Abstract:
An optical leak detection instrument. An electromagnetic source is provided for generating an electromagnetic signal. An interface allows the instrument to communicate with a system under test. A portion of the instrument is provided for receiving the electromagnetic signal. A switch is operatively connected to the electromagnetic source for initiating propagation of the electromagnetic signal. Optionally, a handle is operatively connected to the instrument.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to fault location in fiber optic systems, and more specifically, to an optical leak detection device employing an optical transmitter, a synchronous receiver, an optical filter, and indicators to permit the troubleshooting of optical fiber systems. 
     BACKGROUND OF THE INVENTION 
     The development and implementation of fiber optics has radically changed the world. Using fiber optics, data, voice and video information can be digitized, transmitted and received almost instantly throughout the world. With the development of fiber optics, transmission speeds are typically limited only by the speed and capacity of the sending and receiving means. At the same time, the optical fiber used in fiber optic systems is more reliable and more secure than traditional copper transmission lines. While the use of optical fiber for signal transmission has many advantages, the costs associated with the installation and maintenance of optical links can be significant, particularly when compared to copper links. This is often due to the lack of effective diagnostic tools for troubleshooting optical fiber systems. 
     A basic fiber optic system comprises three main components: a transmitter, a transmission medium, and a receiver. A fiber optic transmitter converts an electrical signal to a light signal, which is subsequently emitted from the transmitter. The light signal is typically within the non-visible spectrum such that there is no visible indication to anyone proximate the fiber optic system that signal is present. The transmission medium carries the light signal from the transmitter to the receiver. The receiver converts the light signal into an electrical signal. While the concept of a basic fiber optic system is easy to envision, actual installation and troubleshooting of a fiber optic system can be a complex and expensive process. 
     Optical fiber is generally constructed in a core and cladding configuration where two dissimilar types of glass are drawn together in a single strand. Because of the differences in the two types of glass, light entering the core of the strand will propagate along the strand by means of reflection until it reaches the far end of a strand or encounters a fault. While optical fiber, a glass strand generally 125 μm in diameter, can be a delicate structure, it tends to be robust in practical application because it is protected by a polymer buffer and up to several layers of jacketing. 
     The robust buffer and jacket design of commercial fiber optic cables virtually eliminates problems within the cable itself. Instead, the vast majority of problems occur in or near a patch cabinet or a splice enclosure where the cable is stripped away and handling of individual strands must occur. 
     Discussion of Related Art 
     As the light (or, more generally, electromagnetic energy) used in fiber optic communication systems is often non-visible, the precise location of a fault is not readily apparent. While existing quantitative test instruments such as optical time domain reflectometers (OTDRs) and loss test sets can locate damaged fibers and fault locations to within a few meters, this level of macroscopic accuracy does not permit the resolution of problems. Such accuracy can isolate a problem to a specific cabinet or splice enclosure but cannot determine where exactly inside a given enclosure the error has occurred. 
     U.S. Pat. No. 6,381,011 for OPTICAL FAULT LOCATOR, by Nickelsberg et al., granted Apr. 30, 2002 discloses a handheld optical fault locator used to determine the distance to a discontinuity in a fiber optic cable, such as a break, nick, cut, scrape, indentation, or the like, a splice, a connector, or the end of the cable. The locator includes an analog front end, a complex programmable logic device (CPLD), a laser diode and drive, a microcontroller, at least one input, and at least one output. 
     U.S. Pat. No. 6,879,741 for SAMPLING END FOR FIBER OPTIC PROBE, by Salerno et al., granted Apr. 12, 2005 discloses a fiber optic probe device having a sampling end positionable over optical fibers. The sleeve could be releasably attached to the fiber optic probe device. A sample chamber including a reflective surface can be formed at the distal end of the sampling end. 
     U.S. Pat. No. 7,245,800 for FIBER OPTIC INTERCONNECT WITH VISIBLE LASER INDICATOR AND FAULT DETECTOR, by Uhlhorn, granted Jul. 17, 2007 discloses an optical transmission system for transmitting optical data. An optical transmitter, an optical receiver and a transmission medium capable of providing a visual indication of transmission status as well as the location of potential faults within the transmission medium are provided in the detector. The optical transmitter supplies a first nonvisible light source for transmitting optical data and a second visible light source providing a visual indication of transmitter operation and possible faults. The first nonvisible light source and the second visible light source are transmitted across the transmission medium whereby they are received by the optical receiver. The optical receiver includes a filter member for removing the visible light source prior to converting the second visible light source into an electrical signal. 
     U.S. Pat. No. 5,138,690 for FIBER IDENTIFIER, by Cox, granted Aug. 11, 1992 discloses a fiber identifier for detecting the presence or absence of an active data signal or a test signal in an optical fiber. The instrument includes a piston which positions a portion of the fiber under test against, an optical detector, the piston being located within a housing, and the housing being attached to a drive rod. The rod is responsive to a levered actuation mechanism, but a damper controls the movement rate of the rod, and hence the piston, to bend the fiber. A spring within the housing is used to limit the pressure applied by the piston against the optical fiber. The housing also includes electrical contacts to sense the position of the piston and, indirectly, the position of the rod. 
     While existing technology can find optical faults in specific circumstances, it would be advantageous to employ a leak detection probe system with a more highly selective and sensitive receiver to detect light leakage from a majority of the aforementioned faults. It would be of further advantage to employ a leak detection probe system which does not require physically handling delicate optical fibers. It would be yet of further advantage for such a probe system to utilize the non-visible light for which a typical fiber system is designed. Moreover, it would be advantageous to employ a visible and/or audible element within the leak detection probe system to indicate the presence of optical energy of interest or the presence of energy leakage due to faults. 
     It is therefore an object of the invention to provide a handheld optical leak detection instrument containing both an optical receiver circuit and optical emitter in a single probing device. 
     It is another object of the invention for the probe device to utilize its own source timing to permit a synchronized detection of the source signal for high sensitivity and rejection of ambient light. 
     It is yet another object of the invention for the source portion of the probing device to be attached to a fiber optic cable and the receiver portion to be used to scan the cable for leakage. 
     It is yet another object of this invention for the probing device to have a narrow or tapered detection tip to allow users to locate a light leak in small areas such as those encountered in a fiber optic splice or break-out enclosure. 
     It is yet another object of the invention for the probing device to work with any wavelength of electromagnetic energy, including visible light, or any form of photodetector. 
     It is yet another object of the invention for the probing device to utilize a tethered or detachable fiber optic wand to couple light to the receiver circuitry. 
     It is yet another object of the invention for the probing device to include lenses or fiber coupled devices in order to make its sensing tip narrower. 
     It is yet another object of the invention for the probing device to have two components with optically or electronically tethered source and receiver units sharing timing signals. 
     It is yet another object of the invention for the probing device to have two components with RF linked source and receiver circuits sharing timing signals. 
     It is yet another object of the invention for the probing device to be compatible with a cellular telephone, radio, or network interface, allowing the reception of receiver timing signals from a remote source. 
     It is yet another object of the invention for the probing device to employ asynchronous detection schemes using the same receiver circuitry. 
     It is yet another object of the invention for the probing device to have optical or electrical filtering in addition to the synchronized detection. 
     It is yet another object of the invention for the probing device to incorporate an audio and/or visual indicator indicating the presence of leakage. 
     It is yet another object of the invention for the output of the probing device to be a numeric display indicating actual detected power levels. 
     It is yet another object of the invention, for the output of the probing device to be a calibrated pass/fail indication. 
     It is yet another object of the invention for the probing device to incorporate a variable intensity lamp at the detection tip in order to illuminate fault locations as they are detected. 
     It is yet another object of the invention for the probing device to incorporate adjustable gain. 
     It is yet another object of the invention for the probing device to incorporate interchangeable heads to allow for different optical filtering or lens configurations. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided an optical leak detection instrument. An electromagnetic source is provided for generating an electromagnetic signal. An interface allows the instrument to communicate with a system under test. A portion of the instrument is provided for synchronously or asynchronously receiving the electromagnetic signal. A switch is operatively connected to the electromagnetic source for initiating propagation of the electromagnetic signal. Optionally, a handle is operatively connected to the instrument for ease of handling and to reduce the likelihood of interference with active optical fibers. 
     The present invention addresses the aforementioned needs. An optical receiver can provide a visual and/or audible indication of the presence of non-visible optical radiation thereby indicating the presence of faults in a fiber link, optical tracer signals, or live data. The inventive instrument comprises a synchronous/asynchronous receiver and synchronous energy source. The receiver is capable of detecting either an internally generated and synchronously modulating signal, an externally generated and modulating tracer signal, and/or light signals carrying communication data. The present invention also includes electronic and field changeable filtering to further differentiate electromagnetic signals of interest from ambient noise signals. 
     The synchronous nature of the internal energy source and receiver pair and the ability to directly connect that synchronous source to optical systems while probing occurs will permit local fault finding sensitivity advances of up to three orders of magnitude over existing technology while maintaining the same level of noise immunity. The field changeable nature of the optical filtering further permits a unique ability to detect specific asynchronous data channel activity in wavelength division multiplexed fiber networks. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A complete understanding of the present invention may be obtained by reference to the accompanying drawings, when considered in conjunction with the subsequent detailed description, in which: 
         FIG. 1  illustrates a fundamental fiber link of the prior art; 
         FIG. 2  illustrates the basic mechanical structures of a fiber link of the prior art; 
         FIG. 3  illustrates patch panel mechanical structures and fault points of the prior art; 
         FIG. 4  illustrates the structure of an optical fiber of the prior art; 
         FIG. 5  is a section view of a length of broken optical fiber of the prior art; 
         FIG. 6  is a section view of a length of bent optical fiber of the prior art; 
         FIG. 7  is a schematic view of a fiber identifier of the prior art; 
         FIG. 8  is a schematic view of an infrared light probe of the prior art; 
         FIG. 9  is a schematic view of a visible fault locator of the prior art; 
         FIG. 10  is a schematic view of an improved fault detection; 
         FIG. 11  is a schematic view of the apparatus in accordance with the present invention; 
         FIG. 12  is block diagram of circuitry in accordance with the current invention; 
         FIG. 13  is a top view of the instrument in accordance with the current invention; 
         FIG. 14  is a bottom view of the instrument in accordance with the current invention; 
         FIG. 15  is a side view of the instrument in accordance with the current invention; and 
         FIG. 16  is a rear view of the instrument in accordance with the current invention. 
     
    
    
     For the sake of clarity and brevity, like elements and components of each embodiment may bear the same designations throughout the description. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention features a novel way of quickly and precisely locating optical cable faults and light leakage areas which are not easily detectable with current fault locating technology. In a first embodiment, the instrument comprises a fiber optic diagnostic reception apparatus for providing an indication of a fault location along a fiber optic path. The fiber optic diagnostic reception apparatus includes a receiver having a detector and filter circuitry and a synchronized light source, wherein the detector captures non-visible light for analysis. Results of the analysis are a combination of visible and audible indications made available to the user. 
     Referring now to  FIG. 1 , there is shown a basic transmitter  1  and receiver  3  schematic diagram of fiber optic operations over an optical fiber or transmission medium  2 , well known in the prior art. Transmitter  1  converts an electrical signal to an electromagnetic signal and receiver  3  reverses the conversion to an electrical signal. 
     An in-depth representation of a physical fiber optic link is shown in  FIG. 2 . It consists again of a transmitter  5  which emits light via connector assembly  6  into fiber optic cord  10 , which is attached to a patch cabinet  20  by way of a connector and adapter assembly  15 . The cabinet may house hundreds of connector assemblies, splices, and strands of fiber coming from a main trunk cable  25 . Over distance, a trunk cable may need to be constructed of several cables which are joined by splices  30  housed in a splice enclosure  35 . At the far end of the link, there is a second patch cabinet  40  and cord  45  before reaching the receiver  50 . 
     A detailed view of a patch cabinet  145  in  FIG. 3  better exemplifies the level of accuracy required in the location and repair of faults. Light entering the cabinet  145  via patch cord  100  must pass through patch connector  105 , through a bulkhead adapter  110 , through a trunk connector  115 , before entering a strand of trunk fiber  120 . The fiber will generally wrap over a management mandrel  125 , pass through a fan-out device  130 , and enter a cable through a breakout point  135  in the trunk cable  140 . Since a bend or fracture may occur at any of these locations within or near the patch cabinet  145 , and since repair costs between these locations may vary by several orders of magnitude, it is critical to have fault isolation capability on the order of centimeters as opposed to meters. A similar mechanical configuration exists in most splice enclosures thereby creating the same cost of repair concerns but with the additional factors of high labor cost and repair time due to physical location issues. To date, only three types of leak indication or detection device have been available for this type of fault location, the fiber identifier, the infrared light probe, and the visible fault locator. 
     Referring now to  FIG. 4 , there is shown a perspective cutaway schematic view of the structure of optical fiber. A glass core  200  is surrounded by cladding  205  which, in turn, is surrounded by buffer coating  210  and, finally, a jacket  215 , all concentrically arranged. Optical fiber cladding  205  is generally covered in a standardized color-coded buffer jacket  215  and visible laser light can be highly attenuated in non-matched color strands. For example, visible fault locator (VFL) devices rarely work well with black, green, brown, and blue colored buffers. In addition, components such as connectors, adapters, and splices often have structures that prevent visible light penetration thereby inhibiting fault detection. These factors limit the usefulness of the device to only a small percentage of potential problems. VFLs also suffer from the results of high attenuation of visible wavelengths in typical communication grade glass, useful operation distances for fault location are generally limited to less than 5 km, a short distance in fiber terms where optical paths can sometimes exceed 100 km. Furthermore, VFLs are often rendered useless in bright ambient light and outdoor conditions because the low level glow from VFL indicated faults simply cannot be seen. 
     Referring now to  FIGS. 5 and 6 , there are shown section views of a broken and a bent optical fiber, respectively, of the prior art. After optical fiber is installed, a variety of fault conditions may either exist or develop over time whereby the optical path may be degraded or broken entirely. The optical fiber may be broken, bent, damaged, crimped, cut, incorrectly routed while connectors or splice junctions may be damaged or poorly assembled. When a break  235  in an optical fiber occurs, light no longer propagates along the strand but instead refracts from the core glass and escapes at the point of damage  240 . The same escape of light may occur when fiber is bent too tightly  245  and the path of light in the core allows it to escape  250 . In both circumstances, light is lost and the communication link is either degraded or broken. 
     Referring now to  FIGS. 7 through 9 , there are shown schematic views of a fiber identifier, infrared light probe, and visible fault locator, respectively, of the prior art. 
     The fiber identifier  270  utilizes a fiber bending and clamping structure  265  to force light out of a fiber  260  for analysis. Fiber identifiers are sometimes used to indirectly locate a fault by repeatedly clamping a section of fiber to follow an active region  275  of fiber until an inactive region  285  is found thereby indicating presence of a fault  280 . Since the patch cabinet represented in  FIG. 3  depicts a typical environment, it can be seen that the use of fiber identifiers for fault location can be financially risky and time consuming. 
     The infrared light probe  325  also has had limited use in the detection of faults and tracing fibers. It is used to search for light leaks  320  from a remote light source  300  attached by connector  310  to a fiber under test. Although capable of detecting infrared emission from transmitters or light sources, current technology probes have the limitation of poor sensitivity which renders them useless in most leak detection applications. Infrared light probes also suffer from interference due to the infrared components of ambient room light and sunlight thereby giving false indications. In addition, as with fiber identifiers, the user often needs to insert the entire hand into the mesh of routed fibers  150  in order to use the device, again a financially risky proposition when working on networks carrying live traffic. 
     To date, the most viable and popular method for rapid and precise fault location is to attach or otherwise incorporate a visible fault locator (VFL)  330 . Typically in the form of a red light emitting laser source, the VFL  330  injects visible light into a fiber system  345  via connector  340  and the user physically looks for visible light emissions to determine fault location  320 . 
     Referring now to  FIG. 10 , the inventive instrument  600  differentiates between three types of non-visible light: asynchronously modulated light, asynchronously modulated light at a frequency of 2 kHz, and most importantly, 500 Hz synchronously modulated light from the functionally attached light source. 
     The first mode of operation, standard asynchronously modulated light detection, permits the user to probe fibers, fiber optic devices, and communications equipment for the presence of either remotely generated optical data traffic, tracer signals, or other types of switched light source. 
     The second mode of operation, asynchronously modulated tone detection, limits detection to only 2 kHz modulated optical signals. The purpose of this additional filtering is to permit fiber path tracing and fault detection with a remote 2 kHz non-visible light source at the exclusion of interfering communication signals. This mode of operation as well as the first mode are similar to existing infrared probe technology. 
     The third mode of operation embodied in the present invention is synchronously modulated tone detection. As opposed to the prior art methods depicted in  FIG. 7-9 , in this mode instrument  600  is connected directly to the fiber under test via patch cord  605  and connector interface  610  to the fiber under test  615  and is used to probe for its own synchronized light signal thereby indicating faults  620 . This method of utilizing internally generated light is used for the location of faults and light leakage often undetectable by existing devices. In this mode, fiber faults may be located through most buffer colors in 250 um and 900 um buffered fibers and many 3 mm jacked fibers. Light leakage may also be detected through many optical connector bodies  675 , connector boots  670 , bulkhead adapters  680 , splices  655  and near fanout devices  690  as well as cable breakout points  695 . Furthermore, in this highly sensitive mode of operation, it is possible to detect the minute light leakage in splices or connectors which are generally considered to be of good quality and from many faults in newer technology bend insensitive fibers. 
     Referring now to  FIG. 12 , a circuit diagram shows the internal workings of the inventive handheld optical leak detector. A power circuit  400  draws energy from a 9V unregulated source and supplies the functional blocks with +/−5VDC regulated power. Also included is sense circuitry which monitors a membrane type power on switch and a low battery indicator. Also included is a master clock  455  which provides timing for internal filtering and audio blocks as well as a 500 Hz master pulse train for the internal laser and synchronous detection circuits. An O/E amplifier block  420  consists of a photodiode and amplifier, which generate a voltage variable signal proportional to received light. The block is a high gain transimpedance type amplifier with a frequency response of DC to ˜30 kHz. 
     A room light filter  425  consists of a multiple notch filter which attenuates the fundamental and harmonic light oscillations emitted by standard indoor fluorescent bulbs before further amplification and filtering. A raw IR indicator  405  receives the signal from the room light filter  425 , blocks any continuous wave components, and sends the signal to a display device. This signal indicates the presence of modulating infrared light from sources other than room light. An asynchronous detector  410  is a phase locked loop (PLL) device designed to operate at 2 kHz or other desired tracer frequency. Any signal near the PLL center frequency at a magnitude of 1.5 mV or greater will digitally indicate a lock. This digital signal is fed to the asynchronous indicator  415  and an audio steering circuit  465 . The asynchronous indicator  415  is a digital of the PLL status fed from the asynchronous detector  410 . The asynchronous indicator  415  indicates the presence of remotely modulated optical tracer tones thereby providing a function similar to that of existing infrared leak detection probes. 
     The critical portion of the circuit, the synchronous detector circuit  430 , is a switched gain amplifier that uses pulses from the master clock circuit  455  to pass or invert signals from the room light filter block  425 . Since the synchronous detector  430  is phase synchronized with an internal laser driver  450 , it provides high noise rejection of all light and electrical signal sources not matching the frequency and phase of the laser output. Synchronous detector  430  also utilizes low pass filtering to complete the detection process. A gain/offset amplifier  435  permits the electrical tailoring of the output from synchronous detector  430  for interface with display and indication components. The gain in this section is user accessible to permit field sensitivity adjustment. 
     A comparator circuit  440  allows a set point to be established for the indication of synchronous light detection, permitting the calibration of the device to a known quantity of light, thereby allowing pass/fail analysis of devices. Synchronous indicator  445  drives a display to give visual indication of internal laser light detection. An audio voltage control oscillator  460  receives the modified voltage variable output of the gain/offset amplifier  435  and generates an audio tone from approximately 10 Hz to 10 kHz. The pitch of this tone varies with the quantity of light being synchronously detected. An audio steering circuit  465  determines the source of audio output, synchronous detector or asynchronous detector. The audio driver  470  receives low power audio frequency signals from the steering circuit and delivers higher current pulses to a speaker. 
     A laser driver  450  uses the master pulse train from the master clock  455  to drive an internal laser. The laser output power is internally adjustable and capable of emitting power levels greater than 0 dBm at a wavelength of 1550 nm. 
       FIGS. 13-16  depict the physical configurations of the inventive instrument.  FIG. 15  is a side view of instrument showing the activation trigger  530  that begins the fault location process. The power cell  535  also acts as the device handle to allow ease of use and proper placement of optical module  501  in close proximity to system under test while keeping the hand at a safe distance. The detector head  505  propinquity to the optical module  501  allows the easy alignment of the components. The circuitry diagrammed in  FIG. 12  is integrated into the spine of the probe  525  for the purpose of being an all in one tool. 
       FIG. 13  is a top view of instrument that encompasses the power switch  515  and power status indicators  510 . 
       FIG. 14  is a bottom view of instrument that shows the audio ports  540  that are driven by the audio driver  470 . This gives an auditory signal to the operator that the point being searched for has been found. 
       FIG. 16  is a rear view of instrument that has a sensitivity switch  550  which allows the device responsiveness to be changed easily and while the device is in use. A display module  555  with leakage indicators  545  presents a visual representation of the results found. The laser output port  520  is used to introduce a light signal into the system under test which is phase synchronized to the internal receiver. Light used from the port  520  internally synchronized source permits the device to achieve up to a 1000× increase in sensitivity while maintaining the same level of noise immunity. 
     Since other modifications and changes varied to fit particular operating requirements and environments will be apparent to those skilled in the art, the invention is not considered limited to the examples chosen for purposes of disclosure, and covers all changes and modifications which do not constitute departures from the true spirit and scope of this invention. 
     Having thus described the invention, what is desired to be protected by Letters Patent is presented in the subsequently appended claims.