SE545314C2 - Method and apparatus for laser beam mudulation and beam steering - Google Patents

Abstract

The present invention relates to A laser emitting device comprising, a spatial modulator comprising a plurality of individually addressable piston or deflection pixel elements, at least one laser emitter attached to a top surface of at least two of said plurality of individually addressable pixel elements, wherein said spatial modulator is configured in operation to phase modulating emitted light from said laser emitters for steering a predetermined light pattern to a predetermined position. The invention also relates to a lidar device and a method for detecting objects.

Description

Technical field of the invention The present invention relates in general to the field of laser beam modulation and beam steering. ln particular, the present invention relates to methods and devices for spatially modulating a plurality of laser emitting sources.

Background of the invention There is a growing interest in high quality digital projection systems that display images that meet 10 or exceeds the quality of movies, especially in large areas.

Projectors based on DLP show the ability to provide the required light throughput, contrast ratio, and colour quality for most desktop to large cinema projection applications. However, existing devices are inherently limited in resolution, typically having no more than 2048 >< 1080 pixels. ln addition, due to the high cost of components and systems, the suitability for higher quality digital 15 cinema projection is limited. Furthermore, the cost, size, weight and complexity of a Philips prism or other suitable combined prism are significant constraints. Furthermore, the need for relatively fast projection Ienses with long working distances due to luminance requirements has a negative impact on the acceptability and ease of use of these devices. ln LiDAR application, a laser source and a beam steering element is used to scan the field of view. 20 Currently, most LiDAR use an architecture of laser and beam steering element which can be complex, inefficient and expensive.

US 2020/0301010 discloses a distance measurement apparatus including a light projector; a sensor to receive light projected from the light projector and reflected from a target object, photoelectrically convert the received light to an electrical signal, and obtain a plurality of phase 25 signals from the electrical signal; and an interface to output distance data indicating a distance to the target object, the distance data being obtained based on the plurality of phase signals. The light projector includes a plurality of light emitters that are arranged two-dimensionally; and circuitry configured to cause the plurality of light emitters to emit light simultaneously in groups. Here groups of emitters are temporally controlled by switching laser beam on and off for achieving a desired laser beam pattern or alternatively a movable mechanism capable of moving a plane with laser sources and uses, as a drive source, a piezoelectric element that expands or contracts the plane in accordance with application of a voltage while intermediate laser sources are switched off. The movable mechanism is moved in accordance with a drive signal, thereby shifting the position of the laser sources in a plane relative to each other. The problem with this distance measurement apparatus is that it has a limited range capability due to the fact that maximum output power is compromised with said modulating technology.

There is a need in the art for an improved laser beam modulating methods and devices which is less complex and more efficient than state of the art products. 0b'|ect of the Invention The present invention aims at obviating the aforementioned problem. A primary object of the present invention is to provide an improved laser emitting device.

Another object of the present invention is to provide an improved lidar device.

Yet another object of the invention is to provide an improved method for detecting objects. Summag of the Invention According to the invention at least the primary object is attained by means of the system having the features defined in the independent claims.

Preferred embodiments of the present invention are further defined in the dependent claims.

According to a first aspect of the present invention it is provided laser emitting device comprising, a spatial modulator comprising a plurality of individually addressable piston or deflection pixel elements, at least one laser emitter attached to a top surface of at least two of said plurality of individually addressable pixel elements, wherein said spatial modulator is configured in operation to phase modulating emitted light from said laser emitters for steering a predetermined light pattern to a predetermined position.

An advantage of this embodiment is an efficient laser emitting device with modulation and beam steering capability.

In various example embodiments ofthe present invention said individually addressable pixel elements are piezo or electrostatically operated piston pixels.

The advantage of these embodiments is a robust and precise modulation technique. ln various example embodiments ofthe present invention said individually addressable pixel elements are electrostatically operated deflection pixels.

The advantage of these embodiments is that it provides for a variety of modulation and beam steering alternatives which may speed up the response time for the emitting device. ln various example embodiments according to the present invention said laser emitter is a VCSEL, edge emitting laser source, LED, super luminescent emitting diode or the like.

The advantage of these embodiments is that almost any type of laser emitters may be used, only the pixel size may limit the use of a particular type of laser emitter. ln various example embodiments according to the present invention it further comprising a polarizer provided in front of said array of laser emitters.

The advantage of these embodiments is that the polarizer adds another dimension of flexibility regarding beam steering and/or beam focusing. ln various example embodiments according to the present invention one or a plurality of laser emitters is configured for polarization modulating emitted light for steering a predetermined light pattern to a predetermined position.

The advantage of this embodiment is that polarization modulation is independent from phase modulation which adds another dimension of fine tuning the beam steering capability and/or beam shaping capability. ln another aspect of the present invention it is provided lidar device comprising, - a laser emitting array module comprising a plurality of laser emitters emitting a laser beam, - a detecting module receiving at least a portion of the laser beam reflected from an object, wherein said laser emitting array module comprises a spatial modulator comprising a plurality of individually addressable piston or deflection pixel elements, at least two of said plurality of individually addressable piston or deflection pixel elements each have at least one of said emitters attached to a top surface thereof, wherein said spatial modulator is configured in operation to phase modulating emitted light from said laser emitters for steering a predetermined light pattern to a predetermined position, a control unit for controlling said plurality of emitters and/or said detecting module.

The advantage of this embodiment is that it provides for a more efficient and less complex lidar device compared to prior art solutions. ln various example embodiments of the lidar device said individually addressable pixel elements are piezo or electrostatically operated piston pixels.

The advantage of these embodiments is a robust and precise lidar device. ln various example embodiments of the lidar device said individually addressable pixel elements are electrostatically operated deflection pixels.

The advantage of these embodiments is that it provides for a variety of modulation and beam steering alternatives for the lidar device which may speed up the response time. ln various example embodiments of the lidar device said laser emitter is a VCSEL, edge emitting laser source, LED, super luminescent emitting diode or the like.

The advantage of these embodiments is that almost any type of laser emitters may be used, only the pixel size may limit the use of a particular type of laser emitter. ln various example embodiments of the lidar device further comprising a polarizer provided in front of said array of laser emitters.

The advantage of these embodiments is that the polarizer adds another dimension of flexibility regarding beam steering and/or beam focusing for the lidar device. ln various example embodiments of the present invention at least one pixel element is configured for polarization modulating emitted light from said at least two laser emitters for steering a predetermined light pattern to a predetermined position.

The advantage of this embodiment is that polarization modulation is independent from phase modulation which adds another dimension of fine tuning the beam steering capability and/or beam shaping capability. ln another aspect ofthe present invention the laser emitting device may be used in display applications, for instance big screen projector displays.

The advantage of this embodiment is that it provides for a display technique with high pixel intensity and adjustable field of view which may make it particularly suitable for long distance projector distance. ln another aspect of the present invention it is provided method for detecting objects, the method comprising: activating at least two of a plurality of laser emitters in a laser emitter array, wherein said laser emitters are provided on a top surface of a spatial modulator, detecting by a detector light from at least two of said emitters reflected by an object, determining a location of the object in response to the detecting, phase modulating emitted light constructively or destructively from said laser emitters by moving piston or deflection pixel elements in said spatial modulator for steering a predetermined light pattern to a predetermined position.

The advantage of this embodiment is that it provides for a more efficient and less complex detection method compared to prior art solutions. ln various example embodiments according to the present method said spatial modulator 30 and said detector is provided in a vehicle, an aerospace device or a robot.

The advantage of these embodiments is that it provides for an efficient method for autonomous vehicle technology, rocket docking technology or robot technology.

The advantage of these embodiments is that it provides for a robust and precise detection method. ln various example embodiments according to the present method wherein said laser emitter is a VCSEL, edge emitting laser source, LED, super luminescent emitting diode or the like.

The advantage of these embodiments is that almost any type of laser emitters may be used, only the pixel size may limit the use of a particular type of laser emitter. ln various example embodiments according to the present method further comprising the step of polarization modulating emitted light from said laser emitters for steering a predetermined light pattern to a predetermined position.

The advantage of these embodiments is that the polarizer adds another dimension of flexibility regarding beam steering and/or beam focusing for detection method.

Further advantages with and features of the invention will be apparent from the following detailed description of preferred embodiments.

Brief description of the drawings A more complete understanding of the abovementioned and other features and advantages 15 of the present invention will be apparent from the following detailed description of preferred embodiments in conjunction with the appended drawings, wherein: Fig. 1 depict an example embodiment of a laser array according to the present invention.

Fig. 2a depicts an example embodiment of a laser element according to the present invention 20 belonging to a laser array in retracted position.

Fig. 2b depicts an example embodiment of a laser element according to the present invention belonging to a laser array in extracted position.

Fig. 3 depicts an example embodiment of a laser array and a far field pattern according to the present invention.

Fig. 4 depicts a LiDAR device according to an example embodiment of the present invention.

Fig. Sa depicts a first example embodiment of phase modulation pattern from a laser array according to the present invention.

Fig. 5b depicts a second example embodiment of phase modulation pattern from a laser array according to the present invention.

Fig. 6 depicts a first example embodiment of polarization modulation pattern from a laser array according to the present invention.

Detailed description of preferred embodiments of the invention Fig. 1 depict an example embodiment of a VCSEL (Vertical Cavity Surface Emitting Laser) /laser array 100 according to the present invention. Each VCSEL/laser Pixel 110 in the array 100 are individually addressable. Beams from each VCSEL/laser pixel 110 can be made to interfere with each other constructively and destructively in the far field, depending on the phase difference created by a piston mode operation or a deflection mode operation of each pixel. This interference of beams from each VCSEL/laser may steer the beam in the far field for scanning the required field of view. Field of view is determined by the pixel pitch of the VCSEL/laser array. VCSEL/laser in the VCSEL/laser array will require to have similar peak wavelength. A master laser can also be used to make the array operate at the wavelength in order to achieve beam interference from each VCSEL/laser source in the array 100. In figure 1 an array having 6 rows and 12 columns of VCSEL/laser elements, i.e., 72 individually addressable VCSEL/laser elements. The array may comprise more or less VCSEL/laser elements such as 4x4, 10x10, 100x100, 1000x1000 etc. The VCSEL/laser array may comprise a spatial modulator comprising a plurality of individually addressable pixel elements. The pixel elements may be electrostatically or piezoelectrically movable elements. The pixel elements may be of piston type, i.e., movement in one direction only or a deflection type where the pixel may be deflected around an axis in positive or negative direction. Electrostatically addressable deflection type pixels in a spatial modulator may be addressable in a similar way as the digital micromirror device (DMD) from Texas Instruments where individual pixel elements may be set in on or off position by using an electrostatically attraction force between said pixel elements and a substrate. Electrostatically addressable deflection type pixels in a spatial modulator may alternatively be addressable in a similar way as Micronic Laser Systems Spatial Light Modulator (SLM) where each pixel elements are electrostatically addressable in 64 positions between fully flat and fully deflected. Pixel elements of piston type may also be addressable in on-off fashion, digital mode, where the pixel element 25 may be fully extracted or fully retracted. Alternatively, piston type pixel elements may be addressable in grey level fashion, analog mode, where there one or a plurality of extracted/retraced addressable positions of the pixel element in between the fully extracted position and the fully retracted position.

A laser emitter is attached to a top surface of the individually addressable pixel elements in the spatial modulator. The spatial modulator is configured to phase and/or polarization modulating emitted light from said laser emitters.

Fig. 2a depicts an example embodiment of a laser element 110 according to the present invention belonging to a laser array in retracted position. The laser element 110 may be arranged on a substrate 120 and in between the laser element and said substrate a movable element 130 35 may be arranged. The movable element may be of piston type or deflection type as mentioned hereinabove and the and the movable element may be moved by electrostatic forces or piezoelectric forces. Fig. 2b depicts an example embodiment of a laser element 110 according to the present invention belonging to a laser array in extracted position. Here the movable element 130 is set so that the laser element 110 is further away from the substrate 120 compared to the 5 laser element 110 in figure 2a. The laser/VCSEL emits a beam Laser/VCSEL 110 in the array 100 can also be replaced with an edge emitting laser source and can used for beam steering in the far filed similarto VCSEL source.

Beams 140 from a laser/VCSEL array 100 can also be steered by modulating polarisation of VCSEL array 100. An amplitude pattern can be written to VCSEL array 100. This amplitude pattern can be translated into polarisation modulation of VCSELs 110 in the VCSEL array 100. VCSEL array 100 may be followed by a static polariser with defined polarisation axis allowing only one polarisation state.

A Beam of a VCSEL array may be steered by spatially modulating the VCSEL array Each VCSEL Pixel 110 in the array 100 may be individually addressable. Beams from each VCSEL 15 pixel 110 may be made to interfere with each other constructively and destructively in the far field, depending on the phase difference created by the piston mode operation or the deflection mode operation. This interference of beams 140 from each VCSEL 110 may steer the beam in the far field for scanning a required field of view, for instance an object of interest.

A beam 140 from a VCSEL array 100 can be steered by spatially modulating VCSEL array 100. Each VCSEL act as a pixel in a VCSEL array 100. A phase pattern can be implemented on the pixel array for intended beam pattern and location in the far field. Each pixel 110 in the pixel array 100 will have unique phase information. Each VCSEL pixel will contribute to the resultant beam in the far filed. A beam or pattern can be formed and (or) steered in the far field based on the phase information of each VCSEL pixel. This phase information can be executed by operating each VCSEL 25 110 in the array 100 in a piston mode or deflection mode.

Figure 3 depicts an example embodiment of a laser array 100 and a far field patterncreated by the beams 140 from the laser array according to the present invention. ln figure 3 all pixel elements, laser emitting sources, are in the same position, i.e., on, off or any level in between. The far field pattern may be manipulated by setting individual laser emitting elements 30 in the laser array at different position and thereby, by constructive or destructive interference, steer and focus a light beam pattern in the far field. The beam pattern may scan a predetermined area in the far field by changing the positions of the individual laser elements 110 in the laser array 100. The beam maybe focused or defocused in the far field depending on the position pattern of the spatial modulator.

P30934Fig. 4 depicts a LiDAR device 800 according to an example embodiment of the present invention. The lidar device 800 comprises a VCSEL/laser array 100, a lens 300, a detector 200 and a control unit 700. A spatially modulated VCSEL array 100 may offer an intelligent scanning of a target in contrast to raster scan or Flash LiDAR architecture, reducing bulky and complex data processing time and solutions. Fig 4 illustrates an example configuration of a distance measurement apparatus Lidar 800. As illustrated in FIG. 4, the distance measurement apparatus 800 includes a VCSEL array, the transmitter 100, the detector (receiver) 200 and a distance measurement control unit 700. The transmitter includes a VCSEL array 100, where each VCSEL are provided on a movable mechanism as disclosed hereinabove. The control unit 700 controls the individual light emitters 110 in the VCSEL array 100 and also controls the received light pattern on said detector 200 for determining the shape of and/or the distance to an object in the far field 400. The lens 300 is used for focusing the light pattern onto said detector 200. The detector 200 may for instance be a single photon avalanche diode (SPAD) array. Beams 140 from the laser array 100 provides for a predetermined pattern in the far field. Reflected beam 240, from a potential object in the far field 400, is detectable by the detector The VCSEL array 100 includes a plurality of light emitters that are two-dimensionally arranged in the X-Y plane. The VCSEL array 100 may comprise hundreds, thousands, or millions of light emitters The movabie mechanism 130 of each pixel element/light emitter may be capable of translating the light emitter 110 in z-direction. ln alternative embodiments the light emitters 110 may be deflected in order to phase modulate beams from a plurality of emitters 110 in the VCSEL array 100. As a drive source, a piezoelectric element may be used that is expandable or contractible in accordance with application of a voltage, for movement in Z-direction. The light emitter 100 is attached to the movabie mechanism 130, and the movabie mechanism 130 is moved in accordance with a drive signal, thereby shifting the position of the light emitter 110 in Zdirection.

Fig. Sa depicts a first example embodiment of phase modulation pattern 282 in far field from a laser array 100 according to the present invention. At least one pattern of the contracted/extracted pixels will create a desired pattern in far field in a desired position. Fig. 5b 30 depicts a second example embodiment of phase modulation pattern 170 from a laser array 100 according to the present invention. Here the pattern of contracted/extracted pixels are changed compared to the pattern in figure 5a for creating a focused beam at a desired position. By constantly changing the pattern of the pixel elements, i.e., by constantly changing the position of the movabie elements 130 in the laser array 100, a desired laser pattern maybe scanned over a 35 predetermined area. Optical power in the far field may be scaled up according to the present invention by combining beams from all VCSELs/laser emitters 110 coherently and optical power from all beams from said laser emitters 110 may be projected into a specific predetermined direction.

Figure 6 depicts a first example embodiment of polarization modulation pattern 284 from a laser array 100 according to the present invention. Here a polarizer 600 with a predetermined polarization pattern is arranged in front of the laser array 100. The polarization pattern of the polarizer 600 may be fixed or alterable. Polarization modulation of the light emitted by the laser emitters 110 in the laser array 100 is achieved by altering polarization state of individual laser emitters electrically. Polarization modulation is independent from phase modulation. Scanning a 10 predetermined light pattern in the far field is performed by amending the position of the deflection or piston pixel elements in the laser array 100 in a predetermined fashion. Any type of scanning pattern may be achieved. Scanning patterns may be stored in a look-up table, i.e., in the look up table there is for each and every setting of the modulator a corresponding resulting light pattern in the far field. ln order to create a predetermined scanning pattern for a predetermined 15 light pattern one might beforehand choose from the look up table a desired light pattern and its corresponding position in the far field in order to create a desired scanning path in the far field. The light pattern that is to be scanned in the far field may be a single focused or unfocused light beam, a plurality of focused or unfocused light beams or a predetermined light pattern. ln various example embodiment the scanning of a predetermined light pattern in the far field may be a combination of altering the pixel element positions in the laser array 100 and the polarization of the laser emitters 110. The polarisation may be altered from a laser emitter 110 by changing its driving current, by changing the temperature of the laser emitter and/or by applying a stress externally. Polarisation can also be changed by putting birefringent material /polariser in front of the laser emitter(s).

The laser array 100 may be used in consumer electronics as displays and cameras, automotive Industry as LiDAR application for sensing, ranging, detection, automatic cruise control (ACC), Advance driver assist (ADAS), aerospace Industry as LiDAR application for docking station, satellite debris detection or the like.

The laser emitters in the laser array 100 can be switched all on at once so it can operate in a so-called flash mode. ln alternative example embodiments the laser emitters in the laser array can also be switched on to project a pattern in the field of view, e.g., the laser emitters can be switched on in a line, a point or a pattern to scan the field of view. The scanning of the far field may be made in any type of pattern such as, but not limited to, a serpentine or raster pattern, line wise pattern where a new line always starts from one end which may be left or right, column wise 35 where a new column always starts from the top or bottom, a spiral out scanning pattern where a predetermined area of the far field is covered starting at origo and working outwards or spiral in scanning pattern where one starting at the periphery of the predetermined area and scan towards origo.

VCSEL based beam steering technology may be used for LiDAR application.

Piston mode VCSEL based optical phase array may be used for LiDAR application. Spatially modulated VCSEL array may be used for LiDAR application and phase modulated VCSEL array may be used for LiDAR application.

Feasible modifications of the invention The invention is not limited only to the embodiments described above and shown in the drawings, which primarily have an iilustrative and exemplifying purpose. This patent application is intended to cover all adjustments and variants of the preferred embodiments described herein, thus the present invention is defined by the wording of the appended claims and the equivalents thereof. Thus, the equipment may be modified in all kinds of ways within the scope ofthe appended claims.

Throughout this specification and the claims which follows, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or steps or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims (6)

1. A laser emitting device comprising, - a spatial modulator comprising a plurality of individually addressable piston or 5 deflection pixel elements, - at least one laser emitter attached to a top surface of at least two of said plurality of individually addressable pixel elements, wherein said spatial modulator is configured in operation to phase modulating emitted light from said laser emitters for steering a predetermined light pattern to a predetermined position.

2. The laser emitting device according to claim 1, wherein said individually addressable pixel elements are piezo or electrostatically operated piston pixels.

3. The laser emitting device according to claim 1, wherein said individually addressable pixel 15 elements are electrostatically operated deflection pixels.

4. The laser emitting device according to any one ofthe preceding claims, wherein said laser emitter is a VCSEL, edge emitting laser source, LED, super luminescent emitting diode or the like.

5. The laser emitting device according to any one of the preceding claims, further comprising a polarizer provided in front of said array of laser emitters.

6. The laser emitting device according to any one ofthe preceding claims, wherein one or a 25 plurality of laser emitters is configured for polarization modulating emitted light for steering a predetermined light pattern to a predetermined position.