We analyse the stochastic polarization fluctuations in a vertical cavity surface emitting laser (VCSEL) under the influence of electro-optical feedback and show that the dynamics can be modeled as a bistable system with time-delayed memory. Assuming an asymmetric potential, we show the existence of a regime in which the systems dynamic displays excitability. We calculate the relevant residence time distributions and correlation times and compare our system to a well known discrete model for excitability. Finally, we present experimental data that demonstrates excitable behaviour in the polarization dynamics of a VCSEL and, in particular, show the appearance of coherence resonance.
The polarisation dynamics of vertical cavity surface emitting lasers
(VCSELs) in the bistable regime is well described by Kramers theory
for noise induced transitions. By employing feedback, a memory mechanism can be introduced, which make the dynamics of the system
non-Markovian. Here we analyse theoretically and experimentally the
residence time distribution of the bistable systems in the presence
of noise and time-delayed feedback, using an opto-electronic feedback cycle for a VCSEL. We demonstrate and explain various non-exponential features of the residence time distribution using a continuous as well as a two-state model. Additionally we compare the results to an electronic Schmitt trigger, which represents an experimental realization of the two-state model.
An analysis of the transverse and longitudinal mode structure of broad area quantum dot lasers emitting at 1060 nm is presented. In particular, temperature is shown to play an important role in the stabilisation of the transverse mode structure of the devices. In addition, the investigation of the interaction between these transverse modes, through the measurement of the spatial intensity correlation, shows that the laser retains some modal properties in the unstable regime. Finally, measurements of spectral correlations between longitudinal mode groups display a strong dependency on their respective transverse mode structures indicating the importance of spatial overlap.
We analyse the dynamics of a self-pulsating semiconductor laser with optical feedback. Without re-injection of light the laser displays periodic oscillations. At very weak feedback levels we observe an amplitude instability whose frequency increases with the feedback level until the laser enters the low frequency fluctuation regime
commonly observed in cw lasers with optical feedback. We show that such behaviour can be observed within the framework of the Lang Kobayashi equations for self-pulsating semiconductor lasers.
We analyse theoretically and experimentally the residence time distribution of bistable systems in the presence of noise and time-delayed feedback. The feedback provides a memory mechanism for the system which leads to non-Markovian dynamics. We demonstrate and explain various non-exponential features of the residence time distribution using a two-state as well as a continuous model. The experimental results are based on a Schmitt Trigger where the feedback is provided by a computer generated delay loop and on a semiconductor laser with opto-electronic feedback.
Microcavity semiconductor lasers are important devices from both practical and fundamental viewpoints. Practically, these lasers/resonators are excellent candidates for the next generation of all-optical network components, including switches and filters, because of their size and low power consumption. We will present a novel packaging scheme which further facilitates these applications. This scheme involves the bonding of the optically pumped micro-resonator to a piece of multi-mode fiber. The laser is optically pumped directly and the emission is collected through another multi-mode fiber. This raises the possibility for 'all fiber' packaging schemes where the micro-resonator is sandwiched between two pieces of optical fiber. The pump and signal light can be injected in at one end and the output collected at the other. This illustrates the potential that these devices have for all optical network applications. In addition, the dynamic properties of these lasers are not well understood because the low level of laser light (order of nanoWatts) makes experimental analysis difficult. We will present experimental results that highlight some of the future challenge, which will have to be overcome if these devices are to realise their potential.
Proc. SPIE. 4646, Physics and Simulation of Optoelectronic Devices X
KEYWORDS: Polarization, High power lasers, Physics, Numerical simulations, Semiconductor lasers, Near field, Profiling, Laser damage threshold, Vertical cavity surface emitting lasers, Near field optics
We present a simple broad area semiconductor laser which uses a current spreading layer to modify the transverse gain profile. The device exhibits excellent spatial coherence to total output powers of 2.5 W under pulsed operation. Devices have been focused down to a spot size of approximately 5 micrometers FWHM at 2.5 W with the beam profile and position remaining stable over the entire range of operation. Under CW operation, thermal effects reduce spatial coherence leading to a significantly increased spot size and loss of beam stability. This work demonstrates the advantages of modifying the transverse gain profile and how it can be used to produce high brightness devices required for single mode fiber coupling.
We outline physical models and simulations for suppression of self-focusing and filamentation in large aperture semiconductor lasers. The principal technical objective is to generate multi-watt CW or quasi-CW outputs with nearly diffraction limited beams, suitable for long distance free space transmission, focusing to small spots or coupling to single-mode optical fibers. The principal strategies are (1) optimization of facet damage thresholds, (2) reduction of the linewidth enhancement factor which acts as the principal nonlinear optical coefficient, and (3) design of laterally profiled propagation structures in lasers and amplifiers which suppress lateral reflections.