10 September 2013 FDTD modeling of chip-to-chip waveguide coupling via optical quilt packaging
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We present Finite-Difference Time-Domain (FDTD) simulations to explore feasibility of chip-to-chip waveguide coupling via Optical Quilt Packaging (OQP). OQP is a newly proposed scheme for wide-bandwidth, highly-efficient waveguide coupling and is suitable for direct optical interconnect between semiconductor optical sources, optical waveguides, and detectors via waveguides. This approach leverages advances in quilt packaging (QP), an electronic packaging technique wherein contacts formed along the vertical faces are joined to form electrically-conductive and mechanically-stable chip-to-chip contacts. In OQP, waveguides of separate substrates are aligned with sub-micron accuracy by protruding lithographically-defined copper nodules on the side of a chip. With OQP, high efficiency chip-to-chip optical coupling can be achieved by aligning waveguides of separate chips with sub-micron accuracy and reducing chip-to-chip distance. We used MEEP (MIT Electromagnetic Equation Propagation) to investigate the feasibility of OQP by calculating the optical coupling loss between butt coupled waveguides. Transmission between a typical QCL ridge waveguide and a single-mode Ge-on-Si waveguide was calculated to exceed 65% when an interchip gap of 0.5 μm and to be no worse than 20% for a gap of less than 4 μm. These results compare favorably to conventional off-chip coupling. To further increase the coupling efficiency and reduce sensitivity to alignment, we used a horn-shaped Ge-on-Si waveguide and found a 13% increase in coupling efficiency when the horn is 1.5 times wider than the wavelength and 2 times longer than the wavelength. Also when the horizontal misalignment increases, coupling loss of the horn-shaped waveguide increases at a slower rate than a ridge waveguide.
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Tahsin Ahmed, Tahsin Ahmed, Thomas Butler, Thomas Butler, Aamir A. Khan, Aamir A. Khan, Jason M. Kulick, Jason M. Kulick, Gary H. Bernstein, Gary H. Bernstein, Anthony J. Hoffman, Anthony J. Hoffman, Scott S. Howard, Scott S. Howard, } "FDTD modeling of chip-to-chip waveguide coupling via optical quilt packaging", Proc. SPIE 8844, Optical System Alignment, Tolerancing, and Verification VII, 88440C (10 September 2013); doi: 10.1117/12.2024088; https://doi.org/10.1117/12.2024088

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