| 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 interfemometer ( 24 ). The interrogation unit ( 40 ) includes an optical circuit with Mach-Zehnder or Sganac/Michelson interferometer arrangement.
|
