra‐broadband operation for next generation integrated photonic systems. image

Scalable orbital-angular-momentum sorting without destroying photon states

Single photons with orbital angular momentum (OAM) have attracted substantial attention from researchers. A single photon can carry infinite OAM values theoretically. Thus, OAM photon states have been widely used in quantum information and fundamental quantum mechanics. Although there have been many methods for sorting quantum states with different OAM values, the nondestructive and efficient sorter of high-dimensional OAM remains a fundamental challenge. Here, we propose a scalable OAM sorter which can categorize different OAM states simultaneously, meanwhile, preserving both OAM and spin angular momentum. Fundamental elements of the sorter are composed of symmetric multiport beam splitters (BSs) and Dove prisms with cascading structure, which in principle can be flexibly and effectively combined to sort arbitrarily high-dimensional OAM photons. The scalable structures proposed here greatly reduce the number of BSs required for sorting high-dimensional OAMstates. In view of the nondestructive and extensible features, the sorters can be used as fundamental devices not only for high-dimensional quantum information processing, but also for traditional optics.

Multivariate quantum memory as controllable delayed multi-port beamsplitter

The addressability of parallel spatially multimode quantum memory for light allows one to control independent collective spin waves within the same cold atomic ensemble. Generally speaking, there are transverse and longitudinal degrees of freedom of the memory that one can address by a proper choice of the pump (control) field spatial pattern. Here we concentrate on the mutual evolution and transformation of quantum states of the longitudinal modes of collective spin coherence in the cavity-based memory scheme. We assume that these modes are coherently controlled by the pump waves of the on-demand transverse profile, that is, by the superpositions of waves propagating in the directions close to orthogonal to the cavity axis. By the write-in, this allows one to couple a time sequence of the incoming quantized signals to a given set of superpositions of orthogonal spin waves. By the readout, one can retrieve quantum states of the collective spin waves that are controllable superpositions of the initial ones and are coupled on demand to the output signal sequence. In a general case, the memory is able to operate as a controllable delayed multi-port beamsplitter, capable of transformation of the delays, the durations and time shapes of signals in the sequence. We elaborate the theory of such light-matter interface for the spatially multivariate cavity-based off-resonant Raman-type quantum memory. Since, in order to speed up the manipulation of complex signals in multivariate memories, it might be of interest to store relatively short light pulses of a given time shape, we also address some issues of the cavity-based memory operation beyond the bad cavity limit.

Suppression laws for multiparticle interference in Sylvester interferometers

Quantum interference of correlated particles is a fundamental quantum phenomenon which carries signatures of the statistics properties of the particles, such as bunching or antibunching. In the presence of particular symmetries, interference effects take place with high visibility, one of the simplest cases being the suppression of coincident detection in the Hong-Ou-Mandel effect. Tichy et al., [Phys. Rev. Lett. 104, 220405 (2010)] recently demonstrated a simple sufficient criterion for the suppression of output events in the more general case of Fourier multiport beam splitters. Here we study the case in which ${2}^{q}$ particles (either bosonic or fermionic) are injected simultaneously in different ports of a Sylvester interferometer with ${2}^{p}\ensuremath{\ge}{2}^{q}$ modes. In particular, we prove a necessary and sufficient criterion for a significant fraction of output states to be suppressed, for specific input configurations. This may find application in assessing the indistinguishability of multiple single-photon sources and in the validation of boson sampling machines.

Multiphoton quantum interference with high visibility using multiport beam splitters

Multiphoton states can be produced in multiple parametric down-conversion (PDC) processes. The nonlinear crystal in such a case is pumped with high power. In theory, the more populated these states are, the deeper is the conflict with local realistic description. However, the interference contrast in multiphoton PDC experiments can be quite low for high pumping. We show how the contrast can be improved. The idea employs currently accessible optical devices, the multiport beam splitters. They are capable of splitting the incoming light in one input mode to $M$ output modes. Our scheme works as a positive operator-valued measure filter. It may provide a feasible Clauser-Horne-Shimony-Holt-Bell inequality test, and thus can be useful in, e.g., schemes reducing communication complexity.

Many-particle interference beyond many-boson and many-fermion statistics

Identical particles exhibit correlations even in the absence of inter-particle interaction, due to the exchange (anti)symmetry of the many-particle wavefunction. Two fermions obey the Pauli principle and anti-bunch, whereas two bosons favor bunched, doubly occupied states. Here, we show that the collective interference of three or more particles leads to much more diverse behavior than expected from the boson–fermion dichotomy known from quantum statistical mechanics. The emerging complexity of many-particle interference is tamed by a simple law for the strict suppression of events in the Bell multiport beam splitter. The law shows that counting events are governed by widely species-independent interference, such that bosons and fermions can even exhibit identical interference signatures, while their statistical character remains subordinate. Recent progress in the preparation of tailored many-particle states of bosonic and fermionic atoms promises experimental verification and applications in novel many-particle interferometers.

Two-Photon Path-Entangled States in Multimode Waveguides

We experimentally show that two-photon path-entangled states can be coherently manipulated by multimode interference in multimode waveguides. By measuring the output two-photon spatial correlation function versus the phase of the input state, we show that multimode waveguides perform as nearly ideal multiport beam splitters at the quantum level, creating a large variety of entangled and separable multipath two-photon states.