VCSEL electrical packaging analysis and design guidelines for multi-GHz applications

The introduction of the vertical cavity surface emitting laser (VCSEL) diode structure has created the need for enhanced performance, low cost, optical packages capable of supporting data rates as high as 5 Gb/s. The popular laser packages, such as the TO-46 and the TO-56 "cans", which have been traditionally used for edge emitting laser diodes at much lower frequencies, cannot support this dramatic increase in data rates. Package parasitics and severe impedance discontinuities, inherent in the TO-46 and TO-56, impose stringent frequency limitations and dramatically effect the integrity of the electrical signals. Because electrical waveform control is essential for proper laser diode operation, these high frequency performance problems must be identified and overcome. This paper will describe electromagnetic and SPICE modeling techniques which were used to create equivalent circuits of the TO-36 and the TO-56 cans for comparison to measured results to achieve model verification. Subsequently, the models were used to determine frequency limitations associated with the TO-46 and the TO-56 laser cans. Additionally, the specific problems associated with the operation of a VCSEL laser package operating at high frequencies (i.e. >1 Gb/s) were identified; possible solutions for typical driving configurations were then developed. The lessons learned from the analysis of the TO-46 and TO-56 cans were used to determine a rudimentary set of VCSEL package design guidelines. Finally, these guidelines were used to design and model a conceptual VCSEL laser package, dubbed optical package for advanced lasers (OPAL), capable of operation to data rates as high as 5 Gb/s. The modeling techniques used to match the TO-46 and the TO-56 time domain and frequency domain simulations to measurements were extrapolated to create a model of OPAL, and to evaluate it at high frequencies.