Installation Planning

LPB & RTB

Tool for System Planning

Power Budgeting Definition

Power Budgeting dan Pemilihan Perangkat

System Design Choices: Photodetector, Optical Source, Fiber

• Photodetectors: Compared to APD, PINs are less expensive and more stablewith temperature. However PINs have lower sensitivity.

• Optical Sources: 1- LEDs: 150 (Mb/s).km @ 800-900 nm and larger than 1.5

(Gb/s).km @ 1330 nm 2- InGaAsP lasers: 25 (Gb/s).km @ 1330 nm and ideally around

500 (Gb/s).km @ 1550 nm. 10-15 dB more power. However more costly and more complex circuitry.

• Fiber: 1- Single-mode fibers are often used with lasers or edge-emitting

LEDs.2- Multi-mode fibers are normally used with LEDs. NA and

should be optimized for any particular application.

Use of Power Budgets

Anggaran terpenuhi jika daya terima di detektor ≥ sensitifitas penerima

Link Power/Loss Analysis

Margin System][]/[][2

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kmLkmdBdBlP

dBmPdBmPdBP

fcT

RsT

Total Power Loss

Receiver Sensitivities vs. Bit Rate

The Si PIN & APD and InGaAsP PIN plots for BER= . The InGaAs APD plot is for BER= .

910

1110

Link Loss Budget [Example 8.1]

Power Margin

Transmission Types

• Two types of transmissions:1. Link (point to point)

2. Networka. point to multipointb. Meshc. Ring

Elements of Link/ Network Design

• Transmitter : Operating wavelength (), Linewidth (),Rise time, Bit-rate, Line format, Power

level

• Fiber : SMF/MMF, Fiber type – SMF28, DSF, etc, Cable loss, Spool length

• Rx : PSEN, PSAT, Rise time

Elements of Link/ Network Design (cont.)

• Connection: No. of splice, Splice lossNo. of connectors, Connector Loss

• In Line Devices: Splitter, Filter, Attenuator, Amplifier

Insertion loss, Gain

The Main Problems• Attenuation and

Loss• Dispersion

The Main Question • In Digital System - Data Rate

- Bit Error Rate• In Analog System - Bandwidth

- Signal to Noise Ratios

System Factor Considerations Type of Fiber Single-mode or Multimode Operating Wavelength 780, 850, 1310 and 1550 nm

typical Transmitter Power Typically expressed in dBm Source Type LED or Laser Receiver Sensitivity and Overload Characteristics

Typically expressed in dBm

Detector Type PIN Diode, APD or IDP

Factors for Evaluating Fiber Optic System Design

System Factor Considerations Modulation Code AM, FM, PCM or Digital Bit Error Rate (BER) (Digital Systems Only)

10-9 ,10-12 Typical

Signal to Noise Ratio Specified in decibels (dB) Number of Connectors Loss increases with the number of

connectors Number of Splices Loss is Loss increases with the

number of splices Environmental Requirements

Humidity, Temperature, Exposure to sunlight

Mechanical Requirements Flammability, Indoor/Outdoor Application

Factors for Evaluating Fiber Optic System Design (cont.)

Optical Transmitter/ Sources LEDs

Output PowerModulation BandwidthCenter WavelengthSpectral WidthSource SizeFar-Field Pattern

Laser DiodesOutput PowerModulation BandwidthCenter Wavelength, Number of ModesChirp, LinewidthMode Field of the Gaussian beam

Optical FiberMultimode Fiber

AttenuationMultimode DispersionChromatic DispertionNumerical ApertureCore Diameter

Single-Mode FiberAttenuationChromatic DispersionCutoff WavelengthSpot Size

Optical Receiver/ Photodiode

Risetime/BandwidthResponse Wavelength RangeSaturation LevelMinimum Detection Level

Simple Link

TX RX

Medium and Devices

OA OA

Link Budget Considerations

Three types of budgets:

(1) Power Budget(2) Bandwidth or Rise Time Budget

(3) ?

dB, dBm, mW

dB = 10 log (P1/P2)dBm Value % of 1 mW Power Application

0.0 100% 1.0 mW Typical laser Peak Output

-13.0 5% 50.0W Typical PIN Receiver Sensitivity

-30.0 0.1% 1.0W Typical APD Receiver Sensitivity

-40.0 0.01% 100.0W Typical LED Peak Output

dB Power Out as a % of Power In

% of Power Lost

Remarks

1 79% 21% - 2 63% 37% - 3 50% 50% ½ the power 4 40% 60% - 5 32% 68% 6 25% 75% ¼ the power

7 20% 80% 1/5 the power

8 16% 84% 1/6 the power

9 12% 88% 1/8 the power

10 10% 90% 1/10 the power

Decibel to Power Conversion

dB Power Out as a % of Power In

% of Power Lost

Remarks

25 0.3% 99.7% 1/300 the power

30 0.1% 99.9% 1/1000 the power

40 0.01% 99.99% 1/10,000 the power

50 0.001% 99.999% 1/100,000 the power

Decibel to Power Conversion

IS THIS SYSTEM GOOD?

Example: Power Budget Measurement for Long Haul Transmission

PTx = 0 dBm

185 km

PSEN = -28 dBmSplice

Attenuation Coefficient, = 0.25 dB/km

Dispersion Coefficient, D = 18 ps/nm-km

Number of Splice = 46

Splice Loss = 0.1 dB

PMargin = 6 dB

Connector Loss = 0.2 dB

Connector

CONCLUSION: BAD SYSTEM!!

Simple Calculation…. Fiber Loss = 0.25 dB/km X 185 km

= 46.3 dB

Splice Loss = 0.1 dB X 46 = 4.6 dB

PMargin = 6 dB

Total Losses = 46.3 + 4.6 + 0.4

= 51.3 dB

Power Budget, PRX ≥ PSEN !!

PRX = -57.3 dB

PRX = PTX – Total Losses – PMargin

= 0 – 51.3 – 6

Connector Loss = 0.2 dB X 2 = 0.4 dB

How To Solve?Answer… Place an amplifier

But… What is the gain value??

Where is the location?And…

First we calculate the amplifier’s gain..

Gain PSEN - PRX

Gain -28 – (-57.3)

Gain 29.3 dBTo make it easy, Gain 30 dB

Now…Where to put the amplifier?

Three choices availablefor the location

Power Amplifier – At the transmitter

Preamplifier – At the receiver

In Line – Any point along fiber

Let us check one by one…Power Amplifier: PTX + Gain = POUT

0 + 30 = 30 dBm

But is there any power amplifier with 30 dBm POUT?

NO, THERE ISN’T

Hence …

What about Preamplifier?

POUT received = -57 dBm

Remember…

Preamplifier with 30 dB available? Yes

But, can it take –57 dBm?

Typically, NO

Hence …

Let us check In Line Amplifiers

30 dB gain amplifier available here…

But, What value can it take?

Typically –30 dBm

So…

Now, we can find the location…

Where is the –30 dBm point?

PTX – Loss At That Point = 0 dBm – 30 dB

Loss At That Point = -30 dBm

30 = x Length of That Point

Remember = 0.25,Point Length = 30/0.25

= 120 kmBut 120 km from Tx,

No. of splice = 120/4

= 30

Assume Other Loss = 0, Loss At That Point = Fiber Loss,

Splice Loss = 0.1 dB x 30 = 3 dB

Also remember connector loss at amplifier and Tx…

2 connectorsConnector Loss = 0.2 dB x 3 = 0.6 dB

Total Losses = Fiber Loss + Splice Loss + Connector Loss

Actually, at 120 km,

= 30 + 3 + 0.6 = 33.6 dB

33.6 dB > 30 dB!! NOT GOOD!

Now, We have excess of 3.6 dB…Find the distance,

Fiber Loss Length = 3.6/0.25 = 14.4 km

Good Location = 120 km – 14.4 km = 105.6 km

+ 1 connector at Tx

Let us confirm the answer…At 105.6 km from Tx,

Fiber Loss = 0.25 x 105.6 = 26.4 dB

No. of Splice at 105.6 km = 105.6/4 =26.4 = 27

Splice Loss = 0.1 x 27 = 2.7 dB

Total Losses = 26.4 + 2.7 = 29.1 dB

29.1 dB < 30 dB !!

CONFIRM…105.6 KM IS A GOOD LOCATION!!

PTx = 0 dBm

185 km

PSEN = -28 dBmSplice Connector

105.6 KM

IS THIS SYSTEM GOOD?

PTx = -15 dBm

500 m

Using 850nm

PSEN = -25 dBm

Attenuation Coefficient, = 4.5 dB/km

Dispersion Coefficient, D = 18 ps/nm-km

Number of Splice = 0

Splice Loss = 0 dB

PMargin = 2 dB

Connector Loss = 0.5 dB

Server A Server B

Example: Power Budget Measurement for LAN

BANDWIDTH BUDGET

• Calculate the total rise times Tx, Fiber, Rx

• Calculate Fiber rise time, TFiber

Tfiber = D x x L

D = Dispersion Coefficient = LinewidthL = Fiber Length

Tx Rise Time, TTX = normally given by manufacturerRx Rise Time, TRX = normally given by manufacturer

System Rise Time

Total Rise time, Tsys:

Tsys=1.1(TTX2+TRX

2+Tfiber2)1/2

Dispersion Analysis (Rise-Time Budget)

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Bandwidth Budget

TX RX

Medium and Devices

T’

Δτ = T’ - T

T

OA OA

What is a good Rise time?For a good reception of signal Tsys < 0.7 x Pulse Width (PW)

PW = 1/BitRate for NRZ1/2BitRate for RZ

System rise-Time & Information Rate

• In digital transmission system, the system rise-time limits the bit rate of the system according to the following criteria:

periodbit RZ of %35

periodbit NRZ of %70

sys

sys

t

t

Pengkodean Transmisi Optik

Two-level Binary Channel Codes

Example: Rise Time Budget Measurement for Long Haul Application

Tx rise time, TTX = 0.1 ns

Rx rise time, TRX= 0.5 ns

Linewidth() = 0.15 nm

Dispersion Coefficient, D = 18 ps/nm-kmFiber length = 150km

Bit Rate = 622MbpsFormat = RZ

Fiber rise time, TF =Length x D x Linewidth()

= 150 km x 18 x 0.15 nm

= 0.4 ns

Total Rise time, TSYS = 1.1 TLS2 + TPD

2 + TF2

= 1.1 0.01 + 0.25 + 0.16

Simple Calculation….

TSYS = 0.77 ns

Let say,Bit Rate = STM 4 = 622 MbpsFormat = RZ

Tsys < 0.7 x Pulse Width (PW)

Pulse Width (PW) = 1/(622x106)= 1.6 ns

0.77 ns < 0.7 x 1.6 ns

0.77 ns < 1.1 ns !!

Good Rise Time Budget!!

Let say,Bit Rate = STM 16 = 2.5 GbpsFormat = RZ

Tsys < 0.7 x Pulse Width (PW)

Pulse Width (PW) = 1/(2.5x109)= 0.4 ns

0.77 ns < 0.7 x 0.4 ns

0.77 ns ≥ 0.28 ns !!

Bad Rise Time Budget!!

Budget Summary    Option Power

BudgetBandwidth

BudgetFinancial

A Source (LED vs. LD)        

  Δλ 

850nm Mediocre Bad Cheap

    1310nm Good Good Less expensive

    1550nm Very good Very good Expensive

  Modulation Bandwidth

LED NA Bad Cheap

    LD NA Good Expensive

  Output Power LED Mediocre NA Cheap

    LD Good NA Expensive

  Radiation pattern LED (far-field pattern)

NA Bad Cheap

    LD (Gaussian beam)

NA Good Expensive

           

Budget Summary

B Fiber Option Power Budget

Bandwidth Budget

Financial

  Attenuation MM Mediocre Mediocre Cheap

    SM Good Good Expensive

  Dispersion MM Mediocre Mediocre Cheap

    SM Good Good Expensive

  Numerical Aperture (NA)

MM Mediocre Mediocre Cheap

    SM Good Good Expensive

  Core Diameter MM Mediocre Mediocre Cheap

    SM Good Good Expensive

           

Budget SummaryC Receiver (PIN vs.

APD)

Option Power Budget Bandwidth Budget

Financial

  Rise time/ Bandwidth

PIN Mediocre Mediocre Cheap

    APD Good Good Expensive

  Response wavelength range

PIN Mediocre Mediocre Cheap

    APD Good Good Expensive

  Saturation Level PIN Mediocre Mediocre Cheap

    APD Good Good Expensive

  Minimum detection level

PIN Mediocre Mediocre Cheap

    APD Good Good Expensive

Cost/Performance Considerations

Components considerations such as :– Light Emitter Type – Emitter Wavelength – Connector Type – Fiber Type – Detector Type

Link Power Budget Table [Example 8.2]

• Example: [SONET OC-48 (2.5 Gb/s) link]

Transmitter: 3dBm @ 1550 nm; Receiver: InGaAs APD with -32 dBm sensitivity @ 2.5 Gb/s;

Fiber: 60 km long with o.3 dB/km attenuation; jumper cable loss 3 dB each, connector loss of 1 dB each.

Component/loss parameter

Output/sensitivity/loss

Power margin (dB)

Laser output 3 dBm

APD Sensitivity @ 2.5 Gb/s

-32 dBm

Allowed loss 3-(-32) dBm 35

Source connector loss

1 dB 34

Jumper+Connector loss

3+1 dB 30

Cable attenuation 18 dB 12

Jumper+Connector loss

3+1 dB 8

Receiver Connector loss

1 dB 7(final margin)

Sample Power Budget Calculation

excercise

Solution

Example

• Laser Tx has a rise-time of 25 ps at 1550 nm and spectral width of 0.1 nm. Length of fiber is 60 km with dispersion 2 ps/(nm.km). The InGaAs APD has a 2.5 GHz BW. The rise-time budget (required) of the system for NRZ signaling is 0.28 ns whereas the total rise-time due to components is 0.14 ns. (The system is designed for 20 Mb/s).

Example: Transmission Distance for MM-Fiber• NRZ signaling, source/detector: 800-900 nm LED/pin or AlGaAs

laser/APD combinations. ; LED output=-13 dBm;fiber loss=3.5 dB/km;fiber bandwidth 800 MHz.km; q=0.7; 1-dB connector/coupling loss at each end; 6 dB system margin, material dispersion ins 0.07 ns/(km.nm); spectral width for LED=50 nm. Laser ar 850 nm spectral width=1 nm;

laser ouput=0 dBm, Laser system margin=8 dB;

910BER

Example:Transmission Distance for a SM Fiber• Communication at 1550 nm, no modal dispersion, Source:Laser;

Receiver:InGaAs-APD (11.5 log B -71.0 dBm) and PIN (11.5log B-60.5 dBm); Fiber loss =0.3 dB/km; D=2.5 ps/(km.nm): laser spectral width 1 and 3.5 nm; laser output 0 dBm,laser system margin=8 dB;