Printable laser-emitting ‘droplets’ offer new display technology

30 Dec 2024

Tsukuba group creates compact laser emitter by arranging droplets on circuit board.

Researchers at the University of Tsukuba, Japan, have developed a novel method for rapidly creating laser light sources in large quantities using an inkjet printer that ejects laser-emitting droplets.

By applying an electric field to these droplets, the researchers demonstrated that switching the emission of light on and off is possible. Furthermore, they successfully created a compact laser display by arranging these droplets on a circuit board.

The achievement is described in Advanced Materials.

Displays for TVs, PCs, and smartphones are continually improving in picture quality, clarity, and energy efficiency. Laser displays are anticipated to represent the next-generation model. Particularly regarding brightness and color reproducibility, laser displays have the potential to overcome the intrinsic limitations of conventional light-emitting devices, such as OLEDs and liquid crystals.

However, to be effectively used as displays, the components must be miniaturized beyond current levels and laid out in high density and large quantities. In this study, the researchers found that droplets of a specific organic liquid, ejected by an inkjet printer, emit laser light. The laser light can be switched on and off by applying an electric field to the droplets. These droplets are extremely small (30 µm in diameter) and can be densely arranged in large quantities over areas as large as several centimeters.

When an electric field is applied to the droplet by positioning it between electrodes, the spherical droplet deforms into an ellipsoidal shape, causing the laser light emission to cease. This demonstrated that the droplet functions as an electrically switchable “laser pixel”. Additionally, the researchers discovered that the laser emission of each pixel can be individually controlled in a 2×3 array of these droplets.

Further improvements in the configuration of electrical devices and laser performance are expected to contribute significantly to the future development of commercial laser displays.

Paper abstract

Following is the abstract from the paper in Advanced Materials.

“Conventional laser panel displays are developed through the mass integration of electrically pumped lasers or through the incorporation of a beam steering system with an array of optically pumped lasers. Here (we report) a novel configuration of a laser panel display consisting of a non-steered pumping beam and an array of electrically Q-switchable lasers.

“The laser oscillator consists of a robust, self-standing, and deformable minute droplet that emits laser through Whispering-Gallery Mode resonance when optically pumped. The laser oscillation is electrically switchable during optical pumping by applying a vertical electric field to the droplet.

“Electromagnetic and fluid dynamics simulations reveal the deformation of the droplet into a prolate spheroid under the electric field and associated attenuation of quality factor (Q-factor), leading to the halt of the laser oscillation. A 2 × 3 array of droplets is fabricated by inkjet printing as a prototype of a laser panel display, and it successfully achieves the pixel-selective switching of the oscillation.”

Conclusion: “A novel electrically switchable droplet laser and its array is demonstrated. The droplets are deposited by inkjet printing with high precision and scalability, and its laser oscillation is switchable by applying an electric field using a pair of electrodes. Fluidic dynamics and electromagnetic simulations revealed the deformation of the droplet and the concomitant Q-attenuation. This novel device configuration for laser switching will contribute to future advancements in laser displays, although the pumping energy and the lifetime of the laser dyes must be improved beforehand.”