Multi-spectral imager having an expanded spectral region

Abstract

Disclosed is a multispectral imager designed for analyzing a spectral region of interest, comprising an image sensor (100) formed of an array of macropixels and including first and second photosensitive pixels (115) dedicated to first and second spectral bands, respectively; and a filtering structure (150) including first and second interference filters (160) superimposed on the first and second photosensitive pixels (160), respectively, and arranged to transmit first and second electromagnetic radiation belonging to the first and second spectral bands, respectively, wherein a wavelength half that of the second electromagnetic radiation is located in the spectral region of interest; and a filtering layer (170) superimposed on the second photosensitive pixels (115) and configured to block the passage of a third electromagnetic radiation having a wavelength half that of the second electromagnetic radiation.

Description

Technical Field

[0001] The present invention relates to a multispectral imager capable of instantaneously obtaining a two-dimensional image in which the spectrum is decomposed at each point.

Background Art

[0002] Many applications in astronomy, mineralogy, chemistry, and agriculture require the acquisition of spectral images of an object or scene, that is, images spectrally limited to specific bands of the electromagnetic spectrum in the visible, infrared, or ultraviolet range.

[0003] Multispectral or hyperspectral imagers make it possible to obtain such images consisting of two-dimensional images in which the spectrum is extracted at each point. The term hyperspectral imaging has been conventionally used when the extracted spectrum is highly resolved, that is, formed by a large number (typically more than 100) of relatively narrow spectral bands (typically 5 to 15 nm), and multispectral imaging when the spectrum is relatively broad (typically 15 to 40 nm) and formed by fewer spectral bands (typically 4 to 20).

[0004] A first method for obtaining a multispectral image is to use a scanner equipped with a one-dimensional sensor that scans the scene to be analyzed, called a "push broom scanner".

[0005] A second method is to employ a two-dimensional array of basic photosensitive sensors, a so-called Focal Plane Array (FPA), for performing instantaneous multispectral imaging, that is, "snapshot imaging", which is a method for capturing an image during a single integration period of a sensor array.

[0006] The present invention is in a situation of acquiring a multi-spectral image according to this second method, and US Patent Application Publication No. 2019 / 0145823 discloses a multi-spectral imager based on an image sensor comprising a two-dimensional array formed by an array of photosensitive pixels and a set of basic filters each associated with one of the photosensitive pixels.

[0007] The photosensitive pixels are each specialized for a given spectral band, that is, they are intended to receive and measure radiation of wavelengths included in this band, and a set of photosensitive pixels dedicated to a single spectral band forms a sub-image, and each point of the sub-image belongs to one of a plurality of macro-pixels respectively formed by a group of pixels and the associated filters.

[0008] Structurally, each basic filter is superimposed on the basic filter of the photosensitive pixel to which it is associated, and defines its spectral band by filtering the incident electromagnetic radiation.

[0009] Here, the basic filters are each constituted by Fabry-Perot interference filters.

[0010] Devices such as the device of US Patent Application Publication No. 2019 / 0145823 are designed to analyze only a relatively small range of spectral regions with a width of about 300 nm so that one spectral band does not contaminate another spectral band.

[0011] In practice, for example, in order to study the spectral region of 400 to 1000 nm (visible and near-infrared regions), there are, for example, two different multi-spectral imagers dedicated to the spectral regions of 400 to 700 nm and 700 to 1000 nm respectively.

[0012] It is desirable that a single device be able to perform multi-spectral imaging for an extended spectral region.

[0013] Japanese Patent Application Publication No. 2017 / 0163901 (A1) relates to an optical system capable of forming a plurality of small-sized images each forming a copy of an image of a scene to be analyzed, wherein each thumbnail image is detected by a separate part of a color image capture element, and a multispectral imaging system disposed on a combination between a narrowband filter and a color filter incorporated in the image capture element.

[0014] U.S. Patent Application Publication No. 2015 / 0138560 (A1) and German Patent Application Publication No. 112013-002-560 (T5) relate to a spectroscopic sensor including two opposing mirrors forming a laser cavity. SUMMARY OF THE INVENTION

[0015] An object of the present invention is to increase the range of spectral regions analyzable by a single multispectral imager.

[0016] More specifically, the present invention is a multispectral imager designed to analyze a spectral region of interest including a first spectral band and a second spectral band different from the first spectral band, the multispectral imager comprising: an image sensor formed of an array (110) of macro pixels each including a first photosensitive pixel and a second photosensitive pixel dedicated to the first spectral band and the second spectral band different from the first spectral band, respectively; a filtering structure including a first interference filter and a second interference filter disposed so as to be respectively superposed on the first photosensitive pixel and the second photosensitive pixel and transmit a first electromagnetic radiation belonging to the first spectral band and a second electromagnetic radiation belonging to the second spectral band, respectively; wherein a wavelength half of the wavelength of the second electromagnetic radiation is located in the spectral region of interest; and further comprising a filtering layer configured to be superposed on the second photosensitive pixel and block the passage of a third electromagnetic radiation having a wavelength half of the wavelength of the second electromagnetic radiation.

[0017] An essential advantage of the multispectral imager according to the present invention is the ability to analyze an extended spectral region without being contaminated by the secondary resonance of the interference filter.

[0018] Furthermore, such a multispectral imager does not require a specific image sensor and can thus be based on standard commercially available image sensors, facilitating development and significantly reducing the cost of this imager.

[0019] A multispectral imager having such a structure, involving operations based on the use of macro pixels and a filtering layer of the pixel structure, has other advantageous features.

[0020] It enables excellent spatial resolution because it uses the entire photosensitive surface of the sensor. Furthermore, since such a structure is in close proximity between the image sensor, the interference filtering structure, and the filtering layer, it ensures that there are few problems related to the respective field of view angles of each pixel of the scene being captured.

[0021] The multispectral imager according to the present invention may have the following characteristics. - The wavelength of half of the wavelength of the second electromagnetic radiation may be located within the first spectral band. - The filtering layer may form a high-pass filter configured to block the first electromagnetic radiation and transmit the second electromagnetic radiation. - The filtering layer may be structured so as not to overlap with the first photosensitive pixels. - The filtering layer may be composed of a layer of red organic material. - The filtering layer may be formed by a mosaic of basic filters and may be further superimposed on the first photosensitive pixels and configured to transmit the first electromagnetic radiation to the first photosensitive pixels. - The filtering layer may include an array of organic filters configured to transmit spectral bands in the visible spectral region respectively. - The organic filters may be configured to transmit blue, green, and red emission bands respectively, and - The array of organic filters may be a Bayer array.

Brief Description of Drawings

[0022] The present invention will be better understood and other advantages will become apparent by reading the detailed description of embodiments shown by the accompanying drawings as non-limiting examples.

Figure 1A

Figure 1B

Figure 1C

Figure 1D

Figure 2

Figure 3

Figure 4

Figure 5

[0023] FIGS. 2 (A, C, and D) and FIGS. 3 (A, B, and C) show the spectral responses of the optical filters, with the transmittance on the Y-axis and the wavelength on the X-axis represented in nanometers.

Modes for Carrying Out the Invention

[0024] [Description of the First Specific Embodiment According to the Present Invention] FIG. 1A shows a cross-sectional view of the structure of a multi-spectral imager having 16 channels according to the present invention, including a sensor substrate 105, and an array of photosensitive pixels 115 dedicated to each of 16 spectral bands of interest centered on wavelengths λ1 to λ 16 respectively, an image sensor 100 including an array of photosensitive pixels 115 dedicated to each of 16 spectral bands of interest centered on wavelengths λ1 to λ

[0025] To specialize the sensitivity of the photosensitive pixels to the incident radiation, specializing each pixel to a given spectral band is a combination of an array of interference filters and a filtering layer.

[0026] The plurality of macro-pixels 110 forming the array of macro-pixels shown in FIG. 1B are each formed of a group of pixels dedicated to one of the spectral bands of interest and an associated filter.

[0027] FIG. 1C shows, in a plan view of one of these macro-pixels 110, that each is formed from a 4×4 array of photosensitive pixels 115, and the photosensitive pixels are centered on the center wavelengths λ1 to λ 16 of 16 spectral bands that are each dedicated, i.e., specified by 430, 468, 506, 544, 582, 620, 658, 696, 734, 772, 810, 848, 886, 924, 962 and 1000 nm.

[0028] The filtering layer 170 may take a continuous form or may be composed of discrete elements such as a mosaic of basic filters, and may or may not have a homogeneous composition and properties throughout its extent. Here, as shown in FIG. 2B representing the filtering layer 170 on the scale of the macro-pixel 110, for the high wavelengths λ1 to λ 16It is uniformly formed from a red organic resin that is superimposed on a photosensitive pixel dedicated to a spectral band centered thereon and is structured so as not to exist in pixels dedicated to spectral bands centered on low wavelengths λ1 to λ5.

[0029] Here, the filtering layer 170 forms a high-pass organic filter having a cut-off wavelength located at about 590 nm as shown in FIG. 2C). However, any type of filter such as an absorption, reflection, interference or plasmonic filter can be used, provided that it has an appropriate spectral response (here a high-pass) and can be structured on the scale of the photosensitive pixels.

[0030] When a filter is said to be superimposed on a photosensitive pixel, it should be understood here that this filter is shifted in a direction perpendicular to its formation surface from the pixel and is arranged to block the incident radiation in order to block or transmit the incident radiation on that pixel.

[0031] In this specification, the terms "block" and "transmit" should not be understood in the sense of complete block and complete transmission. For example, it must be understood according to the use in the field of optical filters, such as by blocking at least 80% and transmitting at least 30% of the electromagnetic radiation, which corresponds to the examples considered in this specification.

[0032] Therefore, when a filtering layer superimposed on a photosensitive pixel is said to be configured to transmit radiation to that photosensitive pixel, it will be understood that such a filtering layer is transparent to that radiation (transmitting at least 30% of that radiation) and enables that radiation to pass through the filtering layer and irradiate that photosensitive pixel.

[0033] This does not prevent the first element forming the first part of the filtering layer from being able to transmit the first radiation of a given wavelength, nor does it prevent the second element forming the second part of the filtering layer from being able to block the second radiation of that given wavelength.

[0034] The imager may further include a microlens array 120 configured to reproduce the arrangement of the photosensitive pixels so as to correspond to, and only to, one of the lenses at each pixel, and to concentrate the incident radiation on the photosensitive surface of the photosensitive pixels, thereby enhancing the sensitivity of the imager.

[0035] While limiting the phenomenon of crosstalk (where the radiation intended to be received by a given pixel is contaminated by the radiation intended to be received by an adjacent pixel), even at a fairly large angle of incidence (e.g., greater than 30°), the elements of this imager require proximity between the image sensor, the interference filtering structure, and the filtering layer such that the path of the incident radiation passes through the photosensitive pixel and the interference filter superimposed thereon, respectively.

[0036] Such proximity can be obtained by direct contact between the elements (160, 170) formed on the sensor substrate 105 and the elements (115, 120) formed on the filter substrate 155, or optionally via a thin protective layer, and then by attaching the substrates (105, 155) to each other by means of an adhesive strip 157 disposed around these substrates (105, 155).

[0037] The elements 160, 170, 115, and 120 are not separated by the thickness of one or two of these substrates and are interposed between the two substrates 105 and 155 to maintain the required proximity.

[0038] In practice, the imager shown in Figure 1A is associated with an optical focusing system (not shown) that includes the photosensitive pixels 115, the interference filter 160, and one or several lenses located at a distance from their substrates 155.

[0039] The interference filter can be, for example, Fabry - Perot filters formed by a resonant cavity configured between two mirrors.

[0040] Such a filter transmits electromagnetic radiation when the electromagnetic radiation enters a resonant state within the cavity, that is, when its wavelength satisfies the condition of belonging to a spectral band centered on a given wavelength defined by the following formula [1]:

[0041]

Number

[0042] where k is an integer greater than or equal to 1 that defines the resonance order being considered. When the condition is satisfied, that is, when the wavelength belongs to a spectral band centered on a given wavelength defined by the following formula [1], the electromagnetic radiation is transmitted. Here, in the formula, k is an integer of 1 or more that defines the resonance order being considered,

[0043]

Number

[0044] is the refractive index of the cavity with respect to the wavelength λ k and e is the physical thickness of the cavity.

[0045] The width of the spectral band transmitted by such a filter is characterized by the height at the intermediate height of the resonance peak, which can range from a few nanometers to dozens of nanometers and can depend on the structure and materials used for the filter.

[0046] When k = 1, it is a first - order resonance, and the nominal transmission band of the filter is a band centered on λ1. However, other resonance orders that satisfy the transmission condition of formula [1] are associated with integers k greater than 1, such as the second - order when k is equal to 2, the third - order when k is equal to 3, and so on.

[0047] By allowing the transmission of radiation of the corresponding wavelength, the secondary resonance order effectively limits the spectral range that a given multispectral imager can actually analyze.

[0048] In fact, an interference filter designed to transmit the first radiation as a useful signal by primary resonance will also transmit a second radiation of a wavelength approximately half that of the first radiation (within the scattering index of refraction) by secondary resonance, contaminating the measurement of the useful signal to the point of rendering the measurement of the useful signal unusable.

[0049] Therefore, in the spectral region analyzed by the multispectral imager, to prevent the signal from being contaminated by the presence of wavelengths approximately half as short as other wavelengths in the same region, the use of an overall high-pass filter covering all of the photosensitive pixels, or in the case of CMOS detection technology, the properties of the material used to detect radiation, such as silicon, limit the range of the analyzable spectral region to exclude wavelengths approximately half as short as other wavelengths in the same region.

[0050] In this way, it is prevented that half of the wavelength of the electromagnetic radiation located in the high spectral band (with respect to wavelength) of the spectral region to be analyzed is located in the low spectral band (with respect to wavelength) of the same spectral region.

[0051] In fact, blocking the radiation transmitted by the secondary resonance of a filter dedicated to the high spectral band on an overall scale for the entire multispectral imager is equivalent to blocking the low spectral band that can be analyzed by the same multispectral imager.

[0052] Figure 2 shows a graph of the spectral responses of 16 interference filters associated with 16 photosensitive pixels in a spectral region ranging from 400 to 1100 nm. The transmission peaks have a width at half height between 20 and 50 nm and have transmission peaks due to primary and secondary resonances.

[0053] In this example, in the absence of the filtering layer 170, radiation with wavelengths less than about 550 nm is transmitted to the photosensitive pixels dedicated to high wavelengths (i.e., relatively long wavelengths) by the secondary resonance of the associated interference filter, as shown by the resonance peaks of the box where the primary resonance peak at low wavelengths (i.e., relatively short wavelengths) coincides with the secondary resonance peaks of the interference filter having nominal transmissions corresponding to high wavelengths.

[0054] In the present invention, the filtering layer 170 enables radiation in the low spectral band (with respect to wavelength) to pass through the photosensitive pixels dedicated to these low spectral bands, while solving the problem of contaminating useful signals in the high spectral band (with respect to wavelength) by blocking radiation of shorter wavelengths, not overall for all photosensitive pixels, but particularly in the photosensitive pixels dedicated to these high spectral bands.

[0055] Specifically, in this embodiment, the filtering layer 170 is individually structured in the photosensitive pixels so as to overlap only the pixels dedicated to the high spectral band and not exist at the level of the pixels dedicated to the low spectral band.

[0056] In fact, the filtering layer 170 has an array structure, and each of its elements reproduces the structure of the macro pixel 110 in terms of its geometric shape and dimensions. The structure formed in this example is an array of 4×4 photosensitive pixels 115.

[0057] Therefore, the filtering layer 170 here has wavelengths λ6 to λ respectively 16It is formed by elements respectively superimposed on the dedicated photosensitive pixels 115, each element corresponding to a photosensitive pixel and vice versa.

[0058] In this particular embodiment, these elements form a continuous filtering layer 170 on the scale of the macro pixel 110, superimposed on only the first part of one macro pixel 110 so as not to block the incident radiation passing through the second part of the same macro pixel, as shown in B) of FIG. 2.

[0059] Therefore, the multispectral imager according to the present invention can analyze an expanded spectral region, for example, ranging from 400 to 1000 nm, over a wider range than that of a conventional multispectral imager without suffering from the above-described contamination phenomenon.

[0060] FIG. 2 shows the spectral response of the combination according to the present invention between the interference filter 160 and the filtering layer 170 consisting of a high-pass filter shown in B), designed to block the radiation corresponding to the second resonance of 11 interference filters λ1 to λ 16 whose wavelength is shorter than the cut-off wavelength of the filtering layer, in D).

[0061] It can be seen that the filtering layer, according to the principle shown in FIG. 1D, covers a wide spectral region and enables the elimination or very significant reduction of the transmission of radiation by the secondary resonance peaks so as to obtain a spectral image having 16 bands that do not suffer from any or many contaminations caused by these secondary resonance peaks.

[0062] The solid arrows indicate the transmission peaks of the 11 dedicated photosensitive pixels, that is, the pixels on which the filtering layer 170 is superimposed, from wavelength λ6 to λ 16 FIG. 1D summarizes the general principle of the present invention. That is, the first interference filter IF1 superimposed on the first photosensitive pixel PP1 has a wavelength λ

[0063] FIG. 1D summarizes the general principle of the present invention. That is, the first interference filter IF1 superimposed on the first photosensitive pixel PP1 has a wavelength λ IRadiation Iλ having a wavelength belonging to a first spectral band centered on I is transmitted, and the second interference filter IF2 superposed on the second photosensitive pixel PP2 transmits radiation Iλ of a second wavelength belonging to a second spectral band centered on the wavelength λ II and contamination radiation Iλ having a third wavelength approximately half of λ II due to the secondary resonance of the second interference filter IF2. The filtering layer FL transmits Iλ II to PP1, transmits Iλ II to PP2, and is configured to block the contamination radiation Iλ I at PP2. II II -P. II

[0064] Actually, it can be considered that the filtering layer FL also blocks radiation having a wavelength half of the wavelength of λ II at PP2.

[0065] The third contamination wavelength Iλ II -P of the radiation may be very close to or equal to λ1, and in particular, since it is within the spectral band of interest centered on λ1 corresponding to the primary resonance peak of IF1, it may be transmitted by the first interference filter IF1.

[0066] The two spectral bands of interest are distinct, i.e., centered on different wavelengths, and preferably do not overlap.

[0067] A first modification of this principle shown in FIG. 1D consists of structuring the filtering layer FL so that it is superposed only on the second photosensitive pixel PP2.

[0068] In this specification, the expression "approximately" means that a 10% difference is allowed between the values of the magnitudes being considered, and is used in particular to take into account the index despersion when positioning the resonance peak.

[0069] Applying this principle to the first specific embodiment in the present invention, λ I and λ II respectively correspond to, for example, λ1 and λ 12 ; PP1 and PP2 correspond to photosensitive pixels 115 dedicated to spectral bands centered on these wavelengths; IF1 and IF2 correspond to interference filters 160 superimposed on PP1 and PP2 respectively; Iλ I and Iλ II correspond to the radiation transmitted by IF1 and IF2 through primary resonance; Iλ II -P corresponds to the radiation transmitted by IF2 through secondary resonance; and the filtering layer FL corresponds to the filtering layer 170.

[0070] Applying the general principle of the present invention to this first embodiment and combining an array of interference filters with a structured high-pass filter on the scale of photosensitive pixels enables the analysis of a sufficiently broad spectral region including a first spectral band and a second spectral band having a wavelength approximately half that of the wavelength of the first spectral band without being subject to contamination by secondary resonance.

[0071] The applications of the present invention are not limited to the Fabry-Perot filters cited here as examples, but rather extend to any type of filter that generates interference of several orders.

[0072] This first embodiment relies on the use of a filtering layer 170 that forms a locally structured high-pass filter so as to be superimposed only on photosensitive pixels dedicated to high spectral bands in order to block the radiation transmitted by the secondary resonance and higher-order resonances of the associated interference filters. However, the present invention is not limited to this configuration, and as shown in the following embodiments, other types of filters such as band-pass filters can be used regardless of whether they are superimposed on a set of photosensitive pixels defining macro pixels.

[0073] [Description of the Second Specific Embodiment According to the Present Invention] The second embodiment of the present invention has the same structure as that of the first embodiment except for the interference filter and the filtering layer, and consists of a 5-channel spectral imager including photosensitive pixels dedicated to five spectral bands centered at wavelengths λ1 to λ5, 450, 550, 650, 865, and 945 nm, respectively. The pixels arranged within the macro pixel 110 are each composed of 16 photosensitive pixels as shown in C) of FIG. 4.

[0074] The first three wavelengths respectively correspond to three interference filters B, G, and R that transmit blue, green, and red radiations in the visible region, and the last two wavelengths respectively correspond to two interference filters NIR1 and NIR2 in the near-infrared region.

[0075] FIG. 3 shows in A) the spectral responses of the five interference filters having five transmission peaks corresponding to wavelengths λ1 to λ5 of the primary resonances of each of the five filters, respectively, and two transmission peaks at 444 nm and 483 nm corresponding to the secondary resonances of the filters NIR1 and NIR2, respectively.

[0076] These last two transmission peaks are sources of contamination as described in the first embodiment, and are removed or significantly reduced by using a filtering layer 170 formed of a conventional Bayer array composed of organic filters Grg, B, Grg.G, and Org.R that transmit the blue, green, and red radiation bands in the visible region, respectively, as shown in B) of FIG. 3.

[0077] FIG. 4 shows in A) the arrangement of the interference filters according to the geometric shape of the macro pixel 110, and each filter is superimposed on one and only one of the photosensitive pixels of a given macro pixel having the primary and secondary resonance peaks of these filters.

[0078] The organic filters are arranged according to the geometric shape of the macro pixel 110, as shown in B) of FIG. 4. Each filter is superimposed on only one of the photosensitive pixels. As a result, the filters NIR1 and NN2 are superimposed on the Org.G and Org.R filters, respectively, so as to block the peaks at 444 nm and 483 nm corresponding to the second resonance.

[0079] More specifically, the macro pixel 110 is formed from four conventional Bayer arrays, each formed from a 2×2 array of elements, an Org.R red filter, an Org.B blue filter, and two Org.G green filters arranged along the diagonal of the Bayer array.

[0080] The filters NIR1 and NN2 are superimposed on the Org.G and Org.R filters in each of the two Bayer arrays arranged along the diagonal of the macro pixel 110.

[0081] The filter arrangements described in detail above and shown in A) and B) of FIG. 4 are advantageous in that, on the one hand, they enable the use of all photosensitive pixels 115, each dedicated to the detection of wavelengths that may reach, and on the other hand, they enable the use of commercially available photosensitive sensors that already contain a Bayer array and are mass-produced, thus being of affordable price, and combined enable high spatial resolution and high sensitivity.

[0082] C) of FIG. 3 shows the result of the combination of the interference filter and the organic filter. The two peaks at 444 nm and 483 nm are very much reduced, while the five peaks of the first resonance remain transmitted.

[0083] A second variant of the general principle of the invention, applied to this second specific embodiment of the invention, is summarized in D) of FIG. 4. That is, λ I and λ IIFor example, it corresponds to λ2 and λ4 respectively. PP1 and PP2 correspond to dedicated photosensitive pixels 115 in spectral bands of interest centered around these wavelengths. IF1 and IF2 correspond to interference filters G and NIR1 superimposed on PP1 and PP2 respectively. Iλ I and Iλ II correspond to the radiation transmitted by IF1 and IF2 through primary resonance. Iλ II -P corresponds to the radiation transmitted by IF2 through secondary resonance at 444 nm. The two parts of the filtering layer FL’ correspond to the two Org.G basic filters of the filtering layer 170 superimposed on PP1 and PP2 respectively.

[0084] The two spectral bands of interest are distinct, i.e., centered around different wavelengths and preferably do not overlap.

[0085] In this variant, the filtering layer is superimposed on two photosensitive pixels. Due to its different spectral responses by pixel, it transmits Iλ I at PP1 while blocking Iλ II -P at PP2.

[0086] In practice, it can be considered that the filtering layer FL’ also blocks the radiation having a wavelength half of the wavelength of λ II at PP2.

[0087] Here, the organic filters form a Bayer array (a specific type of so-called RGB filter) that transmits in the blue, green, and red of the visible spectral region. However, other types of filtering arrays, and in general any type of filter in the form of an array of filters and other transmission bands, such as filters of the RGBE, RYYB, CYYM, or RGBW type, etc., can be envisioned for designing the spectral imager according to the present invention.

[0088] Using an image sensor equipped with a Bayer array in a multispectral imager is extremely advantageous as long as such sensors are widely available at reasonable costs.

[0089] Furthermore, the spectral imager structure of FIG. 1A taken as an example in the above two embodiments corresponds to a structure obtained by hybrid technology, i.e., an image sensor and a filtering structure are manufactured in parallel on two different substrates and then depend on their association including an array of lenses. However, other structures are also suitable, such as a hybrid structure that is the same as that of FIG. 1A but without a lens as shown in A) of FIG. 5, or a hybrid structure in which a filtering layer 170 is formed on a sensor substrate and without or with an array of lenses on a planarization layer 175 as shown in B) and C) of FIG. 5 respectively, and optionally covered by the planarization layer.

[0090] It is also possible to use a structure obtained by monolithic technology, i.e., as shown in D) and E) of FIG. 5, by stacking a photosensitive pixel 115, an interference filter 160, and a filter layer 170 in this order respectively, and stacking a photosensitive pixel 115, a filtering layer 170, optionally a planarization layer 176, and an interference filter 160 in this order respectively, to continuously form all elements of the imager on a single substrate.

[0091] It goes without saying that the present invention is not limited to the embodiments disclosed above and can be modified and combined without departing from the scope of the present invention.

Claims

1. A multispectral imager designed to analyze a region of interest spectrum including a first spectral band and a second spectral band different from the first spectral band, an image sensor (100) formed from an array of macro pixels (110) each including a first photosensitive pixel (115, PP1) dedicated to the first spectral band and a second photosensitive pixel (115, PP2) dedicated to the second spectral band different from the first spectral band, a filtering structure (150) including a first interference filter (160, IF1) and a second interference filter (160, IF2) respectively disposed so as to be superposed on the first photosensitive pixel (115, PP1) and the second photosensitive pixel (115, PP2) and transmit a first electromagnetic radiation (IλI) belonging to the first spectral band and a second electromagnetic radiation (IλII) belonging to the second spectral band, comprising: wherein half the wavelength of the second electromagnetic radiation is located in the region of interest spectrum; further comprising a filtering layer (170, FL; FL') disposed so as to be superposed on the second photosensitive pixel (160, PP2) and configured to block the passage of a third electromagnetic radiation having half the wavelength of the second electromagnetic radiation; wherein the filtering layer (FL) forms a high-pass organic filter having a cut-off wavelength in a spectral region including the first spectral band and the second spectral band, or the filtering layer (FL') includes an array of organic filters (Org.R, Org.G, Org.B) configured to transmit spectral bands within a visible spectral region including the first spectral band and the second spectral band respectively; characterized in that it is a multispectral imager.

2. The multispectral imager according to claim 1, characterized in that half the wavelength of the second electromagnetic radiation is within the first spectral band.

3. The multispectral imager according to claim 1 or 2, characterized in that the filtering layer (170, FL) forms a high-pass filter configured to block the first electromagnetic radiation and transmit the second electromagnetic radiation.

4. The multi-spectral imager according to any one of claims 1 to 3, wherein the filtering layer (170, FL) is structured so as not to overlap with the first photosensitive pixel (160, PP1).

5. The multi-spectral imager according to any one of claims 1 to 4, wherein the filtering layer (FL) is composed of a layer of a red organic material.

6. The multi-spectral imager according to claim 1 or 2, wherein the filtering layer (FL') is formed by a mosaic of basic filters, and is further superimposed on the first photosensitive pixel (PP1) and configured to transmit the first electromagnetic radiation (IλI) to the first photosensitive pixel (PP1).

7. The multi-spectral imager according to claim 1 or 6, wherein the organic filter is configured to transmit blue, green, and red radiation bands, respectively.

8. The multi-spectral imager according to claim 7, wherein the array of the organic filters is a Bayer array.

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