Resonant and Sensing Performance of Volume Waveguide Structures Based on Polymer Nanomaterials.

Organic-inorganic photocurable nanocomposite materials are a topic of intensive research nowadays. The wide variety of materials and flexibility of their characteristics provide more freedom to design optical elements for light and neutron optics and holographic sensors. We propose a new strategy of nanocomposite application for fabricating resonant waveguide structures (RWS), whose working principle is based on optical waveguide resonance. Due to their resonant properties, RWS can be used as active tunable filters, refractive index (RI) sensors, near-field enhancers for spectroscopy, non-linear optics, etc. Our original photocurable organic-inorganic nanocomposite was used as a material for RWS. Unlike known waveguide structures with corrugated surfaces, we investigated the waveguide gratings with the volume modulation of the RI fabricated by a holographic method that enables large-size structures with high homogeneity. In order to produce thin photosensitive waveguide layers for their subsequent holographic structuring, a special compression method was developed. The resonant and sensing properties of new resonant structures were experimentally examined. The volume waveguide gratings demonstrate narrow resonant peaks with a bandwidth less than 0.012 nm. The Q-factor exceeds 50,000. The sensor based on waveguide volume grating provides detection of a minimal RI change of 1 × 10-4 RIU. Here we also present the new theoretical model that is used for analysis and design of developed RWS. Based on the proposed model, fairly simple analytical relationships between the parameters characterizing the sensor were obtained.

Optical and Nonlinear Properties of Photonic Polymer Nanocomposites and Holographic Gratings Modified with Noble Metal Nanoparticles.

Nanocomposites based on transparent polymer matrices containing nanoparticles (NPs) of noble metals are modern-day materials that can be specially designed for photonics, linear and nonlinear optics, laser physics and sensing applications. We present the improved photosensitive nanocomposites doped with Au and Ag NPs allowing fabrication of high effective submicrometer dimensional diffraction structures using holographic method. A general approach for the fabrication of holographic structures using a two-component mixture of the monomers of different reactivity was developed. Two different methods, ex situ and in situ, were studied to introduce Au and Ag NPs in the polymer matrix. The diffusion model of the grating formation upon holographic exposure as well as the process of Ag NP synthesis in a polymer matrix is considered. The influence of the NP size on the polymerization process, material dynamic range and nonlinear properties were investigated. The mechanisms and characteristics of the nanocomposite nonlinear optical response are discussed.

Polarization Gratings in Azobenzene-Based Fully Liquid Crystalline Triblock Copolymer.

Photosensitive liquid crystalline (LC) block copolymers are a universal platform for designing functional materials for optics and photonics. Here, azobenzene LC ABA triblock copolymer containing mesogenic groups in each block is studied as a medium for the recording of polarization holographic gratings. The fast recording of polarization gratings is successfully performed with two orthogonally circularly polarized light beams of a 532-nm laser. It is shown that annealing of the recorded polarization grating increases diffraction efficiency considerably, by a factor of 70, and provokes simultaneous erasing of the surface relief grating if it has been recorded. Holographic behavior of the triblock copolymer is compared with that of an azobenzene homopolymer and a random copolymer, which has the same monomer ratio as the triblock copolymer. The obtained results are expected to allow designing new materials for the polarization of optical elements and holographic data storage.

Continuously tunable polymer membrane laser.

Thin-film organic distributed feedback (DFB) lasers processed with elastomeric polymers allow fabrication of flexible and continuously tunable coherent light sources. So far, the realized laser devices fall short on broad continuous tuning range. We demonstrate that the addition of plasticizers to the polymer matrix and the minimization of the thickness of the laser can reduce mechanical impact and, thus, extend the wavelength tuning range to the full gain range of the active medium. A contact-transfer method is used to transfer gently the ultra-thin membrane DFB laser to a silicone support. A continuous tuning of the laser wavelength up to 77 nm in the orange-red spectral range of a single laser dye was achieved by mechanical stretching of the supporting film with a DFB membrane laser on top.

Holographic Structuring of Elastomer Actuator: First True Monolithic Tunable Elastomer Optics.

Volume diffraction gratings (VDGs) are inscribed selectively by diffusive introduction of benzophenone and subsequent UV-holographic structuring into an electroactive dielectric elastomer actuator (DEA), to afford a continuous voltage-controlled grating shift of 17%. The internal stress coupling of DEA and optical domain allows for a new generation of true monolithic tunable elastomer optics with voltage controlled properties.

Stable selective gratings in LC polymer by photoinduced helix pitch modulation.

A cholesteric mixture based on the nematic liquid crystalline side-chain polymer doped with a chiral-photochromic compound was prepared and used as an active medium for creation of stable polarization selective gratings by phototunable modulation of the helix pitch. Such modulation was fabricated in the polymer mixture by a nonpolarized UV-irradiation with spatially modulated intensity that causes E-Z isomerization of a chiral-photochromic dopant, decreasing its helical twisting power. It was shown that the gratings recorded by UV-exposure through a mask are strongly selective to the handedness of circular polarized light. The studied polymer film forms a right-handed helical structure and, correspondingly, the diffraction of only the right-circularly polarized light was found in the transmittance mode. The maximum diffraction efficiencies were found for the wavelength values between the maxima of selective light reflection. The films obtained open very interesting possibilities for further development of materials with stable gratings operating in the entire visible spectral range. Both the position and the width of the spectral range of an efficient diffraction can be easily controlled by the UV exposure and concentration of the dopant. The materials obtained and methods developed can be used for creation of specific diffraction elements for optics and photonics.

The fabrication of periodic polymer/silver nanoparticle structures: in situ reduction of silver nanoparticles from precursor spatially distributed in polymer using holographic exposure.

A new approach to producing volume periodic polymer-metal nanoparticle structures is presented. Periodic distribution of Ag nanoparticles in a polymer film can be obtained by applying the holographic patterning in the UV or visible spectral range to the composite material comprising photocurable monomers, photoinitiators and a solution of silver nitrate in acetonitrile. Photopolymerization of the composite in the interference pattern provides formation of a highly efficient volume grating composed of periodic polymer regions and Ag precursor-containing regions. Subsequent homogeneous UV irradiation and/or thermo-treatment of the grating causes reduction of silver ions to Ag nanoparticles in the areas of the film containing the metal precursor. Spectroscopic measurements confirm the formation of the nanoparticles in the gratings. Transmission electron microscopy showed a regular spatial distribution of well-defined Ag nanoparticles in a polymer film with a periodicity governed by the geometry of holographic structuring. The average diameter of nanoparticles can be controlled by the wavelength and intensity of holographic exposure as well as the composite formulation. A possible mechanism of silver nanoparticle formation by free radicals as reducing agents is presented.

Large-scale synthesis of organophilic zirconia nanoparticles and their application in organic-inorganic nanocomposites for efficient volume holography.

We present a multigram scale, one-step nonaqueous synthesis route to monodisperse, highly crystalline ZrO(2) nanoparticles. The nanoparticles can be stabilized in nonpolar solvents via a simple functionalization procedure using only minute amounts of organic stabilizers. Their great potential in materials applications is demonstrated by the fabrication of organic-inorganic nanocomposites that can be selectively photopolymerized to inscribe extremely effective and volume holographic gratings with the highest refractive index contrast (n(1) of up to 0.024) achieved so far.