Comparison of wavelength conversion in SOA ainid EDFA fiber ring systems

We report on two types of wavelength conversion techniques that are based on gain saturation effect in semiconductor optical amplifier (SOA) and erbium doped fiber amplifier (EDFA). In these amplifiers the gain saturation occurs when the optical density at the gain medium is high enough to result in depletion of the population inversion by stimulated emission. In each case, the fiber ring laser is assembled using a variable fiber coupler, a narrowband optical filter and the gain medium. For external input power values higher than the determined threshold value of the ring resonator, the gain will be saturated. Because the wavelength of the external laser is different from the oscillating wavelength of the ring resonator, the optical power at the output of the resonator is drastically decreased (low-state). On the other hand, when the input of the external laser is below the threshold value the output power of the resonator increases (high-state). In our experiment the operating wavelengths of the ring resonators are 1314 nm and 1553 nm for the SOA and EDFA respectively. The input signal is modulated around the threshold value for frequencies of 20 MHz and 1 MHz and resonator lengths of around 8 m and 16 m for the SOA and EDFA cases respectively. Both systems exhibit high contrast modulation of 41 dB and 33 dB at the output port for the low/high states of the SOA and EDFA ring lasers respectively.