Japan's AIST touts polarization-diverse silicon photonics optical switch

At OFC next month, Japan's National Institute of Advanced Industrial Science and Technology (AIST) will describe the creation of an integrated optical switch realized via silicon photonics that will accommodate light that is carrying signals in both vertical and horizontal polarizations.

To accommodate dual-polarized modulated transmission, a separate switch circuit must be used for each polarization. An optical switch for such transmission therefore must be twice the size of a similar device that only has to accommodate one polarization. The device that AIST will present in Los Angeles at OFC next month, which the group calls a "fully integrated non-duplicate polarization-diversity silicon-photonic switch," comprises a single 8x8 grid of 2x2 element switches. The researchers say that such a grid with unique port assignments could take the place of two synchronized grids, and thus be used to simultaneously manage both polarizations of light and achieve 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 device also features polarization splitter-rotators integrated onto the chip. The splitter-rotators take the input dual-polarized signals, 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 8x8 grid with the unique port assignments. The polarization splitter-rotator them recombines the switched polarizations into their original state.

The researchers designed the device so that the distance traveled by any signal passing through the 8 x 8 grid is identical, regardless of its path. This means that the attenuation and delay of the signal are also the same.

The new switch is a proof-of-concept design. The researchers are now working to further improve the device and to create a design with a larger number of ports (such as a 32x32 grid) that would enable transmission of a greater amount of data.

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