Technology Research, Based On The Fiber Cone Reflector Device Active Query

The properties of fiber Bragg grating (FBG) and fiber loop mirror (FLM) have been studied experimentally based on the study of their principle. An active interrogating scheme, in which a cased wavelength division multiplexed (WDM) FBGs and an FLM have been employed to act as the end mirrors, has been proposed. An FBG array constructed by with 10 sensor elements was addressed, successfully, by introducing a tunable filter, which performs the function of wavelength scanning and an unbalanced Michelson interferometer demodulator. The research work will be illustrated from the following four aspects:(1) The effects of strain, press and temperature on FBG have been studied based on the Bragg equation. Then the theory of wide band fuse-tapered coupler was introduced. The wide band coupler was manufactured by the pre-pulling manner, which can result different propagation constants of the two fibers. Finally, the reflectivity of the FLM made by 3dB wide band coupler was investigated; it indicated that its reflectivity (transmissivity) can be changed by birefringence.(2)The characters of the FLM made by 2×2 3dB wide band coupler have been studied experimentally, and the results were discussed. It shows that the FLM has a reflectivity greater than 99.9% in the wavelength-flattened band of the coupler (the losses of FLM were neglected).(3)A configuration of linear cavity fiber laser based on FBG and FLM was presented according to the character of FBG and FLM. The distribution of stress in the fiber is changed by a Polarization Controller (PC), which is introduced to twist the fiber ring. The change of the distribution can result the birefringence effect; therefore, the reflectivity (transmissivity) of FLM is varied. The fiber laser has regulated output power in the (0.485, 6.86) mW and tuned laser wavelength in (1555.065, 1557.240) nm by tuning worked wavelength of FBG with triangle cantilever beam.(4)A novel active interrogating setup based on closing cavity was demonstrated according to the characters of FBG and FLM. It can interrogate 10 FBG sensor array placed in the FLM successfully by an F-P filter. The sensing signals of the FBG system were demodulated by unbalanced scanning Michelson interferometer; and phrase-shift signals, the measured strain signals included, were detected by phase meter. The sensor sensitivity of the system, 1.5835 Deg/με, is in good line with the theoretical value of 1.6662 Deg/με, and its resolution was 6ne.