On April 15, Pohang University of Science and Technology (POSTECH) announced that a research team led by Professor Choi Soo-suk from the Department of Electrical and Computer Engineering has developed a new generation of color-tunable laser emission technology. It enables continuous color tuning of laser light at a voltage lower than that of a single AA battery, with color purity dozens of times higher than that of existing OLEDs. The research was recently featured on the cover of Laser & Photonics Reviews, an international journal in the field of optics.
Why Is OLED Color Not Pure Enough?
Color purity depends on how narrow the emission spectrum is. Imagine a beam of light as a crowd: if everyone stands at the exact same spot (the same wavelength), the light will be extremely pure in color. If the crowd is widely scattered (a broad wavelength distribution), the color will appear muddy.An ideal monochromatic light should have an emission bandwidth of approximately 1 nm. However, conventional OLED emitters have a bandwidth of around 40nm. Quantum dot materials perform slightly better, but still have a bandwidth of about 30nm. This is why the red on a screen never quite matches true, pure red—the spectrum is too wide, and the color is "diluted."
This issue is even more critical for holographic displays and next-generation AR and VR devices. These applications require precise control over the phase and diffraction of light, which demands light sources with ultra-narrow spectra at the laser level. The traditional approach of mixing RGB light sources in OLEDs suffers from low light efficiency and limited color gamut, making it unsuitable for these uses.
Why Is OLED Color Not Pure Enough?
Color purity depends on how narrow the emission spectrum is. Imagine a beam of light as a crowd: if everyone stands at the exact same spot (the same wavelength), the light will be extremely pure in color. If the crowd is widely scattered (a broad wavelength distribution), the color will appear muddy.An ideal monochromatic light should have an emission bandwidth of approximately 1 nm. However, conventional OLED emitters have a bandwidth of around 40nm. Quantum dot materials perform slightly better, but still have a bandwidth of about 30 nm. This is why the red on a screen never quite matches true, pure red—the spectrum is too wide, and the color is "diluted."
This issue is even more critical for holographic displays and next-generation AR and VR devices. These applications require precise control over the phase and diffraction of light, which demands light sources with ultra-narrow spectra at the laser level. The traditional approach of mixing RGB light sources in OLEDs suffers from low light efficiency and limited color gamut, making it unsuitable for these uses.
How Was the 1 nm Emission Bandwidth Achieved?
The POSTECH team combined an OLED emitter with chiral liquid crystal (CLC). Chiral liquid crystal molecules are arranged in a helical structure like a spring, which can selectively resonate and amplify light of a specific wavelength. Leveraging this property, the team "filtered" the originally broad emission spectrum of the OLED emitter through the resonant structure of the chiral liquid crystal, compressing the emission bandwidth to approximately 1nm.As a result, the color purity is dozens of times higher than that of conventional OLEDs, reaching the level of laser light sources.
Color Tuning at the Voltage of a Single Battery?
Even more remarkably, the team can actively control the emission wavelength of the laser. The principle is somewhat similar to thermal expansion and contraction. When an electric current is applied to the device, the slight heat generated alters the helical pitch of the chiral liquid crystal, which in turn changes the resonant wavelength and continuously shifts the emission color.Crucially, a voltage below 1.5 V is sufficient to achieve a wavelength modulation range of roughly 135nm, covering the entire visible light spectrum. Previous laser color-tuning technologies either required high voltages or offered only narrow tuning ranges. The ability to cover the full color gamut at 1.5V greatly enhances practical applicability.
What Are the Benefits of a Single Pixel Emitting All Colors?
Current displays consist of three sub-pixels (red, green, and blue) per pixel, which produce various colors by adjusting the brightness ratio of the three. This requires three sets of driving circuits for three sub-pixels, resulting in a complex structure.With POSTECH’s new technology, a single pixel can continuously generate all colors. No color mixing is needed—one device achieves full-color emission. This means display structures can be greatly simplified, pixel density can be increased, and power consumption can be reduced.
Potential Applications
Beyond holographic displays and AR/VR devices, this technology may also be applied to optical communications, biosensors, next-generation optoelectronic semiconductors, and other fields.The research was funded by the Samsung Future Technology Cultivation Fund, and the South Korean display industry is paying close attention to this direction.Professor Choi Soo-suk of POSTECH stated that by integrating display materials with chiral liquid crystals, the technology has realized ultra-high-purity laser emission and precise low-voltage control, and has the potential to become a platform technology that reshapes the structure of displays and optoelectronic devices in the future.
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