A nonlinear vectorial optical field generating device and method

Abstract

The application discloses a nonlinear vector light field generating device and method based on a Moiré nonlinear photonic crystal, relates to the technical field of optical light field regulation and nonlinear optics, and comprises a Moiré nonlinear photonic crystal satisfying nonlinear Raman-Nath diffraction and a quarter-wave plate; wherein the Moiré nonlinear photonic crystal is a fork-shaped nonlinear photonic crystal with the same topological charge in a specific direction polarization, and is sequentially placed according to a Moiré angle; after base frequency light passes through the Moiré nonlinear photonic crystal, nonlinear Raman-Nath diffraction is generated, nonlinear vortex light with polarization directions perpendicular to each other and opposite topological charges is generated in the same diffraction direction, and after superposition through the quarter-wave plate, a nonlinear vector light field is formed; the nonlinear vector light field generating device and method provided by the application are simple, compact and highly integrated, and through design on the Moiré nonlinear photonic crystal structure, a vector light field with an arbitrary polarization state can be generated.

Description

Technical Field

[0001] This invention relates to the fields of optical field manipulation and nonlinear optics, and particularly to a nonlinear vector light field generation device and method based on a moiré nonlinear photonic crystal. Background Technology

[0002] Vector light fields refer to light fields with different polarization states at different positions on the same wavefront at the same time; they are a type of non-uniformly polarized light. Due to their unique spatial polarization distribution, vector light fields have important applications in optical micromanipulation, optical microfabrication, optical imaging, and optical communication. However, the unique spatial polarization distribution of vector light fields, coupled with their polarization sensitivity during nonlinear frequency conversion, makes generating nonlinear vector light fields extremely difficult. Since 2018, researchers have proposed different methods to address this problem, including methods based on cascaded nonlinear photonic crystals, Mach-Zehnder interferometers, and Sagnac rings. For the cascaded nonlinear photonic crystal method, researchers first generate the fundamental frequency vector light field through a complex optical path, and then use two orthogonally placed nonlinear photonic crystals to generate a frequency-doubled vector light field in a three-wave mixing process. The Mach-Zehnder interferometer-based method first divides the fundamental frequency vector light field into two parts, each of which is simultaneously frequency-doubled by a nonlinear photonic crystal. The frequency-doubled light fields are then recombined to form a second-harmonic vector light field. The Sagnac ring-based method uses a dual-wavelength polarizing beam splitter to split the generated fundamental frequency vector light field into two paths. These two orthogonally polarized fundamental frequency beams propagate in opposite directions and undergo nonlinear frequency conversion on their own. Finally, they are superimposed by a polarizing beam splitter to synthesize a frequency-doubled vector light field. It is evident that existing experimental methods for generating nonlinear vector light fields are complex, with cumbersome experimental setups and optical paths, low integration, and cannot directly generate a vector light field simultaneously with nonlinear frequency conversion.

[0003] Therefore, those skilled in the art are dedicated to developing a simple, compact, and highly integrated nonlinear vector light field generation device and method based on a moiré nonlinear photonic crystal. Summary of the Invention

[0004] In view of the above-mentioned deficiencies of the prior art, the technical problem to be solved by the present invention is how to realize a simple, compact, and highly integrated nonlinear vector light field generation device and method.

[0005] To achieve the above objectives, the present invention provides a nonlinear vector light field generation device and method based on a moiré nonlinear photonic crystal.

[0006] A nonlinear vector light field generating device based on a moiré nonlinear photonic crystal includes a moiré nonlinear photonic crystal that satisfies nonlinear Raman-Nice diffraction and a quarter-wave plate. The moiré nonlinear photonic crystal is composed of two fork-shaped nonlinear photonic crystals with the same topological charge polarized in a specific direction, which are placed sequentially according to the moiré angle. When the fundamental frequency light passes through the moiré nonlinear photonic crystal, nonlinear Raman-Nice diffraction is generated, and nonlinear vortex light with mutually perpendicular polarization directions and opposite topological charges is generated in the same diffraction direction. After being superimposed by the quarter-wave plate, a nonlinear vector light field is formed.

[0007] In a preferred embodiment of the present invention, the nonlinear photonic crystal includes nonlinear photonic crystal I and nonlinear photonic crystal II, wherein the polarization direction of nonlinear photonic crystal I is along the y-direction and the polarization direction of nonlinear photonic crystal II is along the x-direction; in order to obtain frequency-doubled vortex light with opposite topological charges, the fork-shaped nonlinear photonic crystal structure of nonlinear photonic crystal I has the fork-shaped direction facing upward, and the fork-shaped nonlinear photonic crystal structure of nonlinear photonic crystal II has the fork-shaped direction facing downward.

[0008] A method for generating a nonlinear vector light field based on a moiré nonlinear photonic crystal includes the following steps:

[0009] Step 1: Prepare two fork-shaped nonlinear photonic crystals with the same topological charge polarized in a specific direction;

[0010] Step 2: Place the nonlinear photonic crystals sequentially according to a certain Mohr angle. When the fundamental frequency light passes through the Mohr nonlinear photonic crystal, nonlinear Raman-Nice diffraction is generated, and nonlinear vortex light with mutually perpendicular polarization directions and opposite topological charges is generated in the same diffraction direction.

[0011] Step 3: The nonlinear vortex light with mutually perpendicular polarization directions and opposite topological charges generated in Step 2 is superimposed through a quarter-wave plate to generate a nonlinear vector light field.

[0012] In a preferred embodiment of the present invention, step 1 further includes:

[0013] The nonlinear photonic crystal includes nonlinear photonic crystal I and nonlinear photonic crystal II, wherein the polarization direction of nonlinear photonic crystal I is along the y direction and the polarization direction of nonlinear photonic crystal II is along the x direction. The nonlinear material is cut in the z direction and the upper and lower surfaces are polished to obtain the sample.

[0014] Nonlinear photonic crystals are prepared by electron beam lithography, laser-induced electric field polarization, metal tip electric field polarization, and room temperature electric field polarization.

[0015] Design a mask with an L-shaped grating pattern based on the required periodicity;

[0016] The pattern on the photomask is transferred to the sample surface; then the electrode is deposited by ion beam sputtering, and finally polarized; after polarization, the light-transmitting surface is polished.

[0017] In a preferred embodiment of the present invention, step 2 further includes: the fork-shaped nonlinear photonic crystal structure of nonlinear photonic crystal I has the fork-shaped direction facing upward, and the fork-shaped nonlinear photonic crystal structure of nonlinear photonic crystal II has the fork-shaped direction facing downward.

[0018] In a preferred embodiment of the present invention, step 2 further includes: the input fundamental frequency light is linearly polarized light polarized along the y-axis, incident on a first fork-shaped nonlinear photonic crystal I with a topological charge of l, and generating a frequency-doubled vortex light with a topological charge of -l polarized along the y-axis in the +1 order nonlinear Raman-Nice diffraction, denoted as... The nonlinear coefficient corresponding to the nonlinear process is d 22 The fundamental pump light then passes through a second fork-shaped nonlinear photonic crystal II with a topological charge of l, generating a frequency-doubled vortex light with a topological charge of +l along the x-polarization path in the +1 order nonlinear Raman-Nice diffraction, denoted as... The nonlinear coefficient corresponding to the nonlinear process is -d 22 The intensity of the frequency-doubled vortex light generated in both instances is the same.

[0019] In a preferred embodiment of the present invention, step 2 further includes: finely adjusting the positions of the two fork-shaped gratings so that the frequency-doubled vortex beams corresponding to the +1st order of diffraction coincide, where the +1st order frequency-doubled vortex beams are represented as...

[0020] In a preferred embodiment of the present invention, step 3 further includes: the nonlinear vortex light with mutually perpendicular polarization directions and opposite topological charges generated in step 2 passes through a quarter-wave plate in a frequency-harmonic band at a 45° angle to the polarization direction of the incident polarized light, specifically as follows:

[0021] In a preferred embodiment of the present invention, a nonlinear vector light field with arbitrary topological charge can be generated by selecting different nonlinear Raman-Nice diffraction orders. Where m is the selected diffraction order.

[0022] In another preferred embodiment of the present invention, a nonlinear photonic crystal structure is further designed, which can generate vector light fields with arbitrary ring number and arbitrary polarization state.

[0023] in is the topological charge of the fork-shaped photonic crystal, and m is the selected diffraction order. α is the azimuth coordinate, n is the radial exponent, r is the radial component of the cylindrical coordinate, r0 is the spot radius, and α0 is the initial phase.

[0024] This invention provides a simple, compact, and highly integrated nonlinear vector light field generation device and method based on a moiré nonlinear photonic crystal; by designing the structure of the moiré nonlinear photonic crystal, a vector light field with arbitrary polarization can be generated. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the fork-shaped nonlinear photonic crystal structure of NPC1 according to a preferred embodiment of the present invention, with the fork-shaped direction pointing upwards.

[0026] Figure 2 This is a schematic diagram of the fork-shaped nonlinear photonic crystal structure of NPC2 according to a preferred embodiment of the present invention, with the fork-shaped direction pointing downwards.

[0027] Figure 3 This is a schematic diagram of an experimental setup for generating a nonlinear vector light field based on a Mohr nonlinear photonic crystal. Detailed Implementation

[0028] The following description, with reference to the accompanying drawings, illustrates several preferred embodiments of the present invention to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0029] In the accompanying drawings, components with the same structure are indicated by the same numerical designation, and components with similar structures or functions are indicated by similar numerical designations. The dimensions and thicknesses of each component shown in the drawings are arbitrary, and the present invention does not limit the dimensions and thicknesses of each component. To make the illustrations clearer, the thickness of some components has been appropriately exaggerated in the drawings.

[0030] Example 1:

[0031] This embodiment provides a nonlinear vector light field generation device based on a moiré nonlinear photonic crystal, including a moiré nonlinear photonic crystal that satisfies nonlinear Raman-Nice diffraction and a quarter-wave plate. The nonlinear photonic crystal includes nonlinear photonic crystal I and nonlinear photonic crystal II. The moiré nonlinear photonic crystal is a fork-shaped nonlinear photonic crystal with the same topological charge polarized in a specific direction. The polarization direction of nonlinear photonic crystal I is along the y-direction, and the polarization direction of nonlinear photonic crystal II is along the x-direction. To obtain frequency-doubled vortex light with opposite topological charges, the fork-shaped nonlinear photonic crystal structure of nonlinear photonic crystal I has its fork-shaped direction facing upwards, and the fork-shaped nonlinear photonic crystal structure of nonlinear photonic crystal II has its fork-shaped direction facing downwards. These are placed sequentially according to moiré angles. When the fundamental frequency light passes through the moiré nonlinear photonic crystal, nonlinear Raman-Nice diffraction is generated, producing nonlinear vortex light with mutually perpendicular polarization directions and opposite topological charges in the same diffraction direction. After being superimposed by the quarter-wave plate, a nonlinear vector light field is formed.

[0032] Example 2:

[0033] This embodiment provides a method for generating a nonlinear vector light field with a topological charge of l. In this embodiment, the preferred nonlinear material is a 0.5 mm thick, 5 mol% MgO lithium niobate crystal cut along the z-axis. Both the upper and lower surfaces of the crystal are well polished, with the larger surface being the light-transmitting surface. First, a mask for a fork-shaped grating pattern with a topological charge of l is designed according to the required period. The fork-shaped structure has a size of 1 × 1 mm. 2 The polarization period is 50 μm, and the duty cycle is 1 / 2. Nonlinear photonic crystals can be fabricated using electron beam lithography, laser-induced electric field polarization, metal tip electric field polarization, and room-temperature electric field polarization, among others. Room-temperature electric field polarization is preferred in this experiment. Room-temperature electric field polarization induces periodic reversal of the domain structure within the ferroelectric crystal by applying a periodic electric field larger than the crystal's coercive field.

[0034] In the experiment, the polarization direction of the nonlinear crystal NPC1 is along the y-direction, and the polarization direction of NPC2 is along the x-direction. To obtain frequency-doubled vortex light with opposite topological charges, the fork-shaped nonlinear photonic crystal structure of NPC1 has its fork-shaped direction pointing upwards, while the fork-shaped nonlinear photonic crystal structure of NPC2 has its fork-shaped direction pointing downwards, as shown below. Figure 1 , 2 As shown. First, the sample is cleaned with an acetone and methanol solution to improve the adhesion between the sample and the photoresist. Then, ultraviolet lithography is performed, involving coating, exposure, and development to transfer the pattern from the photomask to the sample surface. Next, electrodes are deposited using ion beam sputtering, followed by polarization. After polarization, the light-transmitting surface is polished, requiring a polishing precision much smaller than the wavelength scale to ensure the uniformity of the generated light field wavefront. The experimental setup is as follows. Figure 3As shown. The experimental setup consists of a Mohr nonlinear photonic crystal satisfying nonlinear Raman-Nice diffraction and a quarter-wave plate. The input fundamental light is linearly polarized light with a wavelength of 1064 nm, polarized along the y-axis. This light is incident on the first fork-shaped nonlinear photonic crystal NPC1 with a topological charge of l. In the +1st order nonlinear Raman-Nice diffraction, it generates a frequency-doubled vortex light with a wavelength of 532 nm and a topological charge of -l, polarized along the y-axis. This can be represented as... The nonlinear coefficient corresponding to the nonlinear process is d 22 The fundamental pump light then passes through a second fork-shaped nonlinear photonic crystal NPC2 with a topological charge of l. In +1 order nonlinear Raman-Nice diffraction, it generates a frequency-doubled vortex light with a topological charge of +l and a wavelength of 532 nm along the x-polarization direction, which can be represented as follows: The nonlinear coefficient corresponding to the nonlinear process is -d 22 Since the nonlinear coefficients corresponding to the nonlinear interactions occurring sequentially through two nonlinear photonic crystals in the experiment are of the same magnitude, the intensities of the frequency-doubled vortex beams generated in the two experiments are identical. By fine-tuning the positions of the two fork-shaped gratings so that the frequency-doubled vortex beams corresponding to the +1st order of diffraction coincide, the frequency-doubled beams corresponding to the +1st order of diffraction can be expressed as...

[0035] After passing through a quarter-wave plate with a working wavelength of 532 nm at a 45° angle to the polarization direction of the incident polarized light, it can be represented as... The vector light field generated by the corresponding -1 order can be expressed as in Let these represent the polarization basis vectors of the x-axis and y-axis, respectively. It is the angle between the light polarization vector and the x-axis. When m = 1 and l = 1, the generated frequency-doubled vector light is radially polarized vector light.

[0036] Depending on the selected nonlinear Raman-Nice diffraction order, nonlinear vector light fields with arbitrary topological charges can be generated. Where m represents the selected diffraction order. Furthermore, a nonlinear photonic crystal structure can be designed to generate vector light fields with arbitrary ring numbers and arbitrary polarization states.

[0037] in is the topological charge of the fork-shaped photonic crystal, and m is the selected diffraction order. α is the azimuth coordinate, n is the radial exponent, r is the radial component of the cylindrical coordinate, r0 is the spot radius, and α0 is the initial phase.

[0038] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A nonlinear vector light field generation device based on a moiré nonlinear photonic crystal, characterized in that, The nonlinear vector light field generating device includes a moiré nonlinear photonic crystal that satisfies nonlinear Raman-Nice diffraction and a quarter-wave plate. The moiré nonlinear photonic crystal consists of two fork-shaped nonlinear photonic crystals with the same topological charge polarized in a specific direction, placed sequentially according to moiré angles. When the fundamental frequency light passes through this moiré nonlinear photonic crystal, nonlinear Raman-Nice diffraction is generated, producing nonlinear vortex light with mutually perpendicular polarization directions and opposite topological charges in the same diffraction direction. After being superimposed by the quarter-wave plate, a nonlinear vector light field is formed. The fork-shaped nonlinear photonic crystal includes nonlinear photonic crystal I and nonlinear photonic crystal II, wherein the polarization direction of nonlinear photonic crystal I is along the y-direction, and the polarization direction of nonlinear photonic crystal II is along the x-direction. To obtain frequency-doubled vortex light with opposite topological charges, the fork-shaped nonlinear photonic crystal structure of nonlinear photonic crystal I has an upward fork direction, and the fork-shaped nonlinear photonic crystal structure of nonlinear photonic crystal II has a downward fork direction.

2. A method for generating a nonlinear vector light field based on a Moiré nonlinear photonic crystal, characterized in that, The method for generating nonlinear vector light fields includes the following steps: Step 1: Prepare two fork-shaped nonlinear photonic crystals with the same topological charge polarized in a specific direction; Step 2: Place the fork-shaped nonlinear photonic crystals sequentially at a certain Mohr angle. When the fundamental frequency light passes through the Mohr nonlinear photonic crystal, nonlinear Raman-Nice diffraction is generated, and nonlinear vortex light with mutually perpendicular polarization directions and opposite topological charges is generated in the same diffraction direction. Step 3: The nonlinear vortex lights with mutually perpendicular polarization directions and opposite topological charges generated in Step 2 are superimposed through a quarter-wave plate to generate a nonlinear vector light field; the fork-shaped nonlinear photonic crystal in Step 1 includes nonlinear photonic crystal I and nonlinear photonic crystal II, wherein the polarization direction of nonlinear photonic crystal I is along the y-direction and the polarization direction of nonlinear photonic crystal II is along the x-direction. The fork-shaped nonlinear photonic crystal is cut in the z-direction and the upper and lower surfaces are polished to obtain the sample; Fork-shaped nonlinear photonic crystals were prepared using electron beam lithography, laser-induced electric field polarization, metal tip electric field polarization, and room temperature electric field polarization. Design the topology load according to the required period. A mask for a fork-shaped grating pattern; The pattern on the mask is transferred to the sample surface; then, electrodes are deposited using ion beam sputtering, and finally polarized; after polarization, the light-transmitting surface is polished; step 2 also includes: The fork-shaped nonlinear photonic crystal structure of nonlinear photonic crystal I has the fork-shaped direction pointing upwards, while the fork-shaped nonlinear photonic crystal structure of nonlinear photonic crystal II has the fork-shaped direction pointing downwards.

Images