Extending the Lifecycle of Fiber Optic Cables

John CulbertPresident and Partner, Megladon Mfg. GroupAustin, TX

Introduction•Fiber optic cables are considered a weakness in optical networks

•Fiber cables are very fragile and sensitive to damage when handling

•Making fiber optics meet performance expectations and withstand field/installation handling are important challenges

•Industry Best Practices can help us achieve these goals, but robust connector technology can help us avoid the challenges

Outline

1) Common Physical and Mechanical causes for Performance Decline in Fiber Optic Connectors

•Inspection and evaluation criteria•Individual Factors•Case Study Discussions and Experimental Evidence•Industry Best Practices and Prevention Techniques

2) Proposed Solution through Tempering Technology

Scratches and Pitting

Scratches on the end face of a fiber optic surface drastically reduce its performance

Scratches are created by: Improper HandlingImproper CleaningInsertions into Inspection EquipmentMultiple Matings

Any time the end face contacts something other than a cleaning tool or another properly oriented fiber end face, there is the potential for scratches to develop

Scratches and PittingCase Study – International Electronics Manufacturing Initiative (iNEMI)

Scratches have a negative effect on Return Loss (RL), a key fiber performance indicator

Connectors under regular test environment use for 18 months saw return loss increased from -55db to an average of -42db

Conclusions: Scratches significantly degrade optical performance, especially return loss

Zone 3Ferrule Zone 1B

Cladding

Zone 1ACore

Zone 3Ferrule

Zone 1CEpoxy Ring

Zone 2Contact Area

Zone Descriptions

Inspection CriteriaFrom IPC-8497-1 Cleaning Methods and Contamination Assessment for Optical Assembly

Scratches and Pitting

Solutions

•Inspection – Follow inspection criteria. Any scratch can degrade performance•Proper Handling – protect end face at all times. Cap un-used connectors•Proper Cleaning – Use only approved cleaning products to prevent scratching•Carefully insert connectors into inspection ports – even this can create scratches

Prevention

•Proper Technician Training•More robust connectors that withstand handling

Contamination

Contamination

•Consists of dust, dirt and various other forms of debris•Difficult to avoid – Contamination happens anytime you remove the end cap and endface is exposed•Subject to the inspection guidelines mentioned earlier•Prevents even contact between cable end faces during mating•Blocks signal through core•80% of contaminants are silica particles

Contamination

During repetitive connector mating and de-mating cycles, dust particles can accumulate and redistribute at the connector end face.

Electrostatic charge force was one of the mechanisms responsible for the particle accumulation, redistribution and their movement in the core area.

Experimental Dust Applied

Case Study – International Electronics Manufacturing Initiative (iNEMI)

Contamination

5th Mating, 200xCase Study – iNEMI

Particles had a tendency to migrate specifically towords the core over the course of multiple matings

The core is EXTREMELY sensitive to contamination. The accumulation of dust particles seriously impaired fiber performance

A dust particle 5um wide in the core of a SM fiber assembly can effect more than one half of the signal

ContaminationBest Practices – Per IPC-8497-1

•Always inspect and clean fiber connectors before insertion•Clean with dry wipes and cleaning fluid

•Absorbent wipes of woven or entangled nature•Use IPA or other solvent to clean end face•Always clean with dry wipe again after solvent use

•Clean connectors again when re-inserting in another port•Careful – some contamination can lead to scratches during cleaning•See IPC-8497-1 for cleaning methodology

Solutions•Reduction in ESD Generation during cleaning•Smoother end face is more resistant to contamination gathering

Multiple InsertionsMultiple insertions can impact cable performance by:•Creating scratches•Increasing contamination•Migrating contamination towards core of fiber •Damaging epoxy ring

All connectorized fiber assemblies have a limited number of matings that they can withstand and still perform adequately

Multiple Insertions

Based on iNEMI research in 60 % of all examined LC connectors, a series of five repeated matings/demating operations resulted in an increase of IL of 0.5 to 1.1 dB due to particle movement from the ferrule and cladding areas towards the core

Case Study - iNEMI

Multiple Insertions

Exercise Cleanliness Best practices between matings

Verify both connectors are free of contaminants

Prevention

Solutions

Develop connectors that are resistant to the effects of multiple matings

Note that connectorized assemblies have a mating limit – replace cables that have exceeded their life cycle

Inspection Best Practices

Inspection Criteria - Revisited

Zone 3Ferrule

Zone 1BCladding

Zone 1ACore

Zone 3Ferrule

Zone 1CEpoxy Ring

Zone 2Contact Area

Zone Descriptions

Inspection Best PracticesKeys to Successful Inspection

Use Proper Inspection EquipmentBench Top ScopeHandheld Scope, Port Probe

Scratches can be identified @ 200x or 400x magnificationScratches and contamination on the core or cladding is unacceptable

If scratches, re-polish the connectorContamination should be cleaned, then connector re-inspected

Cleaning Best PracticesKeys to Successful Cleaning

Use Proper Cleaning Equipment and TechniqueDry Wipe on soft surface – Hard surfaces may damage ferruleCleaning CassettesIPA or other non-water based cleaning solventAlways use dry wipe after solvent use

Contamination on the core or cladding is unacceptableContamination should be cleaned, then connector re-inspected If contamination contains oils or residues, a solvent must be used

Cleaning Best PracticesFrom IPC-8497-1

Comparison of Cleaning Fluid Properties

Installation Guidelines

•Maximum Cable lengths

•Minimum Bend Radius

•Pull Tension Restriction

Fiber Mechanical Limits

Installation Guidelines

•Never Pull by the Connector•Use Pulling Eye or Grip for Trunks•Monitor Pulling Tension•Use “Straight Pull”•Do not twist cable

Proposed Alternative

Tempered Mating Surface

Accomplished by heat treating mating surface similar to a tempered windshield

Hardness of Mating Surface increases

Smoothness of mating surface increases

Tempered Mating Surface

FeaturesScratch ResistantPromotes minimum insertion loss and return lossHeat anneals mating surface to prevent contaminant leachingHeat “heals” any imperfections near the end of the glassSmooth surface reduces ESD build up (less friction)Smooth surface reduces build up of contaminantsExtended life spanEasy CleaningDurable enough to handle multiple matingsCompatible with all existing connectors

Tempered Mating Surface

BenefitsEasy to installRepeatable Network Performance and ReliabilityReduced Network DowntimeIncreased Customer SatisfactionSaves Time and Money

Tempered Mating Surface

Number of Matings VS Insertion Loss

Tempered Mating Surface

Conclusions

•Scratches and Contamination on Fiber Optic cables drastically reduce performance

•By following industry best practices, we can prevent some scratches and make better efforts to keep connectors clean from contamination

•Following these practices does not guarantee clean connectors and a scratch free surface

•Tempering (heat treated) technology exists that creates a scratch resistant mating surface and extends the life cycle of the product

References(1) “Accumulation of Particles near the Core during repetetive Fiber Conenctor Matings and De-matings.” NFOEC 2007 Presentation. Berdinskikh, Tatiana, March 29, 2007

(2) “Cleaning Methods and Contamination Assessment for Optical Assembly.” OFC 2006 Presentation. Berdinskikh, Tatiana, March 6, 2006

(3) “Degradation of Optical Performance of Fiber Optic Connectors in a Manufacturing Environment.” iNEMI Presentation. Berdinskikh, Tatiana

(5) IPC-8497-1 Cleaning Methods and Contamination Assessment for Optical Assembly

(4) “The Investigation of ESD effects on Mated Fiber Optic Connectors.” iNEMI Presentation. Culbert, John