Search

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.

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.

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.

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.

We demonstrate a μ-branch in Si photonic wire waveguides. The loss measured is as low as 0.3 dB. An H-tree circuit is also demonstrated with clear light outputs from 8 ports.

Less than 0.5 dB bend loss and 5 - 10% polarization conversion were experimentally evaluated for μ-bend in Si photonic wire waveguide. For the polarization stability, the perfect rectangular cross-section is crucial.

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.

We demonstrated an arrayed-waveguide-grating (AWG) demultiplexer using Si photonic wire waveguides, for the first time. We designed and fabricated an AWG of 110 ×93 µm2 size on a silicon-on-insulator substrate. The demultiplexing function was observed in the wavelength range of 1.50–1.57 µm with a channel spacing of ∼6 nm and a free spectral range of > 90 nm. A narrower channel spacing of 1 nm is possible in an area of ∼(500 µm)2, using an optimization of arrayed waveguides and slab waveguides.