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Large electro-optic effects of liquid-crystal materials are attractive in applications to various optical devices in a wider wavelength region. Fundamental optical properties in the submillimeter wave region, such as refractive indices and transmission losses for some cyanobiphenyl nematic liquid crystals, have been investigated for the first time, to our knowledge, with a submillimeter laser. Refractive indices of the liquid crystal materials for ordinary and extraordinary rays are a little larger than those in the visible region, and a larger birefringence comparable with the visible region can also be obtained. Although the loss level is larger by ~2 orders of magnitude than that of quartz plate, which is an excellent window in the submillimeter wave region, the transmission of the liquid crystal cell is high enough.

We investigated the optical properties of a circular photonic crystal (CPC) for which the distance between lattices was systematically distributed. The transmission spectra of CPC composed of alumina cylinders were examined in the frequency region from 0 to 20 GHz. We show that photonic gaps are obtained not only in CPCs but also in phase-shifted CPCs. The isotropic photonic gaps are evidenced by changes in the incident angle of a millimeter wave.

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When a semiconductor substrate is illuminated by an optical beam whose photon energy exceeds its band‐gap energy, free carriers are produced in the substrate, which provides a means of control for the substrate reflectance and transmittance of submillimeter electromagnetic waves. This paper is concerned with submillimeter wave modulation by an optically‐excited semiconductor. High‐resistivity silicon and GaAs are used as the substrate. Continuous radiation with a wavelength of 214 μm is used as the submillimeter wave. A Q‐switched Nd:YAG laser is used to excite the free carriers. The experimental results are presented. Effects of semiconductor substrate material, wavelength of the excitation beam, and incident surfaces of the submillimeter wave and the substrate excitation beam, on the modulation waveforms are analyzed. As an application of the proposed modulation technique, submillimeter wave short pulses with variable duration are successfully generated. © 1998 Scripta Technica. Electron Comm Jpn Pt 2, 80(6): 1–9, 1997

Scanning near-field optical microscopy using a slit-type probe is discussed. The slit-type probe has a width of much less than a wavelength, λ, and a length on the order of λ, and thus has high transmission efficiency. Two dimensional near-field images of objects have been constructed using an image reconstruction algorithm based on computerized tomographic imaging. Experiments performed at 60 GHz (λ=5 mm) show that this type of near-field microscopy can achieve a spatial resolution of better than λ/45 for two dimensional imaging. A method for fabricating a submicron width slit probe at the end of an optical fiber is presented for extending this microscopy to optical waves.

A reflection-type liquid crystal (LC) test cell is prepared with a rectangular waveguide for investigation of a novel method to determine refractive indices and loss parameters of nematic liquid-crystal materials. As the bottom of the test cell is sealed with a glass window and the top of the cell is capped with a metal-tipped movable reflector after the LC materials are injected, both ends of the waveguide test cell have large reflectance. Thus the reflection properties of the LC test cell can be well described by a multiple-beam interference model. A simple method for the determination of refractive indices from the reflection measurement data is proposed based on results of some investigations with the theoretical model. Commercially available LC materials have been measured with this method at a millimeter-wave frequency (50 GHz) by use of a simple experimental setup with a Gunn oscillator and a diode detector.

A bent photonic crystal waveguide was fabricated by use of a lattice pattern of a circular photonic crystal that allowed high transmission for a broad band of wavelengths with a small radius of curvature at a bend. The waveguide was fabricated by use of alumina rods with a diameter of 3 mm. Windows of high transmission as a result of waveguiding were observed near 9 and 15 GHz. By measurement of the relative wave intensity [E]2 along the line defects, the propagation losses in the straight and the bent sections were estimated at 9.3 GHz to be 0.04 and 0.03 dB/mm, respectively.