Dual optical head for optical feeder link in satellite communication systems

Abstract

A laser communication terminal (LCT) comprises separate optical head assemblies (OHAs) for optical signal transmission and reception, with respective pointing systems allowing for separate pointing control of the respective OHAs. In a satellite communication system (SCS) having an optical ground station (OGS) configured for satellite communication coupling with the SCS via an optical feeder link (OFL), the satellite and / or the OGS implement respective dual OHAs (DOHA). In one or more embodiments, the DOHA are configured for use of different optical wavelengths with respect to optical communication beams on uplink and downlink. Several advantages resulting from the use of the DOHA are: isolation of the optical paths carrying the outgoing and incoming beams, and optimization and simplification of the capabilities of the corresponding optics. Furthermore, providing separate pointing control alleviates the need to manufacture DOHA with precise inter-head alignment.

Description

Technical Field

[0001] The technology disclosed herein relates to a laser communication terminal (LCT) with dual optical heads and its use in an optical feeder link (OFL) for a satellite communication system (SCS). Background Technology

[0002] Optical feeder links (OFLs) represent a key innovation in the deployment of satellite communication systems (SCS) that utilize a class of high-throughput satellites required to provide evolving communication services such as broadband internet access. The term "feeder" refers to communication between a ground station and a satellite, including forward link traffic from the ground station to the satellite for transmission to the corresponding terminal within a group of terminals served by the satellite. Feeder communication further includes reverse link traffic from the corresponding terminal to the satellite for relay or retransmission from the satellite to the ground station. Here, the ground station can be understood as one endpoint of the satellite link, and each terminal as the corresponding other endpoint. Terminals are, for example, user terminals belonging to or assigned to subscribers of the SCS.

[0003] In a typical implementation, an OFL includes one or more uplink beams from a ground station to a satellite, and one or more downlink beams from a satellite to a ground station. The term "beam" refers to the directional or guided propagation of a light wave. For example, a laser-based emission source outputs light, which is then focused and guided in a specific direction, where example guiding operations include any or more of collimation, focusing, filtering, beam splitting, deflection, and redirection. The light used to form the beam can be unmodulated or can be modulated according to data or control signaling, such that the beam carries information. In this sense, the beam may or may not transmit optical signals.

[0004] A light beam can contain light at a single wavelength, or it can contain light at more than one wavelength. For example, an optical communication beam transmitted over an OFL between a ground station and a satellite that is part of the OFL can contain light at multiple wavelengths, where each wavelength is a different optical channel signal, and where each optical channel signal is modulated light corresponding to a respective information stream, which itself can include multiplexed forward traffic for multiple terminals.

[0005] Furthermore, more than one beam can propagate along the same optical path but may have different divergences. For example, an OGS can propagate an optical uplink beacon beam and an optical uplink communication beam along the same optical path, allowing the satellite to receive a combination or composite beam containing light at wavelengths used to form the optical uplink beacon beam and at wavelengths used to form the optical uplink communication beam. The optical path on the satellite used to receive such a composite beam can be configured for beam splitting, allowing the constituent beams incident on the satellite to be processed individually or used as a composite beam. Of course, a similar arrangement can be used in the OGS relative to a composite beam incident from the satellite to the OGS.

[0006] Compared to radio frequency (RF) feeder links, OFLs offer significantly higher capacity, but their use presents numerous design and operational challenges. Establishing and maintaining optical alignment between the satellite and the OGS is a key challenge. Here, "optical alignment" refers to the correct orientation of the optics used for beam transmission and reception at both the satellite and ground station. Known approaches to addressing alignment challenges include using a single optical head assembly (OHA), where both optical transmission (TX) and optical reception (RX) functions are implemented via the same optical telescope. Here, the term "optical telescope" broadly refers to an optical system used to focus, collect, or transmit light to or from a distance. Using a single OHA offers several advantages, notably that both the optical transmitter and receiver require only a single alignment system. Of course, the alignment system itself can be complex, such as having two or more alignment sensors of different resolutions to support coarse and fine alignment sensing. Summary of the Invention

[0007] A laser communication terminal (LCT) includes a separate optical head assembly (OHA) for optical signal transmission and reception, wherein a corresponding pointing system allows for individual pointing control of the respective OHA. In an SCS having an optical ground station (OGS) configured for satellite communication coupling with a satellite communication system (SCS) via an optical feedline link (OFL), the satellite and / or OGS implements a corresponding dual OHA (DOHA). In one or more embodiments, the DOHA is configured to use different optical wavelengths relative to the optical communication beams on the uplink and downlink. Several advantages of using the DOHA include: isolation of the optical paths carrying the outgoing and incoming beams, and the ability to optimize and simplify the corresponding optics. Furthermore, providing individual pointing control reduces the need to manufacture DOHAs with precise inter-head alignment.

[0008] One embodiment includes an LCT configured for use at one end of the OFL between the OGS of a satellite and an SCS. The example LCT includes a receiving optical head assembly (ROHA) configured for beam reception, the ROHA including a first pointing system configured to control the pointing direction of the ROHA, and a transmitting optical head assembly (TOHA) configured for beam transmission, the TOHA including a second pointing system configured to control the pointing direction of the TOHA independently of the pointing direction of the ROHA. The LCT also includes a pointing control circuitry configured to control the first pointing system in response to a first alignment signal output from a ROHA alignment sensor camera, and further configured to control the second pointing system in response to a second alignment signal output from a TOHA alignment sensor camera.

[0009] In at least one embodiment, a satellite configured for use in an SCS includes one or more radio frequency (RF) antenna systems and an RF communication payload configured to transmit forward traffic to a corresponding terminal via the one or more RF antenna systems and to receive return traffic from the corresponding terminal via the one or more RF antenna systems. Furthermore, the satellite includes an optical receiver head assembly (ROHA) configured to receive forward traffic via an optical uplink communication beam transmitted by the OGS of the SCS and to transmit return traffic to the OGS via an optical downlink communication beam. The LCT on the satellite includes a receiver optical head assembly (ROHA) configured for beam reception, the ROHA including a first pointing system configured to control the pointing direction of the ROHA, and a transmit optical head assembly (TOHA) configured for beam transmission, the TOHA including a second pointing system for controlling the pointing direction of the TOHA independently of the pointing direction of the ROHA. The LCT also includes a pointing control circuitry configured to control a first pointing system in response to a first alignment signal output from a ROHA alignment sensor camera, and further configured to control a second pointing system in response to a second alignment signal output from a TOHA alignment sensor camera.

[0010] An example OGS configured for use in an SCS includes an interface circuitry system configured to receive forward traffic from the SCS's Communication Processing System (CPS) for forwarding to a corresponding terminal in a terminal served by the SCS's satellite, and configured to transmit return traffic from the corresponding terminal in the terminal toward the CPS. The OGS further includes a communication circuitry system configured to generate a forward communication signal for transmitting the forward traffic and configured to recover a return communication signal for transmitting the return traffic. The OGS further includes an LCT configured to transmit the forward communication signal to the satellite via an optical uplink communication beam and configured to receive the return communication signal via an optical downlink communication beam transmitted by the satellite. The OGS's LCT includes a receiving optical head assembly (ROHA) configured for beam reception, the ROHA including a first pointing system configured to control the pointing direction of the ROHA, and a transmitting optical head assembly (TOHA) configured for beam transmission, the TOHA including a second pointing system for controlling the pointing direction of the TOHA independently of the pointing direction of the ROHA. The LCT also includes a pointing control circuitry configured to control a first pointing system in response to a first alignment signal output from a ROHA alignment sensor camera, and further configured to control a second pointing system in response to a second alignment signal output from a TOHA alignment sensor camera.

[0011] In another embodiment, the method of communication between the satellite and the SCS's OGS via OFL is performed by an LCT at one end of the OFL. The method includes the LCT receiving an optical communication beam incident on the LCT via free-space propagation from a remote LCT at the other end of the OFL. This incident optical communication beam is received via the LCT's ROHA, which has a first pointing system for pointing control of the ROHA. Furthermore, the method includes the LCT transmitting an optical communication beam exiting the LCT via free-space propagation towards the remote LCT. This exiting optical communication beam is transmitted via the LCT's TOHA, which has a second pointing system for pointing control of the TOHA. Further, the method includes performing pointing control separately on the ROHA and TOHA based on corresponding evaluations of a first alignment signal output by a first alignment camera in the ROHA and a second alignment signal output by a second alignment camera in the TOHA.

[0012] Another embodiment includes an SCS comprising an OGS configured to operate at one end of an OFL and a satellite configured to operate at the other end of the OFL. The satellite includes one or more RF antenna systems and an RF communication payload configured to transmit forward link traffic to a corresponding terminal via the one or more RF antenna systems and to receive return link traffic from the corresponding terminal via the one or more RF antenna systems. Furthermore, the satellite includes an LCT having a ROHA configured for beam reception, the ROHA including a first pointing system configured to control the pointing direction of the ROHA, and further having a TOHA configured for beam transmission, the TOHA including a second pointing system for controlling the pointing direction of the TOHA independently of the pointing direction of the ROHA. Even further, the LCT includes a pointing control circuitry configured to control the first pointing system in response to a first alignment signal output from a ROHA alignment sensor camera, and further configured to control the second pointing system in response to a second alignment signal output from a TOHA alignment sensor camera.

[0013] Of course, the present invention is not limited to the features and advantages described above. In fact, those skilled in the art will recognize additional features and advantages after reading the following detailed description and reviewing the accompanying drawings. Attached Figure Description

[0014] Figure 1 This is a block diagram of an example optical ground station and a satellite with a laser communication terminal (LCT), and one or both LCTs use a dual optical head assembly (DOHA).

[0015] Figure 2 This is a block diagram of the DOHA arrangement of a satellite LCT according to one embodiment.

[0016] Figure 3 This is a diagram of an example optical field of view (FoV) of the receiver optical head assembly (ROHA) of the LCT satellite, in which... Figure 4 A corresponding example FoV of the Transmission Optical Head Assembly (TOHA) of the LCT satellite is shown.

[0017] Figure 5 This is a block diagram of the DOHA arrangement of an OGS LCT according to one embodiment.

[0018] Figure 6 This is a diagram of an example optical field of view (FoV) of the OGS LCT receiver optical head assembly (ROHA), where Figure 7 A corresponding FoV example of the OGS LCT's Transmission Optical Head Assembly (TOHA) is shown.

[0019] Figure 8This is a block diagram illustrating example details of a DOHA-based LCT based on an example embodiment.

[0020] Figure 9 It is used for orientation Figure 8 The example of LCT's ROHA FoV shown points to a block diagram of the system.

[0021] Figure 10 yes Figure 8 A block diagram of an example optical arrangement of the ROHA for the LCT is shown.

[0022] Figure 11 yes Figure 8 The example ROHA block diagram of LCT shown here supports electronic devices.

[0023] Figure 12 It is used for orientation Figure 8 The example of the TOHA FoV of LCT shown in the diagram points to the block diagram of the system.

[0024] Figure 13 yes Figure 8 A block diagram of an example optical arrangement for the TOHA of the LCT is shown.

[0025] Figure 14 yes Figure 8 The example TOHA diagram of LCT shown here supports electronic devices.

[0026] Figure 15 This is a block diagram of a satellite communication system (SCS) according to an example embodiment, wherein the OGS and the satellite include Figure 8 The corresponding specific implementation of LCT is shown.

[0027] Figure 16 This is a diagram of the optical feeder link (OFL) arrangement for coupling the OGS to the satellite, according to an example embodiment.

[0028] Figure 17 This is a logic flowchart illustrating the DOHA pointing control method according to an example embodiment.

[0029] Figure 18 This is a diagram illustrating an example search pattern that can be used for beacon beam transmission by an LCT during optical alignment with a remote LCT. Detailed Implementation

[0030] Using an optical feeder link (OFL) between a ground station and a satellite requires precise optical alignment between the optical transceiver at the ground station and the optical transceiver on the satellite. Here, "optical alignment" means that the optical field of view (FoV) is pointing in the correct direction for the transmission / reception of the light beam. Correspondingly, the terms "pointing" and "directing" can be used interchangeably when referring to directional FoV, for example, orienting it according to elevation and azimuth angles through mechanical adjustments within the optical path involved. Example methods of directional FoV involve controlling movable elements within the optical path involved, such as mirrors, lenses, or prisms.

[0031] While known methods of OFL implementation utilize simplified alignment achieved by using a single optical head assembly (OHA) that integrates RX and TX functions into the same shared optical telescope, this paper recognizes that increasing OFL capacity depends on the use of increasingly sophisticated modulation and coding schemes at the optical transmitter. The ability to detect corresponding optical signals requires a higher signal-to-noise ratio (SNR) in the optical receiver, and this requirement favors higher optical transmission (TX) power.

[0032] As TX power increases and receiver sensitivity improves, optical isolation between TX and RX functions within a single OHA becomes increasingly challenging. An advantageous method disclosed herein includes a dual OHA (DOHA) optical transceiver comprising a separate RX OHA (ROHA) and a TX OHA (TOHA). Using separate OHAs optically isolates the RX and TX functions, allowing for corresponding optimization of the RX and TX optics. Furthermore, the disclosed DOHA arrangement provides separate pointing control for the ROHA and TOHA, simplifying the design, assembly, and operation of DOHA-based optical transceivers. A particular advantage is that separate pointing control alleviates the need for precise head-to-head alignment between the ROHA and TOHA, as each is configured to point independently of the other.

[0033] Figure 1 An example arrangement is shown where the Optical Ground Station (OGS) 10 of a Satellite Communication System (SCS) operates at one end of OFL 12, and the SCS satellite 14 operates at the other end of OFL 12. The term "OFL" here can be understood as a logical reference to the beam-based communication coupling between OGS 10 and satellite 14. A beam transmitted from OGS 10 propagates in free space along an optical path defined by the TX pointing direction of OGS 10, where OGS 10 is the beam source and satellite 14 is the beam destination. Similarly, a beam transmitted from satellite 14 propagates in free space along an optical path defined by the TX pointing direction of satellite 14, where satellite 14 is the beam source and OGS 10 is the beam destination.

[0034] OGS 10 includes an optical transceiver 20 comprising one or more OHAs 22 pointed to via one or more pointing systems 24 controlled by a pointing control circuitry 26. Similarly, satellite 14 includes an optical transceiver 30 comprising one or more OHAs 32 pointed to via one or more pointing systems 34 controlled by a pointing control circuitry 36. Unless otherwise stated, the term "Laser Communication Terminal" (LCT) is interchangeable with "optical transceiver," and hereinafter, optical transceiver 20 is referred to as LCT 20 and optical transceiver 30 as LCT 30.

[0035] In the illustrated example embodiment, LCT 30 transmits an optical communication beam 40 for reception at LCT 20, and transmits an optical beacon beam 42 on the same optical axis for reception at LCT 20. Complementarily, LCT 20 transmits an optical communication beam 44 for reception at LCT 30, and transmits an optical beacon beam 46 on the same optical axis for reception at LCT 30.

[0036] In one or more embodiments, the first of LCTs 20 and 30 uses a single OHA that integrates RX and TX functions via shared optics and has a single pointing system, while the second of LCTs 20 and 30 uses a DOHA with corresponding pointing systems for the included ROHA and TOHA. In an example scenario, OGS 10 uses a single OHA and satellite 14 uses a DOHA. In another example scenario, OGS 10 uses a DOHA and satellite 14 uses a single OHA, although the use of a DOHA on satellite 14 may provide certain advantages. In at least one embodiment, OGS 10 and satellite 14 use corresponding DOHAs.

[0037] Figure 2An example DOHA implementation of LCT 30 on satellite 14 is shown, including ROHA 50. According to the illustrated embodiment, ROHA 50 includes an alignment sensing camera 52 and a first pointing system 34-1. The first pointing system 34-1 includes a hierarchical pointing subsystem comprising a beam steering assembly (BSA) 54 as the first pointing subsystem and a fast pointing assembly (FPA) 56 as the second pointing subsystem. In one or more embodiments, the pointing control circuitry 36 implements cooperative, coordinated control of the BSA 54 and FPA 56 for alignment operations, thereby using the FPA 56 for rapid, fine alignment adjustments over a first angular range to handle minor disturbances and precise alignment control, and using the BSA 54 for slower, coarser adjustments over a larger second angular range covering the first angular range. For example, the pointing control circuitry 36 uses BSA 54 for coarse pointing control, such as for initial pointing toward the selected OGS 10 and making large, slow adjustments, and uses FPA 56 for faster, finer pointing control, such as for dynamic fine centering control of the ROHA FoV on the selected OGS 10.

[0038] In one or more embodiments, the alignment sensing camera 52 includes a geometric array or grid of pixels, wherein a particular pixel illuminated by the incident beam indicates the alignment of the ROHA FoV. An alignment sensing signal 60 output by the alignment sensing camera 52 indicates the illumination per pixel. In a particular embodiment, the alignment sensing camera 52 is a four-quadrant sensor and the alignment sensing signal 60 includes a per-quadrant signal indicating the absolute or relative amount of light illuminating each quadrant. With this arrangement, centering of the ROHA FoV on the beam source results in a characteristic illumination pattern or relationship across the four quadrants. Therefore, the centering state or any deviation from that state is detected from the corresponding signal level of the alignment sensing signal 60. In one or more embodiments, a pointing control circuitry system 36 incorporates an analog-to-digital converter (ADC) for the digitization of the alignment sensing signal and for the corresponding comparison of digital samples in the digital processing domain.

[0039] In one or more embodiments, the BSA 54 includes one or more optical elements driven by one or more servo actuators for coarsely shifting the ROHA FoV in terms of elevation and azimuth. Regardless of its implementation, the BSA 54 provides one or more position feedback signals 62 to the pointing control circuitry 36 to track the angular position, and the processing circuitry 36 provides one or more BSA drive signals 64 to adjust the angular position. Similarly, in one or more embodiments, the FPA 56 includes one or more optical elements driven by one or more servo actuators for finely shifting the ROHA FoV in terms of elevation and azimuth. Regardless of its implementation, the FPA 56 provides one or more position feedback signals 66 to the processing circuitry 36 to track the angular position, and the processing circuitry 36 provides one or more FPA drive signals 68 to adjust the angular position.

[0040] LCT 30 further includes a TOHA 70 with an alignment sensor camera 72 and a pointing system 34-2. Pointing system 34-1 is a first pointing system for orienting the ROHA FoV, while pointing system 34-2 is a second pointing system for orienting the TOHA FoV. Having separate pointing systems allows for independent control of the ROHA pointing direction and the TOHA pointing direction, meaning that LCT 30 does not need to rely on precise mechanical alignment between the ROHA 50 and TOHA 70, or otherwise subordinate the pointing control of one head to the other.

[0041] Similar to pointing system 34-1, pointing system 34-2 includes BSA 74 and FPA 76. Further similar to ROHA 50, the alignment sensor camera 72 outputs alignment sensing signals 80—e.g., per-quadrant signals—and BSA 74 and FPA 76 output position feedback signals 82 and 86, respectively. Pointing control circuitry system 36 controls BSA 74 via BSA drive signal 84 and controls FPA 76 via FPA drive signal 88.

[0042] Figure 3 and Figure 4 Corresponding to Figure 2 DOHA example, where Figure 3 The FoV of ROHA 50 on LCT 30 on satellite 14 was depicted, and Figure 4 The FoV of TOHA 70 for LCT 30 is depicted. Each FoV covers a corresponding spatial region and can be logically subdivided into corresponding sectors, where... Figure 3 and Figure 4 Example layout using sixteen sectors.

[0043] Assuming that ROHA 50 and TOHA 70 are each at least coarsely aligned with the selected OGS 10, the OGS 10 "appears" within the respective fields of view of ROHA 50 and TOHA 70. However, as shown, individual alignment control of ROHA 50 and TOHA 70 means that the same OGS 10 can occupy different positions within their respective fields of view. Ideally, by finely controlling the positioning of ROHA 50 and TOHA 70 individually, the selected OGS 10 will appear at the respective center of ROHA FoV and TOHA FoV. In some embodiments, or in some operating conditions, ROHA 50 and TOHA 70 of the same LCT 30 on satellite 14 are always oriented toward the same selected OGS 10, while in other embodiments or in other operating conditions, ROHA 50 and TOHA 70 of the same LCT 30 are each oriented toward one of the two corresponding OGS 10s.

[0044] Figure 5 and Figure 2 Similarly, but an example DOHA implementation at LCT 20 is shown at OGS 10. Although the power, size, optics, and beam characteristics of the DOHA implementation at LCT 30 may differ from those at LCT 20, the basic principles and advantages are likely the same in areas such as optical isolation and individual pointing control of the corresponding OHA.

[0045] exist Figure 5 In the example, LCT 20 includes a ROHA 90 with an alignment sensing camera 92 and a pointing system 24-1 including a BSA 94 and an FPA 96. The alignment sensing camera 92 outputs an alignment sensing signal 100—e.g., a per-quadrant signal—and the BSA 94 and FPA 96 output position feedback signals 102 and 106, respectively. The pointing control circuitry system 26 controls the BSA 94 via a BSA drive signal 104 and controls the FPA 96 via an FPA drive signal 108. LCT 20 further includes a TOHA 110 with an alignment sensing camera 112 and a pointing system 24-2. Similar to pointing system 24-1, pointing system 24-2 includes a BSA 114 and an FPA 116. The alignment sensing camera 112 outputs an alignment sensing signal 120—e.g., a per-quadrant signal—and the BSA 114 and FPA 116 output position feedback signals 122 and 126, respectively. The pointing control circuit system 26 receives the position feedback signal 122 from the BSA 114 and controls the BSA 114 via the BSA drive signal 124. Similarly, the pointing control circuit system 26 receives the position feedback signal 126 from the FPA 116 and controls the FPA 116 via the FPA drive signal 128.

[0046] Figure 6 and Figure 7 Showing Figure 5 The examples depicted are the ROHA and TOHA fields of view of the LCT 20 DOHA arrangement of the OGS 10 and TOHA 110. Of course, the spatial area or volume covered by each such FoV depends on the pointing direction of the FoV.

[0047] and Figure 3 and Figure 4 Similar to the satellite-related fields of view depicted, the fields of view of ROHA 90 and TOHA 110 can be logically divided into sectors. Assuming that ROHA 90 and TOHA 110 are at least coarsely initially optically aligned with the selected satellite 14, the selected satellite 14 appears within each respective ROHA and TOHA field of view, although not necessarily in the same relative position, considering the separate pointing controls used for orienting ROHA 90 and TOHA 110. Furthermore, in at least one embodiment or in at least some operating scenarios, the OGS 10 with the DOHA-based LCT 20 can orient the ROHA 90 of the LCT 20 toward the first selected satellite 14, while orienting the TOHA 110 of the LCT 20 toward the second selected satellite 14. Similarly, in some embodiments or in certain operating scenarios, the DOHA-based LCT 30 on satellite 14 can orient its ROHA for receiving from the first remote LCT and orient its TOHA for transmitting toward the second remote LCT. For example, satellite 14 can act as a relay station between adjacent satellites.

[0048] Figure 8 A DOHA-based LCT 140 with additional example details is depicted. LCT 140 represents another example implementation of LCT 20 in OGS 10 and / or LCT 30 in Satellite 14. In other words, LCT 140 serves as a more general example of a DOHA LCT that can be used in either the OGS or satellite context. Thus, LCT 140 can be customized according to... Figure 2 or Figure 5 Configure any of the specific context details shown.

[0049] The LCT 140 shown includes ROHA 142 and TOHA 144. ROHA 142 includes an optical head 150, which includes an objective lens optics 152, an RX optical telescope 154, and a supporting RX optics 156. The supporting RX optics 156 outputs an optical RX communication signal 158 corresponding to the optical communication beam incident on ROHA 142 via the objective lens optics 152.

[0050] The support electronics 160 of LCT 140 outputs an electrical domain RX communication signal 162 corresponding to the optical RX communication signal 158, for input to a downstream RX circuitry (not shown). The support electronics 160 further includes a pointing control circuitry 164 that receives an alignment sensing signal 166 output from the alignment sensing camera 168 of ROHA 142. The pointing control circuitry 164 outputs one or more pointing control signals 170 to adjust the FoV of ROHA 142. For example, although not shown, ROHA 142 includes a BSA for coarse pointing control of the FoV of ROHA 142 and an FPA for fine pointing control of ROHA 142.

[0051] The TOHA 144 of the LCT 140 includes an optical head 180, which includes an objective lens optics 182, a TX optical telescope 184, and a TX support optics 186. The TX support optics 186 is configured to receive an optical TX communication signal 188 from the TOHA 144 as an output optical communication beam. Support electronics 160 generates the optical TX communication signal 188 in response to an electrical TX communication signal 190 received from a TX communication circuit system (not shown).

[0052] The pointing control circuitry 164 is configured to implement open-loop and closed-loop control of ROHA 142 and TOHA 144, wherein the pointing control of ROHA 142 is separate from the pointing control of TOHA 144. For example, the pointing control circuitry 164 includes one or more microprocessors, digital signal processors, or other programmed circuitry systems that perform the separate pointing controls of ROHA 142 and TOHA 144. When initially pointing to ROHA 142 or TOHA 144, the pointing control circuitry 164 implements open-loop pointing control, and then implements closed-loop pointing control once the incident beam is sensed.

[0053] For closed-loop control of ROHA 142, pointing control circuitry 164 uses alignment sensing signal 166 to determine the optical alignment of ROHA 142 relative to the beam incident on ROHA 142 via objective optics 152, and outputs one or more pointing control signals 170 to ROHA 142. In one or more embodiments, similar to earlier ROHA / TOHA examples, ROHA 142 includes a BSA for coarse, slow pointing control and an FPA for fine, fast pointing control. Therefore, in an example embodiment, the pointing control signals 170 generated by pointing control circuitry 164 include a first control signal for coarse elevation control, a second control signal for coarse azimuth control, a third control signal for fine elevation control, and a fourth control signal for fine azimuth control.

[0054] For closed-loop control of TOHA 144, the pointing control circuitry 164 uses alignment sensing signal 192 to determine the optical alignment of TOHA 144 relative to the beam incident on TOHA 144 via objective optics 182. At this point, it should be noted that while the primary purpose of TOHA 144 is beam transmission, it also functions as an optical receiver, as it senses the incident beam or spool for the limited purpose of detecting and adjusting its optical alignment relative to the incident beam source. As an example, if LCT 140 is on satellite 14, both ROHA 142 and TOHA 144 can be aligned using the same beam transmitted by the selected OGS 10.

[0055] Based on its evaluation of the alignment sensing signal 192 output by the alignment sensing camera 194 of TOHA 144, the pointing control circuitry 164 outputs one or more pointing control signals 196 to TOHA 142. In one or more embodiments, TOHA 144 includes a BSA for coarse, slow pointing control and an FPA for fine, fast pointing control. Therefore, in an example embodiment, the pointing control signal 196 includes a first control signal for coarse elevation control, a second control signal for coarse azimuth control, a third control signal for fine elevation control, and a fourth control signal for fine azimuth control.

[0056] Consistent with the details above, Figure 9An example pointing system 200 for ROHA 142 is shown, which includes a BSA 202 in response to a first control signal 204 and a second control signal 206 for coarse pointing adjustment of the FoV of ROHA 142. The pointing system 200 for ROHA 142 further includes an FPA 208 in response to a third pointing control signal 210 and a fourth pointing control signal 212 for fine pointing adjustment of the FoV of ROHA 142.

[0057] Figure 10 This demonstrates example optical details of the ROHA 142. The incident beam 214 strikes a mirror, as... Figure 8 An example implementation of the objective optics 152 introduced herein includes a BSA 202 incorporated into or otherwise hinged to the objective optics 152 for elevation tilt and azimuth rotation. The BSA 202 depicted in this example includes a first servo actuator 216 that, in response to a first position control signal 204, provides elevation tilt control of the objective optics 152 and outputs a position feedback signal 218. The BSA 202 further includes a second servo actuator 220 that, in response to a second position control signal 206, provides azimuth rotation control of the objective optics 152 and outputs a position feedback signal 222.

[0058] The incident beam 214 contains light at one or more wavelengths and may comprise a single beam or a composite beam—that is, two axially coincident beams incident on ROHA 142. For example, a remote LCT may initially transmit an optical beacon beam for detection at ROHA 142 and may then switch to transmitting an optical communication beam in place of the beacon beam or in addition to the beacon beam. In either case, objective optics 152 deflects the incident beam 214 into the RX optical telescope 154, which guides it onto additional optical elements 224 included in or otherwise acting on the FPA 208. Optical elements 224 are mirrors, and the FPA 208 provides elevation tilt control of optical elements 224 via a third servo actuator 226 and azimuth rotation control of optical elements 224 via a fourth servo actuator 228. The pointing control signals 210 and 212 incident from the pointing control circuit system 164 control the corresponding servo actuators 226 and 228, wherein the corresponding servo actuators 226 and 228 provide the corresponding position feedback signals 230 and 232.

[0059] Optical element 224 deflects the incident light beam 214 into a first collimator 234, where the resulting collimated light illuminates a beam splitter 236. Beam splitter 236 is configured to deflect at least a portion of the incident light beam 214, which is the output from collimator 234, onto an alignment sensing camera 168. In the depicted example, the alignment sensing camera 168 is a four-quadrant sensor with quadrants 238, 240, 242, and 244, where each quadrant includes a light-sensing pixel.

[0060] Beam splitter 236 delivers the remaining beam portion to RX collimator 246, which provides the corresponding collimated light to fiber collimator 250. Fiber collimator 250 couples this light into fiber optic 252 as optical RX communication signal 158. More specifically, optical RX communication signal 158 exists or otherwise transmits information only if the incident beam 214 includes an optical communication beam (i.e., a beam containing modulated light).

[0061] In the example scenario, ROHA 142 controls BSA 202 via pointing control circuitry 164 to point in an open loop toward the remote LCT. Initial pointing is based on the pointing control circuitry 164 knowing the location of the remote LCT. Initial pointing causes ROHA 142 to receive an optical beacon beam transmitted from the remote LCT to aid in fine optical alignment. Specifically, initial pointing positions the remote LCT somewhere within the FoV of ROHA 142 such that the alignment sensor camera 168 is illuminated by the optical beacon beam projected onto it by optical element 236. The location where the projected beam strikes the surface of the alignment sensor camera 168 indicates alignment / misalignment, with the alignment sensing signal 166 output by the alignment sensor camera 168 indicating the location of the remote LCT within the FoV of ROHA 142. Correspondingly, pointing control circuitry 164 controls FPA 208 to “center” the remote LCT within the FoV. In this example, centering the remote LCT in the FoV of ROHA 142 means shifting the FoV in elevation and azimuth as needed to produce equal illumination in the four quadrants of the aligned sensor camera 168.

[0062] After achieving mutual optical alignment with LCT 140, the remote LCT can begin transmitting an optical communication beam consistent with its transmitted optical beacon beam, or it can stop transmitting the optical beacon beam once it has begun transmitting the optical communication beam. In at least one embodiment, the optical beacon beam and the optical communication beam from the remote LCT are at different optical wavelengths, wherein beam splitter 236 deflects at least some of the incident optical beacon beam onto alignment sensing camera 168, and deflects some, but not all, of the incident optical communication beam onto alignment sensing camera 168. One advantage of illuminating alignment sensing camera 168 with a portion of the incident optical communication beam is that it increases the available optical power for alignment detection—that is, it improves the signal-to-noise ratio (SNR) for alignment detection without unduly reducing the corresponding optical RX communication signal 158.

[0063] Figure 11 An example implementation of the supporting electronics 160 relative to ROHA 142 is shown. Optical RX communication signal 158 is received by optical amplifier 300, which provides its output optical signal to optical demultiplexer 302. Here, it is assumed that the optical communication beam incident on ROHA 142 contains light at multiple wavelengths, each such wavelength corresponding to a corresponding optical channel for transmitting a corresponding information stream, which itself may include a multiplexed arrangement of information substreams. Therefore, optical demultiplexer 302 is based on wavelength division multiplexing (WDM) and outputs multiple RX optical channel signals 304, of which five such signals 304-1, 304-2, 304-3, 304-4, and 304-5 are shown only as examples.

[0064] The corresponding optical phase detector (PD) 306 converts the corresponding optical channel signal 304 into an electrical RX communication signal 308, shown as electrical RX communication signal 308-1 corresponding to optical RX channel signal 304-1, electrical RX communication signal 308-2 corresponding to optical RX channel signal 304-2, and so on. The optical PD 306 operates using the corresponding local oscillator (LO) signal 310 output by the corresponding RX oscillator, commonly identified by reference numeral 312. An optical phase-locked loop (OPLL) 314 can be used to provide a reference frequency to the RX oscillator 312.

[0065] In the illustrated embodiment, the TX communication payload 316, which is not considered part of LCT 140, receives electrical RX communication signals 308 for processing or unprocessed retransmission. In the example where LCT 140 is on satellite 14, the TX communication payload 316 may include multiple bend signal transmission paths for transmitting the electrical RX communication signals 308 as radio frequency (RF) downlink signals to corresponding terminals in the terminal group served by satellite 14.

[0066] Here, "bend" means that satellite 14 does not recover the information carried by the electrical RX communication signal 308, but only transmits these signals, which may have been amplified, filtered, and frequency-converted. For example, the corresponding optical channel signal 304 includes radio frequency (RF) modulated light, where the modulation includes the information content. In such embodiments, the electrical RX communication signal 308 is an RF signal. In related embodiments, the corresponding RX optical channel signal 304 includes digitally modulated light, where the TX communication payload 316 modulates the corresponding RF carrier according to such modulation. Alternatively, the TX communication payload 316 may include a processing payload that demodulates and decodes the electrical RX communication signal 308 and then generates a corresponding new outgoing RF signal for transmission.

[0067] The RX BSA elevation driver 320 provides a position control signal 204, while the RX BSA elevation sensor electronics 322 receives a corresponding position feedback signal 218. The RX BSA azimuth driver 324 provides a position control signal 206, while the RX BSA azimuth sensor electronics 326 receives a corresponding position feedback signal 222. The RX FPA elevation / azimuth driver 328 provides pointing control signals 210 and 212, while the RX FPA elevation sensor electronics 330 receives corresponding position feedback signals 230 and 232.

[0068] The RX alignment sensor electronics 332 receives alignment sensing signals 166 from the alignment sensing camera 168 and includes one or more ADCs, for example, to provide digitized samples to an LCT controller 340, which includes, for example, one or more CPUs 342 and a supporting memory 344 for storing one or more computer programs 346 and configuration and operating data 348. In at least one embodiment, the LCT controller 340 includes one or more microprocessors or other digital processing circuitry specifically adapted to execute computer program instructions stored in the memory 344. The LCT controller 340 and its supporting interface electronics should be understood as examples of supporting electronics 160 and the pointing control circuitry 164 included therein. Additional elements of such circuitry include, for example, an optical amplifier (OA) driver / controller 350 for controlling OA 300.

[0069] With targeting Figure 8 The details discussed in the LCT 140 shown are consistent. Figure 12An example pointing system 400 for the TOHA 144 of the LCT 140 is shown. The pointing system 400 includes a BSA 402 responsive to a first control signal 404 and a second control signal 406 for coarse pointing adjustments to the FoV of the TOHA 144 in terms of elevation and azimuth. The pointing system 400 for the TOHA 144 further includes an FPA 408 responsive to a third pointing control signal 410 and a fourth pointing control signal 412 for fine pointing adjustments to the FoV of the TOHA 144 in terms of elevation and azimuth.

[0070] Figure 13 Example optical details of TOHA 144 from the example LCT 140 are shown. The supporting TX optics 186 of TOHA 144 includes a fiber-coupled collimator 420 for receiving an optical TX communication signal 188 via an input fiber optic cable 422. Collimator 420 collimates the optical TX communication signal 188 into an outgoing optical communication beam 424 directed toward a further collimator 428, which then directs it toward a beam splitter 430. Beam splitter 430 deflects a portion of the beam toward an optical storage unit 432 while passing the remainder to a second beam splitter 434. For simplicity, this remaining portion of the light is still referred to as the outgoing optical communication beam 424.

[0071] The supporting TX optics 186 further includes a beacon laser unit 436 that outputs a laser beam in response to a beacon control signal 438. This laser beam serves as an outgoing optical beacon beam 440 to be transmitted by TOHA 144 for use by a remote LCT to optically align itself with LCT 140. A collimator 442 directs the outgoing optical beacon beam 440 toward an optical element 260 (such as a deflecting mirror), which directs the outgoing optical beacon beam 440 to a beamsplitter 430, which directs it toward another beamsplitter 434. This other beamsplitter 434 directs a portion of the light contained in the outgoing beacon beam toward an optical storage device 444, while passing the remainder toward an optical element 446 contained in the FPA 408 of TOHA 144.

[0072] Using this arrangement, when TOHA 144 transmits both the outgoing optical communication beam 424 and the outgoing optical beacon beam 440, beam splitter 430 deflects a portion of the communication beam towards the dump 432, while transmitting the remaining communication beam towards beam splitter 434. Correspondingly, beam splitter 434 transmits the outgoing communication beam incident on it from beam splitter 430, while deflecting a portion of the outgoing beacon beam towards dump 444 and transmitting the remainder towards optical element 446. Therefore, at least a portion of the supporting optical assembly 186 includes a shared optical path for the outgoing beacon and communication beam.

[0073] Optical element 446 guides the outgoing optical communication beam 424 and the outgoing optical beacon beam 440 into the optical telescope 184, which in turn guides the beams onto the optical element as... Figure 8 An example of the objective optics 182 shown. Optical element 182 includes a portion of BSA 402 of TOHA 144, and the figure shows an outgoing optical communication beam 424 and an outgoing optical beacon beam 440 that exit TOHA 144 for free space propagation toward a remote LCT.

[0074] Although the primary function of TOHA 144 is beam transmission, individual alignment control of TOHA 144 requires sensing its alignment relative to a remote LCT. Therefore, TOHA 144 is configured to receive an incident beam 450 on at least a portion of the same optical path used for beam transmission; for simplicity, these incident and outgoing beams are depicted in the diagram via a single bidirectional arrow. The incident beam is, for example, the same optical beacon and / or communication beam incident on ROHA 142, and it is deflected by optical element 182 via TX optical telescope 184 into the main optical path supporting TX optics 186. The depicted optical path guides the incident beam 450 to collimator 452, which directs it to alignment sensing camera 194, which outputs the aforementioned alignment sensing signal 192, for example, a per-quadrant signal from a four-quadrant configuration of alignment sensing camera 194.

[0075] Pointing control circuitry 164 uses alignment sensing signal 192 to sense the FoV of TOHA 144 relative to the incident beam 450, or in other words, the optical alignment relative to the remote LCT of the transmission beam 450. Pointing control circuitry 164 uses BSA 402 for coarse pointing control of TOHA 144 and FPA 408 for fine pointing control of TOHA 144. In one or more embodiments, pointing control circuitry 164 implements open-loop pointing control via BSA 402, for example, positioning FPA 408 at its default or nominal center position for initial alignment of TOHA 144 with the remote LCT. The same initial alignment method can also be implemented for ROHA 142.

[0076] This initial alignment positions the beam 450 somewhere within the FoV of TOHA 144, and then alignment sensor signal 192 instructs pointing control circuitry 164 to perform the fine FPA adjustment required to center the incident beam 450 within the FoV. From there, pointing control circuitry 164 can "track" the incident beam 450 by using BSA 402 to compensate for slow misalignment trends while using FPA 408 to compensate for smaller, faster disturbances. In this context, tracking means controlling BSA 402 / FPA 408 to keep the incident optical beacon beam centered within the TOHA FoV. The pointing control circuitry 164 performs the same tracking control for the ROHA FoV separately.

[0077] The pointing control circuitry 164 determines the current positions of BSA 402 and FPA 408 in terms of elevation and azimuth based on position feedback signals. A first servo actuator 460 of BSA 402 responds to a first position control signal 404 to control the elevation angle of optics 182 and provides a corresponding position feedback signal 462. A second servo actuator 464 of BSA 402 responds to a second position control signal 406 to control the azimuth angle of optics 182 and provides a corresponding position feedback signal 466. A first servo actuator 470 of FPA 408 responds to a third pointing control signal 410 to control the elevation angle of optics 446 and provides a corresponding position feedback signal 472. A second servo actuator 474 of FPA 408 responds to a fourth pointing control signal 412 to control the azimuth angle of optics 182 and provides a corresponding position feedback signal 476.

[0078] Another point of interest in the figure is the hinge of the optics 260 used to “scan” the outgoing optical beacon beam 440. For example, using the LCT 140 implemented in OGS 10, OGS 10 can scan the outgoing optical beacon beam 440 within its optical FoV as part of a favorable pointing, acquisition, and tracking (PAT) algorithm.

[0079] Multiple hinge methods are possible. Figure 13 Only example methods based on servo actuator 480 for azimuth rotation of optical element 260 and servo actuator 482 for elevation rotation of optical element 260 are shown. Az control signal 484 controls azimuth rotation and provides corresponding position feedback via position feedback signal 486. Similarly, E1 control signal 488 controls elevation rotation and provides corresponding position feedback via position feedback signal 490.

[0080] Figure 14 Example details of the supporting electronics 160 of LCT 140 in one embodiment regarding the control of TOHA 144 are shown. Figure 11 The LCT controller 340 introduced in the document is configured to perform or otherwise coordinate such control, for example, based on the execution of stored computer program instructions.

[0081] The additional circuitry includes a TX BSA elevation driver 500, which operates under the control of an LCT controller 340 and outputs a first position control signal 204. The corresponding TX BSA elevation sensor electronics 502 receives a corresponding position feedback signal 462. A TX BSA azimuth driver 504 operates under the control of an LCT controller 340 and outputs a second position control signal 206. The corresponding TX BSA azimuth sensor electronics 506 receives a corresponding position feedback signal 466. A TX FPA elevation and azimuth driver 508 operates under the control of an LCT controller 340 and outputs a third position control signal 210 and a fourth position control signal 212. The corresponding TX FPA elevation / azimuth sensor electronics 510 receives corresponding position feedback signals 472 and 476.

[0082] The TX alignment camera sensor electronics 512 interfaces the alignment sensor camera 194 of TOHA 144 with the LCT controller 340, for example, by digitizing the alignment sensing signal 192 output by the alignment sensor camera 194. Further interface details include a beacon laser control circuit 514, which is configured to provide the LCT controller 340 with on / off control of the beacon laser unit 436 of TOHA 144, and modulation control in some embodiments.

[0083] Furthermore, the LCT controller 340 controls the optical power amplifier (OPA) 516 via the OPA driver 518, wherein the OPA 516 is configured to output the optical TX communication signal 188 received in TOHA 144 for transmission via the input fiber 422 as an outgoing optical communication beam 424. Assuming that the optical TX communication signal 188 is formed as a combined optical signal comprising multiple optical channel signals 520 (e.g., optical channel signals 520-1 to 520-5), the supporting electronics 160 includes an optical multiplexer 522 configured to combine the optical channel signals 520 via WDM to generate the optical TX communication signal 188 as a combined or composite optical signal having multiple optical channel signals 520 multiplexed in the optical frequency domain.

[0084] Each optical channel signal 520 corresponds to a different electrical domain RX communication signal 524 output by the RX communication payload 526, which is not considered part of the LCT support electronics 160. Although the RX communication payload 526 outputs electrical domain RX communication signals 524 for optical transmission by the LCT 140, the designation "RX" indicates that these RX communication signals 524 are received for optical transmission by the LCT 140.

[0085] Taking five optical channel signals 520-1, 520-2, 520-3, 520-4, and 520-5 as an example, each optical channel signal 520 is at a corresponding optical wavelength and is modulated by a corresponding optical modulator 528 according to a corresponding one of the electrical domain RX communication signals 524. This corresponding optical modulator provides the corresponding LO signal 530 at the correct frequency via a corresponding TX oscillator among a plurality of TX oscillators 532. One or more OPLLs 534 operating under the control of the LCT controller 340 can be configured to provide a reference frequency signal to the TX oscillator 532.

[0086] In one or more embodiments, scan control circuitry 536 interfaces LCT controller 340 with servo actuators 480 and 482 for scan control of the emitted optical beacon beam 440. For example, scan control circuitry 536 includes corresponding driver circuitry for driving servo actuators 480 and 482 in response to digital and / or analog signals output from LCT controller 340. In one or more embodiments, scan control circuitry 536 further includes level shifting or buffering circuitry configured to interface position feedback signals 486 and 490 with LCT controller 340. Thus, when performing beacon beam scanning, LCT controller 340 “moves” the emitted optical beacon beam 440 within the optical FoV via signals 484 and 488, and reads the current “position” of the emitted optical beacon beam 440 via signals 486 and 490.

[0087] Figure 15 An example satellite communication system (SCS) 600 is shown, including an OGS 602 communicatively coupled to a satellite 604 via an OFL 606. The OGS 602 includes a first LCT 140-1 as described above, wherein the LCT 140-1 transmits one or more optical uplink beams 608 as part of the OFL 606, such as optical uplink communication beams and optical uplink beacon beams. Correspondingly, the satellite 604 includes an LCT 140-2 as described above, wherein the LCT 140-2 transmits one or more optical downlink beams 610, such as optical downlink communication beams and optical downlink beacon beams.

[0088] Figure 16 An example arrangement of OFL 606 is shown, in which LCT 140-1 in OGS 602 transmits an optical uplink (UL) beacon beam 612 and transmits an optical UL communication beam 614 at the same or different times, for example, transmitting multiple optical channel signals at corresponding optical wavelengths. LCT 140-2 on satellite 604 transmits an optical downlink (DL) beacon beam 616 and transmits an optical DL communication beam 618 at the same or different times. In at least one embodiment, the optical UL communication beam is at a first optical wavelength DL2.

[0089] In one or more embodiments, the optical UL communication beam 614 is at a first optical wavelength, the optical DL communication beam 618 is at a second optical wavelength, the optical UL beacon beam 612 is at a third optical wavelength, and the optical DL beacon beam 616 is at a fourth optical wavelength. In at least one such embodiment, the first and third optical wavelengths are within the first optical wavelength range, and the second and fourth optical wavelengths are within the second optical wavelength range, wherein the first and second optical wavelength ranges do not intersect.

[0090] For one or more embodiments, saying that the optical UL communication beam 614 is at a first optical wavelength can be understood as meaning that the optical UL communication beam 614 is based on an optical carrier having a carrier center frequency corresponding to the first optical wavelength. In fact, the optical UL communication beam 614 can contain light at more than one optical wavelength, such as centered at the carrier center frequency, and the same is true for the optical DL communication beam 618. This arrangement allows the optical communication beam to transmit multiple information streams, such as multiple RF communication signals.

[0091] In one or more embodiments, the optical wavelengths of the optical UL beacon beam 612 and the optical UL communication beam 614 are close. For example, the optical wavelength of the optical UL communication beam 614 is 1550 nm, and the optical wavelength of the optical UL beacon beam 612 is 1590 nm. Similarly, in the same or other embodiments, the optical wavelengths of the optical DL beacon beam 616 and the optical DL communication beam 618 are close. For example, the optical wavelength of the optical DL communication beam 618 is 1064 nm, and the optical wavelength of the optical DL beacon beam 616 is 974 nm.

[0092] Return to Figure 15 In addition to OGS 602, the ground segment 620 of SCS 10 also includes a core network 622, which includes one or more computer servers or other computer systems configured to operate as a communication processing system (CPS) 624, operable to interface SCS 600 with one or more external networks 626, such as the Internet. In one or more embodiments, CPS 624 is configured to receive incoming packet streams targeted to corresponding terminals in a group of terminals 628 served by satellite 604 and provide them as forward traffic for DL ​​transmissions performed by satellite 604 to OGS 602 for reception by target terminals 628, which may include user terminals or other subscriber endpoint devices.

[0093] OGS 602 includes an interface circuitry system 630, such as a data network interface circuitry system, configured to interface OGS 602 with CPS 624. Communication circuitry system 632 generates one or more TX communication signals corresponding to forward traffic incident from CPS 624 to OGS 602 via interface circuitry system 630. In one embodiment, terminals 628 are distributed over a geographical area called a satellite service area covered by satellite 604. The satellite service area is logically divided into multiple beam coverage areas, wherein satellite 604 transmits RF DL beams covering the respective beam coverage areas.

[0094] Correspondingly, in the example embodiment, the communication circuitry 632 in OGS 602 generates an RF forward beam signal for each beam coverage area, wherein each such signal includes multiplexed forward traffic for a terminal 628 located within the corresponding beam coverage area. LCT 140-1 forms its optical UL communication beam 614 as a multiplexed optical signal comprising multiple optical channel signals, each optical channel signal transmitting a corresponding forward beam signal from the forward beam signal. Continuing in the forward direction, LCT 140-2 in satellite 604 receives the optical UL communication beam 614 as an incident optical RX communication beam, and its output can be understood as a recovered version of the corresponding RF signal of the RF forward beam signal. See, for example, [link to example description]. Figure 11 The electrical domain RX communication signal 308 is depicted in the figure.

[0095] Satellite 604 includes a TX communication payload 316 as described above, which uses one or more RF antenna systems 642 to transmit an RF DL communication signal 644 corresponding to the electrical forward flow signal provided to it by LCT 140-2. In one or more embodiments, the RF DL communication signal 644 is transmitted as part of an RF user link 646 via RF beamforming corresponding to a beam coverage area. The TX communication payload 316 may be a bend-tube payload without signal decoding, or it may be a processed payload that performs signal decoding and remodulation for transmission.

[0096] The corresponding terminals in terminal group 628 transmit return traffic via RF UL signals 648, which are received via one or more RF antenna systems 642 on satellite 604. The RX communication payload 526, as previously described, provides these signals, or signals derived therefrom, to LCT 140-2 as electrical return traffic signals for transmission to OGS 602 via optical DL communication beam 618. LCT 140-1 provides corresponding recovered versions of these return traffic signals to CPS 624.

[0097] Although Figure 15The illustration simplifies the representation by showing one OGS 602 and one satellite 604, but in one or more embodiments, the SCS 600 includes multiple OGS 602s and multiple satellites 604. For example, a given satellite 604 may be supported by different OGS 602s at different times. Furthermore, one or more OGS 602s may include more than one LCT 140-1, where each LCT 140-1 is capable of supporting a corresponding OFL 606, meaning that one such OGS 602 may utilize the same satellite 604 or multiple satellites 604 to simultaneously support two or more OFL 606s. Similarly, in one or more embodiments, at least one satellite 604 of the SCS 600 includes more than one LCT 140-2, which increases the capacity of the satellite 604 because it can simultaneously exchange forward / reverse traffic over more than one OFL 606.

[0098] Figure 17 A method 1700 for operation at LCT 140-2 on satellite 604 is illustrated. The LCT controller 340 initially performs (box 1702) open-loop pointing of ROHA 142 and TOHA 144 individually based on its current position and orientation, as well as the location of the selected OGS 602. In one or more embodiments, SCS 600 includes multiple geographically distributed OGS 602s, and satellite 604 is capable of switching from one OGS 602 to another, utilizing the LCT controller 340 to redirect ROHA 142 and TOHA 144 as needed.

[0099] Assuming the selected OGS 602 performs complementary open-loop pointing of ROHA 142 and TOHA 144 in its LCT 140-1, LCT 140-2 will begin receiving the optical UL beacon beam 612 from the OGS 602. Correspondingly, LCT 140-1 will begin receiving the optical DL beacon beam 616 from LCT 140-2.

[0100] Method 1700 continues with the acquisition process (box 1704), where the LCT controller 340 in LCT 140-2 uses the optical UL beacon beam 612 detected by the alignment sensing camera 168 of ROHA 142 and the alignment sensing camera 194 of TOHA 144 to acquire optical alignment relative to LCT 140-1. Similarly, the LCT controller 340 in LCT 140-1 uses its alignment sensing cameras 168 and 194 to perform its own optical alignment of ROHA 142 and TOHA 144 relative to LCT 140-2. Once acquired, LCT 140-1 and LCT 140-2 begin transmitting their respective optical communication beams 614 and 618, and method 1700 continues tracking during ongoing communication (box 1706). Tracking involves the LCT controller 340 in LCT 140-2 controlling the BSA / FPA of its ROHA 142 and its TOHA 144 to maintain the optical alignment of ROHA 142 and TOHA 144 with LCT 140-1. The same or similar tracking operations are performed in LCT 140-1 and OGS 602.

[0101] More specifically, in order to establish a communication link between a given OGS 602 and a given satellite 604 in SCS 600, the corresponding LCT 140-1 (OGS) and 140-2 (satellite) first perform a spatial pointing, acquisition, and tracking (PAT) sequence to optically co-align with each other. To accelerate the acquisition time, in one or more embodiments, the corresponding beacon beam carries a modulated service channel with coded beacon pointing data. Consider the following example (PAT) sequence.

[0102] The pointing operations in the PAT sequence include LCT 140-1 and 140-2, which use known GPS and orbital data to roughly point their beacons toward each other in an open-loop manner using their respective BSAs in ROHA and TOHA.

[0103] After pointing, the acquisition operation begins. In one or more embodiments, the satellite beacon has a sufficiently large divergence angle such that the initial pointing causes the satellite's beacon beam to immediately illuminate the OGS 602, thereby allowing the OGS 602 to acquire the satellite 604 relatively quickly. However, to improve the available signal at the satellite 604, the communication beam transmitted by the OGS 602 can have a narrower divergence angle, while the beacon beam transmitted by the OGS 602 has the same narrow divergence angle.

[0104] The OGS 602 therefore "scans" its outgoing beacon beam within its optical FoV, for example, via a movable mirror (such as... Figure 13The El / Az control of the optical element 260 shown affects the beacon beam but not the optical FoV. See also Figure 18 This demonstrates OGS TOHA's FoV, whose transmission is based on the outgoing optical beacon beam sensed by satellite 604. Despite Figure 18 A spiral scan or search mode on the FoV is shown, but other modes, such as horizontal or diagonal raster scan, can be used. In any case, the LCT controller 340 in the LCT 140-1 of the OGS 602 modulates the outgoing beacon beam at least during the acquisition phase of the PAT algorithm, such that the outgoing beacon beam dynamically encodes the scan path or the corresponding FoV sector traversed by the scan path. In other words, different modulation codes applied to the beacon beam correspond to different scan positions.

[0105] According to satellite 604 Figure 18 The example depicts a scenario where, within the optical FoV of OGS 602, LCT 140-2 of satellite 604 will typically not detect the beacon beam from OGS 602 unless / until the beacon beam is scanned through sector numbered "12" in the example. Alternatively, while satellite 604 may detect the UL beacon beam from OGS 602 for more than one scanned sector of the FoV of OGS 602, the detected beam will be strongest for the sector in which satellite 604 is located.

[0106] LCT 140-2 demodulates the detected optical UL beacon beam from OGS 602 to recover the coded sector information, and it modulates its own optical DL beacon beam with the sector information to feed the sector information back to OGS 602. In the example shown, when OGS 602 scans its optical uplink beacon beam through sector 12 of its optical FoV, satellite 604 detects the optical uplink beacon beam (or detects it most strongly), recovers the corresponding sector code modulated onto the optical UL beacon beam by OGS 602, and returns the recovered code to OGS 602 by modulating its optical DL beacon beam with the recovered sector code.

[0107] Upon receiving the recovered sector code, OGS 602 knows that the satellite is positioned in or near sector 12 of its optical FoV, and it initiates a new scan on or around sector 12, possibly with increased sector resolution. Specifically, in one or more embodiments, the scan is based on higher-resolution sectorization around the position determined according to previous scans. Therefore, the modulation codes in a single scan may not correspond to the same absolute FoV position they represented in previous scans. In any case, OGS 602 may perform one or more additional scans to refine its optical alignment, and for each additional scan, FPA adjustments may be performed, for example, to finely center the FoV on the “position” of the remote LCT determined in the previous scan. After the alignment based on the scans is completed, the satellite 604 will be positioned at the center of the optical FoV of OGS 602 within tolerance and error constraints.

[0108] With OGS 602 and Satellite 604 subsequently optically aligned, an optical UL / DL communication beam can be established, where the FPA in OGS 602 and Satellite 604 is now used to actively maintain optical alignment and compensate for drift and vibration. Additionally, both LCT 140-1 and 140-2 begin to compensate for lead pointing angle.

[0109] It is worth noting that, benefiting from the teachings presented in the foregoing description and related drawings, those skilled in the art will conceive of modifications and other embodiments of the disclosed invention. Therefore, it should be understood that the invention is not limited to the specific embodiments disclosed, and that modifications and other embodiments are intended to be included within the scope of this disclosure. Although specific terminology may be used herein, it is used only in a general and descriptive sense and not for limiting purposes.

Claims

1. A laser communication terminal (LCT) configured for use at one end of an optical feeder link (OFL) between a satellite and an optical ground station (OGS) in a satellite communication system, said LCT comprising: A receiving optical head assembly (ROHA) configured for receiving a beam, the ROHA including a first pointing system configured to control the pointing direction of the ROHA; A transmission optical head assembly (TOHA) configured for beam transmission, the TOHA including a second pointing system for controlling the pointing direction of the TOHA independently of the pointing direction of the ROHA; as well as A pointing control circuit system is configured to control the first pointing system in response to a first alignment signal output from a ROHA alignment sensor camera, and is further configured to control the second pointing system in response to a second alignment signal output from a TOHA alignment sensor camera.

2. The LCT of claim 1, wherein the ROHA is configured to receive an incident optical communication beam at a first optical wavelength, and the TOHA is configured to transmit an outgoing optical communication beam at a second optical wavelength.

3. The LCT of claim 2, wherein the ROHA is configured to receive an incident optical beacon beam at a third optical wavelength, the first optical wavelength and the third optical wavelength being within a first optical wavelength range and the second optical wavelength being outside the first optical wavelength range, wherein the ROHA includes a shared optical path configured to direct the incident optical beacon beam toward the ROHA alignment sensor camera and to direct at least a portion of the incident optical communication beam toward a receiving (RX) fiber collimator.

4. The LCT of claim 3, wherein the shared optical path of the ROHA is further configured to guide a portion of the incident optical communication beam toward the ROHA alignment sensor camera, such that one or both of the incident optical beacon beam and the incident optical communication beam can be used by the pointing control circuitry to control the pointing of the ROHA.

5. The LCT of claim 3 or 4, wherein the TOHA is configured to receive the incident optical beacon beam, wherein the TOHA includes a shared optical path of the TOHA, the shared optical path being configured to direct the incident optical beacon beam toward the TOHA alignment sensor camera and to direct the outgoing optical communication beam for transmission from the TOHA.

6. The LCT of claim 5, wherein the TOHA is further configured to transmit an outgoing optical beacon beam for use by a remote LCT at the other end of the OFL, the shared optical path of the TOHA being configured to guide the outgoing optical beacon beam for transmission from the TOHA.

7. The LCT according to claim 6, wherein the outgoing optical beacon beam is at a fourth optical wavelength, the second optical wavelength and the fourth optical wavelength are within the range of the second optical wavelength, and the range of the second optical wavelength does not overlap with the range of the first optical wavelength.

8. The LCT according to any one of claims 1 to 7, wherein the ROHA includes a first optical telescope dedicated to the ROHA, and the TOHA includes a second optical telescope dedicated to the TOHA.

9. The LCT according to any one of claims 1 to 8, wherein the pointing control circuitry is configured to control the pointing direction of the ROHA in response to a first alignment signal output by the ROHA alignment sensor camera, and to control the pointing direction of the TOHA in response to a second alignment signal output by the TOHA alignment sensor camera.

10. The LCT of claim 9, wherein each of the ROHA alignment sensor camera and the TOHA alignment sensor camera includes a first four-quadrant sensor, wherein the first alignment signal includes a detection signal for each quadrant, indicating the amount of light illuminating the quadrant.

11. The LCT according to any one of claims 1 to 10, wherein the first pointing system and the second pointing system each include a first pointing control element configured to provide coarse pointing adjustment and a second pointing control element configured to provide fine pointing adjustment.

12. The LCT of claim 11, wherein the pointing control circuitry is configured to implement a pointing, capturing, and tracking (PAT) algorithm for each of the ROHA and the TOHA as an OHA, wherein the PAT algorithm comprises the pointing control circuitry: Initially pointing at the OHA on an open-loop basis to initiate beacon beam reception; and Closed-loop pointing control of the OHA is performed in response to beacon beam reception.

13. The LCT according to any one of claims 1 to 12, wherein the pointing control system is configured to align at least initially with a first of the ROHA and the TOHA, determine alignment assistance information based on the alignment with the first, and use the alignment assistance information to align the second of the ROHA and the TOHA more quickly.

14. A satellite configured for use in a satellite communication system (SCS), said satellite comprising: One or more radio frequency (RF) antenna systems; An RF communication payload configured to transmit forward traffic to a corresponding terminal via the one or more RF antenna systems, and to receive return traffic from the corresponding terminal via the one or more RF antenna systems; as well as The LCT according to any one of claims 1 to 13, wherein the LCT is configured to receive the forward traffic via an optical uplink communication beam transmitted by an optical ground station (OGS), the OGS being included in the SCS; and is further configured to transmit the return traffic to the OGS via an optical downlink communication beam.

15. An optical ground station (OGS) configured for use in a satellite communication system (SCS), said OGS comprising: An interface circuit system is configured to receive forward traffic from the Communication Processing System (CPS) of the SCS for forwarding to a corresponding terminal in a terminal served by the SCS's satellite, and is configured to transmit return traffic from the corresponding terminal in the terminal toward the CPS. A communication circuit system configured to generate a forward communication signal for transmitting the forward traffic and configured to recover a return communication signal for transmitting the return traffic; as well as The LCT according to any one of claims 1 to 13, wherein the LCT is configured to transmit the forward communication signal to the satellite via an optical uplink communication beam and is configured to receive the return communication signal via an optical downlink communication beam transmitted by the satellite.

16. A method for communication between a satellite and an optical ground station (OGS) in a satellite communication system via an optical feeder link (OFL), the method being performed via a laser communication terminal (LCT) at one end of the OFL and comprising: An optical communication beam is received from a remote LCT at the other end of the OFL via free space propagation, the incident optical communication beam being received via a receiving optical head assembly (ROHA) of the LCT, the ROHA having a first pointing system for pointing control of the ROHA; The remote LCT transmits an optical communication beam emitted from the LCT via free space propagation. The emitted optical communication beam is transmitted via the LCT's transmission optical head assembly (TOHA), which has a second pointing system for pointing control of the TOHA. as well as Pointing control is performed separately on the ROHA and the TOHA based on the corresponding evaluation of the first alignment signal output by the first alignment camera in the ROHA and the second alignment signal output by the second alignment camera in the TOHA.

17. The method of claim 16, wherein performing pointing control individually on the ROHA and the TOHA comprises individually detecting the optical alignment of the ROHA and the TOHA relative to an optical beacon beam originating from the remote LCT and incident on both the ROHA and the TOHA after initial pointing of the ROHA and the TOHA, and wherein individually detecting the optical alignment of the ROHA and the TOHA comprises detecting the optical alignment of the ROHA via a first alignment sensing camera in the ROHA and detecting the optical alignment of the TOHA via a second alignment sensing camera in the TOHA.

18. The method of claim 16, wherein performing pointing control separately on the ROHA and the TOHA comprises initially pointing the OHA to at least one of the ROHA and the TOHA on an open-loop basis as an initial pointing OHA, and performing further pointing adjustment on the initially pointing OHA in response to detecting the beam position of an optical beacon beam transmitted by the remote LCT and illuminating the alignment detection camera of the initially pointing OHA as a result of the initial pointing.

19. The method according to any one of claims 16 to 18, wherein the incident optical communication beam is at a first optical wavelength and the outgoing optical communication beam is at a second optical wavelength spaced apart from the first optical wavelength.

20. A satellite communication system (SCS), comprising: Optical ground station (OGS), which is configured to operate at one end of the optical feeder link (OFL); A satellite, configured to operate at the other end of the OFL, comprises: One or more radio frequency (RF) antenna systems; An RF communication payload, configured to transmit forward link traffic to a corresponding terminal via the one or more RF antenna systems, and to receive return link traffic from the corresponding terminal via the one or more RF antenna systems; and Laser communication terminal (LCT), which includes: A receiving optical head assembly (ROHA) configured for receiving a beam, the ROHA including a first pointing system configured to control the pointing direction of the ROHA; A transmission optical head assembly (TOHA) configured for beam transmission, the TOHA including a second pointing system for controlling the pointing direction of the TOHA independently of the pointing direction of the ROHA; and A pointing control circuit system is configured to control the first pointing system in response to a first alignment signal output from a ROHA alignment sensor camera, and is further configured to control the second pointing system in response to a second alignment signal output from a TOHA alignment sensor camera.

21. The SCS of claim 20, wherein the ROHA is configured to receive an incident optical communication beam at a first optical wavelength, and the TOHA is configured to transmit an outgoing optical communication beam at a second optical wavelength.

22. The SCS of claim 21, wherein the ROHA is configured to receive an incident optical beacon beam at a third optical wavelength, the first optical wavelength and the third optical wavelength being within a first optical wavelength range and the second optical wavelength being outside the first optical wavelength range, wherein the ROHA includes a shared optical path configured to direct the incident optical beacon beam toward the ROHA alignment sensor camera and to direct at least a portion of the incident optical communication beam toward a receiving (RX) fiber collimator.

23. The SCS of claim 22, wherein the shared optical path of the ROHA is further configured to guide a portion of the incident optical communication beam toward the ROHA alignment sensor camera, such that one or both of the incident optical beacon beam and the incident optical communication beam can be used by the pointing control circuitry to control the pointing of the ROHA.

24. The SCS of claim 22 or 23, wherein the TOHA is configured to receive the incident optical beacon beam, wherein the TOHA includes a shared optical path of the TOHA, the shared optical path being configured to direct the incident optical beacon beam toward the TOHA alignment sensor camera and to direct the outgoing optical communication beam for transmission from the TOHA.

25. The SCS of claim 24, wherein the TOHA is further configured to transmit an outgoing optical beacon beam for use by a remote LCT at the other end of the OFL, and the shared optical path of the TOHA is configured to guide the outgoing optical beacon beam for transmission from the TOHA.

26. The SCS according to claim 25, wherein the outgoing optical beacon beam is at a fourth optical wavelength, the second optical wavelength and the fourth optical wavelength are within the range of the second optical wavelength, and the range of the second optical wavelength does not overlap with the range of the first optical wavelength.

27. The SCS according to any one of claims 20 to 26, wherein the ROHA includes a first optical telescope dedicated to the ROHA, and the TOHA includes a second optical telescope dedicated to the TOHA.

28. The SCS according to any one of claims 20 to 27, wherein the pointing control circuitry is configured to control the pointing direction of the ROHA in response to a first alignment signal output by the ROHA alignment sensor camera, and to control the pointing direction of the TOHA in response to a second alignment signal output by the TOHA alignment sensor camera.

29. The SCS of claim 28, wherein each of the ROHA alignment sensor camera and the TOHA alignment sensor camera includes a first four-quadrant sensor, wherein the first alignment signal includes a detection signal for each quadrant indicating the amount of light illuminating the quadrant.

30. The SCS according to any one of claims 20 to 29, wherein the first pointing system and the second pointing system each include a first pointing control element configured to provide coarse pointing adjustment and a second pointing control element configured to provide fine pointing adjustment.

31. The SCS of claim 30, wherein the pointing control circuitry is configured to implement a pointing, capturing, and tracking (PAT) algorithm for each of the ROHA and the TOHA as an OHA, wherein the PAT algorithm comprises the pointing control circuitry: Initially pointing at the OHA on an open-loop basis to initiate beacon beam reception; and Closed-loop pointing control of the OHA is performed in response to beacon beam reception.

32. The SCS according to any one of claims 20 to 31, wherein the pointing control system is configured to align at least initially the first of the ROHA and the TOHA, determine alignment assistance information based on the alignment of the first, and use the alignment assistance information to align the second of the ROHA and the TOHA more quickly.

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