Optical amplifier based on lithium tantalate doped with rare earth element lithium niobate waveguide and manufacturing method thereof

Abstract

The invention discloses an optical amplifier based on a lithium niobate waveguide doped with rare earth elements on lithium tantalate and a manufacturing method, and relates to the technical field of optical communication. Comprising a lithium tantalate substrate layer, a rare earth element-doped film lithium niobate device layer and an upper cladding which are sequentially stacked from bottom to top, the rare earth element-doped film lithium niobate device layer is provided with a ridge waveguide, the height and the width of the ridge waveguide are micron-level, and two end surfaces of the ridge waveguide are respectively coupled with optical fibers. Compared with a currently reported lithium niobate film nanometer waveguide optical amplifier, the lithium niobate film nanometer waveguide optical amplifier has the advantages that the mode size is larger, the effective waveguide length is longer, the overall gain effect of the device is larger, and the saturation output power is high. The ridge waveguide and the lensed optical fiber / high numerical aperture optical fiber have good mode matching, so that the difficulties of low coupling efficiency, high device insertion loss and low output power and saturation power in similar nano waveguide optical amplifiers are effectively solved, the performance is greatly improved, the manufacturing cost is reduced, and the optical fiber amplifier has practical application potential.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technology, and in particular to an optical amplifier based on a rare earth element-doped lithium niobate waveguide on lithium tantalate and a manufacturing method thereof. Background Art

[0002] Optical amplifiers are one of the key parts in long-distance optical communication technology. In 1980, the invention of the first erbium-doped fiber amplifier (EDFA) provided an important means for amplifying optical signals, making long-distance optical fiber communication a reality and greatly promoting the development of modern optical communication technology. Erbium ions are a common rare earth element ions with a multi-level structure. They can achieve efficient population inversion under the action of pump light (pump wavelength is 980 nanometers or 1480 nanometers) and stimulate radiation under the induction of signal light, thereby providing stable, low-noise broadband gain for traditional optical fiber communication bands (C bands). Therefore, EDFA plays an important role in the application of optical communication and laser technology. With the continuous advancement of optical fiber communication technology, higher requirements are put forward for the performance, size, and integration of optical amplifiers. It is necessary to continuously explore new materials and new technologies to meet the needs of scientific and technological development.

[0003] At present, common optical amplifiers mainly include erbium-doped fiber amplifiers (EDFA), ytterbium-doped fiber amplifiers (YDFA), semiconductor optical amplifiers (SOA), fiber Raman amplifiers (RFA), fiber Brillouin amplifiers (BFA), optical parametric amplifiers (OPA), etc. Erbium-doped fiber amplifiers have the advantages of high gain, low noise, wide bandwidth, and mature technology, but they require a fiber length of 1-100 meters, resulting in large device size, making it difficult to achieve miniaturization and integration, and the fiber is greatly affected by uneven temperature; semiconductor optical amplifiers have low power consumption and are easy to integrate, but they have a large noise coefficient, poor stability, and cannot operate continuously for a long time. Fiber Raman amplifiers, fiber Brillouin amplifiers, and optical parametric amplifiers all work based on the principle of nonlinear optics to achieve optical amplification, but they have high requirements for the coherence of the pump light, and the scope of miniaturization and integration applications is also subject to certain restrictions.

[0004] With the development of integrated optoelectronic technology, referring to the development route of EDFA, on-chip integrated rare earth element-doped waveguide amplifiers are considered to be an effective way to solve the bottleneck of chip-level gain and laser generation. In recent decades, people have studied a large number of host materials and waveguide configurations, and have successfully developed high-performance on-chip optical amplifiers and lasers on platforms such as erbium-doped silicon nitride, erbium-doped lithium niobate, and thulium-doped aluminum oxide. In 2022, the Swiss Federal Institute of Technology in Lausanne produced a high-performance erbium-doped silicon nitride waveguide amplifier, which can achieve an on-chip gain of 30dB in the low-power C-band, basically reaching the level of commercial EDFA; in 2023, a German research team jointly prepared a thulium-doped aluminum oxide waveguide amplifier with a mode spot size of 30 square microns, achieving an on-chip output of 1W in the NIR-IIc band.

[0005] Compared with other material platforms, lithium niobate has become one of the most popular materials due to its wide transparency window, high nonlinear properties, electro-optic / acousto-optic effects and piezoelectric properties. In recent years, the emergence of lithium niobate on insulator (LNOI) or thin film lithium niobate (TFLN) has promoted the rapid development of lithium niobate-based integrated optics and applications. Compared with traditional bulk lithium niobate, the thin film lithium niobate structure inherits the excellent physical properties of bulk lithium niobate, and can also use lithography, etching and other technologies to prepare various complex waveguide shapes, thereby localizing the light field intensity at the micro-nano scale. This not only greatly reduces the size of the device, but also enables high integration with other photonic devices.

[0006] At present, the waveguide optical amplifier based on the LNOI platform mainly studies the nanowaveguide optical amplifier made of erbium-doped nanothin film lithium niobate (Er:TFLN). However, there is a large mode mismatch between the nanowaveguide and the standard single-mode optical fiber, which leads to high coupling loss, affecting the input of the pump light and the output of the signal light, resulting in a large overall insertion loss of the device, limiting its scope of application. Although the on-chip gain is currently large, the actual fiber-to-fiber net gain is unsatisfactory. In contrast, the micron-scale waveguide optical amplifier based on the Er:LNOI platform can effectively reduce coupling loss and expand the absorption and emission cross-sections, but because it is impossible to introduce waveguide bending, it is subject to certain limitations in device size and effective gain length. As described in the Chinese patent with publication number CN118033814A, further lengthening the micron-scale doped lithium niobate waveguide on insulator has certain difficulties and cannot be overcome.

[0007] Therefore, those skilled in the art are committed to developing a waveguide optical amplifier with low optical fiber insertion loss and high net gain. Summary of the invention

[0008] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is to develop a waveguide optical amplifier that is compatible with optical fibers and has a high efficiency net gain. In view of the disadvantage that the existing micron-thin-film lithium niobate erbium-doped amplifier cannot be miniaturized, a new method is proposed to realize a spiral single-mode waveguide structure, so that the device can be miniaturized to form a practical device, which can be expected to be industrialized in the future.

[0009] To achieve the above-mentioned purpose, the present invention provides an optical amplifier based on a rare earth element-doped lithium niobate waveguide on lithium tantalate, comprising a lithium tantalate substrate layer, a rare earth element-doped thin film lithium niobate device layer and an upper cladding layer stacked in sequence from bottom to top, wherein the rare earth element-doped thin film lithium niobate device layer is provided with a ridge waveguide, wherein the height and width of the ridge waveguide are both at the micron level, and both end faces of the ridge waveguide are coupled with optical fibers respectively.

[0010] In a preferred embodiment of the present invention, in the rare earth element-doped thin film lithium niobate device layer, the rare earth element concentration is greater than 0.1 mol%.

[0011] Preferably, the rare earth element is selected from any one or both of erbium and ytterbium.

[0012] In a preferred embodiment of the present invention, the material of the upper cladding layer is selected from any one of silicon dioxide and tantalum pentoxide.

[0013] In a preferred embodiment of the present invention, the rare earth element doped thin film lithium niobate device layer and the lithium tantalate substrate layer have the same cutting direction, which is X-cut or Z-cut.

[0014] In a preferred embodiment of the present invention, the thickness of the lithium tantalate substrate layer is 0.3-1 mm; the thickness of the rare earth element doped thin film lithium niobate device layer is 2-10 microns; the thickness of the upper cladding layer is 0.5-1 micron; the length of the ridge waveguide is 10 cm-1 m, and the width is 2-10 microns.

[0015] In a preferred embodiment of the present invention, the optical fiber is a lens fiber or a fused high-value aperture fiber, and the core size of the optical fiber is slightly smaller than or equal to the size of the ridge waveguide, and the output spot size of the optical fiber matches the mode size in the ridge waveguide.

[0016] In a preferred embodiment of the present invention, the ridge waveguide is configured as a spiral structure, and the spiral bending radius is greater than or equal to 1 mm.

[0017] The present invention also discloses a method for preparing an optical amplifier based on a rare earth element-doped lithium niobate waveguide on lithium tantalate as described above, comprising the following steps:

[0018] Step 1, doping lithium niobate with rare earth elements at a predetermined concentration; bonding a rare earth element-doped thin film lithium niobate device layer to a lithium tantalate substrate layer by a crystal bonding technique, and then making the rare earth element-doped thin film lithium niobate device layer reach a preset thickness by chemical mechanical polishing;

[0019] Step 2, sputtering metal chromium onto the thin-film lithium niobate layer by magnetron sputtering, and then defining the spiral waveguide pattern on the chromium layer with photoresist by ultraviolet lithography, and then using a dry etching process to transfer the waveguide pattern to the chromium layer in sequence, and then to the thin-film lithium niobate layer, and preparing a ridge waveguide structure on the lithium niobate thin-film layer, and then polishing the waveguide sidewall by a chemical mechanical polisher to reduce the roughness, and finally removing the residual photoresist and metal chromium on the surface by wet etching;

[0020] Step 3, depositing an upper cladding layer on the rare earth element doped thin film lithium niobate device layer in step 2 by PECVD;

[0021] Step 4: polish the two end faces of the ridge waveguide, then perform input and output optical coupling through optical fiber, and finally obtain an optical amplifier based on lithium niobate waveguide doped with rare earth elements on lithium tantalate through device packaging.

[0022] In a preferred embodiment of the present invention, in step 2, the dry etching depth is greater than half the thickness of the lithium niobate thin film.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The optical amplifier based on lithium niobate waveguide doped with rare earth elements on lithium tantalate provided by the present invention, wherein the lithium tantalate crystal is similar to the lithium niobate crystal lattice and can be bonded, and the refractive index of lithium tantalate is only slightly smaller than that of lithium niobate, which reduces the refractive index contrast of the lithium niobate waveguide, so that the micron lithium niobate waveguide degenerates into a single-mode waveguide. Compared with the lithium niobate thin film waveguide optical amplifier reported so far, the single-mode characteristics of the lithium niobate micron ridge waveguide on lithium tantalate can be used to prepare a spiral long-distance waveguide, and light amplification is achieved by doping (rare earth ions), the distance is lengthened, and there is a larger mode volume and effective waveguide length, the overall gain effect of the device is greater, and the saturated output power is high. There is a good mode matching between the ridge waveguide and the lens fiber / high numerical aperture fiber, which effectively solves the difficulties of low coupling efficiency, high device insertion loss, low output power and saturation power in similar nano waveguide optical amplifiers, greatly improves the performance and reduces the production cost, and has more practical application potential.

[0025] The present invention dopes rare earth elements in lithium niobate waveguides based on lithium tantalate, which can combine the good gain effect of rare earth elements with the integrated low-loss waveguide based on the thin-film lithium niobate platform, and can achieve high net gain per unit length, thereby realizing an efficient on-chip optical amplifier. The lithium tantalate substrate can suppress the generation of high-order modes in the lithium niobate waveguide, and at the same time, combined with a reasonable waveguide bending structure, an on-chip spiral structure waveguide can be realized, which greatly increases the effective length of the waveguide per unit length of the chip.

[0026] The present invention uses lithium niobate doped with rare earth elements on micron-sized lithium tantalate with a thickness of 2 to 10 microns, which increases the size of the light spot, increases the gain area, has a higher gain, is directly compatible with optical fibers, and can be integrated with lithium niobate devices on micron-sized lithium tantalate.

[0027] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the structure of an optical amplifier according to Embodiment 1 of the present invention;

[0029] Figure 2 This is a schematic diagram of the structure of the optical amplifier according to Embodiment 1 of the present invention. DETAILED DESCRIPTION

[0030] The following describes several preferred embodiments of the present invention with reference to the drawings in the specification, so that the technical content is clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the protection scope of the present invention is not limited to the embodiments mentioned in the text.

[0031] In the drawings, components with the same structure are indicated by the same numerical reference numerals, and components with similar structures or functions are indicated by similar numerical reference numerals. The size and thickness of each component shown in the drawings are arbitrarily shown, and the present invention does not limit the size and thickness of each component. In order to make the illustration clearer, the thickness of the components is appropriately exaggerated in some places in the drawings.

[0032] Example 1

[0033] like Figure 1As shown, in an embodiment of the present invention, the present invention provides an optical amplifier based on a straight waveguide of lithium niobate doped with rare earth elements on lithium tantalate, comprising a lithium tantalate substrate layer 1, a rare earth element doped thin film lithium niobate device layer 2, and a silicon dioxide or tantalum pentoxide upper cladding layer 3, wherein the silicon dioxide or tantalum pentoxide upper cladding layer 3, the rare earth element doped thin film lithium niobate device layer 2 and the lithium tantalate substrate layer 1 are stacked in sequence to form a three-layer structure, thereby achieving good optical confinement, and a ridge waveguide is arranged on the rare earth element doped thin film lithium niobate device layer 2, and the height and width of the ridge waveguide are both in the micron level.

[0034] In the present invention, the height and width of the ridge waveguide are both 5 microns, and the length is 10 centimeters. The light in the ridge waveguide propagates in the fundamental mode. The core size 4-1 of the optical fiber 4 used for coupling is slightly smaller than or equal to the size of the ridge waveguide 2. The optical fiber 4 used for coupling can be made into a lens fiber or fused with a section of high numerical aperture optical fiber to achieve the purpose of reducing the spot size, wherein the mode size in the ridge waveguide matches the output spot size 4-2 of the optical fiber 4 used for coupling to reduce the coupling loss. In the optical communication band, the coupling loss is generally below 1.5 dB.

[0035] In addition, in the present invention, the thickness of the upper cladding layer of silicon dioxide or tantalum pentoxide is 0.5 micrometers. The introduction of the upper cladding layer can form a proper refractive index gradient and form a protective layer at the same time.

[0036] The optical amplifier based on lithium tantalate doped with rare earth element lithium niobate waveguide provided by the present invention has a larger mode volume and effective waveguide length, a larger overall gain effect of the device, and a high saturated output power compared to the currently reported lithium niobate thin film waveguide optical amplifier. The rare earth element doped lithium niobate ridge waveguide with a waveguide width and height of 5 microns has a good mode matching with the lens fiber / high numerical aperture fiber, effectively solving the difficulties of low coupling efficiency, high device insertion loss, low output power and saturation power in similar nano waveguide optical amplifiers, greatly improving performance and reducing production costs, and having more practical application potential.

[0037] Example 2

[0038] like Figure 2 As shown, in an embodiment of the present invention, the present invention also provides another optical amplifier based on lithium tantalate doped with rare earth element lithium niobate micron spiral waveguide. It includes a lithium tantalate substrate layer 1, a rare earth element doped thin film lithium niobate device layer 2, and a silicon dioxide or tantalum pentoxide upper cladding layer 3, wherein the silicon dioxide or tantalum pentoxide upper cladding layer 3, the rare earth element doped thin film lithium niobate device layer 2 and the lithium tantalate substrate layer 1 are stacked in sequence to form a three-layer structure, achieving good light confinement, and a ridge waveguide is provided on the rare earth element doped thin film lithium niobate device layer 2, and the height and width of the ridge waveguide are both in the micron level.

[0039] Among them, the thickness of the silicon dioxide or tantalum pentoxide upper cladding layer 3 in this embodiment is 1 micron, the thickness of the rare earth element doped thin film lithium niobate device layer 2 is 3 microns, and the thickness of the lithium tantalate substrate layer 1 is between 0.3 and 1 mm. The ridge waveguide is 3 microns high and 3 microns wide, and a bend is introduced to form a spiral, and the bending radius is greater than or equal to 1 mm. The light in the curved ridge waveguide still propagates in the fundamental mode mode, and no high-order mode is introduced, so as to achieve a shorter waveguide chip length and smaller size, and a small size of the packaged waveguide optical amplifier device.

[0040] The tangent direction of the rare earth element doped thin film lithium niobate device layer 2 is X-cut or Z-cut, and the tangent direction of the lithium tantalate substrate layer 1 is X-cut or Z-cut. Generally, the tangent directions of the two are the same.

[0041] In the embodiment of the present invention, the length of the ridge waveguide 2 is 10 cm to 1 m, and in order to reduce the area of ​​the optical amplifier, a curved portion may be introduced into the waveguide to realize a spiral waveguide. In this case, the length of the waveguide is 20 cm.

[0042] Preferably, the focusing spot diameter of the lens optical fiber used for coupling in the 1550 nanometer band is 3 microns, which matches the ridge waveguide mode with a height of 3 microns and a width of 3 microns.

[0043] Example 3

[0044] A method for preparing an optical amplifier based on a straight waveguide of lithium niobate doped with rare earth elements on lithium tantalate comprises the following steps:

[0045] Step 1, doping lithium niobate with rare earth elements at a predetermined concentration; bonding the rare earth element-doped thin film lithium niobate device layer 2 to the lithium tantalate substrate layer 1 by crystal bonding technology, and then making the rare earth element-doped thin film lithium niobate device layer reach a preset thickness by chemical mechanical polishing;

[0046] In this step, a predetermined concentration of rare earth elements is doped into lithium niobate, and the predetermined concentration is preferably greater than 0.1 mol%;

[0047] For the optical amplifier with rare earth element-doped lithium niobate waveguide on lithium tantalate, the thickness of the lithium tantalate substrate layer is 0.3-1 mm; the thickness of the rare earth element-doped thin film lithium niobate device layer is 2-10 μm; the thickness of the upper cladding layer is 0.5-1 μm; the length of the ridge waveguide is 10 cm-1 m, and the width is 2-10 μm.

[0048] For example, in Example 1, the height of the ridge waveguide is 5 microns, the width is 5 microns, and the length is 10 centimeters; in Example 2, the height of the ridge waveguide is 3 microns, the width is 3 microns, and the length is 20 centimeters.

[0049] Step 2: Sputter metallic chromium onto the thin-film lithium niobate layer by magnetron sputtering, define the spiral waveguide pattern on the chromium layer with photoresist by ultraviolet lithography, and then use a dry etching process to transfer the waveguide pattern to the chromium layer in sequence, and then transfer it to the thin-film lithium niobate layer, prepare a ridge waveguide structure in the lithium niobate thin-film layer, and then polish the waveguide sidewalls with a chemical mechanical polisher to reduce the roughness, and finally remove the residual photoresist and metallic chromium on the surface by wet etching.

[0050] In this step, the dry etching depth is greater than half the thickness of the lithium niobate thin film.

[0051] Step 3, depositing a layer of silicon dioxide or tantalum pentoxide upper cladding on the optical amplifier of lithium niobate waveguide doped with rare earth elements on lithium tantalate by PECVD or the like;

[0052] In this step, the predetermined thickness of the deposited upper cladding layer is greater than or equal to 0.5 micrometers. For example, the thickness of the upper cladding layer in Example 1 is 0.5 micrometers, and the thickness of the upper cladding layer in Example 2 is 1 micrometer.

[0053] Step 4: Polish the two end faces of the ridge waveguide; couple the input and output light through lens fiber or high numerical aperture fiber; finally, through device packaging, a high-efficiency optical amplifier with small size, high amplification efficiency and high output power based on lithium tantalate-doped rare earth element lithium niobate waveguide is realized.

[0054] The core of the lens fiber is slightly smaller than or equal to the size of the ridge waveguide, and the focusing spot of the lens fiber matches the mode of the ridge waveguide.

[0055] The present invention dopes rare earth elements in lithium niobate waveguides based on lithium tantalate, which can combine the good gain effect of rare earth elements with the integrated low-loss waveguide based on the thin-film lithium niobate platform, and can achieve high net gain per unit length, thereby realizing an efficient on-chip optical amplifier. The lithium tantalate substrate can suppress the generation of high-order modes in the lithium niobate waveguide, and at the same time, combined with a reasonable waveguide bending structure, an on-chip spiral structure waveguide can be realized, which greatly increases the effective length of the waveguide per unit length of the chip.

[0056] The present invention uses lithium niobate doped with rare earth elements on micron-sized lithium tantalate with a thickness of 2 to 10 microns, which increases the size of the light spot, increases the gain area, has a higher gain, is directly compatible with optical fibers, and can be integrated with lithium niobate devices on micron-sized lithium tantalate.

[0057] In an example of the present invention, the spectral range of the signal light used for amplification is 1525-1570 nanometers, and the pump light used is generated by a 980-nanometer laser diode. After passing through a fiber polarization controller, it is combined by a 980-nanometer / 1550-nanometer wavelength division multiplexer, and is coupled into a lithium niobate ridge waveguide through the end face of a single-mode lens fiber at the input end by end face coupling, that is, a unidirectional pumping mode; using a bidirectional pumping method, the output signal light and the input pump light can be split at the output end through another single-mode lens fiber and another 980-nanometer / 1550-nanometer wavelength division multiplexer, that is, a bidirectional pumping mode.

[0058] The preferred specific embodiments of the present invention are described in detail above. It should be understood that ordinary technicians in the field can make many modifications and changes based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by technicians in the technical field based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. An optical amplifier based on lithium tantalate doped with rare earth element lithium niobate waveguide, characterized in that: It includes a lithium tantalate substrate layer, a rare earth element-doped thin film lithium niobate device layer and an upper cladding layer stacked in sequence from bottom to top. The rare earth element-doped thin film lithium niobate device layer is provided with a ridge waveguide, the height and width of the ridge waveguide are both at the micron level, and both end faces of the ridge waveguide are coupled with optical fibers respectively.

2. The optical amplifier based on lithium tantalate-doped rare earth element lithium niobate waveguide according to claim 1, characterized in that: In the rare earth element-doped thin film lithium niobate device layer, the rare earth element concentration is greater than 0.1 mol%.

3. The optical amplifier based on lithium tantalate-doped rare earth element lithium niobate waveguide according to claim 2, characterized in that: The rare earth element is selected from any one or two of erbium and ytterbium.

4. The optical amplifier based on lithium tantalate-doped rare earth element lithium niobate waveguide according to claim 1, characterized in that: The material of the upper cladding layer is selected from any one of silicon dioxide and tantalum pentoxide.

5. The optical amplifier based on lithium tantalate-doped rare earth element lithium niobate waveguide according to claim 1, characterized in that: The rare earth element doped thin film lithium niobate device layer and the lithium tantalate substrate layer have the same cutting direction, which is X-cut or Z-cut.

6. The optical amplifier based on lithium tantalate-doped rare earth element lithium niobate waveguide according to claim 1, characterized in that: The thickness of the lithium tantalate substrate layer is 0.3-1 mm; the thickness of the rare earth element doped thin film lithium niobate device layer is 2-10 μm; the thickness of the upper cladding layer is 0.5-1 μm; the length of the ridge waveguide is 10 cm-1 m, and the width is 2-10 μm.

7. The optical amplifier based on lithium tantalate-doped rare earth element lithium niobate waveguide according to claim 1, characterized in that: The optical fiber is a lens fiber or a fused high-value aperture fiber, and the core size of the optical fiber is slightly smaller than or equal to the size of the ridge waveguide, and the output light spot size of the optical fiber matches the mode size in the ridge waveguide.

8. The optical amplifier based on lithium tantalate-doped rare earth element lithium niobate waveguide according to claim 1, characterized in that: The ridge waveguide is configured as a spiral structure, and the spiral bending radius is greater than or equal to 1 mm.

9. A method for preparing an optical amplifier based on a rare earth element-doped lithium niobate waveguide on lithium tantalate as claimed in claim 1, characterized in that: The steps include: Step 1, doping lithium niobate with rare earth elements at a predetermined concentration; bonding a rare earth element-doped thin film lithium niobate device layer to a lithium tantalate substrate layer by a crystal bonding technique, and then making the rare earth element-doped thin film lithium niobate device layer reach a preset thickness by chemical mechanical polishing; Step 2, sputtering metal chromium onto the thin-film lithium niobate layer by magnetron sputtering, and then defining the spiral waveguide pattern on the chromium layer with photoresist by ultraviolet lithography, and then using a dry etching process to transfer the waveguide pattern to the chromium layer in sequence, and then to the thin-film lithium niobate layer, and preparing a ridge waveguide structure on the lithium niobate thin-film layer, and then polishing the waveguide sidewall by a chemical mechanical polisher to reduce the roughness, and finally removing the residual photoresist and metal chromium on the surface by wet etching; Step 3, depositing an upper cladding layer on the rare earth element doped thin film lithium niobate device layer in step 2 by PECVD; Step 4: polish the two end faces of the ridge waveguide, then perform input and output optical coupling through optical fiber, and finally obtain an optical amplifier based on lithium niobate waveguide doped with rare earth elements on lithium tantalate through device packaging.

10. The preparation method according to claim 9, characterized in that: In step 2, the dry etching depth is greater than half the thickness of the lithium niobate thin film.

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