Laser-Fiber Connection

1
Chapter 5

• Laser-Fiber Connection

2
Content

• Launching optical power into a fiber
• Fiber-to-Fiber coupling
• Fiber Splicing and connectors

3
Coupling Efficiency
5-1
Source
Optical Fiber
4
Radiance (Brightness) of the source

• B Optical power radiated from a unit area of the
  source into a unit solid angle watts/(square
  centimeter per stradian)

5
Surface emitting LEDs have a Lambertian pattern
5-2
6
Edge emitting LEDs and laser diodes radiation
pattern
5-3
For edge emitting LEDs, L1
7
Power Coupled from source to the fiber
5-4
8
Power coupled from LED to the Fiber
5-5
9
Power coupling from LED to step-index fiber

• Total optical power from LED

5-6
5-7
10
Equilibrium Numerical Aperture
11
Examples of possible lensing schemes used to
improve optical source-to-fiber coupling
efficiency
12
Laser diode to Fiber Coupling
13
Fiber-to-Fiber Joint

• Fiber-to-Fiber coupling loss
• Low loss fiber-fiber joints are either
• 1- Splice (permanent bond)
• 2- Connector (demountable connection)

5-8
14
Different modal distribution of the optical beam
emerging from a fiber lead to different degrees
of coupling loss. a) when all modes are equally
excited, the output beam fills the entire output
NA. b) for a steady state modal distribution,
only the equilibrium NA is filled by the output
beam.
15
Mechanical misalignment losses
Lateral (axial) misalignment loss is a dominant
Mechanical loss.
5-9
16
Longitudinal offset effect
Losses due to differences in the geometry and
waveguide characteristics of the fibers
5-10
E R subscripts refer to emitting and receiving
fibers.
17
Experimental comparison of Loss as a function of
mechanical misalignment
18
Fiber end face
Fiber end defects
19
Fiber splicing
Fusion Splicing
20
V-groove optical fiber splicing
21
Optical Fiber Connectors

• Some of the principal requirements of a good
  connector design are as follows
• 1- low coupling losses
• 2- Interchangeability
• 3- Ease of assembly
• 4- Low environmental sensitivity
• 5- Low-cost and reliable construction
• 6- Ease of connection

22
Connector Return Loss