Patent Publication Number: US-2021191108-A1

Title: Hybrid optical fiber mems scanner

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of International Patent Application No. PCT/US2019/039088, filed Jun. 25, 2019, entitled “HYBRID OPTICAL FIBER MEMS SCANNER,” which claims the benefit of priority to U.S. Provisional Patent Application No. 62/690,279, filed Jun. 26, 2018, entitled “RASTER SCANNED PROJECTOR WITH MICROELECTROMECHANICAL SYSTEM SCANNER,” U.S. Provisional Patent Application No. 62/691,560, filed Jun. 28, 2018, entitled “HYBRID OPTICAL FIBER MEMS SCANNER,” and U.S. Provisional Patent Application No. 62/840,298, filed Apr. 29, 2019, entitled “HYBRID OPTICAL FIBER MEMS SCANNER,” the entire disclosures of which are hereby incorporated by reference, for all purposes, as if fully set forth herein. This application is related to International Patent Application No. PCT/US2019/039084, filed Jun. 25, 2018, entitled “RASTER SCANNED PROJECTOR WITH MICROELECTROMECHANICAL SYSTEM SCANNER,” the entire disclosure of which is hereby incorporated by reference, for all purposes, as if fully set forth herein. 
    
    
     BACKGROUND OF THE INVENTION 
     Modern computing and display technologies have facilitated the development of systems for virtual or augmented reality experiences, where digitally reproduced images or portions thereof are presented to a viewer in a manner wherein they seem to be, or may be perceived as real. A virtual reality, or “VR,” scenario typically involves presentation of digital or virtual image information without transparency to other actual real-world visual input; an augmented reality, or “AR” scenario typically involves presentation of digital or virtual image information as an augmentation to visualization of the actual world around the viewer. 
     Despite the progress made in these display technologies, there is a need in the art for improved methods and systems related to augmented reality systems, particularly, display systems. 
     SUMMARY OF THE INVENTION 
     Since the advent of the smartphone, the great utility of having a versatile and always available device capable of general purpose computing and multimedia communication has been realized by the public at large. Nonetheless a pronounced drawback of smartphones is the relatively small screen size. Smartphone display screens are a small fraction of the size of even small laptop computer screens. 
     It is now contemplated that smartphones will eventually be replaced or indispensably supplemented by augmented reality glasses that will, among other things, effectively provide users with a relatively large field of view 3D imagery output system that is accessible to users, at will, whether for business or entertainment purposes. 
     Beyond merely exceeding the screen size afforded by a laptop and without the encumbrance of carrying a laptop, augmented reality glasses will provide new mixed reality applications that seamlessly integrate the real world and virtual content. This will not only preserve the user&#39;s engagement with the real world, but also enable new types of augmentation of the physical world, such as, for example: automatically generated contextually relevant information overlaid on automatically recognized real world objects; communication between remotely situated persons through 3D avatars of each party presented at the other party&#39;s location; and mixed reality games that include virtual content behaving realistically, e.g., respecting boundaries of physical objects in the real world. 
     One form of augmented reality includes a set of transparent eyepieces that is configured to couple light from left and right sources of imagewise modulated light to a user&#39;s eyes. Thus, the user can view the real world while simultaneously or concurrently viewing virtual imagery. Separate left and right imagery that is stereoscopically correct may be provided. Additionally, the curvature of the wavefront of light carrying the imagery can be controlled based on the intended distance of virtual objects included in the virtual imagery from the user. Both of the foregoing measures contribute to the user&#39;s perception that viewed imagery is three dimensional. 
     It would be desirable to reduce the size and weight of augmented reality glasses to values approaching those of typical eyeglasses. An obstacle to doing so is often the source of imagewise modulated light. Even highly miniaturized projectors based on 2D focal plane array light modulators as Liquid Crystal on Silicon (LCoS), or Digital Micromirror Device (DMD) will typically occupy a few cubic centimeters of volume and weight a few grams. One highly compact source of imagewise modulated light is the fiber scanner. The fiber scanner includes an optical fiber extending through a piezoelectric drive tube. Construction of the fiber scanner involves painstaking manual assembly procedures which would be a cost issue for a mass produced product. 
     This disclosure describes various embodiments that relate to transducers for manipulating fiber or cantilevered beam scanners. In particular, a MEMS based transducer is described for manipulating a fiber or cantilevered beam in a circular or spiral pattern. 
     A fiber scanner is disclosed and includes the following: an optical fiber; a transducer assembly comprising a first subassembly and a second subassembly, wherein at least one of the first subassembly or the second subassembly includes a multi-section channel configured to at least partly receive the optical fiber in a configuration where the optical fiber extends lengthwise in the multi-section channel, the multi-section channel including a flexibly attached hub portion configured to transfer motion to the optical fiber, and at least one transducer mechanically coupled to the flexibly attached hub portion. 
     In some embodiments, the flexibly attached hub portion is connected to a remaining portion of the at least one of the first subassembly or the second subassembly by a first flexure and a second flexure. 
     In some embodiments, the channel is a multi-section channel, each of the first subassembly and the second subassembly including a monolithic component that defines a portion of the multi-section channel and also including the flexibly attached hub portion. The optical fiber is disposed in the multi-section channel defined by the first subassembly and the second subassembly. 
     In some embodiments, the monolithic component of each of the first subassembly and second subassembly includes kinematic alignment features to secure against relative slippage of the first subassembly and the second subassembly. 
     In some embodiments, the kinematic alignment features include aligned grooves in the monolithic component of the first subassembly and the second subassembly. 
     In some embodiments, the kinematic alignment features further include cylinders disposed in the aligned grooves. 
     In some embodiments, the channel includes a fixed portion adjacent to the flexibly attached hub portion and spaced apart from the flexibly attached hub portion to allow for motion of the flexibly attached hub portion. 
     In some embodiments, the optical fiber includes a first portion having a first diameter, a second portion having a second diameter and a third portion having a third diameter. The second portion is located between the first portion and the third portion, and the first portion is aligned with the fixed portion of the channel and the third portion is aligned with the flexibly attached hub portion. 
     In some embodiments, the transducer assembly further includes at least one capacitive sensing region. 
     In some embodiments, the at least one capacitive sensing region includes at least a first capacitive sensing electrode disposed proximate to the optical fiber and a second capacitive sensing electrode disposed proximate to the optical fiber and where at least a portion of the optical fiber disposed proximate to the first capacitive sensing electrode and the second capacitive sensing electrode is covered with electrically conductive material. 
     In some embodiments, the at least one transducer includes a first piezoelectric transducer and a second piezoelectric transducer, the flexibly attached hub portion includes a first side and a second side and the first piezoelectric transducer is attached to the first side of the flexibly attached hub portion and the second piezoelectric transducer is attached to the second side of the flexibly attached hub portion. 
     In some embodiments, in each of the first subassembly and the second subassembly, the transducer includes a first piezoelectric transducer and a second piezoelectric transducer such that the fiber scanner includes at least four piezoelectric transducers. Each flexibly attached hub portion includes a first side and a second side and the first piezoelectric transducer is attached to the first side of the flexibly attached hub portion and the second piezoelectric transducer is attached to the second side of the flexibly attached hub portion, the flexibly attached hub portions of the first subassembly and second subassembly positioned adjoining each other forming a flexibly attached hub encompassing the optical fiber. 
     An optical scanner is disclosed and includes the following: a cantilevered optical member; and a transducer assembly having a first subassembly and a second subassembly. The first and second subassemblies define a multi-section channel configured to at least partly receive the cantilevered optical member in a configuration where the cantilevered optical member extends lengthwise in the multi-section channel. The multi-section channel includes a flexibly attached hub portion configured to transfer motion to the cantilevered optical member, the transducer assembly including at least one transducer mechanically coupled to the flexibly attached hub portion. 
     In some embodiments, the cantilevered optical member has a tapered shape with a distal end narrower than a proximal end. 
     An optical scanner is disclosed and includes the following: a first subassembly defining a first side of a multi-section channel and a first hub portion attached to the first subassembly by two or more flexures; an optical fiber coupled to and extending along one or more sections of the multi-section channel; a second subassembly defining a second side of the multi-section channel and a second hub portion attached to the second subassembly by two or more flexures, a first coupling face of the first subassembly being coupled to a second coupling face of the second subassembly; a first piezoelectric actuator having a first end coupled to a fixed portion of the first subassembly and a second end coupled to the first hub portion; and a second piezoelectric actuator having a first end coupled to the second subassembly and a second end coupled to the second hub portion. 
     According to some embodiments of the present invention, an optical scanner includes a base portion, a cantilevered optical member protruding from the base portion, and a transducer assembly comprising one or more piezoelectric actuators coupled to the cantilevered optical member and configured to induce motion of the cantilevered optical member in a scan pattern. 
     In some embodiments of the above optical scanner, the transducer assembly includes a plurality of piezoelectric actuators coupled directly to the cantilevered optical member. 
     In some embodiments, the cantilevered optical member has a tapered shape with a distal end narrower than a proximal end adjacent to the base portion of the optical scanner. 
     In some embodiments, the base portion includes a layer of monocrystalline silicon, and the cantilevered optical member includes a cantilevered beam integrally formed with and protruding from the layer of monocrystalline silicon. 
     In some embodiments, each of the plurality of piezoelectric actuators are oriented in a direction substantially parallel to a longitudinal axis of the cantilevered beam. 
     In some embodiments, the plurality of piezoelectric actuators includes piezoelectric film actuators extending across a surface of the cantilevered optical member. 
     In some embodiments, the plurality of piezoelectric actuators consists of two piezoelectric film actuators configured to drive the cantilevered optical member in a circular scan pattern. 
     In some embodiments, the plurality of piezoelectric actuators comprises two piezoelectric film actuators configured to drive the cantilevered optical member in a circular scan pattern. 
     In some embodiments, the cantilevered optical member has an elongated width along a first plane and include a plurality of waveguides, and the transducer assembly is configured to induce motion of the cantilevered optical member in a second plane orthogonal to the first plane. 
     In some embodiments, the plurality of waveguides in the cantilevered optical member extends through the base portion to optically receive, in a time-sequential manner, a scanning input light beam that scans across the first plane. 
     In some embodiments, the base portion includes a curved section having a contour that tracks a trajectory of a tip of a second cantilevered optical member that emits the scanning input light beam that scans across the first plane. 
     In some embodiments, the second cantilevered optical member includes an optical fiber or a cantilevered beam including a waveguide. 
     In some embodiments, the first plane is a horizontal plane and the second plane is a vertical plane. 
     According to some embodiments of the present invention, an optical scanner includes a base portion, a cantilevered optical member protruding from the base portion, and a transducer assembly comprising one or more piezoelectric actuators coupled to the cantilevered optical member. The cantilevered optical member has an elongated width along a first plane and include a plurality of waveguides. The transducer assembly is configured to induce motion of the cantilevered optical member in a second plane orthogonal to the first plane. 
     In some embodiments of the above optional scanner the base portion includes a layer of monocrystalline silicon. The cantilevered optical member includes a cantilevered beam integrally formed with and protruding from the layer of monocrystalline silicon. 
     In some embodiments, each of the one or more piezoelectric actuators is oriented in a direction substantially parallel to a longitudinal axis of the cantilevered beam. 
     In some embodiments, the one or more piezoelectric actuators include piezoelectric film actuators extending in a direction parallel to the first plane across a surface of the cantilevered optical member. 
     In some embodiments, the first plane is a horizontal plane and the second plane is a vertical plane. 
     According to some embodiments of the present invention, a two-dimensional optical scanner includes a first one-dimensional optical scanner and a second one-dimensional scanner. The first one-dimensional optical scanner includes a first base portion, a first cantilevered optical member protruding from the first base portion, the first cantilevered optical member including a single waveguide, and a first transducer assembly including one or more first piezoelectric actuators coupled to the first cantilevered optical member and configured to induce the first cantilevered optical member to scan a first output light beam in a first plane. The second one-dimensional optical scanner includes a second base portion, a second cantilevered optical member protruding from the second base portion, the second cantilevered optical member having an elongated width along the first plane and include a plurality of waveguides, and a second transducer assembly including one or more second piezoelectric actuators coupled to the second cantilevered optical member and configured to induce the second cantilevered optical member to scan in a second plane, the second plane being orthogonal to the first plane. The plurality of waveguides in the second cantilevered optical member extends through the second base portion to optically receive the first output light beam from the first one-dimensional optical scanner in a time-sequential manner. The first one-dimensional optical scanner and the second one-dimensional optical scanner are optically coupled to form the two-dimensional optical scanner. 
     In some embodiments of the above two-dimensional optical scanner, the second base portion of the second one-dimensional optical scanner includes a curved section having a contour that tracks the trajectory of a tip of the first cantilevered optical member in the first one-dimensional optical scanner to improve coupling between the first one-dimensional optical scanner and the second one-dimensional optical scanner. 
     In some embodiments, the first base portion comprises a layer of monocrystalline silicon, and the first cantilevered optical member including a cantilevered beam integrally formed with and protruding from the layer of monocrystalline silicon. The one or more first piezoelectric actuators the first cantilevered optical member include piezoelectric film actuators disposed on surfaces of the cantilevered beam that are orthogonal to the first plane. 
     In some embodiments of the above two-dimensional optical scanner, the second base portion includes a layer of monocrystalline silicon, and the second cantilevered optical member includes a cantilevered beam integrally formed with and protruding from the layer of monocrystalline silicon. The one or more second piezoelectric actuators in the second cantilevered optical member includes piezoelectric film actuators disposed on surfaces of the cantilevered beam that are orthogonal to the second plane. 
     Other aspects and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
         FIG. 1  shows an exemplary augmented reality system according to an embodiment of the present invention; 
         FIG. 2  shows a top view revealing an exemplary configuration that includes an optical scanner affixed to a rear-facing surface of an eyepiece according to an embodiment of the present invention; 
         FIG. 3  shows a close up view of the optical assembly depicted in  FIG. 2 ; 
         FIG. 4  shows an exploded perspective view of the optical scanner, which includes an upper subassembly, a lower subassembly, and an optical fiber, according to an embodiment of the present invention; 
         FIG. 5  shows a perspective view of the lower subassembly according to an embodiment of the present invention; 
         FIG. 6  shows how solder glass can be distributed across a surface of the lower subassembly for adhesion to the upper subassembly according to an embodiment of the present invention; 
         FIG. 7  shows how the optical fiber can be positioned within a multi-section channel of the lower subassembly according to an embodiment of the present invention; 
         FIG. 8A  shows an optical fiber positioned between the upper and lower assemblies according to an embodiment of the present invention; 
         FIG. 8B  shows piezoelectric actuators coupled with the upper and lower assemblies according to an embodiment of the present invention; 
         FIG. 9  shows an exemplary spiral scan pattern that can be traversed when the optical fiber is actuated according to an embodiment of the present invention; 
         FIG. 10  shows an electric schematic for a four-phase signal splitter network for driving piezoelectric actuators according to an embodiment of the present invention; 
         FIG. 11  shows a schematic view of capacitive sensor regions and ground regions of the upper and lower assemblies according to an embodiment of the present invention; 
         FIG. 12  shows how the actuation and sensing systems described in  FIGS. 10-11  can be combined to adjust optical output based upon an actual scan pattern being traversed by an optical fiber or cantilevered beam that supports one or more waveguides according to an embodiment of the present invention; 
         FIG. 13  shows a detailed view illustrating the operation of an X′-axis amplitude and phase control module according to an embodiment of the present invention; 
         FIGS. 14A-14D  show another type of MEMS scanner formed using a silicon on insulator wafer construction that includes a base region and cantilevered beam according to an embodiment of the present invention; 
         FIGS. 15A-15D  show an alternative MEMS scanner embodiment utilizing four piezoelectric actuators to maneuver a cantilevered beam according to an embodiment of the present invention; 
         FIGS. 16A-16B  show configurations in which a portion of a silicon layer has been removed to accommodate mounting of all piezoelectric actuators directly to a monocrystalline silicon layer according to an embodiment of the present invention; 
         FIG. 17  shows a perspective view of another MEMS scanner according to an embodiment of the present invention; 
         FIGS. 18A-18B  show perspective views of an optical scanner having a cantilevered member that takes the form of an optical fiber according to an embodiment of the present invention; 
         FIGS. 19A-19C  show various embodiments in which discrete piezoelectric film actuators are used to induce movement of a cantilevered beam of a MEMS scanner  1900  in a scan pattern; 
         FIGS. 20A-20B  show two perspective views of an optical scanner having a tapered cantilevered member according to an embodiment of the present invention; 
         FIGS. 21A-21B  show two top views of an optical scanner having a tapered cantilevered member according to an embodiment of the present invention; 
         FIG. 21C  shows a cross-sectional view of an optical scanner having a tapered cantilevered member according to an embodiment of the present invention; 
         FIG. 21D  shows a perspective view of an optical scanner having a tapered cantilevered member according to an embodiment of the present invention; 
         FIG. 22  shows a perspective view of an optical scanner having a wide cantilevered member according to an embodiment of the present invention; 
         FIG. 23  shows a perspective view of two serially coupled optical scanners having cantilevered members according to an embodiment of the present invention; 
         FIG. 24  shows a perspective view of two serially coupled optical scanners having cantilevered members according to an alternative embodiment of the present invention; and 
         FIG. 25  shows an embodiment in which an optical scanner includes an electromagnetic coil that interacts with a permanent magnet mounted adjacent to the electromagnetic coil to generate vertical oscillation of a pivoting portion of a cantilevered beam assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description, references are made to the accompanying drawings, which form a part of the description and in which are shown, by way of illustration, specific embodiments in accordance with the described embodiments. Although these embodiments are described in sufficient detail to enable one skilled in the art to practice the described embodiments, it is understood that these examples are not limiting; such that other embodiments may be used, and changes may be made without departing from the spirit and scope of the described embodiments. 
     Image generating components are important to the performance of virtual and augmented reality devices. Image generating components also tend to take up space and utilize substantial portions of a system&#39;s energy. One way to address these two problems is to build the image generating components with microelectromechanical system (MEMS) technology. In particular, this disclosure describes an optical scanner configuration built using MEMS technology. 
     The optical scanner can include a transducer assembly that includes two subassemblies formed from silicon wafers that cooperatively form a multi-section channel within which a light carrying component, such as an optical fiber or beam with waveguides, can be secured. Each of the subassemblies can include a partially free-floating hub that forms a portion of the multi-section channel within which the optical fiber is positioned. While specific examples of optical fibers or cantilevered beams will be used for the balance of the disclosure, this should not be construed as limiting and it should be appreciated that an optical fiber, cantilevered beam or other cantilevered member configured to emit light could be utilized in the various disclosed embodiments described herein. Piezoelectric actuators coupled with the hub portion are then able to cooperatively manipulate the optical fiber in a manner that causes the optical fiber to move in a desired scan pattern. A synchronization component can be configured to provide inputs to both the piezoelectric actuators and to light generators optically coupled with the optical fiber so that light emitted by the optical fiber is able to correctly display imagery to a user. In some embodiments, the two assemblies can include capacitive sensing regions configured to enable feedback control by tracking a position of the optical fiber during operation of the optical scanner. 
     These and other embodiments are discussed below with reference to the following figures. However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes only and should not be construed as limiting. 
       FIG. 1  shows an exemplary augmented reality system  100  according to an embodiment of the present invention. As shown in  FIG. 1 , the system  100  includes augmented reality headgear  102 , a handheld controller  104 , and an auxiliary unit  106 . The augmented reality headgear  102  includes a left (user&#39;s left) transparent waveguide set eyepiece (herein below “left eyepiece”)  108  and a right transparent waveguide set eyepiece (herein below “right eyepiece”)  110 . Each eyepiece  108 ,  110  includes surface diffractive optical elements for controlling the flow of imagewise modulated light. Eyepieces  108  and  110  are held in position by optical frame  111 . The left eyepiece  108  includes a left incoupling grating  112 , a left orthogonal pupil expansion (OPE) grating  114  and a left exit (output) pupil expansion (EPE) grating  116 . Similarly, the right eyepiece  110  includes a right input coupling grating  118 , a right OPE grating  120  and a right EPE grating  122 . Imagewise modulated light is transferred via the input coupling gratings  112 ,  118 , OPEs  114 ,  120  and EPE  116 ,  122  to a user&#39;s eye. Alternatively, in lieu of the input coupling grating  112 ,  118 , OPE grating  114 ,  120  and EPE grating  116 ,  122  the eyepieces  108 ,  110  include refractive and reflective features for controlling the coupling of imagewise modulated light to the user&#39;s eyes. 
     A left source of imagewise modulated light  124  is optically coupled into the left eyepiece  108  through the left incoupling grating set  112  and a right source of imagewise modulated light  126  is optically coupled into the right eyepiece  110  through the right incoupling grating set  118 . The input coupling grating sets  112 ,  118  deflect light from sources of imagewise modulated light  124 ,  126  to angles above the critical angle for Total Internal Reflection (TIR) for the eyepieces  108 ,  110 . The OPE grating sets  114 ,  120  incrementally deflect light propagating by TIR down toward the EPE grating sets  116 ,  122 . The EPE grating sets  116 ,  122  incrementally couple light out toward the user&#39;s face including the user&#39;s eyes&#39; pupils. Each eyepiece  108 ,  110  can include multiple waveguide planes used to handle different color components and/or provided with EPE grating sets  116 ,  122  having different grating line curvatures in order to impart different wavefront curvatures (corresponding to different virtual image distances) to imagewise modulated light. 
     The auxiliary unit  106  can include a battery to provide energy to operate the system  100 , and can include a processor for executing programs to operate the system  100 . As shown, the auxiliary unit  106  includes a clip  128  that is useful for attaching the auxiliary unit  106  to a user&#39;s belt. Alternatively, the auxiliary unit  106  can have a different form factor. 
     The augmented reality headgear  102  also includes a left temple arm  130  and a right temple arm  132 . The left temple arm  130  includes a left temple speaker port  134  and the right temple arm  132  includes a right temple speaker port  136 . The handheld controller  104  includes a grip portion  146  and a top  148  that includes a plurality of buttons  150 . The auxiliary unit  106  is coupled to the headgear  102  through a cable  152 , which can, for example, include electrical wires and fiber optics. Wireless connections between the auxiliary unit  106  and the headgear  102  can also be used. World cameras  142  and  144  are shown oriented outwardly to cooperatively cover a front facing portion of a user&#39;s field of view. In this way, augmented reality headgear  102  is able to incorporate digital content with real-world items surrounding the user. In some embodiments, world cameras  142  and  144  can include or cooperatively operate in conjunction with depth detection sensors to fully characterize a user&#39;s surroundings. 
       FIG. 2  shows a top view revealing an exemplary configuration that includes an optical assembly  200  according to an embodiment of the present invention. Optical assembly  200  includes optical scanner  202  affixed to a rear-facing surface of eyepiece  110 . By orientating optical scanner  202  in this manner, an overall thickness of an optical stackup can be reduced. Optical scanner  202  is depicted being affixed to eyepiece  110  by mechanical support structure  204 . In some embodiments, mechanical support structure  204  can instead be affixed to optical frame  111  to avoid adverse interaction between mechanical support structure  204  and eyepiece  110 . In some embodiments, an optically reflective material can be affixed between mechanical support structure  204  and eyepiece  110  in order to reduce the occurrence of light being prematurely decoupled from eyepiece  110 . Light can be delivered to optical scanner  202  by optical fiber  206 . Light from optical fiber  206  is then distributed in a predefined scan pattern by optical scanner  202 . The predefined pattern is then received and transmitted to input coupling grating  118  by collimating and coupling optic  208 . It should be appreciated that other cantilevered structures aside from optical fiber  206  are also possible. For example, a silicon beam including one or more optical waveguides can also be used in lieu of optical fiber  206 . 
       FIG. 3  shows a close up view of optical assembly  200  according to an embodiment of the present invention. In particular, details of collimating and coupling optic  208  are shown and described hereinbelow. Light emitted from optical scanner  202  enters collimating and coupling optic  208  through one of curved refractive surfaces  302 . In some embodiments, light generated by optical scanner  202  can be polarized so that substantially all of it passes through polarizing beam splitter  304 . The light then passes through quarter wave plate  306  at which point it is converted from linearly polarized light to circular polarized light and then reflects off curved mirror  308 . Circular polarized light reflecting off curved mirror  308  results in a reversal of the circular polarization handedness of light. Upon passing through the quarter wave plate  306  a second time, the circular polarized light is then reconverted to linearly polarized light, but with a polarization direction perpendicular to the initial linear polarization. The net effect is that the polarization of the light is reversed so that now instead of passing through beam splitter  304  it reflects off of beam splitter  304  to exit collimating and coupling optic  208  through outcoupling surface  310  to enter input coupling grating  118 . The outcoupling surface  310  may also have some optical power. Additional description related to optical assembly  200  is provided in U.S. patent application Ser. No. 15/927,765, titled “Method and System for Fiber Scanning Projector,” filed on Mar. 21, 2018, the disclosure of which is hereby incorporated by reference in its entirety for all purposes. 
       FIG. 4  shows an exploded perspective view of optical scanner  202 , which includes optical fiber  206  and a transducer assembly having a base portion including both an upper subassembly  402  and a lower subassembly  404  according to an embodiment of the present invention. Optical fiber  206  includes multiple enlarged diameter portions  401  sized to engage a channel defined by the transducer assembly and metallized segment  403  for interaction with capacitive sensor regions of upper and lower subassemblies  402  and  404 . Upper and lower subassemblies  402  and  404  both include piezoelectric actuators  406  coupled to a monolithic component such as a thin silicon substrate. The piezoelectric actuators  406  can be configured to drive optical fiber  206  in a desired scan pattern. Optical scanner  202  can also include kinematic alignment features  408  for aligning upper and lower subassemblies  402  and  404 . In this way, any adverse effects on fiber scanning performance due to misalignment of upper and lower subassemblies  402  and  404  can be mitigated or avoided. In some embodiments, kinematic alignment features  408  can take the form of cylindrical members that are positioned within openings  410  defined by upper and lower subassemblies  402  and  404 . In some embodiments, upper and lower subassemblies  402  and  404  can be formed from a thin layer of silicon or silicon carbide or another material. Upper and lower subassemblies  402  and  404  can also include electrically conductive pathways  412  formed from electrically conductive material such as copper. It should be noted that in some embodiments, upper and lower subassemblies  402  and  404  can be interchangeable. Pathways on interchangeable assemblies can be arranged so that electrically conductive pathways do not overlap. 
       FIG. 5  shows a perspective view of lower subassembly  404  of optical scanner  202  according to an embodiment of the present invention. A hub portion  502  is positioned within an opening  504  defined by lower subassembly  404  and connected to the rest of lower subassembly  404  by flexures  506 . In some embodiments, opening  504  can be performed by a subtractive or stamping manufacturing operation. Flexures  506  accommodate movement of hub portion  502  within opening  504 . Hub portion  502  also defines a portion of a curved multi-section channel  508  designed to accommodate and support a portion of optical fiber  206 . The curvature of multi-section channel  508  is selected in accordance with the shape of the optical fiber that is positioned in the multi-section channel. In the embodiment illustrated in  FIG. 4 , the optical fiber  206  includes multiple enlarged diameter portions  401  sized to match the shape and size of multi-section channel  508 . The increased diameter of enlarged diameter portions  401  allows select portions of optical fiber  206  to remain in direct contact with multi-section channel  508  while other portions of optical fiber  206  are able to move to induce movement of optical fiber  206  in a scan pattern. In particular, section  508 - 1  of multi-section channel  508  is configured to receive a first enlarged diameter portion  401  and section  508 - 2  of multi-section channel  508  is configured to receive a second enlarged diameter portion  401  of optical fiber  206 . In this way, sections  508 - 1  and  508 - 2  can maintain a tight fit with and maintain firm control of the first and second enlarged diameter portions  401  of optical fiber  206 . 
     In some embodiments, a length of optical fiber  206  between enlarged diameter portions  401  can have the same diameter such that fiber  206  has a single enlarged diameter section that can be engaged by both section  508 - 1  and  508 - 2  of multi-section channel  508 . In such a configuration, a length of section  508 - 2  can be lengthened to match and support more, most or all of the portion of the single enlarged diameter section not engaged by section  508 - 1  of multi-section channel  508 . For example, section  508 - 2  can be about two or three times longer than its depicted length to help maintain contact with a larger portion of optical fiber  206 . 
       FIG. 5  also shows how electrically conductive pathways  412 - 1  and  412 - 2  can be configured to route electricity between capacitive sensing regions  510  and electrical pads  512 . Capacitive sensing regions  510  can be metalized and configured to monitor motion of optical fiber  206  during operation of optical scanner  202 . Capacitive sensing regions  510  can be separated by a gap, which allows the two regions to independently sense movement of optical fiber  206 . Electrically conductive pathway  412 - 3  can be configured to route electricity between signal input region  514  and electrical pad  516 . Signal input regions  510  can take the form of a metalized surface area. A conductive coating (e.g., metal coating) is formed over segment  403  of optical fiber  206 . In the assembled scanner  202  metallized segment  403  on the optical fiber  206  extends axially from signal input region  514  to capacitive sensing regions  510 . In the embodiment depicted, the signal input region  514  does not contact metallized segment  403  on the optical fiber  206  however in an alternative embodiment it does. The capacitive sensing regions  510  do not contact metallized segment  403 . In operation, an AC signal is capacitively coupled from signal input regions  514  to the conductive coating  417  and capacitively coupled to varying degrees from the conductive coating  417  to the capacitive sensing regions  510 . The amplitude of the signal that is capacitively coupled from metallized segment  403  to each of the capacitive sensing regions  510  depends on the instantaneous distance between metallized segment  403  and each particular capacitive sensing region  510 . Thus, the position of optical fiber  206  can be sensed by sensing the amplitude of signals coupled into capacitive sensing regions  510 . In the embodiment shown, each of upper and lower subassemblies  402  and  404  includes two capacitive sensing regions  510 ; however, alternatively a different number of capacitive sensing regions  510  is provided. One capacitive sensing regions  510  from each of upper subassembly  402  and lower subassembly  404  may be used in pairs and their signals used as a differential pair to sense the positon of the optical fiber  206 . Lower subassembly  404  also includes tapered protrusions  518 , which can be used as anchoring points for the piezoelectric actuators  406 . 
       FIG. 6  shows how glass frit  602 , which may also be referred to as solder glass, can be distributed across a coupling surface of lower subassembly  404  according to an embodiment of the present invention. In some embodiments, the glass frit can take the form of clear glass with a relatively low melting point. Alternatively, an adhesive is used in lieu of or in addition to the glass frit. Alternatively, another device or method is used to attach the two subassemblies  402  and  404 . Glass frit  602  can act to securely bond lower subassembly  404  to upper subassembly  402 . Glass frit  602  can also be utilized to bond optical fiber  206  to both lower subassembly  404  and upper subassembly  402 . An area across which glass frit  602  is distributed can be selected so that two identical parts can be bonded together in a manner that distributes glass frit  602  across a majority of the surface depicted in  FIG. 6 . 
       FIG. 7  shows how optical fiber  206  can be positioned lengthwise within multi-section channel  508  of hub portion  502  such that a longitudinal axis of optical fiber  206  is aligned with a longitudinal axis of multi-section channel  508 .  FIG. 7  also shows how enlarged diameter portions  401  of optical fiber  206  can have a larger diameter than the rest of optical fiber  206  to match a width of multi-section channel  508 , thereby helping to keep enlarged diameter portions  401  firmly in place, while allowing other portions of optical fiber  206  to maneuver during operation. In particular, metallized segment  403  of optical fiber  206  can be narrower than multi-section channel  508  so that capacitive sensing regions  510  are able to accurately track movement of segment  403  relative to capacitive sensing regions  510  during operation of optical scanner  202 . In some embodiments, a distal end of optical fiber  206  can also be at least partially metallized, allowing other capacitive sensors positioned along tapered protrusions  518  to track movement of the distal end of optical fiber  206 . 
       FIG. 8A  shows optical fiber  206  positioned between upper and lower subassemblies  402  and  404  according to an embodiment of the present invention. In some embodiments, upper and lower subassemblies  402  and  404  can be coupled together using glass frit  602 . In  FIG. 8A , piezoelectric actuators  406  have been removed for the purpose of showing an unobstructed view of an upward-facing surface of upper subassembly  402 . Dashed regions  802  show an area across which piezoelectric actuators  406  extend. In some embodiments, a first end of piezoelectric actuators  406  can be coupled to upper subassembly  402  by attachment pads  804 . In this way, second ends of each of piezoelectric actuators  406  attached to an attachment pad  806  are able to expand and contract longitudinally in order to shift hub portion  502  relative to upper subassembly  402 . A central portion of piezoelectric actuators  406  remain unattached to subassembly  402  and in some embodiments can be elevated above the upward-facing surface of upper subassembly  402  by attachment pads  804  and  806  in order to eliminate friction between piezoelectric actuators  406  and subassembly  402 . The upward-facing surface of upper subassembly  402  also includes electrically conductive pathways  808  for carrying electricity and signals between electrically conductive pads  810  and  812 . An external drive circuit (e.g., see  FIG. 12  below) can be coupled to electrically conductive pads  812 . H-shaped opening  813  helps to electrically isolate capacitive sensing regions  510  from each other allowing for a total of four different capacitive sensing regions  510  to monitor movement of optical fiber  206 . 
       FIG. 8B  shows piezoelectric actuators  406  coupled with upper and lower subassemblies  402  and  404  according to an embodiment of the present invention. Piezoelectric actuators  406  are depicted attached to upper subassembly  402  using electrical pads  804  and  806 . In some embodiments, piezoelectric actuators  406  can be electrically coupled to electrically conductive pathways  808  by wire bonding electrical pads  810  to electrical pads  814  of piezoelectric actuator  406  using wire  816 . Wire  816  can be configured to bend and/or flex to accommodate movement of piezoelectric actuator  406 . In embodiments where wire  816  is attached to piezoelectric actuator  406  directly above electrically conductive pad  804 , wire movement can be reduced or eliminated as the end of piezoelectric actuator  406  undergoes very little movement during expansion and contraction. 
       FIG. 9  shows an exemplary spiral scan pattern  902  that can be traversed when optical fiber  206  is actuated according to an embodiment of the present invention. While arrows show scan pattern  902  turning in a clockwise pattern it should be understood that scan direction can vary. For example, after a clockwise scan has been completed, a counter-clockwise scan can be initiated from a central region of spiral scan pattern  902 , thereby resulting in a reversal in direction of depicted scan pattern  902 . The depicted grid of squares  904  can represent pixel locations traversed by spiral scan pattern  902 . Because a speed of optical fiber  206  can vary over the course of spiral scan pattern  902 , a rate at which light is modulated through optical fiber  206  can be adjusted to keep pace with the speed of the optical fiber so that different colors of light being emitted correctly correspond to pixel locations at squares  904 . For example, since optical fiber  206  can travel more slowly through a central portion of scan pattern  902 , a rate at which light signals are modulated can be slowed as a light emitting portion of optical fiber  206  approaches the central portion or the rate can remain substantially the same resulting in a higher spatial resolution at the central portion of scan pattern  902 . It should be understood that other variations and permutations of the modulation rate are possible. 
       FIG. 10  shows an electric schematic for a four-phase signal splitter network  1000  for driving piezoelectric actuators  406  according to an embodiment of the present invention. As illustrated in  FIG. 4 , piezoelectric actuators  406  can be coupled to upper and lower subassemblies  402  and  404 . For purposes of clarity, piezoelectric actuators are illustrated separated from the rest of the piezoelectric scanner. In some embodiments, four phases are applied to piezoelectric actuators  406  arranged on opposing sides of a fiber scanning assembly. Signal generator  1002  provides outputs that are connected to electrically conductive pathways  808 , which are in turn, connected to corresponding actuation inputs. Signal generator  1002  is also connected to a first 90° phase shifter  1004  and a second 90° phase shifter  1006 , which are connected to piezoelectric actuators  406 - 1  and  406 - 4 . Thus, signal generator  1002 , in concert with the phase shifters  1004  and  1006  provides four phases that are 90° out of phase with respect to each other. 
     For the purposes of discussion of  FIG. 10 , it can be considered that all of the piezoelectric actuators  406  are poled in the same vertical direction. The four piezoelectric actuators  406  can be considered to be grouped in two pairs. A first pair is taken to include a first piezoelectric actuator  406 - 1  and a third piezoelectric actuators  406 - 3 , while a second pair is taken to include a second piezoelectric actuator  406 - 2  and a fourth piezoelectric actuator  406 - 4 . The four-phase splitter network  1000  is configured such that within each of the aforementioned pairs of actuators, the electric field directions established by network  1000  within piezoelectric actuators with each pair are oppositely directed. Accordingly, when one member of each pair is induced by the applied field acting through the agency of the piezoelectric effect to contract, the other member of the pair will be induced to expand. As shown in  FIG. 4  one member of each pair is part of the upper subassembly  402  and the other member of each pair is part of the lower subassembly  404 . Additionally, the two members of each pair are on opposite sides of the optical scanner  202  with one of each pair being in the foreground of  FIG. 4  and the other of each pair being disposed toward the background of  FIG. 4 . The two pairs, i.e., the first pair of piezoelectric actuators  406 - 1  &amp;  406 - 3  and the second pair of piezoelectric actuators  406 - 2  &amp;  406 - 4 , can be said to drive two perpendicular axes (denoted X′-axis and Y′-axis) of the scanner  202 . For the purposes of discussion, one can imagine the X′-axis rotated about the rest axis of the optical fiber  206  from the plane at which the upper subassembly  402  and lower assembly meet of the scanner and the Y′-axis perpendicular to rest axis of the optical fiber and perpendicular to the X′-axis. 
     Although as shown in  FIG. 10 , a single signal generator  1002  is supplying a signal to all four piezoelectric actuators  406 , as will be discussed below, alternatively, circuitry may be provided to provide separate phase and amplitude controlled signals to the first (X′-axis) pair of piezoelectric actuators  406 - 1 ,  406 - 3  and second (Y′-axis) pair of piezoelectric actuators  406 - 2 ,  406 - 4 . 
       FIG. 11  shows a schematic view of capacitive position sensing components of the optical scanner  202  according to certain embodiments. Referring to  FIG. 11 , the sensing regions  510  and signal input regions  514  (see also  FIG. 5 ) of the upper and lower subassemblies  402  and  404  are shown. A sense signal generator  1115  is coupled to the signal input regions  514 . The sense signal generator  1115  generates a sensing signal that has a frequency that may be much higher than the frequency used to drive the piezoelectric actuators  406 . Piezoelectric actuators are capacitively coupled to the metalized portion  704  ( FIG. 7 ) of the optical fiber  206  (see  FIGS. 2-4, 7, 8A, and 8B ). The frequency of the sensing signal can be much higher than a fundamental resonant frequency of the optical fiber  206 , e.g., at least, 10, 100 or 1000 times higher. Accordingly, the sensing signal may not excite any significant mechanical vibration that would disturb the operation of optical scanner  202 . The sensing signal that is capacitively coupled into the metalized portion  704  ( FIG. 7 ) of the optical fiber  206 , is coactively coupled out of the metalized portion  704  ( FIG. 7 ) of the optical fiber  206  through the sensor regions  510  (which may take the form of conductive electrodes). The sensor regions  510  include a first sensor region  510 - 1  and an oppositely located second sensor region  510 - 2  which operate as a pair to detect the position of the optical fiber  206  in the X′-axis direction and a third sensor region  510 - 3  and an oppositely located fourth sensor region  510 - 4  which operate as a pair to detect the position of the optical fiber  206  in the Y′-axis direction. According to alternative embodiment, only a single sensor region is used to sense the X′-axis position and/or the Y′-axis position. Sensing signals picked up by the first sensor region  510 - 1  and the second sensor region  510 - 2  are input to a first differential amplifier  1102  to which the first and second sensor regions  510 - 1 ,  510 - 2  are coupled. Similarly, the third sensor region  510 - 3  and the fourth sensor region  510 - 4  are coupled to a second differential amplifier  1104 . 
     In operation, the magnitude of the sensing signal capacitively coupled to each particular sensing region  510  will increase as the metalized portion  704  of the fiber approaches closer to the particular sensing region. Differential amplifiers  1102  and  1104  are configured to compare position information monitored by opposing sensor regions  510 . For example, analysis of a differential between sensor regions  510 - 1  and  510 - 2  is used to track the optical fiber positions  1106  depicted in  FIG. 11 . The sensor readings processed by differential amplifiers  1102  and  1104  are then received by demodulators  1108  and  1110 , which serve to eliminate the high frequency component of the sensing signal and extract X′ and Y′ modulated signals. The modulation of the X′ and Y′ modulated signals is due to the varying capacitance between the metalized portion  704  of the optical fiber  206  and the signal input regions  514  and the sensor regions  510 , and hence is indicative of the X′ and Y′ instantaneous position of the fiber. Digital signal processor  1112  can then be configured to receive inputs from demodulators  1108  and  1110  in order to track a two-dimensional position of the scanning fiber optic cable. In some embodiments, digital signal processor  1112  can also include models and/or lookup tables that allow it to extrapolate a position of a tip of the scanning fiber optic cable based on the sensor readings originating from sensor regions  510 .  FIG. 11  shows how digital signal processor can output X′, Y′ and phase difference between the X′ direction oscillation and Y′ direction oscillation of the scanning optical fiber, which can be used for feedback control in some embodiments. In normal operation there is about a 90 degree phase difference between the X′ direction oscillation and the Y′ direction oscillation so that the tip of the optical fiber  206  follows a helical trajectory.  FIG. 11  also shows how the sense signal generator  1115  can be coupled to ground  1114 . It should be noted that while four different capacitive sensing regions  510  are depicted, alternative configurations with as few as two adjacent capacitive sensing regions  510  are also possible and deemed to be within the scope of the disclosure. 
       FIG. 12  shows how the actuation and sensing systems described in  FIGS. 10-11  can be combined to adjust optical output based upon an actual scan pattern being traversed by an optical fiber or cantilevered beam that supports one or more waveguides according to an embodiment of the present invention. Graphics Processing Unit (GPU)  1202  includes a frame buffer, which includes image information for a select number of frames of virtual information for display to a user of an augmented reality system. Spiral scan address sequence generator  1204  can be configured to supply a sequence of addresses corresponding to a spiral path of the optical fiber or cantilevered beam. Random access read circuit  1206  can be configured to read data from the frame buffer of GPU  1202  with data from spiral scan address generator  1204 . The data read out from the frame buffer can include red, blue and green (RGB) pixel values that are first converted from digital to analog by digital/analog converters  1207  and then used to control an amount of power delivered by red, green and blue laser driver amplifiers  1208 ,  1210  and  1212  to corresponding laser diodes  1214 ,  1216  and  1218 . Each of laser diodes  1214 ,  1216  and  1218  is optically coupled to optical scanner  202 . 
     Movement and control of optical scanner  202  begins with timing signal generator  1220 , which helps to synchronize X′-axis and Y′-axis amplitude and phase control modules  1222  and  1224 . X′-axis and Y′-axis amplitude and phase control modules  1222  and  1224  in turn cooperatively drive piezoelectric actuators  406 . Capacitive sensing regions  510  provide optical fiber position information to X′-axis and Y′-axis amplitude and phase control modules  1222  and  1224  as described in the text accompanying  FIG. 13 . These sensor readings help to identify any discrepancies in timing between the scan pattern being executed by optical scanner  202  and timing provided by timing signal generator  1220 . In this way, any undesired alterations in scan pattern can be controlled by feedback. 
     Alternatively or additionally, capacitive sensing regions  510  could be used to provide sensor readings of the instantaneous position of optical fiber  206  to the spiral scan address sequence generator  1204  in order to allow the spiral scan address generator  1204  to select the correct pixel values corresponding to the instantaneous position of optical fiber  206  from the frame buffer. 
       FIG. 13  shows a detailed view illustrating the operation of X′-axis amplitude and phase control module  1222  according to an embodiment of the present invention. It should be appreciated that this description can also apply to Y′-axis amplitude and phase control module  1224 . The signal generated by timing signal generator  1220  can be received by oscillator  1302 , phase detector  1304  and amplitude ramp function generator  1306 . Oscillator  1302  uses the timing signal received from timing signal generator  1220  to initiate and synchronize an oscillating signal input. For example, a sinusoidal input could be initiated and synchronized with the received timing signal. Alternatively, a chirped signal that has a frequency variation that takes into account nonlinearities of the restoring forces of the optical fiber  206 . The result being that an oscillating input is generated and reliably synchronized with outputs from timing signal generator  1220 . Phase detector  1304  is used to adjust the output of oscillator  1302  using data from capacitive sensing regions  510 , which track actual movement of optical scanner  202 . By comparing data from timing signal generator  1220  and demodulated data from capacitive sensing regions  510 , phase detector  1304  is able to provide an offset value to variable phase shifter  1308 , which can be utilized to shift the phase of the signal generated by optical scanner  202  so that an output of optical scanner  202  matches an input generated by timing signal generator  1220 . 
     Similarly, demodulated sensor readings from capacitive sensing regions  510  can also be used to regulate an amplitude of a signal generated by oscillator  1302 . Amplitude ramp function generator  1306  can be configured to modulate the amplitude signal to match a circular or spiral scan pattern. In the case of a spiral scan pattern the amplitude slowly increases and decreases over the duration of the scan. Amplitude detector  1310  receives the demodulated sensor readings detected by capacitive sensing regions  510 , which are compared with an output from amplitude ramp function generator  1306  by differential amplifier  1312  in order to determine how much if at all the amount of movement of optical scanner  202  differs from a desired amplitude. Any difference between the signals is then applied to amplifier  1314 , which can boost or attenuate the drive signal prior to it being received by a two-phase signal splitter network  1316 . Two-phase signal splitter network  1316  distributes the signal to 1 st  and 2 nd  Transducers, which each include two piezoelectric actuators  406 , in order to keep a light emitting component of optical scanner  202  in motion. 
       FIGS. 14A-14D  show another type of MEMS scanner  1400  formed using a silicon on insulator wafer construction that includes a base or handle region  1402  and cantilevered beam  1404  according to an embodiment of the present invention.  FIG. 14A  shows how a portion of base region  1402  and cantilevered beam  1404  can be formed from a layer of monocrystalline silicon  1406 , also referred to as a single crystal silicon layer. In some embodiments, the monocrystalline silicon portion of base region  1402  and cantilevered beam  1404  can be about 100 microns thick, thereby allowing for deflection of cantilevered beam  1404  during operation of MEMS scanner  1400 . A waveguide  1408  can be formed along an upper surface of base region  1402  and cantilevered beam  1404 . Cantilevered beam  1404  with waveguide  1408  can be referred to as a cantilevered optical member. In some embodiments light can be received by waveguide  1408  from a fiber optic cable engaging notch  1410  defined by base region  1402 . Base region  1402  can be used to secure MEMS scanner  1400  to another structure. 
     Base region  1402  can also include a layer of silicon  1412  that is coupled to monocrystalline silicon layer  1406 . In some embodiments, monocrystalline silicon layer  1406  can be bonded to silicon layer  1412  by a compression bonding operation resulting in the two layers being bonded via a silicon oxide layer. Silicon layer  1412  can be configured to provide structural support to base region  1402  and can be about 200 microns or twice as thick as monocrystalline silicon layer  1406 , which can have a thickness of about 100 microns. In some embodiments, silicon layer  1412  can provide a mounting surface to which one or more actuation structures can be affixed. As depicted in  FIG. 14A , the actuators can include three piezoelectric actuators  1414  configured to cooperatively maneuver cantilevered beam  1404  in a desired scan pattern. Each of actuators  1414 - 1  and  1414 - 2  can extend between a notch defined by monocrystalline layer  1406  and one of lateral protrusions  1416 . Since piezoelectric actuators  1414 - 1  and  1414 - 2  lie substantially in the same plane as monocrystalline layer  1406 , actuation of piezoelectric actuators  1414 - 1  and  1414 - 2  induce lateral movement of cantilevered beam  1404 . A length of lateral protrusions  1416  helps to define how much movement is induced by piezoelectric actuators  1414 - 1  and  1414 - 2 . It should be noted that in some embodiments, lateral protrusions  1416  can be substantially shorter where it is desirable for piezoelectric actuators to engage cantilevered beam  1404  closer to a central axis of cantilevered beam  1404 . Alternatively, a cantilevered beam  1404  could be configured entirely without lateral protrusions  1416 , where cantilevered beam  1404  is wide enough to accommodate attachment of piezoelectric actuators  1414 - 1  and  1414 - 2  to opposing sides or edges of cantilevered beam  1404 . 
     Actuating piezoelectric actuators  1414 - 1  and  1414 - 2  can generate lateral movement of cantilevered beam  1404 , while periodically actuating piezoelectric actuator  1414 - 3  can generate vertical movement of cantilevered beam  1404 . In this way, actuators  1414  can generate a two-dimensional scan pattern. In some embodiments, the scan pattern can be a circular scan pattern. It should be noted that control of piezoelectric actuators  1414  can be controlled in accordance with the control methods described in conjunction with  FIGS. 12-13 . In some embodiments, strain gauge(s) positioned on or adjacent to cantilevered beam can be configured to track movement of cantilevered beam  1404  and can provide feedback for the previously described control methods. 
       FIG. 14B  shows a perspective side view of MEMS scanner  1400  according to an embodiment of the present invention. In particular,  FIG. 14B  more clearly shows a scale of cantilevered beam  1404  relative to base region  1402 .  FIG. 14B  also shows an exemplary depth of notches  1418  formed in monocrystalline silicon layer  1406  that accommodate and provide a channel within which one end of piezoelectric actuators  1414 - 1  and  1414 - 2  can rest. A wall defining each of notches  1418  can also include an electrical interface configured to supply electrical signals to piezoelectric actuators  1414  for controlling piezoelectric actuators  1414 - 1  and  1414 - 2 . 
       FIG. 14C  shows a perspective view of a lower side of MEMS scanner  1400  according to an embodiment of the present invention. In particular, a clearer view of piezoelectric actuator  1414 - 3  is shown. A first end of piezoelectric actuator  1414 - 3  engages a notch defined in silicon layer  1412 . In some embodiments, signals for driving piezoelectric actuator  1414 - 3  can be routed through silicon layer  1412  and/or monocrystalline silicon layer  1406 . A second end of piezoelectric actuator  1414 - 3  engages a block of silicon  1420  protruding from a downward-facing surface of cantilevered beam  1404 . When piezoelectric actuator  1414 - 3  expands and contracts, the resulting force on silicon block  1420  creates a lever arm that exerts a force on cantilevered beam  1404  resulting in rotation of cantilevered beam about the y-axis and vertical movement of light being emitted from waveguide  1408 . 
       FIG. 14D  shows a perspective view of an upper side of MEM scanner  1400  according to an embodiment of the present invention. Each one of protrusions  1416  of cantilevered beam  1404  includes a notch  1422  for accommodating one of piezoelectric actuators  1414 . Notch  1422  can help in alignment of piezoelectric actuators  1414  with protrusions  1416 . The depth of notch  1422  can be set to help accommodate a desired length of piezoelectric actuators  1414 .  FIG. 14D  also shows how a height of the piezoelectric actuator can exceed the height of lateral protrusions  1416 . For example, a height of piezoelectric actuator  1414  can be about 150 microns while the height of lateral protrusions  1416  can be about  100  microns. It should be appreciated that in some embodiments it can be desirable to use piezoelectric actuators having the same height as lateral protrusions  1416 . In this way, proper alignment of piezoelectric actuators can be more easily achieved with lateral protrusions  1416 . 
       FIGS. 15A-15C  show an alternative MEMS scanner embodiment utilizing four piezoelectric actuators to maneuver a cantilevered beam. MEMS scanner  1500  includes a base region  1502  and cantilevered beam  1504 .  FIG. 15A  shows how a portion of base region  1502  and cantilevered beam  1504  can be formed from a layer of monocrystalline silicon  1506 . In some embodiments, the monocrystalline silicon portion of base region  1402  and cantilevered beam  1404  can be about 100 microns thick, thereby allowing for deflection of cantilevered beam  1404  during operation of MEMS scanner  1500 . A waveguide  1508  can be formed along an upper surface of base region  1502  and cantilevered beam  1504 . In some embodiments, light can be received at waveguide  1508  from a fiber optic cable engaging notch  1510  defined by base region  1502 . 
       FIG. 15A  also shows how base region  1502  can also include a layer of silicon  1512  that is coupled to monocrystalline silicon layer  1506 . In some embodiments, monocrystalline silicon layer  1506  can be bonded to silicon layer  1512  during a compression bonding operation resulting in the two layers being bonded by a silicon oxide layer. Silicon layer  1512  can be configured to provide structural support to base region  1502  and can be about 200 microns or twice as thick as monocrystalline silicon layer  1506 , which can have a thickness of about 100 microns. In some embodiments, monocrystalline silicon layer  1506  can provide a mounting surface to which one or more actuation structures can be affixed. As depicted in  FIG. 15A , the actuators can include piezoelectric actuators  1514 - 1 - 1514 - 4 , which are configured to cooperatively maneuver cantilevered beam  1504  in a desired scan pattern. The distance over which lateral protrusions  1516  protrude from cantilevered beam  1504  helps to define how much rotation is induced by piezoelectric actuators  1514 - 1  and  1514 - 2 . In this embodiment, piezoelectric actuators  1514 - 3  and  1514 - 4 , which are mounted to a downward facing surface of base region  1502 , can be positioned directly beneath respective piezoelectric actuators  1514 - 1  and  1514 - 2 , which are mounted to an upward facing surface of base region  1502 . In this way, an amount of lateral rotation about the z-axis of cantilevered beam  1504  can be substantially the same for any of piezoelectric actuators  1514 . However, since piezoelectric actuators  1514 - 3  and  1514 - 4  are attached to cantilevered beam  1504  by way of silicon blocks  1520 , thereby creating a different lever arm size, a length and/or operating characteristic of piezoelectric actuators  1514 - 3  and  1514 - 4  can be changed so that an amount of vertical rotation about the y-axis can be similar to or the same as the amount of rotation generated by piezoelectric actuators  1514 - 1  and  1514 - 2 . 
       FIG. 15B  shows a perspective view of a lower side of MEMS scanner  1500  according to an embodiment of the present invention. In particular, a clearer view of piezoelectric actuators  1514 - 3  and  1514 - 4  is shown. A first end of piezoelectric actuators  1514 - 3  and  1514 - 4  engage a downward facing surface of silicon layer  1512 . In some embodiments, signals for driving piezoelectric actuator  1414 - 3  can be routed through silicon layer  1512  and/or monocrystalline silicon layer  1506 . A second end of each of piezoelectric actuator  1514 - 3 ,  1514 - 4  engages a respective block of silicon  1520 , which protrudes from a downward-facing surface of lateral protrusions  1516 . In this embodiment, piezoelectric actuators  1514  each apply shearing forces to cantilevered beam  1504  imparted through a bond between piezoelectric actuators  1514 , monocrystalline layer  1506 , silicon layer  1512 , lateral protrusions  1516 , and silicon blocks  1520 . When piezoelectric actuator  1414 - 3  expands and contracts, the resulting force on silicon block  1520  creates a lever arm that exerts a force on cantilevered beam  1504 , resulting in rotation of cantilevered beam about the y-axis and vertical movement of light being emitted from waveguide  1508  as well as rotation of cantilevered beam  1504  about the z-axis and horizontal movement of light being emitted from waveguide  1508 . By sequentially actuating piezoelectric actuators  1514  a circular scan pattern can be induced as is described above. 
       FIG. 15C  shows a front perspective view of MEMS scanner  1500  according to an embodiment of the present invention. In particular, dimensions of waveguide  1508  are more clearly shown as waveguide  1508  protrudes slightly from an upper surface of cantilevered beam  1504 . Furthermore, a rectangular configuration of piezoelectric actuators  1514 - 1 - 1514 - 4  results in a symmetric amount of lateral movement/rotation being provided by actuation of each of piezoelectric actuators  1514 . 
       FIG. 15D  shows a front perspective view of another MEMS scanner embodiment  1550  according to an embodiment of the present invention. In this embodiment, lower piezoelectric actuators  1514 - 3  and  1514 - 4  are positioned inboard of upper piezoelectric actuators  1514 - 1  and  1514 - 2 . By positioning piezoelectric actuators  1514 - 3  and  1514 - 4  inboard of the upper piezoelectric actuators, an effective lever arm can be equalized, thereby reducing the likelihood of different modes of vibration. As depicted, lever arms  1522  and  1524  are substantially the same length. Piezoelectric actuators  1514 - 3  and  1514 - 4  are also coupled to a single silicon block  1520 . Using a single block in lieu of two discrete silicon blocks can vary. 
       FIGS. 16A-16B  show configurations in which a portion of a silicon layer has been removed to accommodate mounting of all piezoelectric actuators directly to a monocrystalline silicon layer according to an embodiment of the present invention.  FIG. 16A  shows how MEMS scanner  1600  can include a silicon layer  1602  that is offset from one edge of monocrystalline silicon layer  1606  to expose a portion of a downward facing surface of monocrystalline silicon layer  1606 . In this way, all of piezoelectric actuators  1604  can be vertically offset the same distance above or below cantilevered beam  1608 .  FIG. 16B  shows a similar MEMS scanner  1650  design where only notched portions of silicon layer  1602  are removed to accommodate the ends of piezoelectric actuators  1604 - 3  and  1604 - 4 . 
       FIG. 17  shows a perspective view of another MEMS scanner  1700  according to an embodiment of the present invention. Monocrystalline silicon layer  1702  includes two protrusions  1704  in addition to cantilevered beam  1706 . Protrusions  1704  are coupled to lateral protrusions  1708  by flexures  1710 . Flexures  1710  can be designed to attenuate vertical and lateral deflection of cantilevered beam  1706 . Flexures  1710  can help limit movement of a portion of cantilevered beam  1706  that includes lateral protrusions  1712  during actuation of piezoelectric actuators  1714 . By limiting the movement of the portion of cantilevered beam  1706  in this way, an effective length of the cantilevered beam can be substantially reduced. In some embodiments, an overall length of cantilevered beam  1706  can be about 2 mm while the portion of cantilevered beam  1706  extending past lateral protrusions  1712  can be about 1 mm. 
       FIGS. 18A-18B  show perspective views of an optical scanner using a cantilevered member taking the form of an optical fiber according to an embodiment of the present invention. In particular,  FIG. 18A  shows an exploded perspective view of parts making up optical scanner  1800 . In particular, four piezoelectric actuators  1802  taking the form of piezoelectric columns are configured to actuate optical fiber  1804  by exerting force upon hub structure  1806 . Hub structure  1806  defines a central opening  1808  sized to receive optical fiber  1804  and four lateral protrusions  1810  for receiving and securing piezoelectric actuators  1802  to optical fiber  1804 . Each of lateral protrusions  1810  can include a notch  1812  for receiving a first end of each of piezoelectric actuators  1802 . A base portion or supporting structure  1814  includes recesses  1816  for receiving a second end of each of piezoelectric actuators  1802  and a central opening  1818  through which optical fiber  1804  extends. Supporting structure  1814  can take the form of a silicon substrate that includes electrically conductive traces for carrying signals to piezoelectric actuators  1802 . 
       FIG. 18B  shows a perspective view of optical scanner  1800  fully assembled according to an embodiment of the present invention. Similar to previous embodiments, piezoelectric actuators  1802  can be configured to sequentially actuate to maneuver a cantilevered member, which in this embodiment takes the form of optical fiber  1804 , in a scan pattern similar to the scan pattern depicted in  FIG. 9 . An interference fit between optical scanner  1804  and material defining opening  1808  of hub structure  1806  allows for movement and rotation of optical fiber  1804  when lateral protrusions  1810  of hub structure  1806  are acted upon by piezoelectric actuators  1802 . In some embodiments, piezoelectric actuators can be adhesively coupled to hub structure  1806  and supporting structure  1814 . While four lateral protrusions  1810  are depicted, it should be appreciated that a different number of piezoelectric actuators and corresponding lateral protrusions is also possible. For example, three, five or six piezoelectric actuators could be utilized to generate a desired scan pattern. It should also be appreciated that the piezoelectric actuators could be rotated in any desired orientation such as an X or any other similar pattern. 
       FIGS. 19A-19C  show various embodiments in which discrete piezoelectric film actuators are used to induce movement of a cantilevered beam of a MEMS scanner  1900  in a scan pattern according to an embodiment of the present invention. MEMS scanner  1900  can be formed using a silicon on insulator wafer construction that includes a base region  1902  and cantilevered beam  1904 .  FIG. 19A  shows how a portion of base region  1902  and cantilevered beam  1904  can be formed from a layer of monocrystalline silicon  1906 . In some embodiments, the monocrystalline silicon portion of base region  1902  and cantilevered beam  1904  can be about  100  microns thick, thereby allowing for deflection of cantilevered beam  1904  during operation of MEMS scanner  1900 . A waveguide  1908  can be formed along an upper surface of base region  1902  and cantilevered beam  1904 . In some embodiments light can be received by waveguide  1908  from laser diodes  1909 - 1 ,  1909 - 2  and  1909 - 3 , which are secured to a surface of monocrystalline silicon  1906 . In some embodiments, laser diodes  1909 - 1  can be a red laser diode, laser diode  1909 - 2  can be a blue laser diode, and laser diode  1909 - 3  can be a green laser diode. In some embodiments additional laser diodes could be added to allow for a larger variety of colors to be produced and propagated through waveguide  1908  by mixing light generated by two or more of laser diodes  1909 . Base region  1902  can be affixed to a support structure along the lines of mechanical support structure  204  in  FIG. 2  to secure MEMS scanner  1900  in place and to align a distal end of cantilevered beam with additional optics for propagating the light released from the distal end of waveguide  1908 . 
     Base region  1902  can also include a layer of silicon  1912  that is coupled to monocrystalline silicon layer  1906 . In some embodiments, monocrystalline silicon layer  1906  can be bonded to silicon layer  1912  by a compression bonding operation resulting in the two layers being bonded by a silicon oxide layer. Silicon layer  1912  can be configured to provide structural support to base region  1902  and can be about 200 microns or twice as thick as monocrystalline silicon layer  1906 , which can have a thickness of about 100 microns. In some embodiments, silicon layer  1912  can provide a mounting surface to which one or more actuation structures can be affixed. 
       FIG. 19A  also depicts four piezoelectric film actuators  1914  configured to cooperatively maneuver cantilevered beam  1904  in a desired scan pattern. Each of actuators  1914 - 1  and  1914 - 2  can be actuated in the same or different directions to impart different forces upon cantilevered beam  1904 . Since piezoelectric film actuators  1914 - 1  and  1914 - 2  lie substantially in the same plane, an input that causes both of piezoelectric actuators  1914 - 1  and  1914 - 2  to expand longitudinally would induce movement of cantilevered beam  1904  downward, in the −y direction, whereas an input causing piezoelectric film actuators  1914 - 1  and  1914 - 2  to contract longitudinally would induce movement of cantilevered beam  1904  upward in the +y direction. Concurrent actuation of all four of piezoelectric film actuators  1914  could increase the amount of force being exerted upon cantilevered beam  1904 . For example, sending a contraction signal to piezoelectric film actuators  1914 - 1  and  1914 - 2  and an expansion signal to piezoelectric film actuators  1914 - 3  and  1914 - 4  would induce movement of cantilevered beam  1904  upward, in the +y direction. Sending an expansion signal to piezoelectric film actuators  1914 - 1  and  1914 - 3  and a contraction signal to piezoelectric film actuators  1914 - 2  and  1914 - 4  would induce lateral movement of cantilevered beam  1904  in the +x direction while reversing those signals would induce movement of cantilevered beam  1904  laterally in the −x direction. 
       FIG. 19B  shows an alternative configuration for MEMS scanner  1900  in which piezoelectric film actuators  1914 - 5 ,  1914 - 6 ,  1914 - 7  and  1914 - 8  are arranged on lateral surfaces of cantilevered beam  1904 . This configuration has the benefit of placing piezoelectric film actuators  1914 - 5 - 1914 - 8  on a different surface from waveguide  1908 , thereby allowing for piezoelectric actuators  1914  to occupy a larger area of cantilevered beam  1904 . Contraction and expansion inputs can be adjusted to achieve movement of cantilevered beam  1904  in the +x, −x, +y and −y directions. For example, by sending a contraction signal to piezoelectric actuators  1914 - 5  and  1914 - 6  and an expansion signal to piezoelectric film actuators  1914 - 7  and  1914 - 8  movement of cantilevered beam in the +y direction can be achieved. By applying differential signals to piezoelectric actuators  1914  a circular scan pattern of cantilevered beam  1904  can be established. Vertical and horizontal patterns are also possible where a line scan pattern is desired. 
       FIG. 19C  shows another alternative configuration of MEMS scanner  1900  in which piezoelectric film actuators  1914 - 1  and  1914 - 2  are positioned on an upward facing surface of cantilevered beam  1904 . Piezoelectric film actuators  1914 - 1  and  1914 - 2  can maneuver cantilevered beam  1904  in +x, −x, −y and +y directions and consequently are able to drive cantilevered beam  1904  in single axis or circular scan patterns as discussed above. For example, supplying a contraction signal/input to piezoelectric film actuator  1914 - 1  and an expansion signal/input to piezoelectric film actuator  1914 - 2  moves cantilevered beam  1904  laterally in the +x direction. 
     It should be noted that piezoelectric actuators  1914  can be controlled in accordance with the control methods described in conjunction with  FIGS. 12-13 . In some embodiments, strain gauge(s) positioned on or adjacent to cantilevered beam  1904  can be configured to track movement of cantilevered beam  1904  and can provide feedback for the previously described control methods. 
       FIGS. 20A-20B  show perspective views of an optical scanner having a tapered cantilevered member according to an embodiment of the present invention.  FIGS. 20A-20B  illustrate two perspective views of an optical scanner  2000  from two slightly different viewing angles. As shown in  FIGS. 20A-20B , optical scanner  2000  is similar to optical scanner  1900  of  FIGS. 19A-19C . One notable difference is that optical scanner  2000  has a tapered cantilevered member, also referred to as a cantilevered beam. It should be noted that the tapered architecture illustrated in  FIG. 20A  is applicable to the other cantilevered beams discussed throughout this specification and illustrated in the drawings. Thus, although some embodiments of the present invention are illustrating using rectangular or parallelepiped geometrical structures, modification of these structures to incorporate one or more tapered cantilevered beams is included within the scope of the present invention. Therefore, it will be appreciated that the tapered cantilever architecture illustrated in  FIG. 20A  is applicable to a variety of the other cantilever architectures discussed herein. 
     In some embodiments, optical scanner  2000  can be formed using silicon-based MEMS technology, for example, in a silicon-on-insulator substrate. As shown in  FIGS. 20A-20B , optical scanner  2000  includes a base region  2002 , which can include a first silicon layer  2006  and a second silicon layer  2012 . In some embodiments, the first silicon layer  2006  can be a single crystalline silicon layer. Optical scanner  2000  also includes a cantilevered beam  2004  formed in an extended portion of the first silicon layer  2006 . In some embodiments, the monocrystalline silicon portion of base region  2002  and cantilevered beam  2004  can be about  100  microns thick, thereby allowing for deflection of cantilevered beam  2004  during operation of MEMS optical scanner  2000 . A waveguide (not shown in  FIGS. 20A-20B , but similar to waveguide  1908  in  FIGS. 19A-19C ) can be formed along an upper surface of base region  2002  and cantilevered beam  2004 . The cantilevered beam  2004  and the associated waveguide can be referred to as a cantilevered optical member. In some embodiments, light can be received by the waveguide from laser diodes  2009 - 1 ,  2009 - 2  and  2009 - 3 , which are secured to a surface of monocrystalline silicon  2006 . In some embodiments, laser diodes  2009 - 1  can be a red laser diode, laser diode  2009 - 2  can be a blue laser diode, and laser diode  2009 - 3  can be a green laser diode. In some embodiments, additional laser diodes could be added to allow for a larger variety of colors to be produced and propagated through the waveguide by mixing light generated by two or more of laser diodes  2009 . Base region  2002  can be affixed to a support structure along the lines of mechanical support structure  204  in  FIG. 2  to secure optical scanner  2000  in place and to align a distal end of the cantilevered beam with additional optics for propagating the light released from the distal end of the waveguide. 
     The second layer of silicon  2012  of base region  2002  can be coupled to the first silicon layer  2006 . In some embodiments, the first silicon layer  2006  can be bonded to the second silicon layer  2012  by a compression bonding operation resulting in the two layers being bonded by a silicon oxide layer. The second silicon layer  2012  can be configured to provide structural support to base region  2002  and can be about 200 microns or twice as thick as monocrystalline silicon layer  2006 , which can have a thickness of about 100 microns. In some embodiments, the second silicon layer  2012  can provide a mounting surface to which one or more actuation structures can be affixed. 
     Optical scanner  2000  can also have a transducer assembly including one or more piezoelectric film actuators configured to cooperatively maneuver cantilevered beam  2004  in a desired scan pattern. As shown in  FIGS. 20A-20B , piezoelectric film actuator  2014  lies substantially in a top plane of cantilevered beam  2004 , a voltage input that causes piezoelectric actuator  2014  to expand longitudinally would induce movement of cantilevered beam  2004  downward, in the −y direction, whereas a voltage input causing piezoelectric film actuator  2014  to contract longitudinally would induce movement of cantilevered beam  2004  upward in the +y direction. Therefore, cantilevered beam  2004  is configured to scan in a vertical direction, as shown in  FIG. 20A  in the −y direction and the +y direction. In some embodiments, a second piezoelectric film actuator can be formed on a bottom surface of cantilevered beam  2004  to enhance the scanning motion. 
     As shown in  FIGS. 20A-20B , cantilevered beam  2004  has a tapered shape or a triangular shape, with a proximal end  2021  adjacent to the base portion  2002  and a distal end  2022  at a tip region of the cantilevered beam  2004 . In the taper or triangular cantilevered beam  2004 , the distal end  2022  is narrower than the proximal end  2021 . In some embodiments, the size of distal end  2022  can be selected according to the cross-sectional dimension of the waveguide. In some embodiments, cantilevered beam  2004  can have a length from 1000-4000 microns, a base width between 300-1000 um, and a thickness between 50-150 um. An advantage of the tapered cantilevered beam is that the narrower tip region enables the cantilevered beam to have a greater deflection at a given frequency over a non-tapered cantilever. 
       FIGS. 21A-21B  show two top views of an optical scanner having a tapered cantilevered member according to an embodiment of the present invention.  FIG. 21C  shows a cross-sectional view of an optical scanner having a tapered cantilevered member according to an embodiment of the present invention. 
       FIG. 21D  shows a perspective view of a portion an optical scanner having a tapered cantilevered member according to an embodiment of the present invention. As shown in  FIG. 21D , a portion of optical scanner  2100  includes a base region  2102  and a cantilevered beam  2104 . Optical scanner  2100  also includes a piezoelectric film actuator  2114  disposed substantially in a top plane of cantilevered beam  2104 . Piezoelectric film actuator  2114  includes a piezoelectric layer  2114 - 1  sandwiched between a top electrode  2114 - 2  and a bottom electrode  2114 - 3 . In some embodiments, piezoelectric layer  2114 - 1  can be a PZT (lead zirconate titanate) layer, top electrode  2114 - 2  can be a gold layer, and bottom electrode  2114 - 3  can be a platinum layer or a conductive metal oxide, such as SrRuO 3 . Further, a first conductive connector  2131  is connected to the top electrode  2114 - 2  through a wire bond  2133 , and a second conductive connector  2132  is connected to the bottom electrode  2114 - 3 . Depending on the voltage applied between the top electrode and the bottom electrode, cantilevered beam  2104  can be made to deflect upward or downward, and to scan in a vertical direction. 
       FIG. 22  shows a perspective view of an optical scanner having a wide cantilevered member according to an embodiment of the present invention. As shown in  FIG. 22 , optical scanner  2200  is similar to the optical scanners described above in connection to  FIGS. 19A-19C, 20A-20B, and 21A-21D . One notable difference is that optical scanner  2200  has a cantilevered member, or cantilevered beam, having an elongated width that can accommodate multiple waveguides. The cantilevered beam can also be referred to as a multi-waveguide cantilevered beam. 
     As shown in  FIG. 22 , optical scanner  2200  includes a base region  2202  and a cantilevered beam  2204 . Optical scanner  2200  also includes a transducer assembly  2214  that can include one or more piezoelectric film actuators. In  FIG. 22 , a first piezoelectric film actuator  2214 - 1  is disposed substantially in a top plane of cantilevered beam  2204 , and a second piezoelectric film actuator  2214 - 2  is disposed substantially in a bottom plane of cantilevered beam  2204 . With proper bias voltages, piezoelectric film actuators  2214  enables cantilevered beam  2204  to deflect or scan in the x-y plane to form a one-dimensional optical scanner. 
     As shown in  FIG. 22 , cantilevered beam  2204  has a thickness T and an elongated width W. In some embodiments, the width W is greater than the thickness T. Cantilevered beam  2204  is configured to carry multiple waveguides  2208  and to provide a one-dimensional scan of multiple output beams  2229 . The cantilevered beam  2204  and the associated waveguides  2208  can be referred to as a cantilevered optical member. The thickness T and width W can be selected to accommodate the number of waveguides needed for a particular application. For example, cantilevered beam  2204  can be configured to support 2-1,000 waveguides In some embodiments, cantilevered beam  2204  can have a thickness between 5-50 microns and a width between 300-3,000 microns. 
       FIG. 23  shows a perspective view of two serially coupled optical scanners having cantilevered members according to an embodiment of the present invention. As shown in  FIG. 23 , optical scanner  2300  includes a first optical scanner  2310  and a second optical scanner  2320 . Both first optical scanner  2310  and second optical scanner  2320  are one-dimensional optical scanners, and they are optically coupled in series to form optical scanner  2300 , which is a two-dimensional optical scanner. 
     The first optical scanner  2310  is similar in structure to the optical scanners described above in connection to  FIGS. 19A-19C, 20A-20B , and/or  21 A- 21 D. The first optical scanner  2310  includes a base region  2312  and a cantilevered beam  2314 . Optical scanner  2310  also has a transducer assembly  2317  that includes one or more piezoelectric film actuators. In  FIG. 23 , a first piezoelectric film actuator  2317 - 1  is disposed substantially on one side wall of cantilevered beam  2314 , and a second piezoelectric film actuator  2317 - 2  is disposed substantially on an opposite sidewall of cantilevered beam  2314 . With proper bias voltages, transducer assembly  2317  enables cantilevered beam  2314  to deflect or scan in the x-z plane to form a one-dimensional optical scanner. In the embodiment of  FIG. 23 , optical scanner  2310  includes a single waveguide  2318  for receiving an input light beam and projecting a scanning output light beam  2319 . The cantilevered beam  2314  and the associated waveguides  2318  can be referred to as a first cantilevered optical member. 
     The second optical scanner  2320  is similar to optical scanner  2200  of  FIG. 22 . As shown in  FIG. 23 , the second optical scanner  2320  includes a base region  2322  and a cantilevered beam  2324 . Optical scanner  2320  also has a transducer assembly  2327  that includes one or more piezoelectric film actuators. In  FIG. 23 , a first piezoelectric film actuator  2327 - 1  is disposed substantially in a top plane of cantilevered beam  2324 , and a second piezoelectric film actuator  2327 - 2  is disposed substantially in a bottom plane of cantilevered beam  2324 . In this configuration, both the first piezoelectric film actuator  2327 - 1  and second piezoelectric film actuator  2327 - 2  are parallel to the first plane (the x-z plane) and orthogonal to the second plane (the x-y plane). With proper bias voltages, transducer assembly  2327  enables cantilevered beam  2324  to deflect or scan in the x-y plane to form a one-dimensional optical scanner. Similar to cantilevered beam  2204  in optical scanner  2200  in  FIG. 22 , cantilevered beam  2324  has a width W that is greater than its thickness T. Cantilevered beam  2324  is configured to include multiple waveguides  2328  that extend through the base portion  2322  and to provide a one-dimensional scan of multiple output light beams  2329 . The cantilevered beam  2324  and the associated waveguides  2328  can be referred to as a second cantilevered optical member. The thickness T and width W can be selected to accommodate the number of waveguides needed for a particular application. 
     As shown in  FIG. 23 , the output light beam  2319  from first optical scanner  2310  is optically coupled to an input port of second optical scanner  2320 . Optical scanner  2310  scans in a first direction, and optical scanner  2320  scans in a second direction that is orthogonal to the first direction. Therefore, the output light beam  2319  from optical scanner  2310  is coupled to the multiple waveguides in optical scanner  2320  in a time-sequential manner. In this configuration, the first optical scanner  2310  provides a much faster horizontal scan (in the x-z plane) than a vertical scan (in the x-y plane) provided by the second optical scanner  2320 . Thus, the two-dimensional optical scanner  2300  can be configured to produce a raster scan using two one-dimensional optical scanners. 
       FIG. 24  shows a perspective view of two serially coupled optical scanners having cantilevered members according to an alternative embodiment of the present invention. As shown in  FIG. 24 , two-dimensional optical scanner  2400  includes a first optical scanner  2410  and a second optical scanner  2420 . The first optical scanner  2410  is similar to optical scanner  2310  in  FIG. 23  and the second optical scanner  2420  is similar to optical scanner  2320  in  FIG. 23 . Both first optical scanner  2410  and second optical scanner  2420  are one-dimensional optical scanners, but provide scans in two orthogonal planes, the x-z plane and the x-y plane, respectively. They are optically coupled in series to form two-dimensional optical scanner  2400 . The first optical scanner  2410  provides a one-dimensional scan of a single light beam, and the second optical scanner  2420  receives the output light beam from the first optical scanner  2410  and provides a one-dimensional scan of multiple light beams. The first optical scanner  2410  has a base portion  2412  and a cantilevered beam  2414 . The second optical scanner  2420  has a base portion  2422  and a cantilevered beam  2424 . In this configuration, the first optical scanner  2410  provides a much faster horizontal scan (in a first plane, the x-z plane) than a vertical scan (in a second plane, the x-y plane) provided by the second optical scanner  2420 . Two-dimensional optical scanner  2400  can be configured to produce a raster scan using two one-dimensional optical scanners. Optical scanner  2400  is similar to optical scanner  2300  in  FIG. 23 . Therefore, similar components and functions are omitted here. 
     It is noted that the base region  2422  of the second optical scanner  2420  includes a curved section  2431  having a contour that tracks the trajectory of the tip region of cantilevered beam  2414  in optical scanner  2410  to improve the coupling between the waveguide optical scanners  2410  and  2420 . In some embodiments, the distance between the tip of cantilevered beam  2414  in optical scanner  2410  and the input port of optical scanner  2420  is kept constant and small, for example, between 5 nm to 400 nm. 
       FIG. 25  shows an embodiment in which an optical scanner  2500  includes a flat electromagnetic coil  2502  that interacts with a permanent magnet  2504  mounted adjacent to electromagnetic coil  2502  to generate vertical oscillation of a pivoting portion  2506  of a cantilevered beam assembly  2508 . Routing modulated current through electromagnetic coil  2502  generates a shifting magnetic field that interacts with a magnetic field emitted by permanent magnet  2504  to induce oscillation of pivoting portion  2506  about an axis extending through both pivoting portions  2506 . A rate at which the current is modulated within electromagnetic coil  2502  can be set to achieve a desired rate of rotation of pivoting portion  2506  of cantilevered beam assembly  2508  relative to a stationary portion  2512  of optical scanner  2500  about axis of rotation  2514 . Pivoting portion  2506  and stationary portion  2512  can have a thickness of about  100  microns, in some embodiments. The shape of electromagnetic coil  2502  can have a rectangular geometry that matches the shape of a region of pivoting portion  2506  in order to maximize an area across which electromagnetic coil  2502  extends. In some embodiments, spreading electromagnetic coil  2502  over a larger area in this manner allows for a stronger and/or more efficient magnetic field to be generated by electromagnetic coil  2502 . It should be appreciated that the shape of electromagnetic coil  2502  can vary widely to match any desired shape of pivoting portion  2506 . For example, circular, polygonal, and elliptical geometries of electromagnetic coil  2502  are also possible. 
       FIG. 25  also shows how the rotation of pivoting portion  2506  can be defined by flexures  2516 , which connect pivoting portion  2506  to stationary portion  2512 . Flexures  2516  can be sized to accommodate a desired amount of rotation of pivoting portion  2506 . Flexures  2516  can be configured to establish a pathway across which one or more electrically conductive pathways is able to transmit power to energize laser diodes  2518 , which generate light that is transmitted to cantilevered beam  2510  via waveguide  2519 . In addition to helping transmit light, one or both of flexures  2516  can be configured to accommodate an electrically conductive pathway configured to carry electricity for powering electromagnetic coil  2502  and piezoelectric film actuators  2520 - 1  and  2520 - 2  arranged in a configuration similar to the one depicted in  FIG. 19C . Piezoelectric film actuators  2520  can be configured to maneuver cantilevered beam  2510  in a direction  2522  in a plane parallel to pivoting portion  2506  by providing differential inputs into piezoelectric film actuators  2520 - 1  and  2520 - 2 . In this way, piezoelectric actuators can be configured to induce horizontal movement of cantilevered beam  2510  and the combination of electrically conductive coil  2502  and permanent magnet  2504  can maneuver cantilevered beam  2510  vertically. This configuration provides a much faster horizontal scan than a vertical scan, which works well to produce a raster scan. 
     Optical scanner  2500  could also be configured to produce a circular scan, and this would allow optical scanner  2500  to be able to switch between different scan patterns. Switching between scan modes can be beneficial where a particular operating mode has more content toward a central region of its display than a peripheral region, as a circular scan is able to focus more light in a central region than out toward its periphery, while a raster scan is better suited for an even distribution of light across a display. 
     In some embodiments, optical scanner  2500  could also be configured to produce a circular scan use both magnetic and piezoelectric actuations as described above. In these embodiments, the position of the base of the piezoelectric-driven cantilever is made co-incident with the axis of rotation  2514 , through the torsion bars or flexures  2516 , of the magnetically driven base, so that the tip of the cantilever, in its deflection, traces out a spherical path with substantially the same radius of curvature in X and Y. In some embodiments, the position of the base of the cantilever is located such that the X and Y radius of curvature are the same, as depending on the bending mechanics/curvature of the piezo driven cantilever, its base may need to be different from the axis of rotation of the magnetically driven base to achieve equal radius of curvature of the tip motion. 
     In some embodiments, optical scanner  2500  could also be configured to produce a circular scan as described in the configuration accompanying  FIG. 19C . In these embodiments, to transition to a circular scan pattern, pivoting portion  2506  could include a locking mechanism that prevents movement of pivoting portion  2506  relative to stationary portion  2512 . While performing the circular scan, no current would need to be circulated through electrically conductive coil  2502 . In this way, horizontal and vertical motion of cantilevered beam  2510  could be induced by piezoelectric film actuators  2520 - 1  and  2520 - 2 . 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of specific embodiments are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the described embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.