精密光學薄膜的製鍍，需要精確的膜層厚度監控才能完成。本文陳述了五種膜厚監控方法：計時監控法、石英震盪監控法、傳統光學監控法、光學導納軌跡監控法，以及反射係數相位擷取監控法，並分析各種方法的優點與缺點。計時監控法與石英震盪監控法簡單便宜，但無法知道鍍上去薄膜的折射率，因此精密光學薄膜一般會以光學鍍膜的監控來完成。導納軌跡監控法具有視覺識別效果，容易做膜厚誤差補償，而且不需另加硬體，在傳統的光學監控機台加上軟體即可完成，因此容易實現。反射係數相位擷取監控法是非常精確的監控方法，但必須要有一組干涉儀及陣列偏振相位CCD相機，因此機台的總價位比傳統光學鍍膜機要高一些，但比加裝橢圓偏振儀要簡單、精確，所佔空間小，對振動不敏感且便宜。

High quality thin fi lm optical fi lters need high precision fi lm thickness monitoring during the deposition. There are several methods can do the thickness monitoring, named as time-counting monitoring, quartz-oscillation monitoring, traditional optical monitoring, optical admittance loci monitoring and phase-extraction monitoring. Each method
has its advantage and disadvantage. Since no information about refractive index of the depositing thin film can be provided by time-counting monitoring or quartz-oscillation monitoring, optical monitoring is preferred if an optical filter needs film thickness controlled very precisely during the deposition, although time-counting monitoring and
quartz-oscillation monitoring are cheaper and simpler. Optical admittance loci monitoring has an advantage of visual control so that it has a better error correction mechanism. Besides it can be applied on a traditional optical coating machine by the implantation of software without any additional hardware. Phase-extraction monitoring is
the most precise monitoring method, it needs the installation of an interferometer and a camera with polarization array, however, it is vibration insensitive, compact and cheaper than using ellipsometer and having much better performance than an ellipsometric system.