Jiali Liao

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.

Generation and analysis of both in-phase and out-phase radially polarized femtosecond-pulse beam

Abstract. Both in-phase and out-phase radially polarized femtosecond-pulse (RPFP) beams have been generated with one phase-only liquid crystal spatial light modulator, which effectively modulates the phase retardation distributions of a pulse beam wavefront by two reflections. The intensity distributions and polarizing properties of both in-phase and out-phase RPFP beams are detected, and the temporal properties of in-phase RPFP beams are investigated in detail. Experimental results indicate that we effectively produce an RPFP beam. And the temporal duration of the output in-phase RPFP beam is 183 fs about 14 fs shorter than the input Gaussian femtosecond-pulse beam. The temporal durations of arbitrary polarized components of an in-phase RPFP beam vary less than 3.5%.

Double-slit interference of radially polarized vortex beams

Abstract. Both radially polarized (RP) and radially polarized vortex (RPV) beams are generated by an experimental setup with one phase-only liquid crystal spatial light modulator which efficiently modulates the phase retardation distributions of input beam by twice reflections. The polarizing properties and double-slit interference of both RP and RPV beams are investigated in detail. Misplacement and tilt appear in double-slit interference fringes of both RP beams and RPV beams in simulations and experiments. The fringe tilt number F in the intermediate region is proportional to the topological charge l of RPV beams with the approximate relation Fs(l)=0.8125l in simulations and Fe(l)=0.8182l in experiments. The double-slit interference method can be utilized to determine and analyze the topological charge of the beams.

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.

Analysis of femtosecond optical vortex beam generated by direct wave-front modulation

Abstract. The generation of femtosecond optical vortex beam based on direct wave-front modulation with phase-only liquid crystal spatial light modulator is demonstrated. The spatial and temporal properties of the generated femtosecond vortices are investigated in detail. The experimental results show remarkable agreement with the results of the theoretical analysis and simulations, and indicate that the method we utilized can efficiently generate femtosecond optical vortex beam of arbitrary topological charge. The temporal and spectral properties of the femtosecond pulsed beam are hardly affected by the phase dislocation imposed on the wave-front.

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.

Generation of radially polarized femtosecond pulse beam with a polarization plates array

With both ultrafast optical properties of femtosecond pulse and cylindrically symmetric polarization properties of radially polarized light, the radially polarized femtosecond pulse beam has significant applications in super-high density optical storage and ultra-intense lasers. A scheme for generating radially polarized femtosecond pulse beam by a polarization plates array is proposed, in which a phase-only liquid crystal spatial light modulator (LC-SLM) is used to load different phase retardation distribution in transverse into linearly polarized femtosecond pulse beam. Associated with a quarter wave plate, the input linearly polarized femtosecond pulse beam will be converted to radially polarized femtosecond pulse beam at the back of the polarization plates array. The experimental results indicate that the scheme can be well used to generate radially polarized light, and more effective results can be obtained with the increase of sectored polarization plates.

Generation of flat temporal phase distribution of optical pulse by photonic crystal waveguides

We generate a flat temporal-phase distribution optical pulse by 1.3-mm-long photonic crystal waveguide. The effect of coupled pulse energy on the temporal-phase distribution of the output pulse is analyzed by numeral simulating. Simulation results indicate that the root mean square of the output pulse phase decreases to 0.0095 with the optimum coupled pulse energy, which is about 30 pJ, and the narrowest output pulse width is 418 fs. The generation of a flat temporal-phase distribution optical pulse on-chip scale results in potential application prospect in optical communication, pulse compression, pulse shaping and other nonlinear optical application fields.

CCD non-uniformity effects on position accuracy of star sensor

The photoelectric response and the character of the CCD non-uniformity are analyzed in this paper. Based on the analysis, the model of CCD non-uniformity effects on position accuracy of the star spot is established. A correction method based on the least square estimation is used to correct the CCD photoelectric response non-uniformity. The effect of CCD non-uniformity on position accuracy of star sensor before and after the compensation is simulated. The results show that the position accuracy of the star sensor has been improved obviously after compensation. In addition, the differences of the photo response non-uniformity and the mean photo response coefficient do not influence the results of the compensation according the analysis.