09-07-2013, 03:29 PM
Temperature Sensing Characteristics Of Single-Mode–Multimode–Single-Mode Structures
ABSTRACT
Author present a comprehensive study of the strain and temperature-sensing characteristics of single-mode–multimode– single-mode (SMS) structures based on the modal interference of guided modes of graded index multimode fiber (MMF) section spliced in between two single-mode fibers. Their study shows that for the SMS structure with a geo2-doped MMF there exists a critical wavelength on either side of which the spectrum shows opposite spectral shift with a change in temperature/ strain, whereas for structures with a p205doped MMF it shows monotonic red shift with increasing temperature/strain.
Using different MMFs, both the red and blue spectral shifts have been observed experimentally. It has also been found that the SMS structure has higher sensitivity toward this critical wavelength.
FIBER optic devices based on the modal interference among guided modes of a multimode fiber (MMF), spliced in between two single-mode fibers (SMFs), have been an active area of research due to their low cost, ease of fabrication, and the freedom they offer in tailoring the output spectrum. These so-called SMS devices have been extensively used for various applications such as sensors, modulators, power splitters, optical switches and directional couplers, bandpass filters, and fiber lenses. Recently, some studies have been done seeking possible applications of SMS devices in the area of temperature and strain sensors utilizing both the step index and the graded index multimode fibers. In one end of a 5 cm long MMF has been fusion spliced with an SMF and its temperature sensitivity has been studied.
Recently, author have experimentally investigated SMS structures using different graded index MMFs, out of which one MMF shows red spectral shift with respect to increasing temperature/ strain, second one shows blue spectral shift with increasing temperature/strain.