On-Chip Photonics with Erbium Doped Silicon Laser

Erbium doped silicon has been analytically studied for its prospective application in on-chip optical communication. Laser functionality at 1.54 mum line of erbium emission has been analyzed. Erbium atoms in silicon host have been considered as defect centers offering strong recombination routes to injected carriers. Excitation process of erbium from the ground state to the higher excited state has been explained by an electron-hole mediated process involving the erbium sites. Emission rates of erbium through intra 4f shell transitions by spontaneous and stimulated processes have been equated with the rate of excitation. Detailed analysis on rate equations show the feasibility of achieving population inversion and lasing threshold for incorporation of 10¹⁹ cm^-3 of optically active erbium sites. Based on a quasi-two level laser analysis, low threshold current densities of the order of A/cm² have been estimated for a laser cavity length of 1 mum. Linear increase of laser output with drive current has been simulated. Modulation compatibility of erbium doped silicon lasing system has been studied by introducing small signal components at various operating conditions. Direct modulation with frequencies up to Gega Hertz level was found feasible. The 3 dB bandwidth of laser response shows strong dependence with the power output. Rate equations of laser operation were also solved for large signal conditions. Turn-on delays of the order of tens of nanoseconds have been estimated. The time delay was found to reduce with higher drive currents.