Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-06-02
2002-07-02
Chan, Jason (Department: 2733)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200
Reexamination Certificate
active
06414773
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical digital communication apparatus for transmitting and receiving digital data by using light.
2. Description of Related Art
As a conventional optical digital data communication apparatus is constituted by a transmission section and a reception section. In the transmission section, an infrared LED or a laser diode is driven by a digital electric signal corresponding to digital data to be transmitted, and an infrared signal corresponding to the data is radiated into space.
The reception section receives the infrared signal radiated from the transmission section by an infrared-receiving element such as a photodiode and convert the infrared signal into an analog electric signal. In addition, in the reception section, the obtained analog electric signal is amplified and then converted into a digital signal by a comparator or the like.
An infrared digital data communication apparatus generally performs communication between modules each having both of a transmission section and a reception section. However, the infrared digital data communication apparatus may perform communication between a module having only a transmission section and a module having only a reception section.
However, as one of factors which limits a communication distance, there is disturbance optical noise. As disturbance optical noise in the infrared digital data communication apparatus, noise such as sunlight, radiation light from an incandescent lamp or radiation light from a fluorescent lamp are known. In order to remove influence of such disturbance optical noise, various countermeasures are made in reception sections.
As a main countermeasure for removing influence of such disturbance optical noise, an arrangement of an optical filter, a device of the position of a light-receiving element, or the like is performed in an optical manner, and a method of using a filter is performed in an electric manner. However, according to these methods, shielding or filtering prevents receiving of disturbance optical noise, or received disturbance optical noise is removed by an electric filter. As a result, the disturbance noise cannot be completely removed.
For this reason, the present applicant has proposed an optical digital communication apparatus having the following arrangement in Japanese Patent Application No. 8-348878 (Japanese Patent Application Laid-Open No. 9-321705), Japanese Patent Application No. 8-348873 (Japanese Patent Application Laid-Open No. 9-321704), or the like. That is, two different optical signals are received to be converted into electric signals, and the level difference between the electric signals is detected to make it possible to remove a noise component.
An arrangement disclosed in Japanese Patent Application No. 8-348878 (Japanese Patent Application Laid-open No. 9-321705) is shown in
FIG. 2
(to be referred to as a first prior art hereinafter). The optical digital communication apparatus shown in
FIG. 2
converts a digital electric signal serving as an object of transmission into an optical signal in a transmission section
1
, emits the optical signal from the transmission section
1
to a reception section
2
, and converts the optical signal received by the reception signal
2
into an electric signal.
The transmission section
1
is constituted by a digital signal input terminal
11
, a drive circuit
12
, a light-emitting element
13
, a linearly polarizing plate
14
, and a ¼-wavelength plate
15
.
The light-emitting element
13
is driven through the drive circuit
12
by a digital signal DS
1
input to the digital signal input terminal
11
and serving as an object of transmission, and an optical signal is output from the light-emitting element
13
.
In addition, the optical signal is linearly polarized by the linearly polarizing plate
14
arranged on the light-emitting side of the light-emitting element
13
, and then is emitted by the ¼-wavelength plate
15
into space as a circularly polarized light component or an elliptically polarized light component.
On the other hand, the reception section
2
is constituted by ¼-wavelength plates
21
A and
21
B, linearly polarizing plates
22
A and
22
B, light-receiving elements
23
A and
23
B constituted by PIN photodiodes, and a subtraction circuit
24
.
The light-receiving element
23
A receives an optical light radiated from the transmission section and converts the optical signal into an electric signal DS
2
to output the electric signal DS
2
. The light-receiving element
23
B receives disturbance light scattered in space and converts the disturbance light into an electric signal DS
2
′ to output the electric signal DS
2
′.
A ¼length plate
21
A and a linearly polarizing plate
22
A are arranged on the light incident side of the light-receiving element
23
A. The ¼length plate
21
A and the linearly polarizing plate
22
A convert circularly polarized light components or elliptically polarized light components radiated from the transmission section
1
into linearly polarized light components to cause the linearly polarized light components to be incident on the light-receiving element
23
A.
The ¼length plate
21
B and the linearly polarizing plate
22
B are arranged on the light incident side of the light-receiving element
23
B. The ¼length plate
21
B and the linearly polarizing plate
22
B convert circularly polarized light components or elliptically polarized light components having a rotating direction which is different from that of the circularly polarized light components or the elliptically polarized light component radiated from the transmission section
1
into linearly polarized light components to cause the linearly polarized light components to be incident on the light-receiving element
23
B.
The output signals DS
2
and DS
2
′ from the two light-receiving elements
23
A and
23
B are input to the subtraction circuit
24
. An electric signal DS
3
having a voltage level obtained such that the subtraction circuit
24
subtracts the voltage level of the electric signal DS
2
′ output from the other light-receiving element
23
B from the voltage level of the electric signal DS
2
output from the light-receiving element
23
A is output.
On the other hand, the main electric system circuit of the transmission section
1
and the reception section
2
has the arrangement shown in FIG.
3
. More specifically, the drive circuit
12
in the transmission section
1
is constituted by resistors
121
to
124
and a transistor
125
, and the digital signal DS
1
is input to one terminal of the resistor
121
. The other terminal of the resistor
121
is connected to the base of the transistor
125
and one terminal of the resistor
122
, and the emitter of the transistor
125
is connected to the one terminal of the resistor
123
. A predetermined voltage +V is applied to the other terminals of the resistors
122
and
123
. Furthermore, the collector of the transistor
125
is connected to the anode of the light-emitting element (LED)
13
through the resistor
124
, and the cathode of the light-emitting element (LED)
13
is grounded.
With the arrangement, the transistor
125
is switching-operated in response to the digital signal DS
1
to apply a voltage to the light-emitting element
13
, thereby driving the light-emitting element
13
.
In the reception section
2
, the subtraction circuit
24
is constituted by a resistor
241
and an amplifier
242
, and one terminal of the resistor
241
is connected to the anode of the light-receiving element (photodiode)
23
A, the cathode of the light-emitting element (photodiode)
23
B, and the input terminal of the amplifier
242
, and the other terminal of the resistor
241
is grounded. Furthermore, a predetermined positive voltage +V
1
is applied to the cathode of the light-receiving element
23
A, and a predetermined negative voltage −V
1
is applied to the anode of the light-receiving ele
Aoki Mikio
Masuzawa Kazutaka
Chan Jason
Leung Christina Y
Lowe Hauptman & Gilman & Berner LLP
Taiyo Yuden Co. Ltd.
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