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
  • H04B10/071—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using a reflected signal, e.g. using optical time domain reflectometers [OTDR]
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
  • G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
  • G01M11/31—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter and a light receiver being disposed at the same side of a fibre or waveguide end-face, e.g. reflectometers
  • G01M11/3109—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR
  • G01M11/3118—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR using coded light-pulse sequences
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
  • G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
  • G01M11/39—Testing of optical devices, constituted by fibre optics or optical waveguides in which light is projected from both sides of the fiber or waveguide end-face

Definitions

• an optical B-ISDN subscriber line is usually implemented in such a way that at the end of that part of the optical subscriber line for which the network operator is responsible, ie at the so-called U ß interface, the optical line with a Network Termination (NT1) has been completed (CCITT Rec. 1.432).
• NT1 Network Termination
• This NTI line termination includes optoelectric and electro-optical converters, correctly terminates the network-side part of the connection line with regard to operation, administration and maintenance (OA) and provides a standardized bidirectional broadband interface, the so-called Tg-, in the direction of the subscriber. Interface, also called user network interface (UNI), available.
• OA administration and maintenance
• Tg- bidirectional broadband interface
• UNI user network interface
• connection configurations which contain a real NTI line termination in the area of responsibility of the network operator, this is relatively problem-free and comprehensive, since in the so-called overhead of the B-ISDN signal (in the bytes provided in the STM-1 frame) or with pure cell transmission in the OAM cells provided for this purpose, a wealth of relevant OAM information can be continuously transmitted in both directions between the NTI line termination and the switch or the corresponding network-side broadband subscriber line unit, and there in the NT1- Suitable electrical, optical or at least logical loops between forward and backward direction can be formed at the line termination.
• a method for monitoring the part of an optical broadband connection line, in particular the subscriber line, lying between an optical fiber connection unit, in particular the exchange-side subscriber line unit, and a defined passive optical interface is already known in the fiber optic connection unit, a sinusoidal pilot tone signal of lower amplitude with a frequency that lies outside the spectral range occupied by the information signal to be transmitted is added to the electrical control signal of the optical transmitter provided there, at the passive interface a small part of the the connection unit optical signal transmitted to the subscriber is branched off, if necessary by reflection deliberately caused by an optical plug connection provided at the passive interface, and is led back in the direction back to the connection unit, where it is provided in the connection unit ⁇ that optical receiver is converted into an electrical signal together with the optical signal received by the subscriber, and that the pilot tone signal contained therein is branched off by means of a frequency-selective filter and in its amplitude of a one- or multi-stage threshold value decision is thrown, the result of which is a measure of the quality of
• the evaluation of the reflected signal can be impaired or made more difficult by the fact that the desired reflection at the passive interface are covered by additional reflections at other points on the optical connecting line to be monitored, and the invention now shows a way of reducing the conditions caused by such additional reflections. counter impairments in the evaluation of the desired reflection.
• the invention relates to a method for monitoring the part of an optical broadband connection line, in particular the subscriber connection line, lying between an optical fiber connection unit, in particular the exchange-side subscriber connection unit, and a defined passive optical interface;
• this method is characterized in that a binary pseudo-noise random signal is also transmitted from the fiber optic connection unit together with the information signal to be transmitted in the downstream direction via the optical broadband connection line, with a small portion from the passive interface of the optical downstream signal transmitted by the connection unit in the upstream direction is led back to the connection unit, where it is reflected in the optical receiver provided there, together with portions of the optical reflected at other reflection points on the optical broadband connection line
• Downstream signal and the optical upstream signal received via the optical broadband connection line is converted into an electrical signal, and that this electrical signal and the original, but corresponding to the signal propagation time on the broadband connection line from the fiber optic connection unittowards the passive interface and back again time-delayed pseudo-noise binary signal is fed to a signal correlator having a multiplier with
• the invention advantageously enables simple and secure monitoring of an optical broadband connection line between an exchange-side connection unit and a defined passive optical interface, which limit the network operator's range of words; the exchange-side connection unit can also be set apart from the actual exchange, and likewise the passive optical interface does not have to be provided directly in front of a subscriber location.
• the bias current of a laser diode provided as an optical transmitter in the fiber optic connection unit can be amplitude-modulated with the binary pseudo-noise random signal.
• the binary pseudo-noise random signal it is also possible for the binary pseudo-noise random signal to be additively superimposed on the electrical control signal of the optical transmitter provided there in the fiber optic connection unit.
• the electrical control signal of the optical transmitter provided there has a frequency range occupied by the information signal to be transmitted horizontal pilot tone signal modulated with the binary pseudo-noise random signal is added;
• the supported pseudo-noise binary signal sequence must then be demodulated on the receiver side before the correlation.
• the time delay can advantageously be implemented in such a way that the pseudo-noise binary signal required on the transmitter side and the time-delayed pseudo-noise binary signal to be fed to the correlator are provided by two separate pseudo-noise Generators with correspondingly different start values (presetting shift register chains) are generated.
• Clarified 1 shows the monitoring of an optical broadband connection line with only one optical fiber
• FIG. 2 shows the monitoring of an optical broadband connection line with two separate optical fibers for the two transmission directions
• FIG. 1 schematically shows, in a scope necessary for understanding the invention, a bidirectional fiber optic (light waveguide) telecommunication system with a (preferably monomode) fiber optic connecting line OAL with only one optical fiber for the transmission of the optical Signals of both transmission directions are shown; this optical connection line, which in the exemplary embodiment according to FIG. 1 extends between a subscriber line unit LT on the exchange side and a subscriber station TSt, may be to be monitored from the exchange point up to a passive optical interface PNT1.
• the passive interface PNT1 is realized with an optical plug connection, in which the optical see end face of the connector part arranged on the switchboard may be provided with a reflective layer r.
• a small part of the optical signal transmitted from the connection unit LT to the subscriber station TSt is branched off at the passive interface PNT1 and is led back to the connection unit LT in the reverse direction. In the exemplary embodiment according to FIG. 1, this takes place in such a way that a part of the light transmitted from the connection unit LT is reflected at the passive interface PNT1.
• the optical signal returned to the connection unit LT is converted there into an electrical signal in the optical receiver e ⁇ o (possibly together with the optical signal received from the subscriber station TSt).
• the wavelength of the switching-side laser transmitter e / o is approximately 1.3 ⁇ , for example, approximately equal to the wavelength of the electro-optical converter (not shown in detail in FIG.
• the wavelengths used for the two transmission directions must not be exactly or almost exactly the same.
• the wavelengths are therefore designated 1.3 ⁇ - and 1.3 ⁇ +.
• an optical window lying at 1.55 ⁇ for example, can also be used.
• the optical signals of the two transmission directions are transmitted in different optical windows, for example at 1.3 ⁇ in one transmission direction and at 1.55 ⁇ in the other transmission direction, then the reflection point on the passive optical interface PNT1 can also be designed to be wavelength-selective, so that essentially only the optical signal transmitted in the direction of the subscriber station TSt and containing the pseudo-noise (PN) binary signal is partially reflected.
• PN pseudo-noise
• FIG. 2 schematically shows an embodiment of a bi-directional fiber optic telecommunication system with a (preferably monomode) fiber optic connection line OAL, which has a separate optical fiber for each direction of transmission, to the extent necessary for understanding the invention.
• the optical signals of the two transmission directions can be transmitted on the same wavelength or on different wavelengths.
• This optical connection line OAL which in the exemplary embodiment according to FIG. 2 in turn extends between an exchange-side subscriber line unit LT and a subscriber station TSt, may in turn be monitored from the exchange side up to a passive optical interface PNT1.
• a PN binary signal is again added to the information signal to be transmitted via the fiber optic connection line OAL.
• a small part of the optical signal transmitted from the connection unit LT to the subscriber TSt is in turn branched off at the passive interface PNT1 and is guided in the reverse direction back to the connection unit LT.
• 2 indicates that on the side of the passive optical interface PNT1 facing the connection unit LT there are branching devices V in the form of passive optical couplers, between which an optical feedback path R runs.
• the coupling or decoupling of the optical signals can take place by means of asymmetrical passive optical couplers.
• the method according to the invention is based on the correlation of a pseudo-noise (PN) bit sequence generated by a generator G with the reflected portion of an optical signal, the mean value of which is the same by means of the laser bias current i ß ias " ⁇
• the bias current i ß ias of the laser diode (line termination on the subscriber line side) is amplitude-modulated with the random sequence of the PN generator G with a small stroke of, for example, 10%.
• the information signal to be transmitted in the downstream direction from the fiber optic connection unit LT via the optical broadband connection line OAL and on the other hand with its mean value modulated with the PN bit sequence is at all possible reflection points the optical broadband connection line OAL and thus also more or less strongly reflects the passive optical interface causing a defined (desired) reflection (eg with a degree of reflection of 10%).
• the optical signal received by the connection unit LT in the upstream direction contains the TSt information signal originating from the subscriber station TSt, reflected portions of the LT information signal transmitted in the downstream direction, reflected portions of the PN binary signal and interference
• This signal is now, if necessary amplified, but not yet (time) regenerated, with the PN sequence delayed by a delay period ⁇ , which corresponds to the signal propagation time from the connection unit LT to the passive interface PNTI and back again correlated, ie multiplied and then integrated over several PN sequences;
• the amplitude of the output signal resulting from the correlation corresponds to the reflected signal components with an optical signal transit time lying in the range of the time delay ⁇ .
• This correlation signal is finally monitored for the occurrence of the pseudo-noise binary signal reflected by the passive interface PNT1 in accordance with the signal transit time, which can be done by means of an amplitude threshold decision. Threshold value decisions are generally known, so that no further explanation is required for this. It should be particularly noted in this connection that the correlation signal can also be subjected to a not only one-stage, but multi-stage threshold value decision, the result of which additionally forms a measure of the quality of the optical connection line OAL between the fiber optic connection unit LT and the passive interface PNT1 .
• the time delay ⁇ can advantageously be realized in that the PN sequences for the pre-current modulator A (in Fig.l) and for the correlator X, J (in Fig.l and Fig.2) from two separate PN generators (G, G in Fig. 2) formed with shift register chains, in which different Starting values in the form of a correspondingly different pre-assignment of their shift register chains are specified by a microprocessor ⁇ P.
• the choice of these starting values determines the time delay ⁇ of the PN sequence fed to the correlator X, J (in FIGS. 1 and 2) compared to that to the modulator (A in FIG. 1; e / o in FIG. 2) PN sequence supplied.
• the achievable signal-to-interference ratio of the integrated signal and thus of the correlator output signal depends on the parameters of the optical signal components, but essentially also on the integration time.
• the correlator output signal (integration result) can be A / D converted and further processed in the subsequent microprocessor ⁇ P. If the group speed of the optical signal is known, the distance of the reflection location can be calculated.
• the microprocessor ⁇ P can initially also take on the setting of various time delays ⁇ in one calibration process in order to determine all the reflection components on the individual sections of the route.
• 3 shows schematically the course of the correlator output signal as a function of the time delay ⁇ .
• the measuring points highlighted on the correlation curve have a stood, which corresponds to the length of a single bit of the PN sequence.
• the correlation curve may be based on a clock rate of 100 kHz and a pseudo-noise bit sequence with a length of 2 5 -l bit (and thus a period of 310 ⁇ s); the group speed of the signal on the optical route may be 0.2 km / ⁇ s.
• a return and return time or time delay ⁇ of 200 ⁇ s in the example corresponds to a distance of the reflection location of 20 km;
• the passive interface PNT1 (in Fig.l and Fig.2) may be located at this distance in the example. Taking into account the double transit time of the signal towards the reflection location and back again, there is a spatial resolution ⁇ l ⁇ 1 km and a monitorable route length l max of a maximum of 31 km.
• the monitoring of the part of the optical part between the fiber optic connection unit LT (in FIG. 1 and FIG. 2) and the defined passive optical interface PNT 1 (in FIG. 1 and FIG. 2) is then carried out Broadband connection line OAL (in Fig.l and Fig.2) is then selected a fixed time delay ⁇ of 200 ⁇ s in the example, in order to ensure the timely occurrence of the pseudo reflected by the passive interface PNTl (in Fig.l and Fig.2) 3 to monitor the noise binary signal on the basis of the occurrence of a correspondingly high correlator output signal amplitude A, as is shown in FIG.
• the time delay ⁇ for normal operation is expediently chosen so that it at least is approximately equal to the signal transit time from the fiber optic connection unit LT to the passive optical interface PNT1 (in FIGS. 1 and 2) and back, because then the amplitude distance a to the direct current component ucs (undesired correlation signal) of the correlator output signal is particularly large.
• This DC component is due on the one hand to the fact that the number of -1 signal elements in a PN sequence is not equal to the number of +1 signal elements, and on the other hand to the fact that in addition to that from the passive interface PNT1 (in FIG .l and Fig.2) originating from the reflection signal, other signals also reach the correlator input.
• a corresponding PN amplitude signal can also be additively superimposed on the electrical information signal, as is also indicated in FIG. 2.
• the overall signal then modulates the optical output power of the laser.
• a pilot tone signal modulated with the pseudo-noise binary signal can also be added in the fiber optic connection unit LT to the control signal of the optical transmitter provided there whose frequency is outside of the upstream direction transmitting information signal occupied frequency range; In the receiver part, the PN binary signal sequence that is carried must then be demodulated again before the correlation.
• the invention is not tied to the fact that, at a switching center, subscriber-specific fiber optic connection units (LT in FIG. 1 and FIG. 2) each have a subscriber-specific optical connection line (OAL in FIG. 1 and FIG 2) are provided; Rather, the invention can also be used in a passive optical network in which a plurality of subscribers or, generally speaking, decentralized telecommunication devices are each connected to an optical splitter via a separate optical connecting line, which is connected directly or is connected via at least one further optical splitter to a common switching-side fiber optic connection unit via an optical waveguide bus.
• a passive optical interface PNT1 Seen from the switching side, in front of the branches, a passive optical interface PNT1 is provided, with the aid of which monitoring of the optical transmission path from the switching side is possible at least up to this interface; the statements made in relation to FIG. 1 (or in the case of a two-fiber version FIG. 2) apply in a corresponding manner.

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Citations (3)

• 1994
  • 1994-12-01 CA CA 2178952 patent/CA2178952A1/en not_active Abandoned
  • 1994-12-01 EP EP95902036A patent/EP0734622A1/de not_active Withdrawn
  • 1994-12-01 WO PCT/DE1994/001424 patent/WO1995017053A1/de not_active Application Discontinuation
  • 1994-12-01 JP JP7516447A patent/JPH09506748A/ja active Pending
  • 1994-12-01 RU RU96114955A patent/RU2115245C1/ru active

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