A giant step toward the practical application of next-generation 40 Gbps optical packet networks

Yokogawa Electric Corporation announced in Japan that the company has developed a prototype of a 40 Gbps optical packet network system and succeeded in demonstrating for the first time ever the practicality of using such a network to transmit image data. This success in transmitting image data over an optical packet network system paves the way for an environment in which data packets just like those in existing LANs will be passed between computers at ultra-high speeds. Yokogawa displayed this network system at Fiber Optics Expo 2005 (FOE2005), an optical communications trade fair held at the Tokyo Big Sight exhibition center from January 19 to 21.

Development Background
The number of subscribers to ADSL, FTTH, CATV and other broadband Internet access services grew three and a half times between 2002 and 2004. As a result, data communications traffic has more than doubled each year and experts are now predicting that the core network will have insufficient capacity to meet demand within a few years.
  As with the core networks, sooner or later corporate, regional, and other types of LANs will undoubtedly experience capacity shortfalls. The day when LANs like these will have to handle much larger volumes of data, including video, is drawing near. The Internet data centers (IDC) and broadcasting stations having to handle such high volumes of data will have to build 40 Gbps networks.
  Achieving 40 Gbps speeds with existing optical communications technologies requires a direct one-to-one connection between a server and a user terminal. Unlike existing LANs, this method does not have the flexibility to support connections to multiple terminals, and this is proving to be a bottleneck in the achievement of ultrahigh-speed communications networks.
  In order to build an ultrahigh-speed optical communications network having the same flexibility as a LAN, data must be divided into relatively small chunks like the packets that are exchanged over the Internet. To implement optical packet communications, a system developer must obtain and skillfully combine optical switching devices,*1 optical label recognition circuits,*2 optical buffers,*3 and clock/data recovery circuits.*4 Each of these requires state-of-the-art technology, and experts say it is extremely difficult for any single company to develop all four types.

Overview of the Network System Prototype
The network system prototype employs Yokogawa’s newly developed 40 Gbps Optical Packet Switch, and Optical Media Manager, which is an optical packet transmitter/receiver that is equipped with an Ethernet interface. With its ring topology, this network system prototype supports the connection of multiple terminals. The signal transmission quality of this optical packet network is also well suited to the actual conditions that the system would encounter in practical use. With this system prototype, it is possible for ten terminals in different locations to simultaneously download a two-hour movie (equivalent to one DVD) from a server in just ten seconds.
  Yokogawa’s successful development of the 40 Gbps Optical Packet Switch, first announced in February 2004, was based on more than 20 years of research into the use of compound semiconductor technology for optical communications. This switch is a combination of an optical switching device, which is capable of directly switching optical packet signals at ultrahigh speeds without having to temporarily convert them to electrical signals, and an optical label recognition circuit, which controls the optical switching device according to the destination information carried by the optical packet signals, and an optical buffer, which prevents conflicts between signals when they are simultaneously output to the same port on the 40Gbps Optical Packet Switch.
  Also incorporated in the prototype is an Optical Media Manager developed by Yokogawa that contains a clock/data recovery circuit for securely recovering data on the receiving side that has not been synchronized with the transmitting side.
  Yokogawa is the only company to date that has succeeded in achieving a practical implementation of all of these fundamental technologies.

Yokogawa’s Approach to the Photonic Networks Business
Yokogawa plans to continue testing the usability of this newly developed 40 Gbps optical network technology and to commercialize it by 2006. The company will focus on the huge LAN market, including IDCs, broadcasting stations, and enterprises, while concurrently developing peripheral devices and even higher-speed products.
  In addition, Yokogawa has moved ahead of the competition by successfully developing driver modules for optical modulators, photodiode modules, and other technologies that will be vital to the realization of 40 Gbps optical transmission systems. These are key components of laboratory measuring instruments and optical communications equipment, and Yokogawa will continue to nurture their further development as part of the communications modules business.
  Overall, Yokogawa estimates that its entire optical communications equipment business, the aforementioned two businesses, will be generating annual sales of 100 billion yen by the year 2010.

*1 Optical switching device: A device designed to directly route optical signals by turning currents through compound semiconductors on and off without having to convert the signals. Yokogawa has realized an optical path switching speed of less than two nanoseconds (two-billionths of a second). This is the world’s fastest current-injected waveguide-type optical switch, with a switching speed a million times faster than an optical switch that uses a movable mirror.

*2 Optical label recognition circuit: A hybrid optoelectronic device comprising a high-speed photodetector for reading the destination information recorded in the header part of an optical packet signal and a high-speed electronic circuit for processing that information. This device controls the optical switching device by using the recognized destination information.

*3 Optical buffer: In order to prevent data corruption caused when two optical packet signals carrying the destination information instructing that they be output to the same port, simultaneously enter the optical packet switch, one of them must be delayed. However, there is currently no such technology for storing light as is in the memory. This optical buffer is a technology for introducing optical packet signals into the optical fiber and delaying them in proportion to the length of the fiber.

*4 Clock/data recovery circuit: In conventional optical communication, the transmitting and receiving sides are connected on a one-to-one basis and dummy data is constantly flowed between them even when the communication link is turned off. This dummy data is used to synchronize the timing signals (clock signals) for reading transmitted data on the transmitting and receiving sides. In the case of optical packet networks, however, there is no way of knowing when and through which path the data is sent. It is therefore impossible to synchronize the clock signals. To solve this problem, optical packet networks require a function for asynchronously recovering clock signals and data on the receiving side for each arriving packet.