Semiconductor Optical Amplifiers and their Application for All Optical Wavelength Conversion

Abstract

All optical networks and switches are envisioned as a solution to the increasing complexity and power consumption of today’s communication networks who rely on optical fibers for the transmission of information but use electronics at the connecting points on the network (nodes) to perform the switching operation. All optical networks, in contrast, will use simple signalling methods to trigger all optical switches to forward the optical data, from one optical fiber to another, without the need to convert the information carried by the optical signal into an electric one. This may save up to 50% of the total power consumption of the switches and will allow for simple scaling of the transmission rates. While all optical networks may offer significant breakthroughs in power consumption and network design, they fall back on one essential aspect, contention resolution. In traditional communication networks and in particular those who carry data (which has long surpassed voice traffic, in bandwidth), the nodes on the network use huge amounts of electronic random access memory (RAM) to store incoming data while waiting for their forwarding to be carried out. The storage of data, also called buffering, is essential in resolving contention which occurs when two incoming streams of data need to be forwarded to the same output port at the same time. In contrast all optical switches, who do not convert the data signals into the electrical domain, cannot use electronic buffers for contention resolution. They can however use the unique properties of light signals which at moderate power levels can propagate along the same transmission media without interference if they have different wavelengths. This means that if two competing light signals need to be switched to the same output port, their successful forwarding can be accomplished by assigning them different wavelength. This can be done completely in the optical domain by means of all optical wavelength conversion. Large optical networks, require optical amplifiers for signal regeneration, especially so if the signal is not regenerated through optical to electrical to optical conversion. Semiconductor Optical Amplifiers (SOAs) are a simple, small size and low power solution for optical amplification. However, unlike fiber based amplifiers such as EDFAs, they suffer from a larger noise figure, which severely limits their use for long haul optical communication networks. Nevertheless, SOAs have found a broad area of applications in non-linear all optical processing, as they exhibit ultra fast dynamic response and strong non-linearities,