Cross-correlation frequency-resolved optical gating and dynamics of temporal solitons in silicon nanowire waveguides

Abstract

We demonstrate the evolution of picosecond pulses in silicon nanowire waveguides by sum frequency generation cross-correlation frequency-resolved optical gating (SFG-XFROG) and nonlinear Schrödinger equation (NLSE) modeling. Due to the unambiguous temporal direction and ultrahigh sensitivity of the SFG-XFROG, which enable observation of the pulse accelerations, the captured pulses' temporal and spectral characteristics showed remarkable agreement with NLSE predictions. The temporal intensity redistribution of the pulses through the silicon nanowire waveguide for various input pulse energies is analyzed experimentally and numerically to demonstrate the nonlinear contributions of self-phase modulation, two-photon absorption, and free carriers. It indicates that free carrier absorption dominates the pulse acceleration. The model for pulse evolution during propagation through arbitrary lengths of silicon nanowire waveguides is established by NLSE, in support of chip-scale optical interconnects and signal processing.

Controlling free-carrier temporal effects in silicon by dispersion engineering

“…For example, the acceleration of the pulse stems from the free-carrier generated blue components traveling faster in time due to the strong anomalous dispersion of the waveguide [3]. In this work we demonstrate pulse temporal advances up to more than six times the initial pulse duration T FWHM , notably larger than any prior reported acceleration [34,35]. Apart from those known effects, here we report a significant nonlinear pulse broadening associated with the FCD-GVD interaction, which we now examine in detail.…”

Nonlinear silicon photonics analyzed with the moment method

“…17 represents effective pulse broadening due to TPA suppressing the pulse peak more strongly and is also second-order to the dispersive effect in PhC. However, the TPA and FCA temporal effects can be dominant in nanowire waveguides due to their smaller dispersion [26]. The FCD blueshift can be seen in Eq.18 (remember that n F C < 0).…”

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

“…The nearly flat form of the temporal phase distributions further support the high-order soliton compression at 1550nm and the fundamental soliton holding at 1555nm center wavelength. At the same time, the spectral blue shift induced by the FCD [28] is about 0.5 nm and 0.2 nm for 1550nm and 1555nm center wavelength respectively. For the input pulses with 1550nm center wavelength, the output pulse profiles for various input pulse energies are shown in Fig.…”

“…The group index is about 10 at 1550nm wavelength and will increase with the longer wavelength, which will enhance the nonlinear effects and make the input pulse interact sufficiently with the waveguide so as to induce large nonlinear changes in a short optical length. With the slow light enhancement, the group velocity dispersion (GVD) and the third order dispersion are about 1000 ps 3 /m at 1550nm and −2000 ps 2 /m at 1555nm wavelength respectively, which are about 10 3 times of which for the Si nanowires [28] so that the access Si nanowires can be neglected for the analysis. The evolution of picosecond pulses in the PhCWs can be governed by the NLSE model with auxiliary carrier dynamics as below [5,12]…”

“…With advantage of unambiguous temporal direction and high sensitivity, the sumfrequency generation cross-correlation frequency-resolved optical gating (SFG-XFROG), which derives from second-harmonic generation frequency-resolved optical gating (SHG-FROG), has been widely performed in ultrashort pulses measurements [25][26][27][28]. We applied the SFG-XFROG technique to investigate the pulse evolution in the Si PhCWs, particularly the pulse acceleration and the ultra-low power pulse evolution.…”