JP2004015324A - Optical transmitter and optical transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein the conventional optical transmitter has a constitution being apt to be complicated for changing the spread angle of a light beam, the light-receiving angle, the emitting direction and the light-receiving angle. <P>SOLUTION: An optical transmitter 10 is composed of a light source 12 for emitting a light beam for wirelessly transmitting information, and a micromirror array unit 14 having micromirrors disposed in a matrix form for reflecting the light beam emitted from the optical source toward a light-receiving means 11 disposed at a distant place. An optical space transmitter 11 is composed of a light-receiving means 13 for receiving a light beam for wirelessly transmitting information, and a micromirror array unit 15 having micromirrors disposed in a matrix form for reflecting the light beam emitted from the light-transmitting means disposed in the distant place toward the light-receiving means. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a space optical transmission device for transmitting information by wireless transmission of a light beam.
[0002]
[Prior art]
In a conventional optical space transmission system, a transmission signal is modulated into an optical signal in an optical transmission device on the transmission side, and the optical signal is emitted as a light beam toward an optical transmission device on the reception side provided opposite thereto. The emitted light beam is transmitted in the air space and received by the optical transmission device on the receiving side. The optical transmission device on the receiving side transmits and receives an information signal by demodulating the optical signal transmitted from the transmitting side by the light beam.
[0003]
However, in the optical space transmission system as described above, the path of the light beam may fluctuate due to the fluctuation of the atmosphere or the like. In addition, the light beam emission direction may fluctuate because a slight deformation is likely to occur at a place where the optical transmission device is installed, for example, a roof of a building due to a temperature change.
[0004]
If the arrival position of the light beam on the receiving side fluctuates due to such external factors, the reception level of the optical transmission device on the receiving side decreases, and in the worst case, communication is interrupted.
[0005]
Similarly, if the light beam incident on the receiving side is no longer directed in an appropriate direction due to deformation of the installation location or the like on the receiving device side, the reception level is reduced or reception is disabled.
[0006]
In order to solve such a problem, a light beam is emitted from the optical transmission device so as to increase the diameter of the light beam received on the receiving side. To ensure a stable reception level.
[0007]
The receiving side is also designed to have a certain light receiving angle (an angle range in which the light can be received).
[0008]
FIG. 7 shows an example of a conventional optical space transmission system. In FIG. 7, the left side is the free-space optical transmission device 50 on the transmission side, and the right side is the free-space optical transmission device 71 on the reception side. On the transmitting side, the light beam emitted from the light source 72 is converted by the optical system 73 into a slightly divergent, substantially parallel light beam 76. On the other hand, also on the receiving side, the optical system 75 is designed so as to have a light angle slightly widening with respect to the parallel light, and the light beam converged by the optical system 75 is received by the light receiving element 74.
[0009]
In such an optical space transmission system, when changing the beam emission angle or the light receiving angle, it is general to change the relative positional relationship by mechanically moving an optical system, a light source, or a light receiving element. In such a case, the relative positional relationship between the light emitting element 72 and the lens 73 in FIG. 7 is moved to change the spread angle. Similarly, the receiving side also changes the relative positional relationship between the light receiving element 74 and the lens 75 to vary the light receiving viewing angle.
[0010]
In the optical space communication, two-way simultaneous communication is generally performed, and a transmission unit and a reception unit are configured in the space optical transmission device, and operate as a transceiver. When the transmitting optical axis of the own device and the receiving optical axis match, the automatic tracking function detects the light incident direction from the partner device and matches the transmitting and receiving optical axis of the own device with the optical axis direction from the partner device. Although it can be mounted, a means for changing the transmission / reception beam direction is required.
[0011]
As a method of changing the transmission / reception beam direction, the angle of the entire apparatus or the entire optical system is changed, the angle is changed by using a mirror in the optical system, and the position is changed between the lens and the light transmitting / receiving element. And so on.
[0012]
FIG. 8 shows an example. The light beam emitted from the light emitting element 81a at the divergent angle 83 is emitted by the lens 82 as a substantially parallel beam 85.
[0013]
On the other hand, when the beam emission direction is changed, it can be realized by changing the relative position between the light emitting element (light source) 81a and the lens. When the light emitting element 81a is moved to the position 81b in FIG. 8, the light beam 84 incident on the lens 82 is emitted from the lens 82 into the space in the form of an emission beam 86, and the beam direction changes.
[0014]
These methods are used not only for realizing the automatic tracking function, but also for adjusting the beam direction when the apparatus is installed.
[0015]
A configuration for changing the relative positional relationship between the light transmitting / receiving element and the optical system will be described with reference to FIG.
[0016]
In the upper part of FIG. 6, a light beam having a divergence angle 65 is emitted from the end face of the light emitting element 61, the beam divergence angle is narrowed by the lens 62, and transmitted to space at a beam divergence angle 68 that is almost parallel. Is done. In order to reduce the beam divergence angle and increase the light reception power density at the receiver, the light emitting element 61 is moved on the optical axis in a direction away from the lens 62 as shown in the lower part of FIG. Of the output light from the light emitting element 61, the light signal in the angle range 66 that is effectively incident on the lens 62 has a smaller beam emission angle 68 than in the previous case, and can be closer to parallel light.
[0017]
[Problems to be solved by the invention]
However, since the divergent angle 65 of the light output from the light emitting element 61 is constant, the light component 67 that does not effectively enter the lens 62 becomes invalid, and the optical power transmitted to the space through the lens 62 decreases. There is a disadvantage that it will.
[0018]
If the curvature of the lens 62 can be changed without changing the relative positional relationship between the light emitting element 61 and the lens 62, effective divergence angle control can be performed, but a lens or lens group capable of changing the curvature should be configured. Is very difficult and the configuration becomes complicated. Further, a precise mechanism and accurate control are required so that the injection direction does not change.
[0019]
In general, in optical space communication, in order to obtain sufficient received light power, it is necessary to reduce the beam diameter at a reception point as much as possible, and a precise mechanism is required. Therefore, it is difficult to configure an optical space transmission device that can freely change the beam emission angle and the light reception angle, and the configuration becomes complicated because a movable mechanism is provided.
[0020]
Furthermore, not only the beam divergence angle but also beam shape control may be required. Generally, in the optical space transmission apparatus, the receiving angle on the receiving side is set to be wide as described above. However, if a strong light source such as the sun is present in the background on the transmitting side, the strong light enters the light receiving element. Therefore, the intended light beam cannot be received clearly.
[0021]
FIG. 5 shows a state of the transmitting device observed from the receiving device. A strong separate light source 43 such as the sun enters a reception range 42 including the transmission side device 41 as viewed from the reception side device.
[0022]
In particular, sunlight has much higher optical power (energy) than the optical power of the light beam from the transmitting device 41. Therefore, even if a little sunlight enters the light receiving angle, a communication error may occur.
[0023]
In a conventional optical transmission device using a lens, the receiving angle is set narrower with respect to the incident strong background light as described above, and the relative positional relationship between the light receiving element and the lens 62 is changed as shown in FIG. However, there is a problem that it is difficult to secure stable communication against fluctuations in the installation environment and the like.
[0024]
On the other hand, when performing beam pattern shaping control or the like, it is necessary to prepare an optical system for controlling the beam emission angle and the light receiving angle separately from the optical system for controlling the same.
[0025]
Furthermore, the beam pattern shape (and the power density distribution) to be shaped and controlled is uniquely determined by the prepared optical system and cannot be freely changed.
[0026]
Further, in the case of changing the beam emission direction and the light receiving direction, in the configuration shown in FIG. 8, the optical power output from the light emitting element 81a is not used effectively similarly to the method of controlling the beam emission angle and the light receiving angle. There is a problem.
[0027]
Specifically, the portion indicated by 87 in FIG. 8 does not effectively enter the lens 82 and becomes a useless component that is not transmitted to space. When the light receiving element 81 is considered, the effective light receiving angle becomes narrower than the angle 85 corresponding to the original light receiving angle as shown by 86, and the receiving efficiency is reduced.
[0028]
Further, the optical system configured for each purpose is a solidified lens, a prism, or the like, and it is difficult to change them individually or simultaneously at a high speed.
[0029]
[Means for Solving the Problems]
In order to achieve the above object, in the optical space transmission apparatus according to the first aspect of the present invention, a light source for emitting a light beam for wirelessly transmitting information and a micromirror are arranged in a matrix and emitted from the light source. A micromirror array unit that reflects the light beam toward a light receiving unit installed at a remote place.
[0030]
In the optical space transmission apparatus according to the second aspect of the present invention, a light receiving unit for receiving a light beam for wirelessly transmitting information and a micromirror are arranged in a matrix, and the optical transmission unit is provided at a remote place. A micro mirror array unit for reflecting the emitted light beam toward the light receiving means.
[0031]
Thereby, the direction of each of the micromirrors constituting the micromirror array unit is independently changed so that useless components of the light beam emitted from the light source are reduced, and without providing a complicated mechanism. It is possible to control the divergence angle, converging angle, pattern shape and reflection direction of the light beam reflected by the micro mirror array unit.
[0032]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows an outline of an optical space transmission system according to an embodiment of the present invention. In the system of the present embodiment, instead of the lenses and prisms used in the conventional system, a micromirror array unit configured by arranging a large number of micromirrors, each of which can independently control the direction, in a matrix, is used. It is used.
[0033]
In FIG. 1, reference numeral 10 denotes a transmission-side optical space transmission device (hereinafter, referred to as a transmission-side device), and reference numeral 11 denotes a reception-side optical space transmission device (hereinafter, referred to as a reception-side device).
[0034]
The transmitting device 10 reflects a light emitting element (light source) 12 such as a semiconductor laser and a light beam (modulated according to information to be transmitted) emitted from the light emitting device 12 toward the receiving device 11. And a control circuit 18 for independently controlling the direction of each mirror constituting the micro mirror array unit 14.
[0035]
On the other hand, the receiving side device 11 includes a light receiving element 13, a micro mirror array unit 15 for reflecting the light beam emitted from the transmitting side device 10 toward the light receiving element 13, and individual components constituting the micro mirror array unit 15. And a control circuit 19 for independently controlling the direction of the mirror.
[0036]
In the system configured as described above, the light beam emitted from the light emitting element 12 of the transmitting device 10 is reflected by the micro mirror array unit 14. The reflected light beam 16 has its divergence angle (that is, beam diameter), pattern (shape) and emission direction, and light receiving direction by controlling the direction of each mirror constituting the micromirror array unit 14 through the control circuit 18. Can be variably set. The direction of each micromirror is controlled so that the light beam 16 emitted to the space has a certain divergence angle.
[0037]
On the other hand, the light beam 17 emitted from the transmitting device 10 and incident on the receiving device 11 is condensed by the micro mirror array unit 15 of the receiving device 11 and is incident on the light receiving element 13. At this time, the direction of each mirror is controlled so as to have a certain light receiving angle and to form a small spot on the light receiving element 13.
[0038]
Further, the control circuits 18 and 19 of the transmission side and reception side apparatuses 10 and 11 include a distance (transmission distance) between the transmission side apparatus 10 and the reception side apparatus 11, scintillation, weather, transmission side apparatus 10 and reception side apparatus 11, The spread angle and the light receiving angle of the light beam that are optimal for the size and shape of the building existing between them and the transmission conditions such as the shaking of the gantry on which the transmitting and receiving devices 10 and 11 are respectively installed. The direction of each mirror is controlled so as to set the pattern, the emission direction, and the light receiving direction. Although not shown, a detector for detecting the transmission conditions and sending a detection signal to the control circuits 18 and 19 is provided. In addition, for some transmission conditions, the installer may set the direction of the mirror.
[0039]
In the case of changing the beam emitting direction and the light receiving direction, in the configuration of FIG. 1, a uniform angular change may be given to each of the micro mirrors of the micro mirror array units 14 and 15. For example. When it is desired to change the emission angle by 0.2 °, the individual micromirrors may be controlled to move by 0.1 ° in the same direction.
[0040]
The emission direction control and the light receiving direction control can be realized by the same micromirror array units 14 and 15 simultaneously with the light beam divergence angle control and the beam pattern control described above.
[0041]
By configuring the system in this manner, it is possible to easily set the divergence angle, light receiving angle, pattern and emission direction, and light receiving direction of the light beam according to the installation conditions and environment of the transmitting device 10 and the receiving device 11. It is possible.
[0042]
Next, the micro mirror array units 14 and 15 will be described in detail with reference to FIG. Although FIG. 2 shows only the micro mirror array unit 14 provided in the transmitting device 10, the configuration of the micro mirror array unit 15 provided in the receiving device 11 is the same.
[0043]
The micromirror array unit 14 is configured by arranging a large number of micromirrors 14a vertically and horizontally in a matrix. The angle of each micromirror 14a can be variably set by an electric signal from the control circuit 18. Although FIG. 2 shows a mirror array unit composed of a total of 225 micromirrors 14a of 15 vertical × 15 horizontal, the number of micromirrors may be other than this, and the shape of the mirror array unit is not limited. Instead of the square shown in FIG. 2, a circular shape or a polygonal shape may be used.
[0044]
By independently controlling the directions of the individual micromirrors of the micromirror array units 14 and 15 configured as described above, the micromirror array units 14 and 15 perform the function of a condensing optical system.
[0045]
FIG. 3 shows an AA ′ section of the micro mirror array unit 14 shown in FIG. FIG. 3 shows a state in which the light emitting element (point light source) 12 is arranged in front of the micro mirror array unit 14 and emits a light beam that is substantially parallel light.
[0046]
As described above, by controlling the directions of the individual mirrors of the micro mirror array unit 14, it is possible to emit a substantially parallel light beam or to emit a light beam having a larger or smaller divergence angle. .
[0047]
The direction of the micromirror array unit 15 of the receiving device 11 is controlled so that the light from the unnecessary light source existing as the background of the transmitting device 10 is not received by the light receiving element 13. When the unnecessary light source moves like the sun, the direction of the mirror may be controlled according to the movement.
[0048]
Specifically, under the situation as shown in FIG. 5, the micromirror array 15 of the receiving device 11 has an area 55 where the light beam from the transmitting device 10 is incident, as shown in FIG. An area 56 where unnecessary light such as sunlight is incident is formed. In this case, the direction is controlled in the direction below the light receiving element 13 so that the light reflected from the micromirror 57 (the dark part in the drawing) in the area 56 where the unnecessary light is incident does not converge on the light receiving element 113. The micromirrors other than the micromirrors 57 included in the light area 56 constitute a condenser mirror for the light receiving element 13.
[0049]
In this way, the individual micromirrors are controlled so that light other than the incident target light does not enter the light receiving element 13, thereby preventing reception failure.
[0050]
In the present embodiment, the case where the transmission side device and the reception side device are separated has been described. However, transmission and reception including one micro mirror array unit, a light source (light emitting element), and a light receiving element are possible. An apparatus may be configured, and a plurality of the apparatuses may be provided to configure a system.
[0051]
【The invention's effect】
As described above, according to the present invention, it is possible to control the light beam emission angle, light reception angle, and further the light emission direction and light reception direction using the micro mirror array unit. Can be transmitted to the transmission space with as little as possible, and the divergence angle of the light beam can be controlled with a simple configuration.
[0052]
Further, the pattern of the light beam can be controlled at the same time, and the apparatus can be simplified and downsized as compared with the case where a conventional optical system such as a solidified lens is used.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a configuration of an optical space transmission system according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a micro mirror array unit of the optical space transmission system.
FIG. 3 is a diagram illustrating the light condensing action of the micro mirror array unit.
FIG. 4 is a view for explaining a countermeasure when unnecessary light is incident on the micro mirror array unit.
FIG. 5 is a diagram illustrating a case where the sun exists in the background on the transmission side in the conventional optical space transmission system.
FIG. 6 is a diagram illustrating a conventional optical space transmission system.
FIG. 7 is a diagram illustrating a method for controlling a light beam diameter in a conventional optical space transmission system.
FIG. 8 is a view for explaining a method of controlling a light beam emission direction in a conventional optical space transmission system.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Transmitting apparatus 11 Receiving apparatus 12 Light emitting element 13 Light receiving element 14, 15 Micro mirror array unit

Claims (7)

A light source for emitting a light beam for wirelessly transmitting information;
An optical space transmission device, comprising: a micromirror array unit in which micromirrors are arranged in a matrix, and reflecting a light beam emitted from the light source toward a light receiving unit provided at a remote place. . 2. The optical space transmission apparatus according to claim 1, further comprising control means for independently controlling the direction of each of the minute mirrors constituting the minute mirror array unit. 3. The apparatus according to claim 2, wherein at least one of the divergence angle of the reflected light beam, the pattern of the light beam, and the reflection direction can be changed by controlling the direction of each of the micromirrors by the control means. Optical space transmission equipment. A light receiving unit for receiving a light beam for wirelessly transmitting information and a micro mirror are arranged in a matrix, and reflect a light beam emitted from a light transmitting unit installed at a remote place toward the light receiving unit. An optical space transmission device comprising a micromirror array unit. The optical space transmission apparatus according to claim 3, further comprising control means for independently controlling the direction of each of the minute mirrors constituting the minute mirror array unit. 6. The apparatus according to claim 5, wherein at least one of the converging angle of the reflected light beam, the pattern of the light beam, and the reflection direction can be changed by controlling the direction of each of the minute mirrors by the control means. Optical transmission equipment. A space optical transmission system comprising the space optical transmission device according to claim 1 and the space optical transmission device according to claim 4.

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