The basic operation of the Optical Packet Switch is as follows:

Each incoming packet is divided into two individual packets by a splitter.

One of the copied packets is fed to a high-speed label recognition circuit.

The label recognition circuit controls an optical switch device by using the recognized destination information.

The processing time required for label recognition is about 10ns. During this process, the other copied packet passes through a 2 meter delay fiber that slows the packet by 10ns.

The delayed packet reaches the optical switch device just after the switch has been controlled, and is output to the correct port.

By this means, the Optical Packet Switch recognizes the destination address of each packet and directs it to the correct output port.

The optical label in the header of each optical packet contains the destination address. As the packet is in an optical form, recognizing its destination address and controlling the optical switch must be done with very high speed.

Though detailed information on this circuit is confidential, it can be revealed that the circuit achieves the 10ns recognition time by using an optical serial-parallel converter and a hybrid optoelectronic device comprised of high-speed photodiodes and logic circuits.

An optical packet consists of an optical label and a payload. Its length is fixed. The standard NRZ modulation is used as its modulation format. On the assumption that a label swap will be implemented in the future, a sub-gap is positioned between the optical label and the payload.

The live demonstration at multiple exhibitions* showed the optical packet switch's capability to recognize a two-bit difference in an optical label and route an optical packet.

In the demonstration, an electric packet sequence was generated using the program pattern function of a 40G pulse pattern generator (the Yokogawa AP9950). The sequence was converted to an optical packet sequence by an LN modulator. The optical packet sequence was able to be monitored by an oscilloscope and is the yellow pattern (input packets) depicted in the above illustration.

The input packets are switched to either of two ports depending on the optical label. In the above illustration, the packets output to port A are blue and the packets to port B are red.

In this demonstration, the bit rate was 2.5Gbps for the optical label, 40Gbps for the payload, and the length of the packet was 43ns.

* OFC 2004 (February 2004, Los Angeles), N+I 2004 Tokyo (June 2004, Makuhari Messe), and ECOC 2004 (September 2004, Stockholm), FOE 2005 (January 2005, Tokyo), ECOC 2005 (September 2005, Glasgow)