Low timing jitter, sub picoseconds pulse source at 1.55 μm is demonstrated by integrating a fast saturable absorber
mirror (SESAM) with an optically-pumped mode-locked
vertical-extended-cavity-surface emitting laser (ML-VECSEL).
In such a soliton-like pulse-shaping mechanism, short pulse generation requires to control the group delay dispersion
(GDD) in the cavity in order to balance the nonlinear phase shift induced by strong semiconductor gain and absorber
saturation. By using selective etching technology, we controlled the SESAM optical cavity by varying from a resonant to
anti-resonant configuration (which corresponds to a GDD variation from -2000fs2 to +500fs2 at 1.55 μm) in the passive
mode-locking cavity. Using the same VECSEL chip, we observed that the mode-locked pulse duration could be reduced
from several ps to less than one ps with a resonance managed SESAM.
Mode-locked vertical-extended-cavity-surface emitting lasers (ML-VECSEL) are promising candidates for the
generation of stable short pulses at multi-GHz rate. However, the poor thermal behavior of quaternary InP-based
semiconductor compounds often limits the performance of ML-VECSELs operating at 1.55 μm. In this work, we report
on a specific approach using downward heat sinking to optimize the heat dissipation out of the active region. VECSEL
chips with a low thermal resistance are fabricated using a hybrid metal-metamorphic GaAs/AlAs mirror and bonding to a
highly thermally conductive host substrate. We show that superior performance can be obtained with a CVD diamond
substrate, while electroplated copper host substrate can afford a flexible and low cost alternate approach for moderate
(~100 mW) output power. The VECSEL chip assembled with a 1.55μm fast InGaAs(Sb)N/GaAsN semiconductor
saturable absorber mirror (SESAM) produces nearly Fourier transform-limited mode-locked pulses at ~ 2 GHz repetition
frequency, and the RF linewidth of the free running laser is measured to be less than 1000 Hz. When the resonance and
group delay dispersion of the SESAM microcavity are tuned by selective etching of specific top phase layers, the modelocked
pulse width is reduced from several picoseconds to less than 1 ps.
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