Optical device

Abstract

An optical device comprising an electroactive lens may comprise a first and a second optically transparent substrate extending generally parallel to each other and defining an axial direction and transverse directions, a diffractive or refractive lens structure (for instance a Fresnel lens structure) between the first and second substrates defining a blazed cross section, the shape of its blazed cross section being defined by a plurality of upright lens parts and a plurality of slanting lens parts, a first and second electrode formed on the substrate and the lens structure, a sealed cavity between the first and second substrates wherein the lens structure and an LC layer are arranged. Furthermore, an additional layer is arranged on the lens structure, the additional layer comprising a plurality of first zones providing first optical characteristics and a plurality of second zones providing second optical characteristics, different from the first optical characteristics. By having different zones with different optical characteristics the effect of optical defects caused by the geometry of the lens structure may be reduced.

Description

[0001] OPTICAL DEVICE

[0002] FIELD OF THE DISCLOSURE

[0003] The disclosure relates to an optical device for use in eyewear, the optical device comprising an electroactive lens for a tunable transmission of light. The disclosure also relates to the use of the optical device and to a method of manufacturing the optical device.

[0004] BACKGROUND OF THE DISCLOSURE

[0005] Optical devices may comprise one or more tunable or electroactive lenses. Electroactive lenses provide the possibility to change (tune) the optical characteristics of the optical devices upon the application of a voltage or current to the lens.

[0006] Examples of electroactive lenses are described in WO 2019 / 115606 Al and WO 2022 / 090223 Al. Generally, an electroactive lens may comprise a first and a second optically transparent substrate extending generally parallel to each other and defining an axial (z) direction and transverse (x,y) directions, a diffractive lens structure (for instance a Fresnel lens structure) between the first and second substrates defining a blazed cross section, the shape of its blazed cross section being defined by a plurality of upright lens parts and a plurality of slanting lens parts, a first and second electrode formed on the substrate and the diffractive lens structure, a sealed cavity between the first and second substrates wherein the diffractive lens structure and an LC layer are arranged.

[0007] The layer of (nematic) liquid crystal (LC) material, diffractive structure and the electrodes enable the lens to be switched on and off between a state in which the refractive index of the LC material in the direction of the optical axis of the lens matches with the refractive index of the lens to a state in which the refractive index in a direction perpendicular to the optical axis does not match with the refractive index of the lens. The liquid crystal lens can be a lens made entirely of liquid crystal or a lens made of isotropic material filled with liquid crystal.

[0008] A Fresnel lens structure is generally known as a means to substantially reduce the thickness of a conventional lens. The design of such a device is implemented by cutting through the curved surface of a given conventional lens in zones at specified positions and reducing the thickness of each zone. These zones are called Fresnel blazes. In principle, each blaze comprises two main parts: a first main part, herein referred to as the slanting lens part, that may comprise of a smooth curved surface of the lens that extends at a small angle relative to the transversal (for instance, horizontal) direction, and a second main part, herein referred to as the upright lens part, that extends generally in the axial direction (for instance, the vertical direction). The second main part may be thought of as a steep wall. The steep wall can be considered as a reset position for the phase of the light to form a continuous phase front after passing through the Fresnel structure. For proper operation of the electroactive lens, the liquid crystal (LC) molecules of the LC material need a specific orientation with respect to this structure. For instance, in the off state the molecules can be aligned perpendicular with respect to the substrates forming the top and bottom of the cavity. For instance, in such a state it is easy to match the ordinary refractive index of the LC with the refractive index of the Fresnel lens, ensuring there is no (additional) optical power. When applying an electrical field through the transparent electrodes typically residing at the inner side of the cavity, the LC molecules reorient to e.g. a horizontal state, thereby making the extraordinary refractive index active and creating an extra lensing effect.

[0009] The alignment of the LC molecules is typically regulated by implementing alignment layers at both sides of the cavity. Such an alignment layer fixes the orientation of the LC molecules or crystals at the boundary between the alignment layer and the molecules or crystals of the LC layer. The orientation of the LC molecules / crystals in the bulk (in the off state) then is a result of the orientation at both the top and the bottom of the cavity, the elastic forces between the LC molecules (as described by e.g. the Oseen-Frank model), and the geometric design of the cavity (e.g. the height of the cavity, also called the cell gap).

[0010] The most common alignment layers processes are either rubbing or photoalignment. Both typically entail a first deposition and curing of the layer followed by introducing the preferred orientation through a post processing step. In the case of rubbing, this is a linear orientation by mechanically rubbing the layer with a moving cloth mounted on a roller. In the case of photoalignment, this is illuminating the layer with polarized UV light under an angle. In general, this will also lead to alignment in a linear direction, but more complex patterns are possible. Lensing between the LC and the Fresnel structure is obtained by carefully controlling the molecular orientation of the LC in the gap between Fresnel structure and the flat substrate by means of electric field application over the first and second electrodes present on the first and second optically transparent substrates, respectively. LC molecular orientation control is required for both passive and active states of the device, i.e. states with the electric field off and on respectively. To provide a specific orientation to the LC molecules an alignment layer is applied to inner boundaries of the device which are in contact with the LC. In our current device, homogeneous vertical orientation of the LC is achieved by coating the Fresnel structure (and the flat substrate) with a single material. This material defines the LC orientation direction along the surface normal in the off state. Since on the upright parts (i.e. the steep walls) of the Fresnel structure, the surface normal is pointing in orthogonal direction compared to the smooth, slanting lens part, lens surface, LC molecules get misoriented on the steep walls of the structure after filling LC in the device. Hence, at individual steep wall locations, a micrometric GRIN (gradient-index) lens effect is created, causing visibility of Fresnel rings, scattering of light at these particular locations and optical quality degradation. More, generally, the unidirectional alignment of the LC material on the Fresnel structure blaze walls may lead to scattering of a part of incident light and may be directly observed as white rings or defects by human eye.

[0011] Even if under certain conditions, for instance in ambient light situations, these defects are not always visible, an amount of bright light incident on the diffractive lens structure may still result in a contrast decrease at the location of the blazes of the diffractive lens structure. This contrast decrease may reduce the quality of the user experience.

[0012] It is an object to provide an optical device wherein at least one of the above disadvantages has been at least partially removed.

[0013] According to a first aspect, an optical lens for use in eyewear is provided, the optical device comprising an electroactive lens for a tunable transmission of light, the electroactive lens comprising:

[0014] - a first and a second optically transparent substrate, wherein the first and second optically transparent substrates extend generally parallel to each other and define an axial (z) direction and transverse (x,y) directions;

[0015] - a refractive or diffractive lens structure, such as a Fresnel lens structure, made of transparent lens material and arranged between the first and second optically transparent substrate at the side of the second optically transparent substrate, wherein the lens structure defines a blazed cross section, the shape of its blazed cross section being defined by a plurality of upright lens parts and a plurality of slanting lens parts;

[0016] - a first optically transparent electrode formed on the first optically transparent substrate and a second optically transparent electrode formed on the second optically transparent substrate or on the lens structure;

[0017] - a sealed cavity between the first and second optically transparent substrates, wherein in the sealed cavity, the lens structure and nematic liquid crystalline (LC) material forming at least a liquid crystal layer are arranged;

[0018] - an additional layer arranged on the lens structure, the additional layer comprising a plurality of first zones providing first optical characteristics and a plurality of second zones providing second optical characteristics, different from the first optical characteristics; wherein the first zones are primarily located on slanting lens parts and the second zones are primarily located on upright lens parts.

[0019] The inventors came to the insight that a cause of the above-mentioned defects may be found in them specific geometry of the lens structure, more specifically in the relatively abrupt transitions in local orientation of the surface of the lens structure. By defining different zones with suitable optical characteristics, the effect of optical defects caused by the geometry of the lens structure may be reduced. Of importance is that an optical correction is achieved so that no optical defects (or less so) can be observed by the user. This optical effect may be achieved especially well in embodiments wherein the upright lens parts (herein are also referred to as walls or wall parts and generally extending in the above-mentioned axial direction) may be given optical characteristics differing from the optical characteristics of the slanting lens parts (herein also referred to as laying parts).

[0020] It is remarked that the slanted parts may be curved parts and / or (slanting) flat parts. For instance, when the diffractive or refractive structure is a Fresnel lens structure, the slanting parts tend to show a curved shape in cross-section. The slanting lens parts are lens parts generally extending in an oblique direction having an axial component in the axial direction (z) and a transversal component in at least one transversal direction (x and / or y).

[0021] In preferred embodiments the additional layer is an alignment layer and is provided on top of the entire lens structure. The alignment layer determines, among other things, the orientation of the LC molecules in the cavity on the surface when no voltage is applied to the electrodes. The binding of the LC molecules on a surface in a preferred orientation may also be referred to as the anchoring of the LC molecules to the surface. One optical characteristic of the additional layer is the anchoring energy, which is generally expressed in mJ / cm2. However, terms such as “high / strong anchoring energy” and “low / weak anchoring energy” do not refer to absolute values or value ranges, these terms refer to relative values and ratios between different values.

[0022] In embodiments of the present disclosure essentially the entire surface of an upright lens part, and optionally also one or more peripheral portions of one or more slanting lens part adjacent to the upright lens part, form the first zone, whereas the remaining portion or portions of the one or more slanting lens parts form the second zone. In other words, the first zone may be restricted to the upright lens parts only, but in other embodiments the first zone is formed both at the upright lens parts and at a portion of the slanting lens parts. The latter embodiments may have the advantage of easy manufacturing.

[0023] ANCHORING DESIGN

[0024] According to embodiments of the present disclosure the additional layer is an anchoring layer. An anchoring layer (or part of it) may be configured to provide a certain level of anchoring between its contact surface (i.e. the surface in contact with the LC material) and the liquid crystals of the LC material. In case of a strong anchoring the anchoring layer may form an alignment layer configured to align liquid crystals in the neighborhood of the contact surface of the anchoring (i.e. the liquid crystals at a distance within the reach of the anchoring effect) so as to arrange the liquid crystals in a preferred alignment direction. A (relatively) strong anchoring layer may have a relatively strong effect on the LC molecules compared to a (relatively) weak anchoring layer. The anchoring layer (or part of it) may also be configured to provide a weak anchoring between its contact surface and the liquid crystals of the LC material compared to another anchoring layer, or even no practical anchoring at all. In this situation the liquid crystals in the neighborhood of the contact surface tend to be arranged in arbitrary directions or in the direction of a strong anchoring layer located remotely from the anchoring layer.

[0025] In preferred embodiments wherein the additional layer on the lens structure is an anchoring layer and the anchoring layer has a contact surface in contact with the LC layer, the first zones of the contact surface providing the first optical characteristics are embodied as high anchoring zones configured to provide a relatively strong level of anchoring of liquid crystals in the nematic liquid crystalline (LC) material, and the second zones of the contact area are providing the second optical characteristics are embodied low anchoring zones configured to provide a relatively low level of anchoring or substantially no anchoring of liquid crystals in the nematic liquid crystalline (LC) material.

[0026] The first zones (i.e. in these embodiments the low / weak anchoring zones) are primarily located on upright lens parts and the high / strong anchoring zones are primarily located on slanting lens parts. As mentioned above though a small portion of the slanting lens parts may be formed as a weak anchoring zone as well.

[0027] By configuring the upright lens parts to have a weak or no anchoring with the LC crystals, the liquid crystals in the neighborhood of the upright lens part will no longer follow the local topology of the upright lens part (i.e. a steep wall) or less so. Thus means that the amount of visible light scatter at the positions of the upright lens parts will be reduced accordingly, thereby increasing the optical quality of the optical device.

[0028] In a further embodiment the optical device comprises an alignment layer arranged on the first optically transparent electrode. The alignment layer has a further contact surface in contact with the LC layer. The alignment layer is configured to provide a relatively strong anchoring of neighboring liquid crystals in the nematic liquid crystalline (LC) material (and therefore forms an anchoring layer) and is further configured to anchor the liquid crystals in such a way that they become aligned in a preferred direction. This alignment layer on the electrode is located such that it faces the anchoring layer on the lens structure. In specific embodiments the alignment layer on the electrode is configured to linearly align neighboring liquid crystals in the preferred first direction, preferably in a generally axial direction.

[0029] In certain embodiments the level of anchoring between the contact surface of the anchoring layer and neighboring liquid crystals in the low anchoring zones is small enough to provide alignment of the neighboring liquid crystals in one or more directions corresponding with the alignment direction of a remotely located alignment layer on the first optically transparent layer and / or with the alignment direction of the strong anchoring zones. In these embodiments the orientation of the liquid crystals located close to the upright lens part is tuned (at least partially) to the orientation of the liquid crystals located remotely, more specifically the orientation corresponding to the alignment layer on the first optically transparent electrode.

[0030] In embodiments of the present disclosure the contact surface in the high anchoring zone is configured to align neighboring liquid crystals in a second direction, preferably in essentially the same direction as the alignment of the above-mentioned alignment layer and / or preferably in a generally axial direction.

[0031] According to an embodiment the anchoring layer comprises:

[0032] - a first anchoring layer arranged over essentially the entire lens structure, the first anchoring layer configured to provide a relatively low level of anchoring or no anchoring at all with neighboring liquid crystals;

[0033] - a second anchoring layer located only in the high anchoring zones and arranged on the first anchoring layer, the second anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals.

[0034] According to an embodiment the anchoring layer comprises:

[0035] - a first anchoring layer arranged over essentially the entire lens structure, the first anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals when in contact with the first anchoring layer;

[0036] - a second anchoring layer located only in the low anchoring zones and arranged on the first anchoring layer, the second anchoring layer configured to provide a relatively low level of anchoring or no anchoring at all with neighboring liquid crystals.

[0037] According to an embodiment the anchoring layer comprises:

[0038] - a first anchoring layer located only in the high anchoring zones and arranged on the lens structure, the first anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals when in contact with the first anchoring layer;

[0039] - a second anchoring layer located only in the low anchoring zones and arranged on the lens structure, the second anchoring layer configured to provide a relatively low level of anchoring or no anchoring at all with neighboring liquid crystals.

[0040] According to an embodiment the anchoring layer comprises:

[0041] - a first anchoring layer arranged over essentially the entire lens structure, the first anchoring layer configured to provide a relatively low level of anchoring or no anchoring with neighboring liquid crystals when in contact therewith;

[0042] - a second anchoring layer located over essentially the entire first anchoring layer, the second anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals when in contact therewith; wherein a part of the second anchoring layer arranged on the first anchoring layer has been removed, for instance by etching, by ablating or by a similar operation, to locally expose the first anchoring layer, wherein the removed part is the second anchoring layer corresponding to the low anchoring zones.

[0043] According to an embodiment the anchoring layer comprises:

[0044] - a first anchoring layer arranged over essentially the entire lens structure, the first anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals when in contact therewith;

[0045] - a second anchoring layer located over essentially the entire first anchoring layer, the second anchoring layer configured to provide a relatively low level of anchoring or no anchoring at all with neighboring liquid crystals when in contact therewith; wherein a part of the second anchoring layer arranged on the first anchoring layer has been removed, for instance by etching, by ablating or by a similar operation, to locally expose the first anchoring layer, wherein the removed part is the second anchoring layer corresponding to the high the high anchoring zones.

[0046] According to an embodiment the anchoring layer is arranged over the lens structure and is made of anchoring material providing a relatively high level of anchoring with neighboring liquid crystals when in contact with the anchoring layer, wherein the outer surface of high anchoring material of the anchoring layer in the low anchoring zone is treated so as to locally reduce the level of anchoring, for instance by UV exposure of the high anchoring material in the low anchoring zone.

[0047] According to an embodiment the anchoring energy of the surface in the high anchoring zones is substantially higher than the anchoring energy of the surface of the low anchoring zones. The terms high and low anchoring are used as relative terms. In this application, the anchoring of certain zones and layers is adapted with respect to other zones and layers. The ratio between the high anchoring energy of the surface in the high anchoring zones with respect to the anchoring energy of the surface in the low anchoring zones may be selected to lie in the range of 102to 106Specifically, “high anchoring energy / zone” and “low anchoring energy / zone” do not (necessarily) refer to anchoring energies in the ranges commonly referred to as “high” and “low” in the literature, they are relative terms.

[0048] According to an embodiment the anchoring energy in the first zones is two orders of magnitude lower compared to the anchoring energy in the second zones. The order of magnitude of the anchoring energy as used herein corresponds the smallest power of 10 used to represent the anchoring energy. According to an embodiment at least one of the second zones only extends over the surface of an upright lens part and wherein at least one of the first zones only extends over the surface of a slanting lens part.

[0049] According to an embodiment at least one of the first zones only extends over the surface of an upright lens part and over one or more peripheral portions of one or more slanting lens parts.

[0050] According to an embodiment the total width of a second zone in cross-section along a transverse direction (x) is in the range of 1 pm to 45 pm, preferably 3 pm to 25 pm, more preferably in the range of 5 pm to 15 pm, for instance about 10 pm. A coating or layer preferably is about 10 pm wide and / or covers a plurality of the upright lens parts (i.e. a plurality of the upright walls of the lens structure) wall. Furthermore, coated wall portions may be located in the center of the lens.

[0051] According to other embodiments the optical characteristics in the second zones differ from the optical characteristics in the first zones in that the material of the additional layer in the first zone has a relatively small optical absorbance while the material of the additional layer in the second zone has a relatively large optical absorbance (relative to the (spectrum of) light entering the electroactive lens).

[0052] According to an embodiment the material of the additional layer in the second zone is configured to completely or almost completely absorb light received in the electroactive lens.

[0053] According to an embodiment the additional layer comprises in the second zones essentially light-absorbing material and / or in the first zones the additional layer comprises essentially lighttransmitting material.

[0054] According to an embodiment the light-absorbing material comprises ink material, for instance black ink material.

[0055] According to an embodiment the light-absorbing material is a material providing relatively low or no anchoring with the liquid crystals when in contact with the LC material inside the cavity.

[0056] According to an embodiment the light-absorbing material is a material with a high bandgap, for instance, BK-6148 T3 from TOK or a coating. This material shows a visually prominent and unexpected effect of not only being less transparent but also preventing total internal reflection.

[0057] According to an embodiment the additional layer in the second zones comprises:

[0058] - a first layer made of light-absorbing material;

[0059] - a second layer on top of the first layer, wherein the second layer is an anchoring layer configured to provide a high anchoring, for instance an alignment layer as defined herein.

[0060] The additional layer in the first zones may be free from light-absorbing material.

[0061] According to an embodiment the optical characteristics in the second zones differ from the optical characteristics in the first zones in that the material of the additional layer in the first zone has a relatively high transparency while the material of the additional layer in the second zone has a relatively low transparency or almost zero transparency. Again, of course relative to the (spectrum of) light entering the electroactive lens.

[0062] According to an embodiment wherein the total width of a second zone in cross-section along a transverse direction (x) is in the range of 1 pm to 45 pm, preferably 3 pm to 25 pm, more preferably in the range of 5 pm to 15 pm, for instance 10 pm. Preferably, the width of the second zone depends on the feature parameters of the lens structure, more preferably on the dimensions of the upright lens part.

[0063] According to further embodiments an additional layer is arranged on both the lens structure, more specifically on the slanting lens parts and / or on the upright lens parts, and on other structures located inside the sealed cavity, for instance on one or more spacers arranged between the lens structure and the first optically transparent substrate or the first optically transparent electrode formed on the first optically transparent substrate. This means that the other structures may be “hidden” as well so that uniform distribution of the alignment directions of the liquid crystals may be achieved also at the locations where such other (mechanical) structures are located.

[0064] According to further embodiments the optical characteristics of the material of the additional layer involve at least one of an interaction parameter and an absorption parameter, wherein an interaction parameter defines the interaction between the material of the additional layer and liquid crystals of the LC material in the cavity; and wherein an absorption parameter defines the absorption behavior of light in the additional layer.

[0065] According to further embodiments the interaction parameter of a material includes the anchoring energy of the material and / or wherein the absorption parameter of a material includes the level of light absorption of the material.

[0066] The anchoring energy represents the amount of energy needed for LC crystals (molecules) to divert their orientation from a preferential orientation relative to a surface (i.e. relative to a contact surface / alignment surface).

[0067] According to further embodiments the additional layer comprises a first additional layer having first surface features and a second additional layer having second surface features different from the first surface features.

[0068] According to further embodiments the electroactive lens is configured to vary the optical power of the electroactive lens by altering the refractive index of the LC layer in the transverse direction upon application of a voltage to the first and second optically transparent electrodes.

[0069] According to further embodiments the optical is configured to cause the electroactive lens to switch from an the off-state wherein the at least one electroactive lens shows essentially no lens action and an on-state wherein the at least one electroactive lens shows lens action upon application of a voltage from a voltage source connected to the first and second optically transparent electrodes.

[0070] According to further embodiments the liquid crystal material of the at least one electroactive lens has a birefringence An that is in the range of 0.15 - 0.40.

[0071] Another aspect relates to the use of the optical device as defined herein claimed in any of the preceding claims.

[0072] A further aspect relates to a method of manufacturing the optical device as defined herein.

[0073] BRIEF DESCRIPTION OF THE DRAWINGS

[0074] The above and / or other aspects of exemplary embodiments will become apparent and more readily appreciated from the following detailed description of exemplary embodiments, taken in conjunction with the accompanying drawings of which:

[0075] - Figure 1 is a cross-section through an embodiment of an optical device comprising an clcctroactivc lens for a tunable transmission of light, relative to a (x, y, z) coordinate system;

[0076] - Figure 2A is a part of the cross-section of the embodiment of figure 1 , wherein the tilt angle (9) of a crystal of the liquid crystalline (LC) material with respect a transverse direction (specifically, x-dircction) (the figure also showing an enlargement section, as will be explained later);

[0077] - Figure 2B is a partly cut-away side view of the optical device of figure 2A, wherein the twist angle (<p) of a crystal of the liquid crystalline (LC) material with respect to the same transverse (x-) direction;

[0078] - Figure 3 a front view of a part of a pair of spectacles, as an example of a unit wherein the optical device may be mounted;

[0079] - Figure 4 shows an optical contrast map (in a Shack-Hartmann arrangement), representing the results of an optical quality inspection test performed on a prior art optical device;

[0080] - Figure 5 is a map showing a cross-section of an electroactive lens with an indication of the local orientation of the LC molecules or crystals, in an embodiment having an alignment layer showing a constant level of anchoring;

[0081] - Figure 6 shows an example of an electroactive lens with an anchoring layer showing varying levels of anchoring;

[0082] - Figure 7 is a map showing a cross-section of an electroactive lens with an indication of the local orientation of the LC molecules or crystals, in an embodiment having an anchoring layer showing varying levels of anchoring (as in figure 6);

[0083] - Figures 8A-8D are graphs of a cross-section (in an x,z-plane) of a blaze of a lens element according to a prior art example, showing the tilt angle (9) for the OFF-state (figure 8A) and for the

[0084] RECTIFIED SHEET (RULE 91) ISA / EP ON-state (figure 8B) and showing the twist angle (<p) for the OFF-state (figure 8C) and for the ON- state (figure 8D), in case of the application of a mono-anchoring layer on the lens structure;

[0085] - Figures 9A-9D are graphs of a cross-section (in an x,z-plane) of a blaze of a diffractive or refractive lens element according to an embodiment of the present disclosure, showing the tilt angle (9) for the OFF-state (figure 9A) and for the ON-state (figure 9B) and showing the twist angle (<p) for the OFF-state (figure 9C) and for the ON-state (figure 9D), in case of the application of a anchoring layer with varying anchoring on the lens structure;

[0086] - Figures 10-15 arc cross-sections of further embodiments of an optical device using weak anchoring in order to reduce scattering;

[0087] - Figures 16 and 17 arc cross-sections of embodiments of an optical device using light absorption in order to reduce scattering; and

[0088] - Figures 18A-18D arc photographic renderings showing the effect of the application of absorption material in specific zones of the lens structure, wherein figures 18A and 18B represent the prior art in respectively an OFF-state and ON-state and figures 18C and 18D represent an embodiment of the present disclosure wherein black ink material has been applied to these specific zones;

[0089] All the figures arc schematic, not necessarily to scale, and generally only show parts which arc necessary to elucidate example embodiments, wherein other parts may be omitted or merely suggested. Furthermore, all publications and patents cited in this specification arc herein incorporated by reference as if each individual publication or patent were specifically and individually indicated to be incorporated by reference and arc incorporated herein by reference to disclose and describe the methods and / or materials in connection with which the publications arc cited.

[0090] It is noted that, as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation.

[0091] As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope of the present invention. Any recited method can be carried out in the order of events recited or in any other order which is logically possible.

[0092] Figure 1 shows schematically an example of an optical device 1 in accordance with an embodiment of the present disclosure. The optical device 1 comprises a tunable electroactive lens 101. This electroactive lens 101 may be part of a lens, for instance lens of a pair of glasses (cf.

[0093] RECTIFIED SHEET (RULE 91) ISA / EP figure 3). For instance, the electroactive lens 101 may be sandwiched between two lens halves (not shown in figure 1) providing the optical device with a suitable optical power.

[0094] The electroactive lens 101 comprises a first substrate 104 at which a first electrode 106 is formed, a second substrate 105 at which a second electrode 107 is formed, and a volume or cavity

[0095] 108 enclosed between the first and second substrate 104, 106, in the specific embodiment between the electrode 106,107, and sealed by two borders 103 arranged at opposite ends of the electroactive lens 101. The first substrate 104, second substrate 105, first electrode 106 and second electrode 107 may be made of an optically transparent material. For instance, the electrodes 106, 107 may comprise tin-doped indium oxide (ITO) layers and / or indium-zinc oxide (IZO) layers. The first and second electrodes 106, 107 may be connected to an electrical power source (not shown). The power source may be configured to apply a voltage difference between the first and second electrodes when the optical device is switched into an on-state while in an off-state essentially no voltage difference exist between the first and second electrodes.

[0096] The sealed volume or sealed cavity 108 between the optically transparent electrodes 106, 107 contains a lens structure 102 and at least a liquid-crystal (LC) layer 113 formed of liquid crystals. The cavity 108 of the electroactive lens 101 may comprise a lens structure in the form of a Fresnel lens structure although other types of diffractive structures could be employed as well. The lens structure 102 extends in the shown embodiment over only a part of the width of the cavity 108 so that at both lateral ends of the lens structure a respective intermediate space 108a, 108b is present. In other embodiments, however, the lens structure extends to contact the two borders 103 (which borders 103 may be formed by plugs arranged between the first and second substrates 104, 105. Furthermore, the Fresnel-lens structure 102 is positioned in the center of the cavity 108, although in other embodiments the Fresnel-lens structure may be arranged closer to either of the borders 103 of the electroactive lens 101. The Fresnel-lens structure 103 is made of transparent material as well, for instance an isotropic polymeric material.

[0097] Additionally, one or more spacers 109 may be arranged inside volume 108 as well. Spacers

[0098] 109 may be arranged between the Fresnel-lens structure 102 and an opposing electrode 106, 107. For example, as illustrated in figure 1, the Fresnel-lens structure 102 may be arranged on the second electrode 107. The one or more spacers 109 are then arranged between the Fresnel-lens structure 102 and the first electrode 106 and extend through the volume 108. One or more spacers (not shown) may also be arranged in between electrodes 106, 107, extending from the first electrode 106 through the volume 108 to the second electrode 107. Furthermore, on top of the first electrode 106 (or as part of the first electrode 106) an alignment layer 111 is arranged for aligning the LC material 113 inside the cavity 108.

[0099] Furthermore, an additional layer 112 (see especially the enlarged section of figure 1) is arranged on top of the lens structure 102, i.e. on the surface of the lens structure 102 facing the LC material in the cavity 108. The electrodes 106, 107 are configured to alter (tune) the alignment direction of the liquid crystal molecules inside the liquid crystal (LC) layer to thereby alter the refractive index of the liquid-crystal (LC) layer in the transverse direction (x-direction of figure 1) of the electroactive lens 101. More specifically, it is the refractive index in transversal (horizontal) direction which is the one that needs to be either matched or not matched with the Fresnel lens. Thereby a variation in the optical power of the electroactive lens 101 may be obtained. The alignment of the liquid crystal molecules can be changed by activation of the electroactive lens 101. The electroactive lens 101 is configured to be activated using a voltage applied to the optically transparent electrodes 106, 107.

[0100] When no voltage is applied to the electrodes 106,107 the orientation of the liquid-crystal molecules in the cell is determined by the alignment on the contact surfaces (of the alignment layer 111 and the additional layer 112) in the cell. More specifically, the liquid crystal molecules in the liquid crystal (LC) layer exhibit both in-plane and out-of-plane orientation wherein the in-plane alignment direction of the liquid crystals typically coincides with the rubbing or illumination direction of the contact surface. The average upward tilt angle of the liquid crystals from the contact surface plane is then referred to as the (unidirectional) pretilt angle (0) (see figure 2A). When a voltage is applied to the electrodes 106, 107, the electric field generated between the electrodes 106, 107 will cause a different alignment direction of the liquid crystals.

[0101] For example, in a first state, herein also referred to as the off state, i.e. a state wherein no voltage is applied to the optically transparent electrodes 106, 107, the liquid crystals may orient themselves in such a manner that the refractive index of the LC layer in the transverse direction (x- direction) of the electroactive lens 101 essentially matches the refractive index of the lens structure (i.e. Fresnel lens structure) 102. Consequently, the lens structure 102 and the LC layer effectively form a combined optical layer having one and the same refractive index in the transverse (x-) direction (i.e. essentially no optical interface is present in volume 108). In other words, the combined optical layer has an essentially constant refractive index in volume 108, irrespective of the width position (i.e. position along the x-direction shown in figure 1).

[0102] In the shown embodiment the combined optical layer also has two parallel surfaces. Consequently, a beam of light, incident on the electroactive lens 101 when in the first state, will not be collimated or dispersed.

[0103] In a second state, herein also referred to as the on-state, i.e. a state wherein a voltage is applied to the first and second electrode 106,107, the orientation of the liquid-crystal molecules typically becomes parallel with the alignment direction (if any) of the contact surface, so that an additional optical interface is created between the liquid crystals in the LC layer and the lens structure 102. This additional optical interface results in a different refractive index of the combined layer. Therefore, a light beam incident on the electroactive lens 101 will be refracted by the optical interface between the lens structure 102 and the LC-layer, thereby collimating or dispersing rays of the beam incident on the lens structure 102.

[0104] In summary, the first state may be a state wherein no voltage is applied to the electrodes 106, 107 and the second state is state wherein a suitable voltage is applied to the electrodes 106, 107 so that the refractive index of the combined optical layer in the transverse direction of the electroactive element 101 respectively matches and differs from the refractive index of the lens structure 102 (i.e. a Fresnel lens structure). Similarly, in the following description, a switched on state refers to a state wherein additional optical power is provided to the electroactive lens 101 by creating a refracting optical interface between the lens structure 102 and the liquid crystals in the volume 108, while the switched off state refers to a state wherein the refractive index of the liquid crystals in the transverse direction of the electroactive lens 101 matches the refractive index of the lens structure 102 as a result of which no additional power is provided to the electroactive lens 101. Preferably the refractive index of the LC layer (in the switched off state) and Fresnel-lens structure 102 matches the refractive index of the first substrate 104 and / or second substrate 105 as well.

[0105] The Fresnel-lens structure 102 may be a positive Fresnel-lens structure or a negative Fresnel-lens structure. Preferably, the Fresnel-lens structure 102 is a negative Fresnel-lens structure (as illustrated in figure 1). It may differ among applications of the electroactive lens 101 what kind of Fresnel-lens structure 102 is used, for example, different sizes, strengths, shapes of Fresnel-lens structures 102 may be used. The Fresnel-lens structure 102 may be arranged on the electrode 107 that is connected to the second. In embodiments wherein the Fresnel-structure 102 is arranged on electrode 107, the Fresnel structure 102 may be formed on electrode 107 by any technique, for instance by nanoimprint lithography.

[0106] The Fresnel-lens structure 102 may be formed by a plurality of concentric ring-like shapes referred to as ridges or blazes 110. A blaze 110 is formed by a ring-like shape having a crosssection that resembles a triangle-like shape with one of the sides extending in the axial direction (i.e. z-direction) of the electroactive lens 101, referred to as the upright lens part 115, a side that is facing the electrode whereon the Fresnel-lens structure 102 is formed (i.e. x, y-plane), and an oblique side (which may be curved), that provides the refracting optical interface between the Fresnel-lens structure 102 and the liquid crystal in the switched on state, referred to as the slanting lens part 116. The shape of the blazes 110 may be optimized for the specific application of the electroactive lens 101 and the example discussed above, or the exemplary figures are non- limitative.

[0107] The first optically transparent substrate 104 and the second optically transparent substrate 105 may be joined by applying an adhesive between the two substrates, thereby forming at least a portion of the border 103. The border 103 or part of the border may further be formed during the formation of the Fresnel-lens structure 102, for example, during the nanoimprinting step wherein the Fresnel-lens structure 102 is formed.

[0108] In figures 2A and 2B, the electrodes 106 and 107 are spaced in the z-direction. The electrodes together with the borders 103 are spaced apart in a transversal direction (x-direction) and define a volume containing LC material. The LC molecules or crystals are indicated as a longitudinal ellipsoid 205. The tilt angle of an LC molecule or crystal is visualized schematically in figure 2A. The tilt angle 0 is the angle between the z- (upright / vertical) direction and the x-axis (horizontal / transversal) of the system, corresponding to the central axis of the Fresnel lens structure pointing in a normal direction to the plane wherein the Fresnel lens structure is arranged, and the direction wherein the Fresnel blazes are lined up, i.e. an arbitrary radial direction of the Fresnel lens structure. The twist angle cp is the angle of rotation around the z axis, i.e. the angle between the x-axis and the y-axis as indicated in figure 2B. The y axis extends in the plane wherein the Fresnel lens is provided, and perpendicular to the x and the y axis.

[0109] In many LC based devices, the starting position of the LC molecules at one side is either nearly horizontal, with a preferred horizontal direction (e.g. tilt of 3° and a twist of 0°) or a nearly vertical direction, also having a preferential in the horizontal direction (e.g. a tilt of 89° and a twist of 0°). Tilt angles of 0° or 90° are generally avoided because the reorientation of the molecules upon applying an electrical field will occur randomly, leading to a - at least temporary - scattering state. Next to this, the preferential direction on either side of the cavity is generally chosen in an anti-parallel configuration to either avoid twisting of the molecules in the bulk of the cell and / or to ensure a fast response of the LC cell when applying an electrical field.

[0110] As LC is a birefringent material, this tilting and twisting of the LC material causes a shift of the index of refraction. Inhomogeneous tilting and twisting may cause scattering / uncontrolled lensing effects.

[0111] As mentioned before, the mono-alignment of the LC molecules on the blazed contact surfaces of the Fresnel lens in electroactive lenses like the one shown schematically in figure 1 may cause scattering and uncontrolled lensing. The mono-alignment of the LC molecules on the contact surfaces of the Fresnel lens, i.e. the surface of Fresnel blaze walls, or on the surface of the alignment layer provided evenly over the Fresnel blaze walls, may cause inhomogeneous alignment of the LC molecules. As a result of the varying orientation of the lens parts 115, 116 (for instance, the blaze parts of the Fresnel structure), i.e. the orientation shifting from horizontal (in the slanting lens part) to vertical (in the steep wall), the mono-alignment, an LC molecule alignment which is always normal to the contact surface, creates inhomogeneous orientation of the LC molecules or crystals. This inhomogeneous orientation of the LC crystals along the lens causes an inhomogeneous diffraction. Hence, at individual blaze locations, a micrometric lens effect is created, causing Fresnel rings, scattering of light at these upright lens parts and optical quality degradation.

[0112] Figures 3 and 4 are examples showing the optical results of such optical scattering. Figure 3 shows a pair of glasses / spectacles wherein electroactive lenses (only one electroactive lens 100 shown in the figure) have been mounted in a spectacle frame. Figure 4 is a Shack-Hartman map determined by a Shack-Hartmann (or Hartmann-Shack) wavefront sensor (SHWFS) (which is an optical instrument known to, and its working being readily understood by, the skilled person. The optical instrument may be used or emulated for characterizing an imaging system and is a common method to verify the quality of the lens) showing dots of local light intensity as function of x,y position. The map makes clear that concentric defects are generated in the prior art electroactive lenses.

[0113] More specifically, figures 3 and 4 show visual effects of scattering due to inhomogeneous orientation of the LC molecules caused by mono-alignment on the surface of the blazed Fresnel structure. Figure 3 shows a schematic drawing of blaze defects as a result of the undesired interaction between the Fresnel lens and the LC in an optical device when bright light source is illuminating the device from the back. However, when a bright light source is incident on a blazed structure, a contrast decrease in the location of Fresnel blazes is observed as shown in our standard optical quality inspection test. Figure 4 shows a contrast maps in a Shack - Hartmann setup. A dot pattern of the light coming through the LC-Fresnel lens is shown in figure 4. The rings in the dot pattern of figure 4 are a result of scattering of the light around the ring-shaped blazes in the Fresnel structure caused by the steep gradient in the orientations of the LC molecules that are connected to the blaze surface in mono-alignment. Due to the scatter, the local contrast and hence optical quality decreases at the position of the blaze walls. Light scattered from the blaze wall is particularly observable in a dark environment while facing a bright light source.

[0114] As mentioned before, when applying an anchoring layer to an unleveled structure such as a lens structure, the local alignment is typically influenced by the local topology. For instance, when the applied alignment layer is configured to anchor the LC molecules in a direction normal to the surface (as in shown in the embodiment of figure 5), the LC molecules will locally retain their nearly normal orientation with respect to the surface plane. While the impact can be low when the structure is varying slowly, a profound impact can be seen with abrupt changes such as on the upright lens part (see figures 6, 8).

[0115] The impact of this non-ideal alignment is a local increase in visible light scatter since there is a local refractive index variation that acts like a small (micron sized) Gradient Index lens. This scatter is detrimental to the user experience, particularly in specific situations such as driving at night (see figures 3 and 4). Next to this, this scatter deteriorates the optical quality of the lens. Note that in this configuration the scatter is mainly for light with its polarization axis parallel to the preferential direction. Light with a perpendicular orientation will not scatter as it will experience the ordinary refractive index of the liquid crystals, which is matched with the refractive index of the Fresnel lens.

[0116] The current disclosure addresses the scatter caused at the upright lens parts in the lens structure by locally adapting certain optical properties of the lens structure. More specifically, the optical properties are adapted so that in so-called first zones of the lens structure the structure has first optical characteristics while in so-called second zones the structure provides second optical characteristics, different from the first optical characteristics. Referring to figure 6, the slanting lens portions 1161, 1162are part of respective first zones 118, while the upright lens part 115 and (optionally also) small neighboring strips 1163, 1164of the slanting lens portions 1161, 1162form a second zone 117. By adapting the optical characteristics in the first zone relative to those of the second zone, adapting the optical characteristics in the second zone relative to those of the first zone, or adapting the optical characteristics in both the first and second zones, the improvement of the optical quality of the optical device may be achieved.

[0117] More specifically, locally adapting the optical properties of the various lens parts may be accomplished by at least one of:

[0118] 1) adjusting the local alignment on the upright lens portions and / or the slanting lens portions to achieve an improved alignment (i.e. by locally tuning the anchoring level)

[0119] 2) absorbing a portion of the light arriving at the lens structure, more specifically at the upright lens portions thereof.

[0120] A first manner of locally adapting the surface of the lens part(s) will be discussed with reference to figures 5-15 while a second manner will be described thereafter with reference to figures 16-18.

[0121] TUNING ANCHORING LEVEL

[0122] Adjusting the local alignment of the LC molecules / crystals involves varying the (level of) anchoring existing between the LC molecules / crystals in the cavity and the contact surfaces of the different lens parts of the lens structure. The level of anchoring is dependent on the physical concept of anchoring energy. Anchoring energy is defined by the force connecting LC molecules with the alignment molecules of the contact surface and is a known concept in the field of LC1. A clarification about the concept of “anchoring energy” for instance can be found in an article by Yumiko Sato et al, 1992, Jpn. J. Appl. Phys. 31 L579, DOI 10.1143 / JJAP.31.L57 (incorporated herein by reference). By locally changing the level of anchoring or the anchoring energy between the contact surface in a zone of the lens structure and the LC molecules in the cavity, the orientation of the LC molecules within a short distance from the contact surface may be controlled to some extent.

[0123] Figures 5-9 schematically show the difference between the alignment and orientation of the LC molecules in the prior art lens device (figure 5, 8) and in the improved lens device (figure 6, 7, 9-14).

[0124] Figure 5 schematically shows inhomogeneous orientation of the LC molecules due to mono-alignment of the molecules on the blazed surface of the Fresnel structure, whilst figure 7 schematically shows homogeneous orientation as a result of provided locally selective alignment layers on the blazed Fresnel structure.

[0125] Figure 5 is a cross section of part of the optical device in the situation of mono-alignment of the LC molecules on the blazed Fresnel structure. A cavity filled with LC molecules / crystals is formed between combination of a substrate 104, an electrode 106, and an alignment layer 111 (the alignment layer 111 directly facing and in contact with the LC molecules in the cavity) and a combination of a substrate 105 and electrode 107. From the Fresnel structure, one blaze 110 is partly shown. One upright lens part 115 of the blaze 110 and its surroundings are shown in cross section. The orientation of the LC molecules is indicated with T-shaped nails 205. The large arrows 508, 509 passing the Fresnel structure and the LC layer indicate the direction of light rays traveling through the system.

[0126] For instance, referring to figure 5, in the mono-alignment situation, the LC molecules may be aligned with the contact surface of the blazed Fresnel structure such that their orientation always is perpendicular to the surface. The LC molecules follow the direction set by the alignment layer and in this case they therefore align perpendicularly to the surface.

[0127] If we follow this preferential alignment direction on the Fresnel lens side from the first zone 118 primarily on the slanted lens part 116 to the second zone 117 on the upright lens part 115, the orientation of the LC molecules will follow the downward (or upward) orientation at the upright lens part 115. In other words, the LC molecules will locally retain their nearly vertical orientation with respect to the local contact surface. This actually means that the molecules are oriented horizontally when considering the original frame of reference. This horizontal alignment gradually becomes vertical again at larger distances from the upright lens part 115, i.e. in the bulk of the cavity (clearly shown in figure 5). The mono-alignment of the molecules on the surface results in an inhomogeneous orientation field around the upright lens part of the blaze 110. This horizontal alignment gradually becomes vertical again when moving towards the bulk of the cavity.

[0128] The impact of this non-ideal alignment is a local increase in visible light scatter since there is a local refractive index variation that acts like a small (micron sized) gradient Index lens. This scatter is detrimental to the user experience, particularly in specific situations such as driving at night. Next to this, this scatter deteriorates the optical quality of the lens.

[0129] As LC is a birefringent material, this bending and twisting of the LC material causes a shift of the index of refraction and scattering and / or uncontrolled lensing. The change in direction of the large arrows indicates scattering of the light.

[0130] Figure 6 is a schematical representation of an embodiment of an optical device wherein the additional layer on the diffractive or refractive element has different optical characteristics provided in different zones. The figure shows a blaze 410 wherein the additional layer 112 (in this case an anchoring layer) has two zones: the first zone 118 extends along slanting lens parts 116 (more specifically, a first slanting lens part 1161and a second slanting lens part 1162), while the second zone 117 extends along upright lens part 115 and (in this specific embodiment also) small neighboring strips 1163, 1164of the slanting lens parts 116.

[0131] In typical arrangements the width (W) of the second zone 117 in cross-section along a transverse direction (x) is in the range of 1 pm to 45 pm, preferably 3 pm to 25 pm, more preferably in the range of 5 pm to 15 pm, for instance about 10 pm. Preferably, the width of the second zone depends on the feature parameters of the lens structure, more preferably on the dimensions of the upright lens part.

[0132] The anchoring layer 112 is configured to show in the first zone 118 a relatively large level of anchoring (as was the case in the example of figure 5, while in the second zone 117 the anchoring layer 112 shows a relatively small level of anchoring (preferably in the order of magnitude of 2 smaller than the anchoring in the first zone 118). The precise ratio between strong and local anchoring to reduce the zone of misorientation depends on inter alia the thickness of the LC cell, the geometry (width and angle of the Fresnel and blaze structure), the properties of the LC material, and / or on the temperature of the optical device.

[0133] Figure 7 is a map similar to figure 5, but now for the embodiment of figure 6. The figure shows the desired orientation field of the selective alignment situation according to an embodiment of the present invention. From the Fresnel structure, one blaze 110 is partly shown. One upright lens part of the blaze 110 and its surroundings are shown in cross section. The orientation of the LC molecules is indicated with T-shaped nails 205. In this desired situation the orientation of the LC material is homogeneous and light rays travel essentially without perturbation. The large arrow 510 passing through the Fresnel structure and the LC layer again represent the direction of light rays traveling through the optical device 1. The large arrow indicates that the light passing through this optical device 1 system is essentially not scattered (as was the case in the situation shown in figure 5).

[0134] The reason for the absence of scattering in this embodiment is that in different zones there is a differentiation in LC alignment of the LC molecules on the surface of the lens structure. By providing a relatively low level of anchoring in the first zone 117 of the Fresnel structure compared to the anchoring level in the second zone 118, the anchoring energy of the upright lens part 115 of the blaze can become insignificant compared to the anchoring energy of the slanting lens part 116 of the blaze. Because of this weak anchoring or the absence of any anchoring in the second zone, the orientation of the LC molecules in this zone is not significantly distorted by the different orientation of the upright lens part 115 (relative to the slanting lens part 116). The anchoring to other surfaces, for instance the surface of the slanting lens part 116 and / or the surface of the anchoring layer 112, is much stronger than the anchoring to the upright lens part 115. Because of the relatively low anchoring energy of the surface of the upright lens part, the orientation of the LC molecules is relatively unaffected by the upright lens part and less scattering or refraction occurs.

[0135] The orientation of the LC molecules has been confirmed by Finite Element (FE) simulation software commonly used for modeling of LC display devices. A schematic representation of the results of tilt and twist maps of LC director are shown in figures 8 and 9 for the main cross-section of the Fresnel LC lens. Figures 8A-8E and 9A-9E show schematic representations of tilt and twist maps of the LC material around an upright lens part 115 of a blaze, wherein figures 8A-8D represent the situation according to the example of figure 5 and figures 9A- 9E represents the situation according to the example of figures 6, 7 (respectively showing the problematic situation of a mono-alignment layer and the desired situation using selective alignment). The vertical axis indicates the height in the z direction of the system, and the horizontal axis indicates the position in the x direction of the system. The different types of hatching indicate the amount of twist or tilt of the molecules. Four maps are shown in both figures 6 and 7, visualizing the situation of the tilt (top) and the twist (bottom) for both the on state (right) and the off state (left) of the lens. The schematic representation shown in figures 8A-8E and 9A-9D of the twist and tilt are discrete approximations of gradual heat maps.

[0136] Figures 8A-8E shows a schematic representation of the tilt and twist map outputs from FE simulation of LC maps for mono-alignment surface in cross-section. In the off state, a tilt of 0 to 90 degrees is visible around the upright lens part of the blaze, and a twist of 0 and 180 degrees. In the on-state, the map shows tilt angles of 0 degrees, and twist angles of 0 to 180 degrees. Note that the off-state twist values seem to change abruptly, but this is a result of the numerical representation. The real change is small since the tilt values are close to 90 degrees. In principle, no twist and / or tilt variation of the LC material is observed for both states.

[0137] An advantage of the above-discussed embodiments comprising first (high anchoring) zones of the lens structure having a higher level of anchoring than the second (low anchoring) zones is they reduce the scatter both in the ON-state and the OFF-state of the electroactive lens. Furthermore, the low anchoring zone can extend beyond the upright lens part 115 itself (into the peripheral areas of the slanting lens parts), without causing substantial additional distortion in the orientation of the LC molecules / crystals. This resulting in a situation wherein scatter can be reduced in both operational states of the electroactive lens, while still a broader process window for practical implementation and manufacturing in such a zone is feasible.

[0138] There are different ways in which the appropriate variation in the level of anchoring caused by the anchoring layer 112 can be achieved, as will become apparent from the next description of a few possible embodiments of the present disclosure.

[0139] Figure 10 shows an embodiment of an optical device 1 with suitable anchoring layer 112 (comprises of anchoring layer 1121and anchoring layer 1122). The anchoring layer comprises:

[0140] - a first anchoring layer 1121arranged over essentially the entire lens structure, the first anchoring layer configured to provide a relatively low level of anchoring or no anchoring at all with neighboring liquid crystals;

[0141] - a second anchoring layer 1122located only in the high anchoring zones and arranged on the first anchoring layer, the second anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals.

[0142] Figure 11 shows a second embodiment of an optical device 1 with suitable anchoring layer 112. In this embodiment the anchoring layer comprises:

[0143] - a first anchoring layer 1121arranged over essentially the entire lens structure, the first anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals when in contact with the first anchoring layer;

[0144] - a second anchoring layer 1122located only in the low anchoring zones and arranged on the first anchoring layer, the second anchoring layer configured to provide a relatively low level of anchoring or no anchoring at all with neighboring liquid crystals.

[0145] Figure 12 shows a third embodiment of an optical device 1 with suitable anchoring layer 112. In this embodiment the anchoring layer comprises:

[0146] - a first anchoring layer 1121located only in the high anchoring zones and arranged on the lens structure, the first anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals when in contact with the first anchoring layer;

[0147] - a second anchoring layer 1122located only in the low anchoring zones and arranged on the lens structure, the second anchoring layer configured to provide a relatively low level of anchoring or no anchoring at all with neighboring liquid crystals.

[0148] Figure 13 shows a fourth embodiment of an optical device 1 with suitable anchoring layer 112. In this embodiment the anchoring layer comprises:

[0149] - a first anchoring layer 1121arranged over essentially the entire lens structure, the first anchoring layer configured to provide a relatively low level of anchoring or no anchoring with neighboring liquid crystals when in contact therewith; - a second anchoring layer 1122located over essentially the entire first anchoring layer, the second anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals when in contact therewith; wherein a part of the second anchoring layer 1122arranged on the first anchoring layer is (or will be) removed, for instance by etching, by ablating or by a similar operation, to locally expose the first anchoring layer, wherein the removed part is the second anchoring layer corresponding to the low anchoring zones.

[0150] Figure 14 shows a fifth embodiment of an optical device 1 with suitable anchoring layer 112. In this embodiment the anchoring layer comprises:

[0151] - a first anchoring layer 1121arranged over essentially the entire lens structure, the first anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals when in contact therewith;

[0152] - a second anchoring layer 1122located over essentially the entire first anchoring layer, the second anchoring layer configured to provide a relatively low level of anchoring or no anchoring at all with neighboring liquid crystals when in contact therewith; wherein a part of the second anchoring layer 1122arranged on the first anchoring layer is removed, for instance by etching, by ablating or by a similar operation, to locally expose the first anchoring layer, wherein the removed part is the second anchoring layer corresponding to the high the high anchoring zones.

[0153] Figure 15 shows a sixth embodiment of an optical device 1 with suitable anchoring layer 112. In this embodiment the anchoring layer 112 is arranged over the lens structure and is made of anchoring material providing a relatively high level of anchoring with neighboring liquid crystals when in contact with the anchoring layer, wherein the outer surface of high anchoring material of the anchoring layer in the low anchoring zone is treated (as schematically indicated by 125) so as to locally reduce the level of anchoring, for instance by exposing the high anchoring material in the low anchoring zone to a suitable dose of radiation like UV light.

[0154] ADDING ABSORBING MATERIAL

[0155] According to another aspect the optical characteristics in the second zones differ from the optical characteristics in the first zones in that the material of the additional layer in the first zone has a relatively small optical absorbance while the material of the additional layer in second the zone has a relatively large optical absorbance.

[0156] Additionally or alternatively, the scattering of light by the upright lens part 115 can be reduced by applying a light-absorbing material on the lens structure in the second zones of the lens structure. In a preferred embodiment, the light-absorbing material is ink material, for instance black or dark ink material. This ink material may be a low anchoring material or may be combined with a low anchoring material that reduces the effect of the LC twist and tilt.

[0157] In certain embodiments, the layer is deposited below a strong alignment layer to avoid hydrodynamical effects occurring in the LC material due to light absorbance combined with interactions in the LC material. Alternatively, light-absorbing materials with a high bandgap are used in other preferred embodiments that will not participate in hydrodynamical effects in the LC material.

[0158] In a preferred embodiment, the width of the black ink material covers at least the upright lens part 115 to a significant extent in order to hide the twisting and turning of the LC material around the sharp and upright surfaces of the lens structure. The required width can be experimentally derived by measuring the affected zone in a cross polarized image. For optical structures, defining the precise width (W) of the second zone is important since the wider the second zone becomes, the more the light observing area of the lens will become visible for the naked eye (which is not desirable from an ophthalmic point of view) and will reduce contrast of the image. Alternatively, in a preferred embodiment, the width could be extended over such an area that it blocks most of the light in a certain, predefined range of directions. For instance, the range of directions leading towards the pupil is known and depends on the typical location of the pupil of the wearer with respect to the a priori known positions of the blazes. The width of the black ink material may be smaller than the width of the low anchoring layer covering the upright lens part and dependent on the feature parameters of the lens structure, preferably on the dimensions of the upright lens part.

[0159] Figure 16 shows a cross-section of an embodiment of an optical device 1 with a suitable additional layer suitable comprising a thin coating 171 of absorbing material applied on the lens structure (only) on at the second zone 117 of the lens structure 102 and an anchoring layer 172 having a relatively high level of anchoring, applied over essentially the entire surface of the lens element 102.. In the preferred embodiment shown in the figure, the absorbing material is deposited on the lens structure and underneath or before the first additional layer. The absorbing material is configured to absorb incoming light. In a preferred embodiment the absorbing material is a black ink material.

[0160] Figure 17A shows another embodiment wherein the additional layer comprises:

[0161] - a coating 171 made of light-absorbing material, deposited on the lens structure on the second zone substantially;

[0162] - a first anchoring layer 172 arranged over essentially the entire lens structure, the first anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals when in contact with the first anchoring layer; - a second anchoring layer 173 located only in the low anchoring zones, on the second zone of the lens structure substantially, and arranged on the first anchoring layer, the second anchoring layer configured to provide a relatively low level of anchoring or no anchoring at all with neighboring liquid crystals. The additional layer in the first zones is free from light-absorbing material.

[0163] Figure 17B shows another embodiment wherein the additional layer comprises:

[0164] - a coating 171 made of light-absorbing material, deposited on the lens structure on the second zone substantially;

[0165] - a first anchoring layer 172 located only in the high anchoring zones and arranged on the lens structure, the first anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals when in contact with the first anchoring layer;

[0166] - a second anchoring layer 173 located only in the low anchoring zones and arranged on the lens structure, the second anchoring layer configured to provide a relatively low level of anchoring or no anchoring at all with neighboring liquid crystals.

[0167] Figures 18A-18D are photographic renderings showing the effect of the application of black ink in the second zones of the lens structure 102. Figures 18A and 18B represent the prior art wherein a uniform, mono-alignment layer has been applied to the lens structure, in an OFF-state and ON-state respectively, while figures 18C and 18D represent an embodiment of the present disclosure wherein black ink material has been applied to respective second zones of the lens element 102, also in an OFF-state and ON-state respectively. The figures show an improved LC alignment in case the optical characteristics of the lens structure in the area of the second zone have been changed by applying a layer of light-absorbing material.

[0168] In further embodiments both types of embodiments, i.e. the use of black ink material and the use of a low anchoring material are combined. For instance, a low anchoring material can be deposited on top of a layer or coating of black ink material. The benefit thereof is that traditional scattering of a Fresnel lens is eliminated and that the black line can be made narrower, as the LC material no longer twists and turns. Hence, the black layer becomes less visible. The black ink also helps to hide deposition artefacts of the second low anchoring material.

[0169] All methods mentioned herein can be used to hide other similar structures in the LC cell, for instance, spacers, which are vertical pillars imprinted together with the Fresnel lens structure in the process of nanoimprinting.

[0170] Further aspects of the present disclosure are defined in the following enumerated examples (EE):

[0171] 1. Optical device for use in eyewear, the optical device comprising an electroactive lens for a tunable transmission of light, the electroactive lens comprising: - a first and a second optically transparent substrate, wherein the first and second optically transparent substrates extend generally parallel to each other and define an axial (z) direction and transverse (x,y) directions;

[0172] - a diffractive or refractive lens structure, such as a Fresnel lens structure, made of transparent lens material and arranged between the first and second optically transparent substrate at the side of the second optically transparent substrate, wherein the lens structure defines a blazed cross section, the shape of its blazed cross section being defined by a plurality of upright lens parts and a plurality of slanting lens parts;

[0173] - a first optically transparent electrode formed on the first optically transparent substrate and a second optically transparent electrode formed on the second optically transparent substrate or on the lens structure;

[0174] - a sealed cavity between the first and second optically transparent substrates, wherein in the sealed cavity, the lens structure and nematic liquid crystalline (LC) material forming at least a liquid crystal layer are arranged;

[0175] - an additional layer arranged on the lens structure, the additional layer comprising a plurality of first zones providing first optical characteristics and a plurality of second zones providing second optical characteristics, different from the first optical characteristics; wherein the first zones are primarily located on slanting lens parts and the second zones are primarily located on upright lens parts.

[0176] 2. Optical device as defined in EE 1 , wherein essentially the entire surface of an upright lens part, and optionally also one or more peripheral portions of one or more slanting lens part adjacent to the upright lens part, form a first zone, whereas the remaining portion or portions of the one or more slanting lens parts form second zone.

[0177] 3. Optical device as defined in EE 1 or EE 2, further comprising wherein the additional layer on the lens structure is an anchoring layer, the anchoring layer having a contact surface in contact with the LC layer, wherein the first zones of the contact surface providing the first optical characteristics are high anchoring zones configured to provide a relatively strong level of anchoring of liquid crystals in the nematic liquid crystalline (LC) material, and wherein the second zones of the contact area providing the second optical characteristics are low anchoring zones configured to provide a relatively low level of anchoring or substantially no anchoring of liquid crystals in the nematic liquid crystalline (LC) material.

[0178] 4. Optical device as defined in EE 3, further comprising:

[0179] - an alignment layer arranged on the first optically transparent electrode, the alignment layer having a further contact surface in contact with the LC layer, the further contact surface configured to provide a relatively strong anchoring of neighboring liquid crystals in the nematic liquid crystalline (LC) material, so as to align the liquid crystals in a preferred direction. 5. Optical device as defined in EE 4, wherein the alignment layer is configured to linearly align neighboring liquid crystals in the preferred direction, preferably in a generally axial direction.

[0180] 6. Optical device as defined in any of EEs 3-5, wherein in the high anchoring zone the contact surface of the anchoring layer in contact with LC material is configured to align neighboring liquid crystals in a second direction.

[0181] 7. Optical device as defined in EE 6, wherein the LC material is configured to align the neighboring liquid crystals essentially in the same direction as the alignment of the alignment layer and / or preferably in a generally axial direction.

[0182] 8. Optical device as defined in any of EEs 3-7, wherein the level of anchoring between the contact surface of the anchoring layer and neighboring liquid crystals in the low anchoring zones is small enough to provide alignment of the neighboring liquid crystals in one or more directions corresponding with the alignment direction of a remotely located alignment layer on the first optically transparent layer and / or with the alignment direction of the strong anchoring zones.

[0183] 9. Optical device as defined in any of EEs 3-8, wherein the anchoring layer comprises:

[0184] - a first anchoring layer arranged over essentially the entire lens structure, the first anchoring layer configured to provide a relatively low level of anchoring or no anchoring at all with neighboring liquid crystals;

[0185] - a second anchoring layer located only in the high anchoring zones and arranged on the first anchoring layer, the second anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals.

[0186] 10. Optical device as defined in any of EEs 3-9, wherein the anchoring layer comprises:

[0187] - a first anchoring layer arranged over essentially the entire lens structure, the first anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals when in contact with the first anchoring layer;

[0188] - a second anchoring layer located only in the low anchoring zones and arranged on the first anchoring layer, the second anchoring layer configured to provide a relatively low level of anchoring or no anchoring at all with neighboring liquid crystals.

[0189] 11. Optical device as defined in any of the EEs 3-10, wherein the anchoring layer comprises:

[0190] - a first anchoring layer located only in the high anchoring zones and arranged on the lens structure, the first anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals when in contact with the first anchoring layer;

[0191] - a second anchoring layer located only in the low anchoring zones and arranged on the lens structure, the second anchoring layer configured to provide a relatively low level of anchoring or no anchoring at all with neighboring liquid crystals. 12. Optical device as defined in any of the EEs 3-11, wherein the anchoring layer comprises:

[0192] - a first anchoring layer arranged over essentially the entire lens structure, the first anchoring layer configured to provide a relatively low level of anchoring or no anchoring with neighboring liquid crystals when in contact therewith;

[0193] - a second anchoring layer located over essentially the entire first anchoring layer, the second anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals when in contact therewith; wherein a part of the second anchoring layer arranged on the first anchoring layer has been removed, for instance by etching, by ablating or by a similar operation, to locally expose the first anchoring layer, wherein the removed part is the second anchoring layer corresponding to the low anchoring zones.

[0194] 13. Optical device as defined in any of the EEs 3-12, wherein the anchoring layer comprises:

[0195] - a first anchoring layer arranged over essentially the entire lens structure, the first anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals when in contact therewith;

[0196] - a second anchoring layer located over essentially the entire first anchoring layer, the second anchoring layer configured to provide a relatively low level of anchoring or no anchoring at all with neighboring liquid crystals when in contact therewith; wherein a part of the second anchoring layer arranged on the first anchoring layer has been removed, for instance by etching, by ablating or by a similar operation, to locally expose the first anchoring layer, wherein the removed part is the second anchoring layer corresponding to the high the high anchoring zones.

[0197] 14. Optical device as defined in any of the EEs 3-13, wherein the anchoring layer is arranged over the lens structure and is made of anchoring material providing a relatively high level of anchoring with neighboring liquid crystals when in contact with the anchoring layer, wherein the outer surface of high anchoring material of the anchoring layer in the low anchoring zone is treated so as to locally reduce the level of anchoring, for instance by UV exposure of the high anchoring material in the low anchoring zone.

[0198] 15. Optical device according to any of the EEs 3-14, wherein the anchoring energy of the surface in the high anchoring zones is substantially higher than the anchoring energy of the surface of the low anchoring zones.

[0199] 16. Optical device as defined in EE 15, wherein the ratio between the high anchoring energy of the surface in the high anchoring zones with respect to the anchoring energy of the surface in the low anchoring zones lies in the range of 102 to 106. 17. Optical device as defined in any of the preceding EEs, wherein the anchoring energy in the first zones is 2 orders of magnitude lower compared to the anchoring energy in the second zones.

[0200] 18. Optical device as defined in any of the preceding EEs, wherein at least one of the second zones only extends over the surface of an upright lens part and wherein at least one of the first zones only extends over the surface of a slanting lens part.

[0201] 19. Optical device as defined in any of the EEs 1-17, wherein at least one of the first zones only extends over the surface of an upright lens part and over one or more peripheral portions of one or more slanting lens parts.

[0202] 20. Optical device as defined in EE 18 or 19, wherein the total width (W) of a second zone in cross-section along a transverse direction (x) is in the range of 1 pm to 45 pm, preferably 3 pm to 25 pm, more preferably in the range of 5 pm to 15 pm, for instance about 10 pm, depending on the feature parameters of the lens structure.

[0203] 21. Optical device according to any of the EEs 3-20, wherein the optical characteristics in the second zones differ from the optical characteristics in the first zones in that the material of the additional layer in the first zone has a relatively small optical absorbance while the material of the additional layer in the second zone has a relatively large optical absorbance.

[0204] 22. Optical device as defined in EE 21, wherein the material of the additional layer in the second zone is configured to completely or almost completely absorb light received in the associated zone of the electroactive lens.

[0205] 23. Optical device according to EE 21 or 22, wherein in the second zones the additional layer comprises essentially light-absorbing material and / or in the first zones the additional layer comprises essentially light-transmitting material.

[0206] 24. Optical device as defined in any of EEs 21-23, wherein the light-absorbing material comprises ink material, for instance black ink material.

[0207] 25. Optical device as defined in any of EEs 21-24, wherein the light-absorbing material is a material providing relatively low or no anchoring with the liquid crystals when in contact with the LC material inside the cavity.

[0208] 26. Optical device as defined in any of EEs 21-25, wherein the light-absorbing material is a material with a high bandgap.

[0209] 27. Optical device as defined in any of EEs 21-26, wherein the additional layer in the second zones comprises:

[0210] - a first layer made of light-absorbing material; - a second layer on top of the first layer, wherein the second layer is an anchoring layer with sufficient anchoring to have an alignment impact, preferably an anchoring layer configured to provide a relatively high anchoring; while the additional layer in the first zones is free from light-absorbing material.

[0211] 28. Optical device as defined in any of EEs 3-27, wherein the optical characteristics in the second zones differ from the optical characteristics in the first zones in that the material of the additional layer in the first zone has a relatively high transparency while the material of the additional layer in the second zone has a relatively low transparency or almost zero transparency.

[0212] 29. Optical device as defined in EE 18 or EE 19, wherein the total width of a second zone in cross-section along a transverse direction (x) is in the range of 3 pm to 25 pm, preferably in the range of 5 pm to 15 pm, for instance 10 pm.

[0213] 30. Optical device as defined in any of the preceding EEs, wherein an additional layer is arranged on both the lens structure, more specifically on the slanting lens parts and / or on the upright lens parts, and on other structures located inside the sealed cavity, for instance on one or more spacers arranged between the lens structure and the first optically transparent substrate or the first optically transparent electrode formed on the first optically transparent substrate.

[0214] 31. Optical device as defined in any of the preceding EEs, wherein the optical characteristics of the material of the additional layer involve at least one of an interaction parameter and an absorption parameter, wherein an interaction parameter defines the interaction between the material of the additional layer and liquid crystals of the LC material in the cavity; and wherein an absorption parameter defines the absorption behavior of light in the additional layer.

[0215] 32. Optical device according to EE 31, wherein the interaction parameter of a material includes the anchoring energy of the material and / or wherein the absorption parameter of a material includes the level of light absorption of the material.

[0216] 33. Optical device according to any of the previous EEs, wherein the additional layer comprises a first additional layer having first surface features and a second additional layer having second surface features different from the first surface features.

[0217] 34. Optical device according to any of the preceding EEs, wherein the electroactive lens is configured to vary the optical power of the electroactive lens by altering the refractive index of the LC layer in the transverse direction upon application of a voltage to the first and second optically transparent electrodes.

[0218] 35. Optical device as defined in any of the preceding EEs, configured to cause the electroactive lens to switch from an the off-state wherein the at least one electroactive lens shows essentially no lens action and an on-state wherein the at least one electroactive lens shows lens action upon application of a voltage from a voltage source connected to the first and second optically transparent electrodes.

[0219] 36. Optical device as defined in any of the preceding EEs, wherein the liquid crystal material of the at least one electroactive lens has a birefringence An that is in the range of 0.05 to 0.5, preferably in the range of 0.15 to 0.40.

[0220] 37. Use of the optical device as defined in any of the preceding EEs.

[0221] 38. Method of manufacturing an optical device as defined in any of EEs 1-35, the method comprising:

[0222] - providing an optical device comprising

[0223] - first and a second optically transparent substrate, wherein the first and second optically transparent substrates extend generally parallel to each other and define an axial (z) direction and transverse (x,y) directions;

[0224] - a diffractive or refractive lens structure, such as a Fresnel lens structure, made of transparent lens material and arranged between the first and second optically transparent substrate at the side of the second optically transparent substrate, wherein the lens structure defines a blazed cross section, the shape of its blazed cross section being defined by a plurality of upright lens parts and a plurality of slanting lens parts;

[0225] - a first optically transparent electrode formed on the first optically transparent substrate and a second optically transparent electrode formed on the second optically transparent substrate or on the lens structure;

[0226] - a sealed cavity between the first and second optically transparent substrates, wherein in the sealed cavity, the lens structure and nematic liquid crystalline (LC) material forming at least a liquid crystal layer are arranged;

[0227] - arranging an additional layer on the lens structure, the additional layer comprising a plurality of first zones primarily located on slanting lens parts of the lens structure so as to provide first optical characteristics and a plurality of second zones primarily located on upright lens parts of the lens structure so as to provide second optical characteristics, different from the first optical characteristics.

[0228] It is to be understood that this invention is not limited to particular aspects described, and, as such, may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

Claims

CLAIMS1. Optical device for use in eyewear, the optical device comprising an electroactive lens for a tunable transmission of light, the electroactive lens comprising:- a first and a second optically transparent substrate, wherein the first and second optically transparent substrates extend generally parallel to each other and define an axial (z) direction and transverse (x,y) directions;- a diffractive or refractive lens structure, such as a Fresnel lens structure, made of transparent lens material and arranged between the first and second optically transparent substrate at the side of the second optically transparent substrate, wherein the lens structure defines a blazed cross section, the shape of its blazed cross section being defined by a plurality of upright lens parts and a plurality of slanting lens parts;- a first optically transparent electrode formed on the first optically transparent substrate and a second optically transparent electrode formed on the second optically transparent substrate or on the lens structure;- a sealed cavity between the first and second optically transparent substrates, wherein in the sealed cavity, the lens structure and nematic liquid crystalline (LC) material forming at least a liquid crystal layer are arranged;- an additional layer arranged on the lens structure, the additional layer comprising a plurality of first zones providing first optical characteristics and a plurality of second zones providing second optical characteristics, different from the first optical characteristics; wherein the first zones are primarily located on slanting lens parts and the second zones are primarily located on upright lens parts, wherein the additional layer on the lens structure is an anchoring layer, the anchoring layer having a contact surface in contact with the LC layer, wherein the first zones of the contact surface providing the first optical characteristics are high anchoring zones configured to provide a relatively strong level of anchoring of liquid crystals in the nematic liquid crystalline (LC) material, and wherein the second zones of the contact area providing the second optical characteristics are low anchoring zones configured to provide a relatively low level of anchoring or substantially no anchoring of liquid crystals in the nematic liquid crystalline (LC) material.

2. Optical device as claimed in claim 1 , wherein essentially the entire surface of an upright lens part, and optionally also one or more peripheral portions of one or more slanting lens part adjacent to the upright lens part, form a first zone, whereas the remaining portion or portions of the one or more slanting lens parts form second zone.

3. Optical device as claimed in claim 1, further comprising:- an alignment layer arranged on the first optically transparent electrode, the alignment layer having a further contact surface in contact with the LC layer, the further contact surface configured to provide a relatively strong anchoring of neighboring liquid crystals in the nematic liquid crystalline (LC) material, so as to align the liquid crystals in a preferred direction.

4. Optical device as claimed in claim 3, wherein the alignment layer is configured to linearly align neighboring liquid crystals in the preferred direction, preferably in a generally axial direction.

5. Optical device as claimed in any of the preceding claims, wherein in the high anchoring zone the contact surface of the anchoring layer in contact with LC material is configured to align neighboring liquid crystals in a second direction.

6. Optical device as claimed in claim 5, wherein the LC material is configured to align the neighboring liquid crystals essentially in the same direction as the alignment of the alignment layer and / or preferably in a generally axial direction.

7. Optical device as claimed in any of the preceding claims, wherein the level of anchoring between the contact surface of the anchoring layer and neighboring liquid crystals in the low anchoring zones is small enough to provide alignment of the neighboring liquid crystals in one or more directions corresponding with the alignment direction of a remotely located alignment layer on the first optically transparent layer and / or with the alignment direction of the strong anchoring zones.

8. Optical device as claimed in any of the preceding claims, wherein the anchoring layer comprises:- a first anchoring layer arranged over essentially the entire lens structure, the first anchoring layer configured to provide a relatively low level of anchoring or no anchoring at all with neighboring liquid crystals;- a second anchoring layer located only in the high anchoring zones and arranged on the first anchoring layer, the second anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals.

9. Optical device as claimed in any of the preceding claims, wherein the anchoring layer comprises:- a first anchoring layer arranged over essentially the entire lens structure, the first anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals when in contact with the first anchoring layer;- a second anchoring layer located only in the low anchoring zones and arranged on the first anchoring layer, the second anchoring layer configured to provide a relatively low level of anchoring or no anchoring at all with neighboring liquid crystals.

10. Optical device as claimed in any of the preceding claims, wherein the anchoring layer comprises:- a first anchoring layer located only in the high anchoring zones and arranged on the lens structure, the first anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals when in contact with the first anchoring layer;- a second anchoring layer located only in the low anchoring zones and arranged on the lens structure, the second anchoring layer configured to provide a relatively low level of anchoring or no anchoring at all with neighboring liquid crystals.

11. Optical device as claimed in any of the preceding claims, wherein the anchoring layer comprises:- a first anchoring layer arranged over essentially the entire lens structure, the first anchoring layer configured to provide a relatively low level of anchoring or no anchoring with neighboring liquid crystals when in contact therewith;- a second anchoring layer located over essentially the entire first anchoring layer, the second anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals when in contact therewith; wherein a part of the second anchoring layer arranged on the first anchoring layer has been removed, for instance by etching, by ablating or by a similar operation, to locally expose the first anchoring layer, wherein the removed part is the second anchoring layer corresponding to the low anchoring zones.

12. Optical device as claimed in any of the claims preceding claims, wherein the anchoring layer comprises:- a first anchoring layer arranged over essentially the entire lens structure, the first anchoring layer configured to provide a relatively high level of anchoring with neighboring liquid crystals when in contact therewith;- a second anchoring layer located over essentially the entire first anchoring layer, the second anchoring layer configured to provide a relatively low level of anchoring or no anchoring at all with neighboring liquid crystals when in contact therewith; wherein a part of the second anchoring layer arranged on the first anchoring layer has been removed, for instance by etching, by ablating or by a similar operation, to locally expose the first anchoring layer, wherein the removed part is the second anchoring layer corresponding to the high the high anchoring zones.

13. Optical device as claimed in any of the preceding claims, wherein the anchoring layer is arranged over the lens structure and is made of anchoring material providing a relatively high level of anchoring with neighboring liquid crystals when in contact with the anchoring layer, wherein the outer surface of high anchoring material of the anchoring layer in the low anchoring zone is treated so as to locally reduce the level of anchoring, for instance by UV exposure of the high anchoring material in the low anchoring zone.

14. Optical device according to any of the preceding claims, wherein the anchoring energy of the surface in the high anchoring zones is substantially higher than the anchoring energy of the surface of the low anchoring zones.

15. Optical device as claimed in claim 14, wherein the ratio between the high anchoring energy of the surface in the high anchoring zones with respect to the anchoring energy of the surface in the low anchoring zones lies in the range of 102to 106.

16. Optical device as claimed in any of the preceding claims, wherein the anchoring energy in the first zones is 2 orders of magnitude lower compared to the anchoring energy in the second zones.

17. Optical device as claimed in any of the preceding claims, wherein at least one of the second zones only extends over the surface of an upright lens part and wherein at least one of the first zones only extends over the surface of a slanting lens part.

18. Optical device as claimed in any of the claims 1-16, wherein at least one of the first zones only extends over the surface of an upright lens part and over one or more peripheral portions of one or more slanting lens parts.

19. Optical device as claimed in claim 17 or 18, wherein the total width (W) of a second zone in cross-section along a transverse direction (x) is in the range of 1 pm to 45 pm, preferably 3 pm to 25 pm, more preferably in the range of 5 pm to 15 pm, for instance about 10 pm, depending on the feature parameters of the lens structure.

20. Optical device according to any of the preceding claims, wherein the optical characteristics in the second zones differ from the optical characteristics in the first zones in that the material of the additional layer in the first zone has a relatively small optical absorbance while the material of the additional layer in the second zone has a relatively large optical absorbance.

21. Optical device as claimed in claim 20, wherein the material of the additional layer in the second zone is configured to completely or almost completely absorb light received in the associated zone of the electroactive lens.

22. Optical device according to claim 20 or 21, wherein in the second zones the additional layer comprises essentially light-absorbing material and / or in the first zones the additional layer comprises essentially light-transmitting material.

23. Optical device as claimed in any of claims 20-22, wherein the light-absorbing material comprises ink material, for instance black ink material.

24. Optical device as claimed in any of claims 20-23, wherein the light-absorbing material is a material providing relatively low or no anchoring with the liquid crystals when in contact with the LC material inside the cavity.

25. Optical device as claimed in any of claims 20-24, wherein the light-absorbing material is a material with a high bandgap.

26. Optical device as claimed in any of claims 20-25, wherein the additional layer in the second zones comprises:- a first layer made of light-absorbing material;- a second layer on top of the first layer, wherein the second layer is an anchoring layer with sufficient anchoring to have an alignment impact, preferably an anchoring layer configured to provide a relatively high anchoring; while the additional layer in the first zones is free from light-absorbing material.

27. Optical device as claimed in any of the preceding claims, wherein the optical characteristics in the second zones differ from the optical characteristics in the first zones in that the material of the additional layer in the first zone has a relatively high transparency while the material of the additional layer in the second zone has a relatively low transparency or almost zero transparency.

28. Optical device as claimed in claim 17 or 18, wherein the total width of a second zone in cross-section along a transverse direction (x) is in the range of 3 pm to 25 pm, preferably in the range of 5 pm to 15 pm, for instance 10 pm.

29. Optical device as claimed in any of the preceding claims, wherein an additional layer is arranged on both the lens structure, more specifically on the slanting lens parts and / or on the upright lens parts, and on other structures located inside the sealed cavity, for instance on one or more spacers arranged between the lens structure and the first optically transparent substrate or the first optically transparent electrode formed on the first optically transparent substrate.

30. Optical device as claimed in any of the preceding claims, wherein the optical characteristics of the material of the additional layer involve at least one of an interaction parameter and an absorption parameter, wherein an interaction parameter defines the interaction between the material of the additional layer and liquid crystals of the LC material in the cavity; and wherein an absorption parameter defines the absorption behavior of light in the additional layer.

31. Optical device according to claim 30, wherein the interaction parameter of a material includes the anchoring energy of the material and / or wherein the absorption parameter of a material includes the level of light absorption of the material.

32. Optical device according to any of the previous claims, wherein the additional layer comprises a first additional layer having first surface features and a second additional layer having second surface features different from the first surface features.

33. Optical device according to any of the preceding claims, wherein the electroactive lens is configured to vary the optical power of the electroactive lens by altering the refractive index of the LC layer in the transverse direction upon application of a voltage to the first and second optically transparent electrodes.

34. Optical device as claimed in any of the preceding claims, configured to cause the electroactive lens to switch from an the off-state wherein the at least one electroactive lens shows essentially no lens action and an on-state wherein the at least one electroactive lens shows lens action upon application of a voltage from a voltage source connected to the first and second optically transparent electrodes.

35. Optical device as claimed in any of the preceding claims, wherein the liquid crystal material of the at least one electroactive lens has a birefringence An that is in the range of 0.05 to 0.5, preferably in the range of 0.15 to 0.40.

36. Use of the optical device as claimed in any of the preceding claims.

37. Method of manufacturing an optical device as claimed in any of claims 1-25, the method comprising:- providing an optical device comprising- first and a second optically transparent substrate, wherein the first and second optically transparent substrates extend generally parallel to each other and define an axial (z) direction and transverse (x,y) directions;- a diffractive or refractive lens structure, such as a Fresnel lens structure, made of transparent lens material and arranged between the first and second optically transparent substrate at the side of the second optically transparent substrate, wherein the lens structure defines a blazed cross section, the shape of its blazed cross section being defined by a plurality of upright lens parts and a plurality of slanting lens parts;- a first optically transparent electrode formed on the first optically transparent substrate and a second optically transparent electrode formed on the second optically transparent substrate or on the lens structure;- a sealed cavity between the first and second optically transparent substrates, wherein in the sealed cavity, the lens structure and nematic liquid crystalline (LC) material forming at least a liquid crystal layer are arranged;- arranging an additional layer on the lens structure, the additional layer comprising a plurality of first zones primarily located on slanting lens parts of the lens structure so as to provide first optical characteristics and a plurality of second zones primarily located on upright lens parts of the lens structure so as to provide second optical characteristics, different from the first optical characteristics.

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