Abstract:
A colorless, reconfigurable, optical add-drop multiplexer (a colorless ROADM) is disclosed. The ROADM may include a de-interleaver, a diffraction grating, and a lens. The de-interleaver may separate an input signal into a first output signal, comprising odd channels, and a second output signal, comprising even channels. The diffraction grating may receive the first and second output signals from the de-interleaver. The diffraction grating may separate each of the first and second output signals into individual channels. The lens may collimate the individual channels received from the diffraction grating.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to optical computer networks and more particularly to systems and methods for lowering the manual intervention required to reconfigure an add/drop node within an optical network. 
         [0003]    2. Background of the Invention 
         [0004]    Operators of computer networks, as well as those that supply network components to such operators, are seeking to lower the cost-per-bit to transfer data. One area of focus in this cost-reduction effort is driving as much functionality as possible out of the electrical layer and into the optical layer. As a result, reconfigurable optical add-drop multiplexers (ROADMs) have risen in prominence. 
         [0005]    However, first generation ROADMs are constrained in certain areas such as reconfigurability and automation. These constraints are particularly noticable at add/drop nodes, where costly manual intervention is required. Accordingly, what is needed is an improved ROADM that lowers the required manual intervention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    In order that the advantages of the invention will be readily understood, a more particular description of the invention will be rendered by reference to specific embodiments illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through use of the accompanying drawings, in which: 
           [0007]      FIG. 1  is a schematic diagram of one embodiment of an optical network for transferring data; 
           [0008]      FIG. 2  is a schematic block diagram of one embodiment of a ROADM switching node; 
           [0009]      FIG. 3  is a schematic block diagram of one embodiment of a switching subsystem that may be contained within a ROADM switching node; 
           [0010]      FIG. 4  is a schematic diagram of one embodiment of selected components that may be contained within a ROADM including an optical distributor delivering a collimated, two-dimensional array of wavelength-specific light beams to an optical switch; 
           [0011]      FIG. 5  is a schematic diagram of one embodiment of an interleaver performing an interleaving function; 
           [0012]      FIG. 6  is a schematic diagram of one embodiment of an interleaver performing an de-interleaving function; 
           [0013]      FIG. 7  is a schematic diagram providing a side view of an interleaver, lens, and diffraction grating of an optical distributor; 
           [0014]      FIG. 8  is a schematic diagram providing a perspective view of an diffraction grating and collimator lens of an optical distributor; 
           [0015]      FIG. 9  is a schematic diagram providing a top view of one embodiment of a channel (i.e., wavelength) distribution produced by a diffraction grating of an optical distributor; 
           [0016]      FIG. 10  is a schematic diagram providing a front view of one embodiment of a first MEMS mirror array of an optical switch; 
           [0017]      FIG. 11  is a schematic diagram providing a front view of one embodiment of a second MEMS mirror array of an optical switch; 
           [0018]      FIG. 12  is a schematic diagram of an alternative embodiment of an optical distributor delivering a collimated, two-dimensional array of wavelength-specific light beams to an optical switch; and 
           [0019]      FIG. 13  is a schematic diagram of a single-lens embodiment of an optical distributor. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    It will be readily understood that the components of the present invention, as generally described and illustrated in the Figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the invention, as represented in the Figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of certain examples of presently contemplated embodiments in accordance with the invention. The presently described embodiments will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. 
         [0021]    Referring to  FIGS. 1 and 2 , fiber-optic networks  10  are playing an increasingly important role in transmission of data. To provided the necessary capacity or bandwidth, fiber-optic networks  10  (e.g., nodes  12  within a fiber-optic network  10 ) commonly use wavelength-division multiplexing (WDM) to combine many independent optical signals of different wavelengths onto one optical fiber for long distance transmission. Accordingly, routing a signal through a network  10  may include demultiplexing, switching, recombining, and the like. To provide such functionality, one or more nodes  12  within a network  10  may include one or more ROADMs  14  (e.g., ROADM switching nodes  14 ). 
         [0022]    A ROADM  14  may be defined as an optical subsystem (e.g., an all optical subsystem) that enables a remote network operator to control whether a particular wavelength is added, dropped, or passed through a node  12 . A ROADM  14  may be characterized by the degrees of switching provided thereby. In selected embodiments, a ROADM  14  may have somewhere in the range of two to eight degrees of switching. 
         [0023]    Each degree of switching may correspond to a different switching direction and may be associated with a transmission fiber pair. Accordingly, a two degree ROADM  14  may switch in two directions. These two directions may be referred to as East and West. Similarly, a four degree ROADM  14  may switch in four directions, which may be referred to as North, South, East, and West. In  FIG. 2 , a four degree ROADM  14  is illustrated. To support these four degrees of switching, the illustrated ROADM  14  includes at least four switching subsystems  16  (e.g., four wavelength selective switches). 
         [0024]    Referring to  FIG. 3 , in selected embodiments, a switching subsystem  16  may provide “colorless” functionality. That is, first generation ROADMs are typically limited by fixed wavelength assignments. Accordingly, in first generation ROADMs, when a wavelength is selected or rerouted, a transceiver must be manually connected to the correct mux/demux port at the add/drop site. However, in embodiments in accordance with the present invention, a switching subsystem  16  may automate the assignment of add/drop wavelength functionality. Accordingly, a switching subsystem  16  may enable any wavelength (i.e., color) to be assigned to any port of an add/drop site. Moreover, a switching subsystem  16  in accordance with the present invention may enable such an assignment to be made automatically (e.g., under the direction of a controlling software program), without the need for any manual work on site. 
         [0025]    A ROADM  14  in accordance with the present invention may have any suitable configuration. For example, a ROADM  14  may include any suitable combination of electrical hardware, optical hardware, software, or some subset thereof. In selected embodiments, a ROADM  14  may include one or more switching subsystems  16 . Each such switching subsystem  16  may include one or more of an optical distributor  18 , optical switch  20 , channel monitor  22 , amplifier  24 , some other component(s)  26 , or the like. 
         [0026]    An optical distributor  18  may prepare a signal for an optical switch  20 . For example, in certain embodiments, an optical distributor  18  may generate a free space distribution of wavelengths. An optical switch  20  may enable one or more signals to be selectively switched from one circuit to another. A channel monitor  22  may assess the quality of channel data by measuring selected optical characteristics. Accordingly, a channel monitor  22  may ensure correct switching, set levels for dynamic equalization of the gain of an optical amplifier, provide system alarms and error warnings, or the like or some combination thereof. An amplifier  24  may amplify an optical signal. It may do so directly, without first converting the optical signal to an electrical signal. 
         [0027]    Referring to  FIG. 4 , in selected embodiments in accordance with the present invention, a switching subsystem  16  (e.g., a switch  20 ) may employ multiple microelectromechanical system (MEMS) mirror arrays  28  (e.g., arrays  28  of mirrors wherein each mirror pivots about two orthogonal axes). Accordingly, a switching subsystem  16  may be configured to overcome certain disadvantages and capture certain benefits that may be associated with MEMS mirror arrays  28 . 
         [0028]    For example, for a colorless ROADM  14  using three-dimensional MEMS mirror arrays  28 , high deflection angles may make it difficult to properly switch forty channels, ninety-six channels, or the like arrayed in a single line. Also, there may be benefits to incorporating within a MEMs-based ROADM  14  a variable optical attenuation function. While the use of an arrayed waveguide grating (AWG) or a thin-film-based, dense wavelength division multiplexing (DWDM) device may reduce the need for optical attenuation, it may be beneficial to incorporate a wavelength demultiplexer, switch, and attenuation function inside a small module. 
         [0029]    In selected embodiments, to overcome certain disadvantages and capture certain benefits that may be associated with MEMS mirror arrays  28 , a switching subsystem  16  may couple an optical distributor  18  and an optical switch  20 . In certain embodiments, an optical distributor  18  may generate a free space distribution of wavelengths that may be handled by a corresponding switch  20  with selective attenuation and without high deflection angles. 
         [0030]    Referring to  FIGS. 4-6 , in discussing and illustrating a free space distribution of wavelengths, it may be helpful to establish a coordinate axes  30 . For example, it may be helpful to discuss a free space distribution in terms of longitudinal  30   a,  lateral  30   b,  and transverse  30   c  directions extending orthogonally with respect to one another. 
         [0031]    In selected embodiments, to provide a free space distribution of wavelengths, an optical distributor  18  may include an optical interleaver  32 . In operation, an interleaver  32  may interleave multiple input signals to form a single output signal. For example, in selected embodiments or situations, an interleaver  32  may interleave a plurality of “odd” channels  34  with a plurality of “even” channels  36  to form a single composite signal  38 . Alternatively, an interleaver  32  may deinterleave a single input signal to form multiple output signals. For example, in certain embodiments or situations, an interleaver  32  may deinterleave a single composite signal  38  into its constituent odd and even channels  34 ,  36 . 
         [0032]    An optical interleaver  32  in accordance with the present invention may comprise any suitable hardware or be configured in any suitable way. In selected embodiments, an optical interleaver  32  may operate in free space. This may provide a space-efficient and compact overall device and may eliminate the need for fusion splicing and two fiber collimators. However, a fiber-pigtail optical interleaver may still be suitable. 
         [0033]    Referring to  FIGS. 4 and 7 , in certain embodiments, an optical distributor  18  may include an optical diffraction grating  42  (e.g., either a transmissive or reflective diffraction grating). In certain embodiments or situations, an optical diffraction grating  42  may receive the even and odd channels  34 ,  36  from an interleaver  32 . For example, the even and odd channels  34 ,  36  may exit the interleaver  32  as parallel collimated beams. A lens  46  may focus the beams output from the interleaver  32  onto a common spot  44  on the diffraction grating  42 . 
         [0034]    Referring to  FIGS. 4 ,  8 , and  9 , an optical diffraction grating  42  may receive from an interleaver  32  a plurality of light beams focused onto a common spot. The axes of the light beams may be separated by a small angles with respect to a first direction (e.g., a transverse direction  30   c ) from one another. An optical diffraction grating  42  may separate each such signal or beam in another direction (e.g., a longitudinal direction  30   a ). For example, a diffraction grating  42  may separate each light signal or beam into its constituent wavelengths or channels. Accordingly, acting in combination, an interleaver  32  and a diffraction grating  42  may generate a two-dimensional array of channels where each such channel occupies its own space. 
         [0035]    In selected embodiments, an interleaver  32  may deliver two light signals or beams to a diffraction grating  42 . A first light beam may comprise all of the even channels  34 , while a second light beam comprises all of the odd channels  36 . The diffraction grating  42  may distribute the even channels  34  within a first plane  48 . The diffraction grating  42  may distribute the odd channels  36  within a second plane  50 , space from the first plane  48 . The angular spacing between the first and second planes  48 ,  50  may corresponding to or match the angular spacing at which the first and second beams are delivered to the diffraction grating  42 . 
         [0036]    When viewed from a direction orthogonal to the first plane  48 , second plane  50 , or both, the paths of the various channels may be identified. For example, as shown in  FIG. 9 , the path  52  of each of the odd channels  36  may be illustrated using a solid line. The path  54  of each of the even channels  34  may be illustrated using a dashed line. Thus, as illustrated, in addition to a separation in one direction (e.g., a transverse direction  30   c ), the even and odd channels  34 ,  36  may also be spaced from one another in another direction (e.g., a longitudinal direction  30   a ). 
         [0037]    In selected embodiments, an optical distributor  18  may include a second lens  56 . Such a lens  56  may be positioned optically between a diffraction grating  42  and a switch  20 . A second lens  56  may collimate the various channels output by a diffraction grating  42 . Accordingly, an optical distributor  18  may deliver to a switch  20  a collimated, two-dimensional array of wavelength-specific light beams that may be properly handled by the switch  20 . 
         [0038]    Referring to  FIGS. 4 ,  10 , and  11 , a switch  20  in accordance with the present invention may have any suitable configuration. In selected embodiments, a switch may be MEMS-based and include multiple MEMS mirror arrays  28 . For example, in certain embodiments, a switch  20  may include a first MEMS mirror array  28   a  and a second MEMS mirror array  28   b.    
         [0039]    The first and second mirror arrays  28   a,    28   b  may each include a substrate  58  supporting a plurality of mirrors  60 . Each of the mirrors  60  may be pivotally secured to the corresponding substrate  58  to enable two-dimensional pivoting. In selected embodiments, electrostatic actuators may be located in the respective substrates  58 . A voltage may be applied to each of the electrostatic actuators to produce a desired pivoting of a corresponding mirror  60 . 
         [0040]    A first array  28   a  may receive a collimated, two-dimensional array of wavelength-specific light beams from an optical distributor  18 . A first array  28   a  may selectively reflect those channels on to other components within the switch  20 . For example, by pivoting a particular mirror  60  of a first array  28   a,  a corresponding channel may be reflected onto a particular mirror of a second array  28   b.  Pivoting of the particular mirror  60  of the second array  28   b  may result in the channel being reflected into a particular fiber  62 . 
         [0041]    Accordingly, one pivoting mirror  60  of a first array  28   a  may be located in the path of each channel being propagated by an optical distributor  18 . The pivoting mirrors  60  may each pivot relative to a mirror substrate  58  to alter an angle at which the channel is reflected therefrom. The angle may be controlled so that the channel eventually falls on a desired pivoting mirror  60  of a second array  28   b  in line with a respective fiber  62  to which the channel is to be switched. 
         [0042]    In selected embodiments, a mirror  64  may be positioned optically between a first array  28   a  and a second array  28   b.  Accordingly, a mirror  64  may direct the channels from a first array  28   a  to a second array  28   b.  Such a mirror  64  may have any suitable configuration. For example in certain embodiments, a mirror  64  may comprise a single, substantially flat surface. Alternatively, a mirror  64  may be curved to assist in reducing the deflection angles imposed on the mirrors  60  of the first and second arrays  28   a,    28   b.    
         [0043]    A second array  28   b  may receive various channels from a mirror  64  and selectively reflect the channels into a lens array  66 . A lens array  66  may include a plurality of focusing lenses. A lens array  66  may be mounted to a fiber block  68  such that each focusing lens is located optically over the end of a corresponding output optical fiber  62 . For example, a particular mirror  60  of a second array  28   b  may reflect a channel onto a particular lens located within the lens array  66 . The particular lens may then pass (e.g., focus) the channel into the particular fiber  62 . 
         [0044]    The positions and orientations of the various components of an optical distributor  18  and an optical switch  20  may be arranged in any suitable manner. For example, in certain embodiments, a first array  28   a  may be positioned so as to be coplanar with a second array  28   b.  Alternatively, first and second arrays  28   a,    28   b  may be positioned so as to be non-coplanar. 
         [0045]    Similarly, the respective positions and orientations between an optical distributor  18  and an optical switch  20  may be arranged in any suitable configuration. For example, as illustrated in  FIG. 4 , the components  28   a,    28   b,    32 ,  42 ,  46 ,  56 ,  64 ,  66 ,  68  of an optical distributor and switch  18 ,  20  may be substantially coplanar (e.g., bisected by a plane containing the longitudinal and lateral directions  30   a,    30   b ). Alternatively, the components  28   a,    28   b,    32 ,  42 ,  46 ,  56 ,  64 ,  66 ,  68  of an optical distributor and switch  18 ,  20  may be substantially non-coplanar. For example, the components  32 ,  42 ,  46 ,  56  of an optical distributor  18  may be largely bisected by one plane (e.g., a plane containing the longitudinal and lateral directions), while the components  28   a,    28   b,    64 ,  66 ,  68  of an optical switch  20  may be largely bisected by a different plane (e.g., a plane containing the lateral and transverse directions  11   b,    11   c ). 
         [0046]    In selected embodiments, a first array  28   a  may be configured to receive the channels delivered thereto by an optical distributor  18 . For example, in certain embodiments, an optical distributor  18  may output a two-dimensional array of wavelength-specific light beams arranged in two rows of twenty channels. Accordingly, a first array  28   b  may comprise a two-dimensional array of mirrors  60  arranges in two rows of twenty, as shown in  FIG. 10 . 
         [0047]    In certain embodiments, a first array  28   a  may be arranged in an interleaved manner and configured to provide 100% yield. For example, the rows of channels output by an optical distributor  18  may be slightly offset from one another. Accordingly, the rows of mirrors  60  on a first array  28   a  may be similarly offset from one another. 
         [0048]    First and second arrays  28   a,    28   b  need not present identical, multi-dimensional arrays of mirrors  60 . While a first array  28   a  may be configured to match an output of an optical distributor  18 , a second array  28   b  may have mirrors  60  arranged for some other purpose. In selected embodiments, a second array  28   b  may have more mirrors  60  than a first array  28   a.  That is, the second array  28   b  need not have 100% yield. Alternatively, or in addition thereto, the mirrors  60  of a second array  28   b  may be interleaved, arranged to lower the required angles of deflection, arranged to be less sensitive to vibration, and or the like or some combination thereof. 
         [0049]    By employing an optical distributor  18  in accordance with the present invention, a switching subsystem  16  may support the use of larger MEMS mirrors  60  with larger pitch. Moreover, such an arrangement may enable the use of small deflection angles for all mirrors  60 . For example, when using a curved intermediate mirror  64 , deflection angles for all mirrors  60  of the first and second arrays  28   a,    28   b  may be less than five degrees. This may reduce the sensitivity of a switch  20  to vibration. Additionally, a first array  28   a  may have a larger deflection angle in one axis and a smaller deflection angle in another axis. The smaller deflection angle may be used for attenuation and switching only two or four rows. The larger deflection angle may be used for switching in larger space. 
         [0050]    A combination between an optical distributor  18  and a corresponding optical switch  20  may be configured to operate (i.e., pass signal) in a first direction, operate in a second direction opposite to the first direction, or selectively switch between operation in the first direction and operation in the second direction. When operating in the first direction, a combined distributor  18  and switch  20  may receive signal on a single fiber  38  and output signal on several fibers  62  (e.g., forty fibers  62 ). When operating in the second direction, a combined distributor  18  and switch  20  may receive signal on multiple fibers  62  (e.g., forty fibers  62 ) and output signal on a single fiber  38 . Accordingly, the functionality of the various components  28   a,    28   b,    32 ,  42 ,  46 ,  56 ,  64 ,  66 ,  68  may be reversed. 
         [0051]    Referring to  FIG. 12 , in selected embodiments, an optical switch  20  may operate without a mirror  64  positioned optically between the first and second arrays  28   a ,  28   b.  Accordingly, when signal is traveling in the first direction, a first array  28   a  may reflect channels directly to a second array  28   b.  Conversely, when signal is traveling in the second direction, a second array  28   b  may reflect channels directly to the first array  28   a.    
         [0052]    Referring to  FIG. 13 , in certain embodiments, an optical distributor  18  may include a single lens  70 . This single lens  70  may perform the functions of both lens  46 ,  56  included in other embodiments. For example, when signal is traveling in the first direction, a single lens  70  may both direct the even and odd channels  34 ,  36  onto the diffraction grating  42  and collimate the channels output by the diffraction grating  42 . 
         [0053]    When geometric or space considerations dictate, certain embodiments of an optical distributor  18  may include a reflector  72 . For example, in selected embodiments involving a single lens  70 , an optical distributor  18  may include a reflector  72  positioned optically between an interleaver  32  and the lens  70 . This may enable an interleaver  32  to be positioned at an out of the way location. 
         [0054]    The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.