
Illustration of the ultrafast switching of an optical bit. (Source: U. Paderborn)
Computers process information based on arrays of bits. This is typically realized with integrated electronic circuits permanently written onto a semiconductor chip. Researchers from Paderborn University and Technical University Dortmund have now realized an all-optical bit that is temporarily written into a planar semiconductor nanostructure only using light and that can also be reconfigured only using optical techniques. Besides the fundamental interest, this new approach carries promise for future optoelectronic application schemes.
The research teams of Stefan Schumacher (Paderborn University) and Marc Aßmann (Technical University Dortmund) investigate a particular type of vortex state forming inside a quantum fluid excited in a planar semiconductor nanostructure. “The vortices that form can rotate in two different directions. These two directions are then associated with the two values of a bit, zero or one, respectively,” explains Schumacher. The structure is optically excitated with a ring-shaped laser profile, the vortex forming resides in the center of the ring. An additional short laser pulse is then applied to invert the rotation direction of the vortex. This way the optical bit can be reconfigured or switched from zero to one and vice versa.
With their promise for information storage or processing, similar vortex states are currently also being studied in a number of other systems. “Quite often, however, only the existence or creation of the vortex states is investigated. Here, we also demonstrate the efficient control with ultrashort laser pulses. We can actually switch the rotation direction of the vortex and the information stored within the billionth part of a second,” elaborates Xuekai Ma.
“A particular achievement of the present study is the practical and robust implementation of the scheme in the lab. The rotation direction of the vortex is directly measured through the orbital angular momentum of the light emitted,” notes Bernd Berger, who has developed the optical setup as part of his PhD studies at the TU Dortmund. The general concept only requires off-resonant and therefore incoherent optical excitation, which also makes it compatible with electrical approaches. The theoretical idea was developed by Xuekai Ma. In close collaboration with the group of Aßmann in Dortmund, the scheme was then successfully realized in the lab. (Source: U. Paderborn)
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