Optical Engineering Lecture 1

 17 th 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.

 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.”

 Albert Einstein offered the explanation of the photoelectric effect.  1924: Luis de Broglie suggested λ = h/p.

 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.

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

 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.

 The spectrum depends on wavelength.  The two important quantities are wavelength ( λ) and frequency (ν) and both are related to each other as

Source:

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

Source:

Source:

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

 Light rays travel in straight line in a uniform medium.  Rays are bent or deflected at interfaces or in non-uniform media.

 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.

Source: “Fiber Optic Communications,” J.C. Palais, 5 th ed., Pearson/Prentice Hall. Law of reflection: θ i = θ r Snell’s Law: n 1 sin θ i = n 2 sin θ t (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. Optical System Object 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?

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

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

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