Kazuhiko Ogusu

Linear and nonlinear optical properties of Ag-As-Se chalcogenide glasses for all-optical switching

We prepared Ag(x)(As0.4Se0.6)(100-x) chalcogenide glasses by a melt-quenching method and measured their linear and nonlinear optical properties to evaluate their potential applications to all-optical ultrafast switching devices. Their nonlinear refraction and absorption were measured by the Z-scan method at 1.05 microm. The addition of Ag to As2Se3 glass led to an increase in the nonlinear refractive index without introducing an increase in the nonlinear absorption coefficient. The glass with a Ag content of x = 20 at. % revealed high nonlinearity ranging from 2000 to 27,000 times that of fused silica, depending on the incident optical intensity.

Numerical Analysis of the Rectangular Dielectric Waveguide and its Modifications

Dielectric waveguides suitable for millimeter and submillimeter wave integrated circuits are analyzed by applying the generalized telegraphists equations. The dielectric waveguides treated in this paper are the rectangular dielectric image line, the cladded rectangular dielectric image line, the insulated image guide, and the strip dielectric guide. Numerical results of the propagation constant, the power distribution, and the field configuration in these dielectric waveguides are presented. Values for the propagation constants obtained by our method are compared with other theoretical results. Although this work is based on a closed waveguide model, it may be applicable to wide classes of dielectric waveguides with arbitrary dielectric profiles and cross sections.

Brillouin-gain coefficients of chalcogenide glasses

We derived the relation between a figure of merit, M1, for the diffraction efficiency of acousto-optical devices and the Brillouin-gain coefficient, gB. We then estimated the values of gB and the phonon lifetime for typical As2S3 and As2Se3 chalcogenide glasses from known acousto-optical parameters. We found that the magnitude of gB for these two glasses is greater than 20 times that of fused silica.

Dynamic Behavior of Stimulated Brillouin Scattering in a Single-Mode Optical Fiber

We theoretically and experimentally investigate the transient stimulated Brillouin scattering (SBS) in a single-mode fiber. The experiment was conducted using a single-mode pulsed YAG laser and demonstrates that SBS can occur even in the nanosecond region. Due to the transient nature of SBS, pulse narrowing of the transmitted pulse is observed. The experimental results agree with the theory based on the coupled-amplitude equations for the pump, Stokes, and acoustic waves. The steady-state solution of SBS is obtained when the pulse width of the incident pulse is one 100-fold greater than the round-trip time within the fiber. We show that the instability of SBS depends on the magnitude of the nonlinear refractive index of the fiber. SBS instability behavior appears at different pump power levels when the nonlinear refractive index is an order of magnitude larger than that of the fused-silica fiber.

TE waves in a symmetric dielectric slab waveguide with a Kerr-like nonlinear permittivity

The propagation characteristics of TE waves guided by a film with a Kerr-like nonlinear permittivity are investigated theoretically. The dispersion equations for positive and negative nonlinear coefficients are derived by introducing the maximum field amplitude as a parameter for the nonlinearity. Typical numerical results for dispersion characteristics are shown. For a hollow waveguide with positive nonlinear coefficient, the threshold power flow is determined numericlly from the viewpoint of applications to optical power clipping. It is found that the threshold power flow is proportional to the square root of the unperturbed permittivity difference between the film, and cladding.

Optical strip waveguide: a detailed analysis including leaky modes

The propagation properties of strip waveguides are analyzed by a mode-matching technique. Mode coupling, which causes leakage effects, is taken into account in the analysis. The numerical results for the attenuation constants of the first three leaky modes are presented as a function of the strip width. The numerical results obtained by the present method are compared with other theoretical and experimental results. It is found that the higherorder leaky modes have varied and interesting properties, as does the fundamental leaky mode.

Transmission characteristics of optical waveguide corners

Abstract Two-dimensional dielectric waveguide corners with air reflector or metal reflector have been investigated by means of the method of plane-wave expansion, which has the advantage of being compact for optical integrated circuit applications. The operating principle of these waveguide corners is based on the total internal reflection or large partial reflection. The corner losses and field profiles are presented for various waveguide parameters. It is found that the corner loss can be small if the waveguide corner is properly fabricated.

Advanced design of a multichannel fiber Bragg grating based on a layer-peeling method

A multichannel fiber Bragg grating (FBG) design based on a discrete layer-peeling method is described. This novel method enables us to design any kind of multichannel FBG in which the spectrum responses of the channels can be either identical or nonidentical. In particular, a nine-channel dispersion-free FBG and a nine-channel nonlinearly chirped FBG used simultaneously as chromatic dispersion and dispersion slope compensators are described. Unlike the general multichannel FBG designed by a sampling method, these two gratings have ideal flat-topped profiles in both the transmission and the reflection spectra. By optimally detuning the relative phases for the multiple-spectrum channels with an iterative layer-peeling method, we can make maximum use of length-limited photosensitive fiber. Moreover, we show numerically that one can reduce or eliminate the oscillation that inherently exists in the index-change envelope of our multichannel FBG by accepting a decreased extinction ratio of the in-band signal to the out-of-band noises.

Dynamic behavior of reflection optical bistability in a nonlinear fiber ring resonator

We present an analysis of the dynamic behavior of a nonlinear fiber ring resonator when an optical pulse with an arbitrary shape envelope is incident into it through a fiber directional coupler. The transient analysis is based on the extension of a well-known multiple-beam interference method to non-linear transmission problems. The steady-state analyses reported so far predict that the ring resonator exhibits reflection optical bistability in the input-output characteristics under appropriate conditions. But, our transient analysis shows that a nearly periodical oscillation of the transmitted power always takes place at a suitable initial detuning when the resonator has no loss or a small loss. It seems that the present instability is caused by the repetition of accumulation and release of the power in the ring resonator. We can obtain a bistable hysteresis loop by introducing a loss to the directional coupler. The dynamic behavior of bistability in a nonlinear fiber ring resonator with coupler loss is then investigated. It is found that a remarkable undershoot and overshoot occur in the switch-off curve and switch-on curve, respectively.

Dynamic transmission properties of a nonlinear fiber ring resonator.

We present a method for calculating the dynamic input–output characteristics of a nonlinear fiber ring resonator caused by a change in input intensity. It is based on an original method developed by Bischofberger and Shen [Phys. Rev. A 19, 1169 (1979)] to study a transient nonlinear Fabry–Perot resonator. We treat a double-coupler fiber ring resonator, in which two types of optical bistability (transmission bistability and reflection bistability) are available and present the illustrative numerical results for a few cavity parameters. This analysis will be useful for a future experimental verification of optical bistability in fiber ring resonators and for the design of fiber bistable devices.