Abstract
Optical fiber based twist sensors usually suffer from high cross sensitivity to strain. Here we report a strain independent twist sensor based on an uneven platinum coated hollow core fiber (HCF) structure. The sensor is fabricated by splicing a section of ~4.5-mm long HCF between two standard single mode fibers, followed by a sputter-coating of a very thin layer of platinum on both sides of the HCF surface. Experimental results demonstrate that twist angles can be measured by monitoring the strength change of transmission spectral dip. The sensor's cross sensitivity to strain is investigated before and after coating with platinum. It is found that by coating a platinum layer of ~9 nm on the HCF surface, the sensor's cross sensitivity to strain is significantly decreased with over two orders of magnitude less than that of the uncoated sensor sample. The lowest strain sensitivity of ~2.32×10-5 dB/𝜇𝛆 has been experimentally achieved, which is to the best of our knowledge, the lowest cross sensitivity to strain reported to date for optical fiber sensors based on intensity modulation. In addition, the proposed sensor is capable of simultaneous measurement of strain and twist angle by monitoring the wavelength shift and dip strength variation of a single spectral dip. In the experiment, strain and twist angle sensitivities of 0.61 pm/𝜇𝛆 and 0.10 dB/° have been achieved. Moreover, the proposed sensor offers advantages of ease of fabrication, miniature size, and a good repeatability of measurement.
Highlights
Twist/torsion is a key parameter that is frequently encountered for structure health monitoring in numerous applications, such as in evaluating the heath conditions of bridges, buildings, tunnels, dams and pipelines [1]
To address the challenge of strain introduced variations in twist sensitivity, in this work, we propose a strain independent twist sensor based on an uneven platinum coated hollow core fiber structure
Since the operation principle of our proposed twist sensor is based on intensity modulation, for which the twist sensitivity is highly dependent on the dip strength, samples from S1-0 to S4-90 were chosen for twist experimental demonstration in the following experiment
Summary
Twist/torsion is a key parameter that is frequently encountered for structure health monitoring in numerous applications, such as in evaluating the heath conditions of bridges, buildings, tunnels, dams and pipelines [1]. A number of optical fiber based twist sensors utilizing different fiber structures have been proposed. Those sensors can be mainly categorized into two types depending on their operation principles. Interferometer based twist sensors, on the other hand, have advantages of a relatively simple fabrication process and a much higher twist sensitivity, a variety of fiber structure configurations based on different customized and specially designed fibers for monitoring twist have been proposed [9,10,11,12,13,14,15,16,17]. Most of the optical fiber based twist sensors mentioned above suffer from high cross sensitivity to strain, even for the PMFs based twist sensors which have been reported with very low cross sensitivities to temperature [14,16]
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