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

2. Outline Scattering process Types of Scattering Loss
Rayleigh scattering & Mie scattering
Interface scattering
Surface scratch and pit scattering
Conclusion
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3. 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
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4. 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
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5. Volume scattering
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6. 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.
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7. 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
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8. Rayleigh scattering Consider : and we get
Since electric vector may be decomposed into orthogonal components, perpendicular (Er) and parallel (El) :
The corresponding intensity:
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9. 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
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10. 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
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11. surface scattering
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12. 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.
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13. 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
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14. 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
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15. 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:
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16. 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:
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17. Surface scratch and pit scattering
For scratch:
For pit:
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18. Surface scratch and pit scattering
Zuyuan He(2004)
reconsider size , location,
number of scratches
The depth (without consider)
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19. 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
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20. Thanks for your listening!
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