Method for eliminating over-the-top problem of double-wedge scanning system

Abstract

The application discloses a method for eliminating the over-the-top problem of a double-wedge scanning system. The method adds a third wedge to the double-wedge scanning system and proposes a constraint condition for the rotation angle of the third wedge. The addition of the third wedge is equivalent to the introduction of a new degree of freedom into the scanning system, which provides more optional schemes for the angle control of the wedge rotation. As long as the constraint condition of the third wedge can make the rotation angle of the third wedge change smoothly and continuously when passing through the singular point of the system, the rotation angles of the remaining wedges will also change smoothly and continuously, thereby eliminating the over-the-top problem of the double-wedge scanning system at the singular point.

Description

Technical Field

[0001] This invention relates to the field of small scanning and tracking systems in laser communication, specifically to a method for eliminating the overhead problem in dual-wedge scanning systems. Background Technology

[0002] In the field of laser communication, conventional scanning and acquisition systems mainly employ two-axis frame structures and mirror structures. Both of these structures require the assistance of a mechanical servo turntable to achieve beam scanning and pointing, and their large size, weight, and power consumption make them unsuitable for miniaturized designs. Therefore, a new beam scanning and pointing control method, namely the optical wedge scanning system, has been proposed. In comparison, the optical wedge scanning system offers advantages such as compact structure, high pointing accuracy, low optical loss, good dynamic performance, insensitivity to carrier vibration, and a large scanning field of view. It is an ideal choice for designing miniaturized laser scanning systems and is particularly suitable for space laser communication environments.

[0003] Currently, most optical wedge scanning systems employ dual optical wedges. While dual optical wedge scanning technology is relatively mature, it also suffers from drawbacks such as numerous missed scan points, significant aberrations, and the "overshoot problem." In dynamic laser communication, due to the "overshoot problem," dual optical wedge scanning systems may lose track of the target near singular points on the target plane, leading to communication interruption. This is a problem that urgently needs to be solved in dual optical wedge scanning systems. Summary of the Invention

[0004] The purpose of this invention is to provide a method for eliminating the over-the-top problem in a dual-wedge scanning system. By introducing a third optical wedge and appropriate constraints, a smooth and continuously varying optical wedge rotation angle can be obtained, thus avoiding the "over-the-top problem" at singular points in the scanning system.

[0005] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0006] A method for eliminating the over-the-top problem in a dual-wedge scanning system involves adding a third optical wedge to the dual-wedge scanning system and imposing appropriate constraints on the rotation angle of the third optical wedge, so that the rotation angle of the third optical wedge always changes smoothly and continuously.

[0007] Among them, the thickest end of the third optical wedge always faces the direction from the center of the target plane to the target pointing point.

[0008] The constraint conditions of the third optical wedge are applicable to different optical wedge placement methods (i.e., vertical surface in front and inclined surface in back, or inclined surface in front and vertical surface in back).

[0009] The relative positions of the three optical wedges and the target plane should avoid a scanning blind zone in the center of the scanning field of view. Assume the thickness of each of the three optical wedges is d, the wedge angle is β, and the refractive index of the material is n. The positional distances between the first and second optical wedges, the second and third optical wedges, and the third optical wedge and the target plane are d1, d2, and d3, respectively, satisfying d1:d2:d3=λ1:λ2:λ3, d1+d2+d3=B, and λ1+λ2+λ3=1. Then, the critical condition for avoiding a scanning blind zone is:

[0010]

[0011] in:

[0012]

[0013] Among them, by utilizing the constraints of the third optical wedge and the two constraints of the target pointing direction, the angles that each optical wedge should rotate are solved based on the target's motion trajectory using a ray tracing algorithm.

[0014] The first, second, and third optical wedges have the same wedge angle and material refractive index.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] A third optical wedge is added to the dual-wedge scanning system, and constraints are proposed regarding the rotation angle of the third optical wedge. When the rotation angle of the third optical wedge can change smoothly and continuously at the singularity of the system, the rotation angles of the other optical wedges will also change smoothly and continuously, thereby eliminating the "overhead problem" in the dual-wedge scanning system. In addition, the three-wedge scanning system is divided into two groups, and a simple method for solving the inverse problem of the three-wedge scanning system is proposed by combining the three constraints and the ray tracing algorithm. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the placement of the dual optical wedges and beam deflection;

[0018] Figure 2 This is a schematic diagram of the placement of the three optical wedges and beam deflection in an embodiment of the present invention;

[0019] Figure 3 The image shows the inverse kinematics results of a dual-wedge laser when capturing a specific target trajectory;

[0020] Figure 4 This is a diagram showing the inverse kinematics result of a three-light wedge when taking a specific target trajectory in an embodiment of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] It should be noted that the dual-wedge scanning system has an "over-the-top problem" ( Figure 1 The term "overhead problem" refers to the situation where, when the pointing point of the emitted beam of the system approaches the origin of the target plane coordinate system (i.e., the singular point of the system), the beam needs to rotate 90° from one axis to another in the target plane coordinate system. When the two points on the coordinate axis are infinitely close to the origin, the 90° rotation needs to be completed in an instant. At this time, the rotation speed of the double beam tends to infinity. This is the essence of the "overhead problem" of the double beam scanning system.

[0023] like Figure 2 As shown, a third optical wedge is added to the dual-wedge scanning system to address the "over-the-top problem," and constraints are introduced regarding the rotation angle of the third optical wedge. This ensures that the rotation angles of each optical wedge, solved by inverse kinematics of the target trajectory, change smoothly and continuously, thus eliminating the "over-the-top problem" at singularities. Adding the third optical wedge introduces a new degree of freedom to the dual-wedge scanning system, providing more options for controlling the wedge rotation angle. If appropriate constraints are added to the rotation angle of the third optical wedge, ensuring that it changes smoothly and continuously when passing through system singularities, then the rotation angles of the other optical wedges will also change smoothly and continuously, thus eliminating the "over-the-top problem" at singularities in the dual-wedge scanning system.

[0024] Furthermore, the inverse problem solution of the dual-wedge scanning system is based on a ray tracing algorithm. By determining the elevation and azimuth angles of the emitted beam through the target pointing orientation, the rotation angles of the dual wedges can be solved inversely. The elevation angle is the angle between the emitted beam and the wedge rotation axis (z-axis), and the azimuth angle is the angle between the line connecting the pointing point on the target plane and the origin, and the x-axis. The elevation and azimuth angles uniquely determine the pointing orientation of the emitted beam on the target plane.

[0025] After adding the third optical wedge, a constraint condition needs to be added to solve for the rotation angles of the three optical wedges. Appropriate constraints can also solve the "overhead problem" in the dual-wedge scanning system. To facilitate solving for the rotation angles of each optical wedge based on the defined constraints, the wedge angle and refractive index of each optical wedge should be identical.

[0026] In addition, in order to minimize the loss of the beam scanning area, the constraint condition should also ensure that the thickest end of the optical wedge 3 always faces the direction from the center of the target plane to the target pointing point.

[0027] Specifically, this invention provides a method for eliminating the "overhead problem" in a dual-wedge scanning system, comprising the following steps: adding a third wedge to the dual-wedge scanning system; proposing appropriate constraints on the rotation angle of the third wedge to ensure that its rotation angle always changes smoothly and continuously, while the thickest end of the third wedge always faces the direction from the center of the target plane to the target pointing point; using the constraints of the third wedge and the two constraints of the elevation and azimuth angles of the target pointing direction, based on a ray tracing algorithm, the rotation angles of each wedge should be solved inversely according to the target motion trajectory. To facilitate solving the inverse problem of the wedge scanning system, the wedge angles and refractive indices of each wedge should be the same. When solving the rotation angles of each wedge using the above three constraints, the dual wedges and the third wedge are divided into two groups, front and back. First, the rotation angle of the third wedge is solved inversely according to the constraints of the third wedge. Then, starting from the target pointing point, the ray is traced in reverse to the rear surface of the second wedge. Using the elevation and azimuth angles corresponding to the beam pointing direction at this time as constraints, the rotation angles of the dual wedges are then solved inversely.

[0028] Specifically, suppose the target trajectory has m points, where the nth point is a singular point, the trajectory point index is represented by k, k∈[1,m], and the rotation angle of the third optical wedge corresponding to the kth target point is represented by θ3(k). The constraints of the third optical wedge are as follows:

[0029]

[0030] in, Let be the azimuth angle corresponding to the k-th target point. σ(k) is the distance from the k-th target point to the origin of the target plane. max This is the maximum value of the distance. Let the unit coordinate vector of the k-th target point be (x0, y0, z0). T Then its corresponding azimuth angle is:

[0031]

[0032] like Figure 1As shown, in the dual-wedge scanning system, the left side is the first wedge, and the right side is the second wedge. A coordinate system is established with the center of the rear surface of the first wedge as the origin. Both wedges have a wedge angle of β and a refractive index of n. The two wedges rotate counterclockwise at velocities ω1 and ω2, respectively. Initially, both wedges are horizontal with their thinnest ends along the positive x-axis, and their initial rotation angles are both 0°. The incident beam is parallel to the positive z-axis, refracted sequentially through the surfaces of each wedge, and finally intersects the target plane F at point P. For solving the forward problem of the dual-wedge scanning system, based on the ray tracing algorithm, in the three-dimensional coordinate system, the beam is considered as a spatial straight line, and the wedge surfaces are considered as spatial planes. The fundamental geometric elements of these straight lines and planes are represented by matrices, transforming geometric operations into matrix operations. After fixing the wedge placement, the matrix expressions for each wedge surface can be obtained. Using the initial position as a reference, during the wedge rotation process, the matrix expression of the wedge surface changing with the rotation angle can be obtained through the rotation matrix. Given the matrix expression of the incident beam, and based on the law of refraction of spatial vectors, the pointing direction of the refracted beam is calculated plane by plane, starting from the incident beam, ultimately yielding the beam's pointing point on the target plane. For the inverse problem of a dual-wedge scanning system, given a target trajectory, this trajectory is subdivided into multiple target trajectory points. The elevation and azimuth angles corresponding to each target trajectory point are then obtained, allowing the inverse solution to determine the rotation angles of the dual wedges pointing sequentially at each target trajectory point.

[0033] like Figure 2 As shown, a third optical wedge is added to the dual-wedge scanning system. The three wedges rotate counterclockwise at velocities ω1, ω2, and ω3, respectively, with an initial rotation angle of 0° for each wedge. The forward solution process for the three-wedge scanning system is similar to that of the dual-wedge system, except that two tracing surfaces are added. For the reverse solution of the three-wedge scanning system, the dual and third wedges are divided into two groups. First, the rotation angle of the third wedge when pointing to each target trajectory point is solved based on the constraints of the third wedge. Then, the ray is traced backward from the target trajectory point to the rear surface of the second wedge. Using the elevation and azimuth angles corresponding to the beam pointing direction A4 at this time as constraints, the rotation angles of the first and second wedges are solved.

[0034] like Figure 3As shown, for a dual-wedge scanning system, the target first moves along the straight line x = t, y = 0.1. After reaching the y-axis, it turns to the x-axis and continues moving along the straight line x = 0.1, y = t. Based on the ray tracing algorithm, the rotation angle of the dual wedges pointing towards the target's trajectory can be solved. It can be seen that when the target trajectory is a straight line parallel to the y-axis and x-axis respectively, the solved rotation angle of the dual wedges changes almost linearly. However, in the region near the origin, when the straight line trajectory turns from the y-axis to the x-axis, the rotation angle of the dual wedges changes abruptly by 90°. When these two points on the y-axis and x-axis are infinitely close to the origin, the dual wedges need to rotate 90° instantaneously, meaning the rotation speed of the dual wedges is close to infinity. This indicates that the dual-wedge scanning system has an "overshoot problem".

[0035] like Figure 4 As shown, a third optical wedge is added to the dual-wedge scanning system, and the same selection is made. Figure 3 Based on the ray tracing algorithm and the constraints of the third optical wedge, the rotation angles of each optical wedge pointing towards the target's trajectory are solved inversely. It can be seen that the solved rotation angle of the third optical wedge still changes smoothly at the singularity point. At this time, the rotation angles of the other two optical wedges also change smoothly. Compared with the dual-wedge scanning system, this eliminates the abrupt change points in the rotation angles of the optical wedges, thus eliminating the "overhead problem" caused by the system's singularity point.

[0036] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for eliminating the over-the-top problem in a dual-wedge scanning system, characterized in that, A third optical wedge is added to the dual-wedge scanning system, and appropriate constraints are imposed on the rotation angle of the third optical wedge so that the rotation angle of the third optical wedge always changes smoothly and continuously. The constraint conditions for the third optical wedge are shown in the following equation: ； Among them, the target motion trajectory has a total of The point, of which the first Each point is a singular point, and the trajectory point index is... express, , No. The rotation angle of the third optical wedge corresponding to each target point is used express, For the first The azimuth angle corresponding to each target point. , For the first The distance from each target point to the origin of the target plane Then it is the maximum value of that distance; let the first... The unit coordinate vector of each target point is Then its corresponding azimuth angle is: 。 2. The method for eliminating the over-the-top problem in a dual-wedge scanning system according to claim 1, characterized in that, The third optical wedge always points its thickest end toward the direction from the center of the target plane to the target's pointing point.

3. A method for eliminating the over-the-top problem in a dual-wedge scanning system according to claim 1 or 2, characterized in that, Using the constraints of the third optical wedge and the two constraints of the target's pointing direction (pitch and azimuth), the angles that each optical wedge should rotate are solved by back-solving the target's motion trajectory based on the ray tracing algorithm.

4. A method for eliminating the over-the-top problem in a dual-wedge scanning system according to claim 1 or 2, characterized in that, The first, second, and third optical wedges have the same wedge angle and material refractive index.

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