Fujitsu Creates Wavelength Tunable Laser

Fujitsu Laboratories Limited announced their development of a wavelength tunable laser for 10 gigabits per second (Gbps) dense wavelength division multiplexing (DWDM)[1] optical transmission. As a world’s first, the company confirmed stable wavelength tunability and optical fiber long-range transmission of a wavelength tunable laser across 80 kilometers (km), in the form of a XFP-type[2] optical transceiver. This new technology will enable practical application of small, high-performance optical transceivers to support high-capacity and high-reliability optical networks.

Details of this technology have been presented at The Optical Fiber Communication Conference & Exposition (OFC) 2007 being held in Anaheim, California from March 25. The technology is also being exhibited and demonstrated at the Fujitsu booth of the exhibition accompanying the conference.

Along with the arrival of a true broadband communicative and ubiquitous networking society, the amount of data traffic has been rapidly increasing. In order to enable high-capacity optical networks, DWDM systems, which use a single optical fiber for optical signals of several different wavelengths, are being utilized. Wavelength tunable optical transceivers are becoming important as components that enable OADM[3] functionality in next-generation networks, as the transceivers enable reduction of component types required- attributable to the characteristic the transceivers feature in which wavelengths can be switched while being used by the network – and realization of DWDM systems at low overall cost.

Currently, large 300 pin-type devices[4] are used as wavelength-tunable transceivers for DWDM systems. However, in order to make the overall systems smaller and with higher capacity, there is a need to create optical transceivers that are even more compact.

Technological Challenges
In developing a XFP-type wavelength-tunable transceiver for 10 Gbps DWDM transmission, the following issues had to be addressed:

  1. Realization of a wavelength tunable laser featuring easy wavelength control and low power consumption
    Temperature-controlled and external cavity type conventional wavelength tunable lasers consume large amounts of power due to their need for temperature control parts and complex control circuitry, thereby requiring a large area for circuit mounting, and thus were difficult to reduce in size.
  2. Aggregation of functions with the optical modulator

  3. Thus far it had been difficult to reduce the size of conventional wavelength tunable lasers, as it was impossible to integrate them with optical modulators required for achieving long-distance transmission, and as such it was necessary to use the lasers by connecting them with external optical modulators.

Newly Developed Technology
In order to address the aforementioned issues, Fujitsu Labs developed a modulator integrated laser known as a Tunable Distributed Amplification-Distributed FeedBack (TDA-DFB) laser, which integrates the optical modulator with the laser source.

TDA-DFB laser source
Fujitsu Labs developed a wavelength tunable laser that applies changes incurred in the refraction index of the wavelength tuning area, when an electrical current is injected. Since wavelength can be changed by simply controlling the electrical current, it is now possible to control the output wavelength with a simple circuit. Furthermore, since laser temperature can be steady and fixed, the new laser consumes dramatically less power than conventional temperature controlled lasers.

Optical modulator integrated laser
Fujitsu developed a modulator integrated laser that integrates the TDA-DFB laser and optical modulator. In addition to making it possible to providing long-distance transmission capability necessary for 10 Gbps transmission, the new laser enables a more compact laser source.

As a world’s first, Fujitsu Labs evaluated characteristics of the newly developed modulator integrated laser in the form of a XFP-type optical transceiver (Figure 2). Evaluation of the transceiver’s optical fiber long-distance performance across 80km, which is necessary for DMDM transmission, confirmed basic characteristics including stable wavelength tunability for 4 wavelengths over 100 gigahertz (GHz) intervals as established by the ITU-T regulatory organization, and excellent functionality for 10Gbps transmission.

Future Developments
Fujitsu aims to commercialize these technologies in the first half of fiscal 2008 (April – September 2008), and will continue to pursue research and development to further enhance their performance.

Glossary and Notes
[1] Dense Wavelength Division Multiplexing (DWDM): A format for multiplexing of optical fibers, in which multiple optical signals that have different wavelengths are simultaneously used.
[2] XFP-Type: A term standing for 10 Gigabit Small Form Factor Pluggable, a product specification for optical modules in which electric and optical interface can be attached or detached.
[3] Optical Add-Drop Multiplexer (OADM): One of several methods available in which the path of light can be switched without electrical conversion, thereby enabling effective use of wavelength resources.
[4] 300 Pin-Type: A product specification for optical modules that uses 300 pin electric connectors.

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 about 4.8 trillion yen (US$40.6 billion) for the fiscal year ended March 31, 2006.

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.