JP2005303416A - Optical wireless system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical wireless system to prevent light receiving sensitivity from being deteriorated due to a loss or the like of light receiving power. <P>SOLUTION: A first light receiving unit 21 receives a transmission light outputted from a polarized optical beam splitter 51 through a lens 41, and a second light receiving unit 22 receives a reflected light outputted from the polarized optical beam splitter 51 through a lens 42. Then electric signals respectively outputted from the first and second light receiving units 21, 22 are coupled by a signal line 71 and input to a current voltage conversion element 61. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical wireless system that performs wireless communication using light as a carrier (transmission medium).

  In recent years, with the rapid increase in information volume, there has been a demand for large capacity and high speed in exchange and transmission of information data. In order to meet such demands, technological development relating to communication means such as optical communication and wireless communication is being carried out daily at a rapid speed.

  Among the communication means, wireless communication does not require wiring such as a cable, so that it is spreading to offices and homes. Furthermore, among wireless communications, optical wireless communications using light as a carrier has a narrow directivity due to the straightness of light and is strong in security, can be used in hospitals and airplanes because it does not emit electromagnetic waves, and licenses Has been attracting attention for reasons such as unnecessary.

  Hereinafter, a conventional optical wireless system will be described. FIG. 6 is a diagram illustrating conventional optical wireless communication, in which two-way communication using a polarization component is performed by one carrier having the same optical wavelength. This is because if the same optical wavelength is used when performing communication between the first and second transceivers 11 and 111, communication cannot be performed due to interference.

  In FIG. 6, 11 is a first transceiver, 21 and 121 are optical receivers that receive optical signals and convert them into electrical signals, 31 and 131 are light sources such as semiconductor lasers, and 41, 42, 141, and 142 are optical signals. , 51 and 151 are polarization beam splitters for separating the polarization component of the optical signal, 81 is a spatial light having a P-polarization (or S-polarization) component, 111 is a second transceiver, and 181 is an S-polarization ( (Or P-polarized light).

  Hereinafter, a case where the spatial light 81 output from the second transceiver 111 has a P-polarized component will be described. First, the optical signal output from the light source 131 in the second transmitter / receiver 111 is collected by the lens 142, and then only the P-polarized light component is transmitted through the polarization beam splitter 151 to be polarized and separated. Then, it is output from the second transceiver 111 and becomes the spatial light 81.

  The spatial light 81 having the P-polarized component is input to the first transmitter / receiver 11, passes through the polarization beam splitter 51 as it is, is collected by the lens 41, and is input to the light receiver 21.

  On the other hand, the optical signal output from the light source 31 in the first transmitter / receiver 11 is collected by the lens 42, and then the S-polarized component is reflected by the polarization beam splitter 51 to be polarized and separated. Then, it is output from the first transceiver 11 and becomes the spatial light 181.

  The spatial light 181 having the S-polarized component is input to the second transmitter / receiver 111, reflected by the polarizing beam splitter 151, condensed by the lens 141, and input to the light receiver 121.

  As described above, even if the wavelengths of the optical signals are the same, if the planes of polarization do not match, interference does not occur, and bidirectional communication can be performed.

Therefore, in the transmission of the spatial light 81 and 181, it is important to match the optical axis and the polarization plane of the spatial light 81 and the light receiver 21, and the spatial light 181 and the light receiver 121. For example, the optical axis is automatically corrected. As a method, a polarization mechanism is provided to scan a light beam with a preset pattern, detect a deviation of the optical axis and the polarization plane, and perform angle correction so that the optical axis and the polarization plane coincide with each other. (See Patent Document 1).
JP-A-7-99480 (page 18, FIG. 1)

  However, in the conventional optical wireless system, light leakage power is generated in the polarization beam splitter during the correction operation of the optical axis and the polarization angle between the transmitter and the receiver, and the light receiving sensitivity is reduced due to loss of received light power and irregular reflection of reflected light. There was a problem of deterioration. Further, when the light leakage power returns to the light source, the operation of the light source may become unstable.

  The present invention has been made in view of the above points, and the object of the present invention is to reduce the sensitivity of light reception due to loss of received light power and the problem of unstable operation of the light source in an optical wireless system. There is to eliminate.

That is, the invention of claim 1 is a polarization beam splitter that separates the polarization component of an optical signal and outputs reflected light at a predetermined position even when the optical axis or polarization plane is deviated.
First and second lenses for focusing;
First and second light receiving elements for converting an optical signal into an electric signal by receiving light;
A signal line for electrically connecting the first light receiving element and the second light receiving element;
An optical wireless system comprising at least a current-voltage conversion element that converts the electrical signal into a voltage,
Light transmitted by the polarization beam splitter is input to the first light receiving element through the first lens and converted into an electrical signal,
The reflected light from the polarization beam splitter is input to the second light receiving element through the second lens and converted into an electrical signal,
The electrical signals output from the first and second light receiving elements are coupled by the signal line and input to the current-voltage conversion element.

The invention of claim 2 comprises a light source,
First and second polarization beam splitters that separate the polarization components of an optical signal and output reflected light at a predetermined position even when the optical axis or plane of polarization is shifted;
First to third lenses for focusing;
First and second light receiving elements for converting an optical signal into an electric signal by receiving light;
A signal line for electrically connecting the first light receiving element and the second light receiving element;
A Faraday element that changes the polarization angle of the optical signal;
An optical wireless system comprising at least a current-voltage conversion element that converts the electrical signal into a voltage,
One of the transmitted light and reflected light output from the first polarization beam splitter is input to the first light receiving element through the first lens and converted into an electrical signal,
The other output light of the transmitted light or the reflected light output from the first polarizing beam splitter is input to the second polarizing beam splitter after the polarization angle is changed by the Faraday element,
Transmitted light or reflected light output from the second polarizing beam splitter is input to the second light receiving element through the second lens and converted into an electrical signal,
Electrical signals respectively output from the first and second light receiving elements are coupled by the signal line, input to the current-voltage conversion element, and converted into a voltage.
The output light output from the light source is input to the second polarization beam splitter through the third lens,
The transmitted light or reflected light output from the second polarizing beam splitter by the input of the output light from the light source is input to the first polarizing beam splitter after the polarization angle is changed by the Faraday element. It is comprised as follows.

The invention of claim 3 is the optical wireless system according to claim 2,
A second light source;
Third and fourth polarization beam splitters that separate the polarization components of the optical signal and output reflected light at a predetermined position even when the optical axis or plane of polarization is deviated;
4th to 6th lenses for focusing;
Third and fourth light receiving elements for converting an optical signal into an electric signal by receiving light;
A second signal line for electrically connecting the third light receiving element and the fourth light receiving element;
A second Faraday element that changes a polarization angle of the optical signal;
A second current-voltage conversion element that converts the electrical signal into a voltage;
The first polarizing beam splitter and the third polarizing beam splitter are optically connected for bidirectional communication of optical signals,
One of the transmitted light and reflected light output from the third polarizing beam splitter is input to the third light receiving element through the fourth lens and converted into an electrical signal,
The other output light of the transmitted light or the reflected light output from the third polarizing beam splitter is input to the fourth polarizing beam splitter after the polarization angle is changed by the second Faraday element. ,
Transmitted light or reflected light output from the fourth polarizing beam splitter is input to the fourth light receiving element through the fifth lens and converted into an electrical signal,
The electrical signals respectively output from the third and fourth light receiving elements are coupled by the second signal line, input to the current-voltage conversion element, and converted into a voltage.
The output light output from the second light source is input to the fourth polarization beam splitter through the sixth lens,
The transmitted or reflected light output from the fourth polarization beam splitter by the input of the output light from the second light source is changed to the third polarization after the polarization angle is changed by the second Faraday element. It is configured to be input to a beam splitter.

The invention of claim 4 is the optical wireless system according to claim 2 or 3,
At least one of the second and fourth polarizing beam splitters is replaced with a beam splitter that transmits light input from one direction and reflects light input from the other direction. .

  As described above, according to the first aspect of the present invention, since the electric signals output from the first and second light receiving elements are coupled by the signal line and input to the current-voltage conversion element, Loss can be prevented and deterioration of reception sensitivity can be suppressed.

  According to the second aspect of the present invention, the polarization angle can be corrected by further providing the Faraday element that changes the polarization angle of the optical signal, and the loss of the received light power is prevented to suppress the deterioration of the reception sensitivity. be able to. In addition, since a light source is added to the system, it is possible to transmit and receive optical signals.

  According to the invention of claim 3, by connecting the first polarization beam splitter and the third polarization beam splitter optically, the first transceiver having the first polarization beam splitter and the third It is possible to form a second transmitter / receiver including the polarizing beam splitter and to perform bidirectional communication between the first transmitter / receiver and the second transmitter / receiver.

  According to the invention of claim 4, the second or fourth polarization beam splitter configured to output the reflected light at a predetermined position even when the optical axis or the polarization plane is shifted is replaced with a normal beam splitter. Thus, it is advantageous in reducing the cost of the entire system while ensuring the transmission / reception performance of the optical signal.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or its application.

<Embodiment 1>
FIG. 1 shows a configuration of an optical wireless system according to Embodiment 1 of the present invention. In FIG. 1, 11 is a transceiver, 21 and 22 are light receivers (light receiving elements) such as photodiodes that receive optical signals and convert them into electrical signals, 41 and 42 are lenses that collect optical signals, and 51 is light. A polarization beam splitter that separates the polarization component of the signal and outputs reflected light at a predetermined position, 61 is a current-voltage conversion element such as a transimpedance amplifier that converts an electrical signal into a voltage, and 71 is an electrical receiver for the light receivers 21 and 22. A signal line to be connected, 81 is a spatial light having a P-polarized (or S-polarized) component, 90 is a transmitted light output from the polarizing beam splitter 51, and 91 is a reflected light output from the polarizing beam splitter 51.

  Hereinafter, a case where the spatial light 81 has a P-polarized component will be described. The spatial light 81 is input to the transceiver 11 and the transmitted light 90 is output from the polarization beam splitter 51. The transmitted light 90 is input to the light receiver 21 through the lens 41, and is converted from an optical signal to an electrical signal by the light receiver 21.

  On the other hand, the reflected light 91 reflected by the polarization beam splitter 51 in the spatial light 81 is input to the light receiver 22 through the lens 42, and is converted from an optical signal to an electrical signal by the light receiver 22.

  The electric signals output from the light receivers 21 and 22 are coupled by the signal line 71 and input to the current-voltage conversion element 61, and the current-voltage conversion element 61 performs current-voltage conversion processing.

  When the optical axis of the polarization component of the spatial light 81 and the polarization plane of the polarization beam splitter 51 are not shifted, there is almost no reflected light 91 reflected by the polarization beam splitter 51. It becomes possible to perform stable communication without any loss.

  Next, the structure of the polarizing beam splitter 51 will be described with reference to FIG. 2A is a plan view of the polarizing beam splitter 51, and FIG. 2B is a side view of the polarizing beam splitter 51. As shown in FIG.

  As shown in FIG. 2A, the polarization plane that separates the polarization component of the optical signal has an axis passing through the midpoints of the upper and lower sides of the rectangular plane to which the optical signal is input in the polarization beam splitter 51 as the rotation axis C. The trajectory when rotating about the rotation axis C is formed to be a concentric circle. Further, as shown in FIG. 2B, the plane of polarization of the polarization plane has a lower side of a rectangular plane to which an optical signal is input as a rotation axis D, and a locus when rotated about the rotation axis D is a concentric circle. Is formed.

  Therefore, if the polarization beam splitter 51 having a polarization plane having both the shapes shown in FIGS. 2A and 2B is used, an optical signal is reflected at a predetermined position even when the optical axis or the polarization plane is shifted. Is possible. Thereby, even when the optical axis and the polarization plane are deviated due to wind or vibration, the reflected light 91 by the polarization beam splitter 51 can be reflected toward the input part of the light receiver 22 and input to the light receiver 22.

  As described above, according to the first embodiment, the electric signals output from the light receivers 21 and 22 are combined by the signal line 71 and input to the current-voltage conversion element 61 to perform current-voltage conversion processing. As a result, loss of received light power can be prevented and deterioration of reception sensitivity can be suppressed.

  Specifically, in the conventional optical wireless system, as shown in FIG. 3A, communication cannot be performed while correcting the optical axis and the polarization plane. According to the wireless system, communication can be performed while correcting the optical axis and the polarization plane as shown in FIG.

<Embodiment 2>
Next, Embodiment 2 of the present invention will be described. In addition, the same code | symbol is attached | subjected about the same part as Embodiment 1, and only a different point is demonstrated.

  FIG. 4 shows the configuration of the optical wireless system in the second embodiment of the present invention. In FIG. 4, 31 is a light source such as a semiconductor laser, 43 is a lens that collects an optical signal, 52 is a polarization beam splitter that separates the polarization components of the optical signal and outputs reflected light at a predetermined position, and 55 is the polarization angle. A Faraday element to be changed, 92 is reflected light output from the polarization beam splitter 52, 95 is output light output from the light source 31, and 96 is transmitted light output from the polarization beam splitter 52.

  Hereinafter, a case where the spatial light 81 has a P-polarized component will be described. The spatial light 81 is input to the transceiver 11 and the transmitted light 90 is output from the polarization beam splitter 51. The transmitted light 90 is input to the light receiver 21 through the lens 41, and is converted from an optical signal to an electrical signal by the light receiver 21.

  On the other hand, the reflected light 91 reflected by the polarization beam splitter 51 in the spatial light 81 is rotated 45 degrees counterclockwise (or clockwise) with respect to the traveling direction by the Faraday element 55. Then, it is input to the polarization beam splitter 52.

  Here, the polarization beam splitter 52 is arranged to rotate 45 degrees counterclockwise (or clockwise) with respect to the polarization beam splitter 51 with the reflected light 91 as the traveling direction. Then, the reflected light 92 reflected by the polarization beam splitter 52 is input to the light receiver 22 through the lens 43, and is converted from an optical signal to an electric signal by the light receiver 22.

  The electrical signals output from the light receivers 21 and 22 are coupled by the signal line 71 and input to the current-voltage conversion element 61, and current-voltage conversion processing is performed by the current-voltage conversion element 61.

  Next, the output light 95 output from the light source 31 is input to the polarizing beam splitter 52 through the lens 42, and the transmitted light 96 is output from the polarizing beam splitter 52. The transmitted light 96 is input to the polarizing beam splitter 51 after the polarization angle is rotated 45 degrees counterclockwise (or clockwise) with respect to the traveling direction by the Faraday element 55. Then, the reflected light reflected by the polarizing beam splitter 51 becomes the spatial light 181 and is output from the transceiver 11.

  When the optical axis of the polarization component of the spatial light 81 and the polarization plane of the polarization beam splitter 51 are not shifted, there is almost no reflected light 91 reflected by the polarization beam splitter 51. It becomes possible to perform stable communication without any loss.

  As described above, according to the second embodiment, since the Faraday element that changes the polarization angle of the optical signal is provided, the polarization angle can be corrected, and loss of received light power can be prevented to deteriorate reception sensitivity. Can be suppressed. Furthermore, the addition of the light source 31 makes it possible to transmit and receive optical signals.

  In the second embodiment, the polarizing beam splitter 52 has the same structure as that of the polarizing beam splitter 51. However, the present invention is not limited to this, and the output light 95 output from the light source 31 is transmitted and polarized. A normal beam splitter configured to reflect the reflected light 91 reflected by the beam splitter 51 toward the light receiver 22 may be used.

<Embodiment 3>
FIG. 5 shows a configuration of an optical wireless system according to the third embodiment of the present invention. In FIG. 5, 111 is a transceiver, 121 and 122 are light receivers such as photodiodes that receive optical signals and convert them into electrical signals, 131 is a light source such as a semiconductor laser, and 141, 142, and 143 condense the optical signals. Lenses 151 and 152 are polarization beam splitters that separate the polarization components of the optical signal and output reflected light at predetermined positions, 155 is a Faraday element that changes the polarization angle, and 161 is a transimpedance amplifier that converts the electrical signal into a voltage. 171 is a signal line for electrically connecting the light receivers 121 and 122, 81 is spatial light having a P-polarized (or S-polarized) component, 195 is output light output from the light source 131, 181 Is the spatial light of the S-polarized (or P-polarized) component, 190 is the light reflected by the polarizing beam splitter 51, and 191 is the polarization beam. The transmitted light by the splitter 151, 192 light reflected by the polarizing beam splitter 152, 196 is a transmitted light by the polarizing beam splitter 152.

  Hereinafter, a case where the spatial light 81 has a P-polarized component and the spatial light 181 has an S-polarized component will be described. Since the structure of the transceiver 11 is the same as that shown in the second embodiment, only the structure of the transceiver 111 optically connected to the transceiver 11 will be described.

  The spatial light 181 is input to the transceiver 111 and reflected by the polarizing beam splitter 151, and reflected light 190 is output from the polarizing beam splitter 151. The reflected light 190 is input to the light receiver 121 through the lens 141, and is converted from an optical signal to an electric signal by the light receiver 121.

  On the other hand, the transmitted light 191 transmitted through the polarization beam splitter 151 among the spatial light 181 is rotated 45 degrees clockwise (or counterclockwise) with respect to the traveling direction in the polarization angle by the Faraday element 155. Thereafter, the light is input to the polarization beam splitter 152.

  Here, the polarization beam splitter 152 is arranged to rotate 45 degrees clockwise (or counterclockwise) with respect to the polarization beam splitter 152 with the transmitted light 191 as the traveling direction. Then, the reflected light 192 reflected by the polarizing beam splitter 152 is input to the light receiver 122 through the lens 143 and is converted from an optical signal to an electric signal by the light receiver 122.

  The electric signals output from the light receivers 121 and 122 are coupled by the signal line 171 and input to the current-voltage conversion element 161, and the current-voltage conversion element 161 performs current-voltage conversion processing.

  Next, the output light 195 output from the light source 131 is input to the polarization beam splitter 152 through the lens 142, and the transmitted light 196 is output from the polarization beam splitter 152. The transmitted light 196 is rotated 45 degrees clockwise (or counterclockwise) with respect to the traveling direction by the Faraday element 155 and then input to the polarization beam splitter 151. The transmitted light that has passed through the polarizing beam splitter 151 becomes the spatial light 81 and is output from the transceiver 111.

  When the optical axis of the polarization component of the spatial light 181 and the polarization plane of the polarization beam splitter 151 are not deviated, there is almost no transmitted light 191 that passes through the polarization beam splitter 151. It is possible to perform stable two-way communication without any problems.

  As described above, according to the third embodiment, by providing the transceivers 11 and 111, loss of received light power can be prevented and deterioration of reception sensitivity can be suppressed, and both the transceivers 11 and 111 can be prevented. Two-way communication can be performed between them.

  In the third embodiment, the polarization beam splitters 52 and 152 have the same structure as that of the polarization beam splitters 51 and 151, but the present invention is not limited to this, and output light output from the light sources 31 and 131 is used. Ordinary beam splitters configured to reflect the optical signals transmitted through 95 and 195 and output from the polarization beam splitters 51 and 151 toward the light receivers 22 and 122, respectively, may be used.

  As described above, the present invention is extremely useful and industrially effective in an optical wireless system because it can prevent loss of received light power and suppress deterioration in reception sensitivity. The availability of is high.

1 is a diagram illustrating an optical wireless system according to a first embodiment of the present invention. (A) It is a top view which shows a polarizing beam splitter. (B) It is a side view which shows a polarizing beam splitter. (A) It is a figure which shows the conventional communication speed during correct | amending an optical axis or a polarization plane. (B) It is a figure which shows the communication speed of this invention in correcting the optical axis and the polarization plane. It is a figure which shows the optical wireless system which concerns on Embodiment 2 of this invention. It is a figure which shows the optical wireless system which concerns on Embodiment 3 of this invention. It is a figure which shows the optical wireless system which concerns on the prior art example of this invention.

Explanation of symbols

11, 111 Transceiver 21, 22, 121, 122 Light receiver 31, 131 Light source 41, 42, 43, 44, 141, 142, 143 Lens 51, 151 Polarizing beam splitter 52, 152 Polarizing beam splitter 55, 155 Faraday element 61 161 Current-voltage conversion elements 71, 171 Signal line 81 Spatial light 90 Transmitted light 91 Reflected light 92 Reflected light 95 Transmitted light 181 Spatial light 190 Reflected light 191 Transmitted light 192 Reflected light 196 Transmitted light

Claims (4)

A polarization beam splitter that separates the polarization component of the optical signal and outputs reflected light at a predetermined position even when the optical axis or polarization plane is deviated,
First and second lenses for focusing;
First and second light receiving elements for converting an optical signal into an electric signal by receiving light;
A signal line for electrically connecting the first light receiving element and the second light receiving element;
An optical wireless system comprising at least a current-voltage conversion element that converts the electrical signal into a voltage,
Light transmitted by the polarization beam splitter is input to the first light receiving element through the first lens and converted into an electrical signal,
The reflected light from the polarization beam splitter is input to the second light receiving element through the second lens and converted into an electrical signal,
An optical wireless system, wherein electrical signals output from the first and second light receiving elements are coupled by the signal line and input to the current-voltage conversion element. A light source;
First and second polarization beam splitters that separate the polarization components of an optical signal and output reflected light at a predetermined position even when the optical axis or plane of polarization is shifted;
First to third lenses for focusing;
First and second light receiving elements for converting an optical signal into an electric signal by receiving light;
A signal line for electrically connecting the first light receiving element and the second light receiving element;
A Faraday element that changes the polarization angle of the optical signal;
An optical wireless system comprising at least a current-voltage conversion element that converts the electrical signal into a voltage,
One of the transmitted light and reflected light output from the first polarization beam splitter is input to the first light receiving element through the first lens and converted into an electrical signal,
The other output light of the transmitted light or the reflected light output from the first polarizing beam splitter is input to the second polarizing beam splitter after the polarization angle is changed by the Faraday element,
Transmitted light or reflected light output from the second polarizing beam splitter is input to the second light receiving element through the second lens and converted into an electrical signal,
Electrical signals respectively output from the first and second light receiving elements are coupled by the signal line, input to the current-voltage conversion element, and converted into a voltage.
The output light output from the light source is input to the second polarization beam splitter through the third lens,
The transmitted light or reflected light output from the second polarizing beam splitter by the input of the output light from the light source is input to the first polarizing beam splitter after the polarization angle is changed by the Faraday element. An optical wireless system configured as described above. The optical wireless system according to claim 2,
A second light source;
Third and fourth polarization beam splitters that separate the polarization components of the optical signal and output reflected light at a predetermined position even when the optical axis or plane of polarization is deviated;
4th to 6th lenses for focusing;
Third and fourth light receiving elements for converting an optical signal into an electric signal by receiving light;
A second signal line for electrically connecting the third light receiving element and the fourth light receiving element;
A second Faraday element that changes a polarization angle of the optical signal;
A second current-voltage conversion element that converts the electrical signal into a voltage;
The first polarizing beam splitter and the third polarizing beam splitter are optically connected for bidirectional communication of optical signals,
One of the transmitted light and reflected light output from the third polarizing beam splitter is input to the third light receiving element through the fourth lens and converted into an electrical signal,
The other output light of the transmitted light or the reflected light output from the third polarizing beam splitter is input to the fourth polarizing beam splitter after the polarization angle is changed by the second Faraday element. ,
Transmitted light or reflected light output from the fourth polarizing beam splitter is input to the fourth light receiving element through the fifth lens and converted into an electrical signal,
The electrical signals respectively output from the third and fourth light receiving elements are coupled by the second signal line, input to the current-voltage conversion element, and converted into a voltage.
The output light output from the second light source is input to the fourth polarization beam splitter through the sixth lens,
The transmitted or reflected light output from the fourth polarization beam splitter by the input of the output light from the second light source is changed to the third polarization after the polarization angle is changed by the second Faraday element. An optical wireless system configured to be input to a beam splitter. In the optical wireless system according to claim 2 or 3,
At least one of the second and fourth polarizing beam splitters is replaced with a beam splitter that transmits light input from one direction and reflects light input from the other direction. Optical wireless system.

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