RZ-DPSK signal regeneration based on dual-pump phase-sensitive amplification in fibers

All-optical regeneration of differential phase-shift keying signals by means of a phase-sensitive amplification scheme solely based on highly efficient four-wave mixing in fibers is theoretically and numerically studied. The analytical and numerical investigation demonstrates almost ideal phase regeneration accompanied with enhanced amplitude noise suppression in the regime of pump depletion.     

Experimental evaluation of an open-loop all-optical chaotic communication system

An experimental investigation of the performance of an open-loop optical chaotic communication system has been carried out under different optical injection conditions. The most popular message encoding techniques have been considered, tested and compared at gigabit rates and for different levels of optical injection to the receiver, by bit-error-rate (BER) measurements. Different low-pass electrical filters have been implemented for the various message bit-rates tested, in order to employ the most appropriate one for message decoding. The best performance of all the examined encryption methods for messages of 1.5 Gb/s bit-rate emerged for the chaos modulation encryption method and was characterized by Q-factor values up to 5.1, after synchronizing in the strong injection regime, while the corresponding BER of the decoded message was as low as 7/spl middot/10/sup -5/. In order to confirm the secure encryption of the message, BER measurements are also performed for the chaotic carrier into which the message is encrypted.     

Electronic distortion compensation in the mitigation of optical transmission impairments: the view of joint project on mitigation of optical transmission impairments by electronic means ePhoton/ONe1 project

The key design approaches and results in the field of compensation of optical impairment distortion by electronic means, as an outcome of the studies and research innovations developed within the joint project on mitigation of optical transmission impairments by electronic means work group of the ePhoton/ONet European project are presented. The research topics addressed are related to chromatic and polarisation mode dispersion, with particular reference to feed-forward/decision-feedback equaliser and maximum-likelihood sequence estimation-based equalisers as well as pre-distortion schemes. Additionally, the use of electronic compensation in metro/access applications is examined with reference to studies related to the performance enhancement of directly modulated laser transmitters, the compensation of the square-law characteristics of receivers and the equalisation of multi-level format schemes.     

Feedback Phase in Optically Generated Chaos: A Secret Key for Cryptographic Applications

The feedback phase in a chaotic system consisting of a semiconductor laser subject to delayed optical feedback is considered for the first time as a secret key for secure chaotic communications not exclusively based on hardware uniqueness. Extensive numerical simulations illustrate that the feedback phase is of extreme importance as far as synchronization is concerned. The ability of an eavesdropper to attack the intensity-modulated message when a pseudorandom variation of the feedback phase is imposed at the transmitter's side is numerically quantified by bit-error-rate calculations. The analysis demonstrates that the eavesdropper is not able to synchronize and hence to extract the message when he is not aware of the phase variations even if he is equipped with an identical chaotic device.     

Noise characteristics of dual-pump fiber-optic parametric amplifiers

The noise figure (NF) properties of an undepleted and lossless dual-pump fiber-optic parametric amplifier (FOPA) are theoretically and numerically investigated. The theoretical study takes into account the noise characteristics of the two pump waves that are considered to have parallel polarization states for gain maximization. It is shown that noisy pump waves degrade the amplifier's NF, especially when the amplifier is operating at high gain values and when the input signal is high. The theoretical observations are validated by Monte Carlo numerical simulations, and the agreement between them is excellent. Finally, a comparative study concerning the noise characteristics of dual-pump and single-pump FOPAs is performed.     

Investigation of an all-optical wavelength converter with reshaping properties based on four-wave mixing in passive microring resonators

The properties of an all-optical wavelength converter with reshaping characteristics, based on four-wave mixing (FWM) in a passive GaAs-AlGaAs microring resonator side-coupled to a bus waveguide, are investigated in this paper. The reshaping properties are based on the nonlinear FWM transfer function as a result of the two-photon absorption enhanced by the resonance effect. A detailed study of the static and dynamic reshaping characteristics of the wavelength converter has been carried out. Its performance, evaluated by extinction ratio and Q-factor calculations, showed satisfactory regenerative properties up to 10 Gb/s.     

Spectral synchronization in chaotic optical communication systems

The ability of chaotic carriers to synchronize in optical chaotic communication systems is studied experimentally under a spectral domain analysis. Synchronization of high-frequency components up to tens of gigahertz of the chaotic carriers can thus be evaluated. On the contrary, the traditional method of measuring the synchronization through chaotic carrier time-traces is constrained by the limited bandwidth of the real-time oscilloscopes used for such measurements, excluding the contribution of the high-frequency components of the chaotic carriers to the synchronization characterization of the system.     

Impact of dispersion fluctuations on the noise properties of fiber optic parametric amplifiers

The effects of zero-dispersion wavelength (ZDWL) fluctuations on the noise characteristics of fiber optical parametric amplifiers (FOPAs) are investigated. The numerical derivation of the noise figure (NF) in terms of the amplifier operating conditions and the magnitude of ZDWL fluctuations is achieved by utilizing a simulation method based on the three-coupled propagation equations. The numerical analysis shows that the average NF of FOPAs is increased compared with the case of uniform dispersion, especially at high-gain operation. Apart from the NF, the gain-to-NF ratio is also evaluated to assess the amplifier performance for a variety of amplifier operating conditions and dispersion profiles.     

Dynamic Properties of a WDM Switching Module Based on Active Microring Resonators

The switching properties of a resonator consisting of two serially cascaded active microrings (MRs) are reported. The switching is achieved through the variation of the refractive index and the losses of the MRs with current injection, which alters the overall output spectral response. The switch is suitable for optical burst switching systems and metro architectures as it provides fast optical switching in the nanosecond scale with contrast ratio higher than 30 dB for 10-Gb/s intensity modulated signals. The capacity of the switch can be remarkably increased if multiwavelength switching is employed.