Scanning type optical system based on rotating ristoni prism

Abstract

The invention relates to the technical field of scanning type optical design, in particular to a scanning type optical system based on a rotating risli prism, which adopts a four-rotating risli prism combination (germanium-silicon-silicon-germanium) to realize achromatism at a wave band of 3-5 microns, and realizes the achromatism at the wave band of 3-5 microns through an optical axis deflection model and rotating speed ratio optimization. And the wedge angle surface tangent value of the Lessli prism is optimized, and the view field of the existing system is expanded from 8 degrees to 66 degrees, so that the application of the rotary Lessli prism in a scanning type optical system is realized. The system solves the problems of chromatic aberration of the middle infrared band (3-5 microns), view field limitation, system size miniaturization and the like, and has the advantages of high resolution, large view field and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of scanning optical design, and in particular relates to a scanning optical system based on a rotating Risley prism. Background Art

[0002] The Risley prism is an optical element that can deflect and control light. It is widely used in the field of light control and related optical imaging fields (such as laser radar, biomedicine, laser communication, infrared countermeasures, machine vision, super-resolution imaging, etc.). In the field of laser radar, by deflecting the laser light and combining the corresponding control algorithm, laser light scanning within a certain range can be achieved. In addition, the rotating Risley prism system is also used in optoelectronic tracking systems and imaging systems. It can control the deflection direction of the optical axis of the system according to the orientation of the target and the relevant control algorithm to achieve dynamic tracking of the target and dynamic scanning imaging within a large field of view. At the same time, in the field of biomedical imaging, its typical representative is the endoscope system. The rotating Risley prism system can reduce the numerical aperture of the optical system, thereby increasing the depth of field, while improving the image quality and taking into account the application requirements of the endoscope system for large field of view imaging.

[0003] For the design of scanning optical systems based on rotating Risley prisms, the most important issues to be considered in the system are the chromatic aberration introduced by the Risley prism and the distortion caused by beam deflection. For the distortion problem, the image processing technology can be used to eliminate the distortion caused by beam deflection of the Risley prism. However, there are still certain limitations in the current solutions to chromatic aberration. First of all, the current methods of achromatic aberration design are usually glued prisms, gratings, introduction of binary surfaces, and introduction of meta-lenses. However, in the prior art, there are still deficiencies in the achromatic aberration design of Risley prisms with a working band of 3μm-5μm (deflection angle of 21°). For example, the deflection angle of a single Risley prism system is limited, and it is difficult to achieve large field of view scanning. The achromatic aberration design of the Risley prism is difficult to match the needs of the existing small field of view optical system to expand the field of view. It is difficult to achieve a large deflection angle while solving the chromatic aberration problem, and it is also impossible to take into account the miniaturization of the prism size.

[0004] Therefore, there is an urgent need for a design that can expand the small field of view optical system and effectively eliminate the chromatic aberration problem introduced by the Risley prism. Summary of the invention

[0005] In view of this, the present invention aims to provide a scanning optical system based on a rotating Risley prism, which is used to solve the problem of achromatization of the scanning optical system in the mid-wave infrared spectrum and the problem of field of view expansion of the existing small field of view optical system.

[0006] To achieve the above object, the technical solution created by the present invention is implemented as follows: The present invention provides a scanning optical system based on a rotating Risley prism, comprising: an optical system body for imaging or detection and a rotating Risley prism group, wherein the rotating Risley prism group comprises: a first rotating Risley, a second rotating Risley, a third rotating Risley and a fourth rotating Risley, which are sequentially arranged along an optical axis and can rotate coaxially; The material of the first rotation Risley and the fourth rotation Risley is germanium or a mixture doped with germanium; The material of the second rotation Risley and the third rotation Risley is silicon or a mixture doped with silicon.

[0007] Preferably, the operating wavelength range is 3 μm-5 μm.

[0008] Preferably, the absolute value of the tangent of the object side of the first rotating Risley prism is 0.111, and the absolute value of the tangent of the image side is 0.27; The absolute value of the tangent of the object side of the second rotating Risley prism is 0.193, and the absolute value of the tangent of the image side is positive infinity; The absolute value of the tangent of the object side of the third rotating Risley prism is positive infinity, and the absolute value of the tangent of the image side is 0.193; The absolute value of the tangent of the object side of the first rotating Risley prism is 0.27, and the absolute value of the tangent of the image side is 0.111.

[0009] Preferably, the maximum deflection angle of the rotating Risley prism group is greater than the field of view of the optical system body, and the scanning full field of view of the scanning optical system based on the rotating Risley prism is equal to twice the maximum deflection angle of the rotating Risley prism group.

[0010] Preferably, the scanning optical system based on the rotating Risley prism has a full field of view of 66° and a local field of view of 8°.

[0011] Compared with the prior art, the invention can achieve the following beneficial effects: The present invention proposes for the first time the application of a rotating Risley prism in a scanning optical system. By matching an existing optical system with a small field of view with a rotating Risley prism group with a large deflection angle, the field of view of the existing optical system is effectively expanded. The field of view of the system can be expanded to 66°, which is suitable for large-scale detection and imaging.

[0012] In addition, the present invention proposes a four-prism combination design for the first time. By designing the material of a rotating Risley prism, achromatism in the mid-wave infrared (3μm-5μm) spectrum is achieved, the chromatic aberration problem caused by a rotating Risley prism is solved, and the miniaturization of the system structure is taken into account in the process of achromatism. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings: Figure 1 is a structural diagram of a scanning optical system based on a rotating Risley prism provided according to an embodiment of the present invention; Figure 2 is a structural design diagram of a rotating Risley prism assembly provided according to an embodiment of the present invention; Figure 3 is a diagram of an optical axis deflection model of a single Risley prism provided according to an embodiment of the present invention; Figure 4 6 basic structural diagrams of rotating Risley prisms provided according to embodiments of the present invention; Figure 5 is a standard spot diagram of a rotating Risley prism assembly provided according to an embodiment of the present invention; Figure 6 is a vertical axis chromatic aberration diagram of a rotating Risley prism assembly provided according to an embodiment of the present invention; Figure 7 It is a structural schematic diagram of a scanning optical system based on a rotating Risley prism provided in a rotation state 1 (field of view is 25°-33°) according to an embodiment of the present invention; Figure 8 is a standard spot diagram of a scanning optical system based on a rotating Risley prism in a rotation state 1 provided by an embodiment of the present invention; Fig. 9 6 basic structures of the rotating Risley prism provided by the embodiment of the present invention are MTF curves of the scanning optical system based on the rotating Risley prism in the rotating state 1; Fig.10 It is a structural schematic diagram of a scanning optical system based on a rotating Risley prism provided in a rotation state 2 (field of view is -4° to 4°) according to an embodiment of the present invention; Fig.11 is a standard spot diagram of a scanning optical system based on a rotating Risley prism in a rotation state 2 provided by an embodiment of the present invention; Fig.12 6 basic structures of the rotating Risley prism provided by the embodiment of the present invention are MTF curves of the scanning optical system based on the rotating Risley prism in the rotation state 2; Fig.13 3 is a schematic structural diagram of a scanning optical system based on a rotating Risley prism provided according to an embodiment of the present invention in rotation state 3 (field of view is -33° to -25°).

[0014] Reference numerals include: Optical system body 1, first rotating Risley 2, second rotating Risley 3, third rotating Risley 4, fourth rotating Risley 5, full field of view 6, local field of view 7. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical scheme and advantages of the invention clearer, the invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the invention and do not constitute a limitation to the invention. Similar components in different embodiments use associated similar component numbers. In the following embodiments, many detailed descriptions are to enable the invention to be better understood. However, those skilled in the art can easily recognize that some of the features can be omitted in different situations, or can be replaced by other components, materials, and methods. In some cases, some operations related to the invention are not shown or described in the specification, in order to avoid the core part of the invention being overwhelmed by too much description, and for those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations according to the description in the specification and the general technical knowledge in the art.

[0016] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other to form various implementation methods. At the same time, the steps or actions in the method description can also be interchanged or adjusted in a manner that is obvious to those skilled in the art. Therefore, the various sequences in the specification and the drawings are only for the purpose of clearly describing a certain embodiment and are not meant to be a necessary sequence, unless otherwise specified that a certain sequence must be followed.

[0017] In the description of the invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the invention, unless otherwise specified, the meaning of "multiple" is two or more.

[0018] In the description of the invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0019] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0020] See also Figure 1 and Figure 2In one embodiment of the present invention, a scanning optical system based on a rotating Risley prism is provided, and a four-rotating Risley prism combination (germanium-silicon-silicon-germanium) is applied to an existing optical system body 1 to construct a scanning optical system with a 3μm-5μm band, low chromatic aberration, and a large field of view. The structure mainly includes: an existing optical system body 1 for imaging or detection and a rotating Risley prism group, and the rotating Risley prism group is used to adjust the deflection of the optical axis to expand the field of view of the optical system body 1. The rotating Risley prism group includes: a first rotating Risley prism 2, a second rotating Risley prism 3, a third rotating Risley prism 4, and a fourth rotating Risley prism 5, which are arranged in sequence along the optical axis and can rotate coaxially. The working band of the scanning optical system designed in the embodiment of the present invention is the mid-wave infrared (3μm-5μm). By introducing four Risley prisms on the basis of the existing optical system body 1 and designing the wedge angle of each rotating Risley prism, the light deflection angle is controlled to be above 30°, which greatly expands the field of view of the optical system body 1. The materials of the first rotating Risley prism 2, the second rotating Risley prism 3, the third rotating Risley prism 4 and the fourth rotating Risley prism 5 are designed to be germanium, silicon, silicon and germanium respectively. By matching the four materials, the chromatic aberration and the prism volume can be controlled within a smaller range to meet the imaging and detection requirements. In addition, the preparation materials of the first rotating Risley prism 2, the second rotating Risley prism 3, the third rotating Risley prism 4 and the fourth rotating Risley prism 5 can also be reasonably doped. The preparation materials of the first rotating Risley prism 2 and the fourth rotating Risley prism 5 are a mixture doped with germanium, and the preparation materials of the second rotating Risley prism 3 and the third rotating Risley prism 4 are a mixture doped with silicon. The present invention mainly solves the problem of medium-wave infrared with a working band of 3μm-5μm. For the working band in the infrared band, it can also be considered to use ZnS, BaF2, ZnSe, LiF and other materials in sequence to match each other to eliminate chromatic aberration.

[0021] The ability of a Risley prism to deflect light is mainly determined by the following two factors: First, the material of the Risley prism. Different materials have different refractive indices. The higher the refractive index of the material, the greater the deflection angle of the light in the Risley prism.

[0022] Second, the wedge angle of the Risley prism. The larger the wedge angle, the greater the deflection angle of the light.

[0023] Therefore, in order to meet the design requirements, the rotating Risley prism group was optimized as follows: like Figure 3 As shown, for each rotating Risley prism structure, the embodiment of the present invention establishes an optical axis deflection model for analysis, and the optical axis deflection angle of the incident light is expressed as , the wedge angle of the Risley prism is expressed as .

[0024] Assume that the optical axis vector of the incident light is ,but Figure 3 Normal vector of the incident interface of the light on the left side of the Risley prism It can be expressed as: ; in, Represents the rotation angle of the Risley prism.

[0025] Based on the vector form of Snell's law of refraction, we can analyze and obtain the cosine vector of the optical axis after the light passes through a Risley prism. It can be expressed as: ; ; .

[0026] in, Represents a coefficient related to Snell's law of refraction and is an intermediate variable used to calculate the cosine vector of the optical axis outgoing direction.

[0027] Based on the above optical axis deflection model, the calculation is as follows Figure 4 The direction cosine vectors of the optical axis deflection of the six basic structures shown are used and They represent the relative rotation angles of the two Risley prisms.

[0028] The direction cosine vectors of the optical axis deflection of the six basic structures shown in the figure are represented as ①, ②, ③, ④, ⑤ and ⑥ respectively. The specific expression of the direction cosine vector of the optical axis deflection is: ; In formula ①, the coefficient and The expression is: ; .

[0029] ; In formula ②, the coefficient and The expression is: ; .

[0030] ; Although the expressions of formula ③ and ④ are the same, the coefficients in the two formulas are , and The specific values ​​are not the same, specifically: In formula ③, the coefficient , and The expression is: ; ,in, ; ,in, .

[0031] In formula ④, the coefficient , and The expression is: ; ,in, ; ,in, .

[0032] ; Although the expressions of formulas ⑤ and ⑥ are the same, the coefficients in the two formulas are , and The specific values ​​are not the same, specifically: In formula ⑤, the coefficient , and The expression is: ; ,in, ; ,in, .

[0033] In formula ⑥, the coefficient , and The expression is: ; ; ,in, .

[0034] Through the construction of the above six structural models, the corresponding relationship between the light deflection ability of a single Risley prism and its wedge angle and material, as well as the direction cosine vectors of the optical axis deflection under the four rotating double Risley prism structures can be obtained, so as to further analyze a corresponding relationship between the optical axis deflection angle and the relative rotation angle, thereby determining the applicability of different structures in different application backgrounds. At the same time, for the design of a rotating Risley prism group, a combination design can be performed through the above six prism structures, while ensuring a reasonable volume and taking into account a large deflection angle. In order to improve the field of view expansion of an optical system body 1 with a small field of view, the embodiment of the present invention adopts a four-prism combination design of a first rotating Risley prism 2, a second rotating Risley prism 3, a third rotating Risley prism 4 and a fourth rotating Risley prism 5.

[0035] After determining the four-prism combination structure model, the material and wedge angle of each prism are designed, specifically: The propagation path of light with different incident directions in the Risley prism is different, but its ability to deflect light is fixed. The determining factors of this deflection ability are the material of the prism itself and the wedge angle at the top of the prism. The greater the refractive index of the material and the larger the wedge angle, the stronger its ability to refract light and the larger the field of view that can be scanned. As the two prisms rotate relative to each other, the deflection angle of the optical axis also changes, and the local field of view 7 (instantaneous imaging field of view) also changes accordingly, so that the field of view can be scanned, thereby achieving full field of view 6 imaging.

[0036] Since the present invention adopts a four-prism combination design, the refractive pressure of a single Risley prism can be effectively reduced. Such a design can reduce the wedge angle of each Risley prism. The reduction of the wedge angle can also reduce the size of each Risley prism, thereby achieving a larger deflection angle under the condition of a small wedge angle and a small prism volume, thereby achieving a larger scanning field of view. Therefore, the design of a scanning optical system with a large deflection angle can be realized through the Risley prism combination. In this design method, the maximum deflection angle of the Risley prism is the maximum half-field angle of the entire system, and there is no vignetting problem. At this time, the field of view of the system is: the maximum deflection angle of the rotating Risley prism group × 2. Assuming that the field of view of the optical system body 1 is 8 degrees and the maximum deflection angle of the Risley prism group is 30 degrees, the full field of view 6 after the system scan is 60 degrees (that is, the local field of view 7 is 8 degrees and the full field of view 6 is 60 degrees). This design method is suitable for expanding the field of view of an optical system body 1 with a small field of view, cascading a Risley prism group with a large deflection angle, and constructing a scanning optical system, thereby solving the problem that the traditional Risley prism with a large deflection angle is incompatible with the optical system with a small field of view.

[0037] For Figure 2 The detailed design parameters of each prism of the rotating Risley prism group shown are as follows: Table 1 Detailed design parameters of each Risley prism

[0038] The rotating Risley prism set designed with the above parameters is simulated and verified, and the following results are obtained: Figure 5 The standard spot diagram shown and Figure 6 The vertical axis chromatic aberration diagram is shown. It can be seen from the figure that at the maximum deflection angle, the chromatic aberration of the rotating Risley prism group is well corrected. This design can be used for imaging detection and beam control in the 3μm-5μm band.

[0039] In order to verify the application effect of the rotating Risley prism group with the above parameters in the optical system body 1, the embodiment of the present invention also cascades the rotating Risley prism group with the optical system body 1 with specific parameters, and simulates and verifies the scanning optical system obtained after the cascade in the rotating state, as follows: For the parameters and surface shape of the optical system body 1, please refer to the following table and Figure 7 .

[0040] Table 2 Detailed design parameters of the optical system body 1

[0041] Please refer to Figure 7 In the rotation state 1 shown in FIG. 1 , when the field of view is 25°-33°, the scanning optical system designed with the above parameters is simulated and verified, and the following is obtained: Figure 8 The standard spot diagram shown and Fig. 9 As shown in the MTF curve, it can be seen that clear imaging can be achieved and MTF@30lp / mm>0.3.

[0042] Please refer to Fig.10 In the rotation state 2 shown in FIG. 1 , when the field of view is -4° to 4°, the scanning optical system designed with the above parameters is simulated and verified, and the following is obtained: Fig.11 The standard spot diagram shown and Fig.12 As shown in the MTF curve, it can be seen that clear imaging can be achieved and MTF@30lp / mm>0.3.

[0043] Please refer to Fig.13 In the rotation state 3 shown, when the field of view is -33°—-25°, since the rotation state 3 is symmetrical to the rotation state 1 and the rear optical system body 1 is also a rotationally symmetric optical system, the imaging quality in this state is also consistent with that in the rotation state 1.

[0044] The above verification proves that the medium-wave infrared scanning optical system of the embodiment of the present invention can form clear images under different rotation states, and the field of view after scanning can reach 66°. At the same time, the design method takes into account the size and wedge angle of the Risley prism, and has the advantages of large field of view, low chromatic aberration, and small overall structure in the 3μm-5μm mid-infrared band.

[0045] In short, the above description is only a preferred embodiment of this specification and is not intended to limit the protection scope of this specification. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this specification shall be included in the protection scope of this specification.

[0046] The systems, devices, modules or units described in one or more of the above embodiments may be implemented by a computer chip or entity, or by a product having a certain function. A typical implementation device is a computer. Specifically, the computer may be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.

[0047] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0048] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0049] The above is a description of a specific embodiment of the specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in an order different from that in the embodiments and still achieve the desired results. In addition, the processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

Claims

1. A scanning optical system based on a rotating Risley prism, comprising an optical system body for imaging or detection, characterized in that: The invention also comprises a rotating Risley prism group, wherein the rotating Risley prism group comprises: a first rotating Risley, a second rotating Risley, a third rotating Risley and a fourth rotating Risley, which are sequentially arranged along the optical axis and can rotate coaxially; The materials of the first rotation Risley and the fourth rotation Risley are germanium or a mixture doped with germanium; The material of the second rotation Risley and the third rotation Risley is silicon or a mixture doped with silicon.

2. The scanning optical system based on a rotating Risley prism according to claim 1, characterized in that: The working band is 3μm-5μm.

3. The scanning optical system based on a rotating Risley prism according to claim 1, characterized in that: The absolute value of the tangent of the object side of the first rotating Risley prism is 0.111, and the absolute value of the tangent of the image side is 0.27; The absolute value of the tangent of the object side of the second rotating Risley prism is 0.193, and the absolute value of the tangent of the image side is positive infinity; The absolute value of the tangent of the object side of the third rotating Risley prism is positive infinity, and the absolute value of the tangent of the image side is 0.193; The absolute value of the tangent of the object side of the first rotating Risley prism is 0.27, and the absolute value of the tangent of the image side is 0.

111.

4. The scanning optical system based on a rotating Risley prism according to claim 1, characterized in that: The maximum deflection angle of the rotating Risley prism group is greater than the field of view of the optical system body, and the scanning full field of view of the scanning optical system based on the rotating Risley prism is equal to twice the maximum deflection angle of the rotating Risley prism group.

5. The scanning optical system based on a rotating Risley prism according to claim 4, characterized in that: The scanning optical system based on the rotating Risley prism has a full field of view of 66° and a local field of view of 8°.

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