Launching condition dependence of noise reduction effect in radio over fiber systems with graded-index plastic optical fibers

We investigate reflection noise in a multimode fiber (MMF) link with a vertical-cavity surface-emitting laser for restricted mode launching conditions. The results show that microscopically heterogeneous graded-index plastic optical fiber (GI POF) has little reflection noise for any launching offsets whereas the glass MMF has strong dependence of reflection noise spectra on launching offset. By directly observing the backreflected light from the GI POF, we show that the noise reduction effect is attributed to the backreflected beam pattern filling the entire core because of the strong mode coupling in the GI POF. This suggests that the GI POF can allow for low-cost Radio over Fiber (RoF) systems without precise control of launching condition.