Y. Hong

Polarisation-resolved chaos and instabilities in a vertical cavity surface emitting laser subject to optical injection

Instabilities in the polarisation-resolved output of a vertical cavity surface emitting laser (VCSEL) subject to optical injection have been investigated experimentally. It is found that regions of chaotic behaviour exist for both positive and negative detuning from the stable injection locking regime. Outside the chaos regimes, several nonlinear dynamical phenomena including frequency pushing, nearly degenerate four-wave mixing (NDFWM), injection locking, limit cycle and period doubling, were also observed.

Experimental observation of anti-phase polarisation dynamics in VCSELS

Abstract Optical injection from an external laser is found to introduce dynamical instability in the polarisation resolved optical output power of a vertical-cavity surface-emitting laser (VCSEL) operating in a stable regime of polarisation. The dependence of the polarisation instability on the frequency, polarisation and the injection power of the external laser has been studied. The instability seems to occur through gain competition between co-existing orthogonal polarised modes. The fluctuations in orthogonal polarisations are in anti-phase – the total output power of the VCSEL remains constant.

Observation of optical bistability in a GaAlAs semiconductor laser under intermodal injection locking.

Experimental observation of optical bistability in a semiconductor laser under intermodal injection locking is reported for what is believed to be the first time. It is seen that a change in injection power of several microwatts or master laser frequency detuning of a few hundred megahertz can induce a change of as much as several hundred gigahertz in the lasing frequency of the slave laser. The results are in qualitative agreement with theoretical predictions.

Polarization-resolved relative intensity noise measurements of a vertical-cavity surface-emitting laser subjected to strong optical feedback

We experimentally measure the polarization-resolved relative intensity noise (RIN) in two orthogonal polarization states of a vertical-cavity surface-emitting laser (VCSEL) subjected to strong optical feedback. A comparison is made with the RIN of solitary VCSEL. Optical feedback is shown to enhance the RIN in one polarization direction while suppressing the RIN in the orthogonal polarization. The RIN in the dominant polarization mode exhibits complementary behavior to the RIN in the suppressed polarization mode.

Theoretical and experimental study of polarization switching in long-wavelength VCSELs subject to parallel optical injection

We report a theoretical and experimental analysis of the polarization switching found in a single-transverse mode VCSEL when subject to parallel optical injection. We have found a novel situation in which injection locking of the parallel polarization and excitation of the free-running orthogonal polarization of the VCSEL are simultaneously obtained. Analytical expressions for the power of both linear polarizations in the previous steady state are determined. We show that considering two linear polarization modes in a model of a VCSEL subject to parallel optical injection leads to simpler expressions than those found for a VCSEL with only a single linear polarization. We show that the power emitted in both linear polarizations depend linearly on the injected power. The stability region of this solution is measured in the plane injected power versus frequency detuning.

Transverse-mode dynamics of vertical-cavity surface-emitting lasers subject to polarized optical injection

Two-transverse-mode vertical cavity surface emitting lasers (VCSELs) subject to external optical injection is experimentally investigated. The spectra of the VCSEL with two parallel-polarized modes, under optical injection, demonstrate significantly different behaviors, compared to the VCSEL with two orthogonally-polarized transverse modes. In a VCSEL with two orthogonally-polarized transverse modes, the experimental results are good qualitative agreement with the theoretical prediction that the external optical injection can be used to achieve single-mode operation. However, in the case of a two parallel-polarized transverse modes VCSEL, single-mode operation cannot be obtained via optical injection. When the injection frequency is close to one of the modes, the coexistence of the injected beam and the mode gives rise to very rich dynamical behavior, however, the other mode is unperturbed by the optical injection.

Semiconductor lasers subject to polarization-rotated optical feedback

The dynamics of a semiconductor laser subject to polarization rotated (incoherent) optical feedback have been numerical and experimental investigated. The results show that the induced dynamics can be grouped into four regimes (stable, chaotic, pulsed and two-state) and they also show that the TM mode of the laser never lases, at least in the ring cavity configuration studied. In addition, unlike the earlier short cavity work, the boundaries between the regimes in the long cavity case were found to be independent of the external cavity delay time. By focussing on the effects induced by incoherent optical feedback from long external cavities we will show that four regimes of operation can be accessed by varying the external reflectivity. Calculated Lyapunov exponents and a bifurcation diagram clearly delineate these regimes and experimental verification of the transition from stable to chaotic dynamics will be described. The dynamical behaviour exhibited in each regime will be explained in terms of the memory effect introduced by the time delay associated with the external cavity and the natural relaxation oscillations of the solitary laser. It will also be shown that within the pulsed regime the pulse repetition rate is determined by the external reflectivity and injection current and is independent of the external cavity length.

Experimental demonstration of a simple technique for highly efficient polarization insensitive wavelength conversion

Four-wave mixing in a semiconductor optical amplifier (SOA) is an attractive technique for various telecommunication and all optical processing applications such as wavelength conversion and dispersion compensation. Such a scheme should be both insensitive to the polarization of the signal wave and highly efficient. In this paper we have demonstrate an effective and most simple scheme to realize polarization insensitive wavelength conversion with high conversion efficiency.

Optical injection control of polarization pulsations in VCSELs

Vertical cavity surface emitting lasers (VCSEL) exhibit self-pulsations in the polarization-resolved light output at certain bias currents, where the dominant polarization direction suffers a transition from one direction to its orthogonal direction. This pulsation in the polarization resolved output could be controlled by an external optical injection in a master-slave configuration with VCSEL used as slave laser. Experimentally it has been demonstrated that the stabilization linear polarization directions preferred in the solitary VCSEL. The exact frequency of the optical injection to effect stabilization is dependent on the injection power and polarization.

Polarization-resolved chaos in a vertical-cavity surface-emitting laser subject to optical injection

A nearly single mode vertical cavity surface emitting laser (VCSEL) subject to optical injection have been investigated experimentally. It is found that regions of polarization-resolved chaotic behavior exist for both positive and negative detuning from the stable injection locking regime. Outside the chaos regimes, several nonlinear dynamical phenomena including frequency pushing, nearly degenerate four-wave mixing, injection locking, limit cycle and period doubling, were also observed.