1. Fiber Optics DGCA: CAR-66 Module-5 Chapter-5.10
Presented by Arnav Mukhopadhyay
URL:

2. TOPICS Introduction to Fiber Optics
Benefits of using Fiber Optics over traditional systems
Principal behind Fiber Optics
Technical Terms related to Fiber Optics Network
Practical Fiber Optics Network
Optical Network Components
Fiber optical Network in Aircrafts

3. Introduction
Optical fiber is used in High speed ground based long-haul communication, Local Area Network, Passive Optical Network (PON)
First used in Boeing 777 Aircraft for on-board data communication (data rate of 100 MBPS)

4. Fiber Optics Cable Replacement for Coaxial Copper Cable
Fiber uses Light, Coax uses Electrons
Huge Bandwidth
Plastic/Glass Core, reduces weight
Technically, future proof

5. Fiber Optics: Core
Core Refractive Index > Cladding Refractive Index
Guides light through Total Internal Reflection
Transparent material: Polymer (Plastic) or Glass
Core Diameter: μm

6. Fiber Optics: Cladding
Core-Cladding refractive index difference must be very low to avoid material discontinuity
Material: Air or Polymer
Prevent core from absorbing surface impurities
Provide Mechanical Strength
Reduce scattering of light

7. Fiber Optics: Coating It is a special coating, protective buffer
Keep light in the core intact, by preventing:
Thermal Gradient
Magnetic Field intrusion into the core
Pressure
Electric Field
Bending Force
Keep optical qualities intact:
Transparency
Opacity
Refractive Index

8. Fiber Optics: Strength Member
Acts as stuffing to keep cables separated in the same jacket. Analogous to Inner Jacket
Protects the fiber core from:
Excessive Tensile Strength
Excessive compression
Excessive bending stress
These may occur during spooling, installation and operations
Materials to enhance strength: Aramid, Kevlar

9. Fiber Optics: Outer Jacket
Enclosure for the Fiber Optics Cable
The enclosure can house multiple fiber cable within one housing
Prevents:
Damage due to Environment
Mechanical Abuse
Cable Abrasion
Material: Black Polyurethane, Purple coloured Thermoplastic Jacket

10. TOPICS Benefits of using Fiber Optics over traditional systems
Introduction to Fiber Optics
Benefits of using Fiber Optics over traditional systems
Principal behind Fiber Optics
Technical Terms related to Fiber Optics Network
Practical Fiber Optics Network
Optical Network Components
Fiber optical Network in Aircrafts

11. Advantages of Fiber Optics
Light Weight compared to conventional Copper Coax
Physically smaller in size
Exceptionally high bandwidth
Offers very high data rates
Reduced Interference
Relatively low Electromagnetic Interference
Low Noise compared to Coax
Low cross-talk
Relatively Lower (Core) Attenuation compared to Coax
High Reliability and Long Life
Electrical Isolation and No Ground Loops

12. Disadvantages of Fiber Optics
Industry’s resistance to acceptance of new technology
Requires specially qualified personnel for installing and repairing Optical Fiber
Proper Cable layout and Core fabrication procedure is important to prevent:
Loss of light in the core through bending of fiber
Loss of light due to material discontinuity at the core-cladding interface
Don’t use Air Cladding
Reduce refractive indices difference between core and cladding
Use proper refractive index profile to yield proper light mode profile
Scattering of Light due to impurities in the core or on the core-cladding interface
Remove Chloride, Hydroxide, Cobalt, Iron, Copper, Chromium, Vanadium from Core glass
Material absorption of light, prevented by selection of proper material for core

13. TOPICS Principal behind Fiber Optics Introduction to Fiber Optics
Benefits of using Fiber Optics over traditional systems
Principal behind Fiber Optics
Technical Terms related to Fiber Optics Network
Practical Fiber Optics Network
Optical Network Components
Fiber optical Network in Aircrafts

14. Principal of Guiding Light
3D Representation
Clad ( η 𝑐𝑙𝑎𝑑 )
Radial Distance from Core
Core ( η 𝑐𝑜𝑟𝑒 )
Clad ( η 𝑐𝑙𝑎𝑑 ) η
η 𝑐𝑜𝑟𝑒 > η 𝑐𝑙𝑎𝑑
2D Representation
Clad ( η 𝑐𝑙𝑎𝑑 )
Radial Distance from Core
Core ( η 𝑐𝑜𝑟𝑒 = η 𝑐𝑙𝑎𝑑 )
Clad ( η 𝑐𝑙𝑎𝑑 )
Corning SMF-28 Fiber η

15. Principal of Guiding Light
η 𝑐𝑙𝑎𝑑
η 𝑐𝑜𝑟𝑒
Refracted
Ray
Reflected
Ray
Incident
Ray
Normal
Light from Rarer to Denser medium: Speed slows down, Light bend towards the normal
Light from Denser to Rarer medium: Speed increases, Light bend away from the normal

16. Angle of Incidence on Core-Cladding Interface is Small
Principal of Guiding Light
Angle of Incidence on Core-Cladding Interface is Small
𝜃 𝑟−𝑐𝑙𝑎𝑑
η 𝑐𝑙𝑎𝑑
η 𝑐𝑜𝑟𝑒
𝜃 𝑖−𝑐𝑜𝑟𝑒
𝜃 𝑟−𝑐𝑜𝑟𝑒
η 𝑐𝑙𝑎𝑑
Large amount of light leaks in to the cladding.
Light in cladding is lost. Minimize the light leaking into the cladding

17. Principal of Guiding Light
Angle of Incidence on Core-Cladding Interface is Increased but still Small
𝜃 𝑟−𝑐𝑙𝑎𝑑
η 𝑐𝑙𝑎𝑑
η 𝑐𝑜𝑟𝑒
𝜃 𝑖−𝑐𝑜𝑟𝑒
𝜃 𝑟−𝑐𝑜𝑟𝑒
η 𝑐𝑙𝑎𝑑
Amount of light leaking into cladding is reduced

18. (Total Internal Reflection)
Principal of Guiding Light
Angle of Incidence on Core-Cladding Interface is equal to Critical Angle
(Total Internal Reflection)
𝐶𝑟𝑖𝑡𝑖𝑐𝑎𝑙 𝐴𝑛𝑔𝑙𝑒:
𝜃 𝑐 = 𝑠𝑖𝑛 −1 ( η 𝑐𝑙𝑎𝑑 η 𝑐𝑜𝑟𝑒 )
η 𝑐𝑙𝑎𝑑
Corning SMF-28:
η 𝑐𝑜𝑟𝑒 = η 𝑐𝑙𝑎𝑑
𝜃 𝑐 = 𝑠𝑖𝑛 − =85°
η 𝑐𝑜𝑟𝑒
𝜃 𝑖−𝑐𝑙𝑎𝑑 = 𝜃 𝑐
η 𝑐𝑙𝑎𝑑
Light incident at Critical angle travels along the core-cladding interface.
None of the Incident Light leaks into cladding.
The phenomenon is known as Total Internal Reflection.

19. Angle of Incidence on Core-Cladding Interface > Critical Angle
Principal of Guiding Light
Angle of Incidence on Core-Cladding Interface > Critical Angle
𝐶𝑟𝑖𝑡𝑖𝑐𝑎𝑙 𝐴𝑛𝑔𝑙𝑒:
𝜃 𝑐 = 𝑠𝑖𝑛 −1 ( η 𝑐𝑙𝑎𝑑 η 𝑐𝑜𝑟𝑒 )
η 𝑐𝑙𝑎𝑑
Corning SMF-28:
η 𝑐𝑜𝑟𝑒 = η 𝑐𝑙𝑎𝑑
𝜃 𝑐 = 𝑠𝑖𝑛 − =85°
η 𝑐𝑜𝑟𝑒
𝜃 𝑟−𝑐𝑜𝑟𝑒
𝜃 𝑖−𝑐𝑙𝑎𝑑 > 𝜃 𝑐
η 𝑐𝑙𝑎𝑑
All of the Incident light is reflected back into the core
Complete light is guided along the core

20. Cone of Acceptance or Light Cone
Principal of Guiding Light
Cone of Acceptance or Light Cone
η 𝑐𝑙𝑎𝑑
Cone Of
Acceptance
𝜃 𝑎
η 𝑐𝑜𝑟𝑒
Incident
Light
η 𝑐𝑙𝑎𝑑
If angle of incidence light is within the angle limited by the Cone of Acceptance, the light will be guided into and carried by the core, without leaking into the cladding.

21. Principal of Guiding Light
Numerical Aperture
η 𝑐𝑙𝑎𝑑
Numerial Aperture
𝑁𝐴= sin ( 𝜃 𝑎 )
= η 𝑐𝑜𝑟𝑒 2 − η 𝑐𝑙𝑎𝑑 2
η 𝑐𝑜𝑟𝑒
Incident
Light
η 𝑐𝑙𝑎𝑑
The larger the value of Numerical Aperture, the more is the amount of light accepted
But leads to multipath and dispersion, causing signal broadening and loss.
High speed systems uses Fiber with very low value of Numerical Aperture

22. TOPICS Technical Terms related to Fiber Optics Network
Introduction to Fiber Optics
Benefits of using Fiber Optics over traditional systems
Principal behind Fiber Optics
Technical Terms related to Fiber Optics Network
Practical Fiber Optics Network
Optical Network Components
Fiber optical Network in Aircrafts

23. Classification of Optical Fibers
Multi-Mode Fiber
Single-Mode
(Mono-Mode)
Fiber
Core Diameter: 8 – 10 μm
Low value of Acceptance Angle
Prone to damage
Light Source: LASER (Narrow Linewidth) (Costly)
Relatively costly to manufacture
Core Diameter: 50 – 200 μm
High value of Acceptance Angle
Mechanically more sturdy
Light Source: LED (Lambertian Beam, more Linewidth) (Cheap)
Cheaper to manufacture

24. Classification of Optical Fibers
Disadvantages
Multi-Mode Fiber
Single-Mode
(Mono-Mode)
Fiber
Reduction in multipath, reduces Intermodal Dispersion and increases Data Rate
Intrinsic property of the fiber material introduces Chromatic Dispersion
Intermodal Dispersion: Multipath for light rays interact with each other, leading to broadening of pulse.
Results in high ISI and reduce Bitrate
Max. Bitrate: 100 Mbps

25. Classification of Multi-Mode Fibers
Step Index Fiber
Graded Index Fiber
Silica core is doped with Germanium or Fluoride, reducing number of multipath and Intermodal Dispersion
Doping profile is parabolic
Max. Data-rate: 1 GBps-km
High material discontinuity at the core-cladding interface
Increases the number of light multi-path and increases intermodal dispersion
Max. Data-rate: 1 MBps-km

26. Optical Fiber Losses Intrinsic Losses Extrinsic Losses
Losses inherent to the Fiber
Cannot be avoided once the Fiber construction is complete
Is important factor for selecting fiber profile
Losses incurred due to layout of optical network
Can be controlled by selecting proper routing design and using good optical components

27. Optical Fiber Losses Intrinsic Losses Extrinsic Losses Absorption Loss
Bending Loss
Scattering Loss
Launching Loss
Connector Loss

28. Intrinsic Losses: Absorption Loss
Intrinsic Material Absorption:
Interaction of Light with Core material’s atomic constituent
Select a material which exhibit minimum absorption in the band of interest
The band of interest must lie outside the Material’s Atomic Resonance frequency to avoid absorption
Silica glass exhibit IR absorption band outside the optical communication band 0.8 – 0.9 μm and 1.2 – 1.5 μm.
Extrinsic Impurity Ion Absorption:
Caused by metal ion impurities (Fe2+,Cu2+, Cr3+ ions), OH- ion trapped in Silica glass.
Impurities adjusts the material’s absorption spectrum by shifting or introducing new resonant frequency
The OH- absorption for ultrapure optical fiber offers fiber attenuation of at least 0.2 dB/km.

29. Intrinsic Losses: Scattering Loss
Scattering cause light travelling through the core to undergo elastic collision with scattering core (silica atoms, impurity ions), and spread out in all possible directions
These results in loss of light travelling through the core
Scattering loss is about 0.15 dB/km at 1550 nm wavelength

30. Extrinsic Losses: Bending Loss
Macro-Bending Loss
Fiber is mechanically bent so much so that light leaks out of the core
Macro-bend loss increases as bent (radius of curvature) is increased
Corning-SMF 28e SMF (Single Mode Fiber) should not be bent below radius of 3 inches

31. Extrinsic Losses: Bending Loss
Micro-Bending Loss
Small scale bend between core-cladding interface
These are localized bend which can develop due to stress developed during layout, wrapping of fiber in a fiber spool
These can occur due to unclean interface during manufacturing
Micro-bend loss adds 1-2 dB/km attenuation

32. Extrinsic Losses: Launching Loss
When connecting two fiber endings, they must be properly aligned (core axis of both fiber must be aligned)
Misalignment causes reflection and cause lesser amount of light to be accepted by the fiber

33. Extrinsic Losses: Connector Loss
Connectors hold fiber in place
Due to air interface between connector and fiber, reflection takes place
Total light introduced to the fiber is reduced
Modern Connector offers very low losses (~ 0.2 dB)
Rule of Thumb: Estimated Connector loss = 1 dB per connector

34. Attenuation in Optical Fiber
Attenuation causes light intensity to decrease as it travels through the optical fiber
Attenuation is caused by Intrinsic losses and excludes extrinsic losses (technically)
Attenuation is characterized by Attenuation Coefficient
Attenuation Coefficient: The optical power lost per unit distance, due to fiber (intrinsic losses) itself
At 1550 nm (Optical Communication Wavelength), the fiber attenuation is minimum (Attenuation Coefficient ~ 0.2 dB/km)

35. TOPICS Introduction to Fiber Optics
Benefits of using Fiber Optics over traditional systems
Principal behind Fiber Optics
Technical Terms related to Fiber Optics Network
Practical Fiber Optics Network
Optical Network Components
Fiber optical Network in Aircrafts

36. Practical Optical Networks
Boeing 777 is the first commercial aircraft employing optical fiber LAN based on-board data communication network
System was developed during 1980s
The system employs:
AVionics Local Area Network (AVLAN)
Placed in Flight Deck and Electrical Equipment bay
CABin Local Area Network (CABLAN)
Fitted on the top of roof of the passenger cabin
The Network conforms to ARINC 636 standards
Maximum possible data rate is 100 Mbps
Multimode fiber is used for network layout
Multimode fiber are more sturdy (mechanically), cheap to manufacture and easy to layout

37. Practical Optical Networks
Boeing 777
Brouter – Bridge + Router….. Connects multiple LANs together. The Bridge connects and relays data to different interconnected LAN. The Router enables connection to a WAN.

38. Fiber Optic Data Bus Data Source Optical Modulator (Light Source)
Multimode Fiber
Optical Receiver
Sink
LED
Cheap
Broad spectrum (Line width)
Not monochromatic
Low speed (for modulation)
Laser
Costly
Narrow spectrum (Line Width)
Monochromatic
High Speed (for modulation)
Photodiode
Electrical
Signal (IN)
Electrical – Light Conv.
Carry Light through the Core
Light – Electrical Conv.
Elec. Signal (OUT)

39. Fiber Optic Cable Construction
Components:
5 optical fiber
Buffer Coated with Distinct Colours for Identification
Colours: Blue, Red, Green, Yellow, White
2 filler strands (mechanical support)
Separator tape
Aramid Yarn Strength Member
Outer Jacket
Common SMF/MMF-Cable Specs:
Core Dia.
(micron)
Clad Dia. (micron)
62.5
125 50 9

40. Fiber Optic Connectors
Characteristics:
Reliable
Robust
Precise and can be used many number of times
Suitable for installation without using special tools
Low Loss (approx. 0.5 dB/connector; technically approximated as 1 dB/connector)
Low Cost

41. Fiber Optic Connectors
Connectors have following sections:
Alignment Keys and Grooves
Accurately align connectors of optical components
Minimizes connector loss
Guide Pins and Cavities
Guards fiber from damages due to over-tightening
Pins acts as buffer stop, at the bottom of the cavity receptable
Coloured Alignment beads
Coupling nut on plug barrel has Yellow band
Receptable side has Red and Yellow band
Correct connection: Red band of Receptable is at least 50 % covered
3 Threads on both plug and receptable ensure a straight start when they join

42. SMA Connectors SMA stands for Sub-Miniature version A
SMA is popular fiber optics connector used due to its ruggedness
SMA connector have a metal body, with precision hole in the tip
A striped fiber is firmly inserted into the SMA assembly after proper alignment, and secured with epoxy
Strength member is rigidly affixed with the body assembly to improve rigidity
Excess fiber is removed, the polished to desired length to provide optical finish
The connector mates with screw-type coupling mechanism until secure and aligned.

43. TOPICS Introduction to Fiber Optics
Benefits of using Fiber Optics over traditional systems
Principal behind Fiber Optics
Technical Terms related to Fiber Optics Network
Practical Fiber Optics Network
Optical Network Components
Fiber optical Network in Aircrafts

44. Other Network Components
Couplers (3 or 4 ports)
Switches for redirecting the light beams into different strands
Routers for routing signals through the LAN. Comprises of
Switches
Processors
Controllers
Bus Interfaces

45. Bypass Switch Unit (BSU)
Optical Router sends control signals to Bypass Switch Unit (BSU)
BSU Control Signals:
PRI HI : Active HIGH connect BSU to fiber optic ring network
PRI RTN : Active LOW input connect Control signal to Optical Ground
SEC HI : Active HIGH connect BSU to fiber optic ring network
SEC RTN : Active LOW input connect Control signal to Optical Ground
Fiber Optic Interface:
Converts Electrical to Optical signal, and Optical to Electrical Signal
Interfaces BSU with electrical sections of the network

46. (Passive) Coupler Types
Divide input light equally among the output port
Types:
Directional Couplers
Tee Couplers
Star Couplers

47. Optical (Directional) Couplers
Multiple I/O ports for the light to travel
Lights in multiple port interact through light modes which leaks when the core are brought near each other
Light enters through port-1 and exit through Port-3, 4. No light should exit through Port-2.
Losses: Scattering, Absorption, Reflections and Cable Misalignment

48. Tee and Star Couplers Tee Couplers Star Couplers
Shaped as a Star: M-inputs, N-outputs
Delivers optical power to multiple terminals, suitable for connecting large number of terminals
Optical (Insertion) Power loss not directly proportional to the number of terminal ports
Shaped as a T : 1 input, 2 outputs
Divides input light power equally among the 2 output terminals
Optical Power Loss proportional to the number of output (terminal) nodes

49. TOPICS Introduction to Fiber Optics
Benefits of using Fiber Optics over traditional systems
Principal behind Fiber Optics
Technical Terms related to Fiber Optics Network
Practical Fiber Optics Network
Optical Network Components
Fiber optical Network in Aircrafts

50. Application in Aircraft
Due to High-Bandwidth availability, Fiber optics was used in In-Flight Entertainment (IFE) systems
Panasonic IFE on Boeing (

51. Application in Aircraft
In future aircraft, Fly-By-Light (FBL) is going to replace Fly-By-Wire (FBW) systems in both Civilian and Military Aircrafts

52. Fly-By-Light (FBL)
Replace Wire by Optical Fiber (Eliminates Electromagnetic Interference)
Photonics-Controlled Actuator Systems (PCAS) are used to replace Electro-mechanical Actuators (EMA)
All conventional electrical sensors are replaced by optical sensors, which will perform various measurements
FBL systems are 10 % lighter than FBW components
FBL offers more reliability and requires lesser maintenance expenditure
FBL offers more lifetime to the system compared to FBW
FBL utilizes Fiber Optic Data Bus which offers data rate up to 100 Mbps, allowing more bandwidth available for aircraft data communication

53. ARINC 636 Standards Boeing ARINC-636 Transmitter
Boeing ARINC-636 Receiver
Data Rate: 125 Mbps (employed for AVLAN components)
Mounted on a rack on EE (Electronics Equipment) Bay
Bit-Error Rate: 2.5 × 10 −10
Operating Temperature: -40 to C
Transmitter and Receiver are 16-pin Dual-In-Line Package
Employed by Boeing 777 Aircraft
Can couple with 100 or 140 μm optical fiber, with LED light source and PIN photodiode

54. References
James W. Wasson, “Module-05, For B-1 Level Certification, Digital Techniques Electronics Instrument Systems”, Aviation Maintenance Technician Certification Series (2016) (EASA Part 66/147) (ISBN: )
Gerd Kaiser, “Optical Fiber Communication”, 2nd Edition, McGraw Hill (International Ed) (1991) (ISBN: )

55. References
Mike Tooley and David Wyatt, “Aircraft Electrical and Electronics: Systems, Principles, Maintenance and Operation”, Elsevier Pub. (2009) (ISBN: )
A. Garg, R. Islam Linda, T. Chowdhury, “Application of Fiber Optics in Aircraft Control System & Its Development”, International Conference on Computer Communication and Informatics (2014) (DOI: /ECS )
E. Chan, D. Koshinz, A. Kazemi, H. Hager, “Hermetic Fiber Optic Module for Aerospace”, IEEE Avionics, Fiber-Optics and Photonics Technology Conference (2009) (DOI : /AVFOP )