Ultrafast Spin-Lasers*

In times of ultrahigh definition video streaming, cloud computing and Internet of Things, the Internet structure is the key enabler of the global digitization. To meet future communication bandwidth requirements, especially in hyperscale datacenters, new concepts for optical short-range communication systems with high modulation bandwidth and low energy consumption are urgently needed. A very promising approach is to use spin and polarization modulation and their superior dynamics in spin-polarized vertical-cavity surface-emitting lasers (spin-VCSELs) instead of conventional intensity modulated laser devices. Here, the coupling via angular momentum exchange between the spin states of the charge carriers and the photons plays a decisive role [1]. The dynamics of the coupled spin system are typically decoupled from the intensity dynamics of the laser and can be modulated at frequencies > 200 GHz [1]. The modulation response of spin lasers can be described analogously to a driven damped harmonic oscillator with a resonance frequency that can be directly controlled and increased by birefringence in the resonator. Furthermore, the ultrafast modulation response in spin-VCSELs can be obtained for low bias currents and is not severely affected by high temperatures [2]. This opens up new possibilities for high-speed transmission systems with very low power consumption.
Here, we review recent results on ultrafast spin-lasers for the next generation of optical communication systems. Furthermore, we describe the fundamental role of design parameters such as birefringence, dichroism and photon lifetime for the development of optimized devices and discuss novel concepts for future integrated and electrically pumped spin-lasers.

[1] M. Lindemann et al., Nature 568, 212 (2019)
[2] M. Lindemann et al., AIP Advances 10, 035211 (2020)