1. Power Launching and Coupling
Chapter 5
Power Launching and Coupling

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. Fiber-to-Fiber Joint 1) Fiber-to-Fiber coupling loss:
2) Low loss fiber-fiber joints are either:
1- Splice (permanent bond)
2- Connector (demountable connection)
[5-8]

5. Mechanical misalignment losses
Lateral (axial) misalignment loss is a dominant
Mechanical loss.
[5-9]

6. Lateral (axial) misalignment loss: Cont…

7. Example

8. 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.

9. Losses due to differences in the geometry and waveguide characteristics
of the fibers
E & R subscripts refer to emitting and receiving fibers.
[5-10]

10. Experimental comparison of Loss as a function of mechanical misalignment

11. Fiber end face
Before connecting or splicing fiber ends must be properly faced to avoid losses and to improve the coupling efficiency.
The end faces should be polished until all the scratches are removed and they become smooth.
The process involves following steps:
The fiber is scratched to create a stress concentration at the surface.
Fiber is then bent over a curved form with applied tension to produce stress distribution.
Maximum stress occurs at scratch point and crack starts propagating through fiber.

12. Fiber splicing Fusion Splicing
Fusion splicing involves butting two cleaned fiber end faces and heating them until they melt together.
Fusion splicing is normally done with a fusion splicer that controls the alignment of the two fibers to keep losses as low as 0.05 dB.
Fiber ends are first prealigned and butted together under a microscope with micromanipulators.
The butted joint is heated with laser pulse to melt the fiber ends so can be bonded together.

13. V-groove optical fiber splicing
Mechanical splices join two fibers together by holding them tightly with a structure or by gluing the fibers together.
Mechanical splices may have a slightly higher loss and back reflection. These can be reduced by inserting index matching gel.
3) V groove mechanical splicing provides a temporary joint i.e fibers can be disassembled if required. The fiber ends are butted together in a V – shaped groove
Groove :اخدود

14. 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

15. Connector Return Loss

17. Fresnel Reflection or Reflectivity

18. Example

19. Power Coupled from source to the fiber
rs is the source radius

20. Power coupling from LED to step-index fiber
Total optical power from LED:

21. Example

22. Power coupling from LED to graded index fiber
Where rs <a
HW: Try rs >a

23. Equilibrium Numerical Aperture

24. Laser diode to Fiber Coupling
BW degree, but area is small use lenses