Hybrid optical components for advanced quantum applications

Abstract

Quantum technologies have received a large amount of interest and investment in the past couple of decades. With great advances in the field, a desire for more portable systems has emerged, and many strides have been made towards this goal. This thesis seeks to investigate optical components for quantum applications, particularly looking at the feasibility of three technologies for a future of compact systems in volume production, through the lens of cold atom clocks. The first technology is a passively mode-locked laser diode (MLLD) for coherent population trapping (CPT) in the Cs-133 D1 line. CPT is a method of interrogating the frequency standard that is compact as it negates the need for a microwave cavity. Using an MLLD is found to be feasible. The key steps and challenges of fabrication are explained in detail. Two resulting devices are examined in terms of L-I curves and optical spectra. The second technology is an examination of UV nanoimprint lithography (NIL) for the fabrication of gMOT gratings. The gMOT is a grating that enables magneto-optical traps (MOTs) to trap atoms with one trapping laser in Rb-87, instead of three. MOTs are used in atomic clocks for cooling atoms, which increases the clock frequency stability. UV-NIL can allow cost-effective volume production of parts fabricated by electron beam lithography (EBL). The key for future success will be identifying a suitable working stamp and resist mask that may hold up to reactive ion etching (RIE) processes better. The third technology is a monolithically integrated polarisation mode controller (PMC) whose design features a single slot etched in the waveguide. Polarisation modulation is rele- vant for different CPT schemes, and both CPT and gMOT use specific polarisation states in the probe and trapping lasers respectively. Etching trials to quantify the RIE lag of the one-slot PMC design are completed and a strategy for non-destructive process control is proposed using correlations between key parameters. A second PMC design featuring an asymmetrically etched waveguide is evaluated as having equally efficient performance. Based on examination of mode-beating parameters, laser ma- terial designs are proposed that would enable shorter PMC devices through higher core refractive index.

Date of Award	Dec 2023
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	University of Glasgow, Engineering & Physical Sciences Research Council & Kelvin Nanotechnology Ltd
Supervisor	John Marsh (Supervisor), Corrie Farmer (Supervisor) & Robert Bowman (Supervisor)