Polarization-Insensitive Optical Switches Could be the Key to High-Speed Data Transfer

When real-time video calls are made from one cellular phone to another across the globe, huge amounts of data are transmitted across the Internet and telecommunications networks delivering the calls.

At the same time, when higher amounts of data such as ultra-high definition (or 4K and 8K) images are sent and received by people over the largly optical fiber-based networks and the requirement for such communication increases, the requirement for new technologies for transmitting that data at improved speeds, with lower cost and increased energy efficiency, also increases.

One potential way of doing this is to use optical switches with the ability to relay signals conveyed by optical fibers from one circuit to another. Currently, one new technology specifically ensures significant enhancement of the optical switches employed by fiber optic networks.

Researchers from the National Institute of Advanced Industrial Science and Technology (AIST), Japan, have developed an innovative integrated optical switch produced by efficiently using silicon photonics technologies. They will present their research at the Optical Fiber Communication Conference and Exhibition (OFC), held from 19 to 23 March in Los Angeles, California, USA.

A main requirement of optical switches of this kind is the ability to handle light signals using both horizontal and vertical polarizations, because optical signals carry data of both polarizations, a technique referred to as polarization-division multiplexing. The successful execution of the dual transmission requires a separate switch circuit for each polarization. However, this way, the size of the chip is doubled and the cost of the system increases.

The new device, technically known as a “fully integrated non-duplicate polarization-diversity silicon-photonic switch,” comprises of a single 8 x 8 grid of 2 x 2 element switches. The research team discovered that a single 8 x 8 grid containing innovative unique port assignments can match the work of two synchronized grids. Thus, the 8 x 8 grid can be used to simultaneously control dual polarization of light - a technique called 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. 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.

Ken Tanizawa, AIST

In the new device, the chip is integrated with polarization splitter-rotators that capture input light signals of both vertical and horizontal polarizations. The splitter-rotators divide the input light signals into separate polarizations, and rotate one of the polarizations by 90 degrees to match the orientation of the other.

The unique port assignments synchronously switch both polarizations on the single 8 x 8 grid. Then, the polarization splitter-rotators recombine the switched polarizations such that they return to their original form.

The research team designed the device in a way that the distance traveled by any signal that passes via the 8 x 8 grid is similar, irrespective of its path. Hence, the delay and attenuation of the signal are also identical, ensuring a consistently high-quality signal.

As the new switch is a proof-of-concept design currently, the research team is on the course of further improving the device and developing a design that includes larger number of ports, e.g. 32 x 32 grid, that can enable transmission of even greater amounts of data. Apart from improving network flexibility, such improvements can also enable the use of optical switching in prospective energy-efficient optical networks.

Source: http://www.osa.org/en-us/

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