Elliptical light spot rounding device based on liquid crystal plane cylindrical mirror group

Abstract

The utility model discloses an elliptical light spot rounding device based on a liquid crystal plane cylindrical mirror group, which comprises two groups of liquid crystal plane cylindrical mirrors which are oppositely arranged in parallel, each liquid crystal plane cylindrical mirror comprises a glass substrate, a light orientation layer thin film coated on one plane of the glass substrate, and a liquid crystal polymer thin film coated on the light orientation layer thin film, and the liquid crystal polymer films of the two groups of liquid crystal plane cylindrical mirrors are arranged face to face. The ellipse light spot rounding device is simple in structure, light and thin in size, capable of rounding ellipse light spots of a laser diode, and capable of adapting to different light beam characteristics or application requirements by adjusting arrangement of liquid crystal molecules on two groups of liquid crystal plane cylindrical mirrors at the same time.

Description

Technical Field

[0001] The utility model relates to beam rounding technology, in particular to an elliptical spot rounder based on a liquid crystal planar cylindrical lens group. Background Art

[0002] As a kind of semiconductor laser, a laser diode (LD) has the advantages of high efficiency, stability, simple structure, etc., and is widely used in many fields such as optical communication, laser printing, material processing, and medical treatment. Due to the significant difference in the beam quality of the LD in the directions perpendicular and parallel to the PN junction, that is, the beam divergence angle is large in the fast direction and small in the slow direction, the beam will be elliptical rather than circular, and this non-uniformity limits the performance of the LD in high-power density output and high-precision applications. Therefore, beam shaping is required. Beam rounding technology includes various methods, such as rounding the beam through cylindrical lens pairs, deformable prism pairs, and spatial filters, etc.

[0003] Rounding of elliptical laser is achieved based on a refractive cylindrical lens pair, as Figure 1 shown. A refractive cylindrical lens is a one-dimensional lens, which has optical curvature in one dimension (such as the X-axis), while the other dimension (such as the Y-axis) remains flat or has a small curvature. This design enables the cylindrical lens to achieve convergence and divergence only in one dimension. When an elliptical beam passes through the cylindrical lens, since the cylindrical lens has curvature in the X-axis direction, the beam in this direction will be focused or diverged, thereby changing the beam divergence angle. By precisely controlling the focal length and position of the cylindrical lens, the beam divergence angles in the X and Y directions can be made equal, so as to form a circular spot in the far field. However, due to the design and material limitations of traditional refractive cylindrical lenses, they are usually large in volume and heavy in weight, and it is difficult to achieve miniaturization and integration. Summary of the Utility Model

[0004] Purpose of the utility model: The purpose of the utility model is to provide an elliptical spot rounder based on a liquid crystal planar cylindrical lens group with a simple structure, thin and light volume, and realize beam shaping.

[0005] Technical solution: To achieve the above purpose, an elliptical spot rounder based on a liquid crystal planar cylindrical lens group described in the utility model includes two groups of liquid crystal planar cylindrical lenses arranged relatively parallel to each other. The liquid crystal planar cylindrical lens includes a glass substrate, a photo-alignment layer film coated on one plane of the glass substrate, and a liquid crystal polymer film coated on the photo-alignment layer film.

[0006] Wherein, the liquid crystal optical axis of the liquid crystal polymer film is a one-dimensional structure.

[0007] Wherein, the liquid crystal polymer films of the two groups of liquid crystal planar cylindrical lenses are arranged face to face.

[0008] Among them, the glass substrate is a transparent planar structure.

[0009] Beneficial effects: The utility model has the following advantages: 1. The elliptical spot shaper can expand the elliptical spot of the laser diode in one dimension while keeping the other dimension unchanged, achieving the effect of rounding the spot. When used reversely, it has the function of converting a circular spot into an elliptical spot; 2. The elliptical spot shaper can adapt to different beam characteristics or application requirements by adjusting the arrangement of liquid crystal molecules on two groups of liquid crystal planar cylindrical lenses; 3. The elliptical spot shaper has a simple structure, is thin and light in volume, and is conducive to being integrated into a compact optical system for use. Description of the drawings

[0010] Figure 1 It is a schematic diagram of the rounding of elliptical laser by a refractive cylindrical lens;

[0011] Figure 2 It is a schematic diagram of the structure of a liquid crystal planar cylindrical lens;

[0012] Figure 3 It is a schematic diagram of the action of a liquid crystal planar cylindrical lens on left-handed circularly polarized light and right-handed circularly polarized light;

[0013] Figure 4 It is a schematic diagram of the structure of an elliptical spot shaper;

[0014] Figure 5 It is an elliptical spot to be shaped;

[0015] Figure 6 It is a circular spot shaped by the elliptical spot shaper. Detailed implementation manners

[0016] The technical solutions of the present utility model will be described in detail below in conjunction with the embodiments and the drawings.

[0017] As Figure 2 shown, the liquid crystal planar cylindrical lens sequentially includes a glass substrate, a photo-alignment layer film, and a liquid crystal polymer film from left to right. Among them, the glass substrate and the photo-alignment layer film have no effect on the incident light. The glass substrate is a transparent planar structure for carrying the films. The photo-alignment layer film is used to control the arrangement of liquid crystal molecules, and the liquid crystal polymer film is a light modulating material for changing the phase of the laser.

[0018] The liquid crystal planar cylindrical mirror is a geometric phase diffraction optical element with a planar structure, which modulates the light beam based on the principle of geometric phase. By designing the one-dimensional structure of the liquid crystal optical axis, the arrangement of liquid crystal molecules has a specific orientation in one dimension, while remaining uniform in the other dimension (the photo-alignment layer film is a material that orients the arrangement of liquid crystal molecules and can transfer its own arrangement structure to the liquid crystal molecules). This arrangement forms a function equivalent to that of a cylindrical mirror. Compared with a refractive cylindrical mirror, the liquid crystal planar cylindrical mirror has a planar structure, and the thickness of the entire thin film is on the order of a few micrometers. Therefore, the thickness and weight of the entire liquid crystal planar cylindrical mirror depend on the glass substrate used.

[0019] For a circularly polarized laser beam, which includes left-handed circularly polarized light or right-handed circularly polarized light, due to the different responses of the geometric phase brought by liquid crystal molecules to left-handed and right-handed circularly polarized light, the liquid crystal planar cylindrical mirror also has circular polarization selectivity. For example, for left-handed circularly polarized light, it has a focusing function, and for right-handed circularly polarized light, it has a diverging function. Therefore, the modulation effect of the liquid crystal planar cylindrical mirror on the light beam depends on the circular polarization chirality of the incident light. As Figure 3 shown, for the incidence of left-handed circularly polarized light, the function of the liquid crystal planar cylindrical mirror is one-dimensional focusing, with a focal length of f, and the chirality of the outgoing light is reversed to right-handed; for the incidence of right-handed circularly polarized light, the situation is opposite to that of left-handed incidence, the function of the liquid crystal planar cylindrical mirror is one-dimensional divergence, with a focal length of -f, and the outgoing light is reversed to left-handed.

[0020] Based on the circular polarization selectivity of the liquid crystal planar cylindrical mirror, the elliptical spot roundness corrector is composed of two sets of liquid crystal planar cylindrical mirrors, and the liquid crystal polymer film sides of the two sets of liquid crystal planar cylindrical mirrors are placed opposite to each other, as Figure 4 shown. Both sets of liquid crystal planar cylindrical mirrors are one-dimensional structures, and their specific arrangement distributions are different according to different requirements for a complete circle. The first liquid crystal planar cylindrical mirror magnifies the short axis of the incident elliptical light and reshapes the elliptical spot into a circular spot. The function of the second liquid crystal planar cylindrical mirror is to restore the direction and polarization state of the incident light, so that the outgoing light only changes the spot shape relative to the incident light. To avoid the influence brought by the intermediate medium, the glass side faces outward and the film side faces inward.

[0021] The distance between the two sets of liquid crystal planar cylindrical mirrors is the sum of the focal lengths of the two sets of liquid crystal planar cylindrical mirrors. The relationship between the focal lengths of the two sets of liquid crystal planar cylindrical mirrors and the incident elliptical spot is as follows: h long / h short =f2 / f1, where h long is the major axis dimension of the incident elliptical spot, h short is the minor axis dimension of the incident elliptical spot, f1 is the focal length of the first liquid crystal planar cylindrical mirror, and f2 is the focal length of the second liquid crystal planar cylindrical mirror.

[0022] Taking the adjustment of the x-direction dimension as an example, the formula for modulating the optical axis arrangement of the liquid crystal planar cylindrical mirror is:

[0023]

[0024] α is the azimuth angle of the liquid crystal molecules, x is the abscissa, and f is the focal length of the modulated liquid crystal plano-cylindrical mirror.

[0025] As Figure 5 shown, it is the elliptical light spot to be shaped, with a wavelength of 633 nm, an x beam waist of 1.2 mm, and a y beam waist of 2.0 mm. The above elliptical light spot rounder is used to shape it. The focal length of the first liquid crystal plano-cylindrical mirror is designed to be 50.0 mm, and the focal length of the second liquid crystal plano-cylindrical mirror is designed to be 83.3 mm. As Figure 6 shown is the shaped circular light spot. During the shaping process of the elliptical light spot rounder, the first liquid crystal plano-cylindrical mirror performs one-dimensional diffusion on the short axis of the elliptical light spot, and the second liquid crystal plano-cylindrical mirror collimates the diverged light spot.

Claims

1. An elliptical spot rounding device based on a liquid crystal planar cylindrical mirror group, characterized in that, It includes two sets of relatively parallel liquid crystal planar cylindrical mirrors, and the liquid crystal planar cylindrical mirror includes a glass substrate, a photo-alignment layer film coated on one plane of the glass substrate, and a liquid crystal polymer film coated on the photo-alignment layer film.

2. The elliptical spot rounding device based on the liquid crystal planar cylindrical mirror group according to claim 1, wherein The arrangement distribution of the liquid crystal optical axes of the liquid crystal polymer film is a one-dimensional structure.

3. The elliptical spot rounding device based on the liquid crystal planar cylindrical mirror group according to claim 1, characterized in that, The liquid crystal polymer films of the two sets of liquid crystal planar cylindrical mirrors are arranged face to face.

4. The elliptical spot rounding device based on the liquid crystal planar cylindrical mirror group according to claim 1, wherein The glass substrate is a transparent planar structure.

5. The elliptical spot rounding device based on the liquid crystal plane cylindrical mirror group according to claim 1, characterized in that The distance between the two sets of liquid crystal planar cylindrical mirrors is the sum of the focal lengths of the two sets of liquid crystal planar cylindrical mirrors.

6. The elliptical spot rounding device based on the liquid crystal planar cylindrical mirror group according to claim 5, characterized in that, The relationship between the size of the incident elliptical light spot and the focal length of the liquid crystal planar cylindrical mirror is as follows: h long / h short = f2 / f1, where h long is the major axis dimension of the incident elliptical light spot, h short is the minor axis dimension of the incident elliptical light spot, f1 is the focal length of the first liquid crystal plano-cylindrical lens, and f2 is the focal length of the second liquid crystal plano-cylindrical lens.

Images