The topic of spectral line suppression is of major importance when designing impulse radio ultra-wideband (IR-UWB) systems. The presence of spectral lines in the power spectral density (PSD) may limit the maximum transmission power in order to comply with UWB regulations, thus affecting the system performance. Although previous works have shown the advantages of IR-UWB over fiber (UWBoF) implementations, the topic of spectral line suppression in PSD in such systems has not been entirely addressed. This letter proposes a simple IR-UWBoF system using spectral line free convolutional codes (SLF-CCs) to address this topic. Experimental results show that the proposed system offers improved PSD characteristics compared to conventional IR-UWBoF implementations. Furthermore, it is demonstrated that the proposed system is able to deliver spectral line free IR-UWB signals over single-mode fibers up to 30 km