PHYSICS PROJECT ON
Optical Fiber and its Applications
Submitted by:
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CERTIFICATE This is to certify that Sumit Sapra, student , St.Theresa's Convent Sr. Sec. School, of Class XII Karnal has completed theproject titled . Optical Fiber and its Applications during the academic year 2012-13 towards partialfulfillment of credit for the Physics ractical evaluation of AISSCE 2013, and submitted satisfactory report, ascompiled in the following pages, under my supervision. “
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(Teacher’s Signature)
Acknowledgement
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The project could have never been possible without the support of various sources. It is etremel! impossible to thank ever! individual who has helped me in completing this project. Some people have helped in the basic formulari"ation and there were sources that helped me in giving the ideas a ph!sical form#shape .I am etremel! grateful to m! mentor$ %r &aswant 'edhu $ for his invaluable guidance in the project right from the beginning. is vital support helped the project to take a logical and suitable shape. I take this opportunit! to thank the School authorities$ for etending their full support and cooperation in the project.
ast but not the least* I would like to thank ever!one who has o+ered a helping hand when re,uired. NISHITH XII A
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Important Terms
Optical Fiber: An optical fiber (or fibre) is a glass or plastic fiber that carries light along its length. Optical fibers are widely used in fiber-optic communications, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communications.
Refraction: Refraction is the change in direction of a wave due to a change in its speed. This is most commonly observed when a wave passes from one medium to another.
Reflection: Reflection is the change in direction of a wave front at an interface between two different media so that the wave front returns into the medium from which it originated. ommon e!amples include the reflection of light, sound and water waves.
Scattering: "cattering is a general physical process where some forms of radiation, such as light, sound, or moving particles, are forced to
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deviate from a straight tra#ectory by one or more locali$ed nonuniformities in the medium through which they pass.
Attenuation: is the gradual loss in intensity of any %ind of flu! through a medium. &or instance, sunlight is attenuated by dar% glasses, and '-rays are attenuated by lead.
Total Internal Reflection Total internal reflection is an optical phenomenon that happens when a ray of light stri%es a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface. f the refractive inde! is lower on the other side
of the boundary and the incident angle is greater than the critical angle, no light can pass through and all of the light is reflected.
Optical Fiber Cable (OFC) ptical /ibers are used in communication instead of metal wires because signals travel along them with less loss$ and the! are also immune to electromagnetic interference. /ibers are also used for illumination$ and are wrapped in bundles so the! can be used to carr! images$ thus allowing viewing in tight spaces. Speciall! designed 0bers are used for a variet! of other applications$ including sensors and 0ber lasers. ight is kept in the core of the optical 0ber b! total internal re1ection. This causes the 0ber to act as a waveguide. /ibers which support man! propagation paths or transverse modes are called multi2mode 0bers (%%/)$ while those which can onl! support a single mode are called single2mode 0bers (S%/). %ulti2mode 0bers generall! have a larger core diameter$ and are used for short2distance communication links and for applications where high power must be transmitted. Single2mode 0ber are used for most communication links longer than 334 meters (5$644 ft).&oining lengths of optical 0ber is more comple than joining electrical wire or cable. The ends of the 0bers must be carefull! cleaved$ and then spliced together either mechanically or by fusing them together with an electric arc.
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Applications
Optical fiber communication ptical 0ber can be used as a medium for telecommunication and networking because it is 1eible and can be bundled as cables. It is especiall! advantageous for long2distance communications$ because light propagates through the 0ber with little attenuation compared to electrical cables. This allows long distances to be spanned with few repeaters. Additionall!$ the per2channel light signals propagating in the 0ber can be modulated at rates as high as 555 gigabits per second$ although 54 or 748b#s is t!pical in deplo!ed s!stems. 9ach 0ber can carr! man! independent channels$ each using a di+erent wavelength of light (wavelength2division multipleing (:;%)). /or short distance applications$ such as creating a network within an o44 !ards)$ and single2mode 0ber used for longer distance links. =ecause of the tighter tolerances re,uired to couple light into and between single2mode 0bers (core diameter about
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54 micrometers)$single2mode transmitters$ receivers$ ampli0ers and other components are generall! more epensive than multi2mode components.
/iber optic sensors &ibers have many uses in remote sensing. n some applications, the sensor is itself an optical fiber. n other cases, fiber is used to connect anon-fiber optic sensor to a measurement system. *epending on the application, fiber may be used because of its small si$e, or the fact that no electrical power is needed at the remote location, or because many sensors can be multiple!ed along the length of a fiber by using different wavelengths of light for each sensor, or by sensing the time delay as light passes along the fiber through each sensor. Optical fibers can be used as sensors to measure strain, temperature ,pressure and other +uantities by modifying a fiber so that the +uantity to be measured modulates the intensity, phase, polari$ation, wavelength or transit time of light in the fiber. "ensors that vary the intensity of light are the simplest, since only a simple source and detector are re+uired. A particularly useful feature of such fiber optic sensors is that they can, if re+uired, provide distributed sensing over distances of up to one meter.
!trinsic fiber optic sensors use an optical fiber cable, normally a multimode one, to transmit modulated light from either a non-fiber optical sensor, or an electronic sensor connected to an optical transmitter. A ma#or benefit of e!trinsic sensors is their ability to reach places which are otherwise inaccessible. An e!ample is the measurement of temperature inside aircraft #et engines by using a fiber to transmit radiation into a radiation pyrometer located outside the engine. !trinsic sensors can also be used in the same way to measure the internal temperature of electrical transformers, where the e!treme electromagnetic fields present ma%e other measurement techni+ues impossible. !trinsic sensors are used to measure
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vibration, rotation, displacement, velocity, acceleration, tor+ue ,and twisting.
Other uses of optical bers /ibers are widel! used in illumination applications. The! are used as light guides in medical and other applications where bright light needs to be shone on a target without a clear line2of2sight path. In some buildings$ optical 0bers are used to route sunlight from the roof to other parts of the building (see non2imaging optics). ptical 0ber illumination is also used for decorative applications$ including signs$ art$ and arti0cial ?hristmas trees. Swarovski bouti,ues use optical 0bers to illuminate their cr!stal showcases from man! di+erent angles while onl! emplo!ing one light source .ptical 0ber is also used in imaging optics. A co herent bundle of 0bers is used$ sometimes along with lenses$ for a long$ thin imaging device called an endoscope$ which is used to view objects through a small hole. %edical endoscopes are used for minimall! invasive eplorator! or surgical procedures (endoscop!). Industrial endoscopes (see 0berscope or bore scope) are used for inspecting an!thing hard to reach$ such as jet engine interiors. In spectroscop!$ optical 0ber bundles are used to transmit light from a spectrometer to a substance which cannot be placed inside the spectrometer itself$ in order to anal!"e its composition. A spectrometer anal!"es substances b! bouncing light o+ of and through them. =! using 0bers$ a spectrometer NISHITH XII A
can be used to stud! objects that are too large to 0t inside$ or gasses$ or reactions which occur in pressure vessels .ptical 0ber can be used to suppl! a low level of power (around one watt) to electronics situated in a di
@rinciple of peration An optical 0ber is a c!lindrical dielectric waveguide (non conducting waveguide) that transmits light along its ais$ b! the process of total internal re1ection. The 0ber core is surrounded b! a cladding la!er Index
of Refraction ( Refrective Index)
The inde of refraction is a wa! of measuring the speed of light in a material. ight travels fastest in a vacuum$ such as outer space. The NISHITH XII A
actual speed of light in a vacuum is about 44 million meters (56>thousand miles) per second. Inde of refraction is calculated b! dividing the speed of light in a vacuum b! the speed of light in some other medium. The inde of refraction of a vacuum is therefore 5$ b! de0nition .The t!pical value for the cladding of an optical 0ber is 5.7>. The core value is t!picall! 5.76. The larger the inde of refraction$ the slower light travels in that medium. /rom this information$ a good rule of thumb is that signal using optical 0ber for communication will travel at around B44million meters per second. r to put it another wa!$ to travel 5444kilometres in 0ber$ the signal will take 3 milliseconds to
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propagate. Thus a phone call carried b! 0ber between S!dne! and -ew Cork$ a 5B444kilometre distance$ means that there is an absolute minimum dela! of >4milliseconds (or around 5#5>th of a second) between when one caller speaks to when the other hears. Total Internal Reflection :hen light travelling in a dense medium hits a boundar! at a steep angle (larger than the Dcritical angleD for the boundar!)$ the light will be completel! re1ected. This e+ect is used in optical 0bers to con0ne light in the core. ight travels along the 0ber bouncing back and forth o+ of the boundar!. =ecause the light must strike the boundar! with an angle greater than the critical angle$ onl! light that enters the 0ber within a certain range of angles can travel down the 0ber without leaking out. This range of angles is called
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the acceptance cone of the 0ber. The si"e of this acceptance cone is a function of the refractive inde di+erence between the 0berEs core and cladding .In simpler terms$ there is a maimum angle from the 0ber ais at which light ma! enter the 0ber so that it will propagate$ or travel$ in the core of the 0ber. The sine of this maimum angle is the numerical aperture (-A) of the 0ber. /iber with a larger -A re,uires less precision to splice and work with than 0ber with a smaller -A. Single2mode 0ber has a small -A
Types of optical Fibers Single ode Fiber &iber supporting only one mode is called single-mode or mono-mode fiber. The behaviour of larger-core multi-mode fiber can also be modeled using the
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wave e+uation, which shows that such fiber supports more than one mode of propagation (hence the name). The results of such modeling of multimode fiber appro!imately agree with the predictions of geometric optics, if the fiber core is large enough to support more than a few modes.
ulti ode Fiber n a multi-mode fiber, rays of light are guided along the fiber core by total internal reflection. Rays that meet the core-cladding boundary at a high angle (measured relative to a line normal to the boundary), greater than the critical angle for this boundary, are completely reflected. The critical angle (minimum angle for total internal reflection) is determined by the difference in inde! of refraction between the core and cladding materials. Rays that meet the boundary at a low angle are refracted from the core into the cladding, and do not convey light and hence information along the fiber. The critical angle determines the acceptance angle of the fiber ,often reported as a numerical aperture. A high numerical aperture allows light to propagate down the fiber in rays both close to the a!is and at various angles, allowing efficient coupling of light into the fiber. owever, this high numerical aperture increases the amount of dispersion as rays at different angles have different path lengths and therefore ta%e different times to traverse the fiber
Bibliography oo!"#
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Physics
(Part 1&2) - Textbook for Class X /ationalouncil of
ducational Research and Training !"cyclo#edias
$eb"ite"# Image Courtesy: www.google.com0images www.wi%ipedia.org Source an other Information: www.google.com www.wi%ipedia.org
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