SOA performances in presence of an assist light at gain transparency wavelength in co- and in counter-propagative direction

This work describes the theoretical and experimental results to analyze the influence of the assist light injection and to evaluate the enhancement of the SOA saturation output power and gain recovery time in both injection ways. The assist light can be injected inside the SOA cavity in co- or in counter-propagative direction with respect to the optical input signal. The injection of an assist light beam at the gain transparency wavelength is an interesting solution to enhance the SOA characteristics. Actually, ensuring a high optical power level, closed to the transparency condition, inside the SOA active layer can produce carriers. Thus the assist light acts as the bias current and permits the improvement of the SOA performances. In addition to improving the saturation output power, the reduction in carrier lifetime implies a fall in the dynamic gain recovery time, which is essential for all-optical high bit-rate systems.