Topological texture adjustable optical skyrmion generation method and system

Abstract

The invention discloses a topological texture adjustable optical skyrmion generation method and system. The method and the system comprise two core components, namely a liquid crystal spatial light modulator and a variable phase delayer, and a linear polarization fundamental mode Gaussian beam can be regulated and controlled into a topological texture customizable Gaussian beam by adjusting the holographic phase of the liquid crystal spatial light modulator and the control voltage of the variable phase delayer. The topological texture adjustable generation of the optical skyrmion is realized. The system is high in energy utilization rate, high in response speed, rich in topological texture, simple and stable in structure and easy to adjust, and can be widely applied to frontier application scenes such as free space laser communication.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic technology, and in particular to a method and system for generating optical skyrmions with adjustable topological texture. Background Art

[0002] Skyrmion is a topologically protected quasi-particle structure, first proposed by British physicist Skyrme in 1962 when studying the unified field theory of the interaction between mesons and baryons, and later confirmed to exist in the fields of Bose-Einstein condensation, liquid crystal materials, ferromagnets, acoustics and torsion electronics. Among them, magnetic skyrmions have shown high stability, small size, and low driving energy in the research process. They are regarded as the future development direction of storage technology and have received widespread attention from the scientific and industrial communities.

[0003] In recent years, the concept of skyrmions has been introduced into the field of optics and frequently appears in various optical systems. These topological quasiparticles with skyrmion-like texture light field distribution are called optical skyrmions, and the beam whose cross-sectional topological texture distribution is that of optical skyrmions is called skyrmion beam. Typical forms of optical skyrmions mainly include Néel-type, Bloch-type, anti-type and di-type skyrmions of different orders. The optical skyrmions discovered in the early days were Néel-type electric field vector skyrmions arrays in evanescent light fields and Bloch-type spin vector skyrmions under tight focusing conditions. Later, under paraxial conditions, optical skyrmions based on Stokes vector theory were proposed. It is the first type of optical skyrmion that can be transmitted in free space. Its controllable form is also more free than in other optical fields. It can realize special textures such as Néel-type, Bloch-type, anti-type and di-type skyrmions. It is a good carrier of optical information. At the same time, due to its anti-turbulence ability brought by its topological characteristics, it has shown great application potential in the field of free-space laser communication.

[0004] At present, scholars at home and abroad have carried out some research work on the generation of Stokes vector skyrmions, and proposed to use liquid crystal spatial light modulators and holography to generate optical skyrmions with adjustable topological textures, namely Néel-type, Bloch-type and anti-skyrmions. However, these methods have problems such as low energy utilization and complex optical paths that are difficult to build. Later, with the introduction of skyrmions, the concepts of optical skyrmions and other topological quasiparticles continued to enrich, and the textures that the original control methods could produce began to appear limited. Researchers designed a more complex gradient refractive index lens to draw skyrmion textures on the end face of the optical fiber, which to a certain extent solved the problem of the high degree of limitation of the modulatable texture of the original modulation method. However, this made the optical path structure more complicated, requiring high-precision splicing of a large number of components to achieve, and the texture was difficult to replace, which was difficult to adapt to the channel capacity requirements of free-space laser communication. Therefore, it is urgent to develop a method for generating optical skyrmions with low energy loss, simple optical path, adjustable topological texture and rapidity. Summary of the invention

[0005] In view of this, the present invention discloses a method and system for generating optical skyrmions with adjustable topological texture.

[0006] The present invention discloses a method for generating optical skyrmions with adjustable topological texture. By loading a liquid crystal spatial light modulator with a modulation phase to introduce a specific and controllable phase modulation as a fundamental mode Gaussian beam, and then adjusting a variable phase retarder to introduce a phase delay, a fundamental mode Gaussian beam can be regulated to be a skyrmion beam with a customizable topological texture, thereby realizing the adjustable topological texture generation of optical skyrmions.

[0007] Among them, the holographic phase loaded on the liquid crystal spatial light modulator is a spiral phase, and its pure phase modulation function is:

[0008]

[0009] Among them, -s is the spiral phase order, which is used to control the order of generated optical skyrmions, that is, the skyrmion number s; is the angular coordinate; is the initial phase, which is used to control the conversion of optical skyrmions between Néel type and Bloch type.

[0010] The variable phase retarder can introduce an adjustable optical path difference of 0 to λ between the fast axis and the slow axis, and control the conversion of optical skyrmions between the positive type (Néel type or Bloch type), the negative type and the diatomic skyrmion.

[0011] The optical skyrmion generation system with adjustable topological texture of the present invention comprises a laser, a polarizer, a liquid crystal spatial light modulator, and a variable phase retarder, wherein:

[0012] The laser is used to generate a fundamental mode Gaussian beam;

[0013] The polarizer is placed in the laser light path behind the laser, with the polarization direction being 45° to the horizontal plane, and is used to generate a fundamental mode Gaussian beam with a linear polarization of 45°;

[0014] The liquid crystal spatial light modulator is placed in the laser light path behind the polarizer, and is loaded with a spiral phase. When a 45° oblique linearly polarized fundamental mode Gaussian beam enters the liquid crystal spatial light modulator, it can be decomposed into a horizontal linear polarization component and a vertical linear polarization component with equal intensity, wherein the horizontal linear polarization component will be modulated by the spiral phase, and the vertical linear polarization component remains unchanged and still maintains the fundamental mode Gaussian mode. At this time, the lateral topological texture of the outgoing light beam of the liquid crystal spatial light modulator is an optical bipolar.

[0015] The variable phase retarder is placed in the laser light path behind the liquid crystal spatial light modulator, with the fast axis tilted at 45°. By adding a control voltage, the optical diviton outputted from the liquid crystal spatial light modulator can be regulated to be a positive / negative diviton, a skyrmion or other topological quasiparticles.

[0016] The present invention has the following beneficial effects:

[0017] (1) The present invention provides a method for generating optical skyrmions with adjustable topological texture, which is based on pure phase regulation and has high energy utilization and fast response speed.

[0018] (2) The present invention provides a method for generating optical skyrmions with adjustable topological texture, which can generate a variety of optical skyrmions and other topological quasiparticles on demand, and has broad prospects in the field of optical communications.

[0019] (3) The optical skyrmion generation system with adjustable topological texture of the present invention has a simple, stable and easy-to-adjust system structure and can be applied to a variety of cutting-edge application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The schematic diagram of the device of an optical skyrmion generation system with adjustable topological texture of the present invention, wherein 1 is a laser, 2 is a polarizer, 3 is a liquid crystal spatial light modulator, and 4 is a variable phase retarder;

[0021] Figure 2 The spiral phase shifter loaded on the liquid crystal spatial light modulator in the first embodiment of the present invention is Schematic diagram, at this time s = 1,

[0022] Figure 3The simulation and experimental results of a topological texture-adjustable optical skyrmion generation system of the present invention when generating first-order Néel-type skyrmions are shown, corresponding to Example 1, the left side is the Stokes vector distribution diagram of the output light beam obtained by simulation calculation, and the right side is the Stokes vector distribution diagram of the output light beam obtained by experiment;

[0023] Figure 4 The spiral phase shifter loaded on the liquid crystal spatial light modulator in Example 2 of the present invention is Schematic diagram, at this time s = 5,

[0024] Figure 5 The simulation and experimental results of a topological texture-adjustable optical skyrmion generation system of the present invention when generating a 5th-order dipartite, corresponding to Example 2, the left side is the Stokes vector distribution diagram of the output light beam obtained by simulation calculation, and the right side is the Stokes vector distribution diagram of the output light beam obtained by experiment; DETAILED DESCRIPTION

[0025] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0026] First, the principle of a topological texture-adjustable optical skyrmion generation method of the present invention is briefly introduced.

[0027] In a general sense, the Stokes vector skyrmion can be generally regarded as the superposition of beams with orthogonal spatial modes and polarization states, and its expression is:

[0028]

[0029] Among them, u1(r) and u2(r) are two orthogonal spatial light intensity distributions, where the initial phase represents the phase difference between the two modes, |p1> and |p2> are two mutually orthogonal polarization states, usually left-handed circularly polarized light and right-handed circularly polarized light, or horizontally polarized light and vertically polarized light. For optical skyrmions, they can be decomposed on the left / right circularly polarized orthogonal basis {|L>,|R>}, one of which is the fundamental mode Gaussian beam |LG0>, and the other is the single-mode vortex beam |LG -s >, then the s-order optical skyrmion is:

[0030]

[0031] in, is a -s order single mode vortex beam. By choosing the parameters s and The values ​​of s = 1 can give the three common forms of optical skyrmions: Néel type: s = 1, Bloch type: s = 1, Inversion: s=-1, In the present invention, the parameters s and The spiral phase can be loaded on the liquid crystal spatial light modulator To control:

[0032]

[0033] Therefore, by adjusting the parameters s and The order and form of the optical skyrmion can be controlled.

[0034] On this basis, if the polarization orthogonal basis of left / right circularly polarized light in the optical skyrmion is converted into other orthogonal polarization basis, an optical skyrmion with unchanged skyrmion number but obvious texture change can be obtained, and this conversion of orthogonal polarization basis can be achieved by a variable phase retarder. For a wave plate with a phase delay angle of δ and an angle of θ between the fast axis and the x-axis, the Jones matrix is ​​expressed in a rectangular coordinate system:

[0035]

[0036] When θ = ±45°, the Jones matrix can be simplified to:

[0037]

[0038] Considering that the input light of the variable phase retarder is the superposition of horizontal and vertical linear polarization light, the output light of the corresponding components is calculated respectively:

[0039]

[0040] It can be found that the basis of the first term and the second term is orthogonal and the modulus is 1, which is a pair of new unit orthogonal basis. It can be deduced that the output light through the variable phase retarder meets the requirements of generalized skyrmions. When the phase delay angle δ=kπ(k=0,1,2……), the basis is horizontal / vertical linear polarization basis, and the output beam is a dipartite. When δ=kπ+π / 2(k=0,1,2……), the basis is left-handed / right-handed circularly polarized light, and the output is a standard optical skyrmion. When δ is other values, other optical skyrmions can be output. This process can cover all unit polarization orthogonal basis, enrich the polarization texture of optical skyrmions, and greatly improve the types and range of optical skyrmions that we can control.

[0041] The present invention provides an optical skyrmion generation system with adjustable topological texture, such as Figure 1As shown, it is equipped with a laser, a polarizer, a liquid crystal spatial light modulator, and a variable phase retarder, wherein: the laser is used to generate a fundamental mode Gaussian beam; the polarizer is placed in the laser light path behind the laser, and its polarization direction is 45° with the horizontal plane, and is used to generate a fundamental mode Gaussian beam with a linear polarization of 45°; the liquid crystal spatial light modulator is placed in the laser light path behind the polarizer, and is loaded with a spiral phase. When the fundamental mode Gaussian beam with a linear polarization of 45° is incident on the liquid crystal spatial light modulator, it can be decomposed into a horizontal linear polarization component and a vertical linear polarization component with equal intensity, wherein the horizontal linear polarization component will be modulated by the spiral phase, and the vertical linear polarization component remains unchanged and still maintains the fundamental mode Gaussian mode. At this time, the transverse topological texture of the output light beam of the liquid crystal spatial light modulator is an optical diviton; the variable phase retarder is placed in the laser light path behind the liquid crystal spatial light modulator, and its fast axis is placed at a 45° tilt. By adding a control voltage, the optical diviton output after the liquid crystal spatial light modulator can be regulated to be a positive / negative diviton, a skyrmion or other topological quasiparticles.

[0042] The following briefly introduces the modulation performance of a topological texture-adjustable optical skyrmion generation method and system of the present invention in conjunction with the embodiments.

[0043] Example 1: Generation of 1st-order Néel-type skyrmions

[0044] In this embodiment, the laser wavelength λ=1617nm, and the modulation phase loaded on the liquid crystal spatial light modulator is as follows: Figure 2 As shown, where s = 1, The variable phase retarder adjusts the control voltage so that the additional optical path difference is λ / 4, that is, the phase delay angle δ = π / 2. The fundamental mode Gaussian beam passes through the system to obtain a first-order Néel-type skyrmion beam, that is, a first-order Néel-type optical skyrmion. Figure 3 This is the topological texture of the optical skyrmion obtained by numerical simulation and experimental measurement in this embodiment. It can be seen that the experimental results are completely consistent with the numerical simulation results.

[0045] Example 2: Generating a 5-order dichotomy

[0046] In this embodiment, the laser wavelength λ=1617nm, and the modulation phase loaded on the liquid crystal spatial light modulator is as follows: Figure 4 As shown, where s = 5, The variable phase retarder adjusts the control voltage so that the additional optical path difference is λ, that is, the phase delay angle δ = 2π. The fundamental mode Gaussian beam passes through the system to obtain a 5th order double half beam, that is, a 5th order double half beam. Figure 5 This is the topological texture of the optical skyrmion obtained by numerical simulation and experimental measurement in this embodiment. It can be seen that the experimental results are completely consistent with the numerical simulation results.

[0047] The above embodiments show that the optical skyrmion generation method and system with adjustable topological texture of the present invention have good performance.

[0048] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for generating optical skyrmions with adjustable topological texture, characterized in that: By loading the modulation phase into the fundamental mode Gaussian beam through a liquid crystal spatial light modulator to introduce a specific and controllable phase modulation, and then adjusting the variable phase delay to introduce a phase delay, a fundamental mode Gaussian beam can be regulated into a skyrmion beam with customizable topological texture, thereby realizing the adjustable generation of topological texture of optical skyrmions.

2. The method according to claim 1, wherein: The phase modulation introduced by the liquid crystal spatial light modulator is: Among them, -s is the spiral phase order, which is used to control the order of generated optical skyrmions, that is, the skyrmion number s; is the angular coordinate; is the initial phase, which is used to control the conversion of optical skyrmions between Néel type and Bloch type.

3. The method according to claim 1, wherein: When the phase delay angle of the variable phase retarder is kπ (k=0, 1, 2...), the output is a diatomic particle; when the phase delay angle of the variable phase retarder is (kπ+π / 2) (k=0, 1, 2...), the output is a standard optical skyrmion; when the phase delay angle of the variable phase retarder is other values, other optical skyrmions can be output.

4. An optical skyrmion generation system with adjustable topological texture, characterized in that: Including laser, polarizer, liquid crystal spatial light modulator, variable phase retarder: The laser is used to generate a fundamental mode Gaussian beam; The polarizer is placed in the laser light path behind the laser, with the polarization direction being 45° to the horizontal plane, and is used to generate a fundamental mode Gaussian beam with a linear polarization of 45°; The liquid crystal spatial light modulator is placed in the laser light path behind the polarizer, and is loaded with a spiral phase. When a 45° oblique linearly polarized fundamental mode Gaussian beam enters the liquid crystal spatial light modulator, it can be decomposed into a horizontal linear polarization component and a vertical linear polarization component with equal intensity, wherein the horizontal linear polarization component will be modulated by the spiral phase, and the vertical linear polarization component remains unchanged and still maintains the fundamental mode Gaussian mode. At this time, the lateral topological texture of the outgoing light beam of the liquid crystal spatial light modulator is an optical bipolar. The variable phase retarder is placed in the laser light path behind the liquid crystal spatial light modulator, with the fast axis tilted at 45°. By adding a control voltage, the optical diviton outputted from the liquid crystal spatial light modulator can be regulated to be a positive / negative diviton, a skyrmion or other topological quasiparticles.

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