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. 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.

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

7. Lateral (axial) misalignment loss: Cont…

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
Fiber end defects

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 putted 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

16. 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)]

17. Surface emitting LEDs have a Lambertian pattern:
[5-2]

18. Edge emitting LEDs and laser diodes radiation pattern
[5-3]
For edge emitting LEDs, L=1

19. Power Coupled from source to the fiber
[5-4]

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

21. Power coupled from LED to the Fiber
rs source radius
[5-5]

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

23. Example

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

25. Equilibrium Numerical Aperture

26. Examples of possible lensing schemes used to improve optical source-to-fiber coupling efficiency

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