Stimulated Brillouin Scattering in cm-Long Chalcogenide Waveguides
Stimulated Brillouin scattering (SBS) is a nonlinear interaction between a relatively intense pump wave, and a counter-propagating, spectrally detuned probe wave. When the difference between the optical frequencies of the two waves matches the Brillouin frequency shift of the medium WB, the probe wave may be amplified at the expense of the pump. SBS is readily observed in standard silica single-mode fibers over lengths of hundreds of meters.
Chalcogenides (ChGs) are a family of glasses which contain one of the chalcogen elements (e.g. S, Se, or Te). They have a broad transparency window from the visible to the mid-infrared wavelengths, and are well known for their highly-nonlinear refractive index n2, that is up to thousand times greater than that of silica. The large nonlinearity makes ChGs an attractive platform for all-optical signal processing. Nonlinear propagation effects in waveguides written in ChG glass have been used in four-wave-mixing, in wavelength conversion etc.
Recently, SBS amplification was demonstrated in 7 cm-long As2S3 waveguides, defined using a dry-etch process. In this work, we report SBS amplification in As2S3 waveguides defined by a much simpler technique of direct laser-beam writing. 1 cm-long and 4 mm-wide waveguides were patterned in a 1 mm-thick film of As2S3, deposited on a silica-on-silicon substrate. The results provide the first demonstration of SBS amplification in directly-written chalcogenide glass waveguides. The observed gain bandwidth of 200 MHz is considerably wider than previously reported values of ~30MHz. A possible explanation due to multi-mode behavior along with the longitudal evolution of the optical field profile will be discussed.