On-line continuous supply device for large-size SLN growth, crystal growth system and growth method

Abstract

The present invention relates to an online continuous supply device, crystal growth system, and growth method for growing large-sized SLN crystals. The online continuous supply device for growing large-sized SLN crystals includes a supply crucible containing polycrystalline material, a supply pipe, a first heating section for heating the supply crucible to a first temperature, and a second heating section for heating the supply pipe to a second temperature. The supply device of the present invention has a simple structure, the supply pipe is less likely to clog, the mass transfer rate is fast, online supply is possible, and control is easy. In a growth system for growing large-sized SLN crystals, adding a supply melt to the crystal growth melt reduces the impact on the temperature field and composition of the crystal growth melt, effectively solving problems of composition fluctuation, temperature fluctuation, and inclusions caused by supply. As a result, it is possible to precisely control the growth of lithium niobate crystals with a near-stoichiometric composition, enabling mass production of large-sized SLN crystals.

Description

[Technical Field]

[0001] The present invention relates to the field of photoelectric materials technology, and in particular to an online continuous supply device, a crystal growth system and a growth method used for growing large-sized SLN crystals. [Background technology]

[0002] Compared with stoichiometric lithium niobate crystals (CLN), stoichiometric lithium niobate crystals (SLN) eliminate the inherent defects caused by the numerous antipositional niobium ions present in the crystal lattice. This eliminates the inherent defects, resulting in significantly superior optical, nonlinear, and ferroelectric properties. In particular, periodically poled lithium niobate (PPLN) crystals have a significantly lower coercive field than CLN crystals, allowing for periodic poling at low voltages. This facilitates the realization of periodic poling and enables the mass production of thick PPLN crystals. Therefore, mass production of SLN crystals is of great importance for applications such as quantum communication devices and miniature infrared targeting and guidance systems based on PPLN crystals.

[0003] Since the first small SLN crystals were reported in Japan in the 1970s using the double crucible method, no mass-produced SLN crystals / wafers have been sold to date. The reason for this is that SLN crystals are susceptible to compositional segregation of the melt during growth, which can easily result in twins, large numbers of bubbles, and inclusions within the crystals, making mass production difficult. As a result, the development of many devices using SLN crystals has been halted or people have been forced to switch to other solutions that are more complex and less efficient.

[0004] Meanwhile, research into SLN crystal manufacturing technology has continued. In the early 2000s, Shandong University proposed the hanging crucible method, and Chinese Patent Publication No. CN200410024543 disclosed a hanging crucible for growing stoichiometric lithium niobate crystals and a growth method for the same. As shown in Figure 1, the hanging crucible structure is used to produce SLN crystals. Subsequently, Chinese Patent Publication No. CN201110127655 disclosed a continuous feed system for SLN crystal growth. As shown in Figure 2, in this continuous feed system, the lower outlet of a polycrystalline material hopper is connected to an elastic feed tube, which is equipped with two pneumatic shut-off valves spaced apart. The end of the feed tube is connected to a platinum feed tube. The platinum feed tube reaches the surface of the melt in the crucible within the hanging crucible system, and the shut-off valve is controlled by a relay, achieving continuous feeding.

[0005] However, in practical applications, this type of continuous material addition method still has certain limitations. Because it uses a solid-phase supply method, the supply pipe is prone to clogging and the mass transfer rate is slow. Furthermore, it has a relatively large impact on the temperature field of the crystal growth melt, which is unfavorable for maintaining a stable crystal growth temperature field. Furthermore, the diffusion process of the supplied material within the crystal growth melt is slow, which also affects the stability of the melt composition, making it unfavorable for mass production of large-sized SLN crystals. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Chinese patent application CN200410024543 [Patent Document 2] Chinese patent application CN201110127655 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of the drawbacks of the conventional technology, and a first object of the present invention is to provide an online continuous supply device for use in growing large-sized SLN crystals.

[0008] A second object of the present invention is to provide a system for growing large size SLN crystals.

[0009] A third object of the present invention is to provide a method for growing large sized SLN crystals using the growth system. [Means for solving the problem]

[0010] In this method, a LiNbO3 polycrystalline material with a mass equal to the mass of the SLN crystal to be grown is melted in a make-up crucible of an online continuous feeder, and then the make-up melt is added to the crystal growth melt via a feed pipe. The feed pipe is equipped with an independent heating coil, and a PID algorithm is used to adjust the heating power and the weight loss in the make-up crucible, precisely controlling the opening and closing of the feed pipe and the temperature of the make-up melt. This reduces the impact of the make-up melt on the temperature field and composition of the crystal growth melt, solving the problems of composition fluctuation, temperature fluctuation, and inclusions caused by the make-up melt during the growth of large-sized SLN crystals, and achieving accurate and controllable growth of stoichiometric lithium niobate crystals, making mass production possible.

[0011] The present invention is realized by the following technical means. An online continuous supply device used for growing large-sized SLN includes a supply crucible containing polycrystalline material, a first heating unit for heating the supply crucible to a first temperature, a supply pipe, and a second heating unit for heating the supply pipe to a second temperature. The first heating unit is provided outside the supply crucible, the supply crucible having a lower outlet communicating with a supply pipe through the outlet, and the second heating unit is provided outside the supply pipe, the end of which extends into the crystal growth crucible.

[0012] The first heating unit heats the refill crucible to melt the polycrystalline material and form a refill melt. The supply pipe adds the replenishment melt to the crystal growth melt at the second temperature, and causes the molten lithium niobate to flow into the crystal growth crucible, thereby realizing online replenishment.

[0013] The second heating unit is provided for heating the supply pipe, the second temperature being higher than the crystal growth temperature to avoid solidification of the melt in the supply pipe.

[0014] The refill crucible may be a platinum crucible of an intermediate frequency induction heating type, and the first heating unit may be an induction coil wound around the outer periphery of the refill crucible to heat it.

[0015] The supply tube may be a platinum tube with a diameter of 5 to 20 mm.

[0016] The second heating unit may be an induction coil wound around the outside of the supply pipe, or may be an induction coil for medium frequency induction heating to avoid solidification of the melt inside the supply pipe.

[0017] The present invention also provides a crystal growth system for use in growing large sized SLN crystals. The crystal growth system includes a crystal growth device, an online continuous supply device, and a control device. The crystal growth apparatus includes a hanging crucible that accommodates a crystal growth melt and a third heating unit that heats the hanging crucible.

[0018] The hanging crucible includes an inner crucible and an outer crucible, the inner crucible is disposed inside the outer crucible, and the bottoms of the inner crucible and the outer crucible are connected to each other. The inner crucible is a melt cavity for accommodating a crystal growth melt, and a sandwich cavity is formed between the inner crucible and the outer crucible. The end of the supply pipe extends into the sandwich cavity.

[0019] The supply pipe may be provided with an electromagnetic valve switch. The control device may include a control unit electrically connected to the electromagnetic valve switch, the first heating unit, the second heating unit, and the third heating unit, and configured to control the output of each heating unit so as to maintain a constant weight of the crystal growth melt during crystal growth.

[0020] The present invention also provides a method for growing large sized SLN. The method may use the crystal growth system and include the following steps: Step (1): A crystal growth melt is placed in the melt cavity of the crystal growing apparatus, the third heating unit and the control device are activated to heat the hanging crucible, and a crystal is grown by the pulling method. Step (2): During the crystal growth process, the first heating unit is operated to melt the polycrystalline material in the refill crucible at a first temperature to obtain a refill melt. Step (3): activating the second heating unit to supply the replenishing melt at the second temperature through the supply pipe into the sandwich cavity of the crystal growing apparatus, so as to maintain the weight of the crystal growing melt constant;

[0021] In the step (1), the control device may use a PID algorithm to control the output P1(t) of the third heating unit according to equation (1).

[0022]

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[0023] In the step (2), the first temperature may be a temperature at which the polycrystalline material can be heated and melted.

[0024] In step (3), the controller may use a PID algorithm to control the output P2(t) of the second heating unit according to equation (2).

[0025]

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[0026] In step (3), the second temperature may be 10 to 50°C higher than the crystal growth temperature, the heating and melting temperature of the replenishing polycrystalline material may be 10 to 50°C higher than the crystal growth temperature, and the replenishing polycrystalline material may be LiNbO3 polycrystalline material.

[0027] According to the present invention, based on the above configuration, stable online continuous supply can be realized in the growth of large-sized SLN crystals, and stability of composition and temperature can be ensured during the crystal growth process. [Effects of the Invention]

[0028] The technical features and advantages of the present invention are as follows: First, the supply device of the present invention has a simple structure, is less likely to cause blockage of the supply pipe, has a high mass transfer rate, can realize online supply, and is easy to control.

[0029] Second, in the large-size SLN crystal growth system of the present invention, polycrystalline material is melted in a replenishment crucible of an online continuous supply device, and the replenishment melt is added to the crystal growth melt through a supply pipe. This reduces the influence of the addition of the replenishment melt on the temperature field and composition of the crystal growth melt, effectively solving the problems of composition fluctuation, temperature fluctuation, and inclusions caused by replenishment during large-size SLN crystal growth. As a result, precise and controllable growth of stoichiometric lithium niobate crystals is realized, and mass production is also possible.

[0030] Third, in the large-size SLN crystal growth system of the present invention, the supply melt is introduced into the sandwich cavity of the crystal growth device through a supply pipe, and the supply melt is smoothly supplied to the crystal growth melt, so that the weight of the crystal growth melt can be kept constant during the crystal growth process, which prevents the crystal growth interface from changing its temperature field or its relative position in the crucible, avoids fluctuations in crystal growth dynamics due to temperature field gradients, and allows for precise control of crystal growth.

[0031] Fourth, the method of the present invention uses a PID algorithm to adjust the heating power and the weight loss of the make-up crucible, and precisely controls the opening and closing of the supply pipe and the temperature of the make-up melt, thereby reducing the impact on the temperature field and composition of the crystal growth melt when the make-up melt is added to the crystal growth melt, and effectively solving the problems of composition fluctuation, temperature fluctuation and inclusions caused by addition during large-sized SLN crystal growth. [Brief explanation of the drawings]

[0032] [Figure 1] FIG. 1 is a diagram showing a hanging crucible structure described in Patent Document 1. [Figure 2] FIG. 1 is a schematic structural diagram of a continuous supply device for growing SLN crystals described in Patent Document 2. [Figure 3] 1 is a structural schematic diagram of a growth system for growing large-sized SLN crystals according to the present invention. [Figure 4] These are actual photographs of large SLN crystals grown using different growth methods. In the figure, a and b are SLN crystals grown using conventional methods, and they contain inclusions and twins. c and d are SLN crystals grown using the method of the present invention, and they have good crystal shapes, no defects, and are of excellent quality. DETAILED DESCRIPTION OF THE INVENTION

[0033] Specific embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the embodiments shown below are merely examples and are not intended to limit the present invention, and various changes and modifications may be made by those skilled in the art.

[0034] [Embodiment 1] The growth system for growing large-sized SLN crystals comprises a crystal growth apparatus (1), an online continuous supply apparatus (2), and a control device, an example of which is shown in FIG.

[0035] The online continuous supply device (2) includes a supply crucible (21) for storing polycrystalline material, a supply pipe (24), a first heating section (23) for heating the supply crucible (21) to a first temperature, and a second heating section (22) for heating the supply pipe (24) to a second temperature.

[0036] The supply crucible (21) contains a polycrystalline material, such as LiNbO3, preferably in powder form. The supply crucible (21) is an intermediate frequency induction-heated platinum crucible. The first heating element (23) is an induction coil wound around the outer periphery of the supply crucible (21) for intermediate frequency induction heating. The supply crucible (21) has a lower outlet through which it communicates with a supply tube (24). The second heating element (22) is an induction coil wound around the outer periphery of the supply tube (24). This provides intermediate frequency induction heating and prevents solidification of the melt within the supply tube (24). The end of the supply tube (24) extends into the crystal growth crucible and is a platinum tube with a diameter of 10 mm.

[0037] The first heating element 23 heats the refill crucible 21 to melt the refill polycrystalline material and form a refill melt. The first heating element 23 is a heating coil, which may be a copper coil disposed around the refill crucible 21.

[0038] The supply pipe (24) allows the supply melt in the supply crucible (21) to flow into the sandwich cavity, so that the weight of the crystal growth melt does not change during the crystal growth process. The end of the supply pipe (24) of the online continuous supply device extends into the sandwich cavity to add the supplementary melt to the crystal growth melt, which is advantageous in maintaining the stability of the temperature field of the crystal growth system. The supply pipe (24) is preferably a platinum pipe.

[0039] The second heating section (22) is for heating the supply pipe (24) so ​​that the refill melt from the refill crucible (21) flows into the crystal growth melt at a second temperature. The second temperature is set to be higher than the crystal growth temperature, for example, 50°C higher than the crystal growth temperature. This prevents the refill melt from crystallizing during transportation through the supply pipe 24 or when it comes into contact with the crystal growth melt. This allows the continuous supply process to proceed smoothly, allows the refill melt and the crystal growth melt to be mixed quickly and uniformly, and ensures the composition stability of the crystal growth melt during the crystal growth process.

[0040] The online continuous supply device (2) continuously supplies melt to the crystal growth device (1) during the crystal growth process, thereby keeping the weight of the crystal growth melt constant and ensuring the relative stability of the liquid surface of the crystal growth melt.

[0041] The crystal growth apparatus (1) includes a hanging crucible (11) that contains a crystal growth melt and a third heating section (12) that heats the hanging crucible (11). The hanging crucible (11) includes an inner crucible (113) and an outer crucible (112). The inner crucible (113) is disposed inside the outer crucible (112), and their bottoms are connected. The interior of the inner crucible (113) is a melt cavity that contains the crystal growth melt, and a sandwich cavity is formed between the inner crucible (113) and the outer crucible (112). The end of the supply pipe (24) extends into the sandwich cavity.

[0042] A solenoid valve switch is provided on the supply pipe 24. The control device is electrically connected to the solenoid valve switch, the first heating section 23, the second heating section 22, and the third heating section 12, and includes a control section that controls the heating output of each heating section to maintain a constant weight of the crystal growth melt during the crystal growth process.

[0043] This growth system is also applicable to other crystal growth processes that require continuous supply. For example, for a typical 3000 g crystal growth melt, adding 2 g of make-up melt at a temperature 50° C. higher than the crystal growth temperature to the crystal growth melt via the supply tube (24) theoretically results in a temperature change of less than 0.03° C. Furthermore, due to the addition location of the make-up melt and the shielding effect of the inner crucible (113) against temperature fluctuations, the addition of this make-up melt (2 g) has a negligible effect on the actual temperature of the crystal growth melt in the inner crucible (113).

[0044] In the online continuous supply device (2), the heating output of the second heating section (22) is controlled according to the supply rate required for crystal growth, thereby adjusting the temperature of the supply pipe (24) and controlling the melting and solidification of the replenishment melt inside the supply pipe (24). This realizes the function of a continuous supply switch and enables intermittent supply. The weight of the replenishment melt added to the crystal growth melt can be precisely controlled over time, improving the consistency between process control and crystal growth.

[0045] [Embodiment 2] The difference from the large-size SLN crystal growth system described in the first embodiment is that the supply pipe (24) is a platinum pipe with a diameter of 15 mm, and the second temperature is higher than the crystal growth temperature, for example, 40°C higher than the crystal growth temperature.

[0046] [Embodiment 3] The difference from the large-size SLN crystal growth system described in embodiment 1 is that the supply pipe (24) is a platinum pipe with a diameter of 8 mm, and the second temperature is higher than the crystal growth temperature, for example, 30°C higher than the crystal growth temperature.

[0047] [Embodiment 4] The method for growing large sized SLN crystals using the system of embodiment 1 includes the following steps. Step (1): A crystal growth melt is placed in the melt cavity of the crystal growth apparatus (1), the third heating section (12) and the control device are activated, the hanging crucible (11) is heated, the output of the third heating section (12) is controlled, and a crystal is grown by the pulling method. Step (2): In the crystal growth process, the first heating section (23) is operated to heat and melt the polycrystalline material in the refill crucible (21) at a first temperature to obtain a refill melt. Step (3): Activate the second heating section (22) and add the refueling melt into the sandwich cavity of the crystal growth apparatus (1) through the supply pipe (24) at the second temperature, so that the refueling melt is smoothly supplied to the crystal growth melt, thereby maintaining a constant weight of the crystal growth melt during the crystal growth process and obtaining a stable large-sized SLN crystal.

[0048] The control of the heating section is realized by a control device, which uses a PID algorithm to control the heating output P2(t) of the second heating section (22) according to the deviation between the actual added weight of the replenishment melt and the weight of the crystal grown, thereby precisely controlling the replenishment process. In this example,

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[0049] The control device uses a PID algorithm according to the deviation between the actual crystal growth weight and the set value to control the heating output P1(t) of the third heating section (12), thereby controlling the crystal growth process with precision.

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[0050] In the pre-melting step, the polycrystalline material is heated and melted. The melt supplement may be maintained at a first temperature higher than the crystal growth temperature. Preferably, the first temperature is 10 to 50°C higher than the crystal growth temperature.

[0051] [Experimental Example 1] Using the growth system of the first embodiment, a 3-inch SLN crystal was obtained by growing a large-sized SLN crystal. Actual photographs of the crystal are shown in Figures 4(c) and 4(d). As shown in Figures 4(c) and 4(d), the crystal is large-sized SLN, free of defects such as twins, bubbles, and inclusions, and highly transparent. The defects introduced by conventional continuous supply methods were eliminated, resulting in high-quality large-sized SLN crystals. In contrast, SLN crystals grown using the conventional continuous supply method (Chinese Patent Document CN201110127655) have defects such as twins, bubbles, and inclusions. As shown in Figure 4(a), the mirror-like planar defect within the red frame is a twin defect, and the termination of the isodiameter portion of the twin often appears. Shown within the frame is a point defect of an inclusion, which often appears in the isodiameter portion. Within the white dotted frame is a bubble, a linear defect that penetrates from the shoulder growth stage to the isodiameter portion. The triangular defect within the frame shown in Figure 4(b) is an inclusion defect.

[0052] [Application experiment example 1] Using the growth system of Embodiment 1, large-sized SLN crystals were grown in the same manner as in Embodiment 4. First, 1000 g of polycrystalline material powder was charged into the supply crucible (21) in a stoichiometric ratio. The polycrystalline material was prepared in a molar ratio of Li / Nb=50 / 50, mixed for 48 hours, and sintered at 1100°C. Next, the supply crucible (21) was heated using the heating coil of the first heating section (23), and the polycrystalline material powder was heated and melted to a temperature 50°C higher than the crystal growth temperature.

[0053] In the supply step, the supply melt from the supply crucible (21) was added to the crystal growth melt at the second temperature via the supply pipe (24) so ​​that the weight of the crystal growth melt did not change during the crystal growth process.

[0054] Specifically, based on a typical isodiametric growth rate of 3 to 5 g / h (e.g., 5 g / h), the continuous supply process was controlled by controlling the temperature of the supply pipe (24). The supply rate was 0.1 to 2 g / 10 to 20 min (e.g., 1.25 g / 15 min), and the supply melt was supplied to the region between the inner crucible (113) and the outer crucible (112). The supply pipe (24) was heated via the heating coil of the second heating section (22), and the supply melt in the supply pipe was maintained at a second temperature 50°C higher than the crystal growth temperature.

[0055] Therefore, during the crystal growth process, it is possible to ensure that the liquid level of the crystal growth melt in the hanging crucible (11) does not change at all (the relative position of the crystal growth interface is stable), and that the temperature field of the crystal growth melt in the inner crucible (113) does not change at all (the temperature field of the crystal growth interface is stable). As a result, SLN crystals with a uniform composition can be grown.

[0056] Furthermore, in the supply step, the output P2(t) of the second heating part (22) can be controlled by a PID algorithm to realize on / off control of continuous supply.

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[0057] Furthermore, the output P1(t) of the third heating section (12) for crystal growth can be controlled by a PID algorithm, allowing for precise control of the crystal growth process.

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[0058] Using the growth system of the first embodiment and the method of the fourth embodiment, a LiNbO polycrystalline material with a mass equivalent to the SLN crystal to be grown was melted in a supply crucible (21), and the supply melt was transported to the liquid surface of the crystal growth melt through a platinum supply pipe (24). The supply pipe (24) was equipped with an independently positioned heating coil, and a PID algorithm was used to control the output of the heating coil and the weight loss of the supply crucible (21), thereby precisely controlling the opening and closing of the supply pipe (24) and precisely controlling the temperature of the supply melt. This reduces the impact of adding the supply melt to the crystal growth melt on the temperature field and composition of the crystal growth melt, contributing to precise control of crystal growth. As a result, problems such as composition fluctuations, temperature fluctuations, and inclusion introduction due to supplying the melt during the growth of large-sized SLN crystals are resolved, enabling precise control of the growth of lithium niobate crystals with a near-stoichiometric composition. Furthermore, by combining this online continuous supply device and method with the existing hanging crucible (11) structure, the impact of the supply process on the composition and temperature field of the crystal growth melt can be reduced to a negligible level. This ensures that the crystal growth dynamics are not affected during the crystal growth process, which is advantageous for the growth and precise control of large-sized SLN crystals. In this case, the supply material is added to the crystal growth melt in molten form, which is advantageous for solute diffusion, prevents the introduction of bubbles, and improves the stability of the crystal growth melt. By precisely controlling the heating power, the amount of supply material can be easily and accurately controlled, making it easy to synchronize process control with crystal growth.

[0059] Although the present invention has been described above by way of specific embodiments with reference to the accompanying drawings, those skilled in the art will understand that the above embodiments are merely examples for explaining the principles of the present invention and are not intended to limit the scope of the present invention. Various combinations, modifications, and equivalent substitutions can be made to the above embodiments without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0060] 1 Crystal growth equipment 2. Online continuous supply device 11 Hanging crucible 112 outer crucible 113 Inner crucible 12 Third heating section 21 Refill crucible 22 2nd heating section 23 1st heating section 24 Supply pipe

Claims

1. An online continuous supply device for growing large sized SLN crystals, comprising: a supply crucible for containing polycrystalline material; a supply pipe; a first heating section for heating the supply crucible to a first temperature; and a second heating section for heating the supply pipe to a second temperature, the first heating unit is provided outside the replenishing crucible and communicates with the supply pipe through a lower outlet of the replenishing crucible, the second heating unit is provided outside the supply pipe, and an end of the supply pipe extends into the crystal growth crucible; the first heating section heats the refill crucible to melt the polycrystalline material and form a refill melt; the supply pipe adds the replenishment melt to the crystal growth melt at the second temperature, and causes the molten lithium niobate to flow into the crystal growth crucible to realize online supply; the second heating unit heats the supply pipe, and the second temperature is higher than a crystal growth temperature to avoid solidification of the melt in the supply pipe; An online continuous supply device for growing large sized SLN crystals.

2. 2. An online continuous supply device for growing large-sized SLN crystals as described in claim 1, characterized in that the replenishment crucible is an intermediate frequency induction heated platinum crucible, and the first heating section is an induction coil wound around the outer periphery of the replenishment crucible to heat it.

3. 2. The on-line continuous supply device for growing large-sized SLN crystals according to claim 1, wherein the supply pipe is a platinum pipe having a diameter of 5 to 20 mm.

4. 2. The online continuous supply system for growing large sized SLN crystals according to claim 1, wherein the second heating section is an induction coil for intermediate frequency induction heating wound around the outside of the supply pipe, to prevent solidification of the melt within the supply pipe.

5. An online continuous supply system for growing large-sized SLN crystals, comprising a crystal growth apparatus, an online continuous supply apparatus according to any one of claims 1 to 4, and a control device, the crystal growth apparatus comprises a hanging crucible for accommodating a crystal growth melt, and a third heating unit for heating the hanging crucible, the hanging crucible comprising an inner crucible and an outer crucible, the hanging crucible being disposed inside the outer crucible, the inner crucible and the outer crucible having bottoms communicating with each other, the inner crucible being a melting cavity for accommodating a crystal growth melt, a sandwich cavity being formed between the inner crucible and the outer crucible, and an end of the supply pipe being extended into the sandwich cavity; an electromagnetic valve switch is provided in the supply pipe, and the control device includes a control unit electrically connected to the electromagnetic valve switch and each of the heating units, and configured to control the output of each heating unit so as to maintain a constant weight of the crystal growth melt during crystal growth; An online continuous supply system for growing large sized SLN crystals.

6. 6. A method for growing large-sized SLN using the online continuous supply system of claim 5, comprising: Step (1): placing a crystal growth melt in a melt cavity of a crystal growing apparatus, operating a third heating unit and a control device to heat a hanging crucible, and growing a crystal by a pulling method; (2) operating the first heating section during the crystal growth process to melt the polycrystalline material in the refill crucible at a first temperature to obtain a refill melt; (3) activating the second heating section to supply a refill melt into the sandwich cavity of the crystal growing apparatus through the supply pipe at the second temperature, and refilling the melt so that the weight of the crystal growing melt is maintained constant; A method for growing large sized SLNs comprising:

7. 7. The method according to claim 6, wherein the controller uses a PID algorithm to control the output P of the third heating section according to the following equation (1): １ (t) controlling the [Equation 1] where e １ (t) is the crystal growth weight m １ (t) is the difference between the set value and Kp １ , Ki １ , Kd １ are the proportional constant, integral constant, and differential constant, respectively.

8. 7. The method according to claim 6, wherein the first temperature is any temperature capable of heating and melting the polycrystalline material.

9. 7. The method according to claim 6, wherein the controller uses a PID algorithm to control the output P of the second heating section according to the following equation (2): ２ (t) controlling the [Equation 2] where e ２ (t) = m ２ (t)-m １ (t) and m ２ (t) is the actual weight of the replenishment melt, m １ (t) is the crystal growth weight, e ２ (t) is the deviation, and Kp ２ , Ki ２ , Kd ２ are the proportional constant, integral constant, and differential constant.

10. 7. The method of claim 6, In the step (3), the second temperature is 10 to 50° C. higher than the crystal growth temperature; The heating and melting temperature of the polycrystalline material is 10 to 50°C higher than the crystal growth temperature, In the step (3), the polycrystalline material is LiNbO ３ The method is characterized in that the material is polycrystalline.

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