Patent Abstract:
A method of making a high reflectivity micro mirror. A first step involves providing a monolithic bulk crystal silicon having an anisotropic body with a crystalline plane. A second step involves applying chemical agents to selectively remove a portion of the body overlying the crystalline plane to expose a portion of the crystalline plane. Crystalline planes that are present in monolithic bulk crystal silicon have an inherent smoothness which is on an atomic level. The underlying teaching of the present invention is that, instead of attempting to polish or otherwise smooth the surface of the silicon, one should merely expose all or a selected portion of the crystalline plane and use the exposed portion of the crystalline plane as a mirror surface.

Full Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a method of making a high reflectivity micro mirror and a high reflectivity micro mirror fabricated in accordance with the teachings of the method.  
         BACKGROUND OF THE INVENTION  
         [0002]    High reflectivity micro mirrors are used in optical telecom systems, optical scanners, scientific instrumentation and other applications. These mirrors are used as: 1) scanners which scan an optical beam in a desired pattern, 2) servos which allow the position of an optical light beam to be actively adjusted to maintain optimal positioning on a target, such as an optical fibre or a detector 3) switches which allow optical beams to be switched from one position to another.  
           [0003]    At the present time cylindrical crystalline structures of silicon are formed which are referred to as “boules”. These boules are cut into thin membrane silicon wafers which are micromachined until they have a highly reflective surface. U.S. Pat. No. 6,008,128 (Habuka et al) discusses the science involved in smoothing a surface of a silicon wafer until it has a highly reflective surface.  
           [0004]    Thin membrane silicon wafers are fragile, temperature sensitive and prone to distortion due to internal stresses which makes the smoothing process more difficult.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention relates to an alternative method of making a high reflectivity micro mirror and a high reflectivity micro mirror fabricated in accordance with the teachings of that method.  
           [0006]    According to one aspect of the present invention there is provided a method of making a high reflectivity micro mirror. A first step involves providing a monolithic bulk crystal silicon having an anisotropic body with a crystalline plane. A second step involves applying chemical agents to selectively remove a portion of the body overlying the crystalline plane to expose a portion of the crystalline plane, such that a mirror surface is formed which is co-extensive with the exposed portion of the crystalline plane.  
           [0007]    According to another aspect of the invention there is provided a high reflectivity micro mirror which includes a monolithic bulk crystal silicon having an anisotropic body with a crystalline plane. The body has a mirror surface co-extensive with a selectively exposed portion of the crystalline plane.  
           [0008]    Crystalline planes that are present in monolithic bulk crystal silicon have an inherent smoothness which is on an atomic level. The underlying teaching of the present invention is that, instead of attempting to polish or otherwise smooth the surface of the silicon, one should merely expose all or a selected portion of the crystalline plane and use the exposed portion of the crystalline plane as a mirror surface. Once this basic teaching is understood a number of other innovations become possible, as will hereafter be further described.  
           [0009]    It will be appreciated that a crystalline plane can be exposed to such an extent that it becomes part of an exterior surface of the body or access can be provided to a crystalline plane that remains positioned internally within the body. There are various ways to provide access to an internally positioned crystalline plane, for example an inlet passage and an outlet passage can be provided which intersect at the crystalline plane.  
           [0010]    Alignment of reflective elements has long been a problem in the industry. Alignment with atomic accuracy can be obtained by selectively exposing several discrete portions of the crystalline plane. This creates several discrete mirror surfaces along crystalline plane. For example, one can create parallel passages extending along the crystalline plane, intersecting passages extending along the crystalline plane, or several discrete mirror surfaces axially aligned and spaced along the crystalline plane.  
           [0011]    The standard in the industry is to work with monolithic bulk crystal silicon cut into wafers. It will be appreciated, however, that the monolithic bulk crystal silicon need not be in wafer form. A larger monolithic bulk crystal silicon will have several, if not multiple, crystalline planes. Complex structures can be developed by selectively removing a portion of the body overlying selected ones of the several crystalline planes. This creates a complex structure with several mirror surfaces that have a relationship with each other that has atomic accuracy.  
           [0012]    In order to accurately align reflective elements, there is a need for the mirror surface of a wafer to be at a selected angle. The angle required is now achieved by micro machining. With the present invention, it is possible to obtain a crystalline plane in any desired orientation merely by selectively cutting the wafers from a larger monolithic bulk crystal silicon at angles to ensure the crystalline plane of the wafers have an orientation consistent with an intended application.  
           [0013]    In some applications a larger mirror surface or a mirror surface of an unusual shape is required. While there will not be an unusual shaped crystalline plane that will match the unusual shape of mirror surface required, the same effect can be obtained by stacking two or more wafers. The stacked wafers provide a composite mirror surface consisting of the combined mirror surfaces of two or more stacked wafers.  
           [0014]    Although beneficial results may be obtained through the use of the high reflectivity mirror, as described above, even more beneficial results may be obtained when means is provided for selectively adjusting the position or angle of the mirror surface by manipulating the position of the body.  
           [0015]    The invention also makes possible a number of innovated switching devices which will hereinafter be illustrated and described. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to in any way limit the scope of the invention to the particular embodiment or embodiments shown, wherein:  
         [0017]    [0017]FIG. 1 a  is a side elevation view of a high reflectivity micro mirror fabricated in accordance with the teachings of the present invention, with positional adjustment.  
         [0018]    [0018]FIG. 1 b  is a side elevation view of a side elevation view of a high reflectivity micro mirror illustrated in FIG. 1, with rotational adjustment.  
         [0019]    [0019]FIG. 2 a  is a top plan view of the high reflectivity micro mirror illustrated in FIG. 1, with actuator.  
         [0020]    [0020]FIG. 2 b  is a side elevation view of the high reflectivity micro mirror illustrated in FIG. 2 a.    
         [0021]    [0021]FIG. 3 is a perspective view of the high reflectivity micro mirror illustrated in FIG. 1, with a fixed mounting and fibre optic alignment passage.  
         [0022]    [0022]FIG. 4 a  is a side elevation view, in section, showing a first step in fabricating the high reflectivity micro mirror illustrated in FIG. 1.  
         [0023]    [0023]FIG. 4 b  is a side elevation view, in section, showing a second step in fabricating the high reflectivity micro mirror illustrated in FIG. 1.  
         [0024]    [0024]FIG. 4 c  is a side elevation view, in section, showing a third step in fabricating the high reflectivity micro mirror illustrated in FIG. 1.  
         [0025]    [0025]FIG. 4 d  is a side elevation view, in section, showing a fourth step in fabricating the high reflectivity micro mirror illustrated in FIG. 1.  
         [0026]    [0026]FIG. 5 is a side elevation view, in section, showing a fourth step in fabricating the high reflectivity micro mirror illustrated in FIG. 1, with the mirror surface having a differing orientation angle.  
         [0027]    [0027]FIG. 6 is a side elevation view, in section, showing the high reflectivity micro mirrors illustrated in FIGS. 4 b  and  5 , combined to form a composite mirror surface having two differing orientation angles.  
         [0028]    [0028]FIG. 7 is a side elevation view, in section, showing how the high reflectivity micro mirror illustrated in FIG. 6, can be used to direct a light beam in two differing reflection angles.  
         [0029]    [0029]FIG. 8 is a top plan view, in section, showing the high reflectivity micro mirror illustrated in FIG. 1, incorporated in an apparatus that combines light beams.  
         [0030]    [0030]FIG. 9 a  is a top plan view, in section, showing the high reflectivity micro mirror illustrated in FIG. 1, incorporated in an apparatus that switches light beams with a single micro mirror.  
         [0031]    [0031]FIG. 9 b  is a side elevation view, in section, showing the switching apparatus illustrated in FIG. 9 a.    
         [0032]    [0032]FIG. 10 a  is a bottom plan view, in section, showing the switching apparatus illustrated in FIG. 9 a.    
         [0033]    [0033]FIG. 10 b  is a top plan view showing the switching apparatus illustrated in FIG. 9 a.    
         [0034]    [0034]FIG. 11 is a side elevation view, in section, showing the high reflectivity micro mirror illustrated in FIG. 1, incorporated in an apparatus that switches light beams on two planes with two micro mirrors.  
         [0035]    [0035]FIG. 12 is a perspective view of the switching apparatus illustrated in FIG. 11.  
         [0036]    [0036]FIG. 13 is a side elevation view, in section, showing the high reflectivity micro mirror illustrated in FIG. 1, with a beam splitting surface.  
         [0037]    [0037]FIG. 14 is a top plan view, in section, showing the high reflectivity micro mirror illustrated in FIG. 1, with servo rotation.  
         [0038]    [0038]FIG. 15 is a perspective view of a switching apparatus similar to that illustrated in FIG. 11, only having multiple ingress light paths and multiple egress light paths.  
         [0039]    [0039]FIG. 16 is a side elevation view, in section, of a switching apparatus similar to that illustrated in FIG. 15, only having a membrane disposed between the first plane and the second plane to alter properties of the light beams as they pass from the ingress light paths to the egress light paths.  
         [0040]    [0040]FIG. 17 is a perspective view of the switching apparatus illustrated in FIG. 16.  
         [0041]    [0041]FIG. 18 a  is a top plan view, in section, showing the high reflectivity micro mirror illustrated in FIG. 1, incorporated in an apparatus for aligning light beams.  
         [0042]    [0042]FIG. 18 b  is a side elevation view, in section, of the apparatus for aligning light beams illustrated in FIG. 18 a.    
         [0043]    [0043]FIG. 19 a  is a top plan view, in section, showing the high reflectivity micro mirror illustrated in FIG. 1, with an expandable actuator in an expanded condition.  
         [0044]    [0044]FIG. 19 b  is a top plan view, in section, of the high reflectivity micro mirror illustrated in FIG. 19 a,  with the expandable actuator in a contracted condition.  
         [0045]    [0045]FIG. 20 is a top plan view, in section, of the high reflectivity micro mirror illustrated in FIG. 19 a,  with the expandable actuator rotating the body to adjust the angle of the mirror surface.  
         [0046]    [0046]FIG. 21 is a side elevation view, in section, of a high reflectivity micro mirror constructed in accordance with the teachings of the present invention with crystalline plane only partially exposed.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0047]    The preferred embodiment, a high reflectivity micro mirror generally identified by reference numeral  10 , will now be described with reference to FIGS. 1 a  through  21 .  
         [0048]    Structure and Relationship of Parts:  
         [0049]    Referring to FIG. 4 d,  there is provided a high reflectivity micro mirror  10  which includes a monolithic bulk crystal silicon  12  that has an anisotropic body  14  with a crystalline plane  16 . Referring to FIG. 21, body  14  has a mirror surface  18  which is co-extensive with a selectively exposed portion  20  of crystalline plane  16 .  
         [0050]    Referring to FIGS. 4 a  through  4   d,  the preferred method of making high reflectivity micro mirror  10  involves providing monolithic bulk crystal silicon  12  that has anisotropic body  14  with crystalline plane  16 . Chemical agents are then applied to selectively remove a portion of body  14  overlying crystalline plane  16  to expose portion  20  of crystalline plane  16 , such that mirror surface  18  is formed that is co-extensive with exposed portion  20  of crystalline plane  16 . High reflectivity micro mirror  10  can be in a number of configurations depending upon what portions  20  of crystalline plane  16  are selectively exposed. For example, crystalline plane  16  can be exposed to an extent that it becomes part of an exterior surface  22  of body  14  or crystalline plane  16  can be positioned internally within body  14 , as will hereinafter be further described.  
         [0051]    Referring to FIG. 2 a  and  2   b,  there is illustrated an actuator, generally indicated by reference numeral  24 . High reflectivity micro mirror  10  can be positioned through the use of actuator  24 . Actuator  24  includes arms in the form of springs  30  that move in response to an application of an electrical current. In the illustrated embodiment, arms are shown as springs  30 , however it will be appreciated that there are other structures that could operate as arms  30 . Referring to FIG. 1 a,  there is illustrated how selective movement of body  14  axially can thereby shift the position of a beam  26  reflecting from mirror surface  18 . Referring to FIG. 1 b,  and FIG. 14, there is illustrated how selective rotation of body  14  can thereby adjust the reflection angle of mirror surface  18 . Referring to FIGS. 19 a  through  20 , there is illustrated another form of actuator, generally indicated by reference numeral  32 . Referring to FIGS. 19 a  and  19   b,  actuator  32  has arms that are resistors  34  which heat up and expand upon application of an electrical current. Referring to FIG. 20, three parallel arms  34  are provided. It can be seen how unequal expansion of arms  34  effects a partial rotation of body  14 .  
         [0052]    Referring to FIG. 3, advantages can be obtained by using crystalline plane  16  of bulk crystal silicon  12  for purposes of alignment. In the illustrated embodiment, a passage  28  extends across crystalline plane  16 . An optical fibre  37  which shown as the source for light beam  26  is aligned in passage  28 . Once the basic teachings are understood, it will be appreciated that the passages can be arranged in a number of configurations. For example, passages  28  can be arranged as parallel passages or intersecting passages. Regardless of the orientation of the passages, in all cases their alignment will have atomic accuracy as they extend across crystalline plane  16 .  
         [0053]    As illustrated in FIG. 21, crystalline plane  16  does not have to be completely exposed, only that portion required as mirror surface  18  need be exposed. Further, crystalline plane  16  can remain positioned internally within body  14 . Body  14  has an inlet passage  40  and an outlet passage  42  which intersect at a small selectively exposed portion  20  of crystalline plane  16 . This small selectively exposed portion  20  serves as mirror surface  18 . It is also possible to effect alignment by utilizing intersecting crystalline planes  16   a  and  16   b.    
         [0054]    Referring to FIGS. 5 through 7, two or more bodies  14  can be stacked to provide composite mirror surface  18  made up of mirror surfaces of two or more bodies  14 . This can be of benefit when mirror surface  18  of a larger size or unusual shape is required.  
         [0055]    Referring to FIG. 8, high reflectivity micro mirror  10  can be positioned in a housing  44  that has a plurality of ingress light paths  46  and a single egress light path  48 . In the illustrated embodiment, lasers  45  are shown as being the light source. A plurality of monolithic bulk crystal silicon  12  is provided. Each bulk crystal silicon  12  has anisotropic body  14  with crystalline plane  16  and exterior surface  22 . On each body  14 , crystalline plane  16  is in a selected angular orientation and mirror surface  18  is co-extensive with of crystalline plane  16  on exterior surface  22  of body  14 . One of bodies  14  is positioned on each ingress light path  46  and has mirror surface  18  oriented at reflection angle that is adapted to reflect light beam  26  to single egress light path  48 . Bodies  14  can either be fixed, or can be equipped with actuators that are capable of rotating bodies  14 , as illustrated in FIGS. 1 b,    14  and  20 .  
         [0056]    Referring to FIGS. 9 a  through  10   b,  high reflectivity micro mirror  10  can be included in a housing  44  which has a plurality of ingress light paths  46  and a plurality of egress light paths  48 . A plurality of monolithic bulk crystal silicon  12  are also provided. Each monolithic bulk crystal silicon  12  has anisotropic body  14  with crystalline plane  16  and exterior surface  22 . Each crystalline plane  16  is in a selected angular orientation and has a mirror surface  18  that is co-extensive with exposed portion  20  of crystalline plane  16  on the exterior surface  22  of body  14 . Each body  14  is positioned within housing  44  and out of alignment with ingress light path  46 . Several actuators are provided for moving one of bodies  14  into one of ingress light paths  46  until mirror surface  18  is oriented at a reflection angle that is adapted to direct reflected beam  26  along a selected one of egress light paths  48 . An examples of a suitable actuator is illustrated in FIGS. 19 a  and  19   b.    
         [0057]    Referring to FIGS. 11 and 12, high reflectivity micro mirror  10  is provided that includes housing  44  with one ingress light path  46  on a first plane  50  and one egress light path  48  on a second plane  52 . Egress light path  48  is angularly offset from ingress light path  46 . Two monolithic bulk crystal silicon  12  are provided with anisotropic bodies  14 . Crystalline plane  16  of each body  14  is in a selected angular orientation and mirror surface  18  is co-extensive with exposed portion  20  of crystalline plane  16  on exterior surface  22  of body  14 . One of bodies  14  is positioned on first plane  50  in ingress light path  46  with mirror surface  18  oriented at reflection angle that is adapted to reflect light beam  26  to second plane  52 . The other body  14  is positioned on second plane  52  with mirror surface  18  oriented at a reflection angle that is adapted to direct reflected light beam  26  along egress light paths  48 . Housing for high reflectivity micro mirror  10  can have more than one ingress light path  46  and one egress light path  48 . Referring to FIG. 15, high reflectivity micro mirror  10  is provided that is similar to that illustrated in FIGS. 11 and 12 but which includes housing  44  that has a plurality of inlet passages  40  for a plurality of ingress light paths  46  on first plane  50  along with a plurality of outlet passages  42  for a plurality of egress light paths  48  on second plane  52 .  
         [0058]    Referring to FIGS. 16 and 17, high reflectivity micro mirror  10  is illustrated which is similar to that illustrated in FIGS. 12 and 15. However, it is configured so as to include a light penetrable membrane  54  that is placed between first plane  50  and second plane  52 , thereby altering properties of light beam  26  passing from ingress light path  46  to egress light path  48 . Light penetrable membrane  54  can be a light filter or can be adapted to effect light beam modulation.  
         [0059]    Referring to FIG. 13, mirror surface  18  is provided that has a beam splitting surface treatment whereby a refractive surface  56  is adapted to split an input light beam  26   a  into several output light beams  26   b.  In the illustrated embodiment, refractive surface  56  is depicted however it will be appreciated that a diffractive surface and holographic surface are also adapted to split an input light beam  26   a  into several output light beams  26   b.    
         [0060]    Referring to FIGS. 18 a  and  18   b,  there is provided high reflectivity micro mirror  10  which includes housing  44  that has ingress light paths  46  and corresponding egress light paths  48 . Laser  25  is shown as being the source of light beam  26 . Each ingress light path  46  is on a common plane  58  but out of axial alignment with corresponding egress light path  48 . Housing  44  has an interior cavity  60 , a first supporting surface  62  and a second supporting surface  64  in parallel spaced relation. Monolithic bulk crystal silicon  12  has anisotropic body  14  with crystalline plane  16  and an exterior surface  22 . Crystalline plane  16  is in a selected angular orientation and mirror surface  18  is co-extensive with exposed portion  20  of crystalline plane  16  on exterior surface  22  of body  14 . A first body  14   a  is positioned on first supporting surface  62  in ingress light path  46  with mirror surface  18  oriented at a reflection angle that is adapted to reflect light beam  26  to second supporting surface  64 . A pair of angularly offset bodies  14  are positioned on second supporting surface  64  with their mirror surfaces  18  oriented at reflection angles that are adapted to effect a realignment of light beam  26  and reflect light beam  26  back to first supporting surface  62 . A second body  14   b  is positioned on first supporting surface  62  with mirror surface  18  oriented at a reflection angle that is adapted to reflect light beam  26  along corresponding egress light path  48 .  
         [0061]    Summary of the Basic Ideas  
         [0062]    1) Single Crystal Bulk Silicon etching used to achieve mirror surface for use in light beam deflection and switching. Single Crystal Bulk Silicon used with mirror surface on moveable element is etched from same bulk silicon as mirror surface.  
         [0063]    2) Single Crystal Silicon that is anisotropically etched along crystal planes to provide precision alignment of separate elements. An example is v-groove for fiber access that is aligned to crystal mirror along another crystal plane. Alignment is possible to atomic accuracy with respect to angle.  
         [0064]    3) Wavelength splitting element (diffractive, holographic, reflective etc.) is applied to mirror surface to allow for wavelength division demultiplexing on mirror element. The same element can be used to switch beam, beam deflect at controllable angle and demultiplex wavelength of incoming beam. Wavelength splitter, demultiplexer. Can be used for WDM(Wavelength Division Multiplex) fiber optic signals or DWDM (Dense WDM).  
         [0065]    4) Free space Wavelength combiner multiplexer based on several mirror surface elements  
         [0066]    5) Monolithic switch based on incoming signals switched to outgoing paths with using two mirror elements to provide full in out switch selection.  
         [0067]    6) Monolithic switch with frequency selective element to provide switching and frequency selection in single unit.  
         [0068]    7) Intensity or power level control is possible by fine alignment control of actuator. This can allow beam power or signal maximization or signal level compensation or equalization across switch or frequencies which is very useful for WDM.  
         [0069]    8) Multiple control elements can be operated at the same time in a parallel fashion.  
         [0070]    9) The use of servo elements allows laser diode elements to be placed with imperfect alignment. Individual laser diodes do not have to be servo, only their output beam. This allows the laser diodes to be placed closer together on better heat sinking material.  
         [0071]    10) Monolithic beam aligner correction servo for multi laser application.  
         [0072]    1.0 Introduction  
         [0073]    Single crystal silicon referred to above could be quartz sapphire or some other crystalline material. This can be any material that is anisotropically etchable. Typically single crystal materials have this attribute. There is a need for steerable micro-mirrors with high reflectivity. These mirrors could be of use in optical Telecom systems, optical scanners, scientific instrumentation, and other applications. In more detail, these mirrors can be used as: 1) scanners: scanning an optical beam in a desired pattern, 2) servos: allowing the position of the an optical light beam to be actively adjusted to maintain optimal positioning on a target (such as an optical fiber or a detector), and 3) switches: allowing optical beams to be switched from one position to another in, for example, an optical switching system used in Telecom.  
         [0074]    For many of the above applications, a small device (order of 1 to 100&#39;s of microns) and small amounts of power needed for motion are important parameters in developing a practical device. These conditions are satisfied by devices fabricated using the techniques known as silicon micromachining and Micro-electro-mechanical Systems (MEMS). For certain applications, such as Telecom and scientific measurements, there is also a strong desire to have a mirror that causes as small a power loss and minimum beam distortion as possible. For these two criteria to be met, an optically smooth, high reflectivity surface is needed. This has proven difficult to develop using the MEMS processing techniques that are typically used to fabricate steerable micro-mirrors. Herein is described a steerable micro mirror based on a mirror tilted at an angle that is integrated with an actuator that moves the mirror. The basic principle of operation is shown in FIGS. 1 a  and  1   b.  The device consists of two types of fabrication processes are described below; the first is based on bulk silicon micromachining technology, and the second uses the concepts described in the first implementation, but is a more general technique. Both of these techniques allow for the devices to be fabricated using standard microfabrication techniques, which then allows for mass production of steerable high reflectivity micro-mirrors.  
         [0075]    2.1 General Description  
         [0076]    The device consists of two portions: the actuator and mirror (FIGS. 2 a,    2   b,  and  3 ). Using a mirror, which is tilted with respect to the axes of motion of the actuator, gives the device the ability to steer the beam. The actuator can be any MEMS actuator, which produces motion when a voltage or current is applied to the device. Possible actuators are comb drives, or resistively heated springs. The motion of the actuator can be simply linear, which causes a linear displacement of the optical beam or it can move the two edges of the mirror differentially, which will allow the optical beam to be deflected in any direction.  
         [0077]    The central idea of this process is that the tilt of the mirror is created during the fabrication process. In the simplest implementation, the mirror surface is formed by the crystalline planes of silicon. The general outline of the fabrication process is shown in FIGS. 4 a  through  4   d.  The process begins with a substrate that contains three layers. The first layer which is the device layer, is the one that the actuator and the mirror are fabricated from. This layer can be silicon or any other material that an actuator and a bevelled mirror can be fabricated in. The middle layer is a sacrificial layer, that is a layer that is removed the free the structures formed in the top layer. This layer can be formed from any material that can be selectively etched compared to the device layer is compatible with all the processes needed to fabricate the device. The last layer is the substrate. This layer can be any material that gives the device strength to be handled during processing. This can be any material that is compatible with the processing of the sacrificial and device layers. In some implementations, there could be only a single layer; the device layer. The other layers are needed in the other implementation to support the device during processing. If the device layer is thick enough, the requirement for the sacrificial layer and substrate can be removed.  
         [0078]    2.2 Fabrication Process  
         [0079]    In the simplest implementation, the substrate and the device layers are made from silicon. The sacrificial layer can be fabricated from silicon dioxide, doped silicon dioxide, silicon nitride, doped or undoped silicon. A possible structure for the wafers would be a 30 micron thick device layer, on a 1 micron thick silicon dioxide sacrificial layer, and a 500 micron thick silicon wafer. These wafers can be purchased commercially. They are called SOS (silicon/oxide/silicon) or SOI (silicon on insulator) wafers.  
         [0080]    The process flow is:  
         [0081]    1) The actuator is patterned into the device layer using standard lithography and deep reactive ion etching.  
         [0082]    2) The electrical connections can be made to the actuators are made at this point or later in the process using standard metal deposition and lithography techniques.  
         [0083]    3) The mirror surface is fabricated by:  
         [0084]    a) covering the actuator and the electrical contacts with a material that covers all the exposed silicon and electrical contacts and will not be removed by the an isotropic silicon etch. Silicon nitride deposited by plasma enhanced chemical vapor deposition (PECVD) is one such material.  
         [0085]    b) openings in the above masking layer, which are for the fabrication of the mirrors, are made using standard lithographic and etching techniques.  
         [0086]    c) the mirrors are etched using aqueous an isotropic silicon etching techniques. The bevelled mirror is formed by the slower etch rate of the crystalline planes of the silicon that forms the device layer.  
         [0087]    d) the masking layer is removed using standard etching techniques  
         [0088]    4) The actuator and the mirror are ‘freed’ from the substrate by etching the sacrificial layer. This etching is performed using standard etching techniques. For example, for a silicon dioxide layer, HF or buffered HF acid solution could be used.  
         [0089]    5) If the surfaces of the mirrors do not have sufficiently high reflectivity, a layer of a high reflectivity material can be deposited onto that surface. An example of this is to deposit a thin layer of aluminum onto the surface of the mirror.  
         [0090]    An Optically Smooth surface can be formed using aqueous silicon an isotropic etching techniques if;  
         [0091]    a) the device layer is formed from silicon wafers with a minimum of defects.  
         [0092]    b) processing the wafers does not add significant numbers of defects.  
         [0093]    c) the masks are accurately aligned to the crystal directions.  
         [0094]    d) the chemistry of the aqueous silicon etch solutions is modified to create smooth surfaces.  
         [0095]    e) proper etching techniques are used to ensure smooth surfaces.  
         [0096]    2.3 Variation 1: Achieving Different Tilt Angles  
         [0097]    If a silicon wafer is used as the device layer, the mirror will be bevelled at an angle of 54.7 degrees. Other angles can be achieved by using silicon wafers that are cut at different angles to the direction as the device layer. These ‘off-cut’ wafers are bonded to the sacrificial layer and the substrate as needed. The surface of the mirrors will continue to be the planes, but the angle between bevelled mirror surface and the device surface can be arbitrarily chosen as illustrated in FIG. 5). This may be used as a on/off switch or as a deflection from channel  1  output to channel two.  
         [0098]    2.4 Variation 2: Achieving Two or More Distinct Angles on a Single Mirror  
         [0099]    In switching applications, a mirror that has two or more distinct angles would be of great use. This can be achieved by bonding two or more wafers, each of which is cut at a different angle to the direction are used to form the device layer. A mirror surface with a two angle structure is shown in FIG. 6. With the actuator in one position, the optical beam reflects off one surface. If the actuator shifts position sufficiently, the optical beam will reflect off the second angular surface. Now the beam is directed in a significantly different direction.  
         [0100]    3.0 A General Technique for Forming the Bevelled Mirror  
         [0101]    The mirror surface can be formed using other techniques. One such technique is to use polishing to from the bevel. Prior to the fabrication of the actuator, the portion of the device that will become the mirror surface is ground and polished to the desired angle and surface finish. The actuator and other portions of the device are formed using mostly standard lithographic techniques, with a modified photo resist spinning process. The advantage of this technique is that the surface finish on the mirror is not dependent on aqueous anisotropic etching, but rather polishing. This increases the possible materials the devices can be fabricated from.  
         [0102]    4.0  
         [0103]    Resistive capacitive or inductive elements applied to or built into the actuator can be used to achieve motion and servo or mechanical fine control over beam deflection. This can utilize piezio electric effects of the actuator or capacitive electrostatic electrodynamic or magnetic forces can be used to deflect actuator in various ways. This motion can be used to provide:  
         [0104]    1) On off beam switching motion to interact in a major way with light beams.  
         [0105]    2) Power control of output by reducing coupling by increasing miss alignment. Fine control over power levels by small deflections.  
         [0106]    3) Frequency or wavelength selectivity for multiplexing or demultiplexing WDM signals.  
         [0107]    5.0  
         [0108]    Control over actuator position by mechanical motion may be used for translation motion, tilt or beam angle deflection, servo or fine control. Each of these is used to interact with the light beam to rotate or translate the beam vector.  
         [0109]    6.0  
         [0110]    The surface optical coating on actuator mirror surface can be used to provide optical frequency or wavelength splitting for selective switching of individual signals. Incoming beam is WDM and contains many frequency bands or channels. Output beam is split by diffractive or holographic surface on switching element into individual beams. Then a single beam out of the family of beams may be selected and directed to an output channel.  
         [0111]    Advantages over surface micromachining the traditional way of building micro mirrors and actuators:  
         [0112]    1) low number of fabrication steps compared to surface micromachining.  
         [0113]    2) low cost fabrication equipment required compared to surface micromachining.  
         [0114]    3) monolithic elements not subject to stresses and deflections of surface micromachining. No dishing curling warping delaminating which is common in surface micromachining.  
         [0115]    4) single monolith element is used so multiple copies can be produced at same time One set of tooling provides multiple devices.  
         [0116]    5) self aligning by use of crystal planes of single crystal silicon.  
         [0117]    6) monolithic so assembly not required.  
         [0118]    7) simple surface treatment either pre or post process can be used to create elements or other features such as diffractive optical surface on switch element.  
         [0119]    8) because multiple units are fabricated monolithically each will have atomic level alignment for primary angles.  
         [0120]    9) integration of v-groove channels for fiber optic alignment.  
         [0121]    Additional comments regarding FIGS. 1 a  through  21 :  
         [0122]    [0122]FIG. 1 a  shows a translation of mirror surface top original position and translation of mirror showing beam position shift. FIG. 1 b  showing beam angle deflection change. Top shows original beam angle deflection bottom shows mirror angle change giving rise to beam angle deflection change. FIGS. 2 a  and  2   b  are showing substrate  66 , actuator base  68 , actuator element  24  along with mirror surface  18 . FIG. 3 illustrates optic fiber  37  alignment and mirror  18  as well as showing beam path  26 . V-groove  28  for optical fiber  37  alignment along with monolithic mirror  18 . Being single crystal monolithic  12  angles of V-groove  28  are tightly controlled. FIGS. 4 a  through  4   d,  involve the fabrication process.  
         [0123]    1. Starting with device layer  70 , sacrificial layer  72  and substrate  66 .  
         [0124]    2. Fabricate Actuator Base  68   
         [0125]    3. Fabricate Mirror  18   
         [0126]    4. Free Device  74   
         [0127]    5. Not shown is Actuator fabrication which anchors mirror  18  and actuator base  68  to rest of device  70 .  
         [0128]    [0128]FIG. 5 is showing the fabrication of single mirrored surface  18  on crystalline plane  16 . FIG. 6 is showing fabrication using silicon etched along two different crystalline planes  16  of two wafer bodies  14 , at different angles. FIG. 7 is showing actuator  24  in two positions with differing bevel angles causing two differing exit angles of incoming beam  26 . Translation turns into beam angle rotation. FIG. 8 is showing several beams  46  being combined by angled reflection off separately controlled mirrors  18  used to produce a combiner multiplexer device. Space based switch/servo elements used to create space based combiner for WDM. Note that lasers  45  can be roughly aligned where as the mirror actuators  24  provide final adjustment. DEMA stands for Deflector Element Mirror plus Actuator. Laser  45  can be of differing wavelengths or alternatively lasers  45  can be same wavelengths but different data channels and the DEMA elements could be used as on/off switching elements. Alternatively lasers  45  could be the same wavelength and in the combiner could used for increased power by the use of multiple lasers  45  for one output beam  48 .  
         [0129]    [0129]FIGS. 9 a  and  9   b  is showing part of cross point switch and is showing DEMA moving into beam path  46  and deflecting beam  46  with 3 beam rows  46  and 6 switching column elements  16 . Multiple input beams  46  are shown with DEMA elements acting as switches to interrupt and deflect beams  46 . FIGS. 10 a  and  10   b  are illustrating a switch showing path of light  46 . FIG. 11 shows a combined switch using two monolithic elements  14 . FIG. 12 is showing two switching elements  14  of cross point switch. FIG. 13 is showing WDM demultiplex wavelengths using surface optical coating on mirror  18 . Surface treatment provides selective direction of split beam  26  as well as direction through DEMA deflective element  14 . Surface  56  may be holographic or other grating or diffractive surface. Single multifrequency input single frequency output. FIG. 14 shows servo rotation to select frequency of WDM or DWDM wavelength, servo angle back and forth to align selected frequency/wavelength to output port. In this way switch demultiplex and selected attenuation is formed. FIG. 15 shows full access cross point switch. Input channels  46  can be switched to any output channel  48  by the use of two switching elements. Note that with channel splitting (WDM selection) surfaces on channel can be diverted to any output channel  42 . Two monolithic parts  50 ,  52  make input channels  46  and output channels  48  switch. FIG. 16 shows full access cross point switch. Input channels  46  can be switched to any output channel  48  by the use of two switching elements  14 . Additional active or passive elements can be placed in vertical light path to allow for faster switching or light filtering or modulation of signals. The middle layer  54  is placed between the two monolithic layers  50 ,  52 . FIG. 17 shows full crosspoint switch with active element. Note that the direction of light waves does not matter in cross point switch. Each channel can be input  46  or output  48 . FIGS. 18 a  and  18   b  shows the use of laser diode beam corrector using two layer actuator system. Each laser diode beam  46  is placed as best alignment as possible on substrate for cooling substrate is switch and actuator. Laser beams  46 , because of manufacturing and assembly variations, are not parallel beams. FIGS. 19 a  and  19   b  show the actuator construction to achieve translation and rotation in simple construction. Voltage  76  and heating element  78  are also shown. Active elements can be resistors which when current is applied heat up causing expansion. This expansion causes increase in length of the element attached. With three arm elements  34 , rotation and translation can be achieved. If current is applied evenly on all three arms  34  or a balance between the two outer ones and the inner one then translation will be in a linear direction. If there is unbalanced currents in the arms  34  then rotation will occur because of uneven heating which leads to uneven expansion. Several alternative methods could be used including piezio resistive elements or electrostatic attraction actuators or magnetic actuators. FIG. 20 is showing rotation of mirror  18  due to unequal current on actuator arms  34 . FIG. 21 illustrates the exposed portion  20  of body  14 .  
         [0130]    Using a bulk single crystal mirror surface allows further treatment of the surface to create superior mirror structures. This gives a stable mirror platform because of stable and controlled thickness of the base single crystal silicon. In contrast, other methods used to create mirrors such as polysilicon or thin film surfaces are not maintained flat under high temperatures or subsequent mechanical or chemical manufacturing steps. Specifically, high efficiency mirrors are made from very flat surfaces and are further processed by the addition of reflecting surfaces such as aluminum or gold or even dielectric layers. A bulk atomically flat surface of a bulk single crystal allows metal, dielectric or other mirror materials to be added without distorting the underlying flat surface. Further processing by the addition of any passive or active surface to the base mirror plane is much easier on a bulk material than on extant thin film material mirrors.  
         [0131]    Photonic crystals are a new class of material which are being developed now. If photonic crystals are added to the bulk single crystal mirror structure, this will create a powerful new class of devices. For example, it can create a mirror with specific optical attributes, such as filtering and switching at the same time. Photonic crystals, by their nature, are unlikely to be produced on thin mirrors. A bulk single crystal mirror structure will assist in facilitating mirror surfaces treated with photonic crystals.  
         [0132]    In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements.  
         [0133]    It will be apparent to one skilled in the art that modifications may be made to the illustrated embodiment without departing from the spirit and scope of the invention as hereinafter defined in the Claims.

Technology Classification (CPC): 2