KR102338174B1 - Projectors of structured light - Google Patents

Abstract

An optoelectronic device includes a semiconductor substrate and a monolithic array of light emitting elements disposed on the substrate in a two-dimensional pattern rather than in a regular grid.

Description

Projector of structured light

FIELD OF THE INVENTION The present invention relates generally to optical and optoelectronic devices, and more particularly to devices for projection of a pattern.

Compact optical projectors are used in a variety of applications. For example, such a projector can be used to cast a pattern of coded or structured light into an object for the purpose of three-dimensional (3D) mapping (also known as depth mapping). In this regard, United States Patent Application Publication 2008/0240502 discloses a lighting assembly in which a light source, such as a laser diode or LED, transmits a slide with optical radiation to project a pattern onto an object, the disclosure of which is incorporated herein by reference. describe (The terms "optical" and "light" as used in this description and claims generally refer to any and all of visible, infrared, and ultraviolet radiation.) An image is captured, and a processor processes the image to reconstruct a 3D map of the object.

PCT International Publication WO 2008/120217, the disclosure of which is incorporated herein by reference, further describes aspects of the kind of lighting assembly shown in the aforementioned US 2008/0240502. In one embodiment, the slide comprises an array of micro-lenses arranged in a non-uniform pattern. The micro-lens creates a corresponding pattern of focus that is projected onto the object.

Optical projectors, in some applications, project light through one or more diffractive optical elements (DOEs). For example, US Patent Application Publication 2009/0185274, the disclosure of which is incorporated herein by reference, is an apparatus for projecting a pattern comprising two DOEs configured together to diffract an input beam to at least partially cover a surface. describe The combination of DOE reduces the energy in the zero-order (non-diffracted) beam. In one embodiment, the first DOE generates a pattern of multiple beams, and the second DOE functions as a pattern generator to form a diffraction pattern for each beam. A similar kind of arrangement is described in US Patent Application Publication 2010/0284082, the disclosure of which is incorporated herein by reference.

As another example, US Patent Application Publication 2011/0188054, the disclosure of which is incorporated herein by reference, describes a photonics module comprising an optoelectronic component and an optical element in a single integrated package. In one embodiment, an integrated photonic module (IPM) comprises a radiation source in the form of a two-dimensional matrix of optoelectronic elements disposed on a substrate and emitting radiation in a direction orthogonal to the substrate. Such IPMs typically include multiple parallel rows of emitters, such as light emitting diodes (LEDs) or vertical-cavity surface-emitting laser (VCSEL) diodes, that form a grid in the X-Y plane. Radiation from the emitter is directed to an optical module, with a projection lens and a suitable patterned element, which projects the resulting pattern onto the screen.

In many optical projection applications, patterns must be projected over a wide angular range. For example, in the type of 3D mapping application described in the background section above, the pattern of light used to generate the map is preferably projected in a field of 90° or greater. However, in conventional optical designs, achieving adequate optical quality for such a wide field of view (FOV) requires the use of expensive multi-element projection optics. The cost and size of these optics can be very prohibitive for consumer applications, which are generally small and require a low-cost solution.

Embodiments of the invention described below provide an improved apparatus and method for projection of patterned light.

Accordingly, in accordance with an embodiment of the present invention, there is provided an optoelectronic device comprising a semiconductor substrate and a monolithic array of light emitting elements disposed on the substrate in two dimensions rather than in a regular grid.

In the disclosed embodiment, the light emitting device comprises a vertical-cavity surface-emitting laser (VCSEL) diode.

In some embodiments, the two-dimensional pattern of the light emitting device is an uncorrelated pattern.

In one embodiment, the light emitting device comprises first and second sets of light emitting devices, wherein the first and second sets of light emitting devices are interposed on the substrate in respective first and second patterns; interleaved), said device comprising first and second conductors, said first and second sets of light emitting elements such that said device selectively emits light in either or both of said first and second patterns are connected to each to drive them individually. The apparatus includes projection optics configured to project the light emitted by the light emitting element onto an object, and only the first set of light emitting elements are driven to emit the light, so that while projecting the low resolution pattern onto the object, the low resolution mode further comprising an imaging device configured to capture an image of the object in a high resolution mode while both the first and second sets of light emitting elements are driven to emit the light to project the high resolution pattern onto the object can do.

In some embodiments, the device is mounted on a semiconductor substrate, and focuses the light emitted by the light emitting element to project an optical beam comprising a light pattern corresponding to a two-dimensional pattern of the light emitting element on the substrate; and a projection lens configured to focus. The apparatus may also include a diffractive optical element (DOE) mounted on the substrate and configured to stretch a projected optical beam by creating multiple, mutually adjacent replicas of the pattern. The projection lens and DOE may be formed on opposite sides of a single optical substrate.

Alternatively, the apparatus may be configured to project an optical beam comprising a light pattern corresponding to a two-dimensional pattern of the light emitting element on the substrate while stretching the projected optical beam by creating multiple, adjacent copies of the pattern. and a single diffractive optical element (DOE) configured to focus and focus light emitted by the light emitting element and mounted on the semiconductor substrate.

According to an embodiment of the present invention, there is additionally provided a method for pattern projection comprising generating an optical beam having a pattern embedded in the optical beam. An optical beam is projected using a projection lens to cast the pattern into a first area in space having a first angular range. A field multiplier is applied to stretch the optical beam projected by the projection lens to cast the pattern into a second region in space having a second angular range that is at least 50% greater than the first angular range.

According to an embodiment of the present invention, a method of calculating an optoelectronic device is further provided. The method includes providing a semiconductor substrate and forming a monolithic array of light emitting devices on the substrate in a two-dimensional pattern rather than a regular grid.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be better understood from the following detailed description of the above embodiments with reference to the drawings.

1 is a schematic side view of a 3D mapping system according to an embodiment of the present invention;
2 is a schematic top view of a semiconductor die having a patterned emitter array formed thereon, in accordance with an embodiment of the present invention;
3A-3C are schematic side views of an integrated optical projection module, in accordance with an embodiment of the present invention;
4A and 4B are schematic front views of a pattern projected by an optical projection module according to an embodiment of the present invention, and
5 is a top view of a semiconductor die formed with a patterned emitter array in accordance with an alternative embodiment of the present invention.

(survey)

In many optical projection applications, patterns must be projected over a wide angular range. For example, in the type of 3D mapping application described in the background section above, the pattern of light used to generate the map is preferably projected in a field of 90° or greater. In conventional optical designs, achieving adequate optical quality for this wide field of view (FOV) requires the use of expensive multi-element projection optics. The cost and size of these optics can be very prohibitive for consumer applications, which are generally small and require a low-cost solution.

Some embodiments of the invention, described below, address these needs by means of a field multiplier that follows the projection optics in the optical train and stretches the field into which the desired pattern is projected while maintaining the optical quality of the projected pattern. . The addition of a field multiplier makes it possible to project a pattern over a large area using small, inexpensive projection optics that themselves have a relatively narrow FOV.

In a disclosed embodiment, an optical device includes a beam source that generates a patterned optical beam. A projection lens projects a patterned optical beam and, without a field multiplier, casts the pattern into a given area in space having a specific angular range corresponding to the field of view (FOV) of the projection lens. (The term "lens" as used in the context of this description and claims refers to both simple and compound, multi-element lenses, unless expressly indicated otherwise) Field multipliers are in the FOV of the projection lens - lens and space Stretches the inter- intervening, patterned beam to a region in space having an angular range at least 50% greater than the FOV of the projection lens. Depending on the design, the stretched beam following the field multiplier may have a FOV of twice or more of the projection lens.

In some embodiments, the beam source includes a monolithic array of light emitting devices disposed on a semiconductor substrate in a two-dimensional pattern corresponding to a pattern imparted on the optical beam.

(system description)

1 is a schematic side view of a 3D mapping system 20 according to an embodiment of the present invention. System 20 is described herein as an example (but not by way of limitation) of the use of a field multiplier of the kind described below. The principles of the present invention are similarly applicable in other types of optical projection systems that require a wide field of view and may benefit from the miniaturization and low cost advantages provided by the disclosed embodiments.

The system 20 includes a projection assembly 30 that projects the patterned beam 38 onto a surface of an object 28 (in this example at the user's side of the system). The imaging assembly 32 captures an image of the projected pattern on the surface and processes the image to derive a 3D map of the surface. For this purpose, assembly 32 typically includes objective optics as well as a digital processor (not shown) that processes the image to produce a 3D map, and an image sensor 42 that captures the image. include Image capture and processing aspects of system 20 are described, for example, in US Patent Application Publication 2010/0118123 and US Patent Application Publication 2010/0007717 above, the disclosures of which are incorporated herein by reference.

The projection assembly 30 includes a patterned beam generator 34 that projects a patterned illumination beam with a particular FOV, and a field multiplier 36 that stretches the projected beam into a patterned beam 38 generated with a wider FOV. ) is included. In this example, as described in the aforementioned patent application publication, the pattern is in a random or quasi-random arrangement with high contrast light spots on a dark background. Alternatively, other suitable types of patterns (including images) may be projected in this manner.

(Integrated Pattern Generator)

VCSEL arrays can advantageously be used in the manufacture of compact, high intensity light sources and projectors. In a conventional VCSEL array, the laser diodes are arranged in a regular grid, such as a straight grid pattern, or a hexagonal grid pattern, as described in the above-mentioned US Patent Application Publication 2011/0188054. The term "regular grating" as used in the context of this description and claims means a two-dimensional pattern in which the spacing between adjacent elements in the pattern (eg, between adjacent emitters in a VCSEL array) is constant. . In that sense, the term "regular lattice" is synonymous with periodic lattice.

Embodiments of the present invention described below depart from this model and instead provide a VCSEL array in which the laser diodes are arranged in a pattern rather than in a regular grid. Optics may be coupled to project into space a pattern of light emitted by elements of the VCSEL array as a pattern of corresponding spots, each spot comprising light emitted by a corresponding laser diode in the array. In general (but not necessarily), the pattern of laser diode positions in the array, and thus the pattern of spots, shows that the auto-correlation of the positions of the laser diodes as a function of the transverse shift of the diode There is no correlation in the sense that it is not significant for any shift greater than the magnitude. Random, pseudorandom, and quasi-periodic patterns are examples of such unrelated patterns. The projected light pattern will therefore also be independent of each other.

This kind of patterned VCSEL array is particularly useful for yielding integrated pattern projection modules, as described below. Such a module can achieve cost and size reduction with the benefit of simplicity of design and manufacture as well as better performance as compared to the projection devices known in the prior art.

2 is a schematic top view of an optoelectronic device having a semiconductor die 100 in which a monolithic array of VCSEL diodes 102 is formed in a two-dimensional pattern rather than in a regular grid, in accordance with an embodiment of the present invention. The array, having a suitable thin film layer structure to form the laser diode, and a conductor supplying power and a ground connection from the contact pad 104 to the laser diode 102 in the array, yields a VCSEL array known in the art. formed on a semiconductor substrate by the same kind of photolithographic method used to

The arrangement of the irregular gratings of Figure 2 is achieved simply by proper design of the photolithographic mask used to compute the array, in any desired two-dimensional pattern. Alternatively, an irregular array of other types of surface emitting devices, such as light emitting diodes (LEDs), can be similarly produced in this way (although incoherent light sources such as LEDs are less suitable for some pattern projection applications). .

A monolithic VCSEL array of the kind shown in FIG. 2 has the advantage of high power scalability. For example, using current technology, a die with an active area of 0.3 mm 2 can contain 200 emitters, resulting in a total optical power output of about 500 mW or more. A VCSEL diode emits a circular beam and can be designed to emit a circular Gaussian beam in a single transversal mode, which has advantages in creating high contrast and high density spot patterns. Since the VCSEL emission wavelength is relatively stable as a function of temperature, the spot pattern, during operation, will be similarly stable even in the absence of active cooling of the array.

3A is a schematic side view of an integrated optical projection module 110 including a VCSEL array, such as the array shown in FIG. 2 , in accordance with an embodiment of the present invention. The VCSEL die 100 is typically tested at the wafer level, then diced and mounted on an appropriate sub-mount 114 with the appropriate electrical connections 116 , 118 . Electrical connections, and also possible control circuitry (not shown) may be coupled to die 100 by wire bonding conductors 121 .

A lens 120 mounted on a die on an appropriate spacer 122 focuses and projects the output beam of the VCSEL emitter. For temperature stability, glass lenses may be used. A diffractive optical element (DOE) 124 , positioned by spacers 126 , fanning out over an extended angular range creates multiple replicas 128 of the pattern. For example, DOEs include Dammann gratings or similar devices, as described in the aforementioned US Patent Application Publications 2009/0185274 and 2010/0284082.

4A is a schematic front view of an elongated pattern 160 projected by an optical projection module 110 according to an embodiment of the present invention. This figure shows a kind of fan out pattern generated by DOE 124 . The DOE in this example stretches the projected beam into an array of 11 x 11 tiles 162 centered on each axis 164 , although more or fewer tiles could alternatively be yielded. Each tile 162 (having the shape of a distorted square due to pincushion distortion) in FIG. 4A contains a pattern of bright spots 166 that is a replica of the pattern of the VCSEL array.

Generally, the fan out angle between adjacent tiles in this example is in the range of 4-8°. For example, assuming that each such tile contains about 200 spots in an unrelated pattern, corresponding to about 200 laser diodes 102 in the VCSEL array, the 11 x 11 fan out shown in FIG. 4A . Pattern 160 then includes over 20,000 spots. DOE 124 is designed, for example, as described in US Patent Application Publication 2010/0284082, such that projected replicas of a pattern tile a surface or spatial region.

3B is a schematic side view of an integrated optical projection module 130 including an irregular VCSEL array, such as the array shown in FIG. 2 , in accordance with an alternative embodiment of the present invention. In this embodiment, the refractive projection lens 120 of the module 110 is replaced by a diffractive lens 136 . Lens 136 and fan out DOE 134 (similar to DOE 124 ) may be formed on opposite sides of the same optical substrate 132 . Although diffractive lenses are sensitive to wavelength changes, the relative stability of the wavelengths of VCSEL devices makes this approach feasible. DOE 134 is protected by a window 138 mounted on spacer 140 .

3C is a schematic side view of an integrated optical projection module 150 including an irregular VCSEL array, in accordance with another embodiment of the present invention. Here, the functions of the diffractive lens and fan-out DOE are formed on the optical substrate 152 and combined into a single diffractive element 154, which also functions as a window. Element 154 performs both focusing and fan-out functions: it corresponds to a two-dimensional pattern of a light emitting element on a substrate, stretching the projected optical beam by creating multiple, mutually adjacent replicas of the pattern as shown above. The light emitted by the light emitting element is focused and focused on the die 100 to project an optical beam comprising a light pattern that is

During assembling the modules shown in FIGS. 3A-C , the DOE is generally aligned in four dimensions (X, Y, Z, and rotation) with respect to the VCSEL die 100 . The embodiments of 9B and 9C show that the photolithographic process used to produce both the VCSEL array and the DOE/diffractive lens structure is accurate to about 1 μm, and therefore X, Y simply by matching fiducial marks. , and since it allows passive alignment in rotation, it has advantages with respect to alignment. Z-alignment (ie, distance between VCSEL die and DOE and lens) requires only a small range of motion, due to high production accuracy. Z-alignment is thus achieved actively while the VCSEL array is powered, using, for example, a height-measuring device such as a confocal microscope to measure the distance between the VCSEL surface and the DEO surface, Or it can be achieved passively.

The module of FIGS. 3A-C can be used as a pattern projector in the 3D mapping system 20 . The tiled pattern (eg, as shown in FIG. 4A ) is projected onto an object of interest, and imaging module 32 captures an image of the pattern on object 28 . As described above, the processor associated with the imaging module measures, at each point in the image, with respect to a known reference, a local transverse shift of the pattern, and then the depth coordinate of that point by triangulation based on the local shift. find out

Each replica of the pattern, corresponding to one of the tiles 162 in FIG. 4A , is internally uncorrelated, but generally highly correlated with neighboring tiles. Since each replica of the pattern contains a relatively small number of spots 166, distributed in a relatively small angular range, when the transverse shift of the pattern on the object is on the order of more than the pitch of the tiles 162, the depth coordinate There may be ambiguities in To reduce this ambiguity, the VCSEL die 100 can be produced with a larger number of laser diodes, and the optics of the projection module can thus yield more tiles; This solution increases the complexity and cost of both the VCSEL die and the optics.

4B is a schematic front view of an elongated pattern 170 projected by an optical projection module, according to an alternative embodiment of the present invention that addresses the problem of correlation between neighboring tiles. (The DOE-based field multiplier of FIGS. 3A and 3B can be similarly configured to yield a pattern similar to pattern 160 or 170.) The tiled pattern of the interleaved kind shown in FIG. 4B is a fan-out DOE. is calculated by proper design of In the present design, at least some of the tiles of the pattern are offset transversely relative to neighboring tiles by an offset of the order of a fraction of the pitch. In particular, in this example, tile 172 is transversely offset relative to neighboring tile 174 by 1/2 a tile. (The offset is vertical in this example, as is the assumption that only a transverse shift in the horizontal direction is used for depth measurements.)

As a result of this offset between tiles, the range of explicit depth measurements is substantially doubled. Other interleaving, in which adjacent tiles are shifted by one-third or one-quarter of the tile pitch, may provide, for example, a greater clear measurement range. DOEs providing these and other fan-out patterns can be designed using methods known in the art, such as those based on the Gerchberg--Saxton algorithm.

5 is a schematic top view of a semiconductor die 180 having a monolithic VCSEL array formed thereon, in accordance with another embodiment of the present invention. This array is similar to the array of FIG. 2 except that in the embodiment of FIG. 5 there are two groups of VCSEL diodes 182 and 184 driven by separate conductors 186 and 188 . Diodes 182 and 184 are shown in the figures as having different shapes, but this difference in shape is for visual clarity only, and in reality, all VCSEL diodes in both groups generally have the same shape.

The two groups of VCSEL diodes 182 and 184 shown in the figure are to be used together with the high-resolution image sensor 42 in the imaging module 32 ( FIG. 1 ) to implement a zoom function in the depth mapping system 20 . can Separate power lines feeding the two groups may be implemented by feeding separate power traces to the two groups within a single metal layer of the VCSEL die, or by adding metal layers such that each group is powered by a different layer. can The two groups may contain the same or different numbers of diodes depending on the desired performance characteristics of the system. It is assumed that the image sensor supports binning neighboring detector elements (which sacrifices resolution reduction and provides improved sensitivity and speed), cropping the sensing area and adjustable clock rate. These features are provided by a variety of commercially available image sensors.

In wide angle mode, one of the two groups of VCSEL diodes (eg, diode 182 ) receives power while the other group is blocked. As a result, powered groups can be driven at high power to increase the brightness of individual spots in the pattern without exceeding the overall power requirements of the VCSEL die. (Higher power per emitter is possible because of the increased distance between active neighboring emitters in this mode, which reduces the associated thermal effect.) On the other hand, image sensor 42 operates in binning mode and , thus forming a low-resolution image of the entire field of view of the system. Because the detector element of the image sensor is bound, the image sensor can capture and output an image at high speed. The processor measures the transversal shift of the pattern in this image to generate the first low resolution depth map.

The processor may segment and analyze the low resolution depth map to recognize objects of potential interest, such as the human body, within the field of view. In this step, the processor chooses to zoom in on the object of interest. For this purpose, the processor turns on all VCSEL diodes 182 and 184 in both groups to create a high resolution pattern. The processor also instructs the image sensor 42 to operate in cropping mode to scan only the area within the field of view in which the object of interest is found. The image sensor at this stage is generally read at full resolution (within the cropped area) without binning, and thus can capture high resolution images of high resolution patterns. Due to the cropping of the read area, the image sensor can also output images at high speed in high-resolution mode. The processor now measures the transverse shift of the pattern in this latter image to form a high resolution depth map of the object of interest.

The above-described embodiment makes optimal use of both the power resource of the VCSEL-based pattern projector and the detection resource of the image sensor. In both wide angle and zoom modes, the scanning speed and sensitivity of the image sensor is typically adjusted (by binning, cropping, and clock rate adjustment) to provide a depth map of adequate resolution at a constant frame rate such as 30 frames/sec. can be adjusted.

Although some of the above embodiments specifically referenced pattern-based 3D mapping, the pattern projector described above may similarly be used in other applications, including both 2D and 3D imaging applications using patterned light. Accordingly, it is to be understood that the foregoing embodiments have been cited by way of example, and that the present invention is not limited to what has been specifically shown and described above. Rather, the scope of the invention includes all combinations and subcombinations of the various features described above, as well as modifications and variations not disclosed in the prior art, which will occur to those skilled in the art upon reading the foregoing description.

Claims (14)

A photovoltaic device comprising:
semiconductor substrate;
a monolithic array of light emitting elements disposed on the substrate in a two-dimensional pattern; and
a single diffractive optical element (DOE);
The single diffractive optical element is mounted on the semiconductor substrate,
The single diffractive optical element is configured to focus and focus the light emitted by the light emitting elements to project an optical beam comprising a light pattern corresponding to the two-dimensional pattern of the light emitting elements on the substrate, while focusing and focusing the light emitted by the light emitting elements on the substrate. and stretch the projected optical beam to create mutually adjacent replicas. According to claim 1,
the single diffractive optical element is configured to project the light pattern onto a surface of an object,
wherein the photovoltaic device comprises an imaging assembly;
wherein the imaging assembly is configured to capture an image of a light pattern projected on the surface and process the image to derive a 3D map of the surface. According to claim 1,
wherein the light emitting elements comprise vertical-cavity surface-emitting laser (VCSEL) diodes. 4. The method according to any one of claims 1 to 3,
wherein the two-dimensional pattern of the light emitting elements is not a regular grid. 5. The method of claim 4,
wherein the two-dimensional pattern is a pseudo-randum pattern. A method of manufacturing a photovoltaic device comprising:
providing a semiconductor substrate;
forming a monolithic array of light emitting devices on the substrate in a two-dimensional pattern; and
to focus and focus the light emitted by the light emitting elements to project an optical beam comprising a light pattern corresponding to the two-dimensional pattern of the light emitting elements on the substrate, while generating multiple, mutually adjacent replicas of the pattern; mounting a single diffractive optical element (DOE) on the semiconductor substrate to stretch the projected optical beam;
A method of manufacturing an optoelectronic device comprising: 7. The method of claim 6,
Projecting the optical beam includes projecting the light pattern onto a surface of an object,
The method includes capturing an image of a light pattern projected on the surface and processing the image to derive a 3D map of the surface.
A method of manufacturing an optoelectronic device. 7. The method of claim 6,
wherein the light emitting elements comprise VCSEL diodes. 9. The method according to any one of claims 6 to 8,
The method of manufacturing a photovoltaic device, wherein the two-dimensional pattern of the light emitting elements is not a regular grid. 10. The method of claim 9,
wherein the two-dimensional pattern is a pseudo-random pattern. delete delete delete delete

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