WO2023131464A1

WO2023131464A1 - Photodetector device and multi-color sensor

Info

Publication number: WO2023131464A1
Application number: PCT/EP2022/084943
Authority: WO
Inventors: Gunter Siess
Original assignee: ams Sensors Germany GmbH
Priority date: 2022-01-04
Filing date: 2022-12-08
Publication date: 2023-07-13

Abstract

A photodetector device comprises an array of light detector elements (10). A Fabry-Perot filter is arranged in front of the array of light detector elements (10) and having an angle-dependent transmission spectrum. A transfer element arranged to direct the incoming light through the Fabry-Perot filter, so that the angle-dependent transmission spectrum is shifted to form a target spectrum over a light detection surface of a corresponding light detector element (11) of the array of light detector elements (10), respectively.

Description

PHOTODETECTOR DEVICE AND MULTI-COLOR SENSOR

This disclosure relates to a photodetector device and a multi-color sensor .

This patent application claims the priority of German patent application 102022100123 . 7 , the disclosure content of which is hereby incorporated by reference .

Background

Color sensors , such as multi-color sensors , can be used for applications including color or true color recognition . In contrast to dedicated spectrometers , compact sensors meet the demand for ongoing miniaturi zation, including smaller space , fewer color channels and lower cost . Color sensors for ambient light sensing (ALS ) , for example , are often defined by the human eye spectra sensitivity . Such sensors are typically based on classical interference filters stacks for each channel , the optimi zation of H and L material stack allows a speci fic design and processing . Also combinations of multi spectral channels for sALS ( 8 to 12 channels ) need speci fic filter transmittance shapes that are reali zed by interference filters . Especially for sALS sensors using interference filters the number of channels ( >3 ) is the signi ficant cost driver of the device and alterative solutions for getting similar performance at less process steps are needed . Other types of common color sensors rely on dedicated layout of interference filters to design color sensors to meet the requirements of applications . Alternative filter designs are rarely used due to their shortcomings . For example , Fabry-Perot filter can be used for integrated spectrometer applications . Fabry-Perot filter have a very narrow transmission shape ( in the range of 1 % to 2 %*X, X being the wavelength) and a needle-shaped peak . Because of the narrow band width ( FWHM) a high number of sensor channels with a peak separation close to the FWHM is needed to have no blind spectra parts in between . At combining the transmissions of an Etalon gradient range , the detector width defines the FWHM of each detector channel . However, common configurations only allow regular arrangements . For dedicated spectrometers a speci fic integral transmission design often may not be necessary for most spectral applications . For example , detectors may have spectral gaps which create blind spectra regions due to the narrow profile of Fabry-Perot filters . However, gaps can be compensated for by using a second parallel detector line that is shi fted by hal f channel pitch .

Color sensors , such as multi-color sensors typically contain less channels than a spectrometer . The count of channels also increase the resources of electronic, chip si ze and processing ef fort . For VIS ( 400 nm to 700 nm) for example up to 30 channels may be needed in a spectrometer . At low cost multi-color sensor solutions , however, a spectral resolution of 12 or 16 channels in the same range could be suf ficient . An optimi zation of spectral sensitivity shape for spectral sensors may involve adj usted overlap and a constant spectra sum of all channels .

It is an obj ect of the present disclosure to provide a photodetector device and multi-color sensor with an alternative filter design at lower cost . These objective is achieved by the subject matter of the independent claims. Further developments and embodiments are described in the dependent claims.

It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described herein, and may be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments unless described as an alternative. Furthermore, equivalents and modifications not described below may also be employed without departing from the scope of the photodetector device and multi-color sensor device which are defined in the accompanying claims.

Summary

The following relates to an improved concept in the field of photodetectors, in particular multi-color photodetectors. The proposed improved concept seeks to realize a specific transmission function or shape of a Fabry-Perot filter for a photodetector device. This can be achieved in different ways, e.g. by generating specific effective angular distributions. For example, size, shape and distance of an aperture or mask arrangement (such as backside of a lens or diffuser) and detector can be designed regarding to the target transmission shape. Another way to realize a specific transmission function/shape is suggested by nonlinear geometrical arrangements of etalon thickness variation over a detector area . The improved concept suggests the use of speci fic designed gradient of etalon layers to design an application speci fic filter shape ( target spectra ) . Such filter shapes could be Gaussian or cosine to reali ze best performance in less channel spectrometer configurations and also XYZ filter for color matching application, that are reali zed typically as separate interference filters . The improved concept provides a solution to use the angular depending ef fects to manipulate the transmission shape of a Fabry Perot filter and create speci fic shapes of transmission .

In at least one embodiment a photodetector device comprises an array of light detector elements , a Fabry-Perot filter and a trans fer element . The Fabry-Perot filter is arranged in front of the array of light detector elements and has an angle-dependent transmission spectrum . The trans fer element is arranged to direct the incoming light through the Fabry- Perot filter . By way of the trans fer element the angledependent transmission spectrum is shi fted, or adj usted, to form a target spectrum over a light detection surface of a corresponding light detector element of the array of light detector elements , respectively .

Fabry-Perot filter typically have a considerable narrow filter shape and a high number of sensor channels with a peak separation close to the FWHM is needed to have no blind spectra parts in between . The count of channels also increase demands on resources such as electronic, chip si ze and processing ef fort . In order to cover the visual range (VIS 400 nm to 700 nm) up to 30 channels are needed . This was not feasible using Fabry-Perot filter so far . The proposed concept allows for low cost solutions as target spectra can be adj usted using the trans fer element . This way the inherent narrow filter shapes of Fabry-Perot filters can be altered, e . g . broadened, to overlap or establish a constant spectra sum of all channels . Thus , the proposed concept provides an alternative filter design comparing to classical interference filter design . Target filter shapes could be Gaussian, cosine or close to narrow rectangular band pass to reali ze best performance in less channel spectrometer configurations .

The trans fer element is operable to shi ft the angle-dependent transmission spectrum of the Fabry-Perot filter in order to produce a desired target spectrum . In other words , the trans fer element rans fer element is arranged to direct the incoming light through the Fabry-Perot filter, so that the angle-dependent transmission spectrum is adj usted to form a desired target spectrum . Thus , the terms " shi ft" and "adj ust" can be used interchangeably .

In at least one embodiment the Fabry-Perot filter comprises at least one etalon . The at least one etalon is arranged in front of the light detection surfaces of several light detector elements of the array of light detector elements . The etalon may cover the whole array so that a single etalon defines the Fabry-Perot filter .

In at least one embodiment the Fabry-Perot filter comprises an array of etalons . Each etalon from the array of etalons is arranged in front of the light detection surface of a corresponding light detector element , respectively . This way the etalon is pixelated in the sense that individual etalons may cover a corresponding light detector element of the array . A plurality of etalons thus defines the Fabry-Perot filter . In at least one embodiment one or more of the etalons comprise a first and a second reflecting surface . The trans fer element comprises the first and/or second reflecting surface .

The reflecting surfaces , e . g . thin mirrors form an optical cavity . The Fabry-Perot filter has a transmission spectrum which is largely determined by the distances between the reflecting surfaces of the etalon . Optical waves can pass through the optical cavity only when they are in resonance with it .

In at least one embodiment the first and/or second reflecting surface are inclined against each other according to a linear gradient . The linear gradient is set so that the angledependent transmission spectrum is shi fted, or adj usted, to form the target spectrum over the corresponding light detection surface .

A distance between the reflecting surfaces ( or thickness of the etalon) changes along one or more directions according to the linear gradient . The level of inclination provides a process parameter to tune the target spectra to a desired degree .

In at least one embodiment the first and/or second reflecting surface are inclined against each other according to a nonlinear gradient . The non-linear gradient is set so that the angle-dependent transmission spectrum is shi fted, or adj usted, to form the target spectrum over the corresponding light detection surface . Distance between the reflecting surfaces ( or thickness of the etalon) changes along the nonlinear gradient . Using a nonlinear gradient provides a further degree of freedom to tune the target spectra to a desired degree .

In at least one embodiment the trans fer element , as reflecting surface , has a non-linear surface profile . The non-linear surface profile can have a free form and of fers yet another degree of freedom to tune the target spectra to a desired degree .

In at least one embodiment the non-linear surface profile comprises sections which are arranged in front of the light detection surface of the corresponding light detector element . The sections can be tuned to establish a desired target spectrum for a corresponding light detector element .

In at least one embodiment the trans fer element comprises an aperture arrangement comprising one or more apertures . The aperture arrangement is configured to direct the incoming light through the Fabry-Perot filter with a defined angular distribution . The aperture arrangement allows to set the target spectra by means of optical setup and may be defined by means of optical simulation or raytracing . For example , the aperture arrangement may comprise aperture layers with apertures of defined shape and/or number .

In at least one embodiment the aperture arrangement defines the angular distribution so that the incoming light incident on a light detection surface of a corresponding light detector element of the array of light is restricted to angles of incidence which shi ft , or adj ust , the angledependent transmission spectrum to form the target spectrum over the respective light detection surface . The design of the aperture arrangement allows only light beams with a defined distribution of angles of incidence to travel through the device . This way the target spectra are altered by way of shi fting ( adj usting) due to varying incidence .

In at least one embodiment one or more light detection surfaces of a corresponding light detector element of the array of light detector elements is masked by a mask or comprises a shape . The mask or the shape is configured to restrict angles of incidence of incoming light so that the angle-dependent transmission spectrum is shi fted, or adj usted, to form the target spectrum over the respective light detection surface .

The angles of incidence may also be restricted by forming the detector with a speci fic shape or by masking a regular light detector element or the array with a mask of said shape .

In at least one embodiment the aperture arrangement comprises a distribution lens . In addition, or alternatively, the aperture arrangement comprises a distribution di f fuser to direct the incoming light through the Fabry-Perot filter with the defined angular distribution .

In at least one embodiment a multi-color sensor device comprises a light source and a photodetector device according to one or aspects discussed herein . Furthermore , the photodetector device and the light source are integrated in a common module . This way the multi-color sensor device is compact and can be integrated into mobile devices , for example . In at least one embodiment the photodetector device comprises at least three light detector elements . The Fabry-Perot filter is configured to filter at least three di f ferent wavelength bands , respectively, of the incoming light , wherein the at least three di f ferent wavelength bands combine to span a predefined range of wavelengths . The wavelength bands allow to cover larger parts of the electromagnetic spectrum, e . g . as opposed to common narrow band Fabry-Perot filters . Fewer channels may be needed to cover a larger part of the spectrum .

In at least one embodiment the Fabry-Perot filter has a corresponding spectral sensitivity associated with the di f ferent wavelength bands , respectively . A sum of the spectral sensitivities of the di f ferent wavelength bands over the predefined range of wavelengths is a constant value .

The spectral sensitivities of the di f ferent wavelength bands can be configured in such a way that various target spectra result in an energetically proportional manner, without energetic signal loss . In particular, the spectral sensitivities can be configured so that a sum of the spectral sensitivities over a predefined wavelength range is kept constant . In this way, the spectral change in extrema ( flanks or peaks ) within a target spectra are not detected spectrally but instead are detected integrally . The spectral sensitivities of the di f ferent channels are configured so that a summation function provides a uni form distribution over a full spectral range of the multi-spectral sensor device , in which the full spectral range of the multi- spectral sensor device may be defined as the di f ference between the smallest wavelength associated with a peak spectral sensitivity of a filter channel and the largest wavelength associated with a peak spectral sensitivity of a filter channel .

Further embodiments of the multi-color sensor device according to the improved concept become apparent to a person skilled in the art from the embodiments of the photodetector device described above and vice versa .

The following description of figures of example embodiments may further illustrate and explain aspects of the improved concept . Components and parts with the same structure and the same ef fect , respectively, appear with equivalent reference symbols . Insofar as components and parts correspond to one another in terms of their function in di f ferent figures , the description thereof is not necessarily repeated for each of the following figures .

Brief description of the drawings

In the Figures :

Figure 1 shows an example embodiment of a photodetector device ,

Figure 2 shows another example embodiment of a photodetector device ,

Figure 3 shows results of a mathematical concept relating to the trans fer element ,

Figure 4 shows an example embodiment of an etalon with a gradient , Figure 5 shows another example embodiment of an etalon with a gradient ,

Figure 6 shows another example embodiment of an etalon with a gradient ,

Figure 7 shows an example embodiment of a photodetector device ,

Figure 8 shows another example embodiment of a photodetector device ,

Figure 9 shows an example construction of target spectra using an aperture arrangement , and

Figures 10 to 15 show example target spectra using di f ferent aperture arrangement geometries .

Detailed description

Figure 1 shows an example embodiment of a photodetector device . The photodetector device comprises an array of light detector elements 10 , each of which have a light detection surface . The array is integrated in a common integrated circuit . For example , array of light detector elements comprises photodiodes or SPADs as light detector elements .

A Fabry-Perot filter is arranged in front of the array of light detector elements . The Fabry-Perot filter comprises an etalon 20 . The etalon comprises an optical cavity which is formed by two reflecting surfaces , e . g . thin mirrors . A first and a second reflecting surface 21 , 22 are inclined against each other according to a linear gradient . In other words , a distance between the reflecting surfaces ( or thickness of the etalon) changes along one or more directions . The etalon covers the light detection surfaces of the array 10 , when viewed along a direction perpendicular to the light detection surfaces . The reflecting surfaces are essentially flat . A pass band filter 23 is arranged on the first and/or the second reflecting to block higher orders of the etalon .

The Fabry-Perot filter has a transmission spectrum which is largely determined by the distances between the reflecting surfaces of the etalon . Optical waves can pass through the optical cavity only when they are in resonance with it . The ef fective distance an incoming light beam 30 travels between the reflecting surfaces 21 , 22 also depends on the angle of incidence . In fact , the transmission spectrum is angledependent transmission spectrum and spectral shi fts under varying angle of incidence . Light beams which are incident under an inclined beam direction (with respect to normal incidence ) lead to varying phase shi ft inside the etalon, resonance and, ultimately, transmission wavelength .

In regular etalons the reflecting surfaces are parallel , i . e . have the same distance over the whole ef fective surface area . As a consequence the transmission spectrum is the same for all light detector elements given a constant angle of incidence . In such a configuration, the spectrum has a needle-like sharp peak and a very narrow transmission shape around a center wavelength . In this example embodiment , however, the etalon is inclined according to the linear gradient . This leads to varying thickness of the etalon, i . e . changing distance between the reflecting surfaces , along the gradient . As a consequence the transmission spectrum becomes a function of space or location . For example, consider the first reflecting surface 21 is inclined with respect to the second reflecting surface 22 (which is essentially parallel to a plane of the array of light detector elements 10) . Then incoming light is incident into the etalon 20 by way of the first reflecting surface. The effective transmission spectrum then is determined by the location where the light beam enters the cavity. Depending on this location the linear gradient determines a defined effective distance between the reflecting surfaces, and, thus, phase shift, resonance and, ultimately, transmission wavelength. In addition, these parameters remain a function of angle of incidence. In this context, the reflecting surfaces, in particular, the first reflecting surface constitutes a transfer element which directs the incoming light through the Fabry-Perot filter, i.e. etalon, so that the angle-dependent transmission spectrum is shifted.

The resulting angle-dependent transmission spectrum is no longer independent of the location of a given light detection surface either. As the light detector elements are arranged below the Fabry-Perot filter it passes different wavelength bands towards the light detection surfaces. In fact, the etalon transmission broadens to form a wavelength band rather than a needle-like sharp peak. The resulting angle-dependent transmission spectrum resembles a dedicated spectrum for each light detector element, i.e. at the respective light detection surface. In turn, the dedicated spectra (target spectra) are largely determined by the linear gradient, which can be adjusted at will. For example, the transfer element (i.e. the reflecting surfaces) can be manufactured to result in a desired linear gradient, so that predefined target spectra form at the light detection surfaces of their corresponding light detector elements of the array of light detector elements 10 . In fact , the trans fer element can be used to adj ust the target spectra to a large degree of freedom . The individual light detector elements 11 can be considered channels for a color sensor, as they have di f ferent wavelength bands .

Figure 2 shows another example embodiment of a photodetector device . This example is based on the one discussed with respect to Figure 1 . The embodiment di f fers in that the trans fer element , embodied as the first reflective surface 21 , has a non-linear surface profile . The non-linear surface profile can be divided into sections which are arranged in front of the light detection surface of the corresponding light detector element 11 .

The non-linear surface profile provides a further degree of freedom to create target spectra with a desired wavelength band

The proposed concept shows how to reali ze a speci fic transmission function/ shape by gradient and/or non-linear geometrical arrangements of etalon thickness variation over a detector area . Compared to common Fabry-Perot spectrometers with etalons and regular arrangements the approach allows to generate a recipe of thicknesses . Free configurable Gaussian or Cosine transmittance functions can be designed and allows for a single production process . Common Fabry-Perot filters typically generate narrow band filters and are typically used for integrated spectrometer applications . Using modern process technology, however, allows to generate gradient etalon layers as discussed above . Special etching technologies allows to process the full etalon gradient in one step and bring up the potential for low cost solutions . By using such gradient filter configurations on a detector array, the width of the detectors in an array and the etalon gradient defines the bandwidth and separation of the spectral channels .

The speci fically designed gradient and/or non-linear surface profile of etalon layers allows to design an application speci fic filter shape . Such filter shapes could be Gaussian or cosine to reali ze best performance in less channel spectrometer configurations , e . g . XYZ filter for color matching application, that are reali zed typically as separate interference filters . The proposed concept , thus , generates an alternative filter design comparing to classical interference filter design .

Figure 3 shows results of a mathematical concept relating to the trans fer element . The overall etalon surface area which is ef fective for a corresponding light detector element can be described as a histogram of the thickness ( distance between reflecting surfaces ) . Basically, a histogram corresponds to the trans fer function that can be calculated by the inverse of a count of Fabry-Perot transmittances in a relevant spectral range and the target spectra . The calculated histogram can be converted into a linear or freeform like gradient/ shape of the trans fer element with respect to the detector area . Also multiple combinations of pattern in respect to light distribution and angles of incidence (AOI s ) are possible .

Consider a photodetector device with three light detector elements , or channels , such as a XYZ multi-color sensor . For example , XYZ is a color space designed to be consistent with how human beings actually experience optical wavelengths . Graph (1) in the drawing shows the spectral range of the Fabry-Perot filter to be calculated. Two example spectra are depicted with narrow peaks representing transmission 400 and 700 nm (Transmission T as a function of wavelength) . Neighboring orders may be blocked by additional pass band filter 23. The Fabry-Perot mirrors 21, 22 have an example reflectivity of 97.6%. The two example spectra mark the spectral range between 400 and 700 nm. This range can be covered with further example spectra. In this example, the range comprises monochromatic transmission spectra with narrow peaks centered on 1 nm steps, i.e. 400, 401, 402, ..., 699, 700 nm. These spectra are denoted FP400, FP401, FP402, ■■■, FP₆99, and FP₇oo- In a certain sense the set of these spectra provides the spectral base functions for the following example calculation.

Graph (2) shows scaled target spectra that have to be fit using the base set a Fabry-Perot spectra and combinations thereof (Transmission T as a function of wavelength) . For example, in the use case of the XYZ color sensor there may be five target spectra, i.e. an X channel split into two channels Xs and XI, a Y channel, and a Z channel.

In mathematical terms the target spectra can be constructed from the set of spectral base functions using a transfer matrix M. In this sense the transfer element of the photodetector device constitutes an embodiment of the transfer matrix, as it directs an incoming light beam to shift the angle-dependent transmission spectrum to form a target spectra. The transfer matrix M basically describes the ratio of spectral base functions needed to reconstruct or fit the target spectrum. This procedure can be represented as

wherein T denotes the target spectra and TFP represents the set of spectral base functions .

Graph ( 3 ) shows an example set of trans fer matrixes which derive from the equation above for the example XYZ color sensor . Depicted are matrix coef ficients as a function of wavelength . Finally, graph ( 4 ) depicts the reconstructed target spectra ( Transmission T as a function of wavelength) . These derive from T = T_FP ■ M^T where only parts of positive coef ficients have been used . In comparison with graph ( 2 ) a decent level of accuracy can be achieved .

Figure 4 shows an example embodiment of an etalon with a gradient . The calculation concept discussed above can be applied to derive design guidelines for the Fabry-Perot filter . The drawing shows in the upper graph an etalon arranged with a linear gradient in only one direction ( denoted x direction in an x, y, z coordinate system, linear spread to rectangle ) . The array of light detector elements lies in the x, y plane . The lower graph shows the resulting thickness histogram . The y-axis indicates a frequency density ( german : Hauf igkeitsdichte ) or in this case calculated area si zes of etalon thicknesses . This illustrates how many of same thickness is necessary inside the distribution of any thickness . The values indicated on the axis in this and the following graphs have been the basis of example calculations . These serve primarily an illustration purpose and may not necessarily represent dimensions or actual values of possible implementations . Figure 5 shows another example embodiment of an etalon with a gradient . The drawing shows in the upper graph an etalon arranged with a linear gradient in only more direction ( diagonal spread to rectangle , i . e . x and y direction) . The array of light detector elements lies in the x, y plane . The lower graph shows the resulting thickness histogram . For less needed density of lower and higher regions ( at functions that are close to Gaussian or Cosine functions ) it is also possible to arrange the thickness spread over the diagonal .

Figure 6 shows another example embodiment of an etalon with a gradient . The first and/or second reflecting surfaces can be inclined against each other according to a linear or a nonlinear gradient . In fact , the gradient may be linear only for sections . In order to be more independent from homogeneous light distribution of incoming light to the Fabry-Perot filter it is also possible to create multiple sections arranged in a regular or even irregular pattern, e . g . of a square or rectangular distribution like the one shown in Figure 6 . Also complete free form gradients are possible . Shape , gradient and sections can be chosen to meet the constraints defined by the desired target spectra .

Further configurations and designs can also include gradient shapes like free forms and not regular basics , trans fer function and design that respect the angular distribution of the light (monochromatic spectra of Fabry-Perot filter become wider and less needle-like characteristic ) . The light detector elements may be covered with a mask to restrict the set of spectral base functions . The Fabry-Perot filter can be processed directly on chip, on a separate carrier or on an optical part on top of the detector . Figure 7 shows an example embodiment of a photodetector device . The photodetector device comprises an array of light detector elements , each of which have a light detection surface . The array is integrated in a common integrated circuit . For example , array of light detector elements comprises photodiodes or SPADs as light detector elements .

A Fabry-Perot filter is arranged in front of the array of light detector elements . The Fabry-Perot filter comprises an array of etalons . Each etalon forms an optical cavity by two reflecting surfaces , e . g . thin mirrors . A first and a second reflecting surface are essentially parallel to each other . In other words , a distance between the reflecting surfaces ( or thickness of an etalon) is constant for a given etalon . There is one etalon associated with a corresponding light detection surface of the array, respectively . The reflecting surfaces are essentially flat .

The Fabry-Perot filter has a transmission spectrum which basically is determined by the transmission spectra of the etalons . Optical waves can pass through the optical cavities only when they are in resonance with it . The ef fective distance an incoming light beam travels between the reflecting surfaces also depends on the angle of incidence . In fact , the transmission spectra of the etalons are angledependent and spectrally shi fts under varying angle of incidence . Light beams which are incident under inclined beam direction (with respect to normal incidence ) lead to varying phase shi ft inside the etalon, resonance and, ultimately, transmission wavelength .

Furthermore , the photodetector device comprises an aperture arrangement . The aperture arrangement constitutes an embodiment of the trans fer element . A first aperture layer 31 is arranged between the Fabry-Perot filter and the array of light detector elements 10 . The first aperture layer comprises an aperture that has the ef fect to mask a light detection surface of a corresponding light detector element of the array of light detector elements . A second aperture layer 32 is arranged above the first aperture layer and above the Fabry-Perot filter (with respect to a surface normal of the array of light detector elements ) . The second aperture layer comprises two or more apertures which direct incoming light through the Fabry-Perot filter and towards the first aperture layer so that incoming strikes the corresponding light detector element by way of the aperture in the first aperture layer . Furthermore , a distribution di f fuser 33 is arranged above the second aperture layer to direct the incoming light through the Fabry-Perot filter with a defined angular distribution .

Figure 8 shows another example embodiment of a photodetector device . This example is based on the one discussed with respect to Figure 7 . The embodiment di f fers in that the aperture arrangement comprises only the second aperture layer having two or more apertures . Furthermore , a distribution lens 34 is arranged above the second aperture layer to direct the incoming light through the Fabry-Perot filter . The lens and the apertures direct incoming light through the Fabry- Perot filter so that incoming strikes the corresponding light detector element with a defined angular distribution .

Alternatively, the Fabry-Perot filter may also comprises a single etalon with parallel reflecting surfaces covering the light detection surfaces of the array, when viewed along a direction perpendicular to the light detection surfaces . In yet another alternative the Fabry-Perot filter may also comprises a single etalon with inclined reflective surfaces as discussed with respect to Figures 1 and 2.

The aperture arrangement, as transfer element, complemented with the distribution lens or diffuser, allow to realize a specific transmission function/shape by generating specific effective angular distributions. In fact, size, shape and distance of aperture layers (e.g., at a backside of lens or diffuser, or masking the detector) can be designed regarding to desired the target transmission spectra.

Figure 9 shows an example construction of target spectra using an aperture arrangement. The first graph (1) shows transmission spectrum of the etalon under varying angles of incidence. The spectral shift of peak transmission is a known function of reflectance R, refractive index n and thickness of the etalon. These can be considered the spectral base functions. The second graph (2) shows a histogram of angular power distribution, depicted as relative power over angle of incidence. The final transmission spectrum (as depicted in graph (3) ) is the sum over all effective single spectra. The calculation involves the angular spectra multiplied by the histogram of graph (2) . The target AOI distribution that result the target transmission shape can be realized by specific shapes of the apertures, for example. For the spectral combinations all angular depending spectra between 0 deg and the maximum usable AOI are usable.

The angular histogram derives from designing specific geometries for the aperture arrangement, e.g. the first and second aperture layers on the top side of the detector or on the bottom side of the optic. The optic can have a diffuser. In this case the system is more independent to the AOI from the outside. The AOI distribution is generated by the shape of the apertures (diffuser and detector) and the distance between both. The optic can have a lens. A lens may be used at collimated setup, for instance at color matching measurements that includes a defined illumination spot (diameter of spot >> target distance) . A full AOI distribution can be generated by the second aperture layer, bottom of the lens; and the system becomes mostly independent on distance. A comparably small detector is possible in focus length of the lens. Less height is possible at direct contacting the lens and aperture to the detector.

The following figures shows various embodiments to illustrate examples to variate the apertures (size, geometry, shape) and may serve as design guidelines. A useful design is necessary to fulfill application requirements. In general, the approach and calculation of transfer matrixes discussed above can be applied .

Figures 10 to 15 show example target spectra using different aperture arrangement geometries. The drawings are similar in that they show a first graphs (1) in left upper corner show example geometries of the aperture arrangement, with the first and second aperture layers as examples. Furthermore, a shadow indicates where, due to the aperture arrangement, no illumination of the detector takes places. The second graphs (2) in the upper right corners show histograms of angular power distribution, depicted as relative power over angle of incidence. The third graphs (3) show the transmission spectrum of the etalon under varying angles of incidence, i.e. a set of spectral base functions. Graphs (4) show the final transmission spectra, i.e. the sum over all effective single spectra . Geometry parameters such as aperture , detector si ze and height are indicated . The examples assume one etalon with parallel reflective surfaces over the array of light detector elements .

Figure 10 assumes a circular aperture in the second aperture layer and a rectangular aperture in the first aperture layer . This leads to a broad histogram of angular power distribution . In this geometry a broad base of spectral base functions are relevant , which leads to a broad final transmission spectrum .

Figure 11 assumes a rectangular aperture in the second aperture layer and a rectangular smaller aperture in the first aperture layer . This leads to a broad histogram of angular power distribution having peak at smaller AOI s and a plateau at higher AOI s . In this geometry a broad base of spectral base functions are relevant , however, base functions associated with the power peak are dominant . This leads to a final transmission spectrum having a more pronounced peak .

Figure 12 assumes an aperture with two circular segments in the second aperture layer and a square aperture in the first aperture layer . For example , the square area is much smaller than the area circular segments . The histogram of angular power distribution has a broad peak at greater AOI s , i . e . >20 deg . This peak is also reflected in the spectral base functions , and, ultimately, the final transmission spectrum .

Figure 13 assumes concentric circular and ring-shaped apertures in the second aperture layer and a square aperture in the first aperture layer . Both ring-shaped apertures and square aperture have similar area . The histogram of angular power distribution has a broad distribution and no pronounced narrow peak . Conversely, the spectral base functions and final transmission spectrum have a more narrow shape centered at a center wavelength .

Figure 14 assumes one concentric circular and one ring-shaped apertures in the second aperture layer and a square aperture in the first aperture layer . For example , the square area is much smaller than the area circular segments . In this configuration the histogram of angular power distribution has a broad peak at greater AOI s . However, the histogram also shows a second peak at smaller AOI s , i . e . between 0 and 10 deg . This is also reflected in the spectral base functions . The final transmission spectrum shows two similar narrow peaks .

Figure 15 assumes one concentric circular and two ring-shaped apertures in the second aperture layer and a square aperture in the first aperture layer . For example , the square area is much smaller than the area circular segments . In this configuration the histogram of angular power distribution has three broad peaks . This is also reflected in the spectral base functions . The final transmission spectrum shows three similar narrow peaks .

The results of Figures 10 to 15 may serve as guidelines to design a photodetector device . In order to come up with a desired design for an intended applications these examples may give starting points which can be complemented with optical calculations and simulations , e . g . along the mathematical framework discussed above . Furthermore , the trans fer element can be embodiment by the aperture arrangement . It may be further complemented with a dedicated etalon design, i . e . single etalon or array of etalons , with linear or non-linear gradient as well as non-linear surface profiles .

While this speci fication contains many speci fics , these should not be construed as limitations on the scope of the invention or of what may be claimed, but rather as descriptions of features speci fic to particular embodiments of the invention . Certain features that are described in this speci fication in the context of separate embodiments can also be implemented in combination in a single embodiment . Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination . Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination .

Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results . In certain circumstances , multitasking and parallel processing may be advantageous .

A number of implementations have been described . Nevertheless , various modi fications may be made without departing from the spirit and scope of the invention . Accordingly, other implementations are within the scope of the claims .

References

10 array of light detector elements

11 light detector element 20 etalon

21 first reflecting surface

22 second reflecting surface

23 pass band filter

30 aperture arrangement 31 first aperture layer

32 second aperture layer

33 di f fuser

34 lens

40 incoming light beam

Claims

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Claims

1. A photodetector device, comprising:

- an array of light detector elements (10) ,

- a Fabry-Perot filter arranged in front of the array of light detector elements (10) and having an angle-dependent transmission spectrum, and

- a transfer element arranged to direct the incoming light through the Fabry-Perot filter, so that the angledependent transmission spectrum is shifted to form a target spectrum over a light detection surface of a corresponding light detector element (11) of the array of light detector elements (10) , respectively.

2. The photodetector device according to claim 1, wherein

- the Fabry-Perot filter comprises at least one etalon (20) ,

- the at least one etalon (20) is arranged in front of the light detection surfaces of several light detector elements (11) of the array of light detector elements (10) .

3. The photodetector device according to claim 1 or 2, wherein

- the Fabry-Perot filter comprises an array of etalons (20) ,

- each etalon (20) from the array of etalons is arranged in front of the light detection surface of a corresponding light detector element (11) , respectively.

4. The photodetector device according to claim 2 or 3, wherein one or more of the etalons (20) comprises a first and second reflecting surface (21, 22) , and - the transfer element comprises the first and/or second reflecting surface (21, 22) .

5. The photodetector device according to claim 4, wherein

- the first and/or second reflecting surface (21, 22) are inclined against each other according to a linear gradient, and

- the linear gradient is set so that the angle-dependent transmission spectrum is shifted to form the target spectrum over the corresponding light detection surface.

6. The photodetector device according to claim 4 or 5, wherein

- the first and/or second reflecting surface (21, 22) are inclined against each other according to a non-linear gradient, and

- the non-linear gradient is set so that the angle-dependent transmission spectrum is shifted to form the target spectrum over the corresponding light detection surface.

7. The photodetector device according to claim 5 or 6, wherein the transfer element, as reflecting surface (21, 22) , has a non-linear surface profile.

8. The photodetector device according to claim 7, wherein the non-linear surface profile comprises sections which are arranged in front of the light detection surface of the corresponding light detector element (11) .

9. The photodetector device according to one of claims 1 to 7, wherein

- the transfer element comprises an aperture arrangement

(30) comprising one or more apertures, and - the aperture arrangement is configured to direct the incoming light through the Fabry-Perot filter with a defined angular distribution.

10. The photodetector device according to claim 9, wherein the aperture arrangement defines the angular distribution so that the incoming light incident on a light detection surface of a corresponding light detector element (11) of the array of light detector elements (10) is restricted to angles of incidence which shift the angle-dependent transmission spectrum to form the target spectrum over the respective light detection surface.

11. The photodetector device according to one of claims 1 to

10, wherein

- one or more light detection surfaces of a corresponding light detector element (11) of the array of light detector elements (10) is masked by a mask or comprises a shape, and

- the mask or the shape is configured to restrict angles of incidence of incoming light so that the angle-dependent transmission spectrum is shifted to form the target spectrum over the respective light detection surface.

12. The photodetector device according to one of claims 9 to

11, wherein the aperture arrangement (30) comprises a distribution lens (34) and/or a distribution diffuser (33) to direct the incoming light through the Fabry-Perot filter with the defined angular distribution.

13. A multi-color sensor device, comprising a photodetector device according to one of claims 1 to 12, and a light source; wherein the photodetector device and the light source are integrated in a common module.

14. The multi-color sensor device according to claim 13, wherein :

- the photodetector device comprises at least three light detector elements (11) , and

- the Fabry-Perot filter is configured to filter at least three different wavelength bands, respectively, of the incoming light, wherein the at least three different wavelength bands combine to span a predefined range of wavelengths .

15. The multi-color sensor device according to claim 14, wherein :

- the Fabry-Perot filter has a corresponding spectral sensitivity associated with the different wavelength bands, respectively, and

- a sum of the spectral sensitivities of the different wavelength bands over the predefined range of wavelengths is a constant value.