Transcript sylla_20070925.ppt

Polarization-Insensitive Cross
Correlation Using Two-Photon
Absorption in a Silicon Photodiode
Pape Sylla
Cross-correlation in fiber optics
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Used for sampling, pattern recognition,
demultiplexing
So far, done using a nonlinear effect called
sum-frequency generation which takes place
in χ² crystals
Quick overview of nonlinearity
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We are use to linear material response of
materials, which manifest itself in the index of
refraction.
There are nonlinear material response
Limitation of the existing method
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It is polarization dependant, which makes it
unpractical for most application
Remediation: Two photon absorption
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They want to use a quantum nonlinear effect
called two photon absorption (TPA) in silicon,
which is χ³ susceptible.
It is based of the fact that two photons are
simultaneously absorbed by the material to
produce current
Normalized Stokes vectors are located on
a unit sphere
S1
s1 
S0
S2
s2 
S0
Poincare’ sphere:
S1  S2  S2
DOP 
S0
2
2
2
S3
s3 
S0
Observation: in Silicon, TPA is
polarization dependent
In theory
Experiment
Results