Abstract:
The present invention provides a method and apparatus for compact, high-speed, latched optical switching devices utilizing bimorph piezoelectric material. The apparatus employs an optical switching prism, that is capable of interchanging two parallel beams, to construct a 2×2 optical switch. In order to construct compact and high-speed switches, the prism has to be small and light-weigh, thus, the separation of the two parallel beams becomes small. A pair of reflection corner mirror capable of separating these two close parallel beams is used. The switching is performed by vertically inserting the prism into the optical path and only less than one millimeter (limited by the beam size) movement is required. Because the switching is based on beam deflection instead of reflection, it is not vulnerable to vibration.

Description:
FIELD OF INVENTION 
     The invention relates to the field of optics, and more particularly to optical switching. 
     BACKGROUND 
     The use of optical fiber for long-distance transmission of voice and/or data is common today. The continuing demand to increase the data carrying capacity raises the need to utilize the bandwidth of existing fiber-optic cable more efficiently. Wavelength Division Multiplexing (WDM) is an established method for increasing the carrying capacity of existing fiber cable where multiple information channels are independently transmitted over the same fiber using multiple wavelengths of light. Using this method, each light-wave-propagated information channel corresponds to light within a specific wavelength range or “band”. 
     The WDM technique significantly increases the network traffic and consequently necessitates more sophisticated optical switching and routing devices that can quickly route numerous channels among various optical communication lines and that can reliably divert network traffic to alternative routes during network failures. Routine network traffic switching requires optical devices that can perform reproducibly over many thousands of switching operations. Network failure restoration requires a long unused switching device to instantaneously perform according to specification. The present invention addresses these issues. 
     SUMMARY OF INVENTION 
     The present invention provides a method and apparatus for optical switching devices utilizing a bimorph piezoelectric apparatus. The optical switching devices include an arm comprising a piezoelectric material, a first and a second surface and a first end and a second end, wherein the first surface is opposite the second surface, and the first end is opposite the second end; at least one electrode couple to the arm to provide a voltage difference between the first and second surface of the arm; a support coupled to the first end of the arm to firmly support the first end; an object with a convex surface coupled to the second end of the arm; an optical element coupled to the second surface of the arm capable of deflecting an optical signal traveling through; a first magnet proximately located to the object and to the first surface of the of the arm; and a second magnet proximately located to the object and to the second surface of the arm. The apparatus is employed by a switching system where the optical or composite optical signal travels from a collimator via optical fibers, the signal is directed by a reflective element such as a mirror, which is angled in order that the signal is in the path of the aforementioned optical element of the piezoelectric apparatus. The use of a reflective element allows the implementation of a 2×2 optical element such as a glass prism. Furthermore, the weight of the optical element allows a high switching speed, and the size of the optical element allows the beams to separate by as little as 1 mm. The optical devices are of a compact modular design that permits the construction of complex optical devices. 
     The present invention provides a method and apparatus for compact, high-speed, latched optical switching devices utilizing bimorph piezoelectric material. The apparatus employs an optical switching prism, that is capable of interchanging two parallel beams, o construct a 2×2 optical switch. In order to construct compact and high-speed switches, the prism has to be small and light-weigh, thus, the separation of the two parallel beams becomes small. A pair of reflection corner mirror capable of separating these two close parallel beams is used. The switching is performed by vertically inserting the prism into the optical path and only less than one millimeter (limited by the beam size) movement is required. Because the switching is based on beam deflection instead of reflection, it is not vulnerable to vibration. 
     The actuating element of the switch is a piece of bimorph material. One end of the bimorph is mounted on a fixture and the other can be moved up or down. The movement is driven by applying switching voltage onto the bimorph. The switching prism is attached on the moving end. Magnetic latching is applied in the switch. Two small steel balls are attached on the top and bottom surfaces at the moving end of the bimorph. Two small magnets are placed close to the two steel balls, respectively, and form a magnetic bi-stable latching mechanism. 
     The advantages of the proposed optical switches are compactness, high-speed, and low vulnerability to vibration. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a side view of one embodiment of the piezoelectric latching apparatus in its neutral state. 
     FIG. 2A is a side view of one embodiment of the piezoelectric latching apparatus in its “on” position. 
     FIG. 2B is a side view of one embodiment of the piezoelectric latching apparatus in its “off” position. 
     FIG. 3 is a flow chart of the logical process for the positioning of the piezoelectric apparatus. 
     FIG. 4A is top view of one embodiment of the optical switch where the piezoelectric latching apparatus is in its “on” position. 
     FIG. 4B is a top view of one embodiment of the optical switch where the piezoelectric latching apparatus is in its “off” position. 
     FIG. 5 is a flow chart of the 2×2 prism switch and signal deflection. 
    
    
     DETAILED DESCRIPTION 
     The present invention provides method and apparatus for optical switching devices that vertically displaces the switching medium. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the embodiments will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the embodiments shown but is to be accorded the widest scope consistent with the principles and features described herein. 
     FIG. 1 depicts a side view of one embodiment  100  of the present invention. The apparatus  100  comprises two elongate plates  7 A and  7 B consisting of a piezoelectric material such as quartz. The plates are secured together in parallel and supported by mounting elements  9 A and  9 B. One electrode  11 A is implemented between the piezoelectric plates  7 A and  7 B along the shared surface between the plates. A second electrode  11 B and a third electrode  11 C are implemented along the non-shared surfaces of the piezoelectric plates  7 A and  7 B respectively. When secured together, the piezoelectric plates  7 A and  7 B encompass a single arm  13  which comprises a first end  13 A, which is firmly supported by mounting elements  9 A and  9 B, and a second opposing end  13 B which is not tightly mounted. Two permanent magnets  1 A and  1 B are placed on either side of the end  13 B. In addition two solid objects  5 A and  5 B, possibly metallic spheres, are fixed on either surface of the end  13 B. The objects  5 A and  5 B are composed of material such as iron, steel, or nickel that experiences a magnetic force of attraction toward either permanent magnets  1 A or  1 B. Furthermore, an optical element  3  (e.g. glass prism, wave plate, etc) is mounted to the arm  13  along an unshared surface of the plate  7 B and near the metallic sphere  5 A. 
     As depicted in FIG. 1, the end  13 B of the piezoelectric plates  7 A and  7 B is shown to rest exactly between the two permanent magnets  1 A and  1 B in a hypothetical metastable physical state where the upward force of the attraction between the sphere  5 A and the magnet  1 A balances the downward force of the attraction between the sphere  5 B and the magnet  1 B perfectly. However, such an intermediate metastable state cannot physically exist for any finite period of time due to slight perturbations of the position of the arm  13  that results in situations where the opposing forces are unbalanced and the free end  13 B of arm  13  would be pulled by the magnetic force of either magnets until one of the spheres  5 A or  5 B contacts its corresponding magnets  1 A or  1 B. Moreover, the two alternative positions create a pair of stable, “latched” positions. 
     Furthermore, the operation of the present embodiment demands that the electrodes  11 A-C apply differential voltages across the surface of the bonded piezoelectric plates  7 A and  7 B, in order that the differential piezoelectric expansion and/or contraction cause vertical movements of the arm  13 . The electrode  11 A applies a variable voltage while the electrode  11 B maintains a constant voltage and the electrode  11 C is grounded in order to generate and maintain the differential voltages across the piezoelectric plates  7 A and  7 B. The electrode  11 A varies its voltage to direct the arm  13  either upward or downward. Moreover, the end  13 A of the arm  13  is firmly secured leaving  13 B as the only movable portion of the arm  13 . It is therefore possible to achieve precise and rapid control of the position of the end  13 B, and consequently, the position of the prism  3 . 
     FIG. 2A illustrates the piezoelectric apparatus in its latched “on” state, where the optical element  3  intercepts the optical signal  15 . In contrast, FIG. 2B depicts the piezoelectric apparatus in its latched “off” state, where the optical signal  15  is not intercepted by the optical element  3 . Further, because the “off” state of the apparatus  100  requires that the optical element  3  to be non-planar to the optical signal, the piezoelectric apparatus may move the optical element  3  less than 1 mm vertically away from the plane in order to avoid intercepting the optical signal. 
     The flow chart FIG. 3 illustrates the actions taken in cases where the position of the piezoelectric arm  13  is to be reversed. In one embodiment where the desired latching position is “off” and the apparatus  100  is latched “on”, an electric charge is applied to the electrode  11 A in order to reverse the latching position. Conversely, in another embodiment where the desired latching position is “on” and the apparatus  100  is latched “off”, an electric charge similar in magnitude and opposite in polarity is applied to the electrode  11 A in order to latched the apparatus “on”. 
     FIGS. 4A and 4B are top views of an optical switch  200  which embodies the deflection and latching apparatus  100  in both the “on” and “off” state. In both figures, an optical signal or composite optical signals  27  and  29  are transmitted via optical fibers from collimators  19 A and  19 C respectively. The signals are then reflected by the a reflective element  17 A such as a mirror in order that the resulting light beam crosses the “on” position of the 2×2 prism  3  latched by the piezoelectric latching apparatus  100 . FIG. 4A depicts the “on” switch position where the piezoelectric latching apparatus is latched vertically downward and planar to the reflective elements  17 A and  17 B. While the apparatus  100  maintains the “on” position, the 2×2 prism  3  intercepts the signal pathways and deflects the signals to focus onto the reflective element  17 C, which in turn directs the signals  27  and  29  to a crisscross path into the collimators  19 D and  19 B respectively. Conversely, FIG. 4B illustrates the “off” switch position where the piezoelectric latching apparatus is latched vertically upward away from the reflective elements  17 A and  17 B. While the apparatus is in its “off” position, the 2×2 prism  3  does not intercept or deflect the signal pathway and the switch is effectively turned off. As shown in FIG. 3A where the switch  200  is latched in the “on” position, the optical signal  21  is deflected from the straight line path. In FIG. 3B, where the switch  200  is latched in the “off” position, the optical signals are not intercepted by the 2×2 prism  3  and thus travel straight to focus onto the reflective element  17 B, which in turn transmits the signals  27  and  29  to the collimators  19 B and  19 D respectively. Moreover, because the collimators are not placed directly on the sides of the optical element  3 , the space between the beams  27  and  29  could be as small as 1 mm. 
     The flow chart FIG. 5 summarizes different paths the optical signal takes where the piezoelectric apparatus is latched “on” or “off”. The optical signal is transmitted via a collimator, and then reflected by a mirror in order to cross the path of the prism  3 . In one embodiment where the piezoelectric apparatus  100  is latched vertically downward and planar to the reflective elements  17 A and  17 B, the prism deflects the signal to redirect its path. Conversely, in the absence of the prism where the piezoelectric apparatus  100  is latched “off” and vertically upward and non-planar to the reflective  17 A and  17 B, the prism does not intercept the signal, which travels straight without deflection. 
     In another embodiment of the present invention, the optical element  3  is a half-wave plate. The piezoelectric apparatus  100  is latched similarly as in the embodiment where the optical element is a prism, however, the half-wave plate controls beam polarization rather than switching. 
     The present invention has been described with an optical switching device utilizing a bimorph piezoelectric material although one of ordinary skill in the art realizes that other suitable materials may be substituted without altering the essence of the invention. 
     A method and apparatus for optical switching devices utilizing a bimorph piezoelectric electro-mechanical deflection and latching apparatus is herein disclosed. The optical device includes a 2×2 optical prism switch or a half-wave plate utilizing a piezoelectric apparatus. The optical devices in accordance with the present invention are of a compact modular design that allows the construction of more complex optical devices. The optical devices in accordance with the present invention possess the advantages of stable and reproducible operation, high switching speeds relative to other mechanical devices and low sensitivity to slight optical mis-alignments or vibrations.