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JPH01231500

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DESCRIPTION JPH01231500
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
optical microphone, and more particularly to an optical microphone that converts an audio signal
into a corresponding electrical signal based on the Doppler effect on laser light. [Prior Art] A
microphone conventionally used receives an audio signal propagated as a sound wave in the air
with a suitable diaphragm and receives a coil mechanically coupled to the diaphragm. The
change of the current generated in the coil is converted into an electric signal corresponding to
the sound signal and extracted by vibrating around the corresponding magnet. By the way, in the
conventional microphone of this type, since the coil which is wovenly connected to the
diaphragm has a corresponding weight, the kinetic energy of the diaphragm is considerably
attenuated when the coil is moved. It will be. As a result, the efficiency of the microphone C is
lowered, and the sound quality to be reproduced is also deteriorated. Also, in conventional
microphones of this type, the audio signal is converted to a corresponding electrical signal and
then the required wire is used for transmission to the appropriate amplifier, but with the inherent
impedance of that wire When importance is attached to the volume and the sound quality from
the relationship etc., the length of the electric wire is limited. Further, since the electric signal is
transmitted through the electric wire, there is a possibility that it may be mixed as noise to the
original electric signal due to the magnetic influence due to other electromagnetic waves etc. on
the outer periphery of the electric wire. There is. [Problems to be Solved by the Invention] Since
the conventional microphone is configured and operates as described above, the mechanical
energy of the corresponding diaphragm is consumed to move the coil, and the microphone is
When the original efficiency of the system is reduced, or when the volume and the sound quality
are emphasized, there are problems such as the restriction of the length of the wire for
transmission of the electric signal, and the other around the wire There is also a problem that
noise is mixed into the original electrical signal under magnetic influence based on
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electromagnetic waves and the like. The present invention has been made to solve the abovementioned problems, and by utilizing the resistance to electromagnetic induction of light, with
good efficiency, and without deteriorating the sound quality, etc., from the audio signal It is an
object of the present invention to obtain an optical microphone which can transmit a
corresponding conversion signal of [Means for Solving the Problems] An optical microphone
according to the present invention includes a laser light source, a polarization beam splitter, first
and second quarter wavelength plates, a mirror, and a polarization processing unit including an
optical sensor. And an optical microphone functional unit including a diaphragm, and an optical
coupling unit connecting the polarization processing unit and the optical microphone functional
unit.
[Operation] In the present invention, the light beam from the laser light source is split into two
light beams by the polarization beam splitter in the polarization processing unit, one of which is
reflected from the polarization beam splitter, A signal that is returned from the mirror to the
optical sensor as a reference beam through the quarter wave plate, and the other is reflected
from the diaphragm of the optical microphone function unit through the optical coupling unit,
and is subjected to Doppler shift The light is returned to the light sensor as light, which utilizes
electromagnetic resistance of the light, has a good efficiency, and does not deteriorate the sound
quality etc., and converts the corresponding signal from the audio signal. The signal can be
transmitted. DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to describing the
embodiments of the present invention, the principle of the Doppler effect applied to the present
invention will be described in principle. When carrying the beam, as in the case of the radio
signal, appropriate modulation such as amplitude modulation or frequency modulation is
performed. By the way, when natural light is selected as the light beam, it is not considered that
frequency modulation is performed, but when laser light is selected, since this is almost complete
monochromatic light, an appropriate light sensor is selected. By using it, it is possible to detect
both amplitude and frequency modulated signals. Here, the most important matter in using the
light signal as the frequency modulation signal is to measure the moving speed of the diaphragm
by the laser light, which is based on the Doppler effect. The frequency of the light signal reflected
by the moving diaphragm changes in proportion to the moving speed of the diaphragm. Now,
assuming that the light signal of frequency f0 is reflected while the diaphragm is moving at
speed 1, the frequency of the reflected light signal changes by Δf, and the value thereof is as
follows. Δf = (fo / C) Veosθ where C is the speed of light. That is, it is sufficient to detect an
optical signal having a frequency of r0 + Δf that corresponds to the frequency change Δr & なる
。 The above matters will be further described with reference to FIG. 2. FIG. 2 is an explanatory
view of the Doppler effect applied to the present invention. The laser beam emitted from the
laser light source 21 is split into two by the half mirror 22 to be the reference beam B1 and the
signal beam B2. The signal light B2 is reflected by the diaphragm 23, and the corresponding
frequency is set to f0 + Δf. On the other hand, since the frequency of the reference light B1 is f,
when the reference light B1 and the signal light B2 are incident on the optical sensor 24, a signal
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corresponding to .DELTA.f which is the difference between the frequency components of the both
is detected. It will be done.
The difference signal thus obtained is considered to hold a signal corresponding to the current
flowing through the coil of the conventional microphone. Next, an embodiment of the present
invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing
an optical microphone according to an embodiment of the present invention. In FIG. 1, the
randomly polarized laser light emitted from the laser light source 11 is incident on the
polarization beam splitter 12A in the polarization processing unit 12 and is reflected to be
directed to the first quarter-wave plate 12B. It is separated into a shear wave S1 and a
longitudinal wave S2 that transmits and travels to the second quarter wave plate 12E. The
polarization processing unit 12 includes a polarization beam splitter 12A, first and second
quarter wavelength plates 12B and 12E, a mirror 12C1, and an optical sensor 12D. First, when
the reflected shear wave S1 passes through the first quarter wave plate 12B, the wave front is
rotated by 45 ', and after being reflected by the mirror 12C, passes through the first quarter
wave plate 12B again. Do. Here, the wavefront is further rotated by 45 ° to form the
longitudinal wave S2. For this reason, there is no light beam reflected by the polarization beam
splitter 12A and returned to the laser light source 11 side, and all the light beams from the
mirror 12C enter the light sensor 12D as reference light. Next, the longitudinal wave S2
transmitted through the polarization beam splitter 12A toward the second quarter-wave plate
12H passes through the second quarter-wave plate 12E, and its wavefront is 45 °. It rotates and
reaches the second fiber connector 13B at the end of the optical microphone functional unit 14
through the first fiber connector 13A and the optical fiber 13. The optical microphone function
unit 14 includes a condenser lens 14A and a diaphragm 14B. Further, the longitudinal wave S2
returns through the path of the condensing lens 14A-4 diaphragm 14B, the condensing lens 14A,
and the second optical fiber connector 13B, which passes through the second quarter wave plate
12E. When the wavefront rotates by 45 °, it becomes the transverse wave S1. For this reason, in
the polarization beam splitter 12A of the next stage, there is no light beam transmitted to the
laser light source 21 and it will be incident on the light sensor 12D as signal light which is totally
reflected6 and from this light sensor 12D The output of is taken as an electrical signal
corresponding to the change of the moving speed of the diaphragm 14B. As described above, the
optical microphone according to the present invention includes the laser light source, the
polarization beam splitter, the first and second quarter-wave plates, the mirror, and the
polarization including the light sensor. A processing unit, an optical microphone functional unit
including a diaphragm, and an optical coupling unit connecting the polarization processing unit
and the optical microphone functional unit, the light beam from the laser light source being
subjected to the polarization processing Part of the light beam is split into two light beams by a
polarization beam splitter, one of which is reflected from the polarization beam splitter and
directed from the mirror to the light sensor via the first quarter wave plate As reference light,
and the other is reflected from the diaphragm of the optical microphone function unit through
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the optical coupling unit and is Doppler-shifted signal light Is what is returned towards the serial
optical sensor, there is the mechanical moving parts only diaphragm, together with the signal
conversion efficiency is very high, the sound quality is also intended to be remarkably improved.
In addition, since an optical fiber is used for signal transmission, it is not affected by external
electrical or magnetic influences, so that there is no risk that noise may be introduced into the
original signal. There is no need to use a wire with impedance, so that a long distance between
the microphone body and the amplification means does not cause any attenuation of the signal,
nor does it cause a change in the sound acquisition. Furthermore, since the microphone function
unit is configured by only the diaphragm and one optical fiber, the effect that miniaturization and
weight reduction can be easily realized can be achieved.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a schematic configuration view showing an optical microphone according to an
embodiment of the present invention, and FIG. 2 is an explanatory view of a Doppler effect
applied to the present invention.
11 is a laser light source, 12 is a polarization processing unit, 12A is a polarization beam splitter,
12B and 12E are first and second quarter wavelength plates, 12C is a mirror, 12D is an optical
sensor, 13 is an optical fiber, 13A, 13B indicates a first and second optical fiber connector, 14
indicates an optical microphone function unit, 14A indicates a condenser lens, and 14 FIG.
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