Japan’s AIST develops polarization-insensitive integrated optical switch

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Researchers with Japan’s National Institute of Advanced Industrial Science and Technology (AIST) say they have developed a new kind of an integrated optical switch using silicon photonics that can handle light signals with both vertical and horizontal polarizations at the same time.

That matters because optical signals currently carry data with both polarizations via a technique known as polarization-division multiplexing – but doing that requires a separate switch circuit for each polarization, which doubles the size of the chip and increases the cost.

The new device from AIST is called a “fully integrated non-duplicate polarization-diversity silicon-photonic switch” – in plain English, an integrated photonic switch that can handle vertical and horizontal polarizations at the same time. From the press release:

The new device … consists of a single 8 x 8 grid of 2 x 2 element switches. The researchers found that a single 8 x 8 grid with novel unique port assignments could take the place of two synchronized grids, and thus be used to simultaneously manage both polarizations of light, a method known as polarization diversity.

“In this way, the switch chip achieves polarization ‘insensitivity’ without doubling the size and cost of the chip, which is important for broadening the practical application of such photonics integrated devices,” said lead author Ken Tanizawa of AIST. “We strongly believe that a silicon-photonic switch is a key device for achieving sustainable growth of traffic bandwidth in optical networks, including both telecommunications and data communications, and eventually computer communications.”

The new optical switch also integrates polarization splitter-rotators onto the chip:

The splitter-rotators take input light signals with both horizontal and vertical polarizations, divide them into separate polarizations, and rotate one 90 degrees to match the orientation of the other. Both polarizations are synchronously switched on the single 8 x 8 grid with the unique port assignments. The switched polarizations are then recombined by the polarization splitter-rotator so that they return to their original state.

The switch is also capable of transmitting a consistently high-quality signal, thanks to a design feature that ensures the distance traveled by any signal passing through the grid is the same, regardless of its path, which means that the attenuation and delay of the signal are also the same.

The new polarization-diversity switch is a proof-of-concept design that AIST researchers will present at the Optical Fiber Communication Conference and Exhibition (OFC) next month. The research team say they will continue to improve the device and design a version with more ports (possibly a 32 x 32 grid) to handle larger amounts of transmitted data.

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