Fujitsu Limited and Fujitsu Laboratories Limited have announced the development of the world's first semiconductor optical amplifier (SOA)(1) enabling waveform re-shaping of high-speed optical signals at 40Gbps by using quantum dots(2). Optical technology capable of restoring degradation of optical signals to their original quality without converting them into electronic signals is known as all-optical 3R regeneration(3), consisting of re-amplification, re-shaping, and re-timing. The new SOA accomplishes both re-amplification and re-shaping of optical signals through a single semiconductor device, thereby enabling optical regenerators to become further compact and facilitating higher.

New technology developed for this SOA will be the foundation for the realization of future ultra high-speed photonic networks. Research for this technology was partially conducted as part of the project "R&D of High Performance Network Subsystems Using Nano Technology", commissioned by the Ministry of Internal Affairs and Communications (MIC) of Japan.

Details of this development will be presented at the Optical Fiber Communication Conference (OFC) 2005, which starts March 6 in Anaheim, U.S.

For future photonic networks that require high-speed optical signals to be transmitted at high qualities over long distances and flexible interconnect of optical network nodes, all-optical 3R regeneration is extremely effective. Optical 3R regeneration technology consists of three key processes: re-shaping, re-timing, and re-amplification. Re-shaping refers to the suppression of noise and fluctuation of optical signals to re-shape signal waveforms, re-timing reduces timing fluctuations know as timing jitter, and re-amplification amplifies optical signals.

In the past, as optical signals were regenerated by converting them into electronic signals and using electronic circuits for regeneration, optical regeneration required large and complex regenerators. Therefore, various research has been underway to develop all-optical regenerators capable of regenerating optical signals without requiring their conversion into electronic signals.

SOAs can suppress noise and fluctuation when optical signals are on (ON-level), by utilizing a characteristic known as gain saturation, in which the optical gain (amplification rate) falls when a signal is too intense. However, conventional SOAs typically had slow gain saturation response speeds requiring several nanoseconds, thereby impacting the subsequent signal and making such SOAs unusable in all-optical regenerators.

Technology that Fujitsu developed for its new SOA significantly accelerates the response speed of gain saturation. Fujitsu achieved this by observing and focusing on the extremely fast speeds of gain saturation when quantum dots were used. By employing quantum dots, gain saturation response time was accelerated to a few picoseconds, one-thousandth the time that was required with conventional SOAs.

In addition, through improvements in crystal growth technology of quantum dots(4) and by designing a new device structure, Fujitsu realized a quantum dot SOA which easily enables gain saturation while achieving high optical gain and high optical output, at wavelengths of 1550 nanometers (nm) which are used in optical telecommunication.