Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to an optical
modulation/demodulation system in which optical -fibers
are used as the signal transmission path.
In recent times,data communication between
computers or computer and terminal stations is aston-
ishingly increased in various business fields ~uch as
Factory Automation, Office Automation and the link in
which data transmission is performed by means of con-
ventional electrical data transmission system providing
electrical modulation/demodulation devica connected
to telephone or telegram line or coaxial cable. The
data transmission speed of such electrical transmission
system has about 9600 baud at most which is not suffic-
ient to satisfy the requirements of the recent data
communication system. Since such recent data communi-
cation system re~uires additionally a huge amount of
information volume, extremely long distance of repeat-
er's span, high reliable noise free communication and
highly accumulated circuit. An optical data trans-
mission system is applicable to satisfy these require-
ments mentioned above~
As is well known, the data communication
systems are divided into two types of synchronous and
asynchronous data processing.
Under the circumstance, the present invention
is performed to satisfy such requirements of the recent
data communication system of asynchronous type, and it
provides an asynchronous type optical modulation/
demodulation system which can easily be attached to
the conventional data communication system without
substantial modification only by changing the electri-
cal transmission line to an optical fiber cable.
~he present invention will now be described
in more detail by way of embodiments.
Figure 1 is a block diagram of the transmitting
side o~ an embodiment of an optical modulation/demodula
tion system according to the present invention.
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Figure 2 is a block diagram of the receiving
side of an embodiment of an optical modulat-ion/demodula-
tion system according to the present invention.
Figure 3 illustrates the wave forms of signals
at various parts of an asynchronous type of the trans-
mitting side shown in Figure 1. ,,
Figure 4 shows the wave forms of signals at
various parts of an asynchronous type of the rece,iving
side shown in Figure 2.
~0 The optical modulation/demodulation system
according to the present invention enables data trans
mission by means of optical fibers simply by connecting
the system to an electric modulation/demodulation system
used for processing data of international standard. The
present invention further provides an optical modulation/
demodulation system which is applicable to asynchronous
type data transmission and reception system.
The present invention provides an optical
modulation/demodulation system comprising a transmitting
side circuit which is capable of detecting the leading or
the falling edge of a transmission data signal SD, con-
verting the leading and falling detection pulse signal
into the pulse of either positive or negative polarity
- in response to the level of said transmission data
signal SD, overlapping these positive or negative
polarity pulses on the ready for sending signal of a
predetermined level to be used as an input signal for
a luminous elemen~ and thus obtaining an optical output
signal which has been intensity-modulated and a receiving
side circuit which is capable of transmitting the above
optical signal through a light transmission path which
connects the light-emitting element with the light-
receiving element, inputting the signal wh-ich is
received by the light-receiving element, converted to
an electric signal and then outputted to a gain variable
amplifier, obtaining the average of the output, controll-
ing the gain of said gain variable amplifier 50 as to
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keep a predetermined gain by inputting the difference in
the level between said averaged output of the output of
said gain variable amplifier and a pxedetermined l~vel,
deciding the polarity of said electric signal from the
light receiving element by comparing the outpuk of said
gain variable amplifier with said averaged value,of
the same, obtaining a couple of binary signals with
respect to the polarity, in putting said 'binary signals
into the set and reset terminals, of a flip-flop
circuit respectively, outputting a received data
signal from the output side of the flip-flop circuit.
Figure 1 illustrates a block diagram of an
embodiment of the present invention on the transmitting
side. The system comprises a detector circuit 1 to
detect a leading edge of a transmission dat'a"SD and
generate a pulse to feed to a positive polarity pulse
generating circuit 5, a detector circuit 2 to detect a
falling edge of said transmission data signal and
generate a pulse to feed'to a negative polarity gen-
erating circuit 7, a positive polarity pulse generatingcircuit 6 to generate a pulse of positive polarity in
response to the output signal from the detector circuit
1 and feed the same to a driving circuit for the light-
emitting element 9, a negative polarity pulse generating
circuit 7 to generate a pulse of negative polarity in
response to the output signal from the detector circuit
2 and feed the same to the driving circuit for th~ light-
emitting element 9, an average level generating circuit 8
to feed a signal of a predetermined level to the driving
circuit for the light-emitting element 9 when it receives
a ready for sending signal RS and a light-emitting element
10 which is driven by a signal synthesized by the driving
circuit for the light-emitting element 9. The references
d through i denote signals at various parts.
Assuming that a transmission data SD is as
shown in Figure 3(A) and a ready for sending signal RS
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in Figure 3~B), the leading edge detection circuit 1 and
the falling edge detection circuit 2 output signals d
and e at the time when they detect the leading and the
falling edges of the transmission data SD respectively
and feed them to the OR circuit 3 as shown in Figures
3(C) and (D~. The signals d, e are supplied to the .
positive polarity pulse generating circuit 6 and the
negative polarity pulse generating circuit 7 respect-
ively.
The positive polarity pulse generating circllit
6 generates a signal f of Figure 3(E) when it is trigger-
ed by 1 shot at the leading of the signal _ while the
negative polarity pulse generating circuit 7 generates
a signal g of Figure 3(F) when it is triggered by 1 shot
at the leading of the signal e, the signals f, g being
supplied to the light-emitting element driving circuit 9.
The light-emitting element driving circuit 9 is also fed
with a signal h of Figure 3(F) of a predetermined level
which is formed by feeding a ready for sending signal
RS of Figure 3~B~ to the average level generating circuit
8. The circuit 9 then overlaps the signal h on the
positive polarity pulse f and the negative polarity
pulse g so as to output a siynal i of Figure 3(H) for
driving the light-emitting diode 10. In other words,
the light-emitting element 10 is made to output a pre-
determined level as a carrier when the output signal i
from the light-emitting element driving circuit 9 is
at the level of the output signal _ from the average
level generating circuit 8, a level higher than the
predetermined level when it is the level obtained by
overlapping the signal h on the positive polarity pulse
f, and a level lower than the predetermined level when
it is the level obtained by overlapping the signal _
on the negati.ve polarity pulse ~.
Since the leading edge of a signal is detected
on the receiving side to generate a binary signal pulse,
there is a danger for the binary circuit to start at a
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sharp wave front of the signal h to assume a curve indica-
indicated by the dotted line h t in Figure 3(G) by using
a RC circuit or the like. The outpuk i from the light-
emitting element driviny circuit in this case will assume
a curve indicated by the dotted line i~ in Fiyure 3(H),
Figure 2 illustrates a block diagram of a
light receiving side of the optical modulation/demodula-
kion system according to the pre~ent invention. The
optical signal from the light-emitting element shown
in Figure 1 is transmitted by means of optical fibers
OW, received by a light-receiving element of the light-
receiving device shown in Figure 2 and converted into
an e]ectric signal.
The light-receiving device of Figure 2 mainly
comprises a light-receiving element 11 to receive a
light signal transmitted by means of the optical fiber
OW and convert the same into an electric signal, a
gain variable amplifying circuit 12 to amplify the
output electric signal from the light-receiving element
11 to a predetermined level, an averaging circuit 13
to average the output signal from the gain variable
amplifying circuit 12, a carrier detection and decision
circuit 19 to generate a carrier detection signal CD
when the output signal from the averaging circuit 13
exceeds ~he predetermined level, binary circuits 17
and 18 to convert the signal from the gain variable
~nplifying circuit 12 into a binary signal by using the
output signal from the averaging circuit 13 as a float-
ing standard level. A flip-flop 20 outputs a received
data signal RD from the output signals of the binary
circuits 17 and 18~ A comparator circuit 14, a pre-
determined level generating circuit 15 and an error
amplifying circuit 16 are provided for controlling
the amplification factor of the gain varia~le amplify-
ing circuit 12 so as to make the output signal levelof the averaging circuit 13 having the averaged value
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of the output signal o~ gain variable amplifying circuit
12 equal to the predetermined level of the predetermined
level generating circuit 15.
R~-ferences i through m in Figure 2 denote
. 5 signals at various parts. The light signal transmitted
via the optical fiber OW is converted to an electric
signal by the light-receiving eiement 11 to be fed to
the gain variable amplifying circuit 12. For example,
suppose the signal i generated from the light-receiving
element 11 is as shown in Figure 4(A), the gain variable
amplifying circuit 12 amplifies the signal i to a pre-
determined level and outputs a signal k as shown in
Figure 4(B). The signal k is fed to one of the input
terminals of the binary circuits 17 and 18 and the
averaging circuit 13. The averaging circuit 13 averages
the signal k to output the signal 1 as shown in Figure
~(C), and feed the same to the other terminal of the
binary circuits 17 and 18 as well as to the comparative
circuit 14 and the carrier detection/decision circuit 19
The comparative circuit 14 compares the level
of the signal 1 with the standard level fed from the
pxedetermined level generating circuit 15, supplies
the difference in the level to the error amplifying
circuit 16. The error amplifying circuit 16 amplifies
by a suitable amplification factor and supplies to the
gain variable amplifying circuit 12 for the gain con-
trol thereof. The carrier detection/decision circuit
19 decides that a carrier has been transmitted when the
signal 1 exceeds a predetermined level and outputs a
carrier detection signal CD as shown in Figure 4(G).
The binary circuit 17 compares the output
signal 1 from the averaging circuit 13 with a signal
which is obtained by dividing the voltage of the
signal k by a suitable voltage dividing ratio and,
when the level of the signal 1 is lower than the
other, outputs the signal _ as shown in Figure 4(D)
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with the output level "1" ko feed the S terminal of
the flip-flop 20. The binary circuit 18, on the other
handj compares the output siynal k from the averaging
circuit 13 with a signal which is obtained by dividing
the voltage of the ou~put signal 1 at a suitable
voltage dividing ratio and, when the level of the
signal k is lower than the okher, outputs the signal
n as shown in Figure 4(E) with the output level "1"
to feed the R terminal of the flip-flop 20. When
receiving the binary signals m and n, the flip-flop
20 outputs from the Q terminal the received data
signal RD as shown in Figure 4(H)o
As described herein above, according to
the optical modulation/demodulation system of the
present invention, an optical asynchronous data trans-
mission and reception system can be achieved in a very
simple structure.
According to the present invention, an
asynchronous data transmission and reception system
of electrical signals can be replaced by an optical
asynchronous data transmission and reception system
simply by changing electrical communication cable to
optical fiber cable. Therefore, the optical modulation/
demodulation system of the pr~sent invention is widely
applicable and extremely economical.
