TECHNICAL FIELD OF THE INVENTION

The invention relates to the production of optical devices, such as optical lenses.

More precisely the invention relates to a method of producing an optical device and to a corresponding system.

BACKGROUND INFORMATION AND PRIOR ART

It has been sought to produce optical devices such as optical lenses using 3D printing technologies, which could offer significant advantages over conventional methods.

Some 3D printing technologies may however not be well suited to produce optical devices, owing in particular to the internal transparency and accurate shape at interfaces necessary for this kind of products.

SUMMARY OF THE INVENTION

In this context, the invention provides a method of producing an optical device from a volume of a curable composition, comprising the following steps:

- polymerizing a first portion of said volume by irradiating an external surface of said volume with a light irradiation, thereby increasing a transmittance of said first portion for said light irradiation;

- polymerizing a second portion of said volume by irradiating said second portion with said light irradiation through said external surface and the polymerized first portion,

wherein said light irradiation has a light intensity varying over said external surface between a first light intensity and a second light intensity distinct from said second light intensity.

Polymerization is thus performed continuously from portion to portion of the curable composition, which makes it possible to obtain an homogeneous polymerized material, having therefore a good transparency.

In addition, thanks to the use of a light irradiation having a specific distribution, the shape of the optical device obtained can be controlled in accordance with optical requirements.

The invention also provides the following optional (and thus non-limiting) aspects: - said power is varying over time for at least one point of said external surface;

- said light irradiation is in the ultraviolet range;

- said light irradiation is in the visible range;

- said curable composition includes a photo-initiator sensitive to the light irradiation and having photobleaching properties, meaning that it becomes transparent to the light irradiation wavelength after having reacted with the light irradiation;

- said photo-initiator is a Bis Acyl Phosphine Oxide (BAPO) or a 2, 4, 6- trimethylbenzoylphenyl phosphinate (Irgacure TPO);

- said curable composition contains an acrylate;

- the method comprises a step of degassing the curable composition prior to polymerizing said first portion;

- said optical device is an optical lens;

- in particular, the optical device is an ophthalmic lens;

- said curable composition is in a container with a bottom part;

- the optical device is formed by polymerization starting from the bottom part;

- said light irradiation is transmitted through said bottom part;

- said bottom part has a curved shape, spherical or aspheric, facing said volume, whereby the bottom part of the produced optical device has a corresponding curved shape;

- said bottom part has a convex shape facing said volume, whereby the bottom part of the produced optical device has a concave shape;

- said varying light intensity presents a maximum value in the centre of said external surface, usable for example to form a positive optical lens;

- said varying light intensity presents a maximum value at the periphery of said external surface, usable for example to form a negative optical lens;

- said varying light intensity presents a maximum value at the periphery of said external surface, along a first axis, and presents a lower value along an axis perpendicular to said first axis, usable for example to form a toric optical lens;

- said varying light intensity presents a maximum value in a decentered position within said external surface, usable for example to form an optical lens bearing an addition; - said varying light intensity presents a combination of the above patterns;

- said light irradiation is produced by an emitter comprising a spatial light modulator.

The invention also provides a system for producing an optical device, comprising:

- a container containing a volume of a curable composition; and

- an emitter of a light irradiation arranged to irradiate an external surface of said volume through the container, thereby polymerizing a first portion of said volume and increasing a transmittance of said first portion for said electromagnetic radiation, such that a second portion of said volume is polymerized by irradiating said second portion with said electromagnetic radiation through said external surface and the polymerized first portion,

wherein said light irradiation has a light intensity varying over said external surface between a first light intensity and a second light intensity distinct from said second light intensity.

This system may also include a control module for controlling said emitter to produce said varying light intensity.

Optional features presented above in connection with the proposed method may also apply to this system.

The present invention can be used for all kinds of optical devices and elements, such as optical lenses and devices or ophthalmic elements and devices. Non-limiting examples of ophthalmic elements include corrective and non- corrective lenses, including single vision or multi-vision lenses, which may be either segmented or non-segmented, as well as other elements used to correct, protect, or enhance vision, including without limitation contact lenses, intra-ocular lenses, magnifying lenses and protective lenses or visors such as found in spectacles, glasses, goggles and helmets.

DETAILED DESCRIPTION OF EXAMPLE(S)

Illustrative embodiments of the present invention are described in detail below with reference to the attached drawing Figures, wherein

- Figure 1 shows a first example of a system for producing an optical device in an initial step;

- Figure 2 shows the system of Figure 1 in an intermediary step; - Figure 3 shows the system of Figure 1 in a final step;

- Figure 4 shows a second example of a system for producing an optical device in an initial step;

- Figure 5 shows the system of Figure 4 in a final step;

- Figure 6 shows a third example of a system for producing an optical device in an initial step;

- Figure 7 shows the system of Figure 6 in an intermediary step;

- Figure 8 shows the system of Figure 6 in a final step;

- Figure 9 to 1 1 show distinct light distributions successively applied to a container containing a curable composition as in the system above;

- Figure 12 shows a piece of polymerized material obtained by applying these light distributions; and

- Figures 13 to 15 show lenses obtained using the process described above with reference to Figures 1 to 3 for distinct operating conditions.

Figures 1 to 3 show respectively three distinct steps of a method for producing an optical device using an exemplary system for producing an optical device.

This system comprises a container 2 containing a volume of a curable composition 4.

The container 2 comprises a bottom part 6 and lateral walls 8 making it possible to hold the volume of curable composition 4.

The system further comprises a light emitter 10 emitting a light beam B towards the container 2, precisely towards the bottom part 6.

The type of light used may be ultraviolet light, or visible light, for instance. The light emitter 10 comprises for instance a light generator (not represented) generating collimated light rays and a spatial light modulator 12 applied to the collimated light rays such that the light beam B has a light intensity varying over the beam B itself (in a manner controllable thanks to the spatial light modulator 12). The spatial light modulator 12 is for instance adapted to control the distribution of light in the light beam under control by a control module. The spatial distribution (as well as possibly its temporal evolution) can thus be configured by a user programming said control module.

In the present example, as schematically shown in Figures 1 to 3, light intensity is higher in the centre of the beam B than at the periphery of the beam B. At least the bottom part 6 of the container 2 (and possibly the whole container 2) is transparent to light emitted by the light emitter 10 (or, at least, translucent for light emitted by the light emitter 10). In this purpose, the container may be made of quartz, for instance.

As depicted in Figure 1 , light emitted by the light emitter 10 thus irradiates an external surface of the volume of the curable composition 4 (here: the external surface facing the bottom part 6), here through the container 2 (precisely through the bottom part 6 of the container 2). As the light beam B is not homogeneous (here: thanks to the use of the spatial light modulator 12), this light irradiation has a light intensity varying over the external surface between a first light intensity and a second light intensity distinct from said second light intensity.

The curable composition 4 comprises for instance a resin (made of a monomer such as an acrylate, for instance Dipentaerythritol penta-/hexa-acrylate or PETIA) and a photo-initiator, such as Bis Acyl Phosphine Oxide (BAPO).

According to a possible variation, the curable composition may include:

- 2.2 Bis(4-(Acryloxy Diethoxy)Phenyl)Propane(EO4mol), or A-BPE-4, to provide the main optical and mechanical properties (for instance between 25wt% and 95wt%);

- Isobornyl Acrylate, or A-IB,. to adjust the optical and mechanical properties (for instance between 5 wt% and 75wt%);

- 3-methyl-2-buten-1 -ol to prevent yellowing (for instance between 1wt% and 3wt%, here 2wt%);

- 2, 4, 6-trimethylbenzoylphenyl phosphinate, or Irgacure TPO, as a photo-bleachable photo-initiator (for instance between 1 wt% and 5wt%, preferably between 2wt% and 3wt%).

At least part of the curable composition 4 (here the photo-initiator) has photo-bleaching properties, i.e. becomes transparent to the light it receives after having reacted due to this light.

As the beam of light is not homogeneous, polymerization of the curable composition 4 develops first in regions where light intensity is high, here in the centre of the beam B (and thus in the centre of the bottom part 6), leading to the formation of a first polymerized portion 14, as shown in Figure 2.

Due to the photo-bleaching properties of the curable composition 4, the first polymerized portion 14 becomes transparent to light received from the light emitter 10: the transmittance of the first portion 14 for the light received from the light emitter 10 increases while the first portion 14 polymerizes.

Thus, light entering via the bottom part 6 of the container 2 in the region of the first polymerized portion 14 then transmits across the first polymerized portion 14 (as schematically shown in Figure 2) and reaches a second portion 16 of the volume of the curable composition 4, thereby leading to polymerization of this second portion 16 (as shown in Figure 3).

As already noted, owing to variations of light intensity across the light beam B, polymerization develops more rapidly in regions where light intensity is high and the thickness of polymerized material is therefore variable over the bottom part 6 of the container 2.

In the present case, as light intensity is high in the centre of the light beam and decreases towards its periphery, the polymerized material has a convex shape, as visible in Figures 2 and 3.

In its final state shown in Figure 3, the polymerized material obtained

(including the first portion 14 and the second portion 16) forms an optical lens 18. This optical lens 18 can be removed from the container 2 and possibly subjected to post-treatment, such as a final curing (post-polymerization), to obtain a good surface state, in particular.

In this respect, a dedicated anti-adhesive (transparent) layer 20 may be interposed between the bottom part 6 of the container 2 and the curable composition 4 to ease removal of the optical lens 18 from the container 2.

In the example just described referring to Figures 1 to 3, the bottom part 6 of the container 2 has a planar surface facing the curable composition 4 such that the optical lens 18 obtained is a plano-convex optical lens.

The bottom part 6 of the container 2, which defines one of the faces of the optical lens, can however have a non planar shape, as exemplified below.

Figures 4 and 5 show another embodiment of a system for producing an optical device.

As in the previous embodiment, a container 22 holds a volume of a curable composition 24. Examples of curable composition given above also apply in the present embodiment. The curable composition (or at least non-transparent compounds of the curable composition) has photo-bleaching properties, as explained above. The container 22 has a bottom part 26 and lateral walls 28. In the present embodiment, the surface 27 of the bottom part 26 facing the volume of curable composition 24 (here in contact with the volume of curable composition 24), i.e. the top surface of the bottom part 26, has a convex shape, as visible in Figures 4 and 5.

A non-homogeneous light beam B is applied to the external surface of the bottom part 26. This light beam B is here of the same type as the light beam used in the embodiment of Figures 1 to 3 and can thus be generated in a similar manner. Light intensity is thus higher in the centre of the light beam B than at its periphery.

The bottom part 26 (at least) of the container 22 is transparent to light used for the light beam B such that the light beam B irradiates an external surface of the volume of the curable composition 24 (i.e. here the surface in contact with the top surface 27 of the bottom part 26 of the container 22).

In the initial state shown in Figure 4, no portion of the volume of the curable composition 24 has yet polymerized and irradiation by the light beam B through the bottom part 26 thus leads to polymerizing regions of the volume of the curable composition 24 in the vicinity of the bottom part 26, corresponding to a first portion 24 of this volume (schematically shown in Figure 5).

As the light beam is non-homogenous (light intensity being here higher in the centre), polymerization is more active in some regions (here the centre) than in others (here the periphery) and the first (polymerized) portion 34 has consequently a thickness varying over the bottom part 26 of the container 22 (here: a thickness increasing towards its centre).

Thus, at a time intermediate between the initial and final steps, the first portion 34 has polymerized and the transmittance of the first portion 34 has increased due to the photo-bleaching properties of the curable composition.

The light beam B irradiating the bottom part 26 of the container 22 and transmitted across the bottom part 26 thus propagates through the polymerized first portion 34 and thereby reaches a second portion 36 of the volume of the curable composition 24, which consequently polymerizes in turn.

As for the first portion 34, the polymerization of the second portion 36 is faster in regions where light intensity is higher and the second (polymerized) portion 26 thus has a thickness varying over the bottom part 26 of the container 22 (here: a thickness increasing towards its centre).

As shown in Figure 5 (corresponding to the final step of the method for producing an optical device, here an optical lens 38), the polymerized material extends on the convex top surface 27 of the bottom part 26 and has a thickness increasing towards its centre: the polymerized material can thus form a concavo- convex lens 38 which can be used for instance as an optical lens.

As mentioned for the previous embodiment, a final treatment (post- polymerization step) may be applied to the optical lens 38 after removal from the container 22, by subjecting the optical lens 38 removed from the container 22 to light, for instance of the same type as the light beam B mentioned above. This post-polymerization steps makes it possible to obtain a good surface state of the optical lens 38, in particular

Figures 6 to 8 shows yet another example of a system for producing an optical device.

In an initial step shown in Figure 6, a volume of a curable composition 44 is put in a container 42.

The container 42 is here identical to the container 22 of Figures 4 and 5: the container 42 has a bottom part 46 and lateral walls 48 and the surface 47 of the bottom part 46 facing the volume of curable composition 44 (here in contact with the volume of curable composition 44), i.e. the top surface of the bottom part 46, has a convex shape.

The curable composition (or at least non-transparent components of the curable composition) has photo-bleaching properties, as explained above.

A non-homogeneous light beam B' is applied to the external surface of the bottom part 26. This light beam B' has a higher light intensity at its periphery than at its centre. Said differently, the light intensity in the light beam B' decreases towards the centre of the light beam B'. Such a light beam B' can be obtained using a spatial light modulator, as described above referring to Figures 1 to 3.

The bottom part 46 (at least) of the container 42 is transparent to light used for the light beam B' such that the light beam B' irradiates an external surface of the volume of the curable composition 44 (i.e. here the surface in contact with the top surface 47 of the bottom part 46 of the container 42).

In the initial state shown in Figure 6, as no portion of the volume of the curable composition 44 has yet polymerized, irradiation by the light beam B' through the bottom part 46 thus leads to polymerizing regions of the volume of the curable composition 44 in the vicinity of the bottom part 46. However, as the light beam is non-homogenous (light intensity being here higher at the periphery of the light beam B'), polymerization begins in particular at the periphery of the volume of curable composition 44, in first portions 54 schematically shown in Figure 7.

As a consequence, at an intermediary step shown in Figure 7, these first portions 54 have polymerized and the transmittance of these first portions 54 has increased due to the photo-bleaching properties of the curable composition.

The light beam B' irradiating the bottom part 46 of the container 42 and transmitted across the bottom part 46 thus propagates through the polymerized first portion 54, as schematically shown in Figure 7, and thereby reaches second portions 56 of the volume of the curable composition 44, which consequently polymerizes in turn.

As the light beam B' is not homogeneous, this process is more effective in regions where the light intensity is high, leading to a larger thickness in these (here peripheral) regions.

Consequently, in the final step shown in Figure 8, the polymerized material extends on the convex top surface 47 of the bottom part 46 with a thickness decreasing towards its centre: the polymerized material can thus form a double concave lens 58 which can be used for instance as an optical lens.

As mentioned for previous embodiments, a final treatment (post- polymerization step) may be applied to the optical lens 58 after removal from the container 42. This post-polymerization step makes it possible to obtain a good surface state of the optical lens 58, in particular.

In the examples just described, the light beam B, B' irradiating the volume of the curable composition is non homogeneous spatially, but has constant characteristics over time. In other embodiments, light distribution in the light beam could evolve over time, as now explained.

EXAMPLE A

A piece of polymerized material with variable thickness as shown in

Figure 12 was obtained by subjecting a curable composition (having a volume of 38 cm ³ ) placed in a container (identical to the container 2 of Figure 1 ) to a light beam having successively the three distinct light distributions shown respectively in Figures 9 to 1 1 . The curable composition used comprises PETIA (Dipentaerythritol penta- /hexa-acrylate), as a monomer, and 1 % (in weight) of Bis Acyl Phosphine Oxide (BAPO), as a photo-initiator. Light used is visible light.

In Figures 9 to 1 1 , white areas represent parts of the light beam with high intensity (for instance between 10 W.m ^"2 and 100 W.m ^"2 , here about 40 W.m ^"2 ), while black areas represent parts of the light beam with low (or no) light intensity.

Prior to being subjected to the light beam, the curable composition is degassed (here for an hour at 0.09 MPa) to removed dissolved O ₂ .

The light distribution shown in Figure 9 is applied for 5 s.

Then, the light distribution shown in Figure 10 is applied for 5s.

Then, the light distribution shown in Figure 1 1 is applied for 10s.

The piece of polymerized material obtained is shown in Figure 12.

Three distinct thicknesses are clearly visible:

- ei = 1 ,5 mm (obtained by the 10s-long irradiation of the right-hand part of the beam on Figure 1 1 );

- β ₂ = 2,6 mm (obtained by the 15s-long irradiation of the central part of the beam);

- β3 = 3,35 mm (obtained by the 20s-long irradiation of the left-hand part of the beam).

EXAMPLE B

Figures 13 to 15 show plano-convex lenses obtained using the process described above with reference to Figures 1 to 3 for distinct operating conditions, respectively.

The curable composition used comprises PETIA (Dipentaerythritol penta- /hexa-acrylate), as a monomer, and 1 % (in weight) of Bis Acyl Phosphine Oxide (BAPO), as a photo-initiator. Light used is visible light.

The light distribution of the light beam has rotational symmetry around the centre of the light beam (where light intensity is maximum, in the present example).

Operating conditions and characteristics of the obtained lenses

(maximum thickness e _max and minimum thickness e _m i _n ) are given in the table below. Fig. 13 Fig. 14 Fig. 15

Light intensity at centre 10 W.rrf 10 W.m ^" 10 W.rrf

Light intensity at periphery 3 W.rrf 3 W.m ^" 3 W.rrf

Degassing no yes: hard yes: mild

©max 3,36 mm 2,26 mm 4,77 mm

Smin 1 ,63 mm 0,62 mm 2,1 1 mm

The above experiments correspond only to exemplary embodiments of the invention and the values mentioned therein should not therefore be construed as limitative.