Multiparameter measurements using dual-core, polarization maintaining side-hole fiber

Combining temperature measurements with other parameters is essential, as temperature variations are difficult to isolate from environmental influences. Most commercial sensors are designed for single-parameter measurements, assuming negligible external interference. However, in applications such as structural health monitoring, isolating temperature effects is often unfeasible, which may lead to inaccurate results. A common solution involves the use of two separate fibers—one dedicated to temperature sensing only and the other sensitive to both temperature and strain—thus enabling temperature compensation. Nevertheless, this approach is frequently ineffective due to difficulties in maintaining constant spacing between the fibers, resulting in nonuniform thermal conditions. This article presents, for the first time, the design of a dual-core polarization-maintaining side-hole optical fiber. The potential of this side-hole (SH) fiber for multiparameter sensing using spectral interrogation techniques is demonstrated. Owing to its tailored structure, the proposed fiber exhibits a polarization extinction ratio exceeding 30 dB, low transmission losses, bending insensitivity, and—most importantly—differential sensitivity to temperature and strain, as well as to temperature and hydrostatic pressure. These properties were achieved by employing different levels of germanium doping in the two cores (5 mol% and 20 mol%) and by optimizing the geometry of the cores and the adjacent air holes.