An optical fibre is a thin, flexible, and transparent fibre made of glass (high quality silica) or plastic that is used to transmit information in the form of light pulses.
These fibres can carry information, such as text, images, videos, telephone calls, and anything that can be encoded as digital information, across large distances almost at the speed of light.
- Structure: An optical fibre consists of:
- Core, which is the innermost part where light travels.
- Cladding, which surrounds the core and helps contain the light within the core by reflecting it back into the core.
- The core and cladding are usually made of materials with different refractive indices, allowing for the total internal reflection of light within the core.
- The refractive index of the core is higher (denser medium) than the refractive index of the cladding (rarer medium).
Reflection of Light:
- Reflection is the bouncing back of light when it strikes/hits a surface.
- The angle at which the light hits the surface (angle of incidence) is equal to the angle at which it reflects off the surface (angle of reflection), according to the law of reflection.
Refraction of Light:
- Refraction is the bending of light when it passes from one medium to another with a different optical density/ refractive index.
- The speed of light changes as it moves from one medium to another, causing the light to change direction.
Total Internal Reflection:
- Total internal reflection occurs when light travelling from a rarer medium to a denser medium, strikes the boundary of the medium at an angle greater than the critical angle.
- If the angle of incidence is greater than the critical angle, all the light is reflected back into the original medium; none of it is refracted into the second medium.
- This phenomenon is crucial in optical fibres, where it allows light signals to be transmitted over long distances by repeatedly undergoing total internal reflection within the core of the fibre.
How do optical fibres work?
- The phenomenon known as total internal reflection is the basis of guiding light across long distances without a significant loss of optical power.
- With proper adjustments, the light can be kept bouncing within the glass with very little escaping outside. This is how signals encoded as electromagnetic waves can be fed into one end of an optical fibre, and they will reflect and bounce many times between the glass walls as they traverse several kilometres bearing the information in the signals.
Advantages:
- Optical waves have high bandwidth, thus allowing a high data-transmission rate, up to several terabits per second in a single fibre.
- It serves as a medium for carrying optical signals over long distances with minimal loss of signal quality (low signal attenuation).
- Unlike radio or copper-cable-based communication, fibre cables are also insensitive to external perturbations such as lightning and bad weather, and have immunity to electromagnetic interference.
Hence, optical fibres possess the ability to transmit signals over long distances without significant degradation and provide the backbone for internet, telephone, and cable television systems.
Applications:
- Telecommunications: Optical fibres are used to connect telephone lines, cable television systems, and internet service providers.
- Medical imaging: Optical fibres are used in a variety of medical imaging applications, such as endoscopy, ultrasound, and laser surgery. They allow doctors to see inside the body without making a large incision.
- Sensors: Optical fibres are used in a variety of sensors, such as temperature sensors, pressure sensors, and chemical sensors.
- Lighting: Optical fibres are used in a variety of lighting applications, such as decorative lighting, stage lighting, and outdoor lighting.
- Military: Optical fibres are used in a variety of military applications, such as communication, surveillance, and targeting.