The present invention relates generally to a refractive-diffractive switchable lens that creates an image at a position produced by the lens in diffractive state that is different from the image position produced by the lens in refractive state by changing the refractive surface of the lens into diffraction surface, and more particularly to a refractive-diffractive switchable ophthalmic lens that changes image positions by switching between refractive and diffraction surface shapes of far and near foci correspondently for presbyopia correction.
BACKGROUND OF THE INVENTION
The refractive-diffractive switchable lens or diffractive switchable lens of the present invention can be applied outside or within ophthalmic application. In latter case the lens can be called diffractive switchable ophthalmic lens. Ophthalmic lens in the present invention is defined as a diffractive switchable lens suitable for placement outside the eye such as spectacle lens or contact lenses or inside the eye such as aphakic and phakic intraocular lenses or implants placed in posterior or anterior eye chamber and also included are artificial corneas and corneal implants or inlay. For detailed explanation of the lens of the present invention, the ophthalmic application for presbyopia correction is used as a preferred embodiment.
A fixed single power lens provides good quality vision but only within a small range of viewing distances that is usually significantly narrower than the range required from near to far vision. The resulted vision deficiency is called presbyopia. There is a significant effort to develop a lens for presbyopia correction in a form of multifocal refractive or diffractive type lenses that provide multiple foci and also in a form of accommodating lenses that may change their optical surface shapes or positions inside the eye for ocular power increase for near vision. Diffractive switchable optical element according to the present invention is a lens that consequently changes the image positions between distance and near foci or fields by directing light to refractive focus and a different focus position corresponding to a diffraction order. Usually but not necessary the power corresponding to diffraction order is higher the refractive power and this difference is called Add power as a traditional reference to a power difference between near and far foci in presbyopia correction. A refractive-diffractive switchable ophthalmic lens implanted inside the eye is also called diffractive accommodating lens as switching between far and near foci occurs under the action of ciliary muscle. It is important to note that diffractive switchable lens according to the present invention has application outside ophthalmic one in so called engineering optic (microscopes, telescopes, photo-objectives, etc.).
Portney' US Application Serial No: 13/247,840
, "Switchable Diffractive Accommodating Lens" explained accommodation, ciliary muscle action during accommodation and prior art involving in Presbyopia correction. The same application also disclosed Sensor Cell that functioned for (a) sensing a need to focus for far or near and/or (b) actuation of an implantable accommodating lens (phakic, aphakic, corneal inlay) to focus at far or near by a direct interaction with ciliary muscle at the location of the ciliary spur. Equivalent Sensor Cell can also be used with a diffractive accommodating lens of the present invention.
The advantage of the diffractive switchable optic in switching between far and near foci over a refractive optic was described in Portney' US Application Serial No. 13/247,840
, "Switchable Diffractive Accommodating Lens" and also by a large group of researches: Li G, Mathine DL, Valley P, et al. "Switchable electro-optic diffractive lens with high efficiency for ophthalmic application", Proceedings of the National Academy of Science of the USA, 2006; 103: 6100-6104
, in the application to the spectacle lens. The operation of the described by Li G, et al spectacle lens was based on electrical control of the refractive index of thin layer of pneumatic liquid crystal by creating volume diffractive element through refractive index modulation. Though the approach is feasible, it is complicated and expensive to execute and it also requires electric field for its operation which is a challenge for ocular implant or contact lens application. Haddock at el. in US Patent Application 20090256977
introduced further improvement to the above volume diffractive lens manufacturability. The spectacle lenses according to the above design were released by PixelOptics under EmPower name. Similar technology is under development for accommodating IOL by ELENZA, Inc.
A diffractive switchable lens according to the present invention incorporates a switchable cell and optical surfaces. A switchable cell of the present invention is an opto-mechanical device that utilizes mechanical optical switching between far and near foci by changing the optical surface shape between refractive continuous form for one focal position and diffractive form of a periodic structure for a different focal position. Refractive surface focusing ability depends on surface curvatures and diffraction surface focusing ability depends on a diffraction surface periodic structure. An optical surface can be part of a switchable cell or part of a separate optical element that together form diffractive switchable lens. Switchable cell is the center of the present invention for operation of a diffractive switchable lens.
Diffractive optic has been described by a huge volume of papers. For instance, D Faklis and GM Morris, "Spectral properties of multiorder diffractive lenses", Apply Optics 1995; 34(14): 2462-2468
, described diffractive optic of blazed shape, so called surface relief shape of different diffraction orders. This type of diffractive optic is called Kinoform that allows 100% of light to be directed to a single focal position formed by a single diffraction order or multiorder per Faklis and Morris explanation. Diffraction zones forming diffraction surface periodic structure can be of different profiles, rectangular, sine-wave for instance, as well as blazed surface of different profiles (parabolic, linear, sine) of a single order or multiorder composition and any one or a combination of them can be applied to a diffractive switchable lens of the present invention for so called diffraction guiding surface introduced below.
The advantage in using diffractive element is that the focal length of selected diffraction order is defined only by the periodic structure of the diffraction surface which can be built into the diffraction surface design. By the law of formation of a diffraction order, light can only be channeled along discrete diffraction orders of the diffractive lens where light constructive interference can take place thus providing predetermined separation between refractive and diffractive foci or Add power in ophthalmic application. Thus, a difference between refractive and diffractive focal positions of the diffractive accommodating lens of the present invention is predetermined by the switchable cell design itself and not by an external factor as in all refractive accommodating lens designs which makes them inherently unpredictable.
In a simple paraxial form the circular diffraction zones, also called grooves, echelettes or surface-relief profile, can be expressed by the formula:
where grooves radii (rj
) create spherical wavefront of focal length (Fm
) for a given diffraction order (m) and design wavelength (λdesign
In case of surface relief profile and in paraxial approximation, the blaze material thickness (Hm
) to produce 100% efficiency at the focus of m-order diffraction is
where n = refractive index of the lens material and n' = refractive index of the medium adjacent to the diffraction surface.
In case of small spherical aberration, the periodic structure, i.e. diffraction groove periods of the diffractive optic is quite accurately defined by the Eq. 1 for a given focal distance. In case of a significant spherical aberration of a diffractive lens introduced to extend a range of foci around a focus of a selected diffraction order, the calculation of the groove shapes can be conducted numerically equivalent to the method described by Portney in the US Patent Appl. No: 20100066973
for multifocal diffractive lens.
 Portney' US Application Serial No. 13/247,840
, "Switchable Diffractive Accommodating Lens" disclosed diffractive optic with specific adjustment of its periods to create positive spherical aberration which is the most effective for depth of focus increase at a diffraction order. The same form of the diffraction surface periodicity can also be applied to the guiding surface of the diffractive switchable lens of the present invention to expand a range of foci at its diffractive focus.
SUMMARY OF THE INVENTION
A switchable cell in accordance with the present invention consists of at least three elements: (1) optical substrate with diffraction surface on it, (2) elastic film in close proximity or contact with the diffraction surface of the optical substrate, and (3) chamber between elastic film and diffraction surface of the optical substrate filled with optical fluid of refractive index which is equal to or up to about 0.03 unit different from the refractive index of the optical substrate. The chamber is called "transparent chamber" and the optical fluid is called "matching fluid" because desirably, its refractive index matches the refractive index of the optical substrate at least at one of wavelengths. The matching is important in the visual spectrum and desirable in green color part of the spectrum in ophthalmic application. This three elements combination forms "3-element switchable cell". Film that is in contact with the optical substrate diffraction surface is preferable option because it provides more stable switchable cell structure and minimizes the amount of matching fluid transfer for the switchable cell operation. A proximate film position is also possible, say less than about 1 mm between the film and diffraction surface of the optical substrate.
A switchable cell may also consists of five elements: (1) elastic film, (2) optical substrate with diffraction surface, (3) transparent chamber between the elastic film and optical substrate diffraction surface filled with matching fluid, (4) optical membrane situated next to the elastic film at the opposite side from the optical substrate and (5) chamber between the elastic film and optical membrane filled with optical fluid of the refractive index that is differ from the refractive index of the optical substrate at the wavelengths of the switchable cell operation, this is so called "non-matching fluid". The corresponding chamber is called "active chamber". A switchable cell consisting of five elements listed above is called "5-element switchable cell". Thus, 5-element switchable cell comprises of 3-element switchable cell plus optical membrane forming active chamber with elastic film filled with non-matching fluid. The medium exterior to the film at the opposite side from the transparent chamber can be aqueous humour, air, stroma, tear layer, etc., depending on the application of the diffractive switchable lens of the present invention. The exterior medium is either ambient medium in case of 3-element switchable cell or a medium of the active chamber in case of 5-element switchable cell.
The optical substrate or optical membrane each may include flat or curved optical surface either at front or back surface or both surfaces. In a general form, diffractive switchable lens of the present invention consists of front and back optical surfaces and switchable cell situated between them. The diffraction surface of the optical substrate that faces the elastic film is called "guiding surface". Surface relief or blazed shape of the guiding surface is preferable embodiment because it provides highest diffractive efficiency, i.e. largest percent of light concentration in a single diffractive focus. The corresponding surface type will be used in explaining a diffraction switchable optical element of the present invention.
The operation of a switchable cell relies on the ability of matching fluid to optically mask the guiding surface resulting in optical interaction with light by the matching fluid surface shaped by the film instead of an interaction with the guiding surface. Depending how the film shapes the matching fluid, different optical characteristics can be created: (a) refractive surface shape to create refractive state with its refractive focus or, (b) diffraction surface shape with periodic structure to create diffractive state with its diffractive focus. The film itself does not contribute to a focusing ability of switchable cell because of being largely of uniform thickness and, as result, its front and back surfaces are parallel to each other, i.e. they manifest equivalement curvatures / power profiles within the thickness contribution. The external surface of the film facing the external medium is called "formable surface". Because a shape of the matching fluid formed by the film and the formable surface shape are equivalement, the formable surface is used in describing refractive or diffractive state of a switchable cell instead of referencing to a matching fluid surface shaped by the film. Thus, a focusing ability of a switchable cell is defined by the formable surface shape and a difference in refractive indices between non-matching fluid and the optical substrate (substrate).
Refractive formable surface is formed if no pressure difference exists between active and transparent chambers. This is so called relaxed state of a switchable cell as no external actuation is required in the relaxed state. In this condition the formable surface takes largely a shape of a minimum strain or, more specifically, the based surface of the diffraction guiding surface if the film is in contact with the guiding surface. Diffractive formable surface is formed if a pressure in transparent chamber is below a pressure in active chamber or medium exterior to the film and the film largely takes the shape of the guiding surface due to its elasticity. It takes place at some pressure difference called threshold level. This is so called active state of the switchable cell as a pressure difference requires an external actuation. In case of a diffraction guiding surface being a surface relief, i.e. a Kinoform, the formable surface also takes the same Kinoform surface shape to focus light at the focus position defined by the diffraction guiding surface. This is the reason to apply term "guiding" to the diffraction surface of the optical substrate as it "guides" the film shape in the active state.
The film itself is either free-standing or bonded to the guiding surface at the ridges of the diffractive grooves and its shape and, therefore, the shape of the formable surface is defined by the base surface of the diffractive guiding surface in the relaxed state. Formable refractive surface in relaxed state can be flat, curved and aspherized, i.e. of any possible shape of a base surface of the diffraction guiding surface.
There is advantage to allocate relaxed state of a switchable cell in ophthalmic application to provide far focus because of a safety consideration as far focus is desirable fall back state if an actuation of the active state fails. Therefore, the active state is to provide diffractive focus for near focus. In addition, an image formed at the diffractive focus is commonly acceptable for near vision as demonstrated by extensive clinical experience with diffractive multifocal IOLs. In general, it can be in reverse, i.e. far focus or longer focal length is formed by the diffractive focus in active state and near focus or shorter focal length by the refractive focus in relaxed state. In general, switchable states may include at least two active states in addition to refractive state or instead of refractive state with each of these active states providing its own focus position and the switching takes place between two diffractive foci.
The central advantage of a switchable cell according to the present invention is that the refractive focus of the relaxed state coincides with zero order diffractive focus formed by the formable surface Kinoform in the active state producing an image at a non-zero diffractive focus. A separation between the corresponding non-zero diffractive focus and zero order diffractive focus is only controlled by the built-in periodicity of the guiding surface which is responsible for the periodicity of the formable surface in the active state. Therefore, a separation between refractive focus in the relaxed state and diffractive focus in the active state is also controlled only the periodicity of the guiding surface.
The present invention references to a "near focus" provided by an active state of a switchable cell in an ophthalmic application but it can be an intermediate focus or even multi-foci combination if guiding surface is of a multi-zonal structure with each zone providing its own diffractive focus. In general, a reference to a "near focus" used in the present invention is a focus that differs from far focus, i.e. "near focus" may technically reference to near or intermediate focus in terms its correspondence to near or intermediate vision.
A pressure difference between active and transparent chambers of a switchable cell of the present invention is created either by increasing pressure externally to the formable surface and/or reducing pressure in the transparent chamber by an actuation mechanism. Two actuation principles can be used for switching between relaxed and active states:
- (1) "Close actuation system" where each Active and Transparent chamber is connected to the Actuator to transfer the corresponding fluid to the active chamber and from transparent chamber for the active state. The corresponding system is used by the Sensor Cell interaction with a diffractive accommodating ocular implants of the present invention.
- (2) "Open actuation system" where only transparent chamber is connected to the Actuator to transfer matching fluid from the transparent chamber for switching to the active state. The corresponding system can be used in diffractive accommodating aphakic IOL with internal actuation or diffractive switchable contact lens.
In either system, the matching fluid is pulled out from the transparent chamber through a mean of connecting the transparent chamber with the exterior of the switchable cell. This can be in a form of a channel in the substrate of the switchable cell which connects the transparent chamber within all diffractive grooves of the guiding surface to the exterior of the switchable cell.
The performance of a diffractive switchable lens in ophthalmic application (ocular implant, corneal inlay, contact lens and spectacles that are designed for presbyopia correction) relies on two functions:
- (1) Sensing a need by the wearer of the diffractive switchable ophthalmic lens to focus at far or near, and
- (2) Actuation a diffractive switchable ophthalmic lens for the required focus.
Actuation in case of a spectacle lens does not present an issue as it can be accomplished either manually or electrically by using, for instance, a solenoid but sensing for far or near need for automatic actuation the switching between far and near foci is a great challenge not only for the diffractive switchable spectacles of the present invention but for all switchable types of spectacles, electro-optical type as EmPower, for instance, and it is also a subject of the present invention.
Sensing and actuation of diffractive accommodating ocular implant can be accomplished with Sensor cell where external chamber of the Sensor cell is connected to the transparent chamber of the diffractive accommodating implant of the present invention or both external chamber is connected to transparent chamber and internal chamber of the Sensor cell to the active chamber of the switchable cell of the diffractive accommodating implant of the present invention. There is a great challenge of sensing and /or actuation of a diffractive accommodating lens without a help of Sensor cell by using internal sensing and actuation. Sensing for far or near need by a wearer of any switchable IOL or switchable contact lens is a great challenge for presbyopia correction, for instance, by electro-optical ELANZA implant. The system structurally equivalent to one used for sensing the need for far or near focus and actuation of the switching to the desired focus utilized by the diffractive switchable lens of the present invention can also be used for sensing function and triggering to the corresponding far or near focus in any switchable type of ocular implant or contact lens and it is also a subject of the present invention.
Aspects of the invention include the following embodiments:
1. A switchable cell comprising an optical substrate with diffraction guiding surface; an elastic film in close proximity or contact with the diffraction guiding surface, optical fluid filled the transparent chamber between the elastic film and diffraction surface of the optical substrate with its refractive index matching or close to refractive index of the optical substrate; and a mean through which the optical fluid is transposed in or out of the transparent chamber.
2. A switchable cell according to embodiment 1 with diffraction guiding surface being blazed diffraction surface.
3. A switchable cell according to embodiment 2 with the film being bonded at the peaks of the diffraction guiding surface.
4. A switchable cell according to embodiment 1 with formable surface of the film at the film exterior from the diffraction guiding surface of the optical substrate; and the formable surface changes from refractive surface when pressures at both sides of the film are the same to diffraction surface when pressure in the space between the film and substrate is below the pressure over the formable surface.
5. A switchable cell according to embodiment 1 is part of a diffractive switchable ophthalmic lens for presbyopia correction that is either ocular implant, corneal inlay, contact lens or spectacle lens.
6. An accommodating implant comprising an optical anterior member; an optical posterior member separated from the anterior member along the optical axis; an angulated haptic for fixation of the accommodating implant inside the eye and is part of either anterior or posterior member and is in contact with a member which the haptic is not a part of; the separation between anterior and posterior members changes with haptic angulation change; an actuation member bonded to the anterior and posterior members; and an actuation member may include electric or magnetic switch or optical fluid.
7. An accommodating implant according to embodiment 6 with the actuation member which includes actuation chamber connected to the transparent chamber of the switchable cell according to embodiment 1 for optical fluid transfer between the actuation chamber and transparent chamber.
8. A diffractive switchable contact lens comprising a flexible actuation ledge that bends with pressure elevation at the bottom part of the actuation ledge; an actuation level being a part of the actuation ledge and which turns with the actuation ledge bending; an actuation chamber bonded with the actuation level via its membrane and which expands with the actuation level turn; an actuation chamber may include electric or magnetic switch or optical fluid.
9. A diffractive switchable contact lens according to embodiment 8 with the actuation chamber connected to the transparent chamber of the switchable cell according to embodiment 1 for optical fluid transfer between the actuation chamber and transparent chamber.
10 Switchable spectacles comprising a switchable spectacle lens; an IR emitter radiating front surface of the eye viewing though the switchable spectacle lens and located either to the right or left side from the eye viewing though the switchable spectacle lens; an IR sensor located at the opposite side of the switchable spectacle lens in approximately horizontal plane containing IR emitter and IR sensor that is crossed by upper eyelid movement between eye open and close conditions; and a change in radiance received by IR sensor triggers a switching the switchable spectacle lens between far and near foci.
11. Switchable spectacles lens according to embodiment 10 with switchable cell according to embodiment 1 located at the lower part of the switchable spectacle lens.
12. An ophthalmic lens incorporating diffractive surface, said ophthalmic lens comprising diffractive grooves of periodicity defined by groove radii from an optical center; and two consecutive diffractive groove radii closest to the optical center being substantially smaller than diffractive groove radii (rj) of the same order (j) and the same order diffraction (m) and substantially similar focal length (Fm) and the same design wavelength (λdesign) where the radii (rj) are defined by the paraxial form
and, a peripheral diffractive groove having a radius that is similar the same order radius (rj) of the same paraxial form.
BRIEF DESCRIPTION OF THE FIGURES
The advantages and features of the present invention will be better understood by the following description when considered in conjunction with the accompanying drawings, in which:
FIG. 1 shows a simplest form of switchable cell configuration as a circular disc with rectangular cross-section.
FIG. 2 demonstrates a segment of cross-section of preferred embodiment of a switchable cell in the relaxed state. The switchable cell of this embodiment includes two chambers filled with optical fluids, separated by the film with elasticity to change its shape with a difference in pressure between the chambers. This is so called 5-element switchable cell. The film is free-standing or bonded to the diffractive blazed guiding surface of the optical substrate. One chamber (transparent chamber) between the film and guiding surface is filled with an optical fluid of refractive index that matches or very close to the refractive index of the optical substrate. The other chamber (active chamber) at the opposite side of the film from the transparent chamber is filled by a non-matching fluid of the refractive index that is differ from the refractive index of the optical substrate. In a simpler form of 3-element switchable cell, the ambient medium serves the function of a medium in active chamber. The film surface facing the active chamber is formable surface and its shape together with a difference in refractive indices between the substrate and non-matching fluid define a focusing characteristic of the switchable cell in the relaxed state shown.
FIG. 3 demonstrates the same section of the switchable cell cross-section shown on Figure 2, but the switchable cell is in the active state with the matching fluid is largely removed from the transparent chamber. A pressure in transparent chamber is lower a pressure in the active chamber so most of the area of the formable surface takes the shape of the corresponding groove of the guiding surface, i.e. the formable surface largely conforms to the shape of the guiding surface. The elastic film must maintain continuity and, as a result, it has deviations from the guiding surface in the areas close to the step transitions between the diffractive grooves. This is so called smoothing area. Light passing through the formable surface of the conformed diffractive shape concentrates at the diffractive focus of the guiding surface itself as its diffractive shape was defined as being against the non-matching fluid. For instance, if the guiding surface is shapes to create (-1)-order Kinoform if facing the medium of the active chamber, the switchable cell in the active state also forms (-1)-order Kinoform with most light forming image at the focus of the (-1)-order of diffraction of the guiding surface. Only a fraction of light that passes through the smoothing area of the formable surface is spread out outside the active state focus. The light "spread out" must have a significant area because the formable surface shape within the smoothing area manifests significant curvatures. Therefore, it is most likely that the intensity of the highly spread out light at the image plane of the active state diffractive focus is fairly low and, as a result, its impact on the image quality at the diffractive focus is insignificant.
FIG. 4 illustrates front view of switchable cell of diffractive accommodating aphakic IOL with internal actuation. Internal actuation means that the actuation occurs due to an internal interaction between the lens elements. The switchable cell includes at least one but shows two actuation chambers each formed by an elastic membrane with its internal content connected to the transparent chamber of the switchable cell for the matching fluid transfer between the actuation and transparent chambers. The actuation chambers are located at the opposite sides of the switchable cell for balanced actuation. Diffractive accommodating IOL as well as any switchable IOL may also rely on external actuation by the Sensor Cell.
FIG. 5 shows front view of the optical anterior member of the diffractive accommodating aphakic IOL with internal actuation. The anterior member is shaped by the anterior optical surface of the diffractive accommodating lens and largely flat surface posteriorly. The figure 5 also shows a cut out on the back of the anterior member for placement of the switchable cell of the figure 4.
FIG. 6 illustrates front view of the optical posterior member of the diffractive accommodating aphakic IOL with internal actuation. The posterior member is shaped by the posterior optical surface of the diffractive accommodating lens and largely by flat surface anteriorly. In general, the posterior surface of the switchable cell and anterior surface of the posterior member can be curved for a dioptric power contribution. Also, the posterior member may have cut out for placement the switchable cell instead of in the anterior member. The posterior member includes haptics for fixation of the diffractive accommodating lens inside the capsular bag. There are also actuation wings attached to the posterior member optic for bonding to the actuation chambers of the switchable cell shown on the figure 4. Again, the structure can be reversed and haptics can be attached to the anterior member and the actuation wings can be placed either on anterior or posterior member.
FIG. 7 demonstrates a side view of aphakic diffractive accommodating lens assembled with the anterior and posterior members illustrated on the figures 5 and 6 and switchable cell of the figure 4 placed in between. The anterior and posterior members are separated by the width of the actuation members attached to the switchable cell which are bonded to the lens members.
It is known from clinical observations that due to (a) overall implant diameter that reaches the ciliary body, minimum about 13-13.5 mm, and (b) haptics angulation, a conventional IOL commonly moves along the optical axis with accommodation by about 10-100 microns due to a compression of the lens haptics attached to the lens optical body by circumference of the ciliary body. The ciliary body present circumferentially around the internal surface of the eye globe and incorporates ciliary muscle that changes its shape with accommodation thus altering the ciliary body shape affecting a pressure on the haptic as the supporting member of the implant. The magnitude of movement by conventional IOL is insufficient for a meaningful power change of the eye, besides, a movement can either be forward or backward and, therefore, this movement is commonly ignored.
Nevertheless, the diffractive switchable IOL design demonstrated on figure 7, relies on the above clinical observation by using (a) similar overall diameter to respond to a pressure change on an accommodating lens from the ciliary body with eye accommodation and (b) haptics angulation. A compression of the haptics and increase in their angulation with accommodation increases a separation between the anterior and posterior members by tens of microns, i.e. similar magnitude of movement observed with conventional IOL of equivalement lens sizing and haptics angulation. The increase in separation expands the actuation chamber volume because the corresponding actuation member is bonded to anterior and posterior members at its opposite sides. As a result, the matching fluid is pulled out from the transparent chamber of the switchable cell. This in turn, reshapes the formable surface of the switchable cell from the refractive type of the relaxed state for far focus to diffractive type of the active state for near focus. It takes only several hundreds of milliliter of matching fluid transfer to change the switchable cell state and few tens of microns of the separation change is sufficient for the corresponding fluid transfer. With disaccommodation, the haptic takes the original shape reducing the separation into its original relaxed form with the film taking its original shape of formable refractive surface of the minimum strain and the matching fluid is transferred back to the transparent chamber from the actuation chamber.
The structure described in the figure 7 serves (a) sensing for a need for far or near focus by the wearer of the implant and (b) actuation for far or near focus. The same structure of the internal actuation described on figure 7 can be applied for sensing a need for far and near foci in any type of accommodating optic, for instance, in electro-optical switchable lens such as ELENZA type. In latter case, an actuation member includes electric or magnetic switch instead of optical fluid to trigger electro-optical actuation with the separation increase with ocular accommodation.
FIG 8 and FIG 9 demonstrate cross-section views of the switchable cell and actuation members of the diffractive accommodation lens of the figure 7 in relaxed state and active state correspondently. The width of the actuation member and as a result, the actuation chamber along the optical axis in the relaxed state (figure 8) is shown to be narrower than in active state (figure 9) demonstrating the actuation chamber volume increase. The refractive formidable surface of the switchable cell of the figure 8 changes into diffraction surface shown on the figure 9. Formable surface is the posterior surface of the switchable cell in the figures 8 and 9 and is facing the space between anterior and posterior members. As the diffractive accommodating lens is installed in the eye, the space between anterior and posterior members is filled with aqueous humour and formable surface is facing the aqueous humour of the eye which functions as the active chamber of the switchable cell. This is an example of 3-element switchable cell with "Open actuation system".
FIG 10 demonstrates front view of the diffractive switchable contact lens. The overall diameter of the lens is likely ≥ 14 mm to minimize its movement with eye blinking and gaze change. The contact lens includes balance at the bottom of the lens to maintain the lens meridional orientation. The contact lens also includes actuation ledge at the bottom of the lens to facilitate interaction with lower eyelid when viewing or gaze down for near focus. The actuation ledge connection to the contact lens body is such that it bends with a pressure elevation at the side of the actuation ledge that faces down. The contact lens incorporates switchable cell within its optic zone which is connected to the actuation chamber at the lens periphery.
FIG 11 and FIG 12 demonstrate cross-section views of the diffractive switchable contact lens of the figure 10 in relaxed state (figure 11) and active state (figure 12). The switchable cell is located at the lower part of the lens within the optic zone. The guiding surface is facing inside the lens. The base surface of the diffraction guiding surface of the switchable cell in this structure has convex shape to allow the film to be free-standing at the ridges of the guiding surface grooves in the relaxed state. The formable surface faces a narrow anterior chamber towards front of the film which is filled with tear fluid when the lens is fitted on the eye. This chamber functions as active chamber of the switchable cell. The actuation chamber is connected to the transparent chamber for the matching fluid transfer between them. The actuation chamber forming membrane is bonded to the actuation level. The latter turns together with the actuation ledge bend under the pressure from the lower eyelid when the lens wearer looks down for near focus, figure 12. The actuation level turn expands the actuation chamber thus reducing inside pressure that, in turn, pulls out the matching fluid from the transparence chamber for the switchable cell transfer from refractive relaxed state for far focus to diffractive active state for near focus.
A simpler structure is also possible with formable surface being a part of the back surface of the contact lens and facing the tear layer over the anterior surface of the eye. In this arrangement the base surface of the guiding surface is concave and the film is likely bonded to the ridges of the guiding surface grooves to maintain film contact with the ridges. Bonding is an addition manufacture step which is a downside of this structure. It is also possible to have a free-standing film and reply on front surface of the eye to maintain the film proximity to the guiding surface.
In general case, an actuation chamber includes an electrical or magnetic switch responding to the chamber expansion to sense a need for far or near focus by the lens wearer and to trigger switching to far or near focus. With the actuation level turning with the actuation ledge bend under the pressure from the lower eyelid when the wearer of a switchable contact lens looks down for near focus, the actuation chamber containing an electrical or magnetic switch expands triggering the switching from far to near focus.
FIG 13, FIG 14, FIG 15 and FIG 16 depict one half of switchable spectacles that includes switchable spectacle lens to demonstrate sensing a need for far or near focus. The switchable lens may be diffractive switchable lens of the present invention or any type of switchable spectacle lens with the only requirement to utilize the common optical arrangement of bifocal and progressive spectacles for presbyopia correction where the spectacles wearer looks straight forward for far focus and down for near focus. The figure 13 shows front view of right half of switchable spectacles, i.e. framed right switchable spectacle lens in this case. The IR emitter is installed at one side of the switchable spectacle lens either on the switchable spectacle lens periphery or frame, and an IR sensor is installed on the opposite side of the switchable spectacle lens, also either at the switchable spectacle lens periphery or frame. The IR emitter and IR sensor are installed in approximately horizontal plane that is crossed by the upper eyelid movement between open and closed eye conditions. Figure 14 is upper view of the spectacles half shown on the figure 13: the IR radiance is directed towards front surface (cornea and sclera) of the eye ball by the IR emitter and reaches IR sensor upon reflection off the reflective front surface (cornea and sclera) of the eye ball. Figure 15 demonstrates front view of the same half of the spectacles with the wearer is looking down for near focus with the upper eyelid in its lower position. The figure 16 shows the upper view of the figure 15: IR radiance from the IR emitter is fully or partially obstructed by the upper eyelid thus affecting the amount of IR radiance reaching the IR sensor.
Thus, IR radiance received by the IR sensor changes with upper eyelid moving over the front surface of the eye ball by at least 1/3 of total upper eyelid movement from the position of the opened eye for straight forward gaze to the upper eyelid lowest position in closed eye. Change in IR radiation reaching the IR sensor changes the electrical signal generated by it that triggers switching the switchable spectacle lens between far and near foci. A signal threshold for sensing a need for far or near focus for the automatic triggering for far or near focus is individually programmed. In case of a diffractive switchable spectacle lens of the present invention, switchable cell changes between relaxed state for far focus and active state for near focus. The figure 15 shows a switchable cell located at the lower part of the switchable spectacle lens similar to a near zone location in conventional bifocal or progressive spectacles.
The structure described by the figures 13 - 16 serves for sensing a need for far and near foci and can be applied to any switchable spectacles to switch its switchable spectacle lens between far and near foci, for instance, electro-optical switchable lens of EmPower type. In that case, the disclosed sensing system triggers electro-optical switching between far and near foci.
FIG 17 illustrates a use of switchable cell for low vision application to provide magnification for a visually impaired person. It depicts a spectacle like structure with two pairs of diffractive switchable cells, one pair is for far vision when viewing straight forward and another one is for near vision when looking down. Each pair includes front diffractive switchable cell functioning as objective (high positive power lens) and back diffractive switchable lens functioning as eyepiece (high negative power lens) of the Galilean telescope. They are in relaxed state if a person desires only to observe a general surrounding and a corresponding pair is switched to active states to provide magnification either for far or near vision. The size and lightness of a switchable cell allows to combine them into a pair to form a telescope and even to combine several pairs on a single spectacle like frame for far or near viewing.
FIG. 18 provides Longitudinal Spherical Aberration (LSA) at Far focus in the relaxed state by the Diffractive Accommodating Lens.
FIG. 19 provides Longitudinal Spherical Aberrations at Near focus in the active state by the Diffractive Accommodating Lenses with increased depth of focus at (-1) order diffraction.
FIG. 1 shows a simplest form of switchable cell as a circular disc of D ≈ 3-8 mm diameter and rectangular cross-section of W ≈ 0.05-0.4 mm thickness in ophthalmic applications. The optical axis 100 and segment 110 of the switchable cell are shown. The dimensions of a switchable cell might vary significantly in an engineering optic application.
FIG. 2 demonstrates a segment 110 of the cross-section of a preferred embodiment of an switchable cell in relaxed state. The switchable cell of this embodiment includes transparent chamber 120 filled with matching fluid and active chamber 130 filled with non-matching fluid, separated by the film 140. The active chamber 130 is situated between film 140 and membrane 190. The film 140 is free-standing or bonded to the diffractive blazed guiding surface 150 of the optical substrate 160. Guiding surface 150 is shown as blazed diffraction surface of period L as one of the periods within the segment 110. Diffraction surface periods vary, generally following Eq. 1 with an additional variation to introduce spherical aberration for depth of focus increase in the active state. Film can be made of different elastics, for instance with polydimethylsiloxane also known as PDMS. The PDMS is a Si based organic polymer that has found wide applications in MEMS and microfluidic device fabrication, soft lithography, contact lens manufacturing and device encapsulation. The PDMS material is easily available as SYLGARD 184 Silicone Elastomer Kit from Dow Corning, with mixing in a 1 : 10 weight ratio. It is inexpensive and fabrication processes for thin film with PDMS include spin-casting, soft lithography (molding).
The optical substrate 160 can be made of any appropriate optical material used in a target application which maintains guiding surface shape with the film compression in the active state, not too soft material. For instance, in IOL application, it can be silicone material (refractive index 1.41 and higher) or hydrophobic acrylic (refractive index 1.46 to 1.56) or even PMMA. Optical fluids of wide range of refractive indices to serve as matching fluid are available. For instance, Laser Liquid from Cargille Laboratories offers optical fluids between 1.293 - 1.578 refractive indices that are colorless, stable, biocompatible and inert.
The surface facing the active chamber 130 is formable surface 180 which is used to demonstrate optical switching between refractive form of the switchable cell in the relaxed state and diffractive form in the active state.
FIG. 3 demonstrates the same section 110' of the cross-section of the switchable cell, shown in Figure 2, but in the active state. The film 140' between the transparent chamber 120' and active chamber 130' largely takes the shape of the blazed guiding surface 150 thus reshaping the transparent chamber 120'. The formable surface 180' takes period L at the location of the segment 110' and groove height H of the guiding surface 150 to become blazed diffraction surface of the same periodicity and height as the guiding surface 150. The elastic film 140' must maintain continuity and, as a result, it has a deviation from the guiding surface in the areas 200 close to the step transitions 210 between the diffractive grooves, so called smoothing area. The smoothing area depends on a difference in pressure between the active and transparent chambers and reduces as the difference increases.
The channel 170 is shown to penetrate the deepest portions of the grooves of the guiding surface 150 to allow the matching fluid to escape from the transparent chamber 120' as shown by arrow F, during switchable cell transition to the active state or to fill the transparent chamber during its transition back for the relaxed state. In a simpler form, the channel can be made in a form of a Trench channel, i.e. a channel cut across the cross-sections of the grooves. Optical effect of the Trench channel in active state is likely negligible with narrow enough channel, say 100 microns or less. A trench channel can be made during diffraction guiding grooves fabrication thus lowering cost of the production and desirably but not necessarily, made in a radial orientation to minimize a tearing of the film in transitions between relaxed and active states when the film strain changes. It also desirable to round trench channel edges for the same purpose.
Finite Element Analysis (FEA) was conducted to investigate a conformance of the switchable cell film to the guiding surface with a difference in pressure between the chambers. Technically, Conformance is defined as L'/L where L is a selected period of the guiding surface and L' is the width of the film conforming to the shape the guiding surface at the period L. A non-conformed width S of a given groove L is S = L - L' and is smoothing area or S-dimension.
It has appeared that Conformance is proportional to the guiding surface period L and it reduces with the reduction the period L for the same pressure difference between the active and transparent chambers. Therefore, the FEA was conducted for the smallest period of a selected aperture of the switchable cell.
A common aperture in ophthalmic application is 5 mm. This is suitable for any ocular implant and contact lens as the pupil at Near focus is commonly within 5 mm diameter. The smallest period Lmin
was calculated as following:
Focal length F = 400 mm (2.5 D of Add power); Design wavelength λdesign
= 0.54 µm. Assuming 1st order diffraction is used for the guiding surface. Guiding surface diffractive groove radii are defined by Eq. 1 and groove height of the same order by the Eq. 2. PDMS substrate was selected to analyze the mechanics of the large groove height H, i.e. at fairly low refractive index n = 1.400 (PDMS material) against tear layer or aqueous humour of refractive index n' = 1.336. Matching fluid is also has n=1.400 refractive index. This leads to the minimum period Lmin
= 88 µm and groove height H-l
= 8.4 µm.
A selection of 7 mm aperture would lead to Lmin
= 62 microns minimum period for the same material and optical parameters selection.
Film thickness of 10 microns was selected to be comparable with the groove height and for its manufacturability. The film can be "free standing" over the guiding surface or "bonded to ridges" of the guiding blazed diffraction surface, for instance, by oxygen plasma process. "Free standing" setup which does not require additional bonding fabrication step was used and a rounding was added to each ridge peak to prevent tearing of the film with the film potentially sliding over the ridges with film strain changes during transitions between active and relaxed states.
The corresponding Conformance curve is shown in the graph below:
The graph demonstrates a typical Conformance curve shape for different film thicknesses, groove widths and heights - the curve rapidly increases with a pressure difference between the chambers initially and then it is slowing down with approachment to a full conformance to the guiding surface. Each groove of an switchable cell has its own Conformance curve with Conformance curve shifts to the left (lower pressure difference of the horizontal axis) with a groove period increase. Variable film thickness (thicker along a larger period of the guiding surface and thinner along a smaller period) might be beneficial for Conformance consistency for different periods.
General fitting function of a Conformance Curve is:
where y = Conformance and x = pressure difference in PSI units.
In case of the example A above for Lmin
= 88 µm and H = 8.4 µm, the parameters of the Conformance Curve shown in graph above are: a = -0.01; b = 0.82; c = 0.02; d = 0.4 .
Use of materials with different refractive indices for the optical substrate with the same periodic structure of the guiding surface does not impact diffractive focal length and only impacts the groove height H per the Eq. 2. The periodicity is the most important parameter and the outcome of FEA are valid for different substrate materials. The only effect of the groove height reduction is a force threshold reduction for a transition between relaxed and active states of the switchable cell.
A radial strain of the film in relaxed state can be added to the film to facilitate its return to the original shape in the relaxed state. Film stretching in a direction parallel the base surface of the diffraction guiding surface in case of the film contact with the guiding surface. In case of a radial strain, the Conformance curve shifts to the right, i.e. to higher pressure difference in the horizontal axis. A radial strain of the film can be used to control a force threshold of the transition between relaxed and active states of the switchable cell.
The blazed guiding surface may also include its own "smoothing" at the transitions between the grooves, i.e. instead of having close to the theoretical step transition from one groove to another, the transitions are smoothed out. A guiding surface smoothing would allow (a) to use larger tool radius for the guiding surface manufacturing instead of more expensive and easily damaged single-point diamond tool, and (b) to increase cutting feed-rate of the fabrication of the corresponding surface or mold insert also to reduce the fabrication cost.
The question is on a Diffraction Efficiency (DE) of the switchable cell in active state. The DE geometrical definition was used to calculate DE of the ideal (theoretical) Kinoform with the smoothing defined by S-dimension: Diffraction Efficiency equals the sum of all area of the grooves coinciding with the blazed surface of the theoretical Kinoform to the area of the theoretical Kinoform for selected aperture.
A DE reduces with the increase of fraction of the smoothing area width to the groove period. It has appeared that a linear regression function per smoothing width (S-dimension) defines the Diffraction Efficiency for a given aperture of the switchable cell. For instance, for 5 mm aperture used in the Example A above, the DE is determined by:
where DE = Diffraction Efficiency, S is smoothing dimension in microns.
For instance, for 5 mm aperture and pressure difference to achieve conformance of about 0.8 at the minimum period Lmin
= 88 µm, the Diffraction Efficiency of the switchable cell is following:
S ≈ 2H = 16.8 µm, say with a rounding of the groove ridges, S = 20 µm, i.e. ≈23% of the minimum period of 88 µm is allocated to film "smoothing". Per Eq. 4, the DE = 0.85 which is fairly high even in using such conservative assessment of the film conformance.
FIG. 4 illustrates front view of switchable cell 220 with optical axis 100' of diffractive accommodating aphakic IOL 230 with internal actuation. The switchable cell 220 is joint with two actuation members 240, 250 that incorporate actuation chambers 260, 270 correspondently. An actuation chamber is formed by an elastic membrane to enable it to change its volume if the actuation member is stretched out.
FIG. 5 shows front view of the anterior member 280 of the diffractive accommodating aphakic IOL 230 with internal actuation. The anterior member 280 is shaped by the anterior optical surface of the diffractive accommodating lens 230 and largely flat surface posteriorly. The figure 5 also shows a cut out 300 on the back of the anterior member for placement the switchable cell 220 joined by the cut outs 290, 290' for placement the actuation members 240, 250.
FIG. 6 illustrates front view of the posterior member 310 of the diffractive accommodating aphakic IOL 230 with internal actuation. The posterior member 310 includes haptics 320, 330 attached to the posterior member optic body 360 for fixation the diffractive accommodating aphakic IOL 230 inside the capsular bag of the eye. The posterior member optic body 360 is shaped by the posterior optical surface of the diffractive accommodating lens 230 and largely flat surface anteriorly. There are also actuation wings 340, 350 attached to the posterior member optic body 360 to serve for bonding the posterior member 310 to the corresponding actuation members 240, 250.
FIG. 7 demonstrates side view of aphakic diffractive accommodating lens 230 assembled with the anterior and posterior members 280, 310 and the switchable cell 220. The anterior and posterior members 280, 310 are separated by the width of the actuation members 240, 250. The optic diameter of the anterior member 280 is shown to be larger the diameter of optic body 360 of the posterior member 310 in order for the haptics 320, 330 that are coming out from the optic body 360 to be in contact with the anterior member 280 at its periphery. It is also shown a slight cut out 285 at the periphery of the anterior member 280 where the angulated haptic 320 rests. The identical cut out is located at the opposite side of the anterior member 280 for resting of the other haptic 330. The aphakic diffractive accommodating lens 230 is shown in two states: relaxed state by the position of haptics 320, 330 and active state by the position of haptics 320', 330'. Front surfaces of the actuation members 240, 250 are bonded to the posterior of the anterior member 280 and posterior surfaces of the actuation members 240, 250 are bounded to the actuation wings 340, 350 of the posterior member 310. A volume of the actuation chambers 260, 270 expends with the increase in the separation 370 between the anterior members 280 and posterior member 310. The separation 370 increases with the haptics compression and corresponding angulation change from 320, 330 position to 320', 330' position which results in the haptics attached to the optic 360 of the posterior member 310 pushing the anterior member 280 apart from the posterior member 310 by a magnitude ΔI
. This shift is shown by a new position of the anterior member 280'. Separation 370 increase enlarges volumes of the actuation chambers 260, 270 which pulls out the matching fluid from the transparent chamber of the switchable cell 220. This, in turn, switches the formable surface 380 from the refractive state for far focus into formable surface 390 of the diffractive state for near focus.
FIG 8 and FIG 9 demonstrate cross-section views of the switchable cell 220 with actuation members 240, 250 in relaxed state and the switchable cell 220' with actuation members 240', 250' in active state. The width of the actuation members 240, 250 along the optical axis 100' in the relaxed state is shown to be narrower the width of the actuation members 240', 250' in active state. This is to demonstrate that the corresponding actuation chambers 260, 270 in relaxed state is enlarged into actuation chambers 260', 270' in the active state. In turn, it transforms the refractive formidable surface 380 of the switchable cell 220 into diffraction surface 390 of the switchable cell 220'. The formable surface is in contact with aqueous humour in the eye.
FIG 10 demonstrates front view of the diffractive switchable contact lens 400. The contact lens 400 includes balance 410 at the bottom of the lens to maintain the lens meridional orientation. The contact lens 400 also includes the actuation ledge 420 at the bottom of the lens to facilitate interaction with the lower eyelid when viewing down for near focus similar to a performance of an alternating contact lenses. The contact lens 400 includes a switchable cell 440 within the optic zone 460 which joints the actuation chamber 450.
FIG 11 and FIG 12 demonstrate cross-section views of the diffractive switchable contact lens 400 in relaxed state 470, and active state 480 correspondently. The switchable cell 440 is located at the lower part of the lens 400 and consists of optical substrate 490 with its back surface forming a part of the back surface or base of the contact lens 400. The optical substrate 490 can be made of the same material as the contact lens 400 or a different material bonded to the lens depending if the transparent chamber impermeability can be maintained. The guiding surface 500 of the substrate 490 is facing inside the lens with the film 510 free-standing on or bonded to the ridges of the convex shape of the guiding surface 500 in the relaxed state. There is a transparent chamber filled with the matching fluid between the film 510 and guiding surface 500. The formable surface of the film 510 is facing a narrow chamber filled with tear medium when the lens 400 is fitting on the eye. This chamber acts as the active chamber of the switchable cell 440. The actuation chamber 450 is connected to the transparent chamber of the switchable cell 440 for the matching fluid transfer between them to switch between relaxed and active states. The actuation chamber 450 is bonded to the actuation level 520 located inside or adjacent to the actuation ledge 420 shown in relaxed state. As the actuation ledge 420 is bent by the lower eyelid pressure when the contact lens wearer looks down for near focus, the actuation level 520 turns. The actuation level turn expands the actuation chamber 450 in the relaxed state into actuation chamber 450' in the active state by pulling out the matching fluid from the transparent chamber of the switchable cell 440. As the result, the film 510' takes the shape of the guiding surface 500 thus modifying the formable surface into a diffraction surface for near focus. The transition between the relaxed and active states corresponds to a shift by ΔC
distance between unturned actuation level 520 and turned actuation level 520'.
FIG 13, FIG 14, FIG 15 and FIG 16 depict right half 540 of switchable spectacles to demonstrate a sensing a need for far or near focus. The figure 13 shows front view of right half of the spectacles. It consists of frame 650 and switchable spectacle lens 640. The IR emitter 550 is installed at one side of the switchable spectacle lens 640. An IR sensor 560 is installed on the opposite side of the switchable spectacle lens 640, actually two sensors 560, 570 to provide better sensitivity for sensing. Each IR sensor 560 or 570 and IR emitter 550 lie in approximately horizontal planes 620 and 630 correspondently. The depiction of the eye in the figure 13 demonstrates the eye's straight forward gaze for far focus through the switchable spectacle lens 640 with the upper eyelid 580 being in its upper position. Figure 14 is upper view of the spectacles half 540 shown on the figure 13: the IR emission from the IR emitter 600 shown by arrows is reflected off the front surface 590 of the eye ball as shown by solid line 600 and reaches the IR sensor 560 on the opposite side of the frame. Figure 15 demonstrates front view of the same switchable spectacles half 540 in the condition when the wearer looks down for near focus with the upper eyelid 580' in its lower position. The figure 16 shows the upper view of the figure 15: IR emission from the IR emitter 550 is fully or partially obstructed by the upper eyelid 580' thus changing the amount of IR radiance received by the IR sensor 560 or both sensors 560, 570. The intended reflection from the front surface 590 of the eye ball is shown by the broken line 600'. The outcome of the radiation obstruction is a lower electrical signal from the IR sensor which triggers an actuation of the switchable cell from relaxed state for far focus into active state for near focus. The figure 15 showed the switchable cell 610 located at a lower part of the switchable spectacle lens 640.
FIG 17 illustrates the use of switchable cell for low vision application to provide magnification for a visually impaired person. It depicts a spectacle like structure 620 with two pairs of diffractive switchable cells OF
for straight forward far vision (subscript F) and ON
for down near vision (subscript N). A front diffractive switchable cell OF
serves as the objective of the Galilean telescope and back diffractive switchable cell EF
serves as the eyepiece of the corresponding Galilean telescope. High order diffraction can be used to reduce focal lengths in both objective and eyepiece of each pair to shorten the Galilean telescope for its placement onto the spectacle like structure 620.
FIG. 18 demonstrates Longitudinal Spherical Aberration (LSA) at Far focus by the Diffractive Switchable Ophthalmic Lens (Diffractive Accommodating Lens) in the switching cell relaxed state according to the specifications listed in Tables 1 and 2.
Table 1: Eye model specifications where Diffractive Accommodating Lens is placed behind the pupil.
|Optical Characteristics||Dimension in mm; refractive index|
| Anterior surface radius
| Refractive index
| Conic constant (asphericity Q)
||Nominal Q = -0.26|
| Posterior surface radius (mm)
| Central thickness (mm)
|Aperture stop or pupil position from posterior corneal surface (mm)
|Aqueous refractive index
|Vitreous refractive index
Table 2. Relaxed state specifications of the Diffractive Accommodating Lens.
|Optical Characteristics||Dimension in mm; refractive index|
| front surface vertex radius
||17.55; bi-sign aspheric(*)|
| back surface radius
| plano-parallel plate
||Per figures 8|
| front surface radius
| back surface radius
The LSA for Far focus demonstrates positive spherical aberration for up to about 1 mm from the lens center and negative spherical aberration outside 1 mm distance which is the characteristic of bi-sign asphericity.
FIG. 19 demonstrates Longitudinal Spherical Aberrations at Near focus by the Diffractive Accommodating Lenses produced at (-1)-order diffraction with switchable cell being in the active state per specifications of Eye model and Diffractive Accommodating Lens in Tables 1 and 2. The switchable cell is limited to 4 mm diameter of optical aperture in this example.
The LSA at Near focus shown on figure 19 manifests significant positive spherical aberration at (-1)-order diffraction to create retinal image from a near object placed not only around 36 cm viewing distance (2.75 D) but through about 27 cm of near viewing distance, i.e. to offer the increased depth of focus at near of about 1 D. The increase in depth of focus at near is demonstrated by the corresponding LSA shape which starts at shorter near focus position at the lens center and gradually shifts further away to create a negative slope of the power graph which is most effective for a depth of focus increase.
Specification of the guiding surface of the switchable cell with large amount of spherical aberration to extend depth of focus at (-1)-order diffraction is provided in Table 3 where its periodicity (referenced to "Large LSA") is compared with the periodicity that produces spherical wavefront per Eq. 1 (referenced to "Small LSA").
Table 3. Diffractive guiding surface periodicity of the switchable cell of 2.75 D addition (power difference between near and far foci at spectacle plane) with 4 mm aperture.
|Groove radii (mm)||1||2||3||4||5||6||7||8||9||10||11||12||13|
Depth of focus or progressive foci feature at near diffraction focus in active state was increased by modifying the phase coefficients for (-1) order diffraction for spherical wavelength to include spherical aberration that spreads the light along the optical axis at the near diffraction focus either to improve near close up or improve intermediate vision capability in addition to providing near.
A surface position where the optical axis intersects an optical surface is called optical center. Each optical surface of the lens has its own optical center which line up on the optical axis in centered optical system. Diffractive grooves are defined by their radii from the optical center and diffractive grooves periodicity is defined by differences in consecutive groove radii, i.e. groove periods. Per the example of the figure 19, there are 13 grooves within about 4 mm diameter with central two grooves radii the periodicity producing enhanced depth of focus being substantially smaller the corresponding radii of the same orders defined by Eq. 1.
Central groove means closest to the optical center. The periodicity producing the depth of focus increase also has a radius of a peripheral groove that reaches similar magnitude as the groove radius of the same order defined by the Eq. 1, 11th groove per Table 3, in this case. "Substantially smaller" generally means to be by about 10% or more smaller and "similar" generally means to be within about ±10%. The higher order groove radii of the periodicity described exceed groove radii of the corresponding orders per Eq. 1. The described comparison between any diffraction surface in terms of their groove radii that produces extended positive (geometrical) spherical aberration and diffractive surface that produced small amount of spherical wavefront, i.e. groove radii analogous to Eq. 1, is only applicable for the same order of diffraction (1st or higher), by comparing the same order of groove radii, the same design wavelength and substantially similar focal lengths, say within about ±2.5%.
Phase coefficients to enhance depth of focus at a diffraction focus can be applied to a monofocal diffractive non-accommodating lens and multifocal diffractive optics where light is split between far and near foci and near image is formed, for example, by (-1)-order diffraction. Appropriate phase coefficients can be applied to a multifocal diffractive optic that leads to substantially smaller central (closest to the optical center) diffractive groove radii of the periodic structure for enhanced depth of focus than the central groove radii of the periodic structure that produces spherical wavefront, i.e. per Eq.1. In addition, the same periodic structure that increases depth of focus reaches a groove radius towards surface periphery that is similar to the groove radius of the same order that produces spherical wavefront, i.e. equivalent to Eq.1. In case of an annular zone with progressive foci feature at its diffraction focus, the radii of central grooves are defined as starting at the internal side of the annular zone and are also referenced to as "central grooves" or "closest to the optical center grooves".
Although there has been hereinabove described a specific refractive-diffractive switchable optical element in accordance with the present invention for the purpose of illustrating the manner in which the invention may be used to advantage, it should be appreciated that the invention is not limited thereto. That is, the present invention may suitably comprise, consist of, or consist essentially of the recited elements. Further, the invention illustratively disclosed herein suitably may be practiced in the absence of any element which is not specifically disclosed herein. Accordingly, any and all modifications, variations or equivalent arrangements which may occur to those skilled in the art, should be considered to be within the scope of the present invention as defined in the appended claims.