JPS5617600

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DESCRIPTION JPS5617600
Description 1, title of the invention
Optical microphone device
3. Detailed Description of the Invention The present invention relates to an optical microphone
apparatus using an optical fiber, and it is an object of the present invention to faithfully transmit
information of sound received by the optical microphone unit. As microphones conventionally
used, there are da,. The basic operation principle of EndPage: 1 is to move the diaphragm in
proportion to the sound pressure by voice (general sound) and convert this vibration into an
electric signal. Therefore, a connection signal is produced, and the electric signal of this voice is
sent out through the microphone cord extended from the microphone unit to the outside. Since
the voice electric signal sent out is weak, it is easily affected by external noise from the
microphone cord. In addition, if the microphone cord is long, the capacity of the microphone
cord becomes large, which may cause unevenness in the frequency characteristic of the signal 2
to be transmitted. FIG. 1 shows an example of a so-called optical microphone apparatus for
transmitting voice information as an optical signal using an optical fiber, which has been
proposed by the present inventor. FIG. 2 is a block diagram of the transmission system, and
based on these drawings, an optical system 1. 'Has a vibrating diaphragm 101 that moves, and a
microphone case 102 that does not vibrate due to sound pressure, and is fixed to this
microphone case 102 so that the tip of the optical fiber 1o3 is located approximately at the
center of the vibrating film 101. It is attached in proximity. The light emitting element IQ 4 emits
light from the battery 1 via the switch 106 and the current control resistor 107 in series, and
irradiates the vibrating film 101. Reference numeral 108 denotes a light absorbing material,
which covers the periphery of light phi / <103. A part of the light is reflected at a portion of the
diaphragm 101 facing the optical fiber 103 side. In such a state, light from the light emitting
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element 104 is irradiated to the vibrating film 101, and a part of the irradiated light is reflected
and enters the optical fiber 103 from the tip of the light fino <103. Now, if the vibrating
membrane 101 vibrates in response to the sound pressure, the distance between the tip of the
optical fiber 1 o 3 and the vibrating membrane 1 o 1 changes accordingly, and the gap from the
tip of the optical fiber 103 enters The amount of light fluctuates according to the sound pressure.
Therefore, the amount of light proportional to the sound pressure enters the optical fiber 103.
When the signal contained in the optical fiber is referred to as an audio light signal, the audio
light signal can be taken out from the optical microphone unit by an optical fiber microphone
cord comprising an optical fiber.
FIG. 2 receives sound pressure such as voice from the front surface of the above optical
microphone unit 201, and sends out a sound light signal obtained according to the sound
pressure by the above conversion system by the microphone cord 202 of the optical fiber .
Reference numeral 203 denotes a light receiving element, which converts an audio light signal
sent by an optical fiber microphone cord 202 into an electric signal. An amplifier 204 amplifies
the electric signal from the light receiving element 203 and extracts it as an electric signal of
voice. The above configuration is a simple outline of the novel optical microphone casing. It is
considered that the input obtained by using the above-mentioned optical microphone unit and
the microphone of the conventional electromechanical conversion is caused by the thermal noise
of the light receiving element 1 light emitting element and other elements. In addition, (base
transmission is susceptible to noise in the transmission path. The present invention provides an
optical microphone and its system that are not susceptible to the above noise. Hereinafter, an
embodiment of the present invention will be described with reference to the drawings. FIG. 3
shows the structure of the optical self-microphone unit of the first embodiment, and an oscillator
is further incorporated in the optical microphone unit of FIG. 1 described above, and a basic
explanation of the operation is given. As described above, it is a major feature that the light
emitting element 304 is blinked at a high frequency (several hundreds KHz to several MHz) by
the oscillator 309. The waveform of the main part at this time is shown in FIG. -It shows that the
vibrating membrane 301 is continuously fluctuated at time t by the tapping pressure. (B) is an
output waveform in which the light emitting element 304 blinks at a constant frequency. In such
a state, the optical fiber 303 is obtained as an optical signal modulated at a constant frequency
by reflection EndPage: 2 by the vibrating membrane 301. Hereinafter, this optical signal is
referred to as a modulated optical signal, and the-column is shown in FIG. 4 ((+). FIG. 5 shows an
embodiment of an optical microphone apparatus using the above-mentioned optical microphone
unit 501. As shown in FIG. Hereinafter, a signal processing method of the modulated light signal
obtained from the optical microphone unit 501 shown in FIG. 3 will be described. An optical
microphone section 601 whose structure is shown in FIG. 3 is obtained, and a modulated optical
signal corresponding to the sound pressure shown in FIG. 4 (a) is obtained. A signal is sent.
Reference numeral 503 denotes a light receiving element, which converts the transmitted
modulation signal into an electric signal.
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Reference numeral 504 denotes a drive circuit of this light receiving element, and the obtained
electric signal is passed through a band pass filter 505, and a carrier signal is taken out only at
the same frequency component as the oscillator cutting blade built in the optical microphone
unit 601. On the other hand, a part of the modulated signal from the band pass filter 505 is input
to the synchronous detection circuit 507, and is synchronously detected by the fixed carrier
signal extracted by the limiter circuit changer. 1508 ′ ′ F7i removes the carrier component
from the output synchronously detected by the low-pass filter. Therefore, an output of the low
pass filter 508 can be an electrical signal corresponding to the sound pressure. Here, although
the synchronous detection method is used, FIG. 6 shows another embodiment of the optical
microphone device utilizing the directivity of light δ. The optical microphone unit 5o1 has a
built-in light emitting element, wings, and the oscillator 309 except the built-in function
equivalent to that in the microphone amplifier unit, but the optical microphone unit eo1 'output
will be described later. It is derived by the fiber microphone cord mark 2 and is coupled to the
microphone amplifier unit 603 via the optical connector 604. In the inside of the microphone
amplifier unit 603, a directional optical coupler 606 or an optical fiber 606 is connected to the
optical connector 604. In addition, the oscillation output signal of the built-in oscillation circuit
6070 causes the light emitting element cutting edge to blink via the light emitting element drive
circuit 8. The light emitted from the light emitting element 609 is guided through the directional
coupler 605 from the optical fiber 606 and the optical connector 6 G to the microphone cord
602 to the optical microphone 601. At this time, the light from the light emitting element 609 is
not transmitted to the light receiving element 610 side by the action of the directional coupler
605. There are various specific configurations of the directional optical coupler 606, but any
configuration may be used as long as it selects the directivity as described above. On the other
hand, in the light transmitted through the optical microphone unit 601, the vibrating film moves
according to the change in sound pressure, the light is reflected by the vibrating film, and it is
transmitted through the microphone cord of the same optical fiber as shown by the broken
arrow. It is structured to return. This returned modulated light signal has a low reflection surface
for light coming from the optical connector 604, the optical fiber 606, and the directional light
coupling part, and therefore the modulated signal is the light emitting element 609. It is
absorbed by the surface. Further, the modulated light signal to the force light receiving element
610 side is converted into an electric signal by the light receiving element 610. Reference
numeral 611 denotes a light receiving element drive circuit of the light receiving element 610.
The converted electric signal passes through the band-pass filter 612 and is synchronously
detected by the synchronous detection circuit 613 with the carrier signal of the oscillation circuit
607. The low-pass filter 614 except for the carrier signal is extracted as an audio signal. FIG. 7
illustrates the principle of the above-mentioned optical microphone unit, and shows only the
vibrating film and the tip of the optical fiber. Now, it is assumed that the vibration film 701
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changes from the point (a) to the point due to the sound pressure, and the tip of the optical fiber
702 is fixed at the point (C) (a fixed position). The light transmitted from the light emitting
element dull is emitted from the front end face of the light 7 eyepa πη. This emitted light is
EndPage: 311. In order to come, the optical fiber has the characteristic of having the maximum
radiation theta θ determined by the diameter. The arrows in FIG. 7 indicate the optical path of
the light of the maximum radiation angle θ, and since the optical fiber 702 is a cylinder, the
light spreads in a conical shape. From the above, the light emitted from the tip surface (C) of the
optical fiber 702 differs in the spread of the reflected light as viewed at the (+) point depending
on the position of the vibrating film 701. Since the tip of the optical fiber 702 is fixed at point C,
the amount of light entering the optical fiber 702 varies depending on the position of the
vibrating film 701. The solid and broken arrows indicate the optical path system of the maximum
radiation angle θ of light at the position of the vibrating film 701 at the (, l) point and 0) point.
As described above, the light corresponding to the sound pressure is transmitted as the
modulated optical signal) as the modulated optical signal) and processed as shown in FIG. . For
the path, a percival circuit or the like less susceptible to thermal noise can be used in the light
receiving section, and as a result, it is possible to improve the S / N to 12 ′ ′. In addition, since
a constant light signal is converted directly to a modulated light signal according to the sound
pressure by the diaphragm directly in the related art, the modulation characteristic is excellent,
matching with other devices is easy, and the quality as a whole is very high. The present
invention provides an excellent optical microphone device capable of signal transmission.
4. Brief Description of the Drawings-9-Fig. 1 is a cross-sectional view showing the already
proposed optical microphone unit, Fig. 2 is a block diagram of the optical microphone device,
and Fig. 3 is an embodiment of the present invention. FIG. 4 is a waveform chart of the main part,
FIG. 5 is a block diagram of the optical microphone device of the present embodiment, and FIG. 6
is a block diagram showing another embodiment of the present invention. FIG. 7 is a block
diagram of the main part. 3 Iva, 503 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·
band filter, 506611116 @ @ limiter circuit, 507 · 0 · · · synchronization detection circuit, 601 · · · ·
· · · · · · · · · · · Optical microphone unit, 602 · · · 0 · optical fiber, 60311111 @ 11 * 11 microphone
amplifier unit, 605 · · · unidirectional coupler, 607 # · · · · · · · · · · · · · · · · · · · · · · · · · · Light element
drive circuit, 609 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·
Synchronous detection circuit. Name of the agent Attorney Nakao et al. 1 person z9 ノ Fig. 1 Fig.
1 Fig. 2 Fig. 3 End Page: 4 Fig. 4 □ (t) Fig. 5 Fig. 6 Fig. 7 End Page: 5
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