Two-wave competition in ultralong semiconductor optical amplifiers

Abstract

The copropagation of two waves in an ultralong semiconductor optical amplifier (SOA) is considered in theory and experiment. One wave is a modulated signal, whereas the other one is unmodulated (continuous wave). The theory bases on a comprehensive traveling-wave model and predicts an exponential improvement of the signal extinction ratio (ER) of the modulated signal, caused by the presence of the unmodulated signal. Conditions for achieving this two-wave competition (TWC) effect are as follows. The SOA is operated under saturation, both waves are copolarized, they have comparable gain and their spectral correlation is between certain limits. The TWC effect is due to nondegenerate four-wave mixing (FWM) in the saturated part of a long SOA and is expected to have a high-speed potential. In order to check the theoretical predictions, 4-mm-long SOAs are developed and experimentally investigated under the given conditions. The measured ER improves by 1.3 dB for a 5-GHz sinusoidal signal, which compares well with the 2 dB theoretically predicted for this configuration. FWM is identified also experimentally as the basic mechanism. Variation of wavelength detuning, pump current, modulation frequency and ER of the injected signal are used to determine optimum conditions for the given device

Ultrahigh-Frequency Microwave Phase Shifts Mediated by Ultrafast Dynamics in Quantum-Dot Semiconductor Optical Amplifiers

“…1(a) shows the considered wavelength up-conversion configuration based on QD SOAs. It is similar to the small-signal XGM configuration in [12] with a sine-modulated data signal, at optical frequency , as input (given by , where , , and are input power, modulation index, and modulation frequency). The data signal will modulate the gain of the SOA and thus in turn XGM in the amplifier will transfer the modulation to the copropagating continuous-wave (CW) signal at optical frequency as an XGM converted signal with an inverse pattern.…”

“…We here propose a dual-wavelength-configured phase shifter based on dynamic gain gratings induced by high-speed XGM in QD SOAs. In contrast to the usual configuration involving a weak probe and strong pump, this concept utilizes the two-wave competition phenomenon [12], namely the strong interaction between two waves with comparable magnitude, caused by XGM via fast intersubband effects in QDs under a high current injection. The main new results compared to previous works are to numerically demonstrate the potential of QD SOAs for this new application as a simple and compact 180 broadband microwave phase shifter working at frequencies beyond 100 GHz.…”

Extinction Ratio Improvement Due to a Bogatov-Like Effect in Ultralong Semiconductor Optical Amplifiers

“…Since the nonlinear gain is dependent on the photon density , its modulation causes a nonlinear gain pulsation. Furthermore, [6], [11], [13], [15] the fluctuation of the nonlinear gain results in a nonlinear index change due to the -factor of each nonlinear gain mechanism. Fig.…”

“…Since the electrical field beating is the reason for the Bogatovlike effect, only the dynamic term of (1) is of interest: (6) The approach for solving the differential equations in (4) is…”

“…The nonlinear transfer function is obtained due to an additionally injected CW signal. In [6], simulations as well as measurements for sine modulated signals of this regeneration scheme were presented. In addition, a first attempt for an analytic description of the ER improvement, which is based on four-wave mixing (FWM), is given.…”