Abstract
Polarization sensitive optical low-coherence reflectometry (OLCR) is used for measuring the complex fiber Bragg gratings (FBG) reflection coefficient. We determine the beat length directly from oscillations in the OLCR amplitude with a resolution of 10(-6) and a spatial resolution only limited by the minimum beat length or the coherence length of the light source. Using the OLCR amplitude and phase in combination with an inverse scattering algorithm the birefringence is retrieved with a resolution of 2x10(-5) while the spatial resolution is 25 mum. The two developed techniques are applied for measuring position, magnitude and footprint of induced birefringence of an FBG under uniform and non-uniform diametric loading.
Highlights
Optical low coherence reflectometry (OLCR) is an interferometric technique that allows measuring amplitude and phase of the light reflected from the device under test
OLCR was proved to be a powerful tool for the determination of the various properties of fiber Bragg gratings (FBG), such as position, length [1], and impulse response [2] from which the wavelength spectrum or group delay are obtained by Fourier transformation [3, 4]
The spatial resolution is given by half the beat length in this case
Summary
Optical low coherence reflectometry (OLCR) is an interferometric technique that allows measuring amplitude and phase of the light reflected from the device under test. Using the measured impulse response, it is possible to retrieve the complex coupling coefficient of the grating, q(z), through inverse scattering algorithms, such as layer-peeling [5, 6]. The complex coupling coefficient contains information about the refractive index modulation and the local grating period along the grating length. The possibility to monitor changes in local FBG parameters opened new possibilities for high spatial resolution grating characterization and distributed sensing [4, 7,8,9,10]. The complete characterization and sensing applications of the FBG using high-resolution reflectometry methods were mostly limited so far to nonbirefingent gratings
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