Optical Amplifiers Used as Functional Components

The optical amplifier is having a large impact on current research on optical networks, where the Er doped fiber amplifier (EDF) is the prime candidate for creating a transparent optical, analog network. The EDF will most likely be used for preamplification, power boosting, linear repeating because of its advantages of polarization insensitivity, extremely low ”facet” reflectivity, good noise and saturation output power properties. However, the EDF amplifier is limited in versatility: In the semiconductor laser amplifier (SCLA), light amplification is effected by the coupling between the photon field and inverted electron population system, implying that the quasifermi level separation provides an electronic means of monitoring the optical field. Further, since the spontaneous recombination time is of the order of ns, the optical field can be detected (simultaneously with amplification), frequency converted and gated up to bandwidths of ≈ 1 GHz. In the EDF, there is no analog to the electrooptic interface (although the monitoring might be possible to perform optically) and the spontaneous recombination time is on the order of ms. Hence, the SCLA offer unique possibilities, and all of the above functions can be implemented by one single generic structure which is integrable, in contrast to the EDF. But it should also be noted that the ns time scale introduces severe crosstalk problems in multichannel systems.