JPH07177097A - Slave station entry method for optical transmission system - Google Patents

Abstract

PURPOSE:To prevent the impossibility of communication due to optical beat to perform stable optical communication by permitting the entry to a system of a new slave station in accordance with the occurrence of optical beat of an optical signal at the time of originating a call. CONSTITUTION:When the.new slave station is connected to an optical cable, a master station requests all the stations in the system to simultaneously originate calls in a prescribed time. When calls are originated from all the stations, the master station takes in optical signals for calls by an O/E 16, and the occurrence of optical beat is detected by a CPU 11. When optical beat doesn't occur, the entry or the new slave station is permitted. If optical beat occurs, the entry is inhibited because communication is impossible, The new slave station receives calls from all the stations and takes in optical signals for calls by an O/E 26, and the occurrence of optical beat is detected by a beat detecting circuit 51. If it occurs, a driving current control circuit 52 controls a driving circuit 28a in accordance with this occurrence, and supply current setting of an LD 28b in its own station is changed to finely adjust the oscillation signal wavelength, thereby performing the avoiding operation for prevention of the occurrence of optical beat. Thus, the impossibility of communication due to optical beat is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slave station joining method of an optical transmission system for checking a slave station newly added to an optical transmission system composed of a master station and a slave station.

[0002]

2. Description of the Related Art Conventionally, as an optical transmission system of this kind, there is an optical multi-drop system for performing bidirectional transmission of light by using a single mode fiber for a transmission line. In the above optical multi-drop system, a master station and a plurality of slave stations are connected to the transmission line, and normally one slave station is connected to the master station.
They called each station for optical transmission of predetermined data. In addition, when a new slave station is added to the above system, the slave stations are simultaneously called to check whether or not the optical signals collide. In such a system, for example, in the case of LAN (LOCAL AREA NETWORK), CSM
A (CARRIER SENSE MULTIPLE ACCESS) and CSMA / C
D (CARRIER SENSE MULTIPLE ACCESS / COLLISION DETECT
ION) etc.

[0003]

However, in the above optical transmission system, frequency multiplexing is performed using a modem so that a plurality of stations (for example, a plurality of slave stations or a master station and a slave station) simultaneously use transmission lines. In that case, an optical beat is generated, which causes a problem that the line is completely out of communication. Here, when a semiconductor laser is used as the optical oscillation means, the semiconductor laser is set to have a wavelength distribution within a wavelength band (for example, 1.3 micron band) with a predetermined distribution at the time of manufacturing. Of this distributed wavelength,
Arbitrary two are taken out and the wavelength difference is calculated. A problem occurs when the obtained wavelength difference is very small. In other words, if the wavelength difference is large, the frequency at which the optical beat is generated becomes extremely high, and there is no problem outside the range of the operating frequency band 100 MHz. That is, V is the speed of light (in light,
At 3.0 · E (8) m / s, E: EXPONENT (power of 10)), F is the frequency, and U is the wavelength of light, then V = FU. Here, if U = 1.3 micrometers,
The frequency F of light is 2.307E (14), that is, the fundamental frequency is a high frequency of F = 230 GHz.

Usually, the wavelength band fluctuation is several nm. For example, if the fluctuation is 2 nm, the frequency difference is 354.
It will be 8 GHz, which will be outside the normal frequency band used. Further, the frequency difference may appear in the above-mentioned used frequency band (about 100 MHz) when the wavelength difference of the LD coincides with a small value such as several tenths of a pm, that is, a value of 1/10000 of several nm. Therefore, any two or more wavelengths may match within the small wavelength difference. Therefore, it is necessary to check the optical beats to see if they have occurred.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a slave station joining method of an optical transmission system capable of preventing communication failure due to an optical beat and performing stable optical communication. And

[0006]

In order to achieve the above object, the present invention provides an optical transmission system for transmitting an optical signal between a master station and a plurality of slave stations connected to an optical fiber cable which is a transmission line. When a new slave station is connected to the optical fiber cable, the master station issues a call request to all stations in the system so that all stations in the system call all at once, and all stations When a call is made after the predetermined time, there is provided a slave station joining method of the optical transmission system, which permits the new slave station to join the system according to the state of the optical signal at the time of the call.

[0007]

[Effect] Each time a new slave station is connected, the master station requests the slave station to make a simultaneous call, and if there is a simultaneous call, whether or not an optical beat occurs depending on the state of the optical signal at that time. Check to prevent communication failure due to optical beat. Therefore, even in optical communication by frequency multiplexing, a plurality of stations can reliably use the transmission line at the same time, and stable optical communication can be performed.

[0008]

Embodiments of the present invention will be described with reference to the drawings of FIGS. FIG. 1 is a block diagram of an optical multi-drop system that performs bidirectional light transmission using a single mode fiber as a transmission line. In the optical multi-drop system, two optical fiber cables (hereinafter,
It is called "optical cable". ) 1, 2 are connected to the master station 10 and a plurality of slave stations 20, 30 and 40, and normally, the slave stations are called from the master station one by one, and other stations such as the own station or a host device are connected. Optical transmission of data input from.

The branch of the optical cable is usually a closure 3, which is connected to each of the upstream and downstream optical cables 1, 2.
4 and optical cables 5 and 6. The optical branching devices used in the closures 3 and 4 are normally unidirectional and unidirectional, but in some cases communication between slave stations is required. What can be done is preferable. The optical branching device in this case may be configured using, for example, an X coupler and a Y branch.

FIG. 2 is a diagram showing a schematic configuration of the master station 10. In the figure, a master station 10 includes a CPU 11 that executes a process procedure as a master station, a memory 12 that stores program data and the like, and an interface circuit (hereinafter, referred to as “I / "F".) 1
3, 14 and the display circuit 15 for displaying the operation state, and the optical / electrical converters (hereinafter,
It is called "O / E". ) 16, a buffer circuit 17 for temporarily storing information from the O / E 16, an electric / optical converter (hereinafter referred to as “E / O”) 18 connected to the optical cables 5 and 6, and an E / O 18. Driver circuit 1 to drive
It is composed of 9 etc.

In this embodiment, the one-core optical cable may be used at the same time for upstream and downstream, so in this case, an isolator (hereinafter referred to as "ISO") is added to direct the optical signal. It is also possible to set it so that only the optical signal in the required direction is extracted. Memory 12
Stores a process procedure as a master station, program data having a timer function, etc., and the CPU 11 controls each device based on these data to transmit / receive an optical signal to / from a slave station. Running. Also, the CP of the master station 10
U11 has a beat detection function that detects a beat from the optical signal captured by the O / E16. When a new slave station is added, all stations output optical signals, and when a beat is detected from this optical signal, the new slave station detects the beat. The station is prohibited from joining the system.

The I / Fs 13 and 14 are for inputting / outputting data to / from an upper device such as a host computer or a lower device such as a terminal device (not shown). The display circuit 15 is a system (for example, optical cables 1 and 2 or each slave station 2).
(0, 30, 40) indicates whether the operating state is normal or abnormal. O / E16 is optical cable 5
Or, a photodiode (hereinafter referred to as “PD”) that converts an optical signal input from the optical cable 1 or 2 via 6 into an electric signal (photocurrent) is provided, and the PD includes, for example, a pin photodiode or an avalanche. There are photodiodes and the like.

The buffer circuit 17 temporarily stores the data (electrical signal) in the transmission frame fetched by the O / E 16 and reads the above data under the control of the CPU 11. The read data is, for example, I / F13,1
It is output to another machine via the No. 4 terminal. The E / O 18 generates a drive circuit that outputs a drive current corresponding to the electric signal input from the driver circuit 19 and an optical signal that corresponds to the drive current, and the optical cable 1 or 2 via the optical cable 5 or 6.
The light source includes a laser diode element (hereinafter referred to as “LD”), a surface emitting element, an LED element, and the like.

Under the control of the CPU 11, the driver circuit 19 creates a transmission frame based on data (electrical signal) input through the I / Fs 13 and 14, and temporarily stores the created transmission frame (electrical signal). After being accumulated, it is output to the E / O 18. Child stations 20, 30, 40
Since the above configuration is similar, the schematic configuration of the slave station 20 is shown in FIG. 3 as a representative here. In the figure, the configuration of the slave station 20 is different from the configuration of the master station 10 in that all stations output at the same time, the beat is detected from the optical signal captured by the O / E 26, and the E / O 28 is detected according to the detection result. That is, a control circuit 50 for controlling the output of the optical signal is provided.

The memory 22 stores a process procedure as a slave station, program data having a timer function, and the like, and the CPU 21 determines, based on these data.
Each device is controlled to transmit / receive an optical signal to / from the master station 10. Further, the E / O 28, as shown in FIG. 4, for example, generates a drive circuit 28a that outputs a drive current corresponding to an electric signal input from the driver circuit 29, and an optical signal that corresponds to the drive current. LD which is the light source 28b for outputting to the optical cable 1 or 2 via
Consists of.

The control circuit 50, as shown in FIG.
A beat detection circuit 51 that detects the occurrence of a beat and outputs a detection signal from the photocurrent corresponding to the optical signal that is the output of the PD that is the O / E 26, and a drive circuit 28a that corresponds to the output detection signal. Drive current control circuit 52 for controlling the drive current of the. Next, in the optical transmission system having the above configuration, a slave station joining method according to the present invention when a new slave station is connected to an optical cable will be described. When the new slave station is connected to the optical cable, the master station 10 requests all stations in the system to make a call request via the downstream optical cable 2 so that all stations in the system can call simultaneously.
When the master station 10 makes a call via the upstream optical cable 1 from all stations including its own station after the predetermined time,
The optical signal at the time of calling is captured by the O / E 16, and the CPU 11 detects whether or not an optical beat is generated. Here, if no beat occurs, the master station 10 permits the new slave station to join the system. Also, if a beat occurs, the line of the optical cable becomes completely incommunicable, so the master station 1
0 prohibits new slave stations from joining the system.

When a new slave station, for example, the slave station 20 makes a call from all stations via the upstream optical cable 1 after the predetermined time, the optical signal at the time of calling is taken in by O / E,
The beat detection circuit 51 detects whether or not an optical beat is generated. Here, in the new slave station 20 which is prohibited from newly joining by the master station 10, when a beat is generated, the drive current control circuit 52 controls the drive circuit 28a according to the occurrence of the beat, and the LD 28b of the self station is controlled. LD by changing the current setting of
The wavelength of the optical signal oscillated from 28b is finely adjusted, and the avoidance operation is performed so as to prevent the occurrence of an optical beat.

Therefore, in this embodiment, the optical beat is not generated at the next simultaneous call due to the joining of the new slave station 20, so that the master station 10 permits the new slave station 20 to join the system. Therefore, in this embodiment, each time a new slave station is connected, the master station requests all stations to make a simultaneous call, and whether or not an optical beat is generated according to the state of the optical signal at the time of the simultaneous call. To prevent communication failure due to optical beat,
Even in optical communication by frequency multiplexing, a plurality of stations can reliably use the optical cable at the same time, and stable optical communication can be performed.

In the above embodiment, the control circuit 50 of the new slave station controls the E
This is not limited to this, but the present invention is not limited to this. For example, the second and third currents shown in FIG. 5 or FIG.
It is also possible to cope with the configuration of the embodiment. 5 and 6, the same components as those in FIG. 4 are designated by the same reference numerals for convenience of description.

In the second embodiment shown in FIG. 5, the control circuit 50 of the new slave station 20 includes a beat detection circuit 51 for detecting the occurrence of an optical beat from the photocurrent taken in from the PD 26, and the LD2.
The temperature sensor 53 that measures the temperature of 8b, the temperature detection circuit 54 that outputs a detection signal based on the output from the temperature sensor 53, and the two detection signals that have been output are compared, and the Peltier element is determined according to the comparison result. A temperature changing circuit 55 for changing and controlling the set temperature of 56, and a Peltier element 56 arranged near the LD 28b to change the cooling temperature setting of the LD 28b.

In the present embodiment, if new joining is prohibited by the master station 10, if a beat occurs in the new slave station 20, the cooling temperature setting of the LD 28b of its own station is changed according to the occurrence of an optical beat. Then, the wavelength of the light emitted from the LD 28b is finely adjusted, and the avoidance operation can be performed so as to prevent the occurrence of the optical beat. The third embodiment of FIG. 6 is shown in FIGS.
It is a control circuit having a configuration in which the above are combined. This third
In the case of the embodiment, if new joining is prohibited by the master station 10, if a beat is generated in the new slave station 20, the cooling temperature setting of the LD 28b of its own station is changed according to the occurrence of an optical beat. , The wavelength of the light emitted from the LD 28b is finely adjusted. However, if a beat may be generated even by this adjustment, the cooling temperature setting is returned to the original value, and then the drive current control circuit 52 changes the setting of the energization current of the LD 28b of its own station to oscillate from the LD 28b. The wavelength of the optical signal is finely adjusted to avoid the optical beat. In this case, when the set value of the energizing current of the LD 28b becomes equal to or less than the predetermined limit set value, the adjusting operation is stopped and the energizing current is returned to the original value.

Further, in the LD of each station according to the present invention, as shown in FIG. 7, for example, an ISO 61 is arranged on the optical path side of the light emission output via the pigtail optical fiber 60, and the return from the optical cable 5 (or 6) is performed. The light may be adjusted. In this case, the new slave station is provided with a plurality of ISOs 62 and 63 having different physical properties from ISO 61, and the ISO for the return light adjustment is set to ISO 62 or 63 according to the optical beat detected by the beat detection circuit 51. It is also possible to physically change (replace) and finely adjust the wavelength of the light emitted from the LD 28b.

Further, even if the wavelength of the oscillation light of the LD is adjusted as in each of the above-mentioned embodiments, if an optical beat occurs, the new slave station outputs an alarm signal to the display circuit or the like. Then, the LD is stopped, and the system joins the system. Further, in the bidirectional transmission of the above embodiment, the master station and the new slave station detect the occurrence of the optical beat, but the bidirectional transmission and the unidirectional transmission according to the present invention are not limited to this. Is detected only by the master station, this master station notifies the new slave station of the occurrence of a beat via an optical cable, and the new slave station oscillates from the LD according to the notified optical beat. It is also possible to make a fine adjustment and perform an avoidance operation so as to prevent the occurrence of an optical beat. In this case, since the beat detection circuit is unnecessary in each slave station, the number of parts can be reduced.

[0024]

As described above, according to the present invention, in an optical transmission system for transmitting an optical signal between a master station connected to a transmission line and a plurality of slave stations, a new slave station is connected to the transmission line. In this case, the master station makes a call request to all stations in the system so as to make a simultaneous call after a predetermined time, and if there is a call after the predetermined time, the Since the new slave station is allowed to join the system according to the state of the optical signal, for example, the optical beat of the optical signal is generated, communication failure due to the optical beat can be prevented and stable optical communication can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram of an optical multi-drop system using a slave station joining method according to the present invention.

FIG. 2 is a block diagram showing a schematic configuration of a master station shown in FIG.

FIG. 3 is a block diagram showing a schematic configuration of a slave station shown in FIG.

FIG. 4 is a block diagram showing a configuration of a first embodiment of the control circuit shown in FIG.

FIG. 5 is a block diagram showing a configuration of a second embodiment of the control circuit of the same.

FIG. 6 is a block diagram showing the configuration of a third embodiment of the control circuit of the same.

FIG. 7 is a block diagram showing an example of a laser diode element according to the present invention in which an isolator is arranged on the optical path side of light emission output.

[Explanation of symbols]

1, 2, 5, 6 Optical fiber cable 3, 4 Closure 10 Master station 20, 30, 40 Slave station 11, 21 CPU 12, 22 Memory 13, 14, 23, 24 Interface circuit (I /
F) 15,25 Display circuit 16,26 Optical / electrical converter (O / E) 17,27 Buffer circuit 18,28 Electric / optical converter (E / O) 19,29 Driver circuit 50 Control circuit

Claims (5)

[Claims] 1. In an optical transmission system for transmitting an optical signal between a master station connected to a transmission line and a plurality of slave stations, when a new slave station is connected to the transmission line, the master station is When a call request is issued to all stations in the system so that all stations will be called simultaneously after a predetermined time, and a call is made after the predetermined time, the new call is sent according to the state of the optical signal at the time of the call. A method for subscribing to a slave station of an optical transmission system, which permits the slave station to join the system. 2. The slave station joining method for an optical transmission system according to claim 1, wherein the master station permits the new slave station to join the system in response to the generation of an optical beat of the optical signal. 3. All the stations have optical oscillation means for oscillating light, and when the new slave station is not permitted to join the system, the new slave station operates in response to the generation of the optical beat. The slave station joining method for an optical transmission system according to claim 1 or 2, wherein the setting of the energizing current of the optical oscillation means is changed to finely adjust the wavelength of the light emitted from the optical oscillation means. 4. All of the stations have optical oscillation means for oscillating light, and when the new slave station is not permitted to join the system, the new slave station operates in response to the generation of the optical beat. 3. The slave station joining method for an optical transmission system according to claim 1, wherein the cooling temperature setting of the optical oscillation means is changed to finely adjust the wavelength of the light emitted from the optical oscillation means. 5. All the stations have optical oscillation means for oscillating light and return light adjusting means on the output side of the optical oscillation means, and when the system participation of the new slave station is not permitted, the new slave station 3. The station adjusts the return light of the return light adjusting means of its own station according to the generation of the optical beat, and finely adjusts the wavelength of the light oscillated from the optical oscillating means. A method of subscribing to a slave station of the optical transmission system described.