Chapter 1Nonimaging optical systems and

their uses

Irfan Ullah

Department of Information and Communication Engineering

Myongji university, Yongin, South Korea

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Image-forming system

Capable of being used for imaging

Nonimaging system

Do not attempt to form an image of the source.

Introduction

not sphericalsurfaces

Equilibirium temperature T of black body

• σ is the Stefan Boltzmann constant, 5.67 × 10-8Wm-2°K-4

• S is the radiation power density, approximately 1KWm-2

For generating electric power, increase S by a factor C

Focus the image of sun with an image forming system

How large a value of C is theoretically possible?

Can the theoretical maximum concentration be achieved in practice?

Nonimaging collectors

T = 364°K or 90.85°C

Nonimaging (anidolic, meaning “without image”)

F-number N is given by

• f is the focal length• D is the diameter of the entrance pupil (effective aperture)

Nonimaging concentrators are more efficient than image forming systems

Nonimaging collectors cont’d..

Concentration ratio

• A plane entrance aperture of area• A' plane exit aperture of area

Concentration ratio of a linear concentrator

Concentration ratio

Output dimensionsPerpendicular to the line

Is there any limit to the value of C?

Theoretical maximum concentration in a rotational concentrator is

•Condition: rays emerge at all angles up to π/2 from the normal to the exit face

For a linear concentrator

Concentration ratio cont’d..

Source at infinity

Can actual concentrators be designed with the theoretically best

performance?

Can all reflecting surfaces have 100% reflectivity?

Can all refracting surfaces have perfectly antireflective coating?

Can all shapes be made exactly right?

Yes, 2D concentrators can be designed.

Also 3D concentrators, if consider refractive index or infinity thin

surfaces properly

And also rotational symmetric concentrators.

Other approach is to use complex design, or by using materials which are

not possible in practice

Concentration ratio cont’d..

Photomultipliers

These detectors multiply the current produced by incident light by as

much as 100 million times

Limited in size and volume (1 m3)

Optics of visual receptors (retina)

Uses of concentrators

Photomultiplier Principle of Photomultiplier Human eye

Filament

Light emitting diode (LED)

Emitting light into wide angular spread

Problem: efficiently collimate to emit in a certain angular emitted region

Uses of illuminators

Compact fluorescent lamp LEDLED with reflector