2.4 - Optics Flashcards
What is meant by Chromatic Aberration
Aberration means a departure from the expected or proper course
Dispersion is a serious problem that the makers of optical instruments with lenses have to solve.
Dispersion means that red light is brought to a focus further away from a positive lens than blue light is.
This blurs images, an effect called chromatic aberration.
Newton solved the problem for telescopes by designing one in which the light was focuses by a curved mirror
Converging (Convex) lens
If object outside the focus?
if object inside the focus?
Converging (Convex) lens
If the object is outside the focus the image is real and is located at the opposite side of the lens to the object. The image will be inverted (COIRO)
If the object is inside the focus the image is virtual and is located at the same side of the lens to the object. The image is upright
A mirror
a) absorbs come of the light
b) refracts some of the light
c) reflects some of the light
a) absorbs come of the light
What is meant by Attenuation?
The loss of optical power as light travels along the fibre caused by
Absorption
Scattering
Bending losses
In terms of loss of optical power through attenuation.
What causes absorption
Atomic imperfections, impurities (water, oxygen defects)
In term absorptions of loss of optical power through attenuation.
What causes Scattering
Fibre density changes - light scattered in all directions
In terms of loss of optical power through attenuation.
What causes bending
Macrobends - fibre bend radius too small
Microbends - clamping too tight, external forces
What is the speed of light in a vacuum?
3 x 108 m/s
Note in a vacuum, this speed decreases in our atmosphere
Concave Mirrors
When real image and when virtual?
If an object is outside the focus the image is real
If the object is inside or at the focal point the image is virtual
Fibre optics depends on (is based off) the ______ of light rays
total internal reflection
What is the bending or changing of direction of light called
refraction of light
When Launching light into the fibre,
The acceptance cone is ________
The acceptance angle is _____________________
When Launching light into the fibre,
The acceptance cone is three-dimensional
The acceptance angle is 1/2 angle of the maximum cone of light that can enter or exit the fiber
What is the eqaution relating refractory index and how fast light will travel through a substance?
N = C / V
Where
N = index of refraction
C = celerity (speed of light in a vacuum)
V = speed of light in that substance
What is the difference between angle of incidence and angle of refraction?
angle of incidence i is the angle at which light strikes the object
angle of refraction is the bending of light when it goes through or hits an object
In order for light to bounce off a medium and not enter it, it must be _______ to the critical angle
greater
What is the equation for snell’s law and what does it mean
n = sin i / sin r
where n = refractive index
i = angle of incidence
r = angle of refraction
The refractive index determines how much the path of light is bent or refracted when entering a material
What does the refractive index n mean?
The refractive index determines how much the path of light is bent or refracted when entering a material
Make a table with concave/convex mirror/lens under image and image location
To test for a splice of a fibre optic cable, what is used?
OTDR
Optical Time Domain Reflectometer
What are the 2 types of rays found in Fibre optic cables?
Meridional Rays - Rays that pass through the centre axis of the fibre
Skew rays = rays that travel through the fibre without passing through the centre axis
