Patent Description:
State of the art optical 3D sensors need high power light sources and corresponding detectors. Optical alignment complexity, power consumption and eye safety are critical points.

<CIT> discloses a laser sensor module for particle density detection. The laser sensor module may comprise an array of a multitude of laser diodes.

<CIT> discloses a vertical cavity surface emitting laser device with a monolithically integrated photodiode.

<CIT>discloses a vertical cavity surface emitting laser device comprising a photodetector deposited directly onto a top surface of the laser structure.

<CIT> discloses ladar sensor including an optical gain element in the optical receiver path, between the light concentrating and focussing lens, and the focal plane array of optical detectors. This optical gain element may be optically pumped, as in an example of an erbium doped fiber amplifier, or electrically pumped as in the case of a semiconductor optical amplifier.

It is an object of the present invention to provide an improved VCSEL device for an SMI sensor for recording three-dimensional pictures.

According to a first aspect a Vertical Cavity Surface Emitting Laser (VCSEL) device for a self-mixing interference sensor for recording three-dimensional pictures is provided. The VCSEL device is defined in claim <NUM>. The VCSEL device comprises a VCSEL array, a multitude of detectors (e.g. optical detector like photodiodes or photo transistors), a first electrical laser contact and at least one second electrical laser contact. The VCSEL array comprises a multitude of laser VCSELs. The multitude of laser diodes are arranged on a substrate. The common substrate may, for example, be a growth substrate for growing semiconductor layers the VCSEL array consists of or a substrate which is bonded to the VCSEL array in a subsequent processing step. Each laser diode comprises an optical resonator. The optical resonator comprises a first distributed Bragg reflector, a second distributed Bragg reflector and an active layer for light emission. The active layer is arranged between the first distributed Bragg reflector and the second distributed Bragg reflector. The first electrical laser contact and the at least one second electrical laser contact are arranged to provide an electrical drive current to electrically pump the optical resonators of the laser diodes. The first electrical laser contact is a common contact for all laser diodes of the VCSEL array. The at least one second electrical laser contact is arranged to electrically contact at least a subgroup of the multitude of laser diodes of the VCSEL array. Each detector may be arranged to receive laser light from at least one laser diode of the VCSEL array (optical detector). Each detector is arranged to generate a self-mixing interference measurement signal associated to the at least one laser diode upon reception of the laser light (optical detector, electrical detector etc.). Each detector may be associated to one, two, three, four or more laser diodes. A subgroup of the multitude of laser diodes of the VCSEL array may comprise, for example, a column or a row of the VCSEL array. A self-mixing interference signal is generated if a laser diode (VCSEL) emits laser light and a part of the emitted laser light is reflected back to the optical resonator of the respective laser diode. The reflected laser light interferes with the standing wave pattern within the optical resonator or laser cavity resulting in the self-mixing interference signal. The self-mixing interference signal can be detected by means of the detector (e.g. variations of the laser intensity within the optical resonator which can, for example, be detected by means of a photodiode).

The multitude of laser diodes may comprise more than <NUM> laser diodes. The multitude of laser diodes may especially comprise at least <NUM>, preferably at least <NUM> and most preferably at least <NUM> laser diodes. The VCSEL array may even comprise more than <NUM> laser diodes (e.g. VGA resolution of <NUM>×<NUM> pixel and the like).

The VCSEL device may comprise two, three, four or more second electrical laser contacts. Each second electrical laser contact is in this embodiment arranged to electrically drive a corresponding subgroup of laser diodes of the VCSEL array. The second electrical laser contacts may, for example, be an anode laser contacts. A first anode contact may in combination with the first electrical laser contact (common cathode contact) provide an electrical drive current to a first column or row of the VCSEL array. The anode contacts may therefore enable switching on or off the respective subgroup independent from the other subgroups. The detectors may, for example, be arranged in a complementary arrangement with respect to the arrangement of the subgroup of the VCSEL array. The detectors may, for example, be arranged in rows if the laser diodes of the VCSEL array are arranged in columns. This matrix arrangement enables read out of a single self-mixing interference measurement corresponding to one laser diode signal by means of one detector even if one complete column of laser diodes emits laser light and generates a corresponding self-mixing interference signal within each optical resonator. The matrix arrangement simplifies contacting of the detectors but requires a corresponding switching scheme. An alternative approach is to provide one dedicated detector for each laser diode such that it is clear which laser diode generated the respective self-mixing interference measurement signal.

The VCSEL device may according to an alternative embodiment comprise one second electrical laser contact, wherein the first electrical laser contact and the second electrical laser contact are arranged to provide a common electrical drive current to all laser diodes of the VCSEL array. Each detector is in this embodiment associated to one dedicated laser diode to enable identification of the respective self-mixing interference measurement signal. This embodiment may enable a very fast measurement of a <NUM>-D setting or scene.

The detector may be integrated in the optical resonator. The detectors may, for example, be integrated in the first distributed Bragg reflector or the second distributed Bragg reflector. The detectors may, for example, be integrated in an unstructured DBR such that one common detector may be arranged to receive self-mixing interference signals from two, three, four or more VCSELs as described above. The detector may, for example, be integrated in the first (lower) DBR to provide a common detector for neighboring VCSELs.

Each optical resonator may comprise one dedicated detector. Assignment between laser diode and corresponding dedicated detector is in this case unambiguous such that identification of the self-mixing interference signal is simplified.

Each detector may comprise a first detector electrode. The first detector electrode and at least one additional electrode are arranged to read out the electrical self-mixing interference measurement signal. The additional electrode may be comprised by the first electrical laser contact or the second electrical laser contact. The respective laser diode and detector share in this case one electrode or contact. The additional electrode may alternatively be a separate second detector electrode independent from the first electrical laser contact and the second electrical laser contact.

The at least one additional electrode may be the at least one second electrical laser contact(s). The detector is integrated in the second distributed Bragg reflector. The VCSEL array is arranged such that the laser light is emitted via the first distributed Bragg reflector during operation of the VCSEL device. The laser diodes (VCSELs) are in this case so-called bottom emitters which emit the laser light through the substrate if the substrate is not removed in a direction opposite to the side of the substrate next to the optical resonators. The emission wavelength is in this case such that the (GaAs) substrate is transparent (emission wavelength greater than <NUM> in case of GaAs) for example <NUM>. The substrate may alternatively be at least locally removed. The first detector electrodes of the detectors may be contacted by wire bonds. The self-mixing interference measurement signal can be read from each individual detector (e.g. photodiode or photo transistor).

The VCSEL device may alternatively be arranged as a flip chip device. The topmost first detector electrodes may (e.g. completely) cover the mesa of the respective laser diode (VCSEL). The first detector electrodes are (e.g. full) metal contacts that can be flip chipped. The second electrical laser contact(s) of the subgroup(s) (e.g. whole laser array, columns or rows) may, for example, be electrically contacted by means of wire bonds so that each detector (Pixel) can be read by a simple electrical connection. All of the laser diodes (VCSELs) may be operated simultaneously or subgroup by subgroup.

The VCSEL array may according to an alternative embodiment be mounted on a detector chip. The detector chip comprises the detectors. The detector chip may, for example, be a silicon-based detector chip comprising an array of photodetectors, wherein each photodetector is aligned with a corresponding laser diode (VCSEL) comprised by the VCSEL array. The detector chip may alternatively comprise, for example, rows or columns of photodetectors which may be arranged in a matrix arrangement with respect to the subgroups of laser diodes as discussed above.

The VCSEL device comprises at least one optical device arranged to redirect the laser light. The optical device may, for example, comprise a lens, an array of lenses, a diffusor or the like to spread the laser light emitted by the VCSEL array in a defined field-of-view. The at least one optical device may be an optical structure etched in a substrate (e.g. gallium arsenide growth substrate) comprised by the VCSEL array.

According to a further aspect a self-mixing interference sensor for recording three-dimensional pictures comprising a VCSEL device according to any embodiment discussed above is provided. The three-dimensional self-mixing interference sensor further comprises a driving circuit and an evaluator. The driving circuit is arranged to electrically drive the laser diodes by means of the first electrical laser contact and the at least one second electrical laser contact. The evaluator is arranged to evaluate the electrical self-mixing interference measurement signals. The evaluator may, for example, be arranged to determine distances, velocities and/or acceleration of objects based on self-mixing interference signals in each optical resonator or laser cavity of the laser devices comprised by the VCSEL array. The evaluator may further be arranged to reconstruct a three-dimensional picture of the field of view and objects in the field of view based on the multitude of distances, velocities and/or accelerations.

According to a further aspect a mobile communication device may comprise a VCSEL device according to any embodiment described above or a three-dimensional self-mixing interference sensor as described above. The mobile communication device is arranged to present a three-dimensional picture of a scene to a user of the mobile communication device based on self-mixing interference measurement signals of the scene as described above. The evaluation of the self-mixing interference measurement signals may be performed by the laser sensor and/or the mobile communication device. The VCSEL device or the three-dimensional self-mixing interference sensor may further be comprised by <NUM>-D cameras.

According to a further aspect a method of fabricating a Vertical Cavity Surface Emitting Laser, VCSEL, device for a self-mixing interference sensor for recording three-dimensional pictures is provided. The method is defined in claim <NUM>.

The steps need not be performed in the order given. The different layers may be deposited by epitaxial methods like MOCVD, MBE and the like. The substrate may be removed in a subsequent processing step.

It shall be understood that the VCSEL device according to any embodiment described above and the method of fabricating the VCSEL device have similar and/or identical embodiments, in particular, as defined in the dependent claims. Further advantageous embodiments are defined below.

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

In the Figures, like numbers refer to like objects throughout. Objects in the Figures are not necessarily drawn to scale.

Various embodiments of the invention will now be described by means of the Figures.

Self-mixing interference is used for detecting movement of and distance to an object. Background information about self-mixing interference is described in "<NPL> which is incorporated by reference. Detection of movement of a fingertip relative to a sensor in an optical input device is described in detail in International Patent Application No. <CIT> which is incorporated by reference. The principle of self-mixing interference is discussed based on the examples presented in International Patent Application No. <CIT>. A diode laser having a laser cavity or optical resonator is provided for emitting a laser or measuring beam. At its upper side, the device is provided with a transparent window across which an object, for example a human finger, is moved. A lens is arranged between the diode laser and the window. This lens focuses the laser beam at or near the upper side of the transparent window. If an object is present at this position, it scatters the measuring beam. A part of the radiation of the measuring beam is scattered in the direction of the illumination beam and this part is converged by the lens on the emitting surface of the laser diode and re-enters the cavity of this laser. The radiation re-entering the cavity of the diode laser induces a variation in the gain of the laser and thus in the intensity of radiation emitted by the laser, and it is this phenomenon which is termed the self-mixing effect in a diode laser.

The change in intensity of the radiation emitted by the laser or of the optical wave in the laser cavity can be detected by a photodiode or a detector arranged to determine an impedance variation across the laser cavity. The diode or impedance detector converts the radiation variation into an electric signal, and electronic circuitry is provided for processing this electric signal.

<FIG> shows a principal sketch of a first VCSEL device <NUM> with integrated photodiode. The first VCSEL device <NUM> comprises a multitude of VCSELs with integrated photodiode which are arranged on a common substrate <NUM>. The first VCSEL device <NUM> is a bottom emitter emitting laser light (indicated by the arrow) through the substrate <NUM>. Each of the VCSELs with integrated photodiode comprises a first DBR <NUM>, an active layer <NUM>, a first part of a second DBR <NUM>-<NUM>, a second part of the second DBR <NUM>-<NUM> and a detector <NUM>. The detector <NUM> comprises at least one layer which is arranged to detect a variation of the optical wave within the optical resonator or laser cavity built by the first DBR <NUM> and the second DBR <NUM>-<NUM>, <NUM>-<NUM> and the semiconductor layers sandwiched between the first DBR <NUM> and the second DBR <NUM>-<NUM>, <NUM>-<NUM>. The single VCSELs are in this embodiment separated by means of an oxidation opening <NUM> or trench which is subsequently filled with an electrically isolating material. The oxidation opening <NUM> may, for example, be used to provide a current aperture (not shown) in the first DBR <NUM> or the second DBR <NUM>-<NUM>, <NUM>-<NUM>. The VCSELs are electrically contacted by means of a first electrical laser contact <NUM> and at least one second electrical laser contact <NUM>. The first electrical laser contact <NUM> electrically contacts in this embodiment a common current distribution layer (not shown) which is integrated in the non-etched part of the first DBR <NUM> to provide the current to all VCSELs comprised by the VCSEL array. The first VCSEL device <NUM> comprises a multitude of second electrical laser contacts <NUM>, wherein each second electrical laser contact <NUM> contacts one row of VCSELs comprised by the VCSEL array. The rows are arranged perpendicular with respect to the plane of <FIG>. The first DBR <NUM> comprises <NUM> pairs of layers with alternating refractive index to provide a reflectivity of <NUM>% such that the emission of laser light through the substrate <NUM> is enabled. The first DBR <NUM> may, for example, comprise AlGaAs (AlxGa(<NUM>-x)As) layers with different Al concentration (e.g. variation between <NUM>% and <NUM>%) to provide different refractive indices. The first part of the second DBR <NUM>-<NUM> may comprise <NUM> pairs of layers with alternating refractive index and the second part of the second DBR <NUM>-<NUM> may comprise another <NUM> pairs of layers with alternating refractive index to provide sufficient reflectivity. The second part of the second DBR <NUM>-<NUM> of each mesa of the VCSELs is covered by a first detector electrode <NUM> such that each detector <NUM> can be read out by means of the corresponding second electrical laser contact <NUM> and the corresponding first detector electrode <NUM>. A solder bump <NUM> is provided on top of each first detector electrode <NUM> such that the first VCSEL device <NUM> can be mounted in a flip chip arrangement on top of, for example, a submount (not shown) which may comprise evaluations circuitry to evaluate measurement signals generated by means of the first VCSEL device <NUM>.

<FIG> shows a principal sketch of the electrical contacting scheme of the first VCSEL device <NUM> shown in <FIG>. The VCSELs are electrically pumped by means of a current source <NUM> which is contacted to the common first electrical laser contact <NUM> and to the second electrical laser contacts <NUM>-<NUM>, <NUM>-<NUM> such that each row comprising a multitude of laser diodes <NUM> can be operated independent from the other rows. The second electrical laser contacts <NUM> and the first detector electrodes <NUM> are electrically connected with an evaluator (not shown) such that each detector <NUM> can be read out separately to determine the self-mixing measurement signals.

<FIG> shows a principal sketch of a top view of the first VCSEL device <NUM>. The first VCSEL device <NUM> is electrically contacted by means of the common first electrical laser contact <NUM>, the second electrical laser contacts <NUM>-<NUM>, <NUM>-<NUM>. and the solder bumps <NUM>.

<FIG> shows a principal sketch of a second VCSEL device <NUM> comprising a detector chip <NUM>. The second VCSEL device <NUM> comprises in this embodiment a bottom emitting VCSEL array comprising an optical resonator with a first DBR, a second DBR <NUM> and an active layer <NUM> sandwiched between the first DBR <NUM> and the second DBR <NUM>. The active layer <NUM> typically comprises one or several quantum well layers. A first electrical laser contact <NUM> (usually n-contact) is provided on a backside of the substrate <NUM> opposing the side of the substrate <NUM> on which the optical resonators are provided. An at least one second electrical laser contact <NUM> (usually p-contact) is provided on top of the second DBR <NUM>. The first and the second electrical laser contacts <NUM>, <NUM> are arranged to provide an electrical drive current (electrically pump) the optical resonator. The VCSEL device <NUM> may comprise further layers as, for example, current distribution layers, current confinement layers and the like which are not explicitly shown in <FIG> but well known to those skilled in the art. The first electrical laser contact <NUM> as well as the second electrical laser contact(s) <NUM> (both may comprise metal layers) may surround a hole through which laser light <NUM> can be emitted if a drive current above a laser threshold current of the VCSEL device <NUM> is supplied. Emission wavelength of the laser light <NUM> is above <NUM>, preferably above <NUM> such that the substrate <NUM> (GaAs) is essentially transparent for laser light <NUM>. The VCSEL array of the VCSEL device <NUM> is mounted with the second electrode(s) <NUM> on a detector chip <NUM>. The detector chip <NUM> is according to this embodiment arranged to provide electrical connection of the first electrical laser contact <NUM> and the second electrical laser contact (not shown). The detector chip <NUM> further comprises a multitude of detectors <NUM> (e.g. photodiodes). The detectors <NUM> are aligned with the openings of the first electrical laser contact <NUM> and the second electrical contact(s) <NUM>. The reflectivity of the first DBR <NUM> and the second DBR <NUM> is arranged such that the laser light <NUM> is emitted through the substrate <NUM> and an optical device <NUM> (lens) which is etched in the substrate <NUM>. The lenses are arranged to focus the laser light <NUM> to a field-of-view. The laser beams are spread with respect to each other by shifting the lenses with respect to a center of the corresponding VCSEL. The reflectivity of the second DBR <NUM> is such that a defined amount of laser light is received by the respective detector <NUM> to determine the self-mixing interference measurement signal. Each detector is electrically contacted to two contact pads <NUM> which are arranged on the opposite side of the detector chip <NUM>. The contact pads <NUM> may enable mounting of the VCSEL device on, for example, a PCB.

<FIG> shows a principal sketch of a third VCSEL device <NUM> with detector chip <NUM>. The third VCSEL device <NUM> comprises an array of top emitting VCSELs each comprising a first DBR <NUM>, a second DBR <NUM> and an active layer <NUM> arranged between the first DBR <NUM> and the second DBR <NUM>. Reflectivity of the second DBR <NUM> is in this case somewhat lower than the reflectivity of the first DBR <NUM>. Majority of the laser light <NUM> is therefore emitted through e.g. ring shaped second electrical laser contacts <NUM> which are arranged on top of the second DBR <NUM> to electrically contact the rows or columns of VCSELs comprised by the VCSEL array similar as discussed with respect to <FIG> or <FIG>. The second electrical laser contacts <NUM> are electrically isolated with respect to the first DBR <NUM> and the active layer <NUM> by means of an isolating structure <NUM> (e.g. oxide layer). A first electrical laser contact <NUM> is deposited on a backside of substrate <NUM> opposing the side of the substrate <NUM> on which the layer stacks of the first DBR <NUM> and subsequently the active layer <NUM>, second DBR <NUM> and second electrical laser contact <NUM> are processed. The first electrical laser contact <NUM> comprises openings which are aligned with the VCSELs such that laser light <NUM> can be emitted via the substrate <NUM> through the corresponding opening. The substrate <NUM> may alternatively be locally removed to avoid absorption of laser light <NUM> by the substrate <NUM>. The third VCSEL device <NUM> is similarly as discussed with respect to <FIG> mounted on the detector chip <NUM> which comprises an electrical driver (not shown) which is arranged to provide an electrical drive current to the VCSELs by means of the first electrical laser contact <NUM> and the second electrical laser contact <NUM>. The detector chip <NUM> further comprises detectors <NUM>, wherein the detectors <NUM> are aligned with the openings of the first electrical contact <NUM>. The detector chip <NUM> further comprises an evaluator <NUM> which is arranged to receive self-mixing interference measurement signals from the detectors <NUM> to determine distances to, for example, an object to determine a three-dimensional picture of the object. The third VCSEL device <NUM> further comprises one common optical device <NUM>. The common optical device <NUM> is integrated on wafer level by means of a transparent material. The transparent material is deposited on top of the VCSELs. The transparent material is further shaped such that laser light <NUM> emitted by different VCSELs is directed to different directions. The common optical device <NUM> may further comprise integrated micro lenses (e.g. structured layers of different transparent materials) which are arranged to focus the laser light <NUM>. The optical devices as discussed with respect to <FIG> and <FIG> may also be combined with the embodiment discussed with respect to <FIG>.

<FIG> shows a cross-section of self-mixing interference sensor <NUM> according to a first embodiment. The self-mixing interference sensor <NUM> is arranged to determine presence, distances and movements of objects by means of self-mixing interference measurements. The optical sensor <NUM> comprises a VCSEL device <NUM> as discussed above, a transmission window <NUM> and a driving circuit <NUM> for electrically driving the VCSEL device <NUM>. The driving circuit <NUM> is electrically connected to the VCSEL device <NUM> to supply electrical power to the VCSEL device <NUM> in a defined way. The driving circuit <NUM> comprises a memory device for storing data and instructions to operate the driving circuit <NUM> and a processing unit for executing data and instructions to operate the driving circuit <NUM>. The self-mixing interference sensor <NUM> further comprises an evaluator <NUM>. The detectors <NUM> (e.g. photodiodes) comprised by the VCSEL device <NUM> are arranged to determine variations in the standing wave pattern within the laser cavity coupled to the respective photodiode. The evaluator <NUM> comprises at least one memory device like a memory chip and at least one processing device like a micro-processor. The evaluator <NUM> is adapted to receive electrical signals from the VCSEL device <NUM> and optionally from the driving circuit <NUM> to determine distances or movements of one or more objects based on the interference of laser light <NUM> which is reflected by the respective object and the optical standing wave within the respective laser cavity. The evaluator may optionally be arranged to reconstruct a <NUM>-D picture of a scene which is illuminated by means of the self-mixing interference sensor <NUM>.

<FIG> shows a principal sketch of a mobile communication device <NUM> comprising a self-mixing interference sensor <NUM>. The self-mixing interference sensor <NUM> can, for example, be used in combination with a software application running on the mobile communication device <NUM>. The software application may use the self-mixing interference sensor <NUM> for providing a <NUM>-D picture or movie of a scene illuminated by means of the self-mixing interference sensor <NUM>.

<FIG> shows a principal sketch of a process flow of a method of fabricating a VCSEL device <NUM> according to the present invention. A substrate <NUM> is provided in step <NUM>. A VCSEL array comprising a multitude of laser diodes is provided in step <NUM> on the substrate. Each laser diode comprises an optical resonator. The optical resonator comprises a first distributed Bragg reflector, a second distributed Bragg reflector and an active layer for light emission. The active layer is arranged between the first distributed Bragg reflector <NUM> and the second distributed Bragg reflector. A first electrical laser contact is provided in step <NUM>. The first electrical laser contact <NUM> is a common contact for all laser diodes of the VCSEL. An at least one second electrical laser contact is provided in step <NUM>. The first electrical laser contact and the at least one second electrical laser contact are arranged to provide an electrical drive current to electrically pump the optical resonators of the laser diodes. The at least one second electrical laser contact is further arranged to electrically contact at least a subgroup of the multitude of laser diodes <NUM> of the VCSEL array. In step <NUM> detectors are provided. Each detector is arranged to generate an electrical self-mixing interference measurement signal associated to the at least one laser diode upon reception of laser light.

The layers of the first DBR <NUM>, the active layer <NUM>, the second DBR <NUM> and the electrical contacts and any other layer as current injection layers and the like may be deposited by epitaxial methods like MOCVD or MBE.

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

From reading the present 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.

Variations to the disclosed embodiments can be understood and effected by those skilled in the art, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality of elements or steps.

Claim 1:
A Vertical Cavity Surface Emitting Laser, VCSEL, device (<NUM>) for a self-mixing interference sensor (<NUM>) for recording three-dimensional pictures, the VCSEL device (<NUM>) comprises a VCSEL array comprising a multitude of laser diodes(<NUM>) on a substrate (<NUM>), a multitude of detectors (<NUM>), a first electrical laser contact (<NUM>) and at least one second electrical laser contact (<NUM>), wherein each laser diode (<NUM>) is configured as a VCSEL, wherein each laser diode (<NUM>) comprises an optical resonator, wherein the optical resonator comprises a first distributed Bragg reflector (<NUM>), a second distributed Bragg reflector (<NUM>) and an active layer (<NUM>) for light emission of laser light (<NUM>), wherein the active layer (<NUM>) is arranged between the first distributed Bragg reflector (<NUM>) and the second distributed Bragg reflector (<NUM>), wherein the first electrical laser contact (<NUM>) and the at least one second electrical laser contact (<NUM>) are arranged to provide an electrical drive current to electrically pump the optical resonators of the laser diodes (<NUM>), wherein the first electrical laser contact (<NUM>) is a common contact for all laser diodes (<NUM>) of the VCSEL array, and wherein the at least one second electrical laser contact (<NUM>) is arranged to electrically contact at least a subgroup of the multitude of laser diodes (<NUM>) of the VCSEL array, wherein each detector (<NUM>) is arranged to generate an electrical self-mixing interference measurement signal associated to at least one laser diode (<NUM>) upon reception of the laser light (<NUM>), wherein the detectors (<NUM>) are integrated in the optical resonators, wherein the VCSEL device (<NUM>) is configured to generate the self-mixing interference signal when a laser diode (<NUM>) emits laser light and a part of the emitted laser light is reflected back to the to the optical resonator of the respective laser diode (<NUM>) and interferes with the standing wave pattern within the optical resonator, wherein the laser light (<NUM>) is emitted through a substrate (<NUM>).