A method for driving a liquid crystal waveguide beam scanner

Abstract

This invention relates to the field of optical waveguide technology, specifically providing a method for driving a liquid crystal waveguide beam scanner. The method involves calculating the director of liquid crystal molecules under an applied electric field, calculating the dielectric tensor based on the director, obtaining the effective refractive index of the optical waveguide based on the dielectric tensor, calculating the scanning angle under different applied electric fields, establishing the dynamic relationship between the scanning angle and voltage, and designing a driving voltage waveform accordingly to achieve a preset beam scanning process. This invention enables precise and predictable beam scanning, fulfilling specific application requirements.

Description

Technical Field

[0001] This invention relates to the field of optical waveguide technology, and specifically provides a method for driving a liquid crystal waveguide beam scanner that can be used for precise beam control. Background Technology

[0002] The liquid crystal waveguide beam scanner uses a waveguide as the carrier and liquid crystal as the working medium. It achieves beam scanning control through the process of light refraction within the waveguide and coupling with an external prism. It features on-chip integration, all-solid-state operation, high speed, and the ability for continuous two-dimensional scanning. Compared to existing scanning technologies such as traditional mechanical, MEMS, silicon-based optical phased arrays, and liquid crystal optical phased arrays, the liquid crystal waveguide beam scanner offers advantages such as high stability, low power consumption, concentrated beam energy, and a large scanning angle, making it valuable for applications in radar detection, laser communication, and laser displays.

[0003] Traditional liquid crystal waveguide beam scanners often use a uniform square wave voltage during driving, and the dynamic process of beam scanning is relatively fixed, making it difficult to achieve precise and predictable beam control. This severely limits the application of liquid crystal waveguide beam scanners.

[0004] Therefore, there is an urgent need for a liquid crystal waveguide beam scanner driving method that can achieve precise beam control. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a driving method for a liquid crystal waveguide beam scanner. Based on the dynamic variation law of the scanning angle of the liquid crystal waveguide beam scanner, a driving voltage waveform is designed to achieve precise beam control and significantly improve scanning linearity.

[0006] The liquid crystal waveguide beam scanner driving method provided by the present invention includes:

[0007] S1: Determine the dynamic equation for the pointing vector of liquid crystal molecules under an applied electric field;

[0008] S2: Calculate the dielectric tensor of liquid crystal molecules based on the liquid crystal molecule pointing vector;

[0009] S3: Substitute the dielectric tensor into the waveguide structure model of the liquid crystal waveguide beam scanner to solve for the effective refractive index of the waveguide mode;

[0010] S4: Calculate the scanning angle corresponding to the effective refractive index under different applied electric fields, and establish the relationship equation between the driving voltage of the applied electric field and the scanning angle;

[0011] S5: Substitute the preset beam scanning angle change into the relational equation to obtain the driving voltage waveform of the liquid crystal waveguide beam scanner.

[0012] Preferably, in S1, the dynamic equation for the liquid crystal molecule pointing vector θ is:

[0013]

[0014]

[0015] Where, k 33 Let k be the elastic constant of the liquid crystal molecules. 11 γ is the bending elastic constant of the liquid crystal molecules, γ1 is the rotational viscosity coefficient, and D is the bending elastic constant of the liquid crystal molecules. Z Let ε be the z-component of the electric displacement vector, U be the applied voltage of the external electric field on the liquid crystal molecules, and ε be the voltage of the liquid crystal molecules. ⊥ Let ε be the short-axis dielectric constant of the liquid crystal molecules, Δε be the difference in dielectric constants between the liquid crystal molecules, ε0 be the vacuum dielectric constant, and T be the thickness of the liquid crystal cladding.

[0016] Preferably, in S2, the dielectric tensor ε of the liquid crystal molecules LC for:

[0017]

[0018] Where n0 is the ordinary refractive index of the liquid crystal molecules, n e This represents the unusual optical refractive index of liquid crystal molecules.

[0019] Preferably, in S4, after the dielectric tensor is substituted into the waveguide structure model of the liquid crystal waveguide beam scanner, the effective refractive index of the waveguide mode is solved by the finite element method.

[0020] Preferably, it is used to improve the scanning linearity of vehicle-mounted radar or to generate images in laser displays.

[0021] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0022] This invention calculates the relationship between the driving voltage and the instantaneous scanning angle, and designs the driving voltage waveform according to the desired scanning process, thereby achieving precise and predictable beam scanning.

[0023] This invention can be applied to scenarios with specific requirements for the beam scanning process, such as improving scanning linearity in automotive radar and generating images in laser displays. The driving method of this invention can effectively control the scanning angle of the beam, achieving more precise beam control, thereby improving the performance and effectiveness of related applications. Attached Figure Description

[0024] Figure 1 This is a flowchart of a liquid crystal waveguide beam scanner driving method provided according to an embodiment of the present invention;

[0025] Figure 2 This is a structural diagram of a liquid crystal waveguide beam scanner provided according to an embodiment of the present invention;

[0026] Figure 3 This is a curve showing the relationship between the liquid crystal alignment angle and the liquid crystal cladding thickness according to an embodiment of the present invention;

[0027] Figure 4 This is a curve showing the variation of the scanning angle with the driving voltage according to an embodiment of the present invention;

[0028] Figure 5 This is a comparison diagram of the driving voltage waveform designed by the method of the present invention and the traditional driving voltage square wave;

[0029] Figure 6 This is a diagram illustrating the precise beam control effect of the driving method of this invention.

[0030] The reference numerals in the figures include:

[0031] 1. Glass cover plate, 2. Electrode layer, 3. Alignment layer, 4. Liquid crystal cladding, 5. Waveguide core layer, 6. Substrate layer, 7. Coupled substrate, 8. Incident light, 9. Waveguide mode, 10. Outgoing light, 11. Square wave driving voltage, 12. Gradient driving voltage. Detailed Implementation

[0032] In the following description, embodiments of the invention will be described with reference to the accompanying drawings. In the description below, the same modules are denoted by the same reference numerals. Where the same reference numerals are used, their names and functions are also the same. Therefore, their detailed description will not be repeated.

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0034] like Figure 1 As shown, this embodiment of the invention provides a method for driving a liquid crystal waveguide beam scanner, which can perform precise beam control on the liquid crystal waveguide beam scanner, such as... Figure 2As shown, the liquid crystal waveguide beam scanner mainly includes functional layers such as electrode layer 2, alignment layer 3, liquid crystal cladding layer 4, waveguide core layer 5, substrate layer 6, and coupling substrate 7. The coupling substrate 7 acts as a coupling prism, used to couple free-space beams into the waveguide. The substrate layer 6, made of silicon oxide with a refractive index of 1.47 and a thickness of 2 micrometers, is disposed on the upper surface of the coupling substrate 7. The waveguide core layer 5, made of silicon oxynitride with a refractive index of 1.852 and a thickness of 480 nanometers, forms the waveguide structure, guiding the beam propagation within it. A first alignment layer 3 is disposed on the upper surface of the waveguide core layer 5. The liquid crystal cladding layer 4 is disposed on the upper surface of the alignment layer 3, and a second alignment layer 3 is disposed on the upper surface of the liquid crystal cladding layer 4. Both alignment layers 3 have the same material and function, both used to determine the initial alignment direction of the liquid crystal molecules, influencing their behavior under an electric field. The initial tilt angle of the liquid crystal molecules is 2°. An electrode layer 2 is disposed on the upper surface of the second alignment layer 3. The electrode layer 2 is a patterned electrode used to apply voltage. Through patterning design, the arrangement of liquid crystal molecules can be precisely controlled, thereby controlling the scanning direction of the light beam. In addition, a glass cover plate 1, usually made of transparent material such as glass or plastic, is disposed on the upper surface of the electrode layer 2 to protect the waveguide structure below.

[0035] The liquid crystal cladding layer 4 is a positive liquid crystal material, and its thickness T = 4.5 micrometers. The liquid crystal molecules in the liquid crystal cladding layer 4 have an ordinary light refractive index n0 = 1.48 and an extraordinary light refractive index n... e =1.58. When the driving voltage of the liquid crystal cladding 4 changes, the refractive index of the liquid crystal cladding 4 can change under the stimulation of the electric field, and change the effective refractive index of the waveguide mode 9 transmitted in the waveguide structure. Based on this adjustment mechanism and the coupling process between the electrode layer 2 and the coupling substrate 7, continuous scanning of two-dimensional beams can be realized.

[0036] In the operation of the liquid crystal waveguide beam scanner of this embodiment, the incident light 8 is coupled into the waveguide core layer 5 through the coupling substrate 7 and transmitted within the waveguide core layer 5. The wavelength corresponding to the transmitted waveguide mode 9 is 1064 nanometers.

[0037] Since the scanning angle of the two-dimensional beam in the liquid crystal waveguide beam scanner is closely related to the amplitude of the driving voltage, and the scanning angle and driving voltage show a positive correlation, after the driving voltage exceeds the threshold voltage, a higher voltage often leads to a larger scanning angle. Furthermore, both have a monotonic characteristic, meaning a single driving voltage corresponds to a fixed scanning angle. Therefore, when performing precise beam control on the liquid crystal waveguide beam scanner, the relationship between the driving voltage and the scanning angle can be used as the design theory for the driving voltage waveform. Based on the dynamic change law of the desired scanning angle, the driving voltage waveform is designed, and the liquid crystal waveguide beam scanner is driven to perform two-dimensional scanning using the designed driving voltage waveform. The specific steps include:

[0038] S1: First, construct the dynamic equation for the orientation vector of liquid crystal molecules in liquid crystal cladding 4 under the action of an applied electric field:

[0039]

[0040]

[0041] Where, k 33 Let k be the elastic constant of the liquid crystal molecules. 33 =11..6pN, k 11 k is the bending elastic constant of the liquid crystal molecules. 11 =11.2pN, γ1 is the rotational viscosity coefficient, γ1 = 68mpa.s, D Z Let ε be the z-component of the electric displacement vector, U be the applied voltage of the external electric field on the liquid crystal molecules, which is the driving voltage, and ε be the driving voltage. ⊥ ε is the short-axis dielectric constant of the liquid crystal molecule. ⊥ =3.70, Δε is the difference in dielectric constant of the liquid crystal molecules, Δε = 11.36, ε0 represents the vacuum dielectric constant, and T represents the thickness of the liquid crystal cladding, T = 4.5 micrometers.

[0042] Since it is necessary to establish the following relationship between the driving voltage and the scanning angle, it is necessary to calculate the liquid crystal molecule director under a series of different applied electric fields, and then obtain the effective refractive index under different driving voltages, and obtain the scanning angle corresponding to different effective refractive indices. The calculation process is the same for different applied electric fields. In this embodiment, the calculation process is explained only when the driving voltage of the applied electric field is equal to 30V.

[0043] When the applied electric field is 30V, the direction vector θ of the liquid crystal molecule is calculated according to the following dynamic equation:

[0044]

[0045]

[0046] The liquid crystal molecule director is a vector used to describe the average alignment direction of liquid crystal molecules. The calculated director is expressed as an orientation angle, and the relationship between the obtained liquid crystal orientation angle and the thickness of the liquid crystal cladding is as follows: Figure 3 As shown.

[0047] S2: Substitute the liquid crystal molecule pointing vectors obtained under different applied electric fields in S1 into the following formula to calculate the dielectric tensor ε corresponding to the liquid crystal molecule. LC for:

[0048]

[0049] Where n0 is the ordinary refractive index of the liquid crystal molecules, n0 = 1.48, n e n represents the unusual optical refractive index of liquid crystal molecules. e =1.58.

[0050] S3: The dielectric tensor ε obtained in S2 LC The effective refractive index of waveguide mode 9 was calculated using the finite element method by incorporating it into the waveguide structure model of the liquid crystal waveguide beam scanner. Under the condition of an applied electric field driving voltage of 30V, the effective refractive index of waveguide mode 9 was approximately 1.70.

[0051] S4: Based on the law of refraction, the refractive index of liquid crystal molecules changes with the applied voltage. Under different applied electric field conditions, waveguide mode 9 has different effective refractive indices. The instantaneous scanning angle caused by the change in effective refractive index can be calculated. Then, based on the driving voltage of the applied electric field, a relational equation expressing the interaction between the driving voltage of the external electric field and the instantaneous scanning angle can be constructed. This relational equation reflects, for example, the following... Figure 4 The scanning angle is shown as a function of the driving voltage.

[0052] S5: After obtaining the relational equation, the beam scanning angle at each moment can be determined according to the specific beam scanning design. The driving voltage waveform that satisfies the preset beam scanning angle variation can be calculated based on the relational equation. The driving voltage waveform can have any variation form, including but not limited to exponential gradual change, linear gradual change, etc. For example... Figure 5 As shown, this is a gradient drive voltage 12 that optimizes scanning linearity. This gradient drive voltage 12, unlike the traditional square wave drive voltage 11, features a gradient characteristic, resulting in higher scanning control precision and a beam scanning angle that better matches the intended design. For example... Figure 6 As shown, the linearity of the beam scanning process is significantly improved under the drive of the gradually changing driving voltage 12.

[0053] The driving design method of the present invention can design the driving voltage according to the actual scanning requirements. It has good application prospects in fields such as vehicle-mounted LiDAR, laser display image generation, and optical modeling. It can significantly improve the beam scanning control accuracy and the uniformity and accuracy of optical modeling.

[0054] Although embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

[0055] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for driving a liquid crystal waveguide beam scanner, characterized in that, include: S1: Determine the dynamic equation for the orientation vector of liquid crystal molecules under an applied electric field. The dynamic equation is: ； ； in, Let be the elastic constant of the liquid crystal molecules. Let be the bending elastic constant of the liquid crystal molecules. Let be the rotational viscosity coefficient. The z-component of the electric displacement vector. The voltage applied to the liquid crystal molecules by the external electric field, The short-axis dielectric constant of the liquid crystal molecule. This represents the difference in dielectric constants between the liquid crystal molecules. Represents the vacuum permittivity. T Indicates the thickness of the liquid crystal cladding; S2: Calculate the dielectric tensor of liquid crystal molecules based on the liquid crystal molecule pointing vector; S3: Substitute the dielectric tensor into the waveguide structure model of the liquid crystal waveguide beam scanner to solve for the effective refractive index of the waveguide mode; S4: Calculate the scanning angle corresponding to the effective refractive index under different applied electric fields, and establish the relationship equation between the driving voltage of the applied electric field and the scanning angle; S5: Substitute the preset beam scanning angle change into the relational equation to obtain the driving voltage waveform of the liquid crystal waveguide beam scanner.

2. The liquid crystal waveguide beam scanner driving method as described in claim 1, characterized in that, In S2, the dielectric tensor of the liquid crystal molecules for: ； in, The ordinary refractive index of liquid crystal molecules, This represents the unusual optical refractive index of liquid crystal molecules.

3. The liquid crystal waveguide beam scanner driving method as described in claim 1, characterized in that, In step S3, after the dielectric tensor is substituted into the waveguide structure model of the liquid crystal waveguide beam scanner, the effective refractive index of the waveguide mode is solved by the finite element method.

4. The liquid crystal waveguide beam scanner driving method as described in claim 1, characterized in that, Used to improve the scanning linearity of vehicle radar or to generate images in laser displays.

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