Fabrication And Study Of High-temperature Resistant Fiber Gratings

Optical fiber gratings are broadly used in optical fiber sensing andcommunication system owning to their low insertion loss, good wavelength-selectiveproperty, immunity to electromagnetic interference, small size and so on. High-temperature resistant fiber gratings have attracted lots of research interests in recentyears due to their potential applications in several industrial and military areas suchas aerospace, missile and smelting.This paper mainly describes the preparation methods of high-temperature fibergratings, the related spectral properties and the test experiments of theirhigh-temperature characteristics. Following are the main contents:1. The research development of high-temperature resistant fiber gratings isreviewed by classifying them into five types, including type-II gratings, type-IIAgratings, chemical composition gratings (CCG), special ion-doped fiber Bragggratings and long period fiber gratings (LPFG). The fabrication methods, hightemperature performances are analyzed, as well as their merits and drawbacks. Theirfuture developments and applications are discussed.2. CCGs were fabricated in a standard single mode fiber by using theregeneration method after high temperature annealing. Their performance under hightemperature was studied. It was testified that stable CCG with reflectivity up to6dBcan be achieved. Temperature sensitivity of over11.7pm/°C was obtained in a rangeof200~700°C.3. Fiber Bragg gratings were inscribed in polyimide-coated fibers with thephase-mask method. Their performances under high-temperature circumstances werestudied. It was found that the reflectivity is reduced and then stabilized at a fixedvalue during the high temperature annealing process. This value is directlyproportional to the original reflectivity, i.e. the reflectivity before annealing.Temperature sensitivity of10.9~13.9pm/°C is obtained in a temperature range of50~300°C.4. Three different high-temperature fiber Bragg grating sensors were developed for different application environments. Designs with one or two optical fiber pigtails,by using metal and ceramics packaging technologies were studied respectively. Theperformance of a polyimide fiber grating-based sensor was studied before and afterpackaging as an example. Experimental results indicate that the packaging method isfeasible and applicable, having no influence for the grating’s temperatureperformance.