A method for uniform nucleation of periodically polarized potassium titanyl phosphate crystals

Abstract

The present invention discloses a method for uniform nucleation of periodically polarized potassium titanyl phosphate crystals. The method utilizes the depolarization effect caused by the built-in electric field of the material itself to make the inversion domain regress to a state that runs through the crystal but is not merged, so that a complete inversion domain remains on both sides of the metal electrode, that is, orderly nucleation is formed. This will provide an ideal expansion site for subsequent periodic polarization, so that the inversion domain can be directly expanded on this basis, thereby greatly improving the uniformity of the inversion domain after polarization, and has good application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of nonlinear optical crystal materials, and more particularly to a method for uniform nucleation of periodically polarized potassium titanyl phosphate crystals. Background Art

[0002] Laser is one of the greatest inventions of mankind in the 20th century. Due to its unique properties such as high brightness, high directivity, high monochromaticity and high coherence, it plays a vital role in quantum information, medical treatment, communication, industrial processing and scientific research, and is an important force to promote technological progress and innovation. However, since its generation mechanism depends on the transition of atoms or molecules between specific energy levels, this mechanism leads to the limitation of the wavelength of the laser, which limits some applications of the laser. The emergence of nonlinear optics fills this gap, and nonlinear crystal materials are the core of nonlinear optical conversion. Potassium titanyl phosphate is a commonly used nonlinear crystal material, but the phase mismatch caused by material dispersion greatly affects the conversion efficiency of light. The periodically polarized potassium titanyl phosphate based on quasi-phase matching technology can not only effectively compensate for the phase mismatch caused by material dispersion, but also significantly improve the conversion efficiency of light. At present, the most commonly used method for preparing periodically polarized potassium titanyl phosphate is the external electric field method. This method is to photolithograph periodic electrodes on the surface of the crystal and use a high voltage electric field to make the ferroelectric domain inside the crystal periodically reversed. However, due to the high conductivity of the potassium titanyl phosphate crystal itself, the polarization process is not easy to control.

[0003] The potassium titanium phosphate crystals mainly include four stages in the process of periodic polarization, namely, inversion domain nucleation, longitudinal and lateral expansion of inversion domains, inversion domain merging, and inversion domain stabilization. The above four stages are not completely independent and may also occur simultaneously. Among them, the initial nucleation process is particularly important. If a high-voltage electric field greater than the coercive field of the potassium titanium phosphate crystal is directly applied to the potassium titanium phosphate crystal, it will often cause the inversion domain to nucleate disorderly and randomly under the metal electrode, resulting in uncontrollable subsequent expansion of the inversion domain, and the inversion domain morphology is poor, which seriously affects the conversion efficiency.

[0004] Therefore, how to achieve uniform nucleation in the first stage of the periodic poling process is the primary and urgent problem that technicians in this field need to solve. Summary of the invention

[0005] In view of this, in order to achieve uniform nucleation of periodically polarized potassium titanium oxyphosphate, the present invention provides a nucleation method based on material built-in electric field regulation. The method utilizes the depolarization effect caused by the material's own built-in electric field to make the inversion domain regress to a state that runs through the crystal but is not merged, so that a complete inversion domain remains on both sides of the metal electrode, that is, an orderly nucleation is formed. This will provide an ideal expansion site for subsequent periodic polarization, so that the inversion domain can be directly expanded on this basis, thereby greatly improving the uniformity of the inversion domain after polarization, and has good application prospects.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A method for uniform nucleation of periodically polarized potassium titanyl phosphate crystals, comprising the following steps:

[0008] (1) On the Z plane of potassium titanyl phosphate crystal, periodic metal electrodes and full-coverage metal electrodes are respectively fabricated using semiconductor photolithography technology;

[0009] (2) Outputting a triangular wave pulse electric field consisting of a high electric field V1, a low electric field V2 and a stable electric field V3 through a signal generator;

[0010] (3) Testing the inversion domains of the crystal. If two continuous and complete inversion domains with a width of less than 1 / 4Λμm are formed on both sides of the metal electrode, the nucleation polarization is stopped; if two continuous and complete inversion domains with a width of ≥1 / 4Λμm are formed, the crystal is mono-domained and the voltage is lowered and step (2) is repeated; if two continuous and complete inversion domains are not formed, the crystal is mono-domained and the voltage is increased and step (2) is repeated;

[0011] (4) After the nucleation polarization process in step (3) is completed, a pulsed square wave electric field V4 is outputted by a signal generator to expand and merge the inversion domains on both sides of the metal electrode until the inversion domain width is approximately 1 / 2Λμm, thereby completing the polarization process.

[0012] Preferably, in step (1):

[0013] The thickness of the potassium titanyl phosphate crystal is ≥0.5 mm;

[0014] The periodic metal electrode is made on the -Z surface, and the full-coverage metal electrode is made on the +Z surface; or the periodic metal electrode is made on the +Z surface, and the full-coverage metal electrode is made on the -Z surface;

[0015] The metal electrode is gold, copper, chromium, titanium, aluminum or other conductive metal materials;

[0016] The thickness of the metal electrode is 50-500nm;

[0017] The period of the periodic metal electrode is ≥1 μm;

[0018] The width of the periodic metal electrode is ≤1 / 2Λμm;

[0019] The structure of the periodic metal electrode is a long strip structure or a structure that is partially hollow but maintains a long strip shape as a whole;

[0020] Preferably, in step (2):

[0021] The initial value of the high electric field V1 is 0 V / mm, and its final value reaches or exceeds 500 V / mm; the initial value of the low electric field V2 is set to the final value of V1 (i.e. reaches or exceeds 500 V / mm), and its final value is reduced to 1 / 4 of the final value of V1; the initial value of the stable electric field V3 is also set to 1 / 4 of the final value of V1, and its final value gradually decreases to 0 V / mm;

[0022] The electric field slope of the high electric field V1 is ≥10V / ms, the slope of the low electric field V2 is 0V / ms, and the slope of the stable electric field V3 is ≥10V / ms;

[0023] There is a transition zone of at least 5ms between the high electric field V1 and the low electric field V2; there is a transition zone of at least 5ms between the low electric field V2 and the stable electric field V3;

[0024] Preferably, in step (3):

[0025] The voltage is increased or decreased after the monodomainization, and the final value of V1 is increased or decreased by 500V each time, and the final value of V2 is increased or decreased by 125V each time; the change of V2 corresponds to the change of V1, ensuring that the value of V2 is 1 / 4 of V1;

[0026] The Λ is the inversion domain period, and its size can be customized by photolithography according to the use requirements;

[0027] The optimal width of the inversion domain is 1 / 2Λ, that is, the ratio of the inversion area to the non-inversion area is 1:1, at which the performance is optimal;

[0028] Preferably, in step (4):

[0029] The pulsed square wave electric field V4 comprises a pulsed electric field, a relaxation time and a pulse number;

[0030] The pulse electric field is greater than or equal to the coercive field of potassium titanyl phosphate crystal;

[0031] The relaxation time is ≥ 0.1 ms;

[0032] The pulse number is ≥1.

[0033] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0034] The uniform nucleation method of periodically polarized potassium titanyl phosphate provided by the present invention utilizes the depolarization effect caused by the built-in electric field of the material itself to form orderly nucleation, so that the inversion domain of the crystal is easier to control in subsequent expansion, thereby making it easier to obtain a uniform inversion domain, so that the ratio of the inversion area to the non-inversion area is about 1:1, and the conversion efficiency is close to the theoretical maximum value, thereby achieving the purpose of more effectively utilizing potassium titanyl phosphate. In addition, the present invention is simple to operate and the nucleation method is easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0036] Figure 1 The triangular wave pulse electric field used in the present invention for uniform nucleation of potassium titanyl phosphate crystal material;

[0037] Among them, region (I) is the high electric field stage; region (II) is the low electric field stage and the transition zone between the low electric field, the high electric field stage and the stable electric field; region (III) is the stable electric field stage.

[0038] Figure 2 A schematic diagram of the nucleation process of potassium titanyl phosphate crystal material using the technology of the present invention;

[0039] Among them, (a) is the initial state of the ferroelectric domain inside the potassium titanium phosphate crystal material; (b) is the state of the potassium titanium phosphate crystal material after the inversion domain is completely reversed after being subjected to a high electric field; (c) is the nucleation state of the potassium titanium phosphate crystal material after being subjected to a low electric field and a stable electric field.

[0040] Figure 3 This is a real picture of the inversion domain after uniform nucleation using the potassium titanyl phosphate crystal material of the present invention.

[0041] Figure 4 This is a physical picture of the inversion domain after periodic poling is completed using the potassium titanium oxide phosphate crystal material of the present invention. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] Example 1

[0044] This embodiment discloses a method for uniform nucleation of periodically polarized potassium titanyl phosphate crystals, comprising the following steps:

[0045] (1) fabricating a periodic metal electrode on the -Z surface of the potassium titanyl phosphate crystal and a fully covered metal electrode on the +Z surface;

[0046] In this embodiment, the thickness of the potassium titanyl phosphate crystal is 1 mm;

[0047] The metal electrode material is aluminum metal with a thickness of 200nm;

[0048] The period of the periodic metal electrode is 46 μm;

[0049] The width of the periodic metal electrode is 12 μm;

[0050] The shape of the periodic metal electrode is a long strip;

[0051] (2) The signal generator is used to output a signal such as Figure 1 The triangular wave pulse electric field shown is composed of a high electric field V1, a low electric field V2 and a stable electric field V3;

[0052] In this embodiment, the initial value of the high electric field V1 is 0 V / mm, the final value is 8 kV / mm, and the electric field slope is 80 V / ms;

[0053] The initial value of the low electric field V2 was 8 kV / mm, the final value was 2 kV / mm, and the electric field slope was 0 V / ms;

[0054] The initial value of the stable electric field V3 is 2 kV / mm, the final value is 0 V / mm, and the electric field slope is 25 V / ms;

[0055] There is a 10ms transition zone between the high electric field V1 and the low electric field V2, and a 10ms transition zone between the low electric field V2 and the stable electric field V3;

[0056] (3) Test the inversion domain of the crystal. If Figure 3 As shown, two continuous and complete inversion domains with a width of less than 11.5 μm are formed on both sides of the metal electrode, and the nucleation polarization stops;

[0057] If two continuous and complete inversion domains with widths ≥ 23 μm are formed, the final value of V1 after the crystal is monodomainized is reduced by 500 V, and the final value of V2 is reduced by 125 V, and step (2) is repeated;

[0058] If two continuous and complete inversion domains cannot be formed, the final value of V1 after the crystal is monodomainized is increased by 500V, and the final value of V2 is increased by 125V, and step (2) is repeated;

[0059] After the nucleation polarization process in step (3) is completed, a pulsed square wave electric field V4 is outputted by a signal generator to expand and merge the inversion domains on both sides of the metal electrode until the inversion domain width is about 23 μm, thereby completing the polarization process.

[0060] In this embodiment, the electric field of the square wave electric field V4 is 3 kV / mm;

[0061] The relaxation time of the square wave electric field V4 is 20 ms;

[0062] The number of pulses is ≥1. The number of pulses applied varies according to the expansion of the inversion domain, and the pulses are stopped after the expansion reaches the theoretical width.

[0063] Example 2

[0064] (1) fabricating a periodic metal electrode on the -Z surface of the potassium titanyl phosphate crystal and a fully covered metal electrode on the +Z surface;

[0065] In this embodiment, the thickness of the potassium titanyl phosphate crystal is 1 mm;

[0066] The metal electrode material is aluminum metal with a thickness of 200nm;

[0067] The period of the periodic metal electrode is 30 μm;

[0068] The width of the periodic metal electrode is 8 μm;

[0069] The shape of the periodic metal electrode is a long strip;

[0070] (2) The signal generator is used to output a signal such as Figure 1 The triangular wave pulse electric field shown is composed of a high electric field V1, a low electric field V2 and a stable electric field V3;

[0071] In this embodiment, the initial value of the high electric field V1 is 0 V / mm, the final value is 7 kV / mm, and the electric field slope is 50 V / ms;

[0072] The initial value of the low electric field V2 was 7 kV / mm, the final value was 1.75 kV / mm, and the electric field slope was 0 V / ms;

[0073] The initial value of the stable electric field V3 was 1.75 kV / mm, the final value was 0 V / mm, and the electric field slope was 20 V / ms;

[0074] There is a 10ms transition zone between the high electric field V1 and the low electric field V2, and a 10ms transition zone between the low electric field V2 and the stable electric field V3;

[0075] (3) Test the inversion domain of the crystal. If Figure 3 As shown, two continuous and complete inversion domains with a width of less than 7.5 μm are formed on both sides of the metal electrode, and the nucleation polarization stops;

[0076] If two continuous and complete inversion domains with widths ≥ 15 μm are formed, the final value of V1 after the crystal is monodomainized is reduced by 500 V, and the final value of V2 is reduced by 125 V, and step (2) is repeated;

[0077] If two continuous and complete inversion domains cannot be formed, the final value of V1 after the crystal is monodomainized is increased by 500V, and the final value of V2 is increased by 125V, and step (2) is repeated;

[0078] After the nucleation polarization process in step (3) is completed, a pulsed square wave electric field V4 is outputted by a signal generator to expand and merge the inversion domains on both sides of the metal electrode until the inversion domain width is about 15 μm, thereby completing the polarization process.

[0079] In this embodiment, the electric field of the square wave electric field V4 is 2.6 kV / mm;

[0080] The relaxation time of the square wave electric field V4 is 20 ms;

[0081] The number of pulses is ≥1. The number of pulses applied varies according to the expansion of the inversion domain, and the pulses are stopped after the expansion reaches the theoretical width.

[0082] Example 3

[0083] (1) fabricating a periodic metal electrode on the -Z surface of the potassium titanyl phosphate crystal and a fully covered metal electrode on the +Z surface;

[0084] In this embodiment, the thickness of the potassium titanyl phosphate crystal is 1 mm;

[0085] The metal electrode material is aluminum metal with a thickness of 200nm;

[0086] The period of the periodic metal electrode is 10 μm;

[0087] The width of the periodic metal electrode is 3 μm;

[0088] The shape of the periodic metal electrode is a long strip;

[0089] (2) The signal generator is used to output a signal such as Figure 1 The triangular wave pulse electric field shown is composed of a high electric field V1, a low electric field V2 and a stable electric field V3;

[0090] In this embodiment, the initial value of the high electric field V1 is 0 V / mm, the final value is 6 kV / mm, and the electric field slope is 30 V / ms;

[0091] The initial value of the low electric field V2 was 6 kV / mm, the final value was 1.5 kV / mm, and the electric field slope was 0 V / ms;

[0092] The initial value of the stable electric field V3 is 1.5 kV / mm, the final value is 0 V / mm, and the electric field slope is 15 V / ms;

[0093] There is a 10ms transition zone between the high electric field V1 and the low electric field V2, and a 10ms transition zone between the low electric field V2 and the stable electric field V3;

[0094] (3) Test the inversion domain of the crystal. If Figure 3 As shown, two continuous and complete inversion domains with a width of less than 2.5 μm are formed on both sides of the metal electrode, and the nucleation polarization stops;

[0095] If two continuous and complete inversion domains with widths ≥ 10 μm are formed, the final value of V1 after the crystal is monodomainized is reduced by 500 V, and the final value of V2 is reduced by 125 V, and step (2) is repeated;

[0096] If two continuous and complete inversion domains cannot be formed, the final value of V1 after the crystal is monodomainized is increased by 500V, and the final value of V2 is increased by 125V, and step (2) is repeated;

[0097] After the nucleation polarization process in step (3) is completed, a pulsed square wave electric field V4 is outputted by a signal generator to expand and merge the inversion domains on both sides of the metal electrode until the inversion domain width is about 10 μm, thereby completing the polarization process.

[0098] In this embodiment, the electric field of the square wave electric field V4 is 2 kV / mm;

[0099] The relaxation time of the square wave electric field V4 is 20 ms;

[0100] The number of pulses is ≥1. The number of pulses applied varies according to the expansion of the inversion domain, and the pulses are stopped after the expansion reaches the theoretical width.

[0101] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0102] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for uniform nucleation of periodically polarized potassium titanyl phosphate crystals, characterized in that: The following steps are involved: (1) On the Z plane of potassium titanyl phosphate crystal, periodic metal electrodes and full-coverage metal electrodes are respectively fabricated using semiconductor photolithography technology; (2) Outputting a triangular wave pulse electric field consisting of a high electric field V1, a low electric field V2 and a stable electric field V3 through a signal generator; (3) Testing the inversion domains of the crystal. If two continuous and complete inversion domains with a width of less than 1 / 4Λμm are formed on both sides of the metal electrode, the nucleation polarization is stopped; if two continuous and complete inversion domains with a width of ≥1 / 4Λμm are formed, the crystal is mono-domained and the voltage is lowered and step (2) is repeated; if two continuous and complete inversion domains are not formed, the crystal is mono-domained and the voltage is increased and step (2) is repeated; (4) After the nucleation polarization process in step (3) is completed, a pulsed square wave electric field V4 is outputted by a signal generator to expand and merge the inversion domains on both sides of the metal electrode until the inversion domain width is approximately 1 / 2Λμm, completing the polarization process.

2. The method for uniform nucleation of periodically polarized potassium titanyl phosphate crystals according to claim 2, characterized in that: In step (1), if the periodic metal electrode is made on the -Z surface, the full-coverage metal electrode is made on the +Z surface; or if the periodic metal electrode is made on the +Z surface, the full-coverage metal electrode is made on the -Z surface.

3. The method for uniform nucleation of periodically polarized potassium titanyl phosphate crystals according to claim 1, characterized in that: The metal electrode in step (1) is gold, copper, chromium, titanium, aluminum or other conductive metal materials; The thickness of the metal electrode is 50-500nm; The period of the periodic metal electrode is ≥1 μm; The width of the periodic metal electrode is ≤1 / 2Λμm; The structure of the periodic metal electrode is a long strip structure or partially left empty, but the overall structure is a long strip structure.

4. The method for uniform nucleation of periodically polarized potassium titanyl phosphate crystals according to claim 1, characterized in that: In step (2): the initial value of the high electric field V1 is 0 V / mm, and the final value thereof is ≥ 500 V / mm; The initial value of the low electric field V2 is set to the final value of V1, and its final value is 1 / 4 of the final value of V1; The initial value of the stable electric field V3 is 1 / 4 of the final value of V1, and its final value is 0 V / mm.

5. The method for uniform nucleation of periodically polarized potassium titanyl phosphate crystals according to claim 4, characterized in that: In step (2), the electric field slope of the high electric field V1 is ≥10 V / ms, the slope of the low electric field V2 is 0 V / ms, and the slope of the stable electric field V3 is ≥10 V / ms.

6. The method for uniform nucleation of periodically polarized potassium titanyl phosphate crystals according to claim 1, characterized in that: In step (2), there is a transition zone of ≥5 ms between the high electric field V1 and the low electric field V2; and there is a transition zone of ≥5 ms between the low electric field V2 and the stable electric field V3.

7. The method for uniform nucleation of periodically polarized potassium titanyl phosphate crystals according to claim 1, characterized in that: The voltage is increased or decreased after the single domain transformation in step (3): the final value of V1 is increased or decreased by 500V each time, and the final value of V2 is increased or decreased by 125V each time; The Λ is the inversion domain period, and its size is customized by photolithography according to the use requirements; The optimal width of the inversion domain is 1 / 2Λ, that is, the ratio of the inversion area to the non-inversion area is 1:

1.

8. The method for uniform nucleation of periodically polarized potassium titanyl phosphate crystals according to claim 1, characterized in that: The pulsed square wave electric field V4 in step (4) comprises a pulsed electric field, a relaxation time and a number of pulses; The pulse electric field is greater than or equal to the coercive field of potassium titanyl phosphate crystal; The relaxation time is ≥ 0.1 ms; The pulse number is ≥1.

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