Method for eliminating photorefractive effect of ferroelectric crystal based on auxiliary light source packaging

Abstract

A method for eliminating the photorefractive effect of a ferroelectric crystal based on auxiliary light source packaging. A waveguide is prepared on the surface of a ferroelectric crystal, and a main laser is introduced by the waveguide by means of optical fiber coupling; short-wavelength blue-violet light or ultraviolet light is used as an auxiliary light source; the auxiliary light source and the ferroelectric crystal are integrated and packaged, and the ferroelectric crystal is irradiated by means of the auxiliary light source. The integrated packaging comprises the following two packaging methods: 1. keeping the auxiliary light irradiation coaxial with the main laser transmission direction; 2. keeping the auxiliary light irradiation perpendicular to the main laser transmission direction. Using a short-wavelength blue-violet / ultraviolet irradiation method, and performing integrated packaging of a blue-violet / ultraviolet light source and the ferroelectric crystal material, eliminates the photorefractive effect in the ferroelectric crystal. By means of packaging the ferroelectric material, the photorefractive effect generated when the laser is transmitted in the ferroelectric crystal is reduced.

Description

A method for eliminating photorefractive effect of ferroelectric crystal based on auxiliary light source packaging Technical Field

[0001] The invention belongs to the field of ferroelectric materials, and in particular relates to a method for eliminating photorefractive effect of ferroelectric crystals based on auxiliary light source packaging. Background Art

[0002] Ferroelectrics are crystals that exhibit spontaneous polarization within a certain temperature range, and the direction of this spontaneous polarization can be reversed by the reversal of the external electric field. This property of the crystal is called ferroelectricity, and crystals exhibiting ferroelectricity are called ferroelectrics. Ferroelectrics have numerous applications in piezoelectrics, dielectrics, pyroelectrics, electro-optics, and nonlinear optics. Ferroelectric materials come in a variety of forms, including single crystals, polycrystalline materials, inorganic materials, and organic materials. Ferroelectric optical crystals primarily include lithium niobate (LiNbO3), lithium tantalate (LiTaO3), and potassium titanyl phosphate (KTiOPO4). These optical crystals exhibit nonlinear optical effects, including electro-optical effects, anomalous photovoltaic effects, and photorefractive effects. The electro-optical effect is most widely used in the information industry, with high-speed electro-optic modulators constructed using electro-optical crystals widely used in the optical communications industry. The most important application of nonlinear optical effects is laser frequency conversion. For example, the green laser widely used in laser processing converts infrared laser light into 532nm laser light through frequency doubling.

[0003] These ferroelectric optical crystals require laser light to pass through the crystal in order to function. Especially in high-power applications, high-intensity laser light can easily induce effects such as thermal lensing and photorefractive distortion, causing the laser light's shape within the crystal to change, preventing it from maintaining its original shape. This can affect conversion efficiency during use and even lead to irreversible damage, such as crystal damage or fragmentation. Furthermore, the better the intrinsic optical quality of the ferroelectric crystal material, the fewer impurities, and the higher the nonlinear efficiency, the more pronounced the photorefractive effect. For example, in high-power optical parametric oscillators, a focused 1064nm pump laser can easily self-focus and deform within a periodically poled lithium niobate (PPLN) crystal, affecting the intracavity oscillation and causing unstable output laser power, hindering higher-power output. In nonlinear waveguides, such as proton exchange, titanium diffusion, or thin-film lithium niobate waveguides, near-infrared photorefractive distortion caused by effects such as two-photon absorption is also common due to the small mode volume and high optical power density. This can easily cause zero-point drift, output instability, increased loss, and waveguide damage in waveguide devices such as thin-film lithium niobate modulators.

[0004] Summary of the Invention

[0005] Purpose of the Invention: This invention provides a method for eliminating the photorefractive effect in ferroelectric crystals using auxiliary light source packaging. By utilizing short-wavelength blue-violet / ultraviolet light irradiation, the blue-violet / ultraviolet light source is integrated with the ferroelectric crystal material and packaged to eliminate the photorefractive effect in the ferroelectric crystal. By packaging the ferroelectric material, the photorefractive effect generated by laser light transmission through the ferroelectric crystal is reduced.

[0006] Technical solution: The present invention provides a method for eliminating the photorefractive effect of ferroelectric crystals based on auxiliary light source packaging. A waveguide is prepared on the surface of the ferroelectric crystal. The waveguide introduces a main laser through optical fiber coupling. Short-wavelength blue-violet light or ultraviolet light is used as an auxiliary light source. The auxiliary light source and the ferroelectric crystal are integrated and packaged, and the ferroelectric crystal is irradiated by the auxiliary light source. The integrated packaging includes the following two packaging methods: 1. Keeping the auxiliary light irradiation coaxial with the main laser transmission direction; 2. Keeping the auxiliary light irradiation perpendicular to the main laser transmission direction.

[0007] Furthermore, the ferroelectric crystal includes lithium niobate LiNbO3, lithium tantalate LiTaO3, and potassium titanyl phosphate KTiOPO4.

[0008] Furthermore, the wavelength of the auxiliary light source is between 300nm and 500nm, including blue / ultraviolet light emitting diodes (LEDs), blue / ultraviolet xenon lamps, blue / ultraviolet halogen lamps or solid lasers.

[0009] Furthermore, the auxiliary light irradiation is kept coaxial with the main laser transmission direction, and is used in the case where a waveguide exists in the ferroelectric material. The blue-violet light is coupled into the main laser beam transmission waveguide by preparing a grating and a coupling prism on the surface of the ferroelectric material. Specifically, the coupling method of the coaxial transmission of the auxiliary light and the main laser includes: a surface microstructure processing method, a single / multiple evanescent wave coupling prism method, and a single / multiple evanescent wave coupling optical fiber method.

[0010] Furthermore, the surface microstructure processing method includes phase grating, intensity grating, dielectric binary optical structure, and surface plasmon; the single / multiple evanescent wave coupling prism method includes high refractive index materials such as rutile, diamond, zircon, sapphire, quartz crystal, and glass materials; the single / multiple evanescent wave coupling optical fiber method includes quartz crystal and glass materials.

[0011] Furthermore, a method for preparing a grating and a coupling prism on the surface of a ferroelectric material is provided, specifically comprising: arranging auxiliary light sources in a straight line, focusing the auxiliary light through a lens installed in front of the auxiliary light source so that the auxiliary light is focused and irradiated on the surface of a ferroelectric crystal waveguide, and etching the surface of the ferroelectric crystal waveguide to form a phase Bragg grating, coupling the vertically incident auxiliary light into the waveguide;

[0012] According to the grating coupling condition of phase-type Bragg grating in is the wave vector transmitted in the waveguide, is the m-order diffraction wave, is the grating vector corresponding to the grating period, and the effective refractive index of the grating is calculated according to n eff =dc·n1+(1-dc)·n2, where dc represents the duty cycle, n1 represents the effective refractive index of the unetched portion of the waveguide, and n2 represents the effective refractive index of the etched portion of the waveguide. The effective refractive index of the grating n eff =2.275, Assuming the grating period Λ is 500nm, Then, according to the first formula, we can calculate Finally, according to the incident angle corresponding to the first diffraction order in is the eigenwave vector in the crystal, and the incident angle θ is calculated to be 39.5 degrees;

[0013] According to the above calculations, when the period of the refractive index grating is 500 nm, the angle of the auxiliary light source and the focusing lens is 39.5 degrees, so that most of the incident light is converted into first-order diffraction light after grating coupling and enters the waveguide.

[0014] Furthermore, an evanescent wave coupling layer is processed between the grating, coupling prism and ferroelectric crystal by bonding, deposition and sputtering to assist the coupled wave transmission between the coupling element and the ferroelectric material.

[0015] Furthermore, the auxiliary light irradiation is kept perpendicular to the main laser transmission direction, and is used in situations where coupled coaxial transmission is difficult. By encapsulating an auxiliary light source with a specific structure design outside the material, the auxiliary light is focused on the main laser transmission position. Specifically, the coupling method of the auxiliary light and the main laser perpendicular transmission includes: using a lens, an aspheric mirror, a single / multi-point light source, a linear light source, and a surface light source.

[0016] Furthermore, the method of using lenses and aspheric mirrors is as follows: the constituent materials of the lenses include quartz, glass, polymers, and plastics; micromachining processes can also be used to prepare phase gratings, intensity gratings, dielectric binary optical structures, and surface plasmons; the method of using single-point / multi-point light sources, linear light sources, and surface light sources is as follows: when using multi-point light sources, the arrangement of multiple point light sources should be along the main laser transmission direction and arranged at certain intervals; when using linear light sources, the direction of the linear light source is made parallel to the main laser transmission direction; when using point light sources, linear light sources, and surface light sources, the above-mentioned light sources are focused in a focusing manner so that the auxiliary light mainly irradiates the main laser transmission area.

[0017] Furthermore, after the auxiliary light source and the ferroelectric crystal are packaged, there is also a transmission optical window for the main laser, a power supply interface for the auxiliary light source, and a temperature control and heat dissipation electrical interface for the ferroelectric crystal and the auxiliary light source; it also has a temperature control and heat dissipation structure with air cooling, liquid cooling, and contact heat transfer.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0019] Currently, the main methods for reducing photorefractive index in ferroelectric crystals include doping with ions to increase conductivity and raising the temperature (generally to over 100 degrees Celsius) to improve conductivity. Even after adopting these methods, photorefractive index still exists under high-intensity laser irradiation, and no other method can currently address this phenomenon. However, the method proposed in this patent, which uses blue light irradiation, can effectively reduce photorefractive index in this situation, making ferroelectric crystals more suitable for operation under high-intensity laser irradiation. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG1 is a diagram showing the overall appearance of the package of Example 1 of the present invention;

[0021] FIG2 is a cross-sectional view of a device package according to Example 1 of the present invention;

[0022] FIG3 is a partial view of the package of Example 1 of the present invention: LED, lens, grating and waveguide;

[0023] FIG4 is an exploded view of the packaging structure of Example 1 of the present invention. DETAILED DESCRIPTION

[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0025] The purpose of the present invention is to eliminate the photorefractive effects that can cause spot distortion, power instability, and voltage drift during laser transmission in ferroelectric crystals. The basic approach involves encapsulating a blue-violet light source within the device and using it to irradiate the material, thereby increasing the material's conductivity and reducing the spatial electric field and photorefractive effects. To address these issues, the present invention proposes a method that utilizes short-wavelength blue-violet / ultraviolet light, integrating the blue-violet / ultraviolet light source with the ferroelectric crystal material to eliminate the photorefractive effects.

[0026] The main reason for the photorefractive effect of laser in ferroelectric crystals is the uneven charge distribution caused by carrier migration caused by light. The charge generated locally by the laser spot (hereinafter referred to as the main laser) in the crystal cannot be neutralized, causing the refractive index tensor of the crystal to change, resulting in spot shape distortion, increased transmission loss, and transmission power fluctuations.

[0027] Referring to Figures 1 to 4, the basic principle of the present invention is to integrate and package a short-wavelength blue-violet light / ultraviolet light (hereinafter referred to as auxiliary light) light source with a ferroelectric crystal material, irradiate the ferroelectric crystal material with the auxiliary light, excite a large number of carriers in the crystal, reduce the electrical conductivity of the material, and thus neutralize the charge generated by photovoltaics.

[0028] The wavelength of the auxiliary light is between 300nm and 500nm, such as semiconductor lasers with wavelengths of 405nm, 450nm, 473nm, etc., or blue / ultraviolet light-emitting diodes (LEDs), or blue / ultraviolet gas light-emitting tubes (such as xenon lamps, halogen lamps, etc.), or solid-state lasers (such as 355nm), etc.

[0029] The auxiliary light irradiation method can be implemented in two ways: one is to transmit the auxiliary light coaxially with the main laser beam, and the other is to transmit the auxiliary light perpendicularly to the main laser beam.

[0030] 1. The auxiliary light irradiation method described above, which is coaxially transmitted with the main laser beam, is used when a waveguide exists in the ferroelectric material. The blue-violet light is coupled into the main laser beam transmission waveguide by preparing a grating or coupling prism on the surface of the ferroelectric material.

[0031] Specifically, the coupling method for the coaxial transmission of the auxiliary light and the main laser includes but is not limited to surface microstructure processing methods such as phase grating, intensity grating, dielectric binary optical structure, surface plasmon, etc.; the coupling method for the coaxial transmission of the auxiliary light and the main laser includes but is not limited to single / multiple evanescent wave coupling prisms, including high refractive index materials such as rutile, diamond, zircon, sapphire, quartz crystal, glass, etc.; the coupling method for the coaxial transmission of the auxiliary light and the main laser includes but is not limited to single / multiple evanescent wave coupling optical fibers, including materials such as quartz crystal, glass, etc.;

[0032] Specifically, in the above-mentioned method for coupling the auxiliary light to the main laser in a coaxial transmission, an evanescent wave coupling layer can be processed between the coupling components such as the grating, prism, and optical fiber and the ferroelectric material by bonding, deposition, sputtering, etc., to assist the transmission of coupled waves between the coupling components and the ferroelectric material;

[0033] 2. The auxiliary light irradiation method described above, which is perpendicular to the main laser transmission direction, is used in situations where coupled coaxial transmission is difficult. By encapsulating an auxiliary light source with a specific structural design outside the material, the auxiliary light can be focused on the main laser transmission position.

[0034] Specifically, in the above-mentioned coupling method of auxiliary light and main laser transmission perpendicularly, the auxiliary light focusing method can be implemented by using lenses (cylindrical lenses), aspheric mirrors, etc., and the constituent materials of the lenses include quartz, glass, polymers, plastics, etc.; micromachining technology can also be used to prepare phase gratings, intensity gratings, dielectric binary optical structures, surface plasmons, etc.

[0035] Specifically, in the above-mentioned coupling method in which the auxiliary light is perpendicular to the main laser transmission, the auxiliary light source can be a single-point / multi-point light source, a linear light source, a surface light source, etc.; when a multi-point light source is used, the arrangement of multiple point light sources should be along the main laser transmission direction and arranged at a certain interval; when a linear light source is used, the direction of the linear light source should be parallel to the main laser transmission direction; when a point light source, a linear light source and a surface light source are used, the above-mentioned light sources should be focused in a focusing manner so that the auxiliary light mainly irradiates the main laser transmission area.

[0036] 3. In addition, the packaging module of the auxiliary light source and ferroelectric material also has a transmission optical window for the main laser, a power supply interface for the auxiliary light source, and a temperature control and heat dissipation electrical interface for the ferroelectric material and the auxiliary light source; it can also have temperature control and heat dissipation structures such as air cooling, liquid cooling, and contact heat transfer.

[0037] Example 1: Coaxial Method. A waveguide is fabricated on the surface of a ferroelectric periodically poled lithium niobate crystal (PPLN) using methods such as proton exchange, titanium diffusion, and mechanical processing. This waveguide introduces a primary laser (e.g., 1064 nm) via fiber coupling, generating nonlinear effects such as frequency doubling, summing, and difference frequency. At high primary laser power, the photorefractive effect creates an uneven refractive index distribution in the waveguide, increasing waveguide losses and reducing nonlinear effects, impacting device performance.

[0038] This example uses auxiliary light, transmitted coaxially with the primary laser beam, using multiple point-shaped 405nm blue-violet LEDs arranged in a straight line. A lens placed in front of each point LED focuses the auxiliary light onto the surface of a PPLN waveguide. The PPLN waveguide surface is fabricated using lithium niobate etching to create a phase Bragg grating, which couples the vertically incident auxiliary light into the waveguide.

[0039] According to the grating coupling condition of phase-type Bragg grating in is the wave vector transmitted in the waveguide, is the m-order diffraction wave, is the grating vector corresponding to the grating period. The effective refractive index of the grating is calculated based on n eff =dc·n1+(1-dc)·n2, where dc represents the duty cycle (set to 50% in this example), n1 represents the effective refractive index of the unetched waveguide (set to 2.25 in this example), and n2 represents the effective refractive index of the etched waveguide (set to 2.3 in this example). The effective refractive index n of the grating is: eff =2.275, Assuming the grating period Λ is 500nm, Then we can calculate the Finally, according to the incident angle corresponding to the first diffraction order in is the eigenwave vector in the crystal, and the incident angle θ is calculated to be 39.5 degrees.

[0040] According to the above calculations, when the period of the refractive index grating is 500 nm, the angle between the LED and the focusing lens is preferably 39.5 degrees, so that most of the incident light is converted into first-order diffraction light after grating coupling and enters the waveguide.

[0041] Example 2:

[0042] This example provides a design example method for parameters such as grating period and auxiliary light source incident angle. The specific design parameters need to be calculated according to the actual material and processing technology according to this example.

[0043] In the vertical coupling example, the LED illumination method is the same as the previous example, except that the grating coupling is not prepared on the surface of the material. Therefore, the LED light irradiated from above will be perpendicular to the transmitted light.

Claims

1. A method for eliminating the photorefractive effect of a ferroelectric crystal based on auxiliary light source packaging, wherein a waveguide is prepared on the surface of the ferroelectric crystal, and the waveguide is introduced into the main laser through optical fiber coupling, characterized in that: Short-wavelength blue-violet light or ultraviolet light is used as an auxiliary light source, and the auxiliary light source and the ferroelectric crystal are integrated and packaged, and the ferroelectric crystal is irradiated by the auxiliary light source; the integrated packaging includes the following two packaging methods: one, keeping the auxiliary light irradiation coaxial with the main laser transmission direction; two, keeping the auxiliary light irradiation perpendicular to the main laser transmission direction.

2. The method for eliminating the photorefractive effect of ferroelectric crystal based on auxiliary light source packaging according to claim 1, characterized in that: The ferroelectric crystals include lithium niobate LiNbO3, lithium tantalate LiTaO3 and potassium titanyl phosphate KTiOPO4.

3. The method for eliminating the photorefractive effect of ferroelectric crystal based on auxiliary light source packaging according to claim 1, characterized in that: The wavelength of the auxiliary light source is between 300nm and 500nm, including a blue light / ultraviolet light emitting diode LED, a blue light / ultraviolet xenon lamp, a blue light / ultraviolet halogen lamp or a solid laser.

4. The method for eliminating the photorefractive effect of ferroelectric crystal based on auxiliary light source packaging according to claim 1, characterized in that: The auxiliary light irradiation is kept coaxial with the main laser transmission direction, and is used in the case where a waveguide exists in the ferroelectric material. The blue-violet light is coupled into the main laser beam transmission waveguide by preparing a grating and a coupling prism on the surface of the ferroelectric material. Specifically, the coupling method of the coaxial transmission of the auxiliary light and the main laser includes: a surface microstructure processing method, a single / multiple evanescent wave coupling prism method, and a single / multiple evanescent wave coupling optical fiber method.

5. The method for eliminating the photorefractive effect of ferroelectric crystal based on auxiliary light source packaging according to claim 4, characterized in that: The surface microstructure processing method includes phase grating, intensity grating, dielectric binary optical structure, and surface plasmon; the single / multiple evanescent wave coupling prism method includes high refractive index materials such as rutile, diamond, zircon, sapphire, quartz crystal, and glass materials; the single / multiple evanescent wave coupling optical fiber method includes quartz crystal and glass materials.

6. The method for eliminating the photorefractive effect of ferroelectric crystal based on auxiliary light source packaging according to claim 4, characterized in that: The method of preparing gratings and coupling prisms on the surface of ferroelectric materials is specifically as follows: auxiliary light sources are arranged in a straight line, and the auxiliary light is focused by a lens installed in front of the auxiliary light source so that it is focused and irradiated on the surface of the ferroelectric crystal waveguide. The surface of the ferroelectric crystal waveguide is processed into a phase Bragg grating by etching, and the vertically incident auxiliary light is coupled into the waveguide; Grating coupling conditions based on phase-type Bragg grating in is the wave vector transmitted in the waveguide, is the m-order diffraction wave, is the grating vector corresponding to the grating period, and the effective refractive index of the grating According to n eff =dc·n1+(1-dc)·n2, where dc represents the duty cycle, n1 represents the effective refractive index of the unetched portion of the waveguide, and n2 represents the effective refractive index of the etched portion of the waveguide. According to the incident angle corresponding to the first diffraction order, in is the eigenvector in the crystal, and the incident angle θ is calculated so that most of the incident light is converted into first-order diffracted light after grating coupling and enters the waveguide.

7. The method for eliminating the photorefractive effect of ferroelectric crystal based on auxiliary light source packaging according to claim 4, characterized in that: The evanescent wave coupling layer is processed between the grating, the coupling prism and the ferroelectric crystal by bonding, deposition and sputtering methods to assist the transmission of coupled waves between the coupling element and the ferroelectric material.

8. The method for eliminating the photorefractive effect of ferroelectric crystal based on auxiliary light source packaging according to claim 1, characterized in that: The auxiliary light irradiation is kept perpendicular to the main laser transmission direction, and is used in situations where coupled coaxial transmission is difficult. The auxiliary light source with a specific structure design is encapsulated outside the material to focus the auxiliary light on the main laser transmission position. Specifically, the coupling method of the auxiliary light and the main laser perpendicular transmission includes: using a lens, an aspherical mirror, and using a single / multi-point light source, a linear light source, and a surface light source.

9. The method for eliminating the photorefractive effect of ferroelectric crystal based on auxiliary light source packaging according to claim 8, characterized in that: The method of using lenses and aspherical mirrors is as follows: the constituent materials of the lenses include quartz, glass, polymers, and plastics; micromachining technology can also be used to prepare phase gratings, intensity gratings, dielectric binary optical structures, and surface plasmons; the method of using single-point / multi-point light sources, line light sources, and surface light sources is as follows: when using multi-point light sources, the arrangement of multiple point light sources should be along the main laser transmission direction and arranged at certain intervals; when using line light sources, the direction of the line light source is made parallel to the main laser transmission direction; when using point light sources, line light sources, and surface light sources, the above light sources are focused by using a focusing method so that the auxiliary light mainly irradiates the main laser transmission area.

10. The method for eliminating the photorefractive effect of ferroelectric crystal based on auxiliary light source packaging according to claim 1, characterized in that: After the auxiliary light source and the ferroelectric crystal are packaged, there is also a transmission optical window for the main laser, a power supply interface for the auxiliary light source, and a temperature control and heat dissipation electrical interface for the ferroelectric crystal and the auxiliary light source; there is also a temperature control and heat dissipation structure with air cooling, liquid cooling, and contact heat transfer.

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