A thermo-electrical imprinting process has been employed to induce second-order optical nonlinear (SONL) response in amorphous sodo-niobate optical thin films. By characterizing the geometry and the magnitude of the SONL response, a key aspect of thin film’s poling mechanisms compared with bulk glasses was established. This lies in the appearance of a charge accumulation at the film/substrate interface, described by the Maxwell–Wagner effect. A way to minimize this effect was then proven by promoting an induced built-in static field in the plane of the film using a microstructured electrode. A SONL susceptibility as high as 29 pm/V was measured, and its geometry and location were controlled at the micrometer scale. This work paves the way for the future design of integrated nonlinear photonic circuits based on amorphous inorganic poled materials.
A chalcogenide waveguide platform with the combination of GeAsSeTe (IG3)/GeAsSe (IG2) on wet-/dry-etched silicon pedestals is reported. Chalcogenide glasses offer high index contrast and compact footprints, while the post-processing challenges are addressed using Si pedestals. The integration of IG2/IG3 chalcogenides on Si demonstrates ultralow loss of 0.08 ± 0.02 dB/cm at a wavelength of 10 μm. We have measured a thermo-optic coefficient of 1.1x10-4 K-1, which is comparable to Si and GaAs. The combination of simplified fabrication, minimal propagation losses and a strong thermooptic coefficient, positions this waveguide platform as a promising candidate for on-chip tunable long-wave IR spectrometers for practical applications in biomedical diagnostics and environmental sensing.
Molecules have ‘fingerprint’ absorptions in the mid-infrared, enabling their identification via infrared spectroscopy. For applications beyond the lab, such as medical diagnosis, fully integrated mid-infrared spectroscopy on chip would be ideal. Germanium offers low absorption in the mid-IR, making it an ideal candidate for waveguides for mid-IR spectroscopy via the evanescent field. Amorphous germanium could offer a low-cost fabrication route; our work compares methods to deposit amorphous germanium films via RF sputtering, e-beam evaporation and plasma-enhanced chemical vapour deposition (PECVD). In addition to standard germanium waveguides produced by etching a germanium film, an alternative manufacturing method is proposed, where silicon is etched to form pedestals, followed by deposition of amorphous germanium to produce waveguides. Pedestal waveguides offer potential for single-mode operation across a broad wavelength range, making them a strong candidate for spectroscopy applications.
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