Abstract
Polymer optical fibers (POFs) have been proposed for optical strain sensors due to their large elastic strain range compared to glass optical fibers (GOFs). The phase response of a single-mode polymer optical fiber (SM-POF) is well-known in the literature, and depends on the physical deformation of the fiber as well as the impact on the refractive index of the core. In this paper, we investigate the impact of strain on a step-index polymer optical fiber (SI-POF). In particular, we discuss the responsivity of an optical strain sensor which is based on the phase measurement of an intensity-modulated signal. In comparison to the phase response of an SM-POF, we must take additional influences into account. Firstly, the SI-POF is a multi-mode fiber (MMF). Consequently, we not only consider the strain dependence of the refractive index, but also its dependency on the propagation angle . Second, we investigate the phase of an intensity-modulated signal. The development of this modulation phase along the fiber is influenced by modal dispersion, scattering, and attenuation. The modulation phase therefore has no linear dependency on the length of the fiber, even in the unstrained state. For the proper consideration of these effects, we rely on a novel model for step-index multi-mode fibers (SI-MMFs). We expand the model to consider the strain-induced effects, simulate the strain responsivity of the sensor, and compare it to experimental results. This led to the conclusion that the scattering behavior of a SI-POF is strain-dependent, which was further proven by measuring the far field at the end of a SI-POF under different strain conditions.
Highlights
Glass optical fibers (GOFs) are superior to polymer optical fibers (POFs) for data transmission applications because the lower attenuation and the higher bandwidth allow for higher bit rates and longer transmission distances
We have proposed an optical strain sensor based on the phase measurement of an intensity-modulated light wave using an step-index polymer optical fiber (SI-POF) instead [16,17]
Effects such as modal dispersion led to an increased strain responsivity since the modulation phase develops more quickly along an SI-POF than it does along an ideal fiber
Summary
Glass optical fibers (GOFs) are superior to polymer optical fibers (POFs) for data transmission applications because the lower attenuation and the higher bandwidth allow for higher bit rates and longer transmission distances. POF is usually considered only for short-range data transmission [1]. For sensing applications, the mentioned limitations of POFs are often not relevant. There are several advantages which make POFs attractive for sensing tasks. First of all, they are more flexible and robust than GOFs. Due to the large diameter of the core (1 mm) of a step-index polymer optical fiber (SI-POF) and the large numerical aperture (NA), the fiber can be excited with an LED, and the fiber tolerates vibrations and smaller displacements or misalignments
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