Yoshinori Kogami

Single-mode fiber with a plano-convex silicon microlens for an integrated butt-coupling scheme

A single-mode fiber with plano-convex silicon microlens is proposed for butt-coupling between single-mode fibers and high-index-contrast waveguides with fine mode-field diameter. The lensed fiber has two specific features, high focusing power, and null working distance. The theoretical focus-spot diameter at the endface of the lensed fiber is calculated to be as small as 0.56 microm at a wavelength 1.55 microm. A simple fabrication method for the lensed fiber employing chemical etching and rf-sputtering is presented. Experiments showed that the mode-field-diameter of a single-mode fiber was successfully contracted from 10.5 to 1.3 microm with the lensed fiber.

Resonance characteristics of whispering-gallery modes in an elliptic dielectric disk resonator

This paper presents a novel calculation method for resonance characteristics of an elliptic dielectric disk resonator. In the elliptic resonator, electromagnetic energy propagates as a whispering gallery (WG) mode along the edge region of the dielectric disk. In the novel analysis, a local propagation constant of the WG mode at each point of the elliptic disk edge is represented by a propagation constant of a WG mode in a circular disk whose radius of curvature, material constants, and thickness are equal to those of the elliptic disk. Therefore, we can easily calculate the resonance characteristics of the elliptic dielectric disk resonator by applying a conventional technique for the circular dielectric disk. The calculated results of the resonant frequencies and field distribution are well confirmed by experiments.

Characterization of low loss dielectric materials in millimeter wave region using a whispering gallery mode resonator

A new method for measuring the complex permittivity of a low loss material in the millimeter wave region is developed. The heart of the method is a higher order whispering gallery mode resonator which is made of the material under test. The method has a great advantage for millimeter measurements because the dielectric disk resonator does not need a shielding metal structure. Measured results of some plastic and ceramic materials in the 50 to 110 GHz band are presented.

Coupling characteristics of eccentric arranged dielectric disk and ring

An analysis is presented for a novel coupling configuration in which a circular dielectric disk and ring are arranged eccentrically. Whispering gallery (WG) mode coupling characteristics between the dielectric disk and ring are investigated. In this paper, a coupled-mode equation based on the Lorentzs reciprocity theorem is utilized. Distributed coupling coefficients and electric field distributions around the coupling region are obtained numerically through solving the coupled-mode equation. The theory described in this paper is confirmed by comparing measured electric field distributions with calculated ones. Electromagnetic powers flowed along the disk are also calculated. It is shown that coupling quantity of the eccentric configuration would be easily controlled by changing a radius of the disk or ring. The results obtained here will be used to design a WG mode coupled resonator for millimeter wave integrated circuits.

Accurate Evaluation Technique of Complex Permittivity for Low-Permittivity Dielectric Films Using a Cavity Resonator Method in 60-GHz Band

In order to realize modern millimeter-wave applications, the accurate value of complex permittivity of low-permittivity dielectric films with excellent characteristics are needed by circuit designers and material developers. However, there are few accurate measurement methods for dielectric films in the millimeter-wave region. In this paper, an accurate evaluation technique for thin dielectric films using a novel V-band cavity in the 60-GHz band is proposed on the basis of a cavity resonator method. The novel V-band cavity with small excitation holes, which does not affect the resonant electromagnetic fields, is designed and fabricated. The six kinds of thin dielectric film were measured by the proposed technique using the novel cavity. The measured results and the uncertainty analysis validate the accuracy and the usefulness of the proposed method. Moreover, it was verified that this technique can evaluate thin samples with thicknesses of 10 μm or more.

Rugate filters fabricated by a radio frequency magnetron sputtering system by use of an optical in situ monitoring technique.

We propose, for the first time to our knowledge, a new feedback fabrication technique for rugate filters with sinusoidal refractive index distribution. The technique uses an in situ optical monitoring system, in contrast to conventional techniques for rugate filters that are based on time control, which is generally unsuitable for accurate fabrication of a continuous index distribution. We employed a-SiOx:H thin film as the material for the rugate filters because its refractive index can be successively controlled. Using the proposed technique and material, we fabricated near-infrared rugate minus filters having multiple and continuous refractive index distributions. The experimental and calculated spectra were well correlated as a result of applying the proposed feedback fabrication technique.

A Millimeter Wave Filter Using the Whispering-Gallery Mode Dielectric Resonators Coupled Laterally

A millimeter wave BPF constructed from the WG mode dielectric disk resonators is presented. The design chart for the high Q WG mode resonator is obtained from Qu calculation of some WG modes. By using the design chart, high Q WG mode resonator having no influence of unwanted higher order resonances is designed. Designed resonators have different diameter and various Resonance Frequency Separation respectively. A 3 stage maximally flat BPF is constructed so that each resonator may be coupled laterally.on the edge of the disk. Designed center frequency is 62.47 GHz and 3dB bandwidth is 100 MHz. As a result, this BPF has insertion loss of 1.5 dB and some spurious responses which were existed conventional WG mode BPF are reduced considerably.

A novel analysis for eigenvalues of a dielectric disk resonator with a high dielectric constant

A new analysis for eigenvalues of Whispering Gallery Modes on a three-dimensional disk resonator with a high dielectric constant is presented. In this analysis, a Generalized Effective Dielectric Constant Method is applied with some modification. The disk resonator is considered to be decomposed into two-dimensional slab waveguides and a cylindrical dielectric rod resonator. A concept of an effective dielectric constant and a caustic radius are newly introduced to obtain the eigenvalues of Whispering Gallery Modes. As a result of comparison with numerical eigenvalues and experimental ones, it is found that this analytical method is useful even so the dielectric disk resonator has a high dielectric constant.

High precision measurement method for dielectric film materials by a novel V band cavity resonator

Many millimeter wave circuit designers require complex permittivity of low εr film materials with excellent characteristics. However, there are few accuracy measurement methods for film materials in millimeter wave region. In this paper, a high precision measurement method for dielectric film materials in 60GHz band are proposed on the basis of a cavity resonator method. The measured results validate the accuracy and the usefulness of the proposed method and newly developed V band cavity.

An NRD guide excited millimeter wave narrow bandpass filter using whispering gallery mode high-Q resonators

We focused on an NRD guide and the Whispering Gallery (WG) mode high Q sapphire resonator which have the excellent low loss characteristics in millimeter wave region. In this paper, the NRD guide excited millimeter wave narrow bandpass filter using WG mode sapphire resonators was designed and fabricated. As a result, it was reali%ed that the 3-pole bandpass filter with center frequency 58.64GH% and 3dB bandwidth 273MH%. Moreover, its insertion loss was found to be about 1.5dB.