Abstract:
The present invention provides an optical signal quality selection system for optimizing the quality of information transmission. The system splits an incoming optical signal into two equal signals. The split signals are evaluated in optical performance monitors, transmitting an electrical output message to a signal selector relating to the quality of the respective signal. A second electrical message is sent from the optical performance generator to an alarm indicator signal generator, which sends an optical signal to the signal selector to drop the one of the split signals and transmit the non-dropped split signal. An unequipped optical signal from an optical idle signal generator is triggered if no active optical signal is being transmitted.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to the field of communications, and more particularly to the field of communications by the transmission of digital data by optical signals.  
         BACKGROUND OF THE INVENTION  
         [0002]    Current communications technology has adopted optical transmission of data as the medium of choice to obtain the benefits of high bandwidth transmission. As bandwidth increases for transmission through optical network elements, the reliability of the various elements becomes more critical. Although optical signals are known to be less prone to noise or interference, and thus more pure than electrically transmitted signals, the reliability and quality of the optical signal is also more critical because of the volume of data carried. The need for nearly one hundred percent availability drives network cost to a significant extent as it relates to the requirement for redundant equipment and its management to identify and restore a degraded signal within a network. It is generally accepted that a two-fold growth in bandwidth requires a two-fold increase in availability.  
           [0003]    A highly available and reliable system involves component and interface redundancy, fault monitoring, and protection switching. Each of these functions is, in turn, available based on the following factors: component reliability, component redundancy ratio, protection switching speed, protection switching availability, failure detection speed, and detection mechanism availability.  
           [0004]    An optical signal network system designed with adequate availability is more complicated than a similar electrical signal system because fault detection is necessarily at the optical signal level and localization of system faults involves a significant effort.  
           [0005]    Therefore, it is an object of the present invention to provide an automatic optical signal quality selection system that does not require the optical signal to be converted into an electrical format for evaluation.  
           [0006]    It is a further object of the present invention to provide an optical signal quality selection system able to discern between signals having different levels of degradation faster than an external system can detect the degraded signal.  
           [0007]    It is another object of the present invention to provide an optical signal quality selection system able to delete an unacceptable quality signal and to transmit a signal after determining that its quality is acceptable.  
           [0008]    It is another object of the present invention to provide an optical signal quality selection system able to inject an optical idle signal when no active signal is being transmitted through the system.  
           [0009]    These and other objects will become more apparent from the description of the invention to follow.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention provides an optical signal quality selection system for optimizing the quality of optical signal transmission. The system divides an incoming optical signal into two separated signals. The split signals are evaluated by a pair of optical performance monitors, the result of the evaluation is transmitted via an electrical output message to a selector relating to the quality of the respective signal. An optical signal from an optical idle signal generator, also known as an unequipped signal generator, is inserted when no active optical transmission exists in the system. When both signals (A) and (B) fail, an electrical message is sent from the optical performance monitor to an alarm indicator signal generator. If one of the signals (A) and (B) is determined to be better than the other, an optical signal is sent to the signal selector to drop the one of the split signals based on the comparative signal purity as determined by a set of selector state rules, and to transmit the non-dropped split signal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a schematic diagram of the optical signal quality selection system according to the invention.  
         [0012]    [0012]FIG. 2 is a schematic diagram of a selector circuit of the optical signal quality selection system of FIG. 1.  
         [0013]    [0013]FIG. 3 is a selector state logic diagram as used in the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    In accordance with the disclosure contained in FIG. 1, the components and signal paths of the optical signal quality selection system  10  are illustrated diagrammatically. System  10  employs a combination of optical and electrical signals in a data selection system in a unique manner. For reasons of clarity, optical signals are depicted as solid lines and electrical signals are depicted as dotted lines. Input optical signal  12  is divided into split signal A  16  (indicating system side A) and split signal B  18  (indicating system side B) by signal splitter  14 . Split signal A  16  is carried to switch fabric (SF) A  22  where it connects to a designated output path so as to exit as switch output A  30 . Optical performance monitor (OPM) A  36  is connected in a manner to direct a sample probe signal A  34  thereto for evaluation of the optical signal quality according to a number of standard parameters, for example, power level, optical signal to noise ratio, wavelength, and Q factor (pertaining to the compactness of frequency distribution). OPM A  36  derives an evaluative result for switch output signal A  30 , and OPM A  36  generates an electrical message A  38  in response to the evaluative result. Electrical message A  38  is transmitted from OPM A  36  to selector engine  52 , which is described in detail below. Selector circuit  52  transmits an electrical signal  64  to unequipped signal generator (UEQ Gen)  66  if no active, data-bearing, optical signal is being transmitted, and UEQ Gen  66  responds with an optical carrier signal  68  to selector circuit  52 . Thus the evaluation process involves receipt of an input first optical signal, transmission of a first electrical signal, transmission of a second electrical signal, and transmission of an output second optical signal.  
         [0015]    Similarly, from signal splitter  14 , split signal B  18  is carried to SF  24 , from which switch output B  32  is transmitted to signal selector  52  as switch output B  50 . OPM B  46  is connected in a manner to direct a sample probe signal B  44  thereto for evaluation of the signal quality according to the standard parameters noted above. OPM B  46  derives an evaluative result for switch output signal B  50 , and OPM B  46  generates an electrical message B  48  in response to the evaluative result. Electrical message B  48  is transmitted from OPM B  46  to selector circuit  52 , from which a responsive electrical message  56  is sent to optical alarm indicator signal generator (AIS Gen)  58 , which sends an optical signal  60  to selector circuit  52 . As noted above in the description of the signal evaluation and transmission in side A, the sequence is optical, electrical, electrical, optical.  
         [0016]    A further layer of control circuit elements is shown in hierarchical representation in FIG. 1, wherein switch manager  26  serves to control the operation of SF A  22  and SF B  24  through electrical signals  28   a  and  28   b,  respectively. Group manager  82  controls the operation of the components in control circuit  78  through electrical signal  80 . Equipment manager  86 , in higher hierarchy level, controls switch manager  26  and group manager  82  through electrical links  88  and  84 , respectively.  
         [0017]    Referring now to FIG. 2, a detail of the components of control circuit  78  is illustrated with related optical and electrical connections therebetween. Optical switch output A  40  and B  50  connect from SF sides A and B respectively to 4:1 selector  72 . Optical message  60  from AIS Generator  58  and optical carrier signal  68  from UEQ Generator  66  also feed into 4:1 selector  72 . 4:1 selector  72  transmits a single output signal  74  selected from its four input signals based upon a series of input signals and messages from other components of selector engine  52  and selector state logic to be described below in reference to FIG. 3.  
         [0018]    Referring further to FIG. 2, each of the additional components of selector circuit  52  are operative in response to and generate electrical signals. Protection switching logic  92  receives input as electrical message A  38  and electrical message B  48  respectively from OPM A and OPM B. Also, protection switching logic  92  receives input as port identification signal  94  and further as switch map signal  96  from bus interpreter  102 , responding to control signal  80   a  from a control feedback bus with selector state status and OPM A and OPM B status. In addition, protection switch logic  92  transmits selector status signal  98  through bus formatter  100  to the control feedback bus via output  80   b.  Protection switching logic  92  interacts both with selector control interface  70  via bi-directional electrical signal  78  and with generator control interface  80  via bi-directional electrical signal  90 . Further, selector control interface  70  interacts with 4:1 selector via bi-directional electrical signal  76 , and generator control interface interacts with both UEQ generator  66  and with AIS generator  58 . The logic state rules controlling the physical components will be described below in respect to FIG. 3.  
         [0019]    According to the logic circuit depicted in FIG. 3, a set of rules controlling the selections available to the optical signal quality selection system of the invention is laid out. As defined in this set of rules, “F” indicates a failed signal or no signal, and “R” indicates a degraded, but recoverable signal. Thus a result of “R” is superior to a result of “F”. Starting at the upper left, coming out of box select A  320  is criterion OPM(A)≦F, indicating that the output of OPM(A) shows a failed or null A-side signal. In this condition, two choices are possible. If OPM(B)&gt;F  304 , signal B is greater than a fail level, the system selects B  306 ; If OPM(B) is≦F  308 , signal B fails, the system selects AIS  310 , alarm indicator signal. From select AIS  310 , if OPM(B)&gt;R  316 , indicating a good B side signal, the choices are if OPM(A)≦R  322  (degraded A side signal), wherein the system selects B  306  optical signal as the better signal for transmission, and if OPM(A)&gt;R  318  indicating a good A side signal, the system selects A  320  optical signal as the better signal. Thus the logic circuit defaults to signal A when both A and B are good signals. Out of box select B  306 , upper right, the system chooses whether OPM(A)&gt;R  312  (good signal) and proceeds to select A  320 ; or if OPM(B)≦F  314  (failed B side signal) and proceeds to select AIS  310 . From a select B  306  condition, a control=UEQ  324  will lead to select=UEQ  332 . From select=UEQ  332 , a control=None  328  message will select A  320 . Also, select A  320  with a control=UEQ  326  message will result in selecting UEQ  332 .  
         [0020]    As described above, the optical signal quality selection system is useful to differentiate optical signal quality according to selected parameters and established logic rules to obtain an output optical signal with optimal data integrity.  
         [0021]    While the present invention is described with respect to specific embodiments thereof, it is recognized that various modifications and variations thereof may be made without departing from the scope and spirit of the invention, which is more clearly understood by reference to the claims appended hereto.