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Optofluidics offers ultrafast switching

20 May 2009

Organic photonic device shapes up for optical communications, computing applications.

Researchers in Italy are taking advantage of amplified spontaneous emission (ASE) within an optofluidic microchannel to demonstrate ultrafast gain switching. The team claims that its technology could find applications in optical networks and ultimately in all-optical computing (Applied Physics Letters 94 041123).

"We've shown a new approach for organic photonic devices," Jenny Clark, a researcher at Politecnico Di Milano in Milan, told optics.org. "We have combined the unique properties of a conjugated polymer in solution with an optofluidic microchannel to produce an easy-to-integrate all-optical amplifier capable of ultrafast gain switching."

In optical communication systems, it is important to be able to control (switch/modulate) the light within the network at high speed. Therefore, it is necessary for any switching process to have full recovery of the signal within the fastest possible time. The Italian team has demonstrated a switching response time of 350 fs, which corresponds to a possible data transmission rate on the order of terahertz (1012 Hz).

The breakthrough was made possible thanks to the development of reliable femtosecond lasers, which enabled the team to directly write buried microchannels in glass.

In the set-up, a conjugated polymer solution is housed within a 100 µm diameter microchannel. The solution exhibits ASE when illuminated with a 400 nm femtosecond laser. As the light that is generated via ASE is guided through the channel, it can become amplified by other parts of the sample. This results in a line-narrowing of the emission spectrum and an increase in the integrated intensity.

"We exploit the fact that the conjugated polymer chains are isolated in solution to selectively control (quench) the stimulated emission," explained Clark. "The first pump generates excited states in the polymer, which leads to stimulated emission. Since the chains are isolated, they facilitate an ultrafast recovery of stimulated emission."

According to Clark, the breakthrough could provide amplification and switching capabilities for optical communication and optical computing applications. It also provides evidence of ASE in an optical chip, which is a step forward in producing on-chip lasers that can be optically controlled.

As a next step, Clark and colleagues hope to improve the losses of their organic devices by testing different solvents with different refractive indices as well as varying concentrations.

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