Lens array: Difference between revisions
Xinreality (talk | contribs) No edit summary |
Xinreality (talk | contribs) No edit summary |
||
| (5 intermediate revisions by the same user not shown) | |||
| Line 1: | Line 1: | ||
{{see also|Terms|Technical Terms}} | |||
[[Lens array]]s are two-dimensional arrangements of many small lenses (often [[Microlens arrays]]) that manipulate [[light fields]] for imaging or display. In [[Virtual reality]] (VR) and [[Augmented reality]] (AR) systems, lens arrays serve two broad roles: as '''display optics''' that create 3D or light-field images, and as '''sensor optics''' that capture directional light for depth and eye tracking. In displays, lens arrays enable multi-view and focal-plane rendering (e.g. light-field displays or integral imaging) by splitting the image into many sub-images corresponding to different angles or depths.<ref name="Li2019"></ref><ref name="Ng2005"></ref> In sensing, microlens-based ''plenoptic'' or light-field cameras capture the full 4D light field, allowing computational refocusing and depth estimation.<ref name="Ng2005" /> <ref name="Yang2018"></ref> Modern VR/AR prototypes leverage microlens arrays, [[Light field display]] techniques, [[Integral imaging]], holographic waveguide couplers, and specialized lens-array modules for eye tracking and depth sensing. These components appear in devices such as wide-FOV near-eye displays and optical see-through [[Head-mounted display]]s. | |||
==History== | |||
Lens-array technology traces back over a century. Gabriel Lippmann first proposed "integral photography" in 1908, capturing 3D scenes via a lens grid.<ref name="Li2019" /> Early implementations used pinhole arrays (circa 1911) and later simple microlens plates (around 1948) to record and replay light fields.<ref name="Li2019" /> In the mid-20th century, lenticular (cylindrical lens) sheets became popular for autostereoscopic prints and displays (e.g. 3D postcards and packaging), providing separate views for each eye. By the 2000s, advances in digital displays and microfabrication revived lens-array research for head-worn displays. For example, smartphone-scale integral imaging was demonstrated by pairing a display with a matching MLA.<ref name="Li2019" /> In recent years, VR/AR research has produced thin, wide-FOV near-eye displays using sophisticated lens arrays (e.g. polarization optics or metasurfaces)<ref name="Shin2023"></ref>, as well as compact eye-tracking and depth cameras using microlens arrays.<ref name="Yang2018" /><ref name="Microsoft2020"></ref> | |||
== History == | |||
Lens-array technology traces back over a century. Gabriel Lippmann first proposed "integral photography" in 1908, capturing 3D scenes via a lens grid.<ref name="Li2019" /> Early implementations used pinhole arrays (circa 1911) and later simple microlens plates (around 1948) to record and replay light fields.<ref name="Li2019" /> In the mid-20th century, lenticular (cylindrical lens) sheets became popular for autostereoscopic prints and displays (e.g. 3D postcards and packaging), providing separate views for each eye. By the 2000s, advances in digital displays and microfabrication revived lens-array research for head-worn displays. For example, smartphone-scale integral imaging was demonstrated by pairing a display with a matching MLA.<ref name="Li2019" /> In recent years, VR/AR research has produced thin, wide-FOV near-eye displays using sophisticated lens arrays (e.g. polarization optics or metasurfaces)<ref name="Shin2023"> | |||
== Types of lens arrays == | == Types of lens arrays == | ||
| Line 11: | Line 9: | ||
Lens arrays in VR/AR come in several varieties: | Lens arrays in VR/AR come in several varieties: | ||
'''Spherical microlens arrays:''' Regular arrays of small convex (often spherical or aspheric) lenses. These planar MLAs are common for light-field displays and cameras. Pitch (spacing) can range from tens of micrometers (in cameras) up to a few millimeters (in HMD displays).<ref name="Wei2023"> | '''Spherical microlens arrays:''' Regular arrays of small convex (often spherical or aspheric) lenses. These planar MLAs are common for light-field displays and cameras. Pitch (spacing) can range from tens of micrometers (in cameras) up to a few millimeters (in HMD displays).<ref name="Wei2023"></ref><ref name="Jang2021"></ref> Each lenslet has a focal length chosen to suit the application (e.g. to collimate a display or focus on a sensor). | ||
'''Lenticular arrays:''' Arrays of cylindrical microlenses (lenticules) arranged one-dimensionally or two-dimensionally. These produce multiple horizontal viewing zones in glasses-free 3D displays. For example, a lenticular lens array can restrict the exit pupil to certain angles, enabling light-field panels that show different images to each eye.<ref name="Balogh2023"> | '''Lenticular arrays:''' Arrays of cylindrical microlenses (lenticules) arranged one-dimensionally or two-dimensionally. These produce multiple horizontal viewing zones in glasses-free 3D displays. For example, a lenticular lens array can restrict the exit pupil to certain angles, enabling light-field panels that show different images to each eye.<ref name="Balogh2023"></ref> Such arrays are widely used in glasses-free 3D signage and have been adapted to VR/AR light-field display prototypes. | ||
'''Holographic optical element (HOE) arrays:''' These use diffractive hologram patterns that act like an array of lenses. In AR waveguide combiners, ''lens-array holographic optical elements'' have been used to form 2D/3D transparent display screens.<ref name="Liu2012"> | '''Holographic optical element (HOE) arrays:''' These use diffractive hologram patterns that act like an array of lenses. In AR waveguide combiners, ''lens-array holographic optical elements'' have been used to form 2D/3D transparent display screens.<ref name="Liu2012"></ref> A HOE can replace a physical lens array by encoding lens behavior into a recorded interference pattern. In one prototype, a ''lens-array HOE'' was created to build a see-through AR screen.<ref name="Liu2012" /> Other works use holographic micromirror arrays in conjunction with MLAs to couple images into waveguides.<ref name="Jang2021" /> | ||
'''Liquid crystal / tunable lens arrays:''' Some arrays use liquid crystal (LC) or fluidic lenses whose optical power can be electronically changed. For example, a chiral (polarization-sensitive) LC lens array was demonstrated in an AR system to steer light and break conventional FOV limits.<ref name="Wei2023" /> Variable-focus MLAs can allow dynamic focus adjustment or multi-focal displays. | '''Liquid crystal / tunable lens arrays:''' Some arrays use liquid crystal (LC) or fluidic lenses whose optical power can be electronically changed. For example, a chiral (polarization-sensitive) LC lens array was demonstrated in an AR system to steer light and break conventional FOV limits.<ref name="Wei2023" /> Variable-focus MLAs can allow dynamic focus adjustment or multi-focal displays. | ||
| Line 35: | Line 33: | ||
'''Focal cueing and depth enhancement:''' Some VR/AR displays incorporate multiple lens arrays for depth/focus manipulation. For instance, a light-field HMD may use two stacked MLA arrays (a so-called dual-focal arrangement) to enlarge the depth range so that virtual objects at different distances can appear simultaneously in focus. Polarization or liquid crystal arrays have been used to switch between focus planes. These advanced architectures aim to overcome the vergence-accommodation mismatch by aligning virtual image focus with convergence. | '''Focal cueing and depth enhancement:''' Some VR/AR displays incorporate multiple lens arrays for depth/focus manipulation. For instance, a light-field HMD may use two stacked MLA arrays (a so-called dual-focal arrangement) to enlarge the depth range so that virtual objects at different distances can appear simultaneously in focus. Polarization or liquid crystal arrays have been used to switch between focus planes. These advanced architectures aim to overcome the vergence-accommodation mismatch by aligning virtual image focus with convergence. | ||
== Applications in sensing == | ==Applications in sensing== | ||
'''Light-field (plenoptic) cameras for depth and eye tracking:''' Lens arrays are fundamental to plenoptic imaging. Placing an MLA a focal distance in front of an image sensor allows each micro-image to capture rays from different angles.<ref name="Ng2005" /> This effectively samples the full 4D light field of the scene. With computational processing, one can refocus the image after capture or compute depth maps from parallax between the micro-images.<ref name="Ng2005" /> In VR/AR, this is useful both for external depth sensing (scene reconstruction) and internal eye imaging. For example, patents describe using a light-field camera (with MLA) inside an HMD to capture the user's eye. The captured plenoptic data lets the system digitally refocus on various eye regions and compute gaze direction without needing precise IR glints.<ref name="Yang2018" /> This relaxes the geometric constraints on eye-tracker placement. Thus, microlens-based light-field cameras can support both environmental mapping and fine eye tracking in headsets. | '''Light-field (plenoptic) cameras for depth and eye tracking:''' Lens arrays are fundamental to plenoptic imaging. Placing an MLA a focal distance in front of an image sensor allows each micro-image to capture rays from different angles.<ref name="Ng2005" /> This effectively samples the full 4D light field of the scene. With computational processing, one can refocus the image after capture or compute depth maps from parallax between the micro-images.<ref name="Ng2005" /> In VR/AR, this is useful both for external depth sensing (scene reconstruction) and internal eye imaging. For example, patents describe using a light-field camera (with MLA) inside an HMD to capture the user's eye. The captured plenoptic data lets the system digitally refocus on various eye regions and compute gaze direction without needing precise IR glints.<ref name="Yang2018" /> This relaxes the geometric constraints on eye-tracker placement. Thus, microlens-based light-field cameras can support both environmental mapping and fine eye tracking in headsets. | ||
| Line 43: | Line 40: | ||
'''Depth sensors:''' Outside of full light-field cameras, some depth-sensing concepts also use microlenses. One approach is a multi-aperture structured-light projector: an array of tiny beams (formed by a lens array) projects a coded IR pattern for depth triangulation. Another is embedding micro-lenses over depth-sensing pixels to increase fill factor or directivity. In practice, however, most time-of-flight and stereo cameras in VR/AR do not use discrete lens arrays (they use single large lenses or laser projectors). The main use of lens arrays in sensing is thus in light-field capture (including gaze capture) rather than typical ToF or stereo modules. | '''Depth sensors:''' Outside of full light-field cameras, some depth-sensing concepts also use microlenses. One approach is a multi-aperture structured-light projector: an array of tiny beams (formed by a lens array) projects a coded IR pattern for depth triangulation. Another is embedding micro-lenses over depth-sensing pixels to increase fill factor or directivity. In practice, however, most time-of-flight and stereo cameras in VR/AR do not use discrete lens arrays (they use single large lenses or laser projectors). The main use of lens arrays in sensing is thus in light-field capture (including gaze capture) rather than typical ToF or stereo modules. | ||
== Technical specifications == | ==Technical specifications== | ||
Lens-array designs involve several key parameters: | Lens-array designs involve several key parameters: | ||
| Line 61: | Line 57: | ||
Overall, the technical design of a lens array involves a trade-off between FOV, resolution, brightness, and physical thickness. Emerging approaches like metalens arrays promise thinner optics with engineered dispersion<ref name="Li2019" />, which may shift these trade-offs in future systems. | Overall, the technical design of a lens array involves a trade-off between FOV, resolution, brightness, and physical thickness. Emerging approaches like metalens arrays promise thinner optics with engineered dispersion<ref name="Li2019" />, which may shift these trade-offs in future systems. | ||
== Challenges == | ==Challenges== | ||
Lens-array components face several challenges in VR/AR: | Lens-array components face several challenges in VR/AR: | ||
| Line 77: | Line 72: | ||
'''Manufacturing scale and cost:''' Large, high-quality MLAs (especially with small lenslets) are challenging to produce over large areas. Holographic and metasurface arrays often require cleanroom fabrication. For consumer VR/AR, cost-effective replication (e.g. using nanoimprint or injection molding) is crucial but may not yet match the performance of lab prototypes. | '''Manufacturing scale and cost:''' Large, high-quality MLAs (especially with small lenslets) are challenging to produce over large areas. Holographic and metasurface arrays often require cleanroom fabrication. For consumer VR/AR, cost-effective replication (e.g. using nanoimprint or injection molding) is crucial but may not yet match the performance of lab prototypes. | ||
== Future developments == | ==Future developments== | ||
Research on lens-array technology is advancing rapidly. '''Adaptive optics''' will likely play a growing role. Arrays of liquid-crystal or shape-changing lenses could allow dynamic focus control and multi-focal displays (reducing vergence-accommodation conflict). Similarly, '''dynamic wavelength control''' (e.g. polarization or tunable filters in each lenslet) could enable spatiotemporal multiplexing for color and focus. | Research on lens-array technology is advancing rapidly. '''Adaptive optics''' will likely play a growing role. Arrays of liquid-crystal or shape-changing lenses could allow dynamic focus control and multi-focal displays (reducing vergence-accommodation conflict). Similarly, '''dynamic wavelength control''' (e.g. polarization or tunable filters in each lenslet) could enable spatiotemporal multiplexing for color and focus. | ||
'''Metasurfaces and flat optics''' are a major trend. Recent work has demonstrated ''achromatic metasurface waveguides'' for AR: for example, a 2025 Light:Science &Apps paper introduced inverse-designed metasurface couplers that eliminate chromatic aberration across the full visible spectrum and achieve ~45° FOV.<ref name="Achromatic2025"> | '''Metasurfaces and flat optics''' are a major trend. Recent work has demonstrated ''achromatic metasurface waveguides'' for AR: for example, a 2025 Light:Science &Apps paper introduced inverse-designed metasurface couplers that eliminate chromatic aberration across the full visible spectrum and achieve ~45° FOV.<ref name="Achromatic2025"></ref> These metasurface lens arrays are ultrathin and could replace bulky refractive MLAs in future headsets. Cholesteric liquid-crystal metasurface (chiral) lens arrays have already been used to break the field-of-view limit in a scanning AR display.<ref name="Wei2023" /> | ||
'''Integration and compute-optics co-design''' will improve performance. Headsets may co-optimize lens arrays with on-sensor processing. For instance, a microlens array camera could perform onboard refocusing or eye-pose estimation in hardware. Conversely, display side, algorithms could pre-distort images to compensate residual lens aberrations. | '''Integration and compute-optics co-design''' will improve performance. Headsets may co-optimize lens arrays with on-sensor processing. For instance, a microlens array camera could perform onboard refocusing or eye-pose estimation in hardware. Conversely, display side, algorithms could pre-distort images to compensate residual lens aberrations. | ||
| Line 91: | Line 86: | ||
As VR/AR systems aim for wider FOV, thinner form factors, and better realism, custom lens-array designs will continue to evolve. Each new generation of headsets (for example, employing pancake optics, multi-zone optics, or holographic waveguides) tends to reinvigorate lens-array innovation. In sum, lens arrays remain a key enabling technology for immersive displays and interactive sensing, with ongoing research focusing on mitigating their limitations and leveraging novel materials and computation.<ref name="Achromatic2025" /><ref name="Wei2023" /> | As VR/AR systems aim for wider FOV, thinner form factors, and better realism, custom lens-array designs will continue to evolve. Each new generation of headsets (for example, employing pancake optics, multi-zone optics, or holographic waveguides) tends to reinvigorate lens-array innovation. In sum, lens arrays remain a key enabling technology for immersive displays and interactive sensing, with ongoing research focusing on mitigating their limitations and leveraging novel materials and computation.<ref name="Achromatic2025" /><ref name="Wei2023" /> | ||
== References == | ==References== | ||
<references /> | <references> | ||
<ref name="Li2019">Li, X.; Chen, L.; Li, Y.; <i>et al.</i> “A Broadband Achromatic Metalens Array for Integral Imaging in the Visible.” ''Light: Science & Applications'' <b>8</b>, 99 (2019). https://doi.org/10.1038/s41377‑019‑0197‑4</ref> | |||
<ref name="Ng2005">Ng, R.; Levoy, M.; Brédif, M.; <i>et al.</i> “Light Field Photography with a Hand‑Held Plenoptic Camera.” Stanford CSTR 2005‑02 (2005). http://graphics.stanford.edu/papers/lfcamera/</ref> | |||
<ref name="Yang2018">Yang, L.; Guo, Y. “Eye Tracking Using a Light Field Camera on a Head‑Mounted Display.” US Patent Application <b>US 2018/0173303 A1</b>, 21 June 2018.</ref> | |||
<ref name="Shin2023">Shin, K‑S.; Hong, J.; Han, W.; Park, J‑H. “Field of View and Angular‑Resolution Enhancement in Microlens‑Array‑Type VR Near‑Eye Display Using Polarization Grating.” ''Optics Express'' <b>33</b>(1): 263‑278 (2025). https://doi.org/10.1364/OE.546812</ref> | |||
<ref name="Microsoft2020">Microsoft Technology Licensing LLC. “Camera Comprising Lens Array.” US Patent Application <b>US 2023/0319428 A1</b>, 5 October 2023.</ref> | |||
<ref name="Wei2023">Weng, Y.; Zhang, Y.; Wang, W.; <i>et al.</i> “High‑Efficiency and Compact Two‑Dimensional Exit Pupil Expansion Design for Diffractive Waveguide Based on Polarization Volume Grating.” ''Optics Express'' <b>31</b>(4): 6601‑6614 (2023). https://doi.org/10.1364/OE.482447</ref> | |||
<ref name="Jang2021">Darkhanbaatar, N.; Erdenebat, M‑U.; Shin, C‑W.; <i>et al.</i> “Three‑Dimensional See‑Through Augmented‑Reality Display System Using a Holographic Micromirror Array.” ''Applied Optics'' <b>60</b>(25): 7545‑7551 (2021). https://doi.org/10.1364/AO.428364</ref> | |||
<ref name="Balogh2023">Zhang, G.; He, Y.; Liang, H.; <i>et al.</i> “Directional and Eye‑Tracking Light Field Display with Efficient Rendering and Illumination.” ''Micromachines'' <b>14</b>(7): 1465 (2023). https://doi.org/10.3390/mi14071465</ref> | |||
<ref name="Liu2012">Hong, K.; Hong, J.; Yeom, J.; Lee, B. “Two‑Dimensional and Three‑Dimensional See‑Through Screen Using Holographic Optical Elements.” In <i>Digital Holography and Three‑Dimensional Imaging 2012</i>, paper DM2C.6. Optical Society of America (2012). https://doi.org/10.1364/DH.2012.DM2C.6</ref> | |||
<ref name="Achromatic2025">Tian, Z.; Zhu, X.; Surman, P.; <i>et al.</i> “An Achromatic Metasurface Waveguide for Augmented Reality Displays.” ''Light: Science & Applications'' <b>14</b>, 94 (2025). https://doi.org/10.1038/s41377‑025‑01761‑w</ref> | |||
</references> | |||
[[Category:Terms]] | |||
[[Category:Technical Terms]] | |||
[[Category:Virtual reality]] | [[Category:Virtual reality]] | ||
[[Category:Augmented reality]] | [[Category:Augmented reality]] | ||
[[Category:Optical devices]] | [[Category:Optical devices]] | ||
[[Category:Display technology]] | [[Category:Display technology]] | ||