Imaging equipment and methods for operating imaging equipment.

Abstract

This invention relates to an imaging device. The imaging device comprises a Fabry-Perot interferometer (FPI) consisting of two reflective elements capable of transmitting at least a defined portion of the interferometer gap. The length of the interferometer gap is variable within at least the first range. The FPI generates multiple transmission peaks upon receiving light, and the peak wavelength of each transmission peak is variable by changing the length of the interferometer gap. The imaging device also comprises multiple optical filters, each optically passing light within a different wavelength range, wherein each wavelength range has a different mean wavelength. Furthermore, the wavelength ranges of the multiple optical filters are chosen such that each wavelength range includes no more than one of the peak wavelengths at each first-range gap length. This invention also relates to a method of operating the imaging device.

Description

[0001] IMAGING DEVICES AND METHOD OF OPERATING AN IMAGING DEVICE

[0002] TECHNICAL FIELD

[0003] The present disclosure relates generally to the field of imaging devices, and provides particularly an imaging device, and a method of operating the imaging device, which can be used for hyperspectral imaging. The imaging device comprises a Fabry-Perot Interferometer (FPI) element, which generates a plurality of transmission peaks when receiving light. A peak wavelength of each transmission peak can be changed by changing a gap length of an interferometer gap of the FPI element. The imaging device further comprises optical filters, wherein each optical filter passes not more than one transmission peak at each gap length. The imaging device may generate spectral images for a hyperspectral image, wherein each spectral image may be generated for a particular transmission peak and at a particular gap length.

[0004] BACKGROUND

[0005] A Fabry-Perot Interferometer (FPI) can be used for creating a fixed or tunable narrow band filter (also referred to as an “FPI filter”). However, the transmission spectrum of the FPI comprises several harmonic transmission peaks in addition to a main transmission peak. That is, the FPI generates a plurality of transmission peaks when receiving light. This makes it challenging to create an FPI filter, which can be tuned to measure a plurality of narrow peaks of light over a large range of wavelengths.

[0006] For instance, a typical transmission spectrum of an exemplary FPI has harmonic peaks in the visible range of light, i.e., it may include a main peak and a set of harmonic peaks. For example, the main peak may be at Z=(2*d). wherein X is the wavelength of the peak, and d is the gap length of the interferometer gap of the FPI. Further, the harmonic peaks may be generated at Z(n)=(2*d) / (n). wherein n is 2, 3, 4, etc. That is, the wavelength of each transmission peak of the FPI depends on the gap length of the interferometer gap. Due to the harmonic peaks, which are inevitably created by the FPI filter in addition to the main peak, if an image sensor is used to capture light that passes through the FPI filter, the measured data can include the energy from several different wavelengths (i.e., the energy of the main peak and the energy of one or more harmonic peaks), which may be an issue particularly for hyperspectral imaging, which requires narrow band spectral images.

[0007] It is in this respect generally desirable to improve imaging devices that are based on such FPIs, and to improve methods for operating such imaging devices.

[0008] SUMMARY

[0009] In view of the above-mentioned problems and disadvantages, embodiments of the present disclosure aim to improve conventional imaging devices and methods for operating imaging devices, in particular, to improve them for use in hyperspectral imaging.

[0010] An objective is, for instance, to provide an imaging device with an FPI element that is tunable and can measure multiple narrow peaks of light from a wide range spectrum (i.e., over a large range of wavelengths). In particular, a wavelength range of interest is the range of silicon quantum efficiency, in particular, from 400 nm to 950 nm, which includes visible and near infrared electromagnetic radiation. Furthermore, the imaging device should be able to measure the peaks of light having a particular peak width of approximately 20 nm or even less.

[0011] This and other objectives are achieved by the embodiments of the disclosure as described in the enclosed independent claims. Advantageous implementations of the embodiments of the disclosure are further defined in the dependent claims.

[0012] A first aspect of the present disclosure provides an imaging device comprising an FPI element comprising two at least partially transmissive reflecting elements defining an interferometer gap, wherein a gap length of the interferometer gap is changeable in at least a first range, wherein the FPI element is configured to generate a plurality of transmission peaks when receiving light, and wherein a peak wavelength of each transmission peak is changeable by changing the gap length of the interferometer gap, and a plurality of optical filters, each optical filter being configured to pass light in a different wavelength range, wherein each wavelength range has a different mean wavelength, and wherein the wavelength ranges of the plurality of optical filters are selected such that each wavelength range comprises not more than one of the peak wavelengths at each gap length of the first range.

[0013] The imaging device may be, or may be incorporated into, an electronic device, wherein the electronic device may comprise circuitry, and wherein the electronic device may be a digital camera, a digital video recorder, a mobile phone, a smart phone, a gaming station, an augmented reality device, a virtual reality device, a tablet, a pad device, or the like.

[0014] The FPI element may generate several transmission peaks, wherein each transmission peak corresponds to either a main transmission peak or corresponds to one of one or more harmonic peaks. For a certain gap length of the interferometer gap, the FPI element may have a determined transmission spectrum, which includes multiple transmission peaks having different peak wavelengths. Moreover, the transmission spectrum is changeable by changing the gap length of the interferometer gap. In particular, the peak wavelength of each transmission peak is changeable by changing the gap length of the interferometer gap (dependency as explained above). For example, changing the gap length may shift the peak wavelength of each transmission peak to a larger wavelength or to a smaller wavelength.

[0015] The imaging device further comprises the plurality of optical filters, which may be based on optical bandpass filters. Each optical filter passes light in a determined wavelength range having a different mean wavelength, i.e., different than the mean wavelength of the wavelength ranges of the other optical filters. The mean wavelength of a wavelength range may be, for example, the centroid wavelength of that wavelength range.

[0016] The plurality of optical filters are, in particular, selected such that each wavelength range comprises not more than one of the peak wavelengths of the transmission peaks at each gap length of the first range. That is, each optical filter passes, at maximum, one of the peak wavelengths of the transmission peaks, regardless of the gap length of the interferometer gap, at least within the first range. For instance, each wavelength range may comprise exactly one peak wavelength at each gap length of the first range. Thus, an entire range of wavelengths, which is covered by the FPI element, may be divided by the optical filters into the plurality of different wavelength ranges. These wavelength ranges may be non-overlapping.

[0017] With this arrangement of the imaging device, the gap length of the interferometer gap can be changed, e.g. to scan the entire range of wavelengths that is covered by the FPI element, while never having two or more peak wavelengths of the transmission peaks (as generated by the FPI element) inside any of the wavelength ranges of the optical filters. Thus, a plurality of narrow peaks of light (i.e., the transmission peaks) can be measured over a large range of wavelengths, which makes the imaging device particularly useful for hyperspectral imaging. At each gap length, each transmission peak may correspond to one spectral image of a hyperspectral image. The imaging device may accordingly use advantageously the harmonic peaks generated by the FPI element for hyperspectral imaging.

[0018] The imaging device may further comprise circuitry. The circuitry may comprise hardware and software. The hardware may comprise analog or digital circuitry, or both analog and digital circuitry. In some embodiments, the circuitry may comprise one or more processors and a non-volatile memory connected to the one or more processors. The non-volatile memory may carry executable program code, which, when executed by the one or more processors, may cause the device to perform the operations or methods described herein. For instance, executing the program code by the one or more processors may cause the imaging device to change the interferometer gap over the first range and, for instance, to record a hyperspectral image based on spectral images generated for different transmission peaks and / or at different gap lengths of the first range.

[0019] In an implementation form of the first aspect, the wavelength ranges of the plurality of optical filters are selected such that each wavelength range comprises exactly one of the peak wavelengths at each gap length of the first range.

[0020] In a further implementation form of the first aspect, a wavelength spacing is provided between each pair of the wavelength ranges.

[0021] In a further implementation form of the first aspect, the wavelength ranges of the plurality of optical filters do not overlap each other. In a further implementation form of the first aspect, the wavelength ranges comprise two overlapping wavelength ranges forming an overlap region, wherein the overlap region is: less than 10% of each of the two overlapping wavelength ranges, preferably, less than 5% of each of the two overlapping wavelength ranges, most preferably, less than 3% of each of the two overlapping wavelength ranges.

[0022] That is, an overlapping region between at least one pair of wavelength ranges may exist, but each overlapping region is small compared to the wavelength ranges.

[0023] In a further implementation form of the first aspect, the imaging device further comprises an image sensor, wherein the plurality of optical filters are arranged between the image sensor and the FPI element, and wherein the image sensor is configured to generate a plurality of spectral images, wherein each spectral image is generated for a particular transmission peak generated by the FPI element and at a particular gap length of the first range, and wherein the imaging device is configured to generate a hyperspectral image based on a plurality of spectral images generated for different transmission peaks and / or at different gap lengths of the first range.

[0024] In particular, the imaging device may thus be used for providing a hyperspectral camera. While the gap length of the FPI element is changed, not more than one (for example, exactly one) transmission peak is located in each wavelength range of the optical filters at any time, i.e. at each gap length. Not more than one (for example, exactly one) transmission peak may pass through each one of the optical filters, to an adjacent area of the image sensor, at each gap length of the first range. Thus, a hyperspectral image may be generated, wherein the hyperspectral image may be resolved by the different transmission peaks at each of the gap lengths (each transmission peak being recorded in a different area of the image sensor) for each of the gap lengths. That is, the plurality of spectral images (e.g., tens or hundreds of such spectral images) may be obtained when changing the gap length. Each spectral image may thereby be obtained for the same field of view, and / or with a very narrow wavelength e.g. 20 nm. The imaging device may generate the hyperspectral image based on the plurality of spectral images. For example, the imaging device may store the plurality of spectral images to a hyperspectral cube (having an x-coordinate, ay-coordinate, and a spectral curve). Moreover, when there are two or more spectral images with same wavelength, i.e. related to the same peak wavelength of the transmission peak, those images may be averaged to produce one spectral image.

[0025] The image sensor may be any type of image sensor. For example, it may be based on a CMOS image sensor, which may have a silicon photodiode sensitivity range of approximately 400 nm to 1000 nm.

[0026] In a further implementation form of the first aspect, the imaging device further comprises an optical array configured to receive light and guide the light to the FPI element, wherein the FPI element is arranged between the optical array and the plurality of optical filters.

[0027] In a further implementation form of the first aspect, the optical array comprises one lens for each of the optical filters, wherein each lens is configured to guide the light to a different area of the FPI element arranged between the lens and one of the optical filters, and wherein each lens has the same field of view.

[0028] For example, the imaging device may comprise four optical bandpass filters. Furthermore, four (e.g., identical) lenses may be used (i.e., the number of lenses may be equal to the number of optical filers and thus the number of wavelength ranges). The lenses may all have the same field of view. The same field of view of the lenses allows recoding a hyperspectral image of a certain scene.

[0029] In a further implementation form of the first aspect, the plurality of optical filters are based on optical bandpass filters, wherein each optical bandpass filter is configured to pass one transmission peak generated by the FPI element.

[0030] In particular, each optical bandpass filter may pass, at maximum, the one transmission peak at each gap length of the first range. It is possible that at a particular gap length a particular optical bandpass filter does not pass any transmission peak.

[0031] In a further implementation form of the first aspect, the plurality of optical filters comprises four optical bandpass filters arranged in a two dimensional array of 2x2, and wherein each optical bandpass filter is arranged adjacent to a different area of the FPI element. In a further implementation form of the first aspect, the imaging device further comprises a Micro-Electro-Mechanical Systems (MEMS) actuator or a piezoelectric actuator, wherein the imaging device is further configured to change the gap length of the interferometer gap by moving one or both of the two at least partially transmissive reflecting elements using the MEMS actuator or the piezoelectric actuator.

[0032] In a further implementation form of the first aspect, the imaging device is further configured to guide each of the plurality of transmission peaks generated by the FPI element to the respective optical bandpass filter.

[0033] In a further implementation form of the first aspect, the gap length of the interferometer gap is changeable in a movement range of at least 1 lOOnm to 1450nm.

[0034] In a further implementation form of the first aspect, the wavelength ranges of the plurality of optical filters are further selected such that each wavelength range comprises not more than one of the peak wavelengths at the movement range of the interferometer gap.

[0035] In a further implementation form of the first aspect, at least one wavelength range of an optical filter is in the range of:

[0036] 402nm to 470nm, or

[0037] 480nm to 577nm, or

[0038] 590nm to 720nm, or

[0039] 730nm to 970nm.

[0040] In a further implementation form of the first aspect, the image sensor is a CMOS sensor.

[0041] A second aspect of the disclosure provides a method of operating an imaging device comprising generating, by an FPI element of the imaging device, a plurality of transmission peaks when receiving light, wherein the FPI element comprises two at least partially transmissive reflecting elements defining an interferometer gap, wherein a gap length of the interferometer gap is changeable in at least a first range, and wherein a peak wavelength of each transmission peak is changeable by changing the gap length of the interferometer gap, and passing light, by each optical filter from a plurality of optical filters of the imaging device, in a different wavelength range, wherein each wavelength range has a different mean wavelength, and wherein the wavelength ranges of the plurality of optical filters are selected such that each wavelength range comprises not more than one of the peak wavelengths at each gap length of the first range.

[0042] In an implementation form of the second aspect, the wavelength ranges of the plurality of optical filters are selected such that each wavelength range comprises exactly one of the peak wavelengths at each gap length of the first range.

[0043] In a further implementation form of the second aspect, a wavelength spacing is provided between each pair of the wavelength ranges.

[0044] In a further implementation form of the second aspect, the wavelength ranges of the plurality of optical filters do not overlap each other.

[0045] In a further implementation form of the second aspect, the wavelength ranges comprise two overlapping wavelength ranges forming an overlap region, wherein the overlap region is: less than 10% of each of the two overlapping wavelength ranges, preferably, less than 5% of each of the two overlapping wavelength ranges, most preferably, less than 3% of each of the two overlapping wavelength ranges.

[0046] In a further implementation form of the second aspect, the method further comprises generating, by an image sensor of the imaging device, a plurality of spectral images, wherein each spectral image is generated for a particular transmission peak generated by the FPI element and at a particular gap length of the first range, and wherein the plurality of optical filters are arranged between the image sensor and the FPI element, and generating, by the imaging device, a hyperspectral image based on a plurality of spectral images generated for different transmission peaks and / or at different gap lengths of the first range.

[0047] In a further implementation form of the second aspect, the method further comprises receiving light and guiding the light, by an optical array of the imaging device, to the FPI element, wherein the FPI element is arranged between the optical array and the plurality of optical filters. In a further implementation form of the second aspect, the optical array comprises one lens for each of the optical filters, wherein the method further comprises guiding the light to a different area of the FPI element arranged between the lens and one of the optical filters, and wherein each lens has the same field of view.

[0048] In a further implementation form of the second aspect, the plurality of optical filters are based on optical bandpass filters, wherein the method further comprises passing, by each optical bandpass filter, one transmission peak generated by the FPI element.

[0049] In a further implementation form of the second aspect, the plurality of optical filters comprises four optical bandpass filters arranged in a two dimensional array of 2x2, and wherein each optical bandpass filter is arranged adjacent to a different area of the FPI element.

[0050] In a further implementation form of the second aspect, the method further comprises changing, by a MEMS actuator or a piezoelectric actuator of the imaging device, the gap length of the interferometer gap by moving one or both of the two at least partially transmissive reflecting elements using the MEMS actuator or the piezoelectric actuator.

[0051] In a further implementation form of the second aspect, the method further comprises guiding each of the plurality of transmission peaks generated by the FPI element to the respective optical bandpass filter.

[0052] In a further implementation form of the second aspect, the gap length of the interferometer gap is changeable in a movement range of at least 1 lOOnm to 1450nm.

[0053] In a further implementation form of the second aspect, the wavelength ranges of the plurality of optical filters are further selected such that each wavelength range comprises not more than one of the peak wavelengths at the movement range of the interferometer gap.

[0054] In a further implementation form of the second aspect, at least one wavelength range of an optical filter is in the range of: 402nm to 470nm, or

[0055] 480nm to 577nm, or 590nm to 720nm, or 730nmto 970nm.

[0056] In a further implementation form of the second aspect, the image sensor is a CMOS sensor.

[0057] The method of the second aspect achieves the advantages and effects described for the imaging device of the first aspect.

[0058] It has to be noted that all devices, elements, units and means described in the present application could be implemented in the software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

[0059] BRIEF DESCRIPTION OF DRAWINGS

[0060] The above described aspects and implementation forms will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which

[0061] FIG. 1 depicts a schematic view of an imaging device, according to an embodiment of the disclosure;

[0062] FIG. 2 depicts a diagram illustrating an example of a tunable gap length range, and correspondingly changing FPI transmission peaks, and respective pass ranges (i.e., different wavelength ranges) of different optical filters; FIG. 3 depicts another schematic view of the imaging device further comprising an image sensor and an optical array;

[0063] FIG. 4 depicts a schematic of a cross section view of the imaging device;

[0064] FIG. 5 depicts a diagram illustrating a set of wavelength ranges of optical filters, and the FPI peak wavelength obtained at a gap length of 1300 nm;

[0065] FIG. 6 depicts a diagram illustrating exemplary wavelength ranges of four optical filters of the imaging device;

[0066] FIG. 7 depicts an example of a spectral response of an optical filter;

[0067] FIG. 8 depicts a schematic view of the imaging device according to an embodiment of the disclosure being exemplary used for a hyperspectral camera; and

[0068] FIG. 9 depicts a flowchart of a method of operating an imaging device, according to an embodiment of the disclosure.

[0069] DETAILED DESCRIPTION OF EMBODIMENTS

[0070] FIG. 1 depicts a schematic view of an imaging device 100, according to an embodiment of the disclosure.

[0071] The imaging device 100 comprises an FPI element 110, wherein the FPI element 110 comprises two at least partially transmissive reflecting elements 111, 112 defining an interferometer gap 113. In particular, the interferometer gap 113 is formed between the two elements 111 and 112.

[0072] Further, a gap length of the interferometer gap 113 is changeable, in at least a first range, and the FPI element 110 is configured to generate a plurality of transmission peaks when receiving light at each gap length. In order to change the gap length, the transmissive reflective element 111 and / or the transmissive reflective element 112 may be movable, in order to decrease or increase the gap length of the interferometer gap 113. Moreover, a peak wavelength of each transmission peak is changeable by changing the gap length of the interferometer gap 113. This is due to the dependency of each transmission peak, be it a main peak or a harmonic peak, on the gap length (see above). The peak wavelength of each transmission peak can be shifted over a certain wavelength range by changing the gap length over the first range.

[0073] The imaging device 100 further comprises a plurality of optical filters 121, 122, each optical filter 121, 122 being configured to pass light in a different wavelength range. For instance, each wavelength range may be a different mean wavelength. For instance, for two different wavelength ranges, the mean wavelength value of one wavelength range may be smaller than the mean wavelength value of the other wavelength range. Alternatively, or additionally, for two different wavelength ranges, a minimum value of one wavelength range may be smaller than the minimum value of the other wavelength range, and / or a maximum value of the one wavelength range may be smaller than a maximum value of the other wavelength range. Furthermore, the wavelength ranges of the plurality of optical filters 121, 122 are selected such that each wavelength range comprises not more than one (i.e., 0 or 1) of the peak wavelengths at each gap length of the first range.

[0074] The imaging device 100 may comprise processing circuitry (not shown in FIG. 1) configured to perform, conduct or initiate the various operations of the imaging device 100 described herein. The processing circuitry may comprise hardware and software. The hardware may comprise analog circuitry or digital circuitry, or both analog and digital circuitry. The digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable arrays (FPGAs), digital signal processors (DSPs), or multi-purpose processors. In one embodiment, the processing circuitry comprises one or more processors and a non-transitory memory connected to the one or more processors. The non-transitory memory may carry executable program code which, when executed by the one or more processors, causes the imaging device 100 to perform, conduct or initiate the operations or methods described herein.

[0075] FIG. 2 depicts a diagram illustrating an example of a tunable gap length range, and corresponding FPI element transmission peaks, and corresponding optical filter wavelength (pass) ranges. For example, the plurality of optical filters 121, 122 of the imaging device 100 may be based on optical bandpass filters, e.g., each optical filter 121, 122 may be a bandpass filter. Moreover, each optical filter 121, 122 may be configured to pass one of the transmission peaks (a main peak or a harmonic peak) generated by the FPI element 110. The optical filters 121, 122 may be arranged adjacent to the FPI element 110, in particular, they may be arranged after the FPI element 110 with respect to a direction of the incoming light received by and transmitted through the FPI element 110. For example, the FPI element 110 may be a single cavity FPI element 110, i.e., an FPI element 110 having one interferometer gap 113.

[0076] Examples of transmission peaks as a function of the gap length of the interferometer gap 113, and examples of wavelength ranges of four optical (bandpass) filter 121, 122 of a tunable imaging device 110 are shown in FIG. 2. The gap length can exemplarily be tuned from 1100 nm to 1450 nm. The optical filters 121, 122 (e.g., four optical filters) may be arranged as a 2x2 optical array and may pass four different wavelength ranges, respectively. The four optical filters are labelled “Filter 1” to “Filter4” in FIG 2. Each of the optical filters 121, 122 is related to one of four transmission peaks, i.e., each optical filter 121, 122 passes at maximum, the transmission peak it is related to, at each gap length. The transmission peak as a function of the gap length related to Filterl lies in a wavelength range of 402 nm to 470 nm of Filter 1, and is shown with the reference 201. The transmission peak as a function of the gap length related to Filter2 lies in a wavelength range of 480 nm to 577 nm of Filter 2, and is shown with the reference 202. The transmission peak as a function of the gap length related to Filter3 lies in a wavelength range of 590 nm to 720 nm of Filter3, and is shown with the reference 203. The transmission peak as a function of the gap length related to Filter4 lies in a wavelength range of 730 nm to 970 nm of Filter 4, and is shown with the reference 204.

[0077] As it can be derived from FIG. 2, at each gap length of the interferometer gap 113, there is at maximum one transmission peak in each wavelength range of each optical filter 121, 122. The gap length and the wavelength ranges are designed such that there is always zero (0) or one (1) transmission peak inside one wavelength range. The four transmission peaks shown in FIG. 2 move inside the wavelength ranges of the related optical filters 121, 122, when the gap length is changed. FIG. 3 depicts another schematic view of the imaging device 100 further comprising an image sensor 305 and an optical array 301, 302, 303, 304.

[0078] The imaging device 100 of FIG. 3 further comprises the image sensor 305. Moreover, the plurality of optical filters 121, 122, 321, 322 may be arranged between the image sensor 305 and the FPI element 110. In particular, each optical filter 121, 121, 321, 322 may be arranged between the FPI element 110 and a different area (i. e. , here four different areas) of the image sensor 305.

[0079] FIG. 3 shows a view from above of the imaging device 100. The imaging device 100 of FIG. 3 further comprises the optical array comprising lenses 301, 302, 303, 304 that may receive light and guide the light to the FPI element 110. Here, the imaging device 100 exemplarily comprises four lenses 301, 302, 303, 304. All four optical lenses 301, 302, 303, 304 may be arranged inside the same aperture 300. The FPI element 110 (not shown explicitly in FIG. 3) is arranged between the optical array 301, 302, 303, 304 and the plurality of optical filters 121, 122, 321, 322. Each lens 301, 302, 303, 304 may have the same field of view.

[0080] The image sensor 305 may be based on a monochrome CMOS image sensor arranged adjacent to the FPI element 110, and may receive only one narrow channel of light at one gap length to its four different areas (in this example).

[0081] The interferometer gap 113 of the FPI element 110 may be controlled by an actuator (e.g., a MEMS actuator or a piezoelectric actuator). Moreover, when the gap length of the interferometer gap 113 changes, the position of each of the transmission peaks changes, but each transmission peak stays inside the wavelength range of its related optical filter.

[0082] In this example, four spectral images may be captured at each gap length, i.e., one for each of the four transmission peaks. The spectral images for each transmission peak and each gap length may further be stored in a hyperspectral data cube. Moreover, when the whole distance of the designed gap length is scanned, the hyperspectral cube may be completed. Some transmission peak wavelengths may be measured more than once. In this case, the data of the spectral images can be averaged. For example, some wavelength ranges of optical filters 121, 122, 321, 322 may be scanned in two parts such that, for example, the end of the wavelength range is scanned with one transmission peak, and after that the beginning of the same wavelength range is scanned with another transmission peak. However, there is always at maximum one transmission peak in the wavelength range of the optical filter 121, 122, 321, 322 at each gap length of the first range.

[0083] The imaging device 100 may be used to scan and record full visible and very near infrared (VNIR) hyperspectral image from 410 nm to 960 nm with one single FPI element 110, and may be suitable for a smartphone.

[0084] The imaging device 100 may enable obtaining a spectral resolution of about 20nm. For instance, the transmission peak width may be tuned by reflection values of the FPI reflecting element 110. When using the imaging device 100, there might be no need for heavy system level calibration and power hungry after processing. However, a basic calibration that is typical for an FPI element 110 and image sensor 305 may be needed, as it is generally known.

[0085] Reference is now made to FIG. 4 which depicts a schematic of a cross section view of the imaging device 100 (not in scale). The vertical cross-section view depicted in FIG. 4 is exemplary obtained from the cross-section view line 306 shown in FIG. 3.

[0086] The imaging device 100 may comprise four independent optical lenses 301, 302, 303, 304 that see the same field of view. The imaging device 100 may further comprise four custom optical filters 121, 122, 321, 322 arranged adjacent to the FPI element 110, and for filtering out, for each sensor area (or sensor region), the unwanted transmission peak wavelengths of the plurality of transmission peaks of light that are typical to FPI elements. Each sensor area may thus record one transmission peak that can be shifted in the wavelength range of the optical filter it relates to.

[0087] The wavelength ranges of the plurality of optical filters 121, 122, 321, 322 are selected such that each wavelength range comprises not more than one of the peak wavelengths at the movement range of the interferometer gap 113.

[0088] The imaging system 100 comprises exemplarily a 2x2 array of input optics (lenses) that have relatively large field of view, but are capable of guiding light to hit the FPI element 11 in, for instance, an almost perpendicular angle. The four optical lenses 301, 302, 303, 304 may be designed to see the same (or at least a similar) field of view regarding a scene. The light may be guided to the FPI element 110 by the optical lenses 301, 302, 303, 304. All four optical lenses 301, 302, 303, 304 may be arranged inside the same aperture 300 (see FIG. 3). The light may thus get a similar transmission in all four paths through the FPI element 110 (each path being associated with one of the lenses 301, 302, 303, 304). The optical filters 121, 122, 321, 322 are arranged one after each of the four paths through the FPI element 110, and are respectively configured to filter out the unwanted peaks, particularly, different unwanted peaks for each path. Finally, in the bottom is an image sensor 305, e.g. a monochrome CMOS image sensor that may record light intensity. For instance, the image sensor 305 may thus produce spectral images (one per each light path) for each gap length of the interferometer gap 113. As a result, when scanning through the whole gap length range (in the at least a first range) of the interferometer gap 113, a hyperspectral data cube may be generated and stored, wherein the hyperspectral data cube in this example comprises four spectral images per gap length.

[0089] Reference is now made to FIG. 5, which depicts a diagram illustrating a set of wavelength ranges of optical filters 121, 122, 321, 322, and the exemplary transmission peak wavelengths obtained at a gap length of 1300 nm.

[0090] In particular, the gap length is assumed to be 1300nm, and the simulation results for four optical filters 121, 122, 321, 322, having four different wavelength ranges, and four transmission peak wavelengths produced by the FPI element 110 are shown.

[0091] For example, the wavelength range 511 of the optical filter 121 is selected such that the wavelength range 511 comprises exactly one first transmission peak (wavelength) 501, at the gap length of 1300 nm. Further, the wavelength range 512 of the optical filter 122 is selected such that the wavelength range 512 comprises exactly one second transmission peak (wavelength) 502, at gap length of 1300 nm. In addition, the wavelength range 513 of the optical filter 321 is selected such that the wavelength range 513 comprises exactly one third transmission peak (wavelength) 503, at the gap length of 1300 nm. Moreover, the wavelength range 514 of the optical filter 322 is selected such that the wavelength range 514 comprises exactly one fourth transmission peak (wavelength) 504, at the gap length of 1300 nm.

[0092] FIG. 6 depicts a diagram illustrating a selection of exemplary wavelength ranges 511, 512, 513, 514 of four optical filters 121, 122, 321, 322 of the imaging device 100.

[0093] As it can be derived from FIG. 6, a wavelength spacing may be provided between each pair of the wavelength ranges 511, 512, 513, 514.

[0094] Moreover, the wavelength ranges 511, 512, 513, 514 of the plurality of optical filters 121, 122, 321, 322 may be selected such that they do not overlap each other.

[0095] Reference is now made to FIG. 7, which depicts an example of a spectral response 511, 512, 513, 514 of the optical filter 121, 122, 321, 322. The spectral response may define the wavelength range of the optical filter 121, 122, 321, 322 (pass range), which may be in the order of 100-150nm.

[0096] FIG. 8 depicts a schematic view of the imaging device 100 being exemplary used for a hyperspectral camera.

[0097] The imaging deice 100 comprise the optical array 301, 302, 303, 304 configured to receive light and guide the light to the FPI element 110.

[0098] The FPI element 110 of the imaging device 100 may be arranged between the optical array 301, 302, 303, 304 and the plurality of optical filters 121, 122, 321, 322.

[0099] The optical array 301, 302, 303, 304 may comprise one lens for each of the optical filters 121, 122, 321, 322. Each lens may be configured to guide the light to a different area of the FPI element 110 arranged between the lens and one of the optical filters 121, 122, 321, 322.

[0100] Moreover, all of the lenses may have the same field of view. The image sensor 305 of the imaging device 100 may generate a plurality of spectral images. For example, each spectral image may be generated for a particular transmission peak generated by the FPI element 110 and at a particular gap length 113.

[0101] The imaging device 100 may further generate a hyperspectral image based on a plurality of spectral images generated for different transmission peaks and / or at different gap lengths 113. The image sensor 305 may be based on a monochrome CMOS image sensor arranged below the FPI element and may receive only one narrow channel of light at one gap length to its four different areas. For example, when the gap length changes, and when the scanning of the interferometer gap is performed, at each gap length of the first range. A plurality of spectral images may be obtained. Each spectral images may be obtained for the same field of view.

[0102] Moreover, the imaging device 100 may further combine all of the spectral images and may further obtain one hyperspectral data cube. Hence, the imaging device 100 may be able to generate a hyperspectral image based on the spectral images.

[0103] FIG. 9 shows a method 900 of operating an imaging device 100, according to an embodiment of the disclosure.

[0104] The method 900 comprises a step S901 of generating, by an FPI element 110 of the imaging device 100, a plurality of transmission peaks when receiving light, wherein the FPI element 110 comprises two at least partially transmissive reflecting elements 111, 112 defining an interferometer gap 113, wherein a gap length of the interferometer gap 113 is changeable in at least a first range, and wherein a peak wavelength of each transmission peak is changeable by changing the gap length of the interferometer gap 113.

[0105] The method 900 further comprises a step S902 of passing light, by each optical filter 121, 122 from a plurality of optical filters 121, 122 of the imaging device 100, in a different wavelength range, wherein each wavelength range has a different mean wavelength, and wherein the wavelength ranges of the plurality of optical filters 121, 122 are selected such that each wavelength range comprises not more than one of the peak wavelengths at each gap length of the first range. The present disclosure has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed disclosure , from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.

Claims

Claims1. An imaging device (100) comprising: a Fabry -Perot Interferometer, FPI, element (110) comprising two at least partially transmissive reflecting elements (111, 112) defining an interferometer gap (113), wherein a gap length of the interferometer gap (113) is changeable in at least a first range, wherein the FPI element (110) is configured to generate a plurality of transmission peaks when receiving light, and wherein a peak wavelength of each transmission peak is changeable by changing the gap length of the interferometer gap (113); and a plurality of optical filters (121, 122), each optical filter (121, 122) being configured to pass light in a different wavelength range, wherein each wavelength range has a different mean wavelength; and wherein the wavelength ranges of the plurality of optical filters (121, 122) are selected such that each wavelength range comprises not more than one of the peak wavelengths at each gap length of the first range.

2. The imaging device (100) according to claim 1, wherein: the wavelength ranges of the plurality of optical filters (121, 122) are selected such that each wavelength range comprises exactly one of the peak wavelengths at each gap length of the first range.

3. The imaging device (100) according to claim 1 or 2, wherein: a wavelength spacing is provided between each pair of the wavelength ranges.

4. The imaging device (100) according to one of the claims 1 to 3, wherein: the wavelength ranges of the plurality of optical filters (121, 122, 321, 322) do not overlap each other.

5. The imaging device (100) according to claim 1 or 2, wherein: the wavelength ranges comprise two overlapping wavelength ranges forming an overlap region, wherein the overlap region is: less than 10% of each of the two overlapping wavelength ranges; preferably, less than 5% of each of the two overlapping wavelength ranges;most preferably, less than 3% of each of the two overlapping wavelength ranges.

6. The imaging device (100) according to one of the claims 1 to 5, further comprising: an image sensor (305), wherein the plurality of optical filters (121, 122, 321, 322) are arranged between the image sensor (305) and the FPI element (110), and wherein the image sensor (305) is configured to generate a plurality of spectral images, wherein each spectral image is generated for a particular transmission peak generated by the FPI element (110) and at a particular gap length (113) of the first range, and wherein the imaging device (100) is configured to generate a hyperspectral image based on a plurality of spectral images generated for different transmission peaks and / or at different gap lengths (113) of the first range.

7. The imaging device (100) according to one of the claims 1 to 6, further comprising: an optical array (301, 302, 303, 304) configured to receive light and guide the light to the FPI element (110), wherein the FPI element (110) is arranged between the optical array (301, 302, 303, 304) and the plurality of optical filters (121, 122, 321, 322).

8. The imaging device (100) according to claim 7, wherein: the optical array (301, 302, 303, 304) comprises one lens for each of the optical filters (121, 122, 321, 322), wherein each lens is configured to guide the light to a different area of the FPI element (110) arranged between the lens and one of the optical filters (121, 122, 321, 322), and wherein each lens has the same field of view.

9. The imaging device (100) according to one of the claims 1 to 8, wherein: the plurality of optical filters (121, 122, 321, 322) are based on optical bandpass filters, wherein each optical bandpass filter is configured to pass one transmission peak generated by the FPI element (110).

10. The imaging device (100) according to one of the claims 1 to 9, wherein:the plurality of optical filters (121, 122, 321, 322) comprises four optical bandpass filters arranged in a two dimensional array of 2x2, and wherein each optical bandpass filter is arranged adjacent to a different area of the FPI element (110).

11. The imaging device (100) according to one of the claims 1 to 10, further comprising: a Micro-Electro-Mechanical Systems, MEMS, actuator or a piezoelectric actuator, wherein the imaging device (100) is further configured to: change the gap length of the interferometer gap by moving one or both of the two at least partially transmissive reflecting elements using the MEMS actuator or the piezoelectric actuator.

12. The imaging device (100) according to one of the claims 9 to 11, further configured to: guide each of the plurality of transmission peaks generated by the FPI element (110) to the respective optical bandpass filter.

13. The imaging device (100) according to one of the claims 1 to 12, wherein: the gap length of the interferometer gap (113) is changeable in a movement range of at least 1 lOOnm to 1450nm.

14. The imaging device (100) according to claim 13, wherein: the wavelength ranges of the plurality of optical filters (121, 122, 321, 322) are further selected such that each wavelength range comprises not more than one of the peak wavelengths at the movement range of the interferometer gap (113).

15. The imaging device (100) according to one of the claims 1 to 14, wherein: at least one wavelength range of an optical filter (121, 122, 321, 322) is in the range of:402nm to 470nm, or480nm to 577nm, or590nm to 720nm, or730nmto 970nm.

16. The imaging device (100) according to one of the claims 6 to 15, wherein: the image sensor (305) is a Complementary metal-oxide-semiconductor, CMOS, sensor.

17. A method (900) of operating an imaging device (100) comprising: generating (S901), by a Fabry-Perot Interferometer, FPI, element (110) of the imaging device (100), a plurality of transmission peaks when receiving light, wherein the FPI element (110) comprises two at least partially transmissive reflecting elements (111, 112) defining an interferometer gap (113), wherein a gap length of the interferometer gap (113) is changeable in at least a first range, and wherein a peak wavelength of each transmission peak is changeable by changing the gap length of the interferometer gap (113); and passing (S902) light, by each optical filter (121, 122) from a plurality of optical filters (121, 122) of the imaging device (100), in a different wavelength range, wherein each wavelength range has a different mean wavelength, and wherein the wavelength ranges of the plurality of optical filters (121, 122) are selected such that each wavelength range comprises not more than one of the peak wavelengths at each gap length of the first range.

Images