Lightwave Engineering Compact Disc Player ECE-E443 Winter 2005

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

Components Inside a CD Player www.howstuffworks.com ECE-E443

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

Compact Disc ECE-E443 CD read from bottom Pit/ bump www.ee.washington.edu ECE-E443

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 www.hyperphysics.phy-astr.gsu.edu

My Components ECE-E443

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

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

Detector ECE-E443

Optical System ECE-E443 Air (n1) = 1.0 Polycarbonate (n2) = 1.55 Snell’s Law ECE-E443 www.ee.washington.edu

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

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

1’s & 0’s ECE-E443

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. www.ee.washington.edu ECE-E443

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. www.ee.washington.edu ECE-E443

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. www.ee.washington.edu ECE-E443

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

Questions… ? ECE-E443