CN100365447C - Three-channel filter with independently regulatable channel relative position and its regulating method - Google Patents
Three-channel filter with independently regulatable channel relative position and its regulating method Download PDFInfo
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- CN100365447C CN100365447C CNB2004100538133A CN200410053813A CN100365447C CN 100365447 C CN100365447 C CN 100365447C CN B2004100538133 A CNB2004100538133 A CN B2004100538133A CN 200410053813 A CN200410053813 A CN 200410053813A CN 100365447 C CN100365447 C CN 100365447C
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Abstract
The present invention provides a design method for independently regulating the relative positions of three channels in a three-channel optical filter. The present invention adopts three symmetrical structures based on a Fabry-Perot structure. The present invention is different from the traditional narrow band optical filter, and is used for independently regulating the positions of the three 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, the concrete structure and the regulating method of an optical filter, the calculated spectral characteristics of a three-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 three-channel optical filter with adjustable channel positions 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 multichannel 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 channels cannot be designed by using the 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.
S.john and e.yablonovitch et al, in 1987, proposed the concept of photonic crystals, respectively. 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 maintained unchanged, the overall shape of the energy band structure of the photonic crystal is not changed, and only the positions of the peak position of the transmission peak and 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 and multi-channel filters is limited.
Disclosure of Invention
The invention aims to provide a multi-channel narrow-band filter which not only has three channels, but also can independently adjust the positions of the channels and an adjusting method thereof.
The invention provides a three-channel filter with an adjustable channel relative position, which is a brand new design method based on a Fabry-Perot etalon structure and is realized by utilizing a three-symmetrical structure based on 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 reflection 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. The independent adjustment of the three-channel position can be realized by a three-symmetrical structure. This is a completely different design method from the conventional multi-channel band-pass filter.
Based on the design, the 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 d of two materials, respectively H 、d L The physical thicknesses of the two materials correspond to 1/4 wavelength optical thickness, respectively. First, two are made of high and low refractive index materialsFabry-Perot filter symmetric structure, then a new symmetric structure is formed by the two structures, and the structure is called a double symmetric structure. The three-symmetrical structure is characterized in that two identical two-symmetrical structures are coupled together by a coupling layer on the basis of double symmetry, and the two double-symmetrical structures are symmetrical about the coupling layer to form a new symmetrical structure, namely the three-symmetrical structure. The relative positions of the channels in the transmission spectrum of the filter can be changed by adjusting the thicknesses of the seven middle layers in the three-symmetrical structure. The thicknesses of the middle layers of the two Fabry-Perot symmetrical structures are cH and are called middle layers c, the thickness of the middle layer between the two Fabry-Perot symmetrical structures is dL and is called middle layer d, and the thicknesses of the coupling layers of the two Fabry-Perot symmetrical structures are eL and are called e layers. The positions of the three channels can be independently adjusted by adjusting the thicknesses of the layers c, d and e, respectively. 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 three-channel narrow-band filter device adopting an all-dielectric structure. It adopts a three-symmetrical structure based on a Fabry-Perot structure, and can independently and continuously change the positions of three channels by respectively adjusting the thicknesses of the middle layers c, d and e. The following description will be given by taking a three-channel one-dimensional photonic crystal as an example.
The invention is characterized in that the positions of the two channels are respectively controlled by three parameters, namely c, d and e, 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 position of a via and the thickness of a defect layer in a conventional Fabry-Perot structure.
FIG. 2a is a schematic diagram of a double-symmetrical structure according to the present invention.
FIG. 2b is a schematic diagram of a three-symmetrical structure according to the present invention.
Fig. 3 shows the channel variation of the three-channel bandpass filter when c =1.7H and d =0.2L are fixed and e varies in the three-symmetric structure of the present invention.
Fig. 4 shows the channel variation of the three-channel bandpass filter when c =1.7H, e =3.3L is fixed and d varies in the three-symmetrical structure of the present invention.
Fig. 5 shows the channel variation of the three-channel bandpass filter when d =0.4H, e =3.3L is fixed and c varies in the three-symmetric structure of the present invention.
Fig. 6 shows the alternation of the channel positions when c, d and e are alternated in the inventive three-symmetrical structure.
Detailed Description
The following describes a specific method for designing and adjusting the position of the three-channel filter with three symmetric structures according to the present invention with reference to the accompanying drawings.
As can be seen from fig. 1, as the thickness of the intermediate layer c increases, the positions of the two channels are both shifted in the long-wave direction, and 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 according to the present invention. In fig. 3, as e increases from 3.1L to 3.6L, the right channel moves from 701.19nm to 720.35nm, whereas the two left channels remain substantially stationary in their original positions. In fig. 4, as d increases from 0.2H to 0.7H, the middle channel moves from 635.09nm to 696.53nm, whereas the two channels on both sides remain substantially stationary in their original positions. In fig. 5, the left channel moves from 566.50nm to 622.32nm as c increases from 1.7H to 2.2H, however the two channels on the right remain substantially stationary in their original positions. In fig. 6, starting with c =1.7H, d =0.4L, e =3.3L, c, d and e are alternately increased by 0.1 optical thickness until c =2.0H, d =0.6L, e =3.5L. It can be seen from the figure that changing one parameter allows one of the channels to be controlled without affecting the position of the other channel.
Taking the example shown in FIG. 3 as an example, first, the size of the lattice constant, i.e. the single-layer thickness of the reflective film stack on both sides of the spacer layer of the Fabry-Perot structure, is determined according to the position of the desired cut-off band. In the design, the width of the cut-off band is 510-730nm, the design center wavelength is 600nm, and the film structure of the optical filter is as follows:
(HL) n cH(LH) n dL(HL) n cH(LH) n eL(HL) n cH(LH) n dL(HL) n cH(LH) n where c, d and e represent the thickness of the intermediate layer, the position in the film system is shown in FIG. 2b. After the position of the cut-off strip is determined, determining the sizes of c, d and e according to the positions of the three required channels; determining channel 1, by calculating (HL) n cH(LH) n The reflection phase shift of the wavelength of the reflection layer channel 1 on the two sides of the spacing layer of the structure is obtained by the formula (2). Channel 2 and channel 3 are determined in the same way, but the calculated object is different when calculating the reflected phase shift, by calculation (HL) n cH(LH) n dL(HL) n cH(LH) n The reflection phase shift of the reflection layers at the wavelength of the channel 2 on the two sides of the spacing layer of the structure is substituted into the formula (2) to obtain the value of d, and therefore the position of the channel 2 is determined. By calculation (HL) n cH(LH) n dL(HL) n cH(LH) n eL(HL) n cH(LH) n dL(HL) n cH(LH) n Reflecting layers on both sides of the spacer layer of the structure in the channel3, and determining the position of the channel 3 by calculating the size of e according to the formula (2). It can be found from computer simulations that the positions of channels 1,2 and 3 are determined by the sizes of c, d and e, respectively, and the positions of the three channels can be continuously varied. When c and d are calculated, in order to simplify the calculation, (HL) 7 cH(LH) 7 dL(HL) 7 cH(LH) 7 Structures and Fabry-Perot structures rather than the entire three-symmetric film system. The c and e layers can thus be adjusted on the computer to fit the position of channel 1 and channel 2 to the design. After the thicknesses of all designed 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 e =1.TiO 2 2 、SiO 2 The medium pair of the composition is impurity, and the optical filter with the required channel parameter is obtained by adjusting the position and the size of the spacing layer by using a transmission matrix method.
The positions of the two channels are respectively controlled by three parameters, namely c, d and e, can be independently changed, and the positions of the three channels can be randomly adjusted in a cut-off band.
Hereinafter, the left, middle and right three channels are respectively denoted as channel 1, channel 2 and channel 3,
1. the position of channel 3 is adjusted with the positions of channel 1 and channel 2 unchanged:
the positions of channels 1 and 2 do not change when c and d are determined, and the position of channel 3 changes continuously as e changes. When c =1.7, d =0.2, e is equal to 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, respectively, the position of the channel changes as shown in fig. 3.
2. The position of channel 2 is adjusted with the positions of channel 1 and channel 3 unchanged:
the positions of channels 1 and 3 do not change when c and e are determined, and the position of channel 2 changes continuously as d changes. When c =1.7, e =3.3, d is equal to 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, respectively, the position of the channel changes as shown in fig. 4.
3. The position of channel 1 is adjusted with the positions of channel 2 and channel 3 unchanged:
the positions of channels 2 and 3 do not change when d and e are determined, and the position of channel 1 changes continuously with the change of c. When d =0.4, e =3.3, c is equal to 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, respectively, the position of the channel changes as shown in fig. 5.
4. The three channels alternate:
when c, d and e are changed alternately, the positions of the channels are changed alternately, for example, in fig. 6, starting from c =1.7H, d =0.4L, e =3.3L, c, d and e are alternately increased by 0.1 optical thickness until c =2.0H, d =0.6L, e =3.5L, and the change of the channels can be seen that one of the channels can be controlled without affecting the position of the other channel by changing one parameter.
5. Fine adjustment of channel position:
in some cases, the channels may drift slightly during design, which may be corrected for fine tuning of the c, d, and e layers by computer simulation. The main method is to perform correction by performing fine tuning on the control layer of the drift channel, for example, the control layer of channel 1 is the c layer, and so on.
Claims (4)
1. A three-channel filter with independently 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 eL(HL) n cH(LH) n dL(HL) n cH(LH) n H and L are the 1/4 wavelength optical thicknesses of the materials with high and low refractive indexes respectively, and c, d and e are the thickness parameters of the intermediate layer.
2. The three-channel optical filter of claim 1, wherein the relative positions of the channels are independently adjustable, and wherein:
the soft film material of the thin film can be ZnS and MgF 2 And (4) combining.
3. A method for adjusting a three-channel optical filter with independently 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 eL(HL) n cH(LH) n dL(HL) n cH(LH) n H and L are the 1/4 wavelength optical thickness of the material with high and low refractive index respectively, c, d and e are thickness parameters of the middle layer, the positions of the three channels are controlled by the three parameters of c, d and e respectively, the three channels can be independently changed, and the positions of the three channels can be randomly adjusted in the cut-off band.
4. The method according to claim 3, wherein the relative position of the channels is adjustable by the method comprising:
the exact thickness of the c and d layers is fine tuned by the computer.
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| CN103472598B (en) * | 2013-10-12 | 2015-12-09 | 太原理工大学 | A kind of one-dimensional magnetic photonic crystal realizing light isolation |
| CN103576229B (en) * | 2013-11-25 | 2015-07-29 | 杭州科汀光学技术有限公司 | Without the block prism bandpass filter of polarization |
| 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 |
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| CN1308244A (en) * | 2001-01-04 | 2001-08-15 | 复旦大学 | Multiichannel photo crystal filter |
| US6407863B1 (en) * | 1999-04-20 | 2002-06-18 | Ciena Corporation | Dual transmission band interference filter |
| CN1450366A (en) * | 2003-05-06 | 2003-10-22 | 中山大学 | Single-frequency single-angle transmitted total-angle high-reflection one-dimension photon crystal |
| WO2004021527A2 (en) * | 2002-08-30 | 2004-03-11 | Research Electro-Optics, Inc. | Fabry-perot etalon with independently selectable resonance frequency and free spectral range |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6407863B1 (en) * | 1999-04-20 | 2002-06-18 | Ciena Corporation | Dual transmission band interference filter |
| CN1308244A (en) * | 2001-01-04 | 2001-08-15 | 复旦大学 | Multiichannel photo crystal filter |
| WO2004021527A2 (en) * | 2002-08-30 | 2004-03-11 | Research Electro-Optics, Inc. | Fabry-perot etalon with independently selectable resonance frequency and free spectral range |
| CN1450366A (en) * | 2003-05-06 | 2003-10-22 | 中山大学 | Single-frequency single-angle transmitted total-angle high-reflection one-dimension photon crystal |
Non-Patent Citations (2)
| Title |
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| 具有共振腔模式的一维光子晶体结构. 王利等.光学仪器，第26卷第2期. 2004 * |
| 基于Fabry-Perot结构的多通道滤光片的设计. 王利等.光学 精密工程，第11卷第6期. 2003 * |
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