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, optcom@polito.it (2) Istituto Superiore Mario Boella, Torino, Italy, nespola@ismb.it (3) Cisco Photonics Italy, Monza, Italy, fforghie@cisco.com

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 2011 - paper Th.12.LeCervin.5

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 2011 - paper Th.12.LeCervin.5

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 2011 - paper Th.12.LeCervin.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. 742-744, 2011. ECOC 2011 - paper Th.12.LeCervin.5

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 2011 - paper Th.12.LeCervin.5

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 2011 - paper Th.12.LeCervin.5

DFoM for different fiber types 2 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 2011 - paper Th.12.LeCervin.5

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 channels @ 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 2011 - paper Th.12.LeCervin.5

Span Budget vs. PTx,ch - Df = 30 GHz Simulation – BER =3·10-3 Span Budget [dB] Reference PSCF SSMF NZDSF PTx,ch [dBm] ECOC 2011 - paper Th.12.LeCervin.5

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 2011 - paper Th.12.LeCervin.5

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 2011 - paper Th.12.LeCervin.5

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 modulation @ 120 Gbitps 10 channels Nyquist WDM spaced 33 GHz (1.1·RS) 8 spans SSMF or NZDSF ECOC 2011 - paper Th.12.LeCervin.5

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 2011 - paper Th.12.LeCervin.5

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 2011 - paper Th.12.LeCervin.5

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 2011 - paper Th.12.LeCervin.5

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 2011 - paper Th.12.LeCervin.5