Vertical cavity surface-emitting lasers (VCSELs) are the most popular choice as the ultra-fast and energy-efficient transmitters for use in optical interconnection of datacenters and supercomputers. Improvements on the wafer level have made much progress. High speed operations at data rates beyond 40 Gbps were demonstrated through the careful optimization of epi-wafers and device structures, and reached at to NRZ 71 Gbps with electrical equalization employed. But there remain difficulties in increasing the frequency response, which is mostly limited by the relaxation oscillation frequency and paracitics. In this paper, we review the progress of transverse-coupled-cavity VCSELs for increasing the modulation bandwidth and the monolithic lateral modulator integration. The noticeable modulation-bandwidth enhancement can be exhibited owing to “photon-photon resonance effect”. We demonstrated the modulation-bandwidth enhancement of a quasi-single mode VCSEL with a passive optical-feedback-cavity. The 3-dB modulation bandwidth can reach at 30 GHz. Eye opening of large signal modulations at 48 Gbps was obtained. The modeling and future prospect toward the bandwidth enhancement beyond 100GHz will also be presented. In addition, we demonstrated the lateral integration of an ultra-compact electro-absorption modulator with VCSEL. We obtained a sub-volt low driving voltage, and the bandwidth beyond 30 GHz. Our ultra-compact modulator integrated VCSEL can boost the modulation speed far beyond the direct modulation bandwidth for use in next-generation computing and data-center networks. We will also discuss on the multi-level modulation format, wavelength division multiplexing and space division multiplexing toward 400 Gbps or higher per fiber.

Date Published: 4 March 2019
PDF
Proc. SPIE 10924, Optical Interconnects XIX, 109240Q (4 March 2019); doi: 10.1117/12.2511312

Published in SPIE Proceedings Vol. 10924:
Optical Interconnects XIX
Henning Schröder; Ray T. Chen, Editor(s)