CN108931832B - Deep cut-off narrowband filter and optical instrument based on ultra-wide wavelength high reflection - Google Patents
Deep cut-off narrowband filter and optical instrument based on ultra-wide wavelength high reflection Download PDFInfo
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- CN108931832B CN108931832B CN201811140852.5A CN201811140852A CN108931832B CN 108931832 B CN108931832 B CN 108931832B CN 201811140852 A CN201811140852 A CN 201811140852A CN 108931832 B CN108931832 B CN 108931832B
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- 230000003287 optical effect Effects 0.000 title claims abstract description 101
- 229910052709 silver Inorganic materials 0.000 claims abstract description 78
- 239000004332 silver Substances 0.000 claims abstract description 78
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 claims abstract description 74
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims abstract description 74
- 239000000758 substrate Substances 0.000 claims abstract description 57
- ORUIBWPALBXDOA-UHFFFAOYSA-L magnesium fluoride Chemical compound [F-].[F-].[Mg+2] ORUIBWPALBXDOA-UHFFFAOYSA-L 0.000 claims abstract description 48
- 229910001635 magnesium fluoride Inorganic materials 0.000 claims abstract description 48
- 239000004408 titanium dioxide Substances 0.000 claims abstract description 37
- 239000010410 layer Substances 0.000 claims description 157
- 230000001939 inductive effect Effects 0.000 claims description 27
- 239000012528 membrane Substances 0.000 claims description 21
- 239000012790 adhesive layer Substances 0.000 claims description 3
- 239000013078 crystal Substances 0.000 claims description 3
- 239000005304 optical glass Substances 0.000 claims description 3
- 239000002356 single layer Substances 0.000 claims description 3
- 230000035699 permeability Effects 0.000 claims 1
- 230000005540 biological transmission Effects 0.000 abstract description 123
- 229910052751 metal Inorganic materials 0.000 abstract description 16
- 239000002184 metal Substances 0.000 abstract description 16
- 239000004568 cement Substances 0.000 abstract description 3
- 239000010408 film Substances 0.000 description 149
- 238000002834 transmittance Methods 0.000 description 52
- 238000010521 absorption reaction Methods 0.000 description 17
- 230000009977 dual effect Effects 0.000 description 14
- 230000003595 spectral effect Effects 0.000 description 14
- 230000001965 increasing effect Effects 0.000 description 7
- 238000013461 design Methods 0.000 description 6
- 125000006850 spacer group Chemical group 0.000 description 6
- 239000000853 adhesive Substances 0.000 description 5
- 230000001070 adhesive effect Effects 0.000 description 5
- 239000011521 glass Substances 0.000 description 5
- 239000000463 material Substances 0.000 description 4
- 230000035515 penetration Effects 0.000 description 4
- 238000002310 reflectometry Methods 0.000 description 4
- 230000006698 induction Effects 0.000 description 3
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- 239000003822 epoxy resin Substances 0.000 description 2
- 238000003475 lamination Methods 0.000 description 2
- 230000031700 light absorption Effects 0.000 description 2
- -1 middle Chemical compound 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 229920000647 polyepoxide Polymers 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 238000002703 mutagenesis Methods 0.000 description 1
- 231100000350 mutagenesis Toxicity 0.000 description 1
- 239000012788 optical film Substances 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 230000005693 optoelectronics Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/20—Filters
- G02B5/201—Filters in the form of arrays
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/20—Filters
- G02B5/208—Filters for use with infrared or ultraviolet radiation, e.g. for separating visible light from infrared and/or ultraviolet radiation
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/20—Filters
- G02B5/26—Reflecting filters
Abstract
The invention discloses a deep cut-off narrowband filter based on ultra-wide wavelength high reflection and an optical instrument, which comprise a first substrate and a second substrate, wherein a bimetal-triple-permeation filter is arranged on the first surface of the first substrate, an all-dielectric narrowband filter is arranged on the second surface, a bimetal-triple-permeation modified filter is arranged on the first surface of the second substrate, and then the all-dielectric narrowband filter is adhered with the second surface of the second substrate by optical cement. The bimetal-triple-permeation filter and the bimetal-triple-permeation modified filter consist of two layers of silver films and front permeation, middle permeation and rear permeation films separated by the silver films. The all-dielectric narrow-band filter consists of a multilayer double half-wave structure with titanium dioxide and magnesium fluoride alternated. The invention is based on the high reflection of the metal film to realize deep cut-off on ultra-wide wavelength and utilizes the induced transmission of the dielectric film to realize the narrow-band filter with high transmissivity on a specific transmission band, so as to be used for a weak optical signal acquisition system with specific requirements.
Description
Technical Field
The invention relates to the technical field, in particular to a deep cut-off narrowband filter based on ultra-wide wavelength high reflection and a collection system for weak optical signals with specific requirements.
Background
Narrowband filters are commonly used devices in weak optical signal acquisition systems. In order to improve the signal-to-noise ratio, the most basic requirement is that the cut-off band of the narrowband filter must have a sufficiently deep cut-off, while the transmission band must have as high a transmission as possible, which is itself a contradiction.
According to the requirements of new products, the main technical indexes of the narrow-band filter are provided as follows: firstly, the maximum transmission wavelength is 550nm, the half width of a transmission band is less than 10nm, and the maximum transmission is more than 70%; second, the cut-off interval is 400-12000 nm, namely, the visible light region except the transmission band and the near infrared, mid infrared and far infrared regions are included; and thirdly, adopting a reflection type cut-off rather than an absorption type cut-off, wherein the minimum cut-off depth of the whole cut-off band is OD & gtor 4.
The most common method for solving the problem is to use a special absorption type substrate to intercept light, such as ion-colored blue glass or special color glass filter as a substrate, and the substrates can realize transmission in a transmission band wavelength region and absorption in the transmission band wavelength region. Light is prevented from continuing through absorption of light energy by the substrate in the cut-off region, which is commonly referred to as an absorption cut-off. Unfortunately, however: the absorption type cutoff is often limited in depth, and even if the thickness of the substrate is increased, the cutoff requirement cannot be met because the cutoff band of the filter is very wide, for example, the cutoff band of the present narrow-band filter is about 11590nm, and the transmission band width is only 10nm, so even if the cutoff depth of the cutoff band reaches 0.1%, the residual transmission of the cutoff band over the wavelength region 11590nm is integrated, and the noise thereof may be far greater than the transmission band signal, which is obviously not practically applicable. More troublesome is that by using an absorptive cutoff, the light energy absorbed by the substrate is converted to heat, and a narrowband filter is usually placed in front of the signal sensor, so that the heat generated by the substrate radiates to the sensor to generate thermal noise, which is not usually allowed.
The invention aims to provide a narrow-band filter which is used for realizing ultra-wide cut-off band deep cut-off degree based on ultra-wide wavelength and high reflection and realizing high transmissivity in a transmission band by utilizing a transmission induction technology, so as to be used for an optical signal acquisition system with specific requirements. The deep cut-off degree of the ultra-wideband is realized by virtue of the characteristic that the metal film has ultra-wideband high reflection, and meanwhile, the high transmittance of the transmission band is obtained by virtue of the characteristic that the dielectric film can attract the transmittance of the metal film to the maximum value at a specific wavelength, so that the combination of the two is probably the best way for realizing the index of the optical filter. The design proves that the excellent characteristics of deep cut-off degree and high transmissivity of a transmission band at ultra-wide wavelength can be obtained by superposing the two special optical filters, namely the bimetal-three-induced optical filter and the bimetal-three-induced modified optical filter. The cut-off characteristic of the optical filter is realized by adopting the reflection of a metal film instead of the absorption of a substrate material, so that the problem that the temperature of a device is increased due to the absorption of light energy by the optical filter is avoided. That is, achieving deep cut-off with high reflection of the metal film at ultra-wide wavelength and achieving high transmittance with induced design of the dielectric film at transmission band are core problems to be explored and solved by the present invention.
Disclosure of Invention
The invention aims to provide a deep cut-off narrowband filter based on ultra-wide wavelength high reflection and an optical instrument.
The conception of the invention is as follows: the first technical index is: the maximum transmission wavelength is 550nm, the half width of the transmission band is smaller than 10nm, and the maximum transmission is larger than 70%. Obviously, the first technical index can be conveniently realized by using an all-medium narrow-band filter. The second technical index is: the cut-off interval is 400-12000 nm, namely, the visible light region except the transmission band and the near infrared, mid infrared and far infrared regions are included. After the second technical index is added, the all-dielectric narrow-band filter cannot be used, because the cut-off band is too wide, the cut-off can not be realized in such a wide wavelength range by using a dielectric film, so that the absorption type cut-off is realized by using a special absorption type substrate at present, and the absorption type substrate can realize the purposes of wavelength transmission of a specific transmission band and wavelength absorption of a wide cut-off band although the cut-off degree is not too high (such as 0.1 percent on average). The third technical index is: the reflection type cut-off is adopted instead of the absorption type cut-off, and the minimum cut-off depth of the whole cut-off band is OD & gtor 4. After the third technical index is added, the design of the optical filter becomes difficult to start, and therefore, the invention further contemplates the following steps: in the first step, since absorption type cut-off cannot be used, the only possible alternative is to achieve the difficulty of ultra-wideband deep cut-off by means of the ultra-wideband high reflection properties of the metal film, for which purpose the metal to be chosen is practically only silver and aluminum, in particular silver film, since it has the highest reflectivity over the entire wavelength range of 400-12000 nm. In the second step, high reflectivity provides only favorable design conditions for high cut-off, but the problem of high transmittance of the transmission band of the optical filter cannot be solved, because high reflectivity and high transmittance are a pair of contradictions, whether high transmittance band at a specific wavelength can be obtained in the high reflectance band is another technological key, and for this reason, the concept of transmission induction of a metal film by means of a dielectric film is probably the best solution. Through the ingenious design of the dielectric film and the metal film, the transmissivity of the metal film is expected to be attracted at a specific wavelength, so that the transmissivity reaches the maximum value. That is, the high reflection properties of the metal film can be changed to high transmission properties at a specific wavelength by the induction of the dielectric film, which is the attractive place for the interference film-! The present invention refers to such filters as metal-transmission-inducing filters. Unfortunately, filters composed of a single silver-double transmission-inducing film are actually a compromise between cut-off band cut-off and transmission band transmittance, more directly, high cut-off is no longer possible or, conversely, high transmission is no longer possible. In general, the greater the silver film thickness, the higher the cut-off, and the lower the transmittance; otherwise, the cut-off degree is lowered and the transmittance is increased. In fact, even if a plurality of such single silver-double transmission filters are used, the superposition is still difficult to satisfy. And thirdly, further researches show that the optical filter formed by the multi-silver-multi-transmission-inducing film can further improve the transmissivity of a transmission band while maintaining the cut-off degree of the single-silver-double transmission-inducing optical filter, or further increase the thickness of the silver film while maintaining the transmissivity of the single-silver-double transmission-inducing optical filter, and improve the cut-off degree of the optical filter. Through proper optimization, the multi-silver-multi-transmission-inducing filter can not only increase the cut-off degree but also improve the transmissivity compared with the single-silver-double transmission-inducing filter. It should be noted that the multi-silver multi-transmission filter can generate sub-transmission bands at two sides of the main transmission band, and in the multi-silver multi-transmission filter, the number of multi-transmission films is always silver layer number +1, so that the more the number of silver layers in the filter is, the denser the sub-transmission band is, and the larger the transmittance of the sub-transmission band is. Although these sub-transmission bands are very narrow, they still destroy the cut-off in the narrow wavelength region, so that the number of silver layers is not too high, and it is reasonable to select a filter with a double silver-triple transmission structure. And fourthly, the single double-silver-three-transmission-inducing optical filter is difficult to meet the cut-off degree of the whole wavelength cut-off band in practice, so that two groups of different double-silver-three-transmission-inducing optical filters are required to be overlapped, and the optical filter can reach the deep cut-off degree on the ultra-wide wavelength. However, if two identical dual-silver-three-transmission filters are used to overlap, the sub-transmission bands on the long-wave side of the main transmission band are also overlapped together to destroy the cut-off degree on the wavelength, so that one of the dual-silver-three-transmission filters needs to be modified to generate certain wavelength shift on the sub-transmission band on the long-wave side, so the dual-silver-three-transmission filter is called a modified filter. Thus, the double-silver-three-permeability-inducing filter and the double-silver-three-permeability-inducing modified filter are overlapped, and excellent characteristics of deep cut-off at ultra-wide wavelength and high transmissivity of a transmission band can be obtained. And fifthly, the optical filter formed by overlapping the double-silver-three-induced-permeation optical filter and the double-silver-three-induced-permeation modified optical filter provides the minimum cut-off depth of the whole cut-off band to meet OD (optical density) not less than 4 and reach deep cut-off degree at ultra-wide wavelength, and ensures that the optical filter has enough high transmissivity at a transmission band with the wavelength of 550nm, but unfortunately, the requirement that the half width of the transmission band is smaller than 10nm is difficult to realize because the transmission band of the metal film-induced-permeation optical filter is relatively wide and the half width of the transmission band is difficult to adjust, so that a full-medium narrow-band optical filter needs to be overlapped. The full-medium narrowband filter can conveniently adjust the half width of the transmission band through the refractive index, the number of layers, the interference level of the spacing layer and other parameters of the reflection film, and the transmissivity of the transmission band is almost 100 percent, so that the transmissivity of the final narrowband filter cannot be greatly reduced. That is, the deep cut-off narrowband filter based on ultra-wide wavelength high reflection is composed of two bimetal-three transmission-inducing filters which mainly contribute to deep cut-off degree due to ultra-wide wavelength high reflection and keep the transmittance of the transmission band as high as possible, and an all-dielectric narrowband filter which mainly adjusts half width to form a desired narrowband filter.
In order to achieve the above purpose, the specific technical scheme adopted by the invention is as follows:
a deep cut-off narrow-band filter based on ultra-wide wavelength high reflection comprises a bimetal-triple-penetration filter, a first substrate, an all-dielectric narrow-band filter, an optical adhesive layer, a second substrate and a bimetal-triple-penetration modified filter which are sequentially arranged;
the bimetal-triple-permeation filter consists of two layers of silver films and a front permeation film, a middle permeation film and a rear permeation film which are separated by the silver films (namely, the front permeation film, the silver film, the middle permeation film, the silver film and the rear permeation film are sequentially arranged), wherein the middle permeation film is a magnesium fluoride single-layer film, and both the front permeation film and the rear permeation film consist of titanium dioxide with high refractive index and a magnesium fluoride multi-layer film with low refractive index;
the bimetal-triple-permeation modified filter consists of two layers of silver films, and a front permeation film, a middle permeation film and a rear permeation film which are separated by the silver films (consisting of the front permeation film, the silver film, the middle permeation film, the silver film and the rear permeation film which are sequentially arranged), wherein the front permeation film, the middle permeation film and the rear permeation film consist of titanium dioxide with high refractive index and magnesium fluoride multilayer films with low refractive index;
the all-dielectric narrow-band filter consists of a multilayer double half-wave structure with high-refractive-index titanium dioxide and low-refractive-index magnesium fluoride which are alternated.
The first substrate and the second substrate are optical glass or optical crystals.
The dual metal-three-induced-penetration optical filter, the first substrate, the all-dielectric narrow-band optical filter, the optical adhesive layer, the second substrate and the dual metal-three-induced-penetration modified optical filter are sequentially arranged, specifically, the dual metal-three-induced-penetration optical filter is arranged on the first surface of the first substrate, the all-dielectric narrow-band optical filter is arranged on the second surface of the first substrate, the dual metal-three-induced-penetration modified optical filter is arranged on the first surface of the second substrate, and then the all-dielectric narrow-band optical filter on the second surface of the first substrate is adhered with the second surface of the second substrate by optical adhesive.
Further, the number of the film layers of the bimetal-triple permeation filter is 14, and the front permeation film, the silver film, the middle permeation film, the silver film and the rear permeation film are sequentially arranged from the first substrate outwards (namely away from the direction of the first substrate); wherein, the odd number layer is the silver film except that 7 th layer and 9 th layer, and the balance is the titanium dioxide film, and even number layer is the magnesium fluoride film, and the thickness of 1 st to 14 th layer is in proper order: 53.27 69.70, 34.56, 69.47, 56.17, 205.38, 40, 348.83, 40, 200.77, 55.86, 249.79, 44.11, 188.42 in nm.
Further, the number of the film layers of the bimetal-triple-permeation modified optical filter is 17, and the film layers are sequentially a front permeation film, a silver film, a middle permeation film, a silver film and a rear permeation film from the second substrate outwards (namely, far away from the second substrate); the front penetration-inducing film sequentially consists of 6 layers of alternating titanium dioxide films and magnesium fluoride films, wherein the layers are 1 to 6 layers (titanium dioxide films are arranged on the 1 st layer, the 3 rd layer and the 5 th layer, and magnesium fluoride films are arranged on the 2 nd layer, the 4 th layer and the 6 th layer), the thicknesses of the front penetration-inducing film are 54.47, 79.60, 31.33, 75.64, 53.85 and 203.23 respectively, and the unit is nm; the 7 th layer is a silver film with the thickness of 40nm; the medium permeation membrane sequentially consists of magnesium fluoride, titanium dioxide and magnesium fluoride, wherein the 8 th layer is magnesium fluoride, the 9 th layer is titanium dioxide, the 10 th layer is magnesium fluoride, and the thicknesses of the 8 th to 10 th layers are 40.33, 34.25 and 218.4, and the unit is nm; the 11 th layer is a silver film with the thickness of 40nm; the post-permeation film sequentially consists of 6 layers of alternating titanium dioxide films and magnesium fluoride films, wherein the 12 th layer, the 14 th layer and the 16 th layer are titanium dioxide films, the 13 th layer, the 15 th layer and the 17 th layer are magnesium fluoride films, the thicknesses of the 12 th layer to the 17 th layer are respectively 50.6, 99.17, 55.88, 224.98, 50.52 and 193.22, and the unit is nm.
Further, the all-dielectric narrowband filter is a double half-wave structure with 24 layers of film layers: g| [ (HL) 2 H2LH(LH) 2 L] 2 G, where G represents the substrate, H is a high refractive index titanium dioxide film of Quarter Wavelength Optical Thickness (QWOT), L is a low refractive index magnesium fluoride film of Quarter Wavelength Optical Thickness (QWOT), 2L is the spacer layer, i.e., L of twice the thickness, and from the above double half wave structural expression, QWOT of the remaining film layers is equal to 1 except for the QWOT of the two spacer layers of the 6 th layer and 18 th layer which is equal to 2; or watchShown as an optical thickness, since the center wavelength of the narrowband filter is 550nm, the quarter-wavelength optical thickness is 137.5nm, that is, the optical thicknesses of the remaining film layers are 137.5nm except for the optical thicknesses of the 6 th and 18 th spacer layers which are 275 nm.
The number of the film layers of the all-dielectric narrowband filter is 24, the film layers are outwards (namely far from the direction of the first substrate) from the first substrate, the odd layers are H, the H is a high refractive index titanium dioxide layer with quarter-wavelength optical thickness (QWOT), the even layers are L and L is a low refractive index magnesium fluoride layer with quarter-wavelength optical thickness (QWOT) except that the 6 th layer and the 18 th layer are 2L. When the center wavelength of the narrow band filter is 550nm, H is a high refractive index titanium dioxide layer of 137.5nm, L is a low refractive index magnesium fluoride layer of 137.5nm, and 2L is a low refractive index magnesium fluoride layer of 275 nm.
Still further, the QWOT of the last 2 layers, i.e., 23 rd and 24 th layers, of the all-dielectric narrowband filter was optimized from 1 to 1.0219 and 0.6885, respectively, or optical thicknesses of 140.5nm and 94.67nm, respectively.
Namely, the number of the film layers of the all-dielectric narrowband filter is 24, except for 1.0219H which is the 23 rd layer, H which is the high-refractive-index titanium dioxide layer with the optical thickness of one fourth wavelength (QWOT), L which is the low-refractive-index magnesium fluoride layer with the optical thickness of one fourth wavelength (QWOT) which is the 24 th layer, except for 2L which is the 6 th layer and the 18 th layer, and 0.6885L which is the 24 th layer, when the center wavelength of the narrowband filter is 550nm, H is the high-refractive-index titanium dioxide layer with the optical thickness of 137.5nm, L is the low-refractive-index magnesium fluoride layer with the optical thickness of 137.5nm, 2L is the low-refractive-index magnesium fluoride layer with the optical thickness of 275nm, 23 rd layer is the high-refractive-index titanium dioxide layer with the optical thickness of 140.5nm, and 24 th layer is the low-refractive-index magnesium fluoride layer with the optical thickness of 94.67nm.
Further, the optical cement is an optical grade epoxy resin AB cement.
High refractive index material TiO for use in the present invention 2 MgF of low refractive index material 2 And the refractive index of the silver film in the vicinity of the center wavelength of 550nm are shown in table 1.
TABLE 1
The present invention thus far compares the calculation results obtained with metal-transmission filters. When two single silver-double transmission-inducing filters HLH1.74LAg1.74LHLH are overlapped, the silver film thickness of each filter is 55nm, the total silver film thickness is 110nm, and the transmittance of the overlapped filter is 65%; the minimum cut-off depth in the cut-off band is-30 dB, i.e. od=3; the average cut-off of the cut-off band of 400-500 nm is-31 dB, i.e. od=3.1; the average cut-off of 600-1200 nm of the cut-off band is-37 dB, namely od=3.7; the average cut-off of the cut-off band 1200-12000 nm was-59 dB, i.e. od=5.9. When the double-silver-three-permeation-inducing optical filters and the double-silver-three-permeation-inducing modified optical filters are overlapped, the silver film thickness of each optical filter is 80nm, the total silver film thickness is 160nm, and the transmittance of the overlapped optical filters is 80%; the minimum cut-off depth in the cut-off band is-40 dB, i.e. od=4; the average cut-off of the cut-off band 400-500 nm is-43 dB, i.e. od=4.3; the average cut-off of 600-1200 nm of the cut-off band is-46 dB, namely od=4.6; the average cut-off of the cut-off band 1200-12000 nm was-88 dB, i.e. od=8.8. From the above comparison, it can be seen that: firstly, when the single silver-double transmission-inducing filter is overlapped, the transmissivity of a transmission band is lower (65%), and the cut-off degree of a cut-off band meets the requirement only in the range of 1200-12000 nm of long wave; when the double-silver-three-transmission-inducing filter is overlapped, the transmissivity of the transmission band can be improved to 80%, and the cut-off degree of the cut-off band meets the requirements on all wave bands. Second, the increase of the cut-off degree of the double-silver-triple-transmission filter mainly contributes to the increase of the thickness of silver, but if the thickness of silver is increased in the single-silver-double-transmission filter, the cut-off degree is greatly reduced, and the transmittance of the transmission band and the cut-off degree of the cut-off band can be greatly improved only by increasing the number of silver layers, because the double-silver-triple-transmission filter has two silver layers, namely four silver surfaces, and the dielectric film stack positioned in the center of the two silver layers attracts the transmittance of the two silver surfaces at the same time, three dielectric film stacks attract the transmittance of the four silver surfaces, namely, the improvement of the transmittance of the transmission band mainly depends on the attraction effect of the three dielectric film stacks, and the improvement of the cut-off degree is mainly due to the increase of the thickness of the double-silver film.
An optical instrument comprises a signal acquisition system, wherein the signal acquisition system adopts the deep cut-off narrowband filter based on ultra-wide wavelength high reflection.
Compared with the prior art, the invention has the beneficial effects that:
1) Adopting reflection type cut-off. The prior art commonly uses an absorbing substrate to obtain a cut-off over a broad or ultra-broad wavelength range, which can typically reach a residual transmission of 0.1%, i.e. -30dB or od=3. The absorption type cut-off is obtained by absorbing light energy in a wide wavelength or ultra-wide wavelength range, and the cut-off degree is not high. Since the cutoff band is very wide, even if the residual transmittance of 0.1% is integrated over a wide wavelength or ultra-wide wavelength region, the integrated value thereof is likely to exceed the transmittance of the transmission band, which means that noise is likely to exceed the transmission signal; furthermore, the absorption type cut-off can convert absorbed light energy into heat, and the heat generated by the optical filter can radiate to the sensor to generate thermal noise, so that the signal-to-noise ratio is further reduced, and the optical filter loses practical value. The invention adopts the silver film with the highest reflectivity to form the metal-transmission-inducing filter, thus realizing reflection type cut-off, and the invention has the advantages that the reflected light energy cannot be accumulated on the filter to be converted into heat, so the filter can work in a low-temperature environment, and the signal to noise ratio is improved.
2) A new metal-induced penetration filter structure is proposed. The single silver-double transmission filter contemplated earlier in the present invention cannot achieve both deep cut-off and high transmittance, and such a filter can be used alone only when the requirements are not high. This is because the silver film thickness in the single silver-double transmission filter is limited, and it is necessary to increase the silver film thickness in order to increase the cut-off, but the transmittance is drastically reduced at this time, so that only a compromise in the cut-off and transmittance of the filter can be designed. The calculation shows that by adopting the superposition of two single silver-double transmission-inducing filters with the silver film thickness of 55nm, the minimum cut-off depth in a cut-off band of-30 dB or OD=3 can be realized, namely, the cut-off depth is equivalent to the cut-off degree (residual transmittance of 0.1%) of an absorption type cut-off filter, but the transmittance of the filter is only 65% at the moment, and the use requirement of the invention is not met. Therefore, the invention further provides a new scheme of overlapping the double-silver-three-transmission-inducing modified optical filter by using the double-silver-three-transmission-inducing optical filter and a sub-transmission band to generate certain wavelength displacement: due to the adoption of a double-silver film system, the total thickness of the silver film is increased from 110nm to 160nm, so that the minimum cut-off depth in a cut-off band is-40 dB or OD=4, and the whole cut-off band has deeper or very deep cut-off degree; meanwhile, three dielectric film stacks are introduced to induce the transmittance of the silver film surface, so that the transmittance of the optical filter transmission band reaches 80%. Thus, the metal-induced-penetration filter with deep cut-off degree and high transmissivity of the transmission band at ultra-wide wavelength can be obtained.
3) Has prospective technical indexes. The narrow-band filter obtained by the prior art generally adopts absorption type cutoff, the long wave limit of the cutoff band is usually 1200nm, a small number of the cutoff bands can reach the mid-infrared wave band, and the cutoff bands respectively reach more than 10000 nm; the cut-off typically reaches a residual transmittance of 0.1%, i.e. -30dB or od=3; the transmittance of the transmission band varies greatly, for example, 30% to 80%, depending on the cutoff bandwidth, the cutoff degree, and the half width of the transmission band. The invention requires a reflective cut-off, the cut-off interval is 400-12000 nm, namely, the visible light region, the near infrared region, the mid infrared region and the far infrared region are included except the transmission band, in fact, the optical filter is cut-off in a longer wavelength region, and the cut-off is deeper, because the silver film is reflective to microwaves and millimeter waves, and the longer the wavelength is, the higher the reflection is, and therefore the cut-off is deeper; the minimum cut-off depth of the invention in the whole cut-off band is OD=4, wherein the average cut-off degree of the short wave side cut-off band of the transmission band is-43 dB, namely OD=4.3, and the average cut-off degree of the whole cut-off band of the transmission band is-86 dB, namely OD=8.6; the maximum transmission wavelength of the narrow-band filter is 550nm, the half width of the transmission band is 8nm, and the maximum transmission is 77%. It can be seen that the technical index of the invention is very prospective.
Drawings
FIG. 1 is a schematic diagram of the structure of the deep cut-off narrowband filter of the present invention based on ultra-wide wavelength high reflection;
FIG. 2 is a spectral plot of transmittance versus wavelength for an all-dielectric narrowband filter on a K9 glass substrate at 400-1200 nm;
FIG. 3 is a graph of dB versus wavelength for the all-dielectric narrowband filter of FIG. 2 at 400-12000 nm;
FIG. 4 is a spectral plot of transmittance versus wavelength for a single silver-double transmission filter at 400-1200 nm;
FIG. 5 is a graph of dB versus wavelength for the single silver-double transmission filter of FIG. 4 at 400-12000 nm;
FIG. 6 is a spectral plot of transmittance versus wavelength at 400-1200 nm after two single silver-dual transmission filters are superimposed;
FIG. 7 is a graph of dB versus wavelength at 400-12000 nm for two single silver-dual transmission filters shown in FIG. 6 after being superimposed;
FIG. 8 is a spectral plot of transmittance versus wavelength for a dual silver-triple transmission filter of the present invention at 400-1200 nm;
FIG. 9 is a spectral plot of transmittance versus wavelength for a dual silver-triple transmission modified filter of the present invention at 400-1200 nm;
FIG. 10 is a spectral plot of transmittance versus wavelength at 400-1200 nm after the two dual silver-triple transmission filters shown in FIGS. 8 and 9 are superimposed;
FIG. 11 is a graph of dB versus wavelength at 400-12000 nm for two dual silver-triple transmission filters shown in FIGS. 8 and 9 after being superimposed;
FIG. 12 is a spectral plot of transmittance versus wavelength at 400-1200 nm after the two dual silver-triple transmission filters shown in FIG. 10 or FIG. 11 are superimposed with the all-dielectric narrowband filter shown in FIG. 2.
Detailed Description
Fig. 1 is a block diagram of a deep cut narrow band filter based on ultra-wide wavelength high reflection in accordance with the present invention. The optical filter comprises a first substrate 1 and a second substrate 2, wherein the substrate material is optical glass or optical crystal. A metal-transmission inducing filter 5 is arranged on the first surface of the first substrate 1, and an all-dielectric narrow-band filter 3 is arranged on the second surface of the first substrate 1; a metal-induced penetration modification filter 6 is provided on the first surface of the second substrate 2. And then the all-dielectric narrowband filter 3 on the second surface of the first substrate 1 is adhered to the second surface of the second substrate 2 by using optical adhesive 4, wherein the adhesive optical adhesive is optical grade epoxy resin AB adhesive.
The first substrate 1 and the second substrate 2 were each made of K9 glass (chang duming optoelectronics inc.).
FIG. 2 is a spectral plot of transmittance versus wavelength for an all-dielectric narrowband filter 3 on a K9 glass substrate at 400-1200 nm; and FIG. 3 is a graph of dB versus wavelength for the all-dielectric narrowband filter 3 shown in FIG. 2 at 400-12000 nm. In fig. 2, since the half width of the transmission band of the all-dielectric narrowband filter 3 is less than 10nm, the wavelength coordinates are set to 400 to 1200nm for clarity; in fig. 3, however, the dB curve is shown mainly to show the cut-off of the entire cut-off band, so that the wavelength coordinates are set to 400 to 12000nm (similar to the following). The all-dielectric narrowband filter 3 is a double half-wave filter structure with 24 layers of film layers: g| [ (HL) 2 H2LH(LH) 2 L] 2 And G, wherein G represents a substrate, H is a high refractive index titanium dioxide film of Quarter Wavelength Optical Thickness (QWOT), L is a low refractive index magnesium fluoride film of Quarter Wavelength Optical Thickness (QWOT), and 2L is a spacer layer. As can be seen from fig. 2 and 3, the transmission of the all-dielectric narrowband filter 3 at the maximum transmission wavelength of 550nm is high, and if the quarter-wave optical thickness (QWOT) of the last 2 layers of films, i.e. the 23 rd layer and the 24 th layer of films, is optimized from 1 to 1.0219 and 0.6885 respectively, the maximum transmission is almost 100%, and the half-width requirement of the transmission band can be conveniently satisfied, as shown in fig. 2, the half-width is about 9nm. However, the problem with all-dielectric narrowband filters is that the cut-off wavelength band is too narrow, on the short-wave side of maximum transmittance, the cut-off width is less than 100nm, and on the long-wave side is also less than 150nm, it is clear that it is simply not conceivable to achieve the cut-off width of the present invention, since the reflection cut-off bandwidth must be very limited since it is an optical film interference, which is not calculated, and another problem is that many higher order reflection bands must interfere with the transmission band of the narrowband filter, eventually resulting in the transmission band being completely submerged. For this purpose, only the absorption type cut-off of the prior art and the reflection type cut-off proposed by the invention are used to achieveCut-off of ultra-wide wavelength domain.
Example 1
FIG. 4 is a spectral plot of transmittance versus wavelength for a single silver-dual transmission filter of the present invention at 400-1200 nm; FIG. 5 is a graph of dB versus wavelength for the single silver-double transmission filter of FIG. 4 at 400-12000 nm. The single silver-double transmission-inducing filter structure is HLH1.74LAg1.74LHLH, wherein H is a high refractive index titanium dioxide film with Quarter Wavelength Optical Thickness (QWOT), L is a low refractive index magnesium fluoride film with Quarter Wavelength Optical Thickness (QWOT), silver film (Ag) is 55nm in thickness, 1.74L is a spacer layer thickness, and the spacer layer thickness is thinned because the silver film has the characteristic of phase advance, namely, the phase advance value of 1.74L plus the silver film is just equal to 2L. It can be seen that the single silver-double transmission filter hlh1.74lag1.74lhlh is also in fact a double half-wave filter. As can be seen from fig. 4 and 5, the single filter has a minimum cut-off depth of only-22 dB, i.e., od=2.2, although the maximum transmittance at a wavelength of 550nm reaches 80%. For this purpose, two single silver-double transmission filters are used for superposition, and FIG. 6 is a spectral curve of transmittance at 400-1200 nm and wavelength after superposition of two single silver-double transmission filters; FIG. 7 is a graph of dB versus wavelength at 400-12000 nm for two single silver-dual transmission filters shown in FIG. 6 after lamination. As can be seen from fig. 6 and 7, the transmittance of the superimposed filter was reduced to 65%, and the minimum cut-off depth in the cut-off band was-30 dB, i.e., od=3. Obviously, the superposition of two single silver-double transmission-inducing filters still cannot meet the use requirements. For this purpose, the following multi-silver-multi-transmission filter design concept is further proposed.
Example two
Compared with a single silver-double trapping filter, the multi-silver-multi trapping filter not only has increased cut-off degree of a cut-off band, but also has improved transmissivity of a transmission band. However, the multi-silver-multi-transmission filter can generate sub-transmission bands on both sides of the main transmission band, and the more the number of silver layers, the denser the sub-transmission band and the greater the transmittance of the sub-transmission band. Although these sub-transmission bands are very narrow, they still destroy the cut-off of the cut-off band, and thus the present invention has been focused on a double silver-triple transmission filter.
FIG. 8 is a spectral plot of transmittance versus wavelength for a dual silver-triple transmission filter of the present invention at 400-1200 nm. The bimetal-triple-permeation filter consists of two layers of silver films and front permeation, middle permeation and rear permeation films separated by the silver films, wherein the middle permeation is a magnesium fluoride single-layer film, and the front permeation and rear permeation films consist of titanium dioxide with high refractive index and a magnesium fluoride multi-layer film with low refractive index. The number of the film layers of the bimetallic-triple-transmission filter is 14, and the bimetallic-triple-transmission filter sequentially comprises the following components from the substrate to the outside: front, silver, middle, silver, rear, and film; wherein the odd number layer is the titanium dioxide film except that the 7 th layer and the 9 th layer are silver films, and even number layer is magnesium fluoride film, and the thickness of 1 st to 14 th layer is in proper order: 53.27 69.70, 34.56, 69.47, 56.17, 205.38, 40, 348.83, 40, 200.77, 55.86, 249.79, 44.11, 188.42 in nm. The silver film thickness of the double-silver-triple-penetration filter is 80nm, and is thicker than that of the single-silver-double-penetration filter by 25nm, which indicates that the cut-off degree of the double-silver-triple-penetration filter is obviously improved; and the highest transmittance of the transmission band was 88% (see fig. 8), which is also improved over the single silver-double transmission filter, but a very narrow sub-transmission peak appears at wavelength 1090nm, with a transmittance of about 7%. To eliminate this sub-transmission peak, the present invention contemplates modification of the bimetallic-trichromatic filter shown in fig. 8 and is referred to as a bimetallic-trichromatic modified filter in order to shift the wavelength of the sub-transmission peak so that the two bimetallic-trichromatic filters suppress the sub-transmission peak from each other when stacked. FIG. 9 is a spectral plot of transmittance versus wavelength for a dual silver-triple transmission modified filter of the present invention at 400-1200 nm. The bimetal-triple-permeation modified filter consists of two layers of silver films and front permeation film, middle permeation film and rear permeation film which are separated by the silver films, wherein the front permeation film, the middle permeation film and the rear permeation film are all composed of titanium dioxide with high refractive index and magnesium fluoride multilayer film with low refractive index. The film layer number of the bimetal-three-permeation modified optical filter is 17, the silver film thickness is still 80nm, and the film layer comprises the following components in sequence from a substrate to the outside: front, silver, middle, silver, rear, and film; wherein, the front mutagenesis consists of 6 layers of alternating titanium dioxide and magnesium fluoride films with the thickness of 54.47, 79.60, 31.33, 75.64, 53.85 and 203.23 respectively, and the unit is nm; the silver and the medium-permeability are sequentially composed of silver, magnesium fluoride, titanium dioxide, magnesium fluoride and a silver film 5 layers, wherein the thicknesses of the silver and the medium-permeability are respectively 40, 40.33, 34.25, 218.4 and 40, and the unit is nm; the post-permeation film sequentially consists of 6 layers of alternating titanium dioxide and magnesium fluoride films, and the thicknesses of the films are respectively 50.6, 99.17, 55.88, 224.98, 50.52 and 193.22, and the unit is nm. As can be seen from FIG. 9, the highest transmittance of the transmission band is 90%, but the sub-transmission peak is shifted to a wavelength of 1020nm, and the transmittance of the sub-transmission peak is about 10%.
Since a single double-silver-triple transmission filter does not actually satisfy the cut-off degree of the entire wavelength cut-off band, the double-silver-triple transmission filter and the double-silver-triple transmission modified filter must be superimposed. FIG. 10 is a spectral plot of transmittance versus wavelength at 400-1200 nm after the two dual silver-triple transmission filters shown in FIGS. 8 and 9 are superimposed. As can be seen from fig. 10, the filter has a maximum transmittance of 80% at a maximum transmission wavelength of 550 nm. FIG. 11 is a graph of dB versus wavelength at 400-12000 nm for two dual silver-triple transmission filters shown in FIGS. 8 and 9 after lamination. As can be seen from fig. 11, the lowest cut-off depth in the entire cut-off band is od=4, wherein the average cut-off of the short-wave side cut-off band of the transmission band from 400 to 500nm is-43 dB, i.e., od=4.3, and the average cut-off of the entire cut-off band of the transmission band from 600 to 12000nm is-86 dB, i.e., od=8.6. It is worth noting that the filter is also cut-off in the wavelength region above 12000nm and cut-off is deeper, because the metal film is reflective to microwaves and millimeter waves, even centimeter waves, and the longer the wavelength, the higher the reflection and thus the deeper the cut-off.
Example III
The filter formed by overlapping the double-silver-triple-transmission filter and the double-silver-triple-transmission modified filter provides the requirement of the cut-off degree of the whole cut-off band, and ensures that the filter has enough high transmittance in the transmission band with the wavelength of 550nm, but the requirement that the half width of the transmission band is smaller than 10nm is difficult to realize, because the transmission band of the metal-transmission filter is relatively wide and difficult to regulate, particularly when the half width is smaller than 10 nm. To solve this problem, the simplest approach is to superimpose an all-dielectric narrowband filter. The full-medium narrow-band filter can conveniently regulate and control the half width of the transmission band through the refractive index, the number of layers, the interference level of the spacing layer and other parameters of the reflection film, and the transmission rate of the transmission band is almost 100%, so that the transmission rate of the final narrow-band filter is not greatly reduced. FIG. 12 is a spectral plot of transmittance versus wavelength at 400-1200 nm after the two dual silver-triple transmission filters shown in FIG. 10 or FIG. 11 are superimposed with the all-dielectric narrowband filter shown in FIG. 2. The result of the final obtaining of the narrowband filter is: 1) The maximum transmission wavelength of the optical filter is 550nm, the half width of a transmission band is 8nm, and the maximum transmission rate is 77%; 2) Since the superposition of the all-dielectric narrowband filter hardly affects the cut-off degree of the filter shown in fig. 11, it is not drawn here any more, that the average cut-off degree of the filter at 400-500 nm on the short wave side of the transmission band is-43 dB, that is, od=4.3, and that the average cut-off degree of the whole cut-off band at 600-12000 nm on the long wave side of the transmission band is-86 dB, that is, od=8.6; 3) The lowest cut-off depth over the cut-off band is od=4. The technical indexes of the invention not only all meet the technical requirements, but also are very prospective.
Claims (7)
1. The deep cut-off narrowband optical filter based on ultra-wide wavelength high reflection is characterized by comprising a bimetal-triple-penetration optical filter, a first substrate, an all-dielectric narrowband optical filter, an optical adhesive layer, a second substrate and a bimetal-triple-penetration modified optical filter which are sequentially arranged;
the bimetal-triple permeation filter consists of a front permeation membrane, a silver membrane, a middle permeation membrane, a silver membrane and a rear permeation membrane which are sequentially arranged, wherein the middle permeation membrane is a magnesium fluoride single-layer membrane, and the front permeation membrane and the rear permeation membrane are both composed of titanium dioxide with a high refractive index and a magnesium fluoride multi-layer membrane with a low refractive index;
the bimetal-triple-permeation modified optical filter consists of a front permeation membrane, a silver membrane, a middle permeation membrane, a silver membrane and a rear permeation membrane which are sequentially arranged, wherein the front permeation membrane, the middle permeation membrane and the rear permeation membrane are all composed of titanium dioxide with a high refractive index and a magnesium fluoride multilayer membrane with a low refractive index;
the all-dielectric narrow-band filter consists of a multilayer double half-wave structure with high-refractive-index titanium dioxide and low-refractive-index magnesium fluoride which are alternated.
2. The ultra-wide wavelength high reflection based deep cut-off narrowband filter of claim 1, wherein the first substrate and the second substrate are optical glass or optical crystals.
3. The deep cut-off narrowband optical filter based on ultra-wide wavelength high reflection according to claim 1, wherein the number of the layers of the bimetal-three-permeation optical filter is 14, the front permeation film, the silver film, the middle permeation film, the silver film and the rear permeation film are sequentially arranged from the first substrate outwards, the odd layers except the 7 th layer and the 9 th layer are silver films, the rest is titanium dioxide films, the even layers are magnesium fluoride films, and the thicknesses of the 1 st layer to the 14 th layer are sequentially: 53.27 69.70, 34.56, 69.47, 56.17, 205.38, 40, 348.83, 40, 200.77, 55.86, 249.79, 44.11, 188.42 in nm.
4. The deep cut-off narrowband optical filter based on ultra-wide wavelength high reflection according to claim 1, wherein the number of the layers of the bimetal-three-permeation modified optical filter is 17, and the bimetal-three-permeation modified optical filter is a front permeation film, a silver film, a middle permeation film, a silver film and a rear permeation film from the second substrate outwards in sequence;
the front permeability inducing film consists of 6 layers of alternating titanium dioxide films and magnesium fluoride films, wherein the 1 st layer, the 3 rd layer and the 5 th layer are titanium dioxide films, the 2 nd layer, the 4 th layer and the 6 th layer are magnesium fluoride films, the thicknesses of the magnesium fluoride films are 54.47, 79.60, 31.33, 75.64, 53.85 and 203.23, and the unit is nm;
the 7 th layer is a silver film with the thickness of 40nm;
the medium permeation membrane sequentially consists of magnesium fluoride, titanium dioxide and magnesium fluoride, wherein the 8 th layer is magnesium fluoride, the 9 th layer is titanium dioxide, the 10 th layer is magnesium fluoride, and the thicknesses of the 8 th to 10 th layers are 40.33, 34.25 and 218.4, and the unit is nm;
the 11 th layer is a silver film with the thickness of 40nm;
the post-permeation film consists of 6 layers of alternating titanium dioxide and magnesium fluoride films, wherein the 12 th layer, the 14 th layer and the 16 th layer are titanium dioxide films, the 13 th layer, the 15 th layer and the 17 th layer are magnesium fluoride films, and the thicknesses of the 12 th layer to the 17 th layer are respectively 50.6, 99.17, 55.88, 224.98, 50.52 and 193.22, and the unit is nm.
5. The ultra-wide wavelength high reflection-based deep cut-off narrowband filter according to claim 1, wherein the number of layers of the all-dielectric narrowband filter is 24, the layers are outwards from the first substrate, the odd layers are H, the H is a high refractive index titanium dioxide layer with a quarter wavelength optical thickness, the even layers are L except the 6 th layer and the 18 th layer, and the other even layers are L, and the L is a low refractive index magnesium fluoride layer with a quarter wavelength optical thickness.
6. The ultra-wide wavelength high reflection-based deep cut-off narrowband filter according to claim 1, wherein the number of layers of the all-dielectric narrowband filter is 24, the layers of the all-dielectric narrowband filter are outwards from the first substrate, the odd layers except the 23 rd layer is 1.0219H, the other odd layers are all H, H is a high-refractive-index titanium dioxide layer with a quarter-wavelength optical thickness, the even layers except the 6 th layer and the 18 th layer are 2L and the 24 th layer is 0.6885L, and the other even layers are L and L is a low-refractive-index magnesium fluoride layer with a quarter-wavelength optical thickness.
7. An optical instrument comprising a signal acquisition system, wherein the signal acquisition system employs the deep cut-off narrowband filter based on ultra-wide wavelength high reflection of any one of claims 1-6.
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| CN110146949B (en) * | 2019-05-29 | 2022-06-14 | 西北工业大学深圳研究院 | Narrow-band spectrum filtering structure and manufacturing method thereof |
| CN110320583A (en) * | 2019-07-15 | 2019-10-11 | 杭州美迪凯光电科技有限公司 | Three wave crest coating process of visible light |
| CN114063204B (en) * | 2021-10-19 | 2024-02-23 | 福建福特科光电股份有限公司 | Light splitting sheet and preparation method thereof |
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