OPTICAL SWITCHING: All-optical processing reads packet headers

Incorporating news from O plus E magazine, Tokyo

OSAKA—In what they say is the first demonstration of this transmission technique, researchers have succeeded in sending data packets to a destination specified in the address without having to convert the optical signals to electrical signals. The researchers include Naoya Wada at the Optical Communications Technologies Laboratory of the Ministry of Communications and Posts, Kenichi Kitayama at the Osaka University Graduate School Department of Engineering, and colleagues

Communication in venues such as the Internet involves dividing data into smaller units called packets and sending them separately, with destination information such as addresses included in a header. Routers read the header information and send the packets along the correct path. The data are restored at the destination (see figure).

Current networks perform most of their functions, including routing, electrically. Optics are used only in the transfer of information over the length of the path. As the quantity of data transmitted over the Internet steadily increases, it is clear that the electric manipulations will eventually give rise to bottlenecks. All-optical networks solve this problem because they allow optical signals to be manipulated without being converted to electric signals. This experiment has confirmed the proof of principle of an optical routing component in such a network. The biggest challenge lies in creating a header processor that performs without the conventional light-to-electricity conversion.

In the experiment, address information was expressed in a code used in optical code—division multiple access (OCDMA) technology—OCDMA is an optical version of CDMA, which is a familiar technology in cellular phones.

Multiple copies of a row of pulses are made inside the header processor and are compared to the addresses in the table using optical correlation techniques. When the addresses match, a sharp peak is seen. This peak can be used to control an optical switch array. Because the comparisons are done in parallel, the manipulations dramatically shorten the process. A compact (a few square centimeters) optical waveguide device, also developed by the researchers, is used to compare the signals. This stable device is also used to generate the optical code.

PHOTO. In an optical router, a packet enters from the left as an optical signal, which is divided and sent to either an optical gate switch array or a header processor. The header processor reads the packet header, identifies the address, and turns on the optical switches that route the information to the specified destination. The header processor essentially contains a lookup table that matches the address and destination.

During the test an 8-bit address was sent to its correct destination in 35 ps (no data were attached because the experiment was theoretical). This speed translates into processing 100 million packets in one second—approximately 1000 times faster than electrical routing.

Although this experiment focused on making address identification optical, the group hopes to develop an integrated optical routing device by transforming other components such as switch-control components to an optical format.

Courtesy O plus E magazine, Tokyo

CORRECTION

In the October Japanwatch story "Homogeneous superfine silicon particles light up" (p. 48), the name of one research institute was incorrectly given as the Mechanical Research Laboratory. The accurate English translation should read Mechanical Engineering Laboratory, AIST-MITI.