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Authors: Andres Desmet, A. Radosavljevic, J. Missinne, D. Van Thourhout, G. Van Steenberge
Title: Laser Written Glass Interposer for Fiber Coupling to Silicon Photonic Integrated Circuits
Format: International Journal
Publication date: 2/2021
Journal/Conference/Book: IEEE Photonics Journal
Editor/Publisher: IEEE , 
Volume(Issue): 13(1) p.1-12
DOI: 10.1109/JPHOT.2020.3039900
Citations: 16 ( - last update: 14/7/2024)
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Recent advancements in photonic-electronic integration push towards denser multichannel fiber to silicon photonic chip coupling solutions. However, current packaging schemes based on suitably polished fiber arrays do not provide sufficient scalability. Alternatively, lithographically-patterned fused silica glass interposers have been proposed, allowing for the integration of fanout waveguides between a dense array of on-chip silicon waveguides and a cleaved fiber ribbon. In this paper, we propose the use of femtosecond laser inscription for the fabrication of the fused silica glass interposer, allowing for a monolithic integration of waveguides and V-grooves for fiber alignment. The waveguides obtained by Femtosecond Laser Direct Writing (FLDW) have a propagation loss of 0.88 dB/cm at 1550 nm. The mode-field diameter is 12.8 ± 0.4 μ m, allowing for a coupling loss of 1.24 ± 0.32 dB when coupling to a standard single mode optical fiber, passively aligned to the fused silica waveguide by insertion in a V-groove created by Femtosecond Laser Irradiation followed by Chemical Etching (FLICE). The average surface roughness of the etched waveguide facet is 160 ± 5 nm. Scattering loss when coupling to fiber is reduced by use of an index-matching adhesive for fiber fixation. A polished out-of-plane coupling mirror at an angle of 41.5 ∘ injects the light into standard grating couplers, providing a quasi-planar fiber-to-chip package. The excess loss of the proposed solution is limited to 2 dB per interface, including mirror, waveguide and fiber coupling losses.

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