JPH06291733A - Optical fiber communication system - Google Patents

Abstract

PURPOSE:To construct a system receiving a signal in a state that the influence of noise is little at an arbitrary place along an optical fiber by using a leakage type optical fiber and providing a demodulation mechanism where light leaking from an optical fiber side surface is received and it is restored to the original signal on a light receiver. CONSTITUTION:This system is an optical fiber communication system composed of a light source device 1, an optical fiber 2 where light from the light source device 1 is made incident and a light receiver 3 arranged on an arbitrary location along the optical fiber 2, and the light source device 1 has a modulation mechanism changing the light intensity and phases, etc., of a light source in accordance with the change of an inputted signal. In an optical fiber 2, a leakage type optical fiber where light leaks from the side surface is used. The light receiver 3 is provided with a demodulation mechanism receiving light leaking from the side surface of the optical fiber 2 and restoring it to the original signal. By this constitution, a signal can be received at the range where modulated light which is away from a cable reaches without mounting a receiver on the cable itself and a communication system which is strong for electromagnetic waves is provide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a communication system for transmitting information by using an optical fiber.

[0002]

2. Description of the Related Art Conventionally, as this type of system, a radio broadcasting system using a leaky coaxial cable has been used. This modulates the audio signal in the radio frequency band,
By transmitting it to a leaky coaxial cable, it is a system that can receive and demodulate the leaked radio wave at any point along the cable, and it is often used as a wireless communication means in tunnels or along roads. ing.

[0003]

However, since these systems use radio waves, they are easily affected by electromagnetic noise and may not be used in places with strong electromagnetic noise, such as in power cable tunnels. It was
Further, although optical fiber communication is widely used, it is a device that directly attaches a communication device to the optical fiber for communication, and reception at a place apart from the optical fiber cannot be performed, so that it is convenient as in the above wireless system. Was not obtained. On the other hand, as an application technique of light leaking from the side surface of the optical fiber, a display device using a short optical fiber is considered, but there is no application example of communication. Furthermore, the present inventors have proposed an optical fiber capable of leaking visible light from the side surface of a long optical fiber (Japanese Patent Application No. 4-88067).

In view of the above circumstances, the present invention provides an optical fiber communication system that takes advantage of the leaky coaxial communication system and is resistant to electromagnetic noise, and a first configuration thereof is a light source device and a light source device. An optical fiber communication system comprising an optical fiber to which the light from is incident and a light receiving device arranged at an arbitrary position along the optical fiber, wherein the light source device has a light intensity of a light source according to a change of an input signal, The optical fiber includes a modulation mechanism for changing the phase,
It is characterized in that a leaky optical fiber whose light leaks from the side surface is used, and the light receiving device has a demodulation mechanism for returning the light leaked from the side surface of the optical fiber to the original signal.

In the second configuration, a plurality of signals can be simultaneously transmitted, and a plurality of light source devices that emit light of different wavelengths and a plurality of optical fibers to which the light from each light source device is incident are focused. An optical fiber communication system comprising the optical fiber cable and a light receiving device arranged at an arbitrary position along the optical fiber cable, wherein the light source device changes the light intensity, phase, etc. of the light source according to the change of the input signal. The optical fiber uses a leaky optical fiber whose light leaks from the side surface thereof, and the light receiving device receives the light leaking from the side surface of the optical fiber and the wavelength selection mechanism which receives only a specific wavelength. It is characterized by having a demodulation mechanism for returning to the original signal.

Further, in the third configuration, the optical fiber can be used also as a route display, and the optical fiber on which the light from the light source device is incident and the light receiving device arranged at an arbitrary position along the optical fiber. In the optical fiber communication system, the light source device uses a visible light source and modulates the light to enter the optical fiber, or a communication light source different from the visible light source is provided to provide a visible light source. The optical fiber is provided with a mechanism for making the modulated light of the communication light source incident on the optical fiber, the visible light is constantly leaked using a leaky optical fiber in which light leaks from the side surface thereof, and the light receiving device is provided from the side surface of the optical fiber. It is characterized by having a demodulation mechanism for returning the leaked modulated light to the original signal when received.

[0007]

With the first configuration, unlike the conventional leaky coaxial communication system, it is possible to receive a signal in a range where modulated light is far away from the cable without attaching a receiving device to the cable itself. It is possible to realize a communication system that is resistant to electromagnetic noise. These also apply to the following two configurations.

With the above-mentioned second structure, it becomes possible to transmit a plurality of signals at the same time, and the receiving side can selectively use the signals depending on the purpose, or the wavelengths can be assigned to the respective receivers in advance so that the sender can receive the necessary signals. It is possible to send a signal only to the person.

Further, with the third configuration, the optical fiber itself appears to emit light at all times, so that not only can a visible route be visible, but it can also serve as a route indicator in the dark. it can.

[0010]

EXAMPLES Examples of the present invention will be described below. (Embodiment 1) FIG. 1 shows the basic configuration of the system of the present invention. A light source device 1 is provided at one end of an optical fiber 2 (both ends may be provided), and a light receiving device 3 is provided at an arbitrary position along the optical fiber. There is. In this example, the signal is an audio signal, a microphone 4 is connected to the light source device, an optical signal modulated by the audio signal is emitted from the light source device 1, and the light is incident on the optical fiber 2. The optical fiber 2 is configured so that light can be leaked from its side surface, and is a system that demodulates the leaked light into an original audio signal when received by the light receiving device 3 and outputs a sound from the speaker 5. Each component will be described.

The light source device 1 has a structure as shown in FIG.
The input circuit 6 receives a signal from the microphone 4 and the like, and the modulation circuit 7 gives a modulation signal to the light source drive circuit 8 to modulate the light emitted from the light source element 9. Here, for the light source element 9, a general light source such as a light emitting diode or a halogen lamp can be used as the laser.

Next, the light-receiving device 3 has a structure as shown in FIG. 3, amplifies the signal received by the light-receiving element 10 such as a photodiode by an amplifier circuit 11, and the demodulator circuit 12 amplifies the original audio signal. To the speaker 5 and the like via the output circuit 23.

The optical fiber 2 is capable of leaking light from its side surface. For example, as shown in Japanese Patent Application No. 4-88067, the refractive index difference between the core and the cladding is 0.1.
Within the range of 5%, the transmission loss in the wavelength range used is 3 / L (d) with respect to the leakage distance L (km) used.
b / km) centered around plus 70%, minus 3
What is in the range of 0% may be used. FIG. 4 shows the configuration of a cable using the above optical fiber. The optical fiber has a two-layer structure of a core 13 and a clad 14, as shown in FIG. 1C, and is coated with a transparent resin. In order to increase the light emitting area, the optical fiber element wires 15 may be arranged in parallel to form a tape core wire 17 having a transparent resin coating 16 as shown in FIG. Alternatively, a cable using a plurality of the tape core wires 17 may be used. Any structure may be used as long as a sufficient amount of light leakage can be obtained, but a cable structure is preferable in view of ease of installation and mechanical strength.

In this example, as shown in FIG. 1A, an optical fiber element wire 15 made of quartz glass for the core and a thin acrylic plastic material for the clad is used, and a plurality of such optical fiber element wires 15 are arranged in parallel to form silicon or the like. A tape core wire 17 coated with a transparent resin is prepared, and a plurality of the tape core wire 17 is wound around a body 19 made of polyethylene or the like around a tension member 18 such as a steel wire or an FRP rod. The jacket 20 was provided by covering with resin (nylon or the like). In addition, in order to efficiently reflect the leaked light to the outer peripheral side of the cable, a reflector such as silver paper may be interposed between the tape core wire 17 and the body 19.

When a laser light source is used to input 100 mW of light into the optical fiber cable having such a structure, it is possible to obtain leakage light of several mW per 1 m from the side surface of the cable. It can be received by a light receiving device using a diode as a light receiving element.

(Embodiment 2) Next, the configuration shown in FIG.
This is an application of the basic configuration of 1., using a plurality of light source devices 1a, 1b, 1c having different wavelengths (three types in this example), and converging a plurality of optical fibers 2a, 2b, 2c corresponding to each light source device. Using the optical fiber cable 21, the light receiving device 3 is installed at an arbitrary position along this cable. Of course, as the optical fiber, a leaky type is used as in the first embodiment.

The leaked light from the optical fiber cable is a mixture of lights of three wavelengths. As shown in FIG. 6, a wavelength selection mechanism such as a wavelength selection filter 22 is provided in front of the light receiving element 10 to identify the light. Only wavelength signals can be selected and received. After that, it is amplified by the amplifier circuit 11, and this is demodulated by the demodulator circuit 12.
It is the same as in the first embodiment in that the original audio signal is returned to the original audio signal and is output to the speaker or the like via the output circuit 23.
Therefore, according to this example, it becomes possible to transmit a plurality of signals at the same time, and the receiving side can selectively use the signals depending on the purpose.
The wavelength can be assigned to each receiver in advance, and the transmitter can transmit the signal only to the necessary receiver.

(Embodiment 3) Further, a structure in which visible light is made incident on the optical fiber and the light is constantly emitted continuously can be used as the route indication. This example is also basically the same as the configuration of FIG. 1, and a visible light source may be used for this. In this case, two configurations are conceivable, one of which is to use the visible light source as a communication light source and modulate the light intensity of the light source that continuously emits light at all times.

Several modulation methods are conceivable. As shown in FIG. 7, light is continuously emitted at a constant level at all times (see FIG. A), and the light intensity is as shown in FIG. It may be modulated in an analog manner, or may be a method of repeating light emission and extinction in a pulsed manner as shown in FIG. Even with the method of repeating light emission and extinction, if modulation is performed at a speed of several tens of hertz or more, it appears to the human eye to continuously emit light. Of course, the modulation is not limited to these methods, and may be a modulation method generally used for optical communication, such as frequency modulation.

The other is that a light source different from the visible light source is used as a communication light source, and the visible light source is constantly and continuously emitting light to modulate the light of the communication light source. As shown in FIG.
Two light sources, a visible light source 24 and a communication light source 25, are used, and the lights from both light sources are combined by a combiner 26 and incident on a leaky optical fiber. In this case, the wavelength and light intensity of both light sources can be set appropriately,
As in the second embodiment, the light receiving device can receive only the light of the specific wavelength, but it is disadvantageous as compared with the case of modulating the visible light in that the light is lost due to the multiplexing. The light from each light source may be incident on a different optical fiber without being multiplexed. With any of the above configurations, since the optical fiber always emits light and can be viewed, the optical fiber can also function as a route indication in the dark.

[0021]

As described above, according to the present invention,
It is possible to construct a system that receives information transmitted from one end of an optical fiber at an arbitrary location along the optical fiber with less influence of noise as compared with the wireless system. Therefore, it is convenient to use it as a communication means in railway tunnels and power cable caves.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a basic configuration of a system of the present invention.

FIG. 2 is an explanatory diagram of a light source device used in the system of the present invention.

FIG. 3 is an explanatory diagram of a light receiving device used in the system of the present invention.

4A and 4B show an optical fiber used in the system of the present invention, where FIG. 4A is a sectional view of a cable structure, FIG. 4B is a sectional view of a tape core wire, and FIG. 4C is a sectional view of an element wire.

FIG. 5 is a schematic diagram of a system of the present invention capable of simultaneously transmitting a plurality of information.

6 is an explanatory diagram of a light receiving device used in the system of FIG.

FIG. 7 is a graph illustrating a light emitting method of a light source, where (A) is a case where continuous light emission is performed at a constant level, (B) is a case where light intensity is modulated in analog, and (C) is a case where pulse is modulated. Indicates.

FIG. 8 is a schematic diagram of a system of the present invention using two light source devices, a visible light source and a communication light source.

[Explanation of symbols]

 1,1a, 1b, 1c Light source device 2,2a, 2b, 2c Optical fiber 3 Light receiving device 4 Microphone 5 Speaker 6 Input circuit 7 Modulation circuit 8 Driving circuit 9 Light source element 10 Light receiving element 11 Amplifying circuit 12 Demodulating circuit 13 Core 14 Cladding 15 Optical fiber element 16 Resin coating 17 Tape core 18 Tension member 19 Body 20 Outer sheath 21 Optical fiber cable 22 Wavelength selection filter 23 Output circuit 24 Visible light source 25 Communication light source 26 Multiplexer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location H04B 10/00 // G02B 6/28 V 8707-2K

Claims (3)

[Claims] 1. An optical fiber communication system comprising a light source device, an optical fiber on which light from the light source device is incident, and a light receiving device arranged at an arbitrary position along the optical fiber, wherein the light source device is an input device. Light intensity of the light source according to the change of the signal,
The optical fiber uses a leaky optical fiber that leaks light from its side surface, and the light receiving device returns the original signal even if the light leaked from the optical fiber side surface is received. An optical fiber communication system comprising a demodulation mechanism. 2. A plurality of light source devices each emitting light of different wavelengths, an optical fiber cable that converges a plurality of optical fibers to which the light from each light source device is incident, and an arbitrary position along the optical fiber cable. An optical fiber communication system comprising arranged light receiving devices, wherein the light source device has a light intensity of a light source according to a change of an input signal,
A modulation mechanism for changing the phase etc. is provided, the optical fiber is a leaky optical fiber in which light leaks from its side surface, and the light receiving device is a wavelength selection mechanism for receiving only a specific wavelength,
An optical fiber communication system comprising: a demodulation mechanism for returning light leaking from the side surface of the optical fiber to the original signal. 3. An optical fiber communication system comprising a light source device, an optical fiber on which light from the light source device is incident, and a light receiving device arranged at an arbitrary position along the optical fiber, wherein the light source device is visible. It is equipped with a mechanism that uses a light source and modulates the light to enter the optical fiber, or provides a communication light source different from the visible light source and allows the visible light and the modulated light of the communication light source to enter the optical fiber. The optical fiber constantly leaks visible light using a leaky optical fiber that leaks light from its side surface, and the light receiving device demodulates the modulated light leaked from the optical fiber side surface to restore it to the original signal. An optical fiber communication system comprising a mechanism.