Laser video display
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Laser color television (laser TV), or laser color video display, is a type of television that utilizes two or more individually modulated optical (laser) rays of different colors to produce a combined spot that is scanned and projected across the image plane by a polygon-mirror system or less effectively by optoelectronic means to produce a color-television display. The systems work either by scanning the entire picture a dot at a time and modulating the laser directly at high frequency, much like the electron beams in a cathode ray tube, or by optically spreading and then modulating the laser and scanning a line at a time, the line itself being modulated in much the same way as with
digital light processing Digital Light Processing (DLP) is a set of chipsets based on optical micro-electro-mechanical technology that uses a digital micromirror device. It was originally developed in 1987 by Larry Hornbeck of Texas Instruments. While the DLP imagin ...
(DLP). The special case of one ray reduces the system to a monochrome display as, for example, in
black and white television Black-and-white (B&W or B/W) images combine black and white in a continuous spectrum, producing a range of shades of grey. Media The history of various visual media began with black and white, and as technology improved, altered to color. ...
. This principle applies to a direct view display as well as to a (front or rear)
laser projector A laser projector is a device that projects changing laser beams on a screen to create a moving image for entertainment or professional use. It consists of a housing that contains lasers, mirrors, galvanometer scanners, and other optical component ...
system. Laser TV technology began to appear in the 1990s. In the 21st century, the rapid development and maturity of
semiconductor lasers The laser diode chip removed and placed on the eye of a needle for scale A laser diode (LD, also injection laser diode or ILD, or diode laser) is a semiconductor device similar to a light-emitting diode in which a diode pumped directly with e ...
and other technologies gave it new advantages.


History

The laser source for television or
video display A display device is an output device for presentation of information in visual or tactile form (the latter used for example in tactile electronic displays for blind people). When the input information that is supplied has an electrical signal the ...
was originally proposed by Helmut K.V. Lotsch in the German Patent 1 193 844. In December 1977 H.K.V. Lotsch and F. Schroeter explained laser color television for conventional as well as projection-type systems and gave examples of potential applications. 18 years later the German-based company Schneider AG presented a functional laser-TV prototype at IFA'95 in Berlin/Germany. Due to the bankruptcy of Schneider AG, however, the prototype was never developed further to a market-ready product. Proposed in 1966, laser illumination technology remained too costly to be used in commercially viable consumer products. At the Las Vegas Consumer Electronics Show in 2006, Novalux Inc., developer of Necsel semiconductor laser technology, demonstrated their laser illumination source for projection displays and a prototype rear-projection "laser" TV. First reports on the development of a commercial Laser TV were published as early as February 16, 2006 with a decision on the large-scale availability of laser televisions expected by early 2008. On January 7, 2008, at an event associated with the Consumer Electronics Show 2008, Mitsubishi Digital Electronics America, a key player in high-performance red-laser and large-screen HDTV markets, unveiled their first commercial Laser TV, a 65"
1080p 1080p (1920×1080 progressively displayed pixels; also known as Full HD or FHD, and BT.709) is a set of HDTV high-definition video modes characterized by 1,920 pixels displayed across the screen horizontally and 1,080 pixels down the screen ve ...
model. A ''Popular Science'' writer was impressed by the color rendering of a Mitsubishi laser video display at CES 2008. Some even described it as being too intense to the point of seeming artificial. This laser TV, branded "Mitsubishi LaserVue TV", went on sale, November 16, 2008 for $6,999, but Mitsubishi's entire laser TV project was killed in 2012. LG introduced a front projected laser TV in 2013 as a
consumer product A final good or consumer good is a final product ready for sale that is used by the consumer to satisfy current wants or needs, unlike a intermediate good, which is used to produce other goods. A microwave oven or a bicycle is a final good, but ...
that displays images and videos measuring 100 inches (254 centimeters) with a full high-definition resolution of 1920 x 1080 pixels. It can project images onto the screen at a distance of 22 inches (56 centimeters). In China, the Sixth Session of the Seventh Council of the China Electronic Video Industry Association formally approved the establishment of a laser TV industry branch. The establishment of the industry branch also symbolizes that the entire industrial chain connecting the upstream and downstream of the laser TV field is officially opened, in order to make the laser TV industry bigger and stronger. By 2022, sales of laser TVs in the Chinese market will exceed 1 million units, and sales will reach 11.8 billion CNY.


Principle

Laser TV images are reflected by the
screen Screen or Screens may refer to: Arts * Screen printing (also called ''silkscreening''), a method of printing * Big screen, a nickname associated with the motion picture industry * Split screen (filmmaking), a film composition paradigm in which mul ...
and enter the human eye for imaging. The principle of laser TV is to use DLP technology for image display. Take the DMD chip as an example. The DMD chip is the imaging core component of a laser TV. There are millions of small mirrors arranged, and each small mirror can flip in the positive and negative directions at a frequency of tens of thousands of times per second. The light reflects directly on the screen through these small mirrors to form an image. Due to the visual inertia of the human eye, the three
primary colors A set of primary colors or primary colours (see spelling differences) consists of colorants or colored lights that can be mixed in varying amounts to produce a gamut of colors. This is the essential method used to create the perception of a br ...
that are irradiated on the same
pixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a raster image, or the smallest point in an all points addressable display device. In most digital display devices, pixels are the ...
at high speed are mixed and superimposed to form a color.


Technology

Lasers may become an ideal replacement for the UHP lamps which are currently in use in projection display devices such as
rear-projection TV Rear-projection television (RPTV) is a type of large-screen television display technology. Until approximately 2006, most of the relatively affordable consumer large screen TVs up to used rear-projection technology. A variation is a video projec ...
and front projectors. LG claims a lifetime of 25,000 hours for their laser projector, compared to 10,000 hours for a UHP. Current televisions are capable of displaying only 40% of the
color gamut In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain ''complete subset'' of colors. The most common usage refers to the subset of colors which can be accurately represented in a given ci ...
that humans can potentially perceive. Color television requires light in three distinct
wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, t ...
s—red, green, and blue. While red laser diodes are commercially available, there are no commercially available green laser diodes which can provide the required power at room temperature with an adequate lifetime. Instead,
frequency doubling Second-harmonic generation (SHG, also called frequency doubling) is a nonlinear optical process in which two photons with the same frequency interact with a nonlinear material, are "combined", and generate a new photon with twice the energy of ...
can be used to provide the green wavelengths. Several types of lasers can be used as the frequency doubled sources: fibre lasers, inter-cavity doubled lasers, external cavity doubled lasers, eVCSELs, and OPSLs (Optically Pumped Semiconductor Lasers). Among the inter-cavity doubled lasers, VCSELs have shown much promise and potential to be the basis for a mass-produced frequency doubled laser. The blue laser diodes became openly available around 2010. A VECSEL is a vertical cavity, and is composed of two mirrors. On top of one of them is a diode as the active medium. These lasers combine high overall efficiency with good beam quality. The light from the high power IR-laser diodes is converted into visible light by means of extra-cavity waveguided
second-harmonic generation Second-harmonic generation (SHG, also called frequency doubling) is a nonlinear optical process in which two photons with the same frequency interact with a nonlinear material, are "combined", and generate a new photon with twice the energy o ...
. Laser pulses with about 10kHz repetition rate and various lengths are sent to a
digital micromirror device The digital micromirror device, or DMD, is the microoptoelectromechanical system (MOEMS) that is the core of the trademarked DLP projection technology from Texas Instruments (TI). Texas Instrument's DMD was created by solid-state physicist and ...
where each mirror directs the pulse either onto screen or into the dump. Because the wavelengths are known all coatings can be optimized to reduce reflections and therefore speckle.


Characteristics

Laser TV images are reflected by the screen and enter the human eye for imaging. According to ophthalmologists and professional evaluations, laser TV products are display products that are harmless to the naked eye. The screen has no electromagnetic radiation, which is eye-protecting, healthy and comfortable. Compared with paper reading comfort, it is 20% higher. Laser TVs are mainly large-sized, with pure light sources, bright colors, and authenticity, also support 4K display resolution. Laser TVs have lower power consumption than LCD TVs of the same size. For example, a 100-inch laser TV consumes less than 300 watts, which is ½-⅓ of the same size LCD TV. Laser TVs are about one-tenth the weight of LCD TVs of the same size, and people can watch 80-inch laser TVs at a viewing distance of 3 meters.


Assembly


Laser signal modulation

The
video Video is an electronic medium for the recording, copying, playback, broadcasting, and display of moving visual media. Video was first developed for mechanical television systems, which were quickly replaced by cathode-ray tube (CRT) syst ...
signal In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The '' IEEE Transactions on Signal Processing' ...
is introduced to the laser beam by an
acousto-optic modulator An acousto-optic modulator (AOM), also called a Bragg cell or an acousto-optic deflector (AOD), uses the acousto-optic effect to diffract and shift the frequency of light using sound waves (usually at radio-frequency). They are used in lasers ...
(AOM) that uses a
photorefractive The photorefractive effect is a nonlinear optical effect seen in certain crystals and other materials that respond to light by altering their refractive index. The effect can be used to store temporary, erasable holograms and is useful for holog ...
crystal to separate the beam at distinct diffraction angles. The beam must enter the crystal at the specific Bragg angle of that AOM crystal. A
piezoelectric Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied mechanical stress. The word '' ...
element transforms the video signal into vibrations in the crystal to create an image.


Horizontal and vertical refresh

A rapidly rotating polygonal mirror gives the laser beam the horizontal refresh modulation. It reflects off of a curved mirror onto a
galvanometer A galvanometer is an electromechanical measuring instrument for electric current. Early galvanometers were uncalibrated, but improved versions, called ammeters, were calibrated and could measure the flow of current more precisely. A galvan ...
-mounted mirror which provides the vertical refresh. Another way is to optically spread the beam and modulate each entire line at once, much like in a DLP, reducing the peak power needed in the laser and keeping power consumption constant.


Display characteristics

* Maintain full power output for the lifespan of the laser; the picture quality will not degrade * Have a very wide color
gamut In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain ''complete subset'' of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circ ...
, which can produce up to 90% of the colors a human eye can perceive by adjusting the wavelength of the laser * Capable of displaying 3D stereoscopic video * Can be projected onto any depth or shape surface while maintaining focus.


Applications

There are several realizations of laser projectors, one example being based on the principle of a flying light spot writing the image directly onto a screen. A laser projector of this type consists of three main components — a laser source uses the video signal to provide modulated light composed of the three sharp spectral colors — red, green, and blue — which a flexible, fiber-optic waveguide then transports to a relatively small projection head. The projection head deflects the beam according to the pixel clock and emits it onto a screen at an arbitrary distance. Such laser projection techniques are used in
handheld projector A handheld projector (also known as a pocket projector, mobile projector, pico projector or mini beamer) is an image projector in a handheld device. It was developed as a computer display device for compact portable devices such as mobile ph ...
s, planetariums, and for flight simulators and other virtual reality applications. Due to the special features of laser projectors, such as a high depth of field, it is possible to project images or data onto any kind of projection surface, even non-flat. Typically, the sharpness, color space, and contrast ratio are higher than those of other projection technologies. For example, the on-off contrast of a laser projector is typically 50,000:1 and higher, while modern DLP and
LCD projector An LCD projector is a type of video projector for displaying video, images or computer data on a screen or other flat surface. It is a modern equivalent of the slide projector or overhead projector. To display images, LCD (liquid-crystal display ...
s range from 1000:1 to 40,000:1. In comparison to conventional projectors, laser projectors provide a lower luminous flux output, but because of the extremely high contrast the brightness actually appears to be greater.


Development status

In order to further accelerate the adoption of laser displays, the China Ministry of Science and Technology has prioritized the "engineering and development of next-generation laser display technology" as one of the eight major industrial development directions. As related technical problems are gradually resolved, the popularization of laser TV products in households remains a major goal. At the end of December 2019, the CESI Laboratory of the China National Institute of Electronic Standardization and a team of ophthalmologists from Peking Union Medical College Hospital conducted a research project regarding the visual perception and eye strain of laser displays. In the study, 32 subjects were placed in the same environmental conditions comparing a laser TV and a LCD TV. Eye blinking frequency and the subjective perception score were compared and analyzed between the displays. The results found that watching the LCD TV for an extended period of time produced certain symptoms such as eye swelling, eye pain, photophobia,
dry eyes Dry eye syndrome (DES), also known as keratoconjunctivitis sicca (KCS), is the condition of having dry eyes. Other associated symptoms include irritation, redness, discharge, and easily fatigued eyes. Blurred vision may also occur. Symptoms rang ...
, and blurred vision, while watching the laser TV, there was no obvious visual change or eye discomfort. On January 16, 2020, the Laser Television Industry Branch of the China Electronic Video Industry Association released the industry's first White Paper on Laser TV Eye Care in Shanghai. The white paper published the eye-care evaluation data of laser TVs and traditional
LCD TV Liquid-crystal-display televisions (LCD TVs) are television sets that use liquid-crystal displays to produce images. They are, by far, the most widely produced and sold television display type. LCD TVs are thin and light, but have some disadvantag ...
s by ophthalmology experts of China Electronics Technology Standardization Institute's CESI Laboratory and
Peking Union Medical College Hospital Peking Union Medical College Hospital (PUMCH), also known as Beijing Xiehe Hospital (), is a large of teaching hospital in Beijing, China. It was founded in 1921 by Rockefeller Foundation and is affiliated to both Peking Union Medical College (PU ...
, and made scientific suggestions on how to protect the visual health of adolescents. The market for laser TVs has seen an overall compound growth rate of 281% from 2014 to 2019. In 2019, the Hisense Laser TV 80L5 ranked first in the annual TV bestseller list. According to user survey data, more than 93% of users chose laser TVs because of the claimed benefits of eye health protection.


Prospect

Compared with LED backlit LCD TVs, laser TVs have many advantages in large-screen imaging. In terms of technical composition, a laser TV is composed of
laser light A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The firs ...
source, imaging module, circuit control system, and display. The technological progress of each of these units will help to increase market share compared to competing display technologies. Additionally, laser light sources have the advantages of lower manufacturing carbon emissions, higher
color gamut In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain ''complete subset'' of colors. The most common usage refers to the subset of colors which can be accurately represented in a given ci ...
, and higher energy efficiency. The advancement of laser television combined with better optical imaging technology can be lucrative in the future home display market.


Technical challenges

Lasers are the most expensive components of laser televisions. More advanced laser diodes usually need more
semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...
materials to be manufactured, so reducing costs will remain an issue for the industrialization of laser TV for the foreseeable future. Existing laser TV products generally use imported semiconductor devices. In current large-screen display solutions, there are a variety of competing technologies such as LCD,
OLED An organic light-emitting diode (OLED or organic LED), also known as organic electroluminescent (organic EL) diode, is a light-emitting diode (LED) in which the emissive electroluminescent layer is a film of organic compound that emits light i ...
, and upcoming
Micro LED microLED, also known as micro-LED, mLED or µLED, first invented in 2000 by the research group of Hongxing Jiang and Jingyu Lin of Texas Tech University while they were at Kansas State University, is an emerging flat-panel display technology. m ...
displays. Laser TVs must continue to develop to maintain a competitive advantage in order to occupy a larger market share.


References

{{emerging technologies, displays=yes Display technology Emerging technologies