Topic 7 Digital Technique Fiber optics

Malaysian Institute of Aviation Technology
DIGITAL TECH (MECH)
AKD 21102
CHAPTER 7
FIBER OPTIC
Revision 00 Issue 01 Module 5.4

LEARNING OUTCOME
• Data transmission over electrical wire propagation
• Fiber optic data bus
• Fiber optic related terms
• Advantages and disadvantages of fiber optic
• Terminations: cleaving, stripping, splicing and
termination losses
• Couplers, control terminals, remote terminals
• Application of fiber optics in aircraft system

BASIC COMMUNICATION SYSTEM
Transmitter Information
Channel Receiver
•Information travels
•Message is
generated and
from transmitter to the Message is
receiver over this extracted from
put into channel. the information
suitable form channel and put
for transfer •Divided in 2 into its final form
over the categories:
information 1)Unguided channel.
channel - atmosphere
2)Guided channel
- copper, fiber optic

WHAT IS FIBER OPTIC?
• Fiber optics (optical fibers) are long, thin
strands of very pure glass about the
diameter of a human hair. They are
arranged in bundles called optical cables
• Used to transmit high-speed transmission
of data using light over long distances.
• Transmission depend on the optical
property of total internal reflection

A bundle of optical fibers

STRUCTURE

STRUCTURE
• Core - Thin glass centre of the fiber where the
light travels
• Cladding - Outer optical material surrounding
the core that reflects the light back into the core
• Buffer coating - Plastic coating that protects the
fiber from damage and moisture
• Hundreds or thousands of these optical fiber are
arranged in bundles in optical cables. The
bundles are protected by the cable's outer
covering, called a jacket

TOTAL INTERNAL REFLECTION
• Core(n1) and cladding(n2) have different
refraction index (n). n1 is always greater than n2
(n1>n2)

• “When the angle of incidence exceeds a critical
value, light cannot get out of the glass; instead,
the light bounces back in.”
• Numerical aperture (NA)
– measure of maximum core angle for light rays to be
reflected down the fibre by total internal reflection
– Snell’s law : NA= sin θ = √(n2 1
– n2)
2
where n1 = refractive index of the core
n2 = refractive index of the cladding

Total internal reflection of light in a multi-mode optical fiber.

TYPES OF MODE
• 2 types of mode : single-mode fiber and multi-mode fiber
1. Single-mode fiber
– Small core diameter(5-10μm) with an operating wavelength of
around 1.5μm
– Transmitter source : Laser diode (LD)
– Only 1 incident angle i.e only 1 path and at same velocity,
eliminating distortion due to pulse lapping
– providing the least signal attenuation and the highest transmission
speeds, large bandwidth (typically 500 - 1500 MHz.km) and longer
distance.
– Data is sent at multi-frequency (WDM Wave-Division- Multiplexing)

2. Multi-mode fiber
TYPES OF MODE
– large diameter core (typically 100μm) with operating wavelength
around 1μm.
– Transmitter source : light emitting diode (LED)
– Support hundreds or thousands of light rays traveling at different
velocities i.e. many angles of incident
– Problem: pulse broadening causing limitation on bandwidth
– 2 type of multi-mode : Step index and Graded Index
– Easier to launch optical power and facilitate the connecting of similar fibre

DATA TRANSMISSION

DATA TRANSMISSION
Multi-mode (graded index)

TERMINOLOGY
• Attenuation : signal loss within a fibre and measure in
decibels per kilometer (dB/km)
• Star coupler : passive optical coupler which allows the
light signals from each fibre stub to be coupled with
other fibre stub and then into subsystems
• Wavelength Division Multiplexing (WDM) : signal of
different wavelengths are sent down the fibre all together
• Passive optical sensor : optical sensor which do not
require electrical supplies or any electronic processing.
Used to monitor leading and trailing edge flap, spoilers,
ailerons, rudder etc

FIBER OPTIC COMMUNICATION
SYSTEM

TERMINOLOGY: TRANSMISSION
• Optical Source - used to generate light signal. Can be
either light-emitting diode (LED) or an injection- laser
diode (ILD)
• Transmitter - Produces and encodes the light signals
• Optical fiber - Conducts the light signals over a distance.
Light pulses move easily down the fiber- optic line
because of a principle known as total internal reflection.
• Optical regenerator - May be necessary to boost the light
signal (for long distances)
• Optical receiver - Receives and decodes the light
signals. Can be either photodiode or phototransistor

OPTICAL SOURCES
• LD advantages over LED:
– Signal can be modulated at very high speed
– Produce greater optical power (used for long haul
communication cable)
– Have higher coupling efficiency of the optical cable
– Does not suffer from signal broadening due to pulse lapping
• LED advantages over LD
– Higher reliability
– Better linearity
– Lower cost
– More user (used for metro/urban population and point-to-point
connection)

ADVANTAGES OF FIBER OPTIC
• SPEED: Fiber optic networks operate at high speeds i.e.
up into the gigabits
• BANDWIDTH: large carrying capacity
• DISTANCE: Signals can be transmitted further without
needing to be "refreshed" or strengthened.
• RESISTANCE: Greater resistance to electromagnetic,
electrical isolation, low cross talk (interference)
• MAINTENANCE: Fiber optic cables costs much less to
maintain.
• PHYSICAL: Smaller size and weight than coaxial or
copper cable buses
• USER : able to accommodate more user

FIBER OPTIC VS COPPER
The optical fiber cable in the foreground has the equivalent information-carrying
capacity of the copper cable in the background

DISADVANTAGES OF FIBER OPTIC
• Connectors have to be of high integrity
• No DC power transmission
• Minimum bend radii required
• Care when handling - no excessive
pulling, pinching or crimping

MAINTENANCE
1. Repairing the cable by inserting an in-line
splice
- 2 type of splicing : fusion and mechanical
- Cleaving : The controlled breaking of a
fiber so that its end surface is smooth.
2. Termination
3. Testing

FUSION SPLICING
• 4 Basic steps
1.Stripping: removing the cladding using plastic clad silica
(PCS) and cleaning of fiber using alcohol solution
2. Cleaving: cutting of edge surface at 900 using cleaver and
fiber is clean again using alcohol solution

• 4 Basic steps
3. Fusion process :
FUSION SPLICING
– Sleeves are places on the fiber and the 2 ends of the fiber
need to be connected are place on the micro core.
– Testing of compatibility (acceptable angle of cutting), free of
foreign object debris (FOD) and alignment of two fiber optics
are carried out by the micro core splicing machine.
– Errors occurred, correctional action is taken.
– After errors are corrected, fusion splicing took place.

FUSION SPLICING
• Example of error during fusion process

• 4 Basic steps
4. Protection :
FUSION SPLICING
– A sleeve for the fiber is used to protect the splicing area and
act as a strengthening mechanism for the fiber.
– Final testing is simulated using Optical Time Domain
Reflectometer (OTDR).

• 7 Basic steps
1. Preparing the required connector i.e. housing, body, duct
cap and the strain relief boot
2. Preparing the fiber
Termination

• 7 Basic steps
3. Connecting the fiber to connector
4. Cleaving
5. Polishing
Termination

• 7 Basic steps
6. Visual check
7. Testing
Termination

CONNECTORS
• Type A
- used at production breaks i.e. not regularly
connect-disconnect
- Multi channel, in-line (butt type)
- Low loss
• Type B
– Used to connect to the LRUs; frequently
connect-disconnect
– Multi channel, expended beam (ball lens)

TERMINOLOGY OF NETWORK
• Bus Network
- A network topology in which all of the terminals are attached to a
transmission medium serving as a bus
– Commonly called data bus
– The term is used to describe the physical linkage between stations
on a network sharing a common communications
– The bus can only transmit data in one direction, and if any network
segment is severed, all network transmission ceases.

TOPOLOGY
• Bus Network
- Computer directly connected on a main communication line
- A host on a bus network is called a station or workstation. In a bus
network, every station receives all network traffic, and the traffic
generated by each station has equal transmission priority.
Only 1 computer can communicate Each computer
communicate
individually Revision 00 Issue 01 Module 5.10 to network

TERMINOLOGY OF NETWORK
• Star Network
- one of the most common computer network
topologies.
- In its simplest form, a star network consists of one
central switch, hub or computer, which act as a
conduit to transmit messages.
- This consists of a central node, to which all other
nodes are connected; this central node provides a
common connection point for all nodes through a hub

• Star Network
TOPOLOGY

• Advantages
STAR NETWORK
- Better performance
- Isolation of devices
- Centralization: increasing in capacity, or connecting additional
devices to it, increases the size of the network very easily and allows
the inspection of traffic through the network
- Easy to detect faults and to remove parts.
- No disruptions to the network when connecting or removing devices.
- Installation and configuration is easy

• Disadvantages
STAR NETWORK
- High dependence of the system on the functioning of the central hub.
Failure of the central hub renders the network inoperable
- There is central server dependency.
- Expensive to purchase.
- Requires a large amount of cable to be connected.

• Ring Network
- a network topology in which each node connects to exactly two
other nodes, forming a single continuous pathway for signals
through each node - a ring. Data travel from node to node, with
each node along the way handling every packet.
TOPOLOGY

• Advantages
RING NETWORK
- Very orderly network where every device has access to the token
and the opportunity to transmit
- Performs better than a bus topology under heavy network load
- Does not require a central node to manage the connectivity
between the computers
- Quite easy to install and reconfigure since adding or removing a
device requires moving just two connections.
- Point to point line configuration makes it easy to identify and isolate
faults.

• Disadvantages
RING NETWORK
- One malfunctioning workstation can create problems for the entire
network. This can be solved by using a dual ring or a switch that
closes off the break.
- Moving, adding and changing the devices can affect the network
- Communication delay is directly proportional to number of nodes in
the network
- Bandwidth is shared on all links between devices
- More difficult to configure than a Star: node adjunction = Ring
shutdown and reconfiguration

APPLICATION
• In Boeing 777
1.Avionics local area network (LAN)
- Aircraft Information Management System
(AIMS)
- Maintenance Access Terminal (MAT)
2. Cabin LAN
– Zone network controller
– Cabin file server (CFS)

Topic 7 Digital Technique Fiber optics

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