CN100373185C - Relative position independently adjustable channel passband filter - Google Patents

Abstract

The present invention provides a design method capable of independently adjusting position of an optical filter in a channel and position of a passing band, and a symmetrical structure base on a Fabry-Perot etalon is adopted. The present invention is different from a traditional narrow band filter and a band-pass filter, the positions of the channel and the passing band are independently adjusted respectively by changing thickness of a plurality of middle layers, and a coherent phenomenon of the positions of the channel and the passing band during adjusting time is overcome on the foundation of realization of coexistence of the channel and the passing band. The present invention introduces a design idea and a specific structural design of the optical filter, and spectral characteristics, etc. of the channel band pass filter calculated under the design. The designed optical filter can be applied to the technical fields of optical detection instruments, space technologies, etc.

Description

The channel passband filter that relative position can independently be adjusted

Technical field

The present invention relates to a kind of optical filter designs method, be specifically related to the design that a kind of existing passage has the optical filter of passband again.At aspects such as optical instrument, astronomy, remote sensing application prospect is arranged.

Background technology

Traditional hyperchannel bandpass filter generally has following two kinds:

1, based on the hyperchannel bandpass filter of Fabry-Perot etalon

Most typical hyperchannel bandpass filter is a Fabry-Perot etalon structure.This optical filter is a symmetrical structure, two ends are the reflection horizon, the centre is a wall, repeatedly reflection through the reflection horizon, by appropriately choosing the physical thickness of wall, this structure can obtain having the bandpass filter that hyperchannel sees through characteristic, but because all there is relation the position of all passages with the thickness of this wall, the change in location of these passages is concerned with.Therefore, can't go out the adjustable optical filter of passage relative position with this structural design.

2, the hyperchannel bandpass filter of Rugate type

From design point of view, perhaps the hyperchannel bandpass filter of the Rugate type of continuous refractive index structures is arranged is the most attracting, because the Rugate optical filter has perfect mathematic(al) manipulation form.But because the medium that the hyperchannel bandpass filter of the type is adopted requires to be the gradually changed refractive index material, although therefore can design in theory, be coated with technical, more much more difficult than multilayered medium hyperchannel bandpass filter.

People such as S.John in 1987 and E.Yablonovitch have proposed the notion of photonic crystal respectively.Because 1-D photon crystal structurally is similar to the optical multilayer deielectric-coating, therefore from the angle of photonic crystal, by the formation mechanism to 1-D photon crystal spectrum, the electromagnet mode density in the 1-D photon crystal and the analysis and the research of photon state density have formed many new technology.In 1-D photon crystal, cause the variation of photon state density in the crystal behind the insertion defect layer, changed the forbidden band characteristic of 1-D photon crystal, and can in forbidden photon band, form passage.On this basis, people such as Wang Li studies the heterostructure of 1-D photon crystal.The material of two kinds of differing dielectric constants is formed the 1-D photon crystal with different lattice constants, form by the coupling of defect layer and have the heterostructure of doping, and utilize the band gap characteristics of heterostructure to obtain wide rejection zone.Because the modulation that impurity can be with heterostructure, so can in wide rejection zone, obtain two narrow passbands by mixing.It has overcome the shortcoming that the traditional narrow optical filter can not obtain narrow-band-filter at a cut-off bandwidth.And, on the background of broad stopband, obtain more seeing through passage by adjusting the position and the size of defect layer.

An advantage that adopts photonic crystal conceptual design narrow band pass filter is a design effort wave band in advance.Reason is that photonic crystal has " scaling invariance ", if only change grating constant, and it is constant to keep other parameters, and then the overall shape of the band structure of photonic crystal does not change, and just sees through the peak position at peak and the position of rejection zone corresponding moving taken place.

Heterostructure based on the hyperchannel bandpass filter of Fabry-Perot etalon and above-mentioned 1-D photon crystal is difficult to the independent relative position of adjusting each passage, and can't realize the coexistence of passage and passband, thereby limit the range of application of passage bandpass filter.

Summary of the invention

The object of the present invention is to provide a kind of both had passage and passband, can independently adjust the hyperchannel band pass filter of passage and passband position again.

The channel passband filter that passage that the present invention proposes and passband position can independently be adjusted is to be a kind of new method for designing on basis with symmetrical multilayer dielectric film.

In this structure, if the admittance of both sides, middle layer medium is identical, then transmissivity T is:

$T=\frac{T_1{T}_2}{{(1-\sqrt{R_1{R}_2})}^2}\frac{1}{1+\frac{4\sqrt{R_1{R}_2}}{(1-\sqrt{R_1{R}_2})}{\sin }^2\frac{1}{2}({\mathrm{\φ}}_1+{\mathrm{\φ}}_2+-2\mathrm{\δ})}---\left(1\right)$

T wherein ₁, T ₂, R ₁, R ₂Be respectively the transmissivity and the reflectivity of selected rete both sides, φ ₁, φ ₂Be respectively the reflection phase shift of two reflective coatings.

By formula (1) as can be known, if the T of two reflective coatings ₁, T ₂, R ₁, R ₂With reflection phase shift φ ₁, φ ₂Constant, at this moment the amount that can change is the significance bit phase thickness of selected rete $(\mathrm{\δ}=\frac{2\mathrm{\π}}{\mathrm{\λ}}\text{nd})\·$

Work as φ ₁+ φ ₂During-2 δ=2k π (k=± 1,2,3) (2), the transmissivity T that whole film is reaches maximal value.

In this symmetrical structure, the insertion in middle layer has caused the variation of photon state density and electromagnetism mode in the photonic crystal, the repeatedly reflection in the reflection horizon of its both sides and form passage in spectral pattern.Keep the symmetry of film system to form a new passband at the new film layer structure of the both sides of film system introducing.Form channel passband filter.Based on this design philosophy, we have adopted the material of two kinds of differing dielectric constants have been formed the optical filter with symmetrical structure.As shown in Figure 1, wherein: H, L are respectively 1/4 wavelength optical thickness of high low-index material, H=n _Hd _H=L=n _Ld _L=λ/4, n _L=1.44, n _H=2.3 are respectively the refractive index of two kinds of materials; d _H, d _LBe respectively the physical thickness of two kind materials corresponding with 1/4 wavelength optical thickness.Adjust the thickness in five middle layers in the disymmetry structure, can change the relative position of passage and passband in the optical filter transmission spectrum.Wherein the thickness in four middle layers, two symmetrical structure left and right sides is cH, is referred to as middle layer c, and the thickness in middle layer, symmetrical structure center is dL, is referred to as middle layer d, adjusts the position that c and d just can adjust passage and passband independently.This film system can be optimized by adding the coupling rete.

Among the present invention, the material of two kinds of differing dielectric constants can be selected SiO for use ₂And TiO ₂Deng.

The present invention is a kind of channel passband filtering device that adopts full dielectric structure.It adopts symmetrical structure, realizes that the independence of passage and passband position changes continuously; By adjusting the thickness of middle layer c and d, the position of two passage series is changed independently, suitably adjust the thickness in middle layer, can obtain position independence continually varying channel passband 1-D photon crystal.Be that example describes all below with the channel passband 1-D photon crystal.

Description of drawings

Fig. 1 is a series of symmetrical film structural representation of the present invention.

Fig. 2 for the present invention under the constant situation of channel position, appropriate change c and d, the adjustment of the passband position of generation.

Fig. 3 for the present invention under the situation of passband invariant position, appropriate change c and d, the adjustment of the channel position of generation.

Fig. 4 is suitable adjustment c of the present invention and the value of d, the alternate of the passage of generation and passband position,

Embodiment

The c of several block graphicses shown in Figure 2 and the value of d are respectively c=1.4H, d=0.8L, c=1.5H, d=0.743 5 L, c=1.6H, d=0.698L, c=1.7H, d=0.6 59L, c=1.8H, d=0.624L.Suitably adjust d along with c is increased to 1.8 by 1.4, the passband position on the left side progressively moves to right, and the passage on the right keeps motionless in original position all the time.

Keep c=1.4H constant in several block graphicses shown in Figure 3, along with the value of d is increased to 0.7L by 0.2L, it is motionless substantially that the passband position on the left side keeps.And the passage on the right progressively moves right.

As shown in Figure 4, the c of these several channel passband spectrum character diagram correspondences and the value of d are respectively c=1.5H, d=0.4L, c=1.5H, d=0.5L, c=1.6H, d=0.472L, c=1.6H, d=0.6L, c=1.7H, d=0.567 7 L, c=1.7H, d=0.7L, c=1.8H, d=0.662L, c=1.8H, d=0.8L, c=1.9H, d=0.755L, the different variation combination along with c and d can make the position of passage and passband that alternate takes place.

The binary channels Position Design of optical filter and the concrete grammar of adjustment are as follows:

The passage bandpass filter of design symmetrical structure, at first according to the position of required rejection zone, the size of determining grating constant is the single layer optical thickness of the reflection membrane stack of both sides, symmetrical structure middle layer.With the example that is designed to shown in Figure 2, in this design, the rejection zone width is 260nm, and wavelength is 600nm, and the film structure of optical filter is for being the disymmetry structure on basis with symmetrical multilayer dielectric film, and this disymmetry structure is (HL) ²CH (LH) ²L (HL) ²CH (LH) ²DL (HL) ²CH (LH) ²L (HL) ²CH (LH) ², wherein c and d represent the thickness in middle layer.The size of c and d again according to the position of needed passage and passband, is determined after determining in the rejection zone position; Determine earlier passage, the size of d is tried to achieve in the reflection phase shift of passage place wavelength in the reflection horizon, d both sides, middle layer by calculating symmetrical structure by formula (2).Determine that passband uses the same method, but the reflection phase shift of being calculated this moment is by film system (HL) ²CH (LH) ²Producing, is that the symmetrical structure of symcenter produces with certain c layer of the left and right sides promptly.Try to achieve the reflection phase shift of passband place wavelength, through type (2) is obtained the size of c.Can be found that by computer simulation the position of passage is mainly decided by the size of d, the position of passband is mainly decided by the size of c, and the position of passage and passband can change continuously.Because calculate for simplifying when calculating c, calculating object is ((HL) ²CH (LH) ²Symmetrical structure but not the whole series of symmetrical film.Therefore can adjust c on computers, the position of passband and designing requirement are matched.The thickness of all retes of design is all definite, and material therefor can be chosen according to physical condition.That we choose is TiO ₂, SiO ₂, incident medium is air ε=1.TiO ₂, SiO ₂The medium of forming utilizes transfer matrix method to being impurity, by adjusting the thickness in middle layer, the optical filter that obtains having required passage and passband parameter.

Characteristics of the present invention are exactly that the position of two passages can be controlled by two parameter c and two parameters of d, can independent variation, can in rejection zone, at random adjust the position of two passages.

1, adjust the position of passband under the situation that channel position is constant:

Be (HL) all below with structure ²CH (LH) ²L (HL) ²CH (LH) ²DL (HL) ²CH (LH) ²L (HL) ²CH (LH) ²1-D photon crystal be example, design wavelength lambda=600nm, the size of adjusting c and d can obtain as

Situation of change shown in Figure 2 can be adjusted passband under the constant situation of channel position

The position.

2, adjust the position of passage under the situation of passband invariant position:

The size of adjusting c and d can obtain situation of change as shown in Figure 3, can adjust the position of passage under the situation of the invariant position of passband.

3, the position alternate of passage and passband:

Suitable adjustment c and the value of d can make the position alternate of passage and passband, as shown in Figure 4.

Claims (2)

1. channel passband filter that relative position can independently be adjusted is characterized in that:

The dura mater based material of optical filter film is TiO ₂And SiO ₂Combination, the structure of component film system is for being the disymmetry structure on basis with symmetrical multilayer dielectric film, this disymmetry structure is:

(HL) ²CH (LH) ²L (HL) ²CH (LH) ²DL (HL) ²CH (LH) ²L (HL) ²CH (LH) ², wherein, passage and passband see through the position at peak and are adjusted by the thickness of middle layer c in the structure and middle layer d, and wherein, the thickness of middle layer c is cH, and the thickness of middle layer d is dL.

2. the channel passband filter that relative position according to claim 1 can independently be adjusted is characterized in that:

For the position that makes passage and passband coincide with design, the accurate thickness of middle layer c and middle layer d is finely tuned by computer Simulation calculation.

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