5.1 Transmission Losses In
The FOC

• reduction in intensity of
the light beam/ signal strength

• unit: dB/km

• transmission light: ✘100% efficient

• the loss power depends on wavelength of the light & on the propagating material (silica glass)
• typical value (LOW) - 0.35 dB/km at 1300 nm
(single-mode fiber)

5.2 Insertion & Return Loss
In FO Com System

a(dB)=10log^10 (Pout/Pin)

Types Of Transmission
Loss

1. Absorption
   Losses

2. Rayleigh Scattering
   Losses
   

3. Dispersion

• to describe the attenuation/loss
(light signal) for any component/
device inserted in line (splice/connector)

• unit: dB

Insertion Loss(dB)=10log^10
(Pout/Pin)

Return Loss → loss power in signal
returned/reflected by
discontinuity
RL(dB)=10log^10 Pi/Pr

Insertion Loss(IL)

5.4 Apply decibel, dBW and dBM in
Power Measurement Problems

5.3 Decibel, dBW and dBM in Power
Measurement

The decibel (dB) is a logarithmic unit used to express the ratio of two values of a physical quantity, often power or intensity.

FORMULAR DECIBEL
dB = 10 log10 (P1 / P2)

The decibel watt or dBW is a unit for the measurement of the
strength of a signal expressed in decibels relative to one watt.

FORMULAR dBW
Power in dBW = 10 log10 (Power / 1 W)

dBm (sometimes dBmW or decibel-milliwatts) is an abbreviation
for the power ratio in decibels (dB) of the measured power
referenced to one milliwatt (mW).

How to convert Watt to dBm
dBm) = 10 · log10( P(W) / 1W ) + [30]

How to convert dBm to Watt
P(W) = 1W · 10( (P (dBm) - 30) / 10)

How to convert dBW to dBm
P(dBm) = P(dBW) + 30

5.5 Fiber Optic System Design

Transmission Distance

Total distance from the transmitter to the receiver. System complexity increases with transmission distance

System Complexity Increases with Transmission Distance

Type of fiber optic

Single Mode (SM) or Multimode (MM)

(@ )

Information Capabilities

NRZ and RZ coding

(@ )

Transfer Mode / Source type

LED- multimode
LASER- Single Mode

(@ )

Detector type

PIN photodiode or APD photodiode

System architecture

1. Link (point-to-point)
2. Network
   
   

(@ )

Operational Wavelength

MM- 850nm, 1300nm and SM typically

Receiver Sensitivity

minimum average received optical power Pmin required to achieved a fixed BER.

BER- probability of an incorrent identification of a bit by th dicision circuit of a receiver

Perfomance- measured as a low bit error rate (BER)

Insertion Losses

Numbers of connectors and splices

Cable Losses

Attenuation coefficient and bandwith

5.6 Optical Link [Budget]

The link power budget determines the amount of total loss
due to attenuation and other factors that can be introduced
between the transmitter and the receiver and is usually
specified or expressed in decibels (dB).
The link power budget is calculated by taking the difference
between the minimum transmitter power launched in
the fiber, and the minimum receiver sensitivity for a given BER

5.7 Power Link and Rise Time Budget

a. Power Link Budget

b. Rise Times or Bandwidth Budget

PB : PRX > PM

Tx, Fiber,

PRX = PTX – Total Losses + Total Gain - PMARGIN

PRx = PTx - PL +

Total Loss, L = LIL + Lfiber + Lconn. + Lnon-line

Tfiber = D x

5.8 Design Link Badget