Design of deep cut-off negative optical filter

Abstract

The invention provides a design of a deep cut-off negative optical filter. At present, the design thought of a negative optical filter film system mainly applies the main level of a reflecting film system, but the performance of a deep cut-off wave band and a transmission wave band is difficult to guarantee at the same time when the cut-off wave band width is between the main level cut-off width. The optical filter is divided into a front film system and a rear film system, and a high-level reflection band is applied, so that the optical filter achieves the purposes of deep cut-off and high transmission. The front surface film system structure and the rear surface film system structure are Sub (mHnL) S1Air and Sub (pHqL) S2Air respectively, Sub is a substrate, (mHnL) S1 and (pHqL) S2 are optical filter film systems, Air is air, m, n, p and q are matching coefficients of different materials, Chebyshev polynomial characterization shows that the three-level reflection band width depends on the matching coefficients of the materials, the matching coefficients of the different materials are added to form a fixed value, S1 and S2 are film system cycles, and m, n, p and q are the number of cycles of the film systems. H and L respectively represent lambda / 4 optical thicknesses of the high-refractive-index material and the low-refractive-index material, and lambda is a reference wavelength. The design provided by the invention can be widely applied to the design of the deep cut-off negative optical filter.

Description

Technical Field

[0001] The invention relates to the field of optical films, and in particular to the design of a deep cutoff negative filter. Background Art

[0002] In the field of optical thin films, a filter that removes a certain wavelength band from a certain wavelength spectrum is called a negative filter. It usually cuts off a certain spectral range and has high transmittance in other spectral ranges. This kind of filter has important applications in fluorescence analysis systems, laser protection, optical communications, and astronomy filters in the biomedical industry. At present, the film system design idea of ​​deep cutoff negative filters is mainly to apply the main order of the reflective film system. When the cutoff depth of the filter is large and the cutoff width is lower than the main order cutoff width, it is difficult to guarantee the performance of the deep cutoff band and the transmission band at the same time. Summary of the invention

[0003] The purpose of the present invention is to overcome the defects of the prior art and provide a feasible design of a deep cutoff negative filter. At present, the film system design scheme of the deep cutoff negative filter is mainly to achieve the purpose of deep cutoff of the main reflection band by applying the main order of the reflection film system. The present invention adopts the high order reflection film system to provide a new scheme for the design of the deep cutoff negative filter.

[0004] Further research found that the cutoff width of the high-order reflective film system is relatively narrow. When the cutoff band width is lower than the design target cutoff band width, the high-order reflective film system is difficult to realize. Furthermore, the present invention couples two high-order film systems on the same side of the substrate so that the cutoff bands of the two film systems overlap to achieve the design goal. However, the thickness of the film system is too large at this time. Considering the problems of stress between film layers, filtering performance, and equipment process foundation, the present invention cleverly plates the two high-order film systems on the front and rear surfaces of the substrate. By overlapping the cutoff bands of the two film systems on the front and rear surfaces, the width of the cutoff band is "widened". The structure is as follows: Figure 1 shown.

[0005] The present invention can realize accurate filtering of the target light band under certain incident conditions. The front and rear surface film systems are both high-order sub-reflective film systems. By adjusting the number of film stack cycles and the material matching coefficient and the front and rear surface superposition, a wide-band deep-cutoff filter film system is obtained. This design has the advantages of deep cutoff, high transmittance, low process requirements for the coating machine, and high feasibility.

[0006] The Sub in the present invention is a substrate, and the selectable material is one of K9 glass, fused quartz, calcium fluoride and sapphire.

[0007] The combination of high refractive index material and low refractive index material of the present invention is one of Ta2O5 / SiO2, HfO2 / SiO2, TiO2 / SiO2 and Nb2O5 / SiO2.

[0008] The front and rear surface film systems designed by the present invention have low thickness, which reduces the requirements for the coating machine equipment process and can be accurately controlled by conventional monitoring methods, making the present invention highly feasible.

[0009] The deep cutoff negative filter of the present invention is respectively plated with negative filter systems on the front surface and the rear surface of the same substrate.

[0010] The matrix elements of the periodic system M of the two materials can be characterized by Chebyshev polynomials with parameter b(λ):

[0011]

[0012]

[0013] It can be seen that the width of the third-level sub-reflection band can be expressed as:

[0014]

[0015] The film structure of the front surface is Sub|(mHnL)^S1|Air, and the film structure of the rear surface is Sub|(pHqL)^S2|Air.

[0016] The film system described in the present invention realizes the design of the deep cut-off negative filter through commercial film system design software. The film system structure is |(mHnL)^S1|Sub|(pHqL)^S2|Air. A high vacuum coating machine is used to alternately coat high and low refractive index film structures on the front and rear surfaces of the substrate.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The present invention provides a design of a deep cutoff negative filter, especially for a deep cutoff depth and a cutoff bandwidth between the primary and secondary bandwidths of a reflective film system and the high and secondary bandwidths of a reflective film system. First, the initial film system structure of the filter film is designed, and then based on the characteristics of a high cutoff depth and a wide cutoff band, the film system structure is split into front and back double-sided plating. Finally, the film system structure is optimized according to a formula describing the relationship between the physical thickness and optical thickness of the film.

[0019] (2) The present invention provides a design of a deep cutoff negative filter, which uses a high-order sub-reflective film system as the basic structure and a front and back double-sided coating solution, which greatly reduces the film thickness, improves the cutoff, reduces the requirements for coating equipment, and ensures the feasibility of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of deep cutoff negative filter structure

[0021] Figure 2 Transmission spectra of the front, back and double surfaces of the deep cutoff negative filter

[0022] Figure 3 Optical density plots of the front, back, and both sides of a deep cutoff negative filter

[0023] Figure 4 Transmission spectrum of the front surface of the optimized deep cutoff negative filter

[0024] Figure 5 Optical density map of the front surface of the optimized deep cutoff negative filter

[0025] Figure 6 Transmission spectrum of the rear surface of the optimized deep cutoff negative filter

[0026] Figure 7 Optical density map of the back surface of the optimized deep cutoff negative filter

[0027] Figure 8 Transmission spectra of both sides of the optimized deep cutoff negative filter

[0028] Fig. 9 Optical density plot of both sides of a deep cutoff negative filter DETAILED DESCRIPTION

[0029] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0030] A design of a deep cutoff negative filter, characterized in that the front and rear surface film systems of the deep cutoff negative filter are composed of high-order sub-reflection film systems, the position and width of the cutoff band are determined by adjusting the matching coefficient, and the cutoff depth of the cutoff band is improved by increasing the number of periods. According to the above method, the front and rear film systems are respectively plated on the two surfaces of the same substrate, so that the deep cutoff effect of a wider range of spectra can be achieved on both sides. Among them, the front surface film system structure is Sub|(mHnL)^S1|Air, and the rear surface film system structure is Sub|(pHqL)^S2|Air. Among them, Sub represents the substrate, m, n, p, q are the matching coefficients of different materials, and it is found through Chebyshev polynomial characterization that the width of the third-order sub-reflection band of the structure depends on the matching coefficient of the material, and the matching coefficients of different materials in the front and rear surface film systems are added to a constant value, H and L represent the λ / 4 optical thickness of the high refractive index material and the low refractive index material respectively, λ is the reference wavelength, S1 and S2 are the number of film system periods, and Air represents air.

[0031] As an optional embodiment, the substrate of the deep cutoff negative filter is fused quartz, and the front and rear surface films are made of high and low refractive index materials Ta2O5 and SiO2 respectively, with an incident angle of 14°. Among them, the reference wavelength of the front surface film system is 732nm, S1=58, m=1.31, n=2.69; the reference wavelength of the rear surface film system is 790nm, S2=58, p=1.31, q=2.69. The transmission spectra of the front surface, rear surface and double surface are obtained as follows Figure 2 The obtained optical density diagrams of the front surface, back surface and double surface are shown in Figure 3 shown.

[0032] As an optional embodiment, the deep cutoff negative filter designed in the present invention has a cutoff bandwidth of 120nm under an incident condition of 14°, achieves an average transmittance of more than 95% in the 430-680nm and 835-870nm bands, and achieves deep cutoff and reaches OD6 in the 700-820nm band.

[0033] As an optional implementation, the Essential Macleod software is used to optimize the film system designed above, and the optimized front surface transmission spectrum and OD graph are obtained as follows: Figure 4 , Figure 5 As shown in the figure, the optimized rear surface transmission spectrum and OD diagram are shown in Figure 6 , Figure 7 As shown, the optimized double-sided transmission spectrum is shown in Figure 8 As shown, the optical density map of the optimized double-sided is as follows Fig. 9 shown.

[0034] As an optional implementation, the design of a deep cutoff negative filter is characterized in that the front surface film structure of the deep cutoff negative filter is optimized as follows:

[0035] Sub|0.1219H 0.1862L 1.1351H 0.2440L 0.1130H 1.5826L 0.1417H 0.1615L1.1002H 0.0899L 0.4045H0.1507L 0.2209H 1.0096L 0.9458H 1.0864L 0.0751H1.0547L 0.9726H 2.0527L 0.9064H 0.8355L 0.8365H 0.8329L 0.9001H 2.0166L0.8970H 0.8313L 0.8311H 0.8302L 0.8967H 2.0115L 0.9021H 0.8313L 0.8901H0.6912L 0.1269H 0.2683L 0.2790H 1.1756L 0.0598H 1.0094L 0.8977H 0.8467L1.0345H 0.2102L 1.0568H 1.0405L 0.1317H 1.0788L 0.8309H 1.0544L 0.2314H1.0718L 0.7854H 1.0740L 0.2197H 1.0484L 0.8410H 1.0654L 0.1253H 1.0310L0.8684H 0.9436L 0.3345H 0.1886L 0.3014H 0.3213L 1.0696H 2.0626L 0.9870H2.0622L 0.9834H 2.0390L 0.9232H 0.8863L 0.2330H 0.1708L 0.1981H 0.8427L0.8898H 1.0046L 0.1273H 1.0850L 0.1854H 1.0497L 0.2690H 1.0832L 0.7297H1.0748L 0.3000H 1.0627L 0.7629H 1.0861L 0.2140H 1.0404L 0.8555H 1.0521L0.1193H 1.0478L 0.8524H 0.9680L 0.3437H 0.2237L 0.1389H 0.6739L 0.9619H2.0561L 1.0088H 2.1386L 1.0415H 2.2902L 0.2450H 0.1683L 1.4004H 0.5611L|Air.

[0036] As an optional implementation, the design of a deep cutoff negative filter is characterized in that the rear surface film structure of the deep cutoff negative filter is optimized as follows:

[0037] Sub|0.1574H 0.1374L 0.8288H 0.1952L 0.1786H 0.5792L 0.1828H 0.4482L1.1860H 0.3989L 1.1196H 2.1602L 1.1293H 0.3184L 0.3599H 0.1552L 0.3847H0.9552L 0.9557H 2.1328L 1.0153H 1.1264L 0.1060H 1.1812L 1.0504H 2.1890L1.0194H 1.0752L 0.0830H 1.1032L 0.8713H 0.9418L 0.5611H 0.1729L 0.2088H0.4447L 0.9378H 1.0443L 0.1996H 1.0938L 0.8085H 1.0956L 0.2006H 1.0476L0.9560H 0.3872L 0.2380H 0.1638L 0.5653H 0.9503L 0.8730H 1.1045L 0.0997H1.1026L 1.0234H 2.2124L 1.0741H 2.2265L 1.0289H 0.8950L 0.1294H 0.2731L0.1457H 0.9298L 1.0225H 2.2259L 1.0762H 2.2564L 1.0673H 2.1893L 0.9446H0.8878L 0.7538H 0.1169L 0.1710H 0.4567L 1.0048H 0.9797L 0.0958H 1.1297L0.8386H 1.0678L 0.2891H 1.1034L 0.7319H 1.0968L 0.3476H 1.2386L 0.3291H1.24861~0.2859H 1.0843L 0.8402H 1.1100L 0.1778H 1.0969L 0.9677H 2.1541L1.0390H 1.1599L 0.0841H 1.1338L 1.0487H 2.2045L 1.0692H 2.2083L 1.0610H2.1967L 1.0821H 0.3318L 0.0662H 1.5644L 0.1413H 0.2429L 0.2864H 0.6124L|Air.

[0038] As an optional embodiment, the design of the deep cutoff negative filter is that the front surface film system can achieve an average transmittance of 99.78% in the 430-680nm band, a cutoff depth better than OD6 in the 700-770nm band, an average transmittance of 99.97% in the 835-870nm band, and a total thickness of 13.38μm; the rear surface film system can achieve a transmittance of 99.40% in the 430-680nm band, a cutoff depth better than OD6 in the 760-820nm band, a transmittance as high as 99.21% in the 835-870nm band, and a total thickness of about 14.26μm; the double-sided film system can achieve a transmittance higher than 95% in the 430-6580nm band, a cutoff depth better than OD6 in the 700-820nm band, and a transmittance higher than 95% in the 835-870nm band.

[0039] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A design of a deep cutoff negative filter, characterized in that: When the cut-off bandwidth is between the primary sub-bandwidth of the reflective film system and the high-order sub-bandwidth of the reflective film system, the deep cut-off negative filter is coated with high-order sub-reflective film systems on the front and rear surfaces of the same substrate, respectively, so as to achieve deep cut-off processing for a specific light band and transmission processing for a specific light band. The front surface film system structure is Sub|(mHnL)^S1|Air, and the rear surface film system structure is Sub|(pHqL)^S2|Air. Wherein, Sub represents the substrate, m, n, p, q are the matching coefficients of different materials, and it is found through Chebyshev polynomial characterization that the third-order sub-reflection band width of the structure depends on the matching coefficient of the material, and the matching coefficients of different materials in the front and rear surface film systems are added to a constant value, and the position and width of the cut-off band are determined by adjusting the matching coefficient, and the cut-off depth of the cut-off band is improved by increasing the number of periods, H and L represent the λ / 4 optical thickness of the high refractive index material and the low refractive index material respectively, λ is the reference wavelength, S1 and S2 are the number of film system periods, and Air represents air.

2. The deep cutoff negative filter according to claim 1, characterized in that: The Sub is a substrate, and the selectable material is one of K9 glass, fused quartz, calcium fluoride and sapphire.

3. The deep cutoff negative filter according to claim 1, characterized in that: The high refractive index material and the low refractive index material are combined into Ta2O s / SiO2, HfO2 / SiO2, TiO2 / SiO2 and Nb2O s / One of SiO2.

4. The deep cutoff negative filter according to claim 1, characterized in that: The deep cutoff negative filter is composed of alternating dielectric layers of high and low refractive index materials.

5. The deep cutoff negative filter according to claim 1, characterized in that: The design steps are: constructing an optical film system structure; calculating and optimizing the cutoff and transmittance of the optical film system structure at the reference wavelength to obtain the optimized optical film system structure.

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