Comparison of epoxy- and siloxane-based single-mode optical waveguides defined by direct-write lithography

Abstract

This paper reports on the fabrication and characterization of single-mode polymer optical waveguides at telecom and SOI compatible wavelengths; by making a comparison between an epoxy and a siloxane polymer waveguide material system (both commercially-available). The proposed waveguides can be used in short-reach optical interconnects targeting chip-to-chip communication on the interposer level or providing a coupling interface between single-mode optical fibers and photonic integrated circuits (PICs). This technology enables the integration of optoelectronic chips for photonic packaging purposes. First, the single-mode dimensions (4×4μm2 and 5×5μm2) for both materials at selected wavelengths (1.31μm and 1.55μm) were determined based on the refractive index measurements. Then, the waveguides were patterned by a direct-write lithography method. The fabricated waveguides show a high-quality surface with smooth sidewalls. The optical propagation losses were measured using the cut-back method. For the siloxane-based waveguides, the propagation losses were found to be 0.34dB/cm and 1.36dB/cm at 1.31μm and 1.55μm respectively while for the epoxy-based waveguides the losses were 0.49dB/cm and 2.23dB/cm at 1.31μm and 1.55μm respectively.