Dual-band polarization-maintaining optical system

Abstract

According to the dual-band polarization-maintaining optical system provided by the invention, the first dichroic mirror and the second dichroic mirror are spatially orthogonally placed, a first-band light beam is reflected by the first dichroic mirror and the second dichroic mirror in sequence, and after the light beam is reflected by the first dichroic mirror, although the polarization state of the light is subjected to first distortion, when the light is transmitted to the second dichroic mirror, the polarization state of the light is not subjected to second distortion; according to the polarization-maintaining light splitting unit, the roles of the P component and the S component are exchanged, the reflection effect of the second dichroic mirror just compensates and counteracts distortion introduced by the first reflection, the polarization state of a reflected light beam emitted from the whole polarization-maintaining light splitting unit is kept consistent with that of incident light, high-quality polarization-maintaining transmission is achieved, and the polarization-maintaining light splitting efficiency is improved. Therefore, the system can accurately acquire and utilize the polarization information of the target in the specific wave band; the light beam of the second wave band is only transmitted by the dichroic mirror once, polarization-maintaining transmission can be achieved due to the fact that the incident angle is small and the phase difference change of light is small, and then the polarization-maintaining transmission function is achieved.

Description

Technical Field

[0001] This application relates to the field of optical detection technology, and in particular to a dual-band polarization-maintaining optical system. Background Technology

[0002] In the field of multi-band detection, co-aperture band detection has advantages such as high space utilization, high spectral efficiency and coaxial imaging. However, in the process of polarization transmission, because there is a dichroic mirror in the dual-band co-aperture system, the dichroic film needs to reflect the short band and transmit the long band. During the reflection process, phase error will be introduced, resulting in polarization-preserving distortion. Summary of the Invention

[0003] Therefore, it is necessary to provide a dual-band polarization-maintaining optical system to address the shortcomings of existing technologies and solve the problem of polarization-maintaining distortion in existing multi-band detection.

[0004] To solve the above problems, this application adopts the following technical solution: One objective of this application is to provide a dual-band polarization-maintaining optical system, comprising: The polarization-maintaining beam splitter includes a first dichroic mirror and a second dichroic mirror, which are placed orthogonally. Incident light enters the first dichroic mirror and reflects the first wavelength beam therein. The reflected beam enters the second dichroic mirror and is reflected by the second dichroic mirror to form a reflected beam. The first dichroic mirror transmits the second wavelength beam therein to form a transmitted beam. The dual-band imaging unit includes a first imaging lens and a second imaging lens. The first imaging lens is used to receive the reflected light beam and perform imaging, and the second imaging lens is used to receive the transmitted light beam and perform imaging.

[0005] In some embodiments, the incident angles of the light beams entering the first and second dichroic mirrors are opposite.

[0006] In some embodiments, both the first and second dichroic mirrors are provided with an incident angle of 45°.

[0007] In some embodiments, the S component after reflection by the first reflective surface of the first dichroic mirror and the second dichroic mirror becomes the P component of the second reflective surface, and the P component after reflection by the first reflective surface becomes the S component of the second reflective surface.

[0008] In some embodiments, the two metallic reflective surfaces of the first and second dichroic mirrors can be represented by a Jones matrix as follows:

[0009] When two metal mirrors satisfy the orthogonality condition and have equal incident angles, and , r' p This is expressed as the complex reflection coefficient of the first dichroic mirror for p-polarized light. r' s Let be the complex reflection coefficient of the first dichroic mirror for s-polarized light. r'' p This is expressed as the complex reflection coefficient of the second dichroic mirror for p-polarized light. r'' s It is expressed as the complex reflection coefficient of the second dichroic mirror for s-polarized light.

[0010] In some embodiments, the incident light The emitted light passes through the polarization-maintaining beam splitter sequentially and is as follows:

[0011] in: T 1 represents the Jones matrix of the reflection of the first dichroic mirror. T 2 represents the Jones matrix of the reflection of the second dichroic mirror. Ep , Es The Jones vector that constitutes the incident light. E' p , E' s The Jones vector that constitutes the outgoing light.

[0012] In some embodiments, a common aperture unit is also included for receiving beams of the first and second wavelengths and converging the beams of the first and second wavelengths to form the incident light.

[0013] In some embodiments, the common aperture unit is a lens group consisting of multiple lenses.

[0014] In some embodiments, an optical window is also included, the optical window comprising a flat glass plate, through which the incident light enters the first dichroic mirror.

[0015] The present application adopts the above technical solution, and its beneficial effects are as follows: The dual-band polarization-maintaining optical system provided in this application includes a first dichroic mirror and a second dichroic mirror. The first and second dichroic mirrors are placed orthogonally. Incident light enters the first dichroic mirror and reflects the first-wavelength beam therein. The reflected beam then enters the second dichroic mirror and is reflected again to form a reflected beam. The first dichroic mirror transmits the second-wavelength beam therein to form a transmitted beam. In this dual-band polarization-maintaining optical system, the first and second dichroic mirrors are spatially orthogonal. The first-wavelength beam is reflected sequentially by both the first and second dichroic mirrors. After reflection by the first dichroic mirror, although the polarization state of the light undergoes a first distortion, the roles of its P and S components are reversed when it propagates to the second dichroic mirror. The reflection effect of the second dichroic mirror precisely compensates for and cancels the distortion introduced by the first reflection. The polarization state of the reflected beam emitted from the entire polarization-maintaining beam splitter unit is consistent with that of the incident light, achieving high-quality polarization-maintaining transmission. This enables the system to accurately acquire and utilize the polarization information of the target in a specific wavelength band. The beam in the second wavelength band is transmitted through the dichroic mirror only once. Due to the smaller incident angle, the phase difference of the light changes less, achieving polarization-maintaining transmission and thus realizing the function of polarization-maintaining transmission. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the structure of the dual-band polarization-maintaining optical system provided in an embodiment of this application.

[0018] Figure 2 This is a schematic diagram of the polarization-maintaining beam splitter provided in an embodiment of this application. Detailed Implementation

[0019] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. In the description of this application, it should be understood that the terms "upper", "lower", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments.

[0021] Please see Figure 1 and Figure 2 This invention provides a dual-band polarization-maintaining optical system, comprising: The polarization-maintaining beam splitter 100 includes a first dichroic mirror 101 and a second dichroic mirror 102. The first dichroic mirror 101 and the second dichroic mirror 102 are placed orthogonally. Incident light enters the first dichroic mirror 101 and reflects the light beam of the first wavelength band therein. The reflected light beam enters the second dichroic mirror 102 and is reflected by the second dichroic mirror 102 to form a reflected light beam. The first dichroic mirror 101 transmits the light beam of the second wavelength band therein to form a transmitted light beam.

[0022] It can be understood that the first dichroic mirror 101 is the first-stage beam-splitting element of the system. It performs the initial separation of composite light from the common-aperture system based on wavelength (band). The dichroic mirror is designed to highly reflect light in the first band and highly transmit light in the second band. Therefore, when composite light arrives at the first dichroic mirror, the light is "filtered," with the light in the first band being reflected in a specific direction, while the light in the second band passes directly through.

[0023] It can be understood that the second dichroic mirror 102 is the second-stage beam-splitting element of the system, specifically designed to process the first-wavelength light reflected by the first dichroic mirror. It is positioned spatially orthogonal to the first dichroic mirror, responsible for receiving and reflecting the first-wavelength light again, precisely guiding it into the subsequent imaging lens. Its key function is to work in conjunction with the first dichroic mirror to form a polarization-maintaining optical path.

[0024] The dual-band imaging unit 200 includes a first imaging lens 201 and a second imaging lens 202. The first imaging lens 202 is used to receive the reflected light beam and perform imaging, and the second imaging lens 202 is used to receive the transmitted light beam and perform imaging.

[0025] It can be understood that the first imaging lens is an imaging lens group designed for the first band of light. It receives the pure band one light reflected from the dichroic mirror II, performs fine aberration correction and focusing on it, and finally forms a clear, high-quality image on the focal plane (such as a CCD or CMOS sensor).

[0026] It is understandable that the second imaging lens is an imaging lens group designed for the second band of light. It receives the pure second band light transmitted from the dichroic mirror, performs fine aberration correction and focusing on it, and finally forms a clear, high-quality image on another focal plane.

[0027] Furthermore, after beam splitting, the first and second imaging lenses can be optimized independently and specifically. Each lens only needs to be designed for its corresponding single band, which can maximize aberration correction and obtain extremely high image quality without compromising the performance of the other band.

[0028] The dual-band polarization-maintaining optical system provided in this application has the following specific optical path: The first band optical path (reflection path): The incident light enters the first dichroic mirror and reflects the first band of light in it, changing its direction and shooting towards the second dichroic mirror. The first band of light reaches the second dichroic mirror, undergoes a second reflection, and is guided into the first imaging lens. The light undergoes fine imaging in the first imaging lens and finally converges on the focal plane to form an image.

[0029] Incident light enters the first dichroic mirror and transmits the second-wavelength light within it. The second-wavelength light is then directly transmitted through this mirror and enters the second imaging lens. The light undergoes fine imaging in the second imaging lens and finally converges onto the focal plane to form an image.

[0030] As can be understood, this system utilizes two spatially orthogonally placed dichroic mirrors to efficiently separate dual-band composite light into two independent optical paths. Each optical path then passes through a subsequent imaging system optimized for its specific wavelength, ultimately forming clear images of both wavelengths simultaneously on its respective focal plane.

[0031] The dual-band polarization-maintaining optical system provided in this application, for the first band beam, forms a reflection structure similar to an "optical pyramid" by placing the first and second dichroic mirrors spatially orthogonal. This design can compensate for the phase change introduced by a single reflection, ensuring that the polarization state of the outgoing light is consistent with that of the incident light, thus achieving polarization-maintaining transmission of the first band beam. For the second band beam, by designing the incident angle of the first dichroic mirror to be small (e.g., close to 0 degrees), the phase delay introduced when the light passes through the dichroic mirror film can be minimized, thereby making its polarization state change extremely small, similarly achieving approximately polarization-maintaining transmission.

[0032] The above solution ingeniously solves the problem of simultaneously maintaining polarization information in multi-band optical systems, enabling the system to not only perform dual-band imaging but also retain polarization information in the reflected or radiated light of objects, greatly expanding its application potential in polarization remote sensing, material composition analysis, stress detection and other fields.

[0033] Furthermore, the incident angles of the light beams entering the first dichroic mirror 101 and the second dichroic mirror 102 are opposite.

[0034] Furthermore, both the first and second dichroic mirrors are provided with an incident angle of 45°.

[0035] Furthermore, the S component after reflection by the first reflective surface of the first dichroic mirror and the second dichroic mirror becomes the P component of the second reflective surface, and the P component after reflection by the first reflective surface becomes the S component of the second reflective surface.

[0036] It is understandable that using two orthogonally placed dichroic mirrors achieves polarization-preserving transmission for the visible optical system. When linearly polarized light is incident on the dichroic mirror, the ratio of the reflection coefficients of the two polarization components and the phase difference are functions of the incident angle. At a 45° incident angle, the phase difference can be eliminated using two orthogonal mirrors, causing the outgoing light to become the original linearly polarized light. With the two mirrors orthogonally placed, the S-component after reflection by the first mirror becomes the P-component of the second mirror, and vice versa.

[0037] It should be noted that: when linearly polarized light (including E) p and E sWhen two orthogonal components (P and S components) are incident on a mirror at a non-zero angle, their reflectivity and phase changes are typically different. This difference alters the amplitude and relative phase relationship between the two components, potentially transforming linearly polarized light into elliptically polarized light, thus disrupting the original polarization state. This scheme uses a first and second dichroic mirror placed orthogonally, both with a 45° incident angle. After reflection by the first dichroic mirror, the roles of the P and S components are reversed relative to the second dichroic mirror. The S component relative to the first dichroic mirror becomes the P component relative to the second dichroic mirror, and vice versa. If the reflection characteristics of the first and second dichroic mirrors are identical, the attenuation and phase delay caused by the first dichroic mirror on the original S component will be compensated by the effect of the second dichroic mirror on it (now the P component), and vice versa.

[0038] Furthermore, the two metallic reflecting surfaces of the first and second dichroic mirrors can be represented by a Jones matrix as follows:

[0039] When two metal mirrors satisfy the orthogonality condition and have equal incident angles, and , r' p This is expressed as the complex reflection coefficient of the first dichroic mirror for p-polarized light. r' s Let be the complex reflection coefficient of the first dichroic mirror for s-polarized light. r'' p This is expressed as the complex reflection coefficient of the second dichroic mirror for p-polarized light. r'' s This is expressed as the complex reflection coefficient of the second dichroic mirror for s-polarized light. When the reflection angle of the two metal mirrors is set to 45°, the incident beam and the outgoing beam after passing through the orthogonal mirrors remain spatially perpendicular.

[0040] Furthermore, the incident light The emitted light passes through the polarization-maintaining beam splitter sequentially and is as follows:

[0041] in: T 1 represents the Jones matrix of the reflection of the first dichroic mirror. T 2 represents the Jones matrix of the reflection of the second dichroic mirror. Ep , Es The Jones vector that constitutes the incident light. E' p , E's The Jones vector that constitutes the outgoing light.

[0042] It can be understood that the transfer matrix of the entire orthogonal mirror system can be expressed as the product of the Jones matrices of the two mirrors: T total = T2* T1.

[0043] Under the conditions of ideal orthogonality and equal incident angles, the result of this product is an identity matrix (multiplied by a common phase factor i).

[0044] T total = i * [1, 0; 0, 1], which means: [E' p ; E' s ] = i * [E p E s ] Therefore, the polarization vector of the emitted light [E'] p ; E' s The polarization vector of the incident light [E] p E s The polarization is directly proportional to the incident light. Therefore, the polarization state of the outgoing light is exactly the same as that of the incident light, achieving perfect polarization-maintaining transmission.

[0045] It is understandable that the core design of the orthogonal dichroic mirror assembly actively and theoretically perfectly compensates for the polarization state change caused by reflection, achieving high-quality polarization-preserving transmission. This is crucial for applications that rely on precise polarization information. By setting the transmission angle of the second dichroic mirror to near 0 degrees, the influence of the transmission process on the polarization state is minimized, thus approximately achieving polarization-preserving transmission.

[0046] Furthermore, it also includes a common aperture unit 30 for receiving beams of the first and second wavelengths and converging the beams of the first and second wavelengths to form the incident light. The common aperture unit is a lens group composed of multiple lenses.

[0047] It is understandable that setting a common aperture unit 30 at the front end of the incident light reduces the system size and complexity, ensures strict alignment of the two spectral fields of view, and enables the simultaneous acquisition of the target's intensity image and polarization information in two spectral bands, greatly enhancing the ability to detect, identify, and classify substances. In addition, the use of a common aperture optical path improves the spatial utilization and band utilization of the optical path and realizes coaxial imaging, which facilitates post-processing between dual-optical-path imaging.

[0048] Therefore, a common-aperture unit is constructed in front of the incident light, and a dual-band imaging unit is constructed behind the orthogonally reflected light, together forming a dual-band polarization-maintaining optical system. Experimental testing proved the feasibility of this scheme, with the polarization-maintaining transmission efficiency of the first band exceeding 92% and the second band exceeding 95%, meeting the requirements for polarization detection.

[0049] In some embodiments, an optical window is also included, the optical window comprising a flat glass plate, through which the incident light enters the first dichroic mirror.

[0050] It should be noted that an optical window is usually one or two parallel flat glass plates (or crystals, such as sapphire, zinc selenide, etc., depending on the wavelength), which can be coated with an anti-reflective film and has a simple structure.

[0051] The dual-band polarization-maintaining optical system provided in this application features a configuration in which the first and second dichroic mirrors are placed orthogonally in space. The first-band beam is reflected sequentially by the first and second dichroic mirrors. After reflection by the first dichroic mirror, although the polarization state of the light undergoes a first distortion, the roles of its P and S components are reversed when it propagates to the second dichroic mirror. The reflection effect of the second dichroic mirror precisely compensates for and cancels the distortion introduced by the first reflection. The reflected beam emitted from the entire polarization-maintaining beam splitter unit maintains the same polarization state as the incident light, achieving high-quality polarization-maintaining transmission. This allows the system to accurately acquire and utilize the polarization information of the target in a specific band. The second-band beam is transmitted through the dichroic mirror only once. Due to the smaller incident angle, the phase difference change of the light is smaller, enabling polarization-maintaining transmission and thus achieving the function of polarization-maintaining transmission.

[0052] It is understood that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0053] The above are merely preferred embodiments of this application, and only specifically describe the technical principles of this application. These descriptions are only for explaining the principles of this application and should not be construed as limiting the scope of protection of this application in any way. Based on this explanation, any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, as well as other specific embodiments of this application that can be conceived by those skilled in the art without creative effort, should be included within the scope of protection of this application.

Claims

1. A dual-band polarization maintaining optical system, characterized by, Comprising: A polarization maintaining beam splitting unit, comprising a first dichroic mirror and a second dichroic mirror, the first dichroic mirror and the second dichroic mirror are orthogonally placed, an incident light enters the first dichroic mirror and reflects a first waveband of light beams therein, the reflected light beams enter the second dichroic mirror and are reflected by the second dichroic mirror to form a reflected light beam; the first dichroic mirror transmits a second waveband of light beams therein to form a transmitted light beam; A dual waveband imaging unit, comprising a first imaging lens and a second imaging lens, the first imaging lens is used for receiving the reflected light beam and imaging, the second imaging lens is used for receiving the transmitted light beam and imaging.

2. The dual-band polarization maintaining optical system of claim 1, wherein, The incident angles of the light beams entering the first dichroic mirror and the second dichroic mirror are opposite.

3. The dual-band polarization maintaining optical system of claim 2, wherein, The first dichroic mirror and the second dichroic mirror are both provided with an incident angle of 45°.

4. The dual-band polarization maintaining optical system of claim 3, wherein, The S component reflected by a first reflecting surface in the first dichroic mirror and the second dichroic mirror becomes the P component of a second reflecting surface, and the P component reflected by the first reflecting surface becomes the S component of the second reflecting surface.

5. The dual-band polarization maintaining optical system of claim 4, wherein, The two metal reflecting surfaces of the first dichroic mirror and the second dichroic mirror can be represented by a Jones matrix as follows: When two metal mirrors satisfy the orthogonal condition and the incident angles are equal, and , r' p represents the complex reflection coefficient of the first dichroic mirror to p-polarized light, r' s represents the complex reflection coefficient of the first dichroic mirror to s-polarized light, r'' p represents the complex reflection coefficient of the second dichroic mirror to p-polarized light, r'' s represents the complex reflection coefficient of the second dichroic mirror to s-polarized light.

6. The dual waveband polarization maintaining optical system according to claim 5, wherein, The incident light Passing through the polarization maintaining optical element in order, the emergent light is: wherein: T 1 represents the reflection Jones matrix of the first dichroic mirror, T 2 represents the reflection Jones matrix of the second dichroic mirror, Ep , Es the Jones vector of the incident light, E' p , E' s the Jones vector of the emergent light.

7. The dual-band polarization maintaining optical system of claim 1, wherein, Further comprising a co-axial unit for accepting the first waveband and the second waveband of light beams and converging the first waveband and the second waveband of light beams to form the incident light.

8. The dual-band polarization maintaining optical system of claim 1, wherein, The co-axial unit is composed of a lens group composed of multiple lenses.

9. The dual-band polarization maintaining optical system of claim 1, wherein, Further comprising an optical window, the optical window comprises a flat glass, and the incident light enters the first dichroic mirror through the optical window.

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