The Study Of Wavelength Converter Based On XGM In A Semiconductor Optical Amplifier

Wavelength division multiplexing (WDM) techniques offer a very effective utilization of the fiber bandwidth directly in the wavelength domain, rather than in the time domain. In addition, wavelength can be used to perform functions as routing and switching, which becomes an important consideration for realization for an all-optical transparent network layer in the network. The number of wavelengths in WDM networks determines the numbers of independent wavelength addressed, or paths. Although this number may be large enough to fulfill the required information capacity, it often is not large enough to support a large number of nodes. In such cases, the blocking probability rises due to possible wavelength contention when two channels at the same wavelength are to be routed at the same output. One method of overcoming this limitation is to convert signals from one wavelength to another.All-Optical wavelength converters are expected to become key components in the future broadband networks. Their most important use will be for avoidance of wavelength blocking in optical cross connects in WDM networks. Thereby the converters increase the flexibility and the capacity of the network for a fixed set of wavelengths. Equally important, the wavelength conversion function enables decentralized network management concerning the wavelength paths through the network and may facilitate easier protection switching. The potential of wavelength converters has already been demonstrated in a number of system experiments.Several techniques have been proposed to achieve wavelength conversion. The straight forward solution is an electro-optic converter consisting of a detector followed by a laser that retransmits the incoming signal on the new wavelength. Disadvantages of the electro-optic converter such as complexity and large power consumption have , however, directed the interest to all optical wavelength converters. They enable direct translation of the information on the incoming wavelength to a new wavelength without entering the electrical domain. Examples of all optical wavelength converters are: Semiconductor optical amplifiers (SOAs) used in the cross gain modulation (XGM) mode or the cross phase modulation (XPM) mode; SOA's using four wave mixing (FWM); and DBR lasers relying on optical frequency or intensity modulation, et al.The XGM-based wavelength converters are very simple to realize and have shown impressive performance. In this thesis we will concentrate on SOA converters using the XGM conversion scheme that presently seems to be well suited for system use. Important parameters such as extinction ratio(ER), relative intensity noise (RIN) and conversion efficiency will be discussed. The main results of this thesis include:In the theory, we derive the basic velocity equations of SOA-XGM wavelength converters from Helmholtz equation. And we discuss the effect of wavelength conversion range, the probe input power, the probe wavelength, and the signal input power to ER due to the gain model. It can be seen that there is the severe degradation of the ER for wavelength up conversion. Moreover, we investigate the causes of the degradation of ER. Such methods can improve the ER, including improving the gain of the SOA, reducing the probe input power, improving the signal input power.We deduce the infection of some parameters to relative intensity noise(RIN) and conversion efficiency from the basic equation according to the small-signal theory. We derive the transmission function of the input signal and the probe intensity noise for wavelength converters base on XGM. This is used to investigate both signal and noise characteristics analytically. we find there are several contributions to the output probe noise; 1)the direct transmission of the probe input noise which, as a result ,has the same power-density spectrum(PDS), and 2)a narrow-band contribution due to the nonlinear interaction of the field intensities with the carrier density. This contribution is subtracted from the former since a high field intensit...