Holey strain sensor is temperature-independent

Holey optical fibers, also known as microstructured or photonic-crystal fibers, are being applied in numerous sensing and related applications (see www.laserfocusworld.com/articles/229677). Unlike strain sensors made from long-period gratings and fiber Bragg gratings that show temperature dependence, a tapered holey-fiber strain sensor has been developed by researchers at the Centro de Investigaciones en Óptica (Leon, Mexico) that is temperature-independent between 0°C and 180°C.

The sensor was fabricated from a 125-mm-diameter large-mode-area holey fiber with a solid core surrounded by four rings of 2.7-mm-average-diameter air holes (the fifth ring is partially collapsed) arranged in a hexagonal structure. A 30-cm-long section of the holey fiber was fusion-spliced to standard single-mode fiber and then tapered (by heating) to a diameter of less than 39 mm, causing the air holes to collapse. While peaks in the sensor transmission spectrum-caused by interference of multiple modes within the tapered region-shift as a function of applied strain, they do not shift as the temperature is varied. For temperature-independent strain sensing, one or all of the peaks can be monitored; in addition, different wavelengths can be used to interrogate the sensor. Contact Joel Villatoro at [email protected].