We present a detailed overview of stimulated Brillouin scattering (SBS) in
 single-mode optical fibers. The review is divided into two parts. In the first part,
 we discuss the fundamentals of SBS. A particular emphasis is given to analytical
 calculation of the backreflected power and SBS threshold (SBST) in optical fibers
 with various index profiles. For this, we consider acousto-optic interaction in the
 guiding geometry and derive the modal overlap integral, which describes the
 dependence of the Brillouin gain on the refractive index profile of the optical
 fiber. We analyze Stokes backreflected power initiated by thermal phonons, compare
 values of the SBST calculated from different approximations, and discuss the SBST
 dependence on the fiber length. We also review an analytical approach to calculate
 the gain of Brillouin fiber amplifiers (BFAs) in the regime of pump depletion. In the
 high-gain regime, fiber loss is a nonnegligible effect and needs to be accounted for
 along with the pump depletion. We provide an accurate analytic expression for the BFA
 gain and show results of experimental validation. Finally, we review methods to
 suppress SBS including index-controlled acoustic guiding or segmented fiber links.
 The second part of the review deals with recent advances in fiber-optic applications
 where SBS is a relevant effect. In particular, we discuss the impact of SBS on the
 radio-over-fiber technology, enhancement of the SBS efficiency in Raman-pumped
 fibers, slow light due to SBS and SBS-based optical delay lines, Brillouin
 fiber-optic sensors, and SBS mitigation in high-power fiber lasers, as well as SBS in
 multimode and microstructured fibers. A detailed derivation of evolutional equations
 in the guided wave geometry as well as key physical relations are given in
 appendices.

Stimulated Brillouin scattering in optical fibers

Germania glass was prepared from high purity GeO2 powder. Refractive-index dispersion was used to calculate material dispersion and to provide a model for representing the dispersion of GeO2–SiO2 glasses. The wavelength of zero material dispersion is found to be in agreement with theoretical calculations. Modal propagation is modeled for a GeO2 core–silica clad fiber. Results support compositional dependence of profile dispersion in GeO2–SiO2 fibers.

Dispersion in GeO2-SiO2 glasses.

The average electronic polarizability of the oxide ion αO2−(no) of numerous binary oxide glasses (phosphate, borate, silicate, germanate, tellurite and titanate) has been estimated on the basis of the refractive index reported in literature. An optical basicity scale has been proposed on the basis of a good agreement between calculated theoretical optical basicity Λth and refractive index based optical basicity Λ(no) of the glasses. It was established that third-order non-linear optical susceptibility χ(3) of the glasses, also found in the literature, increases with increasing optical basicity and tendency for metallization of the glasses. This is associated with the high electron donor ability of the oxide ions and the small optical band gap. Conventional oxide glasses with low refractive index possess low polarizability, low optical basicity, large metallization criterion and small χ(3). Tellurite and titanate glasses as well as borate glasses containing a large amount of Sb2O3 and Bi2O3 with high refractive index above 2.0 show large polarizability, high optical basicity, small metallization criterion and large χ(3).

Electronic polarizability, optical basicity and non-linear optical properties of oxide glasses

We have investigated a series of glasses and melts along the GeO2–SiO2 join using in situ Raman spectroscopy. The results for both the glasses and melts are consistent with a continuous random network in which there are ‘regions’ that are SiO2-like, GeO2-like and mixed GeO2–SiO2-like. Incorporation of GeO2 into the SiO2 network is initially accommodated via the 3- and 4-membered SiO4 rings which are lost as they convert to larger mixed Ge/Si rings. The LO–TO mode behavior is also consistent with a network that is composed of different ‘regions’ and is similar to that expected from the Bruggeman effective media model. At the highest temperatures there are indications that the mixed Ge/Si rings convert back to small 3-membered GeO4 rings and large SiO4 rings; the small 3- and 4-membered SiO4 rings are not reformed.

The structure of GeO2–SiO2 glasses and melts: A Raman spectroscopy study

High-κ dielectrics on Ge have recently attracted much attention as a potential candidate to replace planar silicon transistors for sub-32-nm generations However, the instability of the high-κ/Ge interface, especially the desorption of germanium monoxide (GeO), hampers the development of Ge-based devices Therefore, the typical GeO2/Ge structure was chosen to investigate GeO desorption In this contribution, we describe the desorption kinetics of GeO, including Ge/GeO2 interface reaction, the diffusion process during GeO desorption, the desorption activation energy of GeO, the different mechanisms of GeO desorption, and the active oxidation of Ge Through annealing GeO2/Ge in an ultrahigh vacuum (UHV), direct evidence for the consumption of Ge substrate has been shown by atomic force microscopy (AFM) measurements of the consumption depth By using thermal desorption spectroscopy (TDS) measurements and studying oxygen-18 isotope tracing, we have clarified that the GeO desorption is not caused by the GeO di

Desorption kinetics of GeO from GeO2/Ge structure

The density and the refractive index for various compositions of binary SiO2GeO2 glass prepared by a flame deposition technique, similar to that used to make low-loss optical waveguides, have been measured by standard Archimedes method and the Becke line method, respectively The density as a function of composition is calculated considering the effective volume of the ions contained in the glass to be invariant The refractive index as a function of composition is also calculated, based on the Lorenz-Lorenz equation, by computing the electronic polarizability of fused silica and germania All calculated results are in good agreement with the observed data

Y.Y. Huang

Papers

Relationship between composition, density and refractive index for germania silica glasses