Device and method for measuring light field distribution

Abstract

The invention relates to a device and a method for measuring light field distribution. The device comprises an aperture mask device which is placed on a spatial domain surface or a frequency domain surface of a to-be-measured optical field and has a light-transmitting area, and the light-transmitting area is used for transmitting a part of the to-be-measured optical field; the optical transmission module is used for modulating a part of the to-be-measured optical field so that Wigner distribution of the to-be-measured optical field can rotate in the phase space along with the propagation process; and the light intensity detection module is used for detecting the two-dimensional light intensity distribution of a part of the to-be-detected light field modulated by the optical transmission module.

Description

Technical Field

[0001] The present application relates to the field of optical measurement technology, and more specifically to a device and method for measuring light field distribution. Background Art

[0002] Since its advent, lasers have been widely used due to their advantages such as high coherence, monochromaticity, directionality, and high energy. In reality, there is no truly completely coherent light, whether it exists naturally or is artificially controlled. In addition, in some usage scenarios, such as optical imaging, laser processing, and optical lithography, excessive coherence can cause problems such as non-uniform illumination, speckle noise, and susceptibility to environmental influences, requiring artificial reduction of coherence. Partially coherent light fields are ubiquitous, and completely coherent light can be regarded as an extremely idealized model of partially coherent light.

[0003] The Wigner distribution of a light field can simultaneously describe the spatial position and spatial frequency of a light field, and can establish a connection between wave optics and geometric optics. It has unique advantages in characterizing partially coherent light fields, describing their propagation processes, and evaluating beam quality. The Wigner distribution of a light field has important applications in the fields of light field coherence measurement, optical imaging, and light field modulation, and accurate measurement of the Wigner distribution of a light field is the basis for its application.

[0004] Unlike fully coherent two-dimensional light fields that can be described by two-dimensional wavefronts, partially coherent two-dimensional light fields need to be described by four-dimensional Wigner distribution. The dimensionality mismatch caused by the high dimensionality of the Wigner distribution is the main difficulty in Wigner measurement. The success of traditional phase space tomography technology requires the premise that the light field itself has prior information, such as the light field is a separable variable or rotationally symmetric. Therefore, the application scope of the traditional Wigner measurement method is severely limited.

[0005] Therefore, a new solution for measuring light field distribution is needed in the art. Summary of the invention

[0006] The purpose of the present application is to provide such a device for measuring light field distribution, which can measure the Wigner distribution of any complex light field without requiring the light field to be measured to have prior information.

[0007] According to the first aspect of the present application, a device for measuring light field distribution is provided. The device comprises: an aperture mask device, which is placed on the spatial domain surface or frequency domain surface of the light field to be measured and has a light-transmitting area, and the light-transmitting area is used to transmit the first part of the light field to be measured; an optical transmission module, which is used to modulate the part of the light field to be measured so that its Wigner distribution rotates in the phase space during the propagation process; and a light intensity detection module, which is used to detect the two-dimensional light intensity distribution of the part of the light field to be measured after being modulated by the optical transmission module.

[0008] Preferably, the device further comprises a motion control module, which is configured to move the light intensity detection module along the optical axis so that the light intensity detection module acquires multiple two-dimensional light intensity distributions of the part of the light field to be measured at multiple positions along the optical axis.

[0009] Preferably, the apparatus further comprises a processing module, wherein the processing module is configured to reconstruct a four-dimensional Wigner distribution of the light field to be measured based on a plurality of two-dimensional light intensity distributions corresponding to different parts of the light field to be measured.

[0010] Preferably, the processing module is further configured to reconstruct a three-dimensional blur function corresponding to the portion of the light field to be measured based on the multiple two-dimensional light intensity distributions.

[0011] Preferably, the processing module is further configured to obtain a four-dimensional fuzzy function of the light field to be measured based on the three-dimensional fuzzy functions of multiple parts of the light field to be measured, and reconstruct the four-dimensional Wigner distribution of the light field to be measured by performing a filtered back projection operation on the four-dimensional fuzzy function.

[0012] Preferably, the aperture mask device is moved or replaced to transmit the second portion of the light field to be measured.

[0013] Preferably, the movement of the aperture mask device includes translation or rotation.

[0014] Preferably, the shape of the light-transmitting area of ​​the aperture mask device includes a linear slit, a curved slit or a small hole array.

[0015] Preferably, the thickness of the aperture mask device is less than 200 μm.

[0016] Preferably, the optical transmission module comprises a rotationally symmetric lens and / or an astigmatic lens.

[0017] Preferably, the optical transmission module comprises: a first light group, used to converge the light field to be measured in a first direction and having a first focal length; and a second light group, used to converge the light field to be measured in a second direction and having a second focal length, the first direction and the second direction are respectively orthogonal to the optical axis.

[0018] Preferably, the first light group is arranged to be at the first focal length away from the spatial plane of the light field to be measured, and at the first focal length away from the aperture mask device.

[0019] Preferably, the second light group is arranged to be twice the second focal length away from the spatial plane of the light field to be measured.

[0020] Preferably, the multiple positions include a first position, a second position and a plurality of third positions located between the first position and the second position, wherein: the two-dimensional light intensity distribution at the first position corresponds to a light intensity projection of the Wigner distribution of the portion of the light field to be measured rotated at a first angle; the two-dimensional light intensity distribution at the second position corresponds to a light intensity projection of the Wigner distribution of the portion of the light field to be measured rotated at a second angle; and the two-dimensional light intensity distribution at the third position corresponds to a light intensity projection of the Wigner distribution of the portion of the light field to be measured rotated at a third angle, wherein the third angle is between the first angle and the second angle.

[0021] Preferably, the first angle is 0° and the second angle is 180°.

[0022] Preferably, the plurality of third positions are evenly distributed between the first position and the second position.

[0023] According to a second aspect of the present application, a method for measuring light field distribution is provided. The method includes: a detection operation, the detection operation including the following steps: (a) filtering the light field to be measured using an aperture mask device, wherein the aperture mask device has a light-transmitting area, and the light-transmitting area is used to transmit a portion of the light field to be measured; (b) modulating the filtered light field so that its Wigner distribution rotates in the phase space during the propagation process; (c) scanning and detecting the modulated light field along the optical axis to obtain an axial stack of two-dimensional light intensity distribution at multiple positions; and a processing operation, the processing operation determining the light field distribution based on the obtained axial stack of two-dimensional light intensity distribution.

[0024] Preferably, the processing operation includes the following steps: (d) reconstructing the three-dimensional ambiguity function of the light field to be measured corresponding to the light-transmitting area based on the axial stack of the two-dimensional light intensity distribution; (f) filling the three-dimensional ambiguity function into the four-dimensional ambiguity function space of the light field to be measured; (g) judging whether the four-dimensional ambiguity function of the light field to be measured is complete; when it is determined that the four-dimensional ambiguity function of the light field to be measured is incomplete, (h) scanning the light field to be measured using an aperture mask device and repeating steps (a)-(g) during the scanning process; or when it is determined that the four-dimensional ambiguity function of the light field to be measured is complete, (i) reconstructing the four-dimensional Wigner distribution of the light field to be measured by performing a filtered back projection operation on the four-dimensional ambiguity function. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present application may be better understood by describing exemplary embodiments of the present application in conjunction with the accompanying drawings, in which:

[0026] Figure 1 A schematic block diagram of a device 100 for measuring light field distribution according to an exemplary embodiment of the present application is shown.

[0027] Figure 2-4 Several examples of aperture mask devices are shown separately.

[0028] Figure 5-6 Example movement modes of the aperture mask device are respectively shown.

[0029] Figure 7 and Figure 8 Examples of devices for measuring light field distribution according to the present application are respectively shown.

[0030] Fig. 9 is a flow chart of a method 900 for measuring light field distribution according to an exemplary embodiment of the present application. DETAILED DESCRIPTION

[0031] The specific implementation methods of the present application will be described below. It should be noted that in the specific description of these implementation methods, in order to provide a concise description, it is impossible for this specification to provide a detailed description of all the features of the actual implementation methods. It should be understood that in the actual implementation of any implementation method, just as in the process of any engineering project or design project, in order to achieve the specific goals of the developer and to meet system-related or business-related restrictions, various specific decisions are often made, and this will also change from one implementation method to another. In addition, it can also be understood that although the efforts made in this development process may be complex and lengthy, for ordinary technicians in the field related to the content disclosed in this application, some changes such as design, manufacturing or production based on the technical content disclosed in this disclosure are just conventional technical means, and should not be understood as insufficient content of this disclosure.

[0032] Unless otherwise defined, the technical or scientific terms used in the claims and description shall have the usual meaning understood by persons with ordinary skills in the technical field to which the present application belongs. The words "first", "second" and similar words used in the patent application description and claims of this application do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "one" or "one" do not indicate a quantitative limitation, but indicate the existence of at least one. Words such as "include" or "comprise" and similar words mean that the elements or objects appearing before "include" or "comprise" include the elements or objects listed after "include" or "comprise" and their equivalent elements, and do not exclude other elements or objects. Words such as "connect" or "connected" and similar words are not limited to physical or mechanical connections, nor are they limited to direct or indirect connections.

[0033] In the present disclosure, a structure may be referred to as being "used for" or "capable of" performing certain tasks even if the structure is not currently being operated. For example, "a light intensity detection module for detection" is intended to cover a light intensity detection module having components that perform that function during operation, even if the light intensity detection module is not currently being used (e.g., not connected to a power source).

[0034] In this application, if there is no special description, all embodiments and preferred embodiments mentioned herein can be combined with each other to form a new technical solution. In this application, if there is no special description, all technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

[0035] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0036] The following describes in detail a device for measuring light field distribution provided according to an embodiment of the present application in conjunction with the accompanying drawings.

[0037] refer to Figure 1-4 ,in Figure 1 : shows a schematic block diagram of a device 100 for measuring light field distribution according to an exemplary embodiment of the present application, Figure 2-4 Several examples of aperture mask devices are shown separately.

[0038] The apparatus 100 for measuring light field distribution may include an aperture mask device 110 , an optical transmission module 120 , and a light intensity detection module 130 .

[0039] The aperture mask device 110 can be placed on the spatial domain surface or the frequency domain surface of the light field to be measured. The aperture mask device 110 has a light-transmitting area for transmitting a portion of the light field to be measured (for example, the first portion). The spatial domain surface of the light field to be measured can be any surface to be measured in the light field to be measured, and the frequency domain surface and the surface to be measured can be converted into each other through Fourier transform. As an example, the shape of the light-transmitting area of ​​the aperture mask device 110 may include a linear slit, a curved slit, or an array of small holes. Note that the present application is not intended to limit the mask pattern (i.e., the shape of the light-transmitting area), which can be specially designed according to the distribution of different light fields. Optionally, the mask pattern is a slit parallel to the coordinate axis (such as Figure 2 As shown in FIG. 1 ), this pattern can make the subsequent supporting algorithm simpler, more intuitive in physical sense, and satisfy the Wigner detection of any complex light field. This slit aperture mask can be used as a universal aperture mask pattern of the present application. In addition, corresponding curved slits (such as Figure 3 ) or a specific distribution of dot masks (such as Figure 4 As shown in FIG. 1 , a specially designed aperture mask can make the scanning method simpler under special conditions, shorten the detection time, or facilitate the measurement of light field information in a specific area.

[0040] The optical transmission module 120 may modulate a portion of the light field to be measured (ie, the light field filtered by the aperture mask device 110 ) so that its Wigner distribution rotates in the phase space during the propagation process.

[0041] The light intensity detection module 130 can detect the two-dimensional light intensity distribution of a part of the light field to be measured after being modulated by the optical transmission module 120. The detected two-dimensional light intensity distribution can be further used to determine the light field distribution of the light field to be measured.

[0042] In some embodiments of the present application, the device 100 may further include a motion control module 140. The motion control module 140 may be configured to move the light intensity detection module 130 along the optical axis so that the light intensity detection module 130 acquires multiple two-dimensional light intensity distributions of a portion of the light field to be measured at multiple positions along the optical axis. Figure 1 As shown, the motion control module 140 can move the light intensity detection module 130 from position A to position B, or from position B to position A. Note that in the present application, the motion control module 140 is optional and not necessary, because other methods (e.g., manual) can also be used to move the light intensity detection module 130, or multiple light intensity detection modules 130 can also be used without moving the detection module 130 along the optical axis.

[0043] In some embodiments of the present application, the apparatus 100 may further include a processing module ( Figure 1 The processing module may be configured to reconstruct the four-dimensional Wigner distribution of the light field to be measured based on multiple two-dimensional light intensity distributions corresponding to multiple parts of the light field to be measured. Note that a separate processing module may be provided to perform the reconstruction operation, or the processing module may be integrated with the light intensity detection module 130.

[0044] Specifically, the processing module can be configured to reconstruct a three-dimensional fuzzy function corresponding to a portion of the light field to be measured based on multiple two-dimensional light intensity distributions of the portion of the light field to be measured. The processing module can also be configured to obtain a four-dimensional fuzzy function of the light field to be measured based on the three-dimensional fuzzy functions of different parts of the light field to be measured, and reconstruct the four-dimensional Wigner distribution of the light field to be measured by filtering and back-projecting the four-dimensional fuzzy function. In the device 100 for measuring the light field distribution of the present application, the aperture mask device 110 selectively transmits the light beam according to the aperture pattern to filter the spatial information or frequency information of the light field respectively, and artificially adds a priori conditions to the light field to be measured to reduce the spatial or frequency dimension of the Wigner distribution of the light field to achieve dimensional matching during measurement; the filtered light field is propagated backward through the optical transmission module, and its Wigner distribution rotates accordingly in the phase space as it propagates; the light intensity detection module 130 records the two-dimensional light intensity at several positions along the optical axis, corresponding to the projection of the light intensity rotated at different angles of the Wigner distribution; according to the Fourier slice theorem, the two-dimensional light The Fourier transform function of the intensity distribution corresponds to a section passing through the origin in the blur function of the light field to be measured (the blur function and the Wigner distribution are in a four-dimensional Fourier transform relationship with each other). By scanning along the optical axis by the light intensity detection module 130, the three-dimensional blur function corresponding to the light-transmitting area of ​​the aperture mask can be reconstructed; after reconstructing the three-dimensional blur function corresponding to the light-transmitting area of ​​the aperture mask, the aperture mask device 110 can be used to scan different areas of the light field to be measured, and the three-dimensional blur functions corresponding to different areas can be reconstructed. After traversing the spatial domain or frequency domain, the complete four-dimensional blur function can be filled in, and finally the complete four-dimensional Wigner distribution of the light field to be measured can be reconstructed by the filtered back projection method.

[0045] In some embodiments of the present application, the aperture mask device 110 can be moved or replaced to transmit the second portion of the light field to be measured. The second portion and the first portion may have a partially overlapping area, or may have different areas from each other.

[0046] In some embodiments of the present application, the movement of the aperture mask device 110 may include translation or rotation. Figure 5-6 1 and 2 show example movement modes of the aperture mask device 110. Figure 5 In the example of FIG. 1 , the aperture mask device 110 is a slit parallel to the x-axis, and the aperture mask device 110 can be moved along the y-axis to scan the light field to be measured. Figure 6 In the example of FIG. 1 , the aperture mask device 110 can be rotated around its center to scan the light field to be measured.

[0047] In some embodiments of the present application, if the aperture mask device 110 is a small hole array, the light field to be measured can be scanned by using a plurality of different aperture mask devices 110 .

[0048] In some embodiments of the present application, the optical transmission module 120 may be a first-order optical system, for example, it may be composed of a rotationally symmetric lens (such as a spherical mirror, an aspherical mirror, etc.) and / or an astigmatic lens (such as a cylindrical lens). For example, in the case where the optical transmission module 120 includes a rotationally symmetric lens, the aperture mask device 110 may be placed in the spatial domain plane of the light field to be measured, and the rotationally symmetric lens may converge the light beam in a first direction and a second direction (the first direction and the second direction are respectively orthogonal to the optical axis), and modulate a portion of the light field to be measured that passes through the aperture mask device 110 so that its Wigner distribution rotates in the phase space as the propagation process progresses.

[0049] In some embodiments of the present application, the scanning of the aperture mask device 110 can be achieved through the motion control module 140. In other words, the aperture mask device 110 can drive the light intensity detection module 130 to move, and can also drive the aperture mask device 110 to move.

[0050] In some embodiments of the present application, in order to reconstruct the complete three-dimensional blur function of the aperture mask light-transmitting area, it is necessary to obtain the projection of the Wigner distribution within the range of 0-180°, and the number of projections will also affect the final measurement accuracy. The number of projections is preferably greater than 20 and is evenly distributed within the range of 0-180°, so the motion control module 140 needs to ensure the range and accuracy of movement. In this way, the multiple positions where the light intensity detection module 130 obtains multiple two-dimensional light intensity distributions may include a first position, a second position, and multiple third positions between the first position and the second position. The two-dimensional light intensity distribution at the first position corresponds to the light intensity projection of the Wigner distribution of a part of the light field to be measured rotated at a first angle; the two-dimensional light intensity distribution at the second position corresponds to the light intensity projection of the Wigner distribution of a part of the light field to be measured rotated at a second angle; and the two-dimensional light intensity distribution at the third position corresponds to the light intensity projection of the Wigner distribution of a part of the light field to be measured rotated at a third angle, wherein the third angle is between the first angle and the second angle. Preferably, the first angle is 0° and the second angle is 180°, and the plurality of third positions are evenly distributed between the first position and the second position so that the obtained plurality of light intensity projections are evenly distributed within the range of 0-180°.

[0051] Figure 7 and Figure 8 Examples of devices for measuring light field distribution according to the present application are shown respectively. In these examples, the aperture mask devices 710 and 810 are common slit aperture mask patterns, and the optical transmission modules 720 and 820 are composed of two cylindrical lenses.

[0052] See also Figure 7, which shows the general optical path of the device 700 for measuring light field distribution, in which the slit aperture mask device 710 is placed in the spatial domain plane (the plane where the light field to be measured is located). The optical transmission module can be composed of two cylindrical lenses 721 and 722. In this example, the slit of the aperture mask device 710 is parallel to the x-axis and is placed in the plane of the light field to be measured (spatial domain plane); the first cylindrical lens 721 focuses in the y direction and is located at a distance f1 behind the light field surface, and f1 is the focal length of the first cylindrical lens 721 in the y direction; the second cylindrical lens 722 focuses in the x direction and is located at a distance 2f2 behind the light field surface, and f2 is the focal length of the second cylindrical lens 722 in the x direction.

[0053] In the device 700, the role of the slit aperture mask parallel to the x-axis is to remove the spatial dimension in the y direction of the original four-dimensional Wigner distribution of the light field to be measured, and then the spatial dimension in the y direction can be reconstructed by scanning the slit along the y direction. The role of the first cylindrical lens 721 is to convert the frequency information in the y direction into the spatial information in the y direction, which can be accurately recorded by the light intensity detection module 730 in subsequent propagation. Preferably, the first cylindrical lens 721 can be a Fourier transform lens. The role of the second cylindrical lens 722 is to modulate the light field so that the Wigner distribution rotates in the phase space during the propagation process and is projected to the light intensity detection module 730 at a specific angle.

[0054] See also Figure 8 , which shows the general optical path of the device 800 for measuring the distribution of the light field, in which the slit aperture mask device 810 is placed in the frequency domain plane (for example, the plane corresponding to the light field to be measured after a Fourier transform). The optical transmission module can be composed of two cylindrical lenses 821 and 822. In this example, the slit of the aperture mask device 810 is parallel to the x-axis; the first cylindrical lens 821 focuses in the y direction and is located at a distance f1 behind the light field surface, and f1 is the focal length of the first cylindrical lens 821 in the y direction. The second cylindrical lens 822 focuses in the x direction and is located at a distance 2f2 behind the light field surface, and f2 is the focal length of the second cylindrical lens 822 in the x direction.

[0055] In the device 800, the function of the first cylindrical lens 821 is to first convert the frequency information in the y direction into the spatial information in the y direction, and the slit aperture mask placed on the rear focal plane of the first cylindrical lens 821 and parallel to the x-axis removes the frequency dimension in the y direction of the original four-dimensional Wigner distribution of the light field to be measured, and then the frequency dimension in the y direction can be reconstructed by scanning the slit along the y direction. The function of the second cylindrical lens 822 is to modulate the light field so that the Wigner distribution rotates in the phase space during the propagation process and is projected to the light intensity detection module 830 at a specific angle. Note that this application does not limit the direction of the above-mentioned coordinate axis. The above-mentioned coordinate axis direction is only for illustrative purposes, and the direction of the slit aperture mask can be determined according to actual needs.

[0056] In the above example, after the light field is modulated by the optical transmission module, the light intensity distribution at an optical axis position corresponds to the rotational projection of the Wigner distribution at a specific angle, and the corresponding relationship between the axial position and the projection angle can be determined by the optical transmission module.

[0057] The thickness of the aperture mask device 110 can be designed according to the wavelength λ of the light source. In some embodiments of the present application, the thickness of the aperture mask device 110 can be less than 200 μm to reduce the measurement error caused by the thickness of the mask device.

[0058] In some embodiments of the present application, the slit length of the aperture mask device 110 may be greater than the maximum size of the light spot on the surface where it is placed, to ensure that the entire light spot can be covered during the scanning process. Taking a slit aperture mask placed on the spatial surface parallel to the x-axis as an example, the aperture mask is scanned along the y-axis, and at this time, the slit length is preferably greater than the maximum width of the light spot in the x-direction.

[0059] According to the measurement uncertainty principle in quantum mechanics, the spatial information and frequency information of the light field are non-commutative conjugate physical quantities and cannot be accurately measured at the same time. In Wigner measurement, the spatial resolution and frequency resolution can be adjusted by the slit width of the aperture mask. Taking the slit aperture mask placed on the spatial domain as an example, the narrower the slit, the higher the spatial resolution and the lower the frequency resolution; the wider the slit, the lower the spatial resolution and the higher the frequency resolution. If the slit aperture mask is placed on the frequency domain, the situation is exactly the opposite. The actual slit width needs to be determined according to the measurement requirements and the wavelength λ of the light source. In device 700, when the finite aperture and aberration of the lens are not considered, the minimum spatial resolution is a and the minimum frequency resolution is λf1 / a, where a is the slit width. In device 800, the minimum spatial resolution is λf1 / a and the minimum frequency resolution is a. In actual measurement, a suitable slit width a should be selected to balance the spatial and frequency resolutions to meet the measurement requirements.

[0060] There is no essential difference in the measurement physics principle between the two cases where the aperture mask device 110 is placed in the space domain and the frequency domain. The difference is reflected in the trade-off between the spatial and frequency resolutions and the scanning speeds in different cases. Preferably, the aperture mask device 110 can be placed in the space domain and the frequency domain where the spot scanning size is smaller, which can reduce the scanning distance of the aperture mask and shorten the overall measurement time.

[0061] The present application includes but is not limited to the above two general optical paths. Other optical path combinations should be considered to be included in the scope of the present application as long as they achieve the corresponding effects. For example, in the above optical path, the second cylindrical lens 722 or 822 is located 2f2 behind the light field. At this time, the imaging system is a 2f-2f system, and the image magnification is 1. This situation is a general object-image relationship. In actual measurement, the object-image relationship can be changed according to the actual size of the light field to be measured and the detection range of the detection system, and the magnification can be controlled to ensure that the subsequent light field can be completely detected.

[0062] The light intensity detection module 130 of the present application can be used to detect the light intensity distribution information after being modulated by the optical transmission module 120, and can move along the optical axis direction with the motion control module 140. The target surface of the photodetector can be used to directly record the light intensity distribution, or it can be used in conjunction with a receiving screen and an imaging system (such as a photographic objective lens and a microscope objective lens, etc.). In some cases, factors such as the pixel sampling frequency of the photodetector and the resolution and magnification of the imaging system will affect the measurement accuracy and must be selected according to actual needs. The present application has no special restrictions on the light intensity detection module 130, and it only needs to meet the complete and accurate recording of the light intensity distribution.

[0063] According to an embodiment of the present application, a method for measuring light field distribution is also provided. Fig. 9 , Fig. 9 is a flow chart of a method 900 for measuring light field distribution according to an exemplary embodiment of the present application. The method 900 can be applied to the apparatuses 100, 700 and 800 described above, for example. Fig. 9 As shown, the method 900 for measuring light field distribution may include a detection operation and a processing operation.

[0064] The detection operation may include the following steps S910 to S930 .

[0065] In step S910, the aperture mask device is used to filter the light field to be measured. In this way, the dimension of the Wigner distribution of the light field to be measured can be reduced, for example, the four-dimensional Wigner distribution of the light field to be measured can be reduced to three dimensions.

[0066] The aperture mask device 110 can be placed in the spatial domain or frequency domain of the light field to be measured. The aperture mask device 110 has a light-transmitting area for transmitting a part of the light field to be measured.

[0067] In step S920, the filtered light field is modulated so that its Wigner distribution rotates in the phase space during the propagation process. For example, the modulation can be performed using the optical transmission module 120, 720 or 820 as described above, which will not be described in detail here.

[0068] In step S930, the modulated light field is scanned and detected along the optical axis to obtain an axial stack of two-dimensional light intensity distribution at multiple positions. For example, the light intensity detection module 130 and the motion control module 140 described above can be used for scanning detection, which will not be described in detail here.

[0069] The processing operation may determine the light field distribution based on the acquired axial stack of the two-dimensional light intensity distributions.

[0070] Specifically, the processing operation may include the following steps S940 to S980.

[0071] In the optional step S940, a three-dimensional blur function corresponding to the light-transmitting area of ​​the light field to be measured is reconstructed according to the axial stack of the two-dimensional light intensity distribution.

[0072] In the optional step S950, the three-dimensional fuzzy function is filled into the four-dimensional fuzzy function space of the light field to be measured.

[0073] In the optional step S960, it is determined whether the four-dimensional blur function of the light field to be measured is complete.

[0074] When it is determined that the four-dimensional ambiguity function of the light field to be measured is incomplete, an optional step S970 may be performed, that is, scanning the light field to be measured using an aperture mask device and repeating steps S910 to S960 during the scanning process.

[0075] When it is determined that the four-dimensional ambiguity function of the light field to be measured is complete, an optional step S980 may be performed, that is, reconstructing the four-dimensional Wigner distribution of the light field to be measured by performing a filtering back-projection operation on the four-dimensional ambiguity function.

[0076] In this way, the four-dimensional Wigner distribution of the light field to be measured can be reconstructed based on the axial stack of multiple two-dimensional light intensity distributions corresponding to multiple parts of the light field to be measured (the light field to be measured is scanned using the transparent area of ​​the aperture mask device).

[0077] In the method 900 for measuring the light field distribution of the present application, the aperture mask device selectively transmits the light beam according to the aperture pattern to filter the spatial information or frequency information of the light field respectively, and artificially adds a priori conditions to the light field to be measured to reduce the spatial or frequency dimension of the Wigner distribution of the light field to achieve dimensional matching during measurement; the filtered light field is modulated and propagates backward, and its Wigner distribution rotates accordingly in the phase space as it propagates; the two-dimensional light intensity at several positions propagating along the optical axis is recorded, corresponding to the projection of the light intensity rotated at different angles of the Wigner distribution; according to the Fourier slice theorem, the Fourier transform function of the two-dimensional light intensity distribution corresponds to a section through the origin in the fuzzy function of the light field to be measured (the fuzzy function and the Wigner distribution are in a four-dimensional Fourier transform relationship with each other), and scanning in the direction of the optical axis allows the reconstruction of the three-dimensional fuzzy function corresponding to the transparent area of ​​the aperture mask. After reconstructing the three-dimensional ambiguity function corresponding to the transparent area of ​​the aperture mask, the aperture mask device can be used to scan different areas of the light field to be measured, and the three-dimensional ambiguity functions corresponding to different areas can be reconstructed. After traversing the spatial domain or frequency domain, the complete four-dimensional ambiguity function can be filled in. Finally, the complete four-dimensional Wigner distribution of the light field to be measured can be reconstructed through the filtered back projection method.

[0078] So far, the device and method for measuring the light field distribution according to the present application have been described, wherein a measurement scheme for the four-dimensional Wigner distribution of the light field based on an aperture mask is proposed, which can measure the four-dimensional Wigner distribution of an arbitrarily distributed light field. According to the Wigner distribution, the generalized phase information, coherence information, spatial and frequency information, etc. of the light field can be obtained. Technical support is provided for the fields of light field coherence measurement, characterization and evaluation of partially coherent light fields, phase imaging, and computational imaging. The Wigner distribution can simultaneously represent the spatial position and spatial frequency characteristics of the signal, which can not only meet the needs of analyzing and processing the correlation characteristics of the spatial and frequency domain information of the partially coherent light field, but also can intuitively visualize the characterization and transmission of the partially coherent light field distribution in the form of approximate light rays, thereby establishing a bridge between wave optics and geometric optics. The Wigner distribution of light fields has important applications in the fields of optical imaging, light field modulation, optical lithography, etc.

[0079] Some exemplary embodiments have been described above. However, it should be understood that various modifications may be made to the exemplary embodiments described above without departing from the spirit and scope of the present application. For example, if the described techniques are performed in a different order and / or if the components in the described systems, architectures, devices, or circuits are combined in different ways and / or replaced or supplemented by other components or their equivalents, suitable results may be achieved, and accordingly, these modified other implementations also fall within the scope of protection of the claims.

Claims

1. A device for measuring light field distribution, comprising: An aperture mask device, the aperture mask device is placed on a spatial domain surface or a frequency domain surface of the light field to be measured and has a light-transmitting area, the light-transmitting area is used to transmit a first portion of the light field to be measured; An optical transmission module, wherein the optical transmission module is used to modulate the part of the light field to be measured so that its Wigner distribution rotates in the phase space during the propagation process; as well as A light intensity detection module is used to detect the two-dimensional light intensity distribution of the part of the light field to be measured after being modulated by the optical transmission module.

2. The device according to claim 1, characterized in that The device also includes a motion control module, which is configured to move the light intensity detection module along the optical axis so that the light intensity detection module obtains multiple two-dimensional light intensity distributions of the part of the light field to be measured at multiple positions along the optical axis.

3. The device according to claim 1, characterized in that The apparatus further includes a processing module configured to reconstruct a four-dimensional Wigner distribution of the light field to be measured based on a plurality of two-dimensional light intensity distributions corresponding to a plurality of parts of the light field to be measured.

4. The device according to claim 3, characterized in that The processing module is further configured to reconstruct a three-dimensional blur function corresponding to the portion of the light field to be measured based on the multiple two-dimensional light intensity distributions.

5. The device according to claim 4, characterized in that The processing module is further configured to obtain a four-dimensional fuzzy function of the light field to be measured based on the three-dimensional fuzzy functions of different parts of the light field to be measured, and reconstruct the four-dimensional Wigner distribution of the light field to be measured by performing a filtered back projection operation on the four-dimensional fuzzy function.

6. The device according to claim 1, characterized in that The aperture mask device is moved or replaced to transmit a second portion of the light field to be measured.

7. The device according to claim 6, characterized in that The movement mode of the aperture mask device includes translation or rotation.

8. The device according to claim 1, characterized in that The shape of the light-transmitting area of ​​the aperture mask device includes a linear slit, a curved slit or a small hole array.

9. The device according to claim 1, characterized in that The thickness of the aperture mask device is less than 200 μm.

10. The device according to claim 1, characterized in that The optical transmission module includes a rotationally symmetric lens and / or an astigmatic lens.

11. The device according to claim 1, characterized in that The optical transmission module comprises: A first light group, used for converging the light field to be measured in a first direction and having a first focal length; and The second light group is used to converge the light field to be measured in a second direction and has a second focal length. The first direction and the second direction are respectively orthogonal to the optical axis.

12. The device according to claim 11, characterized in that The first light group is arranged to be at the first focal length away from the spatial plane of the light field to be measured and at the first focal length away from the aperture mask device.

13. The device according to claim 12, characterized in that The second light group is arranged to be twice the second focal length away from the spatial plane of the light field to be measured.

14. The device according to claim 2, characterized in that The plurality of positions include a first position, a second position, and a plurality of third positions between the first position and the second position, wherein: The two-dimensional light intensity distribution at the first position corresponds to a light intensity projection of the Wigner distribution of the part of the light field to be measured rotated at a first angle; The two-dimensional light intensity distribution at the second position corresponds to a light intensity projection of the Wigner distribution of the part of the light field to be measured rotated at a second angle; and The two-dimensional light intensity distribution at the third position corresponds to a light intensity projection of the Wigner distribution of the portion of the light field to be measured rotated at a third angle, wherein the third angle is between the first angle and the second angle.

15. The device according to claim 14, characterized in that The first angle is 0° and the second angle is 180°.

16. The device according to claim 14, characterized in that The plurality of third positions are evenly distributed between the first position and the second position.

17. A method for measuring light field distribution, comprising: The detection operation comprises the following steps: (a) filtering a light field to be measured using an aperture mask device, wherein the aperture mask device has a light-transmitting area, and the light-transmitting area is used to transmit a portion of the light field to be measured; (b) modulating the filtered light field so that its Wigner distribution rotates in phase space as it propagates; (c) scanning and detecting the modulated light field along the optical axis to obtain an axial stack of two-dimensional light intensity distribution at multiple positions; and A processing operation is performed to determine a light field distribution based on the acquired axial stack of the two-dimensional light intensity distribution.

18. The method of claim 17, wherein the processing operation comprises the following steps: (d) reconstructing a three-dimensional ambiguity function of the light field to be measured corresponding to the light-transmitting area according to the axial stack of the two-dimensional light intensity distribution; (f) filling the three-dimensional fuzzy function into the four-dimensional fuzzy function space of the light field to be measured; (g) determining whether the four-dimensional fuzzy function of the light field to be measured is complete; When it is determined that the four-dimensional ambiguity function of the light field to be measured is incomplete, (h) scanning the light field to be measured using an aperture mask device and repeating steps (a) to (g) during the scanning process; or When it is determined that the four-dimensional ambiguity function of the light field to be measured is complete, (i) a four-dimensional Wigner distribution of the light field to be measured is reconstructed by performing a filtered back-projection operation on the four-dimensional ambiguity function.

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