ROADM Technologies for Flexible - Tbitsec Optical Networks

© 2014 Finisar Corporation

ROADM Technologies for Flexible, Tbit/sec Optical

Networks

Simon Poole

Director, New Business Ventures

© 2014 Finisar Corporation 2

ROADM Proliferation

ROADMs are used to manage transparent traffic

through the intersections of a WDM network;

3 prime functions: Wavelength Switching

Amplification

Signal Integrity Monitoring

2

Switching Cost Relative to OSI Layer


Problem: How to reduce cost of transmission

Increase Capacity

Coherent Nyquist Filtering

Superchannels Flexible Grid

Amplifiers Monitoring

Defragmentation etc

Dual WSS

Amplifiers

Reduce Capex

Route & Select

CD/CDC

Size

Power

Reduce Opex

Cost of Transmission

($/Gb/sec/km)


Increasing Capacity: Nyquist & Superchannels

Third generation coherent

transmitters add a filtering

(digital/analog) at transmitter to

minimise optical bandwidth of

signal (Nyquist output)

A superchannel is a multi-

carrier group of channels that

is operationally managed as a

single channel and which can

be presented to higher

networking layers as a single

higher data rate channel. (May

or may not be Nyquist filtered).

QPSK Re

lati

ve

Po

we

r (d

B)

Normalized Freq (GHz)

16QAM Re

lati

ve

Po

we

r (d

B)

Normalized Freq (GHz)


-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

-25 -20 -15 -10 -5 0 5 10 15 20 25

Rel Freq (GHz)

Rel IL

(d

B)

-3.0

-2.5

-2.0

-22 -21 -20 -19 -18 -17

Rel Freq (GHz)

Rel

IL

(d

B)

Flexible Grid WSS

First generation WSS allocated a

single channel to a single pixel

LCoS-based WSS use a flexible

matrix-based wavelength switching

platform with megapixel matrices

which allows programmable

channel bandwidth


From Fixed-grid to Flexgrid

LCoS technology allows arbitrary channel bandwidth

Trade-off between flexibility and OSS requirements

12.5GHz slices as per ITU G 694.1 (Feb 2012) supports legacy

fixed-grid as well as Flexgrid


Flexgrid & Superchannels

Flexgrid™ + superchannels with

Nyquist Filtering for maximum

Spectral Efficiency

Fixed Grid WSS require

interchannel guard-bands

35 GHz Pass Bands 15 GHz “Dead Zones”

Flexgrid™ WSS +

superchannels allow denser

channel packing by eliminating

inter-channel guard-bands

Up to 5 THz Pass Band, 15 GHz “Dead Zone”


Advanced Flexgrid Functionality

No Limit to Superchannel spectral width

37.5 GHz – 5 THz in 6.25 GHz increments

Intra-channel attenuation control

Attenuation range: 0 to 20 dB

Intra-channel attenuation control of each 6.25 GHz section of a channel

Enables equalization across super channels

Dynamic and scalable channel width

Hitlessly widen, narrow or migrate a channel with 6.25 GHz resolution

Established traffic unaffected

Simplifies defragmentation


Flexgrid WSS: a proven technology

Finisar has deep experience in LCoS WSS since 2004

More than half of Finisar’s shipped WSS feature flexible grid

functionality

Common LCoS Platform

Single WSS: 1x4 – 1x20 Dual WSS: 2x1x20, 2xMxN


Example ROADM Configurations

ROADM design depends on many factors

Network Design

Node Degree(s)

Electronic vs Optical switching

Expandability vs Initial Cost

etc

Traditional Broadcast and Select

Colourless, Directionless (CD)

Colourless, Directionless, Contentionless (CDC)


Broadcast and Select ROADM

Passive split on Drop-side

WSS on Add-side

AWG for wavelength

mux/demux

Fixed Grid

Coloured Add/Drop

100% Add/Drop of 88

channels

2x100 GHz AWGs on

add side for lost cost

Fixed-grid OCM

Classic (B&S) ROADM O

CM

44 ch AWG 88 ch AWG 44 ch AWG

1x9 W

SS

8x8 Span

Crossconnect

8x8 Span

Crossconnect

1x8 s

plitt

er

88 ADD 88 DROP


Colourless, Directionless (CD) ROADM

Typical Requirements

8 degrees with 100% Add/Drop of 96

channels

Flexgrid

NB Limited drop-side filtering – only

works for coherent systems

Typical Modularity

Per degree

• 2x1x16 (Dual) WSS

• Flexgrid OCM

• Pre-amp and booster

Per directional switch

• 2x6x8 per 96 channels

Per 16 channel Add/Drop

• 2x1x16 splitter/couplers

• EDFA per splitter/coupler

CD ROADM

16x1 coupler

OC

M

1x16 W

SS

8x8 Span

Crossconnect

8x8 Span

Crossconnect

1x16 W

SS

To

Directions 2-8

From

Directions 2-8

Drop Port 1

16 ADD 16 DROP

6x8 WSS 8x6 WSS

Drop Ports 2-8

AMP

x6 x6

Add 1

Add Ports 2 - 8

1x16 splitter

8x6 WSS

AMP


Colourless, Directionless, Contentionless, (CDC) ROADM

Typical Requirements

Scalable to 8 degrees with ~30%

Add/Drop of 96 channel systems

Flexgrid

NB No drop-side filtering – only

works for coherent systems

Example Modularity

Per degree

• 2x1x23 (Dual) WSS

• Flexgrid OCM

• Pre-amp and booster

Per 16 channel Add/Drop

• 2x8x16 multicast switch

• Quad low-gain EDFA (2 per

multicast switch)

CDC ROADM O

CM

1x23 W

SS

8x8 Optical

Crossconnect

8x8 Optical

Crossconnect

1x23 W

SS

To

Directions 2 - 8 From

Directions 2-8

Drop Port 1

Drop Ports 2-16

16 ADD 16 DROP

AMP AMP

Add Port 1

Add Ports 2-16

8x16 MCS 8x16 MCS


8 Degree ROADM Comparison


CDC ROADM , 100% Add Drop

100% capacity on each Add/Drop

requires:

1 x 4 splitter

Higher gain amplifiers

Additional MCS on Add/Drop

CDC ROADM O

CM

1x23 W

SS

8x8 Optical

Crossconnect

8x8 Optical

Crossconnect

1x23 W

SS

Drop Port 1

Drop Ports 2-16

Add Port 1

Add Ports 2-16

1x4 splitter

From

Directions 2-8

16 DROP

8x16 MCS

From

Directions 2-8

16 DROP

8x16 MCS

From

Directions 2-8

16 DROP

8x16 MCS

AMP


Optical Amplifiers: Size, Power, SNR


Honey, I shrunk the EDFA…

XFP: 1.5W power

consumption

APPROXIMATE LIFETIME EXPECTATIONS*

Coil diameter

(mm) 10 12 14 18

125µm – 3%

proof tested fiber <1 year <1 year ~3.17 years >50 years

80µm – 2% proof

tested fiber <1 year 0-3.17 years >40 years >50 years

80µm – 3% proof

tested fiber >40 years >50 years >50 years >50 years

*Cost 218 Model, 4m of fibre


EDFA Arrays for ROADMs

Shared electronics – reduces cost, power, size

Uncooled pumps - lower power consumption

Dual EDFA (70x90 mm)

PreAmp and Booster in one box

8 EDFA

(183 x 150 x 18.5 mm)


Hybrid Raman-EDFA

A combination of a counter-propagating Raman pump unit and a

variable gain EDFA

Mesh networks

ULH inline amplification

Hut skipping (for high gain range units)

Overall Gain

Electronics for

AGC Control and Eye Safety

EDFA

980 Pump

Raman

14XX

pump(s)

2 or 3-Pump Hybrid Raman EDFA


Amplifier Trends

Availability of up to 130 channels (37.5 GHz-spaced Nyquist channels within larger superchannels) in the C-band drives higher amplifier output powers.

Mesh topology will drive lower NF (Hybrid Raman-EDFA) and superior dynamics (fast electronics) to allow flexibility in network re-configuration.

Raman and Hybrid Raman-EDFAs will proliferate in long haul systems.

To simplify ROADM control loops, gain uniformity <0.5 dB.

To reduce types of EDFAs used, either gain switched platforms will proliferate or pluggable EDFAs will take off - provided there is no cost penalty


Optical Channel Monitors:

Flexgrid, Superchannels and SDN


OCM Requirements

Spectral power information with high resolution

Intra-channel attenuation in 6.25 GHz spectral slices

Power monitoring of superchannel carriers

Location of center wavelengths of superchannel carriers

Eliminate power differential between adjacent channels

Fast scanning and response time

Superchannel Add/Drop requires OCM, not just a photodiode, to monitor traffic through

Add/Drop paths

Loss of Signal (LoS) and fault detection to support protection and restoration switching

Staring mode - monitoring a fixed frequency

Applications utilizing in-band modulation signals, i.e. wavelength tracking

• Possibly demodulate within the OCM

Some proprietary OSNR measurement techniques


Multi-port Flexgrid Optical Channel Monitor

Grating spectrally disperses light from up to four fibers.

2D MEMS mirror is used to scan the optical spectrum onto an

array of photodiodes.


Example: Multiport Flexgrid OCM

Small size: 100x50x15 mm, Low power: <5 W

Parallel scanning of all ports in 500 ms; no need for dedicated switch

Requires deconvolution of measured signal to provide 6.25 GHz slices

required for attenuation control on Flexgrid WSS

2-4 port OCM


To Summarise…

Improved ROADM subsystems

(Dual WSS, Hybrid amplifiers, Flexgrid OCM, etc) will

enable future-proof ROADM Architectures

to provide transparent Wavelength Management

Capability for future 400 Gb/sec and 1 Tb/sec

ROADM Technologies for Flexible - Tbitsec Optical Networks

Technology

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