Enhancement of a Chaotic Carrier Bandwidth in a Multi-quantum-well Laser Transmitter Using Self-Phase Modulation in an Optical Fiber Feedback Path

We demonstrate theoretically and numerically a novel method of enhancing the bandwidth of a chaotic carrier from a multi-quantum-well laser transmitter using self-phase modulation (SPM) effect in an optical fiber round path. It is deduced theoretically that the nonlinear phase shift arisen from SPM effect has an impact on the gain and bandwidth enhancement factor of the laser. The second order nonlinear effect of the fiber enriches the varieties of the amplitude and the phase of the laser while the nonlinear phase shift produces a lot of new frequencies, which can spread the bandwidth. Numerical results reveal that, with SPM effect, the new bandwidth be can enhanced 4 times more than the bandwidth without the optical fiber path, and the relaxation oscillation frequency of the chaotic laser is increased to being 2 times more than that of the laser without the optical fiber path. It is found numerically that the enhancement of the chaotic bandwidth depends evidently on the optical fiber length, the power into the optical fiber, the coupling-feedback ratio and the second order nonlinear coefficient affect.