A wireless communication system and method

Abstract

The present invention discloses a wireless communication system and method. The system includes: a coherent optical transmitter is connected to an optical-terahertz conversion module through an optical fiber link, and the optical-terahertz conversion module is connected to a coherent terahertz receiver through a wireless link; the coherent optical transmitter is used to select two comb teeth of a first frequency interval from an optical frequency comb, and perform signal modulation on one of the comb teeth to obtain a corresponding optical signal; the optical-terahertz conversion module is used to perform photoelectric detection on the optical signal, convert it to obtain a corresponding terahertz signal, and transmit the terahertz signal to a coherent terahertz receiver through a wireless link; the coherent terahertz receiver is used to generate a terahertz local oscillator signal based on the optical frequency comb, and coherently receive the terahertz signal based on the terahertz local oscillator signal using a terahertz fundamental wave mixing method. The present invention effectively solves the problem that the phase noise of the output signal in the traditional terahertz harmonic mixing scheme is dominated by the background noise and multiplier noise of the radio frequency source.

Description

Technical Field

[0001] The present invention relates to the field of communication technology, and in particular to a wireless communication system and method. Background Art

[0002] The terahertz band has abundant spectrum resources and can support communication rates of over 100 Gigabits or even terabits per second. It has been recognized as one of the key enabling technologies for the next generation of communication networks. Terahertz communication systems include two typical technical routes: pure solid-state electronics and optoelectronics. Among them, the pure solid-state electronics route can generate terahertz waves with power up to milliwatts, but its application is limited by local oscillator leakage, frequency doubling noise, terahertz frequency coordination, modulation bandwidth and transmission capacity. Although the optoelectronics combined technical route has a small transmission power, its high tunability, ultra-wideband modulation and large-capacity transmission capabilities, and easy integration with commercial mature optical networks have attracted widespread attention. However, in existing photon-assisted terahertz wireless communication systems, independent lasers are usually used as light sources, facing the following two problems:

[0003] First, the generated terahertz frequency has large jitter and poor frequency stability, which cannot support some application scenarios that require high-stability and high-purity terahertz (such as terahertz communication, perception, detection, and radar imaging). Second, the generated terahertz phase noise is large, which not only reduces the terahertz front-end transmission signal-to-noise ratio, but also increases the power consumption and complexity of the digital signal processing (DSP) at the receiving end (relying on complex carrier phase recovery algorithms to compensate for frequency offset jitter and phase noise).

[0004] In the traditional terahertz harmonic mixing scheme that uses an optical frequency comb to generate a highly stable and low phase noise terahertz signal, the down-conversion at the receiving end still uses the traditional harmonic mixing method, which causes the phase noise of the output intermediate frequency signal to be dominated by the background noise of the RF source and the frequency multiplication noise of the frequency multiplication chain, and fails to reflect and fully utilize the low phase noise characteristics of the optical frequency comb. Summary of the invention

[0005] The present invention provides a wireless communication system and method, which effectively solves the problem that the phase noise of the output signal in the traditional terahertz harmonic mixing scheme is dominated by the background noise and multiplier noise of the radio frequency source.

[0006] According to one aspect of the present invention, there is provided a wireless communication system, comprising: a coherent optical transmitter, an optical-terahertz conversion module and a coherent terahertz receiver; wherein the coherent optical transmitter is connected to the optical-terahertz conversion module via an optical fiber link, and the optical-terahertz conversion module is connected to the coherent terahertz receiver via a wireless link;

[0007] The coherent optical transmitter is used to select two comb teeth of a first frequency interval from the optical frequency comb, and perform signal modulation on one of the comb teeth to obtain a corresponding optical signal, and transmit the optical signal to the optical-terahertz conversion module through the optical fiber link;

[0008] The optical-terahertz conversion module is used to perform photoelectric detection on the optical signal, convert it into a corresponding terahertz signal, and transmit the terahertz signal to the coherent terahertz receiver through the wireless link;

[0009] The coherent terahertz receiver is used to generate a terahertz local oscillator signal based on an optical frequency comb, and to coherently receive the terahertz signal based on the terahertz local oscillator signal by using a terahertz fundamental wave mixing method.

[0010] According to another aspect of the present invention, a wireless communication method is provided, which is applied to any of the wireless communication systems described above; wherein the wireless communication system comprises: a coherent optical transmitter, an optical-terahertz conversion module and a coherent terahertz receiver; the wireless communication method comprises:

[0011] Selecting two comb teeth of a first frequency interval from the optical frequency comb by the coherent optical transmitter, performing signal modulation on one of the comb teeth to obtain a corresponding optical signal, and transmitting the optical signal to the optical-terahertz conversion module through an optical fiber link;

[0012] Performing photoelectric detection on the optical signal through the optical-terahertz conversion module to convert it into a corresponding terahertz signal, and transmitting the terahertz signal to the coherent terahertz receiver through the wireless link;

[0013] The coherent terahertz receiver generates a terahertz local oscillator signal based on an optical frequency comb, and coherently receives the terahertz signal based on the terahertz local oscillator signal by adopting a terahertz fundamental wave mixing method.

[0014] The technical solution of the present invention effectively avoids the problem of beat frequency crosstalk between signals caused by the dual-comb tooth simultaneous modulation scheme by selecting two comb teeth with a frequency interval from the optical frequency comb at the transmitting end and performing signal modulation on one of the comb teeth; at the same time, by generating a terahertz signal with high stability and low phase noise based on the optical frequency comb at the transmitting end, and generating a terahertz local oscillator signal with the same high stability and low phase noise based on the optical frequency comb at the receiving end, and using a terahertz fundamental wave mixing method to complete the down-conversion of the signal, the output intermediate frequency signal maintains the low phase noise characteristics of the optical frequency comb, thereby effectively solving the problem that the phase noise of the output signal in the traditional terahertz harmonic mixing scheme is dominated by the background noise and multiplier noise of the radio frequency source, thereby effectively improving the transmission signal-to-noise ratio of the terahertz signal in the coherent terahertz communication system.

[0015] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0017] Figure 1 is a structural block diagram of a wireless communication system provided by an embodiment of the present invention;

[0018] Figure 2 is a structural diagram of a coherent optical transmitter provided by an embodiment of the present invention;

[0019] Figure 3 is a structural block diagram of a coherent terahertz receiver provided by an embodiment of the present invention;

[0020] Figure 4 is a structural block diagram of a terahertz local oscillator generator provided by an embodiment of the present invention;

[0021] Figure 5 It is a flowchart of an algorithm implementation of a simplified coherent DSP module provided by an embodiment of the present invention;

[0022] Figure 6 is a structural block diagram of a light-to-terahertz conversion module provided by an embodiment of the present invention;

[0023] Figure 7 It is a schematic diagram of an implementation of an integrated, low-noise Kerr soliton optical frequency comb provided by an embodiment of the present invention;

[0024] Figure 8 It is a physical schematic diagram of a high-Q fiber microcavity in a low-noise Kerr soliton optical frequency comb module provided by an embodiment of the present invention;

[0025] Fig. 9 It is a test schematic diagram of a test Q value of a high-Q fiber microcavity in a low-noise Kerr soliton optical frequency comb module provided by an embodiment of the present invention;

[0026] Fig.10 is a schematic diagram of a spectrum output with different repetition frequencies provided by an embodiment of the present invention;

[0027] Fig.11 It is a schematic diagram of a phase noise curve of an intermediate frequency signal measured when a transmitting end is not loaded with data, provided by an embodiment of the present invention;

[0028] Fig.12 It is a schematic diagram of a bit error rate and input UTC-PD optical power variation curve of three different modulation formats at a 23 Gbaud baud rate provided by an embodiment of the present invention;

[0029] Fig.13 It is a flow chart of a wireless communication method provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0031] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0032] In one embodiment, Figure 1 is a block diagram of a wireless communication system provided by an embodiment of the present invention. This embodiment is applicable to coherent terahertz wireless communication with integrated dual optical frequency combs. The wireless communication system can be implemented in the form of hardware and / or software. Figure 1 As shown, the wireless communication system includes: a coherent optical transmitter 10, an optical-terahertz conversion module 30 and a coherent terahertz receiver 50; wherein the coherent optical transmitter 10 is connected to the optical-terahertz conversion module 30 via an optical fiber link 20, and the optical-terahertz conversion module 30 is connected to the coherent terahertz receiver 50 via a wireless link 40;

[0033] The coherent optical transmitter 10 is used to select two comb teeth of a first frequency interval from the optical frequency comb, and perform signal modulation on one of the comb teeth to obtain a corresponding optical signal, and transmit the optical signal to the optical-terahertz conversion module 30 through the optical fiber link 20;

[0034] The optical-terahertz conversion module 30 is used to perform photoelectric detection on the optical signal, convert it into a corresponding terahertz signal, and transmit the terahertz signal to the coherent terahertz receiver 50 via the wireless link 40;

[0035] The coherent terahertz receiver 50 is used to generate a terahertz local oscillator signal based on an optical frequency comb, and coherently receive the terahertz signal by using a terahertz fundamental wave mixing method based on the terahertz local oscillator signal.

[0036] Among them, the coherent optical transmitter 10 and the coherent terahertz receiver 50 are both based on an optical frequency comb. The coherent optical transmitter 10 based on an optical frequency comb is used to select a pair of two comb teeth with a first frequency interval from a low-noise optical frequency comb. If the power difference between the two comb teeth with the first frequency interval is large, the comb tooth with larger power among the two comb teeth is modulated to ensure that the signal-to-noise ratio of the comb tooth is relatively large after signal modulation, thereby ensuring communication performance; the optical fiber link 20 is used to realize the long-distance transmission of the optical signal; the optical-terahertz conversion module 30 is used to detect the optical signal and realize the conversion of the optical signal to the terahertz signal; the wireless link 40 is used for the wireless transmission of the above-mentioned terahertz signal; the coherent terahertz receiver 50 based on the optical frequency comb is used to generate a low-phase-noise terahertz local oscillator signal based on the optical frequency comb, and complete the coherent reception of the above-mentioned terahertz signal by using the terahertz fundamental wave mixing method. Among them, the low-noise optical frequency comb can be understood as having a phase noise of close to -100dBc / Hz and a floor noise of less than -120dBc / Hz at an offset frequency of 10KHz.

[0037] The technical solution of this embodiment effectively avoids the problem of beat frequency crosstalk between signals caused by the dual-comb tooth simultaneous modulation scheme by selecting two comb teeth with a frequency interval from the optical frequency comb at the transmitting end and performing signal modulation on one of the comb teeth; at the same time, by generating a terahertz signal with high stability and low phase noise based on the optical frequency comb at the transmitting end, and generating a terahertz local oscillator signal with the same high stability and low phase noise based on the optical frequency comb at the receiving end, and using a terahertz fundamental wave mixing method to complete the signal down-conversion, the output intermediate frequency signal maintains the low phase noise characteristics of the optical frequency comb, thereby effectively solving the problem that the phase noise of the output signal in the traditional terahertz harmonic mixing scheme is dominated by the background noise and multiplier noise of the RF source, thereby effectively improving the transmission signal-to-noise ratio of the terahertz signal in the coherent terahertz communication system.

[0038] In one embodiment, Figure 2 is a structural diagram of a coherent optical transmitter provided by an embodiment of the present invention. This embodiment further illustrates the structure of the coherent optical transmitter based on the above embodiment. Figure 2As shown, the coherent optical transmitter 10 includes: a first optical frequency comb 101, a first optical amplifier 102, a first optical filter 103, an electro-optical modulator 104, a polarization controller 105 and an optical coupler 106; wherein the first optical frequency comb 101 is connected to the input end of the first optical amplifier 102, and the output end of the first optical amplifier 102 is connected to the input end of the first optical filter 103, the output end of the first optical filter 103 is respectively connected to the input end of the electro-optical modulator 104 and the input end of the polarization controller 105, and the output end of the electro-optical modulator 104 and the output end of the polarization controller 105 are both connected to the optical coupler 106;

[0039] The first optical frequency comb 101 is used to generate a light wave having a first repetition frequency and comprising at least two coherent comb teeth, and input the light wave into the first optical amplifier 102;

[0040] The first optical amplifier 102 is used to amplify the optical power of the optical wave and input the amplified optical wave to the first optical filter 103;

[0041] The first optical filter 103 is used to filter out a first comb tooth and a second comb tooth of a first frequency interval from at least two coherent comb teeth according to the terahertz communication frequency;

[0042] The electro-optic modulator 104 is used to load the first comb teeth with data to be transmitted;

[0043] The polarization controller 105 is used to adjust the polarization state of the second comb teeth until the second comb teeth are aligned with the polarization of the loaded first comb teeth;

[0044] The optical coupler 106 is used to combine the optical wave signals corresponding to the first comb teeth and the second comb teeth to obtain corresponding optical signals.

[0045] Among them, the power of the first comb tooth is greater than the power of the second comb tooth, that is, the signal modulation is performed on the first comb tooth with larger power among the first comb tooth and the second comb tooth. Of course, in the actual operation process, if the power difference between the first comb tooth and the second comb tooth is small, the second comb tooth can also be loaded with the data to be transmitted, and the polarization state of the first comb tooth can be adjusted. The process of loading data on the first comb tooth can be understood as the process of modulating the data to be transmitted by the coherent optical transmitter on the first comb tooth; the polarization state of the second comb tooth is adjusted to be aligned with the polarization of the loaded first comb tooth through the polarization controller 105, that is, the first comb tooth and the second comb tooth are ensured to be the same square, so as to avoid the first comb tooth and the second comb tooth from being orthogonal, thereby maximizing the terahertz power. The optical wave signal corresponding to the first comb tooth and the optical wave signal corresponding to the second comb tooth are coupled together by the optical coupler 106, that is, converted into one light wave to obtain the corresponding optical signal. In the embodiment, the structure of the coherent optical transmitter 10 based on the optical frequency comb is as follows Figure 2As shown, the first optical frequency comb 101 generates a light wave with a first repetition frequency of f1 and a plurality of coherent comb teeth (the spectrum is shown in FIG. Figure 2 As shown in (i) in FIG. 1 ), the light wave is amplified by the first optical amplifier 102 and then sent to the first optical filter 103 for wavelength selection. The first filter 103 filters out the first frequency interval f according to the required terahertz communication frequency. THz1 = two teeth of mf1 (m is a positive integer), such as Figure 2 As shown in (ii) and (iii) in . It should be noted that when m = 1, the first optical frequency comb 101 is a terahertz repetition frequency optical frequency comb. The actual value of m is limited by the number of comb teeth, comb tooth interval (i.e., repetition frequency), flatness, and comb tooth power of the optical frequency comb, and is generally not more than 10. For example, f1=283GHz, m=1. Subsequently, data is loaded on the first comb tooth in the electro-optic modulator 104, and the polarization state of the second comb tooth is adjusted through the polarization controller 105 to align it with the polarization of the first comb tooth after data loading. Finally, the two are combined through the optical coupler 106 to produce the following. Figure 2 The combined optical signal shown in (iv).

[0046] After being transmitted through the optical fiber link, the combined optical signal is sent to the optical-terahertz conversion module 30, which converts the combined optical signal into a target terahertz signal, and finally transmits it to free space through the transmitting antenna for wireless communication. Since the designed optical frequency comb teeth have strong coherence, the terahertz signal emitted by the optical-terahertz conversion module 30 has high frequency stability and low phase noise characteristics.

[0047] It should be emphasized that conventional coherent terahertz receivers usually use a terahertz harmonic mixing scheme for down-conversion. This scheme first generates a high-frequency local oscillator signal through an RF source and a multi-frequency link, and then uses a terahertz harmonic mixer to achieve down-conversion of the target terahertz signal. However, on the one hand, the RF source is not only bulky and difficult to integrate, but also has an inherent background noise (this noise is usually higher than the phase noise of the terahertz signal generated by the optical frequency comb designed in the present invention); on the other hand, the frequency multiplication link will further deteriorate the system noise level by 20logN (N represents the multiplication factor), resulting in the intermediate frequency signal output after down-conversion by the terahertz harmonic mixing scheme to carry a large phase noise. In this case, even if the transmitter uses an optical frequency comb to generate a terahertz signal with high stability and low phase noise, the intermediate frequency signal output after down-conversion at the receiver will lose the above characteristics. To address this problem, the present invention proposes a coherent terahertz receiving scheme based on an optical frequency comb, which generates a terahertz local oscillator signal with high stability and low phase noise (the phase noise level is equivalent to that of the received terahertz signal) through the optical frequency comb, and outputs an intermediate frequency signal with the same high stability and low phase noise characteristics based on the terahertz fundamental wave mixing scheme. This process will not introduce additional frequency doubling noise.

[0048] In one embodiment, Figure 3 is a structural block diagram of a coherent terahertz receiver provided by an embodiment of the present invention. Figure 3 As shown, the coherent terahertz receiver 50 includes: a receiving antenna 501, a terahertz fundamental wave mixer 502, a terahertz local oscillator generator 503 based on an optical frequency comb, a terahertz amplifier 504, an electrical amplifier 505, an analog-to-digital converter 506 and a coherent DSP module 507; wherein the terahertz local oscillator generator 503 is connected to the input end of the terahertz amplifier 504, the output end of the terahertz amplifier 504 and the receiving antenna 501 are connected to the input end of the terahertz fundamental wave mixer 502, the output end of the terahertz fundamental wave mixer 502 is connected to the electrical amplifier 505, the output end of the electrical amplifier 505 is connected to the input end of the analog-to-digital converter 506, and the output end of the analog-to-digital converter 506 is connected to the coherent DSP module 507;

[0049] Wherein, the receiving antenna 501 is used to receive the terahertz signal transmitted by the wireless link;

[0050] The terahertz local oscillator generator 503 is used to generate a terahertz local oscillator signal;

[0051] The terahertz amplifier 504 is used to amplify the power of the terahertz local oscillator signal;

[0052] The terahertz fundamental wave mixer 502 is used to down-convert the terahertz signal and the power-amplified terahertz local oscillator signal, and output a corresponding intermediate frequency signal;

[0053] The electric amplifier 505 is used to amplify the power of the intermediate frequency signal;

[0054] The analog-to-digital converter 506 is used to convert the power-amplified intermediate frequency signal into a corresponding digital signal;

[0055] The coherent DSP module 507 is used to demodulate the digital signal.

[0056] In one embodiment, Figure 4 is a structural block diagram of a terahertz local oscillator generator provided by an embodiment of the present invention. Figure 4 As shown, the terahertz local oscillator generator 503 includes: a second optical frequency comb 5031, a second optical filter 5032, a second optical amplifier 5033 and a first photodetector 5034; wherein the second optical frequency comb 5031 is connected to the input end of the second optical filter 5032, the output end of the second optical filter 5032 is connected to the input end of the second optical amplifier 5033, and the output end of the second optical amplifier 5033 is connected to the first photodetector 5034;

[0057] The second optical frequency comb 5031 is used to generate a light wave having a second repetition frequency and comprising at least two coherent comb teeth, and input the light wave into the second optical filter 5032;

[0058] The second optical filter 5032 is used to filter out the third comb teeth and the fourth comb teeth of the second frequency interval from at least two coherent comb teeth according to the terahertz communication frequency, and input the third comb teeth and the fourth comb teeth to the second optical amplifier 5033;

[0059] The second optical amplifier 5033 is used to amplify the power of the third comb teeth and the fourth comb teeth, and input the amplified third comb teeth and the fourth comb teeth to the first photodetector 5034;

[0060] The first photodetector 5034 is used to beat the amplified third comb teeth and fourth comb teeth to generate corresponding terahertz local oscillation signals.

[0061] In one example, the signal frequency of the intermediate frequency signal is the absolute value of the difference between the first repetition frequency and the second repetition frequency; wherein the first repetition frequency and the second repetition frequency are not equal. The second optical frequency comb 5031 generates a light wave with a second repetition frequency of f2 and a plurality of coherent comb teeth, and then filters out a light wave with a second frequency interval of f2 through the second optical filter 5032. THz2 = nf2 (n is a positive integer, and f THz2 ≠ f THz1 ) are amplified by the second optical amplifier 5033, and then sent to the photodetector 5034 for beat frequency generation of the required terahertz local oscillator. Figure 4 As shown in (iii). Similar to the first optical frequency comb 101, the actual value of n here is also limited by the number of comb teeth, comb tooth interval (i.e., repetition frequency), flatness, and comb tooth power of the optical frequency comb, and is generally not more than 10. For example, f2=303GHz, n=1. The terahertz local oscillator signal is then amplified by the terahertz amplifier 504 to drive the terahertz fundamental mixer 502 to complete down-conversion, and the signal frequency of the output intermediate frequency signal is f IF = |f THz1 -f THz2 |. The intermediate frequency signal inherits the high frequency stability and low phase noise characteristics of the terahertz signal at the transmitting end and the terahertz local oscillator at the receiving end, and the actual phase noise is the sum of the phase noises of the two. Subsequently, the intermediate frequency signal is amplified by the electrical amplifier 505, converted into a digital signal by the analog-to-digital converter 506, and the subsequent signal demodulation is completed in the simplified coherent DSP module 507.

[0062] In one embodiment, the first optical filter may be a pulse shaping filter. The signal frequency f of the intermediate frequency signal IF> (1 + β) BW; where BW represents the baud rate of the loaded data to be transmitted, and β is the roll-off factor of the pulse shaping filter in the coherent optical transmitter.

[0063] In one embodiment, Figure 5 FIG. 1 is a flowchart of an algorithm implementation of a simplified coherent DSP module provided by an embodiment of the present invention. Figure 5 As shown in FIG. 5 , the simplified coherent DSP module includes the following six modules: down-conversion 5071, resampling 5072, frame synchronization & clock recovery 5073, matched filtering 5074, channel equalization 5075, and bit error rate calculation 5076. It should be noted that for the traditional photon-assisted terahertz wireless communication system based on an independent laser at the transmitting end or a terahertz harmonic mixing scheme at the receiving end, since the intermediate frequency signal obtained carries a large frequency offset jitter and phase noise, the algorithm carrier phase recovery operation (including frequency offset estimation and phase noise compensation algorithm) of the traditional coherent DSP module is indispensable. However, on the one hand, the algorithm consumes resources and increases the cost and power consumption of the terminal; on the other hand, the phase noise varies with the communication rate and the optical fiber transmission distance, and the relevant parameters of the compensation algorithm also need to be adjusted accordingly, which seriously reduces the universality of the receiving DSP module. In the present invention, benefiting from the coherence of the optical frequency comb and the adopted terahertz fundamental wave mixing scheme, the intermediate frequency signal after down-conversion inherits the characteristics of high frequency stability and low phase noise. Therefore, the receiving end can realize signal demodulation by using a simplified coherent DSP module without any carrier phase recovery processing, which not only simplifies the complexity of the DSP module, reduces the cost and power consumption, but also improves the robustness and adaptability of the receiving DSP module.

[0064] In one embodiment, Figure 6 is a structural block diagram of a light-to-terahertz conversion module provided by an embodiment of the present invention. Figure 6 As shown, the optical-terahertz conversion module 30 includes: a third optical amplifier 301, a second photodetector 302 and a transmitting antenna 303; wherein the output end of the third optical amplifier 301 is connected to the input end of the second photodetector 302, and the output end of the second photodetector 302 is connected to the transmitting antenna 303;

[0065] The third optical amplifier 301 is used to amplify the power of the optical signal and input the amplified optical signal to the second photodetector 302;

[0066] The second photodetector 302 is used to convert the amplified optical signal into a terahertz signal;

[0067] The transmitting antenna 303 is used to transmit the terahertz signal to free space for wireless communication.

[0068] like Figure 6As shown, in the optical-terahertz conversion module 30, the combined optical signal is first amplified by the third optical amplifier 301, and then converted into a target terahertz signal (the spectrum is shown in the inset) by the second photodetector 302, and finally the terahertz signal is transmitted to the free space for wireless communication by the transmitting antenna 303. Since the teeth of the optical frequency comb have strong coherence, the terahertz signal emitted by the optical-terahertz conversion module 30 has high frequency stability and low phase noise characteristics.

[0069] In one embodiment, the coherent optical transmitter and the coherent terahertz receiver use an integrated Kerr soliton optical frequency comb module; wherein the Kerr soliton optical frequency comb module includes: a distributed feedback laser (DFB) and an optical fiber microcavity; wherein the distributed feedback laser and the optical fiber microcavity establish communication through a spatial optical connection;

[0070] Distributed feedback lasers are used for direct diode pumping under limited pump power;

[0071] A few-mode fiber microcavity transmitting two constant modes is used to fabricate a few-mode fiber Fabry-Perot resonator (FFPR) as the corresponding fiber microcavity.

[0072] The distributed feedback laser can be referred to as a DFB laser, and the fiber microcavity can be referred to as a FFPR. In actual operation, the DFB laser and the FFPR can establish communication through a wireless connection via a spatial optical connection.

[0073] In one embodiment, the noise limit of the microcavity light comb generated by the fiber microcavity is inversely proportional to the square of the quality factor value of the fiber microcavity.

[0074] In one embodiment, when the offset frequency is much smaller than the half-width at half-height of the resonant cavity, the relationship between the microcavity light comb noise limit and the quality factor Q value of the optical fiber microcavity includes:

[0075]

[0076] Among them, π is the ratio of the circumference of a circle, is Planck's constant, c is the speed of light in vacuum, λ is the wavelength of the pump light in the microcavity optical comb, D is the dimensionless dispersion coefficient, f is the offset frequency, κ is the pump light power and the microcavity parameter threshold power P th The ratio of Q is the quality factor of the fiber microcavity. The half-width at half maximum can be understood as the difference between the frequencies of the two light wavelengths at half the position of the peak power of the resonant spectrum line output, that is, the 3dB bandwidth of the output spectrum. The half-width at half maximum corresponds to half the full-width at half maximum. The narrower the half-width at half maximum, the higher the quality factor Q of the resonant cavity.

[0077] Phase noise is inversely proportional to the square of Q, so the preparation of a high-Q microcavity is a prerequisite for the generation of a low-noise optical frequency comb. In the design of the present invention, both the coherent optical transmitter 10 based on an optical frequency comb and the coherent terahertz receiver 50 based on an optical frequency comb use an integrated, low-noise Kerr soliton optical frequency comb module, which mainly includes devices such as a DFB laser and a high-Q fiber microcavity. Figure 7 It is a schematic diagram of an implementation of an integrated, low-noise Kerr soliton optical frequency comb provided by an embodiment of the present invention; Figure 8 It is a physical schematic diagram of a high-Q fiber microcavity in a low-noise Kerr soliton optical frequency comb module provided by an embodiment of the present invention; Fig. 9 1 is a schematic diagram of testing the Q value of a high-Q fiber microcavity in a low-noise Kerr soliton optical frequency comb module provided by an embodiment of the present invention. The specific implementation scheme of the integrated, low-noise Kerr soliton optical frequency comb module is as follows: Figure 7 As shown, there are three steps:

[0078] S701. Under limited pump power, a 100mW commercially available on-chip single-mode distributed feedback laser (DFB) is used for direct diode pumping to achieve miniaturized and integrated packaging of Kerr soliton combs.

[0079] S702. A few-mode fiber Fabry-Perot resonator (FFPR) is made using a few-mode fiber microcavity that can only transmit two transverse modes. On the one hand, it can ensure the fundamental mode parametric oscillation and avoid the mode cross-effect; on the other hand, the larger fundamental mode field area of ​​the few-mode fiber reduces the noise floor of the terahertz wave.

[0080] S703, using sub-nanometer fine mechanical polishing and high-quality dielectric coating technology to precisely forge FFPR (its structure is as follows Figure 8 As shown in the figure, its Q value is as high as 6.0 × 10 8 The above (experimental test results of microcavity Q value are as follows Fig. 9 As shown in the figure, the miniaturized and integrated Kerr soliton comb has the characteristics of low noise limit.

[0081] Through methods such as gluing and optical path alignment, the volume of the entire optical frequency comb module after final packaging is 85mm (length) × 90mm (width) × 25mm (height).

[0082] In the embodiment, the use of a low-noise Kerr soliton optical frequency comb module replaces the traditional bulky and large radio frequency source in the down-conversion process, which is conducive to the integration and practical development of terahertz terminals.

[0083] The present invention does not limit the supported wireless carrier frequencies (millimeter wave, terahertz and even higher frequency bands) and application scenarios (communication, perception, detection and radar imaging, etc.). This implementation case takes terahertz communication as an example. Among them, the optical frequency comb involved in the present invention includes but is not limited to Kerr optical frequency comb, mode-locked laser, electro-optical frequency comb, etc., the electro-optical modulator includes but is not limited to intensity modulator, phase modulator and IQ modulator, etc., the photodetector includes but is not limited to PIN diode photodetector, single-line carrier photodetector, etc., and the optical filter includes but is not limited to arrayed waveguide grating, optical comb filter, optical wavelength selective switch, etc.

[0084] In one embodiment, Fig.10 FIG. 1 is a schematic diagram of a spectrum output with different repetition frequencies provided by an embodiment of the present invention. Fig.10 (a) indicates that the first repetition frequency is 283 GHz, that is, the repetition frequency of the frequency comb 1 (Comb1) used by the transmitter is 283 GHz; Fig.10 (b) in the figure shows that the second repetition frequency is 303 GHz, that is, the repetition frequency of frequency comb 2 (Comb2) used at the receiving end is 303 GHz. The center frequency of the intermediate frequency signal output after the terahertz wave generated by Comb1 and Comb2 is mixed with the terahertz fundamental wave is around 20 GHz. Fig.11 is a schematic diagram of a phase noise curve of an intermediate frequency signal measured when a transmitting end is not loaded with data, provided by an embodiment of the present invention. Fig.11 As shown in the figure, it can be seen that the noise floor is as low as -130 dBc / Hz. Since the phase noise carried by the intermediate frequency signal is the sum of the phase noise of the terahertz signal at the transmitting and receiving ends, this proves that the 283 GHz terahertz carrier generated by the transmitting end and the 303 GHz terahertz local oscillator generated by the receiving end both have high frequency stability and low phase noise characteristics.

[0085] In one embodiment, Fig.12This is a schematic diagram of the bit error rate (BER) and the optical power change curve of the input single-traveling carrier photodiode (UTC-PD) of three different modulation formats at a 23 Gbaud baud rate provided by an embodiment of the present invention. Among them, the three different modulation formats include: quadrature phase shift keying (QPSK), 16QAM and 64QAM. Among them, QAM is the abbreviation of quadrature amplitude modulation (Quadrature Amplitude Modulation). SD-FEC is the abbreviation of soft-decision forward error correction (Soft-Decision Forward Error Correction), HD-FEC is the abbreviation of hard-decision forward error correction (Hard-Decision Forward Error Correction), Fig.12 The 25% SD-FEC threshold shown here refers to the soft-decision forward error correction bit rate threshold with 25% overhead, which generally corresponds to 4.2×10 -2 ; The 7% HD-FEC threshold refers to the hard decision forward error correction bit rate threshold with 7% overhead, which generally corresponds to 3.8×10 -3 CPE refers to Carrier Phase Estimation. w / CPE is the abbreviation of with CPE, which means with carrier phase estimation; w / o CPE is the abbreviation of without CPE, which means without carrier phase estimation. Fig.12 As shown in the figure, it can be seen that even if CPE is not used in DSP, the performance of the three modulation formats is almost the same as that of the carrier phase estimation, and all meet the SD-FEC bit error rate threshold below 25%. On the one hand, it is once again proved that the Kerr optical frequency comb in this system can generate high frequency stability and low phase noise terahertz waves; on the other hand, it is proved that this system can indeed abandon the carrier phase recovery algorithm (including frequency offset estimation and phase noise compensation modules) relied on by the traditional coherent DSP module. The simplified DSP process can improve the robustness and adaptability of the receiving end and reduce its cost and power consumption.

[0086] The wireless communication system provided by the embodiment of the present invention can execute the wireless communication method provided by any embodiment of the present invention, and has the corresponding functional modules and beneficial effects of the execution method.

[0087] In one embodiment, Fig.13is a flow chart of a wireless communication method provided by an embodiment of the present invention. The wireless communication method in this embodiment is applied to the wireless communication system described in any of the above embodiments; wherein the wireless communication system includes: a coherent optical transmitter, an optical-terahertz conversion module and a coherent terahertz receiver. Fig.13 As shown, the wireless communication method includes:

[0088] S1310, selecting two comb teeth of a first frequency interval from an optical frequency comb through a coherent optical transmitter, performing signal modulation on one of the comb teeth to obtain a corresponding optical signal, and transmitting the optical signal to an optical-terahertz conversion module through an optical fiber link.

[0089] S1320, photoelectrically detecting the optical signal through the optical-terahertz conversion module, converting it into a corresponding terahertz signal, and transmitting the terahertz signal to a coherent terahertz receiver through a wireless link.

[0090] S1330, generating a terahertz local oscillator signal based on an optical frequency comb through a coherent terahertz receiver, and coherently receiving the terahertz signal by using a terahertz fundamental wave mixing method based on the terahertz local oscillator signal.

[0091] The technical solution of this embodiment generates a terahertz signal with high stability and low phase noise based on an optical frequency comb at the transmitting end, generates a terahertz local oscillator signal with the same high stability and low phase noise at the receiving end, and uses a terahertz fundamental wave mixing method to complete the down-conversion of the signal, so that the output intermediate frequency signal maintains the low phase noise characteristics of the optical frequency comb. This can not only effectively improve the transmission signal-to-noise ratio of the terahertz signal at the transmitting end of the coherent terahertz communication system, but also abandon the complex carrier phase recovery algorithm in the DSP of the receiving end, thereby significantly reducing the DSP cost and power consumption of the terahertz terminal.

[0092] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the present invention can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and this document does not limit this.

[0093] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A wireless communication system, characterized in that: include: A coherent optical transmitter, an optical-terahertz conversion module and a coherent terahertz receiver; wherein the coherent optical transmitter is connected to the optical-terahertz conversion module via an optical fiber link, and the optical-terahertz conversion module is connected to the coherent terahertz receiver via a wireless link; The coherent optical transmitter is used to select two comb teeth of a first frequency interval from the optical frequency comb, and perform signal modulation on one of the comb teeth to obtain a corresponding optical signal, and transmit the optical signal to the optical-terahertz conversion module through the optical fiber link; wherein the coherent optical transmitter is used to perform signal modulation on the comb tooth with greater power among the two comb teeth of the first frequency interval; The optical-terahertz conversion module is used to perform photoelectric detection on the optical signal, convert it into a corresponding terahertz signal, and transmit the terahertz signal to the coherent terahertz receiver through the wireless link; The coherent terahertz receiver is used to generate a terahertz local oscillator signal based on an optical frequency comb, and coherently receive the terahertz signal based on the terahertz local oscillator signal by using a terahertz fundamental wave mixing method; The coherent terahertz receiver includes: a receiving antenna, a terahertz fundamental wave mixer, a terahertz local oscillator generator, a terahertz amplifier, an electric amplifier, an analog-to-digital converter and a coherent DSP module; wherein the terahertz local oscillator generator is connected to the input end of the terahertz amplifier, the output end of the terahertz amplifier and the receiving antenna are connected to the input end of the terahertz fundamental wave mixer, the output end of the terahertz fundamental wave mixer is connected to the electric amplifier, the output end of the electric amplifier is connected to the input end of the analog-to-digital converter, and the output end of the analog-to-digital converter is connected to the coherent DSP module; Wherein, the receiving antenna is used to receive the terahertz signal transmitted by the wireless link; The terahertz local oscillator generator is used to generate a terahertz local oscillator signal; The terahertz amplifier is used to amplify the power of the terahertz local oscillator signal; The terahertz fundamental wave mixer is used to down-convert the terahertz signal and the power-amplified terahertz local oscillator signal, and output a corresponding intermediate frequency signal; The electric amplifier is used to amplify the power of the intermediate frequency signal; The analog-to-digital converter is used to convert the power-amplified intermediate frequency signal into a corresponding digital signal; The coherent DSP module is used to perform signal demodulation on the digital signal; The coherent DSP module is composed of the following six modules: down-conversion, resampling, frame synchronization and clock recovery, matched filtering, channel equalization and bit error rate calculation; The coherent optical transmitter comprises: a first optical frequency comb, a first optical amplifier, a first optical filter, an electro-optical modulator, a polarization controller and an optical coupler; wherein the first optical frequency comb is connected to the input end of the first optical amplifier, and the output end of the first optical amplifier is connected to the input end of the first optical filter, the output end of the first optical filter is respectively connected to the input end of the electro-optical modulator and the input end of the polarization controller, and the output end of the electro-optical modulator and the output end of the polarization controller are both connected to the optical coupler; The first optical frequency comb is used to generate a light wave having a first repetition frequency and comprising at least two coherent comb teeth, and input the light wave into the first optical amplifier; The first optical amplifier is used to amplify the optical power of the light wave and input the amplified light wave into the first optical filter; The first optical filter is used to filter out a first comb tooth and a second comb tooth of a first frequency interval from the at least two coherent comb teeth according to the terahertz communication frequency; The electro-optic modulator is used to load the first comb teeth with data to be transmitted; The polarization controller is used to adjust the polarization state of the second comb teeth until the second comb teeth are polarization-aligned with the loaded first comb teeth; The optical coupler is used to combine the optical wave signals corresponding to the first comb teeth and the second comb teeth to obtain corresponding optical signals.

2. The system according to claim 1, characterized in that The terahertz local oscillator generator comprises: a second optical frequency comb, a second optical filter, a second optical amplifier and a first photodetector; wherein the second optical frequency comb is connected to the input end of the second optical filter, the output end of the second optical filter is connected to the input end of the second optical amplifier, and the output end of the second optical amplifier is connected to the first photodetector; The second optical frequency comb is used to generate a light wave having a second repetition frequency and comprising at least two coherent comb teeth, and input the light wave into the second optical filter; The second optical filter is used to filter out the third comb teeth and the fourth comb teeth of the second frequency interval from the at least two coherent comb teeth according to the terahertz communication frequency, and input the third comb teeth and the fourth comb teeth to the second optical amplifier; The second optical amplifier is used to amplify the power of the third comb teeth and the fourth comb teeth, and input the amplified third comb teeth and the fourth comb teeth to the first photodetector; The first photodetector is used to beat the amplified third comb teeth and the fourth comb teeth to generate a corresponding terahertz local oscillation signal.

3. The system according to claim 1, characterized in that The optical-terahertz conversion module comprises: a third optical amplifier, a second photodetector and a transmitting antenna; wherein the output end of the third optical amplifier is connected to the input end of the second photodetector, and the output end of the second photodetector is connected to the transmitting antenna; The third optical amplifier is used to amplify the power of the optical signal and input the amplified optical signal to the second photodetector; The second photodetector is used to convert the amplified optical signal into a terahertz signal; The transmitting antenna is used to transmit the terahertz signal to free space for wireless communication.

4. The system according to claim 1, characterized in that The coherent optical transmitter and the coherent terahertz receiver adopt an integrated Kerr soliton optical frequency comb module; wherein the Kerr soliton optical frequency comb module comprises: a distributed feedback laser and an optical fiber microcavity; wherein the distributed feedback laser and the optical fiber microcavity establish communication through a spatial optical connection; Under limited pump power, the distributed feedback laser is used for direct diode pumping; A few-mode fiber microcavity transmitting two constant modes is used to make a few-mode fiber Fabry-Perot resonant cavity as the corresponding fiber microcavity.

5. The system according to claim 4, characterized in that The noise limit of the microcavity light comb generated by the fiber microcavity is inversely proportional to the square of the quality factor value of the fiber microcavity.

6. The system according to claim 5, characterized in that The noise limit and the quality factor of the fiber microcavity Q The value relationships include: ； in, π is pi, h is Planck's constant, c is the speed of light in vacuum, λ is the wavelength of the pump light in the microcavity optical comb, D is the dimensionless dispersion coefficient, f is the offset frequency, κ is the pump light power and the microcavity parameter threshold power P th The ratio of Q is the quality factor of the optical fiber microcavity.

7. The system according to any one of claims 1-2, characterized in that: The signal frequency of the intermediate frequency signal is the absolute value of the difference between the first repetition frequency and the second repetition frequency; wherein the first repetition frequency and the second repetition frequency are not equal.

8. A wireless communication method, characterized in that: Applied to the wireless communication system according to any one of claims 1 to 7; wherein the wireless communication system comprises: a coherent optical transmitter, an optical-terahertz conversion module and a coherent terahertz receiver; the wireless communication method comprises: Selecting two comb teeth of a first frequency interval from the optical frequency comb by the coherent optical transmitter, performing signal modulation on one of the comb teeth to obtain a corresponding optical signal, and transmitting the optical signal to the optical-terahertz conversion module through an optical fiber link; wherein the coherent optical transmitter is used to perform signal modulation on the comb tooth with greater power among the two comb teeth of the first frequency interval; Performing photoelectric detection on the optical signal through an optical-terahertz conversion module to convert it into a corresponding terahertz signal, and transmitting the terahertz signal to the coherent terahertz receiver through a wireless link; The coherent terahertz receiver generates a terahertz local oscillator signal based on an optical frequency comb, and coherently receives the terahertz signal by using a terahertz fundamental wave mixing method based on the terahertz local oscillator signal; The coherent terahertz receiver includes: a receiving antenna, a terahertz fundamental wave mixer, a terahertz local oscillator generator, a terahertz amplifier, an electric amplifier, an analog-to-digital converter and a coherent DSP module; wherein the terahertz local oscillator generator is connected to the input end of the terahertz amplifier, the output end of the terahertz amplifier and the receiving antenna are connected to the input end of the terahertz fundamental wave mixer, the output end of the terahertz fundamental wave mixer is connected to the electric amplifier, the output end of the electric amplifier is connected to the input end of the analog-to-digital converter, and the output end of the analog-to-digital converter is connected to the coherent DSP module; Wherein, the receiving antenna is used to receive the terahertz signal transmitted by the wireless link; The terahertz local oscillator generator is used to generate a terahertz local oscillator signal; The terahertz amplifier is used to amplify the power of the terahertz local oscillator signal; The terahertz fundamental wave mixer is used to down-convert the terahertz signal and the power-amplified terahertz local oscillator signal, and output a corresponding intermediate frequency signal; The electric amplifier is used to amplify the power of the intermediate frequency signal; The analog-to-digital converter is used to convert the power-amplified intermediate frequency signal into a corresponding digital signal; The coherent DSP module is used to perform signal demodulation on the digital signal; The coherent DSP module is composed of the following six modules: down-conversion, resampling, frame synchronization and clock recovery, matched filtering, channel equalization and bit error rate calculation; The coherent optical transmitter comprises: a first optical frequency comb, a first optical amplifier, a first optical filter, an electro-optical modulator, a polarization controller and an optical coupler; wherein the first optical frequency comb is connected to the input end of the first optical amplifier, and the output end of the first optical amplifier is connected to the input end of the first optical filter, the output end of the first optical filter is respectively connected to the input end of the electro-optical modulator and the input end of the polarization controller, and the output end of the electro-optical modulator and the output end of the polarization controller are both connected to the optical coupler; The first optical frequency comb is used to generate a light wave having a first repetition frequency and comprising at least two coherent comb teeth, and input the light wave into the first optical amplifier; The first optical amplifier is used to amplify the optical power of the light wave and input the amplified light wave into the first optical filter; The first optical filter is used to filter out a first comb tooth and a second comb tooth of a first frequency interval from the at least two coherent comb teeth according to the terahertz communication frequency; The electro-optic modulator is used to load the first comb teeth with data to be transmitted; The polarization controller is used to adjust the polarization state of the second comb teeth until the second comb teeth are polarization-aligned with the loaded first comb teeth; The optical coupler is used to combine the optical wave signals corresponding to the first comb teeth and the second comb teeth to obtain corresponding optical signals.

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