Download Rayleigh scattering

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
Page 2
Solid-State Laser Crystal and Device Laboratory
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
Page 3
Solid-State Laser Crystal and Device Laboratory
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
Page 4
Solid-State Laser Crystal and Device Laboratory
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.
Page 6
Solid-State Laser Crystal and Device Laboratory
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
Page 7
Solid-State Laser Crystal and Device Laboratory
Rayleigh scattering
 Consider :
and we get
 Since electric vector may be decomposed into orthogonal
components, perpendicular (Er) and parallel (El) :
 The corresponding intensity:
Page 8
Solid-State Laser Crystal and Device Laboratory
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
Page 9
Solid-State Laser Crystal and Device Laboratory
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
Page 10
Solid-State Laser Crystal and Device Laboratory
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.
Page 12
Solid-State Laser Crystal and Device Laboratory
Interface scattering
h’=h+1/Kyc+1/Kyu
 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
Page 13
Solid-State Laser Crystal and Device Laboratory
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
Page 14
Solid-State Laser Crystal and Device Laboratory
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:
Page 15
Solid-State Laser Crystal and Device Laboratory
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:
Page 16
Solid-State Laser Crystal and Device Laboratory
Surface scratch and pit scattering
 For scratch:
 For pit:
Page 17
Solid-State Laser Crystal and Device Laboratory
Surface scratch and pit scattering
 Zuyuan He(2004)
reconsider size , location,
number of scratches
The depth (without consider)
Page 18
Solid-State Laser Crystal and Device Laboratory
Conclution
 For volume scattering:
1. Rayleigh scattering accounts for about 96% of attenuation in
optical fiber
2. For small x ,Mie theory reduces to the Rayleigh approximation
 For surface scattering:
1. Interface scattering : roughness at the interface between the
core and the claddings
2. Surface defects : as the depth increases, the degradation also
increases very rapidly
Page 19
Solid-State Laser Crystal and Device Laboratory
Thanks for your listening!
bee6565
Page 20
Solid-State Laser Crystal and Device Laboratory