Method of manufacturing optical article incorporating optical element by inkjet printing

Abstract

A method for manufacturing an optical article is disclosed, the method comprising: providing a base lens substrate having opposing first and second optical surfaces; forming at least one optical element protruding from the second surface of the base lens substrate; and forming at least one second layer extending over the second surface of the base lens substrate and encapsulating the at least one optical element, where the optical element and the second layer are formed of materials having different refractive indices, and the formation of the optical element is performed by inkjet printing. An optical article obtained by applying such a method is also disclosed.

Description

Technical Field

[0001] The present disclosure relates to a method of manufacturing an optical article comprising at least one optical element, such as a microlens, and to an optical article obtained by applying said method. Background Art

[0002] Optical articles such as lenses generally include a base lens substrate that is configured to provide a desired optical function such as a desired optical power.

[0003] Recently, it has been proposed to add one or more protruding optical elements (such as microlenses) to this basic lens substrate. Microlenses can be used, among other things, to slow the progression of myopia by providing an optically blurred image in front of the retina, thereby triggering a stop signal to eye growth.

[0004] Accordingly, various optical lenses are provided that include a central area without lenticules to achieve good vision and that include multiple lenticules in the peripheral field of vision to slow the progression of myopia.

[0005] Various microlens patterns in the peripheral field of view have been proposed. Figure 1a , the first pattern includes a plurality of concentric circles formed by regularly distributed microlenses. This pattern produces an unfocused light signal. Figure 1b , showed another pattern that consisted of an array of microlenses regularly distributed in a ring corresponding to the peripheral field of view of the lens. This pattern produced a defocus signal in front of the retina.

[0006] In both types of optical lenses, microlenses can be molded or machined directly on a particularly precise lathe. However, this process does not allow for individual design of the microlens pattern. In addition, the microlenses are located on the surface of the base lens substrate, making them susceptible to scratches and other damage, and are also prone to cleaning difficulties.

[0007] Alternatively, it has been proposed to replace the microlenses with diffuse dots in the peripheral vision, which can also significantly slow down the progression of myopia, these diffuse dots being formed by light spots obtained by laser processing. Here too, these light spots are on the surface and exposed to dust and dirt.

[0008] Attempts have also been made to embed microlenses into optical articles, for example by molding a first lens with microlenses protruding from its surface and overmolding the first lens with a second lens there. In this way, the microlenses are embedded into the optical article, at the interface of the two materials, and the outer surface of the optical article is smooth and fluent. However, this process and the article obtained are susceptible to delamination. Summary of the invention

[0009] The purpose of this disclosure is to provide a solution to the deficiencies in the prior art.

[0010] In particular, it is an object of the present disclosure to provide a method for manufacturing an optical article comprising optical elements, such as microlenses, wherein the optical article is less susceptible to damage and the manufacturing method can be personalized.

[0011] Accordingly, a method of manufacturing an optical article is disclosed, the method comprising:

[0012] - providing a base lens substrate having opposing first and second optical surfaces;

[0013] - forming at least one optical element protruding from the second surface of the base lens substrate; and

[0014] - forming at least one second layer which extends on the second surface of the base lens substrate and encapsulates the at least one optical element,

[0015] The optical element and the second layer are formed of materials having different refractive indexes, and the formation of the optical element is performed by inkjet printing.

[0016] In an embodiment, forming the optical element by inkjet printing comprises depositing at least one droplet of material for forming the optical element.

[0017] In an embodiment, depositing at least one droplet of material comprises depositing a single droplet of material, the single droplet forming the optical element.

[0018] In an embodiment, depositing at least one droplet of material comprises depositing a plurality of coalesced droplets to form the optical element.

[0019] In an embodiment, the method further comprises a preliminary step of performing a surface treatment on the second optical surface, the surface treatment being configured to provide a desired curved surface for each deposited material droplet.

[0020] In an embodiment, forming the optical element by inkjet printing comprises depositing successive layers of material forming the optical element on the second optical surface of the base lens substrate.

[0021] In an embodiment, the method comprises depositing successive layers of material forming the optical element according to a stepped profile.

[0022] In an embodiment, depositing successive layers of material forming the optical element comprises depositing layers of material forming the optical element on top of previously deposited layers in such a way that the previously deposited layers are encapsulated by the next deposited layers.

[0023] In an embodiment, forming an optical element by inkjet printing includes depositing successive material layers on a second optical surface of a base lens substrate, wherein each material layer includes a first material on a first area for forming the optical element, and a second material on a second area surrounding the first area, the second material being used to form a second layer surrounding the optical element.

[0024] In an embodiment, the optical element has a target bend profile configured to achieve a determined optical function, inkjet printing is performed using a printing device having a resolution determined according to an axis perpendicular to the deposition surface during printing, and the material forming the optical element and the second layer is selected so that the error in the optical function caused by the difference between the target bend profile and the printed profile formed by successive material layers is below a predetermined threshold.

[0025] In an embodiment, the optical element is a microlens having a target curvature profile configured to achieve a determined optical power, and the materials forming the optical element and the second layer are selected so that the optical path deviation of a determined wavelength caused by the difference between the target curvature profile and the printed profile is below a predetermined threshold.

[0026] In an embodiment, the predetermined threshold is lower than or equal to λ / 4, where λ is a determined wavelength.

[0027] In an embodiment, the materials forming the optical element and the second layer are selected such that z(n1-n2) is below a predetermined threshold, where z is the resolution of the inkjet printing device according to an axis perpendicular to the second surface during operation, n1 is the refractive index of the material forming the optical element, and n2 is the refractive index of the material forming the second layer.

[0028] In an embodiment, printing the at least one optical element includes transmitting a digital file including instructions defining printing parameters to a printing device, and the method further includes: when an error in the optical function between the printed profile and the target profile exceeds a predetermined threshold, updating the digital file by correcting the printing parameters of the digital file, and sending the updated file to the printing device.

[0029] In an embodiment, the material used to form the optical element is the material used to form the second layer, to which the nanoparticles are added.

[0030] An optical product is also disclosed, characterized in that the optical product is obtained by implementing the manufacturing method described above.

[0031] The claimed method proposes forming optical elements embedded in optical articles by inkjet printing. Since the optical elements are embedded in the optical article, they are less susceptible to damage and scratches and may not be exposed to dust. In addition, inkjet printing enables printing of specific and personalized optical element patterns, wherein the arrangement of the optical elements and the size of the optical elements can be adjusted according to the needs of the wearer.

[0032] In embodiments, coarse print resolution along the optical axis may be avoided by selecting the materials forming the optical element and the materials forming the layers encapsulating the optical element to have a desired refractive index and by adapting the print pattern according to the refractive index of the materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] For a more complete understanding of the description provided herein and its advantages, reference is now made to the following brief description taken in conjunction with the accompanying drawings and detailed description, wherein like reference numerals represent like parts.

[0034] - Figure 1a and Figure 1b represents an example of an optical article including a microlens pattern on its surface for slowing down the progression of myopia.

[0035] - Figure 2a The main steps of the manufacturing method according to the embodiment are schematically shown.

[0036] - Figure 2b The main steps of a manufacturing method according to another embodiment are schematically shown.

[0037] - Figure 3 Examples of optical products obtained by applying the manufacturing method are schematically shown.

[0038] - Figure 4 is a schematic diagram of the embedded microlens.

[0039] - Figure 5a and Figure 5b Respectively represent the complete target surface of the microlens and its approximation by a step function, and its detailed part.

[0040] - Figure 6a and Figure 6b Respectively for Figure 5a The complete target surface and Figure 5b The detailed part determines the optical path deviation between the target surface and the step function of the light of the wavelength.

[0041] - Figure 7 An example of depositing successive layers of material by inkjet printing to form an optical article according to an embodiment is schematically represented. DETAILED DESCRIPTION

[0042] refer to Figure 2a and Figure 2b , main steps of a method for manufacturing an optical article 1 according to an embodiment of the present disclosure will now be described. Figure 3 An example of an optical product 1 obtained by this method is schematically represented in .

[0043] The method comprises step 100 of providing a base lens substrate 10 having opposite first and second optical surfaces 10a, 10b.

[0044] When the optical article is integrated into a pair of glasses, the first optical surface 10a may be the back surface of the base lens substrate 10 located near the user's eye, and when the optical article is integrated into a pair of glasses, the second optical surface 10b may be the front surface located far from the user's eye. Alternatively, the second optical surface 10b may be the surface located near the eye, and the first optical surface 10a may be the front surface of the base lens substrate 10 located far from the user's eye.

[0045] The base lens substrate 10 may include a single layer or may be formed by a laminate. The base lens substrate may include a plano thin sheet (i.e., a material layer without optical power), a base lens providing optical power, or both, i.e., a base lens providing optical power and a thin sheet complementary to the base lens and having optical functions other than optical power, such as one or more of the following:

[0046] - amplitude filtering,

[0047] - spectral filtering (e.g. edge-pass like short-pass or long-pass, or band-pass filtering, or filtering of a specific color e.g. by tinting, or in combination with photochromic or electrochromic functions, UV absorption, specular reflection, etc.),

[0048] -polarization.

[0049] The plano sheet may be formed of one or several ophthalmic grade functional films (having, for example, polarizing or photochromic properties), optionally with an ophthalmic grade protective film on one or both sides of the ophthalmic grade functional film.

[0050] Suitable transparent resin films or sheets for forming matte sheets (including functional films and protective films) include poly(vinyl alcohol) (PVA) or cellulose acylate-based materials (e.g., cellulose diacetate and cellulose triacetate (TAC)). Other usable sheet materials may include polycarbonate, polysulfone, cellulose acetate butyrate (CAB) or cyclic olefin copolymer (COC), polyacrylate, polyester, polystyrene, copolymers of acrylate and styrene, and poly(vinyl alcohol) (PVA). For example, polycarbonate-based materials include polybisphenol A carbonate; homopolycarbonates such as 1,1'-dihydroxydiphenyl-phenylmethylmethane, 1,1'-dihydroxydiphenyl-diphenylmethane, 1,1'-dihydroxy-3,3'-dimethyldiphenyl-2,2-propane, their copolymerized polycarbonates with each other, and copolymerized polycarbonates with bisphenol A.

[0051] The base lens may be formed in an organic ophthalmic lens, for example made of thermoplastics or thermosetting plastics. In particular, the thermoplastic material may be selected from, for example: polyamides, polyimides, polysulfones, polycarbonates and copolymers thereof, poly(ethylene terephthalate) and polymethyl methacrylate (PMMA).

[0052] The thermosetting material may be selected, for example, from cyclic olefin copolymers, such as ethylene / norbornene or ethylene / cyclopentadiene copolymers; homopolymers and copolymers of allyl carbonates of linear or branched aliphatic or aromatic polyols, such as diethylene glycol bis(allyl carbonate) (CR ) homopolymers; homopolymers and copolymers of (meth)acrylic acid and its esters which may be derived from bisphenol A; polymers and copolymers of thio(meth)acrylic acid and its esters, polymers and copolymers of allyl esters which may be derived from bisphenol A or phthalic acid and allyl aromatic hydrocarbons such as styrene, polymers and copolymers of urethane and thiourethane, polymers and copolymers of epoxy resins, and polymers and copolymers of sulfides, disulfides and episulfides, and combinations thereof. As used herein, (co)polymers are intended to mean copolymers or polymers. As used herein, (meth)acrylates are intended to mean acrylates or methacrylates.

[0053] Examples of substrates suitable for use in the present invention include and Various matrices based on polythiourethane resins are sold by Mitsui Toatsu Chemicals, and these matrices and the monomers used to prepare these matrices are described in, inter alia, U.S. Pat. No. 4,689,387, U.S. Pat. No. 4,775,733, U.S. Pat. No. 5,059,673, U.S. Pat. No. 5,087,758 and U.S. Pat. No. 5,191,055.

[0054] The shape of the base lens is preferably designed to provide an optical power suitable for correcting the wearer's refractive error (eg, myopia or hyperopia).The base lens 12 may be monofocal or multifocal, such as a multifocal progressive lens.

[0055] In addition to the base lens and / or the plano sheet, the base lens substrate 10 may also include other layers, such as, for example, a photochromic Layer or any additional layer which may be deposited on the base lens or the plano-laminate and which has the following optical functions:

[0056] - Amplitude filtering function,

[0057] - spectral filtering functions (e.g. edge-pass like short-pass or long-pass, or band-pass filtering, or filtering of a specific color e.g. by tinting, or in combination with photochromic or electrochromic functions, UV absorption, specular reflection, etc.),

[0058] - Polarization function.

[0059] A base lens may also be a semi-finished lens, which means that the semi-finished lens does not provide the final power of the lens to be manufactured from the semi-finished lens, also called the target power. The semi-finished lens may provide a power that is not the target power, which is obtained by later surface treatment of the semi-finished lens.

[0060] The base lens may also be an unmodified lens, which means that its peripheral shape has not yet been adjusted to the shape of the frame into which it will subsequently be inserted.

[0061] Providing the base lens substrate 10 can be performed according to any technique known to those skilled in the art, such as by casting or inkjet printing the base lens, and any additional layers can be added to the base lens as appropriate by overmolding, inkjet printing, coating, etc.

[0062] The method further comprises: forming 200 at least one, preferably a plurality of optical elements 20 protruding from the second optical surface 10b of the base lens substrate 10. This step is performed by inkjet printing and is described in more detail below. The optical elements protruding from the second optical surface 10b exhibit a height variation over a limited width relative to the surface from which these optical elements protrude. "Protruding" means that each element protrudes outwards from the second optical surface 10b, i.e. away from said surface.

[0063] These optical elements may provide an optical wavefront modification of its intensity, curvature or optical deviation.For example, when the optical element provides a modification of the intensity of the optical wavefront, the optical element may locally absorb the wavefront intensity in the range of 0 to 100%.

[0064] When the optical element provides a modification of the curvature of the wavefront, the optical element may locally modify the wavefront curvature within a range of ±20 diopters.

[0065] When the optical element provides a light deviation, the optical element may be adapted to locally scatter an amount of light within the range of ±1° to ±30°, for example between 1% and 20% of the light comprised.

[0066] "Locally" refers to the intersection between the wavefront and the optical element.

[0067] In an embodiment, the at least one (eg all) optical elements are microlenses.Microlenses are discrete optical elements of microscale or millimeter scale that induce local variations in the optical power of the optical device.

[0068] The microlenses may be spherical, toric, or have an aspherical shape. The microlenses may have a single focus, or cylindrical power, or a non-focused point. In a preferred embodiment, the microlenses may be used to prevent the progression of myopia or hyperopia. In this case, the base lens substrate includes a base lens that provides a power for correcting myopia or hyperopia, and the microlenses may provide a power greater than the power of the base lens if the wearer is myopic, or a power less than the power of the base lens if the wearer is hyperopic, respectively.

[0069] In the sense of the present disclosure, a "microlens" has an outline shape that can be inscribed within a circle having a diameter greater than or equal to 0.5 mm and less than or equal to 10.0 mm.

[0070] The microlenses may be distributed according to a regular or irregular pattern, provided that the pattern includes sufficient areas without microlenses to allow the wearer to obtain clear vision. For example, the microlenses may be regularly distributed along at least one circle, possibly multiple concentric circles, centered on the optical center of the refractive area. According to another example, the microlenses may be regularly distributed in annular segments centered on the optical center of the refractive area.

[0071] The average cylinder of the different microlenses can be adjusted based on the shape of the human retina.

[0072] The refractive zone may include a distance reference point, a near reference point, and a meridian connecting the distance reference point and the near reference point. For example, the refractive zone may include a progressive multifocal lens design that is adapted to a person's prescription or adapted to slow the progression of abnormal refraction in the eye of a person wearing the lens element.

[0073] The meridian corresponds to the locus of intersections of the principal gaze direction with the lens surface.

[0074] Preferably, according to this embodiment, the optical element is configured so that, under standard wearing conditions, along any horizontal segment of the lens, when worn by the wearer, the average sphere and / or average cylinder of the lenticule increases from the intersection of the horizontal segment with the meridian towards the peripheral portion of the lens.

[0075] The average spherical and / or average cylindrical increase functions along a segment may be different depending on the position of the segment along the meridian.

[0076] In particular, the average sphere and / or average cylinder gain function along the segment is asymmetric. For example, under standard wearing conditions, the average sphere and / or average cylinder gain function is asymmetric along the vertical and / or horizontal segment.

[0077] At least one of the microlenses has an optical function such that an image is not focused on the retina of a human eye when the lens element is worn under standard wearing conditions.

[0078] Advantageously, this optical function of the lenticules is combined with a refractive zone having at least one refractive power different from the prescribed refractive power, allowing to slow down the progression of abnormal refraction of the eye of the person wearing the lens element.

[0079] The microlenses may be non-continuous.

[0080] In the sense of the present disclosure, two microlenses are non-contiguous if, for all paths connecting two microlenses, a refractive power based on a prescription for a person's eye can be measured at least along a portion of each path.

[0081] When two microlenses are on a spherical surface, the two microlenses are non-contiguous if, for all paths connecting the two optical elements, the curvature of the spherical surface can be measured at least along a portion of each path.

[0082] According to an embodiment, at least one of the microlenses has an optical function of focusing an image on a location other than the retina.

[0083] Preferably, at least 50%, such as at least 80%, such as all of the microlenses have the optical function of focusing an image on a location other than the retina.

[0084] According to an embodiment, at least one of the microlenses has an aspherical optical function.

[0085] Preferably, at least 50%, for example at least 80%, for example all of the microlenses have an aspherical optical function.

[0086] In the sense of the present disclosure, an "aspherical optical function" is understood as not having a single focus.

[0087] At least one microlens having an aspherical optical function is transparent.

[0088] These microlenses can be added in a defined array, such as a circular array, a square array, or a hexagonal array, or a random array, or other arrays.

[0089] The lenticules may cover a specific area of ​​the lens element, such as the area at the center or any other area.

[0090] Optical element density or amount of focus may be adjusted according to the zone of the base lens substrate. Typically, microlenses may be positioned at the periphery of the base lens substrate to increase the contribution of the optical element to myopia control, thereby compensating for peripheral defocus due to, for example, the peripheral shape of the retina.

[0091] According to an embodiment, the shape of at least one (e.g., all) microlenses is configured to form a caustic surface in front of the retina of the human eye. In other words, such microlenses are configured so that if the light flux passing through the microlens is concentrated on any cross-sectional plane, the cross-sectional plane is located in front of the retina of the human eye, either in a point-like manner in the plane, or in a way that it is never concentrated in a point-like manner in any of these cross-sectional planes.

[0092] According to an embodiment, at least one (eg all) of the microlenses having an aspherical optical function are multifocal refractive microlenses.

[0093] In the sense of the present disclosure, a microlens is a "multifocal refractive microlens", including a bifocal lens (having two focal powers), a trifocal lens (having three focal powers), a progressive multifocal lens (having continuously changing focal power, such as a progressive aspheric surface lens).

[0094] According to an embodiment, at least one multifocal refractive microlens has a toric surface.A toric surface is a surface of revolution that can be produced by rotating a circle or an arc around an axis of revolution that does not pass through its center of curvature (ultimately located at infinity).

[0095] A toric surface lens has two different radial profiles at right angles to each other, thus producing two different focal powers.

[0096] The toric surface component and the spherical surface component of a toric lens produce an astigmatic beam rather than a single point focus.

[0097] According to an embodiment, at least one of the microlenses (e.g., all optical elements) of the microlenses having an aspherical optical function is a toric refractive microlens, for example, a toric refractive microlens having a spherical power value greater than or equal to 0 diopters (δ) and less than or equal to +5 diopters (δ) and a cylindrical power value greater than or equal to 0.25 diopters (δ).

[0098] As a specific embodiment, the toric refractive microlenses can be pure cylindrical, which means that the meridian minimum power is zero and the meridian maximum power is strictly positive, for example less than 5 diopters.

[0099] According to an embodiment, at least one (eg all) of the microlenses have an optical function with high-order optical aberrations.For example, the microlenses are composed of a continuous surface defined by Zernike polynomials.

[0100] Each microlens may have a maximum height, for example a maximum height measured in a direction perpendicular to the surface from which the microlens protrudes, which is less than or equal to 1 millimeter (mm), for example less than or equal to 0.1 mm, such as less than or equal to 100 micrometers (μm), 90 μm, 80 μm, 70 μm, 60 μm, 50 μm, 40 μm, 30 μm, 20 μm, 10 μm, 5 μm, 1 μm, or less, or between any two of the above. In an embodiment, each microlens has a maximum height preferably included between 1 μm and 20 μm, for example equal to 11 μm or 15 μm. The diameter of each microlens may be less than or equal to 10 mm, for example less than or equal to 2.0 mm, 1.5 mm, 1.0 mm, 0.5 mm, 0.1 mm, 80 μm, 60 μm, 40 μm, 20 μm, or less, or between any two of the above. For example, the diameter may be between 2.0 mm and 0.5 mm.

[0101] Thus, the base lens substrate exhibits an average thickness greater at the microlenses than at distances from the microlenses, with the maximum thickness of the substrate being reached at the point of maximum thickness of the microlenses.

[0102] The method for manufacturing an optical article further comprises a step 300 of forming at least one second layer 30 extending on the second optical surface 10b of the base lens substrate 10 and encapsulating the at least one optical element 20. "Encapsulation" means that the entire surface of each optical element 20 is covered and in contact with the material forming the second layer 30, without any gap or any intermediate material in between. Thus, the second layer 30 comprises: a first surface in contact with the optical element and in contact with the second optical surface of the base lens substrate in the area of ​​the base lens substrate without the optical element; and a second surface opposite to the first surface.

[0103] In an embodiment, the second layer may be formed of an organic ophthalmic lens, for example made of a thermoplastic or a thermosetting plastic, the same as the examples provided above with respect to the base lens included in the base lens substrate.

[0104] The material forming the second layer 30 has a refractive index n2 different from the refractive index n1 of the material forming the optical element 20. More specifically, the material forming the second layer 30 may have a refractive index n2 lower than the refractive index n1 of the material forming the optical element 20.

[0105] When the base lens substrate is a semi-finished lens, the manufacturing method may include the step of surface treating the base lens substrate to obtain a finished lens, said surface treating being performed on the surface of the base lens substrate not covered by the second material.

[0106] Various embodiments of manufacturing methods will now be disclosed.

[0107] As described above, each optical element 20 is formed by inkjet printing.

[0108] The problem with inkjet printing is the resolution of current additive manufacturing devices, which is typically about 40 μm in the XY plane (i.e., in the deposition plane of the material) and about 1 μm, for example about 10-15 μm, in the Z direction (i.e., in the direction orthogonal to the deposition plane). These resolutions do not allow for direct implementation of optical functions, such as microlenses with a typical diameter of about 1 mm but a final surface height of 1 μm, diffractive elements with a height on the order of the wavelength, or diffusive elements with a height on the order of the wavelength or less.

[0109] This problem can be avoided by encapsulating the optical element (ie, covering the optical element with a second layer of material) and appropriately selecting the material forming the optical element and the material forming the second layer based on their refractive indices.

[0110] In fact, when the material forming the second layer has a refractive index different from but close to the refractive index of the material forming the optical element, the size of the optical element can be increased.

[0111] For example, refer to Figure 4 , schematically showing an exemplary microlens in contact with a second material forming a second layer of an encapsulated optical element. Let n1 be the refractive index of the material forming the optical element, and n2 be the refractive index of the material forming the second layer. Let D also be the diameter of the microlens, S be its focal power, R be the radius of curvature of the surface of the optical element and h be its height.

[0112] To achieve the desired optical power S, the radius of curvature of the surface is given by:

[0113] R=(n1-n2) / S

[0114] And the final height of the microlens can be calculated as:

[0115]

[0116] Classical parameters for microlenses formed on the surface of the lens at the interface with air may be a diameter of about 1 mm, a focal power of about 3.5 to 4.5 D, and a refractive index of 1.56 (where the refractive index of air is equal to 1) for the unique material forming the base lens substrate and the microlenses, which gives R = 12 to 16 cm and a height h of the microlenses between 0.78 and 1 μm. As mentioned above, this cannot be achieved by inkjet printing due to insufficient Z resolution.

[0117] However, by choosing the refractive index of the second material to be closer to the refractive index of the material forming the microlens, the height of the microlens can be increased, thereby enabling the microlens to be formed by depositing successive layers of material. For n1=1.56, n2=1.5, R=1.3 to 1.7 cm and h=7.2 to 9.4 μm are found.

[0118] Thus, the size of the optical element may be increased by selecting the materials forming the optical element and the second layer, which enables the optical element to be formed by printing superimposed layers of material.

[0119] Thus, according to a first embodiment, the optical element is formed by depositing successive layers of material forming the optical element according to a profile configured to approximate a curved target surface of the optical element. In particular, the profile may be a stepped profile, wherein the steps are considered to be in a direction orthogonal to the deposition plane (hereinafter denoted as direction Z).

[0120] In an embodiment, forming the optical element by inkjet printing comprises depositing a plurality of superposed material layers 21 on the second optical surface 10b of the base lens substrate 10. In the case of a stepped profile, each deposited material layer has a progressively decreasing lateral dimension relative to the previously deposited layer.

[0121] The thickness of a material layer can be determined by the resolution of the additive manufacturing device used for deposition in the Z axis and can be higher than or equal to said resolution. In a preferred embodiment, the thickness of a layer is equal to the resolution of the device along Z, which corresponds to forming as many material layers as technically possible and thus maximally approximating the target surface of the optical element.

[0122] In particular, this embodiment may be performed when the refractive index difference between the material forming the microlenses and the material forming the second layer is below a determined threshold, for example below 0.1, preferably below 0.06, below 0.05 or even below 0.01.

[0123] Given a desired optical function to be achieved by a target curved surface of an optical element, such as:

[0124] - the optical power of the microlenses,

[0125] - the phase and amplitude transmission of the diffractive element,

[0126] - Bidirectional Scattering Distribution Function (BSDF) of the diffuse element,

[0127] A maximum acceptable error in the optical function resulting from a difference between a target curved profile that will achieve the desired optical function and a printed profile that approximates the target curved profile can be determined. The error is a function of the difference in refractive index between the material forming the optical element and the second material and the geometrical difference between the target profile and the printed profile.

[0128] Regarding the optical power, a criterion may be defined based on the optical path deviation between the printed profile and the curved profile. The criterion may be a maximum value of the optical path deviation, which may be less than or equal to λ / 4, where λ may be selected between 400 and 800 nm, for example 555 nm corresponding to the peak sensitivity of the eye. Alternatively, the criterion may be the Marechal criterion for evaluating the quality of an optical system, and the criterion sets the maximum error to λ / 12.

[0129] For a diffuse element, the maximum acceptable error may be defined as the maximum roughness value according to the Z-axis that enables the optical function of the printed element to match the corresponding target curvature profile.

[0130] For diffractive elements, the maximum acceptable error can be defined as the maximum relative error of the wavefront.

[0131] The size of the stepped profile that approximates the target curved profile is constrained by the resolution of the printing device along the Z axis, and therefore it can be determined whether the error is below a maximum acceptable error based on the stepped profile and the refractive index of the selected material. It should be noted that in embodiments, the printed profile may be closer to the target profile than the stepped profile, at least because the printed profile is smoother than the stepped profile, and also because some inkjet printing technologies enable the printing of profiles that are smoother than the stepped profile (see below for embodiments of step 200). In this case, the error between the printed profile and the target profile is less than the error between the stepped profile and the target profile, and therefore, if the error obtained for the stepped profile is acceptable, it will also be acceptable for the printed profile.

[0132] refer to Figure 5a , shows an exemplary curved target profile of a microlens having a desired optical power, a stepped profile that approximates the target profile, and an actual printed profile that is slightly smoother than the stepped profile due to the printing process. Detailed views of these profiles are shown in Figure 6a The abscissa axis represents mm in the plane of the deposition surface and the ordinate axis represents the physical thickness of the layer (expressed in μm).

[0133] As can be seen in these figures, approximating the curved surface of the microlens by a stepped profile introduces errors into the optical function achieved by the optical element. Figure 5a The optical function error of the profile is shown in Figure 5, and corresponds to Figure 6a The error in the detailed view is Figure 6b Shown in. Figure 6a and Figure 6b The horizontal and vertical axes in Figure 5a and Figure 5b The same as in.

[0134] Let ot be the optical thickness of the layer, defined by ot = e(n1-n2), where e is the physical thickness of the layer. If the curved surface is approximated by a stepped profile, where each layer has a thickness equal to e, then at each layer the optical path error varies between a minimum and a maximum value, as Figure 5a and Figure 5b As shown (in this example, the error is alternately negative and positive), and the maximum optical path error between the stepped profile and the target curved profile is equal to the maximum peak-to-valley difference, which is less than or equal to e, that is, it is less than or equal to the resolution of the printing device along z. The corresponding optical path is less than e(n1-n2).

[0135] exist Figure 4 a to Figure 5b In the example shown in , where e equals 10 μm, corresponding to the optical resolution of the printing device, and n1-n2 equals 0.005 (n1=1.56 and n2=1.555), the maximum error of the optical path is 0.050 μm, and the measured error of the optical path of the printed profile (which is smoothed and therefore has a reduced error relative to the step profile) is 0.045 μm.

[0136] Considering that the average wavelength λ is 550nm, an error of 0.045μm corresponds to λ / 12, which meets the Marechal criterion for determining the quality of an optical system. It is also possible to apply a lower criterion to define the maximum acceptable thickness error, such as a threshold of λ / 4.

[0137] refer to Figure 7 The sequential deposition of the material layers forming the optical element together with the formation of the base lens substrate and / or the second layer can be implemented in various ways.

[0138] according to Figure 7In the first example shown in the left part of FIG, a base lens substrate may be formed at step 100, and step 200 may include depositing successive layers of material forming optical elements on a second optical surface of the base lens substrate, wherein the lateral dimensions of each layer decrease relative to the previous layer. Each layer may be at least partially cured, for example by light (e.g., UV irradiation), before the next layer is deposited. Then, the formation of the second layer 300 may be performed by overmolding or inkjet printing the second material between and over the optical elements.

[0139] According to another example, the step 200 of forming the optical element by inkjet printing can be performed according to the teaching of document WO 20220 / 169689, wherein each layer is printed at least partially on top of the previously printed layer in such a way that the previously printed layer is encapsulated by the second printed layer so that the printed material can flow on the surface of the previous layer with a smaller surface area and surround the latter. It is also possible to solidify each layer before depositing the next one. This makes it possible to print convex shapes that better approximate the target curved surface than a stepped profile and therefore reduce the error of the optical function achieved by the optical element.

[0140] according to Figure 7 In another example shown in the right part of , a base lens substrate may be formed at step 100, and step 200 may include depositing successive material layers on a second optical surface of the base lens substrate, wherein each material layer includes a first material on a first area for forming an optical element, and a second material on a second area surrounding the first area, the second material being used to form a second layer surrounding the optical element. Each step of depositing a material layer may include the following sub-steps: depositing the first material, curing the first material, depositing the second material and then curing the second material. Alternatively, a curing delay may be applied, in which case curing is not performed after each printed layer. Thus, according to this example, steps 200 and 300 are performed simultaneously because the optical element and the second layer of material are formed simultaneously, as shown in FIG. Figure 2b Schematically shown in .

[0141] Once the portion of the optical device including the optical element and a portion of the second layer surrounding the optical element is printed, the remainder of the second layer may be formed by inkjet printing, molding, or the like.

[0142] For the first embodiment disclosed above in which the optical element is formed by depositing successive material layers by inkjet printing, a material combination may be chosen with a low refractive index difference, in particular a difference below a given threshold. The threshold depends on the criteria for acceptable errors.

[0143] For example, a wavefront error below the λ / 12 criterion achieves a microlens of high optical quality. With a layer thickness of 10 μm and an average wavelength of 500 nm, the refractive index difference must be below 550. -9 / (12.10 -6 ) = 0.045. In the case of this refractive index combination, the radius of curvature would be 0.0045 / 3.5 = 1.3 mm (where 3.5 corresponds to an exemplary optical power of a microlens), and the height of the structure would be 101 μm, realized in 10 layers.

[0144] If a lower optical quality is accepted (say λ / 4), the refractive index difference should be lower than 0.0135 according to the above parameters. In this case, the height of the structure is 32.6 μm, realized in three layers. It will be assumed that the spreading of the droplets will smooth the edges of each layer without exacerbating this defect.

[0145] According to a second embodiment in which the optical elements are spherical microlenses, each microlens is formed by depositing a single droplet of material or a plurality of coalesced droplets of material on the second optical surface of the base lens substrate, the droplets exhibiting the size and shape of the desired microlens after curing. "Coalesced droplets" means that a plurality of droplets are deposited successively, contacting each other, so that these contacting droplets merge together to adopt the shape of a single larger droplet.

[0146] This second embodiment is particularly (but not exclusively) applicable when the materials forming the microlenses and the second layer have a refractive index that differs by more than the threshold value provided above.

[0147] The desired shape of the microlenses can be obtained by preliminarily performing a surface treatment on the deposition surface that enables the desired contact angle between the deposited droplet and the surface to be obtained. In fact, for a planar uniform surface, it is known that the following relationship exists between the contact angle between the droplet and the surface and the interfacial surface tension between the droplet, the surface and the surrounding air or fluid forming the deposition environment:

[0148]

[0149] where θ is the contact angle between the droplet and the deposition surface, σ SF is the surface tension of the surface / air interface, σ SL is the surface tension of the surface / liquid interface (the liquid corresponding to the deposition material) and σ LF is the surface tension at the liquid / air interface.

[0150] When the contact angle is 90° (corresponding to σ SF =σ LF ), a spherical shape is obtained. Therefore, a preliminary treatment of the surface can be achieved to make σ SF Equal to σLF , which is determined when selecting the deposition material.

[0151] For example, the preliminary treatment may include plasma or corona treatment.

[0152] In case the microlenses are formed from a single droplet of material, the distance between two droplets is calculated to prevent two adjacent droplets from coalescing and thus forming a single larger droplet.

[0153] The step 200 of forming microlenses by inkjet printing also includes the step of curing the deposited microdroplets by exposing them to light (eg, UV light).

[0154] In the case of forming a microlens by depositing a plurality of coalesced droplets, several contacting droplets may be deposited by the same nozzle of a printing device or by a plurality of adjacent nozzles. According to one example, a plurality of droplets may be deposited successively at a constant position by the same nozzle. Accordingly, the droplets are superimposed on each other at the same position, thereby forming a larger droplet. According to another example, a plurality of droplets are deposited successively by the same nozzle, wherein the nozzle is shifted between depositing two droplets, or adjacent nozzles may deposit contacting droplets simultaneously. The contacting droplets merge together, and the resulting droplet is centered at a position between the positions of the initially contacting droplets. In any case, the following parameters may be adapted to ensure that two adjacent droplets are in contact and will coalesce:

[0155] - the volume of the droplet,

[0156] - the distance between the droplet deposition locations,

[0157] - The shape of the deposited droplets.

[0158] Here too, a preliminary surface treatment can be performed in order to control the shape of the deposited droplets, ie to achieve a defined shape.

[0159] In the case where the optical element is formed by depositing successive material layers and the optical element is formed by depositing a single droplet or a plurality of coalesced droplets, the same material can also be used to form the optical element and the second layer, and the refractive index difference between the optical element and the second layer is introduced by introducing nanoparticles of inorganic material. The addition of nanoparticles increases the refractive index of the material. Accordingly, in order to make the material forming the optical element 20 have a refractive index greater than the refractive index of the material forming the second layer 30, nanoparticles can be added to the material forming the optical element. Depending on the type and concentration of the nanoparticles, the refractive index change obtained can be included between 0.0001 and 0.01. The size of the introduced nanoparticles can be between 12 and 20nm to avoid scattering effects.

[0160] Adding nanoparticles to obtain the refractive index difference between the optical element and the second layer enables the optical element and the second layer to be manufactured using initially the same material, in particular the same inkjet printing resin. This has the advantage that it simplifies the process by using only one set of inkjet parameters (viscosity, curing temperature, etc.) and also reduces costs.

[0161] In an embodiment, when printing the optical element, the method may further comprise step 400 of checking the difference between the printed profile and the target profile to determine whether the difference remains below a determined maximum acceptable error. This step may be performed by measuring the printed profile using a profilometer, such as a contact profilometer. If the error exceeds the maximum acceptable error, the optical device 1 may be rejected or compensation may be performed to reduce the error. Compensation is performed by correcting the instructions sent to the inkjet printer to define the specifications of the printed droplets so as to adjust the profile of the printed material and thereby reduce the error.

Claims

1. A method for manufacturing an optical product, the method comprising: - providing (100) a base lens substrate (10) having opposite first and second optical surfaces (10a, 10b); - forming (200) at least one optical element (20) protruding from the second surface of the base lens substrate; as well as - forming (300) at least one second layer (30) extending on the second surface of the base lens substrate and encapsulating the at least one optical element, The optical element (20) and the second layer (30) are formed of materials having different refractive indices, and the formation of the optical element is performed by inkjet printing.

2. The method according to claim 1, wherein: Forming the optical element (20) by inkjet printing includes depositing at least one droplet of material for forming the optical element.

3. The method according to claim 2, wherein: Depositing at least one droplet of material includes depositing a single droplet of material, the single droplet forming the optical element.

4. The method according to claim 2, wherein: Depositing at least one droplet of material includes depositing a plurality of coalesced droplets to form the optical element.

5. The method according to any one of claims 2 to 4, further comprising a preliminary step of performing a surface treatment on the second optical surface, the surface treatment being configured to set a desired curved surface for each deposited material droplet.

6. The method according to claim 1, wherein: Forming the optical element by inkjet printing comprises depositing successive layers of material forming the optical element on the second optical surface (10b) of the base lens substrate.

7. A method according to claim 6, comprising depositing the successive layers of material forming the optical element according to a stepped profile.

8. The method according to claim 6, wherein: Depositing the successive layers of material forming the optical element comprises depositing layers of material forming the optical element on top of previously deposited layers in such a way that the previously deposited layers are encapsulated by the next deposited layers.

9. The method according to any one of claims 1 to 8, wherein: Forming the optical element by inkjet printing includes depositing successive material layers on the second optical surface of the base lens substrate, wherein each material layer includes: a first material on a first area for forming the optical element, and a second material on a second area surrounding the first area, the second material being used to form the second layer surrounding the optical element.

10. The method according to any one of claims 6 to 9, wherein: The optical element has a target curvature profile configured to achieve a determined optical function, the inkjet printing is performed using a printing device having a resolution determined according to an axis perpendicular to a deposition surface during printing, and the materials forming the optical element and the second layer are selected so that an error in the optical function caused by a difference between the target curvature profile and a printed profile formed by the successive material layers is below a predetermined threshold.

11. The method according to claim 10, wherein: The optical element is a microlens having a target curvature profile configured to achieve a determined optical power, and the materials forming the optical element and the second layer are selected so that an optical path deviation of a determined wavelength caused by a difference between the target curvature profile and the printed profile is below a predetermined threshold.

12. The method according to claim 11, wherein: The predetermined threshold is lower than or equal to λ / 4, where λ is the determined wavelength.

13. The method according to any one of claims 10 to 12, wherein: The materials forming the optical element and the second layer are selected so that z(n1-n2) is below the predetermined threshold, where z is the resolution of the inkjet printing device according to the axis perpendicular to the second surface during operation, n1 is the refractive index of the material forming the optical element, and n2 is the refractive index of the material forming the second layer.

14. The method according to any one of claims 10 to 13, wherein: Printing the at least one optical element comprises transmitting a digital file comprising instructions defining printing parameters to the printing device, and the method further comprises updating the digital file by correcting the printing parameters of the digital file when the error of the optical function between the printed profile and the target profile exceeds the predetermined threshold, and sending the updated file to the printing device.

15. A method according to any one of the preceding claims, wherein: The material used to form the optical element (20) is the material used to form the second layer (30), and nanoparticles are added to the material.

16. An optical product, characterized in that: The optical article is obtained by implementing a method according to any one of the preceding claims.

Images