CN100365448C - Double channel filter with regulatable channel relative position and its regulating method - Google Patents
Double channel filter with regulatable channel relative position and its regulating method Download PDFInfo
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- CN100365448C CN100365448C CNB2004100538148A CN200410053814A CN100365448C CN 100365448 C CN100365448 C CN 100365448C CN B2004100538148 A CNB2004100538148 A CN B2004100538148A CN 200410053814 A CN200410053814 A CN 200410053814A CN 100365448 C CN100365448 C CN 100365448C
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Abstract
The present invention provides a design method for independently regulating the relative positions of two channels in a two-channel optical filter. The present invention adopts a bisymmetry structure based on a Fabry-Perot etalon. The present invention is different from the traditional narrow band optical filter, and is used for independently regulating the positions of the two channels by respectively changing the thickness of a plurality of middle layers. The present invention overcomes the defect of coherent position generated by the regulation of the positions of the channels. The present invention introduces the design and the concrete structure of an optical filter, the calculated spectral characteristics of a two-channel band-pass optical filter, etc. The optical filter of the present invention can be applied to the fields of an optical detection instrument, a space technology, etc.
Description
Technical Field
The invention relates to an optical filter device, in particular to a dual-channel optical filter with adjustable relative position of channels and an adjusting method thereof. Has application prospect in optical instrument, astronomy, remote sensing and other aspects.
Background
Conventional multi-channel bandpass filters generally have two types:
1. multi-channel band-pass filter based on Fabry-Perot etalon
The most typical multi-channel bandpass filter is a Fabry-Perot etalon structure. The filter is a symmetrical structure, two ends of the filter are provided with reflecting layers, the middle of the filter is provided with a spacing layer, the structure can obtain the band-pass filter with multi-channel transmission characteristics through multiple reflections of the reflecting layers and proper selection of the physical thickness of the spacing layer, but because the positions of all channels are related to the thickness of the spacing layer, the position changes of the channels are coherent. Therefore, the filter with adjustable relative position of the channels cannot be designed by using this structure.
2. Rugate-type multi-channel band-pass filter
A Rugate-type multi-channel bandpass filter, perhaps with a continuous index structure, is most attractive from a design point of view, since Rugate filters have a perfect mathematical transformation. However, since the medium adopted by the multi-channel band-pass filter of the type is required to be a refractive index gradient material, the design can be performed theoretically, but the multi-channel band-pass filter is more difficult to plate than the multi-layer medium multi-channel band-pass filter.
The concepts of photonic crystals were proposed by s.john and e.yablonovitch et al, respectively, in 1987. Because the one-dimensional photonic crystal is similar to an optical multilayer dielectric film in structure, from the perspective of the photonic crystal, a plurality of new technologies are formed through the analysis and research of the forming mechanism of the spectrum of the one-dimensional photonic crystal, the electromagnetic mode density and the photon state density in the one-dimensional photonic crystal. After the defect layer is inserted into the one-dimensional photonic crystal, the photon state density in the crystal is changed, the forbidden band characteristic of the one-dimensional photonic crystal is changed, and a channel can be formed in the photon forbidden band. On the basis, wangli et al have studied the heterojunction structure of one-dimensional photonic crystals. Two materials with different dielectric constants are formed into one-dimensional photonic crystals with different lattice constants, a doped heterojunction structure is formed by coupling of defect layers, and a wide cut-off band is obtained by utilizing the band gap characteristics of the heterojunction structure. Due to the modulation of the heterojunction structure energy band by the impurities, two narrow pass bands can be obtained in the wide cut-off band by doping. The narrow-band filter overcomes the defect that the traditional narrow-band filter cannot obtain narrow-band filtering in a wide cut-off band. And more transmission channels are obtained on the background of the wide forbidden band by adjusting the position and the size of the defect layer.
One advantage of using photonic crystal concepts to design narrowband filters is that the operating band can be pre-designed. The reason is that the photonic crystal has scale invariance, and if only the lattice constant is changed and other parameters are kept unchanged, the overall shape of the energy band structure of the photonic crystal is not changed, and only the peak position of the transmission peak and the position of the cut-off band are correspondingly shifted.
The Fabry-Perot etalon-based multi-channel band-pass filter and the heterojunction structure of the one-dimensional photonic crystal are difficult to independently adjust the relative position of each channel, so that the application range of the dual-channel filter is limited.
Disclosure of Invention
The invention aims to provide a multi-channel narrow-band filter which not only has multiple channels, but also can independently adjust the positions of the channels and an adjusting method thereof.
The invention provides a double-channel optical filter with adjustable relative channel positions, which is a brand new design method based on a Fabry-Perot etalon structure and is realized by using a double-symmetrical structure on the basis of the Fabry-Perot etalon structure.
In a Fabry-Perot etalon structure, if the admittance of the media on either side of the spacer is the same, the transmission T is:
wherein T is 1 、T 2 、R 1 、R 2 Respectively the transmittance and reflectance, phi, of both sides of the selected film layer 1 、φ 2 The phase shift of the two reflection film layers is respectively.
As can be seen from the formula (1), if T of two reflective film layers is 1 、T 2 、R 1 、R 2 And a reflection phase shift phi 1 、 φ 2 Constant by selecting the effective phase thickness of the film
When phi is 1 +φ 2 Transmission T of the entire film system reaches a maximum at 2 δ =2k pi (k = ± 1,2, 3) (2):
as can be seen from the Fabry-Perot etalon structure, in this symmetrical structure, the insertion of the spacer layer causes the change of the photon density of states and electromagnetic wave modes in the photonic crystal, and the multiple reflections of the reflective layers on both sides form the channel. A symmetrical structure can form a series of independent channels, the number and location of which vary with the thickness of the spacer layer. To achieve independent adjustment of the two channel positions, two symmetrical structures can be used. This is a completely different design method from the traditional two-channel band-pass filter.
Based on the designThe optical filter with a double symmetrical structure is formed by two materials with different dielectric constants. As shown in fig. 1, wherein: H. l, 1/4 wavelength optical thickness of high and low refractive index material respectively, H = n H d H ＝L＝n L d L ＝λ/4，n L ＝1.44、n H =2.3 refractive indices of the two materials, respectively; d H 、d L The physical thicknesses of the two materials correspond to 1/4 wavelength optical thickness, respectively. Firstly, two Fabry-Perot filter symmetrical structures are formed by high-low refractive index materials, and then a new Fabry-Perot filter symmetrical structure is formed by the two structuresThis structure is referred to as a double-symmetrical structure. The relative position of the channel in the transmission spectrum of the optical filter can be changed by adjusting the thicknesses of the three intermediate layers in the double-symmetrical structure. The thicknesses of the middle layers of the two Fabry-Perot symmetrical structures are both cH and are called as middle layers c, the thickness of the middle layer between the two Fabry-Perot symmetrical structures is dL and is called as middle layers d, and the relative positions of the two channels can be independently adjusted by respectively adjusting c and d. The film system can be optimized by adding matching film layers.
In the invention, siO can be selected as the hard film material of two films with different dielectric constants 2 And TiO 2 The soft film material can be MgF 2 And ZnS, and the like.
The invention relates to a double-channel narrow-band filter device adopting an all-dielectric structure. The Fabry-Perot etalon-based double-symmetry structure is adopted to realize independent continuous change of the serial positions of two channels; the positions of the two channel series can be independently and continuously changed by respectively adjusting the thicknesses of the intermediate layers c and d, and the two-channel one-dimensional photonic crystal with the independently and continuously changed positions can be obtained by properly adjusting the thickness of the intermediate layer.
The invention is characterized in that the positions of the two channels are respectively controlled by two parameters c and d, can be independently changed, and can be arbitrarily adjusted in the cut-off band.
Drawings
FIG. 1 is a graph showing the relationship between the channel position and the thickness of a defect layer in a conventional Fabry-Perot structure.
FIG. 2 is a schematic diagram of a double-symmetrical structure according to the present invention.
Fig. 3 is a diagram of the channel variation of the dual-channel bandpass filter when c =1.4H is fixed and d is varied in the dual-symmetric structure of the present invention.
Fig. 4 is a channel variation diagram of the dual-channel bandpass filter when d =0.4L is fixed and c is varied in the double-symmetric structure of the present invention.
Fig. 5 is a diagram showing the channel variation when the double symmetric structures d and c of the present invention are alternately changed.
Detailed Description
The present invention is further described below with reference to the accompanying drawings by taking a two-channel one-dimensional photonic crystal as an example.
As can be seen from fig. 1, as the thickness of the intermediate layer c increases, the channel position moves toward the longer wavelength direction. However, the relative spacing between the channels is always the same and cannot be changed. FIG. 2 is a schematic diagram of a Fabry-Perot based dual symmetry structure of the present invention. Fig. 3 shows that as d increases from 0.3L to 0.9L, the right channel moves from 650.65nm to 708.1nm, whereas the left channel remains stationary in the original position. It can be seen from fig. 4 that the left channel moves from 538.7nm to 600nm as c increases from 1.4H to 2.0H, whereas the right channel remains in the original position. In fig. 5, the double symmetric structures d and c alternate, starting with c =1.4h, d =0.4l, and c and d alternate by 0.1 optical thickness until c =2.0h, d =0.9l. It can be seen from the figure that the positions of the channels are also alternately changed, changing one parameter, changing only the position of one channel, while the position of the other channel is not changed.
Taking fig. 3 as an example, the specific method for designing and adjusting the dual-channel position of the optical filter is as follows:
firstly, the size of the lattice constant, namely the thickness of the reflecting film stack on two sides of the spacer layer of the Fabry-Perot structure is determined according to the position of a required cut-off band. In FIG. 3, the width of the cut-off band is 510-730nm, and the film structure of the filter is (HL) n cH(LH) n dL(HL) n cH(LH) n Wherein n is an integer and c and d are thicknesses of the intermediate layer. After the position of the cut-off strip is determined, determining the sizes of c and d according to the positions of the two required channels; determining channel 1, by calculating (HL) n cH(LH) n The reflection phase shift of the wavelength of the reflecting layer channel 1 on the two sides of the spacing layer of the structure is obtained by the formula (2). The same method is used to determine the channel 2, but the reflection phase shift calculated at this time is generated by two Fabry-Perot structures on both sides of the intermediate layer of the entire film system, the reflection phase shift of the wavelength at which the channel 2 is located is obtained, and the magnitude of d is obtained by the equation (2). From computer simulations it can be found that the position of channel 1 is determined by the size of cIt is determined that the position of the channel 2 is determined by the size of d, and the position of the channel may be continuously varied. Since c is calculated for simplicity, the calculation object is a Fabry-Perot structure rather than the whole double symmetric film system. So that c can be adjusted on the computer to fit the position of the channel 1 to the design. After the thicknesses of all the film layers are determined, the used materials can be selected according to actual conditions. The invention selects TiO 2 、SiO 2 The incident medium is air epsilon =1.TiO 2 2 、 SiO 2 The formed medium pair is impurity, and the optical filter with the required channel parameter is obtained by adjusting the position and the size of the impurity by using a transmission matrix method.
The positions of the two channels are controlled by two parameters c and d respectively, can be independently changed, and can be randomly adjusted in the cut-off band. With the structure as (HL) 7 cH(LH) 7 dL(HL) 7 cH(LH) 7 The one-dimensional photonic crystal of (a) is exemplified by:
1. the position of the channel 2 is adjusted without changing the position of the channel 1:
the center wavelength λ =600nm is designed such that the position of channel 1 does not change when c is determined, and the position of channel 2 changes continuously with the change of d. When c =1.4h, d is equal to 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9L, respectively, the position of the channel changes as shown in fig. 3.
2. The position of the channel 1 is adjusted without changing the position of the channel 2:
the center wavelength λ =600nm is designed such that the position of channel 2 does not change when d is determined, and the position of channel 1 changes continuously with the change in c. When d =0.6l, c is equal to 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0H, respectively, the position of the channel changes as shown in fig. 4.
3. The two channels alternate:
the center wavelength λ =600nm is designed, and when d and c are changed alternately, the positions of the channels are shifted alternately, for example, in fig. 5, starting from c =1.4h, d =0.4l, and c and d are alternately increased by 0.1 optical thickness until c =2.0h and d =0.9l, and the change of the channels can be seen by changing a parameter, one of the channels can be controlled without affecting the position of the other channel.
Claims (4)
1. A dual-channel optical filter with adjustable relative position of channels is characterized in that:
the hard film material of the film is TiO 2 And SiO 2 In combination, the structure of the membrane system is as follows: (HL) n cH(LH) n dL(HL) n cH(LH) n H and L are the optical thicknesses of 1/4 wavelength of the high-refractive index material and the low-refractive index material respectively, and c and d are the thickness parameters of the intermediate layer.
2. The dual channel filter of claim 1, wherein the channel relative position is adjustable by:
the film-based material of the film may beWith ZnS and MgF 2 And (4) combining.
3. A method for adjusting a dual-channel filter with adjustable relative position of channels is characterized in that:
the hard film material of the film is TiO 2 And SiO 2 The combination, the structure of membrane system is: (HL) n cH(LH) n dL(HL) n cH(LH) n H and L are the 1/4 wavelength optical thickness of the high-refractive index material and the low-refractive index material respectively, c and d are the thickness parameters of the middle layer, and the positions of two transmission peaks of the double-channel optical filter with adjustable relative positions are adjusted by the thicknesses of the c layer and the d layer in the structure.
4. The method of claim 3, wherein the method further comprises:
the exact thickness of the c layer was fine-tuned by computer.
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Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN100385266C (en) * | 2005-09-14 | 2008-04-30 | 同济大学 | Two-dimensional pass band channel filter capable of tuning relative position |
| CN100385265C (en) * | 2005-09-14 | 2008-04-30 | 同济大学 | Two-dimensional double-channel optical-filter capalbe of tuning channel relative position |
| CN101303424B (en) * | 2008-06-12 | 2011-02-16 | 中国科学院上海技术物理研究所 | Three-cavity multichannel optical spectrum step type integrated optical filter |
| CN102320164B (en) * | 2011-08-15 | 2014-04-16 | 西北核技术研究所 | Multilayer medium high-reflecting film for variable angle laser incidence |
| CN104297834B (en) * | 2014-11-06 | 2017-02-08 | 沈阳仪表科学研究院有限公司 | Multi-passband optical filter based on nested loop model |
| CN104330844B (en) * | 2014-12-02 | 2017-04-12 | 中国航天科工集团第三研究院第八三五八研究所 | Method applied to correction of reflection phase shift of high-reflection optical dielectric thin film |
| CN106405709B (en) * | 2016-11-16 | 2018-12-28 | 天津津航技术物理研究所 | A kind of broadband cut-off ultra-narrow band pass filter |
| CN108801967B (en) * | 2018-06-21 | 2021-06-15 | 长春理工大学 | Double-passband filter device, infrared thermal imaging detection system and method for detecting methane |
| CN109031494A (en) * | 2018-09-05 | 2018-12-18 | 任磊 | A kind of all dielectric filter pigment |
| CN109683225A (en) * | 2019-02-27 | 2019-04-26 | 成都国泰真空设备有限公司 | A kind of flat sheet membranes edge filter for depolarization |
| CN111123423B (en) * | 2020-03-27 | 2020-06-23 | 上海翼捷工业安全设备股份有限公司 | Double-channel infrared filter combination for flame detection and preparation method and application thereof |
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