Research On The Fabrication And Application Of Fiber Grating And Surface Nanoscale Axial Photonics (SNAP)

As the most perfect optical waveguide till now,optical fiber has the advantages of light weight,low loss,and anti-electromagnetic interference,et al.,and has played an irreplaceable role in optical communications,optical fiber sensing,lighting and other fields.In order to fully utilize its advantages,various kinds of optical fiber devices have been proposed.As an all-in-fiber device,fiber gratings are perfectly compatible with existing optical fiber networks and have been attracting extensive attention in optical communications with applications in filtering and dispersion compensation,since the day they were proposed.With the development of fiber-optic communication,the application of fiber gratings in optical sensing has gained increasing attention.Especially in recent years,with the emphasis on environmental protection and food safety,the concept of “Lab on fiber”,which is based on fiber-optic sensing,has attracted considerable attention.For the "Lab on fiber" application,it is critical to further improve the refractive index sensing performance of fiber grating.Apart from fiber grating,surface nanoscale axial photonics(SNAP)is a new platform for the fabrication of microcavity with low-loss and ultra-high precision,and has potential applications in the next-generation all-optical signal processing.This dissertation will describe an overall study on the fiber gratings and SNAP structures fabricated using ultraviolet lasers and femtosecond lasers,including:1)Point by point inscription of fiber Bragg gratings with a femtosecond laser.Thanks to the flexibility of point by point method,a localized multi-grating structure is proposed and experimentally demonstrated.Using the proposed grating,stable dual-wavelength lasing in Erbium doped fiber is achieved at room temperature.2)Analysis of the sensing characteristics of the long period grating(LPG),verification of the high sensitivity of LPG near the dispersion point,as well as experimental demonstration of the inscription of turning point LPG with a femtosecond laser for the first time.3)Inscription of a localized eccentric LPG with a femtosecond laser to combat the disadvantage of a low refractive index sensitivity for standard LPG near the refractive index of water.In principle,eccentric inscription of the proposed grating with a period of only 15 microns ensures an efficient coupling co-efficient of the higher-order cladding modes,which have a higher refractive index response near the water refractive index.4)Achievement of an ultra-narrow bandwidth LPG.The bandwidth of LPG is found to be inversely proportional to the number of grating periods,so we reduced the grating period to introduce more grating cycles within certain length.Using this scheme,we have successfully demonstrated an LPG with sub-nanometer 3 dB-bandwidth utilizing an UV laser.This is the narrowest bandwidth ever reported in LPGs.5)Femtosecond laser inscription scheme for SNAP structure.In this scheme,femtosecond laser inscription pressurizes the outer surface of the fiber from inside,introducing nanoscale variations in fiber radius.Based on this scheme,microcavities fabrication with sub-angstrom precision is achieved.