The sensitivity of the earphone of an optical telephone that contains a gas filled tube that reacts to small changes in temperature caused by amplitude variations in light to create sound is improved by replacing the gas tube opto-acoustic converter with a strip of a material that reacts forcefully when...http://www.google.com/patents/US4766607?utm_source=gb-gplus-sharePatent US4766607 - Method of improving the sensitivity of the earphone of an optical telephone and earphone so improved
