Abstract

Standard nonimaging components used to collect and integrate light in light-emitting-diode-based projector light engines such as tapered rods and compound parabolic concentrators are compared to optimized freeform shapes in terms of transmission efficiency and spatial uniformity. We show that the simultaneous optimization of the output surface and the profile shape yields transmission efficiency within the étendue limit up to 90% and spatial uniformity higher than 95%, even for compact sizes. The optimization process involves a manual study of the trends for different shapes and the use of an optimization algorithm to further improve the performance of the freeform lightpipe.

© 2008 Optical Society of America

Full Article  |  PDF Article

References

  • View by:
  • |
  • |

  1. F. Fournier and J. Rolland, “Design methodology for high brightness projectors,” J. Display Technol. 4, 86-91 (2008).
    [CrossRef]
  2. J. M. Teijido, F. Ludley, O. Ripoll, M. Ueda, Y. Oshima, T. Yoshida, K. Toyota, K. Yamamoto, T. Nagara, Y. Kato, A. Wajiki, and S. Umeya, “73.2: compact three panel LED projector engine for portable applications,” SID Int. Symp. Digest Tech. Papers (2006).
    [CrossRef]
  3. E. Geissler, “Meeting the challenges of developing LED-based projection displays,” presented at the Photonics in Multimedia Conference, Strasbourg, France, 3-7 April 2006.
  4. M. H. Keuper, G. Harbers, and S. Paolini, “26.1: RGB LED illuminator for pocket-sized projectors,” SID Int. Symp. Digest Tech. Papers 35, 943-945 (2004).
    [CrossRef]
  5. M. R. Krames, O. B. Shchekin, R. Mueller-Mach, G. O. Mueller, Z. Ling, G. Harbers, and M. G. Craford, “Status and future of high-power light-emitting diodes for solid-state lighting,” J. Display Technol. 3, 160-175 (2007).
    [CrossRef]
  6. R. Karlicek, “Photonic Lattice LEDs are new class of light-emitting device,” LEDs Magazine , 20-23 (August 2007).
  7. E. H. Stupp and M. S. Brennesholtz, Projection displays, Wiley SID series in display technology (Wiley, 1999), pp. xviii, 418.
  8. M. P. Krijn, B. A. Salters, and O. H. Willemsen, “LED-based mini-projectors,” presented at the Photonics in Multimedia Conference, Strasbourg, France, 3-7 April 2006.
  9. H. Murat, D. Cuypers, and H. De Smet, “Design of new collection systems for multi LED light engines,” presented at the Photonics in Multimedia Conference, Strasbourg, France, 3-7 April 2006.
  10. S. Ohuchi, T. Miyoshi, T. Imahase, T. Nakashima, and K. Shikita, “Ultra portable LCOS projector with high-performance optical system,” IEEE Trans. Cons. Electron. 48, 388-393(2002).
    [CrossRef]
  11. J.-W. Pan, C.-M. Wang, W.-S. Sun, and J.-Y. Chang, “Portable digital micromirror device projector using a prism,” Appl. Opt. 46, 5097-5102 (2007).
    [CrossRef] [PubMed]
  12. I. Moreno, “Spatial distribution of LED radiation,” Proc. SPIE 6342, 634216 (2006).
  13. W. Falicoff, J. Chaves, and B. Parkyn, “PC-LED luminance enhancement due to phosphor scattering,” presented at the Nonimaging Optics and Efficient Illumination Systems II Conference, San Diego, Calif. 31 July-1 August 2005.
  14. E. Peli, “Contrast sensitivity function and image discrimination,” J. Opt. Soc. Am. A 18, 283-293 (2001).
    [CrossRef]
  15. R. Winston, J. C. Minano, P. Benitez, and W. T. Welford, Nonimaging Optics (Elsevier Academic, 2005), pp. xi, 497.
  16. W. J. Cassarly, “Nonimaging optics: concentration and illumination,” in Handbook of Optics, 2nd ed. (McGraw-Hill, 1995).
  17. L. A. Whitehead and M. A. Mossman, “Off the beaten path with total internal reflection,” Proc. SPIE 6342, 63420U(2006).
    [CrossRef]
  18. L. A. Piegl and W. Tiller, The NURBS Book, 2nd ed. (Springer, 1997), pp. xiv, 646.
  19. X. Ning, R. Winston, and J. O'Gallagher, “Dielectric totally internally reflecting concentrators,” Appl. Opt. 26, 300-305(1987).
    [CrossRef] [PubMed]
  20. J. Rodgers, “Slope error tolerances for optical surfaces,” presented at the SPIE Optifab Conference, Rochester, N.Y., 15-17 May 2007.

2008 (1)

2007 (2)

2006 (3)

J. M. Teijido, F. Ludley, O. Ripoll, M. Ueda, Y. Oshima, T. Yoshida, K. Toyota, K. Yamamoto, T. Nagara, Y. Kato, A. Wajiki, and S. Umeya, “73.2: compact three panel LED projector engine for portable applications,” SID Int. Symp. Digest Tech. Papers (2006).
[CrossRef]

I. Moreno, “Spatial distribution of LED radiation,” Proc. SPIE 6342, 634216 (2006).

L. A. Whitehead and M. A. Mossman, “Off the beaten path with total internal reflection,” Proc. SPIE 6342, 63420U(2006).
[CrossRef]

2004 (1)

M. H. Keuper, G. Harbers, and S. Paolini, “26.1: RGB LED illuminator for pocket-sized projectors,” SID Int. Symp. Digest Tech. Papers 35, 943-945 (2004).
[CrossRef]

2002 (1)

S. Ohuchi, T. Miyoshi, T. Imahase, T. Nakashima, and K. Shikita, “Ultra portable LCOS projector with high-performance optical system,” IEEE Trans. Cons. Electron. 48, 388-393(2002).
[CrossRef]

2001 (1)

1987 (1)

Appl. Opt. (2)

IEEE Trans. Cons. Electron. (1)

S. Ohuchi, T. Miyoshi, T. Imahase, T. Nakashima, and K. Shikita, “Ultra portable LCOS projector with high-performance optical system,” IEEE Trans. Cons. Electron. 48, 388-393(2002).
[CrossRef]

J. Display Technol. (2)

J. Opt. Soc. Am. A (1)

LEDs Magazine (1)

R. Karlicek, “Photonic Lattice LEDs are new class of light-emitting device,” LEDs Magazine , 20-23 (August 2007).

Proc. SPIE (2)

L. A. Whitehead and M. A. Mossman, “Off the beaten path with total internal reflection,” Proc. SPIE 6342, 63420U(2006).
[CrossRef]

I. Moreno, “Spatial distribution of LED radiation,” Proc. SPIE 6342, 634216 (2006).

SID Int. Symp. Digest Tech. Papers (2)

M. H. Keuper, G. Harbers, and S. Paolini, “26.1: RGB LED illuminator for pocket-sized projectors,” SID Int. Symp. Digest Tech. Papers 35, 943-945 (2004).
[CrossRef]

J. M. Teijido, F. Ludley, O. Ripoll, M. Ueda, Y. Oshima, T. Yoshida, K. Toyota, K. Yamamoto, T. Nagara, Y. Kato, A. Wajiki, and S. Umeya, “73.2: compact three panel LED projector engine for portable applications,” SID Int. Symp. Digest Tech. Papers (2006).
[CrossRef]

Other (9)

E. Geissler, “Meeting the challenges of developing LED-based projection displays,” presented at the Photonics in Multimedia Conference, Strasbourg, France, 3-7 April 2006.

R. Winston, J. C. Minano, P. Benitez, and W. T. Welford, Nonimaging Optics (Elsevier Academic, 2005), pp. xi, 497.

W. J. Cassarly, “Nonimaging optics: concentration and illumination,” in Handbook of Optics, 2nd ed. (McGraw-Hill, 1995).

E. H. Stupp and M. S. Brennesholtz, Projection displays, Wiley SID series in display technology (Wiley, 1999), pp. xviii, 418.

M. P. Krijn, B. A. Salters, and O. H. Willemsen, “LED-based mini-projectors,” presented at the Photonics in Multimedia Conference, Strasbourg, France, 3-7 April 2006.

H. Murat, D. Cuypers, and H. De Smet, “Design of new collection systems for multi LED light engines,” presented at the Photonics in Multimedia Conference, Strasbourg, France, 3-7 April 2006.

W. Falicoff, J. Chaves, and B. Parkyn, “PC-LED luminance enhancement due to phosphor scattering,” presented at the Nonimaging Optics and Efficient Illumination Systems II Conference, San Diego, Calif. 31 July-1 August 2005.

J. Rodgers, “Slope error tolerances for optical surfaces,” presented at the SPIE Optifab Conference, Rochester, N.Y., 15-17 May 2007.

L. A. Piegl and W. Tiller, The NURBS Book, 2nd ed. (Springer, 1997), pp. xiv, 646.

Cited By

OSA participates in CrossRef's Cited-By Linking service. Citing articles from OSA journals and other participating publishers are listed here.

Alert me when this article is cited.


Figures (15)

Fig. 1
Fig. 1

Example of a single-element light engine made of a freeform lightpipe. In this configuration the LED (which is mounted on a board) is directly coupled to the microdisplay.

Fig. 2
Fig. 2

Rays that hit the receivers in the simulation software are converted to an illuminance map. Because of the statistical nature of the ray generation process, the illuminance map has statistical noise that depends on the number of rays traced on the size of the cells in the mesh.

Fig. 3
Fig. 3

(a) Transmission efficiency within NA = 0.2 and (b) spatial nonuniformities for hollow tapered rods, solid tapered rods, hollow CPCs, and solid CPCs of various lengths. Data for CPC-like devices is not available for the shortest lengths, as the theoretical shape of the CPC requires a minimum length.

Fig. 4
Fig. 4

Models of the lightpipes used as benchmarks.

Fig. 5
Fig. 5

System configuration. Uniformity and efficiency are measured on a flat plane at the lightpipe output. For a solid lightpipe, an air gap is left between the LED and the lightpipe input face.

Fig. 6
Fig. 6

Evolution of the illuminance pattern at the output of a solid CPC-like lightpipe as length increases from 60 to 95 mm . Local minima in the relative standard deviation of illuminance is observed at 60, 75, and 95 mm .

Fig. 7
Fig. 7

Intensity distributions at nine different positions on the output face of (a) a 60 mm solid tapered rod and (b) a 60 mm solid CPC-type lightpipe. CPCs exhibit a fairly uniform intensity distribution across the device output, which is not the case for tapered rods. For this reason, the performance of tapered rods can be greatly improved by adding an output lens.

Fig. 8
Fig. 8

Tapered rods with (a) a spherical and (b) a Fresnel lens.

Fig. 9
Fig. 9

Transmission efficiency within NA = 0.2 and (b) spatial nonuniformities for solid tapered rods with no lens, a spherical lens, and a Fresnel lens at the rod output.

Fig. 10
Fig. 10

Optimum output radius for rod lengths ranging from 20 to 120 mm .

Fig. 11
Fig. 11

Illuminance pattern at the lightpipe output with a spherical lens, a Fresnel lens, and a Fresnel lens with 1 mm defocus. The images have been generated with a larger receiver mesh ( 200 × 150 ) and 10 7 rays to resolve the pattern caused by the Fresnel lens grooves. Defocus partially gets rid of the ring pattern but produces a slight illuminance falloff on the edges. In a configuration using a reflective microdisplay, the edge falloff observed with a spherical lens can be compensated by the relay lens.

Fig. 12
Fig. 12

Variation of the illuminance map as the central control point is moved up and down for a 30 mm lightpipe. A slight hyperbolic shape can provide good uniformity.

Fig. 13
Fig. 13

Transmission efficiency (%) and spatial nonuniformities (%) for a 30 mm tapered rod with various profile shapes. The x axis corresponds to the horizontal position of the middle control point of the Bezier curve, as depicted in Fig. 12. The y axis is the vertical displacement of the control point relative to the tapered rod position. y = 0 corresponds to a tapered rod shape; y > 0 corresponds to a parabolic shape; y < 0 corresponds to a hyperbolic shape.

Fig. 14
Fig. 14

Illuminance map at the top surface of the Osram Ostar LED. The four-die structure of the emissive area is clearly visible. Light falloff on the edges is gradual, and occurs beyond the ac tual physical size of the die indicated by the white dashed line ( 2.1 mm × 2.1 mm ).

Fig. 15
Fig. 15

Transmission efficiency (%) within NA = 0.2 for a 30 mm tapered rod with a lens for varying lightpipe input height and width. Maximum transmission efficiency is obtained in this case for a 2.24 mm × 2.04 mm input size.

Equations (8)

Equations on this page are rendered with MathJax. Learn more.

E = n 2 d A d ω cos θ n 2 A Ω = n 2 A π sin 2 θ 1 / 2 ,
RSD = σ E ¯ = 1 N i = 1 N ( E i E ¯ - 1 ) 2 .
f max = ν max w μ D FOV ,
C ( ν ) = E max - E min E max + E min ,
E ( x ) = 1 2 [ E max ( 1 + sin x ) + E min ( 1 - sin x ) ] .
E ¯ = 1 2 π 0 2 π E ( x ) d x = E max + E min 2 ,
σ = 1 2 π 0 2 π ( E ( x ) - E ¯ ) 2 d x = E max - E min 2 2 .
RSD ( ν ) = σ E ¯ = C ( ν ) 2 .

Metrics