Heavily-doped semiconductor films are very promising for application in mid-infrared plasmonic devices because the real part of their dielectric function is negative and broadly tunable in this wavelength range. In this work we investigate heavily n-type doped germanium epilayers grown on different substrates, in-situ doped in the 10 17 to 10 19 cm −3 range, by infrared spectroscopy, first principle calculations, pump-probe spectroscopy and dc transport measurements to determine the relation between plasma edge and carrier density and to quantify mid-infrared plasmon losses. We demonstrate that the unscreened plasma frequency can be tuned in the 400 -4800 cm −1 range and that the average electron scattering rate, dominated by scattering with optical phonons and charged impurities, increases almost linearly with frequency. We also found weak dependence of losses and tunability on the crystal defect density, on the inactivated dopant density and on the temperature down to 10 K. In films where the plasma was optically activated by pumping in the near-infrared, we found weak but significant dependence of relaxation times on the static doping level of the film. Our results suggest that plasmon decay times in the several-picosecond range can be obtained in ntype germanium thin films grown on silicon substrates hence allowing for underdamped mid-infrared plasma oscillations at room temperature.The recent push towards applications of spectroscopy for chemical and biological sensing in the mid-infrared (mid-IR)1-8 has prompted the need for conducting thin films displaying values of the complex dielectric functionǫ(ω) = ǫ ′ (ω) + iǫ ′′ (ω) that can be tailored to meet the needs of novel electromagnetic designs exploiting the concepts of metamaterials, transformation optics and plasmonics 9 . In the design of metamaterials, where subwavelength sized conducting elements are embedded in dielectric matrices, if the values of ǫ ′ of the metal and the dielectric are of the same order, but have opposite sign, the geometric filling fractions of the metal and dielectric can be readily tuned to achieve subwavelengthresolution focusing of radiation 10 . Such requirement is met by silver for wavelengths λ around 400 nm. The same condition cannot be achieved in the IR range by using elemental metals, however, because metals possess an extremely high negative value of ǫ ′ not equaled, in

An ideal photonic integrated circuit for nonlinear photonic applications requires high optical nonlinearities and low loss. This work demonstrates a heterogeneous platform by bonding lithium niobate (LN) thin films onto a silicon nitride (Si₃N₄) waveguide layer on silicon. It not only provides large second- and third-order nonlinear coefficients, but also shows low propagation loss in both the Si₃N₄ and the LN-Si₃N₄ waveguides. The tapers enable low-loss-mode transitions between these two waveguides. This platform is essential for various on-chip applications, e.g., modulators, frequency conversions, and quantum communications.

This paper aims to present the design and the achieved results on a CMOS electronic and photonic integrated device for low cost, low power, transparent, mass-manufacturable optical switching. An unprecedented number of integrated photonic components (more than 1000), each individually electronically controlled, allows for the realization of a transponder aggregator device which interconnects up to eight transponders to a four direction colorless-directionless-contentionless ROADM. Each direction supports 12 200-GHz spaced wavelengths, which can be independently added or dropped from the network. An electronic ASIC, 3-D integrated on top of the photonic chip, controls the switch fabrics to allow a complete and microsecond fast reconfigurability

Energy harvesting for Internet of Things applications, comprising sensing, life sciences, wearables, and communications, requires efficient thermoelectric (TE) materials, ideally semiconductors compatible with Si technology. In this work, we investigate the potential of GeSn/Ge layers, a group IV material system, as TE material for low-grade heat conversion. We extract the lattice thermal conductivity, by developing an analytical model based on Raman thermometry and heat transport model, and use it to predict thermoelectric performances. The lattice thermal conductivity decreases from 56 W/(m·K) for Ge to 4 W/(m·K) by increasing the Sn atomic composition to 14%. The bulk cubic Ge0.86Sn0.14 alloy features a TE figure of merit of ZT ∼ 0.4 at 300 K and an impressive 1.04 at 600 K. These values are extremely promising in view of the use of GeSn/Ge layers operating in the typical on-chip temperature range.