This invention relates generally to optical to acoustical transducer means and more particularly to such transducer means employed in a telephone receiver to produce a sound field over the audible range.
Optical acoustical telephones are known. A typical example is shown and discussed in U.S. Pat. No. 4,002,897, entitled, "Optical Acoustical Telephone Receiver", issued to D. A. Kleinman, et al. on Jan. 11, 1977. This patent discloses and telephone receiver for converting optical signals propagated through an optical fiber waveguide into audible acoustic signals by the inclusion of a small optical absorption chamber filled with optical absorbing material, such as dark fibrous material.
More recently, Seymour Edelman, one of the present inventors, was granted a patent on an improvement in such a device The patent is identified as U.S. Pat. No. 4,334,321, entitled, "Opto-Acoustic Transducer And Telephone Receiver", issuing on June 8, 1982. Shown and described therein is a telephone receiver in which information in the form of variations in the intensity of light transmitted along an optical fiber is converted to sound. The variations of light intensity, commonly known as modulated light, are absorbed in a specially treated short length of optical fiber coupled to a diaphragm located in the earpiece of a telephone housing. The absorbing length of the optical fiber becomes heated and cooled as the intensity of the light varies and accordingly expands and contracts, causing a movement of the diaphragm which sets up a sound field transmitted to the ear of a person utilizing the telephone receiver.