Abstract:
An optical wavelength division multiplexing (WDM) device comprising optical components that are integrated together to provide an optical WDM that does not require circulators, that has simplified alignment and that is relatively low in cost. The WDM device comprises an integrated port separator, a dispersive element and a reflector. The integrated port separator comprises various optical components that spatially separate the polarization components of a light beam input through an input port of the integrated port separator. The spatially separated polarization components are output from the integrated port separator and impinge on the dispersive element, which spatially separates the wavelengths associated with the polarization components impinging thereon. The spatially separated wavelengths then impinge on the reflective element and are reflected with angles of polarization that depend on the state of the reflective element. The reflected polarization components maintain their respective wavelengths when they are reflected. However, when they are reflected, they are directed along a path through the integrated port separator that depends on the angles of polarization of the reflected polarization components, which depends on the state of the reflective element.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a wavelength division multiplexer (WDM) and, more particularly, to an optical WDM that is a reflective system and is integrated.  
           [0002]    Optical WDMs enable light of multiple wavelengths to be spatially dispersed such that each wavelength of light is spatially separated from every other wavelength of light. WDM devices typically comprise two major functional portions. The first portion provides spatial demultiplexing (i.e., the dispersion) of the individual wavelengths through the use of a grating (e.g., an array waveguide grating, a filter array, etc.). The second portion then acts on one or more of the spatially dispersed wavelengths for purposes of, for example, attenuation, monitoring, compensation or switching.  
           [0003]    In a reflective system, these wavelengths are then sent back through the same dispersion element, thereby multiplexing them (i.e., combining the wavelengths) again onto one optical fiber. In fiber optic networks, reflective WDM systems are increasingly being used because of their lower complexity, smaller size and lower part count compared to transmissive WDM systems. However, the use of a reflective system requires the use of circulators to separate the incoming and outgoing signals. Circulators are often expensive and difficult to integrate into a small optical system. In addition, systems using polarization sensitive elements are more complex and require another circulator-like separation stage to route a signal between the different ports. In addition to having a large part count, these types of systems typically require precision alignment of several optical components, which is time consuming and expensive.  
           [0004]    Accordingly, a need exists for an optical WDM device that is a reflective system, but that is smaller in size than known reflective WDM systems, that has a smaller part count than known reflective WDM systems, that does not require a circulator, and that does not require alignment of optical components.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention provides an integrated, reflective optical WDM device comprising optical components that are integrated together to provide a reflective WDM device that does not require any circulators, that has simplified alignment due to its integrated characteristics, and that is relatively low in cost. The WDM device comprises the integrated port separator, a dispersive element and a reflector.  
           [0006]    The integrated port separator comprises various optical components that spatially separate the polarization components of a light beam input through an input port of the integrated port separator. The spatially separated polarization components are output from the integrated port separator and impinge on the dispersive element, which spatially separates the wavelengths associated with the polarization components impinging thereon. The spatially separated wavelengths then impinge on the reflective element and are reflected with angles of polarization that depend on the state of the reflective element. The reflected polarization components maintain their respective wavelengths when they are reflected. However, when they are reflected, they are directed along a path through the integrated port separator that depends on the angles of polarization of the reflected polarization components, which depends on the state of the reflective element.  
           [0007]    Preferably, the reflective element comprises an array of liquid crystal display (LCD) pixels, each of which is individually controllable. Thus, the path of each polarization component through the integrated port separator depends on the state of the LCD pixel upon which the polarization component impinges, which depends on the wavelength associated with each polarization component and the manner in which the dispersive element spatially separates the wavelengths to cause the corresponding polarization component to impinge on the reflective element.  
           [0008]    The optical device can be used for various purposes, such as, for example, for protection switching, in add/drop modules and in other applications where a polarization sensitive manipulation of wavelengths is needed or desired. These and other features and advantages of the present invention will become apparent from the following description, drawings and claims.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a schematic diagram of the optical device of the present invention in accordance with one embodiment.  
         [0010]    [0010]FIG. 2A is a top view of the optical device of the present invention shown in FIG. 1.  
         [0011]    [0011]FIG. 2B is a side view of the optical device of the present invention shown in FIG. 1.  
         [0012]    [0012]FIG. 3 is a perspective view of the optical device of the present invention configured in a particular manner using particular components and materials.  
         [0013]    [0013]FIG. 4 is a polarization diagram demonstrating the manner in which the components shown in FIG. 3 perform particular polarization functions for wavelength division multiplexing.  
         [0014]    [0014]FIG. 5A is a polarization diagram demonstrating another embodiment that utilizes a different configuration of components and the manner in which the components perform particular polarization functions to enable wavelength division multiplexing to be performed.  
         [0015]    [0015]FIG. 5B is a top view of the WDM device of the present invention represented by FIG. 5A.  
         [0016]    [0016]FIG. 5C is a side view of the WDM device of the present invention represented by FIG. 5A.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    An example design of the integrated optical WDM of the present invention in accordance with one embodiment is shown in FIGS.  1 - 4 . FIG. 1 is a schematic diagram of the optical WDM  20  of the present invention. The WDM  20  preferably comprises four pigtailed ports, I 1 , O 1 , I 2  and O 2 , which are represented by numerals  21 ,  22 ,  23  and  24 , respectively, a directional stage  25 , a polarization stage  26 , a dispersion element  28  and a reflective element  30  having a plurality of states. The reflective element  30  preferably is an array of liquid crystal cells, or pixels, each having a plurality of states that can be controllably selected.  
         [0018]    Each of the input ports  21  and  23  is configured to receive light from an end of an optical fiber (not shown). Each of the output ports  22  and  24  is configured to output light into an end of an optical fiber. Optics for relaying the light output between the fibers and the integrated WDM optics, may include, for example, gradient-index (GRIN) lenses, micro-lenses or thermally expanded core (TEC) fibers.  
         [0019]    The WDM device  20  can be viewed as having a 2-stage separation in a tree-like structure. In the stage represented by the dashed box  25 , the light entering input ports I 1  and  12  is split into separate polarization beams that are then operated on by various optical components to provide them with a particular polarization. Each polarized beam may comprise a plurality of wavelengths of light. Since the direction of the light is used to define the positions of the light paths I 1  and O 1  and I 2  and O 2 , respectively, the stage  25  will be referred to herein as the directional stage. In the stage represented by dashed box  26 , the path of the light depends on the polarization of the light on the incoming light paths I 1  and I 2  and on the outgoing light paths O 1  and O 2 . Therefore, stage  26  will be referred to herein as the polarization stage because it directs the light based on its polarization.  
         [0020]    For the input beams I 1  and  12  propagating through the stage  26 , the stage  26  provides the polarization components associated with each input beam with a particular polarization that causes light from I 1  and I 2  to be reflected along output paths O 1  and O 2 , respectively, when the reflective element  30  is not rotated, and that causes light from I 1  and I 2  to be reflected along output paths O 2  and O 1 , respectively, when the reflective element  30  is rotated. For the output beams O 1  and O 2 , the polarization of the light depends on the state of the reflective element  30 , which determines how the light will be operated on by the polarization stage  26  when it is reflected by the reflective element  30 .  
         [0021]    It should be noted that the dispersion element  28  receives the polarization components from the polarization stage  26  as they propagate towards the reflective element  30  and disperses (i.e., spatially separates) the wavelengths and their respective polarization components, thereby causing the polarization components to impinge on different pixels of the LC pixel array of the reflective element  30 . As stated above, each pixel has a plurality of states that can be selectively controlled.  
         [0022]    In the preferred embodiment, if the LC pixel upon which polarization components from the I 1  path impinge is not rotated, the polarization components will be output via the O 1  path. Conversely, if the LC pixel upon which polarization components from the I 1  path impinge is rotated by 90°, the polarization component will be output via the O 2  path. Likewise, if the LC pixel upon which polarization components from the I 2  path impinge is not rotated, the polarization components will be output via the O 2  path. Conversely, if the pixel upon which a polarization components from the I 2  path impinge is rotated by 90°, the polarization components will be output via the O 1  path.  
         [0023]    Because the reflected polarization components have signatures of the wavelengths associated with them, outputting the reflected polarization components along a particular path is the equivalent of outputting the wavelengths associated with the reflected polarization components along the particular path. For example, if light input at I 1  comprises certain wavelengths that need to be output via output path O 2  (i.e., dropped, or tapped off, at a certain location in a network) and other wavelengths need to continue in the forward direction (i.e., through output path O 2 ), then certain pixels of the reflective element  30  would be rotated by 90° and other pixels would not be rotated. For the pixels that are rotated, the wavelengths of light associated with the reflected polarization components would be combined by the dispersion element  28  and output via path O 2 . For the non-rotated pixels, the wavelengths of light associated with the polarization components reflected by those pixels would be combined by the dispersion element  28  and output via path O 1 . Thus, it can be seen how light of different wavelengths can switched so that it is output through the O 1  port or the O 2  port, regardless of whether the light is input through input port I 1  or input port I 2 .  
         [0024]    In order to implement the directional stage  25 , preferably walk-off crystals, faraday rotators and half waveplates are utilized to accomplish light path separation. These components are selected and combined in such a way that the light from either of the input ports I 1   21  and I 2   23  that is reflected by the reflective element  30  can only enter the output ports O 1   22  and/or O 2   24 . In other words, reflection of the light back to an input port ca be avoided. In order to implement the polarization stage  26 , a polarization beamsplitter, a wollaston prism, or a walk-off crystal, for example, is used to provide the polarization components with one or more particular angles of polarization. The dispersive element  28  preferably is a grating, such as an arrayed waveguide grating (AWG). The manner in which these components are implemented to accomplish these tasks will be described below in detail with reference to FIG. 4.  
         [0025]    A top view and a side view of the integrated optical WDM  20  are shown in FIGS.  2 A and FIG. 2B, respectively. With reference to the top view of FIG. 2A, the I 1   21  and O 1   22  light paths remain in the same vertical planes over the course of those light paths through the WDM device  20 . Therefore, both light paths, although spatially separated, are represented by the single line labeled  21 ,  22 . Similarly, the I 2   23  and O 2   24  light paths are in the same vertical planes with respect to the top view of FIG. 2A over the course of those light paths through the device  20 . Therefore, both of those light paths, although spatially separated, are also represented by the single line labeled  23 ,  24 .  
         [0026]    In FIG. 2B, the light paths I 1   21  and I 2   23  are in the same transverse planes over the course of those light paths through the device  20  with respect to the side view. Therefore, both light paths, although spatially separated, are represented by the single line labeled  21 ,  23 . Similarly, the O 1   22  and O 2   24  light paths are in the same transverse planes with respect to the side view of FIG. 3B over the course of those light paths through the device  20 . Therefore, both of those light paths, although spatially separated, are represented by the single line labeled  22 ,  24 .  
         [0027]    [0027]FIG. 3 illustrates a perspective view of the WDM  20  of the present invention in accordance with one embodiment, which includes a view of the complete, fullyintegrated package, including the four pigtailed ports I 1   21 , I 2   23 , O 1   22  and O 2   24 . The directional stage  25  is comprised of a first walk-off element (WO 1 )  31 , a compensation element (Comp)  32 , a first Faraday rotator (F 1 )  33 , a first half-waveplate (HWP 1 )  34 , a second walk-off element (W 02 )  35 , a second Faraday rotator (F 2 )  36  and a second half-waveplate (HWP 2 )  37 . The polarization stage  26  comprises a polarization combining and separating stage, which may be, for example, a third walk-off element (WO 3 )  38 .  
         [0028]    [0028]FIG. 3 also illustrates an example of the manner in which a group of wavelengths, λ 1 , λ 2 , λ 3 , λ 4  and λ 5  can be input from one input port, which is I 1  in this example, separated by the dispersion element  28 , and reflected by the reflective element  30  such that some (λ 1 , λ 3 , λ 4 ) of the wavelengths are combined by the dispersion element  28  onto the O 1  path and output through output port O 1  and some (λ 2  and λ 5 ) of the wavelengths are combined by the dispersion element  28  onto the O 2  path and output through output port O 2 .  
         [0029]    The manner in which these components operate in conjunction with one another to accomplish the switching action of the WDM  20  can be seen in FIG. 4. FIG. 4 shows the polarization of each of the components  31 - 38  for each of the light paths  21 - 24 . The blocks  21 A- 21 I show the polarization of each of the components  31 - 38  and LC cell  30 , respectively, along light path I 1   21 . The blocks  22 A- 22 H show the polarization of each of the components  31 - 38 , respectively, along light path O 1   22 . The blocks  24 A- 24 H show the polarization of each of the components  31 - 38 , respectively, along light path O 2   24 . The blocks  23 A- 231  show the polarization of each of the components  31 - 38  and LC cell  30 , respectively, along light path I 2   23 .  
         [0030]    Light that enters the input ports I 1   21  and I 2   23  will have a polarization vector that can be resolved into two orthogonal polarization components. Likewise, light exiting output ports O 1   22  and O 2   24  will have a polarization vector that corresponds to the combination of the two orthogonal polarization components. Essentially, the polarization vector of the respective light signals entering a respective input port is initially resolved into two separate orthogonal polarization components, walked-off in particular directions, and rotated in particular manners so that the light signals from these ports of various wavelengths that pass through the dispersion element  28  and impinge on the reflective element  30  will be reflected, combined and output through either output port O 1   22 , output port O 2   24 , or partially through each of the output ports O 1   22  and O 2   24 . However, the arrangement is such that none, or substantially none, of the light from one of the input ports I 1  or I 2  is reflected back into one of the input ports.  
         [0031]    Also, the polarization components of each of the respective polarization vectors of each of the respective signals will be combined before exiting the output ports O 1  and/or O 2 , as indicated by the plus signs in blocks  22 A and  24 A. Therefore, whereas respective input paths of the directional stage  25  separate the respective polarization vectors into separate polarization components and operate on them in a particular manner, the output paths of the directional stage  25  operate on the respective reflected, separated polarization components in a particular manner and combine the respective polarization components into respective polarization vectors.  
         [0032]    The waveplates  31 ,  34  and  37  may be made of quartz, which is a material typically used to produce waveplates. The walk-off elements  31 ,  35  and  38  may be made of yttrium vanadate or of a rutile material, for example. A walk-off crystal has a polarization direction defined by its crystal structure. The Faraday rotators  33  and  36  may be made of garnet, for example. Faraday rotators rotate light polarization through the application of a magnetic field. The Faraday rotators can be “latched” Faraday rotators. Latched Faraday rotators will continue to rotate light through magnetization even after the magnetic field is no longer being applied to the latched Faraday rotator. Alternatively, a magnet may be embedded in the integrated WDM device  20  adjacent to or in close proximity to the Faraday rotator to enable the necessary magnetic field to be generated.  
         [0033]    These components are known in the art and the manner in which they operate on light signals to separate the polarization vector of a light signal into polarization components and to operate on the polarization components in a particular manner is discussed in detail in U.S. Pat. Nos. 6,088,491 and 6,026,202, which are incorporated by reference herein in their entireties. Therefore, a detailed discussion of the manner in which these components can be implemented to perform the necessary operations will not be provided herein.  
         [0034]    The polarization vector of the light signal entering port I 1  from an optical fiber initially is not separated into separate orthogonal components, as indicated by the small cross in the block  21 A. However, after the incoming light signal passes through WO 1   31 , the horizontal polarization component of the light signal is separated and displaced from the vertical polarization component in the walk-off direction, as indicated by block  21 B. WO 1   31  operates only on the polarization component of the light that is parallel to the walk-off direction of the WO 1   31  (i.e., only on the horizontal polarization component, which is parallel to the walk-off direction indicated by the horizontal arrow in block  31 ). This separates and displaces the horizontally polarized component from the vertically polarized component. Thus, light having a polarization that is parallel to the walk-off direction of WO 1   31  is separated into a beam by WO 1   31  that has the same orientation as WO 1   31 . Light having a polarization that is not parallel to the walk-off direction of WO 1   31  is not displaced, but forms a beam that is coincident with the original light beam and that has a polarization that is orthogonal to the polarization of the displaced beam.  
         [0035]    These beams then pass through the compensation element  32 , which does not change the polarization of the beams, but simply compensates for any light path length differences caused by the walk-off displacement. The light then passes through a first Faraday rotator F 1   33 , which changes the direction of polarization of each of the beams by 45°, as indicated by the lines in block  21 D. The light then passes through a first half waveplate HWP 1   34 , which separately rotates the polarizations of each of the beams such that they both have a horizontal polarization, as indicated by block  21 E. The dashed lines in the HWP 1  component  34  indicate that each portion of the component operates on the polarized beams differently, which is also apparent from the notation in blocks  21 E,  22 D,  23 E and  24 D. Along input path I 1   21 , because the polarization components are horizontal, they will not be affected as they pass through the second walk-off element WO 2   35 , which has a vertical walk-off direction, as indicated by the vertical double-ended arrow in block  35 .  
         [0036]    It should be noted that light propagating along the O 1   22  and O 2   24  light paths in the reverse direction will be spatially displaced by WO 2   35  because, as shown in blocks  22 F,  22 E,  24 F and  24 E, the light beams along these paths are vertically polarized at this point, as indicated by the vertical parallel lines in these blocks and the vertical displacement of those lines between blocks  22 F and  22 E and between blocks  24 F and  24 E. The shift in direction of the O 1 /O 2  light paths with respect to the I 1 /I 2  light paths can be seen in the directional stage  25  from the side view of the device  20  shown in FIG. 2B.  
         [0037]    The light beams traveling along the I 1  light path  21  then pass through the second Faraday rotator F 2   36 , which rotates the polarizations of the beams by 45°, as shown in block  21  G. F 2   36  operates on light traveling along light paths O 1  and O 2  to rotate the polarizations such that they are vertical, as indicated by the lines in blocks  22 G,  22 F,  24 G and  24 F, which enables the O 1  and O 2  light path polarizations to be operated on by WO 2   35  in order to direct those light paths in the direction indicated in the directional stage  25  shown in the side view of FIG. 3B.  
         [0038]    The light beams traveling along I 1  then pass through HWP 2   37 , which rotates the polarizations of both beams into horizontal polarizations, as indicated by the lines in  21 H. The light beams traveling along I 1  then passes through the polarization stage  26 , which corresponds, in this example, to the WO 3  block  38 . The WO 3   38  changes the direction of the light beams such that the beams corresponding to light path I 1  are displaced horizontally in the manner indicated in the polarization stage  26  shown in the top view of FIG. 2A. The horizontal displacement is indicated by the horizontal lines in block  21 H and their movement from the left, upper corner of that block to the right, upper corner of block  21 I.  
         [0039]    The light beams corresponding to light path I 1  having the polarization shown in block  21 I then pass through the dispersion element  28 , which spatially separates all of the wavelengths in the light beams. When the wavelengths of the light beams are spatially dispersed, the polarization components of the light beams impinge on various pixels of the reflective element  30 , depending on the wavelength associated with the polarization components. When the pixel that the polarization components impinge on is not rotated, the light beams corresponding to light path I 1  are reflected by that pixel and combined by the dispersion element such that they pass through WO 3   38 , which displaces the beams horizontally. This horizontal shift in polarization is indicated by the horizontal shift in the position of the lines in block  21 I to the positions shown in block  22 H. Therefore, in this case, the reflected light enters the O 1  light path and is operated on by the elements of the directional stage  25  in the manner indicated by the lines in blocks  22 H- 22 A.  
         [0040]    It should be noted that, in the vertical planes, the O 1  light path tracks the I 1  light path, but is below it in the transverse planes due to WO 2 , as shown in the top view of FIG. 2A and as indicated by the shift of the polarization components in the vertical direction in correspondence with the lines in blocks  22 F and  22 E. It should also be noted that the WO 1   31  combines the polarization components of the light traveling on light paths O 1  and O 2 , respectively, just before they are output through output ports O 1  and O 2 , respectively. This is indicated by the lines in blocks  22 B and  22 A and  24 B and  24 A.  
         [0041]    The different location of the cross in block  23 A compared to the location of the cross in block  21 A indicates the horizontal separation of the beams on input light paths I 1  and I 2 , which is evident from the top view of FIG. 2A. With respect to the I 2  light path, the horizontal polarization component is separated from the vertical polarization component when the light passes through WO 1   31 , as indicated by the polarization notation lines in block  23 B. The polarization changes indicated by the polarization notation in blocks  23 B- 23 G for the I 2  light path are essentially the same as those indicated by blocks  21 B- 21 G, respectively, for the I 1  path. Likewise, the polarization changes indicated by blocks  22 G- 22 A for the O 1  light path are essentially the same as those indicated by blocks  24 G- 24 A for the O 2  light path. However, HWP 2   37  operates on the polarization components of light on light paths I 2  and O 2  in a manner different from the manner in which it operates on the polarization components of light on light paths I 1  and O 1 . HWP 2   37  rotates the polarization components of light on light path I 1  so that they are horizontal, whereas it rotates the polarization components of light on light path I 2  so that they are vertical, as indicated by blocks  21 H and  23 H, respectively.  
         [0042]    Because of this difference, when the polarization of the corresponding LC pixel of the reflective element  30  is not rotated, reflected light on the I 1  light path is combined by the dispersion element  28  according to wavelength onto light path O 1  and is shifted horizontally while maintaining the same polarization, as indicated by blocks  21 I and  22 H. The horizontal shifting of the polarization components is due to the fact that WO 3   38  is a horizontal walk-off crystal. With respect to light traveling along light path I 2 , when the polarization of the corresponding LC pixel of the reflective element  30  is not rotated, the reflected light is combined by the dispersion element  28  according to wavelength onto light path O 2  and passes through WO 3   38  without being shifted and while maintaining its vertical polarization, as indicated by blocks  231  and  24 H. The vertical polarization components are not even shifted due to the fact that WO 3   38  is a horizontal walk-off crystal. With these polarizations, the reflected I 1  light can only enter light path O 1  and the reflected I 2  light can only enter light path O 2 . The reflected light then passes through the directional stage  25  along the respective output light paths and exits the integrated optical WDM  20  through the respective output ports.  
         [0043]    When the corresponding LC pixel of the reflective element  30  is fully rotated (i.e., rotated by 90°), the light on light path I 1  having the polarization indicated by block  21 I is dispersed by the dispersion element  28  and reflected by the rotated pixel with a vertical polarization such as that shown in block  24 H. This light then passes through WO 3   38  unaffected and thus is conditioned only to propagate along the O 2  light path. As stated above, the polarization components have wavelengths associated with them. Therefore, directing polarization components from light path I 1  onto light path O 2  is the equivalent of directing the wavelengths associated with those polarization components from light path I 1  onto light path O 2 .  
         [0044]    With respect to light path I 2 , when the corresponding LC pixel of the reflective element  30  is fully rotated (i.e., rotated by 90°), the light on light path I 2  having the polarization indicated by block  231  is dispersed by the dispersion element  28  and reflected by the rotated pixel with a horizontal polarization such as that shown in block  22 H. This light is conditioned only to propagate along the O 1  light path. Therefore, when the polarization components are combined by the dispersion element  28  according to the wavelengths associated with them, the light naturally will propagate only along light path O 1  to the O 1  output port. As stated above, directing polarization components from light path I 1  onto light path O 2  and from light path I 2  onto light path O 1  is the equivalent of directing the wavelengths associated with those polarization components along those paths. Hence, by controlling the states of the pixels of the reflective element, wavelengths can be selectively separated out by the WDM of the present invention. This allows wavelengths to be selectively separated out and dropped (e.g., switched from I 1  to O 2 ) or added (e.g., all wavelengths of light from I 1  go to O 1  and at least some wavelengths of light from I 2  go to O 1 ). Of course the WDM of the present invention can serve many other purposes. For example, it can be used simply to attenuate light of certain wavelengths by separating out the wavelengths and then discarding them through an output port. Those skilled in the art will understand, in view of the discussion provided herein, the many purposes for which the WDM of the present invention is suited.  
         [0045]    Another example embodiment of the optical WDM device of the present invention will now be described with reference to FIGS.  5 A- 5 C. FIG. 5A illustrates a configuration of various optical components and the manner in which they operate on the polarization components of light to perform the WDM functions. The concepts are generally the same as those described above with reference to FIG. 4, but the configuration of the WDM is different from the configuration of FIG. 4. FIG. 5B illustrates a top view of the components shown in FIG. 5A and the manner in which the polarization components of input light and reflected light propagate through the optical WDM device. FIG. 5C illustrates a side view of the components shown in FIG. 5A and the manner in which the polarization components of input light and reflected light propagate through the optical WDM device.  
         [0046]    With reference to FIG. 5A, the optical WDM device is comprised of a walk-off (W/OFF) element  41 , a half waveplate (HWP) element  42 , a walk-on (W/ON) element  43 , a Faraday rotator  44 , another HWP element  45 , a walk-on (W/ON) element  46 , a dispersion element  47  and a reflective element  50 , which preferably is an array of selectively controllable LC pixels, as in the embodiment of FIG. 4. The block  51  illustrates four light beams, each of which has two polarization components that are orthogonally combined. Light beams  51  and  52  correspond to the O 1  and I 1  light paths, respectively, and light beams  53  and  54  correspond to the I 2  and O 2  light paths, respectively. For incoming light, the W/OFF element  41  displaces the horizontal polarization component  52 A of beam  52 , which corresponds to the I 1  input light, from its vertical component  52 B. Likewise, the W/OFF element  41  displaces the horizontal polarization component  53 A of beam  53 , which corresponds to the I 2  input light, from its vertical component  53 B. For outgoing light to be output from the optical device, the W/OFF element  41  combines the horizontal component  54 A of beam  54 , which corresponds to the output light path O 2 , with its vertical component  54 B. Likewise, the W/OFF element  41  combines the horizontal component  51 A of beam  51 , which corresponds to the output light path O 1 , with its vertical component  51 B. This separating and combining of the polarization components can be seen in block  41  of FIG. 5C.  
         [0047]    The HWP  42  only operates on the separated polarization components in the right side of the box, namely, polarization components  51 A,  52 B,  53 A and  54 B. This can also be seen from block  42  in FIG. 5C in that only half of the polarization components propagate through the HWP  42 . For the separated polarization components  52 B and  53 A of the incoming light, HWP  42  applies a clockwise 90° rotation, as indicated by the horizontal orientations of the dashes in the following box. With respect to the outgoing light, the polarization components  51 A and  53 A are also rotated clockwise by 90° as they pass through the HWP  42  propagating in the direction of the W/OFF element  41 , as shown in the box proceeding the HWP  42 . The W/OFF element  41  then orthogonally combines polarization components  51 A and B and  54 A and B to form two beams, each having two polarization components that are orthogonal to each other.  
         [0048]    With respect to the input light, after the polarization components have been rotated by 90° in the clockwise direction, the input light passes through W/ON element  43 . The input light polarization components  53 A and B, which are now vertically polarized, are shifted upwards. This can be seen from the vertical incline of the I 2  input shown in block  43  FIG. 5B. The input light polarization components  52 A and B of the I 1  input remain horizontally polarized and are not affected as they propagate through the W/ON element  43 , as indicated by the straight I 1  line passing through block  43  in FIG. 6B. With respect to the output light, the W/ON element  43  shifts the polarization components  51 A and B of the output light O 1  down, but leaves them vertically polarized. This shift can be seen by the upward incline in block  43  of FIG. 5B with respect to the direction of the output light. The polarization components  54 A and B of the output light O 2  remain horizontally polarized and are not operated on by the W/ON element  43 , as indicated by the O 2  line passing straight through block  43  in FIG. 5B.  
         [0049]    The Faraday rotator  44  rotates the horizontally and vertically polarized input light polarization components  52 A and B and  53 A and B, respectively, by 45°. The HWP  45  then rotates the input light polarization components  53 A and B and  52 A and B clockwise by 45° such that the input light polarization components  52 A and B are vertically polarized and the input light polarization components  53 A and B are horizontally polarized. The W/ON element  46  then shifts the vertically polarized input light polarization components  52 A and  52 B down such that they are spatially coincident with and orthogonal to the horizontally polarized input light polarization components  53 A and B, respectively. The downward shift of the vertically polarized input light polarization components  52 A and  52 B is indicated by the downward incline in block  46  of FIG. 5B with respect to the direction of propagation of the input light.  
         [0050]    In the opposite direction, the vertically-polarized reflected light polarization components  51 A and B are shifted down to separate them from the horizontally-polarized output light polarization components  54 A and B. When the an LC pixel of the reflective element  50  is in a state in which polarization is not rotated, the spatiallyseparated vertically polarized input light polarization components  52 A and B of input light I 1  will be reflected by the pixel with the same polarization, which is orthogonal to the polarizations of the input light polarization components  53 A and B of the input light I 2 , and to output light polarization components  54 A and B of the output light O 2 . Therefore, the reflected light from port I 1  will only propagate out of the optical device via the O 1  light path because that is the only light path that is capable of properly reseparating and re-combining the output light polarization components. The dispersion element  47  separates the incoming light and combines the reflected light according to wavelength in the manner is discussed above with reference to FIG. 4.  
         [0051]    The reflected I 2  light, which is horizontally polarized, will only propagate out of the optical device via the O 2  light path because that is the only light path that is capable of properly re-separating and re-combining the output light polarization components. On the other hand, if the corresponding pixels of the reflective element  50  is in a state in which the polarization is rotated by 90°, the polarizations of all of the light components reflected by the rotated pixels will be rotated by 90°. Therefore, the vertically-polarized input light polarization components  52 A and B of input light I 1  will be rotated by 90° such that these reflected light components will have a horizontal polarization. With this polarization, the polarization components will be properly re-separated and recombined as they propagate through and out of the optical device via optical path O 2 . Likewise, the polarization of the horizontally-polarized input light polarization components  53 A and B will rotated by 90° such that they will be vertically polarized. With this polarization, the polarization components will be properly re-separated and recombined as they propagate through and out of the optical device via optical path O 1 . Therefore, rotating the angle of polarization of the corresponding pixels of the reflective element  50  by 90° will enable the optical device to function as a WDM because it is capable of separating the light according to wavelength, with each polarization component having a an associated wavelength, and channel the polarization components corresponding to any selected wavelengths from any input port to any output port.  
         [0052]    It should be noted that although the example embodiments shown in FIGS. 4 and 5A each show two inputs and two outputs, the optical WDM device of the present invention may have only one input and two output. Preferably, the WDM device has two inputs and two outputs so that it is bi-directional and is capable of functioning with versatility. Spatial separation of the input light polarization components could occur before the input light is input to the optical device.  
         [0053]    Those skilled in the art will understand the many possible applications of the present invention in view of the discussion provided herein. Of course, orientations of waveplates and crystals other than those shown in FIGS. 4 and 5A can be used to accomplish the goals of the present invention in an integrated form, as will be understood by those skilled in the art in view of the discussion being provided herein. Also, the present invention is not limited to the materials discussed herein for creating the components of the integrated optical WDM of the present invention. For example, as stated above, the reflective element of the present invention can be something other than a liquid crystal cell, and it can be something known now or discovered or developed in the future.  
         [0054]    It should be noted that the above-described embodiments of the present invention are examples of implementations. Those skilled in the art will understand from the disclosure provided herein that many variations and modifications may be made to the embodiments described without departing from the scope of the present invention. All such modifications and variations are within the scope of the present invention.