A 3D FULL WINDSHIELD HEAD UP DISPLAY Philippe Coni, Jean Luc Bardon, Xavier Servantie THALES AVIONICS SAS
Overview A 3D Full Windshield Head Up Display A brief history of HUD in Aircraft Cockpit HUD Values & Issues Full windshield concept Simulated collimation Holographic Windshield approach Introduction to HOE Reflection efficiency (VS direct reflection) Conclusion Paper # (if applicable) 2
A brief history of Head Up Display 1961 Blackburn Buccaneer attack aircraft First HUD introduced in aircraft Used as a Strike sight First HUD application: Mean of targeting Paper # (if applicable) 3
HUD values Symbol appears Eyes Out on landscape No need to look down at displays Improve situational awareness Symbol appears in conformity with landscape Aircraft Collimated image No parallax issue Enable Augmented Reality applications Car Paper # (if applicable) 4
HUD issues Difficulties to install Footprint on overhead (Aircraft) or Large volume under glareshield (Automotive) Aircraft Limited optical performances Poor field of view (Automotive) Small eyebox (Aircraft) Single user Car Paper # (if applicable) 5
HUD : Avionics Combiner in front of the eyes PRO : Large field of view (Typically 30 x 20 ) CONS : Complex mechanism Overhead projection system PRO: Collimated images near infinity CONS: Head clearance CONS: Small Eye Motion Box Aircraft Paper # (if applicable) 6
HUD : Automotive Windshield projection PRO : Large Eye Motion Box CONS : Optical efficiency (Reflection rate less than 20%) HUD Box Car PRO: Nothing on overhead CONS: Narrow field of view (No more than 7 x 4 ) Large volume, large mirror to improve the vertical field of view Paper # (if applicable) 7
HUD : The FOV / EMB compromise HUD: An Optical system Input : Generated picture A 1 (Area, Aperture) Optical system (Folded mirror, relay optics ) Output: Eyebox A 2 (Eye box, Field of view) A1 1 2 A2 Geometrical Etendue An invariant relationship E between optical system, input A 1 and output A 2 A compromise between FOV and EMB Avionics: Small EMB/Large FOV Automotive: Large EMB/Small FOV Paper # (if applicable) 8
Direct Projection: Full Windshield HUD New technology on the rise Cheaper Smaller footprint (Small projector instead of large HUD box) Lighter Wide Field Of View & Eye Box Potentially sharable Needs a transparent projection screen Not collimated Accommodation / Vergence issue 9
The vergence / focus mismatch issue When looking outside: The eye vergence is almost parallel Nearby images displayed on the windshield are duplicated The focus is performed at infinity Nearby images displayed on the windshield are blurry 10
Solving the vergence issue Simulated collimation could be performed thanks to stereoscopy Solves the duplicated image issue Solves the conformity issue if associated with a head tracking system Allows 3D images display (Volumic or in several planes) 11
3D Glasses for a see-through use Need to be highly transparent Technology: Passive, left and right separation performed by spectral filtering (Notch filter) Green band for left eye Green band for right eye P. Coni,et al., A 3D Head Up Display with Simulated Collimation, SAE ASTC 2016, Technical Paper 2016-01-1978, 2016, doi:10.4271/2016-01-1978 12
Remaining issue: Focus & Visual acuity Using Stereoscopy: Vergence is forced at infinity (Symbol and Landscape) Accommodation is performed at infinity (Landscape) Symbol are displayed at short distance (On transparent screen) Symbol appears blurred if the viewing distance is too short Need to find a compromise Unacceptable loss of visual acuity Small visual acuity loss Ideal Ideal screen distance: > 1m70 Acceptable distance: > 0.60 m (With compromise on symbol size) P. Coni,et al., A Full Windshield Head-Up Display using Simulated Collimation, Proceedings of Display Week San Francisco 2016 (Mai 2016) 13
Windshield HUD: The screen problematic Image projected at finite distance: Use of windshield as projection screen Need of a high transmission ratio (> 75%) Need to reemit the image from the projector toward Eye Motion Box Need a contrast ratio greater than 30% (Symbol luminance greater than 30% of outside luminance) First technology tested: Dot patterned glass Issues: Reemits projector image out of EMB Reemits also any other light source (Sun coming from rear) Paper # (if applicable) 14
Windshield HUD: The Holographic solution HOE: Working on spectral dimension of light Narrow bandwidth Better efficiency with a narrow bandwidth light source Better transmission outside working bandwidth Photopic Tr > 76% (Outside working frequency: >90%) Reflective-Diffusing function Done with Holographic Optical Element Optical function: To spread the incoming light over the Eye Box, at a given wavelength Totally transparent out of these conditions Reflection ratio: > 85% Paper # (if applicable) 15
Windshield HUD: First Prototype Spectral Multiplexing on HOE Two Narrow bandwidths One for the left eye Another for the right eye Stereoscopic display by using spectral goggles Proof of concept Stereoscopic display Simulated collimation Issues HOE efficiency for both wavelengths Need of two multiplexed HOE Simulated collimation using Wavelength multiplexing Paper # (if applicable) 16
Windshield HUD: Discussion Windshield HUD using HOE Diffusing / Reflective function is demonstrated Efficiency > 85% compared to automotive windshield (<20%) Sunlight readable Wide eyebox: Sharable by the crew Small cockpit footprint Break the Etendue constraint Need only one pico-projector High luminance pico-projector (Courtesy of Texas Instrument) Unlimited Eye Box: A transparent display shared by the crew Paper # (if applicable) 17
Conclusion Large Field of View Head Up Displays Augmented reality experience in vehicle needs an immersive display, Using the full windshield is proposed as the solution Conventional optics can t achieve this goal and stay with a reasonable size HOE brings the solution The future of Head Up Display will be Holographic! Paper # (if applicable) 18