Optoelectronic arrangement and method for operating an optoelectronic arrangement

Abstract

The invention concerns an optoelectronic arrangement with a housing with a bottom first region surrounding an elevated second region, wherein the second region comprises three openings arranged in a first row, each of the openings and having a transparent cover. A first optoelectronic device is arranged in a first opening, said optoelectronic device comprising a first optoelectronic component a second optoelectronic component. A first light detection device is arranged in a second opening, wherein a distance of the first optoelectronic component to the first light detection device is substantially equal to a distance of the second optoelectronic component to the first light detection device, the first light detection device configured to detect light of the first and the second wavelength. A light absorbing element is arranged in a central opening between the first and second opening and configured to absorb light of the first and the second wavelength.

Description

[0001] OPTOELECTRONIC ARRANGEMENT AND METHOD FOR OPERATING AN OPTOELECTRONIC ARRANGEMENT

[0002] The present application claims priority from German application DE 10 2023 133 601 . 0 dated November 30 , 2023 , the disclosure of which is incorporated in its entirety herein by reference . The present invention concerns an optoelectronic arrangement and a wearable device having such arrangement . The invention also refers to a method for operating an optoelectronic arrangement .

[0003] BACKGROUND

[0004] Wearables , like smart watches or phones , but also suitable clothing may comprise additional functionality that provide vital sign monitoring , generally referred to as VSM . Typical VSM application include , but are not limited to heart rate measurement , blood pressure measurement , oxygen saturation measurement and glucose measurements .

[0005] Such measurements are often based on optical data acquisition, whereas a defined amount of light is emitted onto the subj ect ' s s kin and the reflected or transmitted light is detected and evaluated . Consequently, an important quality factor is the signal-to-noise ratio of such measurement , although it has been found by the inventor that the noise itself may include relevant and useful information in itself . Still , noise from ambient light should be reduced to a large degree and the area of interaction between the emitted light and the skin tissue optimized to obtain good and repeatable results .

[0006] A typical application in this regard is based on Photoplethysmography ( PPG ) measurements , which obtains the signal strength over time and particularly over a plurality of heart beats . The heartbeat can be seen in light reflected from blood vessels , as the different pressure causes an AC signal in the obtained reflected portion of light with a frequency corresponding to heartbeat . The relative amplitude of such signal , i . e . the difference between the lowest amplitude and the highest amplitude in comparison with the DC portion of the overall signal , referred to as perfusion index or PI can provide information for many of the above- mentioned VSM applications . However, it has been observed by the inventor that the sensitivity of the Photoplethysmography measurement depends on various parameters , some of them based on the handling of the measurement device by a user and others based on the set-up of the sensor devices and the data acquisition .

[0007] It is therefore an obj ect of the present application to provide for an optical front-end that has an improved sensitivity of Photoplethysmography ( PPG) measurements and reduces the influence of various parameters .

[0008] SUMMARY OF THE INVENTION

[0009] This and other obj ects are addressed by the subj ect matter of the independent claims . Features and further aspects of the proposed principles are outlined in the dependent claims .

[0010] The inventors observed various aspects when using an optical front end to perform optical measurements , to be used in vital sign monitoring applications . For once , it has been found that the actual contact surface containing the emitter and detector should be as small as possible in order to improve the overall signal quality . More particularly it has been found that if the contact pressure is too small , the so-called perfusion index ( PI ) , which is the ratio of the signal constituents modulated by the heartbeat and the average signal level , i . e . , AC / DC , is small- or at least not stable and / or not well established . The magnitude of the PI is the measure of sensitivity, and it is desirable to achieve the highest possible sensitivity . This can be achieved by reducing the contact surface based on a given pressure of the contact surface onto a sample surface .

[0011] In case of a wearable , such contact pressure can be exerted by a strap . It has been observed that for certain pressures , there is a maximum in the observable perfusion index, with the PI signal increasing with increasing pressure and then reducing again if even more pressure is exerted . As a strap length can usually be varied, an optimum position of the strap is available , and the pressure caused by it can be adj usted . It has been found that an improvement by a factor of 2 . 5 to 4 depending on the used wavelength can be achieved .

[0012] It has also been observed that the proposed structural changes relieve the requirements on the necessary force to obtain good results and hence , a more comfortable strap force range of the strap is possible .

[0013] In addition, the structural changes also take the distance between the sensor and the emitter into account , as the signal strength of the PI is also a function of said distance . Usually, crosstalk, that is light portion not having interacted with the sample , is a large issue . The inventor proposes reducing the cross talk using a dedicated light absorbing element between the sensor and the corresponding emitter . Suppression of the crosstalk by such element as proposed directly reduces the DC value of the signal level and hence raises the AC / DC ratio and thus the PI .

[0014] Finally, it has been found that emitted light may be reflected directly into or close to the emitter . Such light is usually lost . However, by light recycling measures , the forward emission towards the probe sample is increased again and the signal level ( DC ) increased .

[0015] In some aspects , the inventor proposes an optoelectronic arrangement , comprising a housing with a bottom contact surface , said bottom contact surface having a first region and a second region, the first region surrounding the second region . The second region is elevated with respect to the first region . Hence , the bottom contact surface comprises a protruding area, said area forming the second region .

[0016] The protruding area , that is the second region, has a smaller area compared to the bottom contact surface , which causes a higher local contact pressure when the bottom contact is pressed against a sample probe , particular if the sample probe comprises a flexible or yielding surface upon exerting pressure .

[0017] The second region now comprises a plurality of openings , wherein three openings of the plurality of openings are arranged in a first row . Each of the openings also comprise an at least partially transparent cover . A partially transparent cover in this regard shall be understood as a cover that has a very high transmission in certain portions of the visible , UV or infrared spectrum, but may outside those portions optionally act as a filter . Typical transparent covers include SI02 , Sapphire or other glasses . They are usually resistant to scratches or dirt and other substances to ensure a high transmission over a long time .

[0018] In this regard, each of the at least three openings can be flush with a surface of the second region . However it is also possible that they are either recessed with regard to the surface of the second region or protrude the second region . Combinations are also possible . For example the opening with the light emitting device underneath may protrude , while the openings with the light detection devices may be recessed or vice versa . Each opening or some of those may comprise lenses , while other openings may be flush .

[0019] A first optoelectronic device arranged in a first of the three openings . The optoelectronic device comprises a first optoelectronic component configured to emit light of a first wavelength, in particular red light . The optoelectronic device also comprises a second optoelectronic component configured to emit light of a second wavelength, in particular infrared light .

[0020] The optoelectronic arrangement further comprises a first light detection device , in particular a photodetector, arranged in a second of the three openings . In accordance with the proposed principle , a distance of the first optoelectronic component to the first light detection device is substantially equal to a distance of the second optoelectronic component to the first light detection device . In other words , the first and second optoelectronic components are substantially spaced equally apart from the first light detection device . The first light detection device is configured to detect light of the first and the second wavelength . It has now been observed that for the given second region protruding above the surrounding first region, there is a certain pressure or force range being exerted onto the probe sample to obtain good results for optical measurements and in particular oxygen saturation measurements , SPO2 measurement also referred to as ratio of ratios . More particularly, for area sizes in the range of 74 mm2to appr . 250 mm2of the second protruding region a force onto the surface of appr . 130 g to about 450 g , resulting in a corresponding pressure onto the probe sample .

[0021] In some aspects , the proposed optical arrangement comprises a strap or bracelet that can be attached to the probe to be sampled and is configured to exert a force in the range of 1 , 25N to 4 , 5N and in particular between 1 , 75 N and 4 N and in particular between 2 N and 3 . 5 N . Those forces may be of particular use if the emitted light is in the red and infrared portion of the spectrum.

[0022] In some further aspects , the strap and the optical arrangement is configured to be wrapped around a forearm or wrist of a user , such that the plurality of openings arranged in the first row are substantially parallel to the arm of the user . In other aspects , the optical arrangement with the strap is configured such that the optical path when worn by a user lies substantially parallel to the forearm of the user and not perpendicular to it . It has been observed that PI measurements and the ratio of ratios are slightly stronger in the parallel direction, that is parallel to the forearm. Hence it may be generally suitable in some aspects to arrange the first row parallel to the forearm in case of wearables .

[0023] More generally speaking it is proposed in some aspects that the optical arrangement is configured to be arranged onto a user' s s kin such that the first row lies substantial parallel to the main direction of the blood vessels .

[0024] Further in accordance with the proposed principle of the above- mentioned arrangement , a light absorbing element is arranged in a central opening of the three openings between the first and second opening, said light absorbing device is configured to absorb light of the first and the second wavelength .

[0025] The proposed optical arrangement implements various improvements based on the various observations . As a result , the overall Perfusion index and other optical measurements are significantly improved, which in turn allow reducing the overall power consumption . Particularly in wearables with its limited power resource , the reduced consumption results in a longer cycles between recharging .

[0026] In some aspects , the optical arrangement further comprises a fourth and a fifth opening arranged in a second row intersecting the first row . Such intersection may be perpendicular . Such arrangement of the openings may result in the shape of a cross or a T . In some aspects , one of the three openings of the first row, in particular the central opening, is arranged between the fourth and fifth opening . In some other aspects , the central opening is arranged opening at an intersection of the cross or T . In both cases , a light absorbing element is arranged in the central opening .

[0027] In some aspects , the light absorbing element may be a photodiode , or more general the first light detection device .

[0028] In this regard a second optoelectronic device can be arranged in the fourth opening in some aspects , said optoelectronic device comprising a first optoelectronic component configured to emit light of the first wavelength, in particular red light and a fourth optoelectronic component configured to emit light of the second wavelength, in particular infrared light . Likewise , a second light detection device , in particular a photodetector may be arranged in the fifth opening , wherein a distance of the first optoelectronic component to the second light detection device is substantially equal to a distance of the fourth optoelectronic component to the second light detection device , the second light detection device configured to detect light of the first and the second wavelength . Depending on the VSM application, different wavelengths for optical measurement may be required or at least suitable . For example , for PPG measurement indicating the heart rate and used to determine the oxygen saturation, one can use red and infrared light and the resulting ratio of perfusion indices , which is also called the ratio of ratios , i . e . , (AC / DC )red / (AC / DC )IR. This is due to the fact that scattering and absorption of light in tissue is wavelength dependent . Different wavelengths also have different penetration depth into the probe sample . Hence , it is proposed in some aspects that the first and / or second optoelectronic device comprises a third optoelectronic component configured to emit light of a third wavelength, in particular green light .

[0029] However , for light in the green portion of the spectrum it has been observed that the distance between emitter and detector to obtain a high signal-to-noise ratio is different from red or infrared light and in particularly smaller . In some aspects , a distance of the third optoelectronic component to the first light detection device is smaller than a distance of the first and second component to the first light detection device . Likewise , a distance of the third optoelectronic component to the second light detection device is smaller than a distance of the first and second component of the second optoelectronic device to the second light detection device .

[0030] In an alternative embodiment , the first and / or second optoelectronic device may comprise a third optoelectronic component configured to emit light of a third wavelength, in particular green light . Centers of the respective first , second and third optoelectronic components form edges of a virtual triangle with the center of the third optoelectronic component being closest to the respective central opening .

[0031] The light absorbing element arranged in the central opening may be a third light detection device configured to detect light of the first , second and third wavelength . It has been found that a photodetector suitable to detect light of the third wavelength and therefore also of the first and second wavelength act as a light absorber . By arranging said light absorbing element between an optoelectronic device and the light detection device , it has been observed that the crosstalk is significantly reduced and the signal-to-noise ratio enhanced . The reason behind this fact lies most likely in light being reflected close to the sample surface , which then reaches the location between an optoelectronic device and the light detection device . The light absorbing element absorbs such light , thereby preventing crosstalk therefrom.

[0032] The light absorbing element can be a photodetector, which can also be used to detect green light . Hence , the photodetector at the central position can -depending on the desired optical measurement- act as detector or as light absorber . In the latter case , the photodetector may simply be switched off .

[0033] Some aspects concern the arrangement of the optoelectronic components of the optoelectronic device . In some aspects , the first and / or second optoelectronic device comprise a package with a first recess , in which the first and second optoelectronic components are arranged . It is also possible in some aspects that each of the first and second optoelectronic components are arranged in separate recesses of the optoelectronic device . To further increase the light emission therefrom, the recess or recesses may comprise beveled sidewalls . To further improve so-called light recycling ( i . e . light that is reflected for the probe sample back into the recess , the sidewalls may comprise a material with a high reflectivity for light of the first and / or second wavelength . Examples of such material contain TI02 particles .

[0034] In some aspects , in which a third optoelectronic component is present in the optoelectronic device , the package may comprise a second recess , in which the third optoelectronic component is arranged . As for the other recesses , said second recess comprising -in particular beveled- sidewalls having a high reflectivity for light of the third wavelength . It may also have a low reflectivity for light of the first and second wavelength, hence also acting as a light absorbing element for light of such wavelengths . Some aspects concern measures for improving the signal-to-noise ratio . For example , the first and / or second light detection device can comprise a color filter configured to block light in a portion of the spectrum different from the first and second wavelength . Such color filter can also be arranged in or on the transparent cover . In some further aspects , the at least partially transparent cover over the first and / or second light detecting device comprises a color filter or color filtering properties configured to block light in a portion of the spectrum different from the first and second wavelength .

[0035] In some other aspects , the first region of the bottom contact surface comprises a light absorbing coating , in particular a black coating . Alternatively or additionally, the first region of the bottom contact surface can comprise a light absorbing material , in particular a blackened material . A suitable material which is highly absorbent for light of in the red and infrared portion of the spectrum is PEEK, polyetheretherketone . Such material is a high-performance engineering plastic with outstanding resistance to harsh chemicals , and excellent mechanical strength and dimensional stability, which makes it suitable for the second region not to be damaged upon fall , scratches and the like .

[0036] In another aspect , the material of the second and optionally also the first region comprises a lower thermal conductivity, in particular a heat conduction efficient lower than those of metals . It has been observed that a high heat flow properties result in a degradation of the PI signal quality . This may be due to the fact the heat of the s kin is transported by the material away from the region . As a result , the diameter of blood vessels is shrinking and thus reducing the signal . Consequently, the second region should not contain metal , but rather a plastic .

[0037] Some aspects concern the shape and form of the second region . As stated previously, the second region elevated above the first region should be small to exert a certain pressure on the contact surface . Hence , it can be suitable in some instances , if the shape of the second region follows the arrangement of the plurality of openings in the second region. For example, if the arrangement of the plurality of openings in the second region resembles a cross or a T, then the second region may also have the form of a stylized cross or a T in top view. The edges can be rounded. Some other possible forms are a circle or an oval .

[0038] Some further aspect concern fastening means, which can be attached to the optical arrangement. The fastening means are configured to exert an adjustable pressure of the bottom contact surface onto a sample surface, the sample surface comprising in particular skin tissue. This provides a possibility to adjust the pressure, thereby shifting the signal-to-noise ratio to its respective optimum.

[0039] In another aspect, the elevation of the second region with respect to the first region is in the range between 0.5 mm to 3.5 mm and in particular between 1.0 mm to 2.0 mm and in particular less than 1.75 mm. It has been observed that an elevation within such ranges provides good results. In some other aspects, the separation between a center of the first optoelectronic device, in particular a common center of the first and second optoelectronic components of the first optoelectronic device to the first light detecting device is in the range of 5 mm to 15 mm and in particular between 7.5 mm and 12.5 mm and in particular between 7.5 mm and 10 mm and in particular between 8 .0 mm and 9. 0 mm. Likewise, a distance between a center of the second optoelectronic device, in particular a common center of the first and second optoelectronic components of the second optoelectronic device to the second light detecting device is in the range of 5 mm to 15 mm and in particular between 7.5 mm and 12.5 mm and in particular between 7.5 mm and 10 mm and in particular between 8.0 mm and 9.0 mm.

[0040] The above range reflects the observation that a distance smaller than 5 mm results in a lower signal of the perfusion index and a lower sensitivity. The above ranges however offer a good trade-off between the overall size of the device and the signal quality for optical measurements .

[0041] In some further aspects, a distance between a center of the third optoelectronic components to the third light detecting device is in the range between 2 . 5 mm and 5 mm and in particular between 3 mm and 4 mm . Hence , the distance between the emitter for green light and the detector is significantly smaller and slightly less than half the previous distance .

[0042] In some aspects , the first and second optoelectronic devices are substantially identical in construction . They may comprise the similar emitters and / or optoelectronic components of the same type . In some aspects , the first and second light detection devices are identical in construction . Hence , first and second light detection devices may comprise photodetector of the same or similar type . In some aspect , wherein the first , second and third light detection devices are substantially identical in construction . Consequently, three photodetectors can be used in some aspects , which are of the same or similar type and particularly configured to detect light in ranges of the light spectrum covered by the first , second and third wavelength .

[0043] The proposed principle offers a good compromise between competing requirements . For a high sensitivity it would be best to separate optoelectronic components and the photodetector "infinitely" far away from each other, resulting in low DC signal and poor SNR . At the same time to achieve high contact pressure for low strap forces , we have to keep the contact area small , which means the optoelectronic components and the photodiode should be closer together . For low supply currents for the optoelectronic components but high DC signal counts , which are required for best SNR, is tis necessary to bring the optoelectronic components as close as possible to the photodetector .

[0044] The proposed principles implements a small contact area with large enough distances between the optoelectronic components and the light detection devices for red and IR wavelengths . The components and light detection devices are placed on diametrically opposed positions around a circle or another suitable shape . The diameter and area of shape is chosen such, that a relatively high sensitivity is obtained together with sufficient DC signal for red and IR wavelengths . The signal levels are further helped along by the light recycling properties of the proposed arrangement . Some further aspects concern a wearable device , in particular a watch . The wearable device comprises an optoelectronic arrangement in accordance with the proposed principle and a strap forming an adj ustable fastening means to exert a pressure of the bottom contact surface onto the s kin tissue . The housing of the optoelectronic arrangement can also correspond to a housing of the wearable as such, hence , the individual elements of the optoelectronic arrangement are arranged within the housing of the wearable .

[0045] The wearable also comprises an evaluation and control unit coupled to the first and / or second optoelectronic device , the first and / or second light detecting device and the light absorbing device . It is configured to operate those devices to obtain data and determine from said data at least one of heart rate , oxygen saturation and glucose concentration .

[0046] In some further aspects , the wearable may also comprise a pressure sensor and / or a temperature sensor . This enables to obtain the contact pressure during the measurement and subsequently calibrate the measurement or indicate the user to adj ust the fastening of the fastening means and strap , respectively . Similarly, a measurement by the temperature sensor is used to calibrate the subsequent optical measurement . In this regard, it is noted that in some instances , the optoelectronic arrangement as proposed above may comprise the pressure sensor and / or the temperature sensor . In some aspects , the pressure sensor is located on the second region in close vicinity to the at least three openings .

[0047] In some aspects , the housing ( or optoelectronic device in more general terms ) is implemented as a ring, earbud, watch or any other wearable , that may fit in some aspects into a user' s usual environment and can be carried continuously . Said ring, earbud, watch or any other wearable is in communicative connection with the evaluation unit or a mobile or any other device implementing the evaluation and control unit . The ring , earbud, watch or any other wearable may cover a larger portion of the user' s skin, e . g . wrap around the finger , clipped to the ear from both sides and the like . They may contain several emitters and detectors at various location, thus allowing not only to measure at one spot but at several at once or sequentially . As a result thereof , skin irregularity or other issue can be overcome and the overall measurement quality improved .

[0048] Apart from devices and handheld devices , other applications are possible . For example , the optoelectronic arrangement can be implemented in medical devices or laboratory equipment , e . g . for test and measurement purposes . Those devices again can be stationary or mobile . Some more aspects concern mobile displays in which the detectors are directly implemented . In such applications , the display LEDs e . g . for the red and green and even blue color can be used as emitter in accordance with the proposed principle .

[0049] A finger is placed directly on the display surface and then illuminated by the display for obtaining the first and / or second signal . Likewise , the proposed principle can be implemented in VR or AR glasses and devices .

[0050] Another application concerns safety issues , e . g . during certain labor- intensive work but also while driving a vehicle and the like . It is possible to implement such optoelectronic arrangements in accordance with the proposed principle in a car , e . g . on the steering wheel to obtain the perfusion index and from there the noise spectrum during driving . This enables for example to warn drivers of potential health threats while driving .

[0051] In some further aspect , a method for operating an optoelectronic arrangement in accordance with the proposed principle as proposed . The method comprises the step of providing an optoelectronic arrangement with a housing having a bottom contact surface , said bottom contact surface having a first region surrounding an elevated second region . The second region comprises a plurality of openings , wherein three openings of the plurality of openings are arranged in a first row; each of the openings comprising an at least partially transparent cover that is flush with a surface of the second region . The optoelectronic arrangement is fixed onto a user' s s kin to probe a human tissue , such that a defined contact pressure is exerted onto the user' s s kin by the second region of the bottom contact surface , with a smaller contact pressure being exerted onto the user' s s kin by the first region of the bottom contact surface . Light of a first wavelength and / or a second wavelength is then emitted from a first opening towards the user' s s kin to interact with the tissue thereof . Light being reflected into the second opening , located between the first and a third opening, is absorbed by a light absorbing element , thereby reducing any potential crosstalk . Light being reflected into the third opening is detected and evaluated to obtain a perfusion index or any other value related to the optical measurement .

[0052] In some aspects , the light of the first and second wavelength is emitted using a time division scheme . Furthermore , in some aspects , light of a third wavelength, for example green light , can be emitted from a first opening towards the user' s skin to interact with the tissue thereof . Light being reflected into the second opening, located between the first and a third opening, is detected and evaluated to obtain a perfusion index or any other value related to the optical measurement . Hence , light reaching the second opening can either be absorbed, reducing the cross talk or detected and processed further .

[0053] SHORT DESCRIPTION OF THE DRAWINGS Further aspects and embodiments in accordance with the proposed principle will become apparent in relation to the various embodiments and examples described in detail in connection with the accompanying drawings , in which

[0054] Figure 1 shows a perspective view of an embodiment of an optoelectronic arrangement in a smartwatch in accordance with some aspects of the proposed principles ;

[0055] Figure 2 illustrates a top view of the embodiment of an optoelectronic arrangement in a smartwatch in accordance with some aspects of the proposed principles ; Figure 3 shows a more detailed view of the second region of an optoelectronic arrangement in accordance with some aspects of the proposed principle ;

[0056] Figure 4 illustrates a schematic top view of an optoelectronic component used in an optoelectronic arrangement in accordance with some aspects of the proposed principle ;

[0057] Figure 5 shows side views of an optoelectronic component used in an optoelectronic arrangement in accordance with some aspects of the proposed principle ;

[0058] Figures 6A and 6B illustrate different measurement representing the relationship between contact pressure and the obtained perfusion index of an embodiment in accordance with some aspects of the proposed principle in comparison with a predecessor device , which exhibits a lower perfusion index while requiring a larger strap force ;

[0059] Figures 7A and 7B show exemplary measurements illustrating the relationship of the DC and PI in dependence to the distance at a given skin position in accordance with some aspects of the proposed principle ;

[0060] Figure 8 shows a diagram illustrating the signal index over distance in accordance with some aspects of the proposed principle ;

[0061] Figure 9 shows a diagram illustrating the perfusion index over distance for green, red and IR light in accordance with some aspects of the proposed principle ;

[0062] Figure 10 shows a more detailed view of the diagram of Figure 9 for red and IR light in accordance with some aspects of the proposed principle ;

[0063] Figure 11A and 11B illustrate a diagram showing the perfusion index vs the contact force for a signal substantially parallel to the main direction of the blood vessels for red and infrared light ; Figure 12 shows a diagram of the ratio of ratios , relevant for SPO2 applications , indicating the preferred range of force being applied to the probe surface for an embodiment of an optoelectronic arrangement in accordance with some aspects of the proposed principles .

[0064] DETAILED DESCRIPTION

[0065] The following embodiments and examples disclose various aspects and their combinations according to the proposed principle . The embodiments and examples are not always to scale . Likewise , different elements can be displayed enlarged or reduced in size to emphasize individual aspects . It goes without saying that the individual aspects of the embodiments and examples shown in the figures can be combined with each other without further ado , without this contradicting the principle according to the invention . Some aspects show a regular structure or form . It should be noted that in practice slight differences and deviations from the ideal form may occur without , however , contradicting the inventive idea .

[0066] In addition, the individual figures and aspects are not necessarily shown in the correct size , nor do the proportions between individual elements have to be essentially correct . Some aspects are highlighted by showing them enlarged . However , terms such as "above" , "over" , "below" , "under" "larger" , "smaller" and the like are correctly represented with regard to the elements in the figures . So it is possible to deduce such relations between the elements based on the figures .

[0067] Figure 1 illustrates a perspective view (up-side down ) of an optoelectronic arrangement in accordance with some aspects of the proposed principle . The arrangement is integrated in a smartwatch 1 as a wearable device , with the strap being removed from its fastening location 41 for better illustration . Still , the watch 1 is fastened around a user' s wrist , with the strap being adj ustable such that the watch is fastened with the strap so that it fits tight and snugly or loosely around the wrist . The watch comprises a housing that corresponds to the housing 10 of the optoelectronic arrangement . The bottom contact surface 11 is then pressed by the strap onto a user' s wrist or more generally skin surface . By adj usting the strap , the overall contact pressure can be adj usted and varied . The bottom contact surface 11 comprises a first region 12 surrounding a centrally located circular second region 13 . As illustrated, the second central region 13 is elevated and protrudes the first region 2 of the bottom contact surface . The height between the two regions lies in the range between 1 . 0 mm and 1 . 5 mm and is in the present embodiment around 1 . 2 mm .

[0068] The surface of the first and second region may usually be blackened or mad of black or dark material . Its color is changed in the present Figure 1 to improve visibility of the various elements . Further , the surface material and, more generally, the material of both regions is made of a material with a low heat conduction coefficient and in particular a lower heat conduction coefficient than those of metals . Typical material suitable with low heat conduction coefficient include glass , sapphire and plastics . The latter can be doped with a black material , which further provides a high absorption of light of various wavelengths , thereby reducing the crosstalk and improving the measurements , as explained below in greater detail . One material suitable to form the first and / or second region is PEEK or polyetheretherketone . The material has a low heat conduction coefficient but is also highly stable with excellent mechanical strength and dimensional stability .

[0069] The remaining portion of the housing 10 may comprise metal or any other suitable material . The housing 10 also contains power supply, evaluation and control circuitry . In some instance , the top side (here on the bottom and not visible ) may also comprise a display to visualize the measurement results . Buttons 42 are arranged on the side to select certain functionality of the wearable or adj ust parameters thereof .

[0070] The second region 13 comprises five opening 20 to 24 , which are located forming a cross-like structure with a central opening 22 intersecting two rows of opening . The first row comprising openings 20 , 21 and 22 are substantially parallel to the fastening means ( not shown herein) , while the second row comprising openings 23 , 24 and 22 is arranged perpendicular to it . Each opening compriss a substantial quadratic shape with sightly rounded edges . As illustrated, the overall second region is only slightly larger in its diameter than the length of each row . The openings fit into the second region, but the overall space from the outer edge of an opening to the edge of the second region is small and only as large as the mechanical stability requires . As a result , the second region is as small as possible to increase the pressure exerted by the fastening means onto the user' s skin .

[0071] Each opening comprises a cover that is flush with the surface of the second region and transparent to light of the red and infrared wavelength, as explained further below . Typical materials for the cover include all kinds of glass , but also transparent plastics , as long as they are resistant to scratches and do not age under the various light spectra .

[0072] Each opening is arranged above a common carrier , on which a plurality of various devices is arranged . Figure 2 shows the top view of the bottom contact surface 11 with the devices being present . Two opening , namely opening 20 of the first row of openings and opening 23 of the second row of openings , each comprise a light emitting device 50 and 50 ' , respectively . The light emitting devices are of the same type and configured in the present example to emit light within the red, infrared and green spectrum. More particular , the first row, parallel to the fastening means 43 attached to element 41 comprises opening 20 with light emitting device 50 and a second opening 21 opposite the first opening at the other end of second region 13 . The second opening 21 comprises a light detecting device implemented as a photodiode 60 .

[0073] The second row perpendicular to the first row and thus perpendicular to the fastening means 43 comprise a third opening 23 at the left edge of the second region 13 with the light emitting device 50 ' placed therein and a fourth opening on the other end of the second region 13 with a light detecting device in form of a photodiode 60 ' . Photodiodes 60 and 60 ' are both from the same type and configured in the present example to detect light within the red, infrared and green spectrum.

[0074] Furthermore , central opening 22 , the central opening for both rows also contain a photodiode 61 as a light absorbing element , designed to absorb light of the red, infrared and green spectrum. Depending on its operation, the photodiode 61 acts as light absorbing element or as light detecting element , the latter in case the devices 50 or 50 emit green light . Photodiode 61 is of the same type as photodiode 60 and 60 ' , respectively . However, it might be instructive to point out that a centrally located light emitting device , which is a common design choice in current products for vital sign monitoring , does not satisfy the same function . Due to the larger bandgap of green light emitting devices usually used here , red and IR light , i . e . , light with longer wavelength than green light or, equivalently, light with a lower photon energy than the bandgap of the green light emitting device , cannot be ( substantially) absorbed and is thus reflected . Therefore , a common green light emitting device , referred to as green LED cannot be a preferred absorber for red and IR light .

[0075] Similarly, and as a differentiating aspect , the centrally located light detection device cannot feature a filter that reflects longer wavelengths , as is customarily done in some products to suppress ambient light at red and IR wavelengths . The lighting device in accordance with the proposed principle can, however, be used without loss of functionality . Further, with a reverse bias , the centrally located light detection device can be operated in a mode that maximally absorbs the incoming light by effectively reducing the probability for generated electron-hole pairs to recombine .

[0076] In the present embodiment , the first and second rows are positions to form a cross . However, it is also possible to select opening 21 with element 60 as central opening . In such embodiment , the shape of the two rows would resemble a "T" , with the opening 21 being the central opening for the row having openings 23 , 24 and 21 . While this embodiment may be useful in some aspects , it does not offer the symmetrical structure as the embodiment presented in Figures 1 and 2 . The embodiment also contains an optional pressure sensor and an optional temperature sensor, both are not shown in these embodiments . In operation of the arrangement , one can emit light from one of devices 50 in openings 23 and 20 , respectively . When the emitters 50 emit red or infrared light , the photodiode 61 in the central opening is switched off or in reverse mode , thereby acting as a light absorbing element . Hence , light that is reflected from the user' s skin back to the second opening is absorbed therein and will not reach any of the other two openings 21 or 24 . If green light is emitted, the photodiode 61 in central opening 22 is activated to detect light interacting the with user' s tissue and reflected back to the central opening . Consequently, depending on the operation, the photodiode 61 in central opening 22 acts as light absorbing device to reduce the overall cross talk or as light detecting device .

[0077] The perfusion index is often used as a measure of quality for optical measurement and as the basis for various vital sign monitoring applications . Those may include heart rate but also oxygen saturation and SPO2 measurement and glucose measurements . The so-called perfusion index ( PI ) is the ratio of the signal constituents modulated by the heartbeat and the average signal or DC level . It is often abbreviated as the ration AC / DC . As it can be seen, the DC portion includes noise and unwanted signal portions like crosstalk and noise , while the AC portion includes the useful signal portions . Consequently, one aims to reduce such DC portions that do not contain any useful information . On the other hand, the magnitude of the PI is a measure of sensitivity, and it is desirable to achieve the highest possible sensitivity .

[0078] It has been now observed that the contact pressure of an optical front end and the optical arrangement in accordance with the proposed principle with the human s kin and the wrist in case of a smartwatch is central to the performance of optical vital sign monitoring applications . If the contact pressure is too small, the perfusion index (PI) is either small- or at least not sufficiently stable. In some cases, it can even can not be established in a predictable and repeatable way.

[0079] Figure 6A and 6B illustrate the sensitivity for two different optical arrangement configurations VI and V4 for different strap tightness. The x-axis illustrates strap position, i.e. hole positions of the strap and wrist band. Those do not directly correspond to a contact pressure, as they are dependent on the wrist diameter. However, the contact pressure pcis a function of the strap hole position. The first configuration VI is a more conventional design, in which the bottom contact surface is completely flush with circular openings, and does not have two regions with different elevation. The configuration V4 corresponds to the optical arrangement in accordance with the proposed principle .

[0080] Figure 6A illustrates the measurement for light in the infrared portion of the spectrum, Figure 6B for light in the red portion of the spectrum. It is observed that (1) the achievable PI is 2.5 to 3 times higher for red and IR wavelengths . The following table provides the maximum values for various ratios .

[0081] V4 PI RED is at least 2.09x and at most 3x greater than VI PI RED.V4 PI IR is at least 1.63x and at most 2.56x greater than VI PI IR.

[0082] The second observation is that the peak PI values generated by the proposed configuration occur with a lower contact pressure, i.e. at lower strap tightness by two holes. In addition, it seems that the contact pressure has an optimum, that is, lower contact pressures but also higher contact pressures result in a drop of the PI. Also indicated in the same diagrams is the (subjective) wearing experience of the watch over the range of strap settings tested, and it is being observed that , the best PI for the previous configuration VI design occurs in an uncomfortable range , while the proposed configuration V4 design moves the required strap force into a (more ) comfortable range .

[0083] The reduction of strap force required is a consequence of the minimized cross-section ( area ) of the optical front end . The overall shrinkage of the second region to the overall bottom contact surface corresponds to a diameter reduction from about 28mm to appr . 12mm . This corresponds to ~20% of the original area . In addition, the second region of the bottom contact surface is raised above the plane of the backside of the watch, protruding by appr . 1 . 2mm. It is possible to further reduce the contact pressure required by increasing the protrusion, and vice versa .

[0084] At higher contact pressure for this configuration, i . e . strap holes 8 to 10 , the strap and the bottom contact surface will start to impede the pulsatile signal and shore up the blood flow through the extremity, which is not only very uncomfortable but also counterproductive : thus , it is desirable to enable operation of the optical arrangement with adj ustable fastening in a range of contact pressures / strap forces where the PI is maximized, and the fastening means are still comfortable to wear .

[0085] The influence of various pressures and its effects onto the perfuison index and particular the SPO2 application, referred to as ratio of ratio measurements are further illustrated in Figure 11 and 12 .

[0086] Figures 11A and 11B illustrate the perfusion index in response to various forces ( corresponding to the mass ) exerted onto the forearm and in particular onto the surface of the user skin . For this purpose the embodiment of Figure 1 is arranged onto the forearm. Then, a defined forces are exerted onto the housing pressing the wearable of Figure 1 with ca specific force ( corresponding to a mass of 100g , 200g and so forth) onto the user s kin . The perfusion index for red light and infrared light is measured for such different forces . Figure 11A illustrates the result for an arrangement , in which the optical path is substantially parallel to the main direction of the forearm and thus parallel to the main direction of the blood vessels below the skin . Figure 11B is the same measurement , but with the optical path substantially perpendicular to the main direction of the forearm and thus perpendicular to the main direction of the blood vessels below the skin .

[0087] Figure 12 shows the ratio of ratios , that is the ratio of the measured signals for the red and the infrared curve . Several observations can be obtained from the measurements .

[0088] 1 . The measurement has a certain dependency on the position of the forearm and wrist ( not shown in the measurements of Figure 11 and 12 ) , but it seems that areas with a higher density of blood vessels and thinner s kin provide a clearer and stronger signal .

[0089] 2 . The protruding area is pressed int the s kin first and then the first region . Too high forces apparently reduce the signal quality again . This is apparent from Figure 12 , whereas force and pressure in a certain range result in substantially constant values for the SPO2 measurement values . It seems that this pressure and force range is suitable . Strap and bracelets could be designed to exert a pressure and force of a given diameter in said range .

[0090] 3 . The overall diameter for the second area lies in the range ov 12 mm to about 14 mm and was precisely 13 . 7 mm in the embodiment , with a slightly smaller diameter of the optical surface that is primarily in contact with the s kin, i . e . without the rounding at the edge of plane 2 , is approx . 12 . 5mm.

[0091] 4 . The measurement direction provides different signal strength but not fundamental deviation . However, it seems advisable to orient the optical path to be substantially parallel to the blood vessels to increase the interaction and thus increase the overall perfusion index signal strength .

[0092] 5 . For green wavelengths , the dependence on the contact pressure seems to be less pronounced, not shown herein .

[0093] 6 . The broad range of pressure and force in which the ratio of ratios illustrated in Figure 12 is substantially constant offers a window of opportunity to implement flexible straps and bracelets that are configured to exert such force . It has been observed that the given forces are also still comfortable to wear by a user . It was shown that in conventional devices without a protruding section, a significant higher force was necessary to obtain good results , i . e . in the range of 650 g to 800 g . Moreover, the window for a SPO2 measurement ( ratio of ratios ) became smaller, about 100g and was in the range of 650g to 750g of force . This is usually too high and thus uncomfortable to wear for a user .

[0094] Another improvement is achieved by the configuration of the arrangement of light emitters and light detecting device as shown in Figure 1 and 2 as well as in more detail in Figure 3 . Figure 3 illustrates a PCB with the various devices attached to it , which is arranged directly below a second region such that the various devices are located beneath the openings in the second region . The PCB 130 is circumferential with radius LI . In some aspects , as shown for example in Figures 1 or 2 , the circumference LI can correspond to the outer edge of the second region . In the embodiment of Figure 3 , the second region follows the dashed line resembling a cross like structure , thereby further reducing the elevated area further .

[0095] The dashed lines also represent the respective openings . As shown, photodiodes 60 , 60 ' and 61 each of the same type are located on the PCB and carrier 130 below openings 21 , 24 and 22 , respectively . Each photodiode comprises an active detecting area occupying the large amount of the overall opening , i . e . 80% to 95% of the opening, to collect as much light as possible . Bonding wires are connecting the photodiode to contact areas at an edge of each opening , although other configuration for mechanical and electrical connection can be implemented .

[0096] The light emitting devices 50 and 50 ' below openings 20 and 23 are implemented as a so called 3-in-l configuration . Such configuration is explained in greater detail in Figure 4 further below . The distance DI from one light emitting device e . g . 50 ' to the opposite photo diode , e . g . 60 ' for detecting the red and infrared light portion is about 8 . 5 mm measured from the respective centers as shown in the Figure 3 . The distance between the component configured to emit green light of the light emitting devices 50 and 50 ' to the central photodetector is less in the range of about 3 mm to 4 mm and in particular about 3.5 mm. The smaller distance is due to a higher absorption at large distances for the green light.

[0097] In this regard, Figures 7A and 7B shows the relationship between the DC single portion and distance between the emitter and the respective photodiodes, as well as the perfusion index vs the distance. Figure 7A shows the change of the DC portion of the detected signal versus the distance. The points at appr 8.5 mm distance correspond to the configuration wherein the optoelectronic components 500 and 501 for red and infrared light in the embodiment of Figure 3 are spaced part from the center of the photodiode by 8.5 mm (distance DI) , i.e. the distance between elements 50' and 60' or between elements 50 and 60. Likewise, the second points at appr 4.5 mm correspond to the distance between the component of red and infrared light of devices 50 and 50' to the central photodiode 61.

[0098] The right point for the curve marked as GREEN correspond to a distance of 7.5 mm between the components 502 for green light in devices 50 and 50' to the outermost photodiode 60 and 60' . The left point at distance 3.5 mm corresponds to distance D2 shown in Figure 3. The measurements indicate that the central photodiode 61 generates 5.5 times higher signal for the red and infrared portion than the photodiodes 60 and 60' on the outer edges. However, the PI of those diodes 60 and 60' as given in Figure 7B are about 3 times higher, which provides a better result for light in the red and infrared spectrum. This figure stipulates to use a larger distance for optical measurements in the red and infrared portion of the spectrum.

[0099] In contrast, thereto, the central photodiode 61 generates a 36 times higher signal for the green portion at the smaller distance, while the PI could be increased only by 2x with the diode 61 on the outer side.

[0100] As a result, the red and infrared diodes generate 5.5 times more photo current at the central photo diode 61 in comparison to the outer photodiode 60, 60' , but the perfusion index is larger by a factor of 3, which is more desirable. If a reflector is placed in place of the central photodiode 61 , e . g . in the form of a lighting diode with a band gap lager than the energy for red or infrared light , an artificial secondary light source would be created at the central position, which would contribute to the PPG signal due to its reflection of signal portions reflected from the tissue into the central opening . This is undesirable because the actual or effective distance would then no longer be clearly defined and would, for example , be more dependent on the skin type than before . Further, -and also quite relevant- , the perfusion index would be reduced due to additional crosstalk and due to the general distance dependence of the sensitivity .

[0101] At green but also blue or UV wavelengths , the central photodiode 61 generates a 36 times higher signal than the one of opposite photodiodes 60 and 60 ' ; in contrast , the PI would improve by a factor of 2 times with the greater distance .

[0102] It is the general preference that the modulation depth and the perfusion index is larger than the noise level . In an ideal world, this noise is mainly shot noise . Since shot noise scales with the square root of the signal , a 36 times greater signal means that the SNR has improved by a factor of six compared to the outer photodiodes 60 and 60 ' ; conversely, it is possible to improve the perfusion index by only a factor of two ( for green light ) when using the outer photodiodes 60 and 06' . Therefore , for green light , it is more desirable to use the central diode 61 .

[0103] For red and IR light , with a gain of only 5 . 5x in signal level , the signal-to-noise ratio may be improved by ~2 . 3x with the central photodiode 61 , but the loss in sensitivity is 3x , which makes it more desirable to use the outer photodiodes 60 and 61 for red and IR . This principle seems legit for s kin type 2 but should be reasonably applicable also to some other skin types .

[0104] Apart from higher supply currents , there are also considerations of heat development , possible skin and eye strain, and perceptions by the user and by-passers . Another aspect is based on light recycling techniques employed in some aspects with the proposed principle . Light that is reflected from the human skin and tissue directly back into the recess of the emitter device is usually lost . Such light may contribute to a significant portion . Hence , a larger supply current is to be used to obtain the same signal strength . Figures 4 and 5 illustrate several aspects .

[0105] Figure 4 shows a more detailed view with the respective dimension for a lighting device used in the proposed optical arrangement in a 3-in- 1 configuration . The light emitting device 50 comprises two recesses 55 and 55 ' which are of slightly different size and shape . They are centered on an axis and oriented toward the opposing photodiodes ( not shown herein) when placed on the PCB 130 . Two lighting components 500 and 501 are placed in the first recess 55 , whereas the first component 500 is configured to emit red light , while the second component 501 is configured to emit infrared light . Both components are arranged in a symmetrical manner such that their distance to the light detecting device as explained previously are the same . The dimensions given in the embodiment of Figure 4 are based on design and may vary depending on the implementation . The second recess 55 ' contains another light emitting component 502 configured to emit green light . The recess 55 and 55 ' are separated by a barrier to avoid crosstalk from green light into the red light or infrared light .

[0106] The sidewalls can be made of different material and surfaces to improve reflection . Figure 5 shows two different embodiments . In the left configuration, the sidewalls 55 are straight and not beveled . Further , the bottom surface is made of a non-reflecting material as the sidewalls . Consequently, only a portion of light , e . g . appr 45% is inj ected deeper into the probe sample and the human skin, while another portion being reflected into the recess is absorbed and therefore lost for any interaction . The maj ority of light is reflected at the various interfaces , e . g . between the covers of the light emitting device and air or the human tissue .

[0107] In contrast thereto , the right embodiment comprises beveled sidewalls

[0108] 55 with the surface 550 covered by a highly reflective material . Such material may comprise TiO2 , aluminum, silver or another suitable highly reflective material . As a result , light being reflected from the interface to air or to the human s kin surface without interacting with human tissue is reflected into the recess and subsequently recycled . It is reflected again in the recess by the reflective material and can therefore again enter the probe sample and interact with the sample .

[0109] It has been shown that an improvement of the signal level per mA of light component current and mm2 of photodiode active area occurs from 1747 units to 2818 units for green light , from 676 units to 1614 units for red light , and from 1459 units to units 2314 in infrared light . The gain in the signal with all their parameters held equal is due to the light recycling technology that is introduced with the light emitting devices of embodiment 4 with beveled and reflective sidewalls . Effectively, light recycling measures increase the signal strength at least by 50 % at the same light emitting current for all wavelengths .

[0110] Figures 8 , 9 and 10 illustrate several results of measurements making use of the distance and the light recycling . Figure 8 shows the signal dependence on distance between the light source and detector . Figure 9 is the modulation depth or perfusion index, the ratio of AC / DC , which is also called perfusion index ( PI ) .

[0111] While the signal decreases approximately exponentially with distance for all wavelengths , it is apparent from Figure 8 that the decay is faster for green light than for red and IR by about an order of magnitude , e . g . , when looking at separation 5 mm. The fast decay of the green DC signal is due to the absorption and scattering properties of human tissue . It can be compensated, in principle , by higher LED currents to increase the output of the source . However, in practice it may be prohibitive to apply large enough currents , either because of driver capacity- and / or battery life-time limitations , or because the LED is going into thermal roll-over .

[0112] Conversely, when we look at the graphic on the right side , we see that the perfusion index for green light is about lOx larger than the perfusion index for red and IR . While overall , the PI increases with distance for all wavelengths , the PI for green light at the distance of about 3 to 4 mm provides quite enough sensitivity without sacrificing too much overall signal strength as shown in Figure 8 . Hence , it is possible to decrease the current consumption for green light with a smaller distance .

[0113] For red and IR light due to the generally low perfusion index, it is desired to establish a larger separation, e . g . , 7 to 10 mm . Even at this distance , relatively strong signals are anticipated due to the low attenuation . However, it is beneficial to increase the PI , here by 50-100% compared, e . g . , to the distance of 3 mm.

[0114] In addition, due to the light-recycling characteristics , when red or IR is turned on, basically exactly the same- , small area is illuminated on the skin, which results in a defined distance from the source to the detector and virtually identical optical paths , in the sense of sampling the same points on the tissue surface . This is quite useful in certain VSM application for example for SPO2 applications . Similar considerations apply for the green wavelength, i . e . , the illuminated area on the tissue is kept small , resulting in properly defined distances between source and detector ( s ) .

[0115] The TiO2 filler material in the recesses 55 and 55 ' is chosen due to its low absorption and large scattering coefficient , effectively resulting in a highly, diffusely reflective undercast material . The filler material covers the bottom and sidewalls of the recesses . Once the undercast is administered to the package , the rest of the cavities are filled with clear Silicone , resulting in an index contrast between the package and the ambient ( air ) .

[0116] The index contrast of the clear silicone casting leads to reflection of light at the silicone to air interface plus a critical angle , beyond which no light is emitted from the package . The measurements indicate that about 50% of the generated light is internally reflected and lost for the application . However , due to the TiO2 particles , the internally reflected light is scattered with a redistribution of energy over the solid angle . As a result , the probability of leaving the package and entering the probe sample is effectively doubled at least .

[0117] In addition, light recycling is particularly beneficial in vital sign monitoring applications , because about 30% of light is scattered and / or reflected by the s kin : due to the proximity of the tissue to the source , much of this back scattered / ref lected light will be received again by the emitting package and, due to light recycling, also has a second chance to escape and contribute to the measurement signal , much in the same way as the internally reflected photons .

[0118] In summary, the presented new concepts propose several measures to optimize the signal strength and the perfusion index suitable for vital sign monitoring application . Those include to maximize the distance between red and infrared light emitting components and diametrically opposed photodetectors to about 8 . 5 mm for an approximately 12 mm diameter of the second region . The contact force is adj ustable to achieve best PI by minimizing the optical contact area / cross-section of the optical arrangement . This is achieved by a protrusion of the contact bottom surface .

[0119] Potential optical crosstalk between the red and infrared emitter and photodetector is suppressed by a centrally located light absorbing element , which is formed suitable by another photodetector . This helps to maximize the perfusion index for red and infrared light . The centrally located photodiode is also used as photodetector for green light .

[0120] In this regard, a secondary distance for green light is established from the green light emitting component to the central photodetector , keeping the distance from the light emitting component to the photodetector around 3 . 5 mm for green light or less . A significant larger distance for green light would be counterproductive , because green light is very strongly absorbed by tissue . The absorption is so strong that it may not be worth the effort to be compensated by increasing the supply current , i . e . , this approach would exceed the dynamic range of typical driver circuitry and substantially increase current / power consumption .

[0121] Rather , an additional signal gain is achieved for the same supply current and distance between the light emitting component and the photodetector by using a module with light-recycling properties . Finally, an optical barrier is established . PEEK can be used for this purpose as it comprises a high thermal resistance and low heat conductivity . This reduces cooling of the measurement site when the optical arrangement is in contact with the probe sample . A metallic barrier would be not suitable , and other plastic materials may not provide good opacity at all wavelengths , especially the longer IR wavelengths .

[0122] LIST OF REFERENCES

[0123] I optoelectronic arrangement

[0124] 10 housing

[0125] II bottom contact surface

[0126] 12 first region

[0127] 13 second region

[0128] 20, 21 openings

[0129] 22 central opening

[0130] 23, 24 openings

[0131] 41 fastening

[0132] 42 button

[0133] 43 fastening means

[0134] 50, 50' light emitting device

[0135] 51, 52 recess

[0136] 55 sidewall

[0137] 60, 60' light detecting device

[0138] 61 light absorbing device

[0139] 500,501 optoelectronic component

[0140] 502 optoelectronic component

[0141] 550 bevelled sidewall

[0142] LI, L2 circumference

Claims

CLAIMS1 . Optoelectronic arrangement , comprising :A housing with a bottom contact surface , said bottom contact surface having a first region and a second region, the first region surrounding the second region, wherein the second region is elevated with respect to the first region; the second region comprising a plurality of openings , wherein three openings of the plurality of openings are arranged in a first row; each of the openings comprising an at least partially transparent cover ; a first optoelectronic device arranged in a first of the three openings , said optoelectronic device comprising a first optoelectronic component configured to emit light of a first wavelength, in particular red light and a second optoelectronic component configured to emit light of a second wavelength, in particular infrared light ; a first light detection device , in particular a photodetector , arranged in a second of the three openings , wherein a distance of the first optoelectronic component to the first light detection device is substantially equal to a distance of the second optoelectronic component to the first light detection device , the first light detection device configured to detect light of the first and the second wavelength; a light absorbing element arranged in a central opening of the three openings between the first and second opening , said light absorbing device configured to absorb light of the first and the second wavelength .2 . Optoelectronic arrangement , comprising :A housing with a bottom contact surface , said bottom contact surface having a first region and a second region, the first region surrounding the second region, wherein the second region is elevated with respect to the first region; the second region comprising a plurality of openings , wherein three openings of the plurality of openings are arranged in a first row; each of the openings comprising an at least partiallytransparent cover and the two outer opening arranged clos to opposing sides of the second region; a first optoelectronic device arranged in a first of the three openings , said optoelectronic device comprising a first optoelectronic component configured to emit light of a first wavelength, in particular red light and a second optoelectronic component configured to emit light of a second wavelength, in particular infrared light ; a first light detection device , in particular a photodetector , arranged in a second of the three openings , wherein a distance of the first optoelectronic component to the first light detection device is substantially equal to a distance of the second optoelectronic component to the first light detection device , the first light detection device configured to detect light of the first and the second wavelength; the optoelectronic arrangement configured to exert a pressure in the range of 6 , 5 kPas to 60kPas and in particular between 10 kPas and 50 kPas and in particular between 15 kPas and 40 kPas and in Particular between 10 kPas and 30 kPas and in particular between 15 kPas and 25 kPas .3 . Arrangement according to claim 1 , further comprising a fourth and a fifth opening arranged in a second row intersecting the first row in particular perpendicular , wherein one of the three openings of the first row, in particular the central opening , is arranged between the fourth and fifth opening and a light absorbing element is arranged in said opening configured to absorb light of the first and the second wavelength; and / or the five openings form the shape of a cross or a T , wherein a light absorbing element is arranged in the central opening at an intersection of the cross or T configured to absorb light of the first and the second wavelength .4 . Arrangement according to claim 2 , wherein a second optoelectronic device is arranged in the fourth opening , said optoelectronic device comprising a first optoelectroniccomponent configured to emit light of the first wavelength, in particular red light and a fourth optoelectronic component configured to emit light of the second wavelength, in particular infrared light ; a second light detection device , in particular a photodetector , arranged in the fifth opening , wherein a distance of the first optoelectronic component to the second light detection device is substantially equal to a distance of the fourth optoelectronic component to the second light detection device , the second light detection device configured to detect light of the first and the second wavelength .5 . Arrangement according to any of the preceding claims , wherein each of the at least three openings are one of : flush with a surface of the second region recessed with regard to the surface of the second region; protruding with regard to the surface of the second region; and / or comprises a lens with a rounded shape .6 . Arrangement according to any of the preceding claims , wherein the first and / or second optoelectronic device comprises a third optoelectronic component configured to emit light of a third wavelength, in particular green light ; and wherein a distance of the third optoelectronic component to the first light detection device is smaller than a distance of the first and second component to the first light detection device ; and / or wherein a distance of the third optoelectronic component to the second light detection device is smaller than a distance of the first and second component of the second optoelectronic device to the second light detection device .7 . Arrangement according to any of the preceding claims , wherein the first and / or second optoelectronic device comprises a third optoelectronic component configured to emit light of a third wavelength, in particular green light ; and whereincenters of the respective first , second and third optoelectronic components form edges of a virtual triangle with the center of the third optoelectronic component closest to the respective central opening .8 . Arrangement according to any of the preceding claims , wherein the light absorbing element arranged in the central opening is a third light detection device configured to detect light of the first , second and third wavelength .9 . Arrangement according to any of the preceding claims , wherein the first and / or second optoelectronic device comprise a package with a first recess , in which the first and second optoelectronic components are arranged, said recess comprising -in particular beveled- sidewalls having a high reflectivity for light of the first and / or second wavelength .10 . Arrangement according to claims 5 or 6 and 8 , wherein the package comprise a second recess , in which the third optoelectronic component is arranged, said second recess comprising -in particular beveled- sidewalls having a high reflectivity for light of the third wavelength;11 . Arrangement according to any of the preceding claims , wherein the first and / or second light detection device comprise a color filter configured to block light in a portion of the spectrum different from the first and second wavelength; and / or wherein the at least partially transparent cover over the first and / or second light detecting device comprises a color filter configured to block light in a portion of the spectrum different from the first and second wavelength .12 . Arrangement according to any of the preceding claims , wherein the first region comprises a light absorbing coating , in particular a black coating; or comprises a light absorbing material , in particular a blackened material .13 . Arrangement according to any of the preceding claims , wherein the second region comprises one of : a circular shape ; cross like shape ; a T-shape ; and a shape following the arrangement of the plurality of openings In the second region .14 . Arrangement according to any of the preceding claims further comprising : fastening means to exert an adj ustable pressure of the bottom contact surface onto a sample surface , the sample surface comprising in particular skin tissue ; and / or one of a pressure sensor and / or a temperature sensor , said sensors particularly being arranged in the second region .15 . Arrangement according to any of the preceding claims , wherein the optical arrangement is arranged in such way that the is aligned substantially parallel to a main direction of liquid containing vessels of the sample probe , in particular blood vessel beneath the s kin when the optical arrangement is placed onto the skin .16 . Arrangement according to any of the preceding claims , whereinThe elevation of the second region with respect to the first region is in the range between 0 . 5 mm to 3 . 5 mm and in particular between 1 . 0 mm to 2 . 0 mm and in particular less than 1 . 75 mm; and / or a distance between a center of the first optoelectronic device , in particular a common center of the first and second optoelectronic components of the first optoelectronic device to the first light detecting device and / or a distance between a center of the second optoelectronic device , in particular a common center of the first and second optoelectronic components of the second optoelectronic device to the second light detecting device is in the range of 5 mm to 15 mm and in particular between 7 . 5 mm and 12 . 5 mm and in particular between 7 . 5 mm and 10 mm and in particular between 8 . 0 mm and 9 . 0 mm; and / ora distance between a center of the third optoelectronic components to the third light detecting device is in the range between 2 . 5 mm and 5 mm and in particular between 3 mm and 4 mm .17 . Arrangement according to any of the preceding claims , wherein the first and second optoelectronic devices are substantially identical in construction; and / or wherein the first and second light detection devices are substantially identical in construction; and / or wherein the first , second and light detection devices are substantially identical in construction .18 . earable device , in particular a watch, comprising : an optoelectronic arrangement according to one of the preceding claims ; a strap forming an adj ustable fastening means to exert a pressure of the bottom contact surface onto the skin tissue ; an evaluation and control unit coupled to the first and / or second optoelectronic device , the first and / or second light detecting device and the light absorbing device configured to operate those devices to obtain data and determined from said data at least one of : heart rate ; oxygen saturation; and glucose concentration .19 . Method of operating an optoelectronic arrangement , wherein the optoelectronic arrangement comprises :- a housing having a bottom contact surface , said bottom contact surface having a first region surrounding an elevated second region; the second region comprising a plurality of openings , wherein three openings of the plurality of openings are arranged in a row; each of the openings comprising an at least partially transparent cover that is flush with a surface of the second region;- the method comprising :- fixing the optoelectronic arrangement onto a user' s s kin with an adj ustable fastening means such that the first and second region of the bottom contact surface each exert a defined contact pressure onto the user' s , with the contact pressure exerted by the first region being smaller than the contact pressure exerted by the second region; emitting light of a first wavelength and / or a second wavelength from a first opening towards the user' s skin to interact with the tissue thereof ;- absorbing light being reflected into a second opening , located between the first and a third opening, by a light absorbing element ;- detecting light being reflected into the third opening and evaluating the detected light to obtain a value related to the optical measurement , in particular a perfusion index ;Optionally determining the perfusion index using the detected light .20 . Method according to claim 19 , wherein the second region of the bottom contact surface pressed against the skin or tissue with a pressure in the range of 6 , 5 kPas to 60 kPas and in particular between 10 kPas and 50 kPas and in particular between 15 kPas and 40 kPas and in Particular between 10 kPas and 30 kPas and in particular between 15 kPas and 25 kPas .21 . Method according to claim 19 , wherein the second region of the bottom contact surface exerts a force in the range of 1 , 25N to 4 , 5N and in particular between 1 , 75 N and 4 N and in particular between 2 N and 3 . 5 N onto the skin or tissue .22 . Method according to any of claims 19 to 21 , further comprising :Emitting light of a third wavelength, in particular green light , from the first opening towards the user' s skin to interact with the tissue thereof ; detecting light being reflected into the second opening and evaluating the detected light to obtain a value related to the optical measurement , in particular a perfusion index .23 . Method according to any of claims 19 to 22 , wherein the step of detecting light is conducted by a photodetector arranged in the respective openings . 24 . Method according to any of claims 19 to 23 , further comprising :Measuring the pressure exerted by the second region onto the user' s skin;Calibrating at least one of the steps of o determining the perfusion index ; o emitting light ; and o detecting light using a value derived from measuring the pressure .25 . Method according to any of claims 19 to 24 , wherein the step of emitting light and detecting light is conducted such that an optical path lies substantially parallel to blood vessels beneath the user' s s kin .

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