TRIUMPH
Cascadability Performance of
Continuous Spectrum WB/WSS at
10/40/160Gb/s
S. Sygletos, A. Tzanakaki, and I. Tomkos
High Speed Networks and Optical Communications Group
Markopoulou Ave., PO. BOX 68, 190 02 Peania, Athens, Greece
www.ait.gr
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OXC and ROADM Architectures
OXC
ROADM
WB
1
M
M
WB
Drop
n-λ
In
Out
WB
11
Add
Rx
Rx
Tx
Tx
WB
M
M
N
f
N
WB
Drop
Reconfigurability properties are defined by the wavelength blocker (WB)
Thermo-optical
•
Free Space
Acousto-optical
•
Waveguide
•
Electro-optical
•
Hybrid
•
Micro-mechanical
•
•
Low loss
•
Polarization independency •
•
(~msec) switching speed
•
high on/off isolation
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Originate from the presence of gap
and phase discontinuity between the
pixels on the SLM plane
Loss
Loss and group delay ripples appear
at the slot boundaries
Group Delay
Continuous Spectrum WB/WSS
Proposed Model :
Frequency
T f  
i
2

 f  fi  
 
1  A  exp  ln 100  

 f / 2  
2

 f  fi  
e
 
 f   C    f
exp k 

2k i
  f  
A : depth of the amplitude ripple
C : peak to peak value of the group
delay ripple
Δf : spectral width at 1% depth
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Switching Schemes
The WSS device supports 50GHz
channel spacing
Case -A
Case-A : Waveband switching scheme
of 10Gb/s DWDM system at 25 GHz.
Case-B : Channels are located at the
middle of the pixel’s flat pass-band
The system penalty is numerically
evaluated in terms of eye closure
Case -B
λ
The relative effect of loss and group
delay ripples on the system performance
is identified
The cascadabilty performance of an
already commercial available WSS is
also explored
λ
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Results – Case A
Amplitude ripple
4
4
3
2.5
2
1.5
1
0.5
0
-2
1GHz
5GHz
10GHz
15GHz
20GHz
3.5
-0.1dB
-0.2dB
-0.3dB
Eye Penalty (dB)
Eye Penalty (dB)
3.5
3
2.5
2
1.5
1
0.5
-1.5
-1
-0.5
0
0.5
1
Detuning Frequency
1.5
2
x 10
10
0
-2
-1.5
-1
-0.5
0
0.5
1
Detuning Frequency
1.5
2
x 10
The peak loss introduced on the carrier frequency is the dominant
penalty factor
The spectral width of the interpixel area can significantly shrink the
corresponding frequency area of the penalty
10
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Results – Case A
Group Delay Ripple
5
5
4.5
1 psec
2 psec
4 psec
6 psec
8 psec
4
3.5
3
Eye Penalty (dB)
Eye Penalty (dB)
4.5
2.5
2
1.5
1
0.5
0
-2
1GHz
5GHz
10GHz
15GHz
20GHz
4
3.5
3
2.5
2
1.5
1
0.5
-1.5
-1
-0.5
0
0.5
1
Frequency Detuning
1.5
2
x 10
10
0
-2
-1.5
-1
-0.5
0
0.5
1
Frequency Detuning
Maximum penalty may not occur at zero detuning frequency
The degradation strongly depends on the frequency width of the
interpixel region
1.5
2
x 10
10
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Results – Case A
Cascadability Performance
0.7
0.6
0.5
0.4
2
0.3
0.2
0.1
4
6
8
2
4
6
8 10 12 14 16 18 20
Frequency Width (GHz)
GDR (psec)
Insertion Loss (dB)
0.8
20
18
16
14
12
10
8
6
4
2
4
8
10
16
18
20
12
2
4
6
6
8 10 12 14 16 18 20
Frequency Width (GHz)
The degradation introduced by the amplitude dip dominates, and no
more than 4 filters can be cascaded for a 0.2dB peak loss
The maximum penalty due to the GDR effect takes place when this
area extends over the main spectral lobe of the transmitted signal
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Results – Case A
Misalignment Effect
Eye Penalty (dB)
4
No misalinment
2 GHz
4 GHz
6 GHz
3
WSS specifications :
Amplitude dip : 0.2 dB
GDR (p-p)
2
: 6 psec
Frequency Width : 20GHz
1
2
4
6
8 10 12
Cascaded Filters
14
When an amount of random misalignment exists the WSS cascadability
may further improve if system penalties larger than 1-dB are tolerated.
At 2-dB eye closure limit 6 additional WSS devices can be placed in the
cascade when the maximum detuning offset is at 6 GHz.
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Results – Case B
40 Gb/s System
6
12
0.8
10
0.6
8
20
16
20
28
0.4
0.2
2
4
6
8 10 12 14 16 18 20
Frequency Width (GHz)
GDR (psec)
Insertion Loss (dB)
1.0
20
18
16
14
12
10
8
6
4
2
4
6
8
10
28 2016 12
24
2
4
6
8 10 12 14 16 18 20
Frequency Width (GHz)
1st order Gaussian pulses of 6 psec time duration at FWHM have
been considered
The amount of degradation imposed separately by each effect is
negligible
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Results – Case B
160 Gb/s System
0.8
6
8
0.6
16
0.4
12
20
24
28
0.2
2
4
6
8 10 12 14 16 18 20
Frequency Width (GHz)
GDR (psec)
Insertion Loss (dB)
1.0
20
18
16
14
12
10
8
6
4
2
4.0
6.0
8.0
16 12
24 20
28
2
4
6
8 10 12 14 16 18 20
Frequency Width (GHz)
2psec 1st order Gaussian pulses have been assumed
Similar performance with the 40Gb/s system. Cascadability exceeds 28
devices for 20GHz ripple region, 0.2dB peak insertion loss and 6psec GDR
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Results – Case B
Eye Penalty (dB)
2.0
40 Gb/s
160 Gb/s
1.5
1.0
0.5
0.0
3
6
9
12
15
Cascaded Filters
Both 40Gb/s and 160Gb/s systems present similar performance
The combined effect of both amplitude and group delay ripple limits
cascadability to 9 WSS devices for 1dB tolerated penalty
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Conclusions
The specifications of the WB/WSS device and the cascadability
performance has been identified for different switching scenarios and
bit-rates
When the channel is located at the middle of the inter-pixel area (case-A )
a large amount of penalty is introduced due to the inserted loss ripple
When the channel is located in the middle of the single slot pass-band
the cascadability performance is much more advanced
The eye closure degradation accumulates similarly for both 40Gb/s as
well as 160Gb/s line rates
Using the design parameters of an already available device the
corresponding cascadability at 1dB exceeds 10 filter elements
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Modelling of Quantum Dot
Semiconductor Optical Amplifiers
M. Spyropoulou, S. Sygletos, A. Tzanakaki, and I. Tomkos
High Speed Networks and Optical Communications Group
Markopoulou Ave., PO. BOX 68, 190 02 Peania, Athens, Greece
www.ait.gr
TRIUMPH
Rate Equation Model
Homogeneous
broadening
Inhomogeneous
broadening
DE
j-th dot group
j = 0….2M+1
• Size fluctuation follows a Gaussian distribution the FWHM of which
is referred to as Inhomogeneous broadening
• Each dot-group is described by a Lorentzian distribution function
characterized by a FWHM known as Homogeneous broadening
• The gain of the device is a contribution of all the dot-groups which lie
under the homogeneous broadening of the resonant dot-group to
the input photon energy.
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Band structure of quantum dots
• Three discrete energy levels have been considered to describe
carrier dynamics within the dots:
 Continuum state
 Excited state
 Ground state
• Carriers are captured by the wetting layer which lies on top of
the quantum dots
• The upper energy states act as a reservoir of carriers for the
lower energy states
• Optical gain originates mainly from Ground State transitions
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Rate Equation Model
dN w ( z, T ) J N w ( z, T ) N w ( z, T )  j N c , j ( z, T )
 


dT
ed
 w c
 wr
 cw
• Wetting layer:
dNc , j ( z, T )
• Continuum state:
• Excited state:
dT

N c, j ( z, T )
 c g , j

G j N w ( z, T )

N c, j ( z, T )
 w c , j
 c e , j


N j ( z, T )
 g c , j
N c, j ( z, T )
 c  w, j

N c, j ( z, T )

N c, j ( z, T )
 e c , j
r
dNe, j ( z, T ) dNc, j ( z, T ) dN j ( z, T ) dNe, j ( z, T ) dNe, j ( z, T ) dNe, j ( z, T )





dT
 ce, j
 g e, j
r
 ec, j
 e g , j
N j 0 ( z, T )  N j ( z, T )
• Ground state:
dN j
• Propagation
Equation:
dS mn ( z, T )
 g mn n  aloss S mn ( z, T )
dz
dT

teff , j ( Nc, j , Ne, j )
 g gmn ( N j )Smn ( z, T )
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Steady State Gain Curves
• Note that,
– the gain curves for M ≥ 15 coincide
• As the number of groups under homogeneous broadening increases
the saturation power increases as well
– for M = 15 → Psat = 10dBm
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XGM at 40Gb/s
BitRate = 40Gbps with 8ps pulse width and fpump = fprobe+400GHz
BitRate = 40Gbps with 8ps pulse width and fpump = fprobe+400GHz
24
45
40
35
Extinction Ratio of electrical output
Pprobe = -20dBm
Pprobe = -15dBm
Pprobe = -10dBm
Pprobe = -5dBm
Pprobe = 0dBm
Qfactor
30
25
20
15
10
5
0
Pprobe = -20dBm
Pprobe = -15dBm
Pprobe = -10dBm
Pprobe = -5dBm
Pprobe = 0dBm
22
20
18
16
14
12
10
8
6
4
2
0
0
10
20
Input Pump Power (dBm)
30
40
0
10
20
30
40
Input Pump Power (dBm)
Large input pump power is needed to get an acceptable extinction ratio
however patterning effects and jitter arise
The optimum choice need to be found and this will depend on the
specific networking case
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XGM at 40Gb/s
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Further Work
• Study of the XGM phenomenon with two SOAs in
cascade
• Implement multi-wavelength operation of the SOA
• Incorporation of the model in the VPI simulation tool, to
illustrate the performance of the SOA in a network
architecture
•
Perform system level simulations to determine channel
spacing, number of channels that can be regenerated
simultaneously,etc.
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Thank you!
mspi@ait.rg
ssyg@ait.rg
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Simulation Parameters
Parameter
Value
Γinhom
40meV
Γhom
10meV
Number of layers
10
Confinement factor
0.15
De
6
Dc
20
Dg
1
Carrier capture rate
1ps
Relaxation lifetime
10ps
Recombination lifetime in the dots
1ns
Recombination in the wetting layer
0.4ns
2-D coverage of dots
0.15