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1 T. Malica1, D.M. Kane1, J.P. Toomey1, and K. A. Shore2 MQ~Photonics Research Centre and Dept of Physics and Astronomy, Macquarie University, Sydney, Australia 2 School of Electronic Engineering, Bangor University, Wales, UK Précis-Insights into analysis of an experimental semiconductor laser with external optical feedback system gained from simulation with theoretical models. Over the years, theoretical semiconductor laser equation models have enabled the research community to map out semiconductor laser behavior and study dynamics. These dynamics arise on introducing a perturbation to the otherwise stable semiconductor laser. An external cavity mirror providing optical feedback to a laser is one of the easier ways of achieving this, as shown in Fig1. These theoretical models predict regions of stability and provide insights on chaotic behavior and other complex phenomena, thus, informing where certain dynamics might be achieved in experiments, with lasers, within a predefined parameter space. Some of the more well-known and widely used models are Lang-Kobayashi (L-K, limited to weak optical feedback) [1] and the travelling wave model (TWM) [2,3]. The TWM has since evolved to the iterative TWM (ITWM) [4,5] which incorporates multiple reflections for a multi-modal system and can predict the laser dynamics for higher levels of optical feedback compared to the L-K model. Previously, experiments have been performed using a GaAlAs high power laser diode lasing at 830nm semiconductor laser and the system complexity was mapped successfully over a wide range of parameters [6]. In order to verify the accuracy of the theoretical models we performed simulations using both L-K and ITWM with the parameters stated in Table1. We expected similar trends as seen in high resolution maps produced experimentally. Our simulation results suggest otherwise and indicate that varying the external feedback results in, to date, unexpected dynamics where the system transitions more than once between complex and stable dynamics as the level of optical feedback is increased. Hence, there is a need to further critically appraise the ITWM with respect to its validity to describe experimental results. Since the L-K model has been extensively studied and has proven to produce accurate results for low optical feedback levels, we use it as a benchmark to test the accuracy of the ITWM at lower-feedback levels. The results of this comparison and the critical appraisal of the ITWM at higher levels of optical feedback will be presented. Fig1. Schematic diagram of the laser setup with external optical feedback using a mirror where ‘r1’, ‘r2’ and ‘r3’ are the amplitude reflectances of the laser facets and external cavity mirror respectively while ‘τin’ and ‘τRT’ are internal and external round trip times. Parameters Value Symbol Unit Refractive index Carrier lifetime Volume of active region Transparency carrier density External cavity roundtrip time Wavelength Internal cavity length 3.4 2x109 1.5x10-16 n τn V s m-3 1.5x1023 No m-3 0.33x10-9 τext s 850x10-9 300x10-6 λ Lin m m Table1. Parameters used for simulations Acknowledgement TM is supported by an international Macquarie University Research Excellence Scholarship. The development of the iterative travelling wave model code has been contributed to by several researchers including Lloyd Langley at University of Bath and Paul Spencer and Zubaida Sattar at Bangor University. [1] [2] [3] [4] [5] [6] R. Lang and K. Kobayashi, ‘External optical feedback effects on semiconductor injection laser properties’, Quantum Electron. IEEE J. Of, vol. 16, no. 3, pp. 347–355, 1980. F. Sporleder, ‘Travelling wave line model for laser diodes with external optical feedback’. Proceedings-International U.R.S.I. Symposium, 1983. J. Mork, PhD Thesis: Nonlinear dynamics and stochastic behaviour of semiconductor lasers with optical feedback. Denmark Technical University, 1988. I. Pierce, P. Rees, and P. S. Spencer, ‘Multimode dynamics in laser diodes with optical feedback’, Phys. Rev. A, vol. 61, no. 5, p. 53801, Apr. 2000. P. S. Spencer and K. A. Shore, ‘Multimode iterative analysis of the dynamic and noise properties of laser diodes subject to optical feedback’, Quantum Semiclassical Opt. J. Eur. Opt. Soc. Part B, vol. 9, no. 5, p. 819, 1997. J. P. Toomey and D. M. Kane, ‘Mapping the dynamic complexity of a semiconductor laser with optical feedback using permutation entropy’, Opt. Express, vol. 22, no. 2, p. 1713, Jan. 2014.