Recent Advancements in Laser-based AR Engines

Several papers at the Frontiers in Optics and Laser Science conference described advancements in lasers or laser sub-systems for AR glasses. VitreaLab for example, has been developing an LCOS illumination module that includes hundreds of tiny embedded waveguides to direct red, green and blue laser light to the LCOS imager. The innovation here is the laser-writing of these tangled single-mode waveguides in the glass substrate in such a way as to deliver a uniform RGB light source at its output. Each color has its own network of waveguide channels.

They call this device a Quantum Light Chip (QLC) with the latest Gen. 5 design highlighted at the conference. This small angular distribution of the laser sources means the QLC can be more compact and optically efficient compared to an LED light source. Efficiency can also come by shrinking the pulse width but increasing the intensity of the laser light vs. LED illumination. But lasers can have speckle, so VitreaLab adds a MEMS modulator to wiggle the laser light just enough to destroy its coherence.

The Figure below provides the specifications on their Gen 5 engine. But on their roadmap are two additional designs that will offer a 50-degree FOV (~1cc, 10 lm/W, 1440 x 1440, and a 2 mm pupil) and a 30-degree FOV (~0.5 cc, 800 x 800, 10 lm/W, 1.5 mm pupil). The company did not specify if these would be full color, but it does now have a partnership with Brillian RGB to supply the RGB lasers.

VitreaLabs’ Gen 5 LCOS Illumination Engine is Green Only

Taking a different tack was AlphaLum, an ams Osram spin-out, which introduced a 24-channel RGB laser illumination engine for Laser Beam Scanning (LBS) architectures. With conventional LBS, single red, green and blue lasers are combined to illuminate the MEMS mirror simultaneously. The idea here is to parallelize the illumination of the MEMS mirror by modulating and scanning 24 lasers sources as eight full-color RGB pixels spatially separated from each other. That allows for faster scanning and/or more pixels.

AlphaLum’s 24-channle Laser Engine Offer Parallel Laser Beam Scanning

AlphaLum has developed red, green and blue laser modules with 8 lasers per module. Each module has a dedicated driver IC to individually address each laser with pulses as short as 3 ns (4.8 G pulses/second). The laser spots are diffraction limited with a prototype system delivering more than 30 pixels per degree (20/40 vision) and a 60-degree FOV. Color correction is implemented using laser temperature monitoring as the output wavelengths are quite temperature sensitive.

On the development roadmap is further integration to create a 45 x 25 mm solution with a high efficiency of > 21 lm/W.

Kyocera/SLD Laser noted that LBS applications or fiber-coupled applications prefer circular laser beam profile over an elliptical one for increased pixel density or more efficient fiber coupling. The company is working on a solution for single mode operation, but it is trying to reduce the increased threshold current that normally happens when going to a circular profile.

Sony Semiconductor Solutions described an important advancement in miniaturizing diode-pumped solid-state surface-emitting lasers (DPSSEL). The currently available device emits at 1030nm, which is not a visible wavelength, so why the interest? As described in a separate article: Wave-Mixing Display Concept for AR Glasses Revealed, new IR wave-mixing techniques are emerging that will allow two IR laser beams to mix on the surface of a pair of AR glasses to create visible images and symbology. So tiny IR lasers are needed.

Conventional DPSSEL lasers are passively Q-switched offering much higher power in a larger package compared to Vertical Cavity Surface-Emitting Lasers (VCSEL). They must also be optically pumped vs. electrically pumped VCSELs. Sony has managed to shrink the size of these lasers to a tiny 1 mm³ volume. This tiny package can create 450 picosecond pulses with up to 57 kW of optical power or over 300 mW average power. Sony is also developing devices to emit at 946 nm and 1313 nm all for wave-mixing displays.