Sensor unit and method for operating a sensor unit

Abstract

The invention relates to a sensor unit (100) having a waveguide (105, 105a, 105b) coupled to a ring resonator (115) by means of a coupling point (110), wherein the ring resonator (115) is designed to generate a quantum state at at least one output (135). Furthermore, the sensor unit (100) comprises a detection unit (145) having at least one detector (145a) for detecting states present or output at the at least one output (135). The detector (145a) is designed to detect an intensity of a light detected at the output (135) and / or a pinch parameter, and to detect therefrom an applied or output state and / or a rotation parameter of a rotation about a rotation axis (148) of the sensor unit (100).

Description

State of the art

[0001] The present invention relates to a sensor unit and a method for operating a sensor unit, to a corresponding control unit and to a corresponding computer program product.

[0002] Current optical gyroscopes are either too large to guarantee good sensitivity or not sensitive enough for chip-integrated applications. Such gyroscope designs hamper widespread availability and universal applicability, making very precise measurements expensive and available only for specific, specialized applications. Disclosure of the invention

[0003] Against this background, the approach presented here presents a sensor unit, a method for operating such a sensor unit, a control unit that uses this method, and finally a corresponding computer program product according to the main claims. Advantageous embodiments emerge from the respective subclaims and the following description.

[0004] Here, a sensor unit with the following features is presented: - a waveguide coupled to a ring resonator by means of a coupling point, wherein the ring resonator is designed to generate a quantum state (for example using four-wave mixing) at at least one output; and - a detection unit having at least one detector for detecting states present or output at the at least one output, wherein the detector is designed to detect an intensity of a light detected at the output and / or a pinch parameter and to detect therefrom a present or output state and / or a rotation parameter of a rotation of the sensor unit.

[0005] For example, this sensor unit can be compact, specially constructed on a substrate or integrated into a chip. A coupling point in this case can be understood, for example, as a multimode interferometer or an arrangement of closely spaced waveguides (for example within a range of approximately 50 nanometers to one millimeter). This can be used to achieve entanglement of states such as photons in or at the two coupled time periods by means of the Hong-Ou-Mandel effect. An output in this case can be understood as a connection or contact point that enables the output or detection of light. A squeezing parameter can be understood as a value or parameter that describes a reduction in the blur of certain properties of, for example, light, while simultaneously increasing the blur of another property.For example, the phase blur of light can be reduced by increasing the amplitude blur.

[0006] The approach proposed here is based on the finding that the pre-switching of the ring resonator in combination with an evaluation of the intensity of the light detected at the output and / or the squeezing parameter enables a significant improvement in the precision of measuring values. The approach presented here enables the realization of an optical chip-integrated gyroscope that can measure a rotation rate or, in general, a rotation parameter and exhibits high sensitivity. The advantage of the approach presented here is that this is possible in a compact sensor system that can be constructed on-chip. Using a ring resonator, a quantum state, such as single photons and squeezed light, can be generated. By exploiting specific quantum states and measurement methods, a robust sensor across a wide temperature range is possible.

[0007] According to a favorable embodiment, the detection unit can be configured to determine the applied or output state and / or the rotation parameter of the rotation of the sensor unit using an intensity and / or a wavelength of the light transmitted into the waveguide and / or using an intensity and / or a wavelength of the light detected at the output and / or using a length of the resonator and / or using an effective optical refractive index and / or using a mode index parameter. Such an embodiment of the approach proposed here offers the advantage of using these easily detected or known optical parameters of the structure of the sensor unit to determine the applied or output state or a corresponding rotation parameter of the rotation of the sensor unit derived therefrom.

[0008] A particularly advantageous embodiment of the approach proposed here is one that has a second waveguide coupled to the coupling point and / or, bypassing the ring resonator, to a coupling point between the output and the detector. Such an embodiment advantageously enables the determination of physical effects of the light traveling through the ring resonator, which then ensures reliable evaluation of the results by the detector.

[0009] Another conceivable embodiment of the approach proposed here is one in which the output is coupled to at least one further output, wherein the detection unit has at least one further detector for detecting states present at the at least one further output. Such an embodiment advantageously enables the evaluation of different parameters that can be provided by the ring resonator in the different detectors. For example, the values ​​provided by the different detectors can be linked to one another, thereby enabling a particularly precise determination of a physical quantity as a measured value.

[0010] According to a further embodiment of the approach proposed here, the detection unit can be configured to provide a sensor signal using a detection signal from the first detector and a further detection signal from the at least one further detector, in particular wherein the sensor signal represents a rotation rate and / or rotation of the sensor unit. Such an embodiment enables a very accurate or precise determination of the physical quantity using relatively simple technical means.

[0011] Furthermore, an embodiment of the approach proposed here is conceivable which further comprises at least one light source and / or a laser light source which is designed to emit light into the waveguide, in particular wherein a further light source and / or a further laser light source is provided which is designed to emit light into the at least one further waveguide, in particular wherein the light source or the further light source is designed to emit light with different wavelengths. Such an embodiment offers the advantage, on the one hand, of a compactly constructed sensor unit and, on the other hand, of the determination of very precise measurement results by using the favorable properties of the light emitted by the light source and / or the further light source.

[0012] In another embodiment, multiple frequencies can be generated using a single light source. This is possible, for example, using electro-optical modulators outside or on the chip.

[0013] A particularly advantageous embodiment of the approach proposed here is one in which the light source and / or the laser light source can be used as a pump light source and the further light source and / or the further laser light source can be used as a signal light source. Such an embodiment offers the advantage of efficiently exploiting the physical properties of the ring resonator to provide the quantum states, which can then be advantageously evaluated in the detector or detector unit.

[0014] For this purpose, according to one embodiment of the approach presented here, a ring resonator designed to generate a quantum state using four-wave mixing and / or the Kerr effect can be used particularly advantageously. A ring resonator designed in this way is, on the one hand, technically very simple to implement and, on the other hand, provides quantum states that can be advantageously used in the downstream Mach-Zehnder interferometer.

[0015] Another advantageous embodiment of the approach proposed here is one in which the waveguide has at least two partial waveguides, between which the ring resonator is arranged. Such an embodiment offers the advantage that specific wavelengths can be coupled in and / or out more effectively than others. This also has the advantage that no or only minimal interference and / or effects can arise in subsequent optical paths due to the action of a light source.

[0016] In order to specifically couple, for example, light from outside a substrate into a sensor unit and / or to couple out light from inside a substrate from the sensor unit, which is constructed in one piece in its own substrate, according to a particularly advantageous embodiment of the approach proposed here, at least one grating coupler with or without a subsequent taper structure can be provided for coupling light into the waveguide or for outputting light from the output to at least the detector of the detection unit.

[0017] A particularly favorable embodiment of the approach proposed here is one in which at least one phase-shifting element is provided for varying a state guided on the waveguide and / or the further waveguide and / or for changing the resonance condition of the ring resonator, and / or wherein the waveguide comprises a lithium niobate material and / or a lithium niobate material is arranged in an environment at least around the waveguide and / or the ring resonator. Such an embodiment offers the advantage of being able to operate the sensor unit at particularly favorable operating points due to the possibility of a phase variation of a quantum state on the conduction unit in the sensor unit, specifically at which the sensor unit can very sensitively detect a specific physical quantity, such as a rotation rate or a rotation.By using the lithium niobate material, desired vibration modes can be amplified and / or unwanted vibration modes can be suppressed or at least dampened.

[0018] In another embodiment, a phase shifter or the lithium niobate material is located above or on the ring resonator to actively change the resonance conditions in the ring. This has the advantage that the generation of quantum states is more reliable, their properties can be varied, and their generation can be controlled. The phase shifters can be designed, for example, electro-optically with electrodes or thermally with heatable layers, such as metal conductors.

[0019] An embodiment of the approach proposed here is advantageous as a method for operating a sensor unit according to one of the preceding claims, wherein the method comprises the following steps: - sending light into at least the waveguide; and - Evaluating a received light received by at least the detector to obtain a sensor signal.

[0020] The advantages mentioned above can also be realized in a technically simple and efficient manner using such an embodiment.

[0021] The approach presented here further provides a control unit configured to perform or implement the steps of a variant of a method presented here in corresponding devices. This embodiment of the invention in the form of a control unit also allows the problem underlying the invention to be solved quickly and efficiently.

[0022] In this case, a control unit can be understood as an electrical device that processes sensor signals and outputs control and / or data signals depending on them. The control unit can have an interface that can be implemented in hardware and / or software. In a hardware implementation, the interfaces can, for example, be part of a so-called system ASIC, which contains a wide variety of functions of the control unit. However, it is also possible for the interfaces to be separate integrated circuits or to consist at least partially of discrete components. In a software implementation, the interfaces can be software modules that are present, for example, on a microcontroller alongside other software modules.

[0023] Also advantageous is a computer program product with program code that can be stored on a machine-readable medium such as a semiconductor memory, a hard disk memory or an optical memory and is used to carry out the method according to one of the embodiments described above when the program product is executed on a computer or a control unit.

[0024] The approach presented here is explained in more detail below using the attached drawings. They show: Fig. 1 a schematic representation of an embodiment of a sensor unit; Fig. 2 two schematic representations of different designs or connections of the ring resonator to the waveguide or the different sections of the waveguide; Fig. 3 in a schematic diagram representation of quantum states that can be generated via four-wave mixing in several sub-diagrams arranged one above the other; Fig. 4 a flowchart of an embodiment of a method; and Fig. 5 a block diagram of an embodiment of a control unit.

[0025] In the following description of advantageous embodiments of the present invention, the same or similar reference numerals are used for the elements shown in the various figures and having a similar effect, whereby a repeated description of these elements is omitted.

[0026] Fig. 1 shows a schematic representation of an embodiment of a sensor unit 100. The sensor unit 100 comprises a waveguide 105, which is divided, for example, into two subsections 105a and 105b, which are coupled or entangled with a ring resonator 115 via a coupling point 110.

[0027] At least the second subsection 105b is coupled and / or entangled via a coupling point acting as output 135 to an output coupling point 140, which is configured to output quantum states or photons to a detector 145a of a detector unit 145. Furthermore, a further output coupling point 150 is coupled and / or entangled to the output 135, which is configured to output quantum states or photons to a further detector 145b of the detector unit 145.The detector unit 145 is designed, for example, to provide a sensor signal 147 using sensor values ​​from the detector 145a and the further detector 145b, which sensor signal 147 detects, for example, an intensity of a light detected at the output 135 and / or a pinch parameter and, from this, to detect an applied or output state and / or a rotation parameter of a rotation of the sensor unit 100, wherein the rotation parameter represents a rotation rate and / or a rotation of the sensor unit 100 about a rotation axis 148.

[0028] In addition, according to the Fig. 1, an input coupling point 155 is provided for the sensor unit 100, which is connected via a second waveguide 157 to the coupling point 110 and / or, bypassing the ring resonator 155, alternatively or additionally to the output 135 and additionally or alternatively via a waveguide coupling point 160 to the output coupling point 140 and / or additionally or alternatively via the waveguide coupling point 160 to the further output coupling point 150.

[0029] Furthermore, according to the Fig. In the embodiment shown in Figure 1, a 165 is provided, which is configured, for example, as a pump laser light source and is designed to transmit light into the (first) section 105a of the waveguide 105. Alternatively or additionally, a further light source 170 is provided, which is configured, for example, as a signal laser light source and is designed to transmit further light into the input coupling point 155. Furthermore, only the light source 170 can be used without the light source 165. In this case, the light source 170 is used as a pump laser light source and a signal laser light source. This is possible because, in the ring resonator, signal photons of the same wavelength as the pump source can also be generated via four-wave mixing. Photons of different wavelengths can also be generated via an electro-optical modulator outside or on the chip.

[0030] It is also conceivable that grating couplers 175 are used to couple light from the light source 165 to the further light source 170 into the sensor unit 101 if this sensor unit 100 is integrated on a common substrate or chip and the light source 165 and the further light source 170 are arranged outside this substrate or the chip. Similarly, corresponding grating couplers 175 can also be used to couple corresponding quantum states or photons from the output coupling point 140 to the detector 145a and / or from the further output coupling point 150 to the further detector 145b, especially if one or more of the detectors of the detector unit 145 are not integrated on a common substrate with the other components of the sensor unit 100.

[0031] It is also conceivable to use phase shifters or phase shifting elements 180 on and / or in individual conductor components of the components of the sensor unit 100 and / or the ring resonator 115, in particular wherein the phase shifting elements 180 are designed such that they can be controlled individually or jointly in such a way that they can control certain phase shifts or delays of states occurring on the respective conductor components. For this purpose, for example, a Fig. 1, a control unit not shown can be used, which can control the individual phase shift elements 180.

[0032] Fig. 2 shows two schematic representations of different configurations or connections of the ring resonator 115 to the waveguide 105 or the different sections 105a and 105b of the waveguide 105. In the left representation from the Fig. 2 shows the arrangement or interlacing of the ring resonator 115 via the coupling point 115 with the two sections 105a and 105b of the waveguide 105. In the right-hand illustration of the Fig. Figure 2 shows an alternative arrangement of the ring resonator 115 between the first section 105a and the second section 105b of the waveguide 105. An auxiliary coupling point 200 is used, which is arranged opposite the coupling point 110, for example, halfway along the length of the ring resonator 115, and which is configured to output states that run in the ring resonator 115.

[0033] An architecture is thus presented as an example in which a quantum state is generated, for example, via four-wave mixing in a ring resonator 115. For this purpose, a ring resonator structure and two lasers can be used as light sources 165 and 170. One laser then corresponds to the pump laser and the other to the signal laser. The pump laser then pumps the ring resonator 115. The ring resonator structure is designed, for example, in such a way that the resonator condition is met for specific wavelengths. Via four-wave mixing, squeezed or coherently squeezed photons of the wavelength of the signal laser and of other wavelengths for which the resonator condition described in more detail below applies are then generated in the ring resonator 115.

[0034] According to the Sagnac effect, a phase shift of the light occurs in the ring resonator 115, which, among other things, changes the resonance condition of the ring and, according to a specific detection method, leads to a specific interference pattern that can be measured. The ring resonator 115 represents the sensor area.

[0035] With the exemplary embodiment of a sensor unit 100 presented here, light from a laser source can thus be generated as light source 165 either directly on an optical chip or coupled into it via lateral coupling. In a further possibility, the laser can be positioned directly above the grating coupler 175 and guided via a taper structure from the grating coupler 175 into a waveguide 105 or 105a, which, for example, consists of silicon (Si) or silicon nitride (SiN) or comprises such a material. In this case, the laser corresponds to a pump laser. The laser light is coupled into a ring resonator 115 via lateral waveguide coupling or via multimode interferometers. As is usual for resonators, this ring resonator produces a field enhancement and thus a high intensity. At sufficiently high intensity, it is possible to generate squeezed photon pairs via four-wave mixing with Si and SiN.

[0036] The four-wave mixing, like the intensity of the pump light, depends on the resonance condition of the resonator. The resonance condition of the pump light can be described as follows: λres=neffLm, where n eff is the effective optical refractive index, L is the length of the (ring) resonator 115, and m is an integer representing the mode index. The resonance condition of the four-wave mixing is described by the equation: κ=neffωS+neffωI−2neffωPc+2γPp, where in the perfect resonance of the four-wave mixture κ=0 is satisfied. Here the variables ω p , ω s and ω l are the angular frequencies of the pump, signal, and idler modes, c is the speed of light, γ is a constant describing the strength of the four-wave coupling, and P_p is the pump light intensity. If the resonance condition for the pump light is met, the maximum pump light intensity is P pwith frequency ω P present in ring 115. If the resonance condition for the four-wave mixing is fulfilled, the maximum intensity for the generated squeezed quantum states with the frequencies ω s and ω l present at a specific pump light intensity. Due to the Sagnac effect, the effective length of the resonator changes with an applied rotation rate of the sensor unit 110, and thus the resonance condition in the ring resonator 115. This changes the pump light intensity and also the intensity of the resulting quantum states via the four-wave mixing. In addition, the resulting quantum states are subject to the effect that their squeezing changes with changing intensity.

[0037] Fig. Figure 3 shows a schematic diagram of quantum states that can be generated via four-wave mixing in several superimposed sub-diagrams. Here, σ corresponds to a combination of the resonance condition and the pump light intensity. A higher σ corresponds to a higher four-wave mixing intensity (indicated by a higher value x plotted on the abscissa). s ) and up to a value of σ=1 the crushing becomes larger and then smaller again.

[0038] Next to the ring resonator 115, a detection stage in the form of detector unit 145 is placed, which measures the intensity and / or squeezing of the generated light. For this purpose, additional lasers with the frequency of the quantum states are either coupled into the chip or generated directly within it via integrated lasers. This is implemented below by the additional light source 170, with the light from this additional light source 170 being referred to as the signal laser (light).

[0039] In another embodiment, the signal laser is also pumped into the ring resonator 115 to produce squeezed light of higher intensity, also called coherently squeezed light.

[0040] The signal from coupling point 140 or the further coupling point 150 can then be measured using various measurement methods, for example, homodyne detection. Here, the signal laser is combined with the output signal at output 135 in a beam splitter, and the resulting interference is measured by one or two detectors 145a or 145b. The latter case is referred to as balanced homodyne detection, which offers the advantage of low measurement noise. The phase of the signal laser can be varied using phase shifters 180 to optimize detection. In another embodiment, a pure intensity measurement is performed. Here, the output signal is measured directly by a detector 145a. Since the intensity of both the pump light and the squeezed light changes, there is a higher sensitivity than in the classic case.In further embodiments, parity measurement can also be realized using the aforementioned structures. In all variants, the detectors 145a and 145b can be manufactured directly integrated, or the signal can be coupled out via grating couplers 175 or lateral couplers and measured outside the chip on which, for example, the sensor unit is manufactured integrated.

[0041] In another embodiment, a product measurement is used, which is advantageous for measuring pinch marks. For this purpose, 140 and 150 each have two outputs, whose signals are each measured by a detector. This corresponds to a total of four detectors. The measured signals from 140 and 150 are subtracted or added and then multiplied. This also enables the simultaneous analysis of pinch marks and intensity.

[0042] In a further embodiment, a frequency measurement can also be performed by evaluating signal 147. If the resonance condition in ring 115 changes due to an applied rotation rate, the wavelength of the resulting quantum states also varies. However, since the wavelength of signal laser 170 remains the same, the interference between the two at 140 and 150 produces a beat signal that has a different frequency depending on the frequency difference between the two.

[0043] This allows the rotation rate to be determined from the frequency of the measured hover signal.

[0044] As previously described, the entire structure is exemplary in the Fig. 1. Thus, the two lasers used as examples are shown, whose light is coupled into a chip via grating couplers 175. This first enters the ring 115 to generate the four-wave mixing. The waveguide 105 or 105b is then guided via the output 135 and exemplary grating couplers 175 to the detectors 145a or 145b. The path of the signal laser is used to pump the ring resonator 115 and, for example, to serve as a signal for a Mach-Zehnder interferometer input and / or for homodyne detection. It should be noted that each of these uses / paths of the signal laser can also be omitted.Thus, only one vacuum state can be used for the multimode interferometers, or any number of phase shifters can be used in the lowest waveguide path and / or the sensor region, or the order and number of multimode interferometers used in this path can be changed so that the first interferometers already have four outputs.

[0045] According to another embodiment, a phase shifter 180 is located above the ring resonator 115. This allows a closed control loop to be formed by the phase shifter 180 counteracting the Sagnac effect and adjusting the phase (for example, of the light traveling through the ring resonator 115) accordingly. This allows the sensor to be kept in the most sensitive range. The phase shifters 180 can be implemented using thermal or electro-optical effects.

[0046] In a further embodiment, a material with a high second-order susceptibility is located above the ring resonator 115, for example, and / or the waveguide 105 or the conductor of the ring resonator 115 is made directly of this material, which can be periodically poled lithium niobate, for example. This also allows for three-wave mixing. This has the advantage of allowing a higher intensity of the quantum states to be achieved.

[0047] Any combination of the embodiments is also conceivable.

[0048] In a further embodiment, the system can be expanded to include a temperature sensor 185. In combination with one or more of the phase shifters 180, this can compensate for temperature influences in a control loop.

[0049] Fig. 4 shows a flowchart of an embodiment of a method 400 for operating a variant of a sensor unit presented here. The method 400 includes a step 410 of illuminating at least the waveguide with light and a step 420 of evaluating a received light received by at least the detector to obtain a sensor signal. The illumination and / or detection can occur either continuously or at specific times.

[0050] Fig. 5 shows a block diagram of an embodiment of a control unit 500 for executing a variant of the method 400 for operating a variant of a sensor unit presented here, wherein the control unit has a unit 510 for controlling an illumination of at least the waveguide with a light and a unit 520 for evaluating a received light received by at least the detector in order to obtain a sensor signal.

[0051] The embodiments described and shown in the figures are selected only as examples. Different embodiments can be combined with each other completely or with regard to individual features. Furthermore, one embodiment can be supplemented by features of another embodiment.

[0052] Furthermore, the process steps presented here can be repeated and carried out in a different order than that described.

[0053] If an embodiment includes an “and / or” link between a first feature and a second feature, this should be read as meaning that the embodiment according to one embodiment has both the first feature and the second feature and according to another embodiment has either only the first feature or only the second feature.

Claims

[1] Sensor unit (100) with the following features: - a waveguide (105, 105a, 105b) coupled to a ring resonator (115) by means of a coupling point (110), wherein the ring resonator (115) is designed to generate a quantum state at at least one output (135); and - a detection unit (145) having at least one detector (145a) for detecting states present or output at the at least one output (135), wherein the detector (145a) is designed to detect an intensity of a light detected at the output (135) and / or a pinch parameter and to detect therefrom a present or output state and / or a rotation parameter of a rotation about a rotation axis (148) of the sensor unit (100). [2] Sensor unit (100) according to claim 1, wherein the detection unit (145) is designed to determine the applied or output state and / or the rotation parameter of the rotation (148) of the sensor unit (100) using an intensity and / or a wavelength of the light sent into the waveguide (105a) and / or using an intensity and / or a wavelength of the light detected at the output (135) and / or using a length of the resonator (115) and / or using an effective optical refractive index and / or using a mode index parameter. [3] Sensor unit (100) according to one of the preceding claims, comprising a second waveguide (157) coupled to the coupling point (110) and / or, bypassing the ring resonator (115), to a coupling point (140) between the output (135) and the detector (145a). [4] Sensor unit (100) according to one of the preceding claims, wherein the output (135) is coupled to at least one further output (150), wherein the detection unit (145) has at least one further detector (145b) for detecting states present at the at least one further output (150). [5] Sensor unit (100) according to claim 3, wherein the detection unit (145) is designed to provide a sensor signal (147) using a detection signal of the first detector (145a) and a further detection signal of the at least one further detector (145b), in particular wherein the sensor signal (147) represents a rotation rate and / or rotation of the sensor unit (120). [6] Sensor unit (100) according to one of the preceding claims, with at least one light source (165) and / or a laser light source for emitting a light into the waveguide (105), in particular and / or wherein additionally a further light source (170) and / or a further laser light source is provided, which is designed to emit a light into the at least one further waveguide (155, 157), in particular wherein the light source (165) and / or the further light source (170) are designed to emit light with different wavelengths. [7] Sensor unit (100) according to claim 6, wherein the light source (165) and / or the laser light source can be used or are used as a pump light source and the further light source (170) and / or the further laser light source can be used or are used as a signal light source and / or wherein the light source (170) can be used or is used as a pump light source and a signal light source. [8] Sensor unit (100) according to one of the preceding claims, wherein the waveguide (105) has at least second partial waveguides (105a, 105b) between which the ring resonator (115) is arranged. [9] Sensor unit (100) according to one of the preceding claims, with at least one grating coupler (175) for coupling light into the waveguide (105) or for outputting light from the output (135) to at least the detector (145a) of the detection unit (145). [10] Sensor unit (100) according to one of the preceding claims, with at least one phase shifter element (180) for varying a frequency on the waveguide (105), the further waveguide (157) and / or for changing the resonance condition of the ring resonator (115) and / or wherein the waveguide comprises a lithium niobate material and / or a lithium niobate material is arranged in an environment at least around the waveguide (105) and / or the ring resonator (115), in particular wherein the at least one phase shifter element (180) is controlled as a function of a signal from a temperature sensor (185) and / or wherein the detection unit (145) is designed to infer the rotation rate from the frequency of a measured beat signal. [11] Method (400) for operating a sensor unit (100) according to one of the preceding claims, wherein the method (400) comprises the following steps: - transmitting (410) light into at least the waveguide (105); and - evaluating (420) a received light received by at least the detector (145a) in order to obtain a sensor signal (147), in particular in order to obtain information about a rotation of the sensor unit. [12] Method (400) according to claim 11, comprising a step of controlling a phase shifter element (180) using at least one detection signal of the detector (145a) and / or a sensor signal (147) and / or a signal of the at least one light source (165, 170) and / or wherein in the step (410) of transmitting the light is emitted as pulsed light or as continuous light. [13] Control unit (500) which is designed to carry out and / or control the steps (410, 420) of a method (400) according to claim 11 or 12 in corresponding devices (510, 520). [14] Computer program product with program code for carrying out and / or controlling the steps (310, 320) of the method (400) according to claim 11 or 12, when the program product is executed on a control unit (500). [15] A machine-readable storage medium on which a computer program product according to claim 14 is stored.

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