CN117539139B - Polarization interference-free coded aperture correlation holography based on speckle decorrelation - Google Patents

Abstract

The invention discloses a polarized interference-free coded aperture correlation holography based on speckle decorrelation, and relates to the field of computational optical imaging. Based on the interference-free coded aperture correlation holography, holograms containing 0 DEG, 45 DEG and 90 DEG polarization components are recorded by using a single light path and synthesized into a single hologram, the light path structure is simple, meanwhile, the correlation between point source holograms of different polarization angles is reduced by using a speckle rotary decorrelation technology, images corresponding to the 0 DEG, 45 DEG and 90 DEG polarization components are respectively reconstructed from the single hologram, the images of the polarization components are not crosstalked during reconstruction, the calculation error of Stokes parameters is reduced, and the calculation precision of linear polarization angles and linear polarization degrees is improved.

Description

A polarization-free interference-free coded aperture correlation holography based on speckle decorrelation

Technical Field

The invention relates to interference-free coded aperture correlation holography, belongs to the field of computational optical imaging, and in particular to polarization interference-free coded aperture correlation holography based on speckle decorrelation.

Background technique

As a new type of incoherent digital holography, Interferenceless Coded Aperture Correlation Holography (I-COACH) can record and reproduce the three-dimensional information of incoherently illuminated objects. Different from the implementation conditions of other incoherent holography, it can record and store 3D scenes on 2D holograms without using coherent light, two-wave interference, changing the viewpoint of the image sensor, moving any part of the imaging system, and measuring the depth of any part of the scene before the hologram is acquired. At the same time, it has the advantages of no aberration, no speckle noise, low cost and high resolution, and has practical application value in polarization imaging, biomedical imaging, remote sensing imaging and other aspects.

Polarization imaging is a technology that uses the polarization information of light to obtain images. In medical imaging, it can be used to detect fiber structures in tissues; in materials science, it can be used to detect stress distribution and defects in materials; in biology, it can be used to detect molecular structures in cells. Currently, polarization imaging based on coherent digital holography is often represented by the Jones matrix, which requires a highly coherent laser light source, has high requirements for the shooting environment, and has high shooting costs. It is also impossible to completely achieve aberration-free polarization imaging. Polarization imaging based on the incoherent digital holographic system I-COACH uses the Stokes matrix, but its optical path structure is complex, and the correlation between point source holograms PSH (Point Spread Hologram) at different angles is too large, resulting in errors in the calculation results of the Stokes parameters.

The present invention proposes a polarization-free interference coded aperture correlation holography based on speckle decorrelation, which realizes single-channel I-COACH polarization imaging. The optical path structure is simple, and the speckle decorrelation technology is used to reduce the correlation of different polarization angles PSH recorded, reduce the calculation error of Stokes parameters, and improve the calculation accuracy of linear polarization angle AOLP (Angle Of the Linear Polarization) and linear polarization degree DOLP (Degree Of Linear Polarization).

Summary of the invention

The present invention proposes a polarization-free interference-free coded aperture correlation holography based on speckle decorrelation, which can realize high-precision polarization imaging of I-COACH with only a single optical path.

The method comprises the following three steps: S1, recording the object hologram OH (Object Hologram) and PSH corresponding to the polarization angles of 0°, 45° and 90° respectively; S2, PSH rotation decorrelation at different polarization angles; S3, calculating Stokes parameters, AOLP and DOLP.

The horizontal direction of the cross section perpendicular to the propagation direction of the light path is defined as 0°, and the counterclockwise direction is the positive direction.

For the convenience of representation, the abbreviations of optical components are given: Light Emitting Diode LED (Light Emitting Diode); Phase Spatial Light Modulator PSLM (Phase Spatial Light Modulator).

The polarization-free interference-free coded aperture correlation holography based on speckle decorrelation has a specific optical system comprising: a monochromatic LED (1), a first polarizer (2), a first lens (3), a target object (4), a second lens (5), a second polarizer (6), a 1/2 wave plate (7), a third polarizer (8), a PSLM (9), a beam splitter prism (10) and an image sensor (11).

S1: record OH and PSH corresponding to polarization angles of 0°, 45°, and 90°, respectively;

A monochromatic LED (1) emits monochromatic incoherent light, which is converted into 135° linear polarized light after passing through a first polarizer (2). A first lens (3) focuses the light beam emitted from the first polarizer (2) onto a target object (4), thereby achieving critical illumination of the target object (4). A pinhole is first used to simulate an ideal point light source on the target object (4), and diffracted light emitted from the target object (4) is collimated by a second lens (5).

The polarization angle of the second polarizer (6) is rotated to 0°, 45° and 90° in sequence. After the collimated light beam passes through the second polarizer (6), it is changed to 90° by the 1/2 wave plate (7). At this time, the polarization angle of the light beam is the same as the polarization angle of the third polarizer (8). The polarization modulation angle of the PSLM (9) is 90°. A coded phase mask CPM (Coded Phase Mask) synthesized by the Gerchberg-Saxton algorithm is loaded on the PSLM (9). The PSLM (9) is a reflective phase-type spatial light modulator. After the light beam is modulated by the CPM, it is reflected by the beam splitter prism (10) and enters the image sensor (11). The PSH intensities corresponding to the polarization angles of the second polarizer (6) are recorded in sequence on the image sensor (11), which are _IPSH (0°), _IPSH (45°) and _IPSH (90°).

Only the pinhole at the target object (4) is replaced with a resolution plate, and the rest of the optical path settings remain the same. The OH intensities corresponding to the polarization angles of the second polarizer (6) are recorded in sequence on the image sensor (11), namely, I _OH (0°), I _OH (45°), and I _OH (90°).

S2: PSH rotation decorrelation at different polarization angles;

The speckle can be quickly decorrelated by rotating it around the main optical axis, and the minimum rotation angle to ensure that the reconstruction of each polarization angle does not interfere with each other is 3°. Therefore, _IPSH (0°) is rotated 0° around the central pixel point and recorded as _IPSH,0° (0°), _IPSH (45°) is rotated 3° around the central pixel point and recorded as _IPSH,3° (45°), and _IPSH (90°) is rotated 6° around the central pixel point and recorded as _IPSH,6° (90°).

To ensure smooth reconstruction of the image, the OH with the same polarization angle as PSH needs to be rotated by the same angle. Therefore, I _OH (0°) is rotated 0° around the center pixel and recorded as I _OH,0° (0°), I _OH (45°) is rotated 3° around the center pixel and recorded as I _OH,3° (45°), and I _OH (90°) is rotated 6° around the center pixel and recorded as I _OH,6° (90°).

The object hologram OH containing polarization information is expressed as follows:

I _OH =I _OH,0° (0°)+I _OH,3° (45°)+I _OH,6° (90°)

S3: Calculate Stokes parameters, AOLP and DOLP;

The image reconstruction corresponding to the polarization angle is expressed as follows:

in represents the correlation operation; H, V and T represent the reconstruction results of polarization angles of 0°, 90° and 45°, respectively.

The Stokes parameter can be expressed as:

S0＝H+V

S1＝H-V

S2＝2T-S0

AOLP and DOLP can be expressed as:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of a polarization-free interference-free coded aperture correlation holographic system based on speckle decorrelation.

Figure 2 is a flow chart for the implementation of polarization-free interference-free coded aperture correlation holography based on speckle decorrelation.

Fig. 3 Correlation value variation curve of speckle rotation decorrelation of PSH at 0° and PSH at 90°.

Fig. 4 Reconstruction results of polarization angles of 0°, 90°, and 45°: (a) 0°, (b) 90°, (c) 45°.

Fig. 5 Calculation results of Stokes parameters: (a) S0, (b) S1, (c) S2.

Fig. 6 Calculation results of AOLP and DOLP: (a) AOLP, (b) DOLP.

Description of reference numerals:

1. Monochrome LED, 2. First polarizer, 3. First lens, 4. Target, 5. Second lens, 6. Second polarizer, 7. 1/2 wave plate, 8. Third polarizer, 9. PSLM, 10. Beam splitter, 11. Image sensor.

Detailed ways

In order to better explain the implementation process of the present invention, the present invention will be further described in detail with reference to an embodiment below, but the present invention is not limited to this embodiment.

Example

As shown in FIG1 , the wavelength of the monochromatic LED (1) light source is 528 nm, the polarization angle of the first polarizer (2) is set to 135°, the first polarizer (2) changes the light beam emitted by the LED into 135° linear polarized light, and then focuses on the target (4) through the first lens (3), the target (4) first uses a 25 μm pinhole, the distance from the monochromatic LED (1) light source to the first lens (3) is d ₁ , the focal length of the first lens (3) is f ₁ , the distance from the first lens (3) to the target (4) is d ₂ , d ₁ , d ₂ and f ₀ satisfy d ₁ ^-1 +d ₂ ^-1 =f ₀ ^-1 . The distance from the target (4) to the second lens (5) is the focal length f ₁ of the second lens (5), and the diffracted light of the target (4) is collimated after passing through the second lens (5). The collimated light beam passes through a second polarizer (6). To calculate the Stokes parameter, the second polarizer (6) is rotated to 0°, 45° and 90° in sequence. The optical axis of a half wave plate (7) after the second polarizer (6) is rotated to 45°, 22.5° and 90° respectively, so as to adjust the light beam emitted from the second polarizer (6) to 90°. At this time, the polarization angle of the light beam is the same as the polarization angle of the third polarizer (8), thereby satisfying the polarization modulation angle of the PSLM (9).

The 1/2 wave plate (7) adjusts the polarization state of the light beam without affecting the light intensity, thereby ensuring the accuracy of the Stokes parameter calculation. At the same time, the light beam satisfies the polarization modulation angle of the PSLM (9).

A coded phase mask CPM synthesized by a Gerchberg-Saxton algorithm is loaded on PSLM (9). The light beam incident on PSLM (9) is modulated by CPM. PSLM (9) is a reflective phase spatial light modulator. The modulated light beam is reflected by a beam splitter prism (10) and enters an image sensor (11).

According to the rotation of the second polarizer (6) and the 1/2 wave plate (7), the PSH intensity images at 0°, 45° and 90° are recorded on the image sensor (11) in sequence, namely _IPSH (0°), _IPSH (45°) and _IPSH (90°).

Only the pinhole at the target (4) is replaced with a resolution plate, and the other operating settings remain the same. The OH intensity images at 0°, 45° and 90° are recorded on the image sensor (11) in sequence, which are I _OH (0°), I _OH (45°) and I _OH (90°), respectively.

To ensure the calculation accuracy of the Stokes parameters, it is necessary to reconstruct the images corresponding to the polarization angles of 0°, 45°, and 90° separately. During the reconstruction, the correlation between _IPSH (0°), _IPSH (45°), and _IPSH (90°) is too large, resulting in that PSH and OH with different polarization angles can still reconstruct images during the correlation operation. Images with different polarization angles cause crosstalk with each other during reconstruction, which greatly increases the calculation error of the Stokes parameters and affects the calculation accuracy of AOLP and DOLP.

Based on the rotation decorrelation characteristic of speckle, that is, the rotation of speckle around the principal optical axis can make the speckle quickly decorrelated, 135° linearly polarized light was used in the experiment. The 45° polarization component is 0, so I _PSH (45°) only has background noise. Therefore, I _PSH (0°) and I _PSH (90°) were selected to verify the fast decorrelation of speckle. As shown in Figure 3, the correlation intensity between I _PSH (0°) and I _PSH (90°) decreases with the increase of the rotation angle of I _PSH (0°) around the principal optical axis.

The minimum rotation angle that satisfies the mutual non-interference of reconstruction at different polarization angles is 3°. Therefore, I _PSH (0°) is rotated 0° around the center pixel point and recorded as I _{PSH, 0°} (0°), I _PSH (45°) is rotated 3° around the center pixel point and recorded as I _{PSH, 3°} (45°), and I _PSH (90°) is rotated 6° around the center pixel point and recorded as I _{PSH, 6°} (90°).

In order to smoothly reconstruct the images of each polarization component, the OH with the polarization angle corresponding to the PSH needs to be rotated by the same angle to match the rotation angle. Therefore, I _OH (0°) is rotated 0° around the center pixel point and is recorded as I _OH,0° (0°), I _OH (45°) is rotated 3° around the center pixel point and is recorded as I _OH,3° (45°), and I _OH (90°) is rotated 6° around the center pixel point and is recorded as I _OH,6° (90°).

At this time, only PSH and OH rotated by the same angle can reconstruct the image.

The OH including all polarization components is expressed as follows:

I _OH =I _OH,0° (0°)+I _OH,3° (45°)+I _OH,6° (90°)

Image reconstruction of different polarization components is expressed as follows:

in represents the correlation operation; H, V and T represent the images corresponding to the 0°, 90° and 45° polarization components reconstructed from a single hologram, respectively, as shown in Figure 4(a), Figure 4(b) and Figure 4(c), respectively.

The Stokes parameter can be expressed as:

S0＝H+V

S1＝H-V

S2＝2T-S0

S0 is shown in FIG5(a), S1 is shown in FIG5(b), and S2 is shown in FIG5(c).

AOLP and DOLP can be expressed as:

The calculation result of AOLP is shown in Figure 6(a). The average value of the polarization angle image is 132.13°, the theoretical value is 135°, and the error is 2.87°. The calculation result of DOLP is shown in Figure 6(b). The average value of the polarization degree image is 0.91°, the theoretical value is 1°, and the error is 0.09°.

The above description is only a preferred implementation example of the present invention and does not represent the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the principles of the present invention are included in the protection scope of the present invention.

Claims (1)

1. The speckle decorrelation-based polarized interference-free coded aperture correlation holography is characterized in that the specific implementation device comprises a monochromatic Light Emitting Diode (LED) (LIGHT EMITTING Diode), a first polaroid, a first lens, a target object, a second lens, a second polaroid, a 1/2 wave plate, a third polaroid, a phase space light Modulator PSLM (PHASE SPATIAL LIGHT Modulator), a beam splitting prism and an image sensor;

defining the horizontal direction of a cross section perpendicular to the propagation direction of the optical path as 0 DEG, and the anticlockwise direction as the positive direction;

The method comprises the following three steps: s1, respectively recording an object hologram OH (Object Hologram) and a point source hologram PSH (Point Spread Hologram) corresponding to polarization angles of 0 DEG, 45 DEG and 90 DEG; s2, PSH rotation decorrelation of different polarization angles; s3, calculating Stokes parameters, a linear polarization Angle AOLP (Angle Of THE LINEAR Polarization) and a linear polarization degree DOLP (Degree Of Linear Polarization);

S1: the first polaroid changes the light emitted by the monochromatic light emitting diode LED into 135-degree linearly polarized light, the polarization angles of the second polaroid are sequentially rotated to be 0 degrees, 45 degrees and 90 degrees, the corresponding rotation of the optical axis of the 1/2 wave plate is 45 degrees, 22.5 degrees and 90 degrees corresponding to the rotation angle of the second polaroid in order to meet the polarization modulation angle of PSLM, the 1/2 wave plate is utilized to change the polarization angle of a light beam to be 90 degrees under the condition that the light intensity is not changed, and at the moment, the polarization angle of the light beam is the same as the polarization angle of the third polaroid and meets the polarization modulation angle of PSLM; the target uses a 25 μm pinhole, and corresponding to three rotation angles of the second polarizer, PSH of 0 °, 45 ° and 90 ° are recorded on the image sensor in sequence, and are respectively denoted as I _PSH(0°)、I_PSH (45 °) and I _PSH (90 °); the target is replaced by a resolution plate, and OH of 0 DEG, 45 DEG and 90 DEG is recorded on the image sensor in sequence corresponding to three rotation angles of the second polaroid and is respectively marked as I _OH(0°)、I_OH (45 DEG) and I _OH (90 DEG);

S2: PSH with different polarization angles have overlarge correlation with each other, so that the PSH and OH with different polarization angles can still reconstruct images during correlation operation, and the calculation error of Stokes parameters is greatly increased; based on the speckle rotation decorrelation characteristic, namely that the speckle rotates around a main optical axis, the speckle can be rapidly decorrelated, and the minimum rotation angle which meets the condition that the reconstruction of all polarization angles is not interfered with each other is 3 degrees; thus, the rotation of I _PSH (0 °) about the center pixel point is denoted as I _PSH,0°(0°),I_PSH (45 °) about the center pixel point is denoted as I _PSH,3°(45°),I_PSH (90 °) about the center pixel point by 0 °) and the rotation of I _PSH,6° (90 °) about the center pixel point by 6 °; in order to smoothly reconstruct the image of each polarization component, the same angle as OH of the polarization angle corresponding to PSH needs to be rotated, wherein I _OH (0) is selected to rotate around a central pixel point by 0 degrees and is marked as I _OH,0°(0°),I_OH (45 degrees), 3 degrees is selected to rotate around the central pixel point and is marked as I _OH,3°(45°),I_OH (90 degrees), and 6 degrees is selected to rotate around the central pixel point and is marked as I _OH,6° (90 degrees), and at the moment, only PSH and OH which rotate by the same angle can reconstruct the image;

The OH containing all polarization components is represented by the following formula:

I_OH＝I_OH,0°(0°)+I_OH,3°(45°)+I_OH,6°(90°)

The image reconstruction of the different polarization components is represented by the following formula:

Wherein the method comprises the steps of Representing correlation operations, H, V and T representing images reconstructed from a single hologram corresponding to 0 °, 90 ° and 45 ° polarization components, respectively;

s3: stokes parameters can be expressed as:

S0＝H+V

S1＝H-V

S2＝2T-S0

AOLP and DOLP can be expressed as: