A theoretical discussion is given of optical telephone receivers employing the optoacoustic effect, which are here called photophones, for use in an optical‐fiber telephone subscriber loop. The basic receiver consists of an absorption cell, a response‐equalizing device such as a gas column or diaphragm, a tapered acoustic tube acting as a transformer, and an earpiece similar to a conventional telephone earpiece including a response‐equalizing device. These photophones are designed to give a flat (3‐dB) response to intensity modulated light over the telephone voice band 300–3300 Hz. The optoacoustic effect is treated on the basis of a pseudogas model for solid absorbers in the form of a fine mesh disbusrsed in a gas. We find that the sensitivity (the optical power modulation required to produce a sound pressure level SPL = 81 dB in a closed volume of 6 cm3, representing the earpiece pressed against the ear) is 2.8 and 0.9 mW for the air‐filled and xenon‐filled photophones, respectively.
Subject Classification: [43]85.76, [43]85.40, [43]85.60; [43]35.65.