Abstract:
A test and measurement system may include a light source coupled to a 1×(N+M) switch that supplies signals to devices under test as well as reference channels. The outputs from each channel of each device under test, as well as the reference channels, are provided to M 2×(N+1) routing switches in one embodiment. The routing switches are then coupled to M channel detector modules. As a result, it is not necessary to connect and disconnect the switches, making long-term environmental tests viable while avoiding losses from disconnecting and connecting switches in the course of ongoing testing.

Description:
BACKGROUND 
   This invention relates generally to optical communication devices and, particularly, to devices for measuring and testing optical communication devices. 
   Many optical devices, such as arrayed waveguides, may include a large number of channels. In order to test devices with a number of channels, it is generally necessary to provide at least one input channel and one output channel. A test device can be coupled to the output channel. To test another channel, connections must be undone and remade. 
   Remaking the connections during testing may involve a considerable amount of labor for devices that are relatively complex with a number of channels. In addition, repeatedly making and breaking of the connections may skew the test results. For example, losses may arise from fiber connection and disconnection during the test. 
   Thus, there is a need for better ways to test multiple optical components in multiple systems. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic depiction of one embodiment of the present invention; 
       FIG. 2  is a schematic depiction, corresponding to  FIG. 1 , in an example with three devices under test, each having two channels, in accordance with one embodiment of the present invention; 
       FIG. 3  shows the layout of the switching network for the embodiment of  FIG. 1  in accordance with one embodiment of the present invention; 
       FIG. 4  shows the switch layout for the embodiment shown in  FIG. 2  in accordance with one embodiment of the present invention; and 
       FIG. 5  is a flow illustrating the operation of a measurement system in one embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   In accordance with one embodiment of the present invention, a light source  12 , such as a laser light source, may be coupled to a switch  14 . The switch  14  may be a 1×(N+M) switch in one embodiment of the present invention, where N is the number of devices under test (DUT) and M is the number of output channels per device under test. 
   Thus, in  FIG. 1 , there are devices under test  16 , 1−N, each having M output channels  18 . M reference channels  24  may couple from the switch  14  to a switch bank  20 . The number of switches in the bank  20  may equal the number of channels in one embodiment. Each of the M switches in the bank  20  may be a 2×(N+1) switch. The switch bank  20  may be coupled to M channel detector modules  22 , such as power monitors. 
   To provide a concrete example,  FIG. 2  shows the configuration, in accordance with one embodiment of the present invention, where there are three devices under test  16   a , each having two output channels, i.e. N=3 and M=2. In this case, the switch  14   a  is a 1×5 switch that receives an input from a laser source (not shown). Each of the devices under test  16   a  receives a signal from the switch  14   a . The devices under test  16   a  each provide two outputs because they each have two output channels. In addition, the switch  14   a  provides a first reference channel  24   a  and a second reference channel  24   b . The bank  20  may include, in this example, two 1×4 switches  20   a  and  20   b . Alternatively, the bank  20  may include 2×4 switches with common ports labeled C 1  and C 2 . The common ports, C 1 , C 2 , are coupled to a pair of detectors  22 , labeled detector  1  and detector  2 . 
   Referring to  FIG. 3 , the bank  20 , for the embodiment shown in  FIG. 1 , may include M 2×(N+1) switches  20 . Thus, each bank  20  may include a pair of switches  24  that receive a pair of channels for each device under test  16  arranged in a plurality of rows and columns. Thus, each column corresponds to each of the devices under test  16  and one particular channel and each row corresponds to a different channel of each device under test  16 . The last row is provided for the reference channels that provide reference signals for comparison to the test outputs. 
   Again, to provide a concrete example for the switching arrangement shown in  FIG. 2 , the first switch  20   a  includes the switches for the first channel of each device under test  16   a  and a reference switch, as well as a common port C 1  that connects to the detector  1 . Similarly, the switch  20   b  includes the common port C 2  that is coupled to detector  2 . Each of the devices under test  16   a  also has a connection for a second channel and for a reference channel. 
   Thus, referring to  FIG. 5 , in order to set up the switching network, initially, all the switches in  FIG. 3  are set to the reference ports and the references signals are measured through M common ports that are connected to M detectors (block  31 ), and then, the number of devices under test is set equal to one as indicated at  32 . The device under test number  1 , channels  1  to M, are then tested as indicated in block  34 . This corresponds to proceeding through the first row in  FIG. 3. A  check at diamond  36  determines whether N equals the number of devices under test. If so, the flow is complete. Otherwise, the variable N is incremented as indicated at block  38 . 
   The next time though the flow, N now equals 2, so device number  2  channels  1  to M are tested as indicated in block  34 . Again, N does not equal the number of devices under test at diamond  34 , so N is then incremented again. Thus, the test proceeds row by row through the switching network shown in  FIG. 3 , until all the devices under test have been tested and all their channels have been tested. 
   In some embodiments, multi-channel operations over multiple components may use M switches in a configuration of n×(N+1) where M is equal to or larger than the channel count of the components, N is equal to or larger than the number of components under test, n is at least equal to 1, but advantageously is equal to or larger than 2. 
   In some embodiments of the present invention, once all the channels of all the devices under test  16  are connected to the detection modules  22  through the routing switches, they may be monitored without any physical interference to the test system until all the anticipated measurements are done. The measurement system can also be used for long-term reliability testing with high repeatability in some embodiments. As all the channels are coupled before a series of tests, losses coming from fiber connection and disconnection during the tests may be reduced or avoided. 
   According to one embodiment of the present invention, the 1×(N+M) switch  14  governs an optical input through the reference channels and input ports of all the devices under test  16  while M 2×(N+1) switches  20  control routes of data acquisition in which “2×” common ports (C) are designated to testing and referencing, respectively. 
   During referencing, M channels in M 2×(N+1) switches are set for referencing all M ports of N components. During testing, another M channels in M 2×(N+1) switches are set for testing all the M ports of N components. During testing, all the ports of all the devices under test are coupled in the ways shown in FIG.  3  and measurements proceed from the first layer which is occupied by all M ports of device under test  1  to the Nth layer which is occupied by all the M ports of device under test N. Thus, all the ports of all the components are measured. 
   Some embodiments may be useful for long-term reliability testing under various environmental conditions. Once the components are connected to the system as described above, there is no need to interfere with them physically. Only variations in parameters and the components under environmental conditions are then detected. 
   While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.