Abstract

A novel type of liquid microlens, bounded by a microfabricated, distensible membrane and activated by a microfluidic liquid-handling system, is presented. By use of an elastomer membrane fabricated by spin coating onto a dry-etched silicon substrate, the liquid-filled cavity acts as a lens whereby applied pressure changes the membrane distension and thus the focal length. Both plano–convex and plano–concave lenses, individual elements as well as arrays, were fabricated and tested. The lens surface roughness was seen to be ∼9 nm rms, and the focal length could be tuned from 1 to 18 mm. This lens represents a robust, self-contained tunable optical structure suitable for use in, for example, a medical environment.

© 2005 Optical Society of America

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References

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  1. D. Daly, Microlens Arrays (Taylor & Francis, New York, 2001).
  2. J. C. Roulet, R. Völkel, H. P. Herzig, E. Verpoorte, N. F. de Rooij, R. Dändliker, “Microlens systems for fluorescence detection in chemical microsystems,” Opt. Eng. 40, 814–821 (2001).
    [CrossRef]
  3. H.-P. Herzig, Micro-optics (Taylor & Francis, New York, 1997).
  4. B. Berge, J. Perseux, “Variable focal lens controlled by an external voltage: an application of electrowetting,” Eur. Phys. 3, 159–163 (2000).
  5. T. Krupenkin, S. Yang, P. Mach, “Tunable liquid microlens,” Appl. Phys. Lett. 82, 316–318 (2003).
    [CrossRef]
  6. H. Ren, Y.-H. Fan, S.-T. Wu, “Liquid-crystal microlens arrays using patterned polymer networks,” Opt. Lett. 29, 1608–1610 (2004).
    [CrossRef] [PubMed]
  7. J. Chen, W. Wang, J. Fang, K. Varahramyan, “Variable-focusing microlens with microfluidic chip,” Micromech. Microeng. 14, 675–680 (2004).
    [CrossRef]
  8. N. Chronis, G. L. Liu, K.-H. Jeong, L. P. Lee, “Tunable liquid-filled microlens array integrated with microfluidic network,” Opt. Express 19, 2370–2378 (2003), http://www.opticsexpress.org .
    [CrossRef]
  9. A. Casner, J.-P. Delville, “Adaptive lensing driven by the radiation pressure of a continuous-wave laser wave upon a near-critical liquid-liquid interface,” Opt. Lett. 26, 1418–1420 (2001).
    [CrossRef]
  10. M. Madou, Fundamentals of Microfabrication (CRC Press, Boca Raton, Fla., 2002.

2004 (2)

J. Chen, W. Wang, J. Fang, K. Varahramyan, “Variable-focusing microlens with microfluidic chip,” Micromech. Microeng. 14, 675–680 (2004).
[CrossRef]

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

2003 (2)

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

N. Chronis, G. L. Liu, K.-H. Jeong, L. P. Lee, “Tunable liquid-filled microlens array integrated with microfluidic network,” Opt. Express 19, 2370–2378 (2003), http://www.opticsexpress.org .
[CrossRef]

2001 (2)

A. Casner, J.-P. Delville, “Adaptive lensing driven by the radiation pressure of a continuous-wave laser wave upon a near-critical liquid-liquid interface,” Opt. Lett. 26, 1418–1420 (2001).
[CrossRef]

J. C. Roulet, R. Völkel, H. P. Herzig, E. Verpoorte, N. F. de Rooij, R. Dändliker, “Microlens systems for fluorescence detection in chemical microsystems,” Opt. Eng. 40, 814–821 (2001).
[CrossRef]

2000 (1)

B. Berge, J. Perseux, “Variable focal lens controlled by an external voltage: an application of electrowetting,” Eur. Phys. 3, 159–163 (2000).

Berge, B.

B. Berge, J. Perseux, “Variable focal lens controlled by an external voltage: an application of electrowetting,” Eur. Phys. 3, 159–163 (2000).

Casner, A.

Chen, J.

J. Chen, W. Wang, J. Fang, K. Varahramyan, “Variable-focusing microlens with microfluidic chip,” Micromech. Microeng. 14, 675–680 (2004).
[CrossRef]

Chronis, N.

N. Chronis, G. L. Liu, K.-H. Jeong, L. P. Lee, “Tunable liquid-filled microlens array integrated with microfluidic network,” Opt. Express 19, 2370–2378 (2003), http://www.opticsexpress.org .
[CrossRef]

Daly, D.

D. Daly, Microlens Arrays (Taylor & Francis, New York, 2001).

Dändliker, R.

J. C. Roulet, R. Völkel, H. P. Herzig, E. Verpoorte, N. F. de Rooij, R. Dändliker, “Microlens systems for fluorescence detection in chemical microsystems,” Opt. Eng. 40, 814–821 (2001).
[CrossRef]

de Rooij, N. F.

J. C. Roulet, R. Völkel, H. P. Herzig, E. Verpoorte, N. F. de Rooij, R. Dändliker, “Microlens systems for fluorescence detection in chemical microsystems,” Opt. Eng. 40, 814–821 (2001).
[CrossRef]

Delville, J.-P.

Fan, Y.-H.

Fang, J.

J. Chen, W. Wang, J. Fang, K. Varahramyan, “Variable-focusing microlens with microfluidic chip,” Micromech. Microeng. 14, 675–680 (2004).
[CrossRef]

Herzig, H. P.

J. C. Roulet, R. Völkel, H. P. Herzig, E. Verpoorte, N. F. de Rooij, R. Dändliker, “Microlens systems for fluorescence detection in chemical microsystems,” Opt. Eng. 40, 814–821 (2001).
[CrossRef]

Herzig, H.-P.

H.-P. Herzig, Micro-optics (Taylor & Francis, New York, 1997).

Jeong, K.-H.

N. Chronis, G. L. Liu, K.-H. Jeong, L. P. Lee, “Tunable liquid-filled microlens array integrated with microfluidic network,” Opt. Express 19, 2370–2378 (2003), http://www.opticsexpress.org .
[CrossRef]

Krupenkin, T.

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

Lee, L. P.

N. Chronis, G. L. Liu, K.-H. Jeong, L. P. Lee, “Tunable liquid-filled microlens array integrated with microfluidic network,” Opt. Express 19, 2370–2378 (2003), http://www.opticsexpress.org .
[CrossRef]

Liu, G. L.

N. Chronis, G. L. Liu, K.-H. Jeong, L. P. Lee, “Tunable liquid-filled microlens array integrated with microfluidic network,” Opt. Express 19, 2370–2378 (2003), http://www.opticsexpress.org .
[CrossRef]

Mach, P.

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

Madou, M.

M. Madou, Fundamentals of Microfabrication (CRC Press, Boca Raton, Fla., 2002.

Perseux, J.

B. Berge, J. Perseux, “Variable focal lens controlled by an external voltage: an application of electrowetting,” Eur. Phys. 3, 159–163 (2000).

Ren, H.

Roulet, J. C.

J. C. Roulet, R. Völkel, H. P. Herzig, E. Verpoorte, N. F. de Rooij, R. Dändliker, “Microlens systems for fluorescence detection in chemical microsystems,” Opt. Eng. 40, 814–821 (2001).
[CrossRef]

Varahramyan, K.

J. Chen, W. Wang, J. Fang, K. Varahramyan, “Variable-focusing microlens with microfluidic chip,” Micromech. Microeng. 14, 675–680 (2004).
[CrossRef]

Verpoorte, E.

J. C. Roulet, R. Völkel, H. P. Herzig, E. Verpoorte, N. F. de Rooij, R. Dändliker, “Microlens systems for fluorescence detection in chemical microsystems,” Opt. Eng. 40, 814–821 (2001).
[CrossRef]

Völkel, R.

J. C. Roulet, R. Völkel, H. P. Herzig, E. Verpoorte, N. F. de Rooij, R. Dändliker, “Microlens systems for fluorescence detection in chemical microsystems,” Opt. Eng. 40, 814–821 (2001).
[CrossRef]

Wang, W.

J. Chen, W. Wang, J. Fang, K. Varahramyan, “Variable-focusing microlens with microfluidic chip,” Micromech. Microeng. 14, 675–680 (2004).
[CrossRef]

Wu, S.-T.

Yang, S.

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

Appl. Phys. Lett. (1)

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

Eur. Phys. (1)

B. Berge, J. Perseux, “Variable focal lens controlled by an external voltage: an application of electrowetting,” Eur. Phys. 3, 159–163 (2000).

Micromech. Microeng. (1)

J. Chen, W. Wang, J. Fang, K. Varahramyan, “Variable-focusing microlens with microfluidic chip,” Micromech. Microeng. 14, 675–680 (2004).
[CrossRef]

Opt. Eng. (1)

J. C. Roulet, R. Völkel, H. P. Herzig, E. Verpoorte, N. F. de Rooij, R. Dändliker, “Microlens systems for fluorescence detection in chemical microsystems,” Opt. Eng. 40, 814–821 (2001).
[CrossRef]

Opt. Express (1)

N. Chronis, G. L. Liu, K.-H. Jeong, L. P. Lee, “Tunable liquid-filled microlens array integrated with microfluidic network,” Opt. Express 19, 2370–2378 (2003), http://www.opticsexpress.org .
[CrossRef]

Opt. Lett. (2)

Other (3)

M. Madou, Fundamentals of Microfabrication (CRC Press, Boca Raton, Fla., 2002.

H.-P. Herzig, Micro-optics (Taylor & Francis, New York, 1997).

D. Daly, Microlens Arrays (Taylor & Francis, New York, 2001).

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Figures (13)

Fig. 1
Fig. 1

Cross-sectional diagram of a membrane-based microfluidic microlens, showing its implementation as plano–convex and plano–concave lenses. The drawing is to scale for a microlens with diameter d = 400 µm.

Fig. 2
Fig. 2

Microphotograph of two distended plano–convex lenses achieved by application of positive fluidic pressure. The lens diameter of 400 µm is shown.

Fig. 3
Fig. 3

Process summary: (a) Silicon wafer with both side SiO2 layer and with back side opened by RIE; (b) photoresist, spin coated and structured; (c) first ICP RIE etching; (d) spin coating of primer and PDMS; (e) second ICP RIE etching; (f) SiO2 removal; (g) bonding of the Pyrex wafer and patterning of the back-side chromium layer; (h) sawing and filling of the devices.

Fig. 4
Fig. 4

Layout for a lens array with 400-µm lenses.

Fig. 5
Fig. 5

Lens radius of curvature as a function of pressure applied to the liquid optical medium (ethanol and water) as measured by white-light interferometry.

Fig. 6
Fig. 6

Complete lens profile measured by a mechanical profiler for a 500-µm-diameter lens as a function of applied pressure in the range 454 kPa.

Fig. 7
Fig. 7

Measurement setup for focal-length measurement. A collimated laser beam illuminates the lens array from the back side. The light is focused by each lens, such that the lenses of the array are tested in transmission. One determines the focal length for an individual lens by moving the translation stage in the z direction at that point where the beam waist is minimal. The amount by which the translation stage was moved corresponds to the focal length.

Fig. 8
Fig. 8

Focal length of the membrane lenses as a function of applied pressure as measured directly and as calculated from optical surface profile measurements.

Fig. 9
Fig. 9

Wave fronts and MTFs at several pressures: (a) 11, (b) 21, (c) 40, and (d) 54 kPa. The wavelength in this simulation was determined at λ = 550 nm. Dashed curves show the diffraction limits. PV, peak to valley.

Fig. 10
Fig. 10

Contours measured with a white-light interferometer for the tunable lenses operated in (a) plano–convex and (b) plano–concave modes; the measurements are for a 300-µm diameter lens operated at 4 and 0.2 kPa, respectively.

Fig. 11
Fig. 11

Typical Ansys result for a distended membrane, 50 µm thick, with a pressure of 50 kPa.

Fig. 12
Fig. 12

Comparison of maximum lens distension as a function of pressure as measured by interferometry and surface profiling and compared with simulation results.

Fig. 13
Fig. 13

Lens profile as predicted by an Ansys simulation for a 50-µm-thick PDMS membrane with 400-µm diameter.

Tables (2)

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Table 1 Spherical Aberrations

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Table 2 Wave-Front Aberrations

Equations (2)

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R = d 2 8 h + h 2
f = R ( n 1 1 ) ,

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