Non-Symmetric

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Non-Symmetric

• Microstructured Optical Fibres

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Introduction

• Information Age Computers, CDs, Internet
• Need a way to transmit data Optic Fibres
• Other uses medicine, surveillance

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The story so far

• Currently use conventional optic fibres
• Began in the 60s, first used in the 80s
• So far, so good
• Moores Law Economics Need for better fibres

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Problems

• Losses 0.18dB/km at best lose 4 of power/km
• Restricted wavelength
• Dispersion

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Microstructured Optical Fibres(MOFs)

• First thought of 10 years ago
• Fibre air holes MOF
• Lower losses
• Much greater versatility

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Simple Concepts

• Light is contained in the fibre by the holes
• Light propagates along many modes
• Intermodal Dispersion - coupling between modes
• Only want single mode fibres (fundamental mode)

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Polarisation Mode Dispersion

• Fundamental mode two polarisations
• Coupling between different polarisations
• Theory degenerate modes, no coupling
• Heat, stress, manufacture imperfections
• Reality non-degenerate modes, coupling

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Solution?

• Create a non-symmetric fibre birefringence
• Fundamental mode no longer degenerate
• Use only one polarisation eliminate
  polarisation mode dispersion

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My Experiment

• Investigate modes in non-symmetric MOFs
• Computer simulations, using programs written by
  Boris Kuhlmey
• Input parameters and structure
• Program gives information about modes

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Basic parameters

• Used three rings of holes six holes in the
  first ring, 12 in the second, 18 in the third
• Kept hole size constant at 1.30 mm
• Kept wavelength constant at 1.55 mm
• Kept fibre size and refractive indices constant

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Ellipses

• Used Ellipses, varying eccentricity while keeping
  the semi-major axis constant (length a)
  Eccentricity e (1-b2/a2)0.5
• Put cylinders equally along the arc

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Problems/Constraints

• No formula for arc length of an ellipse
  numerical integration
• Cant have eccentricity too close to 1
  cylinders overlap, results inaccurate
• Took 0 lt e lt 0.77

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Input Data
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The Fibre
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Output
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Output (continued)

• The program generates two modes
• Mode 1 Mode 2
• The field shown is the Poynting Vector in the
  z-direction

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The difference?

• The same two modes
• Mode 1
  Mode 2
• The field shown is the E field in the x-direction

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Important Numbers

• Refractive Index b br ibi
• Real Component Normal refractive index e.g.
  Snells Law
• Imaginary Component Loss of the fibre
• Degree of Birefringence Bm br,x - br,y
• Bm gt 10-4 good fibre

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Losses
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Results
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More Results
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Trends?
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Summary

• Losses decrease with eccentricity, with bi,x less
  than bi,y - can create
• Real part of refractive index decreases with
  eccentricity, with br,y less than br,x
• Bm increases with eccentricity according to a
  power law
• Can create highly birefringent fibres using this
  method

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References

• Govind P. Agrawal, Fiber-Optic Communication
  Systems (Wiley and Sons, New York, 2002)
• Thomas White, Microstructured Optical Fibres a
  Multipole Formulation, University of Sydney,
  October 2000
• Boris T. Kuhlmey, Theoretical and Numerical
  Investigation of the Physics of Microstructured
  Optical Fibres, University of Sydney, 2003
• Boris T. Kuhlmey, Ross C. McPhedran, C. Martijn
  de Sterke, Modal cutoff in microstructured
  optical fibers, 2002