Yasuo Kokubun

Antiresonant reflecting optical waveguides in SiO2-Si multilayer structures

A new type of optical waveguide utilizing an antiresonant reflector is described. Implementation in the SiO2‐Si system gave losses as low as 0.4 dB/cm for the TE mode. The TM mode loss is >60 dB/cm, making the device an excellent planar technology integrated optic polarizer.

An eight-channel add-drop filter using vertically coupled microring resonators over a cross grid

An eight-channel add-drop cross-grid vertically coupled microring resonator (VCMRR) filter is proposed and demonstrated. The cross grid comprises a grid-like array of buried channel waveguides which perpendicularly cross through each other, VCMRRs at each of the cross-grid nodes serve as the wavelength selective add-drop filters. Measured crosstalk levels at the crossings are typically less than -30 dB. Rings with a nominal radius of 10 /spl mu/m are used to achieve a free-spectral range of 20 nm and optical bandwidths of 1 nm, while changes of the radii in increments of 50 nm lead to a nominal channel spacing of 5.7 nm.

Microring resonator arrays for VLSI photonics

The analytic theory governing the complete scattering response of two-dimensional (2-D) microring resonator arrays is developed, The method is applicable to arbitrary interconnections of general four-port, single polarization nodes. An 8/spl times/8 cross-grid array of vertically coupled glass microring resonators is fabricated for test purposes.

Heterogeneous multi-core fibers: proposal and design principle

A new type of optical fiber called heterogeneous multi-core fiber (heterogeneous MCF) is proposed towards future large-capacity optical-transport networks and the design principle is described. In the heterogeneous MCF, not only identical but also non-identical cores, which are single-mode in isolation of each other, are arranged so that cross-talk between any pair of cores becomes sufficiently small. As the maximum power transferred between non-identical cores goes down drastically, cores are more closely packed in definite space, compared to a conventional, homogeneous multi-core fiber (homogeneous MCF) composed of only identical cores.

Vertically coupled glass microring resonator channel dropping filters

Air-clad glass microring resonators vertically coupled to buried channel waveguides are experimentally investigated. Ring radii of 10 /spl mu/m, and channel drop bandwidths of 5 nm are reported. Vertical coupling eliminates the need for the etching of fine features, and relaxes the alignment of the resonator with respect to the input and output bus waveguides.

Fabrication technologies for vertically coupled microring resonator with multilevel crossing busline and ultracompact-ring radius

To eliminate the scattering loss at the crossing points of cross-grid busline waveguides, the multilevel crossing structure of the busline waveguides was introduced into a vertically coupled microring resonator (VCMRR) filter. To achieve this structure, two fabrication technologies were newly developed; one is a method to planarize perfectly the top surface of each buried waveguide, and the other is a method to fabricate microring waveguides with very smooth sidewalls. Using the latter method, an ultracompact VCMRR with a ring radius of 5 /spl mu/m was realized and a free spectral range of 37 nm was successfully demonstrated. Next, using the former method, single-ring and quadruple series-coupled ring resonators with multilevel crossing busline waveguides were fabricated. A clear filter response was obtained for the single-microring resonator, and a boxlike filter response was obtained for the quadruple series-coupled microring resonator with multilevel crossing busline waveguides.

Box-like filter response and expansion of FSR by a vertically triple coupled microring resonator filter

The Lorentzian-shape filter response of a microring resonator filter is not suitable for practical use in wavelength division multiplexing (WDM) systems because of the lack of passband flatness, high crosstalk, and the large wing in the rejection band. Therefore, the tailoring of filter response shape is required to improve the performance. The series coupled microring resonator is one of the solutions. We designed and fabricated vertically triple coupled microring resonator add/drop filters with a stacked configuration. A box-like filter response with a flat passband was successfully obtained, and the free spectral range (FSR) was expanded to 25.8 nm owing to the Vernier effect.

Dispersion and radiation loss characteristics of antiresonant reflecting optical waveguides-numerical results and analytical expressions

Propagation characteristics of novel single-mode slab waveguides, ARROW (antiresonant reflecting optical waveguides), ARROW-B, and their modified configurations, are investigated. The dispersion and radiation loss characteristics, field profile, confinement factor, and spot size of these ARROW-type waveguides are analyzed in detail by a mode analysis method using the system interference matrix. Approximate expressions for these characteristics are obtained in simple forms, which provide useful suggestions for the design of these waveguides. Possible combinations of materials and design conditions of ARROW-type waveguides are discussed on the basis of these results. >

Wavelength trimming of a microring resonator filter by means of a UV sensitive polymer overlay

Trimming of the resonant wavelength of a vertically coupled glass microring resonator channel dropping filter with a photo-induced refractive index change in a dip coated polymer overlay is reported. In this letter, the glass microring resonator has a radius of 19 /spl mu/m, a free-spectral range of 10 nm, and a Q value of 800. The maximum wavelength shift observed is 9 nm, which is yielded through an absolute bulk index change in the polymer of 0.044. Trimming is a continuous function of exposure time and dose.

Second-order filter response from parallel coupled glass microring resonators

Ring resonators are coupled in parallel in order to obtain a second order type of wavelength response. The phase relationship between the rings determines the details of the spectral response. The rings used in the experiment have radii of 25 /spl mu/m and are fabricated from compound glass having an index of 1.539. Several resonances are observed to have double peaked box-like response.