1. A novel Figure of Merit to Compare Fibers in Coherent Detection Systems with Uncompensated Links
A. Carena(1), V. Curri(1), G. Bosco(1), R. Cigliutti(1), E. Torrengo(1), P. Poggiolini(1)
A. Nespola(2), D. Zeolla(2)
F. Forghieri(3)
(1) Dip. di Elettronica, Politecnico di Torino, Italy,
(2) Istituto Superiore Mario Boella, Torino, Italy,
(3) Cisco Photonics Italy, Monza, Italy,

2. Why a fiber Figure of Merit?
Which is the best fiber type for long-haul transmission?
For links based on compensation of chromatic dispersion the answer depends on dispersion-map
For coherent-received modulation formats uncompensated links are the best solution
We want to “give a grade” to each fiber type for the use on uncompensated links for coherent-received modulation formats
Fiber Figure of Merit (FoM)
ECOC paper Th.12.LeCervin.5

3. ECOC 2011 - paper Th.12.LeCervin.5
Outline
A novel FoM definition based on system margin
NL interference in uncompensated links (Df = Rs)
FoM: a closed form for Df = Rs
Comparing different fiber types and previous FoM definitions
Simulative validation
What happens if Df > Rs?
Experimental results
Comments and conclusions
ECOC paper Th.12.LeCervin.5

4. The FoM based on system margin
Given a multi-span link setup based on a fiber type operating at BER ≤ BERtarget
Fiber loss Afiber: it is the intrisic loss introduced by the fiber span
Span budget Amax: it is the maximum tolerable loss per span in order to ensure operation at BER ≤ BERtarget
System margin: Amax - Afiber
ECOC paper Th.12.LeCervin.5

5. Nonlinear interference (Df = RS)
Closed-form expression for maximum span budget
(*)P. Poggiolini, A. Carena, V. Curri, G. Bosco, F. Forghieri, “Analytical Modeling of Non-Linear Propagation in Uncompensated Optical Transmission Links,” IEEE PTL, vol 23, issue 11, pp , 2011.
ECOC paper Th.12.LeCervin.5

6. Figure of Merit: analytical expression
For sufficiently large dispersion values …
In order to compare different fibers the FoM difference is considered taking the SSMF as a reference
ECOC paper Th.12.LeCervin.5

7. FoM: previous definitions and applications
Previous FoM definitions
No loss
No dispersion
No dispersion
a [dB/km]
g [1/W/km]
b2 [ps2/km]
DFoM1 [dB]
DFoM2 [dB]
DFoM [dB]
C-band
Nch=10
SSMF
0.21
1.26
-21.3
0.0
PSCF
0.18
1.00
-26.2
4.0
3.4
4.1
NZDSF
0.22
2.00
-3.3
-3.0
-2.8
-7.0
-6.2
ECOC paper Th.12.LeCervin.5

8. DFoM for different fiber types2 4 8 16 32
-10 -8 -6 -4 -2 6 | b
| [ps
/km] D
FoM [dB] a
=0.18 [dB/km]; g
=1 [1/W/km]
=0.21 [dB/km];
=1.26 [1/W/km]
=0.22 [dB/km];
=2 [1/W/km]
PSCF
SSMF
NZDSF
ECOC paper Th.12.LeCervin.5

9. Simulative validation
In order to validate the FoM definition, we simulate the propagation of Nyquist WDM PM-QPSK channels
We matched setup characteristics to the ECOC 2011 paper We.7.B.2 by E. Torrengo et al.
10 PM-QPSK 120 Gbitps (Rs = 30 Gbaud)
8 spans of fiber (SSMF, NZDSF, PSCF)
Target BER = 3·10-3
The OSNR sensitivity matching to the experiment is the following Rx
X 8
EDFA
100 km
VOA
Opt
filter
PM-QPSK Tx …
Polarization diversity coherent Rx
and LMS DSP
ECOC paper Th.12.LeCervin.5

10. Span Budget vs. PTx,ch - Df = 30 GHz
Simulation – BER =3·10-3
Span Budget [dB]
Reference
PSCF
SSMF
NZDSF
PTx,ch [dBm]
ECOC paper Th.12.LeCervin.5

11. What happens if Df > Rs?
The model for PNLI has an analytical closed-form only for Df = Rs
We want to check what happens at larger channel spacings
We run simulations of the considered 10 channels system over 8 fiber spans varying Df from 30 GHz up to 50 GHz
We derived the maximum span budget and consequently the FoM for such scenarios
ECOC paper Th.12.LeCervin.5

12. The FoM definition is independent
DFoM vs. Df
PSCF
4.1dB
Reference: SSMF
NZDSF
-6.3 dB
The FoM definition is independent
of channel spacing
ECOC paper Th.12.LeCervin.5

13. ECOC 2011 - paper Th.12.LeCervin.5
Experimental results
So far, the proposed FoM is confirmed by simulation for most the commercial fiber types and also for channel spacings larger than the symbol rate
We carried on also a validation based on experimental results
We used the set-up whose results were presented in:
E. Torrengo et al., ECOC 2011, paper We.7.B.2
PM-QPSK 120 Gbitps
10 channels Nyquist WDM spaced 33 GHz (1.1·RS)
8 spans SSMF or NZDSF
ECOC paper Th.12.LeCervin.5

14. Simulation vs. experiment - Df = 33 GHz
PTx,ch [dBm]
Span Budget [dB]
NZDSF
SSMF
PSCF
Simulation
PTx,ch [dBm]
Span Budget [dB]
NZDSF
SSMF
Experiment
Points: experimental results
Lines: NL model
DFoM [dB]
Analytical
Simulation
Experiment
SSMF
0.0
NZDSF
-6.2
-6.3
-6.1
PSCF
4.1
N.A.
Excellent agreement
ECOC paper Th.12.LeCervin.5

15. Comments and conclusions
We propose a novel definition for a fiber FoM for uncompensated links and coherent-received modulation formats
It includes simultaneous dependence on nonlinearity, chromatic dispersion and loss
The FoM definition holds for channel spacing from the Nyquist limit up to larger spacing
It has been verified by simulation and with experimental results on PM-QPSK transmission
ECOC paper Th.12.LeCervin.5

16. This work was supported by CISCO Systems within a SRA contract
Acknowledgments
This work was supported by CISCO Systems within a SRA contract
The simulator OptSimTM was supplied by RSoft Design Group Inc.
ECOC paper Th.12.LeCervin.5

17. Span Loss vs. PTx,ch - Df > Rs
PSCF
Df = 33 GHz
Df = 37 GHz
PSCF
SSMF
SSMF
NZDSF
NZDSF
Df = 40 GHz
PSCF
SSMF
NZDSF
ECOC paper Th.12.LeCervin.5