Abstract
We consider an integrated electro-absorption modulator within a coupled-cavity VCSEL structure (EAM-VCSEL). We derive expressions for the modulation transfer function (MTF) of the EAM-VCSEL for small-signal modulation of either VCSEL injection current or EAM losses. For current modulation, the cut-off frequency remains limited by relaxation oscillation frequency. For EAM loss modulation, the MTF curve is much flatter and its shape around the relaxation oscillation frequency displays either a well-pronounced maximum, both a maximum and a minimum or a sharp minimum only depending on the bias point of the EAM losses. Such features have been found experimentally in Marigo-Lombart et al., J. Physiscs: Photonics, 1, 2019, but remained unexplained hitherto. Furthermore, the cut-off frequency remains beyond 100 GHz for moderate and week coupling between the VCSEL and EAM cavities. Such ultrahigh bandwidth modulation is due to the fact that the changes of EAM impact much less the optical power distribution along the EAM-VCSEL and, consequently, the confinement factor and photon density in the VCSEL cavity. The three cases of strong, intermediate and weak coupling are also considered when carrying out the large-signal modulation response of the EAM-VCSEL and a clear open-eye diagram is demonstrated at 100 Gbs for an optimal EAM cavity length.
Highlights
Vertical-cavity surface-emitting lasers (VCSELs) [1,2] are nowadays substituting the traditional edge emitting semiconductor lasers (EEL) in many applications, such as Fiber to the Home links, computer networks, optical interconnects, optical sensing, laser printing, etc
For the case of small-signal modulation of electro-absorption modulator (EAM) losses shown in Figure 4b, the relaxation frequency peak is still well pronounced, its amplitude strongly decreases with α EAM and the modulation curve is flatter compared to the current modulation case
We see that the modulation cut-off frequency for current modulation is much less influenced as compared to the case of strong coupling as the bias absorption of the EAM is increased. This is due to the fact that the changes of α EAM impact much less the optical power distribution along the EAM-VCSEL and, the confinement factor in the VCSEL cavity and photon density
Summary
Vertical-cavity surface-emitting lasers (VCSELs) [1,2] are nowadays substituting the traditional edge emitting semiconductor lasers (EEL) in many applications, such as Fiber to the Home links, computer networks, optical interconnects, optical sensing, laser printing, etc. An impressive small-signal modulation cut-off frequency of about 30 GHz for such an integrated VCSEL with electro-absorption modulator (EAM), i.e., EAM-VCSEL has been reported [14]. We carry out a thorough analysis of the smalland large-signal modulation response of such an integrated EAM-VCSEL based on the coupled-cavity approach as reported in the recent experimental studies [13,14]. EAM-VCSEL for three typical cases of strong, intermediate and small coupling strength
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