WO1998009267A1

WO1998009267A1 - Compact image generator with dual line emitter array

Info

Publication number: WO1998009267A1
Application number: PCT/US1997/014993
Authority: WO
Inventors: Maurice S. Karpman; Allen Becker
Original assignee: Reflection Technology, Inc.
Priority date: 1996-08-28
Filing date: 1997-08-26
Publication date: 1998-03-05
Also published as: JP2001501318A

Abstract

A display includes line emitter arrays (18A and 18B) coordinated with optical cross scanning to produce a virtual image. A line is actuated in sequences to increase resolution, augment color range or both, reducing the number of drivers. A resonant oscillatory mirror (24) scans a complete image at a rate above the flicker perception rate with separate actuations of the line array during forward and reverse scans, or successive scans in the same sense, to form the image. Preferably, a gallium nitride linear array emits light with blue and green components, and wavelength filters present aligned blue and green pixel lines during scanning. An emitter array has two optically and electrically isolated emission regions located at the line position of the optical assembly. One band may be offset along its axis to interleave and form a double density line image. A synchronized switchable filter may determine the color displayed at a given time. Drive or multiplexing circuitry to synchronize with the oscillating mirror may be fabricated on the emitter chip (18).

Description

COMPACT IMAGE GENERATOR WITH DUAL LINE EMITTER ARRAY

Background

This invention relates to display systems, and more particularly to miniature display systems configured to provide resolution comparable to larger display devices generally known in the art. One example of such a miniature device is described in U.S. Patent No. 4,934,773, of Becker. The device of that patent is a miniature display device which can be either hand held or mounted on a head strap, and in which the user peers through an objective lens assembly to view a two-dimensional virtual image. The virtual image is compactly created by a linear array of light emitting diodes (LEDs) which extend for the full length of an image line, and a resonantly oscillating mirror which pivots transverse to the line to scan the intermittently illuminated line over the cross dimension of an image frame. By properly synchronizing the actuation of the LEDs to form each successive line of the image as the mirror oscillates, a full two-dimensional raster image is swept out and appears through the eye piece as a two-dimensional virtual image for direct viewing. By scanning the mirror at a rate greater than about 50 frames per second, blinking effects become negligible and the image appears continuous to the viewer. However, the constraint of applying a line of LEDs having a suitably large number of dots, and having the line fit entirely within the field of view of the objective optics for direct eye viewing imposes some restraints on the dimensions of the device overall and the alignment of various image-creating elements within the device. As described in the aforesaid '773 patent, the device readily produces a monochrome image using single color LEDs in a linear array, and it is also possible to produce a full color virtual image from several colored light emitting arrays. In this case, the LEDs must produce three distinct, and preferably additive primary colors, e.g., red, blue and green, and must be aligned and actuated with suitable timing to superimpose the three colors in the virtual image produced by the scanning mirror. Since in general the red, green and blue color components at each point in the image will differ, the three arrays must be separately energized, and the cost of a full color device therefore increases because of the additional hardware and software required for driving and synchronizing the devices. In addition, the requirement that the three colors be superimposed in the virtual image requires that the different LEDs be mounted within the housing and that optical elements be provided to superimpose their images in a common optical path for viewing. This may, for example, require half-silvered mirrors, one or more sets of relay lenses, or other elements known in the art for combining optical paths of elements in different focal planes. The constraints imposed by eyepiece viewing and the miniaturization of the housing make improvements in the density or color of such multi-color superposition difficult to accomplish without resorting to highly corrected or customized optics, or other costly components. The fact that the linear LED arrays must be mounted on a chip carrier and provided with lines for driving more than several hundred separate image pixels further accentuates the difficulty of this task, since such support circuitry is generally produced on a planar array with the basic emitters. Thus any configuration involving relay lenses or folded optical paths necessarily increases the overall size of the device, as it must accommodate not just plural lines of emitters but plural regions of conductive lines and support circuit material coplanar with the emitters and extending in different positions within the device. Concomitant with the problem of suitably miniaturizing a three-color display and effectively controlling the costs of manufacturing such a device, is the problem of obtaining sufficient resolution to appeal to users of graphics and display devices, who generally have become accustomed to higher and higher screen pixel densities. Compared to items such as LED printers where the large housing enables a relatively great line length with many emitting chips assembled end-to-end to produce, for example a 1024 or 2048 dot line, the constraints on a hand held viewing device are quite severe, and readily allow only a small area, about the size of one chip carrier to be effectively imaged in the eye field for generating the entire virtual display. To increase the dot density beyond that of a normal e.g., single-chip 220-280 emitter dot array would also appear to raise further engineering constraints. Such increase in dot density might require a reduction in size of the basic circuit elements, which would exceed current wire bonding or chip carrier fabrication technology or introduce unacceptably high rates of manufacturing error. To increase resolution by using plural existing chip sets poses the difficulties of aligning different chips for superposition, and providing relatively slight offsets along the direction of the LED array, as well as increasing the wiring requirements.

As a theoretical matter, the existence of LEDs which can be actuated to produce two different colors, for example yellow and red, would appear to allow a color display to be implemented with at least one linear diode array performing double duty, albeit at different times. Another approach would be to utilize a fully integrated full color miniature display device with a liquid crystal display that functions generally identically to the liquid crystal displays commonly used in larger scale devices. Such full color miniature displays, as used for example on video camcorders, typically have a large number of very closely spaced miniature pixels or pixel sets in red, green or blue. The pixels are selectively illuminated to produce a full color display. These devices however tend to be relatively expensive. Thus there is a need for a miniature full color display device having a hardy and effective, but relatively inexpensive, compact construction.

Summary of the Invention A miniature display in accordance with the present invention utilizes a line array of light emitting elements which is split into two or more separately actuable but contiguous lines that are selectively illuminated in coordination with mechanical scanning transverse to the line by a mirror or other optics to produce a two-dimensional virtual image. The line array is actuated in more than one sequence to either increase the resolution, or extend the color range, or both, of the image so created, and a simple switching circuit connects a common driver to the actuated line. In this manner the number of drivers required for the system is reduced while a common optical assembly may image a single chip to double, quadruple or further increase image density. The mechanical scanning element, such as a resonant oscillatory mirror, is operated at a rate above the rate of flicker perception, e.g., over 50 Hz, or at a frequency above this threshold rate. Separate actuations of the line array are coordinated during forward and reverse scans of the mirror, or during successive scans of the mirror in the same sense to create a complete image frame.

In one preferred embodiment, the light emitters are a gallium nitride line array of diode emitters which emit light in a relatively broad band about 500 nm having both blue and green components. In a preferred embodiment, the line array contains optically and electrically isolated emission elements which are arranged in two immediately adjacent linear arays extending along the line so that both appear essentially at the focal position of the optical assembly. One array may be offset one or a fraction of a pixel along the line with respect to the other array so that when independently energized its illuminated positions interleave with those of the adjacent array to produce a double density line image. In other embodiments, a spectral filter is applied to the output of the emitters such that the single array is activated for both blue and green outputs separately. In this embodiment, two line arrays adjacent to each other may be provided as in the first embodiment above, and their outputs filtered so that the blue and green dots are laid down essentially in registry without further mechanical adjustment or fitting required. In other embodiments, the two offset arrays may be separately energized to lay down a double density line of a single color, e.g., blue, selected by one filter, followed by actuation to form a double density line of another color (e.g., green) obtained with another filter. Thus the drivers energize the array at separate times to form the blue and green pixel lines during mirror scanning. For a basic embodiment employing a 240 dot line array, the two offset arrays of elements produce a 480 dot line which may for example be energized at 640 distinct times during the scan of the mirror to produce a 480 by 640 pixel two-dimensional virtual image. By employing separate blue and green filters, separate colors, at 240 dot or 480 dot resolution, are displayed. Each of these separate actuations of a 240 dot segment is referred to herein as a color segment. A color segment may be considered a basic unit in the sense that one set of hardware drivers may drive the segment. In accordance with a further aspect of the present invention, a single driver is multiplexed to drive the light segment in each illuminated interval, with the same hardware employed for the first interval then connected in a second interval to energize a light segment to interleave double density image dots, and/or add a superimposed second color. This is done by actuating each light segment during a separate scan by the mirror of the same image portion. A switchable filter may be synchronized with actuation of the light segment to determine the color being displayed at a given fraction of the frame writing interval which may, for example, occupy one or more half-cycles of the mirror scan for each color.

One method of fabricating the light segments in a gallium nitride emitter array is to form an isolation trench through both the p- and the n-doped nitride layers of the array. The trench isolates the adjacent lines of light emitters electrically as well as optically so that light generated in one line does not reach or emit from the adjacent line. Separate conductors having a width smaller than that of the pixel elements may be laid down over the face of the emitting elements to make electrical connection separately to the two distinct lines of rigidly and closely interconnected emission elements so formed. In this case, the two light segments require no external alignment or adjustment for optical superposition, and the two segments may be made to exactly overlap simply by introduction of a slight phase delay δ in their actuation signals. As noted above, a mechanical mirror operates to scan the direction across the illuminated line in both forward and backward directions. Each line segment is illuminated during all or part of one pass of the mirror, although multiple sub-intervals during forward and back scans, or during successive scans in the same direction, may be employed so long as each color or line segment is actuated to cover the full cross dimension of the display field in a continuous or separate sequence of actuations. In another embodiment, drive or multiplexing circuitry may be fabricated on the light emitter chip with the LED emitters. In either case, the multiplexing circuitry is synchronized with a synch signal from the oscillating mirror to energize the light segment during the appropriate intervals of the forward or back scans of the mirror. When the diode emitters are formed as parallel lines with an isolation trench between adjacent lines of the device, the construction is readily extended to provide three, four or more separate and independent lines of emitters. In one such arrangement, a third independently activated line array emits a red wavelength, thereby providing blue, green and red simultaneously-viewed emitters in a full color display.

Brief Description of Drawings

These and other features of the invention will be understood from the description below taken together with drawings, wherein

FIGURE 1 shows a prior art image generator; FIGURES 2 and 2A show a line emitting chip, and chip carrier, respectively, as utilized in the device of FIGURE 1;

FIGURE 3 shows a first embodiment of the invention;

FIGURE 4 shows a top plan view of a first light emitting array for the embodiment of FIGURE 3; FIGURE 5 shows the top plan view of a second light emitting ray for the embodiment;

FIGURES 6A-6J illustrate fabrication of the light emitting arrays of FIGURES 4 and 5; and

FIGURE 7 shows a full color display.

Detailed Description

FIGURE 1 illustrates generally a prior art miniature video display system 1 of the type to which the present invention is addressed. As shown, the device has a housing 12 into which the user peers through a viewing window 14 at a resonantly oscillating mirror assembly 24, 22 which is directed through focusing optics 20 at a light emitter array 18 which, as more fully explained in the aforesaid U.S. patent 4,934,773, is arranged as a line of light emitters driven by drivers 16 through appropriate circuit connections 26, 28 which synchronize the illumination of the line of lights 18 with oscillation of the scanning mirror assembly 24, 22. As further noted in that patent, the emitter 18 may include plural linear arrays of emitting elements of distinct colors, actuation of which is synchronized with the mirror scans to produce a full color virtual image of the data being displayed.

FIGURES 2 and 2A show by way of practical example, the general appearance of a line array 18 of light emitters as described in that patent. As shown, the emitting region 25 consists of a series of small square regions 25a, 25b... typically having a cross dimension of about 40 micrometers which are connected by conductive leads 27a, 27b.,.. to corresponding lands 29a, 29b As illustrated in FIGURE 2A, the chip 18 is mounted in a chip carrier 30 which provides structural support for mounting it in circuitry and making electrical connections thereto. Chip carrier 30 has a plurality of miniature wire bonds illustrated generally by lines 32 which interconnect the lands 29a, 29b... to the pins or other conductors of the chip carrier 30 and thus to the external wires, circuit boards or other operative circuit connectors. The chip carrier 30 has a cross dimension under one inch and is therefore well configured to sit at the focal plane of the viewing optics 20 (FIGURE 1) and place the entire fine of emitters, 25a, 25b... in the user's field of view. Typically, the line of emitters contains between about 220 and 280 emitting regions 25/. When a multicolor display is contemplated, several such subchips may be arranged, for example on faces of a combining prism, to place each of the necessary colors in the desired focal region of the lens 20.

FIGURE 3 illustrates a corresponding view of a basic embodiment 10 of a multicolor display device in accordance with the present invention. Corresponding components are numbered identically to those of FIGURE 1. As shown in the Figure, an active set of light emitters 18 A, 18B are placed at the focal position of lens 20 and are offset from each other by a slight gap g so that the two rows of emitting elements are parallel to each other. A microscope cover plate 21 or other protective but light transmissive window is preferably provided over the arrays, while a filter element 40 shown in phantom is optionally provided in some embodiments discussed further below. Preferably the light emitting arrays are gallium nitride or other bright emitters, and are arranged in a pattern substantially as shown in FIGURE 2. However, as discussed further below, two and optionally more, lines of these emitting elements are formed on a common substrate and separated by a small gap in a manner that each line can be separately electrically actuated to emit light only in one or the other of the lines so formed.

FIGURE 4 illustrates a first embodiment 38 of the multiple line emitter array as shown in 18A, 18B of FIGURE 3. This array 38 includes a first line of emitters 38a, and a second line of emitters 38b both fabricated together and separated by an isolating barrier trench 38c which extends in a line between the two lines of emitters. As shown wire bond pads 39 corresponding to pads 29a, 29b... of FIGURE 2 are each connected by a single conductive lead to a single emitting element of the array 38a and to an adjacent element of the array 38b across the barrier 38c. As discussed above, the emitter array is preferably a gallium nitride emitter array, that is one in which a p-doped gallium nitride layer forms the top layer of each emitter, and rests on a conductive n-doped gallium nitride sublayer. Both layers are essentially transparent, and are conductive at an appropriate potential, to enable selective actuation at the diode junction formed by each emitting region when a voltage is applied between the line array sublayer and the leads attached to the top layer, i.e., to the top surface of the emitting elements. In addition the wire bond pads 39 connecting the p-doped emission region of each line array, two separate wire bond pads are provided, denoted 19a, 19b which connect to the line arrays at the underlying n-doped gallium nitride layer. Each pad 19a or 19b thus connects to the entire vertical strip of the n-dope layer underlying all elements of the emission line 38a or 38b. Thus by selectively applying a voltage across one of the pads 19a or 19b, and one of the individual emitter pads 39, the emitter in the selected line which is connected to pad 39 is illuminated, without illuminating the adjacent pad whose sublayer is not so energized. In this embodiment, the adjacent or corresponding emitting elements of emitter line 38a and emitter line 38b reside at the same vertical positions, and thus when scanned by the mirror they illuminate the same positions on the virtual image field view by the user. As further illustrated in FIGURE 4, one of these lines, illustratively line 38b has a spectral filter 42 placed over its emitting elements. In this embodiment, the emitters are fabricated to emit over a relatively broad wavelength band encompassing wavelengths from below 490 nanometers to above 510 nanometers, and thus have substantial energy components in both the blue and green bands of the spectrum. Filter 42 is preferably a band pass filter, which may be for example a green filter which passes illumination having a wavelength greater than 500 nanometers, so that only green light passes the filter 42, and the array 38b is seen by the viewer as green in the imaging device 10. Similarly, a shorter wavelength band pass filter may be applied over the line array 38a so that it functions as a blue emitter array. However a blue pass filter is not generally necessary for the above described GaN array, since over ninety percent of the diode emission energy lies in the blue band and the presence of a small amount of green does not impair its value as a blue color source in a multicolor viewing arrangement. The invention is not limited to direct coating of a filter over the line 38b, and other constructions for intermittently filtering the line of emission elements or selectively placing or switching such filter in the optical path are also contemplated, as more fully set forth in applicants' co-pending U.S. patent application serial number 08/540,871 filed on October 1 1, 1995, which application is hereby incorporated herein by reference in its entirety. A copy of that application is attached hereto as Appendix A.

FIGURES 6A-6J illustrate the fabrication of a gallium nitride emission source array split into several lines as shown in FIGURE 4. These drawings are schematic, and provide a conceptual illustration of the construction, but it will be understood that detailed conventional substeps as necessary for growth, isolation and electrical connection to the illustrated array are to be employed with appropriate variations and substitutions as known in the fabrication art. As shown in FIGURE 6 A, a substrate which in current manufacturing technology may be, for example, sapphire or silicon carbide is used to provide a compatible but strong mechanical support. An electrically insulating buffer layer is epitaxially grown on the substrate (FIGURE 6B) and an n-type (GaN) layer is epitaxially grown on the buffer layer (FIGURE 6C). A p-type GaN layer is then epitaxially grown on the n-type layer (FIGURE 6D) and portions of this layer are etched away to expose contact regions for connecting to the n-type layer. An ohmic contact layer is then deposited on one or more areas of the p-type layer and on the exposed areas of the n-type layer. These ohmic contact regions are metalized, and may have wires attached for energizing the device.

Typically when making and LED, the LED is separated from the wafer after this fabrication step, and the metalized layers are electrically connected to a leadframe or substrate. A positive voltage applied to the p-type layer while the n-type layer is grounded will then drive the gallium nitride diode to emit light. In general since both the p-type and n-type layers are conductive, the fabrication of an array introduces further complexities. For making line arrays as described above with respect to FIGURES 3 and 4, a more complex construction is required. Briefly, a trench t is etched through the p-type layer, and ohmic contact layers are deposited on the n-type layer and on each emitter island (FIGURE 6G). The trenches are then filled (FIGURE 6H) to planarize the assembly, and metalization is laid down on the ohmic contact of the n-type layer, the p-type layer and a metalized trace m is placed over the trench connecting these two. Wire bonding, for example, to a chip carrier is also performed as before (FIGURE 6H).

To adapt this construction to the present invention, plural emitter regions are formed by forming a plurality of trenches separating the emission islands into a least two parallel bands, as shown in FIGURE 61. A deep trench T is then formed going entirely through the underlying n-type layer and extending to the insulating epitaxial sublayer. This severs the n-type layer into a first layer band A underlying the line of emitters 38a and a second layer band B underlying the line of emitters 38b. Each of these underlying regions has been exposed through the p-type layer and metalized, so that a separate electrical connection is provided to the band A or B of the sublayer of each array while the p-type layer of each pair of emitters shares a common conductor with its neighbor in the adjacent array. As shown in FIGURE 6J, in the finished chip these conductors extend over the planarized trenches t, T and across the faces of the emitters. In one prototype embodiment, applicant has provided ten micrometer wide conductive leads extending over the face of each thirty-eight micrometer square emission area and across the planarized trenches to interconnect corresponding emitters of the first and second lines.

Turning now to the top plan views of the emitter devices, FIGURE 5 illustrates a second embodiment of a emitter array useful in practicing the invention of FIGURE 3. As shown in FIGURE 5, an emitter array 48 has a first line of emitters 48a and a second line of emitters 48b. Each line of emitters has a fixed pitch P, or number of emission regions per inch, which is the same for each line. Furthermore, in each line the emission regions are spaced apart by a distance approximately equal to the size of the emitter. In this embodiment, however, the emitters of line 48b are positioned offset from the emitters of line 48a so that they fall vertically (as shown) in the space between the corresponding emitters of line 48a. Furthermore each conductor 47 extending from a wire bond pad 49 to an emitter crosses over the face of its corresponding emitter, e.g., 48a and follows a diagonal path across the trench 48c to the adjacent emitter 48b at a one pixel offset. As in the embodiment of FIGURE 4, only two wire bonding pads or contact areas are necessary to access the underlying n-type gallium nitride layer, and these two contacts in conjunction with the wire bond pads 49 provide a two-wire column/row diode addressing scheme to energize the emitters. Advantageously, the number of wire bond pads 49 remains identical to the number of wire bond pads employed for a single line of emitters having pitch spacing P, but in this case a pitch of twice the resolution is obtained by separately energizing the pixels of line 48a (referred to below for simplicity of exposition as the "odd" pixels) and then those of line 48b (the "even" pixels). Advantageously, a single set of drivers fixedly connected to the single set of lands 49 is multiplexed to light up the odd and even pixels.

FIGURE 7 illustrates the overall operation of the device of FIGURE 3 with separately actuated line arrays for image forming.

In this embodiment, a first array 58 is a split line array, such as array 38 of FIGURE 4 or array 48 of FIGURE 5, having two or more separately actuated lines of light emitters l\, F>, carried on the same chip. This array may be actuated as described above to form double density, double color, or double density two color images as described above. A second array 68 is arranged at the focal region adjacent to array 58, and provides a line of light emitters k which produce a third or independent color. Arrays 68, 58 may be mounted on the same chip carrier, and may share wiring to the extent feasible. For example the backplane or column electrode of array 68 may be tied to that of one or more lines of array 58 so that it writes its color during the same scan intervals. In that case, one driver drives array 68, while simultaneously multiplexor 70 applies drive signals from another driver to illuminate a line of elements of array 58. Alternatively, all emitters may be energized by a single driver. In that case a 3: 1 or 6: 1 multiplexor is used to connect the driver to successive lines of emitters lj, I2, k, or a simple switch synchronized to successive scans of the mirror is actuated to write the whole frame of each color in several successive passes. It will be understood that for such operation the resonant mirror may be tuned to oscillate at a multiple of a basic scan rate, so that each color may be displayed and refreshed without flicker.

According to a further aspect of the invention the lines of emitters k, lj, I2, are displaced fixed distances from each other in the cross-sea direction, and these distances correspond simply to an offset of the line number of the frame. The offset between 1_] and I2 may be substantially less than a millimeter, while that of k may be one or several millimeters, depending upon the manner of chip fabrication or mounting. Two accommodate these offsets, the mirror 24 scans more than a full field, and slight timing offsets are applied to the actuation signals so that the correct RGB values of one line of an image frame will overlap in a single line of the virtual image of the emitters in a confocal image plane IP. The invention has been described with reference to several particular embodiments; however, it may take other forms which will occur to those skilled in the art, and all such forms are encompassed within the spirit and scope of the present invention, and its equivalent, as defined by the claims appended hereto. What is claimed is:

Claims

1. A system for generating a two dimensional color virtual image comprising, first and second linear arrays of individual light emitters, electrically isolated from one another and extending in a first direction, signal generating means providing in a first sequence electrical signals to selected emitters of only said first linear array sufficient to generate over a first period of time areas of light of dimension sufficient to create said two dimensional image at a first time and for providing in a second sequence electrical signals only to selected emitters of said second linear array sufficient to generate over a second period of time, offset from said first period of time, areas of light of dimension sufficient to create said two dimensional virtual image at a second time, said first and second linear arrays being formed on a common substrate, and a scanning mirror positioned to receive light from both said linear arrays and to scan in a second direction orthogonal to said first direction superimposing said areas of light in less than l/50th of a second thereby generating said virtual image as an enhanced image with light from both linear arrays.

2. A system in accordance with claim 1 , wherein spacing between individual light emitters in each linear array is substantially equal to dimension of an emitter in said first direction and wherein said first and second linear arrays are offset from each other in said first direction by said dimension of the emitter so that said virtual image has twice the resolution of a single linear array.

3. A system in accordance with either of claims 1 or 2, wherein the color of light from said first array differs from the color of light from said second array so that said scanning mirror superimposes two colors in said enhanced virtual image.

4. A system for generating a two dimensional full color virtual image comprising, first and second separately-actuable linear arrays of individual light emitters, extending in a first direction, said first linear array emitters producing green and blue light, and said second linear array emitters producing red light, said first linear array emitters being formed of GaN, said first linear array having electrically and optically divided elements which are multiplexed with a single driver to combine in a color image.

5. A system according to claim 4, wherein said divided elements are divided into plural lines of closely adjacent elements, the elements of one line being offset from those of an adjacent line so as to interleave therewith when combined in a virtual image.

6. A system according to claim 5, wherein a scanning mirror forms light from the emitters into a virtual image, and wherein a multiplexor actuates different ones of said lines of elements during different scans of said scanning mirror.

7. A system according to claim 6, wherein said different scans are forward and backward scans.

8. A system according to claim 6, wherein said different scans are successive scans in the same direction.

9. A system according to claim 6, further comprising a switchable filter synchronized with said multiplexor to determine color to be produced by a line of elements in said virtual image.

10. A display device comprising a housing a viewing objective a chip carrier at the focal region of said viewing objective, and a linear array of emitting elements mounted in said chip carrier, a scanning mirror in an optical path to the chip carrier and arranged to scan across the linear array to form a two dimensional virtual image, and means for switching said linear array in synchrony with scanning of said mirror, said linear array having two separately actuable lines of light emitting elements and said switching means actuating respective ones of said lines of elements in different scans of said mirror to sweep out a flicker- free two dimensional virtual image.

11. A display device according to claim 10, further comprising a wavelength filter synchronized with scanning of said mirror to alter color of said light emitting elements so that different scans sweep out two different colors of said virtual image.

12. A display device according to claim 10, further comprising a linear array of having a third color, said third color linear array being activated simultaneously with at least one of said two different colors to produce a full color image.

13. A display device according to claim 10, wherein said two separately actuable lines have mutually offset emitting elements which are interleaved with each other by actuation with a phase delay during said successive scans so as to appear on a common line with double density.

14. A two dimensional image display system of the type comprising a linear array of light emitting elements, means for selectively illuminating said elements and means for optically scanning said elements in a cross direction to produce a two dimensional luminous image, wherein said elements are arranged adjacent to each other in a line extending along one direction to form a full line of said image, said line of elements being formed as a patterned emitter layer on a conductive support layer, and having a barrier extending along said one direction through said emitter and support layers to both optically and electrically isolate first portions of said elements on one side of the barrier from second portions of said elements on the other side of the barrier, and means for separately energizing the portions on both sides of the barrier with a single driver to produce two distinct sets of picture elements of said image, said scanning in a cross direction combining said two sets in a two-dimensional vitual image.

15. A two dimensional image display system according to claim 14, wherein said emitting elements emit light extending in a band containing two colors, and further comprising means for placing a filter in the scanning path to produce said two colors separately in said virtual image.

16. A two dimensional image display system according to claim 14, wherein said first portions and said second portions comprise adjacent sets of half density light elements, said means for optically scanning superposing said elements to form a two- dimensional full density virtual image.

17. A two dimensional image display system according to claim 14, wherein the light emitting elements are gallium nitride elements which produce blue and green light simultaneously.

18. A two dimensional image display system according to claim 15, wherein said means for placing moves a filter in coordination with said scanning for selecting one color from the two distinct colors.

19. A two dimensional image display system according to claim 14, wherein said first and second portions alternate with each other along said one direction and are substantially contiguous to each other along said cross direction with front surface conductive traces interconnecting each element of the first portion with a neighboring element of the second portion for actuation by a single driver.

20. A two dimensional image display system according to claim 14, wherein said means for optically scanning scans in said cross-dimension at a rate above about 50Hz.

21. A system for generating a two dimensional virtual image, comprising first and second separately actuable linear arrays of individual light emitters, the arrays extending in a first direction signal generating means for providing in a first sequence electrical signals to selected emitters of only said first linear array sufficient to generate over a first period of time areas of light of dimension sufficient to create said two dimensional image at a first time, and for providing in a second sequence electrical signals only to selected emitters of said second linear array sufficient to generate over a second period of time, offset from said first period of time, areas of light of dimension sufficient to create said two dimensional virtual image at a second time said first and second linear arrays being formed adjacent each other on a common substrate, and a scanning mirror positioned to receive light from both said linear arrays and to scan in a second direction orthogonal to said first direction superimposing said areas of light at a rate effective to form a continuous image wherein each individual light emitter of said first linear array is offset in said first direction from a corresponding individual light emitter of said second linear array so that said scanning interleaves light from said first and second linear arrays to form an enhanced virtual image having greater resolution than a single linear array.