Inscription and characterization of fiber Bragg gratings in multi-mode As2S3 optical fiber at 1550nm using interferometric and phase mask methods

Fiber Bragg gratings (FBGs) in optical fibers are quickly growing in appeal and are being considered by researchers for use as mechanical and chemical sensors in fiber reinforced composite airframes to provide inexpensive, high sensitivity and high density sensor coverage. Such FBG detection systems offer the advantages of being rapid, sensitive, radiation-hard and low density. To date, typical silica-glass optical fibers have been studied. However, the ultimate sensitivity of FBGs in silica fiber is limited by the relatively low photosensitivity of silica glass which leads to low reflectivities of the FBGs. In this project, advantage is taken of the significantly higher photosensitivity of chalcogenide glasses, glasses based upon the chalcogenide elements, S, Se, and Te to inscript FBGs in selected chalcogenide optical fibers, specifically As2S3. Time stability, power level dependence, and temperature dependence were measured for the FBGs written in multi-mode As2S3 optical fiber;FBGs were inscripted in multi-mode arsenic sulfide (As2S 3) glass fibers at 1550 nm by He-Ne laser irradiation using the interferometric and phase mask techniques. In the set up, a broadband light source centered at 1550 nm with a bandwidth of 100nm at half intensity (Agilent Broadband light source 83437A) and an OSA (Agilent HP86412B) were used to analyze the inscribed FBGs and the reflectivity around 1550 nm;Multiple transmission dips were obtained from the FBGs writing experiment using both the interferometric and phase mask techniques that were caused by same mode reflection and neighboring mode coupling. Using the interferrometric method, we obtained FBGs with maximum reflectivity 46.6% at 1526.6 nm. The average effective index change in the glass caused by the He-Ne laser irradiation inducing the FBGs is estimated to be +0.000482. Using a 0/-1 order phase mask, we obtained FBGs of maximum reflectivity 61.9% at 1548.8 nm and the average effective index change is estimated to be +0.000491