Fiber Optics Basics
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Questions and Answers

What is the principle behind the working of an optical fiber?

  • Refraction of light
  • Total internal reflection (correct)
  • Diffraction of light
  • Transmission of sound waves
  • What is the critical angle of incidence?

  • The angle of incidence when the angle of refraction is 90° (correct)
  • The angle of incidence when the reflected ray travels along the boundary
  • The angle of incidence when the refracted ray travels along the boundary
  • The angle of incidence when the angle of reflection is 90°
  • What happens when the angle of incidence is greater than the critical angle?

  • The refracted ray becomes bright
  • The refracted ray becomes weak
  • The reflected ray becomes weak
  • The reflected ray becomes bright (correct)
  • What is the formula to calculate the critical angle of incidence?

    <p>θc = sin(η1/η2)</p> Signup and view all the answers

    What is the purpose of an optical fiber communication system?

    <p>To transmit electronic signals through light</p> Signup and view all the answers

    What is the innermost region of an optical fiber called?

    <p>Core</p> Signup and view all the answers

    What is the phenomenon when light travels from a medium of higher refractive index to a medium of lower refractive index and is reflected back?

    <p>Total internal reflection</p> Signup and view all the answers

    What is the shape of an optical fiber?

    <p>Coaxial</p> Signup and view all the answers

    What is the condition for Rayleigh scattering loss to occur?

    <p>Size of density fluctuation is 1/10th of operating wavelength</p> Signup and view all the answers

    What type of bend in an optical fiber leads to attenuation due to small discontinuities or imperfections in the fiber?

    <p>Microscopic bending</p> Signup and view all the answers

    What is the maximum number of modes supported by a step-index fiber?

    <p>Nmax=v2/2</p> Signup and view all the answers

    What is the advantage of optical fiber over copper cables in terms of security?

    <p>Signal security</p> Signup and view all the answers

    What is the advantage of optical fiber over copper cables in terms of weight?

    <p>Small size and low weight</p> Signup and view all the answers

    What is the application of optical fiber in medical field?

    <p>Endoscopic applications</p> Signup and view all the answers

    What is the benefit of using optical fiber in aircraft or ships?

    <p>Reduces weight and maintains true communication silence</p> Signup and view all the answers

    What is the characteristic of light propagation in graded-index fiber?

    <p>Light propagates in curved fashion</p> Signup and view all the answers

    What is the characteristic of single-mode fiber?

    <p>Propagates only one mode</p> Signup and view all the answers

    What is the range of attenuation in multimode fiber?

    <p>2.6 to 50 dB/km</p> Signup and view all the answers

    What is the classification of optical fibers based on refractive index profile?

    <p>Single mode step index, Multimode step index and Multimode graded index fibers</p> Signup and view all the answers

    What is the diameter of the core in a single mode step index fiber?

    <p>4um</p> Signup and view all the answers

    What is the reason for scattering losses in optical fibers?

    <p>Density fluctuations within the fiber</p> Signup and view all the answers

    What is the unit of attenuation in optical fibers?

    <p>dB/km</p> Signup and view all the answers

    What is the cause of absorption in optical fibers?

    <p>All of the above</p> Signup and view all the answers

    What is the wavelength range of operation for silica glass?

    <p>700nm to 1600nm</p> Signup and view all the answers

    What is the effect of impurities on fiber attenuation?

    <p>Increases fiber attenuation</p> Signup and view all the answers

    What is the term for the reduction of signal strength over the length of the fiber?

    <p>Attenuation</p> Signup and view all the answers

    What is the name of the scattering mechanism that occurs between the ultraviolet and infrared regions?

    <p>Rayleigh Scattering</p> Signup and view all the answers

    What is the type of fiber that has a core diameter of around 100um?

    <p>Multimode step index fiber</p> Signup and view all the answers

    What is the primary purpose of the cladding in an optical fiber?

    <p>To keep light within the core</p> Signup and view all the answers

    What is the outermost region of an optical fiber known as?

    <p>Sheath (Protective Jacket)</p> Signup and view all the answers

    What is the minimum thickness required for the cladding to keep light within the core?

    <p>No specific minimum thickness is required</p> Signup and view all the answers

    What is the condition for total internal reflection to occur in an optical fiber?

    <p>The angle of incidence is greater than the critical angle</p> Signup and view all the answers

    What is the sine of the acceptance angle of an optical fiber called?

    <p>Numerical Aperture (N.A.)</p> Signup and view all the answers

    What is the purpose of the buffer in an optical fiber?

    <p>To protect the fiber from moisture and abrasion</p> Signup and view all the answers

    What is the ratio of the difference between the refractive indices of the core and the cladding to the refractive index of the core?

    <p>Fractional Refractive Index change (Δ)</p> Signup and view all the answers

    What is the maximum angle that a light ray can have relative to the axis of the fiber and still propagate through the fiber?

    <p>Acceptance Angle</p> Signup and view all the answers

    What is the term for the light ray within the cone having a full angle of 2𝜃𝑚?

    <p>Acceptance Cone</p> Signup and view all the answers

    What is the typical length of an optical fiber?

    <p>1 kilometer</p> Signup and view all the answers

    What is a unique property of laser beams that makes them useful for communication?

    <p>High energy density</p> Signup and view all the answers

    In which medical application is laser used to fix detached retinas?

    <p>Eye Surgery</p> Signup and view all the answers

    What is the advantage of using laser beams in surgery?

    <p>Clean cuts and minimal blood loss</p> Signup and view all the answers

    What is the application of lasers in industrial cutting and drilling?

    <p>Drilling and cutting</p> Signup and view all the answers

    What is the term used to describe the type of surgery performed using laser beams?

    <p>Bloodless surgery</p> Signup and view all the answers

    What is the most exciting application of lasers, according to the text?

    <p>Holography</p> Signup and view all the answers

    What is the primary difference between conventional light sources and laser sources in terms of phase?

    <p>Phase</p> Signup and view all the answers

    What is the reason for the high intensity of laser light?

    <p>It is concentrated in a very narrow region</p> Signup and view all the answers

    What is the function of the chromium ions in the ruby crystal?

    <p>To absorb light in the blue and green spectrum</p> Signup and view all the answers

    What is the purpose of the helical photographic xenon flash lamp in the ruby laser?

    <p>To generate a beam of white light</p> Signup and view all the answers

    What is the state of the chromium ions after absorbing the green component of the spectrum?

    <p>Metastable state</p> Signup and view all the answers

    What is the wavelength of the laser beam emitted by the ruby laser?

    <p>6943A0</p> Signup and view all the answers

    What is the application of laser beams in civil construction work?

    <p>To measure distances</p> Signup and view all the answers

    What is the advantage of laser light over conventional light?

    <p>It is highly coherent</p> Signup and view all the answers

    What is the shape of the ruby rod used in the ruby laser?

    <p>Cylindrical</p> Signup and view all the answers

    What is the purpose of the coolant around the ruby rod?

    <p>To cool the ruby rod</p> Signup and view all the answers

    What is the primary purpose of fiber optic devices in industrial applications?

    <p>To inspect or control operations in inaccessible areas</p> Signup and view all the answers

    What is a characteristic of ordinary light?

    <p>It is non-directional and inconsistent</p> Signup and view all the answers

    What happens when a photon of energy is incident on a single free atom in a ground state?

    <p>The atom is excited to a higher energy level</p> Signup and view all the answers

    What is the process by which an excited atom returns to the ground state by emitting a photon of energy?

    <p>Spontaneous emission</p> Signup and view all the answers

    What is the characteristic of laser light that makes it different from ordinary light?

    <p>It is monochromatic and directional</p> Signup and view all the answers

    What is the purpose of pumping in a laser?

    <p>To achieve population inversion</p> Signup and view all the answers

    What is the characteristic of laser light that makes it coherent?

    <p>It emits continuous waves for very long duration</p> Signup and view all the answers

    What is the difference between spontaneous emission and stimulated emission?

    <p>Spontaneous emission is a random process, while stimulated emission is triggered by an external energy</p> Signup and view all the answers

    What is the characteristic of laser light that makes it monochromatic?

    <p>It spreads over a wavelength range of few A0</p> Signup and view all the answers

    What is the purpose of using fiber optic devices in fiber guided missiles?

    <p>To transmit video information to a ground control van</p> Signup and view all the answers

    Study Notes

    Fiber Optics

    • Fiber Optics deals with the transmission of light through glass or plastic as thin as a human hair, designed to guide the light waves along their length.
    • The optical fiber works on the principle of total internal reflection.

    Principle of Total Internal Reflection

    • When a ray of light passes from a denser medium to a less dense medium (rarer), some part of the light is reflected back into the denser medium, and the rest is refracted into the less dense medium.
    • The reflected ray is weak in intensity, but the refracted ray is bright with maximum intensity.
    • As the angle of incidence increases, the angle of reflection also increases, and at some angle of incidence, the angle of refraction is 90°, and the refracted ray travels along the boundary.
    • This angle of incidence is called the critical angle (𝜃𝑐).
    • When the angle of incidence increases slightly, the reflected ray becomes bright, and all the incident light energy is reflected back into the denser medium.

    Construction of Fiber Optics

    • An optical fiber has three coaxial regions: the core, cladding, and sheath (protective jacket).
    • The core is the innermost region, surrounded by the cladding, and the outermost region is the sheath.
    • The core and cladding are made of glass or plastic, and the refractive index of the core is always greater than the refractive index of the cladding.
    • The purpose of the cladding is to keep the light within the core.
    • The sheath or buffer protects the cladding and core from moisture and abrasion.

    Acceptance Angle and Acceptance Cone

    • When a light ray enters a fiber, it makes an angle with the axis of the fiber, and if this angle is greater than the critical angle, the light is totally internally reflected and propagates through the fiber.
    • The acceptance angle is the maximum angle that a light ray can have relative to the axis of the fiber and still propagate through the fiber.
    • The acceptance cone is the light ray within the cone having a full angle of 2𝜃𝑚 that is accepted and transmitted through the fiber.

    Fractional Refractive Index Change and Numerical Aperture

    • The fractional refractive index change (Δ) is the ratio of the difference between the refractive indices of the core and the cladding to the refractive index of the core.
    • The numerical aperture (N.A.) is the sine of the acceptance angle and signifies the light-gathering power of the optical fiber.

    Classification of Optical Fiber

    • There are two main types of optical fibers: single-mode and multimode fibers.
    • Depending on the refractive index profile, there are three types of optical fibers:
      • Single-mode step index fiber
      • Multimode step index fiber
      • Multimode graded index fiber

    Attenuation in Optical Fiber

    • Attenuation is the reduction of signal strength over the length of the light-carrying medium.
    • The main causes of attenuation in optical fibers are:
      • Absorption
      • Scattering
      • Bending
    • Different mechanisms of attenuation include:
      • Intrinsic absorption
      • Extrinsic absorption
      • Rayleigh scattering
      • Microscopic and macroscopic bending

    Advantages of Optical Fiber over Conventional Communication

    • Higher bandwidth
    • Smaller size and lower weight
    • Absence of cross-talk
    • Easy maintenance
    • Signal security
    • Low cost
    • Longer lifespan
    • Electrical isolation

    Applications of Optical Fiber

    • Communication applications (telephone, teleconferencing, cable TV, digital data transmission)
    • Medical field (endoscopic applications, eye surgery, cardiology)
    • Military applications (aircraft, ships, tank wiring, fiber-guided missiles)
    • Industrial applications (inspection or control of operations in inaccessible areas)

    LASER (Light Amplification of Stimulated Emission of Radiation)

    • Laser light is monochromatic, directional, and coherent, with a focused beam and a high intensity.
    • Laser light is produced by stimulated emission, which occurs when an excited atom is forced to emit a photon of the same energy and in phase with the incident photon.

    Characteristics of Laser

    • Monochromaticity
    • Coherence
    • Directionality
    • Divergence
    • Brightness

    Ruby Laser

    • Ruby is a crystal containing chromium ions, which gives it a pink or red color.
    • The chromium ions have absorption bands in the blue and green regions of the visible spectrum.
    • The ruby laser works on a three-level system, with the energy levels of the chromium ions in the crystal lattice.### Energy States and Laser Beam Generation
    • The xenon discharge generates a beam of white light, which is absorbed by Cr3+ ions, exciting them from the ground state (E1) to the excited state (E3).
    • The excited state (E3) is highly unstable, lasting only 10^(-8) seconds, and rapidly loses energy to transition to the metastable state (E2).
    • The metastable state (E2) accumulates Cr3+ ions for a few milliseconds, allowing for population inversion between E2 and E1.
    • Spontaneous emission of a photon by Cr3+ ions at E2 initiates stimulated emission by other ions in the metastable state, producing a strong laser beam.

    Characteristics of Ruby Laser

    • The laser beam is red in color, with a wavelength of 6943A0.
    • The green light plays the role of pumping agent, not the amplified component.
    • The effectiveness of the Ruby laser is low, as only the green component of the pumping light is utilized.

    Applications of Laser

    Scientific Applications

    • Laser beam is used for precision measurement of distances and alignment in civil construction work due to its directionality and coherence.
    • The distance between the Earth and the Moon has been precisely measured using laser beams.
    • Laser can be used for determining the shape of objects and structure deformations.

    Engineering and Industrial Applications

    • Laser is used in communications due to its high directionality and energy density.
    • Laser is used as a heat source for cutting, drilling, welding, etc.
    • Laser can be used to investigate the structure of molecules.

    Medical Applications

    • Laser is used for diagnosis in endoscopy, allowing for the examination and photography of inner body parts using an optical fiber.
    • Laser is used in eye surgery, fixing detached retinas and treating glaucoma and cataract.
    • Laser is used in general surgery, making clean cuts and sealing blood vessels, minimizing blood loss.
    • Laser is used in dentistry to destroy germs in tooth cavities without pain.

    Holography

    • Laser is used in holography to obtain a 3D view of an object.

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    Learn about the fundamental principles of fiber optics, including the transmission of light through thin glass or plastic fibers and the concept of total internal reflection.

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