An Optical Microphone?

The optical microphone principal has now reached a higher level. A technique newly developed by SENNHEISER and PHONE-OR Ltd. makes it possible to realize the principle of the optical converter with remarkable new characteristics.

A beam of light is projected from an optical glass fibre onto a reflective diaphragm. A second glass fibre captures the reflected light and conducts it to a photodetector.

Glass fibres of this type are widely used in high quality data and phone networks, and experience only very minor losses in light transmission. This advantage enables the optical microphone transducer to be placed a considerable distance away from the light source (LED) and photodetector with their associated active electronic components.

As a result this novel microphone system can be applied in locations which have previously been unsuitable for conventional microphones, including locations subject to extreme electric or magnetic fields, e.g. nuclear magnetic resonance imaging, computer tomography, in the vicinity of power output stages, and even in volatile or hazardous environments.

Particularly interesting advantage of this new microphone derives from its diminutive size, which makes it suitable for live applications. Quality microphones of less than 3 mm (1/8") diameter are easily achievable with a frequency responsecomparable to that of the standard for such applications, our classic Sennheiser MIKE 2. Of further importance for these applications is this model's high degree of tolerance to moisture, since the actual transducer function is purely optical, with no sensitive electronic components needed in the capsule.

The new optical microphone has been developed by SENNHEISER, based on the optical converter principle of Phone-Or (US Patent #. 5771091).