Refraction and fibre optics

The thing i always forget to include on wave diagrams

Partial reflection rays

speed of light in another substance equation

speed of light in vacuum/refractive index = speed of light

What does the refractive index show

How much slower that light moves in a substance compared to when its in a vacuum

How do wave properties change when it enters a substance of higher refractive index

Bends towards the normal, and wavelength and speed decrease while frequency remains constant

Conditions for total internal reflection

The medium change is from higher to lower refractive

The angle of incidence is greater than the critical angle

Why do diamonds sparkle

The critical angle is very small, so there is a higher probability that light rays are reflected many times before they emerge so the colours will be more spread out

What is the phenomenon that allows fibre optics to work

Total internal reflection

What layers are there in optical fibres

Core, cladding and sheath

What could happen when 2 fibres touch each othee

Crosstalk (loss of signal into another wire)

Why do we use digital signals instead of analogue

When analogue signals pick up noise (superpose with other waves) it is hard to tell where the peaks and troughs are meant to be

What is latency

How quickly a signal reaches its destination

What is bit rate

How much data is sent per second

What must we do to signal to have a high bit rate

Pulses must be quick and close together

What is a potential issue with high bit rate

Multipath dispersion can render the signal undetectable if all the peaks overlap

What does the sheath do

Prevent scratching to core, prevents crossover and add structural integrity

How can a scratch cause signal loss

Light refracts the wrong way due to changed shape

What does the cladding do (5)

Has a lower refractive index so light totally internally reflects in core

Prevents scratching of core

Reduces mobile dispersion

Increase signal strength

Prevent crossover

Attentuation meaning

Decrease in signal strength as it is absorbed by mediums down the wire

How do we prevent attenuation

Use red or infrared as light doesnt absorb those wavelengths

Signal boosters

Material/chromatic dispersion

Pulse widening due to using different wavelengths of light, which travel different speeds in glass

Modal dispersion meaning

Pulse widening due to path difference in optics

How can we reduce modal dispersion

Reducing the diameter of the core or by reducing it enough for single path dispersion

What is the difference between step index and graded index

Graded index changes the refractive index gradually so it bends back toward the centre more often

How can we prevent modal dispersion

Reducing diameter enough so it is a single mode fibre