Lightwave - Fujitsu develops wavelength-tunable laser

APRIL 3, 2007 -- Fujitsu Laboratories Ltd (search for Fujitsu) has developed what it claims is the world's first wavelength-tunable laser for 10-Gbit/sec DWDM optical transmission. The company has confirmed stable wavelength tunability and long-range transmission of a wavelength tunable laser across 80 km in the form of a XFP-type optical transceiver. Fujitsu says this new technology will enable practical application of small, high-performance optical transceivers to support high-capacity and high-reliability optical networks.

Wavelength tunable optical transceivers are becoming important as components that enable optical add/drop multiplexing (OADM) functionality in next-generation networks. The transceivers enable a reduction in the number of component types required and a lower overall DWDM system cost.

Currently, large, 300 pin-type devices are used as wavelength-tunable transceivers for DWDM systems. However, in order to make the overall systems smaller and higher capacity, optical transceivers must be even more compact.

In developing an XFP-type wavelength-tunable transceiver for 10-Gbit/sec DWDM transmission, two key 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. Thus, they were difficult to reduce in size.

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

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 applies changes incurred in the refraction index of the wavelength tuning area when an electrical current is injected. Since wavelengths 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, says Fujitsu.

Fujitsu Labs evaluated characteristics of the newly developed modulator integrated laser in the form of a XFP-type optical transceiver. Evaluation of the transceiver's optical fiber long-distance performance across 80 km, which is necessary for DMDM transmission, confirmed basic characteristics, including stable wavelength tunability for four wavelengths over 100-GHz intervals as established by the ITU-T regulatory organization, and excellent functionality for 10-Gbit/sec transmission.

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.

Details of this technology were presented last week at The Optical Fiber Communication Conference & Exposition (OFC) 2007 in Anaheim, CA. The technology was also demonstrated in the Fujitsu booth at the exhibition accompanying the conference.

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