Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/20—Filters
  • G02B5/201—Filters in the form of arrays
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/04—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings formed by bundles of fibres
  • G02B6/06—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings formed by bundles of fibres the relative position of the fibres being the same at both ends, e.g. for transporting images
  • G02B6/08—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings formed by bundles of fibres the relative position of the fibres being the same at both ends, e.g. for transporting images with fibre bundle in form of plate
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B2207/00—Coding scheme for general features or characteristics of optical elements and systems of subclass G02B, but not including elements and systems which would be classified in G02B6/00 and subgroups
  • G02B2207/123—Optical louvre elements, e.g. for directional light blocking
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B3/00—Simple or compound lenses
  • G02B3/0006—Arrays

Definitions

• This description relates to an optical filter and more specifically an angular optical filter.
• the present description relates to an angular filter intended to be used within an optical system, for example, a biometric imaging system.
• An angular filter is a device making it possible to filter incident radiation as a function of the incidence of this radiation and thus block the rays whose incidence is greater than a maximum incidence.
• Angle filters are frequently used in conjunction with image sensors.
• One embodiment overcomes all or part of the drawbacks of known angular optical filters.
• One embodiment provides an optical angular filter comprising: a network of pillars in a first transparent material; a matrix of walls in a second opaque material, separating the pillars from each other, the ratio between the refractive indices of the first and second materials depending on the wavelength.
• the difference between the refractive indices of the first and second materials changes sign at a given wavelength.
• the ratio between the refractive indices of the materials is reversed for a given wavelength.
• the refractive index of the first material is, for wavelengths in the infrared range, greater than the refractive index of the second material and, for wavelengths of wave in the visible range, lower than the refractive index of the second material.
• the refractive index of the second material is lower than that of the first material, for at least part of the spectrum.
• the refractive index difference between the two materials is between 0.001 and 0.5.
• the refractive index of the first material is, depending on the wavelength, between 1.55 and 1.65 and is equal, at a wavelength less than said wavelength given wave, of the order of 1.57, preferably 1.57.
• the refractive index of the second material is, at a wavelength lower than said given wavelength, between 1.45 and 1.6.
• the refractive index of the second material is between 1.52 and 1.57 and is, at a wavelength less than said given wavelength, of the order of 1.55, preferably 1.55. According to one embodiment, the refractive index of the second material is between 1.45 and 1.5 and is, at a wavelength less than said given wavelength, of the order of 1.49, preferably 1.49.
• the thickness of the filter is chosen according to the selectivity desired for the angular filter.
• the first and second materials are organic resins.
• the angular filter further comprises an array of microlenses.
• One embodiment provides an image acquisition device comprising an angular filter.
• Figure 1 shows, by a block diagram, partial and schematic, an embodiment of an image acquisition system
• FIG. 2 shows, in a partial and schematic sectional view, an embodiment of an image acquisition device comprising an angular filter
• Figure 3 illustrates in a schematic sectional view, the operation of an embodiment of an angular filter
• Figure 4 illustrates by another schematic sectional view, the operation of an embodiment of an angular filter
• Figure 5 illustrates by yet another schematic sectional view, the operation of an embodiment of an angular filter
• FIG. 6 represents examples of transmittance of angular filters
• FIG. 7 illustrates the operation of a preferred embodiment of an angle filter.
• a layer or a film is said to be opaque to radiation when the transmittance of the radiation through the layer or the film is less than 10%. In the rest of the description, a layer or a film is said to be transparent to radiation when the transmittance of the radiation through the layer or the film is greater than 10%, preferably greater than 50%.
• all the elements of the optical system which are opaque to radiation have a transmittance which is less than half, preferably less than a fifth, more preferably less than a tenth, of the transmittance the weakest of the elements of the optical system transparent to said radiation.
• useful radiation is used to refer to the electromagnetic radiation passing through the optical system in operation.
• optical element of micrometric size refers to an optical element formed on one face of a support whose maximum dimension, measured parallel to said face, is greater than 1 ⁇ m and less than 1 mm.
• each micrometric-sized optical element corresponds to a micrometric-sized lens, or microlens, composed of two diopters.
• each optical element of micrometric size being able to correspond, for example, to a Fresnel lens of micrometric size, to a micron-sized gradient index lens or to a micron-sized diffraction grating.
• visible light is called electromagnetic radiation whose wavelength is between 400 nm and 700 nm
• green light is electromagnetic radiation whose wavelength is between 400 nm and 600 nm, more preferably between 470 nm and 600 nm.
• Infrared radiation is electromagnetic radiation with a wavelength between 700 nm and 1 mm. In infrared radiation, a distinction is made in particular between near-infrared radiation, the wavelength of which is between 700 nm and 1.7 ⁇ m, more preferably between 850 nm and 940 nm.
• Figure 1 illustrates, by a block diagram, partial and schematic, an embodiment of an image acquisition system 11.
• the image acquisition system 11, illustrated in FIG. 1, comprises: an image acquisition device 13 (DEVICE); and a processing unit 15 (PU).
• DEVICE image acquisition device 13
• PU processing unit 15
• the processing unit 15 preferably comprises signal processing means provided by the device 11, not shown in Figure 1.
• the processing unit 15 comprises, for example, a microprocessor.
• the device 13 and the processing unit 15 are preferably connected by a connection 17.
• the device 13 and the processing unit 15 are, for example, integrated in the same circuit.
• Figure 2 shows, in a sectional view, partial and schematic, an embodiment of an image acquisition device 19 comprising an angular filter.
• the image acquisition device 19 shown in Figure 2 comprises, from bottom to top in the orientation of the figure: an image sensor 21; and an angular filter 23, covering the image sensor 21.
• the embodiments of the devices of FIGS. 2 to 5 are represented in space according to a direct orthogonal XYZ frame, the Z axis of the XYZ frame being orthogonal to the upper face of the image sensor. 21.
• the image sensor 21 comprises an array of photon sensors, also called photodetectors.
• the photodetectors are preferably arranged in matrix form.
• the photodetectors can be covered with a protective coating, not shown.
• the photodetectors all have the same structure and the same properties/characteristics. In other words, all the photodetectors are substantially identical within manufacturing tolerances.
• the photodetectors do not all have the same characteristics and may be sensitive to different wavelengths.
• photodetectors can be sensitive to infrared radiation and photodetectors can be sensitive to radiation in the visible range.
• the image sensor 21 further comprises conductive tracks and switching elements, in particular transistors, not shown, allowing the selection of photodetectors.
• the photodetectors are preferably made of organic materials.
• the photodiodes are, for example organic photodiodes (OPD, Organic Photodiode) integrated on a substrate with CMOS transistors (Complementary Metal Oxide Semiconductor, complementary metal oxide semiconductor) or a substrate with thin film transistors (TFT or Thin Film Transistor).
• the substrate is for example made of silicon, preferably of monocrystalline silicon.
• the channel, source and drain regions of TFT transistors are for example made of amorphous silicon (a-Si or amorphous Silicon), indium, gallium, zinc and oxide (IGZO Indium Gallium Zinc Oxide) or low temperature polycrystalline silicon ( LTPS or Low Temperature Polycrystalline Silicon).
• the photodiodes of the image sensor 21 comprise, for example, a mixture of organic semiconductor polymers such as poly(3-hexylthiophene) or poly(3-hexylthiophene-2,5-diyl), known under the name P3HT , mixed with methyl [6,6]-phenyl-C61-butanoate (N-type semiconductor), known as PCBM.
• organic semiconductor polymers such as poly(3-hexylthiophene) or poly(3-hexylthiophene-2,5-diyl)
• P3HT organic semiconductor polymers
• P3HT poly(3-hexylthiophene) or poly(3-hexylthiophene-2,5-diyl
• PCBM methyl [6,6]-phenyl-C61-butanoate
• the photodiodes of the image sensor 21 comprise, for example, small molecules, that is to say molecules having molar masses of less than 500 g/mol, preferably less than 200 g/mol.
• the photodiodes can be inorganic photodiodes, for example, made from amorphous silicon or crystalline silicon.
• the photodiodes are composed of quantum boxes (quantum dots).
• the angular filter 23 comprises, according to the embodiments described, a matrix 31 or layer of holes or openings 33 in a first opaque material, filled with a second transparent material forming a network or a matrix of transparent pillars 33.
• the first material defines opaque walls 35 forming a grid around the transparent pillars 33. of transparent pillars 33 and that the interstices between the pillars are filled with an opaque material forming a grid in each mesh of which there is a transparent pillar.
• the transparency and opacity of the constituent materials of the angular filter is understood in relation to the radiation to which the image acquisition device applies.
• the pillar 33 have, in the XZ plane, a decreasing section in the direction of the sensor 21.
• the walls 35 have, conversely, in the XZ plane, a growth section towards the sensor.
• the pillars and walls have regular sections in the thickness (dimension Z) of the filter 23.
• each pillar 33 (or opening 33 in the angular filter) can have a trapezoidal, rectangular shape or have the shape of a funnel.
• Each pillar 33 seen from above (that is to say in the XY plane), can have a circular, oval or polygonal shape, for example triangular, square, rectangular or trapezoidal.
• Each pillar 33 seen from above, has a preferably circular shape
• the width of a pillar 33 is defined as the characteristic dimension of the pillar 33 in the XY plane. For example, for a pillar 33 having a square section in the XY plane, the width corresponds to the dimension of one side and for a pillar 33 having a circular section in the XY plane, the width corresponds to the diameter of the pillar 33.
• the center of a pillar 33 is the point located at the intersection of the axis of symmetry of the pillars 33 and of the lower face of the level, matrix or layer, 31.
• the center of each pillar 33 is located on the axis of revolution of the pillar 33.
• the role of the angular filter 23 is to control the rays received by the image sensor according to the incidence of these rays on the outer surface of the filter.
• An angular filter makes it possible more particularly to select only the light of a scene to be imaged with an incidence close to the normal.
• An angular filter is generally characterized by the width of the transmission peak at mid-height (in degrees) of its maximum transmittance.
• the angular filter further comprises an array 27 of microlenses 29 of micrometric size, for example plano-convex.
• the array 27 of microlenses 29 is formed on a substrate or support 30 and in contact with the latter, the substrate 30 then being interposed between the microlenses 29 and the matrix 31.
• the substrate 30 may be made of a transparent polymer which does not absorb, at least, the wavelengths considered, here in the visible and near-infrared range.
• This polymer can in particular be poly(ethylene terephthalate) PET, poly(methyl methacrylate) PMMA, polymer of inecyclic olefin (COP), polyimide (PI), polycarbonate (PC).
• the thickness of the substrate 30 can vary between 1 ⁇ m and 100 ⁇ m, preferably between 10 ⁇ m and 100 ⁇ m.
• the substrate 30 can correspond to a colored filter, to a polarizer, to a half-wave plate or to a quarter-wave plate.
• the microlenses 29 can be made of silica, of PMMA, of a positive photosensitive resin, of PET, of poly(ethylene naphthalate) (PEN), of COP, of polydimethylsiloxane (PDMS)/silicone, of epoxy resin or in acrylate resin.
• the microlenses 29 can be formed by creeping blocks of a photosensitive resin.
• the microlenses 29 can additionally be formed by molding on a layer of PET, PEN, COP, PDMS/silicone, epoxy resin or acrylate resin.
• the microlenses 29 are converging lenses each having a focal distance f of between 1 ⁇ m and 100 ⁇ m, preferably between 1 ⁇ m and 70 ⁇ m. According to one embodiment, all the microlenses 29 are substantially identical.
• the microlenses 29 and the substrate 30 are preferably made of transparent or partially transparent materials, that is to say transparent in a part of the spectrum considered for the targeted domain, for example, imaging, over the range of wavelengths corresponding to the wavelengths used during the exposure of an object to be imaged.
• the flat faces of the microlenses 29 face the pillars 33.
• the microlenses 29 are organized in the form of a grid of rows and columns.
• the microlenses 29 are, for example, aligned.
• the repeating pattern of microlenses 29 is, for example, a square in which microlenses 29 are located at the four corners of the square.
• the microlenses 29 are organized in the form of a grid of rows and staggered columns.
• the repeating pattern of the microlenses 29 is, for example, a square in which the microlenses 29 are located at the four corners and in the center of the square.
• the arrangement of the microlenses and, preferably, the meshes of the angular filter are generally hexagonal in shape.
• the thickness or height (in the Z direction) of the matrix 31 is called "h".
• the height "h” of the matrix 31 (and preferably of the angular filter 23) is approximately constant, preferably constant.
• the transparent pillars 33 can all have substantially the same dimensions.
• w the width (in the direction X in the case of a square mesh) of a pillar 33 (measured at the base of the pillar, that is to say at the interface with the substrate 30) .
• the dimension in the orthogonal Y direction is preferably the same as in the X direction.
• the width “w” corresponds to the dimension between the two most distant opposite sides two by two.
• “p” is the repetition pitch of the pillars 33, that is to say the distance between the centers of two successive pillars 33.
• the pitch p can be between 5 ⁇ m and 50 ⁇ m, for example be equal to approximately 12 ⁇ m or approximately 18 ⁇ m.
• the height h can be between 1 ⁇ m and 1 mm, preferably between 5 ⁇ m and 30 ⁇ m, even more preferably between 10 ⁇ m and 20 ⁇ m.
• the width w is, preferentially, comprised between 0.5 ⁇ m and 25 ⁇ m, for example, approximately equal to 10 ⁇ m and even more preferentially comprised between 3 ⁇ m and 6 ⁇ m, for example approximately 4 ⁇ m.
• Each pillar 33 is preferably associated with a single microlens 29 of the array 27.
• the optical axes of the microlenses 29 are preferably aligned with the centers of the pillars 33 of the matrix 31.
• the diameter of the microlenses 29 is , preferably greater than the maximum section (measured perpendicular to the optical axes) of the pillars 33.
• the structure associating the array 27 of microlenses 29 and the matrix 31 is adapted to filter the incident radiation according to its wavelength and the incidence of the radiation with respect to the optical axes of the microlenses 29 of the array 27.
• the structure is adapted to filter the incident rays, arriving on the microlenses, according to their incidences and their wavelengths. In the absence of a microlens, the radiation is less concentrated and focused by the filter nevertheless plays its role of filtering the incident radiation with respect to the axis of the pillars 33.
• the dimensions in the XY plane of the openings of the filter or of the transparent pillars 33 is for example a function of the size of the pixels of the image acquisition device.
• the described embodiments plan to take advantage of particular properties of the constituent materials of the matrix of transparent pillars 33 and of the walls 35 which separate them. More particularly, provision is made to select these materials, preferably organic resins, as a function of their respective refractive indices in order to control the characteristics of the angular filter. More specifically, different refractive indices are provided for the pillars and for the walls.
• the constituent materials of the pillars 33 and the walls 35 preferably being solid materials, but in a simplified embodiment, pillars 33 of air may be provided.
• Figure 3 illustrates by a schematic sectional view, the operation of an embodiment of an angular filter.
• Figure 4 illustrates by another schematic sectional view, the operation of an embodiment of an angular filter.
• Figure 5 illustrates by yet another schematic sectional view, the operation of an embodiment of an angular filter.
• Figures 4 and 5 are schematic representations illustrating the impact of the incidence of a beam of incident rays on the response of the filter.
• a beam of rays of relatively low incidence is assumed and, in the example of FIG. 5, a beam f of relatively high incidence (compared to the low incidence of figure 4.
• FIG. 6 represents examples of angular filter transmittance.
• FIG. 6 Two response curves GEN1 (dotted line) and GEN2 (solid line) of two different angular filters are illustrated in FIG. 6.
• the curves represent the angular transmittance (Angular Transmittance) as a function of the angle of incidence ( Incidence Angle) .
• the GEN1 response symbolizes the response of a usual angular filter in which the transmission of the angular filter as a function of the incidence is mainly conditioned by the dimensions (height and width or section) of the transparent pillars 33.
• the width of the peak half-width (in degrees) of its maximum transmittance is relatively narrow.
• the response GEN2 symbolizes the response of an angular filter according to the embodiments described in which, thanks to the variation in refractive index between the walls 35 and the pillars 33, the effect linked to the dimensions of the pillars to a reflection effect inside them.
• the transmission peak is thus wider than in a usual filter.
• the thickness of the angular filter 23 and more particularly of the matrix or layer 31 is chosen according to the desired selectivity for the angular filter.
• the organic resins constituting the walls 35 and the pillars 33 so that the ratio between their respective refractive indices is a function of the wavelength and, preferably , reverses for a given wavelength between a range of wavelengths to be transmitted and a range of wavelengths to be filtered.
• FIG. 7 illustrates the operation of an embodiment of an angular filter according to this aspect.
• This figure shows examples of trends R33 (solid line) and R35 (dotted shape) of evolution of the refractive index "n" of a constituent resin of the pillars 33 and of a constituent walls 35 as a function of the wavelength X.
• curves R33 and R35 have similar general appearances, the refractive index n decreasing with increasing wavelength.
• the ratio between the respective indices of the resins is reversed for a wavelength X0. That means that the ratio is less (or greater) than 1 for wavelengths less than X0, equal to 1 for a wavelength equal to X0 and greater (respectively less) than 1 for wavelengths greater than X0. More precisely, the ratio of the index of the walls 35 to that of the pillars 33 is less than 1 for wavelengths less than X0 and greater than 1 for wavelengths greater than X0.
• the difference between the refractive indices of the first and second materials changes sign at a given wavelength X0 when the wavelength increases.
• the refractive index of the resin of the walls 35 (dotted curve) is lower than that of the pillars 33 (solid line curve) for wavelengths below X0 , while it is greater for wavelengths greater than X0. Consequently, for a wavelength X1 (or a range of wavelengths) less than X0, the rays are reflected inside the pillars 33 but are not, conversely, absorbed by the walls 35. A Conversely, for a wavelength X2 (or a range of wavelengths) greater than X0, the rays are not reflected inside the pillars 33.
• Infrared filter into the angular filter. Infrared rays (wavelengths less than X0) are filtered while rays in the visible range are favoured. The filter then functions as a color filter for wavelengths above X0.
• the refractive index difference between the two materials is between 0.001 and 0.5.
• the refractive index of the material constituting the walls 35 is, at the wavelength X1, between 1.45 and 1.6.
• the refractive index of the material of the walls 35 is between 1.52 and 1.57 and is, at the wavelength X1, of the order of 1.55, preferably 1.55.
• the refractive index of the material constituting the walls 35 is between 1.45 and 1.5 and is, at the wavelength X1, of the order of 1.49, preferably of 1.49.
• the refractive index of the material constituting the pillars 33 is, at the wavelength Xl, between 1.55 and 1.65 and is, at the wavelength Xl, l order of 1.57, preferably 1.57.
• the filter 23, more particularly the matrix of pillars 33, is made using thin-layer manufacturing technologies, which makes it possible to integrate the filter into an imaging system while maintaining a short distance from the scene. to be imaged with the sensor.
• Figure 8 illustrates the operation of another preferred embodiment of angle filter according to this aspect.
• This figure represents, like FIG. 7, examples of curves R33' (solid line curve) and R35' (dotted curve) of evolution of the refractive index "n" of a constituent resin of the pillars 33 and of a constituent resin of the walls 35 as a function of the wavelength X.
• the general shapes of curves R33' and R35' while respecting the condition that the ratio between the respective indices of the resins is a function of the wavelength and s' inverse for a wavelength X0, have different general appearances.
• the refractive index increases for the walls 35 whereas it decreases for the pillars 33.
• the ratio of the indices (pillars/walls) is greater than 1 for lengths d waves less than X0, equal to 1 for a wavelength equal to X0 and less than 1 for wavelengths greater than X0.

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Solid State Image Pick-Up Elements (AREA)
• Optical Elements Other Than Lenses (AREA)
• Optical Filters (AREA)
• Eyeglasses (AREA)
• Studio Devices (AREA)
• Polarising Elements (AREA)
• Optical Couplings Of Light Guides (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=74860095

Family Applications (1)

Country Status (6)

Families Citing this family (1)

Family Cites Families (5)

• 2020
  • 2020-12-15 FR FR2013270A patent/FR3117614B1/fr active Active
• 2021
  • 2021-12-13 EP EP21836482.6A patent/EP4264341A1/de active Pending
  • 2021-12-13 CN CN202180084601.3A patent/CN116635763A/zh active Pending
  • 2021-12-13 JP JP2023536565A patent/JP2023554061A/ja active Pending
  • 2021-12-13 US US18/267,053 patent/US20230408741A1/en active Pending
  • 2021-12-13 WO PCT/EP2021/085408 patent/WO2022128873A1/fr active Application Filing

Also Published As

Similar Documents

Legal Events