Birefringent Thin Films Research Articles

Thickness and birefringence of thin films assessed by interferometry using a low-cost spectrometer

The interference has significant importance from the viewpoints of fundamental science and applications. Though the experimental exercise and assessment based on numerical data are inevitable to understand the interference, it is challenging to perform classwork using spectrometers in a large teaching room due to the high-cost problems. In this work, the authors assessed low-cost spectrometers' availability and analysis methods for transmittance/reflectivity measurements for polymer films and their educational applications. The results show the accuracy and convenience of the apparatus and the methods.

Optical coating on a corrugated surface to align the polarization of an unpolarized wave without loss

A multilayer comprising birefringent thin films is devised to present to function as a polarization beam splitter and waveplate simultaneously. By arranging such a multilayer on a right triangle-shaped corrugated surface, a polarizer is realized to align the randomly oscillating electric field of an unpolarized wave into a linear polarized wave without loss.

Paper No S6.2: An Advanced Optical Thin Film Structure for Fabricating Multidomain Display

AbstractIn this paper, an advanced optical thin film structure, which can be used for fabricating multidomain display is introduced. It is composed of multilayer patterned birefringent thin films, of which each thin film is formed by a liquid crystal (LC) polymer layer with spatially varying optical axes controlled by a patterned photoalignment layer so that it can spatially modulate light propagation directions and polarizations. The overall thickness of the multilayer films, excluding the substrate, can be less than 1 µm, which offers the flexibility to generate high resolution light wavefront structure and the light diffraction within the film is also suppressed. As a result, the optical thin film can be ideally working as a photomask for exposure on a LC photoalignment layer to generate multidomain alignment structures in a single exposure, which can be applied for the manufacturing of LC multidomain displays. To verify the effectiveness of the proposed photomask, a periodic two‐domain thin film structure has been designed and fabricated and a liquid crystal cell with two‐domain alignment structure has been successfully fabricated in a single exposure with the photomask.

Dual-layer ultrathin film optics: I. Theory and analysis

This paper revisits dual-layer ultrathin film optics, which can be used for functional graded refractive index thin film stack. We present the detailed derivation including s-polarized and p-polarized light under arbitrary incidence angle showing the equivalence between the dual-layer ultrathin films and a negative birefringent thin film and also the approximations made during the derivation. Analysis of the approximations shows the influence of thickness of dual-layer thin films, the incidence angle and desired refractive index of the birefringent film. Numerical comparison between the titanium dioxide/aluminum oxide based dual-layer ultrathin film stack and the equivalent birefringent film verifies the theoretical analysis. The detailed theoretical study and numerical comparison provide a physical insight and design guidelines for dual-layer ultrathin film based optical devices.

Dual-layer ultrathin film optics: II. Experimental studies and designs

This paper presents an experimental study of using dual-layer ultrathin films with a high refractive index and low refractive index to approximate a single-layer thin film with an equivalent intermediate refractive index, which is the basis of the functional graded refractive index thin film stack using dual-layer ultrathin films. Using ion beam deposition, five sets of ultrathin films of titanium dioxide (TiO2) and aluminium oxide (Al2O3) are deposited on silicon with different volume fractions and characterized by spectroscopic ellipsometer for the ordinary/extraordinary refractive index and by spectrophotometer for the reflectance. By designing the sequence of TiO2 and Al2O3 ultrathin films, the measured results show a good agreement between the experiments and simulation of the equivalent birefringent thin film. An application example of using the TiO2 and Al2O3 dual-layer ultrathin films to approximate a single-layer antireflection coating for silicon is presented.

Analysis of angular-selective performances of obliquely deposited birefringent thin film

A slanted columnar TiO2 sculptured anisotropic thin film is prepared using the glancing angle deposition (GLAD) technique. We extend the inference regarding the optical properties of a uniaxial birefringent film based on theoretical analysis to include the more general case of a multilayer biaxial birefringent thin film, the optic axis of which is in the incident plane. We also investigate in detail the symmetrical angularselective transmittance performances of TiO2 biaxial anisotropic thin films for light incident at the same angle but coming from opposite sides of the surface normal. The tilted nanocolumn microstructures of the birefringent thin films induce optical anisotropy. The transmisson spectra for the p-polarized wave of TiO2 biaxial anisotropic thin film measured in the experiment almost overlap at the symmetrical oblique incidence at the ±0 angles, which validates our theoretical derivation.

Phase Shift of Polarized Light after Transmission through a Biaxial Anisotropic Thin Film

Based on the theoretical analysis of biaxial birefringent thin films with characteristic matrix method, we investigate the phase shift on transmission of a tilted columnar biaxial film at normal and oblique incidence over 300–1200 nm for s- and p-polarized waves. Compared with the simplified calculation method, the interference effects of the birefringent thin film are considered to yield more accurate results. The quarter wavelength phase shift calculated with the characteristic matrix method is consistent with that monitored with in situ measurement by two-angle ellipsometry, which validates our complied program for the calculation of the phase shift of the biaxial anisotropic thin film. Furthermore, the characteristic matrix method can be easily used to obtain continuous adjustable phase retardation at oblique incidence, whereas the simplified calculation method is valid for the case of normal incidence. A greater generality and superiority of the characteristic matrix method is presented.

Metal oxide morphology in argon-assisted glancing angle deposition

Glancing angle deposition (GLAD) is a thin film deposition technique capable of fabricating columnar architectures such as posts, helices, and chevrons with control over nanoscale film features. Argon bombardment during deposition modifies the GLAD process, producing films with new morphologies which have shown promise for sensing and photonic devices. The authors report modification of column tilt angle, film density, and specific surface area for 12 different metal oxide and fluoride film materials deposited using Ar-assisted GLAD. For the vapor flux/ion beam geometry and materials studied here, with increasing argon flux, the column tilt increases, film density increases, and specific surface area decreases. With a better understanding of the nature of property modification and the mechanisms responsible, the Ar-assisted deposition process can be more effectively targeted towards specific applications, including birefringent thin films or photonic crystal square spirals.

Polarization Fizeau interferometer based on birefringent thin film

A polarization Fizeau interferometer based on birefringent thin film is presented. The interferometer adopts a birefringent thin film to obtain orthogonally polarized and strictly common-path reference and test beams. Advantages include ease of implementation on large-aperture interferometer, measuring test optics from long distance, and achieving high fringe visibility. The phase shift is obtained by combining a quarterwave plate and an analyzer. The concepts illustrated are verified experimentally.

Topics Related to Surface Science in Automobile Industry

Several R & D topics related to surface science in automobile industry are reviewed in chronological order from early 1970s, including topics on instrumental analysis of surfaces, sputtering and plasma processing, birefringent thin films, all optical sensors, transient analyses of surface chemical reactions in automobile catalysts, recordable CD-Rs which can be played in DVD-ROM drives, solar cells and photochemical reduction of CO2.

Periodically Birefringent Thin Films Grown out of the Isotropic Phase of a Bent-Core Banana-Shaped Liquid Crystal

Periodically birefringent thin films growing out of the isotropic phase of the banana-shaped liquid crystal 1,3-phenylene-bis (4-butoxybenzyldiamine) were investigated with polarized optical microscopy. The gown thin films of the periodic modulation of the birefringent index self-assembled by the banana-shaped LC molecules were attributed to the difference of the molecular composing structures. Further the driving forces of the banana-shaped molecular self-assembly were discussed.

Leakage of light in liquid crystal displays and birefringent thin film compensators

This paper elucidates the physical origin of leakage of light in the dark state of liquid crystal displays (LCDs) and describes birefringent thin film compensators to mitigate the problems. There are two fundamental sources of leakage of light in LCDs. They are the leakage of light through a pair of ideal crossed polarizers, and the leakage of light due to elliptical state of polarization after transmitting through the liquid crystal (LC) cell. The leakage of light in the dark state leads to poor contrast ratios and color instability, particularly at large viewing angles. The paper then describes the employment of sixth-wave (λ/6) plates as well as various wave plates that function as birefringent compensators for eliminating the leakage of light in LCDs.

THIRD ORDER NONLINEAR EFFECT NEAR A DEGENERATE BAND EDGE

We describe the properties of a 1D anisotropic periodic structure, designed to have a band edge with fourth order degeneracy, called a degenerate band edge (DBE). A giant field resonance at the transmission peak frequency closest to this band edge has been verified by rigorous numerical calculation and is supported by experimental evidence. Simulations are presented of the consequences of a χ3 nonlinear index change at a DBE resonant frequency which can provide all-optical switching and transmission self-limiting.

Anisotropic optical thin films finely sculptured by substrate sweep technology

In this paper, we have fabricated for the first time films with different orientations of principal axes but similar principal indices and also films with different principal refractive indices but the same orientations of principal axes. During deposition, the deposition angle and the substrate sweep angle are varied to control separately the porosity (refractive principal indices) and column tilt angle (orientations of principal axes) of a birefringent thin film.

Birefringence enhancement in annealed TiO2 thin films

Postdeposition thermal annealing is used to enhance the form birefringence of nanostructured TiO2 thin films grown by electron-beam evaporation using the serial bideposition technique. Thin films were grown on fused silica substrates using oblique deposition angles between 60° and 75° and repetitive 180° substrate rotations to produce birefringent thin films that are structurally anisotropic. Postdeposition annealing in air, between 200 and 900°C, was used to increase the form birefringence of the films by changing the TiO2 phase from the as-deposited amorphous state to a polycrystalline state that exhibits a greater inherent density and larger bulk refractive index. The optical properties, microstructure, and crystallinity were characterized by Mueller matrix ellipsometry, scanning electron microscopy, atomic force microscopy, and x-ray diffraction. It was found that the in-plane birefringence increased significantly upon thermal annealing, in some cases yielding birefringence values that doubled in magnitude, from 0.11 to 0.22 at a wavelength of 550nm for films annealed at 400°C.

Conjugated Polymers Oriented Organic Thin Films for Nonlinear Optics

ABSTRACT Preparation of oriented thin films of a series of soluble conjugated polymers and characterization of linear and nonlinear optical properties is described and discussed. The orientation of polymer chains leads to an enhanced cubic susceptibility, important for the targeted practical applications of these materials. The refractive indices and the optical birefringence of thin films were determined using the m-lines technique. The nonlinear optical properties were measured by optical third harmonic generation technique and by picosecond z-scan method. The figures of merit for the application of PPV-MDMO polymer in all optical switching are derived. The kinetics of chemical degradation of a conjugated π electron polymer was also studied and the degradation rate was measured.

Effect of Molecular Weight on Photoinduced Birefringence in a Chiral Liquid Crystalline Azodye Polymer

AbstractSummary: The evolution of the photoinduced birefringence in thin films of narrow polymer fractions is studied and compared with the behavior of the non‐fractionated polymer. The Δnind value decreases by increasing the degree of polymerization ($\overline {DP}$) within the oligomeric range but becomes independent of molecular weight starting from a $\overline {DP}$ of ≈70. Thermal pretreatment of the films results in higher photoinduced birefringence. The films show good stability of the photorecording.Birefringence induced after 10 min, Δnind(600) and its growth rate at the same moment versus molecular weight.magnified imageBirefringence induced after 10 min, Δnind(600) and its growth rate at the same moment versus molecular weight.

Optical thickness and anisotropic orientation of a birefringent thin film: analysis from explicit expressions for reflection and transmission coefficients

We present explicit expressions for the reflection and trans- mission coefficients of an anisotropic thin film. In the general case, the optical axis and the incident ray are in arbitrary directions. Multireflected ordinary rays and extraordinary rays in the thin film are coupled to each other at the interface. The degrees of polarization conversion for re- flected and transmitted light from the anisotropic thin film are calculated. The transmittance and reflectance are measured by rotating the polar- ization of the normal incident ray, and the columnar growth plane and film thickness are thus determined. © 2006 Society of Photo-Optical Instrumenta-

Study of orientational order in thin films of disklike heptameric polycyclosiloxane molecules by means of the oblique-polarized-ray method

This paper uses the oblique-polarized-ray method to investigate birefringence in thin films of disklike heptameric polycyclosiloxane (HPCS). The surface birefringence B is determined at various temperatures. It is determined that B is independent of T in the region from room temperature to 40°C, while B decreases to zero in absolute magnitude when the samples are heated further. A theoretical estimate is made of the polarizability anisotropy of HPCS molecules as Delta gamma = -450×10^-25 cm^3. The orientational-ordering parameter of the HPCS molecules relative to the interphase boundaries is determined as = -0.25. It is shown that the sixth-order symmetry axes of the HPCS molecules are oriented predominantly perpendicularly relative to the normal to the surface of the layer. A model is proposed for supermolecular structures, associated with the formation of domains in the form of stacks of predominantly parallel disklike HPCS molecules. © 2005 Optical Society of America

Birefringent non-polarizing thin film design

In this paper, 2×2 characteristic matrices of uniaxially anisotropic thin film for extraordinary and ordinary wave are deduced at oblique incidence. Furthermore, the reflectance and transmittance of thin films are calculated separately for two polarizations, which provide a new concept for designing non-polarizing thin films at oblique incidence. Besides, using the multilayer birefringent thin films, non-polarizing designs, such as beam splitter thin film at single wavelength, edge filter and antireflection thin film over visible spectral region are obtained at oblique incidence.