Abstract:
An apparatus and method are disclosed for visualizing an automatic laser shutdown (ALS) state. An operator is informed of the ALS state by transmitting a visible light with weak power, to an optical fiber, that effuses from the cut position of the optical fiber. The operator recognizes the cut position of the optical fiber by comparing the power of the ALS visible light reflected from the cut surface of the optical fiber and that of the transmitting ALS visible light, and thus restores the cut optical fiber at the recognized position.

Description:
BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION 
     The present invention relates to an optical transmission system, and, more particularly, to an apparatus and method for visualizing an automatic laser shutdown (ALS) state. The invention is capable of visually showing an ALS state to an operator located at a cut position of an optical fiber. 
     2. Background of the Related Art 
     Optical transmission systems utilizing optical fiber form the basis of large-scale communication systems, today. As the capacity of the optical transmission system increases, the power of the main signal transmitted through the optical fiber is proportionately increased. For example, in the case of a wavelength division multiplexing optical transmission system, the main signal power flowing through an optical fiber has increased to a number of watts. With such high power flowing through the very small cross-sectional area of a fiber, it is very important to protect the eyes and skin of an operator located at a cut position, when the optical fiber is cut. 
     Therefore, the ITU-T G.681 (International Telecommunications Union-Telecommunication G.681) Recommendation, which is hereby incorporated by reference, states that a transmission terminal should enter an automatic laser shutdown (ALS) state that disconnects the main optical signals, when the optical fiber of the transmission system is cut. 
       FIG. 1  illustrates an optical transmission system having a series of main optical signal transmission units  1  and  2  interconnected by an optical fiber media. If the optical fiber is cut at point A, such that the main optical signal flowing between the two transmission units  1  and  2  is blocked, transmission system  1  senses this blocking state and disables the transmission of the main optical signal, in accordance with the ITU-T G.681 Recommendation. Thus, the optical transmission system goes into an ALS state. This procedure is called an automatic laser shutdown. Similarly, the ALS procedure is initiated for any type of main optical signal blockage occurring between two transmission units  1  and  2  of an optical transmission system. 
     To determine that a transmission unit  1 ,  2  has entered the ALS state and stopped transmitting, the operator must either check the ALS state of the transmission unit  1 ,  2 , through a user interface of the equipment, or measure the optical power transmitted through the fiber. Oftentimes, the user interface does not provide a convenient way to check the ALS state of a transmission unit  1  and  2 , such as when it is remotely located from the optical fiber cut. If the ALS state is not confirmed prior to handling the fiber, the operator may inadvertently expose himself to the high power optical signal and be injured. Therefore, a means for visually confirming the ALS state, right after the ALS state has been set, is needed. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter. 
     An object of the present invention is to provide an apparatus and method for visualizing an ALS state at a cut position. Another object of the invention is to provide an apparatus and method for visualizing an ALS state that may be easily used in the process of restoring a cut optical fiber. 
     To achieve the above objects, a low-power visible light is conveyed through the optical fiber, when the ALS state is active. This visible light may be seen by the operator, at the cut point, through the surface of the optical fiber. Because the visible light is transmitted at low power it will not injure the operator. The presence of the visible light positively identifies an active ALS state and its absence positively identifies an inactive ALS state. 
     In a first embodiment, the present invention has a main optical signal transmitting/receiving unit for transmitting and receiving a main optical signal of high power; an ALS visualization light source unit for outputting ALS visible light; an ALS visualization connection unit for selectively outputting a main optical signal and ALS visible light according to the state of the system; and a control unit for controlling the operation of the entire system. 
     In a second embodiment, the invention has a visible light source for generating ALS visible light; an optical circulating unit for outputting ALS visible light toward the fiber cut; an optical detector for measuring the power of the ALS visible light reflected from the cut surface of the optical fiber; a light source driving unit for adjusting the output power of the visible light; and a signal processing unit for calculating the distance between the visible light source and the fiber cut by comparing the measured power levels of the visible light at the respective locations. 
     A third embodiment of the invention is a method for visualizing an ALS state, having the steps of: transmitting ALS visible light to an optical fiber when the optical fiber is cut; checking the cut position of the optical fiber by measuring the power of the ALS visible light reflected from the surface of the optical fiber at the cut position; and transmitting a main optical signal to the optical fiber when the optical fiber is restored. 
     The objects of the present invention can be achieved in whole or in part by an apparatus for visualizing an automatic laser shutdown (ALS) state in an optical transmission system, comprising: a visible light source that outputs a visible light; a main signal source that outputs a high power optical signal; and an ALS connection unit that connects the main signal source with an optic medium in a normal system state and disconnects the main signal source from the optic medium and connects the visible light source to the optic medium when an ALS state is initiated. 
     The objects of the present invention can be achieved in whole or in part by a method for visualizing an automatic laser shutdown (ALS) state in an optical transmission system, comprising: detecting a discontinuity in an optic medium; disconnecting a main power signal source from the optic medium when the discontinuity is detected; and connecting a visible light source that outputs visible light to the optic medium after the main signal source is disconnected from the optic medium. 
     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the invention will be described in detail with reference to the following drawings in which like reference numerals refer to like elements wherein: 
         FIG. 1  illustrates an optical transmission system having a series of main optical transmission units interconnected by an optical fiber media; 
         FIG. 2  illustrates an apparatus for visualizing an automatic laser shutdown state in an optical transmission system; 
         FIG. 3  illustrates the ALS visualization light source unit of  FIG. 2  in greater detail; 
         FIG. 4  illustrates the ALS visualization connection unit of  FIG. 2  in greater detail; and 
         FIG. 5  illustrates the process flow of a method for visualizing an automatic laser shutdown state in an optical transmission system. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 2  is a block diagram illustrating an apparatus for visualizing an ALS state. Optical transmission systems  100  and  200  are interconnected by an optical fiber media and constructed identically. Each transmission system  100 ,  200  has a main optical signal transmitting/receiving unit  10  that transmits/receives a main optical signal having a wavelength of 1300 nm-1700 nm; an ALS visualization light source unit  12  that transmits an ALS visible light having a wavelength of 400 nm-900 nm; and an ALS visualization connection unit  14  that selectively passes either the main optical signal or the ALS visible light, according to the state of the system. The main optical signal transmission unit  10  is preferably constructed of an optical transceiver or an optical amplifier. The ALS visualization connection unit  14  outputs the main optical signal to the optical fiber, when the system is in the normal state, and outputs the ALS visible light to the optical fiber when the ALS state is active. 
       FIG. 3  illustrates in greater detail the ALS visible light source unit  12  of FIG.  2 . The visible light source unit  12  comprises an optical circulating unit  20 , an optical detector  22 , a visible light source  24 , a visible light driving circuit  28 , and a signal processing unit  26 . The optical circulating unit  20  receives visible light from visible light source  24  and conveys this light to the fiber cut, via the visualization connection unit  14  and the optical fiber medium. At the cut location, visible light is reflected by the fiber cut back to the optical transmission system  100 ,  200  that generated the visible light. This reflected light is received by the optical circulating unit  20 , via the visualization connection unit  14 , and conveyed to the optical detector  22 . The optical detector  22  measures the power of the received visible light and informs the signal processing unit  26  of the measured value. Signal processing unit  26  serves a dual purpose. Firstly, it adjusts the power of the visible light generated by the visible light source  24  through a control signal that is provided to the visible light driving circuit  28 . Operating in conjunction with the driving circuit  28 , the visible light source  24  modulates the transmitted power level of the visible light in accordance with the control signal. Secondly, the signal processing unit calculates the distance between the cut location and the transmission system  100 ,  200  by comparing the relative power levels of the transmitted light and its reflection. Preferably, the visible light source generates light having a wavelength of 400-900 nm, the optical circulating unit  20  is implemented with an optical coupler, and the visible light source  24  uses a laser diode or a light emitting diode. 
     As illustrated in  FIG. 4 , the ALS visualization connection unit  14  is preferably constructed of an optical switch  30 . The optical switch  30  passes the main optical signal in a normal state and passes the ALS visible light in the ALS state. The ALS visualization connection unit  14  may also be preferably constructed of an optical multiplexer. An optical multiplexer may be used because the wavelength of the main optical signal preferably ranges from 1300 nm to 1700 nm, and the wavelength of the ALS visible light ranges from 400 nm to 900 nm. 
       FIG. 5  illustrates the operational process performed by the transmission unit  100 ,  200  of  FIG. 2  when the ALS state is active. Additionally, the flow chart of  FIG. 5  illustrates the operation of the transmission units  100 ,  200  when the ALS state is inactive, that is, when a normal state exists. 
     When the optical transmission system  100 ,  200  is in the normal state, the main optical signal outputted from the main optical signal transmitting/receiving unit  10  is transmitted to the optical fiber through the ALS visualization connection unit  14 , as illustrated in FIG.  2 . However, if the optical fiber is cut at point A, or a connector is removed from the transmission/receiving equipment, the main high-power optical signal flowing through the optical fiber is disabled by the transmission system  100 ,  200  sourcing it and the sourcing transmission system  100 ,  200  transitions to the ALS state. Therefore, if the disconnection of the main optical signal flowing through the optical fiber is detected, the control unit (not shown) of the optical transmission system  100  is transitioned to the ALS state and the main optical signal outputted from the main optical signal transmitting/receiving unit  10  is disabled in steps S 10  and step S 11 . 
     To disable the transmission of the main optical signal, the control unit switches the optical switch  30  from passing the main optical signal of the transmitting/receiving unit  10  to passing the visible light of the ALS visualization light source unit  12 , by controlling the ALS visualization connection unit  14  in step S 12 . 
     Upon completing the switching operation, the signal processing unit  26  sends a control signal to the visible light driving circuit  28  indicating a particular drive level. In turn, the driving circuit  28  causes the visible light source to generate visible light having a certain power level. The generated visible light is conveyed to the optical fiber that has the cut by the ALS visualization connection unit  14 , after passing through the optical circulating unit  20 . To promote security, the power of the ALS visible light may be kept low. The above-described process is indicated in  FIG. 5  by step S 13 . 
     Afterwards, if the ALS visible light is reflected from the cut surface of the optical fiber, the reflected ALS visible light is inputted to the optical detector  22 , via an optical switch unit  30  and an optical circulating unit  20 . Optical detector  22  measures the power of the reflected ALS visible light and outputs the measured value to the signal processing unit  26 , as indicated in step S 14 . 
     The signal processing unit  26  calculates the distance between the transmission system  100 ,  200  and the reflecting surface of the optical fiber cut by comparing the power of the reflected ALS visible light, detected by the optical detector  22 , and that of the ALS visible light outputted from the visible light source  24 , as indicated in step S 15 . In other words, the signal processing unit  26  calculates the distance between its position and the optical fiber cut surface based on the transmission loss of the ALS visible light, the insertion loss of the optical device, the output power of the ALS visible light from the visible light source  24 , and the power of the reflected ALS visible light measured by the optical detector  22 . Once the distance calculation is complete, signal processing unit  26  adjusts the output power of the visible light source  24  so that it reaches a predetermined level. The signal processing unit  26  adjusts the power by controlling the light source driving circuit  28  in step S 16 . 
     The operator may determine the ALS state by looking for ALS visible light flowing from the optical fiber cut surface. The presence of visible light in the optical fiber indicates an active ALS state and the absence of visible light indicates an inactive ALS state. Additionally, the operator may determine the approximate location of the fiber cut by obtaining a readout of the calculated distance from the signal processing unit  26 . Knowing the approximate distance, the operator may more easily find the cut and restore the optical fiber to operational condition. Moreover, by visually determining the ALS state at the cut site, the operator may avoid being injured by the inadvertent transmission of the main optical signal. 
     The control unit continually checks whether the cut optical fiber is restored in step S 17 . If the cut optical fiber is not restored to normal, steps S 13 -S 16  are repeatedly performed. If the optical fiber is restored to normal, the ALS visible light is turned off in step S 17 . Then, the control unit switches the optical switch  30  of the ALS visualization connection unit  14  to convey the main optical signal, in step S 18 . Finally, if the ALS state is released, the control unit performs a normal optical transmission operation by driving the main optical signal transmitting/receiving unit  10  in step S 19 . 
     Thus, the present invention visually informs the operator of the ALS state by disconnecting the main optical signal, passing the ALS visible light to the optical fiber, and effusing the ALS visible light at the cut position of the optical fiber, when the system is transitioned to the ALS state. If an optical multiplexer is used for the ALS visualization connection unit instead of the optical switch, then steps S 12  and S 19  can be omitted from the above-described process. 
     As described above, the apparatus and method for visualizing an ALS state according to the present invention is effective in that the operator located at the cut position of the optical fiber can be visually informed of the ALS state visually by passing an ALS visible light indicating the ALS state to the optical fiber, when the optical fiber is cut. In addition, the present invention is effective in that the cut optical fiber can be easily restored by calculating the distance between the transmission system  100 ,  200  and the cut position by comparing the power of the ALS visible light reflected from the cut surface of the optical fiber and that of the transmitting ALS visible light 
     The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures.