laser projection display

Report on

Laser Projection Displays

Md. Abul Hasnat

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Abstract

After the invention of lasers, in the past 50 years progress made in laser-based display technology has

been very promising. This technology has long been proposed as a superior alternative to existing

image-display devices like CRTs (cathode-ray tubes), flat panels, and projection systems based on lamps

and LEDs. Compact laser systems, such as edge-emitting diodes, vertical-cavity surface-emitting lasers,

and optically pumped semiconductor lasers, are suitable candidates for laser-based displays. In addition

to this, Laser speckle is an important concern, as it degrades image quality. Typically, one or multiple

speckle reduction techniques are employed in laser displays to reduce speckle contrast. Likewise, laser

safety issues need to be carefully evaluated in designing laser displays under different usage scenarios.

Laser beam shaping using refractive and diffractive components is an integral part of laser displays, and

the requirements depend on the source specifications, modulation technique, and the scanning method

being employed in the display.

Lasers have been attractive to display manufacturers because, from a theoretical and practical

standpoint, they deliver a significantly better image than any other display type. Probably the biggest

single advantage of lasers is their ability to cover a wider color gamut. The laser’s promise has yet to

become a market reality, in part because of the size, power consumption, and cost drawbacks of

available visible laser technology.

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Table of Contents

Introduction ............................................................................................................................................ 4

Optics for Laser Displays .......................................................................................................................... 5

Laser Beam Shaping of Single-Emitter Lasers ....................................................................................... 6

Laser Beam Shaping of Multiemitter Lasers ......................................................................................... 6

Laser requirements ................................................................................................................................. 8

Laser Display Systems .............................................................................................................................. 9

Displays with Single-Axis Scanning ....................................................................................................... 9

Displays with Two-Axis Scanning ........................................................................................................ 10

Displays with Direct Two-Dimensional Modulation ............................................................................ 11

Example of 2D modulated laser display technology ........................................................................ 12

Other Laser-Based Displays ................................................................................................................ 13

Example of different Laser projection displays available in market ........................................................ 13

Laser TV ............................................................................................................................................. 14

Laser projector .................................................................................................................................. 14

Advantages of Laser projection displays ................................................................................................ 15

Superior color .................................................................................................................................... 15

Brightness and contrast ..................................................................................................................... 15

Spanned lifetime ............................................................................................................................... 16

Several issues regarding laser projection displays .................................................................................. 16

Laser Safety ....................................................................................................................................... 16

Speckle in Laser Displays .................................................................................................................... 17

Conclusion ............................................................................................................................................. 18

References ............................................................................................................................................ 19

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Introduction

A display is an output surface and projecting mechanism that shows text, graphic images and video

(sequence of images) to the user, using a cathode ray tube ( CRT ), liquid crystal display ( LCD ), light-

emitting diode, gas plasma, or other image projection technology. The display is usually considered to

include the screen or projection surface and the device that produces the information on the screen.

Most displays in current use employ cathode ray tube ( CRT ) technology similar to that used in most

television sets. The CRT technology requires a certain distance from the beam projection device to the

screen in order to function. Using other technologies, displays can be much thinner and are known as

flat-panel displays . Flat panel display technologies include light-emitting diode (LED), liquid crystal

display ( LCD ), and gas plasma. LED and gas plasma work by lighting up display screen positions based

on the voltages at different grid intersections. LCDs work by blocking light rather than creating it. LCDs

require far less energy than LED and gas plasma technologies and are currently the primary technology

for notebook and other mobile computers. A plasma display panel (PDP) is a type of flat panel display

common to large TV displays. A panel typically has millions of tiny cells in compartmentalized space

between two panels of glass. These compartments, or "bulbs" or "cells", hold a mixture of noble gases

and a minuscule amount of mercury. Depending on the phosphors used, different colors of visible light

can be achieved. Each pixel in a plasma display is made up of three cells comprising the primary colors of

visible light. Displays can be characterized according to: Color capability, sharpness and view ability, the

size of the screen and the projection technology.

Many of the projection display systems use arc lamps, also known as high-intensity discharge(HID) lamps.

Xenon lamps are HID lamps, where the only fill material is the noble gas xenon. Metal-halide lamps are

HID lamps in which the fill material consists primarily of mercury, with a doping of a halide salt of the

desired metal. In several displays, very low end projectors tungsten halogen lamps are used. The other

type of lamp used in projection display technology is Ultra High Performance (UHP) lamps. UHP lamps

have high luminous efficacy 50-60 lm/W. UHP lamps are claimed to have a lifetime of over 10,000 hours.

However, using these lamps current televisions are capable of displaying only 40% of the color gamut

that humans can potentially perceive. The color gamut based on these lamps is less than the gamut of

NTSC. The size of the color gamut produced by the light sources used is considered as a limitation of the

current projection display technologies. In such situation in order to increase the size of color gamut,

lasers may become an ideal replacement of the current light sources in displays. The more

monochromatic is the light source, the nearer of the border line of the color space it is situated. That is

why by using laser the color gamut achieved is as large as possible, because laser lines are situated

practically on the border line of the color space. Therefore, the color gamut of a Laser Display System

(LDS) can be easy to expand beyond NTSC (e.g., 166%). Lasers are currently in use in projection display

devices such as rear projection TV and front projectors in order to produce extended color gamut. Color

gamut comparison of CRT, LCD, LED and laser projector display in CIE color space is shown in fig. 1.

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Figure 1: Comparison between color gamut of CRT, LCD LED and laser projection display in CIE color

space

A laser projection display, is a rear-projection based display technology that replaces the conventional

high-intensity discharge lamps with three colored lasers. The image on the screen is produced like a

conventional rear projection system, by scanning the light source across the screen using

optoelectronics.

The idea of using lasers as light sources for display applications dates back to the 1960s. Such that the

laser display systems seems to be feasible, unfortunately, due to the lack of practical laser devices that

generate red, green, and blue (RGB) lights, it is only recently that diode lasers and miniature diode-

pumped-solid-state lasers (DPSSLs), which emit visible spectrum lights, have become commercially

available. Based on RGB laser lights as primaries, except for expanded color gamut, some other

advantages emerge, for example, longer lifetime, no warm-up time, less noise and power consumption,

higher contrast ratio, simplified optics are needed, and perhaps, a few years later, it will become cost

less. After examination of the development history of the display technologies and of the laser

technologies, it is safe to say, that following the monochromic-display, the full color display, and digital-

display technologies, the laser display technology is the fourth generation display technology which

opens up a new area for laser application.

Optics for Laser Displays

Laser-based displays require special optical components to shape, homogenize, combine, or separate

laser beams. The preferred optical components and the coatings on them show variety according to the

type, power, and the wavelengths of the lasers used. Although there are overlapping techniques, laser

beam shaping can be divided into two categories.

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Laser Beam Shaping of Single-Emitter Lasers

Beam shaping of single-emitter lasers can be done with reflective and diffractive elements, and the

method used mainly depends on the shape and the power of the input beam.

A simple laser beam shaping technique for single emitter lasers that uses refractive elements is shown in

Fig. 2. It consists of two plano aspheric lenses in the standard Galilean beam expander configuration.

The first lens directs the incident rays so that they are uniformly distributed on the second lens. The

second lens collimates the incident beam, the exiting beam propagates almost perfectly collimated, and

the optical path length (OPL) is preserved. This configuration allows creation of large collimated beams

but requires radially symmetric input beams and works for a certain wavelength. If the wavelengths of

the input beam changes, the setup needs adjustment by changing the distance between the two lenses.

On the other hand, it is possible to achromatize the two-lens system by using conventional spherical

components made of standard glass. Inserting doublets or triplets as external compensators at the exit

pupil of the design is a method for color correction. For high-power single-emitter lasers, lens-based

shapers may not be suitable, as their performance deteriorates over time [90]. In order to shape a high

power laser beam into a uniform rectangular profile, two external binary phase reflective DOEs can be

used.

Figure 2: Beam expander configuration with two plano-aspheric lenses.

The methods discussed above use passive optical elements to shape laser beams, which make them

sensitive to the input. Another way of shaping a laser beamis using active optical elements such as

deformable mirrors, which adjust the spatial phase of the beam before propagating to the target.

Laser Beam Shaping of Multiemitter Lasers

Laser diode arrays are effective sources because of their high power supporting capabilities and lower

speckle properties. Delivery of the beam from the array without losing brightness and beam quality is an

important task. Different methods for combining the output of laser diode arrays in the spectral and

phase domains are proposed. Most of the time, individual emitters in the array have different

divergence angles in different axes. A classical method for beam shaping is combining different emitter

outputs using a fiber bundle and focusing them into a single fiber. In order to get maximum efficiency,

bundle dimensions should be as small as possible, which places restrictions on minimum jacketing and

cladding thickness.

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Uniform intensity profiles over an area or along a line from laser diode arrays can be produced using

microlens arrays combined with field lenses. The divergence of the emitted rays can be controlled by

microlens arrays, and the output can be homogenized by combining and mixing the rays from different

emitters. The most common microlens array configuration for creating uniform illumination is known as

the fly’s eye configuration, a schematic of which is shown in Fig. 3(a). It consists of two identical

microlens arrays and a field lens. This system will have reduced interference effects if used after a

telescope configuration with a rotating random diffuser in between, as shown in Fig. 3(b). The first array

of the above configuration is called the field lens array, and the second array is called the pupil lens

array, as it forms the pupil of the system. The combination of two microlens arrays is called a

uniformizer or a tandem lens array. The second microlens array is located at the focal plane of the first

microlens array, and the level of homogenization is inversely proportional to the pitch of the arrays. A

configuration with two identical microlens arrays separated by a focal length can also be used for

exitpupil expansion in display systems and fabrication technologies.

Figure 3: (a) Fly’s eye configuration for beam homogenization. (b) Fly’s eye configuration with a diffuser.

An improved design that uses a multiemitter laser and a fly’s eye configuration to create a uniform laser

line at a plane is shown in fig. 4. Although designed for a laser printer, this method can be applied to

display systems requiring a line illumination, such as the GLV-based system. In this configuration, beams

coming from individual emitters are collimated with the first lenslet array and made to travel through

different field lenses and a tandem lens array. The system uses cylindrical microlens arrays to

homogenize the laser light only along the line axis and keeps its Gaussian profile along the other axis. As

the line is scanned, the intensity along the unhomogenized axis gets averaged. This uniformizer was

adapted for a one-dimensional (1D) scanning-based 3D display, which uses array lasers as light sources.

For full color, an X cube or dichroic mirrors can be used for combining the beams from red, green, and

blue lasers.

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Figure 4: Improved fly’s eye configuration for uniform laser line creation from an array of diode lasers.

Laser requirements

For many years the technology itself kept growth in this segment of the laser industry in check, primarily

because the lasers that generated the desired colors and images were large, expensive, and very high-

maintenance. For example, gas lasers are available with a wide range of wavelengths. However, being

bulky and less efficient makes them unsuitable for the mass production display market. Additionally,

they require external modulators, which increase the cost and complexity of the system. However, with

the advent of more-compact, affordable, and user-friendly solid-state lasers--particularly diode lasers

capable of emitting red, green, and blue (RGB) wavelengths. These lasers are inherently smaller, more

efficient and reliable, and increasingly more versatile and less expensive than ion lasers.

The primary reason lasers are now poised for implementation in displays is that several key

technological improvements have provided reduced power consumption, increased reliability, wider

wavelength selection, higher output from a given package size, and the potential for mass production.

There are several solid-state approaches to generate visible continuous-wave laser light. The principal

methods are edge-emitting diodes (and frequency-doubled diodes), diode-pumped solid-state (DPSS)

lasers, vertical-cavity surface-emitting lasers (VCSELs), and optically pumped semiconductor (OPS) lasers.

OPS lasers are the superior choice for a number of reasons. Because, this is a completely scalable

technology, in terms of both power and wavelength. Fig. 5 shows the structure of an OPSL employing

the side-pumping scheme. In comparison, DPSS lasers are more complex and costly, while the output

power of diodes and VCSELs is limited. Some manufacturers have proposed ganging diodes or VCSELs in

arrays for this application. However, the use of an extended emission area lowers source brightness,

negating one of the main advantages of lasers. It appears that semiconductor lasers are the ideal light

sources for laser projection display applications due to compact size and high electrical to optical

efficiency. Although diode lasers emitting red lights are commercially available, there is none operating

at suitable blue and green wavelengths. DPSSLs, operating at 532 and 473 nm, are the immediate

candidates for laser projection display applications in long time.

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Figure 5: Structure of an OPSL

Requirements of the laser source depend on the architecture of the display. For a flat panel backlit

display, the laser beam M2 parameter can be a few hundred times larger than that of a diffraction

limited beam. Display systems based on the flying spot approach are considered to be more suitable for

mobile devices. Such an approach requires that the laser beam be collimated while maintaining the

small beam size, which places restrictions on the selection of the source. As a TEM00 (transverse

electromagnetic with p=l=0) laser beam can be considered as a true point source, such a beam is the

ideal choice of the designer in this case.

Laser Display Systems

Successful implementations of laser-based displays in the late 1960s were inspired from the cathode ray

tube (CRT), which uses an electron beam to write the image on the screen. Today, advancements in

technology provided us with a variety of means by which a laser-based display can be realized each with

its own advantages and disadvantages. These systems can be broadly classified based on the

architecture being employed as (i) scanned linear architecture type, which uses a 1D array of pixels [GLV

and grating electromechanical system (GEMS)], (ii) scanned beamtype [modulation is internal with diode

current or external using an electro-optic or acousto-optic modulator (EOM or AOM)], and (iii) two-

dimensional (2D) flat panel type [modulation with liquid-crystal display (LCD), digital micromirror device

(DMD), or liquid-crystal-on-silicon (LCoS)]. In addition to this, laser-based displays can replace many

other current technologies without adversely affecting user experience. Successfully demonstrated laser

based display systems are described below.

Displays with Single-Axis Scanning

Displays following this approach use a 1D array of modulators to form a single column of image, which is

then scanned in a direction orthogonal to the length of the line image to form the complete 2D image.

This architecture uses microelectromechanical linear array modulators called the GLV by Silicon

LightMachines, Incorporated, GEMS by Kodak or spatial opticalmodulator (SOM) by Samsung Electro-

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Mechanics. All these devices are MEMS (micro-electro-mechanical systems), which are fabricated on

silicon. GLV and GEMS use electrostatic force to create a grating structure by deflecting tiny reflective

ribbons, while SOM utilizes the piezoelectric effect for the same purpose. By controlling the voltage

applied to these tiny ribbons, their mechanical shift, and thereby the diffraction of light from the overall

grating structure, can be controlled. Following the success of flat diffraction grating structures, devices

with blazed diffraction grating were introduced by Sony. These devices are more efficient, owing to the

fact that the light is being directed to a single diffraction order, and it produced a contrast ratio that is

twice that of the device with a flat grating structure.

Another laser-based display with a similar scanning method is the proposed HELIUM 3D display, which

uses single-axis scanning of modulated laser light for forming 3D images by working in conjunction with

head trackers. Reflective LCoS microdisplays are used for light modulation in this direct view display. The

HELIUM 3D display is autostereoscopic, as it sends left and right images of a 3D image to the

corresponding eyes of the viewer by forming exit pupils at the location of the eyes of the viewer in a

dynamic fashion with the help of head trackers. As shown in the schematic in fig. 6, the display requires

a RGB laser light engine to produce laser line illumination at the modulator plane and a 1D scanner to

produce a 2D image. After this image forming section, there is a dynamic spatial light modulator and a

special front screen assembly to direct images to the viewing zones with the help of head trackers.

Figure 6: HELIUM 3D display schematic.

Displays with Two-Axis Scanning

These types of displays use a slowly converging laser beam, which is modulated by the video signal, to

write the images by scanning the beam on the screen using a pair of scanner mirrors. These types of

raster scanned displays have the advantage of not requiring a projection lens assembly for image

formation. Thus these systems can be very compact and less expensive, making them suitable for the

mobile market. Image formation is very similar to that of the electron gun in a CRT. Vertical and

horizontal movement of the laser beam is achieved by a two-mirror system in which a very fast polygon

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mirror scans the horizontal axis while the other mirror slowly scans the vertical axis. Developments in

MEMS technology has led to the evolution of compact and silent two-axis MEMS scanners that can

replace both mirrors mentioned earlier. The raster scanned projection scheme does not require

projection lenses, as these systems directly write the image on the screen and the image is always in

focus, regardless of the distance of the projection screen or the shape of the projection surface. The

schematic of a flying spot laser projector is shown in fig. 7.

Figure 7: Schematic of a flying spot laser projector.

Diode lasers are more suitable for this type of display, as they are directly modulatable by modulating

the diode current according to the video signal. Most compact laser projectors use this approach, but

other modulator technologies such as AOMs or EOMs can also be used. With the introduction of

miniature MEMS scanner mirrors, this type of projectors became more compact. This miniaturization of

scanner technology led to the introduction of a new class of projectors called pico projectors; these use

directly modulatable diode lasers and two-axis MEMS scanners, which allow a large reduction in size.

Displays with Direct Two-Dimensional Modulation

Direct modulation of the laser light with 2D modulators has the advantage of requiring lower beam

quality from the laser. The optical configuration of the projection system can be seen in Fig. 8.

Figure 8: Schematic of a DMD-based laser projector.

For these types of backlit displays, the required laser beam quality (étendue) depends on the aperture

size of the modulator and its angular acceptance. As the étendue of the modulator is higher than the

laser beam in most cases, inefficiencies

transmissive liquid-crystal (LC) technologies. Mitsubishi introduced LaserVue, a laser

2008. The projector introduced by the company Explay uses reflective LCoS microdispl

microprojector from Alcatel-Lucent uses a single reflective LCoS unit, with color sequential illumination

by employing a modulation frequency of 180 Hz, divided among the three primaries, which results in a

60 Hz full-color image. This projector u

with only 1:5W of electrical power consumption

Example of 2D modulated laser display technology

The laser display principle is based on deflection o

signal is first routed via an input module to a programmable image memory, which adjusts itself

standard (PAL, NTSC, SECAM or HDTV).

display technology has to be downwards

systems. Here, the laser light must be adapted

existing television technology so that

phosphorus compounds in picture tubes. The light source is a laser unit with three wavelengths for the

colors red (630 nm), green (532 nm) and blue (450 nm), whereby the brightness of each is controlled by

an electro-optical modulator in accordance with the

by a polygon mirror with 32 or 25 faces, respectively,

revolutions per second. A galvanometer

produce a variable image size with a fixed projection distance. Since the polygon mirror achieves only a

small deflection angle of 12 deg, the deflector is followed by an optical system to increase divergence,

significantly reducing the depth of the units.

Since the projection lamps (thermal beamers) used in projection technology today emit light throughout

the entire projection area, only a fraction of this light can be used for image projection (aperture loss).



laser beam in most cases, inefficiencies do not arise. There are laser projectors based on reflective and

crystal (LC) technologies. Mitsubishi introduced LaserVue, a laser

The projector introduced by the company Explay uses reflective LCoS microdispl

Lucent uses a single reflective LCoS unit, with color sequential illumination


color image. This projector uses 635nm, 532 nm, and 450nm lasers to produce a 10 lm output

with only 1:5W of electrical power consumption.

Example of 2D modulated laser display technology

The laser display principle is based on deflection of a modulated laser beam (fig. 9

signal is first routed via an input module to a programmable image memory, which adjusts itself

standard (PAL, NTSC, SECAM or HDTV). Color transformation is the next step. It is required because laser

display technology has to be downwards-compatible with existing transmissions and reproduction

systems. Here, the laser light must be adapted via a matrix to the fixed, colo

existing television technology so that color reproduction will be identical to that of conventional

osphorus compounds in picture tubes. The light source is a laser unit with three wavelengths for the

s red (630 nm), green (532 nm) and blue (450 nm), whereby the brightness of each is controlled by

optical modulator in accordance with the received signal. Horizontal deflection is performed

by a polygon mirror with 32 or 25 faces, respectively, which rotates at a speed of maximum

revolutions per second. A galvanometer scanner is responsible for vertical deflection. A vario lens can

uce a variable image size with a fixed projection distance. Since the polygon mirror achieves only a


significantly reducing the depth of the units.

Figure 9: Overview of LDT-components



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do not arise. There are laser projectors based on reflective and

crystal (LC) technologies. Mitsubishi introduced LaserVue, a laser-based television in

The projector introduced by the company Explay uses reflective LCoS microdisplays. The

Lucent uses a single reflective LCoS unit, with color sequential illumination


ses 635nm, 532 nm, and 450nm lasers to produce a 10 lm output

f a modulated laser beam (fig. 9). The video or TV

signal is first routed via an input module to a programmable image memory, which adjusts itself to any

transformation is the next step. It is required because laser

mpatible with existing transmissions and reproduction

via a matrix to the fixed, colorimetric standards of

reproduction will be identical to that of conventional

osphorus compounds in picture tubes. The light source is a laser unit with three wavelengths for the

s red (630 nm), green (532 nm) and blue (450 nm), whereby the brightness of each is controlled by

received signal. Horizontal deflection is performed

which rotates at a speed of maximum 1300

scanner is responsible for vertical deflection. A vario lens can

uce a variable image size with a fixed projection distance. Since the polygon mirror achieves only a




The fundamental difference between laser sources and projection lamps lies in their spatial diffusion

light. The aperture loss is eliminated using lasers, all light is emitted in quasi

projection systems depth of focus is limited, and

laser projection, depth of focus is practically unlimited owing to the use of quasi

beams. No focusing is necessary, and projection on non

Speckle in the projected laser image is created by the coherence properties of the laser light. Unlike

many other laser applications, the coherence properties of laser light are not required in image

projection; there are thus various opportunities of eliminating s

Other Laser-Based Displays

Among the other laser based displays

Blue Optics (LBO), which is based on 2D diffraction from diffraction patterns displayed on a

However, they are not truly holographic and form only a 2D image. Holographic video displays, which

can indeed display 3D images, have also been under active development over the last two decades but

are currently limited by the capabilities

Other display types that successfully exploited the positive aspects of laser light are head

displays. These systems were bulky and heavy, but with the incorporation of new technologies the

finding places in medical, automotive, and

seen through, providing real-world images superimposed with information from external sources.

Example of different Laser projection displays

The major drawback of laser based projection display is high cost and maturity in comparison with the

other display systems. An analysis on available display technologies is performed in terms of market size

and cost. Fig. 10 illustrates the analysis, from which it is clear that laser based displays has the lowest

market size as well as the technology is not matured enough.

Figure 10: Analysis on available display technologies in terms of market size and cost.

mental difference between laser sources and projection lamps lies in their spatial diffusion

light. The aperture loss is eliminated using lasers, all light is emitted in quasi-parallel rays. In all classic

projection systems depth of focus is limited, and the image must be focused on the projection screen.

laser projection, depth of focus is practically unlimited owing to the use of quasi

beams. No focusing is necessary, and projection on non-plane surfaces is simple.

n the projected laser image is created by the coherence properties of the laser light. Unlike


projection; there are thus various opportunities of eliminating speckle directly at the laser source.

Based Displays

Among the other laser based displays one is holographic laser projector by the company named

based on 2D diffraction from diffraction patterns displayed on a

are not truly holographic and form only a 2D image. Holographic video displays, which


are currently limited by the capabilities of the available modulation and computation technologies

Other display types that successfully exploited the positive aspects of laser light are head

displays. These systems were bulky and heavy, but with the incorporation of new technologies the

finding places in medical, automotive, and military applications. These types of wearable displays can be

world images superimposed with information from external sources.

ifferent Laser projection displays available in market



illustrates the analysis, from which it is clear that laser based displays has the lowest

market size as well as the technology is not matured enough.

: Analysis on available display technologies in terms of market size and cost.

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mental difference between laser sources and projection lamps lies in their spatial diffusion

parallel rays. In all classic

the image must be focused on the projection screen. In

laser projection, depth of focus is practically unlimited owing to the use of quasi-parallel (collinear) laser

plane surfaces is simple.

n the projected laser image is created by the coherence properties of the laser light. Unlike


peckle directly at the laser source.

by the company named Light

based on 2D diffraction from diffraction patterns displayed on a microdisplay.

are not truly holographic and form only a 2D image. Holographic video displays, which


of the available modulation and computation technologies.

Other display types that successfully exploited the positive aspects of laser light are head-mounted

displays. These systems were bulky and heavy, but with the incorporation of new technologies they are

military applications. These types of wearable displays can be

world images superimposed with information from external sources.

vailable in market



illustrates the analysis, from which it is clear that laser based displays has the lowest

: Analysis on available display technologies in terms of market size and cost.

Laser TV

A laser TV replaces the conventional high

on the screen is produced like a conventional rear projection system

the market is “LaserVue” (fig. 1

such as Microvision, Alcatel-Lucent, Light Blue Optics (LBO), and Explay, are also developing their own

laser display architectures for the mass market.

First reports on the development of a commercia

with a decision on the large-scale availability of laser televisions expected by early 2008. On January 7,

2008, Mitsubishi Digital Electronics America, unveiled their first commercial Laser TV, a 65"

Laser projector

A laser video projector modulates a laser beam in order to project a raster

work either by scanning the entire picture a dot at a time and modulating the laser dir

frequency, or by optically spreading and then modulating the laser and scanning a line at a time

well implemented, this technology produces the broadest color gamut available.

Among the manufacturer of laser projectors,

produces high-end laser projectors with double amount of colors and high contrast of 50.000:1.

Intended applications are simulation, planetaria and virtual reality.

produces 2000 and 8000 Lumen projectors for large screen high resolution (8K) applications

company “Microvision” produces

company “Light Blue Optics(LBO)” produces

company “JENOPTIK LDT” delivered the first 13

to the German armed forces, where it forms part of a Tornado simulator.

companies producing laser projectors commercially. Fig. 1

r TV replaces the conventional high-intensity discharge lamps with three colored lasers. The image

on the screen is produced like a conventional rear projection system. One of the laser

(fig. 11) a laser rear projection television from Mitsubishi. Other companies,

Lucent, Light Blue Optics (LBO), and Explay, are also developing their own

laser display architectures for the mass market.

First reports on the development of a commercial Laser TV were published as early as February 16, 2006

scale availability of laser televisions expected by early 2008. On January 7,

2008, Mitsubishi Digital Electronics America, unveiled their first commercial Laser TV, a 65"

Figure 11: Mitsubishi LaserVue TV

A laser video projector modulates a laser beam in order to project a raster-based image. The systems

work either by scanning the entire picture a dot at a time and modulating the laser dir

frequency, or by optically spreading and then modulating the laser and scanning a line at a time

this technology produces the broadest color gamut available.

Among the manufacturer of laser projectors, the company “LDT Laser Display Technology GmbH

end laser projectors with double amount of colors and high contrast of 50.000:1.

Intended applications are simulation, planetaria and virtual reality. The company “

umen projectors for large screen high resolution (8K) applications

” produces 10 Lumen Handheld mobile projector and OEM component

(LBO)” produces 35 Lumen projector and OEM component

delivered the first 13-channel laser projection system of the new generation 2

to the German armed forces, where it forms part of a Tornado simulator.

companies producing laser projectors commercially. Fig. 12 shows the laser projector from Sanyo.

Figure 12: Laser projector from Sanyo

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intensity discharge lamps with three colored lasers. The image

One of the laser TV available on

projection television from Mitsubishi. Other companies,

Lucent, Light Blue Optics (LBO), and Explay, are also developing their own

l Laser TV were published as early as February 16, 2006

scale availability of laser televisions expected by early 2008. On January 7,

2008, Mitsubishi Digital Electronics America, unveiled their first commercial Laser TV, a 65" 1080p model.

based image. The systems

work either by scanning the entire picture a dot at a time and modulating the laser directly at high

frequency, or by optically spreading and then modulating the laser and scanning a line at a time. When

this technology produces the broadest color gamut available.

Laser Display Technology GmbH”

end laser projectors with double amount of colors and high contrast of 50.000:1.

The company “Evans and Sutherland”

umen projectors for large screen high resolution (8K) applications. Another

10 Lumen Handheld mobile projector and OEM component. The

35 Lumen projector and OEM component. Another

channel laser projection system of the new generation 2

to the German armed forces, where it forms part of a Tornado simulator. There are many other

the laser projector from Sanyo.

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Advantages of Laser projection displays

Today’s compact solid-state lasers enable the image brightness, greater color gamut, and resolution that

make for great viewing, with the added bonus of longer lifetimes than lamp-based light sources.

However, these lasers cost a lot more than the ultra-high-pressure (UHP) arc lamps they are trying to

displace. The advantages of laser projection displays over other display systems are discussed more

detail in the following sections.

Superior color

The CRT display gamut is noticeably superior to liquid-crystal displays (LCDs), yet still only covers 60% to

70% of the NTSC (National Television Systems Committee) color gamut because of the limited color

saturation (spectral purity) of the phosphor emissions. Moreover, the NTSC color gamut is substantially

smaller than the eye’s total color capabilities. In contrast, the use of three lasers (at 460, 532, and 635

nm) enables coverage of 150% to 170% of the NTSC gamut. This means that laser displays deliver a

wider range of vivid colors making the image far more lifelike than any existing display type. A

comparison between color gamut of laser projection and NTSC is shown in fig. 13.

Figure 13: Comparison between color gamut of laser display and the NTSC (National Television Systems

Committee) television protocol.

Another color-related issue is source aging. With lamps and LEDs, output wavelengths shift as the

devices age, and not necessarily at a constant rate. This means the color reproduction of the projected

image deteriorates over time. With lasers, however, output wavelength does not shift with age, and

color characteristics are maintained simply by holding the laser power constant.

Brightness and contrast

Brightness is another key image parameter and is defined as the total power emitted by a source per

unit solid angle per unit area. A TEM00 (transverse electromagnetic with p=l=0) laser is a true point

source; all the light appears to emanate from the same point in space. This means it can be perfectly

collimated and focused back to a point, limited only by diffraction. In contrast, a lamp or LED emits from

an extended area or volume over a large solid angle. Furthermore, obtaining increased brightness from

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lamps or LEDs virtually always involves increasing the apparent source size. As a result, a TEM00 laser

beam delivers a brightness that is multiple orders of magnitude higher than any lamp or LED.

For laser-projection displays, this translates into increased image brightness and/or resolution.

Projection displays rely on a linear or two-dimensional micromirror MEMs chip. To maintain image

brightness as chip size decreases, the light source must be focused to a smaller spot. For any nonpoint

source, reducing the focused spot size increases the cone angle (f number) of the light beam. However,

both the micromirror and projection optics have limited acceptance angles, so, at some point, the

system will start to throw light away, which eventually decreases image brightness.

As a point of reference, current state-of-the-art LED-based projection television is limited to a maximum

50 in. diagonal. And, even this size requires the use of a high-gain screen containing a lens array to trade

off viewing angle for brightness. A laser source avoids this problem and brightness can be scaled without

limit because increasing laser power doesn’t increase the source size.

Spanned lifetime

The lifetime of the light sources, such as UHP lamps, HID lamps, xenon lamps, and other types of lamps,

are only several hundreds or several thousands hours, and the lamps easily explode due to their high

operation temperature. In comparison to these light sources, laser has longer lifetime. Therefore,

spanned lifetime of laser based display will be more than others.

Several issues regarding laser projection displays

Laser Safety

Laser radiation falls in the category of nonionizing radiation, unlike x rays and gamma rays. Although

there are other risks, such as chemical, electrical, and other secondary hazards associated with a laser

unit, the mostly discussed risks are eye and skin hazards caused by laser radiation. A laser with sufficient

optical power can cause corneal and retinal burns or cataracts, depending on the level of exposure. In

laser based displays, only wavelengths in the range from 400 to 700nm are used. But there may be

spurious emission of infrared or ultraviolet if the technology used for the generation of the primaries

utilize nonlinear optical processes, such as second harmonic generation or sum/difference frequency

generation. However, these can be effectively removed with appropriate filters.

In order to evaluate the hazard potential of a laser-based display system, one has to determine the

maximum possible exposure under a worst-case scenario. If the evaluated exposures are below the

maximum permissible exposure (MPE) for laser radiation laid out by the above-mentioned standards,

the display may be considered eye safe.

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Speckle in Laser Displays

Although a laser-based display can offer a wide color gamut compared with other display technologies,

it also comes with a problem specific to laser light, the speckle patterns, which results from the

coherence of laser light. When an object is illuminated with a coherent light source, such as a laser, the

scattered light has components with different delays, which are caused by the roughness of the

illuminated surface. As the scattered light propagates further, these coherent but de-phased

components interfere and produce a granular intensity pattern called speckle on the screen. speckle

formation is an undesired effect in laser-based display systems, as it destroys the information content

and reduces the resolution.

In order to reduce speckle, many different methods have been suggested. In order to generate

uncorrelated speckle patterns in the spatial dimension, incident angle, wavelength, or polarization of

the light source can be altered. Uncorrelated patterns in the temporal dimension can be created by

placing and moving a scattering surface into the light path. The moving scattering surface creates a time-

varying speckle pattern, and if the movement is fast enough, the speckle will be averaged out by the

human eye. Angular diversity for speckle reduction can be achieved with micro electro mechanical

systems (MEMS) scanning devices working at 2–10 kHz that generate different illumination angles. Using

a broadband source reduces the temporal coherence and, therefore, can effectively reduce speckle

without causing optical loss or design complexity. However, driving multiple laser diodes individually

with different wavelengths is a very complex and costly task and is not useful for a laser-based television

or projector system. In order to overcome this problem, a new laser diode array structure that exhibits

self-induced spectrum widening has been suggested.

If the observer is close to the screen in a projection system, the perceived diameter of the speckle is

typically small, and speckle can be reduced by reducing the temporal or the spatial coherence of the

laser. In the far field, on the other hand, the average size of the speckles appears larger to the observers

eyes; therefore, small phase changes are not sufficient to eliminate the speckle in the far field. In order

to remove speckle in the far field, boiling speckle patterns can be produced by using a diffractive optical

element (DOE). A DOE is used to modulate the spatial phase and the amplitude of the unfocused

scanning laser beam across its diameter. Another method for creating a time-varying speckle pattern is

using a dynamic polymer-based diffraction grating. In this approach, diffracted light coming from the

grating is used as the illumination source after collection and homogenization.

Although the stated speckle reduction techniques reduce the speckle contrast in considerable amounts,

they do not completely remove the speckle noise and hot spot speckles remain. The remaining hot spot

speckles can be removed by implementing both a rotating diffuser and a running screen.

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Conclusion

Currently, the market for laser-based projection displays-that is, rear-projection televisions (RPTVs),

front-projection systems, and pocket projectors-is caught between a technology that offers superior

image quality and a price tag that makes it a hard sell. However, while lasers clearly offer improved

imaging characteristics over other display technologies, the final hurdle to their adoption is cost.

Therefore it is expected the laser technology to penetrate the higher-value applications first, where the

cost can be more readily justified. These applications include digital cinema projectors and specialty

displays such as flight and ship simulators, followed by large-format televisions. Flight simulators, in

particular, are a near-perfect fit for lasers because lasers address one of the biggest limitations of

current CRT-based systems, namely contrast, which has long limited the realism of the images and

hence the entire simulated-motion experience. Then, as production volumes increase and costs

correspondingly drop, laser displays will be ready to penetrate the consumer market.

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References

[1] "Optoelectronic Applications: Projection Displays: Laser-based projectors target consumer market",

Dec 1, 2005. Accessed from: http://www.optoiq.com.

[2] Kishore V. Chellappan, Erdem Erden, and Hakan Urey, "Laser-based displays: a review," Appl. Opt. 49,

F79-F98 (2010)

[3] Guang Zheng Wang, B. Fang, T. Cheng, H. Qi, Y. Wang, Y.W. Yan, B.X. Bi, Y. Wang, Y. Chu, S.W.

Wu, T.J. Xu, J.K. Min, H.T. Yan, S.P. Ye, C.W. Jia, Z.D., Laser Digital Cinema Projector, Journal of Display

Technology, Vol 4, pp 314 - 318, Sept. 2008.

[4] Kranert, J. Deter, C. Gessner, T. Dotzel, W., Schneider Rundfunkwerke AG, Turkheim, Laser display

technology, Proc. of the Eleventh Annual International Workshop on Micro Electro Mechanical Systems,

pp 99 - 104, Jan 1998, Heidelberg.

laser projection display

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