Boston Chapter of the IEEE Photonics Society

Abstract:  Ever since the availability of low loss single mode optical fiber in the early 1980s, fiber optic interferometry has developed into a highly versatile technique for measuring displacement in optical fiber. This has led to a vast range of applications that require measuring displacements in optical fiber ranging in size from 10-10 λ to over 20 λ (i.e. in excess of ten orders of magnitude).

This talk will explain the fundamental limits to measuring displacements in optical fiber both at the smallest extreme due to thermodynamic noise and at the largest extreme due to the breaking strain/mechanical failure of glass fiber as well as recent work on circumventing the thermodynamic noise limit by using hollow core optical fiber. By way of example, applications that span this measurement range will be described that utilize different implementations of fiber optic interferometry for measuring crack growth in structures, underwater acoustics, weak electromagnetic fields, strain gradient and explosive and laser generated shock waves in solids.

Biography:  Dr. Cranch received a PhD in Applied Physics from Heriot-Watt University, Edinburgh and has over fifteen years experience in developing fiber optic sensors for a range of applications. He has lead the development of fiber laser sensor technology for applications in acoustics, magnetics and inertial sensors. He is currently leading programs in ultra-high performance interferometry based on hollow core photonic crystal fibers, fiber optic atomic vapor magnetometry and distributed fiber optic sensing based on correlation domain Brillouin scattering. He has also developed fiber optic pressure and particle velocity sensors for shock wave characterization in solids and liquids. Dr Cranch has published over 60 journal and conference publications with several invited talks at international conferences. He has also written two book chapters, holds five patents and is topical editor for Applied Optics (2010-).