Fabrication And Optical Modulation Characterization Of Azopolymer-Silica Compound Fiber

Evanescent wave has lots of advantages when used in fiber optic sensing and modulation, and polymers are easily tailored and fabricated, so fiber optic components based on the interaction between polymers and the evanescent wave are easily fabricated and have extensive potential value. And the propagating light in the fiber can be optically modulated when photoresponsive azopolymer is compounded with the optical fiber. Take it in consideration that the silica fiber can be easily connected with the optical communication system, here the silica fiber is selected and the cladding is chemically etched to enhance the evanescent wave interaction with the external medium. The refractive index of the azopolymer is controlled to be lower than that of the silica fiber so that the waveguide condition is satisfied, and the azopolymer-silica compound fiber is obtained. The intensity and polarization modulation of the propagating light in the compound fiber is investigated during the azopolymer’s photoisomerization and photo-reorientation processes, and the modulation range is enlarged by precise controlling of the azopolymer’s refractive index. All the details are shown as follows:1. Fluoride azobenzene polymers with low refractive indices were synthesized by free radical solution polymerization and the basic characterizations were measured, also the refractive indices were measured using the prism coupling method; the refractive indices were controlled by changing the copolyme(?)zation ratios and azopolymer with refractive index lower than that of the silica fiber was obtained; the phot(?)isomerization and photo-reorientation characterizations were studied and the refractive indices during the processes were measured.2. The single mode silica optical fiber was etched to the evanescent field range according to the chemical method using hydrofluoric acid, and optical fiber with smooth surface and suitable diameter was obtained by experimental condition control and selection; the azopolymer was coated on the etched section of the optical fiber and the azopolymer-silica compound fiber was obtained; when the azopolymer overlay was irradiated by unpolarized and polarized light, the intensity and the polarization state of the propagating light were tuned continuously and reversibly.3. Polyhedral Oligomeric Silsesquioxanes(POSS) was introduced into the azobenzene polymerization system, and the ternary copolymer was obtained and characterized basically; by controlling the copolymerization ratios the refractive indices and photo-induced birefringences of the ternary copolymers were precisely controlled; using the azobenzene polymer with proper refractive index, the azopolymer-silica compound fiber was obtained and finally an enlarged modulation range of the intensity and polarization state of the propagating light was achieved.4. To improve the stability of the Polydiacetylene(PDA) film, poly(4-vinylpyridine)(P4VP) is used to obtain the hydrogen-bonding complexes of the diacetylene derivatives10,12-tricosadiynoic acid(TDA), and the blue-to-red colorimetric transition was studied; the PDA self-assembly film was incorporated into polymer optical fiber as part of the cladding and the spectrums in different solvent vapors were monitored; based on the evanescent wave interaction between the propagating light and the PDA film and the different diffusivities of the solvents, the differentiation of the solvent vapors was realized.