Abstract
A fiber strain sensor based on a p-phase-shifted Bragg grating and an extended cavity diode laser is proposed. Locking the laser frequency to grating resonance by the Pound-Drever-Hall technique results in a strain power spectral density S(epsilon) (f) = (3 x 10(-19) f(-1) +2.6 x 10(-23)) epsilon(2)/Hz in the Fourier frequency range from 1 kHz to 10 MHz (epsilon being the applied strain), corresponding to a minimum sensitivity of 5 pepsilon Hz(-1/2) for frequencies larger than 100 kHz.
Highlights
Fiber-based optic sensors are known to show several advantages as compared with conventional electro-mechanical sensors, such as electrical passive operation, electromagnetic interference immunity, multiplexing capabilities, and distributed sensing
A fiber strain sensor based on a π-phase-shifted Bragg grating and an extended cavity diode laser is proposed
The proposed fiber sensor has potential applications in the field of ultra-high-resolution ultrasonic hydrophone for medical sensing and sonar systems
Summary
Fiber-based optic sensors are known to show several advantages as compared with conventional electro-mechanical sensors, such as electrical passive operation, electromagnetic interference immunity, multiplexing capabilities, and distributed sensing. The sensor consists of a π-phase-shifted FBG interrogated by a frequency modulated laser radiation emitted from an extended cavity diode laser (ECDL), using the Pound-Drever-Hall (PDH) technique [13]. This technique is widely accepted as the best method of laser frequency stabilization and enables laser frequency noise characterizations with high accuracy. Note the appearance of the sharp resonance peak around the center of the FBG stop band at 1542.77 nm, which turns out to be splitted into two peaks spaced by 7.6 pm (corresponding to ∼ 0.96 GHz) and with resolution-limited full widths at half maximum (FWHM) of 0.4 pm Such a splitting is attributed to a weak birefringence of the fiber induced by the UV writing radiation. The narrowest resonance shows a linewidth of 55 MHz and a minimum reflection of 26%
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