| Small size, small beam divergence, very low threshold current, and wide modulation bandwidth make vertical-cavity surface-emitting lasers (VCSELs) very attractive for optical communications and interconnects. However, their carrier dynamics such as threshold carrier densities and recombination processes are still not well known. Many of these parameters can be obtained from carrier lifetime measurements.;This work presents the results of experimental studies obtained with a recently developed experimental technique for accurate and reliable measurements of carrier lifetimes in VCSELs. This technique is based on a high frequency impedance model of quantum-well lasers. Results on differential carrier lifetimes of gain-guided (lambda = 850 nm) and index-guided (lambda = 980 nm) VCSELs were obtained from laser impedance measurements at subthreshold currents. We also show how to use this new technique to study the effect of lateral diffusion of carriers in index-guided VCSELs with the device size as a parameter.;Different applications of VCSELs use different information coding schemes and require lasers with different characteristics. Digital transmission at high data rates requires VCSELs with high modulation bandwidth and very stable single-wavelength emission. Since VCSELs have a relatively large transverse dimension, the mode structure resulting from optical feedback could be strongly affected, generating either multimode or single mode emission, depending on the amount of feedback. Our work demonstrated single-mode operation of a VCSEL using a fiber Bragg grating as an external reflector. A side mode suppression ratio of 30dB was obtained under static and dynamic bias conditions for a wide range of modulation frequencies.;Analog transmission using VCSELs has large potential for communication applications. Standard cable television systems, radar links, and personal communication systems utilize analog modulation of the signal but require low intermodulation distortion and therefore very high linearity and low noise. The dynamic range is a useful measure to characterize the importance of the third order intermodulation distortion caused by nonlinearities in the modulated VCSEL. The intermodulation distortion usually limits the system performance. Analog modulation experiments on VCSELs were performed and their suitability for analog link applications was demonstrated. |
