PATENT DOCUMENT

Publication Number: US-10025154-B2
Application Number: US-201514794654-A
Country: US
Kind Code: B2

Title: Camera lens filter

Abstract:
An electrically activated lens filter with an electro-optic portion having a radially and circumferentially symmetric electric field gradient is disclosed. More particularly, embodiments of the lens filter include an electro-optic portion having one or more conductive plugs arranged around a center region such that an electric field within the electro-optic portion varies from a maximum at an outer rim to a minimum outside of the center region. The lens filter may include a plurality of front electrodes and rear electrodes accessible in an axial direction for electrically activating front and rear transparent conductive layers, respectively.

Claims:
What is claimed is: 
     
       1. A lens filter, comprising:
 a front transparent conductive layer; 
 a rear transparent conductive layer having an outer region surrounding a perimeter of a center region; 
 an electrochromic layer between the front transparent conductive layer and the rear transparent conductive layer; and 
 one or more conductive plugs arranged along the perimeter at a plurality of points around the center region, each conductive plug extending across the electrochromic layer to provide an electrical short path from the front transparent conductive layer to the rear transparent conductive layer, wherein the electrical short path surrounds the center region such that application of an electrical potential to the front and rear transparent conductive layers in the outer region generates a non-zero electrical potential difference across the electrochromic layer in the outer region and generates zero electrical potential difference across the electrochromic layer in the center region. 
 
     
     
       2. The lens filter of  claim 1 , wherein each conductive plug directly connects the front transparent conductive layer with the rear transparent conductive layer, and wherein each conductive plug creates an electrical short between the front transparent conductive layer and the rear transparent conductive layer. 
     
     
       3. The lens filter of  claim 2 , wherein a plurality of front electrodes along an outer rim of the front transparent conductive layer are separated from a plurality of rear electrodes along an outer rim of the rear transparent conductive layer such that application of the electrical potential to the front electrodes and the rear electrodes generates a radially symmetric electric field gradient in the electrochromic layer from a maximum electrical potential difference across the electrochromic layer at the outer rims to the zero electrical potential difference across the electrochromic layer at the perimeter. 
     
     
       4. The lens filter of  claim 3 , wherein the perimeter is circular. 
     
     
       5. The lens filter of  claim 4 , wherein the front transparent conductive layer and the electrochromic layer extend over the center region. 
     
     
       6. The lens filter of  claim 5 , wherein the electrochromic layer includes a trench along the perimeter, and wherein the one or more conductive plugs include a conductive filler in the trench. 
     
     
       7. The lens filter of  claim 6 , wherein the trench is a continuous trench along the entire perimeter. 
     
     
       8. The lens filter of  claim 7 , wherein the trench extends in an axial direction through the front transparent conductive layer and the electrochromic layer to the rear transparent conductive layer. 
     
     
       9. The lens filter of  claim 4 , wherein the center region is exposed in an axial direction through the front transparent conductive layer and the electrochromic layer. 
     
     
       10. The lens filter of  claim 9 , wherein the front transparent conductive layer and the one or more conductive plugs are contiguous. 
     
     
       11. The lens filter of  claim 4 , wherein the one or more conductive plugs include a set of electrical vias arranged along the perimeter. 
     
     
       12. A lens filter, comprising:
 a front transparent conductive layer having a plurality of front electrodes arranged along an outer rim of the front transparent conductive layer, wherein the plurality of front electrodes are separated along the outer rim by a plurality of circumferential gaps; 
 a rear transparent conductive layer having an outer region surrounding a perimeter of a center region, wherein the rear transparent conductive layer has a plurality of rear electrodes arranged along an outer rim of the rear transparent conductive layer, and wherein the plurality of rear electrodes are exposed in an axial direction through the plurality of circumferential gaps; 
 an electrochromic layer between the front transparent conductive layer and the rear transparent conductive layer; and 
 one or more conductive plugs arranged along the perimeter at a plurality of points around the center region, each conductive plug directly connecting the front transparent conductive layer with the rear transparent conductive layer across the electrochromic layer to provide an electrical short path surrounding the center region such that application of an electrical potential to the front and rear electrodes in the outer region generates a non-zero potential difference across the electrochromic layer in the outer region and generates zero electrical potential difference across the electrochromic layer in the center region. 
 
     
     
       13. The lens filter of  claim 12 , wherein the plurality of front electrodes and the plurality of rear electrodes are distributed evenly along the respective outer rims and are arranged circumferentially about a same diameter. 
     
     
       14. The lens filter of  claim 13 , wherein the plurality of front electrodes includes at least four front electrodes. 
     
     
       15. The lens filter of  claim 14 , wherein the plurality of circumferential gaps include a plurality of holes extending in an axial direction through the front transparent conductive layer and the electrochromic layer to the rear transparent conductive layer. 
     
     
       16. A portable consumer electronics device, comprising:
 a device housing; and 
 a camera module integrated in the device housing, the camera module having an imaging sensor configured to receive light from a scene through a lens filter, wherein the lens filter includes:
 a front transparent conductive layer; 
 a rear transparent conductive layer having an outer region surrounding a perimeter of a center region; 
 an electrochromic layer between the front transparent conductive layer and the rear transparent conductive layer; and 
 one or more conductive plugs arranged along the perimeter at a plurality of points around the center region, each conductive plug extending across the electrochromic layer to provide an electrical short path from the front transparent conductive layer to the rear transparent conductive layer, wherein the electrical short path surrounds the center region such that application of an electrical potential to the front and rear transparent conductive layers in the outer region generates a non-zero electrical potential difference across the electrochromic layer in the outer region and generates zero electrical potential difference across the electrochromic layer in the center region. 
 
 
     
     
       17. The portable consumer electronics device of  claim 16 , wherein each conductive plug directly connects the front transparent conductive layer with the rear transparent conductive layer, and wherein each conductive plug creates an electrical short between the front transparent conductive layer and the rear transparent conductive layer. 
     
     
       18. The portable consumer electronics device of  claim 17  further comprising:
 a plurality of front electrodes arranged along an outer rim of the front transparent conductive layer; 
 a plurality of rear electrodes arranged along an outer rim of the rear transparent conductive layer; and 
 a driver circuit configured to apply the electrical potential to the front electrodes and the rear electrodes to generate a radially symmetric electric field gradient in the electrochromic layer that decreases from a maximum electrical potential difference across the electrochromic layer at the outer rims to zero electrical potential difference across the electrochromic layer at the perimeter. 
 
     
     
       19. The portable consumer electronics device of  claim 18 , wherein the front transparent conductive layer and the electrochromic layer extend over the center region. 
     
     
       20. The portable consumer electronics device of  claim 18 , wherein the center region is exposed in an axial direction through the front transparent conductive layer and the electrochromic layer.

Description:
This application claims the benefit of U.S. Provisional Patent Application No. 62/055,227, filed Sep. 25, 2014, and this application hereby incorporates herein by reference that provisional patent application. 
    
    
     BACKGROUND 
     Field 
     Embodiments related to an electrically activated lens filter with an electro-optic portion having an electric field gradient with radial and circumferential symmetry are disclosed. More particularly, an embodiment related to a lens filter that may be integrated in a camera module to provide an aperture stop, is disclosed. 
     Background Information 
     Camera modules have been incorporated in a variety of consumer electronics devices, including mobile devices such as smart phones, mobile audio players, personal digital assistants, and other portable and desktop computers. A typical camera module includes an optical system used to collect and transmit light from an imaged scene to an imaging sensor. The optical system generally includes at least one lens associated with one aperture stop. The lens collects and transmits light. The aperture stop limits the light collected and includes an aperture through which light is transmitted. The aperture is therefore termed the stop aperture, or alternatively, the camera pupil. The effective diameter of the stop aperture combined with the lens focal length determines the “F number” of the lens. A lens with a lower F number produces a brighter image than a lens with a larger F number and, as a result, reduces the image noise in a low light scene. However, as the F number is reduced, the lens depth of field decreases and, as a result, lens aberrations increase. Thus, there is an optimal aperture size, dependent on the lens and the scene being imaged, to minimize image noise and maximize image resolution. 
     In most portable consumer electronics devices, minimizing device profile is an important design goal. Accordingly, device profile limitations generally prohibit the use of an iris diaphragm as a variable aperture stop. Another way to control the amount of light admitted through the lens to balance image brightness and resolution is to use an electro-optic aperture. Such devices may be sized to fit within the space constraints of portable consumer electronics devices. An electro-optic aperture may include an electro-chromic (EC) medium that attenuates light that is passing through the aperture, in response to a voltage being applied to a pair of transparent conductive layers that sandwich the EC medium. One of the transparent conductive layers may be patterned to include a void in a central portion, so as to form a ring-like aperture stop with an inner aperture area that remains transparent when the EC medium is energized and an outer stop that becomes dark, thereby yielding in effect a smaller pupil size. With this approach, the patterned transparent conductive layer creates a radially uniform electric field in the EC medium, and thus, uniform opacity across the outer stop area of the ring-like aperture stop. Since voltage may be applied at a single location around a circumference of each transparent conductive layer, the electric field may vary substantially in a circumferential direction, with a maximum field located at a point of contact and a minimum field located opposite from the point of contact. This electric field, which may be radially uniform (no-gradient from an outer edge to a center location) and circumferentially non-symmetric (no symmetry and/or uniformity of an electric field about a central axis) may generate opacity with a “top hat” light transmission profile, such that light transmission drops off sharply between the aperture and the stop regions, and varies in a circumferential direction. 
     SUMMARY 
     Lens filters having an electro-optic portion with an electric field gradient that is radially and circumferentially symmetric, particularly for use in portable consumer electronics device applications, are disclosed. In an embodiment, a lens filter includes a front transparent conductive layer, a rear transparent conductive layer having a center region with a circular perimeter, and an electrochromic layer between the front transparent conductive layer and the rear transparent conductive layer. One or more conductive plugs may be arranged along the perimeter, and each conductive plug may extend across the electrochromic layer from the front transparent conductive layer to the rear transparent conductive layer. For example, the electrochromic layer may include a continuous trench along the entire perimeter that is filled by a conductive filler to form a conductive plug. Accordingly, each conductive plug may directly connect the front transparent conductive layer with the rear transparent conductive layer in an axial direction across the electrochromic layer. The conductive plugs may have substantially zero electrical resistivity to create an electrical short around the perimeter. Accordingly, when an electrical potential difference is applied between several front electrodes and rear electrodes that are arranged along an outer rim of the lens filter, a radially symmetric electric field gradient may be generated in the electrochromic layer that varies from a maximum electrical potential difference at the outer rim to zero electrical potential difference at the perimeter. Since the area within the perimeter does not support an electric field, the center region within the perimeter may remain transparent during electrical activation. The conductive plugs may be formed in various manners, including as continuous or discontinuous plugs, e.g., as a set of electrical vias arranged along the perimeter. Furthermore, the conductive plugs may be formed from various materials, e.g., the front conductive layer and the one or more conductive plugs may be contiguously formed. 
     In an embodiment, a lens filter includes a front transparent conductive layer having several front electrodes arranged along an outer rim and separated from one another by several circumferential gaps. The lens filter may include a rear transparent conductive layer having several rear electrodes arranged along an outer rim, and exposed in an axial direction through circumferential gaps in the front transparent conductive layer. The front transparent conductive layer and the rear transparent conductive layer may be separated by an electrochromic layer, and one or more conductive plugs may directly connect the front transparent conductive layer and the rear transparent conductive layer across the electrochromic layer. More particularly, the conductive plugs may be arranged around a center region of the rear transparent conductive layer. In an embodiment, the front electrodes and the rear electrodes are distributed evenly along the outer rims and/or are arranged circumferentially about a same diameter such that electrical activation of the electrodes generates a circumferentially symmetric electric field within the electrochromic layer. For example, there may be at least four front electrodes and as many rear electrodes distributed evenly around the lens filter rim. 
     In other embodiments, a portable consumer electronics device including one or more of the lens filters described above may include, in addition to the lens filter(s), a device housing and a camera module integrated in the device housing. The camera module may include an imaging sensor configured to receive light from a scene through the lens filter. Furthermore, the portable consumer electronics device may include a driver circuit configured to apply an electrical potential difference between the front electrodes and the rear electrodes of the lens filter to generate a radially and circumferentially symmetric electric field gradient with a correspondingly symmetric light transmittance profile. 
     The above summary does not include an exhaustive list of all aspects of the present invention. It is contemplated that the invention includes all systems and methods that can be practiced from all suitable combinations of the various aspects summarized above, as well as those disclosed in the Detailed Description below and particularly pointed out in the claims filed with the application. Such combinations have particular advantages not specifically recited in the above summary. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a pictorial view of a portable consumer electronics device being used in accordance with an embodiment. 
         FIG. 2  is a block diagram of camera-related elements and associated electronics circuitry in a portable consumer electronics device in accordance with an embodiment. 
         FIG. 3  is a cutaway view of a lens filter of a camera module integrated in a device housing of a portable consumer electronics device in accordance with an embodiment. 
         FIG. 4  is a perspective view of a lens filter having an electric field gradient with radial and circumferential symmetry in accordance with an embodiment. 
         FIG. 5  is a cross-sectional view of a lens filter having an electric field gradient with radial and circumferential symmetry in accordance with an embodiment. 
         FIG. 6  is a graph showing a radially symmetric electric field gradient of a lens filter in accordance with an embodiment. 
         FIGS. 7A-7B  are front views of a lens filter having an electric field gradient with radial and circumferential symmetry before and after electrical activation in accordance with an embodiment. 
         FIG. 8  is a graph showing a light transmittance profile for a lens filter in accordance with an embodiment. 
         FIG. 9  is a partial perspective view of an aperture region of a lens filter having a continuous conductive plug around a transparent center region in accordance with an embodiment. 
         FIG. 10  is a partial perspective view of an aperture region of a lens filter having a plurality of conductive plug vias arranged circumferentially around a transparent center region in accordance with an embodiment. 
         FIGS. 11A-11C  are cross-sectional views, taken about line A-A of  FIG. 4 , showing an aperture region of a lens filter in accordance with several embodiments. 
         FIGS. 12A-12B  are partial front views of a plurality of segmented electrodes arranged along an outer rim of a lens filter in accordance with several embodiments. 
         FIG. 13  is a cross-sectional view, taken about line B-B of  FIG. 12A , of a front electrode of a lens filter in accordance with an embodiment. 
         FIGS. 14A-14B  are cross-sectional views, taken about line C-C of  FIG. 12A , of a rear electrode of a lens filter in accordance with several embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments describe lens filters having an electro-optic portion with a radially and circumferentially symmetric electric field gradient, particularly for use in portable consumer electronics device applications. However, while some embodiments are described with specific regard to integration within mobile electronics device, the embodiments are not so limited and certain embodiments may also be applicable to other uses. For example, a lens filter as described below may be incorporated into a camera module that remains at a fixed location, e.g., a traffic camera, or used in a relatively stationary application, e.g., in a desktop computer, or a motor vehicle. 
     In various embodiments, description is made with reference to the figures. However, certain embodiments may be practiced without one or more of these specific details, or in combination with other known methods and configurations. In the following description, numerous specific details are set forth, such as specific configurations, dimensions, and processes, in order to provide a thorough understanding of the embodiments. In other instances, well-known processes and manufacturing techniques have not been described in particular detail in order to not unnecessarily obscure the description. Reference throughout this specification to “one embodiment,” “an embodiment”, or the like, means that a particular feature, structure, configuration, or characteristic described is included in at least one embodiment. Thus, the appearance of the phrase “one embodiment,” “an embodiment”, or the like, in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, configurations, or characteristics may be combined in any suitable manner in one or more embodiments. 
     The use of relative terms throughout the description, such as “front” and “rear” may denote a relative position or direction. For example, a “front face” may be directed in a first axial direction and a “rear face” may be directed in a second direction opposite to the first axial direction. However, such terms are not intended to limit the use of a lens filter to a specific configuration described in the various embodiments below. For example, a front face of a lens filter may be directed in any direction with respect to an external environment, including toward an external device housing or toward an imaging sensor within the device housing. Similarly, the terms “front” and “rear” are not intended to be limiting of a direction along which light may pass through a lens filter, since in various embodiments, light may pass through an aperture of a lens filter in either a rearward direction, e.g., through a front face, or in a frontward direction, e.g., through a rear face. 
     In an aspect, a lens filter includes an electro-optic portion with a radially symmetric electric field gradient such that filter opacity, which varies with electric field, gradually decreases from an outer rim of the lens filter to an aperture region on either side of a central optical axis. The aperture region may include one or more conductive plugs that directly connects a front transparent conductive layer with a rear transparent conductive layer such that an electrical short is created. Furthermore, the electrical short may be continuous and surround a central region of a predetermined diameter to form the stop aperture. As a result, the area within the central region has no electrical potential difference and remains transparent, while the area outside of the continuous short path exhibits opacity that increases from the conductive plug toward an outer rim of the lens filter. Thus, the lens filter transmits light in a manner that transitions smoothly from a maximum to a minimum intensity in a radially symmetric manner. 
     In an aspect, a lens filter includes a plurality of segmented electrodes (or electrode segments) arranged along an outer rim of a front conductive layer and a rear conductive layer of a lens filter to apply voltage to an electro-optic portion and generate a circumferentially symmetric electric field gradient. The electrodes (or electrode segments) of a respective conductive layer may be distributed evenly around the respective outer rim of the conductive layer, and electrodes of one conductive layer may not overlap with electrodes of another conductive layer. Thus, application of a voltage to these electrodes creates an electric field that is regularly arranged and distributed around a central optical axis. Furthermore, in an embodiment, all of the electrodes (on both of the conductive layers) may be exposed in an axial direction to allow all electrodes to be accessed from the same side of the lens filter. 
     Referring to  FIG. 1 , a pictorial view of a portable consumer electronics device is shown being used in accordance with an embodiment. In this example, the portable consumer electronics device  100  is a smart phone having a device housing  102  with a front face that is up against an ear of the user during a phone call. A rear face of the device housing  102  may have an opening through which a camera module  104  is visible. Camera module  104  may enable photographic functionality for the smart phone. In other embodiments, camera module  104  may be integrated within other portable and non-portable consumer electronics devices, e.g., tablet computers, laptop or notebook computers, and/or other devices that can benefit from a low-profile lens filter having an electrically variable aperture. 
     Referring to  FIG. 2 , a block diagram of camera-related elements and associated electronics circuitry in a portable consumer electronics device is shown in accordance with an embodiment. Additional functionality may be implemented in portable consumer electronics device  100 , e.g., communication network interfaces, display screens, touch screens, keyboards, and audio transducers; for conciseness, however, such functionality is not described further here. In an embodiment, camera module  104  includes an optical system having an imaging sensor  200 , a focusing lens  202 , and a lens filter  204 . These optical elements may be aligned along an optical axis  206 . In an embodiment, a mirror or other optical deflector allows one or more of the optical elements to be positioned off of a straight line. Nevertheless, the optical elements may still be considered “aligned along the optical axis” given that light  208  would propagate along optical axis  206  from a scene being imaged through lens filter  204  and focusing lens  202  to imaging sensor  200 . 
     Imaging sensor  200  may be any conventional solid-state imaging sensor such as a complementary metal oxide semiconductor (CMOS) sensor chip, which presents an interface to an exposure controller  210  to receive certain parameters for determining an exposure for taking a picture. The sensor parameters may include pixel integration time, which may be set by exposure controller  210  in accordance with any suitable exposure control algorithm that considers various input variables, e.g., levels of scene illumination and the availability of a flash or strobe illumination. Exposure controller  210  may automatically perform the algorithm to determine an appropriate exposure setting for signal imaging sensor  200  to update its parameters in response to a manual shutter release  212  command, e.g., in response to a mechanical or virtual shutter button being actuated by a user of the device  100 . Exposure controller  210  may be implemented as a programmed processor or as a completely hardwired logic state machine together with stored parameter options. Once a digital image has been captured by imaging sensor  200  under the chosen exposure setting, it may be transferred to an image storage  214 , e.g., a solid state volatile or a non-volatile memory, prior to being further processed or analyzed by higher layer camera functions  216  that yield for example a still picture file, e.g., in a JPEG format, or a video file, e.g., in a digital movie format. 
     Focusing lens  202  may include one or more lens elements that serve to collect and focus light  208  from the scene onto imaging sensor  200 , thereby producing an optical image on an active pixel array portion of imaging sensor  200 . Focusing lens  202  may include either a fixed focus optical subsystem, or a variable focus subsystem that implements an autofocus mechanism. There may also be an optical zoom mechanism as part of focusing lens  202 . In the case of an optical zoom lens and/or an auto focus mechanism, additional control parameters relating to lens position can be set by exposure controller  210  for each exposure to be taken. 
     In  FIG. 2 , lens filter  204  is shown as being positioned in front of focusing lens  202 . However, lens filter  204  may be positioned at any suitable location along optical axis  206  in front of imaging sensor  200 , including between focusing lens  202  and imaging sensor  200 . As described below, lens filter  204  includes an electro-active aperture that effectively implements a camera pupil with an electrically variable size, e.g., an aperture diameter. When lens filter  204  is electrically controlled to provide a small or narrow pupil, highly collimated rays are admitted to imaging sensor  200 , resulting in a sharp focus of a captured image. On the other hand, when the lens filter  204  is electrically controlled to provide a large or wide pupil, un-collimated rays are admitted to imaging sensor  200 , resulting in a captured image that is sharp around an object placed in focus by focusing lens  202 , but blurry in other image areas. Thus, lens filter  204  may determine how collimated the admitted rays of light  208  from the imaged scene are, and thus, may affect a bokeh of the captured image. Furthermore, lens filter  204  may determine the amount of incident light  208  admitted to imaging sensor  200 , and thus, may affect a brightness of the captured image. 
     In an embodiment, control of the effective pupil size of lens filter  204  is achieved using an electronic driver circuit  218 , which may receive a control signal or command from exposure controller  210  representing the desired size of the effective pupil. Driver circuit  218  may translate this input command into a drive voltage that is applied to lens filter  204  to generate an internal electric field gradient, and a corresponding light transmittance profile for lens filter  204 , as described below. 
     Referring to  FIG. 3 , a cutaway view of a lens filter of a camera module integrated in a device housing of a portable consumer electronics device is shown in accordance with an embodiment. As described above, lens filter  204  may be located in any appropriate position along optical axis  206 , including in front of, or behind, focusing lens  202 . For example, lens filter  204  may be attached to a rear wall of device housing  102 . The rear wall may be formed from glass, polycarbonate, or another suitable material that transmits light  208  from a scene being imaged through the opening in the rear face of device housing  102 . In an embodiment, camera module  104  may incorporate multiple lens filters  204 , including one lens filter  204  in front of focusing lens  202  and one lens filter  204  behind focusing lens  202 . The lenses and lens filters of camera module  104  may be supported and maintained in alignment by a supporting barrel or frame of camera module  104 . Thus, the optical elements of camera module  104  may be arranged in any manner appropriate to meet the optical requirements and space limitations of portable consumer electronics device  100 . 
     Referring to  FIG. 4 , a perspective view of a lens filter having an electric field gradient with radial and circumferential symmetry is shown in accordance with an embodiment. Lens filter  204  may include a disk-like structure distributed symmetrically about optical axis  206 . For example, lens filter  204  may be generally circular with an aperture region  402  centered on a central optical axis  206 . Aperture region  402  may include a perimeter  404  delineating a boundary between an aperture area within perimeter  404  and an outer region  406 , e.g., a stop area, outside of perimeter  404 . Thus, outer region  406  may extend radially from perimeter  404  to an outer rim  408  of lens filter  204 . Outer rim  408  may be a region encompassing a sidewall of lens filter  204 , and more particularly, outer rim  408  may include an edge of at least one of several layers in a stack making up lens filter  204 . For example, outer rim  408  may include an outer edge of one or more of a transparent conductive layer or an electrochromic layer of lens filter  204 , which are described in more detail below. 
     Along outer rim  408 , several electrodes (or electrode segments) may be distributed, e.g., in a circumferentially symmetric manner, each of which provides an electrical contact through which driver circuit  218  may apply a control signal, e.g., a voltage, between a front transparent conductive layer  414  and a rear transparent conductive layer  416  of lens filter  204 . The transparent conductive layers may be separated electrically, e.g., by an electrochromic layer  418 , between outer rim  408  and perimeter  404 . Thus, in an embodiment, several front electrodes  409  (e.g., formed as portions or segments of the front layer  414 ) and several rear electrodes  410  (e.g., formed as portions or segments of the rear layer  416 ) may be arranged circumferentially along outer rim  408  and separated from each other by electrochromic layer  418  having non-zero electrical resistance. In an embodiment, front electrodes  409  may be positive electrodes electrically connected with front transparent conductive layer  414  and rear electrodes  410  may be negative electrodes electrically connected with rear transparent conductive layer  416 , although such polarities may be reversed in other embodiments. 
     A circumferentially symmetric distribution of electrodes may include distributing the electrodes (or electrode segments) evenly along outer rim  408  so that, in an embodiment, an angle between radial lines extending from optical axis  206  through adjacent electrodes is the same for all adjacent electrodes. For example, in a case in which four electrodes are evenly distributed along outer rim  408 , the angle between each adjacent electrode will be 90 degrees (360 degrees divided by 4). Accordingly, although the electric field may vary in strength between the adjacent electrodes, e.g., being a maximum near each electrode and a minimum half way between the adjacent electrodes, the variation in field strength may be approximately the same between each pair of adjacent electrodes along outer rim  408 . Thus, the electrical field may be considered to be symmetric in a circumferential direction since the electric field variation has a repeating pattern between each pair of adjacent electrodes. 
     In an embodiment, at least two front electrodes  409  may be separated by one or more circumferential gaps  412 . The circumferential gaps  412  may extend axially through front transparent conductive layer  414  and through the electrochromic layer  418 , exposing a front surface of rear transparent conductive layer  416 . Furthermore, a rear electrode  410  may be disposed on this front surface (e.g., the rear electrode  410  may be formed as a portion or segment of the rear conductive layer  416 ). Thus, the front and rear electrodes  409 ,  410  may be visible from a front side of lens filter  204  and therefore accessible from the front side in an axial direction of optical axis  206  by electrical leads or pins (in order to deliver the control signal or voltage V control ). Accordingly, such electrical connectors may be used to apply a voltage V control  between the front and rear transparent conductive layers  414 ,  416 . 
     The front and rear electrodes  410  may be distributed evenly around outer rim  408  such that application of voltage to each electrode results in a circumferentially symmetric electric field about optical axis  206  of lens filter  204 . In particular, as more front and rear electrodes  410  are electrically activated, the electric field distribution will become more uniform and/or evenly distributed about optical axis  206  of lens filter  204  within a given radial boundary. For example, radially inward of circumferential gaps  412 , the electric field may be symmetric and uniform. In an embodiment, there is no circumferential variation in electric field within a diameter of, e.g., about two-thirds of lens filter  204  diameter. That is, the electric field may be substantially the same at any point within a radius from optical axis  206  equal to two-thirds of a distance from optical axis  206  to outer rim  408 . Thus, the optical transmittance profile of lens filter  204  may be circumferentially symmetric and/or uniform over a majority of lens filter  204  front surface area. Accordingly, while there may be as few as two front electrodes  409  separated by two circumferential gaps  412  that expose two rear electrodes  410 , it is contemplated that there may be at least four front electrodes  409  and four rear electrodes  410  to improve circumferential electric field distribution. In an embodiment, as shown in  FIG. 4 , there may be approximately eight front electrodes  409  evenly spaced around outer rim  408  and separated by eight circumferential gaps  412  exposing eight rear electrodes  410  in an axial direction. In other embodiments, there may be even more, e.g., 10-20 front electrodes  409 , circumferential gaps  412 , and rear electrodes  410 . More particularly, any number of electrodes may be chosen to balance the benefit of circumferentially symmetric and/or uniform electric field distribution with the cost of manufacturing lens filter  204 . 
     Referring to  FIG. 5 , a cross-sectional view of a lens filter having an electric field gradient with radial and circumferential symmetry is shown in accordance with an embodiment. Lens filter  204  includes an electrochromic device having an electrochromic layer  418  between a front transparent conductive layer  414  and a rear transparent conductive layer  416 . In an embodiment, the transparent conductive layers sandwich, e.g., contact either side of electrochromic layer  418 . Driver circuit  218  may be in electrical connection with front transparent conductive layer  414  through one or more front electrodes  409 , and similarly, driver circuit  218  may be in electrical connection with rear transparent conductive layer  416  through one or more rear electrodes  410 . Although driver circuit  218  is shown as being connected to rear electrode  410  along an outer wall or edge of rear transparent conductive layer  416 , this is for illustration purposes, and it is apparent from the description herein that rear electrode  410  may be on a front surface of rear transparent conductive layer  416  and exposed to contact with driver circuit  218  through a circumferential opening in an axial direction. Furthermore, although the electrodes are shown on only one side of lens filter  204  in the cross-sectional view of  FIG. 5  taken through optical axis  206 , there may be front electrodes  409  and rear electrodes  410  positioned circumferentially about outer rim  408 , including at a location diametrically opposite from the electrodes shown in  FIG. 5 . These other electrode pairs may be electrically activated by electrical leads placed in series with the illustrated electrical leads of driver circuit  218 , or may be electrically activated by additional electrical leads connected to driver circuit  218  or to another driver circuit (not shown). Thus, lens filter  204  may incorporate an electrochromic device that may be electrically activated by driver circuit  218 . 
     Front and rear transparent conductive layers  414 ,  416  may include a transparent conductive material, such as indium tin oxide (ITO). Of course, other transparent conductive materials capable of being formed in a thin layer may be used. Although the front and rear transparent conductive layers  414 ,  416  may be electrically conductive, in an embodiment, the transparent conductive material includes a finite resistivity per sheet area, i.e., the transparent conductive layers do not provide a short path across outer region  406  from outer rim  408  to aperture region  402  near a conductive plug  512 . For example, in a case in which the transparent conductive layers are formed from ITO having a uniform thickness of about 20 nm, resistivity of the transparent conductive layers may be on the order of 500 to 2,000 Ω/sq. For example, sheet resistance of the transparent conductive layers may be about 1,000 Ω/sq. Thus, when driver circuit applies voltage to electrodes, a potential difference may be created between front transparent conductive layer  414  and rear transparent conductive layer  416  across electrochromic layer  418 . 
     In an embodiment, electrochromic layer  418  may have several sub-layers. For example, as described further below, electrochromic layer  418  may include an electrolyte medium that includes an ion source material layer, an ion conduction material layer, and an active electrochromic material layer. Other layers or layer terminology may be added or substituted for electrochromic layer  418  within the skill in the art. For example, the ion source material layer may alternatively be referred to as a counter electrode layer. Ion source material layer may store suitable ions, such as lithium ions, that activate the active electrochromic material layer when a sufficient electric field is generated by driver circuit  218 . In an embodiment, ion source material layer is optically transparent to allow light rays from a scene being imaged to transmit through the layer. Ion conduction material layer may allow for high mobility of ions that have been produced by the ion source material layer. More particularly, ion conduction material layer may facilitate transfer of the ions from the ion source material layer into the active electrochromic material layer. The ion conduction material layer may be optically transparent to allow light rays from a scene being imaged to transmit through the layer. In a deactivated state, the active electrochromic material layer may be transparent, but when ions transfer into the active electrochromic material layer, darkening of the active electrochromic material layer, and consequently lens filter  204 , occurs. The darkening of lens filter  204  may occur over the area that an electric field gradient exists, e.g., over outer region  406 , and may be proportional to the electrical potential across the electrochromic layer  418  within that area. 
     The electrochromic device of lens filter  204 , which includes the transparent conductive layers  414 ,  416  and the electrochromic layer  418 , may be supported on a substrate  508 . For example, rear transparent conductive layer  416  may be formed or coupled with substrate  508 . Front transparent conductive layer  414  may or may not appose a respective substrate  508 . For example, in an embodiment, both front and rear transparent conductive layers  414 ,  416  may be formed on or coupled with respective substrates and then brought together to sandwich electrochromic layer  418 . Substrate  508  may be formed from a transparent material, such as glass, polycarbonate, or another material or composition suitable for use in an optical system of portable consumer electronics device  100 . More particularly, in an embodiment, substrate  508  transmits some portion of the visible wavelength range and is sufficiently rigid to support the electrochromic device of lens filter  204 . 
     Optionally, lens filter  204  may include an optical material  510  over at least a portion of one or more of the stack layers. For example, in an embodiment, optical material  510  is an anti-reflection layer formed over front transparent conductive layer  414 . Accordingly, the optical material  510  may be formed with one or more layers that reduce reflections through known techniques, e.g., index-matching, interference, etc. Alternatively, optical material  510  may be an infrared cut-off layer that includes a suitable material to block transmission of infrared light. Optical material  510  may be formed over only a portion of an adjacent transparent conductive layer, or may be patterned, e.g., etched, after forming a uniform layer to selectively expose underlying areas, such as electrodes on the underlying transparent conductive layers. 
     In an embodiment, lens filter  204  includes one or more conductive plug  512  between front transparent conductive layer  414  and rear transparent conductive layer  416 . More particularly, conductive plug  512  may directly connect to front transparent conductive layer  414  at a first end and connect to rear transparent conductive layer  416  at a second end to directly connect one transparent conductive layer with another. As described further below, conductive plug  512  may include a variety of forms. For example, conductive plug  512  may be single annular element that fills a continuous trench formed through at least front transparent conductive layer  414  and electrochromic layer  418  to place the transparent conductive layers in electrical connection. Alternatively, in an embodiment, a plurality of variously sized and shaped conductive plugs  512  may be arranged around a center region  514 , e.g., in a circumferential pattern, to create several discrete connections between the transparent conductive layers along the circumferential pattern. In any case, the one or more conductive plugs  512  may be arranged to create a continuous short path surrounding center region  514  of lens filter  204 , e.g., center region  514  of rear transparent conductive layer  416  or any other lens filter  204  layer. In an embodiment, center region  514  is not electrically shorted. Thus, a radial electrical path extends from front electrode  409  through front transparent conductive layer  414 , into and across one or more conductive plugs  512  to rear transparent conductive layer  416 , and then through rear transparent conductive layer  416  to rear electrode  410 . In an embodiment, no two points of the electrical path intersect, since electrochromic layer  418  may be disposed between the transparent conductive layers. Furthermore, electrical paths between electrode pairs that are diametrically opposite from one another may be separated by a gap or filler between respective conductive plugs on opposite sides of center region  514 . For example, any or all of front transparent conductive layer  414 , electrochromic layer  418 , or rear transparent conductive layer  416  may be omitted or removed, e.g., by forming a hole, within center region  514 . Accordingly, a radially symmetric electric field may be established in lens filter  204 . 
     Referring to  FIG. 6 , a graph showing a radially symmetric electric field gradient of a lens filter is shown in accordance with an embodiment. In an embodiment, conductive plug  512  may be formed from a conductive material that is electrically conductive. For example, conductive plug  512  may be formed from indium, and thus, have an electrical resistivity of essentially zero. Zero resistivity may be, but is not required to be, no resistivity. For example, indium may have a resistivity of about 80 nΩ·m, which may be considered to be essentially zero within the context of this description. Accordingly, conductive plug  512  may cause an electrical short between the locations at which it contacts front transparent conductive layer  414  and rear transparent conductive layer  416 . Given that front transparent conductive layer  414  and rear transparent conductive layer  416  may have non-zero resistivity, i.e., a finite resistivity per sheet area as described above, an electric field gradient may be formed across lens filter  204  when a voltage V control , e.g., an excitation voltage of about one volt, is applied by driver circuit  218  between front electrode  409  and rear electrode  410 . 
     The electric field gradient is apparent through the observation of electrical potential differences across electrochromic layer  418  plotted as a function of radial location on lens filter  204 . Electrical potential difference across electrochromic layer  418  at a point on perimeter  404 , which may also coincide with a location of conductive plug  512 , is essentially zero, since conductive plug  512  creates an electrical short between the transparent conductive layers and thus the voltage level at the front transparent conductive layer  414  equals the voltage level at the rear transparent conductive layer  416 . Conversely, electrical potential difference across electrochromic layer  418  may be at a maximum at a location where voltage is applied, e.g., at front electrode  409  and rear electrode  410  on outer rim  408 . As shown, the electric field gradient may be radially symmetric. That is, the electric field may decrease from a maximum on diametrically opposite sides of outer rim  408  to a minimum at diametrically opposite sides of perimeter  404 . The radially symmetric electric field gradient between outer rim  408  and perimeter  404  on either side of center region  514  of lens filter  204  is illustrated as being linear as a function of radial distance, which may correspond to a uniform thickness of constituent sub-layers of electrochromic layer  418  as shown in  FIG. 5 . However, in another embodiment, the gradient may be non-linear, and the non-linearity of the gradient may result from, e.g., an electrochromic layer  418  having a tapered active electrochromic material layer (not shown) or other material variations that cause resistivity of stack layers to vary differently in the radial direction from perimeter  404  toward outer rim  408 . 
     Referring to  FIG. 7A , a front view of a lens filter that will display an electric field gradient with radial and circumferential symmetry upon electrical activation is shown, in accordance with an embodiment. In an embodiment, outer rim  408  may be darkened by, e.g., application of a protective coating over an outer periphery of lens filter  204  to make the outer rim  408  more robust and/or more suitable for clamping within a supportive barrel or frame of camera module  104 . Furthermore, the darkened portion around outer rim  408  may extend into outer region  406 , creating an inner edge to the darkened portion that may be circular and surround a lighter portion of outer region  406 . Thus, the darkened portion may define a larger aperture size suitable for low light scenes when operating in a large aperture mode. Accordingly, the darkened portion may be an opaque optical material  510 , e.g., a black coating, layered over a portion of front transparent conductive layer  414 . Prior to electrical activation a “large” aperture size may be defined as including both aperture region  402  and at least a portion of outer region  406 , i.e., the portion of outer region  406  not covered by the black coating. In the non-activated state, essentially no electrical potential difference may be applied across electrochromic layer  418 , and thus, outer region  406  of the electro-optic portion of lens filter  204  may be transparent, like aperture region  402  within perimeter  404 . In an embodiment, the black coating may extend over any portion of lens filter  204  that does not support a circumferentially uniform electric field. Thus, any portion of lens filter  204  that remains transparent in a large aperture mode may support a circumferentially uniform electric field in a small aperture mode. 
     Referring to  FIG. 7B , a front view of a lens filter having an electric field gradient with radial and circumferential symmetry after electrical activation is shown in accordance with an embodiment. Upon application of a control voltage to front electrode  409  and rear electrode  410  by driver circuit  218 , an electric field gradient, such as the gradient shown in  FIG. 6 , is generated within electrochromic layer  418 . More particularly, the electric field gradient decreases from a maximum electrical potential difference within electrochromic layer  418  near outer rim  408  to a minimum, e.g., essentially zero, at conductive plug  512  along perimeter  404  and within aperture region  402 . Accordingly, the aperture size of lens filter  204  reduces as electrochromic layer  418  darkens in relation to its internal electric field gradient. Thus, electrochromic layer  418  darkens from a maximum opacity at outer rim  408  to a minimum opacity at perimeter  404 . As the electric field gradient varies radially, so may the opacity profile vary radially. Therefore, a diameter of the aperture may be controlled by the profile, e.g., a diameter, of perimeter  404  along conductive plugs  512 . As shown and described above, opacity may be circumferentially symmetric in relation to a circumferentially symmetric and/or uniform electric field in lens filter  204 . In other embodiments, the electric field may be one of either radially symmetric or circumferentially symmetric, but need not be both. For example, three electrodes may be unevenly distributed around a circumference of the lens, with two electrodes diametrically opposite one another, to create a location with radial symmetry (through the diametrically opposing electrodes), but still provide a lens without a circumferentially symmetric electric field distribution (since an electric field distribution on one side of a plane extending through the diametrically opposing electrodes and the central axis may differ from an electric field on the other side). 
     Referring to  FIG. 8 , a graph showing a light transmittance profile for a lens filter is shown in accordance with an embodiment. Just as opacity of lens filter  204  may vary with radial location, so may the optical transmittance of visible light  208  through lens filter  204  vary from a minimum near outer rim  408 , i.e., at the location of greatest opacity, to a maximum near center region  514  of lens filter  204 , i.e., at the location of least opacity. It may be useful to note at this point that although aperture region  402  and center region  514  may correspond to the same region of lens filter  204 , in an embodiment, they may not be identical areas. For example, aperture region  402  may refer more directly to an optical region at which light transmittance through lens filter  204  is nearly at a maximum, e.g., greater than about 95% of a maximum transmittance, while center region  514  may refer more directly to a physical location radially inward from the one or more conductive plugs  512 . Thus, while light transmission may be high enough in both regions to form part of the stop aperture of camera module  104 , they may not be identical. More particularly, electric field gradient of lens filter  204  may result in an apodized light transmittance profile (and a corresponding apodized light intensity profile on imaging sensor  200 ) as the transmitted light level tapers gradually from a maximum within center region  514  and aperture region  402  to a minimum at outer rim  408 . That is, the light transmittance profile may taper or curve between the maximum and minimum across outer region  406  rather than exhibit a “top hat” light transmittance profile with a sharp drop-off at the aperture region edge. 
     Referring to  FIG. 9 , a partial perspective view of an aperture region of a lens filter having a circular conductive plug around a transparent center region is shown in accordance with an embodiment. In an embodiment, conductive plug  512  includes a single annular plug through front transparent conductive layer  414  and electrochromic layer  418 . For example, the annular plug may continuous or ring-like structure. In an embodiment, conductive plug  512  may include indium, or another conductive material, that is deposited, injected, flowed, or otherwise inserted into a space to create a direct connection between rear transparent conductive layer  416  at a bottom end, and front transparent conductive layer  414  at a top end. Thus, conductive plug  512  may form a continuous electrical short around center region  514 . In the case where conductive plug  512  has an annular profile, the continuous electrical short may be circular. 
     Although conductive plug  512  may be annular, e.g., a circular tube, other embodiments may provide for a different aperture shape. For example, whereas aperture region  402  may have perimeter  404  that is essentially circular and slightly larger than an outer diameter of annular conductive plug  512 , in an alternative embodiment, trench  902  may include any closed shape such as an elliptical, curvilinear, or polygonal, e.g., octagonal, square, star-shaped, cross-sectional profile, shape. Accordingly, the aperture region  402  within perimeter  404  may include a shape corresponding to that of the continuous short formed by conductive plug  512 . That is, aperture region  402  may be defined by the creation of an electrical short, not at the center of aperture region  402 , but rather, along the perimeter  404  of aperture region  402  around center region  514 . 
     Notably, the transparent conductive layers may not be shorted to one another within center region  514 , but the electric field of a material that fills center region  514  may nonetheless be negligible and/or zero, given that voltage is applied at the periphery of lens filter  204  and any electrical potential difference is shorted by conductive plug  512  outside of center region  514 . As there is no voltage and/or electrical potential difference within center region  514  radially inward of conductive plug  512 , the material in the area from optical axis  206  to the edge of center region  514  at conductive plug  512  appears transparent. Center region  514  having no electric field may be sized to achieve a desired light transmittance when lens filter  204  is placed in a small aperture mode, as illustrated in  FIG. 8 . Thus, a profile or diameter of center region  514  may vary according to design requirements. However, in an embodiment, center region  514  around which an electrical short is formed is at least about 2 mm in diameter. For example, center region  514  may have a width or diameter of between about 3-20 mm, e.g., 5 mm, at a location. 
     Referring to  FIG. 10 , a partial perspective view of a center region of a lens filter having a plurality of conductive plug vias arranged circumferentially around a transparent center region is shown in accordance with an embodiment. In an alternative embodiment, rather than having a continuous conductive plug  512  formed around center region  514 , lens filter  204  may include a plurality of conductive plugs  512 , e.g., cylindrical conductive plugs, arranged in a pattern around center region  514 . The plurality of conductive plugs  512  may have various cross-sectional shapes, e.g., circular in the case of cylindrical plugs or polygonal in the case of rectangular plugs. The plurality of conductive plugs  512  may also be arranged in a variety of pattern shapes, including polygonal. Furthermore, although the plurality of conductive plugs  512  may each have a solid cross-section, as in the case of a deposited conductive plug  512 , one or more of the plurality of conductive plugs  512  may also have a non-solid cross-section, e.g., annular, as in the case of some types of electronic vias, e.g., tubular vias. Accordingly, in an embodiment, one or more of the plurality of conductive plugs  512  may be electronic vias, as are known in the art to be inexpensive and easy to manufacture. 
     As described above, conductive plug  512  may be continuous or discontinuous. For example, conductive plug  512  may be an annular conductor or several discrete conductors arranged to create a continuous electrical short. In an alternative embodiment, conductive plug  512  may be a single conductor, e.g., a c-shaped conductor with a cross-sectional profile that is substantially annular such that the ends of the c-shape terminate close to one another. Thus, although the ends are discontinuous, they may be close enough to each other to electrically short an electric field in lens filter  204  and prevent the electric field from creeping into center region  514 . Thus, regardless of the specific structure of conductive plug  512 , the electrical short created between transparent conductive layers  414 ,  416  by conductive plug(s)  512  may be continuous around and/or outside of center region  514 . 
     Still referring to  FIG. 10 , since the electrical shorts provided by the plurality of conductive plugs  512  may be separated from each other across and around center region  514 , the local electric field, as well as the shape of perimeter  404  of aperture region  402 , may not be circular or have the same shape as a geometric chord passing through the conductive plugs  512 . For example, the space between conductive plugs  512  may support some electrical potential difference across electrochromic layer  418 , and accordingly, the opacity of lens filter  204  and the perimeter  404  of aperture region  402  may creep into the intervening space between conductive plugs  512 . Nonetheless, the opacity of lens filter  204  may increase radially from perimeter  404  to outer rim  408  across outer region  406 , similar to the other embodiments described above. Furthermore, the continuous short around center region  514  formed by conductive plug(s)  512  may maintain a transparent stop aperture. 
     Referring to  FIG. 11A , a cross-sectional view, taken about line A-A of  FIG. 4 , showing an aperture region of a lens filter is shown in accordance with an embodiment. In an embodiment, line A-A of  FIG. 4  passes through one or more conductive plug  512  between the transparent conductive layers  414 ,  416 . For example, the conductive plug  512  sections shown may be diametrically opposite portions of a continuous annular conductive plug  512  on either side of center region  514 , as shown in  FIG. 9 . In an embodiment, conductive plug  512  includes a single annular plug filling a trench  902  formed axially through front transparent conductive layer  414  and electrochromic layer  418 . For example, trench  902  may be laser-inscribed through front transparent conductive layer  414  and electrochromic layer  418 . In an embodiment, the laser-inscription may pass into rear transparent conductive layer  416  also. The conductive filler making up conductive plug  512  may be pre-formed, e.g., an indium pin, and inserted into machined holes, or alternatively, the conductive filler making up conductive plug  512  may be a conductive material, e.g., indium, capable of being coated, deposited, injected, or otherwise flowed into the holes to form conductive plug  512 . For example, after forming the trench, indium may be deposited into trench  902  to form the continuous conductive plug  512 . The conductive plug  512  may contact both rear transparent conductive layer  416  at a bottom end, and front transparent conductive layer  414  at a top end, thus forming a continuous electrical short around center region  514 . In the case where conductive plug  512  has an annular profile, the continuous electrical short may be circular. 
     Other manners of manufacturing lens filter  204  with a continuous conductive plug  512  may be used. For example, in an embodiment, rear transparent conductive layer  416  and electrochromic layer  418  may be formed over substrate  508 , and then trench  902  may be etched, laser cut, or otherwise formed by removing material from electrochromic layer  418 , up to rear transparent conductive layer  416 . Conductive plug  512  may be deposited or inserted into trench  902 , and subsequently, front transparent conductive layer  414  may be layered over electrochromic layer  418  having one or more sub-layers, e.g., ion source material layer  1102 , ion conduction material layer  1104 , or active electrochromic material layer  1106  to form an electrical connection with conductive plug  512 . Thus, conductive plug  512  may be fully encapsulated between the layers of the electrochromic device of lens filter  204 , while still providing an electrical short path between the transparent conductive layers  414 ,  416 . 
     Still referring to  FIG. 11A , the conductive plug  512  sections shown may be cross-sectional views of different discrete conductive plugs  512  arranged discontinuously around center region  514 . For example, each rectangular cross section may be a cross-sectional view of a cylindrical conductive plug  512  (as described with respect to  FIG. 10 ) inserted through electrochromic layer  418  to directly connect front transparent conductive layer  414  with rear transparent conductive layer  416 . In another embodiment, conductive plugs  512  may have solid profiles that are arc-like, or have a shape that follows perimeter  404 . For example, where perimeter  404  is circular, several distinct conductive plugs  512  having arc shapes that conform to the circle may be arranged along perimeter  404  to create a continuous electric short between transparent conductive layers  414 ,  416 . Discrete conductive plugs  512  may be disposed within lens filter  204  in several manners. For example, a plurality of circular bores may be formed through electrochromic layer  418  and/or front transparent conductive layer  414  up to rear transparent conductive layer  416 . Circular conductive plugs  512  may be deposited or inserted into the bores to form several discrete electrical shorts between the transparent conductive layers around center region  514 . Similar deposition or insertion methodologies may be used to insert discrete plugs with different shapes and/or volumes. 
     Still referring to  FIG. 11A , center region  514  may be filled by a material with non-zero resistivity. For example, center region  514  within conductive plug  512  may incorporate electrochromic layer  418  having non-zero resistivity. Alternatively, center region  514  may be filled with a different material having non-zero resistivity. For example, center region  514  within conductive plug(s)  512  may be filled with a transparent insulator, such as glass or polycarbonate. Thus, center region  514  may be filled with any material that does not create a short between front transparent conductive layer  414  and rear transparent conductive layer  416 . 
     Referring to  FIG. 11B , a cross-sectional view, taken about line A-A of  FIG. 4 , showing an aperture region of a lens filter is shown in accordance with an embodiment. In an embodiment, a continuous trench  902  may be formed through electrochromic layer  418  to rear transparent conductive layer  416  over substrate  508 . The continuous trench  902  may be circular, and may surround center region  514 . Furthermore, electrochromic layer  418  may remain intact radially inward from the trench  902 . Subsequently, front transparent conductive layer  414  may be coated, deposited, or otherwise disposed over electrochromic layer  418 . A portion of front transparent conductive layer  414  material may flow into and fill trench  902  during the layering of front transparent conductive layer  414 . Accordingly, an electrochromic device having conductive plug  512  formed contiguously with, and from the same material as, front transparent conductive layer  414  may be formed. 
     Although conductive plug  512  may be contiguous with front transparent conductive layer  414 , there may not be an electrical short across the material that fills center region  514 , since conductive filler within trench  902 , which makes up conductive plug  512 , may have lower resistivity than the filler material within center region  514 , e.g., electrochromic layer  418 . Accordingly, any voltage may short across conductive plug  512  rather than the filler within center region  514 . That is, given that such filler material would be radially inward from conductive plug  512 , which forms an electrical short between transparent conductive layers, the filler material may not support an electric field, and thus, may remain transparent in a small aperture mode. 
     Referring to  FIG. 11C , a cross-sectional view, taken about line A-A of  FIG. 4 , of an aperture region of a lens filter is shown in accordance with an embodiment. In an alternative embodiment, lens filter  204  may have all or some of front transparent conductive layer  414  and electrochromic layer  418  removed over center region  514  of rear transparent conductive layer  416 . For example, after forming rear transparent conductive layer  416  and electrochromic layer  418  over substrate  508 , a hole may be formed through electrochromic layer  418  to remove electrochromic layer material over center region  514  of rear transparent conductive layer  416  and create a counterbore with a bottom terminating at rear transparent conductive layer  416  or substrate  508 . Removal may be achieved by etching or micromachining, for example. Subsequently, front transparent conductive layer  414  may be deposited over electrochromic layer  418 . In an embodiment, front transparent conductive layer  414  may entirely fill the void formed over rear transparent conductive layer  416 . As described above, center region  514  of lens filter  204  may nonetheless remain transparent since any electric field may be shorted electrically outward at conductive plug(s)  512 . Alternatively, as shown in  FIG. 11C , at least some portion of the void may be left intact, either by removing front transparent conductive layer  414  material over center region  514 , or by only depositing front transparent conductive layer  414  up to the center region  514 , as depicted. Accordingly, at least some amount of front transparent conductive layer  414  extends beyond electrochromic layer  418  and is layered over a sidewall of electrochromic layer  418  to make contact with rear transparent conductive layer  416 . Thus, in an embodiment, front transparent conductive layer  414  material may form conductive plug  512  along the sidewall of electrochromic layer  418 . More particularly, front transparent conductive layer  414  and conductive plug  512  may be contiguously formed from a same conductive material. 
     It will be appreciated therefore that conductive plug  512  need not have an electrical resistivity of substantially zero. For example, since conductive plug  512  may be formed from the same material as front transparent conductive layer  414 , e.g., ITO, conductive plug  512  may include a resistivity similar to that of front transparent conductive layer  414 . More particularly, conductive plug  512  may be formed from a material with a resistivity higher than indium, and the electrical path between front transparent conductive layer  414  and rear transparent conductive layer  416  may include some voltage drop. Nonetheless, given that the distance between front transparent conductive layer  414  and rear transparent conductive layer  416  may be much less than the radius of lens filter  204 , any voltage drop may be negligible, i.e., the transparent conductive layers may have substantially equal voltages across conductive plug  512  even if conductive plug  512  does not create an electrical short between the layers. 
     Referring to  FIG. 12A , a partial front view of a plurality of segmented electrodes arranged along an outer rim of a lens filter is shown in accordance with an embodiment. As described above with respect to  FIG. 4 , a plurality of electrodes may be distributed around outer rim  408  to provide symmetric and/or uniform distribution of electric field in a circumferential direction. That is, since the electrodes may be equally spaced around outer rim  408 , application of a same voltage to each electrode may produce a circumferentially symmetric voltage distribution. Although the distribution may vary between peaks at the electrodes and minima circumferentially half-way between the electrodes near outer rim  408 , at a location radially inward of outer rim  408 , the distribution may be uniform, i.e., without maxima and minima in the circumferential direction. The degree of circumferential variation and the radial location at which the even distribution of electric field becomes uniform may depend on a circumferential distance between electrodes, given that the variation is due to voltage drops through the transparent conductive layer materials. Thus, the circumferential distance between electrodes may be minimized to increase the number of electrode contacts and the circumferential symmetry/uniformity of the electric field within lens filter  204 . 
     As shown, circumferential gap  412  may have a substantially rectangular, or trapezoidal, shape. Alternatively, circumferential gap  412  may have any other shape that is sized to permit access by an electrical lead in an axial direction to contact an exposed rear electrode  410 . In an embodiment, circumferential gap  412  extends from outer rim  408  to within outer region  406  of front transparent conductive layer  414 . Thus, in an embodiment, circumferential gap  412  may be formed by machining, e.g., micromachining, lens filter  204  to remove front transparent conductive layer  414  and electrochromic layer  418  overlying rear transparent conductive layer  416 . 
     In an alternative embodiment, the segmented structure of lens filter  204  electrodes may include one or more electrodes that extend radially from a central hub. For example, rather than circumferential gaps  412  being formed by the removal of material from front transparent conductive layer  414 , each front electrode  409  may be a separate component, e.g., a thin electrode tab adjoined to front transparent conductive layer  414  along the conductive layer outer periphery. Similarly, rear electrodes  410  may include one or more segmented electrode tabs adjoined to rear transparent conductive layer  416  along the conductive layer outer periphery. Thus, since the electrodes may extend from an electrochromic stack of lens filter  204 , circumferential gaps  412  may not be formed by removal of lens filter  204  material during fabrication, but rather, circumferential gaps  412  may be defined between extensions that are added to lens filter  204  during fabrication. 
     Referring to  FIG. 12B , a partial front view of a plurality of segmented electrodes arranged along an outer rim of a lens filter is shown in accordance with an embodiment. Circumferential gap  412  may not extend from outer rim  408 , but rather, may be a void of any shape and size large enough to permit axial access to rear electrode  410  through front transparent conductive layer  414 . For example, all electrodes may be accessed from a front side of lens filter  204 . Circumferential gap  412  may be formed by machining, e.g., micromachining, a circular, elliptical, rectangular, etc., profile through a previously layered front transparent conductive layer  414  and electrochromic layer  418 . Accordingly, access to rear electrode  410  may be enabled with minimal removal of material to match a profile of a pin or other electrical contact that extends to contact rear electrode  410 . 
     In an embodiment, front electrodes  409  and rear electrodes  410  arranged in a circular fashion may also be arranged about a same diameter. That is, a circle circumscribing front electrodes  409  may have a same diameter as a circle circumscribing rear electrodes  410 . Alternatively, electrodes may be staggered, i.e., front electrode  409  and rear electrode  410  may be along respective profiles circumscribing different diameters. Furthermore, although front electrodes  409  and rear electrodes  410  have been primarily described as being circumferentially offset from one another, e.g., located along different radials of lens filter  204 , in an embodiment, corresponding front electrodes  409  and rear electrodes  410  may be circumferentially aligned, i.e., along a same radial line emanating from optical axis  206 . This may be the case where front electrode  409  on a radial is located at a first distance along a radial of lens filter  204  and rear electrode  410  is located on the same radial at a second distance along the radial greater than the first distance. 
     Referring to  FIG. 13 , a cross-sectional view, taken about line B-B of  FIG. 12A , of a front electrode of a lens filter is shown in accordance with an embodiment. Front electrode  409  may be a surface area on a front face of front transparent conductive layer  414  of the electrochromic device of lens filter  204 . More particularly, front electrode  409  may be a region on the front face of front transparent conductive layer  414 , rather than a separate component. Alternatively, front electrode  409  may include a separate component, such as a deposited contact pad, e.g., an indium pad. For example, in an embodiment, each front electrode  409  may include an electrode pad having a diameter of between about 2-10 mm, e.g., 5 mm, and a thickness between about 0.2-1.0 mm, e.g., 0.6 mm, deposited on front transparent conductive layer  414 . As shown, a portion of lens filter  204  having front electrode  409  may include the entire stack of the electrochromic device, i.e., front transparent conductive layer  414 , electrochromic layer  418 , rear transparent conductive layer  416 , and substrate  508 . This structure may be the same for every front electrode  409  region along outer rim  408  of lens filter  204 . Alternatively, front electrode  409  structures may differ, e.g., may have different pad materials or sizes around the circumference of lens filter  204 . 
     Referring to  FIG. 14A , a cross-sectional view, taken about line C-C of  FIG. 12A , of a rear electrode of a lens filter is shown in accordance with an embodiment. In contrast to a front electrode  409  region of lens filter  204 , a rear electrode  410  region may not include the entire stack of the electrochromic device. That is, electrochromic layer  418  and front transparent conductive layer  414  may be removed over rear transparent conductive layer  416  and substrate  508  to expose a rear electrode  410  surface area on a front face of rear transparent conductive layer  416 . More particularly, rear electrode  410  may be a region on the front face of rear transparent conductive layer  416 , rather than a separate component. The rear electrode  410  region may be large enough to permit contact with an external lead, such as an electrical pin or lead that reaches axially through circumferential gap  412  to contact rear electrode  410 . 
     Referring to  FIG. 14B , a cross-sectional view, taken about line C-C of  FIG. 12A , of a rear electrode of a lens filter is shown in accordance with an embodiment. In an alternative embodiment, rear electrode  410  may be formed as a separate component over rear transparent conductive layer  416 . For example, rear electrode  410  may be deposited as a pad with a height that is approximately the same as the combined thickness of front transparent conductive layer  414  and electrochromic layer  418 . In an embodiment, each rear electrode  410  may include an electrode pad having a diameter of between about 2-10 mm, e.g., 5 mm, and a thickness between about 0.2-1.0 mm, e.g., 0.6 mm, deposited over rear transparent conductive layer  416 . Thus, rear electrode  410  may have a front face that is substantially coplanar with a front face of front transparent conductive layer  414  and/or front electrode  409 . Accordingly, external contacts such as leads or pins connected with driver circuit  218  may contact all electrodes of lens filter  204  at approximately the same axial location. 
     Other electrode configurations may be used to evenly distribute the electric field in a circumferential manner around outer rim  408 . For example, rear electrodes  410  may be accessible along an edge of lens filter  204 , e.g., at a region on an outer wall of rear transparent conductive layer  416 . Alternatively, rear electrodes  410  may be on a rear face of rear transparent conductive layer  416 , and thus, external leads or electrical contacts such as pins may access and contact rear electrodes  410  from behind lens filter  204 . Therefore, the embodiments described above are not limiting of the range of possible configurations to create a lens filter  204  having a transparent center region  514  and an electrochromic portion that supports both a radially symmetric electric field gradient and a circumferentially symmetric and/or uniform electric field. 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope of the invention as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.

Metadata:
Filing Date: 20150708
Publication Date: 20180717
Grant Date: 20180717
Priority Date: 20140925
Inventors: Gleason, Jeffrey N.
YUAN, Xingchao C.
DUNN, Ryan J.
BIE, Linsen
GUO, XI
SCEPANOVIC, MIODRAG
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F2001/1552", "inventive": false, "first": false, "tree": "[]"}, {"code": "G03B7/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "G03B7/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "G03B9/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B5/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "G03B11/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "G03B9/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/58", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/155", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/155", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/163", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B27/58", "inventive": true, "first": false, "tree": "[]"}, {"code": "G03B11/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "G03B11/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "G03B7/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/155", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/58", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/163", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F2001/1552", "inventive": false, "first": false, "tree": "[]"}, {"code": "G03B9/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B5/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B5/005", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 54106005