Patent Publication Number: US-2007098320-A1

Title: Beam steering element with built-in detector and system for use thereof

Description:
BACKGROUND OF THE INVENTION  
      Increasingly large volumes of information are transferred across telecommunications networks to meet the increasing Internet and business communications demands. High speed communications systems in the telecommunications networks often employ fiber optic communications channels with electronic switches and routers to transfer the increasingly large volumes of information. However, a combination of optical data transmission and electronic switching requires numerous optical-to-electrical-to-optical conversions. These conversions create significant overhead in terms of power consumption, bandwidth limitations, size of system components, overall system throughput, and latency. As such, much research has been performed to develop all-optical cross-connect switching systems.  
      In an all-optical cross-connect switching system, optical beams from transmitting apertures are connected to corresponding receiving apertures in the switching system by pointing direction, reflection, refraction, diffraction, or combinations thereof. To set-up optical connections, conventional optical cross-connect systems generally utilize secondary optical beams emitted by an array of light emitting diodes (LEDs) associated with input ports that are used to locate the proper corresponding output or connecting ports, or vice-versa. As part of the set-up process, the connecting ports may employ a detector coupled to a fiber receiving the secondary optical beam to detect the secondary optical beam. However, such a setup requires sophisticated processing, very accurate positioning of the detector components, and sophisticated components. In addition, if the transmission length of the optical beam is long relative to the size of the receiving aperture, the algorithm needed to center the optical beam on the receiving aperture becomes even more complex and/or requires highly sophisticated processing and, thus, more processing time. In an optical cross-connect system, these requirements result in undesirable delay in setting-up connections, higher per-port costs, and lower reliability.  
     SUMMARY OF THE INVENTION  
      An all-optical cross-connect switching system provides optical switching with significantly reduced processing requirements and cost and with increased reliability by associating an optical detector with an optical beam steering element. In one embodiment, the all-optical cross-connect switching system includes (i) a first beam steering element having a reflective surface in optical association with a first optical fiber array and (ii) a second beam steering element having a reflective surface in optical association with a second optical fiber array. In this embodiment, the first and second beam steering elements are optically arranged to direct an optical beam from a first optical fiber in the first optical fiber array to a second optical fiber in the second optical fiber array. Further, in this embodiment, the second beam steering element includes at least one optical detector that provides information about a first position of the optical beam on the second beam steering element, which may be an indication of an angle of the first beam steering element. Based on this information, the angle of the first beam steering element may be adjusted to cause the optical beam to change to a second position on the second beam steering element.  
      Other embodiments of the present invention include the optical beam steering element with built-in detector and a method of manufacturing same. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.  
       FIG. 1  is a block diagram of an optical cross-connect switching system that may employ an embodiment of the present invention;  
       FIG. 2  is a block diagram of an all-optical cross-connect switching system according to an embodiment of the present invention;  
       FIG. 3  is a high-level flow chart of a process for manufacturing an embodiment of a beam steering element used in the switching system of  FIG. 2 ;  
       FIG. 4  is a flow chart of a process for manufacturing another embodiment of the beam steering element;  
       FIG. 5A  is a top view of a square area of semiconductor material used to manufacture an embodiment of the beam steering element;  
       FIG. 5B  is a top view of the semiconductor material of  FIG. 5A  having masking material (e.g., photoresist) on its surface arranged according to a first pattern;  
       FIG. 5C  is a cross-sectional view of the semiconductor material of  FIG. 5B  after ion implantation forming an optical detector;  
       FIG. 5D  is a top view of the semiconductor material of  FIG. 5C  having masking material on its surface arranged according to a second pattern;  
       FIG. 5E  is a cross-sectional view of the semiconductor material of  FIG. 5D ;  
       FIG. 5F  is a cross-sectional view of the semiconductor material of  FIG. 5D  after metal deposition;  
       FIG. 5G  is a top view of the semiconductor material of  FIG. 5F  having masking material on its surface arranged according to a third pattern;  
       FIG. 5H  is a top view of the semiconductor material of  FIG. 5G  after an etching process;  
       FIG. 5I  is a top view of the reflective surface gimbal of the optical beam steering element of  FIG. 5H ;  
       FIG. 6A  is a side view of an embodiment of a beam steering element in operation, according to an embodiment of the present invention;  
       FIG. 6B  is a side view of another embodiment of a beam steering element in operation;  
       FIG. 6C  is a side view of another embodiment of a beam steering element in operation;  
       FIG. 7A-1  is a top view of a portion of an optical beam steering element having four detectors and showing a misaligned optical beam;  
       FIG. 7A-2  is a graph indicating the misalignment of the optical beam of  FIG. 7A-1 ;  
       FIG. 7B-1  is a top view of a portion of the optical beam steering element of  FIG. 7A-1  showing an aligned optical beam; and  
       FIG. 7B-2  is a graph indicating the alignment of the optical beam of  FIG. 7B-1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      A description of preferred embodiments of the invention follows.  
       FIG. 1  is a block diagram of an optical cross-connect switching system  100 . The optical cross-connect switching system  100  includes an optical cross-connect switch  150  (also referred to as a switch fabric) interfacing with an array of input fibers  102   a , . . . ,  102   n  and an array of output fibers  112   a , . . . ,  112   n . The array of input fibers  102   a , . . . ,  102   n  interface with the optical cross-connect switch  150  through a corresponding array of input apertures (e.g., lenses)  104   a , . . . ,  104   n  and input free space interconnects  106   a , . . . ,  106   n . The array of output fibers  112   a , . . . ,  112   n  interface with the optical cross-connect switch  150  through a corresponding array of output apertures  114   a , . . . ,  114   n  and output free space interconnects  116   a , . . . ,  116   n.    
      The optical cross-connect switch  150  reroutes optical signals from the array of input fibers  102   a , . . . ,  102   n  to the array of output fibers  112   a , . . . ,  112   n . Optical cross-connects (OXCs), such as the optical cross-connect switch  150 , perform switching operations in networks, such as ring and mesh networks, to transfer information between or among communicating nodes in the network, such as end user nodes, central offices, content servers, end user nodes, and so forth. Optical cross-connects enable network service providers to switch high-speed optical signals efficiently.  
      Conventional optical cross-connects perform switching electrically. However, as understood in the art, the combination of optical data transmission and electronic switching requires numerous optical-to-electrical-to-optical conversions. Electronic switches typically convert the optical signals received on the input fiber channels  102   a , . . . ,  102   n  into electrical signals, electrically route these signals, convert the electrical signals back into optical signals, and launch them into the output fiber channels  112   a , . . . ,  112   n . These conversions create significant overhead in terms of power consumption, bandwidth limitations, size of system components, overall system throughput, and latency.  
      Electronic switches are often blocking (i.e., disallowing signal fan-out and fan-in) and are non-transparent (i.e., the signal does not stay in optical form, and the signal may depend upon bit rate, format, and coding). Also, in the electronic switching case, the bandwidth of the optical signal must be within the bandwidth of the electronic switch, which can be orders of magnitude less than the bandwidth of the optical signal. Thus, the electronic switch becomes the network system&#39;s bottleneck. As such, much research has been performed to develop all-optical cross-connect switching systems using various mechanisms, such as movable mirrors, movable fibers, acousto-optic diffraction, electro-optic refraction, magneto-optic switching, movable bubbles, and liquid crystal addressable arrays.  
       FIG. 2  is a block diagram of an all-optical cross-connect switching system  200 , according to an embodiment of the present invention, that provides increased cost-effectiveness, increased reliability, and decreased delay. An optical switch  250  according to an embodiment of the present invention includes (i) an input beam steering element  208   a  that has a reflective surface, such as a mirror or multi-layer dielectric, corresponding to an input fiber  202   a  and (ii) an output beam steering element  218   n  with an optical detector corresponding to an output fiber  212   n . The other input fibers  202   b , . . . ,  202   n  and output fibers  212   b , . . . ,  212   n  also have corresponding input and output beam steering elements, respectively (not shown).  
      The all-optical cross-connect switching system  200  employs free space interconnects (e.g.,  206   a  and  216   n ) and uses two two-degree of freedom (e.g., tip and tilt axes) beam steering elements because of spatial and angular requirements for coupling an optical beam  205  into output apertures  214   a , . . . ,  214   n . Thus, in some embodiments, the all-optical cross-connect switching system  200  is a “free-space” system, as opposed to a guided beam, solid state system (i.e., an optical cross-connect switching system employing an electronic switch). In other embodiments, the system  200  may include guided beam, solid state elements. Other beam steering configurations are also possible, such as four one-degree of freedom beam steering elements. The all-optical cross-connect switching-system&#39;s  200  inputs and outputs may be arranged in a two-dimensional array (not shown) in order to achieve economy of space. Thus, to direct the optical beam  205  from a particular input fiber (e.g.,  202   a ) to a particular output fiber (e.g.,  212   n ), the optical beam  205  may be moved in two dimensions. To do so, for example, the input beam steering element  208   a  may provide beam steering in two perpendicular directions. Similarly, and depending on the exact nature of the beam steering mechanism, the output beam steering element  218   a  may also provide two-dimensional beam steering capability. For example, if the apertures are fixed and the switch mechanism provides steering of the beam (as depicted in  FIG. 2 ), the output beam steering element  218   n  may be used to ensure that an output beam  217   n  is positioned optimally in the output aperture  214   n.    
      In the embodiment shown in  FIG. 2 , the input beam steering element  208   a  points an input beam  207   a  to the desired row and column position on the output beam steering element  218   n . The input beam steering element  208   a  may position the input beam  207   a  in the center of the output beam steering element  218   n . The output beam steering element  218   n  may then realign the optical beam  205  to the output aperture  214   n . The output beam steering element  218   n  may direct the optical beam  205  to the center of the output aperture  214   n . Each input fiber  202   a , . . . ,  202   n  and output fiber  214   a , . . . ,  214   n  may use dedicated beam steering elements with two-dimensional beam steering capability. Other embodiments may use four, single-axis, tiltable, beam steering elements instead of two, double-axis, tiltable, beam steering elements. It should be understood that any geometric or coordinate system designs may be employed in other embodiments, optionally in combination with the ones specifically set forth herein.  
      When a connection is first established, the input and output beam steering elements  208   a ,  218   a  (or at least two input and at least two output beam steering elements) may be tilted to prescribed tilt angles. These angles and the corresponding deflection drive signals (e.g., voltages for electrostatically deflected beam steering elements) may be determined for each connection (e.g., input fiber  202   a  and each of output fibers  214   a , . . . ,  214   n ) and may be stored in system memory and recalled when the connection is first established. The stored drive signals, however, may result in tilt angles that are in the vicinity of the desired tilt angles, but are offset by some value due to drift, aging, environmental effects, etc. Thus, the system  200  may optimize the coupling efficiency (i.e., ration of output power to input power) with a scanning/search and an optimization method.  
      An example optimization method may scan the input and output beam steering elements  208   a ,  218   n  incrementally until an optimum or acceptable coupling efficiency is achieved. The size of the tilt increments (degrees) of the scan and, thus, the tilt angle drive signal increments (e.g., voltage), may be small enough so that several increments result in an acceptable coupling efficiency, i.e., several scan positions of the input and output beam steering elements  208   a ,  218   n  may result in an acceptable coupling efficiency. In this case, the system is said to be less sensitive to tilt angle error. If there are fewer tilt angle increments that result in acceptable coupling efficiency, then the system is said to be more sensitive to tilt angle error. The range of the scan may be determined by a maximum error in the angular position. The number of scan increments is the range divided by the increment size. Thus, each scanning axis has a scanning capability of n positions, where n is equal to or greater than the scan range divided by the increment size. The input beam steering element  208   a  may be scanned through its n 2  positions for each position of the output beam steering element  218   n . In such a case, there are n 4  positions for the entire scanning range (all four tilt axes=n×n×n×n). Clever optimization algorithms have been developed (e.g., the hill-climbing algorithm or the rosette pattern) to ease scanning time required to achieve acceptable coupling efficiency. Nevertheless, the amount of continual processing that may be required to establish and maintain multiple connections is a challenging aspect of free-space optical cross-connect switches. Embodiments of the present invention dramatically ease the processing requirements and may be used in conjunction with the clever optimization algorithms.  
      Through use of an embodiment of the present invention, the number of scan positions may be reduced from n 4  to 2n 2 . For instance, if the “spot” position error were 0.1 mm and the scan increment were 0.002 mm, then n=50, for which n 4 =6.25×10 6 , whereas 2n 2 =5000. In other words, an embodiment of the present invention may reduce the total required scanning positions and total scanning time in this example by as much as a factor of 1250.  
      This reduction may be accomplished by separating optical beam alignment into two stages. The first stage may include positioning the input beam  206   a  in the center of the output beam steering element  218   n . This first alignment stage may use one set of two-dimensional scans for which the total scan field is n×n=n 2 . The second stage may include positioning the output beam (with the output beam steering element  218   n ) in the center of the output aperture  214   n . This second alignment stage may use one set of two-dimensional scans for which the total scan field is n×n=n 2 .  
      In practice, positioning the input beam  207   a  on the output beam steering element  218   n  may be less sensitive than positioning the output beam  217   n  on the output aperture  214   n . This means that the input scan field, n input   2 , may be much smaller than the output scan field, n output   2 . Without the two stage alignment process, both scan fields may be restricted to the sensitivity of the output aperture  214   n . Thus, the required scan field with the invention is n input   2 +n output   2 &lt;2n output   2 &lt;&lt;n 4 . It should be understood that in alternative embodiments or other configurations of the switching system  200 , more than two stages of scanning may be performed.  
      This scan field reduction (from n 4  to 2n 2 ) may be accomplished by configuring an optical detector (not shown here, but shown in  FIGS. 5A-5H ) in the output beam steering element  218   n . This optical detector may provide a measured signal to an angle controller  209  for output beam placement optimization on the output beam steering element  218   n . The total number of scan positions required for output beam placement optimization is n 2 −n for each input beam steering element  208   a  axis. A fiber power tap detector  222   n  in the output fiber  212   n , which is used in a conventional optical cross-connect set-up, is used for aligning the output beam steering element  218   n  to the output fiber  212   n  through a feedback circuit. The output beam steering element  218   n  is moved through n positions in each of the two degrees of freedom (two axes) so that there are n 2  positions for output beam  216   n  alignment. Thus, the total scan field is 2n 2 .  
      Continuing to refer to  FIG. 2 , proper alignment of the output beam  217   n  to the output aperture  214   n  results in the maximum coupling of the input signal power to the output fiber  212   n . In practical operations, however, there is an acceptable range of coupling efficiency. Each connection is preferably established and maintained within this acceptable range. Proper alignment of the output beam  217   n  to the output aperture  214   n  may be achieved through use of feedback circuitry  229 .  
      In the embodiment of  FIG. 2 , the feedback circuitry  229  includes a fiber power tap  222   n  placed on the output fiber  212   n . The fiber power tap  222   n  may be a 1% power tap. The fiber power tap  222   n  connects to signal detection circuitry  224   n , which detects an output signal power level on the output fiber  212   n . The signal detection circuitry  224   n  provides the output signal power level reading to optimization feedback circuitry  226   n . Based on the output signal power level reading, the optimization feedback circuitry  226   n  determines how to adjust the angle of the output beam steering element  218   n  to cause the output beam  217   n  to converge into proper alignment with the output aperture  214   n . In this embodiment, beam steering element driver circuitry  228   n  provides an appropriate deflection drive signal to the output beam steering element  218   n  to cause it to tilt to the desired angle, as determined by the optimization feedback circuitry  226 .  
      The signal detection circuitry  224   n  may also detect other optical output signal characteristics to determine the alignment of the optical output beam with the output aperture  214   n . For example, the signal detection circuitry  224   n  may be configured to detect a modulation on the optical output signal. Modulation may be applied to wavelengths (i.e., optical signals) for use in confirming by a cross-connect switch that the switch correctly steered the wavelength or multiple wavelengths to the correct fiber(s).  
      It should be understood that the signal detection circuitry  224   n , the optimization feedback circuitry  226   n , or the beam steering circuitry  228   n  may be, in whole or in part, software executing on a processor, field programmable gate array (FPGA), or other electronic device. Moreover, though represented as discrete components, the feedback circuits  224   n ,  226   n , and  228   n  may be implemented in a single circuit, a combination of circuit and software, or any other mechanism suitable for accomplishing the functions described herein.  
       FIG. 3  is a flow chart of a process for manufacturing or fabricating a beam steering element having an integral detector. The process  300  starts at step  301 . In step  311 , an optical detector is configured of semiconductor material. The American Heritage® Dictionary of the English Language, Fourth Edition defines the term configure as follows: “To design, arrange, set up, or shape with a view to specific applications or uses.” In step  321 , a reflective surface is associated with the semiconductor material. Finally, in step  341 , a portion of the semiconductor material is configured to be a movable beam steering element. The process  300  returns  303  to step  311  to manufacture another optical beam steering element.  
       FIG. 4  is a flow chart of a process for manufacturing the same or another embodiment of the beam steering element. The process  400  starts at step  401 . In step  411 , a first mask defining a p-doped region is formed on a semiconductor material, such as a silicon wafer, having n-doped regions. In step  415 , the masked semiconductor material undergoes ion implantation to form the p-doped region. In step  421 , a second mask is formed on the semiconductor material to define a reflective surface and electrical contacts. In step  437 , the masked semiconductor material undergoes metal deposition to form the reflective surface and the electrical contacts that support connection of the n-doped and p-doped regions to an electrical circuit. In step  441 , a third mask is formed on the semiconductor material to define a gimbal frame and a reflective surface gimbal. Finally, in step  443 , the masked semiconductor material undergoes an etching process to form the gimbal frame (e.g., X-axis gimbal) and the reflective surface gimbal (e.g., Y-axis gimbal). The process  400  then returns  403  to step  411  to manufacture another optical beam steering element.  
       FIGS. 5A through 5H  referred to below further illustrate the process of manufacturing an embodiment of the beam steering element as set forth by the flow chart of  FIG. 4 .  
       FIG. 5A  is a top view of a square area of semiconductor material  500  used to manufacture an embodiment of the beam steering element. The semiconductor material may be a silicon wafer or any other type of semiconductor material (e.g., gallium arsenide (GaAs)) of any shape or size.  
       FIG. 5B  is a top view of the semiconductor material of  FIG. 5A  having masking material (e.g., photoresist)  510   a  on its surface arranged according to a first pattern. The masking material  511  may be applied to the semiconductor material  513  (which is ion implanted beforehand to form an N-doped region) using known photolithography techniques. Specifically, a layer of photoresist may be applied to the surface of the N-doped semiconductor material. The layer of photoresist may then be exposed to light, such as ultraviolet light, to selectively harden the photoresist in specific places to form the desired pattern shown in  FIG. 5B . According to known photolithography techniques, either “positive” or “negative’ types of photoresist may be used. In this case, negative photoresist is used.  
       FIG. 5C  is a cross-sectional view of the masked semiconductor material of  FIG. 5B  after ion implantation  510   b  forming an optical detector. As shown, a P-doped region  515  is formed adjacent to the N-doped region  513  in those areas where the hardened masking material (i.e., photoresist) is absent. In another embodiment, the optical detector may be positioned on the semiconductor material by known techniques. Multiple optical detectors separated by gaps may also be configured of the semiconductor material. Multiple optical detectors may be isolated on the semiconductor material so that a set of reference signals are used to accurately position the optical beam for optimum positioning.  
       FIG. 5D  is a top view of the semiconductor material of  FIG. 5C  having masking material on its surface arranged according to a second pattern  520   a . As shown, the unmasked portions of the semiconductor material define a reflective surface  523  and a contact  525 .  
       FIG. 5E  is a cross-sectional view of the masked semiconductor material  520   b  of  FIG. 5D . As shown, the masking material  521  exposes a portion of the P-doped region where metal may be deposited to form a contact.  
       FIG. 5F  is a cross-sectional view of the masked semiconductor material  530  of  FIG. 5D  after metal deposition. Metal  537  is deposited on the unmasked portions to form contacts to the N-doped region and a reflective surface. The material for the reflective surface may be gold, silver or any other composition having reflective properties.  
       FIG. 5G  is a top view of the semiconductor material of  FIG. 5F  having masking material on its surface arranged according to a third pattern  540 . The third pattern defines where the semiconductor material is completely removed  543 ,  545  to form a gimbal frame (by removing the semiconductor material at the unmasked portions of the semiconductor material indicated by reference numeral  543 ) and a reflective surface gimbal (by removing the semiconductor material at the unmasked portions of the semiconductor material indicated by reference numeral  545 ).  
       FIG. 5H  is a top view of the semiconductor material  550  of  FIG. 5G  after an etching process. The areas indicated by reference numeral  583  have had the semiconductor material completely removed to form a gimbal frame  572  movable about torsion hinges  570   a  and  570   b . The torsion hinges  570   a ,  570   b  form a vertical axis about which the gimbal frame  572  rotates or twists. The areas indicated by reference numeral  585  have had the semiconductor material removed to form the reflective surface gimbal, which is movable about torsion hinges  574   a  and  574   b . The torsion hinges  574   a ,  574   b  form a horizontal axis about which the reflective surface gimbal twists. In this embodiment only a part of the semiconductor material is configured to be a movable beam steering element. However, in other embodiments, the entire beam steering element may be configured to be movable.  
      The n-electrode  557  and the p-electrode  555  of the p-n diode detector are coupled to outside electronics (not shown) through a p-electrode metallization interconnect  559   a  and an n-electrode metallization interconnect  559   b , respectively. The p-n diode detector may be operated in a conventional back-biased manner for improved sensitivity for optical-to-electrical conversion.  
       FIG. 5I  is a top view of the reflective surface gimbal  560  of  FIG. 5H . The reflective surface gimbal  560  includes a reflective surface  565  surrounded by the detector region  565 . Again, the reflective surface gimbal “twists” about torsion hinges  576   a  and  576   b.    
       FIG. 6A  is a side view of an embodiment of a beam steering element  600  in operation according to the principles of the present invention. The reflective surface  607  is patterned on the beam steering element to cover the center of the detector region defined by the p-doped region  605 . Thus, impinging light  690  may be detected at uncovered detector region(s)  608   a ,  608   b  and provide a signal through a p-electrode contact  609   a  and a n-electrode contact  609   b.    
       FIG. 6B  is a side view of another embodiment of a beam steering element in operation  610 . Reflective surfaces  617   a ,  617   b , . . . ,  617   n  are patterned on the beam steering element  610  in a manner allowing impinging light  692  to be detected at gaps  616   a ,  616   b  between the reflective surfaces  617   a ,  617   b , . . . ,  617   n . Again, the diode detector of the beam steering element includes a p-doped region  615  with a corresponding p-electrode contact  619   a  and an n-doped region  613  with a corresponding n-electrode contact  619   b.    
       FIG. 6C  is a side view of another embodiment of a beam steering element in operation  620 . In this embodiment, the reflective surface  627  is patterned on the beam steering element  620  to cover the entire detector region formed of a p-doped region  625  and a n-doped region  623 . In this embodiment, the reflective surface  627 , however, is thin enough (i.e., transmits enough optical energy) to allow impinging light  694  to be detected by the detector.  
       FIG. 7A-1  shows an embodiment of an optical beam steering element  700   a  having four pads or contacts  709   a ,  709   b ,  709   c , and  709   d , each of which is coupled to a respective optical detector (not shown). A reflective surface (not shown) may be located in the center of the optical beam steering element  700   a . The detector region surrounding the reflective surface may be divided into four regions or quadrants (marked generally by numerals 1-4) corresponding to the four detectors (not shown).  
       FIG. 7A-2  is a graph  705   a  of output detector signals from the four quadrants of optical detectors that can be used to determine a position of the optical signal beam  701  on the optical beam steering element  700   a . When an optical signal beam  701  departs from the reflective surface, optionally indicated by an optical alignment beam  702  with a larger diameter than the optical signal beam  701 , the output detector signals can be used to determine a position of the beam  701  on the optical beam steering element  700   a . In this instance, the different output detector signal levels from each of the detectors corresponding to the contacts  709   a - d  (i) indicate that each of the detectors is exposed to unequal portions of an optical alignment beam  702  and (ii) indicate a misaligned, optical, signal beam  701 , which is oriented in the center of the optical alignment beam  702 . As described above, the output detector signals may be provided to the angle controller  209  for optimizing output beam placement on the optical beam steering element  700   a.    
       FIG. 7B-1  is a top view of a portion of the optical beam steering element of  FIG. 7B . In this instance, equal output detector signal levels from each of the detectors (i) shows that each of the detector regions are exposed to equal portions of an optical alignment beam  702  and (ii) indicates an aligned optical signal beam  701 . Thus, the output detector signals may be used to position the center of the optical signal beam  701  and achieve optimum alignment.  
       FIG. 7B-2  is a graph  705   b  indicating the correct alignment by way of equal signals produced by each of the optical detectors corresponding to contacts  709   a - d.    
      It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, a method, or a computer readable medium such as a computer readable storage medium or a computer network wherein program instructions are sent over optical or electronic communication lines.  
      The tilt range for a typical MEMS beam steering element is six to eight degrees, resulting in a beam deflection angle range of twelve to sixteen degrees. Typical voltage range for a MEMS element is 40 volts. The spot alignment range (circular) to a collimated fiber is typically 10 microns to achieve an acceptable power coupling range of −3 dB (3 dB down from maximum coupling). An optical alignment path may be 10 cm to 1 meter. The −3 dB angular alignment range is then 0.01 to 0.1 milliradians. The voltage increment, assuming a linear relationship, is approximately 3 millivolts. There are, thus, 104 or 214 increments in the full tilt range of the MEMS element. There are four such tilt ranges −4×214 or 216 requiring a 16-bit processor to control the voltage to the accuracy required throughout the range.  
      While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.  
      It should be understood that embodiments of the optical beam steering element and system may also be employed in applications of spectral regions outside of the visible optical spectrum, such as: infrared, x-ray, ultraviolet, and so forth.  
      It should also be understood that software used to control beam steering elements may be stored in a computer-readable medium, such as a CD-ROM or computer memory, and loaded/executed by a digital processor configured to execute the software in a manner adapted to interface directly or via other electronics causing the beam steering elements to steer a beam and detect optical energy with the optical detector as described herein.  
      It should also be understood that the optical detector described herein may be any known optical detector, such as a metal-semiconductor-metal (MSM) photodetector or an avalanche photodiode (APD).