Two-wave competition in ultralong semiconductor optical amplifiers

• Published in: IEEE journal of quantum electronics 2005-10, Vol.41 (10), p.1260-1267
• Main Authors: Bramann, G., Wunsche, H.-J., Busolt, U., Schmidt, C., Schlak, M., Sartorius, B., Nolting, H.-P.
• Format: Article
• Language: English
• Subjects: Erbium; Exact sciences and technology; Four-wave mixing (FWM); Fundamental areas of phenomenology (including applications); High speed optical techniques; Laser optical systems: design and operation; Nonlinear optics; nonlinear wave propagation; Optical interferometry; Optical mixing; Optical modulation; Optical pumping; Optical saturation; Optical signal processing; Optics; Physics; Receivers & amplifiers; Resonators, cavities, amplifiers, arrays, and rings; Semiconductor optical amplifiers; semiconductor optical amplifiers (SOA); Wave optics; Wave propagation, transmission and absorption
• ISSN: 0018-9197; 1558-1713
• DOI: 10.1109/JQE.2005.854600

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.