Optical Disk Drive
The optical storage device that most of us are familiar with is the compact disc. A CD can store huge amounts of digital information on a very small surface that is incredibly inexpensive to manufacture. The design that makes this possible is a simple one: The CD surface is a mirror covered with billions of tiny bumps that are arranged in a long, tightly wound spiral. The CD player reads the bumps with a precise laser and interprets the information as bits of data.
A CD is made by injection-molding piece of polycarbonate plastic. During manufacturing, this plastic is impressed with the microscopic ridges that make up the long, spiral track. A thin, reflective aluminum layer is then coated on the top of the disc, covering these ridges. A Laser beam then passes through the CD's polycarbonate layer, reflects off the aluminum layer and hits an optical device that detects changes in light. This sensor detects these changes in reflectivity, and the electronics in the CD drive interpret the changes as data bits. We currently use these materials because of their optical properties, durability and their low cost.
Just recently research has been done to make storage devices out of doped glasses. New developments have led to optical memory glass. One of these glass devices 1cm cubed has the ability to store 10,000 MB or 1 terabyte of information.