Sujit Bandyopadhyay

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.

VCSEL polarization control by optical injection

The stability of the polarization-resolved (PR) light output of a commercial vertical-cavity surface-emitting laser (VCSEL) has been studied with and without the presence of external optical injection in a master-slave configuration. Pulsations in the PR light output are observed in the solitary laser at certain bias current. It has been observed here for the first time that optical injection can stabilize the polarization of a VCSEL operating in a pulsation regime.

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.

Spectral signatures of the dynamics of current-modulated vertical-cavity surface-emitting lasers subject to optical feedback

The dynamics of current-modulated vertical-cavity surface-emitting lasers (VCSELs) with optical feedback has been studied experimentally. The nature of the dynamics is classified by measured power spectra. It is shown that when the depth of the current modulation is increased the VCSEL dynamics exhibits transitions from a regime governed by the optical feedback through a regime where both optical feedback and modulation contribute to a regime where the current modulation controls the dynamics. Such a transition through three regimes of dynamical behavior has also been identified, at different bias currents, when the modulation frequency is varied. A dynamical resonance having a complicated dependence on the external cavity length is also revealed. The measurements are in good 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.

Noise characteristics of a single-mode laser diode subject to strong optical feedback

An experimental study has been performed of the relative intensity noise (RIN) of a semiconductor laser in optical feedback regimes I to V. At low bias current, a low RIN is observed with low feedback ratio, the RIN increased in the coherence collapse regime (regime IV) and decreased in regime V. The RIN in regime V is lower than that of the solitary laser. For higher bias current, a higher feedback ratio is needed for the semiconductor laser to transit from regime IV to V. The measurements are found to be in good qualitative and quantitative agreement with theoretical predictions.

Polarization-independent optical spectral inversion without frequency shift using a single semiconductor optical amplifier

Two schemes for polarization-independent spectral inversion without frequency shift have been experimentally demonstrated. Both schemes use two pump beams and a polarization-insensitive semiconductor amplifier. Polarization-independent optical spectral inversion without frequency shift was obtained for lower wavelength detuning between the two pump beams in the first scheme and for large wavelength detuning in the second scheme. Combining these two schemes allows polarization-independent spectral inversion without frequency shift to be obtained over a quite wide frequency range. The results are in good qualitative agreement with theoretical predictions.

Polarization dynamics in VCSELs subject to optical injection

The dynamics of VCSEL subject to optical injection is investigated. This study is interesting in that it may define new techniques to control the light polarization. Optical injection may also induce new instabilities related to polarization competition. Different situations are explored, which differ by the polarization state of the solitary VCSEL and/or that of the injected field. In this work, the authors show numerical results obtained from an extension of the San Miguel, Feng and Moloney model to optical injection.

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.