Grating-assisted demodulation of interferometric optical sensors

Abstract

Accurate and dynamic control of the operating point of an interferometric optical sensor to produce the highest sensitivity is crucial in the demodulation of interferometric optical sensors to compensate for manufacturing errors and environmental perturbations. A grating-assisted operating-point tuning system has been designed that uses a diffraction grating and feedback control, functions as a tunablebandpass optical filter, and can be used as an effective demodulation subsystem in sensor systems based on optical interferometers that use broadband light sources. This demodulation method has no signaldetection bandwidth limit, a high tuning speed, a large tunable range, increased interference fringe contrast, and the potential for absolute optical-path-difference measurement. The achieved 40-nm tuning range, which is limited by the available source spectrum width, 400-nm͞s tuning speed, and a step resolution of 0.4 nm, is sufficient for most practical measurements. A significant improvement in signal-to-noise ratio in a fiber Fabry-Perot acoustic-wave sensor system proved that the expected fringe contrast and sensitivity increase.

Pressure sensor based on the fiber-optic extrinsic Fabry-Perot interferometer

“…These features make the linear demodulation particularly be used in dynamic measurement of small perturbations, such as the detection of ultrasonic [38][39][40], vibration [41], partial discharge [42], and dynamic strain [34]. The drawbacks of operating with the linear demodulation method are limited dynamic range and the challenge for the static operating point control or stabilization [39,43].…”

Stabilization of a fiber Fabry–Perot interferometric acoustic wave sensor

“…However, they suffer from the fringe fading problems that result from random polarization rotation. They are also unstable because of drift in the source wavelength and temperature-induced path-length changes [3].…”

“…Grating-assisted demodulation, tuning static OPD and using a tunable light sources have been developed to stabilize the operating point [3,11], which carry through complicated, expensive or non-practical. Previously we propose and design a circuit feedback Q point stabilization acoustic wave detection method, experimental results show that the method works well, but this feedback method may introduce noises, and the Q point tracing invalidated as the temperature keep changing when the sensor was working, a power replacement was needed to settle this problem.…”

Stabilization of optical Fabry–Perot sensor by active feedback control of diode laser

“…The highest sensitivity can be obtained at the quadrature point (Q point) [12,13], where the curve has the highest derivative and a linear response. However, it places difficulty and constraint to fix the working point at the Q point in the sensor fabrication and packaging [14]; and the sensor may also encounter with various environmental perturbations, causing it stray off the Q point.…”

“…However, it places difficulty and constraint to fix the working point at the Q point in the sensor fabrication and packaging [14]; and the sensor may also encounter with various environmental perturbations, causing it stray off the Q point. Several techniques have been developed to stabilize the Q point, such as intentionally applying an acoustic bias [15], gratingassisted demodulation [12], and tuning static OPD [16] or source wavelength [13,17]. However, tuning OPD is not suitable for a packaged FFPI.…”