CN203535253U - Low pass filter - Google Patents

Abstract

The utility model discloses a low pass filter for a high-pixel image sensor. The low pass filter comprises a first quartz crystal piece, a quarter-wave plate and a second quartz crystal piece which are arranged in sequence along the light path direction. An infrared cut-off film is plated on the light incidence side surface of the first quartz crystal piece. A restrained wavelength shifting film is plated on the light outgoing side surface of the second quartz crystal piece. According to the utility model, the infrared cut-off film cuts off light in an infrared wave length zone, and the restrained wavelength shifting film has the advantages of ultraviolet cut-off, visible light high transmission, and small wavelength shift caused by an incidence angle. The low pass filter is low in cost, light in weight and small in size; and since the restrained wavelength shifting film is an optics multilayer film system, the low pass filter is stable and reliable in performance and meanwhile has a blue glass stable transmission-transition wavelength cut-off function, an ultraviolet cut-off function and an antireflection film function.

Description

A kind of low-pass filter

Technical field

The utility model relates to the low-pass filter that a kind of high pixel image processing sensor is used, and belongs to optical field, is mainly used in the digital products such as the slr camera of high pixel, micro-one camera, smart mobile phone and panel computer.

Background technology

Along with developing rapidly of digital imaging technique, the pixel number of CCD image sensor or CMOS constantly increases, and pixel dimension is more and more less, and image resolution ratio is more and more higher.The pixel dimension of existing market main flow imageing sensor is 3～10 microns, and resolution reaches millions pixel.Along with diminishing of pixel dimension, the raising of resolution, the low-pass filter that high pixel image processing sensor is used requires also more and more harsher.

The low-pass filter major function that high pixel image processing sensor is used can be described below: the discrete pixel light electric explorer that is a kind of Si base as CCD image sensor or the CMOS of digital image system, its photaesthesia wavelength zone is about 400nm to 1100nm.In this wavelength zone, what human eye can be seen is mainly the visible ray of wavelength 420～650nm; And be invisible from the light human eye of 700～1100nm, be called near infrared light.Because the photaesthesia wavelength zone of CCD and CMOS is 400～1100nm, in other words, imageing sensor can be simultaneously to visible ray and near infrared light imaging, but this two width image human eye looks like different, if near infrared light is not filtered, visible images and near infrared light image will stack so, and image has just fogged.And our human eye just can only be seen visible images originally, there is no need the near infrared light image of seeing that sensor is experienced, Here it is, and wave filter will end one of reason of near infrared light; Secondly, near infrared light is a kind of thermo-optical, can cause sensor and produce thermonoise, finally makes image resolution ratio and degradation in contrast, and this is two of the wave filter reason that will end near infrared light.In addition, although wavelength is less than the ultraviolet light of 400nm, can not make sensor experience the picture of publishing picture, because the photon energy of ultraviolet light is high, long-term irradiation can reduce the serviceable life of sensor, therefore wave filter also must have the function of cut-off ultraviolet light.The way of cut-off near infrared light and ultraviolet light is all to adopt optical interference film at present, but will certainly there is angular effect in optical interference film in principle, the object that is same color produces obvious aberration owing to entering the different meetings of angle of imageing sensor, therefore wave filter must be stablized transmission-cut-off transition wave-length with smalt, with removal of images aberration.Person more very, when obtaining target image with image system, the radio-frequency component of imageing sensor can reflex in fundamental component, cause so-called Moire fringe, at this moment, image is obscured the periodic frequency spectrum of generation is overlapping, even occurs pseudo-colours striped, have a strong impact on image definition and contrast, this absolutely not allows in high pixel image processing sensor.At present, the method for eliminating this Moire fringe is mainly to adopt birefringece crystal.The function of the low-pass filter that from the above, high pixel image processing sensor is used mainly contains three aspects: end near infrared light and ultraviolet light, stablize transmission-cut-off transition wave-length and eliminate Moire fringe.In high pixel image processing sensor, low-pass filter is the extremely important Primary Component that can not more get over.

Now with the low-pass filter of high pixel image processing sensor, mainly adopt following structure: three bauerite crystal wafers add lastblock smalt, then on quartz crystal slice or smalt, plate infrared cut coating, ultraviolet cut-on film and antireflecting film.Three bauerite crystal wafers can be eliminated x, the Moire fringe on y both direction; Smalt can be stabilized in transmission-cut-off transition wave-length of wave filter (at transmissivity T=50% place) near 650nm, because this wavelength can not change because of the angle of incidence of light of target image, thereby can obtain the image of homogeneous color.But this structure has two problems: be first smalt used only has Japan's exclusive dealing so far, and expensive, and also because mechanical property is crisp, easily broken while cutting into small pieces, chemical stability is also poor, perishable in air; Next is that the gross thickness of low-pass filter is thicker, and this low-pass filter need to directly be attached to before sensor, and larger filter thickness can cause larger image aberration, and this must be avoided in high pixel image processing sensor.

Utility model content

For overcoming the problems referred to above, the low-pass filter that the utility model provides a kind of high pixel image processing sensor to use, this low-pass filter thin thickness, picture quality is good, production cost is low, can be widely used in the digital products such as the slr camera of high pixel, micro-one camera, smart mobile phone and panel computer.

Design of the present utility model is: first, defect for smalt, the wave length shift that can exploration realize transmission-cut-off zone of transition by means of film design is reduced in the scope that meets request for utilization with the variation of incident angle, thereby realizes the function of the stable transmission-cut-off transition wave-length that replaces smalt.Secondly, can exploration further reduce the gross thickness of wave filter, if replacing, suppressed wave length shift film falls smalt, the thickness of smalt has not just had, and then, if can reduce again sheet number or the thickness of quartz crystal, can further reduce the gross thickness of wave filter, finally reduce the aberration that dull and stereotyped wave filter causes in imaging optical path.

To achieve these goals, the utility model proposes a kind of new filter construction, with suppressed wave length shift Thin Film Filter, replace now using smalt, with the quarter-wave plate of a slice very thin thickness, replace that quartz crystal slice now mediating with position in three quartz crystal slices, like this, not only overcome the problem that smalt exists, and greatly reduced the gross thickness of wave filter.Therefore, structure of the present utility model not only can improve picture quality, and can greatly reduce production costs.

A kind of low-pass filter, comprise the first quartz crystal slice, quarter-wave plate, the second quartz crystal slice that along optical path direction, set gradually, wherein, on the light light incident side surface of described the first quartz crystal slice, be coated with infrared cut coating, on the beam projecting side surface of described the second quartz crystal slice, be coated with suppressed wave length shift film.

In the utility model, infrared cut coating is by the light cut-off of infrared wavelength region, suppressed wave length shift film has the features such as wave length shift that ultraviolet cut-on, the high transmission of visible ray and incident angle cause is little, and suppressed wave length shift film has the function that ultraviolet cut-on film, antireflecting film and smalt have concurrently.

As preferably, described infrared cut coating comprises alternatively distributed high refractive index layer and low-index layer, and described high refractive index layer is Ti ₃o ₅layer, Nb ₂o ₅layer or ZnS layer, described low-index layer is SiO ₂layer.The high refractive index layer of above-mentioned material and the combination of low-index layer can make infrared cut coating have good IR-cut function.

Further preferably, described infrared cut coating comprises and adds up to 44 layers, and is alternatively distributed high refractive index layer Ti ₃o ₅with low-index layer SiO ₂, wherein, since the thickness of first each layer of quartz crystal slice, be followed successively by 12.63, 35.09, 76.55, 9.28, 29.64, 340.5, 97.77, 133.0, 88.22, 128.9, 87.1, 127.4, 86.4, 127.6, 85.39, 129.0, 84.36, 131.5, 84.0, 133.8, 83.17, 136.7, 84.19, 142.5, 91.87, 162.5, 113.8, 176.3, 104.2, 160.3, 109.6, 180.9, 114.0, 167.8, 103.1, 170.8, 116.6, 180.4, 109.0, 153.8, 18.6, 6.91, 70.51, 79.14, unit is nm.This infrared cut coating, wavelength 420～650nm is high transmission band, average transmittance is 99.8%, and wavelength 700～1100nm is rejection zone, average reflectance is 99.4%.This infrared cut coating has extraordinary transmissivity in visible wavelength district, at infrared wavelength region, has extraordinary reflectivity, and IR-cut function is excellent.

As preferably, described suppressed wave length shift film comprises the first coupling film system, main film system and the second coupling film system outwards setting gradually from described the second quartz crystal slice, and wherein, the first described coupling film system comprises alternatively distributed low-index layer SiO ₂with high refractive index layer Ti ₃o ₅, described main film is to comprise alternatively distributed low-index layer SiO ₂with high refractive index layer Ti ₃o ₅, the second described coupling film system comprises alternatively distributed high refractive index layer Ti ₃o ₅with low-index layer SiO ₂and be inserted in high refractive index layer Ti ₃o ₅with low-index layer SiO ₂between intermediate-index layer Ta ₂o ₅or HfO ₂.The first coupling film system is adjacent with the second quartz crystal slice, be mainly used in mating the optical admittance between the second quartz crystal slice and main film system, main film is near the drift value that major decision transmission-cut-off transition wave-length 650nm, incident angle causes, the second coupling film system is adjacent with air, for mating the optical admittance between main film system and air, in order to reach optimum matching effect, inserted intermediate-index layer Ta ₂o ₅or HfO ₂.In described suppressed wave length shift film, high refractive index layer is selected the Ti that refractive index is higher ₃o ₅, the refractive index of suppressed wave length shift film is higher, and angular effect is less, thereby obtains the insensitive suppressed wave length shift film of incident angle.

Further preferred, low-index layer SiO in the first described coupling film system ₂thickness be 16～318nm, high refractive index layer Ti in described the first coupling film system ₃o ₅thickness be 15～165nm, the low-index layer SiO in the first coupling film system ₂with high refractive index layer Ti ₃o ₅thickness discrete all very large.Low-index layer SiO in described main film system ₂thickness be 48～93nm, high refractive index layer Ti in described main film system ₃o ₅thickness be 274～295nm, the low-index layer SiO of main film system ₂with high refractive index layer Ti ₃o ₅thickness discrete all less.In main film system, high refractive index layer Ti ₃o ₅thickness and low-index layer SiO ₂the ratio of thickness be far longer than 1, light is mainly propagated in high refractive index film, make suppressed wave length shift film insensitive to incident angle.High refractive index layer Ti in the second described coupling film system ₃o ₅thickness be 29nm～135nm, low-index layer SiO in described the second coupling film system ₂thickness be 22nm～113nm, intermediate-index layer Ta in described the second coupling film system ₂o ₅or HfO ₂thickness be 80～85nm.

Again further preferably, the first described coupling film system comprises that the number of plies is 20 layers and alternatively distributed low-index layer SiO ₂with high refractive index layer Ti ₃o ₅, from the thickness of outside each layer of described the second quartz crystal slice, being followed successively by 175,41,16,165,225,15,46,59,304,46,318,48,306,76,83,22,151,144,29,65, unit is nm; Described main film is to comprise that the number of plies is 23 layers and alternatively distributed low-index layer SiO ₂with high refractive index layer Ti ₃o ₅, from the thickness of described first outside each layer of coupling film system, being followed successively by 93,274,57,288,54,290,54,290,54,290,54,290,54,292,53,293,51,295,48,295,48,277,72, unit is nm; The second described coupling film system comprises that the number of plies is 5 layers, from outside each layer of described main film system, is respectively high refractive index layer Ti ₃o ₅, low-index layer SiO ₂, intermediate-index layer Ta ₂o ₅, high refractive index layer Ti ₃o ₅and low-index layer SiO ₂, its thickness is followed successively by 29,22,82,135,113, and unit is nm.Suppressed wave length shift film under this actual conditions has the features such as wave length shift that ultraviolet cut-on excellent performance, the high transmission of visible ray and incident angle cause is little, therefore, this suppressed wave length shift film has the function that ultraviolet cut-on film, antireflecting film and smalt have concurrently, thereby, can greatly reduce production costs low, while is lightweight, volume is little, and because suppressed wave length shift film itself is exactly an optical multilayer system, stable and reliable for performance.

As preferably, the projection of the optical axis of the projection (perpendicular to the cross section of thickness direction) of the optical axis of the first described quartz crystal slice on the xsect of described the first quartz crystal slice and described the second quartz crystal slice on the xsect of described the second quartz crystal slice is orthogonal, can guarantee so all can suppress the Moire fringe that high-frequency harmonic causes in two vertical direction.

As preferably, the first described quartz crystal slice and the thickness of the second quartz crystal slice equate, making it be divided into o light equates with the distance of separation of e light, the spatial-cut-off frequency of two quartz crystal slices equates, picture point separately can be controlled in micron dimension (in same pixel), therefore can not produce too much influence to low frequency imaging signal, but avoid the Moire fringe of high frequency.

As preferably, the thickness of described the first quartz crystal slice and the second quartz crystal slice is 0.85mm, quarter-wave plate adopts plastic slide, thickness is 0.1mm, adopt the first quartz crystal slice and second quartz crystal slice of above-mentioned thickness, the fundamental frequency signal that spatial frequency is less than cutoff frequency 100lp/mm can transmit substantially through low-pass filter, not too large on the impact of imaging signal, but spatial frequency is greater than the high-frequency signal of cutoff frequency 100lp/mm and is subject to larger inhibition, the Moire fringe that therefore, can suppress high-frequency signal.Low-pass filter of the present utility model only needs two bauerite crystal wafers and a slice plastics quarter-wave plate, and the gross thickness of whole low-pass filter is about 1.80mm, and imaging aberration can significantly reduce, and weight can obviously alleviate.

Compared with prior art, the beneficial effects of the utility model are:

One, to pixel dimension, be the imageing sensor of 5 microns, because the low-pass filter of prior art need to adopt three bauerite crystal wafer and smalts, the thickness of every bauerite crystal wafer is 0.85mm, add that smalt thickness is 0.5mm, and the thickness of infrared cut coating, ultraviolet cut-on film and antireflecting film is all micron-sized, the thickness of comparing quartz crystal slice and smalt is negligible, therefore the gross thickness of whole low-pass filter is about 3.05mm; And low-pass filter of the present utility model only needs two bauerite crystal wafers and a slice plastics quarter-wave plate, the gross thickness of whole low-pass filter is about 1.80mm, and imaging aberration can significantly reduce, and weight can obviously alleviate.

Two, not only price, Heavy Weight, volume are large for the smalt of prior art, and machinery, chemical property is poor, this is to be made by ion coloring principle because of this smalt, so its mechanical property is crisp, thermal expansivity is high, stress is large, moisture resistance gas and acid and alkali corrosion poor performance, this can cause the fabrication yield of wave filter greatly to reduce, and production cost improves greatly; And low-pass filter of the present utility model adopts suppressed wave length shift film to replace smalt, not only cost is low, lightweight, volume is little, and because suppressed wave length shift film itself is exactly an optical multilayer system, stable and reliable for performance, and have the function that smalt is stablized the function of transmission-cut-off transition wave-length, ultraviolet cut-on function and antireflecting film concurrently simultaneously.

Accompanying drawing explanation

Fig. 1 is smalt low-pass filter and the low-pass filter structure schematic diagram of the present utility model of prior art, wherein, (a) be the structural representation of the smalt low-pass filter of prior art, (b) be the structural representation of low-pass filter of the present utility model;

Fig. 2 is low-pass filter principle of work explanation schematic diagram of the present utility model;

Fig. 3 is the schematic diagram of the optical axis position of the first quartz crystal slice 1 of the present utility model, quarter-wave plate 2 and the second quartz crystal slice 3, wherein, (a) be the optical axis position of the first quartz crystal slice 1, (b) being the optical axis position of quarter-wave plate 2, is (c) optical axis position of the second quartz crystal slice 3;

Fig. 4 is the MTF curve of low-pass filter of the present utility model;

Fig. 5 is infrared cut coating light splitting transmission characteristic of the present utility model;

Fig. 6 is the thickness of the every tunic of suppressed wave length shift film of the present utility model and the corresponding relation figure of refractive index;

The light splitting transmission characteristic that Fig. 7 is suppressed wave length shift film of the present utility model when 0 ° and 30 ° of incident angles.

Embodiment

Fig. 1 is smalt low-pass filter and the low-pass filter structure comparison of the present utility model of prior art, wherein, (a) is the smalt low-pass filter of prior art, is (b) low-pass filter of the present utility model.In high pixel image processing sensor, at least need to use 2 above quartz crystal slices.Fig. 1 (a) and (b) refer in the situation that obtains same filter effect and carry out structure comparison.In Fig. 1 (a), the 7th, thickness is about the smalt of 0.5mm, and on light light incident side surface, be coated with infrared cut coating and ultraviolet cut-on film 11, and 8,9,10 be all quartz crystal slice, pixel dimension to 5 microns, its thickness is 0.85mm, then on the beam projecting side surface of quartz crystal slice 10, is coated with antireflecting film 12, and the smalt low-pass filter gross thickness of prior art is 3.05mm.In Fig. 1 (b), for low-pass filter of the present utility model, comprise the first quartz crystal slice 1, quarter-wave plate 2, the second quartz crystal slice 3 that along optical path direction, set gradually, wherein, on the light light incident side surface of the first quartz crystal slice 1, be coated with infrared cut coating 5, on the beam projecting side surface of the second quartz crystal slice 3, be coated with suppressed wave length shift film 6.The thickness of the first quartz crystal slice 1 and the second quartz crystal slice 3 is 0.85mm, and quarter-wave plate 2 adopts plastic slide, and thickness is 0.1mm, and the gross thickness of low-pass filter of the present utility model is 1.80mm.

Fig. 2 is low-pass filter principle of work of the present utility model explanation.The principle of work of low-pass filter is to utilize the birefringence principle of light, when light impinges perpendicularly on birefringece crystal, if the angle of incident light and optical axis is θ (Chang Cheng position angle, this angle), and n _oand n _ebe respectively the refractive index of ordinary light in crystal (o light) and non-ordinary light (e light), the thickness that T is crystal, o light with the distance d that e light separates is

$d=T\frac{({{\mathrm{<figure-callout\; id="0"\; label="n"\; filenames="HDA0000393681610000031.png,HDA0000393681610000032.png"\; state="\{\{state\}\}">n</figure-callout>}}_0}^2-{n_e}^2)\mathrm{tg\&theta;}}{{{\mathrm{<figure-callout\; id="0"\; label="n"\; filenames="HDA0000393681610000031.png,HDA0000393681610000032.png"\; state="\{\{state\}\}">n</figure-callout>}}_0}^2{\mathrm{<figure-callout\; id="2"\; label="tg"\; filenames="HDA0000393681610000011.png"\; state="\{\{state\}\}">tg</figure-callout>}}^2\mathrm{\&theta;}+{{\mathrm{<figure-callout\; id="2"\; label="n\; e"\; filenames="HDA0000393681610000011.png"\; state="\{\{state\}\}">n</figure-callout>}}_e}^2}$

When θ=45 °, d obtains maximum value.Quartz is positive crystal, at wavelength 589.3nm, n _o=1.54424, n _e=1.55335, known pixel dimension is 5 microns, i.e. o light and the distance d=5 micron that e light separates can obtain the thickness T=0.85mm of crystal.

As can be seen from Figure 2, the natural light of incident enters the first quartz crystal slice 1 after infrared cut coating 5, is divided into two kinds of mutually perpendicular linearly polarized lights of direction of vibration of o light and e light in the first quartz crystal slice 1, and o light is d=5 micron with the distance that e light separates; When this two bunch polarized light incides on quarter-wave plate 2, if its light vector respectively with fast, the become ± 45° angle of slow axis of quarter-wave plate 2, two bunch polarized lights of incident have become two bundle circularly polarized lights after quarter-wave plate 2; Two bundle circularly polarized lights are divided into respectively o light and two kinds of mutually perpendicular linearly polarized lights of direction of vibration of e light in the second quartz crystal slice 3 again, if two quartz crystal slice thickness are equal, the distance of separating is still 5 microns, finally forms 45 microns of square picture points.Because the picture point of separating is all micron dimension (in same pixel), thus can not produce too much influence to low frequency imaging signal, but avoided the Moire fringe of high frequency.

Fig. 3 is the optical axis position of the first quartz crystal slice 1 of the present utility model, quarter-wave plate 2 and the second quartz crystal slice 3.For the distance d maximum that allows o light and e light separate, as shown in Fig. 3 (a), the optical axis 13 of the first quartz crystal slice 1 and the angle that impinges perpendicularly on the incident light direction z axle on the first quartz crystal slice 1 surface, be that azimuth angle theta is 45 °, optical axis 13 is-45 ° with the angle of x axle, and optical axis 13 is at x, the projection on the plane of crystal that y axle forms and the angle (this angle often claims rotation angle) of x axle are 0 °, with the angle of y axle be 90 °.The distance d that o light and e light separate has determined the spatial-cut-off frequency of low-pass filter, therefore, selects the thickness T of the first suitable quartz crystal slice 1 ₁can make the low-pass filter of different spaces cutoff frequency.Pixel is less, and crystal thickness is thinner, and spatial-cut-off frequency is larger.Fig. 3 (b) expression quarter-wave plate 2(plastics wave plate) fast axle 14, slow axis 15 and become ± 45° angle of the light vector of incident ray polarized light, the quarter-wave plate 2 that this plastics are made can make o light and e light in whole visible region, all produce the optical path difference of 1/4 wavelength, according to the optical path difference formula of quarter-wave plate 2: Δ=| n _o-n _e| T ₂=λ/4, wherein, T ₂be the thickness of quarter-wave plate 2, λ is wavelength.In quarter-wave plate 2 thickness T ₂in definite situation, the optical path difference that meet whole visible region is 1/4 wavelength, | n _o-n _e| variation must increase and increase regularly with wavelength, this technology breaks through now.As shown in Fig. 3 (c), the optical axis 16 of the second quartz crystal slice 3 and the angle that impinges perpendicularly on the incident light direction z axle on the second quartz crystal slice 3 surfaces, be that azimuth angle theta is 45 °, the angle of optical axis and y axle is-45 °, and optical axis is at x, the rotation angle that projection on the plane of crystal that y axle forms becomes with x axle is 90 ° of angles, and the angle of y axle is 0 °.Consider easily manufactured, the rotation angle of the rotation angle of the second quartz crystal slice 3 and the first quartz crystal slice 1 is mutually orthogonal, the second quartz crystal slice 3 and the first quartz crystal slice 1 optical axis are separately at x, projection on y plane of crystal is orthogonal, can guarantee at x like this, in y direction, suppress the Moire fringe that high-frequency harmonic causes simultaneously.Because the utility model is selected the thickness T of the second quartz crystal slice 3 ₃thickness T with the first quartz crystal slice 1 ₁equate, therefore the spatial-cut-off frequency of two quartz crystal slices equates.

Fig. 4 is the degree of modulation transport function MTF curve of low-pass filter of the present utility model.The relation of transport function MTF and d can be expressed as

$\mathrm{MTF}=\left|\cos \frac{\mathrm{\&pi;<figure-callout\; id="2"\; label="df"\; filenames="HDA0000393681610000011.png"\; state="\{\{state\}\}">df</figure-callout>}}{{2\mathrm{sf}}_n}\right|$

In formula, s is Pixel Dimensions, f _nnyquist limit frequency during for pixel s, can obtain the transport function (the transmitance T coordinate of Fig. 4) of different frequency f with above formula.In the utility model, owing to selecting the thickness T of the first quartz crystal slice 1 ₁thickness T with the second quartz crystal slice 3 ₃equate T ₁=T ₃=0.85mm, by s=5 micron, d=5 micron, can obtain nyquist limit frequency, and the spatial-cut-off frequency of two quartz crystal slices is all 1/ (2d)=100lp/mm.As seen from Figure 4, two MTF-f curves of x direction (solid line) and y direction (dotted line) are actually overlapping; The fundamental frequency signal that spatial frequency is less than cutoff frequency 100lp/mm can transmit substantially through low-pass filter, not too large on the impact of imaging signal, but spatial frequency is greater than the high-frequency signal of cutoff frequency 100lp/mm and is subject to larger inhibition, the Moire fringe that therefore, can suppress high-frequency signal.

Fig. 5 is infrared cut coating light splitting transmission characteristic of the present utility model.The preferred high-index material of infrared cut coating 5 is Ti ₃o ₅, low-index material is SiO ₂.As a kind of most preferably scheme of the present utility model, total rete number is 44 layers, by alternatively distributed high refractive index layer Ti ₃o ₅with low-index layer SiO ₂form, be directly plated on the surface of the first quartz crystal slice 1 light light incident side.Refractive index and the thickness of each tunic are listed in table 1.As seen from Figure 5, wavelength 420～650nm is high transmission band, and average transmittance is 99.8%, and wavelength 700～1100nm is rejection zone, and average reflectance is 99.4%.

Table 1

Rete sequence number	?	1	2	3	4	5	6	7	8	9	10	11
													Material	Quartzy	Ti 3O	5SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5

Refractive index	1.465	2.42	1.46	2.42	1.46	2.42	1.46	2.42	1.46	2.42	1.46	2.42
													Thickness (nm)	?	12.63	35.09	76.55	9.28	29.64	340.5	97.77	133.0	88.22	128.9	87.1

Continued 1

12	13	14	15	16	17	18	19	20	21	22	23	24
													SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2
1.46	2.42	1.46	2.42	1.46	2.42	1.46	2.42	1.46	2.42	1.46	2.42	1.46
													127.4	86.4	127.6	85.39	129.0	84.36	131.5	84.0	133.8	83.17	136.7	84.19	142.5

Continued 1

25	26	27	28	29	30	31	32	33	34	35	36	37
													Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5
2.42	1.46	2.42	1.46	2.42	1.46	2.42	1.46	2.42	1.46	2.42	1.46	2.42
													91.87	162.5	113.8	176.3	104.2	160.3	109.6	180.9	114.0	167.8	103.1	170.8	116.6

Continued 1

38	39	40	41	42	43	44	?
								SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Air
1.46	2.42	1.46	2.42	1.46	2.42	1.46	1.0
								180.4	109.0	153.8	18.6	6.91	70.51	79.14	?

Fig. 6 is the thickness of the every tunic of suppressed wave length shift film of the present utility model and the corresponding relation figure of refractive index.Total rete number of suppressed wave length shift film is 40～60 layers, and in the present embodiment, total rete number is 48 layers.As seen from Figure 6, suppressed wave length shift film 6 comprises three parts that outwards set gradually from the second quartz crystal slice 3: the first coupling film system, main film system and the second coupling film system.The first coupling film system is between the second quartz crystal slice 3 and main film system, and totally 20 tunics, are mainly used in mating the optical admittance between the second quartz crystal slice 3 and main film system; The first coupling film system comprises alternatively distributed low-index layer SiO ₂with high refractive index layer Ti ₃o ₅, low-index layer SiO in the first coupling film system ₂thickness at 16～318nm, high refractive index layer Ti in the first coupling film system ₃o ₅thickness at 15～165nm, low-index layer SiO ₂with high refractive index layer Ti ₃o ₅thickness discrete all very large.Main film system between the first coupling film system and the second coupling film system, totally 23 tunics, main film system comprises alternatively distributed low-index layer SiO ₂with high refractive index layer Ti ₃o ₅, near the drift value that incident angle causes major decision transmission-cut-off transition wave-length 650nm, the low-index layer SiO in main film system ₂thickness at 48～93nm, the high refractive index layer Ti in main film system ₃o ₅thickness is at 274～295nm, and the high refractive index layer that main film is and the thickness of low-index film are discrete all less.The second coupling film system is adjacent with air, for mating the optical admittance between main film system and air; The second coupling film system is only 5 tunics in the present embodiment, in order to reach optimum matching effect, has inserted one deck intermediate-index layer Ta ₂o ₅, its thickness is 82nm.In suppressed wave length shift film, refractive index and the thickness of each tunic are listed in table 2.

Table 2

Rete sequence number	?	1	2	3	4	5	6	7	8	9	10
												Material	Quartzy	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5
Refractive index	1.465	1.46	2.42	1.46	2.42	1.46	2.42	1.46	2.42	1.46	2.42
												Thickness (nm)	?	175	41	16	165	225	15	46	59	304	46

Continued 2

11	12	13	14	15	16	17	18	19	20	21	22	23
													SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2
1.46	2.42	1.46	2.42	1.46	2.42	1.46	2.42	1.46	2.42	1.46	2.42	1.46
													318	48	306	76	83	22	151	144	29	65	93	274	57

Continued 2

24	25	26	27	28	29	30	31	32	33	34	35	36
													Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5
2.42	1.46	2.42	1.46	2.42	1.46	2.42	1.46	2.42	1.46	2.42	1.46	2.42
													288	54	290	54	290	54	290	54	290	54	292	53	293

Continued 2

37	38	39	40	41	42	43	44	45	46	47	48	?
													SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ti 3O 5	SiO 2	Ta 2O 5	Ti 3O 5	SiO 2	Air
1.46	2.42	1.46	2.42	1.46	2.42	1.46	2.42	1.46	2.10	2.42	1.46	1.0
													51	295	48	295	48	277	72	29	22	82	135	113	?

In fact, suppressed wave length shift film 6 of the present utility model is except the example shown in Fig. 6, according to the concrete application requirements of suppressed wave length shift film, those skilled in the art can design it under the situation of knowing suppressed wave length shift membrane structure feature of the present utility model: select high as far as possible index medium membrane material, the thickness of selecting high refractive index layer is the more than 3 times of low refractive index film layer thickness, and be that both sides add coupling film system at main film, then by film design software (as TFCal), be optimized design, can obtain the concrete number of plies of required suppressed wave length shift film and the thickness of every tunic.

The light splitting transmission characteristic that Fig. 7 is suppressed wave length shift film of the present utility model when 0 ° and 30 ° of incident angles.This curve obtains by the illustrative structure of Fig. 6, and wherein, the thickness of the second quartz crystal slice 3 is 0.85mm.As preferred implementation of the present utility model, the performance that Fig. 7 reaches is: the average transmittance of ultraviolet region (350～400nm) is 0.16%, the average transmittance of visible region (420～620nm) is 99.2%, and the average reflectance of infrared region (680～770nm) is 99.7%; Different incidence angles is obtained simultaneously, when the incident angle that incides low-pass filter when light is 0 ° and ± 30 ° (in actual applications, because the angle of incidence of light inciding on low-pass filter has been dwindled in the design of photographic lens greatly, therefore incident angle ± 30 ° can be used for wide-angle), in near transmission-cut-off zone of transition shortwave 415nm, transmissivity is that the wave length shift at 50% place is 6.3nm, and near transmission-cut-off zone of transition long wave 650nm, transmissivity is that the wave length shift at 50% place is 6.8nm.The wave length shift of transmission-cut-off zone of transition that this explanation suppressed wave length shift film 6 of the present utility model changes with incident angle meets real requirement completely, can replace prior art special smalt used.Because the suppressed wave length shift film shown in Fig. 6 has the features such as wave length shift that ultraviolet cut-on, the high transmission of visible ray and incident angle cause is little simultaneously, therefore suppressed wave length shift film 6 has the function that ultraviolet cut-on film, antireflecting film and smalt have concurrently.

For the situation of suppressed wave length shift film 6 more of the present utility model with transmission-cut-off zone of transition wave length shift of now using cutoff filter under same incident angle, to existing with cutoff filter at angle of incidence of light the transmitted spectrum while being 0 ° and ± 30 ° done calculating, in near transmission-cut-off zone of transition wavelength 650nm, transmissivity is that the wave length shift at 50% place is 27nm, and this value is almost 4 times of transmission-cut-off zone of transition wave length shift of suppressed wave length shift film 6 of the present utility model.

Claims (9)

1. a low-pass filter, it is characterized in that, comprise the first quartz crystal slice, quarter-wave plate, the second quartz crystal slice that along optical path direction, set gradually, wherein, on the light light incident side surface of described the first quartz crystal slice, be coated with infrared cut coating, on the beam projecting side surface of described the second quartz crystal slice, be coated with suppressed wave length shift film.

2. low-pass filter according to claim 1, is characterized in that, described infrared cut coating comprises alternatively distributed high refractive index layer and low-index layer, and described high refractive index layer is Ti ₃o ₅layer, Nb ₂o ₅layer or ZnS layer, described low-index layer is SiO ₂layer.

3. low-pass filter according to claim 1 and 2, is characterized in that, described infrared cut coating comprises and adds up to 44 layers, and is alternatively distributed high refractive index layer Ti ₃o ₅with low-index layer SiO ₂, wherein, since the thickness of first each layer of quartz crystal slice, be followed successively by 12.63, 35.09, 76.55, 9.28, 29.64, 340.5, 97.77, 133.0, 88.22, 128.9, 87.1, 127.4, 86.4, 127.6, 85.39, 129.0, 84.36, 131.5, 84.0, 133.8, 83.17, 136.7, 84.19, 142.5, 91.87, 162.5, 113.8, 176.3, 104.2, 160.3, 109.6, 180.9, 114.0, 167.8, 103.1, 170.8, 116.6, 180.4, 109.0, 153.8, 18.6, 6.91, 70.51, 79.14, unit is nm.

4. low-pass filter according to claim 1, it is characterized in that, described suppressed wave length shift film comprises the first coupling film system, main film system and the second coupling film system outwards setting gradually from described the second quartz crystal slice, wherein, the first described coupling film system comprises alternatively distributed low-index layer SiO ₂with high refractive index layer Ti ₃o ₅, described main film is to comprise alternatively distributed low-index layer SiO ₂with high refractive index layer Ti ₃o ₅, the second described coupling film system comprises alternatively distributed high refractive index layer Ti ₃o ₅with low-index layer SiO ₂and be inserted in high refractive index layer Ti ₃o ₅with low-index layer SiO ₂between intermediate-index layer Ta ₂o ₅or HfO ₂.

5. low-pass filter according to claim 4, is characterized in that, low-index layer SiO in the first described coupling film system ₂thickness be 16～318nm, high refractive index layer Ti in described the first coupling film system ₃o ₅thickness be 15～165nm;

Low-index layer SiO in described main film system ₂thickness be 48～93nm, high refractive index layer Ti in described main film system ₃o ₅thickness be 274～295nm;

High refractive index layer Ti in the second described coupling film system ₃o ₅thickness be 29nm～135nm, low-index layer SiO in described the second coupling film system ₂thickness be 22nm～113nm, intermediate-index layer Ta in described the second coupling film system ₂o ₅or HfO ₂thickness be 80～85nm.

6. low-pass filter according to claim 4, is characterized in that, the first described coupling film system comprises that the number of plies is 20 layers and alternatively distributed low-index layer SiO ₂with high refractive index layer Ti ₃o ₅, from the thickness of outside each layer of described the second quartz crystal slice, being followed successively by 175,41,16,165,225,15,46,59,304,46,318,48,306,76,83,22,151,144,29,65, unit is nm;

Described main film is to comprise that the number of plies is 23 layers and alternatively distributed low-index layer SiO ₂with high refractive index layer Ti ₃o ₅, from the thickness of described first outside each layer of coupling film system, being followed successively by 93,274,57,288,54,290,54,290,54,290,54,290,54,292,53,293,51,295,48,295,48,277,72, unit is nm;

The second described coupling film system comprises that the number of plies is 5 layers, from outside each layer of described main film system, is respectively high refractive index layer Ti ₃o ₅, low-index layer SiO ₂, intermediate-index layer Ta ₂o ₅, high refractive index layer Ti ₃o ₅and low-index layer SiO ₂, its thickness is followed successively by 29,22,82,135,113, and unit is nm.

7. low-pass filter according to claim 1, it is characterized in that, the projection of the optical axis of the projection of the optical axis of the first described quartz crystal slice on the xsect of described the first quartz crystal slice and described the second quartz crystal slice on the xsect of described the second quartz crystal slice is orthogonal.

8. low-pass filter according to claim 1, is characterized in that, the first described quartz crystal slice and the thickness of the second quartz crystal slice equate.

9. low-pass filter according to claim 1, is characterized in that, the first described quartz crystal slice and the thickness of the second quartz crystal slice are 0.85mm, and quarter-wave plate adopts plastic slide, and thickness is 0.1mm.

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