If the fiber attenuation is 0. Absorption loss results in dissipation of some optical power as hear in the fiber cable. Although glass fibers are extremely pure, some impurities still remain as residue after purification. The amount of absorption by these impurities depends on their concentration and light wavelength. IN 3 Intrinsic absorption by basic constituent atom of fiber. Absorption by Atomic Defects x Atomic defects are imperfections in the atomic structure of the fiber materials such as TS missing molecules, high density clusters of atom groups.
These absorption losses are negligible compared with intrinsic and extrinsic losses. The radiation dames the internal structure of fiber. The damages are proportional to the intensity of ionizing particles. This results in increasing attenuation due to atomic defects and absorbing optical energy. The total dose a material receives is expressed in rad Si , this is the unit for measuring D radiation absorbed in bulk silicon.
A major source of attenuation is from transition of metal impurity ions such as iron, chromium, cobalt and copper. The effect of metallic impurities can be reduced by glass refining techniques. IN impurities dissolved in glass.
Vibrations occur at wavelengths between 2. The absorption peaks occurs at , and nm. These are first, second and third overtones respectively. Between these absorption TS peaks there are regions of low attenuation. Thus intrinsic absorption sets the fundamental lower limit on absorption for any particular material.
Absorption occurs when a photon interacts with an electron in the valene band and excites it to a higher energy level. The inherent IR absorption is due to interaction between the vibrating band and the electromagnetic field of optical signal this results in transfer of energy from field to the band, thereby giving rise to absorption, this absorption is strong because of many bonds present in the fiber.
CI x The loss in infrared IR region above 1. As glass is composed by randomly connected network of molecules and several oxides e. These two effects results to variation in refractive index and Rayleigh type scattering of light. There are two causes during the manufacturing of fiber. The random changes. IN because of this are impossible to eliminate completely.
When light ray strikes such zones it gets scattered in all directions. The amount of scatter depends on the size of the discontinuity compared with the wavelength of the light so the shortest TS wavelength highest frequency suffers most scattering.
The overall losses in this fibers are more as compared to single mode fibers. Careful control of manufacturing process can reduce mie scattering to insignificant levels.
This is shown in Fig. TS CI x As the core bends the normal will follow it and the ray will now find itself on the wrong side of critical angle and will escape.
The sharp bends are therefore avoided. EN k is wave propagation constant. This small microbending is TS not visible. The losses due to this are temperature related, tensile related or crush related. These effects can be minimized during installation and testing.
IN Macrobending x The change in spectral attenuation caused by macrobending is different to microbending. Usually there are no peaks and troughs because in a macrobending no light is coupled TS back into the core from the cladding as can happen in the case of microbends.
The losses are eliminated when the bends are straightened. The losses can be minimized by not exceeding the long term bend radii. IN where, P r is power density of that model at radial distance r. Pulse spreading in fiber is EN referred as dispersion. Dispersion is caused by difference in the propagation times of light rays that takes different paths during the propagation. The light pulses travelling down the fiber encounter dispersion effect because of this the pulse spreads out in time domain.
Dispersion limits the information bandwidth. The distortion effects can be analyzed by D studying the group velocities in guided modes. Information Capacity Determination TU x Dispersion and attenuation of pulse travelling along the fiber is shown in Fig. At certain distance the pulses are not even distinguishable and error will occur at receiver.
Therefore the information capacity is specified by bandwidth- distance product MHz. For step index bandwidth distance product is 20 MHz. Group Delay x Consider a fiber cable carrying optical signal equally with various modes and each mode. IN contains all the spectral components in the wavelength band. All the spectral components travel independently and they observe different time delay and group delay in the direction of propagation. The velocity at which the energy in a pulse travels along the fiber is known as group velocity.
Group velocity is given by, TS … 2. Material Dispersion. IN x Material dispersion is also called as chromatic dispersion. Material dispersion exists due to change in index of refraction for different wavelengths. The time delay is different for different wavelength components.
This results in time dispersion of pulse at TS the receiving end of fiber. The amount of material dispersion depends upon the chemical composition of glass. TU Example 2. Find the the material-dispersion-induced pulse spreading at nm for an LED with a 75 nm spectral width [Jan.
Since multimode optical fibers carry hundreds of modes, they will not have observable waveguide dispersion. EN x As frequency is a function of wavelength, the group velocity of the energy varies with frequency. The produces additional losses waveguide dispersion. The propagation constant b varies with wavelength, the causes of which are independent of material dispersion. D Chromatic Dispersion TU x The combination of material dispersion and waveguide dispersion is called chromatic dispersion.
These losses primarily concern the spectral width of transmitter and choice of correct wavelength. TS x A graph of effective refractive index against wavelength illustrates the effects of material, chromatic and waveguide dispersion. Attenuation is therefore also at minimum and makes nm a highly attractive operating wavelength. Modal Dispersion x As only a certain number of modes can propagate down the fiber, each of these modes carries the modulation signal and each one is incident on the boundary at a different.
IN angle, they will each have their own individual propagation times. The net effect is spreading of pulse, this form o dispersion is called modal dispersion. It is moderately present in graded index fibers and almost eliminated in single mode step index fibers.
Higher Order Dispersion x Higher order dispersive effective effects are governed by dispersion slope S. Also, where,. The pulse broadening is studied with the help of wave equation. TS Chirped Gaussian Pulses x A pulse is said to b e chirped if its carrier frequency changes with time.
IN where, S is dispersion slope. This results in pulse broadening is know as polarization mode dispersion PMD. The effects of PMD must be compensated. The higher order modes travelling in outer regions of the core, will travel faster than the lower order modes travelling in high refractive index region.
If the index profile is carefully controlled, then the transit times of the individual modes will be identical, so eliminating modal dispersion. S pulse width due to intermodal delay distortion. S pulse width resulting from pulse broadening within each mode. D From this the expression for intermodal pulse broadening is given as: TU … 2. IN coupling. The energy from one mode is coupled to other mods because of: - Structural imperfections. TS - Refractive index variations.
D The improvement in pulse spreading by mode coupling is given as : TU where, C is constant independent of all dimensional quantities and refractive indices. For a CI graded index fiber, the effect of distance on pulse broading for various coupling losses are shown in Fig. IN TS x Significant mode coupling occurs of connectors, splices and with other passive components of an optical link.
TU - Low attenuation. TS x Basic design — optimization includes the following : - Cut-off wavelength. CI - Bending loss. Refractive Index Profile x Dispersion of single mode silica fiber is lowest at nm while its attenuation is minimum at nm. For archiving maximum transmission distance the dispersion null should be at the wavelength of minimum attenuation. Therefore a variety of core-cladding refractive idex configuration fivers. Such as nm — optimized fibers, dispersion shifted fibers, dispersion — flattened fibers and large effective core area fibers.
The two configurations of nm — optimized single mode fibers are : a Matched cladding fibers. IN b Dressed cladding fibers. Typical diameter is 9. Typical diameter is 8. Fig 2. Two configurations of dispersion shifted fibers are : a Step index dispersion shifted fiber. Dispersion Flattened x Dispersion flattened fibers are more complex to design.
It offers much broader span of wavelengths to suit desirable characteristics. Two configurations are :. Different formulae are used to. IN calculate dispersions for variety of fiber at different wavelength. Cut-off Frequency of an Optical Fiber x The cut-off frequency of an optical fiber is determined not only by the fiber itself modal dispersion in case of multimode fibers and waveguide dispersion in case of single mode fibers but also by the amount of material dispersion caused by the spectral width of transmitter.
IN Bending Loss Limitations x The macrobending and microbending losses are significant in single mode fibers at nm region, the lower cut-off wavelengths affects more.
D EN TU x The bending losses are function of mode-filed diameter, smaller the mode-field diameter, the smaller the bending loss. If the bend radius is TS less, the losses are more and when the radius is more, the bending losses are less.
Briefly explain material dispersion with suitable sketch. Give expression of pulse broadening in graded index fiber. State the significance of mode coupling in optic fiber communication.
Explain in detail the design optimization of single mode fibers. Elaborate dispersion mechanism in optical fibers. The optical signal is then launched into the fiber. Optical source is the major component in an optical transmitter. Characteristics of Light Source of Communication TS x To be useful in an optical link, a light source needs the following characteristics: i It must be possible to operate the device continuously at a variety of temperatures for many years.
EN iii For fiber links, the wavelength of the output should coincide with one of transmission windows for the fiber type used. D v To reduce material dispersion in an optical fiber link, the output spectrum should be narrow. TU vi The power requirement for its operation must be low. TS ix Better linearity of prevent harmonics and intermodulation distortion. CI xiii Low weight and low cost. As the carriers are not confined to the immediate vicinity of junction, hence high current densities can not be realized.
IN between p-type and n-type layers. The middle layer may or may not be doped. The carrier confinement occurs due to bandgap discontinuity of the junction. Such a junction is call heterojunction and the device is called double heterostructure. LEDs are best suitable optical source. A heterojunciton is a junction formed by dissimilar semiconductors. Double heterojunction DH is formed by two different semiconductors on each side of active region. IN TS x The crosshatched regions represent the energy levels of freecharge.
The two materials have different bandgap energies and different refractive indices. The changes in bandgap energies create potential barrier for both holes and electrons. The free charges can recombine only in narrow, well defined active layer side. D x A double heterjuction DH structure will confine both hole and electrons to a narrow active layer.
Under forward bias, there will be a large number of carriers injected into TU active region where they are efficiently confined. Carrier recombination occurs in small active region so leading to an efficient device.
Antoer advantage DH structure is that the active region has a higher refractive index than the materials on either side, hence light emission occurs in an optical waveguide, which serves to narrow the output beam.
Surface emitting LED. Edge emitting LED. Both devices used a DH structure to constrain the carriers and the light to an active layer. A circular well is etched through the substrate of the device. A fiber is then connected to accept the emitted light. IN TS x At the back of device is a gold heat sink. The current flows through the p-type material and forms the small circular active region resulting in the intense beam of light. The beam intensity is maximum along the normal.
The radiation pattern decides the coupling efficiency of LED. IN guiding layers. The refractive index of guiding layers is lower than active region but higher than outer surrounding material. Thus a waveguide channel is form and optical radiation is directed into the fiber. The beam is Lambartian in the plane parallel to the junction but diverges TU more slowly in the plane perpendicular to the junction.
In this plane, the beam divergence is limited. In the parallel plane, there is no beam confinement and the radiation is Lambartian. To maximize the useful output power, a reflector may be placed at the end of the diode opposite the emitting edge. Linear relationship between optical output and current. Modulation bandwidth is much large. Not affected by catastrophic gradation mechanisms hence are more reliable.
ELEDs have better coupling efficiency than surface emitter. ELEDs are temperature sensitive. Usage :. LEDs are suited for short range narrow and medium bandwidth links.
Long distance analog links. TS Light Source Materials x The spontaneous emission due to carrier recombination is called electro luminescence. To encourage electroluminescence it is necessary to select as appropriate semiconductor EN material.
The semiconductors depending on energy bandgap can be categorized into, 1. Direct bandgap semiconductors. Indirect bandgap semiconductors. In direct bandgap semiconductors the electrons and holes on either side of bandgap have same value of crystal momentum. Hence direct recombination is possible. The recombination occurs within to sec. The recombination in these semiconductors is quite slow i. In direct bandgap. IN semiconductor, electrons and holes can recombine directly without need of third particle to conserve momentum.
In these materials the optical radiation is sufficiently high. Some tertiary allos Ga1-x Alx As are also used. The width of emission spectrum at half CI power 0. IN Different materials and alloys have different bandgap energies.
TS x The bandgap energy Eg can be controlled by two compositional parameters x and y, within direct bandgap region. Two expression relating Eg and x,y are — EN … 3. Example 3. Find the wavelength emitted by this source. Solution : Comparing the alloy with the quartenary alloy composition. In1-x Gax As P1-y it is found that. Rnr is non-radiative recombination rate. It is also known as bulk recombination life time. The external quantum efficiency is used to calculate the emitted power.
The external quantum. IN efficiency is defined as the ratio of photons emitted from LED to the number of photons generated internally. It is given by equation … 3.
Determine the total carrier recombination life time and optical power generated internally if the peak emission wavelength si nm and the drive currect is 40 mA. The current injected is 40 Ma. Calculate — TU i Bulk recombination life time. Simple design. Ease of manufacture. Simple system integration. Low cost. High reliability. Disadvantages of LED 1. The average life time of a radiative recombination is only a few nanoseconds, therefore nodulation BW is limited to only few hundred megahertz.
Low coupling efficiency. Large chromatic dispersion. The operation of the device may be described by the formation of an electromagnetic EN standing wave within a cavity optical resonator which provides an output of monochromatic highly coherent radiation. Principle : D x Material absorb light than emitting. Three different fundamental process occurs between the two energy states of an atom.
TU 1 Absorption 2 Spontaneous emission 3 Stimulated emission. These processes are represented by the simple two-energy-level diagrams. TS Where E1 is the lower state energy level. E2 is the higher state energy level.
The frequency of the absorbed or emitted radiation f is related to the difference in energy E between the two states. If E1 is lower state energy level. The emission process can occur in two ways. A By spontaneous emission in which the atom returns to the lower energy state in EN random manner. B By stimulated emission when a photon having equal energy to the difference between the two states E2 — E1 interacts with the atom causing it to the lower state with the creation of the second photon.
Hence the light associated with emitted photon is of same frequency of incident photon, and in same phase with same polarization. The bouncing back and forth of light wave cause their intensity to reinforce and build-up. The result in a high brilliance, single frequency light beam providing amplification. Emission and Absorption Rates x It N1 and N2 are the atomic densities in the ground and excited states.
Rate of spontaneous emission. T is absolute temperature. The oscillator is formed by a resonant cavity providing a selective feedback.
The cavity is normally a Fabry-Perot resonator i. EN two parallel plane mirrors separated by distance L, D TU TS CI Light propagating along the axis of the interferometer is reflected by the mirrors back to the amplifying medium providing optical gain. The current at which lasing starts is the threshold current. Above this current the output power increases sharply.
IN x In DFB laster the lasing action is obtained by periodic variations of refractive index along the longitudinal dimension of the diode. IN x Lasing light amplification occurs when gain of modes exceeds above optical loss during one round trip through the cavity i.
If R1 and R2 are the mirror reflectivities of the two ends of laser diode. Now the expression for lasing expressing is modified as, TS … 3. IN Power Current Characteristics x The output optic power versus forward input current characteristics is plotted in Fig. Below the threshold current Ith only spontaneous TS emission is emitted hence there is small increase in optic power with drive current.
At threshold when lasing conditions are satisfied. The optical power increases sharply after the lasing threshold because of stimulated emission. For a Gaussian output the gain and frequency are related by expression — … 3.
At low drive current, the laser operates as an inefficient Led, When drive current crosses threshold TU value, lasing action beings. This enables the laser to easily couple to single mode fiber and reduces the amount of uncoupled light i.
Simple economic design. High optical power. Production of light can be precisely controlled. Can be used at high temperatures. Better modulation capability. High coupling efficiency. Low spectral width 3. Ability to transmit optical output powers between 5 and 10 mW. Ability to maintain the intrinsic layer characteristics over long periods. Disadvantages of Laser Diode 1. At the end of fiber, a speckle pattern appears as two coherent light beams add or subtract CI their electric field depending upon their relative phases.
Laser diode is extremely sensitive to overload currents and at high transmission rates, when laser is required to operate continuously the use of large drive current produces unfavourable thermal characteristics and necessitates the use of cooling and power stabilization.
Principle of operation Spontaneous emission. Stimulated emission. Output beam Non — coherent. Spectral width Board spectrum 20 nm — nm Much narrower nm. Data rate Low. Very high. Transmission distance Smaller. Temperature sensitivity Less sensitive.
More temperature sensitive. Coupling efficiency Very low. Multimode step index multimode Single mode Sl Multimode 8. Circuit complexity Simple Complex Life time hours. Cost Low. TU Linearly proportional to drive Proportional to current Output power current. Threshold current 5 to 40 Current required Drive current 50 to mA peak. Wavelengths available 0. Long distance high data Applications Moderate distance low data rate. LASER 1. The main requirement of light detector or photodector is its fast response.
For fiber optic communication purpose most suited photodetectors are PIN p-type- Instrinsic-n-type diodes and APD Avalanche photodiodes D x The performance parameters of a photodetector are responsivity, quantum efficiency, response time and dark current. The cut-off wavelength is TS determined by bandgap energy Eg of material. IN where, Ip is average photocurrent.
Pin is average optical power incident on photodetector. TS x Absorption coefficient of material determines the quantum efficiency. It is normally expressed in percentage. EN Detector Responsivity D TU x The responsivity of a photodetector is the ratio of the current output in amperes to the incident optical power in watts.
Responsivity is denoted by … 3. Germanium pin photodiode at 1. In GaAs pin photodiode at 1. As the intensity of optical signal at the receiver is very low, the TS detector has to meet high performance specifications. D x At present, these requirements are met by reverse biased p-n photodiodes. In these devices, the semiconductor material absorbs a photon of light, which excites an electron TU from the valence band to the conduction band opposite of photon emission.
The photo generated electron leaves behind it a hole, and so each photon generates two charge carriers. The increases the material conductivity so call photoconductivity resulting in an increase in the diode current.
The diode equation is modified as — TS … 3. Is is photo generated current due to incident optical signal. IN TS x Three regions can be seen forward bias, reverse bias and avalanche breakdown. If the diode is operated in this mode, the EN frequency response of the diode is poor and so photovoltaic operation is rarely used in optical links.
Under these condition, the exponential term in equation 3. They are usually very sensitive detectors. Unfortunately V-I characteristic is very steep in this region and so the bias voltage must be tightly controlled to prevent spontaneous breakdown.
IN TS x Sufficient reverse voltage is applied so as to keep intrinsic region free from carries, so its resistance is high, most of diode voltage appears across it, and the electrical forces are strong within it. The incident photons give up their energy and excite an electron from EN valance to conduction band.
Thus a free electron hole pair is generated, these are called as photocarriers. These carriers are collected across the reverse biased junction resulting in rise in current in external circuit called photocurrent.
If forward biased, they conduct large amount of current. In TU photovoltaic mode, no bias is applied to the detector. In this case the detector works very slow, and output is approximately logarithmic to the input light level. Real world fiber optic receivers never use the photovoltaic mode.
The output in this case is a TS current that is very linear with the input light power. It does not provide internal gain. The combination of different semiconductors operating at different wavelengths allows the selection of material capable of responding to the desired CI operating wavelength. Characteristics of common PIN photodiodes Sr. Rise time Tr nS 0. Bandwidth B GHz 0. Jdiff is diffusion current density due to carriers generated outside depletion region.
Pn is hole concentration in n-type material. EN Pn0 is equilibrium hole density. Substituting in equation 3. TS ii Diffusion time of photocarriers outside the depletion region. By considering the photodiode response time the effect of diffusion can be calculated. CT is sum of photodiode and amplifier capacitance.
Avalanche Photodiode APD x When a p-n junction diode is applied with high reverse bias breakdown can occur by two separate mechanisms direct ionization of the lattice atoms, zener breakdown and high. IN velocity carriers impact ionization of the lattice atoms called avalanche breakdown. APDs uses the avalanche breakdown phenomena for its operation. The APD has its internal gain which increases its responsivity. In this region, the E-field separates the carriers and the electrons drift into the avalanche region where carrier multiplication occurs.
Thus APDs are usually biased just below breakdown, with the bias voltage being tightly controlled. The middle semiconductor layer acts as optical absorbing layer. A Schottky barrier is formed at each metal semiconductor interface junction , which prevents flow of electrons.
D x When optical power is incident on it, the electron-hole pairs generated through photo absorption flow towards metal contacts and causes photocurrent. Each MSM photodetectors had distinct features e. An inverted MSM photodetector shows high responsivity when illuminated from top. APD 1. Questions Optical Source. List the characteristics of light sources required in optical communication. Describe the construction and working of LED.
Explain the structure of surface emitting and edge emitting LEDs. Deduce the expression at internal quantum efficiency and internally generated optical power for LED.
From this expression how external efficiency and power is calculated? Explain the principle of laser action. Explain also the spontaneous and stimulated emission process. Give the necessary conditions for lasing threshold. Explain the structure of — i Fabry-Perot resonator.
Derive expression for lasing condition and hence for optical gain. Explain the power current characteristics of laser diode. Give the expression for — TU i External quantum efficiency. State the significance of each parameter in the expression. TS Optical Detector 1. With a proper sketch briefly explain the structure of PIN diode. Explain the following term relating to PIN photodiode with proper expressions. CI i Cut-off wavelength. Explain the structure and principle of working of APD.
Deduce the expression for total current density for APD. How the response time of APD is estimated? Give expression for passband of APD detector. The interconnection of fiber causes some loss of optical power. Different techniques are used to interconnect fibers. A permanent joint of cable is. IN referred to as splice and a temporary joint can be done with the connector. The fiber — to — fiber coupling efficiency is given as — TS … 4. If the radiation cone of emitting fiber does not match the acceptance cone of receiving fiber, radiation loss takes place.
The magnitude of radiation loss depends on the degree of misalignment. Different types of mechanical misalignments are shown in Fig. Angular misalignment x Angular misalignment occurs when fiber axes and fiber end faces are no longer parallel. The axial offset reduces the common core area of two fiber end faces as shown in Fig.
IN x The optical power coupled is proportional to common area of two fiber cores. The common area is given by expression — TS … 4. D x The coupling efficiency for step index fiber is the ratio of common core area to the end- face area.
These includes, - Variation in core diameter. IN - Core area ellipticity. TS The user have less control over these variations since they are related to manufacturing process. EN x Coupling loss when emitter fiber radius aE and receiving fiber radius aR is not same, is given as — … 4. TS x Coupling loss when numerical apertures of two fibers are not equal, to expressed as — … 4. The end faces should be polished until all the scratches are removed and they become smooth. The process involves following steps.
The fiber is scratched to create a stress concentration at the surface. Fiber is then bent over a curved form with applied tension to produce stress distribution. Maximum stress occurs at scratch point and crack starts propagating through fiber. TS D EN TU TS Precaution x If the stress distribution is not properly controlled, fiber can fork into several cracks, various types of defects can be introduced in the fiber, few of them are mentioned here.
CI Sr. Defect Type Description A sharp protrusion, that prevents the core from coming to close 1. Lip contact. Roll off Rounding-off of the edge of fiber. Chip A localized fracture. Hackle Irregularities across fiber end.
Mist Similar to hackle. Step An abrupt change in end face surface. Shattering Result of uncontrolled fracture. And the process of joining two fibers is called as splicing. TS x Typically, a splice is used outside the buildings and connectors are used to join the cables within the buildings. Splices offer lower attenuation and lower back reflection than connectors and are less expensive.
The butted joint is heated with electric arc or laser pulse to melt the CI fiber ends so can be bonded together. These can be EN reduced by inserting index matching gel. The fiber ends are butted together in a V — shaped groove as shown in Fig. Radiance is defined as the optical power radiated into a solid angle per unit emitting surface area. Radiance is important for defining source to fiber coupling efficiency. Source Output Pattern x Spatial radiation pattern of source helps to determine the power accepting capability of fiber.
Where the polar axis is normal to the emitting. The emission pattern of Lambartian output is shown in Fig. IN x Both radiations in parallel and normal to the emitting plane are approximated by TS expression — … 4. Power Coupling Calculation D x To calculate power coupling into the fiber, consider an optical source launched into the TU fiber as shown in Fig. The coupled power P can be calculated as — … 4. Numerical aperture for graded index fiber is given by, D EN … 4. The power couple TS is reduced by factor, … 4.
R is the Fresnel reflection or reflectivity. In order to improve the coupling efficiency miniature lens is placed between source and fiber. Microlens magnifies the emitting area of source equal to core area. The power coupled increases by a factor equal to magnification factor of lens. See Fig. Rounded — end fiber. Spherical — surfaced LED and Spherical-ended fiber.
Taper ended fiber. Non imaging microsphere. Cylindrical lens, 6. Imaging sphere. EN x There are some drawbacks of using lens. Complexity increases. Fabrication and handling difficulty. Precise mechanical alignment is needed. At this junction certain amount of optical power approximately 0.
Also excess power loss occurs due to non propagating modes scattering out of fiber. This CI excess loss is shown in terms of fiber numerical aperture NA. EN x If the optical powers of measured in long fiber lengths under equilibrium of modes, the effect of equilibrium numerical aperture NAeq is significant.
Optical power at this point is given by, D … 4. TS x The degree of mode coupling is mainly decided by core — cladding index difference.
Hence NAeq is important while calculating launched optical power in telecommunication systems. Also LEDs are cost effective and reliable. Ps is total source output power. Suitable connector is chosen as per the requirement and cost. These are —.
Subscriber Channel SC connector. Straight Tip ST connector. MT-RJ connector. It has push-pull type locking system. It is more reliable than SC connector. ST connector has bayonet type locking system. Low coupling loss. Inter-changeability — No variation is loss whenever a connector is applied to a fiber. Ease of assembly. Low environmental sensitivity. Low cost — The connector should be in expensive also the tooling required for fitting.
Reliable operation. Ease of connection. Repeatability — Connection and reconnection many times without an increase in loss. Connector Types x Connectors use variety of techniques for coupling such as screw on, bayonet-mount, TS puch-pull configurations, butt joint and expanded beam fiber connectors.
Butt Joint Connectors CI x Fiber is epoxied into precision hole and ferrules are used for each fiber. The fibers are secured in a precision alignment sleeve. But joints are used for single mode as well as for multimode fiber systems. Two commonly used butt-joint alignment designs are : 1. IN TS x In tapered sleeve or biconical connector mechanism, a tapered sleeve is used to accommodate tapered ferrules.
The fiber end separations are determined by sleeve length and guide rings. Following are the basic steps for installing fibers — i Cut the cable one inch longer than the required finished length. Cut the exposed strength members and remove fiber coating. Never clean the fiber with dry tissue.
This prevents direct stress on the fiber. Connector Return Loss x At the connection point of optical link low reflectance levels are desired since the optical reflections can be source of unwanted feed back into the laser cavity. Due to this unwanted feedback the optical frequency response may degrade, also it generates internal noise within the source affecting overall system performance. IN connection model. CI R is reflectivity constant.
Recommended Questions 1. State the considerations for power coupling and power launching in a fiber optic system. Derive the expression for power coupling to a step index fiber by a surface emitting LED.
Derive the expression for power coupling to a graded index fiber by a surface emitting LED. Explain various types of misalignments in fiber cables. Derive the expression for power received by fiber for axial misalignment.
Give the expressions for various fiber-related losses. State the steps involved in cleaving process 8. Explain controlled fracture technique of cleaving. Define finer splicing. Explain different types of splicing. State the factors on which the power launching capability of source is dependent.
What is lensing schemes? With simple sketch show different lensing scheme. State the TS drawback of lensing schemes also. Explain equilibrium numerical aperture. Write note on laser diode to fiber coupling. State the principles of good connector design. List the steps involved in process of installing fiber optic connectors. IN quantum limit, eye diagrams, coherent detection, burst mode receiver operation, Analog receivers. TS D EN TU x Noise generated in receiver must be controlled precisely as it decides the lowest signal level that can be detected and processed.
Hence noise consideration is an important factor in receiver design. Another important performance criteria of optical receiver is average error probability. All noise sources are Gaussian in statistics. All nose sources are flat in spectrum. All noise sources are uncorrelated statistically independent.
Tb is bit period. Preamplifier circuit must be designed with the aim of optimizing these characteristics. Low — impedance preamplifier LZ TS 2. High — impedance preamplifier HZ 3. Transimpedance preamplifier TZ 1. Low — impedance preamplifier LZ x In low-impedance preamplifier, the photodiode is configured in low — impedance CI amplifier.
The bias resister Rb is used to match the amplifier impedance. Rb along with the input capacitance of amplifier decides the bandwidth of amplifier. Therefore the low — impedance amplifier are used where sensitivity is of not prime concern. This can be achieved by — - Reducing input capacitance by selecting proper devices. As the high impedance circuit has large RC time constant, the bandwidth is reduced. IN of high input impedance pre-amplifier.
TS EN x High-input impedance preamplifier are most sensitive and finds application in long — D wavelength, long haul routes. A differentiating, equalizing or compensation network at the receiver output corrects for this integration.
Transimpedance preamplifier TZ TS x The drawbacks of ghigh input impedance are eliminated in transimpedance preamplifier. If the link does not work, then you can send your request to us by clicking here or comment below.
This book is very useful for the practical purpose of the subject optical fiber and communication. This book provides a comprehensive account of fiber-optic communication systems.
The 3rd edition of this book is used worldwide as a textbook in many universities. This 4th edition incorporates recent advances that have occurred, in particular two new chapters. The second chapter focuses on new techniques such as all-optical regeneration that are under development and likely to be used in future communication systems.
All other chapters are updated, as well. If you found this blog helpful to you for finding an optical fiber communication book pdf easily than comment below we are happy to help you. And if you have any rare pdf for optical fiber communication than please share us at collectallpdf gmail. Anonymous April 28, at PM. Social Plugin. Most Recent.
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