In this paper, athermal silicon waveguides using bridged subwavelength grating (BSWG) structures are proposed and investigated. The realization of temperature-independent BSWG waveguides for both polarizations is demonstrated numerically and experimentally. SU-8 polymer is used as the cladding material to compensate for the positive thermo-optic (TO) coefficient (dn/dT) of silicon. We investigate the dependence of the effective TO coefficient of BSWG waveguides on both the bridge width and grating duty cycle. The BSWG waveguides have a width of 490 nm, a height of 260 nm, and a grating pitch of 250 nm. Athermal behavior is achieved for both the transverse-magnetic (TM) and the transverse-electric (TE) polarized light for a variety of bridge width and duty cycle combinations. Furthermore, the BSWGs can be designed to be athermal for both TE and TM polarization simultaneously.

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Journal Optics Express
Ibrahim, M. (Marc), Schmid, J.H. (Jens H.), Aleali, A, Cheben, P. (Pavel), Lapointe, J. (Jean), Janz, S. (Siegfried), … Ye, W.N. (2012). Athermal silicon waveguides with bridged subwavelength gratings for TE and TM polarizations. Optics Express, 20(16), 18356–18361. doi:10.1364/OE.20.018356