Flat-panel laser displays through large-scale photonic integrated circuits

Abstract

Laser-based displays are highly sought after for their superior brightness and colour performance¹, especially in advanced applications such as augmented reality (AR)². However, their broader use has been hindered by bulky projector designs and complex optical module assemblies³. Here we introduce a laser display architecture enabled by large-scale visible photonic integrated circuits (PICs)^4-7 to address these challenges. Unlike previous projector-style laser displays, this architecture features an ultra-thin, flat-panel form factor, replacing bulky free-space illumination modules with a single, high-performance photonic chip. Centimetre-scale PIC devices, which integrate thousands of distinct optical components on-chip, are carefully tailored to achieve high display uniformity, contrast and efficiency. We demonstrate a 2-mm-thick flat-panel laser display combining the PIC with a liquid-crystal-on-silicon (LCoS) panel^8,9, achieving 211% of the colour gamut and more than 80% volume reduction compared with traditional LCoS displays. We further showcase its application in a see-through AR system. Our work represents an advancement in the integration of nanophotonics with display technologies, enabling a range of new display concepts, from high-performance immersive displays to slim-panel 3D holography.

Fig. 1. Concept of flat-panel laser displays.

a, Schematic of a conventional laser projector using free-space illumination. It consists of laser sources, collimating lenses, dichroic mirrors, beam-shaping elements, a polarizing beam splitter and a display panel. b, Schematic of the proposed flat-panel laser display. A PIC is used to replace the free-space illumination module and integrated directly onto the display panel, achieving a compact flat-panel form factor. c,d, Comparison of LED and laser illumination. c, Typical LED lightguide illuminators, or backlights, use several layers of diffusers and light filters to tailor the spatial, angular, spectral and polarization characteristics of light, resulting in low optical efficiency. d, The PIC illuminator eliminates the need for lossy diffusers and filters by guiding and tailoring the light characteristics on-chip.

Fig. 2. Device design and fabrication.

a, Schematic of the flat-panel laser display stack. The PIC is placed between a LCoS display panel and a polarizer. It expands the laser inputs over an area to illuminate the LCoS panel. The LCoS panel then reflects the light and modulates its polarization spatially, which is converted into intensity modulation after passing through the polarizer. b, Polarization rotation at the liquid crystal layer. In the dark state, the liquid crystal molecules are aligned vertically, leaving polarization unchanged, so the reflected light is blocked by the cross-polarizer. In the bright state, the liquid crystal molecules form a twisted structure that rotates the polarization of light by 90° on reflection, resulting in a bright state. c, Schematic of the PIC layout. d, Zoom-in view of the grating emitters. The RGB emitters are placed side by side, sharing the same core and grating layers. For each emitter, the grooves transverse to the core waveguide are short gratings for light extraction. The grating pitch determines the emission direction and the grating length determines the divergence angle. The grooves parallel to the core waveguide are impedance-matching structures. They are introduced between adjacent emitters to minimize the scattering loss. e, Cross-section view of the PIC stack. It consists of a 50-nm SiN core (t_c), a 170-nm SiO₂ spacer (t_s) and a 55-nm AlO_x grating layer (t_g). The core waveguide widths (w_r/g/b) and the grating pitches (p_r/g/b) are optimized separately for R, G and B. f, Optical image of a 200-mm-diameter PIC wafer. g, Optical image of the device before the wafer is transferred to the glass substrate (see Methods). h, SEM image of the cross-sectional layer stack. i, SEM image of the Y-splitters. Scale bars, 5 mm (g), 500 nm (h), 3 μm (i).

Fig. 3. Display performance analysis.

a, Key display performance factors and the corresponding PIC design space. b, Simulated grating strength as a function of the SiO₂ spacer layer thickness t_s for R, G and B. The SiN core thickness and the AlO_x grating layer thickness are fixed at 50 nm and 55 nm, respectively. c, Simulated brightness uniformity, colour uniformity and light extraction efficiency as a function of t_s. The green shading represents the allowable range for brightness uniformity, min/max > 0.8. The orange shading represents the allowable range for colour uniformity, Δu′v′ < 0.01. d, Measured uniformity map of a fabricated PIC illuminator. The device size is 6.0 mm by 4.8 mm. e, Zoom-in view of the PIC emitters. f, Schematic of the grating emitters. g, Simulated far-field intensity profiles for Y-polarization (transverse to the polarizer transmission axis). The dashed circle represents the target cone angle. h, Simulated far-field intensity profiles for X-polarization (parallel to the polarizer transmission axis). i, Line, simulated PER as a function of the light collection half angle. Star, measured PER at 11° half cone angle. j, Simulated diffraction efficiency into the ghost orders. KPI, key performance indicator. Scale bars, 1 mm (d), 20 μm (e).

Fig. 4. Measured display images under direct view and AR configurations.

a, The assembled flat-panel laser display shown on top of a dime coin. A fibre is attached to the PIC for light input. The flex cable is for LCoS control. The light sources and laser controllers are not shown in the photo. b, Colour performance of this work in comparison with standard colour spaces. c–f, Measured display images. g, Photo of the handheld AR set-up used in the experiment. h, Conceptual visualization of an AR system integrated with a form-factor-optimized flat-panel laser display. i,j, Images captured by a camera at the eye position of the AR set-up in panel g, showing the displayed virtual objects and real world of an office. Image credit: NASA.

Fig. 5. New display concepts enabled by PICs.

a, Concept of zonal illumination. Zonal illumination can enhance image contrast and efficiency by turning on the illumination only where needed. It can be realized by using active PIC modulators. b, Schematic of a PIC-enabled holographic display. The PIC provides a tailored illumination field, which feeds into one or several layers of spatial light modulators (SLMs) for hologram generation. A flat lens, such as a holographic optical element, is then used to project and magnify the image.