Optimized 4 and 8 Dimensional Modulation Formats for Variable Capacity in Optical Networks

Copyright © Ciena Corporation 2016. All rights reserved.

Optimized 4 and 8 Dimensional Modulation Formats for Variable Capacity in Optical Networks

Michael Reimer, Shahab Oveis Gharan, Andrew D. Shiner and Maurice O’Sullivan

March 21, 2016


Four available dimensions of the optical field: In-phase (I) and quadrature (Q) components of two polarizations.

2D symbols encoded on I and Q of each orthogonal polarization.Data on each polarization can be decoded independently of data on other polarization.

X-pol

Y-pol

Encoded symbol2D symbols encoding 1 bit


4D symbols encoded across I and Q of two orthogonal polarizations.Examples: PS-QPSK, 32-SP-QAM, 128-SP-QAM, etc.

4D symbols encoding 2 bits

X-pol

Y-pol

Encoded symbol

E. Agrell, et al., J. Lightwave Technol. 27(22), 2009P. Poggiolini, Opt. Expr., 18(11), 2010M. Chagnon, et al., Opt. Expr., 21(25) 2013R. Rios-Muller, et al., Proc. ECOC, Th.2.D.2, 2013H. Sun, et al., Proc. ECOC, Th.2.D.3, 2013


OSNR (dB)

BER

3% bit error rate

4D-8QAM PM-8QAM

0.48 dB

35 GBd signaling rate

Example: 4D encoding at 8QAM capacity Linear performance advantage can be realized through novel 4D encoding.

Control of optical power characteristics through constellation “power-balancing”.

Constant 4D symbol modulus for reduced inter-channel nonlinear interference.

Example: 4D-8QAM - 4D constant modulus encoding at PM-8QAM equivalent capacity.

0.48 dB OSNR improvement at 0.03 BER relative to PM-8QAM.

� + � = constant for all symbols


X-pol

Y-pol

Encoded symbol8D symbols encoding 4 bits

8D symbols encoded across I and Q of two orthogonal polarizations of two time slots (or optical wavelengths, spatial modes, etc.)

D. Millar, et al., Opt. Expr., 22(7), 2014D. Millar, et al., Proc. OFC, M3A.4, 2014T. Eriksson, et al. Proc. ECOC, Th.2.D.4, 2013.A. D. Shiner, et al., Opt. Expr., 22(17), 2014


Linear performance advantage can be realized through novel 8D constellation designs.

e.g. 0.62 dB OSNR improvement at 0.03 BER relative to PM-BPSK using 8D biorthogonal constellation.

OSNR (dB)B

ER

3% bit error rate

8D biorthogonal PM-BPSK

0.62 dB


Example: 8D Biorthogonal


Poincaré sphere

WDM spectrum

Reduced cross polarization modulation (XPolM)

8D polarization balanced channel



Control over the temporal characteristics of transmit symbols: “polarization-balancing”

A. D. Shiner, et al., Opt. Express, 22(17), 2014




Control over the temporal characteristics of transmit symbols: “polarization-balancing”

Simplified hardware implementation.PM-BPSK spectral efficiency requires decoding of 16 symbols in 8D space.

Example: 8D-2QAM - 8D pol. balanced encoding at PM-BPSK equivalent capacity.

A. D. Shiner, et al., Opt. Express, 22(17), 2014Poincaré sphere

Reduced cross polarization modulation (XPolM)

8D polarization balanced channel


3% pre-FEC (uncoded) bit error rate

BPSK

OSNR (dB)

8D QPSK 16QAM

BER

8QAM


Track required OSNR (ROSNR) for an example 0.03 pre-FEC BER over range of capacity. ROSNR dependent on Euclidean and Hamming distance properties of the modulation.



0.03 pre-FEC (uncoded) BER

25% overhead

PM-32QAM10 bits/interval

PM-STARQAMPM-16QAM8 bits/interval


PM-QPSK4 bits/interval

PM-BPSK2 bits/interval

Standard QAM

Shannon



PM-STARQAMPM-16QAM8 bits/interval


Standard QAM

PM-32QAM

PM-16QAM PM-STARQAM

PM-8QAM

PM-QPSK PM-BPSK

Shannon

PM-BPSK2 bits/interval

PM-QPSK4 bits/interval


4D Set partitioning

32-SP-QAM5 bits/interval



128-SP-QAM

64-SP-QAM

32-SP-QAM

R. Rios-Muller, et al., Proc. ECOC, Th.2.D.2, 2013H. Sun, et al., Proc. ECOC, Th.2.D.3, 2013

Shannon


4D Constant modulus formats

PS-QPSK3 bits/interval

6Pol-QPSK~ 4.6 bits/interval

PM-8PSK6 bits/interval

8Pol-QPSK5 bits/interval

PM-8PSK

8Pol-QPSK

PS-QPSK

P. Poggiolini, Opt. Expr., 18(11), 2010M. Chagnon, et al., Opt. Expr., 21(25) 2013H. Bulow, Proc. OFC, OWG.2, 2009

6Pol-QPSK

K. Kojima, Proc. ECOC, P.3.25, 2015

Shannon


Time Domain Hybrid QAM (TDHQ) Constellations of differing cardinality within a single TDHQ frame.

Shannon


Time Domain Hybrid QAM (TDHQ)

Shannon

Constellations of differing cardinality within a single TDHQ frame.

Increased ROSNR apparent at � ≤ � ≤ � b/s/Hz.Q. Zhuge, Proc. OECC, 2015

M. Reimer, Proc. SPPCom, 2015


Constellations of differing cardinality within a single TDHQ frame.

Increased ROSNR apparent at � ≤ � ≤ � b/s/Hz.

> 0.5 dB ROSNR improvement through 4D format optimization.

4D Numerical Optimization

Q. Zhuge, Proc. OECC, 2015

M. Reimer, Proc. SPPCom, 2015Shannon


Region enlarged

0.54 dB

4D Numerical Optimization



0.53 dB


Region enlarged

4D-8QAM0.48 dB

4D-8QAM: 4-dimensional encoding of 64 symbols (6 bits).

Constant 4D symbol modulus.



8D polarization balanced formats

X-constellation / 8D Biorthogonal2 bits/interval

Establish performance bounds of 8D pol-balanced formats.

8D polarization balanced2 – 4 bits/interval

A. D. Shiner, et al., Opt. Express, 22(17), 2014

Shannon


8D polarization balanced formats Establish performance bounds of 8D pol-balanced formats.

Cost of 8D pol-balancing:3 dB ROSNR per 1 b/s/Hz increase in capacity.

Linear performance advantage with 8D pol-balancing up to 2.4 b/s/Hz (PS-QPSK)

3 dB ROSNR per 1 b/s/Hz

Shannon

8D polarization balanced2 – 4 bits/interval

X-constellation / 8D Biorthogonal2 bits/interval


Dis

pers

ion

(ps/

nm)

Distance (km)

Txpo

wer

spe

ctru

m (d

B)

Wavelength (nm)

�� , 50 GHz WDM spacing

System margin: dBs of additional noise that can be tolerated before FEC limit. Difference between line-delivered OSNR and OSNR required for FEC limit (ROSNR).

Measured 2430 km reach with PM-8QAM.

PM-8QAM2430 km

System margin

Zero margin reach


Single 4D-8QAM, PM-8QAM interferers

PM-8QAM2430 km

2600 km

7% increased reach (170 km) measured for 4D-8QAM in presence of PM-8QAM WDM nonlinear interference.

Dis

pers

ion

(ps/

nm)

Distance (km)

Txpo

wer

spe

ctru

m (d

B)

Wavelength (nm)



4D-8QAM 2950 km

PM-8QAM2430 km

2600 km

Significant reduction of inter-channel nonlinear interference due to constant 4D symbol modulus.

20% measured increase in reach (520 km) with 4D-8QAM.

Dis

pers

ion

(ps/

nm)

Distance (km)

Txpo

wer

spe

ctru

m (d

B)

Wavelength (nm)



Polarization and time-switched QPSK: 1 bit selects time slot, 1 bit selects polarization, 2 bit QPSK symbol

0.62 dB improvement in OSNR required for 0.03 BER relative to PM-BPSK.

8D symbols encoding 4 bits.2 of 16 possible symbols shown.

X-pol

Y-pol

Encoded symbol

Y-polarized time slot

X-polarized time slot

Zero amplitude

Zero amplitude


Dis

pers

ion

(ps/

nm)

Distance (km)

� = ��

�= ��

Increased nonlinear interference due to amplitude variations of 8D Biorthogonal. Max reach < PM-BPSK despite 0.62 dB improvement in required OSNR (ROSNR).

Zero margin reach (km)

Pow

er (d

Bm

)

PM-BPSK nonlinear polarization sensitivity

Large effective area fiber (LEAF), � ≈ 70 ��90% inline optical dispersion compensation, 6.5 dB NF9 WDM channels, 38 GHz separation35 GBd signaling rate


Poincaré sphere

Identify an 8D rotation that: Equalizes the symbol modulus between time slots. Achieves orthogonal polarization states between time slots (polarization balancing).

8D rotation preserves the linear performance advantage of 8D biorthogonal.

8D symbols encoding 4 bits.2 of 16 possible symbols shown.

X-pol

Y-pol

Encoded symbol

A. D. Shiner, et al., Opt. Expr., 22(17), 2014


> 30% increase in reach (3600 km) relative to PM-BPSK achieved through polarization balancing.

> 40% reach increase (> 4000 km) relative to standard 8D Biorthogonal


Pow

er (d

Bm

)

Dis

pers

ion

(ps/

nm)

Distance (km)

� = ��

�= ��



��

Polarization state of interfering BPSK channels

Interfering WDM channels

Central “probe” wavelength

Best case polarization orientation

Worst case polarization orientation

�

�

Poincaré sphere

PM-BPSK performance varies with polarization state of interfering PM-BPSK WDM channels due to XPolM.

XPolM

XPolM


< 0.05 dB margin difference with respect to WDM polarization state.

“Best case” pol. alignment

2D projection of X-const. symbols

“Worst case” pol. alignment


8D-PB-QPSK: 8D polarization balanced format with QPSK projection (3 bits/interval). > 25% increase in reach (2200 km) relative to PS-QPSK.


Pow

er (d

Bm

)

Dis

pers

ion

(ps/

nm)

Distance (km)

� = ��

�= ��



Single 8D-2QAM, PM-BPSK interferers

Wavelength (nm)

Txpo

wer

spe

ctru

m (d

B)

Dis

pers

ion

(ps/

nm)

65 �, 50 GHz WDM spacing

� = ��.� ��

Distance (km)PM-BPSK


1.2 dB measured increase in system margin with 8D polarization balancing.

Minimal temporal variation of BER observed with 8D-2QAM.

1.2 dB margin

8D-2QAM

PM-BPSK

� = ��.� ��Temporal variation of � (dB)

8D-2QAM

PM-BPSK


�= ��

� = �� SSMF

Improvement due mainly to the increased Euclidean distance of the multidimensional encoding.~ 16% and 13% increased reach at 5 and 6 bits/interval, respectively, using optimized 4D.> 6% increased reach with 8D pol-balancing up to 3 bits/interval spectral efficiency.

Dis

pers

ion

(ps/

nm)

Distance (km)

Max

imum

reac

h (k

m)

2 Pol. Capacity (b/s/Hz)


Dis

pers

ion

(ps/

nm)

�= ��

� = ��

Max

imum

reac

h (k

m)

LEAF, 90% CD comp

≥ 20% increased reach at 5 and 6 bits/interval using optimized 4D formats.

> 25% increased reach with 8D pol-balancing up to 3 bits/interval spectral efficiency.

Distance (km)


Z. Tian, L. Berg, M. Hubbard and P. Mehta, Ciena Submarine Line System Development


Linear advantage of X-const. provides 0.6 dB margin improvement relative to PM-BPSK, with optimum electronic dispersion pre-compensation.

Power (dBm)

Rel

ativ

e m

argi

n (d

B)

PM-BPSK, 50% electronic CD pre-comp

X-const.

PM-BPSK, no electronic CD pre-comp

BPSK no CD pre-comp

BPSK with CD pre-comp

4000 km standard single mode fiber (SSMF)Dispersion uncompensated9 WDM channels, 38 GHz separation35 GBd signaling rate


Phase conjugate twin wave (PCTW) QPSK – unitary transformation of PM-BPSK, with optimum electronic CD pre-compensation and appropriate receiver DSP.

PCTW-QPSK performance equal to PM-BPSK with optimum CD pre-compensation.

Linear advantage of X-const. improves margin by 0.6 dB relative to PCTW-QPSK.

PCTW-QPSK, 4 dBm X-constellation, 4 dBm

X. Liu, et al., Nat. Photon., vol. 7, pp. 560-568 (2013)

PM-BPSK with optimum CD pre-comp

� = �� (� + �)

�

8D


Symbol DOP 1.0

4000 km LEAF90% inline optical CD compensation-1 dBm power

A

B

A

B

X

Y

Effective symbol polarization

� × cross-polarized symbols

AB

B

A

�� × co-polarized symbolsX

Y


Symbol DOP 0.75


AB

X

Y


AB

B

A

�� × co-polarized symbolsX

Y



Symbol DOP 0.5


X

Y

A B


AB

B

A

� × co-polarized symbolsX

Y



Symbol DOP 0.25


X

Y

AB

�� × cross-polarized symbols

AB

B

A


Y



Symbol DOP 0


X

Y

A

B

�� × cross-polarized symbols

AB

B

A


Y


X-constellation


Distance (km)

Dis

pers

ion

(ps/

nm)

�= ��

� = �� SSMF

~ 2 dB SNR variation across range of spectral efficiency. Nonlinear signal-to-noise ratio (SNR) ~ constant for all amplitude modulated formats. Moderate SNR improvement through 8D pol-balanced encoding.


Non

linea

r SN

R (d

B)

-1 dBm launch powerWith electronic CD pre-comp


Dis

pers

ion

(ps/

nm)

Distance (km)

� = ��

� = ��

LEAF, 90% CD comp



Non

linea

r SN

R (d

B)

Nonlinear signal-to-noise ratio (SNR) ~ constant for amplitude modulated formats.

≥ 4 dB nonlinear SNR improvement through 8D pol-balanced encoding.


Dis

pers

ion

(ps/

nm)

Distance (km)

� = ��

� = ��

LEAF, 90% CD comp



Non

linea

r SN

R (d

B)



4D power balancing (constant symbol modulus)


Dis

pers

ion

(ps/

nm)

Distance (km)

� = ��

� = ��

LEAF, 90% CD comp



Non

linea

r SN

R (d

B)



4D power balancing (constant symbol modulus)

8D polarization balancing

Optimized 4 and 8 Dimensional Modulation Formats for Variable Capacity in Optical Networks

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