Abstract

We present a new lithographic technique based on a hybrid photothermal process to modulate the refractive index in commercial SU-8 photoresist. Owing to a difference in cross-linking, the refractive index of unexposed SU-8 cross-linked by thermally induced polymerization is 0.0072 higher than that of SU-8 cross-linked by UV exposure and postbaking. Making use of this property, we fabricated two thick, flat-topped index-modulated diffractive optical elements (DOEs) that contain different phase distributions and measured their wavefront reconstruction. The good experimental reconstructions of the index DOEs demonstrate the potential to extend the refractive-index modulation technique for the fabrication of three-dimensional optical elements without needing a development step.

© 2006 Optical Society of America

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References

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    [CrossRef]
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    [CrossRef] [PubMed]

2004 (1)

2003 (1)

R. Feng and R. J. Farris, J. Micromech. Microeng. 13, 80 (2003).
[CrossRef]

2001 (1)

A. Cusano, G. Breglio, M. Giordano, A. Calabrò, A. Cutolo, and L. Nicolais, J. Opt. A, Pure Appl. Opt. 3, 126 (2001).
[CrossRef]

2000 (2)

A. L. Bogdanov and S. S. Peredkov, Microelectron. Eng. 53, 493 (2000).
[CrossRef]

O. M. Efimov, L. B. Glebov, and V. I. Smirnov, Opt. Lett. 25, 1693 (2000).
[CrossRef]

1994 (1)

1992 (1)

J. de Boer, R. J. Visser, and G. P. Melis, Polymer 33, 1123 (1992).
[CrossRef]

Bennamane, B.

Bogdanov, A. L.

A. L. Bogdanov and S. S. Peredkov, Microelectron. Eng. 53, 493 (2000).
[CrossRef]

Breglio, G.

A. Cusano, G. Breglio, M. Giordano, A. Calabrò, A. Cutolo, and L. Nicolais, J. Opt. A, Pure Appl. Opt. 3, 126 (2001).
[CrossRef]

Calabrò, A.

A. Cusano, G. Breglio, M. Giordano, A. Calabrò, A. Cutolo, and L. Nicolais, J. Opt. A, Pure Appl. Opt. 3, 126 (2001).
[CrossRef]

Cusano, A.

A. Cusano, G. Breglio, M. Giordano, A. Calabrò, A. Cutolo, and L. Nicolais, J. Opt. A, Pure Appl. Opt. 3, 126 (2001).
[CrossRef]

Cutolo, A.

A. Cusano, G. Breglio, M. Giordano, A. Calabrò, A. Cutolo, and L. Nicolais, J. Opt. A, Pure Appl. Opt. 3, 126 (2001).
[CrossRef]

Darraud, C.

de Boer, J.

J. de Boer, R. J. Visser, and G. P. Melis, Polymer 33, 1123 (1992).
[CrossRef]

Decossas, J. L.

Efimov, O. M.

Farris, R. J.

R. Feng and R. J. Farris, J. Micromech. Microeng. 13, 80 (2003).
[CrossRef]

Feng, R.

R. Feng and R. J. Farris, J. Micromech. Microeng. 13, 80 (2003).
[CrossRef]

Gagnadre, C.

Giordano, M.

A. Cusano, G. Breglio, M. Giordano, A. Calabrò, A. Cutolo, and L. Nicolais, J. Opt. A, Pure Appl. Opt. 3, 126 (2001).
[CrossRef]

Glebov, L. B.

Hardman, R.

R. Hardman, MicroChem Corporation, 1254 Chestnut Street, Newton, Massachusetts 02464 (personal communication, 2005).

Melis, G. P.

J. de Boer, R. J. Visser, and G. P. Melis, Polymer 33, 1123 (1992).
[CrossRef]

Nicolais, L.

A. Cusano, G. Breglio, M. Giordano, A. Calabrò, A. Cutolo, and L. Nicolais, J. Opt. A, Pure Appl. Opt. 3, 126 (2001).
[CrossRef]

Peredkov, S. S.

A. L. Bogdanov and S. S. Peredkov, Microelectron. Eng. 53, 493 (2000).
[CrossRef]

Smirnov, V. I.

Stejny, J.

Tao, S. H.

Vareille, J. C.

Visser, R. J.

J. de Boer, R. J. Visser, and G. P. Melis, Polymer 33, 1123 (1992).
[CrossRef]

Yuan, X.-C.

Appl. Opt. (2)

J. Micromech. Microeng. (1)

R. Feng and R. J. Farris, J. Micromech. Microeng. 13, 80 (2003).
[CrossRef]

J. Opt. A, Pure Appl. Opt. (1)

A. Cusano, G. Breglio, M. Giordano, A. Calabrò, A. Cutolo, and L. Nicolais, J. Opt. A, Pure Appl. Opt. 3, 126 (2001).
[CrossRef]

Microelectron. Eng. (1)

A. L. Bogdanov and S. S. Peredkov, Microelectron. Eng. 53, 493 (2000).
[CrossRef]

Opt. Lett. (1)

Polymer (1)

J. de Boer, R. J. Visser, and G. P. Melis, Polymer 33, 1123 (1992).
[CrossRef]

Other (1)

R. Hardman, MicroChem Corporation, 1254 Chestnut Street, Newton, Massachusetts 02464 (personal communication, 2005).

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Figures (3)

Fig. 1
Fig. 1

Flow chart showing the cross-linking of two samples of SU-8 2005 by different fabrication procedures.

Fig. 2
Fig. 2

Schematic illustration of index DOE fabrication: (a) acids formed in the UV exposed region, (b) exposed region cross-linked at low temperature in the presence of an acid catalyst, (c) high-temperature ( 170 ° C ) triggered cross-linking of the unexposed region, (d) fabricated DOE with slight surface relief, (e) scanning-electron microscope photograph of the index DOE (tilted 65° from the horizontal) as depicted in (d), (f) new layer of SU-8, exposed and cured on the DOE to achieve a flat-topped surface.

Fig. 3
Fig. 3

Experimental measurement of the reconstruction of (a) the letter A and (b) a Bessel beam.

Equations (2)

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n 2 1 n 2 + 2 = 4 π N 3 M ϵ ρ β ,
θ = 2 π λ ( n 1 n 2 ) h ,

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