Beam Splitter Research Articles

Nonuniformity of diffractive splitting and receiver-transmitter alignment for large-field-of-view hundred-beam-scale LiDAR

To meet the spatial perception requirements for autonomous ship navigation in common scenarios such as ocean navigation, port entry and exit, and lock passage, commercial vehicle-mounted LiDAR technology falls short of demands in aspects such as sensing distance, field of view, angular resolution, and spatial sampling density. This paper proposes a hundred-beam-scale LiDAR scheme based on large-field-of-view diffractive beam splitting and a fiber array for echo reception and presents an in-depth investigation of the angular nonuniformity of diffractive beam splitting and the microradian-scale alignment for such hundred-beam-scale large-field-of-view LiDAR. This paper considers a combination of split-beam transmission based on a high-order diffractive optical element (DOE) and echo reception based on a high-precision fiber-optic line array. The nonlinear angular characteristics of the DOE are deduced and analyzed for a large field of view. The units of the receiving fiber-optic array are designed to offset the influence of the angular nonlinearity of the DOE, ensuring high-precision receiver–transmitter alignment of the hundred-beam-scale LiDAR for beams at any order of diffraction and helping to reduce system errors. The above-described LiDAR system has undergone laboratory testing and practical engineering verification, and it provides a new optical solution for LiDAR systems at the hundred-beam scale with a large field of view, a small divergence angle, and high sampling density. The presented system achieves a registration accuracy of 66.5 μrad with 128 beams and a 10-degree field of view, greatly improving signal reception efficiency. Such LiDAR systems have a wide range of applications, including space docking, target identification, lunar and planetary exploration, and ground-based vehicle-mounted LiDAR.

Quantum plasmonic sensing by Hong–Ou–Mandel interferometry

We propose a quantum plasmonic sensor using Hong–Ou–Mandel (HOM) interferometry that measures the refractive index of an analyte, embedded in a plasmonic beam splitter composed of a dual-Kretschmann configuration, which serves as a frustrated total internal reflection beamsplitter (BS). The sensing performance of the HOM interferometry, combined with single-photon detectors, is evaluated through Fisher information for estimation of the refractive index of the analyte. This is subsequently compared with the classical benchmark that considers the injection of a coherent state of light into the plasmonic BS. By varying the wavelength of the single photons and the refractive index of the analyte, we identify a wide range where a 50% quantum enhancement is achieved and discuss the observed behaviors in comparison with the classical benchmark. We expect this study to provide a useful insight into the advancement of quantum-enhanced sensing technologies, with direct implications for a wide range of nanophotonic BS structures.

Efficient determination of Born-effective charges, LO-TO splitting, and Raman tensors of solids with a real-space atom-centered deep learning approach

We introduce a deep neural network (DNN) framework called the Real-space Atomic Decomposition NETwork (radnet), which is capable of making accurate predictions of polarization and of electronic dielectric permittivity tensors in solids and aims to address limitations of previously available machine learning models for Raman predictions in periodic systems. This framework builds on previous, atom-centered approaches while utilizing deep convolutional neural networks. We report excellent accuracies on direct predictions for two prototypical examples: GaAs and BN. We then use automatic differentiation to efficiently calculate the Born-effective charges, longitudinal optical-transverse optical (LO-TO) splitting frequencies, and Raman tensors of these materials. We compute the Raman spectra, and find agreement with ab initio results. Lastly, we explore ways to generalize the predictions of polarization while taking into account periodic boundary conditions and symmetries.

High-efficiency three-port beam splitter under normal incidence

A fused-silica three-port grating under TE-polarized normal incidence is designed and manufactured with improved diffraction efficiency (DE) and bandwidth. A physical explanation of the grating diffraction is provided using the simplified mode method (SMM), and parameters of the grating structure were optimized using rigorous coupled-wave analysis (RCWA). For a given set of optimized parameters, a transmitted three-port grating with an area of 170mm×170mm was fabricated by scanning beam interference lithography (SBIL), and diffraction properties were investigated. The average DEs for the +1, 0, and 1 orders of the 25 sampling points are 29%, 30%, and 31% at a 632.8 nm incident wavelength. Additionally, the measured DEs of the +1, 0, and 1 orders all exceed 25% at the wavelength range from 613 to 653 nm.

Ultra-high extinction ratio polarization beam splitter using an antisymmetric grating-assisted multimode waveguide

We have proposed and demonstrated a polarization beam splitter (PBS) with an ultra-high extinction ratio (ER) utilizing an antisymmetric grating-assisted multimode waveguide (AGMW) and an asymmetric directional coupler (ADC) on a silicon-on-insulator (SOI) platform. The AGMW structure is designed to facilitate the conversion of the forward TE0 mode into the backward TE1 mode. Upon injection of the TE0 mode, it transforms into the backward TE1 mode, subsequently undergoing conversion back to a TE0 mode through the ADC and ultimately dropping out from the designated port. In contrast, the injected TM0 mode traverses the device with minimal impact. The simulation results indicate that, for the TE0 mode, a bandwidth of 70 nm with an insertion loss (IL) below 0.65 dB and an ER over 40 dB is achieved. Similarly, for the TM0 mode, the bandwidth with the IL below 0.13 dB and an ER over 40 dB is 90 nm. Experimental validation confirms that, within the measured wavelength range from 1500 to 1580 nm, the bandwidth with an ER exceeding 30 dB is 61 nm for the TE0 mode and 78 nm for the TM0 mode.

The control of the symmetry of quantum beam splitting in the hybrid nanosystem

The control of the symmetry of quantum beam splitting in the hybrid nanosystem

Laser wireless power transmission based on spherical reflector intra-cavity beam splitting

The powersphere is an energy reception device in a laser wireless power transmission system, converting light into electricity, and also has a certain effect of light uniformity. However, in the actual application process, limitations due to laser power, photovoltaic cell absorption rate, and direct irradiation area restrict light uniformity, thus reducing photoelectric conversion efficiency. A spherical reflector at the center of the powersphere to enhance internal reflection and improve light uniformity was proposed. Utilizing LightTools software, we established a simulation model to simulate the energy distribution of light on the powersphere after reflection by the sphere, analyzing light uniformity and constructing an experimental platform for validation. Results show the reflector significantly boosts uniformity, doubling the powersphere’s output power and reducing voltage and current disparities, thereby enhancing system conversion efficiency.

Compact and High-Efficiency Liquid-Crystal-on-Silicon for Augmented Reality Displays

Compact and high efficiency microdisplays are essential for lightweight augmented reality (AR) glasses to ensure longtime wearing comfort. Liquid-crystal-on-silicon (LCoS) is a promising candidate because of its high-resolution density, high brightness, and low cost. However, its bulky illumination system with a polarizing beam splitter (PBS) cube remains an urgent issue to be overcome. To reduce the volume of the LCoS illumination system, here, we propose a compact structure with four thin PBS cuboids. Through simulations, the optical efficiency of 36.7% for an unpolarized input light can be achieved while maintaining reasonably good spatial uniformity. Such a novel design is expected to have a significant impact on future compact and lightweight AR glasses.

1283-1460 nm continuously tunable, watt-level bismuth-doped phosphosilicate fiber laser and its frequency doubling to a visible laser.

We report, to the best of our knowledge, the first demonstration of an O + E-band tunable watt-level bismuth-doped phosphosilicate fiber laser and its frequency doubling to tunable red laser. Benefiting from the two types of bismuth active centers associated with silicon and phosphorus introduced in one fiber, an ultrabroad gain is available in the designed low-water-peak bismuth-doped phosphosilicate fiber (Bi-PSF) pumped by a self-made 1239 nm Raman fiber laser. The high-efficiency tunable lasing is achieved with a maximum output power of 1.705 W around 1320 nm and a slope efficiency of 33.0%. The wavelength can be continuously tuned from 1283 to 1460 nm over a 177 nm spectral range, almost covering the whole O+E-bands. We further employ a polarization beam splitter in the cavity to output an O + E-band linear-polarization laser for second-harmonic generation by a designed multi-period MgO2:PPLN crystal, and a 650-690-nm tunable visible laser is correspondingly obtained. Such an O+E-wideband tunable high-power laser and the SHG red laser may have great potential in the all-band optical communications, biophotonics, and spectroscopy.

Solar disk integration polarimeter: An automated disk‐integration full‐Stokes‐vector solar feed for the Potsdam Echelle Polarimetric and Spectroscopic Instrument spectrograph

AbstractWe introduce a new solar feed for the PEPSI nighttime spectrograph of the LBT. It enables spectroscopy of the Sun‐as‐a‐star in circular polarization (CP) and linear polarization (LP) with a spectral resolution of 250,000 (≈0.025Å or ) for the wavelength range 383–907 nm. The polarimeter is a dual‐beam design with a modified Wollaston prism as beam splitter and linear polarizer combined with a retractable super‐achromatic retarder. The Wollaston beam diameter is 14 mm and large enough that it does not require a classical telescopic feed anymore. Both polarimetric beams are re‐imaged into respective integration spheres from which two fibers feed the scrambled light to the spectrograph. The system is fully automated in the sense that it finds the Sun in the morning, closes the guider loop, observes a predefined number of individual spectra, and moves to a home position at the end of the day. Among the scientific aims is Zeeman–Doppler imaging of the Sun as a star over the next activity cycle. Our first‐light application detects a clear Stokes‐V/I profile with a full amplitude of on, for example, October 13, 2023, suggesting a solar disk‐averaged line‐of‐sight net magnetic field of +0.37±0.02 G. Comparison of this value with a contemporary full‐disk line‐of‐sight magnetogram suggests an unsigned mean field of about ≈13 G.

New stacks design of polarized and non-polarized beam splitters

New stacks design of polarized and non-polarized beam splitters

Portable 5-DOF measurement system using a parallel beam generation method for linear axis detection

Geometric error detection is crucial for evaluating the accuracy of the linear axis. However, the practicality of traditional dual-beam detection systems is limited by the parallelism of beams. This study proposes a portable 5-DOF measurement system using a novel parallel beam generation method. Two orthogonal corner cube retroreflectors (CCRs) and a beam splitter (BS) are utilized to achieve two measuring beams with excellent parallelism, which is determined solely by the CCR. The theoretical parallelism of beams is analyzed and experimentally verified. Two position sensitive detectors (PSDs) and one autocollimator are used to measure two straightness errors and three angular errors, and the detection deviations are modelled and compensated. The experiment proves that dual beam that are generated on the basis of the above structure could achieve a parallelism of 5.9′′ without careful adjustment. The designed 5-DOF measurement system has a straightness measurement range of ± 400 µm and an angle measurement range of ± 300′′. The repeatability of the system is 2.20 µm for straightness errors, 1.58′′ for yaw error, 1.82′′ for pitch error and 5.04′′ for roll error detection. The designed 5-DOF measurement system has the advantages of a simple structure and stable accuracy and is very practical in measuring the geometric errors of machine tools.

Loss-Assisted Anomalous Hong-Ou-Mandel Interference Based on Nonunitary Multilayer Graphene.

Hong-Ou-Mandel interference is an intrinsic quantum phenomenon that goes beyond the possibilities of classical physics, and enables numerous applications in quantum information science. While the photon-photon interaction is fundamentally limited to the bosonic nature of photons and the restricted phase responses from commonly used unitary optical elements, we present that a nonunitary material provides an alternative degree of freedom to control the two-photon quantum interference, even revealing anomalous quantum interference paths that do not exist in a unitary configuration. An elaborate lossy multilayer graphene that can work as a nonunitary beam splitter is used to explore its tunability over the effective photon-photon interaction in spatial modes, and to verify the particle exchange statistics by its experimental implementation in quantum state filter. This scheme is further extended to observe four-dimensional quantum interference patterns on the lossless and lossy beam splitters, and thus show its applicability even in higher-dimensional Hilbert space.

Delayed-focus micro-angle measurement optical system based on structural segregation

In this paper, we propose a delayed-focusing type micro-angle measurement optical system based on the Cassegrain structure (cassette structure), analyze the basic cassette structure and the Galilean laser beam expanding system, and determine the primary and secondary mirror structure as a reflective focusless system as a determining module. This focusless system emits and receives parallel light, and the light source and detector separated by the beam splitter are designed as replaceable modules. Additionally, the imaging quality of the system can be optimized, or the effect of meeting different imaging requirements can be achieved, by changing the number and type of corrective mirrors and the parameters of the specific glass elements in the replaceable modules. After the final optimization, the radius of the imaging spot of the combined mirror group can be limited to 6.1 µm; the modulation transfer function is better than 0.6 at 100 lp/mm; the difference between the meridian and the arc-vector curves is less than 0.1; and the theoretical angular accuracy reaches 0.2″. The delayed-focusing system structure is analyzed under different temperature fields to provide guidance for the design of the subsequent structure temperature control. Comparison and analysis with commonly used angle measurement optical systems are also made. It is concluded that the structure meets the requirements for use in the on-orbit environment, completes the reuse of the established structural modules, and further saves the manufacturing cost, which provides a feasible solution to the problem of monitoring the small angular changes in the field of space.

Atom interferometer using spatially localized beam splitters

Atom interferometer using spatially localized beam splitters

Design of beam splitters with different beam splitting ratios by using double defect layered 1D ternary photonic band gap structures

Design of beam splitters with different beam splitting ratios by using double defect layered 1D ternary photonic band gap structures

Design and Fabrication of Metasurfaces-Based Polarizing Beam Splitter with Tailored Deflection Angles for 940-nm Wavelength

Design and Fabrication of Metasurfaces-Based Polarizing Beam Splitter with Tailored Deflection Angles for 940-nm Wavelength

Reflective anomalous beam splitter (RABS) metasurface for millimeter-wave (mm-Wave) frequency

Metasurfaces have gained a considerable amount of interest in the past decade for their capabilities to manipulate electromagnetic (EM) waves in different manners. They have offered multiple functionalities in terms of wave control depending on the given application. In terms of wave control, particularly EM beam splitting, it can be challenging compared to the given literature review, to achieve a wide number of beam-splitting reflections and coverage for multiple incident angles simultaneously. In this paper, we focus on the design of a metasurface based on the methodology of high periodicity supercell design (5.76λ) and impedance modulation to achieve a various number of beam-splitting angles, while maintaining the same coverage at multiple incident angles for millimeter-wave (mm-Wave) frequencies. Following the generalized phase law of reflection alongside proper optimization of the surface impedance, the proposed reflective anomalous beam splitter (RABS) metasurface is designed to be polarization independent, and high reflection efficiency is achieved with a wave beam split into 11 different directions while operating for multiple incident angles simultaneously, making it a promising candidate to overcome challenges for various mm-Wave communication applications, especially in expanding 5G coverage in non-line of sight regions at a 28 GHz frequency band. The performance of the RABS metasurface is evaluated using both full-wave simulations and experimental measurements, which demonstrate its effectiveness in achieving 11 efficient reflective anomalous beams with a reflection efficiency of up to 96.65% and 97.36% in TE and TM modes at 28 GHz.

Three-dimensional polarization-dependent full-wavelength beam splitter written by femtosecond laser in LiNbO3 crystal

We report on the fabrication of Y-branched waveguide beam splitters with cladding structures in LiNbO3 crystal by direct femtosecond laser writing. The femtosecond laser writes tracks near the surface of the crystal, constructing a square structure based on the Type II geometry. The waveguide beam splitters support the propagation of full-wavelength light from the visible to mid-infrared, which was experimentally and numerically investigated. In addition, it has been found that the guidance is only along the vertical (i.e., TM) polarization, which is due to the different refractive indices in the longitudinal and transverse directions. The femtosecond-laser writing here also represents an alternative for fabricating complex integrated light guiding in crystals.

Data-driven solutions and parameter discovery of the extended higher-order nonlinear Schrödinger equation in optical fibers

In this paper, we investigate an extended higher-order nonlinear Schrödinger equation that includes third-order and fourth-order dispersion terms. By considering higher-order effects, the equation can more accurately simulate and predict the propagation behavior of ultrashort pulses in optical fibers, e.g., pulse splitting, compression and stability. In the optical fiber sensors, the sensitivity and resolution of the sensor can be improved by utilizing nonlinear effects. The analysis of the extended higher-order nonlinear Schrödinger equation helps to understand how nonlinear effects affect the sensing signal, thereby designing more accurate sensors. Specific coefficients of each term in the equation are studied for different scenarios, such as optical fiber design and signal propagation in optical communications. Under certain conditions, the extended higher-order nonlinear Schrödinger equation can be degenerated into the Hirota equation or the Lakshmanan–Porsezian–Daniel equation. With the development of numerical algorithms, the utilization of deep neural networks for solving equations has become increasingly attractive. With given initial conditions and boundary conditions, the physical information is embedded into the neural network in the form of loss functions. We efficiently derive numerical solutions to the extended equation for one-soliton, two-soliton and rogue-wave cases by training weights and biases in physics-informed neural networks. Compared with traditional numerical methods, physics-informed neural networks yield lower prediction errors with less data volume, thus will reduce the cost and time consumptions for data sampling in practical engineering. Furthermore, we solve the inverse problem associated with the extended equation. This approach is critical for extracting fundamental parameters of optical systems from observable data, thereby deepening our understanding of complex optical behavior and helping to improve the performance of optical fiber communication technologies.