Photophone performance

A photophone consisting of a light guiding fiber, an absorption cell containing charred cotton suspended in air, an exponentially tapered tube, and a standard earpiece volume has been made and tested. The pressure in the earpiece versus the frequency in the 300–3300-Hz telephone band for a given optical power input agrees well with the theory of the preceding paper. We conclude that the charred cotton suspended in air can be treated simply as light-absorbing air. Measurements were also made on a photophone which included an air column equalizer to resonate with the absorption cell in order to flatten the frequency response. The high-frequency (1500–3300 Hz) response was enhanced as expected thought not quite as much as predicted. Subject Classification: [43]85.76, [43]85.40, [43]85.60.