Abstract:
An optical communication channel switch includes an aberration corrected spectrometer adapted for receiving plural channels of communication in a one dimensional array of sites where each site corresponds to a source, and a channel selector for selectively switching channels. After receiving the plural channels, the aberration corrected spectrometer provides the channels in a two dimensional array in which channels are distributed in rows (or columns) of similar frequency and different sources and in columns (or rows) of differing frequency and common sources. The channel selector selectively switches channels among sites in the two dimensional array and provides a single dimensional reconfigured array of frequency separated channels that is combined into the two dimensional array. Another aberration corrected spectrometer receives the selectively switched two dimensional array and combines the channels into a single dimensional array of sites having one or more frequency separated channels.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Serial No. 60/170,801 filed Dec. 15, 1999; the disclosure of which is incorporated herein by reference. This claims priority under 35 U.S.C. § 120, application No. 09/674,217 filed Oct. 27, 2000, which is U.S. National Phase of PCT/US99/09270 filed Apr. 29, 1999, which claims priority to U.S. Provisional Application No. 60/083,471 filed Apr. 29, 1998. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable  
         BACKGROUND OF THE INVENTION  
         [0003]    Spectrometers are known and used to provide a spectral image of a scene. FIG. 8 illustrates an example of a known spectrometer  800 . In this spectrometer  800 , light from an image  810  passes through a slit  820  and a first concave mirror  830  of a reflective assembly  835  receives an image  812 . The first mirror  830  is in a light path from the slit  820  and reflects light to a convex diffraction grating  860 . The convex diffraction grating  860  receives the reflected light from the first mirror  830 . The diffraction grating  860  spectrally disperses the image received from the first mirror  830  into a spectral image  814 . A second concave mirror  840  of the reflective assembly  835  receives the spectral image  814  from the diffraction grating  860  and reflects the spectral image  814  to a detector  850 , such as a CCD array of a camera or other device.  
           [0004]    Preferably, the diffraction grating  860  is a known aberration corrected convex diffraction grating, which provides for simultaneous high spatial and spectral imaging resolution and low distortion. By using the aberration corrected convex diffraction grating, the spectrometer  800  provides a high resolution that may function for a wide variety of applications such as optical communication channel switching.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    An optical communication channel switch includes an aberration corrected spectrometer adapted for receiving plural channels of communication in a one dimensional array of sites where each site corresponds to a source, and a channel selector for selectively switching channels. After receiving the plural channels, the aberration corrected spectrometer provides the channels in a two dimensional array in which channels are distributed in rows (or columns) of similar frequency and different sources and in columns (or rows) of differing frequency and common sources. The channel selector selectively switches channels among sites in the two dimensional array and provides a single dimensional reconfigured array of frequency separated channels that is combined into the two dimensional array. Another aberration corrected spectrometer receives the selectively switched two dimensional array and combines the channels into a single dimensional array of sites having one or more frequency separated channels. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0006]    The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:  
         [0007]    [0007]FIG. 1 illustrates an optical communication switching system according to an embodiment of the present invention;  
         [0008]    [0008]FIG. 2 illustrates an array of switching channels according to an embodiment of the present invention;  
         [0009]    [0009]FIG. 3 illustrates an optical communication switching system utilizing a circulator according to another embodiment of the present invention;  
         [0010]    [0010]FIG. 4 illustrates a parallel stage optical communication switching system according to another embodiment of the present invention;  
         [0011]    [0011]FIG. 5 illustrates a system for switching channels in a two dimensional array according to an embodiment of the present invention;  
         [0012]    [0012]FIG. 6 illustrates a single spectrometer system for another embodiment of the present invention;  
         [0013]    [0013]FIG. 7 illustrates a two dimensional array of channels generated by the single spectrometer system illustrated in FIG. 6; and  
         [0014]    [0014]FIG. 8 illustrates a known spectrometer. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    Referring to FIG. 1, an optical communication channel switching system is shown for an embodiment of the invention. The system generally comprises first and second aberration corrected spectrometers  1  and  2  connected by a switch and manager  110  that is controlled by a processor  120 . In the first spectrometer  1 , light of an image  12  from a communication link, such as an optical fiber bundle, passes through a connector  10  onto a first concave mirror  20 . The first mirror  20  is in a light path from the connector  10  and reflects light to a first aberration corrected convex diffraction grating  30 . The first diffraction grating  30  receives the reflected light from the first mirror  20  and spectrally disperses the image received from the mirror  20  into a spectral image  16 . A second concave mirror  40  receives the spectral image  16  from the first diffraction grating  30  and reflects the spectral image  16  to a detector  50 .  
         [0016]    The spectrometer  1  receives multiple communication channels in a one dimensional array  210  where each site corresponds to a source (l 1 , l 2 , . . . l n ) as shown in FIG. 2. For instance, the sources (l 1 , l 2 , . . . l n ) may be vertical inputs of optical fibers. The spectrometer  1  generates a two dimensional array of channels  220  arranged according to frequency and source. For example, the columns of the array  220  may be arranged to have the same frequency and different sources and the rows may be arranged to have the same source and different frequencies. An example of this configuration is shown in FIG. 2 where the array  220  includes rows of sources (l 1 , l 2 , . . . l n ) and columns of frequencies (λ 1 , λ 2 , . . . λ n ). It is realized that this configuration can be arranged as desired. For instance, the rows may include frequencies and the columns may include sources.  
         [0017]    Within this array  220 , the switch and manager  110  may selectively switch to different array sites so that a one dimensional array  230  of frequency separated channels may be output from the second aberration corrected spectrometer  2 . The switch and manager  110  may be a MEMS device, an LCD array, a bubble switch, or a waveguide. The selectable switching performed by the switch and manager  110  is controlled by a processor  120 . For example, the processor  120  may control the switching of a channel position between sites within the array  220 , between sites of the same frequency and different sources within the array  220 , or between sites of different frequencies within the array  220 .  
         [0018]    A detector  60  detects the output of frequency separated channels from the switch and manager  110 . Then, a third mirror  70  of the second spectrometer  2 , which is aligned in the light path, receives a spectral image  22  of these reconfigured channels. The third mirror  70  reflects the spectral image  22  onto a second aberration corrected convex diffraction grating  80 . A fourth concave mirror  90  is in the light path of the refracted light signal received from the second diffraction grating  80 . The fourth mirror  80  reflects the light toward a connector  100  aligned in the light path. The light passes through the connector  100  and forms a one dimensional image array  102  that passes onto a communication link.  
         [0019]    An embodiment of this system may also include a zero-order detector  130  and an optical spectral analyzer  140  as illustrated in FIG. 1. The zero-order detector  130  is aligned for receiving the zero-order signal of the image  12 . This zero-order signal is then input to the spectral analyzer  140  for use as a monitor of the received image. The spectral analyzer  140  may include a television monitor for viewing each channel of the received image.  
         [0020]    Referring to FIG. 3, an optical communication switching system utilizing a circulator for selectively switching signals is shown according to another embodiment of the invention. A circulator  300  receives a signal  302  and a signal  304  is selectably input to an aberration corrected spectrometer  310 . In this spectrometer  310 , light passes through a communication link to a connector  320 . A first concave mirror  330  receives the signal from the connector  320 . The first mirror  330  is aligned in a light path with the connector  320  and an aberration corrected convex diffraction grating  340 . The diffraction grating  340  receives the reflected light from the first mirror  330  and spectrally disperses the received signal into a spectral image  306 . A second concave mirror  350  receives the spectral image  306  from the diffraction grating  340  and reflects the spectral image  306  to an array of reflectors  360 .  
         [0021]    The reflector array  360  reflects back all of the spectral image  306  toward the second mirror  350 . The spectral image  306  is then reflected toward the diffraction grating  340 . The diffraction grating  340  directs a refracted image toward the first mirror  330  so that the refracted image is received at the slit  320 . A signal  308  is received by the circulator  300  and is output as signal  312 .  
         [0022]    The source may include a vertical input of optical fibers connected to multiple circulators so that a one dimensional array of sources is input to this switching system. A two dimensional array of channels arranged according to frequency and source will then be generated at the reflector arrays  360  from this input. The reflector arrays  360  may be MEMS devices designed such that desired frequencies are prevented from being reflected back. Also, the reflector arrays  360  may be connected to a processor  370  which selectively controls the frequencies that may be reflected back. Thereafter, a one dimensional array of reconfigured channels is output to the circulators.  
         [0023]    Referring to FIG. 4, a channel switch having parallel stages is shown. A signal  402  is transmitted over a communication link and is received by a multiplexor  400 , which directs signals  404  and  406  toward first and second channel switch stages  420  and  460  respectively. The first and second channel switch stages  420  and  460  comprise similar elements and perform similar functions as in the switching systems described in the previous embodiments. The first channel switch stage  420  includes a connector  422  for receiving the signal  404  from a communication link. This signal  404  is received by a first concave mirror  424 , and reflected towards a first aberration corrected convex diffraction grating  428 . A spectral image is directed from the diffraction grating  428  toward a second concave mirror  426  which reflects this image toward a detector  430 . A switch and manager  440  receives this signal and can selectively switch channels via a processor associated therewith.  
         [0024]    The reconfigured channels from the switch and manager  440  are received by a detector  442 , directed toward a third concave mirror  444 , and reflected towards a second aberration corrected convex diffraction grating  448 . The second diffraction grating  448  directs a refracted signal towards a fourth concave mirror  446  and reflects the signal towards a connector  450  for outputting a signal  452  over a communication link.  
         [0025]    Similarly, the second channel switch stage  460  includes a connector  462  for receiving the signal  406  from the multiplexor  400  via the communication link. This signal  406  is received by a first concave mirror  464 , and reflected towards a first aberration corrected convex diffraction grating  468 . A spectral image is directed from the diffraction grating  468  toward a second concave mirror  466  which reflects this image toward a detector  470 . A switch and manager  480  receives this signal and can selectively switch channels via a processor associated therewith.  
         [0026]    The reconfigured channels from the switch and manager  480  are received by a detector  482 , directed toward a third concave mirror  484 , and reflected towards a second aberration corrected convex diffraction grating  488 . The second diffraction grating  488  directs a refracted signal towards a fourth concave mirror  486  that reflects the signal towards a connector  490  for outputting a signal  492  over a communication link.  
         [0027]    The first and second stages  420  and  460  are arranged to operate in parallel and provide redundancy. The output signals  452  and  492  are input to a switch  496 . The switch  496  may select one of the signals for outputting therefrom as signal  498 . Therefore, if one of the stages fails to operate, the system may switch over to the other stage to ensure that communication switching is provided. It will be appreciated that more than two parallel stages may be provided. The number of stages provided can then be selected based on the desired amount of redundancy for ensuring the communication switching.  
         [0028]    With respect now to FIG. 5 there is illustrated a system for switching the channels as they appear on a first two dimensional array  510 , as illuminated by an aberration corrected spectrometer as shown above. The array  510  is a two dimensional (M×N) array as noted above and for the purpose of switching between sites in the array each site illumination is applied to a two dimensional (M×N) switching unit  512 . The illumination from each site is applied to corresponding light pipes or optical fibers in a bundle  514  for transmission to the switching unit  512 . Typically the light at each site is applied to the corresponding fiber in the bundle  514  by an array  516  of lenses that focus the light onto the core of the fiber.  
         [0029]    The switching unit  512  diverts the light associated with each site to a different site as specified by a processor  518  and applies the thus switched light to fibers in an output bundle  520  through focusing lenses in an output array  522  to an array  524  (M×N) as before for use by the second aberration corrected spectrometer.  
         [0030]    While other means may be used to transfer the light between the arrayed light  510  and the switching unit  512  and the output array of light  524 , the apparatus described above allows for the remote location of the spectrometers and switching unit for ease of servicing or replacement.  
         [0031]    The switching unit  512  is implementable in a variety of ways. Where switching involves only switching, including elimination, of channels of the same wavelength, a MEMS switch of micro machined silicon for example may be used under control of processor  518  to direct by way of mirrored surfaces of a set of MEMS arrays the light from one array location to another location at the same wavelength. The switched to channel must have been vacant, switched elsewhere itself or eliminated to avoid the presence of two channels in the same array location or site. A set of input and output bubble switches as it is known in the art may also be used for the same purpose. Where channels are to be switched between wavelengths a frequency converter or modulator is used in conjunction with MEMS or bubble switches as mention above to, at some point in the switching, change the wavelength to one appropriate to the array location where the channel is to be switched.  
         [0032]    In another embodiment of the invention as illustrated in FIGS. 6 and 7, a single spectrometer is used to provide the function of two, albeit with only half of the number of channels that could otherwise be handled. As shown in FIG. 6 a single spectrometer of grating  614  and mirrors  610  and  612  as described above receives at a single dimension input array  614  the light from a bundle  616  of fibers. The light from these is spectrally spread into a two dimensional array  618  of reflectors which are switchable between a reflect and deflect or absorb state controlled by a processor  620  to determine which channels are returned through the spectrometer to the input array  614  for application to the output fibers in a bundle  622 .  
         [0033]    The number of fibers and thus channels is one half the number the system could handle with two spectrometers because the fibers are interleaved between input fibers  710 , shown in FIG. 7, in the bundle  616  and output fibers  720  in the bundle  622 . The channel switch array  618  is shown in array  714  to have the input spectra  718  and output spectra alternating as well. The switch array  618  includes a mirror system or the equivalent to transport or block the light from one input spectra  718  to individual channels in the corresponding output spectra  716  using, MEMS devices, bubble switches and mirrors, or any other light control elements. Alternatively, the geometry of the spectrometer of FIG. 6 can be structured so that the input and output bundles  710 ,  720  could be entirely separated at opposite ends of the input array  614  and the array  714  be a direct reflection back of the incoming light, or not as the CPU  620  designates.  
         [0034]    Having described various embodiments of the invention, it will be apparent to those skilled in the art that other embodiments incorporating these concepts may be used. Accordingly, it is submitted that the invention should not be limited to the described embodiments but rather should be limited only by the spirit and scope of the appended claims.