CN209248064U - Low degree of polarization two dimension binary blazed grating - Google Patents
Low degree of polarization two dimension binary blazed grating Download PDFInfo
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- CN209248064U CN209248064U CN201822264272.9U CN201822264272U CN209248064U CN 209248064 U CN209248064 U CN 209248064U CN 201822264272 U CN201822264272 U CN 201822264272U CN 209248064 U CN209248064 U CN 209248064U
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Abstract
The utility model discloses a kind of low degree of polarization two dimension binary blazed gratings, it is the identical column sub-wavelength micro structure transmission-type grating of height, and raster unit is in periodic arrangement in two orthogonal directions.Each raster unit includes multiple subelements, and different subelement width are equal but medium duty ratio is different.It is provided by the utility model two dimension binary blazed grating, grating flute profile be etc. height diadactic structure, can by the single steps exposure method such as electron beam exposure or laser direct-writing be made, compared to ideal pattern sawteeth groove production be easier to；Also there is the diffraction characteristic of high-diffraction efficiency and low polarization sensitivity, and the grating type imaging spectrometer in reference wave strong point no polarization, suitable for high s/n ratio and high actinometry required precision simultaneously.
Description
Technical field
The utility model relates to a kind of low degree of polarization two dimension binary glitterings of transmission-type suitable for grating type imaging spectrometer
Grating belongs to diffraction optical element and spectral imaging technology field.
Background technique
The eighties in last century, with the development need that earth observation is applied, imaging spectral technology rises.It is to combine sky
Between imaging technique and spectral imaging technology emerging field, greatly widened people space remote sensing field, agricultural resource visit
It surveys, the application range of mineral resources and geological prospecting, military detecting, biologic medical etc..
Core element of the diffraction grating as grating type imaging spectrometer, its performance directly affect spectrometer system
Energy.The grating of high-diffraction efficiency can effectively improve system signal noise ratio, to improve detectivity.The grating of low polarization sensitivity
It can reduce spectrometer polarization sensitivity, to improve detection accuracy.Zigzag balzed grating, can get Gao Yan in specific level
Efficiency is penetrated, but it is polarization-sensitive element, and the sawteeth groove of ideal pattern is difficult production.
Zigzag balzed grating, can be equivalent by binary blazed grating, and the binary blazed grating of suitable shape has low polarization
The diffraction characteristic of degree.Binary blazed grating is by a series of consistent one-dimensional barcode of height or two-dimentional cylindricality sub-wavelength feature micro-structure
Composition, can admirably be equivalent to zigzag balzed grating, and such diadactic structure utilizes the works such as laser direct-writing or electron beam lithography
Skill is easy to manufacture.
In the binary blazed grating of existing literature report, mostly Polarization-Sensitive one-dimensional binary balzed grating, and do not make
For diffraction element use.Such as document " Artificial distributed-index media fabricated by zero-
Order gratings " (Stork W, Streibl N, Haidner H, et al. [J] Optics Letters,
1991,16 (24): 1921-3.), " Artificial index surface relief diffraction optical
Elements " (Babin S V, Sheridan J T. [C] // Proceedings of SPIE, 1993,1751:202-
213.) it is used as the one-dimensional binary balzed grating, of anti-reflection layer in.Also there is the relevant report of two-dimentional binary blazed grating, but do not make
For diffraction element use.Such as document " Binary blazed grating-based polarization-independent
Filter on silicon on insulator " (Wu D, Sui X, Yang J, Zhou Z. [J] Frontiers
Of Optoelectronics, 2012,5 (1): 78-81.) in be used as high reflectance resonance filter two-dimentional binary glittering
Grating.
Up to now, the low degree of polarization binary blazed grating and its design method report of imaging spectrometer are had no.For into
One step improves the performance of grating type imaging spectrometer, especially detectivity and detection accuracy, needs to design high diffraction effect
Rate, low polarization sensitivity and balzed grating, easy to manufacture.
Summary of the invention
The utility model is in view of the deficienciess of the prior art, provide a kind of with high-diffraction efficiency, low polarization sensitivity
And transmission-type two dimension binary blazed grating easy to manufacture, for reducing grating type imaging spectrometer polarization sensitivity to improve its spy
Survey precision.
To realize foregoing invention, the utility model provides a kind of low degree of polarization two dimension binary blazed grating, it is height
Identical column sub-wavelength micro structure transmission-type grating along line of rabbet joint direction y and the orthogonal to that direction x, is being in periodically respectively
Arrangement raster unit, the screen periods in the direction y are less than incident wavelength, and the screen periods in the direction x are greater than incident wavelength；Each grating
Unit includes several subelements, the equal length in the direction each subelement x, and is less than incident wavelength；Each subelement equivalent refraction
Raten(m) meet condition:
,
Wherein,n 1For air refraction,n 2For grating layer dielectric material refractive index,mFor subelement ordinal number, MFor a light
Subelement number in grid unit；
Column sub-wavelength micro structure in each subelement,f x (m)Withf y (m)With subelement ordinal numbermIt is sequentially increased, it is described
'sf x (m)、f y (m)The dielectric material duty ratio of respectively each subelement x and the direction y.
Two dimension binary blazed grating provided by the utility model, Preferable scheme is that: a raster unit is included
Subelement number is 4~10.
Compared with prior art, the protrusion effect of the utility model is:
1. two dimension binary blazed grating provided by the utility model, the diffraction with low polarization sensitivity and high-diffraction efficiency
Characteristic, and in reference wave strong point no polarization, the polarization sensitivity of grating type imaging spectrometer is advantageously reduced, to improve detection
Precision.
2. grating flute profile be etc. height diadactic structure, can pass through the single steps such as electron beam exposure or laser direct-writing expose legal system
, the sawteeth groove production compared to ideal pattern is easier to.
Detailed description of the invention
Fig. 1 is the bathtub construction schematic top plan view of two-dimentional binary blazed grating provided by the embodiment of the utility model；
Fig. 2 is the vertical view signal of some raster unit in two-dimentional binary blazed grating provided by the embodiment of the utility model
Figure；
Fig. 3 is the side view signal of some raster unit in two-dimentional binary blazed grating provided by the embodiment of the utility model
Figure；
Fig. 4 is the principle that two-dimentional binary blazed grating provided by the embodiment of the utility model is equivalent to zigzag balzed grating,
Flow diagram；
Fig. 5 is the schematic top plan view of some subelement in two-dimentional binary blazed grating provided by the embodiment of the utility model
Figure；
Fig. 6 is the three dimensional structure diagram of two-dimentional binary blazed grating provided by the embodiment of the utility model；
Fig. 7 is the diffraction efficiency curve of two-dimentional binary blazed grating provided by the embodiment of the utility model.
In figure: 1. raster units；2. the first column sub-wavelength micro structure；3. the second column sub-wavelength micro structure；4. third
Column sub-wavelength micro structure；5. the 4th column sub-wavelength micro structure；6. the 5th column sub-wavelength micro structure；7. the 6th column Asia wave
Long micro-structure；8. the first subelement；9. the second subelement；10. third subelement；11. the 4th subelement；12. the 5th subelement；
13. the 6th subelement；14. the 7th subelement.
Specific embodiment
Technical solutions of the utility model are further described with reference to the accompanying drawings and examples.
Embodiment 1
The present embodiment provides a kind of low degree of polarization two dimension binary blazed gratings, for reducing the inclined of grating type imaging spectrometer
Shake susceptibility, to improve its detection accuracy.
Referring to attached drawing 1,2 and 3, they are respectively the bathtub construction vertical view of two-dimentional binary blazed grating provided in this embodiment
The schematic side view and schematic top plan view of schematic diagram, some raster unit；In Fig. 1, y is along line of rabbet joint direction, and the direction x and y are just
It hands over, raster unit 1 is in periodic arrangement in two orthogonal directions of x and y, and the direction x screen periods are T, and the direction y screen periods ared y；From Figure 2 it can be seen that a raster unit provided in this embodiment includes 7 subelements, it is followed successively by the first subelement 8, the second son
Unit 9, third subelement 10, the 4th subelement 11, the 5th subelement 12, the 6th subelement 13 and the 7th subelement 14；Each
The width in the direction subelement x and y is respectivelyd xWithd y, (d yNamely the screen periods in the direction y)；Without medium material in first subelement 8
Material, the last one subelement 14 is interior to be full of dielectric material；As seen from Figure 3, raster unit provided in this embodiment, in grating substrate
Include the identical column sub-wavelength structure of 6 height on 15, respectively is the first column sub-wavelength micro structure 2, the second column
Sub-wavelength micro structure 3, third column sub-wavelength micro structure 4, the 4th column sub-wavelength micro structure 5, the 5th micro- knot of column sub-wavelength of
Structure 6 and the 6th column sub-wavelength micro structure 7.
Referring to attached drawing 4, the principle of zigzag balzed grating, is equivalent to for two-dimentional binary blazed grating provided in this embodiment
Flow diagram, Fig. 4 (a) be zigzag balzed grating, flute profile, the light of normal incidence after grating slot phase change amount be Φ=
2π(n 2-n 1)h/λ, whereinn 2For VPG medium Refractive Index of Material,n 1For air refraction,hIt is high for the position of light incidence groove face
Degree, λ is incident wavelength.In a screen periods, incident ray phase change amount Φ π from 0 to 2 linearly becomes balzed grating,
Change, this except throughhOutside the sawteeth groove of linear change is realized, the rectangular channel that can also pass through refractive index linear change in slot is real
Existing, such as Fig. 4 (b), rectangle groove height is identical as serrated slot apex height.The periodic arrangement of structure shown in Fig. 4 (b) is in technique
It is difficult realization, the achievable structure proximate of technique need to be used.Specifically, the raster unit of refractive index consecutive variations is discrete to have
The subelement for limiting a homogeneous refractive index, such as Fig. 4 (c), subelement refractive indexn(m) meet following formula (1):
(1)
WhereinMFor discrete subelement number,mFor subelement ordinal number, different subelement refractive index fromn 1It arrivesn 2Linear change；
Using again by EFFECTIVE MEDIUM THEORY, but column sub-wavelength binary knot that duty ratio different identical with each subelement medium refraction index
Structure is equivalent, such as Fig. 4 (d), solves dielectric material duty ratio in each subelement, realizes the equivalent refractive index and formula of each subelement
(1) corresponding.In this way, zigzag balzed grating, shown in Fig. 4 (a) can the binary blazed grating as shown in Fig. 4 (d) it is equivalent.
Referring to attached drawing 5, for a subelement top view of two-dimentional binary blazed grating provided in this embodiment.Column structure
Refractive Index of Material isn 2, ambient enviroment refractive index isn 1, the subelement where it can be equivalent to uniformly by column sub-wavelength structure
Medium, equivalent refractive index and column sub-wavelength structure are in two orthogonal direction duty ratiosf xWithf yIt is related, adjustmentf xWithf yValue
Can get arbitrarily fromn 1Extremelyn 2Equivalent refractive index, in the present embodiment, discrete subelement numberMIt is 7, subelement ordinal numbermRespectively
It is followed successively by positive integer 1~7, the equivalent folding of subelement can be made by adjusting the dielectric material duty ratio of each subelement cylindrical structure
Penetrate raten(m) meet the condition of formula (1):
(1)
And equivalent refractive index is also related with the polarization state of incident light, TE polarization state equivalent refractive indexn eTE With TM polarization state
Equivalent refractive index n eTM Meet formula (2) and formula (3) respectively.It can be by adjustingf xWithf yIt controls simultaneouslyn eTE Withn eTM , and exist
Suitablyf xWithf y, maken eTE =n eTM , such grating is no polarization.
Formula (2) is as follows:
(2)
WhereinMeet
,
Formula (3) is as follows:
(3)
WhereinMeet
；
In the present embodiment, each subelement x and the direction y width are respectivelyd x=472.9nm,d y=473nm；Grating layer is situated between
Material and base material are silica, and refractive index isn 2=1.46, grating upper layer is covered as air, and refractive index isn 1=1。
Grating depth H=1.2 μm, each subelement equivalent refractive index meet formula (1) andn eTE =n eTM , each column sub-wavelength structure duty
Than meeting formula (2) and (3), the reference wavelength of groove design is 0.7 μm.For each subelement, all meetn eTE (m)=n eTM (m), therefore the grating is effect free of birefringence, grating slot is unrelated with polarization to the Spatial transmission of transmitted light, thus real
Referring now to the diffraction characteristic of no polarization at wavelength.
Table 1 is each subelement cylindrical sub-wavelength structure of two-dimentional binary blazed grating provided by the embodiment of the utility model
Duty ratio and corresponding subelement equivalent refractive index value.
Table 1
| Subelement | f x | f y | n eTE | n eTM |
| 1 | 0 | 0 | 1.000 | 1.000 |
| 2 | 0.502 | 0.301 | 1.077 | 1.077 |
| 3 | 0.595 | 0.497 | 1.153 | 1.152 |
| 4 | 0.712 | 0.651 | 1.230 | 1.231 |
| 5 | 0.822 | 0.795 | 1.307 | 1.307 |
| 6 | 0.921 | 0.918 | 1.383 | 1.383 |
| 7 | 1 | 1 | 1.460 | 1.460 |
Seen from table 1, in a raster unit provided by the utility model, each subelement cylindrical structure height phase
Together, the dielectric material duty ratio in the direction x and yf xWithf yDifference, and be sequentially increased with subelement ordinal number；Nothing in first subelement
Dielectric material, the last one subelement is interior to be full of dielectric material.
Fig. 6 show the three dimensional structure diagram of two-dimentional binary blazed grating provided by the embodiment of the utility model, flute profile
Structure is corresponding with data in table 1.
Fig. 7 is the diffraction efficiency curve of two-dimentional binary blazed grating provided by the embodiment of the utility model.In reference wavelength
TE and TM polarization state diffraction efficiency is respectively 79.5% and 79.6% at 0.7 μm, and polarization sensitivity is only 0.06%, be can be ignored.0.6μ
TE and TM polarization state diffraction efficiency is above 70% in the mu m waveband of m~0.8, and polarization sensitivity is only larger at wave band both ends, maximum
Value is 2.8%.The two dimension binary blazed grating has low polarization sensitivity and high-diffraction efficiency, is suitable for high s/n ratio and high spoke
Penetrate the grating type imaging spectrometer of measurement accuracy requirement.
Most energy of incident light can be concentrated in a certain order of diffraction by balzed grating, greatly improve spreading out for grating
Penetrate efficiency.The raster unit of two dimension binary blazed grating provided by the utility model is in two orthogonal directions of x and y in periodically row
Cloth, each raster unit include multiple subelements, and each subelement width is equal and is less than lambda1-wavelength, in different subelements
Column structure shape it is different.When each column structure is designed as suitable shape, two-dimentional binary blazed grating can be fabulous etc.
Effect is zigzag balzed grating, and has the diffraction characteristic of low polarization sensitivity and high-diffraction efficiency.Due also to this is practical new
The two-dimentional binary blazed grating flute profile that type provides such as is at the diadactic structure of height, and it is single can to pass through electron beam exposure or laser direct-writing etc.
It walks exposure method to be made, the sawteeth groove compared to ideal pattern is more easy to manufacture.
Claims (2)
1. a kind of low degree of polarization two dimension binary blazed grating, it is characterised in that: it is the identical column sub-wavelength micro structure of height
Transmission-type grating is in periodic arrangement raster unit (1) respectively along line of rabbet joint direction y and the orthogonal to that direction x, the direction y
Screen periods are less than incident wavelength, and the screen periods in the direction x are greater than incident wavelength；Each raster unit includes several height lists
Member, the equal length in the direction each subelement x, and it is less than incident wavelength；Each subelement equivalent refractive indexn(m) meet condition:
,
Wherein,n 1For air refraction,n 2For grating layer dielectric material refractive index,mFor subelement ordinal number, MFor a grating list
Subelement number in member；
Column sub-wavelength micro structure in each subelement,f x (m)Withf y (m)With subelement ordinal numbermIt is sequentially increased, it is describedf x (m)、f y (m)The dielectric material duty ratio of respectively each subelement x and the direction y.
2. two dimension binary blazed grating according to claim 1, it is characterised in that: the son that a raster unit is included is single
First number is 4~10.
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