optical amplification of ofc signal - nitttrchd.ac.in
TRANSCRIPT
Dr. Umesh TiwariScientist
V-4 (PHOTONICS)E.mail: [email protected]
CSIR-CSIO, SECTOR 30, CHANDIGARH - 160 030
Optical Amplification of OFC Signal
Outline
Optical fiber communication
Optical amplification
Erbium doped fiber amplifiers
Raman fiber amplifiers
Study and performance analysis of
Raman/EDFA hybrid amplifier
Summary
Attenuation Plot (in dB) with wavelength for optical Fiber
4
Introduction
•
Attenuation -
Optical amplification at regular intervals (~70-80 km)
•
Dispersion -
Dispersion compensating fiber
MUX: Multiplexer
DEMUX: Demultiplexer
DCF: Dispersion compensating fiberA: Amplifier
TX
: Transmission fiber
MUX DEMUX
LaserDiodes
Receivers
ATX DCF A
λ1 , λ2….. λnλ1 , λ2….. λn
A
Optical transmission
Information transmitted digitally in the form of optical pulses on various optical carrier frequencies
•Attenuation-Problem in detection at receiver (receiver sensitivity)Two major issues:
Dispersive medium
•Dispersion-Different frequencies components in a pulse travel with different group velocities-Overlap between pulses
Transmission loss
Overcoming attenuation
•
For
long distance transmission, loss needs to be overcome periodically
•
Electronic regenerators
•
Optical amplifiers
Electronic Regeneration
•
Regeneration with Retiming and Reshaping
•
Limited by speed of electronics
•
Single wavelength only
•
Capacity upgradation difficult and expensive3R
RxTx
Traditional Optical Communication System
Loss compensation: Repeaters at every 20-50 km
Optical Amplification
PLUS
•
No need of high speed electronics
•
Transparent to bit rate and format
•
Simultaneous amplification of multiple λ
MINUS
•
Adds noise
Optically Amplified Systems
EDFA = Erbium Doped Fibre Amplifier
Optical Fiber AmplifiersOptical Fiber Amplifiers
OpticalAmplifier
λn…….. λ1. λ2 λn…….. λ1. λ2
Desirable characteristics of an optical amplifier:
• Large gain bandwidth-wider range of signal wavelengths can be simultaneously amplified by the same amplifier
• Gain flatness-All the signal wavelengths get same amplified by the same amount
General Structure of an optical amplifier
Principal types of optical amplifiers
•
Erbium doped fiber amplifier (EDFA)•
For operation in the S-,C-
and L-bands
•
Raman fiber amplifier (RFA)•
All wavelength bands
•
Semiconductor optical amplifier (SOA)•
All wavelength bands
Different amplifier configuration
•
Booster amplifier
•
In-line amplifier
•
Preamplifier
Tx Rx
Boosteramplifier
In-line amplifier
Preamplifier
Pump Source
WDMErbium Doped
Fibre
IsolatorIsolator
= Fusion Splice
Input Output
980 nm signal
1550 nm data signal
Pow
er le
vel
980 nm signal
1550 nm data signal
Pow
er le
velPower
interchangebetween
pump and data
signals
Representation of the Principle of an EDFA
Source: Master 7_5
Erbium Doped Fiber Amplifier (EDFA)
• Erbium has broad emission around 1550 nm where silicaoptical fibers have minimum loss
• Using population inversion Er
doped silica fibers behaveas optical amplifiers
980 nmPump Laser
Doped fiber
Isolator
WDM CouplerSignal
17
Energy level diagram of Erbium ions
• Pump at 980 nm used to create population inversion between levels E2 and E1
• Stimulated emission between E2 and E1 leads to amplification
Absorption and Emission Cross Section*
E2
E3
E1
980 nm
1480 nm1520 - 1570 nm
*B Pedersen et al., J. Lightwave Tech., 9, 1105, 1991
Amplified spontaneous emission (ASE)
•
Erbium atoms in the excited state emit photons spontaneously
•
This emission is not coherent with the signal
•
Like signal this spontaneous emission also gets amplified
•
ASE appears in the both forward as well as backward direction
•
Wavelength range 1525 to 1570 nm
•
Power density 10 to 100 µw/nm
( ) BGhnP spASE Δ−= 12 ν
ASE noise in EDFA:
The output ASE noise is
Where212 /)( NNNnsp −=
Noise Figure: F = 2 nsp
ASE Spectrum
20
Erbium Doped Fiber Amplifiers: Analysis
22
22
0 ( ) 11 ln 11
p
p
bp pa p
b
dP N P z u w u edz w w
we
σ −Ω
−Ω
⎡ ⎤⎛ ⎞ ⎛ ⎞+⎛ ⎞⎢ ⎥⎜ ⎟= − − + −⎜ ⎟⎜ ⎟⎢ ⎥⎜ ⎟⎜ ⎟⎝ ⎠ ⎜ ⎟ ⎝ ⎠⎢ ⎥+⎝ ⎠⎣ ⎦
22
22
0 ( ) 11 ln 11
s
s
bs sa s
b
dP N P z v w v edz w w
we
σ −Ω
−Ω
⎡ ⎤⎛ ⎞ ⎛ ⎞+⎛ ⎞⎢ ⎥⎜ ⎟= − + + −⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥⎜ ⎟⎝ ⎠ ⎝ ⎠⎢ ⎥+⎝ ⎠⎣ ⎦
Pump and signal power evolution equations are given as*
*A.Ghatak and K.Thyagarajan, “Introduction to Fiber Optics”, Cambridge University Press, (1999).
21
0
( )ps
p
P zv
Pη=
0
( )1
s s
s s
P zuP
ηη
=+
0 0
( ) ( )p s
p s
P z P zwP P
= +
( )0 (1 )s s
ssa sp s sa se sp
h hI
t tν ν
σ η σ σ= =
+ +
0p
pp a sp
hI
tν
σ=
ses
sa
ση
σ=
20 0s s sP Iπ= Ω2
0 0p p pP Iπ= Ω
10
0
( )( )( )
K WVaJ UU K W
Ω =
with:
22
Simulation Results
Variation of pump power along the fiber length
• Linear decrease for high pump powers• Exponential for lower pump powers
23
• For every input pump power there is an optimum length of the fiber
Variation of signal power along fiber length
24
• Threshold pump power for transparency, beyond whichgain increases with increasing pump power
Variation of gain with input pump power for different fiber lengths
25
Pump and signal power evolution equations are given as*
PaP
eP
p PdzdP
P12 )N-(N Γ= σσ
Contribution of forward and backward ASE is also taken into consideration
* P.C. Becker,N.A. Olsson, J.R. Simpson “Erbium Doped Fiber Amplifiers”
Academic Press, (1999)
sas
es
s PdzdP
s12 )N-(N Γ= σσ
NP
AhP
AhP
Ah
PAh
PAh
PAhN
PPP
eP
aP
jAs
ea
jsss
es
as
PPP
aP
jAs
a
jsss
as
j
jj
j
j
1)()()()(
)(
2
+Γ+
+Γ+
Σ+Γ+
Γ+ΓΣΓ=
νσστν
νσστ
νσστ
ντσν
ντσ
ντσ
ννν
νν
26
Noise Figure
Noise figure is ratio between SNR at the input and the SNR at the output
*Noise Figure related with the gain and forward ASE spectral density:
*B Pedersen et al., J. Lightwave Tech., 9, 1105, 1991
Gh
LS
F s
sASE⎟⎟⎠
⎞⎜⎜⎝
⎛+
=
+
1),(νν
For practical purpose noise figure calculated as;
GBhNGNF inout
ν−
=
27
Variation in gain of the amplifiers due to two factors:
PDL of optical components like isolators and directional couplers
PDG due to the polarization hole burning (PHB).
Polarization Dependent Gain (PDG)
⎟⎟⎠
⎞⎜⎜⎝
⎛∗=
Min
MaxdB P
PPDG log10
PDG defined as:
o u t i nE D F A
W W
N -G NN 1 1N F = + = +h ν G B G h ν G B G
Measurement of source spontaneous emission [2]
ASE = ASE
Spectra
Wavelength
Pn1
Pn2
eSourceNoisGainPP nn ×−+2
21
Ideally an EDFA should amplify the signal without producing any additional output. However, broadband emission takes place in the form of ASE as shown
Erbium doped fiber amplifiers
Input Monitor
Output Monitor
Co-
directional
Pump
Contra-
directional
Pump
Erbium Doped Fiber
WDM Coupler
WDM CouplerIsolator IsolatorTap
CouplerTap
Coupler
980 nm 980 nm
1525-1565 nm (C-band)
Steps in designing the amplifier
•
Characterized each component for their insertion loss, isolation and wavelength dependence
•
Studied the dependence of gain on the bend radius of the EDF
•
Chose an optimal radius of 5 cm for the coil •
Optimized the splice machine for splicing an EDF with SMF-28
•
The optimum length for a given pump power was found from the Optiwave
Software Package. In this
case it was around 13.5 mts
Experimental Results (Single Channel)
Noise Measurement Bandwidth = 0.5 nm
OA
Pin1
(λ) Pout1
(λ)
PASE
(λ)
EDFA Input Reference Plane
EDFA Output Reference Plane
MUX DEMUX
TX1
TX2
TX3
TXN
RX1
RX2
RX3
RXNPin2
(λ)
Pin3
(λ)
PinN
(λ)
Pout2
(λ)
Pout3
(λ)
PoutN
(λ)
Multi-Channel Characterization
( )0 0( ) 10 ( ) 10( ) 10 log 10 10 ( )wP PBBSG Pλ λλ λ= − −
PBBS(λ), P0w(λ), P0(λ) are measured in dBm
and G(λ) is measured in dB
Multi-Channel Testing –
Results
•
λ1
= 1530.33 nm•
λ2 = 1533.47 nm•
λ3 = 1536.61 nm•
λ4 = 1539.77 nm•
λ5 = 1542.94 nm•
λ6 = 1547.72 nm•
λ7 = 1552.52 nm•
λ8 = 1557.36 nm
Polarization Dependent Gain Spectra
Experimental Results (Electrical Characteristics)Eye Patterns (a) at the output of the transmitter, and (b) at the output of the EDFA
Presented at Photonics -2006
No significant degradation in the Eye pattern due to insertion of the EDFA is observedBit Error Rate - 1.3 x 10-9 (at received power level of -30.75 dBm and transmission rate of 2.5 Gbps)
Final Fabrication (In collaboration with Tejas
Networks, Bangalore and Optiwave
Photonics, Hyderabad)
Optical SpecificationsAmplifier Type
: BoosterOperational Wavelength
: C -
BandNo. of Channels
: OneInput Signal Power (Pin)
: -
25 dBm
to– 5 dBm
Total Output Power @Pin = -25dBm
: + 10 dBmTotal Output Power @Pin = -5dBm : + 15 dBmSmall Signal Gain
: + 34 dBNoise Figure
: ≤
5 dBPolarization Dependent Loss
: 0.20 dBPolarization Mode Dispersion
: 0.04 ps
Electrical SpecificationsPower Supply
: ±
12 V, 2 APower Consumption
:18 WMode of Operation
:Automatic Current Control & Power Control
DESIGN & DEVELOPMENT OF MIDDESIGN & DEVELOPMENT OF MID--STAGE STAGE ERBIUM DOPED FIBRE AMPLIFIERERBIUM DOPED FIBRE AMPLIFIER
Front view of fabricated MSA-EDFA
1530 1535 1540 1545 1550 1555 15602
4
6
8
10
12
14
16
18
20
22
24
26
28
24681012141618202224262830
Out
put P
ower
(dB
m)
Gai
n (d
B)
Wavelength (nm)
Output power Gain
1530 1533 1536 1539 1542 1545 1548 1551 1554 1557 15600
5
10
15
20
25
30
0
5
10
15
20
25
30
Noi
se F
igur
e (d
B)
Gai
n (d
B)
Wavelength (nm)
Multi Channel Gain Multi Channel Noise Figure
Need for an optical amplifier with provision of access to signals at mid-
stage for various functional elements such as :
Optical add-drop multiplexerDispersion Compensator VOA to achieve variable gain
EDF L1
GFFInput
ChannelsOutput
Channels
EDF L2
Gain Flattening Issues in MSA-EDFA
Wavelength (nm)Wavelength (nm)Wavelength (nm)
Gai
n (d
B)
Tra
nsm
issi
on (d
B)
Gai
n (d
B)
38
39
Raman Amplifier
Virtual Energy State
hνpump
hνSignal
ΔEphonon
Lower Energy State
SignalSignal
Pump
Description of Stimulated Raman Scattering
Raman gain curve*
*G.P. Agrawal, Non Linear Fiber Optics, Academic press, 3rd ed.,2001
41
The following equations for signal and pump evolution
ss s s p s
pp p p p s
d P P g P Pd zd P
P g P Pd z
α
α
= − +
± = − −
( )
eff
r p ss
gg
KAν ν−
=
pp s
s
g gνν
=
(m-1W-1) is the Raman gain coefficient of fiber normalized with respect to the effective area of the fiber i.e.
sg
Raman Amplifiers: Modeling Equations
•
Ps,p
= Power at signal and pump wavelength•
αp, αs
= Attenuation co-efficient at pump and signal•
K = Polarization factor•
= Effective Raman gain coefficient at signal and pump wavelength
•
Aeff
= Fiber effective area
sgs,p
Evolution of signal and pump powers for co-directional pumping in a SMF
Ps
(in) = -40 dBm
λs
= 1550 nm
Pp
(in) = 30 dBm
λp
= 1450 nmsignal
pump
Evolution of signal and pump powers for contra-directional pumping in a SMF
signal
pump
Ps
(in) = -40 dBm
λs
= 1550 nm
Pp
(in) = 30 dBm
λp
= 1450 nm
Experimental Results
WDMCoupler
WDMCoupler
Tunable Laser
OSA
1450 nmpump
Liquid Paraffin
Corning Vast®
DCF
Residual Pump
Isolator IsolatorTunable
LaserWDM
CouplerWDM
CouplerOSA
Experimental setup for the measurement of Raman gain
G = exp (gR
P0
Leff
/Aeff
)
Pump1455 nm
Pump
5.3 kmDCF
Index matching
Liquid
Signal
DCF based Raman amplifier
Gain profile of a multi-pumped RFA
Flattened gain profile with optimized pump powers
λ1 = 1420 nmλ2 = 1450 nmλ3 = 1480 nm
ΔG=1 dB
ΔG=2.1 dB
51
5.3 km
DCF
Residual pump
13 m
EDF1450 nm
Pump
5.3 km
DCF
1450 nm
Pump
13 m
EDF
Residual pump
5.3 km
DCF
1450 nm
Pump
13 m
EDF
Residual pump
Hybrid II Hybrid III
Hybrid I
J.H. Lee et al., Journal of Lightwave Technology 23, 3484 (2005).
Different Raman/EDFA Hybrid Amplifier Configurations
52
•
Hybrid amplifier offers several advantages
•
High Gain, low noise figure, High pump efficiency
•
Compensates both dispersion and loss
•
DCF has much higher Raman gain co- efficient
•
Amplification band expansion easily achieved within the transparency window of optical fiber
•
Wavelength Division Multiplexing (WDM) is the most suited methods for increasing the transmission capacity
•
Polarization dependent gain (PDG) modified the signal to noise ratio (SNR) and such an SNR modification leads to performance degradation
Need of Hybrid Amplifier
DCF
Residual pump
53Multi-channel gain and noise figure of hybrid I configuration
Results
5.3 km
DCF
Residual pump
13 m
EDF1450 nm
Pump
54Multi-channel gain and noise figure of hybrid II configuration
Results
5.3 km
DCF
1450 nm
Pump
13 m
EDF
Residual pump
55
Polarization Dependent Gain Spectra
Ref: Tiwari et al. Opt. Comm. 281 (2008) 1593FIO - 2007, San Jose, USA
PMD/PDL analyzer setup
•
Multi-channel performance and PDG measurements studied for first time
•
A trade off exists in the deployment of these amplifiers
•
Hybrid I has best PDG and BER
•
Hybrid II lowest noise figure
•
Hybrid III best pump efficiency
56
Multi-channel Gain and Noise figure Characterization of Raman/EDFA Hybrid Amplifiers
57
New Raman/EDF Hybrid Amplifier with Enhanced Performance
1450 nmPump
5.3 kmDCF
Residual pump
13 mEDF
Schematic of New Raman/EDF Hybrid Amplifier
Simulation and experimental characterization of the new Raman/EDFA hybrid amplifier have been studied
The EDF is followed by a DCF section, and EDF section in the co-pump geometry
58
1520 1530 1540 1550 1560 1570
68
101214161820222426 Input signal power @ - 20 dBm
Input signal power @ - 5 dBm
Input signal power @ - 10 dBm
Simulated Measured Measured Measured Simulated Simulated
Gai
n (d
B)
Wavelength (nm)1520 1530 1540 1550 1560 15700
2
4
6
8
10
12
14
Noi
se F
igur
e (d
B)
Wavelength (nm)
Simulated: Input signal power @ - 5 dBm Simulated: Input signal power @ - 10 dBm Simulated: Input signal power @ - 20 dBm Measured: Input signal power @ - 5 dBm Measured: Input signal power @ - 10 dBm Measured: Input signal power @ - 20 dBm
Simulated and measured gain and noise figure plot
Results
59Photonics -2008, IIT Delhi & SPIE Best Paper AwardRef: Tiwari et al. Opt. Comm. 282 (2009) 1563
-16 -14 -12 -10 -8 -6 -40.0
0.3
0.6
0.9
1.2
1.5
1.8
2.1
2.4
PDG
(dB
)
Signal Power (dBm)
Hybrid II Hybrid III Hybrid I Novel Configuration
•
Best noise figure and lowest gain ripple•
Experimental and simulated results are in close agreement•
Polarization dependant gain (PDG) is smallest
Comparison of PDG of different configurations with signal power
Results
Highlights:
Multi-channel gain comparison between measured (solid line) and simulated (dotted line) gain
60
EDFA /SOA hybrid amplifier for broadband amplification
With increased capacity requirements, wide gain bandwidth amplifiers have become important In order to improve the performance of wide band amplifiers EDFA and SOA can be utilized in conjunctionBy combining the properties of EDFA and SOA, the amplification bandwidth can be enhanced by about 15-20 nmThe various parameters have been optimized to achieve the best performance of EDFA/SOA hybrid amplifierSince SOA suffers from significant polarization dependent gain (PDG), while the EDFA is known to have smaller PDG, and there is a need to study the PDG characteristics of EDFA/SOA in conjunction
n -
InP
InGaAsPp -
Inp
p+ InGaAs
Injection Current
Input signal
Amplified output
Metallization
Active Region
Essentially a Semiconductor Laser diode with Anti-reflection coating on facets
Semiconductor Optical amplifier
6262
SOA SOA --
FeaturesFeatures
••
Small size , electrical pumping Small size , electrical pumping ••
Broad gain spectrum ( 30 ~ 50 nm)Broad gain spectrum ( 30 ~ 50 nm)
••
Exploitable nonlinear characteristicsExploitable nonlinear characteristics••
Compatibility with photonic integrated circuitsCompatibility with photonic integrated circuits
••
Diverse range of applicationsDiverse range of applications––
optical switching, wavelength convertersoptical switching, wavelength converters
––
logic gates, multiplexers, fliplogic gates, multiplexers, flip--flopsflops
ASE spectra
In presence of signal- ASE gets suppressed - Peak shifts towards higher wavelengths
64
Schematic of experimental setup of EDFA/SOA hybrid amplifier studied*
EDFA/SOA Hybrid Amplifier
In the first configuration the EDFA section in the co-pump geometry is followed by an SOA. In other configuration SOA is followed by EDFA section in the co-pump geometry
The hybrid amplifier in the proposed configurations are experimentally characterized in terms of single channel gain, noise figure, multi channel gain, and PDG
SOA
10 mEDF
980 nmPump
10 mEDF
SOA
980 nmPump
Schematic of experimental setup of SOA/EDFA hybrid amplifier studied
*C. H. Yeh et al., Laser Phys. Lett.4, 433 (2007).
65
1510 1520 1530 1540 1550 1560 1570 1580 1590 16000
5
10
15
20
25
30
35
40
0
5
10
15
20
25
30
35
40
Noi
se F
igur
e (d
B)
NF: - 25 dBm I/PNF: - 15 dBm I/P
NF: - 5 dBm I/P
Gain: - 5 dBm I/P
Gain: - 15 dBm I/P
Gain: - 25 dBm I/P
Gai
n (d
B)
Wavelength (nm)
1520 1540 1560 1580 1600 16200
5
10
15
20
25
30
35
40
0
5
10
15
20
25
30
35
40
Noi
se F
igur
e (d
B)
Gai
n (d
B)
Wavelength (nm)
Gain: - 25 dBm I/P Gain: - 15 dBm I/P Gain: - 5 dBm I/P NF: - 5 dBm I/P NF: - 15 dBm I/P NF: - 25 dBm I/P
Results
Measured Gain (G) and Noise figure (NF) comparison for three different I/P power
levels EDFA/SOA Hybrid
Measured Gain (G) and Noise figure (NF) comparison for three different I/P power
levels SOA /EDFA Hybrid
Simulated Gain (G) and Noise figure (NF) comparison for three different I/P power
levels EDFA/SOA Hybrid
1520 1540 1560 1580 1600 16200
5
10
15
20
25
30
35
40
0
5
10
15
20
25
30
35
40
Noi
se F
igur
e (d
B)
Gai
n (d
B)
Wavelength (nm)
Gain @- 5dBm Gain @- 15dBm Gain @- 25dBm NF @ - 5dBm NF @- 15dBm NF @- 25dBm
66
Measured Gain (G) and Noise figure (NF) comparison
1520 1540 1560 1580 1600
5
10
15
20
25
30
35
40
0
5
10
15
20
25
30
35
40
Gai
n (d
B)
Wavelength (nm)
Gain: EDFA Gain: EDFA/SOA Gain: SOA/EDFA Gain: SOA NF: EDFA NF: EDFA/SOA NF: SOA/EDFA NF: SOA
Noi
se F
igur
e (d
B)
P (980 nm) = 127 mW, 150 mA SOA current
67
Results
Comparison of measured PDG spectrum of the different amplifier configuration at -5
dBm signal input power
• Multi channel gain characteristics are quite different from single channel case, and gain tilt is observed due to spectral hole burning
• A better gain flatness was observed for -15 dBm and -5 dBm signal input power• Reported, for the first time, comparison of the PDG characteristics• Improvement in the PDG of the hybrid amplifier is demonstrated
Photonics-2012, IIT Madras
Highlights:
1530 1540 1550 1560 15700.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
PDG
(dB
)
Wavelength (nm)
EDFA EDFA_SOA SOA SOA_EDFA
Optical Amplifier: Comparison
Source: Internet
The measured PDG of fabricated EDFA was quite comparable with PDG of commercially available EDFA
The gain spectra for the multichannel case was significantly different form the single channel case.
Hybrid II amplifier has been demonstrated to have a low noise figure.
The new Raman/EDFA configuration presented in this analysis hasnot only the best noise figure performance but also has lowest gain ripple.
Experimental and simulated results are in close agreement.
Simulation and experimental characterization of single channel
gain and noise figure of a EDFA /SOA hybrid amplifier is presented.
We have reported, for the first time, comparison of the PDG characteristics.
CONCLUSION
References
1. A.Ghatak and K.Thyagarajan, “Introduction to Fiber Optics”, Cambridge University Press, 1999.
2. P.C. Becker,N.A. Olsson, J.R. Simpson “Erbium Doped Fiber Amplifiers” Academic Press, 1999.
3. G.P. Agrawal, Non Linear Fiber Optics, Academic press, 3rd ed.,2001.
4. C. Headly and G.P. Agrawal “ Raman amplification in Fiber Optical communication systems, Elsevier Academic Press,2005.
5. M.N. Islam, “Raman Amplifiers for Telecommunications 1”, Springer-Verlag New York, Inc., 2004.