PROFESSIONAL D-ILA PROJECTOR

Transcription

1 PROFESSIONAL D-ILA PROJECTOR

2 CONTENTS Prefae 3 Projetor Development History and Bakground 3 From ILA TM Projetors to D-ILA TM Projetors 4 Struture and Basi Operating Priniples of D-ILA TM 5 Features of D-ILA TM 6 Single D-ILA TM Color Projetor 7 Comparison with Competitive Systems 8 D-ILA TM Piture Reprodution 9 Summary : The Future of D-ILA TM 10 Referene Materials (Illumination & Optis) 11

3 Prefae Large-sreen video is fast beoming an indispensable display devie for appliations that require greater presene, appeal, and information distribution apabilities than is possible with onventional monitors. This shift to larger sreens is mainly being failitated by projetors, beause they offer greater flexibility in terms of display size and greater ompatness relative to the size of the display. At the same time, however, it is neessary that the projetion devie the key omponent of the projetor is apable of withstanding a onsiderable degree of heat and light sine very high levels of light are onentrated on a relatively small surfae. The need for omplex, advaned tehnology to attain high resolution further ompliates the issue. Even now, engineers around the world are working to develop the next generation of high-performane projetors. In this doument we will examine the basi operating priniples, features, and future prospets of D-ILA TM. An understanding of these basis will both aid in the introdution of new projetors and enable urrent projetors to be used more effetively. Projetor Development History and Bakground In the 1940s, as blak-and-white TVs were fast beoming a fixture in households in Ameria and elsewhere, the development of largesreen displays was already underway. Initially, oinident with the development of TV reeivers, the primary projetion method was CRT based. However, limits on light output soon led to the development of the light valve system, whih made it possible to ontrol more powerful light soures. In the 1950s, a blak-and-white Eidophor system was ommerialized using oil film target tubes. In the 1960s, both projetors and TVs were onverted to olor systems. In the ase of projetors, a onfiguration of three oil film target tubes was used. In the 1970s, the Talaria system was introdued. Here, olor signals were multiplexed and the number of oil film target tubes was redued. This system enabled light output of a few thousand lumens, ompared to the few hundred lumens possible with CRTs. The Eidophor and Talaria devies that used oil film target tubes required large vauum devies. This inreased the size and ost, as well as requiring more maintenane, due to the hemial hanges in the oil film. By this time, however, researh had already begun on the possibility of using liquid rystal for use in future flat panel displays and various display boards. By the 1980s, some manufaturers had begun applying transmissive and refletive liquid rystals to projetors. By the beginning of the 1990s, LCD projetors had been ommerialized for the general market and and ILA TM projetors followed soon afterwards. In the mid-1990s, DLP TM projetors were introdued. These used a DMD TM devie, whih modulated light with the mehanial vibration of ultra-small mirrors. With LCD projetors and ILA TM projetors already on the market, projetion systems entered a new and muh more ompetitive era. Table 1 lists the types of projetion methods and Figure 1 shows onept diagrams for eah type of projetion system. Table 1: Types of Projetion Systems Projetion system Self-light-emitting type Non-light-emitting type (light bulb) Transmissive type Refletive type CRT projetor tube TFT LCD Oil film target ILA (Image Light Amplifier) 3

4 Figure 1: Conept Diagrams and Features for Eah Projetion System Configuration Conept Diagram Features CRT CRT Signal input Projetion lens Mature tehnology and low ost No pseudo-signals with no pixels Can handle speially shaped sreens Resolution and light output inversely related Low output Large size and weight Oil film target type Lamp Vauum hamber Spherial mirror Eletron beam Oil film Light olleting lens Projetion lens Mirror bar Signal input Writing and reading are separated, so light output is higher No pseudo-signals with no pixels Can handle speially shaped sreens High devie osts Long startup time for vauum devie High maintenane osts Large size and weight Deterioration in S/N ratio due to film surfae harateristis LCD ILA DLP Lamp Signal input LCD Projetion lens Light olleting lens Polarizing plate PBS Signal input CRT Light olleting lens ILA Projetion lens Lamp Light olleting lens Light olleting lens Lamp DMD Signal input Projetion lens Can easily be made small and light Can be produed at low ost Easy optial onfiguration Resolution and light output inversely related Large devie required for high light output Contrast limited (horizontal orientation) Provides both resolution and light output No pixels and no pseudo-signals Aperture ratio 100% High ontrast Writing and reading are separated, so high light output easily produed Can handle speially shaped sreens Large size and weight Diffiult to produe at low ost Uses natural light, giving it a high light effiieny ratio (in priniple) High-speed response makes sreen sequene olor easy Tones managed easily with digital swithing operations The devie proess inludes mehanially moving parts and is ompliated. Yields and osts are issues. The pixel pith is restrited, so high resolutions require larger devies. The drive logi is omplex. Meanwhile, following the development of onventional TVs, due to the maturity of the tehnology and their relatively low ost, CRT projetors had for many years dominated the projetor market. However, in spite of tehnologial advanes, these projetors remained plagued by insuffiient light output and bulky, heavy designs. Eventually the CRT projetion system was relegated to use in home projetion TVs and speialist appliations, while designs of other projetors were modified to inorporate to the newer systems. Similarly, the Eidophor and Talaria devies were phased out beause the vauum devies they required means that they were too large, heavy and expensive to ompete with the newer systems. From ILA TM Projetors to D-ILA TM Projetors Around the start of the 1970s, researh was arried out at Hughes Airraft into opti writing spatial modulation devies and in the 1980s, projetors using this devie ame into pratial use (even though they were restrited to still-piture images). Continuous improvements eventually made it possible for these devies to han- 4 dle moving images and by the end of the 1990s, the tehnology for moving images was firmly established. At the same time, JVC (Vitor Company of Japan, Limited), was arrying out researh and development on projetion methods suitable for the antiipated large-sreen pitures. Determining that the opti writing spatial modulation devies were optimum for this purpose, JVC s R&D foused on pratial implementation of this tehnology. Hughes Airraft and JVC joined fores to develop a marketable projetor and in 1993 introdued the ILA TM (Image Light Amplifier) projetor. This was immediately reognized in the market as the new standard for large sreen projetors in the seond half of the 1990s. As Figure 2 shows, the ILA TM projetor devie is omprised of a number of layers of 0 thin-film that are sandwihed between two glass substrates. The thin-film struture has four layers: an optoeletrial ondutive layer, a light ut-off film, dieletri mirrors, and liquid rystal with ultra-fine proessing to generate pixels. As Figure 1 shows, the devie operates with two-dimensional CRT optial images as the writing light, forms the images in the optoeletrial ondutive layer, and varies the impedane of the opti-

5 eletrial ondutive layer aording to the strength of the optial image. As a result, the AC voltage applied to the liquid rystal layer hanges to math the optial image and optial modulation is applied to the reading light. The modulated light is branhed at the PBS (Polarized Beam Splitler) surfae to the light soure side and the projetion side linked with the strength of the writing light. The features of the ILA TM projetors are as follows. ➀The reading light that determines the optial output is refleted by dieletri mirrors, with an aperture ratio of 100%, so high brightness projetion is possible. ➁The writing light that determines the resolution is ultra-low, so the CRT beam size is ultra fine. Conseguently very high resolution an be easily attained. ➂The liquid rystal vertial layout, one onsidered diffiult for mass prodution, is mass produed for the first time, providing very high ontrast. ➃There is no pixel struture, so distortion-free reprodution, free of any pseudo-images is possible for all types of input signals. In other words, by separating the light output (whose phase is easily shifted), and the resolution, the writing light and the reading light (with dieletri mirrors), this is the first tehnique to provide both very high light output and high resolution. Furthermore, this system has the added advantage of distortion free image ombined with very high ontrast. This allows superior quality images from the ILA TM projetor. Figure 2: Basi Composition of ILA TM Devie dia appliations. JVC has developed its own new projetion method that resolves Issues ➀ and ➁ while retaining the high light output, high resolution, and high ontrast provided by ILA TM projetors. To meet market demand for a mainstream projetion tehnique for the 21st entury, JVC introdued its "D-ILA TM Multimedia Projetor" at the beginning of Struture and Basi Operating Priniples of D-ILA TM As Figure 3 shows, the basi struture of D-ILA TM devies is LCOS (Liquid Crystal on Silion). Aluminum refletive eletrodes, orresponding to eah pixel, are laid out on the CMOS board making up the X-Y matrix that selets the pixel address. After this surfae is flat proessed, the vertial film is formed. On the other glass board, the transparent eletrode layer and the vertial film are plaed. The liquid rystal layer is sealed between the faing films. Figure 3: Basi Struture of D-ILA TM Devies Glass Substrate Alignment Layer Transparent Eletrode Liquid Crystal Refletive Eletrode Wiring Shield Layer ITO Eletrode Dieletri Mirror Glass Substrate Photo Sensor Projetion Light Writing Light Si Substrate Soure Gate Drain Capaitor Setional view Wiring Layer Front view Optial Glass Substrate Alignment Layer Liquid Crystal ITO Eletrode Light Bloking Layer While ILA TM projetors are high-resolution projetors that realize light output of up to 12,000 lumens, boundary resolution of 1,600 TV lines, and ontrast of over 1,000 to 1, some problemati issues remain. ➀Beause the ILA TM is used as the projeting devie and a CRT for the writing light, two key devies are required. As a result, osts an quikly esalate as does size and weight. ➁The writing opti image is formed with an eletron beam that has a diameter, so even though the boundary resolution is high, as the optial image spatial frequeny rises, the MTF (modulation transmission funtion) gradually dereases. This an lead to diminished legibility of very small letters. In reent years, thanks to inreases in omputer apaity and speed, together with dereasing osts, presentations whih inlude graphis and text have beome ommonplae. It is expeted that ➁ above may redue the suitability of ILA TM projetors for multime- The D-ILA TM devie s refletive tehnique involves laying out the pixel address seletion setion and the light modulation setion liquid rystal in three dimensions. The entire surfae, exept for the insulation setion between pixel eletrodes, is used as a refletive surfae, so a very high aperture ratio is possible. Also, thanks to the high aperture ratio, high intensity light an be handled, making it easy to onvert to higher light output. The vertial orientation that has proven itself on ILA TM projetors, is used for the liquid rystal layer, so high ontrast is obtained. Depending on the optial system seleted, a ontrast of over 1,000 to 1 is possible. The resolution is determined by the size of the ells on the CMOS board. Given the sub-miron saling of urrent CMOS memory ICs, even the pixels for full HDTV (1,920 x 1,080 pixels) an be fitted onto a CMOS board of less than 1 inh aross, providing ultrahigh resolution. 5

6 Figure 4: Basi Struture of D-ILA TM Projetor Video signal D-ILA devie PBS Light olleting lens Projetion lens Figure 4 shows how a D-ILA TM projetor operates. The natural light from the light soure is separated by the PBS (polarized beam splitter) into a P wave omponent (light vibrating parallel to the surfae) and an omponent (light vibrating perpendiular to the surfae.) The P wave omponent proeeds straight through the PBS. Sine it is unneessary light, it is not used. Only the omponent reahes the D-ILA TM elements. The light that has reahed the elements passes through the liquid rystal layer, is refleted by the pixel eletrodes, passes through the liquid rystal layer again, and reahes the PBS. At this time, the omponent that was modulated in the liquid rystal layer is onverted into P waves and after it has passed through the PBS, is projeted onto the sreen through the projetion lens. On the other hand, the omponent that was not modulated is refleted by the PBS and returns to the light soure, so it does not ontribute to the projetion image. Figure 5 shows the opti modulation harateristis for the vertially oriented liquid rystal. (a) is for when there is no modulation and (b) is for when there is modulation. When the input signal to the devie is blak, voltage is not applied to the pixel eletrode, the liquid rystal layer remains in its vertial orientation (as shown in the diagram), the light axis of and liquid rystal long axis are parallel, and opti modulation does not take plae in the liquid rystal layer. The light input, as s, is output as it is (without modulation) and refleted by the PBS. As a result, this light does not reah the sreen and it reprodues the blak state. The high ontrast harateristi of the vertially oriented liquid rystal is for blak reprodution, when the liquid rystal is not modulated. This is how true blak is obtained. (b) shows the state in whih voltage is applied to the pixel eletrode. Sine the liquid rystal is the n type, the long axis tilts in the diretion perpendiular to the applied eletri field. At this time, the axis of the inoming light and the long axis of the liquid rystal interset. Due to the ompound refration of the liquid rystal, the light is onverted into elliptially polarized light and irularly polarized light, a P wave omponent is generated, and the projeted optial image is formed on the sreen. The maximum modulation of the liquid rystal ours when all the s oming into the devie are onverted into P waves to reprodue a white image. Figure 5: Modulation Charateristi of Vertially Oriented Liquid Crystal When not modulated (a) When modulated (b) Features of D-ILA TM The features of D-ILA TM are as shown in Table 2. Beause of the high aperture ratio, any rise in the temperature of the devie due to photothermal onversion and any malfuntioning of drive elements due to photoeletri onversion is minimal. Therefore, it is possible to handle high intensity light. Moreover, the resolution is determined by the CMOS proess saling, as disussed above. So pixel pithes of only a few mirons are possible and, as mentioned previously, the pixels for full HDTV (1,920 x 1,080 pixels) an fit onto a CMOS board less than 1 inh aross. Also, the vertial orientation of the liquid rystal is fully utilized. The high light output, high resolution, and high ontrast of the onventional ILA TM are retained, while shape, weight, and ost issues of the ILA TM are resolved by onverting the writing method from an optial image to diret writing with eletrial signals. Table 2: D-ILA TM Projetor Features High resolution High aperture ratio High light output High ontrast High-speed response Compat, lightweight Currently, this is the element with the highest possible density. When pixel size is the same, it provides the highest resolution; when resolution is the same, it has the smallest pixel size. As long as the insulation between pixel eletrodes is maintained, the size of the nonopening setion an be minimized, so resolution an be raised with only a minimal redution in the aperture ratio. The aperture ratio and light output are proportional and the non-opening setion is small. As a result, photothermal onversion is minimal, the light withstand level for the elements is high, and powerful light soures an be used. The vertially oriented rystal provides a nomodulation state, so the highest ontrast of a few thousand to one an be attained for the element alone. With the refletive type, light is modulated while it goes bak and forth. As a result, the thikness of the liquid rystal layer is half that of the transmissive type, the eletri field boundary strength gw is double, and highspeed response is possible. The high pixel density and high aperture ratio allows the elements to be light and ompat. Development of olor projetors Figure 6 shows the onfiguration of a three-d-ila TM projetor. The first and seond fly-eye lens plates and the PS omposite plates sandwihed between them onvert the natural white light of the light soure into. This raises the operating effiieny of the light soure and improves the uniformity of the amount of light on the sreen at the same time. Subsequently, the light is separated into RGB (red, green, blue) omponents through olor photospetrometry and eah olor is input to the orresponding PBS. The omponent, refleted by the PBS, beomes the P wave omponent modulated by the liquid rystal as shown in Figure 4 and disussed above. Only this omponent passes through the PBS, while the RGB is synthesized by the ross-dihroi prism, and projeted onto the sreen as a olor image through the projetion lens. The three-panel projetor is the most fundamental method for handling olor. This is a system in whih the light utilization effiieny is high and projetor performane, olor reprodution, ontrast, and 6

7 resolution are determined diretly by the devie harateristis. On the other hand, tiny differenes in registration and uniformity among the R, G, and B devies an diretly influene the piture quality. Sine three devies are required and olor separation and olor synthesis optial systems are neessary, this an lead to high ost and large size. Therefore, although the three-panel system is suitable for professional use, it is not suitable for onsumer systems whih require lower pries. In order to develop an affordable onsumerlevel system, it is neessary to redue the number of devies and further redue the size and ost of the optial systems. Figure 6: Struture of Three-D-ILA TM Projetor Projetion lens B-PBS R-PBS Blue D-ILA Color separation ross-dihroi G-PBS Green D-ILA Single D-ILA TM Color Projetor Mirror Lamp R/G Light olleting lens Mirror Methods proposed for reduing the number of devies inlude ( i ) surfae sequening that multiplexes the olors on the time axis and (ii) simultaneous point sequening that multiplexes the olors in spae. Surfae sequening synhronizes with the field frequeny and applies the RGB light sequentially. It has the advantage that the devie resolution is output as is, but it requires that the field drive frequeny is three times the inoming frequeny. Also, due to time differene, olor mixing, field fliker, et., pseudo-signals an our easily, depending on the olor disruption and drive onditions. The point sequene method alloates eah pixel within the sreen and features simultaneous equations. Color disruption, olor mixing, and fliker are less likely to our and quality equivalent to that of a three-panel type projetor, an be obtained. However, three times the number of pixels are required relative to the resolution, making ultra-high density devies indispensable. The problem with both methods is with the basi priniple; that is, if the olors are simply multiplexed, the light utilization effiieny drops to 1/3. For single D-ILA TM projetors, the high-density harateristi of the devie itself is utilized. By ombining this with a hologram olor filter, it has been possible to develop single D-ILAs TM that minimize the drop in light utilization effiieny. These were first shown in late 1999 and introdued to the market during 2000 in the form of onsumer projetion TVs. Figure 7 shows basi priniples of the struture and olor multiplexing for the D-ILA TM hologram devie used in the single-panel system. The pixel eletrodes are formed on the CMOS IC board and the devie omprises an orientation film, liquid rystal layer, and transparent eletrodes. This is the same as for D-ILA TM devies. However, by plaing a hologram olor filter (HCF) on top of the transparent struture, the RGB point sequene is established for eah pixel. This hologram raises the diffration effiieny for the inoming pure white light with the aim of improving the light utilization effiieny and making the light ome in at an angle. As the figure shows, after the light is split into RGB omponents and passes through the liquid rystal layer, it is onentrated on eah pixel eletrode by the diffration wavelength dependene. The RGB light is refleted by R G B the pixel eletrodes, passes through the liquid rystal layer again, and arrives at the HCF. Sine this light omes into the HCF at a right angle, it passes through the HCF with almost no diffration effet. While the light is passing bak and forth through the liquid rystal layer, it is optially modulated aording to the input signal level the same as with D-ILA TM devies and projetion light orresponding to that amount is reated. When shifting to the olor system, this devie requires three times as many pixels as the required resolution. All this an be made possible thanks to the high density harateristis of D-ILA TM. Figure 7: Struture of D-ILA TM Hologram Devie B G R Hologram olor filter Refletive pixel eletrode B G R B G R B G R White inoming light Liquid rystal layer Silion substrate Figure 8 shows the onfiguration of the single D-ILA TM projetor with the D-ILA TM hologram devie. The light from the light soure travels via the old mirror, the visible light omponent is onentrated by the light olleting lens, aligned as a straight-line polarized light omponent at the inoming-side PBS, and input to the D-ILA TM hologram devie at an angle. Only the light that has been optially modulated in the devie passes through the output-side PBS and is projeted onto the sreen through the projetion lens. Figure 8: Basi Struture of Single D-ILA TM Lamp Hologram D-ILA devie Table 3: Devie Dimensions Mirror Light olleting lens Projetion lens Table 3 gives the speifiations for the urrently used D-ILA TM devie and the D-ILA TM hologram devie. The hologram devie attains a horizontal pixel pith of 22.8/3 = 7.6µm, enabling the highest density level and seuring an aperture ratio of 88%. The ontrast makes use of the vertial orientation and reahes a few thousand to one for the devie itself. Though it depends on a ombined optial system, it is possible to seure a ontrast ratio of 1,000:1 in a projetor. D-ILA devie D-ILA hologram devie Pixel size (diagonal) inh (4:3) 1.22 inh (16:9) Number of pixels 1,365 x 1,024 dots 1,280 (x3) x 1,028 dots Pixel pith 13.5x13.5 µm 22.8/3=7.6 µm Aperture ratio 93% 88% Contrast ratio (theoretial) >2,000:1 >1,000:1 Response speed Rising + falling < 16 ms Rising + falling < 16 ms 7

8 Comparison with Competitive Systems Figure 9 shows the omposition of urrent mainstream projetion devies and Table 4 ompares the performane of the various methods with the triple olor method. DLP TM swithes the double stable angle of miro-mirrors digitally to modulate the light path and reprodues tones aording to hanges in light. Sine natural light is used as is, high light utilization effiieny an be expeted. However, there is a strong relationship between mirror weight and the twisted hinge, restriting pixel size flexibility. It is estimated that the best pixel pith that an urrently be attained is from a few µm to 20+µm. Shifting to higher resolutions will require larger hip surfae areas and is expeted to ause deterioration of pixel yields and make mass prodution diffiult. LCDs use transmissive light, so the optial onfiguration of the system is relatively simple. Even with a triple system, the devie an easily be made ompat and lightweight and low ost an be attained. On the other hand, sine transmissive light setion, the address lines, signal lines, and drive elements are all laid out on the same surfae, an inrease in the number of pixels will derease the aperture ratio. Beause in this system, resolution and light output generally have an inverse relationship, it is more appropriate for mobile and portable units than for ultra-high resolution and ultrahigh brightness. Figure 9: Struture of Eah Projetion Devie D-ILA 0.9": 1,400,000 pixels DMD 1.1": 1,300,000 pixels LCD 1.3" or 1.8": 1,300,000 pixels Devie Liquid rystal polarized modulation Analog gradation Uses polarized light (PS omposition is needed) Ultra high density Ultra high aperture ratio Miro mirror angle modulation Digital gradation Uses natural light Limited pixel pith High aperture ratio Yield diffiulty Liquid rystal light modulation Analog gradation Uses polarized light (PS omposition is needed) Low density Low aperture ratio Optial system Refletive type Quasi-shurilen separation Close relationship between one angle and devie angle (More freedom of F value, High light effiieny ratio) 3P omposition Middle light path length Refletive type PBS separation Inverse relationship between one angle and ontrast (Teleen system, Limited F value, Phase ompensation) 3P/4P omposition Long light path length Transmissive type Polarization plate separation Inverse relationship between light amount and temperature of polarization plate (Adoption of intake side PBS, Large devie size) 4P omposition Short light path length High Resolution Devie size omparison for the same resolution The smaller the size, the higher the resolution D-ILA (operable limit) Single D-ILA made possible D-ILA an have both high resolution and high brightness High Brightness Available spae for devie s light utilization The larger the size, the higher the brightness D-ILA (urrent model) DMD Single-panel olor projetion is possible S-D-ILA LCD LCD DMD D-ILA As mentioned above, beause D-ILA TM has pixel densities and aperture ratios superior to other systems, it is possible to produe ultra-high light output and ultra-high resolution. Also, by using the high density harateristi, the size of the pixel hip an be redued ompared to other units at the same resolution. This means that this system is appliable to portable and mobile systems. The D-ILA TM system is onsidered ideal for the highresolution era of the 21st entury. 8

9 Table 4: Performane Comparison for Different Systems Resolution Aperture ratio High pixel density High light output Light effiieny ratio Contrast ratio Ease of optial onfiguration Element ost (yield) D-ILA DLP LCD (1365 x 1024) (93%) (7 µm pith) (10 klm or more possible) (Polarized light) (Vertial orientation) (1280 x 1024) (91%) (17 µm pith) (10 klm or more realized) (Natural light) Fair Fair (1280 x 1024) Fair (65%) Fair (25 µm pith) (larger pixels for higher output) (Polarized light) Fair (Transmissive type) The only methods to eliminate this are either ( i ) a omplete inphase state or (ii) to use the sampling theorem shown in the figure and sample with a spatial frequeny of at least double the input signal (display with resolution 2x or greater). The in-phase state means a display of 1:1 with the number of pixels for S-XGA input. Also, when displaying XGA input using the number of pixels for S-XGA, the edges are not displayed and the pixels are displayed 1:1. For this reason, many projetors have a funtion that allows the resizing mode to be swithed off. On the other hand, when the resolution of the projetor itself is lower than that of the input signals, it is impossible to display images without the generation of pseudo-signals. The pitures in Figure 11 show the stage of generation of pseudosignals depending on the resolution, using a irular zone hart a typial pattern with various spatial frequenies. As an be seen from this reprodued image, it is not simply enough that the projetor resolution be equal to or greater than the resolution of the input signals. Rather it must be suffiient to ensure that pseudo-signals are not generated when input signals are reprodued. Response speed Real time harateristi Development to single-panel projetor Fair (Frame memory) (Surfae sequene) Fair (Larger pixels) Figure 11: Speifi Example of Pseudo-Signals (Example of moire due to irular zones) D-ILA TM Piture Reprodution Cirular zone hart VGA S-VGA ➀ High-resolution Naturally, the larger the sreen, the greater resolution is required. Current resolution requirements an generally be separated into that for omputer displays entering on text and graphis on the one hand and video displays on the other. Even for omputer displays, S-XGA level resolution an be supported adequately. At the workstation level, most requirements for U-XGA resolution an be handled. On the other hand, for video displays, although full support for 720p/1080i is hoped for with the future standardization of HDTV, this has not yet been ommerialized. To respond to the need for high-resolution displays and display various types of signals from different multimedia appliations, many projetors use a resizing tehnique with pixel density onversion. However, if the projetor resolution is insuffiient, the display image is ompressed and information is lost Also, even if the resolution is greater than that of the input signals, resampling an generate pseudo-signals alled fold-bak distortion. Figure 10 shows this state. The spatial frequeny of the input signal and side-band omponents generated with the sampling frequeny whih orresponds to the projetor s pixels are mixed in. This results in the generation of a pseudo-signal (shown with diagonal lines) that produes fold-bak distortion when onverted into low-band omponents. This appears as moire and jaggedness and auses drasti deterioration of the piture quality. Relative energy Figure 10: Pseudo-Signals due to Sampling Input signal band Fold-bak distortion (pseudo-signal) Spatial frequeny Side band Sampling frequeny (number of pixels) State with Fold-Bak Distortion Ourring Relative energy Input signal band Spatial frequeny Side band Sampling frequeny (number of pixels) State with Fold-Bak Distortion Not Ourring XGA S-XGA Q-XGA Considering the variety of multimedia signal formats, it is obvious that higher and higher resolution will be needed to ompletely avoid the generation of pseudo-signals. The high-density onfiguration of D-ILA TM is ideal for this. ➁ High aperture ratio We have already mentioned how a high aperture ratio is good for high light output beause it improves light effiieny and minimizes light absorption. It also has a major impat on the quality of reprodued pitures. For example, when the input signal is all white, if it is projeted with a low aperture ratio, lattie stripe noise and extraneous pseudo-signals will be generated in the original piture. Therefore, the higher the aperture ratio, the fewer the artifats so that the image reprodued will be smoother. The irular zone hart (disussed above) in Figure 12 shows how the aperture ratio affets the amount of fold-bak distortion (pseudo-signal) that appears in the reprodued image. On the left, we an see the image ondition when the aperture ratio is 90%, and on the right, we see the results when the aperture ratio is 65%. It is obvious that the higher the aperture ratio, the less fold-bak distortion ours. 1/2 fold-bak distortion is signifiantly redued, and there is almost no 1/4 distortion whatsoever at the high aperture ratio. The impat of fold-bak distortion on the reprodued image also depends on the frequeny of the band that the distortion is folded bak to; the lower the band, the lower the piture quality. Here again, a devie with a high aperture ratio that produes minimal 9

10 1/2 or 1/4 fold-bak distortion is definitely advantageous. The D-ILA TM devie allows a high aperture ratio to be maintained even when resolution is inreased. With both high resolution and high aperture ratio, the D-ILA TM devie is muh better at reduing fold-bak distortion than other types of devies. Figure 12: Fold-Bak Distortion Status At Different Aperture Ratios High aperture ratio (90%) b a Low aperture ratio (65%) b with vertial orientation, and smaller size with high pixel density make it the ideal projetion solution for large-sreen display systems. Figure 13 shows the urrent state of D-ILA TM devies and prototypes suh as an HDTV-ready single-panel hologram D-ILA TM, Q- XGA mode for full HDTV, as well as a devie with 4000x1000-pixel apability. These examples make it abundantly lear that the D-ILA TM system has enormous potential for development. It is safe to say that D-ILA TM is the only urrent system that an handle even higher performane. When ommerialization of D-ILA TM began, the system offered S- XGA resolution apability. This is still more than suffiient to meet the majority of urrent market demands for high resolution and high piture quality, but it is only natural that piture performane requirements will ontinue to rise. In order to meet this market demand, JVC is working to boost D-ILA TM performane to onform with future needs and form the basis of the next generation of large-sreen image systems. a a a Figure 13: Various Types of D-ILA TM Devies b b a a b : 0 fold-bak distortion :1/2 fold-bak distortion :1/4 fold-bak distortion 0.7" S-XGA ➂ Contrast Generally, text and other information an be viewed adequately at a ontrast ratio of 50:1 or higher. Most audienes will aept a ontrast ratio of 100:1 or higher for text and data. This is the ase when the peak signal is displayed at 100% on the sreen. However, if viewing a dark video soure (a night-time sene, for example), the peak signal level falls below 1/3 and the ontrast on the sreen falls below 1/3, reduing ontrast ratio. This is the main reason that many data projetors, whih are used mainly for text display, set their ontrast ratios between 100:1 200:1. However, nowadays with video images begining to be inorporated frequently in omputerbased presentations, even data projetors are starting to need the same level of ontrast required in a video system. Under these irumstanes, it is neessary that the projetor omponents themselves offer high-ontrast performane. Again, D-ILA TM, with its vertially oriented liquid rystals, whih has a high ontrast of a few thousand to one, provides an exellent solution for future development. 0.9" S-XGA Summary: The Future of D-ILA TM 1.3" Q-XGA The key advantage of the D-ILA TM system is that it enables the highest density pixel integration, making it suitable for high resolution piture reprodution. Also, even at higher resolutions, there is almost no drop in the aperture ratio, so very high light output is possible. Beause the D-ILA TM system provides both high light output and high resolution, it meets all the performane requirements of projetors. Moreover, D-ILA TM s other benefits suh as higher ontrast 10

11 Referene Materials (Illumination & Optis) Current projetors reprodue a projeted image by modulating the angle and polarization of the light emitted by the light soure aording to the input signal. This means that the illumination optial system used to onentrate the light from the lamp and the harateristis of the lamp used in the light soure are two of the most ritial element tehnologies in the projetor. This doument disusses the general theory of the lamp and the illumination optial system in order to provide a better understanding of how a projetor works. Light soure harateristis The harateristis required of lamps are; 1) high light emitting effiieny, 2) emission of light flux with the brightness point diameter required for treating the light soure as a point light soure, 3) wide enough spetrum for good olor performane, and, 4) long servie life. In addition to the usual important fators suh as small size, light weight, and low ost safety, ease of handling, impat on the environment, and a broad range of other diverse fators must be taken into aount. Typial lamps used in projetors inlude Xenon lamps, metal halide lamps (below MH), and ultra-high-pressure merury lamps (below UHP). All three types use short-ar type eletrial disharge tubes that provide high brightness and are nearly point light soures. The table shows typial performane for these lamps, as well as for a halogen lamp the basi type of white inandesent lamp. The figure shows the light spetrum harateristis for these lamps and for natural daylight. Xenon lamps are eletri disharge lamps that emit light by disharging eletriity in high-pressure Xenon gas that is at atmospheres at normal temperature and atmospheres when the lamp is lit. Xenon lamps have the following advantages. ➀The light spetrum harateristis are ontinuous and lose to sunlight in the visible light spetrum. Color performane is extraordinarily good. ➁The brightness is high and the lamp is nearly a point light soure. ➂Instantaneous lighting and re-lighting are possible. ➃The light spetrum distribution is stable over time, as well as when the power flutuates our. ➄High-power types are possible. Xenon lamps have the following disadvantages. ➀A rare gas is used, so osts are high. ➁Servie life is shorter than for MH and UHP lamps, making running osts high. ➂The pressure inside the lamp is high even at normal temperatures and are is required when handling. As an be seen in the figure, these harateristis espeially the olor spetrum harateristis that are similar to natural daylight make Xenon lamps a popular hoie in projetors that emphasize the quality of the reprodued images, as well as in large projetors that require very high illumination. MH lamps are eletrial disharge tubes that add a variety of metal halides to high-pressure merury. Vaporization pressures are at least 10 atmospheres when the lamp is lit. The merury primarily funtions as an impat gas and ontributes to lamp voltage stability. The light emission spetrum is primarily the work of the bromine and iodine metal halides. MH lamps have the following advantages. ➀Diversity, beause the spetrum harateristi and olor temperature an be seleted by hoosing the appropriate metal halide. ➁Long servie life is possible. ➂The light emission effiieny is omparatively high. MH lamps have the following disadvantages. ➀The spetrum harateristis hange as the lamp starts up and over time. ➁The brightness is lower than for Xenon and UHP lamps (making it diffiult to use these lamps as point light soures). ➂Charateristis an vary onsiderably due to the addition of multiple hemial ompounds. Given these harateristis, MH lamps are frequently used in medium-size projetors where light output and olor performane of at least a ertain level are required. UHP lamps are eletri disharge tubes that emit light with ultrahigh-pressure merury. Vaporization pressures are at least 100 atmospheres when the lamp is lit. By taking advantage of the fat that the ontinuous spetrum inreases when the luminane spetrum of the merury vapor disharge tube is given ultra-high pressure, these lamps have the following advantages. ➀Short ars an be attained easily and the lamp an reate a point light soure. ➁Manufaturing osts are low and, beause the effetive servie life is long, running osts are low. UHP lamps have the following disadvantages. ➀The long-wavelength spetrum is severely insuffiient and it is diffiult to reprodue warm olors. ➁Only low-power types are possible, so this type of lamp is not suited to very high light output. Given these harateristis, UHP lamps are frequently used in omparatively inexpensive projetors. Table: Representative Charateristis by Lamp Type Xenon Metal halide H (light output half-redution) Ultra-high pressure merury (UHP equivalent) Halogen Power 100 W W 100 W W 100 W -220 W 50 W-2000 W Light emission effiieny lm/w lm/w 100 lm/w lm/w Brightness 1000 d/mm d/ mm d/mm 2 60 d/mm 2 Color temperature 5600 K 5000 K-7000 K 7000 K-8000 K 2800 K-3200 K Ar length 1-3 mm mm mm _ Starting time (stable) A few seonds seonds seonds Instantaneous Light modulation Change in olor temperature with time Change in light output over time Servie life Possible (No olor temperature hange) Ultra-small hange Derease with time H (light output half-redution) Not possible Relatively large hange Derease with time Not possible Small hange Slightly derease with time H (remaining ratio) Possible (Large hange in olor temperature) Change Derease with time H (depends on usage onditions) 11

12 1.0 Figure: Light Soure Spetrum Charateristi Relative strength Natural daylight Metal halide Xenon Ultra-high-pressure merury illumination system. The integrator (see below) is frequently used in ombination with polarization onversion elements (primarily with D-ILA TM and LCD projetors whih use polarization onversion),while the light pipe is used with DLP TM projetors (whih use natural light). 0.8 Figure: Light Pipe Conept Diagram Light B Light Pipe 0.2 Light A Wavelength[nm] Light C In general, Xenon lamps are used for high light output and high olor performane, UHP lamps for low prie and ompat size, and MH lamps for appliations that fall somewhere in between. However, as performane of the lamps themselves is improving it is possible that projetor performane will be revolutionized in the near future by even higher brightness points (point light soures), higher effiieny, and higher olor performane. Lamps are one of the most ritial omponents of projetors. Figure: Integrator Diagonal View Conept Diagram Outgoing surfae D-ILA Illumination optial system ➀ Uniform illumination Various improvements allow more effetive and uniform illumination of the projetion devie with the light from the lamp. In addition to optimization of refletors and light olleting lenses, light pipes and integrators made up of fly eye lenses have been used for dramati performane improvements. Inoming surfae Fly eye 2 As the figure shows, a light pipe is a square pillar that repeatedly and ompletely reflets inoming light on its glass surfaes. This onverts the light flux distribution that is non-uniform, at the inoming surfae, into a uniform light flux distribution at the pipe outgoing surfae. At the same time, the light utilization effiieny is improved through effiient onversion that mathes the light pipe outlet surfae shape to the shape of the surfae to be illuminated. Fly eye 1 Figure: Integrator Setional Diagram FEP1 FEP2 Field lens Lamp Projetion devie As the figure shows, an integrator omprises two fly eye plates (FEP) of miro lenses. The light oming from the lamp via the refletor is input to FEP1. The images on eah of the miro lenses pass through the miro-lenses of FEP2 and are projeted onto the projetion devie. In other words, the light soure image of one lamp is split as many ways as the number of miro lenses on FEP1 to improve the equivalent uniformity. Also, the integrator onverts the light to a shape similar to the shape of the projetion devie and thus improves the light utilization effiieny of the 12

13 ➁ Polarization onversion elements In projetion systems that utilize light modulation through the multiple refration of liquid rystal, the light from the light soure is divided into two diretions of perpendiularly polarized omponents. Only one of the polarized omponents is used; the other, unused polarized omponents, beome extraneous and light utilization effiieny drops. In order to improve light utilization effiieny, the extraneous light is onverted into useful polarized light with a light polarization onversion element. Figure A and Figure B show typial onfigurations for polarization onversion elements. In eah system, the light input setion of the polarization onversion element is divided into multiple setions and light polarized in one diretion passes through eah split surfae. The refleted polarized light has its polarization onverted 90 at a 1/2-wavelength plate. This is onverted to light with the same polarization at the output surfae of the light polarization onversion element. Figure A: Polarization Conversion Element 1 Light from light soure FEP1 Polarization onversion FEP2 element Light utoff mask Light utoff mask Light utoff mask Mirror PBS P wave Mirror PBS P wave Mirror Figure B: Polarization Conversion Element 2 1/2-wavelength plate 1/2-wavelength plate Figure A shows the polarization onversion method using ultra-small PBS. The light oming from FEP1 of the integrator (disussed above) is olleted so that light olletion setions and non-olletion setions repeat at equal intervals. This light is input to the polarization onversion element. In the polarization onversion element, the P wave (omponent polarized parallel to the paper surfae) of the light, oming in from light olletion setions, passes through the ultra-small PBS. It is then onverted to s (light polarized perpendiular to the paper surfae) by a 1/2-wavelength plate and output. On the other hand, s input at the ultra-small PBS are refleted by mirror surfaes and output to the non-olletion setions. As a result, s are output to the entire surfae as light whose polarization has been onverted. This improves light utilization effiieny. Figure B uses one PBS prism. The s (omponent polarized perpendiular to the paper surfae) in the light oming from FEP1 of the integrator, (disussed above), are refleted at the PBS surfae and input to FEP2, where setions with and without 1/2-wavelength plates repeat. The s refleted at the PBS pass through FEP2 as is. The P waves (omponent polarized parallel to the paper surfae), on the other hand, are onverted to s by 1/2-wavelength plates loated in front of FEP2. As a result, the light from FEP2 is light over the entire surfae, so light polarization onversion is obtained. FEP1 PBS surfae Light from Light Soure Mirror surfae :1/2-wavelength plate P wave P wave P wave FEP2 Although the light utilization effiienies of urrent projetors vary greatly aording to the brightness (point light soure harateristis) of the light soure and the size of the projetion devie, light utilization effiieny is still limited to about 20 perent even when well-mathed parameters are used. In order to raise light utilization effiieny, the effiieny of the illumination optial system and the lamp light emission needs to be improved even more. DLP TM (Digital Light Proessing TM ) and DMD TM (Digital Miromirror Devie TM ) are the trademarks of Texas Instruments Inorporated in the United States. DMD TM is an ultra-preision eletroni devie developed by Texas Instruments Inorporated. 13

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