Test Plan for PMD Testing of a WDM

Receiver

Henry Yaffe, PrincipalJanuary 2004

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Recommended Test Program

• Process Establish test procedure (automation recommended)

Schedule time in front of systems

• Experiments:

1. Measure bare receiver

2. Use NRT PMD Source to map to Joint Probability Distribution Function

• Analyze data - Calculate Total Outage Probability for different mean span PMDs.

• Addendum If desired, add more impairments (CD, non-linearities) and re-measure

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Test Basis: System Margin (OSNR) as Performance Benchmark

Back to Back

Back-to-back

40 ps PMDC

60 ps PMDC

80 ps PMDC

60 ps uncompensated

BER vs. OSNR

OSNR

BER

Relative OSNR Penalties

10-12

10-6

Recommended: 10-12 BER as limit (else, each test is too time-consuming)

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Recommended Tests to Acquire OSNR Performance for 25 Ps PMD

40/2263

20/566

40/00/0 60/0

40/1386

20/118355/1097

20/0

40/894

55/1598

55/229770/2051

75/1183

75/148880/1587

80/0

Ex.: 17 states can adequately cover the 25psec (25%) contour DGD (ps)

SOPMD (ps2)

0 0

20 05661183

40 089413862263

55 109715982297

60 0

70 2051

75 11831488

80 01587

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Acquiring the data

Test basis: Set & maintain all system parameters Vary OSNR for a given PMD state & measure BER

Characterization process:1. Set PMD state

2. Set OSNR

3. Set RX power

4. Record: payload, B3 BERs, error counts, elapsed time, OSNR, and RX power every 30 seconds

5. Continue recording for >5 min and <30 min (or 10 hits)

6. Increment OSNR, repeat

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Test Stand Required for PMD Testing

Automated BER v OSNR at fixed RX power•Allows efficient measurement of many PMD states• Decreases data acquisition time by 3-4x •* Polarization scrambler 3 is not needed if no optical PMDC is used

Tx EDFA

Tunable

Filter

OSA

Powermeter

10 %

10 %

90/10

Polarization scramblers

BERT

90/10

Attenuators

25 km

SMF-281 2 3* 5 6 7

8910*

11

12

Rx

PMDE

PMDC*

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Test Setup – Equipment Key

1. Launch Polarization Scrambler – ensures no launch at SOP, which could create artificially high-quality eye

2. PMDE – controllable PMD source

3. PMDE Output Polarization Scrambler (optional, only use with 10) – randomly varies SOP to provide “speed” input

4. Fiber spool – source of “residual” chromatic dispersion (appropriate for chirped systems)

5. EDFA input attenuator – ASE noise control (OSNR)

6. EDFA – ASE source

7. EDFA output attenuator – power control

8. OSA – OSNR measurement

9. DWDM Filter – models DWDM effects

10. PMDC (optional) – compensates for PMD

11. Power meter – power measurement to maintain constant Rx dBm

12. BERT – measure BER as performance output

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Test Conditions

• To establish consistent and verifiable test results Testing should be conducted PMD as the only impairment A benchmark system operating level should be set and maintained

(Rx power, etc.)

• For a given WDM system: Maintain a constant received power (dBm) level Turn FEC off (or measure pre-FEC) Turn SBS Suppression off (if used) Maintain a fixed (preferably zero, to avoid confusing effects) level

of residual chromatic dispersion at the RCVR

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Benefits of Automation Can Rapidly Acquire Data to Model Real-world Performance

• For network-realistic PMDC characterization: Reasonable sampling of PMD states is required Try to define points where DGD & SOPMD performance degrades Probability of reaching any those states is relevant to system

performance

• Testing each data point is time-consuming: Need ~1hr for good statistics at 10-12 BER Measure for minimum of 5-10 minutes for full SOP coverage BER v OSNR curves (3-4 points) takes 1 to 2 hours

• Automation improves confidence of characterization Can characterize 10 to 20 PMD states in 24 hours with

automation– Compare to ~ 5 to 8 manually per 8 hour shift

OSA, power meter, 2 attenuators, BERT, PMDE are GPIB interfaced

PMD, test time, polling time, OSNRs, and RX powers set by user