Abstract:
The present invention uses the deflection of a piezoelectric element to move an optical element into contact with the face of an optical path to redirect an optical signal. In its undeflected state, the optical signal is reflected from the angled face of the optical path by internal reflection. When the piezoelectric actuator moves the optical element into contact with the angled face of the optical path, the index of refraction of the optical path is matched and the optical signal enters the optical element and passes through.

Description:
BACKGROUND 
     Piezoelectric materials and magnetostrictive materials (collectively referred to below as “piezoelectric materials”) deform when an electric field or magnetic field is applied. Thus piezoelectric materials, when used as an actuator, are capable or controlling the relative position of two surfaces. 
     Piezoelectricity is the general term to describe the property exhibited by certain crystals of becoming electrically polarized when stress is applied to them. Quartz is a good example of a piezoelectric crystal. If stress is applied to such a crystal, it will develop an electric moment proportional to the applied stress. 
     This is the direct piezoelectric effect. Conversely, if it is placed on an electric field, a piezoelectric crystal changes its shape slightly. This is the inverse piezoelectric effect. 
     One of the most used piezoelectric materials is the aforementioned quartz. Piezoelectricity is also exhibited by ferroelectric crystals, e.g. tourmaline and Rochelle salt. These already have a spontaneous polarization, and the piezoelectric effect shows up in them as a change in this polarization. Other piezoelectric materials include certain ceramic materials and certain polymer materials. Since they are capable of controlling the relative position of two surfaces, piezoelectric materials have been used in the past as valve actuators and positional controls for microscopes. Piezoelectric materials, especially those of the ceramic type, are capable of generating a large amount of force. However, they are only capable of generating a small displacement when a large voltage is applied. In the case of piezoelectric ceramics, this displacement can be a maximum of 0.1% of the length of the material. Thus, piezoelectric materials have been used as valve actuators and positional controls for applications requiring small displacements. 
     Two methods of generating more displacement per unit of applied voltage include bimorph assemblies and stack assemblies. Bimorph assemblies have two piezoelectric ceramic materials bonded together and constrained by a rim at their edges, such that when a voltage is applied, one of the piezoelectric materials expands. The resulting stress causes the materials to form a dome. The displacement at the center of the dome is larger than the shrinkage or expansion of the individual materials. However, constraining the rim of the bimorph assembly decreases the amount of available displacement. Moreover, the force generated by a bimorph assembly is significantly lower than the force that is generated by the shrinkage or expansion of the individual materials. 
     Stack assemblies contain multiple layers of piezoelectric materials interlaced with electrodes that are connected together. A voltage across the electrodes causes the stack to expand or contract. The displacement of the stack is equal to the sum of the displacements of the individual materials. Thus, to achieve reasonable displacement distances, a very high voltage or many layers are required. However, convention stack actuators lose positional control due to the thermal expansion of the piezoelectric material and the material(s) on which the stack is mounted. 
     Due to the high strength, or stiffness, of piezoelectric material, it is capable of opening and closing against high forces, such as the force generated by a high pressure acting on a large surface area. Thus, the high strength of the piezoelectric material allows for the use of a large valve opening, which reduces the displacement or actuation necessary to open or close the valve. 
     With a conventional piezoelectrically actuated relay, the relay is “closed” by moving a mechanical part so that two electrode components are in contact. The relay is “opened” by moving the mechanical part so the two electrode components are no longer in contact. The electrical switching point corresponds to the contact between the electrode components of the solid electrodes. Conventional piezoelectrically actuated relays, however, do not latch easily. If latching is available, a residual charge in the piezoelectric material is used or switch contacts that contain a latching mechanism is used. 
     Conventional optical relays and relay arrays use the creation of bubbles in the optical path to switch the optical signals and do not latch. Further, bubble type relays tend to have large power consumption and to generate unwanted heat. 
     SUMMARY 
     The present invention uses the deflection of a piezoelectric element to move an optical element into contact with the face of an optical path to redirect an optical signal. In its undeflected state, the optical signal is reflected from the angled face of the optical path by internal reflection. When the piezoelectric actuator moves the optical element into contact with the angled face of the optical path, the index of refraction of the optical path is matched and the optical signal enters the optical element and passes through. Coatings that match the index of refraction of the optical path can be used on the optical element for higher efficiency. The optical switch actuator can use a bending mode piezoelectric element to displace the optical element. The optical switch actuator can also use other modes of piezoelectric elements to displace the optical element. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. 
     FIG. 1 shows a side view of a piezoelectric optical relay in accordance with the invention. 
     FIG. 2 shows a top view of an optical layer of a piezoelectric optical relay with the optical element undeflected in accordance with the invention. 
     FIG. 3 shows a top view of an optical layer of a piezoelectric optical relay with the optical element deflected in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a side view of a piezoelectric optical relay  100  in accordance with the invention. Three layers of the relay  100  are shown. The top layer  110  is a cap layer that acts to seal the top of the relay. The middle layer  120  is an optical layer which houses the actuation means and optics of the relay. The bottom layer  130  is a cap layer which acts to seal the bottom of the relay. Any of the three layers  110 ,  120 ,  130  can be used to hold the electrical connections used to supply power to the actuation means of the relay. Preferrably, the middle optical layer  120  contains the electrical connections used to supply power to the actuation means of the relay. 
     Referring now to FIG. 2, a top view of the optical layer  120  of the piezoelectric optical relay  100  in accordance with the invention is shown. An optical wave guide  140  passes through the layer  120 . The wave guide  140  enters at a first point  142  where an optical signal enters the relay  100 . The wave guide  140  diverges in the center of the optical layer  120 . Two signal out paths  144 ,  146  stem from the divergence of the optical wave guide  140 . 
     The wave guide  140  diverges in the center of the optical layer  120  inside of a chamber  150 . The chamber  150  houses the actuation means for the relay  100 . Inside the chamber  150  is a moveable optical path wedge  160 , a diaphragm  170  which sits below the wedge  160  and is attached thereto, and a piezoelectric element  180 . The wedge  160  is moveable in and out of a notch  190  in the wave guide  140 . 
     The chamber  150  comprises at least two ledges  152 ,  154  which act as supports to which the diaphragm  170  is attachable. The diaphragm  170  attaches to the underside of the ledges  152 ,  154 . It is understood that the side walls of the chamber can be straight, without ledges. In such case, the diaphragm  170  attaches to the side walls. It will be obvious to those skilled in the art that many methods of attaching the diaphragm to the sidewalls is possible. For example only, the diaphram can be laminated to the sidewalls or the sidewalls can have notches sized to the diaphragm. Also as an example, the ledge could be upside-down of that shown in FIG. 1 so that the diaphragm sits on the ledge. 
     The piezoelectric element  180  is operable utilizing any mode of piezoelectric actuation. Preferrably, the piezoelectric element  180  is a bending mode piezoelectric element. The piezoelectric element  180  is attached to the diaphragm  170 . Preferably the piezoelectric element  180  is laminated to the diaphragm  170  but it is understood that any method of maintaining enough proximity between the diaphragm and the piezoelectric element so that they will bend together and move the optical element is sufficient. The diaphragm  170  can be made of any material that is flexible. Preferably the diaphragm is made of stainless steel; alternative materials include brass, beryllium copper, spring steel, or piezoelectric material polarized and wired opposite to the piezoelectric element  180  so that when one expands the other shrinks to produce the bending action. Polymer may also be used. The circuit traces for the piezoelectric element  180  are not shown in FIG.  3 . 
     In operation, the switching mechanism of the invention operates by displacement of the piezoelectric elements  180 . In a preferred embodiment, the bending mode piezoelectric element  180  bends downward. Bending of the piezoelectric element  180  causes the diaphragm  170  to deflect downward. Downward deflection of the diaphragm  170  causes the optical element  160  to insert into the notch  190 . The circuit traces for the piezoelectric element  180  are not shown in FIG.  3 . 
     FIG. 3 shows a top view of an optical layer  120  of a piezoelectric optical relay  100  with the optical element  160  deflected in accordance with the invention. Optical element  160  is deflected into the notch  190  so that an optical signal traveling entering at the first point  142  of the wave guide  140  will not reflect off of the angled face of the notch and be deflected along the waveguide toward port  146 . When the piezoelectric element  180  bends the diaphragm  170  and moves the optical element  160  into contact with the face of the optical path  140 , the index of refraction of the optical path  140  is matched and the optical signal enters the optical element  160 . The optical signal travels through the optical element  160  and through signal out path  144 . In a preferred embodiment of the invention, the optical element  160  is coated with a coating that matches the index of refraction of the optical path. The coating may be a material that is similar to the optical path and is typically composed of thin layers of transparent metal oxides. In a more preferred embodiment of the invention, the coating acts as a filter so that only the wavelength of choice is passed and all others are reflected. The filter works when the triangular element is down and in contact with the waveguide. When the triangular element is up, all of the wavelengths are deflected toward waveguide  146  by internal reflection. 
     Also in a preferred embodiment of the invention, the optical element  160  is triangular. It is understood that other shapes of optical elements can be used which provide for reflection into optical path  146  when not engaged and for refraction into optical path  144  when engaged. It is understood by those skilled in the art that the invention is not limited to the bending piezoelectric element  180  shown in the figures. For example, the piezoelectric element can be an extension mode piezoelectric element, a shear mode piezoelectric element or other mode of piezoelectric element capable of bending the diaphragm.