JPH0242834A - Optical space transmission communication device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical space transmission communication device that performs wireless communication using optical signals using free space as a transmission path.

Conventional technology Optical space transmission communication equipment consists of a transmitter that electrically modulates a signal such as voice, converts the modulated signal into an optical signal using a light emitting source, and sends it out into free space, and a receiver that receives the optical signal from the transmitter. Optical communication is performed with a receiver that receives and demodulates light using an element, using free space as an optical signal transmission path.

Conventionally, in such optical space transmission communication devices, optical signals from the light emission source of the transmitter are diffused into free space without being restricted to a certain direction, and the diffused optical signals are transmitted to a light receiving element with a wide directional characteristic. I was receiving it with a different receiver. Therefore, for example, when attempting to transmit only to a limited area within a room, the output of the optical signal sent from the transmitter is adjusted to limit the transmission capacity.

Problems to be Solved by the Invention However, as with the conventional optical space transmission communication device described above, it is difficult to transmit to a limited area by adjusting the output of the optical signal to limit the transmission capacity. In this case, the magnitude of the output of the optical signal must be delicately adjusted depending on each limited area to which transmission is to be performed, and this adjustment operation is difficult. In addition, since the optical signal is diffused and sent out from the transmitter without any directionality, the boundary between the area to which it is intended to be transmitted and the area where it is not desired to be transmitted is not clear, and some areas where it is not desired to be transmitted are The optical signal will also reach the Furthermore, when trying to transmit to a limited area, the output of the optical signal is reduced.

The present invention has problems such as poor S/N ratio due to the influence of disturbance light noise etc. 3 Therefore, an object of the present invention is to transmit and receive optical signals within a limited area of free space. An object of the present invention is to provide an optical space transmission communication device that can perform sensitive adjustment without requiring difficult adjustment operations.

Means for Solving the Problems The present invention provides a transmitter that electrically modulates a signal such as voice, converts the modulated signal into an optical signal by a light emitting source, and sends it into free space, and an optical signal from the transmitter. In an optical space transmission communication device that performs optical communication using free space as an optical signal transmission path between a receiver that receives and demodulates the light with a light receiving element, the transmitter is provided with It is characterized by the fact that it is equipped with a condensing means that condenses the optical signal into a limited area of free space, while giving the receiver's light-receiving element sharp directional characteristics that only receive light from a limited direction. This is an optical space transmission communication device.

According to the present invention, an optical signal from a light emitting source of a transmitter is condensed in a fixed direction by a condensing means and sent out, while at a receiver, an optical signal is input from a fixed direction by a light receiving element with sharp directional characteristics. Since only the optical signals coming from the transmitter are received, by aligning the transmitter's optical signal sending direction and the receiver's receiving direction, the optical signal can be transmitted and received from the transmitter to the limited area where the receiver is located. It is done sensitively.

Embodiment FIG. 1 is a sectional view showing a main part of a transmitter 1 of an optical space transmission communication device which is an embodiment of the present invention, and FIG. !12 is a sectional view showing the main parts.

In the transmission tR1 shown in Figure 1, an opening 4 is formed in a part of the transmitter housing 3, and a light emitting source 5 that outputs an optical signal is provided inside the transmitter housing 3 behind this opening 4. It is being A light emitting diode with wide directional characteristics is used as the light source 5, and infrared rays are output as an optical signal. A cylindrical lens holder 6 is attached to the opening 4 of the transmitter housing 3 in order to send out the optical signal output from the light emitting source 5 in the direction of a limited area of free space outside the transmitter housing 3. An optical lens 7 is held by the lens holder 6.

The reflecting mirror 8 is for condensing the optical signal output from the light emitting source 5 onto the optical lens 7 side, and is configured to move forward and backward along the axial direction of the optical lens 7 together with the light emitting source 5 within the lens holder 6. It is set in. That is, by moving the light emitting source 5 back and forth, the distance between the light emitting source 5 and the optical lens 7 is variably adjusted, thereby adjusting the size of the limited area for transmitting the optical signal. A Fresnel lens is used as the optical lens 7, so that adjustment to limit the area to which the optical signal is transmitted can be easily performed.

FIG. 3 is a block diagram showing the basic mechanism of the transmitter 1 connected to the light emitting source 5 described above. In FIG. 3, an amplifier 9 is a circuit for amplifying the input audio signal a. In the next stage of amplifier 9, the output is frequency-varied i.
ll (FrequencyModulation;
An FM modulator 10 (hereinafter referred to as FM modulation) is connected. The FM modulator 10 is connected to a drive circuit 11 that drives the light emitting source 5 described above according to its output.

On the other hand, in the receiver 2 shown in FIG. 2, a part of the receiver driftwood 12 is recessed to form a hood 13 that blocks light incident from directions other than a certain direction.

A light-receiving element 14 for receiving the optical signal sent from the transmitter 1 described above is arranged at a position f&recessed from the opening of the hood 13 to a certain depth with its light-receiving surface facing the opening of the hood 13. has been done. The light-receiving element 14 has a sharp directional characteristic, and is designed to hardly receive light other than infrared light that is incident from the normal direction of the light-receiving surface.

FIG. 4 shows a receiver 2 connected to the above-mentioned light receiving element 14.
FIG.

In FIG. 4, a demodulator 15 is a circuit that demodulates the output obtained by photoelectric conversion of the light receiving element 14. This demodulator 15 is connected to a speaker 17 via an amplifier 16.

FIG. 5 is an explanatory diagram showing a configuration in which the above-described transmitter 1 and receiver 2 are installed in an exhibition hall such as an art museum or a museum. In FIG. 5, a transmitter 1 is mounted at a predetermined position on the ceiling 20 of the exhibition hall with its optical lens 7 facing the floor 21 of the exhibition hall. On the other hand, a receiver 2 is installed on the floor 21 of the exhibition hall at a position almost opposite to the transmitter 1.
is installed with the opening of the hood 13 facing the ceiling 20. This receiver 2 is for receiving the optical signal S sent out from the above-mentioned transmitter 1, and at a place away from the installation position of this receiver 2, there is an optical signal S sent out from another transmitter 1 (not shown). Another receiver 2a is installed to receive the optical signal transmitted.

Next, the operation of the optical space transmission communication device of this embodiment will be explained using the installation configuration shown in FIG. 5 as an example.

In the transmitter 1, the audio signal a input to the amplifier 9 shown in FIG. A drive circuit 11 that receives a modulation signal from the FM modulator 10 drives the light emitting source 5 in accordance with the modulation signal. As a result, the light emitting source 5 outputs an FM signal based on infrared light as the optical signal S.

The optical signal S output from the light emitting source 5 is focused on the optical lens 7 side by the reflecting mirror 8 shown in FIG. It is sent out within a limited area R1. The size of the region R1 at this time is the size of the light emitting source 5 in the transmitter 1.
The distance between the light emitting source 5 and the optical lens 7 can be changed by moving the light source 5 forward or backward.

On the other hand, the receiver 11i2 on the floor 21 is installed in a position where the hood 13 receives the optical signal S transmitted from the transmitter 1 without blocking it, so the optical signal S transmitted from the transmitter 1 is received.
is received by the light receiving element 14. This light receiving element 14
The output photoelectrically converted by the demodulator 15 shown in FIG.
The signal is demodulated into an audio signal before FM modulation. The demodulated signal is amplified by an amplifier 16 and made into sound by a speaker 17.

At this time, for the receiver 2a installed in a region R2 that is outside the region R1 of the floor surface 21, the optical signal S sent from the transmitter 1 is reflected within the region R1 of the floor surface 21. , and further the optical signal S1 reflected from the ceiling 20 is incident. However, in this case, the apparent transmission ratio M of the optical signal S1 (distance until the optical signal S1 reaches the receiver 2a from the transmitter 1) is Since the distance is more than three times the transmission distance, the amount of light of the optical signal S1 is significantly reduced.

Therefore, if the receiving sensitivity of this receiver 2a is set to be the same as that of the receiver 1a2 in the region R1, the optical signal S from the transmitter 1 will not be received by the receiver 2a. That is, on the floor surface 21, there is an area R1 where the optical signal S from the transmitter 1 can be transmitted, and an area R2 where it cannot be transmitted.
The boundaries become clear. In this way, audio information for explanatory exhibits corresponding to each exhibit is played within a limited area in front of each exhibit in the exhibition hall.

As mentioned above, since there is a clear boundary between the region R1 where the optical signal S from the transmitter 1 can be transmitted and the region R2 where it cannot be transmitted, the wavelength of the infrared light used for transmission and reception, the transport method,
Even if the constants (for example, the value of the carrier frequency) that determine the carrier conditions are exactly the same for each transmitter 1, there will be no interference between audio information at adjacent locations.

In addition, in the above embodiment, the case where the receiver 2 is installed in each limited area where the optical signal S sent out from each transmitter 1 can be received has been described, but the invention is not limited to this.
The user carries one receiver 2 and moves from the transmission area of any transmitter 1 (area where the optical signal S can be received) to the transmission area of another transmitter 1, and the signal is transmitted from each transmitter R1. The optical signals S may be received sequentially. In this case, there is no need to perform a tuning operation on the receiver 2 each time the receiver moves to each transmission area, and the respective audio information can be received as is.

Effects of the Invention As described above, according to the optical space transmission communication device of the present invention, the optical signal output from the light emitting source of the transmitter is focused in a certain direction by the condensing means and transmitted, while the receiver The light receiving element with sharp characteristics is configured to receive only optical signals incident from a certain direction, so by aligning the transmitter's optical signal sending direction and the receiver's receiving direction, Optical signals can be transmitted and received within a limited area where a receiver is located with high sensitivity without requiring difficult adjustment operations.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the main part of a transmitter 1 of an optical space transmission communication device which is an embodiment of the present invention, and FIG. 3 is a block diagram showing the basic mechanism of the transmitter 1,
FIG. 4 is a block diagram showing the basic mechanism of the receiver 2, and FIG.
The figure is an explanatory diagram showing an example of an installation configuration of an optical space transmission communication device. 1... Transmitter, 2... Receiver, 5... Light emitting source, 7
...Optical lens, 8...Reflector, 13...Hood, 14...Photodetector element Patent attorney Keiichi Saikyo

Claims (1)

[Claims] A transmitter that electrically modulates a signal such as voice, converts the modulated signal into an optical signal using a light emitting source, and sends it out into free space; and a light receiving element that receives the optical signal from the transmitter. In an optical space transmission communication device that performs optical communication with a receiver that receives and demodulates light using free space as a transmission path for optical signals, the transmitter has a A light beam is characterized in that a condensing means is provided to condense light within a limited area of free space, and the light receiving element of the receiver is given sharp directional characteristics to receive light only from a limited direction. Space transmission communication device.