Spin injection into a commercial vertical cavity surface emitting laser

: the interplay of spin and photon dynamics.

Abstract

Spintronics exploits the spin degree of freedom of electrons - the electrons’ “natural magnet” - to manipulate information. The quantum-mechanical connection in semiconductors between electron spin and photon polarisation leads to optical writing and reading of spin by appropriate control of optical excitation and detection of excitation polarisation. In this thesis I exploit this process to optically orientate spins in vertical cavity surface emitting lasers (VCSELs), leading to the operation of spin lasers in commercial devices.
I review the extensive literature and summarise the behaviour of spins in semiconductors, particularly examining the relevance to VCSELs, outlining selection rules, spin-relaxation channels, and the role of cavity anisotropies (birefringence and dichroism).
I demonstrate the injection spin into a commercial laser at room temperature using circularly polarised optical pumping and measured the emitted circular polarisation via Stokes polarimetry. I found that near the ∼793 nm cavity dip the emitted light reached steady-state |S3| up to ∼ 0.22, whereas near ∼810 nm it was ≲ 0.06. This behaviour was replicated using a spin-flip model with physically realistic VCSEL parameters.
Fine tuning of the excitation wavelength further revealed features showing the strong dependence of the magnitude and direction of the excitation wavelength, explained by the birefringence of the pump mode.
Preliminary results using an axial magnetic field and polarisation-selective optical feedback revealed practical "tuning knobs" for future studies of spin and polarisation manipulation.
Overall, the work demonstrates that commercial VCSELs - devices you can buy off the shelf - already contain all the ingredients needed for spin controlled lasing, even though they were not designed with spintronics in mind.

Date of Award	20 Jan 2026
Original language	English
Awarding Institution	University of Bristol
Supervisor	Edmund G H Harbord (Supervisor) & Krishna Coimbatore Balram (Supervisor)