Polarizer filter and polarimetric image sensor incorporating such a filter

Abstract

Polarizer filter and polarimetric image sensor incorporating such a filter. This description relates to a polarizer filter (PF) intended to be arranged opposite an image sensor comprising a plurality of pixels. The filter comprises, for each pixel, a polarizing structure (111) having a plurality of parallel metal bars (701), each bar being coated with an absorbing stack (703) comprising: – a tungsten layer (705); – a silicon layer (707) coating the tungsten layer; and – a dielectric layer (709) coating the silicon layer. Figure for the abstract: Fig 7

Description

Title of the invention: Polarizing filter and polarimetric image sensor incorporating such a filter. Technical field

[0001] This description relates generally to image sensors, and more particularly to so-called polarimetric image sensors, adapted to record information relating to the polarization of the captured light. Previous technique

[0002] Measuring the polarization information of light during image acquisition can be of interest for numerous applications. In particular, it enables the implementation of image enhancement processes, tailored to the specific application. For example, it makes it possible to attenuate or, conversely, enhance reflections on an image from any surface that causes specular reflection, such as glass, water, or the surface of an eye. Furthermore, it makes it possible to detect manufactured objects in a natural environment, as these objects generally exhibit a polarization signature.Among the applications that can benefit from polarization information measurement, we can also mention industrial control applications, biomedical applications, for example applications for the detection of cancer cells (the latter polarize light due to their fibrous nature), contrast enhancement applications for image capture in scattering media (fog, underwater imaging, etc.), or even distance mapping or depth image acquisition applications, in which polarization can provide information on the orientation of the surface of manufactured objects, and thus help 3D reconstruction in addition to another modality such as active illumination by structured light or by time-of-flight measurement.

[0003] To measure polarization information, it has already been proposed to successively acquire, using the same sensor, several images of the same scene, placing a polarizer opposite the sensor at each acquisition and changing the polarizer between two successive acquisitions. This results in relatively bulky acquisition systems, with a mechanism in front of the sensor, for example, a motorized rotating wheel or plate on which the different polarizers are mounted, allowing the polarizer to be changed between two acquisitions. Another limitation is related to the need to successively acquire several images of the scene to record several polarization states. This can be particularly problematic when the scene changes over time.

[0004] To overcome these limitations, it has been proposed to place a polarizing filter array opposite the image sensor. However, a limitation remains that the polarizing filters block part of the light signal received by the acquisition system. Thus, the overall sensitivity or overall quantum efficiency of the acquisition system is relatively low.

[0005] It would be desirable to overcome at least in part certain limitations of known solutions for acquiring polarimetric images. Summary of the invention

[0006] To this end, one embodiment provides a polarimetric image sensor formed in and on a semiconductor substrate, the sensor comprising: - a plurality of pixels, each comprising a photodetector formed in the semiconductor substrate; - a polarizing filter disposed on the side of an illumination face of the photodetectors, the filter comprising, for each pixel, a polarization structure; and - a polarization router comprising a two-dimensional metasurface disposed on the side of the polarizer filter opposite the photodetectors, the metasurface comprising a two-dimensional array of dots.

[0007] According to one embodiment, said plurality of pixels comprises at least first and second pixels adapted to measure radiation according to distinct first and second polarizations respectively, the polarization structure of the first pixel being adapted to transmit mainly radiation according to the first polarization and the polarization structure of the second pixel being adapted to transmit mainly radiation according to the second polarization.

[0008] According to one embodiment, a first part of the two-dimensional metasurface located directly above the first and second pixels is adapted to transmit predominantly: - radiation along the first polarization towards the polarization structure of the first pixel; and - radiation along the second polarization towards the polarization structure of the second pixel.

[0009] According to one embodiment, the first and second polarizations are linear polarizations along first and second directions forming angles of 0° and 90° respectively with respect to a reference direction.

[0010] According to one embodiment, said plurality of pixels further comprises third and fourth pixels adapted to measure radiation according respectively to distinct third and fourth polarizations, different from the first and second polarizations, the polarization structure of the third pixel being adapted to transmitting mostly radiation according to the third polarization and the polarization structure of the fourth pixel being adapted to transmit mostly radiation according to the fourth polarization.

[0011] According to one embodiment, a second part of the two-dimensional metasurface, different from the first part and located directly above the third and fourth pixels, is adapted to transmit predominantly: - radiation along the third polarization towards the polarization structure of the third pixel; and - radiation according to the fourth polarization towards the polarization structure of the fourth pixel.

[0012] According to one embodiment, the third and fourth polarizations are linear polarizations along third and fourth directions forming angles of 45° and 135° respectively with respect to the reference direction.

[0013] According to one embodiment, each polarization structure comprises a plurality of parallel metallic bars.

[0014] According to one embodiment, each metal bar is coated with an absorbent stack.

[0015] According to one embodiment, the absorbent stack comprises: - a layer of tungsten; - a layer of silicon, coating the tungsten layer; and - a dielectric layer, coating the silicon layer.

[0016] According to one embodiment, the pads of the two-dimensional metasurface are made of amorphous silicon.

[0017] According to one embodiment, the pads of the two-dimensional metasurface are laterally surrounded by silicon oxide.

[0018] According to one embodiment, the plots of the two-dimensional metasurface have sub-wavelength lateral dimensions.

[0019] According to one embodiment, the sensor further comprises a plurality of first microlenses extending opposite a pair of adjacent pixels of the sensor.

[0020] According to one embodiment, the first microlenses each have an elongated shape.

[0021] According to one embodiment, the first microlenses are: A) arranged on the side of a face of the two-dimensional metasurface opposite to the photodetectors; or B) interposed between the photodetectors and the two-dimensional metasurface.

[0022] According to one embodiment, the sensor further comprises a plurality of second microlenses distinct from the first microlenses and arranged on the side of one face of the two-dimensional metasurface opposite the photodetectors, each second microlens extending opposite a pair of adjacent pixels of the sensor.

[0023] According to one embodiment, each second microlens has an elongated shape.

[0024] According to one embodiment, each first microlens further extends opposite the first part or the second part of the metasurface.

[0025] Furthermore, one embodiment provides for a polarimetric image sensor formed in and on a semiconductor substrate, the sensor comprising: - a plurality of pixels, each comprising a photodetector formed in the semiconductor substrate; - a polarization router comprising a two-dimensional metasurface disposed on the side of an illumination face of the photodetectors, the metasurface comprising a two-dimensional array of dots; and - a plurality of first microlenses extending opposite a pair of adjacent pixels of the sensor.

[0026] According to one embodiment, the first microlenses are arranged on the side of the polarization router opposite to the photodetectors.

[0027] According to one embodiment, the first microlenses are interposed between the photodetectors and the two-dimensional metasurface.

[0028] According to one embodiment, said plurality of pixels comprises, opposite one of the first microlenses, first and second pixels adapted to measure radiation according to respectively distinct first and second polarizations, a first part of the two-dimensional metasurface located directly above the first and second pixels being adapted to transmit predominantly: - radiation according to the first polarization towards the first pixel; and - radiation according to the second polarization towards the second pixel.

[0029] According to one embodiment, the rows of plots in the first part of the two-dimensional metasurface are identical to each other.

[0030] According to one embodiment, the first part of the two-dimensional metasurface is adapted to focus the incident radiation mainly along a direction parallel to the rows of studs.

[0031] According to one embodiment, said plurality of pixels further comprises third and fourth pixels adapted to measure radiation according respectively to distinct third and fourth polarizations, different from the first and second polarizations, a second part of the two-dimensional metasurface located directly above the third and fourth pixels being adapted to transmit predominantly: - radiation according to the third polarization towards the third pixel; and - radiation according to the fourth polarization towards the fourth pixel.

[0032] According to one embodiment, the sensor further comprises a polarizing filter interposed between said plurality of pixels and the two-dimensional metasurface, the filter comprising, for each pixel, a polarization structure.

[0033] According to one embodiment, the polarization structure of the first pixel is adapted to transmit mainly radiation according to the first polarization and the polarization structure of the second pixel is adapted to transmit mainly radiation according to the second polarization.

[0034] Furthermore, an embodiment provides a polarizing filter intended to be arranged opposite an image sensor comprising a plurality of pixels, the filter comprising, for each pixel, a polarization structure comprising a plurality of parallel metal bars, each bar being coated with an absorbing stack comprising: - a layer of tungsten; - a layer of silicon, coating the tungsten layer; and - a dielectric layer, coating the silicon layer.

[0035] According to one embodiment, the metal bars are made of a material other than tungsten, preferably aluminum.

[0036] According to one embodiment, the tungsten layer has a thickness greater than 40 nm, preferably greater than 60 nm.

[0037] According to one embodiment, the metal bars are made of tungsten.

[0038] According to one embodiment, the metal bars and the tungsten layer have a cumulative thickness greater than 40 nm, preferably greater than 60 nm.

[0039] According to one embodiment, the silicon layer has a thickness of between 20 and 100 nm, preferably between 30 and 50 nm, for example equal to about 39 nm.

[0040] According to one embodiment, the dielectric layer is made of silicon oxide.

[0041] According to one embodiment, the dielectric layer consists of a stack of several layers of dielectric materials with refractive indices lower than that of silicon.

[0042] Furthermore, one embodiment provides for a polarimetric image sensor formed in and on a semiconductor substrate, the sensor comprising: - a plurality of pixels, each comprising a photodetector formed within the semiconductor substrate; and - a polarizing filter as described, the filter being positioned on the side of an illumination face of the photodetectors.

[0043] According to one embodiment, the first, second, third and fourth polarizations are linear polarizations along first, second, third and fourth directions forming angles of 0°, 90°, 45° and 135° respectively with respect to a reference direction.

[0044] According to one embodiment, the sensor further comprises a polarization router including a two-dimensional metasurface disposed on the side of the polarizer filter opposite the photodetectors, the metasurface comprising a two-dimensional array of dots.

[0045] According to one embodiment, the two-dimensional metasurface comprises: - a first part located directly above the first and second pixels, adapted to transmit primarily: radiation according to the first polarization towards the first pixel; and radiation according to the second polarization towards the second pixel, and - a second part located directly above the third and fourth pixels adapted to transmit predominantly: radiation according to the third polarization towards the third pixel; and radiation according to the fourth polarization towards the fourth pixel. Brief description of the drawings

[0046] These features and advantages, as well as others, will be described in detail in the following description of particular embodiments, given by way of non-limiting example, in relation to the accompanying figures, among which:

[0047] [Fig.1A] and [Fig.1B] are respectively an exploded perspective view and a cross-sectional view of an example of a polarimetric image sensor according to an embodiment;

[0048] [Fig.2] is a schematic and partial top view of an example embodiment of the polarizer filter of the sensor of figures IA and IB;

[0049] [Fig.3] is a schematic and partial top view of an example embodiment of the sensor polarization router of Figures IA and IB;

[0050] [Fig.4A] and [Fig.4B] are respectively an exploded perspective view and a cross-sectional view of another example of a polarimetric image sensor according to an embodiment;

[0051] [Fig.5] is a schematic and partial top view of an example embodiment of the sensor polarization router of Figures 4A and 4B;

[0052] [Fig.6A] and [Fig.6B] are respectively an exploded perspective view and a cross-sectional view of another example of a polarimetric image sensor according to an embodiment;

[0053] [Fig. 7] is a schematic and partial cross-sectional view of the polarizing filter of the sensor of figures 6A and 6B;

[0054] [Fig. 8] is a cross-sectional view of another example of a polarimetric image sensor according to one embodiment; and

[0055] the [Fig.9] a cross-sectional view of another example of a polarimetric image sensor according to one embodiment. Description of the implementation methods

[0056] The same elements have been designated by the same reference numerals in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same reference numerals and may have identical structural, dimensional and material properties.

[0057] For the sake of clarity, only the steps and elements necessary for understanding the described embodiments have been shown and are detailed. In particular, the photodetection elements and the electronic control circuits for the described image sensors have not been detailed, as the described embodiments are compatible with common implementations of these elements. Furthermore, the applications of the described image sensors have not been detailed, as the described embodiments are compatible with all or most known applications of polarimetric image acquisition systems.

[0058] Unless otherwise specified, when referring to two elements connected together, this means directly connected without intermediate elements other than conductors, and when referring to two elements coupled together, this means that these two elements can be connected or linked through one or more other elements.

[0059] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "superior", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures.

[0060] Unless otherwise specified, the expressions "approximately", "about", "in the order of", and "in the order of" mean to within 10%, preferably to within 5%, or, when referring to angular values, to within 10°, preferably to within 5°.

[0061] Fig.1A and Fig.1B are respectively an exploded perspective view and a cross-sectional view of an example of a polarimetric image sensor 100 according to one embodiment.

[0062] The sensor 100 is formed in and on a substrate 101. The substrate 101 is for example made of a single-crystal semiconductor material, for example single-crystal silicon.

[0063] The sensor 100 comprises a plurality of pixels P formed in and on the semiconductor substrate 101. In top view, the pixels P are for example arranged in a matrix according to rows and columns.

[0064] The sensor 100 further includes, on the side of a first face of the substrate 101, called the front face, corresponding to the lower face of the substrate 101 in the orientation of figures IA and IB, a stack 103 of insulating and conductive (e.g. metallic) layers, called the interconnect stack, in which interconnection elements (e.g. conductive interconnection tracks and vias) of the sensor pixels P are formed.

[0065] In the example of figures IA and IB, the sensor 100 is a backside illumination sensor, also called a BSI sensor (from the English "Back Side Illumination"), that is to say that the light rays from the scene to be imaged illuminate the substrate 101 from its back side, that is to say its side opposite the interconnection stack 103, namely its upper face in the orientation of figures IA and IB.

[0066] Each pixel P of the sensor 100 comprises a photosensitive region 105 formed in the substrate 101. Each photosensitive region 105 comprises, for example, a photodetection element 107, for example, a photodiode or photodetector. In the example shown, the photosensitive regions 105 of the pixels P are separated laterally from each other by insulating walls 109. The insulating walls 109 are, for example, made of a dielectric material, for example, silicon oxide. By way of alternative (not detailed in the figures), the insulating walls 109 comprise outer lateral walls made of a dielectric material, for example, silicon oxide, and a central wall made of an electrically conductive material, for example, doped polycrystalline silicon or a metal. In this example, the insulating walls 109 extend vertically through the entire thickness of the substrate 101.The thickness of substrate 101 is, for example, between 1 and 20 µm, or for example between 3 and 10 µm. As an alternative, the insulation walls 109 can be omitted.

[0067] Each pixel P is surmounted by a polarization structure 111 arranged opposite the photosensitive region 105 of the pixel, on the side of the illumination face of the photodetector 107, that is to say on the side of the upper face of the substrate 101 in the orientation of figures IA and IB. The set of polarization structures 111 located above the pixels P of the sensor 100 forms, for example, a polarization filter or polarizing filter FP.

[0068] Each polarization structure 111 is adapted to transmit predominantly light radiation according to a predefined polarization.

[0069] In the example of Figures IA and IB, the sensor comprises several pixels P whose respective polarization structures 111 have polarization orientations These pixels are different and thus adapted to transmit mostly light rays with different polarizations. This allows the intensities of received light radiation with different polarizations to be measured using distinct P pixels. In other words, the sensor includes at least first and second P pixels designed to measure the intensities of received light radiation with first and second polarizations respectively, for example, orthogonal linear first and second polarizations.As an example, the 111 polarization structure of the first pixel has a transmission coefficient of radiation along the first polarization greater than its transmission coefficient of radiation along the second polarization, and the 111 polarization structure of the second pixel has a transmission coefficient of radiation along the second polarization greater than its transmission coefficient of radiation along the first polarization.

[0070] Polarizing structures are, for example, metallic structures comprising apertures and transmitting radiation predominantly according to a predefined polarization, and absorbing or reflecting radiation according to other polarizations. Metallic structures are, for example, made of aluminum or copper. Alternatively, other metals may be used, for example silver, gold, tungsten, or titanium.

[0071] By way of example, a filling material 115, for example a dielectric material, for example silicon dioxide, silicon nitride, alumina (Al2O3), tantalum oxide, or hafnium oxide, fills the openings formed in the metallic structures. In this example, the material 115 further covers the polarization structures 111, forming a planarization layer 115. Alternatively, the openings of the polarization structures 111 may be left empty or filled with air.

[0072] In practice, the choice of patterns and the dimensioning of the polarization structures 111 can be carried out using known electromagnetic simulation tools.

[0073] By way of example, the pixels P are distributed into macropixels M, each comprising at least two adjacent pixels P, for example, four adjacent pixels P. In each macropixel M, the pixels P of the macropixel have different polarization structures. Thus, in each macropixel M, the pixels P of the macropixel measure intensities of received light radiation according to different polarizations.

[0074] The sensor 100 further comprises a two-dimensional (2D) metasurface MS located opposite the pixels P. More precisely, the metasurface MS is arranged on the side of the polarizing filter FP opposite the photodetectors 107. The metasurface MS comprises a two-dimensional array of pads 117 of a first material, for example amorphous silicon, surrounded laterally by a second material, for example the material 115, for example, silicon dioxide. More generally, the first material has a higher refractive index than the second material. The 117 pads of the MS metasurface have sub-wavelength lateral dimensions, meaning that the largest lateral dimension of each 117 pad is smaller than the principal wavelength intended to be measured by the underlying P-pixel, i.e., the wavelength at which the quantum efficiency of the P-pixel is maximal. For example, for P-pixels intended to measure visible or near-infrared radiation, for example, radiation with a wavelength less than 1 pm, the largest dimension of each 117 pad is between 10 and 500 nm, for example, between 30 and 300 nm.

[0075] The metasurface MS corresponds, for example, to a polarization router or sorter adapted to implement an optical function of polarization routing or sorting to the different underlying polarization structures 111 of the polarizing filter FP. In practice, the metasurface MS comprises, opposite each pixel P, a plurality of pads 117 of varying lateral dimensions. The dimensions and arrangement of the pads 117 are defined according to the optical function to be performed. For example, to perform the polarization routing or polarized light routing function, pads 117 may have asymmetrical shapes in top view, for example rectangular or elliptical, it being understood that the pads 117 may have any shape in top view.The pads 117 can have vertical flanks, i.e., orthogonal to the upper face of the substrate 101, oblique flanks, or stepped flanks, comprising at least one step. Furthermore, each pad 117 can be made of a single material or a stack of layers of different materials. The pattern of the MS metasurface can be defined using an electromagnetic simulation tool, for example, by using inverse design methods, such as those described in the article entitled "Phase-to-pattern inverse design paradigm for fast realization of functional metasurfaces via transfer leaming" by Zhu, R., Qiu, T., Wang, J. et al. Nat. Commun. 12, 2974 (2021), or in the article entitled "Matrix Fourier optics enables a compact full-Stokes polarization camera" by Rubin et al. (SCIENCE - Volume 365 - Issue 6448 - July 5, 2019). .

[0076] The pads 117 of the MS metasurface preferably all have the same height, for example, of the same order of magnitude as the principal wavelength intended to be measured by each pixel P, for example, between 20 nm and 2 pm, preferably between 50 nm and 750 nm, for radiation with wavelengths less than 1 pm. Providing pads 117 of constant height over the entire sensor surface advantageously simplifies the fabrication of the MS metasurface.

[0077] In the example illustrated in Figures IA and IB, the polarization sorter of sensor 100 includes a single MS metasurface. As an alternative, the polarization sorter of the 100 sensor could include several metasurfaces, for example analogous to the MS metasurface.

[0078] Fig. 2 is a schematic and partial top view of an example embodiment of the FP polarizer filter of sensor 100 of figures IA and IB.

[0079] Figure 2 illustrates more specifically the polarization structures of the pixels P of a single macropixel M. In this example, each macropixel M comprises four adjacent pixels P(1), P(2), P(3), and P(4) adapted to measure intensities of received light radiation according to four different polarization orientations P1, P2, P3, and P4, for example, linear polarizations along four directions forming angles of 0°, 90°, 45°, and 135° with respect to a reference direction. In this example, the four pixels P(1), P(2), P(3), and P(4), symbolized by dashed squares in Figure 2, are arranged in a matrix of two rows and two columns.

[0080] Polarization structures 111 are, for example, metallic grids each comprising a plurality of regularly spaced parallel metallic bars, transmitting radiation mainly according to a linear polarization perpendicular to the metallic bars, and absorbing radiation according to other polarizations.

[0081] As an alternative, the number of pixels P per macropixel M may be different from four. Furthermore, the described embodiments are not limited to linear polarization structures 111. As an alternative, each macropixel M may comprise one or more linear polarization structures 111 and / or one or more circular polarization structures 111.

[0082] By way of example, the polarization structures 111 of the pixels P in the same position in the different macropixels M of the sensor are adapted to transmit predominantly the same polarization orientation.

[0083] By way of example, the polarization structures 111 of the same polarization orientation in the different macropixels M of the sensor are all identical, up to manufacturing dispersions.

[0084] As an alternative, the polarization structures 111 of the same polarization orientation in the different macropixels M of the sensor have patterns adapted according to the position of the macropixel M on the sensor, to take into account the principal direction of incidence of the light rays received by the macropixel.

[0085] Although not illustrated in Figures IA and IB, each pixel P of the sensor 100 may include a color filter arranged above the polarization structure and adapted to transmit light predominantly in a specific wavelength range. The color filters are, for example, arranged above the layer of Planarization 115, for example, in contact, by their lower face, with the upper face of layer 115. Different pixels P may include different color filters. For example, the sensor includes pixels P with a color filter adapted to transmit predominantly red light, pixels P with a color filter adapted to transmit predominantly green light, and pixels P with a color filter adapted to transmit predominantly blue light. For example, the pixels P of the same macropixel M include identical color filters, and the pixels P of neighboring macropixels M include different color filters. The color filters are, for example, made of colored resin.

[0086] By way of example, the polarization structures 111 of the same polarization orientation in the different macropixels M of the sensor have patterns adapted according to the color of the pixel, that is to say the range of wavelengths transmitted predominantly by the color filter of the pixel.

[0087] By way of non-limiting example, for linear polarizers of the type illustrated in [Fig.2], made of aluminium with a silicon oxide filling, and intended to operate at visible and / or infrared wavelengths, the dimensioning of the metal bars can be as follows: - for blue light with a wavelength of around 450 nm (and / or for light with a higher wavelength, for example infrared light), the metal bars can have a height between 50 and 100 nm, a width of around 60 nm and a repetition period of around 180 nm; - for green light with a wavelength of around 530 nm (and / or for light with a higher wavelength, for example infrared light), the metal bars can have a height between 50 and 100 nm, a width of around 70 nm and a repetition period of around 210 nm; - for red light with a wavelength of approximately 610 nm (and / or for light with a longer wavelength, for example infrared light), the metal bars can have a height between 50 and 100 nm, a width of approximately 80 nm and a repetition period of approximately 240 nm; and - for infrared light with a wavelength of around 940 nm or higher, the metal bars can have a height between 50 and 100 nm, a width of around 90 nm and a repetition period of around 280 nm.

[0088] In practice, for the sake of simplifying manufacturing processes, it is preferable that the height of the metal bars of the polarization structures 111 be the same in all pixels P of the sensor. Thus, compromises can be made between the manufacturing complexity of the polarizers 111 and their polarization filtering performance.

[0089] Fig. 3 is a schematic and partial top view of an example embodiment of the sensor polarization router of Figures IA and IB.

[0090] Fig. 3 illustrates more particularly an example of the shape and arrangement of the plots 117 of the metasurface MS in the vertical position of a macropixel M. In this example, the macropixel M comprises, as previously explained in relation to Fig. 2, the four adjacent pixels P(1), P(2), P(3) and P(4) adapted to measure intensities of light radiation received according respectively to the four different polarization orientations P1, PS2, PS3 and PS4.

[0091] In the example shown, the metasurface MS comprises a first part MS(1), located directly above pixels P(1) and P(2), and a second part MS(2), located directly above pixels P(3) and P(4). In this example, the first part MS(1) of the metasurface MS has a pattern adapted to implement a routing function for light rays received according to the two polarization states P1 and PS2 towards the polarization structures 111 of the two pixels P(1) and P(2) of the macropixel M, respectively. Similarly, the second part MS(2) of the metasurface MS has a pattern adapted to implement a routing function for light rays received according to the two polarization states PS3 and PS4 towards the polarization structures 111 of the two pixels P(3) and P(4) of the macropixel M, respectively. The components of the incident flux polarized according to the states P1, PS2, PS3, and PS4 are thus deflected towards the pixels P(1), P(2), P(3), and P(4) of the macropixel M, respectively.A photon arriving above pixel P(1) or pixel P(2) will then be sorted into PSI or PS2, and a photon arriving above pixel P(3) or pixel P(4) will be sorted into PS3 or PS4.

[0092] Compared to a polarimetric sensor based on polarizing filters, this advantageously improves the quantum efficiency of the sensor since the entire flux collected opposite each macropixel M is transmitted to the four pixels P(1), P(2), P(3) and P(4) of the macropixel.

[0093] In the example shown, each part MS(1), MS(2) of the metasurface MS is adapted to focus the incident light along two orthogonal axes Ox and Oy, the axes Ox and Oy corresponding respectively to the horizontal axis and the vertical axis, in the orientation of [Fig.3].

[0094] The plots 117, for example, have a constant pitch, that is, a constant center-to-center distance, over the entire metasurface MS. As an example, the pitch of the plot matrix 117 of the metasurface MS is between 250 and 300 nm. In the example shown, parts MS(1) and MS(2) of the metasurface MS each have a perimeter of substantially rectangular shape. This corresponds, for example, to a case where the pixels P of the sensor each have, in top view, a perimeter of substantially square shape, the rectangle formed by each part MS(1), MS(2) of the metasurface MS then having, for example, lateral dimensions substantially equal to those of a rectangle formed by a pair of adjacent pixels P. For example, each part MS(1), MS(2) of the metasurface MS has a length between 4 and 8 pm and a width equal to approximately half the length, for example, between 2 and 4 pm. This example is not limiting, however; the parts MS(1) and MS(2) of the metasurface MS could, for example, have lateral dimensions smaller than those mentioned above, for example, less than 1 pm in a case where the pixels P have a spacing of approximately 0.5 pm or 1 pm.

[0095] By way of alternative, each part MS(1), MS(2) of the metasurface MS can have a perimeter of arbitrary shape, for example, a square. This corresponds, for example, to a case where the pixels P of the sensor each have, in top view, a perimeter of substantially rectangular shape, the square formed by each part MS(1), MS(2) of the metasurface then having, for example, lateral dimensions substantially equal to those of a square formed by a pair of pixels P adjacent along their longer side. An advantage of providing that each part MS(1), MS(2) of the metasurface MS has a square shape is that this facilitates spatial sampling of the image acquired by the pixels P of the sensor 100.

[0096] The pattern of the portion of the metasurface MS located directly above the macropixel M can be repeated identically (within manufacturing dispersions) opposite all the other macropixels M of the sensor.

[0097] As an alternative, the pattern of the portion of the metasurface MS can vary from one macropixel M to another, depending on the position of the macropixel on the sensor, to take into account in particular the principal direction of incidence of the rays arriving on the metasurface MS from the scene to be imaged.

[0098] Fig. 4A and Fig. 4B are respectively an exploded perspective view and a cross-sectional view of another example of a 400 polarimetric image sensor according to one embodiment.

[0099] The polarimetric image sensor 400 of Figures 4A and 4B includes elements common to the polarimetric image sensor 100 of Figures IA and IB. These common elements will not be detailed again below.

[0100] The sensor 400 of Figures 4A and 4B differs from the sensor 100 of Figures 1A and 1B in that the sensor 400 lacks the polarizing filter FP and comprises, on the side of the polarization router opposite the photodetectors 107, a plurality of microlenses 401. In the example shown, each microlens 401 has an elongated shape extending opposite a pair of adjacent pixels P of the sensor 400. Each microlens 401 has, for example, in top view, an oval or rectangular cross-section with rounded corners. This corresponds, for example, to a case where the pixels P of the sensor each have, in top view, a substantially square perimeter, each microlens 401 then having, for example, lateral dimensions equal to those of a rectangle formed by a pair of adjacent pixels P. In the example shown, the 401 microlenses are refractive microlenses.

[0101] By way of alternative, each microlens 401 may have any shape, for example a circular or square perimeter with rounded corners, in top view. This corresponds, for example, to a case where the pixels P of the sensor each have, in top view, a perimeter of substantially rectangular shape, the circle or square formed by the perimeter of each microlens 401 then having, for example, respectively a diameter or a side substantially equal to the side of a square formed by a pair of pixels P adjacent by their longer side.

[0102] By way of example, each microlens 401 is made of flowable resin.

[0103] Fig. 5 is a schematic, partial top view of an example embodiment of the sensor 400 polarization router of Figures 4A and 4B.

[0104] [Fig.5] illustrates more particularly an example of the shape and arrangement of the pads 117 of the metasurface MS of the sensor 400 in line with a macropixel M. In this example, the macropixel M comprises, as previously explained in relation to [Fig.2], the four adjacent pixels P(1), P(2), P(3) and P(4) adapted to measure intensities of light radiation received according respectively to the four different polarization orientations P1, PS2, PS3 and PS4.

[0105] In the example shown, the metasurface MS comprises, as previously explained in relation to [Fig.3], the first part MS(1) located directly above pixels P(1) and P(2), and the second part MS(2) located directly above pixels P(3) and P(4). In this example, the first part MS(1) of the metasurface MS has a pattern adapted to implement a routing function for light rays received according to the two polarization states P1 and PS2 to the two pixels P(1) and P(2) of the macropixel M, respectively. Similarly, the second part MS(2) of the metasurface MS has a pattern adapted to implement a routing function for light rays received according to the two polarization states PS3 and PS4 to the two pixels P(3) and P(4) of the macropixel M, respectively. The components of the incident flux polarized according to the states P1, PS2, PS3, and PS4 are thus deflected to the pixels P(1), P(2), P(3), and P(4) of the macropixel M, respectively.A photon arriving above pixel P(1) or pixel P(2) will then be sorted into PSI or PS2, and a photon arriving above pixel P(3) or pixel P(4) will be sorted into PS3 or PS4.

[0106] In the example shown, the lines of plots 117 in part MS(1) of the metasurface MS are identical to each other. Similarly, the lines of plots 117 in part MS(2) of the metasurface MS are identical to each other.

[0107] In the example shown, each microlens 401 extends over a portion MS(1) or MS(2) of the metasurface MS and is adapted to focus the incident light along the orthogonal axes Ox and Oy (the horizontal axis and the vertical axis, in The orientation of [Fig. 5]) on the underlying MS(1) or MS(2) portion of the MS metasurface. As an example, each microlens 401 exhibits astigmatism and, more specifically, has a focal length along the Oy axis strictly shorter than the focal length along the Ox axis. This corresponds, for example, to a case where the sensor's P pixels each have, in top view, a roughly square perimeter. Alternatively, each microlens 401 does not exhibit astigmatism. This corresponds, for example, to a case where the sensor's P pixels each have, in top view, a roughly rectangular perimeter, with each microlens 401 having a roughly circular perimeter. As an example, each microlens 401 has a focal length along the Oy axis of the order of the distance separating the microlens from the upper face of the substrate 101 (the face of the substrate 101 opposite the interconnection stack 103).Furthermore, in this example, each part MS(1), MS(2) of the MS metasurface is adapted to focus the incident light mainly, or even exclusively, along an axis parallel to the rows of studs 117, here the Ox axis. Thus, in this example, focusing is achieved jointly by the microlenses 401 and by the MS metasurface.

[0108] This simplifies the design and implementation of the MS metasurface of the 400 sensor compared to the MS metasurface of the 100 sensor. For example, it allows, in the 400 sensor, a MS metasurface of less thickness than in the case of the 100 sensor, the shape of the MS metasurface of the 400 sensor being able to be adapted to generate phase jumps and phases in the vicinity of the corners of each part MS(1) and MS(2) less than the case of the MS metasurface of the 100 sensor.

[0109] As an alternative, focusing can be achieved primarily or even solely by the 401 microlenses, with the MS metasurface then, for example, lacking a focusing function. This further simplifies the design and fabrication of the MS metasurface.

[0110] Fig. 6A and Fig. 6B are respectively an exploded perspective view and a cross-sectional view of another example of a 600 polarimetric image sensor according to one embodiment.

[0111] The polarimetric image sensor 600 of Figures 6A and 6B comprises elements common with the polarimetric image sensor 400 of figures 4A and 4B. These common elements will not be detailed again below.

[0112] The 600 sensor of Figures 6A and 6B differs from the 400 sensor of Figures 4A and 4B in that the 600 sensor comprises, in addition to the microlenses 401 and the metasurface MS, a polarizing filter FP interposed between the substrate 101 and the metasurface MS. The polarizing filter FP of the 600 sensor is, for example, analogous to the polarizing filter FP of the 100 sensor previously described in relation to Figures IA and IB.

[0113] [Fig.7] is a schematic and partial cross-sectional view of the FP polarizer filter of the sensor 600 in Figures 6A and 6B. [Fig.7] is more particularly a detailed view of a part of the FP polarizer filter delimited by a dashed box 601 in [Fig.6B].

[0114] According to one embodiment, the FP filter comprises, for each pixel P, a polarization structure 111 comprising a plurality of parallel metal bars 701, each bar being coated with an anti-reflective or absorbing stack 703 comprising, in order from the top face of the bars 701: - a layer of tungsten 705; - a layer of silicon 707, for example amorphous silicon, coating the tungsten 705 layer; and - a dielectric layer 709, coating the silicon layer 707.

[0115] For example, the 701 metal bars are made of tungsten or aluminium.

[0116] Layer 709 is, for example, a silicon oxide layer or a silicon nitride layer. Alternatively, layer 709 may consist of a stack of several layers of dielectric materials with refractive indices lower than that of silicon, for example, one or more silicon oxide layers and one or more silicon nitride layers.

[0117] The thicknesses of the layers 705, 707 and 709 of the stack 703 are chosen so that the stack 703 has, for a central wavelength X0 of the photodetector 107, an absorption coefficient greater than that of the material 115. The stack 703 is dimensioned so that, for the central wavelength X0 of the photodetector 107 and for incident radiation substantially orthogonal to the mean plane of the stack 703, more than 50%, preferably more than 80%, even more preferably more than 95%, of the radiation entering the stack 703 is absorbed in the stack 703 in a single pass. In other words, more than 50%, preferably more than 80%, even more preferably more than 95%, of radiation entering through the top face of stack 703 is absorbed in stack 703 and is not reflected back to the region in material 115.For example, for the center wavelength X0, approximately 90% of the radiation entering the 703 stack is absorbed in the 703 stack in a single pass. For example, more than 50%, preferably more than 80%, and even more preferably more than 90% of all radiation in the wavelength range between 920 nm and 960 nm is absorbed in a single pass in the 703 stack. Preferably, more than 50%, preferably more than 80%, and even more preferably more than 90% of all radiation in the FP filter's passband is absorbed in a single pass in the 703 stack.

[0118] To maximize absorption in stacking 703, the thickness of the layer of The tungsten 705 layer is preferably relatively thick, for example greater than 40 nm and preferably greater than 60 nm in the case where the metal bars 701 are made of a material other than tungsten. Alternatively, in the case where the metal bars 701 are made of tungsten, the bars 701 and the layer 705 have, for example, a combined thickness greater than 40 nm and preferably greater than 60 nm.

[0119] Numerical simulations allow adjustment of the required silicon thickness to maximize absorption, depending on the various parameters of the 703 stack and / or the central wavelength X0. As an example, the thickness of the 705 silicon layer is between 20 and 100 nm, preferably between 30 and 50 nm, for example equal to about 39 nm.

[0120] In the FP polarizer filter of the 600 sensor, the presence of the absorbing structure 703 advantageously reduces the detection of parasitic radiation in the near infrared, and thus improves image quality.

[0121] Fig. 8 is a cross-sectional view of another example of a polarimetric image sensor 800 according to one embodiment.

[0122] The polarimetric image sensor 800 of [Fig.8] includes elements common to the polarimetric image sensor 400 of Figures 4A and 4B. These common elements will not be detailed again below.

[0123] The 800 sensor of [Fig.8] differs from the 400 sensor of Figures 4A and 4B in that, in the 800 sensor, the microlenses 401 are interposed between the photodetectors 107 of the P pixels and the two-dimensional metasurface MS of the polarization router.

[0124] In this example, the microlenses 401 are located in the planarization layer 115. The microlenses 401 are made of a material having an optical index higher than that of the material of the planarization layer 115. In the case where the planarization layer 115 is made of silicon oxide, the microlenses 401 are formed for example, for example by shape transfer, in a layer of silicon nitride or amorphous silicon.

[0125] Interposing the microlenses 401 between the metasurface MS and the photodetectors 107 allows, for example, the incident radiation to be distributed within a cone defined by a lens (not shown) placed in front of the sensor 100, more precisely defined by an aperture f / Dp of this lens, where f represents the focal length and Dp the diameter of the lens's entrance pupil. An advantage of interposing the microlenses 401 below the metasurface MS is that it allows the angles of incidence related to the cone of distribution of the incident radiation to be smaller than those that would be produced, under analogous conditions, if the microlenses 401 were arranged above the metasurface MS. This advantageously facilitates the design and manufacture of the metasurface MS, the metasurface MS being, for example, designed and optimized for be used at a given angle of incidence, for example at normal incidence, and have an angular acceptance lower than that of a "classical" refractive optic such as a lens.

[0126] However, placing the microlenses 401 between the metasurface MS and the photodetectors 107 is likely to cause undesirable crosstalk, meaning that some of the radiation incident directly above a given macropixel M may reach at least one of the macropixels adjacent to that macropixel. This is particularly true when the metasurface MS has a weak or even non-existent focusing power (i.e., a very long or even infinite focal length), as the incident radiation is then mostly, or entirely, deflected by the metasurface MS according to its polarization. The crosstalk phenomenon is more pronounced when the deflection caused by the metasurface MS is significant and the distance between the metasurface MS and the microlenses 401 is large.

[0127] To overcome this drawback, the metasurface MS is, for example, designed and manufactured to have a focusing function such that the radiation deviated according to its polarization, for example, the radiation deviated by the first part MS(1) of the metasurface MS according to P1 and PS2 for pixels P(1) and P(2) of a macropixel M, reaches only the underlying microlens 401. Each part MS(1), MS(2) of the metasurface MS has, for example, a focal length fl greater than the focal length f2 of the underlying microlens 401.

[0128] By way of example, the focal length fl of each part MS(1), MS(2) of the metasurface MS is given by the following formula: [Math 1] fi < XmLi 11 - 2

[0129] In equation [Math 1] above, 0 represents the angle of deflection of a polarization by the metasurface (polarization PSI or PS2, for part MS(1) of the metasurface MS, or polarization PS3 or PS4, for part MS(2) of the metasurface MS), and D represents the maximum lateral dimension of the underlying microlens 401 (for example the major axis of the microlens 401, in the case where the microlens 401 has an ellipsoidal section).

[0130] The deflection angle 0 corresponds for example to a deviation angle, by the metasurface MS, of radiation arriving, under normal incidence, at the center of the part MS(1), respectively MS(2), of the metasurface MS as a function of the polarization PSI or PS2, respectively PS3 or PS4, of the incident radiation.

[0131] Another solution for avoiding, or mitigating, the phenomenon of diaphoty is set out below in relation to [Fig.9].

[0132] Fig. 9 is a cross-sectional view of another example of a 900 polarimetric image sensor according to one embodiment.

[0133] The 900 polarimetric image sensor of [Fig. 9] includes elements common to the 800 polarimetric image sensor of [Fig. 8]. These common elements will not be detailed again below.

[0134] The 900 sensor of [Fig. 9] differs from the 800 sensor of [Fig. 8] in that the 900 sensor further comprises, on the side of the polarization router opposite the photodetectors 107, a plurality of microlenses 901 distinct from the microlenses 401. The microlenses 901 are, for example, analogous to the microlenses 401. In the example shown, each microlens 901 has an elongated shape extending opposite a pair of adjacent pixels P of the 900 sensor, for example pixels P(1) and P(2) or pixels P(3) and P(4) of one of the macropixels M. Each microlens 901 has, for example, in top view, an oval or rectangular cross-section with rounded corners. This example is not exhaustive, however; the 401 microlenses can, as an alternative, have any shape, for example circular or square with rounded corners, as previously explained. In the example shown, the 901 microlenses are refractive microlenses.

[0135] By way of example, each microlens 901 is made of flowable resin.

[0136] In the example shown, the microlenses 901 have a focal length f3 greater than the focal length f2 of the microlenses 401.

[0137] By way of example, the focal length f3 of each microlens 901 is given by the following equation: [Math 2] n < Dxd 1 2tan9xd2

[0138] In equation [Math 2] above: - 0 represents the deflection angle of a polarization by the metasurface (the PSI or PS2 polarization, for the MS(1) part of the MS metasurface, or the PS3 or PS4 polarization, for the MS(2) part of the MS metasurface); - D represents the maximum lateral dimension of the underlying microlens 401 (for example the major axis of the microlens 401, in the case where the microlens 401 has an ellipsoidal section); - dl represents the distance between the lower face of the microlens 901 and the lower face of the metasurface MS, in the orientation of [Fig.9]; and - d2 represents the distance between the lower face of the MS metasurface and the lower face of the 401 microlens, in the orientation of [Fig.9].

[0139] Various embodiments and variations have been described. A person skilled in the art will understand that certain features of these various embodiments and Variants could be combined, and other variants will appear to a person skilled in the art. From the indications in this description, a person skilled in the art is particularly able to foresee, in sensors 100 and 400, a polarizing filter having a structure analogous to the polarizing filter of sensor 600, that is to say comprising a plurality of parallel metal bars coated with an absorbing stack.

[0140] In addition, although not shown, the sensors 800 and 900 previously described in relation to Figures 8 and 9 may include a polarizing filter interposed between the photodetectors 107 and the microlenses 401, for example a polarizing filter identical or analogous to the FP polarizing filter of sensor 600 or the FP polarizing filter of sensor 100.

[0141] Moreover, the embodiments described are not limited to the examples of dimensions and materials mentioned in this description for the realization of metasurfaces.

[0142] Although examples of backside illumination (BSI) sensor embodiments have been described above, the described embodiments can be adapted to frontside illumination (FSI) sensors. In this case, the photosensitive region of each pixel is illuminated through the interconnect stack 103. The polarizing filter and / or the polarizing router are then formed on the front side (lower face in the orientation of [Fig. 1B]) of the substrate, before the formation of the interconnect stack 103.

[0143] Furthermore, in the case of a front-facing illumination sensor, the polarization structures 111 can be formed in one or more metallic levels of the interconnect stack 103. This makes it possible to avoid introducing an additional step for the fabrication of the polarization structures 111.

[0144] Furthermore, the described embodiments are not limited to the examples presented above of polarization structures 111 made of opaque metallic motifs laterally surrounded by a transparent dielectric material. As an alternative, the polarization structures 111 can be made of transparent or semi-transparent materials exhibiting a refractive index contrast, so as to improve the transmission of the polarizers. For example, for polarization structures intended to operate in the near-infrared, for example at a wavelength of approximately 940 nm, silicon motifs, for example amorphous silicon, surrounded by a dielectric material with a lower refractive index, for example silicon oxide, can be used.For pixels intended to measure visible radiation, patterns made of silicon nitride or titanium oxide can be used, surrounded by a dielectric material with a lower refractive index, for example silicon oxide.

[0145] It will also be noted that, in a rear-facing illumination sensor of the type described in relation to Figures IA and IB, depending on the thickness of the substrate 101 and the wavelength intended to be measured by the pixels, part of the incident light radiation can pass through the entire thickness of the substrate and be reflected on metallic tracks of the interconnect stack 103, before being absorbed in the photosensitive region 105 of the pixels.

[0146] Reflection on the metal tracks of the interconnect stack can lead to at least partial polarization of the light in a direction dependent on the orientation of said metal tracks. Preferably, for each pixel P of the sensor, the metal tracks of the interconnect stack 103 located opposite the pixel are oriented in a direction chosen according to the pixel's polarization, for example, so as to favor the polarization of the reflected light in the polarization orientation intended to be measured by the pixel. Thus, preferably, the metal tracks of the interconnect stack 103 located opposite pixels intended to measure different polarizations have different orientations.

[0147] Furthermore, the described embodiments are not limited to the application examples described above for visible sensors. Other wavelength ranges can benefit from polarizing pixels. For example, the described embodiments can be adapted to infrared sensors for measuring radiation with wavelengths between 1 and 2 pm, for example based on InGaAs or germanium.

[0148] Furthermore, although above examples have been described in which the PSI and PS2 polarizations are orthogonal and the PS3 and PS4 polarizations, rotated 45° with respect to the PSI and PS2 polarizations respectively, are orthogonal, a person skilled in the art is able to adapt the embodiments of this description to cases where the PSI and PS2 polarizations are not orthogonal and / or the PS3 and PS4 polarizations are not orthogonal, the PS3 and PS4 polarizations being able in addition to being rotated by a different angle of 45° with respect to the PSI and PS2 polarizations.

[0149] Finally, the practical implementation of the described embodiments and variants is within the reach of a person skilled in the art, based on the functional specifications given above. In particular, a person skilled in the art will be able, based on the specifications in this description, to design, dimension, and fabricate the metasurfaces and polarizing filters and / or microlenses of the sensor pixels, so that these structures cooperate to achieve the desired effect of improving the trade-off between the sensitivity and the polarization extinction coefficient of the pixels.

Claims

Demands

1. Polarizing filter (PF) intended to be disposed opposite an image sensor (100; 400; 600; 800; 900) comprising a plurality of pixels (P), the filter comprising, for each pixel, a polarizing structure (111) comprising a plurality of parallel metal bars (701), each bar being coated with an absorbing stack (703) comprising: - a tungsten layer (705); - a silicon layer (707), coating the tungsten layer; and - a dielectric layer (709), coating the silicon layer.

2. Filter according to claim 1, wherein the metal bars (701) are made of a material other than tungsten, preferably aluminum.

3. Filter according to claim 2, wherein the tungsten (705) layer has a thickness greater than 40 nm, preferably greater than 60 nm.

4. Filter according to claim 1, wherein the metal bars (701) are made of tungsten.

5. Filter according to claim 4, wherein the metal bars (701) and the tungsten layer (705) have a cumulative thickness greater than 40 nm, preferably greater than 60 nm.

6. Filter according to any one of claims 1 to 5, wherein the silicon layer (707) has a thickness of between 20 and 100 nm, preferably between 30 and 50 nm, for example about 39 nm.

7. Filter according to any one of claims 1 to 6, wherein the dielectric layer (709) is made of silicon oxide.

8. Filter according to any one of claims 1 to 6, wherein the dielectric layer (709) is made up of a stack of several layers of dielectric materials with refractive indices lower than that of silicon.

9. Polarimetric image sensor (100; 400; 600) formed in and on a semiconductor substrate (101), the sensor comprising: - a plurality of pixels (P) each comprising a photodetector (107) formed in the semiconductor substrate; and - a polarizing filter (FP) according to any one of claims 1 to 8, the filter being disposed on the side of an illumination face of the photodetectors.

10. Sensor (100; 600; 800; 900) according to claim 9, wherein said plurality of pixels (P) comprises at least first and second pixels (P(1), P(2)) adapted to measure radiation according to distinct first and second polarizations respectively, the polarization structure (111) of the first pixel (P(1)) being adapted to transmit predominantly radiation according to the first polarization and the polarization structure (111) of the second pixel (P(2)) being adapted to transmit predominantly radiation according to the second polarization.

11. Sensor (100; 600; 800; 900) according to claim 10, wherein said plurality of pixels (P) further comprises third and fourth pixels (P(3), P(4)) adapted to measure radiation according to third and fourth distinct polarizations, different from the first and second polarizations, the polarization structure (111) of the third pixel (P(3)) being adapted to transmit predominantly radiation according to the third polarization and the polarization structure (111) of the fourth pixel (P(4)) being adapted to transmit predominantly radiation according to the fourth polarization.

12. Sensor (100; 600; 800; 900) according to claim 11, wherein the first, second, third and fourth polarizations are linear polarizations along first, second, third and fourth directions forming angles of 0°, 90°, 45° and 135° respectively with respect to a reference direction.

13. Sensor (600; 800; 900) according to any one of claims 9 to 12, further comprising a polarization router comprising a two-dimensional metasurface (MS) disposed on the side of the polarizer filter (FP) opposite the photodetectors, the metasurface comprising a two-dimensional array of dots (117).

14. Sensor (600; 800; 900) according to claim 13, in its dependence on claim 11 or 12, wherein the two-dimensional metasurface (MS) comprises: - a first part (MS(1)) located directly above the first and second pixels (P(1), P(2)) adapted to transmit predominantly: radiation according to the first polarization towards the first pixel (P(1)); and radiation according to the second polarization towards the second pixel (P(2)), and - a second part (MS(2)) located directly above the third and fourth pixels (P(3), P(4)) adapted to transmit mainly: radiation according to the third polarization towards the third pixel (P(3)); and radiation according to the fourth polarization towards the fourth pixel (P(4)).

15. Sensor (600; 800; 900) according to any one of claims 9 to 14, further comprising a plurality of first microlenses (401) extending opposite a pair of adjacent pixels (P(1), P(2)) of the sensor.

16. Sensor (600; 800; 900) according to claim 15, wherein the first microlenses (401) each have an elongated shape.

17. Sensor (600; 800; 900) according to claim 15 or 16, in its dependence on claim 13 or 14, wherein the first microlenses (401) are: A) disposed on the side of a face of the two-dimensional metasurface (MS) opposite to the photodetectors (107); or B) interposed between the photodetectors and the two-dimensional metasurface.

18. Sensor (900) according to claim 17, in its option B), further comprising a plurality of second microlenses (901) distinct from the first microlenses (401) and arranged on the side of a face of the two-dimensional metasurface (MS) opposite the photodetectors (107), each second microlens extending opposite a pair of adjacent pixels (P(1), P(2)) of the sensor.

19. Sensor (900) according to claim 18, wherein each second microlens (901) has an elongated shape.

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