JPH0481372B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides
The present invention relates to an optical communication device that enables bidirectional communication of digital signals through a single optical transmission path (for example, one optical fiber or the same space).

[Summary of the invention]

This invention provides a bidirectional optical communication device using a single transmission path, which is provided with an optical transmission circuit, an optical output control circuit, an optical reception circuit, a frequency determination circuit, a clock control circuit, and a line diagnosis circuit, and the optical output control circuit provides a power source. The output of the optical transmitter circuit that outputs encoded data including clock information is stopped for a certain period of time after power-on or reset operation, and during that time the optical receiver circuit receives and decodes the optical signal on the transmission path. From the regenerated clock, the clock control circuit eliminates the effects of crosstalk caused by using a single transmission path by selecting a transmit clock frequency that is different from the transmit clock frequency of the communication device with which it is communicating. By separating each frequency, long-distance optical communication is possible, and by automatically performing these operations, operability and operability are improved. Furthermore, in the present invention, even after the line is set up, the line diagnosis circuit constantly compares the regenerated clock frequency with the own transmission clock frequency, so that even if a failure occurs in the other party's communication equipment or a problem with the transmission line, it can be detected immediately. This makes it possible to significantly improve operability.

[Conventional technology]

Conventionally, in single-line bidirectional communication using a single transmission path, such as one optical fiber, or optical space bidirectional communication using the same space, the signal sent by one party is mixed with the signal from the other party. There is a problem of crosstalk. The reason for this is that in the case of single-wire bidirectional communication, crosstalk due to insufficient separation between each wavelength in wavelength division multiplexing communication,
In the same wavelength communication using an optical coupler, there is crosstalk due to reflected light at the optical fiber connection point, while in the case of optical space bidirectional communication, there is crosstalk due to floating objects (such as dust) in the space. Crosstalk occurs due to light scattering and light reflection from structures (indoors, walls, ceilings, desks, etc.).

Conventionally, as a countermeasure for this problem, in wavelength division multiplexing communication, the spacing between each wavelength is widened sufficiently, and in communication with the same wavelength, a polarizing beam splitter is used in the optical coupler to remove near-end reflections with different polarization directions, and only far-end reflections are reflected light. This can be done by reducing the reflected light by taking advantage of the fact that This was handled by adjusting the value voltage.

[Problem that the invention seeks to solve]

However, in the above-described method, wavelength division multiplexing communication requires a highly accurate demultiplexer to separate wavelengths from each other and an optical transmitter whose wavelengths are sufficiently far apart, making the device extremely expensive. In same-wavelength communication, even if a polarizing beam splitter is used as an optical coupler, far-end reflection remains, so the effect becomes smaller as the transmission distance becomes shorter. The method that uses threshold voltage adjustment not only has the disadvantage of having to adjust the threshold voltage every time the device is installed, but also has the disadvantage that when the signal light is weak, the difference between the signal voltage and the threshold voltage is very large. Because they are small and the bit error rate easily deteriorates due to variations in the elements used or environmental changes such as temperature, long-distance communication with weak signal light has been impossible.

An object of the present invention is to provide a single transmission path bidirectional optical communication device that reduces the effects of crosstalk on a single transmission path, enables long-distance communication, and significantly improves operability, operability, and reliability. It is about providing.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention provides an optical transmission circuit and an optical transmission circuit that encode transmission data using a frequency clock signal in a communication device, perform electrical-to-optical conversion, and output the data to an optical transmission line. an optical output control circuit that controls whether or not to output an optical signal from the optical transmission line; and an optical output control circuit that performs optical-to-electrical conversion on the optical signal input from the optical transmission line, and then performs decoding processing to reproduce and output the clock signal and data. an optical receiving circuit that determines the frequency of the recovered clock signal from the optical receiving circuit and outputs a signal indicating its status; and an optical output control circuit that controls the optical transmitting circuit so that no optical signal is output. A clock control circuit that determines its own transmission clock frequency based on the output of the frequency determination circuit in the same state and stores that state (frequency), and an optical output control circuit that outputs an optical signal from the optical transmission circuit. A line diagnosis circuit that diagnoses the status of communication lines such as the other party's communication equipment and transmission line based on the frequency judgment circuit output in a controlled state and the signal from the clock control circuit that outputs a signal indicating its own transmission clock frequency. The system is configured to use at least the following, to reduce the effects of crosstalk and improve operability, operability, and reliability.

[Effect]

In the single transmission path bidirectional optical communication device with the above configuration, the output of the optical transmitter circuit is stopped when the power is turned on or when a reset operation is performed. By selecting a different clock frequency using the clock control circuit, the communication device becomes a different clock frequency from that of the other communication device. Therefore, it is possible to easily distinguish between a signal from a communication device of the other party and a signal outputted by oneself received due to crosstalk by frequency separation. In addition, if no signal is input to the optical receiving circuit at first, by using a clock with a predetermined frequency and outputting it from the optical transmitting circuit, it is possible to use a clock with a predetermined frequency and output it from the optical transmitting circuit. When the other party selects a different frequency, the clock frequencies between them become different. Furthermore, even if some kind of failure occurs during communication between both communication devices and communication becomes impossible, it can be detected simply by monitoring the regenerated clock frequency. In other words, the line diagnostic circuit compares the regenerated clock frequency and its own transmitting clock frequency, and if the former is the same as the latter, the other party's communication device is not operating, or there is a transmission line abnormality such as a broken optical fiber. You can determine that your own output light is being input due to crosstalk. In addition, if the regenerated clock frequency is different from your own transmit clock frequency and is outside the specified range, the other party's communication device may be producing abnormal output, or the optical transmission path characteristics may have significantly deteriorated. It can be determined that

From the above, the effects of crosstalk can be reduced and long-distance transmission becomes possible.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. FIG. 1 shows one embodiment of the present invention, FIG. 2 shows a timing chart when determining a line, that is, determining a clock frequency, and FIG. 3 shows a timing chart during operation. In FIG. 1, data DO taken in from an interface circuit 80 in charge of communication with an external data terminal (not shown) is sent to an optical transmission circuit 10. Therefore, the output data DO is the transmission clock output from the clock control circuit 50.
The signal is output after passing through an encoding circuit 12 that encodes it into a self-clock code using CKT and an E/O conversion circuit 11 that performs electrical-to-optical conversion and outputs an optical signal. Here, as the encoding method, Muncha star code, CMI code, etc. can be considered, but the present invention is not limited thereto. The optical output is transmitted to one optical fiber 1 through the coupler 70 and sent to the other party's communication device (indicated as station B in the figure). on the other hand,
The signal light sent from the other party's communication device via the optical fiber 1 is separated from the output light by the coupler 70 and sent to the optical receiving circuit 30. At this time, coupler 7
Due to crosstalk caused by 0 and optical fibers, a portion of its own output light is mixed with the input light and sent to the optical receiving circuit 30. In the optical receiving circuit 30, an optical signal is first converted into an electrical signal by an O/E conversion circuit 31 that performs optical-to-electrical conversion, and then a decoding circuit 32 reproduces and separates the signal into data DI and clock CKR. A method for separating data DI and clock CKR will be explained by taking as an example a case where a Manchester code, which is a typical example of a self-clock code, is used as a transmission/reception signal. FIG. 4 shows a timing chart when a Manchester code is formed as a transmission signal from certain data and a clock, and FIG. 5 shows its circuit. As shown in FIG. 5, by exclusive ORing the clock and data, a Manchester code as shown in FIG. 4 can be obtained. When such a Manchester code is received, since the Manchester code includes clock information in the data, the receiving side can easily separate the clock signal and the data, that is, decode it. An example of this decoding circuit is shown in FIG. In the Manchiesta code,
Since there is always an edge in the center of each bit, digital PLL (Phase Locked Loop) technology is used to clock the received signal (for example, to synchronize with the rising or falling edge of the center edge of each bit). This clock and Manchester code are input to a flip-flop through an inverter and an AND circuit, as shown in Figure 6, and taken out as data DI. Of these, data DI will be sent to an external data terminal through the interface circuit 80.

The optical output control circuit 20 is a circuit that controls whether or not to output an optical signal from the E/O conversion circuit 11.
Controlled by control signal RST. Decoding circuit 3
The reproduced clock CKR output from the clock 2 is sent to a frequency determination circuit 40, where the clock frequency is checked. The output of the frequency determination circuit 40 indicates the reproduced clock frequency of the received signal, and is sent to the clock control circuit 50 and the line diagnostic circuit 60.

In a state where line settings must be made immediately after power is turned on or after a reset operation, the optical output control circuit 20 uses the control signal RST to stop the output of the E/O conversion circuit 11 for a certain period of time, and Prevent your own optical signal from being output to the fiber. At this time, the optical receiving circuit 30 is operating, so if the communication device on the other end is operating (outputting an optical signal), it outputs data DI and clock CKR. On the other hand, if the other party is not yet operating, no optical signal is input, so nothing is output. This situation is shown in the timing chart of FIG. FIG. 2a shows a case where the user starts up before the other party, and since the user is not transmitting while RST is off, there is nothing in the regenerated clock CKR. Figure 2b shows the case where the other party starts up before itself, and only the signal from the other party is received while RST is off, so the reproduced clock CKR contains the frequency used by the other party's communication device. . While the RST is off, the clock control circuit 50 inputs the output of the frequency judgment circuit that receives such a clock CKR and outputs the frequency judgment result, and selects the clock that should be used by the clock that is different from the frequency used by the other party. The frequency is determined there and the clock CKT is sent to the optical transmitter circuit 1.
It is sending to 0. In the timing chart in Figure 2, the clock CKT with the frequency determined while RST is off is sent to the optical transmitter circuit when RST is turned on, and at the same time optical output is also performed. It reproduces and outputs (CKR) a clock with the same frequency as the clock used by. After that, after the other party starts up, the signal sent by the other party is regenerated and a normal line is established. Second
In Figure b, a normal line is established by transmitting the clock CKT of the frequency determined while RST is off after RST is turned on.

Below, in the optical transmission circuit, how the crosstalk of the own station and the signal from the other station are distinguished, and
We will also explain how CKR is obtained.
In a normal optical receiving circuit, when only the crosstalk from the own station is input, the optical signal is converted into an electrical signal, and the clock is extracted and data is recovered.

On the other hand, when a signal from the other station is being input, the power of the signal light is sufficiently larger than the crosstalk of the own station (in terms of optical power ratio, the crosstalk of the other station is For example, it is about 1/10 or less), so the crosstalk component of the optical signal of the own station only acts as noise, and in the end only the optical signal from the other station is converted into an electrical signal, and clock extraction and data reproduction are performed. become.

From the above, when only the local station is optically transmitting, it means that only the crosstalk of the local station is being received, so if the recovered clock (CKR) and the transmit clock (CKT) of the local station are equal. becomes. or,
When the other station is transmitting, the crosstalk of the own station is treated as noise and the clock is extracted only from the signal from the other station, so the reproduced clock (CKR) and the own station's transmit clock (CKT) will be different.

Therefore, as shown in Figure 2a, when the other station has not yet transmitted, that is, when it is only receiving its own crosstalk, CKR and CKT are equal, and neither the own nor the other station is transmitting. If you are
CKR and CKT are different because clock extraction is performed only on the signal from the other station.

Also, in Figure 2b, the other station is transmitting from the beginning, and in this case, clock extraction is performed only on the signal from the other station from the beginning, so CKR and CKT are different from the beginning. .

As described above, after the line between both communication devices is set up, the line status can be constantly checked by comparing the own transmitting clock frequency and the received clock frequency. In FIG. 1, a line diagnostic circuit 60 which receives a signal indicating its own clock frequency from the clock control circuit 50 and a signal indicating the received clock frequency from the frequency determination circuit 40 compares both signals. is going on. For example, when two types of frequencies are used, exclusive OR may be used to compare these signals. That is, only when these signals are different (when operating normally) is a high level outputted as a status signal. If the two clocks are different or the receiving clock frequency is within a certain range, the line is judged to be normal; on the other hand, if both are the same or the receiving clock frequency is outside the specified range, the line is judged to be normal. It is determined that this is an abnormality, and that there is a phenomenon in which the user's own signal is being received due to crosstalk and there is no signal from the other party. The timing chart in FIG. 3 shows the above. In FIG. 3a, in a normal state, the transmitting clock CKT and the receiving clock CKR are different, and the line status signal ST indicating the state is high. FIG. 3b shows an abnormal state in which the status signal ST is low. Therefore, section A is in a normal state, section B is in an abnormal state, and it is called CKT.
Since the CKRs are equal, it can be determined that the own output signal is being received due to crosstalk. It is assumed that the main cause is a power outage, failure, or fiber break in the other party's equipment. Section C is also in an abnormal state and the CKR is irregular.
This phenomenon occurs when a signal that is on the verge of the threshold voltage of the O/E conversion circuit of the optical receiver circuit is received. By the way, in the line diagnostic circuit, CKT
When comparing CKT and CKR, if two types of frequencies are used, judge whether CKT and CKR are the same or different; if two or more frequencies are used, CKR falls within a certain range. This can be handled by determining whether or not the situation is true.

In FIG. 1, the clock control circuit 50 includes an oscillation circuit 51, a variable frequency divider circuit 52, and a control logic circuit 53.
It is composed of. The oscillation circuit 51 oscillates at a frequency several times higher than the transmission clock frequency, and the frequency is divided by the variable frequency divider circuit 52 to the transmission clock frequency at a predetermined frequency division ratio. This frequency division ratio is controlled by control logic circuit 53. This is the control logic circuit 5
3, a control signal is sent from the optical output control circuit 20 while the optical output control circuit 20 is stopping the output of the optical transmission circuit 10. During this time, the control logic circuit 5
3 captures and simultaneously stores the output indicating the clock frequency of the received signal from the frequency determination circuit 40;
The stored information is also output to the variable frequency divider circuit. At this time, if the other party is transmitting, the variable frequency divider circuit 52 outputs a clock signal having a frequency different from the clock frequency of the other party's signal based on the information from the frequency determination circuit 40. The circuit is configured to select a frequency division ratio. A simple value such as 1/9, 1/10, or 1/11 is preferable for the frequency division ratio, and the circuit can be realized using only a counter and some gate circuits.

The LED display circuit 81 inputs the status information ST of the line diagnostic circuit, and has the function of turning on the LED if ST is true, and turning it off if ST is false, thereby indicating the line status to the user. Status information ST is also input to the interface circuit, and is used for purposes such as communicating with an external data terminal only when ST is true. In other words, if the line is abnormal or if the line is being set up, communication with the outside can be forcibly stopped to prevent erroneous data exchange.

As explained above, the optical output control circuit automatically operates after startup (after power-on or reset operation), and the line is automatically set during that period, resulting in very good operability. Furthermore, since the clock control circuit can be easily constructed, it not only increases the reliability of the circuit itself, but also has great flexibility in that it can easily cope with changes in the clock frequency of the device. Furthermore, the line diagnostic circuit is extremely effective because it can diagnose the line simply by comparing the frequencies of its own transmitting clock and receiving clock.

In the communication device according to the present invention, it is suitable to use two values as frequencies to simplify the circuit. In other words, in FIG. 1, the variable frequency divider circuit 52, the control logic circuit 53, and the frequency determination circuit 40 of the clock control circuit 50 are configured to select between the two, resulting in a very streamlined circuit configuration. be. In this case, it was confirmed that as long as the method for determining the two frequency values satisfies Equation (1), satisfactory characteristics as a communication device can be obtained.

ΔM＞ΔF＞Δm...(1) Here, ΔF is the difference between two frequencies, Δm is the minimum frequency difference that can be determined by the frequency determination circuit, and ΔM is the maximum frequency that can be decoded by the decoding circuit of the optical transmission circuit. It shows the difference. In equation (1), the upper limit of the frequency difference is determined by the fact that the decoding circuit treats data with a clock of either frequency in common, so the larger the frequency difference, the more likely decoding errors will occur due to timing discrepancies. On the other hand, the lower limit exists in the sense that the smaller the frequency difference, the more the discrimination error occurs when the frequency determination circuit distinguishes between the two. When specifically creating the communication device of the present invention, there are several possible implementation methods for the decoding circuit and frequency determination circuit, but no matter what kind of circuit is adopted, as long as it satisfies equation (1). Since the function as a communication device can be fully fulfilled, the degree of freedom in design increases.

In Figure 1, the flow of data and clocks is shown by solid lines, and the flow of control signals is shown by broken lines. However, when actually creating a circuit, it becomes more complicated, and the necessary signals, especially control signals, are shown as As an electronic circuit design engineer, it is natural to expect that the number of lines and additional circuits will increase, but even in such a situation, as long as the gist of the present invention is followed, it is within the scope of the present invention. Needless to say.

〔Effect of the invention〕

As described above, according to the present invention, by alleviating the problem of bidirectional communication on a single transmission path due to the influence of crosstalk, it is possible to not only easily enable long-distance transmission, but also to simplify line setup and maintenance. Since it is equipped with an automatic function, it has become possible to significantly improve operability, operability, and reliability at a low cost, and its value is high.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of the communication device of the present invention, and FIG.
Figures a and b are timing charts at startup, Figures a and b are timing charts during operation, Figure 4 is a timing chart for Munciesta encoding, and Figure 5 is an example of a Mankiesta encoding circuit. FIG. 6 is a diagram showing an example of a decoding circuit. 1... Optical fiber, 10... Optical transmission circuit, 11
... E/O conversion circuit, 12 ... Encoding circuit, 20
... Optical output control circuit, 30 ... Optical receiving circuit, 31
...O/E conversion circuit, 32 ...Decoding circuit, 40
...Frequency determination circuit, 50...Clock control circuit, 51...Oscillation circuit, 52...Variable frequency division circuit,
53... Control logic circuit, 60... Line diagnostic circuit,
70...Optical coupler, 80...Interface circuit, 81...LED display circuit.

Claims (1)

[Claims] 1. An optical transmission circuit that encodes transmission data from a transmission clock signal having a certain frequency value, converts it into an optical signal, and outputs it to an external optical transmission line; and from the optical transmission circuit. an optical output control circuit that controls whether or not to output an optical signal; an optical receiving circuit that converts an optical input signal from an optical transmission line into an electrical signal, decodes it, and reproduces and outputs a recovered clock signal and data; a frequency determination circuit that determines the frequency of the reproduced clock signal and outputs a signal indicating the reception clock frequency; an oscillation circuit that outputs a dividing clock signal of a predetermined frequency; and a power source controlled by the optical output control circuit. In a state in which no optical signal is output from the optical transmission circuit for a certain period of time after turning on or after a reset operation, capturing and storing the output of the frequency determination circuit using a control signal of the optical output control circuit;
a control logic circuit that outputs the stored information; and a transmission clock signal having a frequency different from that of the regenerated clock signal when there is an optical input signal from the optical transmission line according to the output of the control logic circuit. A frequency division ratio is selected so as to output a transmission clock signal of a predetermined frequency when there is no optical input signal from the optical transmission line, and a frequency division ratio is selected such that a transmission clock signal of a predetermined frequency is output. a clock control circuit including a variable frequency divider circuit that divides the frequency-dividing clock signal of the oscillation circuit by a frequency division ratio and outputs the frequency-divided clock signal to the optical transmitter circuit as the transmission clock signal; and a clock control circuit for controlling the optical output control circuit. Therefore, whether the signal from the frequency determination circuit in a state where an optical signal is output from the optical transmission circuit and the signal indicating the own transmission clock frequency stored in the clock control circuit are the same or different. A single transmission path bidirectional optical communication device comprising a line diagnostic circuit that compares the values and outputs the comparison results to an interface circuit connected to an external data terminal. 2. The single transmission line bidirectional optical communication device according to claim 1, wherein the transmission clock frequency has two values. 3 The transmitting clock frequency has two values, and if the frequency difference is ΔF, the minimum frequency difference that can be determined by the frequency determination circuit is Δm, and the maximum frequency difference that can be decoded by the optical receiving circuit is ΔM, then ΔM＞ A single transmission path bidirectional optical communication device according to claim 1, characterized in that ΔF>Δm.