用于光腔衰荡光谱测量的多支路掺铒光纤飞秒光梳系统

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

报道了用于光腔衰荡光谱测量的多支路掺铒光纤飞秒光梳系统.该系统以“9”字型全保偏掺铒飞秒光纤激光器为激光源.利用自制的锁相环电路,获得的重复频率和载波包络相移频率秒级稳定度分别为5.85× 10^(-18)/τ^(1/2)和4.95× 10^(-18)/τ^(1/2).为了满足CO, CH;等分子吸收光谱测量,利用啁啾放大和非线性光谱展宽技术,采用多支路结构,将飞秒光梳直接输出光谱由1500—1600 nm分别扩展至8个目标波长(1064, 1083, 1240, 1380, 1500,1600, 1750和2100 nm)处,各目标波长处的单模功率均大于300 n W,满足光腔衰荡光谱测量实验的需求.

In this paper, we demonstrate an optical frequency comb(OFC) based on an erbium-doped-fiber femtosecond 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 at the specific wavelengths to meet the requirement for application in the spectral measurement. The OFC is developed 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 the environmental perturbation. Using the chirped pulse amplification and highly nonlinear fibers, the broad spectra at the specific wavelengths are obtained. By optimizing the parameters of the pulses, the power of per mode at each 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-2f interference. The signal-to-noise ratio of the fceo is about 35 dB with a 300-kHz resolution bandwidth. By controlling the intra-cavity electro-optic modulator and piezoactuator, the frep is stabilized with high bandwidth and large range(about megahertz bandwidth and 3 kHz range). The fceo is stabilized by using feedback to the pump current of the femtosecond laser dynamically. The in-loop frequency instability degree of the fceo,evaluated by the Allan deviation, is approximately 4.95 × 10^(-18)/τ^(1/2) at 1 s and integrates down to 10–20 level after 2000 s, while that of the frep is well below 5.85 × 10^(-18)/τ^(1/2) The all polarization-maintaining erbium fiberbased femtosecond optical frequency comb with multi-application branches we demonstrate in this paper is efficient and reliable for many other applications including optical frequency metrology and optical atomic clocks.