JPH04225130A - Light transmitting apparatus - Google Patents

Abstract

PURPOSE:To make it possible to test a light transmitting path simply at any time without using a special apparatus under the normal operating state by scrambling a transmitting signal with pseudo-random signal having a specified bit period, and transmitting the signal into the light transmitting path. CONSTITUTION:A transmitting signal (b) of ordinary business data which is outputted from a transmitting device 11 is scrambled with a scrambling circuit 12 by using a pseudo-random signal (c) having the bit period longer than reciprocating delay time in a light transmitting path 15. The synthesized signal (e) is converted into a light signal (f) in an E/O (electricity/light) converter 16. The signal is sent into the transmitting path 15 through a spectrophotometer 17. The split 17 light signal (g) is converted into an electric signal (h) in an O/E converter 18. The signal is inputted into a correlation processing part 20. In the processing part 20, the correlation coefficient of the light signal (h) and the synthesized signal (e) which is delayed in a delay circuit 21 is obtained. A data analyzing part 22 computes the signal reflecting position of the light signal (g) in the transmitting path 15 based on the correlation data and the delay time inputted from the circuit 21. Thus, the position of the wire breakdown or the damage in the transmitting path 15 is specified.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to an optical transmission device that converts a transmission signal output from a transmission device into an optical signal and transmits it to a terminal device via an optical transmission line. The present invention relates to an optical transmission device that has a function to monitor and test the status of an optical transmission device.

0002

2. Description of the Related Art In an optical communication system using optical communication, as shown in FIG. ing. When the master station A sends and receives various data on a time-sharing basis between the terminals B to D, the format of the communication signal a transmitted on the optical transmission line 1 is configured as shown in FIG. ing.

That is, the communication signal a is composed of a large number of consecutive frames 2 divided into predetermined lengths T0. The frame length T0 is set to, for example, 2.5 ms. In one frame 2, transmission data signals Dab, Dac, and Dad to be transmitted from the master station A to each of the terminals B, C, and D are set at the beginning. Then, a guard time Tg in a no-signal state is set after the transmission data signals Dab, Dac, Dad. Next to the guard time Tg, a transmission data signal Dba to be transmitted from the terminal B to the master station A is incorporated, and furthermore, the guard time Tg
Another shorter guard time Tg1 is provided, and after this guard time Tg1, a transmission data signal Dca to be transmitted from the terminal C to the master station A is incorporated. Further thereafter, a transmission data signal Dda to be transmitted from terminal D to master station A via guard time Tg2 is incorporated.

The leading guard time Tg is provided so that each transmission data signal from the master station A does not conflict with each transmission data signal from each terminal B to D on the optical transmission line 1, and the guard time The value of Tg is set to be longer than the time required for the optical signal to travel back and forth over the longest distance of the optical transmission line 1, that is, the round trip delay time. Guard times Tg1 and Tg2 are also provided between the transmission data signals Dba, Dca, and Dda from terminals B to D to master station A.
This has a function of preventing the transmission data signals Dba, Dca, and Dda from competing on the optical transmission path 1, taking into account the setting error of the distance between each terminal B, C, and D. .

Furthermore, in each transmission data signal, as shown in the figure, a preamble is set at the beginning, then an overhead indicating the type of signal is set, and finally actual data is set.

[0006] In ping-pong transmission having such a configuration, it is necessary to periodically check whether the optical transmission line 1 through which the communication signal a is transmitted is operating normally. Furthermore, even when a new optical communication system is constructed, it is necessary to confirm that the optical transmission line 1 operates normally. Specifically, each optical fiber constituting the optical transmission line 1 is not disconnected;
Measure the length of the optical fiber and the transmission loss of the optical fiber.

As a test procedure for this optical transmission line 1, for example, a test optical pulse signal is sent from the master station A to each terminal B, C, and D via the optical transmission line 1, and each terminal B to D receives a test optical pulse signal. , checks whether the test optical pulse signal received from master station A is addressed to itself and whether the received optical level is within an allowable range. Furthermore, the test optical pulse signal is sent from the master station A side to the optical transmission line 1, the backscattered light of the test optical pulse signal transmitted from the master station A side is observed, and the attenuation characteristics of the signal level of the backscattered light are measured. A method has also been developed to identify disconnected or damaged locations from discontinuities.

[0008]

[Problem to be Solved by the Invention] When constructing a new optical communication system, it is possible to spend sufficient time conducting each of the above-mentioned tests before starting operation of this system. Once the communication system is in operation, it is necessary to interrupt the operation of the optical communication system and conduct a test. However, when this optical communication system is integrated into a general public line, it is not recommended to suspend normal operations for a certain period of time to test the optical communication system once it is in operation. extremely difficult.

[0009] Furthermore, every time regular inspection and repair work is carried out, the master station A is removed from the optical transmission line 1 and the optical transmission line 1 is
For example, it is necessary to attach a test device such as an optical pulse test device (OTDR) to the device for testing. Also, insert an optical switch in advance between master station A and optical transmission line 1, attach the test equipment to the optical switch only when conducting a test, and switch the optical switch to the test equipment side. It is possible to conduct the test using However, in any case, a separate dedicated test device is required.

The present invention has been made in view of the above circumstances, and by scrambling a transmission signal with a pseudo-random signal having a predetermined bit period and transmitting the scrambled signal to an optical transmission path, in normal operating conditions, It is an object of the present invention to provide an optical transmission device that can easily test an optical transmission line at any time without using a separate dedicated test device.

[0011] Furthermore, it is an object of the present invention to provide an optical transmission device in which the data transmission efficiency does not deteriorate even when transmitting and receiving signals are transmitted over the same optical transmission path, as in the case of ping-pong transmission. The purpose is to

0012

[Means for Solving the Problems] In order to solve the above problems, the present invention provides an optical transmission device that converts a transmission signal output from a transmission device into an optical signal and transmits the optical signal to a terminal device via an optical transmission line. , a pseudorandom signal generation circuit that outputs a pseudorandom signal having a bit period longer than the round trip delay time for an optical signal to travel back and forth through an optical transmission line, and a scrambler that scrambles a transmission signal output from a transmission device with a pseudorandom signal. circuit and an E that converts the scrambled composite signal into an optical signal using this scrambling circuit.
/O converter, an optical splitter that sends the optical signal output from this E/O converter to an optical transmission line and separates the optical signal input from this optical transmission line, and this optical splitter an O/E converter that converts the separated optical signal into an electrical signal;
A delay circuit that delays the composite signal output from the scrambling circuit, and a composite signal delayed by this delay circuit and an O/
A correlation processing unit that calculates the correlation between the output signal of the E converter and a signal reflection within the optical transmission line of the optical signal input from the optical transmission line based on the correlation data of this correlation processing unit and the delay time of the delay circuit. It also includes a data analysis section that calculates the distance to the location.

[0013] In yet another optical transmission device of the invention,
In addition to the above-mentioned means, the apparatus includes a signal processing section that receives and processes signals transmitted from the terminal device.

[0014]

[Operation] With the optical transmission device configured as described above, the normal transmission signal outputted from the transmission device is scrambled with a pseudo-random signal. A pseudorandom signal has a constant bit period. Even if the pseudo-random signals are the same, if the bit strings differ by even one bit, there is no correlation at all. That is, it has a property that the correlation coefficient becomes 1 only when the bit string data constituting the bit period completely match. When a transmission signal is scrambled with a pseudorandom signal having such properties, the scrambled composite signal has a correlation of 1 only for the same composite signal. Therefore, when this composite signal is converted into an optical signal and sent to the optical transmission line, the backscattered light of the composite signal being transmitted toward the terminal device, or the Fresnel reflected light at the singular point or end of the optical transmission line, is transmitted. When light is received and converted into an electrical signal at the side, the only signal that correlates with the received signal with a value of 1 is the scrambled and delayed composite signal in the delay circuit.

Therefore, the signal reflection position on the optical transmission path of the input backscattered light or Fresnel reflected light can be calculated from the delay time of the composite signal when the correlation is 1. Therefore, the position of disconnection or damage on the optical transmission path can be identified.

Furthermore, by setting the bit period of the pseudorandom signal to be longer than the round trip delay time for the optical signal to travel back and forth through the optical transmission line under test, it is possible to receive the same composite signal repeatedly in a short period of time. Prevented in advance.

Note that by converting the optical signal received at the terminal side into an electrical signal and canceling the scrambling, the original transmission signal can be demodulated. That is, the test can be conducted during normal business hours.

Furthermore, in other inventions, even if the transmit signal and the receive signal are transmitted on the same optical transmission line, as in ping-pong transmission, the guard time is not used to transmit and receive the test optical signal. , there is no need to set a long guard time for the test.

Furthermore, since the distance to the terminal device can be determined, there is no need to take extra guard time for fluctuations in the length of the transmission path, and automatic setting of time slots is also possible.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of an optical transmission device according to an embodiment. The transmission signal b output from the transmission device 11 is input to the scrambling circuit 12. A pseudorandom signal c as a pseudorandom signal outputted from a pseudorandom signal generation circuit 13 as a pseudorandom signal generation circuit is applied to the scrambling circuit 12.

For example, as shown in FIG. 2, the pseudorandom signal generation circuit 13 has N registers 13a connected in series, and the output of the Nth register 13a and the output of the (N-1)th register 13a. The exclusive OR signal of is obtained using the exclusive OR gate 13b and
A clock signal d having a period Tc is applied to each register 13a from a clock signal generating circuit 13c. Such a pseudo-random signal generation circuit 13 outputs a pseudo-random signal c having a bit period of (2N-1). Therefore, the actual period is a value obtained by multiplying (2N-1) by the clock period Tc.

[0023] This period (2N -1) Tc is the round trip delay represented by the time required for an optical signal to travel back and forth through the optical transmission line 15 made of an optical fiber that connects this optical transmission device and the terminal device 14. The number of stages N of the register 13a is set so that the time is slightly longer than the current time. That is, when the communication signal a as shown in FIG. The guard time Tg is set longer than the guard time Tg provided between the data signal and the data signal.

For example, if the code transmission rate of transmission signal b is 10
MHz (clock period 0.1 μs), optical transmission line 1
5 round trip distance is 10 x 2km (required time 100μs)
), the number of stages N of the register 13a is 10 or more.

The scrambling circuit 12 scrambles the input transmission signal b by adding a pseudo-random signal c to the input transmission signal b. A composite signal e obtained by scrambling the pseudorandom signal c in the scrambling circuit 12 is converted into an optical signal f by an E/O (electrical/optical) converter 16 consisting of, for example, a laser oscillator, and then sent via an optical branching device 15. The signal is sent to the optical transmission line 15. Inside the terminal device 14,
The received optical signal f is returned to the original transmission signal using a scramble demodulation circuit.

Then, the terminal device 14 transmits a transmission signal to the transmission device 11 at the timing shown in FIG. Therefore, the optical transmission line 15 includes a transmission device 1 as shown in FIG.
In addition to the transmission signal transmitted from the terminal device 1 to the terminal device 14, the adjacent transmission signal a is transmitted from the terminal device 14 to the transmission device 11 via the guard time Tg.

The optical branching device 17 has the function of transmitting the optical signal f output from the E/O converter 16 to the optical transmission line 15 as it is, and separating the optical signal input from the optical transmission line 15. Optical signal g separated by optical splitter 17
is converted into an electrical signal by an O/E (optical/electrical) converter 18, amplified by an amplifier 19, and input to a correlation processing section 20.

On the other hand, the composite signal e output from the scrambling circuit 12 is delayed by a delay circuit 21 and then input to the correlation processing section 20. The correlation processing section 20 is the amplifier 1
The correlation coefficient between the output signal h of 9 and the composite signal e delayed by the delay circuit 21 is calculated, and the calculated correlation data is sent to the data analysis section 22. The data analysis unit 22 calculates the signal reflection position in the optical transmission line 15 of the optical signal g input from the optical transmission line 15 based on the correlation data input from the correlation processing unit 20 and the delay time input from the delay circuit 21. calculate.

Furthermore, the output signal h of the amplifier 19 is input to the signal processing section 23. This signal processing section 23 is composed of a data reproducing section 23a and a clock reproducing section 23b, and is configured to handle the transmission signal i transmitted from the terminal device 14 to the transmission device 11.
is restored and transmitted to the transmission device 11.

Next, the reason why the operating state of the optical transmission line 15 made of an optical fiber can be monitored and tested in a normal operating state using the optical transmission apparatus shown in FIG. 1 will be explained.

FIG. 3 shows the backscattered light k input from the optical transmission line 15 and the optical transmission when one optical pulse signal j is applied to the optical transmission line 15 at time t0 from the optical transmission device side. 3 is a diagram showing the relationship between the signal level of the output signal h of the amplifier 19 and the elapsed time t when the optical signal g caused by the Fresnel reflected light m reflected at the end of the path 15 is converted into an electrical signal. FIG. As time passes, the optical pulse signal j
As the signal moves far within the optical transmission path 15, the signal level decreases in a curved manner. If damage is present at a particular position within the optical transmission line 15 or the optical transmission line 15 is bent at an acute angle, the curve changes significantly at that position.

Since the speed of light propagating within the optical transmission line 15 is known, the damage position can be calculated by detecting the discontinuous points at times t1 and t2. Further, the length of the optical transmission path 15 can be detected by determining the time (t3 - t0) until the Fresnel reflected light m. Note that if this length is shorter than the length at the time of construction, it can be determined that the optical fiber is broken, and the location of the break can be identified.

In this way, if it can be specified to which optical pulse signal j the output signal h of the amplifier 19 corresponds, the optical transmission line 15 can be tested.

In this method, a normal transmission signal b output from the transmission device 11 is scrambled with a pseudo-random signal c to obtain a composite signal e. Therefore, even if the composite signal e is the same composite signal e within the bit cycle period of the pseudo-random signal c, if the bit data is shifted by even 1 bit, the correlation function of both composite signals will be Even if calculated, it will be [0]. Then, the correlation coefficient becomes [1] only when there is a complete match.

That is, as shown in FIG. 4, the composite signal e
is output at time t0, the output signal h of the amplifier 19 consisting of the reflected signal k reflected at each position of the optical transmission line 15 and the reflected signal m from the terminal end, and the composite signal e delayed by the delay circuit 21. When the correlation function with 1 indicates [1], the reflected signal from the corresponding position corresponds to the composite signal e sent to the optical transmission line 15. Therefore, the delay time of the delay circuit 21 at this point is the time required for the output optical signal to reach the corresponding position. Therefore, the distance to the corresponding position can be calculated from this delay time and the propagation speed of light.

Therefore, it is possible to specify the reflection position of the corresponding reflected light at the time when the signal level of the output signal h suddenly changes. Therefore, the position of damage or disconnection within the optical transmission line 15 can be identified. Additionally, the attenuation rate of the optical signal at each position can be measured.

According to the optical transmission device configured as described above, the pseudo random signal c is simply scrambled with the normally transmitted signal b transmitted from the transmission device 11 to the terminal device 14, and the pseudo random signal c is scrambled at each position of the optical transmission line 15. It is possible to specify which bit in the composite signal e the reflected backscattered light and the Fresnel reflected light reflected at the end correspond to. Therefore, in an optical communication system incorporating this optical transmission device, the optical transmission line 15 can be monitored and tested under normal operating conditions.

[0038] Therefore, unlike the conventional method, there is no need to interrupt the normal operation of the optical communication system in order to perform the test. In other words, the test can be carried out at a leisurely pace by selecting a time convenient for the operator. Alternatively, the data analysis section 22
Automatic monitoring is possible depending on how the processing is done.

Furthermore, unlike the conventional method, there is no need to separately prepare a dedicated test device such as an optical pulse test device in order to conduct the test.

[0040] Also, an optical transmission line 15 using an optical fiber
In this method, the length of the optical transmission line 5 can be constantly monitored by detecting Fresnel reflections from the termination and connection points, so the output of each signal in the communication signal a can be adjusted according to changes in the optical transmission line length. Timing can be reset. Therefore, collisions between signals can be prevented.

Furthermore, since the guard time Tg of the no-signal state in the communication signal a shown in FIG. 7 is not used for the test signal, it is not necessary to set this guard time Tg particularly long in order to carry out the test. Furthermore, even if the transmission speed (bit rate) of the transmission signal b is the same, the card time Tg shown in FIG. 7 can be set to the necessary minimum value. As a result, data transmission efficiency in the optical communication system can be improved.

FIG. 5 is a block diagram showing a schematic configuration of an optical transmission device according to another embodiment of the present invention. The same parts as in the embodiment of FIG. 1 are given the same reference numerals. Therefore, detailed explanation of the overlapping parts will be omitted.

In this embodiment, the transmission device 11 and the terminal device 14 are connected by two optical transmission lines 15a and 15b. Then, one optical transmission line 15a is connected to the transmission device 11.
The other optical transmission path 15b is used when transmitting data from the terminal device 14 to the transmission device 11. Therefore, the optical signal n outputted from the terminal device 14 is converted into an electrical signal by the O/E converter 24 on the optical transmission device side via the optical transmission line 15b, and after being amplified by the amplifier 25, the optical signal n is shown in FIG. The signal processing section 26 having the same configuration as the signal processing section 23 returns the signal to the original transmission signal o. The transmission signal o is then input to the transmission device 11.

Even with an optical transmission device having such a configuration, monitoring and testing of the optical transmission line 15a on the transmitting side can be performed by scrambling the pseudo-random signal c with the transmission signal b output from the transmission device 11. Can be implemented. Therefore, it is possible to obtain substantially the same effect as the embodiment shown in FIG.

[0045] When monitoring and testing the optical transmission line 15b on the receiving side, each of the circuits described above may be attached to the terminal device 14 side.

[0046]

Effects of the Invention As explained above, according to the optical transmission device of the present invention, the transmission signal for transmitting each data of normal business output from the transmission device can be transmitted with a transmission signal that is longer than the round trip delay time in the optical transmission path. A pseudorandom signal having a bit period is scrambled and transmitted to an optical transmission line, and the correlation between the signal input from the optical transmission line and the delayed signal of the transmitted composite signal is determined. Therefore, under normal operating conditions, the optical transmission line can be easily monitored and tested at any time without using a separate dedicated test device.

Furthermore, even if the transmitting signal and the receiving signal are transmitted over the same optical transmission path, as in ping-pong transmission, there is no need to extend the guard time between the signals for monitoring and testing. Therefore, the data transmission efficiency does not particularly deteriorate in order to perform the test.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a schematic configuration of an optical transmission device according to an embodiment of the present invention;

[Fig. 2] A circuit diagram showing a pseudo random signal generation circuit of the same embodiment device,

[Fig. 3] Diagram for explaining the operating principle of the device of the embodiment,

[Fig. 4] A time chart showing the operation of the same embodiment device;

FIG. 5 is a block diagram showing a schematic configuration of an optical transmission device according to another embodiment of the present invention;

[Figure 6] Schematic diagram showing a general optical communication system,

[
FIG. 7 is a format diagram showing the structure of communication signals transmitted through the optical transmission line of the system.

[Explanation of symbols]

11... Transmission device, 12... Scramble circuit, 13... Pseudo random signal generation circuit, 14... Terminal device, 15, 15a
, 15b... Optical transmission line, 16... E/O converter, 17... Optical splitter, 18... O/E converter, 19, 25... Amplifier, 20
...Correlation processing section, 21...Delay circuit, 22...Data analysis section,
23, 26...Signal processing section.

Claims (2)

[Claims] 1. An optical transmission device that converts a transmission signal output from a transmission device (11) into an optical signal and transmits the optical signal to a terminal device (14) via an optical transmission path (15, 15a),
a pseudorandom signal generation circuit (13) that outputs a pseudorandom signal having a bit period longer than a round trip delay time for the optical signal to travel back and forth through the optical transmission line; A scrambling circuit (12) that scrambles with a random signal, an E/O converter (16) that converts the composite signal scrambled by this scrambling circuit into an optical signal, and this E/O
an optical splitter (17) that sends the optical signal output from the converter to the optical transmission line and separates the optical signal input from the optical transmission line; an O/E converter (18) that converts it into an electrical signal, a delay circuit (21) that delays the composite signal output from the scramble circuit, and the composite signal delayed by this delay circuit and the O/E converter. a correlation processing unit (20) that calculates a correlation between the output signal of the optical transmitter and the output signal of the optical transmission line; An optical transmission device including a data analysis unit (22) that calculates a distance to a signal reflection position within the interior. 2. The optical transmission device according to claim 1, further comprising a signal processing unit (23, 26) for receiving and processing a signal transmitted from the terminal device.