Tatsuhiko Fukazawa

Low Loss Intersection of Si Photonic Wire Waveguides

We fabricated a low loss elliptical intersection of Si photonic wire waveguides on a silicon-on-insulator substrate. An insertion loss of less than 0.1 dB was achieved at a wavelength of 1.55 µm. The experimental loss characteristic closely agreed with the theoretical one. We also used this intersection as a suspension of an air-bridge-type waveguide and evaluated a low loss characteristic similar to that mentioned above.

Estimation of polarization crosstalk at a micro-bend in Si-photonic wire waveguide

The singlemode Si-photonic wire waveguide allows sharp bends, which significantly expands the design flexibility of optical devices and circuits. Here, the suppression of the polarization crosstalk at a sharp bend will be an important issue, since a large crosstalk affects the performance of devices and circuits. In this study, the three-dimensional (3-D) finite-difference time-domain (FDTD) simulation showed that the crosstalk at a 90/spl deg/-bend with a radius of 0.35-1.75 /spl mu/m is less than -25 dB at a wavelength of 1.55 /spl mu/m. In the experiment, the crosstalk from TE-like to TM-like polarization was evaluated to be -13 dB to -10 dB. This large value was explained by a small tilt of waveguide sidewalls, which seriously increased the crosstalk. In addition, it was found in the calculation that some combinations of bends increase or decrease the crosstalk, and that a U-shape bend is the most effective for the suppression of the crosstalk.

H-Tree-type optical clock signal distribution circuit using a Si photonic wire waveguide

We fabricated an ultra small H-tree-type optical signal distribution circuit on a silicon-on-insulator substrate. We used a micron-size bent-waveguide-type optical branch in a Si photonic wire waveguide and observed clear light output from eight output ports for laser light of 1.5 µm wavelength. The fluctuation of distributed light intensity was 2–5 dB. It was caused by a nonuniform branching ratio, and can be reduced by improving asymmetric corner shapes of each branch.

Mach–Zehnder Interferometers Composed of µ-Bends and µ-Branches in a Si Photonic Wire Waveguide

We fabricated compact Mach–Zehnder interferometers consisting of µ-branches and/or µ-couplers in a Si photonic wire waveguide. Clear interference spectra with a maximum extinction ratio of more than 20 dB and an alternating light output between two output ports were observed. A high diffraction order of 300 was also demonstrated within a small foot space of 30×20 µm2.

Ultrasmall filters and low loss intersection by Si photonic wire waveguides

We demonstrate 10-/spl mu/m-order-size Mach-Zehnder interferometer and AWG composed of Si photonic wire waveguides. We also demonstrate a small intersection with an elliptical slab region in this waveguide, which exhibited the almost lossless transmission.

Si photonic wire components and microfilters on SOI substrate

We designed and fabricated some components and devices by using Si photonic wire waveguides on SOI substrate. Because of the very high index contrast between the core and claddings, the waveguide allows a μ-bend. We applied this bend to form a μ-branch and μ-intersection, which exhibited a low of less than 0.3 dB in the experiment. The H-tree optical signal distribution circuit, the Mach-Zehnder interferometer, and the arrayed waveguide grating demultiplexer were demonstrated by this waveguide, for the first time. Although a more careful design and precise fabrication technologies are necessary for future high performance, this waveguide is expected to miniaturize any kind of conventional silica based devices by a factor over 10000 and realize more sophisticate functions by the dense integration of devices.