CN108333789A - A kind of the vortex light preparation method and device mostly logical based on matrix spiral phase plate - Google Patents

Abstract

The invention relates to a method and device for preparing vortex light based on matrix spiral phase plate multipass. The vortex light is a special light field with a helical wavefront, and the matrix helical phase plate is a transparent optical diffraction element used to prepare the vortex light. The beam with Gaussian distribution passes through the matrix spiral phase plate to obtain vortex light, and the direction of the vortex light is changed by a mirror with an incident angle of 0 degrees, so that the vortex light passes through the matrix spiral phase plate in the reverse direction according to the original optical path, and the topological charge is carried out in the form of negative numbers Double; on this basis, the loss generated when passing through the beam splitter is reduced by controlling the polarization state of the beam. A vortex light preparation device based on matrix helical phase plate multipass is proposed, which includes laser, polarizer, polarizing beam splitter, matrix helical phase plate, quarter wave plate, mirror and image sensor. The method has the advantages of simple optical path, low cost and high conversion efficiency, belongs to the field of vortex light preparation, and can be applied to the vortex light preparation of large topological charges.

Description

Method and device for preparing vortex light based on matrix helical phase plate multi-pass

technical field

The invention relates to a method and device for preparing vortex light based on matrix spiral phase plate multipass. The vortex light is a special light field with a helical wavefront, and the matrix helical phase plate is a transparent optical diffraction element used to prepare the vortex light. The vortex light with large topological charge can be obtained by the multi-pass method of the matrix spiral phase plate. The method has simple optical path and high efficiency, belongs to the field of vortex light preparation, and can be applied to the preparation of vortex light with large topological charge.

technical background

Vortex light is a kind of light beam whose equiphase plane is helical and has orbital angular momentum. The phase of the vortex light contains the angular phase factor exp(ilθ), where l is the orbital angular momentum topological charge of the vortex light, and θ is the azimuth angle. The commonly used preparation methods of vortex light include mode conversion method, computational holography method, spatial light modulator method, Q plate method and matrix spiral phase plate method. The mode conversion method is low in cost and does not have strict restrictions on the optical power, but this method has extremely high requirements for the accuracy of the optical path construction; the computational holography method can theoretically prepare large topological charge vortex light, but the conversion efficiency of this method is low, The vortex light of a single mode cannot be generated; the spatial light modulator is small in size and the quality of the vortex light prepared is high, but the device is expensive and has limitations on the incident angle and incident light power; the Q-plate structure is simple, the response speed is fast, and it is convenient Fast, but currently only vortex lights with small topological charges can be prepared.

The matrix spiral phase plate method can make up for the shortcomings of the above preparation methods. This method has high energy conversion efficiency and can prepare vortex lights with large topological charges. This method has a simple structure and is widely used, but once the matrix helical phase plate is fabricated, it can only generate vortex light with a specific topological charge. To prepare vortex lights with various topological charges, it is necessary to purchase multiple combinations of vortex light matrix spiral phase plates, which will increase the laboratory’s financial burden. If the existing matrix spiral phase plates can be used to prepare various topological charges, it will greatly improve the experimental results. Room device utilization efficiency.

Contents of the invention

The technical solution of the present invention is to solve the problem that the existing matrix spiral phase plate can only prepare specific topological charge vortex light, and propose a method and device for preparing vortex light based on matrix spiral phase plate multi-pass. The optical path of this method is simple , low cost, high conversion efficiency, and can easily double the number of vortex optical topological charges that can be obtained from the current matrix spiral phase plate.

The technical solution of the present invention is: the present invention relates to a method and device for preparing vortex light based on matrix spiral phase plate multi-pass. First, a beam with a Gaussian distribution passes through the matrix spiral phase plate, and the outgoing light can obtain a spiral phase. That is, the vortex light with the corresponding topological charge is obtained, and secondly, the rotation direction of the vortex light is changed through a mirror with an incident angle of 0 degrees, so that the vortex light passes through the matrix spiral phase plate in reverse according to the original optical path, so that the topological charge of the vortex light is The negative number form is doubled to complete the preparation of vortex light; on the basis of this method, a vortex light preparation device based on matrix helical phase plate multi-pass is proposed, which includes a laser (1), a polarizer (2), a polarization beam splitter prism (3), matrix spiral phase plate (6), quarter-wave plate (7), mirror 1 (4), mirror 2 (5), mirror 3 (8), mirror 4 (11), A beam splitting prism (9) and an image sensor (10). The rotation direction of the vortex light is changed by the mirror 3 (8), so that the topological charge number of the vortex light changes from l to -l, and the helical phase factor exp(-ilθ) is obtained when passing through the matrix spiral phase plate in reverse, and the topological charge is completed when it exits The negative number of the number is doubled, that is, the topological charge number of the vortex light prepared at the time of exit is -2l, where θ is the azimuth angle. The polarization state control in the process of doubling the vortex optical topological charge is completed by the polarizer (2), the polarization beam splitter prism (3), the quarter-wave plate (7) and the mirror 3 (8), theoretically, making The vortex light is completely reflected by the polarization beam splitter prism (3), which improves the preparation efficiency of the vortex light and reduces loss. The schematic diagram of the device is shown in FIG. 1 .

Principle of the present invention is:

The polarization state of the vortex light after passing through the polarizer is linearly polarized light, and the incident quarter-wave plate produces e light and o light in the same phase, and the phase difference is φ when it exits, and the amplitude is A _e and A _o respectively. Two vortex lights, the trajectory equation of the composite light vector endpoint is:

The optical path difference produced by the quarter-wave plate is Δ=(m+1/4)λ, m=0, ±1, ±2,..., and its phase difference is:

φ=(2m+1)π/2, m=0, ±1, ±2, ... (2)

Substitute formula (2) into (1) to get:

This equation is a standard elliptic equation, when the incident light is π/4, The outgoing light is a circularly polarized light, and its equation is:

Among them, E ₁ and E ₂ are expressions of the amplitude of vortex light.

After the Gaussian light passes through the polarizer, its polarization state is linearly polarized, and after entering the polarization beam splitter, it is divided into two columns of light whose polarization states are perpendicular to each other. Wherein, the transmitted light beam is changed from a quarter-wave plate to circularly polarized light (the quarter-wave plate is set to 45 degrees), and the circular polarization rotation is changed after being reflected by a mirror. When passing through the quarter-wave plate again, the polarization state of the beam becomes linearly polarized, but it is perpendicular to the polarization direction before entering the quarter-wave plate for the first time, so that the second time by the quarter-wave plate The light beam emitted by the sheet is completely reflected by the polarization beam splitter prism, which greatly improves the preparation efficiency of vortex light. The schematic diagram of the device is shown in Figure 1.

Assuming that a beam of Gaussian light is incident on the matrix helical phase plate, the expression before the incident is:

Among them, E ₀ is the amplitude, ω ₀ is the radius of the light waist, ω(z) is the light intensity down to When the beam radius, r is the distance from the center of the optical axis. When Gaussian light emerges from the matrix spiral phase plate for the first time, its expression is:

When the vortex light is reflected by the mirror, its expression is:

When the vortex light passes through the matrix spiral phase plate in reverse, its expression is:

At this time, the topological charge of the outgoing vortex light is -2l.

When setting up the device, pay attention to the distance between the reflector 3 (8) and the matrix spiral phase plate (6). The distance between the two should not be too close in order to reduce the optical path, because Gaussian light obtains the spiral phase factor. The singularity will not be generated immediately, and it needs a certain distance to form gradually. The simulated light intensity distribution of Gaussian light after obtaining the helical phase factor of 1mm, 1cm, and 10cm is shown in Figure 2.

Compared with existing solutions, the scheme of the present invention has the main advantages of:

(1) The optical path is simple, and there is no high precision requirement for the construction of the optical path.

(2) The cost is low, and the same matrix spiral phase plate can be reused to double the topological charge by using this method.

(3) The conversion efficiency is high. The control of the polarization state by the experiment and the device greatly improves the conversion efficiency of the prepared vortex light.

(4) It effectively compensates for the shortcoming that the matrix spiral phase plate can only generate vortex light with a specific topological charge once it is fabricated, and provides a reliable method for the flexible use of the matrix spiral phase plate.

Figure 1 is a schematic diagram of the preparation of vortex light;

Figure 2 is a simulation diagram of the vortex light intensity distribution when the topological charges are 1 and 10;

Fig. 3 is the vortex light intensity distribution diagram of 10, 12, 14, 16 topological charges produced by multi-pass;

Figure 4 is the interference diagram of vortex light and reference light generated by multi-pass with topological charges of 10, 12, 14, and 16;

specific implementation plan

The implementation object of the present invention is a matrix spiral phase plate. Taking the VPP-m633 produced by RPC PHOTONICS as an example, the specific implementation steps are as follows: first, the Gaussian beam is produced by the laser (1), and the polarization of the Gaussian beam is guaranteed by the polarizer (2). The state is linearly polarized, and the light beam enters the polarization beam splitter prism (3) after being emitted by the polarizer, and is divided into two beams of linearly polarized light whose polarization states are perpendicular to each other, and one is reflected by the reflector 4 (11) and enters the beam splitter prism (9) as The reference light is to be interfered with the vortex light; secondly, another branch enters the matrix spiral phase plate (6) to make the Gaussian light carry the spiral phase factor _exp(ilθ) , and the vortex light enters the quarter-wave plate ( 7), so that the polarization state of the light beam is circularly polarized, when the light beam passes through the mirror 3 (8), the helical phase factor exp(ilθ) of the reflected light becomes exp(-ilθ), and the circular polarization state is reversed, Where l is the topological charge, θ is the azimuth angle. Then, after the beam passes through the quarter-wave plate (7) again, its polarization state becomes linearly polarized and is perpendicular to the linear polarization direction before incidence, and the vortex light continues to transmit through the matrix spiral phase plate (6) for topological charge When the negative number doubles, its spiral phase factor changes from exp(-ilθ) to exp(-2ilθ), and its topological charge is -2l. Finally, the prepared vortex beam enters the beam splitter (9) through the mirror 4 (11), and after interference with the reference light, the image sensor (10) detects the interference fringe to judge the quality of the doubled vortex beam , the interference fringes of the vortex light with the topological charges of 10, 12, 14, and 16 and the reference light are shown in Fig. 4 .

The contents not described in detail in the present application belong to the prior art known to those skilled in the art.

Claims (3)

1. A method and device for preparing vortex light based on matrix helical phase plate multi-pass. First, a beam with Gaussian distribution passes through the matrix helical phase plate, and the outgoing light can obtain a helical phase, that is, a vortex with corresponding topological charge can be obtained. The vortex light, secondly, changes the rotation direction of the vortex light through a mirror with an incident angle of 0 degrees, so that the vortex light passes through the matrix spiral phase plate in reverse according to the original optical path, so that the topological charge of the vortex light is doubled in the form of a negative number to complete the preparation of the vortex light; On the basis of this method, a vortex light preparation device based on matrix helical phase plate multi-pass is proposed, which includes laser (1), polarizer (2), polarization beam splitter prism (3), matrix helical phase plate ( 6), quarter-wave plate (7), reflector 1 (4), reflector 2 (5), reflector 3 (8), reflector 4 (11), dichroic prism (9) and image sensor ( 10). 2. the vortex light preparation method and device based on matrix helical phase plate multipass according to claim 1, is characterized in that: change the vortex light hand direction by reflector 3 (8), make the vortex light topological charge change from 1 The number is -l, and the helical phase factor exp(-ilθ) is obtained again when passing through the matrix helical phase plate in reverse, and the negative number of the topological charge is doubled at the time of exit, that is, the topological charge of the vortex light prepared at the time of exit is -2l, where θ is the azimuth angle. 3. the vortex light preparation method and device based on matrix spiral phase plate multipass according to claim 1, is characterized in that: through polarizer (2), polarizing beam splitter prism (3), quarter-wave plate ( 7) and reflector 3(8) complete the polarization state control in the process of doubling the topological charge of vortex light. In theory, the vortex light is completely reflected by the polarization beam splitter prism (3), which improves the preparation efficiency of vortex light and reduces the loss .