Achromatic Retarder Research Articles

Complete polarization state generator composed of one fixed polarizer and two rotating retarders

We discuss all possible responses of a linearly polarized light passing through two linear retarders. Based on this theory, a complete polarization state generator (PSG) composed of a fixed polarizer and two rotating retarders is proposed. The restriction on the phase retardances of the two retarders is given, and the procedures to determine the orientations of the two retarders to generate any pre-specified elliptical polarization state are presented. Compared with the traditional PSG, our design has the advantage that the working wavelength can be selected in a rather broad range. At the same time, our system only requires two normal linear retarders, and is thus cheaper than the PSG composed of achromatic or variable retarders. In addition, by selecting the retardance values of the two retarders, our complete PSG can also be designed to show a good broadband property, such as generating a specific polarization for an extended range of wavelengths under white light illumination. Finally, the comprehensive analysis of a linearly polarized light passing through two linear retarders presented in our paper is also inspiring for the design of other related systems.

Efficient broadband polarization retarder via shortcuts to adiabaticity.

The use of two-level atomic systems in quantum optics allows for the design of highly efficient and broadband achromatic retarders through the application of adiabatic passage and composite pulse techniques. In this work, we propose shortcuts to adiabaticity to improve broadband polarization retarders with shorter lengths. We achieve this by inversely engineering the relative refractive indices and further optimizing them with respect to the perturbation of input wavelength. Our results are compared with adiabatic and composite protocols, demonstrating that our method provides the advantage of integrating efficiency and robustness.

Achromatic terahertz quarter-wave Fresnel rhomb retarder

Achromatic terahertz (THz) quarter-wave retarder is widely desired to manipulate the polarization states of broadband THz beams, which are essential for spectroscopic applications, such as circular dichroism spectroscopy and steering THz vortex beams. A retarder based on Fresnel reflection exhibits the potential for designing an achromatic THz quarter-wave retarder. However, special care should be taken to make a Fresnel retarder capable of manipulating the beam ellipticity by simply rotating its fast axis without affecting its propagation path. Hereby, we design a 4-bounce achromatic quarter-wave Fresnel rhomb retarder free of affecting beam propagation, which can easily change the input beam's ellipticity by simply rotating the retarder's fast axis.

47.1: Green Technology of Photoalignment Layer Coating from H2O solution for Achromatic Polymerizable Liquid Crystal Retarder

Combination of several films from polymerizable liquid crystal (PLC) into single device system with complex properties faces a fabrication issue due to chemical compatibility and mutual alignment effect of the neighbouring layers. Eco-friendly green technology of high anchoring azo-dye photoalignment layer coating from water solvent provides efficient solution to hinder interlayer interaction of bottom PLC layer avoiding its chemical damage and providing unique photoalignment pattern for top PLC retarder. The advanced possibilities of green technology of photoalignment layers coated from H2O solution are demonstrated through fabrication of achromatic quarter-wave retarder system comprising formation of polimerizable liquid crystal layers on top of one another with arbitrary azimuthal photoalignment direction. The merge of photoaligned PLC retarders into single multi-layer anisotropic structure opens new approach to fabrication of thin-film phase devices with complex optical properties.

Fast tunable metamaterial liquid crystal achromatic waveplate

Abstract Photonic metamaterials combined with liquid crystals (LCs) for tunability is a great niche for building miniature devices with high performance such as fast flat tunable lenses, tunable filters, and waveplates. Sub-wavelength or nano-grating surfaces are homogenized to uniaxial waveplates with negative birefringence of unique dispersion when the period is less than the wavelength by at least a few times. This uniaxial metasurface, combined with the LC layer, is shown to act as a tunable retardation achromatic waveplate with 8 μm thick LC layer operating over wide spectral and angular ranges, as compared to using two nematic liquid crystal (NLC) retarders of thicknesses on the order of 30–60 μm, when no metasurface is used. Hence the device becomes miniature and 50× faster due to the thinner liquid crystal layer. The silicon nano-grating of 351 nm pitch and 0.282 fill factor is designed and fabricated to operate in the short-wave infrared range (SWIR). Switching between three achromatic retardation levels: full-, half-, and quarter-waveplates is accomplished by changing the applied voltages on the NLC cell with a switching time of a few milliseconds. This device has applications in fast broadband shutters, low coherence phase shift interferometry, ellipso-polarimetry, dynamic control of light intensity, and smart windows.

Toward practical weak measurement wavefront sensing: spatial resolution and achromatism.

The weak measurement wavefront sensor detects the phase gradient of light like the Shack-Hartmann sensor does. However, the use of one thin birefringent crystal to displace light beams results in a wavelength-dependent phase difference between the two polarization components, which limits the practical application. Use of a Savart plate, which consists of two such crystals, can compensate for the phase difference and realize achromatic wavefront sensing when combined with an achromatic retarder. We discuss the spatial resolution of the sensor and experimentally reconstruct a wavefront modulated by a pattern. Then we obtain the Zernike coefficients with three different wavelengths before and after modulation. Our work makes this new wavefront sensor more applicable to actual tasks like biomedical imaging.

Zero-order achromatic variable-wave retarder in standard single-mode optical fiber

In this work, we present numerically and experimentally a zero-order achromatic variable-wave retarder (AVWR) in a standard optical fiber. The model is based on Pancharatnam’s model including three concatenated variable wave retarders (VWR). The results show high degree of achromaticity over 100 nm from 1500 to 1600 nm covering the Erbium band. In order to explain the AVWR ellipticity and azimuth behavior, we carry out a numerical simulation based on the Jones matrix formulation and compared it directly with a single VWR.

Study on superachromatism of a quarter-wave retarder for the visible range of the spectrum

Achromatic retarders are key components used in optical system design. Various researchers have proposed different combinations of quarter-wave plates that exhibit good achromatic behavior over a broad wavelength range. One of the pioneering works in this area was that of Pancharatnam, who proposed a combination of three wave plates where the fast axis of the first and the last wave plates were parallel, and both quarter-wave and half-wave achromatic retarders were obtained by proper orientation of the central wave plate. In this paper the superachromatic behavior of a quarter-wave retardation system, consisting of three wave plates, is studied in the spectral range from 500–700 nm (i.e., the visible range), centered around the design wavelength of 575 nm. It will be shown that, if the second and third wave plates of the proposed configuration are oriented at 67.5° and 90°, respectively, a retardation variation of as low as ±0.13∘ is observed over the said visible range, indicating the superachromatic nature of the proposed system.

Super-achromatic Quarter-wave Phase Retarder for Visible, Near Infrared and Short Wave Infrared Region Applications-=SUP=-*-=/SUP=-

Phase retarders are essential components in optical system design as they can control the phase shifts associated with the vector components of incoming light waves and hence, decide the state of polarization. Different optical systems are designed to work at different wavelength spectrums. Most of these developments focus on the different wavelength regions between visible to infrared, of which the near infrared and short-wave infrared ranges are popular domains for defense and remote sensing applications. In this present communication, a super achromatic quarter-wave phase retarder consisting of four birefringent plates of different materials, i. e. KDP, crystalline quartz, ADP and ZnS has been proposed, to cover the visible, near infrared and short wave infrared regions from 400-2100 nm. As circularly polarized light is less affected by atmospheric conditions the use of an achromatic broadband quarter-wave phase retarder as proposed is quite useful. The proposed system shows acceptable performance over the intended range of wavelengths. Keywords: Wave plates, Super achromatic, Retarder, SWIR.

Ultrasensitive broadband infrared 4 × 4 Mueller-matrix ellipsometry for studies of depolarizing and anisotropic thin films

The authors present a second-generation broadband 4×4 Mueller-matrix (MM) ellipsometer for ultrasensitive infrared-spectroscopic (8000−800cm−1) studies of complex nanometer-thin films. In a modular design, the instrument employs retractable achromatic retarders and various sets of tandem polarizers. Using high-transmittance free-standing wire-grid polarizers, the device reaches an unparalleled precision of up to 5⋅10−5 in the important fingerprint region, even for block-offdiagonal MM elements. Broadband and signal-to-noise optimized access to the full 4×4 MM provides in-depth information on the sample’s polarimetric properties and opens the door for detailed explorations of depolarizing and anisotropic materials. The authors discuss examples of highly depolarizing nonuniform polyimide membranes, uniaxial-to-biaxial anisotropy changes in ultrathin polymer films, and azimuthal off-axis effects in 2D-structured silica arrays. Diverse optical modeling approaches based upon anisotropic layer stacks and rigorous coupled-wave analysis are used to quantify the optical, structural, and chemical properties of the sample.

An Achromatic Quarter-Wave and Half Wave Phase Retarder Combination Operating in Near Infrared (NIR) Region

Optical phase retarders are major components in design of different optical systems. Normally these retarders exhibit retardance which varies with wavelength. But achromatic phase retardation is necessary in optical system design. These achromatic phase retarders can be designed using different waveplates, sub-wavelength grating (SWG), liquid crystals, and polymers etc in different wavelength ranges. Present communication focus on designing of quarter-wave phase retarder in the near infrared range (NIR) with waveplates of different birefringent materials having different thicknesses. This system in NIR range shows comparable performance with those developed with SWGs and it also removes some drawbacks. The proposed system deals with an achromatic combination of four birefringent plates in 800–2000 nm range using Sapphire, CdSe, Calcite, and Rutile crystals having good transmittance in the NIR range. This system can also be used as a half wave phase retarder in NIR.

Design of a superachromatic quarter-wave retarder for near-infrared region using flower pollination algorithm

Phase retarders normally exhibit strong wavelength dependence. However, for use with polychromatic light, achromatic retarders, which exhibit ideally nearly identical characteristics over a wide wavelength region, are in demand. Designing such a superachromatic retarder is a challenging task for an optical system designer where retardation will be almost constant within a wide range of wavelengths. The present investigation considers a system consisting of wave plates made of different materials, which focus on near-infrared wavelength range, viz. 800 to 2000 nm. Here, a flower pollination algorithm has been used for this nonlinear optimization problem. With the help of the mentioned optimization technique, the optimal values of thicknesses of wave plates are calculated for which the system act as a quarter-wave plate. The obtained result shows a significant improvement in terms of maximum deviation of retardation for the above-mentioned wavelength range. The proposed methodology holds promise for optimizing the design of optical systems.

Broadband infrared Mueller-matrix ellipsometry for studies of structured surfaces and thin films.

We present a high-optical-throughput infrared Mueller-matrix (MM) ellipsometer for the characterization of structured surfaces and ultrathin films. Its unprecedented sensitivity of about 10-4 in the normalized MM elements enables studies of the complex vibrational fingerprint of thin organic films under different ambient conditions. The ellipsometer acquires quadruples of MM elements within a few 10 s to min, rendering it interesting for process and in-line monitoring. It uses retractable achromatic retarders for increased signal to noise, and tandem wire-grid polarizers for improved polarization control. We demonstrate several scientific and industry-related applications. First, we determine the 3D profile of μm-sized trapezoidal SiO2 gratings on Si from azimuth-dependent MM measurements. Data modeling based on rigorous coupled-wave analysis is employed to quantify grating structure and orientation. We then monitor polymer relaxation processes with a time resolution of 47 s. Measurements of polymer films as thin as 7.7 nm illustrate the sensitivity of the device. We finally couple a liquid flow cell to the ellipsometer, highlighting the prospects for in situ infrared MM studies of thin films at solid-liquid interfaces.

Achromatic linear retarder with tunable retardance.

We present a universal design and proof-of-concept of a tunable linear retarder of uniform wavelength response in a broad spectral range. It consists of two half-wave retarders (HWR) between two quarter-wave retarders (QWRs), where the uniform retardance can be tuned continuously by simply rotating one of the HWRs. A proof-of-concept of this design is built by using commercially available Fresnel rhomb retarders that provide retardation with almost wavelength uniformity in the visible and near infrared from 450 to 1550nm. The design is universal, since other achromatic QWRs and HWRs could also be employed. The system is experimentally demonstrated to control the state of polarization of a supercontinuum laser.

Broadband achromatic phase retarder based on metal-multilayer dielectric grating**Project supported by the National Natural Science Foundation of China (Grant No. 11274188)

A new achromatic phase retarder based on a metal-multilayer dielectric grating structure is designed using the rigorous coupled wave analysis method and the genetic algorithm. The optimized phase retarder can maintain phase retardation around 90° from 900 nm to 1200 nm, and the maximum deviation is less than 4.5% while the diffraction efficiencies of TE and TM waves are both higher than 95%. Numerical analysis shows the designed phase retarder has a high fabrication tolerance of groove depth, duty cycle and incident angle. This achromatic phase retarder is simple in design and stable in performance, and can be widely used in optical systems.

Polarization modeling and predictions for DKIST part 2: application of the Berreman calculus to spectral polarization fringes of beamsplitters and crystal retarders

We outline polarization fringe predictions derived from an application of the Berreman calculus for the Daniel K. Inouye Solar Telescope (DKIST) retarder optics. The DKIST retarder baseline design used six crystals, single-layer antireflection coatings, thick cover windows, and oil between all optical interfaces. This tool estimates polarization fringes and optic Mueller matrices as functions of all optical design choices. The amplitude and period of polarized fringes under design changes, manufacturing errors, tolerances, and several physical factors can now be estimated. This tool compares well with observations of fringes for data collected with the spectropolarimeter for infrared and optical regions at the Dunn Solar Telescope using bicrystalline achromatic retarders as well as laboratory tests. With this tool, we show impacts of design decisions on polarization fringes as impacted by antireflection coatings, oil refractive indices, cover window presence, and part thicknesses. This tool helped DKIST decide to remove retarder cover windows and also recommends reconsideration of coating strategies for DKIST. We anticipate this tool to be essential in designing future retarders for mitigation of polarization and intensity fringe errors in other high spectral resolution astronomical systems.

Field deployable pushbroom hyperspectral imaging polarimeter

Hyperspectral imaging polarimetry enables both the spectrum and its spectrally resolved state of polarization to be measured. This information is important for identifying material properties for various applications in remote sensing and agricultural monitoring. We describe the design and performance of a ruggedized, field deployable hyperspectral imaging polarimeter, designed for wavelengths spanning the visible to near-infrared (450 to 800 nm). An entrance slit was used to sample the scene in a pushbroom scanning mode across a 30 deg vertical by 110 deg horizontal field-of-view. Furthermore, athermalized achromatic retarders were implemented in a channel spectrum generator to measure the linear Stokes parameters. The mechanical and optical layout of the system and its peripherals, in addition to the results of the sensor’s spectral and polarimetric calibration, are provided. Finally, field measurements are also provided and an error analysis is conducted. With its present calibration, the sensor has an absolute polarimetric error of 2.5% RMS and a relative spectral error of 2.3% RMS.

A simple analytical method to obtain achromatic waveplate retarders

A new linear and analytical method to design achromatic retarders using waveplates is proposed. The root of this procedure is a generalization of the Hariharan method, which supposes a set of waveplates with fast axes aligned. Hence, it imposes a set of contour conditions over the overall retardation with the aim of determining the thicknesses of the waveplates. Our method proposes a polynomial approximation of the birefringences, thus removing the contour condition. Analytic expressions for calculating the thicknesses of the waveplates are then derived, showing a non-explicit dependence on the wavelength. Moreover, the overall retardation obtained by this method is close to the optimal retardation curve achieved by minimizing the merit function of the achromatism degree.

Effect of tilt on the performance of a quarter-wave prism retarder

The rhomb-type achromatic prism retarder utilizes the phase difference introduced at the glass–air interface, where the beam of light undergoes total internal reflection. With the proper choice of glass materials and the number of total internal reflection, it is possible to obtain a desired phase difference. The phase difference introduced is also dependent on the angle of incidence of the light beam at the glass–air interface. A small change in angle of incidence causes a considerable change in phase difference. The change in the phase difference introduced with the change in external angle of incidence of the light beam in an achromatic prism-type quarter-wave retarder is studied both theoretically and experimentally. The experimental results obtained are found to be in accordance with the theoretical results.

Beam steering for virtual/augmented reality displays with a cycloidal diffractive waveplate.

We proposed a switchable beam steering device with cycloidal diffractive waveplate (CDW) for eye tracking in a virtual reality (VR) or augmented reality (AR) display system. Such a CDW diffracts the incident circularly polarized light to the first order with over 95% efficiency. To convert the input linearly polarized light to right-handed or left-handed circular polarization, we developed a broadband polarization switch consisting of a twisted nematic liquid crystal cell and an achromatic quarter-wave retardation film. By cascading 2-3 CDWs together, multiple diffraction angles can be achieved. To suppress the color dispersion, we proposed two approaches to obtain the same diffraction angle for red, green, and blue LEDs-based full color displays. Our device exhibits several advantages, such as high diffraction efficiency, fast response time, low power consumption, and low cost. It holds promise for the emerging VR/AR displays.