Long-term aging with highly stable performances of 1.55-μm DFB lasers for microwave optical links

At the present time, due to their improved spectral characteristics accompanied by low noise and high linearity of current-light output power features, 1.55 μm DFB lasers are key components of analog microwave fibre optical links. These devices are the most frequently used as both the optical source and RF/optical modulator. Especially in the case of direct intensity modulation links, stringent requirements repose on these devices together in terms of performances and reliability, the latter being a crucial issue for the viability of the optical links. This paper deals with the investigation on the reliability of 1.55 μm strained quantum well ridge DFB lasers. Long term ageing tests were performed during 12,000 hours at 80°C ambient temperature and a constant bias current of 140 mA corresponding to 10 mW output power. These tests ended, none failure or decrease of the optical power was observed. A detailed evaluation based on crucial parameters for direct microwave modulation as static characteristics, emission spectra and relative intensity noise (RIN) has revealed only negligible changes after ageing.