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Laser integration and photonics chip packaging are the two key challenges that require attention to drive down
the cost/bit metric for silicon photonics based optical interconnects. We try to address the latter by demonstrating optical interfaces that fit well in an overall scheme of 2.5D/3D electro-optic integration needed for a high
performance computing environment.
A through-substrate coupling interface provides the benefit of bonding a silicon photonic chip face-up on a
package substrate such that the device-side of the chip remains accessible for die-stacking and fiber-array packaging, thereby offering a promising alternative to flip-chip based packaging. In this paper, we demonstrate
three through-substrate coupling elements to enable alignment tolerant and energy-efficient integration of silicon
photonics with board-level or package-level optical interconnects : (i) a downward directionality O-band grating coupler with a peak -2.3 dB fiber-to-silicon waveguide coupling efficiency; (ii) polymer microlenses hybrid
integrated onto the substrate of a silicon photonic chip to produce an expanded collimated beam at λ=1310
nm for a distance of more than 600 µm; (iii) a ball lens placed in a through-package via to result in a 14 µm
chip-to-package 1-dB lateral alignment tolerance for coupling into a 20×24 µm squared cross-section board-level
Microlenses integrated on the substrate-side can greatly relax alignment tolerances for interfacing photonic integrated circuits. This is demonstrated on a 750um thick chip with standard grating couplers (operation wavelength 1550nm). High quality silicon microlenses (surface roughness below 20 nm) were realized by transfering reflowed photoresist into the silicon substrate using reactive ion etching. The microlens allows interfacing the chip from the backside with an expanded beam, drastically increasing lateral alignment tolerances. A 1dB alignment tolerance of ±8um and ±11um (along and perpendicular to the grating coupler direction, respectively) was experimentally found when a 40um mode field diameter beam was used.
Adsorption of molecules on high-surface-area materials is a fundamental process critical to many fields of basic and applied chemical research; for instance, it is among the simplest and most efficient principles for separating and remediating polluted water. However, established experimental approaches for investigating this fundamental process preclude in situ monitoring and thus obtaining real-time information about the ongoing processes. In this work, mid-infrared attenuated total reflection (ATR) spectroscopy is introduced as a powerful technique for quantitative in situ monitoring of adsorption processes and thus enrichment of traces of organic pollutants from aqueous solution in ordered mesoporous silica films. The synthesis, functionalization, and characterization of two silica films with 3D hexagonal and cubic pore structure on silicon ATR crystals are presented. Benzonitrile and valeronitrile as model compounds for aromatic and aliphatic water pollutants are enriched in hydrophobic films, while the matrix, water, is excluded from the volume probed by the evanescent field. Enrichment times of 200 and >100, respectively, yielding detection limits in the low ppm range. Furthermore, fast and complete desorption of the analyte, ensuring reliable regeneration of the sensor, was verified. Lastly, we derive and experimentally validate equations for ATR spectroscopy with thin film adsorption layers to quantify the absolute mass of adsorbed pollutant in the film. The excellent agreement between recorded absorptions at target wavenumbers of the target analytes and corresponding simulations corroborates the validity of the chosen approach