1. Optical Feedback in a Curved-Facet Self-Pulsing Semiconductor Laser
Olwen Carroll, John Houlihan,
Yann Tanguy, Guillaume Huyet and Brian Corbett*
Optoelectronics Research Group, Physics Dept., National University of Ireland, Cork, Ireland
* National Microelectronics Research Center, National University of Ireland, Cork, Ireland

2. Outline Curved facet laser Experimental setup Increasing feedback
Complex behaviour
Broadening of the spectrum
LFF, Coherence collapse
Conclusions and future work

3. The device High power laser Internal focus
Application to optical amplifiers
Internal focus
Spatially tailored injection profile
Astigmatic beam
Focal point moves with current
Moves less with high magnification

4. Spatial Coherence
Laser focus width remains constant with increasing current for the free running laser
Spatial Coherence and feedback
Under strong feedback, the focal point becomes bigger, so we have a loss of spatial coherence

5. Temporal properties Laser run pulsed to avoid Heating Time series
Detector 30 ps rise time
6 GHz oscilloscope
26 GHz ESA

6. Frequency vs current
Pulsation frequency squared increases linearly with pump current
Same as Relaxation oscillations

7. Origin of self pulsation
Devices have a region which is not pumped
Umpumped region acts as a saturable absorber
But does not affect spatial coherence as the focal point remains small

8. Effect of optical feedback
Can we observe coherence collapse in a self-pulsating semiconductor laser?
Effect on spatial coherence?

10. Time series vs feedback
When feedback increase,
Intensity fluctuations
Events with no fluctuations
Number of events increases
With feedback
Route to complexity

11. Statistical analysis of the events
Measured the time between consecutive events.
Two events per trace to reconstruct the probability distribution
Exponential decay suggests a noise induced instability

12. Characterisation of events
The amplitude of the oscillations varies with time
Measured Hilbert phase and amplitude
Phase increased linearly
Amplitude modulation

14. Moderate feedback levels
Signatures of oscillations at the round trip frequency
Time series show complicated oscillations

16. Low frequency spectra
When the feedback increases, low frequency components appear in the power spectra
This corresponds to power drop outs, LFF

17. LFF Regime Power drop outs
Characteristic Frequency decreases with feedback increase (same as cw laser under optical feedback)

18. Conclusions
Described the behaviour of a self pulsing laser under the influence of optical feedback
See the presence of instabilities similar to those observed in the case of a cw laser under optical feedback
Described the route to LFF as a noise induced amplitude modulation
Future
Have a theoretical understanding

19. Acknowledgements
Vista project
Wild project
Science Foundation Ireland

20. Short cavities
With increasing feedback in a short external cavity relaxation frequency increases until it locks to a particular frequency and the external cavity modes appear