CN1046830C - Fiber Optic Cable Monitoring System - Google Patents

Abstract

Methods and systems for monitoring the condition of a fiber optic communications cable. Two laser sources are used and the optical signal attenuation at two different wavelengths is monitored simultaneously to determine and analyze the mechanical state of the cable structure. A specific detector code is assigned to each joint and the sensor, a water activated battery sensor, drives the optical joint detector by moisture detection. The moisture entering the connector piece being monitored wets the wrapping tape, energizing the sensor to generate sufficient electrical energy to drive the timing and code generators and modulation circuitry in the detector unit. The modulated optical signal is monitored at the device terminal and the location of the decoded alarm detector is addressed.

Description

Fiber Optic Cable Monitoring System

The present invention relates to the monitoring of communication cables, and more particularly to the monitoring of fiber optic communication cables.

Telephone and some other communication cables are subject to environmental and human-caused damage and wear. Severe weather conditions such as high winds, snow, rain, torrents, and lightning can damage exposed cables. Hazards may be from nearby structures or acts of vandalism. Ingress of rainwater or groundwater into damaged cable cores or splices is a major cause of service interruptions (broken wires). Accordingly, various efforts have been made to keep the cable in a state of repair and to prevent water from entering the cable structure.

Often, damage does not result in an immediate loss of service, but rather in the gradual deterioration of the cable system, which often results in cable failure and service interruption. Future repairs to it must be done in a very urgent situation. On the one hand, it will cost a lot of repair costs, and on the one hand, it will also cause loss of income.

From the first major cable installations to the present, some maintenance monitoring systems have been in use to provide early warning of cable failures. This allows people to schedule maintenance without loss of service and costly repairs. The earliest systems used air pressure to prevent water from breaking through the cable or fittings, and detected faults by measuring the velocity of the airflow into the cable section.

Modern telephone cables, including fiber optic cables, are often filled with a water barrier compound to prevent water from entering the cable core. While providing good resistance to water attack, filled compositions also impede or severely restrict air flow, thus rendering air pressure monitoring systems useless. To overcome this limitation and provide maintenance monitoring for populated telephone cables, all-electronic systems were developed, such as those described in US Patent No. 4,480,251 to McNaughton et al. and US Patent No. 5,077,526 to Vokey et al.

Fiber optic cables constructed for certain applications, including as in overhead power transmission fixed conductors or suspended below phase conductors on towers, are dielectrically insulated Material. Therefore, conventional cable and joint monitoring methods requiring metallic electrical conductor components such as those described in the McNaughton et al. and Vokey et al. patents are no longer applicable.

OTDR technology has been used to monitor fiber optic cables and connectors. This technique shoots a pulse of light into the fiber and measures the reflected energy to determine the increase in energy loss. These methods are costly and require detection of specific moisture in the fiber bender in the connector assembly in an attempt to monitor water ingress, and furthermore, the characteristics of the connector bender are not always predictable and must be known precisely to each The exact optical distance of the connector. While active detection devices at the splice point would be preferred, the major difficulty is that with all dielectric cables there is no practical means of providing power to the splice to operate these devices.

According to one aspect of the present invention, a kind of moisture sensing signal generator is provided here, it comprises:

An electronically controlled code signal generating device is used to generate a fault signal according to the received electrical energy; an optical modulation device is coupled with the code signal generating device to generate a coded optical signal in response to the generation of the fault signal; and The sensor electrolysis device is electrically connected with the code signal generating device, the sensor device does not work when it is dry, and it works when it comes into contact with water to generate electrical energy and provide the electrical energy to the code signal generating device.

The moisture sensing signal generator is used to signal the penetration of moisture through the connector of the containing connector device, and the connector device maintains the alignment of the end optical fiber ends of the two optical fiber cables;

The light modulator includes displacement means for selectively displacing one of the fiber ends of one cable relative to a corresponding fiber end of the other cable;

The code signal generating means is coupled to the shifting means for selectively activating the shifting means.

The moisture detection sensor device includes two metal parts and a water-soluble ionizable solid between the metal parts.

Each of said metal members comprises an elongated strip encased within a porous electrically insulating material.

The metal parts and ionizable solids include a moisture detection strip.

The material of one of the metal parts is magnesium, the material of the other metal part is copper, and the ionized solid is copper sulfate.

The code signal generating device includes a device for generating an electrical signal.

The code signal generating means includes means for generating pulsed electrical signals.

According to another aspect of the present invention, there is provided a sensor unit for optical docking, which is used to signal the docking interference package connector of two optical fiber cables penetrated by moisture, the sensor unit comprising:

a butt joint, located at said butt joint, for maintaining alignment of the ends of the respective optical fibers of said cable;

a displacement device for selectively displacing one of the optical fiber ends of one cable relative to the corresponding optical fiber end of the other cable;

signal generating means, coupled to said mobile device, for selectively activating said mobile device; and

A moisture detection device, in response to the existence of moisture in the closing part, activates the signal generating device, and the moisture detection device includes: a moisture detection sensor device, in response to the contact of the sensor device with water, generate a voltage.

The moisture detection device includes: an elongated ribbon wrapped around the docking device.

The moisture detection device includes: two spaced apart metal parts for substantially extending the length of the strip, and the ionized solid is located between the two metal parts.

The signal generating means includes: means for generating encoded electrical signals.

The displacement device includes: a magnetic component coupled to the end of one optical fiber; an electromagnet adjacent to the magnetic component and electrically coupled to the signal generating device.

These aspects of the invention will be described in more detail below with reference to the accompanying drawings.

Embodiments of the invention are shown by way of example in the drawings. in:

Fig. 1 is a schematic diagram of a monitoring system according to the present invention;

Fig. 2 is the schematic diagram of fiber optic transmitter;

Fig. 3 is the schematic diagram of photodetector unit;

Figure 4 is a sectional view of a joint;

Fig. 5 is the sectional view of moisture detection sensor device;

Fig. 6 is a graph representing the coupling loss of the optical fiber connector relative to the offset of the optical fiber end;

Figure 7 is a schematic diagram of the optical receiver;

Figure 8 is a schematic diagram of an alternative embodiment of a photodetector unit;

Figure 9 is a graph showing the coupling loss of a fiber optic splice versus the axial separation of the fiber tip.

Referring to the drawings, and in particular FIG. 1 , a fiber optic cable monitoring system 10 associated with a fiber optic cable 12 is shown. The fiber optic cable shown is a single mode (sm) fiber optic cable with a length of up to 100Km. The illustrated cable includes a splice 14 portion along its length. Typically, a complete cable will contain many connectors. The cable includes a plurality of optical fibers 16 .

System 10 includes an optical transmitter unit 18 at one end of the cable and an optical receiver 20 at the other end. Most particularly as shown in FIG. 2, the light emitter is a dual wavelength laser emitter comprising a stabilized laser source 22 emitting light at a wavelength of 1300 nm and a second stabilized laser source 24 emitting light at a wavelength of 1550 nm. The laser source 22 is connected to a modulation amplifier 26 . Inputs to the amplifier include bias input 30 , modulation input 28 and negative feedback 32 . The modulation input has a frequency F1 at which to modulate the emitted 1300 nm optical signal. Laser 24 is likewise associated with amplifier 33 having modulation input 34 , bias input 36 and negative feedback 38 . The frequency of the modulation signal F2 is different from the modulation frequency F1. These lasers are combined into a wave-splitting multiplexing coupler 40 . The coupler combines the optical outputs of the lasers and splits the optical energy equally into N output ports. A fiber to be monitored is connected to each of these output ports. The pair of lasers then provides optical power to several monitored fibers or cables.

At the receiving end of the fiber is an optical receiver 20 (FIG. 7) that intercepts and detects laser light from each monitored fiber at a PIN detection diode 42. The light is converted by the diode into an electrical signal that Amplified by preamplifier 44. The electrical signal contains frequency components F1 and F2 which are separated by bandpass filters 46 and 50 and measured by measurement circuits 48 and 52 . The optical attenuation of the fiber length at both wavelengths is calculated from the measured amplitudes.

The photoreceiver also includes a pulse detector 54 for monitoring pulses generated in the photodetector unit. The photodetector unit will be described in more detail later.

The output of the optical receiver is sent to a multiplexer 56 which scans the output from each fiber being monitored and provides an input to a central office terminal 58; An alarm is issued when the detected fiber attenuation exceeds a predetermined maximum attenuation. The terminal also includes a decoding circuit 60 for decoding the pulses from the pulse detector 54 .

Referring particularly to FIGS. 3 , 4 and 5 , connector 14 includes a modulator 62 for generating pulses in the light emitted by each fiber for detection by pulse detector 54 . The modulator includes a connector 64 with a V-groove 66 that aligns the ends of the fiber being monitored passing through the cable connector. At the splice, the fiber optic tip 70 has a small ferrous metal element 72 attached to its top surface. It is located immediately under one pole of the modulator electromagnet 74 . The ferromagnet 74 is electrically connected between the moisture detection sensor 76 and the collector 78 of the driving transistor 80 . The emitter of the transistor 80 is connected to the moisture detection sensor 76 and its base 84 is connected to a code generator 86 which in turn is connected to a clock 88 . Both the code generator and the clock are connected across the terminals of the moisture detection sensor 76 .

The detection sensor 76 is a one meter strip 90 having magnesium conductors 92 and copper conductors 94 extending the length of the strip. Each conductor is embedded and pasted in the permeable PVC plastic isolation layer. Between the two conductors, the spacer material 96 separating them is a water soluble ionosphere of copper sulfate. In use, the moisture detection sensor tape is wrapped around the splice bracket 97 (FIG. 4) to form the splice. If water seeps into the junction box, the water dissolves the electrolyte salts, creating electrolyte that excites the sensor to generate a DC voltage. Separation of the sensor components ensures essentially unlimited life in the dry state, the sensor then acting as a battery driving the clock, code generator, driver and modulator electromagnets. The driver provides code current pulses to the electromagnet under the control of the clock and code generator. The current pulses in the electromagnet coils create magnetic pulses that attract the ferromagnetic member 72 attached to the fiber tip 70 , thereby pushing the fiber tip out of alignment with the fiber tip 68 . As shown in Figure 6, misalignment of the fiber tip on the order of 5 microns or more will significantly reduce the coupled optical energy and produce an AM pulse stream at a rate determined by the code generator.

The energy required to deflect a 125 micron glass fiber by 5 to 10 microns is very small. These detector circuits are designed using low voltage microwatt CMOS integrated circuits. As a result, a single sensor battery one meter long can power the modulator and some of the associated circuitry for several weeks. Detection of wet joints is thus guaranteed.

As mentioned earlier, the optical receiver intercepts and detects the laser light from the fiber being monitored and converts it into an electrical signal. The pulses detected by the pulse detector 54 are decoded in a decoding circuit to identify the connector from which the pulses occurred. For these purposes, the code generator 86 for each connector will generate a unique pulse signal.

The optical attenuation across the fiber at the two monitor signal wavelengths is calculated from the measured amplitude of each converted electrical signal. Any additional fiber attenuation above rating is analyzed.

If a similar increase in attenuation is measured at both wavelengths, then this increase in attenuation can be assumed to be due to microbending, which may be caused by cable extrusion or temperature-related structural changes in the cable. If a noticeable increase in attenuation is only detected at 1550nm, the problem may be related to macrobending, which is usually caused by kinks in the cable or breaks in the fiber.

An alternative embodiment of a light detector is shown in FIG. 8 . This embodiment differs from the embodiment shown in FIG. 3 in that the modulator employs a capillary type connector 100 in which the fiber ends are aligned in a ferrule 102 . One end 104 of the fiber is fixed and the other end is movable but biased towards the fixed end by a spring. A ferrous ferrule 108 is secured to the movable end of the fiber. The modulator coil 110 surrounds the optical fiber adjacent to the ferrule 108 . When energized, the coil draws the fiber end 106 away from the fiber end 104, thus modulating the signal on the fiber.

A plot of coupling loss versus axial fiber tip separation is given in FIG. 9 . Fiber motion is performed at an amplitude level greater than the offset required to produce the same coupling loss.

Where the modulator and associated electrical and mechanical components may not be conveniently mounted into a connector bracket or other connector assembly used in a connector assembly, suitable locations on the back or side of the bracket may be utilized.

While one embodiment of the invention has been described above, it should be understood that other embodiments can also be made within the scope of the invention. Thus, for example, the photodetector unit may employ modulators other than the electromagnetic ones shown. For example, a piezoelectric crystal or some other electromechanical modulation device could be used to change the electrical pulse to a mechanical deflection and subsequent coupling decay. Any other device that functions as an optical switch can be used. Moisture detection sensors can be made from any two metals selected as long as they provide a suitable semi-electrolytic reaction in the presence of a suitable electrolyte. It should therefore be understood that the invention is not to be considered limited to the particular embodiments disclosed. The invention is limited only by the appended claims.

Claims (13)

1. A kind of moisture sensing signal generator, is characterized in that, comprises: An electric control code signal generating device, which is used to generate a fault signal according to the received electric energy; optical modulation means, coupled with said code signal generating means, in response to the generation of the fault signal, and generate a coded optical signal; and The electrolytic sensor device is electrically connected with the code signal generating device, the sensor device does not work when it is dry, and it works when it is in contact with water, generating electric energy and providing the electric energy to the code Signal generating device. 2. The moisture sensing signal generator according to claim 1, characterized in that: The moisture sensing signal generator is used to signal the penetration of moisture through the connector of the containing connector device, and the connector device maintains the alignment of the end optical fiber ends of the two optical fiber cables; The light modulator includes displacement means for selectively displacing one of the fiber ends of one cable relative to a corresponding fiber end of the other cable; The code signal generating means is coupled to the shifting means for selectively activating the shifting means. 3. The moisture detection signal generator according to claim 1 or 2, characterized in that said moisture detection sensor device comprises two kinds of metal parts and a water-soluble ionizable solid between the metal parts. 4. 3. The moisture sensing signal generator of claim 3, wherein each of said metal members comprises an elongated strip encased in a porous electrically insulating material. 5. 4. The moisture sensing signal generator according to claim 4, wherein said metal member and said ionizable solid comprise a moisture detection strip. 6. The moisture sensing signal generator according to claim 5, wherein the material of one of the metal parts is magnesium, the material of the other metal part is copper, and the ionized solid is copper sulfate. 7. The moisture sensing signal generator according to claim 1, wherein said code signal generating means comprises means for generating electrical signals. 8. A moisture sensing signal generator according to claim 7, wherein said code signal generating means comprises means for generating pulsed electrical signals. 9. An optical docking sensor unit is used to send out the signal of the docking interference packaging connector of two optical fiber cables penetrated by moisture, and it is characterized in that the sensor unit includes: butt joints, located at said butt joints, for maintaining alignment of the ends of respective corresponding optical fibers of said cables; a displacement device for selectively displacing one of the optical fiber ends of one cable relative to the corresponding optical fiber end of the other cable; signal generating means, coupled to said mobile device, for selectively activating said mobile device; and A moisture detection device, in response to the existence of moisture in the closing part, activates the signal generating device, and the moisture detection device includes: a moisture detection sensor device, in response to the contact of the sensor device with water, generate a voltage. 10. 9. An optically coupled sensor unit according to claim 9, wherein said moisture sensing means comprises: an elongated ribbon wrapped around said docking means. 11. The optically connected sensor unit according to claim 10, wherein said moisture detection means comprises: two spaced metal parts for substantially extending the length of said strip; between the two metal parts described above. 12. 9. An optical link sensor unit according to claim 9, wherein said signal generating means comprises means for generating an encoded electrical signal. 13. The optical connection sensor unit according to claim 12, wherein said displacement means comprises: a magnetic member coupled to said one optical fiber end; an electromagnet adjacent to said magnetic member and The signal generating device is electrically coupled.

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