WO2002086572A1

WO2002086572A1 - Collapse based integrated electrostatic active optical elements and method for manufacture thereof

Info

Publication number: WO2002086572A1
Application number: PCT/US2002/012269
Authority: WO
Inventors: Babak Amirparviz; Kadhair Al-Hemyari
Original assignee: L3 Optics, Inc.
Priority date: 2001-04-18
Filing date: 2002-04-18
Publication date: 2002-10-31

Abstract

A collapse-based integrated electrostatic active optical element (40) includes the first electrode (3) and a second electrode (6) disposed across a gap (g) from each other. The gap (g) is less than the critical distance for instability of the first electrode (3) so that when a voltage differential is applied across the electrodes (3, 6), the first electrode collapses towards the second electrode (6). An optical element (4) is affixed at one end of the first electrode (3) so that a small movement of the electrode (3) translates to a large movement of the optical element (4).

Description

COLLAPSE BASED INTEGRATED ELECTROSTATIC

ACTIVE OPTICAL ELEMENTS AND METHOD

FOR MANUFACTURE THEREOF

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to Provisional Application Number 60/284,671 filed on April 18, 2001.

BACKGROUND OF THE INVENTION

This invention is directed to an actuator for an optical element, and more particularly, to a collapse based integrated electrostatic actuator.

It is known in the fiber optics art to include active (moving) elements in order to control the signal as it passes along an optical path. One such method for controlling a moving member is with a thermal actuator. An optical element is attached to a member having a relatively high coefficient of thermal expansion. The member is heated causing expansion of the member moving the optical element, such as a mirror, into and out of the optical path to control the optical signal. This structure has been satisfactory, however, it suffers from the disadvantage that a large amount of energy and time is required to raise the temperature of the member to the prescribed temperature to effect movement of the optical element. Furthermore, energy is required to maintain the temperature if latching is desired.

Electric actuators have also been contemplated in the art. A piezo-electric actuator includes a piezo-electric element which flexes when a voltage is applied to the element. An optical element is affixed to the piezo-electric element so that the optical element can be moved into and out of the optical path by applying the voltage to the piezo-electric element. This actuator for an active optical element suffers from the disadvantage that it, too, requires energy to latch into position and the piezo-electric effect can degrade over time. Accordingly, an actuator for an active optical element which overcomes the shortcomings of the prior art is desired.

SUMMARY OF THE INVENTION

An actuator includes a first conductor and a second conductor spaced from the first conductor across a gap. The gap is smaller than the critical distance for instability of the first actuator. A voltage source is coupled to each of the first conductor and second conductor for applying a voltage between the first conductor and second conductor, causing the first conductor to collapse (move towards) upon the second conductor. An optical element, such as a mirror, opaque member, translucent member or the like being affixed to the first conductor.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawing figures which are not to scale, and which are merely illustrative and wherein like reference numerals depict like elements throughout the several views:

Fig. 1 is a sectional, schematic view of a collapse based integrated electrostatic optical element constructed in accordance with the invention; Figs. 2A, 2B are sectional views of a portion of a conductor of the collapse based integrated electrostatic optical element as constructed in accordance with an embodiment of the invention before a voltage is applied and after a voltage is applied, respectively;

Fig. 3 is a schematic view of a collapse based integrated electrostatic active optical element constructed in accordance with another embodiment of the invention; Fig. 4 is a top plan sectional schematic view of a collapse based integrated electrostatic active optical element constructed in accordance with yet another embodiment of the invention;

Fig. 5 is a top plan sectional schematic view of a collapse based integrated electrostatic active optical element constructed in accordance with yet another embodiment of the invention; and

Figs. 6A-6F are sectional views of the steps of the process for forming a collapse based integrated electrostatic active optical element in accordance with the invention. DETAILED DESCRIPTION OF THE PERFERRED EMBODIMENTS

This invention is based on a collapse mode of electrostatic actuation for optical elements. Electrostatic actuation utilized in the embodiments of the invention provides motion in micro scale, as needed for the nanoscale sized optical elements as well as zero power latching of the optical elements. The use of collapse mode electrostatic actuation allows for optical elements which can be easily integrated with other optical components either by using micro fabrication technologies or other known manufacturing methods. The embodiments below are given by way of example only and the collapse based electrostatic actuator of the invention can be used to make a number of devices such as optical switches, variable optical attenuators, variable filters, array systems and the like.

Reference is made to Fig. 1 wherein a collapse based integrated electrostatic active optical element, generally indicated as 40 is provided. The collapse based integrated electrostatic active optical element includes a first conductor 3 and a second conductor 6 separated from each other across a gap g. Conductor 3 includes an optical element 4 thereon. Element 4 can be any optically active element such as a mirror, a variable optical attenuator, a filter, an opaque block or the like. In a preferred embodiment optical element 4 is integrally formed with conductor 3. A voltage source 8 is coupled across conductor 3 and conductor 6 to apply a voltage differential between the conductors. Preferably conductor 3 is anchored at one end while its other end, which is coupled to optical element 4, is free to move.

The environment for the collapse based integrated electrostatic active optical element is along an optical path 2 of a light signal. Here, by way of example, optical path 2 is defined by a first waveguide 1 and a second waveguide 1 separated across a gap f.

In operation, a voltage differential is applied to the two opposing conductors 3, 6. This induces an attractive electrostatic force between the two. The electrostatic force between the two charged objects induces motion on a micro scale. However, because optical element 4 is along an arm the motion is amplified at the optical element end of conductor 3. In the case of conductors or semi-conductors, application of a voltage differential across conductors 3, 6 induces an attractive electrostatic force between the two. Depending upon the retentive force holding the conductors in place, there exists an instability point. This is the point where the attractive force overcomes the rigidity inherent in conductor 3. If the distance between the conductors is smaller than the critical distance for instability, the two objects collapse against each other. This attraction is used in the present invention to generate motion in microscale with small voltages to achieve large displacements. As conductor 3 is attracted and collapses towards conductor 6, optical element 4 rotates and moves to the position showed in shaded line. Therefore, a small movement as shown towards the base of conductor 3 translates into a large movement of optical element 4.

The shapes of opposing electrodes 3, 6 can be modified in order to optimize the collapse effect at a proper voltage. Because movement of conductor 3 is a function of the voltage differential applied between the two conductors 3, 6, the position of electrode 3 can be determined by measuring the capacitance change between electrodes 3, 6. Voltage source 8 can be incorporated into drive circuitry including a readout of the capacitance change to determine the position of the actuator. The frequency response and the optical and electrical properties of the overall device can be modified by changing the design of optical element 4 or placing the device in a fluid environment.

One must avoid a total collapse of electrode 3 upon electrode 6 or a short-circuit will occur as they contact each other. Short-circuiting as a result of arcing may even occur without contact if gap g becomes significantly small as electrode 3 moves towards electrode 6. One approach to prevent short-circuit is to coat the sides of electrodes 3, 6 with a dielectric material.

Reference is now made to Figs. 2A, 2B in which another embodiment of the invention for preventing short-circuit is provided. Like numerals are utilized to indicate like structure, this embodiment utilizing a projection affixed to one of the conductors to contact the moving conductor preventing further movement before gap g shrinks to a range within which a short-circuit may occur.

A second conductor 6^' is formed with a channel 7 therein. A protrusion 10 extends through channel 7 into gap g beyond a front-facing surface 9 of conductor 6'. On an opposed surface of conductor 6^', a retaining structure 99 is provided to maintain protrusion 10 affixed to conductor 6^'. Protrusion 10 is separated from conductor 6^' and container 99 by an insulating gap 13. As a result, for ease of manufacture, protrusion 10 can be formed as a conductor from the same materials as conductor 6^'

Fig. 2A shows the relative positioning of conductor 3 and conductor 6^' prior to the application of a voltage. Upon application of a voltage, as shown in Fig. 2B conductor 3 moves in the direction of the right-handed head of double-headed arrow A and contacts protrusion 10 preventing further movement of conductor 3 across gap g preventing short-circuit. Again, this approach is particularly attractive for microfabrication of the device using a Deep Reactive Ion Etching (DRIE) or Bosch processing.

Reference is now made to Fig. 3 in which the optical element is latched in accordance with another embodiment of the invention. Again, like numerals are utilized to indicate like structure. Again, a first electrode 3 is disposed across a gap from a second electrode 6. Electrode 3 includes an optical element 4 affixed at one end. A drive circuit 8 (including a voltage source) provides a voltage differential across conductors 3, 6. A latching mechanism 14 includes an arrowhead 17 which engages optical element 4 as the arrowhead 17 is shaped to engage the corner formed by conductor 3 and optical element 4. Therefore, after activation and movement of optical element 4, latching mechanism 14 operates to hold optical element 4 in the actuated position even upon the removal of the voltage differential between conductors 3, 6. Latching mechanism 14 may be connected to a microacruator of its own for release. This may be done utilizing an actuator system similar to that for controlling conductors 3, 6 which controls optical element 4. It should be noted that an arrow- and corner-latching shape are utilized by way of example only, any shaped latching mechanism in combination with an optical element shape to engage the latching mechanism may be utilized.

In the above two embodiments, the motion of optical element 4 is not linear. It is often desirable to utilize linear motion in controlling the optical element to provide consistency in the effect provided by the optical element as it passes through an optical path. Reference is now made to Fig. 4 wherein a collapse-based integrated electrostatic active optical element 50 exhibiting linear motion of the optical element is provided.

Collapse-based integrated electrostatic active optical element 50 includes an optical element 21. A first conductive arm 27 is affixed at one surface of optical element 21. A second symmetrical conductive arm 28 is connected to optical element 21 at an opposed surface of optical element 21. Each of conductive arms 27, 28 is coupled to a conductive anchor 25 by a respective conductive arm 24.

A conductive anchor is disposed across a gap h from each of conductive arms 27,

28 to provide an equal voltage differential to conductive arms 27, 28. The drive circuit 26 including a voltage source and capacitance readout is coupled across conductive anchor 25 and conductive anchor 22 such that a voltage differential is applied to conductive anchor 25 and conductive anchor 26 resulting in a voltage differential between conductive anchor 22 and conductive arms 27, 28 respectively. This voltage differential causes conductor arms 27, 28 to collapse towards conductive anchor 22 when a voltage is applied in a manner similar to that described above with the previous embodiments.

Optical element 21 is disposed along an optical path 19 between a first waveguide 20 and a second waveguide 20^'. As a result of activation and release of conductive arms 27, 28 optical element exhibits reciprocating motion in the directions of double-headed arrow C. Therefore, upon the application of a voltage, i.e., upon the collapse of conductors 27, 28, optical element 21 moves out of the optical path allowing an optical signal to pass between waveguides 20, 20^' unaffected. Upon release, optical element 21 moves into optical path 19 to operate upon the optical signal by either blocking the signal, filtering the signal, attenuating the signal or like.

Because of the symmetry of conductors 27, 28 and their motion relative to optical element 21 , optical element is restrained in its movement and moves in a linear direction.

Reference is now made to Fig. 5 in which a preferred application of the collapse- based integrated electrostatic active optical element is provided. Specifically, the optical element is utilized in a 2x2 switch 60. Switch 60 includes a first waveguide 20^' which intersects a second waveguide 23 ^'. A trench 38 is formed across the intersection of waveguide 20^' with waveguide 23 ^'. Waveguides 20^', 23 ^', forming an optical path 19^'. An optical element 21 ^' is disposed in and moves within trench 38. Optical element 21 ^' is coupled to a first conductor 27^' at one side of optical element 21 ^' and a second conductor 28^', being the mirror image of conductor 27^' at an opposed side of optical element 21 ^'. Each of conductors 27^', 28^' are coupled to a respective conductive anchor 25^'.

A conductive anchor 22^' is disposed in facing relationship with each of conductors 27^', 28 ^' across a gap k. A drive circuit including a voltage source and capacitance readout is coupled to conductive anchors 25^', 22 ^' so as to provide a voltage differential between conducting anchor 22^' and respective conductors 27^', 28 ^'.

When a voltage differential is applied by drive circuit 26^', are conductors 27^',

28 ^' are attracted towards conductor 22^' collapsing arms 27^', 28 ^' towards conductive anchor 22^' causing optical element 21 ^' to move in trench 38 to withdraw from optical path 19^'. When no voltage is applied, conductors 27^', 28 ^' are released, returning to the position shown in Fig. 5 wherein optical element 21 ^' resides within optical path 19^'. As a result, optical element 21 ^' exhibits reciprocating movement in the direction of double- headed arrow D within trench 38. In a preferred embodiment optical element 21 ^' is a double-sided mirror, so that when in the optical path 19^' an optical signal is switched between waveguide 20^' and waveguide 23^'.

Reference is now made to Figs. 6A-6F wherein a possible microfabrication process for manufacture of 2x2 switch 60 is provided. As shown in Fig. 6A an SOI wafer is formed, beginning with a silicon wafer body 31. A top silicon layer 29 is disposed on wafer body 31 so as to bury an oxide layer 30 there between. As shown in Fig. 6B electrical contact metals 32 are patterned on silicon layer 29. Deep trenches 34 are etched into silicon layer 29 to define moving parts 33 and stationary parts 35 as shown in Fig. 6C. Buried oxide layer 30 is then etched to release moving parts 33 as shown in Fig. 6D. A second metal deposition 36 is performed to defined the mirror surfaces on movable parts 33 and stationary parts 35. Lastly, second metal deposition 36 is removed by an ion milling process from the tops of stationary parts 35 and moving parts 33 to produce movable double-sided mirrors 37 as shown in Fig. 6F.

The process described above is the preferred method for manufacture as it takes advantage of deep trench etching processes, which allows optical element 4 to be integrally formed with conductor 3 and better insures the precision and accuracy with which the product is made. However, it is possible to form the mirrors in a separate step by other processes, such as wet etching in order to achieve better optical qualities.

While there have been shown and described fundamental novel features of the invention as applied to inferred embodiments thereof, it will be understood that various omissions and substitutions and changes in the form and details of the disclosed invention may be made by those skilled in the art without departing from the spirit and scope of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

Claims

CLAIMSWHAT IS CLAIMED IS:

1. A collapse-based integrated electrostatic active optical element comprising: a first conductor; an optical element affixed to the first conductor; a second conductor disposed across a gap from said first conductor, the gap being less than the critical distance for instability of the first conductor, wherein when a voltage differential is applied across said first conductor and said second conductor, said first conductor collapses towards said second conductor.

2. The collapse-based integrated electrostatic active optical element of claim 1 , further comprising a drive circuit for applying a voltage differential between said first conductor and said second conductor.

3. The collapse-based integrated electrostatic active optical element of claim 2, wherein said drive circuit monitors a change in capacitance between said first electrode and said second electrode to determine the position of said optical element.

4. The collapse-based integrated electrostatic active optical element of claim 1, wherein said optical element is integrally formed with the first electrode.

5. The collapse-based integrated electrostatic active optical element of claim 1 , wherein said second conductor is formed with a channel therein; a protrusion extends through the channel into the gap and comes in contact with said first conductor when a voltage differential is applied between the first conductor and second conductor.

6. The collapse-based integrated electrostatic active optical element of claim 5, wherein said protrusion is electrically isolated from said second conductor.

7. The collapse-based integrated electrostatic active optical element of claim 1 , further comprising a latching mechanism, said latching mechanism having a shape for engaging the optical element when there is no voltage differential between the first electrode and the second electrode.

8. The collapse-based integrated electrostatic active optical element of claim 1, wherein said optical element is one of a mirror, attenuator, or filter.

9. The collapse-based integrated electrostatic active optical element of claim 1 , further comprising a third conductor, the first conductor being affixed to the optical element at a first surface of the optical element, the third conductor being coupled to the optical element at an opposed surface of the optical element; wherein said second conductor is a conductive anchor disposed symmetrically across the gap from each of the respective first and third conductors so that when a voltage differential is applied between the first and third conductors and the second conductor, the first conductor and third conductor each collapse towards said second conductor.

10. The collapse based integrated electrostatic active optical element of claim 9, further comprising a second conductive anchor, a first arm for conductively coupling said conductive anchor to said first conductor and a second arm for conductively coupling said second conductive anchor to said third conductor, wherein a charge applied to said second conductive anchor is applied to both said first conductor and third conductor.

11. The collapse based integrated electrostatic active optical element of claim 10, further comprising a voltage source and readout circuit operatively coupled between said second conductor and said first and third conductors for applying a voltage differential between said first and third conductors and said second conductor and determining a change in capacitance between said first and third conductors and said second conductor as said first conductor and third conductor collapse toward said second conductor.

12. The collapse based integrated electrostatic active optical element of claim 9, further comprising a first waveguide, a second waveguide, intersecting said first waveguide, a trench disposed within said first waveguide and second waveguide at said intersection, bifurcating said first waveguide and said second waveguide, respectively; said optical element being disposed within said trench, said first waveguide and second waveguide defining respective first and second optical paths, said optical element being disposed within said first and second optical paths when no voltage differential is applied between said first and third conductors and said second conductor, and is disposed out of the optical path when said first and third conductors are collapsed towards said second conductor.