Monolithically Integrated Transceiver Chips for Bidirectional Optical Data Transmission

Vertical-cavity surface-emitting lasers (VCSELs) emitting at 850 nm wavelength are known for their attractive optical features and a continuously growing range of applications. The main goal of the present thesis is to demonstrate the feasibility of a monolithical integration of VCSELs with PIN-type photodiodes (PDs) for the operation as transceiver (TRx) chips in optical data links. The project milestones comprise the chip and the epitaxial layer design of the VCSEL–PIN PD device based on a traditional AlGaAs/GaAs material system, its fabrication development, electro-optical characterizations, and data transmission in a bidirectional optical link over a single, two-side butt-coupled standard graded-index (GI) multimode fiber (MMF). The monolithic design lowers the costs in the semiconductor technology as well as in packaging and additionally avoids the use of external optics, even though it is employed with a single 50 µm core diameter GI MMF. Thus, the very compact optical link saves space, weight, and module cost.
Deep insights into the electro-optical properties of VCSELs and PIN PDs are given by the theoretical description and measurements. The limitations of small-signal modulation responses are of main interest of this thesis. Thus, the dynamic characteristics including the extraction of modeled parasitics are presented. Also the electrical and optical crosstalk between the integrated devices and both transmission channels as well as the fiber alignment tolerances are covered. The results in optical data transmission consisting of various experiments in half-duplex and full-duplex mode, both free-space and fiber-coupled over a single MMF are comprised.
The monolithic TRx design is well suited for low-cost, compact optical links over distances of a few hundred meters. Capable to handle data rates of up to 10 Gbit/s and more, these TRx chips can be employed, e.g., to upgrade existing standard MMF networks to bidirectional operation or in mobile, low-cost, automotive networks.