Passively synchronized three-color Er-Yb-Nd all-PM-fiber mode-locked laser system

Synchronized three-color mode-locked lasers offer a powerful new dimension to vibrational microscopy, particularly in the realm of broadband coherent Raman techniques like Stimulated Raman Scattering (SRS) and coherent anti-Stokes Raman scattering. We report on the realization of a synchronized three-color all-polarization-maintaining (PM) fiber laser system operating in a mode-locking regime with emission wavelengths of 1.56, 1.03, and 0.92 μm. The different wavelengths are passively synchronized, using the cross-phase modulation effect in common passive PM-fibers between the three laser resonators, to a temporal pulse jitter lower than 400 fs over an integration time of 1 s. A comprehensive characterization of the synchronization mechanism and laser relative intensity noise is also reported. This three-color laser system, based on Er-, Yb-, and Nd-doped fiber lasers, represents the core technology for a new concept of multiplex SRS microscopy, which enables simultaneous fast acquisition of broad spectra in both the C-H stretching (2800-3100 cm^-1) and the fingerprint (1000-1700 cm^-1) regions.