According to the previous researches, all-optical converters based on FWM and XGM conversion schemes at present are well suited for system use. Both performances of optical networks with FWM and XGM conversion are examined in this paper. From the results, we find that the benefit obtained by full range conversion can be achieved by using FWM conversion with the degree of conversion d=1 or 2, when the number of wavelengths on a fiber is small. But with the increase in number of wavelengths, higher conversion degree is required to achieve the performance of full range. As for the case of XGM conversion, our results show that the performance of XGM is worse distinctly than full range conversion because of its asymmetric conversion, no matter the number of wavelengths is large or small. In order to improve the performances of the networks with limited range conversion in the case of large number of wavelengths, three simple wavelength assignment algorithms (FUWC, LUWC and MSW) are proposed. We apply these algorithms to the case of Ring and Mesh-torus. Through simulation, we find that our algorithms do greatly reduce the blocking probabilities of networks with limited range conversion.