Patent Description:
Several approaches have been developed for obtaining extended depth of field of an optical apparatus. Recent technologies involving extended depth of field for various optical applications, including ophthalmic applications, are using annular grooves across a standard lens to create a phase retardation that leads to an interference pattern along the focal distance which, when controlled properly, can provide an extended depth of field. An example of this approach is described in <CIT>. Other techniques for extending the depth of field include presenting diffractional optic elements that can diffract the optical signal into different diffraction orders thereby realizing a bi-focal or multi-focal lens that allows a clear vision for different object distances using a single passive lens. Both technologies implement phase reshaping by introducing a lateral (i.e., along the surface of the lens) geometrical lens reshaping that produces the required phase retardation along a few microns in the longitudinal axis of the lens.

<CIT> relates to patterning a contact lens surface with plurality of nano structures.

Aspects and embodiments are directed to a phase-adjusting element configured to provide extended depth of field for an associated optical lens in an environment where liquid may be present. In particular, aspects and embodiments are directed to a phase-adjusting element that operates in essentially the same manner despite the presence of liquid in the surrounding environment, and/or is configured to account for the presence of liquid, and which therefore may provide a substantially liquid-invariant extended depth of field for the associated optical lens, as discussed further below.

According to the claimed invention a lens comprises a first region, a second region and a plurality of nanostructures formed on a surface of the first region and the plurality of nanostructures having a lateral width and are spaced apart from another by a spacing, the lateral width is at least one or several wavelength(s) at the lower end of the visible spectrum and the spacing being smaller than the optical wavelength; wherein the refractive index of the first region is different to the refractive index of the second region due to the plurality of nanostructures contained by the first region ; and wherein the plurality of nanostructures formed in the first region extend away from a base of the first region, wherein the first region comprises a series of concentric annular regions with a second region disposed between each adjacent pair of concentric annular regions.

In one example of the lens, the plurality of nanostructures extend away from a base of the first region. In one example, the spacing between adjacent nanostructures of the plurality of nanostructures is less than approximately a shortest wavelength of visible light in free space. In another example, the spacing between adjacent nanostructures of the plurality of nanostructures is less than approximately <NUM> nanometers. Each nanostructure of the plurality of nanostructures may have a height that is less than or equal to the depth of the first region. The first region may include, for example, a circular region, an annular region, or a plurality of concentric regions. In one example, the nanostructures are uniformly spaced apart from one another. In another example, the spacing between the adjacent nanostructures decreases from a largest spacing at a center of the first region to smallest spacing at edges of the first region. In another example, the spacing between the adjacent nanostructures is sufficiently small to prevent water from penetrating between the nanostructures at atmospheric pressure. The lens may be, for example, an ophthalmic contact lens, an intraocular lens, a spectacle lens, or any of numerous other types of optical lenses.

According to another embodiment, a lens having a depth of field comprises a phase-adjusting region formed in a lens surface of the lens, the phase-adjusting region extending into the lens by a depth and configured to extend the depth of field of the lens, and a plurality of nanostructures formed in the phase-adjusting region, the plurality of nanostructures extending away from a base of the phase-adjusting region, wherein a spacing between adjacent nanostructures of the plurality of nanostructures is less than approximately <NUM> nanometers.

In one example of the lens, each nanostructure of the plurality of nanostructures has a height that is less than or equal to the depth of the phase-adjusting region. The phase-adjusting region may be, for example, a circular region or an annular region. In one example, lens further comprises at least one additional phase-adjusting region, and at least one corresponding additional plurality of nanostructures formed in the at least one additional phase-adjusting region. In one example, the nanostructures are uniformly spaced apart from one another. In another example, the spacing between the adjacent nanostructures decreases from a largest spacing at a center of the phase-adjusting region to smallest spacing at edges of the phase-adjusting region. In another example, the spacing between the adjacent nanostructures is sufficiently small so as to prevent water from penetrating between the nanostructures at atmospheric pressure. A density of the plurality of nanostructures and the depth of the phase-adjusting region may be selected based at least in part on a predetermined desired average refractive index of the phase-adjusting region. The lens may be an ophthalmic contact lens, or any of numerous other types of optical lenses, as discussed above.

Where technical features in the figures, detailed description or any claim are followed by references signs, the reference signs have been included for the sole purpose of increasing the intelligibility of the figures, detailed description, and claims. Accordingly, neither the reference signs nor their absence are intended to have any limiting effect on the scope of any claim elements. The figures are provided for the purposes of illustration and explanation and are not intended as a definition of the limits of the invention. In the figures:.

As discussed above, several technologies for extending the depth of field of a lens implement a phase-adjusting element to reshape the phase of the optical signal passing though the lens, thereby achieving an extended depth of field. To maintain accurate phase reshaping, the refractive index difference between the phase-adjusting element and its surroundings must be controlled with high precision. In liquid environments, however, the presence of the liquid in the phase-adjusting element can significantly alter the refractive index of the element. For example, in ophthalmic applications the variable presence of tears in the eyes can create a large uncertainty with respect to the refractive index of the space surrounding the phase-adjusting element at any given time. Aspects and embodiments are directed to a phase-adjusting element having a structure that provides liquid-invariant performance of the phase-adjusting element. In one embodiment, the phase-adjusting element includes at least one region having an array of nanostructures formed therein. The region(s) produce a phase retardation in the longitudinal axis of the lens (i.e. along an optical axis of the lens) to achieve extended depth of field for the lens, and the nanostructures inhibit micro fluidic movement within the phase-adjusting element to provide liquid-invariant phase reshaping, as discussed further below.

References in the singular or plural form are not intended to limit the presently disclosed systems or methods, their components, acts, or elements. The use herein of "including," "comprising," "having," "containing," "involving," and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. References to "or" may be construed as inclusive so that any terms described using "or" may indicate any of a single, more than one, and all of the described terms. Any references to front and back, left and right, top and bottom, upper and lower, and vertical and horizontal are intended for convenience of description, not to limit the present systems and methods or their components to any one positional or spatial orientation.

Referring to <FIG>, there is illustrated a block diagram of an imaging apparatus <NUM> according to one embodiment which is configured to image an object <NUM>. The imaging apparatus <NUM> includes a lens <NUM>, a phase-adjusting element <NUM>, and a detector <NUM>, and may also include a processor <NUM> configured to process images from the light detected by the detector <NUM>. The phase-adjusting element <NUM> is configured to provide liquid-invariant extended depth of field for the lens <NUM>, as discussed further below. The phase-adjusting element <NUM> may be a separate element attached to the lens <NUM> or located close thereto, or may be implemented integral with the lens <NUM>, for example as a surface relief on the lens as discussed further below. For example, the phase-adjusting element <NUM> may include a pattern of spaced apart, optically transparent regions <NUM> that have a different refractive index and/or different thickness compared to other regions of phase-adjusting element and/or lens and thus affect the phase of the light passing therethrough. The phase differences caused by the region(s) <NUM> are small, for example, less than π. In order to extend the depth of field of the lens <NUM>, the phase differences caused by the region(s) <NUM> are designed to create a constructive/destructive interference pattern of the light passing through the phase-adjusting element. If a liquid enters the region(s) <NUM>, the refractive index of the region will change, and therefore the phase difference will change as well, resulting in a change in the interference pattern caused by the phase-adjusting element <NUM>. To avoid this situation, according to one embodiment, the region(s) <NUM> of the phase-adjusting element <NUM> are "roughened" to prevent liquid from entering the region(s); thereby improving the robustness of the extended depth of field of the lens <NUM> in environments where liquid may be present.

The imaging apparatus <NUM> may be used in a wide variety of equipment and applications, such as, for example, cameras, machine vision applications, photography, television systems, video conference systems, radar imaging systems, endoscopy and passive bio-medical inspections, tomography, display panels, etc. Embodiments of the imaging apparatus may also be used in ophthalmic applications, such as a contact lens, a spectacle lens, an intraocular lens, or any other lens used around or inserted into any part of the eye. In these applications, the detector <NUM> may be the retina and the processor <NUM> may include part of the brain.

As discussed above, according to one embodiment, the phase-adjusting element <NUM> is implemented integral with the lens <NUM>. Accordingly, referring to <FIG>, there is illustrated a diagram of a lens <NUM> including a phase-adjusting element according to one embodiment. The lens <NUM> has a surface <NUM> which has a modulated relief thereby comprising a plurality of regions including a first region <NUM> and a second region <NUM>. The first region <NUM> being recessed and having a depth <NUM> relative to the second region <NUM>. A plurality of nanostructures <NUM> are formed in the first region <NUM>, extending upward from the base of the first region, as illustrated in <FIG>. The phase-adjusting element <NUM> comprises the combination of the modulated lens surface <NUM> and the plurality of nanostructures <NUM>. As used herein, the term "nanostructure" is intended to refer to a structure of intermediate size between molecular and microscopic (micrometer-sized), and which is small relative to the size of the overall object in which it is formed. The term "nanostructure" as used herein does not require the structure to be smaller than <NUM> nanometers in a given dimension.

Referring to <FIG>, the first region <NUM> has a lateral width <NUM> that is at least one wavelength at the lower (red) end of the visible spectrum. In one example, the lateral width <NUM> of the first region is large compared to the wavelengths of visible light, for example, at least several wavelengths at the lower end of the visible spectrum. Thus, the surface relief of the lens <NUM> does not cause diffraction of visible light passing through the phase-adjusting element because the surface relief is laterally large compared to the wavelengths of visible light. The nanostructures <NUM> each have a lateral width <NUM> and are spaced apart from one another by a spacing <NUM>. This spacing <NUM> may be made small such that the light wave is substantially unaffected other than to see change in the average index of refraction of the first region. The spacing <NUM> may be selected based on at least the following factors. First, the spacing <NUM> is less than approximately one wavelength at the higher (blue) end of the visible light spectrum to avoid scattering diffraction and prevent generation of undesired diffraction orders. Second, as discussed further below, the density of the nanostructures (determined by the spacing <NUM>) and the depth <NUM> of the first region <NUM> are selected to provide a desired average index of refraction for the first region. In addition, the spacing <NUM> is selected to prevent micro fluidic movement in the first region <NUM>, as also discussed further below. The height of the nanostructures <NUM> may be up to approximately the depth <NUM>. In one embodiment, the depth <NUM> of the first region <NUM> is small, for example, less than the optical wavelength.

According to one embodiment, the array of nanostructures <NUM> forms a binary grating that has an average index of refraction. Because the spacing <NUM> between the nanostructures <NUM> is smaller than the optical wavelength, the array of nanostructures does not diffract visible light; instead the light "sees" the first region <NUM> as a whole having an average index of refraction, determined by the material of the nanostructures and the interstitial substance (e.g., the surrounding liquid or air), rather than an array of distinct nanostructures. As a result, the phase-adjusting element is not diffractive to visible light passing therethrough; instead substantially all the light remains in the zeroth order. Accordingly, the phase-adjusting element may be termed "non-diffractive" to visible light. In one embodiment, the phase-adjusting element is also not refractive in that it does not provide optical power. It is to be appreciated that although in one embodiment the phase-adjusting element is not refractive, the associated optical lens <NUM> may be refractive. As used herein, the term "non-diffractive" is intended to mean a structure that may be not diffractive (as described above) and also not refractive (as described above).

The phase-adjusting element <NUM> may be formed using any of a variety of techniques, depending for example on the material of the lens <NUM> and whether or not the phase-adjusting element <NUM> is integral with the lens or a separate element. For example, the phase-adjusting element may be formed by selectively etching the lens surface <NUM> to create the modulated relief and array of nanostructures. In this example, the nanostructures <NUM> may be formed simultaneously with the pattern of the surface relief, and are made of the same material as the lens itself. The etching process may be a chemical etching process or a mechanical etching process. In another example, the nanostructures may be formed using a deposition process to deposit or "grow" the nanostructures on the surface <NUM> of the lens <NUM>, in which case the nanostructures may comprise the same material as the lens or a different material.

In the example illustrated in <FIG>, the first region <NUM> is an approximately circular region formed in the surface of the lens <NUM>, as illustrated in <FIG>. However, it is to be appreciated that the first region <NUM> may assume numerous shapes, not limited to the example illustrated in <FIG> and <FIG>. For example, referring to <FIG> there is illustrated another example of a lens <NUM> in which the first region <NUM> is an annular region (as illustrated in <FIG>). The first region <NUM> may also assume numerous other shapes, such as, but not limited to, rectangular, square, and other geometric or non-geometric shapes of the same lateral width or different lateral widths. In addition, although <FIG> illustrates a single first region <NUM>, the phase-adjusting element may include multiple first regions <NUM>, and multiple second regions <NUM>, and is not limited to a single first region or single second region. For example, the first region <NUM> may comprise a series of concentric annular regions, optionally including a central substantially circular region, with a second region <NUM> disposed between each adjacent pair of concentric first regions. In addition, the shape of the first region <NUM> may vary depending on the shape of the lens <NUM>. Furthermore, the shape of the nanostructures is not limited to the triangular shape illustrated in <FIG>. The nanostructures may have any of a variety of shapes, which may depend (at least in part) on the manufacturing process used to form the nanostructures, and which may include, for example, rectangular, dome, cylindrical or random shapes.

The phase retardation caused by the first region <NUM> depends on the average index of refraction of the region, which is determined by the depth <NUM> and the density of the nanostructures <NUM>. The depth <NUM> can be calculated according to the following equation: <MAT>.

In equation (<NUM>), δ is the depth <NUM>, λ<NUM> is the nominal wavelength of the light, n is the refractive index of the lens, neff is the average refractive index of the first region <NUM>, given by equation (<NUM>) below, and Δϕd is the desired phase retardation that the first region <NUM> is configured to provide.

In equation (<NUM>), Δx is the average width <NUM> of the nanostructures <NUM>, M is the number of nanostructures in the first region <NUM>, and L is the lateral width <NUM> of the first region <NUM>. Accordingly, the depth <NUM> of the first region <NUM> can be calculated based on a known desired phase retardation and a known average index of refraction of the first region, and the average index of refraction can be determined based on a known lateral width <NUM> of the first region and the size and density of the nanostructures <NUM> within the first region.

Any of the above-mentioned parameters may be varied, subject to certain constraints (such as, for example, manufacturing capability, and suitable materials for the lens, optical constraints, etc.) to achieve a structure for the phase-adjusting element that achieves a desired phase retardation and therefore a desired interference pattern to extend the depth of field of the lens <NUM>. One optical constraint is the density of the nanostructures <NUM>. In particular, the spacing <NUM> between the nanostructures <NUM> may be less than approximately the nominal optical wavelength λ<NUM> to avoid generating undesired diffraction orders. In one example, the spacing <NUM> between the nanostructures <NUM> is less than <NUM> nanometers (nm), for example, in a range of approximately <NUM> to <NUM>. The spacing <NUM> may be made smaller than the shortest wavelength in the visible spectrum such that the phase-adjusting element is non-diffractive to visible light. The nanostructures <NUM> may be made nearly adjacent, particularly as advances in modern chemical processing techniques have made it possible to achieve a very dense structure with good repeatability; however, as the density of the nanostructures in the first region <NUM> increases, the average refractive index of the first region also increases. Therefore, to maintain a given average refractive index, for a denser array of nanostructures <NUM>, the depth <NUM> of the first region <NUM> may be increased, according to equations (<NUM>) and (<NUM>) given above. In one example, a depth <NUM> of approximately <NUM> micrometer (µm) to approximately <NUM> is presently practical for ophthalmic contact lenses.

According to one embodiment, the nanostructures <NUM> are sufficiently closely spaced to create a surface tension that is greater than the pressure of the liquid; hence the array of nanostructures will maintain a steady state environment within the first region <NUM> even in the presence of the liquid. For example, for ophthalmic contact lenses, the nanostructures may be sufficiently closely spaced to prevent tears from entering the first region <NUM> at approximately atmospheric pressure (experienced at or near the Earth's surface). The lens <NUM> including the phase-adjusting element can be configured to account for two steady state conditions in which micro fluidics movement inside the first region <NUM> is substantially prevented. In the first configuration, the array of nanostructures <NUM> prevents liquids from penetrating the first region <NUM> between the nanostructures in a hydrophobic material. In the second configuration, the nanostructure <NUM> are either made from a hydrophilic material or such a material is provided in the space between the nanostructures <NUM> of the first region <NUM> such that the space between these nanostructures is constantly filled with the surrounding liquid. The configuration of the lens <NUM> may be selected based on an expected environment in which the lens is to be used. For example, in environments where liquid is only sporadically present, the first configuration may be preferred. The following simulations, which demonstrate performance of an example of the lens <NUM> including an embodiment of the phase-adjusting element, assume a hydrophilic material and therefore demonstrate performance of the structure for the more severe diffraction case since the wavelength of the light is shorter due to the presence of the liquid.

An example of the phase-adjusting element <NUM> including a nanostructure array was simulated using Comsol Multiphysics, a modeling and simulation program available from the COMSOL Group, to solve Maxwell's wave equation via the finite element method. A reference phase-adjusting element, including recessed region without any nanostructure array, was also simulated to provide reference data with which to compare the simulation results obtained for the example phase-adjusting element <NUM>. For both simulations, the illumination was a normally incident TE polarized plane wave having a wavelength λ<NUM> of <NUM> in free space.

A diagram of the simulated reference element <NUM> is illustrated in <FIG>. The reference element has a recessed region <NUM>, corresponding to the first region <NUM> of lens <NUM> in <FIG>, formed in a surrounding material <NUM>. The recessed region <NUM> has a width <NUM> of <NUM> µm and a depth <NUM> (δ) that matches the π condition of equation (<NUM>): <MAT>.

In equation (<NUM>), Δn is the difference between the refractive index of the surrounding material <NUM> and the refractive index of the environment <NUM>. For the simulations, the surrounding material is specified as BK7 optical glass having a refractive index of <NUM>, and the environment <NUM> is specified as water having a refractive index of <NUM>. Accordingly, from equation (<NUM>), the recessed region had a depth δ = <NUM>. The total width of the simulated structure is <NUM> millimeters (mm) and the length (in the dimension of the depth <NUM>) is <NUM>.

Referring to <FIG> there is illustrated the simulated phase distribution of the perpendicular electric field along the reference element <NUM> of <FIG>. <FIG> demonstrates that the phase difference between the recessed region <NUM> and the surrounding material <NUM> is linearly summed along depth the recessed region <NUM> with a phase delay of π generated at the end of the <NUM> recessed region. Thus, the reference element <NUM> implements an inverting phase plate.

Referring to <FIG> there is illustrated a diagram of a simulated example of a phase-adjusting element <NUM> including a nanostructure array formed in a first region <NUM> corresponding to the first region <NUM> in <FIG>. Surrounding the first region <NUM> is the second region <NUM>, corresponding to the second region <NUM> in <FIG>. <FIG> is an enlarged view of the portion of the phase-adjusting element <NUM> enclosed in box 6B in <FIG>, illustrating the nanostructures <NUM> formed in the first region <NUM>. In the simulated example, <NUM> nanostructures <NUM> are defined in the first region <NUM> and the nanostructures <NUM> are uniformly spaced (i.e., arranged in a regular pattern across the width <NUM> of the first region <NUM>) with period of <NUM> and a duty cycle of <NUM>% (i.e., each nanostructure is <NUM> wide and the spacing between adjacent nanostructures is <NUM>). The width <NUM> of the first region <NUM> is <NUM>, the same as the width <NUM> of the reference element. The material of the second region <NUM> is specified as BK7 with a refractive index of <NUM>. As can be seen in <FIG>, and as discussed above, for the simulation, the water <NUM> entirely fills the space between the nanostructures <NUM> in the first region <NUM>. Thus, the average refractive index for the first region can be calculated based on the refractive indexes of the BK7 (from which the nanostructures are made) and the water, and the duty cycle. From equation (<NUM>), to maintain the same phase shift of π as generated by the reference element, the depth <NUM> of the first region <NUM> is made to be <NUM>.

Reference is now made to <FIG> illustrating the phase distribution of the perpendicular electric field along the simulated phase-adjusting element <NUM>. As can be seen with reference to <FIG>, the phase of the electric field of the light in the first region <NUM> accumulates a linear phase shift along the depth of the first region <NUM> and maintains a plane wave phase front in both the first region <NUM> and the second region <NUM>. The phase along the end of the first region <NUM> shows a phase difference of nearly π and the propagating field maintains the phase difference until the end of the simulated phase-adjusting element <NUM>. Thus, the phase-adjusting element with the nanostructures <NUM> realizes an inverting phase shifter that produces a plane wave front with no diffraction caused by the nanostructures.

Cross sections of the phase along the direction of light propagation are illustrated in <FIG> and <FIG>. <FIG> illustrates the phase for the phase-adjusting element <NUM> discussed above having a spacing of <NUM> between the nanostructures. As can be seen with reference to <FIG>, the phase delay in the first region <NUM> shows a constant phase along the first region and the phase delay is linear with the light propagation inside the first region <NUM>. <FIG> illustrates the phase for an example of the phase-adjusting element <NUM> with the nanostructure array having a period of <NUM> and a duty cycle of <NUM>%. Thus, in the example of <FIG>, each nanostructure <NUM> is <NUM> wide and the spacing between adjacent nanostructures is <NUM>. The other dimensions and characteristics of the phase-adjusting element <NUM> are the same as discussed above. This increased spacing approaches the wavelength of the light in BK7. As can be seen with reference to <FIG>, the ripple in the phase implies a minor diffraction pattern caused by the larger spacing between the nanostructures <NUM>. Accordingly, in order to avoid any type of diffraction, the spacing between the nanostructures may be kept under approximately a half wavelength (in free space) to account for the shortening of the wavelength of the light as it passes through the material of phase-adjusting element.

Referring again to <FIG>, the visible distortion <NUM> in the phase at the edge of the first region <NUM> is caused by the sharp transition between the first region <NUM> which contains the nanostructures and the second region <NUM> due the difference in the refractive index between the two regions. This distortion may be reduced by "softening" the transition between the first region and the second region, for example, by implementing a graded change in the refractive index. In one embodiment, the spacing <NUM> between the nanostructures <NUM> is made variable with a largest spacing (and therefore lowest refractive index) toward a center of the first region <NUM> and a smallest spacing (and therefore highest refractive index, closest to the refractive index of the second region <NUM>) toward the edges of the first region. By implementing a slowly increasing spacing <NUM> from the edges of the first region to the center of the first region, the average refractive index of the first region can be made to transition more gradually from that of the second region, reducing any edge distortion in the phase. It is to be appreciated that many variations in the spacing <NUM> between the nanostructures can be implemented. For example, the spacing <NUM> may be uniform, may increase from the edges of the first region <NUM> towards the center of the first region, may be "stepped" (i.e., groups of nanostructures may each have a specified spacing which may differ from group to group), may vary differently along different axes of the phase-adjusting element, or may be random.

Claim 1:
A lens comprising:
• a first region (<NUM>);
• a second region (<NUM>); the first region having a depth relative to the second region; and
• a plurality of nanostructures (<NUM>) formed on a surface (<NUM>) of the first region (<NUM>) each of the plurality of nanostructures (<NUM>) having a lateral width (<NUM>), the nanostructures spaced apart from another by a spacing (<NUM>), wherein the lateral width (<NUM>) of the first region is at least one wavelength at the red end of the visible spectrum and the spacing (<NUM>) is smaller than approximately one wavelength at the blue end of the visible spectrum;
wherein the refractive index of the first region (<NUM>) is different to the refractive index of the second region (<NUM>) due to the plurality of nanostructures contained by the first region (<NUM>) ; and
wherein the plurality of nanostructures (<NUM>) formed in the first region (<NUM>) extend away from a base of the first region (<NUM>),
characterized in that the first region (<NUM>)
comprises a series of concentric annular regions with a second region (<NUM>) disposed between each adjacent pair of concentric annular regions.