We demonstrate a compact, diode-pumped Nd:GdVO4 laser with a repetition rate of 9.66 GHz and 0.5-W average output power. The laser is passively mode locked with a semiconductor saturable absorber mirror (SESAM), yielding 12-ps-long sech2-shaped pulses. For synchronization of the pulse train to an external reference clock, the SESAM is mounted on a piezoelectric transducer. With an electronic feedback loop of only a few kilohertz loop bandwidth we achieved a rms timing jitter of 146 fs (integrated from 10 Hz to 10 MHz). This is an upper limit because it is mostly limited by the measurement system. The laser setup with a simple linear cavity has a footprint of only 130 mm x 30 mm.
Systematic study on the effects of the waveguide thickness Wg has been carried out for 200-μm-wide stripe separate-confinement-heterostructure lasers in the range of Wg=0.22–1.2 μm while the width of single quantum well is kept constant at 10 nm. The internal loss αi is reduced from 1.7 to 1 cm−1 when Wg is increased from 0.22 to 1.2 μm. It is shown that αi is not determined by the free-carrier absorption of clad layers, but primarily by Γ, the optical confinement factor, most probably due to scattering at the quantum well/waveguide interfaces. The external differential quantum efficiency ηd monotonically increases with Wg for pulsed operation. By contrast, ηd is maximum at Wg=0.8 μm for continuous-wave (cw) operation. Both the threshold carrier density and the threshold temperature sensitivity increases with Wg for Wg⩾0.8 μm, which decreases ηd in cw operation. When 200-μm-wide devices (20%/97% coated) were life tested at 2 W and 30 °C, the median degradation rate shows a minimal value of 3×10−6 h−1 at Wg=0.8 μm, which is 7 times smaller than that at Wg=0.22 μm. The facet temperature measured by the modulation reflectance is also minimized at Wg=0.8 μm. In broad-waveguide lasers with increasing Wg, the increase in carrier overflow competes with the reduction of optical power density, and thus self-absorption in the quantum well, which determines the optimal Wg.
The characteristics of broadband superluminescent diodes (SLDs) are presented. The longitudinal bandgap modulated InGaAs/GaAs multiple quantum wells of broadband SLDs are grown by selective area metal organic vapour phase epitaxy (MOVPE) growth. The centre wavelength was 1060 nm. The 3 dB bandwidth was 130 nm and the 10 dB bandwidth was 174 nm. The output power was 0.3 mW.
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