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Proceedings Paper

Ultralow-loss waveguide crossings for the integration of microfluidics and optical waveguide sensors
Author(s): Zheng Wang; Hai Yan; Zongxing Wang; Yi Zou; Chun-Ju Yang; Swapnajit Chakravarty; Harish Subbaraman; Naimei Tang; Xiaochuan Xu; D. L. Fan; Alan X. Wang; Ray T. Chen
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Paper Abstract

Integrating photonic waveguide sensors with microfluidics is promising in achieving high-sensitivity and cost-effective biological and chemical sensing applications. One challenge in the integration is that an air gap would exist between the microfluidic channel and the photonic waveguide when the micro-channel and the waveguide intersect. The air gap creates a path for the fluid to leak out of the micro-channel. Potential solutions, such as oxide deposition followed by surface planarization, would introduce additional fabrication steps and thus are ineffective in cost. Here we propose a reliable and efficient approach for achieving closed microfluidic channels on a waveguide sensing chip. The core of the employed technique is to add waveguide crossings, i.e., perpendicularly intersecting waveguides, to block the etched trenches and prevent the fluid from leaking through the air gap. The waveguide crossings offer a smooth interface for microfluidic channel bonding while bring negligible additional propagation loss (0.024 dB/crossing based on simulation). They are also efficient in fabrication, which are patterned and fabricated in the same step with waveguides. We experimentally integrated microfluidic channels with photonic crystal (PC) microcavity sensor chips on silicon-on-insulator substrate and demonstrated leak-free sensing measurement with waveguide crossings. The microfluidic channel was made from polydimethylsiloxane (PDMS) and pressure bonded to the silicon chip. The tested flow rates can be varied from 0.2 μL/min to 200 μL/min. Strong resonances from the PC cavity were observed from the transmission spectra. The spectra also show that the waveguide crossings did not induce any significant additional loss or alter the resonances.

Paper Details

Date Published: 13 March 2015
PDF: 8 pages
Proc. SPIE 9320, Microfluidics, BioMEMS, and Medical Microsystems XIII, 932012 (13 March 2015); doi: 10.1117/12.2078384
Show Author Affiliations
Zheng Wang, The Univ. of Texas at Austin (United States)
Hai Yan, The Univ. of Texas at Austin (United States)
Zongxing Wang, Omega Optics, Inc. (United States)
Yi Zou, The Univ. of Texas at Austin (United States)
Chun-Ju Yang, The Univ. of Texas at Austin (United States)
Swapnajit Chakravarty, Omega Optics, Inc. (United States)
Harish Subbaraman, Omega Optics, Inc. (United States)
Naimei Tang, Omega Optics, Inc. (United States)
Xiaochuan Xu, Omega Optics, Inc. (United States)
D. L. Fan, The Univ. of Texas at Austin (United States)
Alan X. Wang, Oregon State Univ. (United States)
Ray T. Chen, The Univ. of Texas at Austin (United States)
Omega Optics, Inc. (United States)

Published in SPIE Proceedings Vol. 9320:
Microfluidics, BioMEMS, and Medical Microsystems XIII
Bonnie L. Gray; Holger Becker, Editor(s)

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