Using and Characterizing
Bend-Insensitive Multimode Fiber in Data Centers
Tony Irujo, Sales Engineer
Nov. 13, 2014
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Agenda
•
•
Quick Review of Bend-Insensitive Multimode Fiber (BIMMF)
–
Definition
–
Benefits
–
How it works
Considerations for Testing BIMMF Links
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BIMMF – Quick Review
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Standard vs. Bend-Insensitive Multimode Fiber –
Macrobend Specifications
Macrobend Test
100 turns
37.5 mm radius
Diameter
36.8 mm radius
Standard 50/125
fiber
Bend Insensitive
Multimode Fiber
850 nm d 0.5dB
1300 nm d 0.5dB
850 nm d 0.5dB
1300 nm d 0.5dB
850 nm d 1.0dB
1300 nm d 1.0dB
850 nm d 0.1dB
1300 nm d 0.3dB
NOT DEFINED
850 nm d 0.2dB
1300 nm d 0.5dB
Baseball
2 turns
15 mm radius
22.4 mm radius
Golf Ball
2 turns
7.5 mm radius
9.0 mm radius
Dime
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Benefits of Bend-Insensitive Multimode Fiber
•
BIMMF provides an opportunity to re-design cable management for improved space efficiency
•
Denser, more compact trays and shelves improve airflow and cooling in data center racks
and cabinets
•
Smaller bend radii allow shorter distances between an adapter faceplate and door front.
•
BIMMF provides relief from strict cable management policies for standard multimode fiber,
but bend radius control and good installation and routing practices must not be abandoned!
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Multimode Channel Insertion Loss Budgets Declining
•
Increasingly tight system attenuation requirements!
1.5 dB for 40/100 Gb/s
Ethernet on OM4
fiber!!
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Improving Channel Insertion Loss
Improved Macrobend Performance
(Lower Bend Loss)
Lower fiber attenuation for
lower cable attenuation
Tighter geometries to lower
connection loss
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What Makes BIMMF Bend-Insensitive?
Standard Multimode Fiber
Bend-Insensitive Multimode Fiber
Guided Modes
Multimode Fiber Core Index of Refraction Profile
Standard Core
Cross-Section
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Leaky Modes
Trench Added to
Index Profile for
Improved
Macrobend Performance
BIMMF Core
Cross-Section
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What Makes BIMMF Bend-Insensitive?
Standard Multimode Fiber
Index Profile
(Graded Index)
n1
n2
n1
n2
Bend-Insensitive Multimode Fiber
Index Profile
(Graded Index,
with trench)
n1
n1
n2
n2
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Standard Multimode Fiber and BIMMF Fiber Appearance
“Halo” provides a visual
indicator of BIMMF
Core
A properly designed
BIMMF trench has
no effect on
system performance!
Clad
BIMMF
“Halo”
Core
Clad
Connector
End Face Photographs
Of Standard Fiber
and BIMMF
Standard 50 µm Fiber
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BIMMF 50 µm Fiber
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Identification of BIMMF
Method 2: Read the Jacket Printing
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Identification of BIMMF
Method 3: Test the Jumper
•
Two turns around a 10 mm radius mandrill
•
Attenuation less than
0.2 dB  Bend insensitive Multimode Fiber
•
Attenuation greater than
0.2 dB  Standard Multimode Fiber
This method is the best way to validate
if a jumper is bend insensitive.
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Testing BIMMF Links
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Use Encircled Flux Compliant Launch (EFL)
•
Recommend using Encircled Flux compliant launch.
•
With BIMMF, light in the “halo” region can travel 10’s of meters (leaky modes),
resulting in poor characterization of performance.
“Leaky” Modes
n1
n2
•
Using an EF Launch helps mitigate this effect.
•
CPR / HOM launches are better than Overfilled Launch (OFL) but not as good as EFL.
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Use non-BIMMF, Reference Grade Test Cords
•
•
Launch Cord
–
Using a BIMMF test lead can result in as much as 0.5 dB error
in the loss measurements.
–
Reference grade cords help preserve encircled flux condition.
Receive Cord
–
Using a BIMMF receive cord can result in ~0.1 dB error, usually overly optimistic.
–
Helps filter any leaky modes that may result in measurement errors.
–
Ensures that core size and NA of jumper being tested are near nominal target.
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Testing BIMMF Links
Launch Cord
Std MMF
Large area
Detector
EFL light
source
Receive Cord
Std MMF
Launch Cord
Std MMF
EFL light
source
Detector
power is
zeroed
A
B
Large area
Detector
Insertion
loss is
measured
Link to be tested
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Example of a Duplex Link Test
Encircled
flux launch
conditioner
Link being tested
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Conclusion
•
BIMMF is being widely deployed.
•
BIMMF provides benefit:
–
Reduced fiber management footprint.
–
• (Must still adhere to bend radius control.)
Reduced Channel Insertion Loss.
•
BIMMF interoperates seamlessly with standard MMF.
•
Due to leaky modes in BIMMF, there are considerations for link testing:
•
–
Use Encircled Flux Launch condition.
–
Use non-BIMMF, reference-grade test leads at launch and receive.
BIMMF standardization is nearing completion in IEC. Will then be adopted in TIA.
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Thank You
Visit www.ofsoptics.com for more information.
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