Fig. 1. Principle of operation. (a) Simplified experimental setup of the DCANDi laser; (b) (top) schematic diagram of the Δfrep modulation; (middle) temporal walk-off of the two combs under modulation; (bottom) enhancement of interferogram repetition rate under modulation.

Fig. 2. DCANDi simulation routine results. (a) Modulation of the δωΔ in DCANDi due to modulation of pump2 power; (b) comparison of the expected evolution of Δfrep calculated from cavity β2 coupled with ωΔ (red circle) with the Δfrep retrieved from pulse timing (black).

Fig. 3. Basic performance of DCANDi laser. (a) Optical spectra of the two combs without modulation; (b) evolution of repetition rate difference under slow pump modulation; (c) DC interferogram under 1 kHz modulation; interferogram during (d) forward and (f) backward temporal scanning; RF spectrum obtained from (e) forward and (g) backward interferogram.

Fig. 4. (a) Evolution of the δωΔ in DCANDi calculated from the spectral evolution measured using DFT; (b) evolution of Δfrep due to the β2 coupled with δωΔ calculated using Eq. (2).

Fig. 5. Precise characterization of DC time-delay evolution during dynamic modulation. (a) Spectrogram during one Δfrep switching; (b) pulse separation evolution obtained by performing FFT on (a); (c) Δfrep evolution obtained from (b); (d) PSD of relative timing jitter calculated from 1000 consecutive round trips before (red) and after (blue) the transition, as marked in (b); (e) integrated timing jitter calculated from (d).

Fig. 6. Characterizing the relaxation time constant of SESAM. (a) Experimental setup. Pump-probe technique is employed in a reflection geometry. (b) Measured pump-probe signal using conventional DC technique for 600 ms; (c) mean response of the SESAM calculated by averaging nine pump-probe signals in (b); (d) measured pump-probe signal using proposed dynamic Δfrep modulation technique for 5 ms; (e) mean response of the SESAM calculated by averaging nine pump-probe signals in (d).

Fig. 7. Logic of the DCANDi simulation.

Fig. 8. (a) Evolution of center wavelength for direction 1 (black) and direction 2 (red) for the case of Δfrep=−2.5  Hz; (b) comparison of the saturated gain spectrum of direction 1 (black) and direction 2 (red) at different points along the YDF marked in (a), which are the beginning, middle, and end of the YDF. The insets are zoomed-in to the gain peaks, and the dotted lines in the inset denote the center of the gain peak for each direction.

Fig. 9. (a) Evolution of center wavelength for direction 1 (black) and direction 2 (red) for the case of Δfrep=+2.5  Hz; (b) comparison of the saturated gain spectrum of direction 1 (black) and direction 2 (red) at different points along the YDF marked in (a), which are the beginning, middle, and end of the YDF. The insets are zoomed-in to the gain peaks, and the dotted lines in the inset denote the center of the gain peak for each direction.

Fig. 10. Characterization of compressed pulse using a conventional FROG setup. In the figure, (a) and (b) are the measured and reconstructed spectrogram of comb 1, with (c) showing the retrieved pulse shape of comb 1. The Gaussian fitted pulse duration is 171 fs. Similarly, (d) and (e) are the measured and reconstructed spectrogram of comb 2, with (f) depicting the retrieved pulse shape of comb 2. The Gaussian fitted pulse duration is 185 fs.

Fig. 11. (a) Response of Δfrep to change in pump2 power. (b) Change in output power for direction 1 (black) and direction 2 (red) as a function of change in pump2 power. Note that the pump1 power is fixed at 1.26 W for this measurement.

Fig. 12. Modulation of pump power by a square wave of (a) 1 kHz and (b) 5 kHz frequency. The insets show the zoomed-in picture of the first rising edge of the square wave. The amplitude of modulation is 250 mV.

Fig. 13. (a) Error signal of the unlocked (blue) and locked (red) case measured with an oscilloscope; (b) FFT of the error signals in (a).

Fig. 14. Normalized spectral evolution along (a) direction 1 and (b) direction 2 while the pump2 is modulated, measured using the DFT technique.