Device for realizing quasi-phase matching based on pyroelectric field induced polarization ferroelectric domain

Abstract

The invention discloses a device for realizing quasi-phase matching based on a pyroelectric field induced polarization ferroelectric domain, and the device is characterized in that the ferroelectric domain of a lithium niobate crystal is erased along an optical axis through employing a laser erasing technology, and a grating array structure is formed; then generating a pyroelectric field in the lithium niobate crystal by using a quenching process under vacuum to induce a ferroelectric domain to be polarized from the erasing position to the surface of the crystal along the optical axis, so that the polarized ferroelectric domain is also distributed in a grating array manner; the fundamental wave is subjected to frequency multiplication conversion through a ferroelectric domain polarization area, and the peak value of the frequency multiplication light spot power changing along with the wavelength of the fundamental wave is measured to be matched with the peak value calculated under the quasi-phase matching condition, so that quasi-phase matching is realized. Any external electric field is not needed, and a pyroelectric field opposite to the polarization direction can be generated in the crystal. The pyroelectric field can enable the ferroelectric domain to be reversed, and meanwhile the refractive index cannot be changed. According to the invention, the ferroelectric domain of the pyroelectric field polarized lithium niobate crystal is utilized, and frequency multiplication conversion meeting quasi-phase matching conditions is realized.

Description

Technical Field

[0001] The present invention relates to the field of quasi-phase matching technology, in particular to the quasi-phase matching technology of ferroelectric domain polarization, and specifically to a quasi-phase matching device based on pyroelectric field-induced polarization of ferroelectric domains. Background Art

[0002] The second harmonic generation (SHG) process is one of the most fundamental nonlinear optical effects, in which an intense pump beam excites the nonlinear response of dipoles in the medium (nonlinear polarization) as a source of frequency doubling of the new wave. In 1961, Franken et al. first experimentally demonstrated the SHG process, and experimental nonlinear optics was born. A large number of studies have shown that frequency conversion processes, including sum and difference frequency conversion, can be performed in a medium with a second-order nonlinear coefficient χ (2) The nonlinear light is generated in optical materials such as ferroelectric crystals, semiconductors, and some isotropic media such as glass. However, due to the existence of dispersion effects, there is a phase mismatch between the fundamental wave and the generated nonlinear light during the nonlinear conversion process, which causes the nonlinear light beam to oscillate periodically with the propagation distance in the medium and cannot achieve stable output. The second-order nonlinear coefficient of periodic modulation χ (2) It can compensate for the mismatched phase, improve the nonlinear conversion efficiency, and realize the quasi-phase matching process. Quasi-phase matching technology is easy to implement in ferroelectric crystals and is widely used in the development of high-quality, pure and stable light sources at new frequencies, promoting the development of laser pointers, high-energy laser sources, laser material processing, nonlinear optical microscopy, optical signal processing, quantum communication, quantum sensing and quantum computing.

[0003] Ferroelectric materials commonly used in the optical field include LiNbO3, LiTaO3 and KTP crystals. Spontaneous polarization exists in these crystals, and the regions with the same polarization direction are called ferroelectric domains. Ferroelectric domains have two opposite polarization directions, and the change of polarization direction is accompanied by the second-order nonlinear coefficient χ (2) The external electric field can reverse the polarization direction of the domain, thereby realizing the second-order nonlinear coefficient χ (2) Spatial modulation. This polarization technology was first applied to the processing of one-dimensional (1D) periodic domain structures, achieving collinear quasi-phase matching. With the promotion of polarization technology in two-dimensional (2D) structures, multi-channel quasi-phase matching technology was born. When polarization technology is used for deep processing, it will inevitably cause the domain structure to broaden and the processing accuracy cannot be guaranteed. Three-dimensional (3D) structures were first realized by femtosecond laser processing. The focused pulsed laser can locally reduce the nonlinear coefficient χ of the crystal. (2) , forming a weakly modulated quasi-phase matching. Compared with the domain inversion structure, the nonlinear conversion efficiency of this method is low. Summary of the invention

[0004] In view of this, in order to solve the above-mentioned problems in the prior art, the present invention proposes a quasi-phase matching device based on pyroelectric field-induced polarization of ferroelectric domains, which utilizes pyroelectric field to polarize ferroelectric domains of lithium niobate crystals to form a grating array structure, thereby realizing frequency doubling conversion that meets the quasi-phase matching conditions.

[0005] The present invention solves the above problems by the following technical means:

[0006] In a first aspect, the present invention provides a quasi-phase matching device based on pyroelectric field-induced polarized ferroelectric domains, wherein the device firstly uses a laser erasing process to erase the ferroelectric domains of a lithium niobate crystal along an optical axis to form a grating array structure;

[0007] Then, a quenching process under vacuum is used to generate a pyroelectric field in the lithium niobate crystal to induce the ferroelectric domain to polarize from the erased position along the optical axis toward the crystal surface, so that the polarized ferroelectric domain is also distributed in a grating array.

[0008] The fundamental wave undergoes frequency doubling conversion through the ferroelectric domain polarization region, and the peak value of the frequency doubling spot power that varies with the fundamental wave wavelength is measured to be consistent with the peak value calculated under the quasi-phase matching condition, thus achieving quasi-phase matching.

[0009] Preferably, the fundamental wave undergoes frequency doubling conversion of different orders satisfying quasi-phase matching through the ferroelectric domain polarization region, and the formula is expressed as:

[0010]

[0011] in are the reciprocal lattice vectors of the fundamental wave and the doubled frequency light, is the reciprocal lattice vector of the polarized ferroelectric domain structure inverse space, expressed as:

[0012]

[0013] in, is the unit vector in the x and y directions in the rectangular coordinate system, p and q are arbitrary integers; the reciprocal lattice vector required for the 0-level frequency-doubled spot is For the positive and negative 1-level frequency-doubled light spots, the inverse lattice vectors are and For the positive and negative double frequency spots, the inverse lattice vectors are and

[0014] Preferably, the laser erasing process is a femtosecond laser erasing process.

[0015] In a second aspect, the present invention provides a system for preparing a quasi-phase matching device based on pyroelectric field-induced polarized ferroelectric domains, which is used to prepare the quasi-phase matching device based on pyroelectric field-induced polarized ferroelectric domains, and includes a laser erasing process subsystem and a vacuum quenching process subsystem;

[0016] The laser erasing process subsystem includes a first laser, a gradient attenuation plate, a first half-wave plate, a first objective lens, a magnesium-doped lithium niobate crystal, a three-dimensional nano-translation stage and a computer;

[0017] The first laser emits laser light along the z direction, and the energy of the laser light is controlled by a gradient attenuation plate to compensate the energy in depth of the laser processing. After passing through the first half-wave plate, the polarization changes to the x direction. After passing through the first objective lens, the laser light is focused onto a magnesium-doped lithium niobate crystal. The lithium niobate crystal is placed on a three-dimensional nano-translation stage. The three-dimensional nano-translation stage is controlled by a computer to make the laser light scribe lines along the z direction under the crystal surface. In this process, the laser focus moves from deep to shallow, and the same structure is continuously scribed along the x and y directions to form a grating array structure.

[0018] The quenching process subsystem includes a vacuum temperature control platform, an illumination light source, a first polarizer, a second polarizer, a second objective lens and a CCD;

[0019] The laser processed lithium niobate crystal is placed on a vacuum temperature control platform, slowly heated to 180-220°C, then vacuumed, and then rapidly cooled to room temperature. During the cooling process, a pyroelectric field opposite to the spontaneous polarization direction is generated, which will cause the ferroelectric domain to reverse from the laser processing area along the optical axis z direction to the crystal surface, so that the polarized ferroelectric domain is also distributed in a grating array;

[0020] The illumination light source illuminates the crystal, and the orthogonal first polarizer and second polarizer are placed above and below the lithium niobate crystal respectively to ensure that only the laser processing area and the domain inversion area are illuminated, and then magnified by the second objective lens and finally collected by the CCD to achieve real-time observation of the domain structure of the lithium niobate crystal.

[0021] Preferably, the laser erasing process subsystem further comprises an optical shutter, which is arranged between the first laser and the gradient attenuation plate and is used to control the opening and closing of the laser.

[0022] Preferably, the first laser emits laser light with a wavelength of 800 nm, a pulse width of 34 fs and a repetition frequency of 1 kHz along the z direction.

[0023] In a third aspect, the present invention provides a quasi-phase matching system based on pyroelectric field induced polarized ferroelectric domains, including the quasi-phase matching device based on pyroelectric field induced polarized ferroelectric domains, and also includes a second laser, a second half-wave plate, a polarization beam splitter, a third half-wave plate, a lens and a filter;

[0024] The second laser emits laser light along the x direction, and the energy of the laser light is controlled by the second half-wave plate and the polarization beam splitter. The polarization direction of the laser light is then controlled along the y direction by the third half-wave plate. Finally, the laser light is focused by a lens onto the polarization region on the device for realizing quasi-phase matching based on pyroelectric field induced polarization ferroelectric domains. The fundamental wave is filtered out by a filter and the doubled frequency signal is observed.

[0025] Preferably, the second laser emits laser light with a pulse width of 140 fs, a repetition frequency of 80 MHz and a power of 400 mW along the x direction.

[0026] Preferably, the focal length of the lens is 75 mm.

[0027] Compared with the prior art, the beneficial effects of the present invention include at least:

[0028] The present invention combines laser processing with heat treatment, does not require any external electric field, and can generate a pyroelectric field in the crystal that is opposite to the polarization direction. The pyroelectric field can reverse the ferroelectric domain without causing a change in the refractive index. The present invention uses the pyroelectric field to polarize the ferroelectric domain of the lithium niobate crystal to form a grating array structure, thereby achieving frequency doubling conversion that meets the quasi-phase matching condition. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 The present invention is a schematic diagram of the principle of realizing quasi-phase matching based on ferroelectric domains polarized by pyroelectric field; wherein (a) is a lithium niobate crystal polarized by pyroelectric field; (b) is the quasi-phase matching condition of the polarized ferroelectric domains of the lithium niobate crystal in the reciprocal space on the xoy plane;

[0031] Figure 2The invention is based on the processing diagram of ferroelectric domains polarized by pyroelectric field, wherein (a) the optical path of femtosecond laser erasing ferroelectric domains of lithium niobate crystal; (b) the morphology of ferroelectric domains erased by yoz plane under microscope; (c) the morphology of ferroelectric domains erased by xoy plane under microscope; (d) the optical path of ferroelectric domains polarized by pyroelectric field of lithium niobate crystal produced by vacuum quenching; (e) the morphology of ferroelectric domains polarized by yoz plane under microscope;

[0032] Figure 3 It is a quasi-phase matching characterization optical path diagram of the present invention;

[0033] Figure 4 It is a quasi-phase matching result diagram of the first-order frequency doubling light spot of the present invention, wherein (a) is the power diagram of the first-order frequency doubling light spot when the fundamental wave incident power is 0.4W and the wavelength increases from 890nm to 916nm, (b) is the diagram of the frequency doubling light spot when the fundamental wave wavelength is 904nm, (c) is the quasi-phase matching diagram of the positive and negative first-order frequency doubling light spots in the reciprocal space on the xoy plane, and (d) is the power diagram of the first-order frequency doubling light spot when the fundamental wave power increases from 40mW to 460mW. DETAILED DESCRIPTION

[0034] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be pointed out that the described embodiments are only part of the embodiments of the present invention, not all of them. 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.

[0035] The present invention may also be implemented or applied through other different specific examples, and the details in this specification may also be modified and changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0036] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0037] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. Secondly, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0038] Example 1

[0039] like Figure 1 As shown, the present invention provides a quasi-phase matching device based on pyroelectric field-induced polarized ferroelectric domains. The device first uses a femtosecond laser erasing process to erase the ferroelectric domains of a lithium niobate crystal along the optical axis direction (z direction) to form a grating array structure;

[0040] Then, a quenching process under vacuum is used to generate a pyroelectric field in the lithium niobate crystal to induce the ferroelectric domain to polarize from the erased position along the optical axis (z direction) toward the crystal surface, so that the polarized ferroelectric domain is distributed in a grating array with a period of 4 microns.

[0041] The fundamental wave undergoes frequency doubling conversion through the ferroelectric domain polarization region, and the peak value of the frequency doubling spot power that varies with the fundamental wave wavelength is experimentally measured to be consistent with the peak value calculated under the quasi-phase matching condition, proving that quasi-phase matching has been achieved.

[0042] This embodiment provides a quasi-phase matching technology based on pyroelectric field induced polarization of ferroelectric domains. The ferroelectric domain structure is as follows: Figure 1 As shown in (a), the periodic grating array is generated by erasing the ferroelectric domains with a femtosecond laser, and then a pyroelectric field is generated through a quenching process to polarize the ferroelectric domains along the erased area toward the crystal surface, with a period of Λ. Figure 1 (b) is the reciprocal space of the polarized ferroelectric domain structure, with a period of The fundamental wave undergoes frequency doubling conversion of different orders satisfying quasi-phase matching through the ferroelectric domain polarization region. The formula can be expressed as:

[0043]

[0044] in are the reciprocal lattice vectors of the fundamental wave and the doubled frequency light, is the reciprocal lattice vector of the polarized ferroelectric domain structure inverse space, which can be expressed as:

[0045]

[0046] in, is the unit vector in the x and y directions in the rectangular coordinate system, and p and q are arbitrary integers. The reciprocal lattice vector required for the 0-level frequency-doubled spot is For the positive and negative 1-level frequency-doubled light spots, the inverse lattice vectors are and For the positive and negative double frequency spots, the inverse lattice vectors are and

[0047] Example 2

[0048] like Figure 2 As shown, Figure 2 The processing scheme of lithium niobate crystal pyroelectric field induced polarized ferroelectric domains is demonstrated, which is mainly divided into two steps: laser erasing and vacuum quenching. The present invention provides a preparation system for a quasi-phase matching device based on pyroelectric field induced polarized ferroelectric domains, which is used to prepare the quasi-phase matching device based on pyroelectric field induced polarized ferroelectric domains, including a laser erasing process subsystem and a vacuum quenching process subsystem;

[0049] The laser erasing process subsystem includes a first laser, an optical shutter, a gradient attenuation plate, a first half-wave plate, a first objective lens, a magnesium-doped lithium niobate crystal, a three-dimensional nano-translation stage and a computer;

[0050] Laser erasure Figure 2 As shown in (a), the first laser emits a laser with a wavelength of 800nm, a pulse width of 34fs, and a repetition frequency of 1kHz along the z direction (optical axis direction). The opening and closing of the laser is controlled by an optical shutter, and the energy of the laser is controlled by a gradient attenuation plate to compensate for the energy in the depth of the laser processing. After passing through the first half-wave plate, the polarization changes to the x direction. After the laser passes through the first objective lens with a numerical aperture of 0.75, it is focused on a 5% magnesium-doped lithium niobate crystal. The lithium niobate crystal is placed on a three-dimensional nano-translation stage, and the three-dimensional nano-translation stage is controlled by a computer (Labview software) to make the laser scribe a line 100nm below the crystal surface along the z direction, with a line segment length of 50 microns. In this process, the laser focus moves from deep (150 microns) to shallow (100 microns), and the gradient attenuation plate controls the laser energy to gradually change from 240nJ to 150nJ. Continue to carve the same structure along the x and y directions to form a grating array structure with a period of Λ=4μm in the x and y directions. The laser processed structure is as follows on the yoz plane: Figure 2 As shown in the dashed area in (b), on the xoy plane Figure 2 (c) is shown in the dashed area.

[0051] The quenching process subsystem includes a vacuum temperature control platform, an illumination light source, a first polarizer, a second polarizer, a second objective lens and a CCD;

[0052] Figure 2 The device shown in (d) is used to quench the laser-processed lithium niobate crystal under vacuum and observe its ferroelectric domains in real time. The laser-processed lithium niobate crystal is placed on a vacuum temperature control platform, and the lithium niobate crystal is slowly heated to 180-220°C, then evacuated, and then cooled to room temperature at a rate of 30°C / min. During the cooling process, a pyroelectric field opposite to the spontaneous polarization direction is generated, which will cause the ferroelectric domain to reverse along the z direction from the laser processing area, so that the polarized ferroelectric domains are distributed in a grating array. The illumination light source illuminates the crystal, and the orthogonal first and second polarizers are placed above and below the lithium niobate crystal, respectively, to ensure that only the laser processing area and the domain reversal area can be illuminated, and then magnified by the second objective lens with an NA of 0.25, and finally collected by the CCD to achieve real-time observation of the domain structure of the lithium niobate crystal. The polarized ferroelectric domains are shown in Figure 2 (e) The dashed area is indicated by colored stripes.

[0053] Example 3

[0054] like Figure 3 As shown, the present invention provides a quasi-phase matching system based on pyroelectric field induced polarized ferroelectric domains, including the quasi-phase matching device based on pyroelectric field induced polarized ferroelectric domains, and also includes a second laser, a second half-wave plate, a polarization beam splitter, a third half-wave plate, a lens and a filter;

[0055] Figure 3 The fundamental wave is frequency-doubled by utilizing the polarized ferroelectric domains. The second laser emits a laser with a pulse width of 140fs, a repetition frequency of 80MHz, and a power of 400mW along the x-direction. The energy of the laser is controlled by the second half-wave plate and the polarization beam splitter. The polarization direction of the laser is then controlled along the y-direction by the third half-wave plate. Finally, the laser is focused by a lens with a focal length of 75mm and hits the region of the polarized ferroelectric domain induced by the pyroelectric field to achieve quasi-phase matching. The frequency-doubled signal is observed after the fundamental wave is filtered out by a filter.

[0056] When the fundamental wave incident power is 0.4W and the wavelength increases from 890nm to 916nm, the power of the first-order frequency-doubled spot is as follows: Figure 4 As shown in (a), it can be observed that at 904nm, the frequency-doubled laser power is the highest, indicating that the quasi-phase matching condition is achieved at this time. Figure 4 (c) is the quasi-phase matching diagram of the positive and negative 1-order frequency-doubled light field in the reciprocal space. The required reciprocal lattice vector is and Through theoretical calculation, the fundamental wavelength of 900nm satisfies the quasi-phase matching condition. The slight difference between the actual measurement and the theory may be caused by the deviation of the actual processing cycle. When the fundamental wavelength is 904nm, the frequency-doubled spot is as follows: Figure 4(b) As shown in Figure 2, when the fundamental wave power increases from 40mW to 460mW, the first-order frequency-doubled spot power is as follows: Figure 4 As shown in (d), it has a quadratic relationship with the fundamental wave power.

[0057] The present invention combines laser processing with heat treatment, does not require any external electric field, and can generate a pyroelectric field in the crystal that is opposite to the polarization direction. The pyroelectric field can reverse the ferroelectric domain without causing a change in the refractive index. The present invention uses the pyroelectric field to polarize the ferroelectric domain of the lithium niobate crystal to form a grating array structure, thereby achieving frequency doubling conversion that meets the quasi-phase matching condition.

[0058] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A quasi-phase matching device based on pyroelectric field induced polarization ferroelectric domains, characterized in that: The device first uses a laser erasing process to erase the ferroelectric domain of the lithium niobate crystal along the optical axis to form a grating array structure; Then, a quenching process under vacuum is used to generate a pyroelectric field in the lithium niobate crystal to induce the ferroelectric domain to polarize from the erased position along the optical axis toward the crystal surface, so that the polarized ferroelectric domain is also distributed in a grating array. The fundamental wave undergoes frequency doubling conversion through the ferroelectric domain polarization region, and the peak value of the frequency doubling spot power that varies with the fundamental wave wavelength is measured to be consistent with the peak value calculated under the quasi-phase matching condition, thus achieving quasi-phase matching.

2. The quasi-phase matching device based on pyroelectric field induced polarization ferroelectric domains according to claim 1, characterized in that: The fundamental wave undergoes frequency doubling conversion of different orders satisfying quasi-phase matching through the ferroelectric domain polarization region, and the formula is expressed as: in are the reciprocal lattice vectors of the fundamental wave and the doubled frequency light, is the reciprocal lattice vector of the polarized ferroelectric domain structure inverse space, expressed as: in, is the unit vector in the x and y directions in the rectangular coordinate system, p and q are arbitrary integers; the reciprocal lattice vector required for the 0-level frequency-doubled spot is For the positive and negative 1-level frequency-doubled light spots, the inverse lattice vectors are and For the positive and negative double frequency spots, the inverse lattice vectors are and 3. The quasi-phase matching device based on pyroelectric field induced polarization ferroelectric domains according to claim 1, characterized in that: The laser erasing process is a femtosecond laser erasing process.

4. A system for preparing a quasi-phase matching device based on pyroelectric field induced polarization ferroelectric domains, used for preparing a quasi-phase matching device based on pyroelectric field induced polarization ferroelectric domains as claimed in any one of claims 1 to 3, characterized in that: It includes a laser erasing process subsystem and a vacuum quenching process subsystem; The laser erasing process subsystem includes a first laser, a gradient attenuation plate, a first half-wave plate, a first objective lens, a magnesium-doped lithium niobate crystal, a three-dimensional nano-translation stage and a computer; The first laser emits laser light along the z direction, and the energy of the laser light is controlled by a gradient attenuation plate to compensate the energy in depth of the laser processing. After passing through the first half-wave plate, the polarization changes to the x direction. After passing through the first objective lens, the laser light is focused onto a magnesium-doped lithium niobate crystal. The lithium niobate crystal is placed on a three-dimensional nano-translation stage. The three-dimensional nano-translation stage is controlled by a computer to make the laser light scribe lines along the z direction under the crystal surface. In this process, the laser focus moves from deep to shallow, and the same structure is continuously scribed along the x and y directions to form a grating array structure. The quenching process subsystem includes a vacuum temperature control platform, an illumination light source, a first polarizer, a second polarizer, a second objective lens and a CCD; The laser processed lithium niobate crystal is placed on a vacuum temperature control platform, slowly heated to 180-220°C, then vacuumed, and then rapidly cooled to room temperature. During the cooling process, a pyroelectric field opposite to the spontaneous polarization direction is generated, which will cause the ferroelectric domain to reverse from the laser processing area along the optical axis z direction to the crystal surface, so that the polarized ferroelectric domain is also distributed in a grating array; The illumination light source illuminates the crystal, and the orthogonal first polarizer and second polarizer are placed above and below the lithium niobate crystal respectively to ensure that only the laser processing area and the domain inversion area are illuminated, and then magnified by the second objective lens and finally collected by the CCD to achieve real-time observation of the domain structure of the lithium niobate crystal.

5. The system for preparing a quasi-phase matching device based on pyroelectric field induced polarization ferroelectric domains according to claim 4, characterized in that: The laser erasing process subsystem further includes an optical shutter, which is arranged between the first laser and the gradient attenuation plate and is used to control the opening and closing of the laser.

6. The system for preparing a quasi-phase matching device based on pyroelectric field induced polarization ferroelectric domains according to claim 4, characterized in that: The first laser emits laser light with a wavelength of 800 nm, a pulse width of 34 fs and a repetition frequency of 1 kHz along the z direction.

7. A quasi-phase matching system based on pyroelectric field induced polarization of ferroelectric domains, comprising a quasi-phase matching device based on pyroelectric field induced polarization of ferroelectric domains as claimed in any one of claims 1 to 3, characterized in that: Also includes a second laser, a second half-wave plate, a polarization beam splitter, a third half-wave plate, a lens and a filter; The second laser emits laser light along the x direction, and the energy of the laser light is controlled by the second half-wave plate and the polarization beam splitter. The polarization direction of the laser light is then controlled along the y direction by the third half-wave plate. Finally, the laser light is focused by a lens onto the polarization region on the device for realizing quasi-phase matching based on pyroelectric field induced polarization ferroelectric domains. The fundamental wave is filtered out by a filter and the doubled frequency signal is observed.

8. The quasi-phase matching system based on pyroelectric field induced polarization ferroelectric domains according to claim 7, characterized in that: The second laser emits laser light with a pulse width of 140 fs, a repetition frequency of 80 MHz and a power of 400 mW along the x direction.

9. The quasi-phase matching system based on pyroelectric field induced polarization ferroelectric domains according to claim 7, characterized in that: The focal length of the lens is 75 mm.

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