Photonic Devices - Couplers

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Photonic Devices - Couplers
Optical fibre couplers
A basic photonic device used to split or combine
light to or from different fibres. A building
block of passive optical networks.
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Photonic Devices - Couplers
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Photonic Devices - Couplers
How a four-port 5050 splitter works

• Light entering Port 1 propagates into the
  coupling region where the waveguides are close
  together.
• The evanescent tail of the field of the first
  waveguide overlaps into the second and light
  leaks across - This is evanescent coupling.

• The splitting ratio for light leaving Ports 2
  and 3 can be adjusted to any desired value by
  adjusting the amount of coupling, or the length
  of the coupling region- the most common split is
  5050.
• The splitting ratio also depends on the
  wavelength of the light.

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Photonic Devices - WDM couplers
A 2 channel Wavelength Division Multiplexer (WDM)

• We aim to split two wavelengths from one fibre
  into two outputs, to separate two channels of
  information, or combine two into one fibre.
• We contrive to make a coupler with a splitting
  ratio at one desired wavelength of zero (the
  light all comes out of the primary waveguide)
  while at the other desired wavelength, total
  cross coupling occurs.

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Photonic Devices - Bragg Gratings
A Bragg grating is a periodic refractive index
variation written along the fibre core. If the
optical period is l0 / 2, the grating reflects
wavelength l0 selectively, very useful in
filtering communication channels in or out.