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Energy Express

  • Editor: Bernard Kippelen
  • Vol. 19, Iss. S4 — Jul. 4, 2011
  • pp: A740–A746
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Three-dimensional illumination system using dielectric liquid lenses

Yen-Sheng Lu, Ling-Yu Tsai, Kuo-Cheng Huang, C. Gary Tsai, Chih-Cheng Yang, and J. Andrew Yeh  »View Author Affiliations


Optics Express, Vol. 19, Issue S4, pp. A740-A746 (2011)
http://dx.doi.org/10.1364/OE.19.00A740


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Abstract

A 25-pixel illumination system composed of a 5 × 5 dielectric liquid-lens (DLL) zoom module array, 25 light-emission diodes (LEDs), and a secondary optical lens demonstrates 3D light field manipulation. LEDs function as 2D illumination pixels while the DLL module array performs longitudinal illuminance adjustability by zooming each illumination pixel. A test on the similarity of two illuminance patterns between experiments and simulations shows a normalized cross correlation (NCC) higher than 0.8, indicating the feasibility of the system design. Also, the illumination system is further applied to correct a distorted light pattern on a 45° tilt screen as well as to perform light compensation on distance-differential objects.

© 2011 OSA

1. Introduction

Light has been extensively used in our daily lives since the invention of the incandescent light bulb by Thomas Edison. The illuminance of a point-of-light source is inversely proportional to the travel distance of light, squared. Such an illumination phenomenon induces a non-uniform illumination on distance-differential objects (the objects with different distances from the light source) so that the object closer to the source appears brighter. Highly controllable illumination is still desired to improve quality of life and comfort via room atmosphere, decoration, captured image quality, public security, and so forth. A typical solution to the problem of increasing light controllability is to introduce a lens module to focus, magnify, or zoom the projected beam of light, providing longitudinal adjustability of illuminance (i.e., one-dimensional light field controllability) [1

1. J. R. Richardson, “Motor-controlled lens system,” US Patent 5,029,992 (July1991).

,2

2. A. Uke and S. Wright, “Multi-lens zoom system and method for flashlights,” US Patent App. 11/668,605 (February 2007).

]. Still, non-uniform light distribution could be improved to some extent, but it remains an issue. To further enhance planar light field controllability, the pixel concept of illumination, usually achieved by an LED array, was introduced to permit individual adjustment of the outgoing light intensity based on each pixel [3

3. P. Schreiber, S. Kudaev, P. Dannberg, and U. D. Zeitner, “Homogeneous LED-illumination using microlens arrays,” Proc. SPIE 5942, 59420K (2005). [CrossRef]

]. To really achieve spatial light manipulation, our approach is to implement zoom ability on each pixel of an LED array.

In the study, we demonstrate the integration of dielectric liquid zoom lenses with 2D illumination LED pixels to form a 3D illumination system where the design is primarily based on paraxial ray approximation using OSLO and TracePro simulation software. To equip focus or zoom ability, methods that could be employed include mechanically tuning the spacing between solid lens modules [1

1. J. R. Richardson, “Motor-controlled lens system,” US Patent 5,029,992 (July1991).

,2

2. A. Uke and S. Wright, “Multi-lens zoom system and method for flashlights,” US Patent App. 11/668,605 (February 2007).

], redistributing the refractive index distribution of liquid crystals [4

4. T. Nose, S. Masuda, and S. Sato, “A liquid crystal microlens with hole-patterned electrodes on both substrates,” Jpn. J. Appl. Phys. 31(Part 1, No. 5B), 1643–1646 (1992). [CrossRef]

7

7. C. C. Cheng, C. A. Chang, C. H. Liu, and J. A. Yeh, “A tunable liquid-crystal microlens with hybrid alignment,” J. Opt. A, Pure Appl. Opt. 8(7), S365–S369 (2006). [CrossRef]

], and deforming liquid-lens profiles [8

8. B. Berge and J. Peseux, “Variable focal lens controlled by an external voltage––an application of electrowetting,” Eur. Phys. J. E 3(2), 159–163 (2000). [CrossRef]

17

17. C. C. Yang, C. G. Tsai, and J. A. Yeh, “Miniaturization of dielectric liquid microlens in package,” Biomicrofluidics 4(4), 43006 (2010). [CrossRef]

]. Among them, liquid lenses driven by electrowetting or dielectric forces is one promising solution because of low power consumption, no moving parts, high transparency, and special miniaturization potential of large pixel systems [11

11. C. C. Cheng, C. A. Chang, and J. A. Yeh, “Variable focus dielectric liquid droplet lens,” Opt. Express 14(9), 4101–4106 (2006). [CrossRef] [PubMed]

17

17. C. C. Yang, C. G. Tsai, and J. A. Yeh, “Miniaturization of dielectric liquid microlens in package,” Biomicrofluidics 4(4), 43006 (2010). [CrossRef]

]. A small form factor along with high power efficiency could lead to portable illumination systems in the future. The illumination system proposed demonstrated light controllability, including spatial light pattern manipulation, correction of distorted light patterns, and a 3D flashlight for the camera. The experimental data such as illuminance patterns were captured and compared with simulation predictions via normalized cross correlation (NCC) to estimate the similarity of light patterns and to show the feasibility of the illumination system design [18

18. C. C. Sun, T. X. Lee, S. H. Ma, Y. L. Lee, and S. M. Huang, “Precise optical modeling for LED lighting verified by cross correlation in the midfield region,” Opt. Lett. 31(14), 2193–2195 (2006). [CrossRef] [PubMed]

].

2. The 3D illumination system

The 3D illumination system consists of a 5 × 5 dielectric liquid-lens zoom module array, 25 LEDs, and a secondary optical lens shown in Fig. 1(a)
Fig. 1 (a) Schematic of the 3D illumination system. The 5 × 5 module array is positioned under the secondary optical lens. (b) Schematic of the single module. Each single module is composed of two face-to-face dielectric liquid lenses and one LED.
. LED illumination pixels assembled in a 2D array in combination with zoom liquid lenses provide light controllability over space for each single module. Figure 1(b) depicts the composition of a single module that contains one LED, two face-to-face dielectric liquid lenses (P1 and P2), and a spacer in between the two liquid lenses. The face-to-face assembly permits larger beam convergence and more light transmission. The dielectric liquid lenses, the core components of the system, realize the zoom ability for each pixel as the focal length of each liquid lens is adjusted via applied voltages. The voltages biased at the liquid lenses are controlled by a microprocessor PICI18F4550 (Microchip Technology Inc., USA) that converts digital signals to voltages we want via pulse width modulation and interface of an inter-integrated circuit (I2C). LED power is adjusted using a digital I/O controller, manipulating the light intensity of each pixel. A secondary optical lens is employed to reduce excessive overlapping of the light beams so that the light pattern can be distributed with higher uniformity.

The system for dynamic light projection onto treasure, jewelry, and antiques with 3D appearance is designed to fully control light patterns in the range of 30 to 60 cm from the illumination system (i.e., within 2X distance variation). The design is primarily based on paraxial ray approximation using OSLO and TracePro simulation software. The LED (Everlight Electronics, 59-146UWD/TR8) has a spot diameter of 2 mm and a viewing angle of ± 25.0°. Each single module has a divergence angle varying from ± 14.0° to ± 7° under a dielectric liquid-lens (DLL) voltage of 40 Vrms, achieving angular magnification of two times and illuminance variation of four times. The spacing between the LED and P1 and that between P1 and P2 are 0.72 mm and 5.22 mm, respectively. The module design is symmetric along the x and y axes. The pitch of adjacent liquid lenses varies a bit to satisfy the secondary lens. For row assembly, the separation gap between the first and second row/column and between the fourth and fifth row/column (close to the outer edges of the secondary lens) is a distance of 14.63 mm. The separation gap between the second and third row/column and third and fourth row/column is a distance of 15.93 mm. The secondary optical lens made of BK7 is designed to have a radius of −294.12 mm, a lens thickness of 15 mm, and a diameter of 50 mm.

The system assembly started from each single module in which LEDs were integrated with two liquid lenses and one spacer. Two liquid lenses were axially aligned face-to-face with the insertion of a spacer in between them using a laser aligner, minimizing tilt and de-center aspects. The lens set was then individually mounted onto a LED-embedded PCB as shown in Fig. 2(a)
Fig. 2 (a) Side view of the packaged single module. The two liquids lenses are positioned face-to-face and fixed on the same optical axis. (b) Top view of the illumination system. The 5 × 5 module array is positioned under the secondary optical lens
, forming a single module. Each single module was plugged into the control circuit board. The secondary optical lens was positioned in front of the 5 × 5 module array. After assembly, the 3D illumination system is shown in Fig. 2(b).

3. Experimental results

3.1 Performance of dielectric liquid lenses

Dielectric liquid lenses consist of two iso-density immiscible liquids that have a refractive index difference of 0.11 and a dielectric constant difference of 43 [15

15. C. G. Tsai, C. N. Chen, L. S. Cheng, C. C. Cheng, J. T. Yang, and J. A. Yeh, “Planar liquid confinement for optical centering of dielectric liquid lenses,” IEEE Photon. Technol. Lett. 21(19), 1396–1398 (2009). [CrossRef]

17

17. C. C. Yang, C. G. Tsai, and J. A. Yeh, “Miniaturization of dielectric liquid microlens in package,” Biomicrofluidics 4(4), 43006 (2010). [CrossRef]

]. Mixed alcohol and silicone oil are used as the sealing liquid and the liquid droplet, respectively. The droplet profile along with the refractive index difference determines the optical powers of the liquid lenses. Each liquid lens has a volume of 5 mm3, corresponding to the droplet diameter of 4.7 mm at the rest state. As DLL voltage is applied, the dielectric force produced on the interface of the two liquids squeezes the droplet, resulting in the change of the effective focal length (EFL). When the applied DLL voltage increased from zero bias to 40 Vrms, the corresponding EFL varied from 53.8 mm to 19.5 mm for the liquid lenses (see Fig. 3
Fig. 3 Focal length variation as a function of driving voltage. The liquid lens at zero bias had a focal length of 53.8 mm. The focal length changed to 19.5 mm when the lens was biased at 40 Vrms.
.). The response time of the DLL was measured to be 400 ms for the full-range tuning. Each single module containing two face-to-face liquid lenses had a divergence angle of ± 14.0° and ± 7.0° when both of the two liquid lenses were set at zero bias and 40 Vrms, respectively, obtaining 2X angular magnification (14/7 = 2) and 4X illuminance variation.

3.2 Light pattern similarity test

The illumination system assembled was first investigated by a similarity test to verify the spatial light controllability. The similarity of two illuminance patterns can be estimated by normalized cross correlation (NCC) [18

18. C. C. Sun, T. X. Lee, S. H. Ma, Y. L. Lee, and S. M. Huang, “Precise optical modeling for LED lighting verified by cross correlation in the midfield region,” Opt. Lett. 31(14), 2193–2195 (2006). [CrossRef] [PubMed]

]. The test was conducted by projecting the letter H onto the screens at 30 cm and at 60 cm from the system, as shown in Fig. 4
Fig. 4 H-shape illuminance patterns at distances of 30 cm and 60 cm from the system. The bias setting of all illuminating pixels was changed to 40 Vrms to obtain a highly similar illuminance pattern. Compared with the reference pattern at 30 cm, the one at 60 cm has an NCC value of 0.9 and an illuminance difference about 7.7%.
. To form the letter H at 30 cm away, all LEDs were turned on except the ones in the gray region (see Fig. 4). The DLL voltages at the corner pixels 1, 5, 21, and 25 were set to be 25 Vrms to converge the light at the corners, and the DLL voltages of other pixels at 6, 10, 11–15,16, and 20 were set at zero bias. For the screen located at 60 cm, the DLL voltages of all LED-on pixels were changed to 40 Vrms to increase the illuminance. The H patterns at the two different distances were measured to have nearly the same geometrical dimensions––20 cm in height and 20 cm in width. MATLAB software was used to convert captured light patterns at 30 cm and 60 cm to illuminance patterns by eliminating hue and saturation information [19

19. S. C. Chapra, Applied Numerical Methods with MATLAB for Engineers and Scientists (McGraw-Hill Higher Education, 2008).

]. The illuminance pattern was calibrated with respect to the central illuminance of the light pattern measured by the lux meter (LUTRON, LX-1108). Illuminance at the center of the pattern H was directly measured to be 91 and 84 lux at 30 cm and 60 cm, respectively. The resultant illuminance difference was about 7.7%, much smaller than the illuminance decay of 75%, due to the 2X distance variation in nature. The NCC between the two experimental illuminance patterns was calculated to be about 0.9, showing the system can project similar light patterns from 30 to 60 cm. As compared with simulation predictions, the experimental illuminance patterns at 30 or 60 cm have an NCC higher than 0.8 shown in Table 1

Table 1. NCC Between Simulation Predictions and Experiment Results for Capital H Pattern at 30 and 60 cm Away from Illumination System

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, implying the feasibility of the illumination system design.

3.3 Correction of light pattern distortion on 45° tilted screen

3.4 Lighting compensation demonstration

For lighting applications, the illumination system was used to compensate for unwanted light distribution for a better image capture. Desired illumination is sometimes difficult to obtain with commercial flashlights. For instance, illumination merely on one side of objects (e.g., due to sunset or sunrise or in an unmanageable environment) might cause some pictures to be overexposed or underexposed. A lighting test was performed on a tiger doll positioned at 30 cm away. The test-bed setup is shown in Fig. 6
Fig. 6 (a) Lighting demonstration on a single target, non-uniform illumination on a tiger doll projected by a commercial flashlight from the right-hand side. (b) Uniform illumination obtained by turning on LEDs at pixels no.1, 2, 6, 7, 11, 12, and 16–25 and setting the DLL voltage at zero bias.
. Initially, it was illuminated by a commercial flashlight on the right-hand side, as shown in Fig. 6 (a). The doll image that was captured appeared to be dimmer at the left-hand side due to insufficient illumination. To increase illuminance properly, LEDs at pixels 1, 2, 6, 7, 11, 12, and 16-25 were turned on with the DLL voltage set at zero bias. With this setting, the features of the doll on the left-hand side displayed clearly, as shown in Fig. 6(b). The other plan was to investigate the capability of simultaneous lighting compensation on distance-differential objects (see Fig. 7
Fig. 7 Lighting demonstration on two distance-differential targets. (a) By turning on LEDs at pixels 9,12,14, and 17 and with setting the DLL voltage at zero bias, the princess was dimmer due to the longer distance. (b) Lighting compensation was executed by setting the DLL voltage at pixels 9 and 14 to be 40 Vrms.
). Two doll images, a Mickey Mouse and a princess, were positioned at 30 cm and 60 cm away from the illumination system, respectively. Four LEDs at pixels 9, 12, 14, and 17 were turned on with the DLL voltage set at zero bias. Illuminance decay by the inverse-square law made the princess doll dimmer by 75% as compared to the Mickey Mouse doll. To have equal illuminance, the voltage of liquid lenses at pixels 9 and 14 were increased to 40 Vrms to converge the light beams onto the princess doll. As a result, the princess doll appeared to be equally bright with the Mickey Mouse doll, each one having benefitted from the zoom ability of each pixel.

4. Conclusion

Obtaining 3D light controllability is greatly desired in order to enhance convenience and comfort in our daily life. We integrate dielectric liquid zoom lenses with 2D illumination LED pixels to form a 25-pixel, 3D illumination system. The illumination system was used to execute a light pattern similarity test, distorted light pattern correction, and lighting compensation demonstration. From the investigation of NCC between experimental data and simulation predictions, the system has an NCC higher than 0.8 in the spatial light pattern test and an NCC close to 0.7 in the image correction test, showing the feasibility of our illumination system design.

References and links

1.

J. R. Richardson, “Motor-controlled lens system,” US Patent 5,029,992 (July1991).

2.

A. Uke and S. Wright, “Multi-lens zoom system and method for flashlights,” US Patent App. 11/668,605 (February 2007).

3.

P. Schreiber, S. Kudaev, P. Dannberg, and U. D. Zeitner, “Homogeneous LED-illumination using microlens arrays,” Proc. SPIE 5942, 59420K (2005). [CrossRef]

4.

T. Nose, S. Masuda, and S. Sato, “A liquid crystal microlens with hole-patterned electrodes on both substrates,” Jpn. J. Appl. Phys. 31(Part 1, No. 5B), 1643–1646 (1992). [CrossRef]

5.

H. W. Ren, Y. H. Fan, and S. T. Wu, “Liquid-crystal microlens arrays using patterned polymer networks,” Opt. Lett. 29(14), 1608–1610 (2004). [CrossRef] [PubMed]

6.

H. W. Ren, D. W. Fox, B. Wu, and S. T. Wu, “Liquid crystal lens with large focal length tunability and low operating voltage,” Opt. Express 15(18), 11328–11335 (2007). [CrossRef] [PubMed]

7.

C. C. Cheng, C. A. Chang, C. H. Liu, and J. A. Yeh, “A tunable liquid-crystal microlens with hybrid alignment,” J. Opt. A, Pure Appl. Opt. 8(7), S365–S369 (2006). [CrossRef]

8.

B. Berge and J. Peseux, “Variable focal lens controlled by an external voltage––an application of electrowetting,” Eur. Phys. J. E 3(2), 159–163 (2000). [CrossRef]

9.

T. Krupenkin, S. Yang, and P. Mach, “Tunable liquid microlens,” Appl. Phys. Lett. 82(3), 316–318 (2003). [CrossRef]

10.

S. Kuiper and B. H. W. Hendriks, “Variable-focus liquid lens for miniature cameras,” Appl. Phys. Lett. 85(7), 1128–1130 (2004). [CrossRef]

11.

C. C. Cheng, C. A. Chang, and J. A. Yeh, “Variable focus dielectric liquid droplet lens,” Opt. Express 14(9), 4101–4106 (2006). [CrossRef] [PubMed]

12.

C. C. Cheng and J. A. Yeh, “Dielectrically actuated liquid lens,” Opt. Express 15(12), 7140–7145 (2007). [CrossRef] [PubMed]

13.

H. W. Ren and S. T. Wu, “Variable-focus liquid lens,” Opt. Express 15(10), 5931–5936 (2007). [CrossRef] [PubMed]

14.

H. W. Ren, H. Q. Xianyu, S. Xu, and S. T. Wu, “Adaptive dielectric liquid lens,” Opt. Express 16(19), 14954–14960 (2008). [CrossRef] [PubMed]

15.

C. G. Tsai, C. N. Chen, L. S. Cheng, C. C. Cheng, J. T. Yang, and J. A. Yeh, “Planar liquid confinement for optical centering of dielectric liquid lenses,” IEEE Photon. Technol. Lett. 21(19), 1396–1398 (2009). [CrossRef]

16.

C. G. Tsai and J. A. Yeh, “Circular dielectric liquid iris,” Opt. Lett. 35(14), 2484–2486 (2010). [CrossRef] [PubMed]

17.

C. C. Yang, C. G. Tsai, and J. A. Yeh, “Miniaturization of dielectric liquid microlens in package,” Biomicrofluidics 4(4), 43006 (2010). [CrossRef]

18.

C. C. Sun, T. X. Lee, S. H. Ma, Y. L. Lee, and S. M. Huang, “Precise optical modeling for LED lighting verified by cross correlation in the midfield region,” Opt. Lett. 31(14), 2193–2195 (2006). [CrossRef] [PubMed]

19.

S. C. Chapra, Applied Numerical Methods with MATLAB for Engineers and Scientists (McGraw-Hill Higher Education, 2008).

OCIS Codes
(080.0080) Geometric optics : Geometric optics
(080.4295) Geometric optics : Nonimaging optical systems

History
Original Manuscript: March 16, 2011
Revised Manuscript: May 1, 2011
Manuscript Accepted: May 2, 2011
Published: June 3, 2011

Citation
Yen-Sheng Lu, Ling-Yu Tsai, Kuo-Cheng Huang, C. Gary Tsai, Chih-Cheng Yang, and J. Andrew Yeh, "Three-dimensional illumination system using dielectric liquid lenses," Opt. Express 19, A740-A746 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-S4-A740


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References

  1. J. R. Richardson, “Motor-controlled lens system,” US Patent 5,029,992 (July1991).
  2. A. Uke and S. Wright, “Multi-lens zoom system and method for flashlights,” US Patent App. 11/668,605 (February 2007).
  3. P. Schreiber, S. Kudaev, P. Dannberg, and U. D. Zeitner, “Homogeneous LED-illumination using microlens arrays,” Proc. SPIE 5942, 59420K (2005). [CrossRef]
  4. T. Nose, S. Masuda, and S. Sato, “A liquid crystal microlens with hole-patterned electrodes on both substrates,” Jpn. J. Appl. Phys. 31(Part 1, No. 5B), 1643–1646 (1992). [CrossRef]
  5. H. W. Ren, Y. H. Fan, and S. T. Wu, “Liquid-crystal microlens arrays using patterned polymer networks,” Opt. Lett. 29(14), 1608–1610 (2004). [CrossRef] [PubMed]
  6. H. W. Ren, D. W. Fox, B. Wu, and S. T. Wu, “Liquid crystal lens with large focal length tunability and low operating voltage,” Opt. Express 15(18), 11328–11335 (2007). [CrossRef] [PubMed]
  7. C. C. Cheng, C. A. Chang, C. H. Liu, and J. A. Yeh, “A tunable liquid-crystal microlens with hybrid alignment,” J. Opt. A, Pure Appl. Opt. 8(7), S365–S369 (2006). [CrossRef]
  8. B. Berge and J. Peseux, “Variable focal lens controlled by an external voltage––an application of electrowetting,” Eur. Phys. J. E 3(2), 159–163 (2000). [CrossRef]
  9. T. Krupenkin, S. Yang, and P. Mach, “Tunable liquid microlens,” Appl. Phys. Lett. 82(3), 316–318 (2003). [CrossRef]
  10. S. Kuiper and B. H. W. Hendriks, “Variable-focus liquid lens for miniature cameras,” Appl. Phys. Lett. 85(7), 1128–1130 (2004). [CrossRef]
  11. C. C. Cheng, C. A. Chang, and J. A. Yeh, “Variable focus dielectric liquid droplet lens,” Opt. Express 14(9), 4101–4106 (2006). [CrossRef] [PubMed]
  12. C. C. Cheng and J. A. Yeh, “Dielectrically actuated liquid lens,” Opt. Express 15(12), 7140–7145 (2007). [CrossRef] [PubMed]
  13. H. W. Ren and S. T. Wu, “Variable-focus liquid lens,” Opt. Express 15(10), 5931–5936 (2007). [CrossRef] [PubMed]
  14. H. W. Ren, H. Q. Xianyu, S. Xu, and S. T. Wu, “Adaptive dielectric liquid lens,” Opt. Express 16(19), 14954–14960 (2008). [CrossRef] [PubMed]
  15. C. G. Tsai, C. N. Chen, L. S. Cheng, C. C. Cheng, J. T. Yang, and J. A. Yeh, “Planar liquid confinement for optical centering of dielectric liquid lenses,” IEEE Photon. Technol. Lett. 21(19), 1396–1398 (2009). [CrossRef]
  16. C. G. Tsai and J. A. Yeh, “Circular dielectric liquid iris,” Opt. Lett. 35(14), 2484–2486 (2010). [CrossRef] [PubMed]
  17. C. C. Yang, C. G. Tsai, and J. A. Yeh, “Miniaturization of dielectric liquid microlens in package,” Biomicrofluidics 4(4), 43006 (2010). [CrossRef]
  18. C. C. Sun, T. X. Lee, S. H. Ma, Y. L. Lee, and S. M. Huang, “Precise optical modeling for LED lighting verified by cross correlation in the midfield region,” Opt. Lett. 31(14), 2193–2195 (2006). [CrossRef] [PubMed]
  19. S. C. Chapra, Applied Numerical Methods with MATLAB for Engineers and Scientists (McGraw-Hill Higher Education, 2008).

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