We demonstrate wavelength conversion based on four-wave mixing in a semiconductor optical amplifier of signals with quadrature amplitude modulation (QAM). We first demonstrate wavelength conversion of 16 Gbaud 16-QAM signals over the entire C-band using two co-polarized pumps with low power penalty at the forward error correction threshold (FEC) for a wide range of input optical-signal-to-noise-ratio (OSNR). We also demonstrate for the first time wavelength conversion of 5 Gbaud 64-QAM signals in a semiconductor optical amplifier with bit-error rate below the FEC threshold over the entire C-band and investigate the dependence of the power penalty on input OSNR with a single pump configuration.
We propose a novel treatment that enhances the accuracy of the E ective Index Method (EIM) when used for gain-guided oxide-con ned VCSELs. If a thin oxide is placed at or near a z-eld null position, the di raction caused by the oxide becomes negligible. Gain-guiding subsequently dominates and causes the EIM to break down. To circumvent this problem, we propose to use an arti cial index-guided di raction e ect to simulate the gain-guided di raction e ect. This is achieved by increasing the oxide thickness and making a correction to the oxide index by t a k i n g a w eighted sum between the original oxide index and the center region index at the oxide layer position. The weight is speci cally chosen to be the mean z-eld (normalized to its local z-eld variation) at the position of the oxide. We s h o w that this simple correction to the EIM successfully simulates the gain-guided di raction e ect and produces the correct transverse phase variation for oxide-apertured VCSELs when gain-guiding becomes the dominant mechanism. Therefore, the improved EIM is able to produce resonant wavelengths which are in excellent agreement to those of the vector Green's function method for the COST-268 VCSEL model, both in the gain-guided and index-guided regimes. Comparisons with an experimental model have also been made and excellent agreement i s s h o wn.
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