Browse Prior Art Database

Optical Microphone

IP.com Disclosure Number: IPCOM000100894D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 7 page(s) / 233K

Publishing Venue

IBM

Related People

Bandara, U: AUTHOR [+4]

Abstract

An optical microphone is proposed which may be used to advantage in speech recognition systems or future optical communication and computer systems.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 34% of the total text.

Optical Microphone

       An optical microphone is proposed which may be used to
advantage in speech recognition systems or future optical
communication and computer systems.

      The optical microphone consists of a cantilever beam array
forming part of a Fabry-Perot resonator (etalon) (Fig. 1).  In the
etalon, characteristic vibrations of the cantilever beams are
produced in response to acoustic waves of speech (Fig. 2).  These
vibrations are transmitted to the optical interference signal.  The
optical signal of such an array thus supplies the spectral
information of speech (amplitude, resonance frequency and bandwidth),
without requiring work- and time-consuming standard signal processing
techniques, such as filtering, digitization and Fourier
transformation.  In contrast to the prior art, the cantilever beam
array in the optical microphone may be dimensioned such that speech
is encoded more efficiently and accurately, using a reduced number of
computer means.
   First version of optical microphone (for optical communication)

      In the simplest version, the optical microphone consists only
of a Fabry-Perot resonator (etalon) which is filled with air or other
media (fluids, polymers suitable for optimum acoustooptic conversion)
(Fig. 1).  Sound waves of speech lead to density variations in the
etalon, which modulate the amplitude of the laser interference signal
in the transmission (or reflection) mode.  This microphone version is
particularly suitable for high data rate transmission in future
optical communication by light guides using pulsed or continuous
laser light.
   Second version of optical microphone (for speech recognition)

      The optical microphone for speech recognition consists of a
cantilever beam array forming part of a Fabry-Perot resonator
(etalon) (Fig. 3).  The laser light used is expanded and pulsed.

      The sound waves of speech produce characteristic cantilever
beam vibrations which in turn modulate the Fabry-Perot interference
signal.  The optical signal is then fed with or without the aid of
light guides to a photodiode array.  It already provides spectral
information (such as amplitude, resonance frequency, resonance
frequency bandwidth) of the vibrating cantilever beams i and of
speech without the use of electronic computer-assisted Fourier
transformation.  For a defined cantilever beam array, the
characteristic frequencies (in this case the basic frequencies) and
the associated bandwidths of the individual cantilever beams i are
known, so that only the amplitudes of the optical signal Ai are to be
measured.  If the amplitude (intensity variation) exceeds a
particular threshold As, the digital value of Ai is measured and
associated with the values fi, Wfi of the ith cantilever beam.  This
eventually leads to vector sequences of spectral parameters which are
used for encoding.  The length of the vectors is determined by the
number of cantilever beams N.  For a spe...