E. Bravi

Analysis of distortion effects in subcarrier-multiplexed (SCM) externally modulated lightwave systems: a generalized approach

A generalized analysis is presented for the evaluation of intermodulation distortion effects in case that external intensity modulators are used for the transmission of analog/digital (AM/QAM) channels in an SCM based optical access network. The proposed model can provide useful information to select external modulator and system parameters for performance optimization.

Analysis of the performance of subcarrier multiplexed (SCM) optical systems

Abstract In addition to the distortion effect due to the quadratic phase response of single-mode optical fiber, other impairments affect subcarrier multiplexed (SCM) optical transmission systems when using either semiconductor lasers or intensity external modulators at the transmitter in the case of hybrid AM/QAM channeling. In the first case several effects are considered, which give rise to different distortion phenomena: intrinsic “dynamic” distortions due to interaction of photons and electrons in a semiconductor laser, clipping impulsive noise, AM-FM conversion effect due to the joint action of semiconductor laser static and dynamic chirping and fiber chromatic dispersion, nonlinear distortions due to the Kerr effect, interferometric noise due to the joint action of semiconductor laser chirping and optical fibre multiple reflections. In the case of an external intensity modulator, the distortion noise due to its intrinsic nonlinear response is analyzed. The analysis provides useful information about the design and the performance evaluation of SCM based optical access networks.

Effect of the turn-on delay of a semiconductor laser on clipping impulsive noise

The performance of hybrid multichannel AM/QAM fiber-optic transmission systems is constrained by clipping impulsive noise, which must be suitably taken into account to select system parameters. In this letter, the influence of semiconductor laser turn-on delay is considered in the evaluation of the effects due to clipping impulsive noise.

Statistical analysis of clipping filtered impulsive noise

In the performance evaluation of hybrid multi-channel AM/QAM fiber-optic transmission systems, the effect of clipping impulsive noise must be suitably considered to tradeoff the system parameters. In this letter, the statistical characteristics of clipping impulsive noise are analyzed in the presence of bandpass filtering in order to provide useful information for the design of these systems.

Analysis of the distortion noise due to optical fiber reflections in subcarrier-multiplexed (SCM) lightwave systems

In hybrid analog/digital optical systems based on subcarrier-multiplexing technique, the joint action of semiconductor laser chirping and multiple reactions in optical fiber gives rise to an interferometric noise affecting the performance. So far, this effect has been evaluated assuming that the delay between transmitted and reflected optical signals is so large that such signals can be considered uncorrelated. In this letter, such approximation has been overcome so that the effect due to interferometric noise can be evaluated for any distance between reflection points.

Experimental confirmation of the theoretical analysis of distortion effects in analog externally modulated lightwave systems

A generalized analysis for the evaluation of intermodulation distortions due to nonlinear response of a Mach-Zehnder external intensity modulator has been proposed in this letter. The analysis holds for every modulating signal that can be assumed as a Gaussian process (e.g., subcarrier multiplexing (SCM) and CDMA). In this letter, an experimental confirmation of the theoretical results and a proposal for standard definition are presented.

Experimental and Theoretical Evaluation of Distortion Effects on SCM Optical Transmissions Due to the Joint Action of Static Chirping, Dynamic Chirping and Dispersive Channel

In optical CATV systems based on subcarrier-multiplexing technique, the joint action of semiconductor laser chirp and fiber chromatic dispersion gives rise to intermodulation distortion phenomena affecting the transmission performance. This problem has been explained analytically, leading to a model valid for every kind of modulating signal and explored in the case of a Gaussian process. In this paper, the model is developed for the important specific case of an analogue SCM modulating signal. The results are assessed experimentally.

Distortions due to the joint action of static and dynamic chirping and dispersive fibre in SCM optical systems: theory and experiment

The propagation of an SCM signal in a dispersive optical fibre, considering the AM-FM conversion effect due the semiconductor laser static and dynamic chirping has been analyzed. An analytical model was suitable extended in order to derive closed expressions for the composite second order and composite triple beat distortion induced. The comparison with the developed theory was done in the case of a mismatch liaison, consisting of an analogue 1550 nm DFB laser coupled with different lengths of standard fibre. Good agreement was found within the measurement uncertainty.

Analysis of Transmission of Sub-Carrier Multiplexed Signals through the Optical Transport Network

The transmission of analog SCM signals through the optical layer of the transport network is analyzed and discussed, in order to assess the possibility of exploiting the core network for the transport of video channels, without the need of dedicated communication systems. The utilized analytical model, allowing the transmission performance to be evaluated, is reported. Some performance evaluation results are reported, taking into consideration two relevant network typologies: metropolitan networks and regional networks. The results allow the feasibility of the considered approach to be assessed, considering the available technology.

Effect of optical fiber reflections on the performance of sub-carrier-multiplexed (SCM) lightwave systems

Hybrid analog/digital Sub-Carrier-Multiplexing (SCM) technique is effective for broadband optical access networks designed for video broadcasting and interactive services. These systems are flexible in service management and channeling can be optimized to exploit the available bandwidth. A significant impairment in these systems is introduced by optical fiber multiple reflections, which give rise to an interferometric noise affecting the performance. So far, this effect has been evaluated assuming that the delay between transmitted and reflected optical signals is so large that such signals can be considered uncorrelated. In this paper, the interferometric noise due to optical fiber reflections is analyzed in SCM hybrid analog/digital systems independently of the position of the reflection points. The proposed model leads to a closed expression for the power spectral density of such noise source, which provides useful information for the system design and permits an accurate performance evaluation.