Digital holographic speckle suppression imaging system based on rotating ball lens

Abstract

The invention provides a digital holographic speckle suppression imaging system based on a rotary spherical lens, and belongs to the technical field of digital holographic speckle suppression imaging systems. In order to solve the technical problems of complex light path structure, low imaging quality and high manufacturing cost of a laser modulation element in the existing speckle noise suppression, the adopted technical scheme is as follows: a laser beam emitted by a laser device is modulated by a filter and modulated by a first half-wave plate in intensity and polarization state; the incident light is modulated by the rotating ball lens, filtered by the diaphragm, and finally divided into an object beam and a reference beam by the polarization splitting prism; the object light beam is reflected by the first reflector to irradiate a sample object and is reflected back to the beam splitter prism; after the reference beam is reflected by the second reflector, the polarization state of the reference beam is consistent with that of the object beam through the second half-wave plate, and the reference beam is interfered at the CCD camera after being combined by the beam splitter prism to form an interference pattern; the method is used for suppressing the speckle noise of the digital holographic imaging system.

Description

Technical Field

[0001] The invention provides a digital holographic speckle reduction imaging system based on a rotating ball lens, belonging to the technical field of digital holographic speckle reduction imaging systems. Background Art

[0002] With the continuous development of science and technology, people's research on microscopic objects has become more and more in-depth. The use of more accurate observation methods can improve the observation effect. Digital holographic microscopy technology, as an emerging microscopic observation method, has been widely used in microscopic scenes in many fields such as materials science, biomedicine, and industrial inspection. However, because digital holographic microscopy technology uses highly coherent laser as the light source, when inspecting rough objects, the emitted detection laser will scatter and form speckle noise, which will seriously affect the imaging quality.

[0003] In current technology, the main solutions for suppressing the above-mentioned speckle noise include: replacing low-coherence light sources, using digital image processing algorithms for filtering, and using laser modulation elements. Among them:

[0004] The speckle noise in digital holography essentially comes from the high coherence of the light source. Therefore, replacing the light source with a low-coherence light source can fundamentally suppress the speckle noise. However, the optical path of the digital holographic imaging system using a low-coherence light source is complex, and the low-coherence light source reduces the resolution of the imaging system.

[0005] Digital image processing algorithms can directly process imaging results in computers, but the suppression effect is limited by the algorithm itself. The ability to suppress speckle noise has certain limitations, making it difficult to significantly improve the quality of digital holographic imaging.

[0006] With the advancement of materials science, many new materials can now be used to produce corresponding components to modulate lasers. However, the existing laser modulation components have the problems of high production costs and complex mechanical motion structures. Summary of the Invention

[0007] In order to solve the technical problems existing in the background technology, the present invention adopts the following technical solutions: providing a digital holographic speckle reduction imaging system based on a rotating ball lens, comprising a laser, a filter, a first half-wave plate, a rotating ball lens, an aperture, a polarization beam splitter prism, a first reflector, a second reflector, a second half-wave plate, a beam splitter prism, a sample object, and a CCD camera;

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

[0009] The object light beam is reflected by the first reflecting mirror, irradiates the sample object, and is reflected back to the beam splitter prism;

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

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

[0012] The rear end of the rear clamping plate passes through a through hole provided on the rear bracket and is connected to the driving end of the motor. The motor drives the rear clamping plate to rotate, thereby driving the ball lens and the front clamping plate to rotate.

[0013] The center positions of the front and rear clamping plates do not coincide with the rotation center of the motor, so that the center position of the spherical lens during rotation does not coincide with the rotation center of the motor, and the eccentricity between the two is set to d;

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

[0015] The voltage across the motor is controlled by a control board, and the rotation speed of the ball lens is controlled by changing the applied voltage.

[0016] The material of the spherical lens is specifically K9 glass, the radius R of the spherical lens is 5 mm, and the internal refractive index n is 1.517;

[0017] The width w of the aperture is 3 mm, and the distance from the rotating ball lens is 10 mm;

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

[0019] When the system is in use, the incident light angle is dynamically changed by controlling the rotating spherical lens to suppress speckle noise. When the incident light passes through the rotating spherical lens, the spherical lens deflects the incident light, generating a dynamic optical path difference when the spherical lens rotates, reducing the spatial coherence of the laser, destroying the coherence conditions for the formation of speckle noise, and suppressing speckle noise in the digital holographic microscopy system.

[0020] The specific method of controlling the rotating ball lens to dynamically change the angle of incident light is:

[0021] Define the deflection θ of the laser by the spherical lens r The calculation formula for `and the emission position r` is:

[0022] ;

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

[0024] ;

[0025] At the same time, to ensure image intensity, the relationship between the eccentricity d and the width w of the aperture should satisfy:

[0026] ;

[0027] To ensure the suppression effect of speckle noise, the relationship between the rotation speed ω of the ball lens and the successive exposure time T should satisfy:

[0028] .

[0029] Compared with the prior art, the present invention has the following advantages: the present invention uses a rotating spherical lens to achieve laser modulation, and dynamically changes the angle of incident light by rotating the spherical lens to suppress speckle noise. When the incident light passes through the rotating spherical lens, the spherical lens deflects the incident light, generating a dynamic optical path difference, significantly reducing the spatial coherence of the laser, destroying the coherence conditions for the formation of speckle noise, thereby suppressing digital holographic speckle noise and improving the quality of digital holographic reproduction images. At the same time, the digital holographic image processing algorithm is used to further suppress speckle noise in the reproduction image, improve the quality of the reproduction image, and enhance the signal-to-noise ratio of the system. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0031] Figure 1 Schematic diagram of the structure of the digital holographic speckle reduction imaging system of the present invention;

[0032] Figure 2 Schematic diagram of the structure of the rotating ball lens of the present invention;

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

[0034] Figure 4 This is a diagram showing the working principle of the rotating ball lens of the present invention;

[0035] In the figure, the numbers are: 1 for the laser, 2 for the filter, 3 for the first half-wave plate, 4 for the rotating ball lens, 5 for the aperture, 6 for the polarization beam splitter, 7 for the first reflector, 8 for the second reflector, 9 for the second half-wave plate, 10 for the beam splitter, 11 for the sample object, and 12 for the CCD camera.

[0036] 41 is a front bracket, 42 is a front clamping plate, 43 is a ball lens, 44 is a rear clamping plate, 45 is a rear bracket, and 46 is a motor. DETAILED DESCRIPTION

[0037] like Figures 1 to 4 As shown, the present invention provides a digital holographic speckle suppression imaging system based on a rotating spherical lens, which is used to suppress speckle noise in a digital holographic imaging system. The system mainly generates an optical path difference in the laser by rotating the spherical lens, and modulates the incident angle of the laser to suppress the digital holographic speckle noise and improve the quality of the digital holographic reproduction image.

[0038] like Figure 1 As shown, in order to achieve the above-mentioned purpose, the structure of the digital holographic speckle reduction imaging system provided by the present invention is as follows:

[0039] It includes a laser 1, a filter 2, a first half-wave plate 3, a rotating ball lens 4, an aperture 5, a polarization beam splitter prism 6, a first reflector 7, a second reflector 8, a second half-wave plate 9, a beam splitter prism 10, a sample object 11, and a CCD camera 12;

[0040] During the experiment, it is necessary to first adjust the relative position of the rotating ball lens 4 to ensure that the rotation center of the ball lens coincides with the optical axis of the main light path; first, the laser beam is emitted by the laser 1, and after the intensity is modulated by the filter 2 and the polarization state is modulated by the first half-wave plate 3, the incident light angle is modulated by the rotating ball lens 4 in turn, and filtered by the aperture 5, and finally divided into an object beam and a reference beam by the polarization splitter prism 6; the object beam is reflected by the first reflector 7 and irradiated on the sample object 11, and reflected back to the spectroscopic prism 10; the reference beam is reflected by the second reflector 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, and finally combined by the spectroscopic prism 10 and interfered 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 ball lens 4 is specifically composed of a front bracket 41, a front clamping plate 42, a ball 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 clamping plate and the ball lens 43 to rotate. During installation, the front clamping plate 42 and the rear clamping plate 44 clamp the ball lens 43. The front clamping plate 42 and the rear clamping plate 44 have a bottom plate and a clamping structure; the center of the bottom plate of the rear clamping plate 44 is connected to the motor 46, and the center of the clamping structure is at a certain distance from the rotation center of the motor. The clamping structure coincides with the center of the ball lens 43, thereby ensuring that when the ball lens 43 rotates, the center of the ball is at a certain distance from the rotation center of the motor, that is, the eccentricity d, and the eccentricity d is set to 1mm.

[0042] The rear end of the rear clamping plate 44 passes through the through hole set in the rear bracket 45 and is connected to the driving end of the motor 46. The motor 46 drives the rear clamping plate 44 to rotate, and then 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 spherical lens used in the rotating spherical lens 4 is made of K9 glass, 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 the distance from the rotating spherical lens is 10 mm. The laser beam diameter is 0.65 mm, and the rotation speed of the spherical lens is controlled by changing the voltage applied to both ends of the motor.

[0044] The present invention achieves speckle noise suppression by dynamically changing the incident light angle by providing a rotating spherical lens. When the incident light passes through the rotating spherical lens, the spherical lens deflects the incident light, generating a dynamic optical path difference, significantly reducing the spatial coherence of the laser, destroying the coherence conditions for the formation of speckle noise, and thus achieving speckle noise suppression. 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 can effectively suppress speckle noise in the digital holographic microscopy system.

[0045] like Figure 4 As shown, the deflection θ of the laser by the spherical lens proposed in the present invention is r The relationship between `, the emission position r` and the rotation speed ω, the eccentricity d, the refractive index n of the spherical lens, and the radius R of the spherical lens is:

[0046] ;

[0047] in ;

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

[0049] ;

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

[0051] .

[0052] In an embodiment of the present invention, parameters such as speckle contrast, peak signal-to-noise ratio (PSNR), and root mean square error (RMSE) were used to evaluate the effectiveness of the present invention in suppressing speckle noise. The intensity reconstructed image obtained by the present invention when detecting a silicon plate circular hole array was compared with those obtained using a conventional method and a conventional image processing algorithm. The experimental results are shown in Table 1 below. Compared with the conventional method, the speckle contrast of the intensity reconstructed image obtained using the proposed scheme was significantly reduced to 0.105, a decrease of 76.19%. The speckle contrast of the intensity reconstructed image obtained using the conventional method was 0.439. The proposed scheme also improved the PSNR of the intensity reconstructed image to 9.917 dB and reduced the RMSE to 0.106. These data demonstrate the effective suppression of speckle noise by the proposed scheme.

[0053] Table 1 Noise suppression experimental data under different methods

[0054]

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

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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: It includes a laser (1), a filter (2), a first half-wave plate (3), a rotating ball lens (4), an aperture (5), a polarization beam splitter (6), a first reflector (7), a second reflector (8), a second half-wave plate (9), a beam splitter (10), a sample object (11), and a CCD camera (12); The laser (1) emits a laser beam outward, and after the laser beam passes through the filter (2) to modulate the intensity and the first half-wave plate (3) to modulate the polarization state, it passes through the rotating ball lens (4) to modulate the incident light angle, passes through the aperture (5) for filtering, and is finally divided into an object beam and a reference beam by a polarization splitter prism (6); The object light beam is reflected by the first reflector (7) and irradiated on the sample object (11), and is reflected back to the beam splitter prism (10); After being reflected by the second reflector (8), the reference beam 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, the reference beam is combined by the beam splitter prism (10) and interferes at the CCD camera (12) to form an interference pattern, which is recorded by the CCD camera (12).

2. The digital holographic speckle reduction imaging system based on a rotating ball lens according to claim 1, characterized in that: The rotating ball lens (4) comprises a front bracket (41), a front clamping plate (42), a ball lens (43), a rear clamping plate (44), a rear bracket (45), and a motor (46). Bearings for supporting the rotation of the front and rear clamping plates and the ball lens (43) are provided between the front bracket (41) and the front clamping plate (42), and between the rear bracket (45) and the rear clamping plate (44). 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) passes through a through hole provided in the rear bracket (45) and is connected to the driving end of the motor (46), and the motor (46) drives the rear clamping plate (44) to rotate, 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 spherical lens (43) does not coincide with the rotation center of the motor (46) when the spherical lens (43) rotates, and the eccentricity between the two is set to 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.

3. The digital holographic speckle reduction imaging system based on a rotating ball lens according to claim 2, characterized in that: The voltage across the motor (46) is controlled by a control board, and the rotation speed of the ball lens (43) is controlled by changing the applied voltage.

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

5. The digital holographic speckle reduction imaging system based on a rotating ball lens according to claim 4, characterized in that: When the system is in use, the incident light angle is dynamically changed by controlling the rotating spherical lens (4) to suppress speckle noise. When the incident light passes through the rotating spherical lens (4), the spherical lens (43) deflects the incident light. When the spherical lens (43) rotates, a dynamic optical path difference is generated, which reduces the spatial coherence of the laser, destroys the coherence condition for the formation of speckle noise, and suppresses the speckle noise in the digital holographic microscopy system.

6. The digital holographic speckle reduction imaging system based on a rotating ball lens according to claim 5, characterized in that: The specific method of controlling the rotating ball lens (4) to dynamically change the angle of incident light is: Define the deflection θ of the laser by the ball lens (43) r The calculation formula for `and the emission position r` is: ； Where ω is the rotation speed, d is the eccentricity, n is the refractive index of the spherical lens, R is the radius of the spherical lens, and the deflection θ of the laser is r `Satisfy: ； At the same time, to ensure image intensity, the relationship between the eccentricity d and the width w of the aperture should satisfy: ； In order to ensure the effect of suppressing speckle noise, the relationship between the rotation speed ω of the ball lens (43) and the successive exposure time T should satisfy: 。

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