Optimal design, fabrication, and characterisation of GeO<sub>2</sub>-SiO<sub>2</sub> doped silica multimode-interference couplers

H. N. J. Fernando; M. Hayden; P. J. Hughes

doi:10.1117/12.662860

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20 April 2006 Optimal design, fabrication, and characterisation of GeO₂-SiO₂ doped silica multimode-interference couplers

H. N. J. Fernando; M. Hayden; P. J. Hughes

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Proceedings Volume 6183, Integrated Optics, Silicon Photonics, and Photonic Integrated Circuits; 61830V (2006) https://doi.org/10.1117/12.662860
Event: SPIE Photonics Europe, 2006, Strasbourg, France

Abstract

Article reports low loss (better than 0.09dB/cm) germano-silicate planar devices, operating at 1550nm wavelength, with optical combiner/splitters exhibiting greater splitting uniformity (~ 0.08dB) based on multimode interferences with index contrast ~ 0.7%. Excess loss of the device was improved by 0.41dB by designing output access waveguides with two S-bends operating in the Whispering-Gallery-Mode regime (WGM). The total S-bend loss was improved by inserting a straight waveguide between two cured sections, instead of two oppositely curved sections as in the conventional S-bends. This is expected to reduce transition loss about four times the transition loss between two oppositely curved sections. Optimised offsets, between waveguides of different radii, and widening of curved sections resulted in low excess loss while preserving device compactness. The separation of the output access waveguides was limited to just 250μm, for pigtailing/butt-coupling of SMF fibres, to ensure device compactness for future high-density packaging. Silica and doped-silica on silicon films were formed at low temperature, <350°C, with high deposition rates, greater than 1600 Angstroms/min, using plasma enhanced chemical vapour deposition (PECVD) technology that suits for mass production. Fabricated lightwave circuits were characterised with special care in order to avoid ambiguities that would arise from power fluctuation in the launching laser source during measurements.

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H. N. J. Fernando, M. Hayden, and P. J. Hughes "Optimal design, fabrication, and characterisation of GeO₂-SiO₂ doped silica multimode-interference couplers", Proc. SPIE 6183, Integrated Optics, Silicon Photonics, and Photonic Integrated Circuits, 61830V (20 April 2006); https://doi.org/10.1117/12.662860