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Optical Fibers Restore Old Records

Photonics Spectra
Nov 1997
Jennifer L. Morey

LAUSANNE, Switzerland -- A group of scientists at the Federal Institute of Technology's (EPFL) metrology lab has designed an optical stylus that can play old 78-rpm records that are too fragile or damaged to be played on a traditional record player.
On a record, spiral grooves with varying depths carry a musical formula. When the disc is played on a turntable, a diamond needle converts the depth of the grooves into sound. Unlike modern vinyl records, however, early records were made of resin or wax. With time, the weight of the diamond needle would scratch and sometimes wear away the grooves on the disc, making it unplayable.

Digital stereo with a twist
The new fiber instrument is a thousand times lighter than a traditional needle and therefore can be used multiple times without creating additional damage to the record. It works on some of the most severely damaged recordings by touching an optical fiber to previously unexposed areas of the record groove. A beam from a semiconductor laser similar to that found in a compact disc player passes through the fiber and creates a light spot that moves up and down according to the depth of the grooves. The end of the fiber acts like a mirror and reflects the light to an electronic position detector. The rapid up-and-down movement of the fiber is converted into sound, while the slow sideways tracking of the fiber toward the center of the record determines the recording speed.
Philippe Robert, who developed the device with colleagues at the EPFL, said that the optical stylus is intended for professional use only and that there are no plans to market it for use in the home. Agencies such as the Swiss National Archive, Radio Suisse Romande and Télévision Suisse Romande are already using the device to restore recordings made in the early part of this century, including speeches by Adolf Hitler, Winston Churchill and Queen Elizabeth II when she was just a teen-ager.



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