Focal plane assembly for multi-access free space optical communications transceivers

Systems and methods are described for providing high throughput connectivity between multiple network nodes, such as satellites in Earth orbit or ground stations, using a multi-access free space optical communications transceiver. The transceiver includes a focal plane assembly with an array of moveable optical fibers or fiber bundles, multi-core fibers, or a combination thereof. Each optical fiber bundle may include a centrally-located data fiber with guide fibers disposed around the data fiber. A controller may align a tip of the data fiber with a focal spot associated with incoming optical signals based on measured power levels of optical signals received in the guide fibers. The data fiber may be a multi-mode fiber (MMF) and circuitry in the transceiver may couple signals from the MMF into separate single-mode fibers (SMF) and then coherently combine signals from the SMFs.

TECHNOLOGY BACKGROUND

Field

The present disclosure relates to optical communications, and more particularly to providing high throughput connectivity for free space optical communications.

Description of the Related Technology

Communications connectivity is desirable for many applications. Internet connections, cellular connectivity, satellite communications, and other telecommunications technology rely on such connectivity. However, existing solutions have limited bandwidth which limits the amount of data that can be communicated. Improvements to communications technology are therefore desirable.

SUMMARY OF VARIOUS FEATURES

The embodiments disclosed herein each have several aspects no single one of which is solely responsible for the disclosure's desirable attributes. Without limiting the scope of this disclosure, its more prominent features will now be briefly discussed. After considering this discussion, and particularly after reading the section entitled “Detailed Description of Certain Illustrative Embodiments,” one will understand how the features of the embodiments described herein provide advantages over existing systems, devices, and methods for optical communications technology.

The development relates to systems, devices, and methods for high throughput optical communications technology. The development may be used, for example, between ground-based networks and spacecraft in Earth orbit, deep space, or in orbit around other celestial bodies. As the size and cost of satellites has been falling (see, e.g., CubeSats and other low cost satellites), and launch costs have been falling with the rise of re-useable rockets and ridesharing, increasing numbers of spacecraft are launched each year. Some companies have disclosed plans to launch entire constellations of earth orbiting satellites which may benefit from the development. For example, SpaceX has disclosed plans to launch over 12,000 satellites (split between 200 mile and 700 mile orbits) to provide worldwide satellite-based internet coverage. Individual satellites and satellite constellations can benefit from the developments disclosed herein.

These and other applications, such as Earth imaging and Internet of Things (IoT) satellites, benefit from or even require high bandwidth communication links. For example, an imaging satellite that captures new imagery and/or video daily (or on each orbital pass) may require a communication link with sufficient bandwidth to send each day's (or each orbital pass's) imagery to a ground station. More importantly, immediate link availability after image acquisition is a highly desired and currently unavailable feature for a space-to-ground network. As further example, a satellite constellation providing worldwide internet coverage may require high-speed communication links both within the constellation and between the constellation and a ground station. The current development is capable of meeting the connectivity needs of these and other applications.

The development relates to free space optical (FSO) communications systems methods. The FSO development may rely upon modulated laser light traveling in a line of sight path, and can provide high bandwidth communications in point-to-point links while avoiding the electromagnetic interference issues of radio communications. The optical communications described herein use light propagating in free space to wirelessly transmit data. The communications signal may be transmitted using a laser. The optical communications signals may have a particular wavelength and/or frequency, or may have several particular wavelengths and/or frequencies. The optical signals may be used for data communication. High speeds or rates of data communication are provided by the systems and methods herein. The rate of data transmission may be, for example, at least 0.1 gigabit per second (Gbps), at least 1 Gbps, at least 100 Gbps, at least 200 Gbps, at least 500 Gbps, at least 1 terabit per second (Tbps), or more.

In some embodiments, systems and methods for providing high throughput connectivity between various network nodes, such as between satellites in Earth orbit and ground stations, using a multi-access free space optical transceiver, are described. The multi-access free space optical transceiver may include an array of moveable optical fiber bundles. Each optical fiber bundle may include a centrally-located data fiber with guide fibers disposed around the data fiber. Control circuitry may measure power levels of optical signals received in the guide fibers and may use differences in the measured power levels between guide fibers in a given fiber bundle to align the data fiber with a focal spot associated with incoming optical signals. The multi-access free-space optical transceiver may be included within a communications relay satellite at GEO in order to relay communications between low earth orbit (LEO) satellites and at least one ground station.

Systems and methods are described for providing high throughput connectivity between multiple network nodes (satellites, ground stations, etc.) using a transceiver with a focal plane assembly having an array of moveable optical fibers, movable fiber bundles and/or moveable multi-core fibers. Each optical fiber bundle may include a centrally-located data fiber with guide fibers disposed around the data fiber. A controller may align the data fiber with a focal spot associated with incoming optical signals based on measured power levels of optical signals received in the guide fibers.

In some embodiments, a focal plane solution for a free-space optical communications transceiver is described. The transceiver may be a multiple-to-one transceiver, but the features may be used with other transceiver types as well. Features are described for efficient direct fiber coupling and dynamic tracking of moving nodes transmitting data to, or receiving data from, one node. Features are described for acquiring and maintaining an optical communications channel (transmit and receive) between one node and multiple nodes simultaneously using only one optical antenna. Features are described for dynamic fine-tracking of a moving spot of light in the focal plane of an optical system. A novel design to allow for direct fiber coupling of light onto a guided channel for high-speed optical communications and tracking of moving targets are described. Some embodiments may use of 3D micro-printing to allow for the use of a single multi-core fiber to be used for both tracking and high-speed communications.

DETAILED DESCRIPTION OF CERTAIN ILLUSTRATIVE EMBODIMENTS

In order to satisfy growing demand for high-bandwidth connectivity between, for example, ground-based networks, spacecraft, airborne vehicles, and ground stations, the present disclosure provides a network architecture to enhance optical communications. The network described herein allows for high-bandwidth free space optical communications. “Free space” as used herein has its usual and customary meaning and may refer to, without limitation, mediums such as air, lower and upper planetary atmospheres, near space, outer space, vacuums, or the like. This may be in contrast with, for example, mediums such as solids, for instance optical fiber cable.

The communication may be between a constellation of satellites in Low Earth Orbit (LEO) and one or more ground stations via a relay satellite (sometimes referred to as a repeater). The relay satellite may also relay free space optical communications between satellites (in LEO and in Medium Earth Orbit (MEO)), ground stations, aircraft (e.g., commercial aircraft, military aircraft, high-altitude balloons, pseudo-satellites, etc.), ships (e.g., watercraft of varying sizes), land vehicles, and other network users. The relay satellite may be, in some embodiments, in a relatively high orbit to increase the number of satellites within line of sight of the relay satellite. As examples, the relay satellite may in a Geosynchronous or Geostationary Earth Orbit (GEO), a Medium Earth Orbit (MEO), or a High Earth Orbit (HEO). Additionally, the relay satellite may have optics with a field of view wide enough to encompass the Earth and satellites in LEO.

In general, Low Earth Orbits (LEO) may include orbits having an altitude of less than approximately 1,200 miles or orbits with an orbital period of no more than approximately 128 minutes and an eccentricity of less than 0.25. Geostationary or Geosynchronous Earth Orbit (GEO) may include orbits with an orbital period that matches the Earth's sidereal day (e.g., the Earth's rate of rotation measured relative to distant stars, which is one revolution approximately every 23 hours, 56 minutes, and 4 seconds). A geostationary orbit is a particular kind of geosynchronous orbit that lies in Earth's equatorial plane such that objects in a geostationary orbit appear stationary to observers on Earth's surface. Objects in geosynchronous orbits in orbital planes angled with respect to the equatorial plane may appear to wander around a fixed point in the sky when viewed by an observer on Earth's surface. “GEO” as used herein may include both geostationary and geosynchronous orbits. The GEO orbiting object may therefore remain over, or generally around, the same point on the ground as the earth orbits. A GEO object may remain with a given field of view or line of sight for a particular position on the ground. Medium Earth Orbits (MEOs) may be the orbits between LEO and GEO, while High Earth Orbits (HEOs) may be orbits above GEO.

A relay satellite may have multi-user optical communication abilities, in which multiple LEO satellites and/or other nodes simultaneously connect via separate free space optical paths to the relay satellite. Such arrangements may enable the relay satellite to communicate with multiple LEO satellites simultaneously. In some embodiments, the relay satellite includes an array of optical fibers disposed at the focal plane of an optical antenna (which may occasionally be referred to as a telescope or camera system), and each optical fiber may be moveable within at least a sub-region of the array. A relay satellite may, in some embodiments, have multiple optical antennas with one or more moveable optical fibers in a focal plane of each of the optical antennas for multi-access communication. With such arrangements, each optical fiber can be moved within the array to achieve direct fiber coupling, where the optical fiber is directly coupled to the optical signals of an associated free space optical path.

FIG. 1is a schematic representation of an embodiment of a free space optical (FSO) communications network100architecture including a repeater102on a satellite in orbit about Earth. As shown inFIG. 1, the network100may include a repeater102of the orbiting relay satellite. Repeater102may, in at least some embodiments, be configured for operation at GEO or non-geosynchronous orbit (NGSO), or other orbits such as HEO, MEO, or LEO. Repeater102may also be configured to establish and maintain simultaneous free space optical communications links104a-104ewith network users such as spacecraft106aand106b, airborne vehicle108, and/or ground stations110aand110b. Each of the network users or nodes (e.g., spacecraft106aand106b, airborne vehicle108, and ground stations110aand110b) may have an optical transceiver terminal. In some embodiments, the ground stations110aand110bmay be located at disparate sites chosen to maximize the amount of time at least one of the ground stations has a clear view, unobstructed by clouds, of the repeater102.

The communications links established with the repeater102may provide communications between any of the nodes of the network100. The repeater102may allow for communications between any of one or more of a first group of nodes with any of one or more of a second group of nodes. The first or second groups of nodes may include any of the spacecraft106aand/or106b, the airborne vehicle108, the ground station110aand/or110b, the data center112, the cloud access114, the end user116. Other nodes may be included, such as communications systems associated with ships at sea and automobiles. Thus the particular architecture shown is merely one example embodiment.

Network100may also include connections with terrestrial networks. As an example, network100may couple to terrestrial networks through ground stations. In the example ofFIG. 1, network100connects, via ground station110b, to data center112, network114(which may be a wide area network such as the Internet), and end user116.

In some embodiments, the repeater102may be used in other contexts. The repeater102may be used on the ground or on the other nodes of the network100. The repeater102may be used on satellites in orbit about other planets in space. The repeater102may be used to communicate with nodes that are in orbit about other planets in space. There may be multiple, for example two or more, repeaters102in the network100.

FIG. 2is a block diagram of an embodiment of a transceiver200that may incorporate the repeater102and be used with the GEO satellite in the network100. The transceiver200includes an optical antenna210shown as a wide field of view (FOV) optical assembly, a focal plane assembly212including an array of optical fibers213or215or216, and electronics214including electronics for signal processing and control. The focal plane assembly212and the array of optical fibers213may include an array of actuators, as further described herein, for example with respect toFIG. 3. Optical signals may be received through the optical antenna210from an external network node1,2,3. . . N. The signals may be collected and sorted for processing in the focal plane assembly212. Some of the network nodes include satellites in LEO (e.g., satellites moving at a high velocity, often across the FOV of optical assembly210). In such cases, maintaining each communications link network node may involve dynamically positioning one or more optical fibers using coarse positioning actuator or actuators to maintain that link as the associated network node travels across the FOV of the optical assembly210, as further described herein. The electronics214may then analyze the signals and control the focal plane assembly212or components thereof.

The transceiver200may, alternatively or additionally, be included within other nodes of the network100such as satellites106aand106b, ground stations110aand110b, airborne vehicle108, and/or other nodes. The transceiver200may be a single optical antenna multiple-to-multiple transceiver supporting multiple external optical links uniquely coupled to multiple (and respective) data channels within the transceiver. The transceiver200may therefore support multiple bidirectional communications channels using a single optical antenna. As shown inFIG. 2, the multi-access free-space optical communications transceiver200may simultaneously couple to multiple network nodes (e.g., Node1to Node “N”).

The transceiver200may include a processor and/or memory. The control circuit or circuitry described herein may include the processor and/or the memory. The memory may be local or remote and have instructions stored thereon. The processor may execute the instructions stored in memory to perform the various functions and methods described herein, for example receiving communications signals, analyzing the signals, controlling drivers and fiber or lens array positions, performing image analysis, communicating with other components of the repeater102aand/or transceiver200, controlling the attitude and/or trajectory of the satellite, transmitting communications, performing predictive modeling of the shape of a focal spot of incoming optical signals (which may be used for fine positioning adjustments of one or more optical fibers), etc.

Transceiver200may include components such as a wide field of view (FOV) optical assembly210; a focal plane assembly212, which may include an array of optical fibers213or215or216; and signal processing, control, and electronics214. Details of the focal plane assembly213and array of optical fibers213as well as the signal processing, control, and electronics214are discussed below in connection with at leastFIG. 3.

The optical assembly210may include a single optical antenna. The single optical antenna may collect incoming optical signals and transmit outgoing optical signals using a field of view (FOV). The FOV may be relatively wide. The optical assembly210may focus incoming optical signals (transmitted from other network nodes) onto a focal plane (e.g., onto the focal plane assembly212). On the focal plane, the location of the focal spot may vary with the position of the origin of the corresponding incoming optical signal. The optical assembly210may transmit outgoing optical signals from a focal spot to an external network node, where the focal spot is selected in order to aim the optical signals at the external network node. In some embodiments, the optical assembly210includes a single optical antenna having a relatively wide FOV. In other embodiments, the optical assembly210includes an array of individual optical antennas. The individual optical antennas may each have a relatively wide FOV (e.g., a FOV of at least 10 degrees, at least 15 degrees, at least 20 degrees, at least 25 degrees, at least 30 degrees, at least 35 degrees, at least 40 degrees, at least 45 degrees, etc.). In other embodiments, the individual optical antenna may each have a relatively narrow FOV, where the narrow FOVs are offset but overlapping such that the overall FOV is relatively wide. In such embodiments, the focal plane assembly212may be an array of focal plane assemblies, each of which is coupled to a respective one of the individual optical antennas. In other such embodiments, the array of individual optical antennas may be coupled to a common focal plane assembly212. In some other embodiments, the focal plane assembly212may be an array of single optical fibers (or fiber bundles of the type shown inFIGS. 4 and 7) and the optical assembly212may include an array of individual optical antennas (each having a relatively narrow FOV as described above), where each individual optical antenna is coupled to a different one of the single optical fibers.

The FOV of optical assembly210may be enough that the transceiver200(particularly when implemented within the repeater102of a relay satellite) can “see” satellites in LEO, regardless of their position within their respective orbit (excepting when the satellites pass behind the Earth). Thus, the optical assembly210may be modified depending on the desired orbital altitude (a higher orbit may require a smaller FOV to capture the same region of space). If the transceiver200is implemented within a network node positioned at or near geostationary orbit (GEO), the Earth may have an angular size (from the relay satellite's perspective) of just over 20 degrees. Accordingly, it may be desirable to configure optical assembly210to have a field of view slightly larger than 20 degrees to also cover low earth orbits (which increase the desired angular size).

Therefore, the field of view can be various sizes in various embodiments. As examples, the optical assembly210may have a field of view of at least 2 degrees, at least 4 degrees, at least 10 degrees, at least 15 degrees, at least 20 degrees, at least 25 degrees, at least 30 degrees, at least 35 degrees, at least 40 degrees, at least 45 degrees. As further example, the optical assembly210may have a field of view of 2 degrees, of 4 degrees, of 10 degrees, of 15 degrees, of 20 degrees, of 25 degrees, of 30 degrees, of 35 degrees, of 40 degrees, or of 45 degrees. As further example, the optical assembly210may have a field of view of approximately 2 degrees, of approximately 4 degrees, of approximately 10 degrees, of approximately 15 degrees, of approximately 20 degrees, of approximately 25 degrees, of approximately 30 degrees, of approximately 35 degrees, of approximately 40 degrees, or of approximately 45 degrees. “Approximately” may refer to a value within +/−5 degrees of the given value for a given value or, for values of 10 degrees or less, within +/−50% of the given value.

As shown inFIG. 2, focal plane assembly212may include an array213or215or216of optical fibers. The optical fibers may be mounted on electro-mechanical or piezoelectric (PZT) actuators that provide at least two degrees of freedom (e.g., provide controlled movement within the focal plane), in order to, for each individual optical channel, dynamically position an optical fiber at the focal spot associated with incoming (or outgoing) free space optical signals. In order to support multiple network connections, multiple optical fibers may be individually positioned, such that there is a single active fiber that is properly positioned for each network connection. One advantage of this type of arrangement is scalability. In particular, the number of optical fibers can be increased (and the optics modified to enlarge the focal plane and/or the patrol area of each fiber shrunk) in order to increase an available number of simultaneous connections.

FIG. 3is a schematic representation of an embodiment of a focal plane assembly212and associated signal processing, control, and electronics, which may be used as the focal plane assembly212and the signal processing, control, and electronics214ofFIG. 2.

As shown inFIG. 3, focal plane assembly212and the array213of optical fibers1may include an array of actuators2. Each actuator2may be configured to dynamically position a respective single mode optical fiber, multi-mode optical fiber, few- mode optical fiber, large mode area (LMA) fiber, and/or multi-core optical fiber1and associated end-cap3. Optical fiber1may include a bundle of any of these fibers, for example, a bundle of single-mode fibers, a bundle of multi-mode fibers, or a bundle with both single-mode and multi-mode fibers. Optical signals coming from an external network node may be focused onto a spot within a focal plane where the position of that spot depends on the position of the external network node within the FOV of the optical assembly210. In some embodiments, some of the network nodes include satellites in LEO (e.g., satellites moving at a high velocity, often across the FOV of optical assembly210). In such cases, maintaining each communications link network node may involve dynamically positioning one or more optical fibers to maintain that link as the associated network node travels across the FOV of the optical assembly210. Thus, each actuator or set of actuators2may dynamically position a respective optical fiber1and/or associated end-cap in order to maintain tracking with a moving spot of converging light4coming from a particular network node.

In some embodiments, each actuator or set of actuators2may have a limited patrol area (e.g., each actuator may only be configured to move its respective optical fiber1and end-cap3only within a sub-region of the focal plane). When a focus spot4nears or reaches the edge of a patrol area of a first actuator and associated first optical fiber, a handoff may occur whereby an adjacent second actuator and associated second optical fiber are positioned at the focus spot4and communications are shifted from the first optical fiber to the second optical fiber. Any data lost due to interruption in data communications during the handoff may be recovered via re-transmission of the data and/or error correction techniques.

Detailed views of an optical fiber bundle1and associated end-cap3are shown inFIGS. 4 and 5. As shown inFIG. 4, each optical fiber or optical fiber bundle1may include an end cap3. Each fiber bundle1may include a single cladding and multiple fiber cores. Fiber bundles with a single cladding and multiple fiber cores may be referred to as a multi-core fiber and, depending on the size (e.g., diameter) of the optical fibers, the optical fibers may be single mode (SM) or multi-mode (MM) or few-mode (FM). Fiber bundles with multiple fiber cores and a single cladding may, in some embodiments, be formed at least partially with three-dimensional micro-printing (e.g., end caps3, cladding, and components other than the optical fibers may be 3D printed). Alternatively, each fiber bundle1may include multiple cores, each having a separate cladding. The end cap3may be configured with an optical funnel such as optical funnel402, which may be a hollow taper, for each optical fiber within the fiber bundle. Each optical funnel402may improve coupling between free space optical signals and its respective optical fiber. In at least some embodiments, the surfaces of each optical funnel402may be selectively optically reflective to further improve coupling between free space and the optical fibers. In general, some or all of the optical fibers in each bundle may have an associated optical funnel, and the dimensions and shapes of the optical funnels may vary or may be similar to each other.

FIG. 4illustrates each optical fiber bundle1. The bundle includes a data fiber404, a plurality of guide fibers406, and a beacon fiber408. While fibers404and408are generally referred to as a data fiber and a beacon fiber, respectively, fiber408may, if desired, convey signals modulated (e.g., encoded). The data fiber404may be centrally located within the bundle1. In some embodiments, each fiber bundle1may include three guide fibers406disposed around the data fiber404. In other embodiments, each fiber bundle may include more than three guide fibers (such as the six guide fibers disposed around a central data fiber as shown in bundle410ofFIG. 4) disposed around the data fiber404. By positioning the guide fibers406around the data fiber404, the guide fibers406may be used in fine-tuning the position of the optical fiber bundle1(e.g., in aligning the data fiber404with a focal spot of incoming optical signals).

When the incoming light from a particular network node (e.g. a LEO satellite, an airborne vehicle, a ground station, another GEO satellite, etc.) reaches the focal plane assembly212through the optical antenna210and is within the patrol area of one of the focal plane actuators2, the actuator2may coarsely position its associated fiber1tip and end cap3with enough accuracy that sufficient power is injected in one or more guide fibers through the end cap3. In some embodiments, the initial position of an actuator2may be determined based on the predicted location of the focal spot for a particular network node, which may be predicted on information such as the ephemeris (e.g., known orbital trajectory) of the network node.

Referring toFIG. 3, guide fibers may be coupled to high sensitivity photodetectors5, which may be configured to measure the power levels of optical signals injected into the guide fibers. Actuator controller7may obtain the measured power levels from the high sensitivity photodetectors5and, based on those measurements, command actuator drivers8to adjust the position of the relevant actuator2(e.g., to move the relevant actuator2closer towards an ideal position in which the coupling efficiency between incoming free space optical signals and an active data fiber404, shown inFIG. 4, is maximized). Thus, the guide fibers, high sensitivity photodetectors5, actuator controller7, actuator drivers8, and actuators2may form a closed-loop control system capable of maintaining fine tracking as a spot of light associated with incoming free space optical communications moves across the patrol area of an actuator, due to the relative motion of the communicating nodes or other effects such as vibrations.

In particular, if the fiber bundle1is mis-aligned from the desired focal spot, the incoming optical signals may be guided not into the data fiber404but into the guide fiber(s)406that is/are under the focal spot. Thus, the guide fiber(s)406under the focal spot receives a higher power level of optical signals, as compared to guide fiber(s)406on the opposite side of the data fiber404. The control circuitry7then utilizes these differences in power levels from the different guide fibers406to adjust the fiber bundle1and move the data fiber404towards the focal spot. By continuously adjusting the position of the fiber bundle1, based on measured power levels in the guide fibers406, the control circuitry7can implement a closed- loop control system for maintaining the data fiber404at the moving focal spot.

In alternative embodiments, information in addition to or other than feedback from the guide fibers406may be used in performing fine pointing (e.g., fine adjustment of the position of actuators2and their associated optical fibers1). As examples, control circuitry7may position the actuators2and associated optical fibers1using known ephemeris of a target network node, using star trackers to identify the position and/or orientation of the transceiver, etc. Star trackers may use imaging sensors to view one or more star clusters and analyze the observations, e.g. compare the observations to a database of known star clusters, to determine the orientation of the transceiver.

In still other alternative embodiments, data can be transmitted to external network nodes by modulating the beacon signal13. In such embodiments, the splitter10and isolator11may be omitted and the functionality of signal generator12integrated into the beacon generator13. In embodiments in which a modulated beacon signal, such as beacon signal13, is utilized to transmit data, the transceiver200may transmit the beacon signal and associated data in a point-to-multipoint manner (e.g., the data encoded in the beacon signal may be a broadcast that is available to all network nodes that are in a line of sight with transceiver200and that are within the FOV of optical assembly210).

As shown inFIG. 5, in some embodiments a micro-lens14can be included as part of end cap3. The micro-lens14may improve coupling between free space optical signals and an optical fiber such as the data fiber404.

Returning toFIG. 3, once a particular fiber bundle1is aligned with a focal spot of incoming optical signals, the data fiber404of that bundle may be coupled to the free space optical signals. Optical signals in the data fiber404are then conveyed to splitter10and high-speed photodetector6. Isolator11may prevent the incoming optical signals from traveling towards optical signal generator12. If desired, the incoming optical signals may be amplified, by an amplifier, before reaching the high-speed photodetector6. High speed photodetector6may convert incoming optical signals into electrical signals (e.g., digital signals) for storage, retransmission, and/or use in data processing unit9. There may be a high speed photodetector for each and every optical fiber bundle1or, if desired, multiple optical fiber bundles1may share a photodetector and there may be optical multiplexing components, optical splitting components, or other such components to enable the photodetector to receive optical signals from a single fiber bundle1at a time.

In various embodiments, the transceiver may include an optical signal generator12that generates optical signals encoding data in order to transmit the data to other network nodes. Optical signals from generator12may be injected into a data fiber of the fiber bundle (e.g., data fiber404or a separate transmitting fiber) using beam splitter10.

If desired, the transceiver may transmit a beacon signal using beacon generator13. The beacon signal from beacon generator13may, as an example, be injected into a dedicated fiber such as beacon fiber408ofFIG. 4. The beacon signal may be used to external communication nodes in pointing their optical systems at the transceiver.

The data fiber404of a fiber bundle may be a single-mode optical fiber (SMF), a few mode fiber (FMF), or a multi-mode fiber (MMF). In embodiments in which the data fiber404is a few or multi-mode fiber (FMF or MMF), the transceiver may be implemented with the alternate architecture shown inFIG. 6. In particular, a data fiber that is an FMF or MMF may have a larger diameter central fiber core15. Optical signals coupled into the FMF or MMF optical fiber15may be coupled to a spatial mode multiplexing device16(e.g., a photonic lantern or other multiplexing device). Each mode of optical signals coupled from the optical fiber15to device16may be coupled, by spatial modes multiplexing device16into a different single mode fiber (SMF)17. As a result, each SMF17carries the same signal with varying intensities, but which are not necessarily in-phase. The different SMFs17are coupled to a recombination unit18that coherently reconstructs the signal, thus increasing signal level. The recombined signal may then be conveyed to the high-speed photodetector6, and the electrical signal is then converted to a digital signal for storage, retransmission, and/or use in data processing unit9. The optical signal may or may not be amplified before reaching the photodetector6.

If desired, a fiber bundle may be formed from multiple separately-clad optical fiber (as opposed to multiple optical fibers sharing a common cladding). An arrangement of this type is illustrated inFIG. 7. One advantage of forming each fiber bundle from separately-clad optical fibers is that the fiber tips can more easily be positioned at different planes. In particular,FIG. 7illustrates a central fiber700, which may be used for receiving optical signals, a fiber702, which may be used for transmitting optical signals, and surrounding guide fibers704, which may be used for guiding the fiber into position as discussed herein. As shown inFIG. 7, the guide fibers704may be offset from the plane of the central fiber700and fiber702. Offsetting the guide fibers704in this manner (or in the direction opposite to that which is illustrated inFIG. 7) can advantageously defocus the beacon signals to achieve a more divergent beam and thereby increase the likely hood that the beacon signals are received by an external network node. Micro-lenses, such as the micro-lens14ofFIG. 5, can, if desired, be included in the arrangement ofFIG. 7, e.g., to improve coupling between free-space optical signals and one or more of the optical fibers700,702, and704.

Each of the processes, methods, and algorithms described herein and/or depicted in the attached figures may be embodied in, and fully or partially automated by, code modules executed by one or more physical computing systems, hardware computer processors, application-specific circuitry, and/or electronic hardware configured to execute specific and particular computer instructions. For example, computing systems can include general purpose computers (e.g., servers) programmed with specific computer instructions or special purpose computers, special purpose circuitry, and so forth. A code module may be compiled and linked into an executable program, installed in a dynamic link library, or may be written in an interpreted programming language. In some implementations, particular operations and methods may be performed by circuitry that is specific to a given function.

Some or all of the processes, methods, and algorithms described herein and/or depicted in the attached figures may be performed locally (e.g., on an assembly such as a relay satellite in which the functions are performed). Some or all of the processes, methods, and algorithms described herein and/or depicted in the attached figures may be performed remotely (e.g., on remote computing resources). As an example, ground-based computing resources may perform scheduling functionality. In particular, ground-based computing resources may determine when a relay satellite should establish and/or break connections with particular LEO satellites.

Further, certain implementations of the functionality of the present disclosure are sufficiently mathematically, computationally, or technically complex that application-specific hardware or one or more physical computing devices (utilizing appropriate specialized executable instructions) may be necessary to perform the functionality, for example, due to the volume or complexity of the calculations involved or to provide results substantially in real-time.

The various features and processes described above may be used independently of one another, or may be combined in various ways. All possible combinations and subcombinations are intended to fall within the scope of this disclosure. Various modifications to the implementations described in this disclosure may be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other implementations without departing from the spirit or scope of this disclosure. Thus, the inventive aspects are not intended to be limited to the implementations shown herein, but are to be accorded the widest scope consistent with this disclosure, the principles and the novel features disclosed herein.

Certain features that are described in this specification in the context of separate implementations also can be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation also can be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially described in the inventive aspects as such, one or more features from an inventive combination aspect can in some cases be excised from the combination, and the inventive combination aspect may be directed to a subcombination or variation of a subcombination. No single feature or group of features is necessary or indispensable to each and every embodiment.