Bo-Ji Huang

Si-rich SiNx based Kerr switch enables optical data conversion up to 12 Gbit/s

Silicon photonic interconnection on chip is the emerging issue for next-generation integrated circuits. With the Si-rich SiNx micro-ring based optical Kerr switch, we demonstrate for the first time the wavelength and format conversion of optical on-off-keying data with a bit-rate of 12 Gbit/s. The field-resonant nonlinear Kerr effect enhances the transient refractive index change when coupling the optical data-stream into the micro-ring through the bus waveguide. This effectively red-shifts the notched dip wavelength to cause the format preserved or inversed conversion of data carried by the on-resonant or off-resonant probe, respectively. The Si quantum dots doped Si-rich SiNx strengthens its nonlinear Kerr coefficient by two-orders of magnitude higher than that of bulk Si or Si3N4. The wavelength-converted and cross-amplitude-modulated probe data-stream at up to 12-Gbit/s through the Si-rich SiNx micro-ring with penalty of −7 dB on transmission has shown very promising applicability to all-optical communication networks.

Enriching Si quantum dots in a Si-rich SiNx matrix for strong χ(3) optical nonlinearity

To meet the demand of all-optical data processing applications, the SiNx layer with enriching Si quantum dots (Si-QDs) for achieving strong optical nonlinearity is demonstrated with its χ(3) coefficient enhanced by three orders of magnitude larger than that of stoichiometric Si3N4. With excessive Si concentration enriched from 16.3% to 23.4%, the dense Si-QDs apparently self-assemble in the SiNx matrix with an average size of ∼0.95 nm and volume density of 5 × 1019 # cm−3. The Si-QD doped Si-rich SiNx not only enlarges its third-order nonlinear absorption coefficient from 0.01 to 1.8 m GW−1, but also increases its nonlinear refractive index from 5.7 × 10−13 to 9.2 × 10−12 cm2 W−1 at a wavelength of 800 nm, as attributed to the localized excitons with decreased effective Bohr radius in quantum confined Si-QDs. Such a SiNx:Si-QD material enables strong optical nonlinearity in compact nonlinear nanophotonic waveguide devices developed for future all-optical data processors.

Degenerate Four-Wave Mixing in Si Quantum Dot Doped Si-Rich SiNx Channel Waveguide

The degenerate four-wave-mixing (DFWM) effect in Si quantum dot doped SiNx (SiN_x :Si-QD) channel waveguide has been preliminarily demonstrated. By enhancing the optical nonlinearity of SiN_x at 1550 nm with doped Si-QDs, the DFWM can be enhanced with its conversion efficiency of -46 dB in the SiN_x :Si-QD channel waveguide with length of 8 mm. The nonlinear refractive index of the SiN_x:Si-QD is estimated to be 3 × 10-14cm2/W. The chromatic dispersion analysis indicates that the SiN_x :Si-QD channel waveguide exhibits 3-dB conversion bandwidth of larger than 16 nm. Such a SiN_x :Si-QD waveguide is free of multi-photon absorption at 1550 nm even when injecting an intense laser pulse as large as 1.3 GW/cm². These results show great potential of Si-QD doped SiN_x waveguide for nonlinear optical processing.

All-Optical Cross-Absorption-Modulation Based Gb/s Switching With Silicon Quantum Dots

In silicon quantum dots (Si-QDs), the sub-bandgap cross-absorption-modulation (XAM) has been preliminarily observed and confirmed as a new kind of wavelength conversion process to enable ultrafast optical switching. By using the Si-QD doped Si-rich SiCx micro-ring resonator waveguide with a quality factor of 1.7 × 104 under an optimized gap spacing of 700 nm away from the bus waveguide, the XAM effect induces a wavelength-converted picosecond all-optical switching between pump and probe signals, which is attributed to a specific free-carrier absorption at probe wavelength caused by the two-photon-absorption induced carriers. The non-degenerate pump-probe analysis also shows a weak Kerr nonlinearity related ultrafast switching response from the changing envelope of the XAM probe pulse at red-shifted wavelength. These observations declare that the nano-scale Si-QDs can provide sufficiently large XAM effect to enable the ultrafast all-optical switching capability for pulsed optical logic applications. To confirm, the Si-QDs doped Si-rich SiCx waveguide modulator-based 1.2 Gb/s all-optical format inversion of a PRZ-OOK data-stream is demonstrated for the first time.

Composition ratio dependent refractive index and optical bandgap of nonstoichiometric Si 1−x Ge x on silicon

Nonstoichiometric Si_1-xGe_x films fabricated by plasma enhanced chemical vapor deposition (PECVD) with different flounce ratios are demonstrated to show the composition ratio dependent optical properties, including refractive index, bandgap and optical absorption. By increasing the fluence ratio from 0.2 to 0.5, the refractive index of Si_1-xGe_x film raises from 3.527 to 3.927, with the absorption coefficient enlarging from <;<;1cm^-1 to 31.12 cm^-1.