Yanhua Hong

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.

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.

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.

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.

Experimental demonstration of VCSEL-based chaotic optical communications

Message encoding and decoding using chaotic vertical-cavity surface-emitting lasers (VCSELs) has been experimentally demonstrated. A 200-MHz message has been successfully encoded in an external-cavity VCSEL transmitter and decoded in a stand-alone VCSEL receiver. Message recovery has been achieved with 9-dB signal-to-noise ratio.

Locking characteristics of a side-mode injected semiconductor laser

This paper is focused on an experimental study of the injection-locking bandwidth and the relaxation oscillation frequency in a side-mode injection-locked semiconductor laser. It is shown that, for such a laser, the injection-locking bandwidth and the relaxation oscillation frequency are related to the injection power and the wavelength of the target injection mode. At fixed launched injection power, the injection-locking bandwidth and relaxation oscillation frequency can be increased when the injection wavelength is detuned to the short-wavelength side of the free-running wavelength, while the relaxation oscillation frequency decreases when the injection wavelength is set to the long-wavelength side of the free-running wavelength. The results are in good agreement with theoretical predictions.

Real-time experimental demonstration of low-cost VCSEL intensity-modulated 11.25Gb/s optical OFDM signal transmission over 25km PON systems

The feasibility of utilising low-cost, un-cooled vertical cavity surface-emitting lasers (VCSELs) as intensity modulators in real-time optical OFDM (OOFDM) transceivers is experimentally explored, for the first time, in terms of achievable signal bit rates, physical mechanisms limiting the transceiver performance and performance robustness. End-to-end real-time transmission of 11.25 Gb/s 64-QAM-encoded OOFDM signals over simple intensity modulation and direct detection, 25 km SSMF PON systems is experimentally demonstrated with a power penalty of 0.5 dB. The low extinction ratio of the VCSEL intensity-modulated OOFDM signal is identified to be the dominant factor determining the maximum obtainable transmission performance. Experimental investigations indicate that, in addition to the enhanced transceiver performance, adaptive power loading can also significantly improve the system performance robustness to variations in VCSEL operating conditions. As a direct result, the aforementioned capacity versus reach performance is still retained over a wide VCSEL bias (driving) current (voltage) range of 4.5 mA to 9 mA (275 mVpp to 320 mVpp). This work is of great value as it demonstrates the possibility of future mass production of cost-effective OOFDM transceivers for PON applications.

Wideband Chaos With Time-Delay Concealment in Vertical-Cavity Surface-Emitting Lasers With Optical Feedback and Injection

Both the time-delay signature and the bandwidth of chaos have been investigated in four schemes of chaos generation in vertical-cavity surface-emitting lasers (VCSELs). The results show that suppression of the TD signature and the enhanced bandwidth of chaos can be obtained simultaneously in two schemes - a chaotic beam unidirectionally injected into a CW VCSEL and a CW VCSEL mutually coupled to a chaotic VCSEL. However, suppression of the TD signature and the enhanced chaos bandwidth cannot be achieved simultaneously in two other schemes - a CW optical beam unidirectionally injected into a chaotic VCSEL and two mutually coupled CW VCSELs.

Enhanced chaos synchronization in unidirectionally coupled vertical-cavity surface-emitting semiconductor lasers with polarization-preserved injection

We experimentally study chaos synchronization in unidirectionally coupled vertical-cavity surface-emitting semiconductor lasers (VCSELs) with polarization-preserved and polarization-selected optical injection. The measurements show, in agreement with theoretical predictions, that the maximum cross coefficient of 0.884 obtained with polarization-preserved optical injection is significantly higher than the maximum cross coefficient of 0.724 obtained with polarization-selected optical injection.