Signal generation system, transmitter and transceiver

Abstract

The invention provides a signal generation system. The signal generation system comprises an external modulation laser, an optical splitter, a Mach-Zehnder modulator, a phase shifter, an attenuator, a coupler and a photoelectric conversion unit. According to the invention, Mach-Zehnder modulation is carried out on optical carriers through asymmetric double single side band signals, and millimeter wave / terahertz signals in the form of optical signals are obtained through destructive interference between output signals of a phase shifter and an attenuator and optical signals subjected to Mach-Zehnder modulation. And finally, millimeter wave / terahertz signals in an electric signal form are obtained through the photoelectric conversion unit. Millimeter wave / terahertz signals are generated by adopting a single push-pull Mach-Zehnder modulator and attenuator optical double-single-side-band modulation, transmitter precoding and a complex and expensive I / Q modulator are avoided, the complexity and cost of the system can be effectively reduced, meanwhile, the frequency interval can be flexibly adjusted, and the system performance is improved. And the tunable range of the system is increased.

Description

Technical Field

[0001] This application relates to the field of wireless communication, and more specifically, to techniques for generating wireless communication signals. Background Technology

[0002] 5G technology places higher demands on communication performance indicators, making increasing channel bandwidth and expanding available spectrum key strategies. The gradual shift of wireless communication towards millimeter-wave / terahertz bands is an inevitable trend. Traditional methods of generating millimeter-wave / terahertz signals using all-electronic devices are limited by the bandwidth of these devices and cannot meet the requirements of wireless communication. Photon-assisted millimeter-wave / terahertz signal generation based on optical heterodyne technology is a superior option.

[0003] Currently, there are two main types of photon vector millimeter-wave / terahertz signal generation technologies based on external optical modulation. The first type is based on a single-drive electro-optic intensity modulator or phase modulator, combined with transmitter precoding. These products have a simple structure and high cost-effectiveness, but the use of precoding will shorten the Euclidean distance of the transmitter signal constellation, thus limiting the system performance. The second type is based on a single in-phase / quadrature (I / Q) modulator, which has a relatively complex and expensive structure. Furthermore, the I / Q modulator has three DC biases, which will increase the instability and adjustment difficulty of the system. Summary of the Invention

[0004] This invention provides a signal generation system, a transmitter, and a transceiver to solve the technical problems of limited performance of systems based on precoding technology and the complexity, instability, and difficulty in adjustment of systems based on I / Q modulators in the prior art.

[0005] Firstly, a signal generation system is provided, comprising: Externally modulated lasers are used to generate optical carrier waves; A beam splitter is used to divide the optical carrier into a first subcarrier and a second subcarrier; A Mach-Zehnder modulator (MZM) is used to acquire a driving signal and modulate the first subcarrier according to the driving signal to generate a first optical signal, wherein the driving signal is an asymmetric dual single-sideband signal. A phase shifter is used to phase shift the second subcarrier; An attenuator is used to attenuate the phase-shifted second subcarrier to generate a second optical signal; A coupler is used to couple and superimpose the first optical signal and the second optical signal to generate a third optical signal; The photoelectric conversion unit is used to convert the third optical signal into an electrical signal, wherein the electrical signal is a millimeter-wave signal or a terahertz signal.

[0006] Based on the signal generation system described above, the millimeter-wave / terahertz signal generation achieved by using a single Mach-Zehnder modulator (MZM) avoids the use of transmitter precoding and complex and expensive I / Q modulators, which can effectively reduce the complexity and cost of the system, while allowing the frequency interval to be flexibly adjusted, thus increasing the tunable range of the system.

[0007] In conjunction with the first aspect, in some implementations of the first aspect, the system further includes a digital signal processor and a digital-to-analog converter, wherein, The digital signal processor is used to generate sideband signals, wherein the sideband signals are digital signals; The digital-to-analog converter is used to generate the driving signal based on the sideband signal, wherein the driving signal is an analog signal; The driving signal includes a first vector modulation signal, a second vector modulation signal, a first unmodulated sideband signal, and a second unmodulated sideband signal; The frequency of the first unmodulated sideband signal is a first frequency, and the frequency of the second unmodulated sideband signal is a second frequency; the first frequency is greater than the second frequency, and both are greater than zero; the frequency of the first vector modulated signal is the opposite of the first frequency, and the frequency of the second vector modulated signal is the opposite of the second frequency.

[0008] In conjunction with the first aspect, in some implementations of the first aspect, the phase difference between the phase-shifted second subcarrier and the first subcarrier is... .

[0009] In conjunction with the first aspect, in some implementations of the first aspect, the optical splitter includes a first input port, a first output port, and a second output port; One end of the MZM is connected to the first output port; One end of the phase shifter is connected to the second output port, and the other end of the phase shifter is connected to one end of the attenuator; The coupler includes a second input port, a third input port, and a third output port. The second input port is connected to the other end of the MZM, and the third input port is connected to the other end of the attenuator. The third output port is optically connected to the photoelectric conversion unit.

[0010] In conjunction with the first aspect, in some implementations of the first aspect, the photoelectric conversion unit includes a Mach-Zehnder interferometer (MZI), a first photoelectric converter, and a second photoelectric converter, wherein the conversion of the third optical signal into an electrical signal includes: The MZI is used to acquire the third optical signal and separate the third optical signal into a fourth optical signal and a fifth optical signal; The electrical signal includes a first electrical signal and a second electrical signal; The first photoelectric converter is used to generate the first electrical signal based on the fourth optical signal, and the second photoelectric converter is used to generate the second electrical signal based on the fifth optical signal.

[0011] In conjunction with the first aspect, in some implementations of the first aspect, the separation of the third optical signal into a fourth optical signal and a fifth optical signal satisfies the first condition: The first frequency is equal to 1.25 times the free spectral range of the MZI; The second frequency is equal to 0.75 times the free spectral range of the MZI; The carrier frequency of the electrical signal is equal to twice the free spectral range of the MZI.

[0012] In conjunction with the first aspect, in some implementations of the first aspect, the system further includes a transmission optical fiber, wherein the transmission optical fiber is disposed between the coupler and the photoelectric conversion unit, wherein the transmission optical fiber is a single-mode optical fiber, and at least one optical fiber amplifier is disposed on the transmission optical fiber.

[0013] In a second aspect, a signal transmitter is provided, comprising the signal generation system and antenna as described in any one of the first aspects, the antenna being used to transmit the millimeter-wave signal or terahertz signal.

[0014] Thirdly, a signal transceiver is provided, comprising the signal generation system and the signal receiver described in any one of the first aspects, wherein the signal receiver is used to receive another millimeter-wave signal or a terahertz signal and to process the other millimeter-wave signal or terahertz signal.

[0015] In summary, based on the above-described technical solution conceived in this invention, the following beneficial technical effects can be achieved: (1) The signal generation system, signal transmitter, and signal transceiver described in this invention use a single Mach-Zehnder modulator (MZM) to generate millimeter-wave / terahertz signals, avoiding the use of transmitter precoding and complex and expensive I / Q modulators, which can effectively reduce the complexity and cost of the system, while allowing the frequency interval to be flexibly adjusted, thus increasing the tunable range of the system.

[0016] (2) The signal generation system, signal transmitter, and signal transceiver described in this invention adopt optical dual single-sideband modulation. In the dual single-sideband driving signal, not only are there two vector modulation signals, but also two unmodulated sidebands located in different frequency bands in the optical domain. Therefore, crosstalk between symmetrical sidebands can be effectively avoided.

[0017] (3) The signal generation system, signal transmitter, and signal transceiver described in this invention use a Mach-Zehnder interferometer (MZI) to divide the optical signal into two parts, and then two millimeter-wave / terahertz signals of the same frequency are generated by two PDs, thereby realizing the generation of multiple millimeter-wave / terahertz signals. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a signal generation system provided in an embodiment of this application; Figure 2 This is a schematic diagram of sideband signal generation provided in an embodiment of this application; Figure 3 This is the electric spectrum of the driving signal provided in the embodiments of this application; Figure 4 It is the electrical spectrum of a traditional symmetrical dual single-sideband modulated signal; Figure 5 This is a schematic diagram of another signal generation system provided in an embodiment of this application; Figure 6 These are the spectrum diagrams of the third, fourth, and fifth optical signals provided in the embodiments of this application; Figure 7 This is the electrical spectrum diagram of two 16QAM electric vector millimeter wave signals provided in the embodiments of this application; Figure 8 This is a schematic diagram of another signal generation system provided in an embodiment of this application; Figure 9 This is a schematic diagram of a signal transmitter provided according to an embodiment of this application; Figure 10 This is a schematic diagram of a signal transceiver provided according to an embodiment of this application; Figure 11 This is a simulation system built based on the signal generation system provided in the embodiments of this application; Figure 12 It is the output spectrum of the Mach-Zehnder modulator in the simulation system; Figure 13 It is the output spectrum of the coupler in the simulation system; Figure 14 These are the two 16QAM signals after the PD beat frequency in the simulation system; Figure 15 This is the constellation diagram of two 16QAM signals generated in the simulation system; Figure 16 This refers to the EVM performance of a 16QAM signal after 20km SMF transmission in the simulation system. Figure 17 The curves show the EVM performance versus γ value of a 16QAM signal after 20km SMF transmission in the simulation system. Figure 18 This is the effect of the attenuation of the attenuator in the simulation system on the bit error rate; Figure 19 The curves show the bit error rate (BER) of the 16QAM signal versus the PD input power in the simulation system. Figure 20 It is a graph showing the bit error rate (BER) of the 16QAM signal versus the transmission distance in the simulation system. Detailed Implementation

[0019] The technical solutions in this application will now be described in conjunction with the accompanying drawings. To facilitate understanding of the embodiments of this application, the following explanations will be provided first.

[0020] In this application, “at least one” means one or more, and “more than one” means two or more.

[0021] In this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" or "for example" in this application should not be construed as being more preferred or advantageous than other embodiments or designs. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of the invention described below can be combined with each other as long as they do not conflict with each other.

[0022] In one embodiment of this application, such as Figure 1 As shown, a signal generation system is provided for generating millimeter wave (MW) or terahertz (THz) signals for wireless communication. This signal generation system can be installed in network-side equipment of the wireless communication system, such as a base station (BS). Specifically, the base station can be a generation Node B (gNB) in a 5G New Radio (NR) system, or a related node in other wireless communication systems; no limitation is made here. The signal generation system can transmit the generated MW or terahertz signals through an integrated antenna or other methods to achieve wireless communication; no limitation is made here.

[0023] Specifically, Figure 1The signal generation system shown includes: an externally modulated laser (EML) 1, an optical divider (OD) 2, a Mach-Zehnder modulator (MZM) 3, a phase shifter (PS) 4, an attenuator (ATT) 5, a coupler 6, and a photoelectric conversion unit 7. These devices can be combined into the signal generation system of this embodiment via optical connections. It is understood that... Figure 1 The markings and components shown are for illustrative purposes only, and this application may also include other implementations.

[0024] In this embodiment, the externally modulated laser 1 is used to generate an optical carrier. It is understood that the optical carrier in this embodiment is a carrier of optical signals and does not directly carry information; the information is loaded onto the optical carrier through modulation technology. Furthermore, this optical carrier can be coherent light operating in the optical communication frequency band, with a center frequency of [missing information]. For example, it could be 193.1 Hz, or other frequencies, which can be adjusted according to actual needs and are not limited here.

[0025] Furthermore, in this embodiment, the externally modulated laser 1 can be an external cavity laser (ECL), whose generated optical carrier signal has the following electric field intensity: (1.1) In equation (1.1), The amplitude of the optical carrier wave. This is the center frequency of the optical carrier.

[0026] In this configuration, the optical splitter 2 is used to split the optical carrier into two paths, referred to as the first subcarrier and the second subcarrier, respectively. The first subcarrier is used to input the Mach-Zehnder modulator 3 so that information is loaded onto the first subcarrier through Mach-Zehnder modulation.

[0027] The Mach-Zehnder modulator 3 is used to acquire the drive signal and modulate the first subcarrier according to the drive signal to generate the first optical signal. It is understood that this drive signal is an electrical signal.

[0028] Furthermore, in this embodiment, the driving signal is an asymmetric dual single-sideband signal. It can be understood that a sideband refers to a frequency band generated above and below the center carrier frequency by the modulated signal, and its bandwidth is determined by the bandwidth of the modulating signal and the modulation method used. In this embodiment, a vector modulation signal and an unmodulated sideband are generated on the two asymmetric edges of the optical carrier spectrum, respectively. These vector modulation signal and unmodulated sideband are mutually asymmetric dual single-sideband signals, or a pair of asymmetric dual single-sideband signals. Modulating the optical carrier with the asymmetric dual single-sideband signal of this embodiment effectively solves the sideband crosstalk problem present in traditional symmetric dual single-sideband modulation methods.

[0029] Furthermore, in this embodiment, the Mach-Zehnder modulator 3 can be a push-pull Mach-Zehnder modulator, and its output optical field can be expressed as: (1.2) In equation (1.2), The electric field strength of the input optical signal, i.e., the electric field strength of the first subcarrier, It is a half-wave voltage. and This is the DC bias voltage for the 3 Mach-Zehnder modulator. and These represent the real and imaginary parts of the driving signal, respectively.

[0030] In this embodiment, phase shifter 4 is used to shift the phase of the second subcarrier. The phase-shifted second subcarrier is then input to attenuator 5 for attenuation, resulting in a second optical signal. This allows the optical carrier in the first optical signal to coherently cancel out the second optical signal. This implementation significantly increases the flexibility of system tuning by using optical phase shifters and attenuators instead of costly optical filters.

[0031] Coupler 6 is used to couple and superimpose the first and second optical signals to generate a third optical signal. It is understood that the first optical signal is obtained by the Mach-Zehnder modulator 3 modulating the first subcarrier according to the driving signal. Therefore, the first optical signal includes a center carrier, first-order sideband signals, and higher-order sideband signals. The center carrier, i.e., the 0th-order optical carrier, is redundant and should be canceled out. Therefore, by coupling and superimposing the first and second optical signals through coupler 6, the optical carriers can be coherently canceled to obtain the third optical signal. It is understood that the third optical signal only contains asymmetric positive and negative first-order optical sideband signals, i.e., optical millimeter-wave signals or optical terahertz signals.

[0032] The photoelectric conversion unit 7 is used to convert the third optical signal into an electrical signal, which is a millimeter-wave signal or a terahertz signal. The third optical signal is a millimeter-wave signal or a terahertz signal in the form of an optical signal. Through a photoelectric conversion device such as a PD, the millimeter-wave signal or terahertz signal in the form of an optical signal can be converted into a millimeter-wave signal or a terahertz signal in the form of an electrical signal.

[0033] Furthermore, beam splitter 2 can be a 50:50 splitter, allowing the input signal to be equally divided into two output signals. Specifically, it includes a first input port, a first output port, and a second output port. The first input port is connected to the external modulation laser 1, the first output port is connected to the Mach-Zehnder modulator 3, and the second output port is connected to the phase shifter 4, thus splitting the optical carrier generated by the external modulation laser 1 into two paths, which are then input to the Mach-Zehnder modulator 3 and the phase shifter 4, respectively. It is understood that beam splitter 2 can also be a 50:50 splitter with other splitting ratios, or other types of beam splitters; this is not limited here.

[0034] Furthermore, in this embodiment, coupler 6 can be a two-in-one coupler, allowing two input signals to be coupled into one output signal. Specifically, it includes a second input port, a third input port, and a third output port. The second input port is connected to the Mach-Zehnder modulator 3, the third input port is connected to the attenuator 5, and the third output port is connected to the photoelectric conversion unit 7, thereby coupling and superimposing the first and second optical signals into a third optical signal. It is understood that coupler 6 can also be other types of couplers, and this is not limited here. Furthermore, all connections mentioned in this embodiment refer to optical connections.

[0035] It is understood that the signal generation system provided according to this embodiment uses only a Mach-Zehnder modulator and does not employ precoding and optical filters, which greatly reduces the cost and complexity of the transmitter. Moreover, since it is not limited by the bandwidth of the device, it greatly increases the tunable range of the system and can be used to generate millimeter-wave signals or terahertz signals.

[0036] In some implementations, such as Figure 2 As shown, a method for generating drive signals for a signal generation system is also provided. In this method, the signal transmission system may further include a digital signal processor (DSP) 10 and a digital to analog converter (DAC) 11.

[0037] The digital signal processor 10 is used to generate sideband signals. It is understood that the sideband signals are digital signals, and as mentioned above, a sideband refers to a frequency band generated on both the upper and lower sides of the center carrier frequency after modulation, and its bandwidth is determined by the bandwidth of the modulation signal and the modulation method used.

[0038] The digital-to-analog converter 11 is used to generate the driving signal based on the sideband signal. It is understood that the driving signal is an analog signal, and, as previously mentioned, it is an asymmetric dual-single-sideband signal. This is achieved by generating a vector-modulated signal and an unmodulated sideband on each of the two asymmetric edges of the optical carrier spectrum. The vector-modulated signal and the unmodulated sideband are asymmetric dual-single-sideband signals, or a pair of asymmetric dual-single-sideband signals.

[0039] Specifically, the driving signal may include a first vector modulation signal, a second vector modulation signal, a first unmodulated sideband signal, and a second unmodulated sideband signal. It is understood that vector modulation, also known as complex modulation or IQ modulation, involves separating baseband digital information into two independent components: I (in-phase) and Q (quadrature) components. These I and Q components are then combined to form the baseband modulation signal. In this embodiment, the first vector modulation signal and the second vector modulation signal are electrical signals that carry baseband digital information through vector modulation.

[0040] Specifically, such as Figure 2 As shown, the first vector modulation signal, the second vector modulation signal, the first unmodulated sideband signal, and the second unmodulated sideband signal can be denoted as signals b, a, d, and c, respectively. Based on this, the driving signal can be denoted as signal e. It can be understood that signal e is the sum of signals a, b, c, and d. For example... Figure 2 As shown, the frequencies of signals d and c can be denoted as... , And satisfy the following relationship: Then the frequencies of signals b and a are respectively , .

[0041] Specifically, signals a, b, c, and d can be represented by the following expressions: (2.1) In equation (2.1), S1(t) and S2(t) are two independent normalized vector modulation baseband signals with the same peak-to-peak value. Signals a and d are asymmetric double single-sideband signals, or a pair of asymmetric double single-sideband signals; signals b and c are asymmetric double single-sideband signals, or a pair of asymmetric double single-sideband signals. Based on this, signal e can be represented by the following expression: (2.2) In equation (2.2), a, b, c, d, and γ are five positive constants. The real and imaginary parts of signal e are expressed as follows: (2.3) (2.4) In equations (2.3) and (2.4), a, b, c, d, and γ are five positive constants. Based on this, the electrical spectra of signals a, b, c, d, and e are as follows: Figure 3 As shown. Preferably, the relative amplitudes of signals a, b, c, and d can be adjusted by the digital signal processor 10 to optimize the performance of the millimeter-wave or terahertz signal generated by the signal generation system of this embodiment. For example, as... Figure 4 As shown, a conventional symmetrical dual single-sideband signal spectrum is provided, in which a vector-modulated signal and an unmodulated sideband are generated on each side of the optical carrier spectrum. Crosstalk generated between the symmetrical vector-modulated signals degrades transmission performance. It is understood that by applying the driving signal provided in this embodiment to the signal generation system of this application, an asymmetric dual single-sideband signal modulation method is adopted, which can effectively avoid crosstalk between the symmetrical sidebands.

[0042] In some implementations, when the Mach-Zehnder modulator 3 is a push-pull Mach-Zehnder modulator, and it operates at the quadrature bias point, the output first optical signal can be expressed in detail as follows:

[0043]

[0044] In the above formula, This represents the modulation index of the Mach-Zehnder modulator 3. It is a half-wave voltage. The amplitude of the radio frequency drive signal. Let A represent the Bessel function, where A is a constant. Preferably, in the case of small-signal modulation, i.e., the modulation index... The values ​​of higher-order Bessel functions can be ignored (n≧2), and the output of Mach-Zehnder modulator 3, i.e., the first optical signal, can be approximately described as follows: (2.5) In equation (2.5), the frequency is the center frequency. The amount of " The first optical signal, i.e., the zero-order optical carrier in the first signal, is redundant as mentioned above and should be canceled out. By coupling and superimposing the first and second optical signals through coupler 6, the optical carriers can be coherently canceled to obtain the third optical signal. It can be understood that the third optical signal only contains asymmetric positive and negative first-order optical sideband signals, i.e., optical millimeter-wave signals or optical terahertz signals. Specifically, the third optical signal can be represented as follows: (2.6) In some implementations, such as Figure 5 As shown, another signal generation system is also provided, in which the photoelectric conversion unit 7 includes: a Mach-Zehnder interferometer (MZI) 71; a first photoelectric converter (PD) 72; and a second photoelectric converter 73.

[0045] The Mach-Zehnder interferometer 71 is used to acquire the third optical signal and separate it into a fourth and a fifth optical signal. A first photoelectric converter 72 converts the fourth optical signal into a first electrical signal, and a second photoelectric converter 73 converts the fifth optical signal into a second electrical signal. The first and second electrical signals are the millimeter-wave or terahertz signals to be generated in this application.

[0046] like Figure 5 As shown, the third, fourth, and fifth optical signals can be denoted as signals f, g, and h, respectively, and the first and second electrical signals can be denoted as signals i and j, respectively.

[0047] As mentioned earlier, signal f only contains asymmetric positive and negative first-order optical sideband signals, i.e., optical millimeter-wave signals or optical terahertz signals. Specifically, as shown in equation (2.6), signal f at the center frequency... The positive and negative sides have a frequency of , The four first-order components are, respectively, the carrier frequency is The optical 16QAM signal and carrier frequency are The optical unmodulated sideband, with a carrier frequency of Another optical 16QAM signal and carrier frequency are Unmodulated optical sidebands.

[0048] When the first condition is met, the Mach-Zehnder interferometer 71 separates the optical signal f into two parts, one of which carries a carrier frequency of f. The optical 16QAM signal and carrier frequency are The unmodulated optical sidebands are defined as the inner band signal. Another portion carries a carrier frequency of... Another optical 16QAM signal and carrier frequency are The optically unmodulated sideband is defined as the out-band signal. The first condition is expressed in detail below: (3.1) In equation (3.1), FSR is the free spectral range of the Mach-Zehnder interferometer 71. It is understood that FSR is a constant rather than a range, and F represents the carrier frequency of the millimeter-wave or terahertz signal to be generated in this application. Based on this, the signals g and h separated by the Mach-Zehnder interferometer 71 can be expressed in detail as follows: (3.2) (3.3) For example, the spectra of signals f, g, and h are as follows: Figure 6 As shown.

[0049] Furthermore, by performing photoelectric conversion on signals g and h to obtain signals i and j, it can be understood that beat frequencies are applied to the optical 16QAM signal and the optical unmodulated sideband contained in signals g and h, respectively, to generate two 16QAM vector millimeter-wave signals or terahertz signals. Beat frequency refers to the frequency difference between two waveforms with similar but not identical frequencies. When the frequencies of two waveforms are close, they interfere with each other in a special way, producing a new waveform with a frequency equal to the difference between their frequencies. The electrical vector signals i and j obtained by PD beat frequency can be expressed in detail as follows:

[0050]

[0051]

[0052] (3.4)

[0053]

[0054]

[0055] (3.5) In equations (3.4) and (3.5), μ represents the responsivity of the PD. Based on equations (3.4) and (3.5), it can be seen that this embodiment can obtain two frequencies of... The 16QAM electrical vector millimeter-wave signal, i.e., signals i and j. Since the vector signal is only modulated on the optical sideband on one side of the center carrier, the vector signal obtained after beat frequency has a frequency doubling but no phase doubling, thus avoiding the use of precoding technology and making it suitable for multi-output communication scenarios.

[0056] For example, the electrical spectra of signals i and j are as follows: Figure 7 As shown.

[0057] In some implementations, such as Figure 8 As shown, another signal generation system is also provided, which further includes a transmission optical fiber 8 and an optical fiber amplifier 9. The transmission optical fiber 8 is disposed between the coupler 6 and the photoelectric conversion unit 7. It can be understood that this transmission optical fiber is used to realize the optical connection between the coupler 6 and the photoelectric conversion unit 7, and the length of the transmission optical fiber can be adjusted to meet the needs of different transmission distance scenarios.

[0058] Furthermore, at least one fiber amplifier 9 is also provided on the transmission fiber 8. It is understood that the optical signal attenuates during transmission. In scenarios where the transmission fiber is long, the degree of optical signal attenuation cannot be ignored. If it is not addressed, it will affect the transmission quality. By providing at least one fiber amplifier 9, the optical signal can be amplified to meet the needs of long-distance transmission.

[0059] Preferably, the transmission fiber 8 is a single-mode fiber (SMF). It is understood that single-mode fiber refers to fiber that has only one transmission mode, has low transmission loss, and does not experience intermodal dispersion, making it suitable for long-distance transmission scenarios where lasers are used as light sources.

[0060] In some implementations, such as Figure 9 As shown, a signal transmitter is also provided, comprising at least any of the aforementioned signal generation systems and an antenna, wherein the antenna is used to transmit millimeter-wave signals or terahertz signals generated by the system. It is understood that the technical features described in the above system embodiments are also applicable to this embodiment; therefore, details not described in detail can be found in the above embodiments.

[0061] In some implementations, such as Figure 10As shown, a signal transceiver is also provided, comprising at least any of the aforementioned signal generation systems and a signal receiver, wherein the signal receiver is used to receive another millimeter-wave signal or a terahertz signal and process the other millimeter-wave signal or terahertz signal. It is understood that the technical features described in the above system embodiments are also applicable to this embodiment; therefore, any details not described in detail can be found in the above embodiments.

[0062] In some implementations, exemplarily, based on Figure 8 The signal generation system shown is simulated using Virtual Photonic Integration (VPI) software. The simulation system consists of the following components: Figure 11 As shown. The simulation system connects an oscilloscope (OSC) to the output of each of the two millimeter-wave or terahertz signals to receive the raw data of the generated millimeter-wave or terahertz signals. Further, the external modulation laser 1 can be an external cavity laser with a center frequency of 193.1 THz, a power of 10 dBm, and a linewidth of 100 kHz for its output continuous coherent light. The Mach-Zehnder modulator 3 can be a push-pull Mach-Zehnder modulator with a half-wave voltage of 4 V, an insertion loss of 5 dB, and operates at a quadrature bias point. Furthermore, the required generated millimeter-wave signal carrier frequency is 40 GHz, f... s1 and f s2 They were set to 25GHz and 15GHz respectively.

[0063] Based on this, the baseband signal is generated offline using MATLAB, and further generated as a driving signal through PRB generation, QAM mapping, low-pass filtering, and DAC conversion. This driving signal is an asymmetric dual single-sideband signal. The optical carrier of the input push-pull Mach-Zehnder modulator is modulated using this driving signal, and the spectrum of the output signal is shown below. Figure 12 As shown, the spectrum of the output signal of the push-pull Mach-Zehnder modulator includes the center carrier, positive and negative first-order sidebands, and other higher-order subcarriers. Preferably, the suppression effect of higher-order subcarriers can be affected by adjusting the voltage value of the driving signal. Specifically, higher-order subcarriers can be suppressed by reducing the voltage of the driving signal. It is understood that the voltage value of the driving signal also affects the power suppression ratio of the center carrier and the positive and negative first-order sideband signals. If the driving signal voltage value is too small, it is not conducive to the subsequent generation of vector millimeter-wave signals. Preferably, the peak voltage of the driving signal can be set to 1V, which can better balance the suppression of higher-order subcarriers and the generation of vector millimeter waves.

[0064] Furthermore, by adjusting the phase shift and attenuation levels of phase shifter 4 and attenuator 5, the two optical signals output from Mach-Zehnder modulator 3 and attenuator 5 are coherently superimposed in coupler 6. The specific degree of phase shift and attenuation can be adjusted according to actual conditions and is not limited here. The coherently superimposed optical signal suppresses the 0th-order optical carrier and contains only two pairs of asymmetric positive and negative first-order optical sidebands, as shown in the spectrum. Figure 13 As shown.

[0065] Furthermore, the transmission fiber 8 is configured as an SMF-28 single-mode fiber with a length of 40km, an attenuation coefficient of 0.2dB / km, and a nonlinear effect coefficient of 2.6e-20m² / W; the fiber amplifier 9 is configured as an erbium-doped fiber amplifier (EDFA) with a gain of 20dB. The optical signal output from the coupler 6 is input into the aforementioned single-mode fiber for transmission to simulate and verify the performance of millimeter-wave or terahertz signals in long-distance transmission scenarios, and the erbium-doped fiber amplifier compensates for the power loss caused by fiber transmission.

[0066] Furthermore, the asymmetric double single-sideband optical millimeter-wave signal is split into two parts using a Mach-Zehnder interferometer 71. One part carries a carrier frequency of... The 15GHz optical 16QAM signal and the 25GHz unmodulated optical sideband are defined as the inner-band signal; another part carries a carrier frequency of... Another optical 16QAM signal at 25 GHz and an optically unmodulated sideband with a carrier frequency of 15 GHz are defined as the outer-band signal. With a free spectrum (FSR) of 20 and a delay time of 5e-11 s in a Mach-Zehnder interferometer, the inner-band and outer-band signals can be completely separated. The separated inner-band and outer-band signals are then photoelectrically converted by two parallel single-ended photoelectric converters (PDs), thereby generating a co-frequency vector millimeter-wave signal.

[0067] Furthermore, a variable optical attenuator (VOA) can be added before the PD to adjust the PD's input optical power for bit error rate measurement. The PD's responsivity is set to 0.65 A / W to simulate actual transmission conditions. The photocurrent output spectrum after PD beat frequency is shown below. Figure 14 As shown.

[0068] Furthermore, the electrical millimeter-wave signal after PD beat frequency is received using an oscilloscope (OSC), and the received data is imported into MATLAB for offline digital signal processing. Specifically, this includes baseband down-conversion, clock recovery, constant-mode algorithm equalization for QPSK modulation, cascaded multi-mode algorithm equalization for 16QAM modulation, carrier recovery, and other steps. The recovered 16QAM millimeter-wave signal constellation diagram is shown below. Figure 15 As shown.

[0069] It is understandable that the effective power of the vector millimeter-wave signal generated by the system depends on the power of the unmodulated sideband and the vector modulated signal. Therefore, the effective power of the vector millimeter-wave signal can be adjusted by changing the values ​​of the inner-band signal c / a and the outer-band signal d / b. For example, in a transmission scenario of a 40GHz 2Gb / s 16QAM signal transmitted over a 20km SMF fiber, when the input PD power is fixed at -9.7dBm, the transmission error vector magnitude (EVM) performance is as follows: Figure 16 As shown in the figure, the optimal EVM performance is achieved when the inner and outer band frequency ratios are 1.5 and 2, respectively, with corresponding EVM values ​​of 9.3% and 9.5%. Therefore, in the following simulations, the c / a and d / b ratios are fixed at 1.5 and 2.

[0070] Furthermore, such as Figure 17 The figure shows the EVM performance versus γ value curves of a 40GHz 2Gb / s 16QAM signal transmitted simultaneously in the inner and outer bands over a 20km SMF fiber. In the simulation, the input power to the PD was fixed at -9.7dBm. As the γ value increased, the EVM performance of the outer band signal gradually improved, while the inner band signal showed the opposite trend. The overall EVM performance of both the inner and outer band signals was best when the γ value was 1.1. Therefore, in the following simulations, the γ value was fixed at 1.1.

[0071] Furthermore, such as Figure 18 The figure shows the bit error rate (BER) and attenuation curves of a 40GHz 2Gb / s 16QAM signal transmitted simultaneously in the inner and outer bands of a 20km SMF optical fiber. Attenuation refers to the degree to which attenuator 5 attenuates the input optical signal, affecting the suppression of the optical carrier. Understandably, controlling the attenuation of attenuator 5 can minimize the system's BER. Specifically, as shown... Figure 18 As shown, the bit error rate is minimized when the attenuation of the attenuator is set to 5.031dB.

[0072] Furthermore, such as Figure 19The figure shows the relationship between bit error rate (BER) performance and PD input power when transmitting transmitter data modulated with 2 / 4 Gbaud 16QAM via a 40 GHz millimeter-wave carrier. Specifically, in a back-to-back (BTB) transmission scenario, the BER of both inband and outband signals reaches the Hard Decision Front Error Correction (HD-FEC) threshold when the symbol rate is 2 Gbaud / s and the received optical power is -18.37 dBm, and when the symbol rate is 4 Gbaud / s and the received optical power is -18.25 dBm.

[0073] Furthermore, such as Figure 20 The figure shows the relationship between fiber length and bit error rate (BER). Specifically, the 40GHz band signals generated in both the inner and outer bands have a BER of less than 3.8 × 10⁻³ over a transmission distance of 60 km. Furthermore, comparing the BER performance of ordinary SMF fiber and nonlinear dispersive fiber (NLSF) with a nonlinear exponent of 26e⁻²⁰ m² / W, the BER performance of the signal transmitted via SMF is superior to that transmitted via NLSF. This is mainly due to the influence of nonlinear factors in NLSF on signal transmission performance. The nonlinear fiber is a fiber type used in VPI simulation software, which can add a certain nonlinear exponent to simulate the nonlinear effects of signals during fiber transmission; the other parameters are basically the same as those of SMF.

[0074] Understandably, the above simulation analysis verifies the requirements of the technical solution of this application for the ratios c / a, b / d, γ values, and the attenuation. The simulation results show that the technical solution of this application has strong feasibility. When the attenuation is controlled within a certain range, the output millimeter wave signal performance can be maintained well.

[0075] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0076] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0077] In the several embodiments provided in this application, it should be understood that the disclosed system can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0078] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0079] In addition, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0080] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0081] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A signal generation system, characterized in that, include: Externally modulated lasers are used to generate optical carrier waves; A beam splitter is used to divide the optical carrier into a first subcarrier and a second subcarrier; A Mach-Zehnder modulator (MZM) is used to acquire a driving signal and modulate the first subcarrier according to the driving signal to generate a first optical signal, wherein the driving signal is an asymmetric dual single-sideband signal. A phase shifter is used to phase shift the second subcarrier; An attenuator is used to attenuate the phase-shifted second subcarrier to generate a second optical signal; A coupler is used to couple and superimpose the first optical signal and the second optical signal to generate a third optical signal; The photoelectric conversion unit is used to convert the third optical signal into an electrical signal, wherein the electrical signal is a millimeter-wave signal or a terahertz signal.

2. The system according to claim 1, characterized in that, The system also includes a digital signal processor and a digital-to-analog converter, wherein, The digital signal processor is used to generate sideband signals, wherein the sideband signals are digital signals; The digital-to-analog converter is used to generate the driving signal based on the sideband signal, wherein the driving signal is an analog signal; The driving signal includes a first vector modulation signal, a second vector modulation signal, a first unmodulated sideband signal, and a second unmodulated sideband signal; The frequency of the first unmodulated sideband signal is a first frequency, and the frequency of the second unmodulated sideband signal is a second frequency; the first frequency is greater than the second frequency, and both are greater than zero; the frequency of the first vector modulated signal is the opposite of the first frequency, and the frequency of the second vector modulated signal is the opposite of the second frequency.

3. The system according to claim 1, characterized in that, The phase difference between the phase-shifted second subcarrier and the first subcarrier is .

4. The system according to claim 1, characterized in that, in: The beam splitter includes a first input port, a first output port, and a second output port; One end of the MZM is connected to the first output port; One end of the phase shifter is connected to the second output port, and the other end of the phase shifter is connected to one end of the attenuator; The coupler includes a second input port, a third input port, and a third output port. The second input port is connected to the other end of the MZM, and the third input port is connected to the other end of the attenuator. The third output port is optically connected to the photoelectric conversion unit.

5. The system according to any one of claims 1-4, characterized in that, The photoelectric conversion unit includes a Mach-Zehnder interferometer (MZI), a first photoelectric converter, and a second photoelectric converter. The conversion of the third optical signal into an electrical signal includes: The MZI is used to acquire the third optical signal and separate the third optical signal into a fourth optical signal and a fifth optical signal; The electrical signal includes a first electrical signal and a second electrical signal; The first photoelectric converter is used to generate the first electrical signal based on the fourth optical signal, and the second photoelectric converter is used to generate the second electrical signal based on the fifth optical signal.

6. The system according to claim 5, characterized in that, in, The driving signal includes a first vector modulation signal, a second vector modulation signal, a first unmodulated sideband signal, and a second unmodulated sideband signal; The frequency of the first unmodulated sideband signal is a first frequency, and the frequency of the second unmodulated sideband signal is a second frequency; the first frequency is greater than the second frequency, and both are greater than zero; the frequency of the first vector modulated signal is the opposite of the first frequency, and the frequency of the second vector modulated signal is the opposite of the second frequency; The separation of the third optical signal into the fourth and fifth optical signals satisfies the first condition: The first frequency is equal to 1.25 times the free spectral range of the MZI; The second frequency is equal to 0.75 times the free spectral range of the MZI; The carrier frequency of the electrical signal is equal to twice the free spectral range of the MZI.

7. The system according to claim 6, characterized in that, The system further includes a transmission optical fiber, wherein the transmission optical fiber is disposed between the coupler and the photoelectric conversion unit, wherein the transmission optical fiber is a single-mode optical fiber, and at least one optical fiber amplifier is disposed on the transmission optical fiber.

8. A signal transmitter, characterized in that, Includes a system and antenna as described in any one of claims 1 to 7, wherein the antenna is used to transmit the millimeter-wave signal or terahertz signal.

9. A signal transceiver, characterized in that, The system and signal receiver included in any one of claims 1 to 7, the signal receiver being used to receive another millimeter-wave signal or terahertz signal and to process the other millimeter-wave signal or terahertz signal.

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