We present a numerical simulation on the effect of the linewidth
enhancement factor on the intensity noise and operation of laser diodes
subject to strong optical feedback. The simulation are based on an improved
time-delay rate equations model of a single-mode laser that takes into account
the multiple round-trips of the lasing field in the fiber cavity and is applicable
under any arbitrary strength of optical feedback [1]. The analyses are
performed in terms of the temporal trajectory of the laser intensity, bifurcation
diagram and relative intensity noise. The model is applied to stimulate output
characteristics and intensity noise in InGaAs/InP lasers in a wavelength of 980
nm. The simulation results indicted that the laser under strong optical
feedback mainly operates in Cw, pulsation or chaos operation depending on
the linewidth enhancement factor value [2]. When the linewidth enhancement
factor is low, the regime of strong optical feedback is characterized by either
continuous-wave (CW) operation or pulsation. The pulsation frequency is
locked at the frequency separation of the external cavity modes. When the
linewidth enhancement factor is medium, the laser exhibits pulsing and
unstable dynamics like chaotic operation over wide range of strong optical
feedback. At higher values of the linewidth enhancement factor the pulsing
operation becomes more dominant over wider range of strong optical
feedback. The corresponding RIN level is close to or higher than the level of
the solitary laser depending on optical feedback strength and the linewidth
enhancement factor. The optical feedback noise is found to be as low as the
quantum noise level when the laser is operated in pulsing region and at higher
values of the linewidth enhancement factor.
References
[1] S. Abdulrhmann, M. Ahmed, T. Okamoto, W. Ishimori and M. Yamada “An
improved analysis of semiconductor laser dynamics under strong feedback”,
IEEE J. Select. Topics Quantum., 9(5), 1265-1278, 2003.
[2] S. Abdulrhmann and Minoru Yamada “Numerical Simulations of the Effect of
the Linewidth Enhancement Factor on the Operation of Pumping Lasers under
Optical Feedback”, The Second Arab International Conference in Physics and
Materials Science (CPMS), Alexandria, Egypt,October 27 - 29, 2007.