Filtering effects of cascaded flex-grid roadms with high spectral resolution filters on the...

Pablo Torres-Ferrera (1,2), José Manuel Rivas-Moscoso (1), Dimitrios Klonidis (1),

Dan M. Marom (3), Ramón Gutiérrez-Castrejón (2) and Ioannis Tomkos (1)

(1) Athens Information Technology, Greece

(2) Institute of Engineering, UNAM, Mexico

(3) Applied Physics Department, Hebrew University of Jerusalem, Israel

Filtering effects of cascaded Flex-grid ROADMs

with High Spectral Resolution filters on the

transmission of Nyquist and quasi-Nyquist WDM

super-channels

2NOV 2014 13th ICOCN, Suzhou, China

Outline

Objective

Simulation environment

• N-WDM and qN-WDM transmitter and receiver.

• Flex-grid ROADM with coarse and fine granularity filtering stages

Simulation results

• OSNR vs Back-to-Back BER

• Filter-concatenation studies

Conclusions


Objective

Investigate N-WDM and qN-WDM super-channel (SCh) transmission over a flexible ROADM node-based network in which filtering is performed at two levels:

• Fiber link level: switches super-channels (SCh) as a whole. Uses WSS coarse-granularity filters1.

• Super-channel level: switches sub-channels within super-channel. Uses HSR fine-granularity filters2 with free spectral range (FSR) = 200 GHz (maximum SCh bandwidth).

WSS Coarse HSR Fine

Resolution 7.5 GHz 0.8 GHz

Spectral addressability 6.25 GHz 0.1 GHz

Insertion Loss 5 dB 15 dB

1As reported in D4.3 of FOX-C project. 2As reported in ECOC 2014, paper PD.4.1.


Setup for the MATLAB/VPI co-simulation platform with N ROADMs and 5 uncompensated 80-km fiber spans between ROADMs


Parameters of conventional SMF fibre:

Attenuation [dB/m] 2.00E-4

Dispersion [s/m2] 17

Dispersion Slope [s/m3] 60

γ coeff [1/(W·km)] 1.2

PMD [s/m1/2] 3.16E-15

Super-channel

TxSuper-channel

Rx

SCh1

SCh2

SCh3

5 5

SCh1

SCh2

SCh3

N

WS

S

WS

S

Booster Pre-Amp

AddDrop

Analysed SCh.


Super-channel Tx:

Simulation environment: N-WDM and qN-WDM

IQ-MZM

PPG

PPG

Nyquist

shaping

filter

PBCCW

PBS

IQ-MZM

PPG

PPG

Nyquist

shaping

filter

PBCCW

PBS

Pol-X

Pol-Y

Ch1

Ch7

.

.

.

Super-Channe1 Tx

Pol-X

Pol-Y

MU

X

QBias

/2

IQ-MZM

Q

IIBias

PPG: pulse pattern generator

PBC: polarisation beam combiner

PBS: polarisation beam splitter

Mod format: DP-QPSK

Symbol rate (Rs): 25 Gbaud

Sub-channel spacing (Δf)

N-WDM : 25.0 GHz

qN-WDM : 26.8 GHz

(i.e. 1.07143·Rs)

Super-channel BW:

7 Δf + 12.5 GHz (SCh GB) =

N-WDM : 187.50 GHz

qN-WDM : 200.00 GHz

f= RS


Simulation environment: N-WDM and qN-WDM

Super-channel Rx:

PBS

PBS Sx

Sy

LOy

LOxIx

Qx

Iy

Qy

DS

P

Balanced

photodetector

DFBIntensity

modulator splitter

50/50

211

-1 PRBS

(3.5 or 7)

Gb/s

BPG

4:1

MUX

QPSK↔16QAM

to

Balanced

photodetector

DFBIntensity

modulator splitter

50/50

211

-1 PRBS

(3.5 or 7)

Gb/s

BPG

4:1

MUX

QPSK↔16QAM

to

Balanced

photodetector

DFBIntensity

modulator splitter

50/50

211

-1 PRBS

(3.5 or 7)

Gb/s

BPG

4:1

MUX

QPSK↔16QAM

to

Balanced

photodetector

DFBIntensity

modulator splitter

50/50

211

-1 PRBS

(3.5 or 7)

Gb/s

BPG

4:1

MUX

QPSK↔16QAM

to

LOCh1

Ch1

Pol-X

Pol-Y

PBS

PBS Sx

Sy

LOy

LOxIx

Qx

Iy

Qy

DS

P

Balanced

photodetector

DFBIntensity

modulator splitter

50/50

211

-1 PRBS

(3.5 or 7)

Gb/s

BPG

4:1

MUX

QPSK↔16QAM

to

Balanced

photodetector

DFBIntensity

modulator splitter

50/50

211

-1 PRBS

(3.5 or 7)

Gb/s

BPG

4:1

MUX

QPSK↔16QAM

to

Balanced

photodetector

DFBIntensity

modulator splitter

50/50

211

-1 PRBS

(3.5 or 7)

Gb/s

BPG

4:1

MUX

QPSK↔16QAM

to

Balanced

photodetector

DFBIntensity

modulator splitter

50/50

211

-1 PRBS

(3.5 or 7)

Gb/s

BPG

4:1

MUX

QPSK↔16QAM

to

LOCh7

Ch7

Pol-X

Pol-Y

.

.

.

Super-Channel Rx

Super-Channel Splitter

1:7

Conventional Polarization

Diversity COH-Rx with:

- 90° Optical Hybrid &

balanced photo detectors.

(Optical to Electrical)

- DSP standard algorithms

for DP-QPSK modulation

format:

• ADC (2SpS)

• MIMO CMA &

Freq. EQ for

CD/PMD

compensation.

• CPE Viterbi-Viterbi

for phase correction.


Simulation environment: Flex-grid ROADM

Design and operation of the flex-grid ROADM node:

Three super-channels with

seven 25-GBaud sub-channels

each.

WS

S

WS

S

AddDrop

-3dB-15dB

BS

-5dB

BP

BS

-5dB

BP

BS

BP

Dropped super-channel

(Broadcast and select)

HSR

Channel to be added


Results


Simulation results: OSNR vs Back-to-Back BER

OSNR vs Back-to-Back BER (X- and Y-Pol average):

Rx OSNR of central sub-channel to achieve BER=1E-3:

N-WDM = 18 dB qN-WDM = 14 dB

fsub-Ch= 25 GHz

BtB 4-dB penalty for N-WDM as compared to qN-WDM due to strong linear

XTalk in central sub-channels.

N-WDM qN-WDM

fsub-Ch= 26.8 GHz

Rx OSNR [dB]Rx OSNR [dB]


BER vs reach for dropped sub-Ch3 (X- and Y-Pol average):

Simulation results: Filter-concatenation studies

N-WDM qN-WDM

Add

-15dB

HSR

Analysed Sub-channels:

4 and 7

Add/Dropsub-Ch3

f = 25 GHz f = 25.9 GHz f = 26.8 GHz

w/ROADM

PtP



N-WDM: Very bad PtP-performance for central sub-Ch 4 due to BtB 4-dB penalty. Therefore, the central sub-Ch limits the maximum reach, but the edge sub-Ch7 experience very fast performance degradation due to filtering (no GB between sub-Chs).

qN-WDM: Closer PtP-performance between central and edge sub-Chs than in N-WDM. w/ROADM: For f = 25.9 GHz sub-Ch7 limits the transmission (worst performing sub-Ch after 2300 km). For f = 26.8 GHz central sub-Ch4 limits transmission. Due to positive impact of a wider f, the faster degradation of edge sub-Ch is not enough to limit reach.


N-WDM qN-WDM

f = 25 GHz f = 25.9 GHz f = 26.8 GHz

w/ROADM

PtP



• 1-stage filtering: Only WSS coarse filters (in orange).

Very low impact on the performance due to guard band between SChs.

• 2-stage filtering: Both coarse-granularity WSS and HSR filters (in blue).

HSR fine filtering-stage is responsible for the difference between PtP-and w/ROADM-case.

Simulation results: Filter-cascading studies

qN-WDMN-WDM

f = 25 GHz f = 25.9 GHz f = 26.8 GHz




N-WDM qN-WDM

Add

-15dB

HSR

Analysed Sub-channels:

5 and 7

Add/Dropsub-Ch6

f = 25 GHz f = 26.8 GHz



N-WDM qN-WDM

Sub-channel spacing (f ) GHz 25 25.9 26.8

Super-channel Bandwidth (BWSCh) GHz 187.5 193.75 200

Spectral efficiency (b/s/Hz) 3.73 3.61 3.5

Add/Drop sub-Ch3

Maximum reach wo/ROADM (PtP) km 2600 5000 5150

Maximum reach w/ROADM km 2450 3600 5000

Number of ROADMs SCh go through 4 8 10

Add/Drop sub-Ch6

Maximum reach wo/ROADM (PtP) km 2550 * 5100

Maximum reach w/ROADM km 2450 * 4800

Number of ROADMs SCh go through 4 * 10

BER vs reach with and without ROADM nodes:



N-WDM qN-WDM

Sub-channel spacing (f ) GHz 25 25.9 26.8

Super-channel Bandwidth (BWSCh) GHz 187.5 193.75 200

Spectral efficiency (b/s/Hz) 3.73 3.61 3.5

Add/Drop sub-Ch3

Maximum reach wo/ROADM (PtP) km 2600 5000 5150

Maximum reach w/ROADM km 2450 3600 5000

Number of ROADMs SCh go through 4 8 10

Add/Drop sub-Ch6

Maximum reach wo/ROADM (PtP) km 2550 * 5100

Maximum reach w/ROADM km 2450 * 4800

Number of ROADMs SCh go through 4 * 10

BER vs reach with and without ROADM-nodes

= -0.12 = -0.11

1.9x

1.5x

1.0x

1.3x

= -0.23

2x

2x


Conclusions


Conclusions

Edge sub-channels experience the highest filter-concatenation degradation due to the non-ideal roll-off of both coarse- and fine-granularity filters, especially if the spectral gaps between sub-Chsand SChs are not sufficiently wide. The impact of fine-filtering is predominant.

For N-WDM: BtB 4-dB OSNR penalty due to strong linear Xtalk. Central sub-Chs limit the maximum reach, even if the edge sub-Chssuffer higher degradation due to filter-concatenation.

For qN-WDM (f = 25.9 GHz) the edge sub-channels limit the maximum reach due to filter-concatenation.

For qN-WDM (f = 26.8 GHz) the central sub-Chs limit transmission. Due to positive impact of a larger guard-band between sub-Chs, the faster degradation of edge sub-Ch is not enough to limit the reach.

By slightly reducing spectral efficiency, a substantial increase in maximum reach can be achieved, especially when ROADMs are considered.


Thank you

谢谢


Backup



G = 8 dB G = 10 dB

G = 10 dB

IL = 5 dBIL = 5 dBPin = -2dBm/ch

Pout = -2dBm/ch

P = -7dBm

WSS Coarse-granularity stage

IL = 3 dB (splitter) IL = 15 dB (HSR filter)

Padd = -2dBm

This module acts

as a splitter. Filters

were deactivated.

Fine-granularity stage (HSR)



Coarse WSS for fiber-link stage

BP and BS filters

Shape: Convolution(Erf, Rectangular)

Resolution = 7.5 GHz

Dispersion = 6.25 GHz

Coarse and fine granularity Add and Drop modules

for fibre-link and super-channel stages

BS = BandStop

BP = BandPass

IL = 5 or 15 dB

Ideal

(IL = 0 dB)

HSR for super-channel level switching

BP and BS filters

Shape: Convolution(Erf, Rectangular)

Resolution = 0.8 GHz

Dispersion = 0.1 GHz

IL = 5 dB or

3 dB (splitter)

Filtering effects of cascaded flex-grid roadms with high spectral resolution filters on the...

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