Method for preparing ferroelectric crystal optical superlattice by using pyroelectric effect, superlattice and application

Abstract

The invention discloses a method for preparing a ferroelectric crystal optical superlattice by using a pyroelectric effect, the superlattice and application, and belongs to the field of electronic and optical devices. The method comprises the following steps: preparing a ferroelectric crystal material carrying an electrode pattern; the ferroelectric crystal material carrying the electrode pattern is heated, the heating temperature is 50-200 DEG C, and within the temperature range, the ferroelectric crystal material carrying the electrode pattern excites the polarization reverse direction of the ferroelectric crystal material by using the pyroelectric performance of the ferroelectric crystal material; the annealing step is carried out, and the annealing rate is 50-150 DEG C / h; and heating and annealing are cycled for 1-10 times to obtain the aluminum alloy. The limitation of an external electric field polarization method on different electrode structures is broken through by creating a novel polarization process, different superlattice crystals based on electrodes of various structures are prepared, and the application scene and the application field of ferroelectric crystal materials are further expanded.

Description

Technical Field

[0001] The present invention belongs to the field of electronic and optical devices, and relates to nonlinear optical crystal material technology and laser technology, and specifically to a method for preparing a ferroelectric crystal optical superlattice by utilizing the pyroelectric effect, a superlattice and an application thereof. Background Art

[0002] Ferroelectric crystal optical superlattice is a nonlinear optical material based on quasi-phase matching technology. Optical superlattices with different microstructures are developed through ferroelectric domain engineering, which can achieve efficient and flexible nonlinear frequency conversion and multi-dimensional control of the light field. The basic structural unit of the optical superlattice consists of a pair of positive and negative domains. For example, in ferroelectric crystals such as lithium niobate and lithium tantalate, the spontaneous polarization directions in the positive and negative domains are parallel and anti-parallel to the z-axis of the crystal, respectively. Repeating such basic structural units forms a one-dimensional periodic optical superlattice. If two groups of structural units are arranged according to a certain rule, a two-component quasi-periodic optical superlattice is formed. The optical superlattice microstructure can provide a rich variety of reciprocal lattice vectors to compensate for the wave vector mismatch caused by material dispersion in the process of nonlinear optical parameters, and obtain efficient nonlinear frequency conversion efficiency. It has now shown great potential in the fields of optical shaping, laser light sources and quantum communications.

[0003] The existing technology for preparing optical superlattices is mainly through the external electric field method. After annealing, polarization and other post-processing procedures are carried out on the native lithium niobate crystal, it is cut and polished into chips, and then conductive electrodes are plated on the chips using micro-nano processing lithography technology. Finally, a voltage of a special waveform is applied to achieve periodic reversal of the ferroelectric domain of the chip.

[0004] The above-mentioned prior art preparation methods still have the following technical problems. First, the process involved needs to be pressurized at high temperature, which makes it difficult to accurately control the growth and production of domain structures. Pressurization at high temperature will also make it impossible to obtain two-dimensional optical superlattice materials due to the limitation of electrode structure. Second, the electrodes constructed for two-dimensional optical superlattice cannot fully connect the circuit, so the external electric field polarization scheme cannot meet the requirements of all types of optical superlattice preparation.

[0005] This shows that the prior art needs to be further improved. Summary of the invention

[0006] One of the purposes of the present invention is to provide a method for preparing ferroelectric crystal optical superlattice using the pyroelectric effect. By creating a new polarization process, the limitations of the external electric field polarization method for different electrode structures can be broken through, and the preparation of different superlattice crystals based on various structural electrodes can be realized, further expanding the application scenarios and application fields of ferroelectric crystal materials.

[0007] In order to achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a method for preparing a ferroelectric crystal optical superlattice using the pyroelectric effect, comprising the following steps: S1, preparing a ferroelectric crystal material carrying an electrode pattern: using a ferroelectric crystal material as a raw material, and uniformly vapor-depositing conductive electrodes on its front and back sides respectively; spin-coating photoresist on the surface of the ferroelectric crystal material with the vapor-deposited conductive electrodes; and sequentially subjecting the surface of the ferroelectric crystal material with the spin-coated photoresist to photolithography, development, baking, metal corrosion and photoresist removal to obtain a ferroelectric crystal material carrying an electrode pattern.

[0008] S2, heating-annealing: heating the ferroelectric crystal material carrying the electrode pattern, the heating temperature is 50-200°C, within this temperature range, the ferroelectric crystal material carrying the electrode pattern uses its own pyroelectric properties to excite its polarization in the opposite direction; when the heating time is 300 s, an annealing step is performed, and the annealing rate is 50-150°C / h.

[0009] S3. Cycle S2 1 to 10 times to obtain a ferroelectric crystal optical superlattice.

[0010] In the above-mentioned method for preparing a ferroelectric crystal optical superlattice using the pyroelectric effect, in S1, the above-mentioned ferroelectric crystal material is lithium niobate, lithium tantalate, potassium tantalate niobate or a thin film of any one of them.

[0011] In the above-mentioned method for preparing a ferroelectric crystal optical superlattice using the pyroelectric effect, the above-mentioned ferroelectric crystal material is lithium niobate.

[0012] In the above method for preparing a ferroelectric crystal optical superlattice using the pyroelectric effect, in S2, the above heating temperature is 200° C. and the annealing rate is 100° C. / h.

[0013] In the above-mentioned method of preparing a ferroelectric crystal optical superlattice using the pyroelectric effect, S2 is cycled 10 times.

[0014] Another object of the present invention is to provide a ferroelectric crystal optical superlattice, which is prepared by using the above-mentioned method for preparing a ferroelectric crystal optical superlattice using the pyroelectric effect.

[0015] The above-mentioned ferroelectric crystal optical superlattice has a two-dimensional structure.

[0016] Another object of the present invention is to provide an application of the above-mentioned ferroelectric crystal optical superlattice in a nonlinear frequency conversion crystal device.

[0017] The preparation principle of the ferroelectric crystal optical superlattice prepared by the present invention using the pyroelectric effect is as follows: the phenomenon of the change of the spontaneous polarization intensity of the polar crystal due to the change of the external temperature is called the pyroelectric effect. The crystal with this property is called the pyroelectricity of the crystal. A basic feature of the ferroelectric crystal is that it has the pyroelectric effect, which can be generated without adding an additional electric field. When the external temperature changes, there will be a certain pyroelectric effect. After the ferroelectric crystal is lower than its own Curie temperature, it will spontaneously have asymmetry in a certain direction due to the lack of the crystal's own lattice vibration mode, and a certain degree of phase change will occur. If the pyroelectric is heated, the dipoles in the material lose their direction due to thermal vibration, and its spontaneous polarization level will decrease, resulting in a decrease in the number of free charges bound to the surface of the material. If the crystal is in an open circuit state, the free charges remain on the electrode surface and generate a potential on the material, thereby constructing a built-in electric field inside the crystal, and the crystal polarization is achieved by applying an external electric field to the crystal to achieve high voltage. Therefore, the pyroelectric effect can be used to prepare the ferroelectric crystal optical superlattice.

[0018] The ferroelectric crystal material selected by the present invention is lithium niobate, lithium tantalate or potassium tantalate niobate, or a thin film of lithium niobate, lithium tantalate or potassium tantalate niobate. When the ferroelectric crystal material is heated to 50-200°C, it releases electric charge. The pyroelectric property of the ferroelectric crystal material is used to stimulate the reverse direction of its polarization. Combined with the annealing process, the annealing rate is controlled to be 50-150°C / h, so that the domain structure reversal of the portion with the electrode pattern can be achieved.

[0019] Compared with the prior art, the present invention brings the following beneficial technical effects: (1) In terms of the selection of raw materials, the ferroelectric crystal material selected by the present invention, such as lithium niobate, has pyroelectric properties. After being heated to a certain temperature, it can release electric charge by itself, eliminating the process steps that require additional pressurization in the prior art; in addition, through the close combination of heating-annealing process, the domain structure inversion of the part with electrode pattern can be achieved. Compared with the external electric field polarization in the prior art, the present invention does not require an external electric field, and utilizes the pyroelectric properties of the crystal itself, combined with metal electrodes to obtain an optical superlattice crystal material consistent with the electrode design.

[0020] (2) With the help of the polarized electrode structure of the present invention, the limitation of using an external electric field to prepare optical superlattice materials, that is, the inability to obtain two-dimensional optical superlattice materials due to the limitation of the electrode structure, can be solved, and the preparation of different superlattice crystals based on various structural electrodes can be realized, thereby expanding the application scenarios and fields of ferroelectric crystal materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Flow chart of preparing ferroelectric crystal optical superlattice according to the present invention.

[0022] Figure 2 This is a diagram of the lithium niobate inversion domain structure obtained by the pyroelectric effect in an embodiment of the present invention.

[0023] Figure 3 Domain core distribution of lithium niobate crystal optical superlattice prepared in Examples 1 to 4, wherein (a) corresponds to Example 2, (b) corresponds to Example 3, (c) corresponds to Example 4, and (d) corresponds to Example 1.

[0024] Figure 4 Domain core distribution of lithium niobate crystal fiber superlattice prepared in Example 1, Example 10, Example 11, and Example 12, wherein (e) corresponds to Example 10, (f) corresponds to Example 11, (g) corresponds to Example 12, and (h) corresponds to Example 1. DETAILED DESCRIPTION

[0025] The present invention proposes a method for preparing a ferroelectric crystal optical superlattice using the pyroelectric effect, a superlattice and an application. In order to make the advantages and technical solutions of the present invention clearer and more specific, the present invention is further described below in conjunction with specific embodiments.

[0026] In the description of this application, unless otherwise specified, " / " means "or", for example, A / B can mean A or B. "And / or" in this article is only a way to describe the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone.

[0027] The above-mentioned raw materials in the present invention can be purchased through commercial channels.

[0028] The main technical concept of the present invention is to change the preparation process of optical superlattice in the prior art, which is mainly reflected in the elimination of the original pressurization step. Through the selection of ferroelectric crystal materials and the combination of heating-annealing process, the preparation of different superlattice crystals based on various structural electrodes is realized.

[0029] The present invention provides a method for preparing a ferroelectric crystal optical superlattice by utilizing the pyroelectric effect. Figure 1 As shown, the process comprises the following steps: the first step is to prepare a ferroelectric crystal material carrying an electrode pattern: (1) using a ferroelectric crystal material as a raw material, and uniformly depositing conductive electrodes on its front and back surfaces respectively; preferably, the ferroelectric crystal material is lithium niobate, lithium tantalate or potassium tantalate niobate, or a thin film of lithium niobate, lithium tantalate or potassium tantalate niobate.

[0030] (2) Spin-coating photoresist on the surface of the ferroelectric crystal material with the evaporated conductive electrode. The purpose of this step is to make the surface of the ferroelectric crystal material have metal strips, which can be regular strips or other patterns.

[0031] (3) The surface of the ferroelectric crystal material on which the photoresist is spin-coated is subjected to photolithography, development, baking, metal etching, and photoresist removal in sequence to obtain a ferroelectric crystal material carrying an electrode pattern.

[0032] The second step is heating-annealing: the ferroelectric crystal material carrying the electrode pattern is heated at a temperature of 50 to 200°C. Within this temperature range, the ferroelectric crystal material carrying the electrode pattern uses its own pyroelectric properties to excite its polarization in the opposite direction; when the heating time is 300 s, an annealing step is performed at an annealing rate of 50 to 150°C / h.

[0033] Step 3: Repeat step 2 1 to 10 times to obtain a ferroelectric crystal optical superlattice.

[0034] As a further preference, in the above-mentioned method for preparing a ferroelectric crystal optical superlattice using the pyroelectric effect, the ferroelectric crystal material is lithium niobate.

[0035] As a further preference, in the above-mentioned method for preparing a ferroelectric crystal optical superlattice using the pyroelectric effect, the heating temperature is 200° C., the annealing rate is 100° C. / h, and the number of annealing cycles is 10 times.

[0036] The present invention is described in detail below with reference to specific embodiments.

[0037] Embodiment 1: The ferroelectric crystal material of this embodiment is lithium niobate.

[0038] The specific steps are as follows: Step 1, prepare a ferroelectric crystal material with an electrode pattern: (1) uniformly deposit conductive electrodes on the front and back sides of lithium niobate. (2) spin-coat photoresist on the surface of the lithium niobate crystal material with the conductive electrode deposited. (3) sequentially perform photolithography, development, baking, metal etching and photoresist removal on the surface of the lithium niobate crystal material with the photoresist spin-coated to obtain a lithium niobate crystal material with an electrode pattern.

[0039] The second step is heating-annealing: the lithium niobate crystal material carrying the electrode pattern is heated to 200°C. At this temperature, the ferroelectric crystal material carrying the electrode pattern uses its own pyroelectric properties to excite its polarization in the opposite direction. When the heating time is 300 s, an annealing step is performed at an annealing rate of 100°C / h for 10 min to bring it to room temperature.

[0040] Step 3: Repeat step 2 ten times to obtain a lithium niobate crystal optical superlattice.

[0041] Figure 2 This is a diagram of the inversion domain structure of the lithium niobate crystal optical superlattice prepared in this embodiment.

[0042] Example 2: The difference from Example 1 is that the heating temperature of this example is 25°C.

[0043] Example 3: The difference from Example 1 is that the heating temperature of this example is 100°C.

[0044] Example 4: The difference from Example 1 is that the heating temperature of this example is 150°C.

[0045] The domain core distribution of the lithium niobate crystal optical superlattice prepared in Examples 1 to 4 was observed. Figure 3 As shown in (a), (b), (c), and (d), it is concluded that the domain distribution is optimal when the heating temperature is 200°C. When the heating temperature continues to increase, such as increasing to 250°C, it will reach the threshold of the crystal pyroelectric effect, and there will be no better effect. As the temperature rises, the thermal stress inside the crystal will cause dislocation rows and slip line defects inside the lattice, which can easily lead to crystal rupture.

[0046] Example 5: The difference from Example 1 is that the ferroelectric crystal material of this example is lithium tantalate.

[0047] Example 6: The difference from Example 1 is that the ferroelectric crystal material of this example is potassium tantalate niobate.

[0048] Example 7: The difference from Example 1 is that the ferroelectric crystal material of this example is a thin film of lithium niobate.

[0049] Embodiment 8: The difference from Embodiment 1 is that the ferroelectric crystal material of this embodiment is a thin film of lithium tantalate.

[0050] Example 9: The difference from Example 1 is that the ferroelectric crystal material of this example is a thin film of potassium tantalate niobate.

[0051] Example 10: The difference from Example 1 is that in the third step of this example, the annealing cycle is performed once to obtain a lithium niobate crystal optical superlattice.

[0052] Example 11: The difference from Example 1 is that in the third step of this example, the annealing cycle is performed three times to obtain a lithium niobate crystal optical superlattice.

[0053] Example 12: The difference from Example 1 is that in the third step of this example, the annealing cycle is repeated five times to obtain a lithium niobate crystal optical superlattice.

[0054] The domain core distribution of the lithium niobate crystal fiber superlattice prepared in the above-mentioned embodiment 1, embodiment 10, embodiment 11, and embodiment 12 is analyzed. Figure 4 As shown, Figure 4(e) corresponds to Example 10, (f) corresponds to Example 11, (g) corresponds to Example 12, and (h) corresponds to Example 1. Figure 4 It is known that the best effect is achieved when the number of cycles in Example 1 is 10. When the number of cycles continues to increase, such as when the number of cycles is 15, dislocation rows and slip line defects will be generated inside the lattice due to thermal stress, thereby causing the crystal to break.

[0055] Parts not described in the present invention can be implemented by referring to the existing technology.

[0056] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present application and are not intended to be limiting of the present application. As long as they are within the spirit and scope of the present application, appropriate changes and modifications to the above embodiments are within the scope of protection of the claims of the present application.

Claims

1. A method for preparing a ferroelectric crystal optical superlattice using the pyroelectric effect, characterized in that: The following steps are involved: S1. Preparation of ferroelectric crystal materials carrying electrode patterns Using ferroelectric crystal material as raw material, uniform conductive electrodes are evaporated on its front and back surfaces respectively; Spin-coating a photoresist on the surface of the ferroelectric crystal material on which the conductive electrode is evaporated; The surface of the ferroelectric crystal material on which the photoresist is spin-coated is subjected to photolithography, development, baking, metal corrosion and photoresist removal in sequence to obtain a ferroelectric crystal material carrying an electrode pattern; S2, heating-annealing The ferroelectric crystal material carrying the electrode pattern is heated at a temperature of 50 to 200° C. Within this temperature range, the ferroelectric crystal material carrying the electrode pattern uses its own pyroelectric properties to excite its polarization in the opposite direction; when the heating time is 300 seconds, an annealing step is performed at an annealing rate of 50 to 150° C. / h; S3. Cycle S2 1 to 10 times to obtain a ferroelectric crystal optical superlattice.

2. The method for preparing a ferroelectric crystal optical superlattice using the pyroelectric effect according to claim 1, characterized in that: In S1, the ferroelectric crystal material is lithium niobate, lithium tantalate, potassium tantalate niobate or a thin film of any one of them.

3. The method for preparing a ferroelectric crystal optical superlattice using the pyroelectric effect according to claim 1, characterized in that: The ferroelectric crystal material is lithium niobate.

4. The method for preparing a ferroelectric crystal optical superlattice using the pyroelectric effect according to claim 1, characterized in that: In S2, the heating temperature is 200°C and the annealing rate is 100°C / h.

5. The method for preparing a ferroelectric crystal optical superlattice using the pyroelectric effect according to claim 1, characterized in that: In S3, S2 is cycled 10 times.

6. A ferroelectric crystal optical superlattice, characterized in that: The optical superlattice is prepared by the method for preparing a ferroelectric crystal optical superlattice by utilizing the pyroelectric effect as described in any one of claims 1 to 5.

7. The ferroelectric crystal optical superlattice according to claim 6, characterized in that: The ferroelectric crystal optical superlattice is a two-dimensional structure.

8. An application of a ferroelectric crystal optical superlattice, characterized in that: The application is the application of a ferroelectric crystal optical superlattice as described in claim 6 in a nonlinear frequency conversion crystal device.

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