Ioannis Zacharopoulos

Performance engineering of metropolitan area optical networks through impairment constraint routing

We demonstrate the use of impairment constraint routing for performance engineering of transparent metropolitan area optical networks. Our results show the relationship between blocking probability and different network characteristics such as span length, amplifier noise figure, and bit rate, and provide information on the system specifications required to achieve acceptable network performance.

IMPROVED PERFORMANCE OF A WAVELENGTH CONVERTER BASED ON DUAL PUMP FOUR-WAVE MIXING IN A BULK SEMICONDUCTOR OPTICAL AMPLIFIER

Very high conversion efficiency (6.5 dB for 23.4 nm down-wavelength shift and 4.5 dB for 16 nm up-wavelength shift) is reported, using four-wave mixing in a bulk semiconductor optical amplifier. Based on a dual pump configuration where wavelength conversion is achieved by shifting one of the pumps, superior performance has been achieved in terms of both efficiency and the converted signal-to-background amplified spontaneous emission noise ratio, especially for very large wavelength shifts. Simple theoretical considerations are also discussed for the explanation of the improved performance of the converter.

On the polarisation sensitivity and performance optimisation of a dual pump four wave mixing based wavelength converter

This paper presents a detailed investigation of the performance of a wavelength conversion scheme. The converter is based on four wave mixing in semiconductor optical amplifiers using two parallel polarised pumps. Measurements of the conversion efficiency and the signal to background noise ratio of the two replicas of the signal, for the cases of the signal polarisation being either parallel or orthogonal relative to the pump waves have been carried out. These measurements will reveal the polarisation sensitivity of this scheme which appears to be less than 1 dB when the wavelength spacing between the signal and its closest spaced pump is larger than 12 nm. The experimental results are supported in a satisfactory way by theoretical considerations. A simple theoretical expression describing the polarisation sensitivity have been derived and the theoretical results are in good agreement with those experimentally obtained. A performance comparison of the conversion scheme using semiconductor optical amplifiers with different lengths but the same structure is also performed. Through the following study the optimum operational conditions for this wavelength conversion scheme will be determined.

Mechanisms of wave mixing and polarisation sensitivity of the wavelength conversion in semiconductor optical amplifiers using two parallel polarised pumps

We report on an experimental and theoretical study of wavelength conversion based on four wave mixing (FWM) in a bulk semiconductor optical amplifier (SOA), using two parallel polarised pumps. The mechanisms responsible for the generation of the frequency converted products of the input signal are discussed. It is shown that the polarisation sensitivity of this scheme depends strongly on the position of the signal wavelength relative to the pump wavelengths.

Experimental investigation of wavelength conversion based on four-wave mixing in a three-electrode distributed feedback laser

A wavelength converter based on four-wave mixing in a three-electrode distributed feedback laser is experimentally investigated. The output power and the signal to background noise ratio characteristics of the converted waves were measured for highly nondegenerate conditions, up to 2 THz detuning frequency. The dependence of the converted wave power on the pump and probe input power has been also investigated. Moreover, a comparison with a highly performing converter based on four-wave mixing in a 1.5-mm-long semiconductor optical amplifier has been carried out.

Influence of fiber nonlinearities in the performance of an all-optical fiber-based demultiplexer

The four wave mixing (FWM) process in nonlinear media can be used for all optical demultiplexing of high bit-rate optical time division multiplexed channels. Interaction of the optical time division multiplexed signal and a pulsed pump with a repetition frequency equal to the desired output bit-rate, results in generation of a new wave at a new wavelength which carries the information of one of the de-multiplexed channels. Dispersion shifted fiber (DSF) is an adequate nonlinear medium in which the four wave mixing process takes place. In this work a detailed theoretical study of an all-optical demultiplexer based on four wave mixing in dispersion shifted fibers is presented for different demultiplexing input/output bit-rates. The four wave mixing process in dispersion shifted fibers is studied through numerical simulation of the non- linear Schroedinger equation, taking into account all fiber nonlinearities. The performance of the demultiplexer is characterized in terms of efficiency, Q-factor, suppression of adjacent channels and eye pattern for each de-multiplexed channel. These characteristics are studied for different fiber lengths, pulsewidths, powers, etc. This detailed characterization of the operational conditions of the demultiplexer will reveal its limitations and hints for its optimal design will be proposed.

Comparison of multipoint and midspan spectral inversion in high-bit-rate optical links

In long distance high bit rate optical links, the combined effect of fiber dispersion, nonlinearities and polarization mode dispersion determines the system performance. Mid-span spectral inversion (MSSI) has been proposed for dispersion and nonlinearity compensation. Although the use of spectral inverters in more than one point along the optical link has been discussed in the past, their impact on the transmission performance has never been examined in a detailed and quantitative way. In this work a comparison of the transmission performance when using MSSI or multi-point spectral inversion (MPSI) is presented, for 10- and 40- Gb/s signal transmission and for various transmission conditions. The transmission is described by the non-linear Schroedinger equation and the performance is estimated through the Q-factor analysis of the received optical signal. The comparison starts assuming ideal inverters where the complex conjugate of their input signal is generated at the output. In this case, the MPSI method appears to be more effective in compensating the dispersion and the nonlinearities, allowing highly performing transmission. The results are different when a real spectral inverter based on four-wave mixing in highly nonlinear dispersion shifted fibers is considered. In this case no improvement in the transmission performance can be observed.

Dual-pump wave mixing in semiconductor optical amplifiers: performance enhancement with long amplifiers

We demonstrate experimentally the improvement of the performance of the dual pump wave mixing scheme in semiconductor optical amplifiers, using long amplifier chips and high optical pump powers. The optical amplifiers used in the experiment had a ridge waveguide structure with bulk active layer and antireflective-coated angled facets. Measurements of the conversion efficiency and SBR as a function of wavelength shift are presented for a wavelength shift of more than 40 nm. The above measurements are carried out for three amplifier lengths (500 micrometers , 1000 micrometers , and 1500 micrometers ) and for different levels of the optical power of the two pumps. It will be shown that an increase in the amplifier length from 500 micrometers to 1500 micrometers results to an increase of more than 25 dB for the efficiency and more than 20 dB for the SBR. This improvement combined with the inherent advantages of the dual pump scheme (almost constant SBR and high efficiency for large wavelength shifts) results in a highly performing wavelength converter/phase conjugator, suitable for many applications.