Numerical Analysis of the Frequency Chirp in Quantum-Dot Semiconductor Lasers

Abstract

We present a numerical model for the analysis of the chirp dynamics of quantum-dot (QD) semiconductor laser under large signal current modulation. The model is based on the multipopulation rate equation formalism, and it includes all the peculiar characteristics of the active QD material such as the inhomogeneous broadening of the gain spectrum, the presence of an excited state confined in the QDs and the presence of nonconfined states due to the wetting layer and the barrier. In this paper the model is applied to the analysis of the chirp of two QD single-mode lasers emitting from the ground state and from the excited state, respectively. In order to make comparisons of the chirp in various operating conditions, we define some equivalent parameters for quantifying the adiabatic and transient contributions to the chirp. These parameters are then used to analyze the chirp as function of the bias current, of the modulation depth and of the modulation frequency. All the various simulation results show that the carrier accumulation in the QD states, poorly involved in the stimulated emission process and the carrier dynamics in these states, can cause a nonzero chirp under current modulation even for the ideal condition of zero linewidth enhancement factor (or -parameter) at the laser threshold.

Nonlinear and Nonequilibrium Dynamics of Quantum-Dot Optoelectronic Devices

“…Furthermore, a strong dependence on the pump current has been observed [SU05a,JIA12]. Theoretical works have shown that the α-factor measurements in quantum-dot lasers will yield different results depending on the measurement procedure and operating parameters [MEL06,GIO07,LIN12a].…”

“…Even then, however, the averaged values calculate to α J ≈ 2.1 for the pump-current perturbation and α E ≈ 0.73 with the injected optical pulse. Thus, even around the same fixed point, no uniform value of an average α can be defined [GIO07,LIN12b]. The α- factor is therefore an inappropriate measure for describing the gain dynamics of the quantum-dot medium.…”

Lyapunov exponents of quantum dot laser systems under optical feedback: influence of cavity length

“…In the above equations tph is the photon lifetime in the laser cavity, c is the free-space light velocity, nr is the active material refractive index, k is the intensity of feedback light, w0 is the angular frequency of the solitary laser, td is the external cavity roundtrip time and δf is the frequency chirp calculated according to (Gioannini, 2007). Finally, the terms inside the summation operator is the material gain coupling cavity photons and carriers of the ground-, first-and second-excited states.…”

Measurement and analysis of optical gain spectra in 1.6 to 1.8 μm InAs/InP (100) quantum-dot amplifiers

“…C g = πe 2h /cn r ε 0 m 2 0 is a constant; N W is the number of QD layers; H act is the average active quantum dot layer thickness; |P σ G S,E S | 2 Capture time from WL to ES τ c0 = 1 ps (Bogaart et al 2005) Capture time from ES to GS τ d0 = 1 ps (Bogaart et al 2005) Carrier escape time from WL to SCH τ qe =3 ns (Gioannini and Montrosset 2007) Carrier recombination time in SCH τ sr = 4.5 ns (Gioannini and Montrosset 2007) Carrier recombination time in WL 2 ps < τ qr < 100 ps Fit…”

“…The modeling of QD materials is more involved than the modeling of bulk or quantum well gain material due to the inhomogeneous character of the QD gain material. Extensive QD models have been presented especially for In x Ga 1−x As/GaAs QD materials (Sugawara et al 2000;Gioannini and Montrosset 2007) but also for InAs/InP QD materials (Grillot et al 2009) Here we have simplified a commonly used QD amplifier model to calculate the small signal gain spectrum of the amplifiers and to fit a number of the model parameters to the experimental data. Three important parameters are the electron-hole transition energies of the wetting layer (WL), the excited state (ES) and the ground state (GS).…”