Abstract
The optical Vernier effect magnifies the sensing capabilities of an interferometer, allowing for unprecedented sensitivities and resolutions to be achieved. Just like a caliper uses two different scales to achieve higher resolution measurements, the optical Vernier effect is based on the overlap in the responses of two interferometers with slightly detuned interference signals. Here, we present a novel approach in detail, which introduces optical harmonics to the Vernier effect through Fabry–Perot interferometers, where the two interferometers can have very different frequencies in the interferometric pattern. We demonstrate not only a considerable enhancement compared to current methods, but also better control of the sensitivity magnification factor, which scales up with the order of the harmonics, allowing us to surpass the limits of the conventional Vernier effect as used today. In addition, this novel concept opens also new ways of dimensioning the sensing structures, together with improved fabrication tolerances.
Highlights
The fast development in many research fields utilizing optical fibers along with the specific technical challenges in their use places strong pressure and new challenges for current optical fiber sensing research
The strain was applied to FPI1, for all three cases of different reference Fabry–Perot interferometers (FPIs)
The presence of internal envelopes, which are different from the upper envelope, typically monitored in the fundamental optical Vernier effect, provides intersection points better suited to tracking the wavelength shift used for sensing
Summary
The fast development in many research fields utilizing optical fibers along with the specific technical challenges in their use places strong pressure and new challenges for current optical fiber sensing research. Researchers are driven to find new solutions for improved fiber sensors. In one such improvement, the Vernier effect was applied to fiber sensors. This effect, known for many years due to its application in calipers, consists of two measurement scales with slightly different periods so that the overlap of both improves measurement accuracy [1,2]. The optical Vernier effect makes use of two interferometers with slightly shifted interferometric frequencies, normally arranged in series (cascaded configuration) [3]
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