Low speckle laser line generator

Abstract

A laser line generating assembly for projecting a low speckle laser line is provided. The laser line generation assembly includes a laser source, a beam splitter, and a sub-beam converter. The laser source generates a laser beam having temporal coherence. The beam splitter splits the laser beam into a plurality of incoherent sub-beams that propagate in the same propagation plane. The sub-beam converter generates a plurality of sheets of laser light, each sheet of laser light being associated with a respective one of the sub-beams. Each laser light sheet extends in a propagation plane. The laser light sheet intersects the projection plane to define at least partially overlapping laser line elements to form the low speckle laser line, the laser line elements having respective speckle patterns that are at least partially uncorrelated.

Description

Technical Field

[0001] The technical field generally relates to mitigating speckle in laser lines and, more particularly, to laser line generation assemblies and laser line generators for projecting a low speckle laser line on a projection plane. Background Art

[0002] The term "speckle" is used in the art to refer to the random, granular pattern that can be observed in the projection of a laser line or 2D shape on a rough surface. The appearance of light reflected from such a surface often includes variations in intensity, or bright and dark "spots" in the reflected pattern, resulting in shapes that deviate from the uniform intensity lines that are typically used for a variety of applications. The speckle effect is a result of the constructive and destructive interference of light waves that occurs when coherent light, such as a laser beam, is used as a light source.

[0003] Speckle is often considered problematic for applications using laser line generators. For example, in industrial machine vision systems, an object is illuminated by a laser line and the deviations of the reflected light from the shape and spatial characteristics of the illumination pattern are analyzed to provide information about the illuminated surface. The light intensity variations of speckle can lead to measurement errors.

[0004] There is still a need to improve laser line generation to mitigate the effects of speckle. Summary of the invention

[0005] According to one aspect, there is provided a laser line generation assembly for projecting a low speckle laser line on a projection plane, the laser line generation assembly comprising:

[0006] - a laser source generating a laser beam having a temporal coherence characterized by a coherence length;

[0007] -Laser line generator, including:

[0008] a beam splitter configured to split the laser beam into a plurality of incoherent sub-beams propagating in the same propagation plane; and

[0009] a sub-beam converter generating a plurality of laser light sheets, each laser light sheet being associated with a corresponding one of the sub-beams, each laser light sheet extending in a propagation plane, the laser light sheets intersecting the projection plane to define at least partially overlapping laser line elements to form the low speckle laser line, the laser line elements having respective speckle patterns that are at least partially uncorrelated.

[0010] In some embodiments, the beam splitter is disposed upstream of the sub-beam converter along the path of the laser beam. In other embodiments, the sub-beam converter is disposed upstream of the beam splitter along the path of the laser beam.

[0011] In some embodiments, the beam splitter includes an optical cavity that reflects the laser beam multiple times, wherein the optical path of the laser beam in each pass is longer than the coherence length, and each pass generates one of the sub-beams.

[0012] In some embodiments, the optical cavity includes a high reflectivity reflector and a partially reflective reflector extending in parallel. The optical cavity may include a rectangular transparent block, and the high reflectivity reflector and the partially reflective reflector may be defined by a reflective coating disposed along the respective rear and front surfaces of the rectangular transparent block. The reflective coating may be a metal or dielectric component. In some embodiments, the reflective coating defining the partially reflective reflector may be configured so that all sub-beams contain substantially the same optical power. In some embodiments, the reflective coating defining the partially reflective reflector may have a varying thickness along the front surface. In some embodiments, the optical cavity may include a light input including a portion of the rear surface of the rectangular transparent block that does not define the reflective coating of the high reflectivity reflector.

[0013] In some embodiments, the optical cavity can include an optical input positioned to receive the laser beam within the optical cavity at an input angle a having a non-zero value relative to a normal N to a plane of the high reflectivity reflector.

[0014] In some embodiments, the beam splitter includes a plurality of partially reflective mirrors sequentially positioned in the path of the laser beam.

[0015] In some embodiments, the beam splitter includes a transparent block made of a low reflectivity material and an input block made of a high reflectivity material, the input block having sides adjacent to sides of the transparent block.

[0016] In some embodiments, the sub-beam converter includes a diffraction grating.

[0017] In some embodiments, the sub-beam converter includes a diffuser.

[0018] In some embodiments, the sub-beam converter includes one or more line generating lenses.

[0019] In some embodiments, the sub-beam converter includes a line-generating microlens array.

[0020] In some embodiments, the sub-beam converter includes a cylindrical lens.

[0021] In some embodiments, the sub-beam converter also includes a beam conditioning block.

[0022] In some embodiments, the sub-beam converter includes:

[0023] a line generating lens disposed in the path of the laser beam between the laser source and the optical cavity and designed to fan out the laser beam in one direction within a propagation plane, so that each of the plurality of sub-beams has a fan-out shape within the propagation plane; and

[0024] - a volume diffraction grating located on the propagation plane so as to intersect the plurality of sub-beams, the volume diffraction grating diffracting each sub-beam into a plurality of diffraction orders distributed along one direction in the propagation plane, thereby providing a plurality of images of the sub-beams;

[0025] Wherein multiple images of each sub-beam form a laser light sheet associated with the corresponding sub-beam. The line generating lens can be a non-cylindrical lens or a linear diverging lens. The volume diffraction grating can include a planar glass substrate and a holographic pattern engraved or light-induced in the planar glass substrate. The volume diffraction grating can alternatively include a planar glass substrate and a plurality of metasurfaces deposited on the surface of the planar glass substrate. In one variation, the laser source is a single-mode laser diode. In some embodiments, the beam conditioning block is located before or after the volume diffraction grating. In some embodiments, a pseudo-telecentric illumination module is disposed between the volume diffraction grating and the projection plane. The pseudo-telecentric illumination module can include a first lens and a second lens, the first lens having a curvature configured to redirect the laser light sheet emitted from the volume diffraction grating into a pseudo-parallel light sheet, and the second lens having a curvature configured to focus the pseudo-parallel laser light sheet to form a thin line on the projection plane.

[0026] In some embodiments, the beamlet converter includes a series of line generating lenses located in the path of the beamlets and each designed to fan out a corresponding beamlet in the beamlet, and a cylindrical lens located between the series of line generating lenses and the projection plane.

[0027] In some embodiments, the beamlet converter is configured to convert each beamlet into a point source that generates a corresponding laser light sheet.

[0028] In some embodiments, the beam splitter and the sub-beam converter are integrated into a monolithic component.

[0029] According to another aspect, there is provided a laser line generator for projecting a low speckle laser line on a projection plane, the laser line generator being configured to receive as input a laser beam having a temporal coherence characterized by a coherence length, the laser line generator comprising:

[0030] - a beam splitter configured to split the laser beam into a plurality of incoherent sub-beams propagating in the same propagation plane; and

[0031] a sub-beam converter generating a plurality of laser light sheets, each laser light sheet being associated with a corresponding one of the sub-beams, each laser light sheet extending in a propagation plane, the laser light sheets intersecting the projection plane to define at least partially overlapping laser line elements to form a low-speckle laser line, the laser line elements having respective speckle patterns that are at least partially uncorrelated.

[0032] In some embodiments, a beam splitter is disposed upstream of a sub-beam converter along the path of the laser beam. In an alternative embodiment, a sub-beam converter is disposed upstream of the beam splitter along the path of the laser beam.

[0033] In some embodiments, the beam splitter includes an optical cavity that reflects the laser beam multiple times, wherein the optical path of the laser beam in each of the passes is longer than the coherence length, and each of the passes generates one of the sub-beams.

[0034] In some embodiments, the beam splitter includes a plurality of partially reflective mirrors sequentially positioned in the path of the laser beam.

[0035] In some embodiments, the beam splitter includes a transparent block made of a low reflectivity material and an input block made of a high reflectivity material, with a side of the input block adjacent to a side of the transparent block.

[0036] In some embodiments, the sub-beam converter includes a diffraction grating.

[0037] In some embodiments, the sub-beam converter includes a diffuser.

[0038] In some embodiments, the sub-beam converter includes a microlens array.

[0039] In some embodiments, the sub-beam converter includes a cylindrical lens.

[0040] In some embodiments, the sub-beam converter further includes a beam conditioning block, a one-dimensional diffuser, or a grating.

[0041] In some embodiments, the sub-beam converter includes one or more line-generating cylindrical lenses.

[0042] In some embodiments, the beamlet converter is configured to convert each beamlet into a point source that generates a corresponding laser light sheet.

[0043] In some embodiments, the beam splitter and the sub-beam converter are integrated into a monolithic component.

[0044] In some embodiments, the laser source is a single mode laser diode and the sub-beam converter includes a line generating cylindrical lens located between the laser diode and the beam splitter.

[0045] According to another aspect, there is provided a laser line generation assembly for projecting a low speckle laser line on a projection plane, the laser line generation assembly comprising:

[0046] - a laser source generating a laser beam having a temporal coherence characterized by a coherence length;

[0047] a highly reflective reflector and a partially reflective reflector extending in parallel and defining an optical cavity therebetween, the optical cavity having an optical input configured to receive laser light so that the laser beam reflects multiple passes within the optical cavity, the optical path of the laser beam in each pass being longer than the coherence length, each pass generating one of a plurality of incoherent sub-beams propagating in the same propagation plane;

[0048] a line generating lens arranged in the laser beam path between the laser source and the optical cavity and designed to fan out the laser beam in one direction in a propagation plane, so that each of the plurality of sub-beams has a fan-out shape in the propagation plane; and

[0049] a volume diffraction grating located in the propagation plane so as to intersect the plurality of sub-beams, the volume diffraction grating diffracting each sub-beam into a plurality of diffraction orders distributed in the one direction in the propagation plane, thereby providing a plurality of images of the sub-beam;

[0050] Thereby, the multiple images of each sub-beam form a corresponding laser light sheet extending in the propagation plane, which intersects the projection plane to define at least partially overlapping laser line elements to form a low-speckle laser line, the laser line elements having respective speckle patterns that are at least partially uncorrelated.

[0051] In some embodiments, the laser source is a laser diode.

[0052] In some embodiments, the optical cavity includes a rectangular transparent block, and the high reflectivity reflector and the partially reflective reflector are defined by a reflective coating disposed along the respective rear and front surfaces of the rectangular transparent block. The reflective coating may be a metal or a dielectric component. The reflective coating defining the partially reflective reflector may be configured so that all sub-beams contain substantially the same optical power. The reflective coating defining the partially reflective reflector may have a varying thickness along the front surface.

[0053] In some embodiments, the light input consists of a portion of the rear surface of the rectangular transparent block that is free of the reflective coating that defines the high reflectivity reflector.

[0054] In some embodiments, the optical input is positioned to receive the laser beam within the optical cavity at an input angle a having a non-zero value relative to a normal N to a plane of the high reflectivity reflector.

[0055] In some embodiments, the line generating lens is a non-cylindrical lens.

[0056] In some embodiments, the line generating lens is a linear diverging lens.

[0057] In some embodiments, a volume diffraction grating includes a planar glass substrate and a holographic pattern engraved or photoinduced in the planar glass substrate.

[0058] In some embodiments, a volume diffraction grating includes a planar glass substrate and a plurality of metasurfaces deposited on a surface of the planar glass substrate.

[0059] According to another aspect, there is provided a laser line generator for projecting a low speckle laser line on a projection plane, the laser line generator being configured to receive as input a laser beam having a temporal coherence characterized by a coherence length, the laser line generator comprising:

[0060] a highly reflective reflector and a partially reflective reflector extending in parallel and defining an optical cavity therebetween, the optical cavity having an optical input configured to receive a laser beam from the line generating lens such that the laser beam reflects multiple passes within the optical cavity, the optical path of the laser beam within each pass being longer than the coherence length, each pass generating one of a plurality of incoherent sub-beams propagating within the same propagation plane;

[0061] a line generating lens arranged in the path of the laser beam between the laser source and the optical cavity and designed to fan out said laser beam in one direction within a propagation plane, so that each of the plurality of sub-beams has a fan-out shape within said propagation plane; and

[0062] a volume diffraction grating located on the propagation plane so as to intersect the plurality of sub-beams, the volume diffraction grating diffracting each sub-beam into a plurality of diffraction orders distributed along the one direction within the propagation plane, thereby providing a plurality of images of the sub-beam;

[0063] Thereby, the multiple images of each sub-beam form a corresponding laser light sheet extending in the propagation plane, which intersects the projection plane to define at least partially overlapping laser line elements having respective speckle patterns that are at least partially uncorrelated to form a low-speckle laser line.

[0064] In some embodiments, the optical cavity includes a rectangular transparent block, and the high reflectivity reflector and the partially reflective reflector are defined by a reflective coating disposed along the respective rear and front surfaces of the rectangular transparent block. The reflective coating may be a metal or dielectric component. The reflective coating defining the partially reflective reflector may be configured so that all sub-beams contain substantially the same optical power. The reflective coating defining the partially reflective reflector may have a thickness that varies along the front surface.

[0065] In some embodiments, the light input consists of a portion of the rear surface of the rectangular transparent block that is free of the reflective coating that defines the high reflectivity reflector.

[0066] In some embodiments, the optical input is positioned to receive the laser beam within the optical cavity at an input angle a having a non-zero value relative to a normal N to a plane of the high reflectivity reflector.

[0067] In some embodiments, the line generating lens is a non-cylindrical lens.

[0068] In some embodiments, the line generating lens is a linear diverging lens.

[0069] In some embodiments, a volume diffraction grating includes a planar glass substrate and a holographic pattern engraved or photoinduced in the planar glass substrate.

[0070] Advantageously, a laser line generating assembly or laser line generator as described herein may improve the uniformity of the laser line, and / or increase the apparent source size, thereby providing more power within the same laser safety rating.

[0071] After reading the embodiments of the present invention with reference to the accompanying drawings, the features and advantages of the present invention will be better understood. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 is an elevation view of an illustrative laser line generating assembly according to one embodiment.

[0073] Figure 2 yes Figure 1 A schematic side view of a laser line generating assembly; Figure 2A yes Figure 2 Magnified view of area 2A.

[0074] FIG. 3A to FIG. 3D Different variants of beam splitters are schematically shown.

[0075] Figure 4 A diffraction grating used in a sub-beam converter according to one embodiment is schematically shown.

[0076] Figure 5A is a graphical representation of a line sheet formed by a combination of images of sub-beams having a fan-out shape diffracted by a diffraction grating; Figure 5B is a graphical representation of the intensity distribution of the light patterns of incoherent line sheets superimposed to form a line of uniform intensity.

[0077] Fig. 6A and Figure 6B The use of a linear diffuser and a cylindrical lens in a sub-beam converter are schematically shown, respectively.

[0078] Figure 7An embodiment is schematically shown in which the beam splitter and the sub-beam converter are integrated in a single monolithic component.

[0079] Figure 8 A configuration in which a sub-beam converter is located upstream of a beam splitter is schematically shown.

[0080] Fig. 9 The configuration in which the sub-beam converter includes a diffraction grating and a cylindrical lens as a beam conditioning block is schematically shown.

[0081] Fig. 10A and Fig. 10B Is without and with this cylindrical lens Fig. 9 Side view of the laser line generation assembly.

[0082] Fig.11A schematically shows a configuration including a line generating lens between a laser source and a beam splitter; Fig. 11B Schematically shows a similar Fig.11A A configuration comprising a beam conditioning block between the sub-beam converter and the volume diffraction grating; Fig. 11C A configuration comprising a pseudo-telecentric illumination module is schematically shown.

[0083] Fig.12 A configuration comprising a series of line generating lenses is schematically shown.

[0084] FIG. 13A to FIG. 13C A configuration comprising a sub-beam switch based on a cylindrical lens in combination with a beam conditioning block is schematically shown.

[0085] Fig.14 Schematically shown is a configuration in which the sub-beam converter includes a cylindrical lens and a one-dimensional diffuser or grating in combination with a beam conditioning block.

[0086] Fig.15 is a side view of a variation in which the beam conditioning block is embodied by a one-dimensional beam splitter diffraction grating to clone the generated lines into a multi-line pattern.

[0087] Fig.16A and Fig. 16B Top and side views, respectively, of a configuration providing a collimated laser line projector.

[0088] Fig.17A Schematically shows a configuration in which a laser beam is diffused into a laser light sheet upstream of a beam splitter, and the beam splitter comprises an optical cavity with an optical input located midway between a back reflector; Fig. 17B Shows Fig.17A The equivalent point source of the configuration. Fig. 17C Shows Fig.17A A variation of , wherein the beam splitter is positioned at an angle relative to the light sheet; and Fig.17D Shows Fig. 17C The equivalent point source of the configuration. DETAILED DESCRIPTION

[0089] In the following description, similar features in the figures are given similar reference numerals. In order not to unduly obstruct the drawings, certain elements may not be marked in certain figures if they have been mentioned in previous figures. It should also be understood that the elements in the figures are not necessarily drawn to scale, but the emphasis is placed on clearly illustrating the elements and structures of the present embodiment.

[0090] The terms "a", "an" and "one" are defined herein as "at least one", that is, unless otherwise specified, these terms do not exclude plural terms. Terms such as "substantially", "approximately" and "about" that modify values, conditions or characteristics of features of exemplary embodiments should be understood to mean that the values, conditions or characteristics are defined within an acceptable tolerance range for proper operation of the intended application of the exemplary embodiment.

[0091] Unless otherwise specified, the terms "connected" and "coupled" and their derivatives and variations herein refer to any structural or functional connection or coupling between two or more elements, whether direct or indirect. For example, the connection or coupling between elements may be mechanical, optical, electrical, logical, or any combination thereof.

[0092] In this specification, the terms "light" and "optical" and their derivatives and variations are used to refer to radiation in any appropriate region of the electromagnetic spectrum. Thus, the terms "light" and "optical" are not limited to visible light, but may also include, but are not limited to, the infrared or ultraviolet regions of the electromagnetic spectrum. Furthermore, those skilled in the art will appreciate that the definitions of the ultraviolet, visible, and infrared ranges in terms of spectral ranges and the dividing lines therebetween may vary depending on the technical field or definition being considered, and are not intended to limit the scope of application of the present technology.

[0093] In order to provide a more concise description, some quantitative expressions given herein may be qualified with the term "about". It should be understood that, whether or not the term "about" is explicitly used, each amount given herein is intended to refer to the actual given value, and is also intended to refer to the approximate value of the given value reasonably inferred based on ordinary skills in the art, including the approximate value generated due to the experimental and / or measurement conditions of the given value.

[0094] In this specification, the term "about" means within an acceptable error range for a particular value as determined by one of ordinary skill in the art, which depends in part on how the value is measured or determined, i.e., the limitations of the measurement system. Measurements of 10% accuracy are generally considered acceptable and include the term "about".

[0095] In this specification, when a wide range of values ​​is provided, any possible narrower ranges within the boundaries of the wide range are also considered. For example, if a wide range of values ​​from 0 to 1000 is provided, any narrower ranges between 0 and 1000 are also considered. If a wide range of values ​​from 0 to 1 is mentioned, any narrower ranges between 0 and 1, i.e., decimal values, are also considered.

[0096] According to some aspects, a laser line generation assembly and an associated laser line generator for projecting a low speckle laser line on a projection plane are provided.

[0097] A laser line can be understood as a one-dimensional or quasi-one-dimensional distribution of laser light that intersects the projection plane. The laser line generally has a limited length and a small thickness within the projection plane. For example, in some typical embodiments, the length of the laser line can be between about 50 mm and about 300 mm. However, it is easy to understand that in other embodiments, the laser line can be as short as about 0.1 mm or shorter, or as long as about 5000 mm or longer, without deviating from the protection range. In addition, in some typical embodiments, the thickness of the laser line can be, for example, between about 50 μm and about 500 μm. However, it is easy to understand that in other embodiments, the laser line can be as thin as about 5 μm or thinner, or as thick as about 5000 μm or thicker, without deviating from the protection range. The laser line generation assembly described herein can be used in various applications in which an object is illuminated by a laser line exhibiting low speckle. Such applications include, for example, industrial machine vision systems, etc., in which an object is illuminated by a laser line, and the deviation of the reflected light from the shape and spatial characteristics of the illumination pattern is analyzed to provide information about the illuminated surface. Other examples of use include projectors, visual alignment applications, and visual art applications.

[0098] refer to Figure 1 , Figure 2 and Figure 2A , shows a laser line generating assembly 30 according to one embodiment.

[0099] The laser line generation assembly 30 generally includes a laser source 32 configured to generate a laser beam 34 and a laser line generator 40. As explained in detail below, the laser line generator 40 includes one or more modules, components and / or devices that together transform the laser beam 34 into a low speckle laser line 31 at a projection plane 38.

[0100] Figure 1 , Figure 2 and Figure 2AA Cartesian coordinate system XYZ is used, where the Z axis corresponds to the light propagation direction of the laser beam 34 and the X axis corresponds to the orientation of the low speckle laser line 31. Thus, the XZ plane corresponds to the propagation plane 36 of the light in the entire assembly 30, and the XY plane corresponds to the projection plane 38. It is readily understood that this reference system is provided only for ease of reference. It is also readily understood that in some variations, the light may be deflected at various points between the light source 32 and the projection plane 38 such that the propagation direction or plane changes.

[0101] It will be readily appreciated that in some embodiments, the laser source 32 and the laser line generator 40 may be provided as a single system, while in other embodiments, the laser line generator 40 may be provided independently of the laser source 32. For example, in such a case, the laser line generator 40 may include a fiber optic input (not shown) connectable to an optical fiber carrying the laser beam 34 and configured to inject the laser beam 34 into the laser line generator 40. In other variations, the laser beam from the laser source may be optically coupled to the laser line generator in a free space configuration.

[0102] The laser source 32 can be based on any type of gain medium, such as, for example, a gas laser, a solid-state laser, a fiber laser, a dye laser, or a semiconductor (diode) laser. In some embodiments, the laser source is embodied by a laser diode, such as, for example, a Fabry-Perot (FP) laser diode, a distributed feedback (DFB) laser diode, a distributed Bragg reflector (DBR) laser diode, a quantum cascade (QCL) laser diode, a vertical cavity surface emitting laser (VCSEL) laser diode, etc. In some variations, the laser diode can be a spatial multimode laser diode. In other variations, the laser diode can be a single-mode laser diode.

[0103] As is known in the art, the light waves that make up the laser beam have strong coherence, i.e., they have a fixed phase relationship between their respective electric field values ​​at the same moment in time at different locations (spatial coherence) and at the same location at different times (temporal coherence). The temporal coherence of the laser beam 34 is characterized by the coherence length, which is defined as the propagation distance at which the coherence decays significantly. The coherence length is a commonly used parameter in laser optics, and its evaluation or determination (e.g., measurement with a Michelson or Mach-Zehnder interferometer) is well known in the art.

[0104] In some embodiments, the laser line generator 40 includes a beam splitter 42 configured to split the laser beam 34 into a plurality of incoherent sub-beams 44a ... 44n that propagate in the same propagation plane 36, and a sub-beam converter 90 that generates a plurality of laser light sheets 94a ... 94n, each laser light sheet 94a ... 94n being associated with a corresponding sub-beam in the sub-beams 44a ... 44n. Each laser light sheet 94a ... 94n also extends within the propagation plane 36. As will be explained in detail below, the laser light sheets 94a ... 94n intersect the projection plane 38 to define at least partially overlapping laser line elements 96a ... 96n to form the low speckle laser line 31. The laser line elements 96a ... 96n have respective speckle patterns that are at least partially uncorrelated.

[0105] Beam splitter

[0106] Those skilled in the art will readily appreciate that the temporal coherence between different sub-beams from the same source laser beam may be destroyed if the sub-beams follow different optical paths, thereby providing different delays between the associated electric fields. For example, in some embodiments, e.g. Figure 1 and Figure 2 In the embodiment of the embodiment of the invention, the beam splitter 42 may include an optical cavity 46 defined by a parallel rear reflector 48 and a front reflector 50. It will be readily appreciated that in the context of this specification, the designations of "front" and "rear" are used by convention only to refer to positions relative to the propagation plane 36, with the front reflector 50 being located on one side of the propagation plane 36 and the rear reflector 48 being located on one side of the laser source 32. The optical cavity 46 reflects the laser beam 34 through multiple passes, each pass corresponding to the propagation of light from one reflector to another and back. Each of these passes generates one of the sub-beams 44 extracted from the optical cavity 46 at the front reflector 50. The optical path traveled by the laser beam 34 in each of the multiple passes is longer than the coherence length of the laser beam, so that the sub-beams have no temporal coherence with each other. In some embodiments, for this design using an optical cavity of typical dimensions, any coherence length less than about 1 or 2 millimeters may be considered, for example, the distance between the rear reflector and the front reflector is between about 2 mm and about 10 mm. In other variations, the beam splitter may be sized to accommodate laser beams with longer coherence lengths. Thus, a cavity size between about 10 mm and about 25 mm may be used. Some multimode diodes inherently have coherence lengths of several hundred microns. Alternatively, the coherence length of a typical diode may be reduced to several hundred microns by providing the laser beam in a pulsed manner, thereby using a cavity size between about 0.5 mm and about 5 mm.

[0107] It is also easy for a person skilled in the art to understand that various configurations can be used to implement the beam splitter 42. FIG. 3A to FIG. 3D, for illustration purposes only, an example of such a configuration is shown.

[0108] More specifically refer to Figure 3A In some embodiments, the back reflector 48 of the optical cavity 46 is a high reflectivity reflector, while the front reflector 50 is a partially reflective reflector. For example, this configuration can be implemented in a rectangular transparent block 52 made of glass or other suitable material, with reflective coatings 57, 59 on its back surface 56 and front surface 58, each of which is designed according to the desired reflectivity. For example, the reflective coatings 57, 59 can be metal (e.g., aluminum layer) or dielectric (e.g., magnesium fluoride (MgF2), multilayer, Bragg mirror) components. The optical input 54 receives the laser beam 34 in the optical cavity 46 at an input angle α having a non-zero value relative to the normal N of the plane of the back reflector 48. In the illustrated embodiment, the optical input 54 is, for example, embodied by a portion of the back surface 56 of the transparent block 52, which is free of the reflective coating 57 and otherwise covers the rest of the back surface 56, and the transparent block 52 is positioned relative to the laser beam 34 according to the incident angle α. When the laser beam 34 enters the transparent block 52, its propagation direction may be deviated due to refraction at the interface between the material of the transparent block 52 and the surrounding air. After entering the transparent block 52, the laser beam 34 reflects back and forth between the rear reflector 48 and the front reflector 50. Whenever the laser beam 34 reaches the front surface 58 of the transparent block, a portion of the light is transmitted out of the optical cavity 46, thereby defining one of the sub-beams 44. According to the law of reflection, the remaining portion of the laser beam 34 is reflected at a reflection angle β equal to the incident angle.

[0109] In some embodiments, the front surface reflective coating 59 is configured so that all sub-beams 44a, ... 44n contain substantially the same optical power. This can be achieved, for example, by varying the thickness or number of sub-layers of the reflective coating 59 along the front surface 58. In some embodiments, the front surface reflective coating 59 can cover the entire front surface 58 of the transparent block 52, while in other variations, it can be disposed only at the location where the laser beam 34 strikes the front surface 58.

[0110] refer to Figure 3B, another example of an embodiment of the beam splitter 42 is shown. In the variation shown, the beam splitter 42 also includes an optical cavity 46 formed by a transparent block 52, the rear surface 56 of which is provided with a high reflectivity reflective coating 57. However, in this embodiment, the optical input 54 includes an input diffraction coupler 60, which receives the laser beam 34 according to an input angle perpendicular to the rear surface 56 of the transparent block 52, that is, the transparent block 52 is positioned so that the rear surface 56 is perpendicular to the propagation direction of the laser beam 34. The input diffraction coupler 60 is preferably embodied by a diffraction grating, which diffracts the laser beam 34 into non-zero diffraction orders. The diffraction grating can be engraved in the transparent block 52 or photoinduced in a photoresist, or embodied by a metasurface deposited on the rear surface 56 of the transparent block 52. For example, the diffraction grating can be configured to minimize zero-order light transmission and maximize ±1-order light transmission. According to Figure 3B The beam splitter 42 of the illustrated embodiment also includes a plurality of output diffraction couplers 62 positioned along the front surface 59 of the transparent block 56 to output portions of the laser beam 34 as sub-beams 44. The output diffraction couplers 62 may also be embodied, for example, by an engraved or light-induced diffraction grating or a metasurface deposited on the front surface 58 of the transparent block 52. The output diffraction couplers 62 are preferably configured such that each sub-beam 44 contains substantially the same optical power.

[0111] refer to Figure 3C , shows another example of a beam splitter 42 according to another embodiment. In this variation, the beam splitter 42 does not use an optical cavity, but instead splits the laser beam 34 by a plurality of partial reflectors 76, which are sequentially located in the path of the laser beam 34 and at a 45° angle relative to the propagation direction of the laser beam 34. The beam splitter 42 is positioned so that the laser beam 34 enters at normal incidence. In the variation shown, the beam splitter can be formed by a plurality of trapezoidal glass sheets 78, which are assembled to form a rectangular block 80, with a layer of semi-reflective material 82 extending at the interface between consecutive sheets 78. Of course, other geometric shapes can be used to achieve the same result.

[0112] refer to Figure 3D, shows yet another example of a beam splitter 42 according to an embodiment. In this variation, the beam splitter includes two blocks made of different glass materials: a transparent block 52 serving as an optical cavity 46, and an input block 64 having a side 66 adjacent to a side 74 of the transparent block 52. The transparent block 52 is made of a low reflectivity material, such as fused silica or other optical glass materials, such as N-bk7, N-SF2. The transparent block 52 has: a rear surface 56, which is provided with a rear surface high reflectivity coating 57, forming a high reflectivity rear reflector 48, and a parallel front surface 58, which is provided with a partially reflective front surface coating 59 designed to have a gradually increasing light transmission distribution, forming a partially reflective front reflector 50. The input block 64 is made of a high reflectivity material, such as, for example, N-SF6 or N-SF5. In the variation shown, the beam splitter is positioned so that the laser beam 34 enters the input block 64 at normal incidence through the rear surface 68 of the input block 64 and travels forward through the input block 64 toward the inclined front surface 70 provided with a reflective coating 71, thus acting as a mirror 72. The laser beam 34 is then reflected toward the common interface between the input block 64 and the adjoining side surfaces 66 and 74 of the transparent block 52. The difference in refractive index between the materials of the transparent block 52 and the input block 64 and the angle at which the laser beam 34 strikes the side surface 66 of the input block causes the laser beam 34 to enter the transparent block 52 at an angle close to the critical angle at which total internal reflection begins. This causes the laser beam 34 to enter the transparent block 52 at a very small angle relative to the side surface 74 of the transparent block 52 and therefore strike the front and back reflectors 48, 50 at angles close to normal incidence. This configuration causes the laser beam 34 to pass through the optical cavity a large number of times, thereby generating a large number of sub-beams 44.

[0113] Sub-beam converter

[0114] review Figure 1 and Figure 2 As mentioned above, the laser line generator 40 also includes a sub-beam converter 90, which generates a plurality of laser light sheets 94a, 94b, ... 94n.

[0115] The expression "light sheet" may be understood as light waves co-propagating in a plane in parallel, gradually diverging or gradually converging, such that a cross section of the light sheet forms a line. Preferably, the light sheet 94 has a diffraction-limited thickness transverse to the propagation plane 36. The laser light sheets 94a, 94b, ... 94n intersect the projection plane 38 to define at least partially overlapping laser line elements 96a, 96b, ... 96n to form a low-speckle laser line 31. The laser line elements 96a, 96b, ... 96n have respective speckle patterns that are at least partially uncorrelated.

[0116] More specifically refer to Figure 2 And further reference Figure 2A, the beam splitter 42 and the sub-beam converter 90 are configured together to produce a plurality of light sheets 94. Each light sheet 94 is incoherent with respect to the other light sheets 94, so that their respective intensities simply add up on the projection plane 38 in the region where they overlap, without intensity modulation caused by interference effects. Furthermore, since each individual light sheet 94 is coherent, it will produce a speckle pattern on the image plane of the observer. If the plurality of light sheets 94 illuminate a point P on the projection plane 38 at different incident angles θ1, θ2, as Figure 2A As shown, the speckle pattern produced at the image position of the observer 39 will be uncorrelated from light sheet to light sheet. The incoherent sum of uncorrelated speckle patterns will result in a speckle pattern with lower contrast. In one implementation, the minimum angle of incidence difference Δθ between two rays R1, R2 from two light sheets 94a, 94b at the same point P on the projection plane 38 is preferably about 1 degree or slightly larger or smaller so that their respective speckle patterns are uncorrelated. Smaller angles may still reduce the speckle contrast to an acceptable level. The angular difference is a function of the respective geometries of the viewing instrument at the observer 39, the laser source 32, and the projection plane 38.

[0117] For example, in some embodiments, the sub-beam converter 90 converts each sub-beam 44a, 44b, ... 44n into a point source 92a, 92b, ... 92n. Each point source 92a, 92b, ... 92n generates a corresponding one of the laser light sheets 94a, 94b, ... 94n. The point sources 92a, 92b, ... 92n from the plurality of sub-beams 44a, 44b, ... 44n are separated from each other to obtain the desired uncorrelated speckle pattern. It will be readily appreciated by those skilled in the art that the sub-beam converter 90 may include or be composed of various optical components or combinations of optical components that are easy to convert the sub-beam 44 into a laser light sheet 94, i.e., to induce divergence in the light rays constituting each sub-beam. As will be explained below by various examples, this can be achieved using diffraction gratings, lenses, etc.

[0118] See also Figure 4, in some embodiments, the sub-beam converter 90 may be embodied by or include a volume diffraction grating 98, which may be designed for transmission or reflection. The diffraction grating 98 may, for example, be a holographic pattern engraved or photoinduced into a planar glass substrate or into multiple metasurfaces deposited on the surface of a planar glass substrate. It will be readily appreciated that the volume diffraction grating may alternatively be embodied by any diffraction component or combination of components that diffracts a sub-beam into multiple diffraction orders. Each sub-beam 44 strikes the diffraction grating 98 at a different point and produces a corresponding laser light sheet 94. The use of a diffraction grating may keep the line thickness near the diffraction limit in the propagation plane 36. As is well known in the art, the grating has parameters such as grating period and depth that provide an image of each sub-beam 44 as multiple diffraction orders depending on the wavelength of the light. Reference Figure 5A , in one example, shows an example of the intensity distribution I of a line element generated from one of the point sources on the projection plane. The diffraction grating generates similar light patterns from each point source, which are superimposed on the projection plane to form a low speckle line. Figure 5B As shown, since the point sources are mutually incoherent, their respective light patterns are averaged to obtain a line of uniform intensity. A person skilled in the art will readily appreciate that other parameters of the laser line generator, such as the size, shape and distance between different optical components, are selected to provide uniform illumination of another desired light intensity distribution over the length of the line.

[0119] refer to Fig. 6A In another example, the sub-beam converter 90 can be embodied by or include a linear diffuser 100. The linear diffuser 100 can be, for example, a refractive microlens or a diffractive diffuser. Those skilled in the art will appreciate that, unlike a diffraction grating, a diffuser diffuses the light in each sub-beam in a random manner. Each sub-beam 44 strikes the diffuser 100 at a different point, and the light intensity therein is randomly diffused within the propagation plane, thereby generating a corresponding laser light sheet 94.

[0120] refer to Figure 6BIn another variation, the sub-beam converter 90 may include a cylindrical lens 110. In this implementation, all of the sub-beams 44 from the beam splitter 42 have been dispersed into light sheets 94a, 94b, ..., 94n (e.g., using one or more line generating lenses, as further explained below), which are converged into a focal plane 111 by the cylindrical lens 110. The relative position of the projection plane 38 relative to the focal plane 111 of the cylindrical lens 110 determines the size of the resulting laser line 31, and the resulting light sheet defocusing averages the intensity distribution of each sub-beam, thereby producing a more uniform illumination laser line. If the focal plane 111 of the cylindrical lens 110 is exactly located on the projection plane 38, all of the sub-beams 44a, 44b, ..., 44n will overlap each other. However, if the projection plane 38 is slightly offset compared to the focal plane 111 of the cylindrical lens 110, there will be a slight offset between each of the sub-beams 44, which may be beneficial or unhelpful, depending on the intensity distribution of the laser source 32.

[0121] Although in the above examples, the beam splitter 42 and the sub-beam converter 90 are described as physically separate components, in some variations, they can both be integrated into a single monolithic component. Figure 7 A variation is shown in which the beam splitter 42 has a Figure 3C A similar configuration is shown in which a plurality of partial reflectors 76 are sequentially positioned in the path of the laser beam 34 and form a 45° angle relative to the propagation direction of the laser beam 34. The beam splitter 42 is positioned so that the laser beam 34 enters at normal incidence. The sub-beam converter 90 is embodied by a series of integrated diffraction gratings 102a, 102b, ... 102n, which are located on the front surface 58 of the beam splitter 42, in the path of each sub-beam 44. The integrated diffraction gratings 102 generate the light sheet 94 directly from the front surface 58 of the beam splitter 42.

[0122] See also Figure 8 , shows an alternative embodiment in which a sub-beam converter 90 is located upstream of the beam splitter 42. The sub-beam converter may be, for example, a volume diffraction grating 98 aligned with the light input 54 of the beam splitter 42. The beam splitter shown in the illustrated embodiment is made of a plurality of partially reflecting mirrors 76, as described with reference to FIG. Figure 3C The diffraction grating 98 generates a seed light sheet 104 which is partially transmitted and partially reflected at each partial reflector 76. As a result, a plurality of laser light sheets 94 are directly output by the beam splitter 42. In fact, in this variation, the sub-beam converter 90 provides pre-conversion of the sub-beams into laser light sheets.

[0123] It will be readily appreciated that the laser line generating assembly 30 may include one or more additional components or assemblies for directing, focusing, shaping, filtering, or otherwise acting on the light.

[0124] Configuration example of laser line generation component

[0125] By way of example only and not limitation, different optical configurations of the laser line generating assembly 30 are described below.

[0126] refer to Fig. 9 , shows a configuration of a laser line generation assembly 30 for projecting a low speckle laser line on a projection plane 38 according to one embodiment. The laser line generation assembly 30 shown includes a laser source 32 that generates a laser beam 34 having a temporal coherence characterized by a coherence length. The laser source 32 can be embodied, for example, by a gas laser, a solid-state laser, a fiber laser, a dye laser, or a semiconductor (diode) laser. In some embodiments, the laser source is embodied by a laser diode, such as a Fabry-Perot (FP) laser diode, a distributed feedback (DFB) laser diode, a distributed Bragg reflector (DBR) laser diode, a quantum cascade (QCL) laser diode, a vertical cavity surface emitting laser (VCSEL) laser diode, etc. In some embodiments, Fig. 9 The configuration is suitable for using a single-mode laser diode as the laser source 32, but multi-mode laser diodes may also be used.

[0127] Still refer to Fig. 9 , the laser line generating assembly 30 shown also includes a beam splitter 42. The beam splitter may correspond to FIG. 3A to FIG. 3D Any variation shown in or its equivalent. Fig. 9 The laser line generation assembly 30 also includes a sub-beam converter 90 that generates a plurality of laser light sheets 94a, 94b, ... 94n. The sub-beam converter 90 may be embodied, for example, by any of the above-described variations. In one example, the sub-beam converter 90 may be a volume diffraction grating, such as a holographic pattern engraved or photoinduced into a planar glass substrate or a plurality of metasurfaces deposited on a surface of a planar glass substrate. Each laser light sheet 94a, 94b, ... 94n extends within the propagation plane 36. The laser light sheets 94a, 94b, ... 94n intersect the projection plane 38 to define at least partially overlapping laser line elements 96, 96b, ... 96n to form a low speckle laser line 31, the laser line elements 96, 96b, ... 96n having respective speckle patterns that are at least partially uncorrelated.

[0128] Fig. 9The laser line generation assembly 30 shown in FIG. 1 also includes a beam conditioning block 108 located downstream of the sub-beam converter 90. The beam conditioning block 108 may be embodied by any optical component that has a desired effect on the laser light sheet 94. In one example, the beam conditioning block 108 may be embodied by a cylindrical lens 110 located downstream of the volume diffraction grating 98 to focus the light in the propagation plane 36 at the projection plane 38. Fig. 10A and Fig. 10B is a side view of the laser line generating assembly without and with such a cylindrical lens, showing the difference in the optical path. In some variations, the beam conditioning block 108 may be embodied by one or more cylindrical lenses, non-cylindrical lenses, spherical lenses, aspherical lenses, or combinations thereof.

[0129] Fig.11A A configuration of a laser line generation assembly 30 for projecting a low speckle laser line on a projection plane 38 is shown according to one embodiment. The laser line generation assembly 30 shown includes a laser source 32 that generates a laser beam 34 having a temporal coherence characterized by a coherence length. The laser source 32 may be embodied, for example, by a gas laser, a solid-state laser, a fiber laser, a dye laser, or a semiconductor (diode) laser. In some embodiments, the laser source is embodied by a laser diode, such as a Fabry-Perot (FP) laser diode, a distributed feedback (DFB laser diode, a distributed Bragg reflector (DBR) laser diode, a quantum cascade (QCL) laser diode, a vertical cavity surface emitting laser (VCSEL) laser diode, etc. In some embodiments, Fig.11A The configuration may be adapted to use a single mode laser diode as the laser source 32, although multi-mode laser diodes may also be used.

[0130] Still see Fig.11A, the laser line generating assembly 30 shown also includes a high reflectivity reflector or back reflector 48 and a partially reflective reflector or front reflector 50, which extend in parallel and define an optical cavity 46 therebetween. For example, the optical cavity 46 may include a rectangular transparent block 52, and the high reflectivity reflector 48 and the partially reflective reflector 50 may be defined by reflective coatings 57, 59 disposed along respective back and front surfaces 56, 58 of the rectangular transparent block 52. The reflective coatings 57, 59 may be metal or dielectric components, as mentioned above. The reflective coating 59 defining the partially reflective reflector 50 may have a thickness that varies along the front surface 58 of the rectangular transparent block 56. The optical cavity 46 has an optical input 54, which is configured to receive the laser beam 34, such that the laser beam 34 is reflected multiple times within the optical cavity 46. The optical input 54 may be positioned to receive the laser beam 34 within the optical cavity 46 at an input angle α having a non-zero value relative to the normal N of the plane of the high reflectivity reflector 48. In some embodiments, the optical input may consist of a portion of the rear surface 56 of the rectangular transparent block 52 that is free of the reflective coating 57 defining the high reflectivity reflector 48. As described above, the optical path of the laser beam 34 in each of the multiple passes is longer than the coherence length. Each pass produces one of the multiple incoherent sub-beams 44a, 44b, ... 44n that propagate in the same propagation plane 36. In some variations, the reflective coating 59 defining the partially reflective reflector 50 is configured so that all sub-beams 44a, 44b, ... 44n contain substantially the same optical power. Those skilled in the art will readily appreciate that in other variations, the reflective coating 59 may be configured to provide a substantially uniform optical power. Fig.11A Use the following configuration in FIG. 3A to FIG. 3D A beam splitter as described in any one of .

[0131] Fig.11A The illustrated laser line generating assembly 30 also includes a line generating lens 112 disposed in the path of the laser beam 34 between the laser source 32 and the optical cavity 46. The line generating lens is designed to fan out the laser beam 34 in one direction ( Fig.11A The laser beam 34 is directed in the x direction in the reference frame of the optical cavity 46. Therefore, each of the multiple sub-beams 44a, 44b, ... 44n output by the optical cavity 46 has a fanned-out shape in the propagation plane. In some embodiments, the line generating lens 112 can be embodied by a non-cylindrical lens 112, which has an appropriate optical design to generate a uniform or pseudo-uniform line. For example, a linear diverging lens can be used, such as the linear diverging lens shown in U.S. Patent No. 4,826,299 (POWELL), the entire contents of which are incorporated herein by reference. Such a lens is sometimes referred to as a "Powell lens" in the art and this specification. The line generating lens 112 can advantageously increase the size of the apparent emitter of the laser source.

[0132] at last, Fig.11A The laser line generating assembly 30 includes a volume diffraction grating 98 positioned in the propagation plane so as to intersect the plurality of sub-beams 44a, 44b, ... 44n. The volume diffraction grating 98 diffracts each sub-beam 44a, 44b, ... 44n into a plurality of diffraction orders that are dispersed in the same direction as the fan-out shape of the sub-beam, i.e., the x-direction in the reference frame of FIG. 11. Thus, the volume diffraction grating 98 diffracts each sub-beam into a plurality of images of itself, such as Figure 5A As shown. Multiple images of each sub-beam 44a, 44b, ... 44n form a corresponding laser light sheet 94a, 94b ... 94n. In other words, the volume diffraction grating converts each sub-beam 44a, 44b, ... 44n into a point source 92a, 92b, ... 92n, thereby generating a corresponding laser light sheet 94a, 94b ... 94n. The diffraction grating 98 can be, for example, a holographic pattern engraved or optically induced into a planar glass substrate or a plurality of metasurfaces deposited on the surface of a planar glass substrate. Each laser light sheet 94a, 94b ... 94n extends within the propagation plane 36. The laser light sheets 94a, 94b ... 94n intersect the projection plane 38 to define at least partially overlapping laser line elements 96, 96b, ... 96n, thereby forming a low-speckle laser line 31, and the laser line elements 96, 96b, ... 96n have respective speckle patterns that are at least partially uncorrelated.

[0133] refer to Fig. 11B , showing that Fig.11A The configuration of the laser line generating assembly 30 has all the same features as the configuration of the laser line generating assembly 30, with the addition of a beam conditioning block 108 located before or after the volume diffraction grating 98. In some embodiments, the beam conditioning block 108 can include a cylindrical or non-cylindrical lens designed and positioned to focus the laser sheets 94a, 94b ... 94n to produce a thin line on the projection plane 38. In other embodiments, the beam conditioning block 108 can be a spherical or non-spherical lens for focusing the line on the projection plane 38 so as to correct the natural curvature of the best focus position to the plane. This variation can provide the thinnest possible line generated on the projection plane 38.

[0134] refer to Fig. 11C , shows the configuration of the laser line generating assembly 30, which has Fig.11A The configuration of FIG. 1 is identical to all features of FIG. 1 , including a pseudo-telecentric illumination module 120 disposed between the volume diffraction grating 98 and the projection plane 38. Those skilled in the art will appreciate that the term "telecentric" applies to optical elements having a constant, non-angular field of view. Fig. 11CIn the illustrated embodiment, the pseudo illumination module 120 includes a pair of cylindrical or non-cylindrical lenses 122 and 124. The first lens 122 has a curvature in the xz plane to redirect the laser light sheets 94a, 94b ... 94n emitted from the volume diffraction grating 98 into a pseudo parallel light sheet. The second lens 124 has a curvature in the yz plane for focusing the laser light sheets 94a, 94b ... 94n to form a thin line on the projection plane 38. The second lens 124 is located at a focal length (1f) relative to the diffraction grating 98.

[0135] Fig.12 A configuration of a laser line generation assembly 30 for projecting a low speckle laser line on a projection plane 38 is shown according to another embodiment. The illustrated laser line generation assembly 30 includes a laser source 32 that generates a laser beam 34 having a temporal coherence characterized by a coherence length. The laser source 32 may be embodied, for example, by a gas laser, a solid-state laser, a fiber laser, a dye laser, or a semiconductor (diode) laser. In some embodiments, the laser source is embodied by a laser diode, such as a Fabry-Perot (FP) laser diode, a distributed feedback (DFB) laser diode, a distributed Bragg reflector (DBR) laser diode, a quantum cascade (QCL) laser diode, a vertical cavity surface emitting laser (VCSEL) laser diode, or the like. In some embodiments, Fig.12 The configuration is suitable for using a single-mode laser diode as the laser source 32, but multi-mode laser diodes may also be used.

[0136] according to Fig.12 The laser line generating assembly 30 of embodiments may include a beam splitter, such as, for example FIG. 3A to FIG. 3D or its equivalent. Fig.12In the illustrated example of , the laser line generating assembly 30 includes a high reflectivity reflector or back reflector 48, and a partially reflective reflector or front reflector 50, which extend in parallel and define an optical cavity 46 therebetween. By way of example, the optical cavity 46 may include a rectangular transparent block 52, and the high reflectivity reflector 48 and the partially reflective reflector 50 may be defined by reflective coatings 57, 59 disposed along respective back and front surfaces 56, 58 of the rectangular transparent block 52. The reflective coatings 57, 59 may be metal or dielectric components, as mentioned above. The reflective coating 59 defining the partially reflective reflector 50 may have a thickness that varies along the front surface 58 of the rectangular transparent block 56. The optical cavity 46 has an optical input 54, which is configured to receive the laser beam 34 downstream from the line generating lens 112, so that the laser beam 34 is reflected within the optical cavity 46 to make multiple passes. The optical input 54 may be positioned to receive the laser beam 34 within the optical cavity 46 at an input angle α having a non-zero value relative to the normal N of the plane of the high reflectivity reflector 48. In some embodiments, the optical input may consist of a portion of the rear surface 56 of the rectangular transparent block 52 that is free of the reflective coating 57 defining the high reflectivity reflector 48. As described above, the optical path of the laser beam 34 in each of the multiple passes is longer than the coherence length. Each pass produces one of a plurality of incoherent sub-beams 44a, 44b, ... 44n that propagate in the same propagation plane 36. In some variations, the reflective coating 59 defining the partially reflective reflector 50 is configured so that all sub-beams 44a, 44b, ... 44n contain substantially the same optical power.

[0137] Still reference Fig.12 , the laser line generating assembly 30 shown includes a sub-beam converter 90, which is embodied by a series of line generating lenses 112a, 112b, ... 112n, which are located in the path of the sub-beams 44a, 44b, ... 44n, followed by a cylindrical lens 108 as a beam conditioning block. The line generating lenses 112 generate corresponding laser light sheets, which are laterally focused to the propagation plane by the cylindrical lens 108. Each light generating lens 112 is designed to focus in one direction ( Fig.12 The line generating lens 112 fans out corresponding sub-beams in the sub-beams 44a, 44b, ... 44n in the x-direction in the reference frame of FIG. In some embodiments, the line generating lens 112 may be embodied by a uniform or pseudo-uniform line cylindrical lens 112 with a suitable optical design. A so-called Powell lens as defined above may be used.

[0138] refer to FIG. 13A to FIG. 13C , shows a further embodiment of a laser line generation assembly 30, which is particularly useful for generating shorter lines than the previous embodiments.

[0139] In all illustrated variations of this embodiment, the illustrated laser line generation assembly 30 includes a laser source 32 that generates a laser beam 34 having a temporal coherence characterized by a coherence length. The laser source 32 may be embodied, for example, by a gas laser, a solid-state laser, a fiber laser, a dye laser, or a semiconductor (diode) laser. In some embodiments, the laser source is embodied by a laser diode, such as a Fabry-Perot (FP) laser diode, a distributed feedback (DFB laser diode), a distributed Bragg reflector (DBR) laser diode, a quantum cascade (QCL) laser diode, a vertical cavity surface emitting laser (VCSEL) laser diode, etc. In some embodiments, Fig.12 The configuration may be adapted to use a single mode laser diode as the laser source 32, although multi-mode laser diodes may also be used.

[0140] according to FIG. 13A to FIG. 13C In an embodiment, the laser line generating assembly 30 may include a beam splitter, such as, for example FIG. 3A to FIG. 3D , or their equivalents. The laser line generating assembly 30 as shown includes a high reflectivity reflector or back reflector 48, and a partially reflective reflector or front reflector 50, which extend in parallel and define an optical cavity 46 therebetween. For example, the optical cavity 46 may include a rectangular transparent block 52, and the high reflectivity reflector 48 and the partially reflective reflector 50 may be defined by reflective coatings 57, 59 disposed along respective back and front surfaces 56, 58 of the rectangular transparent block 52. The reflective coatings 57, 59 may be metal or dielectric components, as mentioned above. The reflective coating 59 defining the partially reflective reflector 50 may have a varying thickness along the front surface 58 of the rectangular transparent block 56. The optical cavity 46 has an optical input 54, which is configured to receive the laser beam 34 downstream from the line generating lens 112, so that the laser beam 34 is reflected within the optical cavity 46 to make multiple passes. The optical input 54 may be positioned to receive the laser beam 34 within the optical cavity 46 at an input angle α having a non-zero value relative to the normal N of the plane of the high reflectivity reflector 48. In some embodiments, the optical input may consist of a portion of the rear surface 56 of the rectangular transparent block 52 in which the reflective coating 57 defining the high reflectivity reflector 48 is absent. As described above, the laser beam 34 has an optical path longer than the coherence length within each of the multiple passes. Each pass produces one of the multiple incoherent sub-beams 44a, 44b, ... 44n propagating in the same propagation plane 36. In some variations, the reflective coating 59 defining the partially reflective reflector 50 is configured so that all sub-beams 44a, 44b, ... 44n contain substantially the same optical power.

[0141] Still refer to FIG. 13A to FIG. 13C, the laser line generation assembly 30 shown comprises a sub-beam converter 90 based on a cylindrical lens 110, in combination with a beam conditioning block 108. The beam conditioning block 108 may be embodied, for example, by a cylindrical lens configured and positioned to focus the line on its coarseness axis. The length of the low speckle laser line 31 is the size of the image of the laser source 32 passing through the laser line generator 40. Fig. 13B In a variation of , an upstream lens, such as, for example, another cylindrical lens or the line generating lens 112 as described above, may be used between the laser source 32 and the beam splitter 42 to increase the size of the image of the laser source 32. Alternatively, as Fig. 13C As shown, a series of line generating lenses 112a, 112b, ... 112n may be located in the path of the sub-beams 44a, 44b, ... 44n between the beam splitter 42 and the sub-beam converter 90.

[0142] Fig.14 A laser line generation assembly 30 for projecting a low speckle laser line at a projection plane 38 is shown according to another embodiment. The laser line generation assembly 30 shown includes a laser source 32 that generates a laser beam 34 having a temporal coherence characterized by a coherence length. The laser source 32 may be embodied, for example, by a gas laser, a solid-state laser, a fiber laser, a dye laser, or a semiconductor (diode) laser. In some embodiments, the laser source is embodied by a laser diode, such as, for example, a Fabry-Perot (FP) laser diode, a distributed feedback (DFB) laser diode, a distributed Bragg reflector (DBR) laser diode, a quantum cascade (QCL) laser diode, a vertical cavity surface emitting laser (VCSEL) laser diode, or the like. In some embodiments, Fig.14 The configuration is suitable for using a single-mode laser diode as the laser source 32, but multi-mode laser diodes may also be used.

[0143] according to Fig.14 The laser line generating assembly 30 of an embodiment of may include a beam splitter, such as, for example FIG. 3A to FIG. 3D or its equivalent. Fig.12In the illustrated example of , the laser line generating assembly 30 includes a high reflectivity reflector or back reflector 48, and a partially reflective reflector or front reflector 50, which extend in parallel and define an optical cavity 46 therebetween. For example, the optical cavity 46 may include a rectangular transparent block 52, and the high reflectivity reflector 48 and the partially reflective reflector 50 may be defined by reflective coatings 57, 59 disposed along respective back and front surfaces 56, 58 of the rectangular transparent block 52. The reflective coatings 57, 59 may be metal or dielectric components, as mentioned above. The reflective coating 59 defining the partially reflective reflector 50 may have a thickness that varies along the front surface 58 of the rectangular transparent block 56. The optical cavity 46 has an optical input 54, which is configured to receive the laser beam 34 downstream from the line generating lens 112, so that the laser beam 34 is reflected within the optical cavity 46 to make multiple passes. The optical input 54 may be positioned to receive the laser beam 34 within the optical cavity 46 at an input angle α having a non-zero value relative to the normal N of the plane of the high reflectivity reflector 48. In some embodiments, the optical input may consist of a portion of the rear surface 56 of the rectangular transparent block 52 in which the reflective coating 57 defining the high reflectivity reflector 48 is absent. As described above, the optical path of the laser beam 34 in each of the multiple passes is longer than the coherence length. Each pass produces one of a plurality of incoherent sub-beams 44a, 44b, ... 44n that propagate in the same propagation plane 36. In some variations, the reflective coating 59 defining the partially reflective reflector 50 is configured so that all sub-beams 44a, 44b, ... 44n contain substantially the same optical power.

[0144] Still reference Fig.14 , the laser line generation assembly 30 shown includes a sub-beam converter 90, which is embodied by a cylindrical lens 110 combined with a one-dimensional diffuser or grating 116, so that the laser light sheets 94 from different sub-beams 44 can overlap on the projection plane 38 and have an offset between them, thereby uniformizing the final power distribution in the low-speckle laser line 31. A beam conditioning block 108 can be provided between the sub-beam converter 90 and the projection plane. Fig.15 In another variation, the beam conditioning block 108 may be embodied by a one-dimensional beam splitter diffraction grating to clone the generated lines into a multi-line pattern.

[0145] See also Fig.16A and Fig. 16B, respectively, show a top view and a side view of another example of an embodiment, wherein the end result is a collimated laser line projector. In this variation, a sub-beam converter 90 disposed upstream of the beam splitter 42 includes a line generating lens 120 and a focusing cylindrical lens 122, which are used to initially convert the incoming collimated laser beam 34 into an initial light sheet 93 of parallel rays without a point source. The initial light sheet 93 then enters the beam splitter 42 to create a plurality of sub-beams, each of which already contains a plurality of laser light sheets 94. In this embodiment, each laser light sheet 94 is defined by parallel rays and therefore has no point sources. The laser light sheets 94 are then refocused by the cylindrical lens 110 onto the projection plane 38 so that they overlap. Since each laser light sheet 94 that overlaps at the projection plane is also collimated, the resulting laser line will be collimated.

[0146] refer to Fig.17A , shows another configuration example of the laser line generating assembly 30. In this example, the beam splitter 42 is embodied by a transparent block 52 having: a rear reflector 48, which is made of, for example, a highly reflective rear surface reflective coating 57, and a front reflector 50, which is made of, for example, a partially reflective front surface reflective coating 59. The sub-beam converter 90 is embodied by a cylindrical lens 110 or a line generating lens as defined above, designed to diffuse the laser beam 34 into the seed light sheet 104. The beam splitter 42 has a light input 54, which is arranged in the middle of the length of the rear reflector, for example, by a small hole in the rear surface reflective coating 57. As Fig. 17B As schematically shown in , the result of this configuration is equivalent to placing multiple point sources 92 at different distances behind the light input 54 of the beam splitter 42. The distances between these different point sources provide sufficient optical path length differences to have incoherent light sheets. In addition, this distance separation provides an angular difference between each sub-beam to produce uncorrelated speckle patterns on the projection plane and reduce overall speckle.

[0147] refer to Fig. 17C , a similar configuration as 17A can be made, but this time, the beam splitter 42 is positioned at an angle relative to the seed light sheet 104. In addition, the input light sheet 54 entering the beam splitter 42 is now located more at the bottom of the splitter 42 rather than around the center. Fig.17D As shown, increasing this angle produces point source separation in the x-axis and z-axis. This positional separation facilitates the angular differences between the individual sub-beams at all positions on the generated line 38. Preferably, the incident angle of the light sheet should be greater than about half of the full divergence angle of the light sheet.

[0148] Of course, many modifications may be made to the embodiments described herein without departing from the scope of protection.

Claims

1. A laser line generating assembly for projecting a low speckle laser line on a projection plane, the laser line generating assembly comprising: - a laser source generating a laser beam having a temporal coherence characterized by a coherence length; - A laser line generator comprising: a beam splitter configured to split the laser beam into a plurality of incoherent sub-beams propagating in the same propagation plane; as well as a sub-beam converter generating a plurality of laser light sheets, each laser light sheet being associated with a corresponding one of the sub-beams, each laser light sheet extending within the propagation plane, the laser light sheets intersecting the projection plane to define at least partially overlapping laser line elements to form the low speckle laser line, the laser line elements having respective speckle patterns that are at least partially uncorrelated. 2 . The laser line generating assembly of claim 1 , wherein the beam splitter is arranged upstream of the sub-beam converter along the path of the laser beam.

3. The laser line generating assembly of claim 1, wherein the sub-beam converter is disposed upstream of the beam splitter along the path of the laser beam.

4. The laser line generating assembly according to any one of claims 1 to 3, wherein the beam splitter comprises an optical cavity that reflects the laser beam for multiple passes, the optical path of the laser beam in each of the passes being longer than the coherence length, each of the passes generating one of the sub-beams.

5. The laser line generating assembly of claim 4, wherein the optical cavity comprises a high reflectivity reflector and a partially reflecting reflector extending in parallel.

6. The laser line generating assembly of claim 5, wherein the optical cavity comprises a rectangular transparent block, and the high reflectivity reflector and the partially reflective reflector are defined by reflective coatings disposed along respective rear and front surfaces of the rectangular transparent block.

7. The laser line generating assembly of claim 6, wherein the reflective coating is a metal or a dielectric component.

8. A laser line generating assembly according to claim 6 or 7, wherein the reflective coating defining the partially reflective reflector is configured such that all of the sub-beams contain substantially the same optical power.

9. The laser line generating assembly of any one of claims 6 to 8, wherein the reflective coating defining the partially reflective reflector has a varying thickness along the front surface.

10. The laser line generating assembly of any one of claims 6 to 9, wherein the optical cavity comprises an optical input comprising a portion of the rear surface of the rectangular transparent block that is free of a reflective coating defining the high reflectivity reflector.

11. The laser line generating assembly according to any one of claims 4 to 10, wherein the optical cavity comprises an optical input positioned to receive the laser beam within the optical cavity at an input angle α having a non-zero value relative to a normal N to a plane of the high reflectivity reflector.

12. The laser line generating assembly according to any one of claims 1 to 3, wherein the beam splitter comprises a plurality of partially reflective mirrors, which are sequentially located in the path of the laser beam.

13. The laser line generating assembly according to any one of claims 1 to 3, wherein the beam splitter comprises a transparent block made of a low reflectivity material and an input block made of a high reflectivity material, the input block having sides adjacent to sides of the transparent block.

14. The laser line generating assembly according to any one of claims 1 to 13, wherein the sub-beam converter comprises a diffraction grating.

15. The laser line generating assembly according to any one of claims 1 to 14, wherein the sub-beam converter comprises a diffuser.

16. The laser line generating assembly according to any one of claims 1 to 15, wherein the sub-beam converter comprises one or more line generating lenses.

17. The laser line generating assembly according to any one of claims 1 to 15, wherein the sub-beam converter comprises a line generating microlens array.

18. The laser line generating assembly according to any one of claims 1 to 17, wherein the sub-beam converter comprises a cylindrical lens.

19. The laser line generating assembly according to any one of claims 14 to 18, wherein the sub-beam converter further comprises a beam conditioning block.

20. The laser line generating assembly according to any one of claims 1 to 13, wherein the sub-beam converter comprises: a line generating lens arranged in the path of the laser beam between the laser source and the optical cavity and designed to fan out the laser beam in one direction within the propagation plane, so that each of the plurality of sub-beams has a fan-out shape within the propagation plane; as well as - a volume diffraction grating located on the propagation plane so as to intersect the plurality of sub-beams, the volume diffraction grating diffracting each sub-beam into a plurality of diffraction orders distributed along the one direction within the propagation plane, thereby providing a plurality of images of the sub-beams; The multiple images of each sub-beam form the laser light sheet associated with the corresponding sub-beam.

21. The laser line generating assembly of claim 20, wherein the line generating lens is a non-cylindrical lens or a linear diverging lens.

22. The laser line generating assembly of claim 20 or 21, wherein the volume diffraction grating comprises a planar glass substrate and a holographic pattern engraved or photoinduced in the planar glass substrate.

23. The laser line generating assembly of claim 20 or 21, wherein the volume diffraction grating comprises a planar glass substrate and a plurality of metasurfaces deposited on a surface of the planar glass substrate.

24. The laser line generating assembly of any one of claims 20 to 23, wherein the laser source is a single mode laser diode.

25. The laser line generating assembly according to any one of claims 20 to 24, further comprising a beam conditioning block located before or after the volume diffraction grating.

26. The laser line generating assembly according to any one of claims 20 to 24, further comprising a pseudo-telecentric illumination module arranged between the volume diffraction grating and the projection plane.

27. The laser line generation assembly of claim 26, wherein the pseudo-telecentric illumination module comprises a first lens and a second lens, the first lens having a curvature configured to redirect the laser light sheet emitted from the volume diffraction grating into a pseudo-parallel light sheet, and the second lens having a curvature configured to focus the pseudo-parallel laser light sheet to form a thin line on the projection plane.

28. A laser line generating assembly according to any one of claims 1 to 13, wherein the sub-beam converter comprises a series of line generating lenses located in the path of the sub-beam and each designed to fan out a corresponding sub-beam in the sub-beam, and a cylindrical lens located between the series of line generating lenses and the projection plane.

29. The laser line generating assembly according to any one of claims 1 to 13, wherein the sub-beam converter is configured to convert each sub-beam into a point source generating a corresponding laser light sheet.

30. The laser line generating assembly according to any one of claims 1 to 13, wherein the beam splitter and the sub-beam converter are integrated in a monolithic component.

31. A laser line generator for projecting a low speckle laser line on a projection plane, the laser line generator being configured to receive as input a laser beam having a temporal coherence characterized by a coherence length, the laser line generator comprising: - a beam splitter configured to split the laser beam into a plurality of incoherent sub-beams propagating in the same propagation plane; as well as a sub-beam converter generating a plurality of laser light sheets, each laser light sheet being associated with a corresponding one of the sub-beams, each laser light sheet extending within the propagation plane, the laser light sheets intersecting the projection plane to define at least partially overlapping laser line elements to form the low speckle laser line, the laser line elements having respective speckle patterns that are at least partially uncorrelated.

32. The laser line generator of claim 31 , wherein the beam splitter is arranged upstream of the sub-beam converter along the path of the laser beam.

33. The laser line generator of claim 31, wherein the sub-beam converter is disposed upstream of the beam splitter along the path of the laser beam.

34. A laser line generator according to any one of claims 31 to 33, wherein the beam splitter comprises an optical cavity which reflects the laser beam for multiple passes, the optical path of the laser beam in each of the passes being longer than the coherence length, each of the passes generating one of the sub-beams.

35. A laser line generator according to any one of claims 31 to 33, wherein the beam splitter comprises a plurality of partially reflective mirrors which are sequentially located in the path of the laser beam.

36. The laser line generator according to any one of claims 31 to 33, wherein the beam splitter comprises a transparent block made of a low reflectivity material and an input block made of a high reflectivity material, the sides of the input block being adjacent to the sides of the transparent block.

37. A laser line generator according to any one of claims 31 to 36, wherein the sub-beam converter comprises a diffraction grating.

38. The laser line generator of any one of claims 31 to 36, wherein the sub-beam converter comprises a diffuser.

39. The laser line generator of any one of claims 31 to 36, wherein the sub-beam converter comprises a microlens array.

40. The laser line generator of any one of claims 31 to 36, wherein the sub-beam converter comprises a cylindrical lens.

41. The laser line generator of claim 40, wherein the sub-beam converter further comprises a beam conditioning block, a one-dimensional diffuser or a grating.

42. A laser line generator according to any one of claims 31 to 36, wherein the sub-beam converter comprises one or more line generating cylindrical lenses.

43. The laser line generator of any one of claims 31 to 42, wherein the sub-beam converter is configured to convert each sub-beam into a point source generating a corresponding laser light sheet.

44. The laser line generator according to any one of claims 31 to 33, wherein the beam splitter and the sub-beam converter are integrated in a monolithic component.

45. The laser line generator of claim 31 wherein the laser source is a single mode laser diode and said sub-beam converter comprises a line generating cylindrical lens located between said laser diode and said beam splitter.

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