DUAL-COMB SPECTROSCOPY USING A DUAL-COMB FIBER LASER BASED ON HYBRID PULSE FORMATION MECHANISMS

\begin{wrapfigure}{r}{0pt} \includegraphics[scale=0.3]{Graph12.eps} \end{wrapfigure} Single-cavity dual-comb fiber laser can generate two ultra-short pulse trains from the same cavity, which could have relatively low common-mode noises and good mutual coherence. They had been demonstrated to be applicable to various dual-comb metrology applications including optical spectroscopy\footnote{X. Zhao, et al., Optics Express, vol. 24, 21833, 2016.}, absolute distance measurement\footnote{B. Lin, et al., IEEE Photonics Journal, 99, 2017.} and so on. Here, broadband dual-comb spectroscopy measurement using a broadband mode-locked dual-comb fiber laser based on hybrid pulse formation mechanisms is demonstrated. Through the dispersion management in the cavity, the bandwidths of both pulses are greatly increased. Dual-comb pulse with broader spectra can be generated when the pump power is above the threshold power. After jointly being amplified by an Erbium-doped fiber amplifier, the 3-$dB$ spectral bandwidths, at the center wavelength of $1550 nm$ and $1555 nm$, have been broadened from $4.4 nm$ and $1.3 nm$\footnote{Y. Liu, et al., Optics Express, vol. 24, 21392, 2016.} to $58.8 nm$ and $8.5 nm$, respectively. Also, the 10-$dB$ width of the overlapped spectra is over $16 nm$, covering $1546 nm$ to $1562 nm$. The repetition rate difference of two pulse trains is $37 Hz$, because of the small difference in their center wavelengths and the low cavity dispersion. Then, typical asynchronous experimental setup is used to measure transmission spectrum of an on-chip microring resonator by averaging over $30$ interferograms. All the resonance spectral features are clearly resolved. This kind of dual-comb fiber lasers could offer extra options for low-complexity, dual-comb metrology applications