Generation and recombination of free carriers in silicon photonics is fundamental to understand several nonlinear optical phenomena and engineer novel devices. Particularly in strip nano-waveguides, the tightly confined optical field results in highly efficient generation of free-carriers, both through linear and nonlinear absorption. Furthermore, the large surface-to-volume ratio results in a nonlinear recombination behavior dominated by a trap-assisted mechanism. Through time-resolved pump-and-probe experiments, we performed a detailed experimental characterization of linear and nonlinear generation rates, as well as recombination dynamics. We developed analytical expressions to determine the carrier density averaged along the waveguide from the measured free-carrier absorption for different input pump power levels. As a result, we were able to discriminate the contributions from two-photon absorption (TPA) and single-photon absorption (SPA), obtaining absorption coefficients of (1.5±0.1) cm/GW and (1.9±0.1) m−1 , respectively. Our results then reveal that the effective TPA within the waveguide is higher than the value reported for bulk silicon, and that SPA plays an important role in carrier generation up to ≈300 mW. With regards to recombination dynamics, our results show a highly nonlinear decay curve with instantaneous carrier lifetime varying as the recombination evolves (initially faster with lifetime of ∼800 ps and slower at final stages of the decay, reaching ∼300 ns). We interpret our results with a theoretical framework based on trap-assisted recombination statistics applied to strip nano-waveguides, and explore its implication to the dynamics of nonlinear nanophotonic devices in which free carriers play a critical role.
In this paper, the impact of the number of channels on the performance of elastic optical networks (EONs) is examined considering a multilevel modulation format and coherent transmission. Network design parameters such as spectral bandwidth and channel symbol error rate (SER), are analysed. We simulated the transmission of quadrature phase shift-keying (QPSK) signals, modulated at 56 and 100 Gbps, to evaluate a proposed flexible spectral allocation method in order to evaluate the effect of number of channels and the required total spectral bandwidth.
Optical injection locking of semiconductor lasers has attracted significant attention due to its applications in laser analysis, modulation characteristic enhancement, and nonlinear dynamics. In many cases, the analysis of the optically injected laser is done by simulation, requiring an accurate laser model and, therefore, an adequate modeling of the gain compression at high photon densities. We use the Kobayashi-Lang rate equations to numerically compare the stable locking range considering four different gain models. Results reveal that at low bias currents, gain compression is significant only under weak injection regime. In contrast, for higher bias current, gain compression must be considered both in weak and strong injection regimes.
Nondegenerate four-wave mixing (NDFWM) in semiconductor gain media is a promising source for wavelength conversion in the wavelength division multiplexed (WDM) systems and for fiber dispersion compensation in long distance fiber links. In contrast to bulk and quantum well (QW) semiconductors, the quantum dot (QD) gain medium is favorable for enhancing the performance of the FWM because of the wide gain spectrum, large nonlinear effect as well as ultrafast carrier dynamics. Especially, the destructive interference can be eliminated due to the reduced linewidth enhancement factor (LEF) for obtaining high efficiency in the wavelength up-conversion. This work reports the NDFWM generation in a dual-mode injection-locked QD Fabry-Perot (FP) laser. The device has a wide gain spectrum with a full width at half maximum of 81 nm, and a peak net modal gain of 14.4 cm-1. The laser exhibits two lasing peaks induced by Rabi oscillation, which provides the possibility for efficient FWM generation. Employing the dual-mode injection-locking scheme, an efficient NDFWM is achieved up to a detuning range of 1.7 THz with a weak injection ratio of 0.44. The highest measured values for both the normalized conversion efficiency (NCE) and the side-mode suppression ratio (SMSR) with respect to the converted signal respectively are -17 dB and 20.3 dB at the detuning 110 GHz.
In this paper, the effects of gridless spectrum allocation in Wavelength Division Multiplexed (WDM) optical networks are examined. The advanced modulation formats and multi-rate transmissions of the signals, which are key parameters in the optical system project, are taken into account. The consumed spectrum, as well as the impact of linear and nonlinear impairments on the signal transmission, are compared to WDM network adopting standard grid and gridless ITU. To analyze the influence of these physical effects, some key network design parameters are monitored and evaluated, such as the guard band size, the signal occupied bandwidth, the laser power and the quality of channels. The applied signal modulation formats were On/Off Keying (OOK), Quadrature Phase Shift keying (QPSK), and Dual Polarization State Phase Modulation (DP-QPSK), whereas the transmission rate per wavelength was varied from 10 Gb/s to 100Ghz. The guard band, signal band, and laser power were swept and the resulted Bit Error Rate (BER) was estimated from the eye-diagram. Analytical calculations and simulations are conducted in order to evaluate the impact of the gridless spectrum allocation on both the spectral consumption and the signal quality of transmission (QoT). Results reveal that a gridless transmission system reduces the spectral consumption while offering an acceptable QoT. This work was carried out with both analytical modeling and numerical calculation using the Optisystem as well as Matlab.
A low cost converged wireline and 60GHz wireless hybrid system utilizing a single wavelength is proposed, employing
two single electrode LiNbO3 modulators for all-optical mm-wave frequency up-conversion and baseband modulation,
respectively. Additionally, a novel 15dBi, broadband, coplanar based, photonic patch array antenna is designed on a
high dielectric substrate for application as an indoor compact photonic-wireless transceiver. In order to evaluate the
fiber-wireless system performance a microwave/optical/wireless design is utilized, employing 3Gb/s orthogonal
frequency division multiplexed (OFDM) broadband wireless and passive optical network (PON) signals, co-propagating
in a single mode fiber (SMF). An acceptable performance is calculated for a 10m indoor wireless channel and a PON
urban link in the order of up to 20km, respectively. At last, a comparison of alternative RoF/PON photonic up
conversion schemes is presented.