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Claims  |
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What is claimed is:
1. An optical-signal transmission apparatus comprising:
an optical transmission medium that transmits an optical signal, having a
plurality of transmission nodes to input signal light into said optical
transmission medium and at least one reception node to output an optical
signal from said optical transmission medium;
a plurality of optical-signal transmission units, provided in
correspondence with said respective transmission nodes, that respectively
generate an optical signal and input the generated optical signal from the
corresponding transmission node into said optical transmission medium, and
generate pulse string optical signals having different light intensity
levels among a plurality of optical-signal transmission units; and
an optical-signal reception unit, provided in correspondence with said
reception node, that obtains a reception signal by obtaining the optical
signal transmitted from said reception node, and separates a signal
component corresponding to an optical signal generated by a desired
optical-signal transmission unit, from among a plurality of signal
components corresponding to the plurality of optical signals generated by
said optical-signal transmitting units, included in the obtained reception
signal.
2. The optical-signal transmission apparatus according to claim 1, wherein
said optical-signal transmission units can freely change the light
intensity levels of the optical signals generated by said optical-signal
transmission units, and
wherein said apparatus further comprises an arbitration unit that performs
arbitration among said plurality of optical-signal transmission units such
that light intensity levels of the optical signals generated by said
optical-signal transmitting units are different from each other.
3. The optical-signal transmission apparatus according to claim 1, further
comprising an intensity-level notification unit that notifies said
optical-signal reception unit of the light intensity levels of the optical
signals generated by said optical-signal transmission units, prior to
generation of the optical signals by said optical-signal transmission
units.
4. The optical-signal transmission apparatus according to claim 1, wherein
said optical transmission medium is an optical fiber, and
wherein said apparatus further comprises a wave combiner that overlays the
plurality of optical signals introduced from said plurality of
transmission nodes and transmits the overlaid optical signal into said
optical fiber.
5. The optical-signal transmission apparatus according to claim 1, wherein
said optical transmission medium is a sheet of optical transmission
medium, and
wherein said apparatus further comprises a light diffusion unit that
diffuses the optical signals introduced from said transmission nodes and
transmits the diffused optical signals into said sheet of optical
transmission medium.
6. The optical-signal transmission apparatus according to claim 1, wherein
said optical-signal reception unit separates a desired signal component by
comparing time-sequential signal levels of the signals received by said
optical-signal reception unit with a plurality of threshold values.
7. An optical-signal transmission apparatus comprising:
an optical transmission medium that transmits signal light, having at least
one transmission node to input signal light into said optical transmission
medium and a plurality of reception nodes to output signal light from said
optical transmission medium;
an optical-signal transmission unit, provided in correspondence with said
transmission node, that simultaneously generates a plurality of pulse
string optical signals having different light intensity levels or
generates a multiplex pulse string optical signal where a plurality of
pulse string optical signals having different light intensity levels are
overlaid, and inputs the optical signals or multiplex optical signal from
the corresponding transmission node into said optical transmission medium;
and
an optical-signal reception unit, provided in correspondence with said
respective reception nodes, that obtains a reception signal by obtaining
the optical signals or multiplex optical signal transmitted from a
corresponding reception node, separates a signal component corresponding
to an optical signal generated by a desired optical-signal transmission
unit, from a plurality of signal components corresponding to the plurality
of optical signals generated by said optical-signal transmission unit,
included in the obtained reception signal.
8. The optical-signal transmission apparatus according to claim 7, further
comprising an intensity-level notification unit that notifies said
optical-signal reception unit of the light intensity levels of the optical
signals to be newly generated by said optical-signal transmission unit,
prior to generation of the optical signals by said optical-signal
transmission unit.
9. The optical-signal transmission apparatus according to claim 7, wherein
said optical transmission medium is an optical fiber, and
wherein said apparatus further comprises a wave divider that divides the
optical signal introduced from said transmission node and transmits the
divided optical signals to said plurality of reception nodes.
10. The optical-signal transmission apparatus according to claim 7, wherein
said optical transmission medium is a sheet of optical transmission
medium, and
wherein said apparatus further comprises a light diffusion unit that
diffuses the optical signal introduced from said transmission node and
transmits the diffused optical signals into said sheet of optical
transmission medium.
11. The optical-signal transmission apparatus according to claim 7, wherein
said optical-signal reception unit separates a desired signal component by
comparing time-sequential signal levels of the signals received by said
optical-signal reception unit with a plurality of threshold values.
12. A signal processing apparatus comprising:
an optical transmission medium that transmits signal light, having a
plurality of transmission nodes to input signal light into said optical
transmission medium and at least one reception node to output an optical
signal from said optical transmission medium;
a first circuit board carrying a plurality of optical-signal transmission
units that respectively emit an optical signal, and simultaneously
generate a plurality of pulse string optical signals having different
light intensity levels or generate a multiplex pulse string optical signal
where a plurality of pulse string optical signals having different light
intensity levels are overlaid;
a second circuit board carrying an optical-signal reception unit that
obtains a reception signal by receiving the optical signals or multiplex
optical signal, and separates a signal component corresponding to an
optical signal generated by a desired optical-signal transmission unit,
from among a plurality of signal components corresponding to the plurality
of optical signals generated by said plurality of optical-signal
transmission units, included in the obtained reception signal;
a support member that supports said first circuit board and said second
circuit board positioned with respect to said optical transmission medium
such that the optical signals generated from said optical-signal
transmission units on said first circuit board are introduced from said
transmission nodes into said optical transmission medium and signal light
transmitted from said reception node is transmitted into said
optical-signal reception unit on said second circuit board.
13. A signal processing apparatus comprising:
an optical transmission medium that transmits signal light, having at least
one transmission node to input signal light into said optical transmission
medium and a plurality of reception nodes to output signal light from said
optical transmission medium;
a first circuit board carrying an optical-signal transmission unit that
simultaneously generates a plurality of pulse string optical signals
having different light intensity levels or a multiplex pulse string
optical signal where a plurality of pulse string optical signals having
different light intensity levels are overlaid, and outputs the optical
signals or multiplex optical signal;
a second circuit board carrying a plurality of optical-signal reception
units that obtain a reception signal by receiving the optical signals or
multiplex optical signal, and separate a signal component corresponding to
a desired optical signal from among a plurality of signal components
corresponding to the plurality of optical signals, included in the
obtained reception signal;
a support member that supports said first circuit board and said second
circuit board positioned with respect to said optical transmission medium
such that the optical signals generated from said optical-signal
transmission unit on said first circuit board are introduced from said
transmission node into said optical transmission medium and the signal
light transmitted from said reception nodes is transmitted into said
optical-signal reception units on said second circuit board. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The present invention relates to an optical-signal transmission apparatus
and a method for optical signal transmission, and a signal processing
apparatus for signal processing including optical signal transmission.
The function of a circuit board used in a data processing system (daughter
board) is increasing by virtue of development of very large-scale
integrated circuit (VLSI). With the increase in circuit function, the
number of signals connected to respective circuit boards increases, and
therefore, a parallel architecture requiring a number of connectors and
connection lines is adopted as a data bus board (mother board) connecting
the respective circuit boards (daughter boards) with a bus structure. The
parallel architecture is developed by multilayered and miniaturized
connection lines so as to improve the bus operation speed. However, signal
delay due to capacity between connection wires and resistance of the
connection wire lowers bus operation speed, and the system processing
speed is restricted by the bus operation speed. Further, a problem occurs
when the apparatus heats with increase in electric consumption. Further,
as transmission-waiting time due to bus occupation influences the system
processing speed, there is a need for simultaneous transmission among a
plurality of circuit boards. Furthermore, the problems of EMI
(Electromagnetic Interference) noise due to high-density bus-connection
wiring seriously disturb improvement in the system processing speed.
That is, as the bus operation speed is limited, the number of the bus wires
is increased in correspondence with increase in data transmission amount.
However, as the number of wires increases, the electric consumption
increases, further, transmission speed reduces due to skew between wires
and further, there is a problem in wiring space. Japanese Published
Unexamined Patent Application No. Sho 64-14631 and Hei 8-328707 disclose
analog bus connection to reduce the number of wires among devices and
facilitate wiring.
FIG. 13 shows an example of the analog bus connection disclosed in Japanese
Published Unexamined Patent Application No. Hei 8-328707.
Apparatuses 401 and 411 are interconnected by an analog bus 406 via two A/D
converters 404 and 407 and two D/A converters 405 and 408.
An n-bit signal generated from the apparatus 401 is introduced via a
transmission path 403 into the D/A converter 405, converted into analog
data, and transmitted onto the analog bus 406. The data passed through the
analog bus 406 is converted into an n-bit digital signal by the A/D
converter 407, and transmitted via a transmission path 409 into the
apparatus 411. On the other hand, a signal transmitted from the apparatus
411 is transmitted via a transmission path 410 into the D/A converter 408,
converted into analog data, and transmitted onto the analog bus 406. The
data passed through the analog bus 406 is converted into a digital signal
by the A/D converter 404, and transmitted via a transmission path 402 into
the apparatus 401.
As described above, the analog bus 406 operates with a multilevel analog
signal, and the apparatuses 401 and 411 operate with a digital signal.
In the analog bus connection as described above, as the signal that passes
through the analog bus 406 is a multilevel analog signal, level change
occurs due to a bus-line resistive component, a leak current and the like.
If the analog bus line is prolonged or a number of apparatuses are
connected to the analog bus, data transmission cannot be accurately
performed without difficulty.
Further, microcomputers and the like often use a plurality of buses in
addition to connection with a number of functional blocks. In such case,
as communication cannot be made among the plurality of buses, the
above-described analog bus connection cannot be realized without
difficulty. To solve this problem, Japanese Published Unexamined Patent
Application No. Hei 8-328707 proposes a circuit to compensate the level
change of analog bus. However, since an electric wire is used as the bus
line, this is not a substantial solution of the problem to prevent the
level change due to wiring resistance. Further, the problems of increase
in electric consumption in case of high-speed bus drive and the skew of
parallel wiring for large-capacity transmission cannot be solved. Further,
in the case where the electric wire is used as the bus line, even if a
multilevel-logic analog bus is employed, although simultaneous multiplex
transmission can be performed in the same direction, bidirectional
simultaneous multiplex transmission cannot be performed.
To realize high-speed transmission, utilization of an intra-system optical
connection technique, i.e., so-called optical interconnection, instead of
electric transmission technique is studied. The optical interconnection
technique has been proposed by Teiji Uchidata (in The 9th Circuit
Packaging Scientific Lecture Meeting), H. Tomimuro, et al., ("Packaging
Technology for Optical Interconnects", IEEE Tokyo, No. 3, pp. 81-86,
1994), and Osamu Wada (Electronics 1993 April., pp. 52-55), as various
applications in accordance with the content of system construction.
As one of the proposed various optical interconnection techniques, Japanese
Published Unexamined Patent Application No. Hei 2-41042 discloses a data
bus employing an optical data transmission method using high-speed and
high-sensitivity light-emission/photoreception devices. In this example, a
serial optical data bus for loop transmission between respective circuit
boards is proposed. The circuit boards respectively have a
light-emission/photoreception device on both front and rear surfaces, such
that the light-emission/photoreception devices on adjacent circuit boards
installed in a system frame are optically connected. In this method,
signal light sent from one circuit board is photoelectric-converted by an
adjacent circuit board, and the signal light is further
electrolight-converted by the circuit board, and sent to the next adjacent
circuit board. In this manner, the respective circuit boards, sequentially
and serially arranged, transmit signal light through all the circuit
boards by repeating photoelectric conversion and electrolight conversion.
By this arrangement, the signal transmission speed depends on the
conversion speed of the photoelectric conversion and electrolight
conversion by the light-emission/photoreception devices on the circuit
boards, and at the same time, is limited by the conversion speed. Further,
as data transmission among the circuit boards is made by using optical
connection via free space by the light-emission/photoreception devices on
the respective circuit boards, all the circuit boards must be optically
positioned with the light-emission/photoreception devices on both front
and rear surfaces of the circuit boards and the circuit boards must be
optically connected. Further, as the optical connection is made via the
free space, interference (cross talk) occurs between adjacent optical
transmission paths, which may disturb data transmission. Further, data
transmission failure might occur by scattering of signal light due to
conditions within the system such as dust. Further, as the respective
circuit boards are serially arranged, the connection is released if any of
the boards is removed, and a spare circuit board to compensate for the
lack of removed is required. That is, the circuit boards cannot be freely
added or removed, and the number of circuit boards is fixed.
Japanese Published Unexamined Patent Application No. Sho 61-196210
discloses a data transmission technique among circuit boards utilizing a
two-dimensional array device. According to this technique, a plate is
provided opposing to a light source having two parallel surfaces, and
circuit boards are optically connected via a light path formed by a
diffraction grating and a reflection device provided on the plate.
However, this method merely connects light emitted from one point to one
fixed point, and cannot connect all the circuit boards as in the
above-described electric bus. Further, as a complicated optical system is
required and positioning is difficult, interference (cross talk) may occur
between adjacent optical data transmission paths due to positional shift
of optical devices, which may cause data transmission failure. Further, as
the connection information between circuit boards is determined by the
diffraction grating and the reflection device on the plate surface, the
circuit boards cannot be freely added or removed resulting in low
extensibility of the system.
Japanese Published Unexamined Patent Application No. Hei 4-134415 discloses
another data transmission between circuit boards utilizing the
two-dimensional array device. According to this technique, a system which
comprises a lens array of a plurality of lenses having a negative
curvature formed on the surface of transparent material having a
refractive index higher than that of air, and an optical system for
introducing light which is generated from a light source from the side
surface of the lens array, is provided in the transparent material.
Further, there is also disclosed another system having a region of low
refractive index or a hologram instead of the plurality of lenses having
the negative curvature. In this method, light that enters from the side
surface is diffused by the plurality of lenses, the region of low
refractive index or the hologram, on the surface, and emitted.
Accordingly, the intensity of output signal may vary in correspondence
with the relation between the entrance position and emission positions on
the surface with the plurality of lenses, the low refractive-index region
or the hologram. Further, as optical input devices of circuit boards must
be provided at the positions of the plurality of lenses having negative
curvature, the low refractive-index region or the hologram, there is no
freedom in arrangement of the circuit boards resulting in low
extensibility of the system. As a means of solving these problems, a
sheet-shaped optical data bus which transmits diffused signal light is
considered. In use of this sheet-shaped optical data bus, the number of
circuit boards is not limited, unlike the method in Japanese Published
Unexamined Patent Application No. Hei 2-41042, further, the difficulty in
optical positioning of the light-emission/photoreception devices as in
Japanese Published Unexamined Patent Application No. Sho 61-196210 can be
solved.
However, all of the above-described optical transmission methods merely
convert a signal from an electronic circuit into an optical signal and
transmit the converted optical signal, and are seriously limited by the
electronic circuits.
Further, Japanese Published Unexamined Patent Application No. Hei 9-98137
discloses bidirectional communication via an optical fiber using optical
signals having different wavelengths.
However, in this method, even though the bidirectional communication is
made via the same optical fiber, the communicable range is limited between
terminals with light-emitting devices and photoreception devices for
transmitting and receiving light of one wavelength. To freely perform
communication among a number of terminals, a plurality of light-emitting
devices and photoreception devices must be provided in the respective
terminals for handling light having various wavelengths, which complicates
the apparatus's structure and increases the cost.
That is, a technique to reduce the number of wires among terminals so as to
facilitate wiring and to freely perform communication among a number of
terminals has not been applied in any of electronic circuits and optical
circuits.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above problems, and has
its object to provide an optical-signal transmission apparatus and a
method which connect a number of terminals (apparatuses, circuit boards
and the like) and freely perform communication among the plurality of
terminals, and a signal processing apparatus using the optical-signal
transmission method.
According to one aspect of the present invention, the foregoing object is
attained by providing an optical-signal transmission apparatus comprising:
an optical transmission medium that transmits an optical signal, having a
plurality of transmission nodes to input signal light into the optical
transmission medium and at least one reception node to output an optical
signal from the optical transmission medium;
a plurality of optical-signal transmission units, provided in
correspondence with the respective transmission nodes, that respectively
generate an optical signal and input the generated optical signal from the
corresponding transmission node into the optical transmission medium, and
generate pulse string optical signals having different light intensity
levels among a plurality of optical-signal transmission units; and
an optical-signal reception unit, provided in correspondence with the
reception node, that obtains a reception signal by obtaining the optical
signal transmitted from the reception node, and separates a signal
component corresponding to an optical signal generated by a desired
optical-signal transmission unit, from among a plurality of signal
components corresponding to the plurality of optical signals generated by
the optical-signal transmitting units, included in the obtained reception
signal.
Further, according to another aspect of the present invention, the
foregoing object is attained by providing an optical-signal transmission
apparatus comprising:
an optical transmission medium that transmits signal light, having at least
one transmission node to input signal light into the optical transmission
medium and a plurality of reception nodes to output signal light from the
optical transmission medium;
an optical-signal transmission unit, provided in correspondence with the
transmission node, that generates a plurality of pulse string optical
signals having different light intensity levels or generates a multiplex
pulse string optical signal where a plurality of pulse string optical
signals having different light intensity levels are overlaid, and inputs
the optical signals or multiplex optical signal from the corresponding
transmission node into the optical transmission medium; and
an optical-signal reception unit, provided in correspondence with the
respective reception nodes, that obtains a reception signal by obtaining
the optical signals or multiplex optical signal transmitted from a
corresponding reception node, separates a signal component corresponding
to an optical signal generated by a desired optical-signal transmission
unit, from among a plurality of signal components corresponding to the
plurality of optical signals generated by the optical-signal transmitting
unit, included in the obtained reception signal.
In the optical-signal transmission apparatus according to the second aspect
of the present invention, in a case where the optical-signal transmission
unit generates a multiplex pulse string optical signal where a plurality
of pulse string optical signals having different light intensity levels
are overlaid, any process may be used for finally obtaining the multiplex
pulse string optical signal. For example, the multiplex pulse string
optical signal may be obtained by generating a multiplex pulse string
electric signal where a plurality of pulse string electric signals having
different signal intensity levels and converting the multiplex pulse
string electric signal into an optical signal. Alternatively, the
multiplex pulse string optical signal may be obtained by converting a
plurality of pulse string electric signals having different signal
intensity levels into pulse string optical signals and overlaying the
pulse string optical signals.
Further, according to another aspect of the present invention, the
foregoing object is attained by providing an optical-signal transmission
method comprising the steps of:
simultaneously introducing a plurality of optical signals having different
light intensity levels or a multiplex optical signal where a plurality of
optical signals having different light intensity levels are overlaid into
an optical transmission medium that transmits signal light;
obtaining a reception signal by receiving the optical signals or multiplex
optical signal transmitted from the optical transmission medium; and
separating a signal component corresponding to a desired optical signal
from the reception signal.
Further, according to another aspect of the present invention, the
foregoing object is attained by providing a signal processing apparatus
comprising:
an optical transmission medium that transmits signal light, having a
plurality of transmission nodes to input signal light into the optical
transmission medium and at least one reception node to output an optical
signal from the optical transmission medium;
a first circuit board sharedly carrying a plurality of optical-signal
transmission units that respectively emit an optical signal, and generate
a plurality of pulse string optical signals having different light
intensity levels for respective optical-signal transmission units;
a second circuit board sharedly carrying a plurality of optical-signal
reception units that obtain a reception signal by receiving the optical
signals or multiplex optical signal, and separate a signal component
corresponding to an optical signal generated by a desired optical-signal
transmission unit, from among a plurality of signal components
corresponding to the plurality of optical signals generated by the
plurality of optical-signal transmission units, included in the obtained
reception signal;
a support member that supports the first circuit board and the second
circuit board positioned with respect to the optical transmission medium
such that the optical signals generated from the optical-signal
transmission units on the first circuit board are introduced from the
transmission nodes into the optical transmission medium and signal light
transmitted from the reception node is transmitted into the optical-signal
reception unit on the second circuit board.
Further, according to another aspect of the present invention, the
foregoing object is attained by providing a signal processing apparatus
comprising:
an optical transmission medium that transmits signal light, having at least
one transmission node to input signal light into the optical transmission
medium and a plurality of reception nodes to output signal light from the
optical transmission medium;
a first circuit board carrying an optical-signal transmission unit that
simultaneously generates a plurality of pulse string optical signals
having different light intensity levels or a multiplex pulse string
optical signal where a plurality of pulse string optical signals having
different light intensity levels are overlaid, and outputs the optical
signals or multiplex optical signal;
a second circuit board carrying a plurality of optical-signal reception
units that obtain a reception signal by receiving the optical signals or
multiplex optical signal, and separate a signal component corresponding to
a desired optical signal from among a plurality of signal components
corresponding to the plurality of optical signals, included in the
obtained reception signal;
a support member that supports the first circuit board and the second
circuit board positioned with respect to the optical transmission medium
such that the optical signals generated from the optical-signal
transmission unit on the first circuit board are introduced from the
transmission node into the optical transmission medium and the signal
light transmitted from the reception nodes is transmitted into the
optical-signal reception units on the second circuit board.
Other features and advantages of the present invention will be apparent
from the following description taken in conjunction with the accompanying
drawings, in which reference characters designate the same name or similar
parts throughout the figures thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part
of the specification, illustrate embodiments of the invention and,
together with the description, serve to explain the principles of the
invention.
FIG. 1 is a block diagram showing the construction of an optical-signal
transmission apparatus using the optical-signal transmission method of the
present invention, according to a first embodiment of the present
invention;
FIG. 2 is a block diagram showing the construction of the optical-signal
transmission apparatus using the optical-signal transmission method of the
present invention, according to a second embodiment of the present
invention;
FIGS. 3A and 3B are graphs showing waveforms of optical signals introduced
into an optical transmission medium from two transmission nodes;
FIG. 4 is a graph showing a waveform of an optical signal transmitted from
a reception node;
FIG. 5 is a graph for explaining signal discrimination processing by a
receiver of an optical-signal reception unit;
FIG. 6 is a schematic diagram showing an example of the optical-signal
transmission unit;
FIG. 7 is a block diagram showing another example of the optical-signal
transmission unit;
FIG. 8 is a block diagram showing an example of the optical-signal
reception unit;
FIG. 9 is a schematic diagram showing the optical-signal transmission
apparatus according to a third embodiment of the present invention;
FIG. 10 is a cross-sectional view cut along an arrow A-A' in FIG. 9;
FIG. 11 is a schematic diagram showing the optical transmission medium of
the optical-signal transmission apparatus according to a fourth embodiment
of the present invention;
FIG. 12 is a perspective view showing an example of a signal processing
apparatus of the present invention; and
FIG. 13 is a block diagram showing an example of connection by an analog
bus disclosed in Japanese Published Unexamined Patent Application No. Hei
8-328707.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will now be described in
detail in accordance with the accompanying drawings.
FIG. 1 is a block diagram showing the construction of an optical-signal
transmission apparatus using an optical-signal transmission method of the
present invention, according to a first embodiment of the present
invention.
In FIG. 1, an optical-signal transmission apparatus 10 has an optical
transmission medium 11, a plurality of (two in FIG. 1) optical-signal
transmission units 12, one optical-signal reception unit 13, and an
arbitration unit 14.
The optical transmission medium 11 has a plurality of (two in FIG. 1)
transmission nodes 111 for introducing signal light into the optical
transmission medium 11 on one optical transmission end (the left end of
the optical transmission medium 11 in FIG. 1), and a reception node 112
for transmitting an optical signal transmitted through the optical
transmission medium 11 on the other optical transmission end (the right
end of the optical transmission medium 11 in FIG. 1). The optical
transmission medium 11 transmits the optical signals introduced from the
transmission nodes 111 to the reception node 112, and outputs the signals
from the reception node 112.
Further, the optical-signal transmission units 12, provided in
correspondence with the respective transmission nodes 111, respectively
generate an optical signal and input the generated optical signal from the
corresponding transmission nodes 111 into the optical transmission medium
11. The optical-signal transmission units 12 respectively have a light
emitter 121 for generating an optical signal, and a transmitter 122 for
generating an electric signal as a base of the optical signal generated
from the light emitter 121 and transmitting the electric signal to the
light emitter 121. The transmitter 122 generates a pulse string electric
signal and inputs the pulse string electric signal into the light emitter
121. The light emitter 121 outputs a pulse strings optical signal based on
the pulse string electric signal.
In the present embodiment, a plurality of (two in FIG. 1) optical-signal
transmission units 12 are provided, and the plurality of light emitters
121 of the optical-signal transmission units 12 output pulse string
optical signals having light intensity levels different from each other.
When the respective light emitters 121 output the optical signals having
different light intensity levels, the light intensity levels of optical
signals by the respective light emitters 121 may be fixedly determined,
however, it may be arranged such that the respective optical-signal
transmission units 12 can freely change the light intensity levels of
optical signals generated in the optical-signal transmission units, and as
shown in FIG. 1, an arbitration unit 14 may be provided to perform
arbitration among the plurality of optical-signal transmission units 12
such that the light intensity levels of the optical signals are different
from each other.
In FIG. 1, the number of the optical-signal transmission units 12 is only
two, and it may be arranged such that the light intensity levels of
optical signals generated from the respective optical-signal transmission
units 12 are set to predetermined levels in advance. However, if the
number of optical-signal transmission units is increased, it is rather
advantageous to provide the arbitration unit 14 to assign light intensity
levels, sequentially from the best level, in consideration of electric
consumption or S/N ratio and the like, than to fixedly set the light
intensity levels of optical signals generated from the respective
optical-signal transmission units.
Regarding the relation between the number of optical-signal transmission
units and the light intensity levels of optical signals, the number of
light intensity levels equals the number of optical-signal transmission
units, or the number of light intensity levels is less than that of
optical-signal transmission units.
The respective signal light generated from the light emitters 121 of the
respective optical-signal transmission units 12 are intriduced from the
respective transmission nodes 111 into the optical transmission medium 11,
and transmitted through the optical transmission medium 11 from the
reception node 112.
The optical-signal reception unit 13 is provided in correspondence with the
reception node 112. The optical signals transmitted from the reception
node 112 are transmitted into a photoreceptor 131 in the optical-signal
reception unit 13, and converted into an electric reception signal. Then,
a receiver 132 separates a signal component corresponding to an optical
signal generated by a desired one of optical-signal transmission units 12,
included in the reception signal obtained by the photoreceptor 131.
FIG. 2 is a block diagram showing the construction of the optical-signal
transmission apparatus using the optical-signal transmission method of the
present invention, according to a second embodiment of the present
invention.
In FIG. 2, the optical-signal transmission apparatus 10 has the optical
transmission medium 11, one optical-signal transmission unit 12, and a
plurality of (two in FIG. 2) optical-signal reception units 13.
The optical transmission medium 11 in the optical-signal transmission
apparatus 10 in FIG. 2 has one transmission node 111 for introducing
signal light to the optical transmission medium 11 on one optical
transmission end (the left end of the optical transmission medium 11 in
FIG. 2), and a plurality of (two in FIG. 2) reception nodes 112 for
transmitting the optical signal transmitted through the optical
transmission medium 11 on the other optical transmission end (the right
side end in FIG. 2). The optical transmission medium 11 transmits the
optical signal transmitted from the transmission node 111 to the
respective reception nodes 112, and outputs the optical signals from the
reception nodes 112.
Further, the optical-signal transmission unit 12, provided in
correspondence with the transmission node 111, generates an optical signal
and inputs the generated optical signal from the corresponding
transmission node 111 into the optical transmission medium 11. Similarly
to the first embodiment in FIG. 1, the optical-signal transmission unit 12
has the light emitter 121 which outputs an optical signal and the
transmitter 122 which generates an electric signal as a base of the
optical signal and transfers the electric signal to the light emitter 121.
However, in FIG. 2, the transmitter 122 generates a plurality of pulse
signals having signal levels different from each other in parallel, or
generates a multiplex pulse signal where a plurality of pulse signals
having signal levels different from each other are overlaid, and inputs
the plurality of pulse signals or the multiplex pulse signal into the
light emitter 121. The light emitter 121 generates a plurality of pulse
string optical signals or multiplex pulse string optical signal based on
the input electric signal(s).
Regarding the relation between the number of optical-signal reception units
and that of intensity levels of optical signals, the number of light
intensity levels may equal that of optical-signal reception units, or the
number of light intensity levels may be less than that of the
optical-signal reception units.
Further, in the present embodiment in FIG. 2, the optical-signal reception
units 13 are provided in correspondence with the plurality (two in FIG. 2)
of reception nodes 112. The optical-signal reception units 13 have the
same function as that of the optical-signal reception unit 13 in FIG. 1.
Hereinbelow, the first embodiment in FIG. 1 will be described in detail.
The following description can also be used for explaining the second
embodiment shown in FIG. 2 as long as the characteristic of the first
embodiment is not changed. Further, the feature of the second embodiment
as shown in FIG. 2 will be described later.
FIGS. 3A and 3B are graphs showing waveforms of optical signals introduced
into the optical transmission medium from two transmission nodes 111. FIG.
4 is a graph showing a waveform of an optical signal transmitted from the
reception node 112.
The light intensity levels of the "1" level optical signals at the
respective transmission nodes 111 are respectively "h1" and "h2"
(h1.noteq.h2). Further, the light intensity levels of the "0" level
optical signals are respectively "11" and "12". As shown in FIG. 4, the
reception node 112 receives a signal waveform which consist of the two
optical signals shown in FIG. 3 are added in the optical transmission
medium 11.
To obtain the light intensity of received signal in more detail, it is
necessary to consider the optical transmission efficiency in the optical
transmission medium 11, the respective combining efficiencies in the
transmission nodes 111 and the reception node 112, the difference among
efficiencies of the respective nodes, and the like. In this embodiment,
variation at each node is ignored. Let .eta.be the total optical-signal
transmission efficiency between the point where the optical signal is
generated from the light emitter 121 of the optical-signal transmission
unit 12 and the point where the optical signal is received by the
photoreceptor 131 of the optical-signal reception unit 13, then the
relation between the optical signals introduced from two transmission
nodes (A, B) and the optical signal transmitted from the recelption node
is represented as the following logical table in Table 1.
TABLE 1
Transmission Node A
logic "0" logic "1"
Transmission logic "0" .eta. .multidot. (l1 + l2) .eta. .multidot.
(h1 + l2)
Node B logic "1" .eta. .multidot. (h2 + 11) .eta. .multidot.
(h1 + h2)
Further, assuming that 11+12=0 holds since the light intensity levels 11
and 12 of the "0" level optical signal can be actually ignored, the table
1 can be simplified as represented as the following logical table 2.
TABLE 2
Transmission Node A
logic "0" logic "1"
Transmission logic "0" 0 .eta. .multidot. h1
Node B logic "1" .eta. .multidot. h2 .eta. .multidot. (h1 +
h2)
As shown in these logical tables, by setting in advance the light intensity
levels of signals to be received by the reception nodes, a desired signal
can be easily discriminated from a signal obtained by adding these
signals. More specifically, a desired signal is discriminated as follows.
FIG. 5 is a graph for explaining signal discrimination processing | | |
