Investigation on the high speed modulation in (GaIn) (NAs)/GaAs lasers

The potential of 1.3 mu m GaInNAs SQW laser diodes for high speed operation is experimentally investigated in this paper, computing the differential gain, dg/dn, at a temperature range suitable for most network applications (293K - 348K) and the small signal modulation bandwidth. The investigation begins with a basic characterization calculating the To, with a value of 56K in a range of temperatures of 293K - 318K. The lasing wavelength at 293K is found to be 1250nm with a linear temperature dependence of 0.377nm/K. Secondly, the paper presents a detailed study of the modulation bandwidth of the device, obtaining a value of 6.06Ghz for the maximum modulation bandwidth at 293K with a modulation efficiency of 0.64GHz/root mA. In a range of temperatures of 293K - 318K, the modulation bandwidth is found to decrease only slightly with the temperature with a slope of 0.0088Ghz/K. Finally, the paper explains the temperature behaviour obtained for the modulation bandwidth studying the temperature dependence of the differential gain, dg/dn. For this evaluation, the value of the differential gain with the current (how the peak gain changes with the sub-threshold bias current applied to the sample), dg/dI, is obtained using the Hakki-Paoli method.(1) Quasi-linear temperature dependence of this value has been obtained with a slope of 3.377cm(-1)A(-1)/K. Using impedance measurements, a relation between the carrier density, n, and the bias current applied to the laser, I, has been obtained. With this relation, we obtained the differential current with the carrier density, dI/dn. Then, we calculated the differential gain dg/dn = dg/dI - dI/dn. At 293K, the differential gain a value of 1.55 (.) 10(-5) cm(2). To conclude we saw how the differential gain, dg/dn, has been found to have similar temperature behaviour as the small signal modulation bandwidth.