Showing papers on "Birefringence published in 2021"

Giant optical anisotropy in transition metal dichalcogenides for next-generation photonics.

Abstract: Large optical anisotropy observed in a broad spectral range is of paramount importance for efficient light manipulation in countless devices. Although a giant anisotropy has been recently observed in the mid-infrared wavelength range, for visible and near-infrared spectral intervals, the problem remains acute with the highest reported birefringence values of 0.8 in BaTiS3 and h-BN crystals. This issue inspired an intensive search for giant optical anisotropy among natural and artificial materials. Here, we demonstrate that layered transition metal dichalcogenides (TMDCs) provide an answer to this quest owing to their fundamental differences between intralayer strong covalent bonding and weak interlayer van der Waals interaction. To do this, we made correlative far- and near-field characterizations validated by first-principle calculations that reveal a huge birefringence of 1.5 in the infrared and 3 in the visible light for MoS2. Our findings demonstrate that this remarkable anisotropy allows for tackling the diffraction limit enabling an avenue for on-chip next-generation photonics. Optical anisotropy in a broad spectral range is pivotal to efficient light manipulation. Here, the authors measure a birefringence of 1.5 in the infrared range and 3 in the visible light for MoS2.

Hydroxyfluorooxoborate Na[B3O3F2(OH)2]⋅[B(OH)3]: Optimizing the Optical Anisotropy with Heteroanionic Units for Deep Ultraviolet Birefringent Crystals

Abstract: Maximizing the optical anisotropy in birefringent materials has emerged as an efficient route for modulating the polarization-dependent light propagation. Currently, the generation of deep-ultraviolet (deep-UV) polarized light below 200 nm is essential but challenging due to the interdisciplinary significance and insufficiency of high-performing birefringent crystals. Herein, by introducing multiple heteroanionic units, the first sodium difluorodihydroxytriborate-boric acid Na[B3 O3 F2 (OH)2 ]⋅[B(OH)3 ] has been characterized as a novel deep-UV birefringent crystal. Two rare heteroanionic units, [B3 O3 F2 (OH)2 ] and [B(OH)3 ], optimally align to induce large optical anisotropy and also the dangling bonds are eliminated with hydrogens, which results in an extremely large birefringence and band gap. The well-ordered OH/F anions in [B3 O3 F2 (OH)2 ] and [B(OH)3 ] were identified and confirmed by various approaches, and also the origin of large birefringence was theoretically discussed. These results confirm the feasibility of utilizing hydrogen involved heteroanionic units to design crystals with large birefringence, and also expand the alternative system of deep-UV birefringent crystals with new hydroxyfluorooxoborates.

Fluorine-Driven Enhancement of Birefringence in the Fluorooxosulfate: A Deep Evaluation from a Joint Experimental and Computational Study

Abstract: Understanding and exploring the functional modules (FMs) consisting of local atomic groups can promote the development of the materials with functional performances. Oxygen-containing tetrahedral modules are popular in deep-ultraviolet (DUV) optical materials, but their weak optical anisotropy is adverse to birefringence. Here, the fluorooxosulfate group is proved as a new birefringence-enhanced FM for the first time. The birefringence of fluorooxosulfates can be 4.8-15.5 times that of sulfates with the same metal cations while maintaining a DUV band gap. The polarizing microscope measurement confirms the birefringence enhancement by using the millimeter crystals experimentally. The theoretical studies from micro and macro levels further reveal a novel universal strategy that the fluorine induced anisotropic electronic distribution in fluorooxo-tetrahedral group is responsible for the enhancement of birefringence. This study will guide the future discovery of DUV optical materials with enlarged birefringence.

Polarization sensing using submarine optical cables

Abstract: Observation of polarization modulation at the output of a submarine link, extracted from a standard coherent telecom receiver, can be used to monitor geophysical events such as sea waves and earthquakes occurring along the cable. We analyze the effect of birefringence perturbations on the polarization at the output of a long-haul submarine transmission system, and provide analytical expressions instrumental to understanding the dependence of the observed polarization modulation on the amplitude and spatial extension of the observed events. By symmetry considerations, we show that in standard single mode fibers with random polarization coupling, if polarization fluctuations are caused by strain or pressure, the relative birefringence fluctuations are equal to the relative fluctuations of the polarization averaged phase. We finally show that pressure induced strain is a plausible explanation of the origin of polarization modulations observed in a long submarine link. The presented analysis paves the way for the transformation of transoceanic fiber optic links during operation into powerful sensing tools for otherwise inaccessible geophysical events occurring in the deep ocean.

Mg 2 In 3 Si 2 P 7 : A Quaternary Diamond-like Phosphide Infrared Nonlinear Optical Material Derived from ZnGeP 2 .

Abstract: Balancing the second-harmonic generation (SHG) coefficient, band gap, and birefringence is a vital but addressable challenge for designing infrared nonlinear optical materials. By applying a "rigidity-flexibility coupling" strategy, a quaternary diamond-like phosphide, Mg2In3Si2P7, with wurtzite-type superstructure was successfully designed and synthesized. Remarkably, it achieved the rare coexistence of giant second-harmonic generation (2 × ZnGeP2 and 7.1 × AgGaS2), suitable band gap (2.21 eV), moderate birefringence (0.107), and wide IR transparent range (0.56-16.4 μm). First-principles calculations revealed that the giant SHG response and large birefringence can be attributed to the synergy of arrangement-aligned [InP4] and [SiP4] tetrahedra. This work not only opens a new avenue for designing advanced infrared nonlinear optical materials but also may spur more explorations on quaternary diamond-like pnictides.

Sn2PO4I: An Excellent Birefringent Material with Giant Optical Anisotropy in Non π-Conjugated Phosphate

Abstract: Exploring non π-conjugated phosphate birefringent crystal with a large birefringence has been a great challenge. Herein, based on the unique two-dimensional layered structure in KBe2 BO3 F2 (KBBF), two new compounds, Sn2 PO4 I and Sn2 BO3 I, were designed and synthesized successfully, maintaining the layer structural feature and enhancing the optical anisotropy of crystals. In particular, the birefringence of Sn2 PO4 I is larger than or equal to 0.664 @546 nm, which is largest among the reported borates and phosphates, even surpassing commercial birefringent crystals YVO4 and TiO2 . This work indicates that a breakthrough in birefringence of inorganic compound was achieved. Also, it provides a guiding idea for exploring large birefringence materials in the future.

Highly dispersive optical solitons in birefringent fibers with four nonlinear forms using Kudryashov's approach

Abstract: This paper exhibits bright, dark, singular as well as combo optical highly dispersive solitons in birefringent fibers. The governing model is considered with four forms of nonlinear refractive index. The existence criteria for such solitons are also listed.

α-SnF2 : A UV Birefringent Material with Large Birefringence and Easy Crystal Growth.

Abstract: The simple binary fluoride α-SnF2 is shown to be an excellent birefringent material with outstanding birefringence, about 14 times that of MgF2 . Furthermore, it exhibits a shorter UV cutoff edge and easy crystal growth at ambient temperature compared to YVO4 and TiO2 . A novel theoretical calculation mode was established to analyze the stereochemical-activity lone-pair (SCALP) contribution to the birefringence (SCB) based on the SCALP's strength and arrangement, and it was found that the large birefringence of α-SnF2 mainly benefits from well-aligned [SnF5 ] polyhedra with a strong SCALP. The exploration of the α-SnF2 birefringent crystal points out the direction of the future search for excellent birefringent materials.

Solution-processed inorganic perovskite crystals as achromatic quarter-wave plates

Abstract: Waveplates are widely used in photonics to control the polarization of light1,2. Often, they are fabricated from birefringent crystals that have different refractive indices along and normal to the crystal axis. Similar optical components are found in the natural world, including the eyes of mantis shrimp3,4 and the iridescence of giant clams5, fish6 and plants7. Optical retardation in biology relies on sophisticated self-assembly, whereas man-made systems comprise multiple-layered materials8–11. Here we report a discovery that bridges these two design principles. We observe wideband achromatic retardation in the visible and near-infrared (532–800 nm) regions for Cs4PbBr6 perovskite crystals embedded with CsPbBr3 nanocrystals. We explain our observations as matched dispersions of the refractive indices of the ordinary and extraordinary rays caused by the ordered embedding of the nanocrystals in the host. The wideband performance and ease of fabrication of these perovskite materials are attractive for future applications. Perovskite crystals of Cs4PbBr6 embedded with CsPbBr3 nanocrystals are shown to act as wideband, achromatic waveplates in the visible and near-infrared regions.

Robust Angular Anisotropy of Circularly Polarized Luminescence from a Single Twisted-Bipolar Polymeric Microsphere.

Abstract: It has long been surmised that the circular polarization of luminescence (CPL) emitted by a chiral molecule or a molecular assembly should vary with the direction in which the photon is emitted. Despite its potential utility, this anisotropic CPL has not yet been demonstrated at the level of single molecules or supramolecular assemblies. Here we show that conjugated polymers bearing chiral side chains self-assemble into solid microspheres with a twisted bipolar interior, which are formed via liquid-liquid phase separation and subsequent condensation into a cholesteric lyotropic liquid crystalline mesophase. The resultant microspheres, when dispersed in methanol, exhibit CPL with a glum value as high as 0.23. The microspheres are mechanically robust enough to be handled with a microneedle under ambient conditions, allowing comprehensive examination of the angular anisotropy of CPL. The single microsphere is found to exhibit distinct angularly anisotropic birefringence and CPL with glum up to ∼0.5 in the equatorial plane, which is 2.5-fold greater than that along the polar axis. Such optically anisotropic solid materials are important for the application to next-generation microlight-emitting and visualizing devices as well as for fundamental optics studies of chiral light-matter interaction.

Polarization-sensitive optical diffraction tomography

Abstract: Polarization of light has been widely used as a contrast mechanism in two-dimensional (2D) microscopy and also in some three-dimensional (3D) imaging modalities In this paper, we report the 3D tomographic reconstruction of the refractive index (RI) tensor using 2D scattered fields measured for different illumination angles and polarizations Conventional optical diffraction tomography (ODT) has been used as a quantitative, label-free 3D imaging method It is based on the scalar formalism, which limits its application to isotropic samples We achieve imaging of the birefringence of 3D objects through a reformulation of ODT based on vector diffraction theory The off-diagonal components of the RI tensor reconstruction convey additional information that is not available in either conventional scalar ODT or 2D polarization microscopy Finally, we show experimental reconstructions of 3D objects with a polarization-sensitive contrast metric quantitatively displaying the true birefringence of the samples

Series of Crystals with Giant Optical Anisotropy: A Targeted Strategic Research.

Abstract: The main commercially used birefringent oxides α-BaB2 O4 and YVO4 have the birefringences of 0.12 and 0.22. We propose a targeted high-throughput screening system to search birefringence-active functional modules (FMs) and large birefringent materials. A series of π-conjugated C-O units [C2 O4 ]2- , [C2 O6 ]2- , [C4 O4 ]2- , and [C6 O6 ]2- are discovered to be birefringence-active FMs. Theoretical and experimental studies on the crystals with C-O units confirm the feasibility of strategy. Based on this, the C-O containing compounds ranging from deep-ultraviolet to near-infrared region with large birefringence from 0.1 to 1.35 are found, and most of them break through the birefringent limit of oxides. The (NH4 )2 C2 O4 ⋅H2 O crystal is grown and its experimental birefringence is 0.248 at 546 nm, which is identified as a promising UV birefringent crystal. The A-site cations play significant roles in optical properties by influencing the density and arrangement of the C-O units.

Nonlinear Optical Oxythiophosphate Approaching the Good Balance with Wide Ultraviolet Transparency, Strong Second Harmonic Effect, and Large Birefringence

Abstract: Ultraviolet (UV) transparency, second harmonic effect and optical birefringence are three vital but mutually restrictive factors in the application of UV nonlinear optical (NLO) materials. It is difficult for traditional phosphates to achieve a good balance among these factors. In this communication, we propose that the structural evolution of the NLO motif from traditional phosphate to oxythiophosphate would enhance the birefringence and second harmonic generation (SHG) effect while maintaining wide UV transparency, which is confirmed by first-principles calculations and preliminary experimental measurements. Following this strategy, we predict that, compared with the well-known NLO phosphate KH2 PO4 , the oxythiophosphate KH2 PO3 S exhibits better balance for the UV NLO performance, including wide UV transparency (UV cutoff down to 203 nm), strong SHG effect (ca. 0.9 pm V-1 ), and large birefringence (ca. 0.1 at 1 μm) with short phase-matching SHG output wavelength (≈214 nm).

Exploring Deep-UV Nonlinear Optical Materials with Enhanced Second Harmonic Generation Response and Birefringence in Fluoroaluminoborate Crystals.

Abstract: Deep-UV (DUV) nonlinear optical (NLO) materials are of vital importance to demanding DUV laser applications; however, those with a large NLO coefficient, wide band gap, and sufficient phase-matching ability are rare. In this work, by combining π-conjugated B3O6 groups and distort AlO3F tetrahedra, we successfully designed and synthesized two fluoroaluminoborates, RbAlB3O6F (RABF) and Cs0.5Rb0.5AlB3O6F (CRABF). In addition, the solid solution CsxRb1-xAlB3O6F (0.2 < x < 0.8) polycrystalline samples were obtained by the standard solid-state reaction. It was shown that all these compounds are NLO-active and possess short UV cutoff edges (<200 nm). Interestingly, although they have the same fundamental structural units, their crystal structures and second harmonic generation (SHG) responses are significantly different owing to the cation effect. Theoretical calculations reveal that both B3O6 and AlO3F groups contribute to the SHG responses. Remarkably, it also indicates that RABF exhibits a large birefringence (Δn = 0.0946 at 1064 nm), which is capable of realizing deep-UV phase matching down to 174 nm. The exploration of fluoroaluminoborates provides a new perspective for searching excellent deep-UV NLO materials.

Kilobyte Cosmic Birefringence from ALP Domain Walls

Abstract: We propose a simple mechanism of forming ALP domain walls without strings. Such ALP domain walls lead to both isotropic and anisotropic birefringence of cosmic microwave background (CMB) polarization, which reflects spatial configuration of the domain walls at the recombination. The polarization plane of the CMB photon coming from each domain is either not rotated at all or rotated by a fixed angle. For domain walls following the scaling solution, the cosmic birefringence of CMB is characterized by $2^{N}$, i.e. $N$-bit, of information with $N = {\cal O}(10^3)$ being equal to the number of domains at the last scattering surface, and thus the name, $kilobyte~cosmic~birefringence$. The magnitude of the isotropic birefringence is consistent with the recently reported value, while the anisotropic one is determined by the structure of domains at the last scattering surface. The detection of both signals will be a smoking-gun evidence for ALP domain walls without strings.

Survey of third- and fourth-order dispersions including ellipticity angle in birefringent fibers on W-shaped soliton solutions and modulation instability analysis

Abstract: In this work, the modified Sardar sub-equation method is used to construct optical soliton solutions to the coupled nonlinear Schrodinger equation (CNLSE) having third-order and fourth-order dispersions describing short-pulse propagation in two-core fibers. Several solutions are determined including W-shaped bright, dark soliton solutions, singular soliton solutions, periodic function solutions and the combined complex soliton solutions. It should be noted that this integration scheme is very powerful mathematical tools for obtaining exact optical soliton solutions of nonlinear evolution equations. Under suitable values for the physical parameters, some representative wave structures are graphically displayed. In addition, the linear stability technic is used to analyze the modulation gain spectra in the birefringence associated with an ellipticity angle. In our knowledge, these obtained results are new in the context of nonlinear birefringent optical fibers.

Real-time multi-functional near-infrared wave manipulation with a 3-bit liquid crystal based coding metasurface.

Abstract: We propose a new generation of reprogrammable multi-functional bias encoded metasurfaces for dynamic wave manipulation using liquid crystals (LC). This metadevice is an array of unit-cells based on LCs to provide the desired phase steps based on its large birefringence property. The presented 3-bit coding metasurface (CM) use 8 states of "000"-"111" to control and manipulate the scattered wave at λ=1.4µm for several applications. The metasurface is introduced in detail and followed by several examples to show its versatility. Steered pencil, regular, and focused vortex beams with different topological charges are realized. The theoretical predictions are confirmed by numerical simulations. The proposed CM enables the realization of multifunctional optical wavefront manipulation and future intelligent optical devices.

Fast-Response Liquid Crystal for Spatial Light Modulator and LiDAR Applications

Abstract: We report a new nematic mixture for liquid-crystal-on-silicon spatial light modulator (SLM) and light detection and ranging (LiDAR) applications. The mixture exhibits a relatively high birefringence (Δn), moderate dielectric anisotropy (Δɛ), low viscosity, and reasonably good photostability. To achieve 2π phase change at 5 V, the response time (on + off) is 2.5 ms at 40 °C with λ = 633 nm, and 5.9 ms with λ = 905 nm. After exposure by a blue laser (λ = 465 nm) with a total dosage up to 20 MJ/cm2, this mixture shows no sign of photodegradation. Widespread applications of this material for high brightness SLMs, LiDAR, near-eye displays, and head-up displays are foreseeable.

Highly birefringent gold-coated SPR sensor with extremely enhanced amplitude and wavelength sensitivity

Abstract: In this manuscript, we present a unique and simply designed surface plasmon resonance-based PCF biosensor that shows high sensing performance. The numerical technique finite element method is utilized to evaluate the fiber's guiding characteristics. Our design has a thin layer of gold (Au) surrounding the fiber, which is a stable plasmonic material. The strategic arrangement of the circular-shaped airholes inside the fiber enhances the overall performance of the sensor. After precise investigation of the various fiber parameters, the maximum amplitude sensitivity was found to be 3.35 × 103 RIU−1 for x-polarization and 5.00 × 103 RIU−1 for y-polarization in a sensing range of refractive index 1.33–1.41. The sensor exhibited a maximum birefringence of 2.23 × 10–3 and a maximum wavelength sensitivity of 3.00 × 104 nm/RIU and 3.25 × 104 nm/RIU for x- and y-polarization, respectively. The sensor resolution (amplitude) is found to be 2.98 × 10–6 for x-polarization and 2.00 × 10–6 for y-polarization, whereas the sensor resolution (wavelength) is 3.33 × 10–6 and 3.08 × 10–6 for x-polarization and y-polarization, respectively. Moreover, we obtained a high figure of merit of 4.48 × 102 RIU−1 for x-polarization and 4.44 × 102 RIU−1 for y-polarization. For its simplicity in design and high performance, this biosensor has a wide range of applications in the field of sensing unknown biomolecules and organic substances.

Broadband and compact polarization beam splitter in LNOI hetero-anisotropic metamaterials.

Abstract: In this paper, theoretical modeling and numerical simulations of a high-performance polarization beam splitter (PBS) based on hetero-anisotropic metamaterials are proposed on the lithium-niobate-on-insulator (LNOI) platform. The hetero-anisotropic metamaterials constructed by sub-wavelength gratings (SWGs) can be regarded as effective anisotropy medium, which exhibits strong birefringence without breaking the geometrical symmetry, contributing to the formation of PBS. Rather than the principle of PBS based on beat-length difference of transverse electric (TE) polarization and transverse magnetic (TM) polarization, the device can realize polarization beam splitting in single beat length, and the footprint of the proposed PBS can be reduced to 8 µm × 160 µm (with S-bend). The simulation results show that the bandwidth is 185 nm (1450∼1634 nm) for TE polarization while the bandwidth is 85 nm (1490∼1575 nm) for TM polarization when the polarization extinction ratio is >20 dB. Furthermore, the insertion loss is less than 1 dB in the range of 1450 to 1650 nm, for both TE and TM polarization. Additionally, the proposed device proves strong robustness of the fabrication tolerance.

Design and numerical analysis of a gold-coated photonic crystal fiber based refractive index sensor

Abstract: In the course of past decade, surface plasmon resonance (SPR) based photonic crystal fiber (PCF) sensors have shown phenomenal advancement Many researchers have proposed a wider range of SPR-based sensors by this time But many of these proposed sensors either show low sensitivity or it is very difficult to fabricate the sensors for real time applications We present a simple circular shaped PCF SPR sensor which is easy to fabricate as well as shows high sensitivity in the visible and near-infrared spectroscopy A chemically stable and inactive plasmonic material, gold is applied to the outer layer of the PCF structure to generate surface plasmon excitation A perfectly matched layer is used to minimize radiation absorption towards the surface The guiding properties and analytical evaluation are carried out using commercially available COMSOL Multiphysics version 54 on the basis of finite element method In x-polarization mode, the maximal value of amplitude sensitivity and wavelength sensitivity (WS) of the proposed sensor is 17573RIU−1 (Refractive Index Unit) and 32,000 nm/RIU respectively In addition to that, the proposed design exhibits high sensor resolution of 1428 × 10–6 and figure of merit of 5872 indicating a high-performance sensor and demonstrates birefringence of 0004 RIU Moreover, the proposed PCF-SPR sensor is composed of only six symmetrical circular air holes, which makes it fabrication friendly Owing to the high performance of the proposed sensor and high fabrication probability makes the sensor a strong contender to be used in biomedical and biochemical applications

Decagonal solid core PCF based refractive index sensor for blood cells detection in terahertz regime

Abstract: The fast and accurate detection of the blood components is very necessary before initiating the treatment of patients. In this article, a decagonal Solid Core Photonic Crystal Fiber (SC-PCF) sensor with very high sensitivity and low confinement loss for efficiently detecting the blood cells is proposed. The solid core with air hole ring gives an extra edge for sensing the biomedical analytes due to the easy infiltration of liquid in the holes of the core. The material used in the background of the PCF is TOPAS. A Perfectly Matched Layer (PML) is used as boundary condition in outer layer of cladding. The Full-Vectorial Finite Element Method (FV-FEM) is used for solving the Maxwell equation and numerical analysis of the model in the THz regime. In results, the highest sensitivity in the terahertz spectrum for glucose, plasma, WBC and RBC are 84.55%, 85.09%, 85.62% and 87.68% respectively. Specifically, more than 85.09% sensitivity for all the blood components makes this sensor very useful for rapid blood sensing. This paper also analyzes the low confinement loss (CL), high effective mode area, low birefringence and beat length at operating frequency in the terahertz spectrum (1THz–4THz) for all the blood components.

An Antimony(III) Fluoride Oxalate with Large Birefringence.

Abstract: Birefringent materials play a key role in modulating the polarization of light and thus in optical communication as well as the laser techniques and science. Designing new, excellent birefringent materials remains a challenge. In this work, we designed and synthesized the first antimony(III) fluoride oxalate birefringent material, KSb 2 C 2 O 4 F 5 , by a combination of delocalized π -conjugated [C 2 O 4 ] 2- groups, stereochemical active Sb 3+ cations, and the most electronegative F element. The [C 2 O 4 ] 2- groups are not in an optimal arrangement in the crystal structure of KSb 2 C 2 O 4 F 5 . Remarkably, KSb 2 C 2 O 4 F 5 exhibits a large birefringence (Δ n = 0.170 @546 nm) that is even better than the well-known commercial birefringent material α -BaB 2 O 4 , whereas the latter features an optimal arrangement of π -conjugated [B 3 O 6 ] 3- groups. Based on the first-principles calculations, this prominent birefringence should be attributed to the alliance of planar π -conjugated [C 2 O 4 ] 2- anions, highly distorted SbO 2 F 2 and SbOF 3 polyhedra with stereochemical activity lone pair. Combination of lone pair electrons and π -conjugated systems enables to boost the birefringence to a large extent and will help to develop high-performance birefringent materials.