A multi-channel optical orbital angular momentum beam shaping optical system

Abstract

The present invention discloses a multi-channel optical orbital angular momentum beam shaping optical system, comprising: an optical fiber light source, a cylindrical lens group and a Fourier transform lens, wherein the optical fiber light source, the cylindrical lens group and the Fourier transform lens are sequentially arranged along the incident direction of light, the cylindrical lens group comprises: a one-dimensional micro-cylindrical lens array and a cylindrical lens, the one-dimensional micro-cylindrical lens array is composed of a plurality of micro-cylindrical lenses of the same structure uniformly distributed in the transverse space, the optical fiber light source is located on the symmetry plane of the cylindrical lens and is placed on the front focal plane of the micro-cylindrical lens, and the cylindrical lens is located on the front focal plane of the Fourier lens; the present invention ingeniously adopts a one-dimensional micro-cylindrical lens array and a single cylindrical lens combination mode, and the light sources of all channels are shaped by the one-dimensional micro-lens array and the cylindrical lens, and the beam shaping of multi-channel optical orbital angular momentum multiplexing is truly realized. The present invention is mainly used in the field of optical technology.

Description

Technical Field

[0001] The invention relates to the field of optical technology, and in particular to a multi-channel optical orbital angular momentum beam shaping optical system. Background Art

[0002] In the information field, industries closely related to the national economy and people's livelihood, such as cloud computing, big data, the Internet of Things, smart cities, and 5G, are developing rapidly, and the demand for network communication capacity is exploding. As the capacity of optical fiber gradually approaches the Shannon limit, the optical communication industry is experiencing a serious capacity crisis and urgently needs new channel resources to continue to support the market's demand for communication capacity. Among the many beam dimensions that can support the growth of communication capacity, optical orbital angular momentum has become one of the best candidate parameters with its obvious advantages. In theory, optical orbital angular momentum multiplexing can provide an unlimited number of multiplexed channel resources for optical communication systems. The technical approaches to achieve optical orbital angular momentum multiplexing mainly include theories and technologies such as beam splitters, Dammann optical vortex gratings, optical integrated devices, optical lanterns, multi-plane conversion technology, and coordinate transformation. At present, the technology for achieving optical orbital angular momentum multiplexing has defects such as high loss, complex system, and poor stability, and has not yet truly solved the problem of low loss.

[0003] In the optical orbital angular momentum multiplexing technology based on coordinate transformation, it mainly includes two aspects: beam shaping optical system and phase modulation optical system. The phase modulation optical system can achieve the conversion requirements by using diffraction elements or free-form surface optical elements. A set of optical phase modulation devices can meet the conversion of multi-channel optical orbital angular momentum beams, which is less constrained by the limitation of spatial size. However, the beam shaping optical system needs to shape the Gaussian point light source output by the single-mode optical fiber into a plane wave, and also needs to shape the circular plane wave into a long strip light spot on the propagation cross section. The key technical difficulty that limits the practical application of multi-channel optical orbital angular momentum space division multiplexing technology is: in the case of multi-channel multiplexing, the lateral space (the narrow side direction of the strip light spot) between optical orbital angular momentum beams with different topological charges is small, which makes it extremely difficult to arrange the shaping optical system in space. This is difficult for a discrete beam shaping optical system to handle. Summary of the invention

[0004] The purpose of the present invention is to provide a multi-channel optical orbital angular momentum beam shaping optical system to solve one or more technical problems existing in the prior art and at least provide a beneficial choice or create conditions.

[0005] The object of the present invention is achieved by adopting the following technical scheme: a multi-channel optical orbital angular momentum beam shaping optical system, comprising: an optical fiber light source, a cylindrical lens group and a Fourier transform lens, wherein the optical fiber light source, the cylindrical lens group and the Fourier transform lens are arranged in sequence along the incident direction of light, the cylindrical lens group comprises: a one-dimensional micro-cylindrical lens array and a cylindrical lens, the one-dimensional micro-cylindrical lens array is composed of a plurality of micro-cylindrical lenses with the same structure uniformly distributed in the lateral space, the optical fiber light source is located on the symmetry plane of the cylindrical lens and is placed on the front focal plane of the micro-cylindrical lens, and the cylindrical lens is located on the front focal plane of the Fourier lens;

[0006] The parameters of the multi-channel optical orbital angular momentum beam shaping optical system meet the following requirements:

[0007] L ideal =2*π*a;

[0008] θ=λ*ζ / (2*π*a);

[0009] β=fA2 / fA11;

[0010] Δxζ=λ*ζ*fB / (2*π*a);

[0011] L = D0*fB / fA11;

[0012] W = D0*fB / fA2;

[0013] d = λ*Δn*fB / (2*π*a);

[0014] DA1 ≥ fA11*(2*NA);

[0015] DA1≤λ*Δn*fB / (2*π*a);

[0016] 1≤N≤96;

[0017] DA2 ≥ N*λ*Δn*fB / (2*π*a);

[0018] Among them, L idealIt represents the ideal length of the circular spot of the optical orbital angular momentum with a topological charge of 1 after the strip spot is converted, a represents the input parameter, θ represents the angle between the optical axis and the light beam with a topological charge of 1 after being converged by the Fourier transform lens, ζ represents the topological charge of the optical orbital angular momentum after conversion, β represents the aspect ratio of the strip spot after being shaped by the cylindrical lens group, fA2 represents the focal length of the cylindrical lens, fA11 represents the focal length of the micro-cylindrical lens, Δxζ represents the lateral spatial deviation between the symmetry plane of the micro-cylindrical lens corresponding to the optical orbital angular momentum beam with a topological charge of ζ and the optical axis of the Fourier transform lens, and fB represents the Fourier The focal length of the Fourier transform lens, L represents the spot length on the rear focal plane of the Fourier transform lens, W represents the spot width on the rear focal plane of the Fourier transform lens, D0 represents the beam waist diameter of the output spot of the fiber light source, d represents the center distance between adjacent micro-cylindrical lenses, λ represents the wavelength of the output light of the fiber light source, Δn represents the difference in topological charges of the optical orbital angular momentum beams of adjacent channels, DA1 represents the light aperture of the micro-cylindrical lens in the lateral space, NA represents the fiber numerical aperture of the fiber light source, N represents the number of micro-cylindrical lenses, and DA2 represents the light aperture of the cylindrical lens in the lateral spatial direction.

[0019] Furthermore, the micro-column lens is arranged orthogonally to the cylindrical lens.

[0020] Furthermore, the optical fiber light source is a single-mode optical fiber light source.

[0021] The beneficial effects of the present invention are as follows: the present invention ingeniously adopts a one-dimensional micro-column lens array and a single-column lens combination, and the light sources of all channels are shaped by the one-dimensional micro-lens array and the cylindrical lens, which truly realizes the beam shaping of multi-channel optical orbital angular momentum multiplexing. By adopting a one-dimensional micro-column lens array, high-precision integrated design and manufacturing technology can be realized, and the high-precision manufacturing process ensures the positional relationship between optical orbital angular momentum beams with different topological charges during multi-channel multiplexing, greatly reducing the difficulty of system assembly and debugging, and realizing a highly integrated, miniaturized and compact design, which is conducive to the design of a miniature multi-channel beam shaping device.

[0022] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0024] Figure 1 It is a structural diagram based on the X-axis and Z-axis planes of a multi-channel optical orbital angular momentum beam shaping optical system provided by the present invention;

[0025] Figure 2 It is a structural diagram based on the Y-axis and Z-axis planes of a multi-channel optical orbital angular momentum beam shaping optical system provided by the present invention;

[0026] The coordinate arrows in the figure represent the X, Y, and Z axes respectively. DETAILED DESCRIPTION

[0027] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0028] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0029] In the description of the present invention, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed" etc. are understood as not including the number itself, and "above", "below", "within" etc. are understood as including the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0030] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0031] Reference Figure 1 and Figure 2 , a multi-channel optical orbital angular momentum beam shaping optical system, comprising: a single-mode fiber light source S, a cylindrical lens group, a Fourier transform lens B and a phase modulation device Q; the cylindrical lens group comprises: a one-dimensional micro cylindrical lens array A1 and a cylindrical lens A2; Figure 1 and Figure 2 In , 1, 2, ..., N represent multiple channels of the light beam. Z is the transmission direction of the light beam, and the XZ plane is defined as the transverse spatial plane, and the YZ plane is defined as the longitudinal spatial plane, which are orthogonal to each other; wherein each micro-cylindrical lens represents a channel.

[0032] The single-mode fiber light source S, the cylindrical lens group and the Fourier transform lens B are arranged in sequence along the incident direction of the light. The cylindrical lens group includes: a one-dimensional micro-cylindrical lens array A1 and a cylindrical lens A2. The one-dimensional micro-cylindrical lens array A1 is composed of a plurality of micro-cylindrical lenses A11 with the same structure uniformly distributed in the transverse space. The single-mode fiber light source S is located on the symmetry plane of the cylindrical lens A2 and is placed on the front focal plane of the micro-cylindrical lens A11. The cylindrical lens A2 is located on the front focal plane of the Fourier lens B. The phase modulation device Q is arranged at the rear focal plane of the Fourier transform lens B. The single-mode fiber light source S is used to output a Gaussian beam. The amplitude distribution of the cross section of the Gaussian beam complies with the Gaussian function. The cylindrical lens group is used to form the Gaussian beam into a Gaussian strip plane beam; the one-dimensional micro-cylindrical lens array A1 is used to output a Gaussian plane beam in the transverse direction (i.e., the X-axis direction); the cylindrical lens A2 is used to output a Gaussian plane beam in the longitudinal direction (i.e., the Y-axis direction). The Fourier transform lens B is used to converge the Gaussian strip plane beam onto the rear focal plane. The phase modulator Q is used to convert the Gaussian strip plane beam into a ring-shaped beam to achieve optical orbital angular momentum beam transformation. The phase modulator Q can achieve the conversion requirements by using a diffraction element or a free-form surface optical element.

[0033] The parameters of the multi-channel optical orbital angular momentum beam shaping optical system meet the following requirements:

[0034] L ideal =2*π*a;

[0035] θ = λ*ζ / (2*π*a);

[0036] β=fA2 / fA11;

[0037] Δxζ=λ*ζ*fB / (2*π*a);

[0038] L = D0*fB / fA11;

[0039] W = D0*fB / fA2;

[0040] d = λ*Δn*fB / (2*π*a);

[0041] DA1 ≥ fA11*(2*NA);

[0042] DA1≤λ*Δn*fB / (2*π*a);

[0043] 1≤N≤96;

[0044] DA2 ≥ N*λ*Δn*fB / (2*π*a);

[0045] Among them, L idealIt represents the ideal length of the circular spot of the optical orbital angular momentum with a topological charge of 1 after the strip spot is converted, a represents the input parameter, θ represents the angle between the optical axis and the light beam with a topological charge of 1 after converging through the Fourier transform lens B, ζ represents the topological charge of the converted optical orbital angular momentum, β represents the aspect ratio of the strip spot after shaping by the cylindrical lens group, fA2 represents the focal length of the cylindrical lens A2, fA11 represents the focal length of the micro-cylindrical lens A11, Δxζ represents the lateral spatial deviation between the symmetry plane of the micro-cylindrical lens A11 corresponding to the optical orbital angular momentum beam with a topological charge of ζ and the optical axis of the Fourier transform lens B, and fB represents the Fourier transform lens B. The focal length of the lens is represented by L, L represents the spot length on the rear focal plane of the Fourier transform lens B, W represents the spot width on the rear focal plane of the Fourier transform lens B, D0 represents the beam waist diameter of the output spot of the single-mode fiber light source S, d represents the center spacing between adjacent micro-cylindrical lenses A11, λ represents the wavelength of the output light of the single-mode fiber light source S, Δn represents the difference in topological charge of the optical orbital angular momentum beams of adjacent channels, DA1 represents the light aperture of the micro-cylindrical lens A11 in the transverse space, NA represents the fiber numerical aperture of the single-mode fiber light source S, N represents the number of micro-cylindrical lenses A11, and DA2 represents the light aperture of the cylindrical lens A2 in the transverse spatial direction. For the convenience of description, at least some of the symbols of the above parameter values ​​are reflected in the attached drawings in the form of numbers, where L1 is the distance from the cylindrical lens A2 to the Fourier transform lens B, which is equal to the focal length value fB of the Fourier transform lens B.

[0046] In order to realize the shaping of the circular Gaussian spot output by the single-mode fiber light source S into a long strip spot for the subsequent phase modulation device Q to convert the optical orbital angular momentum, a cylindrical lens group is first used to shape the Gaussian spot output by the single-mode fiber light source S into a Gaussian strip plane wave; then the strip plane wave is focused onto its rear focal plane by the Fourier transform lens B. The spot is converted into a circular ring spot by the phase modulation device Q placed on the rear focal plane of the Fourier transform lens B, and the optical orbital angular momentum beam conversion is obtained. According to the transformation principle, when the long strip plane wave is translated along the perpendicular direction to the optical axis of the Fourier transform lens B and in its lateral direction, an optical orbital angular momentum beam with different topological charges will be generated. Since the translation amount between adjacent topological charges is very small, it is difficult to use discrete cylindrical lenses to realize the shaping of multi-channel beams with different topological charges. Therefore, when realizing multi-channel multiplexing, the present invention adopts a one-dimensional micro-cylindrical lens array A1, and uses micro-cylindrical lenses A11 uniformly distributed in the lateral space, and the number thereof is the same as the number of multiplexing channels. Different topological charge channel light beams pass through a micro-cylindrical lens A11 separately, but share the cylindrical lens A2. The combination of the single-mode fiber light source S and the micro-cylindrical lens A11 has different transverse spatial positions relative to the optical axis of the Fourier transform lens B, corresponding to optical orbital angular momentum light beams of different topological charges. This solves the problem of dense arrangement of adjacent topological charge channel light beams in the transverse space, and reduces the difficulty of system assembly and debugging through integrated manufacturing. The present invention creatively limits the parameters of each device that constitutes the multi-channel optical orbital angular momentum beam shaping optical system, thereby realizing the multiplexing of multi-channel topological charge optical orbital angular momentum beams.

[0047] In some embodiments, the present invention implements the recombination of eight-channel and sixteen-channel topologically charged optical orbital angular momentum beams.

[0048] For eight channels, the specific parameters are as follows:

[0049] 1) Wavelength λ: 1.55 μm;

[0050] 2) Numerical aperture NA: 0.14;

[0051] 3) Parameter a: 0.1mm;

[0052] 4) Topological charge difference Δn: 2;

[0053] 5) Focal length fA11: 0.7mm;

[0054] 6) Number of micro-cylindrical lenses A11: 8;

[0055] 7) The lateral center distance d between adjacent micro-cylindrical lenses A11 is 0.27 mm;

[0056] 8) The transverse aperture DA1 of the micro-cylindrical lens A11: 0.196mm≤DA1≤0.27mm;

[0057] 9) Focal length of cylindrical lens A2 fA2: 3.5mm;

[0058] 10) Focal length fB of Fourier transform lens B: 55 mm;

[0059] 11) After being shaped by the cylindrical lens group, the aspect ratio of the stripe light spot is β:5;

[0060] 12) The angle θ between the light beam with topological charge 1 and the optical axis after being converged by Fourier transform lens B is 2.47 mrad;

[0061] 13) After transformation by Fourier transform lens B, the spot length on the rear focal plane is L: 0.71 mm and the width is W: 0.14 mm.

[0062] 14) The lateral aperture DA2 of the cylindrical lens A2: ≥4.35 mm.

[0063] For sixteen channels, the specific parameters are as follows:

[0064] 1) Wavelength λ: 0.633 μm;

[0065] 2) Numerical aperture NA: 0.1;

[0066] 3) Parameter a: 0.05mm;

[0067] 4) The topological charge difference between adjacent channels Δn: 1;

[0068] 5) Focal length fA11 of cylindrical lens A11: 0.75 mm;

[0069] 6) The number of micro-column lenses A11 of the one-dimensional micro-column lens array A1: 16;

[0070] 7) The lateral center distance d between adjacent micro-cylindrical lenses A11 is 0.16 mm;

[0071] 8) Horizontal aperture DA1 of micro-cylindrical lens A11: 0.15mm≤DA1≤0.16

[0072] mm;

[0073] 9) Focal length of cylindrical lens A2 fA2: 3.75mm;

[0074] 10) Focal length fB of Fourier transform lens B: 80 mm;

[0075] 11) After being shaped by the cylindrical lens group A, the aspect ratio of the stripe light spot is β:5;

[0076] 12) The angle θ between the light beam with topological charge 1 and the optical axis after being converged by Fourier transform lens B is 2.01 mrad;

[0077] 13) After transformation by Fourier transform lens B, the spot length on the rear focal plane is L: 0.38 mm and the width is W: 0.08 mm.

[0078] 14) The lateral aperture DA2 of the cylindrical lens A2: ≥2.58 mm.

[0079] Through testing, it is shown that both eight-channel and sixteen-channel optical orbital angular momentum beam shaping can be achieved.

[0080] The embodiments of the present invention are described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in the technical field without departing from the purpose of the present invention.

Claims

1. A multi-channel optical orbital angular momentum beam shaping optical system, characterized in that: include: An optical fiber light source, a cylindrical lens group and a Fourier transform lens, wherein the optical fiber light source, the cylindrical lens group and the Fourier transform lens are sequentially arranged along the incident direction of light, the cylindrical lens group comprises: a one-dimensional micro-cylindrical lens array and a cylindrical lens, the one-dimensional micro-cylindrical lens array is composed of a plurality of micro-cylindrical lenses with the same structure uniformly distributed in the transverse space, the optical fiber light source is located on the symmetry plane of the cylindrical lens and is placed on the front focal plane of the micro-cylindrical lens, and the cylindrical lens is located on the front focal plane of the Fourier transform lens; The parameters of the multi-channel optical orbital angular momentum beam shaping optical system satisfy: L ideal = 2*π*a: θ = λ*ζ / (2*π*a); β = fA2 / fA11; Δxζ =λ*ζ*fB / (2*π*a); L = D0*fB / fA11; W = D0*fB / fA2; d =λ*Δn*fB / (2*π*a); DA1 ≥ fA11*(2*NA); DA1≤λ*Δn*fB / (2*π*a); 1≤N≤96； DA2 ≥ N*λ*Δn*fB / (2*π*a); Among them, L ideal It represents the ideal length of the circular spot of the optical orbital angular momentum after the strip spot is converted into a topological charge of 1, a represents the input parameter, θ represents the angle between the optical axis and the light beam with a topological charge of 1 after converging through the Fourier transform lens, ζ represents the topological charge of the optical orbital angular momentum after conversion, β represents the aspect ratio of the strip spot after shaping by the cylindrical lens group, fA2 represents the focal length of the cylindrical lens, fA11 represents the focal length of the micro-cylindrical lens, and Δxζ represents the optical orbital angular momentum beam with a topological charge of ζ. The deviation between the symmetry plane of the micro-cylindrical lens and the optical axis of the Fourier transform lens in the transverse space, fB represents the focal length of the Fourier transform lens, L represents the spot length on the rear focal plane of the Fourier transform lens, W represents the spot width on the rear focal plane of the Fourier transform lens, D0 represents the beam waist diameter of the output spot of the fiber light source, d represents the center spacing between adjacent micro-cylindrical lenses, λ represents the wavelength of the output light of the fiber light source, Δn represents the difference in topological charge of the optical orbital angular momentum beams of adjacent channels, DA1 represents the light aperture of the micro-cylindrical lens in the transverse space, NA represents the fiber numerical aperture of the fiber light source, N represents the number of micro-cylindrical lenses, and DA2 represents the light aperture of the cylindrical lens in the transverse space direction; The micro-column lens is arranged orthogonally to the cylindrical lens; and the optical fiber light source is a single-mode optical fiber light source.

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