Fiber Optics Technology An Overview Dr. BC Choudhary, Professor

Transcription

1 Fiber Optics Technology An Overview Dr. BC Choudhary, Professor National Institute of Technical Teachers Training & Research (NITTTR), Sector-26, Chandigarh

2 LECTURE CONTENTS What is Fiber Optic Technology? Why Optical Transmission and Optical Fibers? OFC Systems & Potential Fiber Optic Sensor Technology Special Class of Optical Fibers. * * *

3 Fiber Optics Technology s Also called Lightwave Technology Fiber Optics Technology uses light as the primary medium to carry information. Light often is guided through optical fibers. Most applications use invisible light (infrared) LEDs or LDs. Invention of LASER (1960) and low loss Optical Fiber Waveguides (1970) An edge toward making the dream of carrying huge amount of information, a reality. NEAR ZERO LOSS & INFINITE BANDWIDTH

4 Lightwave Technology: Application Areas Majority Applications: Telephone Networks Data Communication Systems Cable TV distribution Niche Applications: Optical Sensors Medical Equipment

5 1896 Telecommunication Developments & Issues Communication Exchange of information 2016 Telecommunication Exchange of information over a distance using some type of equipment Information Transmitter Link Transmission medium Receiver Information Generally three basic types of information to be exchanged Voice, Video and Data Analog or Digital? Information is often carried by an EM carrier - frequency varying from few MHz to several hundred THz.

6 Telecom Systems of 1970s Transmission Medium Twisted pair Coaxial cable Radio and Microwave Satellite Signal Type Analog continuous Digital-- discrete High Attenuation 20 db/km Limited Bandwidth KHz to MHz Attenuation and BW limitations

7 Why Fiber Optic Communication? During past three decades, remarkable and dramatic changes took place in the electronic communication industry. A phenomenal increase in voice, data and video communication - demands for larger capacity and more economical communication systems. Lightwave Technology: Technological route for achieving this goal Most cost-effective way to move huge amounts of information (voice, video, data) quickly and reliably.

8 Why Optical Transmission? Capacity! Capacity! and More Capacity! A technical revolution in Electronic Communication Industry to explore for large capacity, high quality and economical systems for communication at Global level. Radio-waves and Trrestrial Microwave systems have long since reached their capacity Satellite Communication Systems can provide, at best, only a temporary relief to the ever-increasing demand. extremely high initial cost of launching The geometry of suitable orbits, available microwave frequency allocations and if needed repair is nearly impossible Next option: OPTICAL COMMUNICATION SYSTEMS!

9 Optical Region THz range The Electromagnetic Spectrum

10 Potential of Optical Transmission? Information carrying capacity of a communications system is directly proportional to its bandwidth; C= BW log 2 (1+SNR); Wider the bandwidth, the greater its information carrying capacity. Theoretically; BW is 10% of the carrier frequency Shanon-Hartley theorem Signal Carrier VHF Radio system; 100 MHz. Microwave system; 6 GHz Lightwave system; 10 6 GHz Bandwidth 10 MHz 0.6 GHz GHz. A system with light as carriers has an excessive bandwidth (more than 100,000 times than achieved with microwave frequencies) Meet the today s communication needs or that of the foreseeable future Communication System with light as the carrier of information A great deal of attention.

11 Major Difficulties Transmission of light wave for any useful distance through the earth s atmosphere is impractical because of attenuation and absorption of ultra high light frequencies by water vapors, oxygen and air particulate. Consequently, the only practical type of optical communication system that uses a fiber guide. What is an optical fiber? A strand of glass or plastic material with special optical properties, which enable light to travel a large distance down its length. Powerful & Intense Optical Sources Invention of LASER (1960) and low loss Optical Fiber Wave guides (1970) An edge toward making the dream of carrying huge amount of information, a reality.

12 Fiber Optic Timeline 1930: Scanning & transmitting television images through uncoated fiber cables. 1951: Light transmission through bundles of fibers- flexible fibrescope used in medical field : First fiber-optic endoscope tested on a patient : Invention of Laser (development, T Maiman) 1966: Charles Kao; proposed cladded fiber optic cables with lower losses as a communication medium. 1970: (Corning Glass, NY) developed fibers with losses below 20 db/km. 1972: Semiconductor Injection laser diodes (room temp.) were developed 1977: GT&E in Los Angeles and AT&T in Chicago sends live telephone signals through fiber optics (850nm, 4dB/km, MMF, 9km) World s first FO link 1980s: 2 nd generation systems; 1300nm, SM, 0.5 db/km, O-E-O 3 rd generation systems; 1550nm, SM, 0.2 db/km, EDFA, 5Gb/s 1993 : Bell Labs sends 10 Billion bits/s through 20,000 km of fibers using a WDM systems and Soliton pulses : NTT, Bell Labs and Fujitsu able to send one Trillion bits per second through single optical fiber. 2000s : Towards achieving, Tb/s, Pb/s of data, All Optical Networks

13 The Nobel Prize in Physics 2009 "For ground breaking achievements concerning the transmission of light in fibers for optical communication" "For the invention of an imaging semiconductor circuit the CCD sensor" Charles K. Kao (b Shanghai, China) 1/2 of the prize Standard Telecommunication Laboratories, Harlow, UK; Chinese University of Hong Kong, Hong Kong, China Willard S. Boyle George E. Smith b b /4 of the prize 1/4 of the prize Bell Laboratories, Murray Hill, NJ, USA Kao s Experiment (1966)

14 Dr. Narinder S Kapany Born in Moga (Punjab) in October 1926

15 Basic Fiber Optic Link TRANSMITTER RECIEVER DRIVER LIGHT SOURCE OPTICAL FIBER DETECTOR MEDIUM FOR CARRYING LIGHT Converts Electrical signal to light Driver modifies the information into a suitable form for conversion into light (Modulation) Source is LED or ILDs whose output is modulated. Detector accepts light, converts it back to electrical signal. Detector is PIN diode or APD Elect. Signal is demodulated to separate out the information

16 Fiber-Optic System Devices Transmitter (Laser diode or LED). Fiber-Optic Cable (MMF, SMF) Receiver (PIN diode or APDs). Backbone of an OFC System : OPTICAL FIBER acts as transmission channel for carrying light beam loaded with information

17 Optical Fiber as Transmission Medium Transmit data as light pulses (first converting electronic signals to light pulses then finally converting back to electronic signals) Light propagate by means of Total Internal Reflection (TIR)

18 Structure of Optical Fiber A dielectric core (doped silica) of high refractive index surrounded by a lower refractive index cladding (SCS, PCS). Basic Structure of a Step-Index Optical Fiber Single mode: 5-10 m Step Index Profile Multimode: 50/62.5 m Graded Index Profile NECESSARY CONDITION FOR TIR: n 1 > n 2

19 Transmission Loss in Optical Glass 1970, First Optical Fiber: Loss 20 db/km at 633nm 1977, losses reduced to 5dB/km at 850nm 1980s, Loss reduced to 0.2 db/km at 1550 nm Dramatic reduction in transmission loss in optical glass Highly pure; Transmitting light through 3 mile thick slab of glass

20 Two Major Communication Issues ATTENUATION (Power loss) Attenuation is signal loss over distance. The light pulses loose their energy and amplitude falls as they travel down the cable. Puts distance limitation on long- haul networks. DISPERSION (Pulse broadening) Dispersion is the broadening of pulse as it travels down. Intermodal (Modal) dispersion Intramodal (Chromatic) dispersion Puts data rate limitation on networks

21 Fiber Attenuation 0.5 db/km at 1310 nm 0.2 db/km at 1550 nm Attenuation in Silica Optical Fibers Limit SNR / distance

22 Fiber Dispersion Dispersion is minimum in SMFs Limit Data Rate

23 Attenuation (db/ km ) Wavelengths of Operation Attenuation in Silica Fibers Optical Windows Wavelength (nm ) 850 nm 1310 nm 1550 nm Both 1310 and 1550 nm are active windows

24 Communication Channel Capacity Communication Medium Carrier Frequency Bandwidth 2 way voice Channels Copper Cable 1 MHz 100 khz < 2000 Coaxial Cable 100 MHz 10 MHz 13,000 Optical Fiber Cables THz 40 THz >3,00,000 or 90,000 Video signals Attenuation in silica OFC 0.2dB/km at 1550nm Pulse Broadening 16 ps/km at 1550 nm

25 Practical Optical Fiber Cable

26 OPTICAL SOURCES LEDs (GaAs, GaAlAs) 850 nm, 1310 nm Low cost easy to use Used for multimode fibers Special edge-emitting LEDs for SMFs Laser Diodes (InGaAsP, InGaAsSb) 850nm, 1310nm, 1550nm Very high power output Very high speed operation Specialized power supply & circuitry Very expensive

27 OPTICAL DETECTORS PIN Diodes (Si, Ge, InGaAs) 850nm, 1310nm, 1550 nm Low cost APDs (Avalanche Photodiodes, GaAlAs) 850nm, 1310nm, 1550 nm High sensitivity- operate at very low power levels Expensive

28 Advantages of Optical Fiber Wide Bandwidth: Extremely high information carrying capacity (~GHz) 3,00,000 voice channels on a pair of fiber Voice/Data/Video Integrated Service 2.5 Gb/s systems from NTT, Japan; 5 Gb/s System, Siemens Low loss : Information can be sent over a large distance. Losses ~ 0.2 db/km Repeater spacing >100 km with bit rates in Gb/s Interference Free Immune to Electromagnetic interference: No cross talk between fibers Can be used in harsh or noisy environments Higher security : No radiations, Difficult to tap signal Attractive for Defense, Intelligence and Banks Networks

29 Compact & light weight Advantages of Optical Fiber: Contd.. Smaller size : Fiber thinner than human hair Can easily replace 1000 pair copper cable of 10 cm dia. Fiber weighs 28gm/km; considerably lighter than copper Light weight cable Environmemtal Immunity/Greater safety Dielectric- No current, No short circuits Extremely safe for hazardous environments; attractive for oil & petrochemicals Not prone to lightning Wide temperature range Long life > 25 years Abundant Raw Material: Optical fibers made from Silica (Sand) Not a scarce resource in comparison to copper.

30 Some Practical Disadvantages Optical fibers are relatively expensive. Connectors very expensive: Due to high degree of precision involved Connector installation is time consuming and highly skilled operation Jointing (Splicing) of fibers requires expensive equipment and skilled operators Connector and joints are relatively lossy. Difficult to tap in and out (for bus architectures) - need expensive couplers Relatively careful handling required

31 OFC- Systems Installed Systems: operating at 1310 nm Low loss; minimum pulse broadening Transmission rate 2-10 Gb/s Regeneration of Signal after every km Conversion of O-E-O signal Current OFC Systems: 1550nm wavelength band Silica has lowest loss, increased dispersion Design of Dispersion Shifted Fibers Lowest loss and Negligible dispersion Signal amplification after km Direct amplification of signal in optical domain Erbium Doped Fiber Amplifier (EDFA)

32 EDFA : Fiber Amplifier Erbium Doped Fiber Amplifier Direct amplification of optical signal Flat gain around 1550nm low loss window BW 12,500 GHz ; Enormous potential

33 Increasing Network Capacity Options More Fibers (SDM) Same bit rate, more fibers Slow Time to Market Expensive Engineering Limited Rights of Way Duct Exhaust W D M Same fiber & bit rate, more ls Fiber Compatibility Fiber Capacity Release Fast Time to Market Lower Cost of Ownership Utilizes existing TDM Equipment Faster Electronics (TDM) Higher bit rate, same fiber Electronics more expensive

34 WDM/DWDM OFC- Systems Coincidence of low-loss window & wide-bw EDFA Possibilities of WDM Communication Systems Capable of carrying enormous rates of information Typical WDM network containing various types of optical amplifiers. Examples: 1.1 Tb/s over 150 km ; 55 wavelengths WDM 2.6 Tb/s over 120 km ; 132 wavelengths WDM

35 Fiber Optics Communication Expressway CISCO raising the speed limit LUCENT adding more lanes NORTEL providing faster transport equipments FORESIGHT Lightwave Communication Systems Employing DWDM, EDFA and Soliton pulses ZERO LOSS & NEAR INFINITE BANDWIDTH Provide with a network capable of handling almost all our information needs.

36 Bandwidth 1982 Bandwidth Evolutionary Landmarks TDM (Gb/s) Optical Fiber Fiber is deployed at a rate of 2000 miles every hour Enablers EDFA + Raman Amplifier Dense WDM/Filter High Speed Opto-electronics Advanced Fiber EDFA + Raman Amplifier EDFA All-Optical Network (Terabits Petabits) 40Gb/s 40 Gb/s Mb/s 565 Mb/s 810 Mb/s (1310 nm, 1550 nm) 1.2 Gb/s 1.8 Gb/s 10 Gb/s 2.4 Gb/s TDM DWDM

37 Optical Fiber Platform

38 Bands in Light Spectrum Approximate Attenuation of Single Mode silica fiber cable Visible Infrared nm O Band ~ nm E Band ~ nm S Band ~ nm C Band ~ nm L Band ~ nm

39 All Wave Optical Fiber LUCENT CORNING OFS HUAWEI

40 Photonic Crystal Fibers (PCFs) PCF: around since 1996 (JC Knight et al, OFC (1996) paper PD3 PCFs are optical fibers with a periodic arrangement of low-index material in a background with higher refractive index. The background material is usually undoped silica & the low index is typically provided by air-holes running along their entire length. Solid core PCF Hollow core PCF

41 Important facts regarding PCFs Photonic crystal fibers have a range of properties that can be dramatically different from those of conventional fibers. Index-guiding PCFs can be endlessly single-mode, highly nonlinear and/or have a wide range of dispersion properties Transparency window: UV to mid-ir region Band gap-guiding PCFs can guide light through air or other gases Hollow core PCFs have allowed significant advances in chemical sensing, gas-based non linear optics, high power delivery, pulse compression PCFs can also be the basis for new generation of practical and compact gas-based laser sources and fiber devices etc...

42 Multicore fiber for SDM Pb/s Transmission NTT Japan (2012) Videos\SDM NTTT Peta bit system of future

43 Optical Fibres Beyond Telecom Optical fibres can also have applications in: Fiber Optic Sensing Medicine Light guidance Biological and genetics research Defence/Guidance Industrial materials processing Next generation lasers Optical data processing Transmitting light beyond the near-ir

44 Fiber Optic Sensors An offshoot of fiber optic communication research Realization of high sensitivity of optical fibers to external perturbations (phase modulation, micro bending loss in cabling, modal noise etc) and its exploitation for development of sensors. (An Alternate School of Thought, 1975) High sensitivity of fibers due to long interaction length of light with the physical variable is the attraction. FOS: Any device in which variations in the transmitted power or the rate of transmission of light in optical fiber are the means of measurement or control to measure physical parameters such as strain, pressure, temperature, velocity, and acceleration etc. FOS: A Boon in Disguise

45 Light Wave Parameters 1. Amplitude / Intensity 2. Phase 3. Wavelength 4. Polarization 5. Time / Frequency Variation in any of these parameters due to external influence will form the working principle of the sensor.

46 Supporting Technology Kapron (1970) demonstrated that the attenuation of light in fused silica fiber was low enough that long transmission links were possible Procedure in Fiber optic sensor systems: Transmit light from a light source along an optical fiber to a sensor, which sense only the change of a desired environmental parameter. The sensor modulates the characteristics (intensity, wave length, amplitude, phase) of the light. The modulated light is transmitted from the sensor to the signal processor and converted into a signal that is processed in the control system. The properties of light involved in fiber optic sensors: reflection, refraction, interference and grating

47 Basic Elements of a Fiber Optic Sensor Beam conditioning optics Modulator Light source Transducer Optical Fiber Detector

48 Type of Fiber Optic Sensors Fiber optic sensors can be divided by: Places where sensing happens Extrinsic or Hybrid fiber optic sensors Intrinsic or All-Fiber fiber optic sensors Characteristics of light modulated by environmental effect Intensity-based fiber optic sensors Spectrally-based fiber optic sensors Interferometeric fiber optic sensors

49 ADVANTAGES Immunity to electromagnetic interference (EMI) and radio frequency interference (RFI) All-passive dielectric characteristic: elimination of conductive paths in high-voltage environments Inherent safety and suitability for extreme vibration and explosive environments Tolerant of high temperatures (>1450 o C) and corrosive environments Light weight, and small size High sensitivity

50 What Does F.O.S. Look Like? Various Fiber Optic Sensors

51 GENERAL USES Measurement of physical properties such as strain, pressure, displacement, temperature, velocity, and acceleration in structures of any shape or size Monitoring the physical health of structures in real time (SHM). Damage detection Used in multifunctional structures, in which a combination of smart materials, actuators and sensors work together to produce specific action Any environmental effect that can be conceived of can be converted to an optical signal to be interpreted ; Eric Udd, Fiber Optic Sensors

52 Monitoring in Structural Engineering Buildings and Bridges: concrete monitoring during setting, crack (length, propagation speed) monitoring, prestressing monitoring, spatial displacement measurement, neutral axis evolution, longterm deformation (creep and shrinkage) monitoring, concrete-steel interaction, and post-seismic damage evaluation Tunnels: multipoint optical extensometers, convergence monitoring, shotcrete / prefabricated vaults evaluation, and joints monitoring Damage detection Dams: foundation monitoring, joint expansion monitoring, spatial displacement measurement, leakage monitoring, and distributed temperature monitoring Heritage structures: displacement monitoring, crack opening analysis, post-seismic damage evaluation, restoration monitoring, and old-new interaction

53 General Purpose FOS

54 Fiber Optic Probe Colorimeter Smart Beds Optical fibers in Textiles

55 Fly by Light System-Airframe & Engine

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57 MEDICAL APPLICATIONS Small, Flexible Non Toxic Chemically Inert Intrinsically Safe Low Maintenance Ease of Use

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59 Advantages of Optical Fibers Medical Illumination Products Thin/Small size Flexible Non Toxic Chemically Inert EM Inert No Cross talk Wide Bandwidth Reliable Ease of Use Image Transmission by Fiber Bundle

60 Fibers are Everywhere

61 Fifty Years of Fiber Optics First quarter of the 21 st century will see a continued growth in the demand for fiber optic components.

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64 Bibliography: The excerpts of this lecture are based on the information drawn from following reference. 1. John M. Senior Optical Fiber Communications: Principles and Practice, 2 nd edn., PHI, Gerd Keiser, Optical Fiber Communica tion 3 rd edn., Mc Graw Hill, videos Govind P. Agrawal, Fiber-Optic Communication Systems John Wiley & sons (Asia) Pte Ltd, 3 rd Edn., Bishnu P. Pal, Fundamentals of Fibre Optics in Telecommunication and Sensor Systems, New Age International Publishers, 2005.

65 Questions?

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