Fabrication of deep UV laser written integrated devices for quantum technology

Abstract

The interest in quantum technologies has gained tremendous scientific attention due to their potential applications in quantum information processing, and sensing. Previous studies on quantum science primarily focused on utilising many laser beams and bulk optics, which makes optical setups sensitive to vibrations and limit scalability. Recently, integrated optics have shown promise in increasing the scalability and portability of many existing quantum optical systems. This work recognises blazed gratings on an integrated platform as a viable method to generate integrated large-scale (mm) free-space beams. We propose a design and fabrication route for an integrated and portable device using small spot direct UV writing to deliver free-space beams for quantum technology. Extensive system calibration and characterisation of the pulsed 213 nm laser in small spot direct UV writing is provided. The waveguides and gratings were fabricated in planar silica, with and without hydrogen loading. A new UV fabrication approach is developed, where UV radiative fluence builds up in multiple passes. The technique suggested that the photosensitivity and grating strength can be substantially improved using the multi-pass writing technique. This writing technique is crucial for inscribing larger and more complex devices, providing a robust photosensitive platform via preexposure, and minimising the artefacts associated with hydrogen out-gassing and the stability of the interferometer. The writing dynamics of the pulsed 213 nm laser are investigated in detail, including the non-typical effects of writing power and fluence on the induced effective change in the refractive index and grating strength. Suitable writing regimes (avoiding damage) are identified where the photosensitivity mechanism is dominant by photochemical changes. Furthermore, a state-of-the-art fabrication system is introduced to develop large-area out-of-plane blazed grating couplers. This is the first example of a holographically fabricated grating coupler to provide large-scale (mm) free-space beams. The fabricated device produces a large-area (4.4 mm × 3.9 mm) free-space beam with dimensions significantly larger than those obtained from etched grating couplers. The coupling efficiency (fibre to free space) of the device was less than 1%. However, the fabricated device was the first prototype, and its efficiency can be significantly enhanced with several improvements in the fabrication process.

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Identifiers

ORCID for Qazi Ahmed: orcid.org/0000-0003-0731-5390

ORCID for James Gates: orcid.org/0000-0001-8671-5987

ORCID for Peter Smith: orcid.org/0000-0003-0319-718X

ORCID for Paul Gow: orcid.org/0000-0002-3247-9082

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