PATENT DOCUMENT

Publication Number: US-10700780-B2
Application Number: US-201916399925-A
Country: US
Kind Code: B2

Title: Systems and methods for adjusting movable lenses in directional free-space optical communication systems for portable electronic devices

Abstract:
A directional free-space optical communication system includes a source device including a laser diode and an endpoint device including a photodiode. The endpoint device and the source device also include an adjustable optics subsystem that increases both angular and positional offset tolerance between the source device and the endpoint device.

Claims:
What is claimed is: 
     
       1. An apparatus for free-space optical communication comprising:
 a substrate; 
 a photosensitive element coupled to the substrate and comprising:
 a first photosensitive area; and 
 a second photosensitive area circumscribing the first photosensitive area; 
 
 a movable lens above the photosensitive element; and 
 a controller coupled to the movable lens and configured to adjust a position of the movable lens based on a first power output from the first photosensitive area and a second power output from the second photosensitive area. 
 
     
     
       2. The apparatus of  claim 1 , wherein the first photosensitive area is positioned in a geometric center of an exterior surface of the photosensitive element. 
     
     
       3. The apparatus of  claim 1 , wherein the second photosensitive area is segmented. 
     
     
       4. The apparatus of  claim 3 , wherein the second photosensitive area includes at least three segments. 
     
     
       5. The apparatus of  claim 4 , wherein:
 the second power output is from a first segment of the at least three segments of the second photosensitive area; and 
 the controller is configured to adjust the position of the movable lens based on a third power output from a second segment of the at least three segments of the second photosensitive area. 
 
     
     
       6. The apparatus of  claim 1 , wherein the controller is configured to adjust the position of the movable lens in response to an increase in the second power output and a decrease in the first power output. 
     
     
       7. The apparatus of  claim 1 , wherein the first photosensitive area and the second photosensitive area are separated by a partition formed from metal. 
     
     
       8. A system for free-space optical communication comprising:
 a first apparatus comprising:
 a light source; 
 a first movable lens above the light source; and 
 a first controller configured to adjust a first position of the first movable lens in a pattern; and 
 
 a second apparatus comprising:
 a photosensitive element comprising:
 a first photosensitive area; and 
 a second photosensitive area; 
 
 
 a second movable lens above the photosensitive element; and 
 a second controller configured to adjust a second position of the second movable lens based on changes in power output from the first photosensitive area and the second photosensitive area. 
 
     
     
       9. The system of  claim 8 , wherein:
 the light source comprises a vertical-cavity surface-emitting laser; and 
 the photosensitive element comprises a photodiode. 
 
     
     
       10. The system of  claim 8 , wherein the second controller is configured to adjust the second position of the second movable lens after the first controller stops scanning. 
     
     
       11. The system of  claim 8 , wherein the second controller is configured to tilt the second movable lens. 
     
     
       12. The system of  claim 11 , wherein the second controller is configured to tilt the photosensitive element with the second movable lens. 
     
     
       13. The system of  claim 8 , wherein the second controller is configured to shift the second movable lens laterally. 
     
     
       14. The system of  claim 8 , wherein:
 the first photosensitive area is circular; and 
 the second photosensitive area surrounds the first photosensitive area. 
 
     
     
       15. The system of  claim 14 , wherein the second photosensitive area is segmented. 
     
     
       16. A method of operating a free-space optical communication system comprising a source device and an endpoint device, the method comprising:
 changing a first position of a first movable lens according to a pattern, the first movable lens positioned over a laser diode in the source device; 
 monitoring a first power output from at least one photosensitive area of a photodiode in the endpoint device; 
 in response to the first power output crossing a first threshold, sending a signal to the source device to stop changing the first position of the first movable lens; 
 changing a second position of a second movable lens positioned over the photodiode; 
 monitoring a second power output from at least one photosensitive area of the photodiode; and 
 in response to the second power output crossing a second threshold, stopping movement of the second movable lens. 
 
     
     
       17. The method of  claim 16 , wherein the pattern is predefined. 
     
     
       18. The method of  claim 16 , wherein changing the first position of the first movable lens is performed, at least in part, by a controller of an adjustable optics subsystem in the source device. 
     
     
       19. The method of  claim 16 , further comprising entering a data transfer mode by the source device and the endpoint device after stopping movement of the second movable lens.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a nonprovisional of and claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Patent Application No. 62/678,215, filed May 30, 2018, and entitled “Systems and Methods for Adjusting Movable Lenses in Directional Free-Space Optical Communication Systems for Portable Electronic Devices,” the contents of which is incorporated by reference as if fully disclosed herein. 
    
    
     FIELD 
     Embodiments described herein relate to free-space optical communication systems and, in particular, to systems and methods for dynamically adjusting movable lenses for such systems incorporated into portable electronic devices. 
     BACKGROUND 
     An electronic device can include a free-space optical communication system to wirelessly transmit, receive, or exchange data with another electronic device. In some cases, the optical communication system may be configured to be directional (e.g., line-of-sight) in order to increase data transfer rates, to increase data transfer privacy, or for any other suitable purpose. 
     However, a conventional directional free-space optical communication system is exceptionally dependent on precise alignment of communicating devices. As such, conventional free-space optical communication systems cannot be incorporated into portable electronic devices that may be moved or repositioned from time to time. 
     SUMMARY 
     Embodiments described herein reference an apparatus for free-space optical communication in a portable electronic device. The apparatus includes a photosensitive element coupled to a substrate. In many embodiments, the photosensitive element includes at least two separated photosensitive areas. The apparatus also includes a movable lens positioned above the photosensitive element. The apparatus additionally includes a controller configured to adjust a position of the movable lens based on a power output from a first photosensitive area of the photosensitive element and a power output from a second photosensitive area—if any—of the photosensitive element. 
     Some embodiments described herein reference a method of operating a free-space optical communication system with a source device and an endpoint device, the method including the operations of: changing a position of a movable lens positioned over a laser diode in the source device according to a pattern; monitoring power output from a photosensitive area of a photodiode in the endpoint device for a maximum and, in response, sending a signal to the source device to stop changing a position of the source device lens; changing a position of a second movable lens positioned over the photodiode in the endpoint device; and monitoring power output from a photosensitive area of the photodiode for another maximum and, in response, stopping movement of the second movable lens. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference will now be made to representative embodiments illustrated in the accompanying figures. It should be understood that the following descriptions are not intended to limit this disclosure to one included embodiment. To the contrary, the disclosure provided herein is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the described embodiments, and as defined by the appended claims. 
         FIG. 1A  depicts a directional free-space optical communication system coupling two electronic devices. 
         FIG. 1B  is a simplified system diagram of the directional free-space optical communication system of  FIG. 1A . 
         FIG. 2A  depicts a simplified representation of a source device and an endpoint device, collimated relative to one another. 
         FIG. 2B  depicts the simplified representation of the collimated devices of  FIG. 2A , viewed along line A-A. 
         FIG. 2C  depicts the simplified representation of the collimated devices of  FIG. 2A , viewed along line B-B. 
         FIG. 2D  depicts the simplified representation of the collimated devices of  FIG. 2A , viewed along line C-C. 
         FIG. 3  depicts a system diagram of a directional free-space optical communication system, such as described herein. 
         FIG. 4A  depicts an endpoint device of a directional free-space optical communication system, such as described herein, including a laterally movable lens. 
         FIG. 4B  depicts the movable lens of  FIG. 4A , shifted in a direction. 
         FIG. 5A  depicts an endpoint device of a directional free-space optical communication system, such as described herein, including an angularly movable optical subassembly. 
         FIG. 5B  depicts the movable lens of  FIG. 5A , tilted in a direction. 
         FIG. 6A  depicts a top view of a photodiode of an endpoint device of a directional free-space optical communication system, such as described herein, depicting a beam spot illuminating a central region of a photosensitive area of the photodiode. 
         FIG. 6B  depicts the photodiode of  FIG. 6A , depicting the beam spot shifted in a direction relative to the central region of the photosensitive area. 
         FIG. 6C  depicts a top view of another photodiode of an endpoint device of a directional free-space optical communication system, such as described herein, depicting a beam spot illuminating more than one photosensitive area of the photodiode. 
         FIG. 7  depicts a top view of another photodiode of an endpoint device of a directional free-space optical communication system, such as described herein, including a segmented photosensitive area and depicting a beam spot illuminating more than one photosensitive area of the photodiode. 
         FIG. 8  is a simplified flow chart showing example operations of a method of positioning a movable lens in a directional free-space optical communication system, such as described herein. 
         FIG. 9  is a simplified flow chart showing example operations of another method of positioning a movable lens in a directional free-space optical communication system, such as described herein. 
     
    
    
     The use of the same or similar reference numerals in different figures indicates similar, related, or identical items. 
     The use of cross-hatching or shading in the accompanying figures is generally provided to clarify the boundaries between adjacent elements and to facilitate legibility of the figures. Accordingly, neither the presence nor the absence of cross-hatching or shading conveys or indicates any preference or requirement for particular materials, material properties, element proportions, element dimensions, commonalities of similarly illustrated elements, or any other characteristic, attribute, or property for any element illustrated in the accompanying figures. 
     Similarly, certain accompanying figures include vectors, rays, traces and/or other visual representations of one or more example paths—which may include reflections, refractions, diffractions, and so on, through one or more mediums—that may be taken by one or more photons originating from one or more light sources shown or, or in some cases, omitted from, the accompanying figures. It is understood that these simplified visual representations of light are provided merely to facilitate an understanding of the various embodiments described herein and, accordingly, may not necessarily be presented or illustrated to scale or with angular precision or accuracy, and, as such, are not intended to indicate any preference or requirement for an illustrated embodiment to receive, emit, reflect, refract, focus, and/or diffract light at any particular illustrated angle, orientation, polarization, color, or direction, to the exclusion of other embodiments described or referenced herein. 
     Additionally, it should be understood that the proportions and dimensions (either relative or absolute) of the various features and elements (and collections and groupings thereof) and the boundaries, separations, and positional relationships presented therebetween, are provided in the accompanying figures merely to facilitate an understanding of the various embodiments described herein and, accordingly, may not necessarily be presented or illustrated to scale, and are not intended to indicate any preference or requirement for an illustrated embodiment to the exclusion of embodiments described with reference thereto. 
     DETAILED DESCRIPTION 
     Embodiments described herein reference electronic devices configured to receive data from other electronic devices via free-space optical communication. 
     As used herein, the phrase “free-space optical communication” refers to the delivery of digital and/or analog information or data from at least one “source device” to at least one “endpoint device” by selectively modulating and/or otherwise controlling the amplitude, frequency, phase, polarization, angle, pulse width, duty cycle, and/or any other suitable characteristic of visible or traditionally non-visible light propagating through a medium (e.g., gases, liquids, vacuum, and so on) that physically separates the source device(s) from the endpoint device(s). 
     Any stationary or portable electronic device can be either (or both) a source device or an endpoint device of a free-space optical communication system, such as described herein. Example electronic devices include, but are not limited to: mobile phone devices; tablet devices; laptop devices; desktop computers; computing accessories; peripheral input devices; home or business networking devices; aerial, marine, submarine, or terrestrial vehicle control devices or networking devices; mobile entertainment devices; augmented reality devices; virtual reality devices; industrial control devices; digital wallet devices; home or business security devices; wearable devices; health or medical devices; implantable devices; clothing-embedded devices; fashion accessory devices; home or industrial appliances; media appliances; and so on. 
     In some embodiments, a free-space optical communication system is “directional” in that focused light or laser light emitted from the source device(s) propagates through a medium between the source device(s) and the endpoint device(s) along a substantially line-of-sight path. A directional free-space optical communication system can facilitate increased data transfer rates (e.g., tens of gigabits per second to terabits per second), increased data transfer privacy, and increased data transfer security relative to conventional device-to-device data communication protocols, such as Wi-Fi, Near-Field Communications, or Bluetooth. 
     As noted above, a directional free-space optical communication system, such as described herein, includes at least a source device and at least one endpoint device. The source device includes at least one focused light source or laser light source and the endpoint device includes at least one photosensitive element. When light emitted from the laser light source of the source device is collimated (e.g., emitted with minimal or negligible beam divergence or convergence) and the photosensitive element of the endpoint device is positioned to accept the collimated light (e.g., the source device and the endpoint device are precisely aligned) a signal applied to modulate the laser light source can be received at the photosensitive element without substantial losses. In other words, the signal received by the photosensitive element can be characterized by a high signal-to-noise ratio that can facilitate a high data transfer rate from the source device to the endpoint device. In this configuration and alignment, the source device and the endpoint device can be described as “optically coupled.” It may be appreciated that, in many embodiments, optically coupled devices can each include one or more light sources and one or more photosensitive elements to enable multi-channel and/or two-way communication and/or multi-device communication (e.g., three or more devices optically coupled). However, for simplicity of description, the embodiments that follow reference a directional free-space optical communication system configured for one-way, single-channel, data transfer from a source device to an endpoint device. 
     In this example, the light source of the source device can be any suitable electrical or electronic light source or combination of light sources, including both multipart and solid-state light sources. In many embodiments, a light source of a source device is a semiconductor light source such as, but not limited to: a vertical-cavity surface-emitting laser (a “VCSEL”); a vertical external-cavity surface-emitting laser; a light-emitting diode; an organic light-emitting diode; a resonant-cavity light-emitting diode; a micro-scale light-emitting diode; a superluminescent light-emitting diode; a broad-area laser diode; a diode-pumped laser; a mode-locked diode laser; an infrared band laser; an ultraviolet band laser; and so on. 
     In some embodiments, the light source of a source device can be optically coupled to one or more passive or active optical structures that direct, collimate, and/or focus light emitted from the light source in a particular direction or manner. Example optical structures can include, but may not be limited to: optical adapters; waveguides; optical fibers; reflectors; lenses; microlenses; beamforming and/or beam-directing lenses or lens structures; beam splitters; beam collimators; polarizers; movable lenses; color filters; cut filters; beam expanders; beam divergers; planar light wave circuits; and so on. 
     The photosensitive element of an endpoint device, such as described herein, can be any suitable photosensitive element or combination of elements, including both multipart and solid-state photosensitive elements operated in either photovoltaic mode (e.g., not reverse biased) or photoconductive mode (e.g., reverse biased). Example photosensitive elements include, but are not limited to: semiconductor photodiodes; semiconductor photodetectors; avalanche diodes; charge-coupled devices; and so on. Further, it may be appreciated that the size and shape of a photosensitive element can vary from embodiment to embodiment. In some cases, a “photosensitive area” of a photosensitive element can take a circular shape, whereas in other cases, the photosensitive area can take another shape (e.g., square, rectangular, octagonal, irregular, polygonal, and so on). Further, some embodiments can include more than one photosensitive area. For example, a first photosensitive area can be inset within a second photosensitive area of the same photosensitive element. In these examples, different photosensitive areas may be formed from different materials, or material combinations, and/or may have different photosensitivity or electrical characteristics (e.g., responsivity, rise time, fall time, reverse bias, dark current, and so on). In further examples, a photosensitive element can be constructed such that its photosensitive area exhibits particular electrical properties, at least in part, as a result of the materials, geometry, or dimensions of the photosensitive area. For example, it may be appreciated that different semiconductor materials (e.g., silicon, germanium, indium-gallium arsenide, gallium phosphide, and so on) may exhibit different electrical properties (e.g., responsivity, rise time, fall time, dark current, and so on) in response to stimulation by different spectral ranges and/or amplitudes of light. Similarly, different photosensitive area geometries and/or dimensions may result in different electrical properties. For example, smaller photosensitive areas may be associated with faster rise times and faster fall times. 
     As with the light source of the source device, in some embodiments, the photosensitive element of an endpoint device can be optically coupled to one or more passive or active optical structures that redirect and/or focus light onto the photosensitive area of the photosensitive element. Example optical structures can include, but may not be limited to: optical adapters; optical fibers; reflectors; lenses; microlenses; beamforming and/or beam-directing lenses or lens structures; beam collimators; polarizers; movable lenses; color filters; cut filters; beam concentrators; planar light wave circuits; and so on. 
     For simplicity of description, the embodiments that follow reference a source device including at least one VCSEL light source (hereinafter, a “laser” or “laser diode”) that emits light in a spectral range including a traditionally non-visible frequency band (e.g., infrared light). Further, although not required for all embodiments, the example VCSEL light source described in reference to many embodiments that follow is presumed to be a Class 1 laser as defined by the American National Standards Association. 
     Similarly, for simplicity of description, the embodiments that follow reference an endpoint device including at least one semiconductor photodiode (hereinafter, a “photodiode”). The photodiode has a generally small, circular photosensitive area (e.g., having a diameter of less than 100 μm, such as 20-50 μm) and is operated in a photoconductive mode. The photosensitive area of this example photodiode is responsive to light in the spectral range emitted by the laser diode of the source device. 
     As noted above, a directional free-space optical communication system, such as described herein, preferably operates when the source device and the endpoint device are precisely aligned such that a considerable quantity (which may vary from embodiment to embodiment) of laser light emitted from the laser diode of the source device illuminates the photodiode of the endpoint device. Conversely, if the source device and the endpoint device are not precisely aligned, partial or total signal loss can occur because the laser diode may not effectively illuminate the photodiode. 
     To account for positional and/or angular offset(s) between the source device and the endpoint device—or, more generally, between the laser diode and the photodiode—many embodiments described herein reference optical structures for either or both the source device and the endpoint device that increase positional and/or angular offset tolerance. 
     For example, in one embodiment, an endpoint device of a directional free-space optical communication system can include an adjustable optics subsystem. In one example, the adjustable optics subsystem includes a movable lens positioned over the photodiode of the endpoint device. In other embodiments, the adjustable optics subsystem includes a movable reflective surface (e.g., mirror) positioned adjacent to the photodiode of the endpoint device. The movable reflective surface may be a flat surface or, in other embodiments, it may be curved (e.g., concave or convex, or any other suitable curvature). For simplicity of description, the embodiments that follow generally reference an adjustable optics subsystem including a single movable lens, but it may be appreciated that this is merely one example; other embodiments can include more than one movable lens, a movable reflective surface, multiple movable reflective surfaces, and/or a combination of movable lenses and reflective surfaces. 
     Continuing the example introduced above, an adjustable optics subsystem, such as described herein, can adjust a position of a movable lens in order to direct and/or otherwise focus laser light emitted from a laser diode of a source device onto a photosensitive area of a photodiode in the endpoint device. In this manner, positional and angular offset tolerance of the directional free-space optical communication system is increased. 
     In some embodiments, an adjustable optics subsystem in an endpoint device can adjust the position of a movable lens based on an output of a photodiode in the endpoint device. For example, if power output from the photodiode is less than a threshold value, the adjustable optics subsystem can cause the movable lens to shift in a selected direction. If power output from the photodiode either decreases or does not change in response to the movement, the adjustable optics subsystem may move the movable lens in another, different, direction until an increase in output power (optionally beyond a threshold, which may be different than the first threshold) is achieved. 
     In some cases, the adjustable optics subsystem can iterate through a number of predetermined and/or predefined positions in order to find an optimal position for the movable lens at which power output from the photodiode is a maximum. In other embodiments, the adjustable optics subsystem can cause the movable lens to follow a predetermined path relative to the photosensitive area of the photodiode (e.g., serpentine path, spiral path, and so on) in order to find an optimal position or set of positions for the movable lens at which power output from the photodiode is a maximum. In other cases, other characteristics of output from the photodiode can be used such as, but not limited to: frequency content; absolute value; voltage; current; and so on. In these and similar examples, the movable lens can be moved to one or more predefined positions. For each predefined position of the movable lens, one or more output characteristics from the photodiode can be obtained. Thereafter, a spatial and/or angular profile or map—corresponding to, in one example, intensity of light received by the photodiode at different positions of the movable lens—can be extrapolated and/or otherwise formed from the one or more output characteristics associated with the one or more predefined positions of the movable lens. Thereafter, the movable lens can be moved to a predefined position or another position based on the spatial and/or angular profile or map. 
     In other cases, the adjustable optics subsystem can adjust the position of the movable lens based on output from one or more sensors within (or in communication with) the endpoint device. For example, in some cases, an endpoint device can include an accelerometer, a gyroscope, magnetoresistance sensor, a magnetometer, or any other suitable sensor. In this example, the adjustable optics subsystem can adjust the position of the movable lens (or a position of more than one movable lens or, in some embodiments, an angle of a reflective surface adjacent to the photodiode) based on output from one or more of the accelerometer, gyroscope, magnetoresistance sensor, or magnetometer. 
     In still further examples, the adjustable optics subsystem can adjust the position of the movable lens based on user input. For example, a user of an endpoint device may provide input corresponding to a direction of a source device. In response to receiving user input, the adjustable optics subsystem can adjust the position of the movable lens in the direction (or in the opposite direction) indicated by the user. For example, in some cases, an endpoint device may be configured to optically couple to more than one source device. In these cases, user input may be provided so that the adjustable optics subsystem moves the movable lens in order to optically couple the endpoint device to a specific or user-selected source device. 
     In still further examples, the adjustable optics subsystem can adjust the position of the movable lens based on, without limitation: an output from one or more optimization algorithms; feedback from another element, system or subsystem of the endpoint device; and so on. It may be appreciated that an adjustable optics subsystem such as described herein can utilize any suitable or appropriate technique, or combination of techniques, to adjust and/or set the position of a movable lens or a movable reflective surface. 
     In some embodiments, a source device can also include an adjustable optics subsystem. For example, the adjustable optics subsystem in a source device can include a movable lens (and/or movable reflective surface) positioned over the laser diode. In this embodiment, the adjustable optics subsystem can adjust a position of the movable lens, biasing the movable lens in one or more directions, in order to direct and/or otherwise focus laser light emitted from the laser diode toward an endpoint device. The adjustable optics subsystem of a source device can be configured in the same manner as described above in reference to the example endpoint device. 
     In certain further embodiments, a source device can include a first adjustable optics subsystem and an endpoint device can include a second adjustable optics subsystem. In this example, the first adjustable optics subsystem can be used to direct laser light emitted from the laser diode in the source device toward the endpoint device. Similarly, the second adjustable optics subsystem can be used to focus laser light received from the source device onto the photosensitive area of the photodiode of the endpoint device. In this manner, the first adjustable optics subsystem and the second adjustable optics subsystem can cooperate to direct laser light emitted from the laser diode onto the photosensitive area of the photodiode of the endpoint device. In further embodiments, the first adjustable optics subsystem and the second adjustable optics subsystem can communicate with one another in order to more quickly and/or more accurately focus laser light emitted from the laser diode onto the photosensitive area of the photodiode. For example, the source device can encode information regarding the position of the movable lens of the first adjustable optics subsystem into the laser light emitted by the laser diode. In this example, the endpoint device can use the information regarding the position of the movable lens of the first adjustable optics subsystem to adjust the position of the movable lens of the second adjustable optics subsystem. In other cases, a position of the movable lens of the first adjustable optics subsystem can be communicated to the second adjustable optics subsystem via an auxiliary or secondary communication channel or protocol, such as via Wi-Fi, Bluetooth, Near-Field Communications, Infrared, or Ethernet protocols. One may appreciate that these are merely examples; in other embodiments, a position of the movable lens of the first adjustable optics subsystem can be communicated to the second adjustable optics subsystem using any other suitable technique. In some further embodiments, relative positions of the movable lenses of the first and second adjustable optics subsystems can be used to determine an angle and/or positional offset between a source device and an endpoint device. 
     These foregoing and other embodiments are discussed below with reference to  FIGS. 1A-9 . 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. 1A  depicts a directional free-space optical communication system  100  communicably and optically coupling two electronic devices, identified as the source device  102  and the endpoint device  104 . In the illustrated example, the source device  102  and the endpoint device  104  are separated by an air gap  106  (e.g., free space). In typical examples, the source device  102  and the endpoint device  104  are battery-operated portable electronic devices, but this may not be required; in some embodiments, one or both of the source device  102  and the endpoint device  104  are substantially stationary. 
     As noted above, the source device  102  and the endpoint device  104  can be any suitable electronic devices; example electronic devices are non-exhaustively listed above. The source device  102  includes a housing  108  enclosing, at least in part, an optical communication module  110  that includes a laser diode. Similarly, the endpoint device  104  includes a housing  112  enclosing, at least in part, an optical communication module  114  that includes a photodiode. In some cases, such as illustrated, the optical communication module  110  can extend at least partially through the housing  108 , although this is not required. In some cases, a protective cover (e.g., lens window) can be provided in the housing  108 . In these embodiments, the optical communication module  110  is positioned behind the protective cover. The optical communication module  114  can be similarly configured in the housing  112 . 
     As noted with respect to other embodiments described herein, the source device  102  and the endpoint device  104  can be configured for multi-channel and/or two-way communication. In these examples, the optical communication module  110  of the source device  102  includes at least one photodiode and the optical communication module  114  of the endpoint device  104  includes at least one laser diode. For simplicity of description, one-way, single-channel communication from the source device  102  to the endpoint device  104  is described below. 
     The laser diode of the optical communication module  110  of the source device  102  emits a beam of light u 1  across the air gap  106  toward the photodiode of the optical communication module  114  of the endpoint device  104 . As noted above, by modulating one or more characteristics of the beam of light u 1 , the source device  102  can communicate digital and/or analog information to the endpoint device  104  (hereinafter referred to as, simply, “data” communicated from a source device to an endpoint device). Example beam characteristics that can be modulated by the source device  102  to communicate data to the endpoint device  104  are non-exhaustively listed above. 
     In some examples, data communicated by the source device  102  to the endpoint device  104  can be encoded according to a particular schema (e.g., code division; time division; quadrature modulation; phase shift keying; frequency-shift keying; amplitude-shift keying; pulse code modulation; and so on) and/or may be encrypted. In other examples, the data communicated by the source device  102  to the endpoint device  104  can conform to a particular data transfer protocol—whether proprietary or standardized—such as, but not limited to: universal serial bus (typically referred to as “USB”); peripheral component interconnect express standard (typically referred to as “PCIe”); controller area network (typically referred to as “CAN”); on-board diagnostics (typically referred to as “ODB” or “ODB-II”); serial peripheral interface bus (typically referred to as “SPI Bus”); high-definition multimedia interface (typically referred to as “HDMI”); Ethernet; integrated drive electronics (typically referred to as “IDE”); serial or parallel advanced technology attachment (typically referred to as “SATA” or “PATA”); inter-integrated circuit bus (typically referred to as “I2C”); and so on. In other cases, more than one protocol, encoding, and/or encryption technique or technology can be used in parallel. 
     The data communicated by the source device  102  to the endpoint device  104  can be any suitable data or data type including but not limited to: real-time data; data streams; data files; configuration files; encryption keys; messages; media files or streams; local or remote network resources or addresses; synchronization data; firmware; software; networking data; human interface device and/or sensor data streams or configurations; and so on. In other cases, data communicated by the source device  102  to the endpoint device  104  can be associated with a secure shell or other remote login session. In other cases, data communicated by the source device  102  to the endpoint device  104  can be associated with a serial data link or serial connection between the source device  102  and the endpoint device  104 . In still further examples, other data or data types—or combinations of data or data types—can be communicated from the source device  102  to the endpoint device  104 . 
     It may be appreciated that the foregoing description of  FIG. 1A , and the various alternatives thereof and variations thereto are presented, generally, for purposes of explanation, and to facilitate a thorough understanding of various possible configurations of a directional free-space optical communication system, such as described herein. However, it will be apparent to one skilled in the art that some of the specific details presented herein may not be required in order to practice a particular described embodiment, or an equivalent thereof. For simplicity of description and illustration,  FIG. 1B  is provided. This figure depicts a simplified block diagram of the source device  102  and the endpoint device  104  of  FIG. 1A , showing various operational and/or structural components that can be included in certain embodiments. 
       FIG. 1B  depicts a simplified system diagram of the directional free-space optical communication system  100  of  FIG. 1A . As shown in the figure, the source device  102  includes a laser diode  116  that emits the beam of light u 1  toward the endpoint device  104  in order to illuminate a photodiode  118  to communicate data to the endpoint device  104 . 
     The source device  102  can (optionally) include an optical structure  120  to adjust one or more characteristics of the beam of light u 1  as it exits the source device  102 . As noted above, the optical structure  120  can be configured to move a movable lens to direct the beam of light u 1  toward the endpoint device  104  in order to accommodate a greater range of positional and/or angular offset(s) of the endpoint device  104  (see, e.g.,  FIGS. 2A-3 ). 
     Similarly, the endpoint device  104  can (optionally) include an optical structure  122  to adjust one or more characteristics—such as a direction—of the beam of light u 1  before the beam of light u 1  illuminates the photodiode  118 . Example characteristics of a beam of light that can be modified by an optical structure, such as described herein, are non-exhaustively provided above. Non-exhaustive example optical structures that can be included in a source device are described below in reference to  FIG. 3 . Non-exhaustive example optical structures that can be included in an endpoint device are described below in reference to  FIGS. 3-5B . 
     The laser diode  116  of the source device  102  is coupled to a drive circuit, identified as the drive circuit  124 . The drive circuit  124  can be any suitable analog or digital circuit or purpose-configured processor, or combination thereof configured to generate direct current and/or alternating current signals suitable to drive the laser diode  116  to emit laser light. The drive circuit  124  is typically configured to control a level of current circulated through the laser diode  116 , although this may not be required; other embodiments may control a voltage applied across the laser diode  116 . The drive circuit  124  can apply any suitable current or voltage waveform to cause the laser diode  116  to emit laser light in any suitable manner (e.g., pulse width, duty cycle, color, frequency, amplitude, and so on). The laser light may be monochromatic or polychromatic. The laser diode  116  may be a single mode or a multi-mode laser. As may be appreciated, the waveform applied to the laser diode  116  corresponds to the data to be communicated from the source device  102  to the endpoint device  104  and will accordingly vary from embodiment to embodiment and will be based on the content of the data to be communicated. 
     The source device  102  can also include other components, including a processor  126 , a memory  128 , a display  130 , an input/output system  132 , an adjustable optics subsystem  134 , and so on. 
     In many configurations, the processor  126  of the source device  102  can be configured to access and execute instructions stored in the memory  128  in order to instantiate any number of suitable classes, objects, virtual machines, threads, pipelines, and/or routines to perform, monitor, and/or coordinate one or more operations of the source device  102 . Further, the processor  126  can be communicably coupled—either directly (e.g., via general-purpose input/output pins) or indirectly (e.g., via an intermediary circuit or integrated circuit)—to each of the hardware components of the source device  102 , including the display  130 , the input/output system  132 , the adjustable optics subsystem  134 , and the drive circuit  124 . In this manner, the processor  126  can coordinate the operation of the various hardware components of the source device  102 . 
     As one example, the processor  126  can cause the display  130  to render a user interface while monitoring a user input sensor (e.g., capacitive touch sensor, capacitive force sensor, and so on) of the input/output system  132  to detect one or more characteristics of a user&#39;s physical interaction with the display  130 . As a result of this construction, a user of the source device  102  is encouraged to interact with content shown on the display  130 . 
     The adjustable optics subsystem  134  of the source device  102  can be configured in a number of ways. In typical implementations, the adjustable optics subsystem  134  includes at least one processor, generally referred to as a controller. The controller of the adjustable optics subsystem  134  is communicably coupled to an actuation mechanism (not shown) configured to move a movable lens of the optical structure  120 . 
     In these embodiments, the controller of the adjustable optics subsystem  134  causes the actuation mechanism to move the movable lens in any suitable direction by any suitable amount. As noted with respect to other embodiments described herein, the controller may be configured to cause the actuation mechanism to move the moveable lens in order to direct laser light emitted from the laser diode  116  in a particular direction, such as toward the endpoint device  104 . 
     In some embodiments, the actuation mechanism of the adjustable optics subsystem  134  is configured to move and/or shift the movable lens of the optical structure  120  in a single, linear direction (e.g., a single degree of freedom). In other cases, the actuation mechanism is configured to move the movable lens in more than one linear direction (e.g., multiple degrees of freedom). In still further embodiments, the actuation mechanism of the adjustable optics subsystem  134  is configured to move and/or shift the movable lens in a vertical direction, relative to the laser diode  116 . In still further embodiments, the actuation mechanism of the adjustable optics subsystem  134  is configured to tilt the movable lens to an angle relative to an exterior surface of the laser diode  116 . In some embodiments, the actuation mechanism can be configured to tilt, move, and/or shift the movable lens. 
     It may be appreciated that the actuation mechanism of the adjustable optics subsystem  134  can vary from embodiment to embodiment. In one example, the actuation mechanism is magnetically controlled. More specifically, the actuation mechanism includes an electromagnet positioned along an axis of the movable lens of the optical structure  120 . The actuation mechanism also includes a permanent magnet (or second electromagnet) coupled to the movable lens and aligned with the electromagnet. The actuation mechanism also includes a centering element formed from an elastic material or structure, such as a spring or an elastomer. The centering element supports the movable lens and exerts a restoring force to re-center the movable lens over the laser diode  116  when the actuation mechanism is not activated. 
     As a result of this construction, the controller of the adjustable optics subsystem  134  can apply a current to the electromagnet in order to attract or repel the permanent magnet (and thus the movable lens) by a certain amount proportional and/or related to both the magnitude of current applied and the restoring force applied by the centering element. As such, by varying the amount of current applied to the electromagnet, the controller of the adjustable optics subsystem  134  can precisely control the position of the movable lens along the axis of the movable lens with which the electromagnet is aligned. 
     In a further implementation of this example, the adjustable optics subsystem  134  can include two or more electromagnets, each associated with, and aligned with, a respective permanent magnet (or secondary electromagnets) coupled to the movable lens of the optical structure  120 . In this embodiment, the controller of the adjustable optics subsystem  134  can precisely control the position of the movable lens along multiple axes. In one embodiment, the adjustable optics subsystem  134  includes two magnetically controlled actuation mechanisms that are positioned ninety degrees offset from one another. In this configuration, one of the two actuation mechanisms can control movement of the movable lens in an “X” direction, whereas the other actuation mechanism can control movement of the movable lens in a “Y” direction. 
     In other embodiments, the actuation mechanism may be implemented differently. Suitable actuation mechanisms include, but are not limited to: piezoelectric actuation mechanisms; magnetostrictive mechanisms; mechanisms implemented with electroactive polymers; mechanisms implemented with shape-memory wire; and so on. For simplicity of description, the embodiments that follow generally reference an adjustable optics subsystem that includes a magnetically controlled actuation mechanism, but it is appreciated that this is merely one example. 
     Returning to the endpoint device  104  depicted in  FIG. 1B , the photodiode  118  is coupled to amplifier  136 . In many embodiments, the amplifier  136  is a transimpedance amplifier, but this may not be required of all embodiments. As with the drive circuit  124  of the source device  102 , the amplifier  136  can be any suitable analog or digital circuit or purpose-configured processor, or combination thereof. The amplifier  136  is typically configured to convert a level of current circulated through the photodiode  118  to a corresponding level of voltage, although this may not be required. 
     In some examples, the amplifier  136  is coupled to a multi-bit analog-to-digital converter (not shown) to quantize the level of voltage output from the amplifier  136  into a series of digitally represented values. 
     In other cases, the amplifier  136  can be coupled to a single-bit analog-to-digital converter or a limiting amplifier configured to generate a sequence of voltages that correspond to digital data (e.g., ones and zeros). In other words, an output of the amplifier  136  can be coupled to an input (e.g., a gate) of a high-speed switching element (e.g., diode, transistor, and so) in order to quantize the voltage output from the amplifier  136  as either a binary one or a binary zero. 
     In still other examples, the amplifier  136  can be coupled to a buffer and/or shift register configured to convert serial information received from the source device into a parallel data. 
     In still further examples, the output from amplifier  136  can be provided directly (with or without a resistor or other elements in series, such as a high-pass filter) to an input of a digital circuit for further processing. As may be appreciated, the waveform output from the photodiode  118  corresponds to the data to be communicated from the source device  102  to the endpoint device  104  and will accordingly vary from embodiment to embodiment and will be based on the content of the data communicated to the endpoint device  104 . 
     Similar to the source device  102  described above, the endpoint device  104  can also include other components, including a processor  138 , a memory  140 , a display  142 , an input/output system  144 , an adjustable optics subsystem  146 , and so on. 
     Similar to the processor  126  of the source device  102  described above, in many configurations, the processor  138  of the endpoint device  104  can be configured to access and execute instructions stored in the memory  140  in order to instantiate any number of suitable classes, objects, virtual machines, threads, pipelines, and/or routines to perform, monitor, and/or coordinate one or more operations of the endpoint device  104 . Further, the processor  138  can be communicably coupled—either directly (e.g., via general-purpose input/output pins) or indirectly (e.g., via an intermediary circuit or integrated circuit)—to each of the hardware components of the endpoint device  104 , including the display  142 , the input/output system  144 , the adjustable optics subsystem  146 , and the amplifier  136 . In this manner, the processor  138  can coordinate the operation of the various hardware components of the endpoint device  104  in a manner similar to that described above in reference to the processor  126  of the source device  102 . 
     Similarly, it may be appreciated that the adjustable optics subsystem  146  can be appropriately configured in the same manner as the adjustable optics subsystem  134  described above. Namely, it is understood that the adjustable optics subsystem  146  can include a controller and an actuation mechanism configured to cooperate to move a movable lens associated with the optical structure  122 . 
     Accordingly, generally and broadly in view of  FIGS. 1A-1B , it is understood that a directional free-space optical communication system can be configured in a number of ways. For example, as noted above, certain electronic devices can operate as both a source device and an endpoint device. In this manner, two-way optical communication can be achieved. Further, in certain embodiments, a source device can include more than one laser diode and an endpoint device can include more than one photodiode. In this manner, multi-channel optical communication can be achieved. 
     Further, although the illustrations of  FIG. 1A-1B  depict optical communication modules as purpose-configured components, this may not be required. For example, in some embodiments, a display or other light source of a source device can be used to transmit data using the techniques and methods described herein. Similarly, a camera or a proximity sensor of an endpoint device can be used to receive data using the techniques and methods described herein. 
     Further, it is appreciated that the specific configuration(s) shown in  FIGS. 1A-1B  are not required. In other cases, a laser diode of a source device and/or a photodiode of an endpoint device can be disposed in portions of an electronic device housing different from the positions shown. 
     Additionally, it may be appreciated that other components and/or systems may be included in particular embodiments. For example, as noted above, in some examples, light emitted from a laser diode of a source device can be configured to conform to a standardized data transfer protocol, such as PCIe. In these embodiments, the endpoint device may include one or more circuits, processors, or components configured to route the information received from the source device directly to a component or subsystem of the endpoint device that responds to the standardized protocol. In this manner, a processor in the source device can directly access and/or control a resource of the endpoint device via the directional free-space optical communication system. 
     Thus, it is understood that the foregoing descriptions of specific embodiments are presented for the purposes of illustration and description. These descriptions are not exhaustive nor intended to limit the disclosure to the precise forms recited herein. To the contrary, 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. 
     For example, in many embodiments, alignment between a source device and an endpoint device in the collimated regime may not be guaranteed.  FIGS. 2A-2D  depict a simplified representation of a directional free-space optical communication system  200  in which a source device  202  and an endpoint device  204  are movable and separated by an air gap  206 . As with other embodiments described herein, a beam of light u 1  emitted from a laser diode in the source device  202  propagates through the air gap  206  along a line-of-sight path toward the endpoint device  204  to illuminate a photodiode in the endpoint device  204 . 
     In many cases, the endpoint device  204  may be movable relative to the source device  202 . In the illustrated embodiment, six axes of potential movement are shown including three translational axes and three rotational axes. More specifically, the endpoint device  204  can move—relative to the source device  202 —in three-dimensional space in an X-direction (e.g., to the left or to the right of the source device  202 ; see, e.g.,  FIG. 2B ), in a Y-direction (e.g., toward or away from the source device  202 ; see, e.g.,  FIG. 2C ), and/or in a Z-direction (e.g., above or below the source device  202 ; see, e.g.,  FIG. 2D ). Similarly, the endpoint device  204  can rotate about the Y-direction axis to an angle Φ (e.g., roll; see, e.g.,  FIG. 2D ), about the X-direction axis to an angle Θ (e.g., pitch; see, e.g.,  FIG. 2C ), and/or about the Z-direction axis to an angle Ψ (e.g., yaw; see, e.g.,  FIG. 2B ). 
     To account for variations in alignment between a source device and an endpoint device of a directional free-space optical communication system, many embodiments optically couple one or more passive or active optical structures or elements—such as reflectors, lenses, waveguides, adjustable optics subsystems, and so on—to either or both the laser diode in a source device or the photodiode in an endpoint device. 
       FIG. 3  depicts a system diagram of a directional free-space optical communication system  300 . As with other embodiments described herein, the system includes a source device  302  and an endpoint device  304  that are separated by an air gap  306 . The source device  302  includes a laser diode  308  and the endpoint device  304  includes a photodiode  310 . The laser light output from the laser diode  308  is modulated and/or otherwise controlled according to a selected data signal or waveform by a drive circuit  312 . In the endpoint device  304 , the photodiode  310  is electrically coupled to an amplifier  314  that may be a transimpedance amplifier configured to convert current output from the photodiode  310  into a variable voltage. In some embodiments, the amplifier  314  also provides a reverse bias to the photodiode  310  so that the photodiode  310  operates in a photoconductive mode and not a photovoltaic mode. 
     In many embodiments, the drive circuit  312  of the source device  302  is formed onto a semiconductor substrate that provides both mechanical support and electrical connection to the laser diode  308 . The drive circuit  312  of the source device  302  can be implemented and/or fabricated in a number of suitable ways. In some examples, the drive circuit  312  and the laser diode  308  are fabricated in the same process or operation, but this may not be required. In some embodiments, the drive circuit  312  may be positioned off-board from a rigid substrate or flexible circuit board to which the laser diode  308  is coupled. It may be appreciated that the simplified layout shown in  FIG. 3  is merely one example and that many other implementations and circuit topologies may be possible. 
     Similarly, the amplifier  314  of the endpoint device  304  can be formed onto a semiconductor substrate that provides both mechanical support and electrical connection to the photodiode  310 . As with the drive circuit  312  of the source device  302 , the amplifier  314  of the endpoint device  304  can be implemented and/or fabricated in a number of suitable ways. In some examples, the amplifier  314  and the photodiode  310  are fabricated in the same process or operation, but this may not be required. In some embodiments, the amplifier  314  may be positioned off-board from a rigid substrate or flexible circuit board to which the photodiode  310  is coupled. As noted above, it may be appreciated that the simplified layout shown in  FIG. 3  is merely one example and that many other implementations and circuit topologies may be possible. 
     The source device  302  also includes an optical adapter  316  configured to reflect and/or diverge a laser light beam emitted from the laser diode  308 , thereby increasing the beam width, divergence angle, and/or beam cross-section by a certain designed amount. In other cases, other beam parameters can be adjusted by the optical adapter  316 . In the illustrated embodiment, the optical adapter  316  also redirects the laser light beam emitted from the laser diode  308  ninety degrees, although this may not be required and/or may vary from embodiment to embodiment. 
     It may be appreciated, however, that diverging and/or redirecting the beam output from the laser diode  308  beyond a threshold amount may be undesirable and may contribute to losses. Accordingly, for embodiments described herein, the optical adapter  316  of the source device  302  is typically configured to modify one or more characteristics of the beam output from the laser diode  308  in order to increase positional and angular offset tolerance of the optical communication system without increasing losses beyond a certain selected threshold amount, which may vary from embodiment to embodiment. 
     In some embodiments, the optical adapter  316  can be associated with an adjustable optics subsystem of the source device  302 . In particular, in some embodiments, the optical adapter  316  can be coupled to an actuation mechanism (not shown) configured to shift and/or tilt the optical adapter  316  to change and/or tune a direction to which light emitted by the laser diode  308  propagates. For example, the actuation mechanism of the adjustable optics subsystem can move the optical adapter  316  in any suitable direction relative to the laser diode  308 . In other embodiments, the optical adapter  316  can be tilted relative to the laser diode  308 . 
     In the illustrated embodiment, the endpoint device  304  can also include an optical adapter  318  configured to reflect and/or concentrate the laser light beam emitted from the laser diode  308  onto the photodiode  310 , thereby increasing the quantity of light (e.g., quantity of photons) received by the photodiode  310 . In the illustrated embodiment, similar to the optical adapter  316  described above, the optical adapter  318  also redirects the laser light beam emitted from the laser diode  308  ninety degrees, although—as noted above—this may not be required and/or may vary from embodiment to embodiment. It may be appreciated that, by concentrating the laser light beam in this manner, the optical adapter  318  of the endpoint device  304  also servers to increase positional and angular offset tolerance of the optical communication system. In other words, in some embodiments, as a result of the wider area across which light is collected by the endpoint device  304 , the photodiode  310  of the endpoint device  304  can remain illuminated by the laser light beam emitted from the laser diode  308  even if the endpoint device  304  is offset from the source device  302  by a small amount. 
     Similar to the optical adapter  316 , the optical adapter  318  can be associated with an adjustable optics subsystem of the endpoint device  304 . The optical adapter  318  can be configured in the same manner described above with respect to the optical adapter  316 . 
     In many embodiments, the optical adapter  316  and the optical adapter  318  are made from the same material, but this may not be required. Example materials for the optical adapter  316  and the optical adapter  318  can include, but may not be limited to flexible or rigid: optically clear polymers; glass; optically-clear ceramics; plastics; and so on. In some cases, the optical adapter  316  and/or the optical adapter  318  can be treated with an optically reflective outer coating, such as a mirrored or metallic coating. In other cases, other appropriate surface finishes and/or external layers can be added. 
     Furthermore, although the optical adapter  316  and the optical adapter  318  are illustrated as above, and separated from the laser diode  308  and the photodiode  310 , respectively, it may be appreciated that this configuration may not be required of all embodiments. For example, in one embodiment, the optical adapter  316  may be optically coupled to an outer surface of the laser diode  308  via an optically clear adhesive, which may be flexible. More particularly, in some embodiments, the optically clear adhesive optically coupling the optical adapters  316 ,  318  to the laser diode  308  and the photodiode  310 , respectively, may also serve as a centering element, at least partially providing a restoring force to the optical adapters  316 ,  318  in embodiments incorporating adjustable optics subsystems in either or both the endpoint device  304  or the source device  302 . 
     In this case, the optically clear adhesive may be selected to provide a smooth refractive index transition from the laser diode  308  to the optical adapter  316 ; the optically clear adhesive may be selected to have a refractive index between that of the optical adapter  316  and the laser diode  308 . It may be appreciated that the photodiode  310  and the optical adapter  318  may be similarly configured. 
     In other embodiments, additional adapters, lenses, and/or reflectors can be included. For example, in some embodiments, the optical adapter  316  can be optically coupled to the laser diode  308  via a second adapter (e.g., a fiber optic cable). In other cases, one or more lenses (e.g., concave, convex, Fresnel, and so on) can interpose the laser diode  308  and the optical adapter  316 . It may be appreciated that the photodiode  310  and the optical adapter  318  may be similarly configured. 
     As noted above, in some embodiments, the source device and the endpoint device can each include additional and/or alternative optical structures—such as optical stabilization subsystems—to increase the quantity of light received by the photodiode of an endpoint device. Generally and broadly,  FIGS. 4A-5B  each depict various implementations of an optical stabilization subsystem that can be bodily incorporated into either or both source devices and endpoint devices, such as described herein. For simplicity of description, the embodiments that follow are described in reference to an example optical stabilization subsystem incorporated into an endpoint device, but it may be appreciated that the systems described below can also be incorporated into a source device such as described herein. 
       FIG. 4A  depicts an endpoint device  400  of a directional free-space optical communication system. As with other endpoint devices described herein, the endpoint device  400  includes a photodiode  402  that is disposed onto and/or coupled (e.g., electrically, mechanically, and so on) to a substrate  404  that can include an amplifier, such as a transimpedance amplifier. The substrate  404  may be flexible or rigid and can be made from any suitable material or combination or layering of materials. In some embodiments, the substrate  404  is formed, at least in part, from a semiconductor material. 
     As noted with respect to other embodiments described herein, the endpoint device  400  of  FIG. 4A  includes an optical stabilization subsystem in order to increase angular and/or positional offset tolerance between the endpoint device  400  and a source device (not shown). 
     More specifically, the photodiode  402  is positioned below a movable lens  406  that is configured to shift in at least one lateral direction. As the movable lens  406  changes position, light entering the lens can be repositioned over a photosensitive area of the photodiode  402 . In a more specific example, if laser light enters the movable lens  406  from a direction normal to an outer surface of the photodiode  402 , such as shown by the laser light beams u 1  and u 2  of  FIG. 4A , repositioning of the movable lens  406  may not be required. In other words, light beams incident ninety degrees from a face of the photodiode  402  may be focused onto the photosensitive area of the photodiode  402  without any movement or shifting of the movable lens  406 . 
     On the contrary, if laser light enters the movable lens  406  from a direction offset from normal to an outer surface of the photodiode  402 , such as shown by the laser light beams u 3  and u 4  of  FIG. 4B , repositioning of the movable lens  406  may be preferred. In other words, light beams not incident ninety degrees from a face of the photodiode  402  may be repositioned and/or refocused onto the photosensitive area of the photodiode  402  by moving, translating, and/or otherwise shifting a position of the movable lens  406 . 
     To facilitate the movement described above, the movable lens  406  is supported, at least in part, by an actuation mechanism  408 . The actuation mechanism  408  includes at least two supports, identified as the supports  410 , that elevate the movable lens  406  an appropriate distance above the photodiode  402 . The distance by which the supports  410  elevate the movable lens  406  may vary from embodiment to embodiment, but it is appreciated that changing the distance between the movable lens  406  and the photodiode  402  may change the extent to which light entering the movable lens  406  is focused onto the photosensitive area of the photodiode  402 . In other words, it may be appreciated that the distance separating the photodiode  402  and the movable lens  406  may vary from embodiment to embodiment and/or based on one or more characteristics of the movable lens  406  (e.g., radius of curvature, focal length, shape, and so on) or one or more characteristics of the photodiode  402  (e.g., size and/or area of the photosensitive area, height of the photodiode  402 , and so on). In some embodiments, the distance between the movable lens  406  and the photodiode  402  is fixed, although this may not be required; in other embodiments, the distance between the photodiode  402  and the movable lens  406  can be dynamically adjusted. 
     The actuation mechanism  408  also includes one or more electromagnets, identified as the electromagnets  412 , that can be selectively actuated to attract and/or repel the movable lens  406  (see, e.g.,  FIG. 4B ). More specifically, the electromagnets  412  are positioned so as to attract or repel permanent magnets (or, in alternative embodiments, additional or auxiliary electromagnets) disposed and coupled to a periphery of the movable lens  406 . Two example permanent magnets are identified in  FIGS. 4A-4B  as the permanent magnets  414 . 
     In typical examples, the optical stabilization subsystem also includes a controller that, in some cases, can be formed into and/or otherwise coupled to the substrate  404 . The controller, as noted above, is configured to apply one or more electrical signals to the actuation mechanism  408 —or, more specifically, to the electromagnets  412  of the actuation mechanism  408 —in order to control movement of the movable lens  406  in particular directions and by particular amounts. 
     More specifically, in the illustrated example, the controller of the optical stabilization subsystem can be configured to control electrical current applied to the electromagnets  412 , thereby causing the electromagnets  412  to each generate a corresponding magnetic field having a specific magnitude and polarity. By controlling the polarity and amplitude of current applied to each of the electromagnets  412 , the controller can effectively control the magnetic fields generated by the electromagnets  412  and, in turn, control the amount or extent to which the magnetic fields generated by the electromagnets  412  attract or repel the permanent magnets  414 . In some examples, the controller can apply current to only one electromagnet at a time, whereas in other examples the controller applies current to multiple electromagnets at the same time. 
     The controller can be a processor, digital circuit, analog circuit, or any combination thereof. In many examples, the controller can be communicably coupled to one or more sensors of the optical stabilization subsystem, the endpoint device  400 , or a sensor in communication with the endpoint device  400 . In these examples, the controller can be configured to move the movable lens  406  in response to receiving input from a sensor (or more than one sensor). 
     For example, in one embodiment, the endpoint device  400  includes an inertial sensor, such as a gyroscopic sensor (also referred to as an angular rate or angular velocity sensor). The inertial sensor can be configured to monitor for, and report, movement of the endpoint device  400 . In response to a movement of the endpoint device  400  reported by the inertial sensor, the controller of the optical stabilization subsystem can be configured to adjust the position of the movable lens  406  to counteract the movement of the endpoint device  400  in substantially real time. For example, if the inertial sensor reports that endpoint device  400  has shifted to the right of the page as shown in  FIGS. 4A-4B , the controller of the optical stabilization subsystem can cause the actuation mechanism  408  to move the movable lens  406  to the left of the page as shown in  FIG. 4B , thereby counteracting the reported movement of the endpoint device  400 . 
     In many examples, the actuation mechanism  408  also includes a centering element  416 . As noted with respect to other embodiments described herein, the centering element  416  can serve to provide a restoring force that resists changes in position of the movable lens  406  caused by the actuation mechanism  408 . In the illustrated embodiment, the centering element  416  is a mechanical spring; although this is merely one example. In other embodiments, the centering element  416  may be implemented in another manner. Example centering elements include, but are not limited to: elastomers; leaf springs; spiral springs; flexion rods; and so on. 
     The foregoing embodiment depicted in  FIGS. 4A-4B  is merely one example construction of an optical stabilization subsystem such as described herein. As such, it may be appreciated that an optical stabilization subsystem can be configured in a manner different than shown. Regardless the particular construction selected for a particular implementation, it may be appreciated that incorporating an optical stabilization subsystem into either or both a source device or an endpoint device of a directional free-space optical communication system, such as described herein, can increase angular and positional offset tolerance between the source device and the endpoint device, thereby improving the range, reliability, and speed of communication between the two devices. 
     Furthermore, it is appreciated that the single degree of freedom construction, as depicted in  FIGS. 4A-4B , is merely one example. In other embodiments, an actuation mechanism of an optical stabilization subsystem can be configured to shift a movable lens (and/or movable reflector) in any suitable direction. For example, in some embodiments, an actuation mechanism can include four electromagnets disposed at ninety-degree intervals around a perimeter or periphery of a movable lens. Each of the four electromagnets can be positioned relative to a permanent magnet coupled to the movable lens. In this example, a controller of the optical stabilization subsystem can be configured to apply current to one or more of the four electromagnets in order to move the movable lens in two dimensions. In other cases, an actuation mechanism can include a different number of electromagnet/permanent magnet pairs. 
     In still further examples, an actuation mechanism, such as described herein, may be configured to operate without generating magnetic fields. Non-magnetic actuation mechanisms that may be appropriately incorporated into an optical stabilization subsystem, such as described herein include, but are not limited to: electrostatic attraction mechanisms; piezoelectric mechanisms; pressure bladder mechanisms; microscopic electromechanical actuators; electroactive polymer mechanisms; shape-memory alloy mechanism; and so on. In some cases, a centering element can also serve to move the movable lens. For example, the centering element may be a spring formed from a shape memory alloy; when supplied with current, the centering element changes shape, changing the position of the movable lens in one or more directions. When the supply of current is terminated, the movable lens can return to a central position. 
     In still further embodiments, an actuation mechanism may be configured to tilt a movable lens (and/or a photodiode or laser diode below the lens) in addition to—or as an alternative to—laterally shifting the movable lens, such as described above in reference to  FIGS. 4A-4B . 
       FIG. 5A  depicts an endpoint device  500  of a directional free-space optical communication system including an optical stabilization subsystem. The endpoint device  500  includes a photodiode  502  and a substrate  504 . The photodiode  502  (and, additionally, an amplifier such as described in reference to other embodiments describe herein) is positioned below, and aligned with, a lens  506 . The lens  506  and the photodiode  502  are supported by an actuation mechanism  508  that includes a pivoting frame  510 . The pivoting frame  510  pivots over a fulcrum point  512  toward or away from a support  514 . A centering element  516  is disposed between the pivoting frame  510  and the support  514  to provide a restoring force that resists changes in position (e.g., angle) of the pivoting frame  510  (see, e.g.,  FIG. 5B ). In this embodiment, a controller of the optical stabilization subsystem can be configured to provide a signal to the actuation mechanism  508  to cause the actuation mechanism  508  to tilt the pivoting frame  510  in a particular direction. In one example, the actuation mechanism can include electromagnets and permanent magnets such as described above in reference to  FIGS. 4A-4B . 
     It may be appreciated that the foregoing description of  FIGS. 4A-5B , and the various alternatives thereof and variations thereto are presented, generally, for purposes of explanation, and to facilitate a thorough understanding of various possible configurations of an adjustable optics subsystem in an endpoint device or source device of a directional free-space optical communication system, such as described herein. However, it will be apparent to one skilled in the art that some of the specific details presented herein may not be required in order to practice a particular described embodiment, or an equivalent thereof. 
     Thus, it is understood that the foregoing descriptions of specific embodiments are presented for the limited purposes of illustration and description. These descriptions are not exhaustive nor intended to limit the disclosure to the precise forms recited herein. To the contrary, 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. 
     For example, a controller of an adjustable optics subsystem can be configured to move and/or tilt a movable lens in response to any appropriate stimulation. For example, a controller of an adjustable optics subsystem in an endpoint device of a directional free-space optical communication system can be configured to monitor power output from the photodiode of the endpoint device to determine whether light received on the photosensitive area of the photodiode is appropriately positioned on the photosensitive area. For example,  FIG. 6A  depicts a top view of a photodiode  600  of an endpoint device of a directional free-space optical communication system. The photodiode  600  is disposed in a component enclosure that defines an exterior surface  602  that defines a photosensitive area illustrated as the central portion  604  of the exterior surface. The central portion  604  is defined in the geometric center of the exterior surface  602 , surrounded by a partition  606  (acting as an aperture) formed from metal. The partition  606  separates the central portion  604  from the remaining portion of the photosensitive area such that the remaining portion of the photosensitive area surrounds the central portion  604 , separated by the partition  606 . In some cases, the photodiode  600  can include a partition formed from another material such as plastic, ink, glass, and so on; metal may not be required for all embodiments and the partition  606  is merely one example. 
     As a result of this construction, a focused beam  608  that is not properly positioned/aligned in the central portion  604  (see, e.g.,  FIG. 6B ) of the photosensitive area can at least partially illuminate the partition  606 , causing power output from the central portion  604  to fall. Once the controller of the adjustable optics subsystem recognizes that power output from the central portion  604  of the photodiode  600  has dropped beyond a threshold value, it can instruct an actuation mechanism to move the movable lens in order to re-center the focused beam  608  relative to the central portion  604  (see, e.g.,  FIG. 6A ). 
     As noted with respect to other embodiments described herein, the controller of the adjustable optics subsystem can move the movable lens in any suitable manner, following any suitable technique. In one example, once a drop in power is detected, the controller of the adjustable optics subsystem can instruct the movable lens to move in a pre-defined pattern, such as a cross pattern. As the movable lens is moved, the controller can monitor power output from the photodiode to determine a location of the movable lens that corresponds to the highest power output. In the case that more than one location of the movable lens corresponds to high power output, an average location (e.g., geometric center of mass of the multiple high-power locations) may be used if the output at that location is above a threshold value. In still other embodiments, the controller of the adjustable optics subsystem can implement a maximization algorithm to determine the coordinate location of the movable lens corresponding to maximum power output from the photodiode. Suitable algorithms can include: watershed algorithms; gradient ascent/descent algorithms; segmentation algorithms; and so on. It may be appreciated that any technique and/or combination of techniques can be used by the controller to determine a position for a movable lens. 
     In some examples, the controller of the adjustable optics subsystem can continually operate in a feedback loop in order to continually adjust the position of the movable lens. Feedback can be received by the controller from any suitable feedback source including, without limitation: inertial sensors; positional sensors; data or information from a source device or endpoint device; output from an optimization algorithm; output power from the central region of the photodiode and/or outer region of the photodiode; and so on. 
     In other cases, the controller of the adjustable optics subsystem can be configured to adjust the position of the movable lens at a particular time (e.g., interval, scheduled time or date, and so on) or in response to a particular trigger. For example, the controller of the adjustable optics subsystem can be configured, in one embodiment, to adjust the position of the movable lens only in response to a request to send or receive data using the directional free-space optical communication system. In other cases, other triggers can be received by the controller including, but not limited to: user input; data or information received from a communication channel different from the directional free-space optical communication system (e.g., Wi-Fi, Bluetooth, Near-Field communication, Ethernet, and so on); data or information received via the directional free-space optical communication system; and so on. 
     In some cases, an adjustable optics subsystem in a source device of a directional free-space optical communication system can cooperate with an adjustable optics subsystem in an endpoint device of the same system. For example, both devices can be placed in a pairing or linking mode. When in the pairing or linking mode, the adjustable optics subsystem in the source device can cause the movable lens to scan in a particular direction or according to a particular scanning pattern and/or predefined pattern (e.g., line-scan vertically and/or horizontally). In some embodiments, when in the pairing or linking mode, the movable lens in the source device is moved at a first, high speed. 
     While the adjustable optics subsystem in the source device is scanning, the adjustable optics subsystem in the endpoint device may be static or may scan at a lower rate than the adjustable optics subsystem in the source device, monitoring power output from the photodiode for an increase in power. Once an increase in power is detected, the endpoint device can signal the source device using an appropriate communication protocol or technique to stop scanning. In some cases, a timestamp can be sent to the source device, but this may not be required. 
     In other cases, the signal from the endpoint device may cause the source device to scan at a second, lower rate or speed within a particular angular range based on, in some examples, the time at which the source device received the signal to stop scanning from the endpoint device. Thereafter, once the adjustable optics subsystem in the source device has determined a position for the movable lens, the adjustable optics subsystem in the endpoint device can begin moving the movable lens in accordance with one or more techniques described herein. In this manner, the adjustable optics subsystem in the source device and the adjustable optics subsystem in the endpoint device cooperate to increase angular and/or positional offset tolerance between the two devices. 
     Still further embodiments can be configured in a different manner. For example, as shown in  FIG. 6C , in some examples, the partition  606  can be thin, relative to the expected cross-sectional area of the focused beam  608 . 
     As a result of this construction, a focused beam  608  that is not properly positioned/aligned in the central portion  604  of the photosensitive area can at least partially illuminate the remaining portion of the photosensitive area of the photodiode  600 , causing power output from the central portion  604  to fall and causing power output from the remaining portion to increase. Once the controller of the adjustable optics subsystem recognizes that power output from the central portion  604  of the photodiode  600  has dropped beyond a threshold value and/or that power output from the remaining portion has increased, it can instruct an actuation mechanism to move the movable lens in order to re-center the focused beam  608  relative to the central portion  604  (see, e.g.,  FIG. 6A ). 
     In still further examples, the remaining portion of the photosensitive area can be segmented. For example,  FIG. 7  depicts a photodiode  700  that, like the embodiments depicted in  FIGS. 6A-6C , includes an exterior surface  702  that defines a photosensitive area. A central portion  704  of the photosensitive area is defined in the geometric center of the exterior surface  702 , surrounded by a partition  706  formed from a material such as metal. The partition  706  separates the central portion  704  from the remaining portion of the photosensitive area. In this embodiment, the remaining portion of the photosensitive area is partitioned, segmented, and/or otherwise separated into four discrete regions evenly distributed around the periphery/perimeter of the partition  706 , labeled as the segments  702   a - 702   d  of the remaining portion of the photosensitive area. In particular, the remaining portion of the photosensitive area is partitioned by a metal mask  710 . 
     As a result of this construction, a focused beam  708  that is not properly positioned/aligned in the central portion  704  of the photosensitive area can at least partially illuminate at least one segment  702   a - 702   d  of the remaining portion of the photosensitive area of the photodiode  700 , causing power output from the central portion  704  to fall and causing power output from the illuminated segment(s) to increase. Once the controller of the adjustable optics subsystem recognizes that power output from the central portion  704  of the photodiode  700  has dropped beyond a threshold value and/or that power output from the remaining portion has increased, it can instruct an actuation mechanism to move the movable lens in order to re-center the focused beam  708  relative to the central portion  704  (see, e.g.,  FIG. 6A ). In this example, re-centering movement of the movable lens may be performed proportionality based on which of the segment(s)  702   a - 702   d  are illuminated. For example, if the segment  702   b  is illuminated, but none of the other segments are illuminated, the controller of the adjustable optics subsystem can cause the movable lens to change position such that the focused beam  708  moves diagonally toward the segment  702   d . Similarly, if the segment  702   b  is illuminated along with the segment  702   a , but neither of the other two segments is illuminated, the controller of the adjustable optics subsystem can cause the movable lens to change position such that the focused beam  708  moves horizontally toward the left of the figure. 
     It may be appreciated that four segments, such as shown, is merely one example. Other embodiments can include a greater or less number of segments, segment patterns or distributions, and so on. Further, in other embodiments, the distribution of segments may not be uniform; in some cases, segments along horizontal regions of a photodiode may have a smaller area than segments along vertical regions of the photodiode. 
     It may be appreciated that the foregoing description of  FIGS. 6A-7 , and the various alternatives thereof and variations thereto are presented, generally, for purposes of explanation, and to facilitate a thorough understanding of various possible configurations of an adjustable optics subsystem in an endpoint device or source device of a directional free-space optical communication system, such as described herein. However, it will be apparent to one skilled in the art that some of the specific details presented herein may not be required in order to practice a particular described embodiment, or an equivalent thereof. 
     Thus, it is understood that the foregoing descriptions of specific embodiments are presented for the limited purposes of illustration and description. These descriptions are not exhaustive nor intended to limit the disclosure to the precise forms recited herein. To the contrary, 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. 
     Generally and broadly,  FIGS. 8-9  depict simplified flow charts corresponding to various ordered and/or unordered operations of methods that may be used to manufacture one or more components such as described herein. It may be appreciated that these simplified examples may be modified in a variety of ways. In some examples, additional, alternative, or fewer operations than those depicted and described may be possible. 
       FIG. 8  is a simplified flow chart showing example operations of a method of positioning a movable lens in a directional free-space optical communication system, such as described herein. 
     The method  800 —which can be performed by one or more controllers of an adjustable optics subsystem, such as described herein—includes operation  802  in which at least one of a source device or an endpoint device of a directional free-space optical communication system, such as described herein, enters a link mode. At operation  804 , a power output (or other suitable output or characteristic, such as voltage, current, or resistance) of a photosensitive element or photodetector is measured. As noted with respect to embodiments described herein, the photosensitive element is typically disposed within an endpoint device. Next, at operation  806 , a lens positioned above the photodetector is adjusted, if necessary. Finally, at operation  808 , a communication link between the endpoint device and the source device can be established via appropriate handshake and/or negotiation. In other words, the device(s) may exit the link mode and may proceed to exchange data or information via the directional free-space optical communication system by entering a communication mode or a data transfer mode. 
     In many cases, a directional free-space optical communication system includes two devices that each can function as a source device and an endpoint device. In these examples, the method  800  can be performed by both communicated devices, either simultaneously or otherwise, in order to ensure that the photodiode of one device is appropriately aligned with the laser diode of the other device and vice versa. 
       FIG. 9  is a simplified flow chart showing example operations of another method of positioning a movable lens in a directional free-space optical communication system, such as described herein. The method  900  begins at operation  902  in which data is received at an endpoint device from a source device of an optical communication system. Next, at operation  904 , an error can be detected that corresponds to an angular offset between the source device and the endpoint device. As described above, the error can be detected based on a received power drop detected in the endpoint device. Next, at operation  906 , a position of a movable lens in the endpoint device can be adjusted to maximize power output. The method then continues back to operation  904 . In other embodiments, a movable lens in an endpoint device can be moved based on historical or recent position information. In some embodiments, a movable lens can be moved based on a predicted future location of a source device (e.g., a prediction based on an estimation algorithm, such as a Kalman filter). 
     In some cases, an angular error detected at operation  904  cannot be corrected by operation  906 . In these cases, an endpoint device may generate a notification to a user and/or to the source device that the communication link between the source device and the endpoint device has been broken. 
     In many cases, a directional free-space optical communication system includes two devices that each can function as a source device and an endpoint device. In these examples, the method  900  can be performed by both communicated devices, either simultaneously or otherwise, in order to ensure that the photodiode of one device is appropriately aligned with the laser diode of the other device and vice versa. 
     One may appreciate that, although many embodiments are disclosed above, the operations and steps presented with respect to methods and techniques described herein are meant as exemplary and accordingly are not exhaustive. One may further appreciate that alternate step order or fewer or additional operations may be required or desired for particular embodiments. 
     Although the disclosure above is described in terms of various exemplary embodiments and implementations, it should be understood that the various features, aspects and functionality described in one or more of the individual embodiments are not limited in their applicability to the particular embodiment with which they are described, but instead can be applied, alone or in various combinations, to one or more of the some embodiments of the invention, whether or not such embodiments are described and whether or not such features are presented as being a part of a described embodiment. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments but are instead defined by the claims herein presented.

Metadata:
Filing Date: 20190430
Publication Date: 20200630
Grant Date: 20200630
Priority Date: 20180530
Inventors: MOMTAHAN, OMID
CHEN, TONG
Assignee: APPLE INC
CPC Classifications: [{"code": "H04B10/07955", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B10/691", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B10/503", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B26/101", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B26/0875", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B10/1141", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B10/1121", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B26/101", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B10/07955", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B26/0875", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B10/503", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B10/1121", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04B10/691", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 68693349