Optical Beam Splitter Research Articles

Design of Photonic Molecule-Based Multiway Beam Splitter/Coupler with Variable Division Ratio

An optical beam splitter is used for dividing an input optical beam into several separate beams with a specific power ratio. Usually, conventional optical beam splitters have bulky dimensions (many optical wavelengths) and a fixed dividing ratio, which significantly limit the design of new miniaturized optical devices and integrated optical circuits. We propose and investigate in detail a novel physical concept of a highly miniaturized (up to two working wavelengths) planar optical resonant splitter/coupler with a switching element comprising a photonic molecule (PM) pair dispersing input optical fluxes in multiple directions with a tailored power ratio. The structural design of the proposed splitter is based on a silicon-on-insulator (SOI) platform and composed of high-quality resonators in the form of electromagnetically coupled submicron-sized microcylinders. The control on the power division ratio and the selection of optical beam directions is realized by tuning the photonic splitter structure to the corresponding resonance of the PM supermode. Compared to known analogs, the proposed design is easy and cheap in fabrication. Because of its tiny dimensions, it is suitable for integration into a “System-on-a-chip” platform and can dynamically change the beam power division ratio by input wave-phase manipulation.

Testing quantum reasoning: Developing, validating, and application of a questionnaire

Clear and rigorous quantum reasoning is needed to explain quantum physical phenomena. As pillars of true quantum physical explanations, we suggest specific quantum reasoning derived from quantum physical key ideas. An experiment is suggested to support such a quantum reasoning, in which a quantized radiation field interacts with an optical beam splitter, leading to experimental results conflicting with classical physical predictions. The results, however, can be explained consistently with a quantum reasoning based on the key ideas of probability, superposition, and interference (PSI). In this quantum optical key experiment the optical beam splitter prepares a superposition of single photon states and a Michelson interferometer is used to detect the superposition via controlled propagation phases. Although different single photon experimental setups (aimed at helping students to gain access to foundational issues in quantum physics) have been discussed in the past, the wave-particle dualism bound to classical physics maintains its predominance as an explanation pattern for the interpretation of these experiments. The study presented here investigates the effect of the quantum optical key experiment on the ability of students to use quantum reasoning based on the key ideas of PSI to overcome the naive wave-particle dualism. The current state of relevant studies that test student access to quantum physics can roughly be divided into two distinct areas: one tests how mathematical abilities help them to understand quantum physics and one tests how nonmathematical representations of a set of specific quantum theoretical traits (“Wesenszüge”) lead to a deeper understanding of quantum physics. There is a lack of questionnaires that focus on the idea of developing quantum reasoning based on superposition, probability, and interference of quantum states combined with a real experiment using true quantum light. In the first part of the article, we describe the physical modeling and present the development of the questionnaire. The set of items has been constructed from newly developed items and combined with well-tested ones. The validation of the set addresses qualitative and quantitative methods. In the second part, we give a pre- and poststudy examination of the impact of the quantum optical key experiment on students’ quantum reasoning. A significant increase in the number of students using quantum arguments is based on PSI reasoning for the explanation of an interference, such as the behavior of single photon states. Though the increase is significant, we found only minor changes in a particular issue to the students’ reasoning when approaching quantum physics as illustrated by a sample of answers given in the second part of the article. The concept of quantum states and the principle of superposition still appear particularly difficult. Published by the American Physical Society 2024

Coherent control of photonic band gaps through the relative phase using modified superradiance lattice.

We report photonic band gaps based on a modified superradiance lattice having reflectivity close to 100% for both the low and high-frequency ranges. We observe that tuning the relative phase between the coupling fields provides additional control over photonic band gaps. We notice that the relative phase can control three input channels of the probe field simultaneously and efficiently. This feature of relative phase over photonic band gaps provides potential in the field of quantum optics. Further, this scheme is experimentally more viable. Rubidium atoms 87Rb can obtain low-frequency (infrared) photonic band gaps. On the other hand, rubidium atoms 85Rb and beryllium ions Be2+ can form high-frequency ultraviolet and soft X-ray photonic band gaps, achieving reflectivities of 80% and 96%, respectively. This scheme holds promise for constructing highly efficient optical switches and beam splitters.

Exploring the fundamental limits of integrated beam splitters with arbitrary phase via topology optimization.

Optical beam splitters are essential for classical and quantum photonic on-chip systems. In integrated optical technology, a beam splitter can be implemented as a beam coupler with two input and two output ports. The output phases are constrained by the conservation of energy. In lossless beam splitters, the phase shift between the output fields is π and zero for excitation from the first and second input ports, respectively. Therefore, for excitation from both inputs, the phase between the output fields, defined as beam splitter phase (BSP), is π. The BSP leads to several phenomena, such as the quantum interference between two photons, known as the Hong-Ou-Mandel effect. By introducing losses, BSP values different than π become theoretically possible, but the design of 2 × 2 beam couplers with an arbitrary phase is elusive in integrated optics. Inspired by the growing interest on fundamental limits in electromagnetics and inverse design, here we explore the theoretical limits of symmetrical integrated beam splitters with an arbitrary BSP via adjoint-based topology optimization. Optimized 2D designs accounting for fabrication constraints are obtained for several combinations of loss and phase within the theoretical design space. Interestingly, the algorithm does not converge for objectives outside of the theoretical limits. Designs of beam splitters with arbitrary phase may find use in integrated optics for quantum information processing.

Single line of sight frame camera based on the RadOptic effect of ultrafast semiconductor detector

A new optical beam splitting method is proposed, based on which the optical frame camera capable of capturing multiple frames in a single exposure is designed and experimentally verified. The operation of the frame camera is based on an ultra-fast response semiconductor detector. It is equipped with an optical beam splitter and an optical imaging module. The ultrafast semiconductor detector receives an optical pulse that produces a transient refractive index change, and ultrafast physical processes are recorded by diffracting the probe laser through the transient phase grating. The interaction of an X-ray pulse with a semiconductor detector to produce a phase grating is simulated, based on the Monte Carlo method. The optical beam splitting mode separates a laser into two optical pulses with a certain time difference in the direction of polarization perpendicular to each other. The imaging module filters the diffracted probe laser in the spectral plane and then images multiple frames. The frame camera was used to record the temporal and spatial distribution characteristics of femtosecond laser pulses with a temporal resolution of 4.1 ps. This frame camera has great potential and value for applying to experimental studies of inertial confinement fusion.

Optical coupling control of isolated mechanical resonators

We present a Hamiltonian model describing two pairs of mechanical and optical modes under standard optomechanical interaction. The vibrational modes are mechanically isolated from each other and the optical modes couple evanescently. We recover the ranges for variables of interest, such as mechanical and optical resonant frequencies and naked coupling strengths, using a finite element model for a standard experimental realization. We show that the quantum model, under this parameter range and external optical driving, may be approximated into parametric interaction models for all involved modes. As an example, we study the effect of detuning in the optical resonant frequencies modes and optical driving resolved to mechanical sidebands and show an optical beam splitter with interaction strength dressed by the mechanical excitation number, a mechanical bidirectional coupler, and a two-mode mechanical squeezer where the optical state mediates the interaction strength between the mechanical modes.

Inverse design of dual-band photonic topological insulator beam splitters for efficient light transmission

The study of optical topological insulators (PTIs) has revealed intriguing optical properties that diversify the ways in which light can be manipulated, offering significant potential for a wide range of applications. This paper presents a machine learning (ML)-based approach for the reverse design of optical PTIs. Using finite element methods, the paper addresses the challenge of computing the band structure of a dual-band model, enabling the construction of a dataset suitable for ML training. With the goal of maximizing dual-band bandgaps, the study employs the random forest algorithm to predict target parameters and further designs topological edge states. Leveraging these boundary state patterns, two different optical PTI beam splitters are devised, and their transmission coefficients and losses are computed. The results demonstrate that optical devices designed using topological boundary states exhibit enhanced stability and robustness. This approach offers a reliable solution for applications in fields such as optical communication and optical sensing.

Low Loss 1 × 16/40 Flat Type Beam Splitters on Thin Film Lithium Niobate Using Photolithography Assisted Chemo‐Mechanical Etching

AbstractIntegrated photonic devices based on thin film lithium niobate (TFLN) have attracted great attention due to their excellent performance. In this work, a flat type TFLN 1×N beam splitter is designed by adjusting the widths of tapered waveguides between free propagation region and arrayed waveguides. Two chips with 16 and 40 output ports, respectively, are manufactured with the femtosecond laser photolithography assisted chemo‐mechanical etching technology (PLACE). The excess losses are measured ≈1.43 and 1.94 dB, respectively. In theory, the flat‐type beam splitter for a single‐mode structure can maintain the flat intensity distribution within a 300 nm wavelength range. Experimentally, different types of output intensity distribution such as tilted or M‐shaped distributions can be obtained with the multimode structure by varying the position of the lensed fiber when the input light is TM‐polarized. This work explores an efficient way for the development of multichannel optical beam splitters.

Quantum Noise Source Based on Shot Noise of a Balanced Photodetector with a Tunable Integrated Optical Beam Splitter

Quantum Noise Source Based on Shot Noise of a Balanced Photodetector with a Tunable Integrated Optical Beam Splitter

Modeling and Improving the Transmission Efficiency of an Optical Beam Splitter Made of Silicon Nitride Si3N4

Modeling and Improving the Transmission Efficiency of an Optical Beam Splitter Made of Silicon Nitride Si3N4

A study on the optimal incident angle of sub-wavelength grating polarization beam splitter

One problem faced by the sub-wavelength grating polarization beam splitter is the lack of a generally-used formula able to conduct accurate calculation of the incident angle. With that background, by the design method of optical film polarization beam splitter, this work realizes an precise calculation under the condition of arbitrary grating constants by transforming the splitter into an optical-film-structure model. According to tests, the incident angles of grating calculated by the method proposed here are consistent with those obtained from the FDTD simulation, illustrating the reliability of applying the polarization beam splitting design method of optical thin films to polarization beam splitting gratings.

Femtosecond Laser Fabrication of SiC Microlens Arrays as Integrated Light Homogenizer and Splitter

Silicon carbide (SiC) plays a vital role in special optics because of its stable physicochemical and excellent optical properties; however, making the fabrication of SiC considerably more difficult. In this study, femtosecond laser-assisted inductively coupled plasma etching (ICP) technology is proposed to achieve the efficient fabrication of large-area microlens arrays on the surface of silicon carbide. As an illustration, the microlens array was used for high-quality beam homogenization (uniformity is up to 90%) of the transmitted and reflected Gaussian light beams with a wavelength of 532 nm. The beam-splitting ratio can be dynamically adjusted (from 1.2 to 3.2) by controlling the angle of the incident light, indicating that the SiC microlens arrays can act as an integrated optical homogenizer and beam splitter. This method demonstrates the broad application prospects of SiC in miniaturized and integrated special optics and provides new ideas for further applications of SiC in integrated optical systems.

Optically controllable high-frequency photonic band gaps using modified superradiance lattice

We report that modified superradiance lattice (2023, Phys. Scr. 98 015 105) can be used to obtain high-frequency photonic band gaps which are controllable using low-frequency light. Here, we also notice that the maximum reflectivity of these photonic band gaps can be achieved via low-frequency light control. This maximum reflectivity remains constant for a certain range of probe detuning depending upon the strength of the control field. We also report that this can lead to experimental realization of the soft x-ray regime (high-frequency) via 61st-order low-frequency light using Be2+ ions, the corresponding reflectivity in this case is 96%. Therefore, one can construct controllable x-ray photonic band gaps which can further be used to devise optical switches, beam splitters, and frequency combs. Moreover, this scheme holds the promise of working efficiently in all types of other configurations where reflection of high-frequency light is needed using nth order low-frequency light.

Mode Conversion Between Beams Carrying Orbital Angular Momentum With Opposite Topological Charges Using Two-Dimensional Multimode Interference Waveguides

Recently, the implementation of rectangular waveguides for generation and manipulation of orbital angular momentum (OAM) modes, has been developed to exploit the outstanding features of these modes in more complex integrated devices. Multimode interference (MMI) structures have been widely used in both one and two dimensions as the basic elements in many integrated optical devices like optical beam splitters, mode converters, couplers, wavelength-division (de)multiplexers, and switches. According to the various applications of OAM modes in quantum and classical communications, the study of their propagation properties in MMI waveguides is useful in order to facilitate the way into higher security and capacity systems. This paper presents the results of numerical investigation of a proposed integrated optical OAM mode converter which is performed based on the mode decomposition properties of propagating OAM modes in 2D MMI waveguides, as well as the fact that any order of OAM mode can be represented as superposition of an odd mode and a quarter-wave shifted even mode. The proposed device, which consists of two MMI waveguides connected by phase shifters and linear waveguides, provides mode conversion between beams carrying OAM with odd opposite topological charges. The design procedure is performed for OAM modes with topological charge values of l = ±1 and l = ±3 using beam propagation method. The proposed device is passive with reciprocal behavior and has the output mode purity of 94% and 82% for beams carrying l = ±1 and l = ±3, respectively.

Gain-gain and gain-lossless PT-symmetry broken from PT-phase diagram

Parity-time (PT) symmetry and broken in micro-/nanophotonic structures have been investigated extensively as they bring new opportunities to control the flow of light based on non-Hermitian optics. Previous studies have focused on the situations of PT-symmetry broken in loss-loss or gain-loss coupling systems. Here, we theoretically predict the gain-gain and gain-lossless PT-broken from the phase diagram, where the boundaries between PT-symmetry and PT-broken can be clearly defined in the full-parameter space including gain, lossless and loss. For specific micro-/nanophotonic structures, such as coupled waveguides, we give the transmission matrices of each phase space, which can be used for beam splitting. Taking coupled waveguides as example, we obtain periodic energy exchange in the PT-symmetry phase and exponential gain or loss in the PT-broken phase, which are consistent with the phase diagram. The scenario giving a full view of PT-symmetry or broken, will not only deepen the understanding of fundamental physics, but also will promote the breakthrough of photonic applications like optical routers and beam splitters.

Parameter error analysis of dual-channel Mach–Zehnder interferometer for molecular Doppler wind lidar

Based on the atmospheric molecular Doppler wind lidar system using dual-channel Mach–Zehnder interferometer (DMZI) double-edge detection, two important DMZI parameters, such as optical path difference and beam splitter transmittance, are analyzed. Furthermore, the changes in DMZI transmission response, wind speed sensitivity, and wind speed measurement errors of the lidar system caused by the errors of these two parameters are simulated. The ratio of the difference between the system measurement error caused by the non-optimal parameter and the optimal parameter to the system measurement error at the optimal parameter is defined as an error proportion factor, which can be used to quantitatively describe the variation of wind speed measurement error caused by the parameter errors. Numerical simulation shows that under the assumption that the horizontal wind speed is 20 m/s and the vertical detection height is 15 km, if this error proportion factor needs to be controlled to less than 1%, the difference δ_Δl0 between the actual and the optimal optical path difference should be controlled in the range of 0 ≤ δ_Δl0 < 3.16 mm. Similarly, if other parameters are optimal, the beam splitter transmittance of DMZI should be controlled in the range of 0.5 ± 0.0407, and the error proportion factor can be less than 1%. The results of this study not only provide theoretical guidance for the parameter selection of DMZI but also provide research ideas and methods for the error analysis of DMZI molecular Doppler lidar based on double-edge detection.

Design and Research of Chromatic Confocal System for Parallel Non-Coaxial Illumination Based on Optical Fiber Bundle.

Conventional chromatic confocal systems are mostly single-point coaxial illumination systems with a low signal-to-noise ratio, light energy utility and measurement efficiency. To overcome the above shortcomings, we propose a parallel non-coaxial-illumination chromatic-confocal-measurement system based on an optical fiber bundle. Based on the existing single-point non-coaxial-illumination system, the optical fiber bundle is used as the optical beam splitter to achieve parallel measurements. Thus, the system can yield measurements through line scanning, which greatly improves measurement efficiency. To verify the measurement performance of the system, based on the calibration experiment, the system realizes the measurement of the height of the step, the thickness of the transparent specimen and the reconstruction of the three-dimensional topography of the surface of the step and coin. The experimental results show that the measuring range of the system is 200 μm. The measurement accurcy can reach micron level, and the system can realize a good three-dimensional topography reconstruction effect.

Key Experiment and Quantum Reasoning

For around five decades, physicists have been experimenting with single quanta such as single photons. Insofar as the practised ensemble reasoning has become obsolete for the interpretation of these experiments, the non-classical intrinsic probabilistic nature of quantum theory has gained increased importance. One of the most important exclusive features of quantum physics is the undeniable existence of the superposition of states, even for single quantum objects. One known example of this effect is entanglement. In this paper, two classically contradictory phenomena are combined to one single experiment. This experiment incontestably shows that a single photon incident on an optical beam splitter can either be reflected or transmitted. The almost complete absence of coincident clicks of two photodetectors demonstrates that these two output states are incompatible. However, when combining these states using two mirrors, we can observe interference patterns in the counting rate of the single photon detector. The only explanation for this is that the two incompatible output states are prepared and kept simultaneously—a typical consequence of a quantum superposition of states. (Semi-)classical physical concepts fail here, and a full quantum concept is predestined to explain the complementary experimental outcomes for the quantum optical “non-waves” called single photons. In this paper, we intend to demonstrate that a true quantum physical key experiment (“true” in the sense that it cannot be explained by any classical physical concept), when combined with full quantum reasoning (probability, superposition and interference), influences students’ readiness to use quantum elements for interpretation.

Versatile optical beam routers based on inversely designed supercell metagratings

Metagratings manipulating the wavefront with a subwavelength volume have been widely explored in recent years for their potential applications in optical beam routers, such as laser beam splitters and combiners. Current metagratings are hampered from practical beam rerouting due to inhibitive computational load of engineering design and expensive nanofabrication cost. In this work, we apply the emerging concept of supercell metagratings, which arranges random binary gratings of a unit cell in a one-dimensional periodicity, to simplify such design and fabrication processes. A high-performance inverse design framework for the supercell gratings is proposed. In such a framework, we use coupled wave algorithm as a fast-converging electromagnetic solver for the forward calculation and particle swarm optimization algorithm for the backward optimization. By manipulating the building blocks of a unit cell, specific diffraction orders of supercell gratings can be intentionally strengthened or eliminated. We finally realize high-efficiency, broadband and multi-functionality optical beam splitters and combiners both in visible and near-infrared regimes. We envision that the proposed method offers an avenue towards the mass production realization of flat optics.

Phase-change material assisted on-chip wavefront shaping for optical switching and beam splitting

On-chip wavefront shaping is indispensable for implementing optical routing and signal processing. By referring to the concept of metasurface used in free space, we can realize the on-chip wavefront shaping to manipulate the guided wave. In this paper, we combine the phase-change material Sb2S3 nanorods with 1D on-chip meta-lens to manipulate the optical routing direction. We use the 1550 nm TE0 mode to realize the functions of 1 × 2 and 1 × 3 optical switching, and then the 1 × 2 and 1 × 3 beam splitting. By combining the function of beam deflection and beam splitting, we can realize tunable beam steering and complex optical flow control.