1. Lightwave Engineering
Compact Disc Player
ECE-E443
Winter 2005

2. Presentation Outline ECE-E443 Components Compact Disc Optical System
Laser
Detector
1’s & O’s
Focusing
Advantages
ECE-E443

3. Components
Inside a CD Player
ECE-E443

4. Compact Disc ECE-E443 Polycarbonate Overall diameter of 120mm
Hole with 15mm diameter
Active data area between 46mm and 117mm
Data from center to outside
Capacity of 74 minutes at 16-bit resolution
ECE-E443

5. Compact Disc ECE-E443 CD read from bottom Pit/ bump
ECE-E443

6. Optical System
The laser used for the CD player is typically Aluminum Gallium Arsenide laser diode. It has a wavelength of 780nm. Our visible range terminates at 720nm.
ECE-E443

7. My Components
ECE-E443

8. Laser ECE-E443 Light Amplification by Stimulated Emission of Radiation
Bells Labs – Arthur Schawlow & Charles Townes
1958, Infrared and Optical Masers
Rod made with partly mirrored surfaced materials
Rod bombarded with light or electrons
Mirrors reflect the light
Intense beam emitted through one of the partial mirrors
Light is formed by stimulating a material’s electrons to give out the laser light or radiation.
Microwave spectroscopy. The inventors were developing a device to help them study molecular structures.
ECE-E443

9. Photodetector Converts light pulses into electrical pulses ECE-E443
Senses light pulses
Converts light pulses into electrical pulses
ECE-E443

10. Detector
ECE-E443

11. Optical System ECE-E443 Air (n1) = 1.0 Polycarbonate (n2) = 1.55
Snell’s Law
ECE-E443

12. 1’s & 0’s
The bump is ¼ wavelength high. Therefore the light striking the land travels ½ of a wavelength further than the light striking the bump. This delay constitutes to the fact that the light reflected from the land is 180 degrees out of phase with the light reflected from the bump. This in turn causes destructive interference.
ECE-E443

13. Website – Constructive vs. Destructive Interference
1’s & 0’s
Website – Constructive vs. Destructive Interference
ECE-E443

14. 1’s & 0’s
ECE-E443

15. Focusing
If the objective lens is closer to the compact disk than the focal length of the object lens, then the cylindrical lens creates an elliptical image on the photodetector array.
ECE-E443

16. Focusing
If the objective lens is further away from the compact disk than the focal length of the object lens, then the cylindrical lens again creates an elliptical image on the photodetector array. But this image is perpendicular to the 1st image.
ECE-E443

17. Focusing
If the disk is right at the focal length of the object lens, then the cylindrical lens does not affect the image and it is perfectly circular.
ECE-E443

18. Advantages of Optical Engineering
No mechanical contact between optical pick-up & disc
Eliminates wear and tear
Removes surface noise
Light can be easily focused to small spot sizes
Increases storage density
Photon is the medium by which information is transferred
Light is the carrier of information
ECE-E443

19. Questions… ?
ECE-E443