Katsuhiro Munakata

Diffraction efficiency increase by corona discharge in photoinduced surface-relief gratings on an azo polymer film

The diffraction efficiency of a surface-relief grating (SRG) was dramatically increased by corona discharge. We fabricated this SRG by applying surface modulation to azo polymer films, using laser interference fringes. The electric charge was deposited upon the SRG by a corona discharge in an oven. The first-order diffraction efficiency measured before and after corona discharge above the glass-transition temperature increased from ~2% to ~40% in a SRG written with a circularly polarized beam. The relief depth of the SRG as measured with an atomic-force microscope also increased, from ~130 nm to ~450 nm. The increase in diffraction efficiency was independent of the writing polarization.

A new holographic recording material and its diffraction efficiency increase effect: the use of photoinduced surface deformation in azo-polymer film

Holographic recording characteristics using a photoinduced surface deformation in a side-chain type azo-polymer film were investigated. Corona charging at temperatures above the glass transition temperature increased the diffraction efficiency of the recorded hologram from 0.24% to about 30% and the relief depth from 20 to 350 nm.

Poled Polymer Etalon Light Modulator on Integrated Circuits

Electrically addressed reflective spatial light modulators with polymeric thin films are fabricated on the surface of an n-type metal-oxide-semiconductor (NMOS) chip. The use of a resonator structure is proposed to minimize the driving voltage. The developed device is composed of 1×5 NMOS transistors and nonlinear polymeric materials sandwiched between aluminum electrodes. The electrooptical polymer consists of disperse red 1 (DR1)-doped poly-methyl-methacrylate (PMMA). Poling was demonstrated on this chip and the light modulation was observed using a lock-in amplifier. A modulation efficiency of 2.0 × 10-5 was obtained.

High-speed light modulation using complex refractive-index changes of electro-optic polymers

We propose a promising type of light modulator using complex refractive-index changes of electro-optic polymers in the wavelength region of absorption. The material used in this study is a high-glass-transition-temperature active-polyimide thin film. The wavelength dependence of electrically induced complex refractive-index changes and the modulation efficiency are evaluated. A modulation efficiency of 33.8% has been realized with 141 V rms applied potential at a wavelength of 633 nm. Very fast modulation at over 25 MHz has been demonstrated.

Spatial filtering using poled polymer etalon light modulators

Spatial filtering using poled polymer light modulators is studied. The use of a resonator structure is proposed to minimize the driving voltage. Side-chain polymer poly-orange tom-1 isophoronedisocyanate is used as a material. The measured electro-optic coefficient r33 is 23 pm/V at the wavelength of 633 nm. Spatial filtering of the input images are realized with 30 V applied voltage.

High-speed spatial light modulator with nonlinear organic material in photonic crystal

An electrically addressed spatial light modulator is designed using poled polymers. Use of photonic crystals are proposed to increase nonlinearity. The contrast ratio of 70:1 was obtained at 1 kHz with 11 Vrms applied voltage.

Spatial light manipulation devices using nonlinear polymeric materials

An electrically addressed spatial light modulator with 5 × 5 pixels is designed using nonlinear polymeric materials. Resonator structure for the material is proposed to minimize the driving voltages. Side-chain polymer poly-orange tom-1 isophoronedisocyanate (r33 = 23 pm/V) is used as a material. A modulation efficiency of 4.7% has been realized with 5.1 Vrms applied voltage at a wavelength of 633 nm. Very fast modulation at over 10 MHz has been demonstrated.

Photoinduced surface deformation on azo-polymer films and its holographic application

We propose a new technique to make a surface relief structure on azo polymer films. Application for light diffuser and holograms are described. The diffraction efficiency of the device was dramatically increased by corona discharge.

Direct fabrication of surface relief electro-optic gratings in azo-polymer films

We describe surface relief electro-optic gratings in azo-polymer films using two fabrication methods. One method uses CW laser beams, the other uses pulsed laser beams. The advantages of these methods are open air operation, short fabrication time and direct etching.

Resonant enhansment modulators using electro-optical effect of poled polymers

Spatial light modulators (SLMs) play very important roles in optical computing, including of optical neural networks and optical image processing.