Tài liệu Continuous Improvement in Fiber Optic Cable Assembly pptx

To help ensure network integrity, service providers have turned to standards organizations, suppliers and independent test agencies to develop programs that can ensure fiber optic cable

Continuous Improvement

in Fiber Optic Cable Assembly

Randy Reagan

Sean Grenon

Curtis Hill

Network Service Providers continue to operate under increasing demands for guaranteed service reliability Providers that are actively deploying new technology and networks are carefully scrutinizing all components that go into

a deployment for performance and reliability Fiber optic cable assemblies are

no exception To help ensure network integrity, service providers have turned

to standards organizations, suppliers and independent test agencies to develop programs that can ensure fiber optic cable assembly performance and reliability Standards organizations have responded by developing

comprehensive requirements such as those found in GR-326-CORE, Issue 3

“Generic Requirements for Singlemode Optical Connectors and Jumper Assemblies.” Suppliers have responded by developing improved fiber optic connector technology resulting in cable assembly products that fully meet and exceed these standards Suppliers have also focused on process improvements across a wide range of areas including product materials, facilities,

automation, testing, training and quality control Independent test agencies have responded by developing thorough test programs that validate connector designs and cable assembly production processes and to ensure connectors meet requirements for both inside plant and outside plant applications The results of continuous improvement efforts have been profound Products offered today are capable of consistent performance that exceeds standards over a wide range of applications and environmental conditions By

comparison, connectors manufactured recently offer incrementally better performance than connectors manufactured just a few years ago By selecting products that have been certified to conform to standards, service providers reap the benefits of an overall more reliable and economic solution

Fiber Optic Cable Assemblies

Today’s telecommunications environment continues to

be a landscape that is constantly changing The

landscape is shaped by many factors including changes

in regulatory rulings, increased competition, new

technology, innovation and the status of the economy in

general For instance the Telecommunications Act of

1996 and subsequent regulatory rulings encouraged

increased competition among service providers and

resulted in an increase of fiber deployment During that

expansion period of the late 1990’s, the fiber optic

industry experienced a scarcity of fiber and components

Suppliers scrambled to expand capacity but still could not

meet the demand of network expansion In that

scenario, where demand exceeded supply, service

providers were often constrained to purchasing

components that were less than optimal

Then, in 2001, the bubble burst for the

telecomm-unication industry Since then we have witnessed a

dramatic reduction in demand Today we are seeing a

paring of competitors to fewer service providers that are

leaner and stronger The contraction in the economy and

telecommunications market has left the remaining

service providers in the driver’s seat with respect to

component procurement Today service providers can

select components such as fiber cable assemblies based

on higher performance and lower cost than ever before

While the telecommunication market has contracted,

service providers are still engaged in network construction

and expansion New networks are needed to service

increased bandwidth requirements in the enterprise and

consumer markets Service providers are deploying new

networks targeting new customers and new revenues

Providers find that in today’s competitive environment,

reliability is more important than ever to their end

customers especially with the increased bandwidth placed

on individual fibers Reliability is also paramount when

fiber cable assemblies are placed in outside plant

(uncontrolled) environments closer to customers

Service providers that are actively deploying new

technology and networks including Fiber-to-the-Premises

(FTTP) are planning to use fiber connectors and cable

assemblies Since there is no way to predict which

end-users will request new services, the optical connector

becomes a key point of flexibility Providers building new passive fiber plants want to build it right the first time and then not have to replace components in the future Therefore they are scrutinizing all components for performance and reliability with a view toward performance over the long term While fiber optic connectors and cable assemblies may represent a small fraction of the overall network cost, they continue to be

a vital link in connecting the entire network together Service providers have learned from experience that the network is only as good as the weakest link and they do not want the weakest link to be fiber cable assemblies

Cable assembly suppliers are faced with seemingly impossible demands; improve product performance, quality, and reliability, and significantly reduce costs The approach taken by leading suppliers is to focus on overall continuous quality improvement This includes incremental changes to product designs to optimize performance and mechanical strength Overall quality improvement also involves changes to the assembly process including improvements in the areas of facilities, training, automation, calibration, testing and quality control Furthermore suppliers have taken initiative to provide independent certification of the improved products and processes As a result of quality and process improvement efforts, manufacturers can now provide a new level of performance and reliability previously not available while passing significant cost savings along to end users

Key Performance Requirements

As advances in systems and components result in higher throughput in communication networks, performance expectations on fiber optic cable assemblies have become more stringent Several key performance parameters for standard SC and LC fiber optic cable assemblies are discussed in this section

Insertion Loss - Many applications being deployed just a few years ago with older style connectors (e.g Biconic,

ST, FC, D4) had a typical insertion loss of 0.5dB That was the best performance available at the time Networks were often constrained by insertion loss of passive connectors Newer applications and network deployments can draw from newer products with

improved performance Insertion loss of less than 0.2dB

is commonplace in SC and LC jumpers deployed today

Many suppliers are even providing ultra-low-loss cable

assemblies1having typical loss less of than 0.1dB These

lower-loss connectors enable network deployments to be

more flexible than ever before

Reflectance – Low reflectance will continue to be a critical

parameter in network deployment especially for high

bit-rate digital transmission and for broadband analog

applications Therefore network planners today specify

connectors and cable assemblies with low return loss

Today’s Ultra Physical Contact (UPC) polished connectors

can easily provide a return loss of less than -55dB Many

suppliers are now able to surpass this mark and provide

typical return loss of less than –58dB with a UPC polish

End Face Geometry - In order to achieve ultra-high

performance with common SC and LC connectors, the

polished end face geometry of the ceramic connector

ferrule is carefully defined to ensure that physical contact

is maintained between mated connectors Critical

parameters including radius of curvature, fiber protrusion

and apex offset are measured on ceramic zirconia

ferrules and compared to standard tolerance that has

been adopted for UPC connectors

Intermateability – Mechanical connectors such as the SC

connectors utilize a latching mechanism for joining

mated connector plugs The latching mechanism is

defined in terms of the specific geometry of the

connector plug, adapter and associated latches The

ferrule position relative to the latches is also carefully

defined dimensionally to ensure proper alignment and

contact force The specific dimensions and tolerances for

optical connectors are contained in the FOCIS (Fiber

Optic Connector Intermateability Standard) require-ment

documents issued under TIE-EIA-604 The performance

of a connector can, in large part, be determined by

conformance to these dimensions

Mechanical Strength – Fiber optic connector performance

is also characterized by the strength of the assembly in

normal handling and use Several standard mechanical

tests have been developed to measure the cable assembly

ability to stand up to proof test loads Tests are defined

for straight pull and side pull to represent normal handling and the strength of the connection

Miniature Cord Size – Ever space-conscious service providers are deploying smaller diameter cable assemblies to avoid congestion when installing new equipment Whereas cords of a few years ago were 3mm

in diameter, today’s cords are 1.6 mm to 2.0 mm in diameter Therefore, the customer wants a much smaller package and is not willing to sacrifice any of the performance objectives already mentioned here to get it

Universal Applications – Traditional fiber optic cable assemblies have most often been deployed into controlled indoor environments However more and more intended applications include Fiber-to-the-Premises require fibers to be used in uncontrolled outdoor environments Instead of having two different products, one controlled and the other uncontrolled, users have proposed to have one cable assembly that will serve either environment Therefore all of the performance parameters discussed in this section are now expected to perform over an environmental range of –40C to +85C

so that the same product can be used in either indoor or outdoor applications

Reliability Requirements

To evaluate connector performance and reliability, service providers have turned to the industry standards organizations and independent test agencies to develop improved standards and test programs that can ensure reliability Telcordia GR-326-CORE, Issue 3, “Generic Requirements for Singlemode Optical Connectors and Jumper Assemblies”2, provides a comprehensive standards document that is widely recognized as the most rigorous baseline for fiber optic cable assembly performance and reliability In addition, intermateability standards published in TIA Fiber Optic Connector Intermateability (FOCIS)3 documents cover various connectors and dimensions critical to mechanical intermateability Also test methods published by the EIA/TIA are widely regarded as the most complete and rigorous standards for testing optical components The Telcordia and EIA/TIA standards contain the best collective technical rationale and cover all of the performance

criteria expected in network applications including

optical, environmental and mechanical requirements

Testing a product to these standards provides a

comprehensive and accurate predictor of a product’s

ability to perform throughout its expected service life

The GR-326-CORE, Issue 3 test sequence is designed to

thoroughly shake out any weakness in the connector

design The test procedure involves measuring the optical

performance while subjecting the cable assembly to the

following sequence

Baseline Performance

Insertion Loss

Reflectance

Endface Geometry

Environmental Tests

Thermal Aging, 85°C, uncontrolled humidity, 7 days

Thermal Cycling, -40°C to 75°C, uncontrolled

humidity, 21 cycles in 7 days

Humidity Aging, 75°C, 95% RH, 7 days

Humidity/Condensation Cycling,-10°C to 65°C, 90%

RH, 14 cycles in 7 days

Post-Condensation Thermal Cycling

Mechanical Tests Vibration

Flex, 100 cycles

Twist, 9 cycles, +360°, -720°, +360°

Proof

Transmission with applied load, straight pull

Transmission with applied load, side Pull

Transmission with applied load, 130°

Impact

Durability

Rematability

Connector Installation

End of Test

Insertion Loss

Reflectance

Endface Geometry

Fiber optic cable assembly suppliers strive to satisfy these

standards The goal is to provide customers with a reliable

product that can stand up to the conditions of these tests

over the life of the product To gage performance suppliers voluntarily submit products to independent 3rd party test agencies These agencies conduct the testing or witness the testing on the product and attest to the validity of the results This may be in the form of a “Certificate of Compliance” or a “Verification Report.” In addition, a supplier may elect to qualify a product for either indoor (controlled environment) or outdoor usage (uncontrolled environment) As described in detail in Telcordia Technologies Special Report SR-4226 4, a Level 1 certification is for indoor use and a Level 2 certification is for both indoor and outdoor use In either case, a full test report with all the raw data is submitted from the test agency directly to the service provider showing how well the product stands up to this rigorous test plan

Product Improvements

The typical connectors specified for networks today, including SC and LC5, are not the same designs of just a few years ago While these designs may look the same and interconnect the same, the designs have evolved and been continuously improved Today’s SC and LC fiber optic connectors and cable assembly designs have been improved to the point where they now provide higher performance and greater reliability than ever Often, changes to materials and components are required to achieve enhanced performance and improvements in cable assembly yields Changes are implemented only after thorough qualification testing to ensure that performance and reliability can be maintained while achieving low product costs The following are examples of areas where design improvements have been implemented:

Ferrule Material – The single mode cable assemblies specified today utilize high quality and high precision zirconia ferrules However not all zirconia ferrules are created equally Therefore, a careful application of material science has been used to understand the hardness and crystalline composition of various ferrule designs Through this research, we can establish the optimal ferrule material composition for achieving consistent end-face geometry and consistency of other performance parameters under conventional polishing techniques The ferrule material is not only optimized at ambient temperatures, but also over

a range of temperature and humidity conditions

Fiber-Ferrule Geometry - Ceramic ferrules are specified

with closely controlled outside diameter, inside diameter

and concentricity The ferrules are readily available with

precision concentricity and inside diameters that are

closely matched to the fiber The end result in assembly is

a tight fit of fiber to ferrule and extremely centered fiber

A centered fiber produces consistently excellent insertion

loss and with physical contact extremely low reflectance

Plastic Materials - Stability of the plastic materials play an

extremely important role in the performance of the

connector and of the lifetime reliability Materials used in

fiber optic cable assemblies must be carefully specified to

achieve performance and reliability over a range of

applications and environmental conditions For instance

the plastic selection significantly can influence the

intermateability especially at extreme temperatures

Therefore the plastics specified for the connector body

components are optimized to produce the desired

stability over a range of harsh environmental conditions

Epoxy Adhesive – One of the key areas of fiber cable

assembly design is the epoxy used to lock the fiber into a

stable position inside the ferrule Under high temperatures,

the fiber can creep and piston if the epoxy is not optimized

for stability over a range of environmental conditions6 In

addition, air bubbles intermixed with the epoxy can cause

havoc if allowed to enter the ferrule, therefore, care in

handling during mixing becomes crucial The art of

selecting epoxy is not as easy as reading a specification

sheet The designer needs to consider the way in which the

epoxy is mixed and applied and then how the fiber is cured

An analysis of these variables and careful experimentation

and qualification can lead to a stabilized epoxy selection

over sustained environmental conditions Often, the course

is to select premixed, degassed and frozen epoxy with the

desired formulation needed to meet the requirements

Mechanical Crimp and Boot – In order to meet stringent

proof test requirements, the designer is faced with a

delicate balance of putting enough pressure on the fiber

cable while making sure that the glass is not stressed

This design problem is especially challenging when trying

to meet the strength requirements using 1.60 mm cord

or 2.0 mm cord However a careful analysis the design

can produce the optimal crimp geometry and pressure

even for the smallest miniature cord This crimp is then translated into connector barrel and crimp sleeve materials and dimensions In addition, the actual crimp dimensions are optimized for automated crimp to achieve a uniform pressure consistent from one connector to the next Finally, the boot is specified to add side-pull strength that allows the connector to stand

up to the rugged mechanical test while maintaining support for the fiber so that bending loss is not excessive

Process Improvements

The entire assembly process for fiber optic cable assemblies

is engineered with the aim of producing connectors that exceed performance in the Telcordia standards Total quality management is utilized to improve every aspect of the process with a cumulative result that is often significant Some of the key process areas improved include:

Facilities - Particulates and contaminants having sub-micron dimensions can adversely affect key fiber optic cable assembly procedures such as polishing and testing

To achieve the high performance now required in fiber optic cable assemblies requires an upgrade of the manufacturing facility to improve the environment This often involves using clean room facilities to provide a controlled and monitored atmosphere for finishing and testing cable assemblies

Training - An updated training program is also instrumental

in achieving new levels of performance A thorough training program emphasizes proper techniques and procedures for cable assembly This includes both basic training and specialized training techniques for high-performance assembly including training in polishing, testing or other specific procedures It may also be necessary to provide appropriate training on clean room techniques in order to achieve maximum benefits of the new environment

Assembly - In the past, the cable assembly process has typically been dominated by manual operations Currently there is a trend towards increased automation throughout the process Automation is especially effective where designs are standardized; for instance, where a single cable and connector type are specified Automated tasks

result in greater consistency and improve the throughput

of the overall assembly line The trend toward automation

has helped to improve yields and performance in the

overall process Manufacturers currently use automation in

the stripping process to help improve consistency and

eliminate occurrence of fiber breakage Automated crimps

are utilized to overcome inconsistencies in hand operation

by applying uniform and complete pressure thus making

the mechanical joining of fiber cord to connector much

more reliable Automated mixing and dispensing machines

bring consistency to epoxy application Newer automated

curing ovens provide complete control of the cure

temperature thus providing a uniform temperature

distribution and duration of epoxy cure New cure cycles

have been developed to provide optimized temperature

and cure duration to ensure a totally cured epoxy Each

parameter of the polishing procedure is optimized to bring

tighter controls to the assembly process The process also

incorporates automated data acquisition and recording so

that product performance can be monitored and improved

using Statistical Process Control (SPC)

Calibration - Equipment used in the manufacture of fiber

optic cable assemblies is subject to repeated use and

wear For instance, stripping tools and polishing pucks

wear over time Polishing paper can wear out throughout

the day Test instruments need periodic adjustments and

recalibration If any one piece of equipment is out of

calibration, it can result in reduced throughput and cost

inefficiencies Therefore, it is imperative to institute a

program for calibration and periodic recalibration for each

piece of equipment used in the cable assembly process

Assembly equipment in the manufacturing cell including

stripping machines, crimping machines, epoxy application

machines, polishing machines and test equipment are

periodically calibrated A carefully designed program of

calibration at optimal intervals is required to maximize the

up-time of the assembly line and avoid rework Samples

are reviewed several times during each shift to ensure the

overall process is in calibration and that product is

meeting end user requirements

Testing – Fiber optic cable assemblies are tested to ensure

that products meet desired performance levels Data is

collected and used to monitor the assembly process and

indicate where further improvements can be made The

improved assembly process also institutes a geometry check on fiber ends using highly automated interferometers to ensure proper radius of curvature and fiber protrusion on the connector ferrule end-face The geometry data is recorded in a database as part of the permanent test record for the product The data is also correlated and used as feedback to continuously maintain tight controls over the process

Verification

As improvements are made to products and processes verification testing is used to measure the degree of improvement As a first step towards verification, suppliers will usually test products internally in their own test lab The test lab at a supplier location typically contains all of the equipment and fixtures to test products to GR-326-CORE, Issue 3 Vendor testing is often done incrementally

as changes are made so that the effect of each individual change can be observed Using this approach, the supplier can gage the value of changes to increase performance or reduce cost The overarching objective is to achieve the reliability standards set forth in the Telcordia requirements

As product design changes are verified, samples are made

on the actual manufacturing line and again verified for performance and reliability

Once internal testing is satisfactorily completed, samples are submitted to an independent test laboratory (e.g Telcordia Technologies, Underwriters Laboratories, National Testing Services, ITS, etc) With this approach product testing will be completed at the independent test laboratory under the observance of the independent test laboratory staff The independent test agency is responsible for carrying out the tests and providing a completely objective and factual report Testing a product

at an independent laboratory may result in a

“Certification” or “Verification” certificate indicating the product conforms to all requirements Since the service provider will use the results of testing for comparative analysis, they often will want to review the facilities and procedures used at the test laboratory before testing to make sure all laboratories provide consistent results Some service providers even provide a certification program for independent test laboratories so that labs can be certified for an entire family of products; e.g optical components

One alternative to testing at an independent laboratory

is to use witness testing With witness testing, the

testing is typically done at the suppliers location and is

witnessed by representatives from the independent test

laboratory This approach also results in a completely

objective and factual report The advantage of this

approach to the supplier is that scheduling can be more

flexible since the supplier’s own technicians and facilities

are used to carry out testing Service providers willing to

accept this approach may also elect to pre-certify the

suppliers optical lab This pre-certification is usually done

as a cooperative effort between the service provider,

supplier and independent test agency The overall

objective is to achieve consistency in the testing so that

results can be used in comparative analysis

Verification does not stop with product performance and

reliability Service providers also want assurance that the

manufacturing process used to make assemblies has the

appropriate quality controls to make them consistently

To achieve this, the supplier uses the GR-326-CORE, Issue

3 Section 8 requirements and guidelines for product

manufacturing to guide the process control To verify

that these process controls are in place, the supplier can

enlist the support of an independent test agency to

conduct a manufacturing audit The test agency staff

will visit the supplier’s manufacturing location to review

appropriate process controls vs the Section 8

requirements In addition, the test agency will observe

product manufacture and select random samples for

further verification back at the independent test lab This

process of manufacturing audit carries the verification

full circle and gives the service provider extensive data

with which to gage the performance, quality and

reliability of the manufactured product

Product verification, both internal and independent

testing, are an integral part of the continuous

improvement process The data gathered from

verification testing is used to identify strengths and

weaknesses in product performance and reliability as

well as improve the overall process for manufacture The

data is extremely important in guiding further product

and process improvement efforts

Continuous Improvement Results

A logical question is how much improvement can be achieved? As a comparison, we reviewed independent test results taken during two distinct points in time; one sample tested in October 1998 and another sample tested in July 2002 The test regiment conducted on both occasions with score of passing results per test is summarized on following page

These results show successful completion of the test program in both 1998 and 2002 resulting in Level 2 certification on both occasions To achieve the Level 2 certification, 100% of the requirements were met In

1998, the product satisfied 45% (18 out of 40) of the objectives and in 2002 the product satisfied 90% (39 out

of 43) objectives While objectives are not mandatory, they do provide an important indicator of the products overall ability to exceed industry requirements This increase from 1998 to 2002 shows a significant increase

in the ability of the product to exceed requirements and meet the stretch goals set in the standards The success in optical performance throughout the 2002 certification program was largely due to consistency in the connector ferrule end-face geometry, stability of material used and robustness of the mechanical design In addition, the manufacturing process developed consistently controls the precision of every parameter at the ferrule end-face resulting in performance and consistency that far exceeds previous levels available in the industry The insertion loss averaging 0.12 dB at end of test is a significant achievement This accomplishment demonstrates that it is possible to 100% satisfy all the very rigorous requirements and tests set in Telcordia GR-326-CORE

In 2002, samples of the same SC 2.0 mm product were tested at both Telcordia Laboratories and Underwriters Laboratories The results of testing at the two independent laboratories were correlated with both laboratories achieving near identical results The product at both laboratories met 100% of the GR-326, Issue 3 requirements and over 90% of the objectives This initiative resulted in Level 2 certification status through Telcordia Technologies Certification program and “Verification” status at UL for indoor and outdoor product use

Test Report Date October, 1998 July, 2002

Ferrule Endface Geometry:

End of Test:

Test Report Date October, 1998 July, 2002

Mechanical tests

(Formerly Bellcore)

As a final step in verification, a GR-326-CORE Section 8

manufacturing audit was conducted at the locations

where samples were produced Underwriter’s Laboratories

conducted the 2002 Section 8 manufacturing audit at the

locations where samples were produced Assembly lines

were audited in both the US and in Mexico The results of

the audit were impressive No major issues were identified

at either manufacturing location In addition, product was

selected at random from the assembly lines at each

manufacturing location and sent back to UL laboratories

for testing The performance testing results at UL

correlated to within ±0.02dB to those tested by the

supplier factories in the US and Mexico Successful

completion of the manufacturing audit provides one more

assurance to the end user that highly reliable products can

be mass-produced and deployed

Future Possibilities

Proponents of total quality methodology recognize that

continuous improvement is a never-ending process

Therefore, the industry will pursue other areas for

improving features, performance and reliability for fiber

optic connectors and cable assemblies Numerous

technology issues and trends will impact how connectors

are used and designed Higher-power lasers are causing

the PC style of connectors to be scrutinized even more

carefully than ever Current connectors should perform

adequately in high-power applications but cleanliness is

paramount Therefore, we may see needs for connectors

that provide for ease of cleaning and maintenance As

newer networks are deployed newer glass designs

including Reduced Water Peak fiber may be used to take

advantage of optical transmission across a broad

spectrum Fiber optic cable assemblies may be

color-coded to identify fiber paths fully certified for wide-band

applications Some of the newer fiber designs also

provide customized mode-field profiles that improve

bend performance in fibers These new fibers allow the

construction of more robust cable assemblies able to

stand up to the rigors of field applications More robust

fiber may be especially important for helping improve the

performance of small form factor connectors in

high-density environments or in harsh environments such as

outside plant applications The small form factor

connector designs themselves may need to be improved

to provide overall better strength so that they can be used in outside plant environments Some applications may require field-mounted connectors Much is needed

to improve the performance and reliability of field-mounted connectors so that they are comparable to cable assembles manufactured in the factory Finally, much is needed in the area of design, standards and testing for multi-fiber connectors so that they can be compared as objectively as ceramic-ferrule Singlemode

PC connectors All of these areas for innovation will generate the need for continuous improvement

Conclusion

Service providers concerned with deploying new networks and new applications are scrutinizing the performance and reliability of fiber optic cable assemblies more than ever In the current environment, service providers can specify higher performance and reliability while achieving significant cost reductions The cause of the service providers has been advanced by a combined effort of standards organizations, suppliers and independent test agencies The results presented in this paper represent best-in class performance and reliability for fiber optic cable assembly The products manufactured today meet or exceed industry standard requirements in every category This claim has been substantiated through independent testing at highly reputable laboratories including Telcordia Technologies and Underwriters Laboratories Continuous improvement methodology will continue to prove valuable as fiber optic connector and cable assemblies are incrementally changed to serve users

in the years to come A program of continuous testing to ensure consistent performance and reliability must accompany incremental continuous improvement

Acknowledgement

The authors acknowledge the contribution of Osman Gebizlioglu and John Peters at Telcordia Technologies and Dave Wuestmann and Nicholas Fedrich at Underwriters Laboratories We also recognize the contributions of colleagues at FONS including Ron Cooper, Jim Henschel, Dan Rocheleau, Ed Santana, Matt Brigham, Kathy Olson and Mike Noonan