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||Buried Polyimide Waveguides on Glass Substrates|
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||A buried polyimide waveguide fabricated on glass substrate using semiconductor processing technologies is presented. The proposed structure is applicable to planar lightwave circuits (PLCs) because of planar surface morphology of the device. Potential applications of the device range from passive optical coupler to active modulators. The fabrication steps of the buried polyimide waveguide include deep etching, polishing of polyimide, global planarization and formation of waveguide end facets. |
Deep glass etching requires a hard etching mask in order to prevent unwanted etching of the under laying material. Chromium(Cr) is one of the best making material because it is easy to grow and hard to etch. The Cr thin film was deposited the glass substrates using a thermal evaporation system.
The glass substrate was etched by reactive ion etching (RIE) using SF6 and O2 (SF6:O2=20:1) mixture. Etching rate of glass and Cr were 0.1µm/min and 130Å/min, respectively. After etch, the polyimide guiding layer of the waveguide was spin-coating at a slow spinning speed onto the glass substrate, and was cured at 300℃for 1.5 hr. The uneven surface of the device was planarized by lapping the polyimide down to the glass substrate. Both the abrasive paper and Al2O3 powder were used in the process. Then a thin layer of SOG (spin-on-glass) was coated on the top of the waveguide to isolated the polyimide from the air. Finally, the end facets of the waveguide were form by RIE etching without further polishing. The propagation loss of the waveguide was measured by conventional cut back method. The polarized lights at 1.3um were launched into the waveguide by end-face optical coupling. The propagation losses of the waveguide are 3dB/cm for TE wave and 4.6dB/cm for TM wave, respectively.
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