# Patent

## Title
Projector lamp having pulsed monochromatic microwave light sources

## Abstract

A light engine for image display projectors has a plurality of monochromatic light sources, typically red, blue and green, combined into one light generation device powered by microwaves pulsed at 3-5 KHz rates. The light engine has a microwave power supply, microwave coupling cavity, a microwave coupler coupling a microwave signal from the microwave power supply to the microwave coupling cavity, and the plurality of monochromatic light sources disposed in the microwave coupling cavity and powered by the microwave signal. The microwave coupling cavity includes a plurality of resonance points, each of the monochromatic light sources being located respectively at one of the resonance points.

## Background
This application claims the benefit of the priority date of U.S. Provisional Patent Application No. 60/921,791, which was filed on Apr. 4, 2007, and which is hereby incorporated herein by reference.


BACKGROUND OF THE INVENTION
1. Field of Invention
This invention generally relates to light engines for image display projectors
2. Prior Art
The separation of light into usable colors is a critical function incorporated into projector light engines. Various technologies, such as the sequential color wheels, prism systems, etc., have been developed for such separation of colors from full visible spectrum or “white” light. Color wheels are particular to reflective image generation devices (“imagers”) such as DLP manufactured by Texas Instruments Corp. and may also used in some LCOS systems available from various suppliers. The light source for projection systems is generally broad spectrum (“white light”) sources such as high intensity discharge (“HID”) lamps manufactured by Philips and others. These lamps are typically use 75 to 150 watts power and provide adequate light for projection but are generally inefficient, light quality degrades over time, extensive cooling is required and HID lamps have lifetime limitations. An emerging technology is the use of light emitting diodes (“LED”), which are solid-state laser light sources. They can be monochromatic and can be pulsed. Table 1 is a description of typical design requirements for an LED light source as incorporated into a light engine. Ideally at least three separate, monochromatic LED's, usually in red, blue and green, would be used. Each respective color is turned on and off at a frequency of 3 to 5 KHz. LED light sources are limited by the total lumens generated per color and the relatively large size of the emitting region (etendue) required. LED's can be long lived but are generally low efficiency and generate significant beat that must be removed.







TABLE 1







CURRENT DESIGN TARGETS FOR LED LIGHT SOURCES










Parameter
Target
Comments
2/07 Add'l Comments CD





Total Flux
(180° Output)
Assume duty cycle <60%
Very dependent on source


Brightness
Red: ~425 average
per color that may be
etendue, imager size, screen



lumens
adjusted randomly.
size and gain. Imager is



Green: ~1500 average
Assuming >70%
currently 0.65′′ diagonal



lumens
collected in 60
moving to 0.45′′ diagonal in



Blue: ~130 average
degree cone
size. Ultimate target is



lumens

1000 nits on screen with 2×





gain.


LED
~12 mm{circumflex over ( )}2 for 0.65′′
Imaged onto a 16:9 device



Emitting
imager
illuminated at ~28° at



Area

approx. f/2.0 × f/2.4



Junction to
□ 1 C/W
Total heat dissipation



Case

capability of system



Thermal

heatsink solution is



Resistance

typically ~.5 C/W during





operation



Operating
2-5 KHz
Typical pulsing rate during
With color sequential


Frequency

operation (per color)
system, switching speed 10




is ~2800 Hz.
uS (full off to full on) and





pulse periods down to 400





uS.


Operating
1%-60%
May be adjusted randomly
Per color per frame


Duty Cycle

(per color)



Variability





Operating
10-45 C.
Typical conditions - varies



Ambient

by OEM product design



Temperature

requirements



Range





Operating
Minimum: 20,000 Hrs
Target 60K hours as



Lifetime
Typical: 60,000 Hrs
minimum



Operating
0%-100%
Operating current may vary



Current

randomly - Ohmic



Variability

Resistance must be low





enough to support stable





turn on at low current levels



Die
Rotation: TBD




placement
X/Y: TBD




tolerance to





package





alignment





features





Target
Red: ~620-630 nm
Nominal Output



Output
Green: ~520-540 nm
Wavelengths (per color)



Wavelengths
Blue: ~455-465 nm
utilizing the best





combination of wavelength,





duty cycle, and intensity for





maximum brightness









3. Objectives
This invention is a method and apparatus for producing a light engine with three separate monochromatic light sources, typically red, blue and green, combined into one light generation device powered by microwaves pulsed at 3-5 KHz rates. The individual light sources are cylindrical or spherical in shape with internal dimensions in any direction generally less than 0.6 mm. They would generally generate power densities exceeding 15,000 watt/cm3.
SUMMARY
The principal claim is a light engine with three separate, microwave powered, pulsed, monochromatic light sources, typically one each in red, green and blue. The light sources are lamps that contain selected light generating materials in a background inert gas contained within sapphire or quartz envelopes.
Another principal claim is a new light source, which is microwave powered, pulsed, and either broad spectrum or monochromatic, with applications for light generation in image display projection system, medical or other industrial uses.
Another principal claim is a microwave powered light engine incorporating three separate monochromatic lamps, with a waveguide coupling structure that has three spatially separated resonance locations, and a power supply that can be controlled to adjust the phase of the microwaves by means of an electronic digital phase shifter used to sequentially shift the phase of the microwaves in order to concentrate the power at the three spatially separated resonance locations corresponding to the location of the lamps.
Another principal claim is a sapphire envelope lamp with a fill of ZnCl2, or ZnBr2 and Xenon to produce emission primarily in the red spectrum between 620 and 630 nm. It may include a blocking filter to transmit only the radiation within the 620 to 630 nm band.
Another principal claim is a sapphire envelope lamp with a fill of ThCl2, or ThBr2 and Xenon to produce emission primarily in the green spectrum between 520 and 540 nm. It may include a blocking filter to transmit only the radiation within the 520 to 540 nm band.
Another principal claim is a sapphire envelope lamp with a fill of InCl2, or InBr2 and Xenon to produce emission primarily in the blue spectrum between 455 and 465 nm. It may include a blocking filter to transmit only the radiation within the 455 to 465 nm band.
A summary comparison of this new light source with the LED specifications above is as follows:







TABLE 2







TRICOLOR MICROWAVE LAMP DESIGN VERSUS LED REQUIREMENTS










Parameter
Target
Comments
GEM Lamp Performance





Total Flux
(180° Output)
Assume duty cycle <60%
Maximum dimension is


Brightness
Red: ~425 average
per color that may be
0.6 mm in major dimension



lumens
adjusted randomly.
in order to better etendue



Green: ~1500 average
Assuming >70%
match with imagers 0.65′′ or



lumens
collected in 60
less in diagonal.



Blue : ~130 average
degree cone
Red ~1000 average lumens



lumens

Green ~10,000 average





lumens





Blue ~2500 average lumens





(More if desired)


LED
~12 mm{circumflex over ( )}2 for 0.65′′
Imaged onto a 16:9 device
Emitting area about 0.36


Emitting
imager
illuminated at ~28° at
mm2


Area

approx. f/2.0 × f/2.4



Junction to
□ 1 C/W
Total heat dissipation
N/A


Case

capability of system
Total power input is about


Thermal

heatsink solution is
40 watts to generate lumens


Resistance

typically ~.5 C/W during
indicated above.




operation



Operating
2-5 KHz
Typical pulsing rate during
Three separate color sources


Frequency

operation (per color)
with a 3-15 KHz switching




is ~2800 Hz.
capability with 10 μS from





full off to full on with





arbitrary off periods.


Operating
1%-60%
May be adjusted randomly
Arbitrary duty cycle


Duty Cycle

(per color)
possible


Variability





Operating
10-45 C.
Typical conditions - varies
10-45 C.


Ambient

by OEM product design



Temperature

requirements



Range





Operating
Minimum: 20,000 Hrs
Target 60K hours as
20,000 to 60,000 Hrs,


Lifetime
Typical: 60,000 Hrs
minimum
higher end of range with





sapphire envelope lamps.


Operating
0%-100%
Operating current may vary
No such limitation


Current

randomly - Ohmic



Variability

Resistance must be low





enough to support stable





turn on at low current levels



Die
Rotation: TBD

N/A


placement
X/Y: TBD




tolerance to





package





alignment





features





Target
Red: ~620-630 nm
Nominal Output
Red ~620-630 nm


Output
Green: ~520-540 nm
Wavelengths (per color)
Green ~520-540 nm


Wavelengths
Blue: ~455-465 nm
utilizing the best
Blue ~455-465 nm




combination of wavelength,





duty cycle, and intensity for





maximum brightness












BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a tricolor microwave lamp engine system, according to an embodiment of the present invention.
FIG. 2 illustrates FIG. 2 illustrates how the position of the resonance changes with time, according to an embodiment of the present invention.
FIG. 3 illustrates a microwave power supply, according to an embodiment of the present invention.
FIG. 4 illustrates a microwave pulse as a function of time, according to an embodiment of the present invention.



DESCRIPTION
The Tricolor Microwave Lamp light Engine comprises, for example, the following components:

    1. Three separate lamps that use single crystal sapphire or quartz envelopes:
    
        One lamp which emits light in the red spectrum, between 620 and 630 nm with a fill of one or more of ZnCl2 or ZnBr2 and one or more of Argon or Xenon background gases.
        One bulb which emits light in the green spectrum, between 420 and 540 nm with a fill of one or more of TlCl2 or TlBr2 and one or more of Argon and Xenon background gases.
        One bulb which emits light in the blue spectrum, between 455 and 465 nm with a fill of one or more of InCl2 or InBr2 and one or more of Argon and Xenon background gases.
    
    
    2. A microwave coupling cavity with three separate resonance positions that are determined by the geometry of the resonance cavity and the phase of the microwaves within the cavity.
    3. A microwave power supply that can be pulsed in time and changed in phase by means of electronic controls.
    4. The three lamps located in three separated positions in the wall of the coupling cavity that generate monochromatic light when the microwaves are focused on the respective lamps.
    4. Optics to collect and focus the light emission from each lamp onto a common optical path.
    5. Band pass filters to remove all light that is not in the desired spectrum band.


FIG. 1 is a schematic drawing of tricolor microwave lamp engine system 100. A microwave coupling cavity 110 has resonance points at three positions. Lamps 101, 102 and 103 are depicted located at three such positions. FIG. 2 illustrates how the position of the resonance changes with time. As the phases of the microwaves are changed the position of highest concentration within the microwave coupling cavity 110 physically moves to a different position. The spatial position of the maximum amplitude of the microwaves is shown for three separate times in FIG. 2. The microwave pulse is depicted in FIG. 4 as a function of time. When the phases are changed in sequence, the colors emitted from the light engine move sequentially from red to green to blue in any desired pattern. The duration of each pulse, the time between pulses and the phase are all independently electronically controlled.
A microwave power supply 109 feeds microwaves to a microwave coupler 108. The light generated by each respective lamp is directed through a lens, which may be coated with a band pass filter material to eliminate light outside of the desired spectrum. The lens focuses the monochromatic light on an optical guide 107 that directs the light into the optical system of a projector. The lens 104 focuses the light from lamp 103. The lens 105 focuses the light from lamp 102. The lens 106 focuses the light from 101.
A schematic drawing of the elements of the microwave power supply are shown in FIG. 3. A key element of this power supply is an electronic microwave phase shifter that allows the phase shift to be programmed digitally.
EXAMPLE 1
The lamp is designed to ignite and emit light during a pulse such as that shown in FIG. 4. The lamp turns off when the intensity of the microwave pulse at that position approaches zero. Previous experiments by Dr. Eastlund have demonstrated that when operating in such a mode power levels of  ̃70,000 watts/cm3 can be coupled onto a lamp.
It is advantageous for small DLP or LCOS imaging devices, less than 0.65′′ in diameter, to have the dimensions of the emitting area from a light source as small as possible while providing sufficient light to project the image generated by the system onto a viewing surface.
With a cylindrical envelope lamp of the subject invention having an internal dimension of approximately 0.3 mm and a length of approximately 0.6 mm, the light output as a function of wavelength is projected to be:

    For red between 620 and 630 nm: 1000 lumens (assuming 50 lumens/watt)
    For green between 520 and 540 nm: 10000 lumens (assuming 500 lumens/watt)
    For blue between 455 and 465 nm: 2500 lumens (assuming 250 lumens/watt)
    The lumens/watt is based on the CIE luminous efficiency curve for day vision.

## Claims

1. An apparatus, comprising:
a microwave power supply;
a microwave coupling cavity;
a microwave coupler coupling a microwave signal from the microwave power supply to the microwave coupling cavity, wherein the microwave coupling cavity includes a plurality of resonance points; and
a plurality of monochromatic light sources disposed in the microwave coupling cavity and powered by the microwave signal, each of the monochromatic light sources being located respectively at one of the resonance points.

2. The apparatus of claim 1, wherein the monochromatic light sources include a red light source, a blue light source, and a green light source.

3. The apparatus of claim 1, wherein the monochromatic light sources are pulsed at a rate that is from 3-5 KHz.

4. The apparatus of claim 1, further comprising means for selectively changing a position of a resonance of the microwave signal from one of the resonance points to another one of the resonance points within the coupling cavity.

5. The apparatus of claim 1, further comprising a means of light collection, a lens or lenses for focusing the light from the plurality of monochromatic light sources into an optical guide.

6. The apparatus of claim 4, wherein the means for selectively changing includes a digital phase shifter.