Diffraction grating with top-layer full-edge-covering configuration, preparation method of diffraction grating, optical device and application of diffraction grating

Abstract

The invention discloses a diffraction grating with a top-layer full-edge-covering structure and a preparation method of the diffraction grating. The diffraction grating comprises a grating substrate (1), a grating film (2) and a full-edge-covering layer (3) with a grating structure on the top layer. The full-edge-covering layer (3) completely covers the upper surface and the side edge of the grating film (2), has a full-edge-covering protection function, can protect the grating film (2) from being eroded by an external extreme environment in the grating preparation and use process, and keeps good optical performance. The diffraction grating is suitable for medium-long wave infrared bands, and the diffraction efficiency polarization is adjustable. According to the preparation method, the compatibility of the grating material and the preparation process is improved, the selectable range of the grating material is greatly widened, and the diffraction grating prepared on the basis of the method has high environmental robustness, can meet application requirements in some extreme environments and has important research significance and practical economic value.

Description

Technical Field

[0001] The present invention relates to the field of diffraction gratings, in particular to a diffraction grating with a top-layer fully wrapped edge configuration, a preparation method thereof, an optical device and applications thereof. Technical Background

[0002] As a high-dispersion optical element, a diffraction grating is a core optical element in the fields of spectroscopy, pulse compression, and spectral beam combining, etc., and has important applications in the fields of atmospheric remote sensing, biomedicine, laser processing, national defense security, and basic physical research, etc.

[0003] A diffraction grating usually includes a grating substrate, a grating film, and a top-layer grating structure. The grating film provides specific optical properties such as reflection, transmission, or filtering, etc., and the top-layer grating structure is used to regulate the phase distribution of the light field to achieve diffraction. The existing preparation methods [Prior Art 1: CN105891925B] are to deposit a grating film on the grating substrate, and then use etching technology to form a grating structure on the top layer of the grating film. Conventional etching processes need to introduce reaction gases such as argon (Ar), trifluoromethane (CHF3), or oxygen (O2) for etching. After etching, a large amount of polymers will be formed on the surface of the grating, and acetone, hydrofluoric acid, or strong acid solutions need to be used to soak and clean to remove the polymers and residual photoresist. This process poses strict corrosion resistance requirements on the grating film material. As a result, many mid-infrared optical materials that are not resistant to acid and alkali, such as germanium (Ge), zinc sulfide (ZnS), zinc selenide (ZnSe) [Prior Art 2: G. Desroches, Optomechanical Properties of Infrared Materials. OPTI 521 - Tutorial], etc., are prone to corrosion during the preparation process, thereby reducing the optical performance or even structural damage, severely limiting the selection range of grating materials. These materials themselves have excellent optical properties and are difficult to be replaced by other materials. Therefore, the situation of incompatibility between the preparation process and the materials often occurs, greatly increasing the preparation difficulty of the grating and also restricting the development of diffraction gratings. [Prior Art 3: CN111378934B] proposed to deposit a layer of SiO2 by ion beam assistance to protect the internal optical thin film from isolating water molecules and improve the stability of the optical thin film, but this scheme did not consider the acid-base corrosion problem faced in the grating preparation process. [Prior Art: CN117631110A] and [Prior Art 5: CN117966133A] proposed to add a protective layer on the top of the optical element. Such schemes belong to adding an additional protective film on the top layer after the optical element is prepared, and cannot completely protect the above-mentioned corrosion-prone grating materials from being damaged during the preparation process. As far as we know, there is currently no solution that can completely solve the above-mentioned problem of incompatibility between the grating materials and the preparation process.

[0004] In addition to the challenges faced during the preparation process, in some special application fields, gratings also face certain extreme environments such as high salt fog, high humidity, or strong oxidation environments. Long-term exposure to these extreme environments can cause damage to the surface materials or structures of the gratings, leading to degradation or even failure of the grating performance. Therefore, while ensuring that the diffraction gratings have high optical performance, it is of great research significance and practical economic value to improve the stability of gratings in the preparation and application environments, optimize the grating preparation process, and extend the service life of gratings. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a diffraction grating with a top-layer full-edge configuration and its manufacturing method in view of the problem of incompatibility between the corrosion-intolerant grating materials and the existing preparation processes. The grating manufactured based on this method has the characteristics of high diffraction efficiency and wide spectrum in terms of performance; in terms of structure, it has a top-layer full-edge configuration, which can provide all-round protection for the grating film and has higher environmental stability compared with traditional diffraction gratings, and can meet the application requirements in some extreme environments; the manufacturing method of the present invention can improve the compatibility between the existing etching process and the grating preparation materials, and greatly expand the optional range of grating materials.

[0006] The technical solution of the present invention is as follows:

[0007] First, the present invention provides a diffraction grating with a top-layer full-edge configuration, which is characterized in that the grating structure from bottom to top is: a grating substrate, a grating film; and a full-edge layer covering the upper surface and the side edges of the grating film. The full-edge layer has a periodic grating structure and is made of a high environmental stability material with acid, alkali, salt corrosion resistance or oxidation resistance, which is used to isolate the erosion of the external environment on the grating film.

[0008] Preferably, the material of the full-edge layer is selected from one of yttrium fluoride (YF3), silicon dioxide (SiO2), or diamond-like carbon (DLC).

[0009] Preferably, the grating film is a single-layer film or a multi-layer film, and the material is selected from one or more of ytterbium fluoride (YbF3), germanium (Ge), zinc sulfide (ZnS), or zinc selenide (ZnSe).

[0010] Preferably, the film-forming area of the full-edge layer is larger than the film-forming area of the grating film to completely wrap the upper surface and the side edges of the grating film, and the lateral extension range of the film-forming area of the full-edge layer covers the exposed area of the grating substrate.

[0011] Preferably, the duty cycle of the periodic grating structure of the full-edge layer is 0.3 - 0.9, the groove depth is 100 - 500 nm, the period is 2.0 - 6.7 μm, and the diffraction grating has a diffraction efficiency of more than 95%.

[0012] Second, the present invention also provides a method for preparing a diffraction grating with a top-layer fully wrapped edge configuration, which is characterized by including the following steps:

[0013] (1) Set a mask on the surface of the grating substrate, and deposit a grating film within the area defined by the mask through a magnetron sputtering coating process; the mask fits on the surface of the grating substrate, and the shielding range of the mask can be freely adjusted according to requirements to adjust the area size of the grating film deposited on the surface of the grating substrate.

[0014] (2) Adjust the size of the mask to expand the film-forming area, and deposit a fully wrapped edge layer on the surface and side edges of the grating film through a coating process, so that the film-forming area of the fully wrapped edge layer is larger than that of the grating film, and the side edges of the grating film are completely wrapped;

[0015] (3) Form a photoresist grating structure on the surface of the fully wrapped edge layer through a holographic exposure process, and transfer the photoresist grating structure into the fully wrapped edge layer through an etching process;

[0016] (4) Immerse the etched sample in a strong acid solution to remove the residual photoresist and etching polymer, and obtain the diffraction grating with the top-layer fully wrapped edge configuration. The strong acid solution is H2O2:H2SO4 (1:4), and the immersion time is 10 - 30 minutes.

[0017] Third, the present invention provides an optical device including the above diffraction grating.

[0018] Preferably, the optical device is applied to spectral analysis, laser processing, laser beam combining, or pulse compression systems under high salt fog, high humidity, or strong oxidation environments.

[0019] The technical effects of the present invention are as follows:

[0020] 1) By completely covering the upper surface and side edges of the grating film with the fully wrapped edge layer and acting together with a high-stability material (such as YF3), the intrusion path of external corrosive media from the side edges of the grating film is blocked, improving the environmental tolerance, so that grating film materials (such as Ge, ZnS, ZnSe) that were originally unable to be used due to poor corrosion resistance can be compatible with the preparation process. The fully wrapped edge structure enables the grating to remain intact under strong acid cleaning and extreme environments (such as strong acid and alkaline, high humidity, strong oxidation environments) (Example 2), solving the problem of performance degradation of traditional gratings caused by side edge corrosion.

[0021] 2) For the diffraction grating prepared based on this method, the average diffraction efficiency in the mid-infrared band can reach more than 95%, has the characteristic of polarization independence, and the high diffraction efficiency bandwidth > 100 nm (Example 1). This grating can meet the urgent needs of high-efficiency diffraction gratings in the fields of mid-infrared spectral analysis, laser beam combining, pulse compression, etc.

[0022] 3) The preparation method of the present invention has a simple process and is also applicable to the preparation processes of various optical micro-structure devices, which is used to broaden the types of materials for preparing various optical micro-structure devices, reduce the difficulty of device preparation, improve the environmental robustness and service life of the devices, and has important economic and practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the mid-infrared holographic planar diffraction grating structure provided by the present invention. In the figure, 1 - grating substrate, 2 - grating thin film, 3 - full-edge layer, D - grating period, f - duty ratio, h - groove depth.

[0024] Figure 2 It is the spectral diagram of the -1st order diffraction efficiency of the mid-infrared diffraction grating designed in Example 1.

[0025] Figure 3 It is the preparation method of the diffraction grating with the top-layer edge-enclosing configuration. In the figure, 1 - grating substrate, 2 - grating thin film, 3 - full-edge layer, 4 - baffle.

[0026] Figure 4 It is the experimental result of the top-layer full-edge configuration and the traditional stacked configuration in Example 1 after being soaked in a strong acid solution. In the figure, (a) the sample of the top-layer edge-enclosing configuration; (b) the result of the sample of the top-layer edge-enclosing configuration after being soaked in a strong acid; (c) the sample of the traditional upper and lower stacked configuration; (d) the result of the sample of the traditional stacked configuration after being soaked in a strong acid. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The technical solutions of the present invention will be further described below in conjunction with the drawings and embodiments, but the protection scope of the present invention should not be limited thereby.

[0028] Example 1:

[0029] Design a diffraction grating with a top-layer full-edge configuration, as Figure 1 shown. The grating substrate 1 uses fused quartz with a size of 50 mm × 50 mm × 1.5 mm. The grating film 2 uses a high-reflection film system with a film system of (LH)^4, where L represents the low-refractive-index material yttrium fluoride (YF3) with a thickness of 729.6 nm; H represents the high-refractive-index material germanium (Ge) with a thickness of 282.7 nm. The size of the grating film 2 is 20 mm × 20 mm. The material of the edge layer 3 is selected as YF3 with a thickness of 2818 nm and a size of 50 mm × 50 mm. The period of the top-layer grating structure is 2500 nm, the groove depth is 2818 nm, the duty ratio is 0.15, the designed wavelength band is 4600 - 4700 nm, and the incident angle is 51.2°. This grating has polarization-independent characteristics, and the average diffraction efficiency exceeds 95%, as Figure 2 shown.

[0030] Example 2: Preparation of a diffraction grating with a top-layer fully wrapped edge configuration, as Figure 3 shown

[0031] Step 1: Grating film deposition:

[0032] Select a fused silica with dimensions of 50 mm × 50 mm × 1.5 mm as the grating substrate 1. After cleaning and drying, place it in the vacuum chamber of a magnetron sputtering coating machine;

[0033] Install a square baffle 4 on the surface of the grating substrate 1, with a transmission aperture of 20 mm × 20 mm, to ensure that the deposition area of the grating film 2 is restricted.

[0034] Use the magnetron sputtering process to deposit a multi-layer dielectric film on the grating substrate 1 as the grating film 2. The film stack of the multi-layer dielectric film is (LH)^4, where L represents the low refractive index material yttrium fluoride (YF3), and H represents the high refractive index material Ge. Under a background vacuum of 8×10 -4 Pa, introduce argon gas with a flow rate of 40 sccm. Under the radio frequency mode, the power is 300 W, the working pressure is 0.5 Pa, and alternately deposit a YF3 film layer with a thickness of 730 nm and a Ge film layer with a thickness of 283 nm, with a size of 20 mm × 20 mm.

[0035] Step 2: Deposition of the fully wrapped edge layer

[0036] Adjust the transmission aperture of the baffle 4 to 50 mm × 50 mm and completely cover the surface of the grating substrate 1.

[0037] Deposit a layer of YF3 film on the surface and sides of the Ge film layer as the fully wrapped edge layer 3. Under a background vacuum of 8×10 -4 Pa, introduce argon gas with a flow rate of 40 sccm. Under the radio frequency mode, the power is 300 W, the working pressure is 0.5 Pa, and deposit a YF3 film with a thickness of 2818 nm.

[0038] Step 3: Preparation of the grating structure

[0039] Spin-coat a photoresist on the surface of the YF3 film with a thickness of 2.8 μm, and form a grating mask with a period of 2500 m at a wavelength of 365 nm through a holographic exposure system.

[0040] Use the reactive ion etching (RIE) process, with a mixed gas of trifluoromethane (CHF3), carbon tetrafluoride (CF4), and argon (Ar) (volume ratio 50:80:10) as the etching gas, a power of 1500 W, an etching pressure (not specified in the original), an etching time of 120 minutes, transfer the grating structure to the YF3 fully wrapped edge layer, with a groove depth of 2818 nm and an aspect ratio of 0.15.

[0041] Step 4: Cleaning and performance testing

[0042] The prepared samples were soaked in concentrated sulfuric acid solution with a concentration of 95% for 30 minutes to remove residual photoresist and etched polymers.

[0043] The grating sample with an all-round edge structure is clear and complete, as Figure 4 shown in (b) below. The gratings in the central region remained intact after soaking.

[0044] Compared with the traditional one without side coating, under the same acid soaking conditions, the side edges of the gratings of the traditional samples were severely corroded and the grating structure collapsed, as Figure 4 (d) shown.

Claims

1. A diffraction grating with a top-layer fully wrapped edge configuration, comprising a grating substrate (1), characterized in that, It also includes a grating film (2) disposed on the grating substrate (1); a full-edge coating layer (3) covering the upper surface and the side edges of the grating film (2), the full-edge coating layer (3) having a periodic grating structure and being made of a high environmental stability material with acid, alkali, salt corrosion resistance or oxidation resistance, for isolating the erosion of the external environment on the grating film (2).

2. The diffractive grating with a top-layer fully wrapped edge configuration according to claim 1, characterized in that The material of the full-edge coating layer (3) is preferably selected from one of yttrium fluoride (YF3), silicon dioxide (SiO2), germanium (Ge), or diamond-like carbon (DLC).

3. The diffractive grating with a top-layer fully wrapped edge configuration according to claim 1, characterized in that, The grating film (2) is a single-layer film or a multi-layer film. Preferably, the material is selected from one or more of ytterbium fluoride (YbF3), yttrium fluoride (YF3), germanium (Ge), zinc sulfide (ZnS), or zinc selenide (ZnSe).

4. The diffractive grating with a top-layer fully wrapped edge configuration according to any one of claims 1-3, characterized in that, The film-forming area of the full-edge coating layer (3) is larger than the film-forming area of the grating film (2) to completely wrap the upper surface and the side edges of the grating film (2), and the lateral extension range of the film-forming area of the full-edge coating layer (3) covers the exposed area of the grating substrate (1).

5. The diffractive grating with a top-layer fully wrapped edge configuration according to claim 4, wherein The duty cycle of the periodic grating structure of the full-edge coating layer (3) is 0.3 - 0.9, the groove depth is 100 - 500 nm, and the period is 2.0 - 6.7 μm.

6. A method for preparing a diffraction grating with a top-layer fully wrapped edge configuration according to any one of claims 1-5, characterized in that, It includes the following steps: ① Set a mask plate (4) on the surface of the grating substrate (1), and deposit the grating film (2) within the area defined by the mask plate (4) through a coating process; ② Adjust the size of the mask plate (4) to expand the film-forming area, and deposit the full-edge coating layer (3) on the surface and the side edges of the grating film (2) through a coating process, so that the film-forming area of the full-edge coating layer (3) is larger than that of the grating film (2) and completely wraps the side edges of the grating film (2); ③ Form a photoresist grating structure on the surface of the full-edge coating layer (3) through a holographic exposure process, and transfer the photoresist grating structure to the full-edge coating layer (3) through an etching process; ④ Immerse the etched sample in a strong acid solution to remove the residual photoresist and etching polymer, and obtain the diffraction grating with the top full-edge coating configuration.

7. The method for preparing a diffraction grating with a top-layer fully wrapped edge configuration according to claim 6, characterized in that, The mask plate is attached to the surface of the grating substrate (1), and the shielding range of the mask plate can be freely adjusted according to requirements to adjust the area size of the grating film (2) deposited on the surface of the grating substrate (1).

8. The method for preparing a diffraction grating with a top-layer fully wrapped edge configuration according to claim 6, characterized in that, The strong acid solution is H2O2:H2SO4 (1:4), and the immersion time is 10 - 30 minutes.

9. An optical device, characterized in that, It includes the diffraction grating according to any one of claims 1 to 5.

10. The optical device according to claim 9 is applied to spectral analysis, laser processing, laser beam combining, or pulse compression systems under high salt fog, high humidity, or strong oxidation environments.

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