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Fabrication of an eyeball-like spherical micro-lens array using extrusion for optical fiber coupling

S C Shen1, C T Pan2,4, K H Liu3, C H Chao2 and J C Huang1

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Batch fabrication of an eyeball-like spherical micro-lens array (ESMA) not only can reduce micro assembly cost, but also can replace conventional ball lenses or costly gradient refractive index without sacrificing performance. Compared to the conventional half-spherical micro-lenses, the ESMA is an eyeball-like spherical lens which can focus light in all directions, thus providing application flexibility for optical purposes. The current ESMA is made of photoresist SU-8 using the extrusion process instead of the traditional thermal reflow process. For the process of an ESMA, this research develops a new process at ambient temperature by spin-coating SU-8 on a surface of a silicon wafer which serves as an extrusion plate and extruding it through a nozzle to form an ESMA. This nozzle consists of a nozzle orifice and nozzle cavity. The nozzle orifice is defined and made of SU-8 photoresist using ultra-violet lithography, which exhibits good mechanical property. The fabrication process of a nozzle cavity employs bulk micromachining to fabricate the cavities. Next, viscous SU-8 spun on the extrusion plate is extruded through the nozzle orifice to form an ESMA. Based on the effect of surface tension, by varying the amount of SU-8 on the plate extruded through different nozzle orifices, various diameters of ESMA can be fabricated. In this paper, a 4 × 4 ESMA with a numerical aperture of about 0.38 and diameters ranging from 60 to 550 µm is fabricated. Optical measurements indicate a diameter variance within 3% and the maximum coupling efficiency is approximately 62% when the single mode fiber is placed at a distance of 10 µm from the ESMA. The research has proved that the extrusion fabrication process of an ESMA is capable of enhancing the coupling efficiency.


PACS

42.79.Bh Lenses, prisms and mirrors

42.82.Cr Fabrication techniques; lithography, pattern transfer

42.81.Qb Fiber waveguides, couplers, and arrays

81.20.Hy Forming; molding, extrusion etc.

85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

42.82.Et Waveguides, couplers, and arrays

Subjects

Electronics and devices

Optics, quantum optics and lasers

Nanoscale science and low-D systems

Condensed matter: structural, mechanical & thermal

Dates

Issue 12 (December 2009)

Received 16 April 2009, in final form 30 September 2009

Published 5 November 2009



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