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Super-high-density display could solve VR issues

Super-high-density LCD displays have been developed that use a new ‘blue-phase’ liquid crystal, allowing for triple the number of pixels on the same size screen with reduced power consumption.

The technology would be beneficial for virtual reality (VR) devices as displays are currently not high resolution enough and individual pixels can be discerned by the viewer due to the close proximity of the headset to the user’s face.

“Today’s Apple Retina displays have a resolution density of about 500 pixels per inch,” said Shin-Tson Wu, who led the research team at the University of Central Florida’s College of Optics and Photonics.

“With our new technology, a resolution density of 1500 pixels per inch could be achieved on the same sized screen. This is especially attractive for virtual reality headsets or augmented reality technology, which must achieve high resolution in a small screen to look sharp when placed close to our eyes.”

Although the first blue-phase LCD prototype was demonstrated by Samsung in 2008, the technology still hasn’t moved into production because of problems with high operation voltage and slow capacitor charging time.

To combat these issues, the researchers combined the new liquid crystal with a special performance-enhancing electrode structure can achieve light transmittance of 74 per cent with an operation voltage of 15 volts per pixel. These operational levels could finally make field-sequential colour displays practical for product development.

“Field-sequential colour displays can be used to achieve the smaller pixels needed to increase resolution density,” said Yuge Huang, first author of the research paper. “This is important because the resolution density of today’s technology is almost at its limit.”

Today’s LCD screens contain a thin layer of nematic liquid crystal through which the incoming white LED backlight is modulated.

Thin-film transistors deliver the required voltage that controls light transmission in each pixel. The LCD subpixels contain red, green and blue filters that are used in combination to produce different colours to the human eye. The colour white is created by combining all three colours. An example of what a traditional LCD looks like at the microscopic level can be seen below.

Blue-phase liquid crystal can be switched, or controlled, about 10 times faster than the nematic type. This sub-millisecond response time allows each LED colour (red, green and blue) to be sent through the liquid crystal at different times and eliminates the need for colour filters. The LED colours are switched so quickly that our eyes can integrate red, green and blue to form white.

“With colour filters, the red, green and blue light are all generated at the same time,” said Wu. “However, with blue-phase liquid crystal we can use one subpixel to make all three colours, but at different times. This converts space into time, a space-saving configuration of two-thirds, which triples the resolution density.”

The blue-phase liquid crystal also triples the optical efficiency because the light doesn’t have to pass through colour filters, which limit transmittance to about 30 percent. Another big advantage is that the displayed colour is more vivid because it comes directly from red, green and blue LEDs, which eliminates the colour crosstalk that occurs with conventional colour filters.

Wu’s team worked with JNC to reduce the blue-phase liquid crystal’s dielectric constant to a minimally acceptable range to reduce the transistor charging time and get submillisecond optical response time.

However, each pixel still needed slightly higher voltage than a single transistor could provide. To overcome this problem, the researchers implemented a protruded electrode structure that lets the electric field penetrate the liquid crystal more deeply. This lowered the voltage needed to drive each pixel while maintaining a high light transmittance.

“We achieved an operational voltage low enough to allow each pixel to be driven by a single transistor while also achieving a response time of less than one millisecond,” said Haiwei Chen, a doctoral student in Wu’s lab. “This delicate balance between operational voltage and response time is key for enabling field sequential colour displays.”

“Now that we have shown that combining the blue-phase liquid crystal with the protruded electron structure is feasible, the next step is for industry to combine them into a working prototype,” said Wu. “Our partner AU Optronics has extensive experience in manufacturing the protruded electrode structure and is in a good position to produce this prototype.”

Wu predicts that a working prototype could be available in the next year. Since AU Optronics already has a prototype that uses the protruded electrodes, it will only be a matter of working with JNC to get the new material into that prototype.

Last month, HTC revealed a virtual reality sensor that enables users of the Vive VR system to bring physical objects into the virtual world. 

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