Wavelength and RF resolved relative intensity noise of supercontinuum generated in telecom fiber based CW cascaded random Raman fiber laser architectures

We experimentally investigate continuous-wave (CW) laser-pumped cascaded random Raman fiber-laser (CRRFL) architectures based on standard telecom fiber for low intensity noise supercontinuum (SC) generation. Our objective is to identify conventional pump laser designs that minimize wavelength and radio frequency (RF) resolved relative intensity noise (RIN) - a key determinant of sensitivity of low coherence interferometry application like ultrahigh-resolution optical coherence tomography (UHR-OCT). Three CW Yb-fiber pump configurations were evaluated: a single-stage fiber Bragg grating (FBG)-based bidirectional linear cavity, an FBG and a unidirectional ring-cavity seeded two-stage master-oscillator power-amplifier (MOPA) systems. Each laser delivered ∼75 W at 1064 nm into 2 km of SMF-28 Ultra, generating up to ∼34 W of SC spanning 1000-1700nm (measurement-limited) with power spectral densities (PSDs) exceeding 50 mW/nm. Spectrally resolved RIN was measured from 1200-1700nm across two RF bands: the quantum-noise-dominated regime (1-40 MHz) and the UHR-OCT relevant regime (10-160 kHz). Ring-based CRRFL SC systems consistently exhibited the lowest integrated rms RIN (∼2.5% in the 1-40 MHz band and ∼0.35% in the 10-160 kHz band), outperforming FBG-based implementations (5% and 0.4%, respectively). Importantly, this improvement persists even when the ring-laser free spectral range (FSR) is matched to that of the FBG laser, confirming that the RIN reduction arises from the intrinsic unidirectional lasing dynamics of the ring cavity rather than cavity FSR differences. To assess application-level relevance, we benchmark our best CRRFL-SMF SC sources against a commercial picosecond photonic crystal fiber (PCF)-based SC system. Across 1200-1700nm, the ring-MOPA-pumped SC exhibits at least a four-fold reduction in spectrally resolved RIN while providing comparable spectral flatness and nearly an order-of-magnitude higher PSD (>50 mW/nm vs ∼5 mW/nm). To our knowledge, this is the first systematic wavelength and RF frequency resolved noise characterization, including an explicit assessment of cavity FSR effects of conventional CW pumped CRRFL based SC sources, establishing their strong potential as low-cost, low-noise alternatives to commercial PCF-SCs for UHR-OCT and other low-coherence interferometry applications.