Pulsed time-of-flight radar for fiber-optic strain sensing

Abstract

This article describes a fiber-optic interrogation device based on the pulsed time-of-flight technique. The apparatus is capable of measuring time delays between wideband reflectors, such as connectors, along a fiber path with a precision of about 280 fs (rms value) and a spatial resolution of about 3 ns (0.30 m) in a measurement time of 25 ms. Potential application areas include measuring integral strain and its derivatives such as cracks, deflections, and displacements, particularly in large civil engineering and composite structures. The operation and basic blocks of the measurement system are presented in detail together with measurement results obtained in laboratory and field conditions. It is shown that by using a fiber loop sensor with a reference fiber, it is possible to achieve a strain precision below 1 microstrain and a measurement frequency of 4 Hz. System performance proved adequate for the study of both static and dynamic phenomena in a bridge deck.

Advanced compact 3D lidar using a high speed fiber coupled pulsed laser diode and a high accuracy timing discrimination readout circuit

“…In applications such as nuclear photomultiplier detectors [1], time-of-flight sensing [2], optical fiber time-domain reflectometry [3], pulsed laser range finding systems [4][5] [6], and so on, high speed of measurement points per second and an accurate timing detector to discriminate the timing points in the readout circuits are required. In the case of a 3D Focal Plane Array (FPA) flash LIDAR/LADAR [7], it has possible time to deal with post-processing in the readout circuits or program space such as filtering, accumulation, correlation, and averaging owing to high speed measurement.…”

Ultrasensitive, high-dynamic-range and broadband strain sensing by time-of-flight detection with femtosecond-laser frequency combs

“…In order to simultaneously achieve high-resolution measurement of static and dynamic strain with a large dynamic range, we propose and demonstrate a new class of fibre strain sensing method by detecting the change in the TOF of the strain-influenced femtosecond optical pulse trains generated from MLL frequency comb sources 22,23 . Strain sensing by time-domain interrogation has been explored since early 1990s 24 , however, their performance was limited by the long pulsewidth (~ns long) and electronic timing discriminator (~10-ps resolution) 24,25 . To overcome these limitations, we employ femtosecond optical pulse trains generated from the MLL frequency comb sources and sub-femtosecond-resolution phase detection between optical pulses and microwave signals.…”