Metasurface Research Could Usurp LCDs as Flat Screen Technology

In many fields of electrical engineering, a major focus of technological advances has always been developing devices that are faster, smaller, and more efficient than the current state of the art. One example of this was the invention of liquid-crystal displays (LCDs) in the late 1960s, which revolutionized the display industry, leading to thinner and more energy-efficient displays. 

However, even with the many benefits of LCDs, they still have their limitations. To overcome these limitations, researchers are looking into metasurfaces as an emerging technology which has the potential to replace LCDs. Along just those lines, last week UNSW Sydney announced that a team of researchers have developed a new proof of concept of metasurfaces as a display technology.

The research team spans a group across three universities, including Nottingham Trent University in the UK, UNSW Canberra, and the Australian National University. In this article, we will explore the new research, we’ll discuss what metasurfaces are, and why they could replace LCD.

 

Researchers Develop Metasurface Display

As described in their paper in Nature, the team of researchers developed a new electrically tunable metasurface that can be programmed across multiple pixels. To achieve this, the researchers used a new technique to enable electrical tunability in the metasurface, which exploits silicon's large thermo-optical effect.

 

A rendering of the researchers’ metasurface device. Image used courtesy of UNSW Sydney

 

Specifically, the team developed a CMOS-compatible method based on silicon's thermo-optical effect to control the optical properties of a silicon hole array metasurface using a localized transparent heater driven by biased voltages of less than 5 V. The heating causes a change in silicon's refractive index, which leads to a shift in the metasurface's resonance, resulting in an abrupt transparency change at the resonant wavelength. 

The resulting device operates at transmission regime, has low optical loss, low input voltage requirements, and operates with higher than video-rate switching speed. Notably, by applying an asymmetric driving voltage, the researchers achieved flash heating and observed a modulation time of 625 μs, which is over ten times faster than the human eye's detection limit. 

 

What Are Metasurfaces?

To put this news into context, it’s important to look more closely at how metasurfaces function. Metasurfaces are two-dimensional arrays of subwavelength elements that manipulate light to produce desired effects.

These subwavelength elements are usually smaller than the wavelength of light they interact with, and they can be designed to alter the properties of the light that passes through them. For example, a major application of these arrays is to selectively transmit or reflect incident light to focus and steer it in a desired fashion.

 

Some of the applications for metasurfaces. Image used courtesy of Hsiao and coauthors

 

Using nanofabrication techniques, metasurfaces today can work with millimeter waves, microwaves, and visible light. The elements can be made of different materials, such as metals or dielectrics, and can be arranged in different patterns to achieve specific effects.

Because of their ability to be fabricated on a nano scale, and their ability to control the direction and polarization of light, metasurfaces have found potential in many applications, including communication systems, sensing, and imaging. 

 

Why Metasurfaces Could Replace LCDs

There is a compelling argument for using metasurfaces in the field of display technology, where many believe they can eventually replace LCDs.

The basic operation of a metasurface-based display would involve a light source, such as an LED, which emits light onto the metasurface. The metasurface then manipulates the light waves to produce the desired effect, such as producing an image or changing the color of the light. This manipulation of light waves is achieved by controlling the phase, amplitude, and polarization of the light waves using the subwavelength elements of the metasurface.

 

Example of a metasurface display. Image used courtesy of Jianxiong Li and coauthors

 

To produce an image, for example, a metasurface could be designed to act as an array of tiny pixels. Each pixel would consist of a subwavelength element that can control the phase, amplitude, and polarization of the light. By adjusting these properties of the light, the metasurface can produce different colors and intensities of light, creating an image.

One advantage of metasurfaces is their ability to produce wider viewing angles than LCDs. LCDs tend to use polarizers to control the direction of light, which can limit the viewing angle of the display. Metasurfaces, on the other hand, can be designed to control the polarization of light, which can lead to wider viewing angles.

Additionally, metasurfaces have the advantage of improved energy efficiency over LCDs.A major source of energy expenditure in LCDs is the need for a backlight to produce images. Metasurface-based displays would not need a backlight, and therefore could lead to much more energy efficient solutions.

 

Beyond Proof-of-concept?

While their research is only a proof-of-concept, the team of researchers highlighted in this UNSW Sydney news are optimistic that their findings are the first step in the right direction towards developing fully commercializable metasurface-based displays.