Planar microlens with front-face angle: design, fabrication, and characterization

Md. Abdullah Al Hafiz; Aron W. Michael; Chee-Yee Kwok

doi:10.1117/1.JMM.15.3.035501

8 July 2016 Planar microlens with front-face angle: design, fabrication, and characterization

Md. Abdullah Al Hafiz, Aron W. Michael, Chee-Yee Kwok

Journal of Micro/Nanolithography, MEMS, and MOEMS, Vol. 15, Issue 3, 035501 (July 2016). https://doi.org/10.1117/1.JMM.15.3.035501

Abstract

This paper studies the effect of microlens front-face angle on the performance of an optical system consisting of a planar-graded refractive index (GRIN) lens pair facing each other separated by a free-space region. The planar silica microlens pairs are designed to facilitate low-loss optical signal propagation in the free-space region between the opposing optical waveguides. The planar lens is fabricated from a 38-μm-thick fluorine-doped silica layer on a silicon substrate. It has a parabolic refractive index profile in the vertical direction, which is achieved by controlled fluorine incorporation in the silica film to collimate the optical beam in the vertical direction. Horizontal beam collimation is achieved by incorporating a horizontal curvature at the front face of the lens defined by deep oxide etch. A generalized 3×3ABCDGH transformation matrix method has been derived to compute the coupling efficiency of such microlens pairs to take front-face angles that may be present due to fabrication variations or limitations and possible input/output optical fiber offset/tilt into considerations. Pairs of such planar GRIN lens with various free-space propagation distances between them ranging from 75 to 2500 μm and with front-face angles of 1.5 deg, 2 deg, and 4 deg have been fabricated and characterized. Beam propagation method simulations have been carried out to substantiate the theoretical and experimental results. The results indicate that the optical loss is reasonably low up to 1.5 deg of front-face angles and increases significantly with further increase in the front-face angle. Analysis shows that for a given system with specific microlens front-face angle, the optical loss can be significantly reduced by properly compensating the vertical position of the input and output fibers.

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Md. Abdullah Al Hafiz, Aron W. Michael, and Chee-Yee Kwok "Planar microlens with front-face angle: design, fabrication, and characterization," Journal of Micro/Nanolithography, MEMS, and MOEMS 15(3), 035501 (8 July 2016). https://doi.org/10.1117/1.JMM.15.3.035501

Published: 8 July 2016

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KEYWORDS

Microlens

Optical fibers

Free space optics

Silica

Beam propagation method

Refractive index

Interfaces

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