Optimization of the frequency response of a semiconductor optical amplifier wavelength converter using a fiber Bragg grating

Cross-gain modulation in a semiconductor optical amplifier (SOA) is one of the simplest techniques for ah-optical wavelength conversion. However, the finite gain recovery time of the semiconductor optical amplifier causes dis tortion and pattern dependence at high bit rates. Here we show that filteri ng the output of a semiconductor optical amplifier wavelength converter wit h the transmission edge of a fiber grating filter improves its frequency re sponse. The grating sharpens the transition between the bits by converting the phase modulation at the edge to useful amplitude modulation, We determi ne the filtering condition that produces the optimum frequency response and reduces bit-pattern dependence for nonreturn-to-zero (NRZ) data, For small modulation, the apparent frequency response increases by the linewidth enh ancement factor alpha(H) of the SOA,In this case, pattern dependence is eli minated completely by the fiber grating filter, For large modulation, patte rn dependence can be substantially reduced, but not completely eliminated, We show that after spectral filtering, the residual pattern dependence of a n SOA depends only on modulation depth, For a given SOA, we find the optimu m grating for minimum conversion penalty at 12 Gb/s for a wide range of ope rating parameters. Using a fiber grating filter reduces the required optica l power for conversion in a semiconductor optical amplifier.