Ultra-compact beam expander structure

Abstract

The invention relates to the technical field of ultra-thin optical devices, and provides an ultra-compact beam expander structure which solves the problems that traditional beam expansion is mainly based on a refraction type lens or reflector system and depends on combination of multi-component optical devices to achieve beam conversion, so that the size of the whole system is large, the weight is large, and miniaturization and integration are not facilitated. The two super-structure lenses are arranged at any position in a light path to achieve the ultrahigh beam expansion ratio, the super-structure material is arranged between the two super-structure lenses, the axes of the two super-structure lenses are located on the same straight line, the ultrahigh beam expansion ratio can be achieved in the extremely short light path on the premise that the optical performance is not sacrificed, and the space utilization efficiency of the optical system is remarkably improved; the phase transfer function of the free space can be realized in a short distance, so that the air gap between the lenses is effectively compressed, the miniaturization of the device is further realized, and the device has important application in the fields of laser processing equipment, free space optical communication terminals, spatial light modulation systems and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of ultra-thin optical devices, and more particularly to an ultra-compact beam expander structure. Background Art

[0002] A beam expander is a system that can proportionally expand the diameter of a collimated input beam and is commonly used in laser scanning, interferometry, or telemetry applications. Traditional beam expanders are mostly based on refractive lens or reflector systems (such as Galilean and Keplerian structures), relying on a combination of multi-component optical devices to achieve beam transformation. This results in a large volume and weight for the entire system, which is not conducive to miniaturization and integration [1]. However, with the rapid development of miniaturized optoelectronic systems (such as portable laser devices and integrated optical modules), the shortcomings of traditional solutions in terms of volume, cost, and reliability have become increasingly prominent, and new design concepts are urgently needed to break through the existing technical bottlenecks.

[0003] In recent years, the development of metalenses has provided new ideas for light field control. Metalenses can realize the design of ultra-thin optical devices through subwavelength structure arrays, and are expected to be applied to beam expansion and contraction systems to achieve miniaturized and integrated beam manipulation [2-4]. However, in order to achieve high beam expansion ratios or complex beam transformations, traditional beam expanders require a cascade design of multiple lenses or mirrors, resulting in an excessively long axial dimension and bulky volume of the optical system. Therefore, how to achieve an ultra-compact, high beam expansion ratio, and low-cost solution through innovative structural design under the traditional refractive optical architecture has become a technical difficulty that the industry urgently needs to overcome.

[0004] 【1】Liu, WB, Du, BB, Ma, YG, et al. Design and Application ofBeam Expander and Reducer Based on Dielectric Metalens. Acta Photonica Sinica53, 1223001 (2024). 【2】Tang, JX, Gong, YD, Pang, K. Two-dimensional metasurface: application and research progress of metalenses. Laser&OptoelectronicsProgress 60, 2100004 (2023). 【3】Chen, J. Research on the key technology of metalens. Master'sthesis. Jiangsu University, Zhenjiang (2022). 【4】Wang, W., Wang, J., Zhang, T., et al. All-dielectric metasurfaces for intensity-controllable beam splitting and polarization conversion. Journal of Physics D: Applied Physics 57, 285103 (2024). Summary of the Invention In response to the shortcomings of the existing technology, the present invention discloses an ultra-compact beam expander structure. By optimizing the lens curvature, spacing and material combination, it can achieve an ultra-high beam expansion ratio in an extremely short optical path without compromising the optical performance of the optical system, thereby significantly improving the space utilization efficiency of the optical system.

[0005] An ultra-compact beam expander structure is provided. The ultra-compact beam expander structure is set at any position in the optical path to achieve an ultra-high beam expansion ratio in the optical path. The ultra-compact beam expander structure includes two meta-lenses for achieving beam control and a meta-material between the two lenses. The two meta-lenses have the same diameter but different focal lengths, and the axes of the two meta-lenses are in a straight line.

[0006] Furthermore, the two metalenses include a metaconcave lens and a metaconvex lens. The focal points of the two metalenses coincide on one side of the metaconcave lens. Along the propagation direction of the light beam, the order is metaconcave lens, metamaterial, and metaconvex lens.

[0007] Furthermore, the phase distribution of the metaconcave lens and the metaconvex lens is: in, is the phase distribution of the metaconcave lens, F 1 is the focal length of the metaconcave lens, is the phase distribution of the metaconvex lens, F 2 is the focal length of the metaconvex lens, l 0 is the operating wavelength, y is the longitudinal coordinate of the metalens in the Cartesian coordinate system.

[0008] Furthermore, the beam expansion ratio of the ultra-compact beam expander structure is M = |F 2 / F 1|>1.

[0009] Furthermore, the thickness of the metamaterial itself d SP Less than the thickness of d eff The free space optical transfer function, compression ratio R = d eff / d SP .

[0010] Furthermore, the compression ratio R Greater than 1.

[0011] Furthermore, the dielectric constant of the metamaterial e and magnetic permeability m In satisfaction e = μ = diag ( 1 / R,R,R ) under the premise of achieving independent regulation.

[0012] In summary, the invention has the following beneficial effects: The present invention utilizes two metalenses with different focal lengths and the same diameter to work together to precisely modulate the phase and amplitude of the transmitted light beam, thereby efficiently achieving the beam expansion function. The metamaterial disposed between the two metalenses can achieve a free-space phase transfer function that far exceeds the thickness of the metamaterial itself at an extremely short distance, effectively compressing the air gap between the two metalenses. The present invention can achieve an ultra-high beam expansion ratio within an extremely short optical path. This feature breaks through the physical limitation of traditional beam expanders, where "the beam expansion ratio is positively correlated with the volume," and is conducive to miniaturization, thereby further reducing the size of the device and ultimately achieving an ultra-compact beam expansion effect. The characteristic impedance of the present invention fully matches the impedance of air, and can achieve a transmittance close to 100%. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of the two-dimensional structure of the present invention.

[0014] Figure 2 Numerical simulation results of the electric field intensity of the traditional meta-lens beam expander: grayscale image of the electric field intensity distribution.

[0015] Figure 3 The numerical simulation results of the electric field intensity of the ultra-compact beam expander of the present invention: a grayscale diagram of the electric field intensity distribution.

[0016] In the figure, 1. metaconcave lens, 2. metaconvex lens, 3. metamaterial. DETAILED DESCRIPTION

[0017] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0018] like Figure 1 and 3 As shown, the present invention discloses an ultra-compact beam expander structure. The ultra-compact beam expander structure can be set at any position in the optical path to achieve an ultra-high beam expansion ratio in an extremely short optical path. It includes two meta-lenses for beam control and a meta-material 3 between the two lenses. The two meta-lenses have the same diameter but different focal lengths, and the axes of the two meta-lenses are aligned. The two meta-lenses include a meta-concave lens 1 and a meta-convex lens 2. The focal points of the two meta-lenses coincide on one side of the meta-concave lens 1 of the ultra-compact beam expander structure. The two meta-lenses work together to precisely modulate the phase and amplitude of the transmitted light beam, achieving efficient beam control. Along the beam propagation direction, the following order is meta-concave lens 1, meta-material 3, and meta-convex lens 2.

[0019] Phase distribution of metaconcave lens 1 and metaconvex lens 2: in, is the phase distribution of metaconcave lens 1, F 1 is the focal length of the metaconcave lens, is the phase distribution of metaconvex lens 2, F 2 is the focal length of the metaconvex lens 2, l 0 is the operating wavelength, y is the longitudinal coordinate of the meta-lens in the Cartesian coordinate system. The beam expansion ratio of the ultra-compact beam expander structure, that is, the ratio of the diameter of the outgoing light to the incident light, is M = | F 2 / F 1|>1.

[0020] Metamaterial 3 is used to compress the air gap between lenses, thereby miniaturizing the beam expansion system. d SP Less than the thickness of d eff The free space optical transfer function, compression ratio R = d eff / d SP , compression ratio R Greater than 1; metamaterials can simulate thickness d eff The free space optical transfer function, while the thickness of the metamaterial 3 itself d SP Much smaller thand eff , when R is infinite, d SP Approaching 0, the dielectric constant of metamaterial 3 e and magnetic permeability m In satisfaction e = μ = diag ( 1 / R, R,R ) under the premise of achieving independent regulation.

[0021] Example: In order to verify the performance effect of the present invention, in this example, the present embodiment performs a light band ( f = 500THz). In the electric field numerical simulation, a 30um*60um air domain was set as the simulation area, and a background electric field along the y-axis was applied. A rectangular metamaterial (the specific structural shape is determined by Figure 1 Given), the metamaterial region is 2 μm long and 60 μm high. The dielectric constant of the metamaterial region is set to (1 / 8, 8, 8) and the magnetic permeability is (1 / 8, 8, 8); the other regions are set to air with a dielectric constant of 1 and a magnetic permeability of 1. In this embodiment, a TM-polarized Gaussian beam is incident from the left onto the metaconcave lens (focal length F 1= -2um), and finally from the right meta-convex lens (focal length F 2= ​​18um) and then expand the beam out. Figure 2 and Figure 3 The numerical simulation results without and with metamaterials are shown respectively. The comparative analysis results show that after the introduction of metamaterials, the field distribution behind the metaconvex lens has changed significantly. Specifically, the field distribution is obviously shifted toward the direction of the lens, and the thickness of the air gap between the lenses is significantly reduced from 16um to 2um, which is greatly compressed. Despite this, the simulation effect of the beam expander is very ideal, and the beam width magnification remains almost unchanged. This result fully proves that the present invention has broken through the physical limitation of the traditional beam expander that "the beam expansion ratio is positively correlated with the volume", and can achieve a high beam expansion ratio within an extremely short optical path without compromising the optical performance of the optical system, thereby significantly improving the space utilization efficiency of the optical system. Finally, after precise measurement and evaluation, the performance parameters of the ultra-compact beam expander are as follows: beam expansion ratio M =9, and the transmittance is as high as 99.3%, which shows the high efficiency and reliability of the present invention in practical applications.

[0022] By optimizing the lens and material combination, the present invention can achieve an ultra-high beam expansion ratio within an extremely short optical path without sacrificing optical performance, significantly improving the spatial efficiency of the optical system. The beam expansion function is achieved using metaconcave and convex lenses. By using metamaterials, the free-space phase transfer function can be achieved over a relatively short distance, effectively compressing the air gap between lenses and further miniaturizing the device. Simulation results show that the designed ultra-compact beam expander can achieve a 9x beam expansion within an extremely short optical path, with a transmittance of up to 99%. This invention has important applications in laser processing equipment, free-space optical communication terminals, and spatial light modulation systems.

[0023] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiment. All technical solutions based on the concept of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. An ultra-compact beam expander structure, characterized in that: The ultra-compact beam expander structure is arranged at any position in the optical path to achieve an ultra-high beam expansion ratio in the optical path, and includes two meta-lenses for achieving beam control, and a meta-material (3) between the two lenses. The two meta-lenses have the same diameter and different focal lengths, and the axes of the two meta-lenses are in the same straight line.

2. The ultra-compact beam expander structure according to claim 1, wherein: The two meta-lenses comprise a meta-concave lens (1) and a meta-convex lens (2); the focal points of the two meta-lenses overlap on one side of the meta-concave lens (1); and along the propagation direction of the light beam, the meta-concave lens (1), the meta-material (3), and the meta-convex lens (2) are arranged in sequence.

3. The ultra-compact beam expander structure according to claim 2, wherein: Phase distribution of the metaconcave lens (1) and the metaconvex lens (2): in, is the phase distribution of the metaconcave lens (1), F 1 is the focal length of the metaconcave lens (1), is the phase distribution of the metaconvex lens (2), F 2 is the focal length of the metaconvex lens (2), λ 0 is the operating wavelength, y is the longitudinal coordinate of the metalens in the Cartesian coordinate system.

4. The ultra-compact beam expander structure according to claim 3, wherein: The beam expansion ratio of the ultra-compact beam expander structure is M = | F 2 / F 1| > 1.

5. The ultra-compact beam expander structure according to claim 1, wherein: The thickness of the metamaterial (3) itself d SP Less than the thickness of d eff The free space optical transfer function, compression ratio R = d eff / d SP .

6. The ultra-compact beam expander structure according to claim 5, wherein: The compression ratio R Greater than 1.

7. The ultra-compact beam expander structure according to claim 6, wherein: The dielectric constant of the metamaterial (3) ε and magnetic permeability μ In satisfaction ε = μ = diag ( 1 / R,R,R ) under the premise of achieving independent regulation.

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