Speckle suppression device

Abstract

The present disclosure provides a speckle suppression device, comprising a wide-strip semiconductor laser group, a collimation module, a stepped phase retarder, a lens module and an illumination surface, the wide-strip semiconductor laser group is used for emitting laser which is spatially incoherent in the slow axis direction; the collimation module is used for collimating the laser; the stepped phase retarder makes the laser after phase delay produce phase difference, which is spatially incoherent in the fast axis direction, outputs a plurality of two-dimensional incoherent sub-beams, the two-dimensional incoherent sub-beams are spatially incoherent in the fast axis direction and the slow axis direction; the lens module is used for focusing the two-dimensional incoherent sub-beams; the illumination surface makes each two-dimensional incoherent sub-beam produce a plurality of incoherent speckles after scattering on the surface of a rough object and superimposes, and obtains a speckle superimposed illumination spot. The present disclosure can improve the efficiency of speckle suppression and solve the problem of uneven illumination of the illumination surface.

Description

Technical Field

[0001] This disclosure relates to the field of laser lighting and display technology, and more particularly to a speckle suppression device. Background Technology

[0002] Semiconductor lasers possess advantages such as small size, high energy conversion efficiency, long lifespan, high brightness, and good monochromaticity, enabling large-area, high-brightness, and wide-color-gamut display effects as a light source. Conventional semiconductor lasers have a spectral bandwidth of 0.1–5 nm, and their beam quality is far superior to ordinary light sources such as LEDs and arc lamps. However, the presence of speckle significantly degrades the image quality of laser illumination and displays. The appearance of speckle stems from the high coherence of the laser, specifically including temporal and spatial coherence. When a laser beam illuminates a rough screen on an optical scale, the amplitude and phase of the light field are randomly modulated. These modulated light fields interfere with each other on the retina of the human eye or detectors such as CCDs, producing bright spots of randomly distributed position and size—the speckle pattern.

[0003] Speckle suppression mainly involves two aspects: First, generating different speckle patterns at different times using vibrating scatterers, diffractive optical elements, homogenizing rods, multimode fibers, screens, or modulation devices (such as deformable mirrors and spatial light modulators), leveraging the persistence of vision to reduce the temporal coherence of the laser. These methods generally require mechanical devices to drive the optical elements to move in a certain pattern, increasing the system's size and power consumption, and potentially generating noise. Second, generating different speckle patterns simultaneously, using spatial superposition to reduce the spatial coherence of the laser. Common methods include: designing chaotic lasers with special cavity shapes to generate a large number of spatial modes; coupling the laser into a multimode fiber of a certain length to generate partially coherent light; using bent multimode fiber bundles or phase delayers to reduce spatial coherence with temporal coherence; and using the Hadamard phase matrix to generate orthogonal phase distributions to produce spatially incoherent subbeams. These methods are also known as passive speckle suppression schemes because the optical elements involved do not require driving. In recent years, passive speckle suppression has gained increasing attention due to its lack of additional power consumption and noise. Speckle suppression is completed within the laser's coherence time (nanosecond level), enabling high-speed speckle suppression. To improve the efficiency of speckle suppression, it typically requires a two-dimensional incoherent sub-beam to uniformly fill the numerical aperture of the projection lens, necessitating a two-dimensional decoherence effect from the decoherentizer. Commonly used decoherentizers in passive speckle suppression include diffractive optical elements and stepped phase retarders. Compared to diffractive optical elements such as Hadamard phase plates, stepped phase retarders are simpler to design and fabricate, achieving the same decoherence effect while reducing costs. However, in actual fabrication, it is difficult to maintain the sharp edges of the stepped surface of the stepped phase retarder, inevitably leading to edge scattering. Edge scattering results in striped dark areas in the transmitted light spot, reducing the uniformity of illumination on the surface.

[0004] Therefore, improving the efficiency of passive speckle suppression and reducing uneven illumination on the lighting surface is an urgent problem to be solved. Summary of the Invention

[0005] In view of the above problems, embodiments of this disclosure provide a speckle suppression device to solve the problems of low speckle suppression efficiency and uneven illumination of the lighting surface.

[0006] This disclosure provides a speckle suppression device, comprising: a wide-strip semiconductor laser array for emitting spatially incoherent laser light in the slow axis direction; a collimation module disposed at the emitting end of the wide-strip semiconductor laser for collimating the laser light; a stepped phase retarder comprising multiple phase delay steps, each of which delays the laser light by a different phase, thereby generating a phase difference in the delayed laser light and outputting multiple two-dimensional incoherent sub-beams, the two-dimensional incoherent sub-beams being spatially incoherent in both the fast and slow axis directions; a lens module disposed at the output end of the stepped phase retarder for focusing the two-dimensional incoherent sub-beams; and an illumination surface disposed at the output end of the lens module, the illumination surface containing a rough object, such that each two-dimensional incoherent sub-beam, after being scattered by the rough object, generates multiple incoherent speckles, which are then superimposed to obtain a speckle-superimposed illumination spot; the centers of the stepped phase retarder, the lens module, and the illumination surface are disposed on the system optical axis, which is the path through which the laser light propagates through the speckle suppression device.

[0007] Optionally, adjacent phase delay steps cause the optical path difference generated by the laser to be greater than the coherence length of the laser.

[0008] Optionally, the phase delay steps are spatially arranged along the fast axis direction.

[0009] Optionally, a beam expander, centered on the optical axis of the system and located at the input end of the stepped phase delayer, is used to expand the spot size of the laser.

[0010] Optionally, the lens module includes: a microlens array disposed at the output end of the stepped phase retarder, with its center located on the optical axis of the system, comprising multiple sub-microlenses, each sub-microlens in the microlens array corresponding to a phase delay step of the stepped retarder, the height of each sub-microlens being the same as the height of a single phase delay step of the corresponding stepped phase retarder, used to cut multiple two-dimensional incoherent sub-beams into multiple unit sub-beams, and to integrate the multiple unit sub-beams in an array; and a focusing lens disposed at the output end of the microlens array, used to focus the multiple unit sub-beams after the array integration onto the illumination surface.

[0011] Optionally, the wide-strip semiconductor laser group includes a first wide-strip semiconductor laser and a second wide-strip semiconductor laser; a collimation module includes a first collimator and a second collimator, the first collimator being disposed at the emitting end of the first wide-strip semiconductor laser for adjusting the direction of the first laser emitted by the first wide-strip semiconductor laser, and the second collimator being disposed at the emitting end of the second wide-strip semiconductor laser for adjusting the direction of the second laser emitted by the second wide-strip semiconductor laser; a beam combining assembly is disposed between the output end of the collimation module and the input end of the beam expander, the center of the beam combining assembly being disposed on the optical axis of the system for combining the first laser and the second laser to form a combined laser beam, the combined laser beam being input to the beam expander.

[0012] Optionally, the output ends of the first wide-strip semiconductor laser and the second wide-strip semiconductor laser are perpendicular to each other, and the first wide-strip semiconductor laser and the second wide-strip semiconductor laser are positioned offset from the optical axis of the system in the fast axis direction.

[0013] Optionally, the first laser and the second laser have different wavelengths.

[0014] Optionally, the beam combining component includes: a half-wave plate disposed at the output end of the first collimator for changing the polarization state of the first laser; and a polarization beam combiner, with a first input end disposed at the output end of the half-wave plate and a second input end disposed at the output end of the second collimator for combining the second laser and the first laser after changing its polarization state into a single beam in the slow axis direction.

[0015] Optionally, the microlens array is spaced at a preset distance from the stepped phase delayer, and the position difference between the illumination dark areas of the first laser and the second laser is proportional to the preset distance.

[0016] The above-described at least one technical solution adopted in the embodiments of this disclosure can achieve the following beneficial effects:

[0017] 1. The speckle suppression device provided in this disclosure uses the spatial hole burning effect of a wide-strip semiconductor laser group to cause speckle filamentation and multi-mode lasing, which reduces the spatial coherence of the laser. The far field of the wide-strip semiconductor laser group exhibits a multi-lobed structure in the slow axis direction, and the beams corresponding to different lobes have spatial incoherence, that is, the wide-strip semiconductor laser emits a laser that is spatially incoherent in the slow axis direction. Each phase delay step of the stepped phase retarder delays the laser phase, making the laser spatially incoherent in the fast axis direction. The stepped phase retarder and the wide-strip semiconductor laser group work together to output a two-dimensional incoherent sub-laser that is spatially incoherent in both the fast and slow axis directions, thereby improving the efficiency of speckle suppression.

[0018] 2. The wide strip semiconductor laser array disclosed herein may include two wide strip semiconductor lasers placed off-axis of the system. The directions of the first laser and the second laser are changed by the first collimator and the second collimator. The positions of the illumination dark areas generated by the first laser and the second laser after passing through the stepped phase retarder overlap, which can improve the problem of uneven illumination caused by edge scattering of the stepped phase retarder.

[0019] 3. The first laser and the second laser of this disclosure have different wavelengths, and the diversity of wavelengths can further suppress speckle. Attached Figure Description

[0020] To gain a more complete understanding of this disclosure and its advantages, reference will now be made to the following description taken in conjunction with the accompanying drawings, wherein:

[0021] Figure 1 This schematically illustrates a multi-lobe structure of a wide-strip semiconductor laser in the far field provided in an embodiment of the present disclosure;

[0022] Figure 2 This schematically illustrates a horizontal structure of a speckle suppression device including a wide-strip semiconductor laser provided in an embodiment of the present disclosure.

[0023] Figure 3 This schematically illustrates a horizontal structure of a speckle suppression device including two wide-strip semiconductor lasers provided in an embodiment of the present disclosure.

[0024] Figure 4 This schematic diagram illustrates an equivalent vertical structure of a speckle suppression device according to an embodiment of the present disclosure;

[0025] Figure 5 This schematically illustrates an edge scattering diagram of a stepped phase retarder provided in an embodiment of the present disclosure;

[0026] Figure 6 A schematic diagram illustrating the striped dark areas generated by edge scattering of a stepped phase retarder;

[0027] Figure 7 This schematic diagram illustrates a light spot on the illumination surface during normal illumination, as provided in an embodiment of the present disclosure.

[0028] Figure 8 This schematically illustrates a light spot at the illumination surface when two wide-strip semiconductor lasers provide an embodiment of the present disclosure illuminate off-axis of the system.

[0029] Figure label:

[0030] 1-First wide-strip semiconductor laser; 2-Second wide-strip semiconductor laser; 3-First collimator; 4-Second collimator; 5-Half-wave plate; 6-Polarization beam combiner; 7-Beam expander; 8-Stepped phase delayer; 9-Microlens array; 10-Focusing lens; 11-Illumination surface. Detailed Implementation

[0031] The embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0032] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0033] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0034] This disclosure provides a speckle suppression device, including a wide-strip semiconductor laser array, a collimation module, a stepped phase retarder, a lens module, and an illumination surface. The wide-strip semiconductor laser array is used to emit spatially incoherent laser light in the slow axis direction. The collimation module is disposed at the emitting end of the wide-strip semiconductor laser array and is used to collimate the laser light. The stepped phase retarder includes multiple phase delay steps, each of which delays the laser light by a different phase, resulting in a phase difference in the delayed laser light, which is spatially incoherent in the fast axis direction, and outputs multiple two-dimensional incoherent sub-beams. The system consists of a two-dimensional incoherent sub-beam that is spatially incoherent along both the fast and slow axes. A lens module is located at the output of the stepped phase retarder and is used to focus the two-dimensional incoherent sub-beam. An illumination surface is located at the output of the lens module and contains a rough object. This causes each two-dimensional incoherent sub-beam to be scattered by the rough object, resulting in multiple incoherent speckles that are superimposed to form a speckle-stacked illumination spot. The centers of the stepped phase retarder, lens module, and illumination surface are located on the system's optical axis, which is the path through which the laser propagates via the speckle suppression device.

[0035] Figure 1This schematically illustrates a multi-lobe structure in the far field of a wide-strip semiconductor laser provided in an embodiment of the present disclosure. Figure 1 It shows multiple lobe-like structures.

[0036] In one illustrative embodiment, the wide-strip semiconductor laser group is a single wide-strip edge-emitting semiconductor laser or an array thereof. See also Figure 1 As shown, it should be understood that the stripe width of a wide-strip-emitting semiconductor laser is around 100 micrometers, and it typically operates with multiple transverse and longitudinal modes. In the slow-axis direction, the spatial burning effect leading to filamentation of the beam and the multi-transverse-mode lasing both reduce spatial coherence. In the slow-axis direction, the far field of a wide-strip-emitting semiconductor laser exhibits a multi-lobed structure, with different positions in the far field representing different spatial modes, thus resulting in spatial incoherence between beams corresponding to different lobes. However, in the fast-axis direction, the active region thickness is only about one micrometer, thus it operates with single-transverse-mode lasing, and the laser beam in the fast-axis direction still possesses spatial coherence.

[0037] In one illustrative embodiment, the collimator module is an aspherical lens or a cylindrical lens with a focal length of 0.3 to 10 mm.

[0038] As an alternative embodiment, adjacent phase delay steps cause the optical path difference generated by the laser to be greater than the coherence length of the laser. The "coherence length of the laser" refers to the distance that a laser beam can propagate while maintaining a certain degree of coherence.

[0039] As an alternative embodiment, the phase delay steps are arranged along the fast axis direction.

[0040] Specifically, the order of the stepped phase delayer is 5 to 20, the height of a single phase delay step is 0.5 mm to 2 mm, and the optical path difference generated by the laser is greater than the coherence length of the laser when the adjacent phase delay steps are adjacent, making the laser incoherent in the fast axis direction.

[0041] See Figure 1 As shown, as an optional embodiment, the speckle suppression device further includes a beam expander, which is centrally located on the optical axis of the system and at the input end of the stepped phase retarder. This expands the laser spot size so that the multi-lobe structure size of the wide-strip semiconductor laser in the far field along the slow axis matches the size of a single sub-microlens of the microlens array.

[0042] Specifically, a beam expander is added between the collimation module and the stepped phase delayer. After collimation by the collimation module, a collimated spot is formed. The input end of the beam expander is placed at a point where the shape of the collimated spot is close to a circle, which can reduce astigmatism and make the expanded spot close to a circle.

[0043] In one illustrative embodiment, the beam expander is a Kepler or Galilean beam expander with a beam expansion factor of 1 to 10 times, so that the lateral size of the expanded laser spot is between 10 mm and 30 mm.

[0044] As an optional embodiment, the lens module includes a microlens array 9 and a focusing lens 10. The microlens array 9 is located at the output end of the stepped phase retarder 8, with its center on the optical axis of the system. It includes multiple sub-microlenses, each of which corresponds to a phase delay step of the stepped retarder. The height of each sub-microlens is the same as the height of a single phase delay step of the corresponding stepped phase retarder. It is used to cut multiple two-dimensional incoherent sub-beams into multiple unit sub-beams and to integrate the multiple unit sub-beams. The focusing lens is located at the output end of the microlens array and is used to focus the multiple unit sub-beams after integration onto the illumination surface.

[0045] Specifically, the microlens array 9 is a single-piece double-sided microlens or a two-piece single-sided microlens. The height of a single sub-microlens is consistent with the height of a single phase step of the stepped phase delayer, and the width is the same as the interval of the multi-lobe structure in the beam-expanded spot. The specifications include 5×5~20×20.

[0046] Specifically, the focusing lens 10 is a spherical or aspherical plano-convex lens.

[0047] Figure 2 The schematic diagram illustrates a horizontal structure of a speckle suppression device including a wide-strip semiconductor laser provided in an embodiment of the present disclosure.

[0048] Specifically, see Figure 2As shown, in the embodiments of this disclosure, the wide-strip semiconductor laser array includes a first wide-strip semiconductor laser 1, and the collimation module includes a first collimator 3. In this embodiment, the speckle suppression device includes the first wide-strip semiconductor laser 1, the first collimator 3, the beam expander 7, the stepped phase delayer 8, the lens module, and the illumination surface 11. Due to the unique multi-transverse mode lasing and speckle filamentation characteristics of the wide-strip semiconductor laser, the far field of the first wide-strip semiconductor laser 1 has spatial incoherence in the slow axis direction, which lays the foundation for efficient speckle suppression. The first collimator 3 is used to collimate the first laser emitted by the first wide-strip semiconductor laser 1, changing the directivity of the first laser beam by translation. The beam expander 7 is used to enlarge the spot size of the first laser. After beam expansion, the first laser passes through the stepped phase delayer 8. Since the phase delay of each phase delay step generates an incoherent sub-beam in the fast axis direction, a two-dimensional incoherent sub-beam can be output at the output end of the stepped phase delayer 8. Two-dimensional incoherent sub-beams pass through a lens module and are focused on the illumination surface 11 to form an illumination spot. Each two-dimensional incoherent sub-beam produces a different speckle pattern after being scattered by a rough object on the illumination surface. The superposition of multiple incoherent speckle patterns can achieve the effect of speckle suppression.

[0049] Figure 5 The schematic diagram illustrates the edge scattering of a stepped phase retarder provided in an embodiment of the present disclosure.

[0050] Figure 6 A schematic diagram of the striped dark area generated by edge scattering of a stepped phase retarder is shown.

[0051] See Figure 5 and Figure 6 As shown, it should be noted that in actual fabrication, it is difficult to keep the edges of the stepped surface of the stepped phase retarder perfectly straight, and edge scattering inevitably occurs. Edge scattering leads to striped dark areas in the transmitted light spot, thereby reducing the uniformity of illumination on the lighting surface. The speckle suppression device provided in this disclosure can achieve a cross-distribution of the striped dark areas generated by the first laser and the second laser at the input end of the microlens array while improving speckle suppression efficiency, thus enhancing the uniformity of illumination.

[0052] Figure 3 The schematic diagram illustrates a horizontal structure of a speckle suppression device including two wide-strip semiconductor lasers provided in an embodiment of the present disclosure.

[0053] Figure 4 The diagram illustrates an equivalent vertical structure of a speckle suppression device provided in an embodiment of the present disclosure.

[0054] See Figure 3 and Figure 4As shown, as an optional embodiment, the speckle suppression device further includes: a wide-strip semiconductor laser group including a first wide-strip semiconductor laser 1 and a second wide-strip semiconductor laser 2; a collimation module including a first collimator 3 and a second collimator 4, the first collimator 3 being disposed at the emitting end of the first wide-strip semiconductor laser 1 for adjusting the direction of the first laser emitted by the first wide-strip semiconductor laser 1, and the second collimator 4 being disposed at the emitting end of the second wide-strip semiconductor laser 2 for adjusting the direction of the second laser emitted by the second wide-strip semiconductor laser 2; and a beam combining assembly disposed between the output end of the collimation module and the input end of the beam expander 7, the center of the beam combining assembly being disposed on the optical axis of the system for combining the first laser and the second laser to form a combined laser beam, the combined laser beam being input to the beam expander.

[0055] As an optional embodiment, the output ends of the first wide-strip semiconductor laser 1 and the second wide-strip semiconductor laser 2 are perpendicular to each other. The first wide-strip semiconductor laser 1 and the second wide-strip semiconductor laser 2 are positioned off-axis of the system optical axis in the fast axis direction, so that the directivity of the first laser and the second laser is distributed on the upper and lower sides of the system optical axis in the fast axis direction. At the same time, the first collimator 3 and the second collimator 4 are translated a certain distance in the fast axis direction, so that the first laser and the second laser coincide at the input end of the beam expander through the beam combining assembly, so that the first laser and the second laser overlap as much as possible when passing through the rear optical system, thereby increasing the effective illumination area and reducing off-axis light loss.

[0056] Specifically, the first wide-strip semiconductor laser 1 and the second wide-strip semiconductor laser 2 are single tubes or arrays of wide-strip edge-emitting semiconductor lasers, and the first collimator 3 and the second collimator 4 are aspherical lenses or cylindrical lenses with a focal length of 0.5mm to 10mm.

[0057] As an optional embodiment, the first laser and the second laser have different wavelengths, and the diversity of wavelengths can further suppress speckle.

[0058] Specifically, the center wavelengths of the first laser and the second laser are more than 2 nm apart, which makes the speckle patterns generated by the first laser and the second laser after being scattered by a rough object on the illuminated surface incoherent.

[0059] As an optional embodiment, the beam combining assembly includes a half-wave plate 5 and a polarization beam combiner 6. The half-wave plate 5 is located at the output end of the first collimator 3 and is used to change the polarization state of the first laser. The first input end of the polarization beam combiner 6 is located at the output end of the half-wave plate 5, and the second input end is located at the output end of the second collimator 4, and is used to combine the second laser and the first laser after changing the polarization state into a beam in the slow axis direction.

[0060] As an optional embodiment, the microlens array 9 and the stepped phase delayer 8 are separated by a preset distance. The position difference between the illumination dark areas of the first laser and the second laser is proportional to the preset distance, so that the striped dark areas generated by the first laser and the second laser are cross-distributed at the input end of the microlens array 9, thereby improving the uniformity of illumination.

[0061] Specifically, see Figure 3 and Figure 4 In another embodiment provided in this disclosure, the speckle suppression device includes: a first wide-strip semiconductor laser 1, a second wide-strip semiconductor laser 2, a first collimator 3, a second collimator 4, a half-wave plate 5, a polarization beam combiner 6, a beam expander 7, a stepped phase retarder 8, a microlens array 9, a focusing lens 10, and an illumination surface 11. The first wide-strip semiconductor laser 1 and the second wide-strip semiconductor laser 2 are positioned off-axis of the system, such that the directivity of the first and second lasers is distributed on the upper and lower sides of the system's optical axis in the fast axis direction. The first collimator 3 and the second collimator 4 are positioned off-axis of the system's optical axis, and are translated a certain distance in the fast axis direction so that the first and second lasers coincide at the beam expander input end through the beam combiner assembly. The half-wave plate 5 is used to change the polarization state of the first laser, rotating its polarization direction by 90°. The first and second lasers, whose polarization directions are perpendicular to each other, are combined into a single beam in the slow axis direction after passing through the polarization beam combiner 6. Beam expander 7 expands the combined laser beam. The expanded laser beam passes through stepped phase delayer 8. Due to the phase delay effect of each phase delay step, incoherent sub-beams are generated in the fast axis direction. In conjunction with the wide-strip semiconductor laser, the output of stepped phase delayer 8 yields two-dimensional incoherent sub-beams. The two-dimensional incoherent sub-beams are integrated by microlens array 9 and focusing lens 10, and overlap at different angles on illumination surface 11 to form a uniform illumination spot. Each sub-beam is scattered by a rough object on illumination surface 11, producing a different speckle pattern. The superposition of multiple incoherent speckle patterns achieves speckle suppression.

[0062] In one illustrative embodiment, the first wide-strip semiconductor laser 1 has a stripe width of 100 μm, a typical power of 1 W, a spectral bandwidth of 0.5 nm near the threshold, and a center wavelength of 638 nm; the second wide-strip semiconductor laser 2 has a stripe width of 100 μm, a typical power of 1 W, a spectral bandwidth of 0.5 nm near the threshold, and a center wavelength of 660 nm.

[0063] In one illustrative embodiment, the first collimator 3 and the second collimator 4 are aspherical plano-convex lenses with an effective focal length of 3mm, and the spot size at 90mm behind the collimator is 2.4mm × 3.2mm.

[0064] Specifically, under the paraxial approximation, the tilt angle of the laser after collimation by the collimator can be expressed as:

[0065]

[0066] Where Δx is the vertical distance between the active region of the wide-strip semiconductor laser and the optical axis of the collimator (in the fast axis direction), and f1 is the focal length of the collimator;

[0067] When off-axis (deviating from the system's optical axis) laser propagates to the input of the beam expander, the distance it deviates along the fast axis is:

[0068]

[0069] Where L1 is the distance between the emitting surface of the wide-strip semiconductor laser and the input end of the beam expander. Correspondingly, the active region of the first wide-strip semiconductor laser 1 deviates from the vertical distance Δx1 of the first collimator 3 by 0.1 mm, the active region of the second wide-strip semiconductor laser 2 deviates from the vertical distance Δx2 of the second collimator 4 by -0.1 mm, f1 is 3 mm, and L1 is 90 mm. Therefore, the collimated first laser deviates from the system optical axis upwards (in the fast axis direction), and the vertical offset s1 when it reaches the input end of the beam expander 7 is 3 mm; the collimated second laser deviates from the system optical axis downwards (in the opposite direction of the fast axis), and the vertical offset s2 when it reaches the input end of the beam expander is -3 mm.

[0070] To ensure that the off-axis first laser and the off-axis second laser coincide as much as possible at the input of the stepped phase delayer 8 and to reduce optical loss caused by the off-axis beam, the centers of the first laser and the second laser need to coincide with the center of the beam expander input. Therefore, the first wide-strip semiconductor laser 1 and the first collimator 3 need to be shifted downward as a whole by 3mm, and the second wide-strip semiconductor laser 2 and the second collimator 4 need to be shifted upward as a whole by 3mm.

[0071] In one illustrative embodiment, the fast axis of the half-wave plate 5 forms a 45° angle with the polarization direction of the first wide-strip semiconductor laser 1, converting the laser emitted by the first wide-strip semiconductor laser 1 from an s-polarization state to a p-polarization state. The polarization beam combiner 6 is a polarization beam splitter with a side length of 25.4 mm. After passing through the polarization beam splitter, the first laser and the second laser are combined into a single beam along the slow axis.

[0072] In one illustrative embodiment, the beam expander 7 consists of two aspherical lenses with effective focal lengths of 10mm and 60mm, respectively, with a distance of 70mm between the two aspherical lenses, and the size of the expanded spot is 13.2mm × 18mm.

[0073] Specifically, according to the principle of conservation of optical expansion, the tilt angle of the expanded laser beam is:

[0074]

[0075] Where N is the magnification factor of the beam expander.

[0076] In one illustrative embodiment, the stepped phase retarder 8 consists of nine steps, each with a height of 1.5 mm and a depth of 1.8 mm. The material is PMMA (Polymethyl Methacrylate), which has a refractive index of 1.49, and the overall dimensions are 16.2 mm × 15 mm × 15 mm. The stepped phase retarder 8 produces different phase delays on the laser beam along the fast axis. When the corresponding optical path difference is greater than the coherence length of the laser beam, incoherent sub-beams can be generated.

[0077] Specifically, the coherence length of the laser is calculated by the following formula:

[0078]

[0079] Among them, L c Let λ be the coherence length of the laser, λ be the center wavelength of the laser, and Δλ be the spectral bandwidth of the laser. Then, the coherence length of the first laser emitted by the first wide-strip semiconductor laser 1 is 0.81 mm, and the coherence length of the second laser emitted by the second wide-strip semiconductor laser 2 is 0.87 mm.

[0080] Specifically, the optical path difference generated by the stepped phase retarder 8 can be expressed as:

[0081]

[0082] Among them, L p Let n be the optical path difference, n be the refractive index of the material, and t be the depth of a single phase delay step in the stepped phase retarder 8. The optical path difference generated by the stepped phase retarder 8 is 0.88 mm, which is greater than the coherence length between the first and second lasers. Therefore, both the first and second lasers can generate effective incoherent sub-beams after passing through the stepped phase retarder 8.

[0083] In one illustrative embodiment, the microlens array 9 is a double-sided integrated structure with dimensions of 14×9, a single-sided focal length of 4mm, and the size of each sub-microlens is 1mm×1.5mm, resulting in an overall size of 15mm×6mm×15mm. Along the slow and fast axes, each sub-microlens corresponds one-to-one with the lobe-like structure and the phase delay step of the stepped phase delayer in the far field of the wide-strip semiconductor laser, respectively. The beams emitted from each sub-microlens are spatially incoherent beams.

[0084] In one illustrative embodiment, the focusing lens 10 is a plano-convex spherical lens with an effective focal length of 50 mm and a light-transmitting aperture of 25 mm. The sub-beams emitted from the microlens array 9 are superimposed on the illumination surface 11 at different angles after passing through the focusing lens.

[0085] Specifically, according to Goodman's speckle theory, the speckle suppression factor generated by the superposition of M incoherent speckle patterns with equal average intensity is:

[0086]

[0087] Where k is the speckle suppression factor, and M is the number of incoherent speckle patterns. Based on the above formula, the speckle suppression factor that this device can produce under ideal conditions with monochromatic illumination can be calculated as follows: Because the speckle suppression device of this disclosure uses two wide-strip semiconductor lasers with a sufficiently large center wavelength spacing for illumination, each wide-strip semiconductor laser can produce a different speckle pattern, thus the final speckle suppression factor is... Therefore, the diversity of wavelengths can further improve the speckle suppression effect.

[0088] Specifically, because the first and second lasers are off-axis (placed away from the system's optical axis), their directivity differs, resulting in differences in the position of the illumination dark area generated by the stepped phase retarder 8. Using the center position as a reference point, the positional difference of the dark area can be calculated using the following formula:

[0089]

[0090] Where L2 is the distance between the output of the stepped phase retarder and the input of the microlens array, n is the refractive index of the material, and l is half the overall thickness of the stepped phase retarder. As shown in the above equation, the positional difference of the dark areas is proportional to L2; therefore, the microlens array 9 and the stepped phase retarder 8 need to be separated by a preset distance. When the positional difference of the dark areas is half the height of the microlens array, the two types of striped dark areas overlap, with the dark area of ​​one stripe being filled by the bright area of ​​the other stripe, thus significantly improving the final illumination uniformity.

[0091] In the embodiments of this disclosure, the half-height of the microlens is 0.75 mm, and d = 0.75 mm. =0.1mm, N=6, f1=3mm, n=1.49, =7.5mm. Substituting these values ​​into the above formula, we get L2=56.3mm, which means the preset distance is 56.3mm.

[0092] Figure 7 The diagram illustrates a light spot on the illumination surface during normal illumination according to an embodiment of the present disclosure.

[0093] Figure 8 The illustration shows a schematic diagram of the light spot at the illumination surface when two wide-strip semiconductor lasers provided in the embodiments of this disclosure illuminate off-axis of the system.

[0094] The simulated illumination spot obtained under normal illumination is shown in Figure 7, and the illumination spot obtained under off-axis illumination is shown in Figure 8. Figure 8 As shown in the comparison, it can be found that off-axis illumination can effectively eliminate the dark areas at the upper and lower edges of the light spot, and the overall illuminance uniformity is improved.

[0095] In summary, the speckle suppression device provided in this disclosure combines a wide-strip semiconductor laser array with a stepped phase retarder to obtain a two-dimensional incoherent sub-beam, which can improve the efficiency of speckle suppression. The wide-strip semiconductor laser array includes a first wide-strip semiconductor laser and a second wide-strip semiconductor laser, which are placed off-axis of the system. The directions of the first and second lasers are changed by a first collimator and a second collimator. The positions of the illumination dark areas generated by the first and second lasers after passing through the stepped phase retarder overlap, which can improve the problem of uneven illumination caused by edge scattering of the stepped phase retarder. Furthermore, the first and second lasers have different wavelengths, which can further improve the efficiency of speckle suppression.

[0096] Those skilled in the art will understand that the features described in the various embodiments and / or claims of this disclosure can be combined or combined in various ways, even if such combinations or combinations are not explicitly described in this disclosure. In particular, the features described in the various embodiments and / or claims of this disclosure can be combined or combined in various ways without departing from the spirit and teachings of this disclosure. All such combinations and / or combinations fall within the scope of this disclosure.

[0097] Although this disclosure has been shown and described with reference to specific exemplary embodiments thereof, those skilled in the art will understand that various changes in form and detail may be made to this disclosure without departing from the spirit and scope of the disclosure as defined by the appended claims and their equivalents. Therefore, the scope of this disclosure should not be limited to the above embodiments, but should be defined not only by the appended claims, but also by their equivalents.

Claims

1. A speckle suppression device, characterized in that, include: Wide stripe semiconductor laser array for emitting spatially incoherent laser light in the slow axis direction; A collimation module, disposed at the emitting end of the wide-strip semiconductor laser array, is used to collimate the laser. A stepped phase delayer includes multiple phase delay steps, each of which delays the laser by a different phase, resulting in a phase difference in the delayed laser, which is spatially incoherent in the fast axis direction, and outputs multiple two-dimensional incoherent sub-beams, which are spatially incoherent in both the fast and slow axis directions. A lens module, disposed at the output end of the stepped phase retarder, is used to focus the two-dimensional incoherent sub-beam; An illumination surface is provided at the output end of the lens module. The illumination surface contains a rough object, such that each two-dimensional incoherent sub-beam is scattered by the rough object to generate multiple incoherent speckles, which are then superimposed to obtain a speckle superimposed illumination spot. The center of the stepped phase retarder, lens module, and illumination surface is located on the system optical axis, which is the path through which the laser propagates through the speckle suppression device.

2. The speckle suppression device according to claim 1, characterized in that, The adjacent phase delay steps cause the optical path difference generated by the laser to be greater than the coherence length of the laser.

3. The speckle suppression device according to claim 1, characterized in that, The phase delay steps are spatially arranged along the fast axis.

4. The speckle suppression device according to claim 1, characterized in that, Also includes: A beam expander, centered on the optical axis of the system and located at the input end of the stepped phase delayer, is used to expand the spot size of the laser.

5. The speckle suppression device according to claim 4, characterized in that, The lens module includes: A microlens array, located at the output end of the stepped phase retarder, with its center on the optical axis of the system, includes multiple sub-microlenses. Each sub-microlens in the microlens array corresponds to a phase delay step of the stepped retarder. The height of each sub-microlens is the same as the height of a single phase delay step of the corresponding stepped phase retarder. It is used to cut multiple two-dimensional incoherent sub-beams into multiple unit sub-beams and to integrate the multiple unit sub-beams in an array. A focusing lens, located at the output end of the microlens array, is used to focus the multiple unit sub-beams after arrangement and integration onto the illumination surface.

6. The speckle suppression device according to claim 5, characterized in that, Also includes: The wide-strip semiconductor laser group includes a first wide-strip semiconductor laser and a second wide-strip semiconductor laser; The collimation module includes a first collimator and a second collimator. The first collimator is disposed at the emitting end of the first wide-strip semiconductor laser and is used to adjust the direction of the first laser emitted by the first wide-strip semiconductor laser. The second collimator is disposed at the emitting end of the second wide-strip semiconductor laser and is used to adjust the direction of the second laser emitted by the second wide-strip semiconductor laser. A beam combining component is disposed between the output end of the collimation module and the input end of the beam expander. The center of the beam combining component is located on the optical axis of the system. It is used to combine the first laser and the second laser to form a combined laser beam, which is input to the beam expander.

7. The speckle suppression device according to claim 6, characterized in that, The output ends of the first wide-strip semiconductor laser and the second wide-strip semiconductor laser are perpendicular to each other, and the first wide-strip semiconductor laser and the second wide-strip semiconductor laser are positioned offset from the optical axis of the system in the fast axis direction.

8. The speckle suppression device according to claim 6, characterized in that, The first laser has a different wavelength than the second laser.

9. The speckle suppression device according to claim 6, characterized in that, The beam combining assembly includes: A half-wave plate is disposed at the output end of the first collimator to change the polarization state of the first laser. A polarization beam combiner has a first input terminal located at the output terminal of the half-wave plate and a second input terminal located at the output terminal of the second collimator, used to combine the second laser and the first laser after changing its polarization state into a single beam in the slow axis direction.

10. The speckle suppression device according to claim 6, characterized in that, The microlens array is spaced at a preset distance from the stepped phase delayer, and the position difference between the illumination dark areas of the first laser and the second laser is proportional to the preset distance.

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