Laser beam scanning

Laser beam scanning (LBS), also called laser beam steering or scanned laser display, is a projection-display method that forms an image by sweeping one or more modulated laser beams across a surface or the eye with a moving mirror, usually a microelectromechanical systems (MEMS) mirror. Instead of illuminating an array of pixels at once, as a panel display does, an LBS engine writes the image one point at a time: red, green, and blue laser diodes are combined into a single beam whose brightness is modulated as the mirror steers it through a raster or Lissajous pattern, so each position of the beam corresponds to a pixel.

In virtual and augmented reality, LBS is used as the light engine for several near-eye displays. Its small size, low power draw, and ability to keep every pixel in focus regardless of the optics make it attractive for smart glasses and optical see-through devices, where the scanned light is coupled into a waveguide display or projected onto a holographic optical element and then to the retina. The best-known VR/AR product to use it is the Microsoft HoloLens 2, whose scanning engine was supplied by MicroVision. LBS has produced compact, see-through displays, but in practice it has delivered lower resolution and worse image uniformity than competing microdisplay technologies, which has limited its adoption.

How it works

An LBS display has three main parts: a light source, a scanning mirror, and the optics that route the scanned light to the viewer. The light source is normally a set of red, green, and blue laser diodes whose beams are collimated and merged through lenses or dichroic combiners into one beam. Because lasers are nearly monochromatic, the combined beam can reach a wide color gamut, and the output is controlled directly by varying the drive current of each diode, so no separate light modulator is needed.

The combined beam strikes a MEMS mirror, a small reflective plate suspended on torsional hinges that tilts under an electrostatic, piezoelectric, or electromagnetic drive signal. As the mirror tilts, it steers the beam across the image field. The brightness of the lasers is modulated in step with the mirror's motion, so the moving spot traces out a two-dimensional image. The field of view of the display is set by the mechanical scan angle of the mirror rather than by the physical size of any panel, which means the field of view can be enlarged without making the imaging device larger.

Two mirror arrangements are common. In a two-mirror (or two-chip) design, one mirror scans the fast axis at its mechanical resonance, often in the tens of kilohertz, while a second mirror scans the slow axis linearly to step the beam down the frame, producing a raster pattern similar to a cathode ray tube. In a single-mirror (one-chip) design, a single two-axis mirror is driven at resonance on both axes at once, tracing a Lissajous pattern. A 2023 study in the journal Optics Express reported that Lissajous scanning can give larger scan angles and better tolerance to external vibration than raster scanning, at the cost of more complex control to keep the fill factor uniform.

Because the laser beam itself is narrow and stays collimated, the projected image is in focus over a wide range of throw distances without focusing optics. LBS is also an additive, emissive method: when the displayed content is black the lasers are simply switched off, so a dark image consumes almost no power and, in a see-through display, lets the wearer see straight through the optic.

Origin and the PicoP platform

The most developed commercial LBS platform came from MicroVision, a company based in Redmond, Washington that grew out of work on scanned-beam retinal displays and that describes itself as a pioneer of the technology. MicroVision adapted scanning techniques it had used in handheld bar-code readers into a miniature projector engine it marketed as PicoP. The engine uses red, green, and blue lasers and a MEMS mirror in a package small enough for handheld and embedded projectors. In 2016 MicroVision and STMicroelectronics agreed to co-market MEMS mirror based LBS solutions, with STMicroelectronics manufacturing the MEMS die to MicroVision's design. The PicoP engine appeared in consumer pico-projectors such as Sony's MP-CL1 mobile projector before the technology was applied to near-eye AR.

Use in VR and AR

Microsoft HoloLens 2

The Microsoft HoloLens 2, announced in 2019, is the highest-profile mixed reality product built on laser beam scanning. The earlier first-generation HoloLens (2016) had used liquid-crystal-on-silicon (LCoS) microdisplays; for the second generation Microsoft switched to an RGB laser engine with MEMS mirrors. Microsoft's advanced optics general manager Zulfi Alam described the change as moving "to lasers" and "instead of using a LCOS or a DLP-type approach" using "these micro-electronic mirrors called MEMS." Microsoft stated the change roughly doubled the diagonal field of view, from about 36 degrees on HoloLens 1 to about 52 degrees on HoloLens 2.

The scanned beams are coupled into a diffractive waveguide display that relays the image to the eye and overlays it on the real world. The engine itself came from MicroVision. In April 2017 MicroVision disclosed a development and supply contract with an unnamed "leading technology company" worth up to about 24 million dollars to build a new generation of MEMS, ASICs, and firmware for a high-resolution LBS product; a 2020 teardown of HoloLens 2 confirmed MicroVision MEMS laser scanning modules inside the device.

Independent analysis found the LBS approach harder to make sharp than panel displays. Optics analyst Karl Guttag, examining HoloLens 2, reported roughly 854 scan lines across about a 29-degree vertical field of view, visible scan-line and interlacing artifacts, flicker at or below 60 Hz, and poorer color uniformity than HoloLens 1, attributing the limits to the mechanical speed and acceleration of the resonant scanning mirror.

Smart glasses: Intel Vaunt, North, and Bosch

Several lightweight smart glasses have used a related variant in which a low-power laser is scanned and reflected off a holographic optical element in the lens straight onto the retina, a form of virtual retinal display. Intel's Vaunt prototype, shown in 2018, used a vertical-cavity surface-emitting laser (VCSEL) to project a monochrome red image of about 400 by 150 pixels onto a holographic reflector in the lens and then to the eye. Intel shut down its wearables group and cancelled Vaunt in April 2018.

The Canadian company North acquired the laser display patents behind Vaunt (originating with Lemoptix and Composyt Light Lab) and used a color laser-to-holographic-combiner display in its Focals glasses, which shipped in early 2019 with a narrow field of view of roughly 15 degrees. North was acquired by Google in 2020 for a reported figure of about 180 million dollars; Google wound down the existing Focals and cancelled the planned Focals 2.0, ending support for shipped units on 31 July 2020.

Bosch Sensortec demonstrated a laser scanning module for smart glasses, Light Drive, at CES 2020 and offered it to high-volume manufacturers as part BML500P. The module uses three laser diodes and a MEMS mirror to scan a holographic element embedded in one lens, which reflects the image onto the retina; Bosch states the complete system weighs under 10 grams and remains readable in bright sunlight.

Advantages and disadvantages

The reported advantages of LBS for near-eye displays are a very small light-engine footprint, often described as no larger than a sugar cube; low power, because the lasers are off for dark content and the engine is additive; a focus-free, always-sharp beam; a wide laser color gamut and high peak brightness for outdoor use; and a field of view that scales with mirror scan angle rather than panel size.

The disadvantages are largely about image quality and have constrained real products. Resolution is bounded by how fast and how far the resonant mirror can swing, which produces visible scan lines, interlacing artifacts, and flicker at low refresh rates, as observed on HoloLens 2. Retinal-projection smart glasses such as Focals had very narrow fields of view and, because the image is thrown through the air to the eye, could be blocked by anything in the line of sight, including the wearer's hair, and presented a single, monoscopic image without depth. Because the light is coherent, scanned-laser displays can also show speckle, a grainy interference pattern, although coverage of the specific products above does not detail their speckle performance.

Current status

As of 2026 laser beam scanning remains a niche AR display method rather than a mainstream one. Microsoft's HoloLens 2 was the main shipping VR/AR product using it, and its supplier MicroVision had by the early 2020s redirected most of its business toward automotive lidar while retaining the underlying MEMS laser scanning platform. The retinal-projection smart glasses that used the approach, Intel Vaunt and North Focals, were both discontinued, and North's technology passed to Google. Most newer consumer AR glasses have instead adopted Micro-OLED, microLED, or LCoS microdisplays paired with waveguides or birdbath optics, while MEMS laser scanning continues to be developed by suppliers such as Bosch and OQmented for compact smart-glasses modules.

See also

• Waveguide display
• Virtual retinal display
• Microdisplay
• Optical combiner