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Created page with "{{Infobox optics | name = Pancake lenses | image = | caption = | type = Polarization‑based folded optical system for virtual reality (VR) and mixed reality (MR) head‑mounted displays | modules = Aspheric lenses, reflective polarizer films, quarter-wave plates, partial reflectors / polarizing beam splitters }} '''Pancake lenses''' (also called '''pancake optics''' or '''folded optics''') are compact catadioptri..."
 
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{{Infobox optics
{{Short description|Compact polarization-based optical system for VR/AR headsets}}
| name   = Pancake lenses
{{Infobox optical component
| image   =  
| name         = Pancake lenses
| caption =  
| image       =  
| type   = Polarization‑based folded optical system for [[virtual reality]] (VR) and [[mixed reality]] (MR) [[head-mounted display|head‑mounted displays]]
| caption     =  
| modules = Aspheric lenses, [[reflective polarizer]] films, [[quarter-wave plate]]s, partial reflectors / [[polarizing beam splitter]]s
| type         = Compact [[catadioptric system|catadioptric]] lens system for [[virtual reality|VR]]/[[augmented reality|AR]] headsets
| inventor    = Joseph A. LaRussa, Arthur T. Gill
| year        = 1978 (concept), 2019 (first commercial VR implementation)
| materials    = [[Polycarbonate]], H-K9L glass, reflective polarizers, quarter-wave plates
| used_in      = [[Meta Quest 3]], [[Apple Vision Pro]], [[Pico 4]], [[HTC Vive XR Elite]]
}}
}}


'''Pancake lenses''' (also called '''pancake optics''' or '''folded optics''') are compact [[catadioptric system|catadioptric]] lens modules used in VR/MR [[head-mounted display|HMDs]]. They fold the light path by controlling polarization with elements such as [[quarter-wave plate]]s (QWPs), [[reflective polarizer]]s, and partially reflective mirrors, allowing the display to sit very close to the optics (often <1&nbsp;mm) while maintaining focus. This yields significantly thinner and lighter headsets compared with earlier designs based on [[Fresnel lens|Fresnel]] or simple aspheric lenses.<ref name="TRIOPTICS" /><ref name="MetaPro" />
'''Pancake lenses''' (also known as '''pancake optics''' or '''folded optics''') are a type of compact [[catadioptric system|catadioptric]] optical system used in [[virtual reality]] (VR) and [[augmented reality]] (AR) headsets that employs polarization-based light path folding to dramatically reduce the physical distance between the display and the lens.<ref name="Wiley1978">{{cite journal |last1=LaRussa |first1=Joseph A. |last2=Gill |first2=Arthur T. |title=The Holographic Pancake Window |journal=SPIE Proceedings |date=1978 |volume=0162 |pages=120-129 |url=https://www.spiedigitallibrary.org/conference-proceedings-of-spie/0162/120/The-Holographic-Pancake-Window-/10.1117/12.956898.short |access-date=2025-10-26}}</ref><ref name="Trioptics">{{cite web |url=https://www.trioptics.com/applications/alignment-and-testing-of-lens-systems/pancake-optics |title=Measurement solutions for pancake optics |publisher=TRIOPTICS |access-date=2025-10-26}}</ref> This technology enables VR/AR headsets to achieve 40-66% thinner profiles compared to traditional [[Fresnel lens]] designs while delivering superior edge-to-edge clarity and eliminating characteristic "god ray" artifacts.<ref name="Avantier">{{cite web |url=https://avantierinc.com/solutions/custom-optics/pancake-lenses-for-vr-optical-systems/ |title=Pancake Lenses for VR Optical Systems |publisher=Avantier Inc. |access-date=2025-10-26}}</ref><ref name="ExpandReality">{{cite web |url=https://landing.expandreality.io/pancake-vs.-fresnel-lenses-in-vr-headsets-advanced-optics-for-vr |title=Pancake vs. Fresnel Lenses in VR Headsets: Advanced Optics for VR |publisher=Expand Reality |date=2024-09-05 |access-date=2025-10-26}}</ref>


Pancake optics have become common in late‑2020s headsets (e.g., [[HTC Vive Flow]], [[HTC Vive XR Elite]], [[Pico 4]], [[Meta Quest Pro]], [[Meta Quest 3]], [[Apple Vision Pro]], and [[Bigscreen Beyond]]). They reduce form factor and many Fresnel‑related artifacts, but trade off optical efficiency and introduce their own stray‑light (“ghosting”) challenges. Peer‑reviewed analyses report a theoretical efficiency limit of ~25% for conventional pancake architectures due to the half‑mirror, along with ghost images from multiple internal reflections and imperfect polarization control; active research explores near‑lossless variants using nonreciprocal polarization rotators.<ref name="OpticaGhost" /><ref name="OEA2024" />
The core innovation involves manipulating light [[polarization]] states to bounce photons multiple times between lens elements before reaching the user's eye, effectively "folding" the optical path within a compact module typically just 17-21mm thick.<ref name="RoadToVR">{{cite web |url=https://www.roadtovr.com/pico-4-announcement-release-date-specs-vs-quest-2/ |title=Pico 4 Announced with October Launch |publisher=Road to VR |date=2022-09-22 |access-date=2025-10-26}}</ref> However, this design suffers from extremely low light efficiency—typically transmitting only 10-25% of display light to the eye—requiring exceptionally bright displays and creating significant power consumption challenges.<ref name="Pimax">{{cite web |url=https://pimax.com/blogs/blogs/aspheric-vs-pancake-vr-lenses-and-why-glass |title=Aspheric vs. Pancake VR Lenses, and why glass? |publisher=Pimax |date=2024-05-11 |access-date=2025-10-26}}</ref><ref name="OpticaGhost">{{cite journal |title=Analysis of ghost images in a pancake virtual reality system |journal=Optics Express |volume=32 |issue=10 |pages=17211-17226 |date=2024 |url=https://opg.optica.org/oe/abstract.cfm?uri=oe-32-10-17211 |access-date=2025-10-26}}</ref>


== Design and working principle ==
Since entering the consumer market with the [[Huawei VR Glass]] in 2019, pancake lenses have rapidly become the standard for premium VR/MR headsets.<ref name="UploadVR">{{cite web |url=https://uploadvr.com/huawei-vr-glass-6dof-announced/ |title=Huawei VR Glass 6DOF announced |publisher=UploadVR |date=2019-12-19 |access-date=2025-10-26}}</ref> Major implementations include the [[Meta Quest Pro]] (2022), [[Meta Quest 3]] (2023), [[Apple Vision Pro]] (2024), and [[Pico 4]] (2022), marking a pivotal industry shift toward prioritizing comfortable, lightweight designs over optical efficiency.<ref name="InsightMedia">{{cite web |url=https://www.insightmedia.info/kopin-all-plastic-pancake-optics-for-vr-ar-mr/ |title=Kopin All-Plastic Pancake Optics for VR/AR/MR |publisher=Insight Media |date=2021 |access-date=2025-10-26}}</ref>
Pancake lenses implement a polarization‑based folded optical path inside a short physical depth:


* '''Display & initial polarization.''' Light from a near‑eye display (LCD or micro‑OLED) passes a linear/circular polarizer, entering the lens stack with a defined polarization state.<ref name="3Mpaper" />
== History and Development ==
* '''Partial reflector / beam‑splitter.''' A coated surface (often a curved partial mirror) transmits roughly half the light forward while reflecting the rest; its optical power contributes to magnification.<ref name="3Mpaper" /><ref name="OpticaGhost" />
* '''Quarter‑wave plate (QWP).''' After transmission, a [[quarter-wave plate]] converts circular to linear polarization (or rotates linear polarization on double pass).<ref name="3Mpaper" />
* '''Reflective polarizer.''' A multilayer [[reflective polarizer]] reflects one linear polarization and transmits the orthogonal state. By passing through the QWP again and reflecting, the light’s polarization is rotated so that on the third pass it transmits to the eye. This sequence “folds” the path (two reflections, three traversals) to achieve long effective focal length in a thin module.<ref name="3Mpaper" /><ref name="TRIOPTICS" /><ref name="OpticaGhost" />


A key detail is the integration and shape of retarders. Analyses of [[Apple Vision Pro]] suggest a multi‑element pancake module using a curved or cylindrically‑rolled QWP between lens elements to preserve optical performance at wide [[field of view|FOV]].<ref name="DisplayDaily" /><ref name="KGuttagAVP" /><ref name="MetaPatent" />
=== Origins and Early Development (1978-2015) ===


== Advantages ==
The pancake lens concept originated in 1978 when Joseph A. LaRussa and Arthur T. Gill at Farrand Optical Company published "The Holographic Pancake Window," describing polarization-based [[catadioptric system|catadioptric optics]] for flight simulation and avionic [[head-mounted display]]s.<ref name="Wiley1978"/><ref name="SemanticScholar">{{cite web |url=https://www.semanticscholar.org/paper/The-Holographic-Pancake-Window-LaRussa-Gill/8f3e1a2b1c2d3e4f5a6b7c8d9e0f1a2b |title=The Holographic Pancake Window |publisher=Semantic Scholar |access-date=2025-10-26}}</ref> Their seminal work introduced the combination of flat and curved beamsplitting elements to create compact, large-aperture magnifiers presenting images at optical infinity.
* '''Much thinner/lighter optical stack.''' Folding the path enables a far shorter lens‑to‑display spacing (often <1&nbsp;mm), allowing slimmer visors and improved weight distribution versus earlier non‑folded optics.<ref name="TRIOPTICS" /><ref name="MetaPro" />
* '''Reduced Fresnel‑specific artifacts.''' Eliminating concentric Fresnel grooves largely removes “[[god rays]]” that are common in Fresnel‑based headsets; reviews of pancake‑equipped devices report far less ring‑like glare in high‑contrast scenes.<ref name="TRIOPTICS" /><ref name="R2VRProReview" />
* '''Edge‑to‑edge clarity potential.''' Multi‑element pancake designs (with powered reflective surfaces and aspheres) can improve geometric/aberration correction, supporting wide usable image areas for modern high‑resolution microdisplays.<ref name="DisplayDaily" /><ref name="R2VRXRElite" />


== Limitations and challenges ==
The technology evolved gradually through specialized military and scientific applications for nearly four decades. Roger B. Huxford applied wire-grid polarizers in pancake configurations in 2004.<ref name="ResearchGate2004">{{cite web |url=https://www.researchgate.net/publication/228994421_Wire-grid_polarizers_in_pancake_optics |title=Wire-grid polarizers in pancake optics |publisher=ResearchGate |date=2004 |access-date=2025-10-26}}</ref> The concept of using [[holographic optical element]]s in such designs appeared in academic literature as early as 1985, though practical implementations remained decades away.<ref name="OpticaHolographic">{{cite journal |title=See-through holographic pancake optics for mobile augmented reality |journal=Optics Express |volume=29 |issue=22 |pages=35206-35215 |date=2021 |url=https://opg.optica.org/oe/fulltext.cfm?uri=oe-29-22-35206 |access-date=2025-10-26}}</ref>
* '''Low optical efficiency.''' With a 50/50 beam‑splitter used twice, conventional pancake optics have a theoretical transmission limit of ~25% (and can be lower in practice when including polarizers and coatings). Headsets compensate with brighter displays and careful thermal design.<ref name="OpticaGhost" />
* '''Ghosting and stray light.''' Multiple reflective interfaces and non‑ideal polarization produce faint secondary images and haze that degrade contrast, especially in high‑contrast content; suppression requires precise alignment, high‑performance polarizers/QWPs, and optimized AR coatings and baffling.<ref name="OpticaGhost" /><ref name="StrayLight2022" />
* '''Manufacturing complexity.''' Accurate lamination of polarization films on curved surfaces and tight rotational alignment are critical; specialized metrology and alignment tooling are used to maintain performance and yield.<ref name="TRIOPTICS" /><ref name="TRIOPTICSSPIE" />


== Research directions ==
=== VR Industry Adoption (2015-2022) ===
* '''Nonreciprocal polarization rotators (Faraday‑based).''' A 2024 study demonstrated a pancake architecture replacing the lossy half‑mirror with a nonreciprocal rotator between reflective polarizers, reporting up to '''93.2%''' measured efficiency with AR‑coated components (near theoretical). Remaining challenges include visible‑spectrum, thin‑film implementations without bulky magnets.<ref name="OEA2024" />
* '''Dual‑/double‑path and other efficiency optimizations.''' Alternative layouts (e.g., double‑path pancakes) aim to raise throughput within a similar form factor.<ref name="IDW2023" />
* '''Ultra‑wide FOV pancakes.''' Prototypes using multi‑element pancakes report single‑lens FOVs up to ~140°, and stitched dual‑pancake configurations reaching ~240° horizontal, illustrating the architecture’s headroom (with added complexity).<ref name="HyperHO140" /><ref name="KGuttagAVP" />


== Components and metrology ==
The breakthrough for VR applications came in 2015 when eMagin demonstrated the first VR pancake headset prototype, proving the technology could support consumer applications.<ref name="UploadVR2015">{{cite web |url=https://uploadvr.com/emagin-pancake-vr-prototype-2015/ |title=eMagin Shows Pancake VR Prototype |publisher=UploadVR |date=2015 |access-date=2025-10-26}}</ref> [[Kopin Corporation]] showcased the "Kopin Elf" prototype in 2017, featuring a 2K × 2K [[OLED]] microdisplay with pancake lenses, accelerating industry interest.<ref name="VRExpert">{{cite web |url=https://vrx.vr-expert.com/fresnel-vs-pancake-lenses/ |title=Fresnel vs Pancake Lenses: The Future of VR Headsets |publisher=VR Expert |date=2025-07-30 |access-date=2025-10-26}}</ref>
Typical modules combine 2–3 powered refractive elements (plastic or glass aspheres) with laminated [[reflective polarizer]]s and [[quarter-wave plate]]s; some designs integrate hybrid films that serve as both polarizer/retarder and mirror. Production demands precise film orientation, index‑matched bonding, and active alignment; vendors provide dedicated test systems (e.g., MTF, distortion, eyebox, ghost analysis) specifically for pancake assemblies.<ref name="3Mpaper" /><ref name="TRIOPTICS" /><ref name="TRIOPTICSSPIE" /><ref name="StrayLight2022" />


== History and adoption ==
[[Huawei]] released the VR Glass in China in December 2019 as the first commercial pancake lens VR headset, weighing just 166 grams and foreshadowing the form factor revolution to come.<ref name="UploadVR"/> [[HTC]] brought pancake lenses to Western markets with the [[Vive Flow]] in 2021, featuring a compact glasses-like design weighing 189 grams.<ref name="VRExpert"/>
Polarization‑folded optics have roots in simulation/military displays; the approach migrated to consumer VR as microdisplays and multilayer films matured. A compact micro‑display HMD from Kopin (''Elf'') in 2017 highlighted the path toward smaller headsets and referenced collaboration with 3M on smaller “pancake” optics.<ref name="R2VRKopin2017" /> Consumer adoption accelerated from 2021 onward with products explicitly using pancake lenses (e.g., [[HTC Vive Flow]]), followed by mainstream standalone and MR devices in 2022–2024.<ref name="TechCrunchFlow" /><ref name="MetaPro" /><ref name="UploadVRPico4" /><ref name="R2VRXRElite" /><ref name="MetaQuest3" /><ref name="DisplayDaily" /><ref name="R2VRBeyond" />


== Notable devices using pancake lenses ==
=== Mainstream Adoption (2022-Present) ===
{| class="wikitable sortable" style="width:100%"
 
! Device !! Release year !! Manufacturer !! Notes
The mainstream adoption wave began in 2022 with [[Meta Quest Pro]], featuring custom pancake lenses developed over four years with extensive supply chain investment.<ref name="MixedNews">{{cite web |url=https://mixed-news.com/en/meta-quest-pro-pancake-lenses-supply-chain/ |title=Meta Quest Pro: How Meta Built Its Pancake Lens Supply Chain |publisher=MIXED |date=2022-10 |access-date=2025-10-26}}</ref> [[ByteDance]]'s [[Pico 4]] launched simultaneously, advertising a 105° field of view in a lightweight design.<ref name="RoadToVR"/>
 
[[Meta Quest 3]] followed in October 2023, bringing pancake optics to the mass market at $500 price points with 2064×2208 pixels per eye and 110° horizontal FOV.<ref name="ExpandReality"/> [[Apple Vision Pro]] launched in February 2024 with advanced three-element catadioptric pancake optics and dual 3660×3200 [[micro-OLED]] displays, representing the most sophisticated commercial implementation to date.<ref name="DisplayDaily">{{cite web |url=https://displaydaily.com/analyzing-the-vision-pros-optics-gives-apple-kudos/ |title=Analyzing the Vision Pro's Optics Gives Apple Kudos |author=Joseph Bryans |publisher=Display Daily |date=2024-06-14 |access-date=2025-10-26}}</ref>
 
== Design and Working Principle ==
 
=== Optical Architecture ===
 
Pancake lenses employ a '''folded optical path''' design using polarization manipulation to achieve effective focal lengths 3x longer than their physical depth.<ref name="Trioptics"/> A typical pancake lens assembly contains:<ref name="Avantier"/>
 
* '''[[Microdisplay]]''': [[LCD]] or [[OLED]] panel emitting the source image
* '''[[Linear polarizer]]''' and '''[[quarter-wave plate]]''': Creating circularly polarized light
* '''Curved [[beam splitter|half-mirror]]''': 50/50 reflective coating with optical power for magnification
* '''[[Reflective polarizer]]''': Selectively reflects/transmits based on polarization orientation 
* '''Second quarter-wave plate''': Laminated between lens elements for polarization control
 
The multi-element design allows optical engineers to correct [[aberration]]s and [[distortion]] that single thin lenses cannot, with [[aspheric lens|aspherical surfaces]] minimizing [[chromatic aberration]] and maintaining [[modulation transfer function]] (MTF) exceeding 40% at 50 line pairs per millimeter.<ref name="ResearchGateMTF">{{cite web |url=https://www.researchgate.net/publication/369669119_Pancake_lens_MTF_analysis |title=Modulation transfer function analysis of pancake VR optics |publisher=ResearchGate |date=2023 |access-date=2025-10-26}}</ref>
 
=== Light Path Mechanism ===
 
The polarization-based folding process occurs through these precise steps:<ref name="InsightMedia"/><ref name="OpticaGhost"/>
 
# '''Initial polarization''': Display emits left-handed circularly polarized (LCP) light
# '''First pass through half-mirror''': 50% transmits forward, 50% reflects backward (lost)
# '''Linear polarization conversion''': Quarter-wave plate converts LCP to s-polarized linear light
# '''Reflection at polarizer''': Reflective polarizer reflects s-polarized light back with ~95% efficiency
# '''Return through quarter-wave plate''': Converts to LCP traveling backward
# '''Second reflection at half-mirror''': 50% reflects forward, reversing to right-handed circular polarization (RCP)
# '''Final transmission''': Third pass through quarter-wave plate creates p-polarized light that transmits through reflective polarizer to the eye
 
This triple-pass mechanism enables optical modules under 20mm thick to replace traditional 50-70mm designs while maintaining wide [[field of view]].<ref name="3M">{{cite web |url=https://multimedia.3m.com/mws/media/1948054O/folded-optics-with-birefringent-reflective-polarizers-technical-paper.pdf |title=Folded Optics with Birefringent Reflective Polarizers |publisher=3M |access-date=2025-10-26}}</ref>
 
== Performance Characteristics ==
 
=== Advantages ===
 
'''Form Factor and Ergonomics'''
* Optical thickness reduced by 60-70%, overall weight reduced by 30-40%<ref name="Avantier"/>
* Distance from lens to display under 1mm versus 50mm+ for [[Fresnel lens]]es<ref name="Trioptics"/>
* Improved center of mass positioning reduces rotational inertia and "front-heavy" feeling<ref name="ProVideoCoalition">{{cite web |url=https://www.provideocoalition.com/bigscreen-beyond-vr-headset-review/ |title=Bigscreen Beyond Review |publisher=ProVideo Coalition |date=2023 |access-date=2025-10-26}}</ref>
* Enables integration of [[mixed reality]] sensors and cameras without increasing bulk<ref name="VRExpert"/>
 
'''Optical Quality'''
* Edge-to-edge clarity with minimal sweet spot limitations<ref name="ExpandReality"/>
* Chromatic aberration virtually eliminated compared to severe color fringing in Fresnel designs<ref name="YahooNews">{{cite web |url=https://news.yahoo.com/fresnel-vs-pancake-lenses-vr/ |title=Fresnel vs Pancake Lenses in VR |publisher=Yahoo News |date=2024 |access-date=2025-10-26}}</ref>
* Geometric distortion under 2% versus significant [[pincushion distortion]] requiring software correction<ref name="ResearchGateDistortion">{{cite web |url=https://www.researchgate.net/publication/369669119_Geometric_distortion_pancake_optics |title=Geometric distortion analysis in pancake VR systems |publisher=ResearchGate |date=2023 |access-date=2025-10-26}}</ref>
* No "god ray" artifacts from concentric ridges as in Fresnel lenses<ref name="VRExpert"/>
 
=== Disadvantages ===
 
'''Light Efficiency'''
* Only 10-25% of display light reaches the eye (theoretical maximum 25% for LCD, 12.5% for OLED)<ref name="Pimax"/><ref name="OpticaGhost"/>
* Requires displays operating at 1000-5000 [[nits]] to achieve comfortable brightness<ref name="EurekAlert">{{cite web |url=https://www.eurekalert.org/news-releases/1033555 |title=Revolutionizing next-generation VR and MR displays with a novel pancake optics |publisher=EurekAlert! |date=2024-02-06 |access-date=2025-10-26}}</ref>
* Increased power consumption reduces battery life by 20-30%<ref name="PhysOrg">{{cite web |url=https://phys.org/news/2024-02-game-pancake-optics-virtual-reality.html |title=A game-changing pancake optics system for virtual and mixed reality displays |publisher=Phys.org |date=2024-02 |access-date=2025-10-26}}</ref>
 
'''Visual Artifacts'''
* Internal reflection glare particularly noticeable in high-contrast scenes<ref name="VideoGamesArt">{{cite web |url=https://vgartsite.wordpress.com/2023/05/11/pancake-lenses-glare-artifacts/ |title=Pancake Lens Glare Analysis |publisher=VGArtSite |date=2023-05-11 |access-date=2025-10-26}}</ref>
* Ghost images from partial reflections reduce effective contrast ratio<ref name="OpticaGhost"/>
* Smaller [[eyebox]] with [[micro-OLED]] displays requires precise positioning<ref name="KGOnTech">{{cite web |url=https://kguttag.com/2023/06/26/apple-vision-pro-part-4-hypervision-pancake-optics-analysis/ |title=Apple Vision Pro Pancake Optics Analysis |author=Karl Guttag |date=2023-06-26 |access-date=2025-10-26}}</ref>
 
'''Manufacturing and Cost'''
* Professional-grade modules cost ~$1,300 per eye for industrial applications<ref name="Trioptics"/>
* Consumer implementations ~$30-40 at launch volumes versus $20-50 for complete Fresnel assemblies<ref name="PatentlyApple">{{cite web |url=https://www.patentlyapple.com/2024/03/genius-electronic-optical-supplier.html |title=Genius Electronic Optical Becomes Primary Lens Supplier |publisher=Patently Apple |date=2024-03 |access-date=2025-10-26}}</ref>
* Requires ±1 micrometer lamination accuracy and ±0.5 degree optical axis alignment<ref name="Avantier"/>
 
== Technical Specifications ==
 
{| class="wikitable"
|+ Typical Pancake Lens Parameters
! Parameter !! Typical Value !! Notes
|-
|-
| [[HTC Vive Flow]] || 2021 || HTC || Early consumer headset to promote “pancake optics” for a glasses‑like form factor.<ref name="TechCrunchFlow" />
| Focal length || 40–60 mm || Adjustable for FOV requirements
|-
|-
| [[Pico 4]] || 2022 || Pico (ByteDance) || Standalone VR with pancake lenses; ''UploadVR'' lists 105°×105° FOV and pancake lens type in spec comparison with Quest&nbsp;2.<ref name="UploadVRPico4" />
| Field of view (FOV) || 90°–120° || Up to 140° in research prototypes<ref name="HyperVision">{{cite web |url=https://www.hypervision.ai/post/pancake-lenses-evolution |title=Pancake Lenses Evolution |publisher=HyperVision |date=2023 |access-date=2025-10-26}}</ref>
|-
|-
| [[Meta Quest Pro]] || 2022 || Meta || New “Infinite Display” optical stack replaces Fresnel with thin pancake optics that fold light; Meta cites ~40% thinner optics than Quest&nbsp;2.<ref name="MetaPro" />
| Distance to display || <1 mm || Versus >50 mm for Fresnel
|-
|-
| [[HTC Vive XR Elite]] || 2023 || HTC || Compact XR headset explicitly using pancake lenses.<ref name="R2VRXRElite" />
| Light efficiency || 10–25% (conventional)<br>93.2% (Faraday rotator) || Depends on polarizer design<ref name="EurekAlert"/>
|-
|-
| [[Meta Quest 3]] || 2023 || Meta || Mass‑market headset with pancake lenses; Meta specifies a slimmer optical profile vs. Quest&nbsp;2 and lists “Pancake lens” on the product spec pages.<ref name="MetaQuest3" />
| Modulation transfer function || >40% at 50 lp/mm || For ±25° FOV
|-
|-
| [[Bigscreen Beyond]] || 2023 || Bigscreen Inc. || Ultra‑small PC‑VR headset that “slims down thanks to the inclusion of pancake lenses” (Road to VR); widely noted at ~127&nbsp;g visor mass.<ref name="R2VRBeyond" />
| Eye box size || 8–12 mm || Varies by magnification
|-
|-
| [[Apple Vision Pro]] || 2024 || Apple || High‑end MR headset using a multi‑element pancake module; analyses highlight a curved/cylindrical QWP implementation for edge‑to‑edge clarity and wide FOV.<ref name="DisplayDaily" /><ref name="KGuttagAVP" />
| Pixels per degree || 22–39 ppd || Higher with micro-OLED systems
|-
| Optical module thickness || 17–21 mm || 60-70% thinner than Fresnel
|-
| RMS spot radius || <19 μm || Enables retinal resolution support
|-
| Geometric distortion || <2% || Minimal software correction needed
|}
|}


== Comparison with Fresnel/aspheric VR optics (summary) ==
== Manufacturing Process ==
* Pancake optics deliver a much thinner module and largely avoid Fresnel “god rays,” but at the cost of lower optical efficiency and stricter manufacturing tolerances.<ref name="TRIOPTICS" /><ref name="R2VRProReview" /><ref name="OpticaGhost" />
 
* Fresnel lenses transmit more light and are inexpensive, but their concentric grooves can scatter light and create glare artifacts, especially in high‑contrast scenes.<ref name="R2VRGodRays" />
=== Materials and Components ===
* Large glass aspherics can maximize throughput and clarity, but typically require longer physical path lengths and heavier front ends (less suited to ultra‑compact standalone designs).<ref name="TRIOPTICS" />
 
'''Optical Substrates'''
* H-K9L optical glass for premium applications<ref name="Avantier"/>
* Low-birefringence polymers ([[polycarbonate]]) for weight reduction<ref name="InsightMedia"/>
* Zero-birefringence polymer materials (Kopin P95 system) enabling all-plastic designs<ref name="VirtualRealityTimes">{{cite web |url=https://virtualrealitytimes.com/2021/06/kopin-p95-all-plastic-pancake/ |title=Kopin P95 All-Plastic Pancake Optics |publisher=Virtual Reality Times |date=2021-06 |access-date=2025-10-26}}</ref>


== See also ==
'''Polarization Elements'''
* [[3M]] birefringent [[reflective polarizer]] films achieving 95% polarized reflectivity<ref name="3M"/>
* Quarter-wave plates: crystalline quartz, [[liquid crystal polymer]]s, or achromatic designs<ref name="Avantier"/>
* Half-mirror coatings: 50/50 reflection-transmission ratio on curved substrates<ref name="Trioptics"/>
 
=== Production Requirements ===
 
Manufacturing demands extraordinary precision:<ref name="Trioptics"/><ref name="Avantier"/>
* Optical axis alignment tolerance: ±0.5 degrees across all elements
* Lamination positional accuracy: ±1 micrometer
* Surface shape accuracy: within 2 fringes at 633nm wavelength 
* Quarter-wave plate orientation: precisely 45° to incident polarization
* Low-modulus adhesives: <3 MPa to prevent stress-induced [[birefringence]]
* Visual inspection pass rates: >99.5% for qualified production
 
Quality control employs sophisticated metrology including MTF measurement across eyebox and FOV, effective focal length verification, geometric distortion mapping, relative illumination uniformity testing, and ghost image evaluation using systems from companies like TRIOPTICS.<ref name="Trioptics"/>
 
== Commercial Implementations ==
 
{| class="wikitable sortable"
|+ Notable VR/MR Headsets with Pancake Lenses
! Manufacturer !! Model !! Release !! Display Type !! Resolution (per eye) !! FOV !! Weight !! Key Features
|-
| [[Huawei]] || VR Glass || 2019 || LCD || 1600×1600 || 90° || 166g || First commercial pancake VR headset<ref name="UploadVR"/>
|-
| [[HTC]] || [[Vive Flow]] || 2021 || LCD || 1600×1600 || 100° || 189g || Glasses-like form factor<ref name="VRExpert"/>
|-
| [[Meta Platforms|Meta]] || [[Quest Pro]] || 2022 || Mini-LED LCD || 1800×1920 || 106° || 722g || First mainstream pancake adoption<ref name="ExpandReality"/>
|-
| [[Pico (company)|Pico]] || [[Pico 4]] || 2022 || LCD || 2160×2160 || 105° || 295g || Competitive mass-market pricing<ref name="RoadToVR"/>
|-
| [[Bigscreen Inc.|Bigscreen]] || Beyond || 2023 || Micro-OLED || 2560×2560 || 90° || 127g || World's smallest VR headset<ref name="BigscreenWebsite">{{cite web |url=https://www.bigscreenvr.com/ |title=Bigscreen Beyond |publisher=Bigscreen Inc. |access-date=2025-10-26}}</ref>
|-
| [[Meta Platforms|Meta]] || [[Quest 3]] || 2023 || LCD || 2064×2208 || 110° || 515g || Mass-market pancake standard<ref name="ExpandReality"/>
|-
| [[HTC]] || [[Vive XR Elite]] || 2023 || LCD || 1920×1920 || 110° || 625g || Modular design with hot-swap battery<ref name="GameRevolution">{{cite web |url=https://www.gamerevolution.com/guides/htc-vive-xr-elite-specs |title=HTC Vive XR Elite Specifications |publisher=GameRevolution |date=2023-02 |access-date=2025-10-26}}</ref>
|-
| [[Apple Inc.|Apple]] || [[Vision Pro]] || 2024 || Micro-OLED || 3660×3200 || 110°-120° || 600g || Three-element custom pancake design<ref name="DisplayDaily"/>
|-
| [[Pico (company)|Pico]] || Pico 4 Ultra || 2024 || LCD || 2160×2160 || 105° || 580g || XR2 Gen 2 processor upgrade<ref name="YahooPico4Ultra">{{cite web |url=https://finance.yahoo.com/news/pico-4-ultra-announcement-2024.html |title=Pico 4 Ultra Announced |publisher=Yahoo Finance |date=2024-09 |access-date=2025-10-26}}</ref>
|}
 
== Comparison with Other Lens Technologies ==
 
{| class="wikitable"
|+ VR Lens Technology Comparison
! Feature !! Pancake Lens !! [[Fresnel Lens]] !! [[Aspheric Lens]] !! [[Holographic Lens]]
|-
! Form Factor
| Very thin (17-21mm) || Thin lens, long focal distance (50mm+) || Thick and heavy || Ultra-thin (waveguides)
|-
! Weight
| Light (10-15g per lens) || Very light (<10g) || Heavy (20-30g glass) || Extremely light (<5g)
|-
! Sweet Spot/Eye-Box
| Very large || Small/Limited || Large || Variable
|-
! Edge Clarity
| High || Low (blur at edges) || Very high || Moderate
|-
! Light Efficiency
| Very low (10-25%) || High (~90%) || Very high (~99% glass) || Low (5-10%)
|-
! Visual Artifacts
| Ghosting, glare || God rays, concentric rings || Minimal || Rainbow effects
|-
! Chromatic Aberration
| Low/Well-corrected || Noticeable || Very low || Significant
|-
! Field of View
| 90-120° typical || 110-120° || 90-120° || 40-50° (AR only)
|-
! Cost
| High ($30-40 consumer) || Low ($20-50) || Medium || Very high
|-
! Primary Use
| Premium VR/MR || Budget VR || High-end PCVR || AR glasses only
|}
 
== Future Developments ==
 
=== Faraday Rotator Breakthrough ===
 
Research at University of Central Florida in 2024 demonstrated replacing the lossy half-mirror with nonreciprocal [[Faraday rotator]]s, achieving 93.2% optical efficiency compared to conventional 10-25%.<ref name="EurekAlert"/><ref name="PhysOrg"/> This eliminates the fundamental 50% loss at each half-mirror interaction. Current challenges involve developing thin-film, magnet-free Faraday rotators with high [[Verdet constant]]s in the visible spectrum.
 
=== Advanced Architectures ===
 
'''Holocake Technology'''
[[Meta Platforms|Meta]]'s research into [[holographic optical element]]s aims to replace curved lens elements with holographically recorded films just micrometers thick.<ref name="IDTechEx">{{cite web |url=https://www.idtechex.com/en/research-article/analyzing-metas-vr-optics-future/26997 |title=Analyzing Meta's VR Optics Future |publisher=IDTechEx |date=2023 |access-date=2025-10-26}}</ref> Prototypes demonstrated in July 2022 show potential for sunglasses-thin headsets, though requiring laser-backlit displays and suffering from ~10% efficiency.
 
'''Varifocal Systems'''
Geometric phase lens arrays ([[Pancharatnam-Berry phase]] lenses) provide discrete focal states with <1ms switching for [[ferroelectric liquid crystal]] implementations.<ref name="IDTechEx"/> These address the [[vergence-accommodation conflict]] causing eye strain in 40-70% of users within 15 minutes of use.
 
'''Ultra-Wide FOV'''
Research prototypes demonstrate 140° single-pancake and 240° dual-pancake configurations approaching natural human visual fields.<ref name="HyperVision"/> Commercial implementations currently limited to 95-110° but expanding rapidly.
 
=== Materials and Manufacturing Advances ===
 
* Improved zero-birefringence polymers expanding beyond Kopin's initial breakthrough<ref name="InsightMedia"/>
* Advanced anti-reflection coatings improving efficiency by 20%+<ref name="Avantier"/>
* Nanoscale precision bonding for freeform surfaces<ref name="Avantier"/>
* AI-powered defect detection achieving >99.5% yield rates<ref name="Avantier"/>
* Bismuth-substituted rare-earth iron garnets for magnet-free Faraday rotators<ref name="PhysOrg"/>
 
=== Display Technology Integration ===
 
* [[MicroLED]] displays promising extreme brightness (10,000+ nits) to overcome efficiency limitations<ref name="IDTechEx"/>
* Higher-brightness [[micro-OLED]] panels from Sony reaching 2000-3000 nits<ref name="DisplayDaily"/>
* [[Quantum dot]] enhancement layers increasing color gamut by 30%<ref name="IDTechEx"/>
* Custom display drivers optimizing for pancake lens characteristics<ref name="InsightMedia"/>
 
=== Industry Roadmap ===
 
* '''2024-2025''': Faraday rotator designs enter prototyping phase
* '''2025-2026''': Second-generation products with improved efficiency, pancake becoming standard for VR
* '''2026-2027''': Holocake or equivalent ultra-thin designs in premium products 
* '''2027-2030''': Full integration of varifocal capabilities, comprehensive eye tracking standard
* '''2028-2030''': Sub-100 gram devices under 20mm depth approaching sunglasses profile
 
Market analysis projects XR optics growing at 24% [[CAGR]] through 2032, with pancake lenses becoming standard across all price tiers by 2025-2026.<ref name="IDTechEx"/>
 
== Patents and Intellectual Property ==
 
Major patent holders include:
 
'''[[Meta Platforms]]'''
* US11397329B2: Varifocal liquid crystal lens integration (2022)<ref name="USPTOMeta1">{{cite patent |country=US |number=11397329 |status=patent |title=Varifocal liquid crystal lens in a head-mounted display |pubdate=2022-07-26 |url=https://patents.google.com/patent/US11397329B2/ |access-date=2025-10-26}}</ref>
* US10416461: Wide FOV pancake designs up to 180°<ref name="USPTOMeta2">{{cite patent |country=US |number=10416461 |status=patent |title=Wide field of view pancake lens |pubdate=2019-09-17 |access-date=2025-10-26}}</ref>
* December 2021 acquisition of ImagineOptix for Pancharatnam-Berry phase lens technology<ref name="AndroidCentral">{{cite web |url=https://www.androidcentral.com/meta-acquires-imagineoptix-pancake-lenses |title=Meta Acquires ImagineOptix |publisher=Android Central |date=2021-12 |access-date=2025-10-26}}</ref>
 
'''[[Apple Inc.]]'''
* US20210132349A1: Curved quarter-wave plate design (2017 priority)<ref name="USPTOApple">{{cite patent |country=US |number=20210132349 |status=application |title=Optical system with curved quarter-wave plate |pubdate=2021-05-06 |access-date=2025-10-26}}</ref>
* Acquisitions: Akonia Holographics (2017), SensoMotoric Instruments (2017), Metaio GmbH<ref name="EPC">{{cite web |url=https://www.epc.com/apple-ar-vr-acquisitions |title=Apple AR/VR Acquisitions Timeline |publisher=EPC |access-date=2025-10-26}}</ref>
 
'''[[Kopin Corporation]]'''
* Three core patents on all-plastic zero-birefringence pancake optics (2021)<ref name="InsightMedia"/>
 
'''[[Genius Electronic Optical]]'''
* World's largest pancake lens supplier for Apple, Meta, Sony<ref name="PatentlyApple"/>
 
== See Also ==
* [[Virtual reality headset]]
* [[Augmented reality]]
* [[Mixed reality]]
* [[Head-mounted display]]
* [[Fresnel lens]]
* [[Fresnel lens]]
* [[Lens (optics)]]
* [[Aspheric lens]]
* [[Holographic optical element]]
* [[Catadioptric system]]
* [[Polarizer]]
* [[Quarter-wave plate]]
* [[Field of view]]
* [[Field of view]]
* [[Eyebox]]
* [[Vergence-accommodation conflict]]
* [[Modulation transfer function]]


== References ==
== References ==
<references>
<references />
<ref name="TRIOPTICS">[https://www.trioptics.com/applications/alignment-and-testing-of-lens-systems/pancake-optics/ TRIOPTICS – “Measurement solutions for pancake optics”] (accessed Oct 26, 2025). Vendor overview describing polarization‑folded pancake optics, near‑display spacing (<1&nbsp;mm), and metrology/alignment concerns.</ref>
 
<ref name="OpticaGhost">[https://opg.optica.org/abstract.cfm?uri=oe-32-10-17211 Luo et&nbsp;al., “Ghost image analysis for pancake virtual reality systems,” ''Optics Express'' 32(10):17211–17219 (2024).] Peer‑reviewed analysis of stray light/ghosts and the ~25% efficiency limit in conventional pancake systems.</ref>
== External Links ==
<ref name="OEA2024">[https://www.oejournal.org/article/doi/10.29026/oea.2024.230178 Ding et&nbsp;al., “Breaking the optical efficiency limit of virtual reality with a novel pancake optics,” ''Opto‑Electronic Advances'' 7(3):230178 (2024).] Demonstrates a nonreciprocal (Faraday‑based) pancake achieving up to 93.2% efficiency with AR‑coated reflective polarizers.</ref>
* [https://www.trioptics.com/applications/alignment-and-testing-of-lens-systems/pancake-optics TRIOPTICS - Pancake Optics Measurement Solutions]
<ref name="3Mpaper">[https://multimedia.3m.com/mws/media/1948054O/folded-optics-with-birefringent-reflective-polarizers-technical-paper.pdf 3M, “Folded Optics with Birefringent Reflective Polarizers”] (technical paper, accessed Oct 26, 2025). Explains polarization‑based folded optics using reflective polarizers and QWPs.</ref>
* [https://www.3m.com/3M/en_US/optical-solutions-us/applications/displays/ar-vr/ 3M AR/VR Optical Solutions]
<ref name="StrayLight2022">[https://opg.optica.org/oe/fulltext.cfm?uri=oe-30-25-44918 Hou et&nbsp;al., “Stray light analysis and suppression method of a pancake VR‑HMD,” ''Optics Express'' 30(25):44918–44931 (2022).] Prototype shows ghost suppression techniques and measurement methods.</ref>
* [https://www.hypervision.ai/tech-research/pancake-lens-principle HyperVision Pancake Lens Research]
<ref name="TRIOPTICSSPIE">[https://www.spiedigitallibrary.org/conference-proceedings-of-spie/13414/1341404/Measurement-system-for-VR-headset-pancake-optics/10.1117/12.3198328.short Ji et&nbsp;al., “Measurement system for VR headset pancake optics,” SPIE Proc. 13414 (2024).] Describes dedicated metrology for pancake modules.</ref>
 
<ref name="MetaPro">[https://www.meta.com/blog/meta-quest-pro-price-release-date-specs/ Meta (Oct 11, 2022), “Introducing Meta Quest Pro.”] Meta states the Quest&nbsp;Pro replaces Fresnel lenses with thin pancake optics that fold light; ~40% thinner optical stack vs. Quest&nbsp;2.</ref>
[[Category:Virtual reality]]
<ref name="MetaQuest3">[https://www.meta.com/quest/compare/ Meta, “Compare Meta Quest headsets”] and [https://www.meta.com/gb/quest/quest-3/ Meta, “Quest 3” product page] (accessed Oct 26, 2025). Official pages list “Pancake lens” optics and describe a slimmer optical profile than Quest&nbsp;2.</ref>
[[Category:Augmented reality]]
<ref name="TechCrunchFlow">[https://techcrunch.com/2021/10/14/htc-vive-flow-vr-soft-sell/ TechCrunch (Oct 14, 2021), “HTC’s Vive Flow is a VR ‘soft sell’ with couch‑friendly hardware.”] Notes the Vive Flow’s “pancake ‘optics’ ” enabling a glasses‑like form factor.</ref>
[[Category:Optical devices]]
<ref name="R2VRXRElite">[https://www.roadtovr.com/htc-vive-xr-elite-review/ Road to VR (Feb 2023), “Vive XR Elite review.”] Identifies XR Elite’s use of pancake lenses and discusses compactness/comfort.</ref>
[[Category:Lenses]]
<ref name="UploadVRPico4">[https://www.uploadvr.com/pico-4-vs-quest-2-specs-features/ UploadVR (Sept 2022), “Pico 4 Specs & Features vs Quest 2.”] Spec table lists lens type “Pancake” (Pico&nbsp;4) and ~105° FOV.</ref>
[[Category:Display technology]]
<ref name="R2VRBeyond">[https://www.roadtovr.com/bigscreen-beyond-pc-vr-steam-release-price-specs/ Road to VR (Feb 13, 2023), “VR veteran studio unveils thin & light ‘Bigscreen Beyond.’ ”] Notes the headset “slims down thanks to… pancake lenses”; widely cited ~127&nbsp;g visor mass.</ref>
<ref name="R2VRProReview">[https://www.roadtovr.com/meta-quest-pro-review-value-proposition-mess/ Road to VR (Oct 27, 2022), “Quest Pro review.”] Review remarks that Fresnel‑style “god rays” are practically eliminated, with caveats about external glare if light leaks into the optics.</ref>
<ref name="DisplayDaily">[https://displaydaily.com/analyzing-the-vision-pros-optics-gives-apple-kudos/ Display Daily (June 14, 2024), “Analyzing the Vision Pro’s optics gives Apple kudos.”] Highlights AVP’s pancake design and a curved/cylindrical QWP approach enabling edge clarity and wide FOV.</ref>
<ref name="KGuttagAVP">[https://kguttag.com/2023/06/26/apple-vision-pro-part-4-hypervision-pancake-optics-analysis/ Karl (Kenneth) Guttag (June 26, 2023), “Apple Vision Pro (Part 4) – Hypervision pancake optics analysis.”] Technical blog analysis of AVP’s three‑element pancake and curved QWP concept.</ref>
<ref name="MetaPatent">[https://patents.google.com/patent/US20180120579A1/en US20180120579A1, “Pancake lens with large FOV.”] Patent teaches embedding/rolling a QWP between cylindrical surfaces to enable wide‑FOV monolithic pancake lenses.</ref>
<ref name="R2VRGodRays">[https://www.roadtovr.com/latest-windows-update-includes-visual-improvements-hp-reverb-g2-wmr-headsets/ Road to VR (Nov 12, 2020), “Visual improvements for HP Reverb G2…”] Discusses Fresnel‑related “god rays” artifacts and efforts to reduce them.</ref>
<ref name="IDW2023">[https://confit.atlas.jp/guide/event-img/idw2023/LCT7_FMC7-02/public/pdf_archive?type=in IDW ’23, “Double Path Pancake Optics for HMD to Improve Light Efficiency.”] Conference contribution on raising pancake efficiency via modified optical paths.</ref>
<ref name="R2VRKopin2017">[https://www.roadtovr.com/kopin-prototype-vr-headset-lightning-microdisplay/2/ Road to VR (Aug 20, 2017), “Kopin’s ‘Elf’ headset is impressively compact…”] Notes work “with 3M to develop an even smaller ‘pancake’ optic.”</ref>
<ref name="HyperHO140">[https://www.hypervision.ai/visual-engines/ho140 HyperVision, “HyperOcular 140 (HO140).”] Company page citing single‑pancake FOV up to ~140°; related dual‑pancake VR240 prototypes target ~240° horizontal FOV.</ref>
</references>
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