OS3 Fiber Day

Fiber to the Home technologyMay 21, 2014 / Erik Radius

GlasOperator / Vodafone

Contents (more or less)

• Optical fiber

– Inner workings

– Fiber types

– Transmitter, receiver

• Transmission

– Link budget calculations

• Optical networks

– Core, Metro, Access

• Architectures

• Access network scenarios

Why do we use light signals in networking?

3

let’s explain this with some

conductor physics

Electrons versus photons

• Electrons in metal wire

– Spin ½, obeys Fermi-Dirac statistics (Fermion)

– Collisions: resistance, restricted flow

– Suitable for lightbulbs & toasters

• Photons in glass

– Spin 1, obeys Bose-Einstein statistics (Boson)

– No collisions: zero resistance, no flow limit

– ‘Superconductors’ for data transport

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A closer look at an optical fiber

• Optical fiber is a compact, low-loss carrier for broadband signals

• Optical fiber consists of 3 main parts

– 1: glass core

– 2: glass cladding

– 3: plastic buffer coating

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Optical fiber inner workings

• Optical signal is contained within the fiber

– Higher index of refraction in core than in cladding

– Total internal reflection at the core/cladding boundary

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Multimode versus Singlemode (1)

• Multimode

– ‘Bigger’ core: 50 / 62,5mm

– Multiple optical modes

supported/transmitted

– Bandwidth*distance product is limited

– Only suitable for shorter distances

(<1km)

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Multimode versus Singlemode (2)

• Singlemode

– Small core: 9mm

– 1 optical mode is supported/transmitted

– Signal may be carried over very large distance

• More information online, e.g.

– http://www.rp-photonics.com/fibers.html

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Transmitter & receiver

• Optical fiber is only a passive waveguide

• Active components at the end points:

– Signal source: laser diode or LED

– Receiver: photo diode

• (Amplitude)modulation of the data stream

– Light signal is the ‘carrier’ wave

• Both digital and analog transmission possible

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Signal loss in optical fiber is wavelength dependent

Power budget: how far can you go

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Optical power budget

• Fiber link design: what is involved

– Fiber type (single mode? multi mode?)

– Fiber length (km)

– Licht source: output power (dBm)

– Detector: receiver sensitivity (dBm)

– Elements in the link that cause additional signal loss

• Fiber link budget or optical power budget

– The amount of light available to make a fiber optic connection

– Provides the maximum distance with the available optics

– Take a minimum of 3dB safety margin into account

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Optical power budget: case #1

• Laser power: -7 dBm

• Fiber attenuation: 0,4 dB per kilometer

• Fiber length: 20 km

• Receiver sensitivity: -29 dBm

• Splice loss: 0,1 dB (max.)

• Connector loss: 0,5 dB (max.)

• # of connectors: 2

• # of splices: 4

Calculate Link Budget: laser power – receiver sensitivity

Calculate Margin: laser power – receiver sensitivity – [link losses]

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Transmitter Receiverfiber

Optical power budget: case #2

• Laser power: +1 dBm

• Fiber attenuation: 0,25 dB per kilometer

• Fiber length: 40 km

• Receiver sensitivity: -12 dBm

• Splice loss: 0,1 dB (max.)

• Connector loss: 0,5 dB (max.)

• # of connectors: 4

• # of splices: 8

Calculate Link Budget: laser power – receiver sensitivity

Calculate Margin: laser power – receiver sensitivity – [link losses]

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Transmitter Receiverfiber

Pros and cons of optical fiber

• Question for you all... Give me

– 3 advantages of optical fiber over metallic wiring

... and ...

– 3 disadvantages

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Fiber networks

• Transport network layers

– Core (+ international) network

– Metro(politan) network

– Access network

• Access network for telecom/cableTV: partial fiber

– Telecom

– Optical fiber up to central office

– Copper connection into the home (xDSL)

– Cable TV

– Optical fiber up to street cabinet

– coax connection into the home

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International networks (submarine cable systems)

National networks

source: GIGAport website

City networks (metro rings)

source: GIGAport website

Fiber penetration in the access network

• Fiber….

– to the Node

– Central office, >300m

– to the Curb/Cabinet

– Street cabinet, <300m

– to the Building/Basement

– Multi-storey buildings

– to the Home

– Into the utility closet (meterkast)

21http://upload.wikimedia.org/wikipedia/commons/3/32/FTTX.png

FTTH cabling concept

• Access network branches off multiple times between centraloffice and the home

• Installed: underground or above ground (!)

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Fiber installationFTTH in Romenia

(Bucharest)

Underground installation

• Several underground deployment methods available

• 1: modular tubes; insert fiber as needed (blown fiber)

• 2: fiber inside rugged cable (buried fiber)

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Miniduct system for access network

• 1, 7, 12, 24 thin tubes in a rugged outdoor cable

• Branching off one or multiple tubes is relatively simple

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Fiber in mini duct

• Install thin cable into duct using airflow

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Fiber connection in the home

• Example optical fiber network terminal

• Services for end user:

– Internet

– Television

– Telephony

• Most often installed in the utility cabinet (‘meterkast’)

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Bidirectional data transmission popular in FTTH

• A Single fiber may be used in two directions

– Different signal wavelengths for uplink vs downlink

– 1500nm downlink

– 1310nm uplink

• Reason?

– Less fiber needed in the field

– fiber management is expensive

– Space in the Central Office is scarce

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Bidirectional fiber optic modules (tranceivers)

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POP fiber management

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Fiber architectures (1): Point-to-point

• point-to-point

– 1 on 1 fiber connection between Central office and Home

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Central Office

Fiber architectures (2): PON

• point-to-multipoint (PON: passive optical network)

– optical splitter in the link, to send same signal to multiple end points

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Central Office

Passive splitter/coupler

PON: shared medium

system reach

PON reach calculation

• Laser power: +2 dBm

• Receiver sensitivity: -26 dBm

• Fiber attenuation: 0,4 dB per km @ 1310nm

• 0,25 dB per km @ 1550nm

• Splice loss: 0,1 dB (max.)

• Connector loss: 0,5 dB (max.)

• # of connectors: 4

• # of splices: 6

• Splitter loss (1:16) 14,0 dB

• Splitter loss (1:32) 17,1 dB

• Splitter loss (1:64) 21,2 dB

• Calculate max. reach (in km) with 1:16 split or 1:64 split

PON versus Point-to-Point: who uses which?

• PON popular with telcos

– USA

– Japan

– Australia

– ‘closed business/network model’

• Point-to-point mostly popular in Europe

– Scandinavia

– Netherlands, France, etc

– ‘open network model’

Thank youMore questions? Ask me!

e.radius@glasoperator.nl