An Optical AC-Amplifier/DC-Suppressor Using Sagnac Interferometer with Semiconductor Optical Amplifier

We describe for the first time a fibre-optic device able to simultaneously reduce/amplify the unmodulated(DC)/modulated(AC) component of an optical carrier in the time-domain, respectively. The configuration is based on a Sagnac interferometer incorporating a semiconductor optical amplifier (SOA) non-linear element. The fast (25 ps) SOA is asymmetrically placed from the midpoint of the loop. The unmodulated component is ideally 100% reflected by the loop whereas the modulated is amplified and switched out to the transmission arm due to the self-phase modulation (SPM) in the SOA. The SPM effect acts only on time-varying optical signals thus partially or totally filtering out the optical DC-offset. Experimental results show 9.1 dB AC-amplification and 11.0 dB DC-suppression by carefully adjusting the polarization of the interfering light beams. Measurements around 200 MHz modulation frequency and as a function of the launched optical power were carried out. The distortion of the output signal was also measured. In order to support the experimental results, numerical simulations using the VPI Transmission MakerTM platform were also carried out.