JP2004032461A - Optical wireless communication system, optical radio transceiver, and optical radio transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical wireless communication system which wirelessly transmits a light signal independently of the sunlight. <P>SOLUTION: The optical wireless communication system for performing communication using a laser beam in a free space includes an optical wireless transmitter and an optical wireless receiver. In the transmitter, two semiconductor lasers having a mutually orthogonal relations in their polarized direction perform complementarily intensity modulation according to an input data signal. In the receiver, a polarized light separation prism separates polarized light, and current/voltage conversion is carried out at a middle point of two photodiodes positioned in series, whereby only a differential signal of the polarized-light separated optical signal currents is converted to a voltage to obtain data signal. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a point-to-point optical wireless communication system, an optical wireless transceiver, and an optical wireless transmitter that are not easily affected by background light noise such as sunlight when transmitting and receiving optical signals in free space.
[0002]
[Prior art]
2. Description of the Related Art An optical wireless communication system for transmitting and receiving an optical signal through free space is promising as a communication system in an area where it is difficult to lay an optical fiber or the like and radio waves cannot be used. For example, in an area such as a hospital where the use of wireless devices is restricted, data communication can be easily performed between buildings without performing large-scale construction such as laying optical fibers. In addition, when using radio waves, a wireless license is required, and companies and individuals other than telecommunications carriers cannot freely perform data communication. However, the optical wireless communication system has an advantage that individuals and companies can freely perform data communication.
[0003]
[Problems to be solved by the invention]
As described above, by installing one pair of optical wireless transceivers, mutual data communication can be easily performed. However, at the installation position of the optical wireless transceiver, there is a possibility that a time zone during which data communication cannot be performed may occur because the sun enters on an extension of the pair of optical wireless transceiver links. Therefore, conventionally, there has been a restriction that the optical wireless transceiver must be installed by selecting an installation direction such that sunlight does not enter the optical wireless transceiver. Alternatively, as shown in JP-A-10-107556, a light receiving element for light signal, a light receiving element for bias circuit, and a circuit in which a resistor is connected in parallel are connected in series, so that the light receiving element is applied to the light receiving element in direct sunlight such as sunlight. There is a device that reduces the influence of sunlight by increasing the bias voltage, but has a disadvantage in that the circuit configuration is complicated.
[0004]
The present invention has been made in consideration of eliminating the restriction on the installation direction of an optical wireless transceiver, and has a simple configuration that enables normal data communication even with background light noise caused by sunlight. , An optical wireless transceiver and an optical wireless transmitter.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the optical wireless communication system of the present invention is an optical wireless communication system that performs wireless communication using light between an optical wireless transmitter and an optical wireless receiver, wherein the optical wireless transmitter is A first semiconductor laser, a second semiconductor laser having a polarization orthogonal to the polarization of the first semiconductor laser, and the first semiconductor laser or the second semiconductor laser corresponding to a mark and a space of an input data signal. Driving means for driving two semiconductor lasers and generating light beams having polarizations orthogonal to each other from the first semiconductor laser or the second semiconductor laser; and a driving means for driving the first semiconductor laser and the second semiconductor laser. A multiplexer for coupling the output light, wherein the optical wireless receiver separates the polarization of the light incident from the optical wireless transmitter into a first polarization light and a second polarization light orthogonal to each other. And the duplexer A first polarized light and a second polarized light are input thereto, and a data signal reproducing unit is provided for obtaining an output data signal in which a mark and a space are identified according to the direction of the polarized light. is there.
[0006]
Further, the optical wireless communication system of the present invention performs wireless communication using light between a first optical wireless transceiver and a second optical wireless transceiver, and transmits the first optical transceiver to the second optical wireless transceiver. The first optical transceiver uses the reflected wave from the reflector provided in the second optical transceiver when transmitting light to the second optical transceiver and performs direction adjustment with respect to the second optical transceiver; In a wireless communication system, the first optical wireless transceiver includes a first semiconductor laser, a second semiconductor laser having a polarization orthogonal to the polarization of the first semiconductor laser, and a mark of the input data signal. And driving the first semiconductor laser or the second semiconductor laser by a positive logic output or a negative logic path output of a transistor differential current switch circuit configured to switch the current of the variable current source in accordance with the space, Driving means for modulating the amount of current of the variable current source with a signal of a constant frequency and generating mutually orthogonally polarized light from the first semiconductor laser or the second semiconductor laser; and the first semiconductor laser. And a combiner for combining the lights output from the second semiconductor laser, respectively, and the reflected light reflected from the second optical transceiver and the received light from the second optical transceiver. A demultiplexer that separates the polarized light into a first polarized light and a second polarized light that are orthogonal to each other, and a first photodetector that receives the first polarized light and has a cathode connected to a positive power supply. A diode, a second photodiode that receives the second polarized light, and a negative power supply is connected to the anode thereof, a capacitor connected to the anode of the second photodiode, one end of which is installed, Second photo A second current-to-voltage converter connected to the anode of the anode, an output of the second current-to-voltage converter and a signal of the predetermined frequency being input, and an output of the second current-to-voltage converter and the predetermined And a synchronous detector for synchronously detecting a signal having the frequency of (i) and (ii) adjusting the direction of the first optical wireless transceiver with respect to the second optical wireless transceiver so that the detection output of the synchronous detector is maximized. Is performed.
[0007]
Further, the optical wireless transmitter of the present invention is used in an optical wireless communication system for performing wireless communication using light between an optical wireless transmitter and an optical wireless receiver, and the transmitting unit is provided with a first unit. A semiconductor laser, a second semiconductor laser having a polarization orthogonal to the polarization of the first semiconductor laser, and the first semiconductor laser or the second semiconductor laser corresponding to a mark and a space of an input data signal. Driving means for driving the first semiconductor laser or the second semiconductor laser to generate lights orthogonal to each other in polarization, and the light output from the first semiconductor laser and the light output from the second semiconductor laser, respectively. And a combiner for coupling.
[0008]
Further, the optical wireless transceiver of the present invention is used in an optical wireless communication system for performing wireless communication using light between optical wireless transceivers, and the transmission unit includes a first semiconductor laser and the first semiconductor laser. A second semiconductor laser having a polarization orthogonal to the polarization of the first semiconductor laser and the first semiconductor laser or the second semiconductor laser corresponding to the mark and space of the input data signal, and Driving means for generating light orthogonal to the wave from the first semiconductor laser or the second semiconductor laser; and a multiplexer for coupling the light output from the first semiconductor laser and the light output from the second semiconductor laser, respectively. A splitter that separates the polarization of light incident from the other optical wireless transceiver into a first polarization light and a second polarization light orthogonal to each other, The polarized light and the second polarized light are Is the force, in which a mark and a space depending on the direction of polarization is characterized by comprising a data signal reproduction section to obtain the output stator signal is identified.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
(First Embodiment)
Hereinafter, a first embodiment according to the present invention will be described with reference to the drawings. FIG. 1 shows a first embodiment of the optical wireless communication system of the present invention.
[0010]
In FIG. 1, a first optical wireless transceiver 100 and a second optical wireless transceiver 200 each include a transmitting unit (101, 201) and a receiving unit (102, 202). And the second optical wireless transceiver 200 have the same configuration. Furthermore, the first optical wireless transceiver 100 and the second optical wireless transceiver 200 are arranged at opposing positions where optical wireless communication can be performed, and the first optical wireless transceiver 100 and the second transceiver 200 are Communication is performed with each other. Here, a description will be given on the assumption that optical wireless communication is performed from the first optical wireless transceiver 100 to the second optical wireless transceiver 200.
[0011]
The data signal input to the transmission unit 101 of the first optical wireless transceiver 101 is amplified by the buffer amplifier 1-1. According to the amplified data signal, the current Ip of the current source 2-1 is switched by a differential switch circuit composed of the first bipolar transistor 3-1 and the second bipolar transistor 4-1. That is, when the data signal input to the base of the first bipolar transistor 3-1 is "H", the first bipolar transistor 3-1 is turned "ON", and the second bipolar transistor 4-1 is turned "OFF". '.
[0012]
The cathode of the first semiconductor laser 5-1 and a first bias current source 7-1 for supplying a bias current to the first semiconductor laser 5-1 are connected to the collector of the first bipolar transistor 3-1. ing.
[0013]
The collector of the second bipolar transistor 4-1 is provided with a cathode of the second semiconductor laser 6-1 and a second bias current source 8-1 for supplying a bias current to the second semiconductor laser 6-1. It is connected.
[0014]
It is assumed that the polarization output from the first semiconductor laser is parallel to the page as shown in FIG. 1, and the polarization output from the second semiconductor laser is perpendicular to the page as shown in FIG. That is, the polarization output from the first semiconductor laser and the polarization output from the second semiconductor laser have an orthogonal relationship. Output lights of two orthogonal semiconductor lasers are multiplexed by the polarizing prism 9-1 and output to the second optical wireless transceiver 200 as an output of the first optical wireless transceiver 100.
[0015]
The first semiconductor laser 3-1 and the second semiconductor laser 4-1 which output orthogonally polarized waves output light complementary to each other based on a data signal input to the first optical wireless transceiver. That is, when the input data signal is “H”, the first bipolar transistor 3-1 is turned “ON”, and the current Ip of the current source 2-1 flows to the first semiconductor laser to output light. At this time, the second bipolar transistor 4-1 is turned OFF, and only the current Ib2 of the second bias current source 8-1 is applied to the second semiconductor laser 6-1 to emit only bias light.
[0016]
Next, when the input data is “L”, the first bipolar transistor 3-1 is turned “OFF”, and only the current Ib1 of the first bias current source 7-1 is supplied to the first semiconductor laser 5-1. And only the bias light emission is obtained. On the other hand, the second bipolar transistor 4-1 is turned “ON”, and the current Ip of the current source 2-1 flows to the second semiconductor laser 6-1 to output light.
[0017]
As a result, when the data input to the first optical transmitter 100 is “H”, the output of the polarizing prism 9-1 outputs polarized light parallel to the paper surface, and when the data is “L”, , Polarized light perpendicular to the plane of the paper is output, and the orthogonal relationship is maintained.
[0018]
The signal light output from the polarizing prism 9-1 is output to the space via a lens (not shown), and the signal light of the second optical wireless transceiver 200 (not shown) provided at a position facing the first optical transmitter 100. The light is condensed by a lens and input to the receiving unit 202.
[0019]
The receiving unit 202 of the second optical receiver 200 separates the signal light from the first optical transmitter 100 into orthogonal polarizations by the polarization splitting prism 10-2. The polarized light horizontal to the plane of the paper goes straight and is input to the first photodiode 11-2. On the other hand, the polarized light perpendicular to the paper is reflected and input to the second photodiode 12-2.
[0020]
The cathode of the first photodiode 11-2 is connected to a positive power supply 13-2. The anode of the second photodiode 12-2 is connected to the negative power supply 14-2. Further, the anode of the first photodiode 11-2 and the cathode of the second photodiode 12-2 are connected to the input of the current-voltage converter 15-2.
[0021]
When light having a larger polarization optical power parallel to the paper than that of the polarization perpendicular to the paper is input to the receiver 22-1 of the second optical wireless transceiver 200, the first photodiode 11 The photocurrent of -2 is larger than the photocurrent of the second photodiode 12-2. This photocurrent flows into the input side of the current-to-voltage converter 15-2, and a voltage is output to the output side of the current-to-voltage converter 15-2.
[0022]
Conversely, when light having a higher polarization optical power perpendicular to the paper than that of the polarization horizontal to the paper is input to the receiving unit 22-1 of the second optical wireless transceiver 200, The photocurrent of the second photodiode 12-2 is larger than the photocurrent of the first photodiode 11-2. This photocurrent flows from the input side of the current-to-voltage converter 15-2, and a voltage having a polarity opposite to that described above is output to the output of the current-to-voltage converter.
[0023]
The signal light output from the first optical wireless transceiver 100 has a polarization parallel to the paper when the data signal input to the first optical wireless transceiver 100 is “H”, and the paper light when the data signal is “L”. The polarization is perpendicular to. Since the output signal light is transmitted in space, the polarization state does not change unlike the propagation in an optical fiber. Therefore, when the data of “H” is input to the first optical wireless transceiver 100, the second optical wireless transceiver 200 receives the signal light of the polarization parallel to the paper. In the second optical wireless transceiver, the photocurrent from the first photodiode 11-2 becomes dominant, the photocurrent flows into the input side of the current-voltage converter 15-2, and the output of the current-voltage converter 15-2 Becomes 'H'.
[0024]
On the other hand, when “L” data is input to the first optical wireless transceiver 100, the first optical wireless transceiver 100 outputs a signal light having a polarization perpendicular to the plane of the paper. The second optical wireless transceiver 200 receives a dominant photocurrent from the second photodiode 12-2 to which a signal light having a polarization perpendicular to the sheet of paper is input, and the current of the current-voltage converter 15-2. The photocurrent flows from the input side, and the output of the current-voltage converter 15-2 becomes “L”.
[0025]
As described above, the second optical wireless transceiver 200 outputs a data signal corresponding to the input data of the first optical wireless transceiver 100.
[0026]
Here, various background lights other than the signal light output from the first optical transmitter 100 are input to the second optical wireless transceiver 200. Consider a case in which sunlight, which has the highest power density among the background lights and is a problem, is input to the second optical wireless transceiver 200 simultaneously with the output signal light of the opposing first optical wireless transceiver.
[0027]
The signal light input to the second optical wireless transceiver 200 is separated by the polarization splitting prism 10-2 into a signal light of a polarization parallel to the paper and a signal light of a polarization perpendicular to the paper. As described above, the polarization of the signal light from the opposing first optical wireless transceiver 100 changes horizontally and vertically depending on the data signal input to the first optical wireless transceiver 100. On the other hand, background light such as sunlight has a random polarization direction.
[0028]
Therefore, the background light power of the two polarized waves separated by the polarization splitting prism 10-2 is split into two. Background light such as sunlight separated into two is input to the first photodiode 11-2 and the second photodiode 12-2, respectively. When the powers of the two separated background lights are substantially equal, the photocurrent caused by the background light flowing through the first photodiode 11-2 and the photocurrent caused by the background light flowing through the second photodiode 12-2 are substantially equal. Be equal. As a result, the photocurrent flowing into the input side of the current-voltage converter 15-2 cancels out, and the voltage due to the background light is not output.
[0029]
Therefore, the second optical wireless transceiver 200 can output a voltage according to the signal light without being affected by the background light even when the signal light includes the background light.
[0030]
Further, when the data signal input to the first optical wireless transceiver 100 is “H” and “L”, the direction of the input current of the current-voltage converter 15-2 of the second optical wireless transceiver 200 is changed. Are opposite to each other. That is, the output of the current-voltage converter 15-2 can be output as a reverse polarity voltage. For this reason, the output from the receiving unit 202 of the second optical wireless transceiver 200 can be configured by AC coupling. By configuring the second optical wireless transceiver 200 with AC coupling, an optical wireless transceiver having a wide dynamic range can be realized.
[0031]
Here, when the data input to the first optical wireless transceiver 100 is “H”, the first optical wireless transceiver 100 outputs polarized light parallel to the plane of the drawing, and the second optical receiver 200 In the above, an example in which 'H' is output when polarized light parallel to the paper surface is received has been shown. The relationship between data and polarization is merely an example, and various modifications are possible, such as parallel polarization in the case of 'L'. In addition, an example has been shown in which the polarization is parallel and perpendicular to the paper. However, the polarization output from the first optical wireless transceiver 100 may be any as long as the polarization is orthogonal.
[0032]
Alternatively, a combination of right-handed circular polarization and left-handed circular polarization may be obtained by inserting a quarter-wave plate or the like into the output of the transmitting unit 101 of the first optical wireless transceiver 100. In this case, a quarter-wave plate is inserted into the input of the receiving unit 202 of the opposing second optical wireless transceiver 200 to return to linear polarization, and then the polarization is separated by the polarization splitting prism. Can be considered.
[0033]
Also, an example has been shown in which the first optical transmitter 100 switches the current flowing through the two semiconductor lasers by using a bipolar transistor differential current switch. The differential current switch may be constituted by a pair of field effect transistors.
[0034]
In the embodiment shown in FIG. 1, an example has been described in which the current of the current source 2-1 is switched by the differential current switch. However, any circuit configuration may be used as long as the two semiconductor lasers can be operated complementarily.
[0035]
In the above description, the optical wireless communication is performed from the first optical wireless transceiver 100 to the second optical wireless transceiver 200. However, the second optical wireless transceiver 200 transmits the first optical wireless transceiver. The optical wireless communication with respect to 100 is performed in the same manner, and the first optical wireless transceiver 100 and the second transceiver 200 can communicate with each other.
[0036]
That is, when input data is input to the transmission unit 22-1 of the second optical wireless transceiver 200, the buffer amplifier 1-2, the current source 2-2, and the first bipolar transistor 3-2 that constitute the transmission unit 22-1 , A second bipolar transistor 4-2, a first semiconductor laser 5-2, a second semiconductor laser 6-2, a first bias current source 7-2, a second bias current source 8-2, a polarizing prism. The signal light is transmitted as signal light having the orthogonal polarization by 9-2, and the signal light is received by the receiving unit 101 of the first optical wireless transceiver 100, and the polarization splitting prism 12-1 constituting the receiving unit 101, Received data can be obtained by the first photodiode 11-1, the second photodiode 12-1, the positive power supply 13-1, the negative power supply 14-1, and the current-voltage converter 15-1.
(Second embodiment)
Next, an optical wireless communication system according to a second embodiment of the present invention will be described. FIG. 2 is a diagram illustrating a configuration of the optical wireless transceiver according to the second embodiment.
[0037]
In FIG. 2, a first optical wireless transceiver 300 and a second optical wireless transceiver 400 each include a transmitting unit (301, 401) and a receiving unit (302, 402). And the second optical wireless transceiver 400 have the same configuration. Further, the first optical wireless transceiver 300 and the second optical wireless transceiver 400 are arranged at opposing positions where optical wireless communication can be performed, and the first optical wireless transceiver 300 and the second transceiver 400 are They communicate with each other.
[0038]
In addition, the first optical wireless transceiver 300 and the second transceiver 400 have a reflector 51 as shown in FIG. 3, and a light emitting unit 52 for transmitting signal light and a signal light near the reflector 51. A light receiving section 53 for receiving light is provided, and when the first optical wireless transceiver 300 sends out signal light from the light emitting section 52 to the second transceiver 400, a part of the signal light is received by the light receiving section 53, The part is reflected by the reflection plate 51 and returns to the first optical wireless transceiver 300 as reflected light, and the first light receiver 300 and the second light receiver 400 take tracking by this returned light.
[0039]
FIG. 2 illustrates a case where optical wireless communication is performed from the first transceiver 300 to the second optical wireless transceiver 400.
[0040]
The first optical wireless transceiver 300 and the second optical wireless transceiver illustrated in FIG. 2 include a buffer amplifier (21-1 and 21-2), first bipolar transistors (23-1 and 23-2), Second bipolar transistor (24-1, 24-2), first semiconductor laser (25-1, 25-2), second semiconductor laser (26-1, 26-2), first bias current Sources (27-1, 27-2), second bias current sources (28-1, 28-2), polarizing prisms (29-1, 29-2), and polarization separating prisms (30-1, 30-2). ), A first photodiode (31-1, 31-2), a second photodiode (32-1, 32-2), a positive power supply (33-1, 33-2), a first current voltage The converters (35-1, 35-2) correspond to the first optical multiplexer of the first embodiment shown in FIG. The buffer amplifiers (1-1, 1-2), the first bipolar transistors (3-1, 3-2), and the second bipolar transistors (4-1, 4-1) of the transceiver 100 and the second optical wireless transceiver 200. 4-2), first semiconductor lasers (5-1, 5-2), second semiconductor lasers (6-1, 6-2), first bias current sources (7-1, 7-2) , A second bias current source (8-1, 8-2), a polarizing prism (9-1, 9-2), a polarization separating prism (10-1, 10-2), a first photodiode (11- 1, 11-2), a second photodiode (12-1, 12-2), a positive power supply (13-1, 13-2), and a current / voltage converter (15-1, 15-2). Therefore, detailed description of the operation is omitted here.
[0041]
The difference between the optical wireless transceiver according to the second embodiment and the optical wireless transceiver according to the first embodiment is that the first bipolar transistor (23-1, 23-2) and the second bipolar transistor ( 24-1, 24-2), the current value Ip of the variable current source (22-1, 22-2) of the differential current switch is sinusoidal by the low frequency signal source (27-1, 27-2). And a second current-voltage converter (36-1, 36-2) and a capacitor (39-1, 39-2) on the anode side of the second photodiode (32-1, 32-2). ) Is connected, and the output signals of the low-frequency signal sources (27-1, 27-2) and the second current-to-voltage converters (36-1, 36-2) are synchronized with the synchronous detectors (38-1, 38-2). ).
[0042]
In the transmitting section 301 of the first optical wireless transceiver 300, the output current value of the variable current source 22-1 is modulated by the amplitude and frequency output from the low frequency signal source 37-1. Due to the change in the current value Ip of the variable current source 22-1, the first semiconductor laser 25-1 and the second semiconductor laser 26-1 are subjected to low-frequency intensity modulation as shown in FIG.
[0043]
The two orthogonal semiconductor laser beams are multiplexed by the polarizing prism 29-1 and output to the atmosphere as signal light from the transmission unit 301 of the first optical wireless transceiver 300 via a lens (not shown).
[0044]
The signal light output to the atmosphere reaches the opposing second optical wireless transceiver 400.
[0045]
The transmitted signal light is partially reflected by the reflection plate 501 provided on the second optical wireless transceiver 400, and returns to the first optical wireless transceiver 300 again. The reflected light is used for tracking between the first optical wireless transceiver 300 and the second optical wireless transceiver 400 as described above.
[0046]
Next, the operation of the receiving section 302 of the first optical wireless transceiver 300 will be described. In the receiving section 302, the reflected light from the second optical wireless transceiver 400 described above and the signal light transmitted from the transmitting section 401 of the second optical wireless transceiver 400 are simultaneously received. The signal light transmitted from the transmitting section 401 of the second optical wireless transceiver 400 is the same as the transmitting section 301 of the first optical wireless transceiver 300 described above. It is transmitted as signal light having orthogonal polarization.
[0047]
In the receiving unit 301 of the first optical wireless transceiver 300, the reflected light reflected by the second optical wireless transceiver 400 is received as weak light, while the signal light transmitted from the second optical wireless transceiver 300 is received. Is strongly incident.
[0048]
The reflected light that has reached the receiving section 302 of the first optical wireless transceiver 300 is separated into orthogonal polarized waves via the polarization splitting prism 30-1. The polarized light parallel to the separated sheet is converted into a photocurrent by the first photodiode 31-1. The polarized light perpendicular to the paper is converted into a photocurrent by the second photodiode 32-1.
[0049]
As shown in FIG. 4, the light of both polarizations transmitted from the first optical wireless transceiver 300 is intensity-modulated by a low-frequency signal, and the reflected light is also intensity-modulated by a low-frequency signal. .
[0050]
Therefore, the signal current that has been subjected to intensity modulation at a low frequency is input to the second current-voltage converter 36-1 as an in-phase current. At this time, the photocurrent converted into a current by the second photodiode 32-1 contains many high-frequency components, and thus flows to the ground side by the capacitor 39-1.
[0051]
At this time, the product of the angular frequency of the low frequency signal and the capacitance of the capacitor 39-1 may be set to 0.02 or less. This is so that when the input impedance of the second DC converter 36-1 is considered to be 50Ω, more than half of the signal current and photocurrent modulated at a low frequency flow into the second current converter 36-1. In order to
[0052]
The signal light transmitted by the second optical wireless transceiver 400, which is input to the receiving unit 302 of the first optical wireless transceiver 300, is separated into orthogonal polarizations via the polarization splitting prism 30-1 in the same manner as described above. You.
[0053]
As for the data signal transmitted by the second optical wireless transceiver 400, the first photodiode 31-1, the second photodiode 32-1, and the first current-voltage converter 35, as in the first embodiment. By -1, positive and negative signals are output according to the polarization of the signal light, and can be extracted as data signals.
[0054]
Also, the in-phase low-frequency signal transmitted by the second optical wireless transceiver 400 is input to the second current-voltage converter 36-1 simultaneously with the in-phase low-frequency signal of the reflected light. That is, the output voltage signal of the second current-to-voltage converter 36-1 has two signals, a low-frequency signal of a reflected wave from the second optical wireless transceiver 400 and a low-frequency signal generated by the second optical wireless transceiver 400. There are spectral components.
[0055]
Here, the low frequency signal frequency of the first optical wireless transceiver 300 of the own station and the low frequency signal frequency of the second optical wireless transceiver 400 are made different in advance, so that the 2 and the output signal of the low-frequency signal source 37-1 are synchronously detected, and only the low-frequency signal frequency component of the reflected wave of the first optical wireless transceiver 300 is selectively detected. And a tracking signal can be obtained.
[0056]
Therefore, by controlling the direction of the first optical wireless transceiver 300 with respect to the second optical wireless transceiver 400 such that the frequency component of the reflected wave is maximized, automatic tracking becomes possible.
[0057]
Here, as the reflecting plate 51, for example, a reflecting plate commonly called a cat's eye installed on a road can be used.
[0058]
Further, the low frequency signal frequency component of the first optical wireless transceiver 300 is selectively extracted by the synchronous detector 38-1, but a bandpass filter is provided inside the second current-voltage converter 36-1. Alternatively, the low frequency component of the first optical wireless transceiver 300 may be extracted in advance.
[0059]
Further, although the frequency of the low-frequency signal is made different between the first optical wireless transceiver 300 and the second optical wireless transceiver 400, the first optical wireless transceiver is designed to prevent harmonic components from leaking into each other. The frequency of 300 and the frequency of the second optical wireless transceiver 400 may be relatively prime.
[0060]
The low-frequency signal frequency may be higher than the frequency component of the sunlight (around 2 Mz, see FIG. 5 of JP-A-7-183849) so that the tracking control is less affected by the sunlight. is important.
[0061]
In the above embodiment, an example of the optical wireless transmission / reception device having both the transmission unit and the reception unit and capable of both transmission and reception has been described. It is also possible to configure an optical wireless transmitter and an optical wireless receiver that perform either transmission or reception operation.
[0062]
【The invention's effect】
As described above, according to the present invention, an optical wireless communication system that is not affected by strong background light such as sunlight is provided by transmitting a data signal by performing modulation with polarization directions orthogonal to each other and transmitting the modulated signal. It becomes possible.
[Brief description of the drawings]
FIG. 1 is a diagram showing an optical wireless transceiver according to a first embodiment of the present invention.
FIG. 2 is a diagram showing an optical wireless transceiver according to another embodiment of the present invention.
FIG. 3 is a diagram showing a reflector according to another embodiment of the present invention.
FIG. 4 is a diagram illustrating an optical signal transmitted from an optical wireless transceiver according to another embodiment of the present invention.
[Explanation of symbols]
1-1, 1-2, 21-1, 21-2 ... buffer amplifier
2-1, 2-2, 22-1, 22-2 ... current source
3-1, 3-2, 23-1, 23-2... First bipolar transistor
4-1, 4-2, 24-1, 24-2... Second bipolar transistor
5-1, 5-2, 25-1, 25-2 ... first semiconductor laser
6-1, 6-2, 26-1, 26-2... Second semiconductor laser
7-1, 7-2, 27-1, 27-2 ... first bias current source
8-1, 8-2, 28-1, 28-2 ... second bias current source,
9-1, 9-2, 29-1, 29-2 ... polarizing prism
10-1, 10-2, 30-1, 30-2 ... polarization splitting prism
11-1, 11-2, 31-1, 31-2 ... first photodiode
12-1, 12-2, 32-1, 32-2... Second photodiode
13-1, 13-2, 33-1, 33-2 ... Positive power supply
14-1, 14-2, 34-1, 34-2 ... negative power supply
15-1, 15-2, 35-1, 35-2 ... current-voltage converter
36-1, 36-2 ... second current-voltage converter
37-1, 37-2 ・ ・ ・ Low frequency signal source
38-1, 38-2 ・ ・ ・ Phase comparator
39-1, 39-2: Capacitor
51 ... Reflector
100, 300 ··· First optical wireless transceiver
101, 201, 301, 401...
102, 202, 302, 402...
200, 400 ... second optical wireless transceiver

Claims (8)

In an optical wireless communication system that performs wireless communication using light between an optical wireless transmitter and an optical wireless receiver,
The optical wireless transmitter,
A first semiconductor laser;
A second semiconductor laser having a polarization orthogonal to the polarization of the first semiconductor laser, and driving the first semiconductor laser or the second semiconductor laser corresponding to a mark and a space of an input data signal. Driving means for generating light having orthogonal polarizations from the first semiconductor laser or the second semiconductor laser;
A multiplexer that combines light respectively output from the first semiconductor laser and the second semiconductor laser,
The optical wireless receiver, a splitter that separates the polarization of light incident from the optical wireless transmitter into a first polarization light and a second polarization light orthogonal to each other,
An optical wireless communication apparatus comprising: a data signal reproducing unit to which the first polarized light and the second polarized light are input and obtains an output data signal for identifying a mark and a space according to the direction of polarization. Communications system. The driving unit is configured to switch the current of the current source in accordance with the mark and the space of the input data signal by a positive logic output and a negative logic output of a transistor differential current switch circuit. 2. The optical wireless communication system according to claim 1, wherein each of said second semiconductor lasers is driven. The data signal reproducing unit,
A first photodiode that receives the first polarized light and has a cathode connected to a positive power supply;
A second photodiode that receives the second polarized light and has a negative power supply connected to the anode thereof;
An anode of the first photodiode and a cathode of the second photodiode, comprising a current-to-voltage converter connected to an input thereof;
The optical wireless communication system according to claim 1, wherein a difference between an output of an anode of the first photodiode and an output of a cathode of the second photodiode is detected. The transmission unit of the optical wireless transmitter used in the optical wireless communication system that performs wireless communication using light between the optical wireless transmitter and the optical wireless receiver,
A first semiconductor laser;
A second semiconductor laser having a polarization orthogonal to the polarization of the first semiconductor laser, and driving the first semiconductor laser or the second semiconductor laser corresponding to a mark and a space of an input data signal; Driving means for generating light having orthogonal polarizations from the first semiconductor laser or the second semiconductor laser,
An optical wireless transmitter, comprising: a multiplexer that combines light output from each of the first semiconductor laser and the second semiconductor laser. The transmission unit of the optical wireless transceiver used in an optical wireless communication system that performs wireless communication using light between optical wireless transceivers,
A first semiconductor laser;
A second semiconductor laser having a polarization orthogonal to the polarization of the first semiconductor laser, and driving the first semiconductor laser or the second semiconductor laser corresponding to a mark and a space of an input data signal. Driving means for generating light having orthogonal polarizations from the first semiconductor laser or the second semiconductor laser;
A multiplexer that combines light respectively output from the first semiconductor laser and the second semiconductor laser,
The receiving unit of the optical wireless transceiver is
A demultiplexer that separates polarization of light incident from the other optical wireless transceiver into a first polarization light and a second polarization light orthogonal to each other;
An optical wireless device comprising: a data signal reproducing unit to which the first polarized light and the second polarized light are inputted and which obtains an output data signal for identifying a mark and a space in accordance with the direction of polarization. Transceiver. While performing wireless communication using light between the first optical wireless transceiver and the second optical wireless transceiver, when transmitting from the first optical transceiver to the second optical transceiver, An optical wireless communication system in which the first optical transceiver adjusts a direction with respect to the second optical transceiver using a reflected wave from a reflector provided in the second optical transceiver,
The first optical wireless transceiver includes a first semiconductor laser;
A second semiconductor laser having a polarization orthogonal to the polarization of the first semiconductor laser, and a transistor differential current switch configured to switch a current of a variable current source in accordance with a mark and a space of the input data signal The first semiconductor laser or the second semiconductor laser is driven by the positive logic output or the negative logic path output of the circuit, and the amount of current of the variable current source is modulated by a signal of a predetermined frequency, so that the signals are polarized mutually. Driving means for generating orthogonal light from the first semiconductor laser or the second semiconductor laser;
A transmission unit including a multiplexer that combines light output from the first semiconductor laser and light output from the second semiconductor laser,
A duplexer that separates reflected light reflected from the second optical transceiver and received light from the second optical transceiver into a first polarized light and a second polarized light whose polarizations are orthogonal to each other. And a first photodiode that receives the first polarized light and has a cathode connected to a positive power supply;
A second photodiode that receives the second polarized light and has a negative power supply connected to the anode thereof;
A capacitor connected to the anode of the second photodiode and having one end installed;
A second current-to-voltage converter connected to the anode of the second photodiode, an output of the second current-to-voltage converter and a signal of the predetermined frequency being input, and the second current-to-voltage converter A synchronous detector for synchronously detecting the output of the signal and the signal of the predetermined frequency,
An optical wireless communication system, comprising: adjusting the direction of the first optical wireless transceiver with respect to the second optical wireless transceiver so that the detection output of the synchronous detector is maximized. 7. The optical wireless communication system according to claim 6, wherein the product of the angular frequency of the specific low-frequency signal and the capacitance of the capacitor is 0.02 or less. 7. The optical wireless communication system according to claim 6, wherein the predetermined frequency of the first optical wireless transceiver is different from a predetermined frequency of the opposing second optical wireless transceiver.

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