VitreaLab’s Demo Kit Gen 1.0: Pure Colours and Exceptional Brightness
VitreaLab has revealed its first portable demo kit of the Laser-lit Chip technology at Photonics West 2022 in San Francisco, CA.
The demo kit showcases the world’s-first Laser-lit Chip: a backlight based on standard display glass, featuring a complex network of thousands of three-dimensional optical waveguides, illuminated by single red, green and blue laser diodes. Light is emitted in a highly-controlled array of laser beams, each positioned at the subpixel position of a standard display surface. The combination of the Laser-lit Chip with a Liquid Crystal layer, as part of a standard LCD stack, creates pure colours and unbeatable bright images.
What is Colour Gamut and Why Is It Important? The term colour gamut can be understood in two different ways.
Firstly, applied to human vision, it denotes the full range of colours the human eye is able to perceive. This is formally represented by a colour diagram such as the one shown in Fig.1a.
The other meaning of the term, as applied to an image reproducing device such as a display, refers to the range of colours the device is capable of reproducing. The colour gamut of a display is most commonly represented on the colour diagram by a triangle whose edges correspond to the three mixing colours selected in the display design, encompassing a fraction of the human eye colour gamut.
Thus, the colour gamut of a display is a key characteristic describing its ability to approximate the quality of real-world images as viewed through our own eyes. Naturally, larger means better and as the technology has developed through the years, different and ever-improving standards for the colour gamut of state-of-the art displays have been devised. A few examples are also depicted in Fig. 1a together with the colour gamut of VitreaLab’s Laser-lit Chip which will be discussed in greater detail below.
What Is Display Brightness? One of the most important attributes of any light source is the energy it delivers to a surface per unit time, in other words, its power in Watts. However, the human eye is not equally sensitive to all colours (i.e. wavelengths) of light. In fact, our sensitivity peaks at green light (specifically, at 555 nm wavelength) and declines rapidly towards the blue and red ends of the spectrum. Fig. 1b shows one of the most widely used luminous efficacy curves of the human eye (under daylight conditions, it looks different in dark environments) .
If we now multiply the power of our light source in Watts with the corresponding luminous efficaiency at the chosen wavelength and the value of 683 lm/W, representing the peak luminous efficaiency of the average human eye, we obtain the luminosity of the light source in lumens. If we further divide by the solid angle into which the light is emitted, we arrive at one of the most important characteristics of a display, namely its brightness in nits.
Typical present-day flagship smartphone displays breach the 1000-nit barrier.
How Does VitreaLab’s Technology Improve the State of the Art? Three different display colour gamuts are shown in Fig. 1a. The smallest triangle corresponds to the DCI-P3 (i.e. Digital Cinema Initiatives — Protocol 3) colour gamut, which is what current flagship smartphones strive to achieve. Typical coverage of the DCI-P3 colour gamut by most such devices is around 90 %.
The middle triangle represents the Rec. 2020 standard which was developed for ultra high-definition TVs and is the main target of current developments in display technology. Even the best displays available today offer a coverage of 60–90 % of the Rec. 2020 colour gamut.
By basing our technology on laser sources and thus taking advantage of the directionality and monochromaticity of the beams emitted by the Laser-lit Chip, we are able to demonstrate an even wider colour gamut, depicted as the largest triangle in Fig. 1a. It already covers 96.5 % of the DCI-P3 standard and a whopping 93.3 % of the Rec. 2020 standard.
Additionally, brightness measurements on one of the first generation VitreaLab demos performed by our partner Corning® revealed a brightness of 59 000 nits for white light. The possibility of achieving such exceptionally high brightness will be beneficial for both traditional 2D displays and augmented reality (AR) applications where the displayed image needs to achieve comparable brightness to ambient objects. For the sake of comparison, the reflection off a concrete block in broad daylight can be as bright as 10000 nits.
The VitreaLab Demo Kits. To demonstrate the merits of the Laser-lit Chip technology at a concept level, we designed a portable demo device. Our demos are packed in a robust, shipping-safe suitcase, with the laser diodes and corresponding driver electronics concealed in the bottom layer. The top layer consists of a Laser-lit chip fed by the laser diodes in the bottom layer through an optical fibre array, and a user interface featuring an ON/OFF button and a potentiometer for controlling the power of each individual laser. A piece of diffuser paper is also included in order to allow for a better viewing experience as the pristine output of the display area is very directional, with the laser power highly concentrated in the vertical beams emanating from the chip. The layout of our Generation 1 demo kits is shown in Fig. 2a. Laser power control is achieved with pulse-width modulation of the supply signal. That is, the laser is powered with a fixed current and intensity control is achieved by rapidly turning the laser on and off with a square-waveform trigger signal with controllable duty cycle from 0 % (i.e. no trigger) to 100 % (i.e. full power). This is done in order to eliminate the dependence of the lasing wavelength of the laser diodes on driving current, which, in turn, provides a more stable coupling into and between waveguides. Fig. 2b depicts the Laser-lit Chip equipped with a liquid-crystal (LC) grid on top (including polariser films, but no colour filters), matched to the chip subpixel positions.
By programming the LC grid with an externally connected Raspberry Pi microcontroller, a fully functional display based on the Laser-lit Chip technology could be demonstrated for the first time. An example RGB image is shown in Fig. 3. For reference, the same test image, displayed by the same LC grid with a standard LED backlight (i.e. a monochrome LCD display), has also been included. Note that images were taken with different exposure times, and in both cases no colour filters were present.
By combining the VitreaLab Laser-lit Chip technology with standard LCD display components, while leaving out polarizer films and colour filters, uniquely bright display devices with highly-controlled light directionality and colour gamut can be created. In Fig. 4. the full brightness of the demonstrator can be experienced with similar settings to Fig. 3b).
Improved uniformity and polarisation control of the Laser-lit Chip will be shown in the upcoming Demo Kit Gen 2.0, to be released at DisplayWeek 2022!
Stay tuned.
Published by Lyubomir Ahtapodov / 2022
