Fiber Delays for 10 Gb Risk Assessment
A. John Ritger
Lucent Technologies
John S. Abbot
Corning, Inc.
25Jun01, FO2.2.1 Portland, ajr
Lucent Technologies
1
Original delays - backbone delays
• Original modeling work by Steve Golowich used piecewise linear
delay vs PMN, with 3 segments + white noise for low order modes.
– Linear change of delay with PMN = “alpha” profile, so we can think of
fiber with 3 linear segments as having core with 3 regions, each with a
different value of alpha
• Backbone delays: 3 piecewise linear segments
– PMN=0 to M1, slope chosen from uniform distribution (-0.025, +0.025)
•
M1 chosen from uniform distribution (0.25*19, 19)
– PMN = M1 to M2, slope chosen from uniform distribution (-0.20,0)
• M2 chosen from uniform distribution (M1, 19)
• Bias to negative delays reflects tendency to run process to get higher 1300 nm
OFL BW
– PMN = M2 to 19, slope chosen from uniform distribution (-0.20, .20)
25Jun01, FO2.2.1 Portland, ajr
Lucent Technologies
2
Original delays - low order modes
• Low order modes modeled as random noise on each of PMN = 1 to 5
• Two sets of delays were used at various time
– SG1 used “tapered random noise”
• for PMN = 1 to 5 add from uniform distribution (-.175, .175)*(6-PMN)/5
– PMN=1 uniform in range (-.175, .175)
– PMN=2 uniform in range (-.14, .14)
– etc
– SG2 used “uniform random noise”
• for PMN = 1 to 5 add from uniform distribution (-.175, .175
– PMN=1 uniform in range (-.175, .175)
– PMN=2 uniform in range (-.175, .175)
– etc
25Jun01, FO2.2.1 Portland, ajr
Lucent Technologies
3
Original delays - discussion
•
Designed to cover a wide range of delays
– uniform distributions of slopes not what expected for a production process
•
Range of low order mode perturbations did not cover the observed range from
the TIA Demonstration Data set
– fibers with isolated delays in PMN ~3-5 are not uncommon in life
•
Calculated OFL’s way too low for a “reasonable” manufacturing process
– “wild” high order mode excursions
•
Majority of delays did not pass any mask of interest
– only about 35% SG1, 17% SG2
– not characteristic of a manufacturing distribution
•
Unrealistically low OFL
– 40 % < 1000 MHz-km, 50% <1500 MHz-km
25Jun01, FO2.2.1 Portland, ajr
Lucent Technologies
4
Original delays - examples
Looks like typical data
25Jun01, FO2.2.1 Portland, ajr
Never see delays as large as this
Lucent Technologies
5
Goals for new delay set
• Realistic OFL distribution
– want >~90 % OFL >1000 MHz-km
• Probe limits of each of the 5 parts of the “Boulder Mask”
• Should generate fiber delays that resemble DMD seen in 10 Gig Demo
cable
– several examples of isolated low order modes
• Few “unrealistic” DMD characteristics
– qualitative, but capture experience
• Limit total failures to <~ 30%
25Jun01, FO2.2.1 Portland, ajr
Lucent Technologies
6
Generating the delays
• Use same basic approach as Golowich, change limits on variation of
backbone slopes to get acceptable OFL behavior, add several different
kinds of random noise for low-order modes
• Iterative approach to meeting the goals
– Generate delays from a simple, random model
– For each set of fiber delays
• Simultate DMD
• Evaluate DMD parameters (dmd(0, 23), etc.
• Calculate OFL
– Evaluate set of fiber delays against goal
– Try different parameters in the random model
25Jun01, FO2.2.1 Portland, ajr
Lucent Technologies
7
New Delay Set - backbone
• Backbone:
– PMN=0 to M1, slope from normal (0, .0125) [vs. uinf(-0.025, 0.025)]
•
M1 chosen from uniform distribution (0.25*19, 19)
– PMN = M1 to M2, slope from normal (-0.020, 0.04) [vs. unif(-0.2,0)]
• M2 chosen from uniform distribution (M1, 19)
• Bias to negative delays reflects tendency to run process to get higher 1300 nm
OFL BW
– PMN = M2 to 19, slope from normal (-.04, .04) [vs. unif(-0.2,.2)]
• OFL BW
– 14% < 1000, 25% < 1500 MHz-km [vs. 40%, 50%]
25Jun01, FO2.2.1 Portland, ajr
Lucent Technologies
8
New Delay Set - Low Order Modes
• Qualitative aspects of observed DMD:
– Isolated perturbations only observed for lowest ~ 5 mode groups
– “tapered” random noise, as used in SG1, gave reasonable agreement with
estimates based on delay differences estimated from profiles of production
profiles
– Magnitude of perturbations smaller for PMN=5 than PMN=1
– Isolated perturbations are not uncommon for first few mode groups
• No single noise term to meet all goals, so use several different LOM
additions:
– “tapered random” noise as used in SG1
– Isolated perturbations for PMN=1 to 4
– Isolated perturbations on pairs of PMNs: (1,2) (2,3) (1,3)
25Jun01, FO2.2.1 Portland, ajr
Lucent Technologies
9
New Delay Set - Final proportions
• Total of 5000 fiber delays, all with same “backbone” variation
• A large dose of engineering judgement was used in arriving at these
proportions
– 1000 delays with no low order perturbations at all
• manufacture will head in this direction when DMD is used for yield
– 2500 delays with “uniform tapered noise”
• a large weighting since this happens to match empirical estimates based on
manufacturing results
– 300 delays with PMN 1 from normal (0, 0.30)
• larger variance to probe limits of dmd(0,18), dmd(5,18) “hole” for
fundamental mode
– 300 delays each with PMN 2, 3, 4 from normal (0, 0.13)
• any isolated delay >~0.3 in these mode groups fails nearly all masks of interest
– 100 delays each with PMN 1,2 2,3, 1,3 from normal (0, 0.13)
• make sure we probe the limits, but do not hit them “too hard”
25Jun01, FO2.2.1 Portland, ajr
Lucent Technologies
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0
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Distribution of DMD values for new delays
0.0
0.5
1.0
1.5
0.0
1.0
1.5
DMD(0, 18) - (ps/m)
0
500
1000
1500
DMD(0, 23) - (ps/m)
0.5
0.0
0.5
1.0
1.5
DMD(5, 18) - (ps/m)
25Jun01, FO2.2.1 Portland, ajr
Lucent Technologies
11
Examples from new delay set
25Jun01, FO2.2.1 Portland, ajr
Lucent Technologies
12
Examples from new delay set
25Jun01, FO2.2.1 Portland, ajr
Lucent Technologies
13