1

Single Fiber, Single wavelength, GbE / FE transceiverODN requirements & performance measurements

ODN = Optical Distribution Network

Meir Bartur, Zonu, Inc.IEEE 802.3 ah interimMay 2002

IEEE 802.3ah May. 2002 2

Dependence on cable plant return loss (action item 4)

n Current plant data n Measurements

u Self reflection Rx interferenceu Self reflections Tx interference

IEEE 802.3ah May. 2002 3

Link reflections – P transmit issues

TransceiverFar

(Low Power Pmin)

TransceiverNear

(High Power Pmax)

Range L (km)

ODN – Optical Distribution Network

Reflection due to ODN (Far end terminated)

Reflection due ORL

Fiber

Channel Loss:* Fiber attenuation (0.5dB/km x 10km)* Connector (0.5 dB x 4)

PRx-signal=Pmin x Channel LossPRx-reflect=Pmax x Channel_Loss^2 x ORL +

Pmax x ODN

Link Penalty:* MPN and others – 3dB allotment

Internal reflection (outside spec scope)

IEEE 802.3ah May. 2002 4

ODN ORL - Background n From major carriers:

u Current networks are >30dB ORLu “Old” networks can be as “bad” as > 20 dB

n Common SC-PC connections are specified >35 (or 40) dbn Low ORL in the ODN “disaster waiting to happen” (= cold

solder joint)n ODN ORL of 20dB allows 23 CURRENT worst-case

connectors

IEEE 802.3ah May. 2002 5

GR909 specifies <-40 dB ORL per connection

IEEE 802.3ah May. 2002 6

Example: Generalized Sensitivity measurement Variable Optical Return Signal

n Measure Transceiver Under Test (TUT) output power P0, ER, tr, tf, etc.n Use calibrated symmetric 2 way splitter combiner (~3.5dB)n Increase the optical attenuation of the reflection leg (#1) to max.n Measure sensitivity by adjusting attenuator #2 (no reflections)n Turn ref. Tx off and reduce reflectance leg attenuator (#1) until power

meter reads the desired P0 – target_ORLn Turn ref. Tx on and re-measure sensitivity under ORL condition

OPTICAL ATTENUATOR

#2

OPTICAL ATTENUATOR

#1

Fiber

Coax

OPTICALPATCHCORD

REFLECTS

~100% POWER

REFERENCE

TRANSCEIVER

TRANSCEIVER UNDER TEST 3dB Splitter

Fiber

Fiber

Fiber

Fiber

BIT ERROR RATE TESTER

Transmit data patterns

Receive data

pattern

RX

Coax

Coax

Coax

TX TX

OPTICALPOWER METER

Transmitter RIN affects sensitivity

Reflections affects sensitivity

IEEE 802.3ah May. 2002 7

Measurements: Rx effectsn Test 1

u Pout = - 6dBmu Measured sensitivity (no reflections)

–23 dBm (model predicts –23.5 dBm; 0.5dB loss due to electrical cross-talk?)

u Introduce ODN reflection 21.4 ORL (-27.4dBm)u Sensitivity measured –22dBm (model predicts–22 dBm)

n Test 2u Signal –18dBm; Sensitivity –22.8dBmu Reflection to cause 1E-12 BER –22.7dBm

u Signal/Reflection 4.7dB both predicted and measured

n Theoretical predictions are accurate and reliable!

IEEE 802.3ah May. 2002 8

Rx Sensitivity –Self Tx signal interference with remote signal due to ORL

Single Fiber Single λ SFP1.25Gb/S 27-1

1.0E-11

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

-26.0 -25.0 -24.0 -23.0 -22.0 -21.0 -20.0 -19.0 -18.0 -17.0 -16.0 -15.0

Sensitivity [dBm]

Bit

Err

or

Rat

e

ORL=28

ORL=26

ORL=23

ORL=21

ORL=20

ORL=19

ORL=17

ORL=15

ORL=14

ORL=13

Weak Tx / MAX Reach (7dB)

Sensitivity spec.

ProposedBaseline

Lowest sensitivity SFP in-house

IEEE 802.3ah May. 2002 9

Tx output –Self Tx signal interference – results in higher RIN and degrades Rx sensitivity

Effect of ORL on Tx output

1.0E-11

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

-28.0 -27.0 -26.0 -25.0 -24.0

Sensitivity

Bit

Err

or

Rat

e

ORL = 14 dB

ORL = 12 dB

ORL = 11 dB

ORL = 10 dB

n Non – issue for FP lasers. Current 1000Base-LX specifications are or 12 dB ORL.

IEEE 802.3ah May. 2002 10

Demonstration

n Utilize 3 dB splitter with un-terminated connection.n Total ORL = ~ 21dB

n This setup tests both effects (on the receiver when “weak”remote signal arrives AND on the transmitter effective RIN)

OPTICAL ATTENUATOR

#2

Coax

REFERENCE

TRANSMITTER

TRANSCEIVER UNDER TEST 3dB Splitter

Fiber

Fiber

Fiber

Fiber

BIT ERROR RATE TESTER

Transmit data patterns

Receive data

pattern

RX

Coax

Coax

Coax

TX TX

IEEE 802.3ah May. 2002 11

Summaryn Single wavelength link with maximum ORL

of the ODN –20 dB is easily achievable with FP lasers

n ODN reflections sensitivity – is much more acute problem for DFB (even for dual wavelength solution) and VCSEL (data required)

IEEE 802.3ah May. 2002 12

VCSEL sensitivity to reflections

IEEE 802.3ah May. 2002 13

SFWG - Single Fiber Single Wavelength GbETheoretical treatment Appendix

n Vipul paper “Cross-Talk in Bi-Di Single Wavelength Single fiber GbE”Demonstrated feasibility

http://grouper.ieee.org/groups/802/3/efm/public/jul01/presentations/bhatt_1_0701.pdf

n Reflections - Link “Engineering” issuesn Test methodology examplesn Results

IEEE 802.3ah May. 2002 14

Link “Engineering” – Vipul’s model adaptation

n Include Transmitter power range (e.g. 5 dB)n Include worst case reflections condition (short

link with minimal losses)n Treat two distinct parameters:

u Transceiver ORLuODN ORL

IEEE 802.3ah May. 2002 15

12 14 16 18 20 22 24 26 28 300

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Return Loss [dB]

Cro

ssta

lk P

enal

ty [

dB]

∆Tdb 5dB=

Effect of 5 dB P transmit power range (Pmax – Pmin)

5 dB Channel Loss

7 dB Channel Loss

Xtalk_Penalty1 x( ) 10 log1

1 1 ∆T+( ) XTALK ODNreturn_loss+

channel_loss x( )return_loss channel_loss x( )⋅+

⋅−

⋅:=

IEEE 802.3ah May. 2002 16

ODN ORL – Open endn Worst Case (un-intended loopback):

u All lumped at the interface (no link loss)u Open Fiber yields –14dB reflectionu High power Tx (Pmax)SD - Signal Detect (assert) = LOS – Loss Of Signal (de-assert)

n Attenuation Link budget (10km) - 7dBn Min power received Pmin – 7dBn SD should be set < Pmin – 7dBn Max reflection Pmax – 14dBn SD should be set > Pmax – 14dB

Pmax – 14dB < SD < Pmin – 7dBSetting at the Tx SD during mfg. will guarantee no

un-intended loopback

IEEE 802.3ah May. 2002 17

ORL totaln To enable simple installation worst case

reflections (for connected link) should not assert SD

n SDassert = Pmin - Channel_Lossmax – XdBn SDassert > Reflectionworst case

n Reflectionworst case = Pmax * (10^-.1*ODN_ORL + 10^-.1* ORL)

n Exampleu Pmin = - 9dBm; Channel_Lossmax= 7dB; Pmax = - 4 dBmu ODN_ORL = 20dB ; ORL = 17 dB (- total ORL = 15.2 dB)

n Since total ORL < Open Connector ORL SD issues are not relevant.

Sensitivity under reflection is treated next.

IEEE 802.3ah May. 2002 18

Transceiver ORL n Worst case situation for 0 dB link insertion

lossn SIGNAL/Reflection = Pmin - (Pmax-ORL)

u Pmax – Pmin = 5dBu For SIGNAL/Reflection = 10 dB requires

ORL = 15 dBn Vipul have shown that SIGNAL/Reflection = 5 dB at the far

end results in penalty < 1.6 dBn Our measurement shows 1dB penalty for SIGNAL/Reflection

= 5.4 dB

n CONCLUSION: ORL of 17dB has plenty of margin