aerospace fibers “lessons learned” - nasa · experience determination 1 aerospace fibers...
TRANSCRIPT
Experience Determination www.nufern.com1
Aerospace Fibers“Lessons Learned”
M.F.SeifertOctober ‘05
Experience Determination www.nufern.com2
Our Mission
Nufern designs, manufactures, sells, and supports lot-controlled specialty fibers, optical fiber laser and amplifier products for leading
edge technology applications.
Experience Determination www.nufern.com3
Nufern Advantage: Better Fiber Performance
• Telcordia GR 20 type testing:• High strength, near theoretical
limit.• High fatigue failure resistance.
Best in the world.• Enable the highest power
integral fiber lasers to date.
• Cost 218 Model indicates 107 year life expectancy.
1.2
1.3
1.4
1.5
1.6
1.7
1.8
-9.0 -7.0 -5.0 -3.0 -1.0
Logarithm of Stress Rate[ln(GPa/s)]
Lo
gar
ith
m o
f F
ailu
re
Str
ess[
ln(G
Pa)
]
Slope 0.0324714SEE 0.0032918
nd 29.80nd+95 37.63nd-95 24.60
1
10
100
100 1000Failure Stress (kpsi)
Failu
re P
roba
bilit
y (%
)
Forbidden Zone
750 kpsi
Experience Determination www.nufern.com4
Custom Clean / Lean Manufacturing Space(Designed for lowest cost, highest yield, in mid volumes)
FiberProduct
Flow
Full TelcordiaQualificationLab
Class 100Draw Facility
Experience Determination www.nufern.com5
Aerospace Fibers• Difficult Application:
– High and wide temperature range.– No emissions wanted in spite of operation in “near vacuum”.– Resistance to radiation of all types and magnitudes.– Resistance to chemicals; ie salt water and organic solvents.– High resistance to, and near zero emissions when burned.– Tolerance for high cyclical stress, shock and vibration.– Tolerance to unfavorable installation techniques.
• Need to be connectorized for maintenance purposes.– Fusion splicing & recoating fiber on an aerospace vehicle is
impractical.
Experience Determination www.nufern.com6
Aerospace Fiber Solutions• Waveguide:
– Multimode (graded and stepped index) used to maximize core diameter and coupling efficiency.
– 50/125µ, 100/140µ, 200µ PCS, etc.• Coating materials:
– Polyimide– Silicone– Acrylate
• Cable structures:– Loose Tube (or semi loose tube)– Tight buffer
AerospaceCable
Fiber
Experience Determination www.nufern.com7
Waveguide design• Early systems had low brightness Tx devices.• Early systems had low bandwidth and insensitive Rx devices.• Couplers were retrofit into existing electrical connector designs.• This dictated:
– Large cores ~ 200µm for maximum target area. – Highest NA ~ 0.375 for maximum light capture.– Custom connectors were developed and implemented.– Low bandwidth. (Max 10MHz/km)
• The large core polymer clad designs were unreliable.• The telecom industry has generated a great deal of standard
125µm robust low cost, high bandwidth connector hardware.– Cost / benefit analysis suggests a move in this direction.
core
cladding
coating
Experience Determination www.nufern.com8
Waveguide Issues• Large core fibers ~ 200µ have inadequate BW for today’s
needs. (< 10MHz km)• Thin Polymer Clad Fibers (PCS, HCS, etc.) suffer from long
term reliability issues, particularly if delivering power. • Crimp & Cleave terminations for PCS fibers exhibit high
variability and reduce available BW.• Installation & service methodologies designed to minimize
microbend stress on fiber are not followed.• Maintenance of large diameter FC (face contact) connectors is
tedious and not followed.• Some designs suffered premature failure. (Carbon coatings
prone to ESD failures)
Experience Determination www.nufern.com9
Hard “Polymer Clad” Fiber Defects
Result: Almost all current systems use glass clad fibers
Hard thin (<5µM)cladding tends to delaminatefrom the glass.It requires a “permanently shrinking”coating (Tefzel™)to stay intact.
Extruded Tefzel™on thin claddeposits hardcontaminantsinto the claddingcausing point sourcesof failure
Delamination Contamination
Experience Determination www.nufern.com10
All Glass Waveguide Trade OffRelative Bandwidth
0
0.5
1
1.5
2
2.5
3
3.5
1.0% 1.1% 1.2% 1.3% 1.4% 1.5% 1.6% 1.7% 1.8% 1.9% 2.0%
Index ∆ (%)
Rel
ativ
e B
and
wid
th (
w.r
.t. 1
.8%
∆) Relative Bandwidth
Microbend loss for various multimode fibers
0
1
2
3
4
5
6
7
8
9
10
1.0% 1.1% 1.2% 1.3% 1.4% 1.5% 1.6% 1.7% 1.8% 1.9% 2.0%
Index ∆ (%)
Rel
ativ
e M
icro
ben
din
g L
oss
(w.r
.t. 6
2.5/
125/
1.8%
) 50 12562.5 125100 140
50/125µ0.22 NA
62.5/125µ0.275 NA
100/140µ0.29NA
100/140µ
• Core Ø & NA => Bandwidth & Bend sensitivity• Core Ø / Clad Ø ratio => Bend sensitivity
50/125µ 62.5/125µ
Micro bend Loss Relative Bandwidth
Experience Determination www.nufern.com11
“Ultimate” aerospace waveguide…
• Glass core & Glass cladding structure (reliability).• Smallest core (maximum bandwidth)• Highest possible Core Ø/Clad Ø ratio (bend
insensitivity)• Largest possible NA (highest tolerance to connector
misalignment)• 125µ outside diameter to utilize telecom hardware.
(minimize cost, maximize connector selection)
Experience Determination www.nufern.com12
High Inherent Radiation Tolerant Fibers
0
5
10
15
20
25
30
0.E+00 1.E+05 2.E+05 3.E+05 4.E+05 5.E+05
Radiation Dose (Rad)
Ind
uce
d A
tten
uat
ion
(dB
/km
)
Radiation: ProtonWavelength: 1310 nmFlux: 1.1x108 Protons/cm2/sFluence: 1.47x1012 Protons/cm2
Dose Rate (Gamma): 33 Rad/sTotal Dose: 500 kRadTemperature 27oC
Nufern PM1300G-80 Radiation Sensitivity 0.102 dB/km-kRad
Data:Light IonRadiation LabBerkley CAJoe Frieble
Panda construction
Experience Determination www.nufern.com13
Fiber Lasers (Amplifiers)
(core Ø / clad Ø)1MW -
100kW -
10kW -
1kW -
100W -
10W -M2 = 1 M2 = 10
BPP 1µ? , FL 1
LFM 49/250200/600
LMA 25/250
LMA 15/130
20/400LMA 22/400/480
SM 10/200
SM 5/125 (classical telecom fiber)
CW regime
pulsed regime
Flat mode pulsed regime
Ganged Fibers-Few LMA-Many SM
Experience Determination www.nufern.com14
Coating Design
• Fiber coating serves two functions:– Protect fiber from chemical attack. (Water most prevalent)
– Protect fiber from microbend stresses.
• Many materials and combinations have been tried.• Full qualification is expensive and time consuming,
as a result some fiber coatings that are essentially experimental have made it into flight hardware because of need and time constraints.
Experience Determination www.nufern.com15
Acrylate Coatings• Were developed for the telecom industry 20 years ago.
– New materials with OI temperatures of > 200ºC are rated from -55ºC to +125ºC with excursions to +180ºC for several 10s of hours.
– Old acrylates (pre 2002) were maximum rated for –5ºC to +85ºC.– Typically applied as a dual coating, the inner a soft high RI material to protect
from microbend forces and absorb leaked core light. The outer layer is hard to provide abrasion resistance and minimize friction.
• Do not perform well when attacked by common organic solvents, and in extreme thermal environments.
• Have proven themselves durable and practical when used as designed.– Provide excellent protection from nicks, bends and moisture.– Are easily stripped clean for termination.– Are telcordia qualified for 22 years service life.– Have an enormous deployment record.
Experience Determination www.nufern.com16
Acrylate Coated Fiber Drawing
Repeatedfor multi –coatapplications
Experience Determination www.nufern.com17
Acrylate (polymer) coatings shrink
Result: Critical applications requiring precision winding or fiberbonding specify thermal post processing.
167
168
169
170
171
172
173
174
175
0 20 40 60 80 100 120 140 160 180
Hours at 85C
Sec
ondar
y B
uffe
r Diam
eter
(um
)
135
136
137
138
139
140
141
Prim
ary B
uffe
r Diam
eter
(um
)
Secondary
Primary
~ 1.49 % Primary
~ 1.52 % Primary + Secondary
Experience Determination www.nufern.com18
Acrylate Coating Life Cycle
AsBuilt
After< 5 years
(acc.)
After< 22 years
(acc.)
After1 year(acc.)
After100 Days@ 175° C
(Nearly black,Crumbling)
Test using Nufern HTA using dual coat Acrylate with OI temperature > 200°COrange / Brown color
Experience Determination www.nufern.com19
Silicone Coatings• Provide a good fiber coating for a modestly higher temperature
range. Typically -25º C to +150º C.– Low RI silicones return escaped core light to the cladding so are
preferred in some power delivery applications. – Show good resistance to many common solvents.
• Present known challenges for the fiber manufacturer, the cable assembler, and the ultimate users:– It is very difficult to clean a stripped fiber thoroughly. – Most bonding agents are effectively released by silicones.– Silicone continues to outgas for the life of the application. It therefore
looses mass and volume over time.
• Silicones generally perform as advertised, and have a significant installed base in many harsh environments.
Experience Determination www.nufern.com20
Polyimide Coatings
• Are hard and durable, with high and wide operating temperature ranges. Typically -65º C to ~ +300º C.
• Fibers are coated with multiple thin layers to ~ 20µm.• Contain ~ 4% water by volume when fully cured.• Exhibit low friction so can not be proof tested conventionally.• Are highly tolerant to most solvents.• Are stripped by immersion in hot ( > 100°C) conc. H2SO4.• Most problems with PI fibers are as a result of improper curing
or poor storage & post processing.• Are sometimes used effectively in combination with Carbon
(hermetic) coatings.
Experience Determination www.nufern.com21
Polyimide (PI) Coating Failures
Typical “under curing”(post application reflow)
Typical “blistering”(inadequate cure between coats)
Experience Determination www.nufern.com22
PI Coating Application Guidelines:
• A 20µm coating on fiber takes ~ 1Hr at elevated temperature to fully cure.
• Drawing layers too quickly (inadequate cure) causes subsequent layer bubbling and allows fiber to move.
• Finished fiber must be stored dry.• Fiber requires an elevated temperature drying cycle
prior to cabling. (entrained moisture flashes to steam)• Cable materials must be extremely dry before used in
cable making process.
Experience Determination www.nufern.com23
Proof Testing Polyimide Coatings
Fiber is drawn through sets of fixed wheels of specified diameter to imparta bending (tensile) stress on the outer surface of the fiber.
Fibercrosssection
Fiber is drawn through 4 sets ofWheels, each at 45° from the others
12
3
4
Experience Determination www.nufern.com24
Clever Alternatives to Stripping PI
1. Terminate in custom large diameter ferrules with intact PI coating.
2. Terminate in standard telecom. ferrules with intact PI coating (suffer some bend loss due to core Ø / clad Ø ratio)
• Because PI coating is relatively thin concentricity error and the resulting error in connector alignment can be managed during the coating process.
Experience Determination www.nufern.com25
Micro Bend Loss for 125µ “No Strip” PI
1.0
5.9
0.4
2.5
0
1
2
3
4
5
6
7
8
80 85 90 95 100 105 110 115 120 125 130 135 140
Cladding Diameter (µm)
Rel
ativ
e M
icro
bend
Los
s
50 um, 1% Delta core
62.5 um, 1.8% Delta core
Necessary claddingDiameter to achieve125µ coating diam. With 32µ (16 x 2)PI.
Experience Determination www.nufern.com26
Atomic “Carbon” Coatings• Can provide an effective hermetic seal against
water or H2 gas ingression.• Reduce the raw tensile strength by about 1/5th but
provide a >5X stress corrosion failure (n) rating increase.
• n values in excess of 100 are possible (common).• Carbon is a semiconductor and the resulting fiber
is ESD Sensitive. (NOT USUALLY ANTICIPATED)• Care must be taken to account for ESD sensitivity
during all steps of manufacture & deployment.• Finished products have been shown to be robust.
Experience Determination www.nufern.com27
Carbon Coatings
Polymer coating
Thin (few monolayer) Carbon coating
Waveguide
SEM STM
Experience Determination www.nufern.com28
Aerospace Cable Construction
• Loose Tube– Largest operating
temperature range– Least negative effect in
high transient temperature conditions.
– Difficult to terminate short lengths < 2m. Excess fiber spirals in tube.
– Cable is somewhat bulky and subject to kinking.
• Tight Buffer– Easiest to terminate– Smallest dimensionally so
gives highest bandwidth/size.
– Has difficulty meeting low operating temperature requirements.
Experience Determination www.nufern.com29
Conclusions
• Waveguides have migrated to “all glass” constructions.– Debate continues on “standards”.
• 3 polymers are variously used. Acrylates are increasingly used “in cabin”.– High desire for a strippable polyimide.
• Carbon coatings are falling from favor because of ESD sensitivity.– High desire for a non conductive atomic hermetic coating.
• Both cable constructions are in common use.
Experience Determination www.nufern.com30
Contact
Martin Seifert860.408.5001
7 Airport Park RoadEast Granby, CT 06026
860.408.5000860.408.5080 fax