ENE 451Optical Engineering

Lecture 1

17th Century, Sir Isaac Newton said that rays of light are streams of very small particles emitted from a light source and they travel in straight line.

Christian Huygens: Experiment about two beams of light intersected emerging unmodified. (Wave Theory of Hooke & Huygens)

Thomas Young: Double Slit Experiment.

Introduction of Light

1821: Augustin Fresnel proposed ‘Fresnel equations’.

James C. Maxwell: Maxwell equations yield a prediction for the light speed.

1900: Max Planck was able to derive the blackbody radiation spectrum. “Atoms emitted light in discrete energy chunks rather than in a continuous manner.”

Introduction of Light

Albert Einstein offered the explanation of the photoelectric effect.

1924: Luis de Broglie suggested λ = h/p.

Introduction of Light

For conclusion, light behaves like waves in its propagation and in the phenomena of interference and diffraction.

However, it also behaves as a particle in its interaction such as in the photoelectric effect.

Introduction of Light

If lights are made up of very small particles called photons, then energy of a photon is

Introduction of Light

hcE hf

Introduction of Light

An electromagnetic disturbance that propagates through space as a wave way be ‘monochromatic’ characterized by a single wavelength, or ‘polychromatic’ represented by various wavelengths.

The distribution of energy among those various waves is called radiation spectrum.

Electromagnetic Spectrum

The spectrum depends on wavelength.

The two important quantities are wavelength (λ) and frequency (ν) and both are related to each other as

Electromagnetic Spectrum

c

Electromagnetic Spectrum

Source: www.yorku.ca

Electromagnetic Spectrum

Source: http://science.hq.nasa.gov

White light: When all the light waves are seen together, they make white light.

Polarizations of Light

Source: www.uwgb.edu/dutchs/petrolgy/genlight.htm

Polarizations of Light

Source: www.molecularexpressions.com/optics/lightandcolor

Polarizations of Light

Source: “Fiber Optic Communications,” J.C. Palais, 5th ed., Pearson/Prentice Hall.

TE polarization

TM polarization

The treatment of light as wave motions allows for a region of approximation in which the wavelength is negligible due to the dimension of relevant components of the optical system.

This region of approximation is called ‘geometrical optics’.

Geometrical Optics

Light rays travel in straight line in a uniform medium.

Rays are bent or deflected at interfaces or in non-uniform media.

Geometrical Optics

When a ray of light is reflected at an interface, the reflected ray remains within the plane of incidence and the angle of reflection equals the angle of incidence.

The transmitted (refracted) ray also remains within the plane of incidence and the sine of the angle of refraction is proportional to the sine of the incident angle.

Geometrical Optics

Geometrical Optics

Source: “Fiber Optic Communications,” J.C. Palais, 5th ed., Pearson/Prentice Hall.

Law of reflection: θi = θr

Snell’s Law: n1sin θi = n2sin θt

(law of refraction)

Image is a visual impression of something produced by reflection from a mirror or refraction through a lens.

It may be defined as the mapping of an illuminated object.

Image

Optical System

Object Image

Pin hole camera

Pin hole camera

tan

From the convention: ,

This yields when 0, 0, 0,and 0

0 implies ' '.

yy

s s

y s

y s

y y s s

y ss s y y

y s

yM magnification

y

M inverted image

A small hole is made in the shutter of a dark room, and a screen is placed at a distance of 1.5 m from the shutter. If a tree outside is 30 m away from the shutter and if the tree casts on the screen an image 20 cm high, how tall is the tree?

Example

Example

Lenses may be classified into 2 categories as◦ Converging lens◦ Diverging lens

Lenses

A thin lens is a lens that its thickness is small relative to its focal length, radius of curvature, and object and image distance.

Thin Lens

f-number or f-stop is the ratio of focal length to lens diameter = f/D.

Thin Lens