Akio Sugita

New structure of silica-based planar lightwave circuits for low-power thermooptic switch and its application to 8 /spl times/ 8 optical matrix switch

We propose a novel structure that reduces the switching power of a silica-based thermooptic switch (TOSW). The structure consists of silicon trenches and heat insulating grooves, which are formed beneath and beside the arms of a Mach-Zehnder interferometer, respectively. We optimize the structure using the differential-element method (DEM) and fabricate a 2 /spl times/ 2 TOSW with a switching power of only 90 mW, namely, 75% less than that of a conventional TOSW. We also obtain an insertion loss of about 1 dB and an extinction ratio of over 30 dB with a response time from 0% to 90% of 4.9 ms. We then use the structure to fabricate an 8 /spl times/ 8 matrix switch and confirm a total power consumption of 1.4 W with an average insertion loss of 7.4 dB and an extinction ratio of 50.4 dB for 64 possible optical paths.

Numerical Calculation of Optical Eigenmodes in Cholesteric Liquid Crystals by 4?4 Matrix Method

Light propagation in helical structures is formulated as an eigenvalue problem based on Berremans 4×4 matrix. Diagonalization of the secular equation is carried out to obtain the optical eigenmodes as a function of wavenumber and propagation direction relative to the helical axis, and sets of the optical eigenmodes are found to be classified into four types, whose appearance strongly depends on the wavenumber and the propagation direction. The selective and total reflections in cholesteric liquid crystals are characterized by the types of the eigenmodes for various angles of incidence.

Experimental Observation of the Total Reflection by a Monodomain Cholesteric Liquid Crystal

The reflection spectra from a monodomain cholesteric liquid crystal are measured for obliquely incident light. The first order reflection region is found to be divided into three regions at a large angle of incidence. The central region shows high reflectivity irrespective of incident polarization and is attributed to the total reflection. The total reflection peak is also observed between the second order reflection peaks even at a small angle of incidence. The reflection spectra are numerically computed by the 4×4 matrix method and are in good agreement with the experiments.

Patterning of Conductive Polypyrrole in Polymer Film

The electrochemical polymerization of pyrrole on an insulating polymer coated electrode the surface of which was fabricated to have conductive patterns, alloys the formation of electrically conducting polypyrrole patterns in the polymer film. Without using a direct lithographic process, a polymer film with a highly anisotropic conductivity where the surface resistance is as low as 200 Ω in 30 µm pitch line patterns, can be obtained in a free standing form.

Optical fiber coupling to single-mode silica-based planar lightwave circuits with fiber-guiding grooves

Abstract To enable alignmentfree optical fiber coupling to single-mode silica-based waveguides, fiber-guiding grooves are fabricated in the same substrate as waveguide circuits.These grooves are used successfully to couple optical fiber to Waveguides. An average, fiber-to-waveguide coupling loss of 0.6 dB per interface is obtained with eight arrayedguiding grooves, and it is expected that this will further be reduced to 0.2 dB per interface. The coupling loss varies by ±0.3 dB during thermal cycling between −10°C and +60°C.

A Method for Studying Optical Eigen Modes in Cholesteric Liquid Crystals by Using Stress Plate Modulators in Tandem

An apparatus has been constructed for the direct study of the optical eigen modes (OEMs). The apparatus consists of an He–Ne laser, a linear polarizer (LP), a stress plate modulator (SPM), another SPM, another LP and a photomultiplier tube (PMT). A sample is placed between the SPMs, and the first combination of LP and SPM acts as a dynamic elliptical polarizer and the second one constitutes the analyzer which is always perpendicular to the polarizer. The output signal from the PMT is recorded in a transient memory and is accumulated and processed by a microcomputer. Taking the OEM propagating along the cholesteric helical axis as a test example, we calculated the temporal change in the PMT output signal; it indicates the existence of an ellipticity which gives zero transmittance. The calculated dependence of the ellipticity on wavelength agrees qualitatively with that of the true OEM, except for the region near or in the characteristic reflection. By performing actual measurement with a monodomain cholesteric film at a certain wavelength, we confirmed that the apparatus works well.

Nanometer patterning by focused low energy electron beam lithography

Focused low energy electron beam was applied for nanometerscale pattern delineation. A resist exposure with an electron energy less than 10 kV causes two problems, that is, a limited penetration depth and the scum formation due to charging-up effect. These problems were solved by using an electrically conducting 2-layer resist system composed of thin top imaging layer of silicone containing resist and conducting CVD carbon film as a bottom resist. Nanometer patterning as fine as 40 nm can be delineated by very low energy electron exposure with no electron energy dissipation in a substrate layer.