CA1165399A - Device for triggering an alarm system in the event of insufficiency of the transmission level, for the receiver module of an optical-fiber transmission system - Google Patents
Device for triggering an alarm system in the event of insufficiency of the transmission level, for the receiver module of an optical-fiber transmission systemInfo
- Publication number
- CA1165399A CA1165399A CA000370462A CA370462A CA1165399A CA 1165399 A CA1165399 A CA 1165399A CA 000370462 A CA000370462 A CA 000370462A CA 370462 A CA370462 A CA 370462A CA 1165399 A CA1165399 A CA 1165399A
- Authority
- CA
- Canada
- Prior art keywords
- filter
- output
- alarm
- optical
- triggering
- 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.)
- Expired
Links
Abstract
A DEVICE FOR TRIGGERING AN ALARM SYSTEM
IN THE EVENT OF INSUFFICIENCY OF THE
TRANSMISSION LEVEL, FOR THE RECEIVER MODULE
OF AN OPTICAL-FIBER TRANSMISSION SYSTEM
Abstract of the Disclosure An alarm-triggering device for the receiver of an optical-fiber transmission system comprises in series a filter which has a passband located externally with respect to the band of frequencies employed for optical-fiber transmission and the input of which is connected to an avalanche photodiode, amplifying means, rectifying means, a voltage comparator circuit, and alarm-triggering means.
IN THE EVENT OF INSUFFICIENCY OF THE
TRANSMISSION LEVEL, FOR THE RECEIVER MODULE
OF AN OPTICAL-FIBER TRANSMISSION SYSTEM
Abstract of the Disclosure An alarm-triggering device for the receiver of an optical-fiber transmission system comprises in series a filter which has a passband located externally with respect to the band of frequencies employed for optical-fiber transmission and the input of which is connected to an avalanche photodiode, amplifying means, rectifying means, a voltage comparator circuit, and alarm-triggering means.
Description
I ~ 39~
This invention relates generally to optical-fiber transmission systems and more particularly to a device for triggering an alarm system in the event of insufficiency of the level of transmission on the line, the device being intended for use in the receiver module of a simplified transmission system ~or a single-fiber optical communications link.
An.optical-fiber transmission system is constit-uted by a transmitter module, a receiver module and a ~ib~r extending between these modules. The transmitter module comprises a light-emitting base constituted by a laser diode, by a control photodiode and a laser/fiber optical coupling system inserted in a connector plug for connect-- ing said transmitter base to the optical-fiber cable, and by an electronic control unit which is intended among other design functions to re~ulate the optical trans-mission power. The receiver module comprises a light-detecting base constituted by a photodetector such as an avalanche photodiode and by a photodiode/fiber optical coupling system inserted in a connector plug for connect-ing said base to the optical-fiber cable, and by an electronic control unit which has the intended function, among others, o. automatically regulating the ~ain of the avalanche photodiodeO For a detailed description of the receiver module, reference may usefully be made for exampl.e to the article published in "The Bell System 3 g ~
Technical Journal", volume 57, No 6, July - August 1978, page 1837, entitled 1'Practical 45 - Mb/s Regenerator for Lightwave Transmission".
In a transmission system which makes use of a num~er of optical fibers, it is a known practice to employ a microprocessor for the management of the receiver module and in particular for triggeri~g an alarm system in the event of insufficiency of the -transmission level.
However, the use of a microprocessor is not lO,justified in the case of a transmission system which makes use of a single optical fiber.
The invention is therefore directed to a device for triggering an alarm system in the event of insuffi-ciency of the transmission level for the receiver of a transmission system which utilizes an optical fiber, comprising :
~ a photodetector with automatic gain regulation ;
- a filter having a passband which is external to the requency band employed for optical-fiber transmission, ~0 the input of said filter being connected to said photo-detector, - ~mplifying means connected to the output of said filter, - rectifying means connected to the output of said amplify-ing means, - a voltage comparator circuit connected to the output of said rectifying means, and ~ 1~53~
- al~rm-triggering means connected to the output of said voltage comparator circuit.
It will ~e noted that the electric circuit of the alarm-triggerlng device described in the foregoing is of particularly simple design.
In accordance with another distinctive feature of the invention, the passband of the filter is external to the frequency band employed for optical-fiber trans-mission.
,J
Other features and advantages of the invention will be more apparent upon consideration of the following description and accompanying drawings, wherein :
- Fig. 1 is a diagram sho~m partly in the form of blocks and representing the receiver module which com~rises a first alternative embodiment of the alarm-triggering device in accordance with the invention ;
- Fig. 2 is a diagram sho~ partly in the ~orm of blocks and representing the receivex module which comprises a secona alternative embodiment of the alarm-triggering device in accordance with the invention ;
- Fig. 3 is a diagram sho~m partly in th~ form of blocks and representing the receiver module which com-prises a third alternative embodiment of the alarm-triggering device in accordance with the invention.
In a first alternative embodiment o~ the -invention which is illustrated in Fig. 1, the alarm-~ ~53~
triggering device 1 in accordance with the invention is connected at A to a photodetectox such as, for example, an avalanche photodiode 2 provided within the receiver module of a transmission system which makes use of a single optical fiber. The input E of an amplifier A1 is connected at A to the avalanche photodiode 2 and said amplifier Al deli~ers at the output Sl pulses ha~ing a peak-to-peak amplitude of 1 voltr for exampl~. A peak-to-peak detector 3 i9 connected to the output Sl of the 'amplifier Al and ensures automatic gain regulation of the a~alanche photodlode 2 ; the output S2 of said detector is connected to a bias circuit 4 of the avalanche photo-diode 2, the output S3 of said bias circuit being connected to said avalanche photodiode. The avalanche photodiode 2 is connected to ground at A through a resistor R.
In the description which now follows, considera-tion will be given to the structure of the alarm-triggering device 1 in accordance with the first alternative embodi-ment shown in Fig, 1.
Said alarm-triggering device 1 comprises a fiLter 5, the input E~ of which is connected to the avalanche photodiode 2 through a resistor R' having a value which is distinctly higher than that of the resistor ~. It will be noted at this point that the filter 5 has a passband which is external to the frequency band employed for trans-mission by the pulse code. More specifically, the mean frequency of the filter 5 can be either lower (the filter 5 in this case is a low-pass filter) or higher (the ilter 5 in this case is a high-pass filter) than the bottom or top limits of the frequency band employed respectiuely for transmission by the pulse code.
The output S4 of the filter 5 is connected to a very-low-nolse ~mplifier 6/ the output S5 o w~ïch is connected to an amplifier 7. At the output S~ of the , amplifier 7 is connected a rectifying circuit comprising 10 ,a diode D and a resistor Rl and, in series~ an integrating circuit comprising a resistor R2 and a capacitor C. The output of said integrating circuit is connected to one of the input terminals E8 of a threshold comparator amplifier 8 whilst the other input terminal Eg of said amplifier 8 is connected to a source of variable reference voltage generated at 9. A resistor R3 and an electroluminescent diode D' for controlling an alarm system are connected in series to the output S~ of the co~parator amplifier 8. It will readily be apparent that the diode D' can be replaced by any other suitable means without thereby departing from the scope of the invention.
In Fig. 2, which illustrates a second alter-native embodiment of the invention, the elements which axe identical with those of Fig. 1 are designated by the same references. The alarm-triggering device 1 is connected to the output S1 of the amplifier Al ; more 3 9 ~
specifically, the input E~ of the filter 5 is connected to the output Sl of the ampliier A1 and the output S4 of said filter 5 is connected directly to the input of the amplifier 7.
In Fig. 3, which illustrates a third embodiment of the inven~ion, the elements which are identical with those of ~ig. 2 are in turn designate* by the same reer-ences. ~he alarm-triggexing device 1 described earlie~
is connected between the output Sl of the amplifier Al and the bias circuit 4 of the avalanche photodiode 2. More precisely, the output S8 of the comparator amplifier 8 is connected to the electroluminescant diode D' and to the input of the bias circuit 4. Thus the gain of the avalanche photodiode 2 is automatically regulated by means of the comparator amplifier 8.
The operation a~d the mode of utilization of-the alarm-tri~gering device in accordance with the invention may be deduced from the foregoing description and will hereinafter be explained in greater detail.
In the first place and under normal operating conditions, that is, with standardized incident optical power, the coded electrical pulses produced by the avalanche photodiode 2 are amplified by the amplifier A
and have a constant amplitude at the output by virtue of a control loop circuit. The peak-to-peak ampli~ude of the pulses is in fact measured by the peak-to-peak detector 3 3~
which consequently delivers a proportional direct-current voltage. This voltage is applied to the bias circuit 4 of the avalanche photodiode 2 and therefore controls the gain of this latter, said photodiode being also provided with temperature drift. This control operation thus makes it possible to maintain a standardized and constant ampli-tude (a peak-to-peak amplitude of 1 volk, for example) of the output signals in spite of any possible variations in ambient temperature and variations in the incident optical power.
Assuming now that there exists an insufficiency of the line transmission level or in other words an in-sufficiency of the incident optical power by reason of the fact that the amplitude of the output signals remains constant, the control system described in the foregoing gives rise to o~erbiasing (with respect to normal biasing) of the a~alanche photodioae 2 which therefore delivers at its output a noise potential of the order of 1 volt, for example.
The principle of alarm-system triggering lies in the use of ~he energy within a frequency band which is not employed for transmission of the pulse code i this is obtained by means of the filter 5, the passband of which is external to the frequency band employed by the pulse code.
Thus, in accordance with the alternative embodiment of Fig. 1, the noise is amplified by the first low-noise ampliier 6 and by the second amplifier 7, then rectified by the recti~ying circuit (D and Rl) and inte-grated by the integrating circuit (R2 and C) in order to produce a direct-current voltage which is proportional to the e~fective value of the noiseO This voltage is then compared with a reference vo~tage generated at 9 by the amplifier 8. If this threshold voltage is attained, the comparator amplifier 8 delivers a contxol signal to the èlectroluminescent diode D' which triggers an alarm system - of any suitable type.
It will be noted that the adjustment of said reference voltage makes it possible to determine the minimum optical alarm power ; for example, if the standard-ized power is - 53 dBm, the alarm power is - 60 dBm.
The oregoing description remains applicable to the alternative embodiments illustrated in Figs. 2 and 3.
It should be added that, in regard to the al-ternative embodiment shown in Fig. 2, the noise is amplified solely by the amplifier 7, ta~ing into account the sufficient - level at the output o~ the amplifier A1. Furthermore, in the alternative embodiment shown in Fig. 3, the alarm-triggering device in accordance with the invention also has the function o ensuring automatic gain regulation of the avalanche photodiode.
This invention relates generally to optical-fiber transmission systems and more particularly to a device for triggering an alarm system in the event of insufficiency of the level of transmission on the line, the device being intended for use in the receiver module of a simplified transmission system ~or a single-fiber optical communications link.
An.optical-fiber transmission system is constit-uted by a transmitter module, a receiver module and a ~ib~r extending between these modules. The transmitter module comprises a light-emitting base constituted by a laser diode, by a control photodiode and a laser/fiber optical coupling system inserted in a connector plug for connect-- ing said transmitter base to the optical-fiber cable, and by an electronic control unit which is intended among other design functions to re~ulate the optical trans-mission power. The receiver module comprises a light-detecting base constituted by a photodetector such as an avalanche photodiode and by a photodiode/fiber optical coupling system inserted in a connector plug for connect-ing said base to the optical-fiber cable, and by an electronic control unit which has the intended function, among others, o. automatically regulating the ~ain of the avalanche photodiodeO For a detailed description of the receiver module, reference may usefully be made for exampl.e to the article published in "The Bell System 3 g ~
Technical Journal", volume 57, No 6, July - August 1978, page 1837, entitled 1'Practical 45 - Mb/s Regenerator for Lightwave Transmission".
In a transmission system which makes use of a num~er of optical fibers, it is a known practice to employ a microprocessor for the management of the receiver module and in particular for triggeri~g an alarm system in the event of insufficiency of the -transmission level.
However, the use of a microprocessor is not lO,justified in the case of a transmission system which makes use of a single optical fiber.
The invention is therefore directed to a device for triggering an alarm system in the event of insuffi-ciency of the transmission level for the receiver of a transmission system which utilizes an optical fiber, comprising :
~ a photodetector with automatic gain regulation ;
- a filter having a passband which is external to the requency band employed for optical-fiber transmission, ~0 the input of said filter being connected to said photo-detector, - ~mplifying means connected to the output of said filter, - rectifying means connected to the output of said amplify-ing means, - a voltage comparator circuit connected to the output of said rectifying means, and ~ 1~53~
- al~rm-triggering means connected to the output of said voltage comparator circuit.
It will ~e noted that the electric circuit of the alarm-triggerlng device described in the foregoing is of particularly simple design.
In accordance with another distinctive feature of the invention, the passband of the filter is external to the frequency band employed for optical-fiber trans-mission.
,J
Other features and advantages of the invention will be more apparent upon consideration of the following description and accompanying drawings, wherein :
- Fig. 1 is a diagram sho~m partly in the form of blocks and representing the receiver module which com~rises a first alternative embodiment of the alarm-triggering device in accordance with the invention ;
- Fig. 2 is a diagram sho~ partly in the ~orm of blocks and representing the receivex module which comprises a secona alternative embodiment of the alarm-triggering device in accordance with the invention ;
- Fig. 3 is a diagram sho~m partly in th~ form of blocks and representing the receiver module which com-prises a third alternative embodiment of the alarm-triggering device in accordance with the invention.
In a first alternative embodiment o~ the -invention which is illustrated in Fig. 1, the alarm-~ ~53~
triggering device 1 in accordance with the invention is connected at A to a photodetectox such as, for example, an avalanche photodiode 2 provided within the receiver module of a transmission system which makes use of a single optical fiber. The input E of an amplifier A1 is connected at A to the avalanche photodiode 2 and said amplifier Al deli~ers at the output Sl pulses ha~ing a peak-to-peak amplitude of 1 voltr for exampl~. A peak-to-peak detector 3 i9 connected to the output Sl of the 'amplifier Al and ensures automatic gain regulation of the a~alanche photodlode 2 ; the output S2 of said detector is connected to a bias circuit 4 of the avalanche photo-diode 2, the output S3 of said bias circuit being connected to said avalanche photodiode. The avalanche photodiode 2 is connected to ground at A through a resistor R.
In the description which now follows, considera-tion will be given to the structure of the alarm-triggering device 1 in accordance with the first alternative embodi-ment shown in Fig, 1.
Said alarm-triggering device 1 comprises a fiLter 5, the input E~ of which is connected to the avalanche photodiode 2 through a resistor R' having a value which is distinctly higher than that of the resistor ~. It will be noted at this point that the filter 5 has a passband which is external to the frequency band employed for trans-mission by the pulse code. More specifically, the mean frequency of the filter 5 can be either lower (the filter 5 in this case is a low-pass filter) or higher (the ilter 5 in this case is a high-pass filter) than the bottom or top limits of the frequency band employed respectiuely for transmission by the pulse code.
The output S4 of the filter 5 is connected to a very-low-nolse ~mplifier 6/ the output S5 o w~ïch is connected to an amplifier 7. At the output S~ of the , amplifier 7 is connected a rectifying circuit comprising 10 ,a diode D and a resistor Rl and, in series~ an integrating circuit comprising a resistor R2 and a capacitor C. The output of said integrating circuit is connected to one of the input terminals E8 of a threshold comparator amplifier 8 whilst the other input terminal Eg of said amplifier 8 is connected to a source of variable reference voltage generated at 9. A resistor R3 and an electroluminescent diode D' for controlling an alarm system are connected in series to the output S~ of the co~parator amplifier 8. It will readily be apparent that the diode D' can be replaced by any other suitable means without thereby departing from the scope of the invention.
In Fig. 2, which illustrates a second alter-native embodiment of the invention, the elements which axe identical with those of Fig. 1 are designated by the same references. The alarm-triggering device 1 is connected to the output S1 of the amplifier Al ; more 3 9 ~
specifically, the input E~ of the filter 5 is connected to the output Sl of the ampliier A1 and the output S4 of said filter 5 is connected directly to the input of the amplifier 7.
In Fig. 3, which illustrates a third embodiment of the inven~ion, the elements which are identical with those of ~ig. 2 are in turn designate* by the same reer-ences. ~he alarm-triggexing device 1 described earlie~
is connected between the output Sl of the amplifier Al and the bias circuit 4 of the avalanche photodiode 2. More precisely, the output S8 of the comparator amplifier 8 is connected to the electroluminescant diode D' and to the input of the bias circuit 4. Thus the gain of the avalanche photodiode 2 is automatically regulated by means of the comparator amplifier 8.
The operation a~d the mode of utilization of-the alarm-tri~gering device in accordance with the invention may be deduced from the foregoing description and will hereinafter be explained in greater detail.
In the first place and under normal operating conditions, that is, with standardized incident optical power, the coded electrical pulses produced by the avalanche photodiode 2 are amplified by the amplifier A
and have a constant amplitude at the output by virtue of a control loop circuit. The peak-to-peak ampli~ude of the pulses is in fact measured by the peak-to-peak detector 3 3~
which consequently delivers a proportional direct-current voltage. This voltage is applied to the bias circuit 4 of the avalanche photodiode 2 and therefore controls the gain of this latter, said photodiode being also provided with temperature drift. This control operation thus makes it possible to maintain a standardized and constant ampli-tude (a peak-to-peak amplitude of 1 volk, for example) of the output signals in spite of any possible variations in ambient temperature and variations in the incident optical power.
Assuming now that there exists an insufficiency of the line transmission level or in other words an in-sufficiency of the incident optical power by reason of the fact that the amplitude of the output signals remains constant, the control system described in the foregoing gives rise to o~erbiasing (with respect to normal biasing) of the a~alanche photodioae 2 which therefore delivers at its output a noise potential of the order of 1 volt, for example.
The principle of alarm-system triggering lies in the use of ~he energy within a frequency band which is not employed for transmission of the pulse code i this is obtained by means of the filter 5, the passband of which is external to the frequency band employed by the pulse code.
Thus, in accordance with the alternative embodiment of Fig. 1, the noise is amplified by the first low-noise ampliier 6 and by the second amplifier 7, then rectified by the recti~ying circuit (D and Rl) and inte-grated by the integrating circuit (R2 and C) in order to produce a direct-current voltage which is proportional to the e~fective value of the noiseO This voltage is then compared with a reference vo~tage generated at 9 by the amplifier 8. If this threshold voltage is attained, the comparator amplifier 8 delivers a contxol signal to the èlectroluminescent diode D' which triggers an alarm system - of any suitable type.
It will be noted that the adjustment of said reference voltage makes it possible to determine the minimum optical alarm power ; for example, if the standard-ized power is - 53 dBm, the alarm power is - 60 dBm.
The oregoing description remains applicable to the alternative embodiments illustrated in Figs. 2 and 3.
It should be added that, in regard to the al-ternative embodiment shown in Fig. 2, the noise is amplified solely by the amplifier 7, ta~ing into account the sufficient - level at the output o~ the amplifier A1. Furthermore, in the alternative embodiment shown in Fig. 3, the alarm-triggering device in accordance with the invention also has the function o ensuring automatic gain regulation of the avalanche photodiode.
Claims (7)
1. A device for triggering an alarm system in the event of insufficiency of the transmission level for the receiver of a transmission system which utilizes an optical fiber, comprising:
- a photodetector having an automatic gain regulation and producing noise in the event of said insufficiency of transmission level;
- a filter connected to said photodetector for filtering said noise, said filter having a passband which is external to the frequency band employed for optical fiber transmission;
- means for amplifying said noise present at the output of said filter;
- means for rectifying said noise present at the output of said amplifying means;
- a circuit for comparing the amplitude of said noise to a threshold amplitude value, said comparing circuit being connected to the output of said rectifying means; and - alarm-triggering means connected to the output of said comparing circuit for producing an alarm signal when said noise amplitude is greater than said threshold value.
- a photodetector having an automatic gain regulation and producing noise in the event of said insufficiency of transmission level;
- a filter connected to said photodetector for filtering said noise, said filter having a passband which is external to the frequency band employed for optical fiber transmission;
- means for amplifying said noise present at the output of said filter;
- means for rectifying said noise present at the output of said amplifying means;
- a circuit for comparing the amplitude of said noise to a threshold amplitude value, said comparing circuit being connected to the output of said rectifying means; and - alarm-triggering means connected to the output of said comparing circuit for producing an alarm signal when said noise amplitude is greater than said threshold value.
2. A device according to claim 1, wherein the input of said filter is connected to the output of an amplifier which is supplied by said photodetector.
3. A device according to claim 2, including means for automatically regulating the gain of said photodetector in accordance with said alarm signal.
4. A device according to claim 1 or claim 2, wherein the mean frequency of said filter is lower than the bottom limit of the frequency band employed for optical-fiber transmission.
5. A device according to claim 1 or claim 2, wherein the mean frequency of said filter is higher than the top limit of the frequency band employed for optical fiber transmission.
6. A device according to claim 1, wherein said amplifying means are constituted by a first low-noise amplifier and a second amplifier connected in series.
7. A device according to claim 1, wherein said photodetector is an avalanche photodiode.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000370462A CA1165399A (en) | 1981-02-10 | 1981-02-10 | Device for triggering an alarm system in the event of insufficiency of the transmission level, for the receiver module of an optical-fiber transmission system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000370462A CA1165399A (en) | 1981-02-10 | 1981-02-10 | Device for triggering an alarm system in the event of insufficiency of the transmission level, for the receiver module of an optical-fiber transmission system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1165399A true CA1165399A (en) | 1984-04-10 |
Family
ID=4119136
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000370462A Expired CA1165399A (en) | 1981-02-10 | 1981-02-10 | Device for triggering an alarm system in the event of insufficiency of the transmission level, for the receiver module of an optical-fiber transmission system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1165399A (en) |
-
1981
- 1981-02-10 CA CA000370462A patent/CA1165399A/en not_active Expired
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