Femtosecond Laser Structuring of Active Optical Fiber Sensors for System Health Monitoring
Abstract
The goal of this project is to develop the science and technology needed for femtosecond Laser Structuring (fLS) of optical fibers including femtosecond Laser Densification Writing (fLDW) of waveguides and femtosecond Laser Milling (fLM) of microchannels; and to fabricate and characterize novel active optical sensors for system health monitoring.The structural integrity of safety-critical aerospace and naval structures is of enduring concern to the navy. Intelligent System Health Management (ISHM) systems can help preventstructural failure of safety-critical future naval structures that cannot be allowed to fail in service. As part of the diagnostic system for ISHM, photonic sensors (especially fiber-optic) have attracted considerable attention. Photonic sensors have proven to bevery versatile in terms of their ability to measure multiple parameters, and have other attractive properties including: light weight; immunity to EMI; and multiplexability of sensors on a single optical fiber. Recently proposed active fiber laser sensors in the literature have shown sensitivity to acoustic emission approaching that of piezo sensors. The proposed work seeks to expand on this work by separating the lasing waveguide from the transport waveguide (the optical core) so as to minimize issuespertaining to gain competition and transport loss.In this work, we propose a novel design for a local active sensor through incorporation of localized gain medium inside a mostly passive transport fiber. This will be achieved via laser milling of orthogonal microchannels in an optical fiber, followed by infilling with a rare-earth doped nanoparticle mixed in a UV curable polymer resin, and subsequent laser densification of core-parallel waveguides containing gratings straddling the active medium to create a laser cavity. These sensors are expected to be much more robust than 3D printed sensors as there is no additional complexity arising from coupling of the sensors to ingress and egress fibers. Applications of these sensors to acoustic emission detection will be demonstrated.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 15, 2023
- Source ID
- N000142312529
Entities
People
- Sridhar Krishnaswamy
Organizations
- Northwestern University
- Office of Naval Research
- United States Navy