Fluorescence detection technology plays an indispensable role in biomedical analysis owing to its rapid speed and high accuracy. With the continuous advancement of fluorescence detection technology towards a broader range of types, faster speeds, higher accuracy, and greater integration capabilities, the number of channels for fluorescence detection equipment has gradually increased from 2?3 to 4?6. The utilization of multiple detection channels allows the simultaneous monitoring of various targets using different fluorescent dyes or viruses, thereby enhancing efficiency and reliability while ensuring precise results and significantly reducing overall detection time. The incorporation of multi-passband filters effectively reduces the optical path volume, minimizes the need for numerous individual filters, and enables seamless integration of equipment, which is an effective approach for achieving multi-channel fluorescence detection.

The working band of the quad-passband filter investigated in this study spans from 300 nm to 1100 nm; therefore, the fused quartz material is meticulously chosen as the substrate. When selecting materials with a high or low refractive index, their optical and chemical properties must be carefully considered. In the visible region, TiO₂, Nb₂O₅, and Ta₂O₅ are commonly employed materials with high refractive index, whereas SiO₂ remains the prevalent choice for materials with a low refractive index. Given that the passband range includes the 390 nm band, it is imperative to select materials that exhibit no absorption within this range. Consequently, Ta₂O₅ is utilized as a material with high refractive index, and SiO₂ serves as an optimal choice for a low-refractive-index material. After thorough analysis of the preceding data, it becomes apparent that precisely regulating and positioning the central wavelength and full width at half-maximum of the optical coating structure presents a primary challenge in designing the quad-passband filter. When employing cyclic nesting theory, the full width at half-maximum of the multi-passband expands as the central wavelength of the passband increases. In this study, it is observed that at longer wavelengths, the full width at half-maximum of the third passband is smaller than those of both the first and second passbands at shorter wavelengths. Consequently, formulas (13) and (14) are inapplicable for optical coating system design in this work. Therefore, we propose an innovative double-combination cyclic nesting model to address the aforementioned issues, which introduces a new array of film system structures into the existing single-cycle nested film system structure. This enables the simultaneous adjustment of parameters for both groups of film systems and simplifies the determination of the multi-passband position and full width at half-maximum. By adjusting the parameters in formula (13), the spectral curve of the proposed initial quad-passband filter is shown in Fig. 7. The design results exhibit an astonishing resemblance between the initial structure and our target spectrum. After optimization with the Macleod software, we obtain the design result of a quad-passband filter with a reasonable film structure and spectral performance. Figure 8 illustrates the transmission spectrum and blocking curve, where the spectral transmittance curve exhibits negligible variation at an error of 0.2%. Based on these results, the final structure of the quad-passband filter is determined as follows: 1.34H1.5L1.5H0.97L1.18H……0.54H0.28L2.91H0.2L0.22H0.45L, comprising a total of 174 layers with a cumulative thickness of 15.7 μm. The selection of magnetron sputtering technology for film preparation is based on the desired total thickness and number of layers in the designed structure. In this study, we utilize the sputtering coating equipment, employing tantalum and silicon as experimental targets. The parameters used for the preparation of Ta₂O₅ and SiO₂ are listed in Table 1. An optical control system is used to monitor and achieve a precise film thickness, thereby facilitating the preparation of a quad-passband filter.

We propose a process method that combines optical and time control. During the deposition of highly sensitive layers, the growth rate is determined based on the average rate of the previous layers, aiming to mitigate the thickness errors of highly sensitive layers, which can optimize the spectral curve. Figure 8 presents spectral curves of the filter prepared after implementing these improvements. The test spectrum of the quad-passband filter demonstrates exceptional conformity with the design. To suppress optical signals beyond the passband range effectively, an extended blocking film should be applied on the opposite side of the filter. However, further elaboration is omitted because of the straightforward structure. Based on our calculations, the passbands possess central wavelengths of 391.2, 479.5, 553.3, and 637.7 nm, accompanied by corresponding full widths at half-maximum of 31.8, 31.5, 24.2, and 31.7 nm, respectively; these values all satisfy the spectral requirements of this work.

In summary, we develop a double-combination cyclic nesting method to design a quad-passband filter that enables precise control over the passband position and bandwidth of the quad-passband filter by simultaneously adjusting the parameters of two Fabry-Perot multi-cavity structures. The integration of optical and rate control enhances the deposition accuracy of the sensitive layer in film production. Furthermore, by applying ion bombardment and preheating techniques to the substrate, the aggregation density and refractive index consistency are improved, thereby optimizing the spectral performance. The resulting quad-passband filter exhibits exceptional characteristics, including super-high peak transmittance (≥96%) for each passband within the range of 300?1100 nm, as well as an excellent blocking ability. It is successfully subjected to rigorous environmental testing, demonstrating its strong adaptability to various environments. This remarkable quad-passband filter has significant potential for applications in fluorescence detection.