Preparation device of large-size multi-period polarized crystal
Through the combination of the displacement stage and the monitoring module, high-quality preparation of large-size multi-period polarized crystals is achieved, the problem of uneven distribution of high-voltage electric field is solved, the nonlinear conversion efficiency is improved, and it is suitable for laser optical applications.
Patent Information
- Application Number
- CN202510540340.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-27
- Publication Date
- 2025-08-29
AI Technical Summary
It is difficult to prepare high-quality large-size multi-period polarized crystals with high-quality, especially due to domain mergers and nonlinear conversion efficiency reductions due to uneven distribution of high voltage electric fields.
The combination device of the displacement stage, polarization module, monitoring module and control module is adopted to achieve accurate polarization of different cycles through discretely designed polarization electrodes and real-time monitoring of current. Combined with the automatic movement of the displacement stage, the uniformity and mass of the high-voltage electric field distribution in each cycle are ensured.
It realizes high-quality preparation of large-size multi-period polarized crystals, meets user needs, improves nonlinear conversion efficiency, and is suitable for applications such as laser optical parametric oscillation and frequency multiplication.
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Figure CN120556149A_ABST
Abstract
Description
Technical Field
[0001] The present disclosure relates to the technical field of nonlinear optical frequency conversion devices, and in particular to a device for preparing a large-scale multi-period polarization crystal. Background Art
[0002] Lithium niobate (LN) and lithium tantalate (LT) crystals have excellent light transmittance properties in the range from visible light to mid-infrared light. By utilizing their ferroelectric properties and adopting quasi-phase matching technology, the phase mismatch caused by dispersion is compensated by periodically modulating the nonlinear polarization rate of the optical crystal, that is, periodically changing the spontaneous polarization direction of the crystal domain. Nonlinear frequency conversion can be achieved through optical parameter generation and frequency doubling to obtain mid-infrared and blue-green laser light sources. They have good application prospects in gas detection, precision measurement, underwater communication, etc.
[0003] Currently, periodically poled lithium niobate (PPLN) crystals have been used in various nonlinear optical devices, including frequency doubling, sum frequency generation, and optical parametric oscillation (OPO). As these applications expand, demands are being placed on PPLN crystals with larger sizes and more periods.
[0004] The currently common method of applying an applied electric field to a crystal involves fabricating periodic electrodes and then applying a high-voltage electric field to the positive and negative surfaces. The domain inversion depth can extend through the thickness of the lithium niobate crystal, with the domain inversion boundary region parallel to the z-axis of the lithium niobate crystal. The domain width can be as small as a few microns. Existing multi-periodic PPLN crystals typically have discrete, closely spaced periods. For example, 29-31.5 μm is common in mid-infrared applications, with the minimum and maximum periods varying by only two or three microns. This is because during periodic poling, a high-voltage electric field is applied to the commonly used liquid or metal electrodes, requiring a polarization reversal field of several kV or even tens of kV. Large differences in period distribution lead to different high-voltage electric field distributions across multiple periods, causing the voltage to preferentially concentrate on the smaller periods for polarization. This ultimately results in excessive duty cycles or domain merging in the smaller periods, resulting in poor quality and reduced frequency conversion efficiency in the multi-periodic PPLN crystal. Therefore, to avoid this competition in high-voltage electric field distribution, multi-periodic PPLN crystals typically employ a continuously tapered period, with periods varying by only a few μm. However, user needs are diverse, and continuously gradient multi-period PPLN crystals cannot meet user needs. Summary of the Invention
[0005] The purpose of the present disclosure is to provide a device for preparing large-sized multi-period poled crystals, which can prepare high-quality large-sized multi-period poled crystals.
[0006] The present disclosure provides a device for preparing a large-scale multi-period polarized crystal, comprising:
[0007] A translation stage is used to place a target crystal, wherein the upper surface of the target crystal is divided into a plurality of periodic regions, and polarized electrodes of a corresponding period are prepared in each periodic region;
[0008] a polarization module, configured to apply a high-voltage electric field to polarization electrodes of different periods of the target crystal for polarization, wherein the lower surface of the target crystal is grounded via a voltage divider resistor;
[0009] A monitoring module, configured to monitor the polarization current flowing through the voltage divider resistor in real time;
[0010] The control module is used to control the polarization module to apply a corresponding high-voltage electric field to the current cycle, and determine whether the polarization of the current cycle is completed based on the polarization current collected by the monitoring module; if the polarization of the current cycle is completed, control the displacement stage to drive the target crystal to move so that the polarization module polarizes the next cycle until all cycles are polarized.
[0011] In a possible implementation, the period values of different periods on the target crystal are set independently.
[0012] In a possible implementation, the polarization electrode is a metal electrode or a transparent electrode.
[0013] In a possible implementation, the width of the polarization electrodes in each period is designed to be between one tenth and one third of the period according to the size of the period.
[0014] In one possible implementation, the polarization module includes: an arbitrary waveform generator and a high-voltage amplifier;
[0015] The arbitrary waveform generator is used to generate a pulse waveform used when polarizing multiple cycles;
[0016] The high-voltage amplifier is used to amplify the pulse waveform into a required pulse high-voltage electric field waveform and apply a high-voltage electric field to the polarization electrode.
[0017] In a possible implementation, the pulse waveform is a triangular wave, a rectangular wave, or other arbitrary waveform with peaks.
[0018] In a possible implementation, the smaller the period, the shorter the pulse used.
[0019] In a possible implementation, the monitoring module includes an oscilloscope.
[0020] In a possible implementation, the apparatus further includes:
[0021] The crystal fixture is used to place the target crystal with the prepared polarized electrode in the insulating oil in the crystal fixture, and the temperature of the insulating oil is the target temperature.
[0022] In a possible implementation, the target crystal is a ferroelectric crystal.
[0023] The advantages of the present disclosure compared with the prior art are:
[0024] The preparation device of the large-scale multi-period polarized crystal disclosed in the present invention includes: a displacement stage for placing the target crystal, the upper surface of the target crystal is divided into multiple periodic regions, and each periodic region is prepared with a polarization electrode of a corresponding period; a polarization module for applying a high-voltage electric field to the polarization electrodes of different periods of the target crystal for polarization, and the lower surface of the target crystal is grounded through a voltage divider resistor; a monitoring module for real-time monitoring of the polarization current flowing through the voltage divider resistor; a control module for controlling the polarization module to apply a corresponding high-voltage electric field to the current period, and judging whether the polarization of the current period is completed based on the polarization current collected by the monitoring module; if the polarization of the current period is completed, controlling the displacement stage to drive the target crystal to move, so that the polarization module polarizes the next period until all periods are polarized. Compared with the existing technology, the present application adopts a discrete structure design of multi-period polarization electrodes, combined with a displacement stage and a monitoring module, which can prepare high-quality large-scale multi-period polarized crystals, thereby meeting user needs. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present disclosure. The same reference symbols are used throughout the drawings to represent the same components. In the drawings:
[0026] Figure 1 A schematic structural diagram of a device for preparing a large-scale multi-period polarized crystal provided by the present disclosure is shown;
[0027] Figure 2 A schematic diagram of the target crystal provided by the present disclosure is shown;
[0028] Figure 3 Schematic diagram showing a large-sized multi-periodic PPLN crystal after cutting and polishing;
[0029] Figure 4 Shows what was observed under the microscope Figure 3 The periodic microstructure of the PPLN crystal shown. DETAILED DESCRIPTION
[0030] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely illustrative and are not intended to limit the scope of the present disclosure. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.
[0031] The accompanying drawings illustrate various schematic diagrams of structures according to embodiments of the present disclosure. These figures are not drawn to scale, and for the purpose of clarity, certain details are exaggerated and certain details may be omitted. The shapes of the various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Those skilled in the art may design regions / layers with different shapes, sizes, and relative positions as needed.
[0032] In the context of the present disclosure, when a layer / element is referred to as being "on" another layer / element, it can be directly on the other layer / element or an intervening layer / element may be present therebetween. In addition, if a layer / element is "on" another layer / element in one orientation, it may be "below" the other layer / element when the orientation is reversed.
[0033] The most important indicator of crystal polarization quality is the duty cycle of the crystal's periodic polarization reversal (the ratio of the polarization area to the period). A duty cycle of 50% is ideal, achieving maximum nonlinear conversion efficiency. Large, high-quality periodically poled lithium niobate (PPLN) crystals have a duty cycle of 40-60% at all locations across the crystal.
[0034] Traditional polarization methods, such as liquid electrode polarization, apply a high-voltage electric field, which polarizes the entire crystal all at once. Polarization with metal electrodes cannot be performed separately for different periods. Alternatively, multiple regions with different periods can be cut into the crystal and then polarized multiple times. Alternatively, multiple periods with similar periods can be polarized at once.
[0035] The disclosed embodiments provide a device for preparing large-scale multi-period polarized crystals. By moving the crystal and applying the optimal polarization electric field for different periods, a multi-period PPLN crystal can be obtained. This device offers advantages such as flexible period design and good polarization uniformity over large sizes. It also features mass production and practical application. This is described below with reference to the accompanying figures.
[0036] Figure 1 The schematic diagram of the structure of the preparation device of a large-scale multi-period polarized crystal provided by the present disclosure is shown. Figure 1 The device for preparing a large-size multi-period polarized crystal includes: a translation stage 10, a polarization module 20, a monitoring module 30 and a control module 40.
[0037] The translation stage 10 is used to place the target crystal. The target crystal's top surface is divided into multiple periodic regions, each of which is equipped with polarization electrodes of a corresponding period. The target crystal can be moved with the translation stage 10, and its movement can be controlled by software. The translation stage enables automatic control of the crystal's movement during the polarization process, allowing for discrete polarization of crystals with multiple periods, enabling the creation of large-scale, multi-period polarized crystals. The multiple periods can be arbitrarily designed.
[0038] Specifically, the target crystal is a ferroelectric crystal, including but not limited to lithium niobate crystal, and can also be a lithium niobate crystal doped with magnesium or other materials, as well as a lithium niobate crystal with a near-stoichiometric ratio, or a lithium tantalate crystal, potassium titanyl phosphate (KTiOPO4, KTP) crystal and other similar ferroelectric crystals.
[0039] For example, multiple periodic electrodes of varying lengths can be pre-fabricated on the surface of a lithium niobate crystal. The lengths are designed based on the desired laser wavelength, and the electrodes within each period are discrete and unconnected. The range of period variations can be quite large, ranging from 3 to 10 periods, or even more, and the periodicity can range from 6 to 14 μm, or even 24 to 40 μm.
[0040] like Figure 2 Shown is a schematic diagram of the target crystal provided by this application, such as Figure 2 As shown, the upper surface of the target crystal is divided into multiple long strips, each with a different period. Specifically, the period values of the different periods on the target crystal are independently set. For example, the multiple periods can be discontinuous and discrete, such as 6μm, 30μm, 15μm, 40μm, and other arbitrary values.
[0041] Specifically, the polarization electrodes are metal electrodes or transparent electrodes, for example, metal electrodes such as aluminum and gold, or transparent electrodes such as ITO.
[0042] Specifically, the width of the polarization electrodes in each period is designed to be between one tenth and one third of the period according to the size of the period.
[0043] The polarization module 20 is used to apply a high voltage electric field to the polarization electrodes of different periods of the target crystal for polarization. The lower surface of the target crystal is grounded via a voltage divider resistor.
[0044] Specifically, this application uses an external high-voltage electric field polarization method, applying a positive high voltage to the positive surface of the crystal and grounding the negative surface. Furthermore, this application uses a voltage divider resistor to monitor the polarization of the crystal in real time over a certain period. When the monitoring current indicates that the polarization of the first period has been completed, the stage is used to move to the next period.
[0045] Specifically, such as Figure 1 As shown, the polarization module 20 includes: an arbitrary waveform generator and a high-voltage amplifier.
[0046] The arbitrary waveform generator is used to generate a pulse waveform used when polarizing multiple cycles; the high-voltage amplifier is used to amplify the pulse waveform into a required pulse high-voltage electric field waveform and apply a high-voltage electric field to the polarization electrode.
[0047] In one possible implementation, the pulse waveform generated by the arbitrary waveform generator can be a triangular wave, a rectangular wave, or other arbitrary waveform with spikes. The smaller the period, the shorter the pulse used. For example, during the poling process, different pulse waveforms can be used for different periods, such as short pulses for small periods and long pulses for large periods.
[0048] A monitoring module 30, configured to monitor the polarization current flowing through the voltage divider resistor in real time;
[0049] Specifically, such as Figure 1 As shown, the monitoring module 30 includes an oscilloscope.
[0050] The control module 40 is used to control the polarization module 20 to apply a corresponding high-voltage electric field to the current cycle, and determine whether the polarization of the current cycle is completed based on the polarization current collected by the monitoring module 30; if the polarization of the current cycle is completed, control the translation stage 10 to drive the target crystal to move so that the polarization module 20 polarizes the next cycle until all cycles are polarized.
[0051] The control module 40 can be specifically a computer, a handheld controller or other equipment, and is in communication with the translation stage 10 , the polarization module 20 , and the monitoring module 30 .
[0052] Specifically, the present application places a crystal with prepared polarized electrodes on a translation stage, monitors the polarization progress in real time during the polarization process, and after completing one cycle of crystal polarization, the software automatically controls the translation to the next cycle, gradually completing multiple cycles of polarization. During the polarization process, the specific conditions such as the pulse waveform of the polarization electric field and the high voltage level are changed according to the size of the cycle, thereby obtaining a high-quality, large-scale, multi-cycle polarized crystal that can be used for laser optical parametric oscillation, frequency doubling, etc. The large size of the polarized crystal prepared by this application can be 10mm-50mm in width, or wider, the thickness of the crystal can be 1mm-10mm, and the length of the crystal can be 10mm-70mm.
[0053] In some embodiments, as Figure 1As shown, the apparatus for preparing a large-scale multi-period polarized crystal provided herein also includes a crystal fixture 50 for placing the target crystal with prepared polarized electrodes in insulating oil within the crystal fixture. The insulating oil is at a target temperature. The insulating oil can be silicone oil with excellent insulating properties, and the target temperature can be set between 80°C and 250°C.
[0054] For example, a multi-period polarization electrode is first prepared on the upper surface of a 3-inch magnesium-doped lithium niobate wafer, such as Figure 2 As shown, the period of each strip area is different, and the period value can be discrete, such as any value between 6-40μm. The polarization electrode on the crystal is an aluminum electrode, and the crystal thickness is 2mm. Then as Figure 1 As shown, the crystal sample with the prepared polarized electrode is placed in the crystal fixture. The crystal fixture is first placed on a heating platform. There is silicone oil with good insulation performance in the fixture. The heating temperature can be set between 80-250°C. After heating, the crystal fixture is placed on a translation stage. The translation stage is controlled by software. The required pulse waveform is designed on the arbitrary waveform generator. After passing through the high-voltage amplifier, the high-voltage electric field is applied to the crystal sample. The oscilloscope monitors the polarization current on the voltage divider resistor in real time and observes the polarization of the first cycle. When the polarization is completed, the translation stage is controlled to move to the next cycle for polarization. This cycle is repeated to complete multiple cycles of polarization on the wafer. Finally, the crystal is cut as required and the light-transmitting surface of the sample is polished, as shown in the figure. Figure 3 The following shows the high-quality large-size, multi-period PPLN crystal obtained. Figure 4 The microscope observations Figure 3 The periodic microstructure of the PPLN crystal shown (period P=29 μm) has a duty cycle of 50% and a maximum nonlinear conversion efficiency.
[0055] The preparation device of the large-scale multi-period polarized crystal disclosed in the present invention includes: a displacement stage for placing the target crystal, the upper surface of the target crystal is divided into multiple periodic regions, and each periodic region is prepared with a polarization electrode of a corresponding period; a polarization module for applying a high-voltage electric field to the polarization electrodes of different periods of the target crystal for polarization, and the lower surface of the target crystal is grounded through a voltage divider resistor; a monitoring module for real-time monitoring of the polarization current flowing through the voltage divider resistor; a control module for controlling the polarization module to apply a corresponding high-voltage electric field to the current period, and judging whether the polarization of the current period is completed based on the polarization current collected by the monitoring module; if the polarization of the current period is completed, controlling the displacement stage to drive the target crystal to move, so that the polarization module polarizes the next period until all periods are polarized. Compared with the existing technology, the present application adopts a discrete structure design of multi-period polarization electrodes, combined with a displacement stage and a monitoring module, which can prepare high-quality large-scale multi-period polarized crystals, thereby meeting user needs.
[0056] The above describes the embodiments of the present disclosure. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present disclosure. The scope of the present disclosure is defined by the appended claims and their equivalents. Without departing from the scope of the present disclosure, those skilled in the art may make various substitutions and modifications, which are intended to fall within the scope of the present disclosure.
Claims
1. A device for preparing large-scale multi-period polarized crystals, characterized in that: include: A translation stage is used to place a target crystal, wherein the upper surface of the target crystal is divided into a plurality of periodic regions, and a polarization electrode of a corresponding period is prepared in each periodic region; a polarization module, configured to apply a high-voltage electric field to polarization electrodes of different periods of the target crystal for polarization, wherein the lower surface of the target crystal is grounded via a voltage-dividing resistor; A monitoring module, configured to monitor the polarization current flowing through the voltage-dividing resistor in real time; The control module is used to control the polarization module to apply a corresponding high-voltage electric field to the current cycle, and determine whether the polarization of the current cycle is completed based on the polarization current collected by the monitoring module; if the polarization of the current cycle is completed, control the displacement stage to drive the target crystal to move so that the polarization module polarizes the next cycle until all cycles are polarized.
2. The device for preparing a large-scale multi-period polarized crystal according to claim 1, characterized in that: The period values of different periods on the target crystal are set independently.
3. The device for preparing a large-scale multi-period polarized crystal according to claim 1, characterized in that: The polarization electrodes are metal electrodes or transparent electrodes.
4. The device for preparing a large-scale multi-period polarized crystal according to claim 1, characterized in that: The width of the polarization electrodes in each period is designed to be between one tenth and one third of the period according to the size of the period.
5. The device for preparing a large-scale multi-period polarized crystal according to claim 1, characterized in that: The polarization module includes: an arbitrary waveform generator and a high-voltage amplifier; The arbitrary waveform generator is used to generate a pulse waveform used when polarizing multiple cycles; The high-voltage amplifier is used to amplify the pulse waveform into a required pulse high-voltage electric field waveform and apply a high-voltage electric field to the polarization electrode.
6. The device for preparing a large-scale multi-period polarized crystal according to claim 5, characterized in that: The pulse waveform is a triangular wave, a rectangular wave or other arbitrary waveforms with peaks.
7. The device for preparing a large-scale multi-period polarized crystal according to claim 5, characterized in that: The smaller the period, the shorter the pulses used.
8. The device for preparing a large-scale multi-period polarized crystal according to claim 1, characterized in that: The monitoring module includes an oscilloscope.
9. The device for preparing a large-scale multi-period polarized crystal according to claim 1, characterized in that: The device further comprises: The crystal fixture is used to place the target crystal with the prepared polarized electrode in the insulating oil in the crystal fixture, and the temperature of the insulating oil is the target temperature.
10. The device for preparing a large-size multi-period polarized crystal according to any one of claims 1 to 9, characterized in that: The target crystal is a ferroelectric crystal.