Independently tunable dual-wavelength fiber oscillator with synchronized pulsed emission based on a theta ring cavity and a fiber Bragg grating array

We present a fiber-integrated laser enabling independent tuning of two emission wavelengths with synchronized pulsed emission. The discrete tuning concept comprises a theta cavity fiber laser (TCFL), a fiber Bragg grating (FBG) array as versatile spectral filter, facilitating tailored tuning ranges, and optical gating to control the emission spectrum. A novel electrical driving scheme uniquely enables independently tunable multi-wavelength emission from a single laser oscillator. Tunable dual-wavelength emission is experimentally investigated with an Ytterbium (Yb)-doped TCFL using an FBG array with 11 gratings. Over a tuning range of 25nm, 55 wavelength pairs have been demonstrated with high signal contrast (~ 40dB) and narrow linewidth (<40GHz). Based on the demands of prospective applications, pulse synchronicity is studied with a fiber-based time-delay spectrometer (TDS) simultaneously measuring the joint temporal and spectral pulse properties down to a single-pulse analysis. Accordingly, tunable and fully synchronized dual-wavelength emission has been verified by driving the TCFL with optimized electrical gating parameters. This unique operation mode achieved in a cost-efficient fiber-integrated laser design targets novel applications e.g. in nonlinear spectroscopy and biophotonics.