Angel Valle

Nonlinear dynamics induced by parallel and orthogonal optical injection in 1550 nm Vertical-Cavity Surface-Emitting Lasers (VCSELs)

We report a first experimental study of the nonlinear dynamics appearing in a 1550 nm single-mode VCSEL subject to parallel and to orthogonal optical injection. For the first time to our knowledge we report experimentally measured stability maps identifying the boundaries between regions of different nonlinear dynamics for both cases of polarized injection. A rich variety of nonlinear behaviours, including periodic (limit cycle, period doubling) and chaotic dynamics have been experimentally observed.

Polarization behavior of birefringent multitransverse mode vertical-cavity surface-emitting lasers

An analysis has been undertaken of the effect of birefringence on the selection of polarization states of a weakly index guided vertical-cavity surface-emitting laser (VCSEL) supporting both a fundamental and a first-order transverse mode. It is shown that for small index steps polarization switching due to spatial-hole burning effects can occur. For larger index steps it is found that higher order modes can emerge which are orthogonally polarized to the dominant polarization of the fundamental mode.

Selection and modulation of high-order transverse modes in vertical-cavity surface-emitting lasers

A theoretical proposal to double the pulse repetition frequency by alternating current modulation of two orthogonal high-order transverse modes of a vertical-cavity surface-emitting laser (VCSEL) is presented. Static and dynamic characteristics of weakly index-guided VCSELs in a multitransverse mode regime are analyzed. An efficient model that takes into account all the transverse modes supported by the waveguide is developed. Mode partition noise in a current modulated VCSEL is studied, taking into account the azimuthal degree of freedom. Different transverse modes can be excited with a probability that is numerically calculated. For high injection currents, modes that are not favored in the steady state can be excited with higher probability. The excitation probability is similar for azimuthally orthogonal modes. This symmetry can be broken by selecting a particular high-order transverse mode by using azimuthal-dependent current profiling. This selection can be achieved over current ranges as wide as ten times the threshold current. Current modulation of this transverse mode is then analyzed. Alternate current modulation of two orthogonal high-order transverse modes is also studied. Alternating modulation of these modes can double the pulse repetition frequency obtained by modulating just one high-order transverse mode, without increasing injected current density levels. This current-induced spatial switching leads to high-frequency beam steering in the laser azimuthal direction.

Transverse Mode Switching and Locking in Vertical-Cavity Surface-Emitting Lasers Subject to Orthogonal Optical Injection

In this paper, we report on theoretical and experimental investigation on polarization and transverse mode behavior of vertical-cavity surface-emitting lasers (VCSELs) under orthogonal optical injection as a function of the injection strength and of the detuning between the injection frequency and the free-running frequency of the solitary laser. As the injection strength increases the VCSEL switches to the master laser polarization. We find that the injection power necessary to obtain such polarization switching is minimum at two different values of the frequency detuning: the first one corresponds to the frequency splitting between the two linearly polarized fundamental transverse modes, and the second one appears at a larger positive frequency detuning, close to the frequency difference between the first-order and the fundamental transverse modes of the solitary VCSEL. We show theoretically that both the depth and the frequency corresponding to the second minimum increase when the relative losses between the two transverse modes decrease. Bistability of the polarization switching is obtained for the whole frequency detuning range. Such a bistability is found for the fundamental mode only or for both transverse modes, depending on the value of the detuning. The theoretical and experimental optical spectra are in good agreement showing that the first-order transverse mode appears locked to the external injection

Polarization selection in birefringent vertical-cavity surface emitting lasers

Summary form only given. Polarisation characteristics of vertical cavity surface-emitting lasers (VCSELs) exhibit significant differences to those of edge-emitting semiconductor lasers. In general the polarization of the fundamental transverse mode can change when the injected current is altered. It has also been noted that the strain induced during the fabrication causes birefringence in VCSELs. In this work we present numerical calculations that demonstrate that small refraction index anisotropies can select the polarization of VCSEL.

Polarization Bistability in 1550 nm Wavelength Single-Mode Vertical-Cavity Surface-Emitting Lasers Subject to Orthogonal Optical Injection

In this paper, we report on an experimental investigation of the bistable behavior of a 1550 nm single transverse and polarization mode vertical-cavity surface-emitting laser (VCSEL) when subjected to orthogonal optical injection. As the master laser wavelength is scanned near the resonance wavelength of the depressed linearly polarized fundamental mode, and for a fixed injected power, the VCSEL exhibits two successive polarization switchings (PSs). Both PSs exhibit bistable regions in such a way that a pure-frequency-induced polarization bistability is found. The width of both bistable regions has been measured as a function of the injected power and for different values of the VCSEL current. While the injection power is lesser than a certain value, the hysteresis width fluctuates around a constant level. Further increase of the injection power leads to a smaller constant value of the hysteresis width. The value of that transition value is independent of the VCSEL current. Power-induced polarization bistability - by fixing the master laser wavelength - is found near the transition value. Clockwise and anticlockwise power-hysteresis cycles are observed for short and long master laser wavelengths, respectively.

High-frequency microwave signal generation using multi-transverse mode VCSELs subject to two-frequency optical injection

In this paper we report a new method of photonic generation of microwave signals using a multi-transverse mode VCSEL subject to two-frequency optical injection. Numerical simulations show that double injection locking involving two transverse modes can be obtained in these systems. We show that the higher-order transverse mode is excited with a much larger amplitude than that of the fundamental transverse mode. The comparison with the case of a single-transverse mode VCSEL subject to similar two-frequency optical injection shows that multi-transverse mode operation of the VCSEL enhances the performance of the photonic microwave generation system. Broad tuning ranges, beyond the THz region, and narrow linewidths are demonstrated in our system. The maximum frequency of the generated microwave signals can be substantially increased if multimode VCSELs are used instead of single-mode VCSELs.

Polarization Switching in Long-Wavelength VCSELs Subject to Orthogonal Optical Injection

Polarization switching (PS) appearing in long-wavelength vertical-cavity surface-emitting lasers (VCSELs) subject to orthogonal optical injection is investigated theoretically and experimentally. We have studied the injected optical power required for PS as a function of the frequency detuning between the injected light and the orthogonal linear polarization of the VCSEL. For a wide range of bias currents applied to the device, the injected power required for the occurrence of PS exhibited a minimum and a plateau with respect to the frequency detuning. The minimum (plateau) was found at negative (positive) frequency detuning. The bistable behavior of the polarization is described. Our experimental results confirm the theoretical predictions of Sciamanna and Panajotov. The levels of the minimum and the plateau were observed to increase as higher bias currents were applied to the VCSEL. A first theoretical and experimental observation of the disappearance and further appearance of PS when increasing the injected power in long-wavelength VCSELs is described. This situation is obtained for small levels of negative frequency detuning and for large enough values of applied bias current. A good overall qualitative agreement is found between our theoretical and experimental results.

Power and wavelength polarization bistability with very wide hysteresis cycles in a 1550nm-VCSEL subject to orthogonal optical injection

We have measured optical power and wavelength polarization bistability in a 1550 nm-Vertical Cavity Surface-Emitting Laser (VCSEL) subject to orthogonally-polarized optical injection into the orthogonal polarization of the fundamental transverse mode. Optical bistability with very wide hysteresis cycles, up to four times wider than previously reported results has been measured for both the optical power and wavelength domain. We also report the experimental observation of three different shapes of polarization bistability, anticlockwise, clockwise and X-Shape bistability, all of them with wide hysteresis cycles. This rich variety of behaviour at the important wavelength of 1550 nm offers promise for the use of VCSELs for all-optical signal processing and optical switching/routing applications.

Polarization- and Transverse-Mode Dynamics in Optically Injected and Gain-Switched Vertical-Cavity Surface-Emitting Lasers

In this paper, we summarize our recent results on nonlinear polarization- and transverse-mode dynamics of vertical-cavity surface-emitting lasers (VCSELs) induced by optical injection (OI) or current modulation. Due to the surface emission and cylindrical symmetry, VCSELs lack strong polarization anisotropy and may undergo polarization switching (PS). Furthermore, VCSELs may emit light in multiple transverse modes. This provides new features to the rich nonlinear dynamics induced in VCSELs by an external perturbation. We demonstrate for the case of orthogonal OI that new Hopf bifurcation on a two-polarization-mode solution delimits the injection locking (IL) region and that PS and IL of first-order transverse mode lead to a new resonance tongue for large positive detunings. Similarly, the underlying polarization-mode competition leads to chaotic-like behavior in case of gain switching and the presence of two transverse modes additionally reduces the possibility of regular dynamics.