Naomichi Okamoto

Fabrication of Surface Relief Grating with Second-Order Nonlinearity Using Urethane-Urea Copolymer Films

Surface relief gratings on azobenzene-substituted urethane-urea copolymer films with large second-order nonlinearity are fabricated by a laser-interferometric method. The surface relief structures are obtained upon exposure to an interference pattern of a polarized Ar+ laser beam, which mainly results from photoablation. The gratings are thermally stable at temperatures higher than glass transition temperature (Tg) of the copolymer. The surface relief gratings with second-order nonlinearity are fabricated after a corona poling process. We report what we believe to be the first experimental observation of the separated second-harmonic generation from the fundamental wave by the surface relief grating with second-order nonlinearity.

Nonlinear optical waveguide fabrication by direct electron-beam irradiation and thermal development using a high Tg polymer

A nonlinear optical waveguide fabrication process for use with dye doped polymer is described. The ridge-type channel waveguide containing the chromophores was fabricated by direct electron-beam irradiation. The electron beam with an energy of 25 kV and dose of 1000 μC/cm2 was exposed directly onto the dye doped polymer film, and then thermal development and corona-poling were performed simultaneously. We could also demonstrate the periodically poled nonlinear optical polymer waveguide on the basis of this new process.

Fabrication technique of a nonlinear optical structure using optical polymeric films by direct electron-beam irradiation

A simple fabrication technique of nonlinear optical structures for use with dye-doped polymer is described. Polymethylmethacrylate, U-100 polymer, and polystyrene were used as the host matrices to fabricate the nonlinear optical waveguide. The periodically poled nonlinear optical polymer structures and ridge-type channel structures were fabricated by direct electron-beam irradiation. The electron beam with 25 kV of energy was exposed directly onto the polymer films containing the nonlinear optical chromophores. We can also demonstrate the fabrication technique of the domain-inverted grating of dye-doped polystyrene film.

Nonpoled polymeric films doped with blue-window pyrylium salt dyes for second-harmonic-generation devices

We have prepared polymer films doped with novel nonlinear organic ionic materials, pyrylium salt dyes, and have investigated the second-order nonlinear optical properties of these guest–host-type polymer films by changing the counterion and alkyl group derivatives. These films have no absorption in the blue-light region and have second-harmonic-generation activity without electric-field poling. The second-order nonlinearity of the nonpoled-polymer film is constant, with no relaxation at room temperature or at high temperatures. We fabricated a second-harmonic-generation device with the nonpoled-polymer film and observed Cerenkov-type phase-matched second-harmonic-generation of a Nd:YAG laser.

Second‐order nonlinearity of nonpoled polymeric thin films doped with pyrylium salts with blue window characteristics

A novel nonlinear organic ionic material, or pyrylium salt dye, is synthesized and doped in the polymer matrix. These guest‐host‐type polymer films, which have no absorption in the blue‐wavelength region, have second harmonic generation (SHG) activities without the electric‐field poling process. The nonlinear optical coefficient d33 is estimated as 1.10 pm/V at a 15 wtu2009% of dye concentration. The nonlinearity is stable at room temperature and at 120u2009°C. The SHG device is fabricated using the nonpoled polymer film, and Cerenkov‐type phase‐matched SHG is observed.

Second harmonic generation from organic nonlinear materials of N-alkyl-4-nitroaniline

Abstract We have systematically investigated a series of new nonlinear organic materials, N-alkyl-4-nitroaniline, by measuring the second harmonic generation (SHG) from powder samples of the five materials with the alkyl chain of different length. It is found that N-butyl-4-nitroaniline (BuNA) shows the largest SHG activity among them, and the SHG intensity measured is 14 times larger than that of urea, in contrast with no SHG activity of para-nitroaniline. It is also found that BuNA is a phase-matchable material and the SHG efficiency has a strong dependency upon the recrystallization solvent used for purifying the reaction product.

Electron-beam irradiation-induced nonlinearity in silicate glass films and fabrication of nonlinear optical gratings

Electron-beam (EB) irradiation on rf-sputtered silicate glass thin films can produce second-order nonlinearity. EB-poled germanosilicate glass film shows a maximum nonlinear optical (NLO) coefficient of d33=0.33u200apm/V. It is found that the nonlinearity is homogeneous throughout the film layer and depends on both the EB current and dose. Moreover, a NLO grating, i.e., χ(2) grating, is realized using a periodic EB writing technique.

High-resolution periodically poled structure in diazo-dye-substituted polymer film based on direct electron-beam writing technique

A periodically poled pattern in diazo-dye-substituted nonlinear optical polymer film is fabricated by direct electron-beam (EB) writing. It is found that the second-order nonlinearity of corona-poled polymer thin film is erased after EB irradiation. Moreover, the exposed region can be easily removed by conventional wet development. A high-resolution periodically poled structure (i.e., χ(2) grating) with a period of 0.60 μm is demonstrated based on the direct EB writing technique.

Simple fabrication of nonlinear gratings in polymer film using simultaneous process of emboss heating and thermal poling

Abstract We introduce a simple fabrication technique of nonlinear polymeric optical waveguide patterns based on the simultaneous process of emboss heating and poling. The polyimide film on the nickel plate was used as master grating. The condition of the fabricated pattern depends on removal temperature and the stability of the master grating is investigated. The submicron surface relief grating with χ(2) is realized in the NLO polymer film.

Study on Electron Beam Lithography with Dye-Doped Polymer Material

Abstract We report the study on electron-beam(EB) lithography with a dye-doped poled polymer. The mechanism of absorption spectrum change and nonlinear characteristics after EB exposure are investigated. Aχ(2) diffraction grating is successfully fabricated in this guest-host polymer material based on direct EB irradiation technique.