P2 Flashcards
Fibre optics used for
Become a vital backbone for modern communication systems
Refractive index
Of a transparent medium is the ratio or the speed of light in vacuum to its speed in the medium
What does light travel best through
A vacuum
How does light travel through a vacuum
Rapidly oscillating electric field generates an oscillating magnetic field, and changing magnetic field in turn generates another nearby oscillating electric field and so the wave progresses rapidly through space
Normal line
A line at right angles to the surface of a transparent medium that passes through a point where a Ray enters or exits the medium. The direction of rays is always described by measuring the angle between the Ray and normal line
Incidence
The direction of incoming ray
Refraction
The bending of the direction of travel, so it describes the direction of an outgoing Ray after bending
Internal reflection
When a wave that is already in an optically dense medium hits the boundary with a less dense medium and energy is reflected back into the denser medium
Critical angle
For a Ray in a medium with. Higher refractive index hitting the boundary with a less dense medium, this is rhe angle of incidence where the refracted Ray would be at 90 degrees
Total internal reflection
All the wave energy is internally reflected. None is lost as a refracted Ray. This happens for all angles of incidence larger than the critical angle
Optical fibres
Long thin cylinders of glass or sometimes plastic
What happens when light is fed into the cut end of the fibre
When hits the side of fibre almost does so at angles greater than the critical angle. That means all Ray of light gets totally internally reflected and keep bouncing down the length of the fibre. No wave energy gets lost through the walls of the fibre although as glass is not perfectly transparent some is gradually absorbed
What happens when light is fed kilometres away
The intensity is still large enough to measure as a signal. If the joints between them qrw carefully made the optical fibres joined ends to end cam pass their light signals on to the next stage in a fibre network again with only a small loss in intensity
Why are light in optical fibres more efficient way of transmitting signals than sending electrical impulses down copper cables
Copper cables suffer from quite large losses due to electrical resistance meaning that after a few hundred metres most of the signal has been attenuated away and amplifiers are needed to boost it up again
How are optical fibres put in place
By installing and jointing
Temporary jointing of optical fibre
Can be temporary using a proprietary connector or permanent
How can permanent joint be achieved
By compression or by a welding process using heat
What does reliability if signal transmission depend on
Quality of fonts between fibres, both along a cable run and also those to the optical transmitter at one end and the optical receiver at the other end
Where do substantial losses of signal intensity occur unless the cable is damaged
The cable to the optical transmitter to the optical reciever
How can the optical signal be boosted
Optical amplifier
What is an optical amplifier
Offshoot of solid state laser technologies, they increase rhe intensity of the beam without needing to convert it back into the electrical signal
Where are fibre optics used
In endoscopes
What are endoscopes
Optical instruments either long tubes rhat can be inserted into a body organ through an opening such as the throat or ear.
How is the image piped back out
Shorter rigid tubular endoscopes use a series of relay lenses
In longer flexible fibrescopes rhe image is also conveyed by a second fibre bundle back to an eyepiece or camera lens
