CN112484864B - Polarization modulation Hartmann-shack wavefront detection device - Google Patents

Abstract

The invention discloses a polarization modulation Hartmann-Shack wavefront detection device, which utilizes the difference in polarization characteristics between the wavefront detection target light and background stray light, and adds a rotatable wave plate and an analyzer in front of a microlens array, Perform polarization modulation on the incident beam to obtain the intensity distribution array under different polarization modulation states, and use the polarization restoration method to obtain the beam polarization information of the corresponding area of a single microlens, finally calculate the wavefront slope and restore the wavefront aberration, and realize the detection of the incident beam wave. front detection. Compared with the traditional Hartmann-Shack wavefront detection device, the patent of the present invention transforms the wavefront detection from the intensity detection dimension to the polarization detection dimension, and separates the target light from the background stray light by using the difference in the polarization characteristics of the target light and the background stray light. , greatly improving the signal-to-background ratio and realizing wavefront detection under strong background. The invention is particularly suitable for the application field of wavefront detection under strong background conditions, expands the application range, improves the detection capability, and has a simple structure.

Description

A polarization-modulated Hartmann-Shack wavefront detection device

technical field

The invention belongs to the technical field of wavefront aberration measurement, in particular to a polarization modulation Hartmann-Shack wavefront detection device.

Background technique

Hartmann-Shack wavefront detection technology is a general classical wavefront phase detection technology, which is widely used in adaptive optics, astronomy, optical detection, biomedicine and other important fields. When the background stray light is not strong, the Hartmann-Shack wavefront detection technology can be applied not only to point source target detection, but also to extended target detection. When the signal-to-background ratio of the target detection is low or the background stray light is strong, the imaging information of the point source target or extended target in the sub-aperture of the Hartmann-Shack sensor microlens array will be submerged, and the contrast will be greatly reduced. Since then, the traditional centroid algorithm or cross-correlation algorithm can effectively extract the position offset of imaging intensity information in a single sub-aperture, which leads to the reduction of wavefront detection accuracy or even failure. Therefore, the traditional Hartmann-Shack wavefront detection technology cannot be used for wavefront detection under the condition of strong background stray light, and the application fields and detection capabilities are greatly limited. Minus fixed threshold (Jiang Wenhan et al., Detection error of Shack-Hartmann wavefront sensor [J]. Acta Quantum Electronics, 02:218, 1998), narrow-band spectral filtering (J.Beckers et al., Using laser beacons for daytimeadaptive optics[J].Experimental Astronomy,11(2):133,2001), Field of view shifted Shack-Hartmann wavefront sensor for daytimeadaptive optics system[J].Optics Letters, 31(19):2821, 2006) and other methods can improve the signal-to-background ratio of wavefront detection to a certain extent, but still cannot realize the application scenarios of strong background stray light wavefront detection.

The root of the above problems lies in the traditional Hartmann-Shack wavefront detection technology. The extraction of wavefront error information stays in the intensity dimension, and the target signal light is integrated with the background stray light, although it can be weakened to a certain extent by reducing the fixed threshold and other means. Background stray light affects, but cannot fundamentally distinguish between the two. Polarization is an inherent property of light, which reflects the transverse wave properties of light. Compared with the traditional intensity imaging technology, the polarization imaging technology can simultaneously obtain the spatial distribution information and physical and chemical information of the target object, which greatly improves the amount of target information, and has the capabilities and characteristics that the traditional intensity imaging does not have.

Based on the above background, the present invention is a polarization-modulated Hartmann-Shack wavefront detection device, which utilizes the difference in the polarization characteristics of target signal light and background stray light to distinguish the incident target signal light and background stray light in the polarization dimension, changing the The traditional Hartmann-Shack wavefront detection device is indistinguishable in the intensity dimension, which significantly improves the signal-to-background ratio and expands the application field and detection accuracy of the Hartmann-Shack wavefront detection device.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is: how to distinguish the incident target signal light and background stray light in the polarization dimension, so as to improve the Hartmann-Shack wavefront detection signal-to-background ratio, and expand the application field and detection accuracy.

The technical scheme adopted by the present invention to solve the above-mentioned technical problems is: a polarization modulation Hartmann-Shack wavefront detection device, which obtains intensity distribution arrays under different polarization modulation states by polarization modulation of an incident beam, and obtains a polarization recovery method by using a polarization recovery method. A single microlens corresponds to the regional beam polarization information, and finally calculates the wavefront slope and restores the wavefront aberration to realize the detection of the incident beam wavefront. Compared with the traditional Hartmann-Shack wavefront detection device, the present invention utilizes the difference in the polarization characteristics of the incident target light and the background stray light to detect the wavefront in the polarization dimension, which is particularly beneficial to distinguish the incident target light from the background stray light and improve the wavefront. The detection signal-to-background ratio expands the application field and detection accuracy of wavefront detection.

The device of the present invention is composed of a wave plate 1 , a wave plate rotating mechanism 2 , an analyzer 3 , a microlens array 4 , a light intensity detector 5 , and a data processor 6 . The incident light including the target light and background stray light enters the polarization modulator composed of the wave plate 1 and the analyzer 3 to modulate the polarization state of the incident light; the incident light after polarization modulation continues to propagate forward, And enter the microlens array 4, and is divided into M×N sub-areas, each sub-area is a micro-lens, which images the divided incident light on the photosensitive surface of the light intensity detector 5, and obtains the corresponding sub-area. Imaging intensity distribution I(m,n).

The wave plate 1 is installed on the wave plate rotating mechanism 2, which can rotate together with the wave plate rotating mechanism 2, and rotate to different positions, and the polarization modulation state of the polarization modulator to the incident light is also different.

Among them, M and N are the number of rows and columns of the microlens array, respectively, and I(m,n) is the intensity distribution detected by the microlens with the serial number (m,n) corresponding to the area of the light intensity detector 5 .

The incident light in different modulation states passes through the wave plate 1 , the analyzer 3 , and the microlens array 4 , and finally the light intensity distribution after reaching the light intensity detector 5 is recorded and output to the data processor 6 . The data processing process is as follows:

A single sub-aperture area can be regarded as a polarization imaging micro-system, and the measured light intensities under different modulation states are denoted as I(m,n,1), I(m,n,2),...,I(m, n,N),1,2,…,N is the polarization modulation state number. The modulation effect of the polarization modulator composed of the wave plate 1 and the analyzer 3 on the polarization state of the incident beam is expressed by the following formula:

Among them, S _in and S ⁱ _out represent the polarization state of the incident light and the initial beam polarization state after polarization modulation, respectively, and M _P (θ) is the analyzer 3-Mueller matrix whose angle between the analyzer direction and the horizontal direction is θ, _MR (α _i ,δ) is the 1-Mueller matrix of the wave plate with the fast axis direction and the horizontal direction at an angle of α _i and a retardation of δ, and i is the polarization modulation serial number in a single measurement. S _in , _S ⁱ _out , MP (θ) and _MR (α _i ,δ) are expressed as follows:

Since the light intensity detector 5 can detect the beam intensity information, the following linear equations for solving the polarization state of the incident light can be obtained after formulas (1) to (4) are simultaneously combined:

in,

After solving the polarization state of the incident light by formula (5), the information such as the degree of polarization and the polarization phase angle of the incident light can be further obtained, as shown in the following formula:

So far, the Hartmann-Shack sub-aperture image after polarization modulation has been transformed from the traditional intensity dimension to the polarization dimension. The degree of polarization and the polarization phase angle are the partial representation forms of the sub-aperture image information in the polarization dimension. Using a single polarization parameter or a polarization characteristic parameter (denoted as P) after fusion of multiple polarization parameters, the position offset and slope in a single sub-aperture can be obtained by applying a centroid algorithm or a cross-correlation algorithm, and finally the wave of the incident beam can be recovered. previous error.

Among them, the present invention does not change the basic principle of Hartmann-Shack wavefront detection, but transforms the wavefront detection beacon from the traditional intensity dimension to the polarization dimension, so that the target light and the background stray light that cannot be distinguished by the traditional intensity dimension are in the polarization dimension. Differentiate, improve the signal-to-background ratio and detection accuracy.

The polarization modulator is composed of a wave plate and an analyzer. The wave plate is mainly used to introduce different polarization phases. It can use a 1/4 wave plate or other wave plates. The material can be made of natural crystals or liquid crystals. Artificial material; the analyzer is mainly used to output linearly polarized light, which can be made of wire grid type or other types of materials such as crystal.

The wave plate needs to be rotated multiple times to form multiple modulations on the incident light. The parameter selection needs to make the coefficient matrix full rank, and the number of measurements should be at least 4 times. The data redundancy introduced by more measurements is conducive to suppressing system noise and improving measurement accuracy.

The polarization modulation Hartmann-Shack wavefront detection device can be applied to different Hartmann-Shack wavefront detection scenarios, and the detection object can be a point target or an extended target.

The polarization degree and polarization phase angle are only common parameters to characterize the polarization information of incident light, and linear polarization degree, circular polarization degree, ellipticity angle or other parameters that can characterize polarization characteristics can also be used according to actual needs, or the above-mentioned polarization characteristics Fusion of parameters.

The light intensity detector 6 can detect the intensity of the incident light beam, and can use a CCD camera, a CMOS camera, or an EMCCD camera, as long as the light intensity detection and collection functions are satisfied.

The principle of the present invention is: using the difference in polarization characteristics between the incident target signal light and the background stray light, performing wavefront detection in the polarization dimension, obtaining intensity distribution arrays under different polarization modulation states, and using the polarization restoration method to obtain the corresponding area of a single microlens Beam polarization information, and finally calculate the wavefront slope and restore the wavefront aberration to realize the detection of the incident beam wavefront. The device of the invention is particularly beneficial to distinguish the incident target light from the background stray light, improve the signal-to-background ratio of wavefront detection, and expand the application field and detection accuracy of wavefront detection

Compared with the prior art, the present invention has the following advantages:

The novel wavefront detection device provided by the invention utilizes the difference in the polarization characteristics of the incident target signal light and the background stray light to transform the target signal light and the background stray light, which cannot be distinguished in the intensity dimension by the traditional Hartmann-Shack wavefront detection technology, into a Polarization dimension to distinguish. Compared with the traditional Hartmann-Shack wavefront detector, the device provided by the present invention has a higher signal-to-background ratio for wavefront detection, which is especially suitable for occasions with strong background stray light, and improves the wavefront detection accuracy.

Description of drawings

FIG. 1 is a schematic diagram of a polarization-modulated Hartmann-Shack wavefront detection device. Among them, 1 is a wave plate, 2 is a wave plate rotation mechanism, 3 is an analyzer, 4 is a microlens array, 5 is a light intensity detector, and 6 is a data processor;

FIG. 2 is a schematic diagram of sub-aperture arrangement of a 19-unit polarization-modulated Hartmann-Shack wavefront sensor;

Figure 3 is the image of the point source target with strong background stray light in the 19-element traditional Hartmann-Shack wavefront detection device (left picture) and the 19-element polarization modulation Hartmann-Shack wavefront detection device (right picture) of the present invention comparison diagram;

Figure 4 shows the image comparison between the 19-element traditional Hartmann-Shack wavefront detection device (left picture) and the 19-element polarization modulation Hartmann-Shack wavefront detection device of the present invention (right picture) for an extended target with strong background stray light Schematic.

Detailed ways

The present invention is further described below in conjunction with the accompanying drawings and specific examples.

As shown in Figure 1, a polarization modulation Hartmann-Shack wavefront detection device is composed of a wave plate 1, a wave plate rotation mechanism 2, an analyzer 3, a microlens array 4, a light intensity detector 5, and a data processor 6 . The incident light including the target light and background stray light enters the polarization modulator composed of the wave plate 1 and the analyzer 3 to modulate the polarization state of the incident light; the incident light after polarization modulation continues to propagate forward, And enter the microlens array 4, and is divided into M×N sub-areas, each sub-area is a micro-lens, which images the divided incident light on the photosensitive surface of the light intensity detector 5, and obtains the corresponding sub-area. Image intensity distribution. The wave plate 1 is installed on the wave plate rotating mechanism 2, which can rotate together with the wave plate rotating mechanism 2, and rotate to different positions, and the polarization modulation state of the polarization modulator to the incident light is also different. The incident light in different modulation states passes through the wave plate 1 , the analyzer 3 , and the microlens array 4 , and finally the light intensity distribution after reaching the light intensity detector 5 is recorded and output to the data processor 6 . The data processing process is shown by formulas (1) to (7) respectively.

So far, the Hartmann-Shack sub-aperture image after polarization modulation has been transformed from the traditional intensity dimension to the polarization dimension. The degree of polarization and the polarization phase angle are the partial representation forms of the sub-aperture image information in the polarization dimension. Using a single polarization parameter or a polarization characteristic parameter (denoted as P) after fusion of multiple polarization parameters, the position offset and slope in a single sub-aperture can be obtained by applying a centroid algorithm or a cross-correlation algorithm, and finally the wave of the incident beam can be recovered. previous error.

FIG. 2 shows a possible arrangement of sub-apertures of the microlens array (19 units) of the polarization-modulated Hartmann-Shack wavefront detection device proposed by the present invention. Figures 3 and 4 show the point source target and the extended target with strong background stray light in the 19-element traditional Hartmann-Shack wavefront detection device (left picture) and the 19-element polarization-modulated Hartmann-Shack wave of the present invention, respectively. Schematic diagram of image comparison of the front detection device (right image). It can be seen from the schematic diagram that using the polarization modulation Hartmann-Shack wavefront detection device of the present invention, the signal-to-background ratio of the point source target and the extended target in a single sub-aperture relative to the background stray light is significantly enhanced, and the wavefront detection beacon The extraction accuracy is higher, and the wavefront detection is more accurate.

It should be pointed out that Figure 2 only gives the single polarization information of the point source target and the extended target, and in practical applications, the polarization phase angle information, polarization ellipticity information and other information that can be characterized can also be given. The parameters of the polarization state and their fusion have many possibilities in the expression of polarization information.

The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited to this, any person familiar with the technology can understand the replacement or increase or decrease within the technical scope disclosed by the present invention, All should be included within the scope of the present invention, therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

The part to which the present invention is described in detail belongs to the known art in the art.

Claims (7)

1. A polarization modulation Hartmann-shack wavefront detection device is characterized in that: the device comprises a wave plate (1), a wave plate rotating mechanism (2), an analyzer (3), a micro-lens array (4), a light intensity detector (5) and a data processor (6), wherein incident light containing target light and background stray light enters a polarization modulator jointly consisting of the wave plate (1) and the analyzer (3) to modulate the polarization state of the incident light; the incident light after polarization modulation continuously transmits forwards and enters the micro-lens array (4) and is divided into M multiplied by N sub-regions, each sub-region is a micro-lens, and the divided incident light is imaged on a photosensitive surface of the light intensity detector (5) to obtain imaging intensity distribution I (M, N) of the corresponding sub-region;

The wave plate (1) is arranged on the wave plate rotating mechanism (2), can rotate together with the wave plate rotating mechanism (2) and rotates to different positions, and the polarization modulation states of the polarization modulator on incident light are different;

m and N are respectively the row number and the column number of the micro-lens array, and I (M, N) is the intensity distribution detected by the micro-lens with the serial number (M, N) corresponding to the area of the light intensity detector (5);

incident light under different modulation states passes through the wave plate (1), the analyzer (3) and the micro-lens array (4), and finally the light intensity distribution after reaching the light intensity detector (5) is recorded and output to the data processor (6), wherein the data processing process is as follows:

the single sub-aperture area can be regarded as a polarization imaging micro-system, the light intensities measured under different modulation states are respectively marked as I (m, N,1), I (m, N,2), …, I (m, N, N),1,2, …, and N are polarization modulation state serial numbers, and the modulation effect of the polarization modulator formed by the wave plate (1) and the analyzer (3) on the polarization state of an incident beam is represented by the following formula:

wherein S is_inAnd Sⁱ _outRespectively representing the polarization state of incident light and the polarization state of the initially set light beam after polarization modulation, M_P(theta) an analyzer (3) with an angle theta between the analyzing direction and the horizontal direction, and M is a Mueller matrix _R(α_iDelta) is an angle alpha between the fast axis direction and the horizontal direction_iA wave plate (1) with a retardation delta, i is a polarization modulation serial number in single measurement, and S_in、Sⁱ _out、M_P(theta) and M_R(α_iδ) expression is as follows:

because the light intensity detector (5) can detect the intensity information of the light beam, the following linear equation for solving the polarization state of the incident light can be obtained after the equations (1) to (4) are combined:

wherein,

after the polarization state of the incident light is solved by equation (5), the polarization degree information DoP and the polarization phase angle information AoP of the incident light can be further obtained, as shown in the following equations:

so far, the Hartmann-shack sub-aperture image after polarization modulation is converted from the traditional intensity dimension to the polarization dimension, the polarization degree and the polarization phase angle are partial representation forms of the sub-aperture image information in the polarization dimension, a single polarization parameter or a polarization characteristic parameter obtained by fusing multiple polarization parameters is used and marked as P, the position deviation and the slope in a single sub-aperture can be obtained by applying a centroid algorithm or a cross-correlation algorithm, and the wavefront error of an incident beam is finally restored.

2. A polarization modulated hartmann-shack wavefront sensor of claim 1, wherein: the device does not change the basic principle of Hartmann-shack wavefront detection, but converts the wavefront detection beacon from the traditional intensity dimension to the polarization dimension, thereby distinguishing the target light which cannot be distinguished by the traditional intensity dimension from the background stray light in the polarization dimension, and improving the signal-to-back ratio and the detection precision.

3. The polarization-modulated hartmann-shack wavefront-sensing device of claim 1, wherein: the polarization modulator consists of a wave plate and an analyzer, wherein the wave plate is mainly used for introducing different polarization phases, the wave plate adopts 1/4 wave plates or other wave plates, and the manufacturing material adopts natural crystals or liquid crystal artificial materials; the analyzer is mainly used for outputting linearly polarized light and is made of a wire grid type or a crystal material.

4. The polarization-modulated hartmann-shack wavefront-sensing device of claim 1, wherein: the wave plate needs to rotate for multiple times to form multiple modulation on incident light, the parameter selection needs to enable the coefficient matrix of the formula (5) to be full-rank, the measurement times are at least 4, more data redundancy introduced by measurement is beneficial to inhibiting system noise, and the measurement precision is improved.

5. The polarization-modulated hartmann-shack wavefront-sensing device of claim 1, wherein: the method is applied to different Hartmann-shack wavefront detection scenes, and a detection object is a point target or an expansion target.

6. The polarization-modulated hartmann-shack wavefront-sensing device of claim 1, wherein: the polarization degree and the polarization phase angle are common parameters for representing polarization information of incident light, or linear polarization degree, circular polarization degree or elliptical polarization angle is adopted according to actual needs, or the linear polarization degree, the circular polarization degree or the elliptical polarization angle is fused.

7. A polarization modulated hartmann-shack wavefront sensor of claim 1, wherein: the light intensity detector (5) can detect the intensity of an incident light beam and adopts a CCD camera, a CMOS camera and an EMCCD camera.

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