Refractive Index Pattern Research Articles

Optical control of orientational bistability in photorefractive liquid crystals

Materials with light-controlled properties are extremely attractive for information technologies and, among the wide range of approaches, that of photorefractive media is particularly relevant1,2. Photorefractivity is observed in photoconductors, where charge carriers photogenerated by non-uniform illumination redistribute over macroscopic distances, and where the resulting electric field modulates the refractive index. This effect has been used in a variety of devices for applications ranging from image treatment to beam steering and medical imaging. Compared with the more commonly studied inorganic crystals, photorefractive non-crystalline organic systems3,4,5,6 offer a more technologically appealing alternative, as these materials are mechanically flexible, can be easily modified chemically and are inexpensive. Here we show how a photogenerated space–charge field can be used to control the switching between the two stable orientational states of ferroelectric liquid crystals. The resulting refractive-index patterns are stable, easily erasable and rewritable. In contrast to more traditional organic photorefractive materials, where the refractive index is continuously modulated by the applied field, the liquid-crystalline device described here is a ‘binary’ system, in which the refractive index n switches between two values (Δn∼3×10−2 in this case, but Δn of the order of 10−1 is, in principle, possible).

Optical circuit design based on a wavefront-matching method

We propose an optical circuit design method for coherent waves as a boundary value problem. The method produces a very compact circuit in which the refractive index pattern is automatically synthesized for given input and output fields with a numerical calculation. We employ the method to design a 1.3/1.55 microm wavelength demultiplexer and also describe the features of a circuit generated by use of the method.

Two-dimensional refractive index patterns with crystalline symmetry

Photosensitive samples of poly-methylmethacrylate containing about 10% residual monomer and the photo-initiator Cp2TiCl2 have been prepared. In a two-beam configuration the formation of a volume phase grating was photo-initiated, and, while the first grating was still growing, a second one was recorded after turning the sample by an arbitrary angle γ. As a result, two-dimensional gratings with the symmetry of a monoclinic crystal (a1 ≠ a2, γ ≠ 90°) were obtained and stabilized by a simple heat treatment.In a diffraction experiment the lattice constants and the amplitudes ΔnI and ΔnII of the overlapping gratings forming the crystal pattern could be deduced from its diffraction pattern and all the diffracted beams were assigned to their Miller indices (h, k).

Direct laser writing of thermally stabilized channel waveguides with Bragg gratings

Thermally stabilized photo-induced channel waveguides with Bragg gratings were fabricated in Ge-B-SiO2 thin glass films by exposure with KrF excimer laser and successive annealing at 600 degrees C. The annealing reversed the photo-induced refractive index pattern and also enhanced its thermal stability. The stabilized channel waveguide with a Bragg grating showed diffraction efficiency of 18.0 dB and 18.7 dB for TE- and TM-like modes, respectively. The diffraction efficiencies and wavelengths for both modes never changed after heat treatment at 500 degrees C, whereas the conventional photo-induced grating decayed even at 200 degrees C.

Preparation of Photo-induced Refractive Index Pattern using Polysilane-Silica Hybrid Thin Films

Preparation of Photo-induced Refractive Index Pattern using Polysilane-Silica Hybrid Thin Films

Reconfigurable electro-optical waveguide for optical processing.

A highly versatile electro-optically induced waveguide is proposed, and some of its applications are discussed. The In(1-s)Ga(s)As(t)P(1-t)-based device can reconfigure an arbitrary refractive-index profile with high speed by using an array of stripe electrodes deposited along the device. This device can act as a variable fractional Fourier transformer or as a beam shaper. Some nonguiding applications based on a specific refractive-index patterning that is normal to the light-propagation direction, such as phase modulation and beam steering, can also be implemented with this device.

Photochemically‐induced refractive index and fluoresence patterning on polymer films

AbstractThe molecular design for large photo‐induced refractive index changes in transparent visible light region was proposed and realized with norbornadiene polymers and poly(vinyl cinnamate). The patterning of pure refractive‐index contract on their transparent films was made with near‐field scanning optical microscopy (NSOM). Reversible fluorescence patterning on polymer films is also presented by using controlled energy transfer from a fluorescent pyromethene to a photochromic diarylethene.

Photoinduced Low Refractive Index Patterning in a Photosensitive Hybrid Material

AbstractLight illumination processing created photoinduced reduction of refractive index as well as volume contraction in an organic-inorganic hybrid material. Whereas both refractive index and film thickness are decreased significantly by the light exposure, transmittance and anti-soiling property of the hybrid film are not affected by the exposure. Direct patterning is possible upon light illumination using the photoinduced change in thickness without any developing process.

Refractive index patterning of tellurite glass surfaces by ultra short pulse laser spot heating

Dot patterns of refractive indices were formed by the laser pulse irradiation on the tellurite glasses. The ternary tellurite glasses of TeO2-Na2O-Al2O3, TeO2-Na2O-GeO2 and TeO2-Na2O-TiO2 doped with 2 mol% of CoO were irradiated by a femtosecond pulse laser beam (800 nm) or by a green light beam (532 nm) from a second harmonic generator of a Q switch pulse YAG laser. The refractive index map of the glass was composed with an He-Ne laser beam by an scanning ellipsometric technique at a resolution of 100 μm × 50 μm, indicating that the spots possessing refractive index lower by about 0.05–0.38 than the surroundings were formed at the region irradiated by the laser beam. The irradiation of the femtosecond laser beam generated the dot patterns roughly equivalent to the beam size. The change of refractive index could be tunable by adjusting laser power, suggesting that the process could be applied to optical recording.

Large Photoinduced Refractive Index Change of Polymer Films Containing and Bearing Norbornadiene Groups and Its Application to Submicron-Scale Refractive-Index Patterning

We measured photoinduced refractive index changes of polymer films containing various norbornadiene compounds. Poly(methyl methacrylate) (PMMA) films containing 51.6 wt% of 5,6-(2-benzofuryl)-2,3-di(trifluoromethyl)-1,4,7,7-tetramethyl-2,5-norbornadiene (NBD4) showed refractive index changes of 0.037 during photoisomerization. A polymer film bearing thiophenyl- and benzofuryl- substituted norbornadiene groups (PolyTBFNBD) showed a refractive index change of 0.05–0.06 for 594–632.8 nm during photoisomerization. This value is the largest value of refractive index change so far in a nonresonant region induced by photochemical reactions. Submicron-scale patterning of pure refractive-index contrast on the PolyTBFNBD film was also demonstrated by using near-field scanning optical microscopy (NSOM).

Hot-wire deposition of photonic-grade amorphous silicon

A new amorphous silicon application related to the patterning of refractive index for the purpose of defining and integrating photonic-device elements is emerging. Photonic device elements include waveguides, splitters, mirrors, optical memories, etc. Hot-wire-deposited amorphous silicon has several attributes that make it an exceedingly attractive matrix for photonic device patterning, including: high hydrogen solubility limits; relatively little sub-gap absorption; low stress; non-peeling films; and fast, economical deposition of thick (≥5 μm) films, as well as optically smooth as-deposited surfaces, even on thick films. The growing catalog of proposed and/or demonstrated amorphous silicon-based optical devices is rapidly expanding.

Holographic scattering as a technique to determine the activation energy for thermal fixing in photorefractive materials

We introduce holographic scattering as a technique to determine the activation energy for thermal fixing of refractive index patterns in photorefractive crystals. After recording a parasitic hologram at ambient temperature, we measured the time dependence of the transmitted intensity at the fixing temperature, to determine the time constant. The temperature dependence of the latter allowed us to evaluate the thermal activation energy. For comparison, we performed an equivalent experiment employing the standard two-wave mixing method. The values obtained using the two techniques agree very well.

Refractive-index patterning using near-field scanning optical microscopy

By using near-field scanning optical microscopy (NSOM), patterning of pure refractive-index contrast on a transparent polymer film has been demonstrated. A thin film of poly(methyl methacrylate) doped with 3-phenyl-2,5-norbornadiene-2-carboxylic acid is irradiated with 325 nm UV light from an NSOM probe, resulting in a refractive-index decrease without changes in complete transparency in the visible region and surface flatness. The transmission NSOM image was obtained by the same probe at an incident wavelength of 442 nm. The relative change of the transmission signal is in agreement with the value deduced from a simple model based on the Rayleigh scattering theory of dielectric media.

Optically defined multifunctional patterning of photosensitive thin-film silica mesophases.

Photosensitive films incorporating molecular photoacid generators compartmentalized within a silica-surfactant mesophase were prepared by an evaporation-induced self-assembly process. Ultraviolet exposure promoted localized acid-catalyzed siloxane condensation, which can be used for selective etching of unexposed regions; for "gray-scale" patterning of refractive index, pore size, surface area, and wetting behavior; and for optically defining a mesophase transformation (from hexagonal to tetragonal) within the film. The ability to optically define and continuously control both structure and function on the macro- and mesoscales is of interest for sensor arrays, nanoreactors, photonic and fluidic devices, and low-dielectric-constant films.

Operating characteristics of an optical filter with a linearly periodic refractive index pattern in the range of ultraviolet light

Using a linear periodic refractive index pattern on the macroscopic scale in a suitable material, a new type of ultraviolet filter is suggested. This structure is able to act as an efficient ultraviolet monochromator. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 23: 36–38, 1999.

Optically induced domain waveguides in SrxBa1−xNb2O6 crystals

Optically induced refractive index patterns, which can be used for waveguides, were formed in SrxBa1−xNb2O6 crystals using an erasable fixing mechanism, based on domains formation by the screening effect. The sign and strength of the refractive index change of the fixed waveguides was controllable by an applied electric field. Fixed patterns are shown to allow the storage of many spatially multiplexed holograms.

Optical Waveguides in Lead Germanate Formed by MeV Proton and Helium Ion Implantation

physica status solidi (a)Volume 166, Issue 1 p. R3-R4 Rapid Research Note Optical Waveguides in Lead Germanate Formed by MeV Proton and Helium Ion Implantation D. Kip, D. Kip Universität Osnabrück, Fachbereich Physik, D-49069 Osnabrück, GermanySearch for more papers by this authorS. Mendricks, S. Mendricks Universität Osnabrück, Fachbereich Physik, D-49069 Osnabrück, GermanySearch for more papers by this authorP. Moretti, P. Moretti Laboratoire de Physico-Chimie des Matériaux Luminescents, Université Claude Bernard Lyon 1, 69 622 Villeurbanne, FranceSearch for more papers by this author D. Kip, D. Kip Universität Osnabrück, Fachbereich Physik, D-49069 Osnabrück, GermanySearch for more papers by this authorS. Mendricks, S. Mendricks Universität Osnabrück, Fachbereich Physik, D-49069 Osnabrück, GermanySearch for more papers by this authorP. Moretti, P. Moretti Laboratoire de Physico-Chimie des Matériaux Luminescents, Université Claude Bernard Lyon 1, 69 622 Villeurbanne, FranceSearch for more papers by this author First published: 29 January 1999 https://doi.org/10.1002/(SICI)1521-396X(199803)166:1<R3::AID-PSSA99993>3.0.CO;2-ECitations: 2AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume166, Issue1March 1998Pages R3-R4 RelatedInformation

Thermally induced self-focusing and optical beam interactions in planar strontium barium niobate waveguides

We present an experimental study of thermally induced self-focusing effects and interactions of incoherent light beams in strontium barium niobate waveguides. Depending on the input power, a single parallel beam is strongly focused inside the sample up to diameters of several micrometers. For higher input power we observe the splitting of the beam in a sequence of several spots. We demonstrate that these thermally induced refractive-index patterns can be used to focus and deflect an incoherent guided probe beam in the waveguide with time constants below 1 ms.

Refractive-index patterning of tellurite glass surfaces by laser spot heating

A dot pattern of a refractive-index change was formed by spot heating with laser-beam irradiation on sodium tellurite glasses. The 15Na2O.85TeO2 (mol. %) glass doped with 2 mol. % of CoO was irradiated by a green light-beam spot (532 nm) approximately 800 microm in diameter from the second-harmonic generator of a Q-switched pulsed YAG laser. The map of the refractive index of the glass was determined with an He-Ne laser beam by a scanning ellipsometric technique at a resolution of 100 microm x 50 microm, indicating that the spots possessing a refractive index lower by approximately 0.05 were formed at the region irradiated by the laser beam.

A high resolution real-time temporal heterodyne interferometer for refractive index topography

A Mach-Zehnder interferometer for two-dimensional refractive index topography is presented which utilizes the temporal heterodyne technique. High scanning rates and excellent phase resolutions are obtained using an image dissector camera and a lock-in amplifier. The setup is applied for investigation of the photorefractive effect. A macroscopic light pattern is recorded and thermally fixed in iron-doped LiNbO3. The evolution of the refractive index pattern during development by homogeneous illumination is observed with the interferometer. The measured refractive index profiles are in good agreement with the results of computer simulations.