WO1999012358A1

WO1999012358A1 - Fiber-coupled beam delivery system for direct-write scanning displays

Info

Publication number: WO1999012358A1
Application number: PCT/US1998/017190
Authority: WO
Inventors: Graham W. Flint; Christhard Deter; Holger Frost
Original assignee: Laser Power Corporation; Ldt Gmbh & Co. Laser-Display-Technologie Kg
Priority date: 1997-08-28
Filing date: 1998-08-19
Publication date: 1999-03-11
Also published as: AU9199598A

Abstract

A laser scanning display system for displaying an image on a screen (195) comprises a plurality of lasers (111, 112, 113) and respective modulators (131-133) that provide modulated laser beams (141-143) responsive to image data (100), which are coupled into optical waveguides (161-163) and supplied to a waveguide termination block (180) that situates the modulated laser outputs in a row defining a linear axis. The display system includes a delay means for introducing a delay interval between each of the modulated laser beams emitted from the row so that each pixel is represented by a sequential combination of modulated laser beams. A scanning system (190) then scans the row of modulated laser outputs along the row's linear axis. The delay interval between the scanned beams and the scanning speed of the scanning system are synchronized so that each pixel in the image is defined by superposing each of said modulated laser beams. In the preferred embodiment, a full color display system is provided by modulating a red laser, a green laser, and a blue laser, and then scanning the modulated red, green, and blue beams in a row across the screen. In order to increase the power at any wavelength, additional laser/modulator assemblies may be employed. In some embodiments, pixels in multiple lines can be written in parallel.

Description

FIBER-COUPLED BEAM DELIVERY SYSTEM FOR DIRECT WRITE SCANNING

DISPLAYS

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to image display systems that scan modulated laser light to produce an image on a screen, and particularly to image display systems that deliver modulated laser light to a scanning system using a fiber optic cable.

2. Description of Related Art

The demand for high quality video projection systems is rapidly increasing. Potentially, video data can provide very high resolution; however, the lack of affordable high quality, high-brightness display systems prevents effective utilization of high resolution data on large screens.

One problem with conventional video projectors has been lack of brightness: a typical broadband source does not produce a great deal of brightness, thereby limiting potential markets. Furthermore, a broadband source of light generates significant heat and occupies a great deal of space. Also, the spectral output of a broadband light source is unpredictable, leading to color variations in the resulting image. In order to provide high brightness and predictable colors, it has been suggested to replace the broadband source with red, green, and blue lasers, which produce narrowband beams at a predictable wavelength. The red, green, and blue beams are then independently modulated and scanned on a screen. Some video projection systems that use lasers are available; however they are very expensive and therefore available only to a very small group of people. Furthermore, such systems are very bulky and consume substantial space.

In order to reduce the size and cost of laser scanning video projection systems, it has been suggested to utilize a long fiber optic cable to connect the laser/modulator unit with the scanning system and screen, thereby allowing the laser/modulator unit to be situated away from the living space, in a location such as a closet, while the scanning system and screen can be place in any suitable location to scan the screen with the light transmitted through the optical fiber. Such a system is disclosed by Deter et al. in U.S. Patent 5,440,352 entitled "Laser-Driven Television Projection System with Attendant Color Correction" and in U.S. Patent 5,485,225 entitled "Video Projection System Using Picture and Line Scanning". In that system, the modulated light from the red, green, and blue lasers is combined into a common beam path using dichroic mirrors and conventional free-space combining techniques before being scanned by the scanning system. The combined beam is then scanned across the screen by the scanning system, each pixel in the image being represented by the red, green, and blue components in the combined beam.

In one embodiment of the system disclosed in the above-mentioned U.S. Patent 5,485,225, the modulated light is combined and then coupled into a single fiber. In another embodiment a separate optical fiber transmits the modulated light from each fiber to the scanning system, where it is combined. One problem with both of these systems is that they require free-space combining and dichroic mirrors (at least), which unfortunately add expense, consume additional space, and provide another failure mechanism.

Another problem with these systems relates to inherent physical limitations upon the use of additional lasers to "scale up" the power as needed. It is not physically possible to combine three or more beams of the same wavelength in free space. The dichroic mirrors disclosed in the above patent can be used only to combine beams that have appreciable spectral separation, thereby limiting dichroic-combined systems to one laser beam at a particular wavelength. Two laser beams of the same wavelength can be combined using a polarizer if both beams are linearly polarized; however, the polarizers add cost and consume space, and furthermore, the requirement that the beams be linearly polarized adds complexity to the system and can reduce efficiency. Thus, even if the costs of beam combining were acceptable, there is an absolute limit of two lasers at one wavelength that can be combined for display on the screen. In principle, then, for a red, green and blue projection system, at most a total of six polarized laser beams - two red, two green, and two blue - can be combined to occupy a common path using both dichroic mirrors and polarizers. One physically possible, but impractical way to incorporate a third beam would be to bring it into focus with the other two beams from a non-common path. To accommodate this extra beam while at the same time preserving a numerical aperture of 0.1 would require that the /-numbers of all the beams be increased from /!5 to /Ϊ10. This, in turn, would drive the minimum focused spot diameter of the red beam from about 3.25 microns to about 6.54 microns; thereby effectively necessitating that both the lasers and their combining components have diffraction limited performance, which is an exceedingly difficult requirement and beyond the capability of many lasers and optical components. Although theoretically possible, the cost and size of such a Utopian system would be prohibitive for most practical uses.

SUMMARY OF THE INVENTION

In order to overcome the limitations of the prior art, a laser scanning display system is described in which additional lasers can be added straightforwardly to provide additional power and/or additional wavelengths. The laser scanning display system for displaying an image on a screen using image data comprises a plurality of lasers and a plurality of modulators coupled to respectively modulate the beams from said plurality of lasers responsive to image data. The modulated laser beams are coupled into optical waveguides, a waveguide termination block situates the modulated laser outputs from the waveguides in a row defining a linear axis, and a scanning system scans the row of modulated laser outputs along the row's linear axis. The system includes a delay means for introducing a delay interval between each of the modulated laser beams so that each pixel is represented by a sequential combination of said modulated laser beams. The delay interval between the scanned beams is synchronized with the scanning speed of the scanning system, so that each pixel in the image is defined by superposing each of said modulated laser beams.

In the preferred embodiment, a full color display system is provided by modulating a red laser, a green laser, and a blue laser, and then scanning the respective beams in a row across the screen. In order to increase the power at any wavelength, additional laser and modulator assemblies may be employed; for example, one embodiment may use three blue laser/modulators, three red laser/modulators, and one green laser/modulator. In some embodiments, pixels in multiple lines can be written in parallel. The foregoing, together with other objects, features and advantages of this invention, will become more apparent when referring to the following specification, claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of this invention, reference is now made to the following detailed description of the embodiments as illustrated in the accompanying drawing, wherein:

Fig. 1 is a block diagram of an embodiment of the laser scanning display system according to the invention; Fig. 2 is a perspective view of a waveguide termination block in which the output ends of the optical fibers are situated in a row;

Fig. 3 is a plan view of the output ends of three optical fibers modified to be situated very closely together- Fig. 4 is a perspective view of a waveguide termination block that comprises the modified optical fibers shown in Fig. 3; Fig. 5 is a perspective view of one embodiment of a waveguide termination block for holding the optical waveguides in a closely positioned configuration, a scanning system for scanning the beams from the waveguide termination block, and a screen on which the beams are scanned;

Fig. 6A is a functional diagram illustrating a first beam from a first optical waveguide being written onto a pixel location on a screen; Fig. 6B is a functional diagram illustrating a second beam from a second optical waveguide being written onto the same pixel location as in Fig. 6A;

Fig. 6C is a functional diagram illustrating a third beam from a third optical waveguide being written onto the same pixel location as in Figs 6A and 6B;

Fig. 7 is a schematic diagram of a preferred embodiment of an RGB laser scanning display system implemented with five solid state lasers including a red laser, a green laser, and three blue lasers;

Fig. 8 is a perspective view of an alternative embodiment of a waveguide termination block, comprising a plurality of waveguides formed therein so that their outputs ends are closely positioned;

Fig. 9 is a plan view of the waveguide termination block of Fig. 8, and also showing fiber optics and lenses for coupling light from the fiber optic cables into the waveguide channels; and Fig. 10 is a diagram of a parallel write scanning system that writes multiple lines in parallel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

This invention is described in a preferred embodiment in the following description with reference to the Figures, in which like numbers represent the same or similar elements.

DEFINITIONS

A laser is a device that produces a highly directed beam of concentrated optical radiation. For purpose of this description, "optical radiation" includes visible wavelengths, infrared wavelengths, and ultraviolet wavelengths. As is well known, the visible wavelengths are divided into colors that correspond to human visual response.

An optical waveguide is any device that transmits optical radiation, such as an optical fiber, or a waveguide channel formed in a block of material.

SYSTEM OVERVIEW

The following description begins with an overview of the scanning display system and the scanning method, and follows with an example of a display system in accordance with the preferred embodiment.

Reference is now made to Fig. 1 which is a block diagram of an embodiment of a laser scanning display system for displaying an image defined by image data 100 supplied in any suitable format from any suitable source. In the preferred embodiment, the image data has a conventional RGB (red, green, blue) format in which each pixel in an image is defined by red data, green data, and blue data representative of the respective color level, which together produce the desired color when combined in the displayed image. However, in alternative embodiments the image data may have other formats (i.e. non-RGB formats).

The image data 100 is supplied to a modulation driver 105 that, responsive to the image data, generates control signals to produce the appropriate output from the lasers and modulators in the display system. The display system includes a first laser 111 that produces a first beam 121, a second laser 112 that produces a second beam 122, and a third laser 113 that produces a third beam 123. Preferably, the first, second and third lasers produce continuous wave ("cw") beams, each generating a beam having a different wavelength (i.e. a different color). In the preferred embodiment the first, second, and third lasers are selected to correspond directly with the RGB image data: the first laser generates a red beam, the second laser generates a green beam, and the third laser generates a blue beam. In alternative embodiments, such as the embodiment shown in Fig. 7, additional lasers may be employed to increase power levels, or in other embodiments additional lasers may be employed to add colors and wavelengths such as infrared.

The laser beams 121,122, and 123 are modulated, respectively, by a first modulator 131, a second modulator 132, and a third modulator 133, responsive to signals from the modulator 105. The modulators 131-133 comprise any suitable type of optical modulator, for example an acousto-optic modulator or an electro-optic modulator. The first, second, and third modulators allow separate modulation of the beams 121-123, and therefore produce a modulated first beam 141, a modulated second beam 142, and a modulated third beam 143. In the preferred embodiment in which the lasers are red, green, and blue, the red laser beam is modulated responsive to red data, the green laser beam is modulated responsive to green data, and the blue laser beam is modulated responsive to blue data.

The modulated laser beams 141, 142, and 143 are then coupled, respectively, via optical couplers 151, 152, and 153 into the input end of optical waveguides 161, 162, and 163. In the preferred embodiment, the optical waveguides each include an optical fiber, either single mode or ultimode, and each optical coupler includes a lens that focuses its respective laser beam into the optical fiber. The optical fibers are then collected into a fiber bundle that is delivered to a waveguide termination block. Reference is now made to Fig. 2 together with Fig. 1. The optical waveguides are routed to a waveguide termination block 180 that positions the output ends of the waveguides so that the modulated output beams 185 can be imaged by a scanning system 190 on a screen 195.

Fig. 2 is a perspective view of one embodiment of a waveguide termination block 180 in which the optical waveguides comprise optical fibers 211, 212, and 213 with a cylindrical cross section. In the illustrated embodiment, the optical fibers carrying the modulated beams are supplied to the waveguide termination block 180, which has an output face 215 that situates the respective output ends 221, 222, and 223 of each fiber in a row defined by a linear axis 230 illustrated by a dotted line, with a uniform spatial separation between the output ends. Particularly, the centers of the output ends are separated by a predetermined distance 240. Each of the optical fibers includes a central core 250 surrounded by a cladding 255. Most of the optical radiation is transmitted through the core, while the cladding aids transmission by directing and maintaining the optical radiation within the core. The output ends 221,

222, and 223 are preferably positioned as closely together as possible; i.e. distance 240 is made as small as possible, which facilitates scanning and superposition of the laser beams upon each pixel in a manner described elsewhere in detail, particularly with reference to Figs. 6A-6C. In the preferred embodiment, the output ends of the optical fibers are situated immediately adjacent to each other; for example, if a 125 micron optical fiber is used, the center-to-center separation between immediately adjacent optical fibers would be 125 microns.

Reference is now made to Figs. 3 and 4 together with Fig. 1. The core of a typical optical fiber is a small fraction of its total diameter: in one example a 125 micron optical fiber has a core diameter of only 15 microns. In the embodiment of Figs. 3 and 4, the optical fibers are modified at their output ends 301, 302, and 303 to remove part of the cladding in order to situate the cores (and therefore the output beams) even more closely. Fig. 3 is a plan view of three optical fibers 311, 312, and 313 with a portion of their cladding removed to be situated more closely together than the embodiment of Fig. 2. The cladding in adjacent sections of the optical fibers may be removed by any suitable method such as grinding, forming them into flat surfaces, and then bonding the fibers together by any suitable means such as epoxy. In Fig. 3, the central fiber 312 is ground to form two approximately flat surfaces 340 on opposing sides of the fiber. The first side fiber 311 is ground at an angle to form an approximately flat surface 350 that meets with the adjacent surface of the central fiber, and the second side fiber 313 is also ground at an angle to form an approximately flat surface 355 that meets with the adjacent surface of the central fiber. When grinding or otherwise forming the flat surfaces, the core of each fiber should remain intact; in other words, only the cladding should be removed. Fig.4 is a perspective view of the resulting bonded optical fiber structure installed in a waveguide termination block, illustrating that the centers of the output ends 301, 302, and 303 of the optical fibers are separated by a predetermined uniform spatial separation 410, which is less than the corresponding center-to-center distance shown in Fig. 2, and less than obtainable even if the optical fibers are immediately adjacent. An alternative embodiment of the waveguide termination block, which is described later with reference to Figs. 8 and 9, includes a plurality of waveguide channels formed in a block of material, which allows positioning the output ends very closely together. Reference is now made to Fig. 5, together with Fig. 1. In the block diagram of Fig. 1, the waveguide termination block 180 supplies its modulated beams 185 to a scanning system 190 that scans the beams from the waveguide termination block across a screen 195 using any suitable components. It should be understood that the image on the screen is formed by scanning the raster lines in any suitable predetermined scanning order, for example from top to bottom, from side to side, or in a diagonal manner. Such scanning systems are well known, one of which is illustrated in U.S. Patent No. 5,440,352, issued August 8, 1995 to Deter et al., and U.S. Patent No. 5,485,225 issued

January 16, 1996 to Deter et al.

Fig. 5 is a perspective view of an embodiment of a scanning system that includes a flat deflecting mirror 510 that is moved by, for example, a galvonometer device to provide a vertical scan along the "y" axis and a polygon mirror 520 rotated at a constant speed to scan horizontally along the "x" axis. Fig. 5 shows the optical waveguides collected into a bundle 505 and supplied to the waveguide termination block 180. A collimator such as lens 530 collimates the output beams from the waveguide termination block 180 (i.e., the lens takes the ends of the fibers as the point sources and then collimates them so that the output beams are substantially parallel, propagating at small angles with respect to each other. The collimated output beams are directed to the rotating faces of the polygon mirror 520, from which they are directed to the deflecting mirror 510. The deflected light then enters an optical system 535 that projects it onto the screen 195. The laser beams remain substantially collimated between the collimator and the optical system

535 that projects it on the screen. Preferably, the optical system 535 not only focuses the deflected light on the screen, but it also enlarges the solid angle covered by the deflecting mirror, and thus, the distance between the screen and the deflecting mirror can be very short. To define the resulting image formed by the scanning system, the screen is divided into a series of horizontal raster lines 540, each including a predetermined number of pixels. SCANNING METHOD

Referring now to Figs. 1, 5, and 6, the image on the screen 195 is defined by a series of parallel raster lines 540, each having a predetermined number of pixels. The adjacent beams from the waveguide termination block 180 are first aligned by the scanning system 190 so that a raster line is aligned with the beam axis 230 (Fig. 2) defined by the waveguide termination block. So aligned, the scanning system then scans the beams across the raster line, thereby scanning the beams across each pixel location on the raster line in a continuous sequential manner. Then the next raster line is scanned. Any suitable order may be used to scan raster lines, for example the raster lines may be scanned from top to bottom, from side to side, or in a diagonal manner. A complete image is written when all raster lines have been drawn on the screen.

Using the method described herein, each complete pixel is written by sequentially superposing each of the modulated beams 185 on a single pixel location, and thus, each pixel on the screen is defined by the superposition of the beams at the respective pixel location. Accordingly, a viewer will perceive each pixel as the precise superposition of the outputs from all fibers; i.e. the viewer will perceive the three separate beams as a single pixel. To accomplish superposition, a delay between adjacent beams is provided, in order to compensate for the small distance between the beams. The amount of delay is chosen to synchronize with the scanning speed. As mentioned above, the adjacent beams should be as closely positioned as possible, which advantageously reduces the delay between the beams and reduces the necessary scanning speed. Furthermore, when the adjacent beams are more closely positioned, better resolution can be obtained due to reduced roll-off in the mirrors of the scanning system.

Reference is now made to Figs. 6A, 6B, and 6C to illustrate a method of writing a single pixel 610 using three modulated scanning beams 611, 612, and 613 supplied from the scanning system 190. The raster line 540 on the screen includes a predetermined number of pixels including the pixel 610. It should be clear that the scanning operation proceeds continuously across the raster line, preferably at a constant speed. For purposes of describing the scanning operation, as illustrated in Fig. 6A, writing the pixel 610 begins at a first time t, at which the first beam 611 is written on the pixel 610. Scanning continues across the screen until at a second time t₂ shown in Fig. 6B the second beam 612 is written on the pixel 610, then scanning continues until finally at a third time t₃ shown in Fig. 6C, the third beam 613 is written on the pixel 610, and at that point the pixel 610 has been completely written by the contributions of the three beams 611, 612, and 613.

Before being scanned, each of the scanning beams 61 1, 612, and 613 has been modulated in some way corresponding to the image and has also been modulated with a delay between adjacent beams. For example, to provide the image, each beam may be modulated in amplitude or, alternatively, each beam may be pulse width modulated. To provide the delay, the modulation signals supplied to the modulators may include the appropriate delay, or other suitable mechanisms may be used such as adjusting an acousto-optic modulator as described below with reference to Fig. 7. The delay, which is related to the scanning speed, is selected so that each beam will sequentially register its contribution at the location of the pixel 610, and therefore the pixel 610 will be viewed as a combination of the contributions written sequentially by each of the beams.

Although the above discussion describes writing only the single pixel 610, it is preferred that several pixels be written in parallel in order to more effectively and efficiently scan an image. For example, the three beams 611, 612, and 613 can be used during the continuous scanning operation to write the respective components of adjacent pixels in parallel: at the first time t, the first beam 611 writes the first pixel 610, the second beam 612 writes a second (adjacent, following) pixel 620 and the third beam 613 writes a third (adjacent, following) pixel 630. At a second time t₂ when the three beams have moved forward by one pixel, the first beam 611 writes a fourth pixel 640 that is adjacent and ahead of the first pixel, the second beam writes the first pixel 610, and the third beam writes the second pixel 620. The parallel scanning operation then continues for the remainder of the raster line and remainder of the scanning operation. The above display system has been described in terms of writing a single line on a screen; however, multiple lines can be written in parallel on the screen by duplicating the display system for each additional line desired to be written in parallel, as will be described later with reference to Fig. 10. Advantages of such a system include a slower polygon rotational speed, which can greatly help to reduce costs. SCANNING SYSTEM EXAMPLE

Reference is now made to Fig. 7, which is a schematic diagram of an example of an RGB laser scanning display system implemented with five solid state lasers including a red laser 701, a green laser 702, and three blue lasers 703, 704, and 705. In this example, the red and green lasers output substantially more power than a single blue laser, and therefore three blue lasers are utilized to increase the on-screen blue power level to approximately match the respective power levels of the red and green lasers. It should be apparent that Rg. 7 illustrates only one way in which additional lasers can be employed to increase power at one or more of the wavelengths, and therefore in any alternative embodiment the number and type of lasers can be selected to provide the desired power level and wavelength combination. In one implemented embodiment, three red lasers, one green laser, and three blue lasers are utilized to match the power at the respective wavelengths. In other alternative embodiments, one or more additional lasers could be employed to expand the spectrum of the image to include one or more wavelengths. For example, an infrared laser may be employed in addition to the standard red, green and blue lasers. In other alternative embodiments, as few as two laser beams could be used.

In Fig. 7, the beams from the lasers 701-705 are directed respectively to acousto-optic ("AO") modulators 711, 712, 713, 714, and 715. Conventional AO modulator optics are used with each AO modulator. The AO modulators 711-715 are connected to receive control signals 720 from the driver 725. Responsive to image signals

100, a processor 728 supplies modulated signals to the driver 725, which responsive thereto provides the desired red, green, and blue outputs from the lasers 701-705. Although the embodiment of Rg. 7 uses AO modulators, it should be apparent that alternative embodiments may utilize any suitable modulator or modulation technique; for example, an electro-optic modulator could be used, or for some applications even a liquid crystal may be used. The modulated light from the acousto-optic modulators 711-715 is coupled respectively via fiber coupling optics and SMA-type fiber connectors 741-745 into conventional singie mode cylindrical fiber optic cables 751-755. The optical fibers 751-755 are then brought together to form a fiber optic bundle 760 which is routed to a monolithic waveguide termination block 770. At an output face 775 of the waveguide termination block, the output ends of the fibers are arranged in a closely-positioned row along an axis 780 with a uniform spatial separation between the output ends thereby providing five output sources which are then imaged on the screen by the scanning system 190 as described elsewhere herein in detail. As also discussed elsewhere in more detail, it is advantageous for the spacing between fibers on the output face 775 to be as close as possible. In operation over time, the scanning system scans the output sources with their linear axis aligned with the scanning direction, in a series of raster lines across the screen. The monolithic nature of the waveguide termination block allows precise registration (overlapping) of each of the five sources on the screen.

In the preferred embodiment, the individual fibers at the output end of the waveguide termination block are closely spaced with a uniform spatial separation: in one embodiment the center-to-center separation is approximately twice the fiber core diameter. This close spacing results in minimal differential delays being required on the part of the AO modulators. For example, in a projection system that provides 1280 x 1024 resolution at 25 interlaced frames per second, with the center-to-center separation being approximately twice the fiber core diameter, the total spread in modulator delay is approximately 0.25 microseconds. Meanwhile, the instantaneous positional spread of the five spots along a raster line in the final image amounts to significantly less than one percent of the width of the image.

Preferably, the spatial separation between the fibers is uniform so that the delay interval between each of the output ends is equal; however, in alternative embodiments the separation between the fibers may be non-uniform (i.e., not equal between each adjacent fiber in the row), as long as the delay interval is adjusted accordingly. It may be useful, for example to accommodate one or more optical fibers that have a different diameter than the other optical fiber. In such an alternative embodiment, any variation in the spatial separation between the fibers in the row is accommodated by the delay mechanism that implements the delay interval between the output beams; in other words, if one of the optical fibers is separated from its adjacent optical fiber by a greater distance, then its corresponding delay interval is adjusted to be greater.

In a preferred embodiment, the differential time delay between the beams is obtained by adjusting the acoustic wave propagation across the aperture of each AO modulator laterally so as to achieve horizontal registration of the red, green, and blue images on the screen. Thus, the differential time delays required in this embodiment can be easily accommodated by the AO modulators, which must have a predetermined alignment in any event. In alternative embodiments, an adjustable electronic delay can be implemented by, for example, a FIFO circuit, which advantageously permits a common laser/modulator assembly to be adapted to the particular spatial separation implemented in the waveguide termination block without requiring mechanical adjustment.

In the example of Fig. 7, the associated solid state lasers, acousto-optic modulators, and fiber optic coupling devices are respectively assembled and enclosed in physically independent laser/modulator modules 791, 792, 793,

794, and 795 that comprise, for example, a metal housing. As a result each module 791-795 is a stand-alone device that outputs a modulated beam on its respective optical fiber responsive to signals from the driver. Advantageously, all free-space optical beams are confined within the modules 791-795, thereby reducing the need for extremely high stability and precise positioning in mounting each component in the assembly to its parent structure. Preferably, the modules 791-795 are designed to be completely sealed during manufacture, and therefore subsequent installation of the assemblies within a projection system requires no optical alignment whatsoever. In such an embodiment, replacement of modules in the field is straightforward and requires only an electronic technician rather than a more highly skilled ( and more costly) professional. At most, such a technician is required to set the differential time delay of each assembly such that it is consistent with the output location of the optical waveguide to which it is connected. In alternative embodiments, the lasers and their respective acousto-optic modulators can be situated in separate assemblies. In one such dual-assembly arrangement (not shown), the laser module includes a focusing lens together with a fiber optic connector which also serves as a seal to the outside environment, and the separate modulator assembly is provided with input and output fiber optic connectors, together with internal collimating and refocusing lenses. The modulator assembly may also be provided with an external means (electrical or mechanical) for setting the appropriate differential time delay. Advantages of the dual assembly approach over the single assembly lie in the greater commonality of parts and in the lower cost and lower complexity of components, which could make field replacement less costly. Disadvantages include higher insertion losses associated with additional fiber optic connectors in the beam path. Future growth of a laser scanning system can be straightforwardly accommodated by adding modulated laser beam sources and fibers. No specific limit exists on the number of optical fibers that can be incorporated into the waveguide termination block, and thus, provided the necessary space and power is available within the overall packaging design, the power or spectrum of a display system such as shown in Fig. 1 can be straightforwardly upgraded by, for example inserting one or more additional laser/modulator assemblies. Advantageously, such upgrades could be made in the field as well as in the factory, because the only significant post-installation adjustment relates to setting the differential time delay.

Reference is now made to Figs. 8 and 9. Rg. 8 is a perspective view of an alternative embodiment of the waveguide termination block 180, this embodiment including a plurality of waveguide channels 810 that begin on an input side 820 and end on an output side 830. The input side 820 is formed in any suitable configuration that facilitates coupling the modulated light beams into the optical waveguides, while the output side 830 is formed so that the output apertures have a predetermined linear configuration. Advantageously, this embodiment of the waveguide termination block allows extremely close positioning of the exit apertures 840. The waveguide channels are formed using any suitable technique such as lithography or ion implantation processes.

Fig. 9 is a plan view of the waveguide termination block of Fig. 8, illustrating a plurality of modulated beams from optical fibers 751-755 being coupled via a plurality of lenses 910 into the plurality of waveguide channels 810.

The embodiment of the waveguide termination block shown in Figs. 8 and 9 has five waveguide channels in order to correspond with the five laser/modulator assemblies shown in Fig. 7; in any particular embodiment the number of waveguide channels can be varied according to the number of modulated beams to be scanned by the scanning system. PARALLEL WRITE DISPLAY SYSTEM Reference is now made to Fig. 10, which is a block diagram of an embodiment of a parallel write display system for writing multiple lines in parallel on a screen. Advantageously, a parallel write system can write pixels at a faster rate and, hence, provide higher image resolution and/or a faster frame rate than a single line scanning system. Furthermore, a parallel write system can reduce scanning system requirements by allowing a slower polygon rotational speed and a slower galvonometer speed, all of which can greatly help to reduce costs. Broadly, the parallel-write display system includes two or more single-line display systems such as described above in which the corresponding rows of output ends are aligned to scan multiple rows in parallel. In Rg. 10, a first light modulating system 1010 supplies modulated laser light to a first optical fiber set 1015. The first light modulating system 1010 includes drivers, lasers, modulators, and optical waveguides (e.g. optical fibers) as described above for example with reference to Fig. 1, that are appropriate for scanning a line in response to image data (Fig. 1). As described in detail above, for example with reference to Fig. 6, the modulated laser beams have a delay between them selected so that each pixel is represented by a superposition of the modulated laser beams. The first optical fiber set 1015 is supplied to a waveguide termination block 180a that arranges the output ends of the optical fibers in a first row 1017. The embodiment of Fig. 10 shows seven optical fibers in the first row for illustration purposes; in any particular embodiment the number of optical fibers in a row will vary dependent upon a number of factors as described above, such as the desired on-screen power level at each wavelength. The scanning system 190 collimates the modulated light from the first row and scans it across the screen 195 in a direction aligned with the axis defined by the first row, to write a first raster line 540a. Similarly, a second light modulating system 1020 supplies modulated laser light to a second set of optical fibers 1025, which are routed to a second waveguide termination block 180b that arranges the output ends in a second row 1027 for writing a second raster line 540b, and a third light modulating system 1030 supplies modulated laser light to a third set of optical fibers 1035, which are routed to a third waveguide termination block 180c that arranges the output ends in a third row 1037 for writing a third raster line 540c. The waveguide termination blocks, shown collectively at 1040, are each arranged so that the first, second, and third rows are parallel, and spaced apart by a suitable predetermined distance. The rows are collectively collimated by an optical system such as a single lens 530 (Fig. 5), and scanned on the screen 195 by the scanning system 190. It should be apparent that any number of single-line display systems can be added to provide additional parallel writing capability within the physical limitations imposed by the scanning system and image data supplied thereto, dependent upon practical considerations such as cost constraints and size limitations.

In an alternative embodiment (not shown), a single waveguide termination block can be substituted for the multiple blocks 180a, 180b, and 180c to collect all sets of optical fibers and arrange them in a series of rows. Such a single waveguide termination block could provide a predictable spatial relationship between the rows of output ends and thereby provide accurate scanning of the multiple lines. Furthermore, the single waveguide termination block could position the rows very closely together, which could ease the optical requirements of the scanning systems.

It will be appreciated by those skilled in the art, in view of these teachings, that alternative embodiments may be implemented without deviating from the spirit or scope of the invention. For example, if a semiconductor laser were used instead of a solid state laser, modulation could be obtained by direct modulation of the control current, thereby eliminating the modulator as a separate optical element. This invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings.

Claims

CLAIMSWHAT IS CLAIMED IS:

1. A method of displaying an image on a screen using image data that defines a plurality of pixels, comprising the steps of: a) modulating a plurality of laser beams with said image data, including introducing a delay between each of the modulated laser beams; b) transmitting said plurality of modulated laser beams respectively through a plurality of optical waveguides; c) emitting said transmitted laser beams in a closely-positioned linear pattern that defines a linear axis; and d) scanning said linear pattern of laser beams on the screen along said linear axis, including the step of synchronizing the delay in the sequential modulation and the scanning speed of the linear pattern so that each pixel in the image is defined by superposing said modulated laser beams.

2. The method of claim 1 wherein said plurality of laser beams includes a first beam having a first wavelength and a first plurality of beams having a second wavelength, and said step of modulating said laser beams includes modulating said first beam and said first plurality of beams with said image data.

3. The method of claim 1 wherein said plurality of laser beams includes red, green, and blue laser beams and said step of modulating said laser beams include modulating said laser beams with image data representative of a full color image.

4. The method of claim 1 wherein said plurality of laser beams includes an infrared laser beam, and said step of modulating said laser beams includes modulating said infrared laser beam with image data representative of an infrared image.

5. The method of claim 1 wherein said modulated laser beams are transmitted respectively through a plurality of optical fibers having output ends arranged in a row, and said modulated laser beams are emitted from said row of output ends.

6. The method of claim 1 wherein said modulated laser beams are transmitted respectively through a plurality of optical fibers, then coupled respectively into a plurality of waveguide channels having output ends arranged in a row, and then emitted from said row of output ends.

7. The method of claim 1 wherein said step of synchronizing the delay in the sequential modulation of the laser beams includes electrically delaying the signals supplied to adjacent modulators.

8. The method of claim 1 comprising the step of modulating said laser beams in an acousto-optic modulator, and wherein said step of synchronizing the delay in the sequential modulation of the laser beams includes adjusting the acoustic wave propagation across the aperture of each acousto-optic modulator.

9. The method of claim 1 and further comprising the step of writing multiple pixels on the screen in parallel.

10. The method of claim 1 wherein said laser beams are emitted in a plurality of linear patterns that define a corresponding plurality of linear axes, and further comprising the step of scanning said plurality of linear patterns on the screen in parallel.

11. A method of displaying a full color image using image data, said image being defined by a plurality of pixel locations arranged in a series of raster lines on a screen, comprising the steps of: a) providing a plurality of laser beams including a red beam, a green beam, and a blue beam; b) modulating said laser beams with said image data, including introducing a delay between each of the modulated laser beams so that each pixel is represented by a sequential combination of modulated laser beams; c) coupling the plurality of modulated laser beams into input ends of a plurality of optical fibers; d) emitting the coupled laser beams from a waveguide termination block that arranges the output ends of the optical fibers in a linear pattern that defines a linear axis; and e) scanning said linear pattern of laser beams on the screen with said linear axis aligned with the raster lines, including the step of producing a pixel in a displayed image by sequentially superposing said modulated laser beams.

12. The method of claim 11 wherein said step of defining a pixel includes the step of synchronizing the delay in the sequential modulation and the scanning speed of the linear pattern

13. The method of claim 11 wherein said step a) further includes providing at least one additional laser beam that has spectral characteristics similar to one of said red, green, and blue beams.

14. The method of claim 11 wherein said step a) further comprises providing two additional blue beams.

15. The method of claim 11 wherein said plurality of laser beams includes an infrared laser beam, and said step of modulating said laser beams includes modulating said infrared laser beam with image data representative of an infrared image.

16. The method of claim 11 wherein said laser beams are modulated with a uniform delay interval, said modulated laser beams are transmitted respectively through a plurality of optical fibers having output ends arranged in a row having a uniform spatial separation, and said modulated laser beams are emitted from said row of output ends.

17. The method of claim 11 wherein said modulated laser beams are transmitted respectively through a plurality of optical fibers, coupled respectively into a plurality of waveguide channels having output ends arranged in a row, and then emitted from said row of output ends.

18. The method of claim 11 wherein said step of introducing a delay between each of the modulated laser beams includes electrically delaying the signals supplied to adjacent modulators.

19. The method of claim 11 and further comprising the step of modulating said laser beams in an acousto-optic modulator, and wherein said step of introducing a delay between each of the modulated laser beams includes adjusting the acoustic wave propagation across the aperture of each acousto-optic modulator.

20. The method of claim 11 and further comprising the step of writing multiple pixels on different raster lines on the screen in parallel.

21. A laser scanning display system for displaying an image on a screen using image data, comprising: a plurality of lasers; a plurality of modulators responsive to image data coupled to respectively modulate the beams from said plurality of lasers; delay means for introducing a delay interval between each of the laser beams; a termination block coupled to said plurality of modulators that situates the modulated laser outputs along at least one linear axis; and a scanning system that scans said modulated laser outputs along said at least one linear axis, said scanning system having the delay interval between said scanned beams synchronized with the scanning speed.

22. The display system of claim 21 wherein said scanning speed and delay interval are synchronized so that each pixel in the displayed image is produced by superposing each of said modulated laser beams.

23. The display system of claim 21 wherein said plurality of lasers includes a red laser, a green laser, and a blue laser.

24. The display system of claim 21 wherein said plurality of lasers includes a red laser, a green laser, and three blue lasers.

25. The display system of claim 21 wherein said plurality of lasers includes an infrared laser.

26. The display system of claim 21 wherein said plurality of lasers includes a first laser having a first wavelength and at least two lasers having a second wavelength.

27. The display system of claim 21 wherein said plurality of lasers includes a first laser having a first wavelength and at least three lasers having a second wavelength.

28. The display system of claim 21 wherein said delay means includes means for electrically modulating the modulation signals supplied to the modulators.

29. The display system of claim 21 wherein said modulators comprise electro-optic modulators.

30. The display system of claim 21 wherein said modulators comprise acousto-optic modulators.

31. The display system of claim 30 wherein said delay means includes means for adjusting the acoustic wave propagation across an aperture of at least one acousto-optic modulator.

32. The display system of claim 21 and further comprising a plurality of waveguides coupled between said plurality of modulators and said termination block, wherein said plurality of optical waveguides comprise a plurality of optical fibers, and said termination block situates the output ends of said optical fibers in said row so that modulated laser beams are emitted from said row of output ends.

33. The display system of claim 21 wherein said termination block includes a plurality of waveguide channels having input ends for receiving modulated laser beams and output ends arranged in said row so that said modulated laser beams are emitted from said row of output ends.

34. The display system of claim 21 and further comprising means for writing multiple pixels on the screen in parallel.

35. The display system of claim 21 wherein said waveguide termination block situates said modulated laser outputs in a plurality of linear patterns that define a corresponding plurality of linear axes, and said scanning system scans said plurality of linear patterns on the screen in parallel.

36. A laser scanning display system for displaying an image using image data on a screen arranged in a series of raster lines, comprising: a plurality of lasers, including a first laser that produces a first beam at a first wavelength, a second laser that produces a second beam at a second wavelength, and a group of at least two lasers that produce a group of beams at a third wavelength; a plurality of modulators responsive to image data, including a first modulator for modulating the first beam, a second modulator for modulating the second beam and a group of at least two modulators for modulating said group of beams at the third wavelength; delay means for introducing a delay interval between each of the modulated laser beams so that each pixel is represented by a sequential combination of said modulated laser beams; a plurality of optical fibers including an optical fiber for transmitting each of said modulated laser beams; coupling means for coupling the modulated laser beams into said optical fibers; a waveguide termination block that situates the modulated laser beams outputted from said optical fibers in a row that defines a linear axis; and a scanning system that scans the row of the waveguide termination block on the screen with said linear axis of the waveguide termination block aligned with the raster lines, said scanning system having the delay interval and the scanning speed synchronized so that each pixel in the image is defined by superposing each of said modulated laser beams.

37. The display system of claim 36 wherein said delay means includes means for electrically delaying the modulation signals supplied to at least one of said modulators.

38. The display system of claim 36 wherein said modulators comprise electro-optic modulators, and said delay means includes means for electrically delaying the modulation signals supplied to at least one of said electro-optic modulators.

39. The display system of claim 36 wherein said modulators comprise acousto-optic modulators, and said delay means includes means for adjusting the acoustic wave propagation across an aperture of at least one of said acousto-optic modulators.

40. The display system of daim 36 wherein said waveguide termination block situates the output ends of said optical fibers in an immediately adjacent configuration.

41. The display system of claim 36 wherein said waveguide termination block includes a plurality of waveguide channels having input ends for receiving modulated laser beams and output ends arranged in said row so that said modulated laser beams are emitted from said row of output ends.

42. The display system of claim 36 and further comprising means for writing multiple pixels on the screen in parallel.

43. The display system of claim 36 wherein said waveguide termination block situates said modulated laser outputs in a plurality of linear patterns that define a corresponding plurality of linear axes, and said scanning system scans said plurality of linear patterns to write a plurality of lines on the screen in parallel.

44. A laser scanning display system for displaying a full color image on a screen using image data, comprising: a plurality of lasers including a red laser, a green laser, and a blue laser; modulation means for modulating the beams from said plurality of lasers responsive to the image data; delay means for introducing a delay interval between each of the modulated laser beams so that each pixel is represented by a sequential combination of said modulated laser beams; a plurality of optical waveguides having an input end for receiving the modulated laser beams, and an output end for emitting said modulated laser beam; a waveguide termination block that situates said output ends in a row that defines a linear axis; and a scanning system that scans said modulated laser outputs along said linear axis, said scanning system having the delay interval between said scanned beams and the scanning speed synchronized so that each pixel in the image is defined by a sequential superposition of said modulated laser beams.

45. The display system of claim 44 wherein said plurality of lasers includes at least three blue lasers.

46. The display system of claim 45 wherein said plurality of lasers includes at least three red lasers.

47. The display system of claim 44 wherein said plurality of lasers includes at least one infrared laser.

48. The display system of claim 44 wherein said modulation means comprises electro-optic modulators.

49. The display system of claim 44 wherein said modulation means comprises acousto-optic modulators.

50. The display system of claim 49 wherein said delay means includes means for adjusting the acoustic wave propagation across the aperture of each acousto-optic modulator.

51. The display system of claim 44 wherein said optical waveguides comprise optical fibers, and said waveguide termination block situates the output ends of said optical fibers immediately adjacent to each other.

52. The display system of claim 44 and further comprising means for writing multiple pixels on the screen in parallel.

53. The display system of claim 44 wherein said waveguide termination block situates said modulated laser outputs in a plurality of linear patterns that define a corresponding plurality of linear axes, and said scanning system scans said plurality of linear patterns to write a plurality of lines on the screen in parallel.