CN110764174B - Dielectric grating narrow-band filter and manufacturing method thereof - Google Patents
Dielectric grating narrow-band filter and manufacturing method thereof Download PDFInfo
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Abstract
The invention provides a medium grating narrow-band filter, which is formed by arranging gratings with special sizes at intervals of a specific distance in the direction vertical to the plane of the gratings, and a plurality of reflecting cavities formed by the gratings are used for narrow-band filtering; when the narrow-band filter is used, light is emitted from the upper part of the filter at a certain angle and is emitted from the bottom after being filtered by the multiple layers of gratings, so that the filtering operation is realized. The invention also comprises a manufacturing method of the narrow-band filter, the transmission center wavelength and the center angle can be adjusted in the working waveband, the thickness of the designed device is in the sub-wavelength order, and the defects of large volume and mass and high preparation difficulty of the existing narrow-band filter are overcome. Meanwhile, the filter has extremely high reflectivity, and the interference of noise signals is greatly reduced; the dislocation along the periodic direction among the gratings is adjusted, so that the transmission peaks show different symmetries and different sensitivities are obtained along different directions; and the characteristics of multi-channel output, flat-top band response and the like can be obtained by a cascading method.
Description
Technical Field
The invention relates to the technical field of micro-nano optics and spectroscopy, in particular to a dielectric grating narrow-band filter and a manufacturing method thereof.
Background
In the conventional optical filtering technology represented by an optical film or a one-dimensional photonic crystal, dozens of layers of films need to be cascaded when complex spectral characteristics (such as broadband high reflection, full-angle high reflection, broadband narrow-angle transmission and narrow-frequency narrow-angle transmission) are realized, and the thickness of the film is accurately controlled to be 1/4 of the wavelength in a medium, which brings great challenges to the preparation of the film and the integration of devices. When the traditional thin film optical device realizes narrow-band transmission filtering, the size is large, the preparation difficulty is high, and the application of the filtering technology in the fields of national defense, aerospace, biomedical treatment and the like is seriously hindered.
Disclosure of Invention
The invention provides a dielectric grating narrow-band filter for overcoming the technical defects of large volume and high preparation difficulty when the traditional thin-film optical device realizes narrow-band transmission filtering.
The invention also provides a manufacture method of the medium grating narrow-band filter.
In order to solve the technical problems, the technical scheme of the invention is as follows:
a medium grating narrow-band filter is formed by arranging gratings with special sizes at intervals of a specific distance in a direction vertical to a grating plane, and a plurality of reflecting cavities formed by the gratings are used for narrow-band filtering; the special size means that the height and the period of the grating are smaller than the working wavelength of the filter; the specific distance refers to the spacing distance between the gratings, wherein Fabry-Perot interference can occur and the near-field coupling effect is ignored; when the narrow-band filter is used, light is emitted from the upper part of the filter at a certain angle and is emitted from the bottom after being filtered by the multiple layers of gratings, so that the filtering operation is realized.
More specifically, each grating itself serves as a high-reflection mirror, and a reflection cavity formed by the two high-reflection mirrors independently realizes filtering or is cascaded with reflection cavities formed by other gratings or gratings to output different required spectral lines.
More specifically, the filter is directly placed in the air or wrapped by using SU-8 photoresist as a supporting material, and the air or SU-8 photoresist is used as an environmental material.
More specifically, the grating is made of high-refractive index materials including titanium dioxide, silicon, germanium, gallium arsenide, indium phosphide or silicon-rich silicon nitride; the environment material adopts low refractive index material comprising air, water, silicon dioxide or SU-8 photoresist.
In the above scheme, the narrow-band filter structure provided by the invention has the characteristics of narrow-band filtering, narrow-angle filtering or narrow-band narrow-angle filtering; the whole structure can be suspended in the air, or can be wrapped by support materials such as SU-8 photoresist and the like, and the air and the SU-8 photoresist are environmental materials at the moment. The grating is made of a medium material with a high refractive index, and the environment material is made of a medium with a low refractive index. The obtained narrow-band filter realizes the adjustability of the transmission center wavelength and the center angle in the working waveband, theoretically, the transmission wavelength bandwidth can reach sub-nanometer, the transmission angle bandwidth can reach sub-milliradian magnitude, the transmissivity can reach 100%, the thickness of the designed device is of the sub-wavelength magnitude, and the defects of large volume and mass and high preparation difficulty of the conventional narrow-band filter are overcome.
In the scheme, the filter has extremely high reflectivity in a broadband full-angle range except for a transmission center, so that the interference of noise signals is greatly reduced; by adjusting dislocation between the gratings along the periodic direction, the transmission peaks can present different symmetries, so that different sensitivities can be obtained along different directions; and the characteristics of multi-channel output, flat-top band response and the like can be obtained by a cascading method. The optical interconnection network has the characteristics of small volume, light weight, high sensitivity, flat-top passband and the like, so that the requirements of the application of the optical interconnection network can be met; or can be used for improving the communication signal-to-noise ratio and missile induced bias interference resistance.
A method for manufacturing a dielectric grating narrow-band filter comprises the following steps:
s1: selecting a grating according to the required transmission wave band, the transmissivity, the symmetry of the transmission peak and whether the flat-top band response is required;
s2: adjusting the thickness of each layer of grating according to the required transmission center wavelength and/or center angle;
s3: further adjusting the spacing between the gratings according to the desired transmission center wavelength and/or center angle;
s4: judging whether flat-top-band response is needed, if so, enabling a primary reflection cavity formed by two gratings to be equivalent to a reflector, cascading with another primary reflection cavity or a grating, realizing the flat-top-band response by adjusting the spacing distance, and executing the step S6; if not, go to step S5;
s5: judging whether a symmetrical transmission peak is needed, if so, adjusting dislocation between the upper grating and the lower grating to realize the symmetrical transmission peak, and executing the step S6; if not, directly executing the step S6;
s6: different magnitudes of transmittance are achieved by adjusting the spacing between the gratings according to the desired transmittance.
In step S1, according to the required transmission band, transmittance, symmetry of transmission peak, and whether a flat-topped rectangular peak is required, the single-layer grating is placed in a working environment with a broadband high-reflection band or an angle range, so that the single-layer grating operates in a dual-mode region and only 0-order diffraction exists, and the duty ratio and the thickness range of the grating can be determined, thereby completing the selection of the grating.
The high transmission center wavelength and center angle, transmission bandwidth, transmittance, symmetry of transmission peak and flat top bandwidth index of the transmission peak of the narrow-band filter are determined by parameters of device materials of the filter, geometric thickness, period, duty ratio, cascade layer number and spacing distance of the grating and dislocation among different layers.
In the scheme, the narrow-band filter can be prepared by combining a plasma chemical vapor deposition method with electron beam exposure and an inductively coupled plasma etching technology; for suspended structures, wet selective chemical etching and CO are applied2Critical point drying techniques.
Compared with the prior art, the technical scheme of the invention has the beneficial effects that:
the medium grating narrow-band filter and the manufacturing method thereof provided by the invention realize the transmission center wavelength and the center angle adjustability in the working waveband, the thickness of the designed device is in the sub-wavelength order, and the defects of large volume and mass and high preparation difficulty of the existing narrow-band filter are overcome. Meanwhile, the filter has extremely high reflectivity, and the interference of noise signals is greatly reduced; by adjusting dislocation between the gratings along the periodic direction, the transmission peaks can present different symmetries, so that different sensitivities can be obtained along different directions; and the characteristics of multi-channel output, flat-top band response and the like can be obtained by a cascading method.
Drawings
FIG. 1 is a schematic diagram of a dielectric grating narrow-band filter;
FIG. 2 is a flow chart of a method for fabricating a dielectric grating narrow-band filter;
FIG. 3 is a diagram of the transmission wavelength spectrum, TM polarization, of a narrow band filter consisting of two silicon dielectric gratings;
FIG. 4 is a diagram of the transmission wavelength spectrum, TE polarization, of a narrow-band filter consisting of two silicon dielectric gratings;
FIG. 5 is a transmission angle spectrum of a narrow angle filter consisting of two silicon dielectric gratings;
FIG. 6 is a spectrum of transmission wavelength versus angle for a narrow-band narrow-angle filter composed of two silicon dielectric gratings;
FIG. 7 is a transmission wavelength spectrum of a flat-top band narrow angle filter formed by two cascaded primary reflective cavities;
FIG. 8 is a spectrum of transmission wavelengths of a narrow band filter consisting of two silicon dielectric gratings, showing linear coordinate transmission;
FIG. 9 is a spectrum of transmission wavelengths of a narrow band filter consisting of two silicon dielectric gratings, showing logarithmic transmission;
FIG. 10 is a transmission wavelength spectrum of a spectral line asymmetric narrow-band filter composed of an upper silicon medium grating and a lower silicon medium grating which are staggered in the period direction;
FIG. 11 is a schematic diagram of the structure of a dislocation grating;
FIG. 12 is a transmission wavelength spectrum of a two-channel narrow-band filter composed of two silicon dielectric gratings;
FIG. 13 is a spectrum of transmitted wavelength versus angle for a narrow band narrow angle filter with a center angle of 15.5 ° consisting of two silicon dielectric gratings;
FIG. 14 is a spectrum of transmitted wavelength versus angle for a narrow band narrow angle filter with a center angle of 65.5 ° consisting of two silicon dielectric gratings;
FIG. 15 is a spectrum of transmission wavelength versus angle for a narrow-band narrow-angle filter composed of two germanium dielectric gratings;
fig. 16 is a transmission angle spectrum of a narrow angle filter consisting of two titanium dioxide dielectric gratings.
Detailed Description
The drawings are for illustrative purposes only and are not to be construed as limiting the patent;
for the purpose of better illustrating the embodiments, certain features of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product;
it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
The technical solution of the present invention is further described below with reference to the accompanying drawings and examples.
Example 1
As shown in fig. 1, a dielectric grating narrow-band filter is formed by arranging gratings with special sizes at certain intervals in a direction perpendicular to the plane of the gratings, and a plurality of reflection cavities formed by the gratings perform narrow-band filtering; the special size means that the height t and the period lambada of the grating are smaller than the working wavelength lambada of the filter; the specific distance refers to an interval distance ts between the gratings, wherein Fabry-Perot interference can occur and the near-field coupling effect is ignored; when the narrow-band filter is used, light is emitted from the upper part of the filter at a certain angle and is emitted from the bottom after being filtered by the multiple layers of gratings, so that the filtering operation is realized.
More specifically, each grating is used as a high-reflection mirror, and a reflection cavity formed by the two high-reflection mirrors realizes independent filtering or cascade output of different spectral lines required by the reflection cavity formed by other gratings or gratings.
More specifically, the filter is directly placed in the air or wrapped by using SU-8 photoresist as a supporting material, and the air or SU-8 photoresist is used as an environmental material.
More specifically, the grating is made of high-refractive-index materials including titanium dioxide, silicon, germanium, gallium arsenide, indium phosphide or silicon-rich silicon nitride; the environment material adopts low refractive index material comprising air, water, silicon dioxide or SU-8 photoresist.
In the specific implementation process, various filter characteristics are obtained by combining the gratings step by step, and the refractive index of the material of the grating is ngThe period, duty cycle (grating width divided by grating period), thickness, and interval between gratings from top to bottom are respectively represented by Λi、dci、ti、tsi(i＝1,2,...n)。
In a specific implementation process, the narrow-band filter structure provided by the invention has the characteristics of narrow-band filtering, narrow-angle filtering or narrow-band narrow-angle filtering; the whole structure can be suspended in the air, or can be wrapped by support materials such as SU-8 photoresist and the like, and the air and the SU-8 photoresist are environmental materials at the moment. The grating is made of a medium material with a high refractive index, and the environment material is made of a medium with a low refractive index. The obtained narrow-band filter realizes the adjustability of the transmission center wavelength and the center angle in the working waveband, theoretically, the transmission wavelength bandwidth can reach sub-nanometer, the transmission angle bandwidth can reach sub-milliradian magnitude, the transmissivity can reach 100%, the thickness of the designed device is of the sub-wavelength magnitude, and the defects of large volume and mass and high preparation difficulty of the conventional narrow-band filter are overcome.
In the specific implementation process, the filter has extremely high reflectivity in a broadband full-angle range except for a transmission center, so that the interference of noise signals is greatly reduced; by adjusting dislocation between the gratings along the period direction, the transmission peaks can present different symmetries, so that different sensitivities can be obtained along different directions; and the characteristics of multi-channel output, flat-top band response and the like can be obtained by a cascading method. The optical interconnection network has the characteristics of small volume, light weight, high sensitivity, flat-top passband and the like, so that the requirements of the application of the optical interconnection network can be met; or can be used for improving the communication signal-to-noise ratio and resisting missile-induced interference.
In the specific implementation process, a typical dielectric grating, such as a rectangular grating, is formed by arranging rectangular dielectric columns at equal intervals along the period direction. Considering each rectangular column as a waveguide, the mode dispersion relation, the reflectivity and the transmissivity of the grating and the electromagnetic field distribution can be solved by adopting a waveguide array mode expansion method. Wide (frequency, angle) band high reflectivity characteristics can generally be obtained when there is only 0 order diffraction within the bimodal region and the grating. The narrow-band filter composed of the high-reflection medium grating can realize a sharp transmission peak with a high quality factor and a low side band; the filtering can be realized on the wavelength, the angle or both simultaneously; the material and the geometric thickness are properly selected, and the central wavelength and the central angle of the transmission peak can be controlled or the bandwidth of the transmission peak can be adjusted to adapt to different requirements. Through multi-grating cascade, the characteristics of multi-channel filtering and flat-top-band response can be further realized.
In the specific implementation process, the invention provides the medium of narrow-band filtering, narrow-angle filtering or narrow-band narrow-angle filtering characteristicsThe mass grating narrow-band filter is obtained according to the Fabry-Perot interference principle: according to the Fabry-Perot interference condition, calculating the reflectivity R of an interference cavity formed by upper and lower high-reflectivity mirrorsFPThe calculation formula is as follows:
wherein R is1、R2The reflectivity of the upper and lower highly reflective mirrors is,
δ is the phase of the light propagating through the intermediate layer (from one end to the other end). At this time, the upper and lower high-reflection mirrors can be single gratings or reflecting cavities formed by the gratings. When R is1＝2And is provided with
(k is an integer) the reflectivity of the interference cavity is zero and the corresponding transmission is 100% without absorption. And this condition is typically satisfied only at a particular wavelength or angle. If the end mirror constituting the cavity has high reflectivity in a wide (frequency, angle) band, a high transmission narrow band spectrum can be obtained in the high reflection of the wide (frequency, angle) band.
Example 2
More specifically, on the basis of embodiment 1, as shown in fig. 2, a method for manufacturing a dielectric grating narrow-band filter includes the following steps:
s1: selecting a grating according to the required transmission wave band, the transmissivity, the symmetry of the transmission peak and whether the flat-top band response is required;
s2: adjusting the thickness of each layer of grating according to the required transmission center wavelength and/or center angle;
s3: further adjusting the spacing between the gratings according to the desired transmission center wavelength and/or center angle;
s4: judging whether flat-top-band response is needed, if so, enabling a primary reflection cavity formed by two gratings to be equivalent to a reflector, cascading with another primary reflection cavity or a grating, realizing the flat-top-band response by adjusting the spacing distance, and executing the step S6; if not, go to step S5;
s5: judging whether a symmetrical transmission peak is needed, if so, adjusting dislocation between the upper grating and the lower grating to realize the symmetrical transmission peak, and executing the step S6; if not, directly executing the step S6;
s6: different magnitudes of transmittance are achieved by adjusting the spacing between the gratings according to the desired transmittance.
More specifically, in step S1, according to the required transmission waveband, transmittance, symmetry of the transmission peak, and whether a flat-top rectangular peak is required, the single-layer grating is placed in a working environment with a broadband high-reflection waveband or an angle range, so as to ensure that the single-layer grating operates in a dual-mode region and only 0-order diffraction exists, and thus the duty ratio and the thickness range of the grating can be determined, and the selection of the grating is completed.
More specifically, the high transmission center wavelength and center angle, transmission bandwidth, transmittance, symmetry of transmission peak, and flat top bandwidth index of transmission peak of the narrow-band filter are determined by parameters of device materials of the filter, geometric thickness, period, duty ratio of grating, number of cascade layers of grating, spacing distance, and dislocation between different layers.
In the specific implementation process, the narrow-band filter can be prepared by combining a plasma chemical vapor deposition method with an electron beam exposure and inductively coupled plasma etching technology; for suspended structures, wet selective chemical etching and CO are applied2Critical point drying techniques.
Example 3
In a specific implementation process, on the basis of embodiment 1, the structure of the dielectric grating narrow-band filter is formed by arranging single gratings at a specific distance in a vertical direction. Polarized light is emitted from the upper part and is in the same plane with the x-axis and the z-axis, and the included angle of the light beam and the z-axis is an incident angle theta; defining the vibration direction of the magnetic field as TM polarization along the y axis, and defining the vibration direction of the electric field as TE polarization along the y axis; the transmission wavelength spectrum of the narrow-band filter composed of the dielectric grating is obtained as shown in FIG. 3, and the filter can realize high transmission (calculated transmittance) at narrow frequencyUp to 100%), the working band is around 1550nm, and TM light is normally incident; selecting a grating material as Si (the refractive index is 3.48), and selecting an environment material as air; the structural parameters are as follows: lambda 620nm, dc 0.58, t1＝t2＝360nm，ts1＝775nm。
Example 4
In the specific implementation process, on the basis of embodiment 1, as shown in fig. 4, by using the transmission wavelength spectrum of the narrow-band filter composed of the dielectric grating, the filter can realize narrow-band high transmission (the calculated transmittance reaches 100%), at this time, the working wavelength band is around 1550nm, and TE light is normally incident; selecting a grating material as Si (the refractive index is 3.48), and selecting an environment material as air; the structural parameters are as follows: Λ 1032nm, dc 0.42, t1＝t2＝227nm，ts1＝1135nm。
Example 5
In the implementation process, the transmission angle spectrum of the narrow-angle filter composed of two silicon dielectric gratings as shown in fig. 5 is obtained, and the filter can realize high transmission at a narrow angle (the calculated transmission rate reaches 99.98%). The working wavelength is 1550nm, the high-transmittance central angle is 32.5 degrees, and TM light is incident at a full angle; selecting Si (the refractive index is 3.48); the structural parameters are as follows: lambda is 600nm, dc is 0.70, t1＝210nm，t2＝330nm，ts1＝742nm。
Example 6
In the specific implementation process, the transmission wavelength-angle spectrum of the narrow-frequency narrow-angle filter composed of two silicon dielectric gratings as shown in fig. 6 is obtained, the filter can realize high transmission (the calculated transmission rate reaches 99.99%) at a narrow frequency and a narrow angle, and the environment material is air. The working wave band takes 1550nm as the center and is 200nm wide; the high-transmittance central angle is 45 degrees, and the central wavelength is 1550 nm; TM light is incident at all angles; selecting a grating material as Si (the refractive index is 3.48); the structural parameters are as follows: 568nm for Λ, 0.58 for dc, t1＝455nm，t2＝568nm，ts1＝568nm。
Example 7
In the implementation, two primary reflective cavities (each composed of two gratings) are shown in FIG. 7) The transmission wavelength spectrum of the flat-top band narrow-band filter formed by cascading can be calculated to obtain that the peak transmissivity of the filter reaches 100%, and the flat-top pass-band width of the filter is about 2nm, wherein the transmissivity of the filter is higher than 99%. The working waveband at the moment is around 1550nm (1540 nm-1560 nm), TM light is incident at a full angle, the high-transmittance central angle is 44 degrees, and the central wavelength is 1550 nm; selecting a grating material as Si (with the refractive index of 3.48) and an environment material as air; the structural parameters are as follows: lambda is 567nm, dc is 0.58, t1＝t3＝454nm，t2＝t4＝567nm，ts1＝ts3＝567nm，ts2＝1146nm。
Example 8
In the specific implementation process, as the transmission wavelength spectrum of the line symmetric narrow-band filter composed of the dielectric grating shown in fig. 8 and fig. 9, the symmetry of the narrow-band transmission line can be clearly seen. The working wavelength is 1550nm, and TM light is incident at 45 degrees; selecting a grating material as Si (the refractive index is 3.48), and selecting an environment material as air; the structural parameters are as follows: lambda 535nm, dc 0.74, t1＝369nm，t2＝541nm，ts1＝460nm。
Example 9
In the specific implementation process, the transmission wavelength spectrum of the spectral line asymmetric narrow-band filter composed of the upper grating and the lower grating which are staggered in the period direction as shown in fig. 10 and the structure of the dislocation grating as shown in fig. 11 have the dislocation amplitude of 0.1 Λ, and the asymmetry of the spectral line can be easily seen by adopting the transmission of logarithmic coordinates. The working wavelength is 1550nm, and TM light is incident at an angle of 45 degrees; selecting a grating material as Si (the refractive index is 3.48), and selecting an environment material as air; the structural parameters are as follows: 537nm for Λ, 0.74 for dc, t1＝370nm，t2＝542nm，ts1462 nm. The upper grating is displaced by 54nm in the periodic direction relative to the lower grating.
Example 10
In the implementation, the transmission wavelength spectrum of the dual-channel narrow-band filter composed of the dielectric grating shown in fig. 12 shows two transmission center wavelengths of 1405nm and 1565nm (calculated peak transmission is 100%). The working waveband at the moment is a communication waveband (1260 nm-1)660nm), normal incidence of TM light; selecting a grating material as Si (the refractive index is 3.48), and selecting an environment material as air; the structural parameters are as follows: Λ 747nm, dc 0.76, t1＝t2＝463nm，ts1＝1060nm。
Example 11
In the specific implementation process, as shown in fig. 13, the transmission wavelength-angle spectrum of the narrow-band narrow-angle filter composed of dielectric gratings and having a center angle of 15.5 ° is obtained, and the filter can realize high transmission at a narrow frequency and a narrow angle (the calculated transmission rate reaches 100%). Working in a communication band (1510nm-1630nm) at the moment, wherein the center wavelength is 1550 nm; TM light is incident at a full angle; selecting a grating material as Si (the refractive index is 3.48), and selecting an environment material as air; the structural parameters are as follows: 764nm, dc 0.58, t1＝534nm，t2＝458nm，ts1＝916nm。
Example 12
In a specific implementation, the transmission wavelength-angle spectrum of a narrow-band narrow-angle filter with a center angle of 65.5 ° composed of dielectric gratings as shown in fig. 14. High transmission at narrow frequency and narrow angle (calculated transmission up to 100%) can be achieved. Working in a communication wave band (1520nm-1580nm) with the central wavelength of 1550 nm; TM light is incident at a full angle; selecting a grating material as Si (the refractive index is 3.48), and selecting an environment material as air; the structural parameters are as follows: Λ 543nm, dc 0.58, t1＝380nm，t2＝326nm，ts1＝760nm。
Example 13
In a specific implementation, the transmission wavelength-angle spectrum of a narrow-band narrow-angle filter composed of dielectric gratings as shown in fig. 15. The obtained filter can realize high transmission at narrow frequency and narrow angle (the calculated transmission rate reaches 100%). The working wave band is middle infrared (9.8-11.4 μm), the high-transmittance central angle is 39 degrees, and the central wavelength is 10.6 um; TM light is incident at a full angle; selecting a grating material Ge (refractive index of 4.0), and an environment material air; the structural parameters are as follows: Λ 3.57 μm, dc 0.70, t1＝2.32μm，t2＝3.03μm，ts1＝3.93μm。
Example 14
In one embodiment, a narrow angle filter composed of dielectric gratings as shown in FIG. 16The transmission angle spectrum of the wave filter is obtained, and the filter can realize sub-milliradian narrow-angle high transmission (the half-height width of the transmission peak is calculated to be 0.3 milliradian, and the transmission rate reaches 99.98%). The operating wavelength at this time was 480.0nm, the high transmission center angle was 800.1mrad (45.84 °), TM light was incident, and the incident angle range was 45 ° (786mrad) to 46.75 ° (816 mrad); selecting high-laser damage threshold TiO2 with the refractive index of 2.5 as a grating material, and selecting air as an environment material; the structural parameters are as follows: lambda 239.9nm, dc 0.56, t1＝t2＝333.4nm，ts1242.3 nm. The submillimeter radian filtering characteristic of the device makes the device possible to be an ideal element for unfocused low-pass filtering in high-energy laser.
It should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.
Claims (6)
1. A method for manufacturing a medium grating narrow-band filter is characterized by comprising the following steps: the medium grating narrow-band filter is formed by arranging gratings with special sizes at intervals of a specific distance in the direction vertical to the grating plane, and a plurality of reflecting cavities formed by the gratings are used for carrying out narrow-band filtering; the special size means that the height and the period of the grating are smaller than the working wavelength of the filter; the specific distance refers to the spacing distance between the gratings, wherein Fabry-Perot interference can occur and the near-field coupling effect is ignored; when the narrow-band filter is used, light is emitted from the upper part of the filter at a certain angle, and is emitted from the bottom after being filtered by the multi-layer grating, so that narrow-frequency and narrow-angle filtering operation is realized; the manufacturing method of the medium grating narrow-band filter specifically comprises the following steps:
s1: selecting a grating according to the required transmission wave band, the transmissivity, the symmetry of the transmission peak and whether the flat-top band response is required;
s2: adjusting the thickness of each layer of grating according to the required transmission center wavelength and/or center angle;
s3: further adjusting the spacing between the gratings according to the desired transmission center wavelength and/or center angle;
s4: judging whether flat-top-band response is needed, if so, enabling a primary reflection cavity formed by two gratings to be equivalent to a reflector, cascading with another primary reflection cavity or a grating, realizing the flat-top-band response by adjusting the spacing distance, and executing the step S6; if not, go to step S5;
s5: judging whether a symmetrical transmission peak is needed, if so, adjusting dislocation between the upper grating and the lower grating to realize the symmetrical transmission peak, and executing the step S6; if not, directly executing the step S6;
s6: different magnitudes of transmittance are achieved by adjusting the spacing between the gratings according to the desired transmittance.
2. The method of claim 1, wherein the dielectric grating narrow band filter comprises: each grating is used as a high-reflection mirror, and a reflection cavity formed by the two high-reflection mirrors independently realizes filtering or is cascaded with reflection cavities formed by other gratings or gratings to output different required spectral lines.
3. The method of claim 2, wherein the dielectric grating narrow band filter comprises: the filter is directly placed in the air or wrapped by using SU-8 photoresist as a supporting material, and the air or the SU-8 photoresist is used as an environmental material.
4. A method for making a dielectric grating narrow band filter according to claim 3, wherein: the grating is made of high-refractive-index materials including titanium dioxide, silicon, germanium, gallium arsenide, indium phosphide or silicon-rich silicon nitride; the environment material adopts a low refractive index material comprising air or SU-8 photoresist.
5. The method of claim 1, wherein the dielectric grating narrow band filter comprises: in step S1, according to the required transmission waveband, transmittance, symmetry of the transmission peak, and whether a flat-top rectangular peak is required, the single-layer grating is placed in a working environment with a broadband high-reflection waveband or an angle range, so as to ensure that the single-layer grating operates in a dual-mode region and only 0-order diffraction exists, and thus the duty ratio and the thickness range of the grating can be determined, and the selection of the grating is completed.
6. The method of claim 5, wherein the dielectric grating narrow band filter comprises: the high transmission center wavelength and center angle, transmission bandwidth, transmissivity, symmetry of transmission peak and flat top bandwidth index of the transmission peak of the narrow-band filter are determined by parameters of device materials of the filter, geometric thickness, period, duty ratio, cascade layer number and spacing distance of the grating and dislocation among different layers.
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