Birefringent Substrates Research Articles

Circular Phase-Dichroism of Chiral Metasurface Using Birefringent Interference.

Circular phase-dichroism (CPD) has been suggested for the characterization of chiral metasurfaces in supplementing the conventional circular dichroism (CD). Conventional CD probes the bulk properties while the CPD, reported recently in 2D chiral metasurfaces using an air-gap Fabry-Perot setup, is based on the surface properties. Here we propose and demonstrate a robust birefringent interference approach to obtain the CPD by replacing the air-gap with a uniaxial birefringent material in which interference is realized by the difference in the refractive indexes for the ordinary and extraordinary components of the material. We measure the transmission phases of metasurfaces fabricated on birefringent sapphire substrates and obtain clear CPDs for chiral metasurfaces but vanishing for achiral metasurfaces. Importantly, our approach can be applied to metasurfaces fabricated on nonbirefringent substrates by add-on birefringent materials. We confirm our results by a Jones matrix method using data obtained from full-wave simulations, and good agreements with experiments are obtained.

Epi-illumination gradient light interference microscopy for imaging opaque structures

Multiple scattering and absorption limit the depth at which biological tissues can be imaged with light. In thick unlabeled specimens, multiple scattering randomizes the phase of the field and absorption attenuates light that travels long optical paths. These obstacles limit the performance of transmission imaging. To mitigate these challenges, we developed an epi-illumination gradient light interference microscope (epi-GLIM) as a label-free phase imaging modality applicable to bulk or opaque samples. Epi-GLIM enables studying turbid structures that are hundreds of microns thick and otherwise opaque to transmitted light. We demonstrate this approach with a variety of man-made and biological samples that are incompatible with imaging in a transmission geometry: semiconductors wafers, specimens on opaque and birefringent substrates, cells in microplates, and bulk tissues. We demonstrate that the epi-GLIM data can be used to solve the inverse scattering problem and reconstruct the tomography of single cells and model organisms.

A novel leaky waveguide grating (LWG) device for evanescent wave broadband absorption spectroscopy in microfluidic flow cells

Evanescent wave (EW) broadband absorption spectroscopy is commonly interfaced with a range of analytical systems, including microfluidic flow cells, for identification and quantitation of species. A miniaturised spectrometer integrated with a microfluidic flow cell is useful to permit on-site analysis of samples. This work reports a novel leaky waveguide grating (LWG) device, which is able to obtain an absorption spectrum of an analyte of interest (in this case, methylene blue) without an external spectrometer. At 600 nm, the spectral resolution and the minimum detectable absorption coefficient of the LWG device is 49.5 nm and 1.65 cm(-1), respectively. The LWG can be fabricated on birefringent substrates such as plastics because the performance of the device is independent of the polarisation of the excitation source. The LWG device was fabricated using microcontact printing and hence can be easily mass produced.

Simulation of light propagation through birefringent substrates with periodical surface microrelief

The simulation of the light diffraction in optical anisotropic materials with the surface microrelief is proposed and improved on the base of approaches developed by Rokushima–Yamakita and Glytsis–Gaylord for layered anisotropic materials. A substrate is divided into a set of thin parallel binary gratings with quasihomogeneous properties along the normal to the layers and then matrices of light wave amplitude at layers’ boundaries are calculated. This optical anisotropic gratings with surface microrelief approach is compared with direct integration of the Maxwell equations by the finite-difference time-domain method. The validity of both methods was checked for gratings with different periods reduced to wavelength as well as for a thin grating. The possibility of creating various optical components on the basis of this effect such as diffraction gratings, optical compensators, and various types of light scattering elements is considered.

A common path interferometer for testing the optical thickness ofpossibly birefringent transparent substrates

We describe a compensated common path lateral shearinginterferometer that allows fast two-dimensional measurements of the opticalthickness of transparent plates. The bench is able to provide accurate resultseven when heterogeneous residual birefringence is present in the sample. Thisbench brings several improvements to an optical system originally built byMr G Nomarski.

Flexible Plastic Liquid Crystal Displays

ABSTRACTFlexible plastic liquid crystal displays (LCDs) offer a number of advantages over traditional glass displays. Roll-to-roll manufacturing of such displays makes possible large size, inexpensive displays. While this type of manufacturing is still in the future, here we report solutions of some of the pressing problems needed to achieve this goal. We utilize liquid crystal effects that do not require polarizers and can therefore utilize commercially available, birefringent substrates such as polyesters and polyethylene terephthalate. We achieve excellent optical and mechanical performance of these flexible displays, even when bent, by creating polymer networks and polymer walls that adhere the front and back substrates and maintain uniform spacing between the substrates. Roll-to-roll processing of flexible plastic displays also requires that the photolithographic techniques used to pattern the electrodes on the current glass LCD’s be replaced by printing techniques and the development of techniques to rapidly etch unwanted electrode material. We must also develop and optimize techniques for rapidly forming polymer walls. Here we report methods of patterning ITO electrodes on flexible plastic substrates using conventional wax transfer printing techniques and rapid etching and cleaning techniques. We also report experiments that elucidate the basic science of rapidly forming polymer walls. We combine these new achievements and understanding and demonstrate their utility by fabricating a flexible plastic LCD using techniques compatible with roll-to-roll manufacturing. Finally, we discuss the critical issues that must be addressed if flexible plastic LCD’s are to reach their full potential.

Image contrast in polarization microscopy of magneto-optical disk data-storage media through birefringent plastic substrates

Using polarized-light microscopy, we have investigated the magnetic domains of perpendicularly magnetized media under several different conditions, including direct observation of the thin-film magnetic layer and observations through the glass or plastic substrates on which the magnetic film was deposited. The results show that the image contrast is reduced with an increasing numerical aperture of the objective lens. They also indicate that the polarization rotation caused by differences between the reflectivity-transmissivity of the p and s components of polarization deteriorate the magnetic image contrast. Furthermore, by comparing the image quality using the same objective lens on samples having different substrates, we found that the images obtained through plastic substrates are worse than those obtained through glass substrates. Birefringence of the plastic substrate is shown to be responsible for the additional degradation of the image contrast.

Polarization-selective computer-generated holograms: design, fabrication, and applications

We constructed polarization-selective computer-generated holograms that apply an independent phase profile during readout by horizontal and vertical light polarizations. These elements are composed of two surface-relief-etched birefringent substrates joined face to face. We describe the design methodology for arbitrary birefringent substrate and gap materials. We show how these holograms are fabricated with standard microelectronics technology and discuss the effects of etching and alignment errors on performance. We demonstrated a diffraction efficiency of 60% with a polarization contrast ratio of >100:1 using a multilevel phase hologram made from two birefringent lithium niobate substrates. We also showed that a single-layer SiO(2) thin-film antireflection coating on all surfaces can reduce reflections from the high-index substrates without significant effect on hologram performance. We also consider some possible applications of this technology and demonstrate experimentally a dual focal-length lens and a self-interconnecting binary 2 × 2 polarization switch.

Polarization-selective computer-generated holograms

We demonstrate polarization-selective computer-generated holograms with independent phase profiles for the two orthogonal linear polarizations. The holograms are made of two surface-relief-etched birefringent substrates joined face to face. We describe their design and fabrication and present experimental results for dual binaryphase computer-generated holograms fabricated in lithium niobate. The first-order diffraction efficiency varied from 6% to 25%, with as much as 40:1 contrast between polarizations. Such elements can be used in compact optoelectronic systems or combined with electro-optic polarization rotators to make electrically controlled optical elements.

Electro-optic waveguide TE ↔ TM mode converter with low drive voltage

We have achieved complete electro-optic TE <--> TM mode conversion in Ti-diffused lithium niobate waveguides with as little as a 2.5-V drive. Because, for birefringent substrates like lithium niobate, TE <--> TM conversion is wavelength dependent, our method is potentially useful for wavelength multiplexing and demultiplexing. Three independently controlled mode converters, each with a 15-A filter bandwidth and with center wavelengths separated by 80 A, have been fabricated on a single substrate.

A ray-optical analysis of thin-film polarization converters

A compact formula is given for the Goos-Haenchen shifts occurring for total internal reflection of light from anisotropic media. This is used in a coupled-wave analysis of polarization conversion in thin-film waveguides deposited on optically birefringent substrates. A numerical example illustrates the considerable influence of the Goos-Haenchen shifts on the conversion length.

Polarization conversion of light in thin-film waveguides

Polarization conversion in optical waveguides on birefringent substrates is discussed with the aid of a coupled wave model. Structures are described which tolerate large thickness variations (up to 45%) while achieving the phase matching necessary for high conversion efficiency. Polarization conversion is experimentally demonstrated in two such arrangements using ADP substrates and organic polymer films. Conversion efficiencies in excess of 98% have been obtained.