report on test methodologies from the february 11th and...

Report on test methodologies from the February11th and 12th lab work

Objective: Test the tests

Stretch Camnitz- LightWave DivisionAgilent Technologies Test Equipment [email protected]

Test methods ReportMar 12, 2002

Proposal to have an open laboratory prior to theFebruary interim meeting• Proposed procedures must be validated on several devices• Follow up and refinement of “Raleigh” modifications through

subsequent serial PMD teleconferences• Test beds built during between Jan 18th and Feb 11th• A “Public” lab (open to anyone)• A “Private” lab (those who signed up were given 3 hours of private

use on the test beds)• Eight participants


Some results from the January meeting inRaleigh• New proposals for stressed eye receiver testing• New proposals for transmitter jitter testing• Report on root causes for difficulties in performing jitter bathtub

stressed receiver test measurements• Verification needed on “real” devices


Test system overview

• Transmitter test bed:• Jitter bathtub

measurement• Transmitter

Dispersion Penalty(TDP) measurement

• Receiver test bed:• “Old” stressed eye• “Simplified” Stress


D4.1 vs D4.0: What hasn’t Changed:

StressedTestSignal

RXUnderTest

SignalQualityMeasurement

TXUnderTest

Calibration


D4.1 vs D4.0: Two Major Changes:

StressedTestSignal

RXUnderTest

SignalQualityMeasurement

TXUnderTest

Calibration

“Simplified” Stress:Additive Amplitude ISI

Replace Jitter BTWith Eye Mask +TDP


Contract Between TX and RX

Bathtub jitterTX must produce less jitter than

stressed eyeRX must successfully receive

stressed eye

• TDP methodology• TX must produce a smaller

sensitivity penalty than stressedeye

• RX must successfully receivestressed eye


Matrix of measured Penalties

Three transmitters

Two receivers

“Verygood”

referencetransmitter

Transmitterunder test

Maximum dispersion 10-12

TDP

dBm

Variableoptical

attenuator

Force decisionpoint +/-0.1? UI

Stressedeye

generator

Testreceiver

CDR

Receiverunder

testCDR

BER

10-12

TDP

dBm

BER

_______________________________________| | Receiver || Transmitter | Test Rx | Rx U.T. || V.good ref. | cal. for TDP | Inform. sens. || Tx U.T. | TDP | || Stressed eye |cal.for str.sens. | Norm. sens. |

from Raleigh, NC, January 2002 Matrix of measured Penalties


Effect of Test Equipment non-ideality

Jitter Bathtub method• Tend to over-estimate jitter of TX• Tend to over-estimate jitter in

stressed RX test signal• These two effects tend to partially

cancel out• But, not all test equipment has

equal non-ideality• How does jitter combine?

• TDP method• Substitutional method:

• first order compensation forjitter in measurement RX

• But what about differencesbetween reference RX?


40 MHzJitter

JitterModulator

LPFPatternGenerator

Modulator OpticalAtten

ErrorDetector

O/EConverter

10.3125 GHzClock

Laser1310/1550 nm

2 GHzSine

DUT

OpticalAtten

ClockRecovery

Rx

Tx

10 dB Coupler

Test Fiber

Test System Block Diagram


Receiver Test

• Unstressed• Simplified

Stress• PRBS31

40 MHzJitter

JitterModulator

LPFPatternGenerator


10.3125 GHzClock

Laser1310/1550 nm

2 GHzSine

DUTRx

Tx

7.5 GHz BT filter


Original Stress vs Simplified Stress

Original Stress:Emphasis on LPFAdded RJ• Hard to Adjust Filter• Need BT measurement to Calibrate• Non-ideal Frequency Response:

• larger pattern dependence• larger Sigma, smaller W

Simplified Stress:Additive Amplitude ISISinusoidal Jitter• Easier to Adjust ISI, SJ• Measure with Oscilloscope• More ideal frequency response• Smaller pattern dependence• W larger, Sigma is smaller


Clean signal- 7.5 GHz BT filter

20 GHz scope BW


Original Stress; 4.5 GHz filter


Original stress-Pattern dependence

PRBS7PRBS31

Log

Erro

r Rat

e


Simplified Stress- 7.5 BT filter

20 GHz scope BW


PRBS 31 – Nostress vs Simplified StressLo

g Er

ror R

ate


PRBS 31 – Nostress vs Simplified Stress Vertical “Q” Plot

Amplitude Slice Setpoint

Log

Erro

r Rat

e


Transmitter Test

• Eye Mask• Bathtub Jitter• TDP (+- 0.1 UI

decision point)• PRBS31

ErrorDetector

O/EConverter

DUT

OpticalAtten

ClockRecovery

Rx

Tx

10 dB Coupler

Test Fiber


Bathtub Curve vs TDP

Bathtub Jitter Measurement• Tests Low and High Probability

Jitter• Does not test Vertical Eye Closure

• Left to eye mask

TDP• Classical TDP tests Vertical Eye

Closure• TDP with Offset sampling point

tests Vertical Eye Closure and Jitter• Sensitivity to Jitter depends on

choice of Sampling Point Offset


RX Frequency response

-12

-10

-8

-6

-4

-2

0

2

0.1 5.1 10.1 15.1 20.1

Frequency GHz

Am

plitu

de d

BRef RX Ref RX 7.5 GHz BT filter


TDP Meas and BT measurement on Simpl stressLo

g Er

ror R

ate

X XDecision points


Reference RX penalties; 7.5 GHz RX BT filter

SimplifiedStress +-10ps

+-1 ps+-10ps

+-1 ps

No Stress

3.5 dB2 dB

Log

Erro

r Rat

e


Effect of Decision Point Offset- ref RX

0

1

2

3

4

5

6

7

8

0 5 10 15 20 25 30 35

Total Decision Point Offset [ps]

Pena

lty d

B

Series1


Direct Tx No Fiber (Pier’s Mask)


Direct Laser Tx With Fiber (Petar’s Mask)


Tx Test; PRBS31; No Stress; “10 km” fiberLo

g Er

ror R

ate


TDP +- 0.1 UI; TX through FiberLo

g Er

ror R

ate

CleanRefSignal

SimplifiedStress

Log

Erro

r Rat

e

2.5 dB penalty


TDP correlation to BT curves

Correlation

0

0.5

1

1.5

2

2.5

3

3.5

0 10 20 30 40 50 60 70

BT width @1E=10 [ps]

Pena

lty d

B

TX DUTs


TDP Table- TX results

3.5 dB penaltyStressed Eye

1 to 3 dB penaltyTX DUT

calibrationClean Source

RX DUTReference RX+/- 0.1 UI


Receiver Test

• Unstressed• Simplified

Stress• PRBS31

40 MHzJitter

JitterModulator

LPFPatternGenerator


10.3125 GHzClock

Laser1310/1550 nm

2 GHzSine

DUTRx

Tx

7.5 GHz BT filter


Rx BER vs OMA – Simplified Stress vs NostressLo

g Er

ror R

ate

SJ ~.25UI

No Stress

Simplified Stress

4 dB


Rx Sensitivity with Simplified StressLo

g Er

ror R

ate


TDP Table

3.5-7 dB penaltyOMA=-11 to –5dBm

3.5 dB penaltyStressed Eye

1 to 3 dB penaltyTX DUT

Nominal sensitivity-18 to –11 dBm

calibrationClean Source

RX DUTReference RX+/- 0.1 UI


Summary

• Simplified Stress BT curves qualitatively similar to actual DML TXcurves

• TDP measured with +-0.1 UI decision point offset correlates with BTcurve

• All TX DUTs measured smaller penalties than simplified stress• Simplified stress induced moderate to large power penalties in RX

DUTs• Simplified Stress/TDP methodology seems to be workable using

optimized test Receiver

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