CA2335584A1

CA2335584A1 - Method and apparatus for modulating an incident light beam for forming a two-dimensional image

Info

Publication number: CA2335584A1
Application number: CA002335584A
Authority: CA
Inventors: Asif Godil; David M. Bloom
Original assignee: Individual
Current assignee: Silicon Light Machines Inc
Priority date: 1998-06-24
Filing date: 1999-06-18
Publication date: 1999-12-29
Also published as: EP1090322A1; CN1313957A; DE69905717D1; AU4702199A; EP1090322B1; JP2002519714A; KR20010053201A; WO1999067671A1; US6215579B1; WO1999067671B1; DE69905717T2; ATE233911T1

Abstract

An apparatus and method for modulating an incident light beam for forming a two-dimensional projection image. The apparatus includes a plurality of elongated elements each having a reflective surface. These are suspended parallel to each other above a substrate with their respective ends supporte d, forming a column of adjacent reflecting surfaces grouped according to displa y elements. Alternate ones of each group are deformable by applying a voltage with respect to the substrate. An approximately flat center section of each deformed element is substantially parallel to and a predetermined distance from a center section of each undeformed element. A light beam incident to t he column of adjacent reflecting surfaces is reflected from a group of elongate d elements when the alternate ones are undeformed and diffracted when the alternate ones are deformed. A distance of movement is controlled or a ratio of between reflection and diffraction periods determines a display intensity for the corresponding display element.

Description

METHOD AND APPARATUS FOR
MODULATING AN INCIDENT LIGHT BEAM
FOR FORMING A TWO-DIMENSIONAL IMAGE
Field of the Invention:
The invention relates to a method and apparatus for modulating a light beam for forming a two-dimensional image. More particularly, the invention relates to a columnar diffraction grating for performing such modulation.
Background of the Invention:
Many applications exist for devices which modulate a light beam, e.g. by altering the amplitude, frequency or phase of the light. An example of such a device is a reflective deformable grating light modulator 10, as illustrated in Fig. 1. This modulator 10 was proposed by Bloom et al., in U.S. Patent No. 5,311,360. The modulator 10 includes a plurality of equally spaced apart, deformable reflective ribbons 18 which are suspended above a substrate 16 having reflective surface portions. An insulating layer 1 I is deposited on the silicon substrate 16. This i.s followed by the deposition of a sacrificial silicon dioxide film 12 and a low-stress silicon nitride film 14. The nitride film 14 is patterned to form the ribbons 18 and portions of the silicon dioxide layer 12 are etched such that the ribbons 18 are held by a nitride frame 20 on an oxide spacer layer 12. For modulating light having a single wavelength ~~~, the modulator is designed such that the thickness of the ribbons 18 and the thickness of the oxide spacer 12 both equal ~,~/4.
The grating amplitude of t'.his modulator 10, defined as the perpendicular distance, d, between the reflective surfaces 22 on the ribbons 18 and the reflective surfaces of the substrate 16, is controlled by applying voltage between the ribbons 18 (the reflective surface 22 of the ribbons 16 servea as a first electrode) and the substrate 16 (a conductive film 24 beneath the substrate 16 serves as a second electrode). In its undeformed state, with no voltage applied, the grating amplitude equals 7~~/2 and the total path length difference between light reflected from the ribbons and the substrate equals 7~~, resulting in these reflections adding in phase. 'thus, in the undeformed state, the modulator 10 reflects light as a flat mirror. The undefo~rmed state is illustrated in Fig. 2 with incident and reflected light indicated as 26.
When an appropriate voltage is applied between the ribbons 18 and the substrate 16, an electrostatic force deforms the ribbons 18 into a down position in contact with the surface of the substrate 16. In the down position, the grating amplitude is changed to equal 7,14. The total path length difference is one-half the wavelength, resulting in the reflections from the surface of the deformed ribbons 18 and the reflections from the substrate 16 interfering destructively. As a result of this interference the modulator diffracts the incident light 26. T'he; deformed state is illustrated in Fig. 3 with the diffracted light in the +/-1 diffraction modes (Di,, D_,) indicated as 28 and 30, respectively.
Adhesion between the ribbons 18 and the substrate 16 during wet processin~;
utilized to create the space below t:he ribbons 18 and during operation of the modulator 10 has been found to be a problem in these devices. Numerous techniques to reduce adhesion have been proposed, including: freeze-drying, dry etching of a photoresist-acetone sacrificial layer, OTS monolayer treatments, use of stiffer ribbons by using shorter ribbons 1 S and/or tenser nitride films, roughening or corrugating one or both of the surfaces, forming inverted rails on the underneath of the ribbons, and changing the chemical nature of the surfaces. Sandejas et al. in "Surface Microfabrication of Deformable Grating Light Valves for High Resolution Displays" and Apte et al. in "Grating Light Valves for High Resolution Displays", Solid State Sensors and Actuators Workshop, Hilton Head Island, SC
(June 1994), have demonstrated that such adhesion may be prevented by reducing the area of contact by forming inverted rails on the underneath of the bridges and by using rough polysilicon films, respectively.
Furthermore, as Apte et al. recognize, a feature of the mechanical operation of the modulator 10 is hysteresis in the deformation of the ribbons 18 as a function of applied voltage. The theorized reason for the hysteresis is that the electrostatic attractive force between the ribbons 18 and the substrate 16 is a non-linear function of the amount of deformation, while the restoring force caused by stiffness and tension of the ribbons 18 is a substantially linear function. Fig. 4 illustrates a simulated hysteresis characteristic where the light output (an indirect indicator of the amount of deformation of the ribbons 18) is shown on the vertical axis and the voltage between the ribbons 18 and the substrate 16 is shown on the horizontal axis. Thus, when the ribbons 18 are deformed into the down v . vUlv : ~rA y IU~,~ca~l:u, Uz ~ , , ~ " _15 = ~- U : 5 : 15 w_ . __" _ ~ , _.~ 65U~3;330170-~ +4.9 89 23954.465 : ~z0 __ __ _ __. _ __ _ _ _.._ ",.___. _ __ F'ATENT
S~LM-02401 position in contact with the substrata 16, they latch izi place, requirizxg a smaller holding voltage than the original applied voltage.
Bloom et al., ih U.S. Patent No. 5,311,350 tefech that this latching feature is desirable as it gives the modulator 10 'the adwarttages of active matrix design without the S r.~eed for active components. In addition, Bloom et al. teach that this latching feature ~s also desirable in low power applicatiozzs where efficient use of availaole power is very important. Recognizing the adhesion problem, however, Bloom et al., teach adding small ridges below the ribbons 18 to reduce the contact area and thereby reduce the adhesio~~
problem. Because the substrate of the modulator 10 is used as an optical surface, however, the manufacturing processes for addizzs; small ridges to the surface is complicated by tse reduirements that the reflecting portions of the substrate lb be smooth with high x~ehecti~erity and be in a plane parallel to tfe ribbons 't8.
Ricco et al, in IJ.$. Patent No. 5,757.,536 teach an electrically programmable diffraction grating. The electrically prn,grammable diffraction grating includes a plura~ity of grating elements suspended from a support frame and means for deforming selected.
ones of the grating elements. The grating elements have a three piece construction in ~Nhich each grating element includes an elongate Central portion located between a pair of Flexible members. The thiclaness of the flexible members is substantially smaller than the ~;entral portion of the grating elements. In this way, the flexible members deform in operation while the central poztian remains rigid while undergoing translation without the ;grating elements contacting a substrate:. Bach gratin;; element is attached to a support frame, which, as taught by IZicco et al., is a kxming superstructure which supports the:
,~atang eleua.ents. Also, as taught by l~icco et al., the grating elements and support frane are fabricated as an upper section separate from a lower section and then combined. Posts formed or the lower portion support fhe upper portion when the upper portion is attached to the lower portion, and, thus, the posts are not integral to both the lower and upper portions.
Conventional displays are formed in two dimensional arrays of pixels. The di:;crete image formed by each of the myriad of pixels are integrated by the eye of the user to form a composite of the pixels representizzg an overall image. Unforttulately, the cost of st,ch a display system increases because as each pixel is replicated to form the entire array the _3 REfLACEMEhtT STET

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cost of making each pixel is similarly replicated. Examples of such pixellatcd disp lays are televisions and eo~mputer monitors. '.fhe pixels for each can be formed of LCD
den ices, or by a CRT.
Therefoz~, what is neroded is a diffraction grating tight valve in whic.$
adhesion between reflective elements and a substrate is reduced or eliminated without resorti ~tg to complicated surface treatments requu~ed for reducing such adhesion.
What is also seeded is a disp~'.ay that lowers the cost of manufacture by redLCing the number of pixels required to build the system w ithaut Io~vering the image qualit y.
S~mam of the Invention' The invention is a diffraction grating light '~alve (GL~; and method of use tt~ercof for modulating an incident light beam for forming a two-dimensional image. The difTxaction grating light valve includes a plurality of elongated elements each of which have a reflective stzzface. The elongated elements arc suspended substantially parallel to I~ each other above a substrate with their respective ends supported and substantially aligned so as to form a column of adjacent reflecting surfaces (GL'V array), '>("he elongated elements are grouped according to display elements. Alternate ones of each group are defor~nable by a applying a voltage v~rith respect to the substrate. An approxirnatcly flat center portion of each deformed elonl;ated element is substantially parallel to and a 2~ predetermined distance from a center portion of each undeforrned element.
The predetermined distance is selected to be appxoximatzly onertbird to ono-fourth of the distance between the undefornaed rsffeetizw surfaces and the substrate such that dEformed elongated elements do not contact the surface of the substrate_ Avoiding contact with the substrate prevents the elongated elements from adhering to the substrate_ rn addition, ~5 limiting the predetermined distance avoids hysteresi.5 in deforming the elongated eZen~ents, A light beam incident to the column of adjace~tt reflecting surfaces is reflected from a group of elongated elements when tt~e aIteznate ones of the group are undeformed. The light beam is diffracted by a group of elongated elements r~hen alternate ones of the ;~,oup are deformed. A ratio of between reflection and difliacti on for a group during a time 3~ period determines a display intensity i:ox the correspondizzg display element_ The light beam is alternately red, green and blue during successive periods. In as alternate REPLACEMENT SHEET

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esnbodiment, the light beam is white light and vc~idtlzs of the elongated.
elements for cac h display element are selected w diffract red, green or blue wavelengths at an appropriate diffraction aclglc. An appropriate intei~,s,ity and color for each display element is formed during respective periods according to the image to be represented by the respective display element.
Light diffracted frozen the column of reflecting surfaces is collected 'by a lens. At the exit pupil of the lens, the light is columnar and representative of a column of the i~~age to be displayed. A light shield having a slit of predetermined width over the length of the column is positioned at the pupil of the second lens such that only a selected portion oa'the Iil;llt passes through the slit. This arrangement of the shield prevents light collected by the f~~st lens other than light diffracted from the approximately flat crater portions of the elongated elements fro~~ passing through the slit. In a~n alternate embodiment, a fixed reflecting surface is placed over the ends of the elongated elements to prevent light fret a b<;ing diffracted other than from the approximately flat center portion of each elongated I S element. A pivotable reflective surface (scanning mincer) is positioned apposite the fight sl-.~ield from the Ions to reflect the light passing through the slit info an eyepiece or onto a display screen. The reflective surface pivots back and forth, in synchronism with the column of display elements modulating the light, to represent colu.~nns of the display image. Accordingly, a two-dimensional color image is swept into the eyepiece or onto t he display screen. The pivotable scanning mirror can be replace with other types of mirro:-arrangements such as a rotating faceted polygon rnirror_ Brief Deseriptior~ of the Drawings:
Fig. 1 illustrates a prior art rafler.tive deformable grating light modulator.
2~ Fig. 2 illustrates the prior art reflective defornn.able grating light modulator in an uWformad state, reflecting incideat light.
Fig. 3 illustrates the prior art reflective deformable grating light modulator in a df;formed state, diffracting incident light.
Fig. 4 illustrates a hysteresis curve for the prior art reflective deformable grating li,~t modulator.
Figs. 5-G and 8 illustrate side sectional views of a process sequence far ~5 REPLACENI~fr SHEET

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Fig. 7 illustrates a top view of a step of the process sequence far manufacturing a columnar diffraction grating light valve according to the present invention.
Fig. 9 illustrates a side sectional view of the columnar diffraction grating light v~.~3ve according to the present invention.
Fig. 10 illustrates a top view of x portion of the GLV including six elongated elnenents corresponding to a single display element.
Fig. 11 illustz~ates a front sectional view of a display element of the GLV
with else si:~c elongated elements undeformed, refl.eciing i.~acident light.
Fig. 12 illustrates a side sectional vierw of a deformed ef.ongated elc~nent of the GLV according to the present invention.
Fig. 13 illustrates a front sectional view of the display element of the GLV
with alternate ones of the six elongated elements deformed, diffracting incident light.
l5 Fig. 14 illustrates top view of an optical display system utilizing the GLV.
Fig. 15 illustrates a side view oi" the optical display system illustrated in Fig. 1~
W lcen along the line C-C'.
Fig. 16 illustrates a side cross sectional view ~f an eyepiece arrangement far u:.e v~,zth the optical display system illustrated in Fig. 14 including an exit pupil.
Fig. 17 illustrates a side cross sectional view of a display screen arrangement fsu use with the optical display system illustrated in Pig. 14 including the exit pupil.
Fig. 18 illustrates an alternate embodiment of the present invention for avaidin~
display of tight di,~fracted from othex than an approximately flat center portion of the Elongated elements_ )Detailed Doscrintion of a Preferred Embodiment:
Figs. 5-6 and 8 illustrate side sectional views of a process sequence for ;manufacturing a coluumnar diffiaction grating light valve (GLV) according to the preset ~invention_ lZ.eferring to Fig. 5, an insulating layer is formed on a silicon substrate 10~).
Preferably, the insulating layer is a composite layer including a field oxide Iayer 102 formed by thermal oxidation and a thin layer of silicon nitride 104 formed over the field REJt'LACFMEl~~'f SFIEET

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oxide layer 1.02. Then, a conducting layer 106 is fornled ones the nitride layer 104 Preferably, the conducting layer 106 its a refractory metal, such as tungsten, malybedanum, titanium-tungsten or tantalum or alternatively conductive Poly-silicon or a diffused conductor. The conducting layer 106 serves as a lower electrode for applying bias ~a selected ones of elongated elements of the GLV. In an alternate embodiment, the conducting layer 106 is formed on a :lower surface of the substrate 100.
Next, a sacrificial layer 108 is formed ever the conducting layer lOb_ The sacrificial layer 108 must be able to be selectively etched witli respect to the conducting layer I06. Preferably, the sacrificial layer 148 is a layer of Poly-silicon which is et4hed with a dry etch of xenon diflouride. Alternatively; the sacrificial layer can be a lay~~ of doped glass, such as boro-phospho-silicate glass or phoso-silicate glasg. The thicla~,as at which the sacrificial layer 108 is applied deteLm~os a distance between the conduct ing layer 106 and elongated elements to 'be formed over the sacrificial layer 108.
As vv i11 be explained herein, the thickness of the: sacrificial layer 108 departs significantly from prior light modulators is that khe sacrificial layer 108 is substantially thicker.
Tn the prof~:rred embodiment, the thickness of the sacrificial layer 108 Ls approximately equal to the expected ~va~~elengfih of incident light. For example, if the expected wavelength is in the visible range (approximately 450-760 nm), the thickness of the sacrificial layer 108 is also within this approximate range. If ths~ expected waYelength is in the ultraviolet rang:
(approximately 200-450 nm) the thiclaiess of the sacrificial layer 108 is also within this approximate range. if the expected v~ravelength is in.the infrared range (approximately 760-2000 nm) the thickness of the sacri~.eial layer 108 is also within this app:oximate ruige.
Referring to Fig. 6, the conducting layer 106 and the sacrificial layer 108 are:
photo-lithographically masked by known techniques a~td then etched sequentially bar appropriate dry or wet etch chemistries, forming a pair of post holes 11G for each elongated element of. the GLUT. Preferably, the post holes 110 are formed at distant a of approximately 75 microns from each other, though smother distance can be utilized. For illustration purposes, the apparent thicknesses of the layers 102-108 are exaggerated relative the distance between the post holes 110.
Fig. 7 illustrates a top view of the GLV after the post holes 110 have been etched as described above. For illustration purposes, Rig. 7 illustrates a column of six pair;; of REPLACEMEN'C SKEET

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Referring to Fia. 8, a layer of resilient material 112 is formed over the sacri~,:lal layer 108 and post holes 110, partially or completely filling the post holes 110. Pref4arably, the resilient material 112 is layer of silican nitzide deposited to a thickness and rcsidaal E;tress defined by a spring foxce necessary to return each elongated element to an up :.tare <tfter a sufficient opposite polarity bias is applied to cancel electrostatic force induced by a bias applied to place the elongated element in a down state. Next, a re~leci5ve layer ! 14 is deposited over the resilient layer I 12. The reflective layer 1 I4 provides a reflective surface for each elongated element of the GLV and serves as an upper electrode for E:pplyirng bias to selected ones of the elongated elements of the GLV.
Preferably, tt~e reflective layer 114 is sputtered atumixtum.
Finally, a photvresist layer I I $ is applied as ;i mask far selectively patterning t he reflective layer 114 and the resilient Iayer 112 for forming the elongated elements. Tn addition, the sacrificial layer 108 is etched, leaving an air space beneath the elongated elements.
Fig. 9 illustrates a side sectional view of an elongated element 200 of the GLY in an undeformed state. Note that in Fig. 9, the sacrificial layer 108 (Figs. 5-6 and 8) beneath the elongated element 200 is replaced by an sir space 202. Thus, the elongated element 200 is suspended by its ends above the surface of the substrate (including its constituent layers). In addition, the photoresist layer t ? 8 (Fig. 8) has been removed.
Fig. 10 illustrates a top view of a portion of the GLV including six elongated e:leraents 200. Note that the Elongated elements 200 have equal widths and are awanged parallel to each other. Tlte elongated elements 200 are also separated from each outer by a srnall space, thus, allov~ng each elongated element 200 to be selectively defiomned with respect to the ethers. The six elongated elements 200 illustrated in Fig. 10 preferably correspond to a single display clement 300. ~'hus, the column of 1920 elongated elements Gyrresponds to a GLV array having 32C) display elements arranged in a column.
Xt will be apparent that the number of display elements will affect a resuliYng display resolution and _g_ REPLACEM'$NT Sf~JEE'F

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that a different number can be solcctnd. In addition, each display element 300 can have a different number of elvngatcd clemczxts 200. For example, a group of two, four, cis',ht, ten pr twelve elongated elements 200 can con~espond 'GO a single display element 300. It is possible that even more elongated el~emcnts could be used to form a single display ~.lemvn,t 300. It is also possible that an odd number of elongated elements 200 could be used for a single display element 300.
Fig. 11 illustrates a front svci:ianat view of the display element 300 with the elongated elements 200 undeformed. The section illustrated in Fig. II is~taken along the line A-A' illustrated in Fig. 9_ The ~undeformod state is achieved by equalizing a bias on each elongated element 200 with respect to th.e conductive layer 106. Note that be~,ause the reflective surfaces of the elongated elements 200 are substantially co planar, light incident to the elongated elements 200 is rcilected.
Fig. 12 illustrates a side sectional view of a deformed elongated element 20~?
of the GL'V. Fig. 12 illustrates that in the deformed state, the elongated element 200 remains 1 S suspended in that it does not come into coni:act ~uvith the surface of the substrate layers beneath the elongated element 200. This iS in contrast to the prior modulator of Fi gs. 1-3.
By avoiding co~~tact between th.e elongated element 200 and surface of the substrata , the problem of adhesion associated witlh the prior modulator is avoided. Note, however, that in the deformed state, the elongatec! element 200 tends to sag. This is because the electrostatic force pulling the elongated element 2.00 tovVard the substrate is distn'bWed evenly along its length, perpendicularly to the length, whereas the tension of the elongated elements 200 is along the length of the elongated element 200. Thus, its reflective surface is curvilinear, rather than flat. Note, however, that for illustration, purposes, in Fig 12, the degree of sagging of tkia elongated element 200 is exaggerated relative to its Icngtl~.
rt has been found, however;, that a center portion 202 {Fig_ 12) of the elongated elements ?00 remains approximately flat, such that a Contrast ratio resulting fmm ~~btaining light diffracted only by the center portion 202 of each elongated element 200 is satisfactory. In practice it has been found that the approximately flat center partio n 202 is approximately one-third the length between the post holes 110. Therefore, when tile distance between past holes is 75 microns, the agproxim.atcly flat center pordoz~ 2t~2 is approximately 25 microns in length.
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Fig. 13 illustrates a front sectional view of the display element 300 with altE~rnatc ones of the elongated alernents 244 defozmed. The section illustrated in Fig.
13 is !.aken alozag the line B-B' illustrated in Fib;. 12. The elongated ribbons 200 that are not moved substantially are held in a desired location by applying a bias voltage thereto. The deformed state in the elongated ribbons 200 that move is achieved by applying an appropriate drive voltage on the alternate ones of the elongated elements 240 with inspect to the conductive layer 106. The p~pendiculat distance d~ is approximately constant ever the approximately flat center portion 202 (Fig. 1 Z'1 and, thus, defines a grating amp litudc for the GLV. The grating amplitude d, can be adjusted by adjusting the d~.ve voltage an the driven elements elongated 200. This makes possible fine tuning of the GL'V
~ar an optimum contrast ratio.
Far appropriately diffracting incident light having a single wavelength (~,,), it is preferred that the ~'rLY have a graCi:ng amplitude dl equal to one fourth of the wavy .length of the incident light (x,,14) for a rna:~mnun contrast ratio in the displayed image. h wiL be apparent, however, that the grating .amplitude d, need only result in a round trip di;;tance equal to one-half the wavelength 7~, plus a whole number of wavelengths a, (i.e. d,= 7~~I4, 3 x,,14, 5 x,,14,..., NR,,/2 + x,1/4).
Referring to Fig. 13, it can tie seen that the lower surface of each deformed elongated element 200 is separated from the surface of the substrate by a distance d2.
24 Thus, the elongaxed elements 200 do not make contact with the substrate during operation of the GL'V'. This avoids the problE~n in prior modulators of adhesion between the reflective ribbons and the substrate. This distance dZ is preferably selected to be approximately two to the three limas the distance d,. Accordingly, in t'ze de~rmc~i state, the elongaxcd elements 200 travel appmxinc~ately one-fourth to one-third of the disc once dz to the substrate. The distance dZ is determined by the thickttass of the sacrificial layer 108 tFigs. 5-6 and 8) plus the distance d,.
Referring to the hysteresis curve illustrated in Fig. 4, because the elongated elements 244 diffract the incident light by traveling only one-third to one-fourth of the distance to the surface of the substrate, hysteresis is avoided. Instead, starting frocn the undeforrned state, the elongated elements 200 deform toward the substrate arid, th~.n, return to the undeforzned state along the same voltage versus Iight intensity cwrvc in early -10~
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Because the end portions of ea~,~,b elongated eh,~tn~nt 200 are not approximately flat, of light diffracted by the end pardons :is collected and displayed, the resulting contrast ~ atio ~~f the display image will tend to be unsatisfactory. Therefore, as explained herein, the ypresent invention provides a light shield for preventing light diffracted ~rom other than the approximately flat center portion 202 of each elongated element 200 fxozn being utilizc.~d for forming the display image. Xa the altenzative, the: light could be optically manipulated so that it only impinges onto the approxmately flat confer portion 202. ?his approach avoids wasting light. .
Fig. 14 illustrates top view of an optical display system .400 utilizing the GLV array 402. An illumination arrangezncnt far illuminating the GLV away 402, includes red, .~'een, . and blue Iight sources 4048, 4046 and 404B, respectively. 'These light sources can tie any convenient source or red, green and blue light and can be semiconductor light emittu ~g devices such as light emitting diodes (LEDs) or senuconductor lasers, or separate diode pumped solid state lasers, or white light with a alternating filters such as a spinnimg disk with three filters to sequentially pass red, green anti blue tight. Tn system 400 light sources 4448, 4046, ana 4048 are assumed to be sources emitting in a generally symmetrical manner. A dichroic filter group 406 allows light from any One of these light sources to be directed toward a collimat3n.g leas 4(7$ propagating generally along a system optical axis z.
Dichroic filter groups or prism blocl.~s which cause three light sources of different color to appear to an optical system to emanate from the same point of origin are well lor~ov.~n in the optical art, for example, Philips prisms. Accordingly, a detailed description of ~~ueh dichroic filter groups is not presented herein.
It is also known to use three separate image formation systems, one each for red, green and blue and to then optically combine these images. The system of the present invention could also comprise three display engines which are combined and then seazmed to form a composite image.
Because the GLVs are formed using semiconductor processing techxiiq~ues, it is REFLACEMENT SHEET

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X5083301?0--~ +49 8;3 2389g.46~5: #29 PATENT ~-SLIv!-02~401 possible to form three parallel linea~~ arrays that are essentially perfectly aligned one to ttae other. Thuee illumination systems, one each for red, green and blue can be confrgurcd to impiuage their respective color of light onto a sinblc; one of the three essentially perfc;ctly aligned GLV linear arrays. In this sway, alignment of the composite image is easier than for conventional composite color syst~_ One common problem in conventional color display systems is commonly 1~r~oyvn as color break up. This results from such systems dasplaying a red frarae, a green frame and a blue frame, in any convenient sequence. This technique is lmown as frame sequential color. Tf an object passes between the viewer and tl~e displayed image a ghost of flat object in one of the colors will appear in the display. Similarly, if the viewer quickly turns their head an artifact of the frame sequential color will appear.
Because the GLV technology can operate at sufficient bandwidth, the systen ~
can be made to operate to provide each of the three display colors for each row of the display as it is scanned. The inventors have coined the phrase 'line sequential color' to describe this technique. The deletea~ious artifacts of frame sequential color are not present.
In line sequential color, as the image is scanned each of the three colors is presented to the linear array of the CiLV in sequence. In analogous terms, all three colors are presented in what is approximately equal to a single display line in a conventional pixellated display.
The unago is formed by scanning a linear array of GLVs. The elongated elements in the linear array are all parallel and perpendicular to the length of the linear artav, 'Ibis avoids any discreetly displaying of adjacent elements. Thus, there is no pixellation between adjacent display elements such as is present in conventional LCD or CRT
displays. Further, because the array is smoothly scanned in a direction perpendicular to the . linear array, there eau be no pixellatyon between the display in that direction eithw. In this way, the image quality is vastly improved over that of conventional display technologies.
Lens 408 is illustrated, fox sinc~plicity as a simple "spherical" lens, i.e having equal refractive power in the x and y axes. In gig. 14, the y axis is in the plane of the illustration and the x axis is perpendicular to the plane of the illustration.
1'he lets 4Q8 collimates light from the tight source in both area. Those familiar with the art to which the present invention pertains, will recognize however, that light output from an end-~12.
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SI:,M-02401 ernifting semiconductor laser is more divergent in one transverse (x or y) axis than the other and is astigmatic. Means for collimating the output beam of such a laser and expanding it to a desired size are well-known in fine optical art and may require one or more spherical, aspherical, tomidal, or ~~ylindrieal (spherical and asphezical) lens elem cats.
Lens 408 is intended to represent a group of one or more such elements.
I?ivergent light 41d from a symmetrically emitting light souzee 404 passes thrQUgh lens 408 and is collimated in both the ;x and y axes. Bi-axially collimated light 412 is then passed through a cylindrical lens 414. The term "cylindrical" here defining that lens 414 has refractive power in one a.~ds (here, y) only. Those familiar with the optical art will rE:cognize that the surface of the lens 4X4 may be other than other than circularly cylindrical. The function of lens 414 is to cause bi-axis,hy collimated light 412 passing therethrough to converge (Fig. 14, tine's 41 ~ in the y axis, and remain collimated (Fig. 15 lines 418) in the x axis. Xt should be noted here that lens 414 may also be farmed from one or more optical elements as discussed above, and is shown as a single element For simplicity.
GLV array 402 is located at a distance from cylindrical lens 414 of about a focal l~~gth (f;) of the lens. GLV array 402 is aligned in the x axis, on the system optical axis ~; which corresponds to the optical axis of lenses 408 and 414. The operating surface of the GLV (elongated elements 200) is inclined to the z axis. J.n Fig, i4, GLV
array 402 is inclined as 45 degrees to the axis, which effectively folds the z axis 90 degrees . This :election of inclination of the GLV array 402 is made here for convenience of illustration and should not be considered limiting.
Fig. 15 i~lusttates a side view of the optical display system ihustrated in Fib. I4 taken along the line C-C'. Zteferring to Fig. 15, light incident on an operating GLV array 402, creates a reiriectcd beam (418) and plus and minus first-order diffracted beams designated by D,., and D,, respectively. These diffracted bums are inclined to the z axis, vin. the x aacis. In the y axis, the diffracted and reflected beams are equally divergent. The diffracted aid reflected beams then p~~ss through a magnifying (positive) lens 420 which is separated from GLV array 402 by a focal length fi of the lens. Lens 420 is shown as a single clement from simplicity, but in practice lens 420 may include two or more elements, Lens 420 provides in effect an eyepieoe lens for system 400 and is preferably on of the -la~
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In the x axis, the reflocted beamu 422 converges to a focal point on the z axis, :~t which is placed an elongated stop 423 .at about an ~xtemal telccentric exit pupil PZ of lens 420, In addition a shield 4~6 is placed in the area of the pupil Pz of lens 420 to spiel d light diffractai from portions of the elongated elements 200 of the GLV array 402 otliex tlxat light diffracted from the approximately flat ce~ntcr portion 202 of each elongated element. Thus, the shield has a slit that is preferably dimensioned so as to only pass light (l?,.,, D.,) diffracted frorz~ the approximately 25 micron center portion 202 of each elongated element 200.
The Schlieren optics of system 400 can be defined as being a part of a teleces ltric optical atxangement 42g including GLV azxay 402 magnifying eyepiece lens 420 and stop 424, with GLV array 402 at about an external object position of lens 420 and stop 4:~4 at about an external (exit) pupil of lens 420. A telecentric system is a system in which the entrance pupil and/or the exit pupil is located at infinity. It is widely used in optical systems designed for metrology because it tends to reduce measurement or position ~;rror caused by slight defocusing of the system. This tendency permits some tolerance in placement of stops and other components of the system in general, and is exploited ~n certain embodiments of the present invention discussed further hereinbelow.
In the y axis (Fig. '14) divergent reflected light 430 (and diffracted light) is collsmated by lens 420. Stop 424 is aligned in the y axis, and intercepts the reflected light.
~ihield 426 absorbs di.ftiacted light othcrr than light diffracted from ttj.e approxinzate3y flat center portions 202 of the GLV array 402. Stop 424 may be selectad to be absorbing or reflectinn. If stop 424 is reflecting, re;fleeted Iight from is returned to GLV array 4?0., I?i~aeted beams D+, and D_,, howev~;, being inclined to the z axits and the eoxresponding incident and reflected beans, converge to focal pc>ints about and below (alternativel.y, on apposite sides of) stop 424 and with the slit of shield 426, thereby passing through exit pupil PZ without being intercepted.
A scanning mirror 432 is located such as to intercept the diffracted beams v~nd direct them toward a viewer's eye 434. What the viewer sees is a magnified virtual image (;at inF~nity) of GLV axray 402. This image is represented in Fig. 5 by line 436, ItEF'LACF,ME'f'T SHEET

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PATENT ~,. _ _ _ , _s2 recogpzi,zi.ng, of course, that tliere is no r,:al imago hero. h will be apparent that the line of the GLV array 402 can represent a row or a column of an image to be displayed.
The aplsropriate remaining rows or columns are then formed as the sca~a progresses. It is po:>sible that other scanning modes can I>e used, suoh as diagonally.
The elongated elements 200 of GLV array 402 are operated to represent, seduentlally, different lines of M x hl' display where M is the number of display elements peg- line, and ~T is the number of lines in the display. Each display element 300 includes multiple elongated elements 200, as discussed above. GLV aaray 402 may be defined ge~ierally as representing, a one-dimensional array of light valves, or one row of displvy eleanents or pixels. In the magnified virtual image, these pixels will have a relative brightness determined by the operating state of ribbon or zibbons 12 of GLV
array 10 Scanning mirror 432 is moved, angularly, by a drive unit 436 about an axis 43 8 as illustrated by arrow A {Fig.l4), scanning; the diffracted beams, and thus the magnified.
virtual image, linearly, across the field of vi~wwv of ttm viewer, as indicated by arrow I3, to rep>resent sequential lines of the display, Mirror 43'_> is moved fast enough to cause the scanned virtual image to appear as a two-dimensional iruage to the r~iower.
The pivc~table sct~nning mirror 432 can be replace mitt. otlier types of mirror arrangements such as .a rotating faceted polygon mirror.
Microprocessor-based electronic control circuitry 440 zs azranged to accept video data and is coupled to GLV array 402 fir using the video data to operate the elongated elements 200 of the GLV array 402 for modulating light diffra ;red therefrom.
The cu~cuitry 440 is arranged such that the light iii diffracted beams D+, and D_t, is uLOd, dated to represent sequential lines of a two-dimensional image representing the video data, as noted above. Contro! circuitry 440 is also coupled to scanning mirror drive unit 435 to synchronize the display of sequential lines and to provide that seduential frames of the irn~age begin at an extreme of the anguhtr excursion range of scanning mirror 432. The speed of the scanning can be controlled to be sinusoidal, saw toothed or any other co~nwenient speed algorithm. All that is necessary is that the scanning speed be synchronized with the presentation of tine data to fhe GLV array 402.
Control circuitry 432 is also eoupled,to light sources d04R, 4046, and 404:3 for switching the sources sequontially, cooperative with operation of GLV azray 402 to provide _15_ REPLACEMENT SHEET

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SLlt~-42401 sequential red, green and bloc resolution image of the array, a4lich, togather, reprcsea~ one resolution line of colored two-dimensional image. In this atrangero.ent, the elongated mcrnbcrs 200 of each display element 300 are appropriately modulated while each of the light sources 4048, 4046 and 4048 ~ sequentially active to provide an appropriate 5. proportion of each of rcd, green az~d blue diffracted light for the display element 300 while the corresponding line of the image is displayed to the ~~iewer. This modulation occurs at a rate that is sufficiently Izigh that the viewer perceives an appropriate combined color for each display element 300.
In an alternate axrangemeztt, light sources 4048, 4046 and 4048 are activated simult;anevusly to illuminate GL~1 array .402 and two additional arrays (not shown) v;.a a dichroic prism block (not shown), placed between ions 420 and the three GLV
arrays Each GLV array would flier be arraaiged to modulate a particular one of the tbiree primary color components red, green, and blue of the imago. The diolwoic prism block may be o~
any well-known type for example an above mentioned Phillips prism block, and wood in this case be arranged such that each GLV array appeared to be located at the same Vistance from, and inclination ta, lens 420. 7:n such arraagem.ent, ~or providing a colored image, light sources 4048, 4046 and 404$ could be replaced by a single white light souro~:, and dichraie prism block 406 omitted.
It should be noted here in the Fig. 14, viewer's eye 434 is illustrated in a leis than ideal position for properly viewing .a magnified virtual image of the display of 5ystc~m 400.
Ideally, for viewing such an image, the viewer's eye should be located ax about exit pupil PZ. 1"hi.s is difficult because of nzinror 432, which is preferably also located at about this exit pupil. This di~culty can be overcome by optically relaying an image of the exit pupil away from the mizrar, to a position at which it is easy to locate a viewers eye, thereby allowing the scamling mirror 432 and the viewer's eye each to be located at about .a pupil position.
Une means of relaying an image of exit pupil Pz is illustrated in Fig. 16 wherein the optical arrangement is shown as optically "unfolded" with scanning mirror represented as a line at exit pupil 1'z of lens 420, that being one preferred posit~iu~n far the scanning mirror 432. In addition, shield 42G is placed in the area of the pupil PZ. Mere, pupil-relaying is accomplished by two lenses 442 end 444 of the same focal length, which -lt~
:REfLACEMENT SHEfiT

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are spaced apart by a distance equal to twice that focal Length to form a unit mag~.i ficatian teleccatric relay which places act image P3 of exit pupil Pz a focal length of lens 444 away from the lens 444, providing adequate eye-relief from Lens 44.4. Those skilled in th a srt will recognize, of course, that lenses 442 and 444 nzay include more than vne lens clement, S and further, that the telecentric relay urran.gement illustrated in Fig. 16 is not the on ly possible optical arrangement for relaying a pupil unagc.
Referring now to Fig. 17, (whe;re again the optzcal system is illustrated as ~unfolded" with scanning mirror 432 reproseated as a Line at exit pugil Pz of Ions 420, that being, here also, one preferrad position for the scarring mirror 432). Shield 425 is also placed in the area of the pupil P2. Eyepiece Ierls 420 may also be used as one elet~ ~cnt, or group of elements, for projecting a magnified real image of the CrLV array 402 vn a screen or on a recording medium, such as would be required to provide a projection displa3 or a device for recording or printing an image. Here, a lens (or group of Iars elements) 446 is positioned to focus a magnified rest image 448 (he~~e, the width) of GLV array 402 at a finite distance from lens 44b. This image could be focussed irt a plane 450 which ec~uld be a viewing screen for providing a projected (apparent) two-dimensional i.rnage, or on a ~
recording medium such a photographic film or paper. In the case of a recorded or pr irtted image, scan mirror 432 could be eliminated, and scmnir~g achieved by moving a recording or printing medium in the scan direction, which, in Eig. x7 is perpendi:eul.ar to the plane of the illustration, i.e., perpendicular to the orientation of the image. This mechanical scanning motion would, of course, need to be synchconized with image generation by electric circuitry 440 as in system 400.
In an alternate embodiment, rather than utilizing the shi eld 4z6 illustrated in F igs.
14-1? to prevent diffracted light from ofiher than the approximately flat center portion 202 (Fig. 12) of each elongated element 200 of the GLV array 402 from reaching the viewer, a reflective element 500 is disposed over the outermost portiou.s of each elongated clement 200. A side sectional view of such a reflective element 504 is illustrated ixt Fig. 18 disposed over a deformed elongated element 200. As can be seen from Fig. lg, the approximately flat center portion 242 (Fig. 12) of the elongated element 204 remai~zs exposed to incident light while the outer portions are covered by the reflective element 500. The reflective clement 500 reflects incident light. Therefore, this reflected light does -1?
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~~ot reach the viewer, nor does it a#'ec~ the image perc;cived by the viewer.
The ref lective ~alement 500 illustrated in Fig. 18 i.s preferably suflaciently thin. that it is in substant~.ally the sarrze plane as the approximately flat center portion 202 of each elongated element ?00 (in the undeformed state). The reflective element 500 carp also be located in a plane p:~.rallel to, spaced apart fmz7~, the reflective surface of the elongated elements Z00 (in the undeformed state) by a distance d3 equal to a whole number N of half wavelengths for the expected incident light (i.e. d3~ 0, ~,,I'2, 7~" 3~,t12, : ~1, ... , N?~,12).
The present invention has been described in terms of specific embodiments incorporating details to facilitate the understanding of the principles of construction .in,3 operation of the invention. Such reference herein to spcciflc embodiments and details thereof is not intended to Iimit the Scope of the clams appended hereto. It will be apparent to those slrilled in the art that modificatiocus may be made in the embodiment chosen for illustration without departing from the pint and scope of the invention.
The embodiment described principally above is for forming a display for human XS viewing. Other types of'displays' are. also contemplated within the present invention. For examlsle, an image could be formed on a rotating drum for transfer to paper in a printing process. In such applications, the Iaght source could also be ultraviolet or infrared. :,uch an image is not visible to a human but is eQually useful.
Specifically, it will be apparent to one of ordinary skill in the azt that the device of the present invention coutd be implemented in several different ways and the apparat3rs disclosed above is only illustrative of the preferred e;mbodirnent of the invention and is in no way a limitation.
_I8_ R~PL.ACEMENT SKEET

Claims

Claims:
What is claimed is:

1. A modulator for modulating an incident beam of light having a wavelength, the modulator comprising:
a. a plurality of elongated elements (200), each having an approximately flat reflective surface disposed between two end, each elongated element having an approximately constant cross-section between the two end, the elements arranged parallel to each other and suspended by their respective ends above a substrate (100); and b. means for deforming selected ones of the elongated elements toward the substrate thereby entering a deformed state wherein the approximately flat reflective surface of each selected element moves toward the substrate by a grating amplitude without the selected elongated elements contacting the substrate such that when the plurality of elongated elements are undeformed the modulator reflects light and such that when the selected ones of the plurality of elongated elements are deformed the modulator diffracts light.

2. The modulator according to claim 1 wherein the light is in a range of wavelengths.

3. The modulator according to claim 1 wherein the light is in a range of visible light wavelengths.

4. The modulator according to claim 1 wherein the light is in a range of ultraviolet light wavelengths.

5. The modulator according to claim 1 wherein the light is in a range of infrared light wavelengths.

6. The modulator according to claim 1 wherein the selected ones of the elongated elements moves approximately one-fourth the wavelength of the light.

7. The modulator according to claim 1 wherein the selected ones of the elongated elements move a controllable distance selected to provide a desired brightness of modulated light.

8. The modulator according to claim 1 wherein the grating amplitude is approximately one-fourth to one-third of a distaace between undeformed elongated elements and the substrate.

9. The modulator according to claim 1 wherein the approximately flat reflective surface comprises approximately one-third of a length of the corresponding elongated element.

10. The modulator according to claim 1 wherein the elongated elements are grouped according to a plurality of display elements arranged in a single linear array wherein when the elongated elements corresponding to a display element are undeformed, the incident beam of light is reflected by the display element, and when alternate ones of the elongated elements corresponding to the display element are selectively deformed, the incident beam of light is diffracted by the display element.

11. The modulator according to claim 10 further comprising an optical arrangement for scanning an image from the single linear array to form a two dimensional image.

12. The modulator according to claim 11 wherein the image from the single linear array is scanned sufficiently fast to be integrated into a single nonflickering image by a user's eye.

13. The modulator according to claim 12 further comprising means for sequentially illuminating the modulator with a plurality of colored light such that the two dimensional image is formed without color break up.

14. The modulator according to claim 12 wherein the two dimensional image is not pixellated.

15. The modulator according to claim 10 wherein a distance of movement on the selected ones of the elongated elements determines an intensity for the corresponding display element.

16. The modulator according to claim 10 wherein a ratio of a period of reflection to a period of diffraction determines an intensity for the corresponding display element.

17. The modulator according to claim 11 further comprising means for only illuminating the approximately flat center portions with the beam of light.

18. The modulator according to claim 11 further comprising means for preventing light diffracted by other than the approximately flat center portions from being displayed by the optical system.

19. The modulator of claim 18 wherein the means for preventing comprises a light shield having a slit for passing light diffracted by the aproximately flat center portions and for blocking light diffracted by other than the approximately flat center portions.

20. The modulator according to claim 18 where the means for preventing comprises a reflective element disposed over the two ends of each elongated element in a plane parallel to the reflective surfaces of undeformed elongated elements by distance equal to a whale number or zero multiplied by half the wavelength of the incident beam of light.

21. The modulator according to claim 10 further comprising an optical arrangement for projecting an imago onto a medium for printing.

22. A method of forming a light modulator on a substrate, the light modulator for modulating an incident beans of light having a wavelength within a visible range of wavelengths, the method comprising steps of:
a. forming a sacrificial layer on the substrate, wherein the sacrificial layer has a thickness that is approximately equal to the wavelength of the beam of light wherein the sacrificial layer is exposed;
b. etching at least four post holes through the sacrificial layer;
c, forming posts in the post holes;
d. forming at least two elongated elements over the sacrificial layer, each elongated element coupled to the substrate by two of the posts one at each end of each elongated element, each elongated element having a reflective surface;
and e. removing the sacrificial layer.

23. The method according to claim 22 wherein the thickness is within a range of 200 to 2000 nm.

24. The modulator according to claim 1 wherein the means for deforming uses an applied voltage such that the deformed state follows a reversible function of the applied voltage.

25. A modulator for modulating an incident beam of light having a wavelength, the modulator comprising:
a plurality of elongated elements (200), each having an approximately flat reflective surface disposed between two ends, the elements arranged parallel to each other and suspended by their respective ends by integrally formed posts (110) above a substrate (100), the posts integrally formed to the elongated elements and the substrate; and b. means for deforming selected ones of the elongated elements toward the substrate thereby entering a deformed state wherein the approximately flat reflective surface of each selected element moves toward the substrate by a grating amplitude without the selected elongated elements contacting the substrate such that when the plurality of elongated elements are undeformed the modulator reflects light and such that when the selected ones of the plurality of elongated elements are deformed the modulator diffracts light.

26. A modulator for modulating an incident beam of light having a wavelength, the modulator comprising:
a. a plurality of elongated elements (200), each hawing an approximately flat reflective surface disposed between two ends, the elements arranged parallel to each other and suspended by their respective ends above a substrate (100) and having no framing superstructure; and b. means for deforming selected ones of the elongated elements toward the substrate thereby entering a deformed state wherein the approximately flat reflective surface of each selected element moves toward the substrate by a grating amplitude without the selected elongated elements contacting the substrate such that when the plurality of elongated elements are undeformed the modulator reflects light and such that when the selected ones of the plurality of elongated elements are deformed the modulator diffracts light.