Manufacturing method and application of long-period grating structure in lithium niobate film

Abstract

The invention relates to the technical field of optical communication and photonic devices, in particular to a manufacturing method and application of a long-period grating structure in a lithium niobate thin film, and the manufacturing method comprises the following specific steps: S1, etching the surface of the lithium niobate thin film to manufacture a ridge-type lithium niobate thin film optical waveguide which comprises a lithium niobate substrate, the upper surface of the lithium niobate substrate is etched to form a ridge-type lithium niobate thin film optical waveguide layer, the two sides of the ridge-type lithium niobate thin film optical waveguide layer are lithium niobate thin film plane layers formed after etching, a SiO2 layer is arranged on the lower end face of the lithium niobate substrate, and a Si substrate is arranged on the lower end face of the SiO2 layer; s2, plating metal plane electrodes on the left and right lithium niobate film plane layers respectively; and S3, 500-1000 V / 5 [mu] s direct current pulse voltage is connected between the metal electrode + and the metal electrode-for 1-10 min, and then annealing treatment is conducted. The process is simple, the cost is reduced, and the produced product is stable in performance in a wide-temperature and complex environment.

Description

Technical Field

[0001] The present invention relates to the technical field of optical communication and photonic devices, and specifically provides a method for fabricating a long-period grating structure in a lithium niobate thin film and its application. Background Art

[0002] As a core functional element in the fields of optical communication and photonic devices, the long-period grating (LPG) plays an important role in key applications such as optical signal processing, mode coupling regulation, and high-sensitivity fiber optic sensing. The current mainstream fabrication technologies are mainly based on two processes: ultraviolet lithography and focused ion beam etching, which have significant industrialization bottlenecks. Lithography technology relies on a high-precision phase mask system and multi-step development processes, resulting in high fabrication costs. Ion beam etching is limited by the strict requirements of the vacuum processing environment and the high cost of equipment maintenance. Especially when facing the application requirements of large-scale optical interconnection networks and distributed fiber optic sensing systems, it is urgent to break through the constraints of existing processing technologies and develop a new LPG fabrication solution with simplified processes, controllable costs, and stable performance. This is of great significance for promoting the industrial application of next-generation optoelectronic devices. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for fabricating a long-period grating structure in a lithium niobate thin film and its application to solve the problems raised in the above background art.

[0004] To achieve the above purpose, the present invention provides the following technical solution: A method for fabricating a long-period grating structure in a lithium niobate thin film, the specific steps are as follows: S1. Etch the surface of the lithium niobate thin film to form a lithium niobate thin film optical waveguide. The lithium niobate thin film optical waveguide includes a lithium niobate substrate. The upper surface of the lithium niobate substrate is etched to form a ridge-type lithium niobate thin film optical waveguide layer. The two sides of the ridge-type lithium niobate thin film optical waveguide layer are lithium niobate thin film planar layers formed after etching. The lower end surface of the lithium niobate substrate is provided with a SiO 2 layer, and the lower end surface of the SiO 2 layer is provided with a Si substrate; S2. Deposit metal planar electrodes on the left and right lithium niobate thin film planar layers respectively. A metal electrode + is deposited on the left lithium niobate thin film planar layer, and a metal electrode - is deposited on the right lithium niobate thin film planar layer; S3. Apply a DC pulse voltage of 500 - 1000V / 5μs between the metal electrode + and the metal electrode - for 1 - 10 minutes. The strong electric field (10 - 20 kV / mm) passes through the middle lithium niobate thin film optical waveguide to drive Li + , Nb 5+Ion displacement induces local polarization reversal in the crystal, forming a stable permanent long-period grating (period 50 - 200 μm); then annealing treatment is carried out, annealing at 400 - 600 °C for 1 - 2 h to eliminate stress and stabilize the polarization region.

[0005] As a further preference of this technical solution, a DC pulse voltage of 1000 V / 5 μs is applied between the metal electrode +4 and the metal electrode -5 for 1 min; then annealing treatment is carried out, annealing at 600 °C for 1 h.

[0006] As a further preference of this technical solution, the lithium niobate crystal substrate is doped with titanium or magnesium elements, with a concentration of 0.5% - 10%.

[0007] In one embodiment, the lithium niobate crystal substrate is doped with titanium elements, with a concentration of 0.5%.

[0008] In one embodiment, the lithium niobate crystal substrate is doped with magnesium elements, with a concentration of 10%.

[0009] In one embodiment, the lithium niobate crystal substrate is doped with titanium and magnesium elements, with a concentration of 5%.

[0010] Application of the lithium niobate optical waveguide with a long-period grating structure prepared by the above method for fabricating a long-period grating structure in a lithium niobate thin film in a mode converter of an optical communication system and the fields of environmental monitoring or biosensing.

[0011] The present invention provides a method for fabricating a long-period grating structure in a lithium niobate thin film and its application, having the following beneficial effects: 1. Permanent structure: After one-time electric field induction, continuous power supply is not required, solving the energy consumption problem of traditional dynamic devices; 2. Simplified process and cost reduction: Abandoning the traditional complex process, shortening the cycle and reducing the cost; 3. High stability: Stable performance under wide temperature and complex environments; 4. Dynamic tuning potential: Although the structure is solidified, wavelength fine-tuning can be achieved through the thermo-optic effect (Δn / ΔT≈1×10 -5 / °C) or secondary electric field regulation; 5. Compatibility: Compatible with silicon-based photonics processes and suitable for integrated optical chips. Description of the Drawings

[0012] Figure 1 It is a schematic structural diagram of the lithium niobate thin film optical waveguide of the present invention; Figure 2 For Figure 1 Top view.

[0013] In the figure: 1. Si substrate; 2. SiO 2Layer; 3. Lithium niobate substrate; 4. Metal electrode +; 5. Metal electrode -; 6. Ridge-type lithium niobate thin film optical waveguide layer; 7. Lithium niobate thin film planar layer. Detailed implementation manners

[0014] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention.

[0015] Embodiment 1 As Figure 1 and Figure 2 shown, in this embodiment, a method for fabricating a long-period grating structure in a lithium niobate thin film is as follows: S1. Etch the surface of the lithium niobate thin film to form a lithium niobate thin film optical waveguide. The lithium niobate thin film optical waveguide includes a lithium niobate substrate 3. The upper surface of the lithium niobate substrate 3 is etched to form a ridge-type lithium niobate thin film optical waveguide layer 6. The two sides of the ridge-type lithium niobate thin film optical waveguide layer 6 are lithium niobate thin film planar layers 7 formed after etching. The lower end surface of the lithium niobate substrate 3 is provided with a SiO 2 layer 2. The lower end surface of the SiO 2 layer 2 is provided with a Si substrate 1; S2. Deposit metal planar electrodes on the left and right lithium niobate thin film planar layers 7 respectively. A metal electrode + 4 is deposited on the left lithium niobate thin film planar layer 7, and a metal electrode - 5 is deposited on the right lithium niobate thin film planar layer 7; S3. Connect a 500 / 5 μs DC pulse voltage between the metal electrode + 4 and the metal electrode - 5 and keep it for 10 min; then perform annealing treatment, annealing at 400 °C for 2 h.

[0016] Further, the lithium niobate crystal substrate 3 is doped with titanium element with a concentration of 0.5%.

[0017] Embodiment 2 As Figure 1 and Figure 2 shown, a method for fabricating a long-period grating structure in a lithium niobate thin film is as follows: S1. Etch the surface of the lithium niobate thin film to form a lithium niobate thin film optical waveguide. The lithium niobate thin film optical waveguide includes a lithium niobate substrate 3. The upper surface of the lithium niobate substrate 3 is etched to form a ridge-type lithium niobate thin film optical waveguide layer 6. The two sides of the ridge-type lithium niobate thin film optical waveguide layer 6 are lithium niobate thin film planar layers 7 formed after etching. The lower end surface of the lithium niobate substrate 3 is provided with a SiO 2 layer 2. The lower end surface of the SiO 2 layer 2 is provided with a Si substrate 1; S2. Deposit metal planar electrodes on the left and right lithium niobate thin film planar layers 7 respectively. Deposit metal electrode +4 on the left lithium niobate thin film planar layer 7, and deposit metal electrode -5 on the right lithium niobate thin film planar layer 7; S3. Apply a DC pulse voltage of 800V / 5μs between metal electrode +4 and metal electrode -5 for 5 minutes; then perform annealing treatment, anneal at 500°C for 1.5 hours to obtain a lithium niobate thin film optical waveguide.

[0018] Furthermore, the lithium niobate crystal substrate 3 is doped with magnesium element with a concentration of 10%.

[0019] Example 3 As Figure 1 and Figure 2 shown, a manufacturing method of a long-period grating structure in a lithium niobate thin film is as follows: S1. Etch the surface of the lithium niobate thin film to form a lithium niobate thin film optical waveguide. The lithium niobate thin film optical waveguide includes a lithium niobate substrate 3. The upper surface of the lithium niobate substrate 3 is etched to form a ridge-type lithium niobate thin film optical waveguide layer 6. The two sides of the ridge-type lithium niobate thin film optical waveguide layer 6 are lithium niobate thin film planar layers 7 formed after etching. The lower end surface of the lithium niobate substrate 3 is provided with a SiO 2 layer 2, and the lower end surface of the SiO 2 layer 2 is provided with a Si substrate 1; S2. Deposit metal planar electrodes on the left and right lithium niobate thin film planar layers 7 respectively. Deposit metal electrode +4 on the left lithium niobate thin film planar layer 7, and deposit metal electrode -5 on the right lithium niobate thin film planar layer 7; S3. Apply a DC pulse voltage of 1000V / 5μs between metal electrode +4 and metal electrode -5 for 1 minute; then perform annealing treatment, anneal at 600°C for 1 hour.

[0020] Furthermore, the lithium niobate crystal substrate 3 is doped with titanium and magnesium elements with a concentration of 5%.

[0021] Control group Existing lithium niobate optical waveguide with a long-period grating structure.

[0022] Take the four optical waveguides in the above 3 examples and a control group respectively to test the loss peak depth and response time at 1550nm. The specific data are as follows: As can be seen from the above table, using the manufacturing method of a long-period grating structure in a lithium niobate thin film disclosed in the present invention, the obtained lithium niobate optical waveguide with a long-period grating structure is superior to the existing lithium niobate optical waveguide with a long-period grating structure in terms of both the loss peak depth of the transmission spectrum and the response time.

[0023] After placing the four optical waveguides in the above three embodiments and a control group in an incubator at 80 °C for 500 hours, the central wavelength drift and insertion loss change of the four optical waveguides were measured respectively. The results are shown in the following table: As can be seen from the above table, by using the method for fabricating a lithium niobate thin film long-period grating structure disclosed in the present invention, the lithium niobate optical waveguide with a long-period grating structure prepared is superior to the existing lithium niobate optical waveguide with a long-period grating structure in terms of high-temperature stability.

[0024] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for manufacturing a long period grating structure in a lithium niobate film, characterized in that: The specific steps are as follows: S1. Etching the surface of a lithium niobate film to form a lithium niobate film optical waveguide, wherein the lithium niobate film optical waveguide comprises a lithium niobate substrate (3), the upper surface of the lithium niobate substrate (3) is etched to form a ridged lithium niobate film optical waveguide layer (6), both sides of the ridged lithium niobate film optical waveguide layer (6) are lithium niobate film planar layers (7) formed after etching, the lower end surface of the lithium niobate substrate (3) is provided with a SiO2 layer (2), and the lower end surface of the SiO2 layer (2) is provided with a Si substrate (1); S2, plating metal planar electrodes on the left and right lithium niobate thin film planar layers (7), respectively, plating a metal electrode + (4) on the left lithium niobate thin film planar layer (7), and plating a metal electrode - (5) on the right lithium niobate thin film planar layer (7); S3, applying a 500-1000V / 5μs DC pulse voltage between the metal electrode + (4) and the metal electrode - (5) for 1-10 minutes; then annealing at 400-600°C for 1-2 hours; Wherein, the lithium niobate crystal substrate (3) is doped with titanium or magnesium elements at a concentration of 0.5%-10%.

2. The method for manufacturing a long period grating structure in a lithium niobate film according to claim 1, characterized in that: A 1000V / 5μs DC pulse voltage is applied between the metal electrode + (4) and the metal electrode - (5) for 1 minute; then annealing is performed at 600°C for 1 hour.

3. The method for manufacturing a long period grating structure in a lithium niobate film according to claim 1, characterized in that: The lithium niobate crystal substrate (3) is doped with titanium element at a concentration of 0.5%.

4. The method for manufacturing a long period grating structure in a lithium niobate film according to claim 1, characterized in that: The lithium niobate crystal substrate (3) is doped with magnesium element at a concentration of 10%.

5. The method for manufacturing a long period grating structure in a lithium niobate film according to claim 1, characterized in that: The lithium niobate crystal substrate (3) is doped with titanium and magnesium elements at a concentration of 5%.

6. A lithium niobate optical waveguide having a long period grating structure manufactured according to the method for manufacturing a long period grating structure in a lithium niobate film according to claims 1-5.

7. An application of the lithium niobate optical waveguide with a long period grating structure according to claim 6 in the fields of optical communication system mode converter, environmental monitoring and biosensing.

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