Sound alerter powered over an optical fiber

An optically powered sound alerter has been constructed which demonstrates the feasibility of converting optical power into sound power with good efficiency and at power levels comparable to those of present telephone ringers. The alerter has an overall optical-to-acoustic efficiency of about 35 percent at 2 mW of acoustic output power. Optical power is converted to electrical power by a 52-percent efficient photovoltaic detector and then into acoustical power by a 72-percent efficient electroacoustic tone generator which uses a piezoelectric transducer. This demonstration establishes that it is technically feasible to deliver optically, via a fiber lightguide, sufficient power to operate a telephone, since all other telephone signaling functions can be accomplished, in principle, with less power and within the context of dielectric lightguide technology. For conventional usage, the design of a telephone alerter must take many factors into consideration, including background noise masking, frequencies not irritating to the customer, satisfactory performance for customers with impaired hearing, etc. These factors have not been addressed here.