阅读说明：本技术 使用偏振特定vcsel的三维成像和感测应用 (Three-dimensional imaging and sensing applications using polarization-specific VCSELs ) 是由 C.高希 让-弗朗西斯.苏仁 于 2019-05-08 设计创作，主要内容包括：使用VCSEL光源产生偏振光,其中偏振光中的至少一些被对象反射或散射。被反射或散射的偏振光中的至少一些被接收在传感器中,所述传感器能够选择性地操作以检测与由所述VCSEL光源产生的所述光具有相同偏振的接收光。在一些情况下,对来自所述传感器的信号进行处理以获得所述对象的三维距离图像,或者使用飞行时间技术进行处理以确定距所述对象的距离。(A VCSEL light source is used to generate polarized light, where at least some of the polarized light is reflected or scattered by an object. At least some of the reflected or scattered polarized light is received in a sensor that is selectively operable to detect received light having the same polarization as the light produced by the VCSEL light source. In some cases, the signals from the sensors are processed to obtain a three-dimensional range image of the object, or processed using time-of-flight techniques to determine the distance to the object.)

1. A module for light imaging and/or light sensing, comprising:

a VCSEL light source operable to produce polarized light; and

a sensor selectively operable to detect received light having the same polarization as light generated by the VCSEL light source, the received light being reflected or scattered by an object external to the module.

2. The module of claim 1, wherein the VCSEL light source is operable to produce linearly polarized light.

3. A module according to any of the preceding claims, wherein the VCSEL light source is operable to produce structured light.

4. The module of any of claims 1 to 3, wherein the VCSEL light source comprises a VCSEL having an asymmetric aperture.

5. The module of claim 4, wherein the asymmetric aperture is oval shaped.

6. The module of any of claims 1 to 3, wherein the VCSEL light source comprises a VCSEL comprising a reflective grating.

7. The module of any of claims 1 to 3, wherein the VCSEL light source includes first and second diffractive Bragg reflectors that are separate from one another and define a laser resonant cavity, the VCSEL light source further including a reflection grating adjacent at least one of the first or second diffractive Bragg reflectors.

8. The module of claim 7, wherein the first diffractive Bragg reflector is partially reflective and the reflective grating is adjacent to the first diffractive Bragg reflector.

9. The module of claim 7, comprising a first reflection grating adjacent to the first diffractive bragg reflector and a second reflection grating adjacent to the second diffractive bragg reflector.

10. The module of claim 7, wherein the reflection grating is a sub-wavelength reflection grating.

11. A module according to any of claims 1 to 3, wherein the VCSEL light source comprises first and second reflective gratings that are separate from each other and define a laser resonant cavity.

12. The module of claim 11, wherein at least one of the first or second reflective gratings is a sub-wavelength reflective grating.

13. The module of any of claims 1 to 12, wherein the VCSEL light source comprises a top emitting VCSEL.

14. The module of any of claims 1 to 12, wherein the VCSEL light source comprises a bottom emitting VCSEL.

15. The module of any one of claims 1 to 14, wherein the module is operable for three-dimensional structured light imaging.

16. The module of any one of claims 1 to 14, wherein the module is operable for three-dimensional time-of-flight ranging.

17. A method, comprising:

generating polarized light using a VCSEL light source, wherein at least some of the polarized light is reflected or scattered by an object; and

receiving at least some of the reflected or scattered polarized light in a sensor that is selectively operable to detect received light having the same polarization as light generated by the VCSEL light source.

18. The method of claim 17, comprising processing signals from the sensors to obtain a three-dimensional range image of the object.

19. The method of claim 17, comprising processing signals from the sensors using time-of-flight techniques to determine distance to the object.

20. The method of any one of claims 17 to 19, wherein the polarized light is linearly polarized light.

21. The method of any one of claims 17 to 20, wherein the polarized light is structured light.

22. A method according to any of claims 17 to 21, comprising generating the polarised light using a VCSEL having an asymmetric aperture.

23. A method according to any of claims 17 to 21, comprising generating the polarised light using a VCSEL comprising a reflective grating.

24. The method of any of claims 17 to 21, comprising generating the polarized light using a VCSEL comprising first and second diffractive bragg reflectors separated from each other and defining a laser resonant cavity, the VCSEL further comprising a reflection grating adjacent to at least one of the first or second diffractive bragg reflectors.

25. The method of claim 24, wherein the first diffractive bragg reflector is partially reflective and the reflective grating is adjacent to the first diffractive bragg reflector.

26. The method of claim 24, wherein the VCSEL includes a first reflection grating adjacent to the first diffractive bragg reflector and a second reflection grating adjacent to the second diffractive bragg reflector.

27. The method of any of claims 17 to 21, comprising generating the polarized light using a VCSEL comprising a sub-wavelength reflection grating.

28. A method according to any of claims 17 to 21, comprising generating the polarised light using a VCSEL comprising first and second reflective gratings separated from one another, the reflective gratings defining a laser resonant cavity.

Technical Field

The present disclosure relates to three-dimensional (3D) imaging and sensing applications using polarization (polization) specific Vertical Cavity Surface Emitting Lasers (VCSELs).

Background

VCSELs can provide a compact, powerful laser source for a variety of lighting applications. The use of VCSELs as illumination sources for structured light imaging systems, light detection and ranging (LIDAR) systems, and other types of 3D sensing and imaging systems is finding application in rapidly growing fields of application. Typical systems for various applications include unpolarized or randomly polarized VCSEL sources. However, the sensitivity of these systems may be limited by optical noise from the environment and scattering of the VCSEL beam by aerosols and other background scattering media.

Disclosure of Invention

The present disclosure describes a 3D light imaging and sensing system using one or more polarized VCSELs. VCSEL light reflected or scattered from an object and having the same polarization as the light emitted by the VCSEL(s) is detected by using an optical sensor that is selectively operable to detect light having the same polarization as the illumination emitted by the VCSEL(s). Optical noise with orthogonal polarization and orthogonal polarization components of VCSEL light scattered from aerosols and similar media are not detected. In some embodiments, the system improves sensitivity. For some applications, an important benefit may be reduced power consumption.

As an example, in one aspect, the present disclosure describes a module for light imaging and/or light, the module comprising: a VCSEL light source operable to produce polarized light; and a sensor selectively operable to detect received light having the same polarization as light generated by the VCSEL light source, wherein the received light is reflected or scattered by an object external to the module.

In another aspect, the present disclosure describes a method that includes generating polarized light using a VCSEL light source, wherein at least some of the polarized light is reflected or scattered by an object. The method also includes receiving at least some of the reflected or scattered polarized light in a sensor that is selectively operable to detect received light having the same polarization as the light generated by the VCSEL light source. In some cases, the method further comprises processing signals from a sensor to obtain a three-dimensional range image of the object, or processing signals from the sensor using a time-of-flight technique to determine a range to the object.

Some implementations include one or more of the following features. For example, in some cases, VCSEL light sources are operable to produce linearly polarized light. Various VCSEL structures can be used to produce linearly polarized light. Thus, in some cases, the VCSEL light source comprises a VCSEL with an asymmetric aperture. In some cases, the VCSEL light source comprises a VCSEL that includes one or more reflective gratings. In some cases, the VCSEL includes a sub-wavelength reflective grating.

In some embodiments, the VCSEL light source comprises a VCSEL, wherein first and second diffractive bragg reflectors are separate from each other and define a laser resonant cavity, wherein the VCSEL light source further comprises a reflection grating adjacent to at least one of the first or second diffractive bragg reflectors. In some cases, the first diffractive bragg reflector is partially reflective, and the reflective grating is adjacent to the first diffractive bragg reflector. In some embodiments, the VCSEL structure includes a first reflection grating adjacent to the first diffractive bragg reflector and a second reflection grating adjacent to the second diffractive bragg reflector. In some cases, the VCSEL light source includes a VCSEL having first and second reflective gratings that are separate from each other and define a laser resonant cavity.

Other aspects, features, and advantages will be apparent from the following detailed description, the accompanying drawings, and the claims.

Drawings

Fig. 1 shows an example of a light imaging or sensing system using a linearly polarized VCSEL light source.

Figures 2A and 2B (collectively figure 2) show examples of VCSEL structures that can operate to produce linearly polarized light. Fig. 2A is a top view and fig. 2B is a cross-sectional side view.

Figure 3 shows another structure of a VCSEL that is operable to produce linearly polarized light.

Figure 4 shows another example of a VCSEL structure that is operable to produce linearly polarized light.

Figure 5 shows another VCSEL structure that can operate to produce linearly polarized light.

Figure 6 shows yet another VCSEL structure that is operable to produce linearly polarized light.

Fig. 7 shows an example of a smartphone comprising a module operable to emit and sense polarized light.

FIG. 8 illustrates an example of a vehicle collision avoidance and surveillance system including a module operable to emit and sense polarized light.

Detailed Description

As shown in fig. 1, a 3D structured light imaging or ranging system 10 includes a polarized VCSEL light source 12 and an optical sensor 14, the optical sensor 14 having a polarizing filter aligned with the polarization of the VCSEL source. Thus, the optical sensor 14 is operable to selectively detect light 13A having the same polarization as the light 13B generated by the VCSEL light source 12. The VCSEL light source 12 can include a single VCSEL (e.g., in the case of a LIDAR system) or multiple VCSELs such as an array of VCSELs (e.g., in the case of a structured light imaging system). The use of VCSELs may be advantageous because they provide a compact, powerful laser source. In some cases, the VCSEL light source 12 and the sensor 14 are housed, for example, in a module. One or more linearly polarized light beams 13B from the VCSEL light source 12 are directed to a region of interest 18 (e.g., outside the module). The light beam 13B produced by the VCSEL light source 12 can include, for example, Infrared (IR), near-infrared, or other wavelengths of light, depending on the requirements of a particular application. In some cases, a passive optical element, such as a lens, is provided to adjust the divergence and direction of the light beam(s). An object 16 outside the module in the path of the VCSEL beam(s) 13B may reflect and scatter radiation 13C from the beam(s) in various directions, e.g. depending on the shape and composition of the object. VCSEL light 13B incident on the object surface at a normal angle may be reflected back to the sensor 14, which sensor 14 may be located near the light source 12. The light 13C reflected back to the sensor 14 will be polarized predominantly with the same linear polarization as the incident light beam 13B emitted from the light source 12.

Structured light imaging systems use structured illumination, which refers to spatially coded or modulated illumination. The structured lighting may have any regular shape (e.g., a line or a circle), or may have a pseudo-random pattern (such as a pseudo-random dot pattern), or may also have a pseudo-random shape or a pseudo-randomly sized shape. In a structured imaging system, the image sensor 14 may be implemented as, for example, an array of pixels. A signal processor may be provided to process the raw image(s) acquired by the sensor 14 and derive an acquired three-dimensional depth map of the object 16.

In a structured light system suitable for, for example, smart phone applications, the light source 12 may be implemented as a VCSEL array, the beam of which is projected into the region of interest 18. The sensor 14 may be implemented as, for example, a camera to record spot images based on reflections from one or more objects 16. The lateral spot position in the recorded image will depend on the distance of the object(s) 16 from the sensor 14 and VCSEL light source 12. The spot image(s) may then be analyzed, for example by a computing device (e.g., signal processor) in a smartphone, to calculate a 3D position of the object 16.

An optical ranging system, such as a time-of-flight (TOF) system, may collect range data for one or more objects 16. The distance data may include, for example, the distance between one or more objects and the optical ranging system. In contrast to structured light imaging systems, in optical ranging systems such as LIDAR systems, the sensor 14 may be implemented as, for example, a single photodetector to receive and record a signal indicative of the time of flight of the pulsed light beam from the single VCSEL to the object 16 and back to the sensor 14. In some cases, sensor 14 includes one or more demodulation photosensors (i.e., pixels). The time of flight may be calculated, for example, by a computing device (e.g., a signal processor), and used to determine the distance to the object 16. For example, the signal processor may use the signals from the pixel(s) to calculate the time it takes for light to travel from the VCSEL light source 12 to the object of interest 16 and back to the focal plane of the sensor 14. Thus, the TOF sensor, along with associated electronics and logic, is operable to resolve distances based on known speed of light by measuring the time of flight of the light signal between the sensor 14 and the point of the object 16. If the VCSEL beam is scanned across the object 16, a complete 3D position record of the object 16 can be obtained.

In some cases, the use of a linearly polarized VCSEL light source 12 can improve the sensitivity of the system 10. VCSEL light reflected or scattered from object 16 with the same polarization is detected by using sensor 14, which is limited to detecting light having the same linear polarization as the light emitted by the VCSEL light source. On the other hand, the sensor 14 will not detect optical noise with orthogonal polarization and orthogonal polarization components of VCSEL light scattered from aerosols and similar media. In some cases, the use of linearly polarized VCSELs in conjunction with polarization sensors may provide increased sensitivity and resolution in various applications. For example, for smart phones and other applications, a potential benefit is reduced power consumption. For other less power sensitive applications, the disclosed techniques may result in a greater range of distances.

Figures 2 to 6 show examples of linearly polarised VCSEL structures. For example, fig. 2A and 2B illustrate an example of a non-circular VCSEL device structure 20 that is operable to produce linearly polarized light using an asymmetric aperture 22. An elliptical or other asymmetric cross-section mesa 24 is etched to provide a VCSEL element. Then, during a subsequent oxidation process for providing the current hole, an asymmetry is formed in the hole shape. For example, in some cases, the VCSEL array mesa 24 is fabricated with an oval cross-section. When forming VCSEL current limiting oxide apertures, they also have a similar but smaller oval shape. This feature results in an oval cross-sectional gain section such that the VCSEL device 20 operates with an oval shaped beam. The ovoid structure results in asymmetric thermal and electrical stresses applied to the VCSEL crystal structure, resulting in refractive index asymmetry. This optical asymmetry causes the VCSEL to lase with a linear polarization aligned with the refractive index asymmetry.

In general, there should be sufficient asymmetry to overcome any other polarization bias in the VCSEL structure. Furthermore, as described above, the VCSEL array layout of figure 2 includes an asymmetric aperture 22 and produces a controlled linear polarization in the oval-shaped output beam. The non-circular VCSEL beam produced by VCSEL structure 20 can have an associated variation in beam divergence properties. Thus, the VCSEL structure 20 may be more useful for applications where such issues are not a concern.

In other embodiments, a VCSEL structure operable to produce linearly polarized light includes one or more reflective gratings. In some cases, these structures may produce a substantially symmetrical circular output beam (i.e., a beam having a circular or substantially circular cross-section). VCSELs can be top emitting or bottom emitting. In some embodiments, the reflective grating is functionally integrated with a Distributed Bragg Reflector (DBR). In other cases, a reflective grating may be advantageously used even without an associated DBR.

As shown in the example of fig. 3, the top-emitting VCSEL structure includes a sub-wavelength reflective grating 30 in combination with a top partially reflective DBR 36. In the example shown, the VCSEL structure is fabricated on top of a substrate 32, and an output beam 39 is transmitted out of the top of the structure. The VCSEL structure comprises a bottom highly reflective DBR 33 and a top partially reflective DBR 36, said top partially reflective DBR 36 transmitting an output light beam 39. The two DBRs 33, 36, which may be implemented as mirrors, form a laser resonator. Between the two DBRs 33, 36 is a gain region 34 comprising a group or stack of multiple quantum wells 31, which multiple quantum wells 31 can be activated, for example, by a current flowing between top and bottom electrical contacts (e.g., electrodes) 37, 38. In some designs, quantum well 31 is activated by shining a laser beam on quantum well 31 to optically pump carriers. In a VCSEL activated by a current, the aperture 35 may be used to concentrate the current in the central region. The hole 35 may be formed, for example, by oxidation, but other techniques such as ion implantation may be used to form an electrically insulating region around the hole.

As shown in fig. 3, a reflective grating 30 is formed on top of the upper DBR 36, the reflectivity of which can be adjusted to optimize the overall combined reflectivity. The combined structure of the reflective grating 30 and the DBR 36 should be designed and fabricated to have the proper phase relationship.

Figure 4 shows another VCSEL structure that is operable to produce linearly polarized light having a circular or substantially circular beam cross-section. The example shown is a bottom emitting VCSEL structure, where the respective reflection gratings 40A, 40B operate in conjunction with an upper DBR 46 and a lower DBR 43, respectively. In this case, the bottom DBR 43 is partially reflective, while the top mirror 46 is highly reflective, so that the output beam 49 is transmitted through the substrate 42. The two DBRs 43, 46, which may be implemented as mirrors, form a laser resonator. Between the two DBRs 43, 46 is a gain region 44 comprising a group or stack of multiple quantum wells 41, which multiple quantum wells 41 can be activated, for example, by a current flowing between top and bottom electrical contacts (e.g., electrodes) 47, 48. A respective one of the reflection gratings 40A, 40B is disposed adjacent to each of the DBRs 43, 46. The holes 45 may be used to concentrate the current in the central region. For example, the VCSEL structure of fig. 4 can be bound in direct contact with a heat sink for more efficient cooling.

In some embodiments, such as where the sub-wavelength reflective grating has a very high reflectivity (e.g., close to 100%), the reflective grating may eliminate the need for an associated DBR. Figure 5 shows an example illustrating a bottom emitting VCSEL structure operable to produce linearly polarized light having a circular or substantially circular beam cross-section. In this case, the VCSEL structure includes the highly reflective sub-wavelength reflective grating 50, but does not include the bottom DBR. The top DBR 56, which may be implemented as a mirror, is highly reflective such that the output beam 59 is transmitted through the substrate 52. The laser cavity is formed between the top DBR 56 and the reflection grating 50 and includes a gain region 54. The gain region 54 includes a group or stack of multiple quantum wells 51, which multiple quantum wells 51 may be activated, for example, by a current flowing between top and bottom electrical contacts (e.g., electrodes) 57, 58. The holes 55 may be used to concentrate the current in the central region.

The details of the reflection grating may vary depending on the particular application. As an example of a known structure, a sub-wavelength reflection grating may comprise a one-dimensional grating structure having lines made of a high refractive index material disposed between low refractive index materials. The difference in refractive index between the high index material and the low index material determines the bandwidth and modulation depth and produces a wider reflection band. The reflection is sensitive to various parameters such as the grating period, the grating thickness, the duty cycle of the grating, the thickness and refractive index of the low index layer under the grating. In some cases, a sub-wavelength reflective grating may include a first layer of low refractive index material, a plurality of periodically spaced apart segments of high refractive index material on the layer of low refractive index material, and a second layer of low refractive index material on the segments of high refractive index material. Other reflective grating structures may also be used.

In some embodiments, each of the top and bottom DBRs may be omitted from the VCSEL structure and may be replaced by a respective reflective grating. Figure 6 shows an example illustrating a top emitting VCSEL structure operable to produce linearly polarized light having a circular or substantially circular beam cross-section. Output beam 69 is transmitted out of the top of the structure formed above substrate 62. In this case, the VCSEL structure includes highly reflective sub-wavelength reflective gratings 60A, 60B, but no bottom or top DBR. The laser cavity is formed between the top reflection grating 60A and the bottom reflection grating 60B and includes a gain region 64. The gain region 64 includes a group or stack of multiple quantum wells 61, the multiple quantum wells 61 being activatable, for example, by current flowing between top and bottom electrical contacts (e.g., electrodes) 67, 68. The holes 65 may be used to concentrate the current in the central region.

In some cases, replacing one or both DBRs with corresponding reflective gratings may also provide other advantages. For example, a shorter length along the optical axis of the VCSEL structure may result in a thinner VCSEL device. In addition, depending on the material used, the resistance can be reduced. The lower resistance may help reduce electrical power dissipation, which in turn may result in higher electrical-to-optical power conversion efficiency. Furthermore, optical absorption losses can be smaller because the use of reflective grating(s) does not require different material doping levels as does the DBR structure(s). These features can lead to higher VCSEL efficiency, with the benefit of lower input power at the same optical output power.

As described above, the combined use of the linearly polarized VCSEL light source 12 and the linearly polarized sensor 14 can improve sensitivity by increasing the signal-to-noise ratio. Ambient light 13D (see fig. 1) that may generate noise signals in the sensor is unpolarized; thus, about fifty percent of this optical noise will be eliminated by the sensor polarization analyzer. Aerosols 19 in the atmosphere (see fig. 1) also tend to scatter light 13E back to the sensor 14. Typically, there are multiple internal reflections inside the aerosol 19, which tend to depolarize the incident linearly polarized light beam. Thus, noise signals from such scattering objects may also be attenuated.

The processing circuitry may be implemented, for example, as one or more integrated circuits in one or more semiconductor chips with appropriate digital logic and/or other hardware components (e.g., read registers, amplifiers, analog-to-digital converters, clock drivers, timing logic, signal processing circuitry, and/or microprocessors). Thus, the processing circuitry is configured to implement various functions associated with such circuitry.

The modules described herein may be used, for example, as proximity sensor modules or as other optical sensing modules such as for gesture sensing or recognition. The module may be integrated into various electronic devices and other devices, such as mobile phones, smart phones, cameras, notebook computers, Personal Digital Assistants (PDAs), tablet computers, and the like. The module may be integrated into various small electronic devices such as a biological device, a mobile robot, a surveillance camera, and the like.

Fig. 7 shows an example of a smartphone 70, said smartphone 70 comprising a module 72 for 3D imaging and/or sensing. The module 72 is operable to emit polarized light and selectively detect an incident light beam having the same polarization as the emitted light beam. Module 72 includes a polarized VCSEL light source 74 that includes one or more VCSELs operable to emit polarized light. In some cases, the light generated by the light source 74 is structured. The module 72 further comprises a polarization-sensitive sensor 76, the polarization-sensitive sensor 76 being operable to selectively sense an incident light beam having the same polarization as the light beam emitted by the light source 74. The VCSEL light source 74 and sensor 76 may be mounted on, for example, a printed circuit board or other substrate 78. Module 72 may also include projection optics 79A and collection optics 79B, which may be implemented as, for example, lenses or other passive optical elements. Signal processing circuit 77 is operable to process the signals detected by sensor 76 and determine, for example, the distance to an object external to smartphone 70 that reflects some polarized light back to the smartphone, and/or for gesture recognition.

In some embodiments, the smartphone 70 has a thickness (t) on the order of a few millimeters (e.g., 5 to 7 mm). By using a linearly polarized VCSEL source, the required imaging sensitivity can be obtained with a higher signal-to-noise ratio, which may result in a lower total power required for operation.

Fig. 8 shows another exemplary application in the context of automotive safety. The collision avoidance sensor and monitoring system may use multiple LIDAR modules to detect objects 82, including other vehicles on the road 86, to analyze potentially dangerous conditions and provide audible or other warnings to the vehicle driver. LIDAR modules 84 (each of which includes a polarized VCSEL light source and corresponding polarization sensitive sensor as described above) may be located at different locations on vehicle 80 or in vehicle 80 to detect objects 82 outside of vehicle 80 and determine their distance from the vehicle. In general, it is desirable that these systems be small, compact and relatively inexpensive, yet still provide good sensitivity in sensing hazardous objects.

In addition to smart phones and other portable computing devices and automotive collision avoidance and surveillance systems, the above-described techniques, modules, and systems may be used in other applications, including but not limited to computer gaming systems.

Various modifications may be made to the foregoing examples. Accordingly, other implementations are within the scope of the following claims.