Launch Condition Analysis

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Fill Conditions

A multimode fiber can be filled anywhere from highly underfilled,
where only one mode is excited (single mode), to overfilled, where
all possible modes are excited.
Overfilled

100
80
60
40
200Underfilled

-40

-20

020

40

-40

-20

020

40

100
80
60
40
20
0100
80
60
40
200-40

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-20

02040

Mandrel Wrapping

In a multimode fiber, there are many possible
optical path for the light to travel through:à Different Modes:•The lower order modes are excited by lightlaunched near the center of the core.
•The higher order modes travel at the outer
diameter of the core.
Higher order modes or Cladding modes areattenuated by bending the fiber, for example
with a mandrel wrap.
Lower order modes à center à tightly coupled
Higher order modes à loosely coupled

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Effect of Launch Condition

Depending on which modes, higher order or lower order, arebeing launched from one fiber into the next fiber, the measured
insertion loss of a non-ideal connector varies.

Lower order modes being coupledLaser

2.5

Lost higher order modes

Losss [dB]

21.5
10.5
00

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51015
CPR [dB]

202530Coupling Power RatioMeasuring Coupling Power RatioMeasuring High-Order Mode PowerStandards

TIA 526-14A
IEC 61280-4

Fiber optic communications subsystems test procedures – Part 1-4:
General communications subsystems –CPR Measurement

FOTP-43 TIA/EAI-455-43A

Output Near-Field Radiation Pattern Measurement of Optical
Waveguide Fibers

FOTP-177 TIA-455-177B
IEC-60793-1-43

Optical Fibers – Measurement Methods and Test Procedures –Numerical Aperture

IEC 61280 1-4

Fiber optic communications subsystems test procedures – Part 1-4:
General communications subsystems –Light source encircled flux
measurement methods

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Measurement Principles - Nearfield

Static detector
CCD

Scanning
Detector

Intensity Profile

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Encircled Flux EF

Encircled flux describes the measurement of light power
distribution from the center of the core to the cladding withrespect to the radial distance. The fraction of cumulative
near field power to total output power as a function of radial
distance from the centre of the core.
It is often quantified as the radius from the center of the fiber
required to encircle 25% and 75% of the light energy
through the fiber.
This value is a crucial factor in ensuring the required datatransmission rate in Gigabit Ethernet systems.

62.5 DIA

1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0

Typical power distribution

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0510

15

20

253035

EF Template.918 ATTENUATION DEVIATION CONSTRAINTS, 850 nm, 50 um
75% SHAPE TOL, LINK CONSTRAINTS (uM SHIFT x #CMPTS, dB Tol) =(2.0 x 2,.07 dB), (3.0 x 2,.07 dB), (4.0 x 2,.07 dB), (5.0 x 2,10%), (2.0 x 5,.07 dB), (3.0 x 5,10%), (4.0 x 5,10%), (5.0 x 5,10%).6.4.5TEMPLATETARGET
OFL

0.1.2

.3

NORMALIZED EF.7.8

EF RADIAL BOUNDS
5 um, .0693 - .1069
10 um, .2706 - .3841
15 um, .5874 - .6997
20 um, .8972 - .9254
22 um, .9658 - .9765

02468101214

RADIUS (um)

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16182022242628EF Requirements per IEC 61280-4-1

Table E1 – EF requirements for 50 mm core fibre cabling at 850 nm
EF Tolerance Range – 50mm, 850 nm, 2X+5X, .07 dB Threshold
Radial Offset (mm)510152022

EF Lower Bound
0.06930.2706
0.58740.89720.9658Target0.08800.32710.64280.9112
0.9711EF Upper Bound
0.10690.38410.69970.9254
0.9765

Table E2 – EF requirements for 50 mm core fibre cabling at 1300 nm
EF Tolerance Range – 50mm, 1300 nm, 2X+5X, .07 dB Threshold
EF Lower Bound
TargetEF Upper Bound
Radial Offset (mm)50.0700
0.0894
0.1089100.2756
0.33200.3889150.5969
0.65070.7059200.9094
0.91780.9263220.9694
0.97330.9772

Table E3 – EF requirements for 62.5 mm fibre cabling at 850 nm
EF Tolerance Range – 62.5mm, 850 nm, 2X+5X, .07 dB Threshold
EF Lower Bound
TargetEF Upper Bound
Radial Offset (mm)50.0425
0.05470.0671
100.1677
0.20960.2517150.3684
0.43660.5052200.6333
0.68920.7460260.9202
0.93280.9455280.9716
0.97700.9824

Table E4 - EF requirements for 62.5 mm fibre cabling at 1300 nm
EF Tolerance Range – 62.5mm, 1300 nm, 2X+5X, .07 dB Threshold
EF Lower Bound
TargetEF Upper Bound
Radial Offset (mm)50.0425
0.05480.0672100.1677
0.21000.2525150.3690
0.43740.5062200.6355
0.69020.745726
0.9236
0.9335
0.943528
0.9734
0.97740.9815

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Numerical Aperture

The Numerical Aperture NA is the sine of the half angle of a fiber’slight acceptance cone. All modes of light entering the fiber at angles
less than the NA will be confined to the core of the fiber.
NA is determined from the measurement of the far-field opticalpower distribution exiting from a two meter length of fiber.

CladdingOLarger NA à larger light acceptance cone

Coreq1

Farfield Measurement
2

Fiber Axis

Angular Intensity, I ()NA = sin

125v

Emission Angle,

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q + q52

Launch Condition Measurement

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OP1021 Launch Condition Analyzer

The OP1021 Launch Condition Analyzer is a convenient andcompact benchtop nearfield and farfield scanner for opticalfibers. Coupled with the software package, OPL-LCA, theuser can scan and easily plot both the nearfield and farfield
patterns of almost any fiber.
The OP1021 comes with 2 internal sources. These areusually one 850nm LED and one 1300nm LED. Both sources
are coupled into a 105/125um step index fiber to provide an
overfilled launch condition into both 50um and 62.5um fibers.

Farfield Measurement• +/- 0.5 radians scan angle• 0.1um step size
• measure numerical aperture NAAdapters forFerrules: 1.25, 1.6, 2, 2.5mm

Nearfield Measurement• +/- 250 µm scan range• 0.1 µm step size
• Meets IEC Standards to measure Encircled Flux
• Auto-align feature to center and focus NearField scanner
Overall Features• Wavelength Independent: measures 850nm to 1625nm• Farfield and Nearfield analysis in one instrument• Integrated OPL LCA software• Directly links to Excel spreadsheet – quick print

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