Kazuhito Matsumura

A fiber lens with a long working distance for integrated coupling between laser diodes and single-mode fibers

A new scheme is proposed for lensed fibers with a long working distance, as used in the coupling between laser diodes and single-mode fibers. The scheme consists of the combination of a hemispherically-ended coreless-fiber tip and an expanded-core fiber. The working distance is measured as 169 /spl mu/m with a relatively low coupling-loss of 4.2 dB at a wavelength of 1.49 /spl mu/m. Tolerances for a 1-dB loss increment for axial-, lateral-, and angular-misalignment are 35, 2.6 /spl mu/m, and 0.8 degrees, respectively. The new configuration is suitable for alignment-free coupling between arrayed laser diodes and an array of single-mode fibers. >

A lensed-fiber coupling scheme utilizing a graded-index fiber and a hemispherically ended coreless fiber tip

A new configuration of lensed fibers as the coupling between laser diodes and single-mode fibers is proposed. The lensed fiber consists of a hemispherically ended coreless-fiber and a quarter-pitch length of a graded-index fiber. Fabrication is quite simple and rapid. Basic characteristics of the new configuration, including long working distances and wide tolerances, are experimentally verified. The new configuration is suitable for integration-oriented coupling between arrayed laser diodes and an array of single-mode fibers.

Fabrication of spatial walk-off polarizing films by oblique deposition

A spatial walk-off polarizer that utilizes form-birefringence in an obliquely deposited thick film is proposed. The film is composed of two substances, slant needle-like microcolumns and resultant fine voids around them. The structure has the uniaxial birefringence whose optic axis is parallel to the column/void axis. The basic operation was confirmed with tantalum-oxide thick films deposited onto beveled silica substrates. The spatial walk-off characteristic has clearly been observed, and the maximum polarization-split angle is measured to be 7.3/spl deg/, being larger than that of existing polarizers such as those made of rutile and calcite. >

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.

Improved analysis for the coupling characteristics of two rectangular dielectric waveguides laid in different layers

A coupled-mode theory proposed by A. Hardy and W. Streifer (J. Lightwave Technol., vol.3, p.1135-46, 1985) and step-like approximation are used in this analysis. Comparison between the present result and the previous one indicates that the present approach is more useful, especially in case of strong coupling. >

Laminated polarizers exhibiting high performance over a wide range of wavelength

A laminated polarizer exhibiting high performance over a wide range of wavelengths has been fabricated for the first time. The polarizer consists of alternate layers of laminated silica film and metal-included semiconductor ultra-thin film as the transparent and absorptive layers, respectively. Extinction ratios of greater than 50 dB with insertion losses of less than 0.4 dB have been obtained over the wavelength range of 0.8-1.55 /spl mu/m. At the wavelength 0.98 /spl mu/m where previously no viable laminated polarizer had been available, the extinction ratio is as high as greater than 60 dB and the insertion loss less than 0.3 dB.

Reflection and transmission characteristics of an uncoincidental junction on rectangular dielectric waveguides

A novel approach to the analysis of an uncoincidental junction in a rectangular dielectric waveguide is presented. The boundary condition equations on the junction plane are presented through the tangential components of guided modes and radiation modes which are excited at the discontinuity. To obtain the reflection and transmission coefficients at the discontinuity, the equations are transformed into the spectral domain by the two-dimensional Fourier transformation. In the spectral domain, the orthogonal relationship between the guided and radiation modes is used to determine the reflection and transmission coefficients approximately. The parameters corresponding to the phase constant of the radiation fields in the spectral domain are defined by using an iterative calculation. The reflection and transmission coefficients are determined exactly. These coefficients are compared with 10-GHz band experiments. The analysis shows good agreement with experimental results. >

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.

Reflection and transmission coefficients of rectangular dielectric waveguide discontinuity with an air gap

Reflection, transmission, and radiation characteristics of rectangular dielectric waveguide discontinuities with an air gap are analyzed. A transverse displacement with the air gap is also treated. The characteristics of this discontinuity have never been analyzed with a conventional slab model. In this analysis, a two-dimensional Fourier transformation and orthogonal relations between guided and radiation modes are utilized. Calculations and experimental results in X-band are compared, and good agreement is found. To discuss the numerical results, the principle of energy conservation is introduced. The discrepancy between the results and this principle is less than 0.0003. >