Fujitsu, HHI Reduce Optical Amplitude Noise with Ultra High-Speed Switch

Fujitsu Laboratories Ltd. and Fraunhofer Institute for Telecommunications, Heinrich Hertz Institut(HHI) announced the development of an ultra high-speed optical switch that uses nonlinear optical fiber[1] to reduce optical amplitude noise[2], which degrades the quality of optical signals when they are transmitted. Employing this technology, suppression of optical amplitude noise using a 107 gigabit per second (Gbps) phase modulated ultra high-speed signal was successfully verified. In addition, in a data transmission test across 320 km, it was verified that data quality after transmission could be received with roughly the equivalent of its quality prior to transmission.

Details of the new technology were presented at the Optical Fiber Communication Conference and Exposition (OFC) and the National Fiber Optic Engineers Conference (NFOEC) 2008 held in San Diego from February 24 to February 28.

In accordance with the rapid growth of broadband internet, there is a need for optical networks that are further efficient and capable of handling high-speed transmission and along with the rapid growth of data transmission volumes. Due to the fact that optical signals are more susceptible to optical amplitude noise as data transmission becomes faster and with greater data volume, there are significant limits to transmission distances that can be achieved. Thus, research and development of new technologies that can reduce optical amplitude noise is necessary.

Technological Challenges
In order to overcome the optical amplitude noise problem, a conventional solution has been to convert optical signals into electrical signals, electrically eliminate the noise impact, and then reconvert the signal back to an optical signal. However, for long-distance data transmission, this method requires much power for optical signal amplification and conversion to electrical signals. Therefore, there is demand for new technologies to enable networks that are more efficient and which consume less power.

Overview of the New Technology
The new technology developed by Fujitsu and HHI employs an ultra high-speed optical switch they developed that is capable of processing optical signals in less than a picosecond[3]. By controlling the power gain of the optical parametric amplification effect[4] from the optical signals, raising it when signals are weak and lowering it when signals are strong, the switch reduces optical noise without the need to convert optical signals into electrical signals.

By placing an ultra high-speed optical switch employing this technology in the middle of an optical transmission link, even after data was transmitted across 320 kilometers with a 107Gbps optical signal modulated by differential phase shift keying(DPSK)[5] data, the transmitted data essentially reproduced without change the characteristics of the data prior to transmission, thereby verifying high-quality optical transmission through this test. Compared to results when the switch is not employed, it was also verified that using the switch makes it possible to roughly double the length of transmission distances.

Furthermore, by optimizing the design of the nonlinear optical fiber, it is possible to cover much wider wavelength ranges than are currently used in optical transmissions, and handle optical signals in a variety of modulation formats.

Future Developments
It is anticipated that this new technology can be applied to optical regeneration, which is a key technology for next-generation ultra high-speed photonic networks.

Fujitsu and HHI will continue their research efforts to develop higher functionality in order to enable practical application of this new technology.

[1] Nonlinear optical fiber: A single-mode optical fiber that has a distinctive structure that increases the nonlinear optical effect. It produces ten times the nonlinear optical effect of conventional optical fibers. In the future, it is expected that the performance will be enhanced by ten- to as much as one hundred-fold above current levels by developing the fiber’s structure and material.
[2] Optical amplitude noise: Spontaneous emission noise generated when using an optical amplifier to amplify optical signals.
[3] Picosecond: One trillionth of a second.
[4] Optical parametric amplification effect: A type of nonlinear optical effect in which when a strong pump optical wave and signal optical wave are input into fiber, a new signal optical wave and idler wave are output. During the process, the optical signal power is amplified.
[5] Differential phase shift keying(DPSK): A phase modulation scheme in which the phase of a signal is modulated by 180 degrees corresponding to the digital data of “0″ or “1″. In this scheme, the phase difference between two successive signals carries data.

About Heinrich Hertz Institut
Research and development activities at the Heinrich-Hertz-Institut (HHI) are concentrated to expand the principles of information technology and to demonstrate new applications for new products in partnership with the industry. The core competencies of HHI are in the areas:

  • Photonic Networks and Systems (highly capacitive and flexible signal transmission)
  • Broadband Mobile Communications (resource management for broadband applications for UMTS and beyond (3GPP LTE))
  • Photonic Components (customized active III-V semi-conducting components)
  • Image Processing (encoder / decoder for video and audio transmission)
  • Interactive Media – Human Factors (2D and 3D display technologies; man machine interface)

About Fujitsu Ltd
Fujitsu Limited (TSE: 6702; ADR: FJTSY) is a leading provider of customer-focused IT and communications solutions for the global marketplace. Pace-setting device technologies, highly reliable computing and communications products, and a worldwide corps of systems and services experts uniquely position Fujitsu to deliver comprehensive solutions that open up infinite possibilities for its customers’ success. Headquartered in Tokyo, Fujitsu reported consolidated revenues of 5.1 trillion yen (US$43.2 billion) for the fiscal year ended March 31, 2007.

About Fujitsu Laboratories Ltd.
Founded in 1968 as a wholly owned subsidiary of Fujitsu Limited, Fujitsu Laboratories Limited is one of the premier research centers in the world. With a global network of laboratories in Japan, China, the United States and Europe, the organization conducts a wide range of basic and applied research in the areas of Multimedia, Personal Systems, Networks, Peripherals, Advanced Materials and Electronic Devices.