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Chapter - 5

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Power Launching and Coupling• How to launch optical power into a particular fiber from some

type of luminescent source?

• How to couple optical power from one fiber to another fiber?• Depends on fiber parameters such as:

▫ Numerical Aperture

▫ Core Size

▫ Refractive Index Profile

▫ Core-Cladding Index Difference

• Depends on source parameters such as:▫ Size

▫ Radiance

▫  Angular Power Distribution

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Radiance

• Radiance or (brightness) B is the optical powerradiated into a unit solid angle per unit emittingsurface area.

• specified in terms of watts per square centimeterper steradian

• Optical power that can be coupled to opticalfiber depends on radiance of the optical source

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Source Output Pattern

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Power Launching versus Wavelength

• Optical power launched into a fiber does notdepend on the wavelength of the source but only on its radiance

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Fiber-to-Fiber Joints

• Permanent Joint

▫ Splice

• Demountable Joint

▫ Connector

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Mechanical Misalignment

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Axial Misalignment

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Longitudinal Misalignment 

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Fiber End-Face Preparation• Grinding and Polishing Technique

• Controlled Fracture Technique

•  Automated Fiber Cleaving Through Lasers

Controlled Fracture procedure for fiber end face preparation

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Fiber End-Face Defects• EIA Fiber Optic Test Procedures (FOTP) 57 and 179 define common end-face defects as

follows:

▫ Lip

Sharp protrusion from the edge of a cleaved fiber

▫ Rolloff (Breakover)

Rounding-off of the edge of the fiber (opposite to lipping)

▫ Chip

Localized fracture or break at the end of the fiber

▫ Hackle

Severe irregularities across a fiber end-face.

▫ Mist

Similar to hackle but much less severe

▫ Spiral or Step

 Abrupt changes in the end-face topology 

▫ Shattering

Result of an uncontrolled fracture and has no defined surface characteristics

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Fiber Splicing

• Splicing Techniques

▫ Fusion (permanent joint)

▫ Mechanical (semi-permanent joint)

 V-Groove Mechanical Splice

Elastic Tube Splice

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Fusion Splice

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   O  p

   t   i  c  a   l   F   i   b  e  r   F  u

  s   i  o  n

   S  p   l   i  c  e  r

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   O  p

   t   i  c  a   l   F   i   b  e  r   F  u

  s   i  o  n

   S  p   l   i  c  e  r

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V-Groove Mechanical Splice

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Elastic Tube Splice

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Optical Fiber Connectors

• Requirements for a good connector design:

▫ Low Coupling Losses

▫ Interchangeability 

▫ Ease of Assembly 

▫ Low Environmental Sensitivity 

▫ Low Cost and Reliable Construction▫ Ease of Connection

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Butt-Joint Connectors 

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Expanded-Beam Connectors

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