TO DETERMINE THE NUMERICAL APERTURE OF A GIVEN OPTICAL FIBER. 2. Sunil Kumar 3. Varun Sharma 4. Jaswinder Singh

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1 TO DETERMINE THE NUMERICAL APERTURE OF A GIVEN OPTICAL FIBER Submitted to: Mr. Rohit Verma Submitted By:. Rajesh Kumar. Suil Kumar 3. Varu Sharma 4. Jaswider Sigh

INDRODUCTION TO AN OPTICAL FIBER Optical fiber: a optical fiber is a dielectric wave guide made of glass ad plastic which is used to guide ad cofie a

2 INDRODUCTION TO AN OPTICAL FIBER Optical fiber: a optical fiber is a dielectric wave guide made of glass ad plastic which is used to guide ad cofie a electromagetic wave ad work o the priciple to total iteral reflectio (TIR). The diameter of the optical fiber may vary from 0.05 mm to 0.5mm. Costructio Of A Optical Fiber:

3 (Where N, N, N3 are the refractive idexes of core, claddig ad sheath respectively) Core: it is used to guide the electromagetic waves. Located at the ceter of the cable maily made of glass or sometimes from plastics it also as the highest refractive idex i.e. N. Claddig: it is used to reduce the scatterig losses ad provide stregth to the core. It has less refractive idex tha that of the core, which is the mai cause of the TIR, which is required for the propagatio of height through the fiber. Sheath: it is the outer most coatig of the optical fiber. It protects the core ad claddig from abrasio, cotamiatio ad moisture. Requiremet for makig a optical fiber:. It must be possible to make log thi ad flexible fiber usig that material. It must be trasparet at a particular wavelegth i order for the fiber to guide light efficietly. 3. Physically compatible material of slightly differet idex of refractio must be available for core ad claddig. Type Of Optical Fibers:. Glass Core + Glasss Claddig. Plastic Core + Plastic Claddig 3. Glass Core + Plastic Claddig

4 Properties Of Differet Types Of Idex Fibers Sigle Mode Step Idex Fiber Multi Mode Step Idex Fiber Multi Mode Graded Idex Fiber diploma of core -5 µm. >80 µm 50-60µm Diameter of claddig 0. 3 Step idex profile Step idex profile Graded idex profile. 4. Fudametal mode i.e. axial mode. 5. Laser are used for a fie beam of light Fudametal as well as higher mode LED s are used Fudametal as well as higher mode. LED s are used 6. NA ad Ǿ max is very small so they are difficult to work with NA ad Ǿ max is large easier to work with NA ad Ǿ max is large easier to work with 7. Dispersio 0. Which is very small ad is cosidered as 0 Dispersio is 5-30 s/km Dispersio is s/km 8. Supports bad width of 000 GHz-Km 9. N max =V /; V=πa(NA)/λ; V.405 0MHz-Km N max = V /; V=πa(NA)/λ; V.405 > GHz-km N max = V /; V=πa(NA)/λ; to οο 0. Used i military applicatio Used i short-rus< km as scatterig losses are large, these are easy to termiate. Used i log-rus ad are easy to termiate, as scatterig losses are less i compariso. Most expesive Least expesive More expesive tha multimode step idex fiber.

5 NUMERICAL APERTURE OF AN OPTICAL FIBER I optics, the umerical aperture (NA) of a optical system is a dimesioless umber that characterizes the rage of agles over which the system ca accept or emit light. The exact defiitio of the term varies slightly betwee differet areas of optics. Multimode optical fiber will oly propagate light eters the fiber withi a certai coe, kow as the acceptace coe of the fiber. The half-agle of this coe is called the acceptace agle, Ǿ max. For step-idex multimode fiber, the acceptace agle is determied oly by the idices of refractio: Where f is the refractive idex of the fiber core, ad c is the refractive idex of the claddig This has the same form as the umerical aperture i other optical system, so it has become commo to defie the NA of ay type of fiber to be Where o is the refractive idex alog the cetral axis of the fiber. Note that whe this defiitio is used, the coectio betwee the NA Ad the acceptace agle of the fiber become oly a approximatio. I particular maufacturers ofte NA for sigle mode fiber is quite differet ad caot be determied fro the idices of refractio aloe. I multimode fiber, the term equilibrium umerical aperture is sometime used. This refer to the umerical aperture with respect to the extreme exit agle of a ray emergig from a fiber i which equilibrium mode distributio has bee established. The umerical aperture of a optical ca be expressed quatitatively as: - N N =( + )={( + )/}( ) (We approximate ( + )/ as ) Hece,

7 Observatio Table S.NO. Distace From Scree From Optical Fiber Distace Of The Spot NA.30cm.cm cm.cm cm 3.0cm

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10 EXPERIMENT OBJECTIVE-: To measure the umerical aperture of the optical fiber. APPARATUS-: Fiber optical traier kit. THEORY-: Numerical aperture of the optical fiber is maximum agle at which the light icidet o the fiber ed is trasmitted log the fiber. The light ray should strike the fiber ed withi its core of acceptace else it is reflected Out of the fiber Cosideratio i umerical aperture measure: - It is very importat that the optical source should be properly aliged with the cable ad the distace from the lauched poit ad cable be properly selected to esure that the maximum amout of optical fiber power is trasferred to the cable. PROCEDURE: - Coect the power supply to the abroad. Coect the frequecy geerator KHz sie wave output to iput of emitter curret. Adjust its amplitude at 5 v. p. p. Coect oe ed of the fiber cable to the output socket of emitter curret ad the other ed to the N.A measuremet. Hold the white scree facig such that its cut face is perpedicular to the axis of the fiber. Hold the white scree with 4 cocetric circles (0,5,0,5mm diameter) vertically at a distace to make the red spot from the fiber coicide with 0mm spot. Record the distace of scree from the fiber from ed perpedicular ad ote the diameter w of the fiber. Capture the N.A. from the formula give below. W N.A. = 4L +W. Vary the distace betwee the scree ad optical fiber cable ad make it coicide with oe of the cocetric circles. Note the distace.. Tabulate the various distace ad diameter of the circle made oe the white scree ad compute the N.A. from the formula give below.

11 FORMULAE Acceptace Agle Ad Acceptace Coe Let s cosider the light propagatio i a optical fiber. The ed at which the light eters the fiber is called the lauchig ed. Let the refractive idex of the core be ad the refractive idex of claddig be ( > ). Let the outside medium from which the light is lauched ito the fiber have a refractive idex 0. Let the light ray eter the fiber at a agle θ i to the axis of the fiber. Let the refracted ray make a agle θ r with the axis ad strike the core claddig iterface at a agle φ. If φ>θ c (critical agle), the rays udergoes TIR at the iterface. As log as φ θ c, the light remais withi the fiber. Applyig sell s law to the lauchig face of the fiber, we get 0Siθ i = Siθr i.e. Siθ = Siθ i r 0 i.e. Siθ i = Si(90 φ) φ 0 i.e. Siθ = Cosφ θ i i θ r 0 Where φ=θ c, θ i =θ max So Siθ = Cosθ max c Now 0 Si = Hece Siθ θ so c = Cosθ c = Si θ max 0 If ( - ) 0, the for all values of θ i <θ max TIR will occur. Assumig 0 =i.e. let the outside medium from which light is lauched ito the fiber be air the, θ max = Si [ c = Numerical Aperture It is the measure of the amout of light ca be accepted by a fiber. It is defied as the Sie of the acceptace agle i.e. ] NA= Si max =

12 i.e. + = + = = ) ( ) )( ( NA because for optical fibers.

Geometrical Optics Fiber optics

Phys 322 Lecture 15 Chapter 5 Geometrical Optics Fiber optics First optical commuicatio Alexader Graham Bell 1847-1922 1880: photophoe 4 years after ivetig a telephoe! Fiberoptics: first lightguide 1870: