Session 4: Termination and Splices

Session 4:

Termination and Splices

2

FO Connectors Specifications Specifications

Loss Repeatability Environment (temp, humidity, vibration,

etc.) Reliability Back reflection Ease of termination Cost

3

Connector Ferrules

4

Connector End Finishes

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Connector Termination Processes

Epoxy/polish Hot-melt (3M trademark) Anaerobic Crimp/Polish Crimp/cleave Mechanical Splice

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Termination - Adhesive/Polish

Stripping The Fiber

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Connector Termination

Applying Adhesive

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Crimping To The Cable

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Cleaving The Fiber

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“Air Polishing”

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Polishing

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Microscope Inspection

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Direct With Core Illuminated

Angle View

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Fiber Optic Splices Permanent terminations for fiber Specifications

Loss Repeatability Environment Reliability Back reflection Ease of termination Cost

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Fiber Optic Splices

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Fiber Optic Splices - Fusion

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Fiber Optic Splices - Mechanical

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Fiber Optic Splices - Cleaving

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Connector & Splice Loss

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Back Reflection (Return Loss) Light reflects at surfaces

between materials of different indices of refraction

Glass to air interface yields about a 4% reflection

Occurs at fiber optic joints

Splices have lower back reflection due to fusing or using index matching fluid

Domed (PC) fiber end faces can minimize air to reduce back reflection

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Continuity Testing With visual tracer or fault locator

Tracer is flashlight or LED Fault locator uses visible red laser

Useful for verifying mechanical splices or prepolished/splice-type connectors

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Insertion Loss Testing

Simulates actual system operation

23

OTDR Testing OTDR testing

OTDRs OTDRs are valuable tools for testing fiber

optics. They can verify splice loss, measure length and find faults.

used to create a blue print of fiber optic cable when it is newly installed.

Later, comparisons can be made between the "blue print" trace and a second trace taken if problems arise.

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OTDR Testing

OTDRs work like "optical RADAR," sending out a test pulse and looking for return signals.

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OTDRs See Backscattered Light

Scattering is the primary loss mechanism in fiber

Some light is scattered back to the source ~1 millionth of signal at 1310 nm

OTDR process Send out high power signal Gather backscatter light Averages signal Display backscatter signal over time

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Typical Result

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Information In The OTDR Display

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Fiber Attenuation and Distance

Attenuation Coefficient = (Psource –Pend)[dB]/fiber length [km]

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2-Point Loss

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Least Squares Loss

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Connector or Splice Loss By 2-Point Method

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Connector 2-Point Loss

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Connector or Splice Loss By “Least Squares”

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Connector Least Squares Loss

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Back Reflection (Optical Return Loss)

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Connector Reflectance

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OTDR Launch Cable

Pulse Suppressor /Testing Initial Connector

Testing Far End Connector

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OTDR Ghosts

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OTDR Pulse Width

Wider pulse = more energy = more range

But wider pulses mean less resolution 1 us => 3x108 m/s x 1x10-6 s = 300 m 1 ns => 3x108 m/s x 1x10-9 s = 0.3 m

41

OTDR Resolution

1. to see an event close to the OTDR;2. to see two events close together.

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OTDRs and Multimode Fibers

• Laser test signal is smaller than core• Underestimates loss significantly

• OTDR is no substitute for insertion loss test

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Good OTDR Traces

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Improving OTDR TracesUsing index matching fluid

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OTDR Measurement ParametersApproximate Settings

Wavelength (850/1300 MM, 1310/1550 SM) generally do both wavelengths

Range (2 to 100+ km) Set to greater than 2X cable length

Pulse width (10 m to 1 km) Set as short as possible for best

resolution Averaging (1 to 1024 averages)

For short cables, 16-64 averages

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Range

• A 5.2 km link taken at ranges of 2 km (green), 5 km (brown) and 10 km (blue).

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Wavelength

• A single fiber at both 850 nm (green) and 1300 nm (blue) wavelengths.

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Pulse Width

• A single fiber measured at shortest (blue), median (brown) and longest (green) pulse widths.

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With 30 ns and 90 ns Pulse Width

90 ns (equivalent to 18 m) pulse width)

30 ns (equivalent to 6 m) pulse width

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Averages

no averaging

averaged 1024 times

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Index of Refraction nor nominal velocity of propagation (NVP)

we need to know n to calibrate the measured length of the fiber.Generally the fiber length is

~1% more than the cable to allow for cable stretching

the fault distance will be at ~ 99% of the distance shown by the OTDR

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1. Items 1,2,3 & 4 are all fiber segments. They all have different slopes. Why?

2. Why does the end of the fiber (5) have such a high reflection?

3. How what is the total length of the fibers ? a. The fibers in each segment have

different attenuation coefficients.b. It is cleaved neatly.c. 35.63 km

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What are we measuring here?

Length and loss or attenuation coefficient of a fiber segment between splices.

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1. What is the splice loss measured here?

2. What is the approximate pulse width used for the OTDR measurement?

a. Splice loss, 0.28 dBb. 300 m

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a. What is event 2 ?b. On very long fibers, what do we change on the

OTDR to get more distance?c. Why is the reflection at the end (5) so strong? d. Why does the trace look more “noisy” at point 3

than point 4 ?

b. Pulse width and range or length of the trace

a. Reflective splice or connector

d. As the OTDR trace goes further from the instrument, the power loss causes worse signal to noise performance – the trace will get noiser as it gets closer to the distance limit.

c. It’s is very nicely cleaved.

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1. This is an extremely long fiber. How long? How much loss?176.67 km, 39.13 dB2. Does it look like this is close to the limit of the OTDR range? Why?Yes, the trace is getting very noisy.

3. Why is there no reflective pulse at the end?It is not well cleaved.

Any Questions?

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Documents

Session 4: Termination and Splices