Hideo Kotani

Direct Writing of Gratings by Electron Beam in Poly(metyl methacrylate) Optical Waveguides

Changes in refractive index and in film thickness caused by electron beam irradiation are studied in poly (metyl methacrylate), PMMA. The index at 0.633 µm increases by 8% and the thickness decreases by 12% after 10-3 C/cm2 irradiation. Utilizing these phenomena, gratings with periods of 0.8 and 2 µm are fabricated in PMMA waveguides as Bragg diffraction beam splitters. The effective index change of a guided mode due to the electron beam irradiation is analyzed. An expression for the diffraction efficiency is derived by the coupled wave theory. The dependence of the diffraction efficiency on the grating length is measured, and fairly good agreement is obtained between the experiment and the theory.

Heterostructure CdS1−xSex−CdS surface lasers for integrated optics

Heterostructure CdS1−xSex−CdS surface lasers which have a larger refractive index and a smaller band gap than CdS substrates were fabricated by vapor phase epitaxy and their laser characteristics at 80 K were studied by using a nitrogen gas laser excitation. The Se profiles which were deduced from the fluorescence wavelength were steplike but graded due to diffusion. The optical gain of the epitaxially grown surface layer was larger than that of CdS single crystal owing to optical confinement. By stripe geometry excitation, an intense axial single−mode output was observed up to the excitation intensity three times as high as the threshold 70 kW/cm2. Optical coupling between the active and passive layers was observed in the samples which have a double epitaxial layer.

Electrooptic Bragg-deflection modulators in corrugated waveguides

An electrooptic Bragg-deflection modulator using a corrugated waveguide is discussed. A coupling between transmitted and diffracted waves caused by a Bragg diffraction grating is controlled by an incident angle change. By combining a grating and a prism deflector, a large angle deflection is performed with a low driving voltage. Numerical examples are presented for LiNbO 3 waveguides, and are compared with those of the modulator where the coupling is controlled by an index change.

X-ray Replication of Masks by Synchrotron Radiation of INS-ES

Synchrotron radiation has been used for X-ray lithography. At an electron energy of 1. 1 GeV, o.4 µm gold layer on 3 µm silicon membrane was sufficient for obtaining good contrast in PMMA for direct SOR total beam. By using the mask of the gold grating pattern with 692 nm period made by holographic method, the grating pattern with a large height-to-width ratio of very narrow line (2.2 µm: 0.2 µm) is obtained in PMMA. This result clearly demonstrates the high collimation of X-ray beam from the synchrotron. Effects of diffraction are observed in replicated patterns when a mask and a wafer are separated and are well explained by the theory of Fresnel diffraction as a function of the slit width, the wavelength and the distance between a mask and a wafer.

Trapped Ar Induced Deformation of Magnetron Sputtered Al Film Overlaid with Plasma SiN Film

Effects of heat treatments on magnetron sputtered Al (SP-Al) films overlaid with plasma silicon nitride (P-SiN) films were investigated. Trapped Ar in SP-Al films during sputtering deforms SP-A1 and/or P-SiN films to cause voids ranging from a few to a hundred micrometers in diameter because of the low permeability for the P-SiN film. In cases of CVD-SiO2 and PSG as overlayer materials, less voids are formed because of their higher permeabilities and their higher deposition temperatures. The voids decrease with decreasing line width of patterned SP-Al films since narrower lines trap less amounts of Ar. In order to reduce the voids, substrate heating at 300°C during sputtering and heat treatment at 450°C in vacuum after sputtering were carried out, resulting in reduction of the voids to about one fifth.