Abstract:
A switchable optical add/drop device ( 1 ) includes a first R-channel ( 20 ) and a second R-channel ( 30 ) opposite to each other. A first path ( 70 ) and second path ( 80 ) are respectively defined between two near ends and two far ends of the first R-channel ( 20 ) and the second R-channel ( 30 ). A first collimator ( 40 ) with an ADD port ( 42 ) and a second collimator ( 52 ) with a DROP port ( 52 ) are disposed about said first R-channel ( 2 ) and said second R-channel ( 30 ). A prism ( 60 ) is removable disposed among the R-channels ( 20, 30 ) and the collimators ( 40, 50 ) for switchably adding/dropping the specific wavelength channel.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to fiber optic communication systems, and particularly to the method of switchably or re-configurably adding/dropping the specific single wavelength channel to/from the multiplex of input wavelengths, and the associated device using the same.  
           [0003]    2. The Related Art  
           [0004]    The optical ADD/DROP multiplexer is mainly used to add and drop one or more wavelength channels at a network node in a fiber optic communication system. With the increasing demands on the fiber optic communication systems, the optical network has been widely used in smaller systems, such as the local telephone or data networks, after proving its success on long haul point to point networks. It is noted that in the smaller system, communication signals are usually transmitted over a limited geographic area to various nodes into the network. A particular node can be re-configured to drop one or more channels from multiple channels, and/or add one or more channels with new information to the transmitted signals for transmission to other nodes in the network.  
           [0005]    Current optical ADD/DROP devices are essentially passive components and lack availability of switching and power control thereof. To achieve the re-configuration capability, a 2×2 switch or two 1×2 switches are used to control the ADD and DROP port(s). This method and the corresponding device can be found in all the suppliers in the market. However, all the popularly used methods have disadvantages of uneven power distribution for the through and dropped channels.  
           [0006]    Therefore, an object of the invention is to provide a new method for switchably or re-configurably add/drop channels to/from the transmitted signal of multiplex wavelength channels, and the corresponding device thereof. Therefore, one can use the device to specifically add and/or drop the selected channels, or allow all the channels to pass through with minimum insertion loss thereof.  
         SUMMARY OF THE INVENTION  
         [0007]    According to an aspect of the invention, a switchable optical ADD/DROP device includes first and second same R-channel modules opposite to each other, two collimators performing in-and-out functions respectively, and a removable prism to commonly define switchable optical path. The R-channel module includes a GRIN lens with a DWDM filter. The multiplexed signal enters the first R-channel module with the specific wavelength channel passing through the filter and along a firstpath directing toward the second R-channel from the one side with the filter thereon while the rest of wavelength channels being reflected to a second path which enters the second R-channel from the other side opposite to the corresponding filter. The prism is adapted to be in a first position where the prism blocks the first path and guide the filtered/dropped specific wavelength channel toward the DROP collimator while simultaneously guide another added specific wavelength channel, if any, from the ADD collimator toward the filter side of the second collimator for entering the second collimator. Under this condition, the added wavelength channel will join the rest of wavelength channels from the second path to leave the second collimator via the OUT port. Alternatively, when the prism is moved to a second position without blocking the first path, the filter wavelength channel will enter the second collimator from the filter side, and join the rest of wavelength channels from the second path, leaving the second collimator via the OUT port. Therefore, the device essentially integrates the switching function and the optical ADD/DROP function together. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a diagram to show a switchable optical ADD/DROP device according to the invention.  
         [0009]    [0009]FIG. 2 is a diagram to show the R-channel used in FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0010]    References will now be in detail to the preferred embodiments of the invention. While the present invention has been described in with reference to the specific embodiments, the description is illustrative of the invention and is not to be construed as limiting the invention. Various modifications to the present invention can be made to the preferred embodiments by those skilled in the art without departing from the true spirit and scope of the invention as defined by appended claims.  
         [0011]    It will be noted here that for a better understanding, most of like components are designated by like reference numerals throughout the various figures in the embodiments. Attention is directed to FIGS. 1 and 2 wherein a switchable optical ADD/DROP device  1  generally comprises the R-channel assembly  10 , the collimator assembly  12  and the switchable prism  60 . The R-channel assembly  10  includes a first R-channel  20  and a second R-channel  30  spatially opposite to each other. The first R-channel  20  includes a GRIN lens  22  and a DWDM filter  24 . A first optical fiber  26  enters the IN port  100  of the first R-channel  20 , and a first path  70  is defined on the filter side (the near end) of the R-channel  20  toward the second R-channel  30  and a second path  80  is defined on the same side (the far end) of the IN port  100 .  
         [0012]    Similarly, the second R-channel  30  includes a GRIN lens  32  and a DWDM filter  34  which is same with the DWDM filter  24 . A second optical fiber  36  is connected to the OUT port  200  of the second R-channel  30 . The first path  70  enters the second R-channel  30  through the filter  34 , and the second path  80  enters the second R-channel  30  on the same side of the OUT port  200 .  
         [0013]    The collimator  12  includes a first collimator  40  and an opposite second collimator  50  being disposed around the first R-channel  20  and the second R-channel  30 , wherein the first collimator  40 , which is generally located on the same side of the first R-channel  20 , defines an ADD port  42 , and the second collimator  50 , which is generally located on the same side of the second R-channel  30 , defines a DROP port  52 .  
         [0014]    A switchable prism  60  is removeably positioned among the first R-channel  20 , the second R-channel  30 , the first collimator  40 , and the second collimator  50 .  
         [0015]    Therefore, in the condition of removal of the switchable prism  60  among the R-channel assembly  10  and the collimator assembly  12 , a multiplexed signal enters the first R-channel  20  from the IN port  100  with a specific wavelength channel penetrates the filter  24  to the first path  70 , while the rest of the wavelength channels are reflected to the second path  80  and directed to the second R-channel  30  around the side of the OUT port  200 . The filtered specific wavelength channel along the first path  70  further penetrates the filter  34  of the second R-channel  30 , entering the second R-channel  30  and further joining the rest of the wavelength channels from the second path  80 , then leaving the second R-channel  30  via the OUT port  200 . It is noted that under this situation the whole assembly functions as a transmission device without any change.  
         [0016]    Differently, in the condition of positioning/existence of the switchable prism  60 , the filtered specific wavelength channel from the first R-channel  20  will hit the switchable prism  60  and be directed, along the dotted line path  90 , to the second collimator  50  and dropped from the DROP port  52 . Simultaneously, the same wavelength channel with new information signal may be added through the ADD port  40  of the first collimator  40  and hit the switchable prism  60  and be guided, along the dotted line path  92 , to the second R-channel  30 . The newly added wavelength channel penetrates the second filter  34  and joins the rest of the wavelength channels from the second path  80  and leaves the second R-channel  30  via the OUT port  200 . Under this situation, the whole assembly functions as a switchable ADD/DROP device.  
         [0017]    In brief, if the prism  60  is present, the device  1  drops a single wavelength (λ drop ) to the DROP port  52  through the prism  60 . In the mean time, the same wavelength (λ add ) can be added through the ADD port  80 . In opposite if the prism  60  is removed, the dropped wavelength passes the second identical DWDM filter  34  and combined with the through channels from the second path  80 . In this case, the device  1  does not affect the spectra of the channels. Therefore, no wavelength is dropped or added. This is the so-called by pass mode.  
         [0018]    The features and the advantages of the invention are as follows.  
         [0019]    (1) The invention achieves the low insertion loss, the uniform bypass mode, even power distribution, the compact size, and the lower cost.  
         [0020]    (2) The invention integrates the switch and optical add/drop function in a single piece. Understandably, the prism used in the invention is one feasible embodiment, and thus other means having the switching function may be applied thereto substitutionally.  
         [0021]    While the present invention has been described with reference to specific embodiments, the description is illustrative of the invention and is not to be construed as limiting the invention. Various modifications to the present invention can be made to the preferred embodiments by those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.  
         [0022]    While the present invention has been described with reference to specific embodiments, the description is illustrative of the invention and is not to be construed as limiting the invention. Various modifications to the present invention can be made to the preferred embodiments by those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.  
         [0023]    Therefore, person of ordinary skill in this field are to understand that all such equivalent structures are to be included in the scope of the following claims.