Multi-branch erbium fiber-based femtosecond optical frequency comb for measurement of cavity ring-down spectroscopy

In this paper, we demonstrate an optical frequency comb (OFC) based on an erbium-doped-fiberfemtosecond laser, for the measurement of cavity ring-down spectroscopy (CRDS) with wavelengths of 1064,1083, 1240, 1380, 1500, 1600, 1750 and 2100 nm. We adopt a multi-branch structure to produce high power atthe specific wavelengths to meet the requirement for application in the spectral measurement. The OFC isdeveloped by using a mode-locked fiber ring laser based on the nonlinear amplifying loop mirror mechanism.The laser is self-starting by introducing a nonreciprocal phase bias in the cavity and insensitive to theenvironmental perturbation. Using the chirped pulse amplification and highly nonlinear fibers, the broad spectraat the specific wavelengths are obtained. By optimizing the parameters of the pulses, the power of per mode ateach target wavelength is greater than 300 nW.The frep is obtained by detecting the output of the femtosecond laser directly, while the fceo is detected by f-2finterference. The signal-to-noise ratio of the fceo is about 35 dB with a 300-kHz resolution bandwidth. Bycontrolling the intra-cavity electro-optic modulator and piezoactuator , the frep is stabilized with high bandwidthand large range (about megahertz bandwidth and 3 kHz range). The fceo is stabilized by using feedback to thepump current of the femtosecond laser dynamically. The in-loop frequency instability degree of the fceo,evaluated by the Allan deviation, is approximately 4.95 x 10-18/t1/2 at 1 s and integrates down to 10-20 levelafter 2000 s, while that of the frep is well below 5.85 x 10-13/t. The all polarization-maintaining erbium fiber-based femtosecond optical frequency comb with multi-application branches we demonstrate in this paper isefficient and reliable for many other applications including optical frequency metrology and optical atomicclocks