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?

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

What is the purpose of an optical fiber communication system?

To transmit electronic signals through light Signup and view all the answers

What is the innermost region of an optical fiber called?

Core 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?

Total internal reflection Signup and view all the answers

What is the shape of an optical fiber?

Coaxial Signup and view all the answers

What is the condition for Rayleigh scattering loss to occur?

Size of density fluctuation is 1/10th of operating wavelength 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?

Microscopic bending Signup and view all the answers

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

Nmax=v2/2 Signup and view all the answers

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

Signal security Signup and view all the answers

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

Small size and low weight Signup and view all the answers

What is the application of optical fiber in medical field?

Endoscopic applications Signup and view all the answers

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

Reduces weight and maintains true communication silence Signup and view all the answers

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

Light propagates in curved fashion Signup and view all the answers

What is the characteristic of single-mode fiber?

Propagates only one mode Signup and view all the answers

What is the range of attenuation in multimode fiber?

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

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

Single mode step index, Multimode step index and Multimode graded index fibers Signup and view all the answers

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

4um Signup and view all the answers

What is the reason for scattering losses in optical fibers?

Density fluctuations within the fiber Signup and view all the answers

What is the unit of attenuation in optical fibers?

dB/km Signup and view all the answers

What is the cause of absorption in optical fibers?

All of the above Signup and view all the answers

What is the wavelength range of operation for silica glass?

700nm to 1600nm Signup and view all the answers

What is the effect of impurities on fiber attenuation?

Increases fiber attenuation Signup and view all the answers

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

Attenuation Signup and view all the answers

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

Rayleigh Scattering Signup and view all the answers

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

Multimode step index fiber Signup and view all the answers

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

To keep light within the core Signup and view all the answers

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

Sheath (Protective Jacket) Signup and view all the answers

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

No specific minimum thickness is required Signup and view all the answers

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

The angle of incidence is greater than the critical angle Signup and view all the answers

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

Numerical Aperture (N.A.) Signup and view all the answers

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

To protect the fiber from moisture and abrasion 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?

Fractional Refractive Index change (Δ) 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?

Acceptance Angle Signup and view all the answers

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

Acceptance Cone Signup and view all the answers

What is the typical length of an optical fiber?

1 kilometer Signup and view all the answers

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

High energy density Signup and view all the answers

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

Eye Surgery Signup and view all the answers

What is the advantage of using laser beams in surgery?

Clean cuts and minimal blood loss Signup and view all the answers

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

Drilling and cutting Signup and view all the answers

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

Bloodless surgery Signup and view all the answers

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

Holography Signup and view all the answers

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

Phase Signup and view all the answers

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

It is concentrated in a very narrow region Signup and view all the answers

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

To absorb light in the blue and green spectrum Signup and view all the answers

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

To generate a beam of white light Signup and view all the answers

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

Metastable state Signup and view all the answers

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

6943A0 Signup and view all the answers

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

To measure distances Signup and view all the answers

What is the advantage of laser light over conventional light?

It is highly coherent Signup and view all the answers

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

Cylindrical Signup and view all the answers

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

To cool the ruby rod Signup and view all the answers

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

To inspect or control operations in inaccessible areas Signup and view all the answers

What is a characteristic of ordinary light?

It is non-directional and inconsistent Signup and view all the answers

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

The atom is excited to a higher energy level 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?

Spontaneous emission Signup and view all the answers

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

It is monochromatic and directional Signup and view all the answers

What is the purpose of pumping in a laser?

To achieve population inversion Signup and view all the answers

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

It emits continuous waves for very long duration Signup and view all the answers

What is the difference between spontaneous emission and stimulated emission?

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

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

It spreads over a wavelength range of few A0 Signup and view all the answers

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

To transmit video information to a ground control van 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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Description

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.