膜厚监控系统的光谱宽度对窄带滤光片性能的影响

讨论了膜厚监控系统的光谱宽度对波分复用窄带滤光片特性的影响，分析了监控过程中所出现的信号异常现象，其主要原因是控制光光谱宽度以及控制波长与滤光片中心波长不一致，所以控制光光谱分辨率必须小于单个法布里-珀罗滤光片最后2层膜折转点波长宽度的一半，即对100GHz的滤光片，监控系统的光谱宽度必须小于0．2nm。一旦产生中心波长偏离，就必定产生厚度控制误差。讨论了高折射率膜和低折射率膜的信号变化规律，发现当中心波长比监控波长长时，虽然信号变化规律正确，但判读到极值时的膜厚变薄。中心波长偏离越长，厚度将越薄。而当中心波长比监控波长短时，信号将出现反转。中心波长越短，反转量越大。最后指出了监控误差对滤光片Tmax和半峰全宽的影响。

Effect of Spectral Width of Thickness-Monitoring System on Performance of Narrow-Band Filters

The effect of spectral width of thickness -monitoring system on performance of wavelength division multiplexing (WDM) filters is discussed. Unusual thickness -monitoring signal during deposition is analyzed, which is because of wide spectral width and deviation between monitoring wavelength and central wavelength of the filter. Therefore the spectral width of thickness -monitoring system must be less than half of the turning wavelength width for last two layers of single Fabry-Perot filter. This means that spectral width should be at least less than 0.2 nm for a 100 GHz filter. When the central wavelength is deviated, the thickness error occurs. The signal change regularity for high index and low index materials is shown. When central wavelength is longer than monitoring wavelength, the thickness becomes thinner; and when central wavelength is shorter than monitoring wavelength, the monitoring signal will change in unusual way. These induce a large thickness error, and make maximum transmittance drop and full width at half maximum (FWHM) increase.