How to reduce absorption?
-Use a core which is extremely transparent.
-use optical fibre repeaters so that the pulse is regenerated before significant absorption has taken place.
What is absorption?
Where some of the signal’s energy is absorbed by the material the fibre is made from. This energy loss results in the amplitude of the signal being reduced.
What is the role of core
allows for transmission of the light in the fibre optic with little absorption.
What is modal dispersion?
Occurs when light pulses in the optical fibre spread out due to different angles of incidence in the original pulse.
What is the role of outer sheath?
Prevents physical damage to the fibre, strengthens fibre and prevents scratches.
How to reduce material dispersion?
Use of monachromatic light stops this
Uses of fibre optics
Communications, such as telephone and internet transmission, medical imaging.
What is material dispersion?
Occurs when white light is used instead of monachromatic light (this is because different wavelengths of light travel at different speeds), so some rays of light reach the end due to higher refractive index.
To reduce modal dispersion
The core needs to be very narrow, means the core has only one path (single node fibre)
What are the condition of total internal reflection?
For it to occur angle of incidence must be greater than the critical angle.
What is pulse broadening caused by?
Material dispersion and modal dispersion.
What is pulse broadening?
-When the signal is broader than the initial signal.
-broadened pulses can overlap each other, leading to information loss. This is because the final pulse would be distorted.
What is the role of cladding?
-Protects core from damage, prevents signal degradation through light escaping the core, (can cause information from signal to be lost).
-keeps signal secure and maintains quality of the original signal (prevents scratching of core).
How does total internal reflection occur in fibre optics?
Core is higher density to cladding, so total internal refraction occurs ( step-index fibre optic).
How is signal degraded?
Degraded by absorption or dispersion, this can cause information to be lost from the fibre optic.
How does Fibre optics work?
-Light is shone at one end of the fibre
-The light hits the boundary between the fibre and the cladding at an angle greater than the critical angle.
-This ensures the light travels down the cable carrying out total internal reflection.
-so the light completes the entire journey inside the fibre optic (so no light is transmitted out).
How is information sent down fibre optics?
As pulses of light ( signal of information).
Advantages of fibre optics over copper wires
-Carry more information
-light does not heat up the fibre.
-no electrical interference and cheaper ( carries signal very quickly )
