AU672502B2 - Automatic laser shut-off circuit (ALS) with protection against inadvertent reactivation - Google Patents
Automatic laser shut-off circuit (ALS) with protection against inadvertent reactivation Download PDFInfo
- Publication number
- AU672502B2 AU672502B2 AU66073/94A AU6607394A AU672502B2 AU 672502 B2 AU672502 B2 AU 672502B2 AU 66073/94 A AU66073/94 A AU 66073/94A AU 6607394 A AU6607394 A AU 6607394A AU 672502 B2 AU672502 B2 AU 672502B2
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- AU
- Australia
- Prior art keywords
- circuit
- switch
- shut
- laser
- signal
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- 230000007420 reactivation Effects 0.000 title claims description 13
- 238000000034 method Methods 0.000 claims description 24
- 230000005540 biological transmission Effects 0.000 claims description 14
- 238000012544 monitoring process Methods 0.000 claims description 8
- 230000002457 bidirectional effect Effects 0.000 claims description 4
- 230000000295 complement effect Effects 0.000 claims description 3
- 239000003365 glass fiber Substances 0.000 claims description 3
- 238000005259 measurement Methods 0.000 claims description 3
- 230000003287 optical effect Effects 0.000 claims description 3
- 230000004913 activation Effects 0.000 description 3
- 230000000875 corresponding effect Effects 0.000 description 3
- 230000001960 triggered effect Effects 0.000 description 3
- 230000015556 catabolic process Effects 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 101100523503 Oryza sativa subsp. japonica RAC5 gene Proteins 0.000 description 1
- 230000001276 controlling effect Effects 0.000 description 1
- 230000002596 correlated effect Effects 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 230000008929 regeneration Effects 0.000 description 1
- 238000011069 regeneration method Methods 0.000 description 1
- 230000000246 remedial effect Effects 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
- H04B10/075—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal
- H04B10/079—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal using measurements of the data signal
- H04B10/0799—Monitoring line transmitter or line receiver equipment
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B2210/00—Indexing scheme relating to optical transmission systems
- H04B2210/08—Shut-down or eye-safety
Landscapes
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Optical Communication System (AREA)
Description
L I _I I I Automatic Laser Shut-off Circuit (ALS) with Protection Against Inadvertent Reactivation TECINIGA-L
FIELD
The invention relates to a process as defined in eprecharacterising part of Claim 1 -t--an arrangement for practising the process.
BACKGROUND OF THE INVENTVIN In modern transmission circuits for digital optical signals, for the purpose -f covering a large range without intermediate regeneration, one employs powerful laser diodes the light of which may injure service personnel when the lightguide used for the transmission breaks. For such transmission circuits one therefore customarily provides the function of automatic laser shut-off, termed ALS in what follows, with which the respective laser transmitter is shut off in the case of breakdown of the transmission circuit. In unidirectional operation of a lightguide, interruption of the transmission is noted via the non-appearance of the Stransmitted signal in the receiving station, and from the same an appropriate message is inputted into monitoring means incorporated in the transmitting station. In bidirectional operation involving one lightguide, a characteristic bit sequence, the so-called directional byte, is inserted into the transmitted signal for the purpose of characterising the direction of transmission. In the case of an interruption of the transmission circuit and a corresponding rise in the gain of the receiving amplifier of the station, by processing the directional byte it is possible to recognise in this way that there is only a misrepresentation of a transmitted signal and that the received optical signal is caused by back-scattering and must originate from the transmitter proper. In connection with remedial measures in such Stransmission breakdown It is necessary to switch on the laser transmitter for measurements and for testing though the ALS function was triggered.
Cyclic start-stop operation with a duration of about 2 sec and a period of about 70 sec must be feasible as well as single manual activation of the laser transmitter for 2 sec or for about 60 sec. The control means have to be designed so that such an activation is possible but that this case cannot be simulated by a failure of the control means and/or the connected computer.
WUMRYO -TTlE IN'1ENTION Thus, the prob m-eft4ce-p- nt-4i ewtn---l-s-delelp the *V t 1 rJ S 0 9 9 8 P 00_4 I L -2- SUMMARY OF THE INVENTION In accordance with one aspect of the present invention, there is provided a process for the automatic shut-off of a laser in a transmission circuit for digital signals comprising a laser transmitter, wherein, as a consequence of transmission failure, the laser transmitter is shut-off by a monitoring means, which recognises the transmission failure, outputting an appropriate alarm signal to a switching device which thereafter generates a shut-off signal to the laser transmitter that is connected to receive said shutoff signal, wherein: after such an automatic laser shut-off, for the purpose of an intended reactivation of the laser transmitter following an external signal, switch-on commands are supplied for the duration of the reactivation, from a module-associated computer controlling the reactivation periodically within a first stop period of a timer to the same timer, and for the duration of an interference-free reception of the switch-on command, the timer outputs a control command to a second correlating circuit acting as the switch-on device which thereafter outputs a switch-on and stop-signal to the laser transmitter.
In accordance with another aspect of the present invention, there is provided an arrangement for practising a process as described, wherein: for unidirectional operation there is provided a first recognition circuit which, 20 in the absence of a received signal, generates a first error signal; that for bidirectional operation via a glass fibre there is provided a second monitoring circuit which, when receiving the directional byte of the station's laser transmitter,, outputs a second error signal; that the outputs of the recognition circuits are connecte with the inputs of a first correlating circuit; that the output of the first correlating circuit is connected with a 25 computer bus related to a module-associated computer and with the signal input of a controlled switch; that the control input of the controlled switch is connected with the computer bus and the signal output of the controlled switch is connected with an input S of a second correlating circuit; that an other input of the second correlation circuit is S• connected with the computer bus for the purpose of instant laser shut-off and a third input is connected with the output of a timer the control input of which is connected with the computer bus; that the output of the second correlating circuit is connected with a control input of the laser transmitter; and that the module-associated computer has a command input for commands from external sources.
BRIEF DESCRIPTION OF THE DRAWINGS In what follows the invention will be explained in detail with reference to an embodiment shown in the drawing. There show: RAC5 Figure 1, an arrangement for ALS control, and IN:\LIBo00642MXL r E '11 II s 2a Figure 2, a truth table characterising the development of the process in the arrangement according to Figure 1.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT As a central control element, the arrangement illustrated in Figure 1 comprises a module-associated computer BGR which communicates via a computer bus RB with a user-specific integrated circuit ASIC. The integrated circuit ASIC comprises the error recognition circuits LOS for recognising complete absence of the transmitted signal and also the directional byte processing circuit C1 with which, in bidirectional operation involving a single glass fiber, a distinction can be made between a genuine transmitted signal from the other station and a received signal which was caused by backscattering and originated from the station's own laser diode. The output signals of the two recognition circuits are correlated in a first correlating circuit VK1, and an alarm signal AL, which is imputed into a delay circ.t AS3, is generated. The delay circuit ASV causes a delay of about 0.5 sec which becomes effective only in the case of a shut-off and which prevents that automatic laser shut-off is triggered by short bit errors, in the once-only recognition of the station-specific directional byte. After that, the alarm signal is applied to the input of a controlled switch GS and to an alarm input ALE of the computer bus.
4* o 4 o IN :LIBI00142:MXL L 3 The controlled switch GS serves for the computer-controlled activation or de-act'vation of the ALS function by applying an appropriate switch command to the control input of the controlled switch GS from the module associated-computer BGR, optionally after a control command obtained from an external terminal EXT via the computer bus RB and a terminal ALS-ED; by virtue of this switch command, either the alarm signal AL is passed on to a second correlating circuit VK2 and, hence, the ALS function is activated or this connection is interrupted.
Another input of the second correlating circuit VK2 is connected with the output of a timer TIM which, only in the case of re-activation of the laser transmitter after automatic laser shut-off, receives start signals with a period of about 2 sec via a terminal LON from the computer bus RB and, in the case of interference-free reception, generates an output signal which is recognised by the second correlating circut VK2 as a switch-on or stop command for the laser transmitter. A third input terminal of the second correlating circuit VK2 is connected with a S* terminal LDOFF of the the computer bus RB through which the module-associated computer applies a command to shut off the laser 20 transmitter LS, which command has a rank higher than any other switch command. The output of the second correlating circuit VK2 provides the laser transmitter LS with the switch-on signal SLEA proper.
The operation of the arrangement according to Figure 1 will be explained further with reference to the truth table shown in Figure 2.
The truth table's first column denoted by ALS-ED charactizes the position of the controlled switch ES of Figure 1, with switch position 1 denoting the closed switch, ES, the activated ALS function. The logic state of the alarm signal AL is indicated in the second column; in the logic So.. state 1, one of the recognition circuits Cl, LOS of Figure 1 has "o 30 generated an alarm signal; in the logic state 0, the operation proceeds without interference; whereas denotes any one of the logic states.
The logic state of the output signal ALSA of the controlled switch GS is indicated in the column ALSA; when the controlled switch GS is closed, this state corresponds to the logic state of the alarm signal AL. Column LDON shows the output signal of the timer TIM, which signal Is effective with higher rank vis-a-vis the output signal ASLA of the controlled switch GS and depends upon the switching commands Inputted from the module-associated computer BGR via the terminal LON into the timer. If in the case of an intended re-activation of the laser transmitter these KRS/0998P n toI 4 commands are received in regular fashion, a continuous signal corresponding to the logic l level is inputted into the second correlating circuit VK2; if this "rewinding" does not take place, the continuous signal and, hence, the laser transmitter LS are switched off after at most 2 sec because then the previous automatic laser shut-off by the ALSA signal becomes effective again. The column LDOFF lists the logic level of the signal which has higher rank than any other input signal of the second correlating circuit and which is outputted, for example, by external triggering, from the module-associated computer PGR via the computer bus RB to the second correlating circuit VK2 for the purpose of instant shut-off of the laser transmitter; the laser is shut off in the case of the logic 1 level.
Column SLEA lists the output signal of the second correlating circuit VK2; here the logic 1 level means that the laser transmitter LS is being switched on or has been switched on. Normal operation with operative but not triggered ALS function corresponds to the second line from above, and normal operation with shut-off ALS function corresponds to the second line from below.
20 The truth table of Figure 2 reflects the interaction of the recognition circuits Cl, LOS and the module-associated computer BGR which periodically rewinds the timer via the LON stop commands. In order to provide safeguards against inadvertent reactivation by computational errors, the generation of the LON stop commands is divided into two processes A, B; the two processes render a result which is stored in an additional register of the user-specific integrated circuit ASIC or in the module-associated computer. The two processes A, B are designed so that, when the operation proceeds properly, their results can be converted into each other by a special algorithm. In the simplest case, the complement can be chosen for the algorithm so that the result of process A must be the complement of the result of process B. Only if this condition is satisfied, a switch-on or stop command LON is generated, with the command rewinding the timer TIM. Processes A and B arp designed so that an other initial value is used in each computer run and, hence, that an other numeric result must be obtained in a quasi-random fashion. This ensures that a correct logic function is not simulated by the computer being "hung" in certain logic states.
KRS/0998P I The logic state 0 of the command signal ALS-ED in the first column of Figure 2 accounts for the case in which the ALS function and, hence, the controlled switch GS are switched off and do not affect the generation of the control signal SLEA for the laser transmitter LS. In this case, the timer and, hence, the LDON signal can be switched to the logic 1 level by means of the LON stop signal so that in this way the laser transmitter can be switched on via the second correlating circuit VK2. As a rule, this mode of operation is used for measurements or if the ALS function or in low-power operation is switched off [sic]; for the sake of simplicity, then the timer TIM is switched to second stop time of about one minute. This is advantageous because then a short failure of the module-associated computer BGR or of the computer bus RB does not cause instant shut-off of the laser transmitter. As expressed by the column LDOFF, if there is danger, the application of a logic 1 pulse to the corresponding input of the second correlating circuit VK2 will then S' switch off the laser transmitter instantly.
see
S.
*oo *ee *l ooe ft ft ot f ft.: f ofo• KRS/0998P
Claims (8)
1. A process for the automatic shut-off of a laser in a transmission circuit for digital signals comprising a !p transmitter, wherein, as a consequence of transmission failure, the laser trai, ._tter is shut-off by a monitoring means which recognises the transmission fa outputting an appropriate alarm signal to a switching device which thereafter generates a shut-off signal to the laser transmitter that is connected to receive the shut-off signal, wherein after such an automatic laser shut-off, for the purpose of an intended reactivation of the laser transmitter following an external signal, switch-on commands are supplied for the duration of the reactivation, from a module-associated computer controlling the reactivation periodically within a first stop period of a timer to the same timer and, for the duration of an interference-free reception of the switch-onl command, the tinier outputs a control command to a second correlating circuit acting as the switch-on device which thereafter outputs a switch-on and stop-signal to the laser transmitter.
2. The process according to claim 1, wherein the switch-on commands are generated by generating process signals in parallel in two independent processes from the output signals of the monitoring means, which process signals characterise the 20 state of switching of the automatic laser shut-off circuit and, after their combination, must result in a predetermined value for generating switch-on-commands.
3. The process according to claim 2, wherein when properly generated, the process signals as digital quantities have complementary values.
4. The process according to claim 1 or 2, wherein the switch-on and switch-off commands are additionally protected against operational and computational errors by a code word preceding these commands, with the generation of this code word being independent of the generation of the switch-on and switch-off commands so 30 that coincidental generation of this combination by chance and, hence, the corresponding error situation are little likely.
The process according to claim 1, wherein the first stop period has a duration of about 2 sec.
6. The process according to claim 1, wherein when the automatic laser shut-off circuit is switched off, the timer is switched to a second stop period. IN.\LIDIO0042:MXL _s
7. The process according to claim 6, wherein the duration of the second stop period is about 60 sec.
8. An arrangement for practising a process according to claims 1 to 7, wherein: for unidirectional operation there is provided a first recognition circuit which, in the absence of a received signal, generates a first error signal; that for bidirectional operation via a glass fibre there is provided a second monitoring circuit which, when receiving the directional byte of the station's laser transmitter, outputs a second error signal; that the outputs of the recognition circuits are connected with the inputs of a first correlating circuit; that the output of the first correlating circuit is connected with a computer bus related to a module-associated computer and with the signal input of a controlled switch; that the control input of the controlled switch is connected with the computer bus and the signal output of the controlled switch is connected with an input of a second correlating circuit; that an other input of the second correlating circuit is connected with the computer bus for the purpose of instant laser shut-off and a third input is connected with the output of a timer the control input of which is connected with the computer bus; that the output of the second correlating circuit is connected i: with a control input of the laser transmitter; and that the module-associated computer 0 20 has a command input for commands from external sources. S9. The arrangement according to claim 8, wherein the first correlating circuit is directly followed by a delay circuit causing a delay of about 0.5 sec of the shut-off operation. :10. A process substantially as herein described in any one of claims 1-7, with reference to Fig. 1, or, Fig. 2, or, Fig. 1 and Fig. 2. 11 An arrangement substantially as herein described in claim 8 or 9, with 3o reference to Fig. 1, or, Fig. 2, or, Fig. 1 and Fig. 2. DATED this Thirteenth Day of August 1996 Siemens Aktiengesellschaft Patent Attorneys for the Applicant SPRUSON FERGUSON IN \,llolO0042 MXL I Automatic Laser Shut-off Circuit (ALS) with Protection Against Inadvertent Reactivation ABSTRACT In order to protect the service personnel of optical transmission circuits which are energised by a laser, there is provided an automatic laser shut-off ALS which can be activated by monitoring circuits. An additional capability of switching on the laser transmitter for measurements even when the ALS function has been activated is required. This reactivation, caused by errors, must not take place unintentionally. Therefore, according to the invention the monitoring circuits, together with a timer which is to be rewound regularly by a module-associated computer, have their outputs connected to a correlating circuit which generates the proper switch-on command for the laser transmitter. 0 e *049 *q* o 0* 0 c a KRS/0998P
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE4321601A DE4321601A1 (en) | 1993-06-29 | 1993-06-29 | Automatic laser shutdown with protection against unintentional restart |
| DE4321601 | 1993-06-29 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| AU6607394A AU6607394A (en) | 1995-01-12 |
| AU672502B2 true AU672502B2 (en) | 1996-10-03 |
Family
ID=6491501
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| AU66073/94A Ceased AU672502B2 (en) | 1993-06-29 | 1994-06-28 | Automatic laser shut-off circuit (ALS) with protection against inadvertent reactivation |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0632607A1 (en) |
| AU (1) | AU672502B2 (en) |
| DE (1) | DE4321601A1 (en) |
| NO (1) | NO942355L (en) |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2195508A (en) * | 1986-09-27 | 1988-04-07 | Stc Plc | Optical fibre transmission system |
| US5136410A (en) * | 1990-01-09 | 1992-08-04 | Ibm Corporation | Optical fiber link control safety system |
-
1993
- 1993-06-29 DE DE4321601A patent/DE4321601A1/en not_active Withdrawn
-
1994
- 1994-06-20 NO NO942355A patent/NO942355L/en not_active Application Discontinuation
- 1994-06-22 EP EP94109662A patent/EP0632607A1/en not_active Ceased
- 1994-06-28 AU AU66073/94A patent/AU672502B2/en not_active Ceased
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2195508A (en) * | 1986-09-27 | 1988-04-07 | Stc Plc | Optical fibre transmission system |
| US5136410A (en) * | 1990-01-09 | 1992-08-04 | Ibm Corporation | Optical fiber link control safety system |
Also Published As
| Publication number | Publication date |
|---|---|
| NO942355L (en) | 1994-12-30 |
| AU6607394A (en) | 1995-01-12 |
| NO942355D0 (en) | 1994-06-20 |
| DE4321601A1 (en) | 1995-01-19 |
| EP0632607A1 (en) | 1995-01-04 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MK14 | Patent ceased section 143(a) (annual fees not paid) or expired |