Conference Paper

# Direct observation of the coherent spectral hole in the noise spectrum of a saturated InAs/InP quantum dash amplifier operating near 1550 nm

Electrical Engineering Dept., Technion, Haifa 32000, Israel

DOI: 10.1364/OE.16.002141 Conference: Optical Communication (ECOC), 2007 33rd European Conference and Ehxibition of Source: IEEE Xplore

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**ABSTRACT:**We investigate the nonlinear propagation of an ultra-short, 150 fs, optical pulse along the waveguide of a quantum dot (QD) laser operating above threshold. We demonstrate that among the various nonlinear processes experienced by the propagating pulse, four-wave mixing (FWM) between the pulse and the two oscillating counter-propagating cw fields of the laser is the dominant one. FWM has two important consequences. One is the creation of a spectral hole located in the vicinity of the cw oscillating frequency. The width of the spectral hole is determined by an effective carrier and gain relaxation time. The second is a modification of the shape of the trailing edge of the pulse. The wave mixing involves first and second order processes which result in a complicated interaction among several fields inside the cavity, some of which are cw while the others are time varying, all propagating in both directions. The nonlinear pulse propagation is analyzed using two complementary theoretical approaches. One is a semi-analytical model which considers only the wave mixing interaction between six field components, three of which propagate in each direction (two cw fields and four time-varying signals). This model predicts the deformation of the tail of the output signal by a secondary idler wave, produced in a cascaded FWM process, which co-propagates with the original injected pulse. The second approach is a finite-difference time-domain simulation, which considers also additional nonlinear effects, such as gain saturation and self-phase modulation. The theoretical results are confirmed by a series of experiments in which the time dependent amplitude and phase of the pulse after propagation are measured using the cross-frequency-resolved optical gating technique.Optics Express 03/2013; 21(5):5715-5736. · 3.53 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**Theoretical results on the extinction ratio (ER) improvement in ultralong semiconductor optical amplifiers (UL-SOAs) are presented indicating a Bogatov-like effect in the saturated section. Starting from general nonlinear gain equations, an analytic description of the Bogatov-like effect is derived in terms of gain coefficients. These equations are used to explain the results of fully numerical simulations. The data signal's ER improves because of a two-step process. First, the data signal cross-gain modulates the additionally injected CW signal. Second, due to this inverse modulation, the data signal's states are differently amplified via the Bogatov-like effect. Since the ER improvement is caused by the fast intraband effects, this simple scheme has the potential for high-speed regeneration.IEEE Journal of Quantum Electronics 07/2009; · 2.11 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**We developed an improved model in order to predict the RF behavior of the SOA valid for any experimental conditions. It takes into account the dynamic saturation of the SOA, which can be fully characterized by a simple measurement, and only relies on material fitting parameters, independent of the optical intensity and bias current. We used this new model to analyze and model the additive noise of the SOA in order to fully characterize the influence of the slow light effect on the microwave photonics link properties. To cite this article: P. Berger et al., C R. Physique 10 (2009). (C) 2009 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.Comptes Rendus Physique 12/2009; 10(10):991-999. · 1.64 Impact Factor

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