Abstract
We report on a novel bend sensor with high flexibility and elasticity based on Bragg grating structures in polymer optical fibers to detect bending for the measurement of movement. The concept is very simple and relies on the inscription of eccentrical Bragg gratings into multimode graded-index polymer optical fibers via contact exposure with a krypton fluoride excimer laser in the ultraviolet region and an optimized phase mask. Depending on the fiber deformation, the lattice constant of the inscribed Bragg grating is strained or compressed due to its position relative to the fiber core. This in turn results in a specific shift of the Bragg wavelength of up to $1.3\text{ nm}$ to the red or blue wavelength region, respectively, which is sufficiently large to be reliably detected. Therefore, as proof of principle, deformation along one axis can be observed with a single Bragg grating with a maximum sensitivity of up to $65\text{ pm/m}^{-1}$ . Moreover, multiple Bragg gratings inscribed into the same polymer optical fiber at different positions around the fiber axis allow to determine the shape deformation of the fiber relative to a reference frame with similar accuracy. Consequently, this technology could form the basis for new applications in the areas of medical diagnostics, robotics or augmented reality, which are lacking affordable sensor systems to date.
Highlights
I N recent years polymer optical fibers with inscribed Fiber Bragg Gratings (FBG) have emerged as potential sensors for various purposes such as strain, temperature, humidity, pressure, vibration or bending [1]–[7]
We report on a novel bend sensor with high flexibility and elasticity based on Bragg grating structures in polymer optical fibers to detect bending for the measurement of movement
We report on production and detection of the eccentric Bragg grating (BG) under the surface of the graded-index core of a Cyclic Transparent Optical Polymer (CYTOP) fiber and validate the sensitivity for detection of bending in a proof-of-principle experiment
Summary
I N recent years polymer optical fibers with inscribed Fiber Bragg Gratings (FBG) have emerged as potential sensors for various purposes such as strain, temperature, humidity, pressure, vibration or bending [1]–[7]. To the usual applications of POF to sense changes in strain, temperature, humidity or pressure, for example in structural health monitoring [18], [19], we here present an FBG sensor to detect bending precisely at one spot. Beforehand, this was performed with uneven or asymmetric fibers [2], [5], [20], by multiple fibers [21], by multi-core fibers [2], [22]–[25] or additional optical elements [26].
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