Frustrated Total Internal Reflection Device

This invention relates to the field of frustrated total internal reflection (FTIR) devices.

U.S. Pat. No. 5,211,987, issued to Laughlin, entitled FTIR Modulator, discloses an apparatus that employs frustrated total internal reflection (FTIR) to modulate and switch beams of light or optical signals. U.S. Pat. No. 5,211,987 is expressly incorporated by reference herein for all purposes.

U.S. Pat. No. 5,221,987, discloses a method of developing frustrated total internal reflection by moving two surfaces into and out of proximal contact with one another. Once these surfaces are brought into proximal contact an electrostatic "bond" is formed between the surfaces. To later separate the surfaces requires breaking the electrostatic bond. Overcoming the bond may add to the difficulty and time required in separating these two surfaces. In one embodiment, U.S. Pat. No. 5,211,987 taught a method of bending one of the surfaces in one plane to address this problem.

The inventor of the inventions disclosed in U.S. Pat. No. 5,211,987 has developed several improvements to the FTIR device disclosed therein that are the subject of this present application.

In accordance with the present invention, an improved FTIR device is provided that substantially eliminates or reduces disadvantages and problems associated with previously developed FTIR devices.

One aspect of the prevention invention provides a device for processing an optical signal having a refractor with a reflecting surface operable to reflect the optical signal by total internal reflection. An actuator has one end coupled to the refractor and an opposing end coupled to a switchplate. The switchplate has a first position spaced apart from the refractor and a second position in proximal contact with the refractor to frustrate the total internal reflection of the optical signal.

Another aspect of the present invention provides a device for processing an optical signal having a refractor with a reflecting surface operable to reflect the optical signal by total internal reflection. An actuator has a first end and a second end and is coupled to the refractor at the first end and the second end. A switchplate is coupled to the actuator between the first and the second end of the actuator. The switchplate has a first position spaced apart from the refractor and a second position in proximal contact with the refractor to frustrate the total internal reflection of the optical signal.

The present invention provides numerous technical advantages. The present invention provides the technical advantages in U.S. Pat. Nos. 5,221,987 and 5,444,801, which are both expressly incorporated by reference herein for all purposes.

Additionally, the present invention provides a technical advantage of a more efficient structure over previously developed FTIR devices. In one embodiment, an actuator is coupled to a refractor at one end and to a switchplate at the opposing end. In a second embodiment, both ends of an actuator are coupled to a refractor and a switchplate is coupled between the two ends of the actuator. These arrangements of components of the FTIR device provide increased speed and reliability of operation. Other technical advantages are readily apparent to one skilled in the art from the following figures, descriptions, and claims.

For a more complete understanding of the present invention and advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which like reference numbers indicate like features and wherein:

FIG. 1 is a schematic diagram illustrating the reflection of an optical signal in the FTIR device of the present invention;

FIG. 2 depicts a perspective view of one embodiment of the FTIR device of the present invention;

FIG. 3 illustrates a side cross-sectional view of the FTIR device of FIG. 2;

FIG. 4 provides a side cross-sectional view of an alternate embodiment of the present inventive FTIR device having a prestressed switchplate;

FIG. 5 shows a bottom perspective view of a switchplate having a contact area for use with the present FTIR device;

FIG. 6 shows a perspective view of another embodiment of the FTIR device of the present invention;

FIG. 7 provides a cross-sectional view of a portion of the FTIR device in FIG. 6;

FIGS. 8A and 8B depict a switchplate of the present FTIR device incorporating a lens into the switchplate;

FIG. 9 depicts a cross-sectional view of a portion of an alternate embodiment of the FTIR device of the present invention;

FIGS. 10A and 10B depict a refractor of the present FTIR device incorporating a lens into the surface of the refractor;

FIG. 11 shows a perspective view of another embodiment of the FTIR device of the present invention;

FIG. 12 shows a perspective view of yet another embodiment of the FTIR device of the present invention;

FIGS. 13-15 illustrate different embodiments of a switchplate adapted to the FTIR devices of FIGS. 11 and 12; and

FIG. 16 illustrates an air gap spacer adapted to the FTIR devices of FIGS. 11 and 12.

Preferred embodiments of the present invention are illustrated in the FIGURES, like numerals being used to refer to like corresponding parts of the various drawings.

FIG. 1 shows FTIR device 10 of the present invention. FTIR device 10 includes first refractor 12, hereinafter refractor 12, which is a right angle prism in the embodiment shown in FIG. 1. Refractor 12 may be formed from many suitable refractive materials and may have many configurations without deviating from the inventive concepts of the present invention. First refractor 12 in FIG. 1 has three surfaces, including first or input surface 14, second or reflecting surface 16, and third or output surface 18. In three dimensions, first, second, and third surfaces are generally, but not necessarily, perpendicular with respect to one another.

FTIR device 10 also includes second refractor or switchplate 20 having contact surface 22 and reflective surface 24. Switchplate 20 may be formed from many suitable refractive materials and may have many configurations without deviating from the inventive concepts of the present invention. Reflective surface 24 of switchplate 20 is at bias angle .theta.26 with respect to contact surface 22. The reflectivity of reflective surface 24 may be caused by total internal reflection or by reflective material. It is noted that reflective surface 24 of switchplate 20 may also be non-reflective or optically absorbing.

The theory behind and operation of FTIR device 10 is fully described in U.S. Pat. Nos. 5,211,987 and 5,444,801, and need not be repeated here for an understanding of the present invention. A summary of the operation of FTIR device 10, however, will be provided.

Switchplate 20 is shown in FIG. 1 as removed or spaced apart from refractor 12. In this position, input optical signal or beam 28 enters refractor 12 at input surface 14. Beam 28 travels in refractor 12 until it reaches reflecting surface 16. Beam 28 is reflected at reflecting surface 16 by total internal reflection (TIR) in accordance with Snell's law as described in U.S. Pat. Nos. 5,211,987 and 5,444,801 forming primary output beam 30 that exits refractor 12 at output surface 18.

In order to change the angle of output beam 30, and in turn, the location of output beam 30 after exiting output surface 18, switchplate 20 is brought into proximal contact with refractor 12. Bringing contact surface 22 of switchplate 20 into proximal contact with reflecting surface 16 of refractor 12 frustrates the total internal reflection in refractor 12. The term proximal contact refers not only to direct contact between refractor 12 and switchplate 20, but also contemplates any spacing or partial contact between refractor 12 and switchplate 20 to frustrate internal reflection to a desired degree. This causes input beam 28' to travel into switchplate 20. In one embodiment, beam 28' is reflected at reflective surface 24 of switchplate 20 as secondary output beam 32. The reflection of beam 28' at reflective surface 24 may or may not be by total internal reflection. Generally, reflective surface 24 may reflect, absorb, or transmit optical beam 28', with or without reflective or absorptive coatings. As shown in FIG. 1, because optical beam 28' travels into switchplate 20 before reflection at reflective surface 24, secondary output beam 32 may exit output surface 18 of refractor 12 at a different location than primary output beam 30. Where secondary output beam 32 exits output surface 18 with respect to primary output beam 30 is a function of bias angle .theta.26 of switchplate 20 as is described in U.S. Pat. No. 5,444,801. Alternatively, by varying the thickness of switchplate 20 and angle .theta.26, primary output beam 30 and secondary output beam 32 can intersect at output surface 18.

Therefore, an input optical signal 28 to FTIR device 10 of FIG. 1, can be processed by switching or modulating the signal. This processing is achieved by moving switchplate 20 with respect to refractor 12. In a first position, switchplate 20 is spaced apart from refractor 12. In a second position, switchplate 20 is in proximal contact with refractor 12 to frustrate the total internal reflection of optical signal 28.

FIG. 2 is a perspective view of one embodiment of FTIR device 10 of FIG. 1. The view of FIG. 2 shows bottom surface 34 and top surface 36 of refractor 12. Formed in top surface 36 of refractor 12 is notch 38. Positioned in notch 38 is actuator 40. In one embodiment of FTIR device 10, actuator 40 is a piezoelectrical device that responds to a control signal. The view of FIG. 2 also shows switchplate 20 having first end 42 and second end 44. First end 42 of switchplate 20 is secured to refractor 12. First end 42 of switchplate 20 may be secured to refractor 12 by any suitable mechanism including bonding or clamping. Actuator 40 is disposed in notch 38 of refractor 12 between refractor 12 and second end 44 of switchplate 20.

In the view shown in FIG. 2, switchplate 20 is in proximal contact with refractor 12. As previously described in connection with discussions relating to FIG. 1, in this position a signal entering refractor 12 through input surface 14 will travel in refractor 12 and into switchplate 20 where it will be reflected at reflective surface 24 of switchplate 20. This signal will then exit at output surface 18 of refractor 12.

To change the path of the optical signal, actuator 40 is activated. Activating actuator 40 causes it to expand so that second end 44 of switchplate 20 moves away from refractor 12. Once actuator 40 supplies sufficient force it bends second end 44 causing peel forces to break the electrostatic forces between contact surface 22 of switchplate 20 and reflecting surface 16 of refractor 12. This causes separation between reflecting surface 16 of refractor 12 and contact surface 22 of switchplate 20. Switchplate 20 has a degree of elasticity to it and the initial separation occurring between switchplate 20 and refractor 12 is near actuator 40. This separation propagates towards first end 42 of switchplate 20 where switchplate 20 is attached to refractor 12. Actuator 40, therefore, causes switchplate 20 to peel away from refractor 12 rather than shearing away from refractor 12. This minimizes the amount of force that actuator 40 must supply to move switchplate 20 with respect to actuator 12, minimizes the instantaneous contact area between refractor 12 and switchplate 20, and also minimizes the time necessary to move switchplate 20 with respect to refractor 12.

Once switchplate 20 is spaced apart from refractor 12 a sufficient distance, approximately two times the wavelength (.lambda.) of the beam in FTIR device 10, then input optical beam 28 reflects by total internal reflection at reflecting surface 16 of refractor 12. This causes primary output beam 30 to exit refractor 12 at surface 18 at a new location as was previously described. Deactivating actuator 40 causes it to contract so that switchplate 20 returns to its at-rest position in proximal contact with refractor 12.

Additionally, controlling the amount of expansion provided by actuator 40 in turn controls the separation between switchplate 20 and refractor 12. This allows FTIR device 10 to be used for either switching or modulating the signal input to FTIR device 10.

Attaching switchplate 20 to refractor 12 at first end 42 prevents virtually all lateral movement of switchplate 20 with respect to refractor 12. This prevents abrasions or contusions from forming on reflecting surface 16 of refractor 12 or contact surface 22 of switchplate 20. Abrasions or contusions will affect the efficiency of the total internal reflection at these surfaces and also affect the proximal contact achievable between these surfaces.

FIG. 3 is a cross-sectional view of FTIR device 10 of FIG. 2 with additional second actuator 46. Second actuator 46 may also be a piezoelectrical device that is responsive to a control signal that is secured to a physical reference. Second actuator 46 provides a driving force to move switchplate 20 into contact with refractor 12. Activating actuator 40 and deactivating actuator 46 moves switchplate 20 away from refractor 12. To return switchplate 20 back into proximal contact with refractor 12, actuator 40 is deactivated and second actuator 46 is activated. Using both actuators to drive switchplate 20 increases the speed at which switchplate 20 can be moved with respect to refractor 12. This allows FTIR device 10 to "switch" faster then previously developed devices.

It is noted that there may be applications of FTIR device 10 where it may be desirable to move switchplate 20 away from refractor 12 a distance sufficient so that a beam traveling in refractor 12 is reflected partially at reflecting surface 16 of refractor 12 and partially at reflective surface 24 of switchplate 20. FTIR device 10 operating in this mode provides a variable beam splitter or attenuator function. When this function is desired both actuators 40 and 46 can be activated a sufficient amount to control the exact spacing between refractor 12 and switchplate 20. This same beam splitter or attenuator function may be incorporated into any embodiments of FTIR device 10.

It is noted that second actuator 46 may be a spring to provide a preloaded stress to switchplate 20 with respect to refractor 12. The spring may be embodied in a cylindrical spring or in a belleville spring. Alternatively, actuator 40 may be embodied in a spring while actuator 46 is embodied in a piezoelectrical device. Either of these configurations provide enhanced switching speeds over previously developed FTIR devices.

FIG. 4 is a cross-sectional view of an alternate embodiment of FTIR device 10. Switchplate 20 is attached at first end 42 to refractor 12 by spacer 48. Switchplate 20 is attached to refractor 12 at first end 42 by bonding or clamping such that switchplate 20 is bent or deflected with respect to refractor 12. The deflection of switchplate 20 provides a force that helps maintain contact surface 22 in proximal contact with reflecting surface 16 of refractor 12. This helps minimize the time necessary for switchplate 20 to return to proximal contact with refractor 12 when actuator 40 is deactivated. This embodiment shown in FIG. 4 can also eliminate the need for second actuator 46 in FIG. 3 or other preloading devices to return switchplate 20 into proximal contact with refractor 12 when actuator 40 is deactivated.

A further enhancement that may be provided to FTIR device 10 is also shown in FIG. 4. Conductive element 50 may be placed on switchplate 20 near second end 44. By placing a second conductive reference 52 near conductive element 50 a capacitor is formed. Second conductive reference 52 should be at a distance that is just greater than the displacement of switchplate 20 when actuator 40 is activated. By measuring the value of the capacitor formed by element 50 and reference 52, the positioning of switchplate 20 can be more accurately controlled. This may be particularly helpful when using any embodiment of FTIR device 10 as a variable splitter or modulator of an optical beam.

Additionally, FTIR device 10 in FIG. 4 may also include preload 54. Preload 54 may be embodied in a clamp or screw. Preload 54 provides a force on switchplate 20 with respect to refractor 12 such that switchplate 20 is deformed in a leaf-spring configuration forcing switchplate 20 against refractor 12.

FIG. 5 is a bottom view of an alternate embodiment of switchplate 20 of FTIR device 10. Even with a super polish on or cleaning of refractor 12 and switchplate 20, however, the surface roughness of contact surface 22 and reflecting surface 16 may be on the order 10.sup.-1 to 10.sup.-2 microns. This surface roughness requires a sufficient pressure be applied to these surfaces to cause an elastic deformation of the abnormalities such that the surfaces may be brought into proximal contact. Since pressure is a force per unit area, the force required to bring contact surface 22 into proximal contact with reflecting surface 16 can be reduced by reducing contact area 56 of contact surface 22. The beam of light in FTIR device 10 will enter switchplate 20 at contact area 56.

Reducing the size of contact area 56 may be achieved by removing a very small amount, nominally two microns, of contact surface 22 such that proximal contact of switchplate 20 with respect to refractor 12 is limited to contact area 56. Contact area 56 may have many shapes and is not limited to that depicted in FIG. 5. Contact area 56 may be formed by etching contact surface 22 of switchplate 20. Additionally, it is recognized that there are many ways to form a contact area 56, such as by adding a contact shim to reflecting surface 16 of refractor 12 or contact surface 22 of switchplate 20, and then etching the shim to the desired shape.

FIG. 6 shows an end perspective view of FTIR device 10 and illustrates an alternate embodiment of device 10. In discussions relating to the previous FIGURES, various methods were described on how to bring contact surface 22 of switchplate 20 into proximal contact with reflecting surface 16 of refractor 12. FIG. 6 illustrates another embodiment for bringing switchplate 20 into proximal contact with refractor 12. In the embodiment of FTIR device 10 in FIG. 6 contact surface 22' of switchplate 20 is convex. The curve of contact surface 22' produces spacing on the edges of switchplate 20 with respect to refractor 12 on the order of a few wavelengths of the optical beam traveling in FTIR device 10. To depress switchplate 20 having curved contact surface 22', bridge 58 may be required with the use of second actuator 46. The legs of bridge 58 on the edges of switchplate 20 help compress the convex surface of contact surface 22' into proximal contact with reflecting surface 16 of refractor 12. When actuator 46 forces bridge 58 against switchplate 20 the center of surface 22' first comes into proximal contact with reflecting surface 16. This reduced area increases the pressure, force per unit area, applied to the contact points between switchplate 20 and refractor 12, and as the force continues switchplate 20 flattens out and conforms to reflecting 16.

FIG. 7 shows a cross-sectional expanded view of the alternate embodiment of FTIR device 10 in FIG. 6. FIG. 7 more clearly shows spacing 60 between reflecting surface 22' of switchplate 20 and reflecting surface 16 of refractor 12. When the force from second actuator 46 is released the edges of switchplate 20 as represented by edge 62 in FIG. 7 return to their original shape breaking the electrostatic contact forces between switchplate 20 and refractor 12. This allows actuator 40, as shown in FIGS. 6 and 7, to use less force to separate switchplate 20 from refractor 12 and also to separate them more rapidly. When second actuator 46 is activated to return contact surface 22' of switchplate 20 into proximal contact with reflecting surface 16 of refractor 12, it applies force to bridge 58 that pushes on the opposing edges of switchplate 20. Switchplate 20 moves towards refractor 12 making proximal contact at the center or apex of contact surface 22'. Second actuator 46 initially produces a great force over a small area thereby deforming contact surface 22' such that the electrostatic forces can take effect at the contact point. Once the electrostatic contact has been made between contact surface 22' of switchplate 20 and reflecting surface 16 of refractor 12, then the electrostatic forces tend to spread in a self-initiating manner causing greater contact of switchplate 20 with respect to refractor 12.

As actuator 46 continues to apply force to bridge 58, the forces on switchplate 20 cause it to deform and flatten completely against refractor 12, resulting. Resulting in proximal contact between surface 22' of switchplate 20 and reflecting surface 16 of refractor 12. This results in a more complete contact of switchplate 20 to refractor 16 and therefore results in greater frustrated total internal reflection of a beam in device 10. This allows FTIR device 10 to be a more efficient optical switch, modulator, or splitter. Convex contact surface 22' of switchplate 20 may be formed by many methods, including, for example, grinding contact surface 22' of switchplate 20 to the desired convex surface. Alternatively, convex contact surface 22' may be formed by placing a convex refracting element on only a portion of contact surface 22 of switchplate 20.

FIG. 8A illustrates one method for forming convex contact surface 22' of FIGS. 6 and 7. FIG. 8A is a bottom view of switchplate 20 having a lens or convex refracting element 64 thereon. Convex refracting element 64 covers only a portion of contact surface 22 of switchplate 20 and provides convex contact surface 22' of FIGS. 6 and 7. Convex refracting element 64 may be formed in contact surface 22 by many methods, including, for example, grinding, polishing, or etching contact surface 22, or alternatively, may be a separate convex refracting element 64 that is bonded to surface 22 of switchplate 20 by an appropriate optically transparent agent. FIG. 8B shows a side view of switchplate 20 of FIG. 8A having convex refracting element 64.

FIG. 9 illustrates a cross-sectional expanded view of an alternate embodiment of FTIR device 10 for achieving the advantages of a curved contact surface between switchplate 20 and refractor 12. In the embodiment of FIG. 9, the curved surface is formed in reflecting surface 16' of refractor 12. FTIR device 10 of FIG. 9 operates substantially in the same way as FTIR device 10 in FIGS. 6 and 7. Because reflecting surface 16' is curved with respect to contact surface 22 of switchplate 20, the amount of force required to bring the surfaces into proximal contact with one another and to later separate the surfaces is greatly reduced over prior known FTIR devices.

Forming convex surface 16' on reflecting surface 16 of refractor 12 may be accomplished by many methods. Reflecting surface 16, for example, can be ground to form the convex surface. Alternatively, the convex surface may be formed by placing a convex refractive element on reflecting surface 16 of refractor 12.

FIGS. 10A and 10B show the formation of convex reflecting surface on refractor 12 through the use of a lens or convex refracting element 66 that is placed on reflecting surface 16. FIG. 10A is a side cross-sectional view of refractor 12 showing a typical convex refracting element 66 on reflecting surface 16 of refractor 12. Axial distance between the apex and the edge of convex refracting element 66 is nominally three microns. FIG. 10B shows a top view of refractor 12 having a convex surface formed by convex refracting element 66

FIGS. 11 and 12 illustrate alternative embodiments of FTIR device 10 that operate in a similar manner described above with reference to FIG. 1 using a bimorph transducer 72. Previous embodiments of the invention use an actuator 40 to push switchplate 20. In certain applications, such an arrangement of components in FTIR device may cause a less efficient coupling between transducer forces and contact forces. In addition, an undesirable oscillation of switchplate 20 may contribute to switch bounce and the difficulty of maintaining a required gap between refractor 12 and switchplate 20 despite the oscillations. Also, the arrangement of some of the previous embodiments used an opposing force to bring switchplate 20 in proximal contact with refractor 12. Therefore, to open switchplate 20, the force applied not only had to overcome electrostatic bonding forces between refractor 12 and switchplate 20, but also the opposing force that was applied to close switchplate 20. FTIR devices 10 described with reference to FIGS. 11 and 12 overcome some of these limitations.

Referring now to FIG. 11, FTIR device 10 includes a refractor 12 having a reflecting surface 16. A bimorph transducer 72 is coupled at one end to refractor 12 using a spacer 78. An air gap spacer 76 is coupled to the opposing end of bimorph transducer 72, and a switchplate 74 is coupled to air gap spacer 76. As described with reference to FIG. 1, the reflective surface 24 of switchplate 74 is at a bias angle .theta.26 with respect to contact surface 22. Switchplate 74 may be placed in a variety of orientations depending on the desired paths of beams 28 and 28' through refractor 12. Spacer 78 may also include this same bias angle to provide a consistent or desired orientation of bimorph transducer 72 with respect to refractor 12.

Bimorph transducer 72 may be constructed from a piezoelectric material, dissimilar metals, or other suitable material that changes physical properties in response to an electrical, thermal, or other appropriate control signal. In one embodiment, bimorph transducer 72 comprises the following series of layers: a first conductive layer, a first piezoelectric layer, a second conductive layer, a second piezoelectric layer, and a third conductive layer. The conductive layers are coupled to leads 79 to impart a voltage potential across the piezoelectric layers. For example, one potential is applied to a first pair of leads 79 to cause first piezoelectric layer to shorten, while another potential is applied to a second pair of leads 79 to cause second piezoelectric layer to lengthen. The potentials applied to leads 79 comprise the control signal to bimorph transducer. Depending on the polarity of the control signal, bimorph transducer 72 deflects in the direction indicated by arrow 80.

In operation, a control signal of a first polarity causes the opposing or uncoupled end of bimorph transducer 72 to bend towards refractor 12 to place switchplate 74 in proximal contact with reflecting surface 16 and to apply a force to contact surface 22. In a particular embodiment, bimorph transducer 72 applies enough pressure to deform the irregularities on the surfaces of switchplate 74 and refractor 12 such that an electrostatic bond is formed between those surfaces. When the control signal to bimorph transducer 72 is returned to zero, the surfaces of refractor 12 and switchplate 74 remain in proximal contact to frustrate the total internal reflection. A control signal of a second polarity causes bimorph transducer 78 to generate sufficient force to break the electrostatic bond and space apart switchplate 74 and refractor 12.

FTIR device 10 may also include a conductive element 50 and a second conductive reference 52 to form a capacitor for controlling the distance between switchplate 74 and reflecting surface 16, as described above with reference to FIG. 4. In one embodiment, conductive element 50 is placed on at least a portion of contact surface 22. For example, conductive element 50 may be placed on the portion of contact surface 22 that does not include contact area 56. Similarly, second conductive reference 52 in this embodiment is placed on a portion of reflecting surface 16 that does not come into proximal contact with contact area 56 of switchplate 74. In another embodiment, conductive element 50 may be placed on bimorph transducer 72, air gap spacer 76, or in any other appropriate location that changes position with the deflection of bimorph transducer 72.

FIG. 12 illustrates an alternative embodiment of FTIR device 10 using bimorph transducer 72. In this embodiment, both ends of bimorph transducer 72 are coupled to refractor 12 using spacers 78a and 78b. A switchplate 74 and air gap spacer 76 are coupled to bimorph transducer 72 between spacers 78a and 78b. In this embodiment, the same control signal on bimorph transducer 72 produces four times the force with one-fourth the displacement indicated by arrow 81 as the cantilever configuration of FIG. 11.

FIGS. 13-15 illustrate different embodiments of switchplate 74 adapted to the FTIR device 10 of FIGS. 11 and 12. FIG. 13 illustrates switchplate 74 having a contact surface 22 and a reflective surface 24. Switchplate 74 operates in a similar manner to switchplate 20 shown in FIGS. 1 and 2 but may be shorter in length and is coupled to bimorph transducer 72 instead of refractor 12. FIG. 14 illustrates switchplate 74a with contact surface 22 having a contact area 56 for proximally contacting refractor 12. Contact area 56 is a portion of the total area of contact surface 22. FIG. 15 illustrates switchplate 74b in which contact surface 22 includes a convex refracting element 64, similar to the one shown in FIGS. 8A and 8B above.

FIG. 16 illustrates air gap spacer 76 having a hole 82 to provide an air gap behind the working area of switchplate 74 to facilitate frustrated total internal reflection. Alternatively, hole 82 may represent any suitable material with a lower index of refraction to provide the appropriate optical characteristics for frustrated total internal reflection. In one embodiment, air gap spacer 76 may not have hole 82, and a reflective coating could be applied to reflective surface 24 of switchplate 74 instead. Also, air gap spacer 76 and switchplate 74 may be integral or separate components. The sizing of hole 82 may adjust the compression dynamics of the switchplate 74 and air gap spacer 76 assembly to provide advantages in the operation of FTIR device 10. Specifically, the ratio of the diameter of hole 82 to the diameter of contact area 56 may be adjusted such that the ratio of peal to shear force can be adjusted in breaking the electrostatic bond between switchplate 20 and refractor 12. This results in less force required and higher speed and reliability in operation of FTIR device 10.

Although the present invention has been described in several embodiments, a myriad of changes, variations, alterations, transformations, and modifications may be suggested to one skilled in the art, and it is intended that the present invention encompass such changes, variations, alterations, transformations, and modifications as fall within the spirit and scope of the appended claims.