loss budget calculation in fiber optic link

LOSS BUDGET CALCULATION OF FIBER

CABLE LINK

SECTION 1: DEFINITION OF TERMS

SECTION 2: LOSS BUDGET CALCULATION STEPS (SAMPLE)

SECTION 3: CALCULATION CASE STUDY

SECTION 1 Definition of terms

• FIBER ATTENUATION LOSS :this is an intrinsic loss of signal over distance

• CONNECTOR LOSS : loss recorded as a result of connectorisation

• SPLICE LOSS : loss recorded as a result of cable splicing

• LINK LOSS : the difference of the signal recorded on a link

• TRANSMITTER : the electronics that inject light into the fiber cable

• RECEIVER SENSITIVITY : This is the lowest optical signal that can be detected by the receiver

Cable operating system wavelength

@850nm

@1300nm

@1310nm

@1550nm

EIA/TIA STANDARDS

OPTICAL FIBER CABLE

WAVELENGHT (nm)

MAXIMUM ATTENUATION (dB/km)

50/125um multimode

850 3.5

1300 1.5

62.5/125um multimode

850 3.5

1300 1.5

Single mode inside plant cable

1310 1.0

1550 1.0

Single mode outside plant cable

1310 0.5

1550 0.5

T586 A&B STANDARDS

OPTICAL FIBER CABLE

WAVELENGHT (nm)

MAXIMUM ATTENUATION (dB/km)

50/125um multimode

850

3.0

1300

1.0

62.5/125um multimode

850

3.0

1300

1.0

Single mode inside plant cable

1310

1.0

1550

1.0

Single mode outside plant cable

1310

0.4

1550

0.4

Connector & Splice loss

Connectors loss 0.75db

Splice loss 0.2db

SPLITTER LOSS

SPLITTER RATIO 1:2 1:4 1:8 1:16 1:32

Ideal Loss / Port (dB) 3 6 9 12 15

Excess Loss (dB) 1 1 2 3 4

Actual Loss (dB) 4 7 11 15 19

SECTION 2: LOSS BUDGET CALCULATION STEPS

(SAMPLE)

STEP 1

CALCULATE THE FIBER ATTENUATION

LOSS

STEP 2 CALCULATE THE

CONNECTOR LOSS

connector loss =number of connectors X the maximum loss value

STEP 3 CALCULATE THE

TOTAL SPLICE LOSS

The number of splice x times the maximum loss value

STEP 4 CALCULATE OTHER COMPONENT LOSS

if ANY

OTHER COMPONENT SUCH AS SPLITER,ATTENUATOR,

STEP 5 CALCULATE THE PASIVE SYSTEM ATTENUATION

This is the addition of fiber loss + connector loss + splice loss + other components loss + safety buffer

STEP 6 CALCULATE THE LINK

LOSS BUDGET

Receiver sensitivity - transmitter’s average output power, (in dBm.)

STEP 7 VERIFY THE SYSTEM

PERFORMANCE MARGIN

Link loss budget - passive system attenuation

STEP 8 DETERMINE THE

RECEIVER’S DYNAMIC RANGE

Receiver maximum allowable input level - receiver

sensitivity

STEP 9 COMPARE

Determine the sum of the system’s performance margin and the safety buffer. The total must be less than the dynamic range.

SECTION 3: CASE STUDY

,

USE THE FOLLOWING INFORMATION TO CALCULATE THE LOSS BUGDET OF THE SPECIFIED LINK

• The system wavelength is 1300 nm. • The fiber type is 50/125 µm. • The average transmitter output power is -15.0

dBm. • The receiver sensitivity is -31.0 dBm. • The receiver’s maximum allowable input level is -

20.0 dBm. • The subject cable has 2 ST connector pairs. • The subject cable has 3 splices. • The subject cable’s length = 9.81 km.

(use TIA/EIA maximum loss per connector pair as 0.75 and 0.3 per splice loss for the calculation).

CABLE ATTENUATION LOSS

9.81 X 1.5 = 14.715dB

CONNECTOR LOSS

2 X 0.75 = 1.5dB

SPLICE LOSS

3 X 0.3 = 0.9dB

CALCULATE THE PASIVE SYSTEM ATTENUATION

14.715 dB + 1.5 dB + 0.9 dB + 2.0 dB = 19.12 dB

Passive System Attenuation = 19.12 dB

Calculate the link loss budget

Rx(max) – Rx (min) -10.0 dBm - (-33 dBm) = 23

dB

Link Loss Budget = 23 dB

Verify the system performance margin

Subtract the passive system attenuation from the link loss budget. 23.0 dB - 19.12 dB = 3.88 dB System Performance Margin = 3.88 dB

Determine the receiver’s dynamic range

Receiver maximum allowable input level - receiver sensitivity -20.0 dBm - (-33.0) dBm = 13 dB Receiver’s Dynamic Range = 13 dB

Determine the sum of the system’s performance margin and the safety buffer.

The total must be less than the dynamic range.

3.88 dB + 2.0 dB = 5.88 dB < 13 dB

INTERPRETAION

• Since the received signal (19.12dB) is less than the receiver dynamic range (23dB) , the fiber electronics (Tx, Rx equipment) in this case study is suitable to handle this cable link

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