Towards optimal light-matter coupling of colloidal quantum dots in optical fibers

For years, colloidal quantum dots (cQDs) have been optimized to offer great optical properties customizable through varying size and composition, and become the mature nanomaterial they currently are. However, their optical properties are affected by their environment. Hence, optical behaviour inconsistencies across experiments emerge from using cQDs inside different matrices. Therefore, their scope of applications has hitherto been greatly limited to specific applications. Recently, a new protocol to incorporate cQDs inside step index polymer optical fibers was developed by Whittaker and co-workers. It enables a cheap and robust fabrication of light-generating optical fibers. In addition to shielding cQDs from their outer environment, optical fibers also support optical modes. Hence, according to cavity quantum electrodynamics principles, these modes must alter the local density of optical states of the system, thus modifying the decay rate for each emitter located within the optical fibers. The current work revealed through finite difference time domain simulations only minimal modifications of the decay rate of a single quantum emitter located at the center of a polystyrene/PMMA core/clad step index fiber. Purcell factors staying within 2.2% of its initial value upon changes of the core radius were obtained. Thus, the Purcell enhancement offered by step index fibers is negligible compared to that of current semiconductor microcavities. Consequently, more exotic fiber geometries that offer greater Purcell effect must be identified before fast and cheap light-generating optical fiber can be made from this fabrication process.