| 摘要 |
A method and an apparatus (10) for characterising a multi-layered structure (28) during formation of said multi-layered structure are disclosed. The method includes the steps of measuring the complex reflectivity of the multi-layered structure (28) at a wavelength outside of the bandgap of the multi-layered structure (28) and calculating a complex coupling coefficient from the measured complex reflectivity of the multi-layered structure (28) continuously or at intervals during the formation process. The apparatus (10) includes an interferometer (24) for creating writing beams (20, 22) to form the multi-layered structure (28), such as a Bragg grating, in an optical fibre (16) and an interrogation unit (40) for measuring the complex reflectivity and for calculating the complex coupling coefficient of the multi-layered structure (28) and for producing a feedback sigal which is communicated back to the interferometer (24). The interrogation unit (40) includes an optical circuit with Mach-Zehnder or Sganac/Michelson interferometer arrangement. |
