Birefringent lens, finch imaging system and method based on birefringent lens

Abstract

The application discloses a birefringent lens, a FINCH imaging system and method based on the birefringent lens, and the birefringent lens comprises a birefringent generation module and an optical path difference compensation module, the birefringent generation module comprises a first birefringent lens and a first lens, and a combined focal plane and a holographic plane are generated; the optical path difference compensation module comprises a third birefringent lens, the third birefringent lens is in an orthogonal relationship with an optical axis of the first birefringent lens and has the same optical power sign, the optical path difference generated by the first birefringent lens is compensated, the optical path difference is controlled within the coherence length of light, and the total optical path of the first polarized light and the second polarized light formed is close. The application uses one to two groups of birefringent lenses with the same optical power sign to compensate the optical path difference, and controls the curvature radii of two surfaces of the lens so that the thickness of each radial position is very close, and the error is also in a small range for all light rays passing through the lens.

Description

Technical Field

[0001] The present invention relates to the field of imaging technology, and in particular to a birefringent lens, and a FINCH imaging system and method based on the birefringent lens. Background Art

[0002] Fresnel Incoherent Correlation Holography (FINCH) is a method for recording and reconstructing holographic images of three-dimensional objects. This technique uses a spectrometer to split an incident light beam into two parts and focus them onto different planes, forming a holographic image by generating interference effects in the overlapping area. These images are then analyzed to reconstruct a three-dimensional image of the sample. This technique uses an incoherent light source for illumination, allowing it to increase spatial resolution to twice the coherent diffraction limit by capturing only a single image. Furthermore, it can achieve an extremely large depth of field through digital focusing technology and can be easily integrated into existing optical microscope systems, demonstrating broad application potential.

[0003] Three main types of beam splitting components are commonly used in FINCH systems: spatial light modulators, which achieve beam separation through their polarization selectivity; birefringent lenses, which achieve beam splitting by exploiting the fact that birefringent materials have different refractive indices for light with different linear polarization states; and metasurface devices, such as geometric phase lenses, which achieve beam splitting by exploiting the principle that light with different optical rotation states has different refractive indices. However, there are still some drawbacks: spatial light modulators have large deviations such as chromatic aberration, aberration, and discrete error, which can reduce image quality; and metasurface devices are extremely difficult to manufacture and mass-produce.

[0004] Therefore, birefringent lenses are the most promising FINCH spectrometers. Birefringent materials, such as barium metaborate and quartz crystals, are widely used in optical systems due to their ability to distinguish light with different polarization states. This property gives birefringent lenses unique advantages in polarization modulation, wavefront control, and optical path difference generation. A major challenge in applying birefringent lenses to FINCH is minimizing the optical path difference between the two separated beams, keeping it below the coherence length of the light, thereby allowing interference to form a hologram. Summary of the Invention

[0005] The present invention addresses the shortcomings of the prior art and provides a birefringent lens, a FINCH imaging system and method based on the birefringent lens.

[0006] A birefringent lens, comprising a birefringence generating module and an optical path difference compensating module;

[0007] The birefringence generating module includes a first birefringence lens and a first lens, generating a combined focal plane and a holographic plane;

[0008] The optical path difference compensation module includes a third birefringent lens, wherein the optical axis of the third birefringent lens is orthogonal to the optical axis of the first birefringent lens, that is, the optical axis direction of the third birefringent lens is perpendicular to the optical axis direction of the first birefringent lens, and the optical power signs are the same;

[0009] The incident light is diverged by the first birefringent lens into two beams of light with different polarization directions, namely the first polarized light and the second polarized light;

[0010] After being focused by the first lens, the first polarized light and the second polarized light are incident on the third birefringent lens and diverge again into two beams of light with different polarization directions. The third birefringent lens compensates for the optical path difference generated by the first birefringent lens and controls the optical path difference within the coherence length of the light, so that the total optical path of the first polarized light and the second polarized light are close.

[0011] As an implementable embodiment, the optical path difference compensation module further includes a second lens, and the second lens and a third birefringent lens form a first doublet lens;

[0012] The first double-cemented lens diverges the focused first polarized light and the second polarized light into two beams of light with different polarization directions.

[0013] As an implementation method, the optical path difference generated by the first birefringent lens is expressed as: ;

[0014] like , then the optical path difference generated at the third birefringent lens is , ,when When the optical path difference compensation is achieved ;

[0015] in, represent the optical path difference produced by the first birefringent lens and the optical path difference produced by the third birefringent lens, respectively. represent the center thickness of the first birefringent lens and the third birefringent lens respectively, represents the difference in refractive index between the two beams in the first birefringent lens, They represent the refractive index when light propagates along the ordinary axis and extraordinary axis of the birefringent material, It represents the difference in refractive index between the two beams in the third birefringent lens.

[0016] As an implementable embodiment, the birefringence generating module further includes a second birefringence lens, and the optical path difference compensating module further includes a fourth birefringence lens;

[0017] The first birefringent lens and the second birefringent lens form a second doublet lens, and the third birefringent lens and the fourth birefringent lens form a third doublet lens;

[0018] The second doublet lens disperses the incident light into two beams with different polarization directions, namely the first polarized light and the second polarized light, which are then focused and adjusted by the first lens to form focused polarized light;

[0019] The focused polarized light enters the third double-cemented lens, which again disperses the focused polarized light into two beams of light with different polarization directions. The two beams of light with different polarization directions propagate along different paths, thereby forming different focal points.

[0020] As an implementation method, the optical axis of the first birefringent lens is perpendicular to the optical axis of the second birefringent lens, the optical axis of the third birefringent lens is perpendicular to the optical axis of the fourth birefringent lens, the optical axis direction of the first birefringent lens is the same as the optical axis direction of the fourth birefringent lens, but the sign of the optical focal length is opposite; the optical axis direction of the second birefringent lens is the same as the optical axis direction of the third birefringent lens, but the sign of the optical focal length is opposite; the fourth birefringent lens is used to compensate for the optical path difference generated by the second birefringent lens, and the third birefringent lens is used to compensate for the optical path difference generated by the first birefringent lens.

[0021] As an embodiment, the optical path difference generated by the first birefringent lens is , the optical path difference produced by the second birefringent lens ; The optical path difference produced by the fourth birefringent lens , the optical path difference produced by the third birefringent lens , then the total optical path difference is ;

[0022] The relationship between the thickness of each lens at the center: 、 , then the first birefringent lens and the third birefringent lens are combined to compensate the optical path difference The second birefringent lens and the fourth birefringent lens are combined to compensate for the optical path difference , 、 When , the optical path difference compensation is achieved;

[0023] in, represent the optical path difference generated by the first birefringent lens, the optical path difference generated by the second birefringent lens, the optical path difference generated by the third birefringent lens, and the optical path difference generated by the fourth birefringent lens, respectively. represent the center thicknesses of the first birefringent lens, the second birefringent lens, the third birefringent lens, and the fourth birefringent lens, respectively. represents the difference in refractive index between the two beams in the first and fourth birefringent lenses, It represents the difference in refractive index between the two beams in the second and third birefringent lenses.

[0024] A FINCH imaging system based on a birefringent lens includes an optical system, a polarization module, a birefringent lens, a quarter-wave plate, and a polarization camera;

[0025] The sample light is collimated by the standard optical system and then forms polarized light through the polarization module;

[0026] Polarized light enters the birefringent lens and is split into a first polarized light and a second polarized light with orthogonal polarizations, and the optical path difference is compensated to form different focal points and focus on different focal planes;

[0027] The quarter-wave plate converts the first polarized light and the second polarized light into orthogonal circularly polarized first polarized light and second polarized light and interferes with each other to construct a holographic image, and the polarization camera acquires the holographic image, wherein the polarization camera is located at the maximum overlap surface, that is, the intersection of the orthogonal circularly polarized first polarized light and the second polarized light.

[0028] As an implementation method, the polarization camera includes a plurality of pixel units, each of which is provided with a micro linear polarizer grid in front of it, and the micro linear polarizer grid can collect light of different polarization states;

[0029] The micro linear polarizer grid has four equally spaced polarization directions, namely 0, π / 4, π / 2 and 3π / 4, and is arranged in a repeating pattern.

[0030] When the phase delay difference between the first polarized light and the second polarized light of the orthogonal circular polarization is 0, π / 2, π and 3π / 2, the synthesized linear polarized light is in the directions of 0, π / 4, π / 2 and 3π / 4, respectively. The images generated when the polarization phase difference is 0, π / 2, π, 3π / 2 are used as a polarization image set, and the polarization image set includes a first polarization image, a second polarization image, a third polarization image and a fourth polarization image.

[0031] As an implementable method, the following steps are also included:

[0032] Obtaining a complex amplitude holographic image based on the first polarization image, the second polarization image, the third polarization image, and the fourth polarization image;

[0033] According to the hologram propagation distance and the complex amplitude holographic image, image reconstruction calculation is performed in the Fresnel diffraction zone to obtain a reconstructed image;

[0034] The first polarization image, the second polarization image, the third polarization image, and the fourth polarization image are respectively represented as follows:

[0035]

[0036]

[0037]

[0038]

[0039] The complex amplitude light field image is expressed as follows:

[0040]

[0041] The reproduced image is represented as follows:

[0042]

[0043] in, , Indicates that the light Projection of the plane and The angle of the axis, Indicates that the light Projection of the plane and The angle of the axis, represents the reconstruction distance of the hologram, expressed as: , when the incident beam is a plane wave, , then it is converted to: , represents the distance between the center of the birefringent lens and the polarization camera, They represent the focal length of the birefringent lens respectively; It represents the curvature radius of the light beam before it enters the birefringent lens. 、 、 、 The subscripts of polarization images represent polarization directions 0°, 45°, 90°, and 135°, respectively. represents the complex amplitude holographic image, Represents the reproduced image, represents the Fourier transform, represents the inverse Fourier transform, represents the complex amplitude transfer function of Fresnel diffraction, They represent the light fields of the first polarized light, i.e., S light, and the second polarized light, i.e., P light, respectively. represents the imaginary unit, Indicates the wave number.

[0044] A method for implementing a FINCH imaging system based on a birefringent lens comprises the following steps:

[0045] The sample light is collimated by the standard optical system and then forms polarized light through the polarization module;

[0046] Polarized light entering the birefringent lens is split into orthogonal first and second polarized light beams, and the optical path difference is compensated for, and the beams are focused on different focal planes. Specifically, the first birefringent lens diverges the polarized light into two beams with different polarization directions, namely the first polarized light and the second polarized light. After being focused by the first lens, the first and second polarized light beams are incident on the third birefringent lens and diverge again into two beams with different polarization directions. The third birefringent lens compensates for the optical path difference generated by the first birefringent lens, making the total optical path lengths of the first and second polarized light beams close, and controlling the optical path difference within the coherence length of the light.

[0047] The quarter wave plate converts the first polarized light and the second polarized light into orthogonal circularly polarized first polarized light and second polarized light and interferes with each other to construct a holographic image, and the polarization camera acquires the holographic image.

[0048] The present invention has significant technical effects due to the adoption of the above technical solutions:

[0049] The present invention uses one or two groups of birefringent lenses with the same optical power sign to compensate for the optical path difference, and controls the curvature radius of the two surfaces of the lens so that the thickness at each radial position is very close, that is, the optical path difference compensation is not only satisfied at the center of the lens, but its error is also within a smaller range for all light passing through the lens.

[0050] Compared with the solution of using a birefringent plate to compensate for the optical path difference in the prior art, the optical path difference compensation of the present invention is more thorough, and can achieve higher interference contrast and a larger imaging range. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0052] Figure 1 is a schematic diagram of a birefringent lens of the present invention;

[0053] Figure 2 1 is a schematic structural diagram of the birefringent lens of the present invention;

[0054] Figure 3 is a detailed schematic diagram of a specific embodiment of a birefringent lens;

[0055] Figure 4 is a detailed schematic diagram of another specific embodiment of a birefringent lens;

[0056] Figure 5Schematic diagram of a FINCH imaging system based on a birefringent lens according to the present invention;

[0057] Figure 6 is a schematic diagram of a micro linear polarizer grid of a polarization camera of the present invention;

[0058] Figure 7 It is a schematic flow diagram of the method of the present invention. DETAILED DESCRIPTION

[0059] The present invention will be further described in detail below with reference to the examples. The following examples are intended to explain the present invention but the present invention is not limited to the following examples.

[0060] Example 1:

[0061] A birefringent lens, such as Figure 1 and 2 As shown, it includes a birefringence generating module 100 and an optical path difference compensating module 200;

[0062] The birefringence generating module 100 includes a first birefringence lens 110 and a first lens 120, which generate a combined focal plane and a holographic plane;

[0063] The optical path difference compensation module 200 includes a third birefringent lens 220. The optical axis of the third birefringent lens 220 is orthogonal to the optical axis of the first birefringent lens 110. That is, the optical axis of the third birefringent lens 220 is perpendicular to the optical axis of the first birefringent lens 110, and the optical powers have the same sign.

[0064] The incident light is diverged into two beams of light with different polarization directions by the first birefringent lens 110, namely, the first polarized light and the second polarized light; the first polarized light and the second polarized light are focused by the first lens 120 and are incident on the third birefringent lens 220, and are diverged into two beams of light with different polarization directions again. The third birefringent lens 220 compensates for the optical path difference generated by the first birefringent lens 110 and controls the optical path difference within the coherence length of the light, so that the total optical path of the first polarized light and the second polarized light formed are close.

[0065] In the actual experimental process, the optical path difference compensation module can be a birefringent plate or a combination of a concave lens and a convex lens. The present invention uses a lens combination. The advantage of the combination of a concave lens and a convex lens in compensating the optical path difference is that the optical path difference compensation effect is better, and the optical path difference can be correctly compensated for by the edge light and the center light. The present invention uses a fixed lens combination, that is, all lenses are fixed in relative position to form a lens as a whole. The fixed lens combination has the following advantages: the first is that it is easy to carry, load and debug; the second is that the optical path difference compensation and aberration correction are more accurate.

[0066] The principle of optical path difference compensation is: total optical path is the thickness of each layer of medium through which light propagates d i and refractive index n i The optical path difference of the two polarized beams is a function of OPD There is a geometric component caused by the difference in physical paths, but this component is smaller than the coherence length and does not prevent light from interfering. However, the difference in refractive index of the birefringent lens in actual optical path difference compensation is sufficient to cause an optical path difference greater than the coherence length. To observe interference, this component must be compensated. Assume d BRL is the thickness of the birefringent lens through which the light passes, and the thickness is equal to d BRL A compensating birefringent lens cut in the same crystal axis direction is placed in an optical system, and its extraordinary axis is rotated 90° relative to the extraordinary axis of the birefringent lens in a transverse plane. Light polarized along the ordinary axis of the birefringent lens is polarized along the extraordinary axis of the compensating birefringent lens, and vice versa. In this way, the curved surface ΔOPD of the birefringent lens is offset by the compensating birefringent lens.

[0067] See attached Figure 3 As shown, attached Figure 3 This is a specific embodiment, the optical path difference compensation module 200 also includes a second lens 2101, the third birefringent lens 220 and the second lens 2101 form a first doublet lens 201; the first doublet lens 201 diverges the focused first polarized light and the second polarized light into two beams of light with different polarization directions.

[0068] With this structure, the optical path difference generated by the first birefringent lens 110 is expressed as: ;

[0069] like , then the optical path difference generated at the third birefringent lens is , ,when When the optical path difference compensation is achieved , represent the optical path difference produced by the first birefringent lens and the optical path difference produced by the third birefringent lens, respectively. represent the center thickness of the first birefringent lens and the third birefringent lens respectively, represents the difference in refractive index between the two beams in the first birefringent lens, They represent the refractive indices of the two beams of light when they propagate along the ordinary axis and extraordinary axis of the birefringent material, It represents the difference in refractive index between the two beams in the third birefringent lens.

[0070] Figure 3The working principle of the birefringent lens is as follows: the light emitted from the object plane is diverged by the first birefringent lens 110 into two beams of light with different polarization directions, namely S-polarized light and P-polarized light. After being focused by the first lens 120, it reaches the first doublet lens 201, where a birefringence effect similar to that of the first birefringent lens 110 occurs again. The S light, i.e., the first polarized light, and the P light, i.e., the second polarized light, propagate along different paths, forming different focal points.

[0071] Since the optical axis of the third birefringent lens 220 is perpendicular to the optical axis of the first birefringent lens 110 and the optical power has the same sign, it can be used to compensate for the optical path difference between the two beams of light. Ultimately, the two polarized lights with different focal lengths can produce a coherent superposition effect on the subsequent holographic imaging plane. The optical path difference is: the optical path difference generated by the first birefringent lens 110 is , you may wish to set it here , then an optical path difference will be generated at the third birefringent lens 220 , , and then , optical path difference compensation can be achieved .

[0072] This embodiment uses a third birefringent lens with the same optical power sign as the first birefringent lens to compensate for the optical path difference, and designs the curvature radius of the two sides of the lens so that the thickness at each radial position is very close, that is, Not only is the error satisfied at the center of the lens, but it also applies to all light rays passing through the lens within a relatively small range. Compared to solutions using birefringent plates to compensate for optical path differences, the optical path difference compensation of the present invention is more thorough, achieving higher interference contrast and a larger imaging range.

[0073] Figure 4 Another birefringent lens design is given. Since multiple birefringent lenses can achieve greater focal length separation and optical path compensation, in the actual embodiment, the Figure 4The structure is used to manufacture the related birefringent lens. The birefringent lens in this example is suitable for being manufactured using materials with a relatively low birefringence index, such as quartz crystal or magnesium fluoride. In this embodiment, the birefringence generating module 100 further includes a second birefringent lens 130; the optical path difference compensation module 200 further includes a fourth birefringent lens 2102; the first birefringent lens 110 and the second birefringent lens 130 form a second doublet lens 101, and the third birefringent lens 220 and the fourth birefringent lens 2102 form a third doublet lens 202; the second doublet lens 101 disperses the incident light into two beams of light with different polarization directions, namely, a first polarized light and a second polarized light, which are focused and adjusted by the first lens 120 to form focused polarized light; the focused polarized light enters the third doublet lens 202, which again disperses the focused polarized light into two beams of light with different polarization directions. The two beams of light with different polarization directions propagate along different paths, thereby forming different focal points.

[0074] The entire birefringent lens comprises a first birefringent lens 110, a second birefringent lens 130, a first lens 120, a third birefringent lens 220, and a fourth birefringent lens 2102. The first birefringent lens 110 and the second birefringent lens 130 form a second doublet lens 101, and the third birefringent lens 220 and the fourth birefringent lens 2102 form a third doublet lens 202.

[0075] The optical axes of first and second birefringent lenses 110 and 130 are perpendicular to each other, splitting the light into two beams with different polarization directions: S-polarized light and P-polarized light. These light is then focused and adjusted by first lens 120. After entering third doublet lens 202, the light undergoes a birefringence effect similar to that of second doublet lens 101. The S-polarized light (first polarized light) and the P-polarized light (second polarized light) continue to propagate along different paths, forming different focal points.

[0076] Because the two optical axes of the third doublet lens 202 are perpendicular to each other, the paths of the two polarized light beams will change again. The optical axis direction of the fourth birefringent lens 2102 is the same as that of the first birefringent lens 110, but the optical power sign is opposite. The optical axis direction of the third birefringent lens 220 is the same as that of the second birefringent lens 130, and the optical power sign is also opposite. The fourth birefringent lens 2102 is used to compensate for the optical path difference of the second birefringent lens 130, and the third birefringent lens 220 is used to compensate for the optical path difference of the first birefringent lens 110. Ultimately, the two polarized light beams can produce a coherent superposition effect on the subsequent holographic imaging plane. The optical path difference is calculated as follows:

[0077] The optical path difference generated by the first birefringent lens 110 , the optical path difference generated by the second birefringent lens 130 The optical path difference generated by the fourth birefringent lens 2102 , the optical path difference generated by the third birefringent lens 220 , then the total optical path difference is ; The relationship between the thickness of each lens at the center: 、 , the first birefringent lens 110 and the third birefringent lens 220 are combined to compensate for the optical path difference The second birefringent lens 130 and the fourth birefringent lens 2102 are combined to compensate for the optical path difference , 、 When , the optical path difference compensation is achieved; further design the curvature radius of each lens on both sides so that the above 、 At each radial position, it is approximately satisfied that The deviation relative to 0 is within a smaller range for all light passing through the lens, that is, the optical path difference of the entire lens is compensated.

[0078] Example 2:

[0079] A FINCH imaging system based on a birefringent lens, such as Figure 5 As shown, it includes a standard optical system 1, a polarization module 2, i.e., a polarizer, a birefringent lens 0, a quarter-wave plate 3, and a polarization camera 4;

[0080] After the sample light is collimated by the standard optical system 1, it is polarized by the polarization module 2. The polarized light enters the birefringent lens 0 and is separated into the first polarized light and the second polarized light with orthogonal polarization. The optical path difference is compensated to form different focal points and focus on different focal planes. The quarter-wave plate 3 converts the first polarized light and the second polarized light into the first polarized light and the second polarized light with orthogonal circular polarization and interferes with each other to construct a holographic image. The polarization camera acquires the holographic image. The polarization camera 4 is located at the maximum overlap surface. Please refer to the attached figure. Figure 2 The red line in the middle represents the maximum overlapping area.

[0081] In one embodiment, the polarization camera 4 includes a plurality of pixel units, each of which is provided with a micro linear polarizer grid. Figure 6 As shown, the micro linear polarizer grid can collect light in different polarization states; the micro linear polarizer grid is provided with four equidistant polarization directions, namely 0, π / 4, π / 2 and 3π / 4, and is arranged repeatedly; when the phase delay difference between the first polarized light and the second polarized light of the orthogonal circular polarization is 0, π / 2, π and 3π / 2, the synthesized linear polarized light is in the directions of 0, π / 4, π / 2 and 3π / 4, respectively, and the images generated when the polarization phase difference is 0, π / 2, π, 3π / 2 are used as the polarization image set, which includes the first polarization image, the second polarization image, the third polarization image and the fourth polarization image.

[0082] In one embodiment, the following steps are further included:

[0083] A complex amplitude holographic image is obtained based on the first polarization image, the second polarization image, the third polarization image, and the fourth polarization image. An image reconstruction calculation is performed in the Fresnel diffraction zone according to the hologram propagation distance and the complex amplitude holographic image to obtain a reconstructed image. The first polarization image, the second polarization image, the third polarization image, and the fourth polarization image are respectively represented as follows:

[0084]

[0085]

[0086]

[0087]

[0088] The complex amplitude light field image is expressed as follows:

[0089]

[0090] The reproduced image is represented as follows:

[0091]

[0092] in, , Indicates that the light Projection of the plane and The angle of the axis, Indicates that the light Projection of the plane and The angle of the axis, represents the reconstruction distance of the hologram, expressed as: , when the incident beam is a plane wave, , then it is converted to: , represents the distance between the center of the birefringent lens and the polarization camera, They represent the focal length of the birefringent lens respectively; It represents the curvature radius of the light beam before it enters the birefringent lens. 、 、 、 The subscripts of polarization images represent polarization directions 0°, 45°, 90°, and 135°, respectively. represents the complex amplitude holographic image, Represents the reproduced image, represents the Fourier transform, represents the inverse Fourier transform, represents the complex amplitude transfer function of Fresnel diffraction, They represent the light fields of the first polarized light, i.e., S light, and the second polarized light, i.e., P light, respectively. represents the imaginary unit, Indicates the wave number.

[0093] Figure 5 The process is as follows: Light emitted from the object plane is collimated by a standard optical system, then polarized by a polarizer and enters the birefringent lens of the present invention. There, it is split into two beams of orthogonal polarization, which are then focused onto different focal planes after optical path differences are compensated. A quarter-wave plate then converts the beams into orthogonal circular polarizations, which then interfere with each other to create a hologram, which is captured by a polarization camera placed at the plane of maximum overlap.

[0094] Each pixel unit of the polarization camera is inlaid with a micro linear polarizer grid, which can independently collect light of different polarization states. The micro linear polarizer grid has four equidistant polarization directions (0, π / 4, π / 2, 3π / 4) and is repeatedly arranged on the image sensor. See the schematic diagram for details. Figure 6 As shown. When the phase delay differences of the orthogonal circularly polarized P light, i.e. the second polarized light, and the S light, i.e. the first polarized light, are 0, π / 2, π, and 3π / 2, respectively, the synthesized linearly polarized light is in the directions of 0, π / 4, π / 2, and 3π / 4, respectively. Therefore, the polarization camera can be used to collect four holograms with phase differences of 0, π / 2, π, and 3π / 2 in one imaging, that is, a four-step phase-shifted hologram can be obtained by a single exposure. Assume that the electric field components of the P light, i.e. the second polarized light, and the S light, i.e. the first polarized light, are E P and E S , the first polarization image, the second polarization image, the third polarization image and the fourth polarization image captured by the polarization camera are expressed as:

[0095]

[0096] Therefore, the complex amplitude light field image is: , and then according to the wavelength λ , wave number k=2π / λ and U , the reconstructed image is calculated in the Fresnel diffraction region and is expressed as follows:

[0097]

[0098] in, , cosα and cosβ The light in xz Plane and yz Projection on a plane z The angle of the axis, z ris the reconstruction distance of the hologram:

[0099]

[0100] in, z h is the distance between the center of the birefringent lens and the polarization camera, They represent the focal length of the birefringent lens, z d Is the curvature radius of the light beam before it enters the birefringent lens. When the incident light beam is a plane wave, z d = ∞ , the above formula is simplified to:

[0101]

[0102] Compared with the main features of traditional systems, the innovation of this system lies in the use of a fixed concave lens and convex lens combination, which has better optical path difference compensation and aberration correction effects, can make the edge light and the central light compensate the optical path difference correctly, and is easy to carry, install and debug.

[0103] Example 3:

[0104] A method for realizing a FINCH imaging system based on a birefringent lens, such as Figure 7 , including the following steps:

[0105] S100: After the sample light is collimated by the standard optical system, it is transformed into polarized light by the polarization module;

[0106] S200: Polarized light enters a birefringent lens and is split into a first polarized light and a second polarized light with orthogonal polarizations. The optical path difference is compensated and the light is focused on different focal planes. Specifically, the first birefringent lens diverges the polarized light into two beams of light with different polarization directions, namely, the first polarized light and the second polarized light. After being focused by the first lens, the first polarized light and the second polarized light are incident on a third birefringent lens and diverge again into two beams of light with different polarization directions. The third birefringent lens compensates for the optical path difference generated by the first birefringent lens, so that the total optical path lengths of the first polarized light and the second polarized light are close, and the optical path difference is controlled within the coherence length of the light.

[0107] S300 , a quarter-wave plate converts the first polarized light and the second polarized light into orthogonal circularly polarized first polarized light and second polarized light and interferes with each other to construct a holographic image, and a polarization camera acquires the holographic image.

[0108] Various changes and modifications can be made without departing from the spirit and scope of the present invention, and all equivalent technical solutions also fall within the scope of the present invention.

[0109] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the various embodiments can be referenced to each other.

[0110] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, apparatus, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0111] The present invention is described with reference to the flowcharts and / or block diagrams of the method, terminal device (system), and computer program product according to the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing terminal device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing terminal device generate instructions for implementing the process in the flowchart and / or block diagram. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0112] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing terminal device to operate in a specific manner, so that the instructions stored in the computer readable memory produce a manufactured product including an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0113] These computer program instructions can also be loaded onto a computer or other programmable data processing terminal device so that a series of operating steps are executed on the computer or other programmable terminal device to produce a computer-implemented process, thereby providing instructions for executing on the computer or other programmable terminal device to implement the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0114] It should be noted that:

[0115] References in this specification to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Therefore, appearances of the phrases "one embodiment" or "an embodiment" in various places throughout this specification do not necessarily refer to the same embodiment.

[0116] Furthermore, it should be noted that the specific embodiments described in this specification may vary in the shapes and names of their components. Any equivalent or simple variations based on the structure, features, and principles described in the patented concept of this invention are included within the scope of protection of this patent. Persons skilled in the art may make various modifications, additions, or substitutions to the described specific embodiments, and these modifications, as long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, shall fall within the scope of protection of this invention.

Claims

1. A birefringent lens, characterized in that: Including a birefringence generating module and an optical path difference compensation module; The birefringence generating module includes a first birefringence lens and a first lens, generating a combined focal plane and a holographic plane; The optical path difference compensation module includes a third birefringent lens, wherein the optical axis of the third birefringent lens is orthogonal to the optical axis of the first birefringent lens, that is, the optical axis direction of the third birefringent lens is perpendicular to the optical axis direction of the first birefringent lens, and the optical power signs are the same; The incident light is diverged by the first birefringent lens into two beams of light with different polarization directions, namely the first polarized light and the second polarized light; After being focused by the first lens, the first polarized light and the second polarized light are incident on the third birefringent lens and diverge again into two beams of light with different polarization directions. The third birefringent lens compensates for the optical path difference generated by the first birefringent lens and controls the optical path difference within the coherence length of the light, so that the total optical path lengths of the first polarized light and the second polarized light are close. The birefringence generating module further includes a second birefringence lens, and the optical path difference compensating module further includes a fourth birefringence lens; The first birefringent lens and the second birefringent lens form a second doublet lens, and the third birefringent lens and the fourth birefringent lens form a third doublet lens; The second doublet lens disperses the incident light into two beams with different polarization directions, namely the first polarized light and the second polarized light, which are then focused and adjusted by the first lens to form focused polarized light; The focused polarized light enters the third doublet lens, which again disperses the focused polarized light into two beams with different polarization directions. The two beams with different polarization directions propagate along different paths, thereby forming different focal points. The optical axis of the first birefringent lens is perpendicular to the optical axis of the second birefringent lens, the optical axis of the third birefringent lens is perpendicular to the optical axis of the fourth birefringent lens, the optical axis direction of the first birefringent lens is the same as the optical axis direction of the fourth birefringent lens, but the sign of the optical power is opposite; the optical axis direction of the second birefringent lens is the same as the optical axis direction of the third birefringent lens, but the sign of the optical power is opposite; the fourth birefringent lens is used to compensate for the optical path difference generated by the second birefringent lens, and the third birefringent lens is used to compensate for the optical path difference generated by the first birefringent lens.

2. The birefringent lens according to claim 1, wherein: Optical path difference caused by the first birefringent lens , the optical path difference produced by the second birefringent lens ; The optical path difference produced by the fourth birefringent lens , the optical path difference produced by the third birefringent lens , then the total optical path difference is ; The relationship between the thickness of each lens at the center: 、 , then the first birefringent lens and the third birefringent lens are combined to compensate the optical path difference ; The second birefringent lens and the fourth birefringent lens are combined to compensate for the optical path difference , 、 When , the optical path difference compensation is achieved; in, represent the optical path difference generated by the first birefringent lens, the optical path difference generated by the second birefringent lens, the optical path difference generated by the third birefringent lens, and the optical path difference generated by the fourth birefringent lens, respectively. represent the center thicknesses of the first birefringent lens, the second birefringent lens, the third birefringent lens, and the fourth birefringent lens, respectively. represents the difference in refractive index between the two beams in the first and fourth birefringent lenses, It represents the difference in refractive index between the two beams in the second and third birefringent lenses.

3. A FINCH imaging system based on a birefringent lens, characterized in that: Includes optical system, polarization module, birefringent lens, quarter wave plate and polarization camera; The sample light is collimated by the standard optical system and then forms polarized light through the polarization module; Polarized light entering the birefringent lens is separated into a first polarized light and a second polarized light of orthogonal polarizations, and the optical path difference is compensated to form different focal points and focus on different focal planes. The birefringent lens includes a birefringence generation module and an optical path difference compensation module. The birefringence generation module includes a first birefringent lens and a first lens, generating a combined focal plane and a holographic plane. The optical path difference compensation module includes a third birefringent lens, wherein the optical axis of the third birefringent lens is orthogonal to the optical axis of the first birefringent lens, i.e., the optical axis direction of the third birefringent lens is perpendicular to the optical axis direction of the first birefringent lens, and the optical powers have the same sign. After being focused by the first lens, the first polarized light and the second polarized light are incident on the third birefringent lens and diverge again into two beams of light with different polarization directions. The third birefringent lens compensates for the optical path difference generated by the first birefringent lens and controls the optical path difference within the coherence length of the light, so that the total optical path lengths of the first polarized light and the second polarized light are close. The birefringence generating module further includes a second birefringence lens, and the optical path difference compensating module further includes a fourth birefringence lens; The first birefringent lens and the second birefringent lens form a second doublet lens, and the third birefringent lens and the fourth birefringent lens form a third doublet lens; The second doublet lens disperses the incident light into two beams with different polarization directions, namely the first polarized light and the second polarized light, which are then focused and adjusted by the first lens to form focused polarized light; The focused polarized light enters the third doublet lens, which again disperses the focused polarized light into two beams with different polarization directions. The two beams with different polarization directions propagate along different paths, thereby forming different focal points. The optical axis of the first birefringent lens is perpendicular to the optical axis of the second birefringent lens, the optical axis of the third birefringent lens is perpendicular to the optical axis of the fourth birefringent lens, the optical axis of the first birefringent lens is in the same direction as the optical axis of the fourth birefringent lens, but the optical power has opposite signs; the optical axis of the second birefringent lens is in the same direction as the optical axis of the third birefringent lens, but the optical power has opposite signs; the fourth birefringent lens is used to compensate for the optical path difference generated by the second birefringent lens, and the third birefringent lens is used to compensate for the optical path difference generated by the first birefringent lens; The quarter-wave plate converts the first polarized light and the second polarized light into orthogonal circularly polarized first polarized light and second polarized light and interferes with each other to construct a holographic image, and the polarization camera acquires the holographic image, wherein the polarization camera is located at the maximum overlap surface, that is, the intersection of the orthogonal circularly polarized first polarized light and the second polarized light.

4. The FINCH imaging system based on a birefringent lens according to claim 3, characterized in that: The polarization camera includes a plurality of pixel units, each of which is provided with a micro linear polarizer grid in front of it, and the micro linear polarizer grid can collect light of different polarization states; The micro linear polarizer grid has four equally spaced polarization directions, namely 0, π / 4, π / 2 and 3π / 4, and is arranged in a repeating pattern. When the phase delay difference between the first polarized light and the second polarized light of the orthogonal circular polarization is 0, π / 2, π and 3π / 2, the synthesized linear polarized light is in the directions of 0, π / 4, π / 2 and 3π / 4, respectively. The images generated when the polarization phase difference is 0, π / 2, π, 3π / 2 are used as a polarization image set, and the polarization image set includes a first polarization image, a second polarization image, a third polarization image and a fourth polarization image.

5. The FINCH imaging system based on a birefringent lens according to claim 4, characterized in that: The following steps are also included: Obtaining a complex amplitude holographic image based on the first polarization image, the second polarization image, the third polarization image, and the fourth polarization image; According to the hologram propagation distance and the complex amplitude holographic image, image reconstruction calculation is performed in the Fresnel diffraction zone to obtain a reconstructed image; The first polarization image, the second polarization image, the third polarization image, and the fourth polarization image are respectively represented as follows: The complex amplitude light field image is expressed as follows: The reproduced image is represented as follows: in, , Indicates that the light Projection of the plane and The angle between the axes, Indicates that the light Projection of the plane and The angle between the axes, represents the reconstruction distance of the hologram, expressed as: , when the incident beam is a plane wave, , then it is converted to: , represents the distance between the center of the birefringent lens and the polarization camera, They represent the focal length of the birefringent lens respectively; It represents the curvature radius of the light beam before it enters the birefringent lens. 、 、 、 The subscripts of polarization images represent polarization directions 0°, 45°, 90°, and 135°, respectively. represents the complex amplitude holographic image, Represents the reproduced image, represents the Fourier transform, represents the inverse Fourier transform, represents the complex amplitude transfer function of Fresnel diffraction, They represent the light fields of the first polarized light, i.e., S light, and the second polarized light, i.e., P light, respectively. represents the imaginary unit, Indicates the wave number.

6. A method for realizing a FINCH imaging system based on a birefringent lens, characterized in that: The following steps are involved: The sample light is collimated by the standard optical system and then forms polarized light through the polarization module; Polarized light entering the birefringent lens is split into orthogonal first and second polarized light beams, and the optical path difference is compensated for, and the beams are focused on different focal planes. Specifically, the first birefringent lens diverges the polarized light into two beams with different polarization directions, namely the first polarized light and the second polarized light. After being focused by the first lens, the first and second polarized light beams are incident on the third birefringent lens and diverge again into two beams with different polarization directions. The third birefringent lens compensates for the optical path difference generated by the first birefringent lens, making the total optical path lengths of the first and second polarized light beams close, and controlling the optical path difference within the coherence length of the light. The birefringent lens includes a birefringence generating module and an optical path difference compensating module; the birefringence generating module includes a first birefringent lens and a first lens, generating a combined focal plane and a holographic plane; the optical path difference compensating module includes a third birefringent lens, wherein the optical axis of the third birefringent lens is orthogonal to the optical axis of the first birefringent lens, i.e., the optical axis direction of the third birefringent lens is perpendicular to the optical axis direction of the first birefringent lens, and the optical powers have the same sign; the first polarized light and the second polarized light are focused by the first lens and incident on the third birefringent lens, and are further diverged into two beams of light with different polarization directions; the third birefringent lens compensates for the optical path difference generated by the first birefringent lens and controls the optical path difference within the coherence length of the light, so that the total optical path lengths of the first polarized light and the second polarized light are close; The birefringence generating module further includes a second birefringence lens, and the optical path difference compensating module further includes a fourth birefringence lens; The first birefringent lens and the second birefringent lens form a second doublet lens, and the third birefringent lens and the fourth birefringent lens form a third doublet lens; The second doublet lens disperses the incident light into two beams with different polarization directions, namely the first polarized light and the second polarized light, which are then focused and adjusted by the first lens to form focused polarized light; The focused polarized light enters the third doublet lens, which again disperses the focused polarized light into two beams with different polarization directions. The two beams with different polarization directions propagate along different paths, thereby forming different focal points. The optical axis of the first birefringent lens is perpendicular to the optical axis of the second birefringent lens, the optical axis of the third birefringent lens is perpendicular to the optical axis of the fourth birefringent lens, the optical axis of the first birefringent lens is in the same direction as the optical axis of the fourth birefringent lens, but the optical power has opposite signs; the optical axis of the second birefringent lens is in the same direction as the optical axis of the third birefringent lens, but the optical power has opposite signs; the fourth birefringent lens is used to compensate for the optical path difference generated by the second birefringent lens, and the third birefringent lens is used to compensate for the optical path difference generated by the first birefringent lens; The quarter wave plate converts the first polarized light and the second polarized light into orthogonal circularly polarized first polarized light and second polarized light and interferes with each other to construct a holographic image, and the polarization camera acquires the holographic image.

Images