FI20245764A1

FI20245764A1 - Optical element and method for designing optical element with high-fresnel zone density

Info

Publication number: FI20245764A1
Application number: FI20245764A
Authority: FI
Inventors: Mikko Kataja
Original assignee: Pixieray Oy
Priority date: 2024-06-14
Filing date: 2024-06-14
Publication date: 2025-12-15
Also published as: WO2025256887A1

Abstract

Disclosed is an optical element (100) and a method for designing an optical element with a high-Fresnel zone density, the optical element comprising: a first substrate (102) and a second substrate (104); an active material (106, 600) encased between the first substrate and the second substrate; a first electrode (108, 502, 602) deposited between the first substate and a first surface of the active material and patterned with a first set of resistors (114A…114N, 506A…506N, 610A…610D) that feeds fractions of a first drive voltage to a plurality of Fresnel zones (106A…106N, 606A…606D) associated with the first surface of the active material; and a second electrode (110, 504, 604) deposited between the first substate and the first surface of the active material and patterned with a second set of resistors (116A…116N, 508A…508N, 612A…612D) that feeds fractions of a second drive voltage to the plurality of Fresnel zones, wherein feeding causes leads to variation in refractive index of the active material such that an OPD follows a preset OPD profile (300A, 300B).

Description

OPTICAL ELEMENT AND METHOD FOR DESIGNING OPTICAL ELEMENT

WITH HIGH-FRESNEL ZONE DENSITY

TECHNICAL FIELD

The present disclosure relates to optical element design by use of liquid- crystal-based active material. The present disclosure also relates to an optical element and a method for designing an optical element with a high-Fresnel zone density.

BACKGROUND

An optical apparatus (such as lenses, filters, polarizers, microscopes, and so on) includes optical elements and an active material. For designing an optical apparatus whose optical power is electrically tuneable, one or more properties of the active material (such as a refractive index of the active material) may be required to be controlled. Based on variations in the one or more properties of the active material, various optical powers can be produced in different portions or regions of the optical elements.

For example, a liquid crystal may be used as the active material in an optical lens. The refractive index of the liquid crystal material may be controlled by applying an electric field (voltage) on the liquid crystal. The application of the electric field may change an orientation of liquid crystal < 20 molecules, which, in turn, may lead to changes in the refractive index of

S the liguid crystal. The change in the refractive index is due to anisotropic

O optical properties (such as birefringence) of the liguid crystal. The change + in the refractive index due to the birefringence of the liquid crystal allows

E using the liguid crystal in designing the optical lens.

S 25 An optical power and an aperture of the optical lens, whose optical power 3 is electrically tuneable, may be limited by the birefringence of the active

N material used for designing the optical lens. This limitation is because the birefringence limits a range within which the refractive index of the active material is allowed to vary. When the range is restricted within a limited range, a difference between the refractive index of the active material and the refractive index of the optical element, which corresponds to the optical power of the lens, is restricted. To circumvent this limitation, the optical lens may be realized as a Fresnel lens that includes a plurality of

Fresnel zones. At each Fresnel zone, a specific voltage may be required to be applied using feed electrodes such that a resulting refractive index change at the corresponding Fresnel zone is linear with respect to the applied voltage. This approach may yield larger Fresnel zones at the centre of the optical lens.

For application of specific voltages at each of the plurality of Fresnel zones, a voltage distribution may be determined. The voltage distribution may indicate the specific voltages required to be applied at the plurality of Fresnel zones for effecting a desired variation of refractive index at different regions of the active material. However, the application of such a voltage distribution across the plurality of Fresnel zones is challenging.

This is because, each Fresnel zone, corresponding to a specific region of the active material, may be required to be driven by a specific voltage.

The requirement may necessitate usage of a separate feed electrode for each Fresnel zone. The usage of multiple feed electrodes may lead to a degradation of performance of the optical lens.

Additionally, at regions between the Fresnel zones, the optical power may

N be reset (for example, reset to "0”). These regions between the Fresnel

N zones may be referred to as Fresnel resets. The Fresnel resets degrade = the performance of the optical lens due to their finite size. As size of the = 25 optical lens increases, proportion of such regions (i.e., the Fresnel reset : zones) with respect to Fresnel zone regions of the optical lens increases.

S The presence of Fresnel reset zones may result in less light collected by

N the lens which results in loss of contrast in the image created by the lens

N and may result in worse performance in applications requiring collection of light. Further, the optical power resets at regions between the Fresnel zones may degrade image quality. This degradation may be due to diffraction, scattering and reflections, and so on that may cause ghost images and flares. Due to unavoidable degradation of the image quality, such optical lenses are rarely used in ophthalmic (i.e., vision correction) applications and imaging applications.

Therefore, considering the foregoing discussion, there exists a need to overcome the aforementioned drawbacks.

SUMMARY

The aim of the present disclosure is to provide an optical element and a method for designing an optical element with a high-Fresnel zone density.

The optical element includes an active element that is associated with a set of Fresnel zones. A count of Fresnel zones that is included in the set of Fresnel zones and the Fresnel zone density of the optical element is sufficiently high such that Fresnel resets (i.e., gaps between adjacent

Fresnel zones of the set of Fresnel zones where optical power resets to "0”) are irresolvable by use of imaging sensors. The aim of the present disclosure is achieved by the provided optical element and the method for designing an optical element with a high-Fresnel zone density as defined in the appended independent claims to which reference is made to. Advantageous features are set out in the appended dependent claims.

N Throughout the description and claims of this specification, the words

N "comprise", "include", "have", and "contain" and variations of these = words, for example "comprising" and "comprises", mean "including but = not limited to", and do not exclude other components, items, integers, or : 25 steps not explicitly disclosed also to be present. Moreover, the singular

S encompasses the plural unless the context otherwise reguires. In

N particular, where the indefinite article is used, the specification is to be

N understood as contemplating plurality as well as singularity, unless the context requires otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an optical element with a high-Fresnel zone density, according to an embodiment of the present disclosure;

FIG. 2 depicts steps of a method for designing an optical element with a high-Fresnel zone density, in accordance with an embodiment of the present disclosure;

FIGs. 3a and 3b are graphs that illustrate optical path difference (OPD) profiles of a high-Fresnel zone density liquid crystal Fresnel lens operable to produce both positive optical power and negative optical power, in accordance with an embodiment of the present disclosure;

FIGs. 4a and 4b are graphs that illustrate voltage distributions to be applied on a high-Fresnel zone density liquid crystal lens for producing positive and negative optical powers respectively, in accordance with an embodiment of the present disclosure;

FIG. 5 illustrates an exemplary resistor network that may be used for application of a voltage distribution at Fresnel zones of a high-Fresnel zone density liquid crystal-based Fresnel lens, in accordance with an embodiment of the present disclosure; and

FIG. 6 illustrates an exemplary active material of a high-Fresnel zone

S 20 density liguid crystal-based Fresnel lens on which electrodes, electrode

O

N segments, and a voltage divider network are deposited, in accordance

O

= with an embodiment of the present disclosure.

E DETAILED DESCRIPTION OF EMBODIMENTS

+

S The following detailed description illustrates embodiments of the present

N 25 disclosure and ways in which they can be implemented. Although some

Al . . ; modes of carrying out the present disclosure have been disclosed, those skilled in the art would recognize that other embodiments for carrying out or practising the present disclosure are also possible.

In a first aspect, the present disclosure provides an optical element, the optical element comprising: a pair of substrates, wherein the pair of substrates include a first substrate and a second substrate; 5 an active material, wherein the active material is encased between the first substrate and the second substrate, wherein a first surface of the active material is in contact with the first substrate, and a second surface of the active material is in contact with the second substrate; a first electrode, wherein the first electrode is deposited between the first substate and the first surface of the active material, wherein the first electrode is patterned with a first set of resistors that enable the first electrode to feed a fraction of a first drive voltage to each Fresnel zone of a plurality of Fresnel zones associated with the first surface of the active material; and a second electrode, wherein the second electrode is deposited between the first substate and the first surface of the active material, wherein the second electrode is patterned with a second set of resistors that enable the second electrode to feed a fraction of a second drive voltage to each Fresnel zone of the plurality of Fresnel <

N 20 zones,

O

N

3 wherein feeding of the fraction of the first drive voltage and s the fraction of the second drive voltage causes an application of a

E voltage distribution at the plurality of Fresnel zones, and +

S wherein the application of the voltage distribution effectuates

N 25 a variation in refractive index of the active material such that an

N Optical Phase Delay (OPD) at the plurality of Fresnel zones follows a preset OPD profile.

In a second aspect, the present disclosure provides a method for obtaining an optical element, the method comprising: obtaining a pair of substrates that include a first substrate and a second substrate; obtaining an active material that is encased between the first substrate and the second substrate, wherein a first surface of the active material is in contact with the first substrate, and a second surface of the active material is in contact with the second substrate; arranging deposition of a first electrode between the first substrate and the first surface of the active material, wherein the first electrode is patterned with a first set of resistors that enable the first electrode to feed a fraction of a first drive voltage to each Fresnel zone of a plurality of Fresnel zones associated with the first surface of the active material; arranging deposition of a second electrode between the first substrate and the first surface of the active material, wherein the second electrode is patterned with a second set of resistors that enable the second electrode to feed a fraction of a second drive voltage to each

Fresnel zone of the plurality of Fresnel zones; and applying a voltage distribution at the plurality of Fresnel zones such < 20 that a variation in refractive index of the active material is effectuated,

S wherein the optical element is obtained based on the application, wherein 8 the application of the voltage distribution is based on the feeding of the

J fraction of the first drive voltage and the fraction of the second drive

E voltage, and wherein the variation in the refractive index causes an

S 25 Optical Phase Delay (OPD) at the plurality of Fresnel zones to follow a 3 preset OPD profile. &

The present disclosure provides the aforementioned first aspect and the aforementioned second aspect to provide an optical element that includes an active material (for example, liquid crystal) associated with a plurality of Fresnel zones. For utilization of entire birefringence range of the active material, one of the surfaces of the active material may be associated with numerous Fresnel zones (i.e., the plurality of Fresnel zones). A count of Fresnel zones associated with the active material may be such that spacings between adjacent Fresnel zones of the plurality of Fresnel zones or optical power resets between the adjacent Fresnel zones is irresolvable for an image sensor (for example, a human eye or a camera system).

The advantage of designing a liquid crystal based-Fresnel lens having a high Fresnel zone density is that the visibility of Fresnel resets, i.e., regions where optical power resets to “0”, is reduced.

The reduction of the Fresnel reset visibility may improve a ratio of a usable region of the liquid crystal based-Fresnel lens and Fresnel reset regions. Increasing Fresnel zone density in a liquid crystal lens may further prevent image quality degradation due to artifacts appearing from

Fresnel resets with large amplitude, i.e., where the optical path difference resets to zero from a large optical path difference, for example, 10 wavelengths, which may lead to a greater utilization of the Fresnel lens in imaging, ophthalmic, and light collection applications. The high-Fresnel zone density design of the optical element may enable usage of smaller

Fresnel zones and liquid crystal cell of lower thickness and lower

N birefringence. Such solutions improve utility of the liguid crystal based-

N Fresnel lenses.

S

+ The usage of an optical element with a high-Fresnel zone density may

E 25 necessitate usage of numerous feeder lines, which may feed different 3 Fresnel zones with different voltages. The usage of multiple feeder lines 5 may degrade the quality of the Fresnel lens. To prevent usage of multiple

N

S feeder lines, the optical element utilizes voltage divider scheme to split two drive voltages, viz., the first drive voltage and the second drive voltage. The voltage divider scheme may be actualized by patterning the first electrode using the first set of resistors and patterning the second electrode using the second set of resistors.

The first drive voltage may be applied at a terminal of the first electrode, patterned in series along the length of the first electrode, may enable driving each Fresnel zone of the plurality of Fresnel zones with a fraction of the first drive voltage by use of resistors of the first set of resistors.

Similarly, the second drive voltage may be applied at a terminal of the second electrode, patterned in series along the length of the second electrode, may enable driving each Fresnel zone of the plurality of Fresnel zones with a fraction of the second drive voltage by use of resistors of the second set of resistors. The application of fractions of the first drive voltage and the second drive voltage at the plurality of Fresnel zones may effectuate variations in the refractive index at different portions of the active material (such as liquid crystal) corresponding to the plurality of

Fresnel zones. The variations of the refractive index are such that the

OPD at the plurality of Fresnel zones follows a preset OPD profile. Thus, an optical element may be designed using only two feed electrodes.

It may be noted that the application of the first drive voltage at a terminal of the first electrode and the application of the second drive voltage at a terminal of the second electrode may result in generation of positive < optical power. However, for generation of negative optical power, the first

S drive voltage may be applied at the terminal of the second electrode and

O the second drive voltage may be applied at the terminal of the first + electrode.

E 25 Throughout the present disclosure, the term "optical element" may refer

S to an optical element whose optical power is electrically tuneable. The 3 optical power may be a positive power or a negative power that may be

N used for focussing or defocusing light respectively. The optical element may be controlled to produce different optical powers at different parts of the optical element. The optical element includes the pair of substrates,

i.e., the first substrate and the second substrate, which are optically transparent. The optical element further includes the active material, which may be a liquid crystal layer of a predefined thickness. The active material is encased between the first substrate and the second substrate of the pair of substrates. The active material includes two surfaces, viz., the first surface and the second surface. The first surface is in contact with the first substrate. The second surface is in contact with the second substrate.

An optical power may be produced at a particular part of the optical element based on creation of a difference between refractive index at a region of the active material and refractive index of a Fresnel zone in the

Fresnel substrate that is in contact with the region of the active material.

The refractive index difference is achieved by varying the refractive index differently in different regions of the active material via application of different voltages in different regions of the active material corresponding to different Fresnel zones of the Fresnel substrate. The optical element may be used as, included in, or a part of, glasses, sunglasses, a head- mounted display (HMD), virtual reality (VR), mixed reality (MR), or augmented reality (AR) goggles (headset).

Throughout the present disclosure, the term "active material" may refer to a material with anisotropic optical properties whose refractive index

N may be controlled (or varied) by application of electric fields to produce

N different magnitudes of optical power at different regions of the active = material. In an example, the active material is a liguid crystal material = 25 that is associated with the plurality of Fresnel zones. Specifically, the : plurality of Fresnel zones are associated with the first surface of the active

S material. Upon application of the electric fields, alignment of liguid crystal

N molecules in the different regions of the liguid crystal (i.e., the plurality

N of Fresnel zones) changes. The change in the alignment leads to the variation in the refractive index at the different regions (different Fresnel zones of the plurality of Fresnel zones). Based on such variation in the refractive index, different optical powers may be produced in the different

Fresnel zones.

In accordance with an embodiment, the different regions, or the plurality of Fresnel zones of the active material, may refer to circular regions that are concentric (i.e., have a common centre which is the centre of the active material). Optionally, the plurality of Fresnel zones corresponds to a plurality of portions of the first surface of the active material. For example, the active material can be a circular plane (i.e., a circular disk), an elliptical plane (i.e., an elliptical disk) of a predefined thickness and a predefined radius. The active material can also be a rectangular plane of predefined thickness. The plurality of portions may be arranged as concentric rings on the first surface. The optical element may be a high-

Fresnel zone density liquid crystal-based Fresnel lens. Optionally, a count of Fresnel zones included in the plurality of Fresnel zones of the optical element is such that Fresnel resets between each pair of adjacent Fresnel zones of the plurality of Fresnel zones are irresolvable for an image sensor (such as a camera system or a human eye).

For example, the optical element (i.e., the high-Fresnel zone density liquid crystal-based Fresnel lens) is designed to function at a wavelength of 550 nanometres and generate an optical power of £2.5 Dioptres. The

N focal length of the high-Fresnel zone density liguid crystal-based Fresnel

N lens is 400 millimetres, and the predefined radius is 11.2 millimetres. The = count of Fresnel zones varies within a range 19-50 and Fresnel zone pitch = 25 varies within a range 0.225-0.7 millimetres. Optionally, distance between : adjacent Fresnel zones of the plurality of Fresnel zones (i.e., Fresnel

S pitch) may depend on the predefined radius of the circular plane and the

N count of Fresnel zones included in the plurality of Fresnel zones.

Al

The high-Fresnel zone density liquid crystal-based Fresnel lens utilizes a smaller portion of a birefringence curve (a graph indicative of variation of refractive index of the active material, i.e., the liquid crystal, with respect to voltage applied to the active material) to yield a certain optical power.

The optical power may be similar to, if not greater than, that yielded by a liquid crystal-based Fresnel lens with a lower Fresnel zone density via utilization of a larger portion of the birefringence curve. Thus, the high-

Fresnel zone density liquid crystal-based Fresnel lens (i.e., the optical element) allows producing higher magnitudes of optical power (positive or negative) using lower drive voltages and/or producing higher magnitudes of optical power with a lower birefringence liquid crystal mixture and/or thinner liquid crystal layer.

In accordance with an embodiment, an optical profile may be determined for the active material. The optical profile may be e.g. a spherical, parabolic or an aspheric lens. The determined optical profile is the preset optical profile that may be indicative of a variation of an optical path difference (OPD) associated with the active material along a radius of the active material (i.e., the circular disk or circular plane constituting of liquid crystal). The OPD may be expressed in terms of wavelengths and may be indicative of a phase delay that a light ray undergoes while passing through different regions (i.e., different Fresnel zones of the plurality of Fresnel zones) of the active material. In an embodiment, size of each Fresnel zone, corresponding to each portion of the plurality of x portions of the first surface of the active material, is constant. a If the optical element is designed to produce a positive optical power, = OPD at portions closer to the centre of the Fresnel zones may be higher = 25 compared to OPD at portions of the Fresnel zones farther from the centre : (or closer to edge of the circular plane). If the optical element is designed

S to operate as a lens with a spherical or parabolic profile, the reguired OPD

N range increases for Fresnel zones that are farther from the centre. The

N higher OPD at Fresnel zones closer to the edge is also due to higher slope of the OPD at portions of the first surface of the active material closer to the edge, compared to slope of the OPDs at portions of the first surface of the active material closer to the centre. Consequently, Fresnel zones corresponding to those portions that are closer to the edge utilize a larger part of the birefringence curve compared to Fresnel zones corresponding to portions closer to the centre which required higher drive voltages to be applied for those zones.

If the optical element is designed to produce a negative optical power,

OPD at the portions of the Fresnel zones near the edge of zone is higher than OPD at Fresnel zones near the centre. Similarly to a positive lens, the OPD range of Fresnel zones increases with the radius of the lens, requiring the use of larger part of the birefringence range of the LC material via application of higher drive voltages.

In accordance with an embodiment, the refractive index of the active material needs to vary at the different Fresnel zones corresponding to different portions of the active material such that the OPD at each of the plurality of Fresnel zones follows the determined preset optical profile.

For effectuating the variation in refractive index of the active material, a potential difference may be applied using feed electrodes, viz., the first electrode and the second electrode, at each of the plurality of portions (corresponding to each of the plurality of Fresnel zones) according to the voltage distribution. In an embodiment, a processor may determine the

N preset optical profile and the voltage distribution. The processor may be

N implemented as one of, but may not be limited to, a microprocessor, a = microcontroller, or a controller. In an example, the processor may be = 25 implemented as an application-specific integrated circuit (AISC) chip, or : a reduced instruction set computer (RISC) chip. 5 The voltage distribution is indicative of potential differences (voltages)

N

S reguired to be applied along the radius of the active material that includes the plurality of Fresnel zones corresponding to the plurality of portions.

The voltage distribution may include a set of voltages whose application causes a variation in the refractive index of the active material such that

OPD at each of the plurality of Fresnel zones conforms to preset optical profile. The set of voltages may include a first subset of voltages and a second subset of voltages. The first subset of voltages are fractions of the first drive voltage and the second subset of voltages are fractions of the second drive voltage. A voltage of the first subset of voltages and a voltage of the second subset of voltages is required to be applied on each of the plurality of Fresnel zones corresponding to the plurality of portions of the first surface of the active material.

For enabling application of the voltage distribution along the radius of the active material (i.e., the plurality of Fresnel zones corresponding to the plurality of portions), two feed electrodes, viz., the first electrode and the second electrode, are employed. The first electrode is deposited between the first substate and the first surface of the active material. The first electrode is patterned with the first set of resistors. The second electrode is deposited between the first substate and the first surface of the active material. The second electrode is patterned with the second set of resistors. Each of the first electrode and the second electrode is deposited on all of the plurality of Fresnel zones, i.e., all of the plurality of portions of the first surface of the active material (i.e., the liquid crystal disk). The patterning of each of the first electrode and the second electrode may x lead to creation of a voltage divider network. The voltage divider network

N can be used for feeding fractions of each of the first drive voltage and the

S second drive voltage at each of the plurality of portions of the first surface = 25 of the active material.

I

: Furthermore, a third electrode is deposited between the second substate

S and a second surface of the active material. The second surface of the

N active material is opposite to the first surface of the active material. The

N third electrode may be connected to a ground terminal.

Optionally, each Fresnel zone of the plurality of Fresnel zones may be associated with two resistors. A first of the two resistors may belong to the first set of resistors patterned on the first electrode and a second of the two resistors may belong to the second set of resistors patterned on the second electrode. The two resistors, associated with each of the plurality of Fresnel zones, facilitate application of the voltage of the first subset of voltages and the voltage of the second subset of voltages along each of the plurality of Fresnel zones. Thus, a fraction of the first drive voltage and a fraction of the second drive voltage is applied at each of the plurality of Fresnel zones.

The high-Fresnel zone density design of the liquid crystal-based Fresnel lens allows usage of smaller electrodes, such as the first electrode and the second electrode, which may embody higher resistances compared to larger electrodes embodying lower resistances. A resistance value of each of the first set of resistors, patterned on the first electrode, may be controlled by adjusting at least one of their width, length, or thickness, or patterning them with holes. A resistance value of each of the second set of resistors, patterned on the second electrode, may be similarly controlled. In accordance with an embodiment, the resistance value of a resistor may be increased by reducing the width or the thickness or by increasing the length. Conversely, the resistance value of the resistor x may be decreased by increasing the width or the thickness, or by reducing

N the length. The resistance value of each resistor of the first set of resistors

S and the second set of resistors is selected such that the application of the = 25 voltage distribution (i.e., fractions of the first drive voltage and fractions

E: of the second drive voltage) along the radius of the active material (i.e.,

S each of the plurality of Fresnel zones corresponding to the plurality of 3 portions of the first surface of the active material) is enabled. oo

N The usage of each of the first electrode and the second electrode (i.e., electrodes embodying higher resistances) may enhance quality of images rendered using the optical element, i.e., the liquid crystal-based Fresnel lens. This may be because the higher-Fresnel zone density design allows achieving a finer control of liquid crystal orientation at each Fresnel zone when a fraction of the first drive voltage and a fraction of the second drive voltage is applied at the corresponding Fresnel zone. The finer control over the refractive index variation of the active material at each Fresnel zone is achieved due to existent connections between the plurality of

Fresnel zones as parallel resistors.

The optical element, i.e., the high-Fresnel zone density liquid crystal- based Fresnel lens, may further include a plurality of electrode segments.

The plurality of electrode segments may be deposited on the first surface of the active material. In accordance with an embodiment, each of the plurality of electrode segments is deposited on each of the plurality of

Fresnel zones corresponding to the plurality of portions of the first surface of the active material (i.e., circular liquid crystal plane). Thus, a count of electrode segments included in the plurality of electrode segments is equal to the count of Fresnel zones included in the plurality of Fresnel zones. Each of the plurality of electrode segments may be connected to each of the first electrode and the second electrode at a specific point on each of the first electrode and the second electrode.

The deposition of the plurality of electrode segments on the plurality of

N Fresnel zones may facilitate connecting the plurality of Fresnel zones and

N the feed electrodes (i.e., the first electrode and the second electrode). = Optionally, each Fresnel zone of the plurality of Fresnel zones is

T 25 associated with a Fresnel zone resistor. A value of the Fresnel zone : resistor may fall in a range of 100 Kilo-Ohms (kQ2)-10 Mega-Ohms (MQ).

S A resistance value of each of the two resistors, associated with each of

N the plurality of Fresnel zones, may be lower than the resistance value of

N the each of the Fresnel zone resistors to which each of the plurality of

Fresnel zones are associated with.

Each electrode segment may connect each Fresnel zone resistor, which is associated with each Fresnel zone, to each of the first electrode and the second electrode at the specific point on each of the first electrode and the second electrode. The connection between a Fresnel zone resistor and the first electrode (via an electrode segment), at a specific point on the first electrode, enables application of the fraction of the first drive voltage (for production of positive optical power) or the fraction of the second drive voltage (for production of negative optical power) on a

Fresnel zone associated with the Fresnel zone resistor. Similarly, the connection between the Fresnel zone resistor and the second electrode (via the electrode segment), at a specific point on the second electrode, enables application of the fraction of the second drive voltage (for production of positive optical power) or the fraction of the first drive voltage (for production of negative optical power) on the Fresnel zone associated with the Fresnel zone resistor.

The first drive voltage may be applied at a first end-terminal of the first electrode. The second drive voltage may be applied at a first end-terminal of the second electrode. Each resistor of the first set of resistors, patterned on the first electrode, may cause a potential drop such that a fraction of the first drive voltage is fed at each Fresnel zone. Similarly, each resistor of the second set of resistors, patterned on the second x electrode, may cause a potential drop such that a fraction of the second

N drive voltage is fed at each Fresnel zone. The feeding of the fraction of

S the first drive voltage and the fraction of the second drive voltage at each = 25 Fresnel zone is due to association of each Fresnel zone with each resistor

ZE of the first set of resistors and each resistor of the second set of resistors.

S The feeding causes application of the voltage distribution at the plurality 3 of Fresnel zones corresponding to the plurality of portions of the first

S surface of the active material, i.e., the liguid crystal layer, such that a positive optical power is produced.

In some embodiments, the first drive voltage may be applied at the first end-terminal of the second electrode. The second drive voltage may be applied at the first end-terminal of the first electrode. Each resistor of the first set of resistors may cause a potential drop such that a fraction of the second drive voltage is fed at each Fresnel zone. Similarly, each resistor of the second set of resistors may cause a potential drop such that a fraction of the first drive voltage is fed at each Fresnel zone. The feeding causes application of the voltage distribution at the plurality of Fresnel zones corresponding to the plurality of portions of the first surface of the active material, i.e., the liquid crystal layer, such that a negative optical power is produced.

Optionally, a value of each resistor of the first set of resistors, a value of each resistor of the second set of resistors, a value of the first drive voltage, and a value of the second drive voltage, is selected based on one or more of the voltage distribution and the preset OPD profile. The preset

OPD profile and the voltage distribution may depend on a specific type and properties of the liquid crystal used as the active material. Therefore, the selection of drive voltages, i.e., the first drive voltage and the second drive voltage, the first set of resistors, and the second set of resistors, are specific to the liquid crystal used as the active material. For example, the first drive voltage may vary within a range of 0.5-4 Volts and the x second drive voltage may vary within a range of 4-12 Volts. a In accordance with an embodiment, the application of a specific voltage = at a Fresnel zone, corresponding to a portion of the active material, = 25 results in a modulation of the Fresnel zone. The value of the specific : voltage reguired to be applied may depend on the voltage distribution.

S The applied voltage is a difference between a specific fraction of the first

N drive voltage and a specific fraction of the second drive voltage. The

N modulation of the Fresnel zone involves realignment of liquid crystal molecules and a consequential change in refractive index at the Fresnel zone corresponding to the portion of the active material. Similarly, based on application of specific voltages at the other Fresnel zones, refractive index at those Fresnel zones corresponding to other portions on the first surface of the active material may undergo variations.

The application of the specific voltages at each of the plurality of Fresnel zones is enabled based on the Fresnel zone resistors associated with at each of the plurality of Fresnel zones, and the selected values of the first drive voltage, the second drive voltage, each resistor of the first set of resistors, and each resistor of the second set of resistors. The change in the refractive index at each of the plurality of Fresnel zones, caused by the application of the specific voltages at each of the plurality of Fresnel zones, is such that OPD at each of the plurality of Fresnel zones follows the preset OPD profile.

If the optical element is operable to function as a positive (focusing) lens, a first fraction of the first drive voltage fed to a first Fresnel zone of the plurality of Fresnel zones may be lower than a second fraction of the first drive voltage fed to the second Fresnel zone of the plurality of Fresnel zones. Furthermore, a first fraction of the second drive voltage fed to the first Fresnel zone may be higher than a second fraction of the second drive voltage fed to the second Fresnel zone. A first voltage, which is a difference between the first fraction of the first drive voltage and the first

N fraction of the second drive voltage, is applied at the first Fresnel zone.

N Similarly, a second voltage, which is a difference between a second = fraction of the first drive voltage and the second fraction of the second = 25 drive voltage, is applied at the second Fresnel zone. 5 Optionally, the first Fresnel zone corresponds to a first portion of the 5 plurality of portions, wherein the second Fresnel zone corresponds to a

N

S second portion of the plurality of portions. The first portion is closer to a center of the circular plane (i.e., the liguid crystal plane) compared to the second portion. The application of the first voltage at the first Fresnel zone and the application of the second voltage at the second Fresnel zone may lead to a first change in the refractive index at the first Fresnel zone and a second change in the refractive index at the second Fresnel zone.

The first change and the second change in the refractive index of the active material leads to the production of a positive optical power (for example, +2.5 Dioptre).

In some scenarios, the first voltage applied at the first Fresnel zone and the second voltage applied at the second Fresnel zone may be inverted.

This leads to changes in each of the first Fresnel zone and the second

Fresnel zone, which, in-turn leads to the production of a negative optical power (for example, -2.5 Dioptre).

Thus, for producing a positive optical power, fractions of the first drive voltage applied (as per the voltage distribution) along the radius of the active material (i.e., the first surface of the active material) needs to proportionately increase from the centre of the first surface to the edge of the first surface. On the other hand, fractions of the second drive voltage applied along the radius of the active material needs to proportionally decrease from the centre of the first surface to the edge of the first surface. For example, the first surface of the circular liguid crystal plane may be associated with four Fresnel zones. The first Fresnel zone may be closest to/in contact the centre and the fourth Fresnel zone may

N be closest to/in contact with the edge of the circular liguid crystal plane.

N In this scenario, the fractions of the first drive voltage applied along the = radius of the first surface of the circular liguid crystal plane = 25 proportionately increases from the first Fresnel zone to the fourth Fresnel : zone. Similarly, the fractions of the second drive voltage applied along

S the radius of the first surface of the circular liguid crystal plane

N proportionately decreases from the first Fresnel zone to the fourth

N Fresnel.

For producing a negative optical power, polarities of each of the fractions of the first drive voltage and the fractions of the second drive voltage applied (as per the voltage distribution) along the radius of the of the first surface of the circular liquid crystal plane may be reversed. The lowest applied voltage (i.e., a fraction of the first drive voltage and/or a fraction of the second drive voltage) is greater than threshold voltage of the circular liquid crystal plane and the highest applied voltage (i.e., a fraction of the first drive voltage and/or a fraction of the second drive voltage) is greater than a voltage level at which the circular liquid crystal plane starts to saturate. Thus, the high-Fresnel zone density liquid crystal-based

Fresnel lens, i.e., the optical element is able to produce positive optical power and negative optical power of various magnitudes by use of the voltage divider network and only two feed electrodes.

The present disclosure also relates to the second aspect as described above. Various embodiments and variants disclosed above, with respect to the aforementioned first aspect, apply mutatis mutandis to the second aspect.

Optionally, the the variation of the refractive index may correspond to a refractive index profile indicative of a first variation of a refractive index difference along the radius or the optical axis of the active material. The voltage distribution is determined based on the refractive index profile

N and a second variation of the refractive index of the active material with & respect to a voltage applied to the active material. + Optionally, each of the plurality of Fresnel zones may be associated with

E 25 a Fresnel zone resistor. A value of the Fresnel zone resistor may fall in a 3 range of 100 Kilo-Ohms-10 Mega-Ohms. 2 Optionally, each Fresnel zone of the plurality of Fresnel zones is further

N associated with two resistors. A first of the two resistors belongs to the first set of resistors and a second of the two resistors belongs to the second set of resistors. A value of each of the two resistors is lower than the value of the Fresnel zone resistor.

Optionally, one or more of a value of each resistor of the first set of resistors, a value of each resistor of the second set of resistors, a value of the first drive voltage, or a value of the second drive voltage, is selected based on the voltage distribution and/or the preset OPD profile.

Optionally, a first fraction of the first drive voltage fed to a first Fresnel zone of the plurality of Fresnel zones is lower than a second fraction of the first drive voltage fed to the second Fresnel zone of the plurality of

Fresnel zones. A first fraction of the second drive voltage fed to the first

Fresnel zone is higher than a second fraction of the second drive voltage fed to the second Fresnel zone.

Optionally, the first Fresnel zone may correspond to a first portion of a plurality of portions of the first surface of the active material. The second

Fresnel zone corresponds to a second portion of the plurality of portions.

The active material may be, for example, a circular plane or an elliptical plane of a predefined thickness and a predefined radius in which case the plurality of portions are arranged as concentric rings on the first surface of the active material that corresponds to the circular plane. The first portion is closer to a center of the circular plane, the elliptical plane, or + the rectangular plane, compared to the second portion.

N

& > In some embodiments, the first electrode is patterned with a first set of = impedances (such as inductors and capacitors). The first set of = impedances enable the first electrode to feed a fraction of a first drive : 25 voltage to each Fresnel zone of a plurality of Fresnel zones associated

S with the first surface of the active material. The first drive voltage is an

N alternating current (AC) voltage. The second electrode is patterned with

N a second set of impedances that enable the second electrode to feed a fraction of a second drive voltage to each Fresnel zone of the plurality of

Fresnel zones. The second drive voltage is an AC voltage.

The drive frequency associated with each of the first drive voltage and the second drive voltage is relatively low (such as of the order of 100

Hertz). At these frequencies, inherent capacitive effects of inductive- capacitive structures are small. However, the capacitive effects become more pronounced at higher drive frequencies.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, there is shown a schematic diagram of an optical element 100 with a high-Fresnel zone density, in accordance with an embodiment of the present disclosure. The optical element 100 includes a pair of substrates. The pair of substrates include a first substrate 102 and a second substrate 104. The optical element 100 further includes an active material 106. The optical element 100 further includes a pair of feed electrodes, viz., a first electrode 108 and a second electrode 110, and a ground electrode, viz., a third electrode 112. The optical element 100 further includes a first set of resistors 114A...114N and a second set of resistors 116A...116N.

The active material 106 is encased between the first substrate 102 and + 20 the second substrate 104. A first surface of the active material 106 is in

S contact with the first substrate 102 and a second surface of the active

O material 106 is in contact with the second substrate 104. The first + electrode 108 is deposited between the first substate 102 and the first

E surface of the active material 106. The first electrode 108 is patterned < 25 with the first set of resistors 114A...114N that enable the first electrode 5 108 to feed a fraction of a first drive voltage to each Fresnel zone of a

O plurality of Fresnel zones 106A...106N associated with the first surface of the active material 106. The second electrode 110 is also deposited between the first substate 102 and the first surface of the active material

106. The second electrode 110 is patterned with the second set of resistors 116A...116N that enables the second electrode 110 to feed a fraction of a second drive voltage to each Fresnel zone of the plurality of

Fresnel zones 106A...106N.

The feeding of the fraction of the first drive voltage and the fraction of the second drive voltage causes an application of a voltage distribution at the plurality of Fresnel zones 106A...106N. The application of the voltage distribution effectuates a variation in refractive index of the active material 106 such that an Optical Phase Delay (OPD) at the plurality of

Fresnel zones 106A...106N follows a preset OPD profile. The variation in the refractive index at each of the plurality of Fresnel zones 106A...106N leads to generation of positive optical power or negative optical power of various magnitudes.

It may be understood by a person skilled in the art that FIG. 1 includes a simplified architecture of the optical element 100, for sake of clarity, which should not unduly limit the scope of the claims herein. It is to be understood that the specific implementation of the optical element 100 is provided as an example and is not to be construed as limiting to specific types of optical elements, active materials, and electrodes. The person skilled in the art will recognize many variations, alternatives, and modifications of embodiments of the present disclosure.

S Referring to FIG. 2, depicted are steps of a method 200 for designing the

O optical element 100 with a high-Fresnel zone density, in accordance with + an embodiment of the present disclosure. At step 202, the pair of

E 25 substrates, including the first substrate 102 and the second substrate 3 104, is obtained. At step 204, the active material 108, which is encased 5 between the first substrate 102 and the second substrate 104, is

O obtained. The first surface of the active material 106 is in contact with the first substrate 102, and the second surface of the active material 106 isin contact with the second substrate 104. At step 206, the deposition of the first electrode 108 between the first substrate 102 and the first surface of the active material 106 is arranged. The first electrode 108 is patterned with the first set of resistors 114A...114N. The first set of resistors 114A...114N enable the first electrode 108 to feed a fraction of the first drive voltage to each Fresnel zone of the plurality of Fresnel zones 106A...106N that are associated with the first surface of the active material 106. At 208, deposition of the second electrode 110 between the first substrate 102 and the first surface of the active material 106 is arranged. The second electrode 110 is patterned with the second set of resistors 116A...116N. The second set of resistors 116A...116N enable the second electrode 110 to feed a fraction of the second drive voltage to each Fresnel zone of the plurality of Fresnel zones 106A...106N. At 210, the voltage distribution is applied at the plurality of Fresnel zones 106A...106N such that the variation in refractive index of the active material 106 is effectuated. The optical element 100 is obtained based on the application of the voltage distribution. The application of the voltage distribution is based on the feeding of the fraction of the first drive voltage and the fraction of the second drive voltage to each Fresnel zone of the plurality of Fresnel zones 106A...106N. The variation in the refractive index causes the OPD at each of the plurality of Fresnel zones 106A...106N to follow the preset OPD profile. x The aforementioned steps are only illustrative and other alternatives can

N also be provided where one or more steps are added, one or more steps

S are removed, or one or more steps are provided in a different seguence = 25 without departing from the scope of the claims herein. = 3 Referring to FIGs. 3a and 3b, are graphs that illustrate OPD profiles 300A

S and 300B of a high-Fresnel zone density liguid crystal-based Fresnel lens

X (i.e., the optical element 100), where the high-Fresnel zone density liguid crystal-based Fresnel lens is operable to produce positive optical power and negative optical power, in accordance with an embodiment of the present disclosure. The OPD profiles 300A and 300B may be determined for the active material 106 included in the optical element 100 based on the refractive index of the active material 106. The OPD profile 300A, as shown in FIG. 3a, is determined if the optical element 100 is operable to produce a positive optical power. The OPD profile 300B, as shown in FIG. 3b, is determined if the optical element 100 is operable to produce a negative optical power. Each of the OPD profiles 300A and 300B may be referred to as the preset OPD profile.

Each of the OPD profiles 300A and 300B are indicative of a variation of an OPD (Y-axis) associated with the active material 106 along a radius (X-axis) of the active material 106 (for example, a circular disk or circular plane constituting of liquid crystal material). The OPD (Y-axis) may be expressed in terms of wavelengths and may be indicative of a delay that a light ray may undergo while passing through different regions of the active material 106. The different regions may refer to a plurality portions of the first surface of the active material 106. The plurality of Fresnel zones 106A...106N may correspond to the plurality of portions of the first surface of the active material 106.

As shown in FIG. 3a, i.e., the OPD profile 300A, OPD range required at

Fresnel zones corresponding to portions closer to the centre of the circular < plane may be lower compared to OPD at Fresnel zones corresponding to

S portions farther from the centre. The higher OPD range at Fresnel zones

O farther from the centre is due to higher slope of the OPD of the target + profile of the lens (i.e. spherical) at portions of the first surface of the

E 25 active material 106 closer to the edge of the circular plane. As shown in 3 FIG. 3b, i.e., the OPD profile 300B, OPD at the Fresnel zones closer to 5 the centre of the circular plane is lower than OPD at Fresnel zones at the

N

S edge. The polarity of the OPD profile 300B is opposite with respect to the polarity of the OPD profile 300A, which may be used for generation of a positive optical power.

Based on application of specific voltages at each of the plurality of Fresnel zones 106A...106N, the refractive index at the plurality of Fresnel zones 106A...106N (i.e., the plurality of portions of the first surface of the active material 106) undergoes variation such that the OPD at each of the plurality of Fresnel zones 106A...106N follows one of the determined

OPD profiles 300A or 300B.

FIGs. 3a and 3b are merely examples, which should not unduly limit the scope of the claims herein. A person skilled in the art will recognize many variations, alternatives, and modifications of embodiments of the present disclosure. For example, OPD profiles could be different for other types of active materials included in the optical element 100.

Referring to FIGs. 4a and 4b, are graphs that illustrate voltage distributions 400A and 400B that are to be applied on a high-Fresnel zone density liquid crystal-based Fresnel lens for producing positive and negative optical powers respectively, in accordance with an embodiment of the present disclosure. Each of the voltage distributions 400A and 400B are indicative of voltages that required to be applied along the radius of the active material 106, i.e., the plurality of Fresnel zones 106A...106N corresponding to the plurality of portions of the first surface of the active material 106. The voltage distribution 400A < includes a first set of voltages whose application on the plurality of

S Fresnel zones 106A...106N causes a variation in the refractive index at

O the plurality of Fresnel zones 106A...106N corresponding to the plurality + of portions of the first surface of the active material 106. The change in

E 25 therefractive index is such that the OPD at each of the plurality of Fresnel 3 zones 106A...106N conforms to the OPD profile 300A. Similarly, the 5 voltage distribution 400B includes a second set of voltages whose

O application on the plurality of Fresnel zones 106A...106N causes a variation in the refractive index at the plurality of Fresnel zones

106A...106N such that OPD at each of the plurality of Fresnel zones 106A...106N conforms to the OPD profile 300B.

Each voltage of the first set of voltages or the second set of voltages is a difference between a fraction of a first drive voltage and a fraction of a second drive voltage. Thus, differences between various fractions of the first drive voltage and various fractions of the second drive voltage are applied on the plurality of Fresnel zones 106A...106N. For example, the active material 106 is a circular plane constituting of liquid crystal material. As shown in FIG. 4a, Fresnel zones corresponding to portions closer to the edge utilize a larger part of the birefringence curve compared to Fresnel zones corresponding to portions closer to the centre. This is because of higher OPDs required at Fresnel zones closer to the edge and lower OPDs at Fresnel zones closer to the centre (see FIG. 3a). To ensure that Fresnel zones closer to the edge utilize a larger part of the birefringence curve, higher voltages may be applied at the Fresnel zones closer to the edge compared to Fresnel zones closer to the centre. For example, a voltage applied at a Fresnel zone closer to the edge is a first difference between a fraction of the first drive voltage and a fraction of the second drive voltage. On the other hand, a voltage applied at a

Fresnel zone closer to the centre is a second difference between a fraction of the first drive voltage and a fraction of the second drive voltage. The

S first difference is greater than the second difference. Such application of a voltages at the plurality of Fresnel zones 106A...106N produces positive : optical power.

E 25 Similarly, as shown in FIG. 4b, Fresnel zones corresponding to portions 3 closer to the centre utilize a smaller part of the birefringence curve 5 compared to Fresnel zones corresponding to portions closer to the edge.

N

S This is because of higher OPD range reguired at Fresnel zones closer to the edge and lower OPDs at Fresnel zones closer to the centre (see FIG. 3b). To ensure that Fresnel zones closer to the edge utilize a larger part of the birefringence curve, higher voltages may be applied at the Fresnel zones closer to the edge. For example, the voltage applied at a Fresnel zone closer to the centre is the first difference and the voltage applied at a Fresnel zone closer to the edge is the second difference (since the first difference is greater than the second difference). Such application of voltages at the plurality of Fresnel zones 106A...106N produces negative optical power.

FIGs. 4a and 4b are merely examples, which should not unduly limit the scope of the claims herein. A person skilled in the art will recognize many variations, alternatives, and modifications of embodiments of the present disclosure. For example, the voltage distributions could be different for other types of active materials included in the optical element 100.

Referring to FIG. 5, there is illustrated an exemplary voltage divider network 500 that may be used for application of a voltage distribution at

Fresnel zones of high-Fresnel zone density liquid crystal-based Fresnel lens (i.e., the optical element 100), in accordance with an embodiment of the present disclosure. The voltage divider network 500 may include a first feed electrode 502, a second feed electrode 504, a first set of resistors 506A...506N, a second set of resistors 508A...508N, a set of

Fresnel zone resistors 510A...510N, and a set of electrode segments < 512A...512N. The first feed electrode 502 is patterned with the first set

S of resistors 506A...506N. The second feed electrode 504 is patterned

O with the second set of resistors 508A...508N. Each Fresnel zone resistor + of the set of Fresnel zone resistors 510A...510N is associated with a

E 25 Fresnelzone of the plurality of Fresnel zones 106A...106N. For example, 3 the first, second, (N-1)t, and Nt Fresnel zones may be associated with 5 Fresnel zone resistors Rzi, Rz2, Rz(n-1), and Rn, respectively. A value of

N

S each Fresnel zone resistor is significantly higher compared to a value of each resistor of the first set of resistors 506A...506N or the second set of resistors 508A...508N.

The voltage divider network 500 can be used for feeding fractions (such as Vi,1, V1,2, ..., Vi,n-1, and Vin) of a first drive voltage (Vi) at the plurality of Fresnel zones 106A...106N. The first drive voltage (Vi) is applied at an end-terminal of the first feed electrode 502. Additionally, the voltage divider network 500 can be used for feeding fractions (such as V2,1, V2,2, ..., V2,n-1, and V2,n) of a second drive voltage (V>) at the plurality of Fresnel zones 106A...106N. The second drive voltage (V2) is applied at an end- terminal of the first feed electrode 502. Each of the plurality of Fresnel zones 106A...106N may be further associated with two resistors. The two resistors include a first resistor belonging to the first set of resistors 506A...506N patterned on the first feed electrode 502 and a second resistor belonging to the second set of resistors 508A...508N patterned on the second feed electrode 504. For example, the first Fresnel zone is associated with the first resistor and the second resistor. The first resistor is the resistor 506A and the second resistor is the resistor 508A.

Similarly, the second Fresnel zone is associated with the resistor 506B and the resistor 508B, the (N-1)'* Fresnel zone is associated with the resistor 506C and the resistor 508C, and the N' Fresnel zone is associated with the resistor 506N and the resistor 508N.

The first set of resistors 506A...506N facilitate application of the fractions (V1,1, V1,2, ...V1,n-1, and Vin) of the first drive voltage (Vi) at the

S plurality of Fresnel zones 106A...106N. The second set of resistors

N 508A...508N facilitate application of the fractions (V2,1, V2,2, ..., V2,n-1, 3 and Van) of the second drive voltage (V2) at the plurality of Fresnel zones 106A...106N. For example, voltages Vi,1 and V2,1 are applied at the first & Fresnel zone. Similarly, voltages V1,2, and V2,2 are applied at the second

S Fresnel zone, voltages V1,n-1 and V2,n-1 are applied at the (N-1)'* Fresnel 3 zone, and voltages Vi,» and Van are applied at the Nt Fresnel zone.

Al

The set of electrode segments 512A...512N may be deposited on the plurality of Fresnel zones 106A...106N. Each electrode segment of the set of electrode segments 512A...512N may be connected to each of the first feed electrode 502 and the second feed electrode 504 at a specific point on each of the first feed electrode 502 and the second feed electrode 504. Each electrode segment (such as the electrode segment 512A) may connect each Fresnel zone resistor (such as the Fresnel zone resistor 510A), which is associated with each Fresnel zone (such as the

Fresnel zone 106A), to each of the first feed electrode 502 and the second feed electrode 504 at the specific point on each of the first feed electrode 502 and the second feed electrode 504. The deposition of the set of electrode segments 512A...512N on the plurality of Fresnel zones 106A...106N facilitate connecting the plurality of Fresnel zones 106A...106N and feed electrodes, i.e., the first feed electrode 502 and the second feed electrode 504. The connection between a Fresnel zone resistor (such as the Fresnel zone resistor 510A) and the first feed electrode 502, via an electrode segment (such as the electrode segment 512A), at a specific point on the first feed electrode 502, enables application of the fraction of the first drive voltage, (such as V11) on a

Fresnel zone (such as the Fresnel zone 106A) associated with a Fresnel zone resistor (such as the Fresnel zone resistor 510A). Similarly, the connection between a Fresnel zone resistor (such as the Fresnel zone resistor 510A) and the second feed electrode 504, via an electrode segment (such as the electrode segment 512A), at a specific point on

S the second feed electrode 504, enables application of the fraction of the

O second drive voltage (such as V2,1) on a Fresnel zone (such as the Fresnel > 25 zone 106A) associated with a Fresnel zone resistor (such as the Fresnel

E zone resistor 510A).

S The feeding of a fraction of the first drive voltage (such as Vi,1) and a 3 fraction of the second drive voltage (such as V3,1) at each Fresnel zone

N (such as the Fresnel zone 106A) is due to association of each Fresnel zone (such as the Fresnel zone 106A) with each resistor (such as the resistor 506A) of the first set of resistors 506A...506N and each resistor

(such as the resistor 508A) of the second set of resistors 508A...508N.

The feeding causes application of voltage distribution (such as the voltage distribution 400A or the voltage distribution 400B) at the plurality of

Fresnel zones 106A...106N corresponding to the plurality of portions of the first surface of the active material 106, i.e., the liquid crystal layer.

A value of each resistor of the first set of resistors 506A...506N, a value of each resistor of the second set of resistors 508A...508N, a value of the first drive voltage Vi, and a value of the second drive voltage V, is selected based on a voltage distribution (such as the voltage distribution 400A or the voltage distribution 400B) and OPD profile (such as the OPD profile 300A or the OPD profile 300B). The expressions of the resistor 506A and the resistor 508A are expressed in equation (1) and equation (2) respectively as follows:

R, AV,

Rya = AV — AV, s (1)

Rz AV.

Raa = AV — AV, N (2) where, R;, is the Fresnel zone resistor 510A, AV =V,, — V,,, AV, =V;, —

Vig, and AV, =V,, — Vog.

Similarly, expressions of each of the other resistors of the first set of

S resistors 506A...506N and other resistors of second set of resistors

O 20 508A...508N associated with a particular Fresnel zone may be > determined recursively by replacing the resistance of the first Fresnel z zone, i.e., Rz,, with a resistance that is a cumulative sum of resistances x of all Fresnel zone resistors and feed electrode resistors associated with 5 all Fresnel zones preceding the Fresnel zone. In equations (1) and (2),

O 25 AVisa difference between a specific fraction of the first drive voltage (V1) and a specific fraction of the second drive voltage (V2) which is applied at each of the plurality of Fresnel zones 106A...106N. Furthermore, AV:

and AV; are differences between two specific fractions of the first drive voltage Vi and two specific fractions of the second drive voltage V> respectively. The feeding of the fractions of the first drive voltage (i.e.,

Vint, Vi,2, ..Vin-1, and Vin) and the fractions of the second drive voltage (i.e., V2,1, V2,2, ..., V2n-1, and Van) at the plurality of Fresnel zones 106A...106N results in change in refractive index at each of the plurality of Fresnel zones 106A...106N, which, in turn, results in production of positive optical power or negative optical power.

FIG. 5 is merely an example, which should not unduly limit the scope of the claims herein. A person skilled in the art will recognize many variations, alternatives, and modifications of embodiments of the present disclosure.

Referring to FIG. 6, there is illustrated an exemplary active material 600 of a high-Fresnel zone density liquid crystal-based Fresnel lens on which feed electrodes, electrode segments, and a voltage divider network are deposited, in accordance with an embodiment of the present disclosure.

The feed electrodes, the electrode segments, and the voltage divider network are deposited on a first surface (as shown in FIG. 6) of the active material 600. The electrodes that are deposited on the active material 600 include a first feed electrode 602 and a second feed electrode 604. < The first surface of the active material 600 is associated with four Fresnel

S zones 606A-606D, viz., a first Fresnel zone 606A, a second Fresnel zone

O 606B, a third Fresnel zone 606C, and a fourth Fresnel zone 606D. The + electrode segments that are deposited on the first surface of the active

E 25 material 600 include a first electrode segment 608A and a second 3 electrode segment 608B, a third electrode segment 608C, and a fourth 5 electrode segment 608D. The voltage divider network comprises of a first

O set of resistors 610A-610D, a second set of resistors 612A-612D, and four Fresnel zone resistors (not shown). The four Fresnel zones 606A- 606D are associated with the four Fresnel zone resistors.

The first feed electrode 602 is patterned with the first set of resistors 610A-610D and the second feed electrode 604 is patterned with the second set of resistors 612A-612D. Each Fresnel zone (such as the first

Fresnel zone 606A) is associated with a resistor (such as the resistor 610A) of the first set of resistors 610A-610D, a resistor (such as the resistor 612A) of the second set of resistors 612A-612D, and a Fresnel zone resistor of the four Fresnel zone resistors. Each electrode segment (such as the first electrode segment 608A) connects each Fresnel zone (such as the first Fresnel zone 606A) with the first feed electrode 602 and the second feed electrode 604. A first drive voltage (V1) is fed to an end-terminal of the first feed electrode 602 and a second drive voltage (V2) is fed to an end-terminal of the second feed electrode 604.

The first feed electrode 602 feeds different fractions of the first drive voltage (V1) to each of the first Fresnel zone 606A, the second Fresnel zone 606B, the third Fresnel zone 606C, and the fourth Fresnel zone 606D. Similarly, the second feed electrode 604 feeds different fractions of the second drive voltage (V2) to each of the first Fresnel zone 606A, the second Fresnel zone 606B, the third Fresnel zone 606C, and the fourth Fresnel zone 606D. The feeding of the fractions of each of the first drive voltage and the second drive voltage is based on the electrode segments (i.e., the first electrode segment 608A, the second electrode

S segment 608B, the third electrode segment 608C, and the fourth

N electrode segment 608D) connecting the four Fresnel zones 606A-606D 3 with the feed electrodes (i.e., the first feed electrode 602 and the second = 25 feed electrode 604) and association of each of the four Fresnel zones & 606A-606D with a resistor of the first set of resistors 610A-610D (such

S as the resistor 610A), a resistor (such as the resistor 612A) of the 3 second set of resistors 612A-612D, and a Fresnel zone resistor.

N

For producing a positive optical power, the voltage applied (as per the voltage distribution 400A) at each of the different Fresnel zones (i.e., the first Fresnel zone 606A, the second Fresnel zone 606B, the third Fresnel zone 606C, and the fourth Fresnel zone 606D) needs to proportionately increase from the centre of the first surface of the active material 600 to the edge of the first surface of the active material 600. The applied voltage at each of the different Fresnel zones is a difference between specific fractions of the first drive voltage and specific fractions of the second drive voltage. The first Fresnel zone 606A is closest to/in contact the centre and the fourth Fresnel zone 606D is closest to/in contact with the edge of the active material 600 (i.e., the circular liquid crystal plane).

Thus, the applied voltage proportionately increases from the first Fresnel zone 606A to the fourth Fresnel zone 606D. The voltage applied at the first Fresnel zone 606A may be the lowest and the voltage applied at the fourth Fresnel zone 606D may be the highest.

For producing a negative optical power, a polarity of voltage applied (as per the voltage distribution 400B) at each of the different Fresnel zones 606A-606D needs to be opposite with respect to a polarity of the voltage applied at each of the different Fresnel zones 606A-606D for producing the positive optical power. For such an application, the first drive voltage (V1) is fed to an end-terminal of the second feed electrode 604 and the second drive voltage (V2) is fed to an end-terminal of the first feed electrode 602.

N FIG. 6 is merely an example, which should not unduly limit the scope of & the claims herein. A person skilled in the art will recognize many > variations, alternatives, and modifications of embodiments of the present

I 25 disclosure. For example, the active material 600 may be of any shape 3 (unlike a circular shape as illustrated in FIG. 6), the first surface of the

S active material 600 may be associated with any number of Fresnel zones,

X and each of the first set of resistors 610A-610D and the second set of resistors 612A-612D may include any number of resistors.

Claims

1. An optical element (100) comprising: a pair of substrates, wherein the pair of substrates include a first substrate (102) and a second substrate (104); an active material (106, 600), wherein the active material is encased between the first substrate and the second substrate, wherein a first surface of the active material is in contact with the first substrate and a second surface of the active material is in contact with the second substrate; a first electrode (108, 502, 602), wherein the first electrode is deposited between the first substate and the first surface of the active material, wherein the first electrode is patterned with a first set of resistors (114A...114N, 506A...506N, 610A...610D) that enable the first electrode to feed a fraction of a first drive voltage to each Fresnel zone of a plurality of Fresnel zones (106A...106N, 606A...606D) associated with the first surface of the active material; and a second electrode (110, 504, 604), wherein the second electrode N 20 is deposited between the first substate and the first surface of the active N O material, <Q I wherein the second electrode is patterned with a second set : of resistors (116A...116N, 508A...508N, 612A...612D) that enable 3 the second electrode to feed a fraction of a second drive voltage to N 3 25 each Fresnel zone of the plurality of Fresnel zones, O N wherein feeding of the fraction of the first drive voltage and the fraction of the second drive voltage causes an application of a voltage distribution (400A, 400B) at the plurality of Fresnel zones, and wherein the application of the voltage distribution effectuates a variation in refractive index of the active material such that an Optical Phase Delay (OPD) at the plurality of Fresnel zones follows a preset OPD profile (300A, 300B).

2. The optical element (100) according to claim 1, wherein each Fresnel zone of the plurality of Fresnel zones (106A...106N, 606A...606D) is associated with a Fresnel zone resistor, and wherein a value of the Fresnel zone resistor falls in a range of 100 Kilo-Ohms (kQ2)-10 Mega-Ohms (MQ).

3. The optical element (100) according to claims 1 and 2, wherein each Fresnel zone of the plurality of Fresnel zones (106A...106N, 606A...606D) is further associated with two resistors, wherein a first of the two resistors belongs to the first set of resistors (114A...114N, 506A...506N, 610A...610D) and a second of the two resistors belongs to the second set of resistors (116A...116N, 508A...508N, 612A..612D), and wherein a value of each of the two resistors is lower than the value of the Fresnel zone resistor.

4. The optical element (100) according to claim 3, wherein one or more of a value of each resistor of the first set of resistors (114A...114N, N 506A...506N, 610A...610D), a value of each resistor of the second set of N resistors (116A...116N, 508A...508N, 612A...612D), a value of the first = drive voltage, or a value of the second drive voltage, is selected based = on at least one of the voltage distribution (400A, 400B) and the preset = < 25 OPD profile (300A, 300B). O

2 5. The optical element (100) according to claim 1, wherein a count of N Fresnel zones included in the plurality of Fresnel zones (106A...106N, 606A...606D) is such that Fresnel resets between each pair of adjacent Fresnel zones of the plurality of Fresnel zones are irresolvable for an image sensor.

6. The optical element (100) according to any of the preceding claims, wherein the plurality of Fresnel zones (106A..106N, 606A...606D) correspond to a plurality of portions of the first surface of the active material (106, 600), wherein the active material is one of a circular plane, an elliptical plane, or a rectangular plane of a predefined thickness, wherein the circular plane is of a predefined radius, wherein the plurality of portions are arranged as concentric rings on the first surface of the active material that corresponds to the circular plane.

7. The optical element (100) according to any of the preceding claims, wherein a distance between adjacent Fresnel zones of the plurality of Fresnel zones (106A...106N, 606A...606D) depends on the predefined radius of the circular plane and the count of Fresnel zones included in the plurality of Fresnel zones.

8. The optical element (100) according to any of the preceding claims, wherein a first fraction of the first drive voltage fed to a first Fresnel zone (606A) of the plurality of Fresnel zones (606A...606D) is lower than a second fraction of the first drive voltage fed to the second Fresnel zone (606B) of the plurality of Fresnel zones, wherein a first fraction of the second drive voltage fed to the first Fresnel zone is higher than a second x fraction of the second drive voltage fed to the second Fresnel zone. O

N 9. The optical element (100) according to claim 8, wherein the first = Fresnel zone (606A) corresponds to a first portion of the plurality of = portions, wherein the second Fresnel zone corresponds to a second = - 25 portion of the plurality of portions, and wherein the first portion is closer 5 to a center of the circular plane compared to the second portion. S 10. A method (200) for obtaining an optical element (100), the method comprising:

obtaining a pair of substrates that include a first substrate (102) and a second substrate (104); obtaining an active material (106, 600) that is encased between the first substrate and the second substrate, wherein a first surface of the active material is in contact with the first substrate, and a second surface of the active material is in contact with the second substrate; arranging deposition of a first electrode (108, 502, 602) between the first substrate and the first surface of the active material, wherein the first electrode is patterned with a first set of resistors (114A...114N, 506A...506N, 610A..610D) that enable the first electrode to feed a fraction of a first drive voltage to each Fresnel zone of a plurality of Fresnel zones 106A...106N, 606A...606D associated with the first surface of the active material; arranging deposition of a second electrode (110, 504, 604) between the first substrate and the first surface of the active material, wherein the second electrode is patterned with a second set of resistors (116A...116N, 508A..508N, 612A..612D) that enable the second electrode to feed a fraction of a second drive voltage to each Fresnel zone of the plurality of Fresnel zones; and applying a voltage distribution (400A, 400B) at the plurality of N Fresnel zones such that a variation in refractive index of the active N material is effectuated, wherein the optical element is obtained based on = the application, wherein the application of the voltage distribution is = based on the feeding of the fraction of the first drive voltage and the = - 25 fraction of the second drive voltage, and wherein the variation in the S refractive index causes an Optical Phase Delay (OPD) at the plurality of X Fresnel zones to follow a preset OPD profile (300A, 300B).

11. The method (200) according to claim 10, wherein each Fresnel zone of the plurality of Fresnel zones (106A...106N, 606A...606D) is associated with a Fresnel zone resistor, and wherein a value of the Fresnel zone resistor falls in a range of 100 kQ-10MQ.

12. The method (200) according to claims 10 and 11, wherein each Fresnel zone of the plurality of Fresnel zones (106A...106N, 606A...606D) is further associated with two resistors, wherein a first of the two resistors belongs to the first set of resistors (114A...114N, 506A...506N, 610A...610D) and a second of the two resistors belongs to the second set of resistors (116A...116N, 508A...508N, 612A..612D), and wherein a value of each of the two resistors is lower than the value of the Fresnel Zone resistor.

13. The method (200) according to any of the claims 10-12, wherein one or more of a value of each resistor of the first set of resistors 114A...114N, 506A...506N, 610A...610D), a value of each resistor of the second set of resistors (116A...116N, 508A...508N, 612A...612D), a value of the first drive voltage, or a value of the second drive voltage, is selected based on at least one of voltage distribution (400A, 400B) and the preset OPD profile (300A, 300B).

14. The method (200) according to any of the claims 10-13, wherein a first fraction of the first drive voltage fed to a first Fresnel zone (606A) of the plurality of Fresnel zones (606A...606D) is lower than a second x fraction of the first drive voltage fed to the second Fresnel zone (606B) N of the plurality of Fresnel zones, wherein a first fraction of the second S drive voltage fed to the first Fresnel zone is higher than a second fraction = of the second drive voltage fed to the second Fresnel zone. I : 25

15. The method (200) according to claim 14, wherein the first Fresnel S zone (606A) corresponds to a first portion of a plurality of portions of the N first surface of the active material (600), wherein the second Fresnel zone * (606B) corresponds to a second portion of the plurality of portions, wherein the active material is one of a circular plane, an elliptical plane,

or a rectangular plane of a predefined thickness, wherein the circular plane is of a predefined radius, wherein the plurality of portions are arranged as concentric rings on the first surface of the active material that corresponds to the circular plane, and wherein the first portion is closer to a center of the circular plane, the elliptical plane, or the rectangular plane, compared to the second portion. + N O N O <Q + I = + O N LO s N O N