Effect of Silica-Nanoparticle Dispersion on Holographic Recording in Methacrylate-Based Photopolymer Films
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0939-O06-01
Effect of Silica-Nanoparticle Dispersion on Holographic Recording in Methacrylate-Based Photopolymer Films Hiroshi Takahashi, Takahiro Naitoh, and Yasuo Tomita Electronics Engineering, University of Electro-Communications, 1-5-1, Chofu-Gaoka, Chofu, Tokyo, 182-8585, Japan
ABSTRACT Transmission volume holograms recorded in two types of methacrylate-based photopolymer films that include benzyl n-butyl phthalate (BBP) or Poly(methyl methacrylate) (PMMA) are studied. It is shown that both BBP and PMMA molecules can be uniformly dispersed into methacrylate monomers and that a refractive index modulation (∆ n) as high as ~0.005 is recorded by optimizing their volume concentrations. Moreover, it is also shown that the additional doping of silica nanoparticles substantially suppresses polymerization shrinkage. INTRODUCTION Because photopolymer materials have many advantages such as shape flexibility, easy processability and low cost, various applications have been suggested and demonstrated utilizing their large ∆ n. These include holographic memories, narrow-band wavelength filters, and 3D displays. Such photopolymers may also be used for dye-doped solid-state distributed feedback (DFB) lasers, in which optical feedback is provided by a distributed periodic modulation of ∆ n [1,2]. In this case, a photopolymer material that improves lasing parameters (e.g., lasing threshold power, slope efficiency and output power stability) must be chosen carefully. Such a photopolymer material must meet several requirements. Firstly, it has to possess an optical feedback structure such as a DFB or a distributed Bragg reflector (DBR) structure for lasing action. Secondly, it has to be highly transparent at a lasing wavelength and to be stable both mechanically and thermally. Thirdly, it has to accept a light-emitting agent as a guest material for high photo-luminescence quantum yield. It was reported that both BBP and PMMA molecules have good affinity with laser dyes and exhibit excellent transparency in the visible [3,4]. It was also reported that doping of silica nanoparticles into a polymer film gave a significant improvement of the physical and chemical properties (e.g., tensile strength, abration resistance, chemical and thermal resistance) [5-7]. This result suggests that the silica-nanoparticle doping improves the mechanical and thermal stabilities of a polymer film since they would effectively suppress the mechanical stress caused by heating and/or polymerization shrinkage. Recently, we have reported the use of inorganic nanoparticles as dopants in methacrylate monomers capable of radical polymerization for permanent holographic storage with high diffraction efficiency and recording sensitivity [8-10]. Here, we report on the use of methacrylate monomers codoped with BBP or PMMA and silica nanoparticles to demonstrate photopolymer materials satisfying all the three requirements. We show that ∆ n as high as 0.005 is recorded under the optimum concentrations of either PMMA or BBP and silica nanoparticles. Additionally,
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