Method for preparing mask-assisted photonic crystal array

Abstract

The invention provides a method for preparing a mask-assisted photonic crystal array, which relates to the technical field of femtosecond laser application, and comprises the following steps: depositing a layer of film on the surface of a substrate material; patterning the thin film through photoetching to obtain a mask; the method comprises the following steps: continuously and dynamically scanning a substrate material of a whole mask coverage area through femtosecond Bessel beams, forming a periodically arranged photonic crystal array unit structure by a material without a film coverage area, and forming a defect area by the substrate material without damage under the film coverage, so as to obtain the photonic crystal array structure. According to the method, the mask is arranged on the surface of the substrate material, so that the substrate material covered by the whole mask can be scanned at one time to obtain the periodically arranged photonic crystal units, defects are introduced, one-time preparation of the photonic crystal array is realized, and the preparation efficiency of the photonic crystal array is greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of femtosecond laser applications, and in particular to a method for preparing a mask-assisted photonic crystal array. Background Art

[0002] A photonic crystal is an artificial microstructure formed by periodically arranging media with different refractive indices, and the purpose of controlling the movement of photons can be achieved by designing the structural parameters of the photonic crystal. The two-dimensional photonic crystal array structure can precisely confine light in two spatial dimensions to achieve the regulation of a fine light field. Subsequently, by fabricating the above structure on the gain medium of a thin-film laser and combining with an external cavity phase-locking technique, a high-power and high-beam-quality laser output can be obtained.

[0003] Currently, the main method for obtaining a high aspect ratio photonic crystal array structure is through femtosecond laser direct writing in the transverse direction. However, when using femtosecond laser direct writing to fabricate a photonic crystal structure, it is necessary to process point by point, which has the disadvantage of low preparation efficiency. Moreover, when fabricating a photonic crystal array structure, it is necessary to periodically introduce defect positions in the photonic crystal array structure, which makes it necessary to precisely plan the processing route during femtosecond direct writing, and the preparation process is complex.

[0004] With the continuous development of application requirements, the existing methods have problems of low efficiency and complex preparation process when fabricating a large-area high aspect ratio photonic crystal array structure. Therefore, realizing the efficient processing of a large-area high aspect ratio photonic crystal array structure has become an urgent problem to be solved at present. Summary of the Invention

[0005] Aiming at the problems in the background art, the present invention provides a method for preparing a mask-assisted photonic crystal array, which realizes the one-time preparation of the photonic crystal array by setting a mask, improves the preparation efficiency of the photonic crystal array, and realizes the efficient preparation of a high aspect ratio photonic crystal array structure.

[0006] To achieve the above object, the present invention provides a method for preparing a mask-assisted photonic crystal array, including:

[0007] Depositing a thin film on the surface of a substrate material;

[0008] Performing patterning on the thin film by lithography to obtain a mask;

[0009] Scanning the entire substrate material covered by the mask with a femtosecond Bessel beam. During the laser processing, the mask serves as a protective layer. The material without the thin film coverage forms a periodically arranged photonic crystal unit structure after laser irradiation, and the material covered by the thin film remains undamaged after laser irradiation to obtain a defect region, thereby achieving the preparation of the photonic crystal array structure.

[0010] As a further improvement of the present invention, the substrate material is a material for preparing a photonic crystal array, including materials such as YAG crystal, ZnS crystal, sapphire, and glass.

[0011] As a further improvement of the present invention, a thin film is deposited on the surface of the substrate material, and the methods adopted include magnetron sputtering method, chemical vapor deposition method, and electroplating method.

[0012] As a further improvement of the present invention, the materials of the thin film include metal materials Cr, Al, and non-metal material silicon dioxide.

[0013] As a further improvement of the present invention, a corresponding mask plate is drawn according to the area where defects need to be introduced in the photonic crystal array to be prepared, and the pattern in the mask plate covers all the areas where defects need to be introduced.

[0014] As a further improvement of the present invention, by using a photolithography process, the pattern on the mask plate is transferred onto the thin film to obtain a patterned mask.

[0015] As a further improvement of the present invention, by using a photolithography process, the pattern on the mask plate is transferred onto the thin film. A layer of photoresist is evenly coated on the surface of the thin film. After pre-baking, the substrate material with the thin film is transferred to a photolithography machine equipped with the mask plate. After exposure, it is placed in a specific developer for development processing. The pattern on the mask plate appears on the photoresist. After hardening treatment, the pattern on the photoresist is transferred onto the thin film through an etching method to form a patterned mask. After removing the glue, the preparation of the mask is completed. The etching methods include dry etching and wet etching.

[0016] As a further improvement of the present invention, the substrate material with the mask is fixed on a displacement stage, and the movement of the substrate material is controlled by the displacement stage, so that the femtosecond Bessel beam performs non-stop dynamic scanning processing on the substrate material.

[0017] As a further improvement of the present invention, the femtosecond Bessel beam directly removes or modifies the material of the substrate material. The photonic crystal array obtained after irradiating with the femtosecond Bessel beam is placed in an etching solution, and a chemical reaction occurs between the etching solution and the irradiated area of the photonic crystal array to etch the substrate material, realizing the optimization of the photonic crystal array structure.

[0018] As a further improvement of the present invention, the processed substrate material is placed in a thin film etching solution to remove the residual mask.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] By setting a mask, the present invention can scan the substrate material in the entire mask-covered area at one time to obtain periodically arranged photonic crystal units and introduce defects, realizing the one-time preparation of a photonic crystal array, greatly improving the preparation efficiency of the photonic crystal array, which is of great significance for the preparation of a large-area photonic crystal array.

[0021] The present invention uses a femtosecond Bessel laser, whose focal depth can be adjusted and controlled, and can realize the longitudinal processing of the substrate material. By directionally removing or modifying the substrate material, it can cope with the preparation of a large-area high aspect ratio photonic crystal array. Combining with mask assistance, it can realize non-stop one-time preparation. Compared with the femtosecond transverse laser direct writing, which can only process point by point with low efficiency when processing the photonic crystal structure, requires precise planning of the processing route, and has a complex preparation process, the method of the present invention greatly improves the processing efficiency of a large-area high aspect ratio photonic crystal array.

[0022] The present invention sets a patterned mask, and realizes the absorption of the femtosecond Bessel laser energy in a specific area through the mask. The material without a thin film covering forms periodically arranged photonic crystal units after being processed by the femtosecond Bessel laser, and the material in the area covered by the thin film is not damaged after the non-stop dynamic scanning of the femtosecond Bessel laser, realizing the introduction of defects, that is, the processing of periodically arranged photonic crystal units for the entire substrate material and the introduction of defects in specific areas, obtaining a photonic crystal array, realizing the precise processing of the photonic crystal array, and improving the preparation quality at the same time.

[0023] The present invention coats a layer of photoresist on the surface of the substrate material, draws a mask plate according to the required photonic crystal array, transfers the pattern on the mask plate to the photoresist through patterning treatment, and after hardening the film, etches and removes the photoresist to obtain a mask, accurately obtaining the required mask, thereby making the finally processed photonic crystal array more accurate. Description of the Drawings

[0024] Figure 1 It is a flowchart of a method for preparing a mask-assisted photonic crystal array disclosed in an embodiment of the present invention;

[0025] Figure 2 It is a photolithography process flow for preparing a patterned mask disclosed in an embodiment of the present invention;

[0026] Figure 3 It is a Bessel beam shaping system disclosed in an embodiment of the present invention;

[0027] Figure 4 It is a femtosecond Bessel processing system disclosed in an embodiment of the present invention;

[0028] Figure 5 It is a schematic diagram of non-stop dynamic scanning disclosed in an embodiment of the present invention.

[0029] Description of Reference Numerals

[0030] 1. Base material; 2. Thin film; 3. Mask; 4. Output end of femtosecond Bessel laser; 5. Photonic crystal array; 6. Photoresist; 7. Mask; 8. Exposure light source; 9. Conical lens; 10. Plano-convex lens; 11. Processing objective lens; 12. Femtosecond laser; 13. Half-wave plate; 14. Polarizer; 15. Attenuator; 16. Mechanical switch; 17. First reflector; 18. Second reflector; 19. CCD; 20. Dichroic mirror; 21. Base material with mask; 22. Translation stage. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0033] like Figure 1 As shown, the present invention provides a method for preparing a mask-assisted photonic crystal array, comprising the steps of:

[0034] S1, depositing a thin film 2 on the surface of a substrate material 1;

[0035] in,

[0036] The base material 1 is a material used to prepare the photonic crystal array 5, including YAG crystal, ZnS crystal, sapphire, glass and other materials.

[0037] The material of the film 2 includes metal materials such as Cr and Al and non-metal materials such as silicon dioxide.

[0038] Furthermore,

[0039] A thin film 2 is deposited on the surface of the base material 1 by methods including magnetron sputtering, chemical vapor deposition, electroplating and the like.

[0040] S2, patterning the thin film 2 by photolithography to obtain a mask 3;

[0041] in,

[0042] The corresponding mask 7 is drawn according to the region where defects need to be introduced in the photonic crystal array 5 to be prepared, and the pattern in the mask 7 covers all the regions where defects need to be introduced.

[0043] The thin film 2 is patterned according to the mask 7 to obtain the mask 3.

[0044] Furthermore,

[0045] During the patterning process, the thin film 2 is selectively removed. The patterning methods include dry etching and wet etching. For wet etching, a thin film etchant is used, and for dry etching, ICP etching is used.

[0046] Specifically, a layer of photoresist 6 is uniformly coated on the surface of the thin film 2. After pre-baking, the substrate material 1 with the thin film 2 is transferred to a lithography machine equipped with the mask 7. After exposure, it is placed in a specific developer for development, so that the pattern on the mask template appears on the photoresist 6. After hardening, the pattern on the photoresist 6 is transferred to the thin film 2 by etching to form the patterned mask 3. After removing the glue, the preparation of the mask 3 is completed.

[0047] S3. The entire substrate material 1 covered by the mask is scanned by a femtosecond Bessel beam. The mask 3 acts as a protective layer during the laser processing. The material without the thin film 2 coverage obtains a periodically arranged photonic crystal unit structure after laser irradiation, and the material covered by the thin film 2 remains undamaged after laser irradiation, obtaining a defect area, thereby achieving the preparation of the photonic crystal array structure.

[0048] Among them,

[0049] The substrate material 1 with the mask 3 is fixed on the displacement stage 22, specifically below the output end 4 of the femtosecond Bessel laser. By controlling the displacement stage 22, the movement of the substrate material 2 is realized, so that the femtosecond Bessel beam performs non-stop dynamic scanning processing on the substrate material 1, achieving the one-time preparation of the large-area high aspect ratio photonic crystal array 5.

[0050] The processed substrate material 1 is placed in a specific thin film etchant to remove the residual mask 3 and then cleaned and dried. The temperature of the etchant includes room temperature or heating.

[0051] The photonic crystal array obtained after femtosecond Bessel beam irradiation is placed in a specific etching solution. The etching solution reacts chemically with the irradiated area of the photonic crystal array to etch the substrate material 1, realizing the optimization of the photonic crystal array structure; for different substrate materials, different specific etching solutions are selected. For example, for YAG crystals, a phosphoric acid etching solution can be selected. The temperature of the etching solution includes room temperature or heating.

[0052] Furthermore,

[0053] The substrate material 1 with the mask 3 can be fixed on the displacement stage 22 by a special mechanical fixture, and the substrate material 1 is precisely moved in the x, y, and z directions through computer control software, so as to realize non-stop dynamic scanning processing of the substrate material 1 in cooperation with the femtosecond Bessel beam.

[0054] In the present invention, the femtosecond Bessel beam can be obtained through a spatial light modulator or through a system combining a conical lens 9 and a telescope; after the femtosecond Bessel beam irradiates the substrate material 1, direct removal or material modification of the substrate material 1 is achieved.

[0055] Example:

[0056] When applying the method of the present invention to prepare a large-area high aspect ratio photonic crystal array 5, the substrate material 1 is selected as a pure YAG crystal with a thickness of 300 μm and an end face diameter of 10 mm, and both end faces of the YAG crystal are polished. The specific process includes:

[0057] Step 1: A Cr thin film 2 is sputtered on the end face of the YAG crystal by magnetron sputtering, and the thickness of the Cr thin film 2 is 300 nm;

[0058] Step 2: As shown in Figure 2 , a positive photoresist 6 is uniformly coated on the surface of the Cr thin film 2 by a spin coater and pre-baked;

[0059] Step 3: Using a lithography machine produced by SUSS, the pre-baked YAG crystal is transferred to the sample stage of the lithography machine for exposure, as shown in Figure 2 ;

[0060] Step 4: As shown in Figure 2 , the exposed YAG crystal is placed in a supporting developer for development, so as to transfer the pattern on the mask plate to the photoresist 6, and post-baking is carried out after development;

[0061] Step 5: As shown in Figure 2 , the YAG crystal after post-baking is placed in a room temperature Cr etching solution to realize the preparation of the patterned Cr mask 3;

[0062] Step 6: As shown in Figure 2 , the YAG crystal after the preparation of the Cr mask 3 is placed in a room temperature degluer to remove the residual photoresist 6 on the end face of the YAG crystal;

[0063] Step 7: The YAG crystal after removing the photoresist 6 is fixed on the three-axis displacement stage 22 by a mechanical fixture;

[0064] Step 8: Start the femtosecond laser 12 to output a Gaussian pulse femtosecond laser, which is modulated and beam-expanded to obtain a femtosecond Bessel beam;

[0065] As shown Figure 3 in Fig., a telescope combination system is formed by combining a cone lens 9 with a bottom angle of 5° and a plano-convex lens 10 with a focal length of f1 and a processing objective lens 11 with an equivalent focal length of f EFL ; a femtosecond laser 12 (center wavelength 800 nm, pulse width 50 fs, repetition frequency adjustable from 1 to 1 KHz, output light is Gaussian distribution, polarization mode is linear polarization) produced by Spectra Physics is adopted;

[0066] As shown Figure 4 in Fig., start the femtosecond laser 12 to output Gaussian pulse femtosecond laser. Control the femtosecond laser flux by combining a half-wave plate 13 and a polarizer 14, add an attenuation sheet 15 to attenuate the laser energy to a certain extent, and then control the on / off of the laser through a mechanical switch 16. Adjust the optical path position through the first reflector 17 and the second reflector 18 so that the Gaussian beam is incident parallel to the cone lens 9;

[0067] The Gaussian beam is modulated by the cone lens 9 into a first-region femtosecond Bessel beam with a depth of focus of Z max , and then is focused by a telescope system formed by combining a plano-convex lens 10 and a processing objective lens 11 with a specific positional relationship to obtain a femtosecond Bessel beam with a depth of focus of Z’ max with high energy density characteristics suitable for processing requirements;

[0068] Step Nine: Control the precise movement of the YAG crystal in the x, y, and z directions through computer control software, and make the movement speed match the repetition frequency of the femtosecond Bessel beam obtained in Step Eight to separate the pulses and realize single-pulse drilling of the YAG crystal by the femtosecond Bessel beam; the femtosecond Bessel beam scans the YAG crystal without interruption dynamically, adopting a line scan scheme with head-to-tail connection. As shown Figure 5 in Fig., a large-area high aspect ratio photonic crystal array 5 is prepared at one time.

[0069] Among them, with a pulse energy of 0.08 mJ, under the condition of a repetition frequency of 100 Hz and a moving speed of the displacement stage of 0.05 cm / s, the non-intermittent and efficient preparation of the photonic crystal array structure is realized in the 2.5 mm×2.5 mm area of the 300 μm thick YAG crystal.

[0070] Furthermore, as shown Figure 4 in Fig., the processing state is observed in real time through a dichroic mirror 20 and a CCD 19.

[0071] Step Ten: Place the obtained large-area high aspect ratio photonic crystal array 5 in a specific thin film etching solution to remove the residual mask 3.

[0072] Step Eleven: Place the obtained large-area photonic crystal array 5 with a high aspect ratio in a phosphoric acid etching solution to further optimize the structure of the photonic crystal array.

[0073] Step Twelve: Set up an optical path diagram to test the waveguide optical field localization performance of the prepared photonic crystal array structure. The excitation light source uses a helium-neon laser. The excitation light source is incident perpendicularly to the end face of the YAG crystal with the photonic crystal array 5 prepared thereon into the crystal interior. Place a CCD 19 behind the other end face of the YAG crystal to detect the optical field distribution characteristics after passing through the photonic crystal array structure.

[0074] Advantages of the present invention:

[0075] By setting a mask, the present invention can scan the entire substrate material at one time to obtain periodically arranged photonic crystal units and introduce defects, realizing the one-time preparation of the photonic crystal array, greatly improving the preparation efficiency of the photonic crystal array, which is of great significance for the preparation of large-area photonic crystal arrays.

[0076] The present invention uses femtosecond Bessel laser, whose focal depth can be adjusted and controlled, and can realize the longitudinal processing of the substrate material. By directionally removing or modifying the substrate material, it can cope with the preparation of large-area photonic crystal arrays with a high aspect ratio. Combined with mask assistance, it can realize non-stop one-time preparation. Compared with the femtosecond transverse laser direct writing, which can only process point by point with low efficiency when processing photonic crystal structures, requires precise planning of the processing route, and has a complex preparation process, the method of the present invention greatly improves the processing efficiency of large-area photonic crystal arrays with a high aspect ratio.

[0077] The present invention sets a patterned mask, and realizes the absorption of the energy of the femtosecond Bessel laser by a specific area through the mask. The material without a thin film coverage forms periodically arranged photonic crystal units after being processed by the femtosecond Bessel laser, and the material under the area covered by the thin film is not damaged after the non-stop dynamic scanning of the femtosecond Bessel laser, realizing the introduction of defects. That is, through the absorption of the energy of the femtosecond Bessel laser by the mask, the substrate material under the mask is not damaged, realizing the introduction of the defect area, and the substrate material not covered by the mask forms periodically arranged photonic crystal units after being processed by the femtosecond Bessel laser. That is, the processing of periodically arranged photonic crystal units and the introduction of defects in specific areas are realized for the entire substrate material, obtaining a photonic crystal array, realizing the precise processing of the photonic crystal array, and improving the preparation quality at the same time.

[0078] The present invention coats a layer of photoresist on the surface of the substrate material, draws a mask plate according to the required photonic crystal array, transfers the pattern on the mask plate to the photoresist through patterning treatment, and after hardening the film and then etching and removing the photoresist, a mask is obtained, accurately obtaining the required mask, thereby making the finally processed photonic crystal array more accurate.

[0079] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a mask-assisted photonic crystal array, characterized in that Including: Depositing a thin film on the surface of a substrate material; Patterning the thin film by photolithography to obtain a mask; Scanning the entire substrate material covered by the mask with a femtosecond Bessel beam. The mask serves as a protective layer during the laser processing. The material without the thin film coverage forms a periodically arranged photonic crystal unit structure after laser irradiation, and the material with the thin film coverage remains undamaged after laser irradiation, resulting in a defect region, thereby achieving the preparation of a photonic crystal array structure.

2. The method for preparing a mask-assisted photonic crystal array according to claim 1, wherein: The substrate material is a material for preparing a photonic crystal array, including YAG crystal, ZnS crystal, sapphire, and glass material.

3. The method for preparing a mask-assisted photonic crystal array according to claim 1, characterized in that: The method for depositing a thin film on the surface of the substrate material includes magnetron sputtering, chemical vapor deposition, and electroplating.

4. The method for preparing a mask-assisted photonic crystal array according to claim 1, wherein: The material of the thin film includes metal materials Cr, Al, and non-metal material silicon dioxide.

5. The method for preparing a mask-assisted photonic crystal array according to claim 1, wherein: Drawing a corresponding mask plate according to the area where defects need to be introduced in the to-be-prepared photonic crystal array. The pattern in the mask plate covers all the areas where defects need to be introduced.

6. The method for preparing a mask-assisted photonic crystal array according to claim 5, characterized in that: Transferring the pattern on the mask plate to the thin film by photolithography process to obtain a patterned mask.

7. The method for preparing a mask-assisted photonic crystal array according to claim 6, characterized in that, Transferring the pattern on the mask plate to the thin film by photolithography process, including: uniformly coating a layer of photoresist on the surface of the thin film. After pre-baking, transferring the substrate material with the thin film to a photolithography machine equipped with the mask plate. After exposure, placing it in a specific developer for development. The pattern on the mask plate appears on the photoresist. After hardening treatment, transferring the pattern on the photoresist to the thin film by etching method to form a patterned mask. After removing the glue, the preparation of the mask is completed. The etching method includes dry etching and wet etching.

8. The method for preparing a mask-assisted photonic crystal array according to claim 1, wherein: Fixing the substrate material with the mask on a displacement stage, and controlling the movement of the substrate material through the displacement stage to enable the femtosecond Bessel beam to perform non-stop dynamic scanning processing on the substrate material.

9. The method for preparing a mask-assisted photonic crystal array according to claim 1, wherein: The femtosecond Bessel beam directly removes or modifies the material of the substrate material. Placing the photonic crystal array obtained after femtosecond Bessel beam irradiation in an etching solution. The etching solution reacts chemically with the irradiated area of the photonic crystal array to etch the substrate material, realizing the optimization of the photonic crystal array structure.

10. The method for preparing a mask-assisted photonic crystal array according to claim 1, wherein: Placing the processed substrate material in a thin film etching solution to remove the residual mask.

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