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Optical fibre Basic physics of OFC Merits & Demerits of OFC Nomenclature of OFC Absorption & attenuation Jointing & termination of OFC Optical sources & Detectors FBG & Applications

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A SEMINAR ON Submitted to:- Ravi Goyal Sir Submitted by:- Ram Niwas Bajya OPTICAL FIBER Contents RAM NIWAS BAJIYA Optical fibre Basic physics of OFC Merits & Demerits of OFC Nomenclature of OFC Absorption & attenuation Jointing & termination of OFC Optical sources & Detectors FBG & Applications OPTICAL FIBER OFC have Fibres which are long, thin strands made with pure glass about the diameter of a human hair RAM NIWAS BAJIYA Total internal reflection At some angle, known as the critical angle c, light traveling from a higher refractive index medium to a lower refractive index medium will be refracted at 90 i.e. refracted along the interface. If the light hits the interface at any angle larger than this critical angle, it will not pass through to the second medium at all. Instead, all of it will be reflected back into the first medium, a process known as total internal reflection Incident angle = RAM NIWAS BAJIYA Optical fiber mode Fibbers that carry more than one mode at a specific light wavelength are called multimode fibres. Some fibres have very small diameter core that they can carry only one mode which travels as a straight line at the centre of the core. These fibres are single mode fibres. RAM NIWAS BAJIYA Optical fiber's Numerical Aperture(NA) Multimode optical fiber will only propagate light that enters the fiber within a certain cone, known as the acceptance cone of the fiber. The half- angle of this cone is called the acceptance angle max. For step-index multimode fiber, the acceptance angle is determined only by the indices of refraction: Where n is the refractive index of the medium light is traveling before entering the fiber nf is the refractive index of the fiber core nc is the refractive index of the cladding RAM NIWAS BAJIYA Medium / Link Carrier Information Capacity Copper Cable (short distance) 1 MHz 1 Mbps Coaxial Cable (Repeater every 4.5 km) 100 MHz 140 Mbps (BSNL) UHF Link 2 GHz 8 Mbps (BSNL), 2 Mbps (Rly.) MW Link (Repeater every 40 km) 7 GHz 140 Mbps (BSNL), 34 Mbps (Rly.) OFC 1550 nm 2.5 Gbps(STM-16 Rly.) 10 Gbps (STM-64) 1.28 Tbps (128 Ch. DWDM) 20 Tbps (Possible)RAM NIWAS BAJIYA Frequency Vs Attenuation In Various Types of Cable More information carrying capacity fibbers can handle much higher data rates than copper. More information can be sent in a second RAM NIWAS BAJIYA Limitations of OFC Difficulty in jointing (splicing) Highly skilled staff would be required for maintenance Precision and costly instruments are required Tapping for emergency and gate communication is difficult. Costly if under- utilised Special interface equipments required for Block working Accept unipolar codes i.e. return to zero codes only. RAM NIWAS BAJIYA Nomenclature for Optical Interface X can be I or S or L or V or U & denotes haul I for intra station (up to 2 km) S for short haul (15 km) L for long haul (40 km at 1310 nm & 80 km at 1550 nm) V for very long haul (60 km at 1310 nm & 120 km at 1550 nm) U for ultra-long haul (160 km at 1550 nm) Optical Interface specified as X.Y.Z RAM NIWAS BAJIYA Y can be 1 or 4 or 16 or 64 & denotes STM Level 1 for STM-1 4 for STM-4 16 for STM-16 64 for STM-64 Z can be 1 or 2 or 3 & denotes fibre type 1 for 1310 nm over NDSF (G.652 fibre) 2 for 1550 nm over NDSF (G.652 fibre) 3 for 1550 nm over DSF (G.653 fibre) 5 for 1550 nm over NZDSF (G.655 fibre) RAM NIWAS BAJIYA Examples of Nomenclature for Optical Interface I.16.1 Intra station STM-16 link on 1310 nm fibre S.16.2 Short haul STM-16 link on 1550 nm fibre (G.652) L.16.2 & L.16.3 Long haul STM-16 link on 1550 nm fibre (G.652 & G.653) S.4.1 Short haul STM-4 link on 1310 nm fibre L.4.1 Long haul STM-4 link on 1310 nm fibre (40 km) S.1.1 Short haul STM-1 link on 1310 nm fibre L.1.1 Long haul STM-1 link on 1310 nm fibre (40 km) RAM NIWAS BAJIYA Absorption & Attenuation Scattering of light due to molecular level irregularities in the glass Light absorption due to presence of residual materials, such as metals or water ions, within the fiber core and inner cladding. These water ions that cause the water peak region on the attenuation curve, typically around 1380 nm. RAM NIWAS BAJIYA Three peaks in attenuation a). 1050 nm b). 1250 nm c). 1380 nm Three troughs in attenuation (Performance windows) a.) 850 nm: 2 dB/km b). 1310 nm: 0.35 dB/km c). 1550 nm: 0.25 dB/km Absorption loss & Scattering loss RAM NIWAS BAJIYA JOINTING AND TERMINATION OF OFC There are two methods for jointing Optical fibre cable. a). splicing b.) connectors a). splicing 1.Fusion Splicing- Fusion splicing provides a fast, reliable, low-loss, fibre-to-fibre connection by creating a homogenous joint between the two fibre ends. The fibres are melted or fused together by heating the fibre ends, typically using an electric arc. Fusion splices provide a high-quality joint with the lowest loss (in the range of 0.01 dB to 0.10 dB for single-mode fibres) and are practically non-reflective. RAM NIWAS BAJIYA 2. Mechanical Splicing- Mechanical splicing is of slightly higher losses (about 0.2 db) and less-reliable performance System operators use mechanical splicing for emergency restoration because it is fast, inexpensive, and easy. Mechanical splices are reflective and non-homogenous RAM NIWAS BAJIYA b). Basics about connectors- Fibre optic connector facilitates re-mateable connection i.e. disconnection / reconnection of fibre Connectors are used in applications where Flexibility is required in routing an optical signal from lasers to receivers Reconfiguration is necessary Termination of cables is required Connector consists of 4 parts: Ferrule Connector body Cable Coupling device RAM NIWAS BAJIYA Optical sources An optical source is a major component of optical transmitters. Fiber optic communication systems often use semiconductor optical sources such as Light emitting diodes ( LEDs) and semiconductor lasers. Some of the advantages are: Compact in size High efficiency Good reliability Right wavelength range Small emissive area compatible with fibre core dimensions Possibility of direct emulation at relatively high frequencies RAM NIWAS BAJIYA Optical Detectors The role of an optical receiver is to convert the optical signal back into electrical signal and recover the data transmitted through the optical fibre communication system. Its vital component is a photo detector that converts light into electricity through the photoelectric effect. Some the advantages are: high sensitivity fast response low noise low cost high reliability RAM NIWAS BAJIYA FBG and Applications The Filter that Bragg Grading Fiber Grating Fiber grating is made by periodically changing the refraction index in the glass core of the fiber. The refraction changes are made by exposing the fiber to the UV-light with a fixed pattern. Glass core Glass cladding Plastic jacket Periodic refraction index change (Gratings) RAM NIWAS BAJIYA Fiber Grating Basics When the grating period is half of the input light wavelength, this wavelength signal will be reflected coherently to make a large reflection. The Bragg Condition r = 2neff in Reflection spectrum reflect Transmission spectrum trans. n (refraction index difference) RAM NIWAS BAJIYA Creating Gratings on Fiber One common way to make gratings on fiber is using Phase Mask for UV-light to expose on the fiber core. RAM NIWAS BAJIYA Characteristics of FBG It is a reflective type filter Not like to other types of filters, the demanded wavelength is reflected instead of transmitted It is very stable after annealing The gratings are permanent on the fiber after proper annealing process The reflective spectrum is very stable over the time It is transparent to through wavelength signals The gratings are in fiber and do not degrade the through traffic wavelengths, very low loss It is an in-fiber component and easily integrates to other optical devices RAM NIWAS BAJIYA Temperature Impact on FBG The fiber gratings is generally sensitive to temperature change (10pm/C) mainly due to thermo-optic effect of glass. Athermal packaging technique has to be used to compensate the temperature drift 1533.8 1534.0 1534.2 1534.4 1534.6 1534.8 1535.0 1535.2 -5 15 35 55 75 Temperature ( ) CenterWavelength(nm) Athermal Normal RAM NIWAS BAJIYA Types of Fiber Gratings TYPES CHARACTERS APPLICATIONS Simple reflective gratings Creates gratings on the fiber that meets the Bragg condition Filter for DWDM, stab