A cascaded mode converter and method for generating high-order Poincaré sphere beams

Abstract

This invention discloses a cascaded mode converter and method for generating high-order Poincaré sphere beams. A vortex waveplate converts uniformly polarized light into a high-order Poincaré sphere beam. Typically, a vortex waveplate of a single order can only produce a single-order Poincaré sphere beam. This invention, by inserting half-waveplates at appropriate positions between multiple vortex waveplates, allows for arbitrary addition and subtraction of the vortex waveplate orders. With a limited number of vortex waveplates, it enables the generation of higher and more diverse orders of high-order Poincaré sphere beams, achieving an exponential increase in the number of orders. The invention includes a laser for generating the initial light source; a polarization adjustment module for adjusting the polarization state at different positions on the high-order Poincaré sphere; and a mode conversion module for generating high-order Poincaré sphere beams with switchable orders. This mode converter has advantages such as simple structure, good stability, and adjustable modes and orders.

Description

Technical Field

[0001] This invention relates to the field of structured light fields, and more specifically to a cascaded mode converter and method for generating high-order Poincaré sphere beams. Background Technology

[0002] Unlike the uniformly polarized light described by the traditional Poincaré sphere, the higher-order Poincaré sphere unifies the geometric representation of vector beams. The transverse intensity of a higher-order Poincaré sphere beam is distributed in a ring shape, and the multiple by which the polarization direction on the cross-section changes with the angle is called the order of the higher-order Poincaré sphere.

[0003] Higher-order Poincaré sphere beams are widely used in various fields due to their unique intensity and polarization distribution, such as particle manipulation, materials processing, optical communication, plasma excitation, and super-resolution imaging.

[0004] Currently, most methods for generating high-order Poincaré sphere beams are based on metasurfaces, spatial light modulators, and vortex waveplates. However, the first two methods are costly and have complex structures. Vortex waveplates have become the most popular device for generating high-order Poincaré sphere beams. However, the optical axis of the vortex waveplate is fixed during the manufacturing process, which means that the order of the vortex waveplate cannot be changed. Usually, a vortex waveplate of a certain order can only generate a high-order Poincaré sphere beam of that order. Summary of the Invention

[0005] The technical problem solved by this invention is to overcome the shortcomings described in the background art and propose a cascaded mode converter that can generate high-order Poincaré sphere beams. It has the characteristics of simple structure, good stability, and adjustable mode and order.

[0006] The technical solution of this invention to solve its technical problem is as follows:

[0007] In a first aspect, the present invention provides a cascaded mode converter for generating a high-order Poincaré sphere beam, comprising a laser, a polarization adjustment module, and a mode conversion module, wherein:

[0008] The laser is used to generate the initial light source;

[0009] The polarization adjustment module is composed of a linear polarizer, a half-wave plate, and a quarter-wave plate cascaded together. The linear polarizer is used to generate linearly polarized light; the half-wave plate is used to change the principal axis direction of the polarized light; and the quarter-wave plate is used to change the ellipticity of the polarized light. The initial light source generated by the laser is used to generate an arbitrary polarization state on a basic Poincaré sphere through the polarization adjustment module.

[0010] The mode conversion module consists of a cascaded vortex waveplate and a half-waveplate. The optical axis of the vortex waveplate changes with the angle, and the half-waveplate is used to modulate the geometric phase of the vortex waveplate. The beam emitted from the polarization adjustment module passes through the mode conversion module, which controls the combination order of the vortex waveplate and the half-waveplate to add or subtract the orders of the vortex waveplates, thereby generating higher-order Poincaré sphere beams of different orders.

[0011] Furthermore, the process of generating higher-order Poincaré sphere beams of different orders is as follows: a half-wave plate is inserted between multiple vortex wave plates to add the orders of the vortex wave plates, and a half-wave plate is added after two vortex wave plates to subtract the orders of the two vortex wave plates. In this way, a variety of higher-order Poincaré sphere beams of different orders can be generated in a controlled manner.

[0012] Furthermore, the vortex wave plate is a q-wave plate based on liquid crystal material or an s-wave plate laser-etched onto silicon glass.

[0013] Secondly, the present invention provides a cascaded mode conversion method for generating higher-order Poincaré sphere beams, which is implemented as follows: a laser generates an initial light source, the initial light source passes through a polarization adjustment module to generate arbitrary polarization states on a basic Poincaré sphere; the beam emitted from the polarization adjustment module then passes through a mode conversion module, which controls the combination sequence of vortex waveplates and half-waveplates to achieve the addition or subtraction of the vortex waveplate orders, thereby generating higher-order Poincaré sphere beams of different orders.

[0014] The advantages of this invention compared to existing technologies are: simpler structure, better stability, and adjustable mode and order. The vortex waveplate can convert uniformly polarized light into a higher-order Poincaré sphere beam; typically, a vortex waveplate of one order can only produce a Poincaré sphere beam of one order. By inserting half-waveplates at appropriate positions between multiple vortex waveplates, arbitrary addition and subtraction of the vortex waveplate orders can be achieved. With a limited number of vortex waveplates, higher and more diverse orders of higher-order Poincaré sphere beams can be generated, with an exponential increase in the number of orders. Furthermore, this mode converter has advantages such as simple structure, good stability, and adjustable mode and order. Attached Figure Description

[0015] The accompanying drawings used in the proposed embodiments will be briefly described below to more clearly illustrate the technical solutions of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of a cascaded mode converter module that can generate high-order Poincaré sphere beams according to the present invention.

[0017] The labels in the figure mean: 1 is the laser, 2 is the polarization adjustment module, and 3 is the polarization conversion module.

[0018] Figure 2 This is a structural diagram of a cascaded mode converter that can generate a high-order Poincaré sphere beam according to the present invention.

[0019] In the diagram, 1 is a laser, 21 is a linear polarizer, 22 is a half-wave plate, 23 is a quarter-wave plate, 31 is the cascaded summation section of a vortex wave plate, 32 is the cascaded subtraction section of a vortex wave plate, 311 and 322 are vortex wave plates, and 312 and 321 are half-wave plates. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] like Figure 1 As shown, the present invention provides a cascaded mode converter capable of generating high-order Poincaré sphere beams, comprising a laser 1, a polarization adjustment module 2, and a mode conversion module 3, wherein:

[0022] The laser can be a semiconductor laser diode, used to generate the initial light source;

[0023] The polarization adjustment module can be composed of a linear polarizer, a half-wave plate, and a quarter-wave plate. The linear polarizer is used to generate linearly polarized light; the half-wave plate is used to change the principal axis direction of the polarized light; and the quarter-wave plate is used to change the ellipticity of the polarized light. The polarization adjustment module can generate all polarization states on the basic Poincaré sphere, thereby changing the position of the final polarization state on a higher-order Poincaré sphere.

[0024] The mode conversion module can be composed of a vortex waveplate and a half-waveplate. The vortex waveplate has an optical axis direction that varies with the angle and can be a q-waveplate based on liquid crystal material or an s-waveplate laser-etched on silicon glass. The half-waveplate is used to modulate the geometric phase of the vortex waveplate to achieve the addition or subtraction of the vortex waveplate orders. The mode conversion module is a cascaded mode converter with switchable orders, which can convert a basic Poincaré sphere beam into higher-order Poincaré sphere beams of different orders.

[0025] The cascaded mode converter capable of generating high-order Poincaré sphere beams is implemented as follows: a laser generates an initial light source, which, through a polarization adjustment module, can generate arbitrary polarization states on a basic Poincaré sphere; the beam emitted from the polarization adjustment module then passes through a mode conversion module, which controls the combination sequence of vortex waveplates and half-waveplates to generate high-order Poincaré sphere beams of different orders.

[0026] The vortex waveplate used in this embodiment of the invention is a spatially variable phase retarder. It can be a q-waveplate based on liquid crystal material, an s-waveplate laser-etched onto silicon glass, or a device with the same function based on other materials. The multiple by which the optical axis of the vortex waveplate changes with the angle is called the order of the vortex waveplate. By changing the polarization state of the incident light, an m-order vortex waveplate can achieve a one-to-one conversion of the polarization states on a basic Poincaré sphere to an m-order higher-order Poincaré sphere. The order of the vortex waveplate is fixed during fabrication. By inserting half-waveplates at specific positions between multiple vortex waveplates—for example, inserting a half-waveplate between two vortex waveplates—their orders can be added together; adding a half-waveplate after two vortex waveplates can subtract their orders. This allows for the controlled generation of various higher-order Poincaré sphere beams. If there are n vortex waveplates with orders m1, m2, ... m... n The order of the higher-order Poincaré obtained by this combination can be any integer from -(m1+m2+m3...) to (m1+m2+m3...). From the perspective of optimal combination, the orders of the n vortex plates can be 1, 3, ..., 3. n-1 3 can be obtained through different combinations. n Different orders of higher-order Poincaré sphere beams, whose order is taken as –(3 n -1) / 2 to (3) n The order of the vortex waveplate can be any integer from -1) / 2. The optimal value for the order of the vortex waveplate is, but it is not the only possible value. More order variations can be achieved using combinations of 1 / 2 waveplates, such as n waveplates with values ​​of 1, 2, ... 2. n-1 When the order of the combination can be (2), n+1 -1) to -(2) n+1 Any integer between -1 and 0.

[0027] Based on the above theoretical analysis, this invention achieves the generation of high-order Poincaré sphere beams with switchable order by using a half-wave plate to modulate the geometric phase of the vortex wave plate.

[0028] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0029] like Figure 2As shown, laser 1 generates a near-linearly polarized initial light source. The beam becomes linearly polarized light after passing through linear polarizer 21. Half-wave plate 22 is used to change the vibration direction of the polarized light, and quarter-wave plate 23 is used to change the ellipticity of the polarized light. By rotating the angle of the optical axes of half-wave plate 22 and quarter-wave plate 23, any polarization state on the basic Poincaré sphere can be obtained. Mode conversion module 3 consists of a cascaded summing section 31 of vortex waveplates and a cascaded subtraction section 32 of vortex waveplates. The number of cascaded summing sections 31 and cascaded subtraction sections 32 of vortex waveplates can be increased as needed, and their arrangement order can be arbitrarily adjusted. Light emitted from polarization adjustment module 2 can be converted into higher-order Poincaré sphere beams of different orders by passing through mode conversion module 3.

[0030] In summary, the innovation of this invention solves the problem that a vortex waveplate of a certain order can only produce a Poincaré sphere beam of one order. With a limited number of vortex waveplates, it enables the generation of higher and more diverse orders of Poincaré sphere beams, achieving an exponential increase in the types of orders. Furthermore, this mode converter has advantages such as simple structure, good stability, and adjustable mode and order.

[0031] Although the invention and its advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made without departing from the spirit and scope of the invention as defined by the appended claims. Furthermore, this application is not intended to be limited to the specific embodiments of the processes, equipment, manufactures, and material compositions, means, methods, and steps described in the specification. Those skilled in the art will readily recognize from the disclosure of this invention those existing or hereafter discovered processes, equipment, manufactures, material compositions, means, methods, or steps that perform substantially the same function or achieve substantially the same result as those described herein in their respective embodiments according to the invention. Therefore, it is intended that the appended claims include such processes, equipment, manufactures, material compositions, means, methods, or steps within their scope.

Claims

1. A cascaded mode converter capable of generating high-order Poincaré sphere beams, characterized in that, This includes a laser, a polarization adjustment module, and a mode conversion module, among which: The laser is used to generate the initial light source; The polarization adjustment module is composed of a linear polarizer, a half-wave plate, and a quarter-wave plate cascaded together. The linear polarizer is used to generate linearly polarized light; the half-wave plate is used to change the principal axis direction of the polarized light; and the quarter-wave plate is used to change the ellipticity of the polarized light. The initial light source generated by the laser is used to generate an arbitrary polarization state on the Poincaré sphere through the polarization adjustment module. The mode conversion module is composed of a cascaded vortex waveplate and a half-waveplate. The optical axis direction of the vortex waveplate changes with the angle. The half-waveplate is used to modulate the geometric phase of the vortex waveplate. The beam emitted from the polarization adjustment module passes through the mode conversion module, which controls the combination order of the vortex waveplate and the half-waveplate to achieve the addition or subtraction of the vortex waveplate order, thereby generating higher-order Poincaré sphere beams of different orders. The process of generating higher-order Poincaré sphere beams of different orders is as follows: a half-wave plate is inserted between multiple vortex wave plates to add the orders of the vortex wave plates, and a half-wave plate is added after two vortex wave plates to subtract the orders of the two vortex wave plates. In this way, a variety of higher-order Poincaré sphere beams of different orders can be generated in a controlled manner.

2. A cascaded mode converter capable of generating high-order Poincaré sphere beams according to claim 1, characterized in that: The vortex waveplate is either a q-waveplate based on liquid crystal material or an s-waveplate laser-etched onto silicon glass.

3. A cascaded mode conversion method based on the converter of claim 1, capable of generating higher-order Poincaré sphere beams, characterized in that: The laser generates an initial light source, which, through a polarization adjustment module, produces arbitrary polarization states on the Poincaré sphere. The beam emitted from the polarization adjustment module then passes through a mode conversion module, which controls the combination sequence of vortex waveplates and half-waveplates to add or subtract the orders of the vortex waveplates, thereby generating higher-order Poincaré sphere beams of different orders.

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