20
th
Australian International Aerospace Congress, 27-28 February 2023, Melbourne
RMIT Classification: Trusted
ISBN number: 978-1-925627-66-4
Normal Paper
Student Paper
Young Engineer Paper
Photonic integrated circuit compatible interrogation
methods for low SWaP optical fibre strain sensing
Luke H. Broadley
1
, Andreas Boes
1,2
, Joel Smithard
3
, Cedric Rosalie
3
, Suzana Turk
3
, Nik
Rajic
3
, Pier Marzocca
4
, and Arnan Mitchell
1
1
Integrated Photonics and Applications Centre, RMIT University, Melbourne, Australia
2
School of Electrical and Electronic Engineering, University of Adelaide, Adelaide, Australia
3
Defence Science and Technology Group, 506 Lorimer Street, Fishermans Bend, Australia
4
Sir Lawrence Wackett Defence and Aerospace Centre, RMIT University, Melbourne, Australia
Abstract
Optical fibre strain sensors are high performance, durable, lightweight, and require relatively
low power, however the systems that are used to interrogate these sensors are typically heavy
and bulky, largely negating the advantages of optical fibre strain sensing in situations where
low size, weight, and power (SWaP) is required. This project looks at addressing the SWaP
concerns of optical fibre interrogation systems via photonic integrated circuit (PIC) compatible
interrogation methods. Using bulk optical components, the use of the Pound-Drever-Hall (PDH)
laser frequency locking technique as a PIC compatible means to interrogate optical fibre strain
sensors is investigated. This proof of concept paves the way to developing ultra-low SWaP
interrogators that can be of the size of a fingernail, leading to new possibilities in strain sensing.
Keywords: SWaP, optical fibre sensors, photonic integrated circuits, Pound-Drever-Hall, strain
sensing, structural health monitoring.
Introduction
Traditional optical fibre strain sensors use fibre Bragg gratings (FBGs) as wavelength selective
mirrors. As strain is applied to the FBG, the reflected wavelength shifts; it is this shift that is
monitored as a strain signal. Such optical fiber strain sensors offer many advantages over
conventional electro-mechanical sensing technologies such as improved sensitivity, immunity
to electromagnetic interference, and form factor [1]. However, in low SWaP requirement
scenarios, such as structural health monitoring (SHM), the size and power requirements of the
bulk optical interrogators can largely negate the advantages of optical fibre strain sensing
systems, limiting their practical use.
Photonic integrated circuits (PICs) have progressed tremendously in the last decade; indeed, it
is now possible to integrate many bulk optical components such as lasers, modulators, and
detectors all on a single chip [2]. The ability to miniaturise the bulk optical components of the
interrogation system onto a single integrated circuit the size of a fingernail will enable the
advancement of SHM applications that previously were thought of as too complex. However,
so far, progress in using PICs as interrogators for SHM applications is limited, in part due to
the complexity of integrating the full complement of optical components required for the
interrogation system onto a single PIC.
