EP4251961A1

EP4251961A1 - Multispectral imager with enlarged spectral domain

Info

Publication number: EP4251961A1
Application number: EP21823963.0A
Authority: EP
Inventors: Stéphane TISSERAND; Laurent Roux
Original assignee: Silios Technologies SA
Current assignee: Silios Technologies SA
Priority date: 2020-11-30
Filing date: 2021-11-18
Publication date: 2023-10-04
Also published as: CA3200228A1; US20240102861A1; FR3116899A1; FR3116899B1; WO2022112688A1; CN116507892A; JP2023551686A

Abstract

Disclosed is a multispectral imager designed for analysing a spectral domain of interest, comprising an image sensor (100) formed of an array of macropixels and comprising a first and a second photosensitive pixel (115) respectively dedicated to a first and a second spectral band, and a filtering structure (150) comprising a first and second interference filter (160) which are superimposed respectively on the first and second photosensitive pixel (115) and which are arranged to respectively transmit a first and second electromagnetic radiation belonging respectively to the first and second spectral bands, the multispectral imager in which a wavelength half of that of the second electromagnetic radiation is located in the spectral domain of interest, and a filtering layer (170) is superimposed on the second photosensitive pixel (160) and configured to block the passage of a third electromagnetic radiation of wavelength half that of the second electromagnetic radiation.

Description

TITLE: Expanded spectral domain multispectral imager.

Technical area

The invention relates to a multispectral imager capable of instantaneously obtaining two-dimensional images whose spectrum is resolved at each point.

Prior technique

Many applications in astronomy, mineralogy, chemistry or agriculture require the acquisition of spectral images of objects or scenes, that is to say images spectrally limited to specific bands of the electromagnetic spectrum, in the visible. , infrared or ultraviolet .

Multispectral or hyperspectral imagers make it possible to obtain such images, which consist of two-dimensional images from which the spectrum is extracted at each point. One speaks conventionally of hyperspectral imaging when the extracted spectra are highly resolved, that is to say formed of numerous (typically more than 100) relatively narrow spectral bands (typically 5 to 15 nm), and of multispectral imaging when the ssoonntt spectra formed of fewer spectral bands (typically between 4 and 20) relatively broad (typically 15 to 40 nm).

A first method for obtaining multispectral images is to use a scanner comprising a one-dimensional sensor scanning a scene to be analyzed, called a “push broom scanner”.

A second method is to use a two-dimensional matrix of elementary photosensitive sensors, matrix called “FPA” for Focal Plane Array in English terminology, in order to practice instantaneous multispectral imaging, or “snapchot imaging”, method for capturing images in a single integration period of the array of sensors,

The present invention falls within the scope of obtaining multispectral images according to this second method, a framework in which patent document US 2019/0145823 discloses a multispectral imager based on an image sensor comprising a two-dimensional matrix formed of a matrix of photosensitive pixels, and a set of elementary filters each associated with one of the photosensitive pixels.

The photosensitive pixels are each dedicated to a given spectral band, that is to say provided to receive and measure radiation of wavelength included in this band, all the photosensitive pixels dedicated to the same spectral band forming a sub-image of which each point belongs to one of a plurality of macropixels each formed of a group of pixels and associated filters.

Structurally, each elementary filter is superimposed on that of the photosensitive pixels with which it is associated, defining its spectral band by filtering the incident electromagnetic radiation,

Here, the elementary filters each consist of a Fabry-Pérot type interference filter.

Devices such as those of US patent 2019/0145823 are designed to analyze only spectral domains of relatively small extents, around 300 nm wide, in order to avoid pollution of one spectral band by another.

In practice, to study, for example, the spectral domain ranging from 400 to 1000 nm (visible and near infrared domain), one therefore uses two distinct multispectral imagers, for example dedicated respectively to the spectral domains 400-700 nm and 700- 1000nm.

It would be desirable for a single device to be able to implement multispectral imaging for an extended spectral domain. Patent application LIS 2017/0163901 Al relates to a multispectral imaging system based on optics making it possible to form a plurality of imagettes each forming a duplicate of an image of a scene to be analyzed, each imagette being detected by a separate portion of a color image capture element, as well as a combination of narrow bandwidth filters and color filters integrated into the image capture element.

Patent documents US 2015/0138560 Al and DE 112013 002 560 T5 relate to a spectroscopic detector comprising two facing mirrors forming a laser cavity.

Disclosure of Invention

The aim of the present invention is to increase the extent of the spectral domain that can be analyzed by a single multispectral imager.

The invention relates more particularly to a multispectral imager designed to analyze a spectral domain of interest comprising a first spectral band and a second spectral band distinct from the first spectral band, comprising an image sensor formed of a matrix of macropixels ( 110) each comprising a first photosensitive pixel and a second photosensitive pixel dedicated respectively to the first spectral band and to the second spectral band distinct from the first spectral band, and a filtering structure which comprises a first interference filter and a second interference filter which are superimposed respectively on the first photosensitive pixel and on the second photosensitive pixel and which are arranged to transmit respectively a first electromagnetic radiation belonging to the first spectral band and a second. electromagnetic radiation belonging to the second spectral band, the multispectral imager being characterized in that a wavelength half that of the second electromagnetic radiation is located in the spectral domain of interest, and in that the multispectral imager comprises additionally a filter layer which is superimposed on the second photosensitive pixel and which is configured to block the passage of a third electromagnetic radiation of wavelength half that of the second electromagnetic radiation.

An essential advantage of a multispectral imager according to the invention is its ability to analyze a widened spectral domain without undergoing pollution due to the resonances of order 2 of the interference filters.

Furthermore, such a multispectral imager does not require any particular image sensor and can therefore be based on standard commercial image sensors, facilitating the development and considerably reducing the cost of this imager.

A multispectral imager having such a structure, with an operation based on the use of macropixels and a filtering layer structured on the scale of a pixel, has other advantageous characteristics.

It makes it possible to use the entire photosensitive surface of the sensor, thus providing excellent spatial resolution.

Moreover, such a structure implies an intimate proximity between the image sensor, the interference filtering structure and the filtering layer, thus ensuring a virtual absence of problems related to the respective angles of view of each of the pixels of a scene to capture.

The multispectral imager according to the invention may have the following characteristics:

- the wavelength half that of the second electromagnetic radiation can be in the first spectral band; the filter layer may form a high-pass filter configured to block the first electromagnetic radiation and transmit the second electromagnetic radiation;

~ the filter layer can be structured so as not to be superimposed on the first photosensitive pixel;

- the filter layer can consist of a layer of red organic material - the filtering layer can be formed from a mosaic of elementary filters, can also be superimposed on the first photosensitive pixel and be configured to transmit the first electromagnetic radiation to the first photosensitive pixel;

- the filtering layer may comprise a matrix of organic filters each configured to transmit a spectral band in the visible spectral range; the organic filters can be configured to transmit bands of blue, green and red radiation respectively; and

- the matrix of organic filters can be a Bayer matrix.

Brief description of the drawings

The present invention will be better understood and other advantages will appear on reading the detailed description of the embodiments taken by way of non-limiting examples and illustrated by the appended drawings, in which:

- Figure 1A illustrates a sectional view of a multispectral imager according to a first embodiment of the invention; FIG. 1B illustrates a plan view of an array of macropixels of the spectral imager of FIG. 1A;

- Figure 1C illustrates a macropixel of Figure 1B;

- Figure 1D illustrates a first variant of the general principle of the invention;

- Figure 2 illustrates the characteristics of the multispectral imager of Figure 1A;

- Figure 3 illustrates the characteristics of a multispectral imager according to a second embodiment of the invention;

- Figure 4 illustrates the structure of the multispectral imager of Figure 3; and

- Figure 5 illustrates structural variants of a spectral imager according to the invention. FIGS. 2 (in A, C and D) and 3 (in A, B and C) illustrate spectral responses of optical filters, with transmission percentages on the ordinate and wavelengths on the abscissa, expressed in nanometers.

Description of a first particular embodiment according to the invention

FIG. 1A illustrates a sectional view of the structure of a 16-channel multispectral imager according to the invention, with an image sensor 100 comprising a sensor substrate 105, an array of photosensitive pixels 115 formed on and/or in this substrate, respectively dedicated to one of sixteen spectral bands of interest, centered respectively on wavelengths λ ₁ to λ ₁₆ , and.a filter structure 150 comprising a substrate, filter 155 as well as a matrix interference filters 160 formed on this substrate and a filter layer 170 formed on the interference filters 160.

It is the combination of the matrix of interference filters and the filtering layer which specialize the sensitivity of the photosensitive pixels to incident radiation, thus dedicating them each to a given spectral band.

A plurality of macropixels 110 forming a matrix of macropixels illustrated by FIG. 1B are each formed of a group of pixels, each dedicated to one of the spectral bands of interest, and associated filters. FIG. 1C illustrates in a plan view of one of these macropixels 110, each formed of a 4×4 matrix of photosensitive pixels 115, the photosensitive pixels being designated by the central wavelengths λ ₁ to λ ₁₆ of the 16 spectral bands to which they are respectively dedicated, 430, 468, 506, 544, 582, 620, 658, 696, 734, 772, 810, 848, 886, 924, 962 and 1000 nm.

The filtering layer 170 could take a continuous form or be composed of discrete elements such as a mosaic of elementary filters, and may or may not have a composition and properties homogeneous over its entire extent; it is here homogeneously formed from a red organic resin structured to be superimposed on the photosensitive pixels dedicated to the spectral bands centered on the high wavelengths λ ₁ to λ ₁₆ and to be absent at the level of the pixels dedicated to the centered spectral bands on the low wavelengths λ ₁ to λ ₅ , as illustrated by FIG. 2 in B) which represents the filtering layer 170 on the scale of a macropixel 110.

The filter layer 170 here forms a high-pass organic filter, with a cut-off wavelength located at approximately 590 nm, as illustrated by FIG. 2 at C), but any type of filter could be used, such as for example filters operating by absorption, reflection, interferential or plasmonic, provided that they have an adequate spectral response (high pass here) and that they can be structured on the scale of the photosensitive pixels.

When we say that a filter is superimposed on a photosensitive pixel, we must here understand that this filter is offset from the pixel in a direction perpendicular to its formation plane and located in such a way as to intercept the incident radiation on this pixel for the block or forward it.

In this document, the terms "block" and "transmit ¾> are not to be understood in the sense of total blocking and total transmission, but must be understood according to usage in the field of optical filters, such as example by blocking at least 80% and transmitting at least 30% of electromagnetic radiation, which corresponds to the examples considered in this description.

Thus, when we say that a filter layer superimposed on a photosensitive pixel is configured to transmit radiation to this photosensitive pixel, it will be understood that this filter layer is transparent to this radiation (transmission of at least 30% of this radiation ) and. allows it to cross it to irradiate this photosensitive pixel. This does not prevent a first element forming a first part of the filter layer from transmitting a first radiation of given wavelength and a second element forming a second part of the filter layer from blocking a second radiation of this given wavelength.

The imager can further comprise an array of microlenses 120 reproducing the arrangement of the photosensitive pixels so that each pixel corresponds to one and only one of the lenses, and configured to concentrate the incident radiation on the photosensitive surfaces of the photosensitive pixels, increasing thus the sensitivity of the imager.

The elements of this imager require an intimate proximity between the image sensor, the interference filtering structure and the filtering layer, so that the incident radiation trajectories pass respectively through a photosensitive pixel and an interference filter which is superimposed on it, even with a substantial angle of incidence (greater than 30° for example) while limiting the phenomena of crosstalk (or "crosstalk" in English, pollution of the radiation intended to be received by a given pixel by a radiation intended to be received by a neighboring pixel),

Such proximity can be obtained by bringing the elements (160, 170) formed on the sensor substrate 105 into direct contact with the elements (115, 120) formed on the filter substrate 155, or optionally via layers thin protection, then by fixing the substrates (105,155) to each other by means of a strip of glue 157 located on the periphery of these substrates (105, 155).

The elements 160, 170, 115 and 120 are interposed between the two substrates 105 and 155 so as not to be separated by the thickness of one or two of these substrates and to maintain the necessary proximity.

In practice, the imager illustrated in FIG. 1A is associated with an optical focusing system (not .illustrated) comprising one or several lenses located at a distance from the photosensitive pixels 115 and from the interference filters 160 and from their substrate 155.

The interference filters can be, for example, filters of the Fabry-Pérot type, formed by a resonant cavity between two mirrors,

Such a filter transmits electromagnetic radiation if it enters into resonance in the cavity, that is to say on the condition that its wavelength belongs to a spectral band centered on a given wavelength defined by the formula [1] following: in which k is an integer greater than or equal to 1 which defines the order of resonance considered, is the index of refraction of the cavity for the wavelength λ _k , and e is the physical thickness of the cavity,

The width of the spectral band transmitted by such a filter is characterized by the height at mid-height of a resonance peak, which can range from a few nanometers to several tens of nanometers, and depends on the structure and the materials used poul ^¬ ie filter.

For k=1, we speak of resonance of order 1; the nominal transmission band of the filter being the band centered on λ ₁ . However, other resonance orders satisfying the transmission condition of formula [1] are associated with integers k greater than 1: order 2 for k equal to 2, order 3 for k equal to 3, etc.

By allowing the transmission of radiation of corresponding wavelengths, the orders of resonance of orders 2 limit in practice the spectral range that a given multispectral imager will be able to analyze,

Indeed, an interference filter designed to transmit as a useful signal a first radiation thanks to a resonance of order 1 will also transmit a second radiation of wavelength approximately half (at the index dispersion of refraction close) to that of the first radiation due to the resonance of order 2, which pollutes the measurement of the useful signal to the point of making it unusable.

Thus, to avoid pollution of the signal by the presence in the spectral domain analyzed by the multispectral imager of wavelengths approximately half shorter than other wavelengths of this same domain, the extent of the analyzable spectral range to exclude the latter, by the use of a global high-pass filter covering all the photosensitive pixels or by the characteristics of the material used for the detection of the radiation, such as silicon in the case of a CMOS detection technology.

In this way, it is avoided that a wavelength twice as short as that of electromagnetic radiation located in a high spectral band (in wavelength) of the spectral domain analyzed is located in a low spectral band ( in wavelength) of this same spectral range.

In fact, globally blocking, on the scale of the entire multispectral imager, the radiation transmitted by resonances of order 2 of the filters dedicated to the high spectral bands comes down to also blocking the low spectral bands that could be wish to analyze with the same multispectral imager.

Figure 2 shows in A) a graph indicating the spectral responses of the 16 interference filters associated with the 16 photosensitive pixels in a spectral range extending from 400 to 1100 nm, with the transmission peaks due to resonances of orders 1 and 2, with widths at mid-height between 20 and 50 nm.

In this example, in the absence of the filter layer 170, radiation of wavelengths less than approximately 550 nm would be transmitted to the photosensitive pixels dedicated to high wavelengths (ie relatively long wavelengths) due to 2nd order resonances of the associated interference filters, as indicated by the resonance peaks of the box Box where the resonance peaks of order 1 of the low wavelengths (ie of relatively short wavelengths) are superimposed and the resonance peaks of order 2 of the interference filters of nominal transmissions corresponding to the lengths d high waves.

In the present invention, the filtering layer 170 solves the problem of pollution of the useful signals of the high spectral bands (in wavelength) by blocking the radiation of shorter wavelengths, not globally on all the photosensitive pixels. , but specifically at the level of the photosensitive pixels dedicated to these high spectral bands, while allowing radiation from the low spectral bands (in wavelength) to pass at the level of the photosensitive pixels dedicated to these low spectral bands.

Concretely, the filtering layer 170 is, in this embodiment, structured at the level of the photosensitive pixels taken individually so as to be superimposed only on the pixels dedicated to the high spectral bands, being absent at the level of the pixels dedicated to the low spectral bands.

In fact, the filtering layer 170 has a matrix structure, each element of which reproduces in geometry and in dimensions the structure of the macropixels 110, structure formed in this example of a matrix of 4×4 photosensitive pixels 115.

Thus, the filtering layer 170 is here formed of elements superimposed respectively on the photosensitive pixels 115 dedicated respectively to the wavelengths λ ₆ to λ ₁₆ , each element corresponding to a photosensitive pixel and vice versa.

In this particular embodiment, these elements form a continuous filtering layer 170 on the scale of a macropixel 110, superimposed on a first portion only of a macropixel 110 so as not to intercept incident radiation passing through a second portion. of the same macropixel, as shown in B) of Figure 2. Thus, a multispectral imager according to the invention can analyze an enlarged spectral range ranging for example from 400 to 1000 n®, of greater range than those of conventional multispectral imagers, without suffering from the pollution phenomenon described above.

FIG. 2 illustrates in D) the spectral response of the combination according to the invention between the interference filters 160 and the filtering layer 170 consisting of the high-pass filter illustrated in B), designed to block the radiation corresponding to the resonances of order 2 11 interference filters λ ₁ to λ ₁₆ , of wavelengths shorter than the cut-off wavelength of the filtering layer.

It can be seen that the filtering layer makes it possible to eliminate or very greatly reduce the transmission of radiation due to resonance peaks of order 2, so as to obtain a spectral image with 16 bands covering a wide spectral range and suffering little or no damage. of pollution caused by these resonance peaks of order 2, according to the principle illustrated by FIG. 1D.

The solid arrows indicate the transmission peaks of the 11 photosensitive pixels dedicated to the wavelengths λ ₆ to λ ₁₆ , pixels on which the filtering layer 170 is superimposed.

FIG. 1D summarizes the general principle of the invention: a first interference filter IF1 superimposed on a first photosensitive pixel PP1 transmits radiation Iλ _I of a wavelength belonging to a first spectral band of interest centered on the length d wave λ _I , a second interference filter IF2 superimposed on a second photosensitive pixel PP2 transmits radiation Iλ _II of a second wavelength belonging to a second spectral band of interest centered on the wavelength λ _II as well as a polluting radiation Iλ _II — P third wavelength approximately half of λ _II due to an order 2 resonance of the second interference filter IF2, and a filtering layer FL which is configured to transmit Iλ _I to PP1 and Iλ _II to PP2, and block the polluting radiation Iλ _II — P at PP2.

In practice, it can be considered that the filter layer FL also blocks radiation with a wavelength half that of λ _II at the level of PP2.

The third wavelength of the radiation, pollutant Iλ _II — P could be very close to or equal to λ ₁ , and could in particular be found in a spectral band of interest, centered on λ ₁ corresponding to the resonance peak of order 1 of IF1, and therefore be transmitted by the first interference filter IF1.

The two spectral bands of interest are distinct, that is to say centered on different wavelengths, and preferably do not overlap.

A first variant of this principle, illustrated by FIG. 1D, consists in structuring the filtering layer FL so as to superimpose it only on the second photosensitive pixel PP2.

In this document, the expression “approximately” means that a deviation of 10% is authorized between the values of the quantities considered, and is in particular used to take account of the index dispersion in the positioning of the resonance peaks,

This principle applied to the first particular embodiment of the invention, λ _I and λ _II correspond for example respectively to λ _I and λ ₁₂ , PP1 and PP2 to the photosensitive pixels 115 dedicated to the spectral bands centered on these wavelengths, IF1 and IF2 to the interference filters 160 superimposed respectively on PP1 and PP2, Iλ _I and Iλ _II on the radiation transmitted by IF1 and IF2 by resonance of order 1 and Iλ _II — P on the radiation transmitted by IF2 by resonance of order 2, and the layer filter layer FL to filter layer 170.

A multispectral imager applying the general principle of the invention to this first embodiment, combining a matrix of interference filters and a high-pass filter structured at the scale of the photosensitive pixels, makes it possible to analyze a domain spectrum sufficiently wide to include a first spectral band and a second spectral band of wavelengths approximately twice as short as those of the first spectral band without suffering from pollution due to the second orders of resonance.

The application of the invention is not limited to filters of the Fabry-Pérot type taken here as an example, but extends to any type of filter producing several orders of interference.

This first embodiment is based on the use of a filter layer 170 forming a high-pass filter locally structured so as to be superimposed only on the photosensitive pixels dedicated to the high spectral bands to block the radiation transmitted by the resonances of order 2 and more of the associated interference filters, but the invention is not limited to this configuration and could use other types of filters such as band-pass filters, superimposed or not on all the photosensitive pixels defining a macropixel, as illustrated by the following embodiment.

Description of a second particular embodiment according to the invention

The second embodiment of the invention consists of a 5-channel spectral imager having a structure identical to that of the first embodiment except for the interference filters and the filtering layer, and comprising photosensitive pixels dedicated to 5 bands spectral centers on wavelengths λ ₁ to λ ₅ , respectively 450, 550, 650, 865 and 945 nm, pixels arranged in macropixels 110 each comprising 16 photosensitive pixels as illustrated by FIG. 4 in C).

The first three wavelengths correspond respectively to three interference filters B, G and R respectively transmitting blue, green and red radiation from the visible range, the last two wavelengths corresponding respectively two interference filters NIR1 and NIR2 of the near infrared range,

FIG. 3 illustrates in A) the spectral response of the five interference filters, with 5 transmission peaks corresponding respectively to the wavelengths λ ₁ to λ ₅ of the first-order resonances of each of the 5 filters, and 2 transmission peaks at 444 and 483 nm corresponding respectively to the second order resonances of the NIR1 and NIR2 filters.

These last two transmission peaks are a source of pollution as explained in the first embodiment, and are eliminated or greatly reduced by using a filter layer 170 formed from a mosaic of elementary filters, here a classic Bayer matrix comprising filters organic Grg,B, Grg.G and Org.R respectively transmitting bands of blue, green and red radiation from the visible range as illustrated by FIG. 3 in B).

FIG. 4 illustrates in A) the arrangement of the interference filters, according to the geometry of the macropixels 110, each filter being superimposed on one and only one of the photosensitive pixels of a given macropixel, with the resonance peaks of orders 1 and 2 of these filters.

The organic filters are arranged according to the geometry of the macropixel 110 as illustrated in B) of FIG. 4, each filter being superimposed on one and only one of the photosensitive pixels, and so that the NIR1 and NIR2 filters are superimposed respectively on Org.G and Org.R filters, so as to respectively block radiation from peaks at 444 and 483 nm corresponding to second order resonances.

More specifically, the macropixel 110 is formed from a 2x2 matrix of 4 conventional Bayer matrices which are each formed from a 2x2 element matrix; a red filter Org.R, a blue filter Qrg.B and two green filters Org.G, the two green filters Org.G being placed along a diagonal of the Bayer matrix. The NIR1 and NIR2 filters are superimposed on an Org filter. G and an Org filter. R of each of two Bayer matrices placed along a diagonal of the macropixel 110.

The arrangement of the filters detailed above and illustrated in A) and B) of FIG. 4 is advantageous in the sense that it allows on the one hand use of all the photosensitive pixels 115 , each being of a wavelength capable of reaching it, and on the other hand a high spatial resolution and has a high sensitivity combined with the possible use of a commercial photosensitive sensor already equipped with a Bayer matrix and mass-produced , therefore at a reasonable cost.

FIG. 3 illustrates in C) the result of the combination of the interference filters with the organic filters; the two peaks at 444 and 483 nm are extremely reduced whereas the 5 peaks of the first order resonances remain transmitted.

A second variant of the general principle of the invention, applied to this second particular embodiment of the invention, is summarized here in D) of FIG. 4; λ _I and λ _II correspond for example respectively to λ ₂ and λ ₄ , PP1 and PP2 to the photosensitive pixels 115 respectively dedicated to the spectral bands of interest centered on these wavelengths, IF1 and IF2 to the interference filters G and NIR1 superimposed respectively at PP1 and PP2, Iλ _I and Iλ _II to the radiation transmitted by IF1 and IF2 by resonance of order 1, Iλ _II — P to the radiation transmitted by IF2 by resonance of order 2 at 444 nm, and two parts of a filtering layer FL' with two elementary filters Org.G of the filtering layer 170 superimposed respectively on PP1 and PP2.

In this variant, the filtering layer is superimposed on the two photosensitive pixels, but it transmits i¾ to PP1 while blocking Iλ _II — P at the level of PP2 due to its spectral response which is different depending on the pixels considered.

In practice, it can be considered that the filtering layer FL′ also blocks radiation with a wavelength half that of λ _II at the level of PP2.

Here, the organic filters form a Bayer matrix, transmitting in the blue, green and red of the visible spectral domain (particular type of so-called RGB filter), but other types of filtering matrices, and in general any type A filter in the form of a matrix of filters and other transmission bands could be envisaged to design a spectral imager according to the invention, such as for example filters of the RGBE, RYYB, CYYM or else RGBW type.

The use of an image sensor equipped with a Bayer matrix in the multispectral imager is extremely advantageous insofar as such sensors are widely available commercially at reasonable costs.

In addition, the spectral imager structure of FIG. 1A taken by way of example in the two embodiments above corresponds to a structure obtained by a hybrid technology, that is to say which is based on the parallel fabrication of an image sensor and a filtering structure on two separate substrates then their association, including an array of lenses, but other structures are also appropriate, such as a hybrid structure identical to that of the figure 1A but without lenses as illustrated by FIG. 5 in A), or even a hybrid structure in which the filtering layer 170 is formed on the sensor substrate and. is optionally covered with a planarization layer 175, with or without an array of lenses above the planarization layer, as illustrated respectively in B) and C) of FIG. 5.

It is also possible to use a structure obtained by monolithic technology, that is to say obtained by the formation in succession of all the elements of the imager on a single substrate, as illustrated in D) and E) of FIG. 5, with respectively a superposition in this order of the photosensitive pixels 115, of the interference filters 160 and of the filtering layer 170 and a superposition in this order of the photosensitive pixels 115, of the filter layer 170, possibly a planarization layer 176, and interference filters 160.

It goes without saying that the present invention cannot be limited to the embodiments described above, which may be modified and combined without departing from the scope of the invention.

Claims

1. Multispectral imager designed to analyze a spectral domain of interest comprising a first spectral band and a second spectral band distinct from the first spectral band, comprising:

- an image sensor (100) formed of a matrix of macropixels (110) each comprising a first photosensitive pixel (115, PP1) and a second photosensitive pixel (115, PP2) dedicated respectively to the first spectral band and to the second spectral band distinct from the first spectral band; and

- a filtering structure (150) which comprises a first interference filter (160, IF1) and a second interference filter (160, IF2) which are superimposed respectively on the first photosensitive pixel (115, PP1) and on the second photosensitive pixel (115, PP2) and which are arranged to respectively transmit a first electromagnetic radiation (Iλ _I ) belonging to the first spectral band and a second electromagnetic radiation (Iλ _II ) belonging to the second spectral band, the multispectral imager being characterized in that:

- a wavelength half that of the second electromagnetic radiation is in the spectral domain of interest,* and

-- the multispectral imager further comprises a filtering layer (170, FL; FL') which is superimposed on the second photosensitive pixel (160, PP2) and which is configured to block the passage of a third electromagnetic radiation with a length of wave half of that of the second electromagnetic radiation.

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

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

4, The multispectral imager according to any one of claims 1 to 3, characterized in that the filter layer (170, FL) is structured so as not to be superimposed on the first photosensitive pixel (160, PP1),

5, The multispectral imager according to any one of claims 1 to 4, characterized in that the filter layer (FL) consists of a layer of red organic material,

6, The multispectral imager according to claim 1 or 2, characterized in that the filtering layer (FL') is formed of a mosaic of elementary filters, is also superimposed on the first photosensitive pixel (PP1) and is configured to transmit the first electromagnetic radiation (Iλ _I ) at the first photosensitive pixel (PP1),

7, The multispectral imager according to claim 1 or 6, characterized in that the filtering layer (FL') comprises a matrix of organic filters (Org.R, Org.G, Org.B) configured to each transmit a spectral band in the visible spectral range,

8, The multispectral imager according to claim 7, characterized in that the organic filters are configured to respectively transmit bands of blue, green and red radiation.

9. The multispectral imager according to claim 8, characterized in that the matrix of organic filters is a Bayer matrix.