LIQUID CRYSTALS
`Applications
`and Uses
`
`V01. 1
`
`Edited by
`Birendra Bahadur
`Display Systems Engineering
`Litton Systems Canada Ltd.
`Etobicoke, Ontario WW 5A7
`Canada
`
`Iiiltltiiitlt-tltyiniiiiiWuHui
`
`\ World Scientific
`
`Singapore 0 New Jersey 0 London 0 Hong Kong
`
`(cid:44)(cid:57)(cid:44)(cid:3)(cid:47)(cid:47)(cid:38)(cid:3)(cid:40)(cid:59)(cid:43)(cid:44)(cid:37)(cid:44)(cid:55)(cid:3)(cid:21)(cid:19)(cid:20)(cid:23)
`|V| LLC EXHI :.
`14
`(cid:59)(cid:44)(cid:47)(cid:44)(cid:49)(cid:59)(cid:3)(cid:57)(cid:17)(cid:3)(cid:44)(cid:57)(cid:44)(cid:3)(cid:47)(cid:47)(cid:38)
`XILINX V.
`"
`(cid:44)(cid:51)(cid:53)(cid:3)(cid:38)(cid:68)(cid:86)(cid:72)(cid:3)(cid:21)(cid:19)(cid:20)(cid:22)(cid:16)(cid:19)(cid:19)(cid:19)(cid:21)(cid:28)(cid:3)
`IPR Case 201
`
`
`
`

`

`Published by
`
`World Scientific Publishing Co. Pte. Ltd.
`P O Box 128, Farrel Road, Singapore 9128
`USA office: Suite 1B, 1060 Main Suect, River Edge, NJ 07661
`UK office: 73 Lynlon Mead, Toaeridge, London N20 8DH
`
`Cover design: By Amir Novin, Kant Wan and Joy Tunnoch.
`Microscope photograph of a polymer dispersed liquid crystal display in
`quiescent mode betweat crossed polarizers.
`
`First published 1990
`First reprint 1993
`
`LIQUID CRYSTALS - APPLICATIONS AND USES (Vol. 1)
`
`Copyright © 1990 by World Scientific Publishing Co. Pte. Ltd.
`
`All rights reserved. This book, or parts thereof; may not be reproduced in anyform
`orby any means, electronic or mechanical, includingphotocopying, recording orany
`information storage and retrieval system now known or to be invented, without
`written pemiission from the Publisher.
`
`ISBN 981-02-0110-9
`
`Printed in Singapore by Utopia Press.
`
`List of Contribun
`
`-~:ar5 in parenthesis indirwr :a/
`
`: Elsadur
`
`(195)
`
`4~ F Bieha
`
`L Castes
`
`kaus
`
`(91)
`(275)
`
`(1)
`
`1's Donne
`
`3.:kenzeller
`
`‘ 1.30
`
`\.
`
`'.
`
`\lsdhusudana
`
`‘
`
`‘-'..‘rozumi
`
`(1‘1
`
`HQ
`
`'5)
`
`
`
`
`
`
`

`

`I
`
`nght Valve and
`Proyectwn Mode LCDS
`
`C
`
`O
`
`S.E. Shields
`W.P. Bleha
`
`Industrial Products Division
`Hughes Aircraft Company
`2051 Palomar Airport Road
`Carlsbad, California 92009
`
`
`
`16.1 Analog—Addressed LCLVs
`16.1.1 Photoactivated LCLVs
`
`Image Input Techniques
`16.1.1.1
`16.1.1.2 Photosensors for LCLVs
`16.1.2 Laser-addressed LCLVs
`16.1.3 Electron-beam-addressed LCLVs
`16.2 Matrix-Addressed LCLVs
`
`16.2.1 Multiplexed Display Applications
`16.2.1.1 Multiplexed Display Fundamentals
`16.2.2 Active Matrix Displays for Projection
`Applications
`16.2.2.1 TFI‘ Characteristics for Projection
`Displays
`16.2.2.2 Environmental Issues Especially
`Affecting TFI‘s Used in LCLVs
`16.2.2.3 Design Issues for Transmissive
`Active Matrix LCLVs
`
`.
`
`16.2.2.4 Design Issues for Reflective Active
`Matrix LCLVs
`
`16.3 Optical Systems for Projection LC Displays
`16.3.1 LC Projection Displays Based on Scattering
`16.3.2 LC Projection Displays Based on Polarization-
`Rotation
`
`437
`
`439
`439
`
`441
`442
`443
`445
`446
`
`447
`447
`
`448
`
`449
`
`451
`
`453
`
`455
`
`457
`457
`
`461
`
`
`
`

`

`438
`
`S. E. Shields & W. P. Bleha
`
`16.3.3 Optical Systems for Color Projection Displays
`16.3.4 Light Sources for Light Valve Projectors
`16.3.5 Projection Screen Technology
`16.4 Examples of LCDs for Projection Applications
`16.4.1 Printing Applications of Projected LCLVs
`16.4.2 Display Applications for Projection LCLVs
`16.4.2.1 Photoconductor-addressed LCLV
`
`Projectors
`16.4.2.2 Laser-addressed LCLV projectors
`16.4.2.3 Multiplexed LCLV Projectors
`16.4.2.4 Active-Matrix addressed LCLV
`
`16.5 Conclusions
`16.6 Acknowledgments
`
`projectors
`
`465
`468
`469
`470
`471
`472
`
`472
`475
`477
`
`479
`484
`484
`
`Liquid crystal (LC) devices do not emit light of their own; rather, they modulate the
`intensity or polarization of light from an external source. This means that the.-
`application to projection devices is only natural. Researchers have taken advantage
`of this circumstance by devising a wide variety of LC devices for use in projectio:
`systems.
`Indeed, there is such a wealth of work which has been done that there a
`no doubt that an entire book could be written about projection uses of LCDs.
`
`In this chapter we will concentrate on DC effects and devices which are current:
`being actively pursued. We intend to cover briefly not only the LC devices
`themselves, but also the other components (light sources, polarizers, etc.) require:
`to make a complete projection LC system. Our treatment of necessity will be bncf
`and superficial; thus we have had to be less complete in terms of describing all a“?
`the work which has been done over the years than we would have wished. Thus a
`number of devices have not been included, due primarily to space limitations.
`
`Our discussion will begin with LC light valves (LCLVs). As summarized in tab'x
`16.1, we have divided them into two classes, based on how the input information a
`entered into the LCLV. Matrix-addressed LCLVs use a discrete structure
`integrated into the device to control the spatial location of the information; analog-
`addressed LCLVs have no inherent structure which localizes the information, b;
`
`make use of the information wherever it happens to have been input. Typicaln
`analog LCLVs are addressed with an optical input from a CRT or a scanned last:
`beam, whereas matrix LCLVs are addressed electrically. After describing the
`LCLVs, we will continue with a discussion of projection systems, including 0th:-
`
`'TZpOl'lCl’ltS such :2
`telude with desc
`‘Qgcntly commerce
`
`—
`_.
`
`H
`
`' 6.1 ANALOG-l
`
`A
`
`.ariety of device
`‘2701 8 LC layer.
`- :
`triage into the
`.-...: mm. the optical
`RT). or from a St.
`: 'ectly by heart:
`r
`n: l C layer is used
`; ~t onto a scree r:
`L‘t'fgfe laser beam.
`
`' 5 1 .1 Photoaci
`
`" : shotoactivazcc’
`- rm} Researci‘
`:ai-to-optical i:
`* : 11ght image a
`.- another source
`
`~
`
`. ape of LCLV
`“'-
`-v :‘ separated by a
`.
`\artmr film a.
`
`_______
`
`~
`
`‘ r“: ““1““ 01?“
`.7; Emcmwrprm. 0.1
`
`1'.
`
`
`
`

`

`16. Light Valve and Projection Mode [CBS 439
`
`
`
`
`components such as light sources and polarizers used in such systems. We will
`conclude with descriptions of a number of actual systems, most of which are
`presently commercially available.
`
`Table 16.1. Classes of liquid crystal light valves
`
`
`
` Analog-addressed Matrix addressed
`
`Photo-activated
`Multiplexed
`Laser addressed
`Active matrix
`Electron-beam addressed
`
`16.1 ANALOG-ADDRESSED LCLVs
`
`A variety of devices have been fabricated which use an analog image input to
`control a DC layer. There are at least two methods which have been used to input
`the image into the LCLV - optical and electrical, using a beam of electrons.
`In
`addition, the optical method can use an image from a lens, from a cathode-ray tube
`(CRT), or from a scanned laser to access the LC layer by using a photosensor layer,
`or directly by heating the LC layer itself. All of these devices have in common that
`the LC layer is used to generate an image which can then be projected using white
`light onto a screen, or used for optical data processing (ODP) using a large-
`aperture laser beam.
`
`16.1.1 Photoactivated LCLVsa
`
`The photoactivated LCLV was invented and developed at the Hughes Aircraft
`Company Research Laboratories in Malibu, California in the 19705.
`It is an
`optical-to-optical image transducer that is capable of accepting a low-intensity
`visible light image and converting it, in real time, into an output image using light
`from another sourcel’z. A photoactivated LCLV is shown in figure 16.1.
`
`This type of LCLV consists of a photoconductor film and a nematic liquid crystal
`layer separated by a light-blocking layer and dielectric mirror (see figure 16.2). The
`photosensor film acts as an imaging, light-controlled voltage modulator for the
`
`a A good review of photosensor LCLVs is given in an article by W.P. Bleha (W.P. Bleha, Laser
`Focus/Electro-optics, October, 1983.)
`
`5M
`
`nodulate the
`us that their
`:n advantage
`
`in projection
`that there is
`L£Ds.
`
`are currently
`: LC devices
`
`etc.) required
`y will be brief
`scribing all of
`shed. Thus a
`tations.
`
`u’ized in table
`information is
`etc structure
`
`nation; analog-
`formation, but
`
`put. Typically
`l swarmed laser
`describing the
`ncluding other
`
`
`
`

`

`440
`
`s. E. Shields & W. P. Bleha
`
`
`
`Figure 16.1. Photograph of a typical photosensor—addressed LCLV.
`
`AC Blaa
`
`_.
`_.
`_.
`Writing
`nghl ”
`:
`a
`_.
`
`Ph I
`d
`t
`o ooon uc or
`
`
`
`Layer
`
`
`Transparent Conducllve Electrodes
`
`quuld Crystal
`Flber Opllc
`e IIgnment Fllma
`
`
`g;
`H
`
`igg
`H
`flag
`..
`j fig;
`._. Prolectlon
`
`PJE’
`LIghI
`
`agar
`:
`
`
`
`wet
`H
`
`: ’54
`._.
`finals
`
`
`Blocking D':|‘:;:'°
`
`|
`
`
`
`qu
`
`Id c
`
`l
`
`I
`rye a
`
`liquid crystal layer. F01
`used. In advanced den]
`the modulated readout 1
`
`light from reaching thI‘
`without these layers)
`
`photosensor is not sensii
`
`In operation, an ac volt:
`conducting layers. Typi
`photosensor. When an
`16.2, the photosensor i
`decrease in impedance
`photosensor being shift
`above its CICCtI'O-Opllt
`
`intensity, including gray
`
`One LC effect which c:
`
`In this configuration. th
`conventional 90° of I}
`
`polarizer and crossed
`reflective-mode LCL\
`beam effectively; a mi:
`the liquid crystal effet
`optical birefringence e
`the liquid crystal. Sim;
`used in transmission; 1!
`that the photosensor h
`infrared .
`
`16.1.1.1 Image Ingutj
`
`A variety of methods
`include direct coupling
`CRTs or scanned laS<
`
`disadvantages, as discu
`
`The CdS-photosenso
`erg/cmz) to be used
`This method of image
`which has worked wit
`
`Figure 16.2. Schematic diagram of a typical photosensor-addressed LCLV.
`
`
`
`

`

`
`
`16. Light Valve and Projection Mode LCDs
`
`441
`
`liquid crystal layer. For real-time response, liquid crystal layers 2-6 um thick are
`used. In advanced devices, a broad-spectral-band dielectric mirror serves to reflect
`the modulated readout light, and the light-blocking layer prevents residual readout
`light from reaching the photosensor. Other, simpler LCLVs (which are made
`without these layers) use wavelengths for the readout light to which the
`photosensor is not sensitive.
`
`In operation, an ac voltage is applied across the device between the two transparent
`conducting layers. Typically 10 volts rms at 10 kHz is used for devices with a CdS
`photosensor. When an image is input through the electrode on the left of figure
`16.2, the photosensor impedance is lowered in response to the input light. This
`decrease in impedance results in a portion of the ac voltage present across the
`photosensor being shifted to the DC layer. This additional voltage drives the layer
`above its electro-optic threshold in a pattern that replicates the input image
`intensity, including gray-scale levels.
`
`One LC effect which can be used with the LCLV is the hybrid field effect mode3.
`In this configuration, the liquid crystal molecules have a twist of 45", rather than the
`conventional 90° of typical twisted-nematic (TN) LC displays. With both the
`polarizer and crossed analyzer on the same side of the LC, as is necessary with
`reflective-mode LCLVs, the 90° TN does not modulate the intensity of the light
`beam effectively; a twist angle of 45° gives the maximum modulation effect. Thus,
`the liquid crystal effect is a hybrid configuration of a 45° TN dark off-state and
`optical birefringence effect to transmit light when a bias voltage is applied across
`the liquid crystal. Simple LCLVs without the mirror or light-blocking layers can be
`used in transmission; this makes possible standard 90° TN operation. This requires
`that thephotosensor be transparent to the projection light, as is true for CdS in the
`infrared .
`
`16.1.1.1 Image Ingut Technigues
`
`A variety of methods have been used for inputting images into a LCLV. These
`include direct coupling of images into the device using lenses, as well as the use of
`CRTs or scanned lasers to input the image. Each of these has advantages and
`disadvantages, as discussed below.
`
`The CdS-photosensor LCLV has sufficient sensitivity (a threshold of about 1
`erg/cmz) to be used with a lens for directly imaging three-dimensional objects.
`This method of image input is most often used in GDP applications. One group
`which has worked with the LCLV in this mode is Gara5, who used the LCLV in
`
`
`
`

`

`442
`
`S. E. Shields & W. P. Bleha
`
`correlation experiments to determine the position and orientation of moving three-
`dimensional objects. Other researchers have used the LCLV to convert an image
`from non-coherent to coherent light, in order to apply techniques such as Fourier-
`plane filtering for image recognition applications.
`
`One common method for generating the input image for a LCLV system is to use a
`cathode-ray tube (CRT).
`In particular, by using a fiberoptic faceplate on the CRT
`and a corresponding fiberoptic substrate in the LCLV one can directly couple the
`light from the CRT phosphor into the photosensor. Alternatively, one can also use
`a lens to image the CRT image onto the photosensor. Both of these techniques
`take advantage of the inherent ease of use of the CRT as an image source.
`
`Several groups have used laser scanning to address the LCLV photosensor directly.
`For LCLVs with a CdS photosensor, which is most sensitive near 515 nm
`wavelengths, an argon-ion laser whose output is at 514 nm is an ideal input source.
`In particular, researchers at Naval Ocean Systems Center in San Diego have used a
`scanned laser to address a LCLV for image projection6. They used a 20 mW Argon
`laser to write the LCLV, and obtained a 1075-line, 30 Hz, interlaced video image
`on the output screen.
`
`1§,1.1,2 Photosensors f_or LCLVs
`
`Photosensors other than CdS have been used to make LCLVs. These include
`
`single crystal silicon, amorphous silicon, and compound semiconductors such as
`GaAs and bismuth silicon oxide7. No one photosensor has been developed.
`however, which is ideally suited for use in LCLVs.
`
`CdS is the material which has been used in most of the photoactivated LCLVs
`which have been built. It has good sensitivity, centered in the green. However, it
`also has limited response speed (about 100 msec), as well as large numbers of traps
`which can cause much slower-decaying artifacts in the displayed image, especially in
`images with gray scale.
`
`Single crystal silicon8 has good sensitivity to light throughout the visible spectrum.
`Its response speed is in the microsecond range. However, due to its relatively high
`conductivity at room temperature (even in intrinsic Jr-type material), it must be
`fully depleted during operation. This requires that the photo-generated charge
`residing at the silicon-silicon dioxide boundary be recombined periodically by
`driving the silicon photosensor into accumulation. In order to limit spreading of
`the charge at the interface, an array of diodes is formed in the silicon material, as
`shown in figure 16.3.
`
`n-lype
`Mlcrodlodee
`
`_.
`
`_o-
`
`_..
`
`_,
`
`—. _.
`
`ertlng
`Ugh!
`
`—’
`
`_.
`
`/
`SI llcon
`PhoIoeonduclor
`
`Figure 16.3. Cm
`LCLV.
`
`Amorphous silicon (:
`relatively fast resporLs
`CdS, as well as a spec
`the spectrum. This In
`but makes possible at
`
`GaAs has also been '
`
`silicon case, a wafer c
`than using a depositec
`
`16.1.2 Laser-addl
`
`I: the last section, or
`::e LCLV is addresse
`
`an image onto a phol
`
`‘1
`
`
`
`Wm..1—
`
`l
`
`
`
`

`

`
`
`16. Light Valve and Projection Mode [£05 443
`
`quuld Crystal
`
`n-type
`'llgnment Fllma
`
`Mlcrodlodea
`
`0 ptlcal Glace
`.L
`
`assess:3103034
`
`0 O0
`
`‘0
`.0.0129.9'.
`.0
`
`O
`.0
`3::0'
`02
`
`‘6O.
`9.
`‘0
`
`0'0.0
`.0
`:3?
`
`'0‘e
`
`'0o020 v
`92?
`
`.i:§.9.
`0 fl
`
`..9
`
`{9;5?
`30:00'.O
`9'
`
`Slllcon
`
`Photoconductor
`
`
`
`”£22:39293_Bd‘““““““‘!
`“YA““““““W
`II|||Il!l|||||||||||l|||||l||l|||||||lI
`
`
`
`
`0 3
`
`erllng
`Ugh!
`
`111111
`
`ProlacIlon
`
`nght
`
`4
`
`Hype
`rlng
`
`
`s"3‘2 Dleleclrlc
`
`Gate
`error
`
`Layer
`
`quld Crystal
`
`hree
`mi:
`met
`
`CRT
`e the
`
`owe
`iques
`
`real).
`5 nm
`)uroe.
`med 3
`
`Argon
`image
`
`lCIUdC
`JCh as
`
`loped.
`
`,CLVs
`:ver. II
`
`I traps
`ially in
`
`ctrum.
`
`.w high
`ust be
`
`:harge
`tlly by
`ling of
`'ial, as
`
`Transparent Conductlve Electrodes
`
`Figure 16.3. Cross-sectional schematic of the single-crystal-silicon photosensor
`LCLV.
`
`It has
`Amorphous silicon (a-Si) has also been used as a photosensor in LCLVs.
`relatively fast response (10-20 msec); however, it suffers from lower sensitivity than
`CdS, as well as a spectral response which is shifted out into the near-infrared end of
`the spectrum. This limits the phosphors which can be used to address a-Si devices,
`but makes possible activation with laser diodes.
`
`GaAs has also been used as a photosensor in LCLng. As in the single-crystal-
`silicon case, a wafer of the semiconductor is mounted onto a glass substrate, rather
`than using a deposited thin film of semiconductor.
`
`16.1.2 Laser-addressed LCLVs
`
`In the last section, on photoactivated LCLVs, we discussed several systems where
`the LCLV is addressed by a laser. In those cases, however, the laser is used to write
`an image onto a photoconductor.
`In this section we will describe LCLVs in which
`
`
`
`

`

`
`
`
`16. Light Valve and Projection Mode [CBS 447
`
`several companies have released more sophisticated units which include the light
`source and projection optics, and which allow a full-color image to be shown. At
`least one manufacturer (Matsushita) has announced the development of a matrix-
`addressed LCLV projector with HDTV resolution“, and many others are in
`development at other companies.
`
`16.2.1 Multiplexed Displays for Projection Applications
`
`The most common technique used to address large area LC flat panel displays is
`multiplexing. It is no surprise that this technology has been applied to projection
`displays. Multiplexed displays are much simpler to fabricate than are active matrix
`displays. However, they do not have as good a performance in terms of contrast,
`response speed, and viewing angle, as do active matrix displays.
`
`16.2.1.1 Multiplexed Display Fundamentals
`
`Figure 16.7 shows a cross-section of a multiplexed display. It consists of two glass
`substrates with transparent conductive stripes. The stripes on the two substrates
`are oriented at right angles to each other; the area defined by the overlap of two
`particular stripes forms an individual pixel. The LC material located between the
`two substrates is oriented in a twisted nematic (TN) configuration, and the
`displayed image is generated in the method characteristic of transparent TN
`displa s.
`
`y
`
`/X ElectrodesGlass Substrate
`
`Spacer
`Particles
`
`Liquid
`Crystal
`
`/Y Electrodes
`
`\
`Glass Substrate
`
`Figure 16.7. Cross section of a multiplexed display (from Schefferls).
`courtesy of Society for Information Display).
`
`(Figure
`
`
`
`

`

`448
`
`S. E. Shields & W. P. Bleha
`
`The applied voltage affecting the LC material at any one pixel is the rms average of
`the difference between the voltages applied on the two conductive stripes defining
`that pixel. For small numbers of pixels it is relatively easy to adjust the timing of
`the signals and their relative amplitudes in order to create differences in voltage
`between different pixels in the array, resulting in some pixels being ON and others
`being OFF. However, this becomes more difficult as the number of lines of the
`display is increased. Alt and Pleshko16 derived the relationship between the
`maximum number of lines and the required voltage ratio between turning the LC
`material ON and turning it OFF. This relationship is:
`
`Von
`V—off _
`
`
`{m + 1}1/2
`/N — 1
`
`161
`I
`
`]
`
`[
`
`As new LC materials with steeper electro-optical response curves have been
`developed, the obtainable ratio has gotten closer to 1, allowing the number of lines
`addressed to be increased.
`In addition, new developments such as supertwisted
`alignment have permitted even larger slopes for this response curve. Presentl)
`multiplexed displays with 480 active lines are being produced by several
`manufacturers for use in computer displays, and at least one group17 has built a
`display prototype using multiplexed ferroelectric LC materials to address over 1000
`lines!
`
`the pixel electrode. T
`although diodes and or
`control line toggles all (
`line is common to one
`
`chapter (on active-matr
`of these devices.
`
`Data Unec :\
`
`\
`
`.‘\K‘
`
`16.2.2 Active Matrix Displays for Projection Applicationsa
`
`Active-matrix displays are beginning to displace multiplexed displaysb. They haw
`the advantage that they can show good gray scale images with better field of view
`than can multiplexed displays. This advantage results form the presence of 3:
`active switch at each pixel. Active-matrix displays are also limited in their number
`of lines not by Alt and Pleshko's relation, but by the difficulty of manufacturing the
`active matrix itself.
`
`A schematic of an active-matrix display is shown in figure 16.8. Each pixel contaim
`a switch which controls when the voltage on the data line is allowed to pass onzr
`
`a. A good general review of active matrix displays is given by Morozumi (S. Morozumi, 1989 5::
`Seminar Lecture Notes, Volume II (May 19), pp. 10.1-10.29 (1989).
`
`‘
`
`.
`
`Figure 16.8. Schemat
`
`
`' 6.2.2.1 fl Character:
`
`\ number of technologi:
`-sed to control a liquid
`1171‘s, polysilicon (p-Sil
`SOS), as well as other ;
`{her than TFTs (such a
`ne assumes that the dex
`-:ructurc used in mos
`
`b. One good example of this is the display chosen for the new Apple Computer Corporanm
`MacIntosh portable computer, which uses an active matrix.
`’
`
`L A good review of TFTs :
`formation Display 27, p 31.1
`
`
`
`

`

`mWwWWm
`
` i5
`
`
`
`16. Light Valve and Projection Mode LCDS
`
`449
`
`the pixel electrode. This switch is most commonly a thin film transistor (TFT),
`although diodes and other nonlinear devices have also been used. Typically each
`control line toggles all of the switches along one row of the display, while each data
`line is common to one column of the display. The reader is urged to read the
`chapter (on active-matrix displays) in order to gain a more thorough understanding
`of these devices.
`
`I
`D: aUnum Control
`
`
`
`Figure 16.8. Schematic view of an active-matrix display.
`
`
`16.2.2.1 TFT Characteristics 19; Projection Displays
`
`A number of technologies exist which might be used to fabricate the active matrix
`used to control a liquid crystal device. These include single crystal silicon (c-Si)
`TFTs, polysilicon (p-Si) 'I‘FTs, amorphous silicon (a-Si) TFTs, silicon-on-sapphire
`(SOS), as well as other addressing schemes which make use of nonlinear devices
`other than TFTs (such as diodes or metal-insulator-metal (MIM) structures)a. If
`one assumes that the device will make use of the common twisted nematic (TN) LC
`structure used in most light valves, then the substrate material should be
`
`a A good review of TFTs and their operation is given in W.E. Howard, Proc. Society for
`information Display 27, p 313-326 (1986).
`
`
`
`

`

`472
`
`S. E. Shields & W. P. Bleha
`
`A number of other groups have also worked with the use of LCLVs to create
`images for printing or other graphics applications. Some of the devices which have
`resulted from this work are detailed in the table in the appendix. Certainly this
`type of application is relatively new, but it may represent a real growth area in the
`future.
`
`16.4.2 Display applications for Projection LCLVs
`
`Projection display applications are the most common application for LCLVs.
`Numerous papers have been published, describing devices designed for this type of
`application. These devices are summarized in appendix tables. We have chosen
`several examples of actual products to describe in more detail below.
`
`16.4.2.1 Photoconductor-addressed LCLV Projectors
`
`A number of projection systems have been built for large screen, military
`command-and-control applications. A representative one described by Ledebuhr3
`uses three CdS-photosensor LCLVs to generate a full-color display. The images
`from the three LCLVs are combined inside the projector, and the resulting full-
`color image is projected using a single projection lens.
`
`A perspective view of the projector optical system is shown in figure 16.28. Notice
`that the arc lamp illumination is polarized by passing through two separate
`MacNeille polarizing beam splitters. Two prisms are used to enhance the display
`contrast. This polarized light is then decomposed by dichroic mirrors into its
`constituent colors. Each color is modulated by a separate LCLV.
`
`After modulation, the light returns through the dichroic mirrors to the second
`polarizing beam splitter, which acts as the system analyzer. The light which passes
`through the prism is relayed to a projection lens (located in the face of the view)
`and projected out of the wide side of the unit onto the screen.
`
`The input images for the three LCLVs are generated by three fiberoptic faceplate
`CRTs. These CRTs are custom 2-inch diameter tubes, with very high resolution
`and light output matched to the requirements of the CdS photosensor. The
`fiberoptic CRT output is optically coupled with optical matching fluid to the
`fiberoptic input window of the LCLV. This directly couples the image from the
`phosphor inside the CRT (where it is generated) through the 6 mm diameter fibers
`in the CRT and the LCLV into the photosensor. The combined modulation
`transfer function (MTF) of a 0.9—mil spot fiberoptic CRT and the LCLV is shown in
`figure 16.29.
`
`
`
`Figure 16.28. Persp
`(Figure courtesy of S
`
`
`
`

`

`I16
`“I
`
`Lb:
`
`0 its
`
`tend
`mus
`
`it“ I
`
`plate
`utio:
`The
`3 the
`n the
`fibers
`
`align
`um in
`
`16. Light Valve and Projection Mode [CBS 473
`
`
`
`Figure 16.28. Perspective view of the projector optical system (from Ledebuhr37).
`(Figure courtesy of Society for Information Display).
`
`
`
`

`

`474
`
`S. E. Shields & W. P. Bleha
`
`10—
`30 20;-
`
`”faMlF
`
`A0
`
`0
`
`200 400 000 800100012001400160018002000
`N LINES
`
`Figure 16.29. Combined MTF of the LCLV addressed by a 0.9-mil fiberoptic CRT
`
`Table 16.6 describes the performance of this system. With a 1.6 kW xenon arc
`lamp, the system achieves a light output of over 1000 lumens.
`
`Table 16.6 Performance data for a full-color LCLV projector
`
`
`
`Characteristic
`
`Performance
`
`
`
`
`
`
`Color range
`Light output (1.0 kW lamp)
`
`Light output (1.6 kW lamp)
`
`Contrast ratio (White)
`Screen size
`Throw distance
`
`Frame rate
`Raster format
`Vertical resolution
`Horizontal resolution
`Image registration
`
`Full color
`> 10001umens (open gate)
`> 6501umens (square aperture)
`> 16001umens (open gate)
`> 1000 lumens (square aperture)
`> 75:1
`1 m to 5 m square
`1 m to 5 m
`
`30 Hz (interlaced)
`1075, 625,525
`> 1024 scan lines
`> 1800 TV-lines (limiting)
`0.25 pixel in white for all
`PD“:ls
`
`
`
`.
`M M
`
`laser-addr
`_
`d h essed 5m“
`uoun t 6 world. H‘
`10 Update an entire
`applications requirin
`:omputer-aided desii
`they appear to be very
`
`_
`
`.
`figure 1630‘ u'
`arge SPICE“ pro].
`Operations.
`
`This CRT/LCLV combination also works well for other large screen display
`applications (including high definition television (HDTV)), with over 1,000 TV
`lines available across the aperture. Commercial projectors based on this system
`have been built for numerous large screen applications, including commercial
`command and control centers such as the one at Electronic Data Systems Corp.
`shown in figure 16.30.
`
`Hitachi has market:
`3000x2000 element r
`square screen. As dc
`smectic LVs to gene
`:rojection lens. Figui
`Projector, while figure
`
`
`
`

`

`480
`
`S. E. Shields & W. P. Bleha
`
`Three companies currently have products available in the marketplace - Seiko
`Epson, Sharp, and Sanyo. In addition, Matsushita has demonstrated a similar
`product. Their present projector products are compared in table 16.8 below.
`
`-34
`Table 16.8. Comparison of Several I F! —LCD Projectors (based on a table by Morozumi
`
`).
`
`Model
`
`Lamp Size
`
`Lamp Type
`
`Beam Splitter
`
`VPJ-700
`
`300 W
`
`Halogen
`
`Dichroic
`
`Image combiner
`
`X-cube
`
`XV-100P
`
`PLC 100-N
`
`150 W
`
`150 W
`
`250 W
`
`Metal Halide
`
`Metal Halide
`
`Metal Halide
`
`Dichroic
`
`Dichroic
`
`Dichroic
`
`Dichroic
`
`Dichroic
`
`On Screen
`
`Projection Lens
`LCLV
`
`Single
`3 TFT—LCDs
`
`Single (zoom)
`3 TFF—LCDs
`
`Single (zoom)
`3 TFT-LCDs
`
`Three lenses
`3 TFF-LCDs
`
`TFI‘ technology
`Driver tech.
`Pixels
`
`(transmissive)
`p-Si
`integrated
`320x220
`
`(transmissive)
`a-Si
`LSIs
`405x221
`
`Pixel Layout
`
`Rows/columns
`
`Active area diag.
`
`1.27 inch
`
`Aperture
`
`47%
`
`Response time
`
`40 msec
`
`Brightness
`Contrast
`
`70 lumens
`70:1
`
`Delta
`
`3 inch
`
`about 50%
`
`30-40 msec
`
`1001umens
`100:1
`
`(transmissive)
`a-Si
`
`476x236
`
`Delta
`
`3.1 inch
`
`40 msec
`
`100 lumens
`100:1
`
`(transmissive)
`a-Si
`LSIs on glass
`650x480
`
`Rows/columns
`
`2.8 inch
`
`50%
`
`40 msec
`
`160 ft-L, gain 6
`100:1
`
`498,000 yen not available
`
`Screen size
`
`40-100 inch
`
`25-100 inch
`
`35-100 inch
`
`40 inch (fixed)
`
`Weight
`Volume
`Price
`
`7.3 kg
`42x27x13 cm3
`
`13.8 kg
`25x60x25 cm3
`
`13.6 kg
`19x63x37 cm3
`
`45 kg
`90x90x40 cm3
`
`480,000 yen
`
`485,000 yen
`
`Figure 16.33. Seikc
`Seiko Epson Corpm
`
`
`
`
`Figure 16.36. Disp
`Morozumi, Seiko E
`
`As of now, the Sanyo projector (which was just introduced near the end of 1989) is
`only available in Japan. Seiko Epson has announced that they will release in
`December, 1989, a new projector product. Known as the VPJ-1000, it will use
`440x480 pixel LCLVs to achieve enhanced resolution. Their present product is
`shown in figure 16.35; figure 16.36 shows a projected image from this unit.
`
`
`
`