Absorption is caused by three different mechanisms:
1)Absorption by atomic defects in the glass composition
2)Extrinsic absorption by impurity atom in the Glass material
3)Intrinsic absorption by the basic constituent atoms of the fibre material
Atomic defects are imperfections in the atomic structure of the fibre material.ex:missing molecules ,high density clusters of atom groups, or oxygen defects in the glass structure. absorption losses arising from these defects are negligible compared with intrinsic and impurity absorption effects.
Radiating damages a material by changing its internal structure. the damage effects depend on the energy of the ionising particles or rays ,(eg; electrons,neutrons or gamma rays), the radiation flux , and the flounce.the total dose a material receives is expressed in units of rad(Si),which is a measure of radiation absorbed in bulk silicon.
1rad(Si)= 100erg/g =0.01j/kg
The basic response of a fibre to ionising radiation is an increase in attenuation owing to the creation of atomic defects , or attenuation centres , that absorb optical energy . for the higher radiation level , the attenuation is larger .
The other dominant absorption factor in fibres are preparation of fibre materials. fibre materials prepared by the direct-melt method is in the presence of impurities .impurity absorption results predominantly from transition metal ions ,such as iron,chromium,cobalt,and copper,and from OH(water) ions.the transition metal impurities which are present in the starting materials used for direct-melt fibres range between 1 and 10 parts per billion ,causing losses from 1 to 10 dB/km. the impurity levels in vapour-phase deposition processes are usually
one to two orders of magnitude lower .Impurity absorption losses occurs either because of electronic transitions between energy levels or because of change transitions from one ion to another.
Intrinsic absorption is associated with the basic fibre material (sio2) and is principle physical
factor that defines the transparency window of a material over a specified spectral region. it
is observed in the ultra violet region and from atomic vibration bands in the near - infrared
region.
The electronic absorption bands are associated with the band gap of the amorphous glass materials.this absorption occurs when a photon interacts with an electron in the valence band and excites it to a higher energy level.
1)Absorption by atomic defects in the glass composition
2)Extrinsic absorption by impurity atom in the Glass material
3)Intrinsic absorption by the basic constituent atoms of the fibre material
Atomic defects are imperfections in the atomic structure of the fibre material.ex:missing molecules ,high density clusters of atom groups, or oxygen defects in the glass structure. absorption losses arising from these defects are negligible compared with intrinsic and impurity absorption effects.
Radiating damages a material by changing its internal structure. the damage effects depend on the energy of the ionising particles or rays ,(eg; electrons,neutrons or gamma rays), the radiation flux , and the flounce.the total dose a material receives is expressed in units of rad(Si),which is a measure of radiation absorbed in bulk silicon.
1rad(Si)= 100erg/g =0.01j/kg
The basic response of a fibre to ionising radiation is an increase in attenuation owing to the creation of atomic defects , or attenuation centres , that absorb optical energy . for the higher radiation level , the attenuation is larger .
The other dominant absorption factor in fibres are preparation of fibre materials. fibre materials prepared by the direct-melt method is in the presence of impurities .impurity absorption results predominantly from transition metal ions ,such as iron,chromium,cobalt,and copper,and from OH(water) ions.the transition metal impurities which are present in the starting materials used for direct-melt fibres range between 1 and 10 parts per billion ,causing losses from 1 to 10 dB/km. the impurity levels in vapour-phase deposition processes are usually
one to two orders of magnitude lower .Impurity absorption losses occurs either because of electronic transitions between energy levels or because of change transitions from one ion to another.
Intrinsic absorption is associated with the basic fibre material (sio2) and is principle physical
factor that defines the transparency window of a material over a specified spectral region. it
is observed in the ultra violet region and from atomic vibration bands in the near - infrared
region.
The electronic absorption bands are associated with the band gap of the amorphous glass materials.this absorption occurs when a photon interacts with an electron in the valence band and excites it to a higher energy level.
The ultra violet edge of the electron absorption bands of both amorphous and crystalline material follow the empirical relation ship
αuv=ceE/E0
which is known as urbach's rule.
the ultra violet loss in dB is αuv= 1542 x X 10-2 exp(4.63)
46.6 x+60 ( λ)
No comments:
Post a Comment