Non-contact detection of laser-generated surface acoustic waves using fiber optic Sagnac interferometer

Surface-bonded fiber optic Sagnac sensors for ultrasound detection

“…Note that the visibility of the surface-bonded fiber optic Sagnac sensor is twice better than that of noncontact type fiber optic Sagnac interferometer reported by Jang et al [7]. In the fiber optic Sagnac interferometer for noncontact measurement of ultrasound by Jang et al [6,7], the half amount of light comes out of the Sagnac loop through the dead port.…”

“…In the fiber optic Sagnac interferometer for noncontact measurement of ultrasound by Jang et al [6,7], the half amount of light comes out of the Sagnac loop through the dead port. In addition, a significant optical loss exists at the probing fiber, which is associated with reflection at a specimen surface and re-entering into the probing fiber core.…”

“…In this study, a surface-bonded fiber optic sensor was developed for remote sensing and multi-point detection of ultrasound; which has the output fringe visibility of 1 and is based on the alternative fiber optic Sagnac interferometer reported by Jang et al [6,7]. The surfacebonded, single mode fiber arm is suitable for the measurement of ultrasound and can be used to detect ultrasonic waves at several points.…”

A new fiber-optic non-contact compact laser-ultrasound scanner for fast non-destructive testing and evaluation of aircraft composites

“…2,5,31,32 A design by this group based on a confocal Fabry-Perot interferometer significantly reduced the influence of the light collection system. Other approaches aimed at minimizing the effects of speckle structure include modifications of a Sagnac interferometer [33][34][35][36][37][38] and interferometer schemes employing photorefractive crystals. 31,[39][40][41] However, the detection sensitivity of all these optical techniques does not approach that of a well-designed, contact piezoelectric transducer.…”

“…1,3,4 For LU inspection of real composite structures used in the aerospace industry, reflections from rough surfaces must be processed effectively. To handle rough surfaces and simultaneously minimize the effects of environmental noise, we employed a Sagnac-based interferometer [33][34][35][36][37] measuring vibration speed instead of displacement. This approach has no reference arm.…”