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{{see also|Terms|Technical Terms}}
{{see also|Terms|Technical Terms}}
[[Microlens Arrays]] ('''MLAs'''), sometimes called '''micro-lens arrays''' or '''lenslet arrays''', are [[optical component]]s consisting of multiple small [[lens]]es (often called '''lenslets''') arranged in a one-dimensional or two-dimensional pattern on a supporting substrate<ref name="RPPhotonics">Microlens arrays - fabrication, parameters, applications - RP Photonics</ref><ref name="ShanghaiOptics">Microlens Array - Shanghai Optics</ref><ref name="TEMICON">Microlens Arrays, MLA - temicon</ref><ref name="PhotonicsDict">Microlens array - Photonics Dictionary</ref>. Each lenslet typically has a diameter significantly less than 10 millimeters, often ranging from tens or hundreds of micrometers down to just a few micrometers, or even sub-micrometer in specialized cases<ref name="RPPhotonics"/><ref name="ShanghaiOptics"/><ref name="Syntec">Microlens Arrays | Single Point Diamond Turning - Syntec Optics</ref><ref name="StandardMLA">Standard Microlens Array - Bön Optics (appears to be distributor for brand, original mfg unclear)</ref>. The array pattern is commonly periodic, such as a square or hexagonal grid, but can also be linear, rectangular, circular, or even random/stochastic for specific applications<ref name="RPPhotonics"/><ref name="ShanghaiOptics"/><ref name="TEMICON"/><ref name="StandardMLA"/>. An array can contain thousands, millions, or even more individual lenslets<ref name="RPPhotonics"/><ref name="AvantierIntro">Introducing Microlens Arrays - Avantier Inc.</ref><ref name="OpticalComponents">Detailed Insights in Microlens Array Products - OPTICAL COMPONENTS</ref>.
[[Microlens Arrays]] ('''MLAs'''), sometimes called '''micro-lens arrays''' or '''lenslet arrays''', are [[optical component]]s consisting of multiple small [[lens]]es (often called '''lenslets''') arranged in a one-dimensional or two-dimensional pattern on a supporting substrate<ref name="RPPhotonics">“Microlens Arrays – fabrication, parameters, applications,” RP Photonics Encyclopedia, accessed 3 May 2025, https://www.rp-photonics.com/microlens_arrays.html</ref>
<ref name="ShanghaiOptics">“Microlens Array,” Shanghai Optics product page, accessed 3 May 2025, https://www.shanghai-optics.com/components/micro-optics/microlens-arrays/</ref>
<ref name="TEMICON">“Microlens Arrays (MLA),” Temicon GmbH, accessed 3 May 2025, https://www.temicon.com/products/micro-nano-structures/microlens-arrays</ref><ref name="PhotonicsDict">“Microlens Array – Definition,” Photonics Dictionary, Photonics Media, accessed 3 May 2025, https://www.photonics.com/EDU/microlens_array/d8465</ref>. Each lenslet typically has a diameter significantly less than 10 millimeters, often ranging from tens or hundreds of micrometers down to just a few micrometers, or even sub-micrometer in specialized cases<ref name="RPPhotonics"/><ref name="ShanghaiOptics"/><ref name="Syntec">“Microlens Arrays | Single‑Point Diamond Turning,” Syntec Optics, accessed 3 May 2025, https://syntecoptics.com/microlens-arrays/</ref><ref name="StandardMLA">“Fused Silica Microlens Arrays,” Thorlabs, accessed 3 May 2025, https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=2861</ref>. The array pattern is commonly periodic, such as a square or hexagonal grid, but can also be linear, rectangular, circular, or even random/stochastic for specific applications<ref name="RPPhotonics"/><ref name="ShanghaiOptics"/><ref name="TEMICON"/><ref name="StandardMLA"/>. An array can contain thousands, millions, or even more individual lenslets<ref name="RPPhotonics"/><ref name="AvantierIntro">“Introducing Microlens Arrays,” Avantier Inc. Knowledge Center, 14 Jun 2024, accessed 3 May 2025, https://avantierinc.com/resources/knowledge-center/introducing-microlens-arrays/</ref><ref name="OpticalComponents">“Comprehensive Overview of Custom, High‑Performance Microlens Arrays,” Chineselens Optics, 30 Jul 2024, accessed 3 May 2025, https://chineselens.com/custom-high-performance-microlens-arrays/</ref>.


MLAs are characterized by their potential for miniaturization, integration into complex systems, and considerable design flexibility<ref name="StandardMLA"/><ref name="ApolloOptics">Injection-molded microlens arrays - Apollo Optical Systems</ref>. They have become a critical enabling technology in [[virtual reality]] (VR) and [[augmented reality]] (AR) devices, where they help solve numerous optical challenges related to [[field of view]], display brightness, visual quality, and [[form factor]]<ref name="Bote">Microlens Arrays: Versatile and Efficient Optical Solutions - Bote Optics Singapore</ref><ref name="OpticalComponents"/><ref name="BrightView">AR-VR - Augmented and Virtual Reality - BrightView Technologies, Inc.</ref>. Beyond VR/AR, they are employed across diverse fields, including [[telecommunication]]s (fiber coupling, optical switches), [[medical imaging]] (endoscopy, [[Optical Coherence Tomography|OCT]]), [[solar energy]] (concentrators), automotive [[LiDAR]], [[laser]] beam homogenization and shaping, [[sensor]] technology ([[Shack-Hartmann wavefront sensor]]s, image sensors), and [[consumer electronics]] (projectors, cameras, displays)<ref name="OpticalComponents"/><ref name="ShanghaiOptics"/><ref name="AvantierIntro"/><ref name="StandardMLA"/><ref name="Bote"/><ref name="GDOptics">Efficient and precise production of microlens arrays using precision glass molding - GD Optics (PDF)</ref>. Microlens arrays play an increasingly important role in next-generation display systems, [[waveguide]] technologies, [[eye tracking]] systems, [[light field display]] technologies, environmental [[sensing]], and [[computational imaging]] applications within the immersive technology sector<ref name="PatentlyApple">Apple Invents an optical system with Microlens Array Projectors to advance time-of-flight sensing for Face ID, delivering more realistic AR/VR features+ - Patently Apple (July 21, 2022)</ref><ref name="BrightView"/><ref name="UltraThinMLA">(2024-03-19) Imaging with high resolution and wide field of view based on an ultrathin microlens array - AIP Publishing</ref><ref name="AvantierMicroOptics">Types of Micro Optics - Avantier Inc.</ref>.
MLAs are characterized by their potential for miniaturization, integration into complex systems, and considerable design flexibility<ref name="StandardMLA"/><ref name="ApolloOptics">“Injection‑Molded Microlens Arrays,” Apollo Optical Systems, accessed 3 May 2025, https://www.apollooptical.com/microlens-arrays</ref>. They have become a critical enabling technology in [[virtual reality]] (VR) and [[augmented reality]] (AR) devices, where they help solve numerous optical challenges related to [[field of view]], display brightness, visual quality, and [[form factor]]<ref name="Bote">“Microlens Arrays: Versatile and Efficient Optical Solutions,” Bote Optics Singapore, 18 Aug 2024, accessed 3 May 2025, https://www.bote.com.sg/knowledges/microlens-arrays/</ref><ref name="OpticalComponents"/><ref name="BrightView">“AR‑VR – Augmented and Virtual Reality,” BrightView Technologies, accessed 3 May 2025, https://www.brightviewtechnologies.com/ar-vr</ref>. Beyond VR/AR, they are employed across diverse fields, including [[telecommunication]]s (fiber coupling, optical switches), [[medical imaging]] (endoscopy, [[Optical Coherence Tomography|OCT]]), [[solar energy]] (concentrators), automotive [[LiDAR]], [[laser]] beam homogenization and shaping, [[sensor]] technology ([[Shack-Hartmann wavefront sensor]]s, image sensors), and [[consumer electronics]] (projectors, cameras, displays)<ref name="OpticalComponents"/><ref name="ShanghaiOptics"/><ref name="AvantierIntro"/><ref name="StandardMLA"/><ref name="Bote"/><ref name="GDOptics">“Efficient and Precise Production of Microlens Arrays Using Precision Glass Molding,” GD Optics white paper (PDF), Jan 2024, accessed 3 May 2025, https://gdoptics.de/wp-content/uploads/2024/01/GDOPTICS_WHITEPAPER_EN.pdf</ref>. Microlens arrays play an increasingly important role in next-generation display systems, [[waveguide]] technologies, [[eye tracking]] systems, [[light field display]] technologies, environmental [[sensing]], and [[computational imaging]] applications within the immersive technology sector<ref name="PatentlyApple">F. Patently, “Apple Invents an Optical System with Microlens Array Projectors to Advance Time‑of‑Flight Sensing for Face ID,” Patently Apple, 21 Jul 2022, accessed 3 May 2025, https://www.patentlyapple.com/2022/07/apple-invents-an-optical-system-with-microlens-array-projectors-to-advance-time-of-flight-sensing-for-face-id-delivering-mor.html</ref><ref name="BrightView"/><ref name="UltraThinMLA">Y. Zhang et al., “Imaging with High Resolution and Wide Field of View Based on an Ultrathin Microlens Array,” *Physical Review Applied* 21 (3): 034035 (2024), DOI 10.1103/PhysRevApplied.21.034035</ref><ref name="AvantierMicroOptics">Types of Micro Optics - Avantier Inc.</ref>.


==Characteristics==
==Characteristics==
Microlens arrays possess several key parameters that define their function and application suitability:
Microlens arrays possess several key parameters that define their function and application suitability:
*'''Materials:''' MLAs can be fabricated from a wide range of optical materials, including various types of [[glass]] (like BK7), [[UV]]-grade [[fused silica]], [[silicon]], [[quartz]], [[zinc selenide]] (ZnSe), [[calcium fluoride]], and numerous optical [[polymer]]s such as [[PMMA]], [[polycarbonate]], and PET<ref name="Syntec"/><ref name="StandardMLA"/><ref name="OpticalComponents"/><ref name="BrightView"/>. The material choice is critical and depends on the target [[wavelength]] range (from deep UV to far [[infrared]]), required [[durability]], thermal stability, compatibility with [[manufacturing]] processes, and cost<ref name="OpticalComponents"/><ref name="Syntec"/><ref name="EdmundOptics">Microlens Arrays - Edmund Optics</ref>. Fused silica, for example, offers excellent transmission from UV (around 193nm) to near-infrared (up to 3µm)<ref name="Syntec"/><ref name="AvantierIntro"/><ref name="EdmundOptics"/>. Silicon is suitable for infrared applications (approx. 1.2µm to 5µm) and integrates well with [[MEMS]] fabrication<ref name="OpticalComponents"/><ref name="Syntec"/>.
*'''Materials:''' MLAs can be fabricated from a wide range of optical materials, including various types of [[glass]] (like BK7), [[UV]]-grade [[fused silica]], [[silicon]], [[quartz]], [[zinc selenide]] (ZnSe), [[calcium fluoride]], and numerous optical [[polymer]]s such as [[PMMA]], [[polycarbonate]], and PET<ref name="Syntec"/><ref name="StandardMLA"/><ref name="OpticalComponents"/><ref name="BrightView"/>. The material choice is critical and depends on the target [[wavelength]] range (from deep UV to far [[infrared]]), required [[durability]], thermal stability, compatibility with [[manufacturing]] processes, and cost<ref name="OpticalComponents"/><ref name="Syntec"/><ref name="EdmundOptics">Microlens Arrays - Edmund Optics</ref>. Fused silica, for example, offers excellent transmission from UV (around 193nm) to near-infrared (up to 3µm)<ref name="Syntec"/><ref name="AvantierIntro"/><ref name="EdmundOptics"/>. Silicon is suitable for infrared applications (approx. 1.2µm to 5µm) and integrates well with [[MEMS]] fabrication<ref name="OpticalComponents"/><ref name="Syntec"/>.
*'''Lenslet Shape and Profile:''' Individual lenslets can have various shapes, including circular, square, or hexagonal footprints<ref name="ShanghaiOptics"/><ref name="StandardMLA"/>. Their optical surfaces can be spherical, [[aspheric lens|aspherical]], cylindrical, or even freeform<ref name="StandardMLA"/><ref name="OpticalComponents"/><ref name="TEMICON"/><ref name="IsuzuGlass">lens array - Isuzu Glass</ref>. Common profiles include<ref name="Article1Ref_Daly1990">Daly, D., Stevens, R. F., Hutley, M. C., & Davies, N. (1990). The manufacture of microlenses by melting photoresist. Measurement Science and Technology, 1(8), 759-766.</ref>:
*'''Lenslet Shape and Profile:''' Individual lenslets can have various shapes, including circular, square, or hexagonal footprints<ref name="ShanghaiOptics"/><ref name="StandardMLA"/>. Their optical surfaces can be spherical, [[aspheric lens|aspherical]], cylindrical, or even freeform<ref name="StandardMLA"/><ref name="OpticalComponents"/><ref name="TEMICON"/><ref name="IsuzuGlass">“Lens Array – Integrated Glass Molded Array,” Isuzu Glass, accessed 3 May 2025, https://www.isuzuglass.com/products/lens-integrated.html</ref>. Common profiles include<ref name="Article1Ref_Daly1990">Daly, D., Stevens, R. F., Hutley, M. C., & Davies, N. (1990). The manufacture of microlenses by melting photoresist. Measurement Science and Technology, 1(8), 759-766.</ref>:
** [[Plano-convex lens|Plano-convex]] (flat on one side, convex on the other)
** [[Plano-convex lens|Plano-convex]] (flat on one side, convex on the other)
** [[Bi-convex lens|Bi-convex]] (convex on both sides)
** [[Bi-convex lens|Bi-convex]] (convex on both sides)
Line 35: Line 37:
*'''Compact Magnifiers / Eyepieces:''' One key application is replacing bulky single-element eyepiece lenses (like traditional refractive lenses or even Fresnel lenses) with MLAs positioned between the [[microdisplay]] and the user's eye<ref name="PhotonicsArticle">(2023-05-10) Advanced Study of Optical Imaging Systems for Virtual Reality Head-Mounted Displays - Photonics</ref><ref name="PolGrating">(2025-01-02) Field of view and angular-resolution enhancement in microlens array type virtual reality near-eye display using polarization grating - Optica Publishing Group</ref><ref name="SuperlensMLA">Compact near-eye display system using a superlens-based microlens array magnifier - Optica Publishing Group (mentions MLA as magnifier)</ref>. Each lenslet magnifies a portion of the microdisplay image. This architecture holds the potential for significantly thinner and lighter [[Head-Mounted Display|HMDs]]<ref name="ThinVR">(2024-10-22) ThinVR: Heterogeneous microlens arrays for compact, 180 degree FOV VR near-eye displays - ResearchGate</ref><ref name="AzumaThinVR">ThinVR: Heterogeneous microlens arrays for compact, 180 degree FOV VR near-eye displays - Ronald Azuma (PDF of paper)</ref>.
*'''Compact Magnifiers / Eyepieces:''' One key application is replacing bulky single-element eyepiece lenses (like traditional refractive lenses or even Fresnel lenses) with MLAs positioned between the [[microdisplay]] and the user's eye<ref name="PhotonicsArticle">(2023-05-10) Advanced Study of Optical Imaging Systems for Virtual Reality Head-Mounted Displays - Photonics</ref><ref name="PolGrating">(2025-01-02) Field of view and angular-resolution enhancement in microlens array type virtual reality near-eye display using polarization grating - Optica Publishing Group</ref><ref name="SuperlensMLA">Compact near-eye display system using a superlens-based microlens array magnifier - Optica Publishing Group (mentions MLA as magnifier)</ref>. Each lenslet magnifies a portion of the microdisplay image. This architecture holds the potential for significantly thinner and lighter [[Head-Mounted Display|HMDs]]<ref name="ThinVR">(2024-10-22) ThinVR: Heterogeneous microlens arrays for compact, 180 degree FOV VR near-eye displays - ResearchGate</ref><ref name="AzumaThinVR">ThinVR: Heterogeneous microlens arrays for compact, 180 degree FOV VR near-eye displays - Ronald Azuma (PDF of paper)</ref>.
*'''Wide Field of View (FOV) Systems:''' To achieve ultra-wide FOVs (for example 180° horizontally, approaching the human visual system's range) while maintaining a compact form factor, researchers are exploring the use of curved MLAs paired with curved displays<ref name="PhotonicsArticle"/><ref name="ThinVR"/><ref name="AzumaThinVR"/>. In such wide-FOV systems, many lenslets are viewed significantly off-axis. To manage image quality (for example reduce distortion, maintain [[eye box]] size) across the entire FOV, heterogeneous MLAs are crucial. In these arrays, the properties (for example shape, focal length, tilt) of the lenslets are custom-designed and vary systematically across the array<ref name="ThinVR"/><ref name="AzumaThinVR"/>. Optimization algorithms are used to design these complex heterogeneous lenslet profiles<ref name="ThinVR"/><ref name="AzumaThinVR"/>.
*'''Wide Field of View (FOV) Systems:''' To achieve ultra-wide FOVs (for example 180° horizontally, approaching the human visual system's range) while maintaining a compact form factor, researchers are exploring the use of curved MLAs paired with curved displays<ref name="PhotonicsArticle"/><ref name="ThinVR"/><ref name="AzumaThinVR"/>. In such wide-FOV systems, many lenslets are viewed significantly off-axis. To manage image quality (for example reduce distortion, maintain [[eye box]] size) across the entire FOV, heterogeneous MLAs are crucial. In these arrays, the properties (for example shape, focal length, tilt) of the lenslets are custom-designed and vary systematically across the array<ref name="ThinVR"/><ref name="AzumaThinVR"/>. Optimization algorithms are used to design these complex heterogeneous lenslet profiles<ref name="ThinVR"/><ref name="AzumaThinVR"/>.
*'''[[Light Field Display]]s:''' MLAs are a cornerstone technology for creating near-eye light field displays<ref name="NvidiaLFD">Nvidia Near-Eye Light Field Display - LightField Forum</ref><ref name="NvidiaSupp">Supplementary Material: Near-Eye Light Field Displays - Research at NVIDIA (PDF)</ref><ref name="TAMULFD">Light-field Display Technical Deep Dive - Texas A&M College of Architecture (PDF)</ref><ref name="ResearchGateLFD">Design and simulation of a light field display - ResearchGate</ref>. By placing a precisely aligned MLA over a high-resolution microdisplay, the light rays originating from different pixels under each lenslet can be controlled in direction<ref name="NvidiaLFD"/><ref name="ResearchGateLFD"/>. Each lenslet projects a "micro-image" (sometimes called an elemental image or [[Hogel|hogel]]) composed of pixels underneath it, and effectively acts as a projector sending different information in different directions<ref name="TAMULFD"/><ref name="OpticaLFD">(2021-09-29) Examining the utility of pinhole-type screens for lightfield display - Optica Publishing Group</ref>. This allows the display to reconstruct a light field that approximates the light rays that would emanate from a real 3D scene. Crucially, this enables the viewer's eye to naturally change focus to different depths within the virtual scene, potentially resolving the [[vergence-accommodation conflict]] (VAC) that plagues conventional stereoscopic displays and causes eye strain<ref name="ElectrowettingLFD">Fabrication of an electrowetting liquid microlens array for a focus tunable integral imaging system - Optica Publishing Group</ref><ref name="Creal">VR IN FOCUS - Creal (PDF)</ref>. This technique is closely related to [[integral imaging]]<ref name="ResearchGateLFD"/><ref name="ElectrowettingLFD"/>. An early NVIDIA research prototype used 1280x720 OLED microdisplays with 1.0 mm pitch microlens arrays (focal length ~3.3 mm) to achieve a 29°x16° light field FOV<ref name="NvidiaSupp"/>. A key challenge remains the trade-off between spatial resolution (image sharpness) and angular resolution (number of views/[[depth cue]]s)<ref name="ResearchGateLFD"/><ref name="TAMULFD"/><ref name="Creal"/>.
*'''[[Light Field Display]]s:''' MLAs are a cornerstone technology for creating near-eye light field displays<ref name="NvidiaLFD">“Nvidia Near‑Eye Light Field Display,” LightField Forum, accessed 3 May 2025, https://lightfield-forum.com/light-field-camera-prototypes/nvidia-near-eye-light-field-display/</ref><ref name="NvidiaSupp">“Supplementary Material: Near‑Eye Light Field Displays,” NVIDIA Research (PDF), 2013, accessed 3 May 2025, https://research.nvidia.com/sites/default/files/pubs/2013-11_Near-Eye-Light-Field/NVIDIA-NELD-Supplement.pdf</ref><ref name="TAMULFD">“Light‑Field Display Technical Deep Dive,” FoVI3D / Texas A&M University (PDF), 2021, accessed 3 May 2025, https://www.arch.tamu.edu/app/uploads/2021/10/FoVI3D_DeepDrive.pdf</ref><ref name="ResearchGateLFD">A. Straßer, *Design and Simulation of a Light Field Display*, BSc thesis, Technical University of Munich, 2019, available at ResearchGate, accessed 3 May 2025, https://www.researchgate.net/publication/344414465_Design_and_simulation_of_a_light_field_display</ref>. By placing a precisely aligned MLA over a high-resolution microdisplay, the light rays originating from different pixels under each lenslet can be controlled in direction<ref name="NvidiaLFD"/><ref name="ResearchGateLFD"/>. Each lenslet projects a "micro-image" (sometimes called an elemental image or [[Hogel|hogel]]) composed of pixels underneath it, and effectively acts as a projector sending different information in different directions<ref name="TAMULFD"/><ref name="OpticaLFD">J. Kim et al., “Examining the Utility of Pinhole‑Type Screens for Lightfield Display,” *Optics Express* 29 (21): 33357‑33366 (2021), DOI 10.1364/OE.433357</ref>. This allows the display to reconstruct a light field that approximates the light rays that would emanate from a real 3D scene. Crucially, this enables the viewer's eye to naturally change focus to different depths within the virtual scene, potentially resolving the [[vergence-accommodation conflict]] (VAC) that plagues conventional stereoscopic displays and causes eye strain<ref name="ElectrowettingLFD">H. Lee et al., “Fabrication of an Electrowetting Liquid Microlens Array for a Focus‑Tunable Integral Imaging System,” *Optics Letters* 45 (2): 511‑514 (2020), DOI 10.1364/OL.377865</ref><ref name="Creal">VR IN FOCUS - Creal (PDF)</ref>. This technique is closely related to [[integral imaging]]<ref name="ResearchGateLFD"/><ref name="ElectrowettingLFD"/>. An early NVIDIA research prototype used 1280x720 OLED microdisplays with 1.0 mm pitch microlens arrays (focal length ~3.3 mm) to achieve a 29°x16° light field FOV<ref name="NvidiaSupp"/>. A key challenge remains the trade-off between spatial resolution (image sharpness) and angular resolution (number of views/[[depth cue]]s)<ref name="ResearchGateLFD"/><ref name="TAMULFD"/><ref name="Creal"/>.
*'''Efficiency, Brightness, and [[Screen-door effect]] Reduction:''' MLAs can improve the overall light efficiency and perceived quality of display systems. In projectors or backlit displays like [[LCD]]s, MLAs can be used to focus light specifically onto the active (transmitting) area of each pixel, reducing light absorption by the surrounding pixel structure (for example [[thin-film transistor]]s)<ref name="ShanghaiOptics"/><ref name="RPPhotonics"/>. This increases brightness and reduces power consumption<ref name="BrightView"/><ref name="ApolloOptics"/>. Manufacturers like Sony have applied MLAs over [[OLED]] microdisplays to increase peak luminance<ref name="DisplayDailySony">(Nov 2021) Emerging Display Technologies for the AR/VR Market - Display Daily</ref>. By directing light more effectively or magnifying the apparent pixel area, MLAs can also help reduce the visible "screen door effect" (the dark gaps between pixels)<ref name="Article1Ref_Lanman2013">Lanman, D., & Luebke, D. (2013). Near-eye light field displays. ACM Transactions on Graphics, 32(6), 1-10.</ref>. Furthermore, MLA-based eyepiece designs can offer inherently better light efficiency compared to polarization-dependent folded optical paths used in [[pancake lens]] designs. Pancake lenses achieve thin form factors by folding the optical path using [[polarizer]]s and [[half-mirror]]s, but this process typically results in very low light efficiency (often cited as 10-25%)<ref name="PolGrating"/><ref name="PancakeReview">(2024-12-09) Fabrication of Microlens Array and Its Application: A Review - ResearchGate (PDF)</ref><ref name="LightTransPancake">(2024-07-05) Catadioptric Imaging System Based on Pancake Lenses - LightTrans</ref><ref name="RedditPancake">What are pancake lenses? - Reddit (Sept 13, 2022)</ref><ref name="LimbakReddit">(2022-05-27) LIMBAK's freeform microlens array is thinner and much more efficient than pancake lenses for VR and MR - Reddit</ref>. Novel freeform MLA designs claim much higher efficiencies (for example 80%) while also achieving thin profiles<ref name="LimbakReddit"/>.
*'''Efficiency, Brightness, and [[Screen-door effect]] Reduction:''' MLAs can improve the overall light efficiency and perceived quality of display systems. In projectors or backlit displays like [[LCD]]s, MLAs can be used to focus light specifically onto the active (transmitting) area of each pixel, reducing light absorption by the surrounding pixel structure (for example [[thin-film transistor]]s)<ref name="ShanghaiOptics"/><ref name="RPPhotonics"/>. This increases brightness and reduces power consumption<ref name="BrightView"/><ref name="ApolloOptics"/>. Manufacturers like Sony have applied MLAs over [[OLED]] microdisplays to increase peak luminance<ref name="DisplayDailySony">(Nov 2021) Emerging Display Technologies for the AR/VR Market - Display Daily</ref>. By directing light more effectively or magnifying the apparent pixel area, MLAs can also help reduce the visible "screen door effect" (the dark gaps between pixels)<ref name="Article1Ref_Lanman2013">Lanman, D., & Luebke, D. (2013). Near-eye light field displays. ACM Transactions on Graphics, 32(6), 1-10.</ref>. Furthermore, MLA-based eyepiece designs can offer inherently better light efficiency compared to polarization-dependent folded optical paths used in [[pancake lens]] designs. Pancake lenses achieve thin form factors by folding the optical path using [[polarizer]]s and [[half-mirror]]s, but this process typically results in very low light efficiency (often cited as 10-25%)<ref name="PolGrating"/><ref name="PancakeReview">(2024-12-09) Fabrication of Microlens Array and Its Application: A Review - ResearchGate (PDF)</ref><ref name="LightTransPancake">(2024-07-05) Catadioptric Imaging System Based on Pancake Lenses - LightTrans</ref><ref name="RedditPancake">What are pancake lenses? - Reddit (Sept 13, 2022)</ref><ref name="LimbakReddit">(2022-05-27) LIMBAK's freeform microlens array is thinner and much more efficient than pancake lenses for VR and MR - Reddit</ref>. Novel freeform MLA designs claim much higher efficiencies (for example 80%) while also achieving thin profiles<ref name="LimbakReddit"/>.
*'''[[Waveguide]] Coupling:''' In AR [[waveguide]] displays, microlens arrays can potentially serve as [[in-coupling]] and [[out-coupling]] elements, efficiently directing light from miniature projectors (like [[microLED]] arrays) into thin waveguides and then out toward the user's eyes. Research suggests pixel-level collimating microlenses could narrow microLED emission angles for better waveguide injection, though adding fabrication complexity<ref name="WaveguideReview">(2023) Waveguide-based augmented reality displays: perspectives and challenges - eLight (SpringerOpen)</ref><ref name="Article1Ref_Kress2019">Kress, B. C., & Meyrueis, P. (2019). Applied digital optics: from micro-optics to nanophotonics. John Wiley & Sons.</ref>.
*'''[[Waveguide]] Coupling:''' In AR [[waveguide]] displays, microlens arrays can potentially serve as [[in-coupling]] and [[out-coupling]] elements, efficiently directing light from miniature projectors (like [[microLED]] arrays) into thin waveguides and then out toward the user's eyes. Research suggests pixel-level collimating microlenses could narrow microLED emission angles for better waveguide injection, though adding fabrication complexity<ref name="WaveguideReview">(2023) Waveguide-based augmented reality displays: perspectives and challenges - eLight (SpringerOpen)</ref><ref name="Article1Ref_Kress2019">Kress, B. C., & Meyrueis, P. (2019). Applied digital optics: from micro-optics to nanophotonics. John Wiley & Sons.</ref>.
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