Abstract

Batch-fabrication of a micro-ball lens array (MBA) could not only reduce micro assembly costs but also replace conventional ball lenses or costly GRINs (Gradient Refractive Index) without compromising performance. Compared with conventional half-spherical micro-lenses, the MBA is a spherical micro-lens that can focus light in all directions, thus providing the flexibility required for optical applications. Current MBAs are made of SU-8 photoresist by an extrusion process rather than the traditional thermal reflow process. The aim of this study was to develop a new process for MBA batch-fabrication, performed at ambient temperature, by spin-coating SU-8 onto a silicon-wafer surface, which serves as an extrusion plate, and extruding it through a nozzle to form an MBA. The nozzle consists of a nozzle orifice and nozzle cavity, the former being defined and made from SU-8 photoresist using ultra-violet (UV) lithography, which results in good mechanical properties. In this paper, the fabrication of 4×4 MBAs with diameters ranging from 60 to 550 um is described. Optical measurements indicated a diameter variance within 3% and a maximum coupling efficiency of approximately 62% when the single mode fiber (SMF) was placed at a distance of 10um from the MBA. The results of this study proved that MBA fabrication by the extrusion process can enhance the coupling efficiency.

©2009 Optical Society of America

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References

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  1. D. Daly, R. F. Stevens, M. C. Hutley, and N. Davies, “The Manufacture of Microlenses by Melting Photoresist,” Meas. Sci. Technol.  1(8), 759–766 (1990).
    [Crossref]
  2. C. S. Lee and C. H. Han, “A novel refractive silicon microlens array using bulk micromachining technology,” Sens. Actuators A Phys.  88(1), 87–90 (2001).
    [Crossref]
  3. S. Sinzinger and J. Jahns, Microoptics, (WILEY-VCH Verlag GmbH, Weinheim, 1999) pp. 85–103.
  4. M. C. Hutley, “Optical techniques for the generation of microlens arrays,” J. Mod. Opt.  37(2), 253–265 (1990).
    [Crossref]
  5. M. T. Gale, M. Rossi, J. Pedersen, and H. Schutz, “Fabrication of continuous-relief micro-optical elements by direct laser writing in photoresists,” Opt. Eng.  33(11), 3556–3566 (1994).
    [Crossref]
  6. H. Yang, C. K. Chao, C.-P. Lin, and S.-C. Shen, “Micro-ball lens array modeling and fabrication using thermal reflow in two polymer layers,” J. Micromech. Microeng.  14(2), 277–282 (2004).
    [Crossref]
  7. T. Hirai and S. Hayashi, “Lens Functions of Polymer Microparticle Arrays,” Colloids Surf. A  153(1–3), 503–513 (1999).
    [Crossref]
  8. N. F. Borrelli, D. L. Morse, R. H. Bellman, and W. L. Morgan, “Photolytic technique for producing microlenses in photosensitive glass,” Appl. Opt.  24(16), 2520 (1985).
    [Crossref]

2004 (1)

H. Yang, C. K. Chao, C.-P. Lin, and S.-C. Shen, “Micro-ball lens array modeling and fabrication using thermal reflow in two polymer layers,” J. Micromech. Microeng.  14(2), 277–282 (2004).
[Crossref]

2001 (1)

C. S. Lee and C. H. Han, “A novel refractive silicon microlens array using bulk micromachining technology,” Sens. Actuators A Phys.  88(1), 87–90 (2001).
[Crossref]

1999 (1)

T. Hirai and S. Hayashi, “Lens Functions of Polymer Microparticle Arrays,” Colloids Surf. A  153(1–3), 503–513 (1999).
[Crossref]

1994 (1)

M. T. Gale, M. Rossi, J. Pedersen, and H. Schutz, “Fabrication of continuous-relief micro-optical elements by direct laser writing in photoresists,” Opt. Eng.  33(11), 3556–3566 (1994).
[Crossref]

1990 (2)

D. Daly, R. F. Stevens, M. C. Hutley, and N. Davies, “The Manufacture of Microlenses by Melting Photoresist,” Meas. Sci. Technol.  1(8), 759–766 (1990).
[Crossref]

M. C. Hutley, “Optical techniques for the generation of microlens arrays,” J. Mod. Opt.  37(2), 253–265 (1990).
[Crossref]

1985 (1)

N. F. Borrelli, D. L. Morse, R. H. Bellman, and W. L. Morgan, “Photolytic technique for producing microlenses in photosensitive glass,” Appl. Opt.  24(16), 2520 (1985).
[Crossref]

Bellman, R. H.

N. F. Borrelli, D. L. Morse, R. H. Bellman, and W. L. Morgan, “Photolytic technique for producing microlenses in photosensitive glass,” Appl. Opt.  24(16), 2520 (1985).
[Crossref]

Borrelli, N. F.

N. F. Borrelli, D. L. Morse, R. H. Bellman, and W. L. Morgan, “Photolytic technique for producing microlenses in photosensitive glass,” Appl. Opt.  24(16), 2520 (1985).
[Crossref]

Chao, C. K.

H. Yang, C. K. Chao, C.-P. Lin, and S.-C. Shen, “Micro-ball lens array modeling and fabrication using thermal reflow in two polymer layers,” J. Micromech. Microeng.  14(2), 277–282 (2004).
[Crossref]

Daly, D.

D. Daly, R. F. Stevens, M. C. Hutley, and N. Davies, “The Manufacture of Microlenses by Melting Photoresist,” Meas. Sci. Technol.  1(8), 759–766 (1990).
[Crossref]

Davies, N.

D. Daly, R. F. Stevens, M. C. Hutley, and N. Davies, “The Manufacture of Microlenses by Melting Photoresist,” Meas. Sci. Technol.  1(8), 759–766 (1990).
[Crossref]

Gale, M. T.

M. T. Gale, M. Rossi, J. Pedersen, and H. Schutz, “Fabrication of continuous-relief micro-optical elements by direct laser writing in photoresists,” Opt. Eng.  33(11), 3556–3566 (1994).
[Crossref]

Han, C. H.

C. S. Lee and C. H. Han, “A novel refractive silicon microlens array using bulk micromachining technology,” Sens. Actuators A Phys.  88(1), 87–90 (2001).
[Crossref]

Hayashi, S.

T. Hirai and S. Hayashi, “Lens Functions of Polymer Microparticle Arrays,” Colloids Surf. A  153(1–3), 503–513 (1999).
[Crossref]

Hirai, T.

T. Hirai and S. Hayashi, “Lens Functions of Polymer Microparticle Arrays,” Colloids Surf. A  153(1–3), 503–513 (1999).
[Crossref]

Hutley, M. C.

M. C. Hutley, “Optical techniques for the generation of microlens arrays,” J. Mod. Opt.  37(2), 253–265 (1990).
[Crossref]

D. Daly, R. F. Stevens, M. C. Hutley, and N. Davies, “The Manufacture of Microlenses by Melting Photoresist,” Meas. Sci. Technol.  1(8), 759–766 (1990).
[Crossref]

Jahns, J.

S. Sinzinger and J. Jahns, Microoptics, (WILEY-VCH Verlag GmbH, Weinheim, 1999) pp. 85–103.

Lee, C. S.

C. S. Lee and C. H. Han, “A novel refractive silicon microlens array using bulk micromachining technology,” Sens. Actuators A Phys.  88(1), 87–90 (2001).
[Crossref]

Lin, C.-P.

H. Yang, C. K. Chao, C.-P. Lin, and S.-C. Shen, “Micro-ball lens array modeling and fabrication using thermal reflow in two polymer layers,” J. Micromech. Microeng.  14(2), 277–282 (2004).
[Crossref]

Morgan, W. L.

N. F. Borrelli, D. L. Morse, R. H. Bellman, and W. L. Morgan, “Photolytic technique for producing microlenses in photosensitive glass,” Appl. Opt.  24(16), 2520 (1985).
[Crossref]

Morse, D. L.

N. F. Borrelli, D. L. Morse, R. H. Bellman, and W. L. Morgan, “Photolytic technique for producing microlenses in photosensitive glass,” Appl. Opt.  24(16), 2520 (1985).
[Crossref]

Pedersen, J.

M. T. Gale, M. Rossi, J. Pedersen, and H. Schutz, “Fabrication of continuous-relief micro-optical elements by direct laser writing in photoresists,” Opt. Eng.  33(11), 3556–3566 (1994).
[Crossref]

Rossi, M.

M. T. Gale, M. Rossi, J. Pedersen, and H. Schutz, “Fabrication of continuous-relief micro-optical elements by direct laser writing in photoresists,” Opt. Eng.  33(11), 3556–3566 (1994).
[Crossref]

Schutz, H.

M. T. Gale, M. Rossi, J. Pedersen, and H. Schutz, “Fabrication of continuous-relief micro-optical elements by direct laser writing in photoresists,” Opt. Eng.  33(11), 3556–3566 (1994).
[Crossref]

Shen, S.-C.

H. Yang, C. K. Chao, C.-P. Lin, and S.-C. Shen, “Micro-ball lens array modeling and fabrication using thermal reflow in two polymer layers,” J. Micromech. Microeng.  14(2), 277–282 (2004).
[Crossref]

Sinzinger, S.

S. Sinzinger and J. Jahns, Microoptics, (WILEY-VCH Verlag GmbH, Weinheim, 1999) pp. 85–103.

Stevens, R. F.

D. Daly, R. F. Stevens, M. C. Hutley, and N. Davies, “The Manufacture of Microlenses by Melting Photoresist,” Meas. Sci. Technol.  1(8), 759–766 (1990).
[Crossref]

Yang, H.

H. Yang, C. K. Chao, C.-P. Lin, and S.-C. Shen, “Micro-ball lens array modeling and fabrication using thermal reflow in two polymer layers,” J. Micromech. Microeng.  14(2), 277–282 (2004).
[Crossref]

Appl. Opt. (1)

N. F. Borrelli, D. L. Morse, R. H. Bellman, and W. L. Morgan, “Photolytic technique for producing microlenses in photosensitive glass,” Appl. Opt.  24(16), 2520 (1985).
[Crossref]

Colloids Surf. A (1)

T. Hirai and S. Hayashi, “Lens Functions of Polymer Microparticle Arrays,” Colloids Surf. A  153(1–3), 503–513 (1999).
[Crossref]

J. Micromech. Microeng. (1)

H. Yang, C. K. Chao, C.-P. Lin, and S.-C. Shen, “Micro-ball lens array modeling and fabrication using thermal reflow in two polymer layers,” J. Micromech. Microeng.  14(2), 277–282 (2004).
[Crossref]

J. Mod. Opt. (1)

M. C. Hutley, “Optical techniques for the generation of microlens arrays,” J. Mod. Opt.  37(2), 253–265 (1990).
[Crossref]

Meas. Sci. Technol. (1)

D. Daly, R. F. Stevens, M. C. Hutley, and N. Davies, “The Manufacture of Microlenses by Melting Photoresist,” Meas. Sci. Technol.  1(8), 759–766 (1990).
[Crossref]

Opt. Eng. (1)

M. T. Gale, M. Rossi, J. Pedersen, and H. Schutz, “Fabrication of continuous-relief micro-optical elements by direct laser writing in photoresists,” Opt. Eng.  33(11), 3556–3566 (1994).
[Crossref]

Sens. Actuators A Phys. (1)

C. S. Lee and C. H. Han, “A novel refractive silicon microlens array using bulk micromachining technology,” Sens. Actuators A Phys.  88(1), 87–90 (2001).
[Crossref]

Other (1)

S. Sinzinger and J. Jahns, Microoptics, (WILEY-VCH Verlag GmbH, Weinheim, 1999) pp. 85–103.

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Figures (7)

Fig. 1.
Fig. 1. Schematic evolution of the volumetric variation of a micro-lens after extrusion: (a) initial stage; (b) steady state.

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Fig. 2.
Fig. 2. Illustration of nozzle

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Fig. 3.
Fig. 3. Process flow chart for the fabrication of eyeball-like spherical micro-lens arrays. (a) Deposit silicon nitride and photoresist SU-8. (b) Define nozzle orifice by photolithography (obverse side). (c) Define nozzle cavity (rear side). (d) Bulk etch the rear side with Teflon for protection. (e) Perform extrusion process. (f) Expose without mask (flooding exposure).

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Fig. 4.
Fig. 4. The relationship between the diameter D of the MBA and the SU-8 nozzle orifice size under different rotational speeds of the spin-coater.

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Fig. 5.
Fig. 5. SEM images of MBAs. (a) SU-8 is extruded through the nozzle orifice before forming MBAs. (b) MBAs of a mushroom shape were formed due to the low UV exposure dosage. (c) A 3×3 MBA array. (d) Cross-sectional and top views of the spherical micro-lens

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Fig. 6.
Fig. 6. Design of the light fields measurement platform.

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Fig. 7.
Fig. 7. Relationship of coupling efficiency to the distance between the spherical micro-lens surface and the fiber.

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Equations (3)

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σ = dF dS
f = n ′ 2 ( n ′ − 1 ) R = 1.2463 ∙ R
BF = f − R

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