CN116413847A - A kind of band-pass filter film with extended band-stop area and its control method - Google Patents

Abstract

The invention discloses a bandpass filter film with an extended band-stop region and a regulating and controlling method thereof. The bandpass filter film consists of a substrate, an admittance matching film stack, a broadband filter film stack, a narrowband filter film stack and a ripple optimizing film stack. In the aspect of functional design, the admittance matching film stack is used for adjusting the central wavelength equivalent interface admittance of 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 for expanding and adjusting a band-stop zone, the narrowband filter film stack is used for designing the band-pass spectrum shape, and the ripple optimizing film stack is used for optimizing ripple performance of the band-pass zone. The method for regulating and controlling the expansion band-stop zone is to realize the movement of the band-stop zone by regulating the thickness of a transition layer between resonant cavities of the broadband filter film stack. The invention has the advantages that the film system main body adopts the film system with regular thickness, can adopt direct optical monitoring, is easy to develop, realizes effective expansion and free adjustment of a band stop zone, and is suitable for developing an integrated optical filter of a multi-channel remote sensing system.

Description

A kind of band-pass filter film with extended band-stop area and its control method

technical field

The invention belongs to the technical field of optical thin films, and in particular relates to a band-pass filter film with extended band-stop area and a control method thereof.

Background technique

A narrowband filter is a precision spectral filter element that passes through a specific operating band and prevents (reflects or absorbs) the transmission of non-operating wavelengths. Commonly used narrow-band filters are composed of a Fabry-Perot bandpass filter film on the front surface and a cut-off film system on the back surface. The Fabry-Perot bandpass filter film structure has a metal-dielectric resonator type and a dielectric resonator type. The metal-dielectric Fabry-Perot resonator has a wide cut-off range from the visible to the infrared, but its band-pass waveform is mostly pyramid-shaped, and it is difficult to achieve a band-pass waveform with good rectangularity. In addition, the channel peak transmits due to the absorption of the metal. The rate is difficult to improve, generally less than 90%. The dielectric Fabry-Perot resonant cavity type is stacked with non-absorbing high and low refractive index films, which can achieve a peak transmittance of more than 99%, and the multi-resonant cavity film system can achieve a highly rectangular transmission spectrum. Limited by the ratio of high and low refractive index of the film material, it is difficult for the dielectric filter film to achieve a wide band stop area. Therefore, the dielectric narrowband filter needs to be plated with a thick cut-off film on the back of the substrate after the Fabry Perot resonator is plated, which brings great stress to the filter and causes the filter Reliability issues, and sometimes even affect the bandpass spectral characteristics of the filter film. In order to prevent the excessively thick film structure from accumulating stress, it is necessary to complete part of the cut-off film structure on the surface of the band-pass filter film, which can not only balance the stress distribution on both sides of the substrate, but also expand the band-stop area of the band-pass filter film. Convenient for spectral matching with other components of the optical system.

Narrow-band filter films have high requirements on spectral waveforms, and it is necessary to compensate the cumulative error of the previous film layers between subsequent film layers when developing the film system, so direct optical monitoring is usually required to complete. In order to expand the band-stop region, the traditional design needs to continue to superimpose the front cut-off or rear cut-off film on the basis of the narrow-band filter film, and these cut-off films are usually irregular films, which cannot continue to be completed by direct optical monitoring, which is difficult Forming an effective development error compensation may eventually cause spectral distortion in the bandpass region or a sub-peak problem in the bandstop region of the completed narrowband filter, which will affect the yield or performance of the filter film development.

Multi-channel space remote sensing instruments need to realize simultaneous detection of multiple spectral bands at the same focal plane, and multi-channel integrated filters are the key optical components. In order to avoid the generation of stray light and channel crosstalk light, it is often required to use a single-chip multi-channel integrated filter, which requires the development of different bandpass filter films in different regions on the same optical substrate, but has a common Bandstops to match other common spectral components. Due to the bottleneck problem of yield and performance control, the design and development of the traditional narrow-band filter film with extended band-stop region has affected the further integration of the number of channels, thereby limiting the development of multi-channel remote sensing instruments. Looking for the design of narrow-band filter films with extended band-stop regions and the development of new technology solutions to improve yield and spectral performance have become an urgent need for the development of multi-spectral and hyperspectral remote sensing technology, and it is also an important development of narrow-band filter technology in the future. direction.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the narrow band-stop region of the traditional band-pass filter film, but there are a large number of irregular film systems in the band-pass filter film with extended band-stop region, which is not conducive to direct optical monitoring and film thickness error compensation in the whole process. The invention provides a band-pass filter film with an extended band-stop area that is easy to be directly monitored optically and a control method thereof, which can be used as a new development scheme of an integrated optical filter, and facilitates the adjustment and spectrum matching of the common band-stop area of multiple channels.

Technical scheme of the present invention is:

The main body of the film system is composed of a wideband pass filter stack combined with a narrow bandpass filter stack. In terms of functional design, the narrowband filter stack is used to obtain the bandpass spectral shape of the target and a certain range of bandstop regions, while the broadband filter stack The optical film stack can bring a wider adjustable band-stop region, and its band-pass region completely covers the band-pass region of the narrow-band filter film stack, which will not affect the final spectral performance.

The specific film structure is: on the transparent substrate 1, the admittance matching film stack 2, the broadband filter film stack 3, the narrow band pass filter film stack 4 and the corrugated optimization film stack 5 are sequentially plated;

The substrate 1 is made of a material that is transparent to the working band;

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

The wideband pass filter film stack 3 comprises at least one wideband pass filter film structure, which is a superposition of one to more 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) the combination of single or multiple multi-half-wave resonators in ^x , where H is a high refractive index film layer with a quarter reference wavelength optical thickness, and L is a low refractive index film layer with a quarter reference wavelength optical thickness Ratio film layer, a represents the proportional coefficient of thickness, the range is 0.5～1.7, x is the cycle number of 5-14;

The narrow band-pass filter stack 4 is a conventional multi-half-wave Fabry-Perot band-pass filter, and the bandwidth is less than the bandwidth of the wide-band pass filter 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, t, v, y are integers, indicating the number of repetition periods;

The corrugation-optimized film stack 5 is a stack of 2-3 layers of high and low refractive index film layers with irregular thickness, which is used to reduce band-pass spectrum ripple.

The control method of the band resistance zone that the present invention adopts is:

Adjust the value of the parameter a in the structure of the broadband filter stack 3, and take different values within the range of 0.5 to 1.7 to change the range of the band-stop zone of the broadband filter stack, and check the specific range of the band-stop zone through the film system design software And determining the value of a realizes the function of adjusting the spectral position of the band stop region of the overall film system.

Under the action of the admittance matching film stack 2, the equivalent interface admittance of the substrate 1 and the admittance matching film stack 2 is the same as the refractive index of the L layer, so the change of the parameter a will not affect the central wavelength transmittance value And the corresponding monitoring curve, which facilitates the implementation of direct optical monitoring, ensures the error compensation of the film system development, and improves the yield.

Compared with prior art, the present invention has following advantage:

1. The combination of wideband pass filter stack and narrow bandpass filter stack is used as the main body of the film system, which expands the range of the band stop area;

2. The main body of the film system is a regular film system with a single reference wavelength, which can be directly monitored to facilitate error compensation and improve yield;

3. By changing the parameter a in the structure of the broadband filter film stack 3, the shape of the final film band-pass spectrum can be kept almost unchanged, but the band-stop region of the overall film structure can be adjusted.

Description of drawings

Fig. 1 is a schematic diagram of the film system structure of the present invention.

Fig. 2 is the transmission spectrum of the filter film in the extended band-stop region according to Embodiment 1 of the present invention.

Fig. 3 is the transmission spectrum of the filter film in the first embodiment of the present invention, where the position of the band-stop area is adjusted in the same band-pass area.

Fig. 4 is the second embodiment of the present invention, the transmission spectrum of the filter film in the common band-stop area of different band-pass areas.

Fig. 5 is the third embodiment of the present invention, the transmission spectrum of the filter film matching the response spectrum of the InGaAs detector.

Detailed ways

Below in conjunction with specific example the present invention will be further described

Embodiment one

In this embodiment, we compare the transmission spectra of the traditional narrow-band filter film and the narrow-band filter film of the present invention. Choose a three-cavity narrow-band filter film with a sapphire substrate, a center wavelength of 550nm, and a bandwidth of 14nm as an example. The coating materials are TiO ₂ and SiO ₂ as the high and low refractive index values.

In order to intuitively describe the advantages of the present invention, we have carried out the design of three film systems, and only increase or decrease the broadband filter film stack for comparison. The structures of the three films are as follows:

Film system 1: 0.437L 0.108H(1H 1L 1H 1L 2H 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 1 h 1L) ³ 0.194H 1.46L

Film system three: 0.437L 0.108H(2H 1L) ¹⁰ (1H 2L 1H 1L) ⁶ (1H 1L 1H 1L 2H 1L 1H 1L1H1L) ³ 0.194H 1.46L

In order to make the comparison more clear, in the three film systems, we have plated the admittance matching film stack on the substrate, that is, there are two layers of 0.437L and 0.108H in the film system, and the last two layers of 0.194H and 1.46L are optimized for ripples. effect. The transmission spectra of the three films are shown in Fig. 2. From the three film systems, we can see that the film system one is designed for the main peak film system of the traditional narrow-band filter film, and its band stop range is very narrow. Through the implementation of film system 2 and film system 3, we have added different broadband filter films to greatly expand the band-stop area, which will simplify the difficulty of plating the cut-off film system in the later stage. At the same time, we can also see that the film structure of the broadband filter film is of regular thickness, which is very conducive to the implementation of direct optical monitoring and error compensation to improve the yield.

In order to achieve cut-off matching with the spectrum of other optical films, sometimes we need to adjust the position of the band stop region. Here, based on film system 3, we will demonstrate the specific control method and adjust the parameter a of the broadband filter stack to obtain film system 4 and film system 5 respectively, as follows:

Film system four: 0.437L 0.108H(2H 0.5L) ¹⁰ (1H 2L 1H 0.5L) ⁶ (1H 1L 1H 1L 2H 1L 1H1L1H 1L) ³ 0.194H 1.46L

Film system five: 0.437L 0.108H(2H 1.7L) ¹⁰ (1H 2L 1H 1.7L) ⁶ (1H 1L 1H 1L 2H 1L 1H1L1H 1L) ³ 0.194H 1.46L

Due to the existence of the admittance matching membrane 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 shown in Figure 3, and the distribution of the band-stop region in the wavelength dimension can be freely adjusted.

Embodiment two

In this embodiment, we take the development of an integrated optical filter for multi-channel remote sensing application as an example to illustrate the implementation of the present invention. Multi-channel integrated optical filters need to be plated with band-pass filter films with different central wavelengths at different positions of the filter. These multi-channel filter films need to have a common band-stop region in order to achieve spectral matching with other optical components in the system. Taking the design of the RGB three-primary color bandpass filter film as an example, consider 455nm, 550nm, and 632nm as the central wavelengths of the three channels, and the bandwidths are 18nm, 25nm, and 29nm respectively. The substrate is made of fused silica, and Ta ₂ O ₅ and SiO ₂ As a high and low refractive index material. Taking respective central wavelengths as reference wavelengths respectively, according to the technical scheme of the present invention, the designed film structure is:

Film system 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,@455nm

Film system seven: (2H 1L) ¹⁴ (1H 2L 1H 1L) ⁸ (1H 1L 1H 1L 2H 1L 1H 1L 1H 1L) ³ 0.262H1.448L,@550nm

Film system 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,@632nm

The main structure of the film system is basically the same, only the center wavelength is changed, and then the parameter a of the broadband filter film stack is properly selected, which is very beneficial to the implementation of different channel coatings. Slightly different from film systems 1 to 5, since the substrate is made of quartz glass, its refractive index is already the same as that of the low-refractive index film SiO ₂ , so there is no need to design a matching film stack. From the results, as shown in Figure 4, although the three channels have different band-pass centers, they all have a common band-stop region of 420-840nm, which is conducive to the spectral matching with the optical system in the later stage, so as to realize the non-band-pass band The full-band band-stop effect.

Embodiment three

In near-infrared optical detection, InGaAs detector is a very important photodetector, and its typical response spectrum range is 800-1700nm. In order to realize the detection of the characteristic spectrum signal of the target, it is necessary for the detector to respond only to the characteristic spectrum. Therefore, the optical filter used needs to realize the band-stop characteristic in the 800-1700nm band in addition to the characteristic spectrum. Taking the design of a filter with a center wavelength of 1300nm and a bandwidth of 20nm as an example, the traditional design needs to be completed by multiple coating methods of narrow-band filter film plus front and rear cut-off films. The structure is complex and difficult to develop. However, by adopting the technical solution of the present invention, the required functions can be realized through simple one-time coating. In this embodiment, we use a silicon substrate to ensure that the 800-1100nm is opaque, and the coating materials are TiO ₂ and SiO ₂ as the high and low refractive index layers respectively. The designed film structure is:

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

In this design, the admittance matching membrane stack 2 only needs a single layer of high-refractive index film, and in order to obtain smaller bandpass ripples, after an optimized design, the ripple-optimized membrane stack 5 has a three-layer membrane structure. From the results, as shown in Figure 5, the transmission sub-peak with a wavelength of less than 1100nm cannot pass through the silicon substrate, and the InGaAs detector does not produce a photoelectric response to the transmitted light with a wavelength greater than 1700nm, thus realizing only The photoelectric response to the 1300nm narrowband spectrum achieves the expected goal.

Claims (2)

1. A band-pass filter film for expanding the band-stop zone, characterized in that: The structure of the band-pass filter film with the extended band-stop region is as follows: on the transparent substrate (1), an admittance matching film stack (2), a wide-band pass filter film stack (3), and a narrow-band pass filter film stack (3) are sequentially plated Membrane stack (4) and corrugated optimized membrane stack (5); The substrate (1) is made of a material transparent to the working band; The admittance matching film stack (2) is a stack of 0 to 2 layers of high and low refractive index film layers; Described wideband pass filter film stack (3) comprises at least a kind of wideband pass filter film structure, and this wideband pass filter film structure is the superposition of one to a plurality of 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 the combination of single or multiple multi-half-wave resonators, where H is a high-refractive-index film layer with a quarter reference wavelength optical thickness, and L is the low The refractive index film layer, a represents the proportional coefficient of the thickness, the range is 0.5 to 1.7, and x is the period number of 5-14; The corrugated optimized film stack (5) is a stack of 2-3 high and low refractive index film layers with irregular thickness. 2. the band-pass filter film of extended band-stop area according to claim 1, is characterized in that: the determination method of the parameter a value described in described broadband pass filter film stack (3) structure is: at 0.5 Take different values within the range of ~1.7 to change the range of the band-stop zone of the broadband filter film stack, and determine the value of a by checking the specific band-stop zone range with the film system design software.

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