Dr. Uri Mahlab

Optical Network from Point to Point

to

MESH networksDr. Uri Mahlab

17 December 2007

TAU

2

Content

The market as a driven force

1st generation optical fiber communication

networks.

Optical technologies for the 1st and 1.5 generation

Enabling technologies for 2nd generation optical networks.

Mesh optical networks.

conclusions

3

Brief history of the optical communication network market

Clients

Service

providers

System

companies

Component

Modules companies

Universities

4

Brief history of the optical communication network market

Bubble Period

Allot of technology

And not real market

requirements

Many start ups

Survival period

Cost reduction

We are back

New real demand

for technology

Nortel share

5

Increase demand for services

6

the market is driven also

by tough standards !!!

7

Market of Tough standards

Add some slides for showing - risks

10

Transition

To absorption of new technologies

form survival situation

11Confidential text here

12

Optical network evolution

13

Design an optical network that answer the basic requirements from two point of views:

OLD requirementsConnectivity

Quality of Signal

Cost effective/ Competitive network

Problem Definition

14

Point to Point Networks – static network connectivity

Confidential text here

Tx site

IL site (Amplification site)

Rx site

15

Optical network components


Channel – Optical fiber:

Source and Sink (EO interfaces Tx/Rx)

Transport equipment

DCF/DCM – Dispersion Compensating Fibers/Modules

Passive components (MUX/DEMUX, filters, splitters, attenuators)

Optical Amplifiers

16

The optical fiber channel

Channel – Optical fiber:

Attenuation

Dispersion

Polarization mode dispersion

Non linearity

Attenuation

Rayleigh scattering is the main mechanism of attenuation

The most used band is 1529 ÷÷÷÷1560 nm called “C-band”

Typical attenuation of the C-band is 0.25 dB/km

Dispersion•Causes signal degradation as it passes

the fiber

•Depends on the wavelength

•It is a serious limitation on the signal

transmission distance

•Can be compensated

17

Optical link

Loss Non-linearity

EEit

EiE

Z

E 2

2

2

||22

γβα

+∂

∂−−=

∂

∂

Non-linear Schrodinger equation

Dispersion

Transmission Impairments

18

Source and Sink


EO interfaces Tx/Rx

LaserVoltage

Light = “1” bit

LaserNo voltageNo light = “0” bit

LaserVoltage

Modulator

Voltage – opaque =

“0” bit

LaserVoltage

Modulator

No voltage – transparent =

“1” bitTransmitter – parameters

Bit Rate

Mean launch power

Extinction ratio (ratio between the “1” power and “0” power)

Dispersion tolerance

Receiver

�Two types: PIN and APD.

�O/E interface.

Regenerates the original data stream.

Parameters such as : Sensitivity, Noise, Bandwidth.

Photodiode Decision circuit

19

Multiplexer/Demultiplexers, Filters, DCF

Passive components (MUX/DEMUX, filters, splitters, attenuators, couplers)

Attenuation=Insertion loss

Bandwidth

Bandwidth shape

Technology

STAR coupler

AWG

λN

λ2

λ1

λ1

λ2

λN

.

.

.

.

.

.

FiberFiber

λ λ, . . .

λ1 2 N

, ,λ λ

, . . .λ

1 2 N, ,

Optical multiplexer Optical demultiplexer

•Needed for compensation of the chromatic dispersion

•Depends on the type of fiber

•Attenuation=Insertion loss

•Dispersion ripple

DCF/DCM - Dispersion compensation fiber/modules

20

Optical amplifiers

Used to amplify the signal and to compensate for the attenuation of the passive components

Important parameters

Gain: G = Pout – Pin

Amplifiers are the source of the optical noise, Noise Figure (NF) is the characteristics of the noise amount emitted by an amplifier

Psat – is the maximum optical power an amplifier can provide

Gain flatness is the difference between the maximum and the minimum gain in the working region

Different type of amplifiers -EDFA, RAMAN, SOA

Single stage

Double stage

10dB Mid-stage

for OADM/DCF

22


ROADM

23

connectivity demands


Due to connectivity demands a “drop point” were forced by the service provider.

Filters for local drop

Splitter � Demux� OADM

Static filter

Limited number of filters / output ports

Concatenation limitation

Insertion loss

24

OADM

Used to demultiplex part of the DWDM channels

Utilizes the same technologies as Muxs + Fiber Bragg Gratings

OADM

λ λ. . .

λ1 2 N

Fiber

λ1 λ1

λ . . . λ2 Nλ λ

. . .λ

1 2 N

25

OADM – Optical Add Drop Multilpexing/filter

OADM – Bragg gratings

Periodical structure written on the fiber

Acts as a filter – reflects one wavelength and transmits other

Add Drop

Fiber Bragg grating

1 2

3λ1 λ2 λ3 λ4 λ1 λ2 λ3 λ4

λ2λ2

Coupler

OADM – parameters

•Through loss

•Add loss

•Drop loss

•Isolation – the amount of power,

which is transferred from one port to

another

26

Until one year ago this was the only network

topology.

Static network – no flexibility.

Each sub-network connects two termination points.

Connectivity and capacity defined in “Day 1” design and can’t be changed

Point to Point Networks - drawbacks

Clients

Service

providers

System

companies

Component

systems

Universities

27

Next Generation optical networks


Client point of viewOLD requirements

Connectivity

Quality of Signal

New requirements

Reconfigurable network

Optical traffic provisioning

Optical quality of service

Vendor point of view

Cost effective network and competitive to answer the demands

� OADM� Proper design

Clients

Service

providers

System

companies

Component

systems

Universities

29


ROADM


Re-configurable Optical Add Drop Multiplexing - ROADM

Sophisticated switch

31

WBWAVELENGTH

BLOCKER

Re-configurable Optical Add Drop Multiplexing - ROADM

WSSWAVELENGTH

SELECTIVE

SWITCH

PLCSilica-based

Planar

Lightwave

circuitOADM

ROADM

OXC

Technologies

&

Architecture

2nd generation

1.5st generation

2.Xnd generation

32

ROADM Module Technologies

LC (Liquid-Crystal) based free-space design for Wavelength Blocker (WB) architecture

MEMs (Micro Electro-Mechanical) based free-space design for Wavelength Switch (WS) architecture

PLC for Broadcast and Select architecture

33

LC Wavelength Blocker

Free space design is bulky and not scalable

Costly engineering design to ensure ruggedness against environmental variations

Cost of materials is high (~$6k), market value low (~$8k), no sign for cost reduction as key components have stabilized to fundamental limits (i.e. limited supplier base, low volumes and acceptable yields)

Diffraction grating

Folding mirror

Spherical Mirror

Liquid

crystal cell

(below)

Optical Bench

Front end

P1

P2

Grating

100x40x20 (mm)

Wavelength Blocker

34

System Architecture: WB

WB and Tunable Filter architecture– architecture optimized for pass-through traffic

Costly solution,

product not suited for metro requirements

Wavelength

Blocker (WB)

$8k

1x2 1x2Wavelength

Blocker

35

MEMs Wavelength Switch

Bulky and costly design; 32 sequential MEMs array

Costly hermetic sealing to ensure moveable flaps (i.e. MEMs chip) does not “stick” because of contaminants

Also, cost of materials is high (~$18k), cost reduction curve still not clear

Current market value is $24k for a 8-channel add/drop

IN

OUTExpress

INAdd

OUTDrop

Fibers

Micro

LensesSelfocLens

Sphericalmirror

DiffractionGrating

32 MEMS

Micro-Mirror Array

36

Micro-Electro-Mechanical Systems (MEMS)

Micro-Electro-Mechanical Systems (MEMS) is the integration of mechanical elements, sensors, actuators, and electronics on a common silicon substrate through microfabrication technology.

Electronics are fabricated using integrated circuit (IC) process sequences (e.g., CMOS, Bipolar, or BICMOS processes).

The micromechanical components are fabricated using compatible "micromachining" processes that selectively etch away parts of the silicon wafer or add new structural layers to form the mechanical and electromechanical devices.

37

System Architecture: WSS

ROADM

Rx Rx Tx Tx

In Out

Any channel

At any port


PLC - planar lightwave circuit

•optical devices that can process optical signals

directly in the optical layer

•essential for the construction of next-generation

advanced optical networks.

•Making full use of the superior characteristics of

waveguides formed by planar lightwave circuit

(PLC) technology.

• can perform highspeed and flexible optical-signal

processing for various purposes.

39

PLC Broadcast and Select

Integrated 32-channel PLC ROADM sub-system-on-a-chip has an equivalent of 192 discrete devices

Mature Silica-on-Silicon technology with no-moving parts reliability

Also, cost of materials is high (~$7k), cost reduction curve dominated by volume

Current market value is $12k for a 32-channel add/drop

planar lightwave circuit

40

ROADM Summary


Local ADD/ DROP features as OADM

Advantages:Reconfigurable

Number of active drops

Connectivity – channel assignment in each port.

First generation of the OXC

Disadvantage:High insertion loss

Non mature technology although proved.

Weak standardization

Still expensive

Based mechanical - ??? Vibration/end of life edge effects

Based PLC – No”Multi degree” feature

42



End to end automation � Insert Lambda turn-up assuming pre-deployment

Any-Port Reconfigurable OADM � OXC

44

Next Generation architecture

fiber

45

Mesh network

What do we expect from the Mesh network

New requirements Dynamic and fast connectivity

Quality of Signal � Quality of Service

Optical traffic provisioning

Cost effective/ Competitive network

Mesh + reconfigurability achieved by ROADM

Physical limitation Fiber/distance

Control plan routing

Reconfigurable elements

OSNR

No Linearity

46

Physical layer design – MESH challenges

Tx OE OE OE OE

You change here

You influence here

OE OE OE

OE OE OE OE

OE OE OE

OE OE OE OE Rx

How do we find a path? WRA

How do we find a protection path? WRAHow we understand that the path we’ve found is good?

Or here

How do we plan?

Or here

Or any other Rx


Physical limitation

•OSNR,

•Chromatic dispersion,

•PMD

•Non linearity

WRA under physical limitations

•FEC

•Line coding techniques RZ , NRZ

•Modulation techniques

Tunable DCMs

EDCs

Pre compensation

PMD compensation

48

Mesh Problem Definition

GivenA set of nodes

Fibers Physical details and infrastructure

Given traffic table connectivity

Constraint Wavelength allocation – Difficult optimization problem

Bit rates

BER/OSNR

cost

ObjectiveFind the Optimum (i.e., minimum cost) network(s)

Optical QoSAdaptive bit Rate / Capacity / Decrease BER to moderate level.


50

conclusions

1) Today market encourages the technology

2) Optical networks transition from static to intelligent

Re-configurable service oriented networks

3) ROADM/OXC are the main Key Technologies

4) Physical limitation are still the main challenge !!!


Thank

you

Dr. Uri Mahlab

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