All-Optical Bit with Planar Semiconductors

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)

Reference: X. Ma et al.: Realization of all-optical vortex switching in exciton-polariton condensates, Nat. Commun.  11, 897 (2020); DOI: 10.1038/s41467-020-14702-5

Link: Center for Optoelectronics and Photonics Paderborn (CeOPP), Universität Paderborn, Paderborn, Germany