Patent Publication Number: US-RE42251-E

Title: Projection-type display devices with reduced weight and size

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application claims priority under 35 U.S.C. §119(e) from co-pending U.S. Provisional Patent Application No. 60/487,692 filed Jul. 16, 2003, which is incorporated by reference herein for all purposes; this application also claims priority under 35 U.S.C. §119(e) from co-pending U.S. Provisional Patent Application No. 60/487,866 filed Jul. 16, 2003, which is incorporated by reference herein for all purposes; this application also claims priority under 35 U.S.C. §119(e) from co-pending U.S. Provisional Patent Application No. 60/487,753 filed Jul. 16, 2003, which is incorporated by reference herein for all purposes; and this application also claims priority under 35 U.S.C. §19(e) from co-pending U.S. Provisional Patent Application No. 60/487,867 filed Jul. 16, 2003, which is incorporated by reference herein for all purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to display devices that project an image. More particularly, the present invention relates to projection-type display devices that employ lasers for light generation. 
     DVD players, VCRs and computer systems such as desktop computers, laptop computers, and video game consoles use a display device to output video information. A number of display technologies are currently available, with cathode ray tube (CRT) monitors and liquid crystal display (LCD) screens being most popular. 
     Projection-type display devices—or ‘projectors’—that cast an image onto a receiving surface are a relatively new display technology, increasing in popularity, and offer image sizes having diagonal spans up to 30 feet. Market concerns for projectors include portability and longevity. 
     Conventional projectors employ a lamp, such as a metal halide lamp, to generate white light. One problem with a white-light emitting lamp is lifetime. Not only does a lamp burn out after about two thousand hours, but luminous power consistency often declines with lamp age. The high price of currently available projectors—and the cost of replacement lamps—compromises market acceptance and projector sales. 
     Based on the foregoing, it should be apparent that alternative light generation options for projection-type display devices would be desirable. 
     SUMMARY OF THE INVENTION 
     The present invention relates to display devices that provide projection-type video output and use diode lasers to generate light. For example, one set of diode lasers may produce red light, while a second set produces blue light. One or more lenses may be employed to reduce divergence in the laser light generated by each diode laser. Optics are employed to expand laser light from its small generated or transmitted flux area to a size suitable for transmission onto an optical modulation device. 
     In one aspect, the present invention relates to a projection-type display device. The display device comprises a first diode laser set. Each diode laser in the first diode laser set includes a) a lasing medium in a lasing chamber for producing first light including a first wavelength between about 400 nanometers and about 700 nanometers, and b) an output lens for emitting the first light. The display device also comprises a second diode laser set. Each diode laser in the second diode laser set includes a) a lasing medium in a lasing chamber for producing second light including a second wavelength between about 400 nanometers and about 700 nanometers, and b) an output lens for emitting the second light. The display device further comprises at least one optical modulation device configured to selectively transmit the first light and the second light according to video data included in a video signal provided to the at least one optical modulation device. The display device additionally comprises an optics system, arranged to receive the first light and the second light before receipt by the at least one optical modulation device, configured to increase flux area for the first light and the second light before receipt by the at least one optical modulation device. The display device also comprises a projection lens system configured to project light transmitted by the at least one optical modulation device along a projection path. 
     In another aspect, the present invention relates to a projection-type display device. The display device comprises a red diode laser set. Each red diode laser in the red diode laser set includes a) a lasing medium in a lasing chamber for producing light including a red wavelength between about 615 nanometers and about 690 nanometers, and b) an output lens for emitting the red light. The display device also comprises a blue diode laser set. Each blue diode laser in the blue diode laser set includes a) a lasing medium in a lasing chamber for producing light including a blue wavelength between about 420 nanometers and about 500 nanometers, and b) an output lens for emitting the blue light. The display device further comprises at least one optical modulation, an optics system configured to increase flux area for the light, and a projection lens system configured to project light along a projection path. 
     In another aspect, the present invention relates to a projection-type display device. The display device comprises a red diode laser set. Each red diode laser in the red diode laser set including a) a lasing medium in a lasing chamber for producing light including a red wavelength between about 615 nanometers and about 690 nanometers, and b) an output lens for emitting the red light. The display device also comprises a blue diode laser set. Each blue diode laser in the blue diode laser set including a) a lasing medium in a lasing chamber for producing light including a blue wavelength between about 420 nanometers and about 500 nanometers, and b) an output lens for emitting the blue light. The display device also comprises a third set of lasers, each laser in the third laser set including a) a lasing medium and lasing chamber for producing third light including a third wavelength between about 510 nanometers and about 570 nanometers, and b) an output lens for emitting the third light. The display device further comprises at least one optical modulation, an optics system configured to increase flux area for the light, and a projection lens system configured to project light along a projection path. 
     Another aspect of the invention relates to a redundant laser set to generate light. The laser set produces a desired amount of light, e.g., for a primary color. A redundant laser set includes more lasers than that needed to produce the desired amount of light. For example, a set of six lasers may only need five lasers to generate and emit the desired amount of light. The sixth laser allows failure of one laser in the set to not compromise operability of the entire set—and the display device. In addition, extra lasers in a laser set also allow the lasers to be cycled for heat purposes and to extend longevity of individual lasers in the set. 
     In yet another aspect, the present invention relates to a projection-type display device. The display device comprises a laser set for producing a desired amount of light. The laser set includes a plurality of lasers. The total number of lasers in the laser set is greater than a number of lasers needed to produce the desired amount of light. Each laser in the laser set produces light in a wavelength range related to a primary color. The display device also comprises control circuitry that determines which of the lasers in the set produces light. The display device further comprises an optical modulation device for selectively transmitting light according to video data included in a video signal provided to the optical modulation device. The display device additionally comprises an optics system, arranged to receive light produced by the laser set before receipt by the optical modulation device, for increasing flux area of the light. The display device also comprises a projection lens system for projecting light transmitted by the optical modulation device along a projection path. 
     In a method aspect, the present invention relates to a method for producing light in a projection-type display device including a plurality of lasers. Each laser in the laser set produces light in a wavelength range related to a primary color. The method also comprises determining which of the lasers in the laser set will produce a desired amount of light. The method further comprises producing the desired amount of light using a number of lasers in the laser set that is less than the total number of lasers in the laser set. 
     In another method aspect, the present invention relates to a method for producing an image using a projection-type display device. The method comprises producing a desired amount of light using a number of lasers in a laser set that is less than the total number of lasers in the laser set. Each laser in the laser set produces light in a wavelength range related to a primary color. The method also comprises increasing flux area of the light before transmission to an optical modulation device. The method further comprises selectively transmitting light according to video data included in a video signal provided to the optical modulation device. The method additionally comprises outputting light transmitted by the optical modulation device along a projection path. 
     To reduce any speckle effects for a projected image cast by a projector onto of a non-specular surface, the present invention may decrease coherence of laser-generated light. In one embodiment, coherence reduction is accomplished by introducing a coherence diffuser in a light path of the laser light. Arranging the coherence diffuser in an unfocused light beam reduces both temporal and spatial coherence in the light. Arranging the rotating diffuser at the focus of a beam reduces only the temporal coherence while maintaining the spatial coherence. 
     In one aspect, the present invention relates to a projection-type display device. The display device comprises a set of lasers for producing light. The display device also comprises a coherence diffuser arranged to intercept light produced by the lasers and to reduce coherence in the light. The display device further comprises at least one optical modulation, an optics system configured to increase flux area for the light, and a projection lens system configured to project light along a projection path. 
     These and other features of the present invention will be presented in more detail in the following detailed description of the invention and the associated figures. 
     Before committing to the Detailed Description, it may facilitate understanding to clarify certain words and phrases used in this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, be proximate to, be bound to or with, have, have a property of, or the like. Support and definitions for certain words and phrases are provided throughout this patent document, and those of ordinary skill in the art should understand that in many, if not most instances, such support applies to prior, as well as future uses of such words and phrases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a schematic of a projection type display device in accordance with one embodiment of the present invention. 
         FIG. 2A  illustrates a simplified diode laser in accordance with a specific embodiment of the present invention. 
         FIG. 2B  illustrates a DPSS laser schematic in accordance with a specific embodiment of the present invention. 
         FIG. 3  illustrates a circuit board with multiple diode lasers installed thereon in accordance with one embodiment of the present invention. 
         FIG. 4A  illustrates a common fiber-optic cabling arrangement in accordance with a specific embodiment of the present invention. 
         FIG. 4B  illustrates a display device in which multiple fiber optic cables transmit light from three laser sets to three light optical modulation devices in accordance with one embodiment of the present invention. 
         FIG. 5A  illustrates a process flow for producing light in a projection-type display device in accordance with one embodiment of the invention. 
         FIG. 5B  illustrates a process flow for producing an image using a projection-type display device in accordance with one embodiment of the invention. 
         FIG. 5C  illustrates a process flow for using a projection-type display device that employs a set of lasers including a plurality of lasers to produce light in accordance with one embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described in detail with reference to a few preferred embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention. 
       FIG. 1  illustrates a schematic of a projection type display device  10  in accordance with one embodiment of the present invention. Display device  10  is configured to produce and project a video image for display on a receiving surface. Display device  10  employs lasers to generate light. In one embodiment, display device  10  uses three sets of lasers—one for each primary color. As shown, display device  10  comprises a red diode laser set  12 , a green laser set  14 , a blue laser set  16 , housing  20 , optical modulation device  44 , fans  62 , power supply  66 , fiber-optic interface  70 , fiber-optic cabling  72 , input/output circuitry  74 , control circuitry  76 , input/output interfaces  78 , coherence diffuser  82 , relay optics  80 , prism structure  110  and projection lens system  112 . 
     Housing  20  defines outer dimensions of display device  10  and an inner chamber  65  within display device  10 . Housing  20  also provides mechanical protection for internal components of display device  10 . As shown, housing  20  comprises four walls  22 a-d, a top wall (not shown), and a bottom wall (not shown). Walls  22  define an inner chamber  65  within housing  20 . Walls  22 a-d comprise a suitably stiff material that grants structural rigidity for display device  10  and mechanical protection for internal components within housing  20 , such as a metal or molded plastic. One or more walls  22 a-d of housing  20  may also include air vents  24  that permit airflow between chamber  65  and an environment external to housing  20 . Vents  24  may also be placed on the top and bottom walls of housing  20 . 
     Power supply  66  provides electrical power to lasers in sets  12 ,  14  and  16  and other components within display device  10  that consume electrical power. Thus, power supply  66  may provide electrical energy to control circuitry  76 , input/output circuitry  74 , fans  62  and optical modulation device  44 . A power cord port  81  receives a power cord, which couples power supply  66  to an AC power source such as a wall power supply. In one embodiment, conversion of AC power to DC power occurs in a transformer included between ends of the power cord, as is common with many laptop computer power cords, thereby reducing the size of power supply  66  and display device  10  and increasing the portability of display device  10 . 
     In another embodiment, power supply  66  comprises at least one rechargeable battery  66 a. Battery  66 a may be recharged using power provided through inlet port  81 . Battery  66 a allows display device  10  to operate on stored energy and without reliance on proximity to an AC power source, which further increases portability of display device  10 . For example, inclusion of a battery in housing  20  extends display device  10  usage to settings where AC and fixed power outlets are not available or within reach. 
     Lasers as described herein, such as those included in sets  12 ,  14  and  16 , produce laser light having a wavelength between about 400 nanometers and about 700 nanometers, which is generally accepted as the visible spectrum. Laser light refers to light that is generated using a lasing mechanism, which in some cases may be manipulated after initial generation to achieve a desired frequency, as will be described in further detail below. Red diode laser set  12 , a blue laser set  14 , and green laser set  16  produce red, green and blue laser light, respectively. 
     In one embodiment, each laser emits substantially collimated light. Collimated light differs from radiant light (e.g., from a lamp or light emitting diode) and is characterized by light that travels in about the same direction. Laser light emitted from each laser in sets  12 ,  14  and  16  may also be characterized as coherent. The coherency of laser light relates to the constancy of the spatial and temporal variations in the light or radiation wave fronts. A high degree of coherence implies a substantially constant phase difference between two points on a series of about equal amplitude wave fronts (spatial coherence); and a correlation in time between the same points on differently wave fronts (temporal coherence). If a laser beam is considered as a plane wave traveling in one direction, it is spatially coherent due to the perpendicularity of wave fronts in the direction of propagation. Also, due to the roughly monochromatic nature of laser light emitted from lasers as described herein, the beam is generally temporally coherent, that is, it will display an about fixed phase relation between a portion of the beam emitted at one time and a portion emitted at another. 
     Red diode laser set  12  is designed or configured to produce red light for use in display device  10 . In one embodiment, each diode laser in red diode laser set  12  generates and emits red light including a wavelength between about 615 and about 690 nanometers. In a specific embodiment, each diode laser in red diode laser set  12  includes a lasing medium and laser cavity configured to generate and emit light including a wavelength between about 625 and about 645 nanometers. Red diode lasers suitable for use in red laser set  12  will be described in further detail with respect to FIG.  2 A. 
     Green laser set  14  is designed or configured to produce green light for use in display device  10 . In one embodiment, each laser in green laser set  14  emits light including a wavelength between about 510 and about 570 nanometers. In a specific embodiment, green diode laser set  14  comprises green laser light emitting diode pumped solid state lasers that each emit green light including a wavelength between about 530 nanometers and about 550 nanometers. Green diode pumped solid state lasers suitable for use in green laser set  14  are described in further detail with respect to FIG.  2 B. 
     Blue laser set  16  is designed or configured to produce blue light for use in display device  10 . In one embodiment, each laser in blue laser set  16  emits blue light including a wavelength between about 420 and about 500 nanometers. In a specific embodiment, blue laser set  16  includes blue diode lasers and each blue diode laser comprises a lasing medium and laser cavity for generating and emitting light including a wavelength between about 430 and about 460 nanometers. Blue diode lasers suitable for use in blue laser set  16  are described in further detail with respect to FIG.  2 A. In another embodiment, blue laser set  16  includes blue laser light emitting diode pumped solid-state lasers, which are described in further detail with respect to FIG.  2 B. 
     In general, the combined power of lasers for each color set may be adapted according to a desired light intensity output for display device  10  and according to the light sensitivity of a viewer to each red, green and blue color, as one skilled in the art will appreciate. The power of an individual laser in a set may vary with design; while the number of lasers in each laser set  12 ,  14  and  16  will vary with the output power of individual lasers used in the set. Further description of the total power for each color, power output from each laser and the number of lasers in each set  12 ,  14  and  16  is described below with respect to FIG.  3 . 
     Returning back to  FIG. 1 , each laser is installed on a circuit board  430 , which mounts each laser installed thereon. Circuitry disposed on each board provides electrical communication for each laser installed on a board  430 . Multiple lasers may be mounted on a single board  430  to reduce space occupied by laser sets  12 ,  14  and  16 . In one embodiment, circuit boards  430  are vertically arranged to permit passive cooling of boards  430  and each laser disposed thereon when display device  10  is turned off and fans  62  are not moving air through chamber  65 . In addition, as described below, circuit boards  430  may be arranged parallel to a major direction of air flow through chamber  65  such that the air passes along both opposing wide area surfaces of each circuit board  430 . The boards may also include one or more heat sinks in heat conduction communication with a laser, for cooling boards  430  and individual lasers. 
     In one embodiment, each laser in sets  12 ,  14  and  16  includes a sensor that provides feedback regarding laser performance. For example, diode lasers in red diode laser set  12  may include a photodiode chip that provides optical feedback from each diode laser. Information from each photosensor is then provided to control circuitry  76  to provide an indication of laser output for each set  12 ,  14  and  16 . 
     Control circuitry  76  provides control signals to components within display device  10 , and may route data from input/output circuitry  74  to appropriate components within display device  10 . Thus, lasers in sets  12 ,  14  and  16  receive control signals from control circuitry  76  that regulate when each laser is turned on/off. More specifically, control circuitry  76  receives video data included in a signal via one or more input ports  78  and input/output circuitry  74 , converts the video data to pixel data on a sequential color frame basis, and delivers the sequential color pixel data to the optical modulation device  44  and to each diode laser. In a combined light transmission path design between lasers in sets  12 ,  14  and  16  and optical modulation device  44  where light is transmitted along a common light path that transmits red, green and blue light in a sequential red, green and blue order, control circuitry  76  synchronizes the timing of colored data sent to optical modulation device  44  and on/off commands sent to red, green and blue lasers  12 ,  14  and  16 , respectively. 
     Control circuitry  76  may also include and access memory that stores instructions for the operation of components within display device  10 . For example, stored heat regulation instructions may specify control signals sent by control circuitry  76  to fans  62 . One or more temperature sensors may also be disposed within housing  20  to facilitate thermal regulation. For example, a temperature sensor may be disposed proximate to circuitry  74  and  76  to monitor temperature levels and participate in closed loop temperature control within display device  10  as determined by stored logic implemented by control circuitry  76 . Alternately, temperature sensors arranged for each diode laser may sense temperature levels for each laser and output information that affects fan  24  usage based on stored instructions for desired diode laser temperature levels. Control circuitry  76  may comprise a commercially available processor, controller or microprocessor such as one of the Intel or Motorola family of chips, for example. 
     Input ports  78  are configured to receive at least one cable, wire, or connector, such as a cable for transmitting a video signal comprising video data from a digital computing device. Common ports suitable for use with input ports  78  include ports that receive S video cable, 6-pin mini DIN, VGA 15-pin HDDSUB, an audio cable, component RCA through an S-Video adaptor, composite video RCA cabling, a universal serial bus (USB) cable, fire wire, etc. Ports  78  may also include an audio output port for receiving a wired connection from speakers included in a headphone or speaker system. 
     Input/output circuitry  74  provides an interface between control circuitry  76  and one or more interfaces from ports  78 . Input/output circuitry  74  and input ports  78  collectively permit communication between display device  10  and a device that outputs a video signal carrying video data. For example, desktop computers, laptop computers, video game consoles, digital cameras, handheld computers, digital video recorders, DVD players, and VCRs, may all output video data to display device  10 . Video data provided to control circuitry  76  may be in a digital or an analog form (e.g., from a VCR). In some cases, input/output circuitry  74  and control circuitry  76  convert analog video signals into digital video signals suitable for digital control of an optical modulation device included in display device  10 , such as a liquid crystal display “LCD” device or a digital micromirror “DMD” device. Input/output circuitry  74  or control circuitry  76  may also include support software and stored logic for particular connector types, such as processing logic required for S-video cabling or a digital video signal. Control circuitry  76  includes or accesses stored logic in memory to facilitate conversion of incoming data types and enhance video compatibility of display device  10 . Suitable video formats having stored conversion instructions within memory accessed by control circuitry  76  may include NTSC, PAL, SECAM, EDTV, and HDTV (1080i and 720p RGBHV), for example. 
     Fans  62 a and  62 b move air through inner chamber  65  of housing  20  for cooling components of display device  10 . In one embodiment, fans  62  draw air in through inlet air vents  24 a on one side of housing  20  and exhaust heated air out of exhaust air vents  24 b after the air has cooled internal components of display device  10  and walls of housing  20 . One skilled in the art will appreciate that fan  62  and vent  24  placement will vary with internal component placement within light source chamber  65 . Specifically, fan  62  placement—and airflow patterns affected by fans  62  within chamber  65 —is designed according to individual temperature regulation requirements and heat generation contributions of components within housing  20 . Typically, laser sets  12 ,  14  and  16  and power supply  66  generate the largest proportion of heat within housing  20 , while control circuitry  76 , optical modulation device  44  and input/output circuitry  74  represent temperature regulation priorities. Correspondingly, inlet air  69  passes in through inlet air vents  24 a, initially passes and cools optical modulation device  44 , control circuitry  76  and input/output circuitry  74  while the air is relatively cool, passes across power supply  66  and lasers  12 ,  14  and  16 , and exits out exhaust air vents  24 b. The exhaust air may also cool fan motors  63 a and  63 b, which rotate fans  62 a and  62 b, respectively. In one embodiment, multiple fans  62  are used to permit a lower profile for housing  20 . As one skilled in the art will appreciate, the number and size of fans  62  used will depend on heat generation within display device  10  and a desired airflow to maintain one or more heat dissipation goals. Chamber  65  may also include one or more vertical or horizontal airflow guides  67  within light source chamber  65  to direct and distribute airflow as desired. In one embodiment, circuit boards  430  for lasers  12 ,  14  and  16  are vertically arranged perpendicular to the direction of airflow within chamber  65  and airflow guides  67  are arranged to direct cooling air across the surfaces of each circuit board  430 . 
     In one embodiment, light output from lasers in each set  12 ,  14  and  16  is provided to fiber-optic cabling  72 . Fiber-optic cabling  72  includes one or more fiber optic cables configured to transmit light from lasers in sets  12 ,  14  and  16  along multiple or common optical paths to relay optics system  80 , which is disposed along a light path between an exit end of fiber-optic cabling  72  and an optical modulation device  44 . Each cable  72  comprises an inlet end  72 a configured to receive light from a laser in one of the sets  12 ,  14  and  16  and an outlet end  72 b configured to outlet the laser light for transmission to relay optics system  80 , and subsequent transmission to optical modulation device  44 . Since fiber-optic cabling  72  may be bent and flexibly positioned, cabling  72  advantageously permits light transmission between lasers in sets  12 ,  14  and  16  and relay optics system  80  regardless of the positioning and orientation between the laser sets and optics system  80 . For example, this allows flexible arrangement of lasers in sets  12 ,  14  and  16 , relay optics system  80  and prism  110 , which may be used to improve space conservation within housing  20 , decrease the footprint of housing  20 , and minimize display device  10  size. 
     The number of fiber optic cables in cabling  72  will vary with design. Multiple fiber-optic cables may be employed in a design where each cable services one or more lasers. Multiple fiber-optic cables may be employed in a design where each cable is configured to transmit a primary color. For example, three fiber-optic cables may be employed in which each cable transmits light from a primary color set  12 ,  14  and  16  along three different optical paths to three primary color dedicated optical modulation devices. Alternately, as shown in  FIG. 1 , a common fiber-optic cable may be used to transmit sequentially emitted red, green and blue light along a common light path to a single mirror-based optical modulation device  44 . Fiber-optic cabling  72  may comprise single mode or multimode fibers such as those readily available from a wide variety of vendors known to those skilled in the art. In some cases, a converging lens is disposed at outlet end  72 b when fiber-optic cable  72  is a single mode fiber to correct for any divergence resulting from light transmission within the single mode fiber-optic cable  72 . 
     Fiber optic interface  70  is configured to facilitate transmission of light from each laser into fiber-optic cabling  72 . Interface  70  may include one or more fixtures that position and hold an inlet end for each fiber-optic cable included in cabling  72  such that light output from each laser transmits into a fiber-optic cable. Interface  70  may also include optics that direct light from the lasers into cabling  72 . In one embodiment, a single fiber-optic cable is used in cabling  72  and fiber optic interface  70  includes a lens system disposed between the outlet of each laser and the inlet of the single fiber-optic cable to direct light from each laser into the single cable. The lens system may comprise at least two lenses: a first lens to direct the light towards the fiber entrance and a second lens that re-collimates light entering the cable. In another embodiment that implements a one-to-one laser to fiber-optic cable  72  relationship, fiber optic interface  70  holds the inlet end for each fiber-optic cable  72  relatively close to the outlet of a single laser to receive light therefrom. Each cable in this case may include a converging lens at its inlet end that facilitates light capture and transmission into the fiber-optic cable. In a specific one-to-one embodiment, each fiber-optic cable in cabling  72  includes a fixture that permits attachment to a laser. For example, conventionally available fiber-optic cables available from vendors such as Ocean Optics Inc. of Dunedin, Fla. include a detachable fixture with a thread that allows screwing and fixing of the fiber-optic cable to a mating thread disposed on a laser housing. In this case, interface  70  comprises the threaded fixture for each fiber-optic cable and a mating thread is added to the laser housing. 
     In a common light path transmission embodiment, light from lasers in each set  12 ,  14  and  16  travels along a common path before receipt by optical modulation device  44 . In this case, red, green and blue light is provided to fiber-optic cabling  72  in a time synchronous manner that corresponds to red, green and blue video data provided in a video signal to optical modulation device  44 . One suitable common light path transmission embodiment is described below with respect to FIG.  4 A. In a multiple light path transmission embodiment, separate fiber-optic cables  72  are provided for red light, blue light and green light from red, green and blue laser sets  12 ,  14  and  16 , respectively, to multiple optical modulation devices  44 . One suitable multiple light path transmission embodiment is described below with respect to FIG.  4 B. 
     In one embodiment, the outlet end  72 b of fiber-optic cabling  72  is positioned and held by an interface  104  such that outlet end  72 b outputs light to relay optics system  80 . In one embodiment, interface  104  secures fiber-optic cable  72  such that slack is provided in fiber-optic cabling  72  between attachment at the interface and attachment at fiber optic interface  70 . The outlet interface  104  may comprise a suitable rigid material such as a molded plastic that is dimensioned to achieve a desired position of outlet end  72 b relative to optics system  80 . Together, fiber-optic cable  72  and the outlet interface  104  direct light generated by light source  64  to optics system  80 . 
     In a specific embodiment, the present invention includes display devices that provide projection-type video output in a portable and flexible design. The design includes a projection chamber, a base, and an interface that permits relative positioning between the projection chamber and base. Suitable examples of flexible display devices are described in commonly owned co-pending patent application naming William J. Plut as inventor, filed on the same day as this application and entitled “POSITIONABLE PROJECTION DISPLAY DEVICES”. This application is incorporated by reference in its entirety for all purposes. 
     Optics system  80  converts light received from fiber-optic cabling  72  to light flux suitable for transmission onto optical modulation device  44  via prism structure  110 . This may include shaping and resizing light flux received from cable  72  using one or more lenses, and may include homogenizing intensity across the light flux distribution. To do so, optics system  80  may comprise one or more lenses suitably spaced and arranged within housing  20 . In one embodiment, lens  80 a is selected and arranged to increase the area of light flux received from fiber-optic cable  72 , while lens  80 b is selected and arranged to convert the divergent light transmitted by lens  80 a into substantially collimated flux for transmission onto optical modulation device  44 . 
     Some projected images produced by a display device that uses lasers for light generation may encounter speckle effects. Speckle is an interference pattern produced when laser light strikes a non-specular surface (a rough surface relative to the wavelength of light). Speckle effects are caused by interference between superimposing waves of coherent light reflected from the non-specular reflecting surface. Since laser light is generally monochromatic and in phase (coherent), when the light is scattered by the non-specular reflecting surface, it becomes out of phase and the waves collide. When two waves out of phase collide, e.g., a wave at a high peak and another at a low peak, the two waves superimpose and may cancel each other out—resulting in a dark space. Cumulatively, speckle often produces a three-dimensional pattern of light and dark spaces, perceivable to a viewer as a dark pattern or spots around the projected image. Speckle may detract from the quality and appearance of the laser-based projected output. Generally, any laser with coherence properties may produce speckle effects. An incandescent light bulb, non-lasing light emitting diode, or white light lamp may also produce speckle effects, however, the speckle effects for these light sources are generally in the micrometer range (or less) and well below perception levels of human vision. Laser speckle, on the other hand, often results in interference patterns in the millimeter range and within human perception levels. 
     In one embodiment, the present invention reduces potential speckle effects for a projected image produced using laser light. To do so, the present invention reduces coherence of the laser light to diminish any potential speckle that results from reflection of the projected image off of a non-specular surface. This may be accomplished by introducing a coherence diffuser in the light path of the laser light within display device  10 . In a specific embodiment, the coherence diffuser is a rotating or vibrating diffuser, such as a transparent rotating glass or plastic screen introduced into the light path. Arranging the coherence diffuser in an unfocused beam reduces both temporal and spatial coherence. Arranging the rotating diffuser at the focus of a beam reduces only the temporal coherence—while maintaining the spatial coherence (the ability for the beam to be focused to a point). 
     Referring back to  FIG. 1 , a rotating diffuser  82  is disposed between lenses  80 a and  80 b. Rotating diffuser  82  comprises a transparent glass screen  84  that is rotated by a motor  86 . As shown in  FIG. 1 , rotating diffuser  82  intercepts an unfocused beam, thereby reducing both temporal and spatial coherence, and reducing potential speckle in the output image. In another embodiment, rotating diffuser  82  is introduced into the light path between the exit the fiber optic cabling  72  and before receipt by lens  80 a. 
     One skilled in the art will appreciate that rotating diffuser  82  may be arranged in other locations along the light path between generation of laser light in laser sets  12 ,  14  and  16  and output of the projected image from projection lens  112 c. For example, rotating diffuser  82  may be arranged proximate to a junction where light from multiple fiber optic cables is transmitted into a common fiber optic cable (FIG.  4 A). In this case, rotating diffuser  82  may be arranged at the focus of a beam to only reduce temporal coherence—while maintaining the spatial coherence (the ability for the beam to be focused to a point). Rotating diffuser  82  may also be arranged to intercept light between a laser and a fiber optic coupling, or between a final relay lens and prism  110 , for example. In one embodiment, the coherence diffuser is arranged to intercept laser light before it is expanded in flux area by any relay optics. Intercepting a small flux area light beam reduces the size of the glass screen  84  and coherence diffuser motor  86 . 
     In one embodiment, optics system  80  comprises a pair of fly-eye lenses arranged in the optical path between lasers in sets  12 ,  14  and  16  and prism  110 , such as between lens  80 b and prism  110 . Cumulatively, the pair of fly-eye lenses re-distribute light uniformly across the flux transmitted onto optical modulation device  44 . The first fly-eye lens includes a plurality of lenses that spatially divide input light flux (e.g., from lens  80 b) into a set of blocks or components that each comprise a portion of the total inlet flux area, and transmits light for each block to a corresponding block in the second fly-eye lens. The second fly-eye lens includes a plurality of lenses, the number of which is the same as the number of lenses in the first lens, and outputs light for each component to an object region to be illuminated in such a manner that the partial luminance fluxes from each lens are superimposed on each other at the object region. 
     In another embodiment, optics system  80  comprises an integrator tunnel disposed in the optical path between lasers in sets  12 ,  14  and  16  and prism  110 , such as between lens  80 b and prism  110 . The integrator tunnel uses total internal reflection to output luminous flux with an about uniformly distributed intensity across a shape determined by an output geometry at output end, which is typically rectangular. The outlet may also be dimensioned to match the aspect ratio of the downstream optical modulation device  44 . The integrator may comprise a solid glass rod such as those known and used in the art. If required, one or more lenses may be arranged to re-size flux output by the integrator tunnel from a size that exists at an output end to a size that is suitable for reception by optical modulation device  44 . 
     Prism structure  110  provides light to optical modulation device  44  at predetermined angles, and transmits light from optical modulation device  44  to the projection lens system  112  along output path  31 . Prism structure  110  comprises prism components  110 a and  110 b that are separated by air space or bonding interface  110 c. Interface  110 c is disposed at such an angle so as to reflect light provided from optics system  80  towards optical modulation device  44 . In addition, interface  110 c allows light reflected by optical modulation device  44  to transmit to projection lens system  112  along output path  31 . 
     Optical modulation device  44  selectively transmits light to provide an output image along output light path  31 . To do so, optical modulation device  44  is supplied with video data included in a video signal and selectively transmits light according to the video data. The video data is typically provided to device  44  on a frame-by-frame basis according to individual pixel values. If the video data is not received by display device  10  in this format, control circuitry  76  in housing  20  converts the video data to a suitable format for operation of optical modulation device  44 . In one embodiment, individual light modulation elements within optical modulation device  44 , which each correspond to an individual pixel on the output image, translate received digitized pixel values into corresponding light output for each pixel. 
     In one embodiment, optical modulation device  44  is a mirror based spatial light modulator, such as a digital micromirror device (or DMD, a trademark of Texas instruments Inc.) commercially available from Texas Instruments, Inc. Any XGA or SVGA resolution chip in the SDR or DDR series is suitable for use with the present invention. In this case, optical modulation device  44  comprises a rectangular array of tiny aluminum micromechanical mirrors, each of which individually deflects about a hinged axis to selectively reflect output image light down output path  31 , and reflect non-image light away from output path  31 . The deflection state or angle of each mirror is individually controlled by changing memory contents of an underlying addressing circuit and mirror reset signal. The array of mirrors is arranged such that each mirror is responsible for light output of a single pixel in the video image. Control signals corresponding to pixel output are supplied to control electrodes disposed in the vicinity of each mirror, thereby selectively deflecting individual mirrors by electromagnetic force according to video data on a pixel by pixel basis. Light reflected by each mirror is then transmitted along output light path  31 , through prism structure  110 , and out of display device  10  using projection lens system  112 . 
     The arrangement of optics system  80  and the faces of prism structure  110  control the illumination angles for optical modulation device  44 . After light reflection by individual mirrors of optical modulation device  44 , reflected light exits prism structure  110  towards lenses  112  along output optical path  31 . Output projection path  31  characterizes a) the direction of image light selectively transmitted by optical modulation device  44  within display device  10 , and b) the direction of light output from display device  10 . For light selectively transmitted by optical modulation device  44 , path  31  extends as a straight line from optical modulation device  44  for elements in their ‘on’ state, through prism structure  110 , and out projection lens  112 c. 
     A projection lens system  112  is disposed along output path  31  configured to project light transmitted by the optical modulation device along path  31  from display device  10 . Projection lens system  112  manipulates image light transmitted by optical modulation device  44  along output path  31  such that a projected image cast on a receiving surface enlarges as distance from output lens  112 c to the receiving surface increases. Projection lens system  112  comprises lenses  112 a,  112 b and external lens  112 c, each of which is disposed centrically along and orthogonal to output light path  31 . Distances between each lens  112  may vary with a desired splay angle from output lens  112 c, as may the number of lenses  112  used. In one embodiment, display device  10  is designed for a short throw distance, such as between about six inches and about 15 feet. Display device  10  may also include one or more buttons or tools that allow a user to manually focus and manually zoom output from projection lens system  112 . 
     In operation, light generated by lasers in sets  12 ,  14  and  16  is collected by and transmitted within fiber-optic cables  72 . Relay lenses  80 a and  80 b convert light transmitted by fiber-optic cable  72  to a luminous flux size suitable for transmission onto optical modulation device  44  via reflection within prism  110 . Light propagating through prism component  110 a reflects off a surface  110 d at interface  110 c by total internal reflection and forms a reflected pre-modulated beam directed towards optical modulation device  44 . The reflected pre-modulated beam travels through prism component  110 a to reach optical modulation device  44 , which selectively transmits light according to video data in a signal that corresponds to an image to be projected. Each mirror in optical modulation device  44  reflects light in its ‘on’ state back into prism component  110 a and through interface  110 c without internal reflection such that the light propagates into prism component  110 b and out an exit face  110 e of prism  110 . Light output through exit face  110 e is characterized by optical path  31 , which propagates through one or more projection lenses  112  that manipulate image light for enlarged display onto a screen or suitable receiving surface. Typically, the image is cast with a splay angle such that the image enlarges as the distance to a receiving surface increases. 
     In one embodiment, red and/or blue laser sets  12  and  16  comprise one or more diode lasers.  FIG. 2A  illustrates a diode laser  400  in accordance with a specific embodiment of the present invention. As the term is used herein, a diode laser refers to a device, system or module that outputs laser light and employs a semiconductor to generate the laser light. Diode laser  400  is also commonly referred to as a semiconductor laser, a laser diode or injection laser. Diode laser  400  comprises lasing medium  402 , output lens  404 , lasing chamber  408 , monitor photodiode chip  412 , housing  414 , leads  416 , control circuitry  418  and correction lens  420 . 
     Lasing medium  402  includes a charge carrier in a semiconductor and generates laser light according to a lasing mechanism. The lasing mechanism, or lasing action, refers to the process by which laser light is generated by diode laser  400 . In one embodiment, lasing medium  402  comprises a material which can be excited to a higher or metastable energy state in which atoms or molecules can be trapped after receiving energy from a pumping system. As a first atom or molecule in the higher state decays, it triggers via stimulated emission, the decay of another atom or molecule in a higher state. When one of the decaying atoms or molecules releases a photon parallel to the axis of the lasing material, it triggers the emission of other photons, all of which will be reflected by reflective faces  409  in the lasing chamber  408 . 
     Lasing chamber  408  contains lasing medium  402  and opposing reflective faces  409  disposed on opposite ends of the lasing chamber. Lasing chamber  408  and reflective faces  409  cumulatively provide a resident cavity in which laser light is generated. For a side emitting design, the reflecting faces  409  allow stimulated light to bounce back and forth through the lasing medium  402  to increasingly generate laser light. For small, edge emitting diode lasers, lasing chamber  408  may be formed inside the semiconductor diode laser chip itself and reflective faces  409  may include cut surfaces of the semiconductor crystal. Alternately, reflective faces  409  may comprise an optically ground, polished and/or coated material. For example, one or both of reflective faces  409  may be anti-reflection coated with external mirrors are added. One of the reflective faces  409  is semitransparent and permits the escape of light from lasing chamber  408  for output of an initial laser beam  415 . 
     For diode laser  400 , the wavelength output light is determined by the lasing medium  402  material and the geometry of lasing chamber  408 . For a red diode laser, lasing medium  404  often comprises two layers of semiconductor material sandwiched together on a semiconductor chip  406  in lasing chamber  408 . Galluium-Arsenide is one suitable lasing medium used to generate red laser light, while other semiconductor materials may be used to generate a desired wavelength of laser output. 
     In one embodiment, a beam from the diode laser chip strikes a photodiode or photodiode chip  412 . Photodiode  412  facilitates feedback control of power output from diode laser  400 . More specifically, diode laser  400  employs a built-in photodiode  412  and optical/electronic feedback control to regulate current—and thus regulate output beam power, as described in further detail with respect to control circuitry  418 . Diode laser  400  thus relies on closed loop regulation using optical feedback to stabilize beam power, which is useful to compensate for temperature variations and to assist consistent output laser light wavelength and intensity. In a specific embodiment, photodiode chip  412  is built-in to the back side of lasing chamber  408 . In another embodiment, diode laser  400  employs a photodiode  412  and optics that are external to lasing chamber  408  to monitor laser light beam output from laser  400  for feedback control and output laser light power regulation. 
     Diode laser  400  relies on input energy to excite lasing medium  402 . Semiconductor lasers are commonly pumped by externally applied current, while optical and electron beam pumping may also be used. Leads  416  provide electrical communication between diode laser  400  and control circuitry  418  disposed on a board  430 . In one embodiment, three leads  416  are included. Two leads provide controlled electrical energy to lasing medium  402  and lasing chamber  408 . Two of the leads  416  also provide electrical communication between photodiode  412  and control circuitry  418 , thereby permitting an output signal from photodiode  412  to control circuitry  418  for closed feedback control of power output from laser data  400 . 
     Control circuitry  418  regulates current provided to diode laser  400 . Typically, diode laser  400  has a minimum current above which lasing action takes place. Thus, when control circuitry  418  receives an on/off command from controller  42  for display device  10 , control circuitry  418  maintains current provided to lasing medium  402  above the lasing current threshold. In addition, diode laser  400  typically has a maximum current threshold, which when exceeded may result in damage to diode laser  400 . In this case, control circuitry  418  prevents current greater than the maximum current threshold from reaching diode laser  400 . The minimum and maximum current thresholds will vary with particular devices, designs and materials, as one of skill in the art will appreciate. In addition, control circuitry  418  may also implement a safety buffer relative to the maximum current threshold such that the maximum current ever seen by the diode laser remains safely below the maximum threshold. Thus, each diode laser operates over an input current range between the minimum lasing current and the maximum current threshold (or a safety level relatively close). Output light power from diode laser  400  may vary with current level within this range. Control circuitry  418  then controls input current to achieve a desired output light power or intensity from diode laser  400 . 
     In one embodiment, output light intensity control for diode laser  400  employs a closed-loop feedback scheme. One suitable closed-loop feedback scheme relies on optical feedback from photodiode  412 , which is arranged inside the diode laser housing  414 . Control circuitry  418  then cooperates with photodiode  412  to provide a current that results in a desired power for light produced by diode laser  400 . A fixed reference, such as a fixed voltage included in the circuit or stored logic for reference by a microcontroller, may be used to designate a desired input current or a desired output light intensity. Control circuitry  418  then controls optical output from diode laser  400  by regulating input current based on feedback with respect to the fixed reference. Control circuitry  418  may thus maintain output laser power at an about constant level regardless of input power variations, such as input power that varies when display device  10  employs a battery that nears the end of its limited resources. Some diode lasers have transient light output power with device temperature. In this case, control circuitry  418  cooperates with photodiode  412  to ensure that light output power is consistent regardless of device temperature. 
     Control circuitry  418  is arranged on printed circuit board  430  and electrically connected to leads  416 . As mentioned above, display device  10  includes power supply  38  that either receives DC input or converts AC voltage to DC voltage for use with in display device  10 . In one embodiment, control circuitry  418  comprises a driver circuit capable of operating on regulated DC input. By providing regulated current, control circuitry  418  thus acts as the pumping system that imparts electrical energy to the atoms or molecules of lasing medium  402 , enabling them to be raised to an excited metastable state and create laser light. 
     Housing  414  defines the outer dimensions of the diode laser  400  package and provides structural support and mechanical protection for components arranged therein. Housing  414  may comprise brass, copper, aluminum or another suitable metal, for example, which are beneficial for heat dissipation. 
     Collimation, astigmatism, divergence, and/or an elliptical profile may be used to characterize laser light produced by a diode laser. Collimation refers to the degree to which the beam remains parallel with distance. Many diode lasers emit a divergent beam, having a splay angle that varies from five to forty degrees in each orthogonal direction. In one embodiment, laser  400  is an edge emitting diode laser. The raw output beam from an edge emitting diode laser is commonly divergent and includes two asymmetries: astigmatism and an elliptical beam profile. The astigmatism and elliptical beam profile are a product of unequal divergence in orthogonal directions. Display devices of the present invention may include one or more lenses that alter a laser beam property such as astigmatism, divergence, elliptical profile and/or increase collimation. 
     In one embodiment, display device  10  comprises optics that alter one or more beam characteristics of an initial laser beam  415  emitted from lasing chamber  408 . As shown in  FIG. 2A , internal lens  420  is disposed within housing  414 , between output lens  404  and lasing chamber  408 , and alters laser light generated within diode laser  400  before exit from output lens  404 . In a specific embodiment, lens  420  is an internal microlens that reduces divergence in one or more directions for initial laser beam  415  and outputs a corrected internal beam  416  from its exit surface having less divergence in one or more directions relative to the incident beam  415 , In another specific embodiment, lens  420  reduces astigmatism for initial laser beam  415  and outputs corrected internal beam  416  having less astigmatism relative to the incident beam  415 . A custom dimensioned convex or positive lens  420  may be employed to reduce divergence. Dimensioning of lens  420  will vary with the divergence in the initial laser beam  415 , which will depend on specific parameters for diode laser  400  such as the shape of the emitting aperture for lasing chamber  408 , as one skilled in the art will appreciate. Lens  420  may comprise any suitably shaped redirection optics, such as a custom-made glass or plastic shaped lens, or one or more prisms. In a specific embodiment, lens  420  is made from glass and ground to a suitable dimensions to correct for any divergence. Diode laser packages with correcting microlenses are also available from Blue Sky Research of Milpitas, Calif. 
     Reducing divergence in beam  415  and collimating output from diode laser  400  simplifies light transmission and subsequent light manipulation within display device  10 . Lens  420  is advantageous since, without the presence of lens  420 , a significant amount of initially generated light may not escape though lens  404  and be wasted before output from lens  404  due to divergence of the initial beam  415  within diode laser housing  414 . Internal lens  420 , however, converts divergent laser light into collimated output before significant light loss within housing  414 . This arrangement allows diode laser  400  to output a larger portion of the total light generated in lasing chamber  408 , thereby increasing output light power and light efficiency for diode laser  400  and display device  10 . 
     Divergence correction may also be performed in other locations. In one embodiment, output lens  404  is dimensioned to correct for any divergence in a laser beam generated in lasing chamber  408 . In another embodiment, a collimating lens is glued, epoxied or otherwise attached to the outside the housing  414 . Alternately, divergence correction and collimation may occur in a lens included in a one-to-one coupling fixture that interfaces a fiber-optic cable to diode laser  400 . 
     Lens  420  may also reduce or alter any astigmatism in initial laser beam  415 . The astigmatism causes the focal length required to collimate the laser beam in orthogonal directions, such as in x and y directions, to differ. Without correction, the asymmetry in orthogonal directions results in a beam with an elliptical profile. In one embodiment, lens  420  is custom shaped to reduce astigmatism. More specifically, lens  420  is ground with an astigmatic curvature to compensate for differing divergences in orthogonal directions of the generated laser light. Thus, lens  420  may unequally reduce divergence in the fast axis relative to the slow axis for diode laser  400 . For example, lens  420  may reduce divergence by 30 degrees in the fast axis and by 5 or 10 degrees in the slow axis. The present invention may alternatively correct for astigmatic variations in the laser output in locations other than internal lens  420 . For example, lens  404 , a lens externally attached to housing  414 , or another downstream lens in the optical path may be dimensioned to reduce astigmatic variations resulting from diode laser usage. 
     In addition, multiple lenses such as lens  420 , lens  404 , a lens externally attached to housing  414 , or another downstream lens in the optical path, may cooperate to cumulatively provide a desired output beam. For example, lens  420  may reduce any initial astigmatism in initial laser beam  415 , but leave a minor amount of divergence in the corrected internal beam  416 , which is subsequently corrected by lens  404 . The specific alterations performed by each lens will depend on the initial beam shape and a desired beam shape for transmission within the display device  10 . In one embodiment, laser light having a circular beam with substantially no divergence is transmitted into a fiber optic cable for subsequent optical manipulation in display device  10 . In another embodiment, laser light having an elliptical beam profile with substantially no divergence is transmitted into fiber optic cables. In this case, the elliptical beam profile encompasses an aspect ratio for the optical modulation device  44 , and is subsequently manipulated and cut to a rectangular size that matches the aspect ratio. Since light initially output from lasing chamber  408  is substantially uniform in intensity across the laser light beam flux, early correction of any unwanted laser beam characteristics advantageously maintains about uniform intensity across the light beam flux. 
     Additional optics configurations may be employed to alter one or more beam characteristics of an initial laser beam  415  emitted from lasing chamber  408 . In one embodiment, output lens  404  corrects for divergence, astigmatism and elliptical output in a custom shaped single lens dimensioned for diode laser  400 . In another embodiment, the elliptical beam profile and astigmatism are corrected at once by coupling the output laser beam into a single mode optical fiber using two lenses. In some case, the output face quality of a fiber optic cable may affect output beam characteristics. A collimating lens disposed proximate to the outlet end of the fiber may then be employed to correct for any divergence in the outlet beam emitted from the fiber. 
     Output lens  404  emits laser light produced within diode laser  400 . An output light beam  438  emitted from output lens  404  thus forms the output for diode laser  400 . Output lens  404  may comprise plastic or ground glass. As described above, output lens  404  may be specially dimensioned to alter one or more characteristics in the output laser light. Lens  404  may also include one or more coatings, such as a coating to filter and remove infrared (IR) energy. In another embodiment, a separate IR filter is arranged within housing  414  to filter infrared energy and prevent it from escaping housing  414 . 
     Diode laser  400  may also include heat dissipation assistance. In one embodiment, board  430  is separated from surrounding components such that airflow via fans  62  cools board  430  and each diode laser  400  disposed thereon. One diode laser  400  design employs a metal housing  414 , which in addition to holding the optics and internal components, acts as a heat sink for the semiconductor diode laser chip  412 . Cooling air provided via fans  62  may thus cool the relatively larger surface area provided by housing  414  to improve temperature regulation of diode laser  400 . Alternately, each diode laser chip  412  may be mounted directly onto a separate heat sink to facilitate removal of heat from the chip. The heat sink may extend from housing  414  to receive cooling air provided by fans  62 . 
     In one embodiment, diode laser  400  is responsible for the generation of red light. In this case, diode laser  400  includes a lasing medium and laser cavity configured to produce and emit light having a wavelength between about 615 and about 690 nanometers. In a specific embodiment, diode laser  400  produces and outputs red light having a wavelength between about 625 and about 645 nanometers. Many commercially available Gallium Arsenide (GaAs)-based red diode lasers output red light in this range. Red diode lasers are widely available from a variety of vendors known to those skilled in the art, such as Lasermate Group Inc. of Pomona Calif. 
     In another embodiment, diode laser  400  is responsible for the generation of blue light. In this case, diode laser  400  includes a lasing medium and laser cavity configured to produce and emit light having a wavelength between about 420 and about 500 nanometers. In a specific embodiment, diode laser  400  produces and outputs blue light having a wavelength between about 430 and about 460 nanometers. Blue diode lasers that output light including a wavelength between about 430 and about 460 nanometers are available from Nichia America Corporation of Mountville, Pa. 
     In one embodiment, green laser set  14  and/or blue laser set  16  comprises one or more diode pumped solid-state (DPSS) lasers. Solid-state lasers generally employ a crystal doped with an impurity within their active lasing medium. A DPSS laser refers to a device, system or module that outputs laser light.  FIG. 2B  illustrates a DPSS laser schematic  450  in accordance with a specific embodiment of the present invention. DPSS laser  450  comprises a pumping light source  451 , lasing medium  452 , output optics  454 , lasing chamber  458 , housing  464 , control circuitry  468 , and optics  470 . 
     Lasing chamber  458  includes a lasing medium  452  on an inlet end and an output coupler mirror  457  on the opposite outlet end. Lasing medium  452  includes a crystal doped with an impurity, which generates laser light in response to input pumping energy. Suitable DPSS lasers may employ a crystal doped with Neodymium (Nd), such as Nd:YAG (Nd:Yttrium Aluminum Garnet) or Nd:YVO 4  (Nd Yttrium Ortho Vanadate). Lasing medium  452  is disposed on a metal heat sink  457  to facilitate heat dissipation. Lasing medium  452  generates energy in an IR region of the spectrum, which is reflected by mirror coatings on lasing medium  452  and output coupler mirror  457 . The mirror coating on the lasing medium  452  transmits the pumping light from light source  451 , while the coating on the coupler mirror  457  passes the visible wavelength output by laser  450 . In one embodiment, a crystal  461  comprising a non-linear electro-optic material is disposed in chamber  458 . When mounted at a suitable orientation along the path of the IR beam, crystal  461  converts a portion of the IR beam generated by medium  452  to visible light having a fraction of the IR wavelength, such as half the IR wavelength. This visible light passes through output coupler mirror  457 , and out from chamber  458 . For green-colored laser output, the DPSS laser is designed for second harmonic output, such as second harmonic 512 nanometer green laser light output from a Nd:YAG lasing medium that produces 1064 IR radiation. DPSS laser  450  may also be designed for higher frequency multiplication. 
     Pumping light source  451  imparts energy into lasing chamber  458  to excite lasing medium  452 . For infrared diode lasers used in pumping light source  451 , the wavelength of the pump diode laser  451  is selected to match an absorption line in lasing medium  452 . For Nd:YAG and Nd:YVO 4 , this is about 800 nm. The pump diode laser  451  may also be attached or mounted onto a metal heat sink for heat dissipation. Optics may also be arranged between the pump diode laser  451  and lasing chamber  458  to modify the pumping laser light beam transmitted therebetween. Alternately, the diode laser may be positioned relatively close to lasing chamber  458  without intermediate optics. 
     Housing  464  defines outer dimensions of the laser  450  package; and provides structural support and mechanical protection for components arranged therein. Housing  464  may comprise brass, copper, aluminum or another suitable metal that improves heat dissipation when in thermal communication with one or more heat generating portions of laser  450 . Each DPSS laser  450  also includes an IR filter  461  that prevents transmission of infrared radiation from housing  464 . Filter  461  may also be provided as a coating a lens included in laser  450 , such as output lens  454 . 
     Optics  470  includes one or more lenses that alter the laser beam produced in lasing chamber  458  to a desired shape and flux area. In one embodiment, optics  470  comprise an expanding lens and collimating lens that increase the flux area and re-collimate the light, respectively. Output lens  454  allows light generated within laser  450  to escape housing  464 . An output light beam  468  emitted from output lens  404  thus forms the output for laser  450 . 
     Control circuitry  468  regulates laser  450  output. In response to on/off commands from controller  42 , circuitry  468  regulates current provided to pumping diode laser  451 , which acts as a pumping system that imparts light energy to the atoms or molecules of lasing medium  452 . Control circuitry  468  is arranged on printed circuit board  430  and electrically connected to leads of the pumping diode laser  451 . Laser  450  also may comprise an optical sensor, such as a monitor photodiode chip, for detecting light output from laser  450 . 
     In one embodiment, DPSS laser  450  is responsible for the production of green light. In this case, DPSS laser  450  produces and emits light having a wavelength between about 510 and about 570 nanometers. In a specific embodiment, DPSS laser  450  produces and emits green light having a wavelength between about 530 and about 550 nanometers. Many commercially available DPSS lasers, such as those available from Lasermate Group Inc. of Pomona, Calif, output green light in this range. In another embodiment, one or more diode pumped solid-state lasers are responsible for the generation of blue light. Similar to green DPSS lasers, blue DPSS lasers employ a doubling or tripling of an infrared line, such as direct doubling of an 800+ nanometer IR diode laser (e.g., doubling of a 946 nanometer line to produce a 473 nanometer blue light). Suitable blue DPSS lasers are available from a variety of vendors, such as Lasermate Group Inc. 
     As mentioned above, one or more lasers are installed on a circuit board  430 , which mounts, and provides electrical communication for, each laser installed thereon.  FIG. 3  illustrates a board  430  with five diode lasers  400 a-e installed thereon in accordance with one embodiment of the present invention. This configuration reduces space for laser sets  12 ,  14  and  16  within display device  10 . Control circuitry  412  on board  430  regulates current provided to each diode laser  400 a-e. Although board  430  shows five diode lasers  400 , it is understood that board  430  may include a combination of diode lasers  400  and DPSS lasers  450 . In one embodiment, diode lasers  400 a-e all output light having a similar wavelength, such as red. In another embodiment, lasers on a single board  430  output different colors. 
     Each color or set  12 ,  14  and  16  produces a desired amount of light, achieved by the cumulative output from individual lasers in each set. The desired amount of light for each color or set  12 ,  14  and  16  may be quantified as a luminous power; and determined in design according to a desired total light intensity output for display device  10 . In one embodiment, each red, green and blue laser set  12 ,  14  and  16  is designed to produce light from about 500 mW to about 10 W in luminous power. In a specific embodiment, each red green and blue laser set  12 ,  14  and  16  outputs between about 1 W and about 3 W. The desired light output for each color or set  12 ,  14  and  16  may also be adapted according to the efficiency of the laser/fiber optic coupling system and other luminous inefficiencies in display device  10 . 
     The power of an individual laser in a color set may vary with design, while the number of lasers in each laser set  12 ,  14  and  16  and on each board  430  will vary with the output power of individual lasers in the set and the total luminous intensity for each color in display device  10 . Output power for each laser  400  or  450  may range from 5 mW up to 10 W, for example. Red diode lasers  400  are commercially available with power outputs up to 500 mW, and up to 1000 mW with suitable drive and current control electronics. Green DPSS frequency doubled frequency doubled Nd: YAG lasers are also commercially available with power outputs ranging from 5 mW each to 10 W each. In one embodiment, each set  12 ,  14  and  16  comprises from 1 to 60 lasers. In another embodiment, from 4 to 20 lasers are suitable to achieve a cumulative power output for an individual color. For example, if 3 W of luminous output power is desired for each color, red diode laser set  12  may include 6×500 mW diode lasers  400  arranged on one or two boards  430  or 3×1000 mW diode lasers  400  arranged on a single board  430 , green laser set  14  may include 6×500 mW DPSS lasers  450  arranged on one or two boards  430  or 3×1000 mW DPSS lasers  450  arranged on a single board  430 , while blue laser set  16  may include 6×500 mW DPSS lasers  450  arranged on one or two boards  430  or 3×1000 mW DPSS lasers  450  arranged on a single board  430 . For larger sets, multiple boards  430  for each color may be implemented and arranged side-by-side. In this manner, significant laser power may be generated in a compact and highly portable package. 
     The desired amount of light output power by each set  12 ,  14  and  16  may also vary with viewer sensitivity to the each wavelength. Since lasers output generally monochromatic light in a small wavelength range, and human vision receives light of different wavelengths with varying magnitude, the ratio of power provided by red, green and blue laser sets  12 ,  14  and  16  may be scaled according to human sensitivity for each wavelength range. Thus, the present invention may employ less or more total output power for a specific primary color or set  12 ,  14  and  16  based on the sensitivity of human vision to each wavelength. Desired total output powers for each color may then vary with the wavelengths used, as one of skill the art will appreciate. For example, red diode lasers  400  may output red light having a frequency of about 635 nanometers, which corresponds to a C.I.E. Phototopic Luminous Efficiency Function coefficient of about 0.21 (a coefficient of 1.0 corresponds to a green at 555 nanometers). Green DPSS lasers  450  may output green light having a wavelength of about 532 nanometers, which corresponds to a coefficient of about 0.89. Blue diode lasers  400  may output blue light having a frequency of about 435, while blue DPSS lasers  450  may output blue light having a frequency of about 473, which corresponds to a coefficient of about 0.10. The coefficients for these wavelengths may then be used to determine desired power output for these lasers when used in sets  12 ,  14  and  16 . 
     In one embodiment, display device  10  includes redundant light supply for each color and each laser set  12 ,  14  and  16 . This implies that each set  12 ,  14  and  16  includes more lasers and a greater maximum luminous power output for each color than needed for normal operation of display device  10 . One or more lasers in each set may then be turned off during normal operation. Thus, in the example described above where 3 W of total luminous output power is desired for red diode laser set  12 , set  12  may include 8×500 mW diode lasers  400  arranged on one or two boards  430  or 4×1000 mW diode lasers  400  arranged on a single board  430 . In the former case, two of the 500 mW diode lasers  400  are turned off during normal usage. In the latter case, one of the 1000 mW diode lasers  400  is turned off during normal usage. Similarly, green laser set  14  may include 8×500 mW DPSS lasers  450  arranged on one or two boards  430  or 4×1000 mW DPSS lasers  450  arranged on a single board  430 , while blue laser set  16  may include 8×500 mW DPSS lasers  450  arranged on one or two boards  430  or 4×1000 mW DPSS lasers  450  arranged on a single board  430 . 
     In one embodiment, each set  12 ,  14  and  16  comprises from 2 and 40 lasers in total. In another embodiment, from 4 to 20 lasers are employed. The number of extra lasers in each set  12 ,  14  and  16  may vary according to design. One factor that may influence the number of extra lasers in each set is the desired longevity of display device  10 . A designer increases the number of extra lasers in each set  12 ,  14  and  16  to increase longevity. Known fatigue limits and lifetimes for individual lasers may also affect the number of extra lasers in each set. In one embodiment, a laser set  12 ,  14  and  16  includes one more laser than the number of lasers needed to produce the desired amount of light. In another embodiment, a laser set  12 ,  14  and  16  includes 2-8 more lasers than the number of lasers needed to produce the desired amount of light. 
     Control circuitry  76  determines which of the lasers in a redundant set  12 ,  14  and  16  produce light. Thus, control circuitry  76  sends on/off commands to circuitry for each laser on board  430  based on stored instructions for the operation of each redundant set. In one embodiment, control circuitry  76  determines which of the lasers in each set  12 ,  14  and  16  produces light based on the operability of each laser in the sets. As mentioned above, a photodiode chip for each laser monitors output light intensity. Control circuitry  76  uses feedback from each photodiode chip to determine which lasers are operable, and adjusts output on/off commands to lasers in each set  12 ,  14  and  16  accordingly. 
     Redundant laser supply is advantageous to prevent failure of an individual laser from compromising output for the entire set, or output for a given primary color. Correspondingly, each laser set  12 ,  14  and  16  may continue to output its desired and intended luminous power and primary color even though an individual laser in the set is no longer operable. In most cases, this increases display device  10  longevity for a given set of lasers, with only a slight increase in cost and size. 
     Periodic shutdown for each laser in a redundant set may also be beneficial for heat dissipation. This allows individual lasers to be heated less over the course of extended usage of display device  10 , such as usage associated with motion picture video viewing. Shutdown for individual lasers in a set may be cyclical based on a predetermined shutdown scheme. For example, in a four laser redundant scheme where three lasers are needed for desired output power in normal usage, each of the four lasers may take turns shutting down for a predetermined time. This gives each laser periodic time to cool, and results in less heat generation for each laser. Alternately, shutdown may be used to protect an individual laser that is heating to a threshold temperature as sensed by a temperature sensor disposed in proximity to the laser. Logic stored in memory and accessible to control circuitry  76  ( FIG. 1 ) then shuts down the laser (and may turn on fans  24 ) to prevent the heating laser from reaching the threshold temperature. Multiple threshold temperatures may be established in this manner; and logic may be implemented that determines which lasers in a redundant set are used when multiple lasers in the set reach a particular threshold temperature. Redundant laser supply also advantageously increases longevity for individual lasers that benefit from periodic shut-down, thereby also increasing longevity for display device  10  on a given laser set. 
     In a specific embodiment, each laser in sets  12 ,  14  and  16  includes a temperature sensor that detects the temperature of each laser in the set. Control circuitry  76  uses feedback from the temperature sensors to determine a) if any lasers are heating to one or more temperature thresholds, and b) the specific temperature of each diode laser to minimize temperature based wavelength drift. Based on this information and stored instructions for each condition, or multiple conditions, control circuitry  76  determines which of the lasers in the set produce light based on the temperature of each laser in the set. The stored logic may also include instructions for special events, such as when multiple lasers reach a predetermined temperature threshold, or when an individual laser reaches a higher or dangerous temperature threshold. 
     Some diode lasers  400  include a temperature based frequency drift that alters the wavelength of output laser light with temperature of the laser. Drift of 0.3 nanometers/degree Celsius are common. Typically, a laser manufacturer knows temperature based frequency drift for a given laser. In this case, redundant laser supply may decrease any temperature-based drift by decreasing the average temperature variation for each laser in a redundant set, thereby increasing light consistency and image quality. 
     Returning back to  FIG. 1 , display device  10  employs a single optical modulation device  44  and a common light path between laser sets  12 ,  14  and  16  and the optical modulation device  44  using fiber optic cabling  72 .  FIG. 4A  illustrates a common fiber-optic cabling arrangement  200  in accordance with a specific embodiment of the present invention. 
     In arrangement  200 , light from each laser  400  and  450  in sets  12 ,  14  and  16  is first transmitted into a fiber-optic cable  202  dedicated to each laser; and subsequently routed and transmitted into a common fiber-optic cable  204 . Each laser dedicated fiber-optic cable  202  receives laser light from an individual laser  400  or  450 , and transmits the light to junction  206 . In one embodiment, each fiber-optic cable  202  attaches directly to an individual laser  400  or  450 . For example, each fiber-optic cable  202  may include a fixture with an inner threaded interface that matches a threaded interface disposed on an outside surface of the diode laser  400  housing. Commercially available fiber-optic cables, such as that available from Ocean Optics Inc. of Dunedin, Fla., may come standard with such coupling and alignment fixtures. In some cases, a short focal length normal or GRIN lens is also mounted at the inlet end of each cable  202  to facilitate laser-to-fiber light transition and collimated transfer into cable  202 . 
     Junction  206  permits transmission of light from fiber-optic cables  202  into converging optics  208 , and into common fiber-optic cable  204 . Converging optics  208  redirect incoming light from each fiber-optic cable  202  into common fiber-optic cable  204 , and comprise a converging lens  208 a that redirects light toward re-collimating lens  208 b, which collimates and re-directs incoming laser light from converging lens  208 a into common optical fiber  204 . In a specific embodiment, the inlet end  204 a of cable  204  is disposed at a focus of converging lens  208 a. Although not shown, junction  206  may also include a rigid structure, such as a suitably dimensioned molded plastic, that holds fiber-optic cables  202  and  204 . In addition, junction  206  may comprise an optical adhesive that adheres cables  202  directly to lens  208 . 
     In one embodiment, the outlet end  202 b the fiber-optic cables are combined into a larger cable  214  that contains multiple fibers. Multiple fiber cables, such as fiber ribbon-based cables and those that employ multiple fibers located circumferentially within a round tube, are commercially available from a variety of vendors known to those skilled in the art. 
     In common fiber-optic cabling arrangement  200 , common fiber-optic cable  204  sequentially delivers red, green and blue light as received from each upstream color dedicated fiber-optic cable  202 , in a timely order as received from cables  202  and determined by laser set  12 ,  14  and  16  timing via controller  76  (FIG.  1 ). An outlet end  204 b of common fiber-optic cable  204  transmits light to lens  80 a, which diverges light received from common fiber-optic cable  204  to increase the flux area of the laser light. Common fiber-optic cable  204  thus sequentially transmits red, green and blue light along a common light path to a single mirror-based optical modulation device  44  as shown in FIG.  1 . In one embodiment, the outlet end  204 b of common fiber-optic cable  204  includes a diverging lens  212  that increases the area of laser light flux emitted from common fiber-optic cable  204  before incidence on lens  80 a. This decreases the optical path distance (and space within display device  10 ) needed to increase the laser flux area from the size occurring within fiber-optic cable  204  to a sizable for subsequent transmission onto optical modulation device  44 . In another embodiment, the outlet end  204 b of common fiber-optic cable  204  includes a rectangular shape that matches the aspect ratio of the downstream optical modulation device  44 . 
     Although the present invention has been described primarily so far with respect to a display device that employs a reflective light modulator of a digital micromirror design in a single light path system, the present invention may also employ other types of light modulators and light path designs. For example, fiber-optic cabling  72  may be arranged for a multiple light path design to transmit light to three primary color dedicated LCD optical modulators, or to three primary color dedicated DMD optical modulators. In the case of an LCD optical modulation device, selective transmission of light comprises selective passage of light through a liquid crystal medium on a pixel by pixel basis.  FIG. 4B  illustrates a display device  10  in which multiple fiber optic cables  72 a-c transmit light from laser sets  12 ,  14  and  16  to multiple light optical modulation devices  44 a-c in accordance with another embodiment of the present invention. 
     Laser sets  12 ,  14  and  16  were described above. In this case, output from each laser  400  or  450  is already collimated by optics in the laser, and provided to a fiber-optic interface  70  that is arranged to receive the light with a space  232  between each interface and each laser. The fiber-optic interface  70  for each laser  400  or  450  is held by a fixture  234  that positions and holds each interface  70  to receive the light from its associated laser. Although laser sets  12 ,  14  and  16  are shown side-by-side with a single fixture  234 , is understood that laser sets  12 ,  14  and  16  may be positioned in different locations in display device  10  and each include their own fixture  234 . This may be advantageous to improve space conservation within housing  20 , decrease the footprint of housing  20 , and minimize display device  10  size. 
     Light from each laser  400  or  450  in sets  12 ,  14  and  16  is thus first transmitted into a fiber-optic cable  202  dedicated to each laser. The light is then subsequently routed through a junction  206 a-c for each primary color, and transmitted into a common fiber-optic cable  204 a-c for each primary color. Junctions  206  and common fiber-optic cables  204  were described above with respect to arrangement  200  in FIG.  4 A. In this case however, each common fiber optic cable  202 a,  202 b, and  202 c services a primary color. More specifically, common fiber optic cable  202 a transmits red light emitted by red diode laser set  12  to relay optics system  80 , fiber optic cable  202 b transmits green light emitted by green laser set  14  to optics system  80 , and fiber optic cable  202 c transmits the light emitted by blue diode laser set  12  to optics system  80 . Similar to  FIG. 1 , optics system  80  converts light receive from fiber-optic cabling  204  to light suitable for transmission onto an optical modulation device  44 . In addition, a pair of fly-eye lenses or an integrator tunnel may be disposed along the light path before each optical modulation device  44  to re-distribute light uniformly across the flux transmitted onto optical modulation device  44 . 
     As shown in  FIG. 4B , optical modulation devices  44 a-c are transmissive type LCD panels that each spatially filter light and provide a color image onto combining optics  236 , which emits a composite image towards projection lenses  112  along optical path  31 . For the triple path design shown in  FIG. 4B , lasers in sets  12 ,  14  and  16  may be left on continuously to provide continuous laser light to optical modulation devices  44 a-c. In this case, control circuitry  76  for display device  10  synchronizes frame and pixel data between each of the optical modulation devices  44 a-c. The triple path design shown in  FIG. 4B  advantageously results in a brighter image than a shared color system that relies on one optical modulation device  44 . 
       FIG. 5A  illustrates a process flow  300  for producing light in a projection-type display device in accordance with one embodiment of the invention. While the present invention will now be described as a method and separable actions for producing light, those skilled in the art will recognize that the subsequent description may also illustrate systems and components, such as a suitably configured controller and software, capable of performing the method and actions. 
     Process flow  300  begins by providing a laser set including a plurality of lasers ( 302 ). A suitable display device including three lasers sets is described above with respect to FIG.  1 . In one embodiment, each laser in the laser set produces light in a wavelength range related to a primary color. For example, a first set is responsible for the generation of red light, a second set responsible for the generation of green light, and a third set responsible for the generation of blue light. In this case, each laser in the first laser set produces light in a wavelength range between about 615 and about 690 nanometers, each laser in the second laser set produces light in a wavelength range between about 510 and about 570 nanometers, and each laser in the third laser set produces light in a wavelength range between about 420 and about 500 nanometers. 
     Process flow  300  determines which lasers in the set produce a desired amount of light ( 304 ). To do so, the control circuitry performs a check to determine if all lasers in the set are operable, and periodically monitors the operability of each laser in a redundant set. Testing each laser and reporting laser response using a photodiode chip arranged to detect light for each laser permits this. Testing may be performed at device start up and at regular intervals, for example. If any lasers are inoperable, they are not called upon by the control circuitry to produce light. If the number of inoperable lasers in the set matches the number of extra lasers in a redundant set, then all operable lasers are used to produce the desired amount of light (without redundant control). 
     If a redundant set includes more operable lasers in the set than the number needed to produce the desired amount of light, then redundant control proceeds for all operable lasers. In one embodiment, process flow 300 cycles power to lasers in a redundant set according to a regular usage interval. The regular usage interval may vary according to known heat generation and heat dissipation rates of each laser within the display device, the total number of lasers in the set, the number of redundant lasers in the set, an initiation period for laser generation, and the type of laser and its sensitivity to heat, for example. DPSS lasers, in particular, are typically sensitive to heat and may include more redundant lasers in the set that are cycled quicker to avoid heat accumulation in each laser. In one embodiment, power to each laser cycles in turn for a period from about 0.1 second to about 10 minutes. In a specific embodiment, power to each laser in a redundant set cycles in turn for a period from about 1 second to about 1 minute. In another embodiment, process flow  300  selects individual lasers for use according to heat control instructions stored in software that is accessible to the control circuitry ( 320 , FIG.  5 C). 
     Process flow  300  then produces the desired amount of light using a number of lasers in the laser set that is less than the total number of lasers in laser set ( 306 ). If lasers in the redundant set are diode lasers, then the control circuitry also regulates the current provided to each laser when turned on. This includes both preventing current greater than a maximum current threshold from reaching each diode laser and maintaining the current above lasing threshold levels for each laser. 
       FIG. 5B  illustrates a process flow  310  for producing an image using a projection-type display device in accordance with one embodiment of the invention. Process flow  310  begins by producing a desired amount of light using a number of lasers in a laser set that is less than the total number of lasers in the laser set ( 306  of FIG.  5 A). 
     In one embodiment, process flow  310  determines which lasers in the set produce a desired amount of light in response to reception of a video signal. Exemplary devices that may output video data to the display device include desktop computers, laptop computers, personal digital assistants (PDAs), cellular telephones, video game consoles, digital cameras, digital video recorders, DVD players, and VCRs. Video data provided to control circuitry  76  may be in a digital or an analog form. Process flow  310  may also convert an incoming analog video signal to a digital video signals for use in the display device. 
     The light generated by lasers in the redundant sets is collected and transmitted along one or more optical paths (as illustrated in  FIGS. 4A and 4B  for example). In one embodiment, fiber-optic cables  72  transmit the light. Relay optics disposed along the optical path increase the flux area of light emitted by the lasers, or transmitted by the fiber-optic cabling, before transmission to an optical modulation device ( 312 ). The relay optics may comprise one or more lenses that increase luminous flux size of the laser light to a size suitable for transmission onto an optical modulation device. 
     The light is then selectively transmitted according to video data included in a video signal provided to an optical modulation device ( 314 ). Referring to  FIG. 1 , which employs a single light path, a digital micromirror “DMD” device  44  and a prism  110 , light propagates through prism component  110 a, reflects off a surface  110 d at interface  110 c by total internal reflection, and forms a reflected pre-modulated beam directed towards optical modulation device  44 . The reflected pre-modulated beam travels through prism component  110 a to reach optical modulation device  44 , which selectively transmits light according to video data in a signal that corresponds to an image to be projected. Each mirror in optical modulation device  44  reflects light in its ‘on’ state back into prism component  110 a and through interface  110 c without internal reflection such that the light propagates into prism component  110 b and out an exit face  110 e of prism  110 . Light output through exit face  110 e is characterized by optical path  31 , which propagates through one or more projection lenses  112  that manipulate image light for enlarged display onto a screen or suitable receiving surface ( 316 ). Typically, the image is cast with a splay angle such that the image enlarges as the distance to a receiving surface increases. 
     Frame and color sequential information output by a laser light generation system can be electrically and digitally controlled (the coordination of  306  and  314  in process flow  310 ). For display devices that employ sequential color provision onto a single optical modulation device such as a DMD, electrical and digital control of laser light generation allows faster and more accurate sequential color synchronization and transmission than mechanical color wheel based systems. This digital control and improved red, green and blue light supply may also lead to reduced flicker and improved light efficiency within the display device. In addition, individual in digital control of each laser also permits computer control of light generation within projection type display device—in contrast to existing binary on-off white light lamp control. As mentioned above, this permits control of redundant laser sets to increase longevity of a laser based light source and display device. 
       FIG. 5C  illustrates a process flow  320  for using a projection-type display device that employs a set of lasers including a plurality of lasers to produce light in accordance with one embodiment of the invention. Process flow  320  controls individual lasers in a redundant laser set according to heat control instructions stored in software that is accessible to control that implements circuitry process flow  320 . 
     In this case, the control circuitry monitors temperature for each laser in the set ( 322 ). Temperature sensors in proximity to each laser that detect temperature of each laser and provide temperature information to the control circuitry allow this. 
     Process flow  320  turns off a heating laser in a redundant laser set when temperature for the heating laser reaches a threshold temperature ( 324 ). The temperature threshold may be set to a known temperature failure level for a laser, or various fractions thereof useful for managing temperature levels for one or more lasers. When a laser reaches a threshold temperature, control circuitry, according to logic stored in memory and accessible to the control circuitry, then shuts down the laser to prevent the heating laser from heating further. Multiple threshold temperatures may be established in this manner. For example, multiple temperature thresholds may be set according to regular temperature intervals to keep all lasers in a redundant set at relatively equal temperature levels regardless of heat generation or heat dissipation rates for each laser. As described above, lasers in a redundant set may be cycled at regular intervals. In this case, the temperature-based control may take priority in determining which lasers are cycled. Thus, if one laser has reached a threshold temperature above the remainder of the lasers, it may be kept from participation in a cycling scheme until it cools below the threshold temperature. 
     In response to turning off one laser for heat purposes, process flow  320  turns on an inactive laser in the laser set ( 326 ). An inactive laser refers to a laser in a redundant set that is not currently emitting light. Logic may be implemented that determines which lasers in a redundant set are used when multiple lasers in the set reach a particular threshold temperature, such as turning on lasers with the currently lowest operating temperature in place of a heating laser that reaches a new threshold temperature that none others in the set have reached. After turning on the new inactive laser, process flow  320  produces a desired amount of light using a number of lasers in a laser set that is less than the total number of lasers in the laser set ( 306  of FIG.  5 A). 
     Temperature based redundant control increases longevity for individual lasers that benefit from periodic shutdown and those whose endurance suffers from elevated heat exposure, thereby also increasing longevity for a display device on a given redundant laser set. In addition, redundant laser supply may also decrease any temperature-based drift by decreasing the average temperature variation for each laser in a redundant set, thereby increasing light consistency and image quality. 
     Laser based systems described herein advantageously provide a light generation option for projection-type display devices that requires low voltage and consumes low power. Diode lasers are more efficient in terms of light generation per input energy, particularly relative to white light lamps. Laser light sources also generate less heat than a white light lamp, thereby easing heat dissipation requirements. This allows for smaller cooling fans that consume less power and require less space. Another advantage of diode lasers is that diode lasers emit relatively monochromatic colored light, thereby eliminating the need for a color wheel and its spatial requirements—and eliminating the color wheel motor which also occupies space, consumes power and generates heat. Cumulatively, these factors each contribute to significantly reduced power consumption for a display device and enable battery-powered projection-type display devices. 
     Laser based designs described herein are also lighter and require less space than white light lamp sources, which enables projection type display devices that are smaller, less weight, and increasingly portable. In addition, the collimated light output from lasers is significantly smaller in cross-sectional flux area and therefore requires less space for optical manipulation, such as smaller lenses, further saving space and reducing display device size. In one embodiment, display device  10  is less than 4 pounds. As mentioned above, walls of housing  20  may comprise a lightweight and stiff molded plastic or metal that reduces overall weight of display device  10 . In another embodiment, display device  10  is less than 2 pounds. 
     Display devices described herein also benefit from highly collimated and substantially coherent light output. This permits increased depth of focus for a projected image; and permits an increased range of focus. For some display device designs, this may eliminate the need for manual focusing tools and thereby further reduce the size and cost of display device. 
     With respect to usage, the present invention may receive analog or digital video signals and data from a range of systems and devices. In addition to personal computers such as desktop computers and laptop computers, a variety of other computer systems and digital devices may output video data to a display device of the present invention. Handheld computers, portable digital assistants and portable digital devices are increasingly integrating video functionality, including the ability to communicate with an external display device. Other portable digital devices such as video games, portable video games, portable digital video recorders and digital cameras may also provide video output to display device described herein. One current trend is hybrid entertainment devices that integrate the functionality of computer systems, stereos, and televisions. In addition, set-top boxes associated with cable television services are becoming much more sophisticated user interfaces as interactive services become available to cable customers. Any of these devices may employ and benefit from video output using a display device as claimed herein. The scope of digital computer systems is expanding hurriedly and creating many systems and devices that may employ the present invention. A merging of television, video, and computer functions into a single device also adds value to the present invention since the sensitivity to image quality and size is high in applications such as motion picture viewing. Video game consoles that use large display devices may particularly benefit from the present invention. Moreover, those skilled in the art will appreciate that the invention may be practiced with other computer system configurations, multiprocessor systems, microprocessor-based or programmable consumer electronics, minicomputers, mainframe computers, and the like. 
     Display devices of the present invention may provide projected images having an image size ranging from inches to many feet, as determined by a user and environment. Image size for a projector typically depends on mechanical factors such as the distance from the projector to the receiving surface and a splay angle for the projection lens system  112  (FIG.  1 ). Display device  10  is well-suited for display of motion pictures and still photographs onto screens. In addition, display device  10  is also useful for conducting sales demonstrations, playing video games, general computer usage, business meetings, and classroom instruction, for example. 
     Although the foregoing invention has been described in some detail for purposes of clarity of understanding, those skilled in the art will recognize that various modifications may be made within the scope of the appended claims. For example, although diode lasers described herein have primarily been described with respect to side emitting Fabry-Perot diode laser designs, it is understood that other designs such as vertical cavity surface emitting diode lasers, other vertical emitting and distributed feedback laser designs may be used. In addition, optics may also be employed to alter other unwanted laser beam characteristics not specifically described above. For example, one or more wedge shaped prisms may be used to alter or correct for any elliptical beam shape in a laser beam, if present. By manipulating the relative orientations of the prisms, the prisms may be used to shape or extend the beam profile in one more directions. Further, although the present invention has been described with respect to fiber-optic cabling for transmission of light between lasers in sets  12 ,  14  and  16  and relay optics that deliver the light to the optical modulation device, it is understood that fiber-optic cabling is not necessary for the present invention. In one embodiment, lasers in sets  12 ,  14  and  16  are arranged to emit light towards optics system  80 , which converts incoming light to a light flux suitable for transmission onto optical modulation device  44  and transmits the light to an optical modulation device  44  without the use of fiber-optic cabling. For example, the lasers may be arranged to emit light towards a first lens that spans the laser light from each laser onto a first fly-eye lens. The invention is, therefore, not limited to the specific features and embodiments described herein and claimed in any of its forms or modifications within the scope of the appended claims.