Abstract:
A light modulator includes elongated elements arranged parallel to each other. In a first diffraction mode, the light modulator operates to diffract an incident light into at least two diffraction orders. In a second diffraction mode, the light modulator operates to diffract the incident light into a single diffraction order. Each of the elongated elements comprises a blaze profile, which preferably comprises a reflective stepped profile across a width of each of the elongated elements and which produces an effective blaze at a blaze angle. Alternatively, the blaze profile comprises a reflective surface angled at the blaze angle. Each of selected ones of the elongated elements comprise a first conductive element. The elongated elements produce the first diffraction when a first electrical bias is applied between the first conductive elements and a substrate. A relative height of the blazed portions are adjusted to produce the second diffraction when a second electrical bias is applied between the first conductive elements and the substrate. In an alternative embodiment, each of the elongated elements includes the first conductive element and multiple elongated elements are arranged in groupings, where each of the groupings includes at least three of the elongated elements. When the multiple elongated elements are at a first height, the incident light reflects from the elongated elements. When relative heights of the multiple elongated elements are adjusted by applying individual electrical biases between the first conductive elements and the substrate, the incident light diffracts into the single diffraction order.

Description:
FIELD OF THE INVENTION 
     This invention relates to the field of light modulators. More particularly, this invention relates to the field of light modulators where an incident light is modulated to produce a blazed diffraction. 
     BACKGROUND OF THE INVENTION 
     Bloom et al. in U.S. Pat. No. 5,311,360, entitled “Method and apparatus for modulating a light beam,” 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 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. 
     Bloom et al. further teach an alternative grating light valve which operates in the reflection mode and in a blazed diffraction mode. The alternative grating light valve includes the elongated elements suspended above the substrate. For the alternative grating light valve, the elongated elements include off-axis neck portions at ends of each of the elongated elements. In the reflection mode, the elongated elements are parallel causing incident light to reflect from the elongated elements and, thus, produce the reflected light. In the blazed diffraction mode, each of the elongated elements is rotated about an axis defined by the off-axis neck portions to produce a blazed diffraction. 
     Because the light modulator is switched between the reflection mode and the blazed diffraction mode and because the reflection mode diffracts small quantities of light into the same angles as does the blazed diffraction mode, a contrast between the non-activated state and the activated state is less than an optimum contrast. Further, the off-axis neck portions are critical to operation of the light modulator which necessitate tight tolerances for the off-axis neck portions making the light modulator relatively difficult to fabricate and also relatively expensive to fabricate. 
     What is needed is a blazed diffractive light modulator which provides higher contrast. 
     What is needed is a blazed diffractive light modulator which is easier to fabricate. 
     What is needed is a blazed diffractive light modulator which is more economical to fabricate. 
     SUMMARY OF THE INVENTION 
     The present invention is a light modulator. The light modulator includes elongated elements arranged parallel to each other and suspended above a substrate. The light modulator operates in a first diffraction mode and in a second diffraction mode. In the first diffraction mode, an incident light diffracts into at least two diffraction orders. In the second diffraction mode, the incident light diffracts into a single diffraction order, which is at a diffraction angle different from diffraction angles for the at least two diffraction orders. 
     Each of the elongated elements comprises a blaze profile. Preferably, the blaze profile comprises a stepped profile across a width of each of the elongated elements where the blaze profile produces an effective blaze at a blaze angle. Alternatively, the blaze profile comprises a surface angled at the blaze angle. 
     Each blaze profile comprises a reflective surface. Each of selected ones of the elongated elements comprise a first conductive element along the elongated element. The elongated elements are coupled to the substrate. The substrate comprises a second conductive element. 
     The elongated elements produce the first diffraction when a first electrical bias, preferably a zero electrical bias, is applied between the first conductive elements of the selected ones of the elongated elements and the second conductive element. A relative height of the blazed portions are adjusted to produce the second diffraction when a second electrical bias is applied between the first conductive elements of the selected ones of the elongated elements and the second conductive element. 
     In an alternative embodiment, multiple elongated elements are arranged in groupings. Each of the groupings includes at least three of the elongated elements and each grouping includes an identical number of the elongated elements. Each of the elongated elements in the alternative embodiment includes the first conductive element. When the multiple elongated elements of each of the groupings are at a first height, the incident light reflects from the elongated elements. When relative heights of the multiple elongated elements of each of the groupings are adjusted by applying individual electrical biases between the first conductive elements and the second conductive element, the incident light diffracts into a single diffraction order. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates an isometric view of the preferred blazed grating light valve (GLV) of the present invention. 
     FIG. 2A illustrates an isometric view of a single elongated element and an underlying substrate of the preferred blazed grating light valve of the present invention. 
     FIG. 2B further illustrates the single elongated element and the underlying substrate of the present invention. 
     FIG. 3 illustrates a cross section of an elongated element of the present invention. 
     FIGS. 4A and 4B illustrate a cross-sectional view of the preferred blazed grating light valve of the present invention in a non-activated state and in a fully activated state, respectively, where an incident light is normal to a grating plane. 
     FIGS. 5A and 5B illustrate the cross-sectional view of the preferred blazed grating light valve of the present invention in the non-activated state and in the fully activated state, respectively, where the incident light is at an oblique angle such that, in the non-activated state, diffracted light is placed in a zero order diffraction and further such that, in the fully activated state, light is placed in a first order diffraction, which is normal to the grating plane. 
     FIGS. 6A,  6 B, and  6 C illustrate a plan view and two orthogonal cross-sectional views, respectively, of a first partially fabricated blazed grating light valve of the present invention. 
     FIGS. 7A,  7 B, and  7 C illustrate a plan view and two orthogonal cross-sectional views, respectively, of a second partially fabricated blazed grating light valve of the present invention. 
     FIGS. 8A,  8 B, and  8 C illustrate a plan view and two orthogonal cross-sectional views, respectively, of a third partially fabricated blazed grating light valve of the present invention. 
     FIGS. 9A,  9 B, and  9 C illustrate a plan view and two orthogonal cross-sectional views, respectively, of a fourth partially fabricated blazed grating light valve of the present invention. 
     FIGS. 10A,  10 B, and  10 C illustrate a plan view and two orthogonal cross-sectional views, respectively, of a fabricated blazed grating light valve of the present invention. 
     FIG. 11 illustrates a first alternative grating light valve of the present invention. 
     FIG. 12 illustrates a second alternative grating light valve of the present invention. 
     FIG. 13 illustrates an alternative elongated element and the underlying substrate of the present invention. 
     FIG. 14A illustrates a third alternative grating light valve in a reflection state. 
     FIG. 14B illustrates the third alternative grating light valve in a first diffractive state, which places diffracted light into a diffraction angle. 
     FIG. 14C illustrates the third alternative grating light valve in a second diffractive state, which places diffracted light into minus the diffraction angle. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The preferred blazed grating light valve is illustrated isometrically in FIG.  1 . The preferred blazed grating light valve  20  includes a substrate  22 , elongated elements  24 , first posts  26  (one shown), and second posts  28  (one shown). The substrate  22  includes a first conductor  30 . The elongated elements  24  each preferably include a first surface  32  and a second surface  34 , both of which are reflective. The first and second surfaces,  32  and  34 , form a blaze profile  36  for each of the elongated elements  24 . One of the first posts  26  and one of the second posts  28  couple each of the elongated elements  24  to the substrate  22 . Each of the elongated elements  24  are also preferably coupled to the substrate  22  at first and second ends (not shown) of the elongated element  24 . 
     One of the elongated elements  24  and a portion of the substrate  22  are further illustrated isometrically in FIG.  2 A. The elongated element  24  includes the first and second surfaces,  32  and  34 , both of which are reflective. The first and second surfaces,  32  and  34 , form the blaze profile  36 . The elongated element  24  is coupled to the substrate by the first and second posts,  26  and  28 , and also at the first and second ends (not shown). Preferably, the elongated element  24 , the first post  26 , and the second post  28  are comprised of a resilient material. Preferably, the resilient material comprises silicon nitride. Preferably, the first and second surfaces,  32  and  34 , comprise a reflector. Preferably, the reflector comprises an aluminum layer. Alternatively, the reflector is a different metal. Further alternatively, the reflector is a multilayered dielectric reflector. The substrate  22  includes the first conductor  30 . Preferably, the substrate  22  comprises silicon and the first conductive layer comprises doped poly-silicon. For a visible spectrum application, the elongated element  24  preferably has a length from the first post  26  to the second post of about 200 μm and a width of about 4.25 μm. 
     The elongated element  24  and the substrate  22  are further illustrated in FIG.  2 B. The elongated element  24  preferably comprises a central portion  42  and first and second outer portions,  44  and  46 . The first outer portion  44  is preferably coupled to the substrate  22  at the first end  38  and the first post  26 . The second outer portion is preferably coupled to the substrate  22  at the second end  40  and the second post  28 . Preferably, the first and second outer portions,  44  and  46 , are also coupled to the substrate  22  by first and second anchors,  29  and  31 , located proximate to the first and second ends,  38  and  40 , respectively. Preferably, the first and second anchors,  29  and  31 , have an oval cross-section with a long axis of the oval cross-section oriented parallel to a length of the elongated elements  24 . By orienting the long axes of the first and second anchors parallel the length of the elongated elements  24 , the first and second anchors,  29  and  31 , are relatively stiff in a tension direction defined by the internal tensile stress within the elongated elements  24 . Preferably, lengths of the first and second outer portion,  44  and  46 , are about as long as the central portion  42 . Alternatively, the lengths of the first and second outer portion,  44  and  46 , are longer or shorter than the central portion  42 . The first and second outer portions,  44  and  46 , assure uniform fabrication of the first and second posts,  26  and  28 , and the elongated elements  24  in the vicinity of the first and second posts,  26  and  28 , and in between the first and second posts,  26  and  28 . 
     A cross-sectional view of the elongated element  24  of the present invention is illustrated in FIG.  3 . The elongated element  24  preferably comprises a rectangular body  48  and a stepped reflector  50 . The rectangular body preferably comprises silicon nitride and the stepped reflector  50  preferably comprises aluminum. The stepped reflector  50  forms the first and second surfaces,  32  and  34 , of the elongated element  24 . The first and second surfaces,  32  and  34 , are preferably separated by a height difference of an eighth wavelength λ/ 8  of an incident light. The first and second surfaces,  32  and  34 , form the blaze profile  36 . The blaze profile  36  forms an effective blaze surface  52  at a blaze angle γ. The blaze angle γ is given by the expression: γ=arctan (λ/(4A)). 
     A first cross-sectional view of the preferred blazed grating light valve  20  of the present invention is illustrated in FIG.  4 A. The first cross-sectional view  60  illustrates the preferred grating light valve  20  in a non-activated state with the elongated elements  24  on a grating pitch A and with the first surfaces  32  defining a grating plane  62 . In the non-activated state, there is preferably a zero electrical bias between the elongated elements  24  and the first conductor  30 . The incident light I of wavelength λ illuminates the preferred blazed grating light valve  20  normal to the grating plane  62 . The preferred blazed grating light valve  20  diffracts light into diffraction orders. For discussion purposes, the diffraction orders are based on a second grating pitch  2 A, which is twice the grating pitch A. 
     In the non-activated state, the incident light I of the wavelength λ is diffracted into a zeroth diffraction order D 0 , a second diffraction order diffraction D 2 , and a minus second order diffraction D −2 . The zeroth order diffraction D 0  is normal to the grating plane  62 . The second order diffraction D 2  and the minus second order diffraction D −2  are at a second order diffraction angle θ 2  given by the expression: θ 2 =arcsin (λ/A). For the preferred blazed grating light valve  20 , the second order diffraction angle θ 2  is less than about 15°. Thus, for the preferred blazed grating light valve  20 , the second order diffraction angle θ 2  is approximately four times the blaze angle γ. 
     Neglecting a first light loss due to absorption by the stepped reflectors  50  and a second light loss by the incident light I passing through gaps between adjacent pairs of the elongated elements  24 , half of the incident light I is diffracted into the zeroth diffraction order D 0  while a quarter of the incident light I is diffracted into each of the second diffraction order D 2  and the minus second diffraction order D −2 . 
     A second cross-sectional view of the preferred blazed grating light valve  20  of the present invention is illustrated in FIG.  4 B. The second cross-sectional view  64  illustrates the preferred grating light valve  20  in an activated state. Preferably, to produce the activated state, alternate ones of the elongated elements  24  are moved toward the substrate  22  by applying an electrical bias between the first conductor  30  and the reflective surface  42  of the alternate ones of the elongated elements  24 . In a fully activated state, the electrical bias moves the alternate ones of the elongated elements  24  by a quarter wavelength λ/ 4  of the incident light I. This results in pairs of the elongated elements  24  forming an effective fully activated height difference of a half wavelength λ/ 2  of the incident light I at the blaze angle γ. 
     In the fully activated state, the incident light I of the wavelength λ is diffracted into a first diffraction order D 1  having a first order angle θ 1 . The first order angle θ 1  is given by the expression: θ 1 =arcsin(λ/2A). For the preferred grating light valve  20  as described here, the first order angle θ 1  is approximately twice the blaze angle γ. 
     A third cross-sectional view of the preferred blazed grating light valve  20  of the present invention is illustrated in FIG.  5 A. The third cross-sectional view  70  illustrates the preferred blazed grating light valve  20  in the non-activated state with the incident light I at an oblique angle θ i  to the grating plane  62 . In the non-activated state, the incident light I is diffracted into an oblique zeroth order diffraction D 0 ′, and an oblique second order diffraction D 2 ′, and an oblique minus second order diffraction D −2 ′. The oblique zeroth order diffraction D 0 ′ is at an oblique zeroth order angle θ 0 ′ with respect to the normal to the grating plane  62 , which is equal to the oblique angle θ i . The oblique zeroth order angle θ 0 ′ and oblique angle θ i  are given by the expression: θ 0 ′=θ i =arcsin (λ/2A). The oblique second order diffraction D 2 ′ is at the oblique angle θ i . The oblique minus second order diffraction D −2 ′ is at an oblique minus second order angle θ −2 ′, which is twice the zeroth order angle θ 0 ′. 
     A fourth cross-sectional view of the preferred blazed grating light valve  20  of the present invention is illustrated in FIG.  5 B. The fourth cross-sectional view  72  illustrates the preferred blazed grating light valve  20  in the activated state with the incident light I at the oblique angle θ i  to the grating plane  62 . In the fully activated state, the incident light I is diffracted into an oblique first order diffraction D 1 ′, which is normal to the grating plane  62 . 
     A first advantage of the preferred blazed grating light valve  20  is that the preferred blazed grating light valve  20  provides a blazed diffraction in the activated state while quickly switching between the non-activated state and the activated state. This is because the elongated elements are translated rather than rotated. 
     A second advantage of the preferred blazed grating light valve  20  is that in the non-activated state none of the incident light I is diffracted into the first diffraction order D 1  for the normal incidence and none of the incident light I is diffracted into the oblique first order diffraction D 1 ′ for the oblique incidence. In a display application where the preferred blazed grating light valve  20  produces an array of pixels and where a bright pixel corresponds to either the first diffraction order D 1  or the oblique first order diffraction D 1 ′, this provides a dark pixel of an image. In a telecommunications application, where the preferred blazed grating light valve  20  operates as a switch and where an on-state of the switch corresponds to either the first diffraction order D 1  or the oblique first order diffraction D 1 ′, this provides an off-state for the switch. 
     A third advantage of the preferred blazed grating light valve  20  is that, in the activated state, the incident light I is diffracted into a single diffraction order which is either the first diffraction order D 1  for the normal incidence or the oblique first order diffraction D 1 ′ for the oblique incidence. In the display application where the preferred blazed grating light valve  20  produces the array of pixels and where the bright pixel corresponds to either the first diffraction order D 1  or the oblique first order diffraction D 1 ′, this simplifies display optics since only the single diffraction order is collected to produce the bright pixel. In the telecommunications application, where the preferred blazed grating light valve  20  operates as the switch and where the on-state of the switch corresponds to either the first diffraction order D 1  or the oblique first order diffraction D 1 ′, this provides efficient utilization of the incident light I since the incident light I is diffracted into the single diffraction order. 
     A fourth advantage of the preferred blazed grating light valve is that because, in the non-activated state, none of the incident light I is diffracted into either the first diffraction order D 1  for the normal incidence or the oblique first order diffraction D 1 ′ for the oblique incidence and because, in the activated state, the incident light I is diffracted into the single diffraction order, the preferred blazed grating light valve  20  provides a high contrast ratio between the non-activated state and the activated state. Typically, this contrast ratio is on an order of a thousand to one. In the display application where the preferred blazed grating light valve  20  produces the array of pixels and where the bright pixel corresponds to either the first diffraction order D 1  or the oblique first order diffraction D 1 ′, this produces a high contrast image. In the telecommunications application, where the preferred blazed grating light valve  20  operates as the switch and where the on-state of the switch corresponds to either the first diffraction order D 1  or the oblique first order diffraction D 1 ′, this produces a high discrimination between the on-state and the off-state. 
     A fifth advantage of the preferred blazed grating light valve  20  is that, because the activated state diffracts the incident light I into the single diffraction order, a depth of focus of either the first diffraction order D 1  for the normal incidence or the oblique first order diffraction D 1 ′ for the oblique incidence is relatively long compared to a diffractive light modulator which diffracts useful light into multiple diffraction orders. In the display application where the preferred blazed grating light valve  20  produces the array of pixels and where the bright pixel corresponds to either the first diffraction order D 1  or the oblique first order diffraction D 1 ′, this allows for simpler optics. In a printing application, which is a type of display application where the bright pixel is typically used to illuminate a cylindrical drum, the longer depth of focus provides a sharper printed image. 
     A first partially fabricated blazed grating light valve of the present invention is illustrated in FIGS. 6A,  6 B, and  6 C. Fabrication of the first partially fabricated grating light valve  80  begins with a silicon substrate  82 . Next, a field oxide layer  84  is formed on the silicon substrate  82  by preferably heating the silicon substrate in an oxygen atmosphere. Preferably, the field oxide layer has a thickness of about 1.0 μm. Following this, a conducting layer  86  is deposited on the field oxide layer  84 . Preferably, the conducting layer  86  has a thickness of about 0.35 μm and comprises doped poly-silicon deposited using an LPCVD (low pressure chemical vapor deposition) process. Subsequently, an etch stop  88  is formed on the conducting layer  86 . Preferably, the etch stop  88  comprises a second field oxide layer formed by heating the poly-silicon in the oxygen environment. Preferably, the etch stop  88  has a thickness of about 200 Å. Next, a sacrificial layer  90  is deposited on the etch stop  88 . Preferably, the sacrificial layer  90  comprises poly-silicon deposited using the LPCVD process. Preferably, the sacrificial layer  90  has a thickness about 1.0 μm. Alternatively, the sacrificial layer has a thickness greater than or about equal to a wavelength λ of the incident light I. 
     A second partially fabricated blazed grating light valve of the present invention is illustrated in FIGS. 7A,  7 B, and  7 C. Fabrication of the second partially fabricated grating light valve  92  begins with the first partially fabricated blazed grating light valve  80  (FIGS. 6A,  6 B, and  6 C). Fabrication of the second partially fabricated grating light valve  92  comprises first and second etching steps using photolithography and a semiconductor etching technique, such as plasma etching. The first etching step etches step producing features  93  into the sacrificial layer  90 . Preferably, the step producing features  93  have a height of an eighth wavelength λ/ 8  of the incident light I. For example, if the incident light is green light having a wavelength λ of 5,280 Å, the height of the step producing features  93  is preferably 660 Å. The second etching step etches post holes  94  into the sacrificial layer  90  and also etches anchor holes (not shown) into the sacrificial layer  90 . The anchor holes form the first and second anchors,  29  and  31  (FIG.  2 B). The second etching step also etches sacrificial layer edges (not shown) where first and second ends,  38  and  40 , of each of the elongated elements  24  couple to the substrate  22  (FIG.  2 B). 
     A third partially fabricated blazed grating light valve of the present invention is illustrated in FIGS. 8A,  8 B, and  8 C. Fabrication of the third partially fabricated blazed grating light valve  100  begins with the second partially fabricated blazed grating light valve  92  (FIGS. 7A,  7 B, and  7 C). Fabrication of the third partially fabricated blazed grating light valve  100  comprises depositing a resilient material  102  on the second partially fabricated grating light valve  92  and then depositing a metal  104  on the resilient material  102 . Preferably, the resilient material  102  comprises silicon nitride. Preferably, the resilient material  102  coats surfaces of the post holes  94  and the anchor holes of the second partially fabricated grating light valve  92 . Alternatively, the resilient material  102  more substantially fills the post holes  94  and the anchor holes. Further alternatively, the resilient material fills the post holes  94  and the anchor holes. (Note that FIGS. 8A and 8B depict the resilient material  102  filling the post holes  94  as a simplification for more easily understood illustrations.) Preferably, the resilient material has a tensile stress of about 1 GPa. Preferably, the resilient material  102  has a thickness of about 920 Å and is deposited using an LPCVD process. Preferably, the metal  104  comprises aluminum having a thickness of about 500 Å. Preferably, the metal  104  is deposited using a physical vapor deposition technique. 
     A fourth partially fabricated blazed grating light valve of the present invention is illustrated in FIGS. 9A,  9 B, and  9 C. Fabrication of the fourth partially fabricated blazed grating light valve  110  begins with the third partially fabricated blazed grating light valve  100  and comprises etching the metal  104  and the resilient material  102  to form fabricated elongated elements  24 A supported by the sacrificial layer  90 . 
     A fabricated blazed grating light valve of the present invention is illustrated in FIGS. 10A,  10 B, and  10 C. Fabrication of the fabricated blazed grating light valve  116  begins with fourth partially fabricated blazed grating light valve  110  and comprises etching the sacrificial layer  90  to completion using a xenon difluoride etch. This produces the fabricated elongated elements  24 A coupled to a fabricated substrate  22 A by fabricated first and second posts,  26 A and  28 A, with each of the fabricated elongated elements  24 A comprising first and second fabricated surfaces,  32 A and  34 A. 
     It will be readily apparent to one skilled in the art that suitable electrical connections for the fabricated blazed grating light valve  116  comprise bond pads, which are well known both in structure and fabrication. Further, it will be readily apparent to one skilled in the art that the fabricated blazed grating light valve  116  is a particular embodiment of the present invention and that accordingly the preferred blazed grating light valve  20  more generally describes the present invention. 
     A cross-sectional view of a first alternative blazed grating light valve of the present invention is illustrated in FIG.  11 . The first alternative blazed grating light valve  20 A replaces the elongated elements  24  of the preferred blazed grating light valve  20  with first alternative elongated elements  24 B. The first alternative elongated elements  24 B comprise a three-step profile  50 A having first, second, and third alternative surfaces,  120 ,  122 , and  124 . A height difference between the first and second alternative surfaces,  120  and  122 , and between the second and third alternative surfaces,  122  and  124 , is preferably a twelfth wavelength λ/ 12  of the incident light I. Thus, the three step profile  50 A forms an alternative blazed profile of the present invention. 
     It will be readily apparent to one skilled in the art that additional steps may be added to the first alternative elongated elements  24 B with a corresponding adjustment in height between adjacent surfaces. 
     A second alternative blazed grating light valve of the present invention is illustrated in FIG.  12 . The second alternative blazed grating light valve  20 B replaces the elongated elements  24  of the preferred blazed grating light valve  20  with second alternative elongated elements  24 C. The second alternative elongated elements  24 C replace the stepped profile  50  of the elongated elements  24  with a flat surface  126  at the blaze angle γ. 
     A third alternative blazed grating light valve of the present invention replaces the elongated elements  24  of the preferred blazed grating light valve  20  with third alternative elongated elements. One of the third alternative elongated elements and the substrate  22  are illustrated in FIG.  13 . The third alternative elongated element  24 D reverses the stepped profile  50  of a central region  128  outside of the central region  128 . In the activated state, the third alternative blazed grating light valve diffracts the incident light I within the central region  128  into the first diffraction order D 1  at the first order angle θ 1  while diffracting the incident light I just outside the central region  128  at minus the first order angle θ 1 . Thus, much of the incident light I diffracted between the first post  26  and the central region and between the central region  128  and the second post  28  is directed away from the first order angle θ 1 , reducing unwanted stray light in downstream optics. 
     A fourth alternative blazed grating light valve of the present invention is illustrated in FIG.  14 A. The fourth alternative blazed grating light valve  20 C comprises fourth alternative elongated elements  24 E. The fourth alternative elongated elements  24 E each comprise a flat reflective surface  130 , which in the non-activated state shown in FIG. 14A, places the flat reflective surfaces  130  in the grating plane  62 . When the fourth alternative blazed grating light valve  20 C is in the non-activated state and is illuminated by the incident light I, the fourth alternative grating light valve  20 C produces the reflected light R. 
     The fourth alternative blazed grating light valve  20 C of the present invention is further illustrated in FIG. 14B showing the fourth alternative blazed grating light valve  20 C in a first activated state. The fourth alternative blazed grating light valve  20 C provides dynamic control of the fourth alternative elongated elements  24 E so that variable groupings of the fourth alternative elongated elements  24 E produce a variable angle blazed diffraction. In the first activated state, six element groups  132  of the fourth alternative elongated elements  24 E produce a six element blazed diffraction D 6  having a diffraction angle θ 6 . Since the six element groups  132  approximate an effective blaze  134 , a height difference from a first point  136  to a second point  138  on the effective blaze  134  is a half wavelength λ/2 of the incident light I. Thus, an actual height difference between lowest and highest elongated elements  24 E is preferably five twelfths wavelength 5γ/12 of the incident light I. 
     In general, an nth element blazed diffraction produces first diffracted light having an nth diffraction angle θ n . The nth diffraction angle θ n  is given by the expression: 
     θ n =arcsin(λ/( n ( w+s ))) 
     where λ=wavelength of the incident light I, n=number of elements in an n element group, w=width of each of the fourth alternative elongated elements  24 E, and s=space between adjacent pairs of the fourth alternative elongated elements  24 E. 
     To produce the nth diffracted light, an nth element group is preferably arranged with outer ones of the fourth alternative elongated elements  24 E having an nth element group height difference (d n ) given by the expression: 
     
       
           d   n =( n− 1)(λ/(2 n ))  
       
     
     In a particular embodiment of the fourth alternative blazed grating light valve  20 C, the fourth alternative elongated elements  24 E have the width w of 2.0 μm and the spaces s of negligible length. Table 1 provides the diffraction angle θ n  and the group height difference d n  for a 5,280 Å green light and the n element grouping of four, five, six, and seven elements. 
     
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 n 
                 θ n   
                 d n   
               
               
                   
               
             
             
               
                 4 
                     3.78° 
                  1,980 Å 
               
               
                 5 
                 3.03 
                 2,112 
               
               
                 6 
                 2.52 
                 2,200 
               
               
                 7 
                 2.16 
                 2,263 
               
               
                   
               
             
          
         
       
     
     The fourth alternative blazed grating light valve  20 C of the present invention is further illustrated in FIG. 14C showing the fourth alternative blazed grating light valve  20 C in a second activated state. In the second activated state, the effective blaze  134  has been reversed by reversing heights of the fourth alternative elongated elements  24 E of the six element groups  132  to produce a reverse six element blazed diffraction D 6 ′. Thus, the dynamic control of the fourth alternative elongated elements  24 E provides an ability to reverse the effective blaze  134  and doubles a number of discrete diffraction angles which the fourth alternative blazed grating light valve  20 C provides. 
     In a telecommunications application, the fourth alternative blazed grating light valve  20 C functions as a variable switch. For example, using the four, five, six, and seven element groups in reversible configurations allows for eight diffractive angles, which provides an eight channel switch. Further, the fourth alternative grating light valve  20 C can be cascaded with eight additional fourth alternative blazed grating light valves  20 C to form a sixty-four channel switch. 
     It will be readily apparent to one skilled in the art that other various modifications may be made to the preferred embodiment without departing from the spirit and scope of the invention as defined by the appended claims.