Volume and Surface Scattering of Fibers Speaker: Shiuan-Li Lin Advisor : Sheng-Lung Huang Solid-State Laser Crystal and Device Laboratory

Outline Scattering process Types of Scattering Loss Rayleigh scattering & Mie scattering Interface scattering Surface scratch and pit scattering Conclusion Solid-State Laser Crystal and Device Laboratory Page 2

Scattering process When a wave interacts with a particle in a way that removes energy in the directional propagating wave and transfers it to other directions Different from absorption: the light isn’t absorbed, just sent in another direction Solid-State Laser Crystal and Device Laboratory Page 3

Types of Scattering Loss Volume scattering (linear) Rayleigh scattering Mie scattering Volume scattering (non-linear) Brillouin scattering Stimulated Raman scattering Surface scattering Interface scattering Surface scratch and pit scattering Solid-State Laser Crystal and Device Laboratory Page 4

Volume scattering Here comes your footer  Page 5

Rayleigh scattering & Mie scattering The main type of linear scattering caused by small-scale (small compared with the wavelength of the lightwave) The size of a scattering particle is parameterized by the ratio x of its characteristic dimension r and wavelength λ: Rayleigh scattering : parameter regime x ≪ 1. Mie scattering : larger particles or for an arbitrary size of x. Solid-State Laser Crystal and Device Laboratory Page 6

Rayleigh scattering Consider a small homogeneous, isotropic spherical particle & a incident electric field E0 ,produced the electric dipole : α is the polarisability of the small particle The oscillating dipole produces a plane polarised elecro magnetic wave (scattered wave) According to electromagnetic solution by Hertz : r :the distance between the dipole and the observation point, γ:the angle between the scattered dipole moment and the direction of observation Solid-State Laser Crystal and Device Laboratory Page 7

Rayleigh scattering Consider : and we get Since electric vector may be decomposed into orthogonal components, perpendicular (Er) and parallel (El) : The corresponding intensity: Solid-State Laser Crystal and Device Laboratory Page 8

Rayleigh scattering The total scattered intensity of light: Combined and get : For Rayleigh scattering in optical fibers: n:the refraction index,  P :the photoelastic coefficient of the glass  β is the isothermal compressibility Tf is a fictive temperature Intrinsic Losses of Silica Fiber Solid-State Laser Crystal and Device Laboratory Page 9

Mie scattering For fibers, Mie scattering occurs in inhomogeneities such as core-cladding refractive index variations, impurities at the core-cladding interface, strains or bubbles Mie Scattering Calculator: Sphere Diameter1microns Refractive Index of Medium1.224 Real Refractive Index of Sphere1.5 Wavelength in Vacuum0.532microns Solid-State Laser Crystal and Device Laboratory Page 10

surface scattering Here comes your footer  Page 11

Interface scattering Interface scattering – due to roughness at the interface between the core and the claddings of the waveguide Tien(1971) has derived an expression for scattering loss due to surface roughness ,based on the Rayleigh criterion Pr: specular reflection power, Pi: incident power, σ: variance of surface roughtness , θ1: is the propagation angle within the waveguide, n1: the refractive index of the core. Solid-State Laser Crystal and Device Laboratory Page 12

σu and σl: surface roughness of upper and lower surfaces, respectively Interface scattering Loss Coefficient due to Interface Scattering: σu and σl: surface roughness of upper and lower surfaces, respectively  kyu and kyl: decay constant of upper and lower surface , respectively h’=h+1/Kyc+1/Kyu Solid-State Laser Crystal and Device Laboratory Page 13

Surface scratch and pit scattering The effects of endface defects are studied by employing wave scattering theory Bidirectional scatter distribution function (BSDF): Ps : scattering light power Pi : incident light power Ωs : soild angle Solid-State Laser Crystal and Device Laboratory Page 14

Surface scratch and pit scattering Elliptical gaussian light beam: The total power incident over a scratch: Assume there are n scratches across the MFD area: The power ratio for a defectless endface: Solid-State Laser Crystal and Device Laboratory Page 15

Surface scratch and pit scattering Define the ratio of scattered power and without scratch: The return loss get the main equation as : For pit analysis: Solid-State Laser Crystal and Device Laboratory Page 16

Surface scratch and pit scattering For scratch: For pit: Solid-State Laser Crystal and Device Laboratory Page 17

Surface scratch and pit scattering Zuyuan He(2004) reconsider size , location, number of scratches The depth (without consider) Solid-State Laser Crystal and Device Laboratory Page 18

Conclution For volume scattering: For surface scattering: Rayleigh scattering accounts for about 96% of attenuation in optical fiber For small x ,Mie theory reduces to the Rayleigh approximation For surface scattering: Interface scattering : roughness at the interface between the core and the claddings Surface defects : as the depth increases, the degradation also increases very rapidly Solid-State Laser Crystal and Device Laboratory Page 19

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