Optical signal transmitter, millimeter wave terahertz signal transmitting device and communication system

Abstract

The application relates to an optical signal transmitter, a millimeter wave terahertz signal transmitting device and a communication system. The optical signal transmitter comprises: a first signal generating circuit for generating a first analog signal; a second signal generating circuit for generating a second analog signal; an optical carrier generator for transmitting an optical carrier; and a modulator, a driving arm of a first polarization direction of the modulator being connected with the first signal generating circuit, a driving arm of a second polarization direction of the modulator being connected with the second signal generating circuit, and an input end of the modulator being connected with the optical carrier generator, so as to generate a polarization multiplexing overlapped single sideband vector signal and send the polarization multiplexing overlapped single sideband vector signal to an optical wireless conversion circuit, wherein the polarization multiplexing overlapped single sideband vector signal carries a first microwave vector signal, a second microwave vector signal, a third microwave vector signal and a fourth microwave vector signal. That is, the optical signal transmitter can realize simultaneous transmission of four signals, and the spectral efficiency is doubled compared with the prior art.

Description

Technical Field

[0001] This application relates to the field of communication technology, and in particular to an optical signal transmitter, a millimeter-wave terahertz signal transmitting device, and a communication system. Background Technology

[0002] As we all know, 6G communication networks need to support a large number of user connections and complex data services, which puts forward an urgent need for high bandwidth and large capacity communication. Therefore, improving spectrum efficiency is a problem worth studying.

[0003] Traditional technologies can only transmit two signals simultaneously, and their spectral efficiency needs further improvement. Summary of the Invention

[0004] Therefore, it is necessary to provide an optical signal transmitter, a millimeter-wave terahertz signal transmitter, and a communication system that can improve spectral efficiency in response to the above-mentioned technical problems.

[0005] In a first aspect, this application provides an optical signal transmitter. The optical signal transmitter includes: a first signal generation circuit for generating a first analog signal, the first analog signal carrying a first microwave vector signal and a second microwave vector signal; a second signal generation circuit for generating a second analog signal, the second analog signal carrying a third microwave vector signal and a fourth microwave vector signal; an optical carrier generator for transmitting an optical carrier; and a modulator, wherein a drive arm of the modulator in a first polarization direction is connected to the first signal generation circuit, a drive arm of the modulator in a second polarization direction is connected to the second signal generation circuit, and an input terminal of the modulator is connected to the optical carrier generator, for modulating the first analog signal and the second analog signal onto the first polarization direction and the second polarization direction of the optical carrier, respectively, to generate a polarization-multiplexed overlapping single-sideband vector signal, and transmitting it to an optical wireless conversion circuit; wherein the polarization-multiplexed overlapping single-sideband vector signal includes a first overlapping single-sideband vector signal in the first polarization direction and a second overlapping single-sideband vector signal in the second polarization direction, the first overlapping single-sideband vector signal carrying the first microwave vector signal and the second microwave vector signal carried by the first analog signal, and the second overlapping single-sideband vector signal carrying the third microwave vector signal and the fourth microwave vector signal carried by the second analog signal.

[0006] In one embodiment, the first analog signal includes a first sub-analog signal and a second sub-analog signal. The first signal generation circuit includes: a first microwave vector signal generator for generating a first microwave vector signal; a second microwave vector signal generator for generating a second microwave vector signal; a first Hilbert converter connected to the first and second microwave vector signal generators for performing a Hilbert transform on the sum of the first and second microwave vector signals to generate a first transformed vector signal; a first digital-to-analog converter connected to the first and second microwave vector signal generators for performing digital-to-analog conversion on the sum of the first and second microwave vector signals to generate the first sub-analog signal; and a second digital-to-analog converter connected to the first Hilbert converter for performing digital-to-analog conversion on the first transformed vector signal to generate the second sub-analog signal.

[0007] In one embodiment, the modulator's first polarization direction drive arm includes a first upper drive arm and a first lower drive arm; the first upper drive arm is connected to a first digital-to-analog converter, and the first lower drive arm is connected to a second digital-to-analog converter to generate a first overlapping single-sideband vector signal.

[0008] In one embodiment, the second analog signal includes a third sub-analog signal and a fourth sub-analog signal. The second signal generation circuit includes: a third microwave vector signal generator for generating a third microwave vector signal; a fourth microwave vector signal generator for generating a fourth microwave vector signal; a second Hilbert converter connected to the third and fourth microwave vector signal generators for performing a Hilbert transform on the sum of the third and fourth microwave vector signals to generate a second transformed vector signal; a third digital-to-analog converter connected to the third and fourth microwave vector signal generators for performing digital-to-analog conversion on the sum of the third and fourth microwave vector signals to generate a third sub-analog signal; and a fourth digital-to-analog converter connected to the second Hilbert converter for performing digital-to-analog conversion on the second transformed vector signal to generate a fourth sub-analog signal.

[0009] In one embodiment, the modulator's second polarization direction drive arm includes a second upper drive arm and a second lower drive arm, the second upper drive arm being connected to a third digital-to-analog converter and the second lower drive arm being connected to a fourth digital-to-analog converter to generate a second overlapping single-sideband vector signal.

[0010] Secondly, this application also provides an optical wireless conversion circuit, comprising: a first optical polarization beamsplitter connected to an optical signal transmitter, used to receive a polarization-multiplexed overlapping single-sideband vector signal transmitted by the optical signal transmitter, and to perform polarization beam splitting on the polarization-multiplexed overlapping single-sideband vector signal to obtain a first overlapping single-sideband vector signal and a second overlapping single-sideband vector signal; wherein, the first overlapping single-sideband vector signal is a signal in the first polarization direction of the polarization-multiplexed overlapping single-sideband vector signal, carrying a first microwave vector signal and a second microwave vector signal, and the second overlapping single-sideband vector signal is a signal in the second polarization direction of the polarization-multiplexed overlapping single-sideband vector signal, carrying a third microwave vector signal and a fourth microwave vector signal; a local oscillator generator used to transmit local oscillator light; and a second optical polarization beamsplitter connected to the local oscillator generator used to perform polarization beam splitting on the local oscillator light to obtain a first local oscillator light and a second local oscillator light in the first polarization direction. The system consists of a second local oscillator beam in two polarization directions; a first optical coupler, connected to a first and a second optical polarization beam splitter, used to couple a first overlapping single-sideband vector signal and the first local oscillator beam to obtain a first coupled signal; a second optical coupler, connected to the first and a second optical polarization beam splitter, used to couple a second overlapping single-sideband vector signal and the second local oscillator beam to obtain a second coupled signal; a first photodetector, connected to the first optical coupler, used to convert the first coupled signal into a first millimeter-wave terahertz signal, the first millimeter-wave terahertz signal carrying a first microwave vector signal and a second microwave vector signal carried by the first overlapping single-sideband vector signal; and a second photodetector, connected to the second optical coupler, used to convert the second coupled signal into a second millimeter-wave terahertz signal, the second millimeter-wave terahertz signal carrying a third microwave vector signal and a fourth microwave vector signal carried by the second overlapping single-sideband vector signal.

[0011] Thirdly, this application also provides a millimeter-wave terahertz signal transmitting device, the device comprising an optical signal transmitter as described in any of the first aspects above and an optical-to-wireless conversion circuit as described in the second aspect above, wherein the optical signal transmitter is connected to the optical-to-wireless conversion circuit.

[0012] Fourthly, this application also provides a communication system. The system includes the millimeter-wave terahertz signal transmitting device and the wireless receiving device described in the third aspect above. The millimeter-wave terahertz signal transmitting device is connected to the wireless receiving device, which is used to receive a first millimeter-wave terahertz signal and a second millimeter-wave terahertz signal transmitted by the millimeter-wave terahertz signal transmitting device.

[0013] In one embodiment, the wireless receiving device includes: a wireless receiving circuit connected to a millimeter-wave terahertz signal transmitting device, for receiving a first millimeter-wave terahertz signal and a second millimeter-wave terahertz signal, and processing the first millimeter-wave terahertz signal and the second millimeter-wave terahertz signal to generate a first digital signal and a second digital signal; and a signal processing circuit connected to the wireless receiving circuit, for processing the first digital signal to obtain a first microwave vector signal and a second microwave vector signal; and processing the second digital signal to obtain a third microwave vector signal and a fourth microwave vector signal.

[0014] In one embodiment, the wireless receiving circuit includes: a first envelope detector connected to a millimeter-wave terahertz signal transmitting device, used to receive a first millimeter-wave terahertz signal and down-convert the first millimeter-wave terahertz signal based on the direct detection method of envelope detection to obtain a down-converted first intermediate frequency (IF) signal; a second envelope detector connected to the millimeter-wave terahertz signal transmitting device, used to receive a second millimeter-wave terahertz signal and down-convert the second millimeter-wave terahertz signal based on the direct detection method of envelope detection to obtain a down-converted second IF signal; a first analog-to-digital converter connected to the first envelope detector, used to perform analog-to-digital conversion on the first IF signal to obtain a first digital signal; and a second analog-to-digital converter connected to the second envelope detector, used to perform analog-to-digital conversion on the second IF signal to obtain a second digital signal.

[0015] In one embodiment, the signal processing circuit includes: a crosstalk cancellation circuit connected to the wireless receiving circuit, used to perform crosstalk cancellation processing on the first digital signal and the second digital signal to obtain a first crosstalk-free signal and a second crosstalk-free signal; a first constellation point separation circuit connected to the first output terminal of the crosstalk cancellation circuit, used to perform constellation point demodulation processing on the first crosstalk-free signal to obtain a first microwave vector signal and a second microwave vector signal; and a second constellation point separation circuit connected to the second output terminal of the crosstalk cancellation circuit, used to perform constellation point demodulation processing on the second crosstalk-free signal to obtain a third microwave vector signal and a fourth microwave vector signal.

[0016] In one embodiment, the crosstalk elimination circuit includes: a signal resampling circuit connected to the wireless receiving circuit, used to resample the first digital signal and the second digital signal to obtain a first resampled signal and a second resampled signal; a signal reconstruction circuit connected to the signal resampling circuit, used to reconstruct the first resampled signal and the second resampled signal to obtain a first reconstructed signal and a second reconstructed signal; and a third Hilbert transformer connected to the signal reconstruction circuit, used to perform Hilbert transformations on the first reconstructed signal and the second reconstructed signal respectively to obtain a third transformed vector signal and a fourth transformed vector signal.

[0017] A polarization demultiplexing circuit, connected to the signal reconstruction circuit and the third Hilbert transformer, is used to perform polarization crosstalk compensation processing on the first reconstructed signal and the third transformed vector signal to obtain a first polarization demultiplexed signal, and to perform polarization crosstalk compensation processing on the second reconstructed signal and the fourth transformed vector signal to obtain a second polarization demultiplexed signal; a channel equalization circuit, connected to the polarization demultiplexing circuit, is used to perform channel equalization processing on the first polarization demultiplexed signal and the second polarization demultiplexed signal to obtain a first crosstalk-free signal and a second crosstalk-free signal.

[0018] Fifthly, this application also provides an optical signal transmission method applied to an optical signal transmitter. The method includes: a first signal generation circuit in the optical signal transmitter generating a first analog signal carrying a first microwave vector signal and a second microwave vector signal, and inputting it to a drive arm of a modulator in the optical signal transmitter in a first polarization direction; a second signal generation circuit in the optical signal transmitter generating a second analog signal carrying a third microwave vector signal and a fourth microwave vector signal, and inputting it to a drive arm of the modulator in a second polarization direction; an optical carrier generator in the optical signal transmitter transmitting an optical carrier and inputting it to the input terminal of the modulator, so that the modulator modulates the first analog signal and the second analog signal onto the first polarization direction and the second polarization direction of the optical carrier, respectively, to generate a polarization-multiplexed overlapping single-sideband vector signal; wherein the polarization-multiplexed overlapping single-sideband vector signal includes a first overlapping single-sideband vector signal in the first polarization direction and a second overlapping single-sideband vector signal in the second polarization direction, the first overlapping single-sideband vector signal carrying the first microwave vector signal and the second microwave vector signal carried by the first analog signal, and the second overlapping single-sideband vector signal carrying the third microwave vector signal and the fourth microwave vector signal carried by the second analog signal.

[0019] Sixthly, this application also provides a communication method applied to a communication system, the communication system including an optical signal transmitter, an optical wireless conversion circuit, and a wireless receiving device. The method includes: the optical signal transmitter generating a polarization-multiplexed overlapping single-sideband vector signal and transmitting it to the optical wireless conversion circuit, wherein the polarization-multiplexed overlapping single-sideband vector signal includes a first overlapping single-sideband vector signal in a first polarization direction and a second overlapping single-sideband vector signal in a second polarization direction; the first overlapping single-sideband vector signal carries a first microwave vector signal and a second microwave vector signal; and the second overlapping single-sideband vector signal carries a third microwave vector signal and a fourth microwave vector signal. The wireless conversion circuit converts the polarization-multiplexed overlapping single-sideband vector signal into a first millimeter-wave terahertz signal and a second millimeter-wave terahertz signal, and transmits them to the wireless receiving device. The first millimeter-wave terahertz signal carries the first and second microwave vector signals carried by the first overlapping single-sideband vector signal, and the second millimeter-wave terahertz signal carries the third and fourth microwave vector signals carried by the second overlapping single-sideband vector signal. The wireless receiving device processes the first and second millimeter-wave terahertz signals to obtain the first, second, third, and fourth microwave vector signals.

[0020] The aforementioned optical signal transmitter, millimeter-wave terahertz signal transmitting device, and communication system include the following: The optical signal transmitter comprises: a first signal generation circuit for generating a first analog signal, the first analog signal carrying a first microwave vector signal and a second microwave vector signal; a second signal generation circuit for generating a second analog signal, the second analog signal carrying a third microwave vector signal and a fourth microwave vector signal; an optical carrier generator for transmitting an optical carrier; and a modulator, wherein a first polarization direction drive arm of the modulator is connected to the first signal generation circuit, a second polarization direction drive arm of the modulator is connected to the second signal generation circuit, and the input terminal of the modulator is connected to the optical carrier generator for splitting the first analog signal and the second analog signal. The signals are modulated onto the first and second polarization directions of the optical carrier to generate a polarization-multiplexed overlapping single-sideband vector signal, which is then sent to the optical wireless conversion circuit. The polarization-multiplexed overlapping single-sideband vector signal includes a first overlapping single-sideband vector signal in the first polarization direction and a second overlapping single-sideband vector signal in the second polarization direction. The first overlapping single-sideband vector signal carries the first and second microwave vector signals carried by the first analog signal, and the second overlapping single-sideband vector signal carries the third and fourth microwave vector signals carried by the second analog signal. In other words, the optical signal transmitter can transmit four signals simultaneously, which doubles the spectral efficiency compared to traditional technologies. Attached Figure Description

[0021] Figure 1This is a schematic diagram of an optical signal transmitter in one embodiment;

[0022] Figure 2 This is a schematic diagram of a first signal generation circuit and a second signal generation circuit in one embodiment;

[0023] Figure 3 This is a schematic diagram of a millimeter-wave terahertz signal transmitting device in one embodiment;

[0024] Figure 4 This is a schematic diagram of a communication system in one embodiment;

[0025] Figure 5 This is a schematic diagram of a signal processing circuit in one embodiment;

[0026] Figure 6 This is a schematic diagram illustrating the constellation point separation and demodulation principle in one embodiment;

[0027] Figure 7 This is a schematic diagram illustrating the generation and elimination of SSBI in one embodiment;

[0028] Figure 8 This is a schematic diagram of another communication system in one embodiment;

[0029] Figure 9 This is a flowchart illustrating a communication method in one embodiment.

[0030] Figure 10 This is a schematic diagram of yet another communication system in one embodiment;

[0031] Figure 11 This is a graph showing the verification results of one embodiment using and not using the KK algorithm;

[0032] Figure 12 This is a graph showing the verification results of the relationship between BER and dual-signal baud rate in one embodiment. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0034] As is well known, 6G communication networks need to support a large number of user connections and complex data services, which urgently requires high-bandwidth, high-capacity communication. Millimeter-wave terahertz wireless communication can provide extremely rich spectrum resources and is expected to play an important role in 6G communication networks. It has broad application prospects in future inter-satellite communication, integrated space-ground communication, and wireless backhaul replacing fiber optics. On the other hand, in order to reduce the deployment cost and power consumption of millimeter-wave terahertz wireless communication, direct detection is more competitive than coherent detection schemes. In a fixed-bandwidth direct-detection millimeter-wave terahertz communication system, how to achieve efficient and low-cost transmission of different signals for multiple users and services is a problem worthy of research.

[0035] Traditional WDM (Wavelength Division Multiplexing) and SCM (Sub-Carrier Multiplexed) technologies achieve simultaneous transmission of multiple wireless signals by multiplexing multiple optical / electrical carriers on optical / wireless channels, respectively. However, this approach does not provide high spectral efficiency for optical / wireless channels.

[0036] In fiber-optic wireless hybrid channels, figuring out how to transmit and demodulate two or more independent signals based on a single carrier can significantly improve the spectral efficiency of WDM or SCM systems while meeting the multi-signal transmission requirements of multi-user, multi-service scenarios.

[0037] Currently, existing methods utilize single-polarization or dual-polarization microwave photonic links to successfully transmit and demodulate two independent wireless signals through overlapping double-sideband spectra, significantly improving the spectral efficiency of traditional double-sideband signal transmission schemes. Additionally, methods for modulation and demodulation of twin-generated single-sideband signals have been proposed, where two independent sidebands with non-overlapping spectra carry different information, thereby achieving higher spectral efficiency.

[0038] However, both of these scenarios employ coherent detection for reception, which involves complex equipment and technology, resulting in high system power consumption. This makes large-scale deployment unsuitable for power-sensitive applications. Furthermore, there is still room for improvement in the spectral efficiency of direct detection millimeter-wave terahertz communication systems.

[0039] Therefore, it is necessary to propose effective technical means to solve the above problems.

[0040] In one embodiment, such as Figure 1 As shown, a schematic diagram of an optical signal transmitter is provided. The optical signal transmitter 11 includes:

[0041] A first signal generation circuit 100 is used to generate a first analog signal, the first analog signal carrying a first microwave vector signal and a second microwave vector signal;

[0042] The second signal generation circuit 200 is used to generate a second analog signal, which carries a third microwave vector signal and a fourth microwave vector signal.

[0043] Optical carrier generator 300 is used to transmit optical carriers;

[0044] Modulator 400, with its first polarization direction drive arm connected to first signal generation circuit 100, and its second polarization direction drive arm connected to second signal generation circuit 200, and its input terminal connected to optical carrier generator 300, is used to modulate a first analog signal and a second analog signal onto the first polarization direction and the second polarization direction of the optical carrier, respectively, to generate a polarization multiplexed overlapping single-sideband vector signal, which is then sent to the optical wireless conversion circuit; wherein, the polarization multiplexed overlapping single-sideband vector signal includes a first overlapping single-sideband vector signal in the first polarization direction and a second overlapping single-sideband vector signal in the second polarization direction, the first overlapping single-sideband vector signal carrying a first microwave vector signal and a second microwave vector signal carried by the first analog signal, and the second overlapping single-sideband vector signal carrying a third microwave vector signal and a fourth microwave vector signal carried by the second analog signal.

[0045] The modulator 400 can be a dual-polarization dual-drive Mach-Zehnder modulator, or simply dual-polarization DDMZM, which has the function of electro-optic modulation. The first polarization direction and the second polarization direction can be two orthogonal directions, represented by the X polarization direction and the Y polarization direction, respectively.

[0046] The first analog signal includes a first sub-analog signal and a second sub-analog signal, which are used to drive the drive arm of the modulator 400 in the first polarization direction.

[0047] The second analog signal includes a third sub-analog signal and a fourth sub-analog signal, which are used to drive the drive arm of the modulator 400 in the second polarization direction.

[0048] The first microwave vector signal, the second microwave vector signal, the third microwave vector signal, and the fourth microwave vector signal can be four wireless signals carrying different information. Furthermore, the spectra of the first microwave vector signal and the second microwave vector signal completely overlap, and the spectra of the third microwave vector signal and the fourth microwave vector signal completely overlap.

[0049] Polarization multiplexed overlapping single-sideband vector signal refers to an optical signal carrying information.

[0050] The first analog signal carrying the first microwave vector signal and the second microwave vector signal means that the first analog signal carries information corresponding to the first microwave vector signal and the second microwave vector signal. Similarly, the second analog signal carrying the third and fourth microwave vector signals, the first overlapping single-sideband vector signal carrying the first and second microwave vector signals, and the second overlapping single-sideband vector signal carrying the third and fourth microwave vector signals all refer to carrying information corresponding to the microwave vector signals.

[0051] Optionally, the principle of the optical signal transmitter 11 outputting polarization-multiplexed overlapping single-sideband vector signal is as follows: After the modulator 400 receives the optical carrier emitted by the optical carrier generator 300, when the first analog signal generated by the first signal generation circuit 100 drives the drive arm of the modulator 400 in the X-polarization direction, the modulator 400 will perform electro-optic modulation on the first analog signal and modulate it onto the X-polarization direction of the optical carrier to generate a first overlapping single-sideband vector signal. The two overlapping single-sideband vector signals are the single-sideband vector signal corresponding to the first microwave vector signal and the single-sideband vector signal corresponding to the second microwave vector signal, respectively.

[0052] When the second analog signal generated by the second signal generation circuit 200 drives the drive arm of the modulator 400 in the Y polarization direction, the modulator 400 will perform electro-optic modulation on the second analog signal and modulate it onto the Y polarization direction of the optical carrier to generate a second overlapping single-sideband vector signal. The two overlapping single-sideband vector signals are the single-sideband vector signal corresponding to the third microwave vector signal and the single-sideband vector signal corresponding to the fourth microwave vector signal, respectively.

[0053] Therefore, the polarization multiplexed overlapping single-sideband vector signal output by the optical signal transmitter 11 carries the first microwave vector signal and the second microwave vector signal in the X polarization direction, and the third microwave vector signal and the fourth microwave vector signal in the Y polarization direction.

[0054] In summary, the optical signal transmitter 11 includes: a first signal generation circuit 100 for generating a first analog signal, the first analog signal carrying a first microwave vector signal and a second microwave vector signal; a second signal generation circuit 200 for generating a second analog signal, the second analog signal carrying a third microwave vector signal and a fourth microwave vector signal; an optical carrier generator 300 for transmitting an optical carrier; and a modulator 400, wherein a first polarization direction drive arm of the modulator 400 is connected to the first signal generation circuit 100, a second polarization direction drive arm of the modulator 400 is connected to the second signal generation circuit 200, and an input terminal of the modulator 400 is connected to the optical carrier generator 300 for transmitting the first analog signal and the second microwave vector signal. The analog signal is modulated onto the first polarization direction and the second polarization direction of the optical carrier to generate a polarization multiplexed overlapping single-sideband vector signal, which is then sent to the optical wireless conversion circuit. The polarization multiplexed overlapping single-sideband vector signal includes a first overlapping single-sideband vector signal in the first polarization direction and a second overlapping single-sideband vector signal in the second polarization direction. The first overlapping single-sideband vector signal carries the first and second microwave vector signals carried by the first analog signal, and the second overlapping single-sideband vector signal carries the third and fourth microwave vector signals carried by the second analog signal. In other words, the optical signal transmitter can transmit four signals simultaneously, which improves the spectral efficiency by two times compared to traditional technology.

[0055] In one embodiment, such as Figure 2 As shown, a schematic diagram of a first signal generation circuit and a second signal generation circuit is provided. The first analog signal includes a first sub-analog signal and a second sub-analog signal. The first signal generation circuit 100 includes:

[0056] A first microwave vector signal generator 111 is used to generate a first microwave vector signal;

[0057] The second microwave vector signal generator 112 is used to generate a second microwave vector signal;

[0058] The first Hilbert converter 113 is connected to the first microwave vector signal generator 111 and the second microwave vector signal generator 112, and is used to perform Hilbert transformation on the sum of the first microwave vector signal and the second microwave vector signal to generate the first transformed vector signal;

[0059] The first digital-to-analog converter 114 is connected to the first microwave vector signal generator 111 and the second microwave vector signal generator 112, and is used to perform digital-to-analog conversion on the sum of the first microwave vector signal and the second microwave vector signal to generate a first sub-analog signal;

[0060] The second digital-to-analog converter 115 is connected to the first Hilbert converter 113 and is used to perform digital-to-analog conversion on the first transformed vector signal to generate the second sub-analog signal.

[0061] The modulator 400 has a first upper drive arm and a first lower drive arm in the first polarization direction; the first upper drive arm is connected to the first digital-to-analog converter 114, and the first lower drive arm is connected to the second digital-to-analog converter 115 to generate a first overlapping single-sideband vector signal.

[0062] The spectra of the first microwave vector signal and the second microwave vector signal generated by the first microwave vector signal generator 111 and the second microwave vector signal generator 112 can completely overlap.

[0063] Optionally, the principle of generating the first overlapping single-sideband vector signal is as follows: the first microwave vector signal and the second microwave vector signal will automatically superimpose during the transmission in the digital domain. Therefore, the first digital-to-analog converter 114 and the first Hilbert converter 113 both receive the sum of the first microwave vector signal and the second microwave vector signal.

[0064] The first sub-analog signal obtained after passing through the first digital-to-analog converter 114, and the second sub-analog signal obtained after passing through the first Hilbert converter 113 and the second digital-to-analog converter 115, are used to drive the first upper drive arm and the first lower drive arm in the X-polarization direction of the modulator 400, respectively, thereby generating the first overlapping single-sideband vector signal in the X-polarization direction.

[0065] The above process can be expressed mathematically as follows:

[0066] Assuming s1(t) and s2(t) represent the first microwave vector signal and the second microwave vector signal, respectively, the driving voltages of the first upper driving arm and the first lower driving arm in the X-polarization direction of the driving modulator 400 are as follows:

[0067]

[0068] Among them, U upper (t) and U lower (t) represent the driving voltages of the first upper driving arm and the first lower driving arm in the X-polarization direction of the driving modulator 400, respectively; This indicates that the Hilbert transform is applied to the real signal s1(t). This indicates that the Hilbert transform of the real signal s2(t) is performed; t represents time.

[0069] When modulator 400 is biased at the quadrature point, the output optical signal E(t) after electro-optic modulation in the X-polarization direction is:

[0070]

[0071] Where A = 1 - j is the optical carrier term, E in (t) represents the light wave output by the optical carrier generator 300, where j represents the imaginary unit. Note that... and Let s1(t) and s2(t) represent the right-sideband signals, respectively, whose spectra completely overlap. Therefore, the X-polarized light signal output by modulator 400 is actually an overlapping single-sideband vector signal with a carrier wave, which is formed by the superposition of two independent single-sideband signals distributed on the same side of the optical carrier wave.

[0072] Compared to the dual-single-sideband modulation scheme where two independent sideband signals are located on opposite sides of the carrier, the overlapping single-sideband transmission scheme proposed in this application can further double the spectral efficiency.

[0073] In one embodiment, such as Figure 2 As shown, the second analog signal includes a third sub-analog signal and a fourth sub-analog signal, and the second signal generation circuit 200 includes:

[0074] The third microwave vector signal generator 211 is used to generate the third microwave vector signal;

[0075] The fourth microwave vector signal generator 212 is used to generate the fourth microwave vector signal;

[0076] The second Hilbert converter 213 is connected to the third microwave vector signal generator 211 and the fourth microwave vector signal generator 212, and is used to perform Hilbert transformation on the sum of the third microwave vector signal and the fourth microwave vector signal to generate the second transformed vector signal.

[0077] The third digital-to-analog converter 214 is connected to the third microwave vector signal generator 211 and the fourth microwave vector signal generator 212, and is used to perform digital-to-analog conversion on the sum of the third microwave vector signal and the fourth microwave vector signal to generate the third sub-analog signal;

[0078] The fourth digital-to-analog converter 215, connected to the second Hilbert converter 213, is used to perform digital-to-analog conversion on the second transformed vector signal to generate the fourth sub-analog signal.

[0079] The modulator 400 has a second polarization direction drive arm including a second upper drive arm and a second lower drive arm. The second upper drive arm is connected to a third digital-to-analog converter 214, and the second lower drive arm is connected to a fourth digital-to-analog converter 215 to generate a second overlapping single-sideband vector signal.

[0080] The principle of generating the second overlapping single-sideband vector signal in this embodiment is similar to that of generating the first overlapping single-sideband vector signal, and will not be repeated here.

[0081] In summary, the final output of modulator 400 is a polarization-multiplexed overlapping single-sideband vector signal, the spectrum of which is shown in the figure below. Figure 2 As shown, four different signals occupy the same frequency band, demonstrating ultra-high spectral efficiency.

[0082] In one embodiment, such as Figure 3 The diagram shows a millimeter-wave terahertz signal transmitting device. The millimeter-wave terahertz signal transmitting device 500 includes an optical signal transmitter 11 and an optical-to-wireless conversion circuit 12, with the optical signal transmitter 11 connected to the optical-to-wireless conversion circuit 12.

[0083] Optionally, the millimeter-wave terahertz signal transmitter 500 also includes an optical fiber link 13, through which the optical signal transmitter 11 transmits the polarization multiplexed overlapping single-sideband vector signal to the optical wireless conversion circuit 12.

[0084] In one embodiment, such as Figure 3 As shown, the optical-to-wireless conversion circuit 12 includes:

[0085] The first optical polarization beamsplitter 121 is connected to the optical signal transmitter 11 and is used to receive the polarization multiplexed overlapping single-sideband vector signal sent by the optical signal transmitter 11, and to perform polarization beam splitting on the polarization multiplexed overlapping single-sideband vector signal to obtain a first overlapping single-sideband vector signal and a second overlapping single-sideband vector signal; wherein, the first overlapping single-sideband vector signal is the signal in the first polarization direction of the polarization multiplexed overlapping single-sideband vector signal, carrying a first microwave vector signal and a second microwave vector signal, and the second overlapping single-sideband vector signal is the signal in the second polarization direction of the polarization multiplexed overlapping single-sideband vector signal, carrying a third microwave vector signal and a fourth microwave vector signal;

[0086] Local oscillator light generator 122 is used to emit local oscillator light;

[0087] The second optical polarization beam splitter 123 is connected to the local oscillator light generator 122 and is used to polarize and split the local oscillator light to obtain the first local oscillator light in the first polarization direction and the second local oscillator light in the second polarization direction.

[0088] The first optical coupler 124 is connected to the first optical polarization beamsplitter 121 and the second optical polarization beamsplitter 123, and is used to couple the first overlapping single-sideband vector signal and the first local oscillator light to obtain the first coupled signal.

[0089] The second optical coupler 125 is connected to the first optical polarization beamsplitter 121 and the second optical polarization beamsplitter 123, and is used to couple the second overlapping single-sideband vector signal and the second local oscillator light to obtain the second coupled signal.

[0090] The first photodetector 126 is connected to the first optical coupler 124 and is used to convert the first coupling signal into a first millimeter-wave terahertz signal. The first millimeter-wave terahertz signal carries the first microwave vector signal and the second microwave vector signal carried by the first overlapping single-sideband vector signal.

[0091] The second photodetector 127 is connected to the second optical coupler 125 and is used to convert the second coupled signal into a second millimeter-wave terahertz signal. The second millimeter-wave terahertz signal carries the third microwave vector signal and the fourth microwave vector signal carried by the second overlapping single-sideband vector signal.

[0092] Optionally, the polarization-multiplexed overlapping single-sideband vector signal is converted into a first millimeter-wave terahertz signal and a second millimeter-wave terahertz signal, i.e., optical-to-wireless conversion. The principle is as follows: the polarization-multiplexed overlapping single-sideband vector signal is split into X and Y polarization directions by the first optical polarization beamsplitter 121, thus obtaining the first overlapping single-sideband vector signal and the second overlapping single-sideband vector signal. At the same time, the local oscillator light from the local oscillator light generator 122 is also split into X and Y polarization directions by the second optical polarization beamsplitter 123, thus obtaining the first local oscillator light and the second local oscillator light.

[0093] Then, in the X-polarization direction, the first overlapping single-sideband vector signal transmitted in the X direction is coupled to the local oscillator light using the first optical coupler 124 to obtain the first coupled signal; in the Y-polarization direction, the second overlapping single-sideband vector signal transmitted in the Y direction is coupled to the local oscillator light using the second optical coupler 125 to obtain the second coupled signal.

[0094] The first coupled signal and the second coupled signal are then photoelectrically converted by the first photodetector 126 and the second photodetector 127 respectively to obtain the first millimeter-wave terahertz signal and the second millimeter-wave terahertz signal. The carrier frequency of the generated millimeter-wave terahertz signal is equal to the center frequency interval between the optical carrier generator 300 and the local oscillator generator 122.

[0095] In one embodiment, such as Figure 4 The diagram illustrates a communication system. The communication system 600 includes a millimeter-wave terahertz signal transmitter 500 and a wireless receiver 700. The millimeter-wave terahertz signal transmitter 500 is connected to the wireless receiver 700. The wireless receiver 700 receives a first millimeter-wave terahertz signal and a second millimeter-wave terahertz signal transmitted by the millimeter-wave terahertz signal transmitter 500 in any of the above embodiments. The first millimeter-wave terahertz signal carries a first microwave vector signal and a second microwave vector signal, and the second millimeter-wave terahertz signal carries a third microwave vector signal and a fourth microwave vector signal.

[0096] Optionally, the communication system 600 also includes an antenna 14, through which the millimeter-wave terahertz signal transmitter 500 transmits the first millimeter-wave terahertz signal and the second millimeter-wave terahertz signal to the wireless receiver 700.

[0097] Among them, antenna 14 can be a MIMO (Multiple-Input Multiple-Output) antenna, with a quantity of 4, such as... Figure 4 As shown.

[0098] In one embodiment, such as Figure 4 As shown, the wireless receiver 700 includes:

[0099] The wireless receiving circuit 15 is connected to the millimeter-wave terahertz signal transmitting device 500 and is used to receive the first millimeter-wave terahertz signal and the second millimeter-wave terahertz signal, and to process the first millimeter-wave terahertz signal and the second millimeter-wave terahertz signal to generate the first digital signal and the second digital signal.

[0100] The signal processing circuit 16, connected to the wireless receiving circuit 15, is used to process the first digital signal to obtain a first microwave vector signal and a second microwave vector signal; and to process the second digital signal to obtain a third microwave vector signal and a fourth microwave vector signal.

[0101] Optional, such as Figure 4 As shown, the wireless receiving circuit 15 includes:

[0102] The first envelope detector 151 is connected to the millimeter-wave terahertz signal transmitter 500. It is used to receive the first millimeter-wave terahertz signal and down-convert the first millimeter-wave terahertz signal based on the direct detection method of envelope detection to obtain the first intermediate frequency signal after down-conversion.

[0103] The first envelope detector 152 is connected to the millimeter-wave terahertz signal transmitter 500 and is used to receive the second millimeter-wave terahertz signal and down-convert the second millimeter-wave terahertz signal based on the direct detection method of envelope detection to obtain the down-converted second intermediate frequency signal.

[0104] The first analog-to-digital converter 153 is connected to the first envelope detector 151 and is used to perform analog-to-digital conversion on the first intermediate frequency signal to obtain the first digital signal.

[0105] The second analog-to-digital converter 154 is connected to the second envelope detector 152 and is used to perform analog-to-digital conversion on the second intermediate frequency signal to obtain the second digital signal.

[0106] The principle of sampling millimeter-wave terahertz signals is as follows: First envelope detector 151 and first envelope detector 152 are used to directly detect the first millimeter-wave terahertz signal and the second millimeter-wave terahertz signal, respectively. The millimeter-wave terahertz signal is down-converted to obtain the first intermediate frequency signal and the second intermediate frequency signal.

[0107] Then, the first analog-to-digital converter 153 and the second analog-to-digital converter 154 are used to convert the first intermediate frequency signal and the second intermediate frequency signal from analog signals to digital signals, so as to obtain the first digital signal and the second digital signal.

[0108] Optional, such as Figure 5 As shown, a signal processing circuit is provided, the signal processing circuit 16 including:

[0109] Crosstalk cancellation circuit 161 is connected to wireless receiving circuit 15 and is used to perform crosstalk cancellation processing on first digital signal and second digital signal to obtain first crosstalk-free signal and second crosstalk-free signal.

[0110] The first constellation point separation circuit 162 is connected to the first output terminal of the crosstalk elimination circuit 161 and is used to perform constellation point demodulation processing on the first crosstalk-free signal to obtain the first microwave vector signal and the second microwave vector signal.

[0111] The second constellation point separation circuit 163 is connected to the second output terminal of the crosstalk elimination circuit 161 and is used to perform constellation point demodulation processing on the second crosstalk-free signal to obtain the third microwave vector signal and the fourth microwave vector signal.

[0112] The signal processing circuit 16 is also a DSP (Digital Signal Processing) circuit. After the first millimeter-wave terahertz signal and the second millimeter-wave terahertz signal pass through the wireless receiving circuit 15 and the crosstalk elimination circuit 161, a first crosstalk-free signal and a second crosstalk-free signal can be obtained. Each path is composed of two wireless signals with overlapping spectra.

[0113] For example, the first crosstalk-free signal contains two different wireless signals, which are separated and demodulated by the first constellation point separation circuit 162 to obtain the first demodulated signal s1(t) and the second demodulated signal s2(t), which are also the first microwave vector signal and the second microwave vector signal.

[0114] like Figure 6As shown, a schematic diagram of constellation point separation demodulation principle is provided. Taking the transmission of two QPSK signals as an example, after passing through the crosstalk cancellation circuit 161, the two QPSK signals with a 90° phase difference are superimposed to form a star-shaped 16QAM constellation diagram. Each constellation point of the star-shaped 16QAM has a unique mapping relationship with the constellation points of the two QPSK signals. For example, constellation point (a) of the output signal after passing through the crosstalk cancellation circuit 161 corresponds to the superposition of constellation point (b) of the first demodulated signal s1(t) and constellation point (c) of the second demodulated signal s2(t). Therefore, under this mapping relationship, the star-shaped 16QAM after passing through the crosstalk cancellation circuit 161 can be decomposed into two independent QPSK signals, namely the first demodulated signal and the second demodulated signal.

[0115] For the second crosstalk-free signal, the processing procedure is similar to that for the first crosstalk-free signal, resulting in the third and fourth demodulated signals. In other words, the four independent wireless signals transmitted by the optical signal transmitter 11 can be successfully demodulated and recovered, namely the first microwave vector signal, the second microwave vector signal, the third microwave vector signal, and the fourth microwave vector signal.

[0116] Then, the bit error rate is calculated for the first, second, third, and fourth microwave vector signals obtained after demodulation.

[0117] In one embodiment, such as Figure 5 As shown, the crosstalk cancellation circuit 161 includes:

[0118] The signal resampling circuit 171 is connected to the wireless receiving circuit 15 and is used to resample the first digital signal and the second digital signal to obtain the first resampled signal and the second resampled signal.

[0119] The signal reconstruction circuit 172 is connected to the signal resampling circuit 171 and is used to reconstruct the first resampled signal and the second resampled signal to obtain the first reconstructed signal and the second reconstructed signal.

[0120] The third Hilbert transformer 173 is connected to the signal reconstruction circuit 172 and is used to perform Hilbert transformation on the first reconstructed signal and the second reconstructed signal respectively to obtain the third transformed vector signal and the fourth transformed vector signal.

[0121] The polarization demultiplexing circuit 174 is connected to the signal reconstruction circuit 172 and the third Hilbert converter 173. It is used to perform polarization crosstalk compensation processing on the first reconstructed signal and the third transformed vector signal to obtain the first polarization demultiplexed signal, and to perform polarization crosstalk compensation processing on the second reconstructed signal and the fourth transformed vector signal to obtain the second polarization demultiplexed signal.

[0122] The channel equalization circuit 175 is connected to the polarization demultiplexing circuit 174 and is used to perform channel equalization processing on the first polarization demultiplexed signal and the second polarization demultiplexed signal to obtain the first crosstalk-free signal and the second crosstalk-free signal.

[0123] The signal resampling circuit 171, signal reconstruction circuit 172, third Hilbert transformer 173, polarization demultiplexing circuit 174, and channel equalization circuit 175 can each be multiple. The following example, using two each of the signal resampling circuit 171, signal reconstruction circuit 172, and channel equalization circuit 175, and one each of the third Hilbert transformer 173 and polarization demultiplexing circuit 174, illustrates the principle of crosstalk elimination.

[0124] First, the X-polarized sampling signal (representing the signal strength information of the first millimeter-wave terahertz signal obtained by envelope detection in the X-polarization direction) is resampled by the first signal resampling circuit 171, specifically by downsampling, to obtain the first resampled signal; similarly, the Y-polarized sampling signal (representing the signal strength information of the second millimeter-wave terahertz signal obtained by envelope detection in the Y-polarization direction) is resampled by the second signal resampling circuit 171 to obtain the second resampled signal.

[0125] Secondly, using two signal reconstruction circuits 172, the overlapping single-sideband vector signals of X-polarization and Y-polarization are reconstructed from the first resampled signal and the second resampled signal, that is, the signal intensity information in the X-polarization direction and the signal intensity information in the Y-polarization direction, respectively. Specifically, the Kramers-Kronig (KK) algorithm can be used for reconstruction, while eliminating the SSBI (Signal-Signal Beat Interference) introduced by square-law envelope detection.

[0126] Note that, without considering polarization crosstalk, since the signal in each polarization direction is composed of two single-sideband signals with overlapping spectra, after envelope detection, the SSBI mainly consists of three parts: (1) X1-SSBI introduced by the beat frequency of X-polarized signal 1; (2) X2-SSBI introduced by the beat frequency of X-polarized signal 2; and (3) C-SSBI introduced by the beat frequency of X-polarized signal 1 and X-polarized signal 2. However, if we consider the case of fiber transmission, the polarization mode dispersion of the fiber will introduce polarization crosstalk, causing the signal in each polarization direction at the receiving end to actually contain signals in both polarization directions at the transmitting end. Therefore, after envelope detection, the composition of the SSBI is more complex. However, in either case, as long as the minimum phase condition is met, the KK algorithm can effectively compensate for the SSBI. After processing by the KK algorithm, the overlapping single-sideband vector signal can be reconstructed, such as Figure 7As shown, a schematic diagram is provided for generating and eliminating SSBI.

[0127] According to formula (2), the real part of the overlapping single-sideband vector signal reconstructed by the KK algorithm can be expressed as:

[0128]

[0129] Where r(t) represents the real signal corresponding to the overlapping single-sideband vector signal obtained by taking the real part of the overlapping single-sideband vector signal.

[0130] It can be seen that the overlapping single-sideband vector signal reconstructed by the KK algorithm contains both s1(t)+s2(t) and their Hilbert transform components. The latter is actually a first-order linear crosstalk term, therefore a third Hilbert transformer 173 is needed to eliminate this crosstalk term through superposition. The principle is as follows:

[0131]

[0132] in, This indicates that the Hilbert transform is applied to the real signal r(t).

[0133] In the case of fiber optic transmission, the overlapping single-sideband vector signals in the X and Y polarization directions after the crosstalk term is eliminated by superposition processing using the third Hilbert converter 173 still have polarization crosstalk. It is necessary to further compensate for the polarization-related crosstalk caused by polarization mode dispersion during fiber optic transmission through the polarization demultiplexing circuit 174. Specifically, CMA (Constant Modulus Algorithm) can be used for polarization demultiplexing to obtain two baseband signals without polarization crosstalk, namely the first polarization demultiplexed signal and the second polarization demultiplexed signal, or the recovered first overlapping single-sideband vector signal and the second overlapping single-sideband vector signal. Each overlapping single-sideband vector signal is composed of two wireless signals with overlapping spectra.

[0134] Channel equalization is performed on the recovered first overlapping single-sideband vector signal and the second overlapping single-sideband vector signal respectively. The two radio signals in the first overlapping single-sideband vector signal after channel equalization are 90° out of phase, presenting a star-shaped 16QAM constellation. The two radio signals in the second overlapping single-sideband vector signal after channel equalization are 90° out of phase, presenting a star-shaped 16QAM constellation.

[0135] In summary, such as Figure 8The diagram shows another communication system, which includes an optical signal transmitter 11, an optical-to-wireless conversion circuit 12, an optical fiber link 13, an antenna 14, a wireless receiving circuit 15, and a signal processing circuit 16, each of which includes the optical signal transmitter 11, optical-to-wireless conversion circuit 12, optical fiber link 13, antenna 14, wireless receiving circuit 15, and signal processing circuit 16 described in any of the above embodiments.

[0136] The communication system also includes an erbium-doped fiber amplifier, which is connected between the fiber optic link 13 and the optical wireless conversion circuit 12 to amplify the optical signal.

[0137] The optical signal transmitter 11 further includes a polarization multiplexer, which comprises:

[0138] An optical beam splitter, connected to a modulator, is used to split polarization-multiplexed overlapping single-sideband vector signals into a first optical signal and a second optical signal.

[0139] An optical fiber delay line is connected to the first output end of an optical beam splitter to delay the first optical signal.

[0140] An adjustable optical attenuator is connected to the second output of the optical beam splitter and is used to attenuate the power of the second optical signal.

[0141] An optical polarization combiner, connected to an optical fiber delay line and an adjustable optical attenuator, combines a delayed first optical signal and a power-attenuated second optical signal to obtain a processed polarization-multiplexed overlapping single-sideband vector signal.

[0142] The processed polarization multiplexed overlapping single-sideband vector signal is transmitted to the optical wireless conversion circuit 12 via optical fiber link 13 and erbium-doped fiber amplifier.

[0143] The optical signal transmitter 11 includes a microwave vector signal transmission circuit, and the microwave vector signal includes a first signal generation circuit 100 and a second signal generation circuit 200.

[0144] Based on the same inventive concept, this application also provides an optical signal transmission method for implementing the optical signal transmitter described above. The solution provided by this optical signal transmission method is similar to the implementation described in the optical signal transmitter above. Therefore, the specific limitations in one or more embodiments of the optical signal transmission method provided below can be found in the limitations of the optical signal transmitter described above, and will not be repeated here.

[0145] In one embodiment, an optical signal transmission method is provided, applied to an optical signal transmitter, the method comprising:

[0146] The first signal generation circuit in the optical signal transmitter generates a first analog signal carrying a first microwave vector signal and a second microwave vector signal, and inputs it to the drive arm of the modulator in the first polarization direction in the optical signal transmitter.

[0147] The second signal generation circuit in the optical signal transmitter generates a second analog signal carrying a third microwave vector signal and a fourth microwave vector signal, and inputs it to the drive arm of the second polarization direction of the modulator;

[0148] The optical carrier generator in the optical signal transmitter transmits an optical carrier and inputs it to the input terminal of the modulator, so that the modulator modulates the first analog signal and the second analog signal onto the first polarization direction and the second polarization direction of the optical carrier, respectively, to generate a polarization multiplexed overlapping single-sideband vector signal;

[0149] The polarization multiplexed overlapping single-sideband vector signal includes a first overlapping single-sideband vector signal in the first polarization direction and a second overlapping single-sideband vector signal in the second polarization direction. The first overlapping single-sideband vector signal carries the first microwave vector signal and the second microwave vector signal carried by the first analog signal. The second overlapping single-sideband vector signal carries the third microwave vector signal and the fourth microwave vector signal carried by the second analog signal.

[0150] Based on the same inventive concept, this application also provides a communication method for implementing the communication system described above. The solution provided by this communication method is similar to the implementation scheme described in the communication system above. Therefore, the specific limitations in one or more communication method embodiments provided below can be found in the limitations of the communication system described above, and will not be repeated here.

[0151] In one embodiment, a communication method is provided, applied to a communication system, the communication system including an optical signal transmitter, an optical-to-wireless conversion circuit, and a wireless receiving device, the method comprising:

[0152] The optical signal transmitter generates a polarization multiplexed overlapping single-sideband vector signal and sends it to the optical wireless conversion circuit. The polarization multiplexed overlapping single-sideband vector signal includes a first overlapping single-sideband vector signal in a first polarization direction and a second overlapping single-sideband vector signal in a second polarization direction. The first overlapping single-sideband vector signal carries a first microwave vector signal and a second microwave vector signal, and the second overlapping single-sideband vector signal carries a third microwave vector signal and a fourth microwave vector signal.

[0153] The optical wireless conversion circuit converts the polarization multiplexed overlapping single-sideband vector signal into a first millimeter-wave terahertz signal and a second millimeter-wave terahertz signal, and sends them to the wireless receiving device. The first millimeter-wave terahertz signal carries the first microwave vector signal and the second microwave vector signal carried by the first overlapping single-sideband vector signal, and the second millimeter-wave terahertz signal carries the third microwave vector signal and the fourth microwave vector signal carried by the second overlapping single-sideband vector signal.

[0154] The wireless receiving device processes the first millimeter-wave terahertz signal and the second millimeter-wave terahertz signal to obtain a first microwave vector signal, a second microwave vector signal, a third microwave vector signal, and a fourth microwave vector signal.

[0155] like Figure 9 The diagram shows a flowchart of a communication method. The method includes the following steps:

[0156] Step 901: A polarization-multiplexed overlapping single-sideband vector signal is generated using an optical signal transmitter. This polarization-multiplexed overlapping single-sideband vector signal carries a first microwave vector signal, a second microwave vector signal, a third microwave vector signal, and a fourth microwave vector signal.

[0157] Specifically, in the optical signal transmitter, a simple dual-polarization DDMZM generates a polarization-multiplexed overlapping single-sideband vector signal. Each polarization carries two different wireless signals, resulting in a total of four independent wireless signals with completely overlapping spectra, thus exhibiting high spectral efficiency. This polarization-multiplexed overlapping single-sideband vector signal can achieve high spectral efficiency long-distance transmission in standard single-mode fiber via the same optical carrier.

[0158] Step 902: Use an optical wireless conversion circuit to convert the polarization multiplexed overlapping single-sideband vector signal into a first millimeter-wave terahertz signal in the first polarization direction and a second millimeter-wave terahertz signal in the second polarization direction.

[0159] Specifically, in the optical-to-wireless conversion circuit, millimeter-wave terahertz signals in both X and Y polarization directions are generated based on polarization diversity optical heterodyne detection technology. The obtained dual-polarization millimeter-wave terahertz signals are then transmitted wirelessly via a 2×2 MIMO antenna.

[0160] Step 903: Using a wireless receiving circuit, down-convert the first millimeter-wave terahertz signal and the second millimeter-wave terahertz signal and perform analog-to-digital conversion.

[0161] Specifically, in the wireless receiving circuit, millimeter-wave terahertz signals in both the X and Y polarization directions are down-converted using a low-cost envelope detection direct detection method.

[0162] Step 904: The signal processing circuit is used to reconstruct, eliminate crosstalk, and perform channel equalization on the analog-to-digital converted signal in sequence.

[0163] Specifically, in the signal processing circuit, firstly, for the signals received in the two polarization directions, the KK algorithm is used sequentially to reconstruct the overlapping single-sideband vector signal from the detected intensity information, while simultaneously eliminating the SSBI introduced by direct detection; secondly, Hilbert transform superposition processing is used to compensate for the first-order linear distortion caused by the Hilbert transform term; thirdly, CMA is used for polarization demultiplexing to compensate for polarization-related crosstalk caused by polarization mode dispersion during fiber transmission. Subsequently, baseband recovery and channel equalization are performed on each of the recovered overlapping single-sideband vector signals in the two polarization directions.

[0164] Step 905: Separate the two signals from the signals with overlapping spectra according to the specific mapping relationship of constellation points, and calculate the bit error rate for each of the X-polarized and Y-polarized signals.

[0165] Compared to traditional technologies, the proposed solution can improve spectral efficiency by two times. Based on polarization multiplexing, low-cost dual-polarization DDMZM, and low-power envelope detector, it can carry four independent wireless signals simultaneously on a single optical / wireless carrier, thereby realizing high spectral efficiency transmission of multiple signals in a fiber-optic wireless converged communication system.

[0166] The following simulation demonstrates the feasibility of this application.

[0167] like Figure 10 As shown, a schematic diagram of another communication system is provided, in which:

[0168] The optical signal transmitter includes the following components: an external cavity laser (ECL), a dual-drive Mach-Zehnder modulator (DDMZM), a digital-to-analog converter (DAC), an optical beam splitter (OS), a delay line (DL), an optical attenuator (ATT), a polarization beam combiner (PBC), and a signal generation circuit (Tx-DSP), wherein:

[0169] The signal generation circuit (Tx-DSP) generates a first pseudo-random sequence (PRBS1) and a second pseudo-random sequence (PRBS2). After mapping PRBS1 and PRBS2 into QPSK signals, they are upsampled and root raised cosine (RRC) pulse shaped, respectively. Then, the two QPSK signals are superimposed (QPSK overlapping). Finally, the superimposed signal is resampled and input to the digital-to-analog converter (DAC).

[0170] Standard single-mode fiber (SSMF), erbium-doped fiber amplifier (EDFA), and antenna.

[0171] The optical-to-wireless conversion circuit includes the following components: a polarized beam splitter (PBS), an optical coupler (OC), an intrinsic light source (LO), a unidirectional moving carrier photodiode (UTC-PD), and a polarized beam splitter (PBS).

[0172] The wireless receiver circuit includes the following components: a zero-bias detector (ZBD) and an analog-to-digital converter (ADC).

[0173] The signal processing circuit (Rx-DSP) first processes the first and second digital signals output from the analog-to-digital converter (ADC) sequentially using resampling, the KK algorithm, baseband recovery, and root-raised cosine filtering (RRC filtering). Then, it employs the constant modulus algorithm (CMA) for depolarization multiplexing, obtaining first and second polarization demultiplexed signals. These are then subjected to channel equalization (LMSequalization) and QPSK separation. The first polarization demultiplexed signal, after QPSK separation, yields two independent first and second QPSK signals. Further bit error rate (BER1) calculations are performed on the first QPSK signal and the second QPSK signal (BER2) to obtain the BER of the first and second QPSK signals in the X-polarization direction. Similarly, after QPSK separation, the second polarization demultiplexed signal can also be used to obtain two independent QPSK signals. Further bit error rate calculation can also yield the bit error rate of the two QPSK signals in the Y polarization (Y pol) direction.

[0174] The parameters of the simulated communication system are as follows: modulation format: QPSK; baud rate: 5.75 GBaud; AWG sampling rate: 92 Gsa / s; DPO sampling rate: 128 Gsa / s.

[0175] The simulation results are as follows: Figure 11 As shown, a verification result graph is provided with and without the KK algorithm. The relationship between the BER (Bit Error Ratio) and GB (Guard Band) of a communication system based on directly probed overlapping single-sideband vector signals is shown in the graphs for both scenarios. Figure 11As shown in Figure (a), the BER (Bachelor's Error Rate) of four independent signals varies with GB at a baud rate of 5.75 GBd. Assuming the bandwidth of the overlapping single-sideband baseband signal s(t) is B, without KK recovery, the BER performance increases with increasing GB. This is due to the influence of the SSBI on the system; as the guard interval increases, the detection signal moves further away from the SSBI, resulting in less interference and thus improved system performance. Meanwhile, with the KK reception scheme, even at very small GBs, the system performance can be improved by at least an order of magnitude when the carrier f... s When the center frequency interval between the overlapping single-sideband baseband signal and the SSBI signal exceeds 0.25 bits, the bit error rate (BER) remains low. This means that the SSBI can be largely eliminated by the KK algorithm at this GB. Considering the trade-off between system bandwidth usage and BER performance, by setting the GB to 0.25 bits, the communication system based on directly probed overlapping single-sideband signals can achieve high bit error rate performance while occupying only a small amount of bandwidth resources to meet the needs of high spectral efficiency multi-signal transmission. Figure 11 (b) and Figure 11 Figure (c) shows the constellation diagrams of the overlapping dual single-sideband signals detected with and without KK receiver at a GB of 0.25B. It can be seen that the system performance is significantly improved after using the KK algorithm. Finally, as the GB exceeds 0.75B, the performance of the schemes using and without KK receiver becomes similar.

[0176] like Figure 12 As shown in the figure, a verification result graph of the relationship between BER and the baud rate of dual signals is provided. It can be seen that as the baud rate increases, the bit error rate performance deteriorates continuously. When the baud rate of each dual signal is 17 GBd and the total signal rate is approximately 68 GBd, the 7% HD-FEC threshold (3.8 × 10⁻⁶) can be reached. -3 The bit error rate performance of the four signals on both X and Y polarizations is basically the same. On the other hand, as the baud rate increases, the performance improvement brought by the KK receiver scheme gradually weakens. This is mainly because as the signal baud rate increases, the impact of system noise on performance also gradually increases, thereby reducing the impact of SSBI on system performance.

[0177] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0178] In this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, for example, two, three, etc., unless otherwise explicitly specified.

[0179] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0180] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0181] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. An optical signal transmitter, characterized in that, The optical signal transmitter includes: A first signal generation circuit is used to generate a first analog signal, wherein the first analog signal carries a first microwave vector signal and a second microwave vector signal; The second signal generation circuit is used to generate a second analog signal, which carries a third microwave vector signal and a fourth microwave vector signal. Optical carrier generator, used to transmit optical carriers; A modulator, wherein the first polarization direction drive arm of the modulator is connected to the first signal generation circuit, the second polarization direction drive arm of the modulator is connected to the second signal generation circuit, and the input terminal of the modulator is connected to the optical carrier generator, for modulating the first analog signal and the second analog signal onto the first polarization direction and the second polarization direction of the optical carrier, respectively, to generate a polarization multiplexed overlapping single-sideband vector signal, and sending it to the optical wireless conversion circuit; The polarization multiplexed overlapping single-sideband vector signal includes a first overlapping single-sideband vector signal in a first polarization direction and a second overlapping single-sideband vector signal in a second polarization direction. The first overlapping single-sideband vector signal carries the first microwave vector signal and the second microwave vector signal carried by the first analog signal, and the second overlapping single-sideband vector signal carries the third microwave vector signal and the fourth microwave vector signal carried by the second analog signal.

2. The optical signal transmitter according to claim 1, characterized in that, The first analog signal includes a first sub-analog signal and a second sub-analog signal, and the first signal generation circuit includes: A first microwave vector signal generator is used to generate the first microwave vector signal; A second microwave vector signal generator is used to generate the second microwave vector signal; A first Hilbert converter is connected to the first microwave vector signal generator and the second microwave vector signal generator, and is used to perform a Hilbert transformation on the sum of the first microwave vector signal and the second microwave vector signal to generate a first transformed vector signal; A first digital-to-analog converter is connected to the first microwave vector signal generator and the second microwave vector signal generator, and is used to perform digital-to-analog conversion on the sum of the first microwave vector signal and the second microwave vector signal to generate the first sub-analog signal; The second digital-to-analog converter, connected to the first Hilbert converter, is used to perform digital-to-analog conversion on the first transformed vector signal to generate the second sub-analog signal.

3. The optical signal transmitter according to claim 2, characterized in that, The modulator's first polarization direction drive arm includes a first upper drive arm and a first lower drive arm; the first upper drive arm is connected to the first digital-to-analog converter, and the first lower drive arm is connected to the second digital-to-analog converter to generate the first overlapping single-sideband vector signal.

4. The optical signal transmitter according to claim 1, characterized in that, The second analog signal includes a third sub-analog signal and a fourth sub-analog signal, and the second signal generation circuit includes: A third microwave vector signal generator is used to generate the third microwave vector signal; A fourth microwave vector signal generator is used to generate the fourth microwave vector signal; The second Hilbert transformer is connected to the third microwave vector signal generator and the fourth microwave vector signal generator, and is used to perform a Hilbert transformation on the sum of the third microwave vector signal and the fourth microwave vector signal to generate a second transformed vector signal; The third digital-to-analog converter is connected to the third microwave vector signal generator and the fourth microwave vector signal generator, and is used to perform digital-to-analog conversion on the sum of the third microwave vector signal and the fourth microwave vector signal to generate the third sub-analog signal; A fourth digital-to-analog converter, connected to the second Hilbert converter, is used to perform digital-to-analog conversion on the second transformed vector signal to generate the fourth sub-analog signal.

5. The optical signal transmitter according to claim 4, characterized in that, The modulator's second polarization direction drive arm includes a second upper drive arm and a second lower drive arm; the second upper drive arm is connected to the third digital-to-analog converter, and the second lower drive arm is connected to the fourth digital-to-analog converter to generate the second overlapping single-sideband vector signal.

6. A light-to-wireless conversion circuit, characterized in that, The optical-to-wireless conversion circuit includes: A first optical polarization beamsplitter, connected to an optical signal transmitter, is used to receive a polarization-multiplexed overlapping single-sideband vector signal transmitted by the optical signal transmitter, and to perform polarization beam splitting on the polarization-multiplexed overlapping single-sideband vector signal to obtain a first overlapping single-sideband vector signal and a second overlapping single-sideband vector signal; wherein, the first overlapping single-sideband vector signal is the signal in the first polarization direction of the polarization-multiplexed overlapping single-sideband vector signal, carrying a first microwave vector signal and a second microwave vector signal, and the second overlapping single-sideband vector signal is the signal in the second polarization direction of the polarization-multiplexed overlapping single-sideband vector signal, carrying a third microwave vector signal and a fourth microwave vector signal; Local oscillator light generator, used to emit local oscillator light; The second optical polarization beam splitter is connected to the local oscillator generator and is used to polarize and split the local oscillator light to obtain the first local oscillator light in the first polarization direction and the second local oscillator light in the second polarization direction. A first optical coupler is connected to the first optical polarization beamsplitter and the second optical polarization beamsplitter, and is used to couple the first overlapping single-sideband vector signal and the first local oscillator light to obtain a first coupled signal; The second optical coupler is connected to the first optical polarization beamsplitter and the second optical polarization beamsplitter, and is used to couple the second overlapping single-sideband vector signal and the second local oscillator light to obtain a second coupled signal; A first photodetector, connected to the first optical coupler, is used to convert the first coupled signal into a first millimeter-wave terahertz signal, wherein the first millimeter-wave terahertz signal carries the first microwave vector signal and the second microwave vector signal carried by the first overlapping single-sideband vector signal; The second photodetector, connected to the second optical coupler, is used to convert the second coupled signal into a second millimeter-wave terahertz signal, the second millimeter-wave terahertz signal carrying the third microwave vector signal and the fourth microwave vector signal carried by the second overlapping single-sideband vector signal.

7. A millimeter-wave terahertz signal transmitting device, characterized in that, The device includes an optical signal transmitter as described in any one of claims 1 to 5 and an optical-to-wireless conversion circuit as described in claim 6, wherein the optical signal transmitter is connected to the optical-to-wireless conversion circuit.

8. A communication system, characterized in that, The system includes the millimeter-wave terahertz signal transmitting device and the wireless receiving device as described in claim 7, wherein the millimeter-wave terahertz signal transmitting device is connected to the wireless receiving device; The wireless receiving device is used to receive the first millimeter-wave terahertz signal and the second millimeter-wave terahertz signal transmitted by the millimeter-wave terahertz signal transmitting device.

9. The system according to claim 8, characterized in that, The wireless receiving device includes: A wireless receiving circuit, connected to the millimeter-wave terahertz signal transmitting device, is used to receive the first millimeter-wave terahertz signal and the second millimeter-wave terahertz signal, and process the first millimeter-wave terahertz signal and the second millimeter-wave terahertz signal to generate a first digital signal and a second digital signal. A signal processing circuit, connected to the wireless receiving circuit, is used to process the first digital signal to obtain the first microwave vector signal and the second microwave vector signal; and to process the second digital signal to obtain the third microwave vector signal and the fourth microwave vector signal.

10. The system according to claim 9, characterized in that, The wireless receiving circuit includes: The first envelope detector is connected to the millimeter-wave terahertz signal transmitting device to receive the first millimeter-wave terahertz signal and down-convert the first millimeter-wave terahertz signal based on the direct detection method of envelope detection to obtain the down-converted first intermediate frequency signal. The second envelope detector is connected to the millimeter-wave terahertz signal transmitting device and is used to receive the second millimeter-wave terahertz signal and down-convert the second millimeter-wave terahertz signal based on the direct detection method of envelope detection to obtain the down-converted second intermediate frequency signal. A first analog-to-digital converter, connected to the first envelope detector, is used to perform analog-to-digital conversion on the first intermediate frequency signal to obtain the first digital signal; The second analog-to-digital converter, connected to the second envelope detector, is used to perform analog-to-digital conversion on the second intermediate frequency signal to obtain the second digital signal.

11. The system according to claim 9 or 10, characterized in that, The signal processing circuit includes: A crosstalk cancellation circuit, connected to the wireless receiving circuit, is used to perform crosstalk cancellation processing on the first digital signal and the second digital signal to obtain a first crosstalk-free signal and a second crosstalk-free signal. The first constellation point separation circuit is connected to the first output terminal of the crosstalk elimination circuit and is used to perform constellation point demodulation processing on the first crosstalk-free signal to obtain the first microwave vector signal and the second microwave vector signal. The second constellation point separation circuit is connected to the second output terminal of the crosstalk elimination circuit and is used to perform constellation point demodulation processing on the second crosstalk-free signal to obtain the third microwave vector signal and the fourth microwave vector signal.

12. The system according to claim 11, characterized in that, The crosstalk cancellation circuit includes: A signal resampling circuit, connected to the wireless receiving circuit, is used to resample the first digital signal and the second digital signal to obtain a first resampled signal and a second resampled signal. A signal reconstruction circuit, connected to the signal resampling circuit, is used to reconstruct the first resampled signal and the second resampled signal to obtain a first reconstructed signal and a second reconstructed signal. The third Hilbert transformer is connected to the signal reconstruction circuit and is used to perform Hilbert transformation on the first reconstructed signal and the second reconstructed signal respectively to obtain the third transformed vector signal and the fourth transformed vector signal. A polarization demultiplexing circuit, connected to the signal reconstruction circuit and the third Hilbert converter, is used to perform polarization crosstalk compensation processing on the first reconstructed signal and the third transformed vector signal to obtain a first polarization demultiplexed signal, and to perform polarization crosstalk compensation processing on the second reconstructed signal and the fourth transformed vector signal to obtain a second polarization demultiplexed signal. A channel equalization circuit, connected to the polarization demultiplexing circuit, is used to perform channel equalization processing on the first polarization demultiplexed signal and the second polarization demultiplexed signal to obtain the first crosstalk-free signal and the second crosstalk-free signal.

13. A method for transmitting optical signals, characterized in that, Applied to an optical signal transmitter, the method includes: The first signal generation circuit in the optical signal transmitter generates a first analog signal carrying a first microwave vector signal and a second microwave vector signal, and inputs it to the drive arm of the modulator in the first polarization direction in the optical signal transmitter. The second signal generation circuit in the optical signal transmitter generates a second analog signal carrying a third microwave vector signal and a fourth microwave vector signal, and inputs it to the drive arm of the second polarization direction of the modulator. The optical carrier generator in the optical signal transmitter transmits an optical carrier and inputs it to the input terminal of the modulator, so that the modulator modulates the first analog signal and the second analog signal onto the first polarization direction and the second polarization direction of the optical carrier, respectively, to generate a polarization multiplexed overlapping single-sideband vector signal; The polarization multiplexed overlapping single-sideband vector signal includes a first overlapping single-sideband vector signal in a first polarization direction and a second overlapping single-sideband vector signal in a second polarization direction. The first overlapping single-sideband vector signal carries the first microwave vector signal and the second microwave vector signal carried by the first analog signal, and the second overlapping single-sideband vector signal carries the third microwave vector signal and the fourth microwave vector signal carried by the second analog signal.

14. A communication method, characterized in that, The method is applied to a communication system, which includes an optical signal transmitter, an optical-to-wireless conversion circuit, and a wireless receiving device. The optical signal transmitter generates a polarization multiplexed overlapping single-sideband vector signal and sends it to the optical wireless conversion circuit. The polarization multiplexed overlapping single-sideband vector signal includes a first overlapping single-sideband vector signal in a first polarization direction and a second overlapping single-sideband vector signal in a second polarization direction. The first overlapping single-sideband vector signal carries a first microwave vector signal and a second microwave vector signal, and the second overlapping single-sideband vector signal carries a third microwave vector signal and a fourth microwave vector signal. The optical wireless conversion circuit converts the polarization multiplexed overlapping single-sideband vector signal into a first millimeter-wave terahertz signal and a second millimeter-wave terahertz signal, and sends them to the wireless receiving device. The first millimeter-wave terahertz signal carries the first microwave vector signal and the second microwave vector signal carried by the first overlapping single-sideband vector signal, and the second millimeter-wave terahertz signal carries the third microwave vector signal and the fourth microwave vector signal carried by the second overlapping single-sideband vector signal. The wireless receiving device processes the first millimeter-wave terahertz signal and the second millimeter-wave terahertz signal to obtain the first microwave vector signal, the second microwave vector signal, the third microwave vector signal, and the fourth microwave vector signal.

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