Patent Description:
This invention relates to an ophthalmic lens for imaging with extended depth of focus.

Extension of the depth of focus of imaging is a common goal of various imaging systems. Techniques for extending the depth of focus of imaging systems have been developed, and are described for example in the following publications:.

An ophthalmic lens according to the present invention is defined in appended claim <NUM>. Embodiments of the claimed invention are defined in the dependent claims.

There is a need in the art in a novel all-optical technique, which provides for appropriately extended depth of focus (EDOF) of an imaging lens unit.

The present invention solves the above need by providing a novel coding mechanism for coding a light field in the vicinity of an imaging lens unit. The present invention takes advantage of the earlier technique developed by the inventors and disclosed for example in the above-indicated patent publications <CIT>, <CIT>, <CIT>.

The main idea of the present invention is based on the understanding of the following: Imaging systems, such as human eye, have a depth of focus (DOF) determined by a number of physical parameters - F/#, illumination spectrum and the aberrations terms (deviations from ideal imaging). For aberration-free system, the DOF could be defined as follows (using Rayleigh <NUM>/<NUM> wave rule of thumb): <MAT> where F/# = D/EFL, D is the system clear aperture, and EFL is the system effective focal length.

Therefore, in order to extend the DOF of such an imaging system, the aperture of the imaging system is usually reduced, unavoidably resulting in the lost of energy and resolution. EDOF technology, developed by the inventors, utilizes phase-only coding (e.g. phase mask), having large spatial features (i.e. low spatial frequency phase transitions), located in the imaging system entrance pupil/aperture plane/exit pupil in order to extend the DOF without reducing the aperture, i.e. causing neither loss of energy, nor loss of resolution. This technique eliminates a need for any image processing in order to restore the image.

Phase coding of the effective aperture of an imaging lens unit for extending the depth of focus of the lens unit results in a total profile of Through Focus Modulation Transfer Function (TFMTF) different from that of the imaging lens unit with no phase coding. The inventors have found that such TFMTF profile defined by the EDOF-based phase coded imaging lens unit can be further optimized to obtain such a TFMTF profile, in which the TFMTF plot components corresponding to the desirably extended depth of focus for different wavelengths overlap in the optimal way. The optimization comprises applying additional coding to the light field in the vicinity of the phase coded effective aperture of the imaging lens unit selected to take into account the EDOF effect to be obtained by the phase coding within the imaging lens unit, e.g. continuous range EDOF or discrete multi-range EDOF, and to compensate for longitudinal chromatic aberrations (LCA) of such EDOF imaging lens unit. Further details of lenses providing phase coding are given in <CIT> and <CIT> both to Zalevsky. Both of said patents are hereby incorporated by reference herein in their entirety.

The LCA cause a shift in the extended focal position for different wavelengths, and could thus smear the performance of the EDOF equipped imaging system. The invention provides for compensating for LCA effect while extending the depth of focusing of the imaging lens unit. To this end, the invention utilizes a dispersion profile coding (chromatic aberrations correction) of the light field which has been or is to be phase coded to thereby provide imaging with the desired profile of extended depth of focus for multiple wavelengths where the wavelengths' TFMTF profiles are desirably overlapping within the EDOF profile. The term "compensating for LCA" as used herein means reducing LCA for a lens relative to the same lens exclusive of the dispersion profile coding.

In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:.

Reference is made to <FIG> illustrating dispersion occurring in an imaging lens unit utilizing EDOF phase coding.

<FIG> shows the simulation results for a Through Focus Modulation Transfer Function (TFMTF) for 100cyc/mm spatial frequency. Four graphs are shown, G<NUM>-G<NUM>, corresponding to four different wavelengths in the range <NUM> - <NUM>. This simulation was carried out with Zemax, using "Arizona Eye model". As shown, there is a relative shift for each wavelength: the plot for wavelength <NUM> is shifted <NUM> away from the corresponding graph for wavelength of <NUM>.

Assuming all wavelengths are weighted the same (are of the same intensity), the resulted plot is illustrated in <FIG>.

Thus, for a given value of the TFMTF, the actual obtainable depth of focus (i.e. providing sufficient contract of the image) is smaller than that for each wavelength, e.g. for TFMTF=<NUM>, about <NUM> focal depth is obtained for each wavelength (<FIG>), while being about <NUM> for the total TFMTF plot (<FIG>).

Hence, there is a need to compensate the dispersion such as to cause the TFMTF plots overlap in the optimal way. It should be understood that the optimal way of overlapping means overlap within the required depth of focus region(s), defined by the specific applications. This may be one continuous region as for example required in ophthalmic applications, or dual- or multi-region depth of focus for example for imagers requiring improved image quality in the near and far vision zones.

The required compensation should take into account that DOF extensions for different wavelengths are different, i.e. larger for longer wavelength and smaller for shorter one, and also the initial depth of focus requirements with respect to a specific imaging lens unit. In other words, the chromatic aberrations correction (dispersion profile coding) should be configured in accordance with the depth of focus profiles, of the imaging lens with the EDOF effect, for the multiple wavelengths, e.g. those of the primary colors.

The present invention solves the above problem by providing an all-optical processor to be applied to a light field incident onto a predetermined imaging lens unit (e.g. passing through the lens unit). This optical processor is formed by passing light through a pattern of spaced apart regions of different optical properties. This pattern defines a phase coder affecting TFMTF profiles for different wavelength components in accordance with predetermined EDOF profiles for certain imaging lens unit, and also defines a dispersion profile coder configured to provide a predetermined overlapping between the TFMTF profiles within the EDOF profile.

Reference is made to <FIG> showing schematically an imaging arrangement <NUM> of the present invention. The imaging arrangement <NUM> includes an imaging lens unit <NUM> and an optical processor <NUM>. The imaging lens unit <NUM> may include one or more optical elements configured and operable to create an image of an object in an imaging plane. The optical processor <NUM> may be a separate unit located close to (up to physical contact with) the imaging lens unit <NUM> (generally located so as to be in the vicinity of the effective aperture of the lens unit) located at either sides of the lens unit or both of them; or may be at least partially incorporated within the lens unit (embedded therein). The optical processor is configured to provide a desired profile of the extended depth of focus for the given imaging lens unit and a desired TFMTF profiles of multiple wavelengths within said profile of the extended depth of focus. As shown in <FIG>, the optical processor <NUM> includes a phase coder (mask) <NUM> defined by a first pattern PC and a dispersion profile coder <NUM> (e.g. mask) defined by a second pattern DC. In this example, the masks <NUM> and <NUM> are shown as being separate elements both separated from the lens unit, the phase coding mask <NUM> being located upstream of the lens unit and the dispersion coding mask <NUM> being located downstream of the lens with respect to the light propagation direction. It should however be noted that for the purposes of the invention the lens <NUM> and the coders <NUM>, <NUM> may be arranged differently. Also, the codes of masks <NUM> and <NUM> may be integrated in a single pattern (mask) being separated from the lens or being integral therewith (e.g. embedded therein).

It should be understood that the imaging arrangement <NUM> is configured with one or more optical powers, to provide predetermined extension profile for the focus (focii) defined by said optical power, and to have a desired chromatic dispersion profile. The phase coder is configured to provide said predetermined extension profile, while substantially not adding any optical power to the lens unit. The desired optical power of the entire imaging arrangement for each wavelength is a sum of the respective optical powers of the elements of such arrangement. The dispersion coder is thus configured with a certain optical power (for each wavelength) selected such that the dispersion coder provides desirable shifts of the TFMTFs within the predetermined depth of focus extension profile. It should be understood that desired TFMTFs may be multi-lobe functions. Accordingly, for the given imaging lens with EDOF assembly, different dispersion codings might be used in order to achieve the desired overlap between different wavelength lobes.

<FIG> illustrates schematically an imaging arrangement <NUM> according to an example of the invention. The same reference numbers identify components common in all examples. The imaging arrangement <NUM> includes an imaging lens unit <NUM> (formed by a single lens in the present example), and an optical processor <NUM> which is carried by opposite sides 12A and 12B of the lens unit. Here, the phase and dispersion coders (patterns PC and DC) are implemented as surface patterns on the lens unit rear and front surfaces 12A and 12B. One of these patterns or both may be in the form of a surface relief; or may be formed by spaced-apart regions of a material having refractive index different from that of the lens.

Reference is made to <FIG> exemplifying the effect of the optical processor according to the light field coding technique of the invention. <FIG> exemplifies a radial profile of the EDOF phase coding pattern PC (mask), which is a phase only, substantially not diffractive pattern designed to provide a desired EDOF profile for said imaging lens unit. <FIG> exemplifies a radial profile of the dispersion profile coding pattern DC, which is a diffractive pattern designed in accordance with the imaging lens with the EDOF profile to desirably shift the EDOF components of different wavelengths within said desired profile. <FIG> shows a combined coding (pattern) applied to the light field propagating in the imaging lens arrangement.

Let us consider the above coding of the imaging lens unit similar to that of the example of <FIG>. The function of the chromatic aberrations corrector (dispersion profile coder), configured for properly shifting the EDOF TFMTF plots, is implemented by a diffractive element (e.g. Fresnel lens).

Diffractive lens focal length, fDiff; has the following wavelength dependency: <MAT> <MAT> where f<NUM> is the focal length for a central wavelength λ<NUM>.

<FIG> shows that application of the appropriately designed diffraction pattern to the EDOF imaging lens provides that the TFMTFs for multiple wavelength are well co-aligned (generally desirably overlap), giving a desired total TFMTF. The latter is shown in <FIG>.

The diffractive lens <NUM> used for dispersion profile coding was simulated as made of PMMA material with total thickness, Tthick, determined as: <MAT> npmma and nair being respective refractive indices. The optical power of such diffractive lens is determined as that of refractive plano-convex lens having power, and in the present example is: <MAT> where R = <NUM> is the radius of the plano-convex refractive lens carrying the above described diffractive pattern. In this example, the diffractive lens is configured for ophthalmic application considering the optical power of the eye lens.

Lenses as described herein can be embodied as any suitable ophthalmic lens. The term "ophthalmic lens" refers to an artificial lens for use with the eye. Preferred ophthalmic lenses are made of biomedical materials suitable for contact with eye tissue. The term "ophthalmic lens" includes but is not limited to intraocular lenses (IOLs), contact lenses, and corneal onlays or inlays.

It will be appreciated that non-optical components may be added in some embodiments of ophthalmic lenses (e.g., in intraocular lenses, one or more haptics may be added). Lenses according to aspects of the present invention can comprise combinations of surfaces having any suitable shape (plano, convex, concave). The illustrated embodiments of lenses have only one zone; however, other embodiments may have multiple zones, the zones having different optical powers.

In some embodiments, the lenses may be embodied as intraocular lenses adapted to provide accommodative movement. For example, a lens according to aspects of the present invention can be used in a dual element accommodative lens as described in <CIT>, or a single element accommodative lens as described in <CIT>.

A pattern may be placed on a surface of the lens by various techniques known in the art. As a first example, the pattern may be lathe cut, lased or etched directly into the lens surface. As a second example, the pattern may be provided on a mold having a molding surface for forming the lens surface, wherein the pattern is transferred to the mold during casting of the lens. For example, a conventional manner of making contact lenses involves casting a mixture of lens-forming monomers in a two-part plastic mold. One mold part includes a molding surface for forming the front lens surface, and the second mold part includes a molding surface for forming the back lens surface. The monomer mixture is polymerized, or cured, while in the two-part mold to form a contact lens. The plastic mold parts are injected molded from a metal tool. For such a method, the pattern may be provided on the metal tools, such as by lathing, and thus transferred to the contact lens surface during the casting process.

Claim 1:
An ophthalmic lens comprising
a phase coder (<NUM>) implemented as a first pattern of spaced-apart regions of different optical properties, being configured to provide an extended depth of focusing to be obtained by said ophthalmic lens;
wherein said first pattern is configured for affecting profiles of a Through Focus Modulation Transfer Function (TFMTF) for different wavelength components of a light field passing through the ophthalmic lens in accordance with a predetermined desired profile of said extended depth of focusing, the first pattern having a first radial profile of said spaced apart regions of different optical properties and being non-diffractive to visible light;
characterized in that
the ophthalmic lens comprises a dispersion profile coder (<NUM>) implemented as a second pattern, wherein
said second pattern is configured in accordance with said ophthalmic lens and said profiles of the TFMTF for different wavelength components affected by said first pattern in accordance with said predetermined profile of the extended depth of focusing to thereby cause shifts of the TFMTF profiles for different wavelength components to improve an overlap of said TFMTF profiles for different wavelength components within said predetermined desired profile of the extended depth of focusing, the second pattern having a second radial profile and being diffractive to visible light;
the first pattern having a low spatial frequency in relation to the second pattern.