Non-polarizing Beam Research Articles

Practical considerations for the amplification of electro-optically detected THz signals

Advances in THz methods and applications require the detection of weak THz pulsed signals. One solution to this problem is to amplify weak signals using optically biased electro-optical (EO) techniques. Several different EO amplification schemes are compared. The simplest of these involves using a non-polarizing beam splitter followed by two quarter-wave plates set to small positive and negative angles, respectively. The signals are then passed through polarizers perpendicular to the polarization of the 800 nm EO detector crystal gating beam. As long as sufficient intensity is present in the gate pulse for linear photodiode detection, amplification of up to 10 times with dynamic ranges for single sweep scans of >104 is obtained.

Single-shot spatial light interference microscopy for dynamic monitoring of membrane fluctuations.

Single-shot spatial light interference microscopy (SS-SLIM) with a pair of non-polarizing beam splitters is proposed for substantially enhancing the speed and efficiency of conventional SLIM systems. Traditional methods are limited by the need for multiple-frame serial modulation and acquisition by spatial light modulators and detectors. Our approach integrates non-polarizing beam splitters to simultaneously capture four phase-shifted intensity images, increasing the imaging speed by at least fourfold while maintaining high quality. This capability is crucial for effectively monitoring the dynamic fluctuations of red blood cell membranes. Furthermore, the potential applications of the SS-SLIM system in biomedical research are demonstrated, particularly in scenarios requiring high temporal resolution and label-free imaging.

NiO thickness measurement using a rectangular-type Sagnac interferometer as the material transport layer in a perovskite solar cell

This work aims to utilize a phase-shifting technique in a rectangular-type Sagnac interferometer (RTSI) to measure the thickness of a thin film of nickel (II) oxide (NiO) in an electron transport layer (ETL) in perovskite solar cell preparation. The NiO layer is deposited on a fluorine-doped tin oxide (FTO) glass substrate. In the RTSI setup, the signal output from the interferometer is divided into the reference and testing arms using a nonpolarizing beam splitter (NPBS). The balanced photodetectors then detect the signal, with the FTO/NiO layer placed in the testing arm and pure FTO in the reference arm. By analyzing the signal intensities at polarization settings of 0° to 180°, the phase shift and thickness of the NiO layer can be determined. The thickness values of FTO and NiO films obtained through three different phase-shifting algorithms of three-, four-, and five-steps are calculated. The obtained NiO thickness values are validated against scanning electron microscopy (SEM). Finally, by considering the NiO thickness value that exhibits the lowest percentage error compared to one from SEM, it is confirmed that the three-step algorithm is the most suitable scheme for obtaining intensities at 0°, 45°, and 90°. Therefore, the proposed setup shows promise as a replacement for SEM in thickness measurements.

One-step jones matrix polarization holography for polarization-sensitive materials using angular-multiplexing

A polarization digital holography (DH) using angular multiplexing was developed for extracting the Jones matrix of anisotropy materials in one step. This technique is implemented by adopting an off-axis interferometric configuration connecting two identical CCD cameras. The combined orthogonal 45° beams is split using a nonpolarizing beam splitter to produce the sample and reference beams. Our method yields two angular-multiplexing polarization interferograms simultaneously, in which the orthogonal fringe directions for each interferogram are modulated by two self-installed retro-reflector mirrors. In this case, the spatially resolved Jones matrix parameters of the polarization-sensitive materials can be determined in one step. The basic feasibility of the scheme is verified by measuring the Jones matrices of polarizing optics, a transmitted spatial light modulator, and synthetic mica plates.

Si-Based Polarizer and 1-Bit Phase-Controlled Non-Polarizing Beam Splitter-Based Integrated Metasurface for Extended Shortwave Infrared.

Metasurfaces, composed of micro-nano-structured planar materials, offer highly tunable control over incident light and find significant applications in imaging, navigation, and sensing. However, highly efficient polarization devices are scarce for the extended shortwave infrared (ESWIR) range (1.7~2.5 μm). This paper proposes and demonstrates a highly efficient all-dielectric diatomic metasurface composed of single-crystalline Si nanocylinders and nanocubes on SiO2. This metasurface can serve as a nanoscale linear polarizer for generating polarization-angle-controllable linearly polarized light. At the wavelength of 2172 nm, the maximum transmission efficiency, extinction ratio, and linear polarization degree can reach 93.43%, 45.06 dB, and 0.9973, respectively. Moreover, a nonpolarizing beam splitter (NPBS) was designed and deduced theoretically based on this polarizer, which can achieve a splitting angle of ±13.18° and a phase difference of π. This beam splitter can be equivalently represented as an integration of a linear polarizer with controllable polarization angles and an NPBS with one-bit phase modulation. It is envisaged that through further design optimization, the phase tuning range of the metasurface can be expanded, allowing for the extension of the operational wavelength into the mid-wave infrared range, and the splitting angle is adjustable. Moreover, it can be utilized for integrated polarization detectors and be a potential application for optical digital encoding metasurfaces.

Quantitative phase-amplitude surface determination in reflection differential interference contrast profilometry.

An approach for measuring the surface profile of the samples with reflection variations using the Nomarski differential interference method is presented. The system is analyzed with Jones's matrices tool, and polarization effects of a non-polarizing beam splitter are taken into account. Equations are also developed to allow the determination of the surface profile from interference intensity when the sample reflectively is not uniform. The validity and accuracy of the measurement are verified by measuring the adhered silicon cantilever on a substrate with high reflectivity. This method is expected to be a valuable tool to inspect elements of micromechanics and microsystems.

Fabrication and performance evaluation of nonpolarizing beam splitter with high splitting ratio in 780 nm band

Fabrication and performance evaluation of nonpolarizing beam splitter with high splitting ratio in 780 nm band

Polarization Sensitivity Measurement Method for Non-Polarizing Beam Splitters

Polarization Sensitivity Measurement Method for Non-Polarizing Beam Splitters

Monolithic mode separator for the first-order spatial mode of light field.

We propose a monolithic mode separator (MS) for the first-order spatial mode of a light field. The principle of the MS is an asymmetric Mach-Zehnder interferometer, which consists of two non-polarizing beam splitters, a right-angle prism, and a pentagonal prism. These optics are glued together as a monolithic one. The phase difference between the two light paths inside the interferometer is temperature controlled. The separation efficiency for two first-order orthogonal Hermite Gaussian (HG) modes, i.e., HG01 and HG10, is 97.5%, and the overall transmission is 77%. The device is intrinsically stable and convenient to be adopted in various experiments.

Improved measurement method for the Faraday rotation distribution using beam splitting.

In this work, two Faraday channels and one shadow channel are constructed by two non-polarizing beam splitters and one reflector to measure the Faraday rotation distribution. The intensity of the Faraday and shadow images is related to the state of polarization (SOP) of the incident light, thus achieving two-dimensional accurate measurement. The measurement sensitivity is influenced by the settings of two polarization analyzers in the Faraday channels and the parameters of beam splitters, which are explored numerically and verified with experiments. The fluctuation of the probe light is eliminated by using three evaluation indexes. Also, the measurement range and error sources under different experimental settings are discussed.

Enhancement of the correlation of the photons of thermal light

The scheme of the arrangement of five 50/50 non-polarizing beam splitters is considered. It may provide for the enhancement of the correlation of the photons of thermal light up to 75%. The correlation of the photons after the arrangement can be measured using ghost imaging, Bell test, Hong-Ou-Mandel interference.

Efficient All-Dielectric Diatomic Metasurface for Linear Polarization Generation and 1-Bit Phase Control.

Optical metasurface has exhibited unprecedented capabilities in the regulation of light properties at a subwavelength scale. In particular, a multifunctional polarization metasurface making use of light polarization to integrate distinct functionalities on a single platform can be greatly helpful in the miniaturization of photonic systems and has become a hot research topic in recent years. Here, we propose and demonstrate an efficient all-dielectric diatomic metasurface, the unit cell of which is composed of a pair of a-Si:H-based nanodisks and nanopillars that play the roles as polarization-maintaining and polarization-converting meta-atoms, respectively. Through rigorous theoretical analyses and numerical simulations, we show that a properly designed diatomic metasurface can work as a nanoscale linear polarizer for generating linearly polarized light with a controllable polarization angle and superior performances including a maximum transmission efficiency of 96.2% and an extinction ratio of 32.8 dB at an operation wavelength of 690 nm. Three metasurface samples are fabricated and experimentally characterized to verify our claims and their potential applications. Furthermore, unlike previously reported dielectric diatomic metasurfaces which merely manipulate the polarization state, the proposed diatomic metasurface can be easily modified to empower 1-bit phase modulation without altering the polarization angle and sacrificing the transmission efficiency. This salient feature further leads to the demonstration of a metasurface beam splitter that can be equivalently seen as the integration of a nonpolarizing beam splitter and a linear polarizer, which has never been reported before. We envision that various metadevices equipping with distinct wavefront shaping functionalities can be realized by further optimizing the diatomic metasurface to achieve an entire 2π phase control.

Pure rotational Raman lidar for full-day troposphere temperature measurement at Zhongshan Station (69.37°S, 76.37°E), Antarctica.

A pure rotational Raman lidar (PRRL) for full-day troposphere temperature measurement was deployed in February 2020 at Zhongshan Station (69.37°S, 76.37°E), Antarctica, by the 36th Chinese National Antarctic Research Expedition. The PRRL emits a 532.23-nm laser light and employs a 203.2-mm telescope to collect atmospheric backscatter. Cubic nonpolarizing beam splitters are introduced to yield a compact optics arrangement. A quasi-single-line-extraction technique is proposed for extracting the molecular Stokes line signals. A lidar container with a window system is customized to house the whole PRRL system for long-term stable operation. An approach using a laser plummet is developed for fast and convenient adjustment of the telescope zenithward. A home-made calibration module is utilized for straightforward visual optics adjustment with ∼35.3-μrad angular positioning accuracy. Both typical daytime and nighttime temperature measurement examples are presented to verify the lidar performance. From a 30-h continuous temperature measurement result, it is found the tropopause is located at ∼10.8 km above ground level with a mean temperature of ∼203 K; significant temperature variability occurs only at the inversion areas, while off which the 1-h temperature profiles are relatively similar in form with an average lapse rate of -8.3 K/km.

Design of optical engines for stellar simulation systems with low extinction ratios

An optical engine (OE) for stellar simulation systems with low extinction ratios (ERs) is proposed. This engine combines two orthogonal polarizers with a non-polarizing beam splitter to suppress the leakage of dark silicon-based liquid crystals (LCOS) in traditional systems. In this paper, a method to calculate the ER based on vector ray tracing is used. The new optical engine (OE) is demonstrated to have lower ERs than traditional systems. The calculations show that the maximum ER is 5×10−5 in the range of ±8°, which is much lower than the ERs of traditional optical engines of 2.5×10−2 . It reduces the ER by three orders of magnitude. The experimental results show that the new OE improves the ERs by 92.68% compared with the traditional system.

Optical interference coating design contest 2019: a non-polarizing beam splitter and a color-mixing challenge [Invited

A non-polarizing beam splitter and a light color-mixing challenge were the topics of the design contest held in conjunction with the 2019 Optical Interference Coatings topical meeting of the Optical Society of America. A total of 10 designers from China, France, Germany, Japan, and the United States submitted over 70 designs for problems A and B. The design problems and the submitted solutions are described and evaluated.

Utilization of the cyclic interferometer in polarization phase-shifting technique to determine the thickness of transparent thin-films

An alternative polarization phase-shifting technique is proposed to determine the thickness of transparent thin-films. In this study, the cyclic interferometric configuration is chosen to maintain the stability of the operation against external vibrations. The incident light is simply split by a non-polarizing beam splitter cube to generate test and reference beams, which are subsequently polarized by a polarizing beam splitter. Both linearly polarized beams are orthogonal and counter-propagating within the interferometer. A wave plate is inserted into the common paths to introduce an intrinsic phase difference between the orthogonal polarized beams. A transparent thin-film sample, placed in one of the beam tracks, modifies the output signal in terms of the phase retardation in comparison with the reference beam. The proposed phase-shifting technique uses a moving mirror with a set of “fixed” polarizing elements, namely, a quarter-wave retarder and a polarizer, to facilitate phase extraction without rotating any polarizing devices. The measured thicknesses are compared with the measurements of the same films acquired using standard equipment such as the field-emission scanning electron microscope and spectroscopic ellipsometer. Experimental results with the corresponding measured values are in good agreement with commercial measurements. The system can be reliably utilized for non-destructive thickness measurements of transparent thin-films.

Ultra-Thin Metamaterial Beam Splitters

Here, we present blueprints for three types of ultra-thin beam splitters based on versatile fishnet metamaterial structures at the 1.55 μ m optical communication wavelength. The thicknesses of the designed polarizing beam splitter and partially polarizing beam splitter are 1/26 of the free-space wavelength, while the thickness of the non-polarizing beam splitter is 1/13 of the free-space wavelength. Numerical simulations show that, compared to other miniaturization approaches including popular dielectric metasurfaces, metal-based metamaterial approach can provide much thinner beam splitters with reasonable performance. Such beam splitters can enable miniaturization of conventional and advanced quantum photonic systems towards higher density, scalability, and functionality.

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.