Designing bright single photon sources with low Q-factors at telecom O band wavelengths

Abstract

Bright quantum dot single photon sources (SPS) have mostly relied on coupling to optical cavities with high quality (Q) factors. Since the Q-factor represents the damping of the optical resonator in time, which can be shown to correspond to the resonance spectrum width, bright sources with high Q-factors rely on the (small) probability of a quantum dot emitting within the very narrow resonance peak. In this thesis I have investigated the possibility of bright emission from emitters in low-Q cavities, which are easier to fabricate and result in a higher device yield than their high-Q counterparts. With the use of computerised numerical modelling methods such as the finite-difference time-domain (FDTD) method and the transfer matrix method (TMM) I have investigated two types of devices: optical micropillars, and emitters exploiting Tamm Plasmons (TPs). In my inspection of the properties of Tamm Plasmon based emitters, I focused on the photonic properties of the interface between the metal and cavity (spacer), revealing considerable effects of the metal layer on the absorption and side emission, the two most significant loss channels. By demonstrating differences in the total extraction efficiency of up to 75% of the peak value within the range considered, I demonstate the benefits of optimising TP structures with the metal-spacer interface in mind. By simulating a variety of micropillars, I examine the cavity quantum electrodynamics (QED). By optimising the active coupling to the cavity with the diameter I demonstrate the theoretical possibility of high-beta (>90%) low-Q (~10^2) micropillars. I then demonstrate how the passive efficiency depends on the ratio of the top and bottom DBR transmissivity, and that internally efficient pillars can be designed with Q-factors in the low 1000s. I also demonstrate the theoretical possibility of exctracting over 80% of QD created photons within numerical apertures easily reached by bulk optics.

Date of Award	21 Jan 2021
Original language	English
Awarding Institution	University of Bristol
Supervisor	Ruth Oulton (Supervisor) & Edmund G H Harbord (Supervisor)