JP3296072B2 - Optical communication device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication technology using an optical fiber. The present invention relates to a communication device capable of performing meeting communication with each other at any place without cutting an optical fiber.

[0002]

2. Description of the Related Art Optical fibers are widely used as optical transmission media in optical transmission systems. In order to maintain and operate this optical transmission system efficiently, it is necessary to connect a monitoring center that monitors the facilities related to the optical transmission system and an actual work site such as a manhole during construction work such as new installation of optical fiber and route change. There is a need for a technology that allows easy communication.

A conventional device for this purpose will be described with reference to FIGS. 7 and 8. FIG. FIGS. 7 and 8 are block diagrams of a conventional apparatus. The conventional device shown in FIG.
No. 19184. In this conventional apparatus, a telephone call can be made between a monitoring center and a work site using one optical fiber 4 without cutting the optical fiber 4 in the middle. That is, this communication device
A leak light generated by bending the optical fiber 4 is demodulated by a demodulation circuit 26.
, And an audio signal is output from the speaker 10,
Further, by changing the bending rate of the optical fiber 4 according to the audio signal input from the microphone 9, the light source 130
The intensity modulation is applied to the continuous light (CW light) from the light source.

A conventional apparatus shown in FIG. 8 is described in a patent application filed by the same applicant, Japanese Patent Application No. 5-273798 (not disclosed at the time of filing the present application). This prior art device includes terminal devices Z1 and Z2, and terminal devices Z1 and Z2.
It comprises one optical fiber 4 connecting the two, and intermediate devices M1 and M2 installed without cutting the optical fiber 4 at an arbitrary position of the optical fiber 4.

The terminal devices Z1 and Z2 will be described with reference to FIG. Reference numeral 9 denotes a microphone for inputting an audio signal and converting it into an electric signal. Reference numeral 11 denotes a modulation circuit, and the microphone 9
Modulates the electric signal from the Reference numeral 130 denotes a light source, which converts an electric signal from the modulation circuit 11 into an optical signal and transmits the optical signal. Reference numeral 14 denotes an optical coupler, and the light source 13
The optical signal from 0 is transmitted into the optical fiber 4 and
The optical signal propagating through the optical fiber 4 is guided to an optical / electrical converter (hereinafter referred to as an O / E converter) 150.
The O / E converter 150 converts a received optical signal into an electric signal. A demodulation circuit 16 demodulates an electric signal from the O / E converter 150. Reference numeral 10 denotes a speaker that outputs an electric signal demodulated by the demodulation circuit 16 as an audio signal.

Next, the intermediate devices M1 and M2 will be described with reference to FIG. Reference numeral 9 denotes a microphone for inputting an audio signal and converting it into an electric signal. A modulation circuit 21 modulates an electric signal from the microphone 9. Reference numeral 20 denotes a diaphragm, which applies a change in bending diameter following an electric signal from the modulation circuit 21 to a bending applying portion of the optical fiber 4 installed in a U-shape, and converts the carrier signal light propagating through the optical fiber 4 into an optical signal. This is to add intensity modulation. Reference numeral 23 denotes a light receiving element as an O / E converter, which receives light leaking from the bending portion of the optical fiber 4 and converts the light into an electric signal.
A demodulation circuit 26 demodulates an electric signal from the light receiving element 23. Reference numeral 10 denotes a speaker that outputs an electric signal demodulated by the demodulation circuit 26 as an audio signal.

[0007] A form of communication between the devices in the communication device will be described with reference to FIG. Communication between the terminal devices Z1 and Z2 is performed by directly transmitting and receiving signal light between the light source 130 and the O / E converter 150. Terminal device Z1,
The communication from Z2 to the intermediate devices M1 and M2 is performed by receiving the signal light from the light source 130 in the light receiving element 23 as the leakage light from the optical fiber bending portion. Calls from the intermediate devices M1 and M2 to the terminal devices Z1 and Z2 are performed by the O / E converter 150 receiving the signal light whose light intensity has been modulated by the diaphragm 20. Intermediate device M
The communication between M1 and M2 is performed by receiving the signal light whose light intensity has been modulated by the diaphragm 20 of the intermediate device M1 in the light receiving element 23 of the other intermediate device M2 as leakage light from the optical fiber bending portion. Do.

[0008] This communication device can make a call between the devices without cutting the optical fiber.

[0009]

The above publication also discloses a structure in which light sources are provided at both ends of the optical fiber 4. A monitoring center is provided at one end, and a reflection connector can be connected to the other end. In such a case, by using the configuration shown in FIG. 7, communication can be performed without disconnecting the optical fiber 4 at another intermediate point. However, since the conventional apparatus uses continuous light as a light source, Rayleigh scattered light generated in the optical fiber is received at the same time as a call signal, which causes a reduction in the signal-to-noise ratio (SNR) of the call signal. When the other end is already drawn into the user building, the total reflection connector 50 cannot be connected to the other end of the optical fiber as shown in FIG.

The present invention has been made in such a background. When a monitoring center is located at one end of an optical fiber and a terminal device for communication can be connected, the other end is under construction and opened. Even if it is at the end, already in the user's building, or when another communication device is connected, the terminal device and the intermediate device connected to any position of the optical fiber It is an object of the present invention to provide a device capable of making a telephone call without cutting an optical fiber.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical communication device capable of making a call with high quality without breaking the optical fiber.
SUMMARY OF THE INVENTION It is an object of the present invention to provide a device capable of making a call without cutting an optical fiber, and to increase the callable distance.

An object of the present invention is to provide an apparatus capable of performing high-quality two-way communication over a long distance without cutting the optical fiber and without accessing the other end of the optical fiber. Aim.

[0013] It is an object of the present invention to provide an apparatus capable of making a telephone call between a terminal device and an arbitrary position of an optical fiber even when main signal communication transmitted to the optical fiber is performed. And

[0014]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a light source for generating a periodic pulse light is used as a light source for a meeting communication. The period (T) is characterized in that when the length of the optical fiber is L and the speed of light in the optical fiber is v, the round-trip propagation time of the optical fiber is set to be longer than 2 L / v.

As a light source for generating the pulse light, a light source for generating N (N is 2 or more) pulse lights in time series having different output light wavelengths from each other is used, so that the communication quality can be further improved. it can. Also in this case, the transmission period (T) of the pulse light is set longer than the round trip propagation time (2 L / v) of the optical fiber for each output light wavelength.

Further, the terminal device (1) includes a relay circuit (18) for coupling the output signal obtained by the demodulation circuit (16) to the input signal of the modulation circuit (11),
Bidirectional communication quality can be further improved.

In the present invention, the pulse light of the light source is preferably selected to have a wavelength different from the wavelength for main signal communication propagated through the optical fiber.

That is, the present invention provides an optical fiber, a terminal device (1) connected to one end of the optical fiber, and a coupling device for leaking light generated by bending the optical fiber in the middle of the optical fiber. The terminal device (1) includes the intermediate devices (2, 3) described above, and includes a light source (12) coupled to the optical fiber, and a modulation circuit (11) that modulates the light source with an input signal. A demodulation circuit (16) for demodulating an output signal from an optical signal arriving at the optical fiber,
The intermediate devices (2, 3) include a demodulation circuit (26) for demodulating the leaked light to obtain an output signal, and a modulation circuit (1) for modulating an optical signal passing through the optical fiber with an input signal.
1, 21), wherein the light source (12) is a light source that generates periodic pulsed light, and the transmission period (T) of the pulsed light is such that the length of the optical fiber is L, and Is the speed of light of v, the round trip propagation time of the optical fiber is 2L
/ V.

Another aspect of the present invention is a terminal device used for the communication device.

[0020]

In order to avoid deterioration of the signal-to-noise ratio (SNR) due to optical signal interference and Rayleigh scattered light in an optical fiber, communication is performed using pulsed light. In addition, the transmission period of the pulse light is set longer than the round trip propagation time of the optical fiber. That is, after waiting for one pulse light to be reflected by the reflection end and returning, the next pulse light is transmitted. By doing so, Rayleigh scattered light and the like superimposed on the received signal are reduced. Therefore, the signal-to-noise ratio (S
NR) can be ensured.

Since the transmission period of the pulse light is set longer than the round trip propagation time of the optical signal in the optical fiber, the frequency band of the communication in which the pulse light can be modulated and communicated is limited by the transmission period. Therefore, the frequency band of communication can be expanded by generating and using pulse light of different wavelengths in time series as the pulse light. That is, high quality communication can be performed by performing wavelength multiplexing using a light source that generates N pulse lights having different output light wavelengths in time series. Also in this case, the transmission cycle of the pulse light for each output light wavelength is set longer than the round trip propagation time of the optical fiber. Thereby, a plurality of communication paths can be set by one optical fiber while ensuring high signal quality. If the signal quality is kept constant, the communicable distance can be increased.

By providing a relay circuit for coupling an output signal obtained by demodulating a signal arriving from an optical fiber to an input of the modulation circuit in the terminal device, the signal arriving at the terminal device can be again converted into a signal in the opposite direction. Therefore, the bidirectional communication quality can be improved.

The wavelength of the pulse light is preferably basically different from the wavelength of the main signal transmitted to the optical fiber. By setting the wavelengths to be different from each other, communication for meetings can be performed even during transmission of the main signal.

If a reflection end is provided at the other end of the optical fiber (the end opposite to the one to which the terminal device is connected), the optical pulse arriving at the other end is reflected, thereby improving the communication quality. . However, even if the other end is not provided with a reflection end, the reflection between the light receiving device and other devices connected to the other end and the reflected light generated by the Fresnel reflection even if the other end is an open end. Communication can be performed. By setting the output light level of the light source to be high, two-way communication is actually possible even by Rayleigh scattered light.

[0025]

【Example】

(First Embodiment) The configuration of the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram of a first embodiment of the present invention.

The present invention relates to an optical fiber 4 having one end provided with a reflection filter 5 serving as a reflection end, a terminal device 1 connected to the other end of the optical fiber 4, and an intermediate part of the optical fiber 4. And a light source 12 (FP-LD, F) that causes the terminal device 1 to make light incident on the optical fiber 4 including intermediate devices 2 and 3 that are coupled to leakage light generated by bending the optical fiber 4.
The terminal device 1 and / or the intermediate devices 2 and 3 are provided with modulation circuits 11 and 21 for modulating the light with an input signal, and an output signal is obtained by demodulating the modulated light. This is an optical communication device including demodulation circuits 16 and 26.

The feature of the present invention resides in that the light source 12 generates pulsed light. The pulse light is controlled by a synchronization signal generator 17, and the transmission period T of the pulse light is 2L / v, where L is the length of the optical fiber 4 and v is the light speed in the optical fiber 4. The round-trip propagation time is set longer than 2 L / v.

The terminal device 1 includes a modulation circuit 11 for modulating an input signal, a light source 12 for converting an electric signal from the modulation circuit 11 into an optical signal, an optical isolator 13, and an optical signal incident on the optical fiber 4. In addition, the backscattered light and reflected light from the optical fiber 4 are received by a light receiving element (PD, Photo Diode)
An optical coupler 14 for guiding the light to the light receiving element 15, a demodulation circuit 16 for demodulating a signal received by the light receiving element 15, and a synchronization signal generator 17 for transmitting a synchronization signal to the modulation circuit 11 and the demodulation circuit 16.

The intermediate devices 2 and 3 are inserted at arbitrary positions of the optical fiber 4 without cutting the optical fiber.
The intermediate device 2 or 3 includes a diaphragm 20 for changing a bending application interval to the optical fiber 4, a modulation circuit 21 for transmitting a modulation signal obtained by modulating an input signal to the diaphragm 20, and a light leaking from the bending application unit. It comprises a light receiving element 23 for receiving light and a demodulation circuit 26 for demodulating a signal received by the light receiving element 23.

A reflection filter 5 is connected to the other end of the optical fiber 4. The reflection filter 5 has a characteristic of reflecting the light wavelength of the meeting communication, and has a characteristic of transmitting the light wavelength of the main signal communication using the optical fiber 4.

Next, the operation of the first embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a diagram showing an optical signal according to the first embodiment of the present invention. FIG. 2 shows time on the horizontal axis and the signal level on the vertical axis. The flow of signals from the terminal device 1 to the intermediate devices 2 and 3 will be described. The signal input to the terminal device 1 is modulated by the modulation circuit 11 in synchronization with the synchronization signal from the synchronization signal generator 17. This signal is converted into a pulsed optical signal as shown in FIG. 2 by the light source 12 and is incident on the optical fiber 4 via the optical coupler 14.

In this optical signal, the signal input by the terminal device 1 is superimposed on the envelope of the pulse light having the pulse width τ and the pulse transmission period T. This optical signal is partially leaked at the bending imparting portions of the intermediate devices 2 and 3, and the light receiving element 2
3 is received. The received signal is transmitted to the demodulation circuit 2
4 demodulates into an audio signal.

The flow of signals from the intermediate device 2 to the terminal device 1 will be described. The signal input to the intermediate device 2 is input to the diaphragm 20 via the modulation circuit 21. The diaphragm 20 changes the bending interval of the optical fiber 4 in accordance with the vibration, and modulates the intensity of the optical signal passing through the optical fiber 4. The optical signal at this time is as shown in FIG. The optical signal modulated by the intermediate device 2 is reflected by the reflection filter 5 at the far end of the optical fiber 4. This reflected light propagates through the optical fiber 4 in the opposite direction, and is received by the light receiving element 15 via the optical coupler 14. The received optical signal is demodulated by the demodulation circuit 16 into an audio signal.

The signal flow between the intermediate devices 2 and 3 will be described. The intermediate device 3 has the same configuration as the intermediate device 2. The internal structure is omitted in the figure. The intermediate device 2 similarly applies intensity modulation to the optical signal passing through the optical fiber 4. This optical signal is similarly received by the light receiving element 23 in the intermediate device 3 and demodulated by the demodulation circuit 26. The optical signal modulated by the intermediate device 3 is reflected by the reflection filter 5 at the far end of the optical fiber 4. This reflected light is received by the light receiving element 23 of the intermediate device 2 and demodulated.

The reflection filter 5 inserted near the far end of the optical fiber 4 reflects light in the maintenance wavelength band used for the meeting communication and transmits light in the transmission wavelength band for main signal communication. This is usually used for fault isolation of an optical subscriber system transmission line. In the case of the new construction of the optical fiber 4, the far end of the optical fiber 4 is in an open state. In this case, too, the optical signal can be reflected by using the Fresnel reflection at the end face, and thereby the meeting communication is performed. be able to. Further, even when the other end of the optical fiber 4 is already drawn into a user building or the like and cannot be entered for maintenance operation of the optical fiber 4, it is connected to the end of the optical fiber 4 in the user device. Meeting communication can be performed using reflection generated between the light receiving element and the like.

According to the present invention, by setting the maintenance wavelength band used for the meeting communication separately from the wavelength for the main signal communication, the meeting communication can be performed even during the main signal communication. That is, as shown in FIG.
By connecting the terminal device 1 to the main signal terminal 60 by using, the meeting communication can be performed between the terminal device 1 and the intermediate device 2. FIG. 3 is a diagram illustrating a connection example of the terminal devices.

Next, the relationship between the transmission cycle of the pulse light transmitted from the terminal device 1, the length of the optical fiber 4, and the transmission signal band will be described. When the terminal device 1 receives the reflected light, the Rayleigh scattered light is simultaneously received and becomes noise, so that the signal-to-noise ratio of the terminal device 1 is degraded. Therefore, the pulse width of the pulsed light is made sufficiently shorter than the pulsed light transmission period, and the pulsed light transmission period is set to be longer than the time interval at which the pulsed light is transmitted and then reflected at the far end of the optical fiber 4 and returned. Set. That is, assuming that the length of the optical fiber 4 is L and the speed of light in the optical fiber 4 is v, the pulse light transmission period T is T ≧ 2L / v. On the other hand, the pulse light delivery period for the sampling period of the modulation signal at the intermediate apparatus 2, the f _c ≦ 1 / the sampling theorem when the cut-off frequency of the modulation frequency is f _c (2T). Thus the pulsed light transmission period T is set to 2L / v ≦ T ≦ 1 / (2f c) ... (1), the call distance (optical fiber length) L _{is, L ≦ v / (4f c} ) ... (2 ). For normal voice band is sufficient for the call if 2 kHz, when the modulated signal band at the intermediate apparatus 2 and 2kHz (f _c = 2kHz), communicable distance of the first embodiment of the present invention apparatus formula From (2), the maximum distance is 25 km.

In order to confirm the effect of the present invention, about 25 k
A 1.3 μm band standard optical fiber of m was used to configure an optical subscriber system transmission line, and as shown in FIG. 1, one terminal device and two intermediate devices were installed and a call test was performed. Intermediate devices 2, 3
Were installed at positions 10 km and 20 km from the terminal device 1, respectively. The reflection filter 5 inserted near the far end of the optical fiber 4 has a wavelength of 1.55 μm used as a maintenance wavelength band.
It has the characteristic of reflecting light in the band with a return loss of 10 dB and transmitting light in the 1.3 μm band used as a transmission wavelength band. The pulse width of the signal light from the terminal device 1 is 1 μm.
s, sending period 250 μs, peak power 10 dBm
And the degree of modulation was about 3%. Also, the intermediate device 2,
The degree of modulation at 3 was also about 3%. At this time, the terminal device 1
A good call was possible in any case between the device and the intermediate devices 2 and 3 or between the intermediate devices 2 and 3. The degree of modulation is preferably set to 1 to 5% so as not to disturb the main signal.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a block diagram of a second embodiment of the present invention. FIG. 5 is a diagram showing signal light according to the second embodiment of the present invention. Figure 5 shows time on the horizontal axis,
The signal level is displayed on the vertical axis. The light source 30 outputs a laser diode (DFB-LD, Distributed Feedb) that outputs two wavelengths and outputs light having a wavelength λ1 (= 1.535 μm).
ack-Laser Diode: Distributed feedback laser diode) 31
And a laser diode 32 that outputs light of wavelength λ2 (= 1.55 μm), and these laser diodes 31 and 32
Multiplexed light from the optical coupler.
The light receiver 40 includes an optical coupler 41 that separates two wavelengths λ1 and λ2, respectively, and light receiving elements 42 and 43 that receive backscattered light and reflected light separated for each wavelength.

As shown in FIG.
A pulse light of wavelength λ1 having a pulse width τ has a transmission period of 2T
The pulse light of the wavelength λ2 having the pulse width τ is output from the laser diode 32 at a transmission period 2T with a delay of T time from the pulse light of the laser diode 31. The pulse lights of these different wavelengths are multiplexed by the optical multiplexing / demultiplexing device 33, and the signal light shown in FIG. 5 is output. The input signal in the terminal device 1 is superimposed on the envelope of the pulse light of two different wavelengths (λ1, λ2). In the light receiver 40,
The backscattered light and the reflected light having different wavelengths are separated and received for each wavelength, and the amplitude modulation component is demodulated.

The relation between the pulse width of the pulse light transmitted from the terminal device 1 and the pulse light transmission period is as described in the first embodiment of the present invention. Since light becomes noise and sensitivity deteriorates, it is necessary to set the transmission cycle of the same wavelength to a time interval longer than the time interval at which the optical pulse is transmitted and then reflected and returned at the far end of the optical fiber 4. Therefore, a pulse light transmission cycle of one wavelength 2
T is 2T ≧ 2L / v. Meanwhile, since the transmission period T of the pulsed light of two wavelengths multiplexed light pulse becomes a sampling period of the modulation signal at the intermediate apparatus 2, the sampling theorem when the cut-off frequency of the modulation frequency is f _c f _c ≤1 / (2
T). Therefore, transmission cycle T is set to L / v ≦ T ≦ 1 / (2f c) ... (3), the call distance L becomes _{L ≦ v / (2f c)} ... (4). Modulation signal band in intermediate devices 2 and 3 is 2 kHz
When (f _c = 2 kHz), communicable distance of the present invention the second embodiment apparatus, the equation (4), twice the maximum 50km in the case of the present invention the first embodiment can be obtained. Also, when the communicable distance is set to a maximum of 25 km, the modulation signal band in the intermediate devices 2 and 3 becomes 4 kHz according to Expression (4), and the band of a signal that can be transmitted is doubled, so that the transmission quality is improved. Similarly, by using a light source that generates light of N different wavelengths and a photodetector that separates and receives the light, an N-times talkable distance or an N-times transmission signal band can be obtained.

In order to confirm the effect of the second embodiment of the present invention, an optical subscriber system transmission line is constituted by a 1.3 μm band standard optical fiber 4 of about 50 km, and as shown in FIG. One and two intermediate devices were installed to make a call. The intermediate devices 2 and 3 were installed at positions 20 km and 40 km from the terminal device 1. The pulse width of the signal light from the terminal device 1 is 1 μm.
s, transmission period T is 500 μs, peak power is 10 dB
m and the degree of modulation was about 3%. The degree of modulation in the intermediate devices 2 and 3 was also about 3%. At this time, good communication was possible in any case between the terminal device 1 and the intermediate devices 2 and 3 or the intermediate devices 2 and 3.

Further, an optical subscriber system transmission line is constituted by a 1.3 μm band standard optical fiber of about 25 km, and as shown in FIG. 4, one terminal device and two intermediate devices are installed to communicate. went. The intermediate devices 2 and 3 are 10 km from the terminal device 1 and 2
It was installed at a position of 0 km. Terminal device 1 and intermediate devices 2, 3
Alternatively, good communication was possible in any case between the intermediate devices 2 and 3, and the transmission signal band was expanded to about 4 kHz.

(Third Embodiment) Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 6 is a block diagram of the device according to the third embodiment of the present invention. The third embodiment of the present invention is provided with a relay circuit 18 for relaying the electric signal of the demodulation circuit 16 to the modulation circuit 11. The signal light modulated by the intermediate device 3 is reflected by the reflection filter 5 at the far end of the optical fiber 4. When the reflected light is received by the light receiving element 23 of the intermediate device 2, there is a case where the signal cannot be received while maintaining a high signal-to-noise ratio (SNR) because the coupling loss between the optical fiber 4 and the light receiving element 23 is large. Therefore, the signal light reflected by the reflection filter 5 is once received by the terminal device 1, relayed to the modulation circuit 21 via the relay circuit 18, and transmitted again from the terminal device 1 to the intermediate device 2. As a result, the signal light level received by the light receiving element 23 of the intermediate device 2 increases, and the signal light can be received while maintaining a high signal-to-noise ratio (SNR).

In order to confirm the effect of the third embodiment of the present invention,
As a result of conducting an experiment similar to that of the first embodiment of the present invention, the signal-to-noise ratio of the communication between the intermediate devices 2 and 3 was improved, and the communication quality was improved.

Instead of the laser diodes 31 and 32 of the light source 30 in the second embodiment of the present invention, one multi-wavelength MQ
By using a W-LD (multiple quantum well laser diode) array, the size of the device can be reduced. Similarly, a multi-electrode DFB-LD (Distributed Feed-Back Lase
r Diode: distributed feedback laser diode) and multi-electrode DB
R-LD (Distributed Bragg-Reflector Laser Diode:
Bragg reflection type laser diode) can also be used.

Further, instead of the optical coupler 41 of the light receiver 40, the light of different wavelengths is temporally separated by using a wavelength selective switch, so that the light receiver 40 is constituted by one light receiving element. Device can be downsized.

In the first to third embodiments of the present invention, the modulation circuit 11 and the demodulation circuit 16 are provided in the terminal device 1. However, the terminal device 1 is provided with only a light source that generates pulsed light at a prescribed transmission cycle. It is also possible to adopt a configuration in which the communication device is installed and communication is performed only between the intermediate devices 2 and 3.

[0049]

As described above, according to the present invention,
It is possible to perform high-quality communication between communication devices performing a telephone call without cutting the optical fiber.

According to the present invention, noise due to reflected light, Rayleigh scattered light, and the like can be reduced, thereby improving communication quality. In the present invention, communication quality can be further improved by using a plurality of wavelengths,
Alternatively, the communicable distance can be increased.

According to the present invention, it is possible to smoothly perform communication between the terminal device and the intermediate device without cutting the optical fiber during the installation work or the optical fiber under maintenance. it can. In the present invention, the communication quality is higher than that in the case of using continuous light because it is not affected by Rayleigh scattered light. In the present invention, meeting communication can be performed without accessing the other end of the optical fiber.

[Brief description of the drawings]

FIG. 1 is a block diagram of a device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing signal light according to the first embodiment of the present invention.

FIG. 3 is a view for explaining a connection example of a terminal station device;

FIG. 4 is a block diagram of a device according to a second embodiment of the present invention.

FIG. 5 is a diagram showing signal light according to a second embodiment of the present invention.

FIG. 6 is a block diagram of a device according to a third embodiment of the present invention.

FIG. 7 is a block diagram of a conventional apparatus.

FIG. 8 is a block diagram of a conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, Z1, Z2 Terminal device 2, 3, M1, M2 Intermediate device 4 Optical fiber 5 Reflection filter 8 Optical handset 9 Microphone 10 Speaker 11, 21 Modulation circuit 12 Light source 13, 140 Optical isolator 14 Optical coupler 15, 23, 42, 43 Light receiving element 16, 26 Demodulation circuit 17 Synchronous signal generator 18 Relay circuit 20 Vibration plate 30, 130 Light source 31, 32 Laser diode 33, 41 Optical splitter 40 Optical receiver 50 Total reflection connector 60 Main signal terminal 63 Optical coupler 150 O / E converter

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Nobuo Kuwaki Nippon Telegraph and Telephone Corporation, 1-6-1, Uchisaiwaicho, Chiyoda-ku, Tokyo (56) References JP-A-61-288298 (JP, A) 5-268170 (JP, A) JP-A-5-19184 (JP, A) JP-A-4-368029 (JP, A) JP-A-2-131636 (JP, A) JP-A-3-26432 (JP, A) B2) (58) Field surveyed (Int. Cl. ⁷ , DB name) H04B 10/00-10/28 H04J 14/00-14/08

Claims (5)

(57) [Claims] An optical fiber and one end of the optical fiber
The connected terminal equipment (1) and the optical fiber
One that couples to the leakage light generated by bending this optical fiber
And at least one intermediate device (2, 3), wherein the terminal device (1) is coupled to the optical fiber.
A light source (12), and a modulator for modulating the light source with an input signal;
A tuning circuit (11) and an optical signal arriving at the optical fiber.
And a demodulation circuit (16) for demodulating an output signal from the intermediate device (2, 3).
A demodulation circuit (26) for obtaining a force signal;
A modulation circuit (1) that modulates a passing optical signal with an input signal.
1, 21), wherein the light source (12) generates a periodic pulsed light.
And the transmission cycle of this pulsed lightTo TReciprocating transmission of the optical fiber
Sowing time2L / v (where the length of the optical fiber is L,
Let the speed of light in this optical fiber be v), Required obi
Range cutoff frequency is f _c When T ≧ 2L / v f _c ≤1 / (2T) Set to An optical communication device, comprising: 2. The light sources that generate the pulsed light are mutually
N pulses (N is an integer of 2 or more) with different output light wavelengths
Light is generated in time series, ThatPulse light transmission periodTo
TAnd the cutoff frequency required for the call _c And when, T ≧2L/ VAnd f_c≤N/ (2T)Or T ≧ 2L / (Nv) and f _c ≤1 / (2T)  The optical communication device according to claim 1, wherein the optical communication device is set to: 3. The terminal device (1) includes a relay circuit (18) for coupling an output signal obtained by the demodulation circuit (16) to an input signal of the modulation circuit (11). 1
Or the optical communication device according to 2. 4. The optical communication apparatus according to claim 1, wherein the pulse light is selected to have a wavelength different from a wavelength for main signal communication propagated through the optical fiber. 5. The optical communication device according to claim 4, wherein a reflection means (5) for the wavelength of the pulse light is provided at the other end of the optical fiber.