Imaging system and imaging method for transmitting light through dynamic scattering medium

Abstract

The invention provides an imaging system and an imaging method for transmitting light through a dynamic scattering medium. The imaging system comprises a light source module, a diffracted light filtering module and an imaging module, the light source module is used for generating coherent light beams irradiating a target object, the diffracted light filtering module is used for filtering diffraction orders in reflected light beams of the target object, and the filtered reflected light beams are used for penetrating through a dynamic scattering medium. And the imaging module is used for collecting the dynamic speckle pattern generated by the dynamic scattering medium and recovering the image of the target object according to the dynamic speckle pattern. The imaging system and the imaging method can be applied to a dynamic scattering medium, the limitation of an optical memory effect is broken through, the amplitude information of a target can be directly obtained from a speckle pattern, and large-view-field imaging is achieved. Meanwhile, the method does not need to intrude into a target surface, does not need priori knowledge of a target and a scattering medium, does not need to keep the scattering medium still, and greatly facilitates practical application.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical imaging, and in particular, relates to an imaging system and an imaging method for light passing through a dynamic scattering medium. Background Art

[0002] From macro to micro, achieving optical imaging is the most basic goal. However, optical aberrations, turbulence and scattering are the main obstacles to achieving this goal. Therefore, the aberrations of light passing through scattering media and the imaging of scattering media have been repeatedly identified as one of the most important problems in optics. At present, many classic methods have been proven to overcome the influence of scattering and can image through scattering media.

[0003] For example, wavefront shaping is an effective method for imaging through scattering media, which controls the propagation of light in scattering media by controlling the wavefront of light. However, most wavefront shaping techniques can only image within the range of the optical memory effect by point-by-point raster scanning of a focus point, and they also have to assume that the imaging target scene contains known objects, namely "guide stars". Recent wavefront shaping techniques use iterative optimization to achieve non-invasive direct imaging of light through scattering media without point-by-point scanning. However, their imaging field of view is still limited to the range of the optical memory effect, resulting in a small imaging field of view. The use of transfer matrix methods is an alternative method that can achieve imaging beyond the range of the optical memory effect. However, they often require the scattering medium to be stationary. For another example, in the field of microscopic imaging, speckle correlation method is a very practical method. It can achieve fast non-invasive imaging in dynamic scattering media by utilizing the translation invariance of speckle, namely the "optical memory effect". However, the optical memory effect is only valid within a very small range, usually only a few hundred microns, which limits the target size of the imaging method and requires that the target object size must be smaller than an optical memory effect range.

[0004] In general, existing scattering imaging methods have certain limitations and cannot achieve imaging of target images beyond the range of the optical memory effect through dynamic strong scattering media. Summary of the invention

[0005] The technical problem solved by the present invention is: how to achieve large-field imaging through a dynamic scattering medium.

[0006] The present application also provides an imaging system for light passing through a dynamic scattering medium, the imaging system comprising:

[0007] A light source module, the light source module is used to generate a coherent light beam for illuminating a target object;

[0008] A diffraction light filtering module, wherein the diffraction light filtering module is used to filter the diffraction orders in the reflected light beam of the target object, and the filtered reflected light beam is used to pass through the dynamic scattering medium;

[0009] An imaging module is used to collect the dynamic speckle pattern generated by the dynamic scattering medium and restore the image of the target object according to the dynamic speckle pattern.

[0010] Optionally, the light source module includes a laser, a beam expander collimator, a first aperture, and a polarizer, the beam expander collimator is used to adjust the wavefront of the coherent light beam generated by the laser, the first aperture is used to adjust the diameter of the coherent light beam, and the polarizer is used to adjust the polarization state of the coherent light beam.

[0011] Optionally, the diffraction light filtering module includes a first lens, a second aperture, and a second lens arranged in sequence, the first lens and the second lens are used to adjust the diameter of the reflected light beam, and the second aperture is used to filter the diffraction order in the reflected light beam.

[0012] Optionally, the imaging module comprises an image acquisition unit and a computing unit, the image acquisition unit is used to acquire a dynamic speckle pattern, and the computing unit is used to restore an image of the target object according to the dynamic speckle pattern.

[0013] Optionally, the imaging system further comprises a dynamic scattering module, wherein the dynamic scattering module comprises a scattering medium and a moving device, wherein the moving device is used to move the scattering medium.

[0014] Optionally, the imaging system further comprises a target image module, wherein the target image module is used to generate and display an image used as a target object.

[0015] The present application also provides an imaging method for light passing through a dynamic scattering medium, the imaging method comprising:

[0016] The above imaging system is used to acquire a dynamic speckle pattern of the target object;

[0017] Acquiring autocorrelation amplitude information of the dynamic speckle pattern;

[0018] Obtaining amplitude information of the target object image according to the autocorrelation amplitude information;

[0019] The phase information of the target object image is obtained according to the amplitude information and a preset phase recovery algorithm, and the final target image is reconstructed according to the amplitude information and the phase information.

[0020] Optionally, when the number of the dynamic speckle patterns is one, the method for obtaining the autocorrelation amplitude information of the dynamic speckle pattern includes:

[0021] A covariance operation is performed on the dynamic speckle pattern to obtain autocorrelation amplitude information.

[0022] Optionally, when the number of the dynamic speckle patterns is a plurality of patterns, the method for obtaining the autocorrelation amplitude information of the dynamic speckle patterns includes:

[0023] A covariance operation is performed on each of the dynamic speckle patterns, and an average value of the covariance operation results of each of the dynamic speckle patterns is used as the autocorrelation amplitude information.

[0024] The present application provides an imaging system and imaging method for light passing through a dynamic scattering medium, which have the following technical effects:

[0025] The imaging system and imaging method can be applied to dynamic scattering media, breaking through the limitations of the optical memory effect, and can directly obtain the amplitude information of the target from the speckle pattern to achieve large field of view imaging. At the same time, the method does not require intrusion into the target surface, does not require prior knowledge of the target and the scattering medium, and does not require the scattering medium to remain stationary, which greatly facilitates practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of an imaging system for light passing through a dynamic scattering medium according to the first embodiment of the present invention;

[0027] Figure 2 It is a flow chart of the imaging method of light passing through a dynamic scattering medium in the second embodiment of the present invention.

[0028] The corresponding relationship between the reference numerals and the component names is as follows:

[0029] 1-light source module, 11-laser, 12-beam expander collimator, 13-first aperture, 14-polarizer, 2-target image module, 3-diffraction light filter module, 31-first lens, 32-second aperture, 33-second lens, 4-dynamic scattering module, 5-imaging module, 51-image acquisition unit, 52-computing unit. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] Before describing the various embodiments of the present application in detail, the technical concept of the present application is first briefly described: the current imaging method through a scattering medium is usually difficult to form a large field of view imaging in a dynamic scattering medium scenario. To this end, the present application provides an imaging system and an imaging method for light passing through a dynamic scattering medium, wherein a light source module is used to generate a coherent light beam, and the coherent light beam irradiates a target object to form a reflected light beam carrying image information, and a diffraction light filter module is used to filter the diffraction orders in the reflected light beam. The filtered reflected light beam passes through a dynamic scattering medium to generate a dynamic speckle pattern, and the image of the target object is restored based on the dynamic speckle image. This imaging method is suitable for dynamic scattering media, and can also break through the limitations of the optical memory effect to achieve large field of view imaging.

[0032] Specifically, if Figure 1 As shown, the imaging system for light passing through a dynamic scattering medium of the first embodiment includes a light source module 1, a diffraction light filtering module 3, and an imaging module 5. The light source module 1 is used to generate a coherent light beam for irradiating a target object, the diffraction light filtering module 3 is used to filter the diffraction orders in a reflected light beam of the target object, the filtered reflected light beam is used to pass through the dynamic scattering medium, and the imaging module 5 is used to collect a dynamic speckle pattern generated by the dynamic scattering medium and restore an image of the target object according to the dynamic speckle pattern.

[0033] In one or more embodiments, the light source module 1 includes a laser 11, a beam expander collimator 12, a first aperture 13, and a polarizer 14. The beam expander collimator 12 is used to adjust the wavefront of the coherent light beam generated by the laser 11, the first aperture 13 is used to adjust the diameter of the coherent light beam, and the polarizer 14 is used to adjust the polarization state of the coherent light beam. Exemplarily, the wavelength of the laser 11 is 532nm and the power is 200mW. The light beam generated by the laser 11 becomes a usable coherent light beam after passing through the beam expander collimator 12. After the first aperture 13 adjusts the diameter of the coherent light beam, the coherent light beam can completely cover the target object.

[0034] Exemplarily, the target object may be a physical picture, or an image displayed on a display screen or an image projected by a projection device. In one or more embodiments, the imaging system further includes a target image module 2, which is used to generate and display an image used as a target object. Among them, the target image module 2 may be a digital micromirror device (DMD) or a spatial light modulator (SLM). For example, the digital micromirror device used in this embodiment has 1920×1080 pixel blocks, and each pixel block is 7.56μm×7.56μm in size. A target image is loaded on the DMD through a computer, and after the coherent light beam is reflected by the DMD, the reflected light beam carries the information of the target image.

[0035] In one or more embodiments, the diffraction light filter module 3 includes a first lens 31, a second aperture 32, and a second lens 33 arranged in sequence, the first lens 31 and the second lens 33 are used to adjust the diameter of the reflected light beam, and the second aperture 32 is used to filter the diffraction order in the reflected light beam. Exemplarily, the diffraction light filter module 3 is a 4f system, the focal lengths of the first lens 31 and the second lens 33 are 175 mm and 83 mm, respectively, and the reflected light beam carrying the target image information has unnecessary diffraction orders, which are filtered by the second aperture 32.

[0036] Exemplarily, the dynamic scattering medium can be a naturally moving scattering medium, or a static scattering medium in motion. The scattering medium can be any substance that can produce strong scattering, including various organic substances, inorganic substances, and biological tissues. In one or more embodiments, the imaging system further includes a dynamic scattering module 4, which includes a scattering medium and a moving device, and the moving device is used to move the scattering medium. For example, the scattering medium is a frosted glass sheet, and the moving device is a two-dimensional moving platform. The frosted glass sheet has a particle size of 120 and a thickness of 1.6 mm, and is a strong scattering medium. The frosted glass sheet is placed on a two-dimensional moving platform, and the distance from the second lens 33 is 83 mm. The two-dimensional moving platform is electrically controlled and moves back and forth at a speed of 3 mm / s in a direction perpendicular to the optical axis. After the reflected light beam propagates to the frosted glass sheet and passes through the frosted glass sheet, a dynamic speckle pattern is formed.

[0037] In one or more embodiments, the imaging module 5 includes an image acquisition unit 51 and a computing unit 52, the image acquisition unit 51 is used to acquire dynamic speckle patterns, and the computing unit 52 is used to restore the image of the target object according to the dynamic speckle patterns. Exemplarily, the image acquisition unit 51 uses an industrial camera CCD, which has 1600×1200 pixel blocks, and each pixel block is 5.56μm×5.56μm in size. The industrial camera CCD can be externally triggered, and the computing unit 52 allows the industrial camera CCD to detect once every 1s. For a target image, in order to improve the contrast of the restored image, in this embodiment, multiple speckle patterns can be collected for target image restoration.

[0038] This embodiment also discloses an imaging method for light passing through a dynamic scattering medium, the scattering imaging method comprising the following steps:

[0039] Step S10: using the above imaging system to acquire a dynamic speckle pattern of the target object.

[0040] Step S20: Obtaining autocorrelation amplitude information of the dynamic speckle pattern.

[0041] Step S30: recovering the amplitude information of the target object image according to the autocorrelation amplitude information.

[0042] Step S40: obtaining phase information of the target object image according to the amplitude information and a preset phase recovery algorithm, and reconstructing the final target image according to the amplitude information and the phase information.

[0043] Exemplarily, in step S10 , the target object is a digital target image with a size of 480×480 pixels, and 10 dynamic speckle patterns of the target object are acquired by using an imaging system and saved in the calculation unit 52 .

[0044] When the autocorrelation amplitude information of the dynamic speckle pattern is obtained in step S20, there are two cases according to the number of dynamic speckle patterns. When the number of dynamic speckle patterns is one, the covariance operation is performed on the dynamic speckle pattern to obtain the autocorrelation amplitude information; when the number of dynamic speckle patterns is several, the covariance operation is performed on each dynamic speckle pattern, and the average value of the covariance operation results of each dynamic speckle pattern is used as the autocorrelation amplitude information. Summing and averaging the covariances of multiple speckle patterns can increase the contrast of the autocorrelation amplitude information of the target image.

[0045] For example, it is assumed that the dynamic scattering module 4 is at the position z=0, and the distance between the imaging module 5 and the dynamic scattering module 4 is z. The coordinates (α, β) and (x, y) represent the coordinates of the dynamic scattering module 4 and the imaging module 5, respectively. The complex amplitude close to the exit surface of the dynamic scattering module 4 can be described as:

[0046]

[0047] Wherein, |O(α,β)| and ψ(α,β) are the amplitude and phase of the incident light beam O of the dynamic scattering module 4, The random phase introduced for the scattering medium.

[0048] Accordingly, the field U(x, y) propagated to the imaging module 5 is described by the diffraction integral formula as follows:

[0049]

[0050] Therefore, the dynamic speckle pattern I(x,y) of the imaging module 5 is:

[0051] I(x,y)=|U(x,y)| 2 .

[0052] Furthermore, the symbol Γ(Δx, Δy) is defined to represent the autocorrelation function of the dynamic speckle pattern:

[0053]

[0054] The normalized covariance function C(Δx, Δy) of the speckle pattern is related to Γ(Δx, Δy) by the average intensity connect:

[0055]

[0056] The numerator on the right side of the equation represents the Fourier transform of O, and the denominator is a normalization constant. Perform an inverse Fourier transform on both sides of the equation:

[0057] FFT -1 [C]∝O★O,

[0058] The symbol "★" indicates the autocorrelation operation. For the target image O, its autocorrelation O★O=FFT -1 [|FFT(O)| 2 ], so C represents the autocorrelation amplitude information of the target image O.

[0059] Furthermore, the amplitude information of the target object image is calculated based on the autocorrelation amplitude information:

[0060]

[0061] for Its formula eliminates the random phase introduced by the dynamic scattering medium and does not utilize the translational invariance of the speckle, that is, the optical memory effect. Therefore, this imaging method is suitable for dynamic scattering media and can achieve large field of view imaging.

[0062] In step S40, the preset phase recovery algorithm can be a classic HIO phase recovery algorithm. First, a certain number of iterations is preset and the initial phase information is randomly generated; the initial phase information is multiplied by the amplitude information obtained in the previous step and an inverse Fourier transform is performed to obtain the original target; the original target is subjected to non-negative real number and existence conditional constraints and it is determined whether the set number of iterations has been reached; if so, the phase information of the target is output, otherwise the phase information is updated and the iteration continues. The phase recovery algorithm can be used to obtain the phase information lost due to scattering, and the final target image can be reconstructed in combination with the amplitude information. Exemplarily, the field of view of the reconstructed digital target image is 9 times the memory effect range. It is worth noting that this embodiment is only for better illustrating the effect of the imaging method, which does not mean that the limit of the imaging method is to restore the target image within a 9-fold memory effect range.

[0063] The specific implementation methods of the present invention are described in detail above. Although some embodiments have been shown and described, those skilled in the art should understand that these embodiments can be modified and improved without departing from the principles and spirit of the present invention, the scope of which is defined by the claims and their equivalents. These modifications and improvements should also be within the scope of protection of the present invention.

Claims

1. An imaging system for light passing through a dynamic scattering medium, characterized in that: The imaging system comprises: A light source module, the light source module is used to generate a coherent light beam for illuminating a target object; A diffraction light filtering module, wherein the diffraction light filtering module is used to filter the diffraction orders in the reflected light beam of the target object, and the filtered reflected light beam is used to pass through the dynamic scattering medium; An imaging module is used to collect the dynamic speckle pattern generated by the dynamic scattering medium and restore the image of the target object according to the dynamic speckle pattern.

2. The imaging system for light passing through a dynamic scattering medium according to claim 1, characterized in that: The light source module includes a laser, a beam expander collimator, a first aperture, and a polarizer. The beam expander collimator is used to adjust the wavefront of the coherent light beam generated by the laser, the first aperture is used to adjust the diameter of the coherent light beam, and the polarizer is used to adjust the polarization state of the coherent light beam.

3. The imaging system for light passing through a dynamic scattering medium according to claim 1, characterized in that: The diffraction light filtering module comprises a first lens, a second aperture, and a second lens which are arranged in sequence. The first lens and the second lens are used to adjust the diameter of the reflected light beam, and the second aperture is used to filter the diffraction order in the reflected light beam.

4. The imaging system for light passing through a dynamic scattering medium according to claim 1, characterized in that: The imaging module comprises an image acquisition unit and a calculation unit. The image acquisition unit is used to acquire a dynamic speckle pattern, and the calculation unit is used to restore an image of a target object according to the dynamic speckle pattern.

5. The imaging system for light passing through a dynamic scattering medium according to claim 1, characterized in that: The imaging system further comprises a dynamic scattering module, wherein the dynamic scattering module comprises a scattering medium and a moving device, wherein the moving device is used to move the scattering medium.

6. The imaging system for light passing through a dynamic scattering medium according to claim 1, characterized in that: The imaging system further includes a target image module for generating and displaying an image serving as a target object.

7. A method for imaging light through a dynamic scattering medium, characterized in that: The imaging method comprises: Using the imaging system according to any one of claims 1 to 6 to acquire a dynamic speckle pattern of a target object; Acquiring autocorrelation amplitude information of the dynamic speckle pattern; Obtaining amplitude information of the target object image according to the autocorrelation amplitude information; The phase information of the target object image is obtained according to the amplitude information and a preset phase recovery algorithm, and the final target image is reconstructed according to the amplitude information and the phase information.

8. The imaging method of light passing through a dynamic scattering medium according to claim 7, characterized in that: When the number of the dynamic speckle patterns is one, the method for obtaining the autocorrelation amplitude information of the dynamic speckle pattern includes: A covariance operation is performed on the dynamic speckle pattern to obtain autocorrelation amplitude information.

9. The imaging method of light passing through a dynamic scattering medium according to claim 7, characterized in that: When the number of the dynamic speckle patterns is a plurality of patterns, the method for obtaining the autocorrelation amplitude information of the dynamic speckle patterns includes: A covariance operation is performed on each of the dynamic speckle patterns, and an average value of the covariance operation results of each of the dynamic speckle patterns is used as the autocorrelation amplitude information.

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