Relative intensity noise and modulation distortion characteristics of vertical-cavity surface-emitting laser diodes

Summary form only given. Vertical-Cavity Surface-Emitting Laser (VCSEL) diodes are seen as effective light sources for future optical-fiber communication and optical signal processing applications. Essential to these applications, however, is the device´s ability to yield a low-distortion and adequately broad band intensity modulation response. Unfortunately, very little has been published so far regarding these characteristics of VCSELs, and in particular their dependence on the higher-order transverse modes that are typically present in the device cavity. Our recent experimental investigations conducted on a number of different circular index guided VCSELs have indicated that the presence of higher-order cavity modes, even for devices exhibiting reasonably good side-mode suppression ratios can modify the shape of the modulation response and often leads to harmonic distortion even at relatively low modulation signal levels. We attribute these effects to the cavity mode interaction that is associated with the optical gain nonlinearity. This mode interaction results in signal (or noise) beating effects. This is also referred to as the spectral down- or up-conversion process or mixing. In order to investigate the influence of these beat effects on the intrinsic modulation response, “parasitic-free” relative intensity noise (RIN) characteristics for different medium-power VCSELs (6-9 μm diameter range) have been measured