Patent Publication Number: US-2011069959-A1

Title: Optical interleaver and deinterleaver

Description:
BACKGROUND 
     An optical interleaver is a three-port passive fiber-optic device that is used to interleave two sets of dense wavelength-division multiplexing (DWDM) channels (odd and even channels) into a composite signal stream. For example, an optical interleaver can be configured to receive two multiplexed signals with 100 GHz spacing and interleaves them to create a denser DWDM signal with channels spaced 50 GHz apart. An optical interleaver can also function as a deinterleaver by reversing the direction of the signal stream passing through the interleaver. 
     Optical interleavers have been widely used in DWDM systems and have become an important building block for optical networks with high-data-rate transmission. Optical interleavers are easier to manufacture in some respects compared to other bandpass filtering technologies, such as thin-film filters and arrayed waveguided gratings. With the increased demand for bandwidth from wideband, wireless, and mobile subscribers, conventional 50 GHz DWDM systems are increasingly unable to provide sufficient bandwidth. 
     BRIEF SUMMARY OF SOME EXAMPLE EMBODIMENTS 
     In general, example embodiments of the invention relate to optical interleavers and deinterleavers. Some example embodiments increase the transmission capacity of long-haul DWDM optical communication systems. 
     In one example embodiment, an optical deinterleaver includes first, second, and third filter cells interleaved with first and second waveplates. The filter cells are configured to filter optical signals propagating on first, second, and third paths of an optical loop. The optical deinterleaver also includes a retro reflector optically coupled with the filter cells and waveplates. The retro reflector is configured to reflect the optical signals between the first path and the second and third paths to form the optical loop. The optical deinterleaver further includes first, second, and third single-fiber collimators optically coupled to the first, second, and third paths of the optical loop, respectively. 
     In another example embodiment, an optical deinterleaver includes first, second, and third filter cells interleaved with first and second half-waveplates. The filter cells are configured to filter optical signals propagating on first, second, and third paths of an optical loop. The optical deinterleaver also includes a retro reflector optically coupled with the third filter cell. The retro reflector is configured to reflect the optical signals between the first path and the second and third paths to form the optical loop. The optical deinterleaver further includes a first, second, and third single-fiber collimator optically coupled to the first, second, and third paths of the optical loop, respectively. The first single-fiber collimator is configured to carry an interleaved optical signal with about 10 Gb/s data in the odd channel and about 10 Gb/s data in the even channel with about 25 GHz channel spacing. The second single-fiber collimator is configured to carry a first deinterleaved optical signal with about 10 Gb/s data. The third single-fiber collimator is configured to carry a second deinterleaved optical signal with about 50 GHz channel spacing. 
     In yet another example embodiment, an optical deinterleaver includes a first, second, and third paths of an optical loop and a retro reflector configured to reflect the optical signals between the first path and the second and third paths to form the optical loop. The first path includes a single-fiber collimator, a first polarization beam displacer, first, second, and third filter cells interleaved with first and second half-waveplates, and a third half-waveplate positioned between the third filter cell and the retro reflector. The second path includes a fourth half-waveplate, the third, second, and first filter cells interleaved with the second and first half-waveplates, a first lateral shift prism, and a second single-fiber collimator. The third path includes the fourth half-waveplate, the third, second, and first filter cells interleaved with the second and first half-waveplates, a second lateral shift prism, and a third single-fiber collimator. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential characteristics of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     Additional features will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the teachings herein. Features of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. Features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To further clarify certain aspects of the present invention, a more particular description of the invention will be rendered by reference to example embodiments thereof which are disclosed in the appended drawings. It is appreciated that these drawings depict only example embodiments of the invention and are therefore not to be considered limiting of its scope. Aspects of the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG. 1  is a front perspective view of an example optical deinterleaver; 
         FIG. 2A  is a schematic top view of various internal components and a first path of an optical loop of the optical deinterleaver of  FIG. 1 ; 
         FIG. 2B  is a schematic right side view of various internal components of the optical deinterleaver of  FIG. 1 ; 
         FIG. 2C  is a schematic left side view of various internal components of the optical deinterleaver of  FIG. 1 ; 
         FIG. 2D  is a schematic top view of various internal components and a second path of the optical loop of the optical deinterleaver of  FIG. 1 ; 
         FIG. 2E  is a schematic top view of various internal components and a third path of the optical loop of the optical deinterleaver of  FIG. 1 ; 
         FIG. 3  is a perspective view of an example pair of polarization beam displacers and half-waveplates of the example optical deinterleaver of  FIG. 1 ; 
         FIG. 4  is a perspective view of an example filter cell of the example optical deinterleaver of  FIG. 1 ; 
         FIG. 5  is a chart of the interleaving functionality of the example optical deinterleaver of  FIG. 1 ; and 
         FIG. 6  is a chart of the insertion loss of the example optical deinterleaver of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF SOME EXAMPLE EMBODIMENTS 
     Example embodiments of the present invention relate to optical interleavers and deinterleavers. Some example embodiments can increase the transmission capacity of long-haul DWDM optical communication systems. 
     Reference will now be made to the drawings to describe various aspects of example embodiments of the invention. It is to be understood that the drawings are diagrammatic and schematic representations of such example embodiments, and are not limiting of the present invention, nor are they necessarily drawn to scale. 
     Reference is first made to  FIG. 1  in which an example optical deinterleaver  100  is disclosed. As disclosed in  FIG. 1 , the example optical deinterleaver  100  includes a housing  102  and first, second, and third single-fiber collimators  104 ,  106 , and  108 . 
     In some example embodiments, the optical deinterleaver  100  is configured to receive at the first collimator  104  an interleaved optical signal with about 10 Gb/s data in the even channels and about 10 Gb/s data in the odd channels. The interleaved optical signal can have about 25 GHz channel spacing. The optical deinterleaver  100  is configured to detinterleave the interleaved optical signals and output through the second and third collimators  106  and  108  two about 10 Gb/s optical signals, each having about 50 GHz channel spacing. 
     With reference now to  FIGS. 2A-2E , additional aspects of the various internal components of the example optical deinterleaver  100  are disclosed.  FIGS. 2A-2E  disclose the example optical deinterleaver  100  without the housing  102 . As disclosed in  FIG. 2A , a single interleaved optical signal  110  enters the example optical deinterleaver  100  through the first collimator  104 . The interleaved optical signal  110  includes about 10 Gb/s data in the even channels and about 10 Gb/s data in the odd channels. Next, the interleaved optical signal  110  passes through a first polarization beam displacer  112  and a waveplate assembly  113  attached to the first polarization beam displacer  112 . The waveplate assembly  113  includes a right waveplate  113   a  and a left waveplate  113   b . As disclosed in  FIG. 2A  and  FIG. 3 , the first polarization beam displacer  112  horizontally divides the interleaved optical signal  110  into a lower right beam  114  and a lower left beam  116 . Next, the lower right beam  114  passes through the right waveplate  113   a  and the lower left beam  116  passes through the left waveplate  113   b . In at least some example embodiments, the right half-waveplate  113   a  is oriented at about 22.5 degrees and the left half-waveplate  113   b  is oriented at about −22.5 degrees. As used herein, the term “oriented at” refers to the orientation of the optical axis angle of a waveplate crystal with respect to the horizontal line. 
     Next, as disclosed in  FIG. 2A , the lower right and left beams  114  and  116  pass through a first filter cell  118   a , a first half-waveplate  120   a , a second filter cell  118   b , a second half-waveplate  120   b , a third filter cell  118   c , and a third lower half-waveplate  120   c . Then lower right and left beams  114  and  116  are reflected by a retro reflector  122 . As disclosed in  FIG. 2A , the elements  104 ,  112 ,  113   a ,  113   b ,  118   a - 118   c , and  120   a - 120   c  make up a first path  124  of an optical loop of the optical deinterleaver  100 . 
     As disclosed in  FIG. 4 , each of the filter cells  118  disclosed in  FIGS. 2A-2E  includes opposing optical polarization beam splitters  126  and  128  displaced from one another by the wedge turners  130  and  132 . In some example embodiments, the filter cells  118   b  and  118   c  are about 25 GHz cells, and the filter cell  118   a  is an about 50 GHz cell. Each of the filter cells  118   a - 118   c  can be similar to any of the “polarization beam splitting cells” or “optical filter cells” disclosed in U.S. Pat. No. 6,694,066, 6,850,364, or 7,173,763, each of which is incorporated herein by reference in its entirety. 
     As disclosed in  FIGS. 2A-2E , the half-waveplates  120  enable the filter cells  118  to be mounted on bases that lie in the same plane by changing the polarization of the lower right and left beams  114  and  116 . In at least some example embodiments, the first half-waveplate  120   a  is oriented at about 30 degrees, the second half-waveplate  120   b  is oriented at about 12 degrees, and the third lower half-waveplate  120   c  is oriented at about 4.5 degrees. 
     As disclosed in  FIG. 2B  and  FIG. 3 , after the lower right beam  114  is reflected by the retro reflector  122 , the lower right beam  114  passes through a second polarization beam displacer  134 . The second polarization beam displacer  134  vertically divides the lower right beam  114  into a middle right beam  136  and an upper right beam  138 . Then, the middle and upper right beams  136  and  138  pass through a fourth upper half-waveplate  120   d , the third filter cell  118   c , the second half-waveplate  120   b , the second filter cell  118   b , the first half-waveplate  120   a , and the first filter cell  118   a . In at least some example embodiments, the fourth upper half-waveplate  120   d  is oriented at about 49.5 degrees. 
     Similarly, as disclosed in  FIG. 2C , after the lower left beam  116  is reflected by the retro reflector  122 , the lower left beam  116  passes through the second polarization beam displacer  134 . The second polarization beam displacer  134  vertically divides the lower left beam  116  into a middle left beam  140  and an upper left beam  142 . Then, the middle and upper left beams  140  and  142  pass through the third half-waveplate  120   c , the third filter cell  118   c , the second half-waveplate  120   b , the second filter cell  118   b , the first half-waveplate  120   a , and the first filter cell  118   a.    
     Next, as disclosed in  FIG. 2D  and  FIG. 3 , the middle right beam  136  passes through the right half-waveplate  113   a  and the middle left beam  140  passes through the left half-waveplate  113   b . Then, the middle right beam  136  and the middle left beam  140  pass through a third polarization beam displacer  144 . The third polarization beam displacer  144  horizontally combines the middle right beam  136  and the middle left beam  140  into a first output beam  146 . Next, as disclosed in  FIG. 2D , the first output beam  146  passes through a first lateral shift prism  148 . The first lateral shift prism  148  is used to shift the first output beam  146  laterally to increase the distance between the second collimator  106  and the first collimator  104 . Finally, the first output beam  146  exits the optical deinterleaver  100  through the second collimator  106 . As disclosed in  FIG. 2D , the elements  134 ,  118   c - 118   a ,  120   d ,  120   b ,  120   a ,  113   a ,  113   b ,  144 ,  148 , and  106  make up a second path  150  of the optical loop of the optical deinterleaver  100 . 
     Similarly, as disclosed in  FIG. 2E  and  FIG. 3 , the upper right beam  138  passes through the right half-waveplate  113   a  and the upper left beam  142  passes through the left half-waveplate  113   b . Then, the upper right beam  138  and the upper left beam  142  pass through the third polarization beam displacer  144 . The third polarization beam displacer  144  horizontally combines the upper right beam  138  and the upper left beam  142  into a second output beam  152 . Next, as disclosed in  FIG. 2E , the second output beam  152  passes through a second lateral shift prism  154 . The second lateral shift prism  154  is used to shift the second output beam  152  laterally to increase the distance between the third collimator  108  and the first collimator  104 . Finally, the second output beam  152  exits the optical deinterleaver  100  through the third collimator  108 . As disclosed in  FIG. 2E , the elements  134 ,  118   c - 118   a ,  120   d ,  120   b ,  120   a ,  113   a ,  113   b ,  144 ,  154 , and  108  make up a third path  156  of the optical loop of the optical deinterleaver  100 . 
     Although the example optical deinterleaver  100  has been discussed herein in terms of its deinterleaver functionality, it is understood that the deinterleaver  100  can also function as an interleaver. With reference now to  FIGS. 2A ,  2 D,  2 E, and  5 , the first about 10 Gb/s beam  146  and the second about 10 Gb/s beam  152  can enter the optical deinterleaver  100  through the collimators  106  and  108 , respectively, and then be combined into a single interleaved optical signal  110  that exits through the collimator  104 . As disclosed in  FIG. 5 , reversing the direction of the signal stream passing through the optical deinterleaver  100  results in a total transmission capacity of 1600 Gb/s in the C Band. 
     With reference finally to  FIG. 6 , a chart  200  of measured insertion loss of the example optical deinterleaver  100  of  FIG. 1  is disclosed. In particular, the chart  200  demonstrates that the example optical deinterleaver  100  exhibits athermal and flat top about 25 GHz channel spacing. 
     The example embodiments disclosed herein may be embodied in other specific forms. The example embodiments disclosed herein are to be considered in all respects only as illustrative and not restrictive.