Tunable Wave Plate Research Articles

Error analysis based on a tunable wave plate polarization interferometric imaging spectrometer

Interference imaging spectroscopy combines modern imaging technology with spectral technology, holding significant importance for object imaging and spectral detection. This article introduces the principle of an adjustable wave plate polarization interferometric imaging spectrometer. The example design specifications are set for an observation wavelength range of 450–780 nm and a maximum resolution of 2 nm at 450 nm, with a 0.5 in detector as the base for calculating the specific dimensions of the Soleil–Babinet compensator. An investigation was conducted on the issues of nonuniform sampling, as well as three types of mechanical errors: flatness, wedge angle tolerance, and optical axis orientation accuracy. Emphasis was placed on discussing the impact of these errors on the instrument’s optical path difference and spectral reconstruction accuracy. This research provides theoretical guidance for the design and engineering of this miniaturized imaging spectrometer.

Jacobian methods for dynamic polarization control in optical applications.

Dynamic polarization control (DPC) is beneficial for many optical applications. It is often realized via tunable waveplates to perform automatic polarization tracking and manipulation. Efficient algorithms are essential to realize an endless polarization control process at high speed. However, the standard gradient-based algorithm is not well analyzed. Here, we model the DPC with a Jacobian-based control theory framework that finds a lot in common with robot kinematics. We then give a detailed analysis of the condition of the Stokes vector gradient as a Jacobian matrix. We identify the multi-stage DPC as a redundant system enabling control algorithms with null-space operations. An efficient, reset-free algorithm can be found. We anticipate more customized DPC algorithms to follow the same framework in various optical systems.

Broadband Graphene-Based Electro-Optic Chiral Polarization Conversion for Terahertz Pulse Shaping

Terahertz (THz) radiation is ideally suited for noninvasive testing and short-distance data transmission. Actively controlling the polarization of THz waves is highly desirable in measurement systems. Although significant developments of THz active devices has been achieved through introducing the electromagnetic resonance structure (e.g., metamaterials), the bandwidth is limited. Here, we propose a graphene-based electrically reconfigurable polarization conversion across a broadband THz region (0.3 to 0.9 THz) for controlling the chiral polarization of terahertz pulse. By electrically controlling the graphene conductivity, we can switch the device reflection in-between total internal reflection and metal mirror reflection to realize a frequency-independent phase change, which enables a tunable waveplate with a high dynamic range for manipulating the polarization of THz waves. Because of the frequency-independent modulation property, we achieved tunable chiral polarization THz waveforms in the time domain for the first time, from right-handed to left-handed polarization. This work opens up a new mechanism for designing novel THz modulators for THz circular dichroism.

Tunable photonic bandgap and reflection phase shift properties of 1D binary photonic crystal consisting of double negative and magnetic cold plasma materials

In this manuscript, by using alternate layers of double negative and magnetic cold plasma materials, we have studied the reflection and reflection phase shift properties of 1D binary photonic crystals. The simulations of the proposed work have been carried out by using the transfer matrix method with the help of MATLAB software. It has been found that the combination of the angle of incidence and external magnetic field under both right hand polarized and left handed polarized configurations can be used for right and left tuning of photonic bandgap (PBG) of the proposed structure under consideration. Under the aforementioned circumstances, the reflection phase shift corresponding to TE and TM waves can be smoothly switched between 0 to π and –π to 0, respectively, across PBGs of the proposed structure. The variation in external magnetic field values from 0 to 6 T and angle of incidence from 0° to 80° can be used for precise tuning of PBG and reflection phase shift between –π and π depending upon TM and TE polarization cases, respectively. This study may open a new gateway for designing externally tunable microwave devices like single to multichannel band-stop filters, buffers that can hold data temporarily, tunable wave plates, and tunable phase retarders.

Tunable wave plates based on phase-change metasurfaces.

Wave plates based on metasurfaces have attracted intensive attention over the past decade owing to their compactness and design flexibility. Although various wave plates have been designed, their working wavelengths are fixed once they are made. Here we present a study on tunable wave plates based on phase-change metasurfaces made of Ge2Sb2Te5 nanopillar structures. The Ge2Sb2Te5 nanopillars can work as a high-efficiency transmissive half- or quarter-wave plate depending on their structural parameters. The working wavelength of wave plate can be tuned via the phase transition of Ge2Sb2Te5. Moreover, the polarization state of the transmitted light at a fixed wavelength can be modified by changing the crystallinity of Ge2Sb2Te5. The features suggest that tunable wave plates may have applications in optical modulators, molecular detection, and polarimetric imaging.

Switchable Quarter-Wave Plate and Half-Wave Plate Based on Phase-Change Metasurface

Wave plates as important polarization control devices are widely used in the applications of biomedical imaging, fiber optical communication, astronomy, semiconductor industry and aerospace etc. To make the wave plate actively tunable, we propose a rectangular antenna-based metasurface based on the phase-changing material Ge2Sb2Te5 (GST) with high transmittance and polarization conversion rate. Before the GST phase transition, the metasurface operates as a quarter-wave plate in the wavelength range of 10.0–11.9 μm. After the GST turning into crystalline state, the metasurface operates as a half-wave plate in the wavelength range of 10.3–10.9 μm. The physical mechanism for the high transmittance efficiency and polarization conversion rate attributes to the combination of the electric dipole and magnetic dipole resonances. Moreover, the adjustable wavelength range can be further extended by changing the geometry of antenna-based GST to selectively enhancing or suppressing the electric and magnetic resonances. This work provides a new strategy for tunable wave plate, which would have the potential in the application of multi-functional integrated optical systems.

Active polarization control with a parity-time-symmetric plasmonic resonator

Control of the polarization state of light is essential for many technologies, but is often limited by weak light-matter interactions that necessitate long device path lengths or significantly reduce the signal intensity. Here, we investigate a nanoscale plasmonic aperture capable of modifying the polarization state of far-field transmitted light without loss in the probe signal. The aperture is a coaxial resonator consisting of a dielectric ring embedded within a metallic film; parity-time ($\mathcal{PT}$) symmetric inclusions of loss and gain within the dielectric ring enable polarization control. Since the coaxial aperture enables near-thresholdless $\mathcal{PT}$ symmetry breaking, polarization control is achieved with realistic levels of loss and gain. Exploiting this sensitivity, we show that the aperture can function as a tunable waveplate, with the transmitted ellipticity of circularly polarized incident light changing continuously with the dissipation coefficient from $\pi/2$ to 0 (i.e. linear polarization). Rotation of linearly polarized light with unity efficiency is also possible, with a continuously-tunable degree of rotation. This compact, low-threshold, and reconfigurable polarizer may enable next-generation, high-efficiency displays, routers, modulators, and metasurfaces.

Generation of intensity-tunable structural color from helical photonic crystals for full color reflective-type display.

A new concept of intensity-tunable structural coloration is proposed on the basis of a helical photonic crystal (HPC). The HPCs are constructed from a mixture of chiral reactive mesogens by spin-coating, followed by the photo-polymerization. A liquid crystal (LC) layer, being homogeneously aligned, is prepared on the HPCs to serve as a tunable waveplate. The electrical modulation of the phase retardation through the LC layer directly leads to the intensity-tunable Bragg reflection from the HPCs upon the incidence of the polarized light. The bandwidths of the structural colors are found to be well preserved regardless of the applied voltage. A prototype of a full color reflective-type display, incorporated with three primary color units, is demonstrated. Our concept of decoupling two mutually independent functions, the intensity modulation by the tunable waveplate and the color reflection by the HPCs provides a simple and powerful way of producing a full color reflective-type display which possesses high color purity, high optical efficiency, the cycling durability, and the design flexibility.

Tunable wave plate based on active plasmonic metasurfaces.

Polarization conversion is highly desired for numerous valuable applications such as remote detection and high-precision measurement. It is conventionally achieved through utilizing bulky birefringent crystals or by delicate tailored anisotropy materials. However, such schemes are not compatible with both dynamic and compact on-chip applications. We propose an active metasurface that can generate tunable ellipticity for arbitrary incident polarization with a non-volatile and reversible modulation method. The metasurface consists of V-shape plasmonic antenna arrays and an interval modulation layer made of the phase change material GST for active phase control. Our approach allows the generation of high-quality arbitrary elliptical polarization states in an ultrathin, non-mechanical, and flexible fashion, representing a significant advance compared with its conventional counterparts.

Tunable plasmonic thin magneto-optical wave plate

Planar periodic plasmonic structures encased in a magnetic host revealed an unexpected polarization transformation. In the proposed thin periodic gold–garnet layer, the near fields strongly modify (enhance) the magneto-optical response of garnet. We show that the configuration of near fields in the magnetized layer can be engineered so that the layer converts the linear polarization to elliptical (or circular) or rotates the plane of polarization over a large angle in the transmission (or Faraday) geometry. Since the helicity of elliptically (circularly) polarized light (or the polarization rotation angle) is altered by reversing the magnetization of garnet, the considered plasmonic structure acts as a tunable wave plate.

Emerging photonic devices based on photonic liquid crystal fibers

Photonic liquid crystal fibers (PLCFs) define a new class of optical waveguides that combines unique properties of microstructured photonic crystal fibers and liquid crystals. Current progress of research in the field of PLCFs means that a new class of emerging photonics devices can be expected, i.e. tunable attenuators, tunable broad-band filters, tunable polarizers (with an arbitrary PDL and a variable axis of polarization), tunable waveplates, and tunable phase shifters with high retardance will appear in the near future. In this work we would like to discuss this perspective, paying special attention to two most challenging technological issues such as control of LC molecules orientation and permanent connecting of PLCFs to standard fibers. Full text: PDF

Study on the tight focusing of the local elliptically polarized beam

When a radially-polarized beam passes through a wave plate, the polarization distribution of the beam strongly depends on the retardation angle and the spatial position. When the retardation angle is changed from 0 to π, the polarization of the beam becomes the local elliptic polarization with non-uniform polarization distribution. The rotating direction of polarization in the first and third quadrants is opposite to that in the second and fourth quadrants. In this paper we have numerically simulated the transverse and longitudinal electric field intensity, the transverse energy flux and the longitudinal angular momentum of the tightly focused beam in the focal plane. Our results show that the sum of the longitudinal angular momentum in the focal plane is zero, but it is varying in different quadrants. The liquid crystal variable retarder (LCVR) is adopted as a real-time continuous tunable wave plate with its retardation angle δ changing from 0 to π by varying the applied voltage. In this case the phase retardation angle δ introduced by the LCVR can be used as a control over the longitudinal electric field intensity and the longitudinal angular momentum.

Electrically tunable liquid-crystal wave plate using quadripolar electrode configuration and transparent conductive polymer layers

We present the realization of an electrically tunable wave plate, which uses a nematic liquid-crystal (LC) phase retarder that allows fast and continuous control of the polarization state. This device is built using a quadripolar electrode design and transparent conductive polymer layers in order to obtain a uniform electric field distribution in the interelectrode area. With this realization, we obtain a high degree of control of the orientation of the electric field and, consequently, of the LC director. Indeed, this modulator outperforms classical bipolar LC cells in both optical path variation (>4 microm) and LC rotation speed (0.4 degrees/micros).

Aerogel waveplates

Optical transmission measurements were made on 98% porosity silica aerogel samples under various degrees of uniaxial strain. Uniaxially compressed aerogels exhibit large birefringence, proportional to the amount of compression, up to the 15% strain studied. The birefringence is mostly reversible and reproducible through multiple compression-decompression cycles. Our study demonstrates that uniaxially strained high porosity aerogels can be used as tunable waveplates in a broad spectral range.

Continuously tunable all-in-fiber devices based on thermal and electrical control of negative dielectric anisotropy liquid crystal photonic bandgap fibers

We infiltrate photonic crystal fibers with a negative dielectric anisotropy liquid crystal. A 396 nm bandgap shift is obtained in the temperature range of 22-80 degrees C, and a 67 nm shift of long-wavelength bandgap edge is achieved by applying a voltage of 200 Vrms. The polarization sensitivity and corresponding activation loss are measured using polarized light and a full broadband polarization control setup. The electrically induced phase shift on the Poincaré sphere and corresponding birefringence change are also measured. According to the results, tunable wave plates working in the wavelength range of 1520-1580 nm and a potential for realizing a polarimeter working at the 1310 nm region are experimentally demonstrated.

Electrically tunable liquid-crystal wave plate in the infrared

Phase retardance of a liquid-crystal-based, electrically tunable wave plate as a function of voltage and incident light intensity at 10.6 microm is measured using the Stokes-MacCullaugh ellipsometry technique. At intensities of up to 900 W/cm(2), device performance is found to be driven by thermal effects and not optically induced reorientation effects.