Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/24—Coupling light guides
  • G02B6/26—Optical coupling means
  • G02B6/35—Optical coupling means having switching means
  • G02B6/351—Optical coupling means having switching means involving stationary waveguides with moving interposed optical elements
  • G02B6/3512—Optical coupling means having switching means involving stationary waveguides with moving interposed optical elements the optical element being reflective, e.g. mirror
  • G02B6/3518—Optical coupling means having switching means involving stationary waveguides with moving interposed optical elements the optical element being reflective, e.g. mirror the reflective optical element being an intrinsic part of a MEMS device, i.e. fabricated together with the MEMS device
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/24—Coupling light guides
  • G02B6/26—Optical coupling means
  • G02B6/35—Optical coupling means having switching means
  • G02B6/351—Optical coupling means having switching means involving stationary waveguides with moving interposed optical elements
  • G02B6/3512—Optical coupling means having switching means involving stationary waveguides with moving interposed optical elements the optical element being reflective, e.g. mirror
  • G02B6/3514—Optical coupling means having switching means involving stationary waveguides with moving interposed optical elements the optical element being reflective, e.g. mirror the reflective optical element moving along a line so as to translate into and out of the beam path, i.e. across the beam path
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/24—Coupling light guides
  • G02B6/26—Optical coupling means
  • G02B6/35—Optical coupling means having switching means
  • G02B6/354—Switching arrangements, i.e. number of input/output ports and interconnection types
  • G02B6/3554—3D constellations, i.e. with switching elements and switched beams located in a volume
  • G02B6/3556—NxM switch, i.e. regular arrays of switches elements of matrix type constellation
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/24—Coupling light guides
  • G02B6/26—Optical coupling means
  • G02B6/35—Optical coupling means having switching means
  • G02B6/3564—Mechanical details of the actuation mechanism associated with the moving element or mounting mechanism details
  • G02B6/3568—Mechanical details of the actuation mechanism associated with the moving element or mounting mechanism details characterised by the actuating force
  • G02B6/357—Electrostatic force
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/24—Coupling light guides
  • G02B6/26—Optical coupling means
  • G02B6/35—Optical coupling means having switching means
  • G02B6/3564—Mechanical details of the actuation mechanism associated with the moving element or mounting mechanism details
  • G02B6/3584—Mechanical details of the actuation mechanism associated with the moving element or mounting mechanism details constructional details of an associated actuator having a MEMS construction, i.e. constructed using semiconductor technology such as etching

Definitions

• the present invention relates to switching in optical networks such as optical communications networks and, more particularly, to an optomechanical valve and to arrays of optical valves generally and this valve m particular.
• An essential component of any communications system is a switch to enable signal routing.
• Various types of devices are used for optical switching. Some transform the optical signal into the electrical domain, where switching is done and then retransform back to the optical domain.
• Others use integrated optics to perform switching, using materials such as lithium niobate. These devices are relatively expensive, their minimum size is limited by the physics of optical wave-guides, they are strongly dependent on wavelength, and they suffer from cross-talk and signal attenuation.
• Micro-mechanical switches are not wavelength dependent and can be very compact. Signal loss occurs mainly at the input from and output into the fibers (which is about the same as for other switching technologies). Air accounts for only a very small portion of the attenuation
• An NxN switch that can route any of its N inputs to any of its N outputs, is simple to realize by an array of mirrors placed in the ray paths.
• a ray By suitably actuating a mirror, or series of mirrors, a ray may be switched into any desired output path. There is no interference among the N inputs, since light-ray paths cross without interaction (Hecht J., "Optical switching promises cure for telecommunications log-jam", Laser Focus World, September 1998, page 69). There is thus almost no cross-talk between data lines.
• the task is mamly the production of tiny mirrors to use as switches in these arrays
• Micro- machmed devices are capable of fulfilling the task, provided that the micro-machining produces optical-grade mirrors to reduce losses. Actuation needs to be fast, simple, and allow reproducible and accurate alignment of the beam inputs and outputs as the mirrors bend the ray
• the ability to deploy large arrays of mirrors is an essential feature of the system. All of these affect switching losses and utility.
• valve and valve array of the present mvention overcome the shortfalls of previous art.
• a microelectromechamcal optical switch that transfers or reflects an input ray using a movable mirror constructed on the surface of a substrate and oriented at 45° to the ray's direction is presented.
• This switch is actuated parallel to the substrate's surface by electrostatic, magnetic, thermal, piezoelectric, or other means.
• electrostatic actuation an envelope-style electrode may be used to obtain larger forces than are obtained in prior art configurations such as comb actuators, to produce faster switching. Designing the electrode edges to have a large perimeter or an irregular shape such as a fractal shape can increase this force even more. It should be noted that the terms “valve” and “switch” are used interchangeably herein.
• Arrays of switches may switch rays from a plurality of inputs to any of a plurality of outputs.
• a three-dimensional switch array disclosed allows this switching to be done with shorter ray paths and fewer mirrors.
• a wavelength separating and combining device that can separate a multi-wavelength beam into a bundle of parallel single- wavelength rays and recombme them is also disclosed.
• an optical switch for switching a light ray including: (a) a substantially planar substrate having a portion that is transparent to the light ray; (b) a switching element having at least one reflective surface substantially parallel to the substrate; and (c) a mechanism for moving the switching element in a direction parallel to the substrate between (1) a first position wherein the light ray traverses the transparent portion of the substrate to a first outlet and (n) a second position wherein the light ray is blocked from traversing the transparent portion of the substrate and reflected by the reflective surface to a second outlet.
• the mechanism moves the switching element substantially rectilmearly.
• the mechanism moves the switching element substantially curvihnearly.
• the substrate includes an opaque portion opposite which the switching element is located when in the first position and a transparent portion opposite which the switching element is located when in the second position.
• the substrate includes a second transparent portion opposite which the switching element is located when m the first position.
• a method for switching either of two light rays wherein- (a) the first ray is switched to an output while the second ray passes unswitched to another output when the switching element is in the first position and (b) the first ray passes unswitched to the latter output while the second ray is switched to the former output when the switching element is m the second position.
• the mechanism includes shape memory alloys.
• the mechanism is thermal.
• the mechanism is piezoelectric.
• the mechanism is electrostatic. According to another embodiment of the present mvention the mechanism is magnetic
• the electrostatic mechanism includes: (a) two planar electrodes serving as stators (1) parallel to the substrate, (u) fixed to the substrate and insulated therefrom, (in) having substantially equal shape and dimensions, and (iv) electrostatically chargeable, with same polarity; (b) a third, insulated, planar electrode that: (1) is movable m a plane parallel to and between the stators in a path such that the third electrode may be at rest in a first position substantially between the stators and in a second position substantially outside the stators, and (n) is attached to the switching element; and (c) a mechanism for alternately charging the electrodes in: (1) a first charge configuration wherein a charge on the third electrode is of opposite polarity to a charge on the stators and (n) a second charge configuration wherein a charge on the third electrode is of same polarity as a charge on the stators.
• stator edges wherebetween the path passes are straight.
• stator edges, and/or the leading edge of the third electrode are circular.
• stator edges, and/or the leading edge of the third electrode have an irregular form such as a fractal form.
• the mechanism includes: (a) one or more stators, each of which: (l) is fixed to the substrate and insulated therefrom, (n) has a circular segment shape, the circle lying m a plane parallel to a surface of the substrate, and (m) is electrostatically chargeable; (b) at least one supporting beam for the switching element, each beam being: (l) flexible, (n) attached at a point to the switching element and at another point to at least one of the stators, (in) insulated from that stator, and (iv) electrostatically chargeable, and (c) a mechanism for alternately charging the stators and the beams m. (I) a first charge configuration wherein a charge on the beams is of opposite polarity to a charge on the stators and (u) a second charge configuration wherein a charge on the beams is of same polarity as a charge on the stators
• the mechanism includes a beam attached at a center to the stator and at both ends thereof to the switching element
• the stators have a quadrant shape and each beam is attached at one end to a stator and at the other end to a switching element.
• the stators include pairs of quadrant-shaped components separated by and tangential to the beam at the point of attachment thereto and so aligned that a radial boundary of each is colhnear through that point of attachment.
• the beams are bistable.
• the mechanism includes: (a) a magnetic field perpendicular to the substrate; (b) one or more supporting beams for the switching element, each beam being: (I) flexible, (n) bistable, (in) attached at an end to the switching element and at another end to the substrate, and (iv) electrically conductive, and (c) a mechanism for causing an electric current to pass through the beams.
• the magnetic field is produced by a permanent magnet.
• the magnetic field is produced by an electro-magnet.
• a two- dimensional matrix of optical switches arranged in rows and columns wherein a switch is positioned at at least some intersections of each row with each column.
• each switch is oriented to be moveable m a direction of motion obliquely, preferably at an angle of 45°, to the rows and columns, and is actuatable independently of each other switch.
• each switch is oriented to be moveable in a direction of motion in and out of the plane defined by the rows and columns, and is actuatable independently of each other switch.
• an optical switches is positioned at each intersection of each row with each column
• a stationary reflective element located at a diagonal of this matrix m place of the switching elements there located and wherein switching elements are positioned only on a reflective side of the stationary reflective element.
• a matrix of switches wherein at least one of the switches includes two reflective surfaces on opposite sides thereof.
• a three-dimensional switch array including a plurality of stacked, substantially identical, two-dimensional matrices of optical switches wherein each switch of one matrix is located opposite a corresponding switch of another matrix.
• a three- dimensional switch array including a plurality of stacked, substantially identical, two- dimensional matrices of optical switches having a stationary reflective element at a diagonal wherein each switching element of one matrix is located opposite a corresponding switch of another matrix.
• a three-dimensional switch array complex including a plurality of successive three-dimensional switch arrays wherein for each switch array except the first switch array: (a) an input face of that switch array faces and is parallel to an output face of a preceding switch array, (b) numbers of rows and columns of each succeeding switch array match numbers of columns and rows respectively of each preceding switch array, and (c) each succeeding switch array is oriented such that the rows and columns thereof are substantially aligned to the columns and rows of the preceding switch array.
• a wavelength separator/recombmer including a first and second mutually parallel diffraction gratings, each including a plurality of diffractive elements on a surface thereof, the two gratings being offset so that a single input beam of light that includes a plurality of wavelengths and that is incident on the surface of one of the gratings, is diffracted by the gratings to produce one separate output beam of light for each wavelength with the separated beams being mutually parallel.
• a method of demultiplexing a colhmated wavelength-multiplexed beam and switching individual wavelength components to respective output ports including the steps of: (a) directing the beam into the wavelength separator and (b) introducing the separated wavelength components into a switch array complex, and (c) switching the components to respective output ports thereof.
• a method of multiplexing a plurality of individual wavelength rays into a single beam including the steps of: (a) introducing the individual wavelength rays into respective input ports of a three-dimensional switch array, (b) switching the rays, as required, to output ports of the array in a suitable alignment for introducing the rays into a wavelength recombmer for combining into a single multiplexed beam
• a method of fabricating the three- dimensional switch array including the steps of: (a) fabricating wafers containing independently actuatable optical switches arranged m equispaced rows and columns, the number of rows thereof being equal to the number of component two-dimensional switch matrices, (l) the first wafer having one column, and (n) each succeeding wafer having one more column than a preceding wafer, until (in) a last wafer having a number of columns equal to a number of input ports in each layer of the stack; (b) aligning the wafers with respect to one another such that: (l) the rows are all in parallel planes, (n) the columns are parallel, and (in) a group of columns in a succeeding wafer is centered opposite a group of columns m the preceding wafer; (c) bonding the aligned substrates together; and (d) dicing the bonded stack substantially parallel to the resulting square cross-section switch array and also substantially parallel to said columns
• a method of fabricating the three-dimensional switch array including further steps, beyond those of the preceding paragraph, of: (a) adding succeeding wafers, each said wafer, as before, containing independently actuatable optical switching elements arranged in equispaced rows and columns, the number of rows thereof being equal to the number of component two- dimensional switch matrices, and each succeeding wafer having one less column than a preceding wafer, and a final wafer having one column; (b) aligning the wafers with respect to one another such that, (l) the rows are all in parallel planes, ( ⁇ ) the columns are parallel, and (in) a group of columns in a succeeding wafer is centered opposite a group of columns m the preceding wafer; (c) bonding the aligned substrates together; and (d) dicing the bonded stack substantially parallel to the resulting square cross-section switch array and also substantially parallel to said columns .
• the two-dimensional matrix of the present invention and the three-dimensional array of the present invention are described below in terms of the optical switch of the present invention, the scope of the present invention includes such matrices and arrays based on any kind of optical switch.
• Figure 1 shows the general switch layout and basic switching motions
• FIG. 1 shows switch zones
• FIG. 3 shows basic switching actions
• Figure 4 illustrates how to obtain a switch that can direct two parallel inputs to separate outlets, by operating a switching element entirely within an optically active zone
• Figure 5 shows envelope actuation of a switching element
• Figure 6 presents two different possible designs for curved beam actuation
• Figure 7 illustrates the use of magnetic actuation
• Figure 8 shows some basic switching actions with two crossed rays
• Figure 9 presents a two variations of a basic switch array
• Figure 10 shows a schematic view of multi-layer switch array
• Figure 1 1 illustrates a 3D switching method involving two multi-layer switch arrays
• Figure 12 shows a wavelength-separation/recombmer device
• FIG. 13 illustrates basic switch fabrication processes
• Figure 14 shows fabrication of a 3D switch array.
• the wave valve of the present invention is intended to be used in fiber-optic communications. It employs mirrors to perform the switching. Mirrors have the advantage of being substantially insensitive to wavelength.
• the active environment is a gas such as air, or a vacuum. This non-interfering environment allows ray paths to cross without interaction, so there is no cross-talk and almost no attenuation by the medium. Most of the losses occur during light transfer from and into the fiber at the switch/fiber interfaces Losses are also introduced by spreading of the beam in space, but use of appropriate lenses and short distances can reduce these
• the mirrors should be small, to allow fast response, low losses, and compactness.
• the mirrors in general, are micro-machmed and, in order to reduce losses, are designed to be very smooth. They are generally planar and placed on a smooth wafer substrate, in contrast to previous art that etches the mirrors into the wafer bulk. In order to enhance switching speed, the mirror moves parallel to the substrate, thus reducing the influence of air resistance This placement also minimizes small deviations of the mirror from the normal (90°) to the substrate that account for part of the losses introduced in prior art systems
• the principles presented here are designed to give higher actuating forces, thus allowing a faster response than previous art Valve configuration and operation.
• the valve consists of a flat mirror, 1, placed at a short distance, d, from and parallel to a substrate, 2.
• Mirror 1 may move to different positions in a plane, 3, parallel to a surface of substrate 2, either substantially curvihnearly, as m the substantially circular, pendulum-like motion, 5 in Figure lc or m a substantially rectilinear motion in any direction, such as 6 or 6A in Figure Id.
• motion is generally parallel or normal to a base line, 7 ( Figure 2), that separates an opaque zone, 8, of substrate 2, wherethrough light 10 can not pass, from a transparent zone, 9, wherethrough light 10 can pass and wherewithin switching takes place.
• Transparent zone 9 may be transparent because substrate 2 exists m zone 8 and is absent in zone 9, or because the material of substrate 2 in zone 9 is transparent to the relevant wavelengths.
• Different embodiments of the principles disclosed here can be devised by those skilled in the art, in which it is possible to distinguish the zones m other ways.
• Mirror element 1 is located opposite an opaque zone, 38, of substrate, 2, while light, 10, transits unobstructed through a transparent zone, 39. In this condition, it is in an OFF state, 1A, as shown in Figure 3a, b. Mirror 1 is movable rectilmearly, parallel to substrate 2, into zone 39, as shown by double-headed arrow 36, to an ON state, IB ( Figure 3c, d). While mirror 1 is m OFF state 1A, light 10 can pass from one side, 39A, of surface 3 to another side, 39B, generally at an angle to said surface.
• ray 10 is inclined at 45° to mirror 1.
• OFF state 1A ray 10 transits the switching zone unimpeded from 10A to 10B.
• ON state IB light is reflected along an alternate path IOC.
• ray 10 has one input state, 10A, and two possible, mutually exclusive, output states, 10B and IOC.
• mirror 1 is movable along a line of motion 46, which lies entirely opposite a transparent part, 49, of plane 3, and, by so doing, can simultaneously create obstructing and non-obstructing states in different parts of zone 49.
• Mirror suspension and actuation elements are placed opposite another, opaque zone, 48, of plane 3.
• m non-obstructing state 41A Figure 4c
• light 10A passes to exit 10B while, in blocking state 41B, light is reflected to an alternate output 10C
• either position of mirror 1 can be designated as ON or OFF ( Figure 4e, f).
• More elaborate applications can be realized by combining two or more switching elements. It is important to note that the rays can traverse the switch in the reverse direction. In this case, inputs interchange with outputs and the switching options, explained above, are reversed.
• the valve consists of mirror 1 which is movable parallel to surface 3 and may be in at least two rest positions. Mirror 1 reflects light at one position and allows its passage at the other.
• thermal, magnetic, piezoelectric, mechanical, electrostatic actuation and actuation methods that rely on shape memory alloys are a few of many actuation methods known m the art.
• a preferred embodiment uses electrostatic actuation.
• Different schemes of electrostatic actuation can be used, among them a comb-d ⁇ ve mechanism (Hirano T. et al, "Design, Fabrication, and operation of submicron-gap comb-drive microactuators", Journal of Microelectromechamcal Systems, vol 1 No. 1, March 1992, page 52.)
• the actuation force depends on the change of the overlapping area between the driver's fingers and comb Since usual fabrication methods limit that area to a small value, a large number of fingers is necessary to produce the required force. Therefore this kind of actuation is generally slow and requires large actuators.
• a different approach to this actuation principle is disclosed here ( Figure 5)
• Overlapping finger 51 and comb 52 form a capacitor ( Figure 5b).
• the attractive force between the movable and static fingers is
• ⁇ 0 is the permittivity of the vacuum
• V an electrical potential 53
• h 0 is width of the fmger
• x is the overlapping length of the fmger in the direction of advance thereof
• g 0 is the gap between the moving finger and the static fingers.
• the production of wide fingers is generally difficult with conventional previous art.
• a fabrication method is disclosed in which the manufacture of wider fingers is easily done. Thus, fewer fingers, or even a single finger, can achieve sufficient force and thus faster switching times of the order of microseconds, compared to milliseconds with previous art.
• the disclosed actuator has an envelope-like configuration in which mirror / fmger (moving electrode) 51 may enter or exit envelope (static actuating electrode) 52.
• At least two actuating electrodes are placed m a way that one set, 52A, actuates to an ON position while the other, 52B, C, actuates to an OFF position. Actuation can be made bistable- if the actuated mirror is supported by buckled beams a snap action to each position of the mirror results
• bistabihty employs electrostatic snap (pull-m) action.
• the actuated element is attracted and adhered to an electrical isolated electrode at the end of its motion. From the equations above, force exerted is given by: ⁇ n 2 8A
• the area change of this actuator should be enlarged, not only the width of the fmger.
• the force can be enlarged further as follows: If the change in position is regarded as constant, dx, then it is possible to enlarge the attack-front perimeter (57, Figure 5c) the electrode crosses. In other words, the actuating electrodes entering line (57) should be enlarged.
• This line can be designed to be circular (57B, Figure 5e) instead of straight.
• the leading edge of electrode 51 may be similarly enlarged.
• Another embodiment increases the front length by using a high-perimeter geometrical form.
• a form can be an irregular form such as a fractal line designed for such application.
• the use of a fractal form can increase the actuating force by the ratio of its perimeter to the straight-line length.
• FIG. 6 Another electrostatic actuation method is presented in Figure 6, in which the post-fix A or B refers respectively to variant embodiments.
• One or more flexible beams, 67A or 67B support a mirror, 61.
• One point of the beam(s), 68A or 68B is fixed in close proximity to a circular segment stator, 69A or 69B, attached to a substrate, 62.
• These stators and beams are conductive and chargeable with opposite polarity.
• Beam 67A or 67B and stator 69A or 69B, respectively, are separated by insulators, 65A or 65B, from each other along the entire circular segment of stator 69A or 69B or, at least, at points where contact may occur, so as to prevent a short circuit ( Figure 6a, b, c, and d).
• stator 69A or 69B should be L. If stator 69B is a quadrant of a circle, the height should be the circle radius and have a value of L.
• FIG. 6e, f Another embodiment of this actuation method ( Figure 6e, f) employs opposed-quadrant stators.
• two quadrant-shaped stators, 69C are separated by one single beam, 67C, so that beam 67C is tangential to both quadrants at a point of contact and both quadrants are oriented so that a radial boundary of each quadrant forms a straight line passing through the point of contact.
• both stators are separated from beam 67C by insulating material, 65C
• insulating material, 65C In this configuration, by use of opposite charges on each member of a stator pair, half of the motion is effected by one member and the other half by the other member, in sequence. This allows a more compact actuator to be constructed.
• FIG. 7 Another embodiment of the valve switch uses magnetic actuation. Magnetic fields can produce higher forces, and thus faster switching speed. The disadvantage is the larger overall volume of the device, even though the switching mechanism, itself, has the same dimensions whatever the actuation mechanism.
• a magnetic field, B is necessary at the switch.
• the field can be produced by conducting loops around each switch; by a permanent magnet, larger than the switch; or by an electromagnet with similar field. These are only some of the available magnetic field application possibilities.
• mirror 71 is supported by beams, 77A and 77B.
• These beams are preferably made as curved beams, m order to allow bistable operation, and are conductive or include a conducting layer wherethrough an electric current, I, may be passed Interaction with the magnetic field induces a lateral force, F, on the beams.
• Appropriate alignment of the magnetic field and the current actuates mirror 71 to a new position ( Figure 7a). Reversing the current produces a reverse force that returns mirror 71 to an original position ( Figure 7b) Higher field values or higher currents produce stronger forces and faster switching.
• the single valve disclosed above is capable of switching light rays. Switching is possible between a single input and two outputs or two inputs into one output.
• the strength of the disclosed device lies m its ability to switch many inputs to many outputs, withm a compact space.
• the disclosed switch can be incorporated into prior art optical devices ( Figure 8).
• Figure 8a, b If the switch is in an OFF state, an input ray, 81 A, emerges at output 81B.
• ray 81 A reflects from mirror 82 and exits from output 81 C
• Another embodiment can be designed ( Figure 8c, d) wherein two inputs, 81 A and 81D, are normal to each other and, in an OFF state, continue to respective outputs 81B and 81 C.
• Actuating mirror 82 flips the output rays to emerge at interchanged outputs 81 C and 81 B respectively. In this latter embodiment, mirror 82 is reflective on both sides.
• each input can act as an output, and vice versa, by reversing the direction of ray propagation.
• an appropriate switching mirror 93 at an intersection of corresponding input and output axes is actuated to an ON state.
• the input is thus redirected to a desired output
• input 91B may be directed to output 92D by actuating switch 93A Since only a one-to-one correspondence is implemented (in the case that broadcast is not implemented), only a single switch is actuated at any time in each row and m each column. A non-blockmg condition exists.
• switches such as the switch illustrated in Figures 8c and 8d are used, and no switches should be actuated along the particular ray path concerned. All the switches of the respective input (or all the switches of the respective output, in the case of additional input) should not be actuated thus allowing unimpeded passage of the rays.
• FIG. 9b another embodiment is presented in which only half of an array is needed.
• a static reflecting element such as a mirror 99, as shown, or a waveguide termination, is placed at a diagonal of the array and that part of the array behind mirror 99 is discarded.
• All actuatable mirrors are double sided. In this configuration, fewer actuatable elements are required to achieve desired output configurations, with the same ray path-length, although a ray may, thereby, encounter more reflecting surfaces, leading to greater light loss.
• the overall switch is smaller, which is an advantage in some fabrication schemes, as will be shown below.
• inputs 96A, B, C, and D are switched to outputs 97A, C, B, and D respectively.
• Input 96A is reflected to output 97A via path ⁇ and input 96D is reflected to output 97D via path ⁇ ; it can be seen that these require no switching.
• Input 96B is, however, switched to output 97C via path ⁇ by reflecting at a back of actuated mirror 98.
• input 96C is switched to output 97B via path ⁇ by reflecting at mirror 98.
• a more elaborate switching device is now disclosed in which shorter paths and fewer switches are possible.
• the disclosed device enables this switching option.
• Other types of switches both of the MEMS (microelectromechamcal system) type, as is the switch of the present invention, and of other types (lithium niobate, liquid crystal, etc.), are also configurable m the arrays of the present invention, with MEMS switches being preferred.
• FIG. 10a An embodiment of this more elaborate device is presented schematically in Figure 10a.
• three switching arrays, a, b, and c, as described m Figure 9a or 9b, are utilized, the arrays being stacked, with corresponding elements vertically above one another.
• Each array operates either independently of the other arrays or in conjunction therewith.
• the arrays are not merely stacked, but may be mutually coupled, to achieve more efficient switching, in a smaller volume, than is possible using prior art switch arrays.
• Inputs, 101 consist of stacked rows, denoted by a, b, c , and vertical columns denoted by I, II, III
• Outputs, 102 are similarly denoted.
• a two-dimensional input array to a three-dimensional switch leading to a two-dimensional output array.
• the previously described device had a one-dimensional input array to a two-dimensional switch, leading to a one-dimensional output array.
• Easy fabrication of this device is described below.
• FIG. 10b A realization of this arrangement is shown m Figure 10b, where a cut-away view of a two- layer array having four switching mirrors m each layer is shown, oriented similarly to the schematic view in Figure 10a.
• inputs 103 may lead to outputs 104.
• the upper layer has inputs 103 la and 103 Ha and outputs 104 la and 104 Ha, and switching mirrors Al, A2, A3, and A4; its possible light paths are illustrated by dotted lines.
• the lower layer has inputs 103 lb and 103 lib and outputs 104 lb and 104 lib, and switching mirrors Bl, B2, B3, and B4; its possible light paths are illustrated by dashed lines Not all light paths will be followed in any given instance There is no interaction between the two layers
• FIG. 10b can also illustrate the smallest realization of the half-array switch illustrated schematically in Figure 9b.
• mirrors Al, A4, Bl and B4 are fixed, mirrors A3 and B3 are absent, and mirrors A2 and B2 are actuable, as before, and also reflective on both sides Light paths beyond mirrors Al, A4, Bl and B4 will no longer be possible As in the previous paragraph, there is no interaction between the two layers.
• FIG. 10 Another use of the 3D switching matrix shown m Figure 10 is in compact switching of a large number of inputs.
• the mam purpose of this use is the reduction of a ray path-length and the number of switches necessary compared with a square switching array.
• a 2D input matrix is utilized.
• Each plane, a, b, and c consists of a non-blockmg array.
• Such an array can be regarded as an operator that transforms the input row, 101 la, 101 Ha, 101 Ilia, at plane a, to output row, 102 la, 102 Ila, 102 Ilia, at plane a, and so on for the other planes. Since each plane is isolated from neighboring planes, the only possible operator action is to change the column index, /, II, III, ..., between input and output.
• Figure 1 lb is illustrated an equivalent switch array complex using the 3D switching matrix of Figure 9b instead of that of Figure 9a, utilizing fixed mirrors along a diagonal of each matrix.
• a 100x100 switch requires only 1350 switches, not including the 100 fixed switches, along the diagonal.
• the three-dimensional arrays of Figures 10b and 11 a can be configured with switches such as the switch illustrated in Figures 8c and 8d; providing the option of placing the arrays in switching states in which some or all input rays traverse the array without being reflected.
• switches such as the switch illustrated in Figures 8c and 8d; providing the option of placing the arrays in switching states in which some or all input rays traverse the array without being reflected.
• special options such as control, can be implemented
• a 3D matrix need not be cubic and the input array may be, for example 10x10, 10x3, etc., provided that the second, rotated 3D matrix has a matching number of rows and columns
• One possible variation is to alter the number of cubes used, applying one, two, three, four, etc , cubes as required.
• Another embodiment includes the addition of a wavelength demultiplexing/multiplexing system to the above methods for use of the disclosed switch m WDM (wavelength division multiplexing).
• information is transmitted through optical fiber, encoded withm a group of different wavelengths.
• a wavelength de-multiplexmg and multiplexing device is necessary to separate the different wavelengths at the entrance to a switch array and, after processing or use, recombme these wavelengths. Rays introduced into the described switch are preferably parallel to one another. A device that can accomplish this is presented.
• diffraction gratings uses a diffraction grating to separate the wavelengths into parallel rays that can be introduced into a 3D switch.
• a similar device receives and recombmes the output bundle of parallel rays for insertion into a fiber.
• the device used ( Figure 12) includes two parallel reflective diffraction gratings, 121 and 122, each with respective diffractive elements such as parallel rulings 124 or 125 on surfaces 126, 127 that face each other.
• the distance between the separated wavelength rays is determined by parameters including the distance d between parallel diffraction gratings 121 and 122 and the spacing of parallel rulings 124, 125.
• a simple mirror would reflect this beam at the same angle with respect to a normal to the surface of the mirror.
• a grating diffracts different wavelengths ( ⁇ l5 ⁇ 2 , ⁇ 3j ...) at different angles ( ⁇ i, ⁇ 2 , ⁇ 3 ⁇ .. ); the sum of incident angle plus angle of diffraction is a function of wavelength. From this, it is clear that different wavelengths will be separated into different angles at diffraction grating 121
• reversing direction provides a device capable of recombinmg wavelengths before insertion into a fiber on output.
• the use of one device at an input to the matrix and a reversed one at an output allows de-multiplexmg, switching, and multiplexing signals in a WDM network.
• the three-dimensional arrays of the present invention may be fabricated using prior art technologies, albeit at a cost that may be uneconomical or impractical. Therefore, the scope of the present invention includes an innovative method of fabricating these arrays.
• the basic device is fabricated on top of a wafer surface, m contrast to previous art, where the mirrors may be etched into the substrate.
• the mirrors which require substantially perfect surface quality, flatness, and parallelism, take advantage of high-quality substrates prepared for the microelectronics industry. Substrates of various dimensions, thicknesses, materials, and surface preparations are available.
• the device can be prepared on any kind of material and the fabrication procedure is independent of substrate material. While the substrate material has no effect on the switches, apart from surface preparation and physical dimensions, it is possible to take advantage of the substrate's properties.
• electronic circuitry may be integrated into the substrate or optical fibers may be set therein, in which case advantage can be taken of features such as the crystallographic planes of the substrate material, as in silicon. Those skilled in the art may find different materials and techniques for the production of these switches.
• Mirror material, 131 generally a metal such as aluminum, is deposited on substrate 132 and patterned using standard methods such as lithography. Generally, mirror 131 is produced on top of substrate 132 at a zone, 133, where substrate material eventually will be absent so that a ray may pass through ( Figure 13b).
• mirror 131 is fabricated above a portion of substrate 132 where substrate material eventually will be present.
• a sacrificial layer, 134 is deposited on top of substrate 132; patterned, if necessary, to allow the deposition of subsequent layers that must penetrate through sacrificial layer 134 to reach substrate 132; and polished prior to deposition and patterning of mirror 131.
• supporting beams 135 are deposited and patterned above sacrificial layer 134.
• Supporting beams 135 can be made of any material; in many cases they are made of metal or are otherwise conductive Supporting beams 135 are fabricated attached to mirror 131 and substrate 132. The number and configuration of supporting beams 135 depend on the application.
• Fabrication of electrodes and conducting lines can be done together, before or after the above-mentioned steps.
• an electrode, 136 is deposited on substrate 132 and covered by a sacrificial layer (134).
• a sacrificial layer 134
• the above-mentioned steps for fabrication of mirror 131 are carried out on top thereof.
• a second electrode of the envelope can be produced in a few ways. In one way ( Figure 13e, f) mirror 131 is covered by a second sacrificial layer, 134A. Second layer 134A is patterned and covered by a second envelope electrode, 137, which is patterned By removing the sacrificial layers, the envelope is formed and mirror 131 is released.
• FIG. 13h Another possibility is depositing and patterning a second envelope electrode 137 on another side of substrate 132 or, as illustrated in Figure 13g, on another substrate, 132A.
• Bonding is done by one of the known wafer-bonding methods, such as fusion bonding. Spacers and electrical connection paths are deposited and patterned as required prior to alignment and bonding.
• the mirror In the case of curved electrode actuation, the mirror can be processed directly on a wafer surface at a ray traverse zone. Supporting beams are deposited and patterned on top of the mirror, as previously explained. It is possible to deposit material for the static curved electrode and to do the patterning simultaneously, followed by insulation deposition and patterning over the static electrode Etching the sacrificial layer and corresponding substrate area releases the movable elements.
• the supporting beams may act also as conducting lines, and there is no need for further fabrication steps.
• the mirror and beams are fabricated and released.
• the construction of a switch array requires more elaborate methods than single-switch fabrication.
• the disclosed method is designed to facilitate accurate construction of a 3D cubic array.
• Single switches, 141 are produced, as described previously, in rows, 143, on a surface, 142, of a substrate. In our example, there are four rows. These switches are also arranged m groups, 145, of regularly spaced columns, 144, each group being separated from a neighboring group by an empty column, 146, at the same column spacing.
• the first group of our example consists of one column of four rows, separated by an empty column from a second group consisting of two columns of four rows followed by another empty column
• the arrangement continues with successive groups of 3x4 and 4x4 to form a set. An entire wafer may be covered with such sets For our example, at least seven such sets are required.
• This procedure is continued with consecutive wafers, a 3x4 group of columns being centered above the 2x3 group, and a 4x4 group being centered above the 3x4 Stacking is then continued in a reverse order, a 3x4 group being centered above the 4x4 group, and so on, until a 1x4 group is placed on top of a second 2x4 group.
• the stack is then bonded.
• the mirrors form a 2D matrix having column, 147, and row, 148, directions oriented at 45° to the surfaces of substrates 142.
• the mirrors are oriented at 45° to these column and row directions.
• the array is four deep.
• switches are actuated by one of the previously specified methods through conducting lines which connect rows, columns, and planes, as appropriate.
• that mirror may be set or reset into an ON or Off position.
• switches may be actuated by moving their mirrors m one of two orthogonal directions: a first direction, m the planes defined by columns 147 and rows 148, at 45° angles to columns 147 and rows 148 (left-right in the plane of Figure 14); and a second direction, in and out of the planes defined by columns 147 and rows 148 (in and out of the plane of Figure 14); or m a linear combination of these two orthogonal directions.
• the switch presented can be used for switching input rays of different wavelengths from numerous input paths to numerous output paths. It is primarily intended for use m communications. Together with the wavelength separation and re-combmation device disclosed above, it is applicable to WDM. Other applications, such as optical computation, etc. , will be evident.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Mechanical Light Control Or Optical Switches (AREA)
• Micromachines (AREA)

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• 2000
  • 2000-02-10 IL IL14306200A patent/IL143062A0/xx unknown
  • 2000-02-10 AU AU28768/00A patent/AU2876800A/en not_active Abandoned
  • 2000-02-10 EP EP00907240A patent/EP1151335A2/de not_active Withdrawn
  • 2000-02-10 CA CA002377377A patent/CA2377377A1/en not_active Abandoned
  • 2000-02-10 WO PCT/US2000/003354 patent/WO2000052835A2/en not_active Application Discontinuation

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