Abstract
A novel technique to achieve ultrafast and ultrahigh-resolution interrogation
of a fiber Bragg grating (FBG) sensor based on interferometric temporal spectroscopy
is proposed and experimentally demonstrated. In the proposed system, two FBGs
with one serving as the sensor grating and the other serving as the reference
grating are connected at two arms of an interferometer. An ultrashort optical
pulse from a pulsed laser is sent to the interferometer. Two pulses will be
obtained due to the reflection of the two FBGs and then both are sent to a
dispersive element to map the sensor grating wavelength shift to a temporal
spacing change between the two dispersed pulses due to the dispersion-induced
wavelength-to-time mapping. A temporal interference pattern is generated between
the temporal pulses. The temporal spacing change is further mapped to the
interference pattern frequency change, leading to a greatly improved interrogation
resolution due to the inherently high sensitivity of a temporal interferometer.
The proposed technique overcomes the fundamental tradeoff between the interrogation
speed and resolution in a temporal-spectroscopy-based FBG interrogation system
and that between the measurement resolution and dynamic range in a dual-wavelength
heterodyne-based interrogation system. An ultrafast real-time interrogation
of an FBG strain sensor with a sampling rate of 48.6 MHz and an interrogation
resolution as high as 0.61 pm are experimentally demonstrated.
© 2011 IEEE
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