Method for stripping single crystal optical fiber from surface of rare earth element doped single crystal material

Abstract

The invention relates to a method for stripping a single-crystal optical fiber from the surface of a rare earth element doped single-crystal material, which adopts an ion beam technology to successfully and directly strip a crystal optical fiber structure from the surface of a rare earth element doped garnet crystal to obtain the single-crystal optical fiber. The length can exceed 1cm, and the device has the capability of guiding optical signal propagation; the physical properties of the crystal material are consistent with those of the crystal material. By means of the optical gain characteristic of the rare earth element doped single crystal material, the single crystal optical fiber can serve as an optical waveguide optical amplifier with excellent performance.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for stripping a single crystal fiber from the surface of a rare earth element doped single crystal material, belonging to the field of optical fiber preparation. BACKGROUND

[0002] An optical fiber is a tubular structure with a cross-sectional diameter in the micron level (a few micron level) and a length of centimeter level or longer, used for guiding the transmission of optical signals. Its refractive index is higher than that of the surrounding medium, and it realizes the conduction of optical signals based on the principle of total reflection. Optical fibers have low optical loss and high energy density, and are widely used in optical signal transmission, regulation and optical amplification. At present, most optical fibers are made of silica material. Taking rare earth element doped fused quartz as an example, it is a key component for realizing optical gain in current fiber optical amplifiers. However, rare earth element doped silica is not an ideal optical gain material, and the optical fiber structure based on this material often needs several meters or even hundreds of meters in length to achieve tens of dB of optical signal gain. In contrast, rare earth element doped crystals are excellent laser gain media with much better performance than rare earth element doped silica. Therefore, using rare earth element doped crystals to construct optical fiber structures is expected to greatly shorten the length of optical amplifiers and show broad prospects in the research and application of miniaturized and small-sized optical amplifiers.

[0003] Rare earth element doped garnet crystals are excellent laser gain media with high thermal conductivity, low optical loss, stable chemical properties, and high emission cross section, which can realize high-power and high-efficiency laser output. Their preparation process is mature, and they are currently highly commercialized laser gain media, widely used in existing solid-state lasers and optical amplifiers. They are rich in variety, including YAG (yttrium aluminum garnet), YAP (yttrium aluminum scandium garnet), GGG (gadolinium gallium garnet), etc., and can be doped with various rare earth elements such as Nd (neodymium), Yb (ytterbium), Er (erbium), Tm (thulium), Cr (chromium), etc., which can realize wide optical signal gain from visible light to mid-infrared band, and have very wide application scenarios. However, due to the high Mohs hardness of rare earth element doped garnet crystals, it is difficult to process and difficult to make into optical fiber structure, and its application scenarios are currently mainly limited to traditional bulk solid-state lasers.

[0004] Ion beam technology is a kind of technical means using energetic particle bombardment target material, through sputtering, doping and other mechanisms, can realize the accurate control of target material surface morphology, damage distribution and physical and chemical properties. In recent years, Y. Tan et al. reported a research result, namely using ion beam technology to bombard YAG crystal, successfully stripped the crystal sheet structure with the thickness within 1 microns, width of 100 microns, length of several millimeters on its surface. These crystal sheets have the characteristics of low surface roughness, which can be further processed into round sheet microcavity structure. Due to the limitation of technology, the ion beam technology can only get the crystal sheet structure by bombarding YAG crystal, however, these crystal sheets have significant differences in structure with optical fiber. Optical fiber requires the cross section to be as close to circular or square as possible, and the size needs to be controlled within several microns, while the length-width ratio of the crystal sheet is too large to meet the structural requirements of the optical fiber, so it cannot be used as a crystal fiber. In addition, the shape of these crystal sheets is irregular, the thickness is uneven, and it presents a sword edge structure, which also limits its further processing into a crystal fiber.

[0005] Therefore, there is an urgent need for a new technical means for preparing a single crystal fiber from a rare earth element doped single crystal material. SUMMARY

[0006] In view of the shortcomings of the prior art, the present application provides a method for stripping a single crystal fiber from the surface of a rare earth element doped single crystal material.

[0007] The method of the present application successfully realizes the direct stripping of a crystal fiber structure from the surface of a rare earth element doped garnet crystal, and obtains a single crystal fiber structure. The single crystal fiber not only maintains the shape and structure characteristics of the optical fiber, but also has similar characteristics to the traditional optical fiber, and the cross section is only square microns, which can be easily stretched and deformed, and is easier to integrate into the existing optical fiber system. It also retains the original crystal fluorescence performance and laser gain characteristics, and can be used as a laser gain medium, which has important application value in the field of optical waveguide optical amplifier.

[0008] The present application is achieved by the following technical means: A method for stripping a single crystal fiber from the surface of a rare earth element doped single crystal material, comprising the following steps: 1) Using a rare earth ion doped garnet crystal as a base material, cutting it into a cuboid crystal, and optically polishing and cleaning the largest surface of the cut crystal; 2) Using heavy ion irradiation to polish the surface of the cleaned crystal, the irradiated ions enter the crystal and stay at a certain depth, forming a damage layer; 3) Using photolithography technology, using photoresist as a mask to shield the surface of the crystal, and obtaining a patterned structure protected by photoresist; 4) using low-energy heavy ion beam to irradiate the crystal surface treated in step 3), the area protected by photoresist will remain, and the area without photoresist protection will be sputter milled and thinned by low-energy heavy ions; 5) using organic solvent to clean the crystal surface treated in step 4) to dissolve the photoresist; 6) dropping the etching solution on the crystal surface treated in step 5), the etching solution directly corrodes and dissolves the damage layer through the groove milled in step 4), so that the patterned structure protected by photoresist in step 4) is separated from the crystal substrate; 7) using PDMS-based thermal release adhesive to collect and transfer the separated patterned structure to obtain a single-crystal optical fiber.

[0009] According to the application, preferably, in step 1), the rare earth ion-doped garnet crystal is an Er:YAG crystal or an Nd:YAG crystal.

[0010] According to the application, preferably, in step 1), the cuboid crystal has a length of 1-3 cm, a width of 1-3 cm, and a height of 0.2-1 cm.

[0011] According to the application, preferably, in step 2), the heavy ion irradiation is performed by using a mega-electron-volt heavy ion, the energy of the mega-electron-volt heavy ion is greater than or equal to 1 MeV, and the relative atomic mass of the heavy ion is greater than 8.

[0012] According to the application, preferably, in step 2), the energy of the mega-electron-volt heavy ion is 2-10 MeV.

[0013] According to the application, preferably, in step 2), the irradiation injection direction forms an angle of 3-8° with the normal direction.

[0014] According to the application, preferably, in step 2), the injected ions stay in the crystal interior at a depth of 1-4 microns.

[0015] According to the application, preferably, in step 2), the injected ions are carbon, oxygen, nitrogen, or sulfur atoms. The injected ions ensure that a damage layer can be formed in the crystal.

[0016] According to the application, preferably, in step 2), the injection dose is greater than or equal to 0.5×10 14 ions / cm 2 .

[0017] According to the application, preferably, in step 2), the injection dose is (1-5)×10 15 ions / cm².

[0018] According to the application, the thickness of the photoresist mask ensures that it can completely block the injected ions, and the width is sufficient to support the entire structure.

[0019] According to the application, preferably, in step 3), the thickness of the photoresist mask is 1-5 microns, and the width of the mask for forming the waveguide is greater than or equal to 3 microns.

[0020] According to the application, preferably, in step 3), the photoresist-protected patterned structure is a spiral structure coiled into a roll. That is, the blocked area forms a spiral fiber structure coiled into a roll.

[0021] According to the application, preferably, in step 4), the energy of the low-energy heavy ion beam is less than or equal to 100 eV.

[0022] According to the application, preferably, in step 4), the energy of the low-energy heavy ion beam is 70-90 eV.

[0023] According to the application, preferably, in step 4), the heavy ions of the low-energy heavy ion beam use gallium ions or argon ions.

[0024] According to the application, preferably, in step 4), the width of the sputtering-formed groove is greater than or equal to 500 nm. This ensures that the subsequent etching liquid can enter the groove.

[0025] The low-energy heavy ion beam of the application can effectively mill the base material, thereby etching the groove, and the width of the groove is greater than 500 nm, ensuring that the etching acid can penetrate into the groove; the milling depth is greater than or equal to the damage layer depth, so that the acid can fully contact the damage layer.

[0026] According to the application, preferably, in step 4), the width of the sputtering-formed groove is 500-800 nm.

[0027] According to the application, preferably, in step 4), the irradiation time makes the milled depth greater than or equal to the depth of the damage layer in step 2).

[0028] According to the application, preferably, in step 5), the organic solvent is acetone.

[0029] According to the application, preferably, in step 6), the etching liquid is a phosphoric acid solution with a mass concentration of 60%-85% or a hydrochloric acid solution with a mass concentration of 15%-35%.

[0030] According to the application, preferably, in step 6), the etching time is 10-20 minutes, and the etching temperature is 100-140℃.

[0031] The etching liquid acid of the application does not introduce any defect pits on the crystal surface, does not damage the surface integrity, and has a large etching rate difference for the damage layer and the undamaged layer, thereby meeting the requirements of stripping the patterned structure; the etching liquid concentration ensures that a 4-micron-wide structure can be etched down in about 15 minutes.

[0032] According to the present application, preferably, in step 7), the PDMS-based thermal release adhesive has good adhesion at room temperature, can adhere the structure from the crystal surface, and can be thermally released at a specific temperature (such as 70-80°C) higher than room temperature, losing adhesion, so as to facilitate the transfer of the structure adhered thereon to a new substrate.

[0033] The PDMS-based thermal release adhesive is prepared according to the prior art in the field.

[0034] Technical features and advantages of the present application: 1. The method of the present application can directly strip the crystal fiber from the bulk crystal, without subsequent processing, and can be directly formed, which is simple and low in cost.

[0035] 2. The crystal fiber prepared by the method of the present application has a cross-sectional width that can be accurately controlled within a few microns, which is similar to the core diameter (3 microns) of the existing communication optical fiber, and is convenient for integration with the existing communication optical fiber.

[0036] 3. The single crystal fiber obtained by the method of the present application not only maintains the shape and structural features of the optical fiber, has similar features to the traditional optical fiber, and has a small cross-section of only square microns, which can be easily stretched and deformed, and is more easily integrated into the existing optical fiber system, and also retains the original crystal fluorescence performance and laser gain characteristics, and can be used as a laser gain medium, and has important application value in the field of optical waveguide optical amplifiers. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 Process schematic diagram for milling a patterned structure using photolithography technology; Figure 2 Operation schematic diagram for realizing structure transfer using PDMS.

[0038] 1, argon ion beam, 2, pattern part without photoresist, 3, photoresist, 4, PDMS-based thermal release adhesive, 5, single crystal fiber, 6, crystal substrate, 7, new substrate.

[0039] Figure 3 Actual object and stretching diagram of the spiral structure single crystal fiber peeled from the surface of the Er:YAG crystal and coiled into a roll, a is the actual object diagram, and b is the stretching diagram.

[0040] Figure 4 Fluorescence performance diagram of the obtained single crystal fiber. DETAILED DESCRIPTION

[0041] The present application will be further described in detail below with reference to the accompanying drawings: Example 1: A method for stripping a single crystal fiber from the surface of a rare earth element doped single crystal material, comprising the following steps: Step 1: Er:YAG crystal is cut into a cuboid with the size of 1 cm in length, 1 cm in width and 0.5 cm in height, and the largest surface (ab surface, i.e. the length-width surface) is selected for optical polishing treatment, and surface cleaning is completed; Step 2: Carbon ion beam with an energy of 2.75 MeV is used to implant the ab surface of the crystal at a dose of 2x10 15 ions / cm², and the implantation direction is at an angle of 7° with the normal direction. After the carbon ions penetrate the ab surface, a damage layer with a thickness of about 0.5 microns is formed at a depth of 2.5 microns in the crystal; Step 3: A coiled spiral structure pattern 2 is prepared on the ab surface using photolithography technology. SU8 photoresist is selected as the photoresist 3, with a thickness of 2 microns. The line width of the mask pattern is 4 microns, and the length is 2.6 millimeters.

[0042] Step 4: Argon ion beam 1 with an energy of 50 eV is used to irradiate and sputter the ab surface. The area protected by the photoresist 3 is retained, and only the area not protected by the photoresist 3 is thinned. The sputtering thinning depth is 4 microns, as shown in Figure 1 ; Step 5: Acetone is used as an organic solvent to dissolve the photoresist 3 on the ab surface, and the crystal surface is cleaned; Step 6: A phosphoric acid solution with a mass concentration of 80% is added to the ab surface treated in step 5, ensuring that the liquid surface completely covers the pattern area 2 formed in step 4. It is heated to 120°C and left for 15 minutes to completely etch the damage layer, and finally realize the separation of the coiled spiral structure single crystal fiber with a thickness of 2 microns from the Er:YAG substrate crystal; Step 7: PDMS-based thermal release adhesive 4 is applied to the surface of the Er:YAG crystal fiber 5, and its viscosity is used to fix the crystal fiber 5, which is removed from the original crystal substrate 6. Then the thermal release adhesive is heated to transfer the fiber to the target new substrate 7, as shown in Figure 2 .

[0043] The actual coiled spiral structure single crystal fiber peeled off from the surface of the Er:YAG crystal is shown in Figure 3 a. Due to the small cross-section of the single crystal fiber, only square microns, and the special spiral structure, it can be easily stretched and deformed, as shown in Figure 3 b. It has similar characteristics to traditional optical fibers and properties that bulk crystals do not have, making it easier to integrate into existing optical fiber systems.

[0044] The crystal fiber has both the structure of an optical fiber and the properties of an Er:YAG crystal. By Figure 4It can be seen that the single crystal fiber still retains the fluorescence performance of Er-doped YAG, has the potential of optical amplification, and generates strong green fluorescence through up-conversion under the pumping of 1478 nm light, and has the potential of application as an optical fiber optical amplifier.

[0045] In order to improve the etching efficiency of the Er:YAG crystal and the yield of finished products, the selection of the PDMS for transfer is systematically studied and large-scale experimental exploration is carried out, and when the thickness of the PDMS is 500 microns and the viscosity is low, the target structure is more easily adhered and released.

[0046] Example 2: A method for stripping a single crystal fiber from the surface of a rare earth element-doped single crystal material, comprising the following steps: Step 1: cutting the Nd:YAG crystal into a cuboid with a size of 2 cm in length, 2 cm in width and 0.8 cm in height, selecting the largest surface (ab surface, i.e. length-width surface) for optical polishing treatment, and completing surface cleaning; Step 2: implanting carbon ions with an energy of 6 MeV into the ab surface of the crystal at a dose of 2x10 15 ions / cm², and the implantation direction is at an angle of 7° with the normal direction, and after the carbon ions penetrate the ab surface, a damage layer with a thickness of about 0.5 microns is formed at a depth of about 4 microns in the crystal; Step 3: using photolithography technology to prepare a coiled spiral structure pattern 2 on the ab surface, the photoresist 3 is SU8 photoresist with a thickness of 2 microns, and the line width of the mask pattern is 5 microns and the length is 3.6 microns.

[0047] Step 4: using an argon ion beam 1 with an energy of 50 eV to irradiate and sputter the ab surface, the area protected by the photoresist 3 is retained, only the area not protected by the photoresist 3 is thinned, the sputtering thinning depth is 6 microns, see Figure 1 ; Step 5: using acetone as an organic solvent to dissolve the photoresist 3 on the ab surface, and cleaning the crystal surface; Step 6: dropping a phosphoric acid solution with a mass concentration of 80% onto the ab surface treated in step 5, ensuring that the liquid surface completely covers the pattern area 2 formed in step 4, heating to 120°C and standing for 17 minutes, so that the damage layer is completely etched, and finally realizing the separation of the coiled spiral structure single crystal fiber with a thickness of 3.5 microns from the Nd:YAG substrate crystal; Step 7: covering the PDMS-based thermal release adhesive 4 on the surface of the Nd:YAG crystal fiber 5, using its adhesion to fix the crystal fiber 5, and moving it away from the original crystal substrate 6. Then heat treatment is carried out on the thermal release adhesive, and the fiber is transferred to the target new substrate 7, see Figure 2 .

[0048] The above merely describes the preferred embodiments of the present patent, and it should be pointed out that, for those skilled in the art, several improvements and replacements can be made without departing from the technical principles of the present patent, and these improvements and replacements should also be considered as the protection scope of the present patent.

Claims

1. A method for stripping a single crystal fiber from a surface of a rare earth doped single crystal material, comprising the steps of: 1) cutting a garnet crystal doped with rare earth ions as a base material into a cuboid crystal, optically polishing and cleaning the largest face of the cut crystal; 2) irradiating the polished and cleaned surface of the crystal with heavy ions, the irradiated ions entering the crystal and residing at a certain depth to form a damage layer; 3) using a photolithography technique, using photoresist as a mask to shield the surface of the crystal, obtaining a patterned structure protected by photoresist; 4) irradiating the surface of the crystal treated in step 3) with a low-energy heavy ion beam, the area protected by photoresist remaining, and the area not protected by photoresist being thinned by low-energy heavy ion sputtering milling; 5) cleaning the surface of the crystal treated in step 4) with an organic solvent to dissolve the photoresist; 6) dropping an etching solution onto the surface of the crystal treated in step 5), the etching solution directly etching and dissolving the damage layer through the grooves milled in step 4), so that the patterned structure protected by photoresist in step 4) is separated from the crystal base; 7) collecting and transferring the separated crystal structure using a PDMS-based thermal release adhesive, obtaining a single crystal fiber.

2. The method of claim 1, wherein, In step 1), the garnet crystal doped with rare earth ions is an Er:YAG crystal or an Nd:YAG crystal, the cuboid crystal has a length of 1-3 cm, a width of 1-3 cm, and a height of 0.2-1 cm.

3. The method of claim 1, wherein, In step 2), the heavy ion irradiation is performed using a mega-electron-volt heavy ion, the energy of the mega-electron-volt heavy ion is greater than or equal to 1 MeV, and the relative atomic mass of the heavy ion is greater than 8. Preferably, the energy of the mega-electron-volt heavy ion is 2-10 MeV.

4. The method of claim 1, wherein, In step 2), the injected ions enter the crystal and reside at a depth of 1-4 microns in the crystal.

5. The method of claim 1, wherein, In step 2), the implanted ions are carbon, oxygen, nitrogen or sulfur atoms, the implantation dose is greater than or equal to 0.5 x 1016 ions / cm2, and the implantation dose is (1-5) x 1016 ions / cm2. 14 2 15 ​​​ 6. The method of claim 1, wherein, In step 3), the thickness of the photoresist mask is 1-5 microns, the mask width for forming a waveguide is greater than or equal to 3 microns, and the patterned structure protected by photoresist is a coiled back structure.

7. The method of claim 1, wherein, In step 4), the energy of the low-energy heavy ion beam is less than or equal to 100 eV, preferably the energy of the low-energy heavy ion beam is 70-90 eV, and the heavy ion of the low-energy heavy ion beam is gallium ion or argon ion.

8. The method of claim 1, wherein, In step 4), the width of the sputtering groove is greater than or equal to 500 nm, preferably the width of the sputtering groove is 500-800 nm.

9. The method of claim 1, wherein, In step 4), the irradiation time is such that the depth of the milled area is greater than or equal to the depth of the damage layer in step 2), and in step 5), the organic solvent is acetone.

10. The method of claim 1, wherein, In step 6), the etching solution is a phosphoric acid solution with a mass concentration of 60-85% or a hydrochloric acid solution with a mass concentration of 15-35%, the etching time is 10-20 minutes, and the etching temperature is 100-140°C.

Images