DE3942817A1 - Terminal appts. for message transmission over optical fibres - guards against laser radiation hazard from broken fibre by automatic opening and reclosure of safety switch - Google Patents

Abstract

Duplex appts. with connections (F1an, F1ab) for the transmission path and connections (F2an, F2ab) for the useful signal incorporates a laser transmitter (LS) and modulator (SM), a photoreceiver (OE) and reception amplifier (EV). The laser safety switch (SD) is operated by a control (St) with two timers (ZG1, ZG2) connected by a changeover switch (US) to an OR gate (G). All four timers are started together as soon as breakage of either fibre changes the logic level at the input to the control (St) from the amplifier (EV). ADVANTAGE - Transmission system can be built-up and started-up automatically after repair of broken glass fibre.

Description

The invention relates to a terminal for the optical Fiber optic communications.

Such a terminal is in the magazine "PKI Technische Mitteilungen" 2/1987, Pp. 77 to 83. From image 4 and the related one Text shows that such a device is a laser transmitter, an optical receiver (in picture 4 with APD receiver designated) and has a laser safety shutdown. in the Figure 4 is both a line terminal and half an intermediate regenerator shown. Under "device" Both types of devices are understood in the following, since the Invention underlying object relates to the part that both for the line end device and for the intermediate regenerator is the same.

Two devices are used to build an optical Communication system over two optical fibers connected to each other, so that the laser transmitter of the first terminal via the first glass fiber with the optical Receiver is connected in the second terminal. It is analogous Laser transmitter of the second terminal via the second glass fiber connected to the optical receiver in the first terminal.

The power of a laser transmitter is so great that one out radiation emerging at an open end of a glass fiber can cause harm to human health. To do this prevent is in every device Laser safety shutdown provided. On the one hand, she is with the output of the associated optical receiver and  on the other hand connected to the associated laser transmitter. Becomes for example, the first fiber if the cable is damaged interrupted, the optical receiver receives in the second Terminal no longer emits radiation and as a result does not emit any radiation Received signal more. This failure of the received signal recognizes the associated laser safety shutdown, the then switches off the associated laser transmitter. Now the optical receiver does not receive any in the first terminal either Radiation and no longer emits an output signal. As before is then described by the associated Laser safety shutdown also the laser transmitter in the first Terminal turned off, causing radiation to leak out the point of interruption is prevented. To the Switching back on after repairing the fiber is in everyone A laser start button is provided for the terminal. To look for one Repair the messaging system back in service to set, this laser start button must be pressed.

The invention has for its object a terminal Specify above type, which is the structure of a Communication system with automatic Restart after repairing a broken one Glass fiber enables.

This object is achieved by a terminal device according to the patent claim solved.

The invention will be described with reference to an embodiment shown in FIGS. 1 to 5. The figures represent:

Fig. 1 shows an optical communication system,

Fig. 2 shows an inventive terminal,

Fig. 3 to 5 Overview of functions.

Figs. 1 will be described first. It means:

EG₁, EG₂: terminals
GF₁, GF₂: glass fibers
SM₁, SM₂: transmitter modulators
LSA₁, LSA₂: laser safety shutdowns
LS₁, LS₂: laser transmitter
EV₁, EV₂: receiving amplifier

The index indicates whether it is the first or the second Assembly acts. Furthermore mean:

F 2 on, F 2 down: Connections for the useful signals
F 1 on, F 1 down: connections for the transmission paths.

The optical communication system shown is a duplex system, i. H. there are two transmission systems with opposite directions of transmission provided with a separate transmission path for each Direction of transmission.

It is initially assumed that the two glass fibers GF ₁ and GF ₂ have not yet been interrupted at the points labeled U ₁ and U ₂ . The useful signal to be transmitted from the first terminal EG ₁ to the second terminal EG ₂ is fed to the first terminal EG ₁ via its connection F 2 to the transmitter modulator SM ₁ , which supplies a correspondingly modulated diode current for operating a laser diode installed in the laser transmitter LS ₁ . This diode current is conducted via a switch provided in the LSA ₁ laser safety shutdown. This switch is initially closed, so that the laser transmitter LS ₁ emits light radiation modulated in accordance with the useful signal. This light radiation passes through the connection F 1 , the first glass fiber GF ₁ and the connection F 1 to the optical receiver OE ₂ in the second terminal EG ₂ . The optical receiver outputs a corresponding reception signal to the reception amplifier EV ₂ on its output. This has a useful signal output AN and a control signal output A _ST . The useful signal is emitted via the useful signal output A _N and the connection F 2 ab. The control signal output AST is connected to the laser safety shutdown LSA ₂ and carries a logical yes signal when the optical receiver OE ₂ receives light radiation and emits a corresponding reception signal to the reception amplifier EV ₂ .

In the opposite direction, that is to say from the connection F 2 on the second terminal EG ₂ to the connection F 2 on the first terminal EG ₁ , the same thing analogously takes place. The yes signals at the control outputs AST ensure that the switches of the laser safety cutoffs LSA ₁ and LSA ₂ in the circuits of the diode currents are kept closed.

The functions described above represent the normal Operating state of the message transmission system, wherein transmission of useful signals in both directions possible is.

Details of the terminals EG ₁ and EG ₂ are described with reference to FIG. 2. This figure applies to both the first and the second terminal. The terminal-specific indices have therefore been omitted from the reference symbols. Otherwise, however, the reference symbols have the same meaning as those in FIG. 1.

The LSA laser safety shutdown is shown in detail. It contains a controller St, a first timer ZG ₁ , a second timer ZG ₂ , a changeover switch US and an OR circuit G. The switch located in the circuit of the diode current ID is designated SD. The control signal output A _{ST of} the receive amplifier EV is connected to inputs of the control St, the two timers ZG ₁ and ZG ₂ and the OR circuit. The outputs of the two timers ZG ₁ and ZG ₂ are connected to a further input of the OR circuit via the changeover switch US, the output of the first timer ZG ₁ to the OR circuit G being switched through in the rest position of the changeover switch US shown here. The output of the second timer ZG ₂ is also connected to an auxiliary input of the control unit St. A dashed line indicates that the changeover switch US is actuated by the control unit St. The output of the OR circuit G is connected to a control input of the switch SD.

The switch SD is designed so that the circuit for the diode current I _D is closed as long as a yes signal is present at the control input. The first timer ZG ₁ is designed such that a no signal is emitted at its output as long as a yes signal is present at its input. After a change from yes to no at the input, the timer is started. There is initially a repetition time of 55 s during which the no signal at the output still remains. After the repetition time has elapsed, the output assumes a yes signal level for 1 s, ie a strobe pulse of 1 s length is sent. After the gating pulse, a new repetition time begins, etc. With the second timer ZG ₂ , the repetition time is 65 s, the other functions are the same as those of the first timer.

Furthermore, the timers are designed to be restart at any time. Occurs during the expiration of the Repeat time a short yes signal at the input, see above With its change from yes to no, the timer becomes new started, d. that is, a new full repetition time begins to run. This has the following effect: a timer that always restarting before its repetition time expires never comes to send its gating pulse.

The control unit St is designed so that a short-term yes Signal at your input when changing from yes to no Switch US placed in the working position. A yes signal on its auxiliary input causes a switch back to the rest position. A downshift is also caused by a longer yes Causes signal at their input.

The functions of the terminals according to the invention in a message transmission system according to FIG. 1 will be described with reference to FIGS. 3, 4 and 5. These figures show signal levels and switch positions as a function of time. The positions of the switches SD and the changeover switch US are indicated in lines 1 , 4 , 6 and 9 . Lines 2 , 3 and 7 show the signal levels at the outputs of the timers ZG ₁ and ZG ₂ . Line 8 shows the output of the timer ZG ₂ in the second terminal; However, since the signal levels of this output are of no interest in the functions described here, no details have been entered. Lines 5 and 10 show the signal levels at the control signal outputs A _{ST of} the receive amplifier EV. Lines 1 to 5 are assigned to the first terminal EG ₁ . Lines 6 to 10 are assigned to the second terminal. In line 11 , which has the meaning of the time axis, some points in time are marked. The timeline is not to scale. Excessively sloping flanks were drawn for the signal level and switch position changes in order to differentiate between cause and effect.

In FIG. 3, the normal operation state, already described, is shown at time _t1. The yes signal at the respective control signal output AST keeps the associated switch SD closed via the direct connection of this output to the associated OR circuit G.

At time t ₂ , the first glass fiber GF _{1 is} interrupted at the point designated U ₁ in FIG. 1. The second glass fiber GF ₂ remains intact. The result is that the optical receiver no longer receives radiation in the second terminal and the signal level at the control signal output A _{ST changes} from yes to no. This opens the switch SD and the optical receiver in the first terminal EG _{1 also} no longer receives radiation. As a result, the signal level at the control signal output A _ST also changes from yes to no and the switch SD is opened. The emission of radiation from the interruption point U ₁ is thus prevented.

Furthermore, all four timers are started at time t ₂ , their respective repetition times initially expiring and their outputs still emitting no signals. The values of 55 s and 65 s for the repetition times indicated in FIG. 2 are nominal values. The actual repetition times may deviate from the nominal value due to the variation in the number of components determining the repetition time. Here it is assumed that the first timer ZG ₁ in the first terminal EG _{1 has} a repetition time of 52 s and that in the second terminal EG _{1 has} a repetition time of 58 s.

At the point in time t ₃ , the repetition time of the first timer ZG ₁ in the first terminal EG _{1 has} expired, and the switch SD is closed for 1 s by the gating pulse, ie the laser transmitter is gated for 1 s. Since the first glass fiber GF _{1 is} still interrupted, this probing has no effect in the second terminal EG ₂ . However, it is different at time t ₄ when the repetition time in the second terminal EG _{2 has} expired. The laser transmitter is also probed. The optical receiver in the first terminal EG ₁ receives this gating pulse via the still intact second glass fiber GF ₂ , and it also appears as a brief yes signal at the control signal output A _ST . The laser transmitter is gated again via the direct connection to the OR circuit G.

At time t ₅ , i.e. when the signal level at control signal output A _{ST changes} from yes to no, three things happen in first terminal EG ₁ : first, first timer ZG _{1 is} restarted so that its repetition time of 52 s expires at time t ₆ . Second, the second timer ZG _{2 is} restarted. Since its repetition time is longer than 58 s, it does not have the time to emit a gating pulse. Thirdly, the switch St puts the US switch into the working position. This has the effect that the gating pulse given by the first timer ZG ₁ at time t ₆ no longer leads to gating of the laser transmitter.

At times t ₇ and t _8, that is to say after the repetition time of 58 s of the first timer ZG ₁ in the second terminal EG _{2 has} expired, the same processes take place as at times t ₄ and t ₅ . Only switching the US switch into the working position is omitted, since it is already in this position. This game continues for as long as you want. Such repeated scanning of the laser transmitters is shown in FIG. 4, times t ₉ and t ₁₁ . At times T ₁₀ and t ₁₃ , ineffective gating pulses of the first timer ZG ₁ occur in the first terminal EG ₁ .

Thus, after the repetition time of 58 s, the first timer in the second end device scans both laser transmitters.In contrast to the times t ₃ and t ₄ , the switch US which has now been actuated means that the laser transmitter in the first end device is only repeated once is sensed after the repetition time has elapsed and therefore only emits radiation once from the interruption point for 1 s. The mean light output and the associated risk to persons are correspondingly lower.

The operations after eliminating the interruption are also shown in the first glass fiber GF ₁ in FIG. 4. This is assumed at time t ₁₂ and initially has no effect. Only when at time t ₁₄ , controlled by the first timer ZG ₁ in the second terminal EG ₂ , the laser transmitter in the first terminal EG _{1 is} gated, does the effect become apparent: The optical receiver in the second terminal EG ₂ again receives light radiation, and the control signal output A _{ST of} the associated receiving amplifier again outputs a yes signal. It causes the switch SD to remain closed again and the control signal output A _ST in the first terminal EG 1 again continuously outputs a yes signal. This evaluates the control unit St, which then switches the switch US back to the idle position at time t ₁₅ . The normal operating state has been restored.

In FIG. 5, the procedures are shown which take place after additional interruption of the second glass fiber GF ₂ at the point U _2. The processes shown in FIG. 5 immediately follow the time t ₁₁ in FIG. 4. At the time t ₁₆ , the timers are restarted, as already at the times t ₇ , t ₉ and t ₁₁ , and the laser transmitter in the first terminal EG ₁ gated. At time t ₁₇ , the second glass fiber is also interrupted. At time t ₁₈ , an ineffective gating pulse of the first timer ZG ₁ occurs again in the first terminal EG ₁ . The consequences of the additional interruption do not appear until time t ₁₉ . Although at times t ₇ , t ₉ and t ₁₁ the laser transmitter is scanned in the second terminal EG ₂ , however, the optical receiver in the first terminal EG ₁ no longer receives light radiation because of this interruption, the control signal output A _ST remains on No level and the second timer ZG ₂ is no longer restarted. It follows that the repetition time also expires in the second timer ZG ₂ . Here it is assumed that this repetition time is 62 s because of the specimen scatter already mentioned.

At time t ₂₀ , the repetition time of 62 s has expired, the second timer ZG ₂ sends a gating pulse and the laser transmitter in the first terminal EG ₁ is gated. The gating pulse of the second timer ZG ₂ causes at time t ₂₁ via the auxiliary input of the control unit St that the changeover switch US is returned to the rest position.

Because of the two interruptions of the glass fibers, any new start of the timers by strobe pulses received from the respective other end device is now avoided, rather all timers now run independently of each other, i.e. each timer generates its own repetition time of 52 s, 62 s or 58 s his last gating pulse another gating pulse. The gating pulses generated in this way occur at times t ₂₂ , t ₂₃ and t ₂₄ , the respective first timer ZG ₁ gating the associated laser transmitter.

The game described above lasts until one of the two interruptions U ₁ or U ₂ is eliminated again. If this happens first in the second glass fiber GF _2, the same happens as at time t ₄ . If the interruption in the first glass fiber GF _{1 is} eliminated first, the same thing happens analogously as at time t ₄ , the terminals having reversed their roles.

In the above-described embodiment, in each Terminal provided two timers, namely a first Timer with the short repetition time of 55 s and on second timer with the long repetition time of 65 s. However, only one timer can be provided in each terminal be, with its component determining the repetition time through the switch US or a similar agent is switched that this one timer either with the short or with the long repetition time. General expressed a timer module is therefore provided, at which is effective for either a short or a long repetition time is.

Because of the already mentioned copy variations, how also mentioned the actual repetition times of their respective nominal values. But they are too other causes of such deviations conceivable, e.g. B. different circuit principles in the Realization of the timers. Definitely must set be how big these deviations may be, or it must be smallest and the largest permissible value for the short Repetition time and the smallest and the largest permissible value be determined for the long repetition time. Care must be taken be the smallest allowable value for the long Repeat time must be equal to or greater than the largest permissible value for the short repetition time.  

The values for the gating time as well as for the short and for the long repetition time can be selected differently from the values of 1 s, 55 s and 65 s mentioned in the exemplary embodiment described above. The value for the gating time is measured according to the transient response of the loop formed from the two laser transmitters and the two optical receivers, including their receiving amplifiers. After the gating time has been measured in this way, the repetition time can be dimensioned such that the average light output is still harmless. The advantage of the invention is that after the interruption of an optical fiber only once, namely at times t ₃ and t ₄ , two gating pulses can occur in quick succession and so a relatively high average light output can emerge from the point of interruption. By switching over to the long repetition time and restarting the respective timer according to the invention it is achieved that later only one gating pulse is still effective and only a low mean light output emerges from the point of interruption.

It doesn't have to after the fiber break inevitably two gating pulses occur. At a the smaller difference in the repetition times overlap two strobes to a single strobe, the can be twice as long as a simple gating pulse. The previously made considerations regarding the exiting however, medium light output also applies in this case.

Only if the tactile and Repeat times of both timers overlap Gating pulses so well that even without using the invention the laser transmitter only for the duration of a simple one Gating pulse is gated. But with one very  little difference, the two timers run in their cycle apart so that the overlap of the strobe always gets smaller and finally two short successive gating pulses with their disadvantageous Consequences occur. That is, the application is also in this case expedient of the invention.

The advantage of the invention is that at Design of the timers no effort to achieve a must drive high accuracy. One can rather be a simple one Principle and cheap components with large number of copies use and still achieves a low leakage medium light output.

In the embodiment shown in FIG. 2, it is provided that the optical receiver is followed by a receiving amplifier which has a control signal output. This is not absolutely necessary. A receiving module can be provided which has an optical receiver and a control signal output, the control signal output emitting a yes signal during the reception of light radiation.

Furthermore, in the exemplary embodiment, a transmission modulator is a Switch SD and a laser transmitter provided, a yes- Signal at the input of the switch SD to switch on the Diode current and thus leads to the scanning of the laser transmitter, and the yes signal is obtained via an OR circuit becomes. This is also not absolutely necessary. It can be Transmitter assembly can be provided, the one laser diode and one or has several control inputs. The transmission module is so trained and the control input is or the Control inputs are so with the control signal output and with the output of the timer or with the outputs of the  Timers connected that during a yes signal on Control signal output or at the output of the timer or on Output of the currently activated timer of the Laser transmitter is gated.

Claims (1)

Terminal device for optical message transmission via glass fibers with the following features:

• a) A receiving module is provided which has an optical receiver (OE, Fig. 2) and a control signal output (A _ST ), the control signal output emitting a yes signal during the reception of light radiation.
• b) A timer module (ZG ₁ , ZG ₂ , St, US) with one input and one output is provided.
• c) The input of the timer module is connected to the control signal output (A _ST ).
• d) The timer module is designed so that the following signal levels occur at its output.
  • d1) A no signal occurs as long as there is a yes signal at the input.
  • d2) After a change from yes to no at the input, a sequence of no and yes signals occurs at the output, this sequence starting with a no signal. The respective no signal has the duration of a short repetition time. The respective yes signal has the duration of a gating pulse.
  • d3) A yes signal at the input of the duration of a gating pulse leads to a switchover to a long repetition time.
  • d4) A yes signal at the input of the duration of a gating pulse during the long repetition time causes the long repetition time to start again.
  • d5) If a yes signal with the duration of a gating pulse is emitted after the long repetition time has elapsed, the system switches back to the short repetition time.
• e) A transmitter module with a laser transmitter (LS) and one or more control inputs is provided.
• f) The transmission module is designed and the control input is or the control inputs are connected to the control signal output (A _ST ) and the output of the timer module that during a yes signal at the control signal output (A _ST ) or on Output of the timer module of the laser transmitter (LS) is gated.