High Speed VCSEL Technology and Applications

Abstract

Historically optical links up to 100–300m distances are served by light emitting devices in the 850 nm spectral range in combination with multimode glass fibers (MMF). As the silicon scaling continues, a single channel data rate is to double each 24 months. Light-emitting diodes had to be replaced by vertical cavity surface emitting lasers (VCSELs) and the data rate increased from 100 Mb/s to 10 Gb/s. At higher data rates problems with further scaling evolved. To avoid the collapse an anti-waveguiding VCSEL cavity design was invented, applied, and presently serves data links operating up to 50–100 Gb/s per channel. Another requirement in data communication is the bandwidth density scaling, with the number of channels per link increasing approximately 5-fold each 10 years, while keeping a similar space for connectors. A coarse short-wavelength division multiplexing allowing 850 nm, 880 nm, 910 nm, and 940 nm wavelengths in a single MMF is introduced. The bandwidth density increase is also possible by using multicore fiber (MCF) coupled to on-chip VCSEL arrays. The data rates up to 224 Gb/s are already reached by 850nm VCSELs. At such data rates significant transmission distance over MMF is only possible by applying ultra-narrow spectrum VCSELs minimizing the chromatic dispersion effects. On-chip mini-arrays of oxide-confined VCSELs allow a high coupling efficiency to MMFs, a narrow spectrum, a high power, a significant transmission distance at high data rates. Coherent lasing in such arrays allow photon-photon resonance engineering aimed at modulation bandwidths ∼50–100 GHz.