【摘要】 随着精密光学薄膜技术的快速发展，光学膜厚监控系统在膜厚精确测量和精准控制领域发挥着日益关键的作用。提出一种基于回溯法的膜厚监控算法，该方法基于光学薄膜基础理论，通过薄膜特征矩阵计算公式，结合膜厚监控系统的光路特点，将包含微小入射角的薄膜矩阵计算透射率公式作为目标拟合公式。基于LabVIEW编程平台，采用迭代优化方法对该拟合公式进行精确求解，最终在直接式光学膜厚监控系统中实现了透过率曲线的实时监控与数据采集。通过对比利用回溯法与前极值法得到的透过率判停位置及膜厚误差，结果表明，回溯法的监控精度优于前极值法。采用回溯法制备了750～1700 nm单面双带通滤光膜，以验证其监控精度。测试结果表明，通带中心波长监控误差小于0.0015%，这表明回溯法可实现非规整膜系的稳定监控。更多还原

【Abstract】 Objective In the context of rapid technological advancement, precision optical thin-film technology has become a critical enabling component across multiple high-value sectors. It is widely applied in high-end display panels within the electronics industry, precision optical diagnostic instruments in medicine, optical communication systems, renewable energy devices, and aerospace-based optical targeting systems. The performance and quality of optical thin films directly affect system reliability and functional integrity in these applications. Currently, foreign direct optical film thickness monitoring systems primarily rely on photometric extremum methods and broadband spectral monitoring techniques, typically operating in the visible to near-infrared spectral range. However, most such systems are subject to export restrictions against China. To address this limitation, this study proposes a novel monitoring algorithm based on a backtracking method to enable stable monitoring of non-uniform film structures.Methods This paper introduces a backtracking method for stable monitoring of non-uniform film structures. The method calculates the ratio K=D/S to determine the transmittance cutoff point, thereby controlling thin-film deposition thickness. This approach enables prediction of the complete spectral curve of the current layer using partial deposition data. When the number of extremum points in the current layer is fewer than two, the algorithm reconstructs the full spectral curve based solely on data from the current layer, without dependence on prior layers. Here, D represents the absolute difference between the transmittance cutoff point and the nearest extremum, while S denotes the absolute difference between adjacent extremum points. By monitoring real-time transmittance variations during deposition, the method fits the spectral characteristics of the current layer using Eq.(5) and computes the K=D/S value to trigger termination of deposition. Within the LabVIEW programming environment, a two-dimensional coordinate system is established using time and transmittance as reference parameters, with the horizontal axis representing monitoring time t and the vertical axis representing real-time transmittance T. After incorporating angular correction terms into the spectral-fitting model, the resulting fitted curve demonstrates improved fidelity to the actual data trajectory, facilitating multi-parameter real-time optical thickness monitoring.Results and Discussions Using an identical light control allocation scheme, a comparative analysis is conducted between the backtracking method and the pre-extremum method with respect to transmittance stop points and film thicknesses(Fig. 8). Experimental results show that the transmittance deviation between the backtracking method and the design target is minimal, yielding an average transmittance termination error of 0.03047%, whereas the pre-extremum method exhibits a significantly higher average error of 1.06203%. Consequently, due to discrepancies in transmittance cutoff points, the resulting deposited film thicknesses also differ. The average thickness deviation relative to the design target is 0.44711 nm for the backtracking method, compared to 1.16167 nm for the pre-extremum method(Tables 1 and 2). This comparative analysis demonstrates that the backtracking method achieves closer alignment with the intended transmittance stop point and nominal film thickness during actual deposition. It effectively corrects computational inaccuracies inherent in the pre-extremum approach, thereby enhancing the precision of direct optical monitoring of film growth. To validate the accuracy of the backtracking method in thickness control, a single-sided double-bandpass optical filter is fabricated. The measured spectral performance yields a center wavelength of 956.1 nm for the first passband with a FWHM of 86.6 nm, and 1310 nm for the second passband with a FWHM of 116 nm. The corresponding monitoring errors for the center wavelengths are 0.00115% and 0.00076%, respectively. These results confirm the stability of the backtracking method in monitoring thick films and suggest its potential applicability in the fabrication of non-uniform multilayer systems.Conclusions This paper presents a novel algorithm, the backtracking method, derived from multilayer thin-film matrix transmittance equations and incorporating an angular factor for stopping criterion determination. Implemented in the LabVIEW environment, the method establishes a two-dimensional coordinate system based on time and transmittance to identify input vectors and assign optimal initial reference values, enabling real-time monitoring of multilayer film thickness across concurrent data streams. Experimental evaluation using a six-layer film system compares the backtracking method with the pre-extremum method-based approach, demonstrating superior accuracy in detecting transmittance cutoff points and estimating film thickness. Furthermore, fabrication of a single-sided dual-bandpass optical filter confirms the stability of the backtracking method during thick-film deposition, indicating its potential for manufacturing non-uniform film structures and improving coated product yield.更多还原