P.S. Spencer

Synchronization of chaos in unidirectionally coupled vertical-cavity surface-emitting semiconductor lasers.

Synchronization of chaos is achieved experimentally in unidirectionally coupled external-cavity vertical-cavity surface-emitting semiconductor lasers operating in an open-loop regime. Synchronization is observed when the polarization of the transmitter is perpendicular to the polarization (x polarization) of the free-running receiver. The ratio of transmitter output to y-polarized receiver output power shows normal (positive-slope) synchronization. However, inverse (negative-slope) synchronization is found to arise between the transmitter output and the x-polarized receiver output power.

Suppression of polarization switching in vertical-cavity surface-emitting lasers by use of optical feedback

The polarization properties of vertical-cavity surface-emitting lasers (VCSELs) subject to optical feedback are studied experimentally. It is thereby demonstrated that polarization-selective optical feedback can be utilized to entirely eliminate VCSEL polarization switching over the entire device operating range.

Modeling of optical synchronization of chaotic external-cavity VCSELs

The performance of a master-slave configuration for effecting the synchronization of chaotic vertical-cavity surface-emitting lasers (VCSELs) is studied using numerical simulations. The dynamical evolution of optically coupled VCSELs is examined using a traveling wave model which is valid in the strong optical feedback regime. It is shown that the proposed configuration is capable of effecting synchronization in a robust manner. The opportunity for exploiting synchronized chaos in secure optical communication systems is indicated.

GHz Bandwidth Message Transmission Using Chaotic Vertical-Cavity Surface-Emitting Lasers

Chaotic message encoding and decoding in unidirectionally coupled vertical-cavity surface-emitting lasers (VCSELs) with polarization-preserved and polarization-selected optical injection has been studied experimentally. A GHz message has been successfully encoded in the chaotic transmitter and decoded from the receiver with polarization-preserved optical injection. In contrast decoding using polarization-selected optical injection was achieved at only 330 MHz. It has also been demonstrated that GHz message extraction can be achieved using both normal and inverse chaos synchronization thus providing an opportunity for exploiting polarization properties of VCSELs for duplexed chaotic message transmission.

Influence of fast gain depletion on the dynamic response of TOAD's

The operating characteristics of the terahertz optical asymmetric demultiplexer (TOAD) devices subject to picosecond control pulses have been investigated taking into account gain saturation and nonlinear gain compression, due to carrier heating and spectral holeburning. It is shown that when the control pulse width is less than /spl sim/2 ps, fast gain depletion process appears in the time resolved gain dynamics of the SOA. The fast depletion process leads to an oscillating output power structure in the switched region. The oscillatory structure is found to persist for over 1 ps and sets a limit on the practical utilization of these devices.

Polarization-preserved and polarization-rotated synchronization of chaotic vertical-cavity surface-emitting lasers

The synchronization process in a vertical-cavity surface-emitting laser (VCSEL) based master-slave configuration, where the master laser has been destabilised by optical feedback from an external mirror, has been investigated. The dynamics of both VCSEL polarization modes have been modeled and used to study the chaos synchronization mechanism in both polarization preserved, and polarization rotated unidirectionally coupled master and slave configurations. Two types of synchronization have been identified in the polarization rotated case, one of which may afford an opportunity to effect multiplexed message encoding using orthogonal laser modes.

Optical injection dynamics of two-mode vertical cavity surface-emitting semiconductor lasers

Two-mode vertical cavity surface-emitting lasers (VCSELs) subject to external optical injection are investigated experimentally. The spectrum of a VCSEL with two parallel-polarized modes demonstrates significantly different behavior compared to that of a VCSEL with two orthogonally-polarized transverse modes. In the latter, external optical injection can be used to achieve single-mode operation. However, in the case of two parallel-polarized transverse modes, VCSEL single-mode operation cannot be obtained via optical injection. In this case, when the injection frequency is close to one of the modes, the coexistence of the injected beam and that mode gives rise to very rich dynamical behavior; however, the other mode is unperturbed by the optical injection.

Optimization of adaptively modulated optical OFDM modems for multimode fiber-based local area networks [Invited]

Focus Issue on Orthogonal-Frequency-Division Multiplexed Communications Systems and Networks The impact of a wide range of different parameters of various components involved in optical modems using adaptively modulated optical orthogonal-frequency-division multiplexing (AMOOFDM) on the transmission performance of AMOOFDM signals is explored thoroughly, in single-channel, unamplified, multimode-fiber (MMF)-based, intensity modulation and direct detection (IMDD) transmission links. Practically available optimum component parameters are identified, based on which the AMOOFDM modems are optimized. It is shown that the optimized AMOOFDM modems enable a >70% increase in the capacity versus reach performance without compromising link loss margins, in comparison with that achieved without modem optimization. In addition, the validity of the identified optimum parameters and the feasibility of the optimized AMOOFDM modems are also statistically verified for implementation in the vast majority of installed MMF links. Statistical investigations show that the optimized AMOOFDM modems can support >50Gbits/s signal transmission over 300m in 99.5% of already installed MMF links with loss margins of >7dB. Furthermore, it is also confirmed statistically that the optimized AMOOFDM modems have excellent performance flexibility and great robustness to various fiber and/or system implementation-related impairments.

Investigation of polarization bistability in vertical-cavity surface-emitting lasers subjected to optical feedback

Polarization bistability in vertical-cavity surface-emitting lasers (VCSELs) subject to optical feedback has been studied both experimentally and theoretically. Optical feedback is shown to reduce the width of the bistability hysteresis loop and, hence, suppress the bistability. It is also demonstrated experimentally that polarization-selective optical feedback can be utilized to eliminate VCSEL polarization switching without inducing instabilities in the device.

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.