阅读说明：本技术 单片结构光投影仪 (Monolithic structured light projector ) 是由 简阿克塞尔埃德蒙泰西尔 朱立安博卡特 于 2019-09-06 设计创作，主要内容包括：本申请提出了一种用于以预定图案生成光点的远场图像的结构光投影仪,其中结构光投影仪包括：光源,其提供非准直光束作为输出；以及专用衍射光学元件,其被设置为截取非准直光束。形成专用衍射光学元件以呈现不均匀的光栅特征图案,其被配置为补偿非准直输出光束的非平面波前和相位延迟,从而提供具有所需的配置的光点的干涉图案作为投影仪的输出。(The present application proposes a structured light projector for generating a far-field image of a light spot in a predetermined pattern, wherein the structured light projector comprises: a light source providing a non-collimated light beam as an output; and a dedicated diffractive optical element arranged to intercept the non-collimated beam. The dedicated diffractive optical element is formed to exhibit a non-uniform grating feature pattern configured to compensate for the non-planar wavefront and phase retardation of the non-collimated output beam, thereby providing an interference pattern of spots having a desired configuration as an output of the projector.)

1. A structured light projector for producing a far field image of a light spot in a defined pattern, comprising:

A light source providing a non-collimated light beam as an output; and

a dedicated diffractive optical element arranged to intercept the non-collimated beam, the dedicated diffractive optical element comprising a non-uniform pattern of a plurality of grating features configured to both compensate for wavefront and phase retardation of the non-collimated beam and diffract the compensated beam to produce as output an interference pattern of spots exhibiting a defined pattern.

2. The structured light projector of claim 1, wherein the non-uniform pattern of the plurality of grating features comprises non-uniform spacing between adjacent grating features.

3. The structured light projector of claim 2, wherein the non-uniform spacing increases in size as measured outward from the central region dedicated to the diffractive optical element.

4. The structured light projector of claim 1, wherein the non-uniform pattern of the plurality of grating features comprises a non-uniform thickness of individual grating features forming the plurality of grating features.

5. The structured light projector of claim 4, wherein the thickness of the grating features decreases as measured outward from a central region of the dedicated diffractive optical element.

6. The structured light projector of claim 1, wherein the non-uniform pattern of the plurality of grating features comprises a non-uniform thickness of the plurality of grating features and a non-uniform spacing between adjacent grating features.

7. The structured light projector of claim 6, wherein each grating feature exhibits any one of a first thickness t1 and a second thickness t2, adjacent grating features being separated by any one of a first spacing W1 and a second spacing W2 to form a compensated high order dedicated diffractive optical element.

8. The structured light projector of claim 1, wherein the light source comprises a single mode light source.

9. The structured light projector of claim 1, wherein the light source comprises a multi-mode light source.

10. the structured light projector of claim 1, wherein the light source comprises a laser source.

11. The structured light projector of claim 10, wherein the light source comprises a Vertical Cavity Surface Emitting Laser (VCSEL).

12. The structured-light projector of claim 11, wherein the vCSEL is inverted to direct the non-collimated light beam through a thickness of the support substrate to exit a major surface of the support substrate.

13. The structured light projector of claim 12, wherein the dedicated diffractive optical element is disposed on a major surface of the support substrate.

14. A structured light projector according to claim 13, wherein the dedicated diffractive optical element comprises a non-uniform arrangement of the plurality of grating features etched in a surface layer formed on a major surface of the support substrate.

15. The structured light projector of claim 1, wherein the light source comprises a single laser diode array, wherein a single dedicated diffractive optical element is disposed above and aligned with the single laser diode array.

16. A method of manufacturing a structured light projector, comprising the steps of:

a) Providing a light source emitting a non-collimated output beam;

b) Analyzing the non-collimated output beam to determine a particular non-planar wavefront and phase delay associated with the non-collimated output beam; and

c) configuring a plurality of grating features of a dedicated diffractive optical element to exhibit a non-uniformity sufficient to compensate for the particular non-planar wavefront and phase retardation, wherein a pattern of the plurality of grating features produces as output an interference pattern having a predetermined pattern of spots.

17. The method of claim 16, wherein in performing step a), a vertical cavity surface emitting laser is provided on a support substrate and is oriented to emit the non-collimated output beam through a thickness of the support substrate, the non-collimated output beam emerging at a major surface of the support substrate.

18. The method of claim 17, wherein in performing step c), the dedicated diffractive optical element is disposed on a major surface of the support substrate to form a monolithic structured light projector.

19. The method of claim 18, wherein the dedicated diffractive optical element is etched directly into a major surface of the support substrate.

20. The method of claim 18, wherein the dedicated diffractive optical element is formed by:

Depositing a layer of semiconductor material on a major surface of the support substrate;

Patterning the semiconductor material layer to present a non-uniform pattern; and

Etching the patterned layer to produce the plurality of non-uniform grating features of the dedicated diffractive optical element.

Technical Field

The present invention relates to a structured light projector, and more particularly, to a monolithic structured light projector that does not require a separate collimator to provide beam shaping.

Background

Structured light projectors are being developed for applications that use specific patterns of light "dots" to project coded light or information patterns. Applications such as 3D sensing, mapping, etc. depend on the use of this type of light source. Fig. 1 is a simplified diagram of a typical prior art structured light projector, including a laser diode 1 that emits a light beam B. As shown, the beam diverges as it exits the laser diode 1. Then, the divergent light beam is guided into the collimator lens 2. The function of the collimator lens 2 is to focus a diverging beam

A set of parallel rays (i.e., collimated beams) that exhibit a planar wavefront is formed. The collimated beam is then directed into a Diffractive Optical Element (DOE)3 which serves to redirect some of the light rays so as to produce an interference pattern of spots, as shown in figure 2. When a collimated beam passes through the grating of the DOE, a pattern of spots is formed by introducing a set of phase delays in the wavefront of the collimated beam. Various types of diffractive elements for this purpose are known in the art, including, inter alia, refractive curved surfaces, fresnel lenses, and the like.

Although useful for providing a structured light output, the combination of collimator and DOE requires careful alignment (with each other and the light source) in order to produce the desired pattern. Alignment tolerances necessarily increase the cost of the projector, as well as the time and effort required to manufacture the assembly. Tight alignment tolerances also affect packaging requirements. The use of individual discrete elements can affect the size of the projector itself, particularly in applications where it is desirable to utilize such an array of projectors to produce a broader and/or more complex pattern of spots.

Disclosure of Invention

The need still exists in the art is addressed by the present invention, which relates to structured light projectors, and more particularly to monolithically integrated structured light projectors that do not require a separate collimator assembly, and which in exemplary embodiments may be fabricated directly on the laser diode light source itself.

in accordance with the present invention, a dedicated diffractive optical element ("dedicated DOE") is used in conjunction with a light source to produce the desired dot pattern output. In particular, the special DOE is formed to exhibit a variable diffraction pattern that compensates for the non-collimated beam exiting the laser such that the beam shape and phase delay associated with the laser output can be matched to the diffraction pattern of the special DOE. More specifically, the diffraction patterns formed in the dedicated DOE are configured to include non-uniform spacing and/or thickness of the included features to counteract the phase retardation inherent to the wavefront of the non-collimated beam. For applications where an array of spots needs to be generated (as shown in figure 2), the non-uniformity of the features forming the dedicated DOE develops in a direction away from the centre of the beam and when the non-collimated beam reaches the dedicated DOE it matches the phase delay. Other non-uniformity configurations are contemplated to be within the scope of the present invention and may be used to create a dedicated dot pattern for a particular application. The pattern of dots may take the form of a regular array, or a random pattern (in most cases pseudo-random), as shown in figure 2.

One exemplary embodiment of the present invention utilizes a Vertical Cavity Surface Emitting Laser (VCSEL) oriented on a supporting substrate such that it emits through the thickness of the substrate, in one case a dedicated DOE fabricated directly on the surface of the substrate. This integrated configuration thus provides a very compact and reliable monolithic structured light projector.

Various embodiments of the present invention may utilize an integrated array of light sources arranged such that their diverging beams do not overlap. A diffraction pattern is generated to provide appropriate compensation for the divergence of the array of light beams. The array may be one-dimensional or two-dimensional.

other embodiments of the present invention may be formed using discrete light sources in conjunction with discrete, dedicated DOEs (as opposed to a monolithically integrated configuration). Since the application-specific DOE eliminates the need for a separate collimator, even these embodiments utilizing discrete application-specific DOEs will be more compact than their prior art counterparts (and also eliminate the collimator-DOE alignment process).

Exemplary embodiments of the present invention take the form of a structured light projector comprising a light source providing as output a non-collimated beam of light and a dedicated diffractive optical element arranged to intercept the non-collimated beam of light to generate a far field image of the light spots in a defined pattern. The dedicated diffractive optical element itself is formed as a non-uniform pattern comprising a plurality of grating features configured to both compensate for the wavefront and phase retardation of the non-collimated beam and diffract the compensated beam to produce as output an interference pattern having a defined pattern of spots.

Other and further embodiments of the present invention will become apparent during the course of the following discussion and by reference to the accompanying drawings.

Drawings

Reference is now made to the drawings,

Fig. 1 is a simplified diagram of a prior art point projector.

Fig. 2 shows an exemplary dot pattern produced by interference of light rays passing through the DOE.

Fig. 3 is a simplified diagram of a structured light projector formed in accordance with the present invention.

Figure 4 shows a specific embodiment of the invention, in this case comprising a combination of a VCSEL light source and a dedicated DOE forming an element with non-uniform spacing to compensate for a diverging beam.

fig. 5 is an enlarged view of the special DOE of fig. 1 and shows the wavefront approaching a diverging beam and the uneven spacing of the elements in the DOE.

Fig. 6 illustrates another embodiment of the present invention, in this case showing the use of an array of light sources with associated dedicated DOEs to form a structured light projector in accordance with the principles of the present invention.

fig. 7 shows another embodiment of the invention, in this case with a non-uniform thickness in the material layers forming the dedicated DOE, the varying thickness being configured to compensate for the diverging beam.

Figure 8 shows yet another embodiment of the invention in which a dedicated DOE is formed to include non-uniform spacing and non-uniform thickness to compensate for beam divergence.

Detailed Description

Fig. 3 is a simplified block diagram of an exemplary structured light projector 10 formed in accordance with the principles of the present invention. Similar to the prior art configuration described above, the light source 12 is used to emit a light beam that diverges as it exits the light source 12 and continues to diverge as a non-collimated beam as it propagates along the output path. In accordance with the present invention, the dedicated DOE 14 is configured to interact with the non-collimated beam and produce a pattern of spots, which may be substantially the same as the spots shown in fig. 2.

as will be discussed in detail below, the specialized DOE 14 is formed to present a non-uniform pattern 16 of grating features 18, as opposed to a typical DOE, which presents a uniform configuration to produce a desired interference pattern. In particular, the pattern 16 may be non-uniform in spacing between adjacent features 18 across the surface of the element 14, or non-uniform in the thickness of the features 18 within the material layers forming the dedicated DOE 14, or a combination of non-uniform spacing and non-uniform thickness. In any case, pattern 16 is specifically formed to compensate for delays in arrival times of different portions of the non-collimated beam of light exiting the light source, thereby forming a desired dot pattern projection of light. In this context, various embodiments of the present invention will now be discussed in detail below.

Exemplary embodiments of the present invention provide the desired non-uniformity in a specialized DOE pattern by controlling the spacing between adjacent features forming a grating pattern, as shown in fig. 4. Fig. 4 shows a monolithically integrated structured light projector in which a dedicated DOE40 of the present invention is formed on the back side 30 of substrate 32 and VCSEL device 34 is mounted on the back side 30 of substrate 32 and serves as the light source for the projector. Also shown in fig. 4 is a metal contact layer 38 of VCSEL 34, which is formed on the opposite side of back surface 30 of substrate 32. In this particular embodiment, the VCSELs 34 are mounted "upside down" (i.e., with the outside surface facing down) so as to emit through the thickness of the substrate 32 (instead of the usual process of exiting from the top surface and entering free space). The divergence of the emitted beam as it propagates through the substrate 32 is illustrated by the dashed lines in fig. 3. Figure 4 also shows the movement of the non-planar wavefront from VCSEL device 34 to specialized DOE 40. In accordance with this particular embodiment of the present invention, specialized DOE40 is formed to exhibit a pattern 42 of non-uniform spacing between adjacent grating features 44. In this particular example, pattern 42 of DOE40 is specifically formed to adjust the spacing between adjacent grating features 44 to match the beam profile of the light emitted by VCSEL 34. That is, the spacing is controlled to compensate for phase delays between the outer regions of the wavefront relative to the center of the wavefront. By providing this compensation in a dedicated diffractive element formed in accordance with the teachings of the present invention, both collimation and diffraction are provided by a single component, resulting in a compact structured light projector arrangement.

In one particular configuration of this embodiment, the specialized DOE40 may be formed by depositing a layer of material 46 (e.g., TiO2) on the metal contact layer 38 and then patterning and etching the layer of material 46 to configure the grating features 44 in the desired pattern 42. Alternatively, pattern 42 may be formed by etching feature 44 directly into metal contact layer 38. The ability to directly create a diffraction pattern in/on the contact layer using conventional, well-known integrated circuit fabrication processes results in an extremely compact structured light projector, the pattern being aligned with the beam emitted by the VCSEL. In any configuration, so long as DOE40 produces a grating pattern of individual features 44 having different values of refractive index, the beam passing through these regions will experience different degrees of diffraction, thereby producing the desired spot beam pattern in the far field. By utilizing some type of non-uniform feature (non-uniform size, shape, spacing, etc.), DOE40 provides collimation of the diverging output beam from VCSEL 34, thus eliminating the need for a separate collimating lens.

Fig. 5 is an enlarged view of specialized DOE40, and fig. 5 shows the non-uniformity in pattern 42, which is specifically configured to match the wavefront of the non-collimated beam output from VCSEL 34. As shown in fig. 5, features 44A in a central region of dedicated DOE40 are relatively close together at intervals (represented by interval SA), and the spacing between features 44A and 44B is increasing (represented as the spacing of SB). In the + x and-x directions from central feature 44A of specialized DOE40, this pitch (SC) with feature 44C is increasing, and so on. According to this particular embodiment of the invention, the interval is controlled to match the phase delay outside the wavefront, as shown by Δ φ in FIG. 5.

As described above, the dedicated DOE of the present invention may be used with an array of light sources configured to replace a structured light projector that is only a single light source. FIG. 6 shows an exemplary configuration including an array of VCSELs 34-1 through 34-N, with the epitaxy of the VCSELs 34-1 through 34-N disposed down on a substrate 60 such that their emitted beams propagate through the thickness of the substrate 60 and exit through an N-type contact layer 62. According to this particular configuration of this array embodiment of the present invention, the VCSEL array is formed as an integrated array on a single substrate, with a plurality of individual dedicated DOEs 70-1 to 70-N disposed on the N-type contact layer 62 of the substrate 60. As shown, each of the DOEs 70-1 to 70-N is aligned with its associated VCSEL 34-1 to 34-N.

In this case, the DOEs 70-1 to 70-N are formed within a layer 72 of a suitable material and are configured to exhibit a desired non-uniform pattern 74-1 to 74-N (non-uniformity in spacing, thickness, or both). Each pattern is formed to interact with its own individual beam to produce a desired pattern of dots from the emitted beam. According to this embodiment of the present invention, the VCSELs 34-1 to 34-N are separated by a predetermined distance d such that their diverging beams do not overlap when passing through the substrate 60. In particular, provided that d is defined as greater than 2 × T × sin (θ), where T is the thickness of the substrate 60 and θ is defined as the lateral divergence of the beam, as shown in fig. 6. In this manner, the particular patterns 74-1, 74-2, formed in the DOEs 70-1 through 70-N may be independently configured to provide an optimal pattern based solely on the divergence characteristics of its associated beams without concern for interference of overlapping beams. Indeed, it should be understood that each DOE may exhibit a different non-uniform diffraction pattern, such that the combination of the various patterns provides the desired dot pattern results. Advantageously, the use of standard integrated circuit fabrication processes allows the structured light projection array to be formed in a straightforward manner.

Furthermore, it should be understood that larger arrays of VCSELs may be used as the light source for the integrated structured light projector of the present invention, including two-dimensional arrays of such devices. In each case, a separate diffraction pattern is generated for generating the spot pattern from each beam.

Figure 7 shows another embodiment of the invention in which the feature thickness of the dedicated DOE element (rather than the feature spacing) is controlled in this case to provide the non-uniformity required to compensate for beam divergence. In particular, fig. 7 shows a specialized DOE 80 formed in a layer of material deposited on an n-type (metal) contact layer 38 (as in the above-described embodiment). The material may be processed sequentially to produce individual grating features 82 of different thicknesses. Here, the thickness of grating feature 82 varies with x in both directions from the center of specialized DOE 80. The thickest feature 82A is shown in the central region of DOE 80, with a pair of slightly less thick features 82B disposed on either side of feature 82A (where tA > tB). The next pair of outwardly extending features 82C is slightly shorter than the features 82B (tB > tC), and so on.

The thickness can be varied by using a series of patterns and etches to control the amount of material removed during each etch step. Or a controlled Reactive Ion Etch (RIE) process may be used to tailor the thickness of the features 82 and create the desired pattern. Other methods of adjusting the thickness of the feature 82 may be used, and in all cases, the thickness is modified in order to control the phase delay associated with the portion of the beam passing through the local feature 82. In particular, the thicker the feature, the longer the phase delay. Thus, by knowing the phase retardation associated with the particular material used to form feature 82 (as a function of the wavelength of light passing through the material), appropriate configurations of thickness non-uniformities can be developed in accordance with the present invention to provide compensation for the non-collimated output beam.

Yet another embodiment of the present invention is shown in fig. 8. Here a special DOE90 is formed to show a combination of uneven spacing of elements and uneven thickness of elements. In this particular configuration, the DOE90 includes a set of features 92 that are formed of either a first thickness t1 or a second thickness t2 (with spacing between adjacent features, as shown). The thicknesses in this particular embodiment may be related in size to provide a 2 pi phase shift for the portion of the wave that passes through the thicker feature (however, this should be considered as only one possible configuration and other values of t1 and t2 that may have been used). Features 92 are also formed to have two different widths, as shown at W1 and W2. This combination of characteristic thickness and width may form a blazed diffractive optical element that also compensates for the non-collimated output beam from the VCSEL 34. In particular, this configuration is used to help deplete the zeroth order mode (i.e., a mode that is not diffractive.)

While the above embodiments illustrate the creation of a single-piece structured light projector, it should be understood that the dedicated DOE may be formed as a separate discrete element and disposed in alignment with the light source, such as shown in the block diagram of fig. 3.

Recall that prior art configurations of structured light projectors require alignment of the collimating lens with a standard DOE and then packaging of the aligned combination into a module. The module then needs to be aligned with the associated light source. As described above, the present invention eliminates these various alignment and packaging steps by combining the collimation and diffraction functions into a single element that can be integrated with a laser light source to form a monolithic structured light projector. The structured light projector of the present invention is robust and very compact. The manufacturing process is greatly simplified and allows extremely compact projection products, which is a key factor for applications in the mobile phone industry (e.g. projectors within smart phones), without the need for additional discrete components.

it will thus be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed previously.