Birefringence Properties Research Articles

Characterization of Birefringent Titanium-Oxide Thin Films Deposited by DC Sputtering

This work presents the characterization of birefringent properties of titanium-oxide thin films using spectrophotometry and double-cavity Fabry-Perot structures. All films were deposited by DC sputtering over tilted substrates and the birefringence was characterized as a function of the deposition angle by the numerical difference between the refractive indexes for s- and p-polarized light beams. As a result, the highest value of birefringence (0.03) was obtained for samples tilted at 21º (having the normal axis as reference). A polarizing narrow-band Fabry-Perot filter centered at 400 and 700nm was designed by means of numerical simulations of the multilayer structures using a MATLAB© toolbox to solve the classical optical equations. Using this designed double-cavity Fabry-Perot structure [Ag(40nm) / TiO2(160nm) / Ag(40nm) / TiO2(164nm) / Ag(40nm)], transmittance ratios (Tp/Ts) for p- and s-polarized light beams resulted 1.70 at a wavelength of 699nm and 1.36 at another wavelength of 393nm (centers of the two narrow-band peaks), which corroborated the birefringent characteristics of the nearly-stoichiometric titania (TiO2) thin films.

Thermodynamic properties for two mixed alkaline earth-transition metal borates of BaZn2B2O6 and Ba2Cd(B3O6)2

Two alkaline-earth metal borates BaZn2B2O6 with NLO property and Ba2Cd(B3O6)2 with birefringent property have been synthesized and characterized by XRD, FT-IR, and chemical analysis. The molar enthalpies of solution of BaZn2B2O6 (s) and Ba2Cd(B3O6)2(s) in 2.00 mL of 1 mol·dm−3 HCl(aq) were measured by microcalorimeter at T = 298.15 K, respectively. The molar enthalpies of solution of CdCl2·2.5H2O(s) and ZnO(s) in the mixture solvent of 2.00 mL of {1 mol·dm–3HCl + H3BO3 + Ba(OH)2·8H2O} (aq) were also measured, respectively. With the incorporation of the previously determined enthalpies of solution of H3BO3 (s) in 2.00 mL of 1 mol· dm–3HCl (aq), Ba(OH)2·8H2O) in the mixture solvent of (2.00 mL of 1 mol·dm−3 HCl + H3BO3) (aq), together with the standard molar enthalpies of formation for CdCl2·2.5H2O(s)/ZnO(s), Ba(OH)2·8H2O(s), H3BO3(s), HCl (aq) and H2O (l), the standard molar enthalpies of formation of – (2703.0 ± 2.2) kJ·mol−1 for BaZn2B2O6 (s) and – (5625.26 ± 5.1) kJ·mol−1 for Ba2Cd(B3O6)2 at T = 298.15 K were obtained on the basis of the appropriate thermochemical cycles.

Polarization state tracing method to map local birefringent properties in samples using polarization sensitive optical coherence tomography.

We propose a method that utilizes the trajectory of output polarization states on the Poincaré sphere to derive depth-resolved birefringent information within samples using a fiber-based polarization sensitive optical coherence tomography. The apparent (or intermediate) optic axis and the local phase retardation are first obtained by fitting a plane to the adjacent output polarization states along depths in the Poincare sphere. A sequence of 3D rotation operation determined by the local birefringent property of the upper layers is then applied to the apparent axis to finally determine the local optic axis. This method requires only one input polarization state and is compatible with both free-space and fiber-based PSOCT systems, simplifying the imaging system setup. The theoretical framework is presented to derive the local phase retardation and optic axis from the output polarization states and then demonstrated by mapping local birefringent information of the mouse thigh tissue in vitro.

Real-time Jones phase microscopy for studying transparent and birefringent specimens.

Tissue birefringence is an intrinsic marker of potential value for cancer diagnosis. Traditionally, birefringence properties have been studied by using intensity-based formalisms, through the Mueller matrix algebra. On the other hand, the Jones matrix description allows for a direct assessment of the sample's anisotropic response. However, because Jones algebra is based on complex fields, requiring measurements of both phase and amplitude, it is less commonly used. Here we propose a real-time imaging method for measuring Jones matrices by quantitative phase imaging. We combine a broadband phase imaging system with a polarization-sensitive detector to obtain Jones matrices at each point in a megapixel scale image, with near video rate capture speeds. To validate the utility of our approach, we measured standard targets, partially birefringent samples, dynamic specimens, and thinly sliced histopathological tissue.

Structure of lead silicate glasses and its correlation with photoelastic properties

Short-range structures of xPbO–(100 − x)SiO2 (x = 50, 60 and 65 mol%) glasses were studied by neutron diffraction and Reverse Monte Carlo modeling. Si–O atomic pair correlation distributions are symmetrical and show peaks in the range: 1.60–1.64 ± 0.02 A. Si4+ are tetrahedrally co-ordinated with oxygen, whereas the Pb–O and O–O atomic pair correlation distributions are broad and asymmetrical due to the existence of wide range of Pb–O and O–O distances in the glass network. The peak positions in the Pb–O atomic pair correlations shift from 2.60 ± 0.05 to 2.42 ± 0.05 A on increasing PbO concentration from 50 to 65 mol%. Pb2+ exist in PbOx (x = 3, 4, 5 and 6) structural units, and the average Pb–O coordination is constant and is in the range of 4.08 ± 0.11 to 4.14 ± 0.08. The O–Si–O bond angles distributions are broad and asymmetrical with peak values in the range of 91° to 109°, and deviate significantly from the value of 109.5° in the ideal tetrahedral structural units. The short-range structural properties of glasses i.e. the cation-oxygen coordination numbers and bond lengths were used to predict the photoelastic properties of the glasses by the Zwanziger model, and it is concluded that xPbO–(100 − x)SiO2 (x = 50, 60 and 65 mol%) glasses should exhibit the properties of zero-stress birefringence.

Diffraction of Electromagnetic Waves from a Round Hole Located between Vacuum and Matter with a Refraction Index Different from One

The diffraction of an electromagnetic wave from a round hole on an opaque screen is studied when there is no vacuum on the opposite sides of the screen, as is usually considered, but on one side there is a refractive medium and on the other—vacuum. The diffraction peculiarities due to the fact that the medium into which the wave penetrates from the vacuum have a refractive index different from one are revealed. The case of diffraction in an anisotropic medium with the property of birefringence is also considered.

Novel input polarisation independent endoscopic cross-polarised optical coherence tomography probe.

Lead by the original idea to perform noninvasive optical biopsies of various tissues, optical coherence tomography found numerous medical applications within the last two decades. The interference based imaging technique opens the possibility to visualise subcellular morphology up to an imaging depth of 3 mm and up to micron level axial and lateral resolution. The birefringence properties of the tissue are visualised with enhanced contrast using polarisation sensitive or cross-polarised optical coherence tomography (OCT) techniques. Although, it requires strict control over the polarisation states, resulting in several polarisation controlling elements. In this work, we propose a novel input-polarisation independent endoscopic system based on cross-polarised OCT. We tested the feasibility of our approach by measuring the polarisation change from a quarter-wave plate for different rotational angles. Further performance tests reveal a lateral resolution of 30 μm and a sensitivity of 103 dB. Images of the human nail bed and cow muscle tissue demonstrate the potential of the system to measure structural and birefringence properties of the tissue endoscopically.

Fabrication and characterization of a novel terpolyester film: An alternative substrate polymer for flexible electronic devices

Designing and development of flexible electronic devices require a detailed investigation of the substrate materials available for the fabrication of the devices. This research work reports the fabrication of a novel film with a copolyester of high trans-1,4-cyclohexandimethanol, terephthalic acid, and naphthalene dicarboxylic acid (PCTN) using melt extrusion. The synthesized amorphous film was uniaxially stretched and thoroughly characterized for their mechanical, thermal, thermo-mechanical, water barrier, and optical (birefringence) properties. Universal testing machine (UTM) and differential scanning calorimetry (DSC) results showed that developed film was having good mechanical and thermal properties, with exceptional dimensional stability, which was confirmed by the thermo-mechanical analyzer (TMA). Results indicated that analyzed properties increase with the increase in the draw ratio (DR). This is due to the increase in the orientation polymeric chains inside the films which were verified by DSC and X-ray diffraction (XRD). Additionally, PCTN film has lower water barrier and birefringence properties compared to conventional polymers such as poly (ethylene terephthalate) (PET), poly (ethylene 2,6-naphthalate) (PEN), and polyimide (PI) films. Based on the exceptional performance properties, novel PCTN film may find a strong position as a substrate for next-generation flexible electronics among various performance materials.

Single-shot multispectral birefringence mapping by supercontinuum vector beams.

We demonstrated a single-shot, multispectral birefringence mapping by use of a supercontinuum (SC) vector beam. The vector beam, which was generated by a pair of axially symmetric wave plates, leads to angular-variant polarization modulation to divide birefringence properties of a sample substrate into Fourier space. This strategy allows multispectral birefringence mapping from a single-shot image captured by a multispectral imaging detector. For SC vector beam analysis, we also compensated the retardance error of the axially symmetric wave plate in the superbroadband spectrum. Resolutions of retardance and azimuthal angle were 0.4° and 0.2°, respectively, and the spatial resolution was 60 µm. Those results are expected to provide us a single-shot, multispectral birefringence mapping with high spatial resolution as compared with using a scanning laser microscope. Our proposal has extendibility to develop high-speed, high-resolution birefringence imaging spectroscopy.

Surface plasmon resonance prism coupler for enhanced circular birefringence sensing and application to non-invasive glucose detection.

A surface plasmon resonance (SPR) prism coupler is proposed for the high-resolution non-invasive (NI) measurement of the circular birefringence (CB) properties of turbid media. The feasibility of the proposed device is demonstrated by means of numerical simulations. It is shown that the SPR sensor enables the CB properties to be detected with a resolution of up to 8.9 × 10-7 RIU (refractive index units) for refractive indices in the range of 1.3∼1.4. Moreover, for tissue phantom solutions containing 2% lipofundin, the device has a detection limit of 3.72 mg/dL. This resolution performance satisfies the detection limit of 10 mg/dL stipulated by the U.S FDA for point-of-care glucose monitoring devices. Thus, the proposed SPR sensor has significant potential for NI glucose sensing in such applications as diabetes detection and management.

Bimetallic Thin-Film Combination of Surface Plasmon Resonance-Based Optical Fiber Cladding with the Polarizing Homodyne Balanced Detection Method and Biomedical Assay Application.

In this work, we present the optical birefringence properties of the optical fiber cladding that exists as an evanescent field where the refractive index (RI) of the analysis solution is applied for optical sensor aspiration. To enhance the performance of the sensor, we have investigated the sensor with different thicknesses of TiO2 coating and bimetallic (Ag-Al) film alloy combinations by thermal evaporation coating. We described a special balanced homodyne detection method for the intensity difference change between the p- and s-polarization lights in the surface plasmon resonance sensing systems, which is strongly determined by the RI of the test medium. The plasmonic optical fiber can measure a very small change of the RI of a glycerol solution, which is a resolution of 4.37 × 10-8 RI unit (RIU). This method has great advantages of a small-sized optical setup, high stability, high selectivity, easy chemical modification, and low cost. Furthermore, because of the experiment results, we observe that our approach can also eliminate the surrounding noise in the Mach-Zehnder interferometer, which shows the feasibility of this proposed technique. We demonstrate the fluorescence enhancement in detecting the C-reactive protein antibody conjugated with fluorescein isothiocyanate by means of near-field coupling between surface plasmons and fluorophores at spectral channels of emission. This technique can also be extended for application in a biomedical assay and in biochemical science, including molecular diagnostics relying on multichannels that require a small volume of the analyte at each channel which would suffer from the weakness of fluorescence if it were not for the enhancement technology.

Photon scattering by a 4π -spherically-focused ultrastrong electromagnetic wave

Author(s): Jeong, TM; Bulanov, SV; Sasorov, PV; Korn, G; Koga, JK; Bulanov, SS | Abstract: The scattering of high-power probe laser pulses by tightly focused ultrastrong laser pulses has been investigated through a semiclassical approach using a perturbative method based on the Born approximation. Under a 4π-spherically-focused ultrastrong light field, the electric permittivity and magnetic permeability tensors for vacuum are calculated from the Euler-Heisenberg Lagrangian to show the nonlinear birefringent property of vacuum. And, from permittivity and permeability tensors, the scattering potential is derived for the Born approximation. The first-order solution of the Born approximation is taken as an electric field scattered from the 4π-spherically-focused laser pulse when a probe laser pulse propagates through the focused laser field. The differential cross section of the nonlinear birefringent vacuum is derived, and the number of photons scattered from the nonlinear birefringent vacuum is analyzed in the laser power range of 10-1000 PW.

Tunable Microwave Photonic Filter Based on LNOI Polarization Beam Splitter and Waveguide Grating

A tunable microwave photonic filter (MPF) based on a polarization beam splitter (PBS) and waveguide grating true-time delay line (TTDL) is proposed and demonstrated experimentally. Taking advantage of the high birefringence property of lithium niobate (LN), the PBS is achieved by a simple structure in a short length. The TTDL consists of an LNOI waveguide grating and flexible electrodes covering along the grating. Owing to the electro-optic effect of LN, a wide tuning range and high tuning accuracy of delay time can be achieved simply by controlling the charging position of the electrodes. With the proposed PBS and TTDL, the MPF exhibits low drive voltage, low power consumption, and high response rate in a simple construction.

Highly sensitive tapered optical fiber coupler-based gas refractive index sensor enhanced by the Vernier effect

Aiming at the problem of the low sensitivity of conventional optical fiber-based gas refractive index sensors, an ultrasensitive tapered optical fiber coupler-based gas refractive index sensor enhanced by the Vernier effect is proposed and demonstrated. The birefringence property of the tapered optical fiber coupler allows it to support two passes of interferences in two orthogonal polarized states, and the superposition of these two interferences forms the Vernier effect. Theoretical analysis and numerical calculations indicate that, for the fiber couplers working in the gas medium when the waist width is within the range of 1.2 to 2.0 μm, the group birefringence difference between the even mode and odd mode equals zero. Thus the sensitivity toward the ambient gas refractive index can be enhanced significantly. To demonstrate these theoretical results, a tapered fiber coupler with a width of 1.6 μm and a length of 16.5 mm was fabricated, and ultrahigh sensitivities up to 22015.4 and −22690.0 nm / RIU were experimentally achieved. The proposed sensor has the merits of being easy to fabricate, having compact structure, and being cost effective. It has significant application prospects in the petrochemical and biomedical detection fields.

Design and analysis of photonic crystal fiber-based plasmonic microbiosensor: an external sensing scheme

In this paper, a highly sensitive gold-coated plasmonic microbiosensor, based on photonic crystal fiber (PCF), is proposed and numerically analyzed. To minimize the fabrication challenge and to aid the real-time detection capability of the sensor, the external sensing approach is utilized here. To introduce birefringence property, two rings with some missing air holes are used. Both the wavelength interrogations, as well as the amplitude interrogation method, have been used to determine the sensitivity of the modeled sensor. To demonstrate better performance, different structural parameters, e.g., the thickness of gold layer, pitch, and the diameter of air holes of the PCF, have been varied and investigated. The sensor shows a maximum possible wavelength sensitivity of 10,000 nm/RIU and a maximum possible amplitude sensitivity of 1250 RIU−1 with a sensor wavelength resolution of $$ 1.0 \times 10^{ - 5} $$ RIU. The proposed sensor exhibits an admirable figure of merit (FOM) of the highest value of 260.86 RIU−1 with an excellent linearity property of resonance wavelength in terms of analyte refractive indices. The designed sensor reveals promise for sensing and detecting different biological and biochemical liquid analytes of refractive index (RI) ranging from 1.33 to 1.39 with having enhanced performance.

Birefringence properties of anti-resonant octagonal-core and nodeless hollow-core fibers.

We present experimental results of birefringence property measurements for two types of negative curvature anti-resonant hollow-core fibers (AR-HCFs). Both AR-HCFs have a core of 50 µm in diameter, providing an effective area of the fundamental guided mode larger than 1000µm2. Measurements were carried out at wavelengths of 2.25, 2.35, and 2.45 µm. The obtained results demonstrate that both fiber types have birefringence axes that do not correspond to core symmetry axes. The proposed technique for the birefringence axes orientation measurement could be applied to other kinds of HCFs at various wavelengths.

Highly Birefringent, Low-Loss, and Near-Zero Flat Dispersion ENZ Based THz Photonic Crystal Fibers

In this paper, we present and compare two experimentally feasible photonic crystal fiber (PCF) designs ( $\textit{Type-I}$ and $\textit{Type-II}$ ) which ensure near-zero flattened dispersion with ultra-high phase and group birefringence at THz frequencies. Both structures are based on a subset of a triangular array of circular air-holes, which define the cladding of the PCF and a central elliptical air-hole which breaks the symmetry of the structure, thus introducing high levels of birefringence. Additionally, we investigate the possibility of further enhancing the birefringence properties of $\textit{Type-II}$ structure by selectively filling the air-holes with Potassium Chloride (KCl) as strong Epsilon-Near-Zero (ENZ) material. Our investigation reveals that significant enhancement of birefringence can be achieved than its original counterpart with birefringence to be as high as 0.0627 at 6.2 THz and near-zero flat dispersion of $-$ 0.54 $\pm$ 0.04 ps/THz/cm over the frequency range of 6.2 $-$ 6.3 THz.

Birefringent and Complex Dielectric Functions of Monolayer WSe2 Derived by Spectroscopic Ellipsometer

Because of its highly anisotropic confinement of its crystal structure, monolayer WSe2 should exhibit a birefringent optical property, i.e., the light of in-plane and vertical polarization will experience different velocity and loss when propagating in the vicinity of such a material. However, most research so far treats monolayer WSe2 as an isotropic material and ignores the important difference upon light–matter interaction at different polarizations. In this work, monolayer WSe2 is studied as a uniaxial crystal with different complex dielectric functions with respect to the in-plane and vertical polarization. The sample is measured by a spectroscopic ellipsometer, followed by a strict modeling process with a series of classic oscillators. The results show that the complex dielectric functions of monolayer WSe2 are clearly polarization-dependent. The obtained data are essential for the design of polarization-dependent integrated optoelectronic devices utilizing monolayer WSe2 as a key functional material.

Detecting human articular cartilage degeneration in its early stage with polarization-sensitive optical coherence tomography.

Detecting articular cartilage (AC) degeneration in its early stage plays a critical role in the diagnosis and treatment of osteoarthritis (OA). Polarization-sensitive optical coherence tomography (PS-OCT) is sensitive to the alteration and disruption of collagen organization that happens during OA progression. This study proposes an effective OA evaluating method based on PS-OCT imaging. A slope-based analysis is applied on the phase retardation images to segment articular cartilage into three zones along the depth direction. The boundaries and birefringence coefficients (BRCs) of each zone are quantified. Two parameters, namely phase homogeneity index (PHI) and zonal distinguishability (Dz), are further developed to quantify the fluctuation within each zone and the zone-to-zone variation of the tissue birefringence properties. The PS-OCT based evaluating method then combines PHI and Dz to provide a G PS score for the severity of OA. The proposed method is applied to human hip joint samples and the results are compared with the grading by histology images. The G PS score shows very strong statistical significance in differentiating different stages of OA. Compared to using the BRC of each zone or a single BRC for the entire depth, the G PS score shows great improvement in differentiating early-stage OA. The proposed method is shown to have great potential to be developed as a clinical tool for detecting OA.

Thermal, Mechanical, and Optical Properties of Maleimide Copolymers Containing Twisted N‐Phenyl Substituents in the Side Chain

AbstractUV absorption spectroscopic measurements and DFT calculations revealed that N‐(alkyl‐substituted phenyl)maleimides with substituents at the ortho position favored a twisted N‐phenyl conformation, due to the steric hindrance between the maleimide ring and the substituted N‐phenyl moiety. High‐molecular‐weight copolymers were synthesized by radical copolymerization of the N‐(alkyl‐substituted phenyl)maleimides with n‐butyl vinyl ether and n‐butyl acrylate. The thermal properties of the copolymers were determined by thermogravimetric analysis and differential scanning calorimetry. The mechanical tensile tests under temperature control revealed the mechanical features of the copolymers depending on their repeating structure and composition. The significant temperature dependence of the modulus and strain of the copolymers was also clarified. Then, the transparency, refractive indices, and birefringence properties of the copolymer films were evaluated. It was confirmed that the maleimide copolymers had negative orientational birefringence with small absolute values and positive photoelastic birefringence. The effect of the conformational structure of the N‐phenyl groups on the thermal, mechanical, and optical properties of the copolymers was discussed.