Design and fabrication of an on-chip entanglement source based on X-cut periodically poled lithium niobate thin films

Abstract

The present invention relates to a design and preparation method for an on-chip entangled source based on an X-cut periodically poled lithium niobate film, comprising: (1) preparing a first set of electrodes and a second set of electrodes with different polarization periods on the lithium niobate film; (2) polarizing the first set of electrodes and the second set of electrodes respectively; (3) applying a voltage to cause domain inversion of the lithium niobate between the electrodes, and directly etching the lithium niobate in the domain inversion region to prepare a lithium niobate waveguide, thereby obtaining a periodically poled lithium niobate waveguide; (4) generating two sets of photon pairs with perpendicular polarization directions through a spontaneous parametric down-conversion process between the first set of electrodes and the second set of electrodes, and preparing a polarization entangled source when the length of the lithium niobate waveguide is less than the coherence length of the pump light; and (5) separating the photon pairs. The design and preparation method for the on-chip entangled source provided in the present application provides a stable and highly integrated on-chip polarization entangled source generation solution that meets the requirements of high integration.

Description

Technical Field

[0001] The present invention relates to a design and preparation method of an on-chip entanglement source based on an X-cut periodically polarized lithium niobate film, and belongs to the field of integrated optoelectronics. Background Art

[0002] Nonlinear optical effects have many applications, including single-photon generation, parametric down-conversion, frequency conversion, or amplification. Utilizing the superior nonlinear coefficient of lithium niobate (LN) crystals, periodically poled lithium niobate (PPLN) waveguides based on quasi-phase matching have high nonlinear conversion efficiency and have always attracted much attention in the field of scientific research. However, the refractive index difference of the waveguide structure in the bulk material is small, which is not conducive to the production of highly integrated optical chips. Lithium niobate on insulator (LNOI) is a nanoscale lithium niobate thin film (TFLN). Compared with bulk materials, the optical microstructure on LNOI can have a smaller size, which can greatly improve the integration of the device while reducing the size and power consumption of the device.

[0003] Periodically poled lithium niobate (PP-TFLN) waveguides are a key component of large-scale integrated optoelectronic chips based on lithium niobate thin-film platforms. X-cut TFLN can be easily poled at room temperature using surface electrodes, fully exploiting the highest nonlinear coefficient of lithium niobate. For many devices, such as quasi-phase-matched waveguide structures for spontaneous parametric down-conversion of photons or second harmonic generation, X-cut TFLN is the preferred orientation, allowing the use of the highest nonlinear coefficient of LN while simultaneously allowing for polarization using coplanar electrodes deposited on the LN surface.

[0004] LNOI's devices have rapidly expanded in traditional optics, including low-loss microring structures, optical superlattices, nonlinear effects, and electro-optical modulators. LNOI has demonstrated significant advantages over traditional optics due to its strong light confinement capabilities and large refractive index contrast. In recent years, research at the quantum level has also rapidly expanded. For research on quantum entanglement, the generation of entangled sources is crucial, particularly polarization-entangled sources commonly used in quantum optics. While discrete optics based on polarized polarization-linked nanostructures (PPLNs) can currently produce high-brightness, high-efficiency, and high-contrast polarization-entangled sources, these are bulky, unstable, and require constant maintenance.

[0005] The present application provides a design and preparation method of an on-chip entangled source based on an X-cut periodically poled lithium niobate film, which provides a stable and highly integrated on-chip polarization entangled source generation solution for traditional discrete optics. Summary of the Invention

[0006] In response to the shortcomings of the existing technology, the present invention provides a design and preparation method for an on-chip entangled source based on X-cut periodically poled lithium niobate thin film; a periodically poled lithium niobate waveguide with two sets of polarization periods is prepared through two electrode structures with different periods; type-II phase matching (TE→TE+TM, the polarization direction of TE mode light and the polarization direction of TM mode light are perpendicular to each other) is adopted to calculate the corresponding polarization periods of two sets of non-degenerate spontaneous parametric down-conversion processes respectively, and for 532nm pump light, collinear signal photons and idler photons with perpendicular polarization directions are generated at 1550nm and 810nm respectively, thereby realizing the preparation of an on-chip non-degenerate polarization entangled source.

[0007] Explanation of terms:

[0008] 1.PP-LNOI: Periodically poled lithium niobate thin films on insulator.

[0009] The technical solution of the present invention is:

[0010] A design and preparation method of an on-chip entanglement source based on an X-cut periodically poled lithium niobate thin film, comprising:

[0011] (1) A chromium electrode pattern is prepared on a lithium niobate film, the chromium electrode pattern including a first set of electrodes and a second set of electrodes arranged in sequence, each of the first set of electrodes and the second set of electrodes including a plurality of pairs of symmetrically arranged chromium electrodes; and the polarization periods of the first set of electrodes and the second set of electrodes are different; for example, software such as Lμmerical, Comsol, and MATLAB can be used to simulate the effective refractive index and the corresponding nonlinear process of the lithium niobate waveguide structure to determine the polarization period, duty cycle, etc. of the two sets of tooth electrodes; the electrode gap is the gap between the tooth ends of two opposite parts of a set of comb-shaped tooth electrodes; and the polarization period is the distance between two adjacent chromium electrodes;

[0012] (2) A corresponding pulse voltage is applied to the first set of electrodes and the second set of electrodes for polarization, and the direction of the pulse voltage is opposite to the polarization direction of the lithium niobate film, so that the lithium niobate between the electrodes undergoes domain inversion; due to the periodic arrangement of the tooth structure of the electrodes, the lithium niobate film undergoes periodic domain inversion.

[0013] (3) Directly etching the lithium niobate film in the domain inversion region to prepare a lithium niobate waveguide to obtain a periodically poled lithium niobate waveguide;

[0014] (4) At the first set of electrodes and the second set of electrodes, two sets of photon pairs with perpendicular polarization directions are generated through a spontaneous parametric down-conversion process. When the length of the lithium niobate waveguide is less than the coherence length of the pump light, a polarization entangled source is prepared;

[0015] (5) By splitting the light according to the wavelength, the simultaneously generated photon pairs are separated to obtain polarization-entangled photon pairs.

[0016] According to the preferred embodiment of the present invention, in step (4), a photon TE with a mode of TE and a wavelength of 532 nm is generated at the first set of electrodes. 532 The spontaneous down-conversion process produces a pair of photons with perpendicular polarization directions, that is, a TE 1550 Photons and a TM 810 Photon(|TE 1550 TM 810 >); At the second set of electrodes, a photon TE mode with a wavelength of 532nm is generated. 532 The spontaneous down-conversion process produces a pair of photons with perpendicular polarization directions, that is, a TE 810 Photons and a TM 1550 Photon(|TE 810 TM 1550 >), when the waveguide length is less than the coherence length of the 532nm pump light, the The polarization entangled source of the form

[0017]

[0018] According to the present invention, preferably, the symmetrically arranged chromium electrodes in the first electrode group or the second electrode group have the same shape, namely, comb-shaped paired chromium electrodes, with the chromium electrodes having arc-shaped serrations. The arc-shaped serrations can reduce current leakage, lower the difficulty of achieving periodic poling by applying voltage, and achieve a better periodic poling effect.

[0019] According to the present invention, the electrode gap of the first group of electrodes is preferably the same as the electrode gap of the second group of electrodes. The electrode gap is the gap between the two opposing tooth ends of one group of electrodes. The two groups are divided because different electrodes correspond to different polarization voltages. Polarizing them separately can achieve better polarization effects. Setting the same gap maximizes the utilization of the inversion region.

[0020] According to the present invention, preferably, the electrode gaps between the first group of electrodes and the second group of electrodes are both 10 μm-40 μm; further preferably, the electrode gaps between the first group of electrodes and the second group of electrodes are both 10 μm.

[0021] According to the present invention, the duty ratio of the first and second electrodes is preferably 25-40%. More preferably, the duty ratio of the first and second electrodes is 35%. Because domain expansion occurs when voltage is applied to achieve domain inversion, the smaller the polarization period, the smaller the electrode duty ratio should be.

[0022] According to the present invention, the polarization period of the first set of electrodes is preferably 5.6 μm, and the polarization period of the second set of electrodes is preferably 11.2 μm. The two polarization periods are calculated based on wt = 1.8 μm, wt represents the upper base of the trapezoid, the lower base is calculated from the upper base of the trapezoid and the sidewall angle θ, 0.6 μm is the thickness of the first layer of lithium niobate material of LNOI, the lithium niobate film etching depth h = 0.16 μm, and the sidewall angle θ = 60°.

[0023] Preferably, in step (2), the polarization effect of the lithium niobate film is characterized using piezoresponse force microscopy (PFM), and then a lithium niobate waveguide is prepared in a region with a duty cycle close to 50% in the domain inversion region to obtain a periodically poled lithium niobate waveguide. Preparing the lithium niobate waveguide in this region has the highest conversion efficiency.

[0024] According to the preferred embodiment of the present invention, in step (2), the specific process of determining the pulse voltage and the number of pulses is as follows:

[0025] 2-1, determine the maximum voltage V of the pulse voltage max The size of V max It should be greater than the coercive field value of lithium niobate × electrode gap d. Too small a voltage will make it difficult to achieve domain inversion, and too large a voltage will cause severe lateral expansion. Therefore, V max Generally, it is less than the coercive field value of lithium niobate × the electrode gap d (1 + 50%). In the actual voltage application process, the voltage 10V higher than the voltage value at which domain inversion can be observed is taken as the maximum voltage V max Perform periodic polarization; preliminarily set the pulse voltage waveform to a trapezoidal wave, which includes a fast rising section, a high voltage duration section, and a slow falling section, and the corresponding time periods are t1, t2, and t3 respectively;

[0026] For example, the coercive field of lithium niobate is 21V / μm. When the electrode gap d is 10μm, the polarization voltage V max Set it between 210-300V, and choose a value slightly larger than the voltage at which lithium niobate just undergoes domain inversion, which can increase the success rate of domain inversion.

[0027] 2-2. Adjust the pulse voltage's corresponding values ​​of t1, t2, and t3, as well as the number of pulses, to achieve an ideal duty cycle of 50% in the domain inversion region. The fast rising edge t1 promotes nucleation site formation and has little effect within the selected range, requiring only limited testing or adopting a fixed value based on experience. Voltages above the coercive field allow domain growth, ensuring that the high voltage duration t2 matches the number of pulses. Compared to a single pulse that completes domain polarization in one go, applying multiple pulses at fixed intervals improves the polarization success rate and prevents electrode damage, but requires a longer application time. The slow falling edge t3 prevents depolarization and has little effect within the selected range, requiring only limited testing or adopting a fixed value based on experience.

[0028] 2-3, determine the pulse voltage V according to step 2-2 max Repeated polarization of lithium niobate films improves the success rate. When reversing the voltage to restore the domain inversion area, a voltage slightly higher than the selected pulse voltage and a greater number of pulses can be used to ensure the recovery effect.

[0029] According to the present invention, preferably, the thickness of the chromium electrode is 100 nm.

[0030] Preferably according to the present invention, the thickness of the lithium niobate film is 600 nm.

[0031] The beneficial effects of the present invention are:

[0032] Although high-brightness, high-efficiency, and high-contrast polarization entangled sources can be produced based on PPLN in discrete optics, these are expensive, bulky, unstable, and require constant maintenance. The integration and miniaturization of quantum optical systems are essential for optical quantum information processing. This application provides a design and preparation method for an on-chip entangled source based on X-cut periodically poled lithium niobate thin films, providing a stable and highly integrated on-chip polarization entangled source generation solution for traditional discrete optics, meeting the requirements of high integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the structure of X-cut lithium niobate film;

[0034] Figure 2 Schematic top view of the chromium electrode structure;

[0035] Figure 3 A top-down diagram of the periodic polarization effect and subsequent waveguide processing position;

[0036] Figure 4 This is a side view of the lithium niobate waveguide structure;

[0037] Figure 5 A method for generating an on-chip non-degenerate polarization entangled source;

[0038] Figure 6 is a waveform diagram of the polarization pulse voltage;

[0039] Figure 7 Schematic diagram of polarization with applied pulse voltage.

[0040] 1. Silicon substrate, 2. SiO2 substrate, 3. Lithium niobate film. DETAILED DESCRIPTION

[0041] The present invention will be further described below with reference to the embodiments and the accompanying drawings, but is not limited thereto.

[0042] Example 1

[0043] A design and preparation method of an on-chip entanglement source based on an X-cut periodically poled lithium niobate thin film, comprising:

[0044] (1) Purchase commercial X-cut lithium niobate thin film wafers, the specific structure is as follows Figure 1 As shown, from bottom to top are silicon substrate 1, SiO2 substrate 2, lithium niobate film 3; a chromium electrode pattern is prepared on the lithium niobate film 3 by electron beam exposure. The chromium electrode pattern is as shown in FIG. Figure 2 As shown, the chromium electrode pattern includes a first group of electrodes and a second group of electrodes arranged in sequence, and the first group of electrodes and the second group of electrodes each include a plurality of pairs of symmetrically arranged chromium electrodes; and the polarization periods of the first group of electrodes and the second group of electrodes are different; for example, software such as Lμmerical, Comsol, and Matlab can be used to simulate the corresponding nonlinear process to determine the duty ratio, electrode gap, and polarization period of the two groups of tooth electrodes; Figure 2 As shown, the electrode gap is the gap between the two opposite tooth ends of a set of comb-shaped tooth electrodes; the polarization period is the distance between two adjacent chromium electrodes;

[0045] According to the quasi-phase matching condition The corresponding polarization period that should be satisfied by the first-order quasi-phase matching of two different sets of nonlinear processes can be calculated.

[0046]

[0047] For |TE 532 >→|TE 1550 TM 810 >, polarization period

[0048] For |TE 532 >→|TE 1550 TM 810 >, polarization period The effective refractive index n of light of different wavelengths and modes eff It can be simulated by software such as Lμmerical and Comsol.

[0049] The thickness of the chromium electrode is 100 nm, and the thickness of the lithium niobate film 3 is 600 nm.

[0050] (2) Apply corresponding pulse voltages to the first set of electrodes and the second set of electrodes for polarization, and the direction of the pulse voltage is opposite to the polarization direction of the lithium niobate film, such as Figure 7 As shown, the lithium niobate between the electrodes and the teeth undergoes domain inversion; due to the periodic arrangement of the electrodes on the tooth structure, the lithium niobate film undergoes periodic domain inversion.

[0051] Polarization effects such as Figure 3As shown in the figure, the black area is reversed due to the applied voltage, and the polarization direction is opposite to the original direction. The area where the domain inversion does not occur is arranged periodically with the area where the domain inversion occurs, which is the periodic polarization of the lithium niobate film 3. (3) Apply a voltage in the opposite direction to the pulse voltage in step (2) to cause the lithium niobate between the electrodes to undergo domain inversion. Lithium niobate is directly etched in the domain inversion area to prepare a lithium niobate waveguide. The lithium niobate waveguide structure is designed as shown in the figure. Figure 4 As shown, a periodically poled lithium niobate waveguide is obtained;

[0052] (4) Through the spontaneous parametric down-conversion process of the first set of electrodes and the second set of electrodes, two groups of photon pairs with perpendicular polarization directions are generated. When the length of the lithium niobate waveguide is less than the coherence length of the pump light, a polarization entangled source is prepared.

[0053] Specifically, in step (4), a photon TE with a mode of TE and a wavelength of 532 nm is generated at the first set of electrodes. 532 The spontaneous down-conversion process produces a pair of photons with perpendicular polarization directions, that is, a TE 1550 Photons and a TM 810 Photon(|TE 1550 TM 810 >); At the second set of electrodes, a photon TE mode with a wavelength of 532nm is generated. 532 The spontaneous down-conversion process produces a pair of photons with perpendicular polarization directions, that is, a TE 810 Photons and a TM 1550 Photon(|TE 810 TM 1550 >), when the waveguide length is less than the coherence length of the 532nm pump light, the The polarization entangled source of the form

[0054]

[0055] (5) Spectroscopy based on wavelengths to separate the photon pairs generated simultaneously. Figure 5 As shown, in discrete optics, light can be split by a dichroic mirror (DM), and in integrated optics, a structure that splits light according to wavelength can also be designed.

[0056] In the first or second electrode group, the symmetrically arranged chromium electrodes have the same shape, being comb-shaped, with the teeth of the chromium electrodes having arc-shaped ends. The arc-shaped ends of the chromium electrodes can reduce current leakage, ease the difficulty of achieving periodic poling by applying voltage, and achieve a better periodic poling effect.

[0057] The electrode gap between the first and second electrodes is identical. The gap is the distance between the two opposing teeth of one set of electrodes. The two groups are separated because different electrodes correspond to different polarization voltages. Polarizing them separately yields better polarization results, and setting the same gap maximizes utilization of the inversion region.

[0058] The electrode gaps of the first and second electrodes are both 10 μm to 40 μm, and the duty ratios of the first and second electrodes are 25% to 40%.

[0059] Example 2

[0060] A design and preparation method of an on-chip entanglement source based on an X-cut periodically poled lithium niobate thin film differs from Example 1 in that:

[0061] The electrode gaps of the first and second electrodes are both 10 μm.

[0062] The duty cycle of the first and second electrodes is 35%. Because domain expansion occurs when voltage is applied to achieve domain inversion, the smaller the polarization period, the smaller the electrode duty cycle should be.

[0063] like Figure 4 As shown in the figure, based on wt = 1.8 μm, wt represents the upper base of the trapezoid, the lower base is calculated from the upper base and the sidewall angle θ, 0.6 μm is the thickness of the first layer of lithium niobate material of LNOI, the lithium niobate film etching depth h = 0.16 μm, and the sidewall angle θ = 60°, the two sets of polarization periods are calculated. The polarization period of the first set of electrodes is 5.6 μm, and the polarization period of the second set of electrodes is 11.2 μm.

[0064] In step (2), the polarization effect of the lithium niobate film 3 is characterized using piezoresponse force microscopy (PFM). Then, a lithium niobate waveguide is fabricated in the domain inversion region where the duty cycle reaches 50%, resulting in a periodically poled lithium niobate waveguide. Fabricating the lithium niobate waveguide in this region has the highest conversion efficiency.

[0065] Example 3

[0066] A design and preparation method of an on-chip entanglement source based on an X-cut periodically poled lithium niobate thin film differs from Example 1 in that:

[0067] 2-1, such as Figure 6 As shown, determine the maximum voltage V of the pulse voltage max The size of V max It should be greater than the coercive field value of lithium niobate × electrode gap d. Too small a voltage will make it difficult to achieve domain inversion, and too large a voltage will cause severe lateral expansion. Therefore, V maxGenerally, it is less than the coercive field value of lithium niobate × the electrode gap d (1 + 50%). In the actual voltage application process, the voltage 10V higher than the voltage value at which domain inversion can be observed is taken as the maximum voltage V max Perform periodic polarization; preliminarily set the pulse voltage waveform to a trapezoidal wave, which includes a fast rising section, a high voltage duration section, and a slow falling section, and the corresponding time periods are t1, t2, and t3 respectively;

[0068] For example, the coercive field of lithium niobate is 21V / μm. When the electrode gap d is 10μm, the polarization voltage V max Set it between 210-300V, and choose a value slightly larger than the voltage at which lithium niobate just undergoes domain inversion, which can increase the success rate of domain inversion.

[0069] 2-2. Adjust the pulse voltage's corresponding values ​​of t1, t2, and t3, as well as the number of pulses, to achieve an ideal duty cycle of 50% in the domain inversion region. The fast rising edge t1 promotes nucleation site formation and has little effect within the selected range, requiring only limited testing or adopting a fixed value based on experience. Voltages above the coercive field allow domain growth, ensuring that the high voltage duration t2 matches the number of pulses. Compared to a single pulse that completes domain polarization in one go, applying multiple pulses at fixed intervals improves the polarization success rate and prevents electrode damage, but requires a longer application time. The slow falling edge t3 prevents depolarization and has little effect within the selected range, requiring only limited testing or adopting a fixed value based on experience.

[0070] 2-3, determine the pulse voltage V according to step 2-2 max Repeated polarization of lithium niobate films improves the success rate. When reversing the voltage to restore the domain inversion, a slightly higher voltage and a higher number of pulses can be used to ensure the recovery effect. For example, during the repeated polarization process, the pulse voltage can be increased by 3-5V and the number of pulses can be increased by 5-10.

Claims

1. A design and preparation method of an on-chip entanglement source based on X-cut periodically poled lithium niobate thin film, characterized in that: include: (1) preparing a chromium electrode pattern on a lithium niobate film, the chromium electrode pattern including a first set of electrodes and a second set of electrodes arranged in sequence, the first set of electrodes and the second set of electrodes each including a plurality of pairs of symmetrically arranged chromium electrodes; and the first set of electrodes and the second set of electrodes having different polarization periods; (2) applying corresponding pulse voltages to the first set of electrodes and the second set of electrodes for polarization, wherein the direction of the pulse voltage is opposite to the polarization direction of the lithium niobate film, so that the lithium niobate between the electrodes undergoes domain inversion; (3) Directly etching the lithium niobate film in the domain inversion region to prepare a lithium niobate waveguide to obtain a periodically poled lithium niobate waveguide; (4) At the first set of electrodes and the second set of electrodes, two sets of photon pairs with perpendicular polarization directions are generated through a spontaneous parametric down-conversion process. When the length of the lithium niobate waveguide is less than the coherence length of the pump light, a polarization entangled source is prepared; including: a photon TE mode with a wavelength of 532nm at the first set of electrodes 532 The spontaneous parametric down-conversion process generates a pair of photons with perpendicular polarization directions, that is, a TE 1550 Photons and a TM 810 Photon(|TE 1550 TM 810 >); At the second set of electrodes, a photon TE mode with a wavelength of 532nm is generated. 532 The spontaneous parametric down-conversion process generates a pair of photons with perpendicular polarization directions, that is, a TE 810 Photons and a TM 1550 Photon(|TE 810 TM 1550 >), when the waveguide length is less than the coherence length of the 532nm pump light, the The polarization entangled source of the form (5) By splitting the light according to the wavelength, the simultaneously generated photon pairs are separated to obtain polarization-entangled photon pairs.

2. A design and preparation method of an on-chip entanglement source based on X-cut periodically poled lithium niobate thin film according to claim 1, characterized in that: In the first group of electrodes or the second group of electrodes, the symmetrically arranged chromium electrodes have the same shape, and the shape of the chromium electrodes is comb-shaped paired-tooth chromium electrodes, and the tooth ends of the chromium electrodes are arc-shaped.

3. A design and preparation method of an on-chip entanglement source based on X-cut periodically poled lithium niobate thin film according to claim 1, characterized in that: The electrode gap of the first group of electrodes is the same as the electrode gap of the second group of electrodes, and the electrode gap is the gap between the tooth ends of two opposite parts of a group of electrodes.

4. A design and preparation method of an on-chip entanglement source based on X-cut periodically poled lithium niobate thin film according to claim 3, characterized in that: The electrode gaps of the first group of electrodes and the second group of electrodes are both 10 μm-40 μm.

5. A design and preparation method of an on-chip entanglement source based on X-cut periodically poled lithium niobate thin film according to claim 4, characterized in that: The electrode gaps of the first and second electrodes are both 10 μm.

6. A design and preparation method of an on-chip entanglement source based on X-cut periodically poled lithium niobate thin film according to claim 1, characterized in that: The duty cycle of the first group of electrodes and the second group of electrodes is 25-40%.

7. A design and preparation method of an on-chip entanglement source based on X-cut periodically poled lithium niobate thin film according to claim 6, characterized in that: The duty cycle of the first group of electrodes and the second group of electrodes is 35%.

8. A design and preparation method of an on-chip entanglement source based on X-cut periodically poled lithium niobate thin film according to claim 1, characterized in that: The polarization period of the first group of electrodes is 5.6μm, and the polarization period of the second group of electrodes is 11.2μm.

9. A design and preparation method of an on-chip entanglement source based on X-cut periodically poled lithium niobate thin film according to claim 1, characterized in that: In step (2), the polarization effect of the lithium niobate film is characterized by piezoresistive force microscopy, and then a lithium niobate waveguide is prepared at a duty cycle of 50% in the domain inversion region to obtain a periodically poled lithium niobate waveguide.

10. A design and preparation method of an on-chip entanglement source based on X-cut periodically poled lithium niobate thin film according to claim 1, characterized in that: In step (2), the specific process of determining the pulse voltage and the number of pulses is as follows: 2-1, determine the maximum voltage V of the pulse voltage max The size of (coercive field value of lithium niobate × electrode gap d) < V max <(coercive field value of lithium niobate × electrode gap d(1+50%)); the pulse voltage waveform is initially set to a trapezoidal wave, which includes a rising section, a high voltage duration section, and a falling section, and the corresponding time periods are t1, t2, and t3 respectively; 2-2, adjust t1, t2, t3 corresponding to the pulse voltage, as well as the number of pulses, so that the duty cycle of the domain inversion region reaches 50%; 2-3, determine the pulse voltage V according to step 2-2 max Repeated polarization of lithium niobate film can improve the success rate.

Images