Modulation-based laminated scanning imaging system and operation method thereof

Abstract

The invention discloses a modulation-based laminated scanning imaging system and an operation method thereof, in a coherent diffraction imaging light path, a modulator with unknown distribution is fixed in front of a CCD (Charge Coupled Device) camera, and complex amplitude information of a measured object and the unknown modulator is reconstructed through a laminated scanning or axial scanning method. The positions of the CCD camera and the modulator are not changed, and the two-dimensional moving table is controlled to move at a certain step length to carry out two-dimensional laminated scanning on the measured object; the positions of the measured object and the modulator are not changed, and the one-dimensional mobile station is controlled to carry out axial lamination scanning on the CCD camera at a fixed step length. And in the algorithm reconstruction process. According to the invention, the modulator is added in an optical path, higher reconstruction precision is obtained, and compared with a CDI algorithm, a fixed precise unknown modulator is added, so that the resolution of coherent diffraction imaging is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the field of optical imaging, and in particular relates to a modulation-based stacked scanning imaging system and an operation method thereof. Background Art

[0002] With the development and progress of science and technology, various industries have put forward higher requirements for precision measurement. Computational imaging, as a high-resolution, high-precision, non-contact technology, has broad application prospects. In precision measurement, since many measurement samples are phase-type objects, they are limited by the working principles of the human eye and the camera, and can only receive the intensity information of the detection light but cannot directly obtain its phase information. The internal morphology structure, material refractive index, and phase information of the reflected light field of an object usually reflect the structure of the object better than the intensity distribution. It is particularly important to reconstruct its phase through known intensity information.

[0003] Phase recovery technology can be divided into two categories: (1) Qualitative imaging for phase observation, mainly including Zernike phase imaging and differential interference phase imaging technology; (2) Quantitative imaging for accurate phase quantification, mainly including interferometric measurement and non-interferometric measurement methods. Non-interferometric measurement methods mainly include Shack-Hartmann wavefront sensing, phase solution based on the Transport of Intensity Equation (TIE), coherent diffraction imaging (CDI), etc. Coherent diffraction imaging calculates the complex amplitude information of the object by inverting the diffraction intensity map generated by the light beam irradiating the object and transmitting it to the image collector. Compared with wavefront sensors, TIE and other methods, it has the advantages of high robustness and high imaging accuracy.

[0004] The coherent diffraction imaging algorithm usually needs to add precise constraints in the optical path to accurately solve the measurement object, but it is usually difficult to accurately calibrate the constraint plane. The multi-frame scanning method is used to simultaneously reconstruct the measured object and the constraint plane information, which improves the imaging accuracy and optimizes the experimental process. Summary of the invention

[0005] The present invention provides a modulation-based stacked scanning imaging system and an operation method thereof, which aims to solve the defects of CDI technology such as low imaging resolution and poor convergence, as well as the problem that coherent modulation imaging technology (CMI) is too dependent on a precise modulator.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A modulation-based stack scanning imaging system comprises a light source 1 consisting of a laser, a beam expander, and a collimating lens, an object to be measured 2, a random phase plate 3, a CCD camera 4, a one-dimensional moving stage 5, and a two-dimensional moving stage 6. The laser emits parallel light as a light source after beam expansion and collimation. The two-dimensional moving stage 6 is connected to the object to be measured 2 to achieve two-dimensional scanning in a direction perpendicular to the optical axis. The random phase plate 3 is a wavefront modulation device and is placed between the object to be measured 2 and the CCD camera. The CCD camera 4 is used to receive a diffracted light field after the modulated plane outgoing wavefront of the object to be measured 2. The one-dimensional moving stage 5 is connected to the CCD camera to achieve one-dimensional feeding along the wavefront transmission direction.

[0008] As a preferred embodiment, the light source 1 is fixed in the horizontal direction, the object to be measured 2 is connected to the two-dimensional moving stage 6 and installed at the output end of the light source 1, an uncalibrated random phase plate 3 is placed behind the object to be measured 2 as a modulator, and the CCD camera 4 is connected to the one-dimensional moving stage 5 and installed behind the random phase plate 3.

[0009] As a preferred embodiment, the optical path is adjusted to ensure that the target surface of the CCD camera, the plane of the object 2 to be measured, and the scanning plane of the two-dimensional moving stage 6 are all perpendicular to the wavefront transmission direction, while ensuring that the one-dimensional moving stage 5 feeds along the optical axis.

[0010] A modulation-based stack scanning imaging operation method is provided. Different diffraction intensity images are obtained by two experimental methods according to the constructed experimental system, and the measured object and the modulation plane are reconstructed. On the basis of the CDI experimental system, a random phase plate with unknown distribution is placed at the front end of the CCD camera as a modulation device. The measured object and the modulator information are reconstructed through multi-frame stack scanning and algorithms. Specifically, the steps are as follows:

[0011] Step 1: Make initial guesses for the illumination light incident on the plane of the object to be measured, the object to be measured, and the modulator, which are P, O, and R respectively;

[0012] Step 2: The parallel light emitted by the light source is incident on the plane of the object to be measured as the illumination light, and the outgoing wavefront of the plane of the object to be measured is, Ψ = O × P;

[0013] Step 3: The outgoing wavefront Ψ of the measured object plane has a transmission distance M, and the incident wavefront of the modulator plane is, in Represents the wavefront transmission process;

[0014] Step 4: The outgoing wavefront at the modulator plane is, Ω = Φ × R;

[0015] Step 5: The modulator plane outgoing wavefront Ω is transmitted over a distance K, and the wavefront information obtained by the CCD camera plane is:

[0016] Step 6: Collect the obtained diffraction intensity map I to update the amplitude information of the plane wavefront of the CCD camera.

[0017] Step 7: Update the CCD camera plane wavefront information and transmit it backwards over a distance K to obtain the updated modulator plane output wavefront. in It represents the process of reverse transmission of wavefront;

[0018] Step 8: Synchronously update the modulator's plane incident wavefront and modulator distribution function.

[0019]

[0020] Step 9: Update the incident wavefront Φ′ of the modulator and transmit it in reverse distance M to obtain the outgoing wavefront on the object plane.

[0021] Step 10: Synchronously update the distribution function of the object under test and the illumination light on the plane of the object under test

[0022]

[0023] Among them, α and β are constants;

[0024] Step 11: The updated illumination light P′, the object under test O′, and the modulator R′ are used as the initial values ​​for the next round of iteration until the information of the object under test, the illumination light, and the modulator converges.

[0025] As a preferred embodiment, the positions of the CCD camera and the modulator remain unchanged, and the two-dimensional moving stage is controlled to move in a certain step length to perform a two-dimensional stacked scan on the object to be measured. After the light source illuminates the object to be measured at different positions, it propagates a distance M through the modulator and then propagates a distance K to the target surface of the CCD camera, thereby obtaining a diffraction spot.

[0026] As a preferred embodiment, the arbitrary position is set to n, and the diffraction intensity corresponding to n is Represents the wavefront transmission process, O n It indicates the information of the object being measured corresponding to the nth scanning aperture, M indicates the distance between the object being measured and the modulator, and K indicates the distance between the modulator and the CCD camera.

[0027] As a preferred embodiment, the position of the measured object and the modulator remains unchanged, and the one-dimensional moving stage is controlled to perform axial stacking scanning on the CCD camera with a fixed step length Δ to obtain the propagation distance M of the light source after passing through the fixed position measured object to the unknown modulator, and the propagation distance K after passing through the unknown modulator n The diffraction spot on the CCD camera target surface.

[0028] As a preferred embodiment, K n=K+(n-1)Δ is the wavefront transmission distance between the modulator and the CCD camera corresponding to the nth scan, and L is the initial distance.

[0029] Technical principle of the present invention: The present invention adds an uncalibrated random phase plate to the coherent diffraction imaging experimental system to modulate the outgoing wavefront of the object under test, thereby improving the imaging accuracy. In the experiment, a two-dimensional scan perpendicular to the optical path plane or a one-dimensional axial scan along the optical path direction is performed, and the diffraction intensity map obtained by the scan is input into the reconstruction algorithm to obtain the complex amplitude distribution of the modulator and the complex amplitude distribution of the object under test. Based on two types of scanning methods, the present invention proposes two types of embodiments and their iterative algorithms: Embodiment 1 reconstructs the fixed modulator and the object under test information on the scanning plane through the diffraction intensity map obtained by the two-dimensional scanning of the plane perpendicular to the optical path; Embodiment 2 reconstructs the fixed modulator and the object under test information through the diffraction intensity map obtained by the axial scanning of the optical axis.

[0030] Beneficial effects:

[0031] In view of the problems of poor convergence, poor reconstruction accuracy and easy falling into local optimal solution in coherent diffraction imaging technology, the present invention proposes a scanning system with unknown modulation, which realizes:

[0032] 1. Add a modulator in the optical path to obtain higher reconstruction accuracy. Compared with the CDI algorithm, the resolution of coherent diffraction imaging is greatly improved by adding a fixed precision unknown modulation device;

[0033] 2. Scan the object to be measured, and restore the two planes through a set of diffraction intensity maps obtained by scanning. Compared with the PIE algorithm, this method adds the reconstruction of the modulator plane data while ensuring the resolution;

[0034] 3. Reconstruct unknown modulator data, avoiding the precise calibration process of complex distributed modulators. Compared with the CMI algorithm, this method does not require precise calibration of the modulator in advance, which greatly simplifies the experimental process and reduces the amount of calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram of the experimental optical path of the present invention.

[0036] Figure 2 It is a schematic diagram of the wavefront transmission process of the present invention.

[0037] Figure 3 It is a flow chart of the wavefront transmission combined algorithm of the present invention.

[0038] Figure 4 It is a schematic diagram of the iterative process corresponding to the second embodiment of the present invention.

[0039] Figure 5It is a schematic diagram of the iterative process corresponding to the second embodiment of the present invention. DETAILED DESCRIPTION

[0040] The following is a detailed description of an embodiment of the present invention in conjunction with the accompanying drawings: This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

[0041] like Figure 1 As shown, the stacked scanning imaging method based on modulation in this embodiment includes a light source 1 composed of a laser, a beam expander, and a collimating lens, an object to be measured 2, a random phase plate 3, a CCD camera 4, a one-dimensional moving stage 5, and a two-dimensional moving stage 6. First, the light source 1 is installed horizontally; the object to be measured 2 is connected to the two-dimensional moving stage 6 and placed at the light source output end; the phase plate 3 is placed behind the object to be measured as a modulator; the CCD camera 4 is connected to the one-dimensional moving stage 5 and placed behind the modulator. The optical path is adjusted to ensure that the target surface of the CCD camera, the plane of the object to be measured, and the scanning plane of the two-dimensional moving stage are all perpendicular to the wavefront transmission direction, and at the same time, the feeding of the one-dimensional moving stage is along the optical axis direction.

[0042] The wavefront transmission process is as follows Figure 2 As shown, the update algorithm flow chart combined with the transmission process is as follows Figure 3 . The illumination light emitted by the light source passes through the object to be measured, and the outgoing wavefront carrying the information of the object to be measured is transmitted to the modulator (random phase plate) plane, and the outgoing wavefront carrying the modulator information is transmitted to the CCD camera plane. Finally, the CCD camera records the intensity information of the wavefront on the plane. In the algorithm, the object to be measured, the illumination light, and the modulator are initially guessed. The illumination light is forwardly transmitted to the modulator plane after passing through the object to be measured; after passing through the modulator plane, it is forwardly transmitted to the CCD camera plane; the diffraction intensity map collected in the experiment updates the CCD camera plane amplitude; the updated CCD camera plane wavefront is reversely transmitted to the modulator plane, and the modulator plane information and the incident wavefront of the modulator plane are synchronously updated. The updated modulator incident wavefront is reversely transmitted to the plane of the object to be measured, and the information of the object to be measured and the illumination light information are synchronously updated; the updated object to be measured, the illumination light, and the modulator are input as known information into the next iteration, and iterate until the distribution functions of the object to be measured, the illumination light, and the modulator converge.

[0043] Embodiment 1: The modulator, CCD camera, and one-dimensional moving stage are stationary; the object to be measured is controlled by the two-dimensional moving stage to perform two-dimensional scanning perpendicular to the direction of light field transmission, and the overlap rate of two adjacent scanning sub-apertures during the scanning process is ensured to be not less than 60%, and a set of diffraction intensity diagrams under different scanning apertures are obtained. The light intensity information recorded on the CCD camera for any point (x, y) in the nth aperture obtained by two-dimensional scanning is represents the wavefront transmission process, On (x, y) represents the information of the object under test corresponding to the nth scanning aperture, M represents the distance between the object under test and the modulator, and K represents the distance between the modulator and the CCD camera.

[0044] The corresponding iterative process is as follows Figure 4 As shown:

[0045] Step 1: Make an initial guess on the distribution functions of the incident illumination light on the plane of the object to be measured, the object to be measured, and the modulator, which are P(x, y), O n (x, y), R(x, y), where O n (x, y) is the information of the object under test corresponding to the nth diffraction intensity image;

[0046] Step 2: After the illumination light passes through the object, the plane outgoing wavefront of the object is Ψ(x, y) = O n (x, y)P(x, y);

[0047] Step 3: Ψ(x, y) transmits the wavefront over a distance M to the modulator plane. The incident wavefront on the modulator plane is in Represents the wavefront transmission process;

[0048] Step 4: After the incident wavefront on the modulator plane passes through the modulator, the outgoing wavefront on the modulator plane is Ω(x, y) = Φ(x, y)R(x, y);

[0049] Step 5: Ω transmits the wavefront over a distance K to the CCD camera plane. The incident wavefront obtained by the CCD camera plane is

[0050] Step 6: Collect the obtained diffraction spot pattern I n (x,y) Update CCD camera plane wavefront

[0051] Step 7: The updated CCD camera plane wavefront is transmitted back to the modulator plane to obtain the updated modulator plane output wavefront in It represents the process of reverse transmission of wavefront;

[0052] Step 8: Update the modulator incident wavefront and modulator distribution function simultaneously

[0053]

[0054] Among them, α and β are constants;

[0055] Step 9: Update the incident wavefront Φ′(x, y) of the modulator and transmit it in reverse direction over a distance M to the plane of the object to be measured, and obtain the outgoing wavefront of the object plane.

[0056] Step 10: Update the distribution functions of the measured object and the illumination light respectively;

[0057]

[0058] Step 11: Determine the updated illumination light P′(x, y) and the object O′ n (x, y), whether the modulator R′(x, y) converges, and outputs the reconstructed result after convergence. If it does not converge, it is used as the initial value for the next round of iteration.

[0059] P(x, y) = P′(x, y); n+1 (x, y) = O′ n (x, y); R (x, y) = R′ (x, y) (5)

[0060] The next iteration translates the object position to the next scanning aperture and repeats the above iteration process.

[0061] Embodiment 2: The object under test, the modulator, and the two-dimensional moving stage are stationary, and the one-dimensional moving stage controls the CCD camera to perform axial scanning with a step length of Δ to obtain a set of diffraction intensity images of the object under test at different diffraction transmission distances after passing through the modulator. For any point (x, y) on the object plane, the corresponding nth diffraction intensity image recorded on the CCD camera is M represents the distance between the measured object and the modulator, K n =L+(n-1)Δ is the wavefront transmission distance between the modulator and the CCD camera corresponding to the nth diffraction intensity image, and L is the initial distance.

[0062] The corresponding iterative process is as follows Figure 5 :

[0063] Step 1: Make an initial guess on the distribution functions of the incident illumination light on the plane of the object to be measured, the object to be measured, and the modulator, which are P(x, y), O(x, y), and R(x, y) respectively;

[0064] Step 2: After the illumination light passes through the object to be measured, the plane outgoing wavefront of the object to be measured is Ψ(x, y) = O(x, y)P(x, y);

[0065] Step 3: The outgoing wavefront Ψ(x,y) of the measured object plane is transmitted over a distance M to the modulator plane, and the incident wavefront of the modulator plane is in Represents the wavefront transmission process;

[0066] Step 4: After the incident wavefront on the modulator plane passes through the modulator, the outgoing wavefront on the modulator plane is, Ω = Φ(x, y)R(x, y);

[0067] Step 5: The modulator plane outgoing wavefront Ω(x, y) propagates a distance K n To the CCD camera plane, the CCD camera plane wavefront is

[0068] Step 6: Experimentally obtained diffraction intensity map I n (x, y) Update CCD camera plane wavefront information

[0069] Step 7: Update the CCD camera plane wavefront reverse transmission distance K n To the modulator plane, get the updated modulator plane output wavefront in It represents the process of reverse transmission of wavefront;

[0070] Step 8: Update the modulator's plane incident wavefront and modulator plane information at the same time.

[0071]

[0072] Among them, α and β are constants;

[0073] Step 9: Update the incident wavefront Φ′(x, y) of the modulator and transmit it in reverse direction over a distance M to the plane of the object to be measured, and obtain the updated outgoing wavefront of the plane of the object to be measured

[0074] Step 10: Update the distribution functions of the object being measured and the illumination light respectively

[0075]

[0076] Step 11: Determine whether the updated illumination light P′(x, y), the object under test O′(x, y), and the modulator R′(x, y) have converged. If they have converged, output the reconstructed result. If they have not reached the threshold, use it as the initial value for the next round of iteration.

[0077] P(x,y)=P′(x,y); O(x,y)=O′(x,y); R(x,y)=R′(x,y) (5)

[0078] The next iteration should adjust the transmission distance between the object to be measured and the modulator to K without changing the position of the object to be measured. n+1 , and repeat the above iterative process.

[0079] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A modulation-based stacked scanning imaging system, characterized in that: It includes a light source 1 consisting of a laser, a beam expander, and a collimating lens, an object to be measured 2, a random phase plate 3, a CCD camera 4, a one-dimensional moving stage 5, and a two-dimensional moving stage 6. The laser emits parallel light as a light source after beam expansion and collimation. The two-dimensional moving stage 6 is connected to the object to be measured 2 to achieve two-dimensional scanning in a direction perpendicular to the optical axis. The random phase plate 3 is a wavefront modulation device and is placed between the object to be measured 2 and the CCD camera. The CCD camera 4 is used to receive the diffraction light field after the plane output wavefront of the object to be measured 2 is modulated. The one-dimensional moving stage 5 is connected to the CCD camera to achieve one-dimensional feeding along the wavefront transmission direction.

2. The modulation-based stack scanning imaging system according to claim 1, characterized in that: The light source 1 is fixed in the horizontal direction, the object 2 to be measured is connected to the two-dimensional moving stage 6 and installed at the output end of the light source 1, an uncalibrated random phase plate 3 is placed behind the object 2 to be measured as a modulator, and the CCD camera 4 is connected to the one-dimensional moving stage 5 and installed behind the random phase plate 3.

3. The modulation-based stack scanning imaging system according to claim 1, characterized in that: The optical path is adjusted to ensure that the target surface of the CCD camera, the plane of the object 2 to be measured, and the scanning plane of the two-dimensional moving stage 6 are all perpendicular to the wavefront transmission direction, and at the same time, the feeding of the one-dimensional moving stage 5 is along the optical axis direction.

4. A method for operating a modulation-based stack scanning imaging system as claimed in claim 1, characterized in that: According to the experimental system built, two experimental methods are used to obtain different diffraction intensity images, reconstruct the object under test and the modulation plane. On the basis of the CDI experimental system, a random phase plate with unknown distribution is placed in front of the CCD camera as a modulation device, and the object under test and modulator information are reconstructed through multi-frame stacking scanning and algorithms. The specific steps include the following: Step 1: Make initial guesses for the illumination light incident on the plane of the object to be measured, the object to be measured, and the modulator, which are P, O, and R respectively; Step 2: The parallel light emitted by the light source is incident on the plane of the object to be measured as the illumination light, and the outgoing wavefront of the plane of the object to be measured is, Ψ = O × P; Step 3: The outgoing wavefront Ψ of the measured object plane has a transmission distance M, and the incident wavefront of the modulator plane is, in Represents the wavefront transmission process; Step 4: The outgoing wavefront at the modulator plane is, Ω = Φ × R; Step 5: The modulator plane outgoing wavefront Ω is transmitted over a distance K, and the wavefront information obtained by the CCD camera plane is: Step 6: Collect the obtained diffraction intensity map I to update the amplitude information of the plane wavefront of the CCD camera. Step 7: Update the CCD camera plane wavefront information and transmit it backwards over a distance K to obtain the updated modulator plane output wavefront. in It represents the process of reverse transmission of wavefront; Step 8: Synchronously update the modulator's plane incident wavefront and modulator distribution function. Step 9: Update the incident wavefront Φ′ of the modulator and transmit it in reverse distance M to obtain the outgoing wavefront on the object plane. Step 10: Synchronously update the distribution function of the object under test and the illumination light on the plane of the object under test Among them, α and β are constants; Step 11: The updated illumination light P′, the object under test O′, and the modulator R′ are used as the initial values ​​for the next round of iteration until the information of the object under test, the illumination light, and the modulator converges.

5. The method for operating a modulation-based stack scanning imaging system according to claim 4, characterized in that: The positions of the CCD camera and the modulator remain unchanged, and the two-dimensional moving stage is controlled to move in a certain step length to perform two-dimensional stacked scanning on the object to be measured. The light source illuminates the object to be measured at different positions, then propagates a distance M through the modulator, and then propagates a distance K to the target surface of the CCD camera, thereby obtaining a diffraction spot.

6. The method for operating a modulation-based stack scanning imaging system according to claim 4, characterized in that: The arbitrary position is set as n, and the diffraction intensity corresponding to n is represents the wavefront transmission process, O n It indicates the information of the object being measured corresponding to the nth scanning aperture, M indicates the distance between the object being measured and the modulator, and K indicates the distance between the modulator and the CCD camera.

7. The method for operating a modulation-based stack scanning imaging system according to claim 4, characterized in that: The position of the measured object and the modulator remains unchanged. The one-dimensional moving stage is controlled to perform axial stack scanning on the CCD camera with a fixed step length Δ to obtain the propagation distance M of the light source after passing through the fixed position measured object to the unknown modulator, and the propagation distance K after passing through the unknown modulator n The diffraction spot on the CCD camera target surface.

8. The method for operating a modulation-based stack scanning imaging system according to claim 4, characterized in that: K n =L+(n-1)Δ is the wavefront transmission distance between the modulator and the CCD camera corresponding to the nth scan, and L is the initial distance.

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