High Birefringence Research Articles

一种同时具备显著增强的双折射和二次谐波效应的类BBO三聚硫氰酸盐

There is presently a great demand for nonlinear optical (NLO) crystals that can demonstrate both strong second-harmonic generation (SHG) and high birefringence in emerging spin-orbit angular momentum photonic technologies. Here we report a new chiral trithiocyanate compound, K4(HC3N3S3)2·H2O, which is composed of highly π-conjugated [HC3N3S3]2− rings and is structurally analogous to commercial NLO crystal β-BaB2O4 (BBO). Compared with BBO, which has optimally arranged π-conjugated [B3O6]3− rings, K4(HC3N3S3)2·H2O does not have an optimal arrangement of [HC3N3S3]2− rings. However, this trithiocyanate exhibits a significantly enhanced SHG response of up to 1.8 times that of BBO and an enhanced birefringence of up to 0.402 at the wavelength of 550 nm (about 3.3 times that of BBO). The first-principles calculations show that the π-conjugated [HC3N3S3]2− is the cause of the superior optical properties of K4(HC3N3S3)2·H2O. These findings demonstrate that the π-conjugated [HC3N3S3]2− is an excellent bi-functional “material gene” and merits more attention in the study of optical integrated devices for emerging photonic technologies.

Design of Single-Polarized Single-mode Photonic Crystal Fiber Without Air Holes in the Cladding

This study proposes a novel single-polarized single-mode (SPSM) photonic crystal fiber (PCF) without air holes in the cladding, and the silicon nitride holes and air holes in the core of the PCF are staggered. Based on the full vector finite element method, the birefringence characteristics with different hole sizes have been discussed in detail, and a SPSM-PCF is achieved through optimizing the core structure. Moreover, the extinction ratio, effective refractive index, dispersion, confinement loss and nonlinearity of the PCF are analyzed. Simulation results show that the PCF can obtain a high birefringence value of 2.142 × 10−3 , a large negative dispersion of −2750 ps/(nm · km), a low confinement loss of 1.57 × 10−7dB/m and a high nonlinear coefficient of 90.5W−1 · km−1 at the wavelength of 1.55 μm. In this paper, the proposed structure has the properties of high birefringence and high negative dispersion, which can be used in fiber laser, optical fiber sensing, dispersion compensation and other fields.

Ultra-high birefringence mid-infrared Ge20Sb15Se65 chalcogenide glass photonic crystal fiber with low confinement loss

This study introduces a Ge20Sb15Se65 chalcogenide-glass-based photonic crystal fiber (PCF) with high birefringence and nonlinearity and ultra-low confinement loss, in which two elliptical air holes are added in the core. The propagation properties of the proposed PCF are investigated in mid-infrared range (3.0–5.0 μm) using the finite element method (FEM). Simulation results indicate that optimizing structural parameters can increase the birefringence and nonlinear coefficient to a maximum of 3.16 × 10−1 and 5937 W−1km−1 (in y-polarization mode), respectively, a significantly low confinement loss reach 10−14 dB m−1 at 3.0 μm wavelength, there can obtain one zero dispersion wavelength in the study band, and the designed structure can be fabricated using available technology. The designed PCF will have promising application in mid-infrared fiber fields, optical communication, super-continuum generation, precision, and nonlinear optics.

High birefringence single-polarization composite structured anti-resonant fiber

We propose a highly birefringent, single-polarization composite structured anti-resonant fiber (CS-ARF). The proposed CS-ARF has an elliptical core, two symmetrically spaced arrays of elliptical air holes, and a six-tube anti-resonant structure. The birefringence and single-polarization characteristics of the proposed CS-ARF were analyzed in detail in the mid-infrared band using the finite element analysis method. The results show that the fiber can achieve birefringence up to the order of 10−2 and single-polarization transmission with a confinement loss (CL) below 10−5 dB/m in the mid-infrared band. When the refractive index of the elliptical core is set at na = 2.70, the designed CS-ARF maintains single polarization in the range of 2.5 μm to 3.197 μm with an extinction ratio of up to 1.08 × 107. In addition, we found that by setting the refractive index of the elliptical core, the CL in the y-polarization direction can be effectively adjusted.

Improved Thermal Stability of a Fiber Optic Gyroscope Using a Geometric Birefringence-Enhanced Polarization- Maintaining Fiber

In this paper, we propose and experimentally demonstrate an interferometric fiber optic gyroscope (IFOG) composed of an optimized elliptical-core Panda polarization-maintaining fiber (PMF) based on a comprehensive analysis of the design principle of PMFs for IFOGs. The improvement mechanism of the geometric birefringence on the performance of the Panda PMF was analyzed using the finite element model, and the optimized structural parameters were selected for fiber fabrication. The extinction ratio, polarization crosstalk, and assembled closed-loop IFOG output were tested and compared for fiber coils wound by different fiber structures under different temperature loads. An angle random walk performance of 0.001723 °/√h was achieved, which is a significant improvement over the traditional IFOG. The experimental results confirmed the proposed design basis that the elliptical-core Panda PMF with both higher birefringence and lower effective mode refractive index can improve the temperature stability of the IFOG.

All-Solid Single-Polarization Anti-Resonant Fiber Base on Anisotropic Glass

A single-polarization solid-core anti-resonant fiber is proposed, and the influence of the fiber core material anisotropy of the solid-core anti-resonant fiber on polarization characteristics is investigated using the finite element method. Single-polarization guidance is achieved by using the anisotropy of optical fiber materials, which also ensures high birefringence. The numerical simulation results indicate that there are two single-polarization intervals (1210–1440 nm and 1490–1560 nm), with a maximum bandwidth of up to 230 nm, when the confinement loss difference between the two orthogonal polarizations exceeds two orders of magnitude. Specifically, when the work wavelength is 1550 nm, a polarization extinction ratio (PER) of 108 is obtained by optimizing the structure parameters. Additionally, the y-polarization fundamental mode (YPFM) can be well confined in the fiber center with a low confinement loss of 0.04 dB/m, while the x-polarization fundamental mode (XPFM) has a huge confinement loss larger than 4.65 dB/m due to the coupling with the tube mode. The proposed single-polarization solid-core anti-resonant fiber has a huge potential in applications such as laser systems, fiber-optic gyroscopes, and optical fiber communications.

Continuous fabrication of polarization maintaining fibers via an annealing improved infinity additive manufacturing technique for THz communications.

We report the design and fabrication of a polarization-maintaining fiber for applications in fiber-assisted THz communications. The fiber features a subwavelength square core suspended in the middle of a hexagonal over-cladding tube by four bridges. The fiber is designed to have low transmission losses, high birefringence, high flexibility, and near-zero dispersion at the carrier frequency of 128 GHz. An infinity 3D printing technique is used to continuously fabricate a 5 m-long polypropylene fiber of ∼6.8 mm diameter. The fiber transmission losses are furthermore reduced by as high as ∼4.4 dB/m via post-fabrication annealing. Cutback measurements using 3 m-long annealed fibers show ∼6.5-11 dB/m and ∼6.9-13.5 dB/m losses (by power) over a 110-150 GHz window for the two orthogonally polarized modes. Signal transmission with bit error rates of ∼10-11-10-5 is achieved at 128 GHz for 1-6 Gbps data rates using a 1.6 m-long fiber link. The average polarization crosstalk values of ∼14.5 dB and ∼12.7 dB are demonstrated for the two orthogonal polarizations in fiber lengths of 1.6-2 m, which confirms the polarization-maintaining property of the fiber at ∼1-2 meter lengths. Finally, THz imaging of the fiber near-field is performed and shows strong modal confinement of the two orthogonal modes in the suspended-core region well inside of the hexagonal over-cladding. We believe that this work shows a strong potential of the infinity 3D printing technique augmented with post-fabrication annealing to continuously produce high-performance fibers of complex geometries for demanding THz communications applications.

P‐12.12: Development and Application of High Birefringence Liquid Crystal Materials

The development of new liquid crystal optoelectronic devices, including laser phase modulation, microwave and terahertz devices, requires liquid crystal materials with high birefringence. In this paper, three new molecular design strategies are proposed, including the introduction of olefin chain, lateral fluorine substitution and new ring core. Four new series of isothiocyanate liquid crystal compounds with high birefringence, low melting point and wide nematic temperature range were synthesized. Based on these new liquid crystal compounds, a liquid crystal mixture with nematic temperature range of ‐40~146 ºC and birefringence of 0.42 was developed. At 19 GHz, the new liquid crystal mixture shows excellent dielectric properties, with dielectric anisotropy of 1.28 and dielectric loss of 0.0087. The new liquid crystal mixture also has very low viscoelastic coefficient. The results at 1550nm and 60 ºC show that the response speed can reach 3.6 milliseconds with 2π phase modulation in the reflection mode.

P‐2.30: Design and Fabrication of an Optical Path Folding Pancake Virtual Reality Head‐mounted Display

Metaverse has been going viral across the globe, and virtual reality head‐mounted displays (VR‐HMDs) as the basic infrastructure and entrance to cater to this evolution of social interaction are showing rapid development recently. Pancake optics based on optical path folding provides the feasibility of VR‐HMDs in the form of glasses and is wide recognition. The pancake system has become the current mainstream owing to its large exit pupil diameter (EPD), high resolution, novel compact, and lightweight. Owing to the use of polarization elements, the birefringence in the lens will change the polarization state of the light, resulting in uneven brightness and stray light, seriously reducing the optical performance of the system, so it is necessary to control the birefringence of the lens. In this study, we proposed a pancake system based on a 2.1‐inch LCD display which achieves 10 mm EPD at 11 mm, diagonal field of view (FOV) of 96°, overall length (OAL) of the system less than 20 mm, and support diopter adjustment from ‐7D to ‐1D. The residual birefringence of the lens can be effectively suppressed in four stages: 1) controlling the thickness ratio between the center and the edge of the lens during the optical design, 2) setting a reasonable position and size of the injection gate and cooling system during the mold design process, 3) adopting reasonable injection parameters during the precision injection molding process and 4) eliminating the birefringence of the lens with the lens annealing process. Ultra‐precision machining and correction of the mold cores have been employed to achieve high surface accuracy and low birefringence of the lens. The optomechanical design, assembly, and adjustment process are discussed. Finally, the prototype of the pancake system is experimentally tested, and the results demonstrate pretty well.

47.2: An Essential Role of Diluters on the Fast Response Time for High Birefringence Liquid Crystals

A new liquid crystal diluter was designed and synthesized to balance trade‐offs between low viscosity, high Δn, and large Δε in the LC mixture. Research results indicated that this diluter had excellent properties of low melting point, high Δn, and large Δε. Meanwhile, in a high‐Δn LC mixture, it could effectively reduce the viscoelastic coefficient (γ1/K11), and increase the As while maintaining an equivalent LC phase temperature range and Δn. It means that the LC diluter plays an essential role to improve the response time of LCs.

Optimization of strip-based hybrid plasmonic terahertz waveguide with distributed Bragg reflector layers

In view of recent developments in the utilization of terahertz (THz) communications technology for the increasing demands of high speed and data rates for various wireless applications, this research work targets the design and analysis of distributed Bragg reflector (DBR)-based hybrid plasmonic THz waveguide. This THz waveguide operates at a frequency range from 2.5 to 3.5 THz. The proposed DBR-based hybrid plasmonic THz waveguide consists of DBR layers of gallium arsenide (GaAs) and aluminum arsenide, high-density polyethylene (HDPE) as substrate, a GaAs stripe for wave-guidance, and few layers of graphene layers in HDPE for better confinement. To increase the light confinement between DBR and graphene, a GaAs strip is placed into HDPE. By altering the width and height of the GaAs strip, the parameters birefringence, mode field diameter (MFD), confinement loss, effective mode area, beat length, and dispersion have been fully examined. The obtained simulation results shows high birefringence of 0.6276, maximum MFD of 45 mm, low confinement loss of 7.5 × 10 − 9 mm − 1, high effective mode area of 16.5 mm2, and low anomalous dispersion of 0.0023 (ps/THz/cm) in the range of 2.5 to 3.5 THz. This optimized THz waveguide may helps to enable in guided THz applications for photonic integrated circuits.

Fluorination Improves the Electro-Optical Properties of Benzoxazole-Terminated Liquid Crystals in High Birefringence Liquid Crystal Mixtures: Experimental and Theoretical Investigations.

Aromatic heterocyclic liquid crystal (LC) materials have received much attention from LC chemists for their high birefringence and large dielectric anisotropy, yet few have reported their properties in LC mixtures. In this work, a series of fluorinated benzoxazole liquid crystal compounds were synthesized to evaluate their electro-optical properties in high birefringence LC mixtures, with the expectation of further establishing the theoretical basis and experimental evidence for their applications in LC photonics. Firstly, the effects of the lateral fluorine substituent positions on the molecular synthetic yield, mesomorphic and solubility properties were comparatively investigated. Afterwards, we focused on the fluorination effects on the core electro-optical properties, including birefringence, dielectric anisotropy and further investigation of the viscoelastic coefficient of high birefringence LC mixtures. Research results showed that the benzoxazole liquid crystal compounds possess low melting points, wide nematic phase intervals and good solubility by appropriate lateral fluorine substitution, which is beneficial to further improve the electro-optical properties of high birefringence LC mixtures. Meanwhile, the theoretical and experimental results corroborate each other to well reveal the structure-property relationship. This study demonstrates that fluorination would promote promising applications of benzoxazole-terminated liquid crystals in emerging LC optical devices.

Highly sensitive sensor for simultaneous underwater measurement of salinity and temperature based on highly birefringent asymmetric photonic crystal fiber

This paper describes a novel compact fiber sensor with high sensitivity for the simultaneous measurement of underwater salinity and temperature by simulation. The structure is based on a highly birefringent, asymmetric, full-circular hole photonic crystal fiber (HB-A-FCH PCF), which achieves the birefringence value of 2.83 × 10-3 at the wavelength of 2.2 µm. In addition, with ethanol-filled specific air holes, the temperature sensitivity of HB-A-FCH PCF is remarkably improved. Therefore, considering the high birefringence property, we simulate a Michelson interferometer-based sensor setup with air holes as fluid microchannels and simultaneously measure salinity and temperature through the spectral responses of the x- and y-polarization state. Theoretical analysis shows the sensor can achieve the salinity and temperature sensitivity up to 5.1472 nm/% and −0.8987 nm/°C in x-polarized fundamental mode, respectively, whereas the salinity and temperature sensitivity up to 4.5386 nm/% and −0.8000 nm/°C in y-polarized fundamental mode, respectively.

Difluorovinyl Liquid Crystal Diluters Improve the Electro-Optical Properties of High-∆n Liquid Crystal Mixture for AR Displays.

A liquid crystal (LC) mixture in liquid crystal on silicon (LCoS) is the core material for augmented reality (AR) displays. However, a LC mixture with high birefringence (Δn) and large dielectric anisotropy (Δε) possesses high viscosity (γ1), which results in a slow response time of LCoS devices for AR displays. This work proposes to apply difluorovinyl-based LC diluters to fine balance the low viscosity, high ∆n, and large ∆ε of the LC mixture for a fast response time. Through studying their effects on the key electro-optical properties of a high-∆n LC mixture, it is found that doping these diluter molecules to a high-∆n LC mixture can decrease the viscoelastic coefficient (γ1/K11), increase ∆ε and the figure of merit, maintain a wide nematic phase temperature range, a high clearing point, and ∆n. It also means that these diluters could effectively regulate the relationship between ∆n, ∆ε, and γ1 in the LC mixtures to achieve a fine balance of various excellent properties and further improve the LC device's response time. The widespread applications of these liquid crystal diluters in emerging liquid crystal optical devices are foreseeable.

Function-Versatile Thermo-Optic Switch Using Silicon Nitride Waveguide in Polymer

A function-versatile thermo-optic switch is proposed and experimentally demonstrated using silicon nitride waveguides embedded in polymer cladding. The device consists of a 1 × 2 input splitter, 2 single-mode waveguides for phase shifting, and a thermally controlled 2 × 2 output coupler to give another degree of freedom in achieving phase-matching conditions. Combining the high waveguide birefringence of the thin silicon nitride waveguide and the excellent thermo-optic property of the polymer material, this device can realize multiple functions by applying different micro-heater powers, i.e., polarization-independent path switching, beam splitting, and polarization beam splitting. For the polarization-independent path switching, the fabricated device has shown a crosstalk suppression better than 10 dB for the TE mode and over 20 dB for the TM mode in the wavelength range from 1500 nm to 1620 nm. For the polarization beam splitting function, the device can reach a polarization extinction ratio greater than 10 dB at selected bands. This simple yet scalable device may find applications in polarization-multiplexed optical communication technology and complex photonic computing networks.

Investigating the cross core octagonal photonic crystal fiber with high birefringence: A design and analysis study

In optical communication systems, the quality of transmitted signals can be compromised by random birefringence, which is caused by irregularities in the core-cladding boundaries. To eliminate this problem, high birefringence can be introduced through an asymmetrical fiber structure. Photonic crystal fibers (PCFs) are an ideal solution due to their high intrinsic index contrast and design flexibility, which allows for high birefringence to be achieved. This paper introduces a new PCF design that takes advantage of these features to provide a higher modal birefringence compared to conventional fibers. The design is a cross-core octagonal-shaped fiber, and its performance is evaluated in terms of birefringence and beat length. The results indicate that the proposed fiber provides a birefringence range of 1.3E-3 to 1.6E-3 for a transmission wavelength range of 1.4 μm to 1.8 μm (S, C, and L Bands) and a minimum beat length range of 1.02 mm to 1.12 mm. This fiber design enables long-haul fiber communication without polarization mode dispersion, even under conditions of external perturbation.

Reducing the Power Consumption of VR Displays with a Field Sequential Color LCD

To achieve 60 pixels per degree (PPD) and 100° field of view (FoV) while keeping a reasonably high aperture ratio for active-matrix liquid crystal displays (LCDs), field sequential color (FSC) is a promising approach. We evaluate the physical properties of a high birefringence nematic LC mixture and then use these data to simulate the performance of a fringe-field switching (FFS) LCD. Such an FFS LCD exhibits a fast average gray-to-gray response time (~1.5 ms) to enable FSC operation. By removing the spatial color filters, FSC operation triples the resolution density and optical efficiency, which are critical to high-resolution density and low power consumption virtual reality applications. Wide color gamut (96.2% of the DCI-P3 standard) and superior color uniformity are also demonstrated using such an FSC LCD.

Polarization-maintaining large-mode-area solid-core anti-resonant fiber for high-power fiber lasers

A polarization-maintaining large-mode-area solid-core anti-resonant fiber is investigated in this work with double-layer anti-resonant elements for improved capability on fundamental mode guidance and higher order mode suppression, and structural and material asymmetry on inner-layer cladding tubes for high birefringence. Mode coupling between fundamental core mode in one polarization direction and mode on two high-index inner cladding tubes is used to enhance the fiber birefringence under large core diameter. Eventually, an optimized design of polarization-maintaining large-mode-area solid-core anti-resonant fiber with the currently largest mode field area of 3026 μm2 and birefringence of 1.20 × 10−5 can be anticipated with the confinement losses for all the higher order modes exceeding 10 dB/m. Moreover, confinement loss below 0.1 dB/m can still be obtained for the fundamental core mode in both polarization direction even under the mode-coupling effect. Active polarization-maintaining anti-resonant fiber is analyzed and the refractive index of the central rare-earth-doped region is optimized for the first time for both well guided signal and pump laser. Large pump absorption coefficient can thus be anticipated from the multimode laser core-pumped active large-mode-area fiber, which facilitates short active fiber length needed for sufficient laser gain. The fiber proposed here offers great potential for the development of high-performance fiber laser sources including high-power single-frequency fiber amplifiers and high-peak-power ultrashort pulsed fiber amplifiers.

High birefringence and near‐zero dispersion control of nonlinear photonic crystal fibers with a double‐cladded coaxial core

AbstractOptical propagation characteristics of high birefringence (HB), near‐zero chromatic dispersion, and small effective mode area are first investigated along with simultaneously effective controllability for the new double‐cladded coaxial core photonic crystal fibers with the breakthrough air‐hole defects at the middle‐top, middle‐bottom, right‐top, and left‐bottom, as pairs, which enable the adaptation of novel systematic approach for design goals in the inner first hexagonal cladding layer. Compared with results (around 3.2 × 10−4) of well‐known HB optical fibers, superior performance for preserving the lightwave polarization state by about three times higher HB levels has been achieved with additive advantages of fabrication from only pure fused silica material and broadly unlimited stable single‐mode operation.

Precision mapping of a silicon test mass birefringence

Excellent mechanical and thermal properties of silicon make it a promising material for the test masses in future gravitational wave detectors. However, the birefringence of silicon test masses, due to impurity and residual stress during crystal growth or external stress, can reduce the interference contrast in an interferometer. Using the polarization–modulation approach and a scanning system, we mapped the birefringence of a float zone silicon test mass in the ⟨100⟩ crystal orientation to assess the suitability of such material for future gravitational wave detectors. Apart from the stress-induced birefringence at the supporting area due to the weight of the test mass, the high resolution birefringence map of the silicon test mass revealed a high birefringence feature in the test mass. At the central 40 mm area, birefringence is in the range of mid 10−9 to low 10−8, which satisfy the requirement for future gravitational wave detectors.