We have developed ultra-broadband Super-Luminescent Emitting Diodes (SLEDs) at 840 nm with a 3-dB bandwidth of
45-75 nm. The SLEDs show high robustness against back-reflections of up to 50% with little change in coherence
length, sidelobe suppression ratio and secondary peak suppression over a wide range of back-reflections. First long-term
measurements do not show any signs of device degradation. Hence, these SLEDs can be employed in OCT systems
without costly broadband optical isolators.
We have fabricated superluminescent light-emitting devices in the 840nm wavelength range with flat top spectral shape.
The novel design allows more than 50nm bandwidth and up to 34mW of optical power at the chip facet. Moreover, the
3dB bandwidth changes by less than 2nm within a driving current range between 120mA and 200mA. This corresponds
to a power level change between 17mW and 34mW, without considerable shape changes, which is one of the main
concerns for many applications. The stability of the spectral bandwidth is also reflected by the central wavelength that
changes by less than 1nm in the same range of currents. The device shows great stability of the optical far field with
respect to the driving current, allowing stable coupling of the emitted beam in optical fibers. We have also measured the
coherence function of this device using an interferometric spectrum analyzer. Results show good side-lobes suppression
ratio of more than 10dB, which remains almost unchanged over the whole range of driving currents.
We report the on the characterisation of 1.3μm emitting GaInNAs quantum well (QW) lasers grown by molecular beam epitaxy using a plasma nitrogen source. Through the optimization of the structural and optical properties as a function of substrate temperature and nitrogen flux conditions, we show that high optical quality structures, which exhibit good room temperature photoluminescence intensity and photoluminescence linewidths <10meV at low temperature, can be routinely achieved. To obtain 1.3μm emission, we employed a structure containing quantum wells with an indium content of 40% and a nitrogen content of 2.5% which have low nitrogen content (1%) lattice matched quaternary GaInNAs barriers, the latter enabling us to grow thick barrier structures without introducing further strain. For unmounted and uncoated 15μm ridge waveguide lasers we have achieved threshold current densities as low as 377Acm<sup>-2</sup> for a 3 QW and record low value of 178Acm<sup>-2</sup> for a single QW device emitting above 1310nm. The devices show excellent temperature characteristics with characteristic temperatures >90°C observed in several structures. In comparison to GaInAs quantum well lasers, the results show that at this composition (2.5%) there is no appreciable degradation of performance due to the presence of nitrogen in these samples. Increasing the nitrogen content by 1% was observed to shift the wavelength to 1390nm, but with a threshold current density increased by a factor of 2 to 830Acm<sup>-2</sup>. The results also indicate that although high quality GaInNAs lasers can be achieved at wavelengths suitable for the 1.31μm optical fibre waveband, the performance of devices with higher N content, and therefore with emission at longer wavelength, are degraded.