CN207281390U - The system for producing local score rank Bezier vortex beams - Google Patents

Abstract

The utility model relates to a system for generating local fractional Bessel vortex beams, which is designed to obtain vortex beams whose topological charges on the transmission direction axis change continuously with distance and with wavelength. The system for generating local fractional-order Bessel vortex beams of the utility model includes: sequentially setting on the beam transmission path to expand the beams, so that the spot size of the beams after the beam expansion process can cover the expanded beams of the spiral slits A mirror and a spiral slit structure; wherein, the spiral slit structure, the spiral slit structure is an optical element that is provided with a light-transmitting, notched spiral slit and the rest of the spiral slit is opaque. Longitudinal manipulation techniques such as the present invention can address many of the challenges faced in remote sensing and multi-data communications and even data encryption.

Description

A system for generating localized fractional Bessel vortex beams

technical field

The utility model relates to a system for generating local fractional order Bessel vortex beams.

Background technique

A vortex beam is a beam with a helical phase distribution, with a phase factor exp[ilθ] in its expression, and each photon in the beam carries an orbital angular momentum of l, where l is called the topological charge. Since the vortex beam has an orbital angular momentum l, the orbital angular momentum carried by it can be transferred to the particles to drive the particles to rotate, and can also realize the capture and translation of micron and submicron particles. People vividly call this tool "" Optical Wrench". In addition, vortex beams also have a great application prospect in information encoding. Information can be encoded and transmitted by using the orbital angular momentum of vortex beams. This new encoding method has many unique advantages: (1) Since the value of the topological charge l can be an integer, zero, or even a fraction, it has a higher encoding ability. (2) It has higher confidentiality. Therefore, it is of great significance to measure the topological charge of vortex beams. Based on the above characteristics, vortex beams have great application prospects in driving particle rotation, information encoding, biomedicine, and optical information transmission.

The designer is actively researching and innovating in order to create a system for generating local fractional Bessel vortex beams, making it more valuable in industry.

Utility model content

In order to solve the above technical problems, the purpose of this utility model is to provide a vortex beam in which the topological charge varies continuously with the transmission distance in the transmission direction, and a vortex beam in which the topological charge varies with the wavelength. A system for generating localized fractional Bessel vortex beams.

In order to achieve the purpose of the above-mentioned utility model, the method for generating a local fractional Bessel vortex beam in the utility model includes: expanding the beam sequentially arranged on the beam transmission path, so that the spot size of the beam after the beam expansion process can be A beam expander covering a helical slit and a helical slit structure;

Among them, the spiral slit structure, the spiral slit structure is provided with a light-transmitting, notched spiral slit on it and the rest of the other parts of the spiral slit are opaque optical parts, the light-transmitting, notched spiral slit The radius of satisfies the following formula

In the formula, r ₀ is the radius of the minimum radius point on the light-transmitting and notched spiral slit, α is the angle between other points on a spiral light-transmitting slit and the point at the minimum radius, and N is a fixed value;

After the expanded beam passes through the spiral slit structure, a vortex in which the topological charge changes continuously with the transmission distance in the transmission direction and the topological charge changes with the wavelength in the transmission direction is generated behind the spiral slit structure. rotating beam.

Further, it also includes a digital sensor arranged on the observation plane behind the spiral slit structure, and the digital sensor records the spot shapes at different distances from the spiral slit structure.

Further, the digital sensor is set to record topological charges at z=1m, z=1.14m, z=1.34m, z=1.56m, z=1.89m from the transmission distance of the spiral slit structure as m=2, m =1.17, m=1.5, m=1.3, m=1 vortex beam.

Further, the transmissive spatial light modulator is loaded with transparent and notched spiral slits and opaque parts to form the spiral slit structure.

By means of the above scheme, the system for generating local fractional Bessel vortex beams of the present invention has at least the following advantages:

The utility model is provided with a spiral slit structure, and the expanded beam passes through the spiral slit structure. When a beam of plane wave is incident on the screen, the angle increments of two similar points on the incident wave along the slit are respectively Δα,(r _α ,α), (r _α +Δα,α+Δα), after different distances, the phase difference to the point (0,0,z) on the observation plane is Δθ=2πΔρ/λ, where Δρ =ρ _α +Δα-ρ _α , if Δρ=lλΔα/2π the phase shift on the entire slit is constant. A vortex beam with a topological charge of l can be obtained on the observation plane, and the center topological charge of the generated vortex beam is inversely proportional to the distance in the propagation distance. Therefore, the utility model can not only obtain the vortex beam whose topological charge varies continuously with the transmission distance in the transmission direction, but also obtain the vortex beam whose topological charge varies with the wavelength.

The above description is only an overview of the technical solution of the utility model. In order to understand the technical means of the utility model more clearly and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiment of the utility model with accompanying drawings. back.

Description of drawings

Fig. 1 is a schematic diagram of a system for generating local fractional Bessel vortex beams according to the present invention; wherein: 1, a laser; 2, a beam expander; 3, a transmissive spatial light modulator; 4, a wavefront detector;

Fig. 2 is the slit structural diagram of the system of the utility model that produces the local fractional order Bessel vortex beam;

Fig. 3 is a schematic diagram of the system for generating local fractional Bessel vortex beams of the present invention and the spiral slits actually loaded on the transmission spatial light modulator and various parameters; the black plane is the added spiral slit, The gray plane is the observation plane.

Detailed ways

Below in conjunction with accompanying drawing and embodiment, the specific embodiment of the utility model is described in further detail. The following examples are used to illustrate the utility model, but not to limit the scope of the utility model.

Explanation: The topological charge of the vortex beam in the transmission process is conserved. In this utility model, the change of the topological charge in the local area on the central axis is aimed at. Therefore, the change of the topological charge mentioned in the utility model with the transmission distance is the change of the local area on the central axis, which is called the local fractional order.

The utility model aims at the continuous change of the topological charge in the distance from the center of the transmission shaft, which means that for the required topological charge, the corresponding topological charge can be obtained only by changing the distance. and retain its non-diffractive properties. And the wavelength can be changed to obtain the required topological charge.

Example 1

In this embodiment, the system for generating local fractional Bessel vortex beams includes:

Laser 1, the laser is a solid-state laser of 100mw, and the laser wavelength emitted by it is 532nm;

Beam expander 2, a beam expander system used to expand the laser beam emitted by the laser, the spot size after beam expansion needs to be larger than the size of the spiral slit;

Spiral slit structure 3: The spiral slit structure is shown in Figure 2, the white is the slit, which is transparent, and the black is the opaque part, and its radius needs to conform to the formula Where r ₀ is the radius of the smallest radius on the spiral slit, α is the angle between other points on a spiral slit and the point of the smallest radius, N is a fixed value, in practical application, the value of N It is necessary to consider the wavelength λ of the light source, the range of the distance z between the expected observation plane and the spiral slit structure, and the range of the topological charge size l to be obtained, and finally satisfy the relationship between N=l×z×λ; r ₀ and N Satisfy

In the present embodiment, let r ₀ =0.028mm, and α is the angle between other points on a helical slit and the point at the minimum radius, because let the wavelength λ be 532nm, let l=2, z=4000/ lmm.

Example 2

In this embodiment, the system for generating local fractional Bessel vortex beams, on the basis of Embodiment 1, also includes a digital sensor, that is, an electronic coupling element, which is used to record the spot shape at different distances, and confirm whether the continuous change is obtained. topological charge. When the beam expanded light passes through the helical slit structure, the topological charges can be observed at the transmission distance z=1m, z=1.14m, z=1.34m, z=1.56m, z=1.89m respectively m=2, m =1.17, m=1.5, m=1.3, m=1 vortex beam. Among them, the phase of the vortex beam can be measured by a wavefront detector.

The working principle of each of the above-mentioned embodiments:

A zero-order Bessel beam can be thought of as the Fourier transform of an annular slit, and thus, the first time a Bessel beam was observed was by placing an annular slit in the focal plane of a convex lens. When a monochromatic plane wave is incident on a screen with an annular slit, in the direction of propagation, the transmitted wave will undergo the same phase shift at the same distance after passing through the ring. This is why a bright spot can be obtained in the center of the spot, that is, it is actually a zero-order Bessel beam. But if the annular slit is destroyed and becomes a helical slit, then in the axial field of the observation plane, the transmitted wave will undergo different phase transfers from different parts of the helical slit. That is, a continuous phase shift is produced along the helical slit, and a phase singularity can be seen on the optical axis.

Construct a slit where r _α and α are the radius and angle, respectively, and r ₀ is the initial radius of the helical slit. ρ _α is the distance from point (r _α ,α,0) to (0,0,z) on the viewing plane. When a plane wave is incident on the screen, the angle increments of two similar points on the incident wave along the slit are Δα, (r _α , α), (r _α + Δα, α + Δα), respectively, after different The phase difference of reaching the point (0,0,z) on the observation plane after a distance is Δθ=2πΔρ/λ, where Δρ=ρ _α +Δα-ρ _α , if Δρ=lλΔα/2π then the phase on the entire slit transfer is constant. This means that the closed loop on the axis of the phase front at the observation plane is 2πl. That is to say, there will be an optical vortex on the observation plane, and l is the topological charge, in order to obtain the spiral phase, a spiral slit is constructed, and its mathematical expression is:

In this way, a vortex beam with topological charge l can be obtained on the observation plane. In addition, after the product of the above expression lz is fixed, l at the center will gradually decrease as the propagation distance increases. That is to say, the topological charge of the center of the generated vortex beam is inversely proportional to the distance in the propagation distance.

When the notch of the spiral slit is much smaller than the radius, the spiral slit can be regarded as an annular slit to some extent. Therefore, the vortex beam can be approximated as a Bessel vortex beam. In the Fresnel approximation, the complex amplitude of the diffracted beam after traveling z distance can be obtained by the following diffraction formula

where T(x,y) is the aperture function of the helical slit.

Through the above expression, the light intensity and phase changes of the vortex beam transmitted with the distance can be simulated. However, the expression of the spiral slit can be proved experimentally by using the program to simulate drawing and loading it on the spatial light modulator.

Since the value of the topological charge can be an integer, zero, or even a fraction, it has a higher encoding ability. Therefore, it also has higher confidentiality. Therefore, it is of great significance to measure the topological charge of vortex beams. Based on the above characteristics, vortex beams have great application prospects in driving particle rotation, information encoding, biomedicine, and optical information transmission. The utility model can not only obtain the vortex beam whose topological charge varies continuously with the distance on the axis of the transmission direction, but also obtain the vortex beam whose topological charge varies with the wavelength. Such vertical manipulation techniques can address many of the challenges faced in remote sensing and multi-data communication and even data encryption.

The above is only a preferred embodiment of the utility model, and is not intended to limit the utility model. It should be pointed out that for those of ordinary skill in the art, they can also do Several improvements and modifications are made, and these improvements and modifications should also be regarded as the protection scope of the present utility model.

Claims (4)

1. A system for generating a local fractional Bessel vortex beam, characterized in that it comprises: beam expansion is arranged sequentially on the beam transmission path, so that the spot size of the beam after the beam expansion process can cover the spiral Slit beam expander and helical slit structure; Among them, the spiral slit structure, the spiral slit structure is provided with a light-transmitting, notched spiral slit on it and the rest of the other parts of the spiral slit are opaque optical parts, the light-transmitting, notched spiral slit The radius of satisfies the following formula <mrow><msub><mi>r</mi><mi>&amp;alpha;</mi></msub><mo>=</mo><msup><mrow><mo>(</mo><msup><msub><mi>r</mi><mn>0</mn></msub><mn>2</mn></msup><mo>+</mo><mfrac><mrow><mi>N</mi><mi>&amp;alpha;</mi></mrow><mi>&amp;pi;</mi></mfrac><mo>)</mo></mrow><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msup></mrow> In the formula, r ₀ is the radius of the minimum radius point on the light-transmitting and notched spiral slit, α is the angle between other points on a spiral light-transmitting slit and the point at the minimum radius, and N is a fixed value; After the expanded beam passes through the spiral slit structure, a vortex in which the topological charge changes continuously with the transmission distance in the transmission direction and the topological charge changes with the wavelength in the transmission direction is generated behind the spiral slit structure. rotating beam. 2. The system producing local fractional Bessel vortex beam according to claim 1, is characterized in that, also comprises the digital sensor that is arranged on the observation plane behind the spiral slit structure, and described digital sensor records distance from spiral slit Spot shapes at different distances from the slit structure. 3. The system for generating local fractional Bessel vortex beams according to claim 2, wherein the digital sensor is arranged at a transmission distance z=1m away from the spiral slit structure, z=1.14m, z= At 1.34m, z=1.56m, and z=1.89m, vortex beams with topological charges of m=2, m=1.17, m=1.5, m=1.3, and m=1 were recorded. 4. The system for generating local fractional Bessel vortex beams according to claim 1, wherein the transmissive spatial light modulator is loaded with light-transmitting, notched spiral slits and opaque parts to form the spiral Slit structure.