Post on 21-Jan-2016
Chapter 5
Power Launching and Coupling
Content
• Launching optical power into a fiber
• Fiber-to-Fiber coupling
• Fiber Splicing and connectors
Coupling Efficiency
s
F
P
P
source the from emittedpower
fiber the into coupledpower [5-1]
Source Optical Fiber
sP FP
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)
FFL log10]dB[ [5-8]
Mechanical misalignment losses
Lateral (axial) misalignment loss is a dominant Mechanical loss.
2/12
2step, 21
2arccos
2
a
d
a
d
a
d
a
AcommF
[5-9]
Lateral (axial) misalignment loss: Cont…
Longitudinal offset effect
Losses due to differences in the geometry and waveguide characteristics of the fibers
ERE
RF
ERE
RF
aL
aaa
aaL
NANAfor NA
NA
for
)log(20)(
)log(20)([5-10]
E & R subscripts refer to emitting and receiving fibers.
Losses due to differences in the geometry and waveguide characteristics of the fibers
ERE
RF
ERE
RF
aL
aaa
aaL
NANAfor NA
NA
for
)log(20)(
)log(20)(
[5-10]
E & R subscripts refer to emitting and receiving fibers.
Experimental comparison of Loss as a function of mechanical misalignment
Fiber splicing
Fusion Splicing
1) Fusion splicing involves butting two cleaned fiber end faces and heating them until they melt together.
2) 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.
3) Fiber ends are first prealigned and putted together under a microscope with micromanipulators. 4) The butted joint is heated with laser pulse to melt the fiber ends so can be bonded together.
V-groove optical fiber splicing
1) Mechanical splices join two fibers together by holding them tightly with a structure or by gluing the fibers together.
2) 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
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
Connector Return Loss
Power Coupled from source to the fiber
210
2220
22stepLED, 2)NA( nBrBrP ss
rs is the source radius
Power coupling from LED to step-index fiber
• Total optical power from LED:
022 BrP ss
arP
r
a
arP
Pss
s
ss
if )NA(
if )NA(
2
2
2
stepLED,
Example
Power coupling from LED to graded index fiber
022 BrP ss
Where rs <a
HW: Try rs >a