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Optical Fiber Ultimate Guide 

Optical Fiber Ultimate Guide

 Basic Structure of an Optical Fiber

 An optical fiber is a flexible, transparent fiber made by the glass (silica) or plastic to a diameter slightly thicker than that of a human hair.

 Optical fiber is a dielectric waveguide and ideally has a cylindrical shape.

 It consists of a core made up of a dielectric material which is surrounded by a cladding made up of a dielectric material of lower refractive index than the core.

 Principles of Light Transmission in a Fiber

 Fiber optics deals with the transmission of light energy through transparent fibers.

 How an optical fiber guides light depends on the nature of light and structure of the optical fiber.

 A light wave is a form of energy that is moved by wave motion.

 In fiber optics, wave motion is the movement of light energy through an optical fiber.

Optical Fiber Ultimate Guide 

Optical Fiber Ultimate Guide 

Light effect

 When light waves strike an object, some of the waves are absorbed by the object, some is reflected by it, and some might pass through it.

 When light strikes an object it is: 1) Reflected 2) Transmitted 3) Absorbed

 Properties of Light

 What happens to the light depends on the material

 Transparent (clear) materials- transmit light.

 Translucent (see-through) materials- scatters the transmitted light.

 Opaque (not see-through) materials- absorbs and reflects.

Properties of Light Transparent (clear) materials

 Those materials that transmit almost all the light waves falling upon them are said to be transparent materials.

 you can clearly see other objects through materials such as glass and clear plastic that allow nearly all the light that strikes them to pass through.

 Properties of Light Translucent (see-through) materials

 The materials through which some light rays can pass but the objects can not be seen clearly because the rays are diffused are known as translucent materials.

 Although objects behind these materials are visible, they are not clear.

 Frosted glass or a piece of oiled paper are examples of translucent materials.

 Properties of Light Opaque (not see-through) materials

 Those materials that are unable to transmit light waves falling upon them are said Opaque materials.

 You cannot see other objects through opaque materials.

 Example: walls of a room etc.

Properties of LightReflection

 Reflected waves are those waves that are neither transmitted nor absorbed but are reflected from the surface of the medium.

 When a wave approaches a reflecting surface such as a mirror; the wave that strikes the surface is called incident wave and the wave that bounces back is called the reflected wave. The amount of incident energy that is reflected from a surface depends on

 The nature of the surface &

 The angle at which the wave strikes the surface

 Properties of LightRefraction

 When a light wave passes from one medium to another medium having a different velocity of propagation, a change in the direction of the wave will occur.

 This change of direction as the wave enters the second medium is called refraction.

 Refraction- bending of light waves due to a change in speed

 Lens, curved glass or transparent material that Refracts light

Properties of LightDiffusion

 When a light wave is reflected from a piece of white paper, the reflected beam is scattered or diffused.

 Since the surface of the paper is not smooth, the reflected light is broken up into many light beams that are reflected in all directions.

Optical Fiber Ultimate Guide 

Properties of LightAbsorption

 A light wave is reflected and diffused from a piece of white paper.

 But if the light beam falls upon a piece of black paper, the black paper absorbs most of the light and a very small amount of light is reflected from the paper.

 If the surface upon which the light beam falls is perfectly black; then there is no reflection; the light is totally absorbed.

 Ray Theory Transmission Ray Optics: basic laws

 Light rays inhomogeneous media are straight lines

 Law of Reflection – Reflection from a mirror or at the boundary between two media of different refractive index: the angle of reflection equals to the angle of incidence i.e. qr = qi

 Snell’s law of Refraction – At the boundary between two media of different refractive index n the angle of refraction qt is related to the angle of incidence qi by ni sin θi = nt sin θt

Ray Theory Transmission

The future of optical fibres - Wire Tech World

 Ray Theory Transmission Refractive index

 The index of refraction of a material is the ratio of the speed of light in a vacuum to the speed of light in the material n = c/v The factor n is the index of refraction (or refractive index) of the medium. For air and gases n ~ 1. At optic frequencies, the refractive index of water is 1.33.

 Glass has many compositions, each with a slightly different n. An approximate refractive index of 1.5 is representative for the silica glasses used in fibers; more precise values for these glasses lie between ~1.45 and ~1.48.

 Refractive Index for Some Materials

 Air ———————————————————————–1.0

 Water ——————————————————————-1.33

 Magnesium fluoride ————————————————-1.38

 Fused silica (SiO2)—————————————————-1.46

 Sapphire (Al2O3)——————————————————1.8

 Lithium niobate (LiNbO3)——————————————-2.25

 Indium phosphide (InP)———————————————-3.21

 Gallium arsenide (GaAs) ———————————————3.35

 Silicon (Si)—————————————————————3.48

 Indium gallium arsenide phosphide (InGaAsP)—————–3.51

 Aluminum gallium arsenide (AlGaAs)—————————–3.6

 Germanium (Ge) ——————————————————-4.0

The index varies with a number of parameters, such as wavelength and temperature.

Ray Theory Transmission Critical Angle (qc)

 The angle at which total internal reflection occurs is called the critical angle of incidence.

 At any angle of incidence (q1) greater than the critical angle, light is totally reflected back to the glass medium.

 For n1 > n2, the angle of refraction q2 is always greater than the angle of incidence q1.  When the angle of refraction q2 is 90o the refracted ray emerges parallel to the interface between the media. The critical angle is determined by using Snell’s Law. The critical angle is given by :

Optical Fiber Ultimate Guide 

Ray Theory Transmission Total internal reflection

 At angles of incidence q1 > qc the light is totally reflected back into the incidence higher refractive index medium. This is known as total internal reflection.

Ray Theory Transmission Acceptance Angle

 The acceptance angle of an optical fiber is defined as the maximum angle of a ray (against the fiber axis) hitting the fiber core which allows the incident light to be guided by the core.

 The sine of that acceptable angle is called the numerical aperture, and it is essentially determined by the refractive index contrast between core and cladding of the fiber, assuming that the incident beam comes from air or vacuum.

 Ray Theory Transmission Numerical Aperture

 The numerical aperture is a measurement of the ability of an optical fiber to capture light. The NA is also used to define the acceptance cone of an optical fiber. Mathematically it is defined as Where n1 is the refractive index of core and n2 is the refractive index of the cladding.

Geometrical Optics Description Optical fibers based on modes or mode types:

 The mode is the one that describes the nature of the propagation of electromagnetic waves in a waveguide.

 it is the allowed direction whose associated angles satisfy the conditions for total internal reflection and constructive interference.

 Based on the number of modes that propagate through the optical fiber, they are classified as:

 Single Mode fibers can propagate only the fundamental mode.

 Multimode fibers can propagate hundreds of modes.

Geometrical Optics Description Single-mode fibers:

In a fiber, if only one mode is transmitted through it, then it is said to be a single-mode fiber. A typical single-mode fiber may have a core radius of 3 μm and a numerical aperture of 0.1 at a wavelength of 0.8 μm.

Optical Fiber Ultimate Guide 

Characteristics of Single-Mode Fiber

 The single-mode fiber has the following characteristics; Only one path is available.

 Core diameter is small

 No dispersion  Higher bandwidth (1000 MHz)

 Used for long haul communication  Fabrication is difficult and costly

Geometrical Optics Description Multimode fibers 

 If more than one mode is transmitted through an optical fiber, then it is said to be a multimode fiber.

 The larger core radius of multimode fibers makes it easier to launch optical power into the fiber and facilitate the end to end connection of similar powers.

Characteristics of Multimode Fiber

The Multimode fibers have the following characteristics:

 More than one path is available

 Core diameter is higher

 Higher dispersion

 Lower bandwidth (50MHz)

 Used for short-distance communication

 Fabrication is less difficult and not costly

 Types of Optical Fibers based on refractive index profile:

Based on the refractive index profile of the core and cladding; the optical fibers are classified into two types:  Step index fiber  Graded index fiber

Geometrical Optics Description Step index fiber 

 In a step-index fiber, the refractive index changes in a step fashion, from the center of the fiber, the core, to the outer shell, the cladding.

 It is high in the core and lowers in the cladding. The light in the fiber propagates by bouncing back and forth from the core-cladding interface.

 The step-index fibers propagate both single and multimode signals within the fiber core.

 The light rays propagating through it are in the form of meridional rays which will cross the fiber core axis during every reflection at the core-cladding boundary and are propagating in a zig-zag manner.

 Step Index Single Mode & Multimode Fibers

Geometrical Optics Description Graded index fibers

 In graded-index fibers, the refractive index of the core varies gradually as a function of radial distance from the fiber center.

 The refractive index of the core decreases as we move away from the center.

 The refractive index of the core is made to vary in the form of a parabolic manner such that the maximum refractive index is present at the center of the core.

Optical Fiber Ultimate Guide 

Electromagnetic Optics

 Electromagnetic radiation propagates in the form of two mutually coupled vector waves, an electric field wave & a magnetic field wave. Both are vector functions of position & time.

 In a source-free, linear, homogeneous, isotropic & non-dispersive media, such as free space, these electric & magnetic fields satisfy the following partial differential equations, known as Maxwell’ equations.

 Electromagnetic Optics

 In Maxwell’s equations, E is the electric field expressed in [V/m], H is the magnetic field expressed in [A/m].

 The solution of Maxwell’s equations in free space, through the wave equation, can be easily obtained for monochromatic electromagnetic wave. All electric & magnetic fields are harmonic functions of time of the same frequency. Electric & magnetic fields are perpendicular to each other & both perpendicular to the direction of propagation, k, known as transverse wave (TEM). E, H & k form a set of orthogonal vectors. typermeabiliMagnetic:[H/m] typermittiviElectric:[F/m]

Electromagnetic Plane wave in Free space Ex z Direction of propagation By z x y k An Electromagnetic wave is a traveling wave which has time-varying electric and magnetic fields which are perpendicular to each other and the direction of propagation Z.

 TE modes and Electric fields distribution

 Dispersion Effect in Optical Fiber

In communication, dispersion is used to describe any process by which an electromagnetic signal propagating in a physical medium is degraded because the various wave characteristics (i.e., frequencies) of the signal have different propagation velocities within the physical medium.

 The dispersion cause that optical pulses to broaden as they travel along with a fiber, the overlap between neighboring pulses, creating errors in the receiver output, resulting in the limitation of information-carrying capacity of a fiber.

Dispersion and Bit Rate

 The higher dispersion the longer the bit interval which must be used

 A longer the bit interval means fewer bits can be transmitted per unit of time

 A longer bit interval means a lower bit rate

Optical Fiber Ultimate Guide 

 Types of Dispersion

 Intermodal dispersion: Different modes propagate at different group velocities.

 Intramodal or Chromatic Dispersion  Material dispersion: The index of refraction of the medium changes with wavelength.

 Waveguide dispersion: The index change across waveguide means that different wavelengths have different delays.  Polarization mode dispersion: If the waveguide is birefringent. Birefringent is an optical property of a material having a refractive index that depends on the polarization and propagation direction of light.

 Dispersion Effect in Optical Fiber Intermodal Dispersion

 In a multimode fiber different modes travel at different velocities.

 If a pulse is constituted from different modes then intermodal dispersion occurs.

 Modal dispersion is greatest in multimode step-index fibers.

 The more modes the greater the modal dispersion.

 Typical bandwidth of a step-index fiber may be as low as 10 MHz over 1 km.

 Dispersion Effect in Optical Fiber Intramodal or Chromatic Dispersion

 Intramodal or Chromatic dispersion (CD) is caused by the fact that single-mode glass fibers transmit light of different wavelengths at different speeds. The ratio of the speed of light in a medium to the speed in a vacuum defines the index of refraction or refractive index of the material.

 Material Dispersion

 This is due to the intrinsic properties of the material, glass.

 Glass is a dispersive medium. We can recall from our high school physics that glass has a different refractive index for different colors.

 Different colors (wavelengths) have different velocity in the glass.

 A type of dispersion that occurs in optical fiber due to the interaction of various wavelengths with the physical matter in the crystalline structure of the glass.

 The refractive index of the glass varies according to the wavelength of the optical signal.

 Material dispersion is the phenomenon whereby materials cause a “bundle” of light to spread out as it propagates.

Dispersion Effect in Optical Fiber Intramodal or Chromatic Dispersion

 Waveguide Dispersion

 This is due to the dispersive nature of the bound medium. In a bound medium like the optical fiber, the velocity is a function of frequency.

 Waveguide dispersion is chromatic dispersion which arises from waveguide effects: the dispersive phase shifts for a wave in a waveguide differ from those which the wave would experience in a homogeneous medium. Waveguide dispersion is important in waveguides with small effective mode areas. But for fibers with large mode areas, waveguide dispersion is normally negligible, and material dispersion is dominant.

 Dispersion Effect in Optical Fiber Polarization mode dispersion

 The polarization mode dispersion is due to unequal velocities of two orthogonal states of polarization.

 The PMD puts the ultimate restriction on the data rate on the long haul single-mode optical fiber.

 The pulse slowly broadens due to the statistical fluctuation of the velocities of the two orthogonal polarizations.

Optical Fiber Ultimate Guide 

Optical Fiber Losses Attenuation in Optical Fibers

 Attenuation limits the optical power which can reach the receiver, limiting the operating span of a system.

 Once the power of an optical pulse is reduced to a point where the receiver is unable to detect the pulse, an error occurs.  Attenuation is mainly a result of

 Light Absorption

 Scattering of light

 Bending losses

 Attenuation is defined as the ratio of optical input power (Pi) to the optical output power (Po).

 The following equation defines signal attenuation as a unit of length: Attenuation.

 Optical Fiber Losses

 Types of Attenuation Absorption Loss

 Caused by the fiber itself or by impurities in the fiber, such as water and metals. Scattering Loss

 Intrinsic loss mechanism caused by the interaction of photons with the glass itself. Bending loss

 Loss induced by physical stress on the fiber.

Optical Fiber Losses Material Absorption Losses

 Material absorption is caused by the absorption of photons within the fiber.

 – When a material is illuminated, photons can make the valence electrons of an atom transition to higher energy levels

 – Photon is destroyed, and the radiant energy is transformed into electric potential energy. This energy can then

 • Be re-emitted (scattering)

 • Frees the electron (photoelectric effects) (not in fibers)

 • Dissipated to the rest of the material (transformed into heat)

 In an optical fiber Material Absorption is the optical power that is effectively converted to heat dissipation within the fiber.

  Two types of absorption exist.

 – Intrinsic Absorption, caused by interaction with one or more of the components of the glass.

 – Extrinsic Absorption, caused by impurities within the glass.

Optical Fiber Ultimate Guide 

Optical Fiber Losses Material Absorption Losses

 Intrinsic Absorption is caused by basic fiber material properties. If an optical fiber is absolutely pure, with no imperfections or impurities, ten all absorption will be intrinsic. Intrinsic absorption in the ultraviolet region is caused by electronic absorption bands. Intrinsic Absorption occurs when a light particle (photon) interacts with an electron and excites it to a higher energy level.

 Extrinsic Absorption is caused by impurities introduced into the fiber material. The metal impurities such as iron, nickel, and chromium are introduced into the fiber during fabrication. Extrinsic Absorption is caused by the electronic transition of these metal ions from one energy level to another energy level.

 Optical Fiber Losses Classification

Optical Fiber Losses Fiber Bend Losses Bending loss is classified according to the bend radius of curvature: 1. Microbend Loss 2. Macrobid Loss

 Microbend Loss is caused by small discontinuities or imperfections in the fiber. Uneven coating applications and improper cabling procedures increase micro bend loss. External forces are also a source of micro bends.

 Optical Fiber Losses Linear Scattering Losses

 Light scattering is a form of scattering in which light in the form of propagating energy is scattered.

 Light scattering can be thought of as the deflection of a ray from a straight path, for example by irregularities in the propagation medium, particles, or in the interface between two media.

 Deviations from the law of reflection due to irregularities on a surface are also usually considered to be a form of scattering.

 When these irregularities are considered to be random and dense enough that their individual effects average out, this kind of scattered reflection is commonly referred to as diffuse reflection. Linear Scattering may be of two types

 Rayleigh Scattering

 Mie Scattering

Optical Fiber Ultimate Guide 

Rayleigh Scattering

 The scattering losses are caused by the interaction of light with density fluctuations within a fiber.

 Density changes are produced when optical fibers are manufactured.

 During manufacturing, regions of higher and lower molecular density areas, relative to the average density of the fiber, are created.

 Light traveling through the fiber interacts with the density areas then partially scattered in all directions.

 In commercial Fibers operating 700nm and 1600nm wavelength, the main source of loss is called Rayleigh Scattering (named after the British physicist Lord Rayleigh).

 Rayleigh Scattering is the main loss mechanism between the ultraviolet and infrared regions.

 Rayleigh scattering occurs when the size of density fluctuations (Fiber defect) is less than one-tenth of the operating wavelength of light.

 As the wavelength increases, the loss caused by Rayleigh Scattering decreases.

 Mie Scattering

 If the size of the defect is greater than one-tenth of the wavelength of light, the scattering mechanism is called Mie Scattering (named after Gustav Mie).

 It is caused by these large defects in the fiber core, scatters light out of the fiber core.

 However, in commercial fibers, the defects of Mie Scattering are insignificant.

 Optical fibers are manufactured with fewer defects.

 Linear scattering may also occur at inhomogeneities and they are comparable in size to the guided wavelength. This type of scattering is because of fiber imperfections such as

 Irregularities in the core-cladding interface.

 Core-cladding refractive index differences along with the fiber.

 Diameter fluctuation.

 Stains and bubbles.

 Scattering intensity can be very large if the scattering inhomogeneities size is greater than one-tenth of the operating wavelength of the light. Such inhomogeneities create scattering in the forward direction and are known as Mie Scattering.

Optical Fiber Losses Nonlinear Optical Effects

 Optical waveguides do not always behave as linear channels where optical output power is equal to optical input power.

 Several nonlinear effects occur which causes scattering.

 Nonlinear Scattering is the transfer of optical power from one mode to be transferred in either the forward or backward direction or other modes at different frequencies.

 The types of nonlinearities are 1. Stimulated Raman Scattering 2. Stimulated Brillouin Scattering 3. Self Phase Modulation 4. Cross Phase Modulation 5. Four-Wave Mixing

Optical Fiber Ultimate Guide 

Stimulated Raman Scattering

 In Stimulated Raman Scattering (SRS) a high-frequency optical photon is generated.

 The Stimulated Raman Scattering (SRS) process is initiated by noise, thermally induced fluctuations in the optical fields, and active vibrational modes.

 An incident pump field (ωP) interacts with the vibrational fluctuations, losing a photon which is downshifted in frequency by the vibrational frequency () to produce a Stokes wave (ωS,) and also an optical phonon (quantum of vibrational energy ).

 The pump decays with propagation distance and both the phonon population and Stokes wave grow together.

 If the generation rate of Stokes light exceeds the loss, stimulated emission occurs and the Stokes beam grows exponentially. Threshold Power PR is given by.

 Stimulated Brillouin Scattering

 In Stimulated Brillouin Scattering (SBS) a high-frequency acoustic phonon is generated.

 The Stimulated Brillouin Scattering (SBS) is the modulation of light through thermal molecular vibrations within the fiber.

 The scattered light appears as upper and lower sidebands which are separated from the incident light by the modulation frequency.

The Kerr Effect

 The Kerr effect is due to the non-linear response of the material. It means that the index of the silica is now depending on the optical field propagation through it.

 The power dependence of the refractive index is responsible for the Kerr-effect.

 Depending upon the type of input signal, the Kerr-nonlinearity has three different effects such as Self-Phase Modulation (SPM), Cross-Phase Modulation (CPM), and Four-Wave Mixing (FWM).

Self Phase Modulation (SPM) 

If an intensity-modulated signal propagates in the fiber, the intensity modulation induces an index modulation of the fiber and in return a phase modulation to the signal.  The signal modulates itself

 The SPM induced phase modulation broadens the signal spectrum. Self-phase modulation (SPM) is a fiber nonlinearity caused by the nonlinear index of refraction of glass. The index of refraction varies with optical power level causing a frequency chirp that interacts with the fiber’s dispersion to broaden the pulse. Nonlinear Optical Effects due to the Kerr Effect

 Nonlinear Optical Effects due to the Kerr Effect

 Cross Phase Modulation (XPM) :

In the case of a multi-channel propagation, the index modulation induced by the Kerr–effect modulates the other channels and vice-versa.

Optical Fiber Ultimate Guide 

 Cross Phase Modulation (XPM)

 In the case of multi-channel propagation at various wavelengths, the different channels modulate themselves via SPM but also each other via the fiber index modulation.

 The efficiency of Cross Phase Modulation (XPM) depends on:

 The fiber chromatic dispersion

 Channel spacing

 Channel power

 XPM induces non-linear crosstalk.

Nonlinear Optical Effects due to the Kerr Effect

 Four-Wave Mixing (FWM); In the case of a multi-channel propagation and under phase-matching conditions, new frequencies are generated in the fiber causing crosstalk and power depletion.

Four-Wave Mixing (FWM)

 Under specific phase and wave vectors matching conditions, four different waves will interact in the fiber in a non-linear way.

 The easiest way to obtain FWM in a fiber is to propagate two waves at angular frequencies w1 and w2 that will create new waves at frequencies w3 and w4 such as

 The phase-matching condition is:

 This phenomenon is strongly dependent on channel spacing and chromatic dispersion.

 The generated waves may cause crosstalk if they are at the same wavelength as incident channels.

Some solutions for the Kerr effect in fibers

 Decrease the field intensity by increasing the effective area.

 In the case of single-channel transmission, the increase of the chromatic dispersion will automatically lower the SPM. But the problem is reported to the chromatic dispersion compensation if DCF is used as SPM may be high in such fibers.

 In the case of multi-channel transmission, the increase of the channel spacing and /or chromatic dispersion will decrease XPM effects.

 Optical fibers consist of

1. A core, having a high refractive index. 2. Cladding. 3. Buffer, protective polymer layer. 4. Jacket, protective polymer layer. Manufacturing Optical Fibres

 Two methods to manufacture optical glass fiber

Draw the fiber from molten glasses, which are placed in two concentric crucibles (Direct melt methods) 2. Draw from a glass rod called preform (Vapor-phase oxidation process)

 Direct Melt Methods -Optical fibers are made directly from the molten state of purified components of silica glasses.

 Vapor –phase Oxidation Process -Highly pure vapors of metal halides react with O2 to form a white powder of SiO2 particles. -The particles are then collected on the surface of the bulk glass and are sintered to form a glass rod. -This rod or tube is called a preform. -Typically 10-25mm dia and 60-120cm long.

 Vapor-phase oxidation process

1. Outside vapor phase oxidation 2. Vapor phase axial deposition 3. Modified chemical vapor deposition

 Direct Melt Methods 1. Drawing the fiber 2. Double Crucible Method 3. Rod-in-Tube method Types of Manufacturing Optical Fibres

Drawing the fiber

The tip of the preform is heated to about 2000°C in a furnace. As the glass softens, a thin strand of softened glass falls by gravity and cools down.

The fiber diameter is constantly monitored as it is drawn.

A plastic coating is then applied to the fiber before it touches any components. The coating protects the fiber from dust and moisture.

The fiber is then wrapped around a spool. Direct Melt Methods

 Double crucible method

• The molten core glass is placed in the inner crucible.

• The molten cladding glass is placed in the outer crucible.

• The two glasses come together at the base of the outer crucible and a fiber is drawn.

• Long fibers can be produced (providing you don’t let the content of the crucibles run dry!).

• Step-index fibers and graded-index fibers can be drawn with this method. Direct Melt Methods,

Rod-in-Tube method

• A rod of core glass is placed inside a tube of cladding glass. The end of this assembly is heated; both glasses is softened and a fiber is drawn.

• Rod and tube are usually 1 m long. The core rod has typically a 30 mm diameter. The core glass and the cladding glass must have similar softening temperatures.

• However, one must be very careful not to introduce impurities between the core and the cladding. Direct Melt Methods

Outside Vapor Deposition (OVD)

 This process is also called the “soot process”.

 Halogens and O2 react in a hot flame to form hot glass soot, which is deposited layer by layer on aluminium oxide or graphite mandrel.

 The central mandrel is removed after deposition.

 In the last step, called sintering, a hollow porous preform is dehydrated and collapsed in a controlled atmosphere, (e. g. helium) to form the desired preform. Vapor-phase oxidation process

Vapor-phase oxidation process

1. In the VAD method, the preform can be fabricated continuously.

2. Starting chemicals are carried from the bottom into oxygen-hydrogen burner flame to produce glass soot which is deposited on the end of a rotating silica rod.

3. A porous preform is then grown in the axial direction.

4. The starting rod is pulled upward and rotated in the same way as that used to grow single crystals.

5. Finally, the preform is dehydrated and vitrified in-ring heaters.

6. This process is preferred for mass production.

Vapor-phase oxidation process

Modified Chemical Vapor Deposition (MCVD)

 The gaseous mixture of reactants is fed at the end of a rotating silica tube.

 This tube is heated by a traversing oxygen-hydrogen burner.

 As a result of chemical reactions glass particles, called soot, are formed.

 These particles are deposited on the internal wall of the tube.

 The soot is then vitrified by the traversing burner to provide a thin glass layer.

 The process is repeated many times as the cladding layers and core layers are formed.

 When the deposition is finished, the temperature of the burner is increased to collapse the tube into a solid preform.

 The entire process is highly automated and all process parameters are precisely controlled.

 Manufacturing Optical Fibres

 Fiber Optic Connectors and Splices Fiber Joints

Fibers must be joined when

You need more length than you can get on a single roll

connecting distribution cable to the backbone

Connecting to electronic source and transmitter

Repairing a broken cable Splices v/s Connectors

A permanent join is a splice

Connectors are used at patch panels and can be disconnected

Requirements of a Good Connector

1. At the connector joint, it should offer low coupling losses.

2. Connectors of the same type must be compatible from one manufacturer to another.

3. In the fiber link, the connector design should be simple so that it can be easily installed.

4. The connector joint should not be affected by temperature, dust, and moisture. That is, it should have low environmental sensitivity.

5. It should be available at a lower cost and have a precision suitable for the application. Fiber Optic Connectors

Joint Alignment type connectors 

Straight Sleeve

Tapered Sleeve

In the straight sleeve connector, there is a metal, ceramic or molded plastic ferrule for each fiber and the ferrule fits into the sleeve.

The fiber is epoxied into the drilled hole of the ferrule.

In the straight sleeve connector or tapered sleeve connector, the length of the sleeve and a guide ring on the ferrules determine the end separation of the fibers.

In the tapered sleeve connector, the ferrules and sleeves are tapered. Fiber Optic Connectors Butt-Joint Alignment Mechanism Straight Sleeve Mechanism Tapered Sleeve Mechanism

The expanded beam connector employing a collimating lens at the end of the transmitting fiber and focusing lens at the entrance end of the receiving fiber.

The collimating lens converts the light from the fiber into a parallel beam of light and the focusing lens converts the parallel beam of light into a focused beam of light on to the core of the receiving fiber.

The fiber-to-lens distance is equal to the focal length of the lens.

The lenses are anti-reflection coated spherical microlenses. Expanded Beam Connector Fiber Optic Connectors.(Optical Fiber Ultimate Guide)

Fiber Optic Splices A Fiber Optic Splice is a permanent fiber joint whose purpose is to establish an optical connection between two individual optical fibers. There are two techniques used for fiber splicing: Mechanical Splicing: A mechanical splice has Mechanical Fixtures and materials that are used to fiber alignment and connection.

Fusion Splicing: A Fusion Splice is a fiber joint which is done by Heat Fuses or by melting the ends of two optical fibers together.

Mechanical Splicing may involve the use of a glass or ceramic alignment tube

The inner diameter of this glass or ceramic tube is slightly larger than the outer diameter of the fiber.

A transparent adhesive is injected into the tube and bonds the two fibers together.

The adhesive also provides index matching between the optical fibers.

This technique relies on the inner diameter of the fiber.

If the inner diameter is too large, splice loss will increase because of fiber misalignment.

If the inner diameter is too small, it is impossible to insert the fiber into the tube. Glass or Ceramic Alignment Tube Splices Mechanical Splicing

Mechanical Splicing V-Grooved Splicing

V-Grooved Splicing may involve sandwiching the butted ends of two prepared fibers between a V-Grooved substrate.

When inserting the fibers into the grooved substrate, the V-Groove aligns the cladding surface of each fiber end.

A transparent adhesive makes the splice permanent by securing the fiber ends to the grooved substrate. Open V-Grooved Splice Spring V-Grooved Splice. Optical Fiber Ultimate Guide

 Optical Loss

Intrinsic Loss  Problems the splicer cannot fix  Core diameter mismatch  Concentricity of fiber core or connector ferrules  Core ellipticity  Numerical Aperture mismatch

 Optical Loss

Extrinsic Loss  Problems the person doing the splicing can avoid  Misalignment  Bad cleaves  Air gaps  Contamination: Dirt, dust, oil, etc.  Reflectance

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