HP PN71452 2_Eribum Doped Fiber Amplifier Testing

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HP 71452BOptical Spe ctrum Analyzer

Product Note 71452-2EDFA Testin g w ith th eTime-Domain-ExtinctionTechnique


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Introduction 3

Limits in Common EDFA Measureme nt Tech nique s 4

Time-Domain-Extinction Tech nique 6

Erbium-Doped Fiber Recovery from Satura t ion 6

Measuremen t Setup and Timing 7

Gain and Noise-F igure Character iza t ion 9

Measuremen t Setup for Insta lled Links 9

Output Power and Signa l-to-Noise Rat io 10

Spect ra l Broadening Measurements 11

Determination of Measurement Accuracy 12

Sources of Measurement Uncer ta in ty 13

Calcula t ion of Tota l Measurement Uncerta in t ies 17

Performing Measurements 18Single Wavelength Opera t ion 18

Mult i-Wavelength Test s 20

System Output Test 22

Appendix A 25

Mult i-Wavelength P rogramming Example 25

Table of Conten ts


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Introduct ion Today, the most common techniques to characterize gain and noisefigure of erbium-doped fiber amplifiers are interpolation of the

amplified spontaneous emission (ASE) and extinction of the

polar ized stimu lus signal. Both techniques rea ch their limits invery advanced amplifiers, and th ey may not work a t all at a system

level.

A new method called time-domain-extinction (TDE) technique has

been developed to overcome t he obsta cles an d to allow even n ew

an d more compreh ensive tests. All HP 7145XB Optical Spectr um

Analyzers (OSAs) include the en ha nced har dware for the

measu remen ts described here. For greatest a ccur acy, Hewlett

Pa ckard recommen ds the H P 71452B. Its perform an ce has been

optimized for characterizing optical amplifiers and systems (e.g.,

links) incorporat ing th em. This pr oduct n ote is part of a series of

Optical-Spectrum -Analyzer documents. For a n introduction to

optical spectru m a na lysis an d for basic informa tion aboutcharacterizing optical amplifiers, see also:

[1] Optical Spectru m Analysis Basics, HP Application Note 1550-4

(HP literature number 5963-7145E)

[2] EDFA Testing with t he Inter polat ion Techn ique, HP P roduct

Note 71452-1(HP literatu re n umber 5963-7146E)

[3] EDFA Noise Gain Profile and Noise Gain Peak Measurements

HP Pr oduct Note 71452-3 (HP litera tu re nu mber 5963-7148E)

[4] D. Baney, J. Du pre, C. Hentschel: Optical Fiber Amplifiers

Measur ement of Gain an d Noise Figure, HP Lightwa ve

Symposium 1993


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Limits in Comm onEDFA Measu reme ntTechniques

In recent year s, optical a mplifiers ha ve been deployed in

transcontinental, submarine, and other state-of-the-art long

distan ce connections. The st ill-growing dem an d r equires even m ore

sophisticat ed systems. Th us, ongoing development s h ave to st eadilyoptimize th e next link t o be put in pla ce. This leads to the limits of

some common measu remen t t echn iques: the ASE int erpolation

technique an d th e polarizat ion extinction t echn ique.

A requiremen t in long hau l systems is to minimize the spectr um of

the amplified spontaneous emission (ASE) received from the

previous or transmitted to the next optical amplifier. To accomplish

this, many erbium-doped fiber amplifiers (EDFAs) have built-in

filters. The filters a re designed so only the signal can pass, an d th e

ASE is att enua ted as mu ch as possible. The spectr al nar rowing

distur bs th e accur acy of the ASE inter polat ion t echn ique which

mak es ASE power measu remen ts typically a few nan ometer s to the

left a nd t o the right of th e signa l.

Optical amplifier

with fi ltersTypical output spectrum(without ou tput f i l ter)

Even with out filtering, it can be difficult to measu re t he ASE

accur at ely. If th e sour ce used in t he test ha s sidemodes, it is hard to

place the ma rker correctly between th e sidemodes. The procedures

Amplif ied source sidemod esmake it difficult to placemarkers au tomatical ly

OUTPUT

SIGNALINPUT

1480 or980 nmPumpLaser

Er3+

Doped Fiber

Coupler IsolatorFilter

MonitorPhotodetector

Filter(optional)WDM


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used in a softwar e-controlled test environm ent require

sophisticat ed algorith ms t o avoid an ASE reading a t t he t op of a

sidemode. Otherwise, the chara cterizat ion of either t he stimu lating

source or th e am plifiers outpu t spectr um (or both) contains errorswhich lead to incorrect gain or noise-figure results. The polarization

extinction technique offers a major impr ovement . The signal from a

tu na ble laser is highly polarized. The E DFA usu ally cha nges its

sta te but not its degree of polar ization. It is possible to suppr ess th e

amp lified signal an d its sidemodes by adding a polarization st at e

contr oller an d a linear polar ization filter between th e EDFA and

th e OSA. Because th e ASE is not very polarized, the OSA still sees

50% of the ASE power (i.e., th e ha lf which pa sses t he filter).

However, at mea sur ements on a system level, the long fibers

between a mplifiers excha nge optical power between sta tes of

polarizat ion. Th is effect prohibits a good extin ction of the sour ce at

th e end where th e spectra l ana lysis tak es place. If the source

cannot be well suppressed, then th e interpolation t echn ique has t o

be used again in conjunction with polarizat ion extinction.

Power

Wavelength

Powe r exchange between polarizationstates in a system


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Time-Domain-Extinction

TechniqueErbium-Doped Fibe r Recovery from Saturation

The core of an optical amplifier, for wavelengths around 1550 nm,

is a single-mode fiber doped with erbium. Th e erbium ions a re

shifted to higher en ergy levels by some pu mp lasers. The a ctivat edelectr ons rema in in a meta sta ble level for some time. Without an y

signal at the amplifiers input , these electrons eventu ally fall down

an d emit some light r an domly. However, if an in put signal is

applied, then t he incoming wave stimu lates t he electr ons to fall

down a nd th us emit t heir energy coherently with th e incoming

wave. This is t he m ain effect of th e optical am plificat ion. Th e

amp lificat ion applies to ran domly emitted photons as well, so the

output spectrum of an optical amplifier consists of an amplified

input spectru m (if applied) an d th e am plified spontan eous emission

(ASE, which represent s t he noise from t he a mplifier).

The more electr ons used for st imulat ed emission, th e fewer rem ain

for ran dom emission (and vice versa). Without a n inpu t signal, th eASE is much higher tha n with a n inpu t signal. Therefore, th e ASE

ha s to be measur ed when th e amplifier is driven into satur at ion by

an input signal.

The t ime-domain-extinction technique (TDE) takes a dvant age of

the fact tha t th e meta st able energy level of th e erbium ion ha s a

time const an t of several hu ndr eds of microseconds. Immediat ely

after the input signa l is turn ed off, the ASE power rema ins at th e

same level it was in th e presence of the inpu t signal. Then it sta rt s

to rise in an exponent ial fash ion u ntil it rea ches the level of an

un driven condition.

The time char acteristics can be tested u sing a laser source being

modula ted a t a low frequen cy. Before th e falling edge of th e

modulated la ser, the a mplifier noise (ASE) has st abilized at a

sat ur ated level. This power is th e sum of the am plified input signal

an d th e ASE wh ich is very small due to th e satu ra tion of th e

am plifier. Immediately after t he falling edge, the out put signa l

consist s of only ASE from th e am plifier; i.e., it doesnt conta in t he

am plified signal an y more, nor has it an y sidemodes or spontan eous

emission from the source. This fact allows accurate characterization

of th e ASE even at th e wavelength of the sa tu rat ing signa l.

ASE time-domain

characterist ics

ASERelaxation

0.0 0.5 1.0 1.50

50

100

150

200

Time (ms)

Power(uW)


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Becau se the power after the edge is up to a thousan d times sma ller

than the power before, the measurement equipment must recover

from th e large signal in a very short time. The n ext figure sh ows

typical recovery per form an ce of the H P 7145XB family of OpticalSpectru m Analyzers. Within t en microseconds a fter th e large signal

ha s disappeared, the OSA can m easur e a 30 dB weaker signal with

an accura cy of better t ha n 0.2 dB.

Time After Falling Edge (us)

0 2 4 6 8 100

0.2

0.4

0.6

0.8

1

ASE

MeasurementError(dB)

Signal / ASE

Ratio: 30 dB

20 dB

25 dB

35 dB

OSA recovery performan ce

Measurement Setup and Timing

Similar to the ASE interpolation technique, the measurement setup

consists of a tu na ble laser source (TLS) and a n optical spectru m

an alyzer (OSA). However, this time th e OSA must ha ve enha nced

dat a-acquisition performa nce as discussed above. The TLS is

modulated int erna lly at 25 kH z squar e wave (on/off), an d its

average output power defines th e satu rat ing condition in th e

EDFA. The trigger cable is u sed to synchronize the da ta acquisition

of th e OSA with t he squa re wave.

Optical Amplifier

Ext. Trig

Mod Out

Tunable Laser

HP 8168A/B/C #003

Optical Spectrum Analyzer

HP 7145XB

25 kHz

The TLS modulat ion ha s 20 s ON and 20 s OFF t imes. Ea ch is

about 5% of the erbium s time const an t. On a timing diagram , the

ASE shows a tr iangle wave form (in t he diagra m on th e next page,

the ASE waveform is calculat ed by subtr acting th e source signal

[times gain] from the output power of the EDFA).

TDE measurement setup


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Because the ASE power is still a function of time, the question

rema ins: Where is th e right point in time t o measure it? The ASE

behavior similar to a low-pass filter with less th an a k ilohertz

rolloff frequen cy gives a clear h int : If th e frequen cy of thestimulating square wave increases, then the triangle wave

decreases its am plitu de. For very high frequencies, it converges to

the average value. In other words, if th e average power of th e

squar e-wave modulated laser is the sa me as t he avera ge power of a

Gbit/s t raffic signal, th en t he a verage of th e tr iangle waveform is

the sa me as t he ASE power in the pr esence of the tra ffic signal.

Fortu na tely, the a verage value can be foun d easily in t he center of

th e rising or falling slope.

TDE timing diagram

Tunable Laser

(Internal Mod.)

40 us

off

-5 dBm

ASE Power

OSA Sample

10 us

+0.5 dB

-20 dBm-0.5 dB

The HP 7145XB family of Optical Spectrum Analyzers can delay

the sa mpling of a data point after th e trigger edge. To measur e the

average power of a signa l, the OSA samples ran domly an d avera ges

the dat a u sing a low-frequency video bandwidth. To measu re t he

ASE only, it delays the trigger by 10 s after the falling edge inorder to hit th e center of th e break of the 25 kHz squa re wave. This

delay is long enough for t he a na log har dwar e to recover from t he

strong a mplified signa l to the th ousand-times-weaker ASE level,

an d to sam ple this value with an accur acy of 0.2 dB or bett er. Note

tha t a t t he sa mple point, t he source is completely turn ed off. The

output spectrum of the amplifier consists of ASE only. Since the

source is tu rn ed completely off when a measu remen t is ma de, any

source sponta neous emission a nd a ny source sidemodes are

removed.

Undriven ASE

Signal + saturatedASE + source SE

Saturated ASE

TDE output screen


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Gain and Noise -Figure Characterization

The gain of the am plifier can be determ ined easily by measu ring

the average power of th e signal before and after t he a mplifier. For

best accur acy, the ASE power is subtra cted from the mea sur edoutput power:

G =P out =

P meas NASE

P in p P in p

G: Gain

Pmeas: Average output power

Pout : Average output power (s igna l only)

P in p: Aver a ge in pu t p ower

NASE ASE power at the s ignal wavelength (see below)

With th e time-domain -extinction technique, the OSA measur es th e

ASE spectrum directly. Therefore, it is not n ecessary to ma ke

corr ections for a ny cont ribution from t he st imulus, a nd the ASE

power can be obtain ed directly at t he wa velength of the signal for

the gain formula above or for the noise-figure calculation:

3

NF =NASE +

1=

NASE x

+1

h x x G xB w G B N h x c 2 x GG

NF: Noise Figure

NASE ASE power [W]

h Planks constant [6.6252 x 10 34 Ws 2]

Signa l frequ ency [Hz], = c /

c Speed of light in vacuum [2.9979 x 108 m/s]

length [m]

Bw Opt ica l s pect r um ana lyze r s nois e bandwid t h [Hz]

B w = BN * v /

BN Calibrated or n ormalized noise bandwidth [m]

The formu las are t he sam e as used by the ASE inter polat ion

technique. The n oise figure cont ains two term s: The first term

represent s th e signal-to-ASE mixing at th e photodetector. The

second one repr esents th e level-dependent shot n oise pr oduced in

the photodetector. The equa tion assu mes th at th e ASE-to-ASE

mixing can be neglected, like in systems u sing nar row bandpa ss

filters or driving the amplifier highly into compression.

Measureme nt Setup for Instal led Links

At the r eceiving end of a system , ther e ar e several chara cteristics of

interest: signal output power, noise spectrum, signal-to-noise ratio,

signal broadening, ASE n ar rowing, an d more. The time-domain-

extinction techn ique can help measu re th ese values as long as a

trigger signal is available. The signa l delay th rough th e link h as t o

be added to the 10 s tr igger delay. Even after inst allation, this

technique can be used if the tr igger signal can be recovered.


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TDE system level setup

Tunable LaserHP 8168A/B/C #003

Optical Amplifier System

Ext. Trig

Optical Spectrum AnalyzerHP 71452B

25 kHz

Clock RecoveryHP 8112A

O/E ConverterHP 83442A

CouplerHP 11890A

In order t o do tha t, a splitt er is used in front of th e OSA. It couples

par t of the signal t o a r eceiver wh ich provides a proper tr igger

signa l (i.e., TTL level) to th e OSA. With a fast ( 1 MHz) clockrecovery, the TDE m ethod is independen t of the link length. The

trigger delay in t he OSA has t o be adjusted only by the delay

thr ough th e clock r ecovery par t. This delay can be calibrat ed out

easily by increment ing th e tr igger delay in th e OSA from 10 t o 50

s. As soon a s the signal sta rts t o appear on t he OSA screen, th e

positive edge of the pulse h as been found. As soon as it star ts t o

disappear, sampling occur s at th e negative edge. From th ere, 10 s

ha ve to be added to the t rigger delay (or 30 s subt ra cted) in order

to sample th e average ASE power.

Output Pow er and Sign al-to-Noise Ratio

By using a low video bandwidth (100 Hz) an d tr iggering ran domly(i.e., ADC tr igger set to FRE E), the OSA char acterizes the a verage

output power a s a function of wavelength. Such a tra ce consists of

the ASE a nd t he signal with a ll possible sour ce spontan eous

emissions, sidemodes, etc. Again, when the sampling occurs

synchronized at t he break s of th e modulated signal, the OSA

measu res t he n oise spectru m only. Therefore, th e signal power a nd

the signal-to-noise rat io at t he signa ls wa velength can be obtained

by measuring the average output power at t he signal peak an d the

noise power a t t he very same wa velength.

Output signal and noise spectrum Output noise spectrum


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Spectral Broadening Measurements

Across a long link, the spectru m of the source signal broadens due

to non-linearities in the fiber. It is ea sy to measu re t his effect a t

power levels clear ly above th e noise level, for exam ple, bymeasuring the source linewidth a nd t he signal width at the output

of the system. The time-domain technique also allows you to look at

signal broadening at power levels close to or even sm aller th an the

ASE power.

The H P 7145XB OSA offers t wo alterna tives to such a

measu remen t: (1) The ASE power spectru m can be su btra cted from

the output power spectru m, an d (2) a bu ilt-in AC mode allows

discrete measu remen t of the m odulated portion of th e received

spectrum.

In t he first case, the average outpu t power as a function of

wavelength an d th e ASE spectru m m ust be chara cterized. Then thedifferen ce is calcula ted u sing tr ace ma th (a built-in function of HP s

OSAs).

The second meth od takes advan ta ge of special signal processing

capabilities in the HP 7145XB series: If the AC mode is active, then

the OSA tak es a sam ple after a positive trigger edge and a sa mple

after a negat ive one and stores only the difference between th e two

samp les in m emory. Again, the delay between th e edge and th e

samp le point can be selected, but th e delay is identical for s amples.

The net effect is tha t only the modulated signal is measur ed and

any non-synchronized component (such as ASE power) is

suppressed.

OSA AC mod e Signal separated from ASE

Tunable Laser(Internal Mod.)

ASE PowerOSA Sample

Optical Power(EDFA Output)


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Determinat ion of Measurement Accuracy

The gain a nd n oise-figure-measur ement un certa inties for a

particular measurement can be calculated based on the

measu remen t t echn ique and t he specifications of th e equipment

used. In this section, t he significan t ga in a nd n oise-figureuncertainty terms are described and values determined using the

time-domain-extinction techn ique. This an alysis assu mes th at t he

EDFA ASE r elaxation t ime const an t is 400 s or greater, allowing

the TDE t echn ique to be u sed effectively. The example un certa inty

calculations are based on the use of the EDFA TDE program of an

HP 71452B Optical Spectrum Analyzer (which h as been calibrated,

see [2]), an d an HP 8168A/B/C Tun able La ser Sour ce providing -10

dBm a verage power. In order to illust ra te t he effects of the swept

wavelength versus single wavelength testing, example

un cert aint ies will be calculated for both mea sur ement situa tions.

The am plifier un der t est h as a gain of 20 dB an d a noise figure of 4

dB. Measurements should be made after th e tuna ble laser and th e

optical spectrum an alyzer h ave been allowed to warm up for onehour an d the auto-align routine has been ru n on th e OSA.

Amplifier gain is calculat ed as th e ra tio of the outpu t power (Pout)

to the inpu t power (Pin). For these examples:

G =Pout =

10 m W= 100

Pin p 100W

An uncerta inty of a given magnitu de affecting th e measu remen t of

either Poutor Pi n , but n ot both, will result in a gain u ncertain ty of

the same magnitude. For example, a 2% error in the measurement

of only Pout will result in a 2% error in the calculated gain. As a

result, th e gain uncerta inty can be determined directly from the

individua l uncertaint ies for the measu remen ts of Pout an d Pin.

Because t his is a r elative measurement, th ose uncertainties that

affect both measurements equally will cancel out and have no effect

on the gain un certa inty.

Amplifier noise figur e is calculat ed bas ed on th e am plifier gain (G)

an d th e am plified spont an eous em ission produced by the a mplifier

(NASE). The va lue ofNASE is equal to the a mplifiers out put noise

level (Nout). Due to the modulation of the source, there is no source

spontan eous emission at the a mplifier out put wh en th e OSA

samples Nout. Therefore,NASE= Nout:

N F=NASE

+1

=A+ C, A =N out , C =

1

hxvxGxBw G hxvxGxBw G

For simplicity, the t erms on the r ight ha nd side of the equat ion will

be referred t o as A an d C in th is ana lysis. The impact of an error in

the m easur ement of G or Nouton th e overa ll noise-figure er ror

depends on th e relative magnitu de of the term (A or C) or t erms

tha t it affects an d how that error mechan ism affects th e other

measurements.


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For a wa velength of 1550 nm an d a ba ndwidth of 0.5 nm, hxv

(Plan ks const an t mu ltiplied by th e laser frequency) is equal t o

1.281 *10-19 watt seconds, an d BW is equal to 62.39 GHz. With a

noise figure of 2.512 (4.0 dB), Noutis equa l to 2.00 W (=NASE) .Solving the noise figure equat ion for th e measu remen t with th e

DFB laser source yields:

NF =2.0x106W

+1

= 2.502 + 0.01 = 2.5121.281x1019Wsx100 x62.39x109 Hz 100

In th is case, the noise figur e calculat ion is dominated by A-term

(2.502), which conta ins t he m easur ed values ofNoutand G. An

un cert aint y of a given ma gnitude in th emeasu remen t of either

Noutor G will result in a noise-figure un certa inty of a similar

magn itude. For example, a 2% error in th e measu remen t of Nout

will resu lt in a (2.502/2.512) * 2% err or in th e calcula ted n oise

figure (assuming t his err or m echa nism does not affect t he otherterm s). In a case such as th is, with large gain an d an extinguished

source-spontaneous emission level, a simplified approximation of

the measu rement u ncertainty could be made by assuming that all

the err ors are a r esult of the A-term , and t he C-term is

insignificant.

Sources of Measurement Uncertainty

This an alysis takes t he conservat ive approach of treating a ll of the

individual measurement uncertainties as systematic - that is,

uniform probability distribution within the specified limits. An

error contr ibution is determ ined for each of the u ncertaint y terms

described below. The total u ncertaint ies are t hen calculat ed using

th e following equa tion:

un certain ty = 2 U2

3

where U is the uncertainty of each individual term. All

uncertainties are expressed as peak values. That is, an un certainty

of 0.04 dB will be written as 0.04 dB.

Connector uncertainty

When a fiber connection is made, either with a connector or splice,

there is an amplitude uncertainty associated with it. Three

conn ections contribute to the gain un cert aint y. They are t he source-to-OSA connection dur ing the sour ce measurem ent (Pinp) the

source-to-EDFA and EDFA-to-optical spectrum analyzer

connections during the output measurement (Pout).

In order t o determ ine the conn ector un certa inty in th e noise figure

measu remen t, th e noise-figure equa tion can be rewritt en

expanding the definition of gain:

NF =NoutxPin p +

Pin p= A + C

PoutxhxvxBw Pout


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The ratioNout / Pout in t he A-term will not be affected by conn ector

uncertainties since the two terms are m easured with th e same

connections. As a result, the A-term (Pinp) ha s th e conn ector

uncertainties associated with the absolute measurement of theinput signa l. The input measu remen t cont ains two conn ector

uncertainties: the source-to-OSA connection during the calibration

an d source measu remen t a nd the source-to-EDFA connection

dur ing the a mplifier test. Becau se the n oise figure is much great er

than 1/ G, the A-term is much greater than the C-term an d the

noise-figure u ncertaint y can be appr oximated a s cont aining two

conn ector u ncertaint ies.

With Connectors: If good qua lity physical-conta ct, fiber-optic

conn ectors are used a nd ma inta ined to ha ve 35 dB minimum

return loss and 0.25 dB maximum mismatch uncertainty, the

cont ribution to the gain u ncertaint y is 3 x 0.25 dB, and t he

cont ribution t o the noise-figure u ncertaint y is 2 x 0.25 dB.

With Fusion Splices: Assuming a maximum mismat ch un certa inty

of 0.05 dB per conn ection, the cont ribution to th e gain u ncertaint y

is 3 x 0.05 dB, and th e cont ribution to the noise-figure u ncertaint y

is 2 x 0.05 dB.

Source stabil i ty

Gain is calculated as the difference between two power

measu remen ts. Any cha nge in th e source power level between th ese

measu remen ts will directly affect t he m easur ement accur acy. The

one-hour stability specification for the HP 8168A Tunable Laser

Source is 0.05 dB (HP 8168B, 8168C is 0.03 dB), an d th is will be

used for the gain measurement uncertainty.

Source repeatabil i ty

When mak ing swept wavelength m easurements, th e tun able laser

source is stepped t hr ough all wavelength s two times. The source

amp litu de repea ta bility will affect swept wavelength

measu remen ts just as t he source stability. This term is n ot a factor

for single wavelength m easur ement s. The amplitude-repeata bility

specificat ion of 0.04 dB for th e HP 8168X Tun able La ser S ource will

be used for the gain measu remen t un certa inty.

Source spontaneou s emiss ion repeatabi l i ty

J 13Compa red to the ASE interpolation techn ique, the time-domain-extinction method has n o need to measu re th e sour ce spont an eous

emission. Therefore, its repeat ability ha s no impact on a ny

uncertainty.

OSA absolute amp litude accu racy

The measu remen t of the inpu t an d out put n oise levels are absolute

amp litu de measu remen ts. The gain calculat ion is based on a

relative measur ement, an d this term is not a factor in the gain

uncertainty.


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15

The a bsolute a mplitude accur acy (see [2]) cont ains two error term s:

the power meter t ra nsfer accur acy (0.1 dB) an d th e uncerta inty of

the OSA conn ection made du ring th e calibration. The conn ection

un cert aint y has already been tak en into accoun t an d does not needto be included a gain.

The power meter t ran sfer a ccur acy affects the A-term . For the

single wavelength an d swept wavelength exam ples, th is term is 0.1

dB * A/NF = 0.1 dB * (2.502/2.512) = 0.0996 dB.

OSA polarization se nsit ivity

The input a nd outpu t signals are highly polarized, an d the

polar ization sensitivity of the optical spectru m an alyzer will add to

the u ncertaint y of the mea sur ement . The amplified spont an eous

emission produced by the EDFA is not significantly polarized. The

HP 71452B Optical Spectru m Analyzer p rovides a polarizat ion

sens itivity of 0.05 dB from 1542 nm t o 1562 nm. Since th e gaincalculation involves two measurements of polarized signals, the

gain un certa inty ter m is 2 * 0.05 dB. This is also the cont ribution of

the gain uncertainty to the noise figure measurement.

OSA sca le fidelity

Scale fidelity reflects the accuracy with which the optical spectrum

ana lyzer can be used to make relative amplitude measurement s.

The gain calculation is based on a r elative measu remen t, and t he

absolut e noise-level measu remen ts can be considered a s r elative

measu remen ts with th e calibration source. The optical spectr um

an alyzer s scale fidelity sp ecification is eit her 0.05 dB or 0.07 dB,

depending on th e optical spectru m an alyzer settin gs and th e

amp litu de ra nge covered. This an alysis will use th e worst-case

condition of 0.07 dB. The contribution to the gain u ncertaint y and

to th e n oise-figure un cert aint y is 0.07 dB.

OSA resolution bandwidth accuracy

The mea sur ed spontan eous em ission levels are a fun ction of the

optical spectrum an alyzer s resolution bandwidth . This ban dwidth

is tak en int o account in th e calculat ion of noise figure an d, as a

result, th e accur acy with which t he resolution ba ndwidth is known

affects the noise-figure accuracy. The actual bandwidth of the 0.5

nm resolution ban dwidth filter is known t o within 3%, which

corr esponds t o a 0.13 dB uncertaint y in t he noise measu remen ts.

OSA interna l etalons

Inter na l etalons in th e optical spectru m an alyzer can cause an

amplitude uncertainty when measuring n arrow linewidth laser

sources. The measur ement of a broadban d signal, such a s

spontan eous emission, is n ot affected by t his m echa nism. This t erm

adds a m aximum u ncertaint y of 0.03 dB to th e gain measur ement

but h as n o affect on t he noise measur ement s. The contribution of

the gain un certa inty to the noise- figure measu remen t is equal to

0.03 dB * (A+C)/NF = 0.03 dB.


16/28

16

Source modulat ion s tabi l ity

The 100% on-off modulation of the tunable laser may cause,

between pulses, modes that oscillate with different efficiencies.

This can be observed as an insta bility of the pulse power up t o 0.5dB (the long-term sta bility is gua ra nteed by a pr ecise inter na l

power cont rol loop). To measu re t he a vera ge power of the

modulated source signal and th e modulat ed out put signal, the OSA

sam ples in a free-run mode (i.e.,without tr igger synchronization),

avera ges the dat a by a low-video bandwidth filter, and finally

smooth es th e tra ce by averaging dat a points being within 80% of

th e resolution bandwidth . The effective num ber of avera ges is

typically around 2,000. Therefore, th e gain u ncertaint y is

0.5/ 2000 =0.011 dB. This is also the contribution of the gain toth e noise-figure un certa inty.

OSA aliasing error

The sampling in free-run mode is controlled by digital circuits

which, in fact, cause only a ps eudo-ra ndom sa mpling. The resu lting

noise du e to aliasin g effects is less t ha n 0.5 dB wh ich is furt her

reduced th rough digital processing to a 0.086 dB or less gain

un certa inty cont ribution. Again, this a lso cont ributes t o the n oise-

figure un certa inty due to G in term A.

OSA trigger d elay

The OSA trigger delay is 10 s with 1 s resolution, and t he ASE

relaxation consta nt is 400 s or grea ter. In th e worst case,

digitizing r esults in a 1/2 coun t error. Therefore, th e relat ive error

in measu ring the t rian gle waveform is:

1+(10s+0.5s)/400s= 1.002442 or 0.0106 dB

1+(10s-0.5s)/400s

OSA pulse reco very

The ph otodetector in t he OSA receives th e complete m odulated

signal, whose pulse amplitude is 3 dB higher t ha n th e average

output power of the amplifier. With the falling edge of the square

wave, the electronics have to recover within microseconds from this

high power level and sett le precisely to the ASE power which ma y

be a thousand times weaker than the pulse. The measurement

error du e to recovery tails at ten microseconds after a 30 dB power

drop to be less than 0.2 dB.


17/28

17

Calculation of Total Measureme nt Unce rtainties

The following table sum ma rizes the err or term s calculat ed for t he

example measur ement s in the previous section an d shows the total

measurement uncertainties. The total uncertainties are calculated2

as 2x U where U is th e un certa inty of each individua l term .3

These un certa inty calculat ions a re based on th e use of linear

interpolation measur ements, as described herein, with an HP 71452B

Optical Spectru m Analyzer calibrated as described in Appendix A.

For th ese exam ple measur ement s, the source power is -10 dBm and

the E DFA un der test ha s a gain of 20 dB an d a n oise figure of 4 dB.

Single Wavelength Measurements Swept Wavelength Measurements

Gain Noise Figure Gain Noise Figure

Splice Uncertainty 3 x 0.05 (splice) 2 x 0.05 (splice) 2 x 0.05 (splice) 2 x 0.05 (splice)

3 x 0.25 (conn.) 2 x 0.25 (conn.) 2 x 0.25 (conn.) 2 x 0.25 (conn.)

Source Stability 0.050 0.050 0.050 0.050

Source Repeatability n/a n/a 0.040 0.040

Modulation Stability 2 x 0.011 2 x 0.011 2 x 0.011 2 x 0.011

OSA Aliasing Error 2 x 0.086 2 x 0.086 2 x 0.086 2 x 0.086

OSA Trigger Delay n/a 0.011 n/a 0.011

OSA Pulse Recovery n/a 0.200 n/a 0.200

OSA Absolute Accuracy n/a 0.100 n/a 0.100OSA Pol. Sensivity 2 x 0.05 2 x 0.05 2 x 0.05 2 x 0.05

OSA Scale Fidelity 0.070 0.07 (Gain) 0.070 0.07 (Gain)

0.07 (Nout)

0.07 (Nout)

OSA RBW Accuracy n/a 0.128 n/a 0.128

OSA Internal Ethalons 0.030 0.030 0.030 0.030 Total

Total Uncertainty

With Splices 0.22 dB 0.37 dB 0.22 dB 0.37 dB

With Connectors 0.54 dB 0.55dB 0.54 dB 0.55 dB


18/28

18

Setup the OSA by hitt ing INSTR PRE SET , AUTO ALIGN ,

an d AUTO MEAS . If desired, adjust the wavelength ran ge

( START , STOP ). Automa tic alignm ent is essen tia l for

accur at e results, an d it should be run every day (or if the OSA

has been moved or exposed to a vibration or mechanical shock).

Hewlett-Packar d also suggests calibrating th e OSA against a

power meter t ra ceable to a na tional stan dar d. See the OSA

man ua ls or [2] for deta ils.

2 Measure the Source Signa l

Activate th e intern al modulation of the TLS at 25 kHz

( OUTPU T POWER , MOD/CW , Freq ), an d enter a TLS

output power which is 3 dB higher th an t he desired average

input power a t t he a mplifier (the modulation ha s 50% duty cycle

which causes the average power to be only one-half of the

displaye CW power). Start th e OSA program for time-domain

measu remen ts by pressing USE R , EDFA TD , th en

Single Test .

1 The TLS shows the wavelength in vacuum. The OSA displays a slightly lowervalue because it m easures th e wavelength in air.

Set up for AUTO ALIGN TLS Screen

PerformingMeasurements

HP offers an OSA program (which is stan dar d in the H P 71452B

an d optiona l for the H P 71450B/71451B) to test EDFAs with th e

time-domain -extinction technique. It chara cterizes gain a nd n oise

figure at a single wavelength or at m ultiple wavelengths, a nd itallows th e measu remen t of the outp ut spectru m of an am plifier or

system. This section discusses in detail how to perform th e

measu remen ts. To describe keystrokes at t he OSA, it u ses th is style

for Front -panel keys an d th is one for softkeys . For other

instr umen ts th e style TLS Key is used.

Single Wavelength Operation

1 Set up t he I n st r um en t s

Conn ect t he outpu t of the TLS to the OSA using two patchcords

an d a t hrough a dapt er (i.e., replace th e amplifier by a

feedthr ough). Select th e desired WAVELEN GTH at th e TLS1,

select -10 dBm OUTPU T POWER (for th e OSA au to

alignment) with modulation tur ned off ( OUTPU T POWER ,

MOD/CW ), an d activate the outp ut.

P: -10.0 dBm: 1545.000 nm

Mod Out


Ext. Trig

Optical SpectrumAnalyzer

HP 7145XB

Feedthrough


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POWER: -10.0 dBmFREQ: 25.0 kHz: 1545.000 nm

19

The OSA menu Setup allows you to change th e trigger delay.

The default is10 s a s needed h ere. It m ay be necessary to select

a different value (for example, when chara cterizing a system).

You ma y also tur n on th e integra tion of th e ASE over a givenwavelength ra nge ( Setup , INTGRT ON ).

Measur e th e source power with Measur e Source (use CONT

SWEEP to acquire dat a an d SINGLE SWEEP to stop). If

necessary, adjust th e TLS power or wavelength . Hit DONE

when th e adjustmen t is complete.

OSA screen TLS screen

3 Character ize the Amplifier

Disable the TLS outpu t, an d insert the optical am plifier. For best

accura cy, do not disconnect pa tchcords from either th e TLS or

th e OSA, an d minimize any fiber m ovement.

Activate the TLS again and press Measur e Amplfr. As soon as

the OSA has taken a t race, it calculates all values and u pdates

th e result ta ble above th e grid.

Amplifier characterization OSA readou t fie ld

To repeat th e measur ement for the sam e amplifier at a different

input power or wavelength (or for a different amplifier), start

again at point 2. To leave th e program, press EXIT .

Optical Amplifier

Ext. Trig

Mod Out


Optical Spectrum AnalyzerHP 7145XB

25 kHz


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20

Multi Wavelen gth Measu remen ts

The EDFA TD program also allows chara cterization of gain and

noise figure over wavelength. In this case, th e stimula ting laser is

set to different wavelengths, and automatic measurements aredone for each step as described before. The OSA interpolates gain

an d noise figur e between th e discrete wa velength s in order t o show

a complete tr ace on t he screen.

Becau se the OSA already uses th e trigger inpu t to synchr onize the

samp ling a nd th e an alog/digita l conversion (ADC) with th e

modulation frequen cy of th e stimulus, alter na tive methods must be

used to tun e the laser over wavelength . One way is to step the TLS

an d the OSA man ua lly. Anoth er way is to use a simple program on

an externa l computer (see appendix).

Performing The Swee p Manual ly

1 Set up t he I n st r um en t sConn ect t he outpu t of the TLS to th e OSA using two patchcords

an d a t hr ough adap ter (i.e., replace the am plifier by a

feedthr ough). Select a TLS wavelength in t he center of th e

desired ra nge, select -10 dBm power (for th e OSA aut o

alignment) with modulation tu rn ed off ( OUTPU T POWER ,

MOD/CW ), an d activate the out put .

Setup th e OSA by hittin g INSTR PRE SET , AUTO ALIGN ,

an d AUTO MEAS . Choose th e OSAs START an d STOP

wavelengths a few nan ometers wider tha n t he intended test

range.

Activate t he inter na l modulation of th e TLS at 25 kH z

( OUTPUT POWER , MOD/CW , Fr eq ), an d enter an

out put power which is 3 dB higher th an t he desired average

input power a t t he a mplifier (the modulation ha s 50% duty cycle

which causes the average power to be only one-half of the

displayed CW power). Hit OUTPU T POWER , -Sweep ,

an d select th e desired wavelength ran ge ( sta rt, stop ), step

size, etc. Choose dwell = 1 an d cycles = 100, th en pres s

Manual .

2 Char acterizing t he Source Over Wavelength

Start the OSA program for time-domain measurements by

pressing USE R , EDFA TD , Multi

Test . The OSAmenu Setup allows you to change th e trigger delay. The

defau lt is 10 s as n eeded here. It ma y be necessary to select a

differen t valu e (for exam ple, when cha ra cterizing a syst em). You

may a lso tu rn on the int egration of th e ASE over a given

wavelength ra nge ( Setup, INTGRT ON ).

Measur e th e source power with Measur e Source . Use th e

SINGLE SWEEP mode. The OSA uses the trigger inpu t to

sample a ccording to the modulation. Therefore, th e sweep mu st

be man ua lly synchronized with th e tun ing of the TLS.


21/28

21

Other wise, the OSA might incorr ectly sam ple outp ut power or

out put noise while the TLS is tu ning.

For each wavelength step, hit TAKE SWEE P th ree tim es then

hit Next at the TLS. During the measurement , the OSA putsa blue marker from the bottom of th e display up to th e signal

peak. Repeat the TAKE SWEEP , Next sequence un til th e

full ra nge of interest is covered th en hit DONE .

3 Characterize the Amplifier Over Wavelength

Disable the TLS outpu t, an d insert th e optical am plifier. For

best accuracy, do not disconnect the patchcords from either the

TLS or the OSA, and minimize any fiber movement.

Activate th e TLS again an d press Measur e Amplfr at the

OSA. For each wavelength step, hit TAKE SWEEP th ree tim es

then hit Next at the TLS. During the first step, the OSA puts

a blue ma rker from th e bott om of the display up to the signal

peak. In th e second step, it uses a pink ma rker t o indicate th e

ASE level. Repeat th e TAKE SWEEP , TAKE SWEEP ,

TAKE SWEEP , Next sequence un til th e full ran ge of

interest is covered th en hit DONE .

4 Display the Result s

Display Data , Data Select allows you to display all the

stored information (gain, noise figure, input power, output

power, etc.) as a fun ction of wavelength .

To repeat th e measu remen t for th e same am plifier at a different

input power or wavelength (or for a different am plifier), star t

again at Point 2. To leave th e program, press EXIT .

Performing The Sw eep by Remote Control

Repetitive steps can be easily aut omated by using an extern al

program. Appendix A lists an HP BASIC example which reduces

the ta sk to these steps:

1 Set up t he I n st r um en t s

Conn ect t he outpu t of the TLS to th e OSA using two patchcords

an d a t hr ough adap ter (i.e., replace the am plifier by a

feedthr ough). Select a TLS wavelength in t he center of th e

desired ra nge, select -10 dBm power (for th e OSA aut oalignment) with modulation tu rn ed off ( OUTPU T POWER ,

MOD/CW ), an d activate the out put .


an d AUTO MEAS . Choose th e OSAs START an d STOP

wavelengths a few nan ometers wider tha n t he intended test

range.

Activate t he inter na l modulation of th e TLS at 25 kH z

( OUTPUT POWER , MOD/CW , Fr eq ), an d enter an


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22

output power which is 3 dB higher tha n th e desired average input

power a t t he a mplifier (the m odulat ion h as 50% duty cycle which

causes the average power to be only one-half of the displayed CW

power).

2 Chara cterizing the Source Over Wavelength

Start the BASIC program. F irst , it will query the instru ments t o

display their identification (check cables or HP-IB addresses if

th e TLS ident ificat ion or t he OSA ident ificat ion isn t disp layed).

The program ask s for the wavelength r an ge an d the stepsize.

Then it m akes a pau se to connect the TLS with t he OSA. After

hitting at the BASIC compu ter, it sta rt s to

cha ra cterize the source. When t his ha s been finished, th e

program a sks t o insert th e optical am plifier.

3 Chara cterize the Amplifier Over WavelengthAgain, hit at the BASIC computer t o sta rt t he

characterization of the amplifier. The program will display

!!! DONE !!! when th is is comp leted.

To repeat th e measu remen t for th e same am plifier at a different

input power or wavelength (or for a different am plifier), sta rt

again at Point 2. To leave th e program, press EXIT .

Sys tem Outpu t Test ( usi ng the OSAs EDFA_TD progra m)

The system output t est uses the TDE technique to measure th e

ASE power level right a t the wavelength of interest . Therefore, it

gets rid of problems (such a s signal broadening, ASE n ar rowing,

ASE filtering) which can pr ohibit a n a ccura te int erpolat ion.

1 I ns tr u men t S et u p

Conn ect t he outpu t of the EDFA (or a link) to the OSA. The

out put ha s to car ry th e 25 kHz squa re-wave signal, and its clock

ha s to be recovered to trigger the OSA (see Measur ement Setup

for Inst alled Links ear lier in th is documen t).


an d AUTO MEAS . Automatic alignment is essential for

accur ate r esults, an d it should be run every day (or if th e OSA


2 Meas u re the S igna l

Turn on ASE integrat ion (if desired) in the Setup menu .

There, you can also select whet her t he instr umen t should

display the signal-to-noise ratio or the noise power.

Start the OSA program for time-domain measurements by

pressing USE R , EDFA TD , th en Outp ut Test . Measur e

the out put power with Measur e Amplfr (use CONT SWEEP

to acquire dat a an d SINGLE SWEEP to stop).


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23

To repeat the m easur ement for the sam e amplifier at a different

input power or wavelength (or for a different amp lifier), sta rt

again at Point 2. To leave the progra m, press EXIT .

System Output Test (manu ally)

Anoth er way of looking at th e output spectr um of an EDFA or a

system is to look at th e ASE only, the s ignal only, or both . This can

be done with th e time-domain t echn iques in a ma nu al operat ion:

1 I ns tr u men t S et u p

Conn ect t he outpu t of the EDFA (or a link) to the OSA. The

output ha s to car ry th e 25 kHz squar e-wave signa l, and its clock

ha s to be brought from th e source using an electrical trigger

cable, or it ha s to be recovered (see Measu rem ent Set up for

Inst alled Links earlier in th is docum ent).

Setup the OSA by hitt ing INSTR PRE SET , AUTO ALIGN ,

an d AUTO MEAS . Automatic alignment is essential for

accur at e results, an d it should be run every day (or if the OSA


2 Measure the Total Output Spectrum

Setup the OSA (for example, CENTE R 1558 nm , SPAN 20

nm , REV LEVEL +10 dBm, RES BW 0.5 nm , Amptd ,

LOG 5 dB/DIV).

A modulat ed signa l may irritat e some of th e aut omatic

functions. Therefore, tur n off au toran ging ( Amptd , MORE ,

AUTORNG OFF), an d lock the tran simpedance of th e

photodet ector ( Ampt d , MORE , TRN SZLK On ).

Fu rt herm ore, force a high averaging ( BW , Swp , VID BW

30 Hz) and decrease t he displayed sweep time th ree to five times

( BW , Swp, SWPTIME 20 s).

The OSA now shows the tota l out put spectru m consisting of the

modulated signa l, amplified sour ce sponta neous emission, a nd

the ASE of the amplifier.

To compare t his mea sur ement with t he following ones, store this

measu rement by pressing Traces , STORE A , an d activate

th e next tra ce with Traces , tr ace B , CLEAR/WRT B .

3 Measure the ASE Spect rum Only

The ASE spectrum can be optained by extinguishing th e signa l:

Pr ess BW , Swp , MORE , MORE , adc trigger a nd

switch from ADCTRIG FREE to ADCTRIG NEGE DGE .

Check th e delay by hit tin g ADCTRIG DELAY (10s for 25

kHz squ ar e-wave modulation).


24/28

The tr ace on t he OSA is the ASE spectru m only. The noise

spectru m is slightly lower compa red t o the tr ace in step 2

becau se it does not conta in t he a mplified source spontan eous

emission an ymore.

Again, store the measu remen t by pressing Traces , tr ace B ,

STORE B , an d activate th e next tra ce with Traces ,

tr ace C , CLEAR/WRT C .

4 Measure the Signa l Only

Becau se th e signal is modulated, it can be detected by an AC

measu rement : Pr ess BW , Swp , MORE , MORE ,

adc tr igger an d switch to ADCTRIG AC . Check th e delay

by hit tin g ADCTRIG DELAY (10s for 25 kH z squa re wave

modulation).

The OSA now measu res th e signa l amplitude becau se it

measu res the pu lse peak a nd subt racts an y offset (such as ASE

power) in the pu lse break. The signal am plitu de is twice as

mu ch as t he average power due to the squa re wave modulat ion.

To calculate the average power, 3 dB has to be subtracted from

an y power rea ding out of this t ra ce.

24

ASE SpectrumSignal Spectrum

Total Output

Output spectra measurements

5 Signal-to-Noise Ratio Measurement

Place a ma rker on tra ce A ( Mark er , MORE , MORE ,

MKR TRA A) an d activate th e delta fun ction ( Mark er ),then place th e delta mar ker on tra ce B ( Mark er , MORE ,

MORE , MKR TRA B). Fu rth ermore, norma lize th e mar kerto measu re th e noise correctly by hitt ing Mark er , MORE ,

MKNOIS E ON). The readout will display th e signa l-to-noise

rat io for a 1 nm noise ban dwidth.


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25

Appen dix A

Multi-Wavelen gth Programm ing Example

1000 !=============================================

1010 ! HP 7145XB OPTION 052 MULTI WAVELENGTH TEST -

1015 ! REMOTE WAVELENGTH CTRL

1020 !=============================================

1030 ! June 7,1995

1040 !

1050 !

1060 DIM S$[255]

1070 Osa=723 ! IEEE 488 bus address

1080 Sweeptime=5 ! seconds

1090 Tls=724 ! IEEE 488 bus address

1100 Tunetime=1 ! seconds

1110 CLEAR SCREEN

1120 !

1130 ! check that all instruments are there

1140 OUTPUT Tls;*IDN?

1150 ENTER Tls;S$

1160 PRINT S$

1170 !

1180 OUTPUT Osa;ID?

1190 ENTER Osa;S$1200 PRINT S$

1210 !

1220 ! ask for the wavelength range

1230 INPUT Wavelength: START (nm) ? ,Wstart

1240 INPUT Wavelength: STOP (nm) ? ,Wstop1250 INPUT Wavelength: STEP (nm) ? ,Wstep

1260 !

1270 !

1280 !

1290 LOCAL Osa

1300 LOCAL Tls

1310 PRINT

1320 PRINT Connect the source to the OSA

1330 BEEP

1340 INPUT Press to continue ...,S$

1350 !

1360 OUTPUT Tls;:OUTPUT OFF

1370 Wvl=Wstart1380 OUTPUT Osa;EDFA_TD_ ; ! TDE user program

1390 WAIT 20 !

1400 OUTPUT Osa;EDFA_TD_ GC; ! multi wvl test

1410 WAIT 15 !

1420 OUTPUT Osa;EDFA_TD_ AC; ! measure source

1430 OUTPUT Tls USING 1440;:WAVE ,Wstart, NM

1440 IMAGE 8A, SDDDD.DDD, 4A

1450 OUTPUT Tls;:OUTPUT ON !

1460 WAIT 15 !

1470 !


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1480 REPEAT

1490 DISP USING 1440;WVL ,Wvl, NM

1500 OUTPUT Tls USING 1440;:WAVE ,Wvl, NM

1510 WAIT Tunetime1520 !

1530 OUTPUT Osa;TS; ! single sweep

1540 WAIT Sweeptime


1560 WAIT Sweeptime


1580 WAIT Sweeptime

1590 !

1600 Wvl=Wvl+Wstep

1610 UNTIL Wvl>Wstop+.0001 ! floating point!!!

1620 !

1630 OUTPUT Osa;EDFA_TD_ D ; ! done!

1640 OUTPUT Tls;:OUTPUT OFF1650 !

1660 LOCAL Osa

1670 LOCAL Tls

1680 !

1690 PRINT

1700 PRINT Insert the optical amplifier

1710 BEEP

1720 INPUT Press to continue ...,S$

1730 !

1740 OUTPUT Tls;:OUTPUT OFF

1750 Wvl=Wstart

1760 OUTPUT Osa;EDFA_TD_ AF; ! measure amplifier

1770 OUTPUT Tls USING 1780;:WAVE ,Wstart, NM

1780 IMAGE 8A, SDDDD.DDD, 4A

1790 OUTPUT Tls;:OUTPUT ON !

1800 WAIT 15 !

1810 !

1820 REPEAT

1830 DISP USING 1440;WVL ,Wvl, NM

1840 OUTPUT Tls USING 1440;:WAVE ,Wvl, NM

1850 WAIT Tunetime

1860 !


1880 WAIT Sweeptime

1890 OUTPUT Osa;TS; ! single sweep1900 WAIT Sweeptime


1920 WAIT Sweeptime

1930 !

1940 Wvl=Wvl+Wstep

1950 UNTIL Wvl>Wstop+.0001 ! floating point !!!

1960 !

1970 OUTPUT Osa;EDFA_TD_ D ; ! done!

1980 OUTPUT Osa;EDFA_TD_ AI; ! display data

1990 WAIT 3


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2000 OUTPUT Osa;EDFA_TD_ AJ; ! data select

2010 WAIT 3

2020 OUTPUT Osa;EDFA_TD_ CA; ! gain & NF

2030 OUTPUT Tls;:OUTPUT OFF2040 !

2050 LOCAL Osa

2060 LOCAL Tls

2070 !

2080 PRINT

2090 PRINT !!! DONE !!!

2100 !

2110 END


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For more information on Hewlett-Pack ard Test & Measu remen tproducts, appl icat ions or servicesplease cal l your local Hewlett-

Pack ard sales offices. A currentlisting is ava ilable via Web throug hAccessHP at http ://www.hp.com.If you do not have access to theinternet please contact one of theHP centers l i sted below and theywil l direct you to your nearestHP representative .

United States:Hewlett-Packard CompanyTest and Measurement Organization5301 Stevens Creek Blvd.Bldg. 51L-SCSant a Clara, CA 95052-80591 800 452 4844

Canada:

Hewlett-Packard Canada Ltd.5150 Spectru m WayMississauga, OntarioL4W 5G1(905) 206 4725

Europe:Hewlett-PackardEuropean Marketing CentreP.O. Box 9991180 AZ AmstelveenThe Netherlands

Japan:Yokogawa -Hewlett-Pa ckar d Ltd.Measurement Assistance Center9-1, Takakura-Cho, Hachioji-Shi,Tokyo 192, J apa n

(81) 426 48 3860

Latin America:Hewlett-PackardLatin American Region Headquar ters5200 Blue La goon Dr ive, 9th F loorMiam i, Florida 33126, U.S.A.(305) 267 4245/4220

Australia/New Zealand:Hewlett-Packard Australia Ltd.31-41 Joseph Str eetBlackburn, Victoria 3130, Australia131 347 Ext. 2902

Asia Pacific:Hewlett-Packard Asia Pacific Ltd.17-21/F Sh ell Tower, Time Squ ar e,

1 Matheson Str eet, Causeway Bay,Hong Kong(852) 2599 7070

Data Subject to ChangeCopyright 1995Hewlett-Packard CompanyP i t d i U S A 7/95

HP PN71452 2_Eribum Doped Fiber Amplifier Testing

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Transcript of HP PN71452 2_Eribum Doped Fiber Amplifier Testing