Transparent optical repeater for satellite, and communication satellite including such a repeater
The transparent optical repeater addresses the challenges of high complexity and power requirements in satellite communication by using a polarization separator and bias-dependent amplifiers, optimizing power usage and maintaining signal quality for efficient data transfer.
Patent Information
- Authority / Receiving Office
- FR · FR
- Patent Type
- Applications
- Current Assignee / Owner
- THALES SA
- Filing Date
- 2024-12-17
- Publication Date
- 2026-06-19
Smart Images
Figure 00000000_0000_ABST
Abstract
Description
Title of the invention: Transparent optical repeater for satellite, and communication satellite comprising such a repeater
[0001] The present invention relates to the field of satellite telecommunications systems and more particularly to free space optical links, acronym FSO for "Free Space Optical" in English, for massive data transfer or "trunking" in English between distant optical ground stations SS01, SS02, via a communication satellite S AT, equipped with an optical repeater, as illustrated in [Fig. 1].
[0002] The present invention can also be implemented for optical stations that are not on the ground, for example for a link between an optical ground station, a satellite with a transparent repeater, and an "optical station" on another satellite, or for a link between an "optical station" on a satellite, a satellite with a transparent repeater, and an "optical station" on another satellite. A regenerative optical repeater, such as that shown in [Fig. 2], is known, in which, in addition to the conventional optical elements of a terminal (amplifiers, demultiplexers, multiplexers, etc.), this solution includes O / E detection means for "optical / electrical" and demodulation, very high-speed digital processing and E / O retransmission means for "electrical / optical" with laser sources and modulators.
[0003] These means of rapid digital processing are combined in the form of a digital processor on board an OBP satellite for "on-board processor".
[0004] A regenerative optical repeater presents a very high level of hardware complexity on board, with a significant impact on the mass, power consumption, and volume on board the satellite. In addition to feasibility and / or compatibility issues with the space environment of high-speed digital technologies, this represents a significant additional cost. Furthermore, this solution is dependent on the modulation format (waveform).
[0005] Following the example of [Fig.2], the regenerative optical repeater comprises: - a set of optical fibers (FO) for transferring optical signals between the optical elements of the repeater, and digital connections (CN) at the input and output of the digital processor (OBP); - a first optical head OHU1 configured to collect optical signals, having two possible orthogonal polarizations, with an orthogonality error of less than 10°, and focus them; - a first low-noise optical amplifier LNOA configured to amplify the optical signals transmitted at the output of the first optical head OHU1 with low added noise of less than 6 dB; - a WDM optical demultiplexer configured to separate by wavelength the signals transmitted at the output of the LNOA low-noise optical amplifier, and deliver the wavelength-separated signals at the output on a plurality of output channels, each corresponding to a wavelength; - an optical / electrical O / E converter, to convert the signals from the output channels of the WDM optical demultiplexer; - the OBP digital processor which demodulates the output signals of the optical / electrical converter O / E, performs digital processing, then modulates the output signals of the OBP; - an electrical / optical E / O converter, to convert the signals from the output channels of the OBP digital processor; - a second high-power optical amplifier (HPOA), per output channel of the electrical / optical E / O converter; - an HPWDM optical multiplexer to multiplex the output signals from the second high-power HPOA optical amplifiers; and - a second optical head 0HU2 configured to transmit the output optical signals from the HPWDM optical multiplexer.
[0006] A transparent optical repeater, as illustrated in [Fig. 3] with polarization-independent HPOA, is also known. This solution comprises only conventional optical means and elements (amplifiers, demultiplexers, filters, power amplifiers, multiplexers, etc.), but no demodulation means, nor very high-speed digital processing or E / O retransmission with laser sources and modulators. An all-optical repeater requires significantly higher power levels (typically +3 dB) beyond the state of the art to achieve a closed link budget for the target data rates, and considering that there is no onboard signal quality regeneration.
[0007] Following the example of [Fig.3], the transparent optical repeater comprises:
[0008] - a set of optical fibers (OF) for transferring optical signals between the optical elements of the repeater;
[0009] - a first optical head 0HU1 configured to collect optical signals, having two possible orthogonal polarizations, with an orthogonality error of less than 10°, and focus them;
[0010] - a first low-noise optical amplifier (LNOA) configured to amplify the optical signals transmitted at the output of the first optical head OHU1 with low added noise of less than 6 dB;
[0011] - a WDM optical demultiplexer configured to separate the wavelengths signals transmitted at the output of the LNOA low-noise optical amplifier, and deliver The output signals are separated by wavelength onto a plurality of output channels, each corresponding to a wavelength;
[0012] - a second LOFA optical amplifier of one wavelength, per channel of WDM optical demultiplexer output;
[0013] - an optical BPF bandpass filter configured to filter noise from the channels of output of the second LOFA optical amplifiers;
[0014] - a third high-power optical amplifier (HPOA), per output channel of the optical bandpass filter (BPF);
[0015] - an HPWDM optical multiplexer for multiplexing the signals from the third high-power optical amplifiers (HPOA); and
[0016] - a second optical head 0HU2 configured to transmit signals at the output HPWDM optical multiplexer output optics.
[0017] However, the highest optical powers are typically obtained by polarization-dependent amplifiers, i.e., those that amplify only one polarization state.
[0018] In order to close the link budget and / or maximize the capacity (throughput) of the link, it is advantageous to use bias-dependent amplifiers.
[0019] Indeed, for a given fixed output power, we gain approximately 3 dB on the total power if we amplify each bias separately by a dedicated power amplifier.
[0020] In addition, the use of bias-dependent amplifiers may be required for reasons of performance (easier gain balancing for example) and / or availability for example.
[0021] A transparent optical repeater with upstream polarization maintenance is also known, which consists of maintaining the polarization state throughout the optical repeater on board the satellite.
[0022] One object of the invention is then to propose an optical repeater configured to be carried on board a satellite enabling to make an optical link in free space, compatible with signals on one or two orthogonal polarization states, without compromising the mass, consumption and volume (MCV) budgets or the performance enabling a massive data transfer between two distant ground stations.
[0023] To this end, the invention relates to a transparent optical repeater configured to be carried on board a satellite, comprising: - a set of optical fibers for transferring optical signals between the elements of the optical repeater; - a first optical head configured to collect optical signals, having two possible orthogonal polarizations, with an orthogonality error of less than 10°, and focus them; - a first low-noise optical amplifier configured to amplify the optical signals transmitted at the output of the first optical head with low added noise of less than 6 dB; - a polarization separator and controller, disposed downstream of the first low-noise optical amplifier, comprising, for each input channel, a channel polarization separator and controller configured to separate the signals according to two possible orthogonal polarizations, control the polarization of the signals, and deliver the polarized separated signals to two respective outputs; - a third high-power optical amplifier, per output channel of the splitter and polarization controller; - a polarization combiner, located downstream of the polarization splitter and controller, configured to recombine the signals from the two input channels; and - a second optical head configured to transmit the output optical signals from the orthogonal polarization combiner.
[0024] In one embodiment, the transparent optical repeater comprises: - an optical demultiplexer, disposed between the first low-noise optical amplifier and the polarization splitter and controller, configured to separate the signals transmitted at the output of the low-noise optical amplifier by wavelength, and to deliver the wavelength-separated signals at the output on a plurality of output channels, each corresponding to a wavelength; and - an optical multiplexer, arranged between the third high-power optical amplifiers and the orthogonal polarization combiner, by set of output channels of the same polarization.
[0025] According to one embodiment, the transparent optical repeater includes a second optical amplifier of one wavelength, per input channel of the splitter and polarization controller.
[0026] In one embodiment, the transparent optical repeater includes an optical bandpass filter configured to filter noise from the input channel(s) of the splitter and polarization controller.
[0027] According to one embodiment, the transparent optical repeater comprises, for each input channel of the polarization splitter and controller, an optical switch configured to be able to transfer optical signals on command through another optical fiber to an external satellite processing device, and retransmit them after processing by the external satellite processing device to the polarization splitter and controller.
[0028] In one embodiment, the external satellite processing device includes an external processor.
[0029] According to one embodiment, a channel polarization separator and controller comprises: - a polarization controller configured to change the polarization of optical signals on command; - a polarization splitter configured to separate the signals according to the two possible orthogonal polarizations on two respective channels; and - a polarization tracking and control module per output channel of the splitter and channel polarization controller, by polarization servo loop.
[0030] According to one embodiment, a channel polarization separator and controller is configured to use low-frequency RF tone detection, a polarization tracking and control module comprising the polarization tracking and control module, and a module for minimizing one polarization or maximizing the other orthogonal polarization, the other polarization tracking and control module comprising the polarization tracking and control module, and a module for minimizing the other polarization or maximizing the polarization.
[0031] In one embodiment, a channel polarization splitter and controller includes a polarization tracking module configured, when the received signals have only one polarization, to use optical power detection, so as to maximize the power on the useful output channel and minimize the power on the other output channel.
[0032] According to one embodiment, a channel polarization splitter and controller includes a polarization tracking module configured to detect a portion of the optical flux of a single polarization channel using a coherent receiver, and a digital processor configured to quantify the ratio of the two polarizations and provide feedback to the polarization controller to have only one polarization in the polarization channel comprising the tracking module.
[0033] In one embodiment, a channel polarization splitter and controller includes a polarization tracking module configured to use interference detection of signals from both polarization channels.
[0034] According to one embodiment, the interference detection of the signals of the two polarization channels is a Hansch Couillaud detection.
[0035] In one embodiment, the interference detection of the signals from the two polarization channels is a heterodyne detection.
[0036] According to another aspect of the invention, a communication satellite comprising a transparent optical repeater as previously described is also proposed.
[0037] The invention will be better understood upon examination of some embodiments, described by way of non-limiting examples and illustrated in the accompanying drawings, in which: - [Fig.1] schematically illustrates a massive data transfer between distant optical ground stations, via a communication satellite, according to the state of the art; - [Fig.2] schematically illustrates a regenerative optical repeater for a communication satellite, according to the state of the art; - [Fig.3] schematically illustrates a transparent optical repeater for a communication satellite, according to the state of the art; - [Fig.4] schematically illustrates a transparent optical repeater for a communication satellite, according to one aspect of the invention; - [Fig.5] schematically illustrates a transparent optical repeater for a communication satellite, according to various aspects of the invention; - [Fig.6] schematically illustrates a transparent optical repeater for a communication satellite of [Fig.4], capable of operating in regenerative mode; - [Fig. 7] schematically illustrates an embodiment of a channel polarization separator and controller, according to one aspect of the invention; and - [Fig.8], [Fig.9], [Fig.10] and [Fig.11] schematically illustrate embodiments of a channel polarization separator and controller of [Fig.7], according to aspects of the invention.
[0038] Across all figures, identical references are similar.
[0039] [Fig.4] schematically illustrates a transparent optical repeater for a satellite communication, according to one aspect of the invention.
[0040] The transparent optical repeater, configured for onboard use on a satellite, comprises: - a set of optical fibers (FO) for transferring optical signals between the elements of the optical repeater; - a first optical head OHU1 configured to collect optical signals, having two possible orthogonal polarizations, with an orthogonality error of less than 10°, and focus them; - a first low-noise optical amplifier LNOA configured to amplify the optical signals transmitted at the output of the first optical head 0HU1 with low added noise of less than 6 dB; - a PCS polarization splitter and controller, disposed downstream of the first low-noise optical amplifier LNOA, comprising, for each input channel, a C-PCS channel polarization splitter and controller configured to separate the signals according to two possible orthogonal polarizations, control the polarization of the signals, and deliver the polarization-separated signals to two respective outputs; - a third high-power optical amplifier HPOA, per output channel of the splitter and PCS bias controller; - a PBC orthogonal polarization combiner, located downstream of the PCS polarization splitter and controller, configured to recombine the signals from the two input channels; and - a second optical head 0HU2 configured to transmit at output the optical output signals of the orthogonal polarization combiner PBC.
[0041] The terms upstream and downstream refer to the direction of signal transmission.
[0042] The present invention comprises a series of optical elements (amplifiers, demultiplexers, multiplexers, etc.) that maintain optical continuity along the entire path of the telecommunications signal.
[0043] It also includes, in a rather central stage, after the fiber input section, after channeling (i.e. optical demultiplexing), active control and polarization separation devices per PCS channel.
[0044] Optical signals are treated in polarization, that is to say either separated into their two orthogonal components if they are double polarized, or entirely projected onto one of the two orthogonal states, if they are single polarized.
[0045] The output stage consists of third high-power, bias-dependent optical amplifiers, which make it possible to supply all available power to a single bias state.
[0046] The different channels are then recombined by a power wavelength multiplexer HPWDM1, HPWDM2, by sets of output channels of the same polarization. The orthogonally polarized channels are finally recombined by an orthogonally polarized combiner PBC.
[0047] The insertion of this PCS polarization separator and controller allows each of the polarizations to be amplified in dedicated polarization-dependent HPOAs, which typically allows a gain of 3 dB on the output power after recombination, and thus allows the double-band link budget to be closed for a given flow rate, under better conditions, or the total flow rate to be increased.
[0048] Alternatively, this can optimize the capacity (throughput) of the transfer link.
[0049] [Fig.5] schematically illustrates, according to other aspects of the invention, a transparent optical repeater for a communication satellite of [Fig.4], further comprising optional elements, represented by dashed lines, which can be added alone or in combination to the elements of [Fig.4].
[0050] The optional elements are: - an assembly comprising a WDM optical demultiplexer, disposed between the first low-noise optical amplifier LNOA and the polarization splitter and controller PCS, configured to separate by wavelength the signals transmitted at the output of the low-noise optical amplifier LNOA, and to deliver at the output the wavelength-separated signals on a plurality of output channels each corresponding to a wavelength; and an HPWDM1, HPWDM2 optical multiplexer, disposed between the third high-power optical amplifiers HPOA) and the orthogonal polarization combiner PBC, by set of output channels of the same polarization; - a second LOFA optical amplifier of one wavelength, per input channel of the splitter and PCS polarization controller; - an optical BPF bandpass filter configured to filter noise from the input channel(s) of the splitter and PCS polarization controller.
[0051] [Fig.6] schematically illustrates an embodiment of [Fig.5], further comprising, for each output channel of the BPF bandpass filter, an OADS optical switch configured to be able to transfer optical signals on command through another optical fiber to an EPD satellite external processing device, and retransmit them after processing by the EPD satellite external processing device to the PCS polarization splitter and controller.
[0052] The OADS optical switches allow the signal to be routed either directly to the PCS polarization splitter and controller or to the EPD satellite external processing device.
[0053] For example, the external satellite processing device EPD can be a processor on board the OBP communication satellite acting as a regenerative repeater.
[0054] OADS optical switches allow optical signals to be routed for transparent or regenerative operation of the payload, which allows this transparent optical repeater to operate in regenerative mode.
[0055] The path following the solid arrow represents the transparent case, while the path following the dashed arrow deals with the regenerative case. In the transparent case, the signal passes from the bandpass filter (BPF) to the splitter and bias controller (PCS).
[0056] In regenerative mode operation, the uplink signal, or signal arriving through the first optical head OHU1, passes from the BPF bandpass filter to the satellite external processing device EPD, in which the optical signal undergoes processing.
[0057] In the case of an OBP processor, the optical signal is demodulated. The data of this signal, once demodulated, can be used in the payload or retransmitted as a new optical signal. This new downlink optical signal, or signal output by the second optical head OHU2, is at the same wavelength but carries either new data or the same data as the uplink signal. This signal, which exits the OBP processor, goes to the PCS polarization splitter and controller via an OADS optical switch.
[0058] [Fig.7] schematically illustrates an embodiment of a C-PCS channel polarization separator and controller, according to one aspect of the invention.
[0059] SMF, for acronym of "SingleMode Fiber" in English, represents single-mode optical fibers in which the polarization evolves freely according to the constraints on the fiber (temperature, mechanical stress...).
[0060] PMF, for acronym of "Polarization Maintaining Fiber" in English, represents single-mode optical fibers that maintain the polarization of light along two orthogonal eigenaxes (slow axis and fast axis); if polarized light is injected along one of these two eigenaxes, the polarization of the light is maintained during propagation.
[0061] The C-PCS channel polarization splitter and controller comprises: - a PC polarization controller configured to change the polarization of optical signals on command; - a PBS (Polarization Beam Splitter) configured to separate signals according to two possible orthogonal polarizations (polarization 1, polarization 2) onto two respective channels, by projecting the components onto the eigenaxes of the component's base. Each output signal contains one of the two components (inverse function of a PBC, acronym for "polarization beam combiner"). - a PMC1, PMC2 polarization tracking and control module via the splitter output channel and a C-PCS channel polarization controller. This is a polarization control loop. - Sampling and analysis of light polarization, - Calculation and generation of the control signal to be applied to the PC polarization controller according to the desired polarization value
[0062] [Fig. 8] schematically illustrates an embodiment of a C-PCS channel polarization splitter and controller of [Fig. 7] configured to use low-frequency RF tone detection. The polarization tracking and control module PMC1 comprises the PMC polarization tracking and control module, and a polarization minimization module M1 or polarization maximization module M2. The polarization tracking and control module PMC2 comprises the PMC polarization tracking and control module, and a polarization minimization module M2 or polarization maximization module M2.
[0063] Assuming that there is one RF tone or one RF tone per polarization (for a dual-polarized signal, the tone fx is on polarization 1 and the tone fY is on polarization 2), by analyzing the tones of the signal from the output channel of polarization 1, the polarization circulating in this channel can be deduced. Tone analysis can be performed using a photodiode.
[0064] If the power of tones fx and fY is measured to be equal, the power distribution of each signal in the polarization state basis {polarization1; polarization2} can be deduced. If, on the other hand, zero power is measured for tone fx, only polarization2 is circulating in this output channel.
[0065] If we want to have all the polarization polarization 1 in the output channel of the polarization polarization 1 (and therefore the polarization polarization 2 in the output channel of the polarization polarization 2 because the two polarizations are orthogonal), it is necessary to control the polarization controller PC in order to minimize the tone f2 in the polarization polarization 1 channel (or minimize fl in the polarization polarization 2 channel).
[0066] [Fig.9] schematically illustrates an embodiment of a C-PCS channel polarization splitter and controller of [Fig.7], comprising a PMC polarization tracking module configured, when the received signals have only one polarization, to use optical power detection, so as to maximize the power on the useful output channel and minimize the power on the other output channel.
[0067] The PMC1 polarization tracking and control module includes the PMC polarization tracking and control module configured to minimize the power of the polarization channel of polarization 1 (or to maximize the polarization channel of polarization 2), and a PMI power tracking module for the polarization channel of polarization 1. The PMC2 polarization tracking and control module includes the PMC polarization tracking and control module configured to minimize the power of the polarization channel of polarization 2 (or of maximization of the polarization channel (polarization polarization!), and a PM2 power tracking module for the polarization channel (polarization polarization!).
[0068] [Fig. 10] schematically illustrates an embodiment of a C-PCS channel polarization splitter and controller of [Fig. 7], comprising a PMC polarization tracking module configured to detect a portion of the optical flux of a single polarization channel, in this case the polarization channel polarization 1 using a coherent RC receiver, and a DSP digital processor configured to quantify the ratio of the two polarizations polarization 1, polarization 2 and provide feedback to the PMC polarization controller to have only one polarization in the polarization channel comprising the tracking module.
[0069] [Fig. 11] schematically illustrates an embodiment of a C-PCS channel polarization splitter and controller of [Fig. 7], comprising a PMC polarization tracking module configured to use interference detection of the signals of the two polarization channels polarization 1, polarization 2, for example by a Hansch Couillaud DHC detection.
[0070] As an alternative to Hansch Couillaud detection (HCD), heterodyne detection can be used.
Claims
Demands
1. A transparent optical repeater configured for onboard satellite, comprising: - an assembly of optical fibers (OF) for transferring optical signals between the elements of the optical repeater; - a first optical head (0HU1) configured to collect optical signals, having two possible orthogonal polarizations (polarization 1, polarization!), with an orthogonality error of less than 10°, and focus them; - a first low-noise optical amplifier (LNOA) configured to amplify the optical signals transmitted at the output of the first optical head (0HU1) with a low added noise of less than 6 dB;- a polarization splitter and controller (PCS), located downstream of the first low-noise optical amplifier (LNOA), comprising, for each input channel, a channel polarization splitter and controller (C-PCS) configured to separate the signals according to two possible orthogonal polarizations, control the polarization of the signals, and deliver the separated polarization signals to two respective outputs; - a third high-power optical amplifier (HPOA), per output channel of the polarization splitter and controller (PCS); - an orthogonal polarization combiner (PBC), located downstream of the polarization splitter and controller (PCS), configured to recombine the signals from the two input channels; and - a second optical head (0HU2) configured to output the optical signals from the output of the orthogonal polarization combiner (PBC).
2. A transparent optical repeater, according to claim 1, comprising: - an optical demultiplexer (WDM), disposed between the first low-noise optical amplifier (LNOA) and the polarization splitter and controller (PCS), configured to separate by wavelength the signals transmitted at the output of the low-noise optical amplifier (LNOA), and to output the wavelength-separated signals on a plurality of output channels, each corresponding to a wavelength; and - an optical multiplexer (HPWDM1, HPWDM2), arranged between the third high-power optical amplifiers (HPOA) and the orthogonal polarization combiner (PBC), by set of output channels of the same polarization.
3. Transparent optical repeater, according to any one of the preceding claims, comprising a second optical amplifier (LOFA) of one wavelength, per input channel of the splitter and polarization controller (PCS).
4. Transparent optical repeater, according to any one of the preceding claims, comprising an optical bandpass filter (BPF) configured to filter noise from the input channel(s) of the splitter and polarization controller (PCS).
5. A transparent optical repeater, according to any one of the preceding claims, comprising, for each input channel of the polarization splitter and controller (PCS), an optical switch (OADS) configured to be able to, on command, transfer optical signals through another optical fiber to an external satellite processing device (EPD), and retransmit them after processing by the external satellite processing device (EPD) to the polarization splitter and controller (PCS).
6. Transparent optical repeater, according to claim 5, wherein the satellite external processing device (EPD) comprises an external processor (OBP).
7. A transparent optical repeater, according to any one of the preceding claims, wherein a channel polarization splitter and controller (C-PCS) comprises: - a polarization controller (PC) configured to change the polarization of optical signals on command; - a polarization splitter (PBS) configured to separate the signals according to the two possible orthogonal polarizations (polarization 1, polarization!) on two respective channels; and - a polarization tracking and control module (PMC1, PMC2) per output channel of the channel polarization splitter and controller (C-PCS), by polarization servo loop.
8. A transparent optical repeater, according to claim 7, wherein a channel polarization splitter and controller (C-PCS) is configured to use low-frequency RF tone detection, a tracking module, and polarization control. (PMC1) comprising the polarization tracking and control module (PMC), and a module (M1) for minimizing one polarization (polarization!) among the two possible orthogonal polarizations (polarization 1, polarization!) or maximizing the other polarization (polarization 1) among the two possible orthogonal polarizations, the other polarization tracking and control module (PMC!) comprising the polarization tracking and control module (PMC), and a module (M!) for minimizing the other polarization (polarization 1) or maximizing the polarization (polarization!).
9. A transparent optical repeater, according to claim 7, wherein a channel polarization splitter and controller (C-PCS) includes a polarization tracking module (PMC) configured, when the received signals have only one polarization, to use optical power sensing, so as to maximize the power on the useful output channel and minimize the power on the other output channel.
10. A transparent optical repeater, according to claim 7, wherein a channel polarization splitter and controller (C-PCS) includes a polarization tracking module (PMC) configured to detect a portion of the optical flux of a single polarization channel using a coherent receiver (RC), and a digital processor (DSP) configured to quantify the ratio of the two polarizations and provide feedback to the polarization controller (PMC) to have only one polarization in the polarization channel comprising the tracking module.
11. A transparent optical repeater, according to claim 7, wherein a channel polarization splitter and controller (C-PCS) includes a polarization tracking module (PMC) configured to use interference detection of signals from both polarization channels.
12. Transparent optical repeater, according to claim 11, wherein the interference detection of the signals of the two polarization channels is a Hansch Couillaud detection (DHC).
13. Transparent optical repeater, according to claim 11, wherein the interference detection of the signals of the two polarization channels is a heterodyne detection.
14. Communication satellite comprising a transparent optical repeater according to any one of the preceding claims.