Patent Publication Number: US-7898729-B2

Title: Combinational PZT and MEMS beam steering

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a non-provisional, and claims the benefit, of commonly assigned U.S. Provisional Patent Application No. 60/945,302, filed Jun. 20, 2007, entitled “Combinational PZT And MEMS Beam Steering,” the entirety of which is herein incorporated by reference for all purposes. 
    
    
     BACKGROUND 
     This disclosure relates in general to piezoelectric light guides and, but not by way of limitation, to piezoelectric light guides as a dithering tool in a beam steering application among other things. 
     Atmospheric conditions often cause beam spreading and/or beam wander in a light beam. In some applications, light beams are used to communicate between a transmitter and a receiver. Due to such atmospheric affects, communication signals directed toward a receiver may be off target. Moreover, because these atmospheric affects are often transient, transmitters often employ beam steering and/or beam dithering protocols to track a receiver and/or adjust the beams transmission. 
     BRIEF SUMMARY 
     In one embodiment, the present disclosure provides for a beam steering system that includes an illumination means, a dithering means, and a scanning means. The illumination means provides a beam of light and may comprise a laser, a laser diode, or another light source. The dithering means, for example, a light guide and at least one piezoelectric element, may be used to dither the beam of light. The scanning means, for example, a microelectromechanical mirror, may be independent from said dithering means and may scan the dithered beam of light toward a target. Moreover, the scanning means may scan at a frequency lower than the frequency of the dithering means. For example, the dithering means may dither the beam of light at a frequency greater than about 10 KHz. In another embodiment the dithering means may dither the beam of light at a frequency between 5 KHz and 50 KHz. As another example, the scanning means may scan the beam of light at a frequency between 50 Khz and 100 KHz. In another embodiment, the scanning means may scan the beam of light at a frequency between 100 KHz and 1 MHz. 
     In another embodiment, the disclosure provides for another beam steering system comprising a light source that provides a beam of light, a piezoelectric tube, a scanning optical element, and a controller. The light source may be a laser. The piezoelectric tube may include a light guide and one or more piezoelectric elements. The piezoelectric tube may be coupled with the light source, such that at least a portion of the beam of light is conducted through the light guide. The scanning optical element may be coupled with the piezoelectric tube. The scanning optical element may include an optical element and a steering device. The controller may be communicatively coupled with the light source, the piezoelectric tube and the scanning optical element; and may include instructions to dither the beam of light with the piezoelectric tube and/or instructions to steer the beam of light with the scanning optical element. 
     In various embodiments, the steering device may include a microelectromechanical device. In various other embodiments, the optical element may include a mirror. The light source may include a laser or laser diode. In some embodiments, the light guide is cylindrical and/or comprises fiber optics. In some embodiments the light guide may include four piezoelectric elements distributed radially about the light guide and/or substantially equidistant from one another. The instructions to dither the beam of light may include instructions to deflect the beam of light such that the beam of light maps out a substantially circular pattern. 
     Another beam steering system is also provided according to another embodiment. The beam steering system may include a laser that provides a beam of laser light, a piezoelectric tube, a scanning microelectromechanical mirror, and a controller. The piezoelectric tube may be cylindrically shaped. The light guide may be housed within the piezoelectric tube and at least four piezoelectric elements may be coupled radially around the piezoelectric tube. The piezoelectric tube may be coupled with the laser such that at least a portion of a beam of laser light from the laser may be conducted through the light guide. The scanning microelectromechanical mirror may include a steering device coupled with the piezoelectric tube. The beam of light may be incident on the scanning microelectromechanical mirror after exiting the piezoelectric tube. The controller may be communicatively coupled with and control the operation of the light source, the piezoelectric tube, and the scanning microelectromechanical mirror. The controller may includes instructions to dither the beam of light with the piezoelectric tube and/or instructions to steer the beam of light with the scanning microelectromechanical mirror. 
     A beam steering method is also provided according to another embodiment. A beam of light is directed toward a light guide. One or more piezoelectric elements coupled with the light guide is activated. The activating dithers the beam of light according to a dither pattern. The dithered light may then be directed toward a steering optical element. The beam of light may then be steered toward a target with the steering optical element. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating various embodiments, are intended for purposes of illustration only and do not limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a beam steering device that includes microelectromechanical mirror and a piezoelectric light guide according to one embodiment. 
         FIG. 2A  shows a steering and dithering plan according to one embodiment. 
         FIG. 2B  shows the resulting steering and dithering pattern according to one embodiment. 
         FIG. 3  shows an end view of a piezoelectric light guide including four piezoelectric elements according to one embodiment. 
         FIG. 4  provides a schematic representation of a computer system that may be used to implement various methods of the invention. 
         FIG. 5  shows a flowchart of another embodiment. 
     
    
    
     In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label. 
     DETAILED DESCRIPTION 
     The ensuing description provides preferred exemplary embodiment(s) only, and is not intended to limit the scope, applicability or configuration of the disclosure. Rather, the ensuing description of the preferred exemplary embodiment(s) will provide those skilled in the art with an enabling description for implementing a preferred exemplary embodiment. It should be understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope as set forth in the appended claims. 
     Various embodiments of the invention provide for a decoupled beam dithering and beam steering device. That is, the dithering mechanism and the beam steering mechanisms are separated and can be independently controlled. This decoupling may allow for high frequency dithering with lower frequency steering, and/or provide low beam deviation dithering with higher beam deviation steering. A piezoelectric light guide may be used as the dithering mechanism. Such devices may have quick response times and may operate at high frequencies. One or more piezoelectric elements, for example, may provide a directional force on the light guide that deviates the beam of light. A microelectromechanical mirror, for example, may be used to steer the dithered beam of light. 
     Referring first to  FIG. 1 , a beam steering device  100  that includes microelectromechanical mirror  160  and piezoelectric tube  150  is shown according to one embodiment. The beam steering device  100  also includes a lens  170 , a laser  110  and a fiber optic  120 . The piezoelectric tube  150  may include a light guide and one or more piezoelectric elements  140 . The light guide may include fiber optics, crystal fibers, or any other type of waveguide. The laser  110  may include any type of laser operating with any wavelength. Indeed, the embodiments provided herein, do not require a specific wavelength and/or laser type. The lens  170  may include any type of optical element for focusing and/or collimating light. The piezoelectric tube  150  or piezoelectric tube, may include one or more piezoelectric elements  140 . In one embodiment, the piezoelectric tube  150  includes four piezoelectric elements  140 . The dithering and beam steering may be decoupled using the microelectromechanical mirror  160  for beam steering, and the piezoelectric tube  150  for dithering and/or nutation. 
     When a beam of light is conducted through the piezoelectric tube  150 , the piezoelectric elements  140  may be activated to deflect the light guide in any direction depending on the placement of the piezoelectric elements  140  about the light guide and/or depending on the applied voltage on the piezoelectric elements  140 . In some embodiments, the piezoelectric elements  140  may be used to deflect the light guide small distances at high frequencies. For example, in one embodiment, the piezoelectric elements  140  may deflect the light guide about ±5 μm. In another embodiment, the piezoelectric elements  140  may deflect the light guide between about ±1 μm and ±10 μm. As another example, in another embodiment, piezoelectric elements  140  may deflect the light guide between about ±10 μm and ±100 μm. In another embodiment, the piezoelectric elements  140  may deflect the light guide at a frequency greater than 1 kHz. In another embodiment, the piezoelectric elements  140  may deflect the light guide at a frequency between 10 kHz and 100 KHz. In another embodiment, the piezoelectric elements  140  may deflect the light guide at a frequency between about 100 kHz and 1 MHz. In another embodiment the piezoelectric elements  140  may deflect the light guide  150  at a frequency greater than 1 MHz. 
     The piezoelectric tube  150  may dither the beam of light according to various dithering patterns. For example, the piezoelectric tube  150  may dither the beam of light in a circular, oval, polygon-shaped and/or rectangular pattern.  FIG. 2A  shows an example of a circular dithering pattern  210 . 
     Returning to  FIG. 1 , dithered light from the piezoelectric tube  150  is incident on the microelectromechanical mirror  160 . The microelectromechanical mirror  160  may be used to steer or scan the light beam. This steering may occur over large angles and at slow frequencies. For example, in one embodiment, the microelectromechanical mirror  160  may steer a beam of light ±1°. In another embodiment, the microelectromechanical mirror  160  may steer a beam of light between +10 and ± 5 ′. In another embodiment, the microelectromechanical mirror  160  may steer a beam of light between ±5° and ±10°. In another embodiment, the microelectromechanical mirror  160  may steer a beam of light at a frequency of about 100 Hz. In another embodiment, the microelectromechanical mirror  160  may steer a beam of light at a frequency between about 10 Hz and 500 Hz. 
       FIG. 2A  shows a raster scan steering pattern  220 . While a fixed steering pattern is shown, the steering pattern may also be random, a linear pattern or vary over time. By combining the steering and the dithering, a pattern of moving circles is produced as shown in  FIG. 2B . This decoupling of the steering and dithering by using a separate device for each, may allow for higher dithering speeds, lighter weight components, higher steering angles, greater portability, simplified controls, etc. Moreover, the controls can be designed to resonate with the piezoelectric elements and/or the microelectromechanical mirror in order reduce power consumption. 
       FIG. 3  shows an end view of a piezoelectric light guide  315  that includes four piezoelectric elements  305  according to one embodiment. The four piezoelectric elements  305  are arrayed approximately 90° from each other around the piezoelectric light guide  315 . Each piezoelectric element  305  may provide a directional force to the piezoelectric light guide  315 , and thus deflect the light guide  315  a small amount. Moreover, opposing piezoelectric elements, such as,  305 -D and  305 -B as well as  305 -A and  305 -C, may coordinate by simultaneously applying positive and negative directional forces. Using these piezoelectric elements  305 , the light guide  315  may be deflected according to any time varying functions. For example, the piezoelectric light guide  315  may be deflected in a circular pattern by varying the electric charge incident on the piezoelectric elements  305  over time using time varying sinusoidal functions. 
     Operation of a beam steering device may be coordinated with a computational system like that shown schematically in  FIG. 4 . The drawing broadly illustrates how individual system elements may be implemented in a separated or more integrated manner. The computational device  400  is shown comprised of hardware elements that are electrically coupled via bus  426 , which is also coupled with the portions of the beam steering device that may include, for example, a microelectromechanical mirror  452 , a laser, and piezoelectric element(s)  454 . The hardware elements include a processor  402 , an input device  404 , an output device  406 , a storage device  408 , a computer-readable storage media reader  410   a , a communications system  414 , a processing acceleration unit  416  such as a DSP or special-purpose processor, and a memory  418 . The computer-readable storage media reader  410   a  is further connected to a computer-readable storage medium  410   b , the combination comprehensively representing remote, local, fixed, and/or removable storage devices plus storage media for temporarily and/or more permanently containing computer-readable information. The communications system  414  may comprise a wired, wireless, modem, and/or other type of interfacing connection and permits data to be exchanged with external devices. 
     The computational device  400  also comprises software elements, shown as being currently located within working memory  420 , including an operating system  424  and other code  422 , such as a program designed to implement methods of the invention. It will be apparent to those skilled in the art that substantial variations may be used in accordance with specific requirements. For example, customized hardware might also be used and/or particular elements might be implemented in hardware, software (including portable software, such as applets), or both. Further, connection to other computing devices such as network input/output devices may be employed. 
       FIG. 5  shows a flowchart of another embodiment. A beam of light is directed toward a piezoelectric light guide as shown in block  505 . For example, a laser beam may be directed toward a piezoelectric light guide. The piezoelectric light guide may then dither the beam of light according to a dithering pattern at block  510 . For example the pattern may be made using a time varying function. As one example, the time varying function may produce a circular or oval dither pattern. The dithered light may then be directed toward a microelectromechanical (MEM) mirror at block  515 . The dithered light may then be steered with the microelectromechanical mirror at block  520 . As described in other embodiments the dithering may occur at high frequencies and produce small deviations in the beam of light, where as the steering may occur at lower frequencies and produce larger deviations in the beam of light. 
     Specific details are given in the above description to provide a thorough understanding of the embodiments. However, it is understood that the embodiments may be practiced without these specific details. For example, circuits, structures, and/or components may be shown in block diagrams in order not to obscure the embodiments in unnecessary detail. In other instances, well-known circuits, processes, algorithms, structures, components, and techniques may be shown without unnecessary detail in order to avoid obscuring the embodiments. 
     Implementation of the techniques, blocks, steps and means described above may be done in various ways. For example, these techniques, blocks, steps and means may be implemented in hardware, software, or a combination thereof. For a hardware implementation, the processing units may be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described above and/or a combination thereof. 
     Also, it is noted that the embodiments may be described as a process which is depicted as a flowchart, a flow diagram, a data flow diagram, a structure diagram, or a block diagram. Although a flowchart may describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be rearranged. A process is terminated when its operations are completed, but could have additional steps not included in the figure. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc. When a process corresponds to a function, its termination corresponds to a return of the function to the calling function or the main function. 
     Furthermore, embodiments may be implemented by hardware, software, scripting languages, firmware, middleware, microcode, hardware description languages and/or any combination thereof. When implemented in software, firmware, middleware, scripting language and/or microcode, the program code or code segments to perform the necessary tasks may be stored in a machine readable medium, such as a storage medium. A code segment or machine-executable instruction may represent a procedure, a function, a subprogram, a program, a routine, a subroutine, a module, a software package, a script, a class, or any combination of instructions, data structures and/or program statements. A code segment may be coupled to another code segment or a hardware circuit by passing and/or receiving information, data, arguments, parameters and/or memory contents. Information, arguments, parameters, data, etc., may be passed, forwarded, or transmitted via any suitable means including memory sharing, message passing, token passing, network transmission, etc. 
     For a firmware and/or software implementation, the methodologies may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. Any machine-readable medium tangibly embodying instructions may be used in implementing the methodologies described herein. For example, software codes may be stored in a memory. Memory may be implemented within the processor or external to the processor. As used herein the term “memory” refers to any type of long term, short term, volatile, nonvolatile, or other storage medium and is not to be limited to any particular type of memory or number of memories, or type of media upon which memory is stored. 
     Moreover, as disclosed herein, the term “storage medium” may represent one or more devices for storing data, including read only memory (ROM), random access memory (RAM), magnetic RAM, core memory, magnetic disk storage mediums, optical storage mediums, flash memory devices and/or other machine readable mediums for storing information. The term “machine-readable medium” includes, but is not limited to portable or fixed storage devices, optical storage devices, wireless channels and/or various other mediums capable of storing, containing or carrying instruction(s) and/or data. 
     While the principles of the disclosure have been described above in connection with specific apparatuses and methods this description is made only by way of example and not as limitation on the scope of the disclosure.