Abstract
This paper comprehensively investigated noise characteristics of superluminal propagation based on low-noise single-frequency Brillouin lasing oscillation with the aid of a population inversion dynamic grating. Thanks to high-degree polarization alignment between the Brillouin pump and the lased Stokes lightwaves in polarization maintaining fibers, efficient Brillouin lasing resonance with over 10-dB relative intensity noise suppression has been demonstrated to activate Brillouin loss-induced anomalous dispersion in the vicinity of pump signals, benefiting a noise-insensitive superluminal propagation along kilometer-long optical fibers with robust resistance to ambient disturbance. Consequently, sinusoidally modulated pump signals experienced the time advancement of 4634.0 ns at the group velocity of 10.63 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> . Results show that the variance of the fractional advancement with polarization maintaining fibers is 2.54 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> which is two orders of magnitude lower than that of conventional single mode fibers. Furthermore, the dependence of the group velocity on the modulation frequency was experimentally investigated, showing good agreement with the theoretical analysis.
Highlights
IN the past few decades, the active manipulation of light group velocity has widely drawn attention due to its practical potentials in areas such as alloptical communication [1]-[3], hyper-sensitivity sensing [4], microwave photonics [5]-[7], and time cloak [8], [9]
We demonstrated stable superluminal propagation along kilometer-long optical fibers based on linearly polarized low-noise Brillouin lasing oscillation with an intra-cavity EDF-induced dynamic grating
At the same Stokes lasing power of 0.40 mW, the stochastic fluctuation of the Stokes lasing emission in single mode fibers (SMFs)-based Brillouin fast light system was apparently observed in the time domain whilst the laser intensity fluctuation obtained with polarization maintaining fibers (PMFs) was reduced to about 0.04 V, one half of the peak-peak fluctuation (i.e., 0.09 V) with SMFs
Summary
IN the past few decades, the active manipulation of light group velocity (namely slow and fast light) has widely drawn attention due to its practical potentials in areas such as alloptical communication [1]-[3], hyper-sensitivity sensing [4], microwave photonics [5]-[7], and time cloak [8], [9]. Due to the appearance of multiple longitudinal modes in long-cavity Brillouin lasing resonators, the propagation distance of this Brillouin lasing fast light is basically limited within dozens of meters, which impedes its applications, e.g., gravitationalwave detection in which the laser beams are basically required to pass through over kilometer-long distance for sensitivity improvement. To this end, dynamic fiber gratings based on unpumped Erbium-doped fibers, serving as a narrowband filter, have been introduced to alleviate the longitudinal modes in long-cavity Brillouin lasing resonators, benefiting a profound extension of superluminal propagation in 500-m long optical fibers [27], [28]. Largescale ambient exposure over hundreds of meters fibers inevitably renders the Brillouin lasing resonance more sensitive
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