Low loss achieved in sol-gel based silica-on-siliconintegrated opticsusing borophosphosilicate glass

Polarisation-independent propagation losses of 0.2 dB/cm are reported for near-infrared silica-on-silicon channel guides formed using sol-gel borophosphosilicate glass deposited by repetitive spin coating and rapid thermal annealing. The low loss is ascribed to a reduction in process temperature, which has allowed a total glass thickness of 30 µm. The use of two dopants allows the glass viscosity to be adjusted independently of its refractive index, simplifying reflow and burial.