Abstract:
Apparatus and methods are provided for controlling a light emission from an end of an optical fiber by utilizing a cover that blocks the light emission at the fiber end, a detector situated between the fiber end and the cover that detects the blocked emission, and a signaling device, such as an LED, associated with the detector that illuminates in response to the detection of the blocked emission. The apparatus and methods may further provide for the filtering out of light from the emission that is not used for communications. The apparatus and methods may also provide for the attenuation of the power of the emission before the emission reaches the detector.

Description:
FIELD OF INVENTION 
   The present invention relates generally to apparatus and methods for controlling the light emissions from an end of an optical fiber. 
   BACKGROUND 
   Optical fibers are used for transmitting electronic signals in high-speed data and communications systems. A standard optical fiber contains an inner light transmitting optical core. Surrounding each fiber is an outer protective casing. Optical fibers are utilized in the telecommunications industry, as well as other industries, as a preferred transmission medium because of their ability to carry large amounts of data at high speeds, over long distances. 
   Optical fibers are often terminated in connectors, so that they can be connected to other fibers or some other device. The “slot” that holds the fiber in position within the connector assembly is known as a ferrule. The precise positioning of the fiber in ferrules is necessary in order to consistently align one end of a fiber with the end of another fiber in a mating connector assembly, or with a device connected to the other end of the connector. 
   In the telecommunications industry, multiple fibers terminating at the back of a Fiber Distribution Frame (FDF) are connected via fibers within the frame to “ports”on the front side of the frame. These ports have rigid sleeves to hold the connectors in place, and apertures for the ferrules. In this way, the ports can be used to connect other optical fibers or electronic equipment plugged into the ports on the front of the frame to the fibers terminating on the back side of the frame. 
   If a port on the front side of an FDF is connected through the frame to the back side, and there is no equipment plugged into the port, there would be a fiber “end”exposed at the port. Further, if there is a “live” (powered) fiber connected to the back side of the FDF and associated with that port, the fiber end at the port would be emitting potentially dangerous light. The power level for some current systems with optical amplifiers is approaching 400 mW. For “next generation” systems it is expected to approach 1 W. At these power levels, the emissions could injure the eyes of a person looking at the port. 
   In order to avoid physical damage to the fiber end at an exposed port, and to avoid possible damage to the eyes of anyone looking at the ports, “dust covers” have been placed over the sleeves to protect both the fiber and the connectors from harmful dust or debris, as well as blocking any laser light emitted from the exposed fiber end. Covers could also be utilized in situations other than an FDF, such as to cover fiber connectors, or to cover fiber ferrules. 
   In the case of covers over sleeves on FDFs, these covers are routinely removed for long periods of time while service personnel are working on the front of the frame, looking at the ports. If a live optical fiber is connected at the back of the frame, and the port is not immediately tested when the cover is removed, the technician could be injured by the emitted light. Further, if the port is “live” for an extended period of time, the plastic cover could be damaged due to opto-thermal effects of the emitted light. 
   It would therefore be advantageous for service personnel to know whether a port is “live” before removing a cover from the port. It would also be advantageous to know if an installed cover is covering a live port, so that such a situation could be addressed before damage is done to the cover, or for other operational reasons. For instance, it may very well be a mistake that a “covered” port is live. Therefore, if there were an indication of this situation on a covered port, the problem could be resolved. 
   It would be further advantageous if the power level of light emitted from an optical fiber under a cover could be reduced while the cover is in place, in order to avoid damage to the cover. 
   It would be further advantageous if there was an indication that light within the spectrum used for communications was present under the cover, as opposed to extraneous light that would not be potentially harmful. 

   
     BRIEF DESCRIPTION OF FIGURES 
       FIG. 1  is a drawing of an exemplary apparatus implemented in accordance with the present invention and using methods of the present invention. 
       FIG. 2  is a drawing of an exemplary apparatus implemented in accordance with the present invention and using methods of the present invention. 
       FIG. 3  is a drawing of an exemplary apparatus implemented in accordance with the present invention and using methods of the present invention on a fiber frame. 
       FIG. 4  is a drawing of an exemplary apparatus implemented in accordance with the present invention and using methods of the present invention on a fiber connector. 
       FIG. 5  is a drawing of an exemplary apparatus implemented in accordance with the present invention and using methods of the present invention on a fiber ferrule. 
       FIG. 6  is a flowchart of an exemplary method of indicating that an optical fiber under a cover is powered in accordance with the present invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a drawing of an exemplary cover  100  implemented in accordance with the present invention and using methods of the present invention. Cover  100  is a cylindrical structure, preferably plastic, and hollow at one end (opening  180 ). Cover sidewall  150  and cover end  160  would be used to cover the end of an optical fiber, or alternatively to cover a connector coupler containing an optical fiber (not shown). Cover  100  could be considered to be a cap or hood to be placed over the fiber end. Cover end  160  would be preferably composed of an opaque material that would block the light emitted from the end of the optical fiber. 
   Support ring  110  is a rigid ring member which holds coating  140 , photo detector  120 , and LED (Light Emitting Diode)  130  in place. Coating  140  may be made up of a material that would filter out a portion of the light spectrum emitted from the optical fiber end in opening  180 . For instance, coating  140  could be designed to filter out the portion of the light spectrum that doesn&#39;t carry communications. As will be seen more clearly below, this could be used to prevent false indications of harmful emissions from the optical fiber. Alternatively, the designated spectrum to be filtered out could be light that would not be harmful to the human eye. This would prevent the LED from illuminating if none of the detected light would be harmful to the eye. The material of coating  140  could be self-supporting within ring  110 , or could be applied to the surface of photo-detector  120 . 
   Alternatively, or additionally, coating  140  may be a material which attenuates the power of the laser light emission passing through it. If the power of the laser beam is such that it could damage cover end  160 , this attenuating layer of coating  140  could reduce the power to a safe level whenever cover  100  is in place over the fiber end. Again, this attenuating material could either be self-supporting within ring  110 , or could be a coating on photo detector  120 . Coating  140  could be designed for various power level applications. 
   Alternatively, coating  140  could contain a combination of attenuating material and filter material, to simultaneously filter out light of a designated portion of the spectrum and reduce the power level of the remaining light. 
   LED  130  is affixed to photo-detector  120 . This combination of photo detector  120  and LED  130  would transform light emitted from the fiber end through the attenuator/filter of coating  140  to electrical energy, which would illuminate LED  130  with light that could be seen by the naked eye. LED  130  could protrude through an aperture in cover end  160 , so that someone looking at cover  100  would be able to see whether LED  130  was illuminated or not. If LED  130  was illuminated, the observer would know that the optical fiber within opening  180  was “live”; i.e., was carrying a light signal. However, as opposed to the light emitted from the optical fiber being dangerous to a technician&#39;s eyes, the light from the LED would be safe. This would allow the technician to take further precautions before removing cover  100  from the optical fiber (or the connector coupler encasing the end of the optical fiber). 
   Alternatively, as shown in  FIG. 2 , instead of protruding through a hole in cover end  260  of cover  200 , LED  230  could be situated underneath cover end  260 , and a portion  270  of cover end  260  over LED  230  could be made of a translucent or transparent material, which would allow a technician to see LED  230  illuminated beneath the surface of cover end  260 . Translucent portion  270  could be sized and situated such that no harmful light from the optical fiber would pass through it. 
   Returning to  FIG. 1 , cover sidewall  150  could be of a “neutral” color, such as green or yellow, whereas cover end  160  could be a bright red, signifying that the cap is non-standard; that the connector underneath cover  100  could be a live unterminated connector or link, and could contain an active, high-powered laser beam; and that the technician should look at LED  130  before removing cover  100 . This could avoid exposure by the technician to invisible radiation and indicate that proper action must be taken to deactivate or terminate the link. 
   Cover  100  is a cover or housing that could be manufactured with the fiber or connector, and would be removable. Alternatively, cover  100  could be a stand-alone cover, including the associated support ring  110 , coating  140 , photo-detector  120 , and LED  130 , which could be placed over the end of an optical fiber or connector in the field. 
   Another variation consistent with the present invention would be to install a support ring  110 , coating  140 , photo-detector  120 , and LED  130  into an existing dust cover in the field, and punching a hole in the end of the dust cover for the LED to protrude therethrough. Cover  100  could be placed over the end of an optical fiber in the field, or could be placed over a fiber/connector combination on a Fiber Distribution Frame, or similar situation. 
     FIG. 3  shows the side view of a port on a fiber distribution frame. The port includes sleeve  320 , which holds connector  330  of fiber  340  in place, and sleeve  360 , which is available to hold a connector in place that is to be plugged into the port. An embodiment of the present invention, cover  350 , is shown placed over sleeve  360 , which would protect sleeve  360  and fiber  340  from dust and debris, and would indicate through an LED (not shown) whether fiber  340  was powered with potentially dangerous light. 
     FIG. 4  shows an embodiment of the present invention wherein the inventive cover  450  is placed over connector  430 , which holds fiber  440 . In this case, connector cover  450  would not only protect connector  430  and fiber  440 , but would indicate whether fiber  440  was powered with potentially dangerous laser light. 
     FIG. 5  shows another embodiment of the present invention wherein the inventive cover  550  is placed over ferrule  560 , which is encased in connector  530 , and holds fiber  540  in place. In this case, cover  550  would not only protect ferrule  560 , and fiber  540 , but would indicate whether fiber  540  was powered with potentially dangerous light. 
     FIG. 6  shows the steps that could be taken to implement an embodiment of the present invention. The first step  610  is to filter the emission, to only allow communications-carrying portions of the laser spectrum to pass through. Step  620  (which could also be accomplished with or before step  610 ) is to attenuate the power of the laser beam before it is detected. It should be understood that both steps  610  and  620  are optional steps, and the invention would be effective without either. Step  630  would be to detect the filtered, attenuated emission from the optical fiber. Finally, step  640  would be to signal, such as with a light, if an emission has been detected at step  630 . 
   The methods and apparatus of the invention can be applied to and/or used with, a wide range of devices. Applications of this invention, in addition to FDFs, include optical devices and subsystems terminated with optical connectors such as optical sources, optical amplifiers, Optical Add Drop Multiplexers (OADM) in Dense Wavelength Division Multiplexing systems. The invention is particularly useful in cases where the devices and/or systems use dangerously high optical power. 
   Numerous additional variations on the methods and apparatus of the present invention described above will be apparent to those skilled in the art in view of the above description of the invention. Such variations are to be considered within the scope of the invention.