Matthew Marko

Phase-resolved observations of optical pulse propagation in chip-scale silicon nanowires

We report phase-resolved temporal measurements of picosecond pulse propagation in silicon chip-scale nanowire waveguides. The nonlinear ultrafast phenomena are examined experimentally with frequency-resolved optical gating and numerically with nonlinear Schrodinger pulse modeling. Pulse broadening and higher-order pulse splitting were observed experimentally and matched remarkably with numerical predictions. The contributions of self-phase modulation and group velocity dispersion, as well as two-photon absorption, free-carrier dispersion, and absorption, are described and discussed, in support of chip-scale nonlinear signal processing and ultrafast processes.

Unambiguous demonstration of soliton evolution in slow-light silicon photonic crystal waveguides with SFG-XFROG.

We demonstrate the temporal and spectral evolution of picosecond soliton in the slow light silicon photonic crystal waveguides (PhCWs) by sum frequency generation cross-correlation frequency resolved optical grating (SFG-XFROG) and nonlinear Schrödinger equation (NLSE) modeling. The reference pulses for the SFG-XFROG measurements are unambiguously pre-characterized by the second harmonic generation frequency resolved optical gating (SHG-FROG) assisted with the combination of NLSE simulations and optical spectrum analyzer (OSA) measurements. Regardless of the inevitable nonlinear two photon absorption, high order soliton compressions have been observed remarkably owing to the slow light enhanced nonlinear effects in the silicon PhCWs. Both the measurements and the further numerical analyses of the pulse dynamics indicate that, the free carrier dispersion (FCD) enhanced by the slow light effects is mainly responsible for the compression, the acceleration, and the spectral blue shift of the soliton.

Demonstration of femtosecond soliton dynamics in silicon photonic nano-wire waveguide

We demonstrate femtosecond pulses evolution in silicon photonic nano-wire waveguides with generalized nonlinear Schrödinger equation modeling along with auxiliary carrier dynamics. The temporal and spectral properties of the output pulses are simulated with increasing input pulse energies, and high-order soliton pulse compression and splitting, along with spectral broadening and red-shift are observed remarkably. The impacts of high-order nonlinear effects, including the self-steepening and intrapulse Raman scattering on the pulse evolution are analyzed, and it indicates that the IRC results in noticeable temporal tailing edge tilting and spectral red-shift, while the impact of the self-steeping can be negligible. The contributions of the third order dispersion and various nonlinear effects on the pulse properties are detailedly investigated to better understand the femtosecond pulses propagation, in support of further chip-scale optical interconnects and signal processing.

Finely engineered slow light photonic crystal waveguides for efficient wideband wavelength-independent higher-order temporal solitons

By orthogonally dual-shifting the air-hole rows in the triangular photonic crystal waveguide, a novel finely engineered slow light silicon photonic crystal waveguide is designed for higher-order temporal solitons and ultrashort temporal pulse compression with a large fabrication tolerance. The engineering of dispersion provides the waveguide with a wide wavelength range with only low anomalous dispersion covering, which makes the compression ratio wavelength-independent and stable even under ultralow input pulse energy. The simulation results are based on nonlinear Schrödinger equation modeling, which demonstrates that the input picosecond pulses in the broad wavelength range with ultralow pJ pulse energy can be stably compressed by a factor of 6 to higher-order temporal solitons in a 250 μm short waveguide.

Soliton Propagation with Cross Phase Modulation in Silicon Photonic Crystal Waveguides

An effort was conducted to numerically determine, by the nonlinear Schrodinger split-step Fourier method, whether using cross-phase modulation (XPM) could cause temporal soliton pulse propagation in a silicon slow-light photonic crystal waveguide (PhCWG) shorter than a millimeter. The simulations demonstrated that, because of the higher powers and shorter scales of photonic crystals, two-photon absorption (TPA) would cause an optical soliton pulse to be extremely dissipative. The model demonstrated, however, that by utilizing XPM, it is possible to sustain a compressed soliton pulse within a silicon PhCWG subjected to TPA over longer relative distances.

Disturbance of soliton pulse propagation from higher-order dispersive waveguides

Optical soliton pulses offer many applications within optical communication systems, but by definition a soliton is only subjected to second-order anomalous group-velocity-dispersion; an understanding of higher-order dispersion is necessary for practical implementation of soliton pulses. A numerical model of a waveguide was developed using the nonlinear Schrödinger equation, with parameters set to ensure the input pulse energy would be equal to the fundamental soliton energy. Higher-order group-velocity-dispersion was gradually increased, for various temporal widths and waveguide dispersions. A minimum pulse duration of 100 fs was determined to be necessary for fundamental soliton pulse propagation in practical photonic crystal waveguides.

Tribological investigations of the load, temperature, and time dependence of wear in sliding contact

An effort was made to study and characterize the evolution of transient tribological wear in the presence of sliding contact. Sliding contact is often characterized experimentally via the standard ASTM D4172 four-ball test, and these tests were conducted for varying times ranging from 10 seconds to 1 hour, as well as at varying temperatures and loads. A numerical model was developed to simulate the evolution of wear in the elastohydrodynamic regime. This model uses the results of a Monte Carlo study to develop novel empirical equations for wear rate as a function of asperity height and lubricant thickness; these equations closely represented the experimental data and successfully modeled the sliding contact.