Abstract
A novel optical fiber sensing technology based on intensity distribution change in orbital angular momentum (OAM) mode is proposed and implemented herein. The technology utilizes a chiral long-period fiber grating (CLPFG) to directly excite the 1st-order OAM (OAM1) mode. The intensity changes in the coherent superposition state between the fundamental mode and the OAM1 mode at the non-resonant wavelength of the CLPFG is tracked in order to sense the external parameters applied to the grating area. Applying this technology to temperature measurement, the intensity distribution change has a good linear relationship with respect to temperature in the range of 30 °C to 100 °C. When the intensity was denoted by the number of pixels with a gray value of one after binarization of collected images, the sensitivity was 103 px/°C and the corresponding resolution was 0.0097 °C. Meanwhile, theoretical and experimental results show that the sensitivity and resolution can be further improved via changing the area of the collected image. Compared with sensing methods based on spiral interference pattern rotation in previous work, this sensing technology has the advantage of exquisite structure, easy realization, and good stability, thus making it a potential application in practices.
Highlights
Publisher’s Note: MDPI stays neutralOrbital angular momentum (OAM) beam [1] is a kind of beam with a helical phase front, which is generally expressed by exp(ilφ), where l represents the topological charge number and φ is the azimuth angle
The method is suitable for high-precision measurement applications, a higher cost and a larger volume spatial orbital angular momentum (OAM) generator was used with regard to jurisdictional claims in published maps and institutional affiliations
Optical fiber sensors based on OAM modes [9] have been proposed and achieved by tracking the rotation angle of the spiral interference patterns resulting from the co-axis interference between OAM modes and Gaussian beams
Summary
Orbital angular momentum (OAM) beam [1] is a kind of beam with a helical phase front, which is generally expressed by exp(ilφ), where l represents the topological charge number and φ is the azimuth angle. Optical fiber sensors based on OAM modes [9] have been proposed and achieved by tracking the rotation angle of the spiral interference patterns resulting from the co-axis interference between OAM modes and Gaussian beams. The phase difference of the two optical paths is changed by heating the sensing fiber, resulting in the rotation of the spiral interference pattern. The OAM generators are a hologram [10], a spiral phase plate [11], and long-period fiber grating and a rotator [12] respectively. The disadvantages of this structure are that the interference pattern is affected by external parameters, is unstable, and is difficult to collect, which has an adverse impact on its practical application. By changing the image area, the sensitivity can be adjusted from 1 px/◦ C to 103 px/◦ C
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