Laser Written Glass Interposer for Fiber Coupling to Silicon Photonic Integrated Circuits

Abstract

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 µm, 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. Using the currently optimized laser parameters, the time required to expose a single V-groove/waveguide combination is around one minute.

Compact packaged silicon photonic Bragg grating sensor based on a ball lens interface

“…This is an established technique which has previously been applied e.g. for the fabrication of optofluidics [15], optical switches [16], V-grooves for fiber alignment [17], and optical resonators [18]. For the current work, the FLICE technology was further optimized specifically for achieving a conical holder with a 45°slope angle.…”

Femtosecond laser written Bragg grating sensors with passive fiber alignment structures in fused silica

“…In order to reduce the time required to write the V-groove, only the contour is written. During etching, the bulk of the V-groove will be lifted out of the substrate, creating the wanted structure [3]. The pulse repetition rate for the fabrication of V-grooves is again 500 kHz.…”

Temperature compensated strain sensor in fused silica by femtosecond laser inscription

“…These V-grooves can be monolithically integrated in the glass circuit. 18,19 3. RESULTS AND DISCUSSION…”