A device and method for suppressing zero-order diffraction spot of spatial light modulator based on coaxial optical system

Abstract

This invention proposes a device and method for suppressing zero-order diffraction spots of a spatial light modulator based on a coaxial optical system. The device comprises a laser coupler, a spatial light modulator, a movable coaxial optical system, and a subsequent imaging system, all coaxially connected via a cage-like fixing assembly. The coaxial optical system includes a first lens, a blocking assembly, and a second lens. The method includes the following steps: S1, a laser source is coupled through the laser coupler and then incident on the spatial light modulator for phase modulation, forming a composite reflected beam containing modulated and unmodulated light; S2, the composite reflected beam is introduced into the coaxial optical system for filtering; S3, the filtered beam is output to the subsequent imaging system to obtain a holographic image with suppressed bright spots. In this application, no modifications to the hardware structure of the spatial light modulator or the holographic algorithm are required. Zero-order diffraction suppression can be achieved by introducing a combination of focal plane separation and anti-pinhole blocking in the optical path, resulting in a simple and easy-to-implement structure.

Description

Technical Field

[0001] This invention relates to the field of optical control and light field shaping, and in particular to a device and method for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system. Background Technology

[0002] Spatial light modulators (SLMs), as important devices capable of flexibly controlling the phase, polarization, and amplitude distribution of light waves, have received widespread attention in optical research and engineering applications in recent years. By loading computer-generated holograms (CGHs) or specific phase codes, SLMs can reconstruct light fields from regular light spots to complex three-dimensional structures, significantly improving the degrees of freedom in light field manipulation. Currently, SLMs are widely used in laser processing, optical communication, optical storage, light trapping, and optical imaging. For example, in laser micromachining, they are used to generate complex structured beams to achieve biomimetic functionalized surface processing; in optical communication and optical storage, they enable high-density light field multiplexing and encoding; and in optical imaging and optical tweezers systems, they are used to flexibly construct multifocal light fields.

[0003] However, existing SLMs have inherent structural limitations. Due to the integrated driving circuitry and liquid crystal array, the surface of an SLM typically contains an unmodulotable region. Incident light from this region is directly reflected without participating in phase modulation, resulting in zero-order diffraction. Even with precise holographic encoding, factors such as gaps between liquid crystal pixels and electrode reflections inevitably produce strong zero-order light, whose energy density is usually significantly higher than that of useful higher-order diffraction light. In practical applications, this zero-order component forms a bright spot at the imaging center, not only obscuring effective optical field information but also reducing laser processing accuracy and affecting holographic imaging quality.

[0004] To reduce zero-order light interference, various suppression schemes have been proposed, such as using a blazed grating to deflect higher-order diffracted light off the optical axis and then using an aperture to shield the zero-order light, or using a spherical lens to shift the phase of the zero-order light along the axial direction, or using interference cancellation to weaken the zero-order component. Although the above methods have improved the zero-order light problem to some extent, they generally suffer from problems such as complex system configuration, insufficient adjustment sensitivity, and poor compatibility with multi-wavelength light fields, making it difficult to meet the requirements of multi-color structured light field manipulation and high-quality holographic imaging.

[0005] Therefore, there is an urgent need for a simple SLM optical processing scheme with collinear optical axes that can efficiently suppress zero-order diffraction light, in order to improve the clarity of light field imaging and the quality of holographic reconstruction, and enhance its applicability to multi-wavelength light field modulation. Summary of the Invention

[0006] The purpose of this invention is to provide a device and method for suppressing zero-order diffraction spots of spatial light modulators based on a coaxial optical system. By introducing an adjustable blocking component and a zero-order light separation mechanism based on the defocus principle into the coaxial optical path, the unmodulated zero-order light of the SLM is effectively suppressed, thereby obtaining high-quality holographic imaging results and solving the problem of image distortion and decreased imaging quality caused by excessively high zero-order diffraction light intensity.

[0007] To achieve the above objectives, this invention proposes a device for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system. The device includes a coupling system, a coaxial optical system, a subsequent imaging system, and a cage-type fixing assembly. The coupling system, coaxial optical system, and subsequent imaging system are sequentially and coaxially arranged along the light propagation direction via the cage-type fixing assembly. The coupling system includes a laser coupler and a spatial light modulator sequentially arranged along the light propagation direction. The coaxial optical system includes a first lens, a blocking assembly, and a second lens sequentially arranged along the light propagation direction, and the coaxial optical system is movably fixed to the cage-type fixing assembly.

[0008] Furthermore, in the device for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system, the subsequent imaging system includes an imaging lens and an imaging structure, and the light beam processed by the coaxial optical system is focused by the imaging lens and then imaged on the imaging structure.

[0009] Furthermore, in the device for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system, the first lens, the second lens, and the imaging lens are all Fourier lenses.

[0010] Furthermore, in the device for suppressing the zero-order diffraction spot of the spatial light modulator based on the coaxial optical system, the cage-type fixing assembly includes a cage-type fixing member and a movable cage rod. Multiple movable cage rods sequentially pass through the cage-type fixing member, the second lens, the blocking assembly, the first lens, and the spatial light modulator, and are fixed on the laser coupler.

[0011] Furthermore, in the device for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system, the shielding assembly includes a fine-tuning stage, a shielding frame, a fine-tuning knob, and a locking knob. The shielding frame is movably fixed to the cage-type fixing assembly via the locking knob. The fine-tuning stage is movably located at the center of the shielding frame via the fine-tuning knob. A shielding object is provided on the fine-tuning stage.

[0012] This invention also proposes a method for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system, comprising the following steps: S1. The incident light from the laser source, coupled by a laser coupler, is injected into the modulation region of the spatial light modulator, causing the incident light to undergo phase modulation on the surface of the spatial light modulator, and the outgoing light from the spatial light modulator forms a composite reflected beam containing modulated light and unmodulated light. S2. The composite reflected beam is introduced into the coaxial optical system for filtering. S3. The beam processed by the coaxial optical system is output to the subsequent imaging system to obtain a holographic image with the central bright spot suppressed.

[0013] Furthermore, in the method for suppressing zero-order diffraction spots of a spatial light modulator based on a coaxial optical system, in S1, a Fresnel lens phase is superimposed on the phase distribution of the spatial light modulator to introduce controlled defocusing into the composite reflected beam, so that the modulated light and the unmodulated light form different focal planes in the propagation direction.

[0014] Furthermore, in the method for suppressing zero-order diffraction spots of spatial light modulators based on a coaxial optical system, in S2, the coaxial optical system includes a first lens, a blocking component, and a second lens arranged sequentially along the light propagation direction. The composite reflected beam undergoes a Fourier transform through the first lens, and the zero-order light formed by the unmodulated light is selectively absorbed or blocked by the blocking component. After the zero-order light is filtered out by the blocking component, the modulated light is focused by the second lens and output as a collimated beam propagating in the horizontal direction.

[0015] Furthermore, in the method for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system, in S2, the blocking component adjusts the position of the blocking object based on the focal point of the zero-order light, that is, the horizontal and vertical fine-tuning knobs cooperate with the fine-tuning stage to perform fine-tuning control of the horizontal and vertical planes, and the locking knob is used to control the axial position of the blocking component on the cage-type fixing component.

[0016] Furthermore, in the method for suppressing zero-order diffraction spots of a spatial light modulator based on a coaxial optical system, in S2, an adjustable spacing structure is provided between the first lens and the second lens. The adjustable spacing structure controls the position of the focal plane of the zero-order light relative to the blocking component by adjusting the lens spacing L between the first lens and the second lens.

[0017] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in: 1. This invention achieves focal plane separation of modulated and unmodulated light by superimposing Fresnel lens phases, and introduces adjustable blocking on the focal plane of unmodulated light, realizing the technical advantages of low loss and selective suppression of zero-order light, effectively solving the problems of zero-order light intensity and imaging blur in SLM systems.

[0018] 2. This invention achieves zero-order light suppression without changing the SLM hardware or CGH algorithm, relying solely on optical path layout and focal plane occlusion. It has the advantages of simple structure, flexible adjustment, low cost and strong applicability.

[0019] 3. The method of the present invention can be applied to various SLM-based optical systems such as holographic display, optical microscopy, structured light 3D imaging, optical tweezers manipulation, and laser processing. It can significantly improve the uniformity of the light field and the imaging quality, and has good application value. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the device for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system in this invention. Figure 2 A schematic diagram of the system principle of the device for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system in this invention; Figure 3 The image shown is an image of the result without processing by the method of suppressing the zero-order diffraction spot of the spatial light modulator based on the coaxial optical system in this invention. It can be seen that there is a strong zero-order diffraction spot in the center. Figure 4 The image shows the effect of the zero-order diffraction spot of the spatial light modulator after being processed by the method of suppressing the zero-order diffraction spot of the spatial light modulator based on the coaxial optical system in this invention, but without superimposing the Fresnel lens phase in the spatial light modulator. It can be seen that the zero-order light is significantly weakened at this time, but the edge of the spot is still not sharp enough. Figure 5 The image shows the imaging effect after the method of suppressing the zero-order diffraction spot of the spatial light modulator based on the coaxial optical system in this invention is used, and the phase of the Fresnel lens is superimposed on the spatial light modulator. It can be seen that the central bright spot has completely disappeared and the energy distribution of the spot is extremely uniform. Detailed Implementation

[0021] The apparatus and method for suppressing zero-order diffraction spots of spatial light modulators based on a coaxial optical system according to the present invention will be described in more detail below with reference to the schematic diagrams, which illustrate preferred embodiments of the present invention. It should be understood that those skilled in the art can modify the present invention described herein while still achieving the advantageous effects of the present invention. Therefore, the following description should be understood as being of general knowledge to those skilled in the art and is not intended to limit the present invention.

[0022] In the description of this invention, it should be noted that the directional terms, such as "center," "lateral," "longitudinal," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. They should not be construed as limiting the specific protection scope of this invention.

[0023] In this invention, unless otherwise explicitly specified and limited, the terms "assembly," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can also refer to a mechanical connection; they can refer to a direct connection or a connection through an intermediate medium; or they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0024] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features. Thus, the use of "first" and "second" to define a feature may explicitly or implicitly include one or more of that feature, and in the description of this invention, "at least" means one or more, unless otherwise explicitly specified.

[0025] The invention is described more specifically by way of example in the following paragraphs with reference to the accompanying drawings. The advantages and features of the invention will become clearer from the following description. It should be noted that the drawings are in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the invention.

[0026] like Figures 1 to 2 As shown, this invention proposes a device for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system. The device includes a coupling system, a coaxial optical system, a subsequent imaging system, and a cage-type fixing assembly. The coupling system, the coaxial optical system, and the subsequent imaging system are coaxially arranged in sequence along the light propagation direction via the cage-type fixing assembly. The coupling system includes a laser coupler 1 and a spatial light modulator 2 arranged in sequence along the light propagation direction. The coaxial optical system includes a first lens 31, a blocking assembly 4, and a second lens 32 arranged in sequence along the light propagation direction. The coaxial optical system is movably fixed on the cage-type fixing assembly.

[0027] Furthermore, such as Figure 2As shown, the post-imaging system includes an imaging lens and an imaging structure. The light beam processed by the coaxial optical system is focused by the imaging lens and then imaged on the imaging structure. Preferably, the imaging structure is a screen or a CCD / CMOS detector. That is, the light field emitted from the cage-like fixed component is focused by the imaging lens and can be directly projected onto the screen at the rear focal plane of the imaging lens to achieve visual imaging, or a CCD / CMOS detector can be used for digital acquisition.

[0028] Furthermore, the first lens 31, the second lens 32, and the imaging lens are all Fourier lenses, and the focal length of the Fourier lens can be selected in the range of 50–100mm to adapt to different imaging magnification and resolution requirements.

[0029] Furthermore, such as Figure 1 As shown, the cage-type fixing assembly includes a cage-type fixing member 51 and four movable cage rods 52. The four movable cage rods 52 sequentially pass through the cage-type fixing member 51, the second lens 32, the shielding component 4, the first lens 31, and the spatial light modulator 2, and are rotatably fixed to the laser coupler 1. That is, the first lens 31, the shielding component 4, and the second lens 32 are all movably fixed to the movable cage rods 52. Simultaneously, an imaging lens is fixed to the outside of the cage-type fixing member 51 on the movable cage rods 52, ensuring that the cage-type fixing assembly and the imaging structure are coaxial. That is, the laser coupler 1, the spatial light modulator 2, the first lens 31, the shielding component 4, the second lens 32, the cage-type fixing member 51, the imaging lens, and the imaging structure are arranged coaxially in sequence. Preferably, the cage-type fixing member 51 adopts a standard 40mm square cage structure, which, together with the movable cage rods 52, supports the various optical elements, ensuring that each optical element is strictly fixed on a unified optical axis, facilitating accurate system assembly and modular expansion.

[0030] Furthermore, such as Figure 1 As shown, the blocking assembly 4 includes a fine-tuning stage, a blocking frame 41, a fine-tuning knob 42, and a locking knob 43. The blocking frame 41 is movably fixed to the cage-type fixing assembly via the locking knob 43. The fine-tuning stage is movably positioned at the center of the blocking frame 41 via the fine-tuning knob 42, and a blocking object is provided on the fine-tuning stage. Preferably, the blocking object is a variable aperture light block or a reverse pinhole structure, the size and position of which can be matched and adjusted according to the focal spot size of the zero-order light to achieve precise suppression of unmodulated light.

[0031] Furthermore, the spatial light modulator 2 is a reflective liquid crystal spatial light modulator, capable of achieving high-precision phase modulation within the range of 0–2π. Its surface contains an unmodulated region that directly reflects light to form zero-order light. In this invention, through defocusing design and coaxial optical path coordination, the interference of this unmodulated reflected light on imaging can be significantly reduced.

[0032] This invention also proposes a method for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system. The method employs the aforementioned apparatus for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system, and includes the following steps: S1. A monochromatic or multicolor laser source, coupled by laser coupler 1, is incident onto a spatial light modulator 2, achieving coaxial incidence of the beam. After reflection by a high-reflectivity mirror, the laser source is incident onto the effective phase modulation region of the spatial light modulator 2. The spatial light modulator 2 modulates the incident light by loading a computer-generated hologram (CGH) or a structured phase pattern to achieve phase-encoded modulation of the incident light, generating the desired diffraction field distribution. In other words, the incident light undergoes phase modulation on the surface of the spatial light modulator 2, causing the outgoing light from the spatial light modulator 2 to form a composite reflected beam containing both modulated and unmodulated light. Simultaneously, to achieve focal plane separation between the zero-order light and the modulated light, improve the focusing uniformity and energy distribution stability of the modulated light field, and enhance the energy concentration and spot symmetry of the final image, a Fresnel lens phase is superimposed on the phase distribution of the spatial light modulator 2. This introduces controlled defocusing into the composite reflection beam of the outgoing light, causing the modulated and unmodulated light to form different focal planes in the propagation direction. Specifically, the focal planes of the zero-order light and the modulated light have a focal length difference along the optical axis, achieving defocus separation and providing a spatial separation basis for subsequent zero-order light filtering. Superimposing the optimized Fresnel lens phase on the hologram of the spatial light modulator 2 enhances the focusing intensity of the modulated light at the focal plane of the Fourier lens, resulting in a higher signal-to-noise ratio and a more uniform energy distribution in the output light field. Experiments show that after this phase-assisted modulation, the sharpness of the reconstructed spot and the uniformity of the light field are significantly improved.

[0033] S2. The composite reflected beam generated after the incident light is reflected by the spatial light modulator 2 is introduced into the coaxial optical system for filtering. The coaxial optical system includes a first lens 31, a blocking component 4, and a second lens 32 arranged sequentially along the light propagation direction. Due to the focal shift caused by the phase of the Fresnel lens, the unmodulated zero-order light and the modulated higher-order diffracted light are focused at different positions. The 4f system composed of the first lens 31 and the second lens 32 is used to achieve spatial blocking of the zero-order light in the Fourier plane. By adjusting the blocking component 4 at the focal plane of the zero-order light, the zero-order light is effectively shielded, while the modulated higher-order diffracted light in the defocused state is allowed to pass through smoothly, avoiding the problem of filtering out effective information at low diffraction angles in the conventional pinhole method. Specifically, the composite reflected beam undergoes a Fourier transform via the first lens 31. The zero-order light formed by the unmodulated light forms a high-intensity bright spot at the center of the Fourier plane. The zero-order light is selectively absorbed or blocked by the blocking component 4 placed at the Fourier plane. After the zero-order light is filtered out by the blocking component 4, the remaining modulated light in a defocused state is focused by the second lens 32 and output as a collimated beam propagating in the horizontal direction.

[0034] S3. The beam processed by the coaxial optical system is output to the subsequent imaging system to obtain a holographic image with the central bright spot suppressed. That is, the beam after zero-order light suppression by the coaxial optical system is focused by the imaging lens to form a high-quality holographic image or structured light distribution on the screen or CCD imaging surface; by comparing the imaging difference between turning the suppression device of the present invention on and off, the effectiveness of the present invention in suppressing zero-order light and improving imaging uniformity and clarity in multi-wavelength scenarios can be verified.

[0035] Furthermore, in S1, the laser source is a three-color laser or a multi-wavelength laser system. The multi-wavelength beams are combined via the laser coupler 1 and coaxially incident on the spatial light modulator 2 to obtain a holographic reconstruction effect of a colored or multi-wavelength light field. Preferably, in this embodiment, a green laser with a wavelength of 533nm is selected.

[0036] Furthermore, in S2, by adjusting the lens spacing L between the first lens 31 and the second lens 32 and the blocking parameters of the blocking component 4, precise spatial separation and suppression of zero-order light and modulated light can be achieved.

[0037] Specifically, to ensure that the light block strictly coincides with the zero-order light focal point, the blocking component 4 adjusts the position of the blocking object based on the zero-order light focal point. That is, the blocking component 4 is equipped with an adjustable three-dimensional micro-displacement mechanism, which includes a two-dimensional fine-tuning structure for adjusting the horizontal and vertical positions and a linear slide rail adjustment structure for axial focal plane matching. Since the blocking object is fixed on the fine-tuning platform, the horizontal and vertical positions of the platform are independently fine-tuned using two fine-tuning knobs 42, respectively, enabling the blocking object to move horizontally and vertically. The axial position of the fine-tuning platform is adjusted along with the blocking component 4. Since the locking knob 43 controls the axial position of the blocking component 4 on the cage-type fixing component, loosening the locking knob 43 loosens the fixed blocking component 4 relative to the moving cage rod 52, allowing the blocking component 4 to move back and forth along the moving cage rod 52. Preferably, the fine-tuning knob 42 can adjust the horizontal and vertical distances by 10–20 μm, and the locking knob 43 can adjust the axial distances by 2–10 mm, effectively and accurately compensating for focal plane shifts caused by different focal lengths or different Fresnel lens phases.

[0038] However, if the position of the obstruction is not accurately adjusted, some of the zero-order light will leak into the second lens 32, resulting in residual bright spots or increased background noise in the imaging plane, thereby reducing the hologram reconstruction quality and contrast. The aforementioned three-dimensional fine-tuning mechanism ensures that the center of the obstruction and the zero-order light focal point are strictly aligned, achieving optimal zero-order light suppression and guaranteeing the purity of the modulated diffracted light.

[0039] Meanwhile, to adapt to the focal length change caused by the phase of the Fresnel lens superimposed on the hologram of the spatial light modulator 2, an adjustable spacing structure is provided between the first lens 31 and the second lens 32. This adjustable spacing structure controls the position of the focal plane of the zero-order light relative to the blocking component 4 by adjusting the lens spacing L between the first lens 31 and the second lens 32. When the lens spacing L increases, the equivalent focal length difference caused by the Fresnel lens phase is amplified, and the focal spot of the zero-order light shifts forward along the light propagation direction; while the Fourier distribution position of the higher-order modulated light remains essentially unchanged. Therefore, by controlling the lens spacing L, precise matching between the focal plane of the zero-order light and the position of the light block can be achieved, forming a zero-order light dynamic suppression strategy "based on focal plane drift".

[0040] However, if the lens spacing L is not properly adjusted, some higher-order diffracted light may fall into the obstruction range of the light block, resulting in energy loss, blurred imaging, or degraded light spot edges. This invention achieves the optimal balance between zero-order light suppression efficiency and structured light integrity by finely adjusting the lens spacing L, ensuring that higher-order diffracted light can pass through smoothly while completely blocking zero-order light.

[0041] Furthermore, this invention is applicable to the 400–700nm visible light and 700–1550nm near-infrared bands and is compatible with various types of reflective and transmissive spatial light modulators 2. By adjusting the diameter and position of the obstruction, the lens focal length, and the pattern type loaded on the spatial light modulator 2, this invention can be used in various application scenarios such as laser holographic imaging, light field shaping, vector light generation, polarization state manipulation, spatial optical communication, and micro-nano optical processing, demonstrating good versatility and scalability.

[0042] In summary, the device and method for suppressing zero-order diffraction spots of spatial light modulators based on coaxial optical systems proposed in this embodiment do not require any modification to the hardware structure or holographic algorithm of the spatial light modulator. Zero-order light suppression can be achieved by introducing a combination design of focal plane separation and reverse pinhole blocking in the optical path. The structure is simple and easy to implement.

[0043] The above are merely preferred embodiments of the present invention and do not constitute any limitation on the present invention. Any equivalent substitutions or modifications made by those skilled in the art to the technical solutions and content disclosed in the present invention without departing from the scope of the present invention shall be deemed to have remained within the protection scope of the present invention.

Claims

1. A device for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system, characterized in that, The system includes a coupling system, a coaxial optical system, a post-imaging system, and a cage-type fixing assembly. The coupling system, the coaxial optical system, and the post-imaging system are arranged coaxially along the light propagation direction via the cage-type fixing assembly. The coupling system includes a laser coupler (1) and a spatial light modulator (2) arranged sequentially along the light propagation direction. The coaxial optical system includes a first lens (31), a blocking assembly (4), and a second lens (32) arranged sequentially along the light propagation direction. The coaxial optical system is movably fixed on the cage-type fixing assembly.

2. The device for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system according to claim 1, characterized in that, The post-imaging system includes an imaging lens and an imaging structure. The light beam processed by the coaxial optical system is focused by the imaging lens and then imaged on the imaging structure.

3. The device for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system according to claim 2, characterized in that, The first lens (31), the second lens (32) and the imaging lens are all Fourier lenses.

4. The device for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system according to claim 1, characterized in that, The cage-type fixing assembly includes a cage-type fixing member (51) and a movable cage rod (52). Multiple movable cage rods (52) pass through the cage-type fixing member (51), the second lens (32), the shielding assembly (4), the first lens (31), and the spatial light modulator (2) in sequence, and are fixed on the laser coupler (1).

5. The device for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system according to claim 1, characterized in that, The shielding assembly (4) includes a fine-tuning platform, a shielding frame (41), a fine-tuning knob (42), and a locking knob (43). The shielding frame (41) is movably fixed to the cage-type fixing assembly via the locking knob (43). The fine-tuning platform is movably located at the center of the shielding frame (41) via the fine-tuning knob (42). A shielding object is provided on the fine-tuning platform.

6. A method for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system, comprising the apparatus for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system as described in claims 1 to 5, characterized in that, Includes the following steps: S1. The incident light of the laser source coupled by the laser coupler (1) is injected into the modulation region of the spatial light modulator (2), so that the incident light generates phase modulation on the surface of the spatial light modulator (2), and the outgoing light of the spatial light modulator (2) forms a composite reflected beam containing modulated light and unmodulated light. S2. The composite reflected beam is introduced into the coaxial optical system for filtering. S3. The beam processed by the coaxial optical system is output to the subsequent imaging system to obtain a holographic image with the central bright spot suppressed.

7. The method for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system according to claim 6, characterized in that, In S1, a Fresnel lens phase is superimposed on the phase distribution of the spatial light modulator (2) to introduce controlled defocusing into the composite reflected beam, so that the modulated light and the unmodulated light form different focal planes in the propagation direction.

8. The method for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system according to claim 7, characterized in that, In S2, the coaxial optical system includes a first lens (31), a blocking component (4), and a second lens (32) arranged sequentially along the light propagation direction. The composite reflected beam undergoes a Fourier transform through the first lens (31), and the zero-order light formed by the unmodulated light is selectively absorbed or blocked by the blocking component (4). After the zero-order light is filtered out by the blocking component (4), the modulated light is focused by the second lens (32) and output as a collimated beam propagating in the horizontal direction.

9. The method for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system according to claim 8, characterized in that, In S2, the blocking component (4) adjusts the position of the blocking object based on the focus of the zero-order light, that is, the horizontal and vertical fine adjustment knobs (42) cooperate with the fine adjustment platform to perform fine adjustment control of the horizontal and vertical planes, and the locking knob (43) is used to control the axial position of the blocking component (4) on the cage-type fixing component.

10. The method for suppressing the zero-order diffraction spot of a spatial light modulator based on a coaxial optical system according to claim 8, characterized in that, In S2, an adjustable spacing structure is provided between the first lens (31) and the second lens (32). The adjustable spacing structure controls the position of the focal plane of the zeroth order light relative to the blocking component (4) by adjusting the lens spacing L between the first lens (31) and the second lens (32).

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