Abstract
Brillouin-Enhanced Four-Wave-Mixing techniques, which couple four optical beams through Brillouin nonlinearity, have gained popularity in the 1980’s largely owing to their phase conjugation properties. Experiments were mainly conducted in liquid cells. The interest in Brillouin-Enhanced Four-Wave-Mixing has reawakened in the 2000’s, following the quest for dynamically reconfigurable gratings in optical fibers. Termed Brillouin Dynamic Grating this time around, it is, in fact, an acoustic wave, optically generated by stimulated Brillouin scattering process between two pump waves. The acoustic wave either carries the coherent information encoded by the pump beams, or in the case of sensing applications, its properties are determined by the environmental parameters. This information, in turn, is imparted to the third phase-matched optical probe wave through the elasto-optic effect. Over the last decade, this mechanism allowed for the realization of many all-optical signal processing functions and has proven instrumental in distributed sensing applications. This paper describes the basics, as well as the state of the art, of BDG-based applications in optical fibers. It also surveys the efforts being done to carry over these concepts to the photonic chip level.
Highlights
In Brillouin-Enhanced Four-Wave-Mixing (BE-FWM) [1,2], the four optical waves interact with each other through a material density wave excited through a combination of a Stimulated BrillouinScattering (SBS) process, that generates a moving optical intensity wave and the phenomenon of electrostriction, where the optical intensity wave gives rise to a corresponding density wave [3].From the late 70’s until the early 90’s, BE-FWM in bulk media was the subject of extensive research, leading to applications such as optical phase conjugation, beam combining and optical path selection [4,5,6]
The Brillouin DynamicGrating (BDG) is, a special case of BE-FWM, where the two optical pump waves determine the spatio-temporal form of the acoustic wave, and by choosing the power of the probe wave to be sufficiently low, the problem at hand becomes that of diffraction from a moving fiber Bragg grating [8]
Silicon offers an abundance of third-order nonlinear effects but its large two-photon absorption (TPA) coefficient hinders device performance [72]. To circumvent this intrinsic drawback, scientists have had to resort to silicon organic/inorganic hybrids [73,74], slotted waveguide [75], or slow-light approaches based on photonic crystal waveguides [76]
Summary
In Brillouin-Enhanced Four-Wave-Mixing (BE-FWM) [1,2], the four optical waves interact with each other through a material density wave excited through a combination of a Stimulated Brillouin. Bayvel and Giles were the first to demonstrate the BE-FWM process in optical fibers in 1990 [7]. The BDG is, a special case of BE-FWM, where the two optical pump waves determine the spatio-temporal form of the acoustic wave, and by choosing the power of the probe wave to be sufficiently low, the problem at hand becomes that of diffraction from a moving fiber Bragg grating [8]. When the BDG plays the role of an all-optical, reconfigurable, signal processing circuit, its key performance specifications are accuracy, optical signal-to-noise ratio, bandwidth, dynamic range, and other application-unique requirements.
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