Vortex beam orbital angular momentum detection device and method based on well-shaped line diffraction
By combining a well-shaped line structure and a focusing lens, the problem of secondary bright spot interference in traditional vortex beam detection is solved, enabling accurate identification and high energy utilization of high-order vortex beams, and extending the detection range to 30th order, making it suitable for vortex beams transmitted over long distances.
Patent Information
- Application Number
- CN202511704525.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-20
- Publication Date
- 2025-12-26
AI Technical Summary
In traditional methods for detecting the orbital angular momentum of vortex beams, it is difficult to distinguish between the secondary and primary bright spots of the diffraction of higher-order vortex beams, leading to detection failure and low energy utilization, especially when transmitting over long distances.
The vortex beam orbital angular momentum detection device, which adopts a well-shaped line structure, uses a well-shaped line structure composed of two sets of mutually orthogonal parallel line pairs and a focusing lens to eliminate secondary bright spot interference, retain the main bright spot information, and identify the topological charge number in the far-field diffraction distribution through the focusing lens.
It improves the detection accuracy and energy utilization of high-order vortex beams, expands the detection range to 30th order, is suitable for weak-intensity vortex beams, and simplifies optical path adjustment.
Smart Images
Figure CN121207321A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of laser information technology, and particularly relates to a vortex beam orbital angular momentum detection device of well type line structure. BACKGROUND
[0002] The orbital angular momentum (OAM) property of vortex beams has important potential applications in the field of super-capacity optical communication, and has special research value in optical micro-manipulation and super-resolution imaging. Therefore, it is of great significance to quickly and accurately detect the OAM of vortex beams for the practical application of vortex light. Topological charge is a quantum number describing the topological structure of vortex beams. The OAM carried by a single photon corresponds to an infinite number of eigenvalues, so the topological charge is also used to describe the orbital angular momentum of vortex beams. At present, the commonly used methods for measuring the topological charge of vortex beams include interference method and diffraction method. The interference method is to introduce reference light to interfere with the vortex beam, or to interfere with each other after splitting the vortex beam to be measured, and the topological charge value of the vortex beam to be measured is determined by the distribution characteristics of the interference field. In 2002, Leach et al. proposed using a Mach-Zehnder interferometer with a Dove prism to detect the orbital angular momentum of single vortex light. In 2012, Ke Xizheng et al. detected the orbital angular momentum of vortex light based on the classical Young double-slit interference experiment. In 2013, Liu Ruifeng et al. proposed an angular double-slit interference method to measure the orbital angular momentum of vortex light. Although the interference method has low cost, it requires many optical elements and the optical path adjustment is complex. The diffraction method is that when the vortex beam irradiates a specially designed diffraction diaphragm, the far-field diffraction will show a special pattern related to the topological charge number, and the topological charge number of the incident vortex beam can be inferred according to the distribution of the diffraction light field. In 2011, Araujo et al. used a triangular aperture to measure the OAM of vortex light, and the topological charge measurement range could reach ±7. In the same year, Mesquita et al. used a square aperture for measurement, and found that the topological charge number of even number could be perfectly measured, but the recognition degree of the diffraction bright spot was not high in the case of odd number. Silva et al. compared the diffraction results of vortex light through square and triangular apertures, and found that when the side length of the square aperture is equal to that of the triangular aperture, the OAM measurement range of the square aperture is more than twice that of the triangular aperture. Compared with the interference method, the diffraction method has a relatively small detection range, but has the characteristics of simple optical path, easy to manufacture, and low cost, so it has a wider application prospect. However, the vortex beam OAM detection method based on small aperture diaphragm also has some problems, such as the requirement that the beam width and the aperture size should match to cause obvious diffraction phenomenon, and there are a large number of diffraction secondary spots in the diffraction far-field distribution that are irrelevant to the topological charge value. The higher the topological charge number, the stronger the interference of the diffraction secondary spot on the diffraction main spot, and when the number exceeds a certain order, the diffraction main and secondary spots cannot be distinguished, thereby affecting the detection and recognition of the OAM of vortex beams. At the same time, the energy proportion of the diffraction main bright spot in the traditional small aperture diffraction method is extremely low, especially the far-field main bright spot with a topological charge of 7 or more, which contains less than 1% of the incident beam energy, which seriously restricts the practical application of the diffraction method in OAM measurement. SUMMARY
[0003] Therefore, the application provides a vortex beam orbital angular momentum measuring device based on a well-type line structure, which is simple in structure and has various functions.
[0004] In order to achieve the above object, the technical scheme provided by the embodiment of the application is as follows: the application provides a vortex beam orbital angular momentum measuring device based on a well-type line structure, which is characterized in that:
[0005] The core of the device is the well-type line structure and a focusing lens. The well-type line structure is composed of two groups of parallel lines that are perpendicular to each other. The spacing of each group of parallel lines can be adjusted flexibly according to the size of the light beam. The two groups of parallel lines are composed of four straight lines in the same plane, and the four straight lines are divided into two groups. The straight lines in each group are parallel to each other and form a group of parallel lines. The two groups of parallel lines are perpendicular to each other. The focusing lens is arranged behind the well-type line structure. The far-field diffraction distribution at the focal plane of the focusing lens shows a special pattern related to the topological charge value, and the topological charge number of the incident vortex light beam can be inferred accordingly.
[0006] Compared with the prior art, the application has the following advantages:
[0007] 1. In the traditional method for measuring OAM based on a diffraction diaphragm, in addition to the diffraction main bright spot related to the OAM characteristics, there are a large number of diffraction secondary bright spots unrelated to the OAM characteristics. The higher the topological order is, the closer the intensity of the diffraction secondary bright spot and the main bright spot is, which seriously interferes with the identification of the main bright spot. When the topological order exceeds a certain value, the main bright spot and the secondary bright spot cannot be distinguished, which leads to the failure of vortex light OAM detection. The well-type line diffraction structure used in the application eliminates the diffraction secondary bright spot that interferes with the identification of OAM and only retains the diffraction main bright spot related to the OAM characteristics. Especially in the detection of high-order vortex light, the application can greatly improve the distinguishability of the diffraction main bright spot and the accuracy of OAM identification;
[0008] 2. In the traditional method for measuring OAM based on a diffraction diaphragm, the diffraction diaphragm blocks most of the light beam energy, and the light beam energy that passes through the diffraction diaphragm is dispersed by the diffraction secondary bright spot, resulting in a very low energy ratio of the diffraction main spot in the far-field distribution. On the contrary, the well-type line diffraction structure used in the application can pass through most of the light beam energy, and the passing light beam energy basically exists in the form of a diffraction main spot. Therefore, the application is especially suitable for measuring weak intensity vortex light beams (such as vortex light beams transmitted at a long distance);
[0009] 3. The orbital angular momentum detection range can reach 30 orders, which is much higher than that of the traditional diffraction measurement method;
[0010] 4. Compared with the method of measuring OAM based on a traditional diffraction diaphragm, the beam width of the light beam is adjusted by the lens group to match the pinhole diaphragm, and the line distance of the well type line can be flexibly adjusted according to the beam width of the vortex beam, so that the experimental light path is simplified and the detection difficulty is reduced. BRIEF DESCRIPTION OF DRAWINGS
[0011] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments described in the present application, and other drawings can be obtained by those skilled in the art without creative labor.
[0012] Figure 1 The well type line diffraction structure in the present application is shown in the figure, which is composed of two groups of parallel line pairs that are orthogonal to each other. The parameters in the figure are as follows: a The line width, b The distance between the line pairs.
[0013] Figure 2 The optical path diagram of the vortex beam orbital angular momentum detection device of the well type line structure in the present application is shown in the figure:
[0014] Figure 3 The topological charge value l The far field main spot distribution of the vortex light after passing through the well type line structure of the present application when the topological charge values are 5 and 8, respectively.
[0015] In order to make the person skilled in the art better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should be within the scope of protection of the present application.
[0016] Figure 1 The well type line diffraction structure in the present application is shown in the figure, which is composed of two groups of parallel line pairs that are orthogonal to each other. The parameters in the figure are as follows: a The line width, b The distance between the line pairs, the line width and the distance between the line pairs can be flexibly adjusted according to the wavelength and the beam size and other parameters.
[0017] Figure 2Figure 1 is a schematic diagram of an optical path of a vortex beam orbit angular momentum detection device according to the present application. The vortex light first passes through the well-type line structure, then passes through the focusing lens placed behind the well-type line structure. The far-field diffraction distribution at the back focal plane of the lens will show a diffraction spot distribution related to the topological charge value, and will be collected by a CCD camera. According to the diffraction spot distribution, the topological charge value of the incident vortex beam can be inferred. At the same time, the offset of the well-type line center position will cause the density of the main spot distribution to change. For example, when the well-type line center position is micron-level offset relative to the optical axis along the upper right, for the vortex light diffraction distribution with a positive topological charge value, the diffraction main bright spot on the upper left will become dispersed, while the diffraction main bright spot on the lower right will become dense. For the vortex light diffraction distribution with a negative topological charge value, the changes are just the opposite. Accordingly, the positive and negative of the vortex light topological charge can be inferred.
[0018] Figure 3 Figure 2 is a far-field main spot distribution of vortex light with a topological charge value of 5 and 8, respectively, after passing through the well-type line structure according to the present application. The wavelength of the vortex light used is 632.8 nm, the line width of the well-type line structure is 0.1 mm, and the line pair spacing is 0.9 mm. It can be seen from Figure 2 that the present application eliminates the diffraction secondary bright spots that interfere with OAM identification, and only retains the diffraction main bright spots related to the OAM characteristics. l Figure 3 With the increase of the topological charge value, the number of diffraction main spots gradually increases, and the number always remains a multiple of 4. When the topological charge is even, the number of diffraction spots is defined as follows: N =2 l When the topological charge is odd, the diffraction pattern shows more complex characteristics, and the total number of diffraction spots corresponding to the odd topological charge can be expressed as: N =2(| l |-1)。
[0019] In the traditional diffraction method, the diffraction aperture blocks most of the light beam energy, and the light beam energy passing through the diffraction aperture is dispersed by the diffraction secondary spots, resulting in that the diffraction main spot energy ratio in the far field distribution is extremely low. For example, the vortex light with a wavelength of 632.8 nm is incident on a rectangular aperture with a side length of 1 mm and a triangular aperture with a side length of 2 mm, respectively, the topological charge value of the vortex light beam is distributed from 1 to 9, the diffraction main spot energy ratio of the vortex light beam passing through the rectangular aperture is rapidly reduced from about 80% (topological charge value 1) to about 10% (topological charge value 4), and then to about 2% (topological charge value 6), and finally to about 0.1% (topological charge value 9). In the far field distribution of the well-type line structure diffraction, for the well-type line structure with a line width of 0.1 mm and a line pair spacing of 0.9 mm, when the topological charge value of the incident vortex light is from 1 to 9, the diffraction main spot energy ratio changes from about 70% (topological charge value 1) to about 80% (topological charge value 9). It can be seen that the diffraction main spot related to the beam orbital angular momentum retains most of the energy of the incident light beam, and there is no secondary diffraction spot interfering with detection, so the diffraction main spot can be clearly identified.
[0020] From the above technical solutions, it can be seen that the device for detecting the topological charge number of a vortex light beam in the form of a well-type line disclosed in the present application optimizes the experimental light path for detecting the topological charge number of a vortex light beam while ensuring various functions.
[0021] It will be obvious to a person skilled in the art that the application is not limited to the details of the above exemplary embodiments, and the application can be implemented in other specific forms without departing from the spirit or essential characteristics of the application. Therefore, the embodiments should be considered as exemplary and non-limiting, and the scope of the application is defined by the appended claims rather than the above description, and all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the application. Any reference signs in the claims should not be considered as limiting the claims involved.
Claims
1. A device for detecting the orbital angular momentum of a vortex beam, characterized in that, It includes a well-shaped line structure arranged sequentially along the optical path, used to diffract the incident vortex beam; A focusing lens, positioned after the well-shaped line structure, is used to converge the diffracted light to its focal plane, forming a characteristic diffraction pattern for identifying topological charge values.
2. The apparatus according to claim 1, characterized in that, The well-shaped line structure consists of two sets of parallel lines that are orthogonal to each other in the same plane.
3. The apparatus according to claim 2, characterized in that, The linewidth (a) of the well-shaped line structure and the spacing (b) of the parallel line pairs are configured according to the wavelength of the incident vortex beam and the waist radius.
4. The apparatus according to claim 1, characterized in that, The characteristic diffraction pattern is an array of multiple diffraction spots, and the number of spots has a definite mathematical relationship with the absolute value of the topological charge of the incident vortex beam.
5. The apparatus according to claim 4, characterized in that, When topological load number l When the number is even, the number of diffraction spots N = 2 l ; When topological load number l When the number is odd, the number of diffraction spots N = 2(| l | - 1).
6. The apparatus according to claim 1, characterized in that, By translating the center position of the well-shaped line structure relative to the optical axis, the density of the diffraction spots in the characteristic diffraction pattern will change asymmetrically, and the direction of this change can be used to determine the sign of the topological charge value.
7. A method for detecting the orbital angular momentum of a vortex beam, characterized in that, The apparatus according to any one of claims 1-6 comprises the following steps: subjecting the vortex beam to be tested to the well-shaped line structure to diffraction; focusing the diffracted light through the focusing lens and acquiring a far-field diffraction pattern at its focal plane; determining the absolute value of the topological charge based on the number of diffracted spots in the far-field diffraction pattern; and determining the sign of the topological charge by observing the direction of change in the density of the diffracted spot distribution after translating the center of the well-shaped line structure.