Patent Publication Number: US-2007110440-A1

Title: Measuring system and method for optical network

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This Non-provisional application claims priority under 35 U.S.C. 119(a) on Patent Application No(s). 094139635 filed in Taiwan, Republic of China on Nov. 11, 2005, the entire contents of which are hereby incorporated by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of Invention  
      The invention relates to a measuring system and method. In particular, the invention relates to a measuring system and method for an optical network.  
      2. Related Art  
      With the rapid growth of the Internet, users have higher demands for transmission bandwidths. Therefore, a broadband optical network becomes one of the best solutions.  
       FIG. 1  shows a conventional optical network. Generally speaking, the optical network  1  is a passive optical network (PON) with a point-to-many-point (P2MP) structure. The optical network  1  has several optical network units (ONU)  11  and an optical line terminal (OLT)  12 . The optical network  1  can adopt the time division multiple access (TDMA) scheme. Therefore, once the ONU&#39;s  11  of the optical network  1  are registered, each of them is assigned with a time slot for devoted signal transmissions. Each ONU  11  can send packets only in the devoted time slot to avoid data collisions.  
      Generally speaking, to test the optical network  1  (such as the error rate and sensitivity), a signal generator  13  is usually disposed at each ONU  11  to provide a control signal  131  and a data signal  132 , which are simultaneously sent to the ONU&#39;s  11 . The control signal  131  is used to control the ONU  11  to turn the data signal  132  into an optical signal  131 ′ to be transmitted to the OLT  12 . A measuring device  14  is disposed at the OLT  12 . After the OLT  12  receives the optical signal  131 ′ transmitted from the ONU&#39;s  11 , the optical signal  131 ′ is converted into the corresponding electrical signal  131 ″. The measuring device  14  then measures the electrical signal  131 ″, thereby determining the sensitivity and error rate of the optical network  1 . However, the above-mentioned measuring method requires several signal generators  13  in order to generate respective control signals  131  and data signals  132  for detection. Therefore, if the optical network  1  has  32  ONU&#39;s  11 ,  32  signal generators  13  are needed for the error detection of the optical network. However, the signal generator  13  is an expensive apparatus. This method thus increases the entire detection cost.  
      Therefore, it is an important subject of the invention to provide a simple measuring system and method for an optical network in order to reduce the measuring cost.  
     SUMMARY OF THE INVENTION  
      In view of the foregoing, the invention is to provide a measuring system and method for an optical network for reducing the overall measuring cost.  
      To achieve the above, a measuring system for an optical network of the invention includes a signal generator, a signal dividing device, and a measuring device. The optical network has a plurality of ONU&#39;s and an OLT. The signal generator generates a data signal, which is delivered to the ONU&#39;s, and a control signal. The signal dividing device receives the control signal and delivers the control signal to one of the ONU&#39;s at a first time and to another ONU at a second time. The measuring device is electrically coupled to the OLT. After the ONU receives the control signal, it delivers the data signal to the OLT. The measuring device then measures the data signal received by the OLT.  
      To achieve the above, the invention also discloses a measuring method for an optical network, which has a plurality of ONU&#39;s and an OLT. The measuring method includes the steps of: providing a data signal to each of the ONU&#39;s, providing a control signal at a first time to one of the ONU&#39;s, which then delivers the data signal to the OLT, providing the control signal at a second time to another one of the ONU&#39;s, which then delivers the data signal to the OLT, and measuring the data signal received by the OLT.  
      As mentioned above, the measuring system and method for an optical network uses a signal dividing device to generate a control signal according to the data signal. The control signal is then delivered to one of the ONU&#39;s at different time slots. It controls one of the ONU&#39;s to deliver the data signal to the OLT, thereby simulating the TDMA transmissions. The data signal received by the OLT is measured in order to determine the error rate and sensitivity of the optical network. In comparison with the prior art, the disclosed measured system and method for an optical network only needs one signal generator to measure the optical network, thus reducing the cost of the entire measuring system.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will become more fully understood from the detailed description given herein below illustration only, and thus is not limitative of the present invention, and wherein:  
       FIG. 1  is a schematic view of the conventional measuring system for an optical network;  
       FIG. 2  is a schematic view of a measuring system for an optical network according to a preferred embodiment of the invention; and  
       FIG. 3  shows the waveforms of various signals from the signal dividing device of the measuring system for an optical network according to the embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements.  
      A preferred embodiment of a measuring system for an optical network is schematically shown in  FIG. 2 .  
      The optical network  3  is a passive optical network (PON) and has several optical network units (ONU) ONU 1 .ONU n  and an optical network terminal (OLT). The ONU&#39;s ONU 1 .ONU n  are connected to the OLT via several optical fibers of different lengths, thereby forming the optical network  3 .  
      The measuring system  2  in this embodiment can be used to measure the sensitivity and error rate in the above-mentioned optical network  3 . The measuring system  2  includes a signal generator  21 , a measuring device  22 , and a signal dividing device  23 . The signal generator  21  is a pulse pattern generator (PPG) for generating a data signal  31 , a control signal  32 , and a pulse signal  33 . The signal generator  21  is connected to the ONU&#39;s ONU 1 .ONU n  for providing the data signal  31  and the control signal  32  to the ONU&#39;s ONU 1 .ONU n . The data signal  31  is for testing, whereas the control signal  32  is used to drive the ONU&#39;s ONU 1 .ONU n . After the ONU&#39;s ONU 1 . ONU n  receive the control signal  32 , the data signal  31  is converted into an optical signal  31 ′, and the optical signal  31 ′ is then delivered to the OLT via an optical fiber. Besides, after the OLT receives the optical signal  31 ′, it generates a corresponding electrical signal  31 ″.  
      The measuring device  22  is electrically coupled to the OLT for measuring the electrical signal  31 ″. The sensitivity and error rate of the optical network  3  are then determined according to the electrical signal  31 ″.  
      In this embodiment, the measuring device  22  is an error detector (ED). The measuring device  22  and the signal generator  21  are synchronized. The data signal  31  generated by the signal generator  21  is compared with the electrical signal  31 ″ to obtain the error rate and reception sensitivity of the optical network  3 .  
      The signal dividing device  23  receives the control signal  32  and is coupled to the ONU&#39;s ONU 1 .ONU n . The signal dividing device  23  is a shift register that can simulate TDMA. In different time slots, it provides the control signal  32  to one of the ONU&#39;s ONU 1 .ONU n  for controlling the ONU&#39;s ONU 1 .ONU n  to deliver the data signal  31  to the OLT for measurement. In this embodiment, the signal dividing device  23  has n flip-flops D 1 .D n .  
      The flip-flops D 1 .D n  are D-type flip-flops, each of the flip-flops D 1 .D n  has a signal input terminal (I 1 .I n ), an output terminal (Q 1 .Q n ), and a trigger terminal (C k ). The number of the flip-flops D 1 .D n  is determined by the number of the ONU&#39;s ONU 1 . ONU n , so that the output terminals Q 1 .Q n  of the flip-flops D 1 .D n  correspond to the ONU&#39;s ONU 1 .ONU n ; respectively.  
      The signal dividing device  23  of this embodiment has the following connections. The input terminal I 1  of the flip-flop D 1  is connected to the signal generator  21  for receiving the control signal  32 . The output terminal Q 1  of the flip-flop D 1  is connected to the input terminal I 2  of the flip-flop D 2 . The output terminal Q 2  of the flip-flop D 2  is connected to the input terminal  13  of the flip-flop D 3 . This pattern continues until the output terminal Q n-1  of the flip-flop D n-1  to the input terminal I n  of the flip-flop D n . Moreover, the trigger terminals C k  of the flip-flops D 1 . D n  are together coupled to the pulse signal  33  of the signal generator  21  to provide the trigger signals of the flip-flops D 1 .D n . Besides, ONU 1  is connected to the output terminal Q 1  of the flip-flop D 1 , ONU 2  is connected to the output terminal Q 2  of the flip-flop D 2 , ONU 3  is connected to the output terminal Q 3  of the flip-flop D 3 , and so on.  
      Due to the properties of the D-type flip-flop, it can deliver the signal at its input terminal to its output terminal after receiving the trigger signal (positive-edge trigger or negative-edge trigger). Therefore, a shift register is formed when the D-type flip-flops are connected in series.  
      Please refer simultaneously to  FIG. 3  for the pulse pattern of the output signal from the signal dividing device  23 . For the convenience of illustration, the drawing only shows the output signals of the output terminals Q 1 .Q 4 . The actions of the signal dividing device  23  are described as follows. After the input terminal I 1  of the flip-flop D 1  receives the control signal  32  generated by the signal generator  21  (here the control signal  32  is assumed to be a high-level signal), the output terminal Q 1  of the flip-flop D 1  provides the control signal  32  at a first time T 1  to the ONU ONU 1 . At a second time T 2 ; the output terminal Q 2  of the flip-flop D 2  provides the control signal  32  to the ONU ONU 2 . At a third time T 3 , the output terminal Q 3  of the flip-flop D 3  provides the control signal  32  to the ONU ONU 3 . At a fourth time T 4 , the output terminal Q 4  of the flip-flop D 4  provides the control signal  32  to the ONU ONU 4 . The actions of other flip-flop D 5 ˜D n  are the same as those described above. At different time slots, the signal dividing device  23  provides the control signal  32  to one of the ONU&#39;s ONU 1 ˜ONU n  in order to simulate the TDMA.  
      The measuring method of the disclosed measuring system  2  is as follows. First, the signal generator  21  generates a data signal  31  to the ONU&#39;s ONU 1 .ONU n . Afterwards, the signal dividing device  23  provides the control signal  32  to the ONU ONU 1  at a first time T 1  for driving the ONU ONU 1  to deliver the data signal  31  to the OLT. At a second time T 2 , the signal dividing device  23  provides the control signal  32  to the ONU ONU 2  for driving the ONU ONU 2  to deliver the data signal  31  to the OLT. At a third time T 3 , the signal dividing device  23  provides the control signal  32  to the ONU ONU 3  for driving the ONU ONU 3  to deliver the data signal  31  to the OLT. This pattern continues so that the ONU&#39;s ONU 1 .ONU n  converts the data signal  31  at different time slots into an optical signal  31 ′ and delivers it to the OLT for achieving TDMA. The measuring device  22  further compares the electrical signal  31 ″ generated by the OLT and the data signal  31  generated by the signal generator  21 , thereby obtaining the error rate of the optical network  3 . Moreover, the measuring device  22  measures the power of the electrical signal  31 ″ to obtain the sensitivity of the optical network  3 .  
      Besides, the measuring system  2  further includes a frequency removing device  24  disposed between the signal generator  21  and the signal dividing device  23 . Since the frequency of the pulse signal  33  generated by the signal generator  21  may not comply with the desired frequency, the frequency removing device  24  then performs the frequency removal on the pulse signal  33 . After the pulse signal  33  of the appropriate frequency is obtained, it is delivered to the signal dividing device  23  as the trigger signal of the flip-flops D 1 .D n .  
      In summary, the measuring system and method for an optical network uses a signal dividing device to generate a control signal according to the data signal. The control signal is then delivered to one of the ONU&#39;s at different time slots. It controls one of the ONU&#39;s to deliver the data signal to the OLT, thereby simulating the TDMA transmissions. The data signal received by the OLT is measured in order to determine the error rate and sensitivity of the optical network. In comparison with the prior art, the disclosed measured system and method for an optical network only needs one signal generator to measure the optical network, thus reducing the cost of the entire measuring system.  
      Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the invention.