JPH0131334B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical communication system, and particularly to an optical data link for communicating between a large number of discretely installed devices.

In recent years, optical communication systems have made remarkable progress, and their applications are expanding to various fields.One of the advanced application forms of optical communication systems is to optically connect multiple optical communication devices discretely in the middle of a single optical transmission path. An optical communication system is being considered in which optical signals are connected and multiplexed transmission of optical signals is performed on a time schedule. This type of optical communication system, which is generally called an optical data link, is superior in terms of system flexibility and economy, and because it uses a non-conductive optical transmission path, it is free from electromagnetic induction. It is not susceptible to disturbances and can send and receive data. This has the advantage that only the optical communication device needs to be in operation, and therefore the reliability of the circuit is high.

However, in the case of optical data links, unlike electrical data links, losses in transmission paths, connection points, branch circuits, etc. are considerably large, so it is difficult to determine which optical communication device the optical signal was sent from. Since the transmission path loss varies greatly depending on the type of optical signal, there is a problem in that a large power change occurs in the time-division multiplexed optical signal. On the other hand, since the operating range of the identification circuit used in the optical receiving circuit is usually not very wide, it may not be possible to receive the signal normally as it is.
Therefore, in order to receive a signal with a large power change, it is necessary to reduce the amplitude change of the input signal of the identification circuit by some method. but,
Since the above-mentioned power change due to multiplexing occurs in a very short period of time, usually less than 1 bit, the automatic gain control method (hereinafter referred to as
The AGC method has the disadvantage that it cannot be applied to optical data links due to its slow response.

Therefore, in the past, optical data links have been limited to configurations that do not cause much difference in transmission loss, have very short distances, and have a small number of connected optical communication devices.

Note that it is possible to adjust the optical transmission power to an appropriate value in advance so that the optical reception power is almost constant. This method is not generally applicable to optical data links, which have one feature of being able to freely add or remove optical communication devices, because the values change, so adjustments are required each time.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical data link which eliminates the above-mentioned drawbacks of the conventional link, allows relatively long-distance transmission, and is capable of connecting a large number of optical communication devices.

According to the present invention, one or more optical communication devices are optically connected in the middle of a single optical transmission path that starts with an optical transmitter and ends with an optical receiver, and uses the optical transmission path. In an optical data link that transmits optical signals in a time-division manner, the optical communication device at least receives an optical signal sent from the starting end of the optical transmission line, and connects the optical signal from the optical communication device to the optical transmission line. It has a detection means for separately detecting the peak power of the optical signals, and controls the optical transmission power of the optical communication device so that the ratio of the peak powers of the two optical signals obtained by the detection means is constant. An optical data link is obtained.

In this optical data link, the ratio of the peak power of an optical signal sent from the starting end of an optical transmission line in each optical communication device to the peak power of an optical signal coupled from the optical communication device to the optical transmission line is determined. It is controlled to remain constant. Therefore, by setting the proportionality constant to an appropriate value, it is possible to reduce power fluctuations in multiplexed optical signals, making it possible to transmit relatively long distances and connect a large number of optical communication devices. Become.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of an optical data link according to a first embodiment of the present invention, which is an optical data link in which three optical communication devices are optically connected in the middle of an optical transmission line. . An optical transmitter 1 and an optical receiver 6 are connected to both ends of the optical transmission line 2, and an optical signal is transmitted from the optical transmitter 1 at predetermined intervals. On the other hand, each optical communication device 4 is connected in the middle of the optical transmission line 2 by an optical combining circuit 3 and an optical branching circuit 5, respectively. This optical communication device 4
The optical communication signal sent out at a predetermined time from the optical signal generating circuit 3 is time-division multiplexed with the optical signal transmitted through the optical transmission line 2 by the optical combining circuit 3. Part of the power of this multiplexed optical signal is branched by the optical branching circuit 5 and input to the receiving circuit of the same optical communication device 4.

FIG. 2 is a block diagram showing the detailed configuration of the optical communication device 4 and its surroundings in this first embodiment.

As mentioned above, the transmission signal 101 is sent to the optical transmission circuit 41.
The signal is converted into an optical signal 102 at , and a portion of the electric power is supplied to the photodetector 42 via the optical combining circuit 3 and the optical branching circuit 5 . The photodetector 42 also receives the optical signal 1 sent from the starting end of the optical transmission line 2.
03 is also supplied via the optical branch circuit 5. These two optical signals are converted into electrical signals by the photodetector 42, then amplified to the required level by the amplifier circuit 43, and then sent out from the optical communication device 4 by using the transmission signal 101 in the signal separation circuit 44. The signal component 104 transmitted from the optical transmission line 2 is separated into the signal component 104 transmitted from the starting end side of the optical transmission line 2, and the other signal, that is, the signal component 105 transmitted from the starting end side of the optical transmission line 2. Among the separated signals, signal component 1 transmitted from the starting end side of optical transmission line 2
05 is regenerated into the original signal in the identification circuit 45. Also, two separated signal components 104,
105 are input to wave height detection circuits 46 and 47, respectively, and their peak powers are detected. Next, the comparison circuit 48 compares the two peak powers, and the optical output of the optical communication circuit 41 is controlled by negative feedback so that they become the same value. Therefore, the peak power of the optical signal coupled from the optical communication device 4 to the optical transmission line 2 matches the peak power of the optical signal being transmitted through the optical transmission line 2, so power changes due to multiplexing can be eliminated. An optical data link can be obtained that is capable of relatively long-distance transmission and that can be connected to a large number of optical communication devices.

FIG. 4 shows the signal format of this embodiment. This format has a transmission rate of 32.77 Mb/s and consists of 16 frames. Each frame consists of 512 bits, a frame identification signal,
501 bits, excluding 11 bits such as frame synchronization signals, can be used as data signals. This example is F
This is a so-called fixed allocation method in which each frame from 0 to F15 is allocated to each node. Specifically, the optical transmitter 1 has F0, F1, F2
Each optical communication device 4 receives the three frames F3, F4,
Each of them occupies a frame of F5. Frames F6 to F15 are empty frames, and in this embodiment, 10 additional nodes can be additionally connected. Moreover, if a demand assignment method is adopted in which free frames are searched for and used freely instead of fixed assignment, even more nodes can be connected.
The optical receiver 6 receives optical signals from all nodes and functions to control the loop, and can control the circulation of signals within the loop, connect signals with the main computer outside the loop, etc. I can do it.

The first optical communication device 4 sends out an optical signal 102 in response to the optical signal 103 from the optical transmitter 1, which includes signals only in frames F0 to F2, with timing adjusted to the time range corresponding to frame F3. I will do it. The timing of this signal transmission is
The transmission signal 101 is based on the reception time of the identification signal of frame F2 included in the output signal from the identification circuit 45.
This can be achieved by adjusting the delivery time.

The signal separation circuit 44 is composed of a high-speed switch that switches electrical signals in two directions. When the transmission signal 101 is not sent out, the reception signal is always connected to the identification circuit 45 side, but when it is sent out,
After an appropriate delay time from the transmission time of the transmission signal 101, the switch is connected to the pulse height detection circuit 47 side, and only the signal in the time domain of frame F3 is transmitted to the pulse height detection circuit 4.
I am trying to send it to the 7th side.

The wave height detection circuits 46 and 47 can be formed using techniques commonly used in communication devices, and can be easily obtained by, for example, full-wave rectification of signal pulses.

Similarly, other optical communication devices 4 send out optical signals with the timing and output matched to the time range of the corresponding frame. The method is the first optical communication device 4
Since this is the same as in the case of , the explanation will be omitted.

FIG. 3 is a block diagram that does not show the detailed configuration of the optical communication device 4 and its surroundings according to the second embodiment of the present invention. The configuration of this embodiment is almost the same as that of the first embodiment, and the difference is that the optical transmission circuit 41 of the first embodiment is
However, in this embodiment, the amount of attenuation of a variable optical attenuator 49 connected between the optical transmitting circuit 41 and the optical combining circuit 3 is changed. Even with this configuration, an optical data link having the same features as the first embodiment can be obtained.

It should be noted that the signal format is the same as in the first embodiment, so a description thereof will be omitted.

Furthermore, in this embodiment, instead of the variable optical attenuator 49, an optical coupler whose degree of coupling can be varied may be used in the optical synthesis circuit 3, and the same effect can be achieved by using a method of controlling the degree of coupling.

In each of the above embodiments, three optical communication devices are connected in the middle of the optical transmission line, but it is also possible to connect any number of optical communication devices, one or more. .

Furthermore, various methods can be considered for varying the output power of the optical transmitter circuit in the first embodiment, but in particular when using a light emitting diode or a semiconductor laser as the light emitting element, simply changing the applied current is possible. This can be easily achieved by

The time division multiplex transmission method shown in each example is as follows:
Generally, TDMA (Time Division Multiple
This is an example of a method called the Access) method.
The embodiments of the present invention are not limited to this, and can be applied to any method that controls communication in a time-division manner. For example, the well-known token passing method, CSMA/CD (Carrier Sense
It can also be applied to multiple access/collision detection) methods.

As detailed above, the configuration of the present invention controls the peak power of the optical signal coupled from each optical communication device to the optical transmission line so as to be proportional to the peak power of the optical signal being transmitted through the optical transmission line. By doing so, it is possible to suppress power fluctuations in the multiplexed optical signal, thereby obtaining an optical data link that is capable of relatively long-distance transmission and to which a large number of optical communication devices can be connected.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an optical data link according to a first embodiment of the present invention, and FIGS. 2 and 3 are detailed block diagrams of an optical communication device and its peripheral embodiments used in the present invention, respectively. FIG. 4 is a diagram showing the format of the optical signal. DESCRIPTION OF SYMBOLS 1... Optical transmitting device, 2... Optical transmission line, 3... Optical combining circuit, 4... Optical communication device, 5... Optical branching circuit, 6... Optical receiving device, 41... Optical transmitting circuit, 4
2...Photodetector, 44...Signal separation circuit, 46,
47... Wave height detection circuit, 48... Comparison circuit, 49
...Optical variable attenuator.

Claims (1)

[Scope of Claims] 1. One or more optical communication devices are optically connected in the middle of a single optical transmission path that starts with an optical transmitter and ends with an optical receiver, and In an optical data link in which each optical signal outputted from the optical communication device is time-division multiplexed and transmitted through the transmission path, the optical communication device is configured to receive signals sent from at least the starting end of the optical transmission path. a detection means for separately detecting the peak power of an optical signal and an optical signal coupled from the optical communication device to the optical transmission line, and a ratio of the peak powers of the two optical signals obtained by the detection means; An optical data link characterized in that the optical transmission power of the optical communication device is controlled so that the optical transmission power is constant. 2. An optical communication device, characterized in that the peak power of the optical signal coupled from the optical communication device to the optical transmission line is approximately equal to the peak power of the optical signal transmitted through the optical transmission line. An optical data link according to claim 1.