Holographic display speckle noise suppression system and method based on controllable fog scattering

Abstract

The invention discloses a laser decoherence and holographic display speckle noise suppression system and method based on controllable fog scattering. The system comprises a laser light source module, an optical shaping module, a fog scattering module and a holographic display module which are arranged in sequence. The fog scattering module generates a scattering medium layer composed of micron-sized fog drops in an ultrasonic atomization or airflow disturbance mode, so that the space and time coherence of the collimated laser is reduced under the action of multiple times of scattering, and therefore speckle noise in holographic display imaging is effectively restrained. By adjusting the particle size distribution, the concentration and the disturbance frequency of the fog drops, continuous controllability of the decoherence intensity can be achieved, and the imaging brightness and the imaging definition are both considered. The system is simple in structure and high in compatibility, and can be directly embedded into an existing computer-generated holographic display system without an additional optical modulation device; and meanwhile, the method has the advantages of low cost, high real-time performance, suitability for a multiband laser system and the like, and is suitable for the optical fields of holographic display, laser projection, interference measurement and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical display and information processing, and particularly relates to a laser de-coherence and holographic display speckle noise suppression system and method based on scattering medium.

[0002] Laser has become the main light source in modern optical display and information processing system due to its good monochromaticity, high brightness and high coherence. In the fields of holographic display, light field imaging, interference measurement and so on, laser provides necessary coherent illumination conditions, so that the optical system can realize high-contrast, high-resolution imaging and information reconstruction. In particular, in computer-generated holographic display (CGH), a spatial light modulator (SLM) is used to load a digital hologram and realize image reconstruction under coherent laser illumination, which is an important method for realizing three-dimensional display and wavefront control.

[0003] However, the high coherence of laser, although conducive to interference and holographic reconstruction, also introduces an unavoidable side effect - speckle noise. When high-coherence light is scattered and interfered on rough surfaces, non-uniform media or display elements, a speckle pattern with random intensity distribution is formed. The speckle superimposes random brightness fluctuations in the reconstructed image, resulting in image details being obscured, contrast being reduced and visual fatigue being aggravated, thereby seriously affecting the imaging quality and viewing effect of holographic display.

[0004] At present, in order to reduce laser speckle noise, researchers have proposed various de-coherence and noise reduction methods. Common techniques include:

[0005] (1) Multi-wavelength mixing method, which reduces coherence by using different wavelengths of laser superposition illumination, but the light source system is complex and color consistency is difficult to control;

[0006] (2) Multi-mode or multi-source light illumination method, which uses multi-mode optical fiber, integrating sphere and other structures to mix multi-mode light field to realize spatial de-coherence, but causes light flux loss and brightness drop;

[0007] (3) Rotating diffuser plate method, which uses a mechanically rotating frosted plate to randomly change the phase of the light field to achieve time-averaged despeckling, but the structure is large, noise and vibration problems are obvious;

[0008] (4) High-speed phase modulation method, which realizes coherence reduction by loading random phase on a spatial light modulator, but is limited by the refresh rate and response time of the SLM, and is difficult to apply in high-frame-rate display.

[0009] The above methods can reduce speckle noise to different extents, but still have problems such as system complexity, high cost, difficult control, and insufficient real-time performance. Especially in compact or mobile holographic display devices, the introduction of mechanical rotation or multi-light source structure significantly increases the volume and power consumption, which is not conducive to system integration and stability.

[0010] Therefore, in order to solve the problem of speckle noise caused by high coherence of laser illumination in the prior art, it is urgent to provide an illumination scheme with simple structure, strong controllability, high stability, and effective reduction of laser coherence. The scheme should be able to significantly suppress the coherence length or speckle contrast while maintaining the system luminous flux and imaging brightness, thereby improving the image quality and visual comfort of the computer holographic display. SUMMARY

[0011] (I) Invention purpose

[0012] The present application aims to provide a laser decoherence and holographic display speckle noise suppression system based on controllable fog scattering. By precisely controlling the particle size distribution, concentration, thickness, and dynamic disturbance mode of the fog scattering medium, the spatial and temporal coherence of the laser is significantly reduced during multiple scattering processes, thereby effectively suppressing the speckle noise in the computer holographic display system and improving the image uniformity and visual comfort.

[0013] (II) Technical solutions

[0014] To achieve the above purpose, the present application provides the following technical solutions:

[0015] A laser decoherence and holographic display speckle noise suppression system based on controllable fog scattering, characterized in that it comprises: a laser light source module for generating a monochromatic laser beam; an optical shaping module for collimating and diffusing the scattered light field to ensure uniform illumination and light flux utilization; a fog scattering module arranged between the beam shaping module and the holographic display module for generating a scattering medium layer composed of micron-sized fog droplets, allowing the laser to undergo multiple random scattering to reduce coherence; a holographic display module for loading digital holograms and realizing image reconstruction, and evaluating the decoherence effect of the fog scattering module according to the speckle noise of the reconstructed hologram.

[0016] Among them, the light source module, because the present application is mainly used for holographic display, the optional light source is a monochromatic laser or a white light laser and other coherent light sources;

[0017] The optical shaping module is sequentially and spacedly arranged with a polarizer, a pinhole filter, and a beam collimating assembly to ensure uniform illumination and light flux utilization.

[0018] The light beam collimation assembly is used for collimating one of the split light beams to obtain parallel light as the reconstruction light of the computer holographic display.

[0019] Optionally, the light beam collimation assembly is any one of a lens, a prism, and an optical fiber waveguide.

[0020] The holographic display module is used for loading a digital hologram and realizing image display. The reconstruction light splitting assembly, the image loading element, and the 4f filtering system are sequentially and interval arranged.

[0021] Optionally, the light splitting assembly is any one of a beam splitter, a beam splitter, an optical fiber, and an optical waveguide.

[0022] The fog scattering module includes an ultrasonic humidifier or a piezoelectric atomizer, and is used for generating fog droplets with a particle size distribution of 0.5-5 μm.

[0023] The dynamic disturbance module includes a fan, an ultrasonic oscillator, or a fluid driving device, and is used for periodically changing the fog density and the flow field structure, so as to realize dynamic change of the fog field.

[0024] Theoretical principle and selection of fog droplet particle size:

[0025] 1. Relationship between optical thickness and coherence

[0026] When the laser beam passes through the fog scattering medium, the light field undergoes multiple scattering and random phase change.

[0027] The relationship between scattering intensity and particle size r and wavelength λ can be described by Mie scattering theory, and the scattering cross section is:

[0028] σ s (r, λ) = Q s (r, λ)πr 2 (1)

[0029] Wherein, Q s is a scattering efficiency factor.

[0030] If the fog droplet density is n and the scattering layer thickness is L, the optical thickness is:

[0031] τ s = nσ s L (2)

[0032] When τ s = 1-3, the light is in a weak to moderate multiple scattering region, and the coherence is obviously reduced.

[0033] 2. Coherence decay model

[0034] The path length variance <ΔL 2 introduced by multiple scattering causes the phase of the light field to be randomized, and the coherence can be expressed as:

[0035]

[0036] The phase variance increases with the number of scattering, so the coherence can be effectively reduced by increasing the scattering cross section or the thickness of the fog layer.

[0037] 3. Optimal range of fog droplet size

[0038] When 2πr / λ≈1, scattering enters the Mie range, with high efficiency, wide directional distribution, and most significant coherence destruction.

[0039] Therefore, in the visible light (λ=400-700nm) band, the fog droplet radius r=0.25-2.5μm (i.e. diameter 0.5-5μm) is preferred, among which the main peak particle size 1-3μm can obtain the maximum coherence effect while ensuring the light flux.

[0040] 4. Dynamic disturbance and time averaging

[0041] If the probe integration time T int , the fog field autocorrelation frequency is f c , then the equivalent independent speckle is M=T int f c , and the speckle contrast satisfies:

[0042]

[0043] When C≤0.2, the visual speckle can be basically ignored.

[0044] Through the fog field disturbance frequency (fan 500-2000Hz or ultrasonic 20-50kHz) regulation, sufficient time de-coherence can be achieved.

[0045] The holographic display module, in sequence, is provided with a hologram loading device, a 4f system (Fourier lens 1, single sideband filter, Fourier lens 2) and an imaging surface, for loading digital holograms and realizing image reconstruction.

[0046] Optionally, the hologram loading element can select any one of a spatial light modulator (SLM) and a digital micromirror device (DMD) according to the type of hologram (phase type / amplitude type).

[0047] The 4f filter system is used for single sideband filtering of the hologram in the frequency spectrum plane, which includes Fourier lens 1, a rectangular filter and Fourier lens 2.

[0048] The imaging surface usually uses a camera to capture images.

[0049] Advantages

[0050] Firstly, the present application can achieve significant de-coherence effect under standard laser illumination conditions without using complex phase modulation, spread spectrum or multi-wavelength synthesis and other means. The scheme can effectively reduce the spatial and temporal coherence of laser by introducing controllable fog scattering device, which not only greatly simplifies the system structure and reduces the overall cost, but also avoids the complex control and error accumulation problems brought by traditional multi-wavelength or high-speed modulation system.

[0051] Secondly, the present application can theoretically realize more than one order of magnitude decrease in coherence length by adjusting the particle size distribution, concentration and disturbance frequency of the fog, while ensuring the luminous flux and illumination brightness, so that the speckle contrast is reduced from about 0.9 to below 0.2, thereby significantly improving the imaging uniformity and visual quality in computer holographic display.

[0052] Thirdly, the present application has good parameter adjustability and real-time control capability. Users can dynamically adjust the fog concentration, particle size or flow field disturbance rate according to actual display requirements to realize continuous and controllable de-coherence intensity, so as to adapt to holographic display systems with different resolution, frame rate or brightness requirements.

[0053] In addition, the present application has high structural compatibility and can be directly embedded in existing computer holographic display systems without changing the original optical path or imaging structure, so as to realize effective suppression of speckle noise on the existing platform.

[0054] Finally, the technical principle of the present application has wide applicability and is not only suitable for visible light laser systems, but also can be extended to near-infrared laser and other optical application fields such as interference measurement, laser projection and precision illumination, which has good universality and promotion value. BRIEF DESCRIPTION OF DRAWINGS

[0055] In order to understand the details of the above-mentioned features of the present application, reference can be made to the embodiments to obtain a more detailed description of the application briefly summarized above. The accompanying drawings relate to preferred embodiments of the present application and are described as follows:

[0056] Figure 1 is a principle conceptual diagram of laser de-coherence based on controllable fog scattering according to the preferred embodiment of the present application;

[0057] Figure 2 is a structure schematic diagram of laser de-coherence and holographic display speckle noise suppression system based on controllable fog scattering for phase type computer holographic display according to the preferred embodiment of the present application;

[0058] In the figure, 201 - light source, 202 - polarizer, 203 - pinhole filter, 204 - beam collimation assembly, 205 - fog generator, 206 - beam splitter, 207 - spatial light modulator, 208 - Fourier lens 1, 209 - mirror, 210 - single sideband filter, 211 - Fourier lens 2, 212 - imaging plane; DETAILED DESCRIPTION

[0059] Various embodiments will now be described in detail with reference to the drawings, one or more examples of which are illustrated in the figures. Each example is provided by way of explanation of the application, not as a limitation. For example, features illustrated or described as part of one embodiment, can be used with or in another embodiment, to result in yet another embodiment. It is intended that the present application encompass these and all such modifications and variations.

[0060] In the following description of drawings, like reference numerals indicate like or similar structures. Generally, only the differences between individual embodiments will be described. Unless specifically stated otherwise, a description of a part or aspect of an embodiment can also apply to a corresponding part or aspect of another embodiment.

[0061] EMBODIMENT

[0062] The laser de-coherence and holographic display speckle noise suppression system and method based on controllable fog scattering of the embodiments of the present application are described below with reference to the accompanying drawings.

[0063] REFERENCE Figure 1 , which shows a flowchart of a laser de-coherence and holographic display speckle noise suppression method based on controllable fog scattering, including a de-coherence process and a holographic display

[0064] As Figure 2 shown, the present embodiment proposes a laser de-coherence and holographic display speckle noise suppression system based on controllable fog scattering. The system is composed of a light source 201, a polarizer 202, a pinhole filter 203, a beam collimation assembly 204, a fog generator 205, a beam splitter 206, a spatial light modulator 207, a Fourier lens 208, a mirror 209, a single sideband filter 210, a Fourier lens 211, and an imaging plane 212. The components are connected in sequence to form an optical path, realizing coherence control based on controllable scattering and holographic reconstruction.

[0065] The core idea of the embodiment is to introduce a controllable fog scattering module (implemented by the fog generator 205) in the traditional computer holographic display light path, to make the laser light field undergo multiple random scattering in the propagation process by adjusting the fog droplet size distribution, concentration and flow field disturbance frequency, thereby significantly reducing its spatial and temporal coherence in theory. When the de-coherent light field irradiates the spatial light modulator 207, speckle noise formed by coherent interference can be suppressed in the reconstructed image, thereby improving image brightness uniformity and visual quality.

[0066] The overall optical path of the system is as follows: the laser light source 201 emits monochromatic laser, which enters the pinhole filter 203 after the polarization direction is controlled by the polarizer 202 to realize spatial filtering and obtain a uniform plane wavefront. The beam enters the fog scattering module 205 after being expanded and collimated by the beam collimation assembly 204.

[0067] The fog generator 205 adopts the ultrasonic atomization principle and uses a piezoelectric ceramic sheet to generate fog droplets with controllable particle size through high-frequency oscillation. The fog droplet size is mainly distributed in the interval of 0.5-5 μm, and the main energy distribution area is 1-3 μm, which is in the Mie scattering interval for the visible light band (400-700 nm). Fog droplets in this particle size interval can introduce strong angular scattering, thereby forming a spatial random phase modulation effect in optics.

[0068] In theory, the coherence of the light field after fog scattering is reduced. According to the spatial correlation function formula (3), when the fog droplet size r is in the interval of 1-3 μm and the fog layer thickness L=30 mm, the optical path difference variance can be increased by more than one order of magnitude, thereby significantly reducing |γ|. In theory, the speckle contrast can be reduced from 0.9 to about 0.2-0.3.

[0069] The light field processed by the fog scattering enters the beam splitter 206 and is divided into reference light and object light. The reference light directly enters the spatial light modulator 207 to form a modulated wavefront; the object light is frequency modulated by the spatial filtering system composed of the Fourier lens 208, the mirror 209 and the single sideband filter 210, and then is spatial frequency inverse transformed by the Fourier lens 211, to finally form a holographic reconstructed image on the imaging surface 212.

[0070] Through this structure, the system can introduce a controllable scattering mechanism while maintaining the integrity of the optical path, thereby realizing theoretical coherence regulation and speckle suppression.

[0071] Simple structure and flexible control: Decoherence can be achieved simply by adding a controllable fog scattering module to the optical path, without the need for complex mechanical structures or high-speed phase modulation devices; adjustable parameters and theoretically continuous control: by adjusting the droplet size, concentration, and perturbation frequency, a continuous transition from fully coherent to quasi-incoherent can theoretically be achieved; good compatibility: the module can be directly integrated with conventional computational holographic display systems, maintaining consistency in optical path structure; clear theoretical feasibility: based on Mie scattering and speckle statistical theory, the obtained coherence and speckle contrast changes are both within reasonable physical ranges; wide potential applications: this theoretical scheme is not only applicable to holographic displays but also to laser illumination, interferometry, laser projection, and other fields, providing a new, non-mechanical approach to laser speckle removal.

[0072] In summary, this embodiment proposes a laser decoherence theoretical system based on controllable fog scattering. By introducing a fog scattering medium with adjustable particle size and controllable concentration into the laser propagation path, the spatial and temporal coherence of the laser can be theoretically significantly reduced. Combining the Mie scattering model and speckle statistical analysis, it is shown that under appropriate parameter conditions, the speckle contrast can be reduced from approximately 0.9 to below 0.2, thereby achieving a highly uniform and low-noise reconstructed light field in computational holography. This scheme has a simple structure and clear physical principles, providing a theoretical basis and design basis for subsequent experimental verification and device development.

[0073] While the foregoing describes embodiments of the present invention, other and further embodiments of the present invention may be devised without departing from the basic scope of the invention, the scope of which is defined by the claims.

[0074] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. Technical features in these embodiments that do not contradict each other can be combined with each other. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A laser decoherence and holographic display speckle noise suppression system based on controllable fog scattering, characterized in that, This includes a laser source module, an optical shaping module, a fog scattering module, and a holographic display module that sequentially construct the optical path; The laser source module is used to generate a laser beam; The optical shaping module is used to collimate and diffuse the laser beam generated by the laser source module to ensure illumination uniformity and luminous flux utilization. The fog scattering module is disposed between the optical shaping module and the holographic display module, and is used to generate a scattering medium layer composed of micron-sized fog droplets, so that the laser processed by the optical shaping module undergoes multiple random scatterings in the scattering medium layer to reduce coherence; The holographic display module is used to load digital holograms and reconstruct images, and to evaluate the decoherence effect of the fog scattering module based on the speckle noise of the reconstructed hologram.

2. The laser decoherence and holographic display speckle noise suppression system based on controllable fog scattering according to claim 1, characterized in that, The laser source module is selected from either a monochromatic laser or a white laser.

3. The laser decoherence and holographic display speckle noise suppression system based on controllable fog scattering according to claim 1, characterized in that, The optical shaping module is sequentially and spaced apart by polarizers, pinhole filters and beam collimation components; The polarizer is used to control the polarization direction of the laser beam, the pinhole filter is used to achieve spatial filtering of the laser beam to obtain a uniform planar wavefront, and the beam collimation component is used to collimate the laser beam into parallel light as the reproduction light for computational holographic display.

4. The laser decoherence and holographic display speckle noise suppression system based on controllable fog scattering according to claim 3, characterized in that, The beam collimation component can be any one of a lens, prism, or fiber waveguide.

5. The laser decoherence and holographic display speckle noise suppression system based on controllable fog scattering according to claim 1, characterized in that, The holographic display module is sequentially and intermittently equipped with a reconstruction beam splitter, an image loading element, and a 4f filtering system; The reconstruction beam splitting component is used to reflect the laser light processed by the fog scattering module onto the image loading element. The image loading element is used to load a digital hologram and modulate the reference light to form a modulation wavefront. The 4f filtering system is used to perform spectral modulation on the object light and realize spatial frequency inverse transformation to complete image reconstruction.

6. The laser decoherence and holographic display speckle noise suppression system based on controllable fog scattering according to claim 5, characterized in that, The reconstructed beam splitting component can be any one of a beam splitter, a beam splitter, an optical fiber, or an optical waveguide.

7. The laser decoherence and holographic display speckle noise suppression system based on controllable fog scattering according to claim 5, characterized in that, The image loading element is selected from either a spatial light modulator (SLM) or a digital micromirror device (DMD) according to the type of digital hologram; when the digital hologram is phase-type, a spatial light modulator (SLM) is selected; when the digital hologram is amplitude-type, a digital micromirror device (DMD) is selected.

8. The laser decoherence and holographic display speckle noise suppression system based on controllable fog scattering according to claim 5, characterized in that, The 4f filtering system includes a Fourier lens 1, a single-sideband filter, and a Fourier lens 2 arranged sequentially. The Fourier lens 1 is used to convert the object light into a spectral signal, the single-sideband filter is used to perform single-sideband filtering on the spectral signal, and the Fourier lens 2 is used to convert the filtered spectral signal into a spatial image signal to achieve image reconstruction.

9. The laser decoherence and holographic display speckle noise suppression system based on controllable fog scattering according to claim 1, characterized in that, The fog scattering module includes a fog generation unit and a dynamic disturbance unit; The mist generation unit uses an ultrasonic humidifier or a piezoelectric atomizer to generate mist droplets with a particle size distribution of 0.5μm to 5μm, and the main peak of the mist droplet particle size distribution is between 1μm and 3μm. The dynamic disturbance unit includes a fan, an ultrasonic oscillator, or a fluid drive device, used to periodically change the fog density and flow field structure to achieve dynamic changes in the fog field and enhance the laser decoherence effect; wherein, the disturbance frequency of the fan is 500Hz to 2000Hz, and the disturbance frequency of the ultrasonic oscillator is 20kHz to 50kHz.

10. A laser decoherence and speckle noise suppression method based on the system according to any one of claims 1 to 9, characterized in that, Includes the following steps: Calculate the digital hologram to be displayed; load the hologram onto a spatial light modulator or a digital micromirror device; pass a collimated laser beam through a controllable fog scattering module to achieve spatial and temporal decoherence; reconstruct the holographic three-dimensional image using a Fourier optical system; analyze the speckle noise characteristics of the reconstructed image, and adjust the parameters of the fog scattering module according to the analysis results to achieve adaptive suppression of speckle noise.

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