Non-polarizing Beam Splitter Research Articles

Frequency and phase relations of entangled photons observed by a two-photon interference experiment

An entangled photon experiment has been performed with a large variation of the temperature of the non-linear crystal generating the entangled pair by spontaneous downconversion. The photon pairs are separated by a nonpolarizing beamsplitter, and the polarization modes are mixed by half wave plates. The correlation function of the coincidences is studied as a function of the temperature. In the presence of a narrow interference filter we observe that the correlation changes between -1 and +1 about seven times within a temperature interval of about 30 degrees C. We show that the common simplified single-mode pair representation of entangled photons is insufficient to describe the results, but that the biphoton description that includes frequency and phase details gives close to perfect fit with experimental data for two different choices of interference filters. We explain the main ideas of the underlying physics, and give an interpretation of the two-photon amplitude which provides an intuitive understanding of the effect of changing the temperature and inserting interference filters.

Simultaneous measurement of retardance and fast axis azimuth based on liquid crystal wave plate group

The simultaneous measurement of retardance and fast axis azimuth based on liquid crystal wave plate group (LCWPG) is presented. The laser beam propagates through an aperture and then splits into two beams by a non-polarizing beam splitter (NPBS). The intensity of the reflected beam is detected by a photomultiplier tube (PMT) as the reference light intensity. The transmitted beam, which passes through a polarizer, a quarter-wave plate, a retarder sample to be measured and the LCWPG successively, is finally detected by another PMT. The LCWPG is composed of four liquid crystal wave plates (LCWPs). In addition, the LCWPG works in six different polarized modulation modes dependent on the voltages applied on each LCWP. The six corresponding sets of light intensity are then measured by the two PMTs. By calculating and deriving from the six sets of light intensity, the retardance and fast axis azimuth of the measured sample can be obtained, respectively. In the experiment, the retardance of a quarter wave plate as the sample is measured when its fast axis is at different angles. The standard deviations of the retardance and the fast axis azimuth of the measured sample are 0.67˚ and 0.85˚, respectively. The effectiveness of the proposed method is verified.

Metal–dielectric broad-angle non-polarizing beam splitters with ultrathin copper layer

A novel metal–dielectric three-layer cube broad-angle non-polarizing beam splitter (nPBS) with an ultrathin copper layer was designed, prepared and characterized. Our nPBS structure (270 nm thick) is optimized around the wavelength of 1064 nm (reflectance in between 25 and 35% and transmittance in between 55 and 65% for the incidence angle range of 35–55°). For comparison, a 24-layer design for 45° incidence angle solution (6193 nm thick) using dielectric–dielectric nPBS was shown. For manufacturing point of view, reducing the layer number in the coating let eliminate undesirable mistakes during preparation of every layer thickness and decrease the time of whole structure fabrication. During or after multilayer deposition it is necessary to minimize the possibility of metal oxidation by choosing material with low affinity to oxygen. Additionally, it is important to reduce the product price by avoiding more expensive metals like gold and silver. Our nPBS structure was prepared in a single process by using of magnetron sputtering. The measured transmittance and reflectance values are in agreement with the design and the target values. Every single layer thickness error analysis was done.

Broadband non-polarizing terahertz beam splitters with variable split ratio

Seeking effective terahertz functional devices has always aroused extensive attention. Of particular interest is the terahertz beam splitter. Here, we have proposed, designed, manufactured, and tested a broadband non-polarizing terahertz beam splitter with a variable split ratio based on an all-dielectric metasurface. The metasurface was created by patterning a dielectric surface of the N-step phase gradient and etching to a few hundred micrometers. The conversion efficiency as high as 81% under the normal incidence at 0.7 THz was achieved. Meanwhile, such a splitter works well over a broad frequency range. The split ratio of the proposed design can be continuously tuned by simply shifting the metasurface, and the angle of emergences can also be easily adjusted by choosing the step of phase gradients. The proposed design is non-polarizing, and its performance is kept under different polarizations.

Using a single-cube beam-splitter as a fringe pattern generator within a structured-light projection system for surface metrology

We show how a sinusoidal fringe pattern can be obtained by using a single cube beam splitter based on the Gates’ interferometer configuration. When an expanded and collimated laser beam hits the binding edge of a nonpolarizing cube beam splitter parallel to the splitter coating, it generates interference fringes at the exit due to the internal reflections and refractions of the laser beam passing through the cube. Unlike common digital projection systems, the proposed optical arrangement generates a perfectly sinusoidal and continuous fringe pattern, minimizing the problems associated with the discretization of a synthetic digital signal. The fast Fourier transform and phase-shifting techniques are used to demodulate the captured fringe patterns. Experimental results are presented for the three-dimensional shape reconstruction of the relief of a coin and of a spherical indentation on a piece of aluminum with a maximum height of about 150 μm. In addition, we evaluate the accuracy and resolution of the proposed measuring device: shape reconstruction accuracy is about 1.4% and axial resolution is 0.15 μm. Due to its simple and compact setup, the proposed system is particularly suited to be miniaturized.

Realization of a robust homodyne quadrature laser interferometer by performing wave plate yawing to realize ultra-low error sensitivity.

The deviation of wave plates' optical axes from their intended angles, which may result from either instability or assembly error, is the main cause of quadrature phase error in homodyne quadrature laser interferometers (HQLIs). The quadrature phase error sensitivity to wave plate angle deviations, which is an effective measure of HQLI robustness, is further amplified by beam splitter imperfections. In this paper, a new HQLI design involving non-polarization beam splitting is presented, and a method of making this HQLI robust by yawing the wave plates in the measurement and reference arms is proposed. The theoretical analysis results indicate that ultra-low quadrature phase error sensitivities to wave plate angle deviations can be realized and that non-polarizing beam splitter imperfections can be adequately compensated for. The experimental results demonstrate that the proposed method can reduce the quadrature phase error sensitivity by more than 1 order of magnitude, from a theoretical value of 1.4°/1° to 0.05°/1°.

Generation of cylindrical vector beams based on common-path interferometer with a vortex phase plate

Cylindrical vector (CV) beams have found increasing applications in physics, biology, and chemistry. To generate CV beams, interferometric technique is popularly adopted due to its flexibility. However, most interferometric configurations for the generation of CV beams are faced with system instability arising from external disturbance, limiting their practical applications. A common-path interferometer for the generation of radially and azimuthally polarized beams is proposed to improve the system stability. The optical configuration consists of a vortex phase plate acting to tailor the phase profile and a cube nonpolarizing beamsplitter to split the input beam into two components with mirror-like spiral phase distribution. The generated CV beams show a high quality in polarization and exhibit a better stability of beam profile than those obtained by noncommon-path interferometric configurations.

High-power electro-optic switch technology based on novel transparent ceramic**Project supported by the National Natural Science Foundation of China (Grant Nos. 61137004, 61405218, and 61535014).

A novel high-power polarization-independent electro-optic switch technology based on a reciprocal structure Sagnac interferometer and a transparent quadratic electro-optic ceramic is proposed and analyzed theoretically and experimentally. The electro-optic ceramic is used as a phase retarder for the clockwise and counter-clockwise polarized light, and their polarization directions are adjusted to their orthogonal positions by using two half-wave plates. The output light then becomes polarization-independent with respect to the polarization direction of the input light. The switch characteristics, including splitter ratios and polarization states, are theoretically analyzed and simulated in detail by the matrix multiplication method. An experimental setup is built to verify the analysis and experimental results. A new component ceramic is used and a non-polarizing cube beam splitter (NPBS) replaces the beam splitter (BS) to lower the ON/OFF voltage to 305 V and improve the extinction ratio by 2 dB. Finally, the laser-induced damage threshold for the proposed switch is measured and discussed. It is believed that potential applications of this novel polarization-independent electro-optic switch technology will be wide, especially for ultrafast high-power laser systems.

Measurement of red blood cell characteristic using parallel phase shifting interferometry

In this research, an interferometric technique is presented for the calculation of the optical path difference (OPD) induced by a red blood cell (RBC) to measure its 3D phase profile, allowing the examination of its morphology which is very important in the biomedical field to diagnose diseases. The developed system is based on a polarized cyclic path interferometer with a nonpolarizing beam splitter in the output, which generates two interferograms with relative phase shifts of π/2. From these two interferograms, which are captured in single-shot of the camera, it is possible to measure the optical phase map using a regularized optical flow algorithm developed by Vargas–Quiroga. The presented measurement system is immune to vibrations caused by environmental disturbances, so it can be implemented outside the laboratory; additionally, the use of two interferograms simplify the number of phase steps required to find the optical phase, and it can be adapted to obtain the optical phase with four interferograms obtained in two shots. Using the proposed technique, the experimental results showing the 3D morphology of RBC are presented.

Sub-nanometer periodic nonlinearity error in absolute distance interferometers.

Periodic nonlinearity which can result in error in nanometer scale has become a main problem limiting the absolute distance measurement accuracy. In order to eliminate this error, a new integrated interferometer with non-polarizing beam splitter is developed. This leads to disappearing of the frequency and/or polarization mixing. Furthermore, a strict requirement on the laser source polarization is highly reduced. By combining retro-reflector and angel prism, reference and measuring beams can be spatially separated, and therefore, their optical paths are not overlapped. So, the main cause of the periodic nonlinearity error, i.e., the frequency and/or polarization mixing and leakage of beam, is eliminated. Experimental results indicate that the periodic phase error is kept within 0.0018°.

Compact interferometer transducer based on surface plasmon phase resonance.

We propose a new monolithic interferometric configuration and implement a novel method for spectroscopic phase shift detection of surface plasmon resonance (SPR) sensors. The interference pattern is obtained using a nonpolarizing beam splitter cube with two attached right angle prisms in such a way that each interference field undergoes two total internal reflections (TIR) at prisms/air interface and one attenuated total reflection (ATR) through surface plasmon interaction. The evanescent part of the interferogram around the Zero optical path difference (ZOPD) is sampled and detected in the far field, thanks to a bidimensional array of scattering optical near-field probes deposited on the corresponding prism surface. A Fourier transform of the sampled interferogram is performed to measure the input light wavelength, while a direct comparison of the interferogram in TM and TE polarization modes allows us to determine the differential phase shift induced by the SPR layer. The phase shift measurement is made possible thanks to a remarkable time stability of the interferogram in the glass bulk. By tuning the input laser wavelength around the resonance, we show a good agreement between experimental and theoretical calculations for both amplitude and phase spectral responses.

The second-order interference of two independent single-mode He–Ne lasers

The second-order spatial and temporal interference patterns with two independent single-mode continuous-wave He–Ne lasers are observed when these two lasers are incident to two adjacent input ports of a 1:1 non-polarizing beam splitter, respectively. Two-photon interference based on the superposition principle in Feynman's path integral theory is employed to interpret the experimental results. The conditions to observe the second-order interference pattern with two independent single-mode continuous-wave lasers are discussed. It is concluded that frequency stability is important to observe the second-order interference pattern with two independent light beams.

Extended linear polarimeter to measure retardance and flicker: application to liquid crystal on silicon devices in two working geometries

We focus on the evaluation of the applicability of the classical and well-established linear polarimeter to the measurement of linear retardance in the presence of phase flicker. This analysis shows that there are large errors in the results provided by the linear polarimeter when measuring the linear retardance of a device. These errors depend on the specific retardance value under measurement. We show that there are some points where this limitation can be used to measure the fluctuation amplitude consistently. An elegant method is further pro- posed, enabling the measurement of the average retardance value, thus extending the applicability of the classical linear polarimeter. Experimental characterization results are provided for various electrical sequences addressed onto a parallel aligned liquid crystal on silicon (LCoS) display. Good agreement is obtained with experiment, thus validating the linear polarimeter methodology proposed. Furthermore, results are provided for the LCoS in two reflection geometries, perpendicular incidence with and without nonpolarizing beam splitter, demonstrating robustness of the method. As a result, the evaluation of both phase modulation range and flicker magnitude for any electrical sequence addressed can be easily obtained, which is very important for optimal use of LCoS displays in applications. © 2014 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.OE.53.1.014105)

Dual-CCD Complete Stokes Simultaneously Imaging Polarimeter and Experimental Data Analysis

Polarization imaging technology that is on the basis of the polarization measurement can change the obtained polarization information into two-dimensional image, from which we can acquire polarization characteristics of target scene just like normal gray image so that this technique is widely used in the fields of military investigation, medical testing, space exploration, meteorology and so on. Traditional imaging polarimeter is time sequence polarization imaging, which is to use sequential rotational polarization components (line polarizer or wave plate etc.) and to combine Fourier analysis method to acquire final Stokes components. But because of the sacrificing of temporal resolution, this technique does not meet the needs of the situation of high-speed dynamic changing scene. While current simultaneously polarization imaging technique commonly uses multiple sets of optical systems and at least four CCD cameras, which have the problems of low energy utilization rate and non-matching performance among the optical sets. To solve the aforementioned problems, we design and implement a set of non-mechanical rotating parts, double Wollaston prisms-based high resolution simultaneously imaging polarimeter. This system uses the specific combination of non-polarizing beam splitter, Wollaston prisms and wave plates to divide the incident target space beam into four optical paths of different polarization states which can be taken into two types: two paths in the reflection part and two paths in the transmission part. Finally the imaging lens converge the beam to different regions of two large array CCD to image four images. To achieve the goal of extracting complete Stokes information, we apply the Stokes vector and Mueller matrix analysis. The article presents systems structure, working theory, calibration method, experiment data analysis and system polarization performance, which provides a good reference for the simultaneously high-speed polarization imaging.

미소면적 광학이방성 정밀 측정을 위한 수직반사형 타원계의 광소자 편광특성 및 측정정밀도 향상 연구

기존의 반사형 타원계에 광분할기와 프리즘 등의 광학소자를 추가하여 <TEX>$8.0{\mu}m$</TEX> 보다 작은 면적에서 시료의 광학이방성을 측정할 수 있는 수직반사형 타원계를 제작하였다. 수직반사 구조를 구현하기 위해 사용된 광학소자들의 편광작용을 보정하여 광학이방성 측정의 정확도를 향상시켰다. 비편광 광분할기를 사용하고 사분파장 위상지연자를 장착하며 광섬유를 제거하고 파장영역을 최적화하여 광학이방성인자 측정값의 표준편차를 0.00083 으로 줄이고 방위각 변화에 따른 rutile 시료의 광학이방성인자의 변동폭을 0.015 이하로 줄일 수 있었다. A normal incidence ellipsometer is fabricated to measure the optical anisotropy of a small spot whose diameter is less than <TEX>$8.0{\mu}m$</TEX>, by adding a beam splitter and a prism to the conventional rotating analyzer type ellipsometer. The polarizing actions of the added optical components are calibrated to improve the accuracy of the anisotropy measurement. The standard deviation of the optical anisotropy factor decreased to 0.00083, and the variation of the optical anisotropy factor of rutile versus sample azimuth angle variation also decreased to 0.015, after adoption of a non-polarizing beam splitter and a quarter wavelength phase retarder, followed by removal of the optical fiber and a careful choice of measurement wavelength.

Design and fabrication of multi-wavelength all-dielectric beam splitter with little polarization deviation

When used at non-normal incident situation, optical thin film spectrum curve will exhibit strong polarization deviation. For many applications, this polarization effect was undesired and should be reduced. In this paper, a multi-wavelength all-dielectric nonpolarizing beam splitter operating at wavelength 532nm, 633nm and 1315nm with incident 45° was designed, which was gained by choosing a initial film stack with little polarization splitting and then utilizing the needle thin film synthesis method and conjugate graduate refine method. Plasma-assisted evaporation deposition technology was made to deposit the thin film system. Experimental study also included an annealing process. Considering numerical and experimental results, we can find that the polarization deviation at wavelength 532nm, 633nm and 1315nm were all very little.

Effect of nonpolarizing beam splitter on measurement error in heterodyne interferometric ellipsometers

The nonlinear error of the ellipsometric parameters (EP) has been investigated by many researchers in terms of the imperfection of polarizing beam splitters (PBS), the elliptical polarization and nonorthogonality of the light beams produced by the laser source and wave plates. To our knowledge, the effect of the nonpolarizing beam splitters (NPBS) on the EP errors has not been reported before. Aiming at the heterodyne interferometric ellipsometer with two acousto-optical modulators we proposed before, the EP errors produced by the NPBS are analyzed and calculated with the Jones matrix algebra in this paper. The theoretical analysis indicates that the misorientation of the NPBS has a major effect on the errors; it must be smaller than 0.02° for obtaining nanometer accuracy. Furthermore, the first NPBS which separates the measurement arm from the reference arm has more important contribution to the EP errors than the second NPBS, which recombines the measurement light and the reference light. In addition, the slight variation of the reflectivity and transmissivity of NPBS has a direct and serious influence on the amplitude ratio error; however, it almost has no effect on the phase difference error. As another important source of error, the influence of NPBS on the measure accuracy needs more emphasis.

非偏振分光镜对干涉式椭偏仪测量精度的影响

A novel heterodyne interferometric ellipsometer was investigated to measure the thicknesses of thin films in the nanometer-accuracy.The depolarization effect of a Nonpolarizing Beam Splitter(NPBS) was characterized by the transmission-induced-retardance(TIR) between p and s components of a polarizing beam,reflectance ratio,transmittance ratio and reflection-induced-retardance(RIR),then a corresponding error model was established.The influence of the depolarization effect and misorientation of a multi-layer dielectric NPBS on the errors of ellipsometric parameters was investigated.Experimental results indicate that the fluctuation of the depolarization effect caused by the environmental temperatures,incident angles and the change of polarizating state has a major impact on the measurement accuracy,and it can not be eliminated by calibration.In order to implement the nanometer-accuracy,the misorientation angle must be smaller than 0.1°.Furthermore,it shows that the NPBS orientation angle errors for recombination of the measurement light and the reference light have more important contribution than another ones to the measurement accuracy.The thickness measurement error of thin film induced by NPBS is about 1.8-2.5 nm,which means that the NPBS is an assignable error source in the Mach-Zehnder interferometric ellipsometer.

Polarization-independent rapidly tunable optical add-drop multiplexer utilizing non-polarizing beam splitters in Ti:LiNbO3

A polarization-independent four-port wavelength-tunable optical add drop multiplexer (OADM) that utilizes non-polarizing relaxed beam splitters has been analyzed and demonstrated in Ti:LiNbO3 at the 1530nm wavelength regime. The design utilizes an asymmetric interferometer configuration with strain induced index grating for polarization coupling along its arms that are shifted in position relative to each other. Experimental results of the filter response agree with theoretical predictions. Electrooptic tuning over a range of 15.7nm at a rate of 0.08nm/V has been measured. A temporal response <46ns to a 20V step change in tuning voltage has been demonstrated. Fiber-to-fiber insertion loss is ~6.5dB.

Design technique for all-dielectric non-polarizing beam splitter plate

AbstractThere are many situations when, for the proper working, an opto-electronic device requiring optical components does not change the polarization state of light after a reflection, splitting or filtering. In this paper, a design for a non-polarizing beam splitter plate is proposed. Based on certain optical properties of homogeneous dielectric materials we will establish a reliable thin film package formula, excellent for the start of optimization to obtain a 20-nm bandwidth non-polarizing beam splitter.