Utilising optical Kerr microresonators for polarisation control, logic gates, and quantum optics applications

When high intensities of light are focused inside of a medium, strange effects occur. Light can self-interact. It can be slowed down based on how bright it is, it can be made to go in one direction but not the other, and it can even be made to c change colour. It is hard to imagine how the world would look if these were effects that we experienced in our everyday lives. Fortunately, it takes a significant amount of effort to make the conditions right for such events to occur, specifically, with high optical intensities required. This thesis details some of these efforts. In this work, I present some applications of Kerr microresonantor based nonlinear and quantum optics. Microresonators are minute devices that can be integrated in photonic circuits. They trap and guide light on a repeating path, with each roundtrip leading to an increase in intensity until nonlinear effects start to occur. I start by explaining how such resonators work, are fabricated, and how nonlinear effects can manifest. Next, an all-optical polarisation controller is introduced, in which the nonlinear splitting of otherwise degenerate polarisation modes is employed. This device could find application in integrated photonic circuits that require fast response times. A similar effect, but this time for counter-propagating light, is then used to demonstrate an all-optical, universal logic gate. Interestingly, a set of such logic gates could be used for the on-chip routing of optical signals to provide low-latency communications for telecoms and distributed computing. Finally, the quantum nature of these nonlinearities is explored, first with the calculation of multi-modal entanglement metrics before then discussing work that is progressing towards a single-photon source. These phenomena show promise for integration into future quantum technologies, in particular in secure quantum communications and for state generation for quantum information processing.Open Acces

Optical memories and switching dynamics of counterpropagating light states in microresonators

The Kerr nonlinearity can be a key enabler for many digital photonic circuits as it allows access to bistable states needed for all-optical memories and switches. A common technique is to use the Kerr shift to control the resonance frequency of a resonator and use it as a bistable, optically-tunable filter. However, this approach works only in a narrow power and frequency range or requires the use of an auxiliary laser. An alternative approach is to use the asymmetric bistability between counterpropagating light states resulting from the interplay between self- and cross-phase modulation, which allows light to enter a ring resonator in just one direction. Logical HIGH and LOW states can be represented and stored as the direction of circulation of light, and controlled by modulating the input power. Here we study the switching speed, operating laser frequency and power range, and contrast ratio of such a device. We reach a bitrate of 2 Mbps in our proof-of-principle device over an optical frequency range of 1 GHz and an operating power range covering more than one order of magnitude. We also calculate that integrated photonic circuits could exhibit bitrates of the order of Gbps, paving the way for the realization of robust and simple all-optical memories, switches, routers and logic gates that can operate at a single laser frequency with no additional electrical power.Comment: 10 pages, 10 figure