Research on a Broadband Optical Monitoring Method with an Improved Error Compensation Mechanism

In modern optical coating production, optical monitoring technology is an indispensable component. The traditional monochromatic monitoring technology used in current commercial and research institutions is usually only for a specific wavelength and cannot fully represent the characteristics of the film in the entire spectral range. Moreover, for non-quarter-wave coating systems (such as multilayer or complex coating systems), a thickness change in a single coating may have a significant effect on the performance of the entire coating system. In this case, it may be difficult to use monochromatic monitoring to accurately determine the thickness of each layer, resulting in reduced monitoring accuracy. At present, although broadband optical monitoring can be monitored over a wide wavelength range, the stop-plating time may be misjudged due to error accumulation during the coating process. To solve these problems, a broadband optical monitoring method with an improved error compensation mechanism is proposed in this paper. An optimal function that combines the absolute error and shape similarity of the transmission spectrum is designed, and the transmission spectrum is optimized by the limited random search method. In addition, a breakpoint algorithm based on parabolic error curve prediction is designed for the first time in this paper, which avoids the problem of excessive deposition thickness encountered by traditional broadband monitoring methods in the automatic coating processes. To verify the effectiveness of the proposed method, a set of hardware verification platforms based on broadband optical monitoring is designed in this paper, and a 30-layer shortwave-pass filter is constructed as an example. Compared with the traditional time monitoring method (CTMM), the proposed broadband optical monitoring method (PBMM) has significant advantages in terms of the matching degree between the transmission spectrum and the target spectrum, as well as the average transmittance in the low-pass band. In summary, the broadband optical monitoring method with an improved error compensation mechanism proposed in this paper provides an effective solution for high-precision optical coating production and has high practical application value and research significance.