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An Investigation of Mode Partitioning in VCSELS

Coe, Paul

HPL-96-143

Keyword(s): mode partitioning; VCSEL

Abstract: Mode partitioning, quantified in terms of a normalised mode partitioning parameter k, was investigated in laser diodes operating under CW and PRBS modulation @ 1.0625 Gbit/s. A comparison was made between VCSELs and Fabry-Perot edge emitters. Individual laser modes, (or in the case of VCSELs, groups of modes), were preselected using an optical spectrum analyser and monitored using a sensitive APD. By monitoring the statistical distribution of the APD signal, the modal fluctuations were recorded and used to calculated k. The value of k was found to be higher, indicating stronger mode partitioning, when the bias current was closer to threshold for CW operation and when the laser was switched rapidly under modulation.

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