Widely wavelength-tunable femtosecond light sources in a compact, robustfootprint play a central role in many prolific research fields and technologies, including medical diagnostics, biophotonics, and metrology. Fiber lasers areon the verge in the development of such sources, yet wide span spectral tunability of femtosecond pulses remains a pivotal challenge. Dispersive wave generation, also known as Cherenkov radiation, offers untapped potentials to serve these demands. In this work, the concept of quasi-phase matching for multi-order dispersive wave formation with record-high spectral fidelity and femtosecond durations is exploited in selected, partially conventionally unreachable spectral regions. Versatile patterned sputtering is utilized to realize height-modulated high-index nano-films on exposed fiber cores to alter fiber dispersion to an unprecedented degree through spatially localized, induced resonances. Nonlinear optical experiments and simulations, as well as phase-mismatching considerations based on an effective dispersion, confirm the conversion process and reveal unique emission features, such as almost power-independent wavelength stability and femtosecond duration. This resonance-empowered approach is applicable to both fiber and on-chip photonic systems and paves the way to instrumentalize dispersive wave generation as a unique tool for efficient, coherent femtosecondmulti-frequency conversion for applications in areas such as bioanalytics, lifescience, quantum technology, or metrology.