Research On Fabrication Method And Application Of Few-mode Fiber Bragg Gratingas

Due to the special characteristics of fiber Bragg grating （FBG） in optical spectrum,it was widely used in the field of optical communication and fiber sensing. Since Hillfabricated the first FBG by standing wave method in1978, it has a constant progress infabrication and application research of FBG. Up to now, the studies of fabricationtechnology of FBG and its application in the sensing field have matured. Because theoptical spectrum of Bragg grating written in the special fiber is different from thenormal single-mode fiber’s, many researchers study their optical properties andpotential applications.As the capacity of optical systems based on single mode fiber （SMF） approach thenonlinear Shannon’s limit, further capacity growth requires new transmission paradigm.With the advent of massive digital signal processing, as an alternative way to keep upwith the capacity demand over a single fiber. Few-mode fiber （FMF） is to be developedbased on this case. There has a less research on few-mode fiber Bragg grating（FM-FBG）, and still has a lot of key problems on fabrication technology and applicationresearch unresolved. For these reasons, the research of FMF on fabrication technologyand sensor characteristics is needed.Firstly, in this paper, we research the fabrication technology of conventionalsingle-mode fiber, and analyze the influence of hydrogen loading in fiber, FBG writing,apodization and annealing in the process. We use the phase mask method and exposurethe hydrogen loaded fiber in UV provided by248nm KrF excimer laser. We produce aFBG which has a high reflectivity, narrow3dB bandwidth and prefect sidebandsuppression.Secondly, based on the principle of self-focusing, we proposed a new structurereduce the coupling loss between the few-mode fiber to a single-mode fiber. Using thenew structure, the reflection peak of FBG written in hydrogen loaded FMF can beobserved, it can verify that the new structure can reduce the coupling loss between FMFand SMF.Lastly, the sensing properties, temperature, strain, bend on the FM-FBG are further investigated, and the experimental results indicate that the novel FM-FBG hassensitivities of temperature, strain, and bending of11.2pm/℃,1.3pm/με, and-636.9pm/m^-1, respectively.