Patent Description:
Communication terminals may transmit and receive optical signals through free space optical communication (FSOC) links. In order to accomplish this, such terminals generally use acquisition and tracking systems to establish the optical link by pointing optical beams towards one another. For instance, a transmitting terminal may use a beacon laser to illuminate a receiving terminal, while the receiving terminal may use a position sensor to locate the transmitting terminal and to monitor the beacon laser. Steering mechanisms may maneuver the terminals to point toward each other and to track the pointing once acquisition is established. A high degree of pointing accuracy may be required to ensure that the optical signal will be correctly received.

<CIT> describes a bi-directional Free Space Optical (FSO) communication unit that may be used in a multi-node FSO communication system. The bi-directional FSO unit may include a co-boresighted optical unit such that received and transmitted beams are coincident through a common aperture.

<CIT> describes a method including receiving axis signals from a multi-axis position sensing detector, generating a reference signal by summing the axis signals, determining a mirror position of a mirror directing the optical beam based on the beam position error of each axis of the multi-axis position sensing detector, and actuating the mirror to move to the mirror position. Each axis signal is indicative of a beam position of an optical beam incident on the multi-axis position sensing detector, each axis signal corresponding to an axis of the multi-axis position sensing detector. For each axis of the multi-axis position sensing detector, the method includes converting a phase of an axis to have a <NUM> degree phase difference from a signal of the axis, generating an axis-phasor signal by summing the axis signals, and comparing the axis-phasor signal and the reference signal to determine a phase difference.

<CIT> describes a detector configuration for use in a free space optical (FSO) node for transmitting and/or receiving optical signals has a plurality of sensors for detecting received optical signals. The plurality of sensors is configured along a common optical path and are used for separate functions. According, the detectors may be optimized for the respective function.

Aspects of the disclosure provide for a method of aligning a tracking system of a communication device. The method includes receiving an optical beam at the communication device, where a first beam portion of the optical beam is received at the tracking system and a second beam portion of the optical beam is received at an optical fiber of the communication device. The method further includes using one or more processors to receive a first signal and a second signal from the tracking system, which are generated based on a position of the first beam portion received at the tracking system, determine a first phase difference based on a first phase of the first signal and a second phase difference based on a second phase of the second signal, wherein the first phase difference is between a first phase of the first signal and a first clock component phase measurement, and the second phase difference is between a second phase of the second signal and a second clock component phase measurement, and determine a first offset for the first signal based on the first phase difference and a second offset for the second signal based on the second phase difference for use in electronically aligning the tracking sensor and the optical fiber by adjusting a setpoint position of the tracking sensor of the tracking system. In addition, the method includes tracking, by the one or more processors, the optical beam using the tracking system and the first and second offsets.

The technology relates to aligning tracking systems of communication terminals as well as aligning those communication terminals. The communication terminals may be geographically separate and may also form at least part of a network, such as a free space optical communication network. Each tracking sensor of the tracking systems is aligned to an optical fiber to more accurately track an incoming signal and aim an outgoing signal. At a first communication device of a first communication terminal, an optical beam is received and diverted to the tracking sensor and the optical fiber. A position of a first beam portion on the tracking sensor is identified. When a second beam portion is received at the optical fiber and the position of the first beam portion is not at or near the center of the tracking sensor, the optical beam is processed to electronically align the tracking sensor and the optical fiber.

The communication terminals are then aligned after the tracking system of each communication terminal is aligned so that an optical beam transmitted from one communication terminal is received at or near a center of the optical fiber of the other communication terminal. An update communication regarding the alignment of the first and second communication terminals may be transmitted optically by the first communication terminal to the second communication terminal. In response to receiving the update communication, the location and/or pointing direction of the second communication terminal may be adjusted. To further align the first and second communication terminals, the center of the optical fiber at the second communication terminal may also be determined, and the location and/or pointing direction of the first communication terminal may also be adjusted.

The features described herein may provide an optical communication system that is more accurately aligned and capable of tracking and adjusting alignment quickly. Furthermore, the alignment of the tracking sensor and the optical fiber of each communication terminal may be performed without adversely affecting the signal-to-noise ratio.

<FIG> is a block diagram <NUM> of a first communication device of a first communication terminal configured to form one or more links with a second communication device of a second communication terminal, for instance as part of a system such as a free-space optical communication (FSOC) system. For example, a first communication device <NUM> includes one or more processors <NUM>, a memory <NUM>, a transmitter <NUM>, a receiver <NUM>, and a steering mechanism <NUM>.

The one or more processors <NUM> may be any conventional processors, such as commercially available CPUs. Alternatively, the one or more processors may be a dedicated device such as an application specific integrated circuit (ASIC) or other hardware-based processor, such as a field programmable gate array (FPGA). Although <FIG> functionally illustrates the one or more processors <NUM> and memory <NUM> as being within the same block, the one or more processors <NUM> and memory <NUM> may actually comprise multiple processors and memories that may or may not be stored within the same physical housing. Accordingly, references to a processor or computer will be understood to include references to a collection of processors or computers or memories that may or may not operate in parallel.

Memory <NUM> may store information accessible by the one or more processors <NUM>, including data <NUM>, and instructions <NUM>, that may be executed by the one or more processors <NUM>. The memory may be of any type capable of storing information accessible by the processor, including a computer-readable medium such as a hard-drive, memory card, ROM, RAM, DVD or other optical disks, as well as other write-capable and read-only memories. The system and method may include different combinations of the foregoing, whereby different portions of the data <NUM> and instructions <NUM> are stored on different types of media. In the memory of each communication device, such as memory <NUM>, calibration information, such as one or more offsets determined for tracking a signal, may be stored.

Data <NUM> may be retrieved, stored or modified by the one or more processors <NUM> in accordance with the instructions <NUM>. For instance, although the system and method is not limited by any particular data structure, the data <NUM> may be stored in computer registers, in a relational database as a table having a plurality of different fields and records, XML documents or flat files. The data <NUM> may also be formatted in any computer-readable format such as, but not limited to, binary values or Unicode. By further way of example only, image data may be stored as bitmaps comprised of grids of pixels that are stored in accordance with formats that are compressed or uncompressed, lossless (e.g., BMP) or lossy (e.g., JPEG), and bitmap or vector-based (e.g., SVG), as well as computer instructions for drawing graphics. The data <NUM> may comprise any information sufficient to identify the relevant information, such as numbers, descriptive text, proprietary codes, references to data stored in other areas of the same memory or different memories (including other network locations) or information that is used by a function to calculate the relevant data.

The instructions <NUM> may be any set of instructions to be executed directly (such as machine code) or indirectly (such as scripts) by the one or more processors <NUM>. For example, the instructions <NUM> may be stored as computer code on the computer-readable medium. The instructions <NUM> may be stored in object code format for direct processing by the one or more processors <NUM>, or in any other computer language including scripts or collections of independent source code modules that are interpreted on demand or compiled in advance. Functions, methods and routines of the instructions <NUM> are explained in more detail below.

The one or more processors <NUM> may be in communication with the transmitter <NUM> and the receiver <NUM>. Transmitter <NUM> and receiver <NUM> may be part of a transceiver arrangement in the communication device <NUM>. The one or more processors <NUM> may therefore be configured to transmit, via the transmitter <NUM>, data in a signal, and also may be configured to receive, via the receiver <NUM>, communications and data in a signal. The received signal may be processed by the one or more processors <NUM> to extract the communications and data.

The transmitter <NUM> may be configured to output a beacon beam <NUM> that allows one communication device to locate another. The transmitter <NUM> may include a beacon transmitter which produces a beacon beam. The beacon beam may be output at a wider angle than the optical communication beam, allowing a communication device that receives the beacon beam to better locate the beacon beam. In other words, the beacon beam may cover a larger solid angle in space than the communication signal. For example, the beacon signal may cover an angular area on the order of a square milliradian, and the communication signal may cover an angular area on the order of a hundredth of a square milliradian.

The transmitter <NUM> may also be configured to transmit a communication signal over a communication link <NUM>. In some examples, the communication signal may be a signal configured to travel through free space, such as, for example, a radio-frequency signal or optical signal. The transmitter <NUM> may include one or more communication link transmitters that are separate from the beacon transmitter. Alternatively, the transmitter <NUM> may include one transmitter configured to output both the beacon beam and the communication signal. In some implementations, a given communication link transmitter may include a semi-conductor device, such as, for example, a light-emitting diode (LED) or a laser diode. In some examples, the given communication link transmitter may include a fiber laser or a solid state laser. Laser diodes may be directly modulated, or in other words, the light output may be controlled by a current applied directly to the given communication link transmitter. The given communication link transmitter may include a single-mode laser diode that supports one optical mode, or the given communication link transmitter may include a multimode laser diode that supports multiple-transverse optical modes. The given communication link transmitter may receive a modulated communication signal from a modulator (not shown), which modulates a received electrical signal. The given communication link transmitter may then convert the modulated electrical signal into an optical communication beam that is configured to establish a communication link with another communication device, and then output the optical communication beam from the first communication device <NUM>.

The transmitter <NUM> may also be configured to output a beacon beam <NUM> that allows one communication device to locate another. In some cases, the transmitter includes one or more communication link transmitters configured to transmit the optical communication beam and a separate beacon transmitter configured to transmit the beacon beam. The beacon beam <NUM> may illuminate a larger solid angle in space than the optical communication beam used in the communication link <NUM>, allowing a communication device that receives the beacon beam to better locate the beacon beam. For example, the beacon beam carrying a beacon signal may cover an angular area on the order of a square milliradian, and the otpical communication beam carrying a communication signal may cover an angular area on the order of a hundredth of a square milliradian.

The transmitter <NUM> of the first communication device <NUM> may be configured to output a beacon beam 20a to establish a communication link 22a with the second communication device <NUM>, which receives the beacon beam 20a. The first communication device <NUM> may align the beacon beam 20a co-linearly with the optical communication beam (not shown) that has a narrower solid angle than the beacon beam 20a and carries a communication signal <NUM>. As such, when the second communication device <NUM> receives the beacon beam 20a, the second communication device <NUM> may establish a line-of-sight with the first communication device <NUM> or otherwise align with the first communication device. As a result, the communication link 22a that allows for the transmission of the optical communication beam (not shown) from the first communication device <NUM> to the second communication device <NUM> may be established.

The receiver <NUM> may include an optical fiber and a tracking system configured to detect the optical beam. The tracking system may include at least a tracking sensor. In addition, the tracking system may also include a lens, mirror, or other system configured to divert a portion of a received optical beam to the tracking sensor and allow the remaining portion of the received optical beam to couple with the optical fiber. For instance, a dichroic mirror or sample mirror may be included in the tracking system and may be configured to divert at or around <NUM>% of the received optical beam to the tracking sensor. A remaining portion of the optical beam, such as at or around <NUM>% of the optical beam, may continue on to the optical fiber. The tracking sensor may include a flat surface configured to detect a position of the optical beam on the flat surface. The tracking sensor may include, but is not limited to, a position sensitive detector (PSD), a charge-coupled device (CCD) camera, a focal plane array, a photodetector, a quad-cell, or a CMOS sensor. The tracking sensor may detect a signal location at the tracking sensor and may convert the received optical beam into an electric signal using the photoelectric effect. The tracking system may track the received optical beam, which may be used to direct the steering mechanism <NUM> to counteract disturbances due to scintillation and/or platform motion.

Furthermore, the one or more processors <NUM> may be in communication with the steering mechanism <NUM> (such as a mirror or a gimbal) for adjusting the pointing direction of the transmitter <NUM>, receiver <NUM>, and/or optical beam. In particular, the steering mechanism <NUM> may be a MEMS <NUM>-axis mirror, <NUM>-axis voice coil mirror, or piezo electronic <NUM>-axis mirror. The steering mechanism <NUM> may be configured to steer the transmitter, receiver, and/or optical beam in at least two degrees of freedom, such as, for example, yaw and pitch. The adjustments to the pointing direction may be made to establish acquisition and connection link, such as communication link <NUM>, between the first communication device <NUM> and the second communication device <NUM>. In addition, the adjustments may optimize transmission of light from the transmitter and/or reception of light at the receiver. In some implementations, the one or more processors <NUM> may provide closed loop control for the steering mechanism <NUM> to adjust pointing direction based upon the optical beam received over the communication link from a transmitting communication device, such as an optical beam received over the communication link 22b from the second communication device <NUM>.

Similarly, the second communication device <NUM> includes one or more processors, <NUM>, a memory <NUM>, a transmitter <NUM>, and a receiver <NUM>. The one or more processors <NUM> may be similar to the one or more processors <NUM> described above. Memory <NUM> may store information accessible by the one or more processors <NUM>, including data <NUM> and instructions <NUM> that may be executed by processor <NUM>. Memory <NUM>, data <NUM>, and instructions <NUM> may be configured similarly to memory <NUM>, data <NUM>, and instructions <NUM> described above. In addition, the transmitter <NUM>, the receiver <NUM>, and the steering mechanism <NUM> of the second communication device <NUM> may be similar to the transmitter <NUM>, the receiver <NUM>, and the steering mechanism <NUM> described above.

Like the transmitter <NUM>, transmitter <NUM> may be configured to output both an optical communication beam and a beacon beam. For example, transmitter <NUM> of the second communication device <NUM> may output a beacon beam 20b to establish a communication link 22b with the first communication device <NUM>, which receives the beacon beam 20b. The second communication device <NUM> may align the beacon beam 20b co-linearly with the optical communication beam (not shown) that has a narrower solid angle than the beacon beam and carries another communication signal. As such, when the first communication device <NUM> receives the beacon beam 20a, the first communication device <NUM> may establish a line-of-sight with the second communication device <NUM> or otherwise align with the second communication device. As a result, the communication link 22b, that allows for the transmission of the optical communication beam (not shown) from the second communication device <NUM> to the first communication device <NUM>, may be established.

Like the receiver <NUM>, the receiver <NUM> includes an optical fiber and a tracking system configured to detect the optical beam with the same or similar features as described above with respect to the receiver <NUM>. In addition, the tracking system may also include a lens, mirror, or other system configured to divert a portion of a received optical beam to the tracking sensor and allow the remaining portion of the received optical beam to couple with the optical fiber. The tracking system of receiver <NUM> may track the received optical beam, which may be used to direct the steering mechanism <NUM> to counteract disturbances due to scintillation and/or platform motion.

The one or more processors <NUM> is in communication with the steering mechanism <NUM> (such as a mirror or a gimbal) for adjusting the pointing direction of the transmitter <NUM>, receiver <NUM>, and/or optical beam, as described above with respect to the steering mechanism <NUM>. The adjustments to the pointing direction may be made to establish acquisition and connection link, such as communication link <NUM>, between the first communication device <NUM> and the second communication device <NUM>. In addition, the one or more processors <NUM> may provide closed loop control for the steering mechanism <NUM> to adjust pointing direction based upon the optical beam received over the communication link from a transmitting communication device, such as an optical beam received over the communication link 22a from the first communication device <NUM>.

As shown in <FIG>, the communication links 22a and 22b may be formed between the first communication device <NUM> and the second communication device <NUM> when the transmitters and receivers of the first and second communication devices are aligned. Using the communication link 22a, the one or more processors <NUM> can send communication signals to the second communication device <NUM>. Using the communication link 22b, the one or more processors <NUM> can send communication signals to the first communication device <NUM>. In some examples, it is sufficient to establish one communication link <NUM> between the first and second communication devices <NUM>, <NUM>, which allows for the bi-directional transmission of data between the two devices. The communication links <NUM> in these examples are FSOC links. In other implementations, one or more of the communication links <NUM> may be radio-frequency communication links or other type of communication link capable of travelling through free space.

As shown in <FIG>, a plurality of communication devices, such as the first communication device <NUM> and the second communication device <NUM>, may be configured to form a plurality of communication links between a plurality of communication terminals and form a network <NUM>. For example, the communication terminals in network <NUM> include two land-based datacenters 205a and 205b (generally referred to as datacenters <NUM>), two ground terminals, or ground stations, 207a and 207b (generally referred to as ground stations <NUM>), and four airborne high altitude platforms (HAPs) 210a-210d (generally referred to as HAPs <NUM>). As shown, HAP 210a is a blimp, HAP 210b is an airplane, HAP 210c is a balloon, and HAP 210d is a satellite. Arrows shown between a pair of communication terminals represent possible communication links <NUM>, <NUM>, <NUM>-<NUM> between the communication terminals.

The network <NUM> as shown in <FIG> is illustrative only, and in some implementations the network <NUM> may include additional or different communication terminals. For example, in some implementations, the network <NUM> may include additional HAPs, which may be balloons, blimps, airplanes, unmanned aerial vehicles (UAVs), satellites, or any other form of high altitude platform, additional ground communication terminals, or other types of communication terminals. In alternate implementations, the network <NUM> is a terrestrial network comprising a plurality of communication devices on a plurality of ground communication terminals. The network <NUM> may be an FSOC network that includes communication terminals having communication devices equipped to perform FSOC, such as the first communication device <NUM> and the second communication device <NUM>. In other implementations, the network <NUM> may additionally or alternatively be equipped to perform other forms of communication, such as radiofrequency communications.

In some implementations, the network <NUM> may serve as an access network for client devices such as cellular phones, laptop computers, desktop computers, wearable devices, or tablet computers. The network <NUM> also may be connected to a larger network, such as the Internet, and may be configured to provide a client device with access to resources stored on or provided through the larger computer network. In some implementations, HAPs <NUM> can include wireless transceivers associated with a cellular or other mobile network, such as eNodeB base stations or other wireless access points, such as WiMAX or UMTS access points. Together, HAPs <NUM> may form all or part of a wireless access network. HAPs <NUM> may connect to the datacenters <NUM>, for example, via backbone network links or transit networks operated by third parties. The datacenters <NUM> may include servers hosting applications that are accessed by remote users as well as systems that monitor or control the components of the network <NUM>. HAPs <NUM> may provide wireless access for the users, and may route user requests to the datacenters <NUM> and return responses to the users via the backbone network links.

The communication devices of geographically separate, or remote, communication terminals may be used to perform a method for aligning the tracking system and the optical fiber as well as aligning the communication devices to one another. At a first communication device, such as first communication device <NUM>, an optical beam may be received and diverted to the tracking sensor and the optical fiber of the first communication device. The optical beam may carry an optical signal, such as a communication or beacon signal received from a second communication device, such as second communication device <NUM>, or a test signal from another source used for calibrating the first communication device. In some instances, <NUM>% or more or less of the optical beam may be diverted to the tracking sensor of the first communication device, while a second beam portion, such as the remaining portion of the optical beam, continues on to the optical fiber of the first communication device.

In <FIG>, flow diagram <NUM> is shown in accordance with some of the aspects described above that may be performed by the one or more processors <NUM> of the first communication device <NUM> and/or the one or more processors <NUM> of the second communication device <NUM>. While <FIG> shows blocks in a particular order, the order may be varied and that multiple operations may be performed simultaneously. Also, operations may be added or omitted.

At block <NUM>, one or more processors, such as one or more processors <NUM> of the first communication device <NUM>, identify a position of the first beam portion of the received optical beam. As an example, the position may be identified using a clock component in the tracking system that detects two time varying signals whose phase relative to the clock component measurements maps to position on the tracking sensor along a first and second perpendicular axes that extend in two directions, such as, a horizontal axis and a vertical axis. In particular, the clock component may measure phase of the two time varying signals at the center of the tracking sensor, such as by using a phase lock loop. The two time varying signals may be a first signal and a second signal, such as an azimuth (or horizontal) signal and an elevation (or vertical) signal. Other position identification methods may be used as well.

As shown in <FIG>, the position of the first beam portion <NUM> may be identified relative to a center <NUM> of the tracking sensor <NUM> of the first communication device. For example, a first dimension midpoint <NUM> of the first beam portion <NUM> may be determined based on phase measurements along the first axis <NUM> that passes through the center <NUM> of the tracking sensor, and a second dimension midpoint <NUM> of the first beam portion <NUM> may be determined based on phase measurements along the second axis <NUM> that passes through the center <NUM> of the tracking sensor. The first dimension midpoint <NUM> and the second dimension midpoint <NUM> may be combined to identify the position of the first beam portion on the tracking sensor. For instance, the first dimension midpoint <NUM> may be determined as a distance from the center <NUM> of the tracking sensor along the first axis <NUM> and may be used as an x-coordinate for the center <NUM> of the first beam portion <NUM> received at the tracking sensor. The second dimension midpoint <NUM> may be determined as a distance from the center <NUM> of the tracking sensor along the second axis <NUM> and may be used as a y-coordinate for the center <NUM> of the first beam portion <NUM> received at the tracking sensor <NUM>.

At block <NUM> of <FIG>, the one or more processors determine that the second beam portion is received at the optical fiber of the first communication device. A position sensor, such as a photodiode, at the optical fiber may detect when an optical beam is coupled with the optical fiber and send a signal to the one or more processors.

At block <NUM>, the first beam portion is processed to electronically align the tracking sensor and the optical fiber. In particular, one or more offsets are determined for use with the tracking sensor that adjusts a setpoint, or target location, of the tracking sensor to be at or near the center of the tracking sensor when an optical beam is received at the optical fiber. As the first beam portion is received at the tracking sensor, a first phase difference between the clock component phase measurements at the center of the tracking sensor and the phase of the first signal along the first axis is determined. A first offset of the one or more offsets for the first signal is determined based on the first phase difference. The first offset may be determined by converting the first phase difference to a number that is added to the first signal to effectively shift the first beam portion along the first axis on the tracking sensor to at or nearer to the center of the tracking sensor. Likewise, a second phase difference between the clock component phase measurements at the center of the tracking sensor and the phase of the second signal along the second axis is determined as the first beam portion is received at the tracking sensor. A second offset of the one or more offsets is determined based on the second phase difference. The second offset may be determined by converting the second phase difference to a number that is added to the second signal to effectively shift the position of the first beam portion along the second axis on the tracking sensor to at or nearer to the center of the tracking sensor. As a result of adding the offsets to the respective signals, the center of the tracking sensor corresponds more closely with a center of the optical fiber, and thus electrically align the tracking sensor and the optical fiber.

At block <NUM>, the one or more processors operate the first communication device using the tracking system with the one or more offsets. Any optical beam portion received at the tracking sensor is processed using the one or more offsets. Namely, the one or more offsets may be added to signals generated at the tracking sensor by a given optical beam portion in order to electronically shift the position of the given optical beam portion to a position more closely corresponding to position of a corresponding optical beam portion on the optical fiber. The one or more offsets may be stored in the memory of the first communication device, such as memory <NUM>. The one or more processors may track any optical beam using the one or more offsets over time.

Additionally or alternatively to the method outlined in <FIG>, the one or more offsets may be determined or adjusted based on signal power received at the optical fiber as shown in <FIG> provides a flow diagram <NUM>, not part of the claimed invention, in accordance with some of the aspects described above that may be performed by the one or more processors <NUM> of the first communication device <NUM> and/or the one or more processors <NUM> of the second communication device <NUM>. While <FIG> shows blocks in a particular order, the order may be varied and that multiple operations may be performed simultaneously. Also, operations may be added or omitted.

At block <NUM>, one or more processors, such as one or more processors <NUM> of the first communication device <NUM>, may identify a position of the first beam portion of the received optical beam in a same or similar manner as at block <NUM>. At block <NUM>, the one or more processors may determine that the second beam portion <NUM> is received at the optical fiber <NUM> of the first communication device in a same or similar manner as at block <NUM>, as illustrated in <FIG>, which shows the cross-section of optical fiber <NUM> receiving the second beam portion <NUM>. The one or more processors may further determine initial characteristics of the second beam portion <NUM>. The initial characteristics of the second beam portion may include an initial position of the second beam portion at the optical fiber based on measurements at the tracking sensor, such as centered at position <NUM>, and an initial signal power of the second beam portion based on an amplitude of the second beam portion detected by the one or more processors via the tracking sensor.

At block <NUM>, the optical beam may be moved such that the second beam portion moves towards a first edge in a first direction (i.e., leftward as shown by arrow <NUM> in <FIG>) from the initial position <NUM>, either by a second communication device transmitting the optical beam or using a steering mirror at the first communication device, until the signal power received at the optical fiber <NUM> from the second beam portion <NUM> decreases by a set threshold amount from the initial signal power. The set amount may be, for example, <NUM> decibels, or more or less. The fiber location where the signal power decreases by the set amount may be determined as the first edge of the optical fiber <NUM>.

At block <NUM>, a first edge position may be identified by the one or more processors as where the first beam portion is positioned on the tracking sensor of the first communication device when the second beam portion <NUM> is at the first edge of the optical fiber <NUM>. Blocks <NUM> and <NUM> may be repeated for a second direction opposite the first direction, a third direction perpendicular to the first direction, and a fourth direction opposite the third direction, as well as any other additional directions, to determine second, third, fourth, or other edges of the optical fiber and corresponding edge positions on the tracking sensor. As shown in <FIG>, the second direction may be rightward from the initial position <NUM>, as shown by arrow <NUM>; the third direction may be upward from the initial position <NUM>, as shown by arrow <NUM>; and the fourth direction may be downward from the initial position <NUM>, as shown by arrow <NUM>. In this example, a left, right, top, and bottom edge of the optical fiber may be determined, as well as a corresponding left, right, top, and bottom edge positions on the tracking sensor.

At block <NUM>, a location of the center of the optical fiber <NUM> may be determined by averaging the position of the detected edges of the fibers. For example, the location of the optical fiber center may be determined by determining a first midpoint <NUM> between the first edge and the opposite second edge, determining a second midpoint <NUM> between the third edge and the opposite fourth edge, and averaging the first and second midpoints. In other implementations, the horizontal component of the first midpoint <NUM> and the vertical component of the second midpoint <NUM> may be used as x- and y-coordinates to identify the location of the optical fiber center.

At block <NUM>, a setpoint position between the detected edge positions on the tracking sensor may be determined and set as corresponding to a center of the optical fiber. For example, the setpoint position may be determined by determining a first midpoint between the first edge position and the opposite second edge position, determining a second midpoint between the third edge position and the opposite fourth edge position, and averaging the first and second midpoints. In other implementations, the horizontal component of the first midpoint and the vertical component of the second midpoint may be used as x- and y-coordinates to determine the setpoint position.

At block <NUM>, one or more offsets may be determined to electronically align the tracking system by adjusting the setpoint position to be closer to the center of the tracking sensor. For example, the first beam portion may be positioned at the setpoint position and a first offset and a second offset may be determined based on a first phase difference and a second phase difference, respectively, in a same or similar manner as described in block <NUM>. Alternatively, a positional difference between the setpoint position and the center of the tracking sensor may be determined, and the first and second offsets may be calculated based on the positional difference. The first offset may be, for example, a number that is added to the first signal to effectively shift the position of the first beam portion on the tracking sensor to at or nearer to the center of the tracking sensor or other setpoint of the tracking sensor. Likewise, the second offset may be, for example, a number that is added to the second signal to effectively shift the position of the first beam portion on the tracking sensor to at or nearer to the center of the tracking sensor or other setpoint of the tracking sensor. As a result, the center of the tracking sensor may correspond more closely with a center of the optical fiber.

At block <NUM>, the one or more processors may operate the first communication device using the tracking system with the one or more offsets. Any optical beam portion received at the tracking sensor may be processed using the one or more offsets. Namely, the one or more offsets may be added to signals generated at the tracking sensor by a given optical beam portion in order to electronically shift the position of the given optical beam portion to a position more closely corresponding to position of a corresponding optical beam portion on the optical fiber. The one or more processors may track the position of any optical beam using the one or more offsets over time.

Operating the first communication device may also include transmitting an update communication regarding the alignment between the first and second communication terminals to a second communication device, such as second communication device <NUM>. The update communication may include a location of the center of the optical fiber of the first communication device or an adjustment to the second communication device based on a difference between a current signal location and the location of the center of the optical fiber. The update communication may cause the location and/or pointing direction of the second communication device to be adjusted to point the signal transmitted from the second communication device towards the location of the optical fiber center at the first communication device. For example, the steering mechanism of the second communication device, such as the steering mechanism <NUM> of second communication device <NUM>, may be used to point the transmitter of the second communication device towards the location of the optical fiber center of the first communication device.

In addition, to further align the first and second communication devices, the location of the optical fiber center at the second communication device may be determined as described above in block <NUM>. The location of the optical fiber center may be transmitted to the first communication device. The location and/or pointing direction of the first communication device may then be adjusted based on the location of the optical fiber center at the second communication device. In some implementations, the alignment method further includes determining an updated location of the center of the optical fiber of the second communication device, and performing a second adjustment of the first communication device based on the updated location. The alignment method may also include determining an updated location of the center of the optical fiber of the first communication device, and performing a second adjustment of the second communication device. With this additional iteration of determining the location of the center of the optical fiber, the alignment of the first and second communication terminals may be improved.

Claim 1:
A method of aligning a tracking system of a communication device (<NUM>, <NUM>), the method comprising:
receiving an optical beam at the communication device, a first beam portion (<NUM>) of the optical beam being received at the tracking system and a second beam portion (<NUM>) of the optical beam being received at an optical fiber (<NUM>) of the communication device;
receiving, by one or more processors, a first signal and a second signal from the tracking system, the first and second signals being generated by a tracking sensor (<NUM>) of the tracking system based on a position of the first beam portion received at the tracking sensor;
determining, by the one or more processors, a first phase difference based on a first phase of the first signal and a second phase difference based on a second phase of the second signal, wherein the first phase difference is between a first phase of the first signal and a first clock component phase measurement, and the second phase difference is between a second phase of the second signal and a second clock component phase measurement;
determining, by the one or more processors, a first offset for the first signal based on the first phase difference and a second offset for the second signal based on the second phase difference for use in electronically aligning the tracking sensor and the optical fiber by adjusting a setpoint position of the tracking sensor of the tracking system; and
tracking, by the one or more processors, the optical beam using the tracking system and the determined first and second offsets.