All-optical modulation based on silicon quantum dot doped SiO x :Si-QD waveguide

Abstract

All-optical modulation based on silicon quantum dot doped SiOx:Si-QD waveguide is demonstrated. By shrinking the Si-QD size from 4.3 nm to 1.7 nm in SiOx matrix (SiOx:Si-QD) waveguide, the free-carrier absorption (FCA) cross section of the Si-QD is decreased to 8 × 10−18 cm2 by enlarging the electron/hole effective masses, which shortens the PL and Auger lifetime to 83 ns and 16.5 ps, respectively. The FCA loss is conversely increased from 0.03 cm−1 to 1.5 cm−1 with the Si-QD size enlarged from 1.7 nm to 4.3 nm due to the enhanced FCA cross section and the increased free-carrier density in large Si-QDs. Both the FCA and free-carrier relaxation processes of Si-QDs are shortened as the radiative recombination rate is enlarged by electron–hole momentum overlapping under strong quantum confinement effect. The all-optical return-to-zero on-off keying (RZ-OOK) modulation is performed by using the SiOx:Si-QD waveguides, providing the transmission bit rate of the inversed RZ-OOK data stream conversion from 0.2 to 2 Mbit/s by shrinking the Si-QD size from 4.3 to 1.7 nm.