A novel approach for an all-fiber mono-laser source for CARS microscopy is presented. An Yb-fiber laser generates 100 ps pulses, which later undergo narrowband in-fiber frequency conversion based on degenerate four-wave-mixing. The frequency conversion is optimized to access frequency shifts between 900 and 3200cm-1, relevant for vibrational imaging. Inherently synchronized pump and Stokes pulses are available at one fiber end, readily overlapped in space and time. The source is applied to CARS spectroscopy and microscopy experiments in the CH-stretching region around 3000cm-1. Due to its simplicity and maintenance-free operation, the laser scheme holds great potential for bio-medical applications outside laser laboratories.