Connecting the world through light Building photonic networks

Hiroyuki Tsuda Laboratory, Department of Electronics and Electrical Engineering, Faculty of Science and Technology, Keio University

Connecting the world through light Building photonic networks

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Todays indispensible Internet was achieved through advances in optical communication technology, which dramatically reduce communication cost per unit information volume and transmission distance. The next-generation Internet, as infrastructure to support a future ubiquitous environment, will require even more advances in optical communication technology. Accordingly, the Tsuda Laboratorys research theme is making communications optical. The Lab aims to enable further progress in network infrastructure by researching optical circuits, photonic networks, and ultrafast optical signal processing.

The Tsuda Lab is looking at all kinds of optical circuits using optical waveguides. In an optical waveguide, paths for light are formed on a substrate, which enclose, bend, or divide light to make it pass through. In particular, silica optical waveguides are useful for multiplexing and demultiplexing different wavelength signals.

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As one application for optical circuits using silica glass, were making and testing prototypes of tunable dispersion compensator circuits. As you can see on the screen, the idea with a dispersion compensator circuit is shown, the optical signals passing through a long-distance optical fiber contain many wavelength components, each of which travels at a slightly different speed, and this makes the waveform deteriorate. Using this circuit, its possible to restore the degraded waveform to the way it was before.

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In a photonic network, wavelength division multiplexing technology is used to send signals with many different wavelengths at once. A PLZT optical waveguide can process these different wavelengths at high speed using voltage signals. Such waveguides are made from the material PLZT, which the Lab developed together with businesses.

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PLZT enables faster operation than silica, so it can be used for switches. And weve used it to co-develop devices called tunable wavelength filters, which extract signals with the required wavelengths at very high speed from multiplexed signals. This is an enlarged photo of a chip that weve actually fabricated. By applying electrical signals to this circuit, we can extract signals with specific wavelengths at high speed. When we first made this device, it was the worlds fastest. So weve been able to make extremely fast switches and tunable wavelength filters.

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The Tsuda Lab is also working on high-speed, ultra-small optical switches 100 times smaller than conventional ones using phase-change materials, like those in DVDs, and silicon wire waveguides. In such ways, the Tsuda Lab will contribute to the future of society by supporting the development of photonic networks, which are becoming increasingly important.

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Whats really interesting about research on communications and optical devices is that device design involves physical design. And network design involves theoretical design, and applications on top of that; in other words, applied research that people will use. Its very interesting to be able to do research where we look at everything, in a vertically integrated fashion.

In network research, the applications are clear: if devices improve, then the network improves right away. I think that in this sense, we can do very interesting research.

Category:

Science & Technology

Tags:

• Keio
• University
• Hiroyuki
• Tsuda
• Laboratory
• Photonic
• network
• PLZT
• optical
• waveguide

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Let there be light ... networks.