In-line and reflective semiconductor optical amplifiers can be effectively utilized as external modulators because they can perform simultaneously amplification and modulation. The reflective device (RSOA- Reflective Semiconductor Optical Amplifier) is more practical in optical distribution network. The main limitation is the modulation bandwidth of the device, because next generation access networks desire high transmission speed. Bandwidth enhancement can be achieved by means of optical equalization thanks to the chirping characteristics of semiconductor optical amplifier. Direct modulation of RSOA produces optical signal modulated both in amplitude and phase.
The limited modulation transfer function can be combined with the converted phase modulation transfer function. The investigation of optical filter with optimal slope provides phase-to-amplitude conversion is a crucial challenge. The simulations describe the slope dependence of the modulation band. The model can take into account the different type of realizable optical filters. However there is a trade-off between modulation efficiency and modulation bandwidth due to the extra insertion loss of the set-off optical filter. In the paper theoretical and simulation investigations are presented with the result of improved modulation bandwidth.