Spin Lasers in the Fast Lane

A new concept for ultrafast semiconductor lasers makes inventive use of the intrinsic angular momentum of electrons, called spin, to break previous speed barriers.

The new spin lasers have the potential to achieve modulation frequencies of well above 100 GHz. They represent a significant step toward high-speed data transmission for the Internet of the future.

By injecting spin-polarized electrons in semiconductor-based microlasers, modulation speeds can be reached that are superior to those of conventional lasers. (Images: Gerhardt et al.)

Researchers at Ruhr University Bochum in Germany report on their results in the journal Applied Physics Letters. Their paper is titled "Ultrafast spin-induced polarization oscillations with tunable lifetime in vertical-cavity surface-emitting lasers."

Optical data transmission by semiconductor lasers is a prerequisite for the globally networked information technology world. The maximum speed of conventional semiconductor lasers has been a limiting factor; typical modulation frequencies are at levels well below 50 GHz.

Relaxation oscillations, as shown in (a) mark the maximum speed achievable in conventional semiconductor lasers. By using spin-polarized electrons, oscillations are generated in the polarization of the light field, which can be much faster than the relaxation oscillations (b). Since the oscillation lifetime can easily be tuned via the current(c), such spin lasers are suited for optical data transmission.

By using spin lasers, Bochum's researchers were able to overcome the previous limits for the modulation speed. In conventional lasers, the spin of the electrons injected is entirely arbitrary, while in spin lasers, only electrons with a previously determined spin state are used. Injecting these spin-polarized electrons forces the laser to work simultaneously on two laser modes with different frequencies.

"This frequency difference can easily be tuned using the so-called birefringence in the resonator, for example, by simply bending the microlaser," said researcher Nils Gerhardt.

By coupling the two laser modes in the microresonator, oscillation with a new frequency occurs, which theoretically can reach well above 100 GHz.

For more information, visit: www.ruhr-uni-bochum.de