Asymmetric Beam Splitter Research Articles

Directional Control of Single-Photon Routing in Asymmetric Quantum Beam Splitter Based on the Additional Quantum Dot

Directional Control of Single-Photon Routing in Asymmetric Quantum Beam Splitter Based on the Additional Quantum Dot

Coherent feedback ground state cooling of the mechanical resonator in quadratic optomechanical system assisted by an atomic ensemble.

We propose a scheme for cooling a mechanical resonator to its ground state in a quadratic optomechanical system, assisted by an atomic ensemble in the unresolved sideband regime. The system features an auxiliary cavity directly coupled to an optical cavity, with a portion of the optical cavity's output field being fed back through an asymmetric beam splitter. Utilizing quantum Langevin and master equations, we derive the optical fluctuation spectrum, the cooling rate, and the mean phonon number of the mechanical resonator. Our results demonstrate that the feedback mechanism substantially enhances the cooling rate. Furthermore, under optimal cooling conditions, the mechanical resonator achieves ground state cooling even with weaker optomechanical coupling strengths and higher auxiliary cavity dissipation rates, thereby mitigating the experimental constraints associated with these parameters. Additionally, we provide the feasible ranges for optomechanical coupling strength and atomic decay rates. Our findings suggest promising avenues for quantum manipulation in nonlinear systems and its applications in macroscopic optical devices.

Multilevel asymmetric coupler MAC polarization beam splitter for Si photonics technology

In this work, we present a new design of an integrated optical polarization beam splitter using the Multilevel Asymmetric Coupler MAC structure. The proposed structure is using CMOS compatible Si/SiO2 technology. The structure is tested using the Finite Difference Time Domain FDTD technique and showed a very good performance. The compromise between the structure footprint on Si and its performance is also investigated. The structure can offer an Extinction Ratio ER greater than 40 dB with a length of 5 µm. It can also be designed with a smaller length of only 2 µm but in this case its ER will be only 20 dB. It has a bandwidth of about 60 nm in which the insertion loss is less than 0.003 dB for the TE wave and less than 0.2 dB for the TM wave.

An ultra-compact broadband polarizing beam splitter utilizing hybrid plasmonic waveguide

Polarizing beam splitter has rather significant applications in polarization diversity circuits and polarization multiplexing systems. In this paper, we present an asymmetric polarizing beam splitter utilizing hybrid plasmonic waveguide. The special hybrid structure with a hybrid waveguide and a dielectric waveguide can limit the energy of TE and TM modes to a different layer. Therefore, we can achieve beam splitting by adjusting the corresponding parameters of the two waveguides. First, we studied the influences of different structure parameters on the real part of the effective mode refractive index of the two waveguides, and obtained a set of parameters that satisfy the condition of strong coupling of TM mode and weak coupling of TE mode. Then, the performance of our proposed polarizing beam splitter is evaluated numerically. The length of the coupling section is only 4.1 µm, and the propagation loss of TM and TE modes is 0.0025 dB/µm and 0.0031 dB/µm respectively. Additionally, the extinction ratios of TM and TE modes are 10.62 dB and 12.55 dB, respectively. Particularly, the proposed device has excellent wavelength insensitivity. Over the entire C-band, the fluctuation of the whole normalized output power is less than 0.03. In short, our proposed asymmetric polarizing beam splitter features ultra-compactness, low propagation loss, and broad bandwidth, which would provide promising applications in polarization multiplexing system and polarization diversity circuits relevant to optical interconnection.

Reverse design of ultracompact micro-nano wavelength beam splitter based on quadratic programming algorithm

Micro-nano wavelength beam splitter is an important beam-splitting device in photonic chips. In this study, the sequence quadratic program is used to design ultra-compact wavelength beam splitters with footprints of 1.5 μm × 1.5 μm. The Y-type dual channel beam splitter can realize TE/TM mode splitting at the same time, the transmissions of TE mode light at 1140 nm and 1200 nm are 80% and 81%, and the extinction ratios are 18.1 dB and 16.3 dB, respectively. The transmissions of TM mode light are 70% and 67%, and the extinction ratios are 18.3 dB and 15.9 dB, respectively. The T-type beam splitter realizes 180° separation angle splitting, and the transmissions of optical power at the wavelengths of 1100 nm and 1170 nm both reach 88%, and the extinction ratios are 16.6 dB and 15.0 dB, respectively. It is the smallest size chip-integrated wavelength beam splitter. The cross-type three-channel beam splitter realizes splitting with a wavelength interval of 50 nm. The transmissions at the wavelengths of 1100, 1150 and 1200 nm are 73%, 66% and 70%, and the extinction ratios are 17.2, 13.8 and 13.8 dB, respectively. The asymmetric three-channel beam splitter realizes splitting with the wavelength interval of 20 nm. The transmissions at the wavelengths of 1200, 1220 and 1240 nm are 61%, 56% and 57%, and the extinction ratios are 10.8, 7.9 and 8.9 dB, respectively. This method has the advantages of a short design period, high design efficiency, simple structure, easy processing, and suitability for designing chip-integrated photonic components. It is expected that it can provide a new idea for designing chip-integrated photonic devices.

Fringe visibility and correlation in Mach–Zehnder interferometer with an asymmetric beam splitter

We study the wave–particle duality in a general Mach–Zehnder interferometer with an asymmetric beam splitter from the viewpoint of quantum information theory. The correlations (including the classical correlation and the quantum correlation) between the particle and the which-path detector are derived when they are in pure state or mixed state at the output of Mach–Zehnder interferometer. It is found that the fringe visibility and the correlations are effected by the asymmetric beam splitter and the input state of the particle. The complementary relations between the fringe visibility and the correlations are also presented.

Asymmetrical photonic spin Hall effect based on dielectric metasurfaces

The photonic spin Hall effect has attracted considerable research interest due to its potential applications in spin-controlled nanophotonic devices. However, realization of the asymmetrical photonic spin Hall effect with a single optical element is still a challenge due to the conjugation of the Pancharatnam–Berry phase, which reduces the flexibility in various applications. Here, we demonstrate an asymmetrical spin-dependent beam splitter based on a single-layer dielectric metasurface exhibiting strong and controllable optical response. The metasurface consists of an array of dielectric nanofins, where both varying rotation angles and feature sizes of the unit cells are utilized to create high-efficiency dielectric metasurfaces, which enables to break the conjugated characteristic of phase gradient. Thanks to the superiority of the phase modulation ability, when the fabricated metasurface is under normal incidence with a wavelength of 1550 nm, the left-handed circular polarization (LCP) light exhibits an anomalous refraction angle of 28.9°, while the right-handed circular polarization (RCP) light transmits directly. The method we proposed can be used for the flexible manipulation of spin photons and has potentials in high efficiency metasurfaces with versatile functionalities, especially with metasurfaces in a compact space.

Design and simulation of asymmetric Y-junction beam splitter with controllable splitting based on adjusted air-hole defect

Design and simulation of asymmetric Y-junction beam splitter with controllable splitting based on adjusted air-hole defect

Continuous-Variable Quantum Secret Sharing Based on Thermal Terahertz Sources in Inter-Satellite Wireless Links.

We propose a continuous-variable quantum secret sharing (CVQSS) scheme based on thermal terahertz (THz) sources in inter-satellite wireless links (THz-CVQSS). In this scheme, firstly, each player locally preforms Gaussian modulation to prepare a thermal THz state, and then couples it into a circulating spatiotemporal mode using a highly asymmetric beam splitter. At the end, the dealer measures the quadrature components of the received spatiotemporal mode through performing the heterodyne detection to share secure keys with all the players of a group. This design enables that the key can be recovered only by the whole group players’ knowledge in cooperation and neither a single player nor any subset of the players in the group can recover the key correctly. We analyze both the security and the performance of THz-CVQSS in inter-satellite links. Results show that a long-distance inter-satellite THz-CVQSS scheme with multiple players is feasible. This work will provide an effective way for building an inter-satellite quantum communication network.

Micro-ring resonator based all-optical Arithmetic and Logical Unit

Silicon photonics is achieving developments in optical computing and information processing. It necessitates the efficient design of Arithmetic Logic Unit (ALU) to perform optical micro-operations such as adder/subtractor, comparator. The earlier work reported for ALU design used Mach-Zehnder Interferometer (MZI), semiconductor optical amplifiers, terahertz optical asymmetric demultiplexer (TOAD) and beam splitter. These approaches make optical circuit larger in size and difficult to integrate with Very Large Scale Integrated Optics (VLSIO). Here, we propose an all-optical ALU exclusively using Micro-Ring Resonator (MRR) to perform addition and comparison. The use of MRR to design ALU makes the proposed design novel and easy to integrate with VLSIO. The operations performed are one-bit addition and one-bit comparison. Beam splitter is replaced by MRR which has resulted in low intensity losses. The performance of the proposed ALU is discussed with simulation results and calculated losses. The output is verified for different input combinations of the half adder and comparator with electric field intensity distribution using 1550 nm wavelength. More losses are observed in comparator circuit as compared to adder circuit. Low losses and less MRR makes ALU design optimized.

Engineering optomechanical entanglement via dual-mode cooling with a single reservoir

We study reservoir-engineered entanglement for a cascaded bosonic system consisting of three modes, where the adjacent pairs couple to each other via both the beam-splitter interaction and the coherent parametric interaction with the interaction strengths being tunable. We focus on an optomechanical realization of the model by combining a nondegenerate parametric amplifier and an auxiliary cavity. A great steady-state cavity-mechanical entanglement can be achieved by optimizing the ratio of the interaction strengths, where the optomechanical cavity enacts the cold reservoir, simultaneously laser cooling the pair of hybrid modes delocalized over the auxiliary cavity and the mechanical oscillator. In comparison with the case of cooling a single delocalized mode, the dual-mode cooling approach allows one to obtain a greater amount of entanglement with higher cooling efficiencies and to explore strong entanglement in much broader parameter regions, where the rotating-wave approximation fails for the single-mode cooling case. Moreover, we show that the steady-state cavity-mechanical entanglement is robust to the mechanical thermal noise of the high temperature. The improved reservoir engineering approach can potentially be generalized to other bosonic systems with asymmetric beam-splitter and parametric interactions.

Quantum-enhanced interferometry with asymmetric beam splitters

In this paper, we investigate the phase sensitivities in two-path optical interferometry with asymmetric beam splitters. Here, we present the optimal conditions for the transmission ratio and the phase of the beam splitter to gain the highest sensitivities for a general class of non-classical states with parity symmetry. Additionally, we address the controversial question of whether the scheme with a combination of coherent state and photon-added or photon-subtracted squeezed vacuum state is better or worse than the most celebrated one using a combination of coherent state and squeezed vacuum state.

Cooling of a Mechanical Oscillator and Normal Mode Splitting in Optomechanical Systems with Coherent Feedback

The ground state cooling of a mechanical oscillator and strong optomechanical coupling are necessary prerequisites for realizing quantum control of the macroscopic mechanical oscillator. Here, we show that the resolved-sideband cooling of a mechanical oscillator in an optomechanical system can be enhanced by a simple coherent feedback scheme, in which a portion of the output field from the cavity is fed back into the cavity using an asymmetric beam splitter. Moreover, we show that the normal mode splitting in the spectra of the movable mirror and the output field in a weakly coupled optomechanical system can be induced by the feedback scheme due to a reduced effective cavity decay rate. We find that the peak separation becomes larger and two peaks of the spectra become narrower and higher with increasing the reflection coefficient r of the beam splitter.

Complementarity via Minimum Error Measurement in a Two-Path Interferometer**Supported by the National Natural Science Foundation of China under Grant Nos 11434011 and 11575058.

We study the fringe visibility and the which-path information (WPI) of a general Mach–Zehnder interferometer with an asymmetric beam splitter (BS). A minimum error measurement in the detector is used to extract the WPI. Both the fringe visibility V and the WPI Ipath are affected by the initial state of the photon and the second asymmetric BS. The condition in which the WPI takes the maximum is obtained. The complementarity relationship is found, and the conditions for equality are also presented.

Fringe visibility and distinguishability in two-path interferometer with an asymmetric beam splitter**Project supported by the National Natural Science Foundation of China (Grant Nos. 11434011, 11575058, and 61833010), the “Science and Technology Innovation Platform and Talent Plan” Excellent Talent Award of Hunan Province, China (Grant No. 2017XK2021), the Science Funds from the Ministry of Science and Technology of China (Grant Nos.

We study the fringe visibility and the distinguishability of a general Mach–Zehnder interferometer with an asymmetric beam splitter. Both the fringe visibility V and the distinguishability D are affected by the input state of the particle characterized by the Bloch vector S = (Sx,Sy,Sz) and the second asymmetric beam splitter characterized by the paramter β. For the total system is initially in a pure state, it is found that the fringe visibility reaches the upper bound and the distinguishability reaches the lower bound when cos β = −Sx. The fringe visibility obtain the maximum only if Sx = 0 and β = π/2 when the input particle is initially in a mixed state. The complementary relationship V2 + D2 ≤ 1 is proved in a general Mach–Zehnder interferometer with an asymmetric beam splitter, and the conditions for the equality are also presented.

Photon statistics without coincidence counting using an unbalanced beam-splitter

We have developed a new method to determine the photon statistics of a light source without the need for coincidence counting. Our method relies on using an asymmetric beam-splitter with intentional asymmetrical losses in a non-photon-number resolving detection system. We observe that the counts from one arm of the beam-splitter, when plotted as a function of the counts from the other arm, follow universal single-parameter curves that hint to the statistics of the photon source. We make a series of measurements on single photons detected from an attenuated laser source and show that the data clearly conforms to the universal curve established exclusively for coherent sources. We also show that the data cannot be fitted to the universal curve for thermal and photon-number sources.

Preparation and non-classicality of non-Gaussian quantum states based on catalytic quantum scissors

Based on the quantum scissor device proposed by Pegg et al, this paper implements a non-Gaussian quantum state preparation scheme. When considering the quantum photocatalysis of single-photon input and single-photon detection, the equivalent operator of catalytic quantum scissors is given in order to understand the physical nature of quantum scissors. When the coherent state is taken as the input state, for an asymmetric beam splitter, the output state can be truncated to zero photon, single photon and two photon components; for a symmetric beam splitter, the output state is only truncated to zero photon and two photon components. The non-classicality of the prepared non-Gaussian quantum states is discussed by the average photon number, signal-to-noise ratio, squeezing effcet and Wigner function. These results show that the output states can present strong non-classicality when modulating the amplitude of the coherent state and transmissivity of beam splitter.

Comparison of nonclassical properties resulting from non-Gaussian operations

Based on an asymmetrical beam splitter (ABS) and conditional measurement, we have investigated the nonclassical properties of non-Gaussian states in a unified form, including photon subtraction, photon addition and quantum catalysis, by deriving analytical expressions for photon number, squeezing effect, Mandel Q parameter and Wigner function. It is found that these properties not only depend on squeezing parameter and measurement, but also on the transmissivity of the ABS. Photon addition and quantum catalysis present a higher probability in the regions of low and high transmissivity, respectively. Although both single-photon subtraction and addition share a clear negative volume, the latter is considered to be a better choice for producing nonclassical states than the two others, if both success probability and negative volume in the small squeezing region are taken into consideration. Quantum catalysis is better in the large squeezing region and with low transmissivity. These results provide some reference for generating such non-Gaussian states.

Beam splitter and router via an incoherent pump-assisted electromagnetically induced blazed grating.

We propose a scheme for a beam splitter and a beam router via an electromagnetically induced blazed grating in a four-level double-Λ system driven by an intensity-modulated coupling field and an incoherent pump field. The blazed grating relies on the incoherent pump process, which helps in inducing large refractivity with suppressed absorption or even gain. Consequently, the weak probe beam can be effectively deflected with high diffraction efficiency, and, meanwhile, its energy is amplified. When using an intensity mask with two symmetric domains in the coupling field, the presented blazed grating provides the possibility of a symmetric beam splitter. The diffraction efficiency and diffraction order of the gratings are sensitive to the intensity of the coupling field, and, thus, the gratings can function as a tunable asymmetric beam splitter or a beam router, which distributes the probe field into different spatial directions. Therefore, the proposed scheme may have potential applications in optical communication and networking.

Complementarity via error-free measurement in a two-path interferometer

We study both wave-like behavior and particle-like behavior in a general Mach–Zehnder interferometer with an asymmetric beam splitter. An error-free measurement in the detector is used to extract the which-path information. The fringe visibility V and the which-path information Ipath are derived, their complementary relation is found, and the condition for the equality is also presented.