Achieving High-Power, Ultra-High Spectral Purity Cascaded Raman Fiber Lasers through Low Intensity-Noise Pump Sources

Abstract

Cascaded Raman fiber lasers (CRFLs) based on random distributed feedback are proven to be wavelength agile where, by simply adjusting the input pump power and wavelength, high-power continuous wave fiber lasers at arbitrary wavelengths were demonstrated [1–3]. However, these systems have limited degree of wavelength conversion or spectral purity defined as the percentage of output power in the desired wavelength band. Recently, use of fiber-based amplified spontaneous emission (ASE) sources have been proposed to increase the spectral purity [4]. In [4] authors attributed relative intensity noise (RIN) of the pump laser, as the reason for reduction in spectral purity. Here, we comprehensively investigate the role of RIN on spectral purity by using three kinds of pump lasers for cascaded Raman conversion. We demonstrate that by using high-power, phase-modulated (PM) narrow-linewidth fiber amplifier as the pump source, ultra-high spectral purity of >97% over the entire Raman stokes orders (from 1.1μm to 1.5μm) can be achieved.