For microdisplays used in augmented reality (AR) devices, liquid crystal on silicon (LCoS) had an advantage over LED on silicon (LEDoS) in brightness, Raontech CEO Brian Kim told TheElec.
LCoS changes the phase of the reflected light while LEDoS forms self-emitting LEDs on the silicon.
Kim’s argument is contradictory to the majority of experts that believe LEDoS will be more optimal for AR devices.
The Raontech CEO said AR glasses must be transparent like conventional glasses so that the wearer’s eyes are visible.
This requires a transparent glass with a thin waveguide lens, he said. Waveguide lens has an optical efficiency of 1% or less, which means AR glasses require an incredibly bright display, the CEO said.
For the wearer of the AR glass to be able to view the outside world, the microdisplay must be placed at the leg of the glass, or on the sides. The screen emitted from these displays is shown in front of the wearer’s eyes through the waveguide lens.
According to Kim, LCoS can use MiniLEDs with 3 million nits in brightness as its light source; these, because of reflection, in effect will be expressed in 300,000 to 400,000 nits in brightness and around 3,000 nits (1% from the waveguide) once it reaches the wearer’s eyes.
Meanwhile, for LEDoS, the sizes of the LEDs are to be reduced to such an extent to micrometers scale that their efficiency also nosedives, the CEO said.
The market has been surprised by this drop in brightness and the technology to overcome this problem will take substantial time to develop, Kim said.
The Raontech CEO also believes OLED on silicon won’t be able to be used in AR glass as it only offers thousands of nits in brightness and at most 10,000 nits will be its limits.
OLEDoS in Apple Vision Pro currently has a brightness of between 1,000 to 3,000 nits and the product is more of a mixed reality (MR) ‘goggle’ than a MR glass, Kim said.
OLEDoS can be used in some AR devices that have tinted glass or are similar to sun glass but they won’t be able to be made thin or be used outside for wearers to move around.