Topic 7 Digital Technique Fiber optics

Malaysian Inst itute of Aviat ion Technology

Revision 00 Issue 01 Module 5.4

DIGITAL TECH (MECH)AKD 21102

CHAPTER 7

FIBER OPTIC


• 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


LEARNING OUTCOME



Malaysian Institute of Aviation Technology

BASIC COMMUNICATION SYSTEM

•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

•Divided in 2 for transfer into its final form categories: over the

information 1)Unguided channel. channel - atmosphere

2)Guided channel

- copper, fiber optic

Transmitter InformationChannel Receiver



Malaysian Institute of Aviation Technology

• 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 opticalproperty of total internal reflection

WHAT IS FIBER OPTIC?



A bundle of optical fibers



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


STRUCTURE



STRUCTURE


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


TOTAL INTERNAL REFLECTION


• “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 = √(n1

2 – n22)

where n1 = refractive index of the core n2 = refractive index of the cladding





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



• 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)


TYPES OF MODE


2. Multi-mode fiber– 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


TYPES OF MODE



DATA TRANSMISSION



Multi-mode (graded index)

DATA TRANSMISSION


• 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


TERMINOLOGY



FIBER OPTIC COMMUNICATION SYSTEM


• 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


TERMINOLOGY: TRANSMISSION


• 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)


OPTICAL SOURCES




• 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 userRevision 00 Issue 01 Module 5.10

ADVANTAGES OF FIBER OPTIC



FIBER OPTIC VS COPPER

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


• Connectors have to be of high integrity • No DC power transmission • Minimum bend radii required • Care when handling - no excessive

pulling, pinching or crimping


DISADVANTAGES OF FIBER OPTIC


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. Termination3. Testing


MAINTENANCE


• 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


FUSION SPLICING


• 4 Basic steps

3. Fusion process : – 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


FUSION SPLICING


• 4 Basic steps

4. Protection : – 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).


FUSION SPLICING


• 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


• 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)Revision 00 Issue 01 Module 5.10

CONNECTORS


• 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.


TERMINOLOGY OF NETWORK


• 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 to networkRevision 00 Issue 01 Module 5.10

TOPOLOGY


• 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


TERMINOLOGY OF NETWORK


• Star Network


TOPOLOGY


• Advantages- 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


STAR NETWORK


• Disadvantages

- 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.


STAR NETWORK


• 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- 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.


RING NETWORK


• Disadvantages- 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 reconfigurationRevision 00 Issue 01 Module 5.10

RING NETWORK


• In Boeing 7771.Avionics local area network (LAN)

- Aircraft Information Management System (AIMS)

- Maintenance Access Terminal (MAT)2. Cabin LAN

– Zone network controller

– Cabin file server (CFS)


APPLICATION

Topic 7 Digital Technique Fiber optics

Engineering