On the Effects of an Antireflection Coating Impairment on the Sensitivity to Optical Feedback of AR/HR Semiconductor DFB Lasers

Abstract

International audienceThe sensitivity to optical feedback of 1.55- mum antireflection (AR)/high-reflection (HR) DFB semiconductor lasers is presented in this paper. The onset of the coherence collapse, which is the most critical feedback regime for optical transmissions, is theoretically investigated with a stress on its dependence with facet phase effects (FPEs). Taking into account FPEs on both facets, the sensitivity to optical feedback is evaluated with respect to both the coupling strength coefficient and the feedback level. The first part of the paper shows that due to the HR-facet, a distribution up to several decibels on the coherence collapse thresholds is predicted over the whole DFB laser population. The second part concentrates on the coherence collapse dependence with respect to the AR coating. Calculations show an enhancement of the coherent collapse threshold distribution up to 10 dB due to the AR coating impairment. These simulations are of first importance for optical transmissions since they show that for AR coatings beyond 10-4, the sensitivity to optical feedback of AR/HR DFB lasers is extremely difficult to evaluate from one laser to another. On the other hand, for AR coatings below 10-4, all feedback performances are directly connected to the laser wavelength, and DFB lasers can be easily selected for high bit rate isolator-free transmission

Regimes of external optical feedback in 5.6 μm distributed feedback mid-infrared quantum cascade lasers

“…Although no coherence collapse operation has been reported in recent experiments conducted on both THz and mid infrared QCLs, 14 it is important to stress that the onset of the coherence collapse is also strongly dependent on the DFB laser structure, as already pointed out for near infrared emitters. 6,27 Further, investigations are required to determine whether the fourth regime of optical feedback observed in the QCL under study does correspond to the coherence collapse. Finally, for very high feedback levels, the laser enters the extended cavity regime, with single-mode operation and high output power.…”

Extensive study of the linewidth enhancement factor of a distributed feedback quantum cascade laser at ultra-low temperature

“…Where C l is the coupling strength coefficient of the front facet that is coupled to the external cavity 26 and τ in the photon roundtrip time in the laser cavity. We use this model for a numerical analysis of the bifurcation diagrams when varying the value of the LEF.…”

Temperature dependence of a mid-infrared quantum cascade laser with external optical feedback

“…Where C l is the coupling strength coefficient of the front facet that is coupled to the external cavity 16 and τ in the photon roundtrip time in the laser cavity. Although the LEF can slightly vary with temperature because of the thermal effects and gain compression, our experimental conditions allow remaining within the quasi-static regime.…”