A scanning optical system based on a rotating Risley prism

Abstract

The present invention relates to the field of scanning optical design technology. Specifically, it provides a scanning optical system based on a rotating Risley prism. This system employs a combination of four rotating Risley prisms (germanium-silicon-silicon-germanium) to achieve achromatic aberration in the 3μm-5μm wavelength band. By optimizing the optical axis deflection model and the rotational speed ratio, as well as the surface tangent of the Risley prism's wedge angle, the system's field of view is expanded from 8° to a full 66°, enabling the application of rotating Risley prisms in scanning optical systems. This system addresses issues such as chromatic aberration, field of view limitations, and system miniaturization in the mid-infrared band (3μm-5μm), offering advantages such as high resolution and a large field of view.

Description

Technical Field

[0001] The present 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] A Risley prism is an optical element that can deflect and control light. It has widespread application in light manipulation and related optical imaging fields, such as LiDAR, biomedicine, laser communications, infrared countermeasures, machine vision, and super-resolution imaging. In the LiDAR field, laser beam deflection, combined with appropriate control algorithms, enables laser beam scanning within a certain range. Furthermore, rotating Risley prism systems are also used in electro-optical tracking and imaging systems. They can control the direction of the optical axis based on the target's orientation and, in conjunction with relevant control algorithms, enable dynamic tracking of the target and dynamic scanning imaging over a very large field of view. In the field of biomedical imaging, a prime example is endoscope systems. Rotating Risley prism systems can reduce the numerical aperture of the optical system, thereby increasing depth of field, improving image quality while meeting the wide field of view imaging requirements of endoscopes.

[0003] When designing a scanning optical system based on a rotating Risley prism, the most important issues to consider are chromatic aberration introduced by the Risley prism and distortion caused by beam deflection. Image processing techniques are currently capable of eliminating the distortion caused by beam deflection in the Risley prism. However, current approaches to chromatic aberration still have limitations. First, achromatic aberration designs typically employ cemented prisms, grisms, the introduction of binary surfaces, and meta-lenses. However, existing achromatic aberration designs for Risley prisms operating in the 3μm-5μm wavelength range (with a 21° deflection angle) remain inadequate. For example, the limited deflection angle of a single Risley prism system makes it difficult to achieve wide-field-of-view scanning. Risley prism achromatic designs struggle to meet the demands of expanding the field of view of existing small-field-of-view optical systems. While addressing chromatic aberration, achieving a large deflection angle is difficult, and miniaturization of the prism is also unacceptable.

[0004] Therefore, there is an urgent need for a design solution 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 achromatism of the scanning optical system in the mid-wave infrared spectrum and the problem of expanding the field of view of the existing small field of view optical system.

[0006] To achieve the above object, the technical scheme of the present application is implemented as follows:

[0007] The application provides a scanning optical system based on rotating Risley prisms, comprising: an optical system body for imaging or detection and a rotating Risley prism group, the rotating Risley prism group comprising, sequentially arranged along an optical axis and coaxially rotatable: a first rotating Risley prism, a second rotating Risley prism, a third rotating Risley prism and a fourth rotating Risley prism.

[0008] The first rotating Risley prism and the fourth rotating Risley prism are made of germanium or a mixture doped with germanium.

[0009] The second rotating Risley prism and the third rotating Risley prism are made of silicon or a mixture doped with silicon.

[0010] Preferably, the working waveband is 3-5 microns.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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 rotating Risley prisms is equal to 2 times the maximum deflection angle of the rotating Risley prism group.

[0016] Preferably, the full field of view of the scanning optical system based on rotating Risley prisms is 66°, and the local field of view is 8°.

[0017] Compared with the prior art, the present application can achieve the following beneficial effects:

[0018] The present application first proposes the application of rotating Risley prisms in a scanning optical system, and matches a small field of view of an existing optical system through a rotating Risley prism group with a large deflection angle, effectively expands the field of view of the existing optical system, and the system field of view can be expanded to 66°, which can be applied to large-range detection and imaging.

[0019] In addition, the application first proposes a four-prism combination design, realizes achromatism in a medium-wave infrared (3-5 μm) spectrum band by material design of a rotating Risley prism, and solves the chromatic aberration problem caused by the rotating Risley prism, and in the process of achromatism, the miniaturization of the system structure is also considered. BRIEF DESCRIPTION OF DRAWINGS

[0020] The accompanying drawings, which form a part of the present application, are intended to provide further understanding of the present application and are incorporated herein for a purpose of explanations of the present application. The present application is shown and described in conjunction with the preferred embodiments thereof, and it is not intended to limit the present application unduly.

[0021] Figure 1 is a structural diagram of a scanning optical system based on a rotating Risley prism according to an embodiment of the present application;

[0022] Figure 2 is a structural design diagram of a rotating Risley prism group according to an embodiment of the present application;

[0023] Figure 3 is a light axis deflection model diagram of a single Risley prism according to an embodiment of the present application;

[0024] Figure 4 is a six basic structure diagram of a rotating Risley prism according to an embodiment of the present application;

[0025] Figure 5 is a standard point column diagram of a rotating Risley prism group according to an embodiment of the present application;

[0026] Figure 6 is an off-axis chromatic aberration diagram of a rotating Risley prism group according to an embodiment of the present application;

[0027] Figure 7 is a structural schematic diagram of a scanning optical system based on a rotating Risley prism in a rotating state 1 (a field of view is 25°-33°) according to an embodiment of the present application;

[0028] Figure 8 is a standard point column diagram of a scanning optical system based on a rotating Risley prism in a rotating state 1 according to an embodiment of the present application;

[0029] Figure 9 is an MTF curve diagram of a scanning optical system based on a rotating Risley prism in a rotating state 1 according to an embodiment of the present application;

[0030] Figure 10 is a structural schematic diagram of a scanning optical system based on a rotating Risley prism in a rotating state 2 (a field of view is -4°-4°) according to an embodiment of the present application;

[0031] Figure 11 is a standard point array diagram of the scanning optical system based on the rotating Risley prism in the rotating state 2 according to an embodiment of the present application;

[0032] Figure 12 is a MTF curve diagram of the scanning optical system based on the rotating Risley prism in the rotating state 2 according to an embodiment of the present application.

[0033] Figure 13 is a structure schematic diagram of the scanning optical system based on the rotating Risley prism in the rotating state 3 (the field of view is -33°—-25°) according to an embodiment of the present application.

[0034] The reference signs in the drawings include:

[0035] 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, partial field of view 7. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and do not constitute a limitation on the present application. In different embodiments, similar elements are associated with similar element signs. In the following embodiments, many details are described in order to make the present application better understood. However, those skilled in the art can easily recognize that some features can be omitted in different cases, or can be replaced by other elements, materials or methods. In some cases, some operations related to the present application are not shown or described in the specification in order to avoid the core part of the present application being overwhelmed by too much description, and it is not necessary for those skilled in the art to describe these related operations in detail according to the description in the specification and the general technical knowledge in the art.

[0037] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other to form various embodiments without conflict. Meanwhile, the steps or actions in the method description can also be sequentially adjusted or adjusted in a manner that is obvious to those skilled in the art. Therefore, the order in the specification and the drawings is only for clear description of a certain embodiment, and does not mean a necessary order, unless otherwise stated that a certain order must be followed.

[0038] In the description of the present 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" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present 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 present 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 the indicated technical features. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0039] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art can understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0040] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0041] See also Figure 1 and Figure 2In one embodiment of the present application, a scanning optical system based on rotating Risley prisms is provided, four rotating Risley prisms (germanium-silicon-silicon-germanium) are applied to the existing optical system body 1 to construct a scanning optical system with a 3-5 μm waveband, 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 for regulating 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 arranged in sequence along the optical axis and coaxially rotatable. The working waveband of the scanning optical system designed in the embodiment of the present application is mid-wave infrared (3-5 μm). 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 deflection angle of the light is controlled to more than 30°, the field of view of the optical system body 1 is greatly expanded, and 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 as germanium, silicon, silicon and germanium respectively. By matching the four materials, the chromatic aberration and the prism volume can be controlled within a small 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 use a mixture doped with germanium, and the preparation materials of the second rotating Risley prism 3 and the third rotating Risley prism 4 use a mixture doped with silicon. The present application mainly solves the mid-wave infrared with a working waveband of 3-5 μm. For the working waveband in the infrared band, materials such as ZnS, BaF2, ZnSe and LiF can also be considered for mutual matching to eliminate chromatic aberration.

[0042] The deflection ability of the Risley prism to the light is mainly determined by the following two factors:

[0043] 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.

[0044] Second, the wedge angle of the Risley prism. The larger the wedge angle, the greater the deflection angle of the light.

[0045] Therefore, in order to meet the design requirements, the rotating Risley prism group is designed and optimized as follows:

[0046] As shown in Figure 3 , for the structure of each rotating Risley prism, the present embodiment establishes an optical axis deflection model for analysis, and the deflection angle of the optical axis of the incident light is expressed as , the wedge angle of the Risley prism is expressed as .

[0047] 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:

[0048] ;

[0049] in, represents the rotation angle of the Risley prism.

[0050] Based on the vector form of Snell's refraction law, 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:

[0051] ;

[0052] ;

[0053] .

[0054] 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.

[0055] Based on the above optical axis deflection model, calculation is as follows Figure 4 The direction cosine vectors of the optical axis deflection of the six basic structures shown are used and represent the relative rotation angles of the two Risley prisms.

[0056] 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:

[0057] ;

[0058] In formula ①, the coefficient and The expression is:

[0059] ;

[0060] .

[0061] ;

[0062] In formula ②, the coefficient and The expression of formula ③ is:

[0063] ;

[0064] .

[0065] ;

[0066] The expression of formula ③ and ④ is same, but the specific value of coefficient , and in the two formulas is not same, specifically:

[0067] In formula ③, the expression of coefficient , and is:

[0068] ;

[0069] , wherein, ;

[0070] , wherein, .

[0071] In formula ④, the expression of coefficient , and is:

[0072] ;

[0073] , wherein, ;

[0074] , wherein, .

[0075] ;

[0076] The expression of formula ⑤ and ⑥ is same, but the specific value of coefficient , and in the two formulas is not same, specifically:

[0077] In formula ⑤, the expression of coefficient , and is:

[0078] ;

[0079] wherein, ;

[0080] wherein, .

[0081] In formula (6), the coefficient , and are expressed as:

[0082] ;

[0083] ;

[0084] wherein, .

[0085] By constructing the above six structure models, the corresponding relationship between the light deflection capability of a single Risley prism and its wedge angle and material, and the direction cosine vector of the optical axis deflection under four kinds of rotating double Risley prism structures can be obtained, so as to further analyze the corresponding relationship between the optical axis deflection angle and the relative rotation angle, so as to determine the applicability of different structures in different application backgrounds. At the same time, for the design of a rotating Risley prism group, the above six prism structures can be combined for design, while ensuring reasonable volume, while taking into account large deflection angles. In order to improve the field of view expansion of the optical system body 1 for a small field of view, the embodiment of the application adopts four-prism combination design 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.

[0086] After determining the four-prism combination structure model, the material and wedge angle of each prism are designed, specifically:

[0087] For light rays of different incident directions, the propagation path in the Risley prism is different, but the deflection capability of the light rays is fixed. The determining factor of the deflection capability is the material of the prism and the wedge angle of the top of the prism. The greater the refractive index of the material and the greater the wedge angle, the stronger the deflection capability of the light rays, and the larger the field of view range that can be scanned. With the relative rotation of the two prisms, 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, and then the full field of view 6 imaging is realized.

[0088] The present application adopts a four-prism combination design, which can effectively reduce the refractive pressure of a single Risley prism. The design can reduce the wedge angle of each Risley prism, and the reduction of the wedge angle can reduce the size of each Risley prism. In this way, a large deflection angle can be achieved in the case of a small wedge angle and a small prism volume, thereby achieving a larger scanning field of view. Therefore, the scanning optical system design with a large deflection angle can be achieved by the combination of Risley prisms. 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 x 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 of the system after scanning is 60 degrees (i.e., 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 the optical system body 1, cascading the Risley prism group with a large deflection angle, and constructing a scanning optical system, thereby solving the problem that the traditional large-deflection-angle Risley prism is not suitable for a small field of view optical system.

[0089] For the rotating Risley prism group as shown in Figure 2 , the detailed design parameters of each prism are as follows:

[0090] Table 1 Detailed design parameters of each Risley prism

[0091]

[0092] The rotating Risley prism group designed according to the above parameters is simulated and verified, and the standard point column diagram as shown in Figure 5 and the vertical axis chromatic aberration diagram as shown in Figure 6 are obtained. As can be seen from the diagrams, at the maximum deflection angle, the chromatic aberration of the rotating Risley prism group is well corrected, and the design can be used in 3-5 μm waveband imaging detection and beam control.

[0093] To verify the application effect of the rotating Risley prism group with the above parameters in the optical system body 1, the rotating Risley prism group is cascaded with the optical system body 1 with specific parameters, and the scanning optical system obtained after the cascade is simulated and verified in the rotating state, as follows:

[0094] The parameters and surface shapes of the optical system body 1 are shown in the following table and Figure 7 .

[0095] Table 2 Detailed design parameters of the optical system body 1

[0096]

[0097] Please refer to Figure 7The simulation verification of the scanning optical system designed according to the above parameters is carried out in the state of the rotation state 1, i.e. the state of the field of view of 25°-33°, to obtain the standard point array diagram as shown in Figure 8 and the MTF curve diagram as shown in Figure 9 From the diagrams, it can be seen that clear imaging can be realized, and MTF@30lp / mm>0.3.

[0098] Please refer to the rotation state 2 as shown in Figure 10 The simulation verification of the scanning optical system designed according to the above parameters is carried out in the state of the rotation state 2, i.e. the state of the field of view of -4°-4°, to obtain the standard point array diagram as shown in Figure 11 and the MTF curve diagram as shown in Figure 12 From the diagrams, it can be seen that clear imaging can be realized, and MTF@30lp / mm>0.3.

[0099] Please refer to the rotation state 3 as shown in Figure 13 In the state of the rotation state 3, i.e. the state of the field of view of -33°--25°, since the rotation state 3 is symmetrical to the rotation state 1, and the rear-end optical system body 1 is also a rotationally symmetrical optical system, the imaging quality in this state is consistent with that in the rotation state 1.

[0100] The above verification proves that the middle-wave infrared scanning optical system in the embodiment of the present application can realize clear imaging in different rotation states, and the scanning field of view can reach 66°. Meanwhile, 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, small overall structure and the like in the 3-5 μm mid-infrared waveband.

[0101] In summary, the above only describes preferred embodiments of the present application, and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0102] The system, device, module or unit illustrated in the above one or more embodiments can be specifically implemented by a computer chip or entity, or by a product with certain functions. A typical implementation device is a computer. Specifically, the computer may, for example, be 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.

[0103] It is also to be noted that the terms "comprising", "including", and any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises a... " does not, without more constraints, exclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the recited element.

[0104] Each of the embodiments in the present specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other. Each of the embodiments focuses on the difference from other embodiments. In particular, for the system embodiments, since they are basically similar to the method embodiments, the description is relatively simple, and the relevant parts can be referred to the part of the method embodiments.

[0105] The above describes specific embodiments of the present specification. Other embodiments are within the scope of the appended claims. In some cases, the acts or steps recited in the claims can be performed in a different order than the order in which the acts or steps are recited in the embodiments and still achieve desirable results. In addition, the processes depicted in the figures do not necessarily require the particular order shown, or sequential order, to achieve the desired results. In certain implementations, multitasking and parallel processing can 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 optical system further comprises a rotating Risley prism group, wherein the rotating Risley prism group comprises a first rotating Risley prism, a second rotating Risley prism, a third rotating Risley prism and a fourth rotating Risley prism, which are sequentially arranged along the optical axis and can rotate coaxially; The material of the first rotated Risley prism and the fourth rotated Risley prism is germanium or a mixture doped with germanium; The second rotated Risley prism and the third rotated Risley prism are made of silicon or a mixture doped with silicon; The absolute value of the object tangent of the first rotating Risley prism is 0.111, and the absolute value of the image tangent is 0.27; The absolute value of the object tangent of the second rotating Risley prism is 0.193, and the absolute value of the image tangent is positive infinity; The absolute value of the object tangent of the third rotating Risley prism is positive infinity, and the absolute value of the image tangent 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.

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

3. The scanning optical system based on a rotating Risley prism according to claim 1, wherein: 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.

4. The scanning optical system based on a rotating Risley prism according to claim 3, wherein: 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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