A digital holographic speckle suppression imaging system based on rotating ball lens

Abstract

The application provides a digital holographic speckle suppression imaging system based on a rotating ball lens, and belongs to the technical field of digital holographic speckle suppression imaging systems; in order to solve the technical problems of complex optical path structure, low imaging quality and high manufacturing cost of laser modulation elements in the current speckle noise suppression, the technical scheme is that: the laser beam emitted by the laser passes through a filter to modulate the intensity, a first half-wave plate to modulate the polarization state, a rotating ball lens to modulate the incident light angle, and an optical stop filter in sequence, and finally is divided into an object beam and a reference beam by a polarization beam splitter prism; the object beam is reflected by a first reflector to irradiate on a sample object and is reflected back to the beam splitter prism; the reference beam is reflected by a second reflector, then passes through a second half-wave plate to make the polarization state of the reference beam consistent with that of the object beam, and finally is combined by the beam splitter prism to interfere at a CCD camera to form an interference pattern; the application is used for suppressing the speckle noise of the digital holographic imaging system.

Description

TECHNICAL FIELD

[0001] The application provides a digital holographic speckle suppression imaging system based on a rotating ball lens, and belongs to the technical field of digital holographic speckle suppression imaging systems. BACKGROUND

[0002] With the continuous development of science and technology, people's research on microscopic objects is more in-depth, and more accurate observation means can improve the observation effect; digital holographic microscopy as a new emerging microscopic observation means has been widely used in microscopic scenes in many fields such as material science, biomedical science and industrial detection, however, since digital holographic microscopy uses high-coherence laser as a light source, when detecting rough objects, the emitted detection laser will be scattered to form speckle noise, which will seriously affect the imaging quality.

[0003] In the current technology, the schemes for suppressing the above-mentioned speckle noise mainly include: replacing a low-coherence light source, using a digital image processing algorithm for filtering, and using a laser modulation element, wherein:

[0004] The speckle noise in digital holography essentially comes from the high coherence of the light source, so replacing the light source with a low-coherence light source can suppress the speckle noise from the root, but the digital holographic imaging system using a low-coherence light source has a complex optical path, and the low-coherence light source reduces the resolution of the imaging system;

[0005] The digital image processing algorithm can directly process the imaging result in the computer, but the suppression effect is limited by the algorithm itself, and the suppression ability of the speckle noise has certain limitations, and it is difficult to greatly improve the digital holographic imaging quality;

[0006] With the progress of material science, many new materials can now be used to make corresponding elements to modulate laser, however, the existing laser modulation elements all have the problems of high manufacturing cost and complex mechanical motion structure. SUMMARY

[0007] In order to solve the technical problems in the background art, the technical scheme adopted by the application is as follows: a digital holographic speckle suppression imaging system based on a rotating ball lens is provided, which comprises a laser, a filter, a first half-wave plate, a rotating ball lens, an aperture, a polarization beam splitter, a first mirror, a second mirror, a second half-wave plate, a beam splitter, a sample object and a CCD camera.

[0008] The laser emits a laser beam outward, and the laser beam is modulated in intensity by the filter and in polarization state by the first half-wave plate, and then sequentially passes through the rotating ball lens to modulate the incident light angle and the aperture to filter, and finally is divided into an object beam and a reference beam by the polarization beam splitter.

[0009] The object beam is reflected by the first reflecting mirror onto the sample object and then reflected back to the beam splitter.

[0010] The reference beam is reflected by the second mirror and then passes through the second half-wave plate to make the polarization state of the reference beam and the object beam consistent. Finally, after being combined by the beam splitter, the beam interferes at the CCD camera to form an interference pattern, which is recorded by the CCD camera.

[0011] The rotating spherical lens includes a front support, a front clamping plate, a spherical lens, a rear clamping plate, a rear support, and a motor. Bearings for supporting the rotation of the front and rear clamping plates and the spherical lens are provided between the front support and the front clamping plate, and between the rear support and the rear clamping plate. The front and rear clamping plates hold the spherical lens.

[0012] The rear end of the rear clamping plate passes through the through hole provided in the rear bracket and is connected to the drive end of the motor. The motor drives the rear clamping plate to rotate, which in turn drives the ball lens and the front clamping plate to rotate.

[0013] The center positions of the front and rear clamps do not coincide with the rotation center of the motor, so that the center position of the ball lens does not coincide with the rotation center of the motor when it rotates, and the eccentricity between the two is set to d.

[0014] The rotating spherical lens needs to be adjusted during the experiment to ensure that the rotation center of the spherical lens coincides with the optical axis of the main optical path.

[0015] The voltage at both ends of the motor is controlled by a control board, and the rotation speed of the spherical lens is controlled by changing the applied voltage.

[0016] The spherical lens is specifically made of K9 glass, with a radius R of 5mm and an internal refractive index n of 1.517.

[0017] The width w of the aperture is 3mm, and the distance between it and the rotating spherical lens is 10mm;

[0018] The laser beam emitted by the laser has a diameter of 0.65 mm.

[0019] When in use, the system suppresses speckle noise by dynamically changing the incident light angle through a rotating spherical lens. When the incident light passes through the rotating spherical lens, the lens deflects the incident light. The rotation of the spherical lens generates a dynamic optical path difference, which reduces the spatial coherence of the laser, destroys the coherence conditions for the formation of speckle noise, and suppresses speckle noise in the digital holographic microscope system.

[0020] The specific method for controlling the dynamic change of the incident light angle by the rotating spherical lens is as follows:

[0021] Define the deflection θ of the laser beam by the spherical lens. r The formula for calculating `the launch position r` is:

[0022] ;

[0023] Where ω is the rotational speed, d is the eccentricity, n is the refractive index of the spherical lens, R is the radius of the spherical lens, and the laser deflection θ r Satisfaction:

[0024] ;

[0025] Meanwhile, to ensure image intensity, the relationship between the offset d and the width w of the aperture stop should satisfy:

[0026] ;

[0027] To ensure effective suppression of speckle noise, the relationship between the rotational speed ω of the spherical lens and the successive exposure times T should satisfy:

[0028] .

[0029] The advantages of this invention compared to existing technologies are as follows: This invention uses a rotating spherical lens to achieve laser modulation, and uses the rotating spherical lens to dynamically change the incident light angle to suppress speckle noise. When the incident light passes through the rotating spherical lens, the spherical lens will deflect the incident light, generating a dynamic optical path difference, which significantly reduces the spatial coherence of the laser, destroys the coherence conditions for the formation of speckle noise, and achieves the suppression of speckle noise in digital holography, thereby improving the quality of digital holographic reconstruction. At the same time, the use of digital holographic image processing algorithms can further suppress speckle noise in the reconstruction, improve the quality of the reconstruction, and improve the signal-to-noise ratio of the system. Attached Figure Description

[0030] The present invention will be further described below with reference to the accompanying drawings:

[0031] Figure 1 This is a schematic diagram of the structure of the digital holographic speckle suppression imaging system of the present invention;

[0032] Figure 2 This is a schematic diagram of the rotating spherical lens of the present invention;

[0033] Figure 3 This is a schematic diagram of the rotating spherical lens clamping structure of the present invention;

[0034] Figure 4 This is a schematic diagram illustrating the working principle of the rotating spherical lens of the present invention.

[0035] In the diagram, the numbers represent: 1 for laser, 2 for filter, 3 for first half-wave plate, 4 for rotating spherical lens, 5 for aperture, 6 for polarizing beam splitter, 7 for first reflecting mirror, 8 for second reflecting mirror, 9 for second half-wave plate, 10 for beam splitter, 11 for sample object, and 12 for CCD camera.

[0036] 41 is the front bracket, 42 is the front clamping plate, 43 is the ball lens, 44 is the rear clamping plate, 45 is the rear bracket, and 46 is the motor. Detailed Implementation

[0037] like Figures 1 to 4 As shown, this invention provides a digital holographic speckle suppression imaging system based on a rotating spherical lens, used to suppress speckle noise in a digital holographic imaging system. It mainly uses a rotating spherical lens to generate an optical path difference in the laser, modulating the incident angle of the laser to suppress speckle noise in the digital holographic system and improve the quality of the digital holographic reconstruction image.

[0038] like Figure 1 As shown, in order to achieve the above objectives, the digital holographic speckle suppression imaging system provided by this invention has the following structure:

[0039] Includes laser 1, filter 2, first half-wave plate 3, rotating spherical lens 4, aperture 5, polarizing beam splitter 6, first reflector 7, second reflector 8, second half-wave plate 9, beam splitter 10, sample object 11, and CCD camera 12;

[0040] During the experiment, the relative position of the rotating spherical lens 4 needs to be adjusted first to ensure that the rotation center of the spherical lens coincides with the optical axis of the main optical path. First, the laser beam emitted by the laser 1 is modulated in intensity by the filter 2 and in polarization state by the first half-wave plate 3. Then, it passes through the rotating spherical lens 4 to modulate the incident light angle and is filtered by the aperture 5. Finally, it is split into an object beam and a reference beam by the polarization beam splitter 6. The object beam is reflected by the first reflecting mirror 7 and illuminates the sample object 11, and is reflected back to the beam splitter 10. The reference beam is reflected by the second reflecting mirror 8 and then passes through the second half-wave plate 9 to make the polarization state of the reference beam consistent with that of the object beam. Finally, after being combined by the beam splitter 10, they interfere at the CCD camera 12 to form an interference pattern, which is recorded by the CCD camera 12.

[0041] like Figure 2 and Figure 3 As shown, the rotating spherical lens 4 is specifically composed of a front bracket 41, a front clamping plate 42, a spherical lens 43, a rear clamping plate 44, a rear bracket 45, and a motor 46. Bearings are placed between each bracket and the clamping plate to support the rotation of the clamping plate and the spherical lens 43. During installation, the front clamping plate 42 and the rear clamping plate 44 clamp the spherical lens 43. The front clamping plate 42 and the rear clamping plate 44 have a base plate and a clamping structure. The center of the base plate of the rear clamping plate 44 is connected to the motor 46. The center of the clamping structure is a certain distance from the rotation center of the motor. The clamping structure coincides with the center of the spherical lens 43, thereby ensuring that the center of the spherical lens 43 is a certain distance from the rotation center of the motor when it rotates, i.e., the eccentricity d. The eccentricity d is set to 1mm.

[0042] The rear end of the rear clamping plate 44 passes through the through hole provided in the rear bracket 45 and is connected to the drive end of the motor 46. The motor 46 drives the rear clamping plate 44 to rotate, which in turn drives the ball lens 43 to rotate. Specifically, the voltage applied to both ends of the motor is controlled by the control board, thereby controlling the rotation speed of the ball lens 43.

[0043] The rotating spherical lens 4 uses K9 glass as its material, with a radius R of 5 mm and a refractive index n of 1.517. The incident beam diameter w of the beam expander is 3 mm, and it is 10 mm away from the rotating spherical lens. The laser beam diameter is 0.65 mm. The rotation speed of the spherical lens is controlled by changing the voltage applied to both ends of the motor.

[0044] This invention uses a rotating spherical lens to dynamically change the incident light angle to suppress speckle noise. When the incident light passes through the rotating spherical lens, the lens deflects the incident light, creating a dynamic optical path difference. This significantly reduces the spatial coherence of the laser, disrupts the coherence conditions for speckle noise formation, and thus suppresses the speckle noise. The rotating spherical lens 4 is placed in the main optical path, between the half-wave plate 3 and the aperture 5. The rotating spherical lens 4 deflects the incident light angle, reduces the spatial coherence of the laser, and effectively suppresses speckle noise in the digital holographic microscope system.

[0045] like Figure 4 As shown, the spherical lens proposed in this invention deflects the laser beam by θ. r The relationship between the exit position r and the rotational speed ω, the eccentricity d, the refractive index n of the spherical lens, and the radius R of the spherical lens is as follows:

[0046] ;

[0047] in ;

[0048] To ensure image intensity, the relationship between the offset d and the width w of the aperture should satisfy:

[0049] ;

[0050] To ensure effective suppression of speckle noise, the relationship between the spherical lens rotation speed ω and the successive exposure times T should satisfy:

[0051] .

[0052] In the embodiments of this invention, parameters such as speckle contrast ratio, peak signal-to-noise ratio (PSNR), and root mean square error (RMSE) are used to evaluate the suppression effect of this invention on speckle noise. The intensity reconstruction image obtained by this invention from the detection of a silicon substrate circular aperture array is compared with the intensity reconstruction images obtained by general methods and general image processing algorithms. The experimental results are shown in Table 1 below. The intensity reconstruction image obtained by the proposed method of this invention has a significantly reduced speckle contrast ratio to 0.105 compared to the general method, a reduction of 76.19%, while the speckle contrast ratio of the intensity reconstruction image obtained by the general method is 0.439. Compared with the general method, the proposed method of this invention improves the PSNR of the intensity reconstruction image to 9.917 dB and reduces the RMSE to 0.106. The above data verify the effective suppression effect of the proposed method on speckle noise.

[0053] Table 1. Experimental data on noise suppression using different methods

[0054]

[0055] This invention proposes a scheme for suppressing speckle noise in digital holography using a rotating spherical lens. This scheme utilizes the deflection characteristics of the spherical lens on the laser. The designed spherical lens rotating device uses a motor as a power source. By controlling the voltage applied to both ends of the motor, the rotation speed of the spherical lens can be controlled. By dynamically changing the incident light angle, the spatial coherence of the incident light is reduced, thereby disrupting the coherence conditions for speckle noise formation and achieving the suppression of speckle noise in digital holography.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A digital holographic speckle reduction imaging system based on a rotating ball lens, characterized by: The laser (1), the filter (2), the first half-wave plate (3), the rotating ball lens (4), the diaphragm (5), the polarization beam splitter prism (6), the first mirror (7), the second mirror (8), the second half-wave plate (9), the beam splitter prism (10), the sample object (11), the CCD camera (12); The laser (1) emits a laser beam outward, which is modulated in intensity by the filter (2) and in polarization state by the first half-wave plate (3), then is modulated in incident light angle by the rotating ball lens (4) and filtered by the diaphragm (5), and finally is split into an object beam and a reference beam by the polarization beam splitter prism (6); The object beam is reflected by the first mirror (7) to irradiate on the sample object (11) and is reflected back to the beam splitter prism (10); The reference beam is reflected by the second mirror (8), then passes through the second half-wave plate (9) to make the polarization state of the reference beam consistent with that of the object beam, and finally is combined by the beam splitter prism (10) to interfere at the CCD camera (12) to form an interference pattern, which is recorded by the CCD camera (12); The rotating ball lens (4) comprises a front support (41), a front clamping plate (42), a ball lens (43), a rear clamping plate (44), a rear support (45) and a motor (46), bearings are arranged between the front support (41) and the front clamping plate (42) and between the rear support (45) and the rear clamping plate (44) to support the front and rear clamping plates and the ball lens (43) to rotate, and the front clamping plate (42) and the rear clamping plate (44) clamp the ball lens (43); The rear end of the rear clamping plate (44) is connected with the driving end of the motor (46) through the through hole of the rear support (45), and the rear clamping plate (44) is rotated by the motor (46), thereby driving the ball lens (43) and the front clamping plate (42) to rotate; The center positions of the front clamping plate (42) and the rear clamping plate (44) do not coincide with the rotation center of the motor (46), so that the center position of the ball lens (43) does not coincide with the rotation center of the motor (46) when the ball lens (43) rotates, and the eccentric distance of the two is d; The rotating ball lens (4) needs to be adjusted in position during the experiment to ensure that the rotation center of the ball lens (43) coincides with the optical axis of the main light path; The specific method for controlling the rotating ball lens (4) to dynamically change the incident light angle is: The deflection θ of the spherical lens (43) to the laser is defined r The calculation formula of the exit position r' is: ； where ω is the rotational speed, d is the eccentricity, n is the refractive index of the ball lens, R is the radius of the ball lens, and the deflection θ of the laser r `is satisfied: ； Meanwhile, to ensure the image intensity, the relationship between the eccentric distance d and the width w of the diaphragm should satisfy: ； To ensure the suppression effect on speckle noise, the relationship between the rotation speed ω of the ball lens (43) and the successive exposure time T should satisfy: 。 2. The digital holographic speckle reduction imaging system based on rotating ball lens according to claim 1, characterized in that: The voltage at both ends of the motor (46) is controlled by the control panel, and the rotation speed of the ball lens (43) is controlled by changing the applied voltage.

3. A digital holographic speckle reduction imaging system based on a rotating ball lens according to claim 2, characterized in that: The material of the ball lens (43) is K9 glass, the radius R of the ball lens (43) is 5 mm, and the internal refractive index n is 1.517; The width w of the diaphragm (5) is 3 mm, and the distance from the diaphragm (5) to the rotating ball lens (4) is 10 mm; The diameter of the laser beam emitted by the laser (1) is 0.65 mm.

4. The digital holographic speckle reduction imaging system based on rotating ball lens according to claim 3, characterized in that: The system, when in use, realizes dynamic change of incident light angle by controlling the rotating ball lens (4) to suppress speckle noise, when the incident light passes through the rotating ball lens (4), the ball lens (43) deflects the incident light, and the dynamic optical path difference is generated when the ball lens (43) rotates, the spatial coherence of the laser is reduced, the coherent condition formed by the speckle noise is destroyed, and the speckle noise in the digital holographic microscopic system is suppressed.

Images