Modeling of strain-induced Pockels effect in Silicon

Enhancing Pockels effect in strained silicon waveguides

The magnitude and origin of the electro-optic measurements in strained silicon devices has been lately the object of a great controversy. Furthermore, recent works underline the importance of the masking effect of free carriers in strained waveguides and the low interaction between the mode and the highly strained areas. In the present work, the use of a p-i-n junction and an asymmetric cladding is proposed to eliminate the unwanted carrier influence and improve the electro-optical modulation response. The proposed configuration enhances the effective refractive index due to the strain-induced Pockels effect in more than two orders of magnitude with respect to the usual configuration.

On the influence of interface charging dynamics and stressing conditions in strained silicon devices

The performance of strained silicon devices based on the deposition of a top silicon nitride layer with high stress have been thoroughly analyzed by means of simulations and experimental results. Results clearly indicate that the electro-optic static response is basically governed by carrier effects. A first evidence is the appearance of a variable optical absorption with the applied voltage that should not occur in case of having a purely electro-optic Pockels effect. However, hysteresis and saturation effects are also observed. We demonstrate that such effects are mainly due to the carrier trapping dynamics at the interface between the silicon and the silicon nitride and their influence on the silicon nitride charge. This theory is further confirmed by analyzing identical devices but with the silicon nitride cladding layer optimized to have intrinsic stresses of opposite sign and magnitude. The latter is achieved by a post annealing process which produces a defect healing and consequently a reduction of the silicon nitride charge. Raman measurements are also carried out to confirm the obtained results.

Investigation of mid-infrared second harmonic generation in strained germanium waveguides

In this paper we present a detailed theoretical investigation of second harmonic generation in strained germanium waveguides operating at the mid infrared pump wavelength of 4 μm. The effective second order susceptibility has been estimated through a multiphysics approach considering the residual stress of the SiN_x cladding film. Furthermore, general physical features have been investigated by means of a comparative analysis of SHG performance as a function of input pump power, linear and nonlinear phase mismatching, effective recombination carrier lifetime, and temperature, taking into account both continuous and pulsed regimes. Finally, periodically poled germanium devices have been explored with the aim to improve the SHG efficiency. In the same operative conditions, efficiencies of 0.6% and 0.0018% have been obtained in poled and not-poled waveguides, respectively.