Localized and stationary dynamic gratings via stimulated Brillouin scattering with phase modulated pumps

Y Antman,A Zadok,L Thevenaz,N Primerov,J Sancho

doi:10.1364/oe.20.007807

Abstract

A novel technique for the localization of stimulated Brillouin scattering (SBS) interaction is proposed, analyzed and demonstrated experimentally. The method relies on the phase modulation of two counter-propagating optical waves by a common pseudo-random bit sequence (PRBS), these waves being spectrally detuned by the Brillouin frequency shift. The PRBS symbol duration is much shorter than the acoustic lifetime. The interference between the two modulated waves gives rise to an acoustic grating that is confined to narrow correlation peaks, as short as 1.7 cm. The separation between neighboring peaks, which is governed by the PRBS length, can be made arbitrarily long. The method is demonstrated in the generation and applications of dynamic gratings in polarization maintaining (PM) fibers. Localized and stationary acoustic gratings are induced by two phase modulated pumps that are polarized along one principal axis of the PM fiber, and interrogated by a third, readout wave which is polarized along the orthogonal axis. Using the proposed technique, we demonstrate the variable delay of 1 ns-long readout pulses by as much as 770 ns. Noise due to reflections from residual off-peak gratings and its implications on the potential variable delay of optical communication data are discussed. The method is equally applicable to the modulation of pump and probe waves in SBS over standard fibers.

Highlights

Stimulated Brillouin scattering (SBS) requires the lowest activation power of all non-linear propagation effects in standard optical fibers
The method relies on the phase modulation of two counterpropagating optical waves by a common pseudo-random bit sequence (PRBS), these waves being spectrally detuned by the Brillouin frequency shift
The output of the pumps distributed feed-back (DFB) was modulated by an electro-optic phase modulator (EOM), which was driven by a PRBS generator

Summary

Introduction

Stimulated Brillouin scattering (SBS) requires the lowest activation power of all non-linear propagation effects in standard optical fibers. In Brillouin optical time domain analysis (B-OTDA), an intense pump wave is used to amplify counter-propagating, typically weaker probe waves [6]. The measurement range of a standard BOTDA can reach tens of km, its spatial resolution is fundamentally restricted to the order of 1 m by the acoustic lifetime: The use of either pump or probe pulses much shorter than τ leads to SBS amplification that is both weaker and spectrally broadened [7]. Dynamic gratings are introduced by two counter-propagating pump waves, separated in frequency by ΩB and co-polarized along one principal axis of the PM fiber. We experimentally demonstrate the generation of cm-scale, stationary and localized dynamic gratings over PM fibers of up to 100 m in length, using PRBS phase modulation of both pumps [31].

Brillouin dynamic gratings driven by phase modulated pumps

Experimental setup

Experimental results: localized and stationary dynamic SBS gratings

Noise due to reflections from correlation sidelobes

Conclusions