A point-by-point femtosecond laser fabrication technique was used to form filament arrays inside single-mode telecommunication fiber. The off-axis positioning of the grating from the neutral axis was key to enabling displacement optical sensing in single mode fiber. Optomechanical responses were enhanced with stress concentration in cantilevered optical fiber. The narrow geometry of the filament array facilitated sensing of a uniform strain field induced by the lateral displacement, or to null the response when filaments were orthogonally oriented. In this way, filament gratings could be overlaid for azimuthally resolved displacement sensing. The ability to measure transverse displacements paves the way toward developing more efficient optical accelerometers.
Optical interposers are promising as a robust, reliable, and scalable technology for high-density coupling between the dissimilar platforms of optical fiber and silicon photonics (SiP) chips. To extend this concept, femtosecond laser micro-structuring was harnessed to develop a multi-level, mirror-waveguide optical circuit platform in fused silica glass. The flexible laser writing facilitated compact, low-profile vertical interconnection between multi-core fibers and SiP circuits, exploiting total internal reflection mirrors and vertical grating couplers. Various design strategies of laying out 3D waveguide fanouts, multi-core fiber sockets, and turn-mirrors were explored in 40 channel systems. The flexible interposer technology is scalable to higher channel counts, while maintaining a small footprint, thus offering a broad solution to challenges in areas of optical interconnects and photonic packaging.
The demand for greater link capacity in datacenters has pushed silicon photonic (SiP) optical interconnects from linear edge coupler arrays to two-dimensional grids of vertical grating couplers. To meet the challenge for low-profile, fiber-to-chip coupling, 3D optical waveguide circuits were integrated with total internal reflection (TIR) mirrors, enabling efficient horizontal fiber coupling and vertical SiP coupling through a fused silica interposer. TIR air disks of 30 µm diameter and ~3 µm thickness were fabricated up to 320 µm circuit depth by femtosecond laser irradiation followed by chemical etching (FLICE). The micro-mirror offered 0.54 to 1.2 dB reflection loss for waveguide-to-waveguide coupling within the interposer, as measured across the 1460 to 1625 nm telecom bands. The efficient TIR mirror lays the groundwork for flexible design of 3D photonic interposers to meet high-density interconnection requirements of SiP circuits to multicore fiber arrays for the telecom industry.
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