Homologous modulation and demodulation device based on space optical communication
The homologous modulation and demodulation device in space optical communication stabilizes the system by using orthogonal polarized lights with shared paths, eliminating the need for precise synchronization and enhancing demodulation performance under varying conditions.
Patent Information
- Application Number
- CN202411348723.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-26
- Publication Date
- 2024-12-27
AI Technical Summary
Existing space optical communication systems require complex coherent demodulation due to the need for precise phase and frequency synchronization at the receiving end, which complicates the system and is sensitive to phase errors and frequency deviations.
A homologous modulation and demodulation device that splits non-polarized light into two orthogonal polarized lights, one of which is modulated and used as a coherent demodulation carrier, maintaining consistent frequency and phase through shared optical paths, eliminating the need for precise synchronization at the receiving end.
The device stabilizes the system by ensuring consistent frequency and phase, reducing complexity and maintaining demodulation performance even with motion-induced Doppler shifts, expanding the system's applicability.
Smart Images
Figure CN119210599A_ABST
Abstract
Description
Technical Field
[0001] The present disclosure relates to the technical field of space optical communication, and more specifically, to a homologous modulation and demodulation device based on space optical communication. Background Art
[0002] In space optical communication, modulation and demodulation are key steps in data transmission. Since the baseband signal itself has a very low frequency, it cannot be sent directly. The baseband signal is loaded onto the light source, which is a process called modulation. Demodulation is the inverse process of the above content, which is the process of converting the received optical signal back to the original data signal.
[0003] There are many modulation methods, including but not limited to amplitude modulation, frequency modulation, phase modulation, polarization modulation, etc. Common modulation methods, such as the use of envelope detection method (incoherent demodulation) for demodulation, are simple to implement and low cost, but it is sensitive to noise and cannot effectively distinguish phase and frequency changes. For some other modulation methods, since their envelope cannot directly reflect the changes of the modulated signal, coherent demodulation methods are required. During coherent demodulation, in order to restore the baseband signal without distortion, the receiving end must provide a coherent carrier with the same frequency and phase, multiply it with the modulated signal, and extract the low frequency to obtain the original signal. Coherent demodulation can effectively utilize the phase and frequency information of the signal. Compared with the envelope detection method, it has many advantages, such as: coherent demodulation can achieve reliable communication under low signal-to-noise ratio conditions; coherent demodulation has a strong suppression ability for phase noise and frequency noise, and can also use orthogonal polarization states to increase information transmission capacity; at the same time, coherent demodulation is applicable to all linearly modulated signals. However, since coherent demodulation has very high requirements for phase and frequency synchronization, any slight phase error or frequency deviation will affect the demodulation performance, resulting in the need for a complex system to maintain frequency and phase synchronization. Summary of the invention
[0004] In view of this, the present disclosure provides a homologous modulation and demodulation device based on spatial optical communication, which is used to solve the technical problem in the prior art that the system is too complicated because the receiving end must provide a coherent carrier with the same frequency and phase during coherent demodulation.
[0005] One aspect of the present disclosure provides a homologous modulation and demodulation device based on spatial optical communication, comprising: a light source for providing unmodulated non-polarized light; a polarization beam splitter for splitting the non-polarized light into two mutually perpendicular polarized light beams, wherein the two polarized light beams propagate along different paths according to different polarization states; a modulator for performing signal modulation on one of the polarized light beams, loading the baseband signal onto a carrier, and outputting a modulated signal; a receiving device for receiving the modulated signal output by the modulator and another unmodulated unmodulated signal, and converting the modulated signal and the unmodulated signal into electrical signals respectively, wherein the optical paths of the modulated signal and the unmodulated signal during spatial transmission are consistent; and a digital-to-analog conversion and signal processing system for performing coherent demodulation processing on the two electrical signals converted by the receiving device to obtain the original baseband signal.
[0006] According to an embodiment of the present disclosure, the receiving device includes: a two-dimensional grating coupler, which is used to couple the modulated signal and the unmodulated signal into the optical waveguide according to different coupling efficiencies to achieve polarization state splitting, wherein the two signal lights with different polarization states after splitting propagate along different paths.
[0007] According to an embodiment of the present disclosure, the receiving device further includes: a polarization rotator for rotating the polarization direction of one of the signal lights output by the two-dimensional grating coupler so that the polarization direction is the same as the polarization direction of the other signal light.
[0008] According to an embodiment of the present disclosure, the receiving device further includes: an optical mixer for performing coherent superposition processing on one optical signal processed by the polarization rotator and another optical signal to extract phase and frequency information.
[0009] According to an embodiment of the present disclosure, the receiving device further includes: a photoelectric detector, which is used to perform photoelectric conversion processing on the two signal lights processed by the optical mixer, and convert the two light signals into electrical signals respectively.
[0010] According to an embodiment of the present disclosure, the digital-to-analog conversion and signal processing system includes: a bandpass filter, which is used to filter the two electrical signals converted by the receiving device, extract the signal within a specific frequency range, and filter out irrelevant noise and high-frequency interference; a multiplier, which is used to multiply the two electrical signals processed by the bandpass filter, extract phase and frequency information, and obtain high-frequency signals and low-frequency signals; a low-pass filter, which is used to filter out high-frequency signals and retain low-frequency signals; and a decider, which is used to decide the low-frequency signal and extract the original baseband signal.
[0011] According to an embodiment of the present disclosure, a polarization beam splitter includes: a grating polarization beam splitter.
[0012] According to an embodiment of the present disclosure, the modulation method of the modulator includes: linear modulation.
[0013] According to an embodiment of the present disclosure, the modulated signal and the unmodulated signal received by the receiving device are transmitted simultaneously.
[0014] According to an embodiment of the present disclosure, the medium in which the modulated signal and the unmodulated signal are transmitted in space is configured to be unable to change the polarization state of the signal light.
[0015] The homologous modulation and demodulation device based on spatial optical communication provided by the embodiment of the present disclosure has at least the following beneficial effects:
[0016] (1) The homologous modulation and demodulation device based on spatial optical communication provided by the embodiment of the present disclosure utilizes the fact that light of different polarization states can be split and combined, and splits the non-polarized light into two orthogonal polarized lights. One of the two orthogonal polarized lights is modulated, and the other is used as a coherent demodulation carrier at the receiving end. The two are transmitted together with the same optical path. Since the two orthogonal polarized lights are generated and separated by the same light source, the frequency and phase of the two orthogonal polarized lights are completely consistent, which improves the stability of the system. At the same time, the receiving end no longer needs to provide a coherent carrier with the same frequency and phase, which greatly reduces the complexity of the system.
[0017] (2) In the homologous modulation and demodulation device based on spatial optical communication provided by the embodiments of the present disclosure, the transmission and reception of the two signal light beams are consistent, which improves the matching degree of phase frequency. Even if the receiving or transmitting end is in motion and there is a Doppler frequency shift phenomenon, it will not affect the coherent modulation, thereby expanding the scope of application of the communication system. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:
[0019] Figure 1 The structure of a homologous modulation and demodulation device based on spatial optical communication according to an embodiment of the present disclosure is schematically shown. DETAILED DESCRIPTION
[0020] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present disclosure. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.
[0021] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.
[0022] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.
[0023] When using expressions such as "at least one of A, B, and C, etc.", they should generally be interpreted according to the meaning of the expression commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).
[0024] In space optical communication, modulation and demodulation are key steps in data transmission. Since the baseband signal itself has a very low frequency, it cannot be sent directly. The baseband signal is loaded onto the light source, which is a process called modulation. Demodulation is the inverse process of the above content, which is the process of converting the received optical signal back to the original data signal.
[0025] There are many modulation methods, including but not limited to amplitude modulation, frequency modulation, phase modulation, polarization modulation, etc. Common modulation methods include envelope detection (incoherent demodulation) for demodulation. For example, in amplitude modulation, the time domain signal can be expressed as:
[0026]
[0027] Among them, m(t) is the modulation signal, when When , the shape of the AM signal envelope is consistent with the shape of the modulating signal m(t). When the above conditions are met, the shape of its envelope is exactly the same as that of the modulating signal, so a simple envelope detection method can be used directly to recover the modulating signal. This method is simple to implement and low in cost, but it is sensitive to noise and cannot effectively distinguish between phase and frequency changes.
[0028] For some other modulation methods, such as suppressed carrier double-sideband signal, the time domain expression is as follows:
[0029]
[0030] Among them, cosω c t is the carrier wave, and its envelope cannot directly reflect the changes of the modulated signal, so a coherent demodulation method needs to be adopted.
[0031] During coherent demodulation, in order to restore the baseband signal without distortion, the receiving end must provide a coherent carrier with the same frequency and phase, multiply it with the modulated signal, and extract the low frequency to obtain the original signal. Coherent demodulation can effectively utilize the phase and frequency information of the signal. Compared with the envelope detection method, it has many advantages, such as: coherent demodulation can achieve reliable communication under low signal-to-noise ratio conditions; coherent demodulation has a strong suppression ability for phase noise and frequency noise, and can also use orthogonal polarization states to increase information transmission capacity; at the same time, coherent demodulation is applicable to all linearly modulated signals. However, since coherent demodulation has very high requirements for phase and frequency synchronization, any slight phase error or frequency deviation will affect the demodulation performance, resulting in the need for a complex system to maintain frequency and phase synchronization.
[0032] Based on this, an embodiment of the present disclosure provides a homologous modulation and demodulation device based on spatial optical communication, including: a light source, a polarization beam splitter, a modulator, a receiving device, and a digital-to-analog conversion and signal processing system.
[0033] The light source is used to provide unmodulated non-polarized light.
[0034] The polarization beam splitter is used to split non-polarized light into two polarized lights that are perpendicular to each other, wherein the two polarized lights propagate along different paths according to different polarization states.
[0035] The modulator is used to perform signal modulation on one of the polarized light beams, load the baseband signal onto the carrier, and output the modulated signal.
[0036] The receiving device is used to receive the modulated signal output by the modulator and another unmodulated signal, and convert the modulated signal and the unmodulated signal into electrical signals respectively, wherein the optical path of the modulated signal and the unmodulated signal during the spatial transmission process is consistent.
[0037] The digital-to-analog conversion and signal processing system is used to perform coherent demodulation on the two electrical signals converted by the receiving device to obtain the original baseband signal.
[0038] The homologous modulation and demodulation device based on spatial optical communication provided by the embodiment of the present disclosure utilizes the fact that light in different polarization states can be split and combined, and non-polarized light is split into two orthogonal polarized lights. One of the two orthogonal polarized lights is modulated, and the other is used as a coherent demodulation carrier at the receiving end. The two are transmitted together, and the optical path is consistent. Since the two orthogonal polarized lights are generated and separated from the same light source, the frequency and phase of the two orthogonal polarized lights are completely consistent, which improves the stability of the system. At the same time, the receiving end does not need to provide a coherent carrier with the same frequency and phase, which greatly reduces the complexity of the system.
[0039] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.
[0040] Figure 1 The structure of a homologous modulation and demodulation device based on spatial optical communication according to an embodiment of the present disclosure is schematically shown.
[0041] like Figure 1 As shown, the homologous modulation and demodulation device based on spatial optical communication of the embodiment of the present disclosure includes: a transmitting end and a receiving end.
[0042] The transmitting end includes: a light source 1, a polarization beam splitter 2, and a modulator 3; the receiving end includes: a receiving device and a digital-to-analog conversion and signal processing system 8.
[0043] The light source 1 is used to provide unmodulated non-polarized light.
[0044] The polarization beam splitter 2 is used to split the non-polarized light into two polarized lights that are perpendicular to each other, wherein the two polarized lights propagate along different paths according to different polarization states.
[0045] The modulator 3 is used to perform signal modulation on one of the polarized light beams, load the baseband signal onto the carrier, and output the modulated signal.
[0046] The receiving device is used to receive the modulated signal output by the modulator and another unmodulated signal, and convert the modulated signal and the unmodulated signal into electrical signals respectively, wherein the optical path of the modulated signal and the unmodulated signal during the spatial transmission process is consistent.
[0047] The digital-to-analog conversion and signal processing system 8 is used to perform coherent demodulation processing on the two-way electrical signals converted by the receiving device to obtain the original baseband signals.
[0048] In this embodiment, light source 1 is a polarization-independent light source, which generates unmodulated non-polarized light for spatial optical communication and enters polarization beam splitter 2 along a specific optical path. Polarization beam splitter 2 includes a grating polarization beam splitter and may also include various types of polarization beam splitters that can split light and generate two orthogonal polarization states. Preferably, a grating polarization beam splitter is selected in this embodiment.
[0049] When the light emitted by the light source 1 is incident on the grating of the polarization beam splitter 2, diffraction will occur, and the diffraction will produce multiple diffraction order beams, among which the zero-order beam is generally not deflected, while the beams of other orders will be deflected at different angles. The diffraction efficiency of light in different polarization states is different in the grating, and the design of the grating can make the light in different polarization states have significant intensity differences in different diffraction orders, and the separated optical signals are propagated in different directions, thereby realizing the separation of polarization states. Therefore, after the unmodulated non-polarized light passes through the polarization beam splitter 2, two polarized lights with orthogonal polarization states are obtained.
[0050] The modulator 3 is located in the optical path of one of the two polarized lights with orthogonal polarization states output by the polarization beam splitter 2, and modulates the polarized light. The modulation method includes linear modulation and modulation method that can use coherent carrier for coherent demodulation. The modulated signal passing through the modulator 3 maintains the same optical path as the unmodulated signal of the other path, and both are emitted at the transmitting end at the same time.
[0051] The modulated signal and the unmodulated signal sent by the transmitter are transmitted in space, and the space needs to satisfy the requirement that there is no medium that can change the polarization state of the signal light, that is, the medium is configured to be unable to change the polarization state of the signal light.
[0052] The receiving device receives the modulated signal output by the modulator 3 and another unmodulated signal, and converts the modulated signal and the unmodulated signal into electrical signals respectively.
[0053] According to an embodiment of the present disclosure, the receiving device may include: a two-dimensional grating coupler 4 , a polarization rotator 5 , an optical mixer 6 and a photodetector 7 .
[0054] The two-dimensional grating coupler 4 is used to couple the modulated signal and the unmodulated signal into the optical waveguide according to different coupling efficiencies to achieve polarization state splitting, wherein the two signal lights with different polarization states after splitting propagate along different paths.
[0055] The polarization rotator 5 is used to rotate the polarization direction of one of the signal lights output by the two-dimensional grating coupler so that the polarization direction of the signal light is the same as the polarization direction of the other signal light.
[0056] The optical mixer 6 is used to perform coherent superposition processing on one optical signal processed by the polarization rotator and another optical signal to extract phase and frequency information.
[0057] The photodetector 7 is used to perform photoelectric conversion on the two signal lights processed by the optical mixer, and convert the two light signals into electrical signals respectively.
[0058] In this embodiment, the signal light received by the receiving end is coupled from the free space (or optical fiber) to the optical waveguide through the two-dimensional grating coupler 4. The two-dimensional grating coupler 4 uses the diffraction effect of the grating structure to achieve efficient coupling of the optical signal. The two-dimensional grating coupler 4 is designed with a specific grating structure so that the optical signals of different polarization states are coupled to the optical waveguide with different efficiencies in different directions, thereby achieving polarization state splitting. The diffraction efficiency and direction of the grating for light of different polarization states can be adjusted by adjusting parameters such as the period, depth and shape of the grating, so that the two optical signals of different polarization states passing through the two-dimensional grating coupler 4 enter two different optical paths respectively.
[0059] After the two-dimensional grating coupler 4 splits the two paths of light, one polarized light passes through the polarization rotator 5, and the other polarized light is not processed. The two polarized light beams pass through the same optical path. The polarization rotator 5 uses the optical rotation effect, which can be understood as dividing the linear polarized light into left-handed circularly polarized light and right-handed circularly polarized light. The propagation speeds of the two circularly polarized light beams in the polarization rotator 5 are inconsistent, causing the polarization direction of the synthesized linear polarized light to rotate. The linear polarized light passing through the polarization rotator 5 becomes consistent with the polarization direction of the other linear polarized light beam received by the receiving end. This process can also allow the two light paths to pass through the polarization rotator 5 at the same time, rotating the polarization state in opposite directions, so as to more conveniently ensure the consistency of the two polarized light beams passing through the optical path.
[0060] After being processed by the polarization rotator 5 and the coherent carrier, the optical mixer 6 simultaneously enters the optical mixer 6, which extracts the phase and frequency information by coherently superimposing the received signal and the LO (local oscillation) signal.
[0061] After the above processing of this embodiment, two signal lights, one signal light carries the transmission information through the modulator 3, and the other signal light is directly used as the LO signal light to be coherently superimposed with the modulated signal light sent together. The phase, frequency and transmission environment of the two light beams are completely consistent, ensuring good coherence.
[0062] The two signal lights obtained after the processing by the optical mixer 6 are respectively converted into photoelectric signals by two photodetectors 7 (PD1 and PD2), so as to convert the optical signals into electrical signals.
[0063] The electrical signal enters the digital-to-analog conversion and signal processing system 8 for processing. By processing the strength of the two electrical signals and extracting the phase information, the digital-to-analog conversion and signal processing system 8 finally realizes coherent demodulation to obtain the original baseband signal.
[0064] According to an embodiment of the present disclosure, the digital-to-analog conversion and signal processing system 8 may include: a bandpass filter, a multiplier, a low-pass filter and a decision device.
[0065] Among them, the bandpass filter is used to filter the two electrical signals converted by the receiving device, extract the signals within a specific frequency range, and filter out irrelevant noise and high-frequency interference.
[0066] The multiplier is used to multiply the two electrical signals processed by the bandpass filter, extract the phase and frequency information, and obtain the high-frequency signal and the low-frequency signal.
[0067] A low-pass filter is used to filter out high-frequency signals and retain low-frequency signals.
[0068] The decision device is used to make a decision on the low-frequency signal and extract the original baseband signal.
[0069] The homologous modulation and demodulation device based on spatial optical communication provided by the embodiment of the present disclosure has the same transmission and reception of two signal light beams, which improves the matching degree of phase frequency. Even if the receiving or transmitting end is in motion and there is a Doppler frequency shift phenomenon, it will not affect the coherent modulation, thereby expanding the scope of application of the communication system.
[0070] The flowcharts and block diagrams in the accompanying drawings illustrate the possible implementation architecture, functions and operations of the systems, methods and computer program products according to various embodiments of the present disclosure. In this regard, each box in the flowchart or block diagram may represent a module, a program segment, or a part of a code, and the above-mentioned module, program segment, or a part of the code contains one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box may also occur in an order different from that marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram or flowchart, and the combination of boxes in the block diagram or flowchart, can be implemented with a dedicated hardware-based system that performs a specified function or operation, or can be implemented with a combination of dedicated hardware and computer instructions. It can be understood by those skilled in the art that the features recorded in the various embodiments of the present disclosure can be combined and / or combined in a variety of ways, even if such a combination or combination is not explicitly recorded in the present disclosure. In particular, without departing from the spirit and teaching of the present disclosure, the features described in the various embodiments of the present disclosure may be combined and / or combined in a variety of ways. All of these combinations and / or combinations fall within the scope of the present disclosure.
[0071] The embodiments of the present disclosure are described above. However, these embodiments are only for illustrative purposes and are not intended to limit the scope of the present disclosure. Although the embodiments are described above, this does not mean that the measures in the various embodiments cannot be used in combination to advantage. Without departing from the scope of the present disclosure, those skilled in the art may make a variety of substitutions and modifications, which should all fall within the scope of the present disclosure.
Claims
1. A homologous modulation and demodulation device based on spatial optical communication, characterized in that: The device comprises: a light source for providing unmodulated, non-polarized light; A polarization beam splitter, used for splitting the non-polarized light into two polarized lights perpendicular to each other, wherein the two polarized lights propagate along different paths according to different polarization states; A modulator is used to modulate one of the polarized light beams, load the baseband signal onto the carrier, and output a modulated signal; A receiving device, used for receiving a modulated signal output by the modulator and another unmodulated signal, and converting the modulated signal and the unmodulated signal into electrical signals respectively, wherein the optical paths of the modulated signal and the unmodulated signal during spatial transmission are consistent; The digital-to-analog conversion and signal processing system is used to perform coherent demodulation processing on the two-way electrical signals converted by the receiving device to obtain the original baseband signal.
2. The homologous modulation and demodulation device based on spatial optical communication according to claim 1, characterized in that: The receiving device comprises: The two-dimensional grating coupler is used to couple the modulated signal and the unmodulated signal into an optical waveguide according to different coupling efficiencies to achieve polarization state splitting, wherein the two signal lights with different polarization states after splitting propagate along different paths.
3. The homologous modulation and demodulation device based on spatial optical communication according to claim 2, characterized in that: The receiving device also includes: The polarization rotator is used to rotate the polarization direction of one of the signal lights output by the two-dimensional grating coupler so that the polarization direction of the signal light is the same as that of the other signal light.
4. The homologous modulation and demodulation device based on spatial optical communication according to claim 3, characterized in that: The receiving device also includes: The optical mixer is used to perform coherent superposition processing on one optical signal processed by the polarization rotator and another optical signal to extract phase and frequency information.
5. The homologous modulation and demodulation device based on spatial optical communication according to claim 4, characterized in that: The receiving device also includes: The photoelectric detector is used to perform photoelectric conversion on the two signal lights processed by the optical mixer, and convert the two light signals into electrical signals respectively.
6. The homologous modulation and demodulation device based on spatial optical communication according to claim 1, characterized in that: The digital-to-analog conversion and signal processing system comprises: A bandpass filter is used to filter the two electrical signals converted by the receiving device, extract the signals within a specific frequency range, and filter out irrelevant noise and high-frequency interference; A multiplier, used to multiply the two electrical signals processed by the bandpass filter, extract phase and frequency information, and obtain a high-frequency signal and a low-frequency signal; A low-pass filter, used to filter out the high-frequency signal and retain the low-frequency signal; The decision device is used to make a decision on the low-frequency signal and extract the original baseband signal.
7. The homologous modulation and demodulation device based on spatial optical communication according to claim 1, characterized in that: The polarization beam splitter comprises: a grating polarization beam splitter.
8. The homologous modulation and demodulation device based on spatial optical communication according to claim 1, characterized in that: The modulation mode of the modulator includes: linear modulation.
9. The homologous modulation and demodulation device based on spatial optical communication according to claim 1, characterized in that: The modulated signal and the unmodulated signal received by the receiving device are transmitted simultaneously.
10. The homologous modulation and demodulation device based on spatial optical communication according to claim 1, characterized in that: The medium in which the modulated signal and the unmodulated signal are transmitted in space is configured to be unable to change the polarization state of the signal light.