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Eindhoven University of Technology
MASTER
An optical amplifier using an erbium-doped fiber
Santbergen, M.T.M.C.
Award date:1992
Link to publication
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tLB EINDHOVEN UNIVERSITY OF TECHNOLOGYFACULTY OF ELECTRICAL ENGINEERING
TELECOMMUNICATIONS DIVISION EC
AN OPTICAL AMPLIFIERUSING AN ERBIUM-DOPED FIBER
by
M.T.M.C. Santbergen
Eindhoven, June 19th, 1992
Report of graduation studyperformed from September 1991 until June 1992Supervisor: prof.ir. G. D. Khoe ..:-Coaches: dr.ir. W.C. van Etten
ir. H.P .A. van den Boom
The faculty of Electrical Engineering of the Eindhoven University of Technologydoes not accept any responsibility regarding the contents of graduation reports.
Summary Ui
Summary
This graduation report is an account of my work for the Telecommunications Division of thefaculty of Electrical Engineering at the Eindhoven University of Technology. In this report theprinciple and the optimization of an Erbium-doped fiber amplifier (EDFA) is reviewed. Noise inErbium-doped fiber amplifiers is exarnined, and furthermore an account of the measurements ofabsorption and fluorescence spectra, amplification and noise figures is given. Finally a comparisonof optica! amplified IM/DD systems and coherent optica! systems is made.
Research in Erbium-doped amplifiers has indicated that pump wavelengths of 980 and 1480 omcan be used to arnplify signals with wavelengths of about 1550 om. An EDFA mainly consists ofan EDF, an optical coupier and a pump light source. Optimization of the EDFA involvesoptimizing gain, coupling efficiency and minimizing bending losses.
Noise in EDFAs consists of shot noise due to the signal and spontaneous emlSSlOn, signalspontaneous beat noise and spontaneous-spontaneous beat noise. For high signal powers and highgain the signal-spontaneous beat noise dominates, and for lower signal powers the spontaneousspontaneous beat noise dominates.
Comparison of optical amplified IMIDD systems with coherent detectioQ systems has shown,under ideal and equal conditions, a mere 3 dB SNR advantage of coherent systems over IMIDDsystems. This means that, through the introduction of EDFAs, the performance of IM/DD systemscan approach the performance of coherent systems. The choice between the two systems now onlyinvolves selectivity, channel spacing, costs and complexity of the receivers.
In preparation to the measurements, the 1480 om pump laser has been built in a housing. Thepump laser is therefore equipped with an adjustable current source and a temperature controller.The 1485/1555 om WDM coupier manufactured at the faculty is also built into that housing.Furthermore a Pascal program is written that transfers data from the Optical Spectrum Analyzer toa personal computer, where it can be written to disk or plotted on paper.
The measurements on the York EDF, using the 1480 om pump wavelength, have shown that thefiber didn't meet it's specifications. The optimum fiber length is much shorter than specified, theabsorption is higher and the amplification is lower than given by the manufacturer.
iv Contents
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1
2. Optical amplifier using an Erbium-doped fiber 22.1. The principle of an Erbium-doped fiber amplifier 2
2.1.1. Three-Ievel laser 22.1.2. Laser threshold condition: population inversion 32.1.3. The Erbium atom doped in optical fiber 5
2.2. Components of the complete amplifier 82.3. Optimization of tbe amplifier 9
2.3.1. Working conditions of fiber amplifiers 92.3.2. Optimization of an Erbium-doped fiber 112.3.3. Optimum length of used York fiber 11
3. Noise in Erbium-doped fiber amplifiers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 123.1. The noise components 123.2. Noise figure 15
4. Comparison of optical amplified IMIDD systems and coherent optical systems4.1. The effects of ASE on a cascade of amplifiers4.2. Optica! amplified coherent detection systems4.3. Comparison of direct and coherent detection systems
. . . . . . .. 18182123
5. Measurements on tbe amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 245.1. Absorption spectrum 24
5.2. Fluorescence spectrum 265.3. Amplification 285.4. Noise figure 315.5. Conclusions 32
6. Conclusions and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 33
References 34
List of abbreviations 35
List of constants and variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 36
Contents V
Appendix A: Specifications of the 1480 run pump laser. . . . . . . . . . . . . . . . . . . . . . . .. 38A.I About the laser 38
A.2 Charaeteristics 39A.3 Test data sheet CQF75-D #517 40
Appendix B: Data sheet of 148511555 nm WDM coupIer 41
Appendix C: Data of York DFI500 Erbium-doped fiber , 42
Appendix D: Power souree for the pump laserD. I Current souree0.2 Temperature controller
0.3 Power Supply
0.4 Housing of the pump laser
.............................. 4343485454
Appendix E: Listings PLOTFILE.PAS and IEEEIO.PAS 55
Introduction 1
1. Introduction
In optica! communication systems we can distinguish between two detection methods: directdetection and coherent detection. With direct detection (DD) the information carrying signa! isrecovered by detecting the power of the received optica! wave. Intensity modulation (IM) is afarm of amplitude modulation. It is not possible to recover FM or PM signaIs with directdetection (that is, if the optica! carrier is modulated), however if the received optica! wave ismixed with light from a loca! oscillator, an IF signa! is created, which contains both the phase andfrequency information of the transmitted signa!. This technique is called coherent detection.
The advantages of coherent systems over IMIDD systems are higher selectivity and moresensitivity. However, to realize such systems, the receiver has to be much more complicated. Thereceiver of an IM/DD system can be kept very simpIe, but for long distances more repeaters arenecessary.
We can amplify the optical signal by means of electronic regenerators or we can use optica!amplifiers. With electronic regenerators the optical signal is converted to an electrical signal,amplified electronica!ly and converted back to an optical signal for ftIrther transmission. Animportant drawback is the resulting electronic bottleneck. By using optical amplifiers this problemcan be solved. There are two types of optical amplifier:
• Semiconductor laser amplifier• Erbium-doped fiber amplifier (EDFA)
The semiconductor laser amplifier has the advantages of smaller size and lower power consumption. However, they are sensitive to polarization and have a large connection loss when connectedto transmission fibers. Therefore it seems that they are most suitable for use when combined withoptical integrated circuits and optoelectronic integrated circuits.
On the other hand, a fiber-type optical amplifier, like the EDFA, is directly connected to the
transmission fiber and connection loss is smal!. The power necessary for amplification is suppliedby pump light. Using this type of amplifier, many new appJications will become possible. The
EDFA has the merits of polarization insensitivity and low power level of pump light. Therefore, it
seems that EDFAs will be easily introduced into practical optica! transmission systems.
In this report the principle and the optimization of an Erbium-doped fiber amplifier will bediscussed (chapter 2). In chapter 3 noise in Erbium-doped fiber amplifiers will be discussed. Acomparison of optical arnplified fM/DD systems and coherent optica! systems will be made inchapter 4 and in chapter 5 absorption and fluorescence spectra, amplitïcation and noise figureswill be measured.
2 Optical amplifier using an Erbium-doped fiber
-2. Optical -amplifier- using-an Erbium::dopeçf fi~er_
In this chapter the optical amplifier will be discussed. First the principles of amplification using anErbium-doped fiber will be explained. Then the different components of the complete amplifier
wiJl be discussed and in the last section the optimization of an Erbium-doped fiber amplifier willbe examined.
2.1. The principle of 8n Erbium-doped fiber amplifier
The ampJification of light by means of an Erbium-doped fiber is based on the optical transitionsbetween different atomie levels. These levels have different energies and different populations. In
an Erbium-doped fiber amplifier (EDFA), optical signals can be amplified by means of a so-calledthree-Ievel laser system.
First the basic principles of the three-Ievel laser system wiJl be discussed [Wintjes].
2.1.1. Three-Ievellaser
Figure 2.1 shows both the relevant energy levels of a three-Ievel laser system and all relevanttransitions between these levels. Electrons are either in the El' the E2 or the E3 energy state. Nh
N2 and N3 are the number of electrons (population density) in the energy state Eh E2 and E3 ,
respectively. Photons can be absorbed or emitted by electrons that make transitions between two
states.
B
E 1 l
'-A 32
13 8 31 A 31 812 8 21
Figure 2.1 7hree-level transitions
A transition can either be spontaneous or stimulated, indicated by the Einstein's A and B coefficients, respectively. In this simplified model Bif equals Bfi. A spontaneous transition occurs if an
electron spontaneously decays to a lower state.
Optical amplifier using an Erbium-doped fiber 3
A stimulated transition is induced by electromagnetic radiation in the appropriate frequency
region. The incident photons promote excitation of electrons to a higher level or de-excitation to alower level if the energy of the incident photons match the energy difference between the two
levels involved. Photons can therefore be absorbed or emitted. Stimulated ernission photons are inphase with the incident photons.
2.1.2. Laser threshold condition: population inversion
To understand which conditions have to be satisfied for light to be arnplified in this system, wemust consider the steady state situation of state Ez. A steady state implies that the number ofelectrons per unit of time arriving at an excited level (stimulated absorption rate) is equal to thenumber of electrons leaving the same level (stimulated emission ratel. We can write the following
rate equations [Wintjes]:
(2.1)
(2.2)
(2.3)
(2.4)
where Wp is the pump power density needed to excite electrons to the upper state (a signal with
photon-energy E)-EJ, W the signal power density (a signal with photon-energy E2-EI ) and NIOI the
total Erbium density.
The stimulated emission rate of photons with energy Ez-EI equals WB21N2 and the stimulatedabsorption rate of photons with energy E2-EI equals WBI~l' Since B21 = Blz, the populationthreshold for amplifying light (producing more photons than absorbing) is: N2 = NI' If Nz > NI
we speak of population inversion.
Combining equations (2.1) - (2.4) the population threshold (Nz/NI = 1), which determines theminimum power needed for amplification at a signal wavelength À = hcl(E2-EI ), can be stated as
follows:
(2.5)
4 Optical amplifier using an Erbium-doped fiber
The population threshold must- be minimized and therefore th~_ restrictions on a suitable three-Ievel
system are:
(2.6)
and1
't = -; the lifetime of state 2..411
(2.7)
(2.8)
State 2 must have a fairly long lifetime to lower the threshold and is therefore called a metastabIe
state. The decay from state 3 to state 2 however, is usually a very fast phonon-assisted non
radiative process and therefore these levels are relatively close together. Of course one would Iike
the probability coefficient 8 13 to be as large as possible. If the pump rate Wp :: Wp B13N1 is high
enough to establish a population inversion, amplification can be accomplished.
Altogether four major conditions must be met to be able to establish amplification in a three-Ievel
system:
1: The existence of a metastabie state;
2: Fast decay from an upper state to this metastabie state;
3: High pump absorption probability;
4: High signal transition probability.
Only a few atoms do have three energy levels with characteristics that fit these requirements.
Erbium, doped in a host glass, is one of them.
Optical amplifier using an Erbium-doped fiber 5
2.1.3. The Erbium atom doped in optical fiber
So far the simplified three·level system. To have a good understanding of the Erbium-doped FiberAmplifier (EDFA) one has to consider the low-Iying energy levels of Erbium atoms doped in fiberglass as shown in figure 2.2 [Wintjes].
Energy ;\.
(eV) (nm)
4E-19 500
2H 11/2
ground state
metastablelevel
\asertranSit lons
15-161'm
_ non-radlatlve
de<:ays
/
qs 312
\ 9/2 ...4
I 912 "4
I 11/2"
4I 13/2
pump
absorpt Ion
I4I 15/2
,
1000
free-orblt
spln-orbit
spilt! Ing
crystal field spl,t!,ng
Figure 2.2 Energy levels ofErbium atoms doped in optica/fiber
Due to broadening of the energy levels (caused by Stark splitting, phonon broadening andtransition broadening) figure 2.2 shows transition bands instead of narrow transition lines.
Furthermore we can see that ao Erbium-doped fiber has several three-Ievel mechanisrns sincepumping cao be done fiom the ground state to one of the six possible upper states. The centralwavelengths of these six pump bands approximately are: 520, 540, 660, 800, 980 and 1480 om.
From all these upper states, Erbium ions cascade non-radiatively to the 411312 metastable statethrough multiphonon emission. Non-radiatively processes are inversely proportional to theexponential of the energy gap separating the two levels involved. The higher the phonon energy,the faster the non-radiative process. The energy gap between the 4113/2 and the 41 15/2 state is high
enough to reduce the decay to a large extent in comparison with the decay from higher pumplevels to the 41 13/2 state. This level is therefore metastabie. The pump transition probability depends
on which specific pump band is used.
6 Optical amplifier using an Erbium-doped fiber
- -All- levels wilt-be thermally- populated _acçQn;ling .10 Boltzman's statistics. This means that the
lower Stark components of both the 41 13/2 and the ground state will be higher populated than -thehigher Stark components. Thus absorption will be stronger at lower wavelengths (from lowercomponents of the ground state to higher components of the 411312 state) and emission will bestronger at higher wavelengths (from lower components of the 41 1312 state to higher components of
the ground state).
This Boltzman distribution thus results in different overall shapes of the absorption and emissionspectra of the metastable state and the ground state. The difference in wavelength between the
absorption and the emission band is called the Stokes shift. The Stokes shift permits the 1480 omband to be used as pump band. At 1480 om, unlike the other pump wavelengths, bath absorptionand emission occurs. As a consequence the population inversion will be somewhat lower than inthe case of, for instance, the 980 nm pump band.
Very important are the various loss processes. Apart from the already mentioned non-radiativedecay that can take place from any level, the most significant loss mechanism is excited stateabsorption (ESA). After excitation of an electron to an upper level, further excitation can occur 10
a still higher energy level through the absorption of anather pump photon or signal photon. This
can be seen in figure 2.3 in case of the 820 nm pump band.
45 3/2 t 800 nm_4_F.dg!...f/2~__-::;", .......I_Slgna I ESA
I.. -
4'11/? -~
4113/2
800 nmabsorpt Ion
4 115/2
Figure 2.3 800 nm signaJ ESA
The effect of ESA is detrimental because it depletes the metastabie level and makes inefficient useof pump energy. The electrons will ultimately return to the metastabIe state by non-radiative decay
but still a pump or signal photon will be lost to heat and therefore the overall pump efficiency wiJlbe reduced. ESA can take place fiom the final pump level (pump ESA) or the metastabie level
(signal ESA). Several higher states exist, resulting in unwanted ESA absorption bands.
OpticaI amplifier using an Erbium-doped fiber 7
Both known ESA bands and pump bands are shown in figure 2.4. As can be seen in this figure,
only the 980 nm and the 1480 nrn pump bands don't show any ESA. These bands are therefore infavor of the other pump bands, where efficient pumping is severely impeded. Within the pump
bands that suffer ESA, the pump wavelength must be adjusted to minimize ESA and maximizepump absorption at the same time.
10
• ESA
cQ 5-'Q.Lo(J"l
.D«
o~~....K.l.u..ul~ur&::W&Lu..L~.....L~.L.UL~......L:=~~m:L.u.o..ucuJ..uu..u..u.w.J
500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600
Wavelength (nm)
Figure 2.4 ESA and pump bands of an Erbium-doped fiber
8 Optical amplifier using an Erbium-doped fiber
2.2. Components of the co-m-plete amplifier - -
The three basic EDFA configurations are shown in figure 2.5 They are cJassified mainly by their
pump light propagation direction. The signa! light co-propagates with the pump light by forwardpumping and counter-propagates to the pump light by backward pumping.
Erblum-Ooped Fiber
Input 0----.,
Pump Light SOlTce
(Laser diode)
(a)
ErDlu",.- Doped FIler
Input~ ~'"'""-__-+
Opt lCallsola:<Y
Output
-+-__-0 Output
'nput o---j
Pump lig'1\ Source(Laser diode)
(c)
Optlcal
8and-Dass
Filter
Output
Figure 2.5 Basic EDFA eonjigurations (a) Forward pump type(b) Baekward pump type (e) Bidirectional pump type
The configurations shown in figure 2.5 cao be used as a power amplifier at the transmitter side inorder to increase output from a weak souree prior to transmission in a long systems fiber, as a
prearnplifier in order to amplify a weak signa! level to a level which is acceptable for the receiver
sensitivity, and as an in-line regenerative repeater.
An EDFA mainly consists of an Erbium-doped fiber, an optica! coupier and a pump light source.
In addition to these, an optica! isolator and/or an optica! band-pass filter is used to improve EDFA
performance.
Optical amplifier using an Erbium-doped fiber 9
Depending on which EDFA configuration is used, the optical isolator either prevents reflections toenter the EDFA from the output side or prevents the amplified signal and the pump signal fromreflecting back to the input of the amplifier (see figure 2.5). The amplified signal passes theoptical isolator with approximately 0.5 dB attenuation, but is attenuated 30-60 dB backwards.
The optical band-pass filter can be used to filter the ampJified spontaneous emission (ASE) inorder to minimize the amplifier saturation as weB as the noise due to ASE build up when more
than one amplifier is used. It can also be used to filter the unabsorbed pump light.
The fiber varies in length from a few meters to several hundreds of meters. Important parametersof the fiber are: the core diameter, the Erbium-radius to core-radius ratio, the erbium concentration and the numerical aperture (NA) or the refractive index difference Á.
The performance of the EDFA is astrong function of the pump band used [Pedersen] and onlythose for which high-power semiconductor laser diodes are available are practical. This restriets
the choice to 980 and 1480 om, where relatively expensive lasers can be obtained and 800 nm forwhich inexpensive laser diodes are available. Unfortunately, pumping in the 800 nm band leads to
relatively poor performance in silica fiber because of the strong ESA as mentioned in the previous
paragraph.
For combining the signal and pump beam we use a wavelength-division-multiplexer (WDM)
coupier. A WDM coupier can be made of fused optica! fibers and can be used for one specificpump band only. It should have a minimum fiber-to-fiber insertion loss for the signal wavelength
and a maximum coupling ratio for the pump wavelength.
2.3. Optimization of the amplifier
In the previous paragraph several criteria that influence the performance of the amplifier (with
respect to the different amplifier components) were already mentioned. The most important factorhowever is the Erbium-doped fiber (EDF) itself. The EDF should be optimized in order to:
• optimize gain• optimize coupling efficiency• minimize bending losses
2.3.1. Working conditions of fiber amplifiers
Before going into the details of EDF optimization we will, with reference to figure 2.6 [Povisen],discuss some general properties of the fiber amplifier. Looking at figure 2.6 we can see that the
operation of the EDFA cao be divided into three regions. In region 1, at smal1 input power levels,
the gain is independent of the signal input power. In this region of operation the quantum
10 OpticaI amplifier using an Erbium-doped fiber
efficiency-of tbe pump power ~ yer'j p()Of, witl1__pu~p photons mainly being converted to uselessphotons of backward and forward ASE.
For higher signal input powers (region 2 of figure 2.6) tbe signal gain curve approaches tbedeclining curve of 'ideal amplification' (defined by unity quantum efficiency of pump photons).
..............
10 010 -2
- 8 0 L..o............~.........~"'""-..................................................-....J.......................................""--"-........J
10 -10
signa I Input power (mW)
Figure 2.6 Gain and ASE to signa/ ratio as presented in {Povlsenj
A number of advantages in operating tbe amplifier in region 2 can be Jisted: a pump efficiencyclose to unity, signal output power higher tban power of tbe ASE, i. e., spectral filtering of tbeoutput signal becomes less important tban in region 1, decreasing gain for increasing signal input
power, i.e., gain control of cascade coupled amplifiers will also be less important tban in region1, and finally tbe noise figure of tbe fiber amplifier exhibits its minimum in region 2.
The extreme signal input power case is covered by region 3 where tbe power of tbe signa! hasreached such magnitudes tbat it dominates tbe population inversion a10ng tbe fiber by establishinga counter-balance between stimulated emission and absorption. Operation of tbe fiber amplifier in
tbis region cannot be recommended since tbe gain is weak, witb tbe random emission andabsorption processes along tbe fiber merely acting as noise sourees on tbe signal.
The shape of tbe gain curve is similar for arbitrary fiber designs (Note tbat tbe numerical values
in figure 2.6 don't correspond with those of tbe fiber we've used). The location of tbe intersectionbetween region 1 and region 2 may vary witb fiber design. In an optimization of tbe fiber design
tbe task is to move tbis intersection to an input power level as smalI as possible or equivalently to
maximize tbe small signal gain.
Optical amplifier using an Erbium-doped fiber 11
2.3.2. Optimization of an Erbium-doped fiber
As mentioned earlier, gain, coupling efficiency and bending losses should be considered. In[PovJsen) is shown that the small signal gain decreases with increasing threshold pump power (thepump power for which the EDFA starts to amplify). This means that gain optimization is independent of the actual pump power and can be performed by minimizing the threshold pump power.
The threshold pump power depends on the design parameters of the fiber and the absorption andemission cross-sections of the Erbium ions. The threshold pump power decreases with increasing
NA, decreasing v and decreasing ad (NA = numerical aperture, v = normalized frequency, ad =Erbium-dopant radius to core-radius ratio). However since the fiber gain saturates for smalIthreshold pump powers [Povisen), there is no advantage in decreasing the threshold pump powerbelow the point of saturation (which depends on the pump power).
Minimum coupling losses require a mode field parameter (MFP) WO as close as possibJe to that ofa standard fiber [Etten]. In order to minimize the bending Josses, the v number of the EDF shouldbe maximized. Furthermore the bending losses decrease when .1 (or NA) increases and thebending radius is constant.
This shows that there is a tradeoff between maximum gain (minimum v) and minimum couplingand bending losses (maximum v).
2.3.3. Optimum length of used Vork fiber
Because several parameters of the purchased fiber weren't known or didn't correspond with thespecifications (see chapter 4), it wasn't possible to calculate the optimum fiber length. An othermethod to establish the optimum fiber length, is measuring the gain for several fiber lengths.These measurements were aJready performed by drs. M. Babeliowsky of PTf Research. Thesemeasurements indicated the optimum fiber Jength to be approximately 1.9 meters.
12 Noise in Erbium-doped fiber amplifiers
3. Noise in Erbium-doped fiber amplifiers _.
The output of the optical fiber amplifier is a combination of the amplified signal and broadbandarnplified spontaneous emission (ASE). There will be shot noise associated with both components.At the detector additional noise terms wiJl be introduced by mixing at the detector of the arnplifiedsignal and the spectral components of the ASE, to give signal-spontaneous beat noise andspontaneous-spontaneous beat noise.
3.1. The noise components
For simplicity , we assume an optical amplifier with unit coupling efficiency, uniform gain G, over
an optical bandwidth Bo' and an input power of Ps at frequency Ws centered in the optical passband
Bo '
The electrical field of the optical signal at the output of the amplifier may be written as [Olsson]
Bo/21lv
e(t) = E.expj«,).l+~,J) + L E.JP~expj«w" +27tköv)t+~k)t~(-BoI2&y)
(3.1)
where Es and cl>s are the amplitude and the phase of the optica! signal, respectively. Esp.k and cl>k arethe amplitude and a random phase for each component of spontaneous emission. ö" is the distance
between the spectrallines of the spontaneous emission.
The photodiode current is given by
i(t) oe e(t) 'e(t)" (3.2)
The spontaneous emission power in the optical bandwidth Bo (i.e. for frequencies ws·Y1.Bo S w ~
ws+ InBo) is given by [Yariv, Olsson]:
(3.3)
where JLsp = N1,I(N1,-NI ) is the atomic inversion factor of the transition. It accounts for the largervalue of N2, and hence larger spontaneous emission power, in atomie (amplifier) systems in which
NI 7Jl!. O. h is Planek's constant and " is the optical frequency.
Noise in Erbium-doped fiber amplifiers 13
With E; ex GPz ' E;.A ex NJw (note that Esp,l isn't a function of k), M = Bj2ó/I and e."lh/l theresponsivity of the photodiode, equation (3.2) cao he written as
AI
+ 2JGPaN,,6v eT) :E cos(21tk6vt+~k-~.r)hv kc-AI (3.4)
JI M+ N(16v ell :E expj«<'>s+21tk6v)t+~I) • E exp-j«(,o).r+2'Rk6v)t+~k)
h~~ ~~
The three terms in (3.4) represent the signal, signal-spontaneous beat noise and spontaneous
spontaneous beat noise, respectively. The power spectrum of is-sp(t) is uniform in the frequeney
interval 0 - Ih.Bo and has a density of:
eT'l)2 12JGP N 6v- '(2M+l)'-S (1 hv 2
1.B2 "
(3.5)
The third term in equation (3.4) can be rewritten as follows:
AI AI
isp_sp(t) = N,,6v e'l :E :E cos(21t(kJ)övt+~k-~J)hv l=-JI jc-M
The de term is obtained for k = j and there are 2M+ 1 such terms:
(3.6)
i dt =N av e'l (2M+l)sp " hv
(3.7)
If we organize the terms in (3.6) according to their frequencies, we can see that the terms with
same absolute frequency but of opposite sign add in phase. Therefore, the power spectrum of the
spontaneous-spontaneous beat noise extends from 0 to Bo with a triangular shape and a power
density near de of
(3.8)
14 Noise in Erbium-doped fiber amplifiers
power spectral denslty
53. (3)
(2)52 f------i--------i'
( 1)S1f--------c-----j------=::,'""'c--.:....--
o Be
B ---7wo
Figure 3. J Noise power spectral densities at the receiver(1) shot noise (2) s-sp beat noise (3) sp-sp beat noise
51, 52 and S3 represent the folIowing values:
2SI = 2 e Tl [GP + P ]
hv s sp
82 = 4( ~~rGPsNo
S3 = 2( eT) )2N2 Bhv 0 D
(3.9)
Note that we didn't take into account the random polarization of the spontanec)Us emission. 50percent of the spontaneous emission has a state of polarization that is orthogonal to the state ofpolarization of the signal. This would result in a reduction of the signal-spontaneous beat noiseand the spontaneous-spontaneous beat noise by a factor of 2.
Noise in Erbium-doped fiber amplifiers 15
3.2. Noise figure
Consider an optical in-Iine amplifier:
Gq
Figure 3.2 Optical amplifier with a power gain G
If we were to detect the signal at the input of the amplifier, the main noise contribution would, inan ideal case (a noiseless receiver), be that of the signal shot noise, sa that the signal-to-noisepower ratio (SNR) at the input to the amplifier is
( 'i..
( P6e" y , "Î'
SNR. = JIL = P6" l/ .-) (3.10)
'" P e" 2hvB J2e-6-B e, hv . e
J ""- j/ ',:/,_ /; Ij
where B, is the electrical bandwidth.
The noise power at the output is that of amplified signal shot noise, shot noise due to ASE, signalspontaneous beat noise and spontaneous-spontaneous beat noise. The SNR at the output of theamplifier is thus [Olsson, Ramaswami]
(3.11)
The spontaneous-spontaneous beat noise is proportional to P~ and can be made negJigible to thesignal-spontaneous beat noise if the signal power P.(z) is not allowed to drop toa far and/or by
optical filtering. We can also neglect the shot noise due to ASE. For large gain G » 1, thesecond term in the denominator of (3.11) dominates and
(3.12)
16 Noise in Erbium-doped fiber amplifiers
11le noise figure NP,· oeing the ratio of the· input SNR to. the output valuez is tllus
(3.13)
which in an ideal three-level amplifier (NI = 0, #Lsp = 1) is equal to 2. The single high-gainoptical amplifier will thus degrade the SNR of the detected signal by a factor of 2 (3 dB).
If we consider the case where the amplifier is used as a preamplifier, the signal power usually isvery low and the third term in the denominator of (3.11) will dominate:
NF for P < .!hv (B -.!B )J:1 D:1 t
(3.14)
We can see that for very low signal powers the NF is inversely proportional to the signal power,
which means an increase of NF for decreasing signal powers. In figure 3.3 NF is shown as afunction of the signal power, for optical bandwidths Bo of 10 GHz, 1 THz and 100 THz,respectively.
20
~
.'" rI~ ,...
1-
m ~"Cl
<l!"-
10::lg'
<l!Cl]0Z
51r
J-70
B=100THZo
B= 10GHzo
, I ,~ , , :, , , , , , ,: , , I-60 -50 -40 -30 -20 -10 0
Signal power (dBm)
Figure 3.3 Noise figure as a junction of the signal power
In figure 3.3 the following values are assumed: gain G = 30 dB, 7/ = 1, #Lsp = 1, À = 1550 omand B. = 5 GHz. The figure shows that optical filtering improves the noise figure for low signalpowers considerably.
Noise in Erbium-doped fiber amplifiers 17
If more than one amplifier is used, noise will accumulate. We can rewrite (3.12) as:
(3.15)
For a cascade of n amplifiers the SNR at the output of the nth amplifier is
(3.16)
1 2hVB,(sm = ----p- 2J.Ll
tHII 6(3.17)
Using equation (3.13), the overall noise figure NFe is given by
NFe = 2f.ll +2J.L2
+ ... + 2f.l"G1 G1GZ,,·G"_1
(3.18)
:::: NP +NFz + '" +
NP,.1
Gel Gen
where Gei is the cumulative gain of the cascade up to the input of the ith amplifier and NFj the
noise figure of the ith amplifier. This formula differs from the Friis' formula, because the noise
figure of an EDFA is defined as the output signal-to-noise ratio compared to the shot noise
limitted SNR, which does not influence the ASE power.
'8 Comparison of optical amplified IM/DD systems and coherent optical systems
.4.. Comparison of. ()ptic:a.1 .amplified IM/DD systems andcoherent optical systems . . .. - ..
In very long fiber links, periodical amplification of the signal will be required. In this chapter we
will discuss the effects of ASE on a cascade of amplifiers and furthermore we will compareseveral system configurations.
4.1. The effects of ASE on 8 cascade of amplifiers
A generalization of expression (3.11) for the SNR of the detected signa} at an arbitrary point z
along the link is to write
SNR(z)(P.~~.~r
+ 4(e'l)2P (z)P (z) +hv " sp
(4.1)
where the last term in the denominator represents the mean-squared thermal noise of the receiver
(at point z) whose effective noise temperature is T,. R is the output impedance of the detector
including the receiver's input impedance. Equation (4.1) neglects the shot noise due to the ASE,
the spontaneous-spontaneous beat noise and intensity fluctuation noise of the souree laser. If the
signa} power P,(z) can be maintained above a certain level by repeated amplification, we can
neglect the receiver noise term. The SNR expression becomes:
SNR(z) (4.2)
where a 100 percent detector quantum efficiency (71 = 1) is assumed. Piz) is the signal power at
z, while P.,,(z) is the total ASE power at Z originating in all the preceding amplifiers (z' <z).
Let us consider the scenario of a long fiber with amplifiers employed serially at fixed and equal
intervaIs (Zo), as illustrated in figure 4.}.
Comparison of opticaI amplified IM/DD systems and coherent optical systems 19
PSP Cz)
P,;,o L ~,o ~,oL Ps,O ~,oL
G Jt1G Jt2 G
0 PsP,o Psp,oL 2Psp,o
+ ~
Zo
nPsP,O
Figure 4.1 A fiber link with periodie amplification
The signal power level Ps(z) at the fiber input and at the output of each amplifier is ps.D' The
signal is attenuated by a factor of L = exp(-azo) over the distance Zo between amplifiers and is
boosted back up by the gain G = V = exp(azo) by each amplifier to the initial level ps•D' The
spontaneous emission power Psp(z) is attenuated by a factor L between two neighboring amplifiers
and increases by an increment of Psp.D at the output of each amplifier. Using equation (3.3) and
assuming G » 1, we can write the SNR of the detected current at the output of the nth amplifier
as
SNR == PlI,o" 2[1 + 21l1ol..,,(exp(<<Zo) - l)]hvBe
where, because of the high signal and ASE levels, we neglected the thermal receiver noise.
(4.3)
Equation (4.3) suggests that the SNR at z can be improved by reducing Zo, i.e., by using smaller
intervals between amplifiers which entails reducing the gain G = exp(azo) of each amplifier. If we
take the limit of equation (4.3) as Zo -+ 0, the whole length of the fiber acts as a distributed
amplifier, with a gain constant g = ex just enough to maintain the signal at a constant value. The
SNR at z for a distributed amplifier is thus
SNR(z) (4.4)
We can compare the (ideaI) distributed amplifier with the discrete amplifier case of equation (4.3),
the case where only one preamplifier is used and the case where no amplifier is used.
20 Comparison of optical amplified IMIDD systems and coherent optical systems
Discreteamplifià-case:
p.,oSNR(z) =-------'~----
2 [l + 2(z./Zo)~.1Jl(exp(uZo) - l)]hv B"
where we used n = z/Zo.
One preamplifier:
p.,oSNR(z) :; ----~~----
2[1 + 2~.1Jl(exp(uz) - l)]hvBt
where a gain G = exp(az) is assumed (compensation for fiber toss).
No amplifiers:
(P,.oexp( -uz)iSNR(z) = -------==-------
4kTRtB
.r ( he\l )22P"oexp(-uz)hvBt
+ -----=----=.
(4.5)
(4.6)
(4.7)
In a low-Ioss optical fiber, say with adB = 0.2 dB/km, the distanee between amplifiers that areplaced Q'l km apart would be 1/ln(10002) = 21.7 km.
80
60
,---, 40
rnD'--' 20rrZUJ 0
-20
-400 50 100
(dl
150 200 250 300
Fiber lengt h (km)
Figure 4.2 SNR's oJdirect detection systems
(a) continuous amplification (b) discrete amplifiers spaeed by Zo = Q'l
(e) one preamplifier (d) no amplification
Comparison of optical amplified IM/DD svstems and coherent opticaI svstems 21
The launched power ps•o is 5 mW, À = 1550 Dm, B. = 109 Hz, and adB = 0.2 dB/km. Curve (b)
is to be read only at multiples of z = a'l = 21.7 km, which are tbe output planes of tbe optica!
amplifiers. Curve (c) assumes a gain G = exp(az) , and curve (d) assumes detection with a
receiver witb T. = 725 K (F = 4 dB) and an input impedance of 1000 O.
Note that if, for example, we need to maintain a SNR exceeding 50 dB, we must use a fiber linkshorter tban 100 km if no amplifier is used, but if optica! amplifiers are used every Zo = a'l
(=21.7 km), fiber lengths in excess of 1000 km can be employed. The advantage of continuous
amplification compared to amplification every cll is seen to be less tban 2.5 dB so tbat the latter
may be taken as a practical optimum. We can also see tbat for short fiber link lengths (z < 40
km) amplification has no advantages.
4.2. Optical amplified coherent detection systems
The signal-to-noise ratio of a coherent detection scheme can be written as [Etten]
SNR(z) (4.8)
where Plo is tbe local oscillator power and Àb and Àd are tbe intensities of tbe Poisson processes of
the background radiation and the dark current.
If we neglect the noise due to tbe background radiation and the dark current and assume that11 = 1, tbe SNR for coherent systems without amplifiers cao be written as
hvB~ +
P,(Z)SNR(z) ::; --------
_1_ . 4JcT~B~(hV)22Pw R e
(4.9)
In practical situations, tbe local oscillator power Plo is much larger tban the signal power Ps(z),when the signa! has traversed a long length of fiber.
If we consider again tbe scenario of a long fiber with amplifiers employed serially at fixed and
equal intervals, as iIlustrated in figure 4.1, we cao write tbe SNR of tbe detected cureent at the
output of tbe nth amplifier as [Olsson]
22 Comparison of opticaI amplified IM/DD systems and coherent optical systems
(e" y2P1•oP",. hvrSNR" = ---------~..:........-~------
e" e" ~~~2eP -B + 4PID-n~ (G - l)eB +--liJ hv e hv sp e R
where the second term in the denominator stands for the local-spontaneous beat noise.
(4.10)
If we take 7J = I, G = exp(azo), n = z/~ and if we neglect the thermal noise, (4.10) can bewritten as
p.. oSNR(z) = --------..::.:.:'-----
[1 + 2(~zo>~.(exp(ClZO) - l)]hvBe
For the case of a distributed amplifier the SNR becomes
P"oSNR(z) = -----"'~--[1 + 21-1.rpClZ]hv Be
(4.11)
(4.12)
80
60
40(IJU'--J 20CCZlf) 0
-20
-400 50 100
(a)
(b)
(c)
150 200 250 300
Fiber length(km)
Figure 4.3 SNR 's of coherent detection systems(a) distributed amplifier (b) discrete amplifiers (e) no amplification
The launched power ps•o is 5 rnW, the local oscillator power P/b is 5 mW, À = 1550 nm, B. =109 Hz, and ~cIB = 0.2 dB/km. Curve (b) is to be read only at multiples of z = a'l = 21.7 km,
which are the output planes of the optical amplifiers. Curve (c) assumes detection with a receiver
with T. = 725 K (NF = 4 dB) and an input impedance of 1000 D.
Comparison of optical amplified IM/OO systems and coherent optical systems 23
4.3. Comparison of direct and coherent detection systems
Note that equations (4.9), (4.11) and (4.12) differ from equations (4.7), (4.5) and (4.4),respectively, with a factor of 2 (3 dB). This means that , under ideal and equal conditions, theSNR of a coherent detection method is 3 dB Jarger than the SNR of a direct detection method.
However, in practice the SNR of an unamplified coherent detection system is 10-15 dB larger thatthe SNR of an unamplified IMIDD system (figure 4.4). With the use of optical amplifiers withIM/DD systems it is now possible to approach the SNR of a coherent detection system (there arereports of differences within 2 dB [Park]).
90 r--------------------,
80
---.J« 70'-----'
0::ZrJ)
60
-- ~ ..";:-'.
(a)
-- direct detect Ion- coherent detect Ion
(b)
(c)
(c) -~---------:~_-===:j
20015010050
50 L..--'-'-----'~~_____'___'_~~---'---'-~.........L___'____'>_~~~_____.L_~~_'_____"_'~-'--"
o
Fiber length (km)
Figure 4.4 Practical SNR 's ofboth direct and coherent detection systems(a) no amplification (b) distributed amplifier (c) discrete amplifiers
Coherent detection methods have advantages over IM/DD systems in terms of higher selectivity(channel selection by means of tuning the local oscillator laser) and smaller channel spacings.IM/DD systems are on the other hand cheaper to realize and are less complex.
24 Measurements on the amplifier
5 . Measurements on the -amplifier _
In preparation to the measurements the 1480 nm pump laser (datasheet in Appendix A) is built ina housing. The pump laser is tberefore equipped with an adjustable current source and atemperature controller (Appendix D). The 1485/1555 nm WDM coupler manufactured at thefaculty (datasheet in Appendix B) is also built in that housing. In order to be able to present the
measured data in a report, a Pascal program is written that transfers the data from the Optica!
Spectrum Analyzer (via an IEEE bus) to a personal computer, where it can be written to disk or
plotted on paper (Appendix E).
The measurements that were performed on the amplifier are the absorption and fluorescencespectra, the amplification and the noise figure.
5.1. Absorption spectrum
The absorption spectrum indicates which wavelengths can be used to pump the EDFA. However,one must keep in mind that several pump bands suffer from ESA (figure 2.4), which will degrade
the EDFA performance severely when using these bands. The absorption spectrum is measuredusing the setup in figure 5.1 :
Optlcal Spectrum
, 0 j~::~:.I"I~h?lPatch ...Cord .:
White Light Souree
iVIQCord
(a)
Erblum-Ooped Optlcal SpectrumFiber Ana Iyzer
I (() I Q lo.s.A.I"I~FiPateh. . ...Cord
(b)
Figure 5.1 Absorption spectrum measurement setup
The Optical Spectrum Analyzer we used is the ANDO AQ-631OB.
The spectrum measured with setup (a) is subtracted from the spectrum measured with setup (b),
resulting in the absorption spectrum in figure 5.2.
Measurements on the amplifier 25
25settings OptICai Spectrum Anallzer
Reference Level ·49d8mCenter Wavelength 9001 I100 rvn
20 5weep Wldth 100 rvnId>vResolutlon SM\Average Times 50
~
COU 15'--'cQ+-'Q~
0 10U1
..0<!:
5
0~~---'--'---l..-J..-'--'--"--,--'-'---'-'-~'--'--'c...L.J~---l..-J..--'---'-~-"--,--"--,--'-'---'-'--C-..J-~c...L.J-'--'---'--'---l..-J..--"--L..J
500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600
Wavelength (nm)
Figure 5.2 Absorption spectrum of1.9 m EDF
Additional measurements, performed with anoptical power meter, are:
• Coupling loss EDF to standard SMF forÀ = 1480 run: 1.7 dBÀ = 1538.6 nm: 1.7 dBÀ = 1551.8 nm: 1.7 dB
The values given in figures 5.2 and 5.3 include2 x 1.7 dB = 3.4 dB coupling losses.
20
m 152-cQ+--'Cl.(;
13 10«
~fefef\Ce Le....elCenter W8!velengtns...~WIOth~Iu~l()n
A...er-eoe Tmes
-<9 d8m1500 rrn2Orrnldl'1Q "'"50
The measurements show that the following pumpbands exist:
1600155015001450
o '-'--~~....L-..~~~_~~~-L...o~~-..J
1400
Wavelength(nm)
Figure 5.3 Absorption spectrum of 1.9 m EDFaround 1500 nm
• 515-545 nm 1
• 645-665 run 1
• 795-815 run 1
• 970-990 nm• 1480-1560 nm
1 These pump bands suffer from ESA (according to figure 2.4)
26 Measurements on the amplifier
5.2. Fluorescenét:fspe-ctrum
The fluorescence spectrum indicates which wavelengths can he amplified using the EDFA. The
spectrum is measured for both the co-propagating pump and the counter-propagating pump and asa function of the pump power coupled into the EDF (5.3, 10.6, 15.9, 21.2 and 28.1 mW,
respectively).
148D nm Erblum·Doped Optlcal SpectrumPUT1l) Laser Fiber Analyzer
I *' I f2xc~u~~re-----'-9~tch--+--1O~I--,--,2,---;,jO.SoA·ln••aCord Cord Cord f
(a)
1480 nm
Pump Laser
I ~LtJ P",hCord
"lhJl.O'!o.s.A.I~~ I I PatenCord
Optlcal Spectrum
WOMCoupier
Erblum·DopedFiber
Patch
Cord
Ana Iyzer(b)
Figure 5.4 F/uorescence spectrum measurement setup(a) co-propagating pump (b) counrer-propagating pump
Additional measurements, performed with an optical power meter, are:
• Attenuation WDM coupier for À = 1480 nm:À = 1538.6 nm:À = 1551.8 nm:
1.6 dB
2.1 dB1.6 dB
Figures 5.5 and 5.6 show that, for both the co-pTopagating and the counter-propagating pump,
signals with wavelengths of approximately 1536 nm and 1552 nm can be amplified. The
differences between the two spectra are due to the wavelength dependenee of the WDM coupleT
(Appendix B). When the spectra in figure 5.6 would be corrected fOT 0 dB attenuation of allwavelengths, the spectra would look similar to those in figure 5.5.
Measurements on the amplifier 27
Sêt tlr'qS (:PtlC.1 Spêctrum Analy'....
150
Ref~encl? levelCent.... W.velerqthSweepW,dthQ.esolut IonAverage TnT1ê!;
-40d~
1525 rrn20 rmldrv1rrn5
160015751550152515001475o1450
3' ~êl
C 100'-'...(l)
3: 281mW00- 212mW
<0 159mW\,!
50o-J l06mWG-O 53mW
Wavelength (nm)
Figure 5.5 F/uorescence spectra of 1.9 m EDFfor co-propagating pump
Settings OWcal Speel'''''' Analyzer
7S
Refererw:::e LevelCenter Wa ...~iengl hSWe€P WodlnResolu!rOnAverage TImes
-~J d&n1525 nrn20 nmld'V1 nm5
~ 50~ef
c'-'...(l)
:;;:00-
IO~ 25
+--'Q.0
o1450 1475 1500 1525 1550 1575 1600
Wavelength (nm)
Figure 5.6 F/uorescence spectra of 1.9 m EDF for counter-propagating pump
(28 Measurements on the amplifier
"-
5.3. Amplification
The amplification of the Erbium-doped fiber is measured as a function of the pump power and forboth the co-propagating and the counter-propagating configuration. The measurement setup isshown in figure 5.7.
1480 nm
Pump Laser
['tIQCord
~15386 I 15518 nm Cord
Signa: Laser (OrB)
WDMCoupier
Erblum-Ooped OptICai Spectrum
Fiber Analyzer
0 2,3({]) 4, 50 5lO.SoAolPatch PatchCord Cord
Ca)
1480 nm
Pump Laser
\~~6O.S.A.
Erbium· OopedFiber
[IlQ2,3~Cora Cord
15385/155; 8 nm
Signa l Laser (DFB)
WDM
CouPIer [21*1Cord
(b)
Patch
CordOptlcal Spectrum
Analyzer
Figure 5.7 Amplification measurement setup (a) co-propagating configuration(b) counter-propagating configuration
Additional rneasurements, performed with an optica! power meter, are:
• Signal power for À = 1538.6 nrn: 0.12 mW (-9.1 dBm)À = 1551.8 nrn: 66.0 IlW (-11.8 dBrn)
• Attenuation 1.9 m EDF, excluding 3.4 dB coupling losses:À = 1480 nm: 5.1 dB (2.7 dB/m)
À = 1538.6 nm: 29.6 dB (15.6 dB/m)À = 1551.8 nm: 16.9 dB (8.9 dB/m)
The signa! powers coupled into the EDF at 1538.6 and 1551.8 nrn are, in case of the co-propagating setup 52.5 IlW (-12.8 dBm) and 30.9 JlW (-15.1 dBm), respectively, and in case of thecounter-propagating setup 83.2 JlW (-10.8 dBm) and 44.7 IlW (-13.5 dBm), respectively. In bothcases the pump signal is attenuated 1.6 + 1.7 = 3.3 dB before entering the EDF.
Measurements on the amplifier 29
-.......- co-gropalj;Jlt'r'lgPUflP --.-. counter~rOP6Q8tngp~
302520
Sq1Il W....lIr'vlh m' 8 rII'lSlQNIPc... 660"W(·"'&cl8'I)
5fltrlg5 C»taI5llec1rll!'l"rtllf2'J
Atr.en:::e l l ·2l dQI'le:-nt .. * ,...tfl t!I!l' 8..."S....,Wdth 02,....~"RnolwloOn 01 m........,,'"'" ~
15105
11
/
",ff
ff
1f
.;
Of-------...-L-+=-------------i
- 20 ...........~...........~............~--.J..~~ ...........~-'-'-~-'--"
o
-15
cQ -5
<1>Z
a.Ecoà; -10-Q
302520
~11~C»II(.t~'''"...,.~
~ferPl'a'lMI ·Ucl'8'r'lcent l'lQttl 'SlB 6 lWl
S....,WdU''1 OZ"""'d...A6olUtoon 01rrn~......~ T"," 5
1510
//
5
5,---------------,
01--------_------.....,
-5éD:sc -10Q~
co~
":::: -150-Ecoà; -20-Q"";-a;z -25
,-30 ,
-350
Pump power In EDF (mW) Pump power In EDF (mW)
Figure 5.8 Net-fiber amplification 1.9 m Erbium-dopedjiber
jor Às = 1538.6 nm (left) and Às = 1551.8 nm (right)
We have also measured the amplification for signal powers < -40 dBm. These results were evenworse than the results shown above and are therefore omitted. From figure 5.8 we can determine
the following figures (the numbers between brackets correspond with the numbers in figure 5.7):
Table 5.1 EDFA amplification measurement results
Ico-propagating pump counter-propagating pump
1538.6 nm 1551.8 nm 1538.6 nm 1551.8 run
Max. net-fiber amplif. ()-004) 1.8 dB 3.3 dB 2.2 dB 4.3 dB
Max. fiber-to-fiber amplif. (2~S) -1.6 dB -0.1 dB -1.2 dB 0.9 dB
Max. EDFA amplif. (I~) -3.7 dB -1.7 dB -3.3 dB -0.7 dB
Pump influence • 36.0 dB 23.9 dB 34.4 dB 24.4 dB
Threshold pump power 17 mW 12 mW 17 mW 9mW
• (Amplification with Ppwnp = max) - (Amplification with Ppwnp = 0)
30 Measurements on the amplifier
. Additional measurementLwerep~rt:.ormed,with a HP 81?54SM laser souree (1310/1550 nm), tomeasure the wavelength dependence of the amplification around i5'36 -rim.These rneasureinents·should indicate a similar shape of the amplification to that of the fluorescence spectrum and thus amaximum at 1536 nm. However, the measurements showed that the maximum amplificationoccurred at a wavelength of approximately 1538 nm. We also measured that the attenuation of theEDF has its maximum at 1535 nm (tabie 5.2).
Table 5.2 WaveJength dependenee of ampJification of 1.9 m EDF around 1536 nm
Peak level (dBm) EDF Fiber-to-fiberWavelength attenuation amplification
(om) after WDM after EDF after EDF (dB) (dB)coupier (Pp = 0) (Pp = max)
1531.7 -28.5 -59.9 -30.4 31.4 -1.9
1532.8 -25.1 -57.9 -25.6 32.8 -0.5
1533.9 -22.1 -61.2 -23.9 39.1 -1.8
1535.1 -22.8 -63.1 -22.3 40.3 0.5
1536.3 -19.4 -59.0 -18.5 39.6 0.9
1537.4 -19.5 -52.0 -17.3 32.5 2.2
1538.6 -23.0 -46.1 -20.2 23.1 2.8
1539.7 -20.6 -38.8 -19.3 18.2 1.3
1540.9 -17.8 -33.0 -15.4 15.2 2.4
Note that the different spectral lines of the laser all have different peak levels. For a moreaccurate measurement (canceling out the signal power dependence of the amplifier), the power ofthe laser souree should be adjusted for eaeh spectral lioe in order to measure with the same peaklevel for all spectrallines. However, measurement with a tunable DFB laser source is preferred.
Measurements on the amplifier 31
5.4. Noise figure
The noise figure is measured witb tbe setup shown in figure 5.9.
1480 nm
Pump Laser
15386 nm
5D MHz Modulated
Signal Laser (DFB)
I~ I f2Cord
~lJL~ Patch
Cord
WDM
Coupier
Erb lum- Doped Electrlca/Spectn.rnFiber Analyzer
0 , ({))I 0 1eoSoAo I
Patch Patch
Cord Cord
(a)
1538 6 nm
Erblum-Doped
Fiber
[jJ,~Q---+----'({))~,,4Cord Cord
50 MHz Modulated
Signa 1Laser (DFB)
(b)
WQM
Coupier
148D nm
Pump Laser
f21~1Cord
~le.S.A·1Patch
CordElectrlcal Spectrum
Analyzer
Figure 5.9 Noise figure measurement setup(a) co-propagating pump (b) counter-propagaring pump
The Electrical Spectrum Analyzer we used is the Hewlett Packard HP70000 System with theHP70810A Lightwave Section with optical input and the HP70206A System Graphics Display.
Tbe 1538.6 om signal laser was modulated with a 50 MHz rectangular wave (Ps = lOJAW). Thesignal level measured at 50 MHz, without tbe amplifier, was -55.8 dBmlHz. Tbe noise level ofthe signal was below the noise level of tbe Spectrum Analyzer (-71.3 dBmlHz). Therefore tbeSNR of the signal without amplification was measured to be ~ 15.5 dB. Tbe SNR of tbe signalwithout the amplifier was calculated, with equation (3.10), to be ~ 130 dB (shot-noise limit).
Tbe SNR of the signal after amplification with co-propagating pump (Pf'II'V' max.) was measured tobe 0.7 dB. Witb counter-propagating pump (Pf'II'V' max.) the SNR was measured to be 2.6 dB.
32 Measurements on the amplifier
This mêaJlS that the -noise figure NF- for the amplifie~ with c.o-propagatinRPump is ~~.8 dB ~
NF,o ~ 129.3 dB and with counter-propagating pump 12.9 dB ~ NFCOIWtr ~ 127.4 dB.
The SNRs after amplification are very low because the signal is attenuated and a lot of noise isintroduced by the fluorescence of the fiber and the shot noise of the pump laser. Optical filteringof the pump signal should therefore increase the SNRs.
5.5. Conclusions
The measurements have shown that the EDF didn't meet it's specifications (Appendix C). Apartfrom the low amplification and high absorption, the optimum fiber length is much shorter than isgiven by the manufacturer, which indicates that the Erbium concentration might be too high.The 1.7 dB coupJing losses, however, are due to the optimization of the EDF for coupJing withdispersion shifted tibers, which have a larger numerical aperture NA than standard single mode
fibers.
The measur~ments indicate that the bands around 530, 660, 800, 980 and 1485 run can be used aspump bands. Furthermore, signals with wavelengths of approximately 1536 and 1552 run can beamplified. The maximum net-fiber amplitication measured with our EDF is 4.3 dB. For thecomplete EDFA amplification this results in an "amplitication" of -0.7 dB. The high noise figureis a result of the attenuation of the signal and the addition of noise by the amplifier.
Judging the amplification and the noise figure, we can see that the counter-propagating setup isslightly in favor of the co-propagating setup. This might he a result of the decline in performanceof the EDFA for lower signaI powers. In case of the counter-propagating setup the pump powercoupled into the EDF is higher than in case of the co-propagating setup.
The measurements aIso show that higher pump powers will not result in a higher ampJificationbecause the amplifier is already in saturation for the maximum pump power (28 mW in EDF).The ampJification of this fiber may on the other hand be increased when a 980 run pump laser isused. As mentioned in chapter 2, at 980 nm only absorption occurs, which will enlarge thepopulation inversion and thus the arnpJification. The use of the 980 nm pump hand also makes iteasier to filter the pump signal from the output of the amplifier, what will reduce the noise at thedetector amd therefore improve the NF.
Furthermore I would Jike 10 point out that there are some variations in the measurement results ofthe absorption and ampJification of the EDF. These are due to different settings of the opticalspectrum analyzer (Resolution and Average Times) and due to the polarization dependence of the
O.S.A ..
Conclusions and recommendations 33
6. Conclusions and recommendations
Research in Erbium-doped amplifiers has indicated that pump wavelengths of 980 and 1480 omcan be used to amplify signaIs with wavelengths of about 1550 om. An EDFA mainly consists ofan EDF, an optical coupIer and a pump light source. An optical isolator and an optical filter can
be used to suppress reflections and reduce the noise generated by the EDFA, respectively.Optimization of the EDFA involves optimizing gain, coupling efficiency and minimizing bending
losses.
Noise in EDFAs consists of shot noise due to the signal and spontaneous emlSSlon, signalspontaneous beat noise and spontaneous-spontaneous beat noise. For high signal powers and highgain the signal-spontaneous beat noise dominates, and for an ideal three-level amplifier the noisefigure is 3 dB. For lower signal powers the spontaneous-spontaneous beat noise dominates and thenoise figure is inversely proportional to the signal power. When amplifiers are used in cascadenoise will accumulate.
Comparison of optical amplified IM/DD systems with coherent detection systems has shown,
under ideal and equal conditions, a mere 3 dB SNR advantage of coherent systems over IM/DDsystems. This means that, through the introduction of EDFAs, the performance of IM/DD systems
can approach the performance of coherent systems. The choice between the two systems now onlyinvolves selectivity, channel spacing, costs and complexity of the receivers.
Measurements on the Vork EDF, using the 1480 nm pump wavelength, have shown that the fiberdidn't meet it's specifications. The optimum fiber length is much shorter than specified, theabsorption is higher and the amplification is lower than given by the manufacturer, which resultsin a high noise figure. Pumping of the fiber does, however, decrease the attenuation of the EDFwith approximately 30 dB.
A recommendation for further research is the use of a 980 om pump laser instead of the 1480 nm
pump laser. Because in this pump band only absorption occurs, this might result in a higher
population inversion and thus a higher amplification. The use of the 980 om pump band also
makes it easier to filter the pump signal from the output of the amplifier, what will reduce thenoise at the detector and therefore imprave the NF. The loss introduced by the WDM coupIer
could also be reduced. However, the best recommendation we can give is to purchase a newErbium-doped fiber, preferably one that is optimized for use with standard SMF.
34 References
References
[Wintjes]
[Pedersen]
[PovIsen]
[Etten]
[Olsson]
[Yariv]
Wintjes, RJ.W.
1he Erbium-doped Fiber Amplifier, Operation And ApplicationIVO-Report, Eindhoven: Instituut Vervolgopleiding, Technische UniversiteitEindhoven, 1991.
Pedersen, B. et al.
"Power Requirements for Erbium-Doped Fiber Amplifiers Pumped in the 800,980, and 1480 run Bands"
IEEE Phor. Technol. Lelt., Vol. 4, No. 1, pp. 46-49, 1992.
Povlsen, J.H. et al."Optimum Design of Erbium Fibre Amplifiers Pumped with Sourees Emitting at
1480 nm"
Electron. Lelt., Vol. 26, No. 17, pp. 1419-1421, 1990.
Etten, W. van and Plaats, J. van der
Fundamentals of Optical Fiber CommunicationsNew York: Prentice Hall International, 1991.
Olsson, N.A.
"Lightwave Systems With Optical Amplifiers"
J. Lighrwave Techno!., Vol. 7, No. 7, pp. 1071-1082,1989.
Yariv, Amnon
Optical Electronics, 4th ed.Philadelphia: Saunders College Publishing, 1991.
[Ramaswami] Ramaswami, R. and Humbiet, P.A.
"Amplifier Induced Crosstalk in Multichannel Optical Networks"J. Lighrwave Technol., Vol. 8, No. 12, pp. 1882-1896, 1990.
[Park] Park, Y.K. et al.
"Long Distanee Transmission with Erbium-Doped Fiber Amplifiers in Direct and
Coherent Detection Systems"
Invited paper ECOC-IOOC '91, pp. 86-96, 1991.
List of abbreviations
List of abbreviations 35
ASEDDE.S.A.EDF
EDFA
ESA
FMIMMFP
NANFO.S.A.PM
SMF
SNRWDM
Amplified spontaneous emissionDirect detection
Electrical spectrum analyzer
Erbium-doped fiber
Erbium-doped fiber amplifierExcited state absorption
Frequency modulationIntensity modulationMode field parameterNumerical apertureNoise figureOptical spectrum analyzerPhase modulationSingle mode fiber
SignaI-to-noise ratioWavelength division multiplexer
36 list of constants and variables
List of·constants and. variables
Constants:
cehk
Variables:
adA
B
B.Bo
eet)
El, E2 , E3
E.
Esp,k
gG
Ge
Geiiet)i.(t).,k
lsp
ir-sp(t)
i~sp(t)
LMNI> N2, N3
NF
NFeNFco
NFcotlnl<r
NF;
NoNr-sp
N~sp
N/()/
Plo
Speed of light in vacuum = 2.99792 H)'l [mIs]Electron charge = 1.60210 10-19 [C]
Planck's constant = 6.62559 10-34 [Is]Boltzmann's constant = 1.38 10-23 [J/s]
Erbium-dopant radius to core-radius ratioEinstein's coefficient for spontaneous emission
Einstein's coefficient for stimulated emissionElectrical bandwidth
Optical bandwidthElectrical field of the optical signal
Energy statesAmplitude of the optical signal
Amplitude of the kth component of the spontaneous emissionGain constant
GainCumulative gain
Cumulative gain of the amplifier cascade up to the input of the ith amplifierPhotodiode current
Photodiode current due to signalDc-term of the photodiode current due to the spontaneous emission
Photodiode current due to signal-spontaneous beat noisePhotodiode current due to spontaneous-spontaneous beat noise
Fiber loss
2M+ 1 = Number of spectral Hnes of the ASE
Number of electrons in the energy state EI, E2, E), respectivelyNoise figure
Cumulative noise figureNoise figure for co-propagating configuration
Noise figure for counter-propagating configurationNoise figure of the ith amplifierSpontaneous emission noise power spectral density
Signal-spontaneous beat noise power spectral density
Spontaneous-spontaneous beat noise power spectral density
Total Erbium density
Local oscillator power
Ppumpp.p.,oPsp
RT.v
al!ll
ó"A
71
À
Àb
Àd
JL, JLspJI
T
cJ>1
cJ>s<Al
list of constants and variables 37
Pump power
SignaJ powerLaunched signaJ power
Spontaneous emission powerOutput impedanee of detector including the receiver's input impedaneeEffective noise temperatureNormaJized frequencyMode field parameterSigna! power density
Pump power densityDistance in fiber link
Distance between two amplifiersAttenuation factor
Attenuation factor in dBDistance between the spectra! components of spontaneous emission
Refractive index differenceCoupling efficiencyWavelengthIntensity of the Poisson process of the background radiation of a photodiodeIntensity of the Poisson process of the dark current of a photodiodeAtomie inversion factorOptical frequency
Lifetime of energy state
Random phase of the kth component of the spontaneous emissionPhase of optical signal
FrequencySignal frequency
1 2 3 4 5 {;
0 o 0
°10 0
,I
1000 Q1 014 13 12 R
BOTTOMVIEW
38 Appendix A: Specifications of the 1480 nm pump laser
.. -Appendix A: Specification$ .9fJ.he 1480 ':lm pump laser
A.1 About the laser
The high-output InGaAsP/InP laser diode has the double-channel, planar, buried-heterostructure(DC-PBH) and emits at a wavelength of 1480 nm. The wavelength is suited for pumping ofErbium~opedoptical fiber amplifiers. The laserdiode is mounted in a hermetically sealed metallicDIL14 package. The front facet of the laser is coupled to a 9/125 JLm single mode fiber pigtail.An InGaAs monitor diode is coupled to the rear facet for monitoring the optical output power. Inorder to achieve a case temperature independent performance, a therrnoelectric cooler and atemperature sensor are incorporated in the package.
In figure A.l the pinning of the 1480 nm pump laser is shown.
1 Cooler anode2 NC) NC4 NC5 L0 anode, therm Istor,
caseGND6 Ne7 PDcathodeB PO anode9 LOcathode
10 LOanode, thermistor.case GND
11 thermistor12 NC13 NC14 Cooler cathoae
Ne =Not Connected
Figure A.1 Pinning ofthe 1480 nm pump laser
Appendix A: Specifications of the 1480 nm pump laser 39
A.2 Characteristics
This data is provided by the manufacturer and is measured at Tcaae = 25°C, Ir = 500mA and~rmiolor = IOkO, unless otherwise specified.
Laser diodeRadiant output power from fiber
Threshold current
Forward voltage dropCentral wavelength
MonitordiodeDark reverse current
(Vmr = 10 V)Monitordiode currentCapacitance at V mr = 10 V
ThermistorResistance at TI == TIb.rmiator E 25°C
Imd
min. 30 mWtyp. 40 mWtyp. 50 mA
max. 100 mA
max. 2.5 Vmin. 1460 nmtyp. 1480 nm
max. 1500 nm
typ. 25 nAmax. 100 nA
min. 15 J.LAtyp. 10 pF
typ. 10 kO
Thermoelectric coolerCooler current at ITcaae - Tt I = 15°C
Cooler voltage at IT..... - TIl = 15°C
l cool max. 1.0 A
Vcool max. 2.1 V
» ".. 020 50 CA)
:.....CI)
40 :en ):>:r+ '01.5 'e. '0
CD
3: 'I» ~
r+ Co
2: .s 30 I» x'..... ·en ~(1) :::>
Ol 1.0 a. :::r<0 .....
Cl) en~ :::> '00 0 20 ,Cl) CD> ..... r+ 0..c ~(J)
.0 (').0.5 -' ClI
0 ...10 Ö·
'''T1 ~i" 11I
,U' 0-0 ' I0 ·0 ...:T0 100 200 300 400 500 0 100 200 300 400 500 (I)
=tt ....Current (mA) :U' ~
Current (mA) 00... 0: ..... ::l
Temp ( 'C) 0 25 40 3'0
60 Ith (mA) 25.9 25.7 254 c3
Ec (mW/A) 133 133 133 '0
iiï50 Rs (Q) 20 18 20 11I~
<[ V30 (V) 093 093 0.93:i 40 IJOmW (mA) 253 252 253.....
Wa.vel. (nm) 1494c(J)"- 30 Rntc (kQ) 100 9.9 98'--:::JU Ipelt (mA) -102 -410 -6790+;;:' 20 Ms (~A/mW) 1.0 1.0 1.0c0:2
10
PHILIPS OPTOELECTRONICS CENTRE0
0 10 20 30 40 50 (Copled by M Santbergen)
LJght output (mW)
»uuCD::J0.x'al
CIII...III
en:TCDCD...S..".coUI----UIUIUI::J
3~c~nocu~
CDJ~Q)
en:::TCDCD~
o.......a~00(J'1
--...a(J'1(J'1(J'1
~
3~c3:(")oc:
'"C-CD...
»"'C"'CCD~
C._.><DJ
·49d9'rt1100 ...00.-.5""(J
~fer~rnLewt
Ctnt'" WI'l'tleorlQUrs....eo WcfthI«wlvliQnAvenQlt Trnn
1485+1555 nm output
1555 rm Ifl)ut
1485 rrn lrou!
5
Wavelength (nm)
OL.-.-....~.L......~__'__'_~L..l__o~_'_'_~....L..1.~ ............c..........~.L......~__'__'_~ ...........~.._...J
600 700 800 900 1000 1100 1200 1300 1400 1500 1500
10
15
20 r------------~---------___,
1485/1555 nm WDM Coup Ier
1555 nm Input
1485 nm Input
·~gd8T'l
1500,."}O tm/dlot,~
(J
·49d8'n1500 fTI'I20rmlarw5""10
1550 1575 1600
srtllngsODtlCfll SoectrtlT'l Ar>etyCE'f
RrtI",.ncelt'l91CtntOl" Wave~ngH·..SWlNIPWrdth~~tlon
....~a~T...-s
Rgfp.-nc:. un,l(l"nlet W.llW!'lpngths..ep WlO1hRloSOIUllOl'lA.frflQtT~
1475 1500 1525
1555 rm lrJ)ut
1425 1450
IQ
0~------~------~",_-----____,l...L----I
Wavelength (nm)
5
Wavelength (nm)
oL.......~-'---'-~~--'-~~-'--'-~___...J~~.o_L~~__'___...~~'_'_~__.J
1400
5
15 ,----------------------------'-------,
10
15
-5
20 ,-------------------------------,
-10
_ 15 '-'--~~........J.~~->-.L~~e-.L~~__'___'~~ .........~~L.._~........J.~~___..J
1400 1425 1450 1475 1500 1525 1550 1575 1500
'"a01cQ::JoU
42 Appendix C: Data of Vork OF' 500 Erbium-doped fiber
The York DF1500 amplifier fiber (serial number: ND712-o1) is designed for use at both 980 omand 1480 om pump-wavelengths. The mode field diameter (MFD) has been designed to match thatof dispersion-shifted telecommunications fiber.
Specifications:
Core composition:
Numerical aperture:Cut-off wavelength:Dopant-concentration:
Fiber geometry:
Cladding diameter:Cladding ovality:Core diameter:Concentricity:
Amplifier performance:
Maximum gain:
Gain coefficient:
Germano-Silicate Glass
0.2-0.22850-970 nm100-140 ppm
125.8 Ilm
1.3%
2.8 ILm
0.93 Ilm
approx. 25 dB1.75 dB/mW (achieved using 16 m of EDF, pumped at 1485 nmand with signal power < -42 dBm at 1535 nm)
Appendix 0: Power souree for the pump laser 43
Appendix 0: Power souree for the pump laser
0.1 Current souree
The principle of the current source is iIlustrated in figure 0.1:
Vref
P1
-vee
Figure D.l Principle of the current source
The variabie voltage V+ on the wiper of the potentiometer is placed over resistor Rl by means offeedback. This results in a current of (V + + Vcd/R1 through the laserdiode.
Because of the extreme sensitivity of the laserdiode to current spikes it is necessary to place acapacitor parallel to and an inductor in series with the laserdiode. To reduce the output-current ofthe opamp a transistor is added to the circuit (figure 0.2).
Vref
P1
-VCC'"
R5
-vce
c
Figure D.2 Current limitation ofthe current source and protection against spikes
44 Appendix 0: Power souree for the pump laser
Limitation of the current through the laserdiode can be realized by resistors R3, R4 and Rs anddiode D;. Take note that -V~e' -.<:: -Vee. -Thisis necessaryto- be able 10 realize à zero currentthrough the laserdiode.
Reference voltage VnJ is obtained by using a reference diode (figure 0.3). A maximum value for
voltage V+ (and thus the current (V+ +Ved/R I through the laserdiode) can be set by replacing PIin figure 0.2 with R7, PI and P2 in figure 0.3:
(D.1)
P2
P1 v+D2
L---r----J6
-vee
Figure D.3 Rejerence voltage and limitation of V+
As can be seen in appendix A the DILl4 package is equipped with a photodiode. This photodiode
can be used to monitor the optical output power of the laser. It is a1so necessary to monitor thelaser-current in order to establish any possible degeneration of the laser. The complete circuit is
iIlustrated in figure 0.4. Note that the numbering given in figure 0.4 differs from the numberingused in previous figures. In table 0.1 the component values for the 1480 nm laser are listed.
These components WIII not be placed on the PCB
-Q...:Yct>
Uc3u
äïenct>..
R7 RB R9 R1D
,2 1 3 Ii __I~~~~~~~_~=_=_~_~_~_O --l.-1--1c)q.76~_ U1 3=Vout I~
::::::: C1
-vcc
46 Appendix 0: Power souree for the pump laser
- Table D. J Listing of component values ofcurrentSOUfce
Components I1
ClC2C3C4CSC6C7CSDlD2D3D4LlLDMIM2PIP2P3P4RlR2R3R4R5R6R7R8R9RlORIlRI2TlTIUIU2
Values
tant. IOlLf22nF
tant. IJLFIJLF
tant. 3.3ILF22nF
tant. IIlFIOnFLED
KA3365VIN4007
Monitor diode220JLH
LaserdiodelOOJLA meterlOOJLA meter
20kOtOkOtOkO5kO
Ik2k433kIMIk
13k8k2130
3E3,3W3E3,3W
3k910k
BC414MJE3055LM790SLM741
Appendix D: Power souree for the pump laser 47
The design of the printed circuit board (PCB) is performed with the programs OrCAD and
Autotrax.
0 J1fm mlO 0iIlIl... 0:: n .... 0L
~g=! QJgo :lI'" ::YI
15 r / dQ C» ..Jl'" "t: ro1cm fT -, ---- f\ +, lÏ
/Ij % E~ ~ ao :J; +>o n +>c "~ cr al'" ro 0 coc: SJCl ;) coI nIU '!! UCl 0Cl C 0-t: /Ij<I( z::'"n 0.....
0.-~
L~_ __ef 0.- co0 - 0 I
~l-C/.)
Figure D.5 PCB-design of current source
P3
OLD L1
-e::J;~ O=~ DJ
J=-O" ~O:O=O D.OND
~+D+ 0tu
l P2 Ct
O·t.8~t- ~u Cl
-c::J- +DD~~~ M+l\J+
5
*~a uu
l~
Figure D.6 Placemenr of the components
::YId-'
LQJ>oa.aI-
couQ..z:.o~coI~
lC/.)
48 Appendix 0: Power souree for the pump laser
-.. - -0.2 Temperature controller._,
The temperature is measured with an NTC resistor which is used in a Wheatstone bridge.
Vref
R1
R T
6V
Figure D. 7 WheatslOne bridge with me resistor
The resistance of the NTC resistor as a function of the temperature can be written as
/(0.2)
where T is the absolute temperature in K and A and B are constants. For the Siemens Kt9 NTCresistor, B equals 3340 K and with RT = tOkO at a temperature of 25°C; this means thatA = 0.136 O. The voltage AV as a function of the temperature reads:
(0.3)
RJ will he chosen in such a way that the relation between ~V and T is as linear as possible at atemperature To:
(0.4)
With (0.2), (0.3) and (0.4) RJ can he determined:
(D.S)
Appendix 0: Power souree tor the pump laser 49
We require the bridge to he in balance for T = To. This puts conditions on the values of Rz andR'j:
AV(TJ =0
Rz = Rl
~ Rr
For example: Rz = Rl = 7kO and R) = RT = 10kO.
(0.6)
(0.7)
Temperature To can be adjusted by adding a potentiometer P in series of resistor R) in figure D.7.
Minimum temperature: TIIIÏD
Maxim T 3340um temperature: max = ----
m(0.~6)3440
With R3 = 8.2kO and P = 5kO: l70e < 1'0 < 30oe.
(D.8)
(D.9)
To keep the temperature constant we use feedback: the temperature signal À V is carried back tothe Peltier element by means of negative feedback. Voltage VR can be used to vary the temperature, but since this is not necessary for our purposes VR equaIs 0 V (figure 0.8).
R5
II
K2BVR
A
-L
lp
Figure D.8 Feedback circuit
Kl presents a differential amplifier (figure D.9) and Kz is the final stage which converts thevoltage on point A linearly to the Peltier current lp and in this manner acts as a current source(figure D.10).
(2P
I )V = K 'A V 0; - +1 'A VB 1 ~
and (0.10)
50 Appendix 0: Power souree for the pump laser
+
6V
P7 R7
P6
P1 >-_.L---o Vs
R6
R7R7
Figure D.9 Differential amplifier
+ 15V
PEL TIER
RB
Ii
l-1SV
Figure D.JO Current souree for Peltier element
The complete circuit of the temperature controller is depicted in figure 0.11 and the component
values for the pump laser are Iisted in table 0.2. Note that the numbering given in figure D.ll
differs from the numbering used in previous figures.
Wheatstone brIdge wrth NTC
+15V
differentlal amplifier f,nalstage
+ 15V .15V
T2
R17R16R15
-15Y-15V
R12
These components wlll not be placed on the PCB
r------,, ,I ,I II ,L J
R10
R 11R9
RB
R7
1=16
P2
R20-15V
R2
D2 R3 R4
R18
oetect,on of extreme temperature
.15V
R1
j----------III
: qFELTIER qIIIL _
.------ --I, ,: 01 '":: ~:!.._---- --!
U'I....
52 Appendix 0: Power souree for the pump laser
Table D.2 -Listingof component va(~fs oftemperature controller
Components 11
DlD2D3D4
NTCPELTIER
PIP2P3P4RlR2R3R4R5R6R7R8R9
RIORIlRl2Rl3Rl4Rl5Rl6R17R18Rl9R20Tl1'2UIU2
Values
LEDKA3365V
tN4148LED
ThermistorPeltier element
SkOtOkO20kOtokO
lk52k46k86k88k24k74k73k33k33k33k310k
Ik10k5k6240
3E3,3W10k42klk5
BC414MJE3055LM4741LM747
Appendix 0: Power souree for the pump laser 53
The design of the printed circuit board for the temperature controller is also performed with theprograms OrCAD and Autotrax.
+0:;>o
o
I- 0 I- 0~
~ 0 .c Ij ~
Q.I
~f'~ :JI
~ Öl ./d
+> "C ,.., -':J +> 0:J % Er .r Nlil ::i 0Ol' +>lil C1- I +>Q lTQ r 0r 0 f:Q
.si_ :l
11 n f:QI: 't!Q 0 U" c
ë1\1 CL,... l-n..... z:.
a:; 0
~ 0U
~CL
tl :LWI-
Figure D.l2 PCB-design of temperature controller
0 '1 ~ tl
-e:::J- ~~ O~'"(I~ ca IIn
~.---~---'~~~~D)21lJ-;:::::]-
--e:J!.~
gU~;9/J ~~
-c::J- -;:::::]-~ll~f""---j~110 JiN
D*~Ol~
Figure D.l3 Placement of componems
:Yld-"
s...QJ>oQ.oI-
f:QUCLlr.oUCl..:LWI-
54 Appendix 0: Power souree for the pump laser
- . -.
0.3 Power Supply
The power supply provides the voltages -]2/15 (adjustab]e), 0 and + 12/15 V and a maximum
current of 2.5 A. The module can be used with the 19 inch cases.
0.4 Housing of the pump laser
The circuits, together with the laser, are built into a module that can be used with the 19 inchcases. The 1485/1555 run WDM coupIer is also built in a ]9 inch module. The fronts of themodules are shown in figure 0.14:
stroom aan
x5mA mW
optisch uit
EB EBtemperatuur
UIT EB AAN EB EB
t(8regelaar te
EC aan hoog
I
EBstroom door laser
1480 nm pomp laser
optisch vermogen
Figure D.14 Fronts of the modules
WDM-eoupler
1555nmin
G1485nmin
G1555+1485 uit
GG
tC8EC
Appendix E: Listings PlOTFILE.PAS and IEEEIO.PAS 55
Appendix E: Listings PLOTFILE.PAS and IEEEIO.PAS
PLOTFILE.PAS
This program enables the user to transfer data from the Optical Spectrum Analyzer (O.S.A.), viathe IEEE bus, to a personal computer, write it to disk and/or to plot the data that is visible on theO.S.A.-screen. The O.S.A. and the plotter shauld be connected ta the computer with a GP-IBcabie. The adresses of the O.S.A. and the plotter should be set to [30] and [05], respectively.When started, the program will prompt the user for input when necessary.
PROGRAM PLOTFILE:
USES IEEEIO,CRT:
VAR Marker,Response,YssKey,Value,SensitivityTemp,Temp1,Error,Stap,x,y,sCoordX,CoordY,Reflev,Swpwd,Hokjes,Ctrwl,Resoln,Avr,YsReceiveResul tInit,AccAB,NegFout,stoppenlblFileStringOutFile
String;Cher:Integer;
Real;Array[O •• 4072J Of Char;Array[1 ..581l Of Real;Booleen;Stri ng [50J;String[20J;Text:
Procedure Number(Var Result:Real);Var Strng : String;
Error : Integer;Begin
Resul t := 0;Error := 0:Strng := ":Temp := Tetrp+1;While (Receive[TempJ <> ',') And (Temp < 4073) 00Begin
Strng:=Strng+Receive[TempJ;Temp:=Tetrp+1;
End:Val(Strng,Result,Error):If (Error <> 0) And (NegFout = False) ThenBegin
IJri teln:Wri teln:Writeln('Fouten in de Data·overdracht.'):Writeln;Writeln('A. Stoppen.'):Writeln('B. Doorgaan, waarbij het programma de foute data aanpast. Het resultaat zal'):Writeln(' dan wat de foute data betreft niet geheel juist zijn.'):Writeln;Writeln('Geef keuze [A/BJ .');Key := Upcase(Readkey):While (Key <> 'A') And (Key <> '8') 00 Key := Upcase(Readkey);If Key = 'B' Then NegFout:=True
Else RunErrorjEnd'If (AccAB) And (Error <> 0) Then Result := 4;
End; {procedure Number}
Procedure Plot;Begin
Writeln('Geef de titel van de te plotten grafiek aub. Maximaal 50 tekens.'):Readln(lbl) :Writeln;Writeln('Het plotten duurt ongeveer 3 minuten.'):
56 Appendix E: Listings PLOTFllE.PAS and IEEEIO.PAS
--(Begin met plottenl _.Wri teln(leeeOut, 'OUTPUT 05; 1NvSlOSP1PAPUO, OPD9367, 0,9367,1047,0, 1041,0,OPUO,
349P09367,349PU9367, ,698POO,698');WritelnCleeeOut,'OUTPUT 05;PU837,1413P0837,7326,9367,7326,9367, 1413,837,1413SP2');
Tenp1 := 0;Tenp := 1413;Stap := RoundC5913 / hokjes);While CTl!q) < 7325 - Stap) 00Begin
Tenp := Tl!q) + Stap;If (ABSCTl!q) - 5848) > 50) or (AccAB = True) ThenBegin
lf CTemp1 =0) ThenBegin
Writeln(leeeOut,'OUTPUT 05;PU837,' ,Temp,'PD9367,' ,Temp);Temp1 := 1;
EndElseBegin
Writeln(leeeOut,'OUTPUT 05;PU9367,' ,Temp,'PD837,' ,Temp);Temp1 := 0;
End;End;
End; <whi le}Tl!q) := 1690;Whi Ie (Temp < 7661) DoBegin
Writeln(leeeOut,'OUTPUT OS;PU' ,Temp,' ,1413PD' ,Temp,' ,7326');Temp := Temp + 853;Writeln(leeeOut,'OUTPUT OS;PU' ,Temp,' , 7326PD' ,Temp,', 1413');Temp := Temp + 853;
End;Writeln(leeeOut,'OUTPUT 05;PU8514,1413PD8S14,7326');If CAccAB = False) ThenBegin
Writeln(leeeOut,'OUTPUT OS;LT2SPZPU9367,5849PD837,5849LTPU887,5900L01SI.3,.3SLCSOSSLBREF' ,CHR(3»;WritelnCleeeOut,'OUTPUT 05;PUO,5900LB' ,Reflev:2:0,chr(3»;Writeln(leeeOut,'OUTPUT OS;PUO,S700LB dB' ,chr(3»;
End·If (ReceiveC69] = '.') Then <output in dB}Begin
CoordX := 822.293;Writeln(leeeOut,'OUTPUT 05;SP3PU837,1413');For Temp := 1 To 581 DoBegin
CoordX := CoordX + 14.707;CoordY := 5849 - (Reflev-ResultCTemp]) * 739.125 / Ys:If (CoordY < 1413)Then Writeln(leeeOut, 'OUTPUT 05;PA' ,Round(CoordX),', 1413PU')Else If (CoordY > 7326)
Then If (Result[Temp] =0) Then Writeln(leeeOut,'OUTPUT 05;PAPU' ,Round(CoordX),' ,7328')Else Writeln(leeeOut,'OUTPUT 05;PA' ,Round(CoordX),' ,7328PU')
Else Writeln(leeeOut,'OUTPUT 05;PAPD',Round(CoordX),' ,',Round(CoordY»;End;
EndElse {output lineair}Begin
CoordX := 822.293;WritelnCleeeOut,'OUTPUT 05iSP3PU837,1413'):For Temp := 1 To 581 DoBegin
CoordX := CoordX + 14.707;If (AccAB = False)Then CoordY := 1413 + Result[Templ * 4436Else If Ys=O.2 Then CoordY := 1413 + ResultCTempJ / Ys * 985.5
Else CoordY := 1413 + Result[Tenp] / Ys * 739.125;If (CoordY = 1413)Then Writeln(leeeOut,'OUTPUT 05 PAPU' ,RoundCCoordX),', 1413')Else lf CCoordY > 7326) Then Wr teln(leeeOut,'OUTPUT 05:PAPU' ,Round(CoordX),' ,7328')
Else Wr teln(leeeOut,'OUTPUT 05;PAPD' , Round(CoordX),, ,',Round(CoordY»;End;
End;
Appendix E: Listings PLOTFILE.PAS and IEEEIO.PAS 57
Writeln(leeeOut,'OUTPUT 05;SP1PU100,7S0SI.3,.SLBSWP , ,S~WO:5:1,'nm/div' ,CHR(3»;writeln(leeeOut,'OUTPUT 05;PR100,-52PRPOO,349');Writeln(leeeOut,'OUTPUT 05;PRPU100,-299lBYS ' ,Ys:5:1,Yss,CHR(3»;Writeln(JeeeOut,'OUTPUT OS;PR100,-52PRPDO,349');writeln(IeeeOut,'OUTPUT 05;PRPU100,-299LBRES ' ,Resoln:4:1,'nm',chr(3»;Writeln(leeeOut,'OUTPUT OS;PR100,-S2PRPOO,349');Writeln(JeeeOut,'OUTPUT OS;PRPU100,-299LBAVR ' ,Avr:3:0,chr(3»;Writeln(JeeeOut,'OUTPUT 05;PR100,-52PRPOO,349');Writeln(IeeeOut,'OUTPUT 05;PRPU100,-299LB' ,Receive[72],chr(3»;Writeln(leeeout,'OUTPUT 05;PAPU100,1150LB' ,Ctrwl-5*Swpwd:6:1,'nm',' ':16,
Ctrwl:6:1,'nm',' ':16,Ctrwl+5*Swpwd:6:1,'nm' ,chr(3»;Writeln(JeeeOut,'OUTPUT OS;PAPU100,401LBWMKR' ,chr(3»;Writeln(JeeeOut,'OUTPUT 05;PAPU100,52LBLMKR' ,chr(3»;Writeln(IeeeOut,'OUTPUT OS;PAPUO,7400LBSPECTRUM ' ,Lbl,chr(3»;Writeln(leeeOut,'OUTPUT OS;PUSP');
End; {Procedure Plot}
, ,Result[x+1]:5:2);
, ,Reflev:5:2,' dam');',Ctrwl:S:1,' nm');, ,Swpwd:3:1,' nm/div');',Resoln:3:1,' mi'>;, ,Avr:3:0);',Ys:3:1,' ',Yss);
Procedure WriteToDisk;Begin
Writeln('Geef de naam van de te bewaren file (max 20 karakters).');Readln(Filestring);AssignCOutFile,Filestring);Rewrite(OutFile);Writeln;Writeln('Header toevoegen aan data-file? (JIN)');Writeln;Key:=Upcase(ReadKey);While (Key <> 'J') And (Key <> 'N') 00 Key := UpcaseCReadKey);If CKey = 'J') ThenBegin
WritelnCOutFile,'Reference LevelWriteln(OutFile,'Center WavelengthWriteln(OutFile,'Sweep WidthWritelnCOutFile,'ResolutionWriteln(OutFile,'Average TimesWriteln(OutFile,'Y'Scale
End;For x := 0 To 580 DoBegin
Writeln(OutFile,(Ctrwl'5*Swpwd)+(10*x/580*Swpwd):9:4,'End-Clo;e(OutFile);
End; {Procedure WriteToDisk}
Aansluitingen kontroleren. Loopt er een GP-JB kabel van de computer naar');de plotter en een GP-IB kabel van de computer naar de AQ-6310B Optical');Spectrum Analyzer?');Staat de plotter aan en zit er A4 papier in?');Zitten de goede pennen in de plotter:');
Pen 1: Zwart');Pen 2: Groen');Pen 3: Rood.');
Analyzer [adres 30] en van de plotter [adres 05]');
Begin {Main program}Stoppen := False;Init := False;While Not(Stoppen) DoBegin
While Not(lnit) DoBegin
ClrScr;Writeln('Plot programma voor Optical Spectrum Analyzer');Writeln('Ook geschikt voor schrijven van data naar disk');Writeln;Writeln;Writeln('VOORBEREJOING:');Writeln;Writeln('1.Writeln('Wri teln('Writeln('2.Writeln('3.Wri teln('Writeln('Writeln('Writeln('4. Zijn de adressen van deWriteln(' goed ingesteld?');Writeln;Writeln;Writeln('Oruk op J indien gereed.');Wri teln;Key:=Upcase(Readkey);While (Key <> 'J') Do Key:=Upcase(Readkey);Init:=True;
End;
58 Appendix E: Listings PLOTFILE.PAS and IEEEIO.PAS
-ctrScr·· .Writel~('Druk op <J> indien data op OSA relevant-fs,·);Writeln;Key:=Upcase(Reedkey);While (Key <> 'J') Do Key:=Upcase(Readkey);
NegFout := False;Writeln(leeeOut,'TIME OUT 26');Writeln(leeeout,'OUTPUT 30;DDATA');Writeln('De data wordt van de Spettrum Analyzer naar de computer gestuurd.');Writeln(leeeout,'ENTER 30 #4073 BUFFER',
Seg(Receive[O]),':' ,Ofs(Receive[O]»;Writeln;Writeln('Data zichtbaar maken op scherm? (JIN).');Key := Upcase(Readkey);While (ley <> 'J') And (Key <> 'N') Do Key := Upcase(Readkey);If (ley = 'J') ThenBegin
For Temp1 := 0 Ta 6 Do Write(Receive[Temp1]);Writeln;For Temp := 1 Ta 580 DoBegin
Write('RESULT=',Temp,' TEMP=' ,Temp*7,' .• ',Temp*7+6,' ');For Temp1:=0 To 6 Do Write(Receive[Temp*7+Temp1]);Writeln;If Temp mod 20=0 Then Key := Readkey;
End;Write('RESULT=581 TEMP=4067..4072 ');For Temp1:=4067 To 4072 Do Write(Receive[Temp1);
End·Writeln;Writeln('Even rekenen •.•. ');
AccAB:=Receive[8]='.';Temp := 0;Temp1 := 1;While (Receive[temp) <> ',') Do Temp:=T~1;
Whi le (Tetrp < 4073) DoBegin
Number(Result[Temp1]);Temp1 := Temp1 + 1;
End;
Writeln(leeeOut,'OUTPUT 30;STATE');Writeln(leeeOut,'ENTER 30 #77 BUFFER' ,Seg(Receive[O),':' ,Ofs(Receive[O]»;Temp := 50;Number(Reflev) ;Temp := 12;Number(Ctrwl);Temp := 25;NI.iN:ler ( Swpwd) ;Temp := 38;Nl.iN:ler(Resoln);Temp := 57;Nl.iN:ler(Avr);
CASE -ROUND(Reflev) MOO 10 Of0,3,6 Hokjes:= 6.67;1,4,8 Hokjes:= 10.6;2,5,9 : Hokjes := 8.43;7 : Hokjes := 5.32;
End·If (Receive[69] = '.') ThenBegin
Tel'I'P :=66;Nl.iN:ler(Ys);Hokjes := 8;Yss := 'dB/div';
End
{Yscale in dB}
Appendix E: Listings PLOTFILE.PAS and IEEEIO.PAS 59
Else If (AccAB : True)Then {lineair geval met AccA/B Of AccB/A}Begin
Yss := '/div ';Ys := 0.2;Hokjes := 6;for Temp := 1 To 581 Do If (Result[Temp] > 1.2) ThenBegin
Ys := 0.5;Hokjes := 8;Temp := 581;
End;EndElse {andere lineaire gevallen}Begin
If (-Round(Reflev) div 28 = 0) Then Yss := '~/div'
Else If (-Round(Reflev+28) div 30 = 0) Then Yss := 'nnVdiv'Else Yss := 'pmldiv';Ys := Reflev;If (-Ys >= 30) Then Ys := Ys + 30;If (-Ys >= 30) Then Ys := Ys + 30;CASE -Round(Ys) Of
28,29,0 Ys := 200;1.2.3 Ys := 100;4.5.6.7 Ys := 50;8.9.10 Ys := 20;11,12.13 Ys:=10;14,15.16.17 Ys:= 5;18,19.20 Ys := 2;21,22.23 Ys·-l·24.25.26.27 YS;: 0:5;
End; {case}End; {Else}
Writeln;Writeln('Plotten Of Bewaren op disk? (P/B)');I.Iriteln;Key:=Upcase(Readkey);While (Key <> 'P') And (Key <> 'B') Do Key := Upcase(Readkey);]f (Key : 'P') Then Plot;If (Key = 'B') Then WriteToOisk;Writeln;Writeln('Stoppen? [JIN]');Key:=Upcase(Readkey);While (Key <> 'J') And (Key <> 'N') Do Key := Upcase(ReadKey);If (Key = 'J') Then Stoppen := True;
End;END.
Register definition for low-level callsText files for IEEE communicetion
60 Appendix E: listings PlOTFllE.PAS and IEEEIO.PAS
IEEEIO.PAS
This Pascal unit is used by the program PLOTFILE.PAS.
Unit leeelO;
( Support file for IEEE 488 epplicetions.
Contains:Var Regs
leeeout, leeeln
Procedure locnIOCTlReadRawModeleeeCClqllete
>Interface
Uses Dos;
Sends locn BREAK cOIlIIIlInd to Personal488Reeds loens from Personal488Sets fi les into "raw" (bill8ry) modeCloses files, shuts down.
VerRegsleeeout, leeeln
Registers;Text;
Procedure IOCTL;Procedure IOCTLRead(Ver Command:String);Procedure RewMode(Var AFile:Text);Procedure IeeeCClqllete;
IIJ1)lementat ; on
Procedure IOCTL;( This is the equivalent of the BASIC statment IOCTL#',"BREAK"
es described in Chapter 6 of the Personal488 manual.>Const Break : String = 'BREAK';Var
IeeeFileHandle : integer absolute IeeeOut;Begin
With Regs 00 BeginAX := S4403; (MS-OOS function code)BX := IeeeFileHandle;CX := length(Break);OS := Seg(Break);OX := Ofs(Break).'
End;MsOos(Regs)
End;
Procedure IOCTlRead(Var Command:String);{ This is the equivalent of the BASIC function IOCTLS as described
in Chapter 6 of the Persoll8l488 manual. >Var
IeeeFileHandle: integer absolute IeeeOut;Begin
With Regs Do BeginAX := S4402; (MS-OOS function code)BX := IeeeFileHandle;CX := 255; (Length)OS := Seg(Command);OX := Ofs(Command)+';MsDos( Regs);Command[Ol := Char(Regs.AX) (Received length>
End'End; ,
Appendix E: listings PlOTFllE.PAS and IEEEIO.PAS 61
Procedure RawMode(Var AFile:Text);( This sets the file into "rBW" Or binary mode. This greatly
improves the efficiency of communication.)Var
FileHandle : integer absolute AFile;Begin
With Regs Do BeginAX := 14400: (MS-DOS Get Device Data function)BX := FileHandle;
End:MsD05 (Regs):Wlth Reg5 Do Begin
AX := 14401:BX := FileHandle;DH := 0; {DH must be O}DL := DL Or $20 (Set Binary Mode bit)
End:MsOos(Regs)
End;
Procedure IeeeComplete:Begin
Close(leeeDut);CloseCl eeel n)
End:
BeginAssign(leeeDut,'leee~ut'); Rewrite(leeeDut);Assign(leeeln,'leeeln'); Reset(leeeln);
RawMode(leeeDut);RawMode(leeeln);
lOCH:Writeln(leeeout,'RESET');Writeln(JeeeDut,'FILL ERROR')
End.
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