In integrated optics, it is very important to provide efficient optical coupling between fibers and waveguide devices. In this letter, we propose a fiber-waveguide coupler, whose guide width varies in propagation direction, and show its better coupling behavior than an uniform coupler.

A simple and practically accurate method for studying rectangular dielectric waveguides is proposed. This method can provide good evaluations of propagation constant and field distribution of the waveguides by analyzing improved equivalent guide models. In this paper, it is applied in studying a novel taper-formed waveguides system. The waveguides system was experimentally demonstrated of being advantageous in its lightwave transmission characteristics. Experimentally obtained results exhibited good agreement with the performances predicted by the system numerical analyses using the proposed waveguide study technique.

Magneto-optical (MO) switches operate with a dynamically applied magnetic field. The MO devices presented in this paper consist of microring resonators (MRRs) fabricated on amorphous silicon-on-garnet platform. Two types of MO switches with MRRs were developed. In the first type, the switching state is controlled by an external magnetic field component included in the device. By combination of MO and thermo-optic effects, wavelength tunable operation is possible without any additional heater, and broadband switching is achievable. The other type of switch is a self-holding optical switch integrated with an FeCoB thin-film magnet. The switching state is driven by the remanence of the integrated thin-film magnet, and the state is maintained without any power supply.

Design of a waveguide-type optical isolator using the Faraday and Cotton-Mouton effects for nonreciprocal and reciprocal mode conversions, respectively, is presented. A noteworthy conclusion is obtained that, comparing with the previous design using a phase-matched waveguide, the device length is reduced by allowing phase-mismatch between TE and TM modes in the waveguide.

A novel nonlinear directional coupler consisting of tapered and uniform waveguides with self-focusing or self-defocusing nonlinear material is proposed to improve all-optical switching characteristics. Its switching characteristics are analyzed by using a beam propagation method based on the Galerkin's finite element technique (FE-BPM), in which nonuniform sampling spacings along the transverse coordinate are adopted. It is presented that the tapered nonlinear directional coupler shows fairly distinct 'high' and 'low' states of output power with steep transition versus input power. This property is discussed in comparison with conventional nonlinear directional couplers consisting of uniform symmetric and uniform asymmetric coupled waveguides. In addition, the effects of loss on the characteristics of tapered nonlinear directional coupler are examined.

The optical absorption loss of Ca doped LPE grown rare earth iron garnet films can be reduced by the reducing treatment. The absorption loss is greatly affected by Ar sputter-etching whereas it is shown that the reducing treatment after O2 sputter-etching is suitable for making low-loss waveguides.

A microfabrication technique using a sputter-etching with Ar, including the process of a mask formation, is described. A Ti etch resistant mask was formed by using a lift-off technique following an electron beam exposure lithography. The sputter-etch rate of YIG, Ta2O5, Ti and Al were determined. Grating patterns with fairly deep grooves were fabricated on YIG and Ta2O5 successfully.

All-optical switching operating at 1.55 µm band in fabricated GaInAsP directional couplers loaded with grating are reported experimentally. These switching operations were realized in spatially separated output ports. The devices are suitable for optical integrated circuits and would operate as all-optical routing switches in practical power level by use of optical Kerr effect and Bragg grating. Using the optical bistability in the device, latching operation for output signal can be realized in spatially separated output ports and the outputs from each port are complementary. Two all-optical gate operations, which are optical inverting operation and optically controlled switching in spatially separated output ports, are also demonstrated, where the signal and control lights have different wavelength.

By combining rubber with carbon and ferrite in an appropriate weight ratio, the material which has both dielectric and magnetic losses, suitable for an electromagnetic-wave absorber, is obtained. The dispersion characteristics of complex relative permittivity and permeability of this material are measured, and equations of both permittivity and permeability are derived in RF frequencies. By using these dispersion equations, we can easily simulate applications using this kind of material as an electromagnetic wave absorvber.

A novel series-tapered nonlinear directional coupler is proposed to improve all-optical switching characteristics. Its switching characteristics are analyzed by using a beam propagation method based on the Galerkin's finite element technique. It is presented that the critical power of the series-tapered nonlinear directional coupler is smaller than conventional uniform symmetric and tapered nonlinear directional couplers.

The single layer absorber has the simplest structure among electromagnetic wave absorbers. To have thin and light materials with wide frequency characteristics for this structure, carbon and ferrite are mixed with rubber in different weight ratios. This new material has both dielectric and magnetic losses, which in a single layer structure, has good absorber characteristics . In the C-band, the relative bandwidth is up to 4.6 times wider, and the absorber is thinner, compared with nonmagnetic lossy dielectric material (i.e., 1.0, 0).

A modified beam propagation method based on the Galerkin's technique (FE-BPM) has been implemented and applied to the analysis of optical beam propagation in a tapered dielectric waveguide. It is based on a new calculation procedure using non-uniform sampling spacings along the transverse coordinate. Comparison with a conventional FE-BPM shows a definite improvement in saving computation time. The differences of a propagation field and a mean square power given by the proposed FE-BPM are discussed in comparison with the conventional FE-BPM.

We have proposed and demonstrated the circuit, which collectively recognizes header. Comparing with conventional schemes, the proposed circuit consists of simple structure. The proposed recognition circuit enables fast all-optical self-routing and contributes to reduce the buffer size for temporary data storage in each switch.

The shielding effect of a new material composed of rubber with carbon and ferrite for microwave oven leakage is investigated. By adding an appropriate amount of carbon, the shielding effect is improved. A large attenuation constant, which is 6 dB/cm larger than that of a rubber ferrite, is relizable.