System for forming a uniform illumination line that can be imaged as a small speckle line

Abstract

Disclosed is a system for forming a uniform illumination line that can be imaged as a small speckle line. The system includes: a laser configured to emit a collimated laser beam; and an illumination fan generator including one or more linear diffusers. The illumination fan generator is arranged and configured to: (i) receive the collimated laser beam, (ii) output a fan of diffused light planes such that the fan of planes diverges from rays formed on the farthest linear diffuser among the one or more linear diffusers, and (iii) cause an illumination line to be formed at the intersection of the fan of planes and an object.

Description

[0001] Relevant information of divisional application

[0002] This is a divisional application. The parent case of this divisional application is a patent application for invention with the application date of January 18, 2019, application number 201910049286.5, and invention title "System for Forming a Uniform Illumination Line that Can be Imaged as a Small Speckle Line". Technical Field

[0003] Describe a technique for generating a planar laser sheet for illuminating an object, such that the illumination line formed at the intersection of the planar sheet and the object is uniform and can be imaged as a despeckled line. Background Art

[0004] Laser is projected from a light source in the form of a sheet or a fan onto an object, and the intersection of the laser and the object forms an illumination line. In many applications, a camera is used to image the illumination line to determine the level of the surface of the object relative to a reference plane or the contour of the object. Bright spots or speckles have an adverse effect on the fidelity of the image of the illumination line. The bright spots are caused by parasitic reflections of the laser from the faceted surface of the object. The speckles are caused by the interference of coherent laser light, which has different phases caused by the reflection of coherent light from the optically rough surface of the object. These effects form an uneven and locally distorted image of the illumination line at (i) the camera that acquires the image of the illumination line, or (ii) the observer who observes the illumination line. Consequently, these effects may reduce the accuracy of laser-based measurements performed on the object. Summary of the Invention

[0005] The techniques described herein use a fan beam generator and a linear diffuser disposed between a light source and an object such that each of the fan beam generator and the linear diffuser diffuses the light transmitted therethrough along a predetermined direction. The fan beam generator itself can be a linear diffuser or can be one of a Powell lens or a cylindrical lens. Additionally, the fan beam generator and the linear diffuser can be moved relative to each other along a predetermined direction. In any of these cases, the laser transmitted through the fan beam generator and the linear diffuser is projected onto the object in the form of a sheet or a fan, where the intersection of the object and the sheet or fan forms an illumination line that (i) is uniform along a predetermined direction and (ii) has a Gaussian profile (or another profile associated with the laser emitted by the source) perpendicular to the predetermined direction, regardless of how the height of the object varies across the span of the illumination line. In the case where the fan beam generator and the linear diffuser are moved relative to each other, the uniform illumination line formed at the intersection of the sheet or fan and the object can be imaged (and / or observed) as a despeckled line.

[0006] According to one aspect of the disclosed technology, a system includes: a laser configured to emit a collimated laser beam; and an illumination fan generator including one or more linear diffusers. The illumination fan generator is arranged and configured to (i) receive the collimated laser beam, (ii) output a diffused light plane fan such that the plane fan diverges from the light rays formed on the farthest linear diffuser among the one or more linear diffusers, and (iii) form an illumination line at the intersection of the plane fan and an object.

[0007] The above and other embodiments may each optionally include, individually or in combination, one or more of the following features. In some embodiments, the linear diffuser includes one of a pseudo-random cylindrical array or a holographic optical element.

[0008] In some embodiments, the illumination fan generator may include a fan beam generator and a linear diffuser having a diffusing direction. Herein, the fan beam generator is arranged and configured to receive the collimated laser beam and form a fan beam, and the fan beam intersects the linear diffuser along light rays parallel to the diffusing direction. Additionally, the linear diffuser transmits the light corresponding to the light rays to form a plane fan. In some cases, the fan beam generator may include a linear diffuser. In some cases, the fan beam generator may include one of a cylindrical lens or a Powell lens. In some embodiments, the divergence angle of the fan beam formed by the fan beam generator is greater than a target divergence angle. Additionally, the spacing "d" between the fan beam generator and the linear diffuser is greater than a predetermined spacing to ensure that the length of the light rays formed by the fan beam on the linear diffuser is greater than a target length "L" X ". Herein, the predetermined spacing is proportional to the target divergence angle and the target length.

[0009] In some embodiments, the system may include a driver configured to move the linear diffuser cyclically relative to the fan beam generator. Herein, the cyclic movement is along the diffusing direction of the linear diffuser. Additionally, the system may include an image acquisition device arranged such that its optical axis forms an acute angle with respect to the diffused light plane fan and configured to form an image of the illumination line as a speckle-free image. Herein, the speckle-free image includes an average of a series of images of instances of the illumination line formed during an exposure time interval. Further, the driver is configured to deactivate the laser when the speed of the cyclic movement is lower than a predetermined speed, and the predetermined speed is inversely proportional to the exposure interval.

[0010] In some embodiments, the illumination fan generator may include a cylindrical shell-shaped linear diffuser arranged with its axis perpendicular to the propagation direction of the collimated laser beam and configured to (i) receive the collimated laser beam at an input portion of the cylindrical shell-shaped linear diffuser, (ii) form a fan-shaped beam along rays parallel to the diffusion direction, the fan-shaped beam intersecting an exit portion of the cylindrical shell-shaped linear diffuser, and (iii) transmit the light corresponding to the rays through the exit portion to form a planar fan. In some embodiments, the divergence angle of the fan-shaped beam formed by the input portion of the cylindrical shell-shaped linear diffuser is greater than the target divergence angle. Additionally, the diameter of the cylindrical shell-shaped linear diffuser is greater than a predetermined diameter to ensure that the length of the diffused light profile formed by the fan-shaped beam on the exit portion of the cylindrical shell-shaped linear diffuser is greater than the target length “L X ”. In this context, the predetermined diameter is proportional to the target divergence angle and the target length.

[0011] In some embodiments, the system may include a driver configured to rotate the cylindrical shell-shaped linear diffuser about its axis, the rotation being along the diffusion direction of the cylindrical shell-shaped linear diffuser. Additionally, the system may include an image acquisition device positioned such that its optical axis forms an acute angle with respect to the planar fan of diffused light and configured to form an image of the illumination line as a speckle-free image. In this context, the speckle-free image includes the average of a series of images of instances of the illumination line formed during an exposure time interval.

[0012] In some embodiments, the system may include an image acquisition device positioned such that its optical axis forms an acute angle with respect to the planar fan of diffused light and configured to form an image of the illumination line as a uniform line.

[0013] Certain aspects of the disclosed techniques may be implemented to achieve one or more of the following potential advantages. For example, according to the disclosed techniques, the quality of the illumination line along and perpendicular to the illumination line is better than that of the illumination line achievable by using only a Powell lens without an accompanying linear diffuser, as disclosed, because the unwanted diffraction and refraction effects caused by the Powell lens may transfer in the image of the illumination line. As another example, the light fan generated according to the disclosed techniques may be effectively Gaussian in a direction perpendicular to the fan plane, while in the fan plane, the illumination profile may be designed to meet various illumination profiles. As yet another example, the disclosed techniques effectively reduce the coherence of the laser without degrading the quality of the illumination line in a direction perpendicular to the line direction. As yet another example, by using a fan-shaped beam generator and then a linear diffuser, the power of the laser contained in the light source can be increased without causing laser safety issues due to the eye observing an extended (potentially high-intensity) light source.

[0014] Details of one or more embodiments of the disclosed technology are set forth in the following drawings and description. Other features, aspects, descriptions, and potential advantages will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figures 1A to 1B Aspects of an example of a laser-based imager that forms a uniform illumination line are shown.

[0016] Figures 2A to 2C Aspects of an example of a laser-based imager that forms a uniform illumination line that can be imaged as a small speckle line are shown.

[0017] Figure 3 Another example of a laser-based imager that forms a uniform illumination line that can be imaged as a small speckle line is shown.

[0018] Figures 4A to 4C Shows that can be Figure 1A , 2A and aspects of a linear diffuser that is part of a laser-based imager of 3.

[0019] Certain illustrative aspects of the disclosed technology are described herein in connection with the following description and drawings. However, these aspects represent only a few of the various ways in which the principles of the disclosed technology may be employed, and the disclosed technology is intended to encompass all such aspects and their equivalents. Other advantages and novel features of the disclosed technology will be readily understood from the following detailed description when considered in conjunction with the drawings. DETAILED DESCRIPTION

[0020] Figure 1A An example of a laser-based imager 100 that uses a uniform illumination line 137 is shown. Imager 100 includes a laser-based illumination fan source 102 and an image acquisition device 140. Source 102 has an optical axis 101 that is oriented (e.g.) along the z-axis herein and is configured to output a diffused light plane fan 135 along the optical axis and parallel to the (x, z) plane. Plane fan 135 is projected onto an object 190, and an illumination line 137 is formed at the intersection of the plane fan and the object. It should be noted that illumination line 137 follows the contour of object 190, whether the object has a curved surface or a flat surface.

[0021] Source 102 includes a laser 110 and an illumination fan generator 120. Laser 110 is arranged and configured to emit a laser as a collimated laser beam 111 along optical axis 101. The wavelength of the laser emitted by laser 110 can be in the range of 400 to 2000 nm. Illumination fan generator 120 is arranged and configured to receive collimated laser beam 111 and produce diffused light plane fan 135.

[0022] The illumination fan generator 120 includes: a fan-shaped beam generator 122 having the same optical axis as the optical axis 101; and one or more linear diffusers having a diffusion direction perpendicular to the optical axis 101, which diffusion direction is (for example) along the x-axis herein. The fan-shaped beam generator 122 and the one or more linear diffusers are distributed along the optical axis 101. The fan-shaped beam generator 122 is arranged and configured to diffuse the collimated laser beam 111 into a fan-shaped beam 123 along the x-axis. In Figure 1A In the example shown, the illumination fan generator 120 includes a single linear diffuser 132 having a diffusion direction perpendicular to the optical axis 101, which diffusion direction is (for example) along the x-axis herein. It should be noted that the fan-shaped beam generator 122 itself can be a linear diffuser having a diffusion direction along the x-axis, or can be one of a Powell lens or a cylindrical lens. In the latter case, each of the Powell lens or the cylindrical lens has optical power in the (y-z) plane and no optical power in the (x,z) plane. The fan-shaped beam generator 122 is supported by a first bracket 124, and the linear diffuser 132 is supported by a second bracket 134 spaced apart from the first bracket, such that the fan-shaped beam generator 122 is disposed between the laser 110 and the linear diffuser 132.

[0023] The laser 110 projects the laser beam 111 onto the fan-shaped beam generator 122 as a beam spot 113. The fan-shaped beam generator 122 transmits the light corresponding to the beam spot 113 to form a fan-shaped beam 123 parallel to the (x,z) plane. It should be noted that when the fan-shaped beam generator 122 is implemented as a linear diffuser, the fan-shaped beam 123 is formed by the transmitted light diffused along the x-axis (and not diffused along the y-axis). When the fan-shaped beam generator 122 is implemented as a Powell lens or a cylindrical lens, the fan-shaped beam 123 is formed by the transmitted light redirected along the x-axis (and not redirected along the y-axis). Thus, the fan-shaped beam generator 122 projects the fan-shaped beam 123 onto the linear diffuser 132 along the x-axis as light rays 127. It should be noted that when the fan-shaped beam generator 122 is implemented as a linear diffuser, the fan-shaped beam 123 of diffused light is projected onto the linear diffuser 132 as diffused light rays 127. The linear diffuser 132 transmits the light corresponding to the light rays 127 to form a diffused light plane fan 135 parallel to the (x,z) plane. It should be noted that the plane fan 135 is a superposition of fan-shaped beams 133 (which are parallel to the (x,z) plane), and each fan-shaped beam is formed by the light irradiated from the corresponding point of the light rays 127 diffused by the linear diffuser 132. Thus, the linear diffuser 132 projects the diffused light plane fan 135 onto the object 190 as a uniform illumination line 137.

[0024] In some embodiments, the linear diffuser 132 can be one of a linear diffuser random cylinder array (e.g., random in radius, numerical aperture (NA), and depth), a pseudo-random engineered cylinder array, or a holographic optical element, each of which is configured to provide a diffused light fan beam 133 when light passes through it at a point corresponding to the ray 127. Each fan beam 133 has a diffusion angle, which in this document is in the (x, z) plane and is determined by the characteristics of the cylinder array (e.g., the values of the radius, NA, and depth). The fan beam generator 122, when implemented as a linear diffuser, can be configured in the same or a similar manner as the linear diffuser 132. It should be noted that the fine structure and pseudo-random nature of the linear diffuser 132 and the fan beam generator 122 when implemented as a linear diffuser enhance the uniformity of the illumination line 137 along the x-axis. At the same time, the profile of the illumination line 137 (and the diffused ray 127) along the y-axis remains substantially the same as the profile of the beam spot 113 along the y-axis.

[0025] The disclosed linear diffuser 132 and the linear diffuser used as the fan beam generator 122 in some embodiments can be implemented as an engineered diffuser with appropriate parameters in the EDL (Engineered Diffuser Line) series manufactured by RPC Photonics of Rochester, New York. For example, Figure 4A is a side view in the (x - z) plane of the linear diffuser 422 in the EDL series. In this document, the surface of the linear diffuser varies along the x-axis (in this document, the x-axis is oriented in the left-right direction), but is constant along the y-axis (in this document, the y-axis is oriented in the in-out-of-page direction). Figure 4B Shows that the measured light intensity of the fan beam formed by the EDL - 40 has a top-hat angular profile 472. In this document, the light intensity of the fan beam is substantially constant within an angular range of [-20°, +20°] relative to the (y - z) plane, and drops abruptly (to substantially zero) at larger angles. More precisely, for an input beam spot with a 5 mm diameter and a detector angle of 0.25°, the full width at 90% (50%) is 39.9° (42.9°). Figure 4B Also shows that the scattering of the linear diffuser EDL - 40 is relatively uniform within the fan beam. Other models allow for a smaller divergence of the fan beam (e.g., a total divergence of 4° for the EDL - 4, as low as + / -2°) or a larger divergence of the fan beam (e.g., a total divergence of 120° for the EDL - 120, up to + / -60°). Figure 4Cis an image of the fan-shaped beam profile 474, which shows that for the linear diffuser in the EDL series, diffusion occurs only along one direction (along the x-axis in this text), and almost no diffusion occurs in the transverse direction (along the y-axis in this text). This ensures that the diffused light plane fan 135 does not thicken / widen, and thus ensures that the irradiation line 137 does not thicken / widen.

[0026] Referring again to Figure 1A , the image acquisition device 140 (e.g., a camera coupled to or integrated into the device housing common with the laser-based irradiation fan source 102) is arranged and configured to image the object 190 as irradiated by the uniform irradiation line 137. Here, the optical axis 142 of the image acquisition device 140 is arranged in the (y, z) plane and forms an acute angle SA (i.e., greater than 0 and less than 90°) with the optical axis 101 of the laser-based irradiation fan source 102. The image acquisition device 140 includes an image sensor and an optical subsystem that forms an image of the irradiation line 137 on the image sensor. In some embodiments, the diffused light plane fan 135, the plane of the image sensor of the image acquisition device 140, and the acute angle SA satisfy the Scheimpflug condition. The image sensor of the image acquisition device 140 is configured to convert the image of the irradiation line 137 into information for generating a digital image of the meridionally irradiated object 190.

[0027] Referring now to Figure 1B , the irradiation fan generator 120 outputs the diffused light plane fan 135 during the operation of the laser-based irradiation fan source. When an observer looks directly at the generator 120, e.g., when the observer's eye 142 is placed on or near the optical axis 101, the plane fan 135 intersects the eye along the contour 139. In these cases, the observer sees the light ray 127 on the linear diffuser 132, so the observer's eye 142 forms an image 145 of the light ray on the retina 144. If the length l X of the line image 145 extends long enough so that the light intensity applied to the retina (∝ optical power / length) does not exceed the safety threshold, then the observer will not experience discomfort or harm. Here, the safety threshold corresponds to a high level of laser safety. Additionally, to ensure that the light intensity on the retina 145 is below the mentioned safety threshold, the length L X of the light ray 127 on the linear diffuser 132 must exceed a specific target for a given input light intensity at the beam spot 113. To maximize the C6 safety correction factor, according to the laser safety standards set forth by the International Electrotechnical Commission (IEC), the length L X must be at least 10 mm, and the diffusion angle must be at least 6°. Thus, the length L X can be 10, 30, 50, or 100 mm. The length L of the light ray 127X can be controlled by: (i) the spacing d along the z-axis between the fan beam generator 122 and the linear diffuser 132, and (ii) the divergence angle of the fan beam 123. For example, for a given divergence angle, the length L X increases / decreases as the spacing d increases / decreases. As another example, for a given spacing d, the length L X increases / decreases as the divergence angle increases / decreases. It should be noted that in Figure 1B , the distance D between the observer's eye 142 and the linear diffuser 132 and the spacing d between the fan beam generator 122 and the linear diffuser 132 are not drawn to scale, and the ratio D / d can be as high as 10.

[0028] It should be noted that for an illumination fan generator having only a fan beam generator (e.g., the fan beam generator 122), if the observer looks directly at the illumination fan generator, then the observer will see a beam spot 113 on the fan beam generator 122. Thus, the observer's eye 142 will form an image of the beam spot 113 on the retina 144. For the same given input light intensity at the beam spot 113 discussed above in connection with the illumination fan generator 120, the light intensity applied to the retina by the image of the beam spot will most likely exceed the safety threshold mentioned. Thus, the illumination fan generator 120 can also meet the high level of laser safety satisfied by conventional illumination fan generators, but the laser power used by the disclosed illumination fan generator is higher than that of conventional illumination fan generators. Typical laser analysis devices or other machine vision devices limited to Class 3R lasers compliant with the IEC 60825 laser safety standard protect eye safety by providing a 5 mW laser beam through a 7 mm aperture at a distance of 100 mm from the apparent source. According to the aforementioned laser safety standard, if the apparent source cannot be imaged onto a point on the eye, then the C6 correction factor can be applied. This factor depends on the angular extent of the source and how the eye images it. Assuming the beam is Gaussian and has negligible thickness transverse to the axis of the fan, and assuming the extended source (i.e., the ray 127) is 10 mm long, C6 will provide a correction factor of ~30 for the AEL (Acceptable Exposure Limit) for the laser-based illumination fan source 102. Thus, the laser 110 of the laser-based illumination fan source 102 can be configured to provide up to 150 mW of laser beam (30x5) through a 7 mm aperture at a distance of 100 mm from the apparent source and still protect eye safety.

[0029] It should be noted that although uniform, the illumination profile 137 - formed at the intersection of the planar fan 135 output by the laser-based illumination fan source 102 with the object 190 - will still have speckle when imaged by the image acquisition device 140 or observed by the observer at an acute angle (e.g., SA). The improvements described below can reduce the speckle mentioned.

[0030] Figure 2A An example of a laser-based imager 200 is shown, where the imager 200 uses a uniform illumination line 237 that can be imaged (and / or observed) as a small speckle line. The imager 200 includes a laser-based illumination fan source 202 and an image acquisition device 240. In some embodiments, the image acquisition device 240 can be the image acquisition device 140 described above in connection with Figure 1A The source 202 has an optical axis 201 that is oriented (e.g.) along the z-axis herein and is configured to output a diffused light plane fan 235 along the optical axis and parallel to the (x, z) plane. The plane fan 235 is projected onto an object 290 and forms an illumination line 237 at the intersection of the plane fan 235 and the object 290.

[0031] The source 202 includes a laser 210 and an illumination fan generator 220. In some embodiments, the laser 210 can be the laser 110 described above in connection with Figure 1A The laser 210 is arranged to emit a laser as a collimated laser beam 211 along the optical axis 201. The illumination fan generator 220 is arranged and configured to receive the collimated laser beam 211 and generate a diffused light plane fan 235.

[0032] The illumination fan generator 220 includes: a sector beam generator 222 having the same optical axis as the optical axis 201; and one or more linear diffusers having a diffusion direction perpendicular to the optical axis 201, which diffusion direction is (e.g.) along the x-axis herein. The sector beam generator 222 and the one or more linear diffusers are distributed along the optical axis 201. The sector beam generator 222 is arranged and configured to diffuse the collimated laser beam 211 into a sector beam 223 along the x-axis. In the Figure 2A example shown, the illumination fan generator 220 includes a single linear diffuser 232 having a diffusion direction that also runs along the x-axis and is spaced apart from the sector beam generator 222 along the z-axis such that the sector beam generator 222 is disposed between the laser 210 and the linear diffuser 232. In some embodiments, the sector beam generator 222 and the linear diffuser 232 can be the sector beam generator 122 and the linear diffuser 132 described above in connection with Figure 1A respectively.

[0033] In Figure 2AIn the example shown, during operation of the source 202, at least one of the fan beam generator 222 and the linear diffuser 232 will cyclically move along the diffusion direction, which in this document is, for example, along the x-axis. Thus, the fan beam generator 222 is supported by the first linear stage 224, and the linear diffuser 232 is supported by the second linear stage 234. In some embodiments, the first linear stage 224 and the second linear stage 234 may include one or more of a guide, a motor, a voice coil, a piezoelectric, etc. The first linear stage 224 is arranged along the beam expansion direction and includes a first linear actuator 252 configured to cyclically move the first linear stage with the fan beam generator 222 in the beam expansion direction. The second linear stage 234 is arranged along the diffusion direction and includes a second linear actuator 254 configured to cyclically move the second linear stage with the linear diffuser 232 in the diffusion direction.

[0034] In Figure 2A the example shown, the source 202 also includes a driver 250 that is coupled to the laser 210 and to the first linear actuator 252 or the second linear actuator 254 or both. In other embodiments, the driver 250 is external to the source 202 and is coupled to the laser 210 and to the first linear actuator 252 and the second linear actuator 254. In this way, the driver 250 can send control signals to the laser 210 and to the first linear actuator 252 and the second linear actuator 254.

[0035] Referring now to the operation of the source 202, the laser 210 projects a laser beam 211 onto the fan beam generator 222 as a beam spot 213. The fan beam generator 222 transmits the light corresponding to the beam spot 213 to form a fan beam 223 parallel to the (x, z) plane. Thus, the fan beam generator 222 projects the fan beam 223 along the x-axis onto the linear diffuser 232 as light rays 227. The linear diffuser 232 transmits the light corresponding to the light rays 227 to form a diffused light plane fan 235 parallel to the (x, z) plane. It should be noted that the plane fan 235 is a superposition of fan beams 233 (which are parallel to the (x, z) plane), each fan beam 233 being formed by the linear diffuser 232 diffusing the light irradiated from the corresponding point of the light rays 227. Thus, the linear diffuser 232 projects the diffused light plane fan 235 onto the object 290 as irradiation lines 237.

[0036] In some embodiments, the fan beam generator 222 is stationary relative to the optical axis 201, and the linear diffuser 232 moves cyclically along the x-axis relative to the optical axis 201 (e.g., the driver 250 deactivates the first linear actuator 252 and activates the second linear actuator 254). In these cases, the fan beam generator 222 can be implemented as (i) a linear diffuser, or (ii) one of a Powell lens or a cylindrical lens. Herein, the stationary ray 227 will be formed at multiple positions of the moving linear diffuser 232, each position having its own local rough profile. Figure 2B Shows that when the linear diffuser 232 moves along the x-axis, the stationary ray 227 will be formed on a first scan path 231 having a length P X The length P X Can be 2, 3, 5, or 10 times larger than the length L of the stationary ray X Such that the local roughness at one "position" of the first scan path is randomly different from the local roughness at any other position of the first scan path. Herein, the positions of the first scan path 231 have the length L of the ray 227 X . In this way, multiple instances of the planar fan 235 formed by the moving linear diffuser 232 will be randomly different from each other, and thus multiple instances of the stationary illumination line 237 formed on the stationary object 290 will also be randomly different from each other. The randomly different speckle patterns corresponding to the multiple instances of the stationary illumination line 237 will be averaged during the exposure time of the image acquisition device 240, so the stationary illumination line 237 will be imaged as a small speckle line by the image acquisition device. It should be noted that in this case, the randomness of the speckle patterns corresponding to the multiple instances of the stationary illumination line 237 is at least partially caused by the random differences in the surface roughness of the linear diffuser 232 at different positions of the first scan path 231.

[0037] In some embodiments, the fan beam generator 222 moves cyclically along the x-axis relative to the optical axis 201, and the linear diffuser 232 is stationary relative to the optical axis 201 (e.g., the driver 250 activates the first linear actuator 252 and deactivates the second linear actuator 254). In these cases, the fan beam generator 222 is implemented as a linear diffuser, and it is referred to as the first linear diffuser 222. In the same context, the linear diffuser 232 is referred to as the second linear diffuser 232. Herein, the stationary spot 213 will be formed at multiple points of the moving first linear diffuser 222, each point having its own local roughness profile. Figure 2C Shows that when the first linear diffuser 222 moves along the x-axis, the stationary spot 213 will be formed on a second scan path 221 having a length p X The length p XIt can be 10, 20, 30, 50 or 100 times larger than the diameter of the beam spot, such that the local roughness at a "point" of the second scan path is randomly different from the local roughness at any other point of the second scan path. In this text, the points of the second scan path 221 have the size of the beam spot 213. In this way, multiple instances of the diffused light fan beam 223 formed by the moving fan beam generator 222 will be randomly different from each other, and thus multiple instances of the stationary diffused light rays 227 formed on the stationary second linear diffuser 232 will also be randomly different from each other. Consequently, multiple instances of the plane fan 235 formed by the stationary second linear diffuser 232 will be randomly different from each other, and thus multiple instances of the stationary illumination lines 237 formed on the object 290 will also be randomly different from each other. The randomly different speckle patterns corresponding to the multiple instances of the stationary illumination lines 237 will be averaged during the exposure time of the image acquisition device 240, so that the stationary illumination lines 237 will be imaged as small speckle lines by the image acquisition device. It should be noted that in this case, the randomness of the speckle patterns corresponding to the multiple instances of the stationary illumination lines 237 is at least partially caused by the random differences in the surface roughness of the first linear diffuser 222 at different points of the second scan path 221.

[0038] In some cases of the latter embodiment, both the first linear diffuser 222 and the second linear diffuser 232 move cyclically along the x-axis relative to the optical axis 201 (e.g., the driver 250 activates both the first linear actuator 252 and the second linear actuator 254). In this text, the phase of the relative movement between the first linear diffuser 222 and the second linear diffuser 232 is controlled by the driver 250 to be different from zero, such that the two linear diffusers are in motion relative to each other. In this case, the randomness of the speckle patterns corresponding to the multiple instances of the stationary illumination lines 237 is at least partially caused by the combination of: (i) the random differences in the surface roughness of the first linear diffuser 222 at different points of the second scan path 221, and (ii) the random differences in the surface roughness of the second linear diffuser 232 at different positions of the first scan path 231.

[0039] Refer again to Figure 2A, to ensure that the irradiation line 237 can be imaged as a small speckle line, the driver 250 causes the first linear stage 224 to hold the fan beam generator 222 stationary relative to the optical axis 201, and causes the second linear stage 234 to cyclically move the linear diffuser 232 along the x-axis relative to the optical axis 201 at a predetermined frequency. When the fan beam generator 222 is implemented as the first linear diffuser 222, to ensure that the irradiation line 237 can be imaged as a small speckle line, the driver 250 causes the first linear stage 224 or the second linear stage 234 or both to cyclically move the first linear diffuser 222 and the second linear diffuser 232 relative to each other and along the x-axis at a predetermined frequency. In either of these cases, the predetermined frequency of the relative motion can be in the range of 0.5 to 500 Hz. The specific value of the relative motion frequency f can be selected based on the desired exposure time Δt and the travel distance ΔX required to reduce the speckle contrast C (e.g., along the first scan path 231 or the second scan path 221). For example, the type of structured linear diffuser used in the irradiation fan generator 220 has features sized approximately 10 to 50 μm. To achieve a Δt = 5 ms (200 Hz) exposure with a speckle contrast C = 10%, the image acquisition device 240 averages over independent random speckle patterns every 5 ms or 20,000 times per second. The speckle pattern changes approximately for each micron traveled along the first scan path 231 and / or the second scan path 221, i.e., δx = 1 μm. It should be noted that the above parameters satisfy the following equation:

[0040]

[0041] According to EQ. (1), for example, a travel ΔX of approximately 1 mm will be sufficient at a relative motion frequency f = 20 Hz. These and other examples determined using EQ.1, such as various values of the travel-per-pattern δx, relative motion frequency, and travel distance, are outlined in Table 1.

[0042] Table 1

[0043] N Δt (ms) δx (μm) f (Hz) ΔX (mm) 100 5 1 20 1 100 5 1 2 10 100 5 1 1 20 100 5 10 20 10 100 5 10 2 100 100 5 10 1 200

[0044] In some embodiments, in addition to enabling the first linear actuator 252 or the second linear actuator 254 or both, the driver 250 may also gate the laser 210 by enabling / disabling the laser in the following manner. For simplicity, the gating will be explained for the case where the driver 250 disables the first linear actuator 252 and enables the second linear actuator 254, so the fan beam generator 222 is stationary relative to the optical axis 201 and the linear diffuser 232 is in motion relative to the optical axis 201. Herein, the driver 250 may enable the laser 210 when the speed of the linear diffuser 232 exceeds a predetermined speed and disable the laser when the linear diffuser has a speed less than the predetermined speed. Such deceleration conditions occur when the linear diffuser 232 changes direction as part of a motion cycle. Gating the laser 210 in this way ensures that there are enough random speckle patterns to average even when the exposure time is extremely short.

[0045] The parameters used to optimize the speckle reduction quality of the illumination beam 237 are the frequency of movement of the diffuser 232 relative to the fan beam generator 222; and the measure of the random variation of: (i) the surface roughness of the (second) linear diffuser 232 at different positions along the first scan path 231, and / or (ii) the surface roughness of the first linear diffuser 222 at different points along the second scan path 221. Another parameter used to optimize the speckle reduction quality of the illumination beam 237 is the difference between the divergence angle corresponding to the fan beam generator 222 (e.g., the first diffusion angle corresponding to the first linear diffuser 222) and the second diffusion angle corresponding to the (second) linear diffuser 232. For example, the divergence (first diffusion) angle is 5°, and the (second) diffusion angle is 40°. In general, the difference between the divergence (first diffusion) angle of the fan beam generator (first linear diffuser) 222 and the (second) diffusion angle of the (second) linear diffuser 232 can be 1%, 5%, 10%, 50%, 100%, 500%, or 1000%. This is because the main function of the (second) linear diffuser 232 is to significantly increase the uniformity of the light beam 127 projected by the fan beam generator (first linear diffuser) 222 onto the (second) linear diffuser and to reduce the speckle of the light beam 127. It should be noted that it is the fine structure and pseudo-random nature of the linear diffusers 222, 232 that enhance the uniformity and reduce the speckle contrast. Another parameter used to optimize the speckle reduction quality of the illumination beam 237 is the spacing d between the fan beam generator 222 and the linear diffuser 232. For example, the spacing d between the fan beam generator 222 and the linear diffuser 232 can be 1, 2, 3, 5, 20, 50, or 100 mm. It should be noted that, for example, the spacing d between the fan beam generator 222 and the second linear diffuser 232 is specified to optimize not only the speckle reduction quality of the illumination beam 237, but also the volume and / or apparent size of the package for the encapsulation generator 220.

[0046] The arrangement and functionality of the image acquisition device 240 are similar to those described above in connection with Figure 1AThe arrangement and functionality of the described image acquisition device 140. Herein, the image acquisition device 240 is arranged and configured to image an object 290 as irradiated by an irradiation line 237. The optical axis 242 of the image acquisition device 240 is arranged in the (y, z) plane and forms an acute angle SA with the optical axis 201 of the laser-based irradiation fan source 202. The image acquisition device 240 includes an image sensor and an optical subsystem that forms an image of the irradiation line 237 on the image sensor. It should be noted that due to the way the source 202 generates the irradiation line 237, the image of the irradiation line 237 formed during the exposure time is uniform and free of speckles. The image sensor of the image acquisition device 240 is configured to convert the image of the irradiation line 237 into information for generating a digital image of the object 290 irradiated by the line.

[0047] Subsequently described is the manner of optimizing the complexity of a laser-based irradiation fan source (e.g., 102 or 202), such as simplifying its components (e.g., the irradiation fan generator (e.g., 120 or 220) and the driver (e.g., 250)).

[0048] Figure 3 Another example of a laser-based imager 300 is shown, where the imager 300 uses a uniform irradiation line 337 that can be imaged (and / or observed) as small speckle lines. The imager 300 includes a laser-based irradiation fan source 302 and an image acquisition device 340. In some embodiments, the image acquisition device 340 can be any of the image acquisition devices 140 or 240 described above in connection with Figure 1A or 2A. The source 302 has an optical axis 301 that is (e.g.) oriented along the z-axis herein and is configured to output a diffused light plane fan 335 along the optical axis and parallel to the (x, z) plane. The plane fan 335 is projected onto an object 390 and forms an irradiation line 337 at the intersection of the plane fan and the object.

[0049] The source 302 includes a laser 310 and an irradiation fan generator 320. In some embodiments, the laser 310 can be any of the lasers 110 or 210 described above in connection with Figure 1A or 2A. The laser 310 is arranged to emit a laser as a collimated laser beam 311 along the optical axis 301. The generator 320 is arranged and configured to receive the collimated laser beam 311 and produce the diffused light plane fan 335.

[0050] The generator 320 includes a linear diffuser 322 supported by a cylindrical rotating stage 324. Herein, the cylindrical rotating stage 324 has a rotation axis 351 perpendicular to the optical axis 301 and a cross-section shaped like a circle parallel to the (y, z) plane. In Figure 3In the example shown, the axis of rotation 351 of the turntable 324 is parallel to the y-axis. The linear diffuser 322 is attached above the entire circumference of the side surface of the turntable 324 and thus forms a cylindrical shell-shaped linear diffuser having a diffusing direction tangent to the cylindrical shell.

[0051] In Figure 3 the example shown, during operation of the source 302, the cylindrical shell-shaped linear diffuser 322 will rotate about the y-axis, i.e., the cylindrical shell-shaped linear diffuser will rotate in the diffusing direction. Thus, the turntable 324 includes a rotational actuator 352 configured to rotate the cylindrical shell-shaped linear diffuser 322 in the diffusing direction. Herein, the source 302 also includes a driver 350 configured to communicate with the rotational actuator 352. In other embodiments, the driver 350 is external to the source 302 and communicates with the rotational actuator 352 via a corresponding communication channel.

[0052] In some embodiments, the diffusing characteristics of the cylindrical shell-shaped linear diffuser 322 may be the same as or similar to those of one of the following: (i) the linear diffusers 122 and 132 described above in connection with Figure 1A and (ii) the linear diffusers 222 and 232 described above in connection with Figure 2A And the cylindrical turntable 324 is configured to transmit the light emitted by the laser 310. For example, the cylindrical turntable 324 may comprise a material transparent to laser light, such as glass or plastic. As another example, the cylindrical turntable 324 may have slots parallel to the plane (x-z) and be filled with a medium (such as air, glass, plastic, etc.) that can transmit the laser light passing through the turntable.

[0053] Referring now to the operation of source 302, laser 310 projects a laser beam 311 onto an input portion 322A of a cylindrical shell-shaped linear diffuser 322 as a beam spot 313. It should be noted that the diffusion direction of the input portion 322A of the cylindrical shell-shaped linear diffuser 322 is along the x-axis. For this reason, the input portion 322A transmits the light corresponding to the beam spot 313 to form a fan beam 323A parallel to the (x, z) plane. Thus, the input portion 322A projects the fan beam 323A along the x-axis onto an output (diametrically opposed) portion 322B of the cylindrical shell-shaped linear diffuser 322 as a diffused light profile 327. It should be noted that the diffusion direction of the output portion 322B of the cylindrical shell-shaped linear diffuser 322 is still along the x-axis because the output portion 322B is diametrically opposed to the input portion 322A. For this reason, the output portion 322B transmits the light corresponding to the diffused light profile 327 to form a diffused light plane fan 335 parallel to the (x, z) plane. It should be noted that the plane fan 335 is a superposition of fan beams 323B (which are parallel to the (x, z) plane), each of these fan beams being formed by the output portion 322B diffusing the light irradiated from a corresponding point of the diffused light profile 327. Thus, the output portion 322B projects the diffused light plane fan 335 onto the object 390 as irradiation lines 337.

[0054] During operation of the source 302, the driver 350 enables the rotary actuator 352, which in turn causes the rotary stage 324 to rotate the cylindrical shell-shaped linear diffuser 322 about the y-axis such that its input portion 322A and output portion 322B continuously move in opposite directions. In this way, stationary (relative to the optical axis 301) beam spots 313 will be formed at multiple points on the moving (relative to the optical axis 301) input portion 322A, each point having its own local roughness profile. Consequently, multiple instances of the integral planar fan 323A formed by the moving input portion 322A will be randomly different from one another, and thus multiple instances of the stationary (relative to the optical axis 301) diffused light profile 327 formed on the moving (relative to the optical axis 301) output portion 322B will also be randomly different from one another. In addition, each of the multiple instances of the stationary diffused light profile 327 will be formed at a different location on the moving output portion 322B, each location having its own local roughness profile. Consequently, multiple instances of the planar fan 335 formed by the moving output portion 322B will be randomly different from one another, and thus multiple instances of the stationary illumination line 337 formed on the stationary object 390 will also be randomly different from one another. The randomly different speckle patterns corresponding to the multiple instances of the stationary illumination line 337 will be averaged over the exposure time of the image acquisition device 340, and thus the stationary illumination line 337 will be imaged by the image acquisition device as a speckle-free line. It should be noted that in this case, the randomness of the speckle patterns corresponding to the multiple instances of the stationary illumination line 337 is caused at least in part by the combination of: (i) the random differences in surface roughness at different points on the input portion 322A, and (ii) the random differences in surface roughness at different locations on the output portion 322B.

[0055] To ensure that the irradiation line 337 can be imaged as a small speckle line, the driver 350 rotates the rotary table 324 at a predetermined rotation frequency to rotate the cylindrical shell-shaped linear diffuser 322. In this way, the input portion 322A and the output portion of the cylindrical shell-shaped linear diffuser continuously move relative to each other along the x-axis at a predetermined speed. The predetermined rotation frequency is proportional to the ratio of the predetermined speed and the diameter of the cylindrical shell-shaped linear diffuser 322 (i.e., the distance along the z-axis between the input portion 322A and the output portion 322B). For diameters in the range of 5 to 25 mm, the predetermined rotation frequency can be in the range of 50 to 500 Hz. The specific value of the diameter of the cylindrical shell-shaped linear diffuser 322 and the rotation frequency can be selected based on a balance of the selected diffuser material, the required eye safety level, and the sector angle of the (diffused light plane sector 235) desired in the field. For example, a 30° (+ / -15°) linear diffuser material can be wound around a bar lens made of glass (e.g., N-SF8 material) with a diameter of 20 mm. The input beam 313 to the bar-lens-based irradiation fan generator 320 will be diffused by approximately + / -5 mm (corresponding to a 10 mm diffused light profile 327) when it reaches the exit face 322B of the bar. The light power at the exit face 322B of the bar "straightens" the fan beam 323A to make it approach a collimated state. Then, the final surface it passes through is the 30° linear diffuser material on the exit face 322B to provide an extended source condition on the exit face and homogenize the diffused light plane sector 235 for laser protection purposes. The rotation frequency at which the cylindrical shell-shaped linear diffuser 322 rotates to reduce the speckle contrast to a predetermined level can be determined as described above in conjunction with Figure 2A as described.

[0056] The arrangement and functionality of the image acquisition device 340 are similar to the arrangement and functionality of the image acquisition devices 140 or 240 described above in conjunction with Figure 1A or 2A. Here, the image acquisition device 340 is arranged and configured to image the object 390 as irradiated by the irradiation line 337. The optical axis 342 of the image acquisition device 340 is arranged in the (y, z) plane and forms an acute angle SA with the optical axis 301 of the laser-based irradiation fan source 302. The image acquisition device 340 includes an image sensor and an optical subsystem that forms an image of the irradiation line 337 on the image sensor. It should be noted that due to the way the source 302 generates the irradiation line 337, the image of the irradiation line 337 formed during the exposure time is uniform and free of speckles. The image sensor of the image acquisition device 340 is configured to convert the image of the irradiation line 337 into information for generating a digital image of the object 390 irradiated by the line.

[0057] In summary, the disclosed technology uses a laser that emits laser light, a fan beam generator, and one or more linear diffusers that have no relative motion or have relative motion between them to irradiate an object with a laser line. Herein, the fan beam generator itself can be a linear diffuser, or can be a Powell lens or a cylindrical lens. For the following reasons, the irradiation lines generated according to the disclosed technology are uniform and can be imaged (and / or observed) as small speckle lines. The angular diversity provided by one or more linear diffusers homogenizes the laser along their common diffusion direction, thereby avoiding diffraction defects and reducing bright spots on the object irradiated with a uniform irradiation line. The relative motion of the linear diffusers causes the speckle pattern of the irradiation line to change during the exposure time without affecting the width of the irradiation line along the transverse direction (perpendicular to the diffusion direction). In addition, the spatial profile of the irradiation line along the transverse direction remains the Gaussian profile of the emitted laser. In this way, at any slice intercepted along the propagation direction perpendicular to the diffusion direction and the transverse direction, the irradiation line will have the original Gaussian profile along the transverse direction, will be uniform in the diffusion direction, and will have a predictable line length controlled by the diffusion angles of two or more linear diffusers.

[0058] Several embodiments have been described in detail above, and various modifications are possible. The disclosed subject matter that includes the functional operations described in this specification can be implemented as an electronic circuit, computer hardware, firmware, or a combination thereof, such as the structural components disclosed in this specification and their structural equivalents.

[0059] For example, a driver (e.g., 150, 250, 350) can include at least a data processing device and a medium. The data processing device can be one or more hardware processors, e.g., a central processing unit (CPU), a graphics processing unit (GPU), or a combination thereof, each of which can include multiple processor cores. The medium is a computer-readable medium that can include both volatile and non-volatile memories, such as random access memory (RAM) and flash RAM. For example, the medium stores instructions that, when executed by the data processing device, cause the driver to implement aspects of the methods disclosed herein. The connectors (shown as dashes in Figure 1A 、 2A and 3) can be one or more of a USB connector, an Ethernet connector, or other network connectors. Generally, a connector can represent any data communication link and power transfer link or a combination thereof implemented either physically through a cable or wirelessly.

[0060] Although this specification contains many details, these should not be construed as limiting the scope of what may be claimed, but rather as descriptions of features specific to particular embodiments. Certain features that are described in this specification in the context of separate embodiments may also be implemented in combination within a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented separately or in any suitable sub-combination in multiple embodiments. In addition, although the features may be described above as acting in certain combinations and even initially claimed as such, in some cases, one or more features from a claimed combination may be excluded from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination.

[0061] Similarly, although operations are depicted in the drawings in a particular order, this should not be construed as requiring that such operations be performed in the particular order shown or in a sequential order, or that all illustrated operations be performed, to achieve the desired result. In some cases, multitasking and parallel processing may be advantageous. In addition, the separation of various system components in the foregoing embodiments should not be construed as requiring such separation in all embodiments.

[0062] Other embodiments are within the scope of the appended claims.

Claims

1. An optical system, which comprises: a laser configured to emit a collimated laser beam; a first linear diffuser including a linear diffused random cylindrical array that is random in radius, numerical aperture, and depth; and a second linear diffuser, wherein the first linear diffuser and the second linear diffuser are arranged and configured to receive the collimated laser beam at the first linear diffuser, project the diffused light from the first linear diffuser so that light rays are formed on the second linear diffuser, output a diffused light plane fan diverging from the light rays, and cause an illumination line to be formed at the intersection of the plane fan and an object, wherein the diffused light from the first linear diffuser includes a fan-shaped beam, wherein the fan-shaped beam diffuses in a first direction and substantially does not diffuse in a second direction transverse to the first direction, and wherein the fan-shaped beam is incident on the second linear diffuser along the diffusing direction of the second linear diffuser.

2. The optical system according to claim 1, wherein the length of the light rays is at least 10 mm.

3. The optical system according to claim 1, wherein the diffusion angle of the plane fan is at least 6°.

4. The optical system according to claim 1, wherein the fan-shaped beam from the first linear diffuser is a superposition of a plurality of fan-shaped beams from corresponding plural cylindrical surfaces of the linear diffused random cylindrical array, and wherein the diffusion angles of the corresponding fan-shaped beams of the plurality of fan-shaped beams are determined by the values of the radius, numerical aperture, and depth for each of the plural cylindrical surfaces.

5. The optical system according to claim 1, wherein the divergence angle of the fan-shaped beam is greater than a target divergence angle, wherein the distance between the first linear diffuser and the second linear diffuser is greater than a predetermined distance so that the length of the light rays is greater than a target length, the predetermined distance being proportional to the target divergence angle and the target length, and wherein when the object includes the retina of an eye, the target length of the light rays corresponds to the intensity of the illumination line on the retina of the eye.

6. The optical system according to claim 1, wherein the first linear diffuser and the second linear diffuser are configured to make the illumination line uniform.

7. The optical system according to claim 1, wherein at least one of the first linear diffuser and the second linear diffuser is configured to move along the diffusing direction of the first linear diffuser.

8. The optical system according to claim 7, wherein the first linear diffuser is configured to move along the diffusing direction.

9. The optical system according to claim 7, wherein the second linear diffuser is configured to move along the diffusing direction.

10. The optical system according to claim 7, wherein at least one of the first linear diffuser and the second linear diffuser is configured to move cyclically along the diffusing direction.

11. The optical system according to claim 10, wherein the phase of the relative movement between the first linear diffuser and the second linear diffuser is not zero.

12. An optical system, which comprises: A laser configured to emit a collimated laser beam; A fan beam generator; And A linear diffuser, wherein the linear diffuser includes a linear diffusive random cylinder array that is random in radius, numerical aperture, and depth, and Wherein the fan beam generator and the linear diffuser are arranged and configured to Receive the collimated laser beam at the fan beam generator, Project a fan beam from the fan beam generator such that the fan beam impinges on the linear diffuser and forms light rays on the linear diffuser, Output a diffused light plane fan that diverges from the light rays, wherein the plane fan diffuses in a first direction and is substantially non-diffusive in a second direction transverse to the first direction, and Cause an irradiation line to be formed at the intersection of the plane fan and an object.

13. The optical system according to claim 12, wherein at least one of the fan beam generator and the linear diffuser is configured to move along the light rays.

14. An optical system, which Comprises: A laser configured to emit a collimated laser beam; A first linear diffuser including a pseudo-random engineered cylinder array that is random in radius, numerical aperture, and depth; And A second linear diffuser, Wherein the first linear diffuser and the second linear diffuser are arranged and configured to Receive the collimated laser beam at the first linear diffuser, Project the diffused light from the first linear diffuser such that light rays are formed on the second linear diffuser, Output a diffused light plane fan that diverges from the light rays, and Cause an irradiation line to be formed at the intersection of the plane fan and an object, wherein the diffused light from the first linear diffuser includes a fan beam, wherein the fan beam diffuses in a first direction and is substantially non-diffusive in a second direction transverse to the first direction, and Wherein the fan beam impinges on the second linear diffuser along the diffusing direction of the second linear diffuser.

15. The optical system according to claim 14, wherein at least one of the first linear diffuser and the second linear diffuser is configured to move along the diffusing direction of the first linear diffuser.

16. An optical system, which Comprises: A laser configured to emit a collimated laser beam; A fan beam generator; And A linear diffuser including a pseudo-random engineered cylinder array that is random in radius, numerical aperture, and depth, and Wherein the fan beam generator and the linear diffuser are arranged and configured to Receive the collimated laser beam at the fan beam generator, Project a fan beam from the fan beam generator such that the fan beam impinges on the linear diffuser and forms light rays on the linear diffuser, Output a diffused light plane fan that diverges from the light rays, wherein the plane fan diffuses in a first direction and is substantially non-diffusive in a second direction transverse to the first direction, and Cause an irradiation line to be formed at the intersection of the plane fan and an object.

17. The optical system according to claim 16, wherein at least one of the fan beam generator and the linear diffuser is configured to move along the light rays.

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