A band-pass filter film with an extended stop band and its regulation method

Abstract

The present invention discloses a band - pass filter film with an extended stop band and its regulation method. The band - pass filter film is composed of a substrate, an admittance - matching film stack, a broadband filter film stack, a narrow - band filter film stack, and a ripple - optimization film stack. In terms of functional design, the admittance - matching film stack is used to adjust the equivalent interface admittance at the center wavelength between the substrate and the admittance - matching film stack to be the same as that of the low - refractive - index film. The broadband filter film stack is used to extend and adjust the stop band. The narrow - band filter film stack is used to design the band - pass spectral shape. The ripple - optimization film stack is used to optimize the ripple performance in the band - pass region. The method for regulating the extended stop band is to realize the movement of the stop band by adjusting the thickness of the transition layer between the resonant cavities of the broadband filter film stack. The advantages of the present invention are that the main body of the film system adopts a film system with regular thickness, direct optical monitoring can be used, the film system is easy to develop, the effective extension and free adjustment of the stop band are realized, and it is suitable for the development of integrated filter for multi - channel remote sensing systems.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical thin films, and particularly relates to a band-pass filter film with an extended stop band region and a regulation method thereof. Background Art

[0002] A narrow-band filter is a precision spectral filtering element that transmits through a specific working wavelength band and blocks (reflects or absorbs) the transmission of non-working wavelengths. Commonly used narrow-band filters are composed of a Fabry-Perot band-pass filter film on the front surface and a cut-off film system on the back surface. The Fabry-Perot band-pass filter film structure has a metal-dielectric resonant cavity type and a dielectric resonant cavity type. The metal-dielectric Fabry-Perot resonant cavity has a wide cut-off range from visible to infrared, but its band-pass waveform is mostly pyramid-shaped, making it difficult to achieve a band-pass waveform with good rectangularity. In addition, due to the absorption of the metal, it is difficult to improve the peak transmittance of the channel, generally less than 90%. The dielectric Fabry-Perot resonant cavity type uses non-absorbing high and low refractive index film layers stacked, which can achieve a peak transmittance of more than 99%, and a multi-resonant cavity film system can achieve a high-rectangularity transmission spectrum. Limited by the ratio of the high and low refractive indices of the film layer materials, it is difficult for the dielectric filter film to achieve a very wide stop band region. Therefore, for a dielectric narrow-band filter, after the Fabry-Perot resonant cavity is deposited, a very thick cut-off film system needs to be deposited on the back surface of the substrate, which brings great stress to the filter and leads to the reliability problem of the filter. Sometimes it even affects the band-pass spectral characteristics of the filter film. In order to prevent the accumulation of stress in the overly thick film system structure, part of the cut-off film system structure needs to be completed on the band-pass filter film surface, which can not only balance the stress distribution on both sides of the substrate, but also broaden the stop band region of the band-pass filter film, facilitating spectral matching with other components of the optical system.

[0003] The narrow-band filter film has high requirements for the spectral waveform. When developing the film system, the subsequent film layers need to compensate for the cumulative errors of the previous film layers. Therefore, direct optical monitoring is usually required to complete it. In order to broaden the stop band region, in traditional designs, a front cut-off or back cut-off film system needs to be further stacked on the basis of the narrow-band filter film. These cut-off film systems are usually non-regular film systems and cannot continue to be completed by direct optical monitoring, making it difficult to form effective development error compensation. Eventually, it may cause deterioration of the band-pass region spectrum or the appearance of sub-peaks in the stop band region of the completed narrow-band filter, thus affecting the yield or performance of the developed filter film.

[0004] Multi-channel space remote sensing instruments need to simultaneously detect multiple spectral bands on the same focal plane. The multi-channel integrated filter is a key optical component among them. To avoid the generation of stray light and channel crosstalk light, a monolithic multi-channel integrated filter is often required nowadays. It is required to develop different band-pass filter films in different regions on the same optical substrate, but with a common band-stop region to match other common spectral components. Due to the bottleneck problems of yield and performance control, the design and development of traditional narrow-band filter films with an extended band-stop region have affected the further integration of the number of channels, thus restricting the development of multi-channel remote sensing instruments. Finding new technical solutions for the design and development of narrow-band filter films with an extended band-stop region to improve the yield and spectral performance has become an urgent need for the development of multi-spectral and hyperspectral remote sensing technologies, and is also an important development direction for the future narrow-band filter film development technology. Summary of the Invention

[0005] The object of the present invention is to overcome the shortcomings that the traditional band-pass filter film has a narrow band-stop region, and the band-pass filter film with an extended band-stop region has a large number of irregular film systems, which is not conducive to full-process direct optical monitoring and film thickness error compensation. A band-pass filter film with an extended band-stop region that is easy to directly optically monitor and its regulation method are provided, which can be used as a new scheme for the development of integrated filters, facilitating the adjustment of the common band-stop region of multiple channels and spectral matching.

[0006] The technical solution of the present invention is as follows:

[0007] The film system main body is composed of a broadband pass filter film stack combined with a narrowband pass filter film stack. In terms of functional design, the narrowband filter film stack is used to obtain the band-pass spectral shape of the target and a certain range of band-stop regions, while the broadband pass filter film stack can bring a wider adjustable band-stop region, and at the same time its band-pass region completely covers the band-pass region of the narrowband filter film stack, without affecting the final spectral performance.

[0008] The specific film system structure is: a guiding admittance matching film stack 2, a broadband pass filter film stack 3, a narrowband pass filter film stack 4, and a corrugation optimization film stack 5 are sequentially deposited on the transparent substrate 1;

[0009] The substrate 1 is made of a material transparent to the working wavelength band;

[0010] The guiding admittance matching film stack 2 is a stack of 0 to 2 high and low refractive index film layers, used to make the interface equivalent admittance value between the substrate and the guiding admittance matching film stack close to that of the low refractive index film;

[0011] The broadband pass filter film stack 3 at least includes one broadband pass filter film structure, and this broadband pass filter film structure is the superposition of one to multiple Fabry-Perot resonators, and its structure can be: (2HaL) x 、(4HaL) x 、(6HaL) x 、(H2LHaL)x 、(H4LHaL) x 、(H6LHaL) x 、(HL2HLHaL) x 、(HL4HLHaL) x 、(HL6HLHaL) x 、(HLH2LHLHaL) x 、(HLH4LHLHaL) x 、(HLH6LHLHaL) x a combination of one or more than half-wave resonators, where H is a high-refractive-index film layer with a quarter-reference-wavelength optical thickness, L is a low-refractive-index film layer with a quarter-reference-wavelength optical thickness, a represents a proportionality coefficient of the thickness, with a range of 0.5 to 1.7, and x is the number of periods from 5 to 14;

[0012] The narrowband-pass filter film stack 4 is a conventional multi-half-wave Fabry-Perot band-pass filter film, with a bandwidth smaller than that of the broadband-pass filter film stack 3, and its structure can be: [(HL) t (2H) v (LH) t L] y 、[(HL) t (2L) v (LH) t L] y and other multi-half-wave resonators and combinations, where t, v, y are integers representing the number of repetition periods;

[0013] The corrugation-optimized film stack 5 is a stack of 2 to 3 layers of high- and low-refractive-index film layers with irregular thicknesses, used to reduce the band-pass spectral corrugations.

[0014] The method for regulating the stopband adopted in the present invention is:

[0015] Adjust the value of parameter a in the structure of the broadband-pass filter film stack 3, take different values within the range of 0.5 to 1.7 to change the stopband range of the broadband filter film stack, and determine the value of a by viewing the specific stopband range through the film system design software, so as to realize the function of regulating the spectral position of the overall film system stopband.

[0016] Under the action of the admittance-matching film stack 2, the equivalent interface admittance between the substrate 1 and the admittance-matching film stack 2 is the same as the refractive index of the L layer. Therefore, the change of parameter a will not affect the central wavelength transmittance value and the corresponding monitoring curve, which is convenient for the implementation of direct optical monitoring, ensures the error compensation in the development of the film system, and improves the yield.

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

[0018] 1. The combination of a broadband band-stop filter film stack and a narrowband band-stop filter film stack is used as the main film system, expanding the range of the band-stop region;

[0019] 2. The main film system is a regular film system with a single reference wavelength, which can be directly monitored, facilitating error compensation and improving the yield rate;

[0020] 3. By changing the parameter a in the structure of the broadband band-stop filter film stack 3, the final band-pass spectral shape of the film system can be kept almost unchanged, but the adjustment of the band-stop region of the overall film system structure can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the film system structure of the present invention.

[0022] Figure 2 It is the transmission spectrum of the filter film for expanding the band-stop region in the first embodiment of the present invention.

[0023] Figure 3 It is the transmission spectrum of the filter film for regulating the position of the band-stop region in the same band-pass region in the first embodiment of the present invention.

[0024] Figure 4 It is the transmission spectrum of the filter film for the common band-stop region in different band-pass regions in the second embodiment of the present invention.

[0025] Figure 5 It is the transmission spectrum of the filter film matching the response spectrum band of the indium gallium arsenide detector in the third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention will be further described below in conjunction with specific examples.

[0027] Embodiment 1

[0028] In this embodiment, we compare the transmission spectra of a traditional narrowband filter film and the narrowband filter film of the present invention. Taking a three-cavity narrowband filter film with a sapphire substrate, a center wavelength of 550 nm, and a bandwidth of 14 nm as an example, the coating materials are selected as TiO2 and SiO2 for high and low refractive index values.

[0029] To intuitively describe the advantages of the present invention, we designed three film systems and compared them only by increasing or decreasing the broadband filter film stack. The structures of the three film systems are as follows:

[0030] Film system 1: 0.437L 0.108H(1H 1L 1H 1L 2H 1L 1H 1L 1H 1L 1H 1L) 3 0.194H 1.46L Film system 2: 0.437L 0.108H(1H 2L 1H 1L) 6(1H 1L 1H 1L 2H 1L 1H 1L 1H 1L) 3 0.194H 1.46L

[0031] Film stack three: 0.437L 0.108H (2H 1L) 10 (1H 2L 1H 1L) 6 (1H 1L 1H 1L 2H 1L 1H 1L 1H 1L) 3 0.194H 1.46L

[0032] For clearer comparison, in all three film stacks, we deposited an admittance-matching film stack on the substrate, that is, the two layers of 0.437L 0.108H in the film stack, and the last two layers of 0.194H 1.46L play a role in corrugation optimization. The transmission spectra of the three film stacks are as Figure 2 shown. From the three film stacks, we can see that film stack one is the main peak film stack design of a traditional narrowband filter, and its band-stop region is very narrow. Through the implementation of film stack two and film stack three, we added different broadband filter films, greatly expanding the band-stop region, which will simplify the deposition difficulty of the later cut-off film stack. At the same time, we can also see that the film stack structures of the broadband filter films are all of regular thickness, which is very conducive to the implementation of direct optical monitoring and its error compensation, improving the yield.

[0033] In order to achieve cut-off matching with the spectra of other optical thin films, sometimes we need to adjust the position of the band-stop region. Here, based on film stack three, we demonstrate the specific regulation method. By adjusting the parameter a of the broadband filter film stack, we can obtain film stack four and film stack five respectively, as follows:

[0034] Film stack four: 0.437L 0.108H (2H 0.5L) 10 (1H 2L 1H 0.5L) 6 (1H 1L 1H 1L 2H 1L 1H 1L 1H 1L) 3 0.194H 1.46L

[0035] Film stack five: 0.437L 0.108H (2H 1.7L) 10 (1H 2L 1H 1.7L) 6 (1H 1L 1H 1L 2H 1L 1H 1L 1H 1L) 3 0.194H 1.46L

[0036] Due to the existence of the admittance-matching film stack 0.437L 0.108H, adjusting the parameter a will not affect the shape of the main peak. The obtained band-stop region regulation effect is as Figure 3As shown, the distribution of the stopband region in the wavelength dimension can be freely adjusted.

[0037] Example Two

[0038] In this example, we take the development of an integrated filter for multi-channel remote sensing applications as an example to illustrate the implementation of the present invention. For an integrated multi-channel filter, band-pass filter films with different center wavelengths need to be deposited at different positions on the filter. These multi-channel filter films need to have a common stopband region to achieve spectral matching with other optical elements in the system. Taking the design of RGB primary color band-pass filter films as an example, considering 455 nm, 550 nm, and 632 nm as the center wavelengths of the three channels, with bandwidths of 18 nm, 25 nm, and 29 nm respectively, the substrate is fused silica, and Ta2O5 and SiO2 are used as high and low refractive index materials. Taking their respective center wavelengths as reference wavelengths, according to the technical solution of the present invention, the designed film stack structures are as follows:

[0039] Film Stack Six: (2H 1.4L) 14 (1H 2L 1H 1.4L) 8 (1H 1L 1H 1L 2H 1L 1H 1L 1H 1L) 3 0.262H1.448L, @455 nm

[0040] Film Stack Seven: (2H 1L) 14 (1H 2L 1H 1L) 8 (1H 1L 1H 1L 2H 1L 1H 1L 1H 1L) 3 0.262H1.448L, @550 nm

[0041] Film Stack Eight: (2H 0.7L) 14 (1H 2L 1H 0.7L) 8 (1H 1L 1H 1L 2H 1L 1H 1L 1H 1L) 3 0.262H1.448L, @632 nm

[0042] The main structures of the film stacks are basically the same, only the center wavelengths are changed, and then the parameter a of the broadband filter film stack is appropriately selected, which is very beneficial to the implementation of coating for different channels. Different from Film Stacks One to Five, since the substrate is quartz glass, its refractive index is already the same as that of the low refractive index film SiO2, and there is no need to design a matching film stack anymore. From the results, as Figure 4 shown, although the three channels have different band-pass centers, they all have a common stopband region of 420 - 840 nm, which is beneficial to the spectral matching with the optical system in the later stage, thereby achieving the stopband effect for the entire wavelength band outside the band-pass range.

[0043] Example 3

[0044] In near-infrared band optical detection, indium gallium arsenide detectors are very important optoelectronic detectors, and their typical response spectral region is 800 - 1700 nm. In order to detect the target characteristic spectral signal, it is required that the detector only responds to this characteristic spectrum. Therefore, the filter used needs to achieve a band-stop characteristic in the 800 - 1700 nm band except for the characteristic spectrum. Taking the design of a filter with a center wavelength of 1300 nm and a bandwidth of 20 nm as an example, the traditional design needs to be completed by multiple coating methods of a narrow-band filter film plus front and back cut-off film systems, with a complex structure and difficult development. However, by adopting the technical solution of the present invention, the required function can be achieved through a simple single coating. In this embodiment, we use a silicon substrate to ensure that it is opaque in the 800 - 1100 nm range. The coating materials are selected as TiO2 and SiO2 as the high and low refractive index layers respectively, and the designed film system structure is:

[0045] Film stack nine: H(1H 2L 1H 1L) 9 [(1H 1L) 3 2H(1L 1H) 3 1L] 3 0.485L 0.155H 1.386L,@1300nm

[0046] In this design, the admittance matching film stack 2 only requires a single-layer high refractive index film. In order to obtain a smaller band-pass ripple, after optimization design, the ripple optimization film stack 5 is a three-layer film structure. From the results, as Figure 5 shown, the transmission sub-peak with a wavelength less than 1100 nm cannot pass through after passing through the silicon substrate, and the indium gallium arsenide detector does not generate a photoelectric response to the transmitted light with a wavelength greater than 1700 nm, thus achieving a photoelectric response only to the 1300 nm narrow-band spectrum and achieving the expected goal.

Claims

1. A band-pass filter film with an extended stop band, characterized in that: The structure of the band-pass filter film with an extended stop band is as follows: a admittance matching film stack (2), a broadband band-pass filter film stack (3), a narrow-band band-pass filter film stack (4) and a ripple optimization film stack (5) are sequentially deposited on a transparent substrate (1); The substrate (1) is made of a material transparent to the working wavelength band; The admittance matching film stack (2) is a stack of 0 to 2 high and low refractive index film layers; The broadband pass filter film stack (3) comprises at least one broadband pass filter film structure, which is a superposition of at least two Fabry-Perot resonators, and its structure is: (2HaL) x , (4HaL) x , (6HaL) x , (H2LHaL) x , (H4LHaL) x , (H6LHaL) x , (HL2HLHaL) x , (HL4HLHaL) x , (HL6HLHaL) x , (HLH2LHLHaL) x , (HLH4LHLHaL) x , (HLH6LHLHaL) x a combination of at least two multi-half-wave resonators, where H is a high refractive index film layer with an optical thickness of a quarter reference wavelength, L is a low refractive index film layer with an optical thickness of a quarter reference wavelength, a represents a thickness proportionality coefficient with a range of 0.5 to 1.7, and x is the number of periods from 5 to 14; The ripple optimization film stack (5) is a stack of 2 - 3 high and low refractive index film layers with irregular thicknesses.

2. The band - pass filter film with an extended band - stop region according to claim 1, characterized in that: The method for determining the parameter a value in the structure of the broadband band-pass filter film stack (3) is as follows: different values are taken in the range of 0.5 to 1.7 to change the stop band range of the broadband filter film stack, and the a value is determined by viewing the specific stop band range through film system design software.

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