A Novel Focal Plane Wavefront Sensor with A Pure Photonic Approach

Abstract

Adaptive Optics (AO) is the major technique for observing celestial objects from ground-based telescopes and wavefront sensors (WFS) are one of the core tools for sensing the phase information of light. Current WFSs embedded in AO systems carry inherited problems that either are not able to correct particular types of wavefront errors (WFEs), or introduce more into the system due to noncommon optical paths. This results in the inability of observing exoplanets and similar objects. It has been long realised that a new generation of WFSs is required to observe Earth-like exoplanets and similarly dim objects. This thesis proposes and introduces a new type of all-photonic focal plane WFS. I will present the findings of using a 19 core photonic lantern (PL) as a novel type of focal plane wavefront sensor (FP WFS) in a laboratory setting. The aim of the experiment is to explore the feasibility of PL as FP WFS using a neural network (NN) in a physical setting. The PL, in theory, is able to function as WFS due to its ability to convert multi mode (MM) inputs to single-modes (SM) outputs and vice versa. While direct detection of the input phase and intensity with a single PL (at a single wavelength) is not possible due to degeneracy, a NN is able to find correlations using non-linear function between the PL's inputs and outputs, hence establishes accurate predictions of the WF inputs. Chapter 1 provides information on the current adaptive optic (AO) technology used in Astronomy, and the presenting challenges of AO in ground-based telescopes. Chapter 2 introduces the two building blocks of the proposed technology, and the reasons why the combination of both PL and NN can restore the distorted WF. The experiment is detailed in Chapter 3 and 4. The results and analysis of the data obtained show a promising technique that is able to resolve WFEs that are currently extremely difficult for current WFSs. Chapter 5 concludes the finding and future research direction.