title: Coherence enhancement of a chirped DFB laser for frequency-modulated continuous-wave reflectometry using a composite feedback loop.
abstract: We demonstrate efficient coherence enhancement of a chirped distributed feedback (DFB) laser for frequency-modulated continuous-wave (FMCW) reflectometry. Both sweep nonlinearity and broadband stochastic frequency noises during the laser chirp are efficiently suppressed by a composite feedback loop. The residual frequency error relative to a perfect linear chirp is shown to be about 89 kHz for a laser chirp of 50 GHz in 100 ms, compared with 44 MHz with the loop open. The broadband frequency noise suppression of the frequency-swept laser greatly improves its coherence, leading to a higher signal-to-noise ratio and a significantly extended measurement range in FMCW reflectometry ranging. We demonstrate a 2 mm transform-limited spatial resolution at a range window of 50 m and a 17.5 cm spatial resolution at an extended measurement range of 750 m, which is about 15 times the intrinsic laser round-trip coherence length.
authors.forename: Jie
authors.initials: J
authors.lastname: Qin
authors.forename: Qian
authors.initials: Q
authors.lastname: Zhou
authors.forename: Weilin
authors.initials: W
authors.lastname: Xie
authors.forename: Yan
authors.initials: Y
authors.lastname: Xu
authors.forename: Shengguo
authors.initials: S
authors.lastname: Yu
authors.forename: Zhangweiyi
authors.initials: Z
authors.lastname: Liu
authors.forename: Yi tian
authors.initials: Yt
authors.lastname: Tong
authors.forename: Yi
authors.initials: Y
authors.lastname: Dong
authors.forename: Weisheng
authors.initials: W
authors.lastname: Hu