Method for operating a self-mixing interferometric sensor and self-mixing interferometric sensor

Abstract

A method for operating a self-mixing interferometric sensor is provided. The sensor comprises: - a VCSEL-array (2) with a plurality of VCSEL-elements (3), each VCSEL-element (3) being configured for self-mixing interferometry, - a photodiode-array (6) with a plurality of photodiode elements (7), each photodiode element (7) being configured for detecting electromagnetic radiation (20) leaking from a backside surface (5) of a VCSEL-element (2), wherein the photodiode elements (7) produce SMI-signals (8). The method comprises the steps: - determining a vital sign (16) from the SMI-signals (8) in a first operation mode, and / or - determining the vital sign (16) from the SMI-signals (8) in a second operation mode. Further, a self-mixing interferometric sensor is provided.

Description

[0001] Description

[0002] METHOD FOR OPERATING A SELF-MIXING INTERFEROMETRIC SENSOR AND SELF-MIXING INTERFEROMETRIC SENSOR

[0003] A method for operating a self-mixing interferometric sensor and a self-mixing interferometric sensor are provided.

[0004] An improved method for operating a self-mixing interferometric sensor and an improved self-mixing interferometric sensor are to be provided.

[0005] These objects are achieved by means of a method having the steps of claim 1 and a self-mixing interferometric sensor with the features of claim 9.

[0006] Improved embodiments and developments of the method for operating a self-mixing interferometric sensor and of the self-mixing interferometric sensor are given in the dependent claims.

[0007] According to an embodiment, the self-mixing interferometric sensor to be operated with the present method comprises a VCSEL-array with a plurality of VCSEL-elements, each VCSEL-element being configured for self-mixing interferometry (short: SMI. For example, the VCSEL-elements are arranged in rows and columns within the VCSEL-array. For example, the VCSEL-elements are formed equally (VCSEL, short for "vertical cavity surface emitting laser").

[0008] The VCSEL-element is configured for generating coherent electromagnetic laser radiation. In particular, the VCSEL-element emits coherent electromagnetic laser radiation during operation of the self-mixing interferometric sensor.

[0009] Particularly, the use of a VCSEL-array compared to the use of a single light source, such as a single VCSEL-element or an edge-emitting laser, enables a large field of view of the self-mixing interferometric sensor.

[0010] The VCSEL-element, particularly, comprises an epitaxial semiconductor layer sequence having an active zone configured for generation of electromagnetic radiation. Particularly, the active zone generates electromagnetic radiation when electrical carriers run through the active zone. For example, the active zone comprises a pn-junction for the generation of electromagnetic radiation and the electromagnetic radiation is generated, when electrical carriers run through the pn-junction. For example, the VCSEL-element emits coherent electromagnetic laser radiation with a single transversal mode. Particularly, the VCSEL-array is a transversal single mode VCSEL-array.

[0011] Further, the VCSEL-element comprises, particularly, an optical resonator. For example, the optical resonator is formed by two mirrors arranged opposite to each other. Within the optical resonator the active zone is arranged as a laser active medium, particularly. During operation of the selfmixing interferometric sensor electromagnetic radiation generated within the active zone is at least partially reflected by the mirrors such that a population inversion is generated within the active zone. At least one of the mirrors of the optical resonator is partially transmissive for the electromagnetic radiation. Therefore, during operation of the VCSEL-element electromagnetic laser radiation is emitted from the partially transmissive mirror. During an operation mode of the self-mixing interferometric sensor, electromagnetic radiation emitted by the VCSEL-element is reflected and / or scattered by a target arranged within the field of view of the self-mixing interferometric sensor and at least partially reenters the optical resonator of the VCSEL-element, particularly. The electromagnetic laser radiation reflected back in the cavity interferes and a modulation of an amplitude and / or a frequency of the electromagnetic laser radiation of the VCSEL occurs. From the modulation of the amplitude and / or the frequency of the electromagnetic laser radiation a distance, a velocity, a vibration and / or a movement of the target can be derived.

[0012] According to a further embodiment, the self-mixing interferometric sensor comprises a photodiode-array with a plurality of photodiode elements. Each photodiode element is configured for detecting electromagnetic radiation leaking from a backside surface of a VCSEL-element, particularly. For example, the photodiode elements of the photodiode-array are equal to each other. Particularly, the photodiode elements produce SMI-signals. At present, the out-put signal of the photodiode elements is called "SMI-signal", even if the signals characterizing the self-mixing interferometry within the optical resonators is generated by the VCSEL elements itself. In other words, the photodiode elements act as monitoring photodiode elements monitoring the modulation of the amplitude and / or of frequency of the electromagnetic laser radiation within the optical resonator of the VCSEL-element.

[0013] Particularly preferably, to each VCSEL-element one single photodiode element is allocated. Particularly, one single photodiode element monitors the modulation of the amplitude and / or of frequency of the electromagnetic laser radiation of one single allocated VCSEL-element.

[0014] According to an embodiment of the method, the photodiode element produces an SMI-signal. The SMI-signal, particularly, indicates the amplitude and / or frequency modulation within the optical resonator of the allocated VCSEL-element, due to the target, for example.

[0015] According to a further embodiment of the method, a vital sign is determined from the SMI-signals in a first operation mode. In other words, the self-mixing interferometric sensor is operated in a first operation mode within the method for operating the self-mixing interferometric sensor, and a vital sign is determined from the SMI-signals of the photodiode elements. Particularly, the target in the field of view of the self-mixing interferometric sensor is a human body and a vital sign of the human body is determined from the SMI-signals.

[0016] According to a further embodiment of the method, the vital sign is determined from the SMI-signals in a second operation mode. In other words, the vital sign, which was determined during the first operation mode is, for example, additionally or as an alternative, determined from the SMI-signals in the second operation mode. Particularly, the first operation mode and the second operation mode are different from each other. For example, during the method it is switched between the first operation mode and the second operation mode. It is possible to operate the self-mixing interferometric sensor in the first operation mode and the second operation mode at the same time. The photodetector elements, particularly, measure SMI-signals including amplitude (speckle information) and phase (information on the deformation of the skin) at the very same time.

[0017] According to an embodiment, the self-mixing interferometric sensor comprises:

[0018] - the VCSEL-array with the plurality of VCSEL-elements, each VCSEL-element being configured for self-mixing interferometry,

[0019] - the photodiode-array with the plurality of photodiode elements, each photodiode element being configured for detecting electromagnetic radiation leaking from a backside surface of a VCSEL-element, wherein the photodiode elements produce SMI-signals,

[0020] and the method for operating the self-mixing interferometric sensor comprises the steps of:

[0021] - determining the vital sign from the SMI-signals in the first operation mode, and / or

[0022] - determining the vital sign from the SMI-signals in the second operation mode.

[0023] It is an idea of the present method to use two different operation modes to determine the same vital sign of a human body. For example, the vital sign with the lower signal-to-noise ratio can be chosen as out-put signal. For example, each VCSEL-element can be operated as a displacement sensor using a signal phase of the SMI-signal and / or can be operated as a camera pixel to enable speckle contrast imaging using the SMI-amplitude. Further, the vital sign extraction can be improved due to additional information by using two different operation modes. Preferably, measurement principles of the two operation modes are complementary to each other. According to a further embodiment of the method, the SMI-signal has a power variation coefficient and / or a phase coefficient of a VCSEL-element. Particularly, each SMI-signal has a variation coefficient and / or a phase coefficient of an VCSEL-element allocated to the photodiode element producing the SMI-signal. For example, some or all SMI-signals have power variation coefficients and / or phase coefficients different from each other.

[0024] The SMI-signal of a VCSEL-element, follows the following f ormular:

[0025] P_SMI,ij(µij,φij) = Pij(1 − µijcos(φij)), wherein

[0026] ij characterizes the position of the VCSEL-element within the VCSEL-array. For example, i indicates the row of the VCSEL-element within the VCSEL-array and j indicates the column of the VCSEL-element within the VCSEL-array. Particularly,

[0027]

[0028] indicates the power variation coefficient of the SMI-signal of the respective VCSEL-element at position ij within the VCSEL-array, while cpij indicates the phase coefficient of the SMI-signal of the respective VCSEL-element at position ij within the VCSEL-array. Particularly, the power variation coefficient

[0029]

[0030] comprises an information of an amplitude of the SMI-signal and the phase coefficient φij comprises an information of a phase of the SMI-signal.

[0031] According to a further embodiment of the method, in the first operation mode a time series of speckle images is generated from the power variation coefficients p^ with time, and the vital sign is derived from the time-series of speckle images, particularly via the variation of speckle contrast. In other words, in the first operation mode, the self-mixing interferometric sensor acts as a camera providing speckle images from the power variation coefficients

[0032]

[0033] .

[0034] Particularly, each VCSEL-element together with the assigned photodiode element form a pixel of the camera.

[0035] In the first operation mode speckle plethysmography is, for example, conducted using the self-mixing interferometric sensor. In other words, the self-mixing interferometric sensor acts as a plethysmograph during the first operation mode. During speckle plethysmography a coherent light source, in the present case the VCSEL-array, illuminates the target, for example a part of a human body. Scattering of the coherent electromagnetic radiation by the target leads to formation of a random speckle pattern recorded by the selfmixing interferometer as a speckle image. In particular, the VCSEL-elements and the allocated photodiode elements act as the pixels of the self-mixing interferometer recording the speckle image.

[0036] During plethysmography coherent electromagnetic laser radiation of the VCSEL-elements is transmitted through tissue of the human body and off the skin, which is deformed by the vascular fluctuations in order to interrogate vascular fluctuations caused by the cardiac cycle, for example. The vascular fluctuations lead to volumetric expansion of the blood caused by the variations of pressure. These variations modulate the transmitted electromagnetic radiation of the VCSEL-elements and lead to speckle images. Particularly, speckle plethysmography monitors a blood flow underneath the skin. Particularly, the scattering of coherent light on blood particles causes a variation of the speckle contrast (i. e. the standard deviation of the potential speckle intensity divided by the mean value). This variation of the speckle contrast happens on a time basis that is, in particular, directly associated with the variation of the blood flow during heart activity.

[0037] Heart activity, such as the heartbeat, leads to a variation of a blood flow in the vessels and, as a consequence, to a slight deformation of the skin leading to changes of the speckle pattern of the speckle images. Also, increased scattering of blood particles in the blood vessels changes the speckle pattern and speckle contrast of the speckle pattern. Monitoring of the speckle pattern allows for the extraction of the vital sign. Particularly, from contrast changes and / or amplitude changes within the speckle pattern of the speckle images the vital sign can be determined. For example, an evaluation of the speckle contrast of the speckle image over time yields the vital sign. Also, a movement of the speckle pattern can be analyzed during the first operation mode in order to determine the vital sign.

[0038] According to a further embodiment of the method, each SMI-signal has a phase coefficient. For example, a relative displacement of a target, such as the skin of a human body, is derived from the phase coefficient in the second operation mode. Particularly, the target is arranged within the field of view of the self-mixing interferometric sensor. From the skin deformation, a heartrate of the body can be derived.

[0039] According to a further embodiment of the method, the vital sign of a body is derived from the phase coefficient in the second operation mode. In other words, the vital sign determined from the phase coefficient in the second operation mode is achieved by monitoring the displacement of the skin. According to a further embodiment of the method, a signal-to-noise ratio of the vital sign in the first operation mode is determined. Further, a signal-to-noise ratio of the vital sign in the second operation mode is determined and the vital sign with the smaller signal-to-noise ratio is then put out. In such a way, the signal-to-noise ratio provided by the self-mixing interferometric sensor can be improved.

[0040] Particularly, the detection using two independent operation modes enables a redundant vital sign monitoring.

[0041] It is also possible to use the vital sign in the first operation mode and the vital sign in the second operation mode as complementary information, which may give access to different types of vital signs. Particularly, the second operation mode based on phase information is more sensitive to deformations of the skin incorporating heart activities, while the second operation mode based on speckle contrast may include more complex signal structures allowing for extraction of elaborate vital signs such as blood pressure and velocity.

[0042] According to a further embodiment of the method, the vital sign is monitored remotely. Particularly, the self-mixing interferometric sensor is positioned in the field of view of the self-mixing interferometric sensor at a distance from the human body of which the vital sign is to be monitored. By monitoring the vital sign remotely and in particular in a non-contact mode, it is possible to increase the safety of humans in various types of environments, for example when steering cars or trains. Further, monitoring of the vital signs of patients in a hospital can be simplified by remote monitoring. The self-mixing interferometric sensor disclosed in the following is particularly configured to be operated by means of the method already described. Therefore, features and embodiments disclosed in connection with the method can also be embodied within the self-mixing interferometric sensor and vice versa.

[0043] According to an embodiment, the self-mixing interferometric sensor is configured for remotely monitoring a vital sign, particularly of a human body being arranged at a distance from the self-mixing interferometric sensor. Particularly, the human body to be remotely monitored is arranged in a field of view of the self-mixing interferometric sensor.

[0044] According to a further embodiment, the self-mixing interferometric sensor comprises a VCSEL-array with a plurality of VCSEL-elements, each VCSEL-element being configured for self-mixing interferometry.

[0045] According to a further embodiment, the self-mixing interferometric sensor comprises a photodiode array with a plurality of photodiode elements, each photodiode element being configured for detecting electromagnetic radiation leaking from a backside surface of a VCSEL-element.

[0046] Particularly, each photodiode element is configured for producing an SMI-signal.

[0047] According to a further embodiment, the self-mixing interferometric sensor is configured to be operated in a first operation mode, determining the vital sign from the SMI-signals, and / or in a second operation mode, determining the vital sign from the SMI-signals. Particularly, it can be switched between the first operation mode and the second operation mode. For example, the second operation mode is carried out after the first operation mode or vice versa.

[0048] According to a further embodiment of the self-mixing interferometric sensor, the VCSEL-array and the photodiode array are integrated in a common semiconductor chip. In other words, the self-mixing interferometric sensor is embodied as a semiconductor chip comprising the VCSEL-array and the photodiode array. For example, semiconductor layers being part of the VCSEL-array and semiconductor layers being part of the photodiode array are deposited one above the other and are part of the semiconductor chip.

[0049] It is an idea to embody the self-mixing interferometric sensor as a semiconductor chip comprising the VCSEL-elements as well as the photodiode elements. In such a way, a compact self-mixing interferometric sensor with small dimensions can be achieved with advantage. The self-mixing interferometric sensor can, for example, be applied in vital sign monitoring in a non-contact / remote mode.

[0050] According to a further embodiment of the self-mixing interferometric sensor, a VCSEL-element and a photodiode element form a pixel of the self-mixing interferometric sensor. Particularly, the pixels of the self-mixing interferometric sensor are configured to act as a camera for recording speckle images.

[0051] According to a further embodiment, the self-mixing interferometric sensor comprises an optical element for shaping a far field pattern of the VCSEL-array. Particularly, the optical element for shaping the far field pattern of the VCSEL-array is arranged on or over a radiation exit surface opposite to a backside surface of the VCSEL-array. Particularly, from the radiation exit surface of the VCSEL-array electromagnetic radiation of the VCSEL-elements is emitted during operation of the self-mixing interferometric sensor. The optical element is, for example, a lens, a lens array, a micro-lens array, a diffractive optical element, or a Fresnel lens. Particularly, the optical element is configured for focusing, concentrating or diverging the electromagnetic radiation emitted by the VCSEL-elements of the VCSEL-array.

[0052] According to a further embodiment of the self-mixing interferometric sensor, the VCSEL-element comprises an epitaxial semiconductor layer sequence with an active zone configured for generation of electromagnetic radiation. For example, the VCSEL elements operate in the SWIR range (SWIR short for "short wave infrared"), particularly between 850 nanometer and 1550 nanometer, limit included. In particular, the active zone is configured for generation of electromagnetic radiation within the SWIR range.

[0053] For example, the epitaxial semiconductor layer sequence may be based on an arsenide compound semiconductor material.

[0054] Phosphide compound semiconductor materials are compound semiconductor materials containing arsenide, such as the materials from the system InxAlyGai-x-yAs with 0 < x < 1, 0 < y < 1 and x+y < 1.

[0055] It is also possible that the epitaxial semiconductor layer sequence is based on a phosphide compound semiconductor material. Phosphide compound semiconductor materials are compound semiconductor materials containing phosphor, such as the materials from the system InxAlyGai-x-yP with 0 < x < 1, 0 < y < 1 and x+y < 1.

[0056] According to a further embodiment of the self-mixing interferometric sensor, the VCSEL-element comprises two Bragg mirrors forming an optical resonator of the VCSEL-element. Particularly, in the optical resonator of the VCSEL-element the active zone of the epitaxial semiconductor layer sequence of the VCSEL-element is arranged as a laser active medium.

[0057] Both Bragg mirrors are, particularly, configured to be at least partially transparent for the electromagnetic radiation of the active zone. Therefore, electromagnetic radiation can be emitted from the radiation exit surface opposite to the backside surface of the VCSEL-element. Also, from the backside surface electromagnetic radiation is leaking and impinging on the photodiode element monitoring the output beam of the VCSEL-element.

[0058] According to a further embodiment of the self-mixing interferometric sensor, the photodiode element is applied to one of the Bragg mirrors, for example directly. In such a way, the photodiode elements can be integrated with the VCSEL-elements in a common semiconductor chip, for example. It is also possible, that further layers, for example a buffer layer is arranged between the Bragg mirror and the photodiode element.

[0059] The Bragg mirror, particularly, comprises or consists of alternating thin layers having different refractive indices. Particularly, the thin layers of the Bragg mirror comprise or consist of dielectric materials. Particularly, thicknesses of the thin layers are adapted such that electromagnetic radiation impinging on the Bragg mirror interferes such that a small bandpass filter is achieved. By tuning the thicknesses and the materials of the thin layers, the bandpass of the Bragg reflector can be adapted precisely in a desired way.

[0060] Further advantageous embodiments and developments of the method for operating a self-mixing interferometric sensor and the self-mixing interferometric sensor result from the exemplary embodiment described below in connection with the Figures.

[0061] Figure 1 shows schematically a sectional view of a selfmixing interferometric sensor according to an exemplary embodiment.

[0062] Figure 2 shows schematically a plan view of the self-mixing interferometric sensor according to the exemplary embodiment of Figure 1.

[0063] Figure 3 shows schematically a sectional view of a pixel of the self-mixing interferometric sensor of the exemplary embodiment of Figures 1 and 2.

[0064] Figure 4 shows a flow diagram of a method for operating a self-mixing interferometric sensor according to an exemplary embodiment.

[0065] Figure 5 shows schematically a step of a method for operating a self-mixing interferometric sensor according to an exemplary embodiment. Figure 6 shows schematically the skin over a vessel with blood flow in two different modes.

[0066] Figure 7 shows schematically an SMI-signal as produced by a photodiode element of a self-mixing interferometric according to an exemplary embodiment.

[0067] Figure 8 shows schematically a speckle image of a self-mixing interferometric sensor according to an exemplary embodiment.

[0068] Figure 9 shows schematically a vital sign derived from a speckle image according to an exemplary embodiment.

[0069] Equal or similar elements as well as elements of equal function are designated with the same reference signs in the Figures. The Figures and the proportions of the elements shown in the Figures are not regarded as being shown to scale. Rather, single elements, in particular layers, can be shown exaggerated in magnitude for the sake of better presentation and / or better understanding.

[0070] The self-mixing interferometric sensor 1 according to the exemplary embodiment of Figures 1 and 2 comprises a VCSEL-array 2 having a plurality of VCSEL-elements 3. Each of the VCSEL-elements 3 is configured for self-mixing interferometry. Particularly, each VCSEL-element 3 has a radiation exit surface 4 emitting electromagnetic radiation during operation. Particularly, the VCSEL-elements 3 of the VCSEL-array 2 emit coherent electromagnetic laser radiation 20. An aperture angle of a VCSEL-element 3 lies, for example, between and including 10° and 30°. The radiation exit surfaces 4 of the VCSEL-elements 3 are part of or form a radiation exit surface of the VCSEL-array 2. Opposite to the radiation exit surface 4 of the VCSEL-elements 3 a backside surface 5 of the VCSEL-element 3 is arranged.

[0071] Further, the self-mixing interferometric sensor 1 comprises a photodiode array 6 with a plurality of photodiode elements 7, each photodiode element 7 being configured for detecting electromagnetic radiation 20 leaking from the backside surface 5 of a VCSEL-element 3. Particularly, the photodiode array 6 is arranged on or over the backside surface 5 of the VCSEL-array 2.

[0072] Particularly, the photodiode elements 7 comprise or consist of silicon and have a pn-junction for detecting electromagnetic radiation. Particularly, the photodiode elements 7 are configured for detecting electromagnetic laser radiation 20 of the VCSEL-elements 3 of the VCSEL-array 2. The photodiode elements 7 produce SMI-signals 8 from the electromagnetic radiation 20 leaking from the VCSEL-element 7 during operation.

[0073] Each VCSEL-element 3 together with an allocated photodiode element 7 form a pixel 9 of the self-mixing interferometric sensor 1 or are a part of a pixel 9 of the self-mixing interferometric sensor 1. The pixels 9 of the self-mixing interferometric sensor 1 can be controlled independently from each other.

[0074] The pixels 9 of the self-mixing interferometric sensor 1 are particularly separated from each other by a dielectric material 10 such as an oxide or a nitride. As can be seen in the plain view of Figure 2 on the radiation exit surface of the of the VCSEL-array 2, the radiation exit surfaces 4 of the VCSEL-elements 3 are separated from each other by the dielectric material 10.

[0075] Further, the self-mixing interferometric sensor 1 according to Figure 1 comprises an optical element 11 to adjust a far field pattern of the VCSEL-elements 3. The optical element 11 is arranged over the radiation exit surface of the VCSEL-array 2.

[0076] Particularly, the far field pattern of the VCSEL-elements 7 illuminates a target, such as human body part 17 within the field of view of the self-mixing interferometric sensor 1 continuously. Particularly, in the far field pattern of the VCSEL-elements 3 no unilluminated gaps exist.

[0077] Figure 3 schematically shows a pixel 9 of the self-mixing interferometric sensor 1 according to the exemplary embodiment of Figures 1 and 2. Particularly, the pixel 9 comprises a VCSEL-element 3 and a photodiode element 7.

[0078] The VCSEL-element 3 has an epitaxial semiconductor layer sequence 12 comprising an active zone 13 configured for generating electromagnetic radiation. The active zone 13 is arranged within an optical resonator 14 of the VCSEL-element 3. The optical resonator 14 is formed by two oppositely arranged Bragg mirrors 15 being partially transmissive for the electromagnetic radiation 20 generated within the active zone 13. From a radiation exit surface 4 the VCSEL-element 3 emits electromagnetic laser radiation 20 during operation while from a backside surface 5 some of the electromagnetic laser radiation 20 produced within the active zone 13 leaks towards the photodiode element 7. The photodiode elements 7 of the photodiode array 6 are, at present, directly attached to the Bragg mirrors 15 of the VCSEL-elements 3. In other words, the photodiode elements 7 and the VCSEL-elements 3 are integrated in a common semiconductor chip. At present, the self-mixing interferometric sensor 1 forms a single semiconductor chip comprising the VCSEL-array 2 and the photodiode array 6.

[0079] According to the method for operating a self-mixing interferometric sensor 1, as for example already described in connection with Figures 1 and 3, a vital sign 16 is determined in a first step SI from the SMI-signals 8 of the photodiode elements 7 in a first operation mode. Further, the vital sign 16 is determined from the SMI-signal 8 in a second operation mode in a second step S2.

[0080] In other words, it is possible to operate the self-mixing interferometric sensor 1 in two different operation modes, the first operation mode and the second operation mode.

[0081] Particularly, the self-mixing interferometric sensor 1 can be switched between the first operation mode and the second operation mode. It is possible to operate the self-mixing interferometric sensor 1 in both operation modes at the very same time.

[0082] It is possible, for example, to determine the vital sign 16 only in the first operation mode or only in the second operation mode. Further, the vital sign 16 can be determined in the first and in the second operation mode. In the latter case, a signal-to-noise ratio is determined from the vital sign 16 determined in the first operation mode and a signal-to-noise ratio is determined from the vital sign 16 determined in the second operation mode, and the vital sign 16 with the smaller signal-to-noise ratio is used as out-put signal of the self-mixing interferometric sensor 1, for example. It is also possible to use the vital sign 16 of the first operation mode and the vital sign 16 of the second operation mode as complementary information, which may allow for access to different types of vital signs.

[0083] Figure 5 shows a self-mixing interferometric sensor 1 according to an exemplary embodiment during operation, for example when being operated using the method according to the exemplary embodiment of Figure 4. The self-mixing interferometric sensor 1 is, for example, constructed as already explained in connection with Figures 1 to 3.

[0084] The self-mixing interferometric sensor 1 is operated to emit coherent electromagnetic laser radiation from the radiation exit surface of the VCSEL-array 2. Within a field of view 21 of the self-mixing interferometric sensor 1 a body part 17 of a human to be monitored remotely by means of the self-mixing interferometric sensor 1 is arranged. In the present case, the body part 17 of the human to be monitored remotely is a palm.

[0085] The palm reflects and / or scatters electromagnetic laser radiation 20 emitted from the VCSEL-elements 3 of the VCSEL-array 2 and sent it back at least partially in the optic resonators 14 of the VCSEL-elements 3 such that electromagnetic radiation 20 generated within the optical resonators 14 is disturbed by interference. This change in amplitude and frequency of the electromagnetic radiation 20 of the VCSEL-elements 3 is detected by the photodiode elements 7 of the photodiode array 6 of the self-mixing interferometric sensor 1, and the photodiode elements 7 produce SMI-signals 8.

[0086] Particularly, Figure 6 shows a surface of a skin 18, for example of the palm as shown in Figure 5, with and without blood flow in a vessel below the skin 18. Due to heart activity the blood flow changes within the vessel over time. If there is no blood flow through the vessel, the skin 18 is does not change its shape over time leading to a constant SMI-signal 18. However, if there is blood flowing in the vessel, the skin surface moves due to the heart activity. As a consequence, also the SMI-signals 8 produced by the photodiode elements 7 of the photodiode arrays 6 changes with the heart activity.

[0087] Figure 7 shows the power P of a SMI-signal 8 varying with time t. The SMI-signal 8 has an amplitude and a phase information. From the amplitude of the SMI-signals 8 of the photodiode array 6, a speckle image 19 can be derived in a first operation mode, as shown in Figure 8, for example. From the phase information a relative displacement of the skin 18 can be determined in a second operation mode.

[0088] Particularly, the amplitude information from the SMI-signals 8 of the photodiode elements 7 monitoring the different VCSEL-elements 3 produces the speckle image 19. From the variation of contrast over time of the speckle images 19, the heartbeat as a vital sign 16 of the monitored human being can be derived in the first operation mode. Particularly, a sequence of speckle images 19 is derived from the SMI-signals 8 of the pixels 9 of the self-mixing interferometric sensor 1. From this sequence, the heartbeat as a vital sign 16 is derived. The heartbeat is, for example, shown in Figure 9 exemplarily.

[0089] For example, a signal-to-noise ratio of the heartbeat determined in the first operation mode and a signal-to-noise ratio of the heartbeat determined in the second operation mode is compared, and the vital sign 16 having the smaller signal-to-noise ratio is put out.

[0090] The present application claims priority of the German application DE 102024131034.0, the disclosure content of which is inserted herein by reference.

[0091] The features and exemplary embodiments described in connection with the Figures can be combined with each other according to further exemplary embodiments, even if not all combinations are explicitly described. Furthermore, the exemplary embodiments described in connection with the Figures may alternatively or additionally have further features according to the description in the general part.

[0092] The invention is not limited to the description of the exemplary embodiments. Rather, the invention comprises each new feature as well as each combination of features, particularly each combination of features of the claims, even if the feature or the combination of features itself is not explicitly given in the claims or the exemplary embodiments. References

[0093] 1 self-mixing interferometric sensor

[0094] 2 VCSEL-array

[0095] 3 VCSEL-element

[0096] 4 radiation exit surface of the VCSEL-element 5 backside surface of the VCSEL-element

[0097] 6 photodiode array

[0098] 7 photodiode element

[0099] 8 SMI-signal

[0100] 9 pixel

[0101] 10 dielectric material

[0102] 11 optical element

[0103] 12 epitaxial semiconductor layer sequence 13 active zone

[0104] 14 optical resonator

[0105] 15 Bragg mirror

[0106] 16 vital sign

[0107] 17 body part

[0108] 18 skin

[0109] 19 speckle image

[0110] 20 electromagnetic laser radiation

[0111] 21 field of view

[0112] SI, S2 step

[0113] μᵢⱼ power variation coefficient

[0114] φᵢⱼ phase coefficient

Claims

Claims1. Method for operating a sel f-mixing interferometric sensor ( 1 ), the sensor comprises:- a VCSEL-array ( 2 ) with a plurality of VCSEL-elements ( 3 ), each VCSEL-element ( 3 ) being configured for sel f-mixing interferometry,- a photodiode-array ( 6 ) with a plurality of photodiode elements ( 7 ), each photodiode element ( 7 ) being configured for detecting electromagnetic radiation ( 20 ) leaking from a backside surface ( 5 ) of a VCSEL-element ( 2 ), wherein the photodiode elements ( 7 ) produce SMI-signals ( 8 ),the method comprises the steps:- determining a vital sign ( 16 ) from the SMI-signals ( 8 ) in a first operation mode, and / or- determining the vital sign ( 16 ) from the SMI-signals ( 8 ) in a second operation mode, wherein the first operation mode and the second operation mode are di f ferent from each other.

2. Method according to the previous claim, whereinthe SMI-signal ( 8 ) has a power variation coefficient (μᵢⱼ) and / or a phase coefficient (φᵢⱼ) of a VCSEL-element ( 3 ).

3. Method according to the previous claim, wherein- in the first operation mode a time series of speckle images ( 19 ) is generated from the power variation coef ficients, and - the vital sign ( 16 ) is derived from the series of speckle images ( 19 ).

4. Method according to any of the previous claims, wherein each SMI-signal ( 8 ) has a phase coefficient (φᵢⱼ).

5. Method according to the previous claim, wherein a relative displacement of a target is derived from the phase coefficient (φij ) in the second operation mode.

6. Method according to any of claims 4 or 5, whereinthe vital sign ( 16) of a body is derived from the phase coefficient (φᵢⱼ) in the second operation mode.

7. Method according to any of the previous claims, wherein - a signal to noise ration of the vital sign ( 16) in the first operation mode is determined,- a signal to noise ration of the vital sign ( 16) in the second operation mode is determined, and- the vital sign ( 16) with the smaller signal to noise ratio is put out.

8. Method according to any of the previous claims, wherein the vital sign ( 16) is monitored remotely.

9. Self-mixing interferometric sensor ( 1 ) for remotely monitoring a vital sign ( 16), comprising:- a VCSEL-array (2 ) with a plurality of VCSEL-elements (3), each VCSEL-element (2 ) being configured for self-mixing interferometry,- a photodiode-array ( 6) with a plurality of photodiode elements (7 ), each photodiode element (7 ) is configured for detecting electromagnetic radiation (20) leaking from a backside surface (5) of a VCSEL-element (3), wherein- each photodiode element (7 ) is configured for producing a SMI-signal ( 8 ),- the self-mixing interferometric sensor ( 1 ) is configured to be operated in a first operation mode determining the vital sign ( 16) from the SMI-signals ( 8 ) and / or in a secondoperation mode determining the vital sign ( 16 ) from the SMI-signals ( 8 ), wherein the first operation mode and the second operation mode are di f ferent from each other.

10. Sel f-mixing interferometric sensor ( 1 ) according to the previous claim, whereinthe VCSEL-array ( 2 ) and the photodiode array ( 6 ) are integrated in a common semiconductor chip.

11. Sel f-mixing interferometric sensor ( 1 ) according to any of claims 9 or 10, whereina VCSEL-element ( 3 ) and a photodiode element ( 7 ) form a pixel ( 9 ) of the sel f-mixing interferometric sensor ( 1 ).

12. Sel f-mixing interferometric sensor ( 1 ) according to any of claims 9 to 11, whereinan optical element ( 11 ) for shaping a far field pattern of the VCSEL-array ( 2 ) is arranged on or over a radiation exit surface of the VCSEL-array ( 2 ) opposite to a backside surface of the VCSEL-array ( 2 ).

13. Sel f-mixing interferometric sensor ( 1 ) according to any of claims 9 to 12, whereinthe VCSEL-element ( 3 ) comprises an epitaxial semiconductor layer sequence ( 12 ) with an active zone ( 13 ) configured for generation of electromagnetic radiation ( 20 ).

14. Sel f-mixing interferometric sensor ( 1 ) according to any of claims 9 to 13, whereinthe VCSEL-element ( 3 ) comprises two Bragg mirrors ( 15 ) forming an optical resonator ( 14 ) of the VCSEL-element ( 3 ).

15. Self-mixing interferometric sensor ( 1 ) according to any of claims 9 to 14, whereinthe photodiode element (7 ) is applied to one of the Bragg mirrors ( 15).

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