High Birefringence Research Articles

Deuterated Liquid Crystals – practical synthesis of deuterium labeled 4-alkyl-4″-isothiocyanato-[1,1ʹ:4ʹ,1″]terphenyls

Liquid Crystals, especially materials exhibiting high birefringence are widely utilized in optoelectronic devices. The lifetime of these organic molecules is crucial to the correct operation of devices as they form the “heart” of the device. Exposition on electromagnetic radiation, in particular from UV–VIS region causes excitation of delocalized electrons and their transfer to higher energy levels. Then, photodegradation processes began to dominate inside organic material. Eventually, the operating parameters of the entire device are deteriorated. Herein we present new reinforced molecules which can be favor in the future applications. In this work we developed the synthetic methodology to a highly birefringent mono-, di-, and tri-fluorinated 4-alkyl-4″-isothiocyanato-[1,1ʹ:4ʹ,1″]terphenyls, where deuterium atoms are located at α and β positions of the terminal alkyl chains. These Deuterated Liquid Crystals have excellent isotopic purity ≥ 95%. The synthetic approach involves mainly deuteration reactions of CC bonds by using effective batch system and transformation of amine group (NH2) into isothiocyanate group (NCS) at the last step. These unique materials show higher photochemical stability vs non-deuterated analogs, while maintaining good optical anisotropy simultaneously. Results indicate a high potential use of Deuterated Liquid Crystals in many types of liquid crystalline devices.

High linear polarization, narrow linewidth hybrid semiconductor laser with an external birefringence waveguide Bragg grating.

We demonstrate a high linear polarization, narrow linewidth hybrid laser composed of a semiconductor gain chip and a high birefringence waveguide Bragg grating (WBG). The laser operates in the C-band, and a maximum output power of 8.07 mW is obtained in the fiber waveguide. With careful temperature tuning, the hybrid laser can operate in a single longitudinal mode state from above the threshold current to 410 mA. The side mode suppression ratio (SMSR) reaches a value of 50.2 dB, and the polarization extinction ratio exceeds 39.6 dB. We numerically analyze the linewidth suppression for the Bragg grating based on adiabatic chirp theory. The hybrid laser shows a narrow linewidth of 4.15 kHz and a low relative intensity noise (RIN) of <-155 dBc/Hz, providing a high-performance light source for coherent light communication.

High thermopower and birefringence in layered mercury-based halides

This work presents a theoretical investigation of mercury-based halides in both bulk and monolayer form. These compounds are direct bandgap semiconductors in bulk and monolayer form as it is evident from the analysis of structural and electronic properties. Birefringence values have been used to ascribe anisotropic optical properties, which may host future opto-electronic device applications. The values of mobilities for both the carriers in HgI2 are consistent with the experimental values. The low value of lattice thermal conductivity and favorable carrier mobilities provide a better scope for thermoelectric properties. The least bandgap of HgI2 further enables thermoelectric applications, and the thermopower is found to be high with a value of 580 μV/K for holes and nearly 320 μV/K for electrons. The thermoelectric efficiency for holes is quite appreciable with a figure of merit zT around 0.5 at 300 K for a carrier concentration of 1019 cm−3. In case of monolayers, the thermopower of HgI2 monolayer is found to be higher than its bulk counterpart. Our findings show that these compounds have robust transport and optical properties, which await future experimental verifications.

Compact integral imaging 2D/3D compatible display based on liquid crystal micro-lens array

ABSTRACT We propose a compact integral imaging 2D/3D compatible display based on a liquid crystal (LC) micro-lens array. The LC micro-lens array is combined with a polarisation switching layer (PSL) to realise the rapid switching of the polarisation direction, it’s a micro-lens array under the y-polarised light, and it’s equivalent to a flat glass under the x-polarised light. The proposed 2D/3D compatible display can be switched between the 2D and 3D display mode only by changing the voltage-driving states of the PSL. An LC material with high birefringence is utilised in the LC micro-lens array. Therefore, the fabricated LC micro-lens array has a short focal length. The LC micro-lens array has the advantages of high fill factor (square lens elements), large pitch, and it can be manufactured in large scale. In addition, the large pitch of the LC micro-lens array provides a large viewing angle for the reconstructed 3D image. An LC micro-lens array with a size of 45 mm×40 mm is fabricated and a compact integral imaging 2D/3D compatible display is developed, and the thickness of the integral imaging 2D/3D compatible display is only 13.48 mm. The structure of the proposed display is simple, compact, and easy to implement. Finally, the principle of the proposed 2D/3D compatible display is experimentally verified.

Direct laser writing spiral Sagnac waveguide for ultrahigh magnetic field sensing

A high-birefringence spiral Sagnac waveguide (SSW) device fabricated via direct laser writing (DLW) using a two-photon polymerization (2PP) technique is proposed, designed, and experimentally demonstrated as an ultrahigh magnetic field sensor. The sensor comprises a Y-style tapered waveguide and an SSW containing two microfluidic channels. The SSW has a total length of ∼ 2.4 mm and a spiral radius of ∼ 200 μm . Due to the asymmetric structure, the SSW has a high birefringence of 0.016, which can be designed as a magnetic field sensor, as a magnetic fluid can be filled into the microfluidic channel changing the guiding mode and the birefringence and consequently leading to a change in phase of the interferometer when the applied magnetic field changes. The experimental results show that the proposed photonic device has a sensitivity to magnetic fields as high as 0.48 nm/Oe within a range from 10 to 100 Oe. The proposed device is very stable and easy to fabricate, and it can therefore be used for weak magnetic field detection.

Design of novel models for optical communication with ultra-high non-linearity, birefringence and low loss profile

This study proposes two tellurite-based PCFs whose are OSOC-PCF (Octa-Spiral with Octagonal Cladding PCF) and DSHC-PCF (Dodeca-Spiral with Hexagonal Cladding PCF) designs with higher nonlinearity and higher birefringence. Result comparisons of proposed PCFs are mentioned and demonstrated in this research study. By applying the finite element method with the assistance of COMSOL Multiphysics, we have investigated and simulated guiding properties like nonlinear coefficient, birefringence, dispersion, bending effect, confinement loss, power fraction, effective material loss. Comparing both designs, the highest nonlinearity is gained by OSOC-PCF reaches up to 7333 W−1 Km−1 around 1.55 μm of wavelength and obtained birefringence of 5.85 × 10−2 wherein, a slight confinement loss occurs. The alluded PCFs possess an upstanding structure that associates operating an easy fabrication process. The convenience of propounded PCFs has plenty of purposes in polarization maintenance, optical communication, faster data communication, and super-continuum generation.

Terahertz Sensor via Ultralow-Loss Dispersion-Flattened Polymer Optical Fiber: Design and Analysis.

A novel cyclic olefin copolymer (COC)-based polymer optical fiber (POF) with a rectangular porous core is designed for terahertz (THz) sensing by the finite element method. The numerical simulations showed an ultrahigh relative sensitivity of 89.73% of the x-polarization mode at a frequency of 1.2 THz and under optimum design conditions. In addition to this, they showed an ultralow confinement loss of 2.18 × 10−12 cm−1, a high birefringence of 1.91 × 10−3, a numerical aperture of 0.33, and an effective mode area of 1.65 × 105 μm2 was obtained for optimum design conditions. Moreover, the range dispersion variation was within 0.7 ± 0.41 ps/THz/cm, with the frequency range of 1.0–1.4 THz. Compared with the traditional sensor, the late-model sensor will have application value in THz sensing and communication.

Light-emitting high birefringence chlorinated bistolanes

Eight both symmetrical and non-symmetrical bistolanes with terminal alkyl-, alkoxy- and alkysulphanyl- chain and lateral chlorine atom have been synthesized via Sonogashira cross-coupling and their mesomorphic, optical and photoluminescence properties have been studied. All compounds exhibit enantiotropic nematic and exhibit high value of birefringence (>0.30). The photoluminescence properties both in the diluted solution, solid states and liquid crystal phase were evaluated. Measured compounds emit fluorescence in all states. The correlation between the compounds structure and their properties have been explained using molecular simulation.

Hybrid hollow-core polarization-maintaining fiber with high birefringence and wide single mode bandwidth

A novel hybrid hollow-core polarization-maintaining fiber is proposed by combining the photonic bandgap mechanism and anti-resonant effect. High birefringence can be achieved by introducing a pair of negative curvature anti-resonant layers into the air core of a 7-cell HC-PBGF to obtain two-fold rational symmetry. Within the wavelength range from 1.45 μm to 1.65 μm, the birefringence reaches up to the magnitude order of 10-3 and high-order mode suppression ratio, which is defined as the ratio of the lowest loss of high-order modes to the highest loss of fundamental modes, is greater than 100. Hence, the proposed fiber can realize high birefringence and single mode simultaneously in the 200 nm wide wavelength range. Besides, an extended structure by changing the position of the anti-resonant layers also proves the advantages of hybrid structure in achieving high birefringence and single mode operation. The proposed hybrid structure owns great potential for polarization-sensitive applications and provides a new idea to design hollow-core polarization-maintaining fibers with high birefringence and single mode.

Normal-dispersion CS2-filled silica fiber with broadband single-polarization property

The CS2-filled silica fiber with two air holes in the cladding can offer high nonlinearity, high birefringence and normal group velocity dispersion (GVD) profiles for both two orthogonally polarized fundamental modes (FMs) by an appropriate choice of the fiber parameters. Furthermore, the highly birefringent CS2-filled fiber assisted by two subwavelength-diameter gold wires can exhibit broadband single-polarization (SP) property because that, only the y-polarized FM guided in the CS2-core can couple to the fundamental surface plasmon polariton (SPP) modes with the field vectors along the radial direction, and then has a much larger losses than the x-polarized FM in the wavelength region beyond 1500 nm. The numerical results show that when the 25-kW 0.1-ps pulse at 1920 nm is coupled into the 0.035-m fiber and linearly polarized along the fast axis, the output pulse exhibits over one-octave supercontinuum (SC) spectrum linearly polarized in the fast axis, and can maintain a linear polarization state across the whole SC spectrum even though the input polarization angle increases to 15° from the fast axis.

Fast-Response Liquid Crystals for 6G Optical Communications

We report two high birefringence and low viscosity nematic mixtures for phase-only liquid-crystal-on-silicon spatial light modulators. The measured response time (on + off) of a test cell with 2π phase change at 1550 nm, 5 V operation voltage, and 40 °C is faster than 10 ms. To improve the photostability, a distributed Bragg reflector is designed to cutoff the harmful ultraviolet and blue wavelengths. These materials are promising candidates for future 6G optical communications.

Introduction and measurement of the effective Verdet constant of spun optical fibers.

We introduce the term effective Verdet constant to describe the effect of spun fiber fabrication parameters on the Faraday polarization rotation sensitivity in response to a longitudinal magnetic field along the fiber. We obtain the expression of the effective Verdet constant of a spun fiber showing that it is always less than that of an ideal fiber free of birefringence by a factor relating to the ratio of spin twist rate to unspun fiber retardation per unit length. The larger the ratio, the closer the effective Verdet constant to that of the ideal fiber is. By measuring the polarization rotation in spun fibers with a highly accurate polarization analysis system made with binary polarization rotators, we experimentally obtain the effective Verdet constants of three different high birefringence spun fibers from three different manufactures at 1310 nm, with values of 1.07 × 10-6 rad/A, 1.05 × 10-6 rad/A, and 1.04 × 10-6 rad/A, respectively, which are 98%, 96%, and 95% of that of the ideal fused silica fiber free of birefringence. Our work is important for understanding the Faraday Effect in the spun optical fibers, as well as for quantifying the Faraday sensitivity of different spun fibers for electrical current and magnetic field sensing applications.

In‐Fiber Switchable Polarization Filter Based on Liquid Crystal Filled Hollow‐Filament Bragg Gratings

AbstractFemtosecond laser filaments are formed by surface aberration to open nano‐hole arrays, passing through the silica cladding and guiding core cross‐section of a standard telecommunication fiber. The hollow filament grating presents a strong capillarity effect to draw nematic liquid crystal (NLC) into homogeneous alignment with the cylindrical walls and presents a high birefringent response in the second‐order Bragg stopband. The NLC provides a strong extinction ratio of up to 20 dB over a ≈5 nm band with only a moderate insertion loss of &lt;1 dB arising between the two polarization states of the shifted stopbands. The Bragg grating follows the thermo‐optic response of the NLC to further offer dynamic tuning and switching of the polarization extinction response without an increase in the insertion loss. The flexible laser writing enables tailoring of the Bragg spectral and polarization responses in the telecommunication C‐band.

Electrically Tuning Characteristics of LC Selectively Infiltrated PCF Sagnac Interferometer

A photonic crystal fiber was selectively infiltrated only two of the air holes near the core with liquid crystal. The selective infiltration caused geometric asymmetry and created high birefringence. Because of the geometric asymmetry, the response to varying electric field is concerned with electric field direction. A Sagnac interferometer was set to investigate the electric tuning characteristics of the selectively infiltrated photonic crystal fiber. The effective refractive-indices of the fiber varies with electric field due to reorientation of liquid crystal molecules. The highest sensitivity was 1.12 nm/V (504 nm/kV/mm) with tuning range of 7 nm when electric field direction was parallel to the connecting line of infiltrated holes. The response time of the selectively infiltrated photonic crystal fiber was studied. The device can be utilized as voltage sensors, electro-optical modulators and filters.

Design and characterization of high birefringence three suspended-cores fiber with few-mode

A three suspended-cores fiber (TSF) is proposed. Different to the traditional three-bridge suspended-core fiber, TSF has three suspended-cores with an air-hole in the center. The mode coupling in TSF is analyzed based on the effective area, and the TSF are optimized to support LP01 mode at both C and L wavelength bands and the LP01 mode has only weak coupling between each fiber core. Due to asymmetry fiber core structure and mode compression, the simulated birefringence of the TSF is 9.3×10−3 at 1.55 μm. Despite the large refractive index difference between core and cladding, TSF can be tailored to support only LP01 and LP11 modes.

A large birefringence and high nonlinearity liquid crystal photonic crystal fiber with low confinement loss

Through filling the liquid crystal E7 into the defect position of the photonic crystal fiber (PCF) which possesses full circular air hole structure, a PCF with adjustable optical performance is designed. The effect of external temperature and magnetic field on its optical properties is analyzed by adopting the finite element method. The results reveal that its confinement loss is reduced, and the dispersion performance is also improved. Besides, the high birefringence bandwidth can covers all the S, C, L and U communication bands and the it reaches to the order of 10−1 at the wavelength of 1.55 μm; a high nonlinear coefficients (about 3 × 105 W−1km−1 and 9 × 105 W−1km−1 in X, Y polarization directions respectively) are also obtained. Most importantly, the optical performance can be adjusted without changing its structural parameters. It provides a new method for obtaining PCFs with good optical performance, and it has potential applications in the fields of polarization control, dispersion management, super-continuum generation and optical fiber sensing.

Optical Waveguides and Terahertz Signal by Finite Element Method: A Survey

This paper examines the use of the Finite Element Method (FEM) in the field of optical waveguides and terahertz signals, with the main goal of explaining how this method aids in recent advances in this field. The basics of FEM are briefly reviewed, and the technique's application to waveguide discontinuity analysis is observed. Second-order and higher-order derivatives result from optical waveguide modeling, which is significant for information exchange and many other nonlinear phenomena. The use of FEM in the improvised design of hexagonal sort air hole porous core microstructure fibers, which produces hexagonal structure cladding and rectangular-shaped air holes in the fiber core for excellent terahertz signal transmission, was also observed. These modifications were intended to improve the fiber's properties in comparison to other structures. This approach verifies that the fiber has high birefringence, low material loss, a high-power fraction, and minimal dispersion varia-tion. The features of square-type microstructure fiber are investigated. A folded-shaped po-rous cladding design is recognized for sensing applications. This type of photonic crystal fiber is also known as FP-PCF since it features circular air holes. The most approximate findings of this application are obtained using FEM. In comparison to many other approach-es for various applications, it is evident that FEM is a powerful and numerically efficient tool. This work does a survey of optical waveguides and terahertz signals using the Finite Element Method. Terahertz signals can be used in conjunction with electromagnetic waves to identify viruses. Thus, Terahertz signals are employed in real-world applications such as fuel adulteration, liquid metal synthesis, and virus detection.

Highly birefringent terahertz fiber with split-ring core

We propose a highly birefringent microstructure fiber with a suspended core for terahertz (THz) waveguiding, which only consists of a spilt-ring structure. Significant properties of the fiber including effective refractive index, birefringence and relative absorption loss have been investigated using the finite element method (FEM). In addition, three vital parameters of the fiber are checked to achieve the optimum property. The effects of the shape of gap in the spilt ring on birefringence and relative absorption loss are also studied. According to the simulation result, high birefringence up to the order of 10−2 is achieved. Owing to the ultra simple structure, the proposed fiber is highly potential to be used satisfactorily in commercial THz systems.

An ultra-high birefringent and nonlinear decahedron photonic crystal fiber employing molybdenum disulphide (MoS2): A numerical analysis

A novel Decahedron photonic crystal fiber (DHn-PCF) is proposed. To sustain high birefringence and nonlinearity, the central elliptical core is filled with a highly nonlinear 2D material molybdenum disulphide (MoS2). The significant performance parameters of the proposed DHn-PCF like birefringence, nonlinearity, confinement loss, and core power fraction has been investigated with change in its structural parameters. Simulation results confirmed an exceptionally high birefringence and nonlinearity of 0.632 and 9.68 × 105 W−1 Km−1 with the outstanding core power fraction of 98.6% for the well-known communication window at 1.55μm. Besides, the effective material loss (EML) and confinement loss (CL) are also found very low as 0.0302cm-1 and 8.7×10-10dB/mfor the same communication window. Therefore, with all these excellent outcomes, the proposed DHn-PCF proves itself a potential candidate for polarization maintenance, residual polarization compensation, dispersion compensator, bio-medical imaging, supercontinuum and solitons generation, high bit data rate telecommunication and sensing application.

Slit Beam Shaping for Femtosecond Laser Point-by- Point Inscription of High-Quality Fiber Bragg Gratings

Fiber Bragg gratings (FBGs) inscribed by using femtosecond laser point-by-point (PbP) technology typically have high birefringence due to the elliptical cross-sectional pattern of refractive index modulations (RIMs) created in the fiber core. Additionally, a highly reflective type II PbP FBG, which has a large coupling coefficient, also exhibits large insertion loss due to the limited RIM area induced by a single femtosecond laser pulse. Here we demonstrate a slit beam shaping method for femtosecond laser PbP inscription of high-quality FBGs, featuring by high reflectivity, low insertion loss, and low birefringence. The slit beam shaping method could reduce the ellipticity in the cross-sectional pattern of RIMs without reducing the cross-sectional area, leading to low birefringence and low insertion loss. The experimental results agree well with numerical calculations. Hence, a high-quality type II PbP FBG, which has high reflectivity of 99.12% (i.e., Bragg resonance attenuation of 20.52 dB), low insertion loss of 0.30 dB, and low birefringence of 1.86 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> , was successfully created by use of a slit width of 0.8 mm. Moreover, an enlarged cross-sectional area was created by use of a slit width of 0.2 mm, resulting in a high ratio of 172.46 of the coupling strength coefficient to the scattering loss coefficient in the fabricated PbP FBG, which exhibits very high reflectivity of 99.99% (i.e., a strong Bragg resonance attenuation of 46.65 dB) and low insertion loss of 0.27 dB. Such high-quality FBGs will be promising in many applications, such as optical fiber communications, sensors, and lasers.