High power, ultra-high spectral purity, broadly wavelength tunable cascaded Raman fiber laser

Abstract

Cascaded Raman fiber lasers is the only proven technology which enables high power continuous wave (CW) fiber laser sources outside rare-earth emission bandwidths. Among these systems, recently demonstrated cascaded Raman fiber lasers based on Random distributed feedback (RDFB) provide wavelength agility enabling high-power, ultra-broad band wavelength tunable fiber lasers. However, these systems are limited in terms of power scaling due to degrading spectral purity with increasing input pump power which in turn limits the applicability of these systems. This is due to conversion of desired wavelength into next higher order Raman stokes with increase in pump power. In this work, we demonstrate a high power, ultra-high spectral purity, broadly wavelength tunable cascaded Raman fiber laser. This was enabled by culmination of two significant advances over the last year. To terminate the Raman cascade at the required output wavelength, we utilized our recently proposed distributed filtered feedback mechanism. To achieve high spectral purity, we used a recently demonstrated technique of using high power fiber based Amplified Spontaneous emission (ASE) sources as the input pump. A maximum output power of ~33W at 1.5μm and ~27W at 1.4μm was achieved. High spectral purity of <97% at the final wavelength was achieved over a wide-range of output powers.