Conventional Beam Splitter Research Articles

Ancilla-free scheme for the photon-addition operation and its application to squeezing and coherence manipulation

The photon-addition operation is the inverse of the photon-subtraction operation and has many important applications in research on photon number statistics in quantum optics. In this study, we propose a scheme for a photon-addition operation with ancilla-free photonic manipulation. This is in strong contrast to conventional photon-addition operations in which a single-photon ancilla is an indispensable resource for photon addition. Moreover, our scheme helps break the exponential decay trend in the probability of success for photon addition operating in large Fock states. Thus, our scheme can be considered as a useful tool for manipulating the photon number of a bright coherent state or a strongly squeezed state in the near future. To be precise, we used the SU(1,1) beamsplitter to replace the conventional beamsplitter, and our work can be considered another important application of the SU(1,1) beamsplitter. The photon-addition operation is applied to both single- and two-mode quantum entangled states, and our results show that SU(1,1)-based photon addition is more powerful and efficient in terms of the fidelity and success probability of the photon-addition operation.

A wide band polarizing beam splitter based on complementary mode modulation in the hyperbolic metamaterial structures

An optimal beam splitter using the polarization mode modulation technique in different alignments of layered hyperbolic metamaterials is presented. The transmission and reflection modes in different arrangements of layered HMMs are studied in the presence of TM and TE waves by analyzing dispersion relations. Results show a duality in the mode modulations between structures aligned in the Y and Z axes. The response of one structure to a beam with zero polarization in terms of transmission and reflection is the same as the response of another to a beam with 90-degree polarization. We utilize this approach to propose a polarizing beam splitter (PBS) based on layered Ag-SiO2 unit cell HMM. FDTD simulations show that in a structure with two complementary outputs, when one of the outputs is in transmission mode, the other output is in reflection mode, and when the incident wave mode is changed from TM to TE, the operating modes of the outputs are reversed. Our structure can be used from 340 nm to Mid-IR with a high extinction ratio, and considering that the outputs work independently, the proposed PBS can prevent the destructive effect of waveguides on each other, which limits conventional beam splitters based on HMMs.

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.

Two-dimensional photonic crystal waveguide 1×5 beam splitter reversely designed by downhill-simplex algorithm

Beam splitter, whose main function is to achieve the splitting, combining and routing of optical signals, is an important component of photonic integrated circuits, passive optical network and other fields. Compared with the conventional beam splitter, photonic crystal beam splitter, which has the virtues of smaller size and higher transmission efficiency, is very suitable for high-density and large-scale integration. The traditional control variable method often used in the optimal design of photonic crystal beam splitter is time-consuming and inefficient. When parameter variables are large, it is difficult for beam splitter to achieve the optimal splitting performance. In addition, it is hard to realize flexible design of beam splitting ratio when optimizing multi-channel photonic crystal beam splitter by this method. In this paper, a novel photonic crystal 1×5 beam splitter, in which two special Y-junction waveguides are introduced into a completely two-dimensional square lattice silicon, is proposed and optimally designed by using downhill-simplex algorithm. Firstly, to determine the optimization range of each variable, the influences of the radius of the dielectric rod in the coupling region and the radius and the lateral offset of the regulating dielectric rod in the center of the two Y-junction waveguides on the five output ports of the 1×5 beam splitter are explored respectively by the plane wave expansion method and finite difference time domain method. The results show that the optical energy coupled from the main waveguide W<sub>1</sub> to the upper Y-junction waveguide and lower Y-junction waveguide can be controlled by optimizing the radius of the dielectric rod in the coupling region. The transmittance of the five output ports can be controlled in proportion by optimizing the lateral offset of the regulating dielectric rods. The total transmittance of the five output ports can be improved, and the output of each port can be adjusted by optimizing the radius of the regulating dielectric rod. Then, according to the specific target of the splitting ratio, using downhill-simplex algorithm, the 1×5 beam splitter with different splitting ratio can be reversely designed by optimizing the radius of the coupling dielectric rod and the radius and the lateral offset of the regulating dielectric rod within the selected optimization range. The total transmittance of the 1×5 beam splitter is above 99%, the additional loss is less than 0.044 dB, and the response time is less than 1ps. Besides, to determine the allowable error range of each optimization variable in actual processing, the machining error of the 1×5 beam splitter is analyzed, which provides a theoretical reference for fabricating the device. Owing to the advantages of flexible splitting ratio design, high optimization efficiency, small size and excellent performance, the proposed 1×5 beam splitter will have broad application prospects in the field of photonic integrated circuits and so on.

All-Dielectric Metasurface-Based Beam Splitter with Arbitrary Splitting Ratio.

The development of optical systems is heading to multi-branch circuit design and miniaturization. A beam splitter is a common device for dividing an incident beam into two separate beams. Conventional beam splitters are constructed using coated prisms or glass plate. Their bulky size, right-angled output direction, and fixed splitting ratio greatly limit the design of optical arrangement and also hinder the system integration. Here, an all-dielectric metasurface composed of symmetric nano-rings as a beam splitter are designed by Finite-Difference Time-Domain method. By changing the inner and outer radiuses of the nano-rings, the wavefront phase of the emergence beam can be adjusted to form a phase gradient, and the incident beam of arbitrary polarization is divided into two beams according to the designed transmittance and angle. The initial phase of the emergence beam can be changed by adjusting the refractive index of the substrate or adding the silicon film to the substrate, and the splitting ratio can be adjusted from 0.5:1 to 1:1. The simulation demonstrates that the metasurface-based beam splitter is independent of polarization and the power efficiency is over 92% with a compact area of 33.6 μm × 33.6 μm. This compact metasurface-based beam splitter has promising potential for enabling new types of compact optical systems and advancing metasurface-based functional integrated photonic applications.

Intelligent design of large angle deflection beam splitter based on method of moving asymptotes

Photonic chip is a kind of integrated device that uses light as a carrier for information transportation and processing. Owing to its advantages of small size, lightweight, and low power consumption, photonic chip has become the most popular research topic nowadays. The beam splitter is a vital part of on-chip integration. For conventional beam splitting elements, Y-type and tree-branch output are the main elements, which are usually realized by interference principles. However, it is appropriate only for simple conventional beam splitter because the propagation direction of light cannot achieve large angle deflection. In the case of relay loading, optical amplification, pumping, and frequency upconversion, the vertical loading is often required without affecting the main optical path. To complete the large-angle deflection beam splitting, one needs to add a mirror to realize it or use a right-angle mirror structure for geometric double-sided reflection and splitting in traditional ways, but these structures are relatively complicated and difficult to complete on-chip integration. Based on previous work on inversely designed multi-channel wavelength routers and wide spectrum efficient focusing devices by using the intelligent algorithm, and combining the years of research on the coherent superposition theory of multi-scattering of the disordered medium, a large angle beam splitter that can realize from the near-infrared band is designed through using the intelligent algorithm. The beam splitter structure is based on AMTIR-1 glass, the part to be etched is air. The composition of AMTIR-1 is Ge<sub>33</sub>As<sub>12</sub>Se<sub>55</sub>. And the size of the structure is only 1 μm × 2 μm. The beam splitter can achieve 180° linear separation of beams in a range from 800 nm to 1100 nm, the beam splitting ratio of the entire waveband is approximately 1∶1, and the gross beam splitting efficiency is stable between 85% and 92%. Compared with several conventional structures with the same size, the efficiency of the beam splitter designed by this algorithm is higher. At the same time, the algorithm has the advantages of fast computation speed and small computation amount, and it can be completed only by ordinary personal computers without the support of hardware such as workstations. This intelligent algorithm can also be applied to the design of various passive photonic devices such as optical polarization splitters, routers, optical isolators, etc., providing an idea and reference for the design of integrated micro-nano photonic devices on high-density sheets.

Theory of HOM interference on coupled waveguides.

It is well known that the Hong-Ou-Mandel (HOM) effect can be realized on beam splitters (BSs) in the form of coupled waveguides. It is believed that in this case, the theory is similar to HOM interference on conventional BSs. In this work, it is shown that if a BS is used in the form of a coupled waveguide, the theory of HOM interference can differ significantly from the known one. It is shown that even in the case of completely identical photons, the visibility of V can essentially differ from unity. The developed theory must be taken into account in quantum optical schemes, where BSs are represented mainly as coupled waveguides.

Freeform characterization based on nanostructured diffraction gratings.

The in-line characterization of freeform optical elements during the production cycle is challenging. Recently, we presented a compact sensor setup for the characterization of the wavefront generated by freeform optical elements in transmission. The sensor is based on a common-path interferometer consisting of diffractive components and Fourier filtering being adapted to the subsequent numerical post processing. Additionally, it offers several degrees of freedom for enlarging the measurement range of the wavefront gradients. In this contribution, we propose an advanced sensor setup for the measurement of wavefronts generated by freeform elements in reflection. The main advantage is the uni-axial illumination of the test object and the measuring system without the need for conventional beamsplitters. Due to this uni-axial arrangement, the main challenge is to avoid the effect of stray light and back reflections on the measurement signal-to-noise ratio. This is achieved by implementing a highly absorbing amplitude grating based on nanostructured silicon. We demonstrate the experimentally realized measurement system and compare its performance to a commercial Shack-Hartmann sensor.

Physical mechanism of beam splitting based on reflective embedded double-layer grating

It is not easy to achieve high performance for conventional beam splitters, such as high efficiency, good uniformity, polarization-independence, and wide bandwidth. A reflective embedded double-layer grating is described for beam splitting. With optimized grating profiles, the novel beam splitter can diffract both TE and TM polarizations into two orders with high performance. For the easy production, the fabrication tolerance is investigated and given. Most importantly, efficiencies more than 45% can be split into two orders within the wide bandwidth of 1412–1647 nm for TE polarization. The beam splitter based on multilayer coatings is sensitive to the incident angle and wavelength. And the bandwidth needs to be improved for the beam splitter based on simple grating. The design is of benefit for the performance improvement of the beam splitter by new grating configuration compared with the conventional simple grating.

In-plane ESPI using an achromatic interferometer with low-coherence laser source

The use of an achromatic interferometer is explored as a means of doing in-plane ESPI measurements using a laser diode as the light source. This interferometer type, which uses a diffraction grating in place of the conventional beamsplitter, has two features that make it suitable for making ESPI measurements over extended areas, even when using a low-coherence laser diode source. First, the parallelogram optical geometry of the interferometer causes all rays passing through to have the same optical path lengths. Second, the interferometer is achromatic, whereby the piezo-actuated mirror that steps the illumination light does so by the same phase angle, independent of wavelength. This latter feature accommodates the spectral impurity of a laser diode source. A periodic variation of fringe visibility is observed in experiments, where narrow ranges of high visibility occur at regular spatial intervals. This behavior derives from the clustered discrete spectral character of laser diode light output. A method to “tune” the interferometer by slightly rotating the diffraction grating is described so as to achieve consistent high fringe visibility throughout the measured images.

Material Survey for a Novel Beam Splitter Separating High-Order Harmonics from High-Average-Power Fundamental Pulses

We have investigated novel beam splitter (BS) materials to relax thermal issues under irradiation of a high-average-power visible and near infrared (VIS–NIR) laser beam. The material should efficiently reflect a high-order harmonic beam in the extreme ultraviolet (XUV) spectral region and transmit a VIS–NIR fundamental laser beam at a Brewster incidence for the latter beam. We have investigated optical and thermo-mechanical properties of crystalline silicon carbide (SiC), diamond, and rutile since they exhibit high transparency and high index of refraction for a VIS–NIR light. We also address thermal issues of conventional opaque BS materials by measuring their thermal distortion. We have shown that crystalline SiC is the most promising candidate among the other materials because of a high reflectivity for XUV light, as well as an ignorable thermal distortion. The surface flatness of a crystalline SiC plate must be improved to realize an applicable BS in the XUV spectral region.

Inherently phase-stable coherent two-dimensional spectroscopy using only conventional optics

We introduce an inherently phase-stable setup for coherent two-dimensional femtosecond spectroscopy in noncollinear box geometry using only conventional beam splitters, mirrors, and delay stages. Avoiding diffractive optics, pulse shapers, and active phase-locking loops, our spectroscopy setup is simple, robust, and works for ultrabroad bandwidths in all spectral regimes (infrared, visible, and ultraviolet).

Wavefront distortion of the reflected and diffracted beams produced by the thermoelastic deformation of a diffraction grating heated by a Gaussian laser beam

It may be advantageous in advanced gravitational-wave detectors to replace conventional beam splitters and Fabry-Perot input mirrors with diffractive elements. In each of these applications, the wavefront distortions produced by the absorption and subsequent heating of the grating can limit the maximum useful optical power. We present data on the wavefront distortions induced in a laser probe beam for both the reflected and diffracted beams from a grating that is heated by a Gaussian laser beam and compare these results to a simple theory of the wavefront distortions induced by thermoelastic deformations.

52.3: An Improved Polarizing Beamsplitter LCOS Projection Display Based on Wire‐Grid Polarizers

AbstractMOXTEK has developed a new polarizer technology for the visible spectrum based on the technology of nanometer‐scale wire‐grids. They have named their technology ProFlux(tm) Polarizers. These polarizers are extremely durable in the LCOS and transmissive light valve projector environment. They also offer very attractive optical performance characteristics as beam splitters in the imaging path, especially for an LCOS‐type system. However, since they are plate beamsplitters, they are not a direct replacement for current cube beamsplitters. The proper optical system architecture based on the MOXTEK ProFlux(tm) technology will exhibit significant improvements in image contrast, contrast uniformity, brightness uniformity, and color uniformity. This paper compares performance of conventional beamsplitter cubes with the ProFlux™ beamsplitter. It suggests optical architectures that favor the characteristics of this new beamsplitter while avoiding the problems characteristic of a plate beamsplitter. Test data on polarizers and example system performance will be presented.

Artificial Star Generation Using Nd:YAG Laser and 1.5 m Telescope.

Topical experimental results of artificial star generation are presented. The generation system utilizes a 1.5 m diameter telescope of CRL for transmitting a laser beam to illuminate the atmosphere and for receiving backscattered light. The light source of transmission used is the second harmonics of a pulse-oscillating Nd: YAG laser. A mirror with a small hole at its center is used as a beam splitter for transmission and reception, and it spares us from a power loss of about 6 dB compared to the use of a conventional beam splitter. We executed the first domestic experiment of artificial star generation by atmospheric Rayleigh-scattering, and succeeded in acquiring image data of artificial stars generated at ranges up to ten plus several kilometers. At the same time, data of Polaris in a neighboring direction were obtained as a reference and image comparison.

Optical fiber monitored by a directional coupler for delivering laser radiation in medical treatments

The safety of therapeutic laser treatments could be strongly improved by introducing real-time monitoring to the fiber delivery system. Since any fiber damage leads to a significant variation of the backscatter, its detection could be exploited to monitor the system, in particular the fiber trip. To assess this potential, the backscattered modal power distribution (BMPD) from flat, bulb, and damaged fiber tips were investigated. The BMPD detection was accomplished by using a conventional beam-splitter method and two directional couplers: a prism-fiber and a fiber-fiber lapped coupler. Unlike the conventional method, use of the couplers allows for the separate detection of backscattered and forward transmitted signals. Therefore variations in the backscatter that are due to only a change in the laser pulse can be determined. Moreover, the directional couplers, because of the amplification of high-index modes, allow for an increase in sensitivity of the method. This was particularly evident in our tests on fiber tips that had been dipped into water to obtain a better simulation of the real working conditions. Finally, the influence of the target on the BMPD was investigated as a function of its distance from the fiber tip. All the tests confirm that the target must be taken into account if the distance is <1 mm, but the monitoring system can also be used when the fiber tip works in contact with the tissue wall provided that one can ensure contact by pushing the tip against the target wall.

AGC Amplifier to Correct for Effects of Light Source Variations in Spectrofluorometric Measurements

An automatic gain control amplifier is described which is designed to correct for fluctuations in the light source of a recording spectrofluorometer. Means are also provided for correcting for the spectral response of the spectrofluorometer components. Two input signals to the AGC amplifier, one the fluorescent signal S2, and the other a reference signal S1 (which senses the light source variations present in S2), are obtained by use of a conventional beam splitter. Variations in S1 cause corresponding changes in gain A in such a way that the output voltage of the AGC amplifier is proportional to the quotient S2/S1. Thus, common variations in the input signals are canceled. Test results show that the instrument corrects for variations in light intensity as high as 20% with less than 1% error. Small step variations in light intensity, typically 10% or less, are corrected for within 200 msec.