To find the numerical aperture of a given optic fibre and hence to find its acceptance angle. Aim of experiment: In this experiment, we measure the numerical aperture. The numerical aperture of optical fibers of the second fiber bundle 52 is larger than the numerical aperture of optical fibers of the first fiber bundle 51. Numerical aperture of the optic fiber is = ………………… Angle of acceptance = ………………. Optical Fiber Communication Note: Answer of questions are in bold options UNIT-1 1. The numerical aperture of an optical fiber is an abstract term for the acceptance angle of the fiber. Thanks. i.e. But no such material exists that has lower refractive index than 1. Graded-index multimode fibers have a […] In this way light can be taken anywhere because fibers have enough flexibility. But the condition of total internal reflection for the propagation of light ray comes into action only when most of the light is collected inside the fiber. The short form of this is NA that illustrates the efficiency with the light which is collected within the fiber to get propagated. However, it is possible to continue the ray theory analysis to obtain a relationship between the acceptance angle and the refractive indices of the three media involved, namely the core, cladding and air. What is the Numerical Aperture of Optical Fiber? an imaging system) is a measure for its angular acceptance for incoming light. The numerical aperture of an optical fiber is determined by the relative magnitudes of the refractive indices in the core and in the cladding. This angle α is known as the acceptance angle of the fiber. Thus several parameters must be taken into consideration, for selecting the appropriate optical fiber for signal propagation. This is the expression for the numerical aperture of an optical fiber, having ƞ1 as the refractive index of core and ƞ2 as the refractive index of the cladding. Simulator . NA= Sin θa where θa, is called acceptance cone angle. So, the ray XA is launched from denser medium to rarer medium by making an angle α with the fiber axis. Since  light is guided through the fiber it is sometimes called an optical wave guide. Numerical aperture (NA) is a critical performance specification for multimode fibers. Consider a light ray (i) entering the core at a point A , travelling through the core until it reaches the core cladding boundary at point B. 4.3 Numerical Aperture. Numerical aperture is abbreviated as NA and shows the efficiency with which light is collected inside the fiber in order to get propagated. The basic construction of an optic fiber is shown in figure (1). Numerical Aperture is defined as the Sine of half  of the angle of fibre’s light acceptance cone. This incident ray propagates inside the fiber and gets reflected completely by the core-cladding interface. But for this, the angle of the incident should be more as compared to the critical angle. Total internal reflection occurs only when the angle of incidence is greater than the critical angle. While, for optical signal propagation, the only motive is not to have high accepting range but also to propagate the accepted signal with minimal attenuation. Light Collection b. In most areas of optics, and especially in microscopy, the numerical aperture of an optical system such as an objective lens is defined by NA= n sin where nis the index of refraction of the medium in which the lens is working (1.0 for air, 1.33 for pure water, and up to 1.56 for oils; see also list of refractive indices), and is the half-angle of the maximum cone of light that can enter or exit the lens. So, let us now understand the numerical aperture for optical fiber in detail. The fractional refractive index change is the fractional difference between the refractive indices of core and cladding. Numerical Aperture is defined as the maximum acceptance angle to allow and transmit light by an optical fiber. Theory Procedure Self Evaluation Simulator Assignment Reference Feedback Sign in to view the content Only an authenticated user can view this page. Problem 1 let n = 1, n 1 = 1.46 and n 2 = 1.45 in the diagram of the optical fiber system Numerical aperture The acceptance angle for an optical fiber was defined in the preceding section. Answer: Numerical Aperture is the measure of the ability of an optical fiber to collect or confine the incident light ray inside it. This means that to be guided through an optic fibre, a light ray must enter the core with an angle less than a particular angle called the acceptance angle of the fibre. However, the greater value of NA will be achieved only when the difference between the two refractive indices is high and for this either, ƞ1 is to be high or ƞ2 to be low. Theory Procedure Self Evaluation Simulator Assignment Reference Feedback Bibliography: Woodward, Bill and Emile B. Husson. Nice explanation of the numerical aperture. 「optical numerical aperture」に関連した英語例文の一覧と使い方(2ページ目) - Weblio英語例文検索 例文検索の条件設定 「カテゴリ」「情報源」を複数指定しての検索が可能になりました。( プレミアム会 … 例文帳に追加 第1ファイバ束51の光ファイバの開口数よりも第2ファイバ束52の光ファイバの開口数の方が大きくされている。 Δ = (η1- η2)/ η1 Theory Consider the geometry of Fig. As long as the light ray intersects the core-cladding boundary at a small  angles, the ray will be reflected back in to the core to travel on to point C where the process of reflection is repeated .ie., total internal reflection takes place. As we have already discussed that light through an optical fiber is propagated by several continuous total internal reflections. Theory . Therefore, for light to be propagated within the core of optical fiber as guided wave, the angle of incidence at core-cladding interface should be greater than θ'c. Numerical aperture is thus considered as a light gathering capacity of an optical fibre. numerical aperture The measurement of the acceptance angle of an optical fiber, which is the maximum angle at which the core of the fiber will take in light that will be contained within the core. The numerical aperture of optical fibers of the second fiber bundle 52 is larger than the numerical aperture of optical fibers of the first fiber bundle 51. 8) In an optical fiber, the concept of Numerical aperture is applicable in describing the ability of _____ a. This  property makes them suitable for data communication, design of fine endoscopes, micro sized microscopes etc. We know light through an optical fiber is propagated through total internal reflection. It is the product of the Procedure . Optical fibers are fine transparent glass or plastic fibers which propagate light using the phenomenon of total internal reflection from diametrically opposite walls. Definition: Numerical Aperture is the measure of the ability of an optical fiber to collect or confine the incident light ray inside it. Numerical aperture of an optical fiber. The numerical aperture of an optical fiber system as the one shown in the diagram below, has been defined and all important formulas found. In order to understand the propagation of light through an optical fibre, consider the figure (2). In this way light may be taken anywhere because fibers have enough flexibility. Then. The numerical aperture of an optical fiber is determined by the relative magnitudes of the refractive indices in the core and in the cladding. Your email address will not be published. Theory . Definition: Numerical Aperture is the measure of the ability of an optical fiber to collect or confine the incident light ray inside it. i.e. As higher the value of NA, better will be the optical fiber. The higher an optical fiber’s NA, the larger the cone of light that can be coupled into its core. Procedure . Acceptance angle or Numerical aperture Let us consider an optical fibre having a core with refractive index n1 and cladding with refractive index n2 such that (n1 > n2). The exact definition of the term varies slightly between different areas of optics. Where n0 is refractive index of medium outside the fiber. For air n0 =1. Qualitatively, NA is a measure of the light gathering ability of a fiber. It also indicates how easy it is to couple light into a fiber. According to Snell’s law, the incident and refracted ray propagate in the same plane. A numerical aperture of optical fibers calculator is included in this site and may be used to check the calculations in the following problems. In the first illustration above, notice that angle A is shown at both the entrance and exit ends of the fiber. let the incident light makes an angle i with the core axis as shown in figure (3). Self Evaluation . As i increases,  θ increases and so θ' decreases. They work under the principle of total internal reflection from diametrically opposite walls. Start button: To start the experiment. By incorporating index of refraction in its definition, NA has the property that it is constant for a beam as it goes from one material to another, provided there is no refractive power at the interface. In optics, the numerical aperture (NA) of an optical system is a dimensionless number that characterizes the range of angles over which the system can accept or emit light. Optical fibers are fine transparent glass or plastic fibers which can propagate light. The figure below shows an optical fiber inside which light ray is focused. Switch on: To switch on the Laser. Theory Consider the geometry of Fig. The refractive index of the launching medium is n 0. The significance of NA is that light entering in the cone of semi vertical angle im only propagate through the fibre. NA is related to acceptance angle. Using Snell’s laws at core cladding interface. 1 Fiber Optic Apparatus: NA Measurements Objective : To measure the numerical aperture (NA) of an optical fiber with the help of Fiber Optic Apparatus and hence to deduce V-number for the optical fiber. So, reflection back in to the core does not take place and the light ray is lost in the cladding. Thus we can say that the light gathering efficiency of an optical fiber is the key characteristic while transmitting a signal through an optical fiber. Procedure for simulator Controls . Rays launched outside the angle specified by a fiber's NA will excite radiation modes of the fiber. The Numerical Aperture (NA) of a fiber is defined as the sine of the largest angle an incident ray can have for total internal reflectance in the core. Then the light gets refracted at an angle θ and fall on the core-cladding interface at an angle where. So, the light is propagated inside the fiber by performing continuous reflections from the cladding. In the case of silica fiber, the difference between these indices cannot be too large, otherwise the residual thermal stresses in … Numerical Aperture is defined as the Sine of half of the angle of fibre’s light acceptance cone. Difference Between Optical fiber and Coaxial Cable, Advantages and Applications of an Induction Generator, Rotor Resistance Control of an Induction Motor, Voltage Regulation of a Synchronous Generator, Two Wattmeter Method of Power Measurement, Difference Between Conduction and Convection, Difference Between Circuit Switching and Packet Switching, Difference Between Static and Kinetic Friction, Difference Between Ductility and Malleability, Difference Between Physical and Chemical Change, Difference Between Alpha, Beta and Gamma Particles, Difference Between Electrolytes and Nonelectrolytes, Difference Between Electromagnetic Wave and Matter Wave. A ray which enters the fiber with an angle greater than the acceptance angle will be lost in the cladding. Numerical Aperture of Optical Fiber.. It indicates the maximum angle at which a particular fiber can accept the light that will be transmitted through it. By Snell’s law at the point of entrance of light in to the optical fiber we get. The higher the value of im or NA more is the light collected for propagation in the fibre. So we can conclude that as the numerical aperture shows the light collecting ability of the fiber thus its value must be high. Pak L. Chu, in Guided Wave Optical Components and Devices, 2006. This is so because an optical fiber that has the greatest light gathering efficiency but does not allow light propagation through it properly, is not of any use. However, it is possible to continue the ray theory analysis to obtain a relationship between the acceptance angle and the refractive indices of the three media involved, namely the core, cladding and air. Measuring Numerical Aperture of Optical Fiber. Because of refraction at the fiber–air interface, the ray bends toward the normal. Or we can say multiple TIR takes place inside the optical fiber for the light ray to get transmitted from an end to another through an optical fiber. Multimode fibers allow propagation of more than 100 modes through them. Measuring Numerical Aperture of Optical Fiber Aim of experiment: In this experiment, we measure the numerical aperture. Therefore, there is maximum value of angle of incidence beyond which, it does not propagate rather it is refracted in to cladding medium ( fig: 3(b)). Basically when the light is emitted from an optical source, then the fiber must be highly efficient so as to collect the maximal emitted radiation inside it. Save my name, email, and website in this browser for the next time I comment. Numerical aperture The acceptance angle for an optical fiber was defined in the preceding section. If η1 is the refractive index of core and η2 is that of cladding. It is among the most basic property of optical fiber. The factors deciding the number modes that can be travelled though a multimode … Numerical aperture is thus considered as a light gathering capacity of an optical fibre. Thanks. Consider a light ray XA, that incident inside the optical fiber. Hence, on applying Snell’s law at medium 1 (usually air) and core interface. (1), where a ray making an angle θi with the fiber axis is incident at I was able to turn in my assignment on time due to this , Your email address will not be published. As we know that an optical fiber is composed of a core which is made up of a very pure form of glass silica and is surrounded by a glass cladding. The Numerical Aperture is an important parameter of any optical fiber, but one which is frequently misunderstood and overemphasized. Numerical aperture is abbreviated as NA and shows the efficiency with which light is collected inside the fiber in order to get propagated. On putting the value of θ from the above equation in equation 1, we get, Applying Snell’s law at core-cladding interface, we get, Substituting the above value in equation 4, Substituting the above value in equation 3, we get. Numerical aperture is commonly used in microscopyto describe the a… NA= Sin θ a where θ a , is called acceptance cone angle. The core  transmits an optical signal while the  cladding  guides the light within the core. An optical fiber with ‘high’ numerical aperture will confine light more strongly in the core, and so support guidance further above cut-off. The numerical aperture of an optical fiber system as the one shown in the diagram below, has been defined and all important formulas found. Numerical Aperture of Optical Fiber.. It is among the most basic property of optical fiber. Otherwise, if the incident angle is less the critical angle then rather being reflected, the ray gets refracted. It is among the most basic property of optical fiber. Feedback . 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