Performances of both 10Gb/s externally modulated optical fiber transmission systems and 2.5Gb/s directly modulated system with MSSI are investigated by numerical simulation. The results show that the pulse broadening due to the second order fiber dispersion can be perfectly compensated by employing MSSI, no matter the original pulses have or have no chirp. In addition, it is also shown that the signal spectra broadened by self phase modulation in fiber can be renarrowed to its original shape. We also report a transmission experiment of 2.5Gb/s directly modulated optical signa over 200km standard single mode fiber. In this system, a spectral inverter which is based on the effect of four wave mixing in dispersion shifted fiber to realize spectral inversion, was inserted at the mid-point of the 200km fiber span. By designing and optimizing a novel configuration, a wavelength conversion efficiency of $MIN@7dB was obtained. The DFB laser used in our 2.5Gb/s directly modulated optical transmitter has a 1.8dB power penalty after 100km fiber transmission, and a BER floor occurred at 10$+$MIN@6$/ after 200km transmission without dispersion compensation. In our experiment, by using MSSI, a receiver sensitivity of $MIN@28.8dBm at BER $EQ 10$+$MIN@10$/ after 200km transmission was achieved and the power penalty is 2.8dB.
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