Low-Power consumption Franz-Keldysh effect plasmonic modulator

In this paper we report on a low energy consumption CMOS-compatible plasmonic modulator based on Franz-Keldysh effect in germanium on silicon. We performed integrated electro-optical simulations in order to optimize the main characteristics of the modulator. A 3.3 dB extinction ratio for a 30 µm long modulator is demonstrated under 3 V bias voltage at an operation wavelength of 1647 nm. The estimated energy consumption is as low as 20 fJ/bit

Ge-rich graded-index Si_1-xGex waveguides with broadband tight mode confinement and flat anomalous dispersion for nonlinear mid-infrared photonics

This work explores the use of Ge-rich graded-index Si1-xGex rib waveguides as building blocks to develop integrated nonlinear optical devices for broadband operation in the mid-IR. The vertical Ge gradient concentration in the waveguide core renders unique properties to the guided optical mode, providing tight mode confinement over a broadband mid-IR wavelength range from λ = 3 µm to 8 µm. Additionally, the gradual vertical confinement pulls the optical mode upwards in the waveguide core, overlapping with the Ge-rich area where the nonlinear refractive index is larger. Moreover, the Ge-rich graded-index Si1-xGex waveguides allow efficient tailoring of the chromatic dispersion curves, achieving flat anomalous dispersion for the quasi-TM optical mode with D ≤ 14 ps/nm/km over a ~1.4 octave span while retaining an optimum third-order nonlinear parameter, γeff. These results confirm the potential of Ge-rich graded-index Si1-xGex waveguides as an attractive platform to develop mid-IR nonlinear approaches requiring broadband dispersion engineering

Carrier multiplication in germanium nanocrystals

Carrier multiplication is demonstrated in a solid-state dispersion of germanium nanocrystals in a silicon-dioxide matrix. This is performed by comparing ultrafast photo-induced absorption transients at different pump photon energies below and above the threshold energy for this process. The average germanium nanocrystal size is approximately 5-6 nm, as inferred from photoluminescence and Raman spectra. A carrier multiplication efficiency of approximately 190% is measured for photo-excitation at 2.8 times the optical bandgap of germanium nanocrystals, deduced from their photoluminescence spectra.Foundation for Fundamental Research on Matter (FOM)info:eu-repo/semantics/publishedVersio

Design and simulation of waveguide-integrated Ge/SiGe quantum-confined Stark effect optical modulator based on adiabatic coupling with SiGe waveguide

We report on the design and simulation of a waveguide-integrated Ge/SiGe quantum-confined Stark effect (QCSE) optical modulator based on the use of a Ge-rich SiGe relaxed buffer on a graded buffer as an optical waveguide. Despite the promising potential of this waveguide platform, efficient and wideband optical integration with a Ge-based active device has not been properly addressed so far. In this paper, via 3D finite-difference time domain simulation, we demonstrate that a simple 2Dtaper is sufficient to enable adiabatic optical coupling from the fundamental mode of the input SiGe waveguide to the fundamental mode of the Ge/SiGe multiple quantum well (MQW) modulator without the excitation of higher-order modes in Ge/SiGe MQWs. The 2D taper shows good fabrication tolerance considering critical variations in its dimensions. Significantly, wideband optical modulation performance in terms of extinction ratio and insertion loss is presented over the whole low-loss spectralrange of the Ge/SiGe MQWs at different electrical bias values, device lengths, and numbers of quantum wells in order to comprehensively report its potential for Si-based optical modulators