CN100592137C - Device for Generating Vector Beam with Arbitrary Polarization Distribution - Google Patents

Abstract

The invention provides a generating device for vector beams with arbitrary polarization distribution, in which a spatial light modulator controlled by a computer, a first lens, a filter, two quarter-wave sheet, second lens and Rochi grating; the spatial light modulator is located on the front focal plane of the first lens, and the filter is set on the back focal plane of the first lens; the filter is also located on the front focal plane of the second lens; the Rochi grating is located on the second The back focal plane of the lens. Two quarter-wave plates are placed against the backlight side of the filter. The invention has the advantage of being able to generate arbitrary vector beams, and more importantly, the device described in the invention can also dynamically generate vector beams in real time. Moreover, the device greatly reduces the influence of coherent noise on beam quality, can generate high-quality vector beams, and the generation method is real-time and dynamic.

Description

Device for Generating Vector Beam with Arbitrary Polarization Distribution

technical field

The invention relates to a generating device for a vector beam, in particular to a dynamic and real-time generating device for a vector beam with arbitrary polarization distribution.

Background technique

Light waves contain information such as frequency, phase, intensity, and polarization. The light beams we use for scientific research are usually unpolarized light or polarized light in the form of linear polarization, circular polarization, and elliptical polarization. The polarization characteristics of these beams are relatively simple, and their polarization distribution is uniform in the plane perpendicular to the beam propagation direction, which is called a uniformly polarized beam. In general, the scalar beam model can be used to analyze and describe its propagation process. When dealing with problems related to these beams, we generally use scalar theory, so such beams can be collectively referred to as scalar beams. In order to make better use of the polarization information of light, the concept of vector beam is proposed. Different from scalar beams, vector beams refer to a type of beams whose polarization forms are complex or whose propagation behavior is sensitive to the vibration direction. The related problems of such beams must be dealt with by vector theory.

In 1993, EG Churin and others at the Institute of Applied Physics in Darmstadt, Germany obtained two vector beams with configurable polarization states (EG Churin, J.Hofeld, and T.Tschudi, "Polarization configurations with singular point formed by computer generated holograms ", Opt. Commun 99, 13-17 (1993)). They use a beam splitter to split a beam of linearly polarized light into two beams whose polarization directions are perpendicular to each other, and then use a 1/4 wave plate to convert the two beams of linearly polarized light into left-handed circularly polarized light and right-handed circularly polarized light, respectively. Two beams of circularly polarized light are symmetrically incident on the prefabricated computational holographic grating, and the grating is adjusted so that the +1st-order diffracted wave of one beam of incident circularly polarized light and the -1st-order diffracted wave of the other circularly polarized light can be coherently superimposed to produce Vector light beam. The disadvantage of this method is that each computational hologram can only generate a corresponding vector beam. To generate vector beams with different polarization states, it is necessary to redesign and make a computational hologram and readjust the optical path, and the generation process is an offline working method. In the following time, due to the difficulty of generating vector beams and the lack of full understanding of their advantages, the research on vector beams was at a standstill. Until 2000, KS Youngworth and TGBrown of the Optical Research Center of the University of Rochester in the United States published an article on Opt.Express, and theoretically calculated the properties of two special vector beams under the focus of a high numerical aperture objective lens, which attracted attention. The results of (KS Youngworth and TGBrown, Opt. Express 7, 77 (2000)). One of the special vector beams, the radially polarized light, can obtain a strong non-propagating longitudinal field component after being focused by a lens with a high numerical aperture, thereby forming a sharp focus, while the other special vector beam, the rotated polarized light, can be focused by A hollow light field is obtained. These theoretical results have aroused widespread attention in the optical field, and optical workers have also begun to invest a lot of energy in the study of vector beams, especially its generation methods. In 2002, Israeli scientist Z.Bomzon and others published an article on Opt.Lett. Using a sub-wavelength dielectric grid with a specific structure that varies with space, two types of radially polarized beams and helical polarized beams were obtained at a wavelength of 10.6 microns. Special vector beams (Z. Bomzon et al, Optics Letters, 27, 285 (2002)). In 2002, M.Neil and others from the University of Cambridge in the United Kingdom designed an optical system using a Wollaston prism and a binary ferroelectric spatial light modulator. A series of vector beams between (MAANeil et al, Optics Letters, 27, 1929 (2002)). In 2005, K.Toussaint et al. of the University of Chicago used a specially designed optical system mainly composed of two diffractive optical elements to generate a vector beam similar to the work of M.Neil (KCToussaint et al, Optics Letters, 30, 2846 (2005)). In 2005, Sato et al. from Tohoku University in Japan used a conical Brewster to design a laser resonator to generate a radially polarized beam. And then in 2006, using the birefringence properties of C-cut Nd:YVO ₄ crystals, a special laser cavity was designed to generate radially polarized beams (Y.Kozawa and S.Sato, Optics Letters, 30, 3063(2005 ); K. Yonezawa, Y. Kozawa, and S. Sato, Optics Letters, 31, 2151 (2006)). In March 2007, C. Maurer and others from the Medical University of Innsbruck in Austria published an article in New Jour.Phys. They used a Wollaston prism and a reflective spatial light modulator to form an optical system to generate a Laguerre-Gaussian beam like this A special class of vector beams (C. Maurer et al,, New J. Phys. 9, 78 (2007)).

In the above studies, the types of vector beams generated are limited, usually of a certain type, such as Laguerre-Gaussian beams, and when different types of vector beams need to be generated, a large adjustment must be made to the optical path , these limitations increase the technical difficulty of generating vector beams and the complexity of experimental operations, which is not conducive to the wider application of vector beams. Vector beams have important application requirements in the fields of biology, medicine, high-energy physics, material science, and precision measurement.

Contents of the invention

Purpose of the invention: In order to overcome the deficiency that the existing technology cannot simultaneously generate multiple arbitrary polarization distribution vector beams in the same optical path, the present invention provides a vector beam that can obtain arbitrary polarization state distribution and coexistence of multiple polarization modes in the same optical path A device for generating vector beams with arbitrary polarization distribution output by beams.

Technical solution: The present invention provides a device for generating vector beams with arbitrary polarization distribution, in which a spatial light modulator controlled by a computer, a first lens, a double hole filter, two A quarter-wave plate, a second lens, and a Ronchi grating (i.e. Rochi grating); the spatial light modulator is positioned at the front focal plane of the first lens, and a dual-hole filter is arranged on the rear focal plane of the first lens; the dual-hole filter At the same time, it is located on the front focal plane of the second lens; the Rochi grating is located on the back focal plane of the second lens. Two quarter-wave plates are placed close to the side of the backlight source of the dual-hole filter, and the optical axes of the two quarter-wave plates are in the x and y directions respectively.

The computer-generated computational hologram is loaded onto the spatial light modulator to form a computational holographic grating, thereby adjusting the phase difference between the ±1st-order diffracted light waves in real time, thereby controlling the polarization state distribution of the output vector beam.

The light source for generating polarized light is composed of a laser and a first linear polarizer, and the first linear polarizer can make the linear polarization state of the beam emitted by the laser more pure.

A rotating frosted glass is arranged between the laser and the first linear polarizer, and its function is to destroy the spatial coherence of light, suppress coherent speckle noise, and make the generated beam more uniform.

In order to make the generation of the vector beam more efficient, the Ronchi grating adopts a phase type Ronchi grating.

Beneficial effects: the present invention has the advantage of being able to generate arbitrary vector beams, and more importantly, the device described in the present invention can also dynamically generate vector beams in real time. Moreover, the device greatly reduces the influence of coherent noise on beam quality, and can generate high-quality vector beams. The generation device can regulate the polarization state of light, which is helpful to excavate and expand the polarization information of photons, so as to open up a new way for more comprehensive use of photon information. It also opens up broader application prospects for vector beams in the fields of biology, medicine, high-energy physics, material science, and precision measurement.

Description of drawings

Fig. 1 is a schematic diagram of the structural design of the present invention.

Fig. 2 is a diagram of a specific embodiment of the device of the present invention.

Fig. 3 is the generation of m=1 single-mode vector beam realized by the device of the present invention.

Fig. 4 is the generation of m=1 dual-mode vector beam realized by the device of the present invention.

Fig. 5 is the generation of a single-mode vector beam in which m is an integer realized by the device of the present invention.

Fig. 6 is the generation of a dual-mode vector beam in which m is an integer realized by the device of the present invention.

Fig. 7 shows the generation of vector beams in which m is a half-integer realized by the device of the present invention.

Fig. 8 is the generation of vector beams with different polarization state distributions realized by the device of the present invention.

Detailed ways

The present invention will be further explained below in conjunction with the accompanying drawings.

Example 1

As shown in Figure 1, the core of the generating device of the arbitrary polarization distribution vector light beam according to the present invention is that a spatial light modulator 2, a first lens 3, a Filter 4, two quarter-wave plates 5, second lens 6 and phase-type Ronchi grating 7; spatial light modulator 2 is located at the front focal plane of first lens 3, and the rear focal plane of first lens 3 is set Filter 4; filter 4 is located at the front focal plane of the second lens 6 at the same time; phase-type Ronchi grating 7 is located at the back focal plane of the second lens 6; two quarter-wave plates 5 are close to the backlight of the filter 4 Set aside. As shown in Figure 2, the complete optimal technical scheme of the generating device of the arbitrary polarization distribution vector beam of the present invention is as follows: the laser we use is the green laser 8 with a wavelength of 532 nanometers of Coherent Company, and the spatial light modulator is Sony Company The transmissive spatial light modulator 2 has a resolution of 1024x768, and the size of each pixel is 14 microns x 14 microns. We set up a 4f optical system to achieve this. This 4f system includes two confocally placed lenses L1 and L2 with a focal length of 400 mm, a spatial light modulator 2 placed on the front focal plane of L1, and a spatial light modulator 2 placed on the back focal plane of L1. The dual-hole filter 4, the λ/4 wave plate 5 close to each hole and the phase type Rochi grating 7 on the rear focal plane of the lens L2. Before the spatial light modulator 2, there is also a linear polarizer 9 for determining the polarization direction of the incident ray polarized light and a piece of rotating frosted glass 10 that destroys the spatial coherence of the light beam, and a laser beam expansion device as shown in Figure 2. three lenses. A linear polarizer 11 for inspecting the vector beam and a charge-coupled device 12 for detecting the vector beam are arranged behind the Rochi grating 7 . Loading the designed computational hologram onto the liquid crystal spatial light modulator 2 to generate the required holographic grating can provide specific phase differences for different diffracted light orders, which is the key to generating vector beams based on the light wave superposition method. A beam of linearly polarized light is incident on the spatial light modulator 2, and is divided into multi-level diffracted light waves after passing through the holographic grating, wherein the phases of the ±1st order diffracted light waves are always opposite. The ±1st-order diffracted light is extracted by the double-hole filter 4 on the L1 rear focal plane, and converted into left-handed circularly polarized light and right-handed circularly polarized light by the λ/4 wave plate 5, and then passed through the Rochi The grating 7 makes the two beams of left-handed and right-handed circularly polarized light re-superimposed collinearly, so that the desired vector beam can be obtained. The polarization state distribution of the vector beam can be detected and determined by the analyzer 11 and the charge-coupled device 12 .

其中ρ和分别为径向坐标和方位角坐标。显然，控制全息光栅的相移δ即可获得不同偏振分布的矢量光束。例如

时，其中m为整数，

是常数，则可生成偏振分布相对于光束中心对称的矢量光束，即柱对称矢量光束，m为非整数时，则是一种非柱对称矢量光束。The principle of light beam splitting and superposition is as follows: a beam of linearly polarized light whose vibration direction is at an angle of 45 degrees to the x-axis is incident on the spatial light modulator, and the spatial light modulator is loaded with a transmittance of t(x, y)= A computational holographic grating of [1+γcos(2πf ₀ x+δ)]/2, where γ and f ₀ are the modulation degree and spatial frequency of the grating, respectively, and δ is the phase shift of the grating stripes. The amplitude of the ±1st-order diffracted light of the grating after passing through the quarter-wave plates with two optical axes in the x and y directions can be expressed by the vector expressions of the x and y vibration components as Where A ₀ is an arbitrary constant factor. After collinear superposition through the diffraction of Rochi grating, the obtained output light can be expressed as

where ρ and are the radial and azimuth coordinates, respectively. Obviously, vector beams with different polarization distributions can be obtained by controlling the phase shift δ of the holographic grating. For example

, where m is an integer,

is a constant, then a vector beam whose polarization distribution is symmetrical with respect to the center of the beam can be generated, that is, a cylindrically symmetric vector beam, and when m is a non-integer, it is a non-cylindrically symmetric vector beam.

The 4f system we designed uses the self-decomposition and self-synthesis of the same beam to generate vector beams. The principle is simple, and the experimental system is easy to implement and easy to operate. The system allows low-coherence incident light, which can greatly reduce the impact of coherent noise on beam quality. The hologram generated by the computer is loaded on the spatial light modulator to form a holographic grating, and different holographic gratings can be generated by changing the computational hologram, providing a specific phase difference for the ±1st-order diffracted light, thereby generating the required vector beam, In principle, vector beams with arbitrary polarization distributions can be generated. Overcomes the limitations of existing technologies with limited variety in generating vector beams. Generating different vector beams does not require any changes to the optical path, only the projected computational hologram needs to be changed, which eliminates the shortcomings of other technologies that must adjust the optical path when generating different vector beams, and provides convenience for the application of vector beams.

Example 2

在四个实验结果中消光方向在竖直方向即

对应的情况是径向偏振的光束，消光方向在水平方向即的分布对应于旋向偏振的光束，消光方向在45度和135度方向对应两种柱对称偏振分布的矢量光束。此图表明，利用我们的4f系统实现了m＝1单模矢量光束的生成。图3中的符号含义：全息光栅的相移取为涡旋位相分布

时的矢量光束，其中

是常数，输出光束场强分布为

A0是常数。图3中第一栏为Polarization，给出矢量光束的偏振态分布；第二栏为CGH，Computer Generated Hologram，计算全息图，投影在空间光调制器上生成全息光栅；第三栏为不加检偏器(Analyzer)时的矢量光束强度分布图；第四栏为加上检偏器后的矢量光束强度分布图，用于检验矢量光束的偏振状态；第二列为

生成一种径向偏振光束；第三列为

生成一种偏振状态介于径向和旋向之间的矢量光束；第四列为生成一种旋向偏振光束；第五列为

生成一种偏振状态介于旋向和径向之间的矢量光束。The 4f optical system is built according to the principle in Figure 1, and the specific experimental system constructed on this basis is shown in Figure 2. Project the computational hologram (CGH) shown in the second column in Figure 3 onto the spatial light modulator, and the cylindrical symmetry vector corresponding to the polarization distribution shown in the first column in Figure 3 can be obtained at the CCD in Figure 2 beam. The beam intensities without linear polarizer 2 and with linear polarizer 2 inserted in front of the CCD are shown in columns 3 and 4 in Figure 3, and the dark spot in the center of the beam is caused by the singularity of the polarization state distribution uncertainty. When the linear polarizer 2 used as an analyzer is inserted in front of the CCD, there will be an extinction direction in the beam intensity distribution, and the extinction direction corresponds to

In the four experimental results, the extinction direction is in the vertical direction, namely

The corresponding situation is a radially polarized beam, and the extinction direction is in the horizontal direction, that is, The distribution of corresponds to the hand-polarized beam, and the extinction directions at 45 degrees and 135 degrees correspond to the vector beams of two kinds of cylindrically symmetric polarization distributions. This figure shows that m = 1 single-mode vector beam generation is achieved with our 4f system. The meaning of the symbols in Figure 3: the phase shift of the holographic grating is taken as the vortex phase distribution

When the vector beam, where

is a constant, the field intensity distribution of the output beam is

A0 is a constant. The first column in Figure 3 is Polarization, which gives the polarization state distribution of the vector beam; the second column is CGH, Computer Generated Hologram, which calculates a hologram, which is projected on the spatial light modulator to generate a holographic grating; the third column is no inspection The vector beam intensity distribution diagram of the polarizer (Analyzer); the fourth column is the vector beam intensity distribution diagram after adding the analyzer, which is used to check the polarization state of the vector beam; the second column is

generates a radially polarized beam; the third column is

Generates a vector beam with a polarization state between radial and handed; the fourth column is Generates a hand-polarized beam; the fifth column is

Generates a vector beam with a polarization state between handed and radial.

Example 3

外模是指分布于半径r＝r₀/2到r＝r₀之间的偏振分布模式，图4中的外模为偏振态可表示为

的偏振分布，其中A₀是常数。图4中第一栏-Polarization，给出矢量光束的偏振态分布；第二栏-CGH，Computer Generated Hologram，计算全息图，投影在空间光调制器上生成全息光栅；第三栏-不加偏振片时的矢量光束强度分布图；第四栏-加上偏振片后的矢量光束强度分布图，用于检验矢量光束的偏振状态；第二列——生成一种内模为径向偏振和外模对应于

的双模矢量光束；第三列——生成一种内模径向偏振和外模旋向偏振的双模矢量光束；第四列-生成一种内模径向偏振和外模对应于的双模矢量光束；第五列-生成一种内外模均为径向偏振，但是偏振态反向的双模矢量光束。The 4f optical system is built according to the principle in Figure 1, and the specific experimental system constructed on this basis is shown in Figure 2. By projecting the computational hologram shown in the second column of Fig. 4 on the spatial light modulator, the vector beam corresponding to the polarization distribution shown in the first column of Fig. 4 can be obtained at the CCD in Fig. 2 . The difference in the polarization state between the inner and outer modes leads to the appearance of a dark band at the boundary in the field intensity distribution, and the dark band gradually becomes clear with the increase of the polarization state difference between the inner and outer modes. Xiangshida's dark band is the clearest. Similar to Example 1, there is also the central singularity and the extinction direction after adding a linear polarizer. Here, the generation of m=1 dual-mode vector beams is realized by using our 4f system. Meaning of the symbols in Figure 4: The experimental results of a class of internal and external dual-mode beams with two polarization modes coexisting are given. The internal mode refers to a polarization distribution distributed between the radius r=0 to r=r ₀ /2 mode, in Figure 4 the internal modes are all radially polarized, and their polarization states can be expressed as

The external mode refers to the polarization distribution mode distributed between the radius r=r ₀ /2 to r=r ₀ , and the external mode in Fig. 4 is the polarization state, which can be expressed as

The polarization distribution of , where A ₀ is a constant. The first column in Figure 4 - Polarization, gives the polarization state distribution of the vector beam; the second column - CGH, Computer Generated Hologram, calculates the hologram, which is projected on the spatial light modulator to generate a holographic grating; the third column - no polarization The vector beam intensity distribution diagram of the film; the fourth column - the vector beam intensity distribution diagram after adding the polarizer, which is used to check the polarization state of the vector beam; the second column - generate an internal model for radial polarization and external polarization Modulus corresponds to

The dual-mode vector beam of the ; third column - generate a dual-mode vector beam with inner mode radial polarization and outer mode handed polarization; fourth column - generate an inner mode radial polarization and outer mode corresponding to The fifth column - generates a dual-mode vector beam in which both the inner and outer modes are radially polarized, but the polarization state is reversed.

Example 4

时的矢量光束实验结果，其中m为整数表示涡旋的拓扑荷，输出场强分布为

其中A₀是常数，

是方位角，图中对应的整数m分别为2，3，5。图5中第一栏-Polarization，给出矢量光束的偏振态分布；第二栏-CGH，Computer 6enerated Hologram，计算全息图，投影在空间光调制器上生成全息光栅；第三栏为不加检偏器(Analyzer)时的矢量光束强度分布图；第四栏为加上检偏器后的矢量光束强度分布图，用于检验矢量光束的偏振状态；第二列-m＝2，生成一种拓扑数m＝2的单模矢量光束；第三列-m＝3，生成一种拓扑数m＝3的单模矢量光束；第四列-m＝5，生成一种拓扑数m＝5的单模矢量光束。The 4f optical system is built according to the principle in Figure 1, and the specific experimental system constructed on this basis is shown in Figure 2. By projecting the computational hologram shown in the second column of Fig. 5 onto the spatial light modulator, a cylindrically symmetric vector beam corresponding to the polarization distribution shown in the first column of Fig. 5 can be obtained at the CCD in Fig. 2 . Similar to Example 1, there is also a central singularity. However, the situation of the extinction direction after adding a linear polarizer is different from Example 1. The extinction direction can be expressed as kπ/m+π/2m, where the integer k=0～m-1, the number of extinction directions and the topological number m equal. For example, in the vector beam with m=2, after adding a linear polarizer, two extinction directions π/4 and 3π/4 appear, which is consistent with the theory. The generation of single-mode vector beams in which m is an integer is realized by using our 4f system. Meaning of the symbols in Figure 5: the phase shift of the holographic grating is taken as the vortex phase distribution

The experimental results of the vector beam at , where m is an integer representing the topological charge of the vortex, and the output field intensity distribution is

where _A0 is a constant,

is the azimuth angle, and the corresponding integer m in the figure is 2, 3, 5 respectively. The first column in Figure 5 - Polarization, gives the polarization state distribution of the vector beam; the second column - CGH, Computer 6enerated Hologram, calculates the hologram, which is projected on the spatial light modulator to generate a holographic grating; the third column is no inspection The vector beam intensity distribution diagram of the polarizer (Analyzer); the fourth column is the vector beam intensity distribution diagram after adding the analyzer, which is used to check the polarization state of the vector beam; the second column -m=2, generates a A single-mode vector beam with a topological number m=2; the third column-m=3 generates a single-mode vector beam with a topological number m=3; the fourth column-m=5 generates a single-mode vector beam with a topological number m=5 Single mode vector beam.

Example 5

的偏振分布，其中A₀是常数，

是方位角，拓扑荷m分别取2，4，7。图6中第一栏-Polarization，给出矢量光束的偏振态分布；第二栏-CGH，Computer Generated Hologram，计算全息图，投影在空间光调制器上生成全息光栅；第三栏为不加检偏器(Analyzer)时的矢量光束强度分布图；第四栏为加上检偏器后的矢量光束强度分布图，用于检验矢量光束的偏振状态；第二列-m＝2表示生成的是一种内模径向偏振和外模m＝2的双模矢量光束；第三列-m＝4表示生成的是一种内模径向偏振和外模m＝4的双模矢量光束；第四列-m＝7表示生成的是一种内模径向偏振和外模m＝7的双模矢量光束。The 4f optical system is built according to the principle in Figure 1, and the specific experimental system constructed on this basis is shown in Figure 2. By projecting the computational hologram shown in the second column of Figure 6 onto the spatial light modulator, a cylindrically symmetric vector beam corresponding to the polarization distribution shown in the first column of Figure 6 can be obtained at the CCD in Figure 2 . Similar to the dual-mode situation in Example 2, a ring appears at the dividing line. The difference from Example 2 is that in the same ring zone, there is a trend of bright and dark changes, and the darkest point is extinguished, and its position appears at (2k-1)π/(m-1), k=0～m-1. consistent with theory. Here, the generation of the dual-mode vector beams in which m is an integer is realized by using our 4f system. Meaning of the symbols in Fig. 6: similar to Fig. 4, a class of dual-mode vector beam field strength distributions with different field strengths of the inner mode and the outer mode are given, and the inner mode refers to the distribution in the radius r=0 to r=r ₀ A polarization distribution mode between /2. In Fig. 6, the internal modes are all radially polarized, and its polarization state can be expressed as The external mode refers to the polarization distribution mode distributed between the radius r=r ₀ /2 to r=r ₀ , and the external mode in Fig. 6 is the polarization state, which can be expressed as

The polarization distribution of , where A ₀ is a constant,

is the azimuth, and the topological charges m are 2, 4, 7 respectively. The first column in Figure 6 - Polarization, gives the polarization state distribution of the vector beam; the second column - CGH, Computer Generated Hologram, calculates the hologram, which is projected on the spatial light modulator to generate a holographic grating; the third column is no inspection The vector beam intensity distribution diagram of the polarizer (Analyzer); the fourth column is the vector beam intensity distribution diagram after adding the analyzer, which is used to check the polarization state of the vector beam; the second column -m=2 indicates that the generated A dual-mode vector beam with internal mode radial polarization and external mode m=2; the third column -m=4 indicates that a dual-mode vector beam with internal mode radial polarization and external mode m=4 is generated; the first Four columns-m=7 means that a dual-mode vector beam with internal mode radial polarization and external mode m=7 is generated.

Example 6

的矢量光束实验结果，其中A₀是常数，

是方位角，拓扑荷m分别取半整数0.5和1.5。图7中第一栏-Polarization，给出矢量光束的偏振态分布；第二栏-CGH，Computer Generated Hologram，计算全息图，投影在空间光调制器上生成全息光栅；第三栏为不加检偏器(Analyzer)时的矢量光束强度分布图；第四栏为加上检偏器后的矢量光束强度分布图，用于检验矢量光束的偏振状态；第五栏-加上竖直方向偏振片的矢量光束强度分布图，用于检验矢量光束的偏振状态；第二列-m＝0.5，生成一种拓扑数是半整数m＝0.5的矢量光束；第三列-m＝1.5，生成一种拓扑数是半整数m＝1.5的矢量光束。The 4f optical system is built according to the principle in Figure 1, and the specific experimental system constructed on this basis is shown in Figure 2. By projecting the computational hologram shown in the second column of Figure 7 onto the spatial light modulator, a vector beam corresponding to the non-cylindrical distribution shown in the first column of Figure 6 can be obtained at the CCD in Figure 2 . Similar to Example 1, there is also a central singularity. The difference from Example 1 is that there is also a horizontal dark line here, which is caused by the sudden change of the upper and lower polarization states. After adding the polarizer 2, the extinction direction will also appear, which is different from the situation in Example 1. The extinction direction here divides the light intensity distribution diagram into 2m lobes, and the transverse dark line always exists. These results are consistent with theory. The generation of vector beams in which m is a half-integer is realized by using our 4f system. Meaning of the symbols in Figure 7: The field strength distribution is given as

The vector beam experimental results of , where A ₀ is a constant,

is the azimuth angle, and the topological charges m take half integers 0.5 and 1.5 respectively. The first column in Figure 7 - Polarization, gives the polarization state distribution of the vector beam; the second column - CGH, Computer Generated Hologram, calculates the hologram, which is projected on the spatial light modulator to generate a holographic grating; the third column is no inspection The vector beam intensity distribution diagram when the polarizer (Analyzer) is used; the fourth column is the vector beam intensity distribution diagram after adding the analyzer, which is used to check the polarization state of the vector beam; the fifth column - adding a vertical polarizer The vector beam intensity distribution diagram of the vector beam is used to check the polarization state of the vector beam; the second column-m=0.5 generates a vector beam whose topological number is a half-integer m=0.5; the third column-m=1.5 generates a vector beam The topological number is the vector beam of the half-integer m=1.5.

Example 7

旋向偏振(AP)：

拓扑荷m＝3：拓扑荷m＝1.5：

其中A₀是常数，是方位角。图8中第一栏-不加检偏器(Analyzer)时同一光束中不同区域包含不同偏振态的矢量光束强度分布图；第二栏-加上水平方向检偏器后的矢量光束强度分布图，用于检验矢量光束的偏振状态；第二列-生成一种不同区域多种模式矢量光共存的矢量光束。The 4f optical system is built according to the principle in Figure 1, and the specific experimental system constructed on this basis is shown in Figure 2. In this example, we realize the situations in the previous examples 1, 3, and 5 in the same vector beam, that is, there are different polarization modes in different regions in the vector beam of this example. The polarization distribution of the light beam is specifically: the upper left quarter area is a radially polarized light mode, the upper right quarter area is a circularly polarized light mode, the lower left quarter area is a polarization mode with m=3, and the right upper quarter area is a polarization mode of m=3. The lower quarter region is the polarization mode for m=1.5. Bright and dark changes appear at the boundary between different polarization modes according to the magnitude of the polarization state difference. Here, we use our 4f system to realize the generation of vector beams containing multiple different polarization distributions in the same beam. The meaning of the symbols in Figure 8: The result of four different vector modes coexisting in different regions in the same beam is given, and the four modes correspond to: radial polarization (RP):

Handed Polarization (AP):

Topological charge m=3: Topological charge m=1.5:

where A ₀ is a constant and is the azimuth. The first column in Fig. 8 - when no analyzer (Analyzer) is added, the different regions in the same beam contain the vector beam intensity distribution diagram of different polarization states; the second column - the vector beam intensity distribution diagram after adding the horizontal analyzer , used to check the polarization state of the vector beam; the second column - generate a vector beam in which multiple modes of vector light coexist in different regions.

Claims (4)

1, a kind of generating apparatus of random polarization distributing vector light beam, it is characterized in that the radiation direction that the edge produces the light source (1) of linearly polarized light sets gradually by computer-controlled spatial light modulator (2), first lens (3), two mesh filter (4), two quarter-wave plates (5), second lens (6) and Ronchi grating (7); Spatial light modulator (2) is positioned at the front focal plane of first lens (3), and the back focal plane of first lens (3) is provided with two mesh filter (4); Two mesh filter (4) is positioned at the front focal plane of second lens (6) simultaneously; Ronchi grating (7) is positioned at the back focal plane of second lens (6); Two quarter-wave plates (5) are close to two mesh filter (4) backlight and are simultaneously placed, and the optical axis of described two quarter-wave plates is respectively at x axle and y direction of principal axis; Described spatial light modulator (2) is loaded into the spatial light modulator (2) that the back forms the calculation holographic grating for the computed hologram that is generated by computing machine; Wherein light source (1) is for producing a branch of direction of vibration and the x axle light source that incides the linearly polarized light on the spatial light modulator in angle of 45 degrees; Described spatial light modulator (2) for loaded transmitance be t (x, y)=[1+ γ cos (2 π f ₀The spatial light modulator of calculation holographic grating x+ δ)]/2, wherein γ and f ₀Be respectively the degree of modulation and the spatial frequency of grating, δ is the phase shift of grating fringe; Described two mesh filter (4) is for being used for extracting the two mesh filter (4) of ± 1 order diffraction light.

2, the generating apparatus of random polarization distributing vector light beam according to claim 1 is characterized in that, the light source of described generation polarized light (1) is made up of laser instrument (8) and first linear polarizer (9).

3, the generating apparatus of random polarization distributing vector light beam according to claim 1 is characterized in that, is provided with rotation frosted glass (10) between laser instrument (8) and first linear polarizer (9).

4, the generating apparatus of random polarization distributing vector light beam according to claim 1 is characterized in that, above-mentioned Ronchi grating (7) adopts the phase-type Ronchi grating.

Images