1. Optical system considerations for rear-projection display 11 March 2003 R. Edward English Jr., Ph.D. Chief Optical Scientist 3M Precision Optics, Inc. Cincinnati, Ohio

2. © 3M 2003 3M Precision Optics A brief history of 3M Precision Optics, Inc. Founded in 1930 as U.S. Watch Crystal Manufacturing Company - became the largest American maker of watch crystals in the 1930’s and 1940’s –Began making plastic watch lenses in 1950’s Changed name in 1970’s to U.S. Precision Lens after achieving major success in plastic lenses for LED calculators and optical components –Invented “Delta” lens design in 1978 Acquired by Corning in 1986 and renamed Corning Precision Lens Incorporated in 2000 –Won Technical Emmy in 1997 for “the processing design and development of high efficiency optics which made possible the growth of the video projector industry” Acquired by 3M in 2002 and renamed 3M Precision Optics, Inc. Headquartered in Cincinnati, OH with over 550,000 square feet of operating space employing over 1,500 employees

3. © 3M 2003 3M Precision Optics Projection television is becoming a commonplace consumer electronic item

4. © 3M 2003 3M Precision Optics Why are projection TVs “grody to the max” ?

5. © 3M 2003 3M Precision Optics Outline of presentation Large area consumer display market overview CRT-based projection system design requirements Lens design and performance General lens design requirements for microdisplay –compare and contrast Summary

6. © 3M 2003 3M Precision Optics The US projection TV market has grown an average of 23% per year since 1999

7. © 3M 2003 3M Precision Optics Many observers predict that the demand for large area displays will continue to grow

8. © 3M 2003 3M Precision Optics CRT-based PTV system components The standard configuration in today’s CRT-based systems comprises –3 CRTs (red, green, blue) commonly called PRT (projection ray tube) –Projection lens (3 per TV) liquid coupled to PRT –Mirror –Screen Lenticular and Fresnel –Cabinet –Electronics ELECTRONICS COUPLER

9. © 3M 2003 3M Precision Optics The lens architecture and design are strongly influenced by system considerations Low cost & high volume Image contrast Brightness –f/1 Optical configuration –compact, wide fov, 3 CRTs, curved faceplate Resolution (NTSC vs. digital vs. HDTV) Thermal environment –liquid coupled Spectral –phosphors, filtering, color-corrected?

10. © 3M 2003 3M Precision Optics The lens design requirements were set to meet consumer digital TV performance 5” raster diagonal (object size for 7” CRT) –350 mm faceplate radius f/1.07 40” to 70” screen diagonal (image size) 77 mm efl Standard RGB phosphors; liquid coupled Four element design (high volume) –non color-corrected Resolution to meet digital TV performance

11. © 3M 2003 3M Precision Optics Modern CRT projection lenses began with Betensky’s Delta lens patent (USP 4,300,817) Weak aspheric front element Biconvex second element provides most of optical power Negative field flattener

12. © 3M 2003 3M Precision Optics The three projected images are angularly converged on the screen The red and blue CRTs are tilted to satisfy the Scheimpflug condition for uniform focus across the screen –The shape of the raster is adjusted to compensate the keystone Additionally, there is about 10% distortion in the projected image, which is pre-corrected by the raster

13. © 3M 2003 3M Precision Optics The three CRT phosphors have very different characteristics

14. © 3M 2003 3M Precision Optics Absorption of side-bands reduces need for color correction and improves color purity SMPTE phosphors w/ ECP

15. © 3M 2003 3M Precision Optics A four element design was developed to meet the requirements acrylic aspheres glass (SK5) fluid faceplate phosphor screen

16. © 3M 2003 3M Precision Optics

17. © 3M 2003 3M Precision Optics Exploded view of PRT light box assembly [courtesy of HED(US)] tube AB lens coupler yoke C lens

18. © 3M 2003 3M Precision Optics The monochromatic MTF meets the performance requirements

19. © 3M 2003 3M Precision Optics A slight adjustment to the C-element flattens the wavelength dependent field shape 0% 35% 70% 85% 100% green red

20. © 3M 2003 3M Precision Optics The lens operates in a thermal environment that ranges from 20°C to 65°C The optical powers in the lens are optimized during design to balance most of the thermal drift –fluid index changes from 1.437 (cold) and 1.423 (hot) For higher performing lenses, a thermal bar is used to “adjust” the focus during operation

21. © 3M 2003 3M Precision Optics Microdisplay technology has improved in cost and performance to enter the consumer market Devices are ~1” on the diagonal –transmissive LCD (high temperature poly-silicon, HTPS) –digital micromirror device (DMD) –reflective liquid crystal on silicon (LCoS) Most devices being integrated into RPTV systems are wide XGA (i.e., 1280x720) –high definition wide screen LCoS available (i.e., 1920x1080) The optical system must generate light, “homogenize” the light, manage color, illuminate device, imprint on/off + gray- scale image scene, and project the image onto the screen

22. © 3M 2003 3M Precision Optics Typical schematic for DMD system

23. © 3M 2003 3M Precision Optics The standard architecture for transmissive LCD uses an X-cube for color management PROJECTION LENS RELAY OPTICS LCD DEVICES DICHROICS LAMP X-CUBE from USP 5,959,778

24. © 3M 2003 3M Precision Optics 3-panel LCoS can use a similar arrangement PROJECTION LENS RELAY OPTICS (not shown) LCoS DEVICE LAMP LCoS DEVICE from USP 6,273,567

25. © 3M 2003 3M Precision Optics Microdisplay system requirements will move lens designs in different directions Still a projection system –total conjugate distances are comparable –thermal effects are important (but environments are different) 1 lens (vs. 3 lenses) –full color correction (<1 pixel vs. ~N/A) –telecentric –f/2.4-2.8 (vs. f/1.1) and magnification of ~50-80x (vs. ~8-13x) Pixelated display –Nyquist frequency of ~50 lpm (vs. ~5 lpm) –distortion correction (<1% vs. 10%) More complex optical system –interaction between illumination system, imager “physics” and lens design is important

26. © 3M 2003 3M Precision Optics USP 6,144,503 USP 5,870,228 USP 5,042,929USP 5,760,965

27. © 3M 2003 3M Precision Optics In the end, the same things will be important Low cost & high volume Image contrast Brightness Optical configuration –compact, wide fov Resolution (HDTV) Thermal environment Color-corrected Low distortion

28. © 3M 2003 3M Precision Optics