High speed modulation of vertical cavity surface emitting lasers

An optical interconnect consisting of a semiconductor laser transmitter, an optical fiber, and a photodetector receiver is a basic component of the physical infrastructure of the internet. The laser embeds information into its output by generating pulses of light, and the bandwidth of the laser limits transmission speed. For short range optical communications, vertical cavity surface emitting lasers (VCSELs) are the most commonly used laser transmitter. This work focuses upon determining which properties of VCSELs indicate whether or not the laser will have a high modulation bandwidth and therefore a high transmission speed. First, small signal theory is applied to a VCSEL diode to derive its small signal frequency response. From this analysis the device characteristics that influence bandwidth may be determined. VCSEL samples fabricated by the Photonic Device Research Group at the University of Illinois (including both oxide-confined VCSELs and photonic crystal VCSELs) are then experimentally tested in order to verify conclusions extracted from theory. Continuous wave measurements are performed on the laser diodes in order to characterize their basic properties (threshold current, emission spectra, maximum power, etc.), and it is speculated whether a device will have a high bandwidth based upon these properties. The samples are then introduced into an optical interconnect and their small signal modulation bandwidths are determined.U of I OnlyUndergraduate senior thesis not recommended for open acces