6.441 Final Project: Theory of Polarization Shift Keying (POLSK) Modulation

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6.441 Final Project Theory of Polarization Shift
Keying (POLSK) Modulation

• Matt Willis
• 5/11/06

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Motivations

• POLSK is of professional interest
• Multi-level transmission that is,
• Intuitive Error Analysis
• Generic Feature of Electromagnetic Waves

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Overview of Optical Communications System
Channel Performance
Input Alphabet
TransmissionMedium
Transmitter
Modulator
Receiver
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Light Modulation Schemes

• Light propagating along z-axis, 1-D transverse
  electric field
• Have amplitude, frequency, and phase at our
  disposal

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Polarization Plane Wave Representation

• Light propagating along z-axis, 2-D transverse
  electric field

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Polarization Poincare Sphere Representation

• Consider the following coordinate transformation
• This transformation defines a sphere called the
  Poincare sphere

where
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Features of the Poincare Sphere Representation

• Linear polarizations (? 0) located along
  (x,y,0) equator
• Circular polarizations are located at North and
  South poles
• If S1 and S2 are orthogonal according to
  Hermitian product, they map onto antipodal points
  on the Poincare sphere

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Encoding Procedure

• Partition the surface area of the sphere into n
  disjoint regions
• Assign to each region a representative vector,
• Choose an encoding function that maps the input
  alphabet onto the set of reference vectors

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Decoding Procedure

• Example 2-POLSK, where E 0,1 --gt (0,0,1),
  (0,0,-1)

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Channel/Noise Model

• State of Polarization is transmitted noiselessly,
  that is
• White shot noise is accumulated during
  photodetection process

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Error Results for 2-POLSK

• Error Condition

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2-POLSK Performance

• Error probability
• BER curve

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N-POLSK Performance

• Freedom in constellation choice