Laser arrangement with optical filter

Abstract

The present invention describes a laser arrangement structure for time-of-flight measurement, the laser arrangement structure comprising at least one laser and at least one filter arranged adjacent to the at least one laser, wherein the at least one laser and the at least one filter each comprise a substrate, a first reflector, a second reflector, and an active layer arranged between the first reflector and the second reflector, wherein the at least one laser is arranged to be able to emit laser light in a first direction, wherein the filter is arranged to be able to receive received light, wherein the received light comprises laser light reflected from an object, the at least one filter having a first reflector, an active layer and a second reflector in a direction of propagation of the received light, wherein the second reflector of the at least one filter has a reflectivity equal to or lower than the reflectivity of the first reflector of the at least one filter, wherein the filter is also arranged to be able to filter the received light so that the laser light reflected from the object and received from the first direction passes through the filter.

Description

Technical Field

[0001] The invention relates to a laser arrangement with a filter for time-of-flight measurement, a detector arrangement for time-of-flight measurement, a time-of-flight camera, a method for determining a depth image and a corresponding computer program carrier. Background Art

[0002] Laser arrangements including, for example, arrays of vertical cavity surface emitting lasers (VCSELs) can be used for infrared illumination devices. Using short pulses, VCSEL arrays are used, for example, in time-of-flight applications. Such applications include, for example, close-range gesture recognition and 3D spatial recognition for portable devices. For such applications, an area of ​​about 1 mm2 with an output power in the range of 1-10 W is discussed. 2 The specific illumination field or field of view is defined by the application (e.g. a time-of-flight camera observing e.g. 70°×50°).

[0003] EP3176888A1 discloses a sensor chip suitable for time-of-flight measurement. The sensor chip includes one or more lasers and photodetectors arranged adjacent to each other on the same semiconductor substrate. The laser or laser structure and the photodetector or photodetector structure are processed on the same wafer in the same processing step. Therefore, the changes between the structures of the laser and the photodetector can be minimized. The resonant photodetector is arranged to be sensitive within the wavelength range of the laser emitted by the laser. The optical passband of the resonant photodetector is wider than the optical passband of the laser cavity of the laser. Therefore, changes in the emission wavelength of the laser light can be compensated, such as caused by the temperature difference between the light emitting laser and the resonant photodetector.

[0004] MOENCH HOLGER ET AL: “VCSEL-based sensors for distance and velocity”, PROCEEDINGS OF THE SPIE-SMART STRUCTURES AND MATERIALS 2005: SMARTELECTRONICS, MEMS, BIOMEMS, AND NANOTECHNOLOGY PROCEEDINGS OF THE SPIE; THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING SPIE-IMT.SOC.OPT.ENG.USA, 100020TH FT.BELLINGHAM WA 98, Vol.9766, 4March 2016, pages 97660A-97660A-1-97660A-11 discloses a VCSEL-based sensor that can measure distance and velocity, wherein the measurement can be based on a time-of-flight method and self-mixing interference.

[0005] US2015 / 0219764A1 discloses a LIDAR sensor for a vehicle. The LIDAR sensor includes a plurality of spaced-apart VCSEL arrays.

[0006] US2016 / 0266242A1 discloses a laser sensor with beam steering capability.

[0007] US2017 / 0102461A1 discloses a distance measuring device including a projector, wherein the projector is configured to project a laser beam to an object at a projection angle. The device also includes a light detector array in which a plurality of light detectors are arranged. Summary of the invention

[0008] It is an object of the present invention to provide an improved laser arrangement for time-of-flight measurements.

[0009] According to a first aspect, a laser arrangement structure for time-of-flight measurement is provided. The laser arrangement structure includes at least one laser and at least one filter arranged adjacent to the at least one laser. The at least one laser and the at least one filter each include a substrate, a first reflector, a second reflector, and an active layer arranged between the first reflector and the second reflector. The at least one laser is arranged to be able to emit laser light in a first direction. The filter is arranged to be able to receive received light. The received light includes laser light reflected from an object. The laser light is emitted by the first reflector of the at least one laser, and the received light is received by the first reflector of the at least one filter. The first reflector of the at least one laser and the first reflector of the at least one filter have equal reflectivity. The second reflector of the at least one laser and the second reflector of the at least one filter have equal reflectivity, or the reflectivity of the second reflector of the at least one filter is reduced relative to the reflectivity of the second reflector of the at least one laser. The filter is also arranged to be able to filter the received light so that the laser light reflected from the object and received from the first direction passes through the filter.

[0010] The at least one laser and the at least one filter may be arranged side by side. The at least one laser may preferably be arranged to be able to emit laser light of a wavelength for which the substrate is transparent. In the case of a GaAs substrate, the wavelength of the emitted laser light may, for example, be longer than about 900 nm (depending on the thickness of the substrate). The substrate may alternatively or additionally be removed so that the reflected laser light may enter the filter via a first reflector, and at least a portion of the reflected laser light filtered by the filter may leave the filter via a second reflector (or vice versa). The laser and the filter are characterized by a semiconductor epitaxial layer stack, which for example comprises a first reflector, a second reflector and an active layer, etc. The first reflector, the second reflector and the active layer may be characterized by having the same optical properties. Therefore, the laser and the filter are preferably processed in the same production process to avoid or at least limit the effects of production differences. The semiconductor layer stack is (substantially) the same for both devices. Therefore, the filter is arranged so that the filter wavelength matches the emission wavelength of the laser during operation. The laser and the filter are thermally coupled in such a way that during operation of the laser arrangement the temperature of the laser and the filter are substantially the same to compensate for thermal shifts of the emission wavelength of the laser. Thus, the laser arrangement is arranged to be able to emit laser light in a first direction and receive reflected laser light from the same first direction, such that the filter suppresses ambient light having a different wavelength and / or reception direction. Thus, the laser arrangement enables a very sensitive detector arrangement (see below).

[0011] The substrate may be a common substrate, wherein the at least one laser and the filter are arranged on the common substrate. The at least one laser is a vertical cavity surface emitting laser (VCSEL). The VCSELs may be processed in parallel so that adjacent VCSEL structures share the same epitaxial layer stack. A first VCSEL structure of two adjacent VCSEL structures may be used as a laser, and a second VCSEL structure of two adjacent VCSEL structures may be used as a filter.

[0012] VCSEL arrays have a laser wavelength extension range of about 10-20 nm and a thermal shift of the wavelength of 0.07 nm / K, resulting in an additional 10 nm extension range, e.g. for automotive conditions from -40° C. to 105° C. Therefore, using two (or more) adjacent VCSEL devices can compensate for production differences and, due to the strong thermal coupling, thermal drifts and different temperatures of the two VCSEL devices can be avoided or at least reduced.

[0013] For laser operation, the first and second reflectors are optimized toward one side which may be the substrate side or the epitaxial side (bottom emitter or top emitter). One of the reflectors (Distributed Bragg Reflector - DBR) may be characterized by a high reflectivity of >99.9%, and the other reflector through which light is emitted may be a lower reflectivity of about 99.5%. The reflectivity of the DBR with a higher reflectivity may be reduced (e.g., by etching or providing additional layers) for use in constructing a VCSEL structure of the filter, such that the two DBRs are characterized by having the same reflectivity (e.g., 99.5%). The same reflectivity of the first DBR and the second DBR (or more generally, the first reflector or the second reflector) enables the transmission of the filter to be optimized for the expected filter wavelength received from the first direction (the emission wavelength of the adjacent VCSEL structure that constructs the laser).

[0014] According to an alternative embodiment, the reflectivity of the first and second DBRs can be reduced (e.g., between 95% and 99.5%) so that only gain switching operation of the laser can be achieved. Such a design will enable higher transmission through adjacent filters at the same time.

[0015] The at least one laser and the at least one filter may be arranged to receive a common drive current. In this embodiment, the at least one laser is characterized by a first threshold current. The at least one filter is characterized by a second threshold current higher than the first threshold current. The at least one laser and the at least one filter may, for example, share a common electrode. Providing different threshold currents (e.g., by different diameters of the corresponding VCSEL structures) enables lasing with the aid of a VCSEL structure (laser) having a lower threshold current (electrical pumping above the laser threshold) and enables high transparency of a VCSEL structure (filter) having a higher threshold current (electrical pumping below the threshold). Therefore, the laser and the filter can be driven by the same drive current. Therefore, the local heating of the laser and the filter is very similar.

[0016] The laser arrangement structure may also include at least one second laser and at least one second filter, wherein each laser and each filter is optically coupled to the optical device. The optical device is arranged so that the laser light emitted by the second laser is emitted in a second direction different from the first direction. The optical device is also arranged to be able to receive the received light. The received light includes the reflected laser light emitted by the second laser. The second filter is also arranged to be able to filter the received light so that the reflected laser light received from the second direction passes through the second filter. The optical device is capable of selectively emitting and receiving laser light at an angle. Two, three, four or more pairs of lasers and corresponding filters may be arranged to be able to emit laser light in different directions and receive reflected laser light from corresponding directions so that the reflected laser light can pass through corresponding filters. One or more subgroups of the paired lasers and corresponding filters may be arranged to emit laser light in the same direction and receive reflected laser light from the direction so that the reflected laser light received from the direction can pass through the filters of the corresponding subgroups. The optics may be a common optics or each laser and each filter may be coupled to a separate optics.

[0017] According to another aspect, a detector arrangement structure for time-of-flight measurement is provided. The detector arrangement structure may be a time-of-flight detector module. The detector arrangement structure comprises at least one laser, at least one optical filter, at least one carrier structure and at least one first driver. The at least one laser and the at least one optical filter comprise a substrate, a first reflector, a second reflector and an active layer arranged between the first reflector and the second reflector. The at least one laser is arranged to be able to emit laser light in a first direction. The optical filter is arranged to be able to receive received light. The received light comprises laser light reflected from an object. The laser light is emitted by the first reflector of the at least one laser, and the received light is received by the first reflector of the at least one optical filter. The first reflector of the at least one laser and the first reflector of the at least one optical filter have equal reflectivity. The second reflector of the at least one laser and the second reflector of the at least one optical filter have equal reflectivity, or the reflectivity of the second reflector of the at least one optical filter is reduced relative to the reflectivity of the second reflector of the at least one laser. The object is arranged within a predetermined detection range, wherein the filter is also arranged to filter the received light so that the laser light reflected from the object and received from the first direction passes through the filter. The at least one laser and the at least one filter are attached to a carrier structure. The carrier structure includes at least one optical sensor. The at least one optical sensor is arranged to detect the received light filtered by the filter. The first driver is arranged to control the at least one laser so as to emit a laser light of a predetermined pulse length. The predetermined pulse length is shorter than 20ns, preferably shorter than 10ns. The predetermined pulse length is shorter than a time period for receiving the laser light reflected from the object within the predetermined detection range.

[0018] A detector arrangement comprising a laser and a separate filter (the laser arrangement described above) may be electrically driven so that a longer laser pulse (longer than the time period for receiving light reflected from the object) may be emitted. Thus, a detector arrangement comprising such a laser arrangement may not be limited by the first driver. In this case, the first driver may be arranged so that a laser of a predetermined pulse length is emitted. In this case, the predetermined pulse length may include any pulse length suitable for providing a reliable time-of-flight measurement.

[0019] The at least one laser and the at least one filter may comprise the same physical structure. This means that the physical structure functions as a laser at a first time in time and as a filter at a second, different time in time.

[0020] The laser and the filter may be arranged on a first chip, which is mounted on a carrier structure (second chip). Optionally, since amplified spontaneous emission (ASE) is emitted in all directions, and the received light after filtering (and / or amplification, see below) is perpendicular to the epitaxial layer structure of the laser, a transparent spacer may be implemented between the two chips (which may be Si chips with vias for electrical connection structures) to further reduce the amount of ASE emitted from the filter to the optical sensor.

[0021] The optical sensor may be arranged to provide a non-linear response when detecting received light. The non-linear response may be able to detect very low light intensities generated by the received light. The optical sensor may, for example, comprise a single photon avalanche diode (SPAD) which is well suited for detecting time-of-flight signals.

[0022] The carrier structure may further comprise at least a first driver arranged to be able to provide at least a drive current to the at least one laser.The integration of the first driver may enable a very compact design.

[0023] The substrate may be a common substrate. The at least one laser and the filter are arranged adjacent to each other on the common substrate. The at least one laser is a VCSEL. The filter may be a VCSEL structure identical to the corresponding VCSEL, or may be a VCSEL structure having an epitaxial layer structure substantially identical to the VCSEL. As discussed above, the use of a common substrate enables advantages with respect to thermal coupling and production differences.

[0024] The at least one laser may be characterized by a first threshold current. In this embodiment, the at least one filter is characterized by a second threshold current that is higher than the first threshold current. The first driver is arranged to provide a first drive current to the at least one laser and the at least one filter. The first drive current is arranged between the first threshold current and the second threshold current. The at least one filter may be, for example, a VCSEL having an active area greater than the active area of ​​the at least one laser (such as the area of ​​the active layer receiving the drive current defined by the corresponding current limiting structure (e.g., oxide aperture)). The filter and the first drive current may be arranged to amplify the reflected laser light received from the object. The first drive current may, for example, be slightly lower than the second threshold current to enable amplification. The reflected light triggers laser emission from the filter, and the light of the filter is detected. The first current may be a common (pulsed) drive current that is provided to both the laser and the filter (a series circuit of the laser and the filter). If the series resistances of the laser and the filter are different, there may be two separate drivers.

[0025] In an alternative embodiment, the first driver may be arranged to provide a first drive current higher than a first threshold current to the at least one laser. The first driver or the second driver may also be arranged to provide a second drive current less than the first threshold current to the at least one optical filter. The at least one laser and the optical filter may be characterized in that they optionally have the same first threshold current. The second drive current may be used to provide sufficient transparency of the optical filter.

[0026] The second drive current through the filter may optionally be increased to just below the laser threshold so that the active layer in the filter acts as an amplifier for reflected laser light included by received light having the correct wavelength and reception angle.

[0027] The second drive current can, for example, enable the filter to emit laser light when receiving reflected laser light. In this embodiment, the DBR can remain unetched (the reflectivity of the first reflector and the second reflector are different). The amplification of the received laser light can provide enough light for the optical sensor, which will be coupled from the high reflectivity side of the DBR towards the optical sensor. Therefore, the use of independent first and second drive currents can improve the flexibility and performance (especially sensitivity) of the detector arrangement.

[0028] The filter (and the laser) may also include a phototransistor (PT) or more specifically a distributed heterojunction bipolar phototransistor (HPT). The HPT includes a collector layer, a photosensitive layer, a base layer and an emitter layer. The HPT is arranged so that there is optical coupling between the active layer and the HPT for providing active carrier confinement by means of the HPT. The phototransistor may be used to start laser emission of the filter by increasing the current in response to absorbing reflected laser light. The phototransistor may be integrated in an optical resonator constituted by two reflectors and an embedded active layer. The phototransistor may preferably be positioned near the active layer (e.g., between the active layer and one of the reflectors).

[0029] According to another embodiment, the at least one laser may be characterized by a first threshold current. The first driver is arranged to be able to provide a first drive current higher than the first threshold current for the predetermined pulse length. The first driver or the second driver is arranged to be able to provide a second drive current lower than the first threshold current to the filter during the detection of the laser reflected from the object within the predetermined detection range. The first driver may, for example, be arranged to be able to provide a first drive current to the laser and optionally to the filter in a first time period (different threshold currents for the laser and the filter) and to provide a second drive current to the filter and optionally to the laser in a subsequent second time (the second drive current must be lower than the laser threshold of the laser). Alternatively, the first driver may be arranged to be able to provide a first drive current to the laser, and the second driver may provide a second drive current to the filter permanently or for a predetermined time period after the predetermined pulse length. Providing the second drive current to the filter during a predetermined time period enables the detection of the reflected laser light in time and therefore in space (given the speed of light, a predetermined range of distances). The filter is transparent or amplifies the reflected laser light only during the predetermined time period.

[0030] The detector arrangement structure may also include at least one second laser and at least one second filter. Each laser and each filter is optically coupled to the optical device. The optical device is arranged so that the laser light emitted by the second laser is emitted in a second direction different from the first direction. The optical device is also arranged to be able to receive the received light. The received light includes the reflected laser light emitted by the second laser. The second filter is also arranged to be able to filter the received light so that the reflected laser light emitted by the second laser and received from the second direction passes through the second filter. As described above, the optical device enables the laser light to be selectively emitted and received at an angle. Two, three, four or more pairs of lasers and corresponding filters can be arranged to be able to emit laser light in different directions and receive reflected laser light from corresponding directions so that the reflected laser light can pass through the corresponding filters.

[0031] According to a third aspect, a time-of-flight camera is provided. The time-of-flight camera comprises a detector arrangement according to any of the above embodiments. The time-of-flight camera further comprises an analysis evaluator. The analysis evaluator is arranged to be able to determine a distance to an object by means of detecting received light.

[0032] According to a fourth aspect, a method for determining a depth image of a scene is provided. The method uses a time-of-flight camera according to the third aspect and comprises the following steps:

[0033] emitting laser light in a plurality of different directions, wherein at least one laser emits laser light in at least one of the plurality of directions,

[0034] filtering received light comprising laser light reflected by an object in the scene for each of a plurality of directions by means of at least one filter for each direction, wherein at least one filter is associated with the at least one laser emitting the laser light in the respective direction, wherein each filter comprises an optical passband within a wavelength range of the laser light for the respective direction,

[0035] detecting the filtered received light by means of at least one optical sensor for each filter,

[0036] The distance to the object is determined using the emission time of the laser and the detection time of the filtered received light.

[0037] A depth image of the scene may be reconstructed based on the determined distances.

[0038] The method may also be characterized by:

[0039] The step of emitting laser light includes the step of providing a driving current to the laser that is higher than a first threshold current of the laser,

[0040] The step of filtering the received light includes the step of providing a heating current to the filter that is below a second threshold current of the filter.

[0041] The heating current is arranged to enable the temperature of the filter to match that of the laser. The heating current is below the bulk laser threshold current of the filter. The heating current also increases transparency and can enable amplification of the received laser light for the corresponding direction as discussed above.

[0042] As discussed above, if the first threshold is lower than the second threshold, the drive current and the heating current may be characterized by the same current intensity.

[0043] According to a fifth aspect, a computer program carrier is provided. The computer program carrier comprises code means which can be stored on at least one storage device included by the time-of-flight camera described above. The code means are arranged so that the method described above can be performed by means of at least one processing device included by the time-of-flight camera.

[0044] The storage device or the processing device may be included by the time-of-flight camera (eg, electrical drive, controller, etc.).

[0045] The storage device may be any physical device arranged to be able to store information, in particular digital information. The storage device may in particular be selected from the group solid-state memory or optical memory.

[0046] The processing device may be any physical device arranged to be able to perform data processing, in particular digital data processing. The processing device may in particular be selected from a group processor, a microprocessor or an application-specific integrated circuit (ASIC).

[0047] It should be understood that the method described above and the time-of-flight camera described above have similar and / or identical embodiments.

[0048] Further advantageous embodiments are defined below. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0050] The present invention will now be described by way of example based on embodiments with reference to the accompanying drawings.

[0051] In the attached picture:

[0052] Figure 1 A schematic diagram of a first detector arrangement is shown.

[0053] Figure 2A schematic diagram of a second detector arrangement is shown.

[0054] Figure 3 A schematic diagram of a third detector arrangement is shown.

[0055] Figure 4 A simplified schematic diagram of a time-of-flight camera is shown.

[0056] Figure 5 A schematic diagram of the principle of a method for recording a depth image is shown.

[0057] In the drawings, like reference numerals refer to like objects throughout. Objects in the drawings are not necessarily drawn to scale. DETAILED DESCRIPTION

[0058] Various embodiments of the present invention will now be described with the aid of the accompanying drawings.

[0059] Figure 1 A schematic diagram of a first detector arrangement 10 for time-of-flight measurement is shown. The detector arrangement 10 comprises a laser arrangement 100 and a carrier structure 150. In this embodiment, the laser arrangement 100 comprises a bottom-emitting VCSEL comprising a first reflector 105 (first DBR), a second reflector 109 (second DBR) and an active layer 107 sandwiched between the first DBR and the second DBR. The active layer 107 typically comprises one or more quantum well layers. The layers of the first DBR are deposited on a substrate 101 (GaAs substrate). The reflectivity of the first DBR (e.g., 99.5% reflectivity) is somewhat lower than the reflectivity of the second DBR (e.g., reflectivity>99.9%). A first electrical contact 103 (typically an n-contact) is arranged on the back side of the substrate 101 opposite to the side of the substrate 101 where the optical resonator is arranged. A second electrical contact 111 (typically a p-contact) is arranged on top of the second DBR. The first electrical contact 103 and the second electrical contact 111 are arranged to be able to provide a drive current (electrical pumping) to the optical resonator. The VCSEL may comprise Figure 1Other layers not explicitly shown in the figure but known to those skilled in the art, such as current distribution layers, current confinement layers, etc., may be provided. The first electrical contact 103 and the second electrical contact 111 (both of which may include metal layers) may surround a hole through which the laser light 121 may be emitted if a drive current higher than the laser threshold current of the laser arrangement 100 is supplied. The emission wavelength of the laser light 121 is greater than 900 nm, preferably greater than 930 nm, so that the substrate 101 is substantially transparent to the laser light 121. The laser arrangement 100 is mounted with a second electrode 111 on top of a spacer 130, which in this embodiment comprises a material transparent to the laser light 121. The spacer 130 is arranged to provide an electrical connection structure (not shown) of the first electrode 103 and the second electrode 111. The spacer 130 is mounted on a carrier structure 150 comprising a first driver, which is arranged to provide a drive current to the VCSEL. The carrier structure 150 also comprises an optical sensor 151. The optical sensor 151 may be, for example, a single photon avalanche diode, which is integrated in the carrier structure and aligned with the openings of the first electrical contact 103 and the second electrical contact 111 .

[0060] Most of the laser light 121 is emitted through the first DBR in the first direction, while a small part is emitted via the second DBR, so that the optical sensor 151 receives the laser light 121 emitted by the VCSEL. Therefore, the optical sensor 151 is arranged to be able to detect the emission time of the laser light 121 emitted by the VCSEL. The portion of the laser light 121 emitted through the substrate 101 can be reflected by an object (not shown). The received light 123 including the reflected laser light 121 received from the first direction enters the optical resonator through the substrate 101. The received light 123 is received after a predetermined pulse length of the laser light 121. Therefore, the first driver 153 is arranged to be able to reduce the drive current below the laser threshold of the VCSEL after a predetermined period of time. The first driver 153 is also arranged to be able to provide a subsequent drive current or a second drive current slightly lower than the laser threshold of the VCSEL to the VCSEL. The second drive current can be provided during a predetermined period of time when the laser starts to emit laser light or after the drive current is reduced to below the laser threshold. The second drive current enables amplification of the reflected laser light 121 received from the same direction as the direction in which the laser emits the laser light 121. The reflected laser light 121 is filtered by means of the layer stack of the optical resonator (and the substrate 101) so that substantially no ambient light reaches the active layer 107. As long as the second drive current is applied, the VCSEL can optionally start emitting laser light when receiving the reflected laser light 121. The filtered reflected laser light 121 or laser pulse (amplified reflected laser light 121) is detected by means of an optical sensor 151. In view of the high reflectivity of the second DBR, amplification (laser pulses) can be particularly advantageous. Therefore, the detector arrangement structure 10 is arranged to be able to determine the flight time of the laser light 121 emitted in the first direction. The spacer arranged between the VCSEL and the carrier structure 150 reduces the amount of amplified spontaneous emission (ASE) emitted from the active layer 107. The VCSEL of the laser arrangement structure 100 is arranged to be able to operate as a laser when receiving a drive current above the laser threshold. In this embodiment, the same VCSEL is also arranged to be able to operate as an optical filter (and amplifier) ​​if a second drive current just below the laser threshold is provided. The first reflector 105 and the second reflector 109 can be grown such that both reflectors are characterized by having the same reflectivity to improve the filter performance.

[0061] Figure 21 shows a schematic diagram of a second detector arrangement 10. The second detector arrangement 10 comprises a laser arrangement 100 mounted on top of a carrier structure 150. The laser arrangement 100 comprises an array of VCSEL structures each comprising an optical resonator having a first reflector 105 (first DBR), a second reflector 109 (second DBR) and an active layer 107 sandwiched between the first and second DBRs. Each VCSEL structure is arranged in contact with a laser beam directed to a laser beam source. Figure 1The bottom emitting VCSEL described above is similar. The main difference is that there are two different types of VCSEL structures. The first VCSEL structure is arranged to be able to emit laser light 121 through the substrate 101. Therefore, the first VCSEL structure is a laser. The second reflector 109 (second DBR) of these first VCSEL structures is completely covered by the second electrode 111. The second VCSEL structure is arranged to be able to filter the received light 123 including the reflected laser light 121. Therefore, the second VCSEL structure is a filter. The second reflector 109 (second DBR) of these second VCSEL structures is partially covered by a second electrical contact 111, for example, in the shape of a ring, so that the filtered received light 123 can pass through the second VCSEL structure through an opening in the second electrical contact 111. The first VCSEL structure and the second VCSEL structure include a common first electrical contact 103. The opening in the first electrical contact 103 is aligned with the first VCSEL structure and the second VCSEL structure to be able to emit laser light 121 and receive received light 123. The laser arrangement structure 100 further comprises an optical device 120, wherein one optical device 120 (e.g. a microlens deposited on the surface of the substrate 101) is associated with one first VCSEL structure or a second VCSEL structure. The laser is arranged to be able to receive a first drive current by means of a second driver 155 included by the carrier structure 150 to emit laser light of a predetermined pulse length (in particular very short pulses in the nanosecond range). The filter is arranged to be able to receive a second drive current by means of a first driver 153 included by the carrier structure. The second drive current is arranged to be able to increase the transparency of the filter during the reception of the received light 123. In this embodiment, the laser and the filter are arranged so that one laser is associated with one filter. The optical device 120 associated with the laser and the associated filter is arranged so that the laser light 121 is emitted in a first direction and the received light 123 is received from the same first direction through the associated filter. The optical device 120 can be, for example, a microlens, wherein a pair of microlenses is associated with the laser and the associated filter. The paired microlenses can be slightly shifted relative to each other to be able to emit laser light 121 and correspondingly receive received light 123 from multiple different directions. The carrier structure 150 also includes an optical sensor 151. The optical sensor 151 is aligned with the filter. The filtered and optionally amplified received laser light 121 is detected by means of the corresponding optical sensor 151. The second DBR of the filter can be optionally etched so that the first DBR and the second DBR of the filter are characterized by having the same reflectivity to optimize the filter performance.

[0062] In an alternative embodiment, two or more filters may be associated with one laser. In addition, two, three, four or more lasers and associated filters may be arranged to emit laser light 121 in the same direction and receive light 123 from that direction, so that the optical sensor 151 receives the filtered reflected laser light 121 from that direction.

[0063] Figure 3 A schematic diagram of a third detector arrangement 10 comprising a laser arrangement 100 and a carrier structure 150 is shown. The laser arrangement comprises an array of top emitting VCSELs, each comprising a first reflector 105, a second reflector 109 and an active layer 107 arranged between the first reflector 105 and the second reflector 109. In this case, the reflectivity of the second reflector 109 is slightly lower than the reflectivity of the first reflector 105. Therefore, most of the laser light 121 is emitted through the annular second electrode 111 arranged on top of the second reflector 109. The first electrode 103 is deposited on the back side of the substrate 101, which is opposite to the side of the substrate 101 on which the first reflector 105 and the subsequent layer stack of the active layer 107, the second reflector 109 and the second electrode 111 are processed. The first electrode 103 comprises an opening aligned with the VCSEL so that the laser light 121 can be emitted through the substrate 101 through the corresponding opening. Each of the top emitting VCSELs is arranged to be able to operate as a laser and also operate as a Figure 1 The laser arrangement 100 and the Figure 2 The VCSEL discussed above is similarly mounted on a carrier structure 150 including a first driver 153, which is arranged to provide a drive current to the VCSEL (or VCSEL structure) by means of the first electrical contact 103 and the second electrical contact 111. The carrier structure 150 also includes an optical sensor 151, wherein the optical sensor is aligned with the opening of the first electrical contact 103. The VCSEL structure is driven in accordance with the embodiment of the present invention. Figure 1The detector arrangement 10 is performed in a similar manner as described above. A first drive current is provided that is higher than the laser threshold of the VCSEL structure to enable the emission of laser pulses having a predetermined pulse length. A second drive current that is lower than the laser threshold is provided to enable effective filtering of the received light 123 including the reflected laser light 121. The detector arrangement 10 also includes a common optical device 120. The common optical device 120 is integrated on a wafer level. Transparent material is deposited on top of the VCSEL structure so that substantially each VCSEL structure emits laser light 121 in a dedicated direction and receives received light 123 including the reflected laser light 121 from the dedicated direction. The reflected laser light 121 received from the direction is filtered and optionally amplified by means of the same VCSEL structure that emitted the laser light 121.

[0064] The substrate 101 and the first reflector 105 may optionally be etched such that the first reflector 105 and the second reflector 109 are characterized by having the same reflectivity as discussed above.

[0065] Figure 4A schematic diagram of a time-of-flight camera 200 is shown. The time-of-flight camera 200 comprises a detector arrangement 10 according to one of the embodiments discussed above. The detector arrangement 10 comprises an array of VCSEL structures operating as lasers and / or filters. The laser is arranged to be able to emit short laser pulses (laser 121) that hit an object 300. A portion of the laser 121 is reflected by the object 300, so that as described above, a received light 123 comprising the reflected laser 121 is received by the detector arrangement 10 and filtered by the filter according to the emission direction of the corresponding laser 121. As discussed above, the filtered reflected laser 121 causes a corresponding electrical signal in the corresponding optical sensor of the detector arrangement 10. The electrical driver 230 may be arranged to be able to electrically drive the VCSEL structures of the laser arrangement 100, or optionally each VCSEL structure or a subgroup of VCSEL structures, respectively. The controller 250 is connected to the electrical driver 230 to, for example, control the start and stop times of the laser pulses emitted by the laser. The controller 250 is also connected to the optical sensor of the detector arrangement 10 to receive the electrical signal caused by the reflected laser light 121 detected by the optical sensor. The time-of-flight camera 200 also includes an optional interface 235 to transmit the start and stop times of the laser light 121 emitted by the corresponding laser or laser group and the reception time of the electrical signal caused by the reflected laser light 121. The transmitted data can be used to calculate the flight time of the laser light 121, and thus calculate the distance between the time-of-flight sensor module 200 and the object 300 for each direction in which the laser light 121 is emitted. The time-of-flight sensor module 200 may alternatively include an analysis evaluator (not shown) electrically connected to the controller 250 (or may include the controller 250 or be included by the controller 250) to determine the distance to the object. The controller may also be arranged to be able to reconstruct a depth image of the object 300 based on the distance measurement by means of a corresponding reconstruction algorithm.

[0066] Preferably, the above discussed (especially for Figure 1 , Figure 2 and Figure 3The epitaxial structure of the laser arrangement 10 discussed) is optimized for high gain and amplification and high output coupling, so that the laser emits only ultra-short gain switching peaks of laser light 121 for high laser currents. After the emission pulse, the current can be reduced or even kept constant to remain in the amplification mode until the reflected laser light 121 included in the received light 123 will return from the longest distance to be measured. Then, for example, the current can be switched off when image processing is performed to reduce the heat in the detector arrangement 100. This optimization of the gain switch can also be achieved by reducing the reflectivity of the high reflector as discussed above, which is very unconventional compared to known VCSEL structures. Because the currents in the application are usually low and pulsed, the epitaxial structure is preferably optimized for low absorption at the expense of higher electrical losses compared to known VCSELs or VCSEL structures. The high resistance can be used to heat the filter with a small current, while the low optical losses allow better amplification and transmission in the filter to enable optimized filtering and optional amplification.

[0067] Figure 5 A schematic diagram of the principle of a method for recording a depth image of a scene is shown. In step 410, laser light 121 is emitted in a plurality of different directions. At least one laser emits laser light in at least one of the plurality of directions. In step 420, received light 123 including laser light 121 reflected by an object 300 in the scene for each of the plurality of directions is filtered by means of at least one filter for each direction. At least one filter is associated with the at least one laser emitting laser light in the corresponding direction. Each filter includes an optical passband within the wavelength range of the laser light for the corresponding direction. In step 430, the filtered received light 123 is detected by means of at least one optical sensor 151 for each filter. In step 440, the distance to the object 300 is determined by means of the emission time of the laser light 121 and the detection time of the corresponding filtered received light 123.

[0068] According to one embodiment, the present invention proposes: first, using the epitaxial structure as a laser, second, using the epitaxial structure as a selective filter with exactly the same wavelength as the laser, and a method of coupling it to a separate array optical sensor 151 to form an ultra-compact light source and a sunlight-resistant detector array for a time-of-flight camera 200. Preferably, the silicon chip (carrier structure 150) containing the array of optical sensors 151 contains a first driver 153 and an optional second driver 155 for electrically driving the laser and optionally optimizing the transmission of the filter. The filter can also be optimized to act as an optical amplifier for the laser light 121 reflected back from the object 300 to be measured to improve sensitivity. Preferably, the semiconductor chip also contains an optical device 120 (especially a wafer-level integrated optical device 120) to form a complete ultra-flat integrated time-of-flight or 3D sensor.

[0069] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive.

[0070] From reading this disclosure, other modifications will be apparent to persons skilled in the art.Such modifications may involve other features which are already known in the art and which may be used instead of or in addition to features already described herein.

[0071] Variations of the disclosed embodiments may be understood and implemented by those skilled in the art by studying the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the singular form does not exclude a plurality of elements or steps. The fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0072] Any reference signs in the claims should not be construed as limiting the scope of the claims.

[0073] List of reference numerals:

[0074] 10 Detector Arrangement Structure

[0075] 100 Laser Arrangement Structure

[0076] 101 Matrix

[0077] 103 first electrical contact

[0078] 105 First Reflector

[0079] 107 Active layer

[0080] 109 Second Reflector

[0081] 111 second electrical contact

[0082] 120 Optical Devices

[0083] 121 Laser

[0084] 123 Receive light

[0085] 130 Spacers

[0086] 150 bearing structure

[0087] 151 Optical Sensor

[0088] 153 First Drive

[0089] 155 Second Drive

[0090] 200 Time of Flight Camera

[0091] 230 electric drive

[0092] 235 interface

[0093] 250 Controller

[0094] 300 objects

[0095] 410 Steps to emitting laser

[0096] 420 Steps for filtering received light

[0097] 430 Steps for detecting the received light after filtering

[0098] 440 Step of determining a distance.

Claims

1. A laser arrangement (100) for time-of-flight measurement, the laser arrangement (100) comprising at least one laser and at least one filter arranged adjacent to the at least one laser, wherein: The at least one laser and the at least one optical filter each comprise a substrate (101), a first reflector (105), a second reflector (109), and an active layer (107) arranged between the first reflector (105) and the second reflector (109), the at least one laser and the at least one optical filter comprising a common first electrical contact (103), wherein the at least one laser is arranged to be able to emit laser light (121) in a first direction, wherein the optical filter is arranged to be able to receive received light (123), wherein the received light (123) comprises laser light (121) reflected from an object (300), wherein the laser light passes through the first reflector (105) of the at least one laser and is reflected by the laser light. 05), and the received light is received by the first reflector (105) of the at least one filter, the first reflector (105) of the at least one laser and the first reflector (105) of the at least one filter have equal reflectivity, wherein the second reflector (109) of the at least one laser and the second reflector of the at least one filter have equal reflectivity, or the reflectivity of the second reflector of the at least one filter is reduced relative to the reflectivity of the second reflector of the at least one laser, wherein the filter is further arranged to be able to filter the received light (123) so that the laser light (121) reflected from the object (300) and received from the first direction passes through the filter, wherein the at least one laser and the at least one filter comprise the same physical structure, the physical structure functioning as a laser at a first time and as a filter at a second, different time, wherein the at least one laser and the at least one filter are aligned accordingly so as to be able to emit laser light (121) and receive received light (123) through the same opening in the corresponding first electrical contact (103), wherein the at least one laser and the at least one filter are arranged adjacent to each other on the same substrate, and during operation of the laser arrangement, local heating of the at least one laser and the at least one filter is similar, so that the filter wavelength remains matched to the emission wavelength in the presence of a thermal shift, And wherein the at least one laser is characterized by a first threshold current, wherein the at least one filter is characterized by a second threshold current that is higher than the first threshold current, wherein the first driver (153) is arranged to be capable of providing a first drive current to the at least one laser and the at least one filter, wherein the first drive current is arranged between the first threshold current and the second threshold current.

2. The laser arrangement (100) according to claim 1, wherein: The at least one laser is a vertical cavity surface emitting laser.

3. The laser arrangement (100) according to any one of the preceding claims, wherein: The laser arrangement structure (100) further comprises at least one second laser and at least one second filter, wherein each laser and each filter is optically coupled to an optical device (120), wherein the optical device is arranged so that laser light (121) emitted by the second laser is emitted in a second direction different from the first direction, wherein the optical device is further arranged to be able to receive received light (123), wherein the received light (123) comprises reflected laser light (121) emitted by the second laser, wherein the second filter is further arranged to be able to filter the received light (123) so that the reflected laser light (121) emitted by the second laser and received from the second direction passes through the second filter.

4. A detector arrangement (10) for time-of-flight measurement, the detector arrangement (10) comprising at least one laser, at least one filter, at least one carrier structure (150) and at least one first driver (153), wherein: The at least one laser and the at least one optical filter comprise a substrate (101), a first reflector (105), a second reflector (109), and an active layer (107) arranged between the first reflector (105) and the second reflector (109), the at least one laser and the at least one optical filter comprising a common first electrical contact (103), wherein the at least one laser is arranged to be able to emit laser light (121) in a first direction, wherein the optical filter is arranged to be able to receive received light (123), wherein the received light (123) comprises laser light (121) reflected from an object (300), wherein the laser light is emitted by the first reflector (105) of the at least one laser and the received light is received by the first reflector (105) of the at least one optical filter, the first reflector (105) of the at least one laser and the first reflector (105) of the at least one optical filter have equal reflectivity, wherein the second reflector (109) of the at least one laser and the at least one optical filter The second reflector of the at least one filter has an equal reflectivity, or the reflectivity of the second reflector of the at least one filter is reduced relative to the reflectivity of the second reflector of the at least one laser, wherein the object (300) is arranged within a predetermined detection range, wherein the filter is further arranged to filter the received light (123) so that the laser light (121) reflected from the object (300) and received from the first direction passes through the filter, wherein the at least one laser and the at least one filter are attached to a carrier structure (150), wherein the carrier structure (150) includes at least one optical sensor (151), wherein the at least one optical sensor (151) is arranged to detect the received light (123) filtered by the filter, wherein the first driver (153) is arranged to control the at least one laser so that the laser light (121) with a predetermined pulse length is emitted, wherein the predetermined pulse length is shorter than 20 ns, so that the pulse length is shorter than a time period for receiving the laser light reflected from the object within the predetermined detection range, wherein the at least one laser and the at least one filter comprise the same physical structure, the physical structure functioning as a laser at a first time and functioning as a filter at a second, different time, wherein the at least one laser and the at least one filter are aligned respectively so as to be able to emit laser light (121) and receive received light (123) through the same opening in the corresponding first electrical contact (103), wherein the at least one laser and the at least one filter are arranged adjacent to each other on the same substrate, and during operation of the laser arrangement, local heating of the at least one laser and the at least one filter is similar, so that the filter wavelength remains matched to the emission wavelength in the presence of a thermal shift, And wherein the at least one laser is characterized by a first threshold current, wherein the at least one filter is characterized by a second threshold current that is higher than the first threshold current, wherein the first driver (153) is arranged to be capable of providing a first drive current to the at least one laser and the at least one filter, wherein the first drive current is arranged between the first threshold current and the second threshold current.

5. The detector arrangement (10) according to claim 4, wherein: The predetermined pulse length is shorter than a time period for receiving laser light (121) reflected from an object (300) within the predetermined detection range.

6. The detector arrangement (10) according to claim 4 or 5, wherein: The optical sensor (151) is arranged to provide a non-linear response when detecting received light (123).

7. The detector arrangement (10) according to claim 4 or 5, wherein: The at least one laser is a vertical cavity surface emitting laser.

8. The detector arrangement (10) according to claim 7, wherein: The optical filter and the first driving circuit are arranged to be able to amplify reflected laser light (121) included in received light (123) received from the object (300).

9. The detector arrangement (10) according to any one of claims 4, 5 and 8, wherein: The first driver (153) is arranged to be capable of providing a first drive current higher than a first threshold current to the at least one laser, wherein the first driver (153) or the second driver (155) is arranged to be capable of providing a second drive current lower than a threshold current of the filter to the at least one filter.

10. The detector arrangement (10) according to claim 9, wherein: The at least one laser is characterized by a first threshold current, wherein the first driver (153) is arranged to be capable of providing a first drive current higher than the first threshold current for the predetermined pulse length, wherein the first driver (153) or the second driver (155) is arranged to be capable of providing a second drive current lower than the first threshold current to the filter during detection of laser light (121) reflected from an object (300) within the predetermined detection range.

11. The detector arrangement (10) according to any one of claims 4, 5, 8, 10, wherein: The detector arrangement (10) further comprises at least a second laser and at least a second filter, wherein each laser and each filter is optically coupled to an optical device (120), wherein the optical device is arranged so that laser light (121) emitted by the second laser is emitted in a second direction different from the first direction, wherein the optical device is further arranged so as to be able to receive received light (123), wherein the received light (123) comprises reflected laser light (121) emitted by the second laser, wherein the second filter is further arranged so as to be able to filter the received light (123) so that the reflected laser light (121) emitted by the second laser and received from the second direction passes through the second filter.

12. A time-of-flight camera (200), comprising a detector arrangement (10) according to any one of claims 4 to 11, the time-of-flight camera (200) further comprising an analysis evaluator arranged to be able to determine a distance to an object (300) by means of detection of received light (123).

13. A method of recording a depth image of a scene using a time-of-flight camera (200) according to claim 12, the method comprising the following steps: emitting laser light (121) in a plurality of different directions, wherein at least one laser emits laser light (121) in at least one of the plurality of different directions, filtering received light (123) comprising laser light (121) reflected by an object (300) in the scene for each of the plurality of different directions by means of at least one filter for each direction, wherein at least one filter is associated with the at least one laser emitting the laser light in the respective direction, wherein each filter comprises an optical passband within the wavelength range of the laser light (121) for the respective direction, detecting the filtered received light (123) by means of at least one optical sensor (151) for each filter, At least one distance to an object (300) is determined by means of the emission time of the laser light (121) and the detection time of the filtered received light (123).

14. A computer program carrier comprising code means capable of being stored on at least one storage device comprised by a time-of-flight camera (200) according to claim 12, wherein: The code means are arranged to enable the method according to claim 13 to be performed by means of at least one processing device comprised by the time-of-flight camera (200).

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