The metal-to-dielectric transition of silver films deposited on single-mode optical fibers is monitored by measurements of the transmission spectra of tilted fiber Bragg gratings inscribed in the core of the fiber. In situ, real-time measurements of the spectrum at wavelengths near 1550 nm during the wet etching of a 50 nm thick silver coating show a sudden and temporary decrease of more than 90% in the amplitudes of the core-to-cladding mode coupling resonances when the film thickness reaches 18 nm. Confirmation that this observation corresponds to the percolation threshold is obtained from simultaneous measurements of the silver coating conductivity during etching and by simulations of the grating response. The characteristic spectral signature of the percolation threshold is only obtained for cladding modes polarized azimuthally in the fiber cross section, i.e., parallel to the film surface.

中文翻译：

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用光纤光栅光学检测纳米级银涂层的渗透阈值

通过测量刻在光纤芯中的倾斜光纤布拉格光栅的透射光谱，可以监控沉积在单模光纤上的银膜的金属-介电转变。原位，对50 nm厚的银涂层进行湿法刻蚀时，在1550 nm附近的波长处的光谱的实时测量显示，当磁芯与包层模式耦合共振的幅度突然且暂时降低90％以上时，膜厚度达到18 nm。可以从蚀刻过程中同时测量银涂层的电导率并通过模拟光栅响应来获得这一观察结果对应于渗滤阈值的确认。渗透阈值的特征光谱特征仅针对在纤维横截面（即平行于薄膜表面）中方位极化的包层模式获得。