Explain the important conditions for TIR to exit in fiber. Derive an expression for maximum acceptance angle of a fiber. Explain the acceptance come of a fiber. Define numerical aperture and state its significance also. Explain the different types of rays in fiber optic.
What is mean by mode of a fiber? Explain the fiber materials used in fabrication requirements. In case of glass fibers how the refractive index can be varied? Briefly explain following techniques of fabrication.
IN modal dispersion. It is also known as fiber loss or signal loss. The signal attenuation of fiber determines the maximum distance between transmitter and receiver. The attenuation also determines the number of.
POF handbook : optical short range transmission systems
IN repeaters required, maintaining repeater is a costly affair. As the signal pulse travels along the fiber length it becomes more broader.
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After sufficient length the broad pulses starts overlapping with adjacent pulses. This creates error in the receiver. Hence TS the distortion limits the information carrying capacity of fiber. Absorption is because of fiber material and scattering due to structural imperfection within the fiber. Microbending of optical fiber also contributes to the attenuation of signal.
Glass is a silicon compound, by adding different additional chemicals to the basic silicon dioxide the optical properties of the glass can be changed. Attenuation Units x As attenuation leads to a loss of power along the fiber, the output power is significantly less than the couples power. Let the couples optical power is p 0 i. IN This parameter is known as fiber loss or fiber attenuation.
Handbook Fiber Optic Data Communication
TS x Attenuation is also a function of wavelength. Optical fiber wavelength as a function of wavelength is shown in Fig. Example 2. Determine —. IN 1 Overall signal attenuation in dB. Each splice introducing attenuation of 1 dB.
IN Example 2. The power at the end of 10 km length of the link working in first windows is — Another system of same length working in second window is Calculate fiber attenuation for each case and mention wavelength of operation. Attenuation in 3rd window:. IN … Ans. Wavelength in 1st window is nm. TS Wavelength in 2nd window is nm. Wavelength in 3rd window is nm. EN Example 2.
POF handbook : optical short range transmission systems
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.
Handbook Of Fiber Optics : Data Communication
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.
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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.