Hybrid encoding signal generation system and method based on actively mode-locked optoelectronic oscillator

Abstract

The application example relates to the field of microwave photonics, in particular to a hybrid encoding signal generation system and method based on an active mode-locked optoelectronic oscillator, which comprises an active mode-locked optoelectronic oscillator, the active mode-locked optoelectronic oscillator is composed of a semiconductor continuous wave laser, a double-drive Mach-Zehnder modulator, an optical fiber, an erbium-doped fiber amplifier, an optoelectronic detector, a radio frequency amplifier, an electric band-pass filter, an electric coupler and an arbitrary waveform generator; the arbitrary waveform generator is used for generating a hybrid encoding signal to modulate an optical carrier. The scheme realizes the organic combination of spontaneous oscillation of a microwave signal and hybrid encoding modulation, and meets the needs of high frequency, high stability and high data transmission rate.

Description

Technical Field

[0001] This application relates to the field of microwave photonics, and more particularly to a method for generating hybrid coded signals based on an active mode-locked optoelectronic oscillator. Background Technology

[0002] An active mode-locked optoelectronic oscillator (AMO) is a microwave signal generation system based on microwave photonics, widely used in optical communication systems, radar signal sources, and high-precision clock synchronization. Through an optoelectronic feedback loop and an active mode-locking mechanism, it can generate microwave signals with high stability and low phase noise. A typical AMO structure includes a laser, a Mach-Zehnder electro-optic modulator, an optical fiber, a photodetector, an optical amplifier, an RF amplifier, and an RF signal source.

[0003] In free-space optical communication, optical signals are susceptible to interference from turbulence and haze during atmospheric transmission. Pulse position modulation (PPM) can improve the signal's noise immunity, while pulse amplitude modulation (PAM) increases the data rate through multi-level amplitude coding. Therefore, combining these two modulation methods for hybrid modulation coding can significantly improve spectral efficiency and data transmission rate while ensuring interference resistance, making it suitable for long-distance and high-bandwidth scenarios. Compared to traditional microwave oscillators based on electronic devices, active mode-locked optoelectronic oscillators, due to their high-Q resonant cavity constructed from long optical fibers, offer advantages such as low phase noise and high frequency stability.

[0004] However, existing active mode-locked optoelectronic oscillators can only generate continuous pulse signals with uniform time intervals and amplitudes. This uniform pulse characteristic limits their application in complex coding and high-density communication. Furthermore, common methods of single-encoding continuous pulse signals suffer from insufficient information capacity and limited anti-interference capabilities, making it difficult to extend to higher bit encoding. On the other hand, traditional microwave oscillators based on electronic devices experience increased phase noise in high-frequency signals due to the thermal noise of these devices. When generating X-band and higher frequency signals (8 GHz and above), the commonly used frequency multiplication techniques based on nonlinear devices significantly increase the phase noise, making it difficult to meet the low phase noise requirements of applications such as radar signal sources and high-precision clock synchronization. Summary of the Invention

[0005] One objective of this application is to provide a hybrid coded signal generation system and method based on an active mode-locked optoelectronic oscillator, in order to solve the technical problems in the prior art where the uniform continuous pulse signal generated by the active mode-locked optoelectronic oscillator limits complex coding applications, and traditional electronic oscillators have large phase noise at high frequencies, making it difficult to meet low noise requirements.

[0006] In a first aspect, a hybrid coded signal generation system based on an active mode-locked optoelectronic oscillator is provided, comprising an active mode-locked optoelectronic oscillator, wherein the active mode-locked optoelectronic oscillator is composed of a semiconductor continuous-wave laser, a dual-drive Mach-Zehnder modulator, an optical fiber, an erbium-doped fiber amplifier, a photodetector, a radio frequency amplifier, an electrical bandpass filter, an electrical coupler, and an arbitrary waveform generator; the semiconductor continuous-wave laser is used to generate an optical carrier, the dual-drive Mach-Zehnder modulator is used to modulate the optical carrier to form a modulated optical signal; the optical fiber is used to transmit the modulated optical signal; and the erbium-doped fiber amplifier is used to modulate the optical carrier. The optical signal is adjusted to obtain a modulated optical signal; the photodetector is used to perform photoelectric conversion on the modulated optical signal to form a photocurrent and obtain a first microwave signal; the radio frequency amplifier is used to amplify the first microwave signal to obtain an amplified first microwave signal; the electric bandpass filter is used to filter the amplified first microwave signal to obtain a target microwave signal; the electric coupler is used to feed the target microwave signal back to the dual-drive Mach-Zehnder modulator and / or output microwave pulses; the arbitrary waveform generator is used to generate a mixed coded signal to modulate the optical carrier.

[0007] In conjunction with the first aspect, in one possible implementation, when the arbitrary waveform generator is not operating in the initial state, the semiconductor continuous wave laser is connected to the first port of the dual-drive Mach-Zehnder modulator, the dual-drive Mach-Zehnder modulator transmits signals to the erbium-doped fiber amplifier through the optical fiber, the erbium-doped fiber amplifier is connected to the photodetector, the photodetector is connected to the radio frequency amplifier, the radio frequency amplifier is connected to the electrical bandpass filter, the electrical bandpass filter is connected to the first port of the electrical coupler, and the second port of the electrical coupler is connected to the second port of the dual-drive Mach-Zehnder modulator, forming a first loop, and the target microwave signal generated by the first loop is the second microwave signal.

[0008] In conjunction with the first aspect, in one possible implementation, in the first circuit, the semiconductor continuous-wave laser generates a first optical carrier, which is modulated by the dual-drive Mach-Zehnder modulator to form a first modulated optical signal; the first modulated optical signal is transmitted through the optical fiber to the erbium-doped fiber amplifier, which adjusts the power of the first modulated optical signal to obtain an adjusted first modulated optical signal; the adjusted first modulated optical signal is photoelectrically converted by the photodetector to form a first photocurrent, resulting in a third microwave signal; the radio frequency amplifier amplifies the third microwave signal to obtain an amplified third microwave signal; the electrical bandpass filter filters the amplified third microwave signal to obtain a second microwave signal; and the electrical coupler feeds the second microwave signal back to the dual-drive Mach-Zehnder modulator.

[0009] In conjunction with the first aspect, in one possible implementation, after forming the second microwave signal corresponding to the first loop, the arbitrary waveform generator is activated, connecting the semiconductor continuous wave laser to the first port of the dual-drive Mach-Zehnder modulator, the arbitrary waveform generator to the third port of the dual-drive Mach-Zehnder modulator, the dual-drive Mach-Zehnder modulator transmitting signals to the erbium-doped fiber amplifier via the optical fiber, the erbium-doped fiber amplifier being connected to the photodetector, the photodetector being connected to the radio frequency amplifier, the radio frequency amplifier being connected to the electrical bandpass filter, the electrical bandpass filter being connected to the first port of the electrical coupler, and the second port of the electrical coupler being connected to the second port of the dual-drive Mach-Zehnder modulator, forming a second loop, wherein the target microwave signal generated by the second loop is the fourth microwave signal.

[0010] In conjunction with the first aspect, in one possible implementation, in the second loop, the arbitrary waveform generator generates the mixed coded signal, the semiconductor continuous wave laser generates a second optical carrier, and the mixed coded signal and the second microwave signal are modulated onto the second optical carrier by the dual-drive Mach-Zehnder modulator to form a second modulated optical signal; the second modulated optical signal is transmitted through the optical fiber to the erbium-doped fiber amplifier, and the erbium-doped fiber amplifier adjusts the power of the second modulated optical signal to obtain an adjusted second modulated optical signal; the adjusted second modulated optical signal is photoelectrically converted by the photodetector to form a second photocurrent, resulting in a fifth microwave signal; the radio frequency amplifier amplifies the fifth microwave signal to obtain an amplified fifth microwave signal; the electric bandpass filter filters the amplified fifth microwave signal to obtain a fourth microwave signal; and the electric coupler feeds the fourth microwave signal back to the dual-drive Mach-Zehnder modulator and outputs the microwave pulse.

[0011] In conjunction with the first aspect, in one possible implementation, the period of the hybrid coded signal is the same as the free spectrum range of the active mode-locked optoelectronic oscillator, and each period of the hybrid coded signal contains three triangular wave signals, the shape and amplitude of which are used for amplitude modulation.

[0012] In conjunction with the first aspect, in one possible implementation, after generating the triangular wave signal, the second circuit generates a pulse signal corresponding to the three triangular wave signals, the period of which is the same as the free spectrum range of the active mode-locked optoelectronic oscillator, and the pulse signal is used for pulse position modulation.

[0013] In a second aspect, a method for generating hybrid encoded signals based on an active mode-locked optoelectronic oscillator is provided, implemented based on the system described in any one of the first aspects, characterized in that it includes:

[0014] The acquired optical carrier is modulated to form a modulated optical signal;

[0015] The modulated optical signal is adjusted to obtain an adjusted modulated optical signal;

[0016] The modulated optical signal after adjustment is converted into a photoelectric signal to obtain a first microwave signal;

[0017] The first microwave signal is amplified to obtain the amplified first microwave signal;

[0018] The amplified first microwave signal is filtered to obtain the target microwave signal;

[0019] Output the target microwave signal.

[0020] In conjunction with the second aspect, in one possible implementation, modulating the acquired optical carrier to form a modulated optical signal includes: acquiring a hybrid coded signal and a second microwave signal, wherein the second microwave signal is a microwave signal formed in the initial state when the arbitrary waveform generator in the system is not working; and modulating the optical carrier according to the hybrid coded signal and the second microwave signal to obtain the modulated optical signal.

[0021] In conjunction with the second aspect, in one possible implementation, the hybrid coded signal includes amplitude modulation and pulse position modulation.

[0022] In the aforementioned scheme of the hybrid coded signal generation system and method based on an active mode-locked optoelectronic oscillator, this scheme utilizes a combination of a semiconductor continuous-wave laser and a dual-drive Mach-Zehnder modulator to achieve efficient modulation of the optical carrier, forming a high-quality modulated optical signal and improving the signal integrity and stability of the system. Optical fiber transmission and an erbium-doped fiber amplifier are used to regulate the modulated optical signal, effectively compensating for transmission loss, ensuring signal strength and quality, and improving the transmission distance and performance of the system. A photoelectric detector achieves photoelectric conversion, efficiently converting the optical signal into a microwave signal. Combined with an RF amplifier and an electrical bandpass filter, the microwave signal is amplified and filtered to obtain a high-purity, high-stability target microwave signal. An electrical coupler feeds the target microwave signal back to the dual-drive Mach-Zehnder modulator, forming a closed-loop feedback to achieve active mode-locking, ensuring the frequency stability and low phase noise of the microwave signal. Furthermore, the introduction of an arbitrary waveform generator allows for the flexible generation of various complex hybrid coded signals, which are then loaded onto the optical carrier. This enables the generated optical or microwave pulses to carry specific coded information, giving the system flexible signal modulation capabilities, enabling complex coding and high-density information transmission, and improving spectral efficiency and anti-interference capabilities. Therefore, this scheme achieves an organic combination of spontaneous oscillation of microwave signals and hybrid coding modulation, meeting the requirements of high frequency, high stability and high data transmission rate. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of a hybrid coded signal generation system based on an active mode-locked optoelectronic oscillator according to an embodiment of the present invention;

[0025] Figure 2 This is a flowchart illustrating a hybrid coded signal generation method based on an active mode-locked optoelectronic oscillator according to an embodiment of the present invention;

[0026] Figure 3 This is a schematic diagram of three triangular wave signals (two periodic waveforms) corresponding to the four-bit binary number 0110 in one embodiment of the present invention;

[0027] Figure 4 This is a waveform diagram of three triangular wave signals (two periodic waveforms) corresponding to the four-bit binary number 0111 in one embodiment of the present invention.

[0028] Figure 5 This is a waveform diagram of three triangular wave signals (two periodic waveforms) corresponding to the four-bit binary number 1111 in one embodiment of the present invention.

[0029] Figure 6 This is a schematic diagram of three pulse signals (two periodic waveforms) corresponding to the four-bit binary number 0110 in one embodiment of the present invention;

[0030] Figure 7 This is a schematic diagram of three pulse signals (two periodic waveforms) corresponding to the four-bit binary number 0111 in one embodiment of the present invention;

[0031] Figure 8 This is a schematic diagram of three pulse signals (two periodic waveforms) corresponding to the four-bit binary number 1111 in one embodiment of the present invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0033] It should be noted that, unless there is a conflict, the various features in the embodiments of this application can be combined with each other, all of which are within the protection scope of this application. Furthermore, although functional modules are divided in the device schematic diagram and a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in a different order than the module division in the device or the order in the flowchart. Moreover, the terms "first," "second," and "third" used in this application do not limit the data or execution order, but only distinguish identical or similar items with essentially the same function and effect.

[0034] The present invention will now be described in detail through specific embodiments.

[0035] The technical solution of this application can be applied to the generation of hybrid encoded signals based on active mode-locked optoelectronic oscillators.

[0036] In view of this, this application proposes a hybrid coded signal generation system based on an active mode-locked optoelectronic oscillator, which will be described in detail below.

[0037] Please see Figure 1 , Figure 1 This is a schematic diagram of the structure of a hybrid coded signal generation system based on an active mode-locked optoelectronic oscillator provided in an embodiment of the present invention. Figure 1 The hybrid coded signal generation system based on an active mode-locked optoelectronic oscillator includes an active mode-locked optoelectronic oscillator, which comprises a semiconductor continuous-wave laser 1, a dual-drive Mach-Zehnder modulator 2, an optical fiber 3, an erbium-doped fiber amplifier 4, a photodetector 5, an RF amplifier 6, an electrical bandpass filter 7, an electrical coupler 8, and an arbitrary waveform generator 9. The semiconductor continuous-wave laser 1 generates an optical carrier, and the dual-drive Mach-Zehnder modulator 2 modulates the optical carrier to form a modulated optical signal. The optical fiber 3 transmits the modulated optical signal, and the erbium-doped fiber amplifier 4 modulates the modulated signal. The optical signal is modulated to obtain a modulated optical signal; the photodetector 5 is used to perform photoelectric conversion on the modulated optical signal to form a photocurrent and obtain a first microwave signal; the radio frequency amplifier 6 is used to amplify the first microwave signal to obtain an amplified first microwave signal; the electric bandpass filter 7 is used to filter the amplified first microwave signal to obtain a target microwave signal; the electric coupler 8 is used to feed the target microwave signal back to the dual-drive Mach-Zehnder modulator 2 and / or output microwave pulses; the arbitrary waveform generator 9 is used to generate a mixed coded signal to modulate the optical carrier.

[0038] Among them, the optical fiber can be a single-mode long optical fiber.

[0039] Among them, the hybrid coded signal can be a microwave signal modulated by a hybrid coded four-bit binary number.

[0040] The microwave pulse can be a target microwave signal or a local target microwave signal.

[0041] Since this scheme includes both the initial state where the arbitrary waveform generator is not started and the state where the arbitrary waveform generator is started, it includes two loops.

[0042] Specifically, the first circuit is the circuit in the initial state when the arbitrary waveform generator is not working. The first microwave signal is equivalent to the third microwave signal below, and the target microwave signal is equivalent to the second microwave signal below. Therefore, the process of the dual-drive Mach-Zehnder modulator 2 modulating the optical carrier to form a modulated optical signal is carried out in the first circuit, forming the first modulated optical signal.

[0043] Specifically, after the second microwave signal corresponding to the first circuit is formed, the arbitrary waveform generator 9 is activated to generate a mixed coded signal. The first microwave signal is equivalent to the fifth microwave signal below, and the target microwave signal is equivalent to the fourth microwave signal below. Therefore, the process of the dual-drive Mach-Zehnder modulator 2 modulating the optical carrier to form a modulated optical signal in the second circuit forms the second modulated optical signal.

[0044] The mixed coded signal generated by the arbitrary waveform generator 9 can contain various modulation formats (such as amplitude, phase, frequency coding, etc.) or specific sequences. This makes the output optical pulse or the microwave pulse output through the electric coupler 8 carry this coded information itself, providing a foundation for subsequent signal processing (such as high-speed communication, radar coding, complex sensing, etc.).

[0045] In this scheme, the dual-drive Mach-Zehnder modulator 2 is not only driven by the target microwave signal from the electrocoupler 8 to achieve mode-locking, but also driven by the hybrid coded signal generated by the arbitrary waveform generator 9 to load these coded information in the optical domain. This dual drive is the key to its achievement of active mode-locking and hybrid coding.

[0046] Therefore, the semiconductor continuous wave laser 1, the dual-drive Mach-Zehnder modulator 2, the optical fiber 3, the erbium-doped fiber amplifier 4, the photodetector 5, the radio frequency amplifier 6, the electrical bandpass filter 7, the electrical coupler 8, and the arbitrary waveform generator 9 work together to form a closed-loop feedback structure, achieving active mode-locked photoelectric oscillation and ensuring high frequency stability and low phase noise characteristics of the microwave signal. Furthermore, by introducing the hybrid coded signal generated by the arbitrary waveform generator 9, the system can not only spontaneously generate high-quality microwave signals but also achieve multi-dimensional signal modulation, meeting the application requirements of high bandwidth and high anti-interference capability.

[0047] In one possible example, in the initial state, the arbitrary waveform generator is not working, the semiconductor continuous wave laser is connected to the first port of the dual-drive Mach-Zehnder modulator, the dual-drive Mach-Zehnder modulator transmits signals to the erbium-doped fiber amplifier through the optical fiber, the erbium-doped fiber amplifier is connected to the photodetector, the photodetector is connected to the radio frequency amplifier, the radio frequency amplifier is connected to the electrical bandpass filter, the electrical bandpass filter is connected to the first port of the electrical coupler, and the second port of the electrical coupler is connected to the second port of the dual-drive Mach-Zehnder modulator, forming a first loop. The target microwave signal generated by the first loop is the second microwave signal.

[0048] In one possible example, in the first loop, the semiconductor continuous-wave laser generates a first optical carrier, which is modulated by the dual-drive Mach-Zehnder modulator to form a first modulated optical signal; the first modulated optical signal is transmitted through the optical fiber to the erbium-doped fiber amplifier, which adjusts the power of the first modulated optical signal to obtain an adjusted first modulated optical signal; the adjusted first modulated optical signal is photoelectrically converted by the photodetector to form a first photocurrent, resulting in a third microwave signal; the radio frequency amplifier amplifies the third microwave signal to obtain an amplified third microwave signal; the electric bandpass filter filters the amplified third microwave signal to obtain a second microwave signal; and the electric coupler feeds the second microwave signal back to the dual-drive Mach-Zehnder modulator.

[0049] In one possible example, after forming the second microwave signal corresponding to the first loop, the arbitrary waveform generator is activated, connecting the semiconductor continuous wave laser to the first port of the dual-drive Mach-Zehnder modulator, the arbitrary waveform generator to the third port of the dual-drive Mach-Zehnder modulator, the dual-drive Mach-Zehnder modulator transmitting signals to the erbium-doped fiber amplifier via the optical fiber, the erbium-doped fiber amplifier being connected to the photodetector, the photodetector being connected to the radio frequency amplifier, the radio frequency amplifier being connected to the electrical bandpass filter, the electrical bandpass filter being connected to the first port of the electrical coupler, and the second port of the electrical coupler being connected to the second port of the dual-drive Mach-Zehnder modulator, forming a second loop. The target microwave signal generated by the second loop is the fourth microwave signal.

[0050] In one possible example, in the second loop, the arbitrary waveform generator generates the mixed-coded signal, the semiconductor continuous-wave laser generates a second optical carrier, and the mixed-coded signal and the second microwave signal are modulated onto the second optical carrier by the dual-drive Mach-Zehnder modulator to form a second modulated optical signal; the second modulated optical signal is transmitted through the optical fiber to the erbium-doped fiber amplifier, which adjusts the power of the second modulated optical signal to obtain an adjusted second modulated optical signal; the adjusted second modulated optical signal is photoelectrically converted by the photodetector to form a second photocurrent, resulting in a fifth microwave signal; the radio frequency amplifier amplifies the fifth microwave signal to obtain an amplified fifth microwave signal; the electric bandpass filter filters the amplified fifth microwave signal to obtain a fourth microwave signal; and the electric coupler feeds the fourth microwave signal back to the dual-drive Mach-Zehnder modulator and outputs the microwave pulse.

[0051] In one possible example, the period of the hybrid coded signal is the same as the free spectrum range of the active mode-locked opto-oscillator, and each period of the hybrid coded signal contains three triangular wave signals, the shape and amplitude of which are used for amplitude modulation.

[0052] The Free Spectral Range (FSR) is a key parameter of an optical ring cavity (composed of components such as optical fiber 3). It refers to the frequency interval between two adjacent longitudinal modes (i.e., the optical wave frequencies that can stably exist within the cavity), or in other words, the range of optical frequencies that the cavity can accommodate. For a stably mode-locked fiber ring, the FSR determines the repetition frequency of the output pulse sequence.

[0053] The period of the hybrid coded signal, being the same as the period of the AWG signal, represents a complete repetition cycle of the hybrid coded signal generated by the AWG, which corresponds exactly to the time required for a light wave to travel one round trip within the photoelectric oscillator cavity (or, in other words, the reciprocal of the FSR). This ensures that the coded signal can act on the modulator periodically and synchronously, coordinating with the mode-locking process within the cavity. Simply put, the coded signal applies its coded information completely only once within each pulse repetition cycle.

[0054] The presence of three triangular wave signals within each cycle indicates that the modulator is modulated by three different triangular wave shapes within each pulse repetition cycle.

[0055] Among them, the period of the mixed coded signal generated by the arbitrary waveform generator is consistent with the free spectrum range of the active mode-locked optoelectronic oscillator, and each period contains three triangular wave signals; the three triangular wave signals are named triangular wave 1, triangular wave 2, and triangular wave 3 in the order of their generation in the time domain from first to last.

[0056] A time width of one-fifth of each cycle for the first triangular wave indicates that the second highest bit of the four-bit binary number is 1, and a time width of one-tenth of each cycle indicates that the second highest bit of the four-bit binary number is 0.

[0057] A time width of one-fifth of each cycle for the second-lowest bit of a four-bit binary number indicates that the second-lowest bit is 1, and a time width of one-tenth of each cycle indicates that the second-lowest bit of a four-bit binary number is 0.

[0058] A time width of one-fifth of each cycle for the No. 3 triangular wave indicates that the least significant bit of the four-bit binary number is 1, and a time width of one-tenth of each cycle indicates that the least significant bit of the four-bit binary number is 0.

[0059] A time interval of three-tenths of a cycle between the peak value of triangle wave 2 and the peak value of triangle wave 1 indicates that the highest bit of the four-bit binary number is 1, and a time interval of one-fifth of a cycle between the peak value of triangle wave 2 and the peak value of triangle wave 1 indicates that the highest bit of the four-bit binary number is 0.

[0060] The following are examples of three triangular wave signals (two-period waveforms) corresponding to three different four-bit binary numbers: Example corresponding to the four-bit binary number 0110 is as follows... Figure 3 As shown, an example corresponding to the four-bit binary number 0111 is as follows: Figure 4 As shown, an example corresponding to the four-bit binary number 1111 is as follows: Figure 5 As shown.

[0061] As can be seen, this embodiment emphasizes the synchronization between the signal and the inherent period (FSR) of the photoelectric oscillator through the specific time-domain structure of the hybrid encoded signal, and how the three triangular waves contained within it are used to precisely control the amplitude of the optical pulse, thereby achieving complex signal encoding. This enables the active mode-locked photoelectric oscillator to not only generate high-quality mode-locked pulses, but also to load specific amplitude modulation information defined by the shape and amplitude of the triangular waves onto the pulses, greatly increasing the system's flexibility and application range.

[0062] In one possible example, after generating the triangular wave signal, the second circuit generates a pulse signal corresponding to the three triangular wave signals, the period of which is the same as the free spectrum range of the active mode-locked optoelectronic oscillator, and the pulse signal is used for pulse position modulation.

[0063] In this modulation, the pulse signal is used for pulse position modulation (PPM). In PPM, information is encoded by changing the position of the pulse signal within each cycle. That is, the timing of the pulse changes according to the input signal. This modulation method has high interference immunity because information is transmitted through pulse position rather than amplitude.

[0064] In this circuit, after the arbitrary waveform generator produces three triangular wave periodic signals with coded information, the second circuit will generate three pulse signals corresponding to the three triangular waves, with periods consistent with the free spectrum range of the active mode-locked optoelectronic oscillator. The three pulse signals are designated as pulse 1, pulse 2, and pulse 3 in the time domain, generated sequentially from first to last.

[0065] A triangular wave with a time width of one-fifth of each cycle can generate a high-amplitude loop pulse signal, while a time width of one-tenth of each cycle can generate a low-amplitude loop pulse signal, thus achieving amplitude modulation coding. The time interval between the second and first triangular waves can control the time interval between the second and first pulses in the three-pulse cycle signal, thus achieving pulse position modulation coding.

[0066] Figure 3 As shown, after the three triangular wave signals corresponding to the four-bit binary number 0110 are modulated on the optical carrier, the active mode-locked optoelectronic oscillator loop will generate three pulse signals corresponding to the binary number 0110, such as... Figure 6 As shown; Figure 4 As shown, after the three triangular wave signals corresponding to the four-bit binary number 0111 are modulated on the optical carrier, the active mode-locked optoelectronic oscillator loop will generate three pulse signals corresponding to the binary number 0111, such as... Figure 7 As shown; Figure 5 As shown, after the three triangular wave signals corresponding to the four-bit binary number 1111 are modulated on the optical carrier, the active mode-locked optoelectronic oscillator loop will generate three pulse signals corresponding to the binary number 1111, such as... Figure 8 As shown.

[0067] As can be seen, by using pulse position modulation with a pulse signal corresponding to the triangular wave signal in this embodiment, the system can effectively encode information in both spatial and temporal dimensions. This not only improves the system's data transmission efficiency but also enhances its resistance to noise and signal distortion, making it suitable for communication applications in high-noise environments. Furthermore, this multi-modulation scheme achieves higher spectrum utilization, enabling the system to transmit more information within limited spectrum resources.

[0068] This scheme utilizes a semiconductor continuous-wave laser combined with a dual-drive Mach-Zehnder modulator to achieve efficient modulation of the optical carrier, forming a high-quality modulated optical signal and improving the system's signal integrity and stability. Fiber optic transmission and an erbium-doped fiber amplifier are used to regulate the modulated optical signal, effectively compensating for transmission loss, ensuring signal strength and quality, and improving the system's transmission distance and performance. A photodetector performs photoelectric conversion, efficiently converting the optical signal into a microwave signal. Combined with an RF amplifier and an electrical bandpass filter, the microwave signal is amplified and filtered to obtain a high-purity, high-stability target microwave signal. An electrical coupler feeds the target microwave signal back to the dual-drive Mach-Zehnder modulator, forming a closed-loop feedback loop for active mode-locking, ensuring frequency stability and low phase noise of the microwave signal. Furthermore, an arbitrary waveform generator is introduced, which can flexibly generate various complex hybrid coded signals and load them onto the optical carrier, enabling the generated optical or microwave pulses to carry specific coded information. This gives the system flexible signal modulation capabilities, allowing for complex coding and high-density information transmission, improving spectral efficiency and anti-interference capabilities. Therefore, this scheme achieves an organic combination of spontaneous oscillation of microwave signals and hybrid coding modulation, meeting the requirements of high frequency, high stability and high data transmission rate.

[0069] It should be noted that in the above embodiments, there is no necessarily a certain order between the steps. Those skilled in the art can understand from the description of the embodiments of this application that the above steps may have different execution orders in different embodiments, that is, they may be executed in parallel or in turn, etc.

[0070] Figure 2 A flowchart illustrating a hybrid coded signal generation method based on an active mode-locked optoelectronic oscillator provided in an embodiment of the present invention is characterized by comprising the following steps:

[0071] S10. Modulate the acquired optical carrier to form a modulated optical signal.

[0072] The optical carrier wave is a pure, very high-frequency light wave generated by a semiconductor continuous-wave laser. It does not carry information itself, unlike the carrier wave in radio broadcasting; it serves as a medium to carry information.

[0073] In communication, modulation refers to the process of altering one or more characteristics (such as amplitude, frequency, and phase) of a carrier wave using a signal carrying information (modulated signal). In this scheme, it can be intensity modulation, that is, using a modulating signal to change the intensity of the optical carrier wave.

[0074] In this context, the modulated optical signal refers to the optical carrier wave that has been modulated. Its intensity is no longer constant, but changes regularly with the modulating signal, carrying the information contained in the modulating signal.

[0075] Specifically, the process of modulating the acquired optical carrier to form a modulated optical signal is accomplished by a dual-drive Mach-Zehnder modulator. It has two inputs that can receive electrical signals. One input receives a mixed-coded signal (containing three triangular waves, etc.) from an arbitrary waveform generator; this signal directly controls the intensity change of the optical carrier, forming the basic modulated optical signal. Simultaneously, the other input receives a target microwave signal fed back from an electrocoupler; this signal is used to "lock" the modulator's state, ensuring the entire loop generates stable mode-locked pulses. Therefore, the modulation process is actually dual-driven.

[0076] S20. The modulated optical signal is adjusted to obtain the adjusted modulated optical signal.

[0077] In this process, the modulated optical signal is first transmitted through a long single-mode optical fiber. Within the fiber, the modulated signal undergoes dispersion, causing the pulse to broaden over time. Simultaneously, the fiber introduces transmission loss, reducing signal power. Although nonlinear effects in single-mode fiber are generally weak, they can still occur under certain conditions. Therefore, after transmission through the fiber, both the shape (broadening) and power (decrease) of the modulated optical signal change. The further modulated signal then enters an erbium-doped fiber amplifier (EDFA). The EDFA's role is to compensate for the optical power lost during fiber transmission and potentially further enhance the signal power. This is an active power regulation process, ensuring sufficient signal strength in subsequent stages (such as photodetectors).

[0078] Therefore, "modulating the modulated optical signal" involves two sub-processes: passively changing the signal shape (broadening) and power (loss) in the optical fiber, and actively adjusting the signal power (amplification) in the EDFA. The resulting "modulated optical signal" refers to the optical signal after transmission broadening and power recovery (or enhancement). This regulated signal has a pulse width, shape, and power level that are more suitable for entering the next photoelectric conversion stage.

[0079] S30. The modulated optical signal after adjustment is converted into a photoelectric signal to obtain a first microwave signal.

[0080] Photoelectric conversion refers to the process of converting light signals into electrical signals using a photodetector. When a light signal shines on the detector, it excites electron-hole pairs, forming a current or voltage that is proportional to the light intensity.

[0081] The first microwave signal is an electrical signal obtained through photoelectric conversion. Since the modulated optical signal is periodically changing (especially in mode-locked mode, it contains a series of equally spaced pulses), its rapidly changing light intensity generates an alternating current / voltage of a corresponding frequency on the photodetector. This frequency is typically in the microwave range (hundreds of MHz to tens of GHz), hence the name "first microwave signal." It contains all the time-domain information of the optical signal.

[0082] S40. The first microwave signal is amplified to obtain an amplified first microwave signal.

[0083] Amplification refers to increasing the strength (power or voltage) of a signal. Since the signal output by a photodetector is usually quite weak, it needs to be amplified to drive subsequent circuits.

[0084] S50. Filter the amplified first microwave signal to obtain the target microwave signal.

[0085] Filtering refers to the process of using an electrical bandpass filter to extract components of a specific frequency range from a signal while suppressing other frequency components.

[0086] An electrical bandpass filter is a circuit or device that allows only electrical signals within a specific frequency range to pass through, while blocking signals outside that range. Its "passband" center frequency is typically set at the desired mode-locked frequency.

[0087] The target microwave signal refers to the microwave signal obtained after filtering, whose frequency and waveform meet the requirements.

[0088] S60, Output the target microwave signal.

[0089] The target microwave signal, after being output from the electrical bandpass filter, enters the electrical coupler. The electrical coupler has two main functions: 1. Feedback: It feeds back a portion of the target microwave signal to one of the drive terminals of the dual-drive Mach-Zehnder modulator (as the mode-locking drive signal) to maintain and stabilize the mode-locked state. 2. Output: It outputs another portion of the target microwave signal as the final output of the system. This output microwave signal is a stable microwave pulse signal obtained by photoelectric conversion of the optical pulse sequence, after amplification and filtering, and can be used for subsequent communication, radar, or other applications.

[0090] This solution effectively loads information into optical signals by modulating the acquired optical carrier, laying the foundation for high-speed, high-capacity information transmission. Adjusting the modulated optical signal improves signal quality, reduces noise and distortion, and ensures the stability and accuracy of subsequent conversion and processing. After photoelectric conversion, the optical signal is successfully converted into a microwave signal, achieving seamless integration of optical and microwave communication and expanding the scope of signal applications. Further amplification of the first microwave signal enhances signal strength, improves the signal-to-noise ratio, and ensures signal integrity during transmission and processing. Filtering removes redundant frequencies and noise, resulting in a purer target microwave signal that meets the system's high signal quality requirements. Finally, a high-quality target microwave signal is output, ensuring stable and accurate transmission to downstream equipment or systems, thus improving the overall performance and reliability of the communication system.

[0091] In one possible example, modulating the acquired optical carrier to form a modulated optical signal includes: acquiring a hybrid coded signal and a second microwave signal, wherein the second microwave signal is a microwave signal formed in the initial state when the arbitrary waveform generator in the system is not working; and modulating the optical carrier according to the hybrid coded signal and the second microwave signal to obtain the modulated optical signal.

[0092] The hybrid coded signal is generated by an arbitrary waveform generator (AWG, i.e., element 9). This signal contains complex information that needs to be loaded onto the optical pulse, which may include encodings of amplitude, phase, time position, etc.

[0093] The second microwave signal refers to the microwave signal generated when the system is in a specific "initial state". The key characteristic of this initial state is that "the arbitrary waveform generator is not working", indicating that no mixed coded signal from the AWG is involved in modulation at this time.

[0094] The modulation process is achieved through a dual-drive Mach-Zehnder modulator. The DD-MZM has two independent driving electrodes. One electrode (or channel) may be driven by a mixed-encoded signal to load complex amplitude or phase information onto the optical pulse (achieving mixed encoding); the other electrode (or channel) is driven by a second microwave signal. This second microwave signal typically drives the modulator to operate in a mode-locked state, or adjusts the pulse envelope, center frequency, etc., to maintain oscillation and mode-locking. By simultaneously applying these two signals to the modulator, complex encoding and mode-locking / pulse shaping can be achieved simultaneously in the optical domain. The resulting modulated optical signal is a sequence of optical pulses carrying mixed-encoded information and in a stable mode-locked state.

[0095] As can be seen, in this embodiment, the hybrid coded signal generated by the AWG is used to load information, while the second microwave signal generated by the system itself in the basic state is used to drive the modulator to maintain the mode-locked state or perform pulse shaping, thereby realizing complex information encoding and stable pulse generation on a single optical pulse sequence.

[0096] In one possible example, the hybrid coded signal includes amplitude modulation and pulse position modulation.

[0097] Amplitude modulation refers to the alteration of the level or power of a mixed-coded signal. In the optical domain, this typically manifests as a change in the intensity (brightness) of a light pulse. For example, a pulse might be modulated to high, low, or zero intensity to represent different data bits (such as binary 1s and 0s).

[0098] Pulse position modulation (PPM) refers to a hybrid coded signal that carries information by changing the position of pulses on the time axis. For example, within a fixed time window, pulses may appear at different preset positions (such as position 1, position 2, position 3, etc.), each representing a different information symbol or data block. PPM is a highly efficient modulation method, especially in power-constrained systems.

[0099] The period of the hybrid coded signal is the same as the free spectrum range of the active mode-locked optoelectronic oscillator. Each period of the hybrid coded signal contains three triangular wave signals, and the shape and amplitude of the triangular wave signals are used for amplitude modulation.

[0100] The Free Spectral Range (FSR) is a key parameter of an optical ring cavity (composed of components such as optical fiber 3). It refers to the frequency interval between two adjacent longitudinal modes (i.e., the optical wave frequencies that can stably exist within the cavity), or in other words, the range of optical frequencies that the cavity can accommodate. For a stably mode-locked fiber ring, the FSR determines the repetition frequency of the output pulse sequence.

[0101] The period of the hybrid coded signal, being the same as the period of the AWG signal, represents a complete repetition cycle of the hybrid coded signal generated by the AWG, which corresponds exactly to the time required for a light wave to travel one round trip within the photoelectric oscillator cavity (or, in other words, the reciprocal of the FSR). This ensures that the coded signal can act on the modulator periodically and synchronously, coordinating with the mode-locking process within the cavity. Simply put, the coded signal applies its coded information completely only once within each pulse repetition cycle.

[0102] The presence of three triangular wave signals within each cycle indicates that the modulator is modulated by three different triangular wave shapes within each pulse repetition cycle.

[0103] Among them, the period of the mixed coded signal generated by the arbitrary waveform generator is consistent with the free spectrum range of the active mode-locked optoelectronic oscillator, and each period contains three triangular wave signals; the three triangular wave signals are named triangular wave 1, triangular wave 2, and triangular wave 3 in the order of their generation in the time domain from first to last.

[0104] A time width of one-fifth of each cycle for the first triangular wave indicates that the second highest bit of the four-bit binary number is 1, and a time width of one-tenth of each cycle indicates that the second highest bit of the four-bit binary number is 0.

[0105] A time width of one-fifth of each cycle for the second-lowest bit of a four-bit binary number indicates that the second-lowest bit is 1, and a time width of one-tenth of each cycle indicates that the second-lowest bit of a four-bit binary number is 0.

[0106] A time width of one-fifth of each cycle for the No. 3 triangular wave indicates that the least significant bit of the four-bit binary number is 1, and a time width of one-tenth of each cycle indicates that the least significant bit of the four-bit binary number is 0.

[0107] A time interval of three-tenths of a cycle between the peak value of triangle wave 2 and the peak value of triangle wave 1 indicates that the highest bit of the four-bit binary number is 1, and a time interval of one-fifth of a cycle between the peak value of triangle wave 2 and the peak value of triangle wave 1 indicates that the highest bit of the four-bit binary number is 0.

[0108] The following are examples of three triangular wave signals (two-period waveforms) corresponding to three different four-bit binary numbers: Example corresponding to the four-bit binary number 0110 is as follows... Figure 3 As shown, an example corresponding to the four-bit binary number 0111 is as follows: Figure 4 As shown, an example corresponding to the four-bit binary number 1111 is as follows: Figure 5 As shown.

[0109] In this modulation, the pulse signal is used for pulse position modulation (PPM). In PPM, information is encoded by changing the position of the pulse signal within each cycle. That is, the timing of the pulse changes according to the input signal. This modulation method has high interference immunity because information is transmitted through pulse position rather than amplitude.

[0110] In this circuit, after the arbitrary waveform generator produces three triangular wave periodic signals with coded information, the second circuit will generate three pulse signals corresponding to the three triangular waves, with periods consistent with the free spectrum range of the active mode-locked optoelectronic oscillator. The three pulse signals are designated as pulse 1, pulse 2, and pulse 3 in the time domain, generated sequentially from first to last.

[0111] A triangular wave with a time width of one-fifth of each cycle can generate a high-amplitude loop pulse signal, while a time width of one-tenth of each cycle can generate a low-amplitude loop pulse signal, thus achieving amplitude modulation coding. The time interval between the second and first triangular waves can control the time interval between the second and first pulses in the three-pulse cycle signal, thus achieving pulse position modulation coding.

[0112] Figure 3 As shown, after the three triangular wave signals corresponding to the four-bit binary number 0110 are modulated on the optical carrier, the active mode-locked optoelectronic oscillator loop will generate three pulse signals corresponding to the binary number 0110, such as... Figure 6 As shown; Figure 4 As shown, after the three triangular wave signals corresponding to the four-bit binary number 0111 are modulated on the optical carrier, the active mode-locked optoelectronic oscillator loop will generate three pulse signals corresponding to the binary number 0111, such as... Figure 7 As shown; Figure 5 As shown, after the three triangular wave signals corresponding to the four-bit binary number 1111 are modulated on the optical carrier, the active mode-locked optoelectronic oscillator loop will generate three pulse signals corresponding to the binary number 1111, such as... Figure 8 As shown.

[0113] As can be seen, in this embodiment, the amplitude modulation and pulse position modulation hybrid coded signal generated by the arbitrary waveform generator enables the active mode-locked optoelectronic oscillator to generate such a signal, thereby achieving the transmission of four-bit binary numbers and solving the problem that existing active mode-locked optoelectronic oscillators cannot generate hybrid coded signals. Pulse position modulation encoding transmits information through the position of the pulse on the time axis, rather than amplitude, frequency, or phase. Therefore, it is not sensitive to amplitude noise such as additive white Gaussian noise. As long as the arrival time of the pulse signal is not completely masked by noise, the receiving end can extract effective information through time synchronization, thus exhibiting high anti-interference capability. Amplitude modulation encoding can improve spectrum utilization. This invention uses a hybrid approach of the two encoding methods, combining their advantages to make the hybrid coded signal generated by the active mode-locked optoelectronic oscillator suitable for scenarios that require a balance between anti-interference capability, bandwidth efficiency, and adaptability to complex environments. It also utilizes both time and amplitude dimensions to transmit information, thereby improving data transmission rate.

[0114] It should be noted that in the above embodiments, there is no necessarily a certain order between the steps. Those skilled in the art can understand from the description of the embodiments of this application that the above steps may have different execution orders in different embodiments, that is, they may be executed in parallel or in turn, etc.

[0115] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. The storage medium can be a magnetic disk, optical disk, read-only memory (ROM), or random access memory (RAM), etc.

[0116] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Therefore, any equivalent variations made in accordance with the claims of this application shall still fall within the scope of this application.

Claims

1. A hybrid coded signal generation system based on an active mode-locked optoelectronic oscillator, characterized in that, The device includes an active mode-locked optoelectronic oscillator, which comprises a semiconductor continuous-wave laser, a dual-drive Mach-Zehnder modulator, an optical fiber, an erbium-doped fiber amplifier, a photodetector, a radio frequency amplifier, an electrical bandpass filter, an electrical coupler, and an arbitrary waveform generator. The semiconductor continuous-wave laser is used to generate an optical carrier, and the dual-drive Mach-Zehnder modulator is used to modulate the optical carrier to form a modulated optical signal. The optical fiber is used to transmit the modulated optical signal. The erbium-doped fiber amplifier is used to adjust the modulated optical signal to obtain an adjusted modulated optical signal; the photodetector is used to perform photoelectric conversion on the adjusted modulated optical signal to form a photocurrent and obtain a first microwave signal; the radio frequency amplifier is used to amplify the first microwave signal to obtain an amplified first microwave signal. The electric bandpass filter is used to filter the amplified first microwave signal to obtain the target microwave signal; The electrocoupler is used to feed the target microwave signal back to the dual-drive Mach-Zehnder modulator and / or output microwave pulses; The arbitrary waveform generator is used to generate a mixed coded signal to modulate the optical carrier; In the initial state, the arbitrary waveform generator is not working. The semiconductor continuous wave laser is connected to the first port of the dual-drive Mach-Zehnder modulator. The dual-drive Mach-Zehnder modulator transmits signals to the erbium-doped fiber amplifier through the optical fiber. The erbium-doped fiber amplifier is connected to the photodetector, the photodetector is connected to the radio frequency amplifier, the radio frequency amplifier is connected to the electric bandpass filter, the electric bandpass filter is connected to the first port of the electric coupler, and the second port of the electric coupler is connected to the second port of the dual-drive Mach-Zehnder modulator, forming a first loop. The target microwave signal generated by the first loop is the second microwave signal. After forming the second microwave signal corresponding to the first loop, the arbitrary waveform generator is activated, connecting the semiconductor continuous wave laser to the first port of the dual-drive Mach-Zehnder modulator, and the arbitrary waveform generator to the third port of the dual-drive Mach-Zehnder modulator. The dual-drive Mach-Zehnder modulator transmits signals to the erbium-doped fiber amplifier via the optical fiber. The erbium-doped fiber amplifier is connected to the photodetector, the photodetector is connected to the radio frequency amplifier, the radio frequency amplifier is connected to the electrical bandpass filter, the electrical bandpass filter is connected to the first port of the electrical coupler, and the second port of the electrical coupler is connected to the second port of the dual-drive Mach-Zehnder modulator, forming a second loop. The target microwave signal generated by the second loop is the fourth microwave signal. In the second loop, the arbitrary waveform generator generates the mixed coded signal, the period of which is the same as the free spectrum range of the active mode-locked photoelectric oscillator.

2. The system according to claim 1, characterized in that, In the first loop, the semiconductor continuous wave laser generates an optical carrier, which is modulated by the dual-drive Mach-Zehnder modulator to form a first modulated optical signal. The first modulated optical signal is transmitted through the optical fiber to the erbium-doped fiber amplifier, which adjusts the power of the first modulated optical signal to obtain an adjusted first modulated optical signal. The adjusted first modulated optical signal is then converted into a first photocurrent by the photodetector to obtain a third microwave signal. The radio frequency amplifier amplifies the third microwave signal to obtain an amplified third microwave signal. The electric bandpass filter is used to filter the amplified third microwave signal to obtain the second microwave signal; the electric coupler is used to feed the second microwave signal back to the dual-drive Mach-Zehnder modulator.

3. The system according to claim 1, characterized in that, In the second loop, the semiconductor continuous wave laser generates an optical carrier, and the hybrid coded signal and the second microwave signal are modulated onto the optical carrier generated by the semiconductor continuous wave laser in the second loop by the dual-drive Mach-Zehnder modulator to form a second modulated optical signal; The second modulated optical signal is transmitted through the optical fiber to the erbium-doped fiber amplifier, which adjusts the power of the second modulated optical signal to obtain an adjusted second modulated optical signal. The adjusted second modulated optical signal is then converted into a second photocurrent by the photodetector to obtain a fifth microwave signal. The radio frequency amplifier amplifies the fifth microwave signal to obtain an amplified fifth microwave signal. The electric bandpass filter is used to filter the amplified fifth microwave signal to obtain the fourth microwave signal; the electric coupler is used to feed the fourth microwave signal back to the dual-drive Mach-Zehnder modulator and output the microwave pulse.

4. The system according to claim 3, characterized in that, Each cycle of the hybrid coded signal contains three triangular wave signals, the shape and amplitude of which are used for amplitude modulation.

5. The system according to claim 4, characterized in that, After generating the triangular wave signal, the second circuit generates a pulse signal corresponding to the three triangular wave signals. The period of the pulse signal is the same as the free spectrum range of the active mode-locked optoelectronic oscillator. The pulse signal is used for pulse position modulation.

6. A method for generating hybrid coded signals based on an active mode-locked optoelectronic oscillator, implemented based on the system described in any one of claims 1 to 5, characterized in that, include: The acquired optical carrier is modulated to form a modulated optical signal; The modulated optical signal is adjusted to obtain an adjusted modulated optical signal; The modulated optical signal after adjustment is converted into a photoelectric signal to obtain a first microwave signal; The first microwave signal is amplified to obtain the amplified first microwave signal; The amplified first microwave signal is filtered to obtain the target microwave signal; Output the target microwave signal.

7. The method according to claim 6, characterized in that, The process of modulating the acquired optical carrier to form a modulated optical signal includes: Acquire a hybrid coded signal and a second microwave signal, wherein the second microwave signal is a microwave signal formed in the initial state when the arbitrary waveform generator in the system is not working; The optical carrier is modulated according to the hybrid coded signal and the second microwave signal to obtain a modulated optical signal.

8. The method according to claim 7, characterized in that, The hybrid coded signal includes amplitude modulation and pulse position modulation.

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