Spintronics seeks to manipulate and use the spin that electrons and photons possess to store and process information. Advances in manipulating the spin of an electron and the associated magnetic moment, recognized by the 2007 Nobel Prize in Physics, were crucial for a dramatic increase in the capacity of computer hard drives using spin-valves. Such spin-valves rely on the concept of magnetoresistance in which the magnetic configuration of a device determines if the current flow is permitted or restricted. While spin-valves remain valuable for magnetically storing and sensing information, they are of limited use for signal processing and digital logic; it would be crucial to consider practical paths to other spin-based device schemes. One such opportunity is afforded in this proposal by reexamining how to improve semiconductor lasers, widely used in DVDs, optical communication, and medicine. In commercial semiconductor lasers, a sufficiently large number of electrons and holes, having an opposite charge, are generated and the excess charge carriers recombine to emit coherent photons that possess the same wavelength and phase. Although photons, electrons and holes all have spin, the working principle of conventional semiconductor lasers is completely unaffected by them, because there is no net imbalance between spins pointing in different directions ('up' and 'down'). The proposed work will provide a closely integrated educational and outreach efforts by organizing a week-long Summer Workshop on Lasers, experiment and theory for high school students and organizing symposia to bridge the gap between the spintronics and optics communities at the annual SPIE Optics and Photonics Conference.
The proposed research builds on recent experimental advances demonstrating that the operation of lasers can be strongly modified by optically or electrically injecting spin-polarized carriers, having thus a spin imbalance. In the steady-state and low-frequency operation changing the polarization of injected carriers in such spin-lasers has already enabled: (a) lasing threshold reduction and enhanced emission intensity as compared to their conventional (spin-unpolarized) counterparts; (b) strong modulation of the emitted light, even at a fixed injection intensity. The most important applications of spin-lasers are still largely unexplored and pertain to an ultrafast operation and their superior dynamical performance. The bandwidth in conventional lasers is typically limited by the relaxation oscillation frequency. However, spin-lasers should enable a large increase in oscillation frequency , and) a novel and much higher frequency scale governing the polarization oscillation of the emitted light. The PI will develop a detailed modeling of spin-lasers and explore how to: (1) tailor the resonant cavity anisotropy to achieve dynamical bandwidths > 100 GHz, (2) reduce parasitic frequency modulation-chirp, and (3) improve switching properties and digital operation; and validate with the experimental data. The PI will study alternative device geometries focused on the recent advances in GaN spin-nanolasers. Conventional metallic interconnects are recognized as the bottleneck in Moore's law scaling and the main source of power dissipation. Since optical interconnects, having lasers as their key element, could address the underlying limitations, this work on spin-lasers may have transformative character and enable novel interconnects.
