Optical single sideband modulation with tunable optical carrier-to-sideband ratio using a modulator in a Sagnac loop

We propose and experimentally demonstrate a cost-effective approach to achieve optical single sideband (OSSB) modulation with tunable optical carrier-to-sideband ratio (OCSR) based on a bi-directional use of an OSSB modulator. The key concept of the proposed scheme is to use an OSSB modulator which is incorporated in a Sagnac loop where a light wave is modulated in the form of SSB modulation along the clock-wise direction while the orthogonal light is not modulated along the counter clock-wise direction due to the velocity mismatch. The signals along two directions are combined together at the output of the Sagnac loop via a polarization beam splitter (PBS). Thus a partial orthogonal SSB (PO-SSB) modulated signal is obtained. The generated signal is then sent into a polarization controller (PC) followed by a polarizer. An OSSB-modulated signal with tunable OCSR from −10 to 27 dB is achieved by adjusting the PC in the experiment. The proposed scheme is wavelength independent, which can support low microwave bandwidth and achieve flexible wavelength tunability.