Two-dimensional wavefront sensing system and data processing method thereof

Abstract

The present disclosure provides a two-dimensional wavefront sensing system comprising a distorted wavefront to be measured, two optical filters, an imaging unit, and a polarization photodetection unit. The two optical filters have similar or identical optical responses, requiring that the amplitude transmittance of s- or p-polarized incident light is proportional to the incident angle within a set incident angle range, that the amplitude transmittance of p- or s-polarized incident light remains constant as the incident angle changes within the set incident angle range, and that the angle between one of the two optical filters and the xz plane is the same as the angle between the other optical filter and the yz plane. The imaging unit is configured to image the distorted wavefront to be measured, located at the object plane of the imaging unit, onto the polarization photodetection unit located at the image plane of the imaging unit. The polarization photodetection unit is configured to detect the polarization intensity of the incident light in the x and y directions after it passes through the two optical filters and the imaging unit. The present disclosure can achieve two-dimensional wavefront sensing with high spatial resolution and a large dynamic measurement range.

Description

Technical Field

[0001] The present disclosure can be applied to fields such as adaptive optics and quantitative phase imaging, and specifically relates to a method and system for performing phase-enhanced visualization and real-time measurement of a two-dimensional light wavefront. Background Art

[0002] Wavefront sensing has a wide range of applications in astronomical adaptive optics, laser communications, laser inertial confinement fusion, and biological quantitative phase microscopy. Traditional wavefront phase sensing methods include Shack-Hartmann wavefront sensors, digital holographic quantitative phase imaging, micro- and nanostructure-based wavefront sensing, and optical filter-based wavefront sensing.

[0003] Among them, Shack-Hartmann wavefront sensors have the highest market share due to their high robustness. However, their spatial resolution is low and they cannot be applied to high spatial resolution scenarios such as phase microscopy. Although digital holographic phase imaging based on interference methods can have high spatial resolution, it is sensitive to environmental perturbations. In recent years, the combination of micro-nanostructures and imaging sensors has enabled stable and high spatial resolution wavefront sensing, but their processing requires precise alignment of the two, and optical crosstalk and low quantum efficiency reduce detection sensitivity. In addition, schemes for wavefront sensing based on optical filter devices with asymmetric angular response have been widely studied. On the one hand, this scheme has the same spatial resolution and high robustness as imaging sensors; on the other hand, it has greater design flexibility and is easy to integrate with various imaging systems. However, this scheme is limited to one-dimensional wavefront detection.

[0004] By using angle-sensitive and polarization-sensitive optical filters composed of multilayer thin films, phase gradients in two orthogonal directions are projected onto light intensity variations in two polarization channels, respectively. This intensity variation can then be captured in a single shot by a polarization camera. This enables all-optical phase visualization and two-dimensional real-time wavefront measurement, promising applications in various wavefront measurement and phase imaging fields. Summary of the Invention

[0005] The present disclosure aims to solve one of the technical problems in the related art at least to a certain extent.

[0006] To this end, the first embodiment of the present disclosure proposes a real-time two-dimensional wavefront sensing system with high spatial resolution and a large dynamic measurement range based on an angle-sensitive and polarization-sensitive optical filter. The system includes a distorted wavefront to be measured, a first optical filter, an imaging unit, a second optical filter, and a polarization photodetection unit arranged along the direction of light propagation. A right-handed coordinate system consisting of an x-axis, a y-axis, and a z-axis is constructed, wherein the direction of light propagation is defined as the z-axis, and the plane where the distorted wavefront to be measured is located is defined as the xy plane.

[0007] The first optical filter and the second optical filter have similar or identical optical responses, that is, the amplitude transmittance of s- or p-polarized incident light is proportional to the incident angle within the incident angle range of [θ1, θ2], and the amplitude transmittance of p- or s-polarized incident light remains constant with changes in the incident angle within the incident angle range of [θ1, θ2], θ1, θ2∈[0°, 90°], and the angle between one of the first optical filter and the second optical filter and the xz plane is the same as the angle between the other optical filter and the yz plane, both being (θ1+θ2) / 2;

[0008] The imaging unit is provided between the distorted wavefront to be measured and the polarization photodetection unit, and is used to image the distorted wavefront to be measured located at the object plane of the imaging unit to the polarization photodetection unit located at the image plane of the imaging unit;

[0009] The polarization photoelectric detection unit is used to detect the polarization intensity of the incident light in the x and y directions after the incident light passes through the imaging system composed of the first optical filter, the imaging unit and the second optical filter.

[0010] In some embodiments, the first optical filter and the second optical filter each include a transparent substrate and a first thin film and a second thin film alternately stacked on the transparent substrate, and the materials making the first thin film and the second thin film have a refractive index difference.

[0011] In some embodiments, the difference in refractive index between materials making up the first thin film and the second thin film is greater than or equal to 0.2.

[0012] In some embodiments, the thickness of each thin film in a single optical filter is from 1 / 20 to one wavelength of the operating wavelength of the two-dimensional wavefront sensing system.

[0013] In some embodiments, the total number of thin film layers contained in a single optical filter is 4 to 50 layers.

[0014] In some embodiments, the distorted wavefront to be measured may be generated by a light beam passing through a transparent medium, a biological cell, or a metal surface.

[0015] In some embodiments, the imaging unit adopts a 4f imaging system, a microscope imaging system or a telescope imaging system.

[0016] In some embodiments, the polarization photodetection unit uses a polarization camera or a photodetector with a polarization splitting function.

[0017] The two-dimensional wavefront sensing system provided by the first embodiment of the present disclosure has the following characteristics and beneficial effects:

[0018] The core component of this system is a multilayer optical thin-film filter composed of two alternately deposited materials with contrasting refractive indices. Through rational design, the amplitude transmittance of the optical filter for s-polarized incident light is proportional to the incident angle over a wide range of incident angles, while the amplitude transmittance for p-polarized incident light remains constant. By rotating two thin-film optical filters with identical optical responses in the imaging optical path by a certain angle in orthogonal directions, the phase gradients in the two orthogonal directions of the distorted wavefront are converted into variations in the intensity of two orthogonally polarized light, thus enabling two-dimensional real-time wavefront measurement. Compared to traditional angle-dependent wavefront sensors, the spatial resolution of this system relies solely on the polarization photodetection unit, enabling the realization of a higher-resolution two-dimensional wavefront sensing system. Furthermore, due to its angle-dependent wavefront detection method, the system is more robust than interferometry. The thin-film optical filters are also easy to process and can be integrated with various imaging systems, demonstrating high compatibility.

[0019] The data processing method of the two-dimensional wavefront sensing system according to any embodiment of the first aspect of the present disclosure provided in the second aspect of the present disclosure includes:

[0020] The equivalent optical transfer function H(k x ,k y )for:

[0021]

[0022]

[0023]

[0024] Where k x and k y are the spatial frequencies of the incident light along the x and y directions, k x =k0·sin(θ x ), k y =k0·cos(θ y ), k0 is the wave vector of the incident light, θ x is the angle between the incident light projected onto the xz plane and the x-axis, θ y is the angle between the incident light projected onto the yz plane and the y-axis, θ is the incident angle in the optical response curve of the optical filter, a and b are two constants, t s0 and t p0 are the amplitude transmittances of s- and p-polarized light of the optical filter at an incident angle of (θ1+θ2) / 2, respectively;

[0025] Calculate the input light intensity I carrying the distorted wavefront to be measured according to the following formula: in (x,y) x-polarized light intensity I x-in (x,y) and y polarized light intensity I y-in The measured x-polarized light intensity I when (x, y) reaches the polarization photodetection unit after passing through the imaging system x-out (x,y) and y polarized light intensity I y-out (x,y):

[0026]

[0027] Where, is the wavefront phase;

[0028] The wavefront phase gradients in the x and y directions are calculated as follows:

[0029]

[0030] Where, I x-ref (x,y) and I y-ref (x, y) are the reference light intensity I of the undistorted wavefront ref (x,y) components along the x and y directions;

[0031] The wavefront phase gradients in the x and y directions are obtained and the wavefront phase is reconstructed using the wavefront reconstruction algorithm. Reconstruction.

[0032] In some embodiments, the wavefront reconstruction algorithm adopts a slope wavefront reconstruction algorithm.

[0033] The data processing method of the two-dimensional wavefront sensing system provided in the second embodiment of the present disclosure has the following characteristics and beneficial effects:

[0034] This two-dimensional wavefront detection system linearly maps the magnitude of phase gradients in two orthogonal directions to variations in light intensity across two polarizations. Polarization photoelectric imaging elements read the intensity variations in both polarization channels and, based on the calibrated optical response curves of thin-film filters, uniquely determine the magnitude of the phase gradient at each spatial location. This data processing is simple, computationally inefficient, and eliminates multi-value solutions. Furthermore, there is no optical crosstalk between sampling points during wavefront measurement, allowing for accelerated computation using parallel computing for large numbers of sampling points. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a structural schematic diagram of the two-dimensional wavefront sensing system provided in the embodiment of the first aspect of the present disclosure.

[0036] Figure 2It is a cross-sectional schematic diagram of an optical filter in a two-dimensional wavefront sensing system provided by an embodiment of the first aspect of the present disclosure.

[0037] Figure 3 This is a curve showing how the amplitude transmittance of a single optical filter changes with the incident angle in the first embodiment of the present disclosure. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of this application more clearly understood, this application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0039] On the contrary, this application covers any alternatives, modifications, equivalents, and solutions made within the spirit and scope of this application as defined by the claims. Furthermore, to facilitate a better understanding of this application, certain specific details are described in detail below in the detailed description of this application. Those skilled in the art will be able to fully understand this application without these details.

[0040] See also Figure 1 The two-dimensional wavefront sensing system provided by the embodiment of the first aspect of the present disclosure includes a distorted wavefront to be measured 100, a first optical filter 200, an imaging unit 300, a second optical filter 400, and a polarization photodetection unit 500 arranged along the light propagation direction, and constructs a right-handed coordinate system consisting of an x-axis, a y-axis, and a z-axis, wherein the light propagation direction is defined as the z-axis, the distorted wavefront to be measured 100 is located in the xy plane, and the first optical filter 200 and the second optical filter 400 are rotated by the same angle around the x-axis and the y-axis, respectively; the placement order of the first optical filter 200 and the second optical filter 400 is not limited to Figure 1 , can also be placed between the distorted wavefront to be measured 100 and the imaging unit 300 or between the imaging unit 300 and the polarization photodetection unit 500; wherein:

[0041] The first optical filter 200 and the second optical filter 400 have similar or identical optical responses, requiring s or p polarization (s polarization direction along the y direction, p polarization direction in the xz plane, see Figure 2 The amplitude transmittance of the incident light (with the polarization direction shown in ) is proportional to the incident angle within the incident angle range of [θ1, θ2], and the amplitude transmittance of the p- or s-polarized incident light remains constant with the change of the incident angle within the incident angle range of [θ1, θ2], θ1, θ2∈[0°, 90°], and the angle between one of the first optical filter 200 and the second optical filter 400 and the xz plane is the same as the angle between the other optical filter and the yz plane, both of which are (θ1+θ2) / 2;

[0042] The imaging unit 300 is provided between the distorted wavefront to be measured 100 and the polarization photodetection unit 500, and is used to image the distorted wavefront to be measured 100 located at the object plane of the imaging unit onto the polarization photodetection unit 500 located at the image plane of the imaging unit;

[0043] The polarization photodetection unit 500 is used to detect the polarization intensity of the incident light in the x and y directions after the incident light passes through the optical system composed of the first optical filter 200 , the imaging unit 300 and the second optical filter 400 .

[0044] In some embodiments, the distorted wavefront 100 to be measured may be generated by a light beam passing through a transparent medium, a biological cell, or a metal surface.

[0045] In some embodiments, see Figure 2 The first optical filter 200 and the second optical filter 400 have the same structure. The first optical filter 200 will now be described as an example. The first optical filter 200 includes a transparent substrate 203 and a first thin film 201 and a second thin film 202 alternately stacked on the transparent substrate 203. The materials making up the first and second thin films 201, 202 have a refractive index difference, which is generally greater than or equal to 0.2. Optionally, the refractive index of the first thin film 201 is less than that of the second thin film 202. Monochromatic light 204 at different incident angles passes through the optical filter and undergoes intensity modulation. The wavelength of the incident light can be designed to range from the ultraviolet to the infrared band. The refractive index materials of the first and second thin films 201, 202 can be selected from different combinations of materials with different refractive indices, such as silicon dioxide and titanium dioxide, or silicon dioxide and silicon. In specific implementations, more materials can be used, and this embodiment is not limited thereto. The substrate 203 can be made of common transparent dielectric materials such as molten glass and quartz. The thickness of each thin film layer in an optical filter should be optimized based on the performance requirements of wavefront detection and the wavelength of the incident light, generally ranging from 1 / 20 of the operating wavelength to one wavelength. This optimization can be achieved using commonly used methods for inverse optimization of multilayer thin films, such as particle swarm optimization and adjoint optimization. The number of thin film layers in an optical filter can be flexibly selected based on design needs, generally requiring no fewer than four layers. A greater number of layers facilitates the optimization of the film's optical response. However, considering the practical processing challenges of thin films, excessive layers can compromise their stability. Therefore, the number of thin film layers in a single optical filter is limited to no more than 50. The optical response of an optical filter requires that the amplitude transmittance of s- or p-polarized incident light (s polarization along the y direction, p polarization in the xz plane) is proportional to the incident angle, exhibiting a monotonically increasing or decreasing trend. The amplitude transmittance of p- or s-polarized incident light should remain constant with changes in the incident angle, meaning that the amplitude transmittance of p- or s-polarized incident light is insensitive to changes in the incident angle.

[0046] In some embodiments, the imaging unit 300 may employ, but is not limited to, a 4f imaging system, a microscope imaging system, and a telescope imaging system.

[0047] In some embodiments, the polarization photodetection unit 500 may include, but is not limited to, a polarization camera and a photodetector with a polarization splitting function.

[0048] In the two-dimensional wavefront sensing system provided by the first embodiment of the present disclosure, since the local angle of incidence of the incident light is proportional to the phase gradient of the wavefront, when the light field carrying the distorted wavefront passes through two optical filters in sequence, the phase gradients in the x and y directions of the distorted wavefront are uniquely and linearly contained in the changes in the polarized light intensity in the y and x directions, respectively. The polarized light intensity in the x and y directions is received and detected by the polarization photodetection unit 500, and the phase gradients in the corresponding directions are obtained from the changes in the polarized light intensity. The wavefront distribution is then derived from the x and y phase gradients using a universal wavefront reconstruction algorithm.

[0049] To further illustrate the working principle of the two-dimensional wavefront sensing system provided by the embodiment of the present disclosure, it is now described in conjunction with the first embodiment.

[0050] In the first embodiment of the present disclosure, the operating wavelength of the two-dimensional wavefront sensing system is 532 nanometers. The first optical filter 200 and the second optical filter 400 each have 8 pairs of alternating silicon dioxide and titanium dioxide thin films, wherein the thickness of each thin film is shown in Table 1 (in Table 1, the thin film with a smaller layer number is closer to the transparent substrate 203). The total thickness of the thin films contained in a single optical filter is 1.07 microns, and the transparent substrate 203 is made of transparent fused quartz with a thickness of 1 mm. The refractive indices of silicon dioxide and titanium dioxide at an operating wavelength of 532 nanometers are 1.46 and 2.33, respectively. Figure 3 As shown, the amplitude transmittance of s-polarized light of the optical filter is t s The amplitude transmittance of p-polarized light decreases monotonically in the incident angle range of 30° to 60°. p It remains constant as the incident angle changes. Figure 1As shown, two identical optical filters (200, 400) are inserted into the 4f imaging optical path. The angle between the first optical filter 200 and the xz plane and the angle between the second optical filter 400 and the yz plane are both 45°. The imaging unit 300 is composed of two convex lenses with the same focal length f, and the distance between the convex lenses is 2f. The distance between the distorted wavefront 100 to be measured and the imaging unit 300 is f, and the distance between the polarization photodetection unit 500 and the imaging unit 300 is f. The spatial resolution of the two-dimensional wavefront sensing system is determined by the spatial resolution of the polarization photodetection unit, which is generally several microns. The spatial resolution of a traditional Shack-Hartmann wavefront sensor is determined by the diameter of the microlens array unit, which is generally hundreds of microns. At the same time, this system does not require a reference optical path and is not easily affected by air disturbances, etc., and has higher robustness than traditional interferometric wavefront measurement systems.

[0051] Table 1 Materials and thickness of each layer of thin film optical filter

[0052] Layer number Material Thickness (nm) Layer number Material Thickness (nm) 1 Silicon dioxide 10.00 9 Silicon dioxide 75.91 2 Titanium dioxide 12.18 10 Titanium dioxide 67.48 3 Silicon dioxide 25.59 11 Silicon dioxide 153.37 4 Titanium dioxide 27.00 12 Titanium dioxide 100.44 5 Silicon dioxide 179.21 13 Silicon dioxide 92.22 6 Titanium dioxide 25.43 14 Titanium dioxide 227.34 7 Silicon dioxide 14.56 15 Silicon dioxide 40.69 8 Titanium dioxide 10.00 16 Titanium dioxide 10.00

[0053] The data processing method of the two-dimensional wavefront sensing system provided in the second embodiment of the present disclosure includes:

[0054] Based on the two-dimensional wavefront sensing system of this embodiment, the equivalent optical transfer function H(k) of the imaging system composed of the first optical filter 200, the imaging unit 300 and the second optical filter 400 can be obtained through calculation and derivation. x ,k y )for:

[0055]

[0056]

[0057]

[0058] Where k x and k y are the spatial frequencies of the incident light along the x and y directions, k x =k0·sin(θ x ), k y =cos(θ y ), k0 is the wave vector of the incident light, θ x is the angle between the incident light projected onto the xz plane and the x-axis, θ y is the angle between the incident light projected onto the yz plane and the y-axis, θ is the incident angle in the optical response curve of the optical filter, a and b are two constants, t s0 and t p0are the amplitude transmittances of s- and p-polarized light of the optical filter at an incident angle of (θ1+θ2) / 2, respectively.

[0059] Furthermore, according to the constructed equivalent optical transfer function H(k x ,k y ) After derivation and calculation, the input light intensity I carrying the distorted wavefront to be measured can be obtained in (x,y) x-polarized light intensity I x-in (x,y) and y polarized light intensity I y-in The measured x-polarized light intensity I when (x,y) reaches the polarization photodetection unit 500 after passing through the imaging system x-out (x,y) and y polarized light intensity I y-out (x,y) is:

[0060]

[0061] Where, Wavefront phase First-order partial derivatives with respect to x and y directions.

[0062] Generally, the incident light intensity distribution is uneven, and the reference light intensity I ref (x, y) to eliminate the influence of uneven light intensity, combined with the reference light intensity I ref (x,y) and input light intensity I in (x,y) relationship I ref (x,y)=b 2 I in (x,y) can be further calculated to obtain the wavefront phase gradient in the x and y directions:

[0063]

[0064] The wavefront phase gradients in the x and y directions are obtained and the wavefront phase is reconstructed using the general slope wavefront reconstruction algorithm. Reconstruction.

[0065] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0066] Although the embodiments of the present application have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and intent of the present application, and that the scope of the present application is defined by the claims and their equivalents.

Claims

1. A two-dimensional wavefront sensing system, characterized in that: The invention comprises a distorted wavefront to be measured, a first optical filter, an imaging unit, a second optical filter and a polarization photodetection unit arranged along the light propagation direction, and constructs a right-handed coordinate system consisting of an x-axis, a y-axis and a z-axis, wherein the light propagation direction is defined as the z-axis and the plane where the distorted wavefront to be measured is located is defined as the xy plane; The first optical filter and the second optical filter have similar or identical optical responses, that is, the amplitude transmittance of s- or p-polarized incident light is proportional to the incident angle within the incident angle range of [θ1, θ2], and the amplitude transmittance of p- or s-polarized incident light remains constant with changes in the incident angle within the incident angle range of [θ1, θ2], θ1, θ2∈[0°, 90°]; the angle between one of the first optical filter and the second optical filter and the xz plane is the same as the angle between the other optical filter and the yz plane, which is (θ1+θ2) / 2; the first optical filter and the second optical filter each include a transparent substrate and a first thin film and a second thin film formed on the transparent substrate and alternately stacked in sequence, and the materials making up the first thin film and the second thin film have a refractive index difference; The imaging unit is provided between the distorted wavefront to be measured and the polarization photodetection unit, and is used to image the distorted wavefront to be measured located at the object plane of the imaging unit to the polarization photodetection unit located at the image plane of the imaging unit; The polarization photoelectric detection unit is used to detect the polarization intensity of the incident light in the x and y directions after the incident light passes through the imaging system composed of the first optical filter, the imaging unit and the second optical filter.

2. The two-dimensional wavefront sensing system according to claim 1, characterized in that: The refractive index difference between the materials making the first thin film and the second thin film is greater than or equal to 0.

2.

3. The two-dimensional wavefront sensing system according to claim 1, characterized in that: The thickness of each thin film in a single optical filter is from 1 / 20 to one wavelength of the working wavelength of the two-dimensional wavefront sensing system.

4. The two-dimensional wavefront sensing system according to claim 1, characterized in that: The total number of thin film layers contained in a single optical filter is 4 to 50 layers.

5. The two-dimensional wavefront sensing system according to claim 1, wherein: The distorted wavefront to be measured can be generated by a light beam passing through a transparent medium, a biological cell or a metal surface.

6. The two-dimensional wavefront sensing system according to claim 1, characterized in that: The imaging unit adopts a 4f imaging system, a microscope imaging system or a telescope imaging system.

7. The two-dimensional wavefront sensing system according to claim 1, characterized in that: The polarization photoelectric detection unit adopts a polarization camera or a photoelectric detector with a polarization splitting function.

8. A data processing method for a two-dimensional wavefront sensing system according to any one of claims 1 to 7, characterized in that: include: The equivalent optical transfer function H(k x ,k y )for: b=t s0 ·t p0 Where k x and k y are the spatial frequencies of the incident light along the x and y directions, k x =k0·sin(θ x ), k y =k0·cos(θ y ), k0 is the wave vector of the incident light, θ x is the angle between the incident light projected onto the xz plane and the x-axis, θ y is the angle between the incident light projected onto the yz plane and the y-axis, θ is the incident angle in the optical response curve of the optical filter, a and b are two constants, t s0 and t p0 are the amplitude transmittances of s- and p-polarized light of the optical filter at an incident angle of (θ1+θ2) / 2, respectively; Calculate the input light intensity I carrying the distorted wavefront to be measured according to the following formula: in (x,y) x-polarized light intensity I x-in (x,y) and y polarized light intensity I y-in The measured x-polarized light intensity I when (x, y) reaches the polarization photodetection unit after passing through the imaging system x-out (x,y) and y polarized light intensity I y-out (x,y): Where, is the wavefront phase; The wavefront phase gradients in the x and y directions are calculated as follows: Where, I x-ref (x,y) and I y-ref (x, y) are the reference light intensity I of the undistorted wavefront ref (x,y) components along the x and y directions; The wavefront phase gradients in the x and y directions are obtained and the wavefront phase is reconstructed using the wavefront reconstruction algorithm. Reconstruction.

9. The data processing method according to claim 8, characterized in that: The wavefront reconstruction algorithm adopts a slope wavefront reconstruction algorithm.

Images