Method and system for spatial and angular uniformation of a beam

Abstract

The present invention includes an imaging projection system that can project uniform illumination onto a dimmer while maintaining a small point spread function. A Fourier optical system may be interposed between the two homogenization structures such that the output of light is uniform in both spatial and angular space when light passes through the system.

Description

[0001] This application is a divisional application of the application with the application number 201980093311.8, titled "Methods and Systems for Spatial and Angular Uniformization of Light Beams", filed on August 30, 2021. Technical Field

[0002] The present invention relates to a method and / or system for spatial and / or angular uniformization of a light beam. Background Art

[0003] In the field of imaging projection, existing projectors typically rely on dimming techniques, such as various types of spatial light modulators, such as light valves (LCD, DLP, or LCOS) or micromirror devices (DMD). The entire modulator, such as a light valve, is illuminated as uniformly as possible and blocks light where it is not needed. The disadvantages of this approach may be:

[0004] 1 / For ordinary video signals, since the modulator discards all light that is not needed for the image, a large amount of light energy is wasted.

[0005] 2 / The ability to block light is not perfect, and when the image is supposed to be black, there is still a small amount of light leakage through the image. This can reduce the contrast because the display of an image that is completely black is not perfectly black (pure black).

[0006] Currently, there is a desire for displays, including projection displays, to be able to produce a wider contrast dynamic range. This means darker black levels and higher peak brightness levels, which can enable more details to be distinguishable in the darker or black regions of the image and can more fully represent very bright image highlights. However, a significant increase in the average image brightness level is not desired because this will mainly force the eyes to adapt to higher levels (which can be painful) without obtaining benefits in terms of the perceived dynamic range.

[0007] Typically, when increasing the peak brightness level, the black or darkest illumination level also increases. In a typical image, more information is encoded near this level, so it is highly undesirable to lose details in this way. Alternatively, a cascade of two light modulators was proposed in US5978142. Although this method effectively reduces black light leakage, it will significantly affect the light transmission efficiency because losses in the first light modulator (such as imaging optics, (reflective) mirrors, etc.) easily reduce the peak brightness level by 50%.

[0008] Furthermore, in a typical high-dynamic-range signal, the ratio between the peak brightness level and the average brightness level becomes larger, so a larger amount of light energy is blocked.

[0009] A more efficient implementation of an HDR projector could be one where only the second dimmer is a light valve type, and where the first dimmer only distributes or redirects light where needed. For the same amount of input illumination light, such a scheme can provide both darker black levels and brighter peak white levels. WO2015054797 proposes such a method, where the first dimmer is a phase modulation based LCOS device.

[0010] Hoskinson and Stoeber described a method using an analog MEMs device as the first dimmer in a paper published in 2008 by the Optical Society of America: "High-dynamic range image projection using auxiliary MEMS mirror array".

[0011] In a light redirecting projector, any light distribution at the location of the first dimmer can be converted to the desired light distribution at the second dimmer. However, it is still desirable for the light distribution on the first dimmer to be uniform. This will spread the heat load on the first dimmer and optimally utilize the resolution and étendue (light-gathering power) of the device.

[0012] For a circular beam with a Gaussian profile, the peak power illumination load on the first dimmer can be a multiple of the peak power illumination load with a top-hat shaped uniform rectangular illumination profile. Figure 1A ) shows a circle representing the projection of a circular beam with a Gaussian profile, which is fitted into a uniform 16:9 rectangle. The beam circle only covers 44% of the total area of the rectangle. This can cause the local temperature to far exceed the normal operating range of the device and / or significantly shorten the service life. If the light of the circular beam is uniformly distributed within the rectangle, as Figure 1B ) shows, it would be preferred.

[0013] Although the non-uniform illumination profile can be calibrated and accounted for when calculating the required light redirection, the stability of the profile will be crucial. For example, if multiple discrete laser sources are combined to illuminate the first dimmer, it is possible that the temperature difference effect or aging effect between the discrete laser sources results in a difficult-to-predict, changing illumination profile during the life of the device.

[0014] Thus, preferably, the light beams from a plurality of discrete laser sources are appropriately mixed such that each light source contributes equally and uniformly to all positions on the first dimmer. Another advantage is that this will minimize the laser speckle effect in the image, especially if lasers from slightly different wavelengths are combined for the respective primary colors.

[0015] In addition, the angular spread of the illumination beam affects performance. In an ideal scenario, the laser beam is perfectly collimated so that all parts of the beam propagate in the same direction. Then, the optical system can focus the beam onto a single focal point. However, real-life laser sources do not provide perfectly collimated beams and may have a certain degree of divergence, or angular spread around the propagation axis or optical axis. Thus, when attempting to focus the beam, this light propagation will be visible as a blurred spot around the optical axis. This spread can be referred to as the system point spread function (PSF).

[0016] In the light steering system, the focal point can be located in the intermediate image plane, such as at a stationary or moving diffuser located at a distance from the first dimmer. Due to beam divergence, the spot at the intermediate image plane will have a finite size. Then, the minimum size of the light steering beam spot at the intermediate image (and thus in the final image) can be based on the angular spread at the first dimmer position and the distance between the first dimmer and the intermediate image plane. In a typical configuration, the angular spread of the illumination of the first dimmer can be less than + / -0.1°. The system PSF can also be used in the calibration step for calculating the true luminance level profile at the intermediate image. For multiple light sources, temperature differences or aging differences may change the way the laser or light energy is distributed in angular space, causing the luminance distribution in the point spread function to change. Therefore, since the stability of the calibration step depends on the stability of the angular spread of the illumination light, it is desirable to minimize the influence of differences in characteristics such as temperature and aging.

[0017] Figure 2 An incompletely collimated light or laser beam 20 with an angular spread 21 is shown. It is reflected by a dimmer 22 to form an intermediate image on a moving diffuser 23 located in the intermediate plane 24. The beam spot on the moving diffuser 23 has a spread 25 around the ideal focal point 26 (on the optical axis). The spread 25 can be described by the point spread function. Figure 2 Also included are incident beams 27, 28 which have a similar angular spread and thus contribute to a substantially identical PSF.

[0018] Figure 3Illustrates how to change the angle and spatial light distribution through collimation (solid arrows) or imaging (dashed arrows). If light is transmitted through an optical fiber and the light from the optical fiber is collimated onto a first dimmer, then the angular luminance profile 31 of the light emitted by the optical fiber determines the spatial light distribution 32 on the phase modulator. The spatial distribution 30 of the light emitted by the optical fiber is converted into an angular light distribution 33 on the phase modulator and can thus be directly associated with the shape of the point spread function. If the light at the optical fiber exit is imaged onto the phase modulator, then the spatial uniformity 30 of the light will determine the spatial uniformity 32 of the light projected onto the phase modulator. The angular uniformity 31 of the light determines the angular uniformity 33 of the light projected onto the phase modulator, thus determining the shape of the point spread function.

[0019] In both cases, the spatial and angular distributions of the light at the optical fiber exit are key parameters.

[0020] When the illumination angle profile is smooth (e.g., Gaussian), the calibration of the imaging projection system can be improved. On the other hand, if the illumination angle profile is very irregular, a small difference in the alignment between the actual PSF position and the assumed PSF position may result in a large difference between the actual dimmer illumination and the envisioned dimmer illumination. Finally, this will result in a large error in the final image. Figure 4A Illustrates an example of a smooth luminance level profile, and Figure 4B Illustrates an example of an irregular luminance level profile in which the luminance level changes abruptly with angle. These are only cross-sections, and the requirement for the luminance level to vary smoothly with angle applies in two dimensions. SUMMARY OF THE INVENTION

[0021] An object of the present invention is to provide a method and / or system for spatial and / or angular homogenization of a light beam.

[0022] In one embodiment of the present invention, a system for providing a uniform light beam for use with a light source is provided. The system may include at least two homogenization structures, such as a first and a second homogenization structure or at least a first and a second homogenization structure. Any or all of the homogenization structures may be, for example, optical fibers, each homogenization structure having an input (portion) and an output, i.e., each having an input plane and an output plane. The system may also include a Fourier optical system having a first focus and a second focus. The light source, the first homogenization structure, the Fourier optical system, and the second homogenization structure may be placed adjacent to and continuously with each other. The Fourier optical system may be positioned such that the output (or output plane) of the first homogenization structure may coincide with the first focus of the Fourier optical system, and the input (e.g., input plane) of the second homogenization structure may coincide with the second focus.

[0023] Additionally or alternatively, at least one of the two first homogenizing structures and the second homogenizing structure may include a cross-sectional area having a rectangular shape.

[0024] Additionally or alternatively, at least one of the first and second homogenizing structures may have a cross-sectional area, while the dimmer may have an image area, and the aspect ratio of the cross-sectional area of at least one of the first and second homogenizing structures may be the same as the aspect ratio of the area of the dimmer. The dimmer may be a spatial dimmer or a light valve, and either the spatial dimmer or the light valve may be transmissive or reflective.

[0025] Additionally or alternatively, the first homogenizing structure may be bent with a bending radius. Additionally or alternatively, the first homogenizing structure may adopt different bending radii at different time points.

[0026] Additionally or alternatively, at least one of the first and second homogenizing structures may be a conventional integrator. At least the first and second homogenizing structures may be conventional integrators. Additionally, the system may include a diffuser, and the diffuser may be located between the position where the light source can be placed and the first homogenizing structure.

[0027] In another embodiment of the present invention, a method for using with a light source and providing a uniform light beam is provided. The method utilizes at least two homogenizing structures such as optical fibers, each homogenizing structure having an input (portion) and an output, such as an input plane and an output plane, and having a Fourier optical system, the Fourier optical system having a first focus and a second focus. The method may include placing the light source, the first homogenizing structure, the Fourier optical system, and the second homogenizing structure in close proximity and continuously with each other. It may also include positioning the Fourier optical system such that the output (or output plane) of the first homogenizing structure coincides with the first focus of the Fourier optical system, and the input (e.g., input plane) of the second homogenizing structure coincides with the second focus of the Fourier optical system.

[0028] Additionally or alternatively, at least one of the first homogenizing structure and the second homogenizing structure may have a cross-sectional area, and the method may include configuring the above area into a rectangular shape.

[0029] Additionally or alternatively, at least one of the first homogenizing structure and the second homogenizing structure has a cross-sectional area, and the dimmer may have an image area, wherein the method may include configuring the aspect ratio of the cross-sectional area of at least one of the first homogenizing structure and the second homogenizing structure to be the same as the aspect ratio of the area of the dimmer.

[0030] Additionally or alternatively, the method may include bending the first homogenization structure with a bending radius. Additionally or alternatively, the bending radius may vary with a frequency (i.e., vary periodically along the first homogenization structure).

[0031] Additionally or alternatively, the method may include implementing at least one of the at least first homogenization structure and the second homogenization structure as a conventional integrator. Additionally, there may be a diffuser, and the method may include placing the diffuser between the location for the light source and the first homogenization structure.

[0032] In another embodiment of the present invention, there is provided an optical component for use with a light source and for providing a uniform light beam. The system may include at least two homogenization structures such as optical fibers, each homogenization structure having an input (portion) and an output, such as an input plane and an output plane. The system may further include a Fourier optical system having a first focus and a second focus. And the light source, the first homogenization structure, the Fourier optical system, and the second homogenization structure may be placed adjacent to and continuously with each other. The Fourier optical system may be positioned such that the output of the first homogenization structure (e.g., the output plane) coincides with the first focus of the Fourier optical system, and the input of the second homogenization structure (e.g., the input plane) coincides with the second focus of the Fourier optical system.

[0033] Additionally or alternatively, at least one of the at least first homogenization structure and the second homogenization structure may include a cross-sectional area having a rectangular shape.

[0034] Additionally or alternatively, at least one of the at least first homogenization structure and the second homogenization structure has a cross-sectional area, and the dimming device may have an image area, and the aspect ratio of the cross-sectional area of at least one of the at least first homogenization structure and the second homogenization structure is the same as the aspect ratio of the area of the dimming device.

[0035] Additionally or alternatively, the first homogenization structure may be bent with a bending radius. Additionally or alternatively, the first homogenization structure may adopt different bending radii at different time points.

[0036] Additionally or alternatively, at least one of the at least first and second homogenization structures may be a conventional integrator. Additionally or alternatively, the optical component may include a diffuser, and the diffuser may be placed between the location for the light source and the first homogenization structure.

[0037] In another set of embodiments related to an independent aspect of the present invention, an image projection system for use with a light source is provided. The image projection system includes a dimmer and a homogenizing structure. The homogenizing structure has an elongated shape and is adapted to receive light from the light source and direct the light onto the dimmer. The homogenizing structure has a rectangular structure, such as a rectangular cross-section, and one or more bends.

[0038] The homogenizing structure may include a cross-sectional area having a shortest side, and each bending radius is at least 200 to 1000 times greater than the shortest length of the cross-sectional area.

[0039] The homogenizing structure may have a cross-sectional area that is rectangular.

[0040] The homogenizing structure may include a cross-sectional area having corners, and the shape of each corner is rounded with a radius of curvature.

[0041] The homogenizing structure may have a cross-sectional area, and the dimmer may have an image area. The aspect ratio of the cross-sectional area of the homogenizing structure is the same as the aspect ratio of the image area of the dimmer.

[0042] In another aspect, the present invention provides a method for diffusing light in an image projection system for use with a light source. The image projection system includes a dimmer and a homogenizing structure. The homogenizing structure has an elongated shape and is adapted to receive and direct light onto the dimmer. The method includes bending the homogenizing structure at one or more locations.

[0043] The homogenizing structure may include a cross-sectional area having a shortest side, and the method includes the step of configuring each bending radius to be at least 200 to 1000 times greater than the shortest length of the cross-sectional area.

[0044] The homogenizing structure may have a cross-sectional area, and the method includes configuring the cross-sectional area to be rectangular.

[0045] The homogenizing structure may include a cross-sectional area having corners, and the method includes configuring the shape of each corner to be a rounded shape defining a radius of curvature.

[0046] The homogenizing structure may have a cross-sectional area, and the dimmer may have an image area. The method includes configuring the aspect ratio of the cross-sectional area of the homogenizing structure to be the same as the aspect ratio of the image area of the dimmer. Description of the Drawings

[0047] Figure 1A and Figure 1B shows a cross-section of an illumination beam.

[0048] Figure 2 Shows an illumination beam with a non-ideal collimation having a spatial extent and an angular extent about the optical axis.

[0049] Figure 3 Shows how the collimation or direct imaging of a light beam affects its angular and spatial light distribution.

[0050] Figure 4 shows smooth and irregular brightness distribution profiles.

[0051] Figure 5 Shows four sub-light sources entering a homogenizing structure.

[0052] Figure 6A and Figures 6B to 8A and Figure 8B Shows an embodiment of the present invention including spatial and angular light distribution charts.

[0053] Figure 9A and Figure 9B Shows an embodiment of the present invention including an angular light distribution chart.

[0054] Figure 10 Shows an embodiment of the present invention including an angular light distribution chart.

[0055] Figure 11 Shows an embodiment of the present invention including spatial and angular light distribution diagrams.

[0056] Figures 12 to 14 Shows an embodiment of the present invention including a bipolar homogenizing structure system.

[0057] Figure 15 Shows an embodiment of the present invention including spatial and angular light distribution charts for a two-stage homogenizing structure system.

[0058] Define

[0059] The "point spread function" (PSF) describes the spread or blur of light near the focus on the surface of a light beam due to beam divergence. The spatial distribution of the PSF can describe the area on which the light spreads on a physical surface. The angular light distribution can describe the different angles at which the light beam impinges (illuminates) on a physical surface.

[0060] An "optical fiber" can be a flexible fiber made of a transparent material such as glass, silica, or plastic. The diameter of an optical fiber is typically in the sub-millimeter range.

[0061] An "optical diffuser" or "diffuser" can be an optical component capable of scattering light in any direction.

[0062] A "dimmer" can be an optical component capable of modulating the light beam incident (shining) thereon. A dimmer can be referred to as an "amplitude modulator", which can modulate the amplitude of the incident light. This can be achieved by technologies such as liquid crystal display (LCD), digital light processing (DLP), or liquid crystal on silicon (LCoS), digital micromirror device (DMD), or any other technology that can introduce a controllable amplitude change to the light beam. Another dimmer can be referred to as a "phase modulator", which can modulate the phase of the incident light. This can be achieved by technologies such as LCoS, microelectromechanical systems (MEMS), or any other technology that can introduce a controlled phase shift to the light beam.

[0063] A "homogenizing structure" is an optical component capable of homogenizing a light beam. It is usually elongated, with an inlet or input and an outlet or output. When the light beam is inserted or input into the homogenizing structure, it reflects on the inner wall of the homogenizing structure. The reflection characteristics of the homogenizing structure depend on its geometry and the material it is made of. For example, an integrating rod made of fused quartz or glass usually has a square or circular cross-section. Alternatively, it can be an optical fiber with a high refractive index core, which has a rectangular, square, or hexagonal cross-section surrounded by a low refractive index cladding material.

[0064] "Uniform": For a spatial light distribution, if the brightness level at each position is better than 70%, preferably better than 80% of the average brightness level across the cross-section of the light beam, then the brightness level can be said to be uniform.

[0065] For an angular light distribution, if it is constant or smooth (monotonic, without local maxima), then the brightness observed from different angles within that range is uniform. For example, this can be a Gaussian distribution with a ramp-up and ramp-down near the edges or a top-hat distribution. The ripple in the middle of the distribution is preferably less than 5%, or more preferably less than 2%.

[0066] A "Fourier transform optical system" is a system of optical components capable of transforming a light beam according to the Fourier transform. For example, if the distribution of light in a linear space enters a Fourier system, the output can be described as a similar distribution of light in, for example, the frequency space or the angular space. Detailed Description

[0067] The present invention will be described with reference to specific embodiments and with reference to certain drawings, but the present invention is not limited thereto, but is only limited by the claims. The described drawings are merely illustrative and not restrictive. In the drawings, for purposes of illustration, the dimensions of some elements may be exaggerated and not drawn to scale. When the term "comprising" is used in this specification and claims, it does not exclude other elements or steps. In addition, the terms "first", "second", "third", etc. in the specification and claims are used to distinguish between similar elements and not necessarily to describe a sequence or chronological order. It should be understood that the terms so used are interchangeable under appropriate circumstances, and the embodiments of the present invention described herein can be operated in other orders different from those described or illustrated herein.

[0068] According to an embodiment of the present invention, the light steering system may have a first light modulator illuminated with a beam providing a uniform rectangular light spot and having a smooth angular light distribution. In the case where the light source includes a plurality of discrete laser sources, these light sources are preferably properly mixed. In an ideal case, each light source has a uniform contribution to each position on the first dimmer, and also has a uniform contribution to the entire angular range. In this way, the system can become less sensitive to a reduction (or failure) in the optical power of a single light source. Additionally, if beams having multiple wavelengths are superimposed, speckle patterns can be reduced by means of wavelength diversity.

[0069] The spatial distribution of illumination can determine how the light energy is distributed over different highlight regions of the image. If this spatial illumination profile changes, the light distribution over different highlights will fluctuate, e.g., some highlight regions will become brighter while other regions become darker. A phase algorithm can be used for the light steering beam to reduce the sensitivity to non-uniform and / or varying input illumination beams, and the phase algorithm can include mixing light from different positions. If each highlight region receives light from each position on the panel, the non-uniformity of the illumination of the phase panel can be largely eliminated. However, more efficient phase algorithms (see WO2015184549) attempt to minimize the steering angle and direct, for example, preferably the light at the upper right corner of the phase panel to the highlight in the upper right corner of the middle image. In order to be able to use these more efficient algorithms, it is important to ensure uniform and stable illumination on the phase panel.

[0070] As Figure 3 shown, the angular light distribution determines the shape of the illumination light described by the point spread function at the middle image (which is equal to the shape of the smallest focused highlight). If the angular light distribution profile changes, the distribution of the illumination light within the point spread function also changes. This can lead to changes in the high-frequency brightness level and thereby 4 lead to color changes in an RGB full-color system.

[0071] Proper homogenization of the illumination light that preferably transmits a stable light profile to the first dimmer in both the spatial domain and the angular domain. Ideally, the homogenization structure provides such uniformity regardless of the characteristics of the light at its entrance. If multiple laser sources are coupled at its entrance, each laser source will preferably contribute equally to each position and each angle at the phase modulator, thereby eliminating temperature differences and aging effects and minimizing laser speckle.

[0072] Methods for improving the spatial and angular uniformity of an array of individual laser sources are disclosed in WO 2012139634, which discloses a system including two integrator stages. Each of the two integrator stages can have a diffuser in front, and the output of the first integrator stage can be imaged onto a diffuser in front of the second integrator stage.

[0073] For a light steering projection system, it is desirable to keep the point spread function small, as this allows small highlight features in the image to be resolved. Therefore, the angular spread of the illumination beam incident on the first dimmer is preferably kept small. However, conventional homogenization structures, such as solid rod integrators or hollow light pipes, can only properly mix the incoming beams when the beam has sufficient angular spread and / or the integrator or pipe is very long. Therefore, conventional rod integrators or light pipes may not be suitable for light steering projection systems.

[0074] However, if the cross-section of an integrator rod of conventional length is small enough, a viable angular spread can be obtained with it. For example, it can be about 100 times smaller than the size of the first dimmer. Then, an angular spread of + / -0.1° at the first dimmer can be converted to an angular spread of + / -10° at the integrator rod, which can be sufficient to provide good integration over a limited length. For example, this length can be 50 - 100 times the height of the integrator rod. Assuming the height of the first dimmer is about 1 cm, then the height of the integrator rod is 100 μm (the minimum length can be 5 to 10 mm).

[0075] An integrator rod with the above small cross-section can be implemented using, for example, an optical fiber with a fused silica core having a rectangular, square, or hexagonal cross-section. For example, Leoni offers multimode special optical fibers (https: / / www.leoni-fiber-optics.com / en / products-and-services / fibers / multimode-sp ecial-optical-fibers / ). Custom cross-sections can be produced.

[0076] These optical fibers transmit a top-hat intensity distribution at their output. The output can be imaged onto the first dimmer, and a uniform brightness distribution over the entire first dimmer can be achieved (if the optical fiber has the same shape as the modulator).

[0077] An ideal rectangular optical fiber (i.e., an optical fiber having a rectangular cross-section) will reflect the angular light distribution at its input in the horizontal and vertical directions, but there will be no angular homogenization. If multiple light sources are coupled with inputs from different angles, the output image may include angular gaps between discrete (light) sources.

[0078] Embodiment 1, optical fiber

[0079] Figure 5 A light source is shown that includes four sub-light sources 50 that are coupled at the entrance of an optical fiber 52 for use with various embodiments of the present invention from four different angles (e.g., three degrees relative to the normal or optical axis 51). The sub-light source beams are superimposed at the input (plane) 53. The sub-light source beams span an angle of + / - 1.5 degrees, and thus there are gaps in the angular space. The light distribution at the input is neither spatially uniform nor angularly uniform. Based on the above measurements, the spatial and angular radiation patterns were simulated. The results can be represented by spatial and angular radiation distribution charts, where the x-axis and y-axis each extend in a linear spatial and angular space. The intensity level on the right hand side represents the radiance.

[0080] At the input 53, the light source 50 delivers a non-uniform illumination spot, as shown in the Figure 6A spatial distribution chart. The diameter of the spot having the above dimensions is approximately 20 μm. Figure 6B A corresponding angular light distribution is shown that includes gaps in the angular space, i.e., there is no radiation at these angles or directions.

[0081] Figure 5 And the beam of FIG. 6 can be input into a rectangular optical fiber having a cross-section of, for example, 160×90 μm and a length of 20 cm. Figure 7A And Figure 7B each show the spatial and angular radiation distributions at the output plane of the optical fiber. Therefore, Figure 7A the spatial distribution in Figure 7B exhibits good uniformity. However,

[0082] Embodiment 2, asymmetry

[0083] The sub-light or laser sources at the input can be arranged in an asymmetric angular configuration. This can result in the superposition of four angular profiles (or radiation distributions) at the output (section):

[0084] - Input profile without reflection (mirror image)

[0085] - Input profile with only horizontal reflection (mirror image)

[0086] - Input profile with only vertical reflection (mirror image)

[0087] - Input profile with both horizontal and vertical reflection (mirror image)

[0088] By considering this reflection (mirror image) effect, the gap in the angular space at the output can be reduced or eliminated. It should also be noted to avoid creating large areas of overlap.

[0089] Figure 5 The sub-light sources of Figure 8A can be coupled into the rectangular optical fiber at four discrete angles, which are asymmetrically distributed around the normal direction. The gap in the angular light distribution chart can be selected to be similar in size to the angular coverage of each input source. In Figure 8A the angular light distribution obtained at the input can be seen. Figure 8B The angular light distribution at the output is shown. The different sub-images include Figure 8A The angular light distribution of the input angular light distribution in and the angular light distribution of the images with horizontal and / or vertical reflection (mirror image). The resulting angular light distribution is gapless. Some overlap still produces a higher intensity for certain angles.

[0090] However, since the mirror images now have minimal overlap, the four light sources no longer mix in the angular space. Each (light) source has its own four output points, and the temperature difference or aging effect will cause a change in the angular light distribution.

[0091] Embodiment 3, Bending

[0092] The embodiments of the present invention can be beneficial because they introduce a controllable amount of diffusion to obtain beam mixing. The bending of the optical fiber can be used together with other embodiments of the present invention, but it involves an independent and isolated embodiment of the present invention.

[0093] Due to the very small cross-section of the fiber optic integrating rod, conventional diffusers can no longer be used. The grain size of the diffuser needs to be much smaller than the cross-section of the optical fiber, and the diffuser needs to be very close to the fiber entrance so as not to scatter any light. Even more complex is the extremely high power density.

[0094] The inventors have found that a controlled diffusion can be introduced by slightly bending the optical fiber. Due to the mirror (reflection) effect, bending in one direction will result in an increase in the symmetry of the distribution in the angular space. Therefore, the final angular light distribution will be the incoming angular light distribution plus or minus a few degrees.

[0095] By arranging the rectangular optical fiber in a three-dimensional S-shape, diffusion can be increased along the x-axis and y-axis in angular space. The amount of diffusion around the horizontal axis can be chosen to be the same as or different from the amount of diffusion around the vertical axis.

[0096] Figure 9A It shows how the above exemplary optical fiber has been bent in the horizontal and vertical directions with a bending radius of 10 cm. In addition, using four sub-light sources as shown in Figure 5 , the angular light distribution at the output does not exhibit gaps, see Figure 9B . The spatial light distribution (not shown here) also remains uniform. In addition, the bending can vary with time (i.e., vibrate) to produce an effect equivalent to that of a moving diffuser. This can reduce the speckle effect in the output image.

[0097] Whenever the optical fiber changes its bending direction, the diffusion angle increases. The amount of increased diffusion is based on the bending radius. Similar to the cascading of ordinary Gaussian diffusers, the effect is not cumulative but is given by the square root of the sum of the squares of the diffusion angles, as shown in Equation 1.

[0098]

[0099] Figure 10 An exemplary embodiment of the present invention is shown, which includes an optical fiber 100 (e.g., rectangular), where each angle gradually evolves on a one-dimensional vertical S-shaped bend of the optical fiber. The angular light distributions 101 to 107 at seven points (labeled "1" to "7") from left to right on the optical fiber are shown. After the straight optical fiber portion at point 1, the initial angular light distribution 101 is the same as the angular light distribution emitted at the optical fiber entrance. At the start of the first bend at point 2, the light rays transition from the straight optical fiber portion to the bent optical fiber portion, such that the reflection angle increases and the angular light distribution 102 begins to expand in one direction. When the light continues to propagate along the optical fiber with a constant bending radius and bending direction, the angle increase caused by the light bouncing (reflecting) on one side of the optical fiber is compensated by the angle decrease caused by the light bouncing (reflecting) on the other side of the optical fiber, and the total angular distribution no longer expands. However, through the vertical gap starting to be filled, a vertical mirror effect can be seen at point 103. At point 104, the mirroring (reflecting) operation is completed (the vertical gap is filled). Whenever the bending direction changes, this effect is repeated, and the result corresponds to that of adding an additional diffuser. From point 5 to point 6 and then to point 7, the enhanced effect of vertical diffusion can be gradually seen. However, due to the square root law of Equation (1), the influence of the fourth bend at point 7 is relatively small. The same type of S-shaped bend can also be applied in the other direction to obtain horizontal diffusion.

[0100] It has been observed that whenever an optical fiber transitions from a straight section to a bent section, a certain amount of one-dimensional diffusion is increased. The amount of diffusion can be related to the bending radius. Continuing with the same bending radius and bending direction will no longer affect the angular light distribution. However, bending the optical fiber back to a straight shape and then bending it in the opposite direction can further increase the amount of diffusion (although not in a linear manner). Therefore, by controlling the trajectory and bending radius of the optical fiber, the desired amount of diffusion can be customized.

[0101] The bending radius of the optical fiber can be 200 to 1000 times larger than its height, for example, for a 0.1 mm optical fiber height, the bending radius is 100 mm. The angle after the first bend (point 4) can expand by approximately + / - 0.75 degrees. The angle after the full S curve (at point 7) can expand by approximately + / - 1.5 degrees.

[0102] Embodiment Four, Rounded Cross-Section Corners

[0103] Current optical fiber production processes may result in optical fibers having rounded cross-section corners, so these corners have a radius of curvature. Therefore, overfilling may be required to keep the rounded cross-section corners outside the effective area of the first dimmer, which will result in optical losses. It is desirable to minimize the rounding of the optical fiber cross-section corners to minimize such optical losses.

[0104] However, the rounding of the cross-section corners can introduce an effect of radial mixing in the angular space. Therefore, it may no longer be necessary to apply bends in the horizontal and vertical directions to produce a sufficient diffusion effect. Introducing a bend in any direction may be sufficient, and the rounded cross-section corners will provide radial mixing. For example, the radius of rounding of the cross-section corners can preferably be less than 5% of the optical fiber width to minimize overfilling. However, preferably, the radius is still large enough, for example, greater than 1% of the optical fiber width, to introduce sufficient radial mixing over a limited length of 1 - 2 meters.

[0105] A single rectangular optical fiber with rounded corners can introduce mixing at three levels:

[0106] 1 / Spatial uniform mixing on the rectangular cross-section, providing a uniform rectangle (possibly with rounded corners) at the output.

[0107] 2 / Axial angular uniform mixing by bending the optical fiber. The amount of bending should be minimized to be sufficient to close the axial distance between adjacent laser diodes.

[0108] 3 / Radial angular uniform mixing possibly caused by the rounded cross-section corners, thus eliminating the gaps in the angular space between adjacent diodes in the radial direction.

[0109] Embodiment Five, Straight Optical Fiber

[0110] In an exemplary embodiment, a straight optical fiber is provided. For example, it has a cross-section of 315×166 μm, with corner rounding having a radius of, for example, 50 μm, and a length of 1 meter.

[0111] A point light source, such as a laser having a square angular profile of + / -6.5 degrees in the horizontal and vertical directions, is positioned to project light into the optical fiber. The point light source can be located at a distance of 300 μm in front of the fiber entrance, such that there is a reduced area at the entrance, for example, only an area of 66×66 μm is illuminated.

[0112] Figure 11 An embodiment of the present invention is shown, which includes the above-mentioned optical fiber 110 and spatial light distribution profiles 111 to 117 and angular light distribution profiles 121 to 127 evolving at respective points 1 to 7. Points 1 to 7 are located at the fiber entrance, 1 cm, 5 cm, 10 cm, 20 cm, 50 cm, and 100 cm from the fiber entrance respectively. The members (situations) at each position are summarized in Table 1.

[0113] The spatial uniformity 112 at point 1 after 1 cm is not yet perfect. And the corresponding radial mixing as illustrated in the angular light distribution 122 is also incomplete. At point 3 after 5 cm, the spatial uniformity is almost perfect, and at point 4 after 10 cm, as seen in the angular light distribution 124, the radial mixing is also almost complete to fully cover.

[0114] In this example, the cross-section corner rounding is relatively large (radius is 15% of the fiber width). However, since the amount of radial mixing is expected to be proportional to the radius / width ratio, and we see proper angular mixing after 10 cm, even if the ratio is 10 times smaller (for example, the radius is 1.5% of the fiber width), the optical fiber is expected to provide sufficient radial mixing over a length of 1 meter.

[0115] Table 1

[0116]

[0117]

[0118] Embodiment Seven, Double-Stage Homogenization, Collimator

[0119] Additionally or alternatively, in another embodiment of the present invention, spatial and angular uniformity can be improved by implementing a two-stage homogenization scheme that includes an "optical fiber" or "integrator rod" and "Fourier transform optics" or just "Fourier optics". Such Fourier optics can be used as a "converter" between angular space and linear space. The Fourier optics can be positioned such that the exit of the first homogenization structure coincides with the first focal point of the Fourier optics, and the input of the second homogenization structure coincides with the second focal point of the Fourier optics. At the exit of the first stage, good spatial uniformity can be obtained, but the angular uniformity may not yet be optimal. The Fourier optics can convert the angular light distribution at the exit of the first homogenization stage into a spatial distribution at the entrance of the second homogenization stage; and vice versa (the spatial distribution at the exit of the first homogenization stage into the angular light distribution at the input of the second homogenization stage). The second stage fixes the non-uniformities in the spatial distribution and provides a spatially uniform exit. This also maintains the uniform angular light distribution presented at its entrance, assuming the shape of the distribution is square or rectangular and the corners are sharp enough. Thus, at the exit of the bipolar system, both spatial and angular uniformity are fully ensured and are practically independent of the input characteristics. Multiple (light) sources are properly mixed spatially and angularly, eliminating the problems of temperature differences or aging effects and providing optimal speckle reduction. In most cases, the natural divergence of the (one or more) laser beams will be sufficient to achieve good mixing over a reasonable length of the first fiber stage. And no additional diffusion will be needed, which would unnecessarily increase the optical spread of the laser beam. If the beam quality of the laser beam is too good, a small level of diffusion introduced by controlled bending of the first fiber stage or by placing a diffuser in front of the first integrator rod will be sufficient to achieve good mixing over a reasonable optical length of a few centimeters.

[0120] The Fourier optics can be implemented with, for example, an optical lens system.

[0121] Patent application WO2012139634 discloses a two-homogenization structure scheme. However, the optical lens system between the two stages is configured to image the exit of the first stage onto the entrance of the second stage, and a diffuser is placed in front of each stage.

[0122] Figure 12FIG. 0 shows an embodiment of the present invention, which includes a system 130 with a dual homogenization structure solution and a Fourier lens 131. In this embodiment, the output from the second homogenization structure 136 can be expanded and collimated onto a dimmer 138. The light beam (not shown) from the light source 132, such as a laser, can be square and have a sub-light source 139, and before entering the first homogenization structure 135, such as a rectangular integrating rod or an optical fiber, it passes through a focusing lens 133 and a static or moving diffuser 134. The diffuser can have a relatively low angular spread and is preferably adapted to work with the first homogenization structure 135, such as a rectangular integrating rod or an optical fiber, in this regard. At the exit of the first homogenization structure 135, there is a Fourier optical component, such as a Fourier lens 131, and then the light beam can enter the second homogenization structure 136, such as a square integrating rod or an optical fiber, before being collimated by a collimating lens 137 onto the dimmer 138.

[0123] The system 130 can be an optical steering system, where the dimmer 138 is the first dimmer among two (or more) dimmers. Alternatively, the system 130 can be a conventional single-dimmer system, where the dimmer 138 is the only dimmer.

[0124] If the first homogenization structure 135 is a rectangular integrating rod or an optical fiber, the aspect ratio of its cross-section can determine the ratio of the horizontal to vertical angles at the exit of the second stage. The collimating lens 137 after the bipolar integrator (or homogenization system) can convert or transform the horizontal and vertical angles into a uniform rectangular spot at the modulator 138. In this case, the first homogenization structure 135 is preferably rectangular with the same aspect ratio as the modulator 138. The spatial uniformity at the exit of the second homogenization structure 136 determines the angular light distribution after collimation. The second homogenization structure 136 can be square to create a symmetric PSF in the optical steering system. For a single-dimmer system, the square homogenization structure 136 can create and approximate a circular aperture in the optical path.

[0125] The minimum cross-section of the required second homogenization structure is determined by the angular subtense of the light source emitted in the first optical fiber. In the optical steering system, this cross-section is preferably kept as small as possible to maintain the point spread function as small as possible.

[0126] Although a circular or hexagonal point spread function may be more preferred, it is not possible to use a circular or hexagonal cross-section geometry for the second homogenization structure because only rectangular or square optical fibers will maintain the angular light distribution generated by the first stage. In addition, the circular cross-section geometry will not produce the required spatial uniformity.

[0127] In the case of implementing the second homogenization structure with optical fibers, rounding at the cross-sectional corners is not desirable because radial mixing will interfere with the requirements for maintaining the horizontal and vertical angular light distributions presented at the input of this stage. Therefore, it is desirable to limit the corner rounding to the minimum achievable and limit the length of the second stage to the minimum length required to obtain sufficient spatial mixing.

[0128] Embodiment Seven, Dual-Stage Homogenization, Imaging

[0129] Figure 13 Another embodiment of the present invention is shown, where the second homogenization structure 146 can be rectangular and the first homogenization structure 145 can be square. The light beam (not shown), such as a laser, from the light source 142 can be rectangular and have sub-light sources 149, and passes through a focusing lens 143 and a static or moving diffuser 144 before entering the first homogenization structure. The static or moving diffuser 144 can have a low angular spread and is preferably adapted to work with the first homogenization structure. In this embodiment, the output from the second homogenization structure 146 can be directly imaged onto the dimmer 148 by means of an imaging lens 147.

[0130] For a system with light control (including at least two dimmers), the first homogenization structure 145 can then determine the shape of the point spread function in the intermediate image. For a monotonic dimmer system, the first homogenization structure 145 can create and approximate a circular aperture in the optical path. The first homogenization structure 145 is preferably square or hexagonal in shape.

[0131] The second homogenization structure can provide radial (angular light distribution) mixing. The above-mentioned second homogenization structure includes an optical fiber with rounded cross-sectional corners. It can also convert a square or hexagonal angular light distribution into a more desirable circular distribution.

[0132] If the light source array is, for example, circular or square, rounding at the cross-sectional corners in the first homogenization structure can be tolerated. Then, there will be a circular (light) spot at the entrance of the second homogenization structure, which can match the shape (e.g., rectangular) of the second homogenization structure, but will result in unused system optical expansion.

[0133] Alternatively, the laser array can have a rectangular shape and an aspect ratio suitable for the dimmer. To maintain the rectangular angular distribution profile, the first homogenization structure should preferably be square, and the angle of corner rounding and the fiber length should be minimized.

[0134] Embodiment Eight, Dual-Stage Conventional Homogenization Structure

[0135] In another embodiment of the present invention, a two-stage homogenization or integration (uniformity) system is provided, which includes two conventional integrators, such as fused silica rods or hollow light pipes ("integrators"), preceded by a diffusing element (or "diffuser"), and including intermediate imaging (Fourier) optics and a dimming device. The "integrator" can be a "homogenization structure". This arrangement can be similar to Figure 12 or the arrangement shown in FIG. 13.

[0136] Examples of conventional integrators can be hollow light tunnels https: / / materion.com / - / media / files / precision-optics / data-sheets-2012 / light-tunnel-da ta-sheet.pdf?la=en&hash= 1B2EE007DE55470622DCA2D0A90842D6EDD0C01A , or solid rods https: / / www.newport.com / f / light-pipe-homogenizer .

[0137] An array of laser sources can be focused into the first square integrator. The second integrator can have a rectangular cross-sectional aspect ratio that matches the cross-sectional aspect ratio of the dimming device. The Fourier optics can be placed between the integrators to convert the angular light distribution at the output of the first homogenization structure into a spatial light distribution at the entrance of the second homogenization structure (and similarly, the uniform spatial light distribution at the exit of the first homogenization structure can be converted into a uniform angular light distribution at the entrance of the second homogenization structure).

[0138] To utilize all the available optical expansion at the entrance of the second homogenization structure, the angles at which the light from the laser array is coupled are ideally also asymmetrically distributed. This can be achieved if the laser array is arranged as a rectangle with the same cross-sectional aspect ratio as the dimming device and if the first homogenization structure is square. In this way, the angular light distribution of the light emitted into it is maintained, which is not the case for, for example, hexagonal rods.

[0139] In addition, a static or movable diffuser can be placed before the first homogenization structure, enabling good mixing with a minimum rod length. The static or movable diffuser can have a low angular spread and is preferably adapted to work with the first homogenization structure. However, a diffuser is not required before the second homogenization structure.

[0140] The cross-section of the first homogenization structure can determine the system aperture, where the system aperture becomes square instead of circular. If the physical aperture in the illumination system or the projection lens is circular, the above-mentioned system square aperture should be adapted to this circular aperture. The light loss caused by the unused optical étendue can be compensated by the improved adaptation of the light beam at the entrance of the integrating rod and by the elimination of the second diffuser. Overall, the optical étendue is better utilized, and more laser diodes can be coupled into the system, or the focal ratio number (f-number) of the system can be increased, which further benefits the contrast of the projector and reduces the size of the optical components.

[0141] In a preferred embodiment, the physical system apertures in the illumination system and the projection lens are also square.

[0142] Advantageously, the mixing of the individual light sources in the array, such as laser diodes, is almost perfect in both the spatial domain and the angular domain. For example, wavelength diversity for speckle reduction can be achieved by using only one light source, such as a laser diode, for each wavelength. By the method of WO 2012139634, a small number of light sources, such as laser diodes, will result in the need for a very strong diffuser to close the angular gap between the light sources, such as laser diodes, having the same wavelength. A strong diffuser will increase the PSF diameter, which is not desirable in a light steering system. It should be noted that in order to achieve optimal speckle reduction via angular diversity, it is recommended to move or vibrate the diffuser located in front of the first homogenization structure.

[0143] Embodiment Nine, bipolar, fiber optic homogenization structure

[0144] Figure 14 An embodiment of the present invention is shown, including a system 150 having a first homogenization structure 151, such as a rectangular optical fiber, with a cross-section of, for example, 160×90 μm. The system 150 can further include a second homogenization structure 152, such as a square optical fiber, which, for example, has a cross-section of, for example, 175×175 μm. A Fourier lens 153 is located between the two homogenization structures. The Fourier lens 153 is, for example, a fused silica ball lens, for example, having a diameter of 0.5 mm. The lengths of both optical fibers can be, for example, 30 mm.

[0145] Figure 15 The corresponding spatial light distributions 161 to 165 and angular light distributions 171 to 175 are shown respectively. The light source 180 can be a four-light source arrangement as Figure 5 shown. The entrance 181 and the exit 182 of the first homogenization structure 190 are further shown. The entrance 184 and the exit 185 of the second homogenization structure 191 are further shown.

[0146] At the entrance 181 of the first homogenization structure 190, the spatial distribution 161 is, for example, a square illumination spot of 40 μm, which does not completely fill the cross-section of the rectangular optical fiber. The corresponding angular light distribution 171 shows four discrete angles associated with four (light) sources.

[0147] At the exit 182 of the first homogenization structure 190, the spatial distribution 162 is a uniform filling corresponding to the cross-section of the rectangular optical fiber. However, the corresponding angular light distribution 172 remains at four discrete angles. This is because the symmetric angular profile remains horizontal and the vertical mirroring has no effect.

[0148] When the light has passed through the spherical lens 183, as indicated by the arrow, the spatial and angular profiles have "switched positions" (with some slight distortion and blurring). Thus, at the entrance 184 of the second homogenization structure 191, the spatial distribution 163 is now spread out at four discrete positions, and the corresponding angular light distribution 173 is homogeneous within a filled rectangle.

[0149] At the exit 185 of the second homogenization structure 191, the spatial distribution 164 is a uniform square profile, and the angular light distribution 174 is a filled rectangle identical to the entrance angular distribution 173 (since there is no effect of horizontal and vertical mirroring (reflection)). In the case where the second homogenization structure is an optical fiber with rounded cross-section corners, the final spatial and angular distributions will be represented as 165 and 175 respectively.

[0150] Thus, the gaps in the angular profile present at the input are closed without introducing any diffusion. Due to the spherical aberration of the Fourier lens, some blurring may be observed near the edges.

[0151] Even if only one of the four light sources is activated (operating), the angular and spatial output distributions still remain unchanged. The same is true when modifying the angle at which a single light source is coupled. Thus, even when the spatial and / or angular light distribution at the input changes, Figure 15 the setup described in can also provide stable angular and spatial distribution profiles.

[0152] Therefore, if the inputs of different primary colors from the light sources are different, the present invention can provide uniform illumination for each dimmer and the same uniform point spread function for each primary color. The best achievable common point spread function is limited by the primary color with the largest optical extension amount.

[0153] Although the present invention has been described above with reference to specific embodiments, this has been done for the purpose of elucidating the invention and not for limiting it. Those skilled in the art will understand that various adjustments and different combinations of the disclosed features are possible without departing from the scope of the invention.

Claims

1. An image projection system for use with a light source, the image projection system including a dimmer and a homogenizing structure having an elongate shape and adapted to receive light from the light source and direct the light onto the dimmer, wherein, The homogenizing structure has a rectangular structure and one or more bends, the homogenizing structure including a cross-sectional area having corners, wherein the shape of each of the corners is rounded, and wherein each bend radius is at least 200 to 1000 times greater than the length of the sides of the cross-sectional area.

2. The image projection system according to claim 1, wherein The homogenizing structure has a rectangular cross-section.

3. The image projection system according to claim 1, wherein The dimmer has an image area, and the aspect ratio of the cross-sectional area of the homogenizing structure is the same as the aspect ratio of the image area of the dimmer.

4. The image projection system according to claim 1, characterized in that, The homogenizing structure is adapted to assume different bend radii at different points in time, or the homogenizing structure is adapted to assume bend radii that vary with frequency.

5. The image projection system according to claim 1, wherein Comprising: A light source, At least a first homogenizing structure and a second homogenizing structure, each of the homogenizing structures having an inlet and an outlet, A Fourier optical system having a first focal point and a second focal point, wherein The light source, the first homogenizing structure, the Fourier optical system, and the second homogenizing structure are positioned adjacent to and continuously with each other, And the Fourier optical system is positioned such that the outlet of the first homogenizing structure coincides with the first focal point of the Fourier optical system, and the inlet of the second homogenizing structure coincides with the second focal point of the Fourier optical system.

6. The image projection system according to claim 1, wherein The shape of each of the corners is rounded with a radius of curvature, and the radius of curvature is less than 5% of the width of the homogenizing structure and greater than 1% of the width of the homogenizing structure.

7. A method for use with a light source and for diffusing light in an image projection system, the image projection system including a dimmer and a homogenizing structure, the homogenizing structure having an elongated shape and being adapted to receive light from the light source and direct the light onto the dimmer, the homogenizing structure including a cross-sectional area having corners, The method includes bending the homogenizing structure at one or more locations, the method including configuring each of the corners to be rounded corners, The method further includes the step of configuring each bend radius to be at least 200 to 1000 times greater than the length of the sides of the cross-sectional area.

8. The method according to claim 7, wherein The homogenizing structure has a cross-sectional area that is rectangular.

9. The method according to claim 7, wherein The dimmer has an image area, and the method includes configuring the aspect ratio of the cross-sectional area of the homogenizing structure to be the same as the aspect ratio of the image area of the dimmer.

10. The method according to claim 7, wherein The homogenizing structure assumes different bend radii at different points in time.

11. The method according to claim 10, wherein The bend radius varies with a frequency.

12. The method according to claim 7, wherein The rounded corners define a radius-of-curvature rounding, and the radius of curvature is less than 5% of the width of the homogenizing structure and greater than 1% of the width of the homogenizing structure.

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