diffractive optical element

Abstract

Techniques for designing diffractive optical elements (DOEs), such as diffusers and other optical beam-shaping elements, can involve designing DOE unit cells over an area smaller than the entire area of ​​the DOE and then distributing the unit cells across the surface for the DOE. Height translations are introduced for at least some of the unit cells distributed across the surface, where the height translations correspond to respective phase translations for the DOE's intended operating wavelength. In some cases, phase wrapping is introduced to translate height variations between unit cells into unit cells comprising sub-unit structures with heights within a range corresponding to a specified phase range at the operating wavelength.

Description

[Technical Field]

[0001] REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Provisional Patent Application No. 62 / 988,124, filed March 11, 2020. The disclosure of the prior application is incorporated herein by reference.

[0002] Field of Disclosure The present disclosure relates to diffractive optical elements (DOEs). [Background technology]

[0003] background A DOE is an optical component operable to modify the phase and / or amplitude of incident light to create a desired light output pattern with a specified function. A DOE may have, for example, a multi-level structure formed on the surface of a substrate. The pattern may, for example, be etched into the surface of a rigid substrate, or replicated in a polymer on the surface of the substrate, or may be fabricated purely in the polymer. In some cases, the depth of the pattern may be on the order of the wavelength of light, or may be application-specific, and may be tailored to the refractive index of the material of the DOE.

[0004] When designing a diffractive optical element such as a DOE diffuser, taking into account the entire active area of ​​the diffuser in an attempt to optimize the design can be disadvantageous in several ways. This can lead to computational complexity, especially when designing over a large area. For example, in some cases, a 500 x 500 nm 2 2x2mm with pixel resolution 2This would control 16 million pixel elements for a diffuser. Furthermore, although the numerical complexity may be reduced by using an Iterative Fourier Transform Algorithm (IFTA), this may introduce various undesirable design limitations. Such limitations may relate, for example, to the amount of control over the optimization algorithm. In this case, the evaluation plane is in the far field, the resolution of the evaluation plane is given by the resolution of the design plane, and the method is based on a thin element approximation. Summary of the Invention [Means for solving the problem]

[0005] Disclosure Overview This disclosure describes techniques for designing diffractive optical elements (DOEs), such as diffusers and other optical beam-shaping elements. The techniques may involve designing DOE unit cells over an area smaller than the entire area of ​​the DOE and then distributing the unit cells (e.g., periodically) across the surface for the DOE. Height translations may be introduced for at least some of the unit cells distributed across the surface, where the height translations correspond to respective phase translations for the intended operating wavelength of the DOE.

[0006] In some cases, phase wrapping can be introduced to translate height variations between unit cells into unit cells with sub-unit structures having heights within a range corresponding to a specified phase range (e.g., 0π to 2π) at the operating wavelength. That is, after introducing height translation into a unit cell, the heights of individual sub-units corresponding to phase values ​​outside the specified range (e.g., outside the range of 0π to 2π) are folded back to heights corresponding to phase values ​​within the specified range (e.g., 0π to 2π).

[0007] In one aspect, the present disclosure describes a diffractive optical element including a plurality of periodically repeating unit cells, the unit cells being composed of an optical material and distributed across a common plane. Each unit cell in the plurality of unit cells includes a plurality of sub-unit cells, the plurality of sub-unit cells being arranged to provide an optical effect to incident light of a predetermined operating wavelength. Each of the plurality of sub-unit cells in each particular unit cell of the plurality of unit cells has a sub-unit height that is different from the height of each of adjacent sub-unit cells in the plurality of sub-unit cells of the same unit cell. The plurality of unit cells includes at least one base unit cell and other unit cells that are not the base unit cell, and each of the non-base unit cells in the plurality of unit cells is a height-translated version of the base unit cell relative to the common plane.

[0008] Some implementations include one or more of the following features. For example, in some cases, each of the height-translated versions of the base unit cell corresponds to a respective phase shift at the operating wavelength. Further, in some cases, each of the respective phase shifts is a respective integer multiple of (½)π at the operating wavelength. In some implementations, the plurality of sub-unit heights spans 4, 8, or 16 discrete levels relative to the common plane.

[0009] In some implementations, adjacent ones of the plurality of sub-unit cells in the same unit cell have different heights corresponding to respective phase shifts equal to integer multiples of (½)π at the operating wavelength.

[0010] The present disclosure also describes a diffractive optical element including a plurality of unit cells distributed on a common plane and composed of an optical material. Each unit cell in the plurality of unit cells includes a plurality of sub-unit cells, the plurality of sub-unit cells being arranged to provide an optical effect to incident light of a predetermined operating wavelength. Each of the plurality of sub-unit cells in each particular unit cell of the plurality of unit cells has a sub-unit height that differs from the height of each of adjacent sub-unit cells in the plurality of sub-unit cells of the same unit cell. The plurality of unit cells includes at least one base unit cell and other unit cells that are not the base unit cell, and each of the non-base unit cells in the plurality of unit cells is a phase-wrapped version of a height-translated version of the base unit cell relative to the common plane.

[0011] Some implementations include one or more of the following features. For example, in some cases, a height difference between any two of the subunits in the diffractive optical element corresponds to a respective phase shift of 2π or less at the operating wavelength. Further, in some cases, each of the respective phase shifts is a respective integer multiple of ½π at the operating wavelength. In some implementations, the plurality of subunit heights span 4, 8, or 16 discrete levels relative to the common plane.

[0012] In some implementations, adjacent ones of the plurality of sub-unit cells in the same unit cell have different heights corresponding to respective phase shifts equal to integer multiples of (½)π at the operating wavelength.

[0013] In some implementations, the optical effect is substantially diffuse lighting. Some implementations include one or more of the following advantages. For example, the technique can be relatively computationally efficient, which in some cases can be advantageous in terms of feasibility, design time, and numerical techniques (e.g., full-wave solvers, non-FFT-based scalar propagation, freeform surface shaping). Furthermore, introducing height translation to the unit cells can help counteract diffraction that would result from distributing the unit cells periodically across a surface. Such diffraction can destroy the diffuser effect. That is, distributing the unit cells periodically across a surface can cause the unit cells to interfere with each other, resulting in a grating effect, which destroys the diffusing properties and replaces them with high-intensity diffraction spots. Introducing height translation to the unit cells obviates this problem.

[0014] Additionally, phase wrapping can help reduce the number of levels in the resulting DOE design, which in turn can reduce the number of etching steps required during the manufacturing process.

[0015] This disclosure also describes modules that include a diffractive optical element. The module may include a light-emitting component, a light-sensing component, or both a light-emitting component and a light-sensing component. The diffractive optical element may be positioned to intersect an emitted or incident light wave and to modify one or more properties of the emitted or incident light wave as it passes through the diffractive optical element.

[0016] Other aspects, features, and advantages will become apparent from the following detailed description, the accompanying drawings, and the appended claims. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram showing an example of a DOE structure. [Figure 2] FIG. 1 illustrates an example of a unit cell for designing a DOE. [Figure 3] FIG. 3 illustrates an example of a periodic distribution of the unit cells of FIG. 2 across a common plane. [Figure 4] FIG. 4 shows a height-translated version of the unit cell of FIG. 3. [Figure 5A] FIG. 5 shows an example of a prototype unit cell based on the example of FIG. 4. [Figure 5B] FIG. 5B illustrates a phase-wrapped version of the prototype unit cell of FIG. 5A. [Figure 6] FIG. 5 shows a phase-wrapped version of the height-translated unit cell of FIG. 4. [Figure 7] FIG. 1 illustrates an example of an optoelectronic module incorporating a DOE according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0018] Detailed Description FIG. 1 shows an example of a DOE, such as a diffuser or other beam-shaping element. In some implementations, as shown in FIG. 1, DOE 10 includes a multi-level (e.g., stepped) structure having N levels, where N is at least 2 (e.g., 4, 8, or 16). Examples of suitable materials for DOE 10 include silicon, polysilicon, fused silica, aluminum oxide (Al2O3), metals, dielectrics, and / or semiconductors. Materials for DOE 10 can be selected, for example, based on having a particular refractive index at a specified operating wavelength (e.g., in the infrared or visible range).

[0019] One of the initial tasks in fabricating a DOE is to determine a pixel or other layout design based on the desired optical performance and design criteria of the optical element. In this context, a pixel refers to the smallest building block used in optical design. Typically, each pixel in a design may have, for example, a regular polygon (e.g., a rectangle or square) and its sides may have dimensions of approximately a few hundred nanometers (nm) or less. The layout design may include pixel layouts corresponding to individual DOEs as well as an overall layout for wafer-level production. The pixels within a DOE structure may have different depths. Thus, the pixel layout design may include multiple levels, each corresponding to a different depth. In some cases, there may be as many as four, eight, or even sixteen different levels, with the specific number of levels depending on the optical performance and optical functions required for a particular application. The pixel layout design includes the respective patterns or other layouts of pixels for each level and may include, for example, microstructures and / or nanostructures. A master tool is then prepared based on the pixel layout design. Thus, the master tool may include a multi-level structured surface corresponding to the pixel layout design, which can be transferred (e.g., by replication) to other materials.

[0020] 2-6 illustrate operations in a process for designing a DOE. As shown in FIG. 2, a four-level unit cell 20 includes a base 21. In the illustrated example, the unit cell 20 includes subunits 22A, 22B, 22C, 22D, and 22E, each of which defines a contiguous area of ​​the unit cell 20 and extends to a height defined by a respective one of the four levels. The height of each level of the unit cell 20 corresponds to a respective phase shift at the operating wavelength for which the DOE is designed. Thus, in the illustrated example, subunits 22A and 22D extend to a first height corresponding to a first phase shift of (3 / 2)π. Similarly, subunit 22E extends to a second height corresponding to a second phase shift of π, subunit 22C extends to a third height corresponding to a third phase shift of (½)π, and subunit 22B extends to a fourth height corresponding to a fourth phase shift of 0. Depending on the design, the number and arrangement of subunits may vary. Additionally, depending on the design, the unit cell may have a different number of levels (e.g., 2, 8, 16).

[0021] Next, as shown in Figure 3, the design process may include distributing unit cells 20 periodically across the surface designated for the DOE. Thus, at this stage, the design includes a one- or two-dimensional pattern of unit cells, each identical to unit cell 20. While Figure 3 shows only seven unit cells (i.e., unit cells 20, 20A-20F), the design may have many more unit cells distributed across the area designated for the DOE. For example, in some cases, the design may include a distribution of approximately 50 x 50 unit cells.

[0022] The periodic distribution of unit cells 20 across the surface tends to cause diffraction, which can result in degradation or loss of the diffuser effect. To counteract such diffraction, a subsequent operation in the design of the DOE involves introducing height translations for at least some of the unit cells distributed across the surface, where the height translations of the unit cells correspond to respective phase translations at the intended operating wavelength for the DOE. That is, as shown in the example of FIG. 4, the heights of at least some of the unit cells are translated by amounts corresponding to a phase shift of (½)π, (−½)π, π, or −π at the operating wavelength.

[0023] In FIG. 4 , unit cells 20C and 20F are translated upward by an amount corresponding to a phase shift of π, while unit cell 20D is shifted upward by an amount corresponding to a phase shift of (½)π. On the other hand, unit cells 20A and 20E are translated downward by an amount corresponding to a phase shift of (−½)π. Unit cells 20A and 20B are not translated upward or downward. In general, the selection of which unit cells to translate and whether to translate upward or downward for a given unit cell can be made randomly. In some implementations, the height translation can correspond to a different phase shift than those described above. Introducing height translation to the unit cells can help cancel out diffraction that would result from distributing the unit cells periodically across a surface.

[0024] Another consequence of the height translations for the unit cells described above in connection with FIG. 4 is that the number of levels in a DOE design can increase to five or more. That is, in the example of FIG. 4, the subunits of the unit cells have at least seven different heights (i.e., corresponding to −π, (−½)π, 0π, (½)π, π, (3½)π, 2π, and (5½)π). In some implementations, having a larger number of levels can provide a more robust design. However, increasing the number of levels can also increase the complexity of the manufacturing process for the DOE. Therefore, in some implementations, it is desirable to perform additional operations to reduce the number of levels in the final DOE design. As described below, one technique for performing such operations employs phase wrapping.

[0025] Phase wrapping can be introduced to translate height variations between unit cells into unit cells with sub-unit structures having heights within a range corresponding to a specified phase range (e.g., 0π to 2π) at the operating wavelength. That is, after introducing height translation into a unit cell, the heights of individual sub-units corresponding to phase values ​​outside the specified range (e.g., outside the range of 0π to 2π) are folded back to heights corresponding to phase values ​​within the specified range (e.g., 0π to 2π). Figures 5A and 5B, described below, show examples of phase wrapping.

[0026] Figure 5A shows four prototype unit cells corresponding to the various translated unit cells in Figure 4. The first prototype unit cell corresponds to translated unit cells 20C and 20F in Figure 4, the second prototype unit cell corresponds to translated unit cell 20D in Figure 4, the third prototype unit cell corresponds to translated unit cells 20 and 20B in Figure 4, and the fourth prototype unit cell corresponds to translated unit cells 20C and 20E in Figure 4. During phase wrapping, each sub-unit (in any of the prototype unit cells) having a height corresponding to a phase less than 0π is increased by a height corresponding to a phase shift of 2π. Similarly, each sub-unit (in any of the prototype unit cells) having a height corresponding to a phase greater than or equal to 2π is decreased by a height corresponding to a phase shift of -2π.

[0027] For example, the leftmost prototype unit cell in FIG. 5A corresponds to unit cells 20C and 20F in FIG. 4 and includes five subunits 30A, 30B, 30C, 30D, and 30E, each with heights of (5 / 2)π, π, (3 / 2)π, (5 / 2)π, and 2π, respectively. The height of the first subunit 30A corresponds to a phase of 2π or greater. Thus, phase wrapping reduces the height of the first subunit to a height corresponding to a phase of 0π, as shown by subunit 30a in FIG. 5B. The heights of the second and third subunits 30B and 30C correspond to phases within a defined range (i.e., 0π to 2π), and therefore the heights of these subunits remain unchanged (see subunits 30b and 30c in FIG. 5B). The heights of the fourth and fifth subunits 30D and 30E correspond to a phase of 2π or greater. Thus, phase wrapping reduces the height of the fourth subunit to a height corresponding to a phase of (½)π, as shown by subunit 30d in FIG. 5B. Similarly, phase wrapping reduces the height of the fifth subunit to a height corresponding to a phase of 0π, as shown by subunit 30e in FIG. 5B. As a result of phase wrapping, the prototype unit cells of FIG. 5A corresponding to unit cells 20C and 20F are transformed into phase-wrapped prototype unit cell 32A, as shown in FIG. 5B.

[0028] Similarly, the prototype unit cell of FIG. 5A corresponding to unit cell 20D is transformed into phase-wrapped prototype unit cell 32B, as shown in FIG. 5B. Similarly, the prototype unit cell of FIG. 5A corresponding to unit cells 20 and 20B is transformed into phase-wrapped prototype unit cell 32C, as shown in FIG. 5B. Similarly, the prototype unit cell of FIG. 5A corresponding to unit cells 20A and 20E is transformed into phase-wrapped prototype unit cell 32D, as shown in FIG. 5B.

[0029] Next, unit cells 20, 20A-20F of FIG. 4 are replaced with phase-wrapped prototype unit cells 32A-32D, respectively. That is, unit cell 20 is replaced with prototype unit cell 32C, unit cell 20A is replaced with prototype unit cell 32D, unit cell 20B is replaced with prototype unit cell 32C, unit cell 20C is replaced with prototype unit cell 32A, unit cell 20D is replaced with prototype unit cell 32B, unit cell 20E is replaced with prototype unit cell 32D, and unit cell 20F is replaced with prototype unit cell 32A. The result is shown in FIG. 6, in which unit cells 20 and 20A-20F of FIG. 4 have been converted into phase-wrapped unit cells 20'' and 20a-20f, respectively.

[0030] A DOE design based on the phase-wrapped unit cell of Figure 6 can be realized using only four separate levels (i.e., fewer than would be required for the unit cell shown in Figure 4). By folding the DOE structure back to the original number of levels (four in this example), the manufacturing process for the DOE can be simplified.

[0031] As mentioned above, in some cases, a master tool can be prepared based on the resulting pixel layout design (e.g., the layout design resulting after random height translation as shown in FIG. 4 or the layout design resulting after phase wrapping as shown in FIG. 6). The master tool can include a multi-level structured surface corresponding to the pixel layout design. The structured surface can then be transferred (e.g., by replication) to a substrate to fabricate DOEs, for example, on a mass production scale.

[0032] In some cases, for example, additive lithography processes can be used to create the various levels of a master tool design. Additive lithography techniques allow for careful control of the resist exposure and reflow processes to create master tools for complex multi-level optical elements. Optical designs can be converted into multi-level diffractive structures, which can then be divided into multiple masking patterns.

[0033] In some implementations, additive lithography techniques include depositing a first layer of resist on the top surface of a wafer (e.g., by spin coating) and selectively exposing the resist layer using a first mask via a lithography technique, such as electron beam lithography (EBL). The exposed portions of the resist layer are then developed and removed, leaving selected areas of the wafer surface uncovered by the resist. Next, the wafer is etched from the wafer surface to form openings to a first depth in the areas of the wafer not covered by the resist. The remaining portions of the resist may then be removed. By repeating the above steps with additional layers of resist and masks, different levels in the DOE design can be formed. Combining different lithography and etching processes results in multiple regions of different depths corresponding to the different levels required for the master tool. The details of the various masks used for the lithography and etching steps can be specified based on the pixel layout design. In this manner, a master tool can be fabricated based on the pixel layout design described above.

[0034] For example, after fabrication of a master tool, the master tool can be used to fabricate one or more (negative) sub-masters or replicas, which can then be used directly or indirectly to replicate DOEs, e.g., as part of a mass production manufacturing process. DOE fabrication may optionally be performed at the wafer level, where tens, hundreds, or thousands of DOEs are replicated in parallel using the same sub-master or other tool derived from the master. In some cases, the structured elements of the master (or sub-master) are replicated in a liquid or plastically deformable material, which is then cured to dimensionally stabilize the structured elements, and the structured elements (e.g., DOEs) are removed. These replicating, curing, and removal steps are repeated across different portions of the substrate to form replicas of the same structured elements.

[0035] In some implementations, instead of using a master tool to replicate the DOE elements, the DOE structures can be etched directly into the substrate for the DOE elements based on the pixel layout design.

[0036] DOEs can be fabricated using the techniques described above. For example, in some cases, DOEs fabricated according to the techniques described above include a plurality of periodically repeating unit cells, each unit cell being composed of an optical material and distributed across a common plane. Each unit cell in the plurality of unit cells includes a plurality of sub-unit cells, the plurality of sub-unit cells being arranged to provide an optical effect to incident light of a predetermined operating wavelength. Each of the plurality of sub-unit cells in each particular unit cell of the plurality of unit cells has a sub-unit height that differs from the height of each of adjacent sub-unit cells in the plurality of sub-unit cells of the same unit cell. The plurality of unit cells includes at least one base unit cell and other unit cells that are not the base unit cell, and each of the non-base unit cells in the plurality of unit cells is a height-translated version of the base unit cell relative to the common plane.

[0037] In some implementations, each of the height-translated versions of the base unit cell corresponds to a respective phase shift at the operating wavelength. For example, in some cases, each of the respective phase shifts is a respective integer multiple of ½π at the operating wavelength. In some cases, adjacent sub-unit cells of the plurality of sub-unit cells in the same unit cell have different heights corresponding to respective phase shifts equal to integer multiples of ½π at the operating wavelength.

[0038] In some implementations, the DOE includes a plurality of unit cells, optionally distributed on a common plane and composed of an optical material. Each unit cell in the plurality of unit cells includes a plurality of sub-unit cells, the plurality of sub-unit cells being arranged to provide an optical effect to incident light of a predetermined operating wavelength. Each of the plurality of sub-unit cells in each particular unit cell of the plurality of unit cells has a sub-unit height that is different from the height of each of adjacent sub-unit cells of the plurality of sub-unit cells in the same unit cell. The plurality of unit cells includes at least one base unit cell and other unit cells that are not the base unit cell, and each of the non-base unit cells of the plurality of unit cells is a phase-wrapped version of a height-translated version of the base unit cell relative to the common plane.

[0039] In some cases, the height difference between any two of the sub-units in the diffractive optical element corresponds to a respective phase shift of less than or equal to 2π at the operating wavelength. Further, in some cases, each of the respective phase shifts is a respective integer multiple of ½π at the operating wavelength. In some implementations, the heights of adjacent sub-unit cells of the plurality of sub-unit cells in the same unit cell differ by an amount corresponding to a respective phase shift equal to an integer multiple of ½π at the operating wavelength.

[0040] In some implementations of DOEs, the optical effect is substantially the product of diffuse illumination. In some cases, the operating wavelength is in the infrared portion of the electromagnetic spectrum. The optical material can be, for example, silicon, silicon oxide, sapphire, fused silica, or any metal, dielectric, or polymer with suitable material properties to produce the optical effect.

[0041] The height of the subunits in a particular one of the DOEs can span an integer number of discrete levels, for example. In some implementations, the height of the subunits spans four discrete levels relative to a common plane. In other implementations, the height of the subunits spans eight or sixteen discrete levels relative to a common plane. Some implementations may incorporate other numbers of discrete levels.

[0042] In some implementations, a DOE as described in this disclosure may be integrated into an optical or optoelectronic system that includes, for example, a device operable to emit or detect light at an operating wavelength λ. As shown in FIG. 7 , module 400 includes a substrate 402 and a light-emitting component 404 coupled to or integrated with substrate 402. Light-emitting component 404 may include, for example, a laser (e.g., a vertical-cavity surface-emitting laser), a light-emitting diode, or a laser diode. Light (e.g., infrared or visible light) 406 generated by light-emitting component 404 passes through a housing and is further transmitted to optical device 408 (e.g., a DOE described in this disclosure). Optical device 408 is operable to interact with light 406 such that modified light 410 is transmitted out of module 400. For example, module 400 may use optical device 408 to generate one or more of structured light, diffused light, or patterned light. The housing may include, for example, a spacer 412 that separates the light-emitting component 404 and / or the substrate 402 from the optical device 408 .

[0043] In some implementations, a light-emitting component is mounted to direct incident light into the unit cell of the DOE, and the light-emitting component is operable to emit incident light at an operating wavelength and to provide an optical effect.

[0044] In some implementations, module 400 in FIG. 7 is a light-sensing module (e.g., an ambient light sensor), component 404 is a light-sensitive component (e.g., a photodiode, pixel, image sensor), light 406 enters module 400, and light 410 is modified by optical device 408. For example, optical device 408 (e.g., a DOE described in this disclosure) can focus patterned light onto light-sensitive component 404. In some implementations, module 400 can include both a light-emitting component and a light-sensing component. In some implementations, the light-sensitive component is operable to collect reflected light from a scene or object, the reflected light being generated by illuminating the scene or object with an optical effect. For example, module 400 can emit light, which interacts with its environment and is then received again by module 400, allowing module 400 to function, for example, as a proximity sensor or a three-dimensional mapping device. The above-described modules can be part of, for example, a time-of-flight camera or an active stereo camera. The module may be integrated into a system, for example a mobile phone, a laptop, a television, a wearable device, or a car.

[0045] The optical device 408 (e.g., a DOE as described in this disclosure) may provide advantages to the module 400 compared to a module that does not include the optical device 408 as described in this disclosure. For example, the optical properties of the optical device 408 and the module 400 may be improved.

[0046] Various aspects of the subject matter and functional operations described herein (e.g., relating to the design and / or manufacture of DOEs) can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, or in combinations of one or more of these. Thus, some aspects of the subject matter described herein can be implemented as one or more computer program products, i.e., as one or more modules of computer program instructions encoded on a computer-readable medium for execution by or controlling the operation of a data processing apparatus. The computer-readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter that provides a machine-readable propagated signal, or one or more combinations of these. In addition to hardware, the apparatus can include code that creates an execution environment for the computer program, e.g., code that constitutes processor firmware.

[0047] Various modifications may be made within the spirit of the disclosure, and accordingly, other implementations are within the scope of the following claims.

Claims

1. 1. An apparatus comprising: a diffractive optical element, the diffractive optical element comprising: the optical element includes a plurality of unit cells distributed on a common plane and made of an optical material, each unit cell in the plurality of unit cells including a plurality of sub-unit cells, the plurality of sub-unit cells being arranged to produce an optical effect on incident light of a predetermined operating wavelength, and each of the plurality of sub-unit cells in each particular unit cell of the plurality of unit cells having a sub-unit height that is different from the heights of each of adjacent sub-unit cells in the same unit cell; the plurality of unit cells includes at least one base unit cell and other unit cells that are not the base unit cells, each of the plurality of unit cells that are not the base unit cells being a phase-wrapped version of a height-translated version of the base unit cell relative to the common plane; the phase wrapping is a process of folding the height of each sub-unit cell to a height corresponding to a phase value within a specified phase range at the operating wavelength; Device.

2. 2. The apparatus of claim 1, wherein a height difference between any two of the subunits in the diffractive optical element corresponds to a respective phase shift of less than or equal to 2π at the operating wavelength.

3. 3. The apparatus of claim 2, wherein each of the respective phase shifts is a respective integer multiple of (1 / 2)π at the operating wavelength.

4. 4. The apparatus of claim 1, wherein the plurality of sub-unit heights span four discrete levels relative to the common plane.

5. The apparatus of claim 1 , wherein the plurality of sub-unit heights span eight discrete levels relative to the common plane.

6. The apparatus of claim 1 , wherein the plurality of sub-unit heights spans 16 discrete levels relative to the common plane.

7. 10. The device of claim 1, wherein adjacent ones of the plurality of sub-unit cells in the same unit cell have heights that differ by amounts corresponding to respective phase shifts equal to an integer multiple of (½)π at the operating wavelength.

8. 8. The device of claim 1, wherein the optical effect is substantially diffuse lighting.

9. further comprising a light-emitting component; 9. The device of claim 1, wherein the light emitting component is mounted to direct the incident light towards the plurality of unit cells, the light emitting component being operable to emit the incident light at the operating wavelength.

10. 10. The apparatus of claim 9, wherein the light emitting component comprises at least one of a light emitting diode, a laser diode, or a vertical cavity surface emitting laser.

11. further comprising a photosensitive component; 11. The apparatus of claim 9 or 10, wherein the light-sensitive component is operable to collect reflected light from a scene or object, the reflected light being generated by illuminating the scene or object with the optical effect.

12. 12. The device of claim 1, wherein the operating wavelength is in the infrared portion of the electromagnetic spectrum.

13. 13. The apparatus of claim 1, wherein the plurality of unit cells distributed on a common plane comprises a plurality of periodically repeating unit cells distributed on the common plane.

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