阅读说明：本技术 一种基于软边小孔的涡旋光轨道角动量检测方法 (Vortex light orbit angular momentum detection method based on soft-edge small hole ) 是由 熊晗 庄京秋 于 2021-10-07 设计创作，主要内容包括：本发明公开了一种基于软边小孔的涡旋光轨道角动量检测方法。所述涡旋光轨道角动量检测方法采用软边小孔作为衍射光阑,涡旋光经过软边小孔形成远场的衍射分布,根据远场分布中主亮斑的数量来确定涡旋光的轨道角动量,所述软边小孔是一个内边缘具有一定程度软化因子的小孔,利用软边对衍射效应的收敛性来增强衍射分布中最外围主亮斑对相邻次亮斑的相对强度,提高主亮斑的可识别度和轨道角动量的可检测范围,小孔形状可以是圆形、三角形、矩形和多边形以及各种环形,所述一定程度软化因子是指软化因子可以根据具体情况来调整和优化以获得最佳的检测效果。(The invention discloses a vortex light orbit angular momentum detection method based on a soft-edge small hole. The vortex light orbital angular momentum detection method adopts the soft-edge small holes as diffraction diaphragms, vortex light forms far-field diffraction distribution through the soft-edge small holes, the orbital angular momentum of vortex optical rotation is determined according to the number of main bright spots in the far-field distribution, the soft-edge small holes are small holes with softening factors at certain degrees on the inner edges, the convergence of the soft edges on diffraction effects is utilized to enhance the relative strength of the outermost main bright spots in the diffraction distribution to adjacent secondary bright spots, the identifiability of the main bright spots and the detectable range of the orbital angular momentum are improved, the small holes can be round, triangular, rectangular, polygonal and various rings in shape, and the softening factors at certain degrees can be adjusted and optimized according to specific conditions to obtain the optimal detection effect.)

1. A vortex light orbit angular momentum detection method based on a soft-edge small hole is characterized by comprising the following steps: vortex light passes through the soft-edge small holes to form far-field diffraction distribution, and orbital angular momentum of vortex rotation can be obtained according to the number of main bright spots in the diffraction distribution.

2. The soft-edged pinhole-based vortex optical orbital angular momentum detection method as claimed in claim 1, wherein: the soft-edged orifice has a softening factor at its inner edge to some extent, and the shape of the orifice includes, but is not limited to, circular, triangular, rectangular, polygonal, and various rings.

3. The soft-edged pinhole-based vortex optical orbital angular momentum detection method as claimed in claim 1, wherein: the soft edge factor can be adjusted and optimized according to specific conditions so as to achieve the best detection effect.

Technical Field

The invention relates to the fields of vortex light and light diffraction transmission and the like, in particular to a vortex light orbital angular momentum detection method based on a small hole.

Background

At present, with the development of wireless communication technology, people have an increasing demand for bandwidth capacity of a communication network, but the capacity of a communication system cannot be increased on a large scale by means based on frequency, wavelength, polarization state and the like, and people begin to turn their eyes to vortex beams. Vortex beams, which are beams with a helical phase distribution, have been one of the hot spots in recent years since Allen et al discovered in 1992 that vortex beams carry Orbital Angular Momentum (OAM). Orbital angular momentum of the vortex beam can be used for encoding information, OAM has infinite modes, and all the modes are mutually orthogonal, so that theoretically, communication capacity can be infinitely increased by using the vortex beam. As early as 2004, Gibson Graham pioneered the use of vortex rotation for information transmission in free space, confirming the possibility of OAM for information transmission.

For the application of vortex rotation, the detection of the orbital angular momentum of vortex light is a very important and critical step. Currently, methods commonly used for detecting OAM are mainly classified into interferometry and diffractometry. In 2009, guoshishan et al studied the spatial spectrum in the far-field diffraction intensity distribution of vortex light passing through a circular aperture, and found that the spatial spectrum consists of alternately bright rings and dark rings, and the number of the bright rings completely coincides with the topological charge number of the vortex rotation. Hickmann et al have studied vortex light diffraction based on triangular holes in 2010, and found that a triangular bright spot array changing along with topological charge number appears in diffraction distribution, and the topological charge number of vortex rotation is obtained by subtracting 1 from the number of main bright spots on one side of the bright spot array. The main bright spots are diffraction spots with normalized intensity close to 1 in the diffraction distribution under the condition of low-order topological load, the diffraction spots with normalized intensity close to 0 are called secondary bright spots, the normalized intensity of the main bright spots is continuously reduced along with the increase of the order of the topological load, and the normalized intensity of the secondary bright spots is continuously improved. When the relative intensity of the outermost main bright spot and the adjacent sub bright spot is not large, the main bright spot cannot be accurately identified in the diffraction distribution diagram, and the vortex light detection means based on the small holes reaches the limit. Hickmann et al, based on triangular holes, can only be used to measure lower order vortex rotation of no more than 10 orders. Mesquita et al, 2011 improved pinhole detection by diffracting and analyzing eddy optical rotations with rectangular holes and expanded the upper limit of pinhole detection to about 20 orders.

For the development of the fields of optical communication and the like, the identifiability of the main bright spot in diffraction distribution is improved, and accurate and rapid automatic detection of vortex light is guaranteed; the detection application range of the orbital angular momentum is expanded, and the selectable vortex light range in practical application is favorably increased. Therefore, how to further improve the identifiability of the main bright spot and the application range based on the pinhole detection have important and practical significance.

Disclosure of Invention

In view of the above, the invention provides a method for detecting vortex optical orbital angular momentum based on a soft-edge pinhole. Compared with the existing hard-edge small hole, the method improves the identifiability of the main bright spot, and greatly expands the identification capability and detection range of detecting the vortex light orbital angular momentum by using the small hole.

In order to achieve the above purpose, the technical solutions provided by the embodiments of the present invention are as follows:

a vortex light orbital angular momentum detection method based on a soft-edge small hole enables vortex light to form far-field diffraction distribution through the soft-edge small hole, and orbital angular momentum of vortex optical rotation can be obtained through the number of main bright spots in the diffraction distribution.

As a further improvement of the invention, the soft-edged orifice has a softening factor at its inner edge to a certain extent and a convergence on diffraction to a certain extent, and the shape of the orifice includes, but is not limited to, circle, triangle, rectangle, polygon, various rings, and the like.

As a further improvement of the invention, the soft edge factor can be adjusted and optimized according to specific situations so as to achieve the optimal vortex light detection effect.

The invention has the beneficial effects that:

compared with the common hard-edge small hole, the soft-edge small hole has certain convergence on the far-field diffraction of vortex optical rotation, and can improve the relative strength of the outermost main bright spot to the adjacent secondary bright spot in the diffraction distribution, thereby improving the identifiability of the main bright spot and being beneficial to ensuring the accurate and rapid automatic detection on the orbital angular momentum of the vortex light;

due to the improvement of the identifiability of the main bright spots, the soft-edge small holes can detect higher-order vortex optical rotation which cannot be detected by the original hard-edge small holes in a certain range, so that the application range based on the small hole detection is expanded, and the selectable vortex optical range in practical application is favorably increased;

the softening factor is adjusted and optimized to achieve the best detection effect, so that the identifiability of the main bright spot and the vortex light detection range can be further improved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required in the description of the embodiments or the prior art will be briefly introduced below, it is obvious that the drawings in the following description are only some embodiments described in the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a far field intensity distribution diagram of vortex light carrying different orbital angular momentums after being diffracted by soft-edge and hard-edge small holes (taking a rectangular hole as an example) respectively;

FIG. 2 is a diagram of the lateral intercept of the vortex light in the far field intensity distribution after diffraction by soft-edge and hard-edge apertures, respectively (taking a rectangular aperture as an example).

Detailed Description

In order to make those skilled in the art better understand the technical solution of the present invention, the technical solution in the embodiment of the present invention will be clearly and completely described below with reference to the drawings in the embodiment of the present invention, and it is obvious that the described embodiment is only a part of the embodiment of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

By using a small hole (such as a rectangular hole, a triangular hole, a circular hole, a polygonal hole, various rings, and the like) as a transmission diaphragm, a diffraction distribution of a far field is formed when vortex light passes through the small hole, and orbital angular momentum of vortex rotation can be obtained according to the number of main bright spots with relatively bright centers of the diffraction distribution. Under the condition of lower-order topological charge, the contrast multiple of the main bright spots at the outermost periphery of the diffraction distribution and the adjacent secondary bright spots on the normalized intensity is higher, so that the main bright spots and the secondary bright spots are easy to distinguish, namely, the topological charge order of vortex rotation is easy to obtain.

The adoption of the soft-edge small holes can improve the identifiability of the main bright spots:

referring to fig. 1 and 2, assuming a gaussian laser beam with a wavelength of 632.8 nm and a beam diameter of 0.5 mm, the beam will form a beam with a specific topological charge (assuming that the beam is a gaussian laser beam with a specific topological charge) after passing through a spatial light modulator with vortex-type phase modulationn) The vortex light is then split by vortex rotation and passed through a hard-edge and soft-edge aperture (taking a rectangular aperture with a side length of 0.5 mm as an example). When diffraction fringes formed in the up-down direction and the left-right direction are superposed together, a light spot array arranged horizontally and vertically is formed on the interference pattern. The results of the hard rectangular aperture far field diffraction simulated by Matlab program are shown in FIG. 1(b), which showsnIndicating the topological charge number of vortex light, Soft representing Soft edge pinholes, Hard representing Hard edge pinholes, solid line arrow pointing to the outermost main bright spot, and dotted line arrow pointing to the adjacent secondary bright spot. FIG. 2(b) is a light intensity distribution curve taken along the middle transverse direction in FIG. 1 (b). As can be seen from FIG. 2(b), when the number of topological charges is usednWhen the diffraction distribution of the hard-edge pinholes is equal to 8-order, the normalized intensity value of the outermost main bright spot in the diffraction distribution of the hard-edge pinholes is 0.95, the normalized intensity value of the adjacent secondary bright spots is about 0.36, the intensity contrast value of the two is up to 2.64 times, the main bright spot and the secondary bright spot are easily distinguished, and the topological charge number of the vortex optical rotation can be known by identifying the number of the bright spots in each row on the central dot matrix.

According to the invention, the hard edge of the small hole is changed into the soft edge with a certain softening factor (in the example, the softening factor value corresponds to a 14-order super-Gaussian function), so that the beam diffraction of the small hole with the soft edge has certain convergence, and the intensity contrast value of the main bright spot and the secondary bright spot in far-field diffraction distribution can be improved. The far field diffraction simulation results of the soft rectangular aperture are shown in fig. 1(a) and 2 (a). As can be seen from the figure, when the topological charge number isnWhen the number is 8, the normalized intensity value of the outermost main bright spot obtained by the soft-edge small hole is 1.00, the normalized intensity value of the adjacent secondary bright spot is about 0.29, the contrast value of the intensity of the main bright spot and the secondary bright spot is 3.45 times, the contrast value is increased by 31 percent compared with 2.64 times of that of the hard-edge small hole, and the identifiability is higher. The simulation results thus demonstrate that: compared with the conventional hard-edge small hole, the soft-edge small hole can improve the relative intensity or the identifiability of the main bright spot in the vortex light diffraction distribution.

The detection range of vortex rotation can be improved by adopting the soft-edge small holes:

referring to fig. 1 and 2, under the conditions of hard-edge pinhole diffraction and topological charge number of 8 th order, the intensity contrast value of the outermost main bright spot and the adjacent secondary bright spot is 2.64 times, when the topological charge number is increased to 20 th order, the normalized intensity value of the outermost main bright spot is about 0.60, and the normalized intensity value of the adjacent secondary bright spot is about 0.44, at which time, the intensity contrast value of the main bright spot and the secondary bright spot is reduced to only 1.36 times, and because the main bright spot is difficult to distinguish and identify, the detection range of the hard-edge rectangular hole reaches the limit, as shown by the diffraction spot in fig. 1(b 5). Under the conditions of diffraction of the soft-edge small holes and 20-order topological charge number, the normalized intensity value of the outermost main bright spot obtained by simulation is about 0.66, the intensity contrast value of the adjacent secondary bright spots is about 0.37, the intensity contrast value of the main bright spot and the secondary bright spot is 1.78 times, the contrast value is still 31% higher than that of the hard-edge small holes by 1.36 times, and the main bright spot can still be identified as shown by the diffraction light spot in the figure 1(a 5). The simulation results show that: the soft-edge aperture can identify 20-order vortex beams which cannot be identified by the hard-edge aperture, so that the detection range of the vortex beams can be expanded.

The adoption of the optimized soft-edge small hole can further improve the identifiability and the detection range of the vortex optical rotation:

the softening factor used in the above example corresponds to a 14 th order super-gaussian function, and the relative intensity of the primary and secondary bright spots is increased by about 31% compared to that of the hard-edged pinhole, regardless of whether the topological load is 8 th order or 20 th order. The softening factor can also be optimized to further improve the identifiability of the main bright spots and obtain the optimal vortex light detection effect.

According to the technical scheme, the method for detecting the vortex optical orbital angular momentum based on the soft-edge small hole can expand the identifiability and the detection range of detecting the vortex optical rotation topological charge number based on the small hole, and provides a new idea for the application of the vortex optical rotation in the fields of information technology and the like, particularly for the development of the optical communication technology with high capacity and high channel.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.

Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.