Gain-switched GaAs vertical-cavity surface-emitting lasers

The authors have gain-switched GaAs vertical-cavity surface-emitting lasers (VCSELs) using sinusiodal electrical modulation at rates between 1.5 and 8 GHz and devices with operating wavelengths between 820 and 860 nm. The shortest pulse obtained directly from such lasers was 24 ps. The time-bandwidth products were between 0.6 and 3, which is smaller than those observed for gain-switched, single-frequency, edge-emitting lasers. Some of the excess bandwidth is caused by linear chirp, which was compensated using linear dispersion in single-mode optical fiber. The shortest compressed pulse was 15 ps. The pulses contained significant nonlinear chirp, however, which reduced the expected compression factor for linear dispersion to a factor of 2. The timing jitter for gain-switched pulse trains was 4-6 ps, which is comparable to that observed for the edge-emitting lasers. Device design tradeoffs which affect the duration of the pulses from gain-switched VCSELs are discussed.<
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