Optimization of modulation techniques for suppression of GEMRS in frequency transfer systems

Guided entropy mode Rayleigh scattering in optical fibers has been shown to have detrimental effects in optical fiber links for radio frequency transfer, optoelectronic oscillators (OEOs), and broadband analog optical fiber links. We have previously shown that GEMRS-induced noise can be suppressed via sinusoidal dithering of the laser drive current. Previously, we had hypothesized that this suppression is due to the laser frequency modulation it induces. In this work, we show for the first time GEMRS suppression via external phase modulation, thereby confirming that suppression is achieved via the frequency modulation component of the laser current dither. This result provides further evidence that GEMRS is a laser-driven, phase-dependent effect. Additionally, external modulation offers several advantages over the previously demonstrated intra-cavity modulation, including greater bandwidth and improved flexibility in implementation.