Abstract:
A light modulator includes elongated elements and a support structure. The elongated elements are arranged in parallel. Each element includes a light reflective planar surface with the light reflective planar surfaces lying in one or more parallel planes. The support structure is coupled to the elongated elements to maintain a position of the elongated elements relative to each other and to enable movement of each elongated element between a first modulator configuration and a second modulator configuration. In the first modulator configuration, the elongated elements act to reflect an incident light as a plane mirror. In the second modulator configuration, selected groups of elements are deflected and act to diffract the incident light along one or more of a plurality of diffraction planes. The groups of elements are configured according to one of a plurality of selectable group configurations. Each group configuration corresponds to one of the plurality of diffraction planes.

Description:
FIELD OF THE INVENTION 
     The present invention relates to diffractive light modulators. More particularly, this invention relates to diffractive light modulators with dynamically rotatable diffraction planes. 
     BACKGROUND OF THE INVENTION 
     Bloom et al. in U.S. Pat. No. 5,311,360, entitled “Method and Apparatus for Modulating a Light Bean,” teach a grating light valve which operates in a reflection mode and a diffraction mode. The grating light valve includes elongated elements suspended above a substrate. In the reflective mode, reflective surfaces of the grating light valve cause incident light to constructively combine to form reflected light. In the diffractive mode, the reflective surfaces of the grating light valve are separated by about a quarter wavelength of the incident light to produce diffracted light. When the grating light valve is in the diffractive mode, the grating light valve predominantly diffracts light into a plus one diffraction order and a minus one diffraction order but also diffracts a small amount of light into higher diffraction orders. The incident light diffracts according to the direction of periodicity. In the case of the grating light valve, the direction of the periodicity is perpendicular to the elongated elements. Therefore, in the diffraction mode, the light is diffracted in a diffraction plane perpendicular to the elongated elements. 
     In WDM (wavelength division multiplex) optical communication, multiple component wavelengths of light each carry a communication signal. Each of the multiple component wavelengths of light form a WDM channel. Many applications require switching of a signal from one channel to another. Other applications require the equalization of the output signals as well as excellent extinction in the non-switched fibers. For example, switching an input light signal from one channel to another can be achieved by using a diffractive light modulator, such as a grating light valve, to diffract the input light into a first order of light, while reflecting very little light, ideally no light, as specularly reflected zero order light. The diffracted light is diffracted along a known diffraction plane and the first order light is collected as output for an output port of a switch. The diffracted first order light can also be attenuated by controlled means, thereby equalizing the light that has been “switched” into the first order. It is common practice to perform the switching and equalizing functions at the same physical location for convenience, maintenance, and economic advantages. 
     Although light can be diffracted into higher orders than the first order for switching and attenuation applications, it is easier and more efficient to diffract and collect light into and out of the first order. However, not much flexibility is provided with only one first order per diffraction plane. 
     What is needed is a diffractive light modulator that produces multiple diffraction planes. What is further needed is a diffractive light modulator that produces multiple diffraction planes and dynamically utilizes the multiple diffraction planes. 
     SUMMARY OF THE INVENTION 
     An embodiment of the present invention includes a light modulator. The light modulator includes elongated elements and a support structure. The elongated elements are arranged in parallel. Each element includes a light reflective planar surface with the light reflective planar surfaces lying in one or more parallel planes. The support structure is coupled to the elongated elements to maintain a position of the elongated elements relative to each other and to enable movement of each elongated element between a first modulator configuration and a second modulator configuration. In the first modulator configuration, the elongated elements act to reflect incident light as a plane mirror. In the second modulator configuration, selected groups of elements are deflected and act to diffract the incident light along one or more of a plurality of diffraction planes. The groups of elements are configured according to one of a plurality of selectable group configurations. Each group configuration corresponds to one of the plurality of diffraction planes. 
     Each element includes a first edge and a second edge. In an active optical area, the first edge is preferably linear and is formed at a first edge angle relative to a lengthwise axis of the elongated element. The second edge is also preferably linear within the active optical area and is formed at a second edge angle relative to the lengthwise axis of the elongated element. The first edge angle is preferably zero and the second edge angle is preferably non-zero. Each group configuration includes at least two adjacent elements such that one of the first edge and the second edge of a first end element of the group configuration forms a first outer group edge, and one of the first edge and the second edge of a second end element of the group configuration forms a second outer group edge. The edge angles of the first and second outer group edges are the same. Alternating groups of elements can be deflected a distance of about one-quarter the wavelength of the incident light thereby diffracting the incident light along a first diffraction plane perpendicular to the outer group edge. One or more elements of each group of a remaining groups of elements can be deflected a distance within a range of zero to about one-quarter the wavelength of the incident light, thereby diffracting a portion of the incident light along a second diffraction plane perpendicular to a non-deflected element edge nearest the one or more elements. A selectable diffraction plane is formed perpendicular to the outer group edge of each group configuration. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a first and preferred embodiment of the diffractive light modulator according to the present invention. 
     FIG. 2A illustrates a top-down view of the diffractive light modulator according to the first embodiment. 
     FIG. 2B illustrates a cross-section of the elongated elements of the diffractive light modulator a reflection mode according to the first embodiment. 
     FIG. 3A illustrates a top-down view of the first embodiment of the diffractive light modulator in a first diffraction mode. 
     FIG. 3B illustrates a cross-section of the elongated elements of the first embodiment of the diffractive light modulator in the first diffractive mode. 
     FIG. 3C illustrates an exemplary diffraction pattern along a first diffraction plane while in the first diffraction mode. 
     FIG. 4A illustrates a top-down view of the first embodiment of the diffractive light modulator in a second diffraction mode. 
     FIG. 4B illustrates a cross-section of the elongated elements of the first embodiment of the diffractive light modulator in the second diffractive mode. 
     FIG. 4C illustrates an exemplary diffraction pattern along a second diffraction plane while in the second diffraction mode. 
     FIG. 5A illustrates a top-down view of a second embodiment of the diffractive light modulator in a third diffraction mode. 
     FIG. 5B illustrates a cross-section of the elongated elements of the second embodiment of the diffractive light modulator in the third diffractive mode. 
     FIG. 5C illustrates an exemplary diffraction pattern along the first diffraction plane while in the third diffraction mode. 
     FIG. 6A illustrates a top-down view of the second embodiment of the diffractive light modulator in a fourth diffraction mode. 
     FIG. 6B illustrates a cross-section of the elongated elements of the second embodiment of the diffractive light modulator in the fourth diffractive mode. 
     FIG. 6C illustrates an exemplary diffraction pattern along a third diffraction plane while in the fourth diffraction mode. 
     FIG. 7A illustrates a top-down view of the second embodiment of the diffractive light modulator in a fifth diffraction mode. 
     FIG. 7B illustrates a cross-section of the elongated elements of the second embodiment of the diffractive light modulator in the fifth diffractive mode. 
     FIG. 7C illustrates an exemplary diffraction pattern along a fourth diffraction plane while in the fifth diffraction mode. 
     FIG. 8A illustrates a first example of a 1×2 switch and attenuation application of the diffractive light modulator according to the first embodiment of the present invention. 
     FIG. 8B illustrates a second example of a 1×2 switch and attenuation application of the diffractive light modulator according to the first embodiment of the present invention. 
     FIG. 9 illustrates a single saw-tooth edge pattern for the elongated elements. 
     FIG. 10 illustrates a saw-tooth edge pattern for the elongated elements. 
     FIG. 11 illustrates a sinusoid edge pattern for the elongated elements. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of a light modulator of the present invention create controllable structures that, depending on the configuration, rotate a diffraction plane such that diffracted light is similarly rotated. By selectively configuring the light modulator to diffract light along one of a plurality of selectable diffraction planes, a first order of diffracted light is essentially directed to one of a plurality of different locations. Each location corresponds to one of the plurality of diffraction planes. One advantage of directing light into selective diffraction planes is in switching applications. First order diffracted light can be collected at the different locations, each different location corresponding to an output port of a switch. 
     A diffractive light modulator  13  according to a first and preferred embodiment of the present invention is shown in FIG.  1 . Preferably, the diffractive light modulator is a grating light valve. The diffractive light modulator  13  comprises elongated elements  15  suspended by first and second posts,  14  and  16 , above a substrate  20 . Preferably, the elongated elements  15  are ribbons of the grating light valve, and each ribbon is separated by a constant gap width. The substrate  20  comprises a conductor  18 . In operation, the diffractive light modulator  13  operates to produce modulated light selected from a reflection mode and one of two diffraction modes. Preferably, the incident light comprises wavelength division multiplexed (WDM) signals where each wavelength comprises an optical channel, as is well known in the art. Each channel impinges appropriate ones of the elongated elements  15  on the diffractive light modulator  13 . Preferably, each channel impinges  12  elongated elements  15 . FIG. 1 illustrates the elongated elements  15  corresponding to a single optical channel. It is understood that the diffractive light modulator  13  can include more, or less, elongated elements  15  than that shown in FIG.  1 . It is also understood that each optical channel can impinge more, or less, than  12  elongated elements  15 , as appropriate. 
     The elongated elements  15  comprise a conducting and reflecting surface  22  and a resilient material  24 . Preferably, the resilient material  24  comprises silicon nitride. Preferably, the conductive and reflective surface  22  comprises aluminum. Alternatively, the conductive and reflective surface  22  comprises a different metal, and the resilient material comprises a different resilient material. Each elongated element  15  includes a first edge and a second edge. In the preferred embodiment, the first edge is linear and parallel to a lengthwise axis of the elongated element  15 , and the second edge is linear and is formed at an angle to the lengthwise axis of the elongated element  15  within an active optical area (FIG.  2 A). Within the preferred embodiment, the first edge is referred to as a straight edge and the second edge is referred to as a diagonal edge. The active optical area is an area of the diffractive light modulator  13  on which the incident light impinges the elongated elements  15 . The portion of the second edge that is at an angle to the lengthwise axis includes the active optical area. Preferably, a remaining portion of the second edge, which is outside the active optical area, is parallel to the lengthwise axis of the elongated elements  15 . 
     FIG. 2A illustrates a top-down view of the diffractive light modulator  13  according to the preferred embodiment. FIG. 2B illustrates a cross-section of the elongated elements  15  of the diffractive light modulator  13  according to the preferred embodiment. Both FIGS. 2A and 2B illustrate the diffractive light modulator  13  in a reflection mode. In the reflection mode, the conducting and reflecting surfaces  22  of the elongated elements  15  form a plane so that incident light I (FIG. 2B) reflects from the elongated elements  15  to produce reflected light R (FIG.  2 B). 
     FIG. 3A illustrates a top-down view of the first embodiment of the diffractive light modulator  13  in a first diffraction mode. FIG. 3B illustrates a cross-section of the elongated elements  15  of the diffractive light modulator  13  in the first diffractive mode. In the first diffraction mode, adjacent pairs of elongated elements  15  are configured as groups. Each group includes a first group edge and a second group edge. While in the first diffraction mode, the first group edge and the second group edge are the straight edges of the two elongated elements  15  comprising the group, where the straight edges are the linear edges parallel to the lengthwise axis of the elongated elements  15 . 
     In the first diffraction mode, an electrical bias causes alternate groups of the elongated elements  15  to move toward the substrate  20 . As shown in FIGS. 3A and 3B, ribbons  3 ,  4 ,  7 ,  8 ,  11  and  12  are the elongated elements  15  that are moved according to the first diffraction mode. The electrical bias is applied between the reflecting and conducting surfaces  22  of the alternate groups of the elongated elements  15  and the conductor  18 . The electrical bias results in a height difference between the alternate groups of the elongated elements  15  and non-biased ones of the elongated elements  15 . A height difference of a quarter wavelength λ/4 of the incident light I produces maximum diffracted light including plus one and minus one diffraction orders, D+1 and D−1, as shown in FIG.  3 B. 
     It will be readily apparent to one skilled in the art that the conducting and reflecting surface  22  can be replaced by a multilayer dielectric reflector and a conducting element where the conducting element is buried within each of the elongated elements  15 . Further, it will be readily apparent to one skilled in the art that the conducting and reflecting surface  22  can be coated with a transparent layer such as an anti-reflective layer. 
     In the first diffractive mode, the straight edges of each group form “steps.” These straight edges are parallel to each other and the steps lie in the same plane, and therefore form a periodicity. Light diffracts in the direction of the periodicity. In general, if there is periodicity in one-dimension, then there is diffraction in one-dimension. If there is periodicity in two-dimensions, then there is diffraction in two-dimensions, and so on. As shown in FIG. 3A, the direction of the periodicity while in the first diffraction mode is perpendicular to the straight edges of the elongated elements  15 . Therefore, the diffracted light is directed along a first diffraction plane  30 . 
     FIG. 3C illustrates an exemplary diffraction pattern along the first diffraction plane  30 . The diffraction pattern serves only to illustrate the possible locations of the diffracted light while the diffractive light modulator  13  is in the first diffraction mode. While in the first diffraction mode, the incident light I is primarily diffracted into the plus and minus first order along the diffraction plane  30 . Trace amounts of the incident light I are diffracted into the higher order lights, for example a plus and minus second order, a plus and minus fourth order and a plus and minus sixth order. The circular shape of the diffraction pattern is for illustrative purposes only and should not serve as a limitation on the actual diffraction pattern. In the reflection mode, the reflected light R is specularly reflected as zero, “0”, order light. The diffraction pattern corresponding to the zero order light should approximate the shape of the incident light impinging the diffractive light modulator less attenuation, if any. The diffraction pattern corresponding to the “+1” and “−1” order light are smaller than the “0” order light because when light is diffracted, it is diffracted into the plus and minus first orders as well as the higher orders. Therefore, the diffracted light is distributed over more orders. The size of any one of the diffraction patterns can also vary depending on any attenuation that is performed. 
     FIG. 4A illustrates a top-down view of the first embodiment of the diffractive light modulator  13  in a second diffraction mode. FIG. 4B illustrates a cross-section of the elongated elements  15  of the diffractive light modulator  13  in the second diffractive mode. In the second diffraction mode, adjacent pairs of elongated elements  15 , different from those in the first diffraction mode, are configured as groups. Each group includes a first group edge and a second group edge. In this second diffraction mode, the first group edge and the second group edge are the diagonal edges of the two elongated elements  15  comprising the group, where the diagonal edges are the linear edges formed at an angle to the lengthwise axis of the elongated elements  15 . An electrical bias causes alternate groups of the elongated elements  15  to move toward the substrate  20 . As shown in FIGS. 4A and 4B, ribbons  1 ,  4 ,  5 ,  8 ,  9  and  12  are the elongated elements  15  that are moved according to the second diffraction mode. It is understood that although it is preferred that each group comprises a pair of adjacent elongated elements  15 , the end ribbons  1  and  12  are not part of a group pair in the second diffraction mode. This is due to the “odd-man-out” nature of reconfiguring the elongated elements  15  into groups, as is expected. The electrical bias results in a height difference between the alternate groups of the elongated elements  15  and non-biased ones of the elongated elements  15 . A height difference of a quarter wavelength λ/4 of the incident light I produces maximum diffracted light including plus one and minus one diffraction orders, D+1 and D−1, as shown in FIG.  4 B. 
     In the second diffractive mode, the diagonal edges of each group form steps. Since the diagonal edges are parallel to each other and the steps lie in the same plane, the diagonal edges form a periodicity. As shown in FIG. 4A, the direction of the periodicity, while in the second diffraction mode, is perpendicular to the diagonal edges of the elongated elements  15 . While in the second diffraction mode, light is diffracted similarly as in the first diffraction mode, except that the diffracted light is directed along a second diffraction plane  40 . 
     FIG. 4C illustrates an exemplary diffraction pattern along the second diffraction plane  30 . The diffraction pattern illustrated in FIG. 4C is similar to that illustrated in FIG. 3C related to the first diffraction mode, except that the diffraction pattern of the second diffraction mode is directed along the second diffraction plane  40 . If the diagonal edge is formed at an angle θ1 (FIG. 3A) to the diffraction plane  30 , then the diffraction plane  40  lies at an angle 90-θ1 (FIG. 4C) to the diffraction plane  30 . 
     The first embodiment of the diffractive light modulator  13  can be used as a 1×3 switch. In this case, the zero order light is collected as the output of a first output port, the first order light in the diffraction plane  30  is collected as the output of a second output port, and the first order light in the diffraction plane  40  is collected as the output of a third output port. Preferably, only the plus first order light or the minus first order light is collected along the diffraction plane  30  for the second output port, and only the plus first order light or the minus first order light is collected along the diffraction plane  40  for the third output port. Alternatively, both the plus and minus first order light is collected along the diffraction plane  30  for the second output port, and both the plus and minus first order light is collected along the diffraction plane  40  for the third output port. 
     It is understood that although the first edge is preferably a straight edge parallel to the lengthwise axis of the elongated elements  15 , the first edge can be a linear edge at an angle to the lengthwise axis. The first edge and the second edge are at different angles to the lengthwise axis in order to produce two different diffraction planes when in operation 
     FIG. 5A illustrates a top-down view of a second embodiment of the diffractive light modulator of the present invention. Each elongated element  15  includes a first edge and a second edge. In the second embodiment, the first edge is linear and parallel to a lengthwise axis of the elongated element  15 , and the second edge is linear and is formed at a plus or minus angle to the lengthwise axis of the elongated element  15  within an active optical area. Within the second embodiment, the first edge is referred to as a straight edge and the second edge is referred to as a diagonal edge. As illustrated in FIG. 5A, alternating pairs of elongated elements  15  preferably form mirror shapes of each other due to the plus or minus angle of the diagonal edge. Ribbons  1 ,  2 ,  5 ,  6 ,  9  and  10  include the diagonal edge at the minus angle to the lengthwise axis. Ribbons  3 ,  4 ,  7 ,  8 ,  11 , and  12  include the diagonal edge at the plus angle to the lengthwise axis. In other words, the pattern of the elongated elements  15  repeats every fifth element. The active optical area is an area of the diffractive light modulator  13  on which the incident light impinges the elongated elements  15 . The portion of the second edge that is at an angle to the lengthwise axis includes the active optical area. Preferably, a remaining portion of the second edge, which is outside the active optical area, is parallel to the lengthwise axis of the elongated elements  15 . 
     In the second embodiment, the diffractive light modulator  13  operates in a reflection mode and one of a plurality of diffraction modes. In the reflection mode, the conducting and reflecting surfaces  22  of the elongated elements  15  form a plane so that incident light I reflects from the elongated elements  15  to produce reflected light R. 
     The second embodiment of the diffractive light modulator  13  shown in FIG. 5A is in a third diffraction mode. FIG. 5B illustrates a cross-section of the elongated elements  15  of the diffractive light modulator  13  in the third diffractive mode. In the third diffraction mode, adjacent fours of elongated elements  15  are configured as groups. Each group includes a first group edge and a second group edge. In the third diffraction mode, the first group edge and the second group edge are the straight edges of the first and fourth elongated elements  15  comprising the group, where the straight edges are the linear edges parallel to the lengthwise axis of the elongated elements  15 . 
     In the third diffraction mode, an electrical bias causes alternate groups of the elongated elements  15  to move toward the substrate  20 . As shown in FIGS. 5A and 5B, ribbons  5 ,  6 ,  7 , and  8  are the elongated elements  15  that are moved according to the third diffraction mode. The electrical bias is applied between the reflecting and conducting surfaces  22  of the alternate groups of the elongated elements  15  and the conductor  18 . The electrical bias results in a height difference between the alternate groups of the elongated elements  15  and non-biased ones of the elongated elements  15 . A height difference of a quarter wavelength λ/4 of the incident light I produces maximum diffracted light including plus one and minus one diffraction orders, D+1 and D−1, as shown in FIG.  5 B. 
     In the third diffractive mode, the straight edges of each group form steps. Since the straight edges are parallel to each other and the steps lie in the same plane, the straight edges form a periodicity. As shown in FIG. 5A, the direction of the periodicity while in the third diffraction mode is perpendicular to the straight edges of the elongated elements  15 . Therefore, the diffracted light is directed along the first diffraction plane  30 . 
     FIG. 5C illustrates an exemplary diffraction pattern along the first diffraction plane  30 . While in the third diffraction mode, the diffraction pattern serves only to illustrate the possible locations of the diffracted light while the diffractive light modulator  13  is in the third diffraction mode. While in the third diffraction mode, the incident light I is primarily diffracted into the plus and minus first order along the diffraction plane  30 . Trace amounts of the incident light I are diffracted into the higher order lights, for example a plus and minus second order, a plus and minus fourth order and a plus and minus sixth order. The circular shape of the diffraction pattern is for illustrative purposes only and should not serve as a limitation on the actual diffraction pattern. In the reflection mode, the reflected light R is specularly reflected zero, “0”, order light. The diffraction pattern corresponding to the zero order light should approximate the shape of the incident light impinging the diffractive light modulator less attenuation, if any. The diffraction pattern corresponding to the “+1” and “−1” order light are smaller than the “0” order light because when light is diffracted, it is diffracted into the plus and minus first orders as well as the higher orders. Therefore, the diffracted light is distributed over more orders. The size of any one of the diffraction patterns can also vary depending on any attenuation that is performed. 
     FIG. 6A illustrates the second embodiment of the diffractive light modulator  13  in a fourth diffraction mode. FIG. 6B illustrates a cross-section of the elongated elements  15  of the diffractive light modulator  13  in the fourth diffractive mode. In the fourth diffraction mode, adjacent fours of elongated elements  15 , different from those in the third diffraction mode, are configured as groups. Each group includes a first group edge and a second group edge. In this fourth diffraction mode, the first group edge and the second group edge are the diagonal edges at the minus angle to the lengthwise axis of the elongated elements  15 . An electrical bias causes alternate groups of the elongated elements  15  to move toward the substrate  20 . As shown in FIGS. 6A and 6B, ribbons  1 ,  6 ,  7 ,  8 , and  9  are the elongated elements  15  that are moved according to the fourth diffraction mode. It is understood that although it is preferred that each group comprises four adjacent elongated elements  15 , the end ribbon  1  and the partial group of ribbons  10 ,  11  and  12  are not part of a complete group of four in the fourth diffraction mode. This is due to the “odd-man-out” nature of reconfiguring the elongated elements  15  into groups, as is expected. The electrical bias results in a height difference between the alternate groups of the elongated elements  15  and non-biased ones of the elongated elements  15 . A height difference of a quarter wavelength λ/4 of the incident light I produces maximum diffracted light including plus one and minus one diffraction orders, D+1 and D−1, as shown in FIG.  6 B. 
     In the fourth diffractive mode, the diagonal edges at the minus angle of each group form steps. Since the diagonal edges at the minus angle are parallel to each other and the steps lie in the same plane, the diagonal edges at the minus angle form a periodicity. As shown in FIG. 6A, the direction of the periodicity, while in the fourth diffraction mode, is perpendicular to the diagonal edges at the minus angle of the elongated elements  15 . While in the fourth diffraction mode, light is diffracted similarly as in the third diffraction mode, except that the diffracted light is directed along a third diffraction plane  45 . 
     FIG. 6C illustrates an exemplary diffraction pattern along the third diffraction plane  45  while in the fourth diffraction mode. The diffraction pattern illustrated in FIG. 6C is similar to that illustrated in FIG. 5C related to the third diffraction mode, except that the diffraction pattern of the fourth diffraction mode is directed along the third diffraction plane  45 . If the diagonal edge at the minus angle is formed at an angle θ2 (FIG. 5A) to the diffraction plane  30 , then the diffraction plane  45  lies at an angle 90-θ2 (FIG. 6C) to the diffraction plane  30 . 
     FIG. 7A illustrates the second embodiment of the diffractive light modulator  13  in a fifth diffraction mode. FIG. 7B illustrates a cross-section of the elongated elements  15  of the diffractive light modulator  13  in the fifth diffractive mode. In the fifth diffraction mode, adjacent fours of elongated elements  15 , different form those in the third and fourth diffraction modes, are configured as groups. Each group includes a first group edge and a second group edge. In this fifth diffraction mode, the first group edge and the second group edge are the diagonal edges at the plus angle to the lengthwise axis of the elongated elements  15 . An electrical bias causes alternate groups of the elongated elements  15  to move toward the substrate  20 . As shown in FIGS. 7A and 7B, ribbons  1 ,  2 ,  3 ,  8 ,  9 ,  10 , and  11  are the elongated elements  15  that are moved according to the fifth diffraction mode. It is understood that although it is preferred that each group comprises four adjacent elongated elements  15 , the end ribbon  12  and the partial group of ribbons  1 ,  2  and  3  are not part of a complete group of four in the fifth diffraction mode. This is due to the “odd-man-out” nature of reconfiguring the elongated elements  15  into groups, as is expected. The electrical bias results in a height difference between the alternate groups of the elongated elements  15  and non-biased ones of the elongated elements  15 . A height difference of a quarter wavelength λ/4 of the incident light I produces maximum diffracted light including plus one and minus one diffraction orders, D+1 and D−1, as shown in FIG.  7 B. 
     In the fifth diffractive mode, the diagonal edges at the plus angle of each group form steps. Since the diagonal edges at the plus angle are parallel to each other and the steps lie in the same plane, the diagonal edges at the plus angle form a periodicity. As shown in FIG. 7A, the direction of the periodicity, while in the fifth diffraction mode, is perpendicular to the diagonal edges at the plus angle of the elongated elements  15 . While in the fifth diffraction mode, light is diffracted similarly as in the third diffraction mode, except that the diffracted light is directed along a fourth diffraction plane  50 . 
     FIG. 7C illustrates an exemplary diffraction pattern along the fourth diffraction plane  50  while in the fifth diffraction mode. The diffraction pattern illustrated in FIG. 7C is similar to that illustrated in FIG. 5C related to the third diffraction mode, except that the diffraction pattern of the fifth diffraction mode is directed along the fourth diffraction plane  50 . If the diagonal edge at the plus angle is formed at an angle −θ2 (FIG. 5A) to the diffraction plane  30 , then the fourth diffraction plane  50  lies at an angle −(90-θ2) (FIG. 7C) to the diffraction plane  30 . 
     The second embodiment of the diffractive light modulator  13  can be used as a 1×4 switch. In this case, the zero order light is collected as the output of a first output port, the first order light in the diffraction plane  30  is collected as the output of a second output port, the first order light in the diffraction plane  45  is collected as the output of a third output port, and the first order light in the diffraction plane  50  is collected as the output of a fourth output port. Preferably, only the plus first order light or the minus first order light is collected along the diffraction plane  30  for the second output port, only the plus first order light or the minus first order light is collected along the diffraction plane  45  for the third output port, and only the plus first order light or the minus first order light is collected along the diffraction plane  50  for the fourth output port. Alternatively, both the plus and minus first order light is collected along the diffraction plane  30  for the second output port, both the plus and minus first order light is collected along the diffraction plane  45  for the third output port, and both the plus and minus first order light is collected along the diffraction plane  50  for the fourth output port. 
     Although it is preferred that the second edges are diagonal within the active optical area, it is understood that the second edges can be diagonal over a length larger than the active optical area, up to the entire length of the elongated element. It is preferable that the diagonal edge is made within the active optical area to enable use of smaller angles θ from the diffraction plane  30 . To clarify, since the length of the elongated elements  15  is large relative to the width, a diagonal edge along the entire length of the elongated element  15  is only marginally less than 90 degrees from the diffraction plane  30 . Such a large angle only rotates the diffraction plane by a correspondingly small degree from the diffraction plane  30 . A smaller angle rotates the diffraction plane by a correspondingly larger degree, which produces better de-coupling of the diffracted light in the two diffraction planes. 
     It is understood that although the first edge is preferably a straight edge parallel to the lengthwise axis of the elongated elements  15 , the first edge can be a linear edge at an angle to the lengthwise axis. The first edge and the second edge are at different angles to the lengthwise axis in order to produce different diffraction planes when in operation. 
     FIGS. 2B,  3 B, and  4 B depict the first embodiment of the diffractive light modulator  13  in the reflection mode, first diffraction mode, and second diffraction mode, respectively. For a deflection of the alternate groups of the elongated elements  15  of less than a quarter wavelength λ/4, the incident light I both reflects and diffracts producing the reflected light R and the diffracted light including the plus one and minus one diffraction orders, D+1 and D−1. In other words, by deflecting the alternate groups of the elongated elements less the quarter wavelength λ/4, the diffractive light modulator  13  produces a variable reflectivity. By varying the reflectivity in this manner, each incident light can be equalized to a specified intensity. It should be born in mind that terms like “equalize” and “equalization” as used with respect to the present invention are to be broadly interpreted with respect to regulating the power levels of component light signals to any pre-determined level of relative power levels. Accordingly, the term “equalize” as used herein is not to be limited to any one particular curve or ratio, but simply constitutes a regulation or normalization of signal power against any pre-determined curve or ratio of power levels at different frequencies. It is understood that other embodiments, including the second embodiment, of the present invention can also produce a variable reflectivity. 
     In the case of the first embodiment, the diffractive light modulator  13  can also be used for switching and attenuating. When used solely as a switch, light is directed into output port  1 ,  2  or  3 , as described above. When used as a switch and attenuator, one of the output ports, say output port  3 , is used as a “throw away” port to direct attenuated light. For example, an input signal (incident light I) is to be switched to port  2  and equalized to a level 90% of its input level. To switch and attenuate the input signal, 90% of the input signal is directed by diffraction to output port  2  while 10% of the input signal is directed by diffraction to output port  3 . Since output port  3  is not collected as a switched output port, the 10% portion of the input signal directed to output port  3  is effectively “thrown away.” 
     FIG. 8A illustrates a first example of a 1×2 switch and attenuation application of the diffractive light modulator  13  according to the first embodiment of the present invention. In this case, output port  1  (collected zero order light) and output port  2  (collected plus first order light in diffraction plane  30 ) are switching ports, and output port  3  (plus first order light in diffraction plane  40 ) is a throw away port. The configuration of the elongated elements  15  in FIG. 8A is similar to the configuration in FIG. 4B such that any diffracted light is diffracted along the diffraction plane  40 . In FIG. 8A however, the ribbons  1 ,  4 ,  5 ,  8 ,  9 , and  12  are not moved into the maximum diffraction position of λ/4. The ribbons  1 ,  4 ,  5 ,  8 ,  9 , and  12  in FIG. 8A are configured for variable reflectivity, and therefore, only diffract a portion of the incident light I into the diffraction plane  40 . In this manner, an input signal (incident light I in FIG. 8A) is switched to port  1  (reflected light R in FIG. 8A) and a portion of the input signal is attenuated and thrown away at the output port  3  (diffracted light D+1 in FIG.  8 A). The configuration of the elongated elements  15  shown in FIG. 8A creates a superposition of reflected light in the diffraction plane  30 , and the diffraction pattern in the diffraction plane  40 . The net result is attenuated light at the output port  1 . 
     FIG. 8B illustrates a second example of a 1×2 switch and attenuation application of the diffractive light modulator  13  according to the first embodiment of the present invention. In this case, output port  1  (collected zero order light) and output port  2  (collected plus first order light in diffraction plane  30 ) are switching ports, and output port  3  (collected plus first order light in diffraction plane  40 ) is a throw away port. The configuration of the elongated elements  15  in FIG. 8B is similar to the configuration in FIG. 3B in that ribbons  3 ,  4 ,  7 ,  8 ,  11 , and  12  are moved to maximum diffraction position to diffract light along the diffraction plane  30 . In FIG. 8B, however, the ribbons  2 ,  6 , and  10  are also moved which creates a periodicity corresponding to the diffraction plane  40 . This periodicity creates diffraction along the diffraction plane  40 . In this manner, an input signal (incident light I in FIG. 8B) is switched to port  2  (diffracted light D+1 in FIG. 8B) and a portion of the input signal is attenuated and thrown away at the output port  3  (not shown in FIG.  8 B). The configuration of the elongated elements  15  shown in FIG. 8B creates a superposition of diffraction patterns in both the diffraction plane  30  and the diffraction plane  40 . The net result is attenuated light at the output port  2 . Similarly, the second embodiment of the diffractive light modulator can be used as a 1×3 switch and attenuator. 
     The edges of the elongated elements  15  are not restricted to a single linear  5  direction, as in the straight edge or the diagonal edge. FIGS. 9-11 illustrate exemplary edge patterns for the elongated elements  15 . The edge patterns illustrated in FIGS. 9-11 are preferably used in attenuation applications. Alternatively, these edge patterns can be used for switching and attenuation applications. FIG. 9 illustrates a single saw-tooth edge pattern. In a diffraction mode where the single saw-tooth forms the outer edges of a group, two additional dimensions of periodicity exist, one according to each side of the saw-tooth. The three dimensions of periodicity form three simultaneous diffraction planes  30 , 60  and  62 . In the case where the saw-tooth forms an isosceles triangle with the lengthwise axis of the elongated element  15 , the diffraction plane  60  is formed at an angle φ1 to the diffraction plane  30 , and the diffraction plane  62  is formed at an angle −φ1 to the diffraction plane  30 . In the diffraction mode, where the ribbons are deflected to form a step at the saw-tooth edge, light is diffracted along diffraction planes  30 ,  60  and  62 . 
     FIG. 10 illustrates a saw-tooth pattern. In a diffraction mode where the saw-tooth pattern forms the outer edges of a group, the saw-tooth pattern in FIG. 10 forms three simultaneous diffraction planes  70 ,  71  and  72 . In the case where each saw-tooth in the saw-tooth pattern forms an isosceles triangle with the lengthwise axis of the elongated element  15 , the diffraction plane  70  is formed at an angle φ2 to the diffraction plane  30 , and the diffraction plane  72  is formed at an angle −φ2 to the diffraction plane  30 . The diffraction plane  71  is formed perpendicular to the diffraction plane  30 . Due to the higher frequency of the saw-tooths in FIG. 10 as compared to FIG. 9, the angle φ2 is greater than φ1. In the diffraction mode, light is diffracted along diffraction planes  70 ,  71  and  72 . 
     FIG. 11 illustrates a sinusoid edge pattern. In a diffraction mode where the sinusoid pattern forms the outer edges of a group, the sinusoid pattern provides an additional periodicity in a direction parallel to the lengthwise axis of the elongated element  15 , and therefore forms an additional diffraction plane  80  perpendicular to the diffraction plane  30 . 
     The present invention has been described in terms of specific embodiments incorporating details to facilitate the understanding of the principles of construction and operation of the invention. As such, references herein to specific embodiments and details thereof are not intended to limit the scope of the claims appended hereto. It will be apparent to those skilled in the art that modifications can be made in the embodiment chosen for illustration without departing from the spirit and scope of the invention.