Hybrid coded signal generation system and method based on active mode-locked optoelectronic oscillator

Abstract

The embodiment of the invention relates to the field of microwave photonics, in particular to a hybrid coded signal generation system and method based on an active mode-locked optoelectronic oscillator. 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 optical fiber amplifier, a photoelectric detector, a radio frequency amplifier, an electric band-pass filter, an electric coupler and an arbitrary waveform generator. The arbitrary waveform generator is configured to generate a hybrid coded signal to modulate an optical carrier. According to the scheme, the spontaneous oscillation of the microwave signal and the hybrid coded modulation are organically combined, and the requirements of high frequency, high stability and high data transmission rate are met.

Description

TECHNICAL FIELD

[0001] The embodiment of the present application relates to the field of microwave photonics, in particular to a hybrid encoding signal generation method based on an active mode-locked optoelectronic oscillator. BACKGROUND

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

[0003] In free-space optical communication, optical signals are easily disturbed by turbulence, haze, and other factors when transmitted in the atmosphere. Pulse position modulation can improve the noise immunity of signals, and pulse amplitude modulation can improve the data rate through multi-level amplitude encoding. Therefore, combining the two modulation methods for hybrid modulation encoding can significantly improve the spectral efficiency and data transmission rate while ensuring anti-interference, which is suitable for long-distance and high-bandwidth scenarios. Compared with traditional microwave oscillators based on electronic devices, the active mode-locked optoelectronic oscillator has the advantages of low phase noise and high frequency stability due to the high-Q resonant cavity formed by the long optical fiber.

[0004] However, the existing active mode-locked optoelectronic oscillator can only generate continuous pulse signals with uniform time intervals and amplitudes. This uniform pulse characteristic limits its application in complex encoding and high-density communication. In addition, the common single encoding method for continuous pulse signals has the problems of insufficient information capacity and limited anti-interference, making it difficult to expand to higher bit encoding. On the other hand, when generating high-frequency signals (8GHz and above), the phase noise of the generated signal will increase due to the thermal noise of electronic devices. The frequency multiplication technology based on nonlinear devices commonly used in generating X-band and higher frequency signals (8GHz and above) will significantly increase the phase noise of the signal, making it difficult to meet the demand for low phase noise signals in radar signal sources and high-precision clock synchronization applications. SUMMARY

[0005] One purpose of the embodiment of the present application is to provide a hybrid encoding signal generation system and method based on an active mode-locked optoelectronic oscillator to solve the technical problems that the uniform continuous pulse signal generated by the active mode-locked optoelectronic oscillator in the prior art limits complex encoding applications, and the phase noise of the traditional electronic oscillator is large at high frequencies, making it difficult to meet the low noise requirement.

[0006] In a first aspect, a hybrid encoding signal generation system based on an actively mode-locked optoelectronic oscillator is provided, comprising an actively mode-locked optoelectronic oscillator 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 band-pass 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; 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 to 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 electrical band-pass filter is used to filter the amplified first microwave signal to obtain a target microwave signal; the electrical coupler is used to feed back the target microwave signal to the dual-drive Mach-Zehnder modulator and / or output a microwave pulse; and the arbitrary waveform generator is used to generate a hybrid encoding signal to modulate the optical carrier.

[0007] In combination with the first aspect, in a possible implementation manner, when in an initial state, the arbitrary waveform generator does not work, the semiconductor continuous wave laser is connected with a 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 with the photodetector, the photodetector is connected with the radio frequency amplifier, the radio frequency amplifier is connected with the electrical band-pass filter, the electrical band-pass filter is connected with a first port of the electrical coupler, a second port of the electrical coupler is connected with a second port of the dual-drive Mach-Zehnder modulator, a first loop is formed, and the target microwave signal generated by the first loop is a second microwave signal.

[0008] With reference to the first aspect, in a possible implementation manner, in the first loop, the semiconductor continuous wave laser generates a first optical carrier, the first optical carrier is modulated by the double-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, the erbium-doped fiber amplifier adjusts the power of the first modulated optical signal to obtain an adjusted first modulated optical signal, the adjusted first modulated optical signal is optoelectronically converted by the photodetector to form a first photocurrent, and a third microwave signal is obtained, the radio frequency amplifier is configured to amplify the third microwave signal to obtain an amplified third microwave signal, the electrical band-pass filter is configured to filter the amplified third microwave signal to obtain the second microwave signal, and the electrical coupler is configured to feed back the second microwave signal to the double-drive Mach-Zehnder modulator.

[0009] With reference to the first aspect, in a possible implementation manner, after the second microwave signal corresponding to the first loop is formed, the arbitrary waveform generator is started, the semiconductor continuous wave laser is connected to the first port of the double-drive Mach-Zehnder modulator, the arbitrary waveform generator is connected to the third port of the double-drive Mach-Zehnder modulator, the double-drive Mach-Zehnder modulator is connected 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 band-pass filter, the electrical band-pass filter is connected to the first port of the electrical coupler, the second port of the electrical coupler is connected to the second port of the double-drive Mach-Zehnder modulator, a second loop is formed, and the target microwave signal generated by the second loop is a fourth microwave signal.

[0010] In combination with the first aspect, in a possible implementation manner, in the second circuit, the arbitrary waveform generator generates the hybrid coded signal, the semiconductor continuous wave laser generates a second optical carrier, the hybrid coded signal and the second microwave signal are modulated to the second optical carrier by the double-drive Mach-Zehnder modulator to form a second modulated optical signal; the second modulated optical signal is transmitted by the optical fiber to the erbium-doped fiber amplifier, 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 optoelectronically converted by the photodetector to form a second optical current to obtain a fifth microwave signal; the radio frequency amplifier is configured to amplify the fifth microwave signal to obtain an amplified fifth microwave signal; the electrical bandpass filter is configured to filter the amplified fifth microwave signal to obtain the fourth microwave signal; and the electrical coupler is configured to feed back the fourth microwave signal to the double-drive Mach-Zehnder modulator and output the microwave pulse.

[0011] In combination with the first aspect, in a possible implementation manner, a period of the hybrid coded signal is the same as a free spectral range of the actively mode-locked optoelectronic oscillator, and each period of the hybrid coded signal contains three triangular wave signals, shapes and amplitudes of the triangular wave signals are used for amplitude modulation.

[0012] In combination with the first aspect, in a possible implementation manner, after the triangular wave signal is generated, the second circuit generates a pulse signal corresponding to the three triangular wave signals, a period of the pulse signal is the same as the free spectral range of the actively mode-locked optoelectronic oscillator, and the pulse signal is used for pulse position modulation.

[0013] The second aspect provides a hybrid coded signal generation method based on an actively mode-locked optoelectronic oscillator, and the method is implemented based on the system of any one of the first aspect, and the method comprises the following steps of: modulating the obtained optical carrier to form a modulated optical signal; adjusting the modulated optical signal to obtain an adjusted modulated optical signal; optoelectronically converting the adjusted modulated optical signal to obtain a first microwave signal; amplifying the first microwave signal to obtain an amplified first microwave signal; filtering the amplified first microwave signal to obtain a target microwave signal; outputting the target microwave signal.

[0014] In a possible implementation of the second aspect, the modulation of the obtained optical carrier to form a modulated optical signal comprises: obtaining a hybrid coded signal and a second microwave signal, the second microwave signal being a microwave signal formed when any waveform generator in the system is not working in an initial state; and modulating the optical carrier according to the hybrid coded signal and the second microwave signal to obtain the modulated optical signal.

[0015] In a possible implementation of the second aspect, the hybrid coded signal comprises amplitude modulation and pulse position modulation.

[0016] In the scheme implemented by the hybrid coded signal generation system and method based on the actively mode-locked optoelectronic oscillator, the semiconductor continuous wave laser and the double-drive Mach-Zehnder modulator are combined to achieve efficient modulation of the optical carrier, form a high-quality modulated optical signal, and improve the signal integrity and stability of the system; the optical fiber transmission and the erbium-doped fiber amplifier are used to adjust the modulated optical signal, effectively compensate the transmission loss, ensure the signal strength and quality, and improve the transmission distance and performance of the system; the optoelectronic detector is used to realize the photoelectric conversion, efficiently convert the optical signal into a microwave signal, cooperate with the radio frequency amplifier and the electric band-pass filter to realize the amplification and filtering of the microwave signal, and obtain a target microwave signal with high purity and high stability; the electric coupler feeds back the target microwave signal to the double-drive Mach-Zehnder modulator to form a closed-loop feedback, realize the active mode-locking, and ensure the frequency stability and low phase noise of the microwave signal; further, the arbitrary waveform generator is introduced to flexibly generate various complex hybrid coded signals and load them on the optical carrier, so that the generated optical pulses or microwave pulses can carry specific coded information, endow the system with flexible signal modulation capability, realize complex coding and high-density information transmission, and improve the spectral efficiency and anti-interference capability. Therefore, the scheme realizes the organic combination of the self-oscillation and the hybrid coded modulation of the microwave signal, and meets the requirements of high frequency, high stability and high data transmission rate. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the description of the embodiments of the present application. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative labor.

[0018] Figure 1 is a structure schematic diagram of a hybrid coded signal generation system based on an actively mode-locked optoelectronic oscillator in an embodiment of the present application; Figure 2 is a flowchart of a hybrid coded signal generation method based on an actively mode-locked optoelectronic oscillator in an embodiment of the present application; Figure 3 is a waveform diagram of three triangular wave signals (two periodic waveforms) corresponding to the four-bit binary number 0110 in an embodiment of the present application; Figure 4 is a waveform diagram of three triangular wave signals (two periodic waveforms) corresponding to the four-bit binary number 0111 in an embodiment of the present application; Figure 5 is a waveform diagram of three triangular wave signals (two periodic waveforms) corresponding to the four-bit binary number 1111 in an embodiment of the present application; Figure 6 is a waveform diagram of three pulse signals (two periodic waveforms) corresponding to the four-bit binary number 0110 in an embodiment of the present application; Figure 7 is a waveform diagram of three pulse signals (two periodic waveforms) corresponding to the four-bit binary number 0111 in an embodiment of the present application; Figure 8 is a waveform diagram of three pulse signals (two periodic waveforms) corresponding to the four-bit binary number 1111 in an embodiment of the present application. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not used to limit the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0020] It should be noted that the various features in the embodiments of the present application can be combined with each other without conflict, and all fall within the scope of protection of the present application. In addition, although the functional modules are divided in the device schematic diagram, and the logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in a different order from the module division in the device or the order in the flowchart. Furthermore, the "first", "second", "third" and the like used in the present application do not limit the data and execution order, but only distinguish the same items or similar items with basically the same function and effect.

[0021] The present application will be described in detail below through specific embodiments.

[0022] The technical scheme of the present application can be applied to the scene of generating hybrid coded signals based on an actively mode-locked optoelectronic oscillator.

[0023] Therefore, the present application proposes a hybrid coded signal generation system based on an actively mode-locked optoelectronic oscillator, which will be described in detail below.

[0024] Please refer to Figure 1 , Figure 1 The structure schematic diagram of the hybrid encoding signal generation system based on the active mode-locked optoelectronic oscillator is provided for the embodiment of the present application, and in the Figure 1 The hybrid encoding signal generation system based on the active mode-locked optoelectronic oscillator comprises an active mode-locked optoelectronic oscillator, which is composed of a semiconductor continuous wave laser 1, a double-drive Mach-Zehnder modulator 2, an optical fiber 3, an erbium-doped fiber amplifier 4, a photodetector 5, a radio frequency amplifier 6, an electrical band-pass filter 7, an electrical coupler 8 and an arbitrary waveform generator 9; the semiconductor continuous wave laser 1 is used to generate an optical carrier, the double-drive Mach-Zehnder modulator 2 is used to modulate the optical carrier to form a modulated optical signal, the optical fiber 3 is used to transmit the modulated optical signal, the erbium-doped fiber amplifier 4 is used to adjust the modulated optical signal to obtain an adjusted modulated optical signal, the photodetector 5 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 6 is used to amplify the first microwave signal to obtain an amplified first microwave signal, the electrical band-pass filter 7 is used to filter the amplified first microwave signal to obtain a target microwave signal, the electrical coupler 8 is used to feed back the target microwave signal to the double-drive Mach-Zehnder modulator 2 and / or output a microwave pulse, and the arbitrary waveform generator 9 is used to generate a hybrid encoding signal to modulate the optical carrier.

[0025] The optical fiber can be a single-mode long optical fiber.

[0026] The hybrid encoding signal can be a hybrid encoding four-bit binary number modulated microwave signal.

[0027] The microwave pulse can be the target microwave signal or a local target microwave signal.

[0028] Since the present scheme includes an initial state in which the arbitrary waveform generator is not started and a state in which the arbitrary waveform generator is started, two loops are included.

[0029] Specifically, the first loop is a circuit when the arbitrary waveform generator is not working in the initial state, 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 in which the double-drive Mach-Zehnder modulator 2 is used to modulate the optical carrier to form a modulated optical signal is a first modulated optical signal in the first loop.

[0030] Specifically, after the second microwave signal corresponding to the first microwave signal is formed, the arbitrary waveform generator is started, and the arbitrary waveform generator 9 is used to generate a hybrid coded signal. Then, 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 dual-drive Mach-Zehnder modulator 2 is used to modulate the optical carrier to form a modulated optical signal, and in the second loop, a second modulated optical signal is formed.

[0031] The hybrid coded signal generated by the arbitrary waveform generator 9 can contain various modulation formats (such as amplitude, phase, frequency coding, etc.) or specific sequences, which makes the output optical pulse or microwave pulse output through the electrical coupler 8 itself carry these coded information, providing a basis for subsequent signal processing (such as high-speed communication, radar coding, complex sensing, etc.).

[0032] In this scheme, the dual-drive Mach-Zehnder modulator 2 is not only driven by the target microwave signal from the electrical coupler 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 driving is the key to achieving active mode locking and hybrid coding.

[0033] 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, realize active mode-locked optoelectronic oscillation, and ensure high frequency stability and low phase noise characteristics of the microwave signal. Further, 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 realize multi-dimensional signal modulation to meet the application requirements of high bandwidth and high anti-interference.

[0034] In one possible example, when the initial state is that the arbitrary waveform generator does not work, the semiconductor continuous wave laser is connected with 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 with the photodetector, the photodetector is connected with the radio frequency amplifier, the radio frequency amplifier is connected with the electrical bandpass filter, the electrical bandpass filter is connected with the first port of the electrical coupler, the second port of the electrical coupler is connected with the second port of the dual-drive Mach-Zehnder modulator, a first loop is formed, and the target microwave signal generated by the first loop is a second microwave signal.

[0035] In one possible example, in the first loop, the semiconductor continuous wave laser generates a first optical carrier, the first optical carrier is modulated by the dual-drive Mach-Zehnder modulator to form a first modulated optical signal; the first modulated optical signal is transmitted by the optical fiber to the erbium-doped fiber amplifier, the erbium-doped fiber amplifier adjusts the power of the first modulated optical signal to obtain an adjusted first modulated optical signal; the adjusted first modulated optical signal is optoelectronically converted by the photodetector to form a first photocurrent to obtain a third microwave signal; the radio frequency amplifier is used to amplify the third microwave signal to obtain an amplified third microwave signal; the electrical bandpass filter is used to filter the amplified third microwave signal to obtain the second microwave signal; and the electrical coupler is used to feed back the second microwave signal to the dual-drive Mach-Zehnder modulator.

[0036] In one possible example, after the first loop corresponding to the second microwave signal is formed, the arbitrary waveform generator is started, the semiconductor continuous wave laser is connected with the first port of the dual-drive Mach-Zehnder modulator, the arbitrary waveform generator is connected with the third port of the dual-drive Mach-Zehnder modulator, the dual-drive Mach-Zehnder modulator is connected with the erbium-doped fiber amplifier through the optical fiber, the erbium-doped fiber amplifier is connected with the photodetector, the photodetector is connected with the radio frequency amplifier, the radio frequency amplifier is connected with the electrical bandpass filter, the electrical bandpass filter is connected with the first port of the electrical coupler, the second port of the electrical coupler is connected with the second port of the dual-drive Mach-Zehnder modulator, a second loop is formed, and the target microwave signal generated by the second loop is a fourth microwave signal.

[0037] In one possible example, in the second loop, the arbitrary waveform generator generates the hybrid coded signal, the semiconductor continuous wave laser generates a second optical carrier, the hybrid coded signal and the second microwave signal are modulated to the second optical carrier through the double-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, 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 to obtain a fifth microwave signal; the radio frequency amplifier is used to amplify the fifth microwave signal to obtain an amplified fifth microwave signal; the electrical bandpass filter is used to filter the amplified fifth microwave signal to obtain the fourth microwave signal; and the electrical coupler is used to feed back the fourth microwave signal to the double-drive Mach-Zehnder modulator and output the microwave pulse.

[0038] In one possible example, the period of the hybrid coded signal is the same as the free spectral range of the actively mode-locked optoelectronic oscillator, and each period of the hybrid coded signal contains three triangular wave signals, and the shapes and amplitudes of the triangular wave signals are used for amplitude modulation.

[0039] In one possible example, the period of the hybrid coded signal is the same as the free spectral range of the actively mode-locked optoelectronic oscillator, and each period of the hybrid coded signal contains three triangular wave signals, and the shapes and amplitudes of the triangular wave signals are used for amplitude modulation.

[0040] In one possible example, the period of the hybrid coded signal is the same as the free spectral range of the actively mode-locked optoelectronic oscillator, and each period of the hybrid coded signal contains three triangular wave signals, and the shapes and amplitudes of the triangular wave signals are used for amplitude modulation.

[0041] In one possible example, the period of the hybrid coded signal is the same as the free spectral range of the actively mode-locked optoelectronic oscillator, and each period of the hybrid coded signal contains three triangular wave signals, and the shapes and amplitudes of the triangular wave signals are used for amplitude modulation.

[0042] The period of the hybrid coded signal generated by the arbitrary waveform generator is consistent with the free spectral range of the actively mode-locked optoelectronic oscillator, and each period contains three triangular wave signals; the three triangular wave signals are sequentially recorded as No. 1 triangular wave, No. 2 triangular wave and No. 3 triangular wave according to the order of generation in time domain from early to late; The time width of the No. 1 triangular wave in each period is one fifth, indicating that the second highest bit of the four-bit binary number is 1, and the time width is one tenth, indicating that the second highest bit of the four-bit binary number is 0; The time width of the No. 2 triangular wave in each period is one fifth, indicating that the second lowest bit of the four-bit binary number is 1, and the time width is one tenth, indicating that the second lowest bit of the four-bit binary number is 0; The time width of the No. 3 triangular wave in each period is one fifth, indicating that the lowest bit of the four-bit binary number is 1, and the time width is one tenth, indicating that the lowest bit of the four-bit binary number is 0; The time interval between the peak value of the No. 2 triangular wave and the peak value of the No. 1 triangular wave in each period is three tenths, indicating that the highest bit of the four-bit binary number is 1, and the time interval between the peak value of the No. 2 triangular wave and the peak value of the No. 1 triangular wave in each period is five tenths, indicating that the highest bit of the four-bit binary number is 0; The following gives an example of three triangular wave signals (two period waveforms) corresponding to three different four-bit binary numbers: the example corresponding to the four-bit binary number 0110 is shown in FIG. 1; Figure 3 The example corresponding to the four-bit binary number 0111 is shown in FIG. 2; Figure 4 The example corresponding to the four-bit binary number 1111 is shown in FIG. 3. Figure 5

[0043] It can be seen that, in the embodiment, through the specific time domain structure of the hybrid coded signal, the synchronization of the signal with the inherent period (FSR) of the optoelectronic oscillator is emphasized, and how the three triangular waves contained therein are used to accurately control the amplitude of the optical pulse, thereby realizing complex signal coding, so that the actively mode-locked optoelectronic oscillator not only can generate high-quality mode-locked pulses, but also can load specific amplitude modulation information defined by the triangular wave shape and amplitude on the pulses, greatly increasing the flexibility and application range of the system.

[0044] In one possible example, after generating the triangular wave signals, the second loop generates pulse signals corresponding to the three triangular wave signals, the period of the pulse signals is the same as the free spectral range of the actively mode-locked optoelectronic oscillator, and the pulse signals are used for pulse position modulation.

[0045] ​The pulse signal is used in pulse position modulation (PPM). In PPM, information is encoded by varying the position of the pulse signal within each cycle. In other words, the temporal position of the pulse changes in response to the input signal. This modulation method offers high immunity to interference because information is conveyed through pulse position rather than amplitude.

[0046] After the arbitrary waveform generator generates three triangular wave cycles with encoded information, the second loop generates three pulse signals corresponding to the three triangular waves, with periods that also coincide with the free spectrum range of the active mode-locked optoelectronic oscillator. The three pulse signals are recorded as pulse 1, pulse 2, and pulse 3 in the order in which they are generated in the time domain. A triangular wave with a time width of one-fifth of each cycle can generate a loop pulse signal with a high amplitude, and a triangular wave with a time width of one-tenth of each cycle can generate a loop pulse signal with a low amplitude, thereby realizing amplitude modulation coding; the time interval between triangular wave No. 2 and triangular wave No. 1 can control the time interval between pulse No. 2 and pulse No. 1 in the three pulse cycle signals, thereby realizing pulse position modulation coding.

[0047] Figure 3 After the three triangle wave signals corresponding to the four-bit binary number 0110 modulate the optical carrier, the active mode-locked optoelectronic oscillator loop will generate three pulse signals corresponding to the binary number 0110, as shown in FIG. Figure 6 As shown; Figure 4 After the three triangle wave signals corresponding to the four-bit binary number 0111 modulate the optical carrier, the active mode-locked optoelectronic oscillator loop will generate three pulse signals corresponding to the binary number 0111, as shown in FIG. Figure 7 As shown; Figure 5 After the three triangle wave signals corresponding to the four-bit binary number 1111 modulate the optical carrier, the active mode-locked optoelectronic oscillator loop will generate three pulse signals corresponding to the binary number 1111, as shown in FIG. Figure 8 shown.

[0048] As can be seen, by using pulse position modulation (PPM) corresponding to a 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.

[0049] In the scheme, a semiconductor continuous wave laser is combined with a double-drive Mach-Zehnder modulator to realize efficient modulation of the optical carrier, form a high-quality modulated optical signal, and improve the signal integrity and stability of the system; optical fiber transmission and erbium-doped fiber amplifier are used to adjust the modulated optical signal, effectively compensate for transmission loss, ensure signal strength and quality, and improve the transmission distance and performance of the system; photoelectric conversion is realized through a photodetector, and the optical signal is efficiently converted into a microwave signal, which is amplified and filtered by a radio frequency amplifier and an electric band-pass filter to obtain a high-purity and high-stability target microwave signal; an electric coupler feeds back the target microwave signal to the double-drive Mach-Zehnder modulator to form a closed-loop feedback, realize active mode locking, and ensure the frequency stability and low phase noise of the microwave signal; further introduction of an arbitrary waveform generator can flexibly generate various complex hybrid coded signals and load them onto the optical carrier, so that the generated optical pulses or microwave pulses can carry specific coded information, giving the system flexible signal modulation capability, enabling complex coding and high-density information transmission, and improving spectral efficiency and anti-interference capability. Therefore, the scheme realizes the organic combination of self-oscillation and hybrid coding modulation of the microwave signal, and meets the requirements of high frequency, high stability and high data transmission rate.

[0050] It should be noted that in the above various embodiments, there is no certain sequence between the above steps, and those skilled in the art can understand from the description of the embodiments of the present application that the above steps can have different execution sequences in different embodiments, that is, they can be executed in parallel, or they can be exchanged and executed, etc.

[0051] Figure 2 The flowchart of the hybrid coded signal generation method based on the active mode-locked optoelectronic oscillator provided by the embodiment of the present application, characterized in that the method comprises the following steps: S10, modulating the obtained optical carrier to form a modulated optical signal.

[0052] The optical carrier is a pure and high-frequency light wave generated by a semiconductor continuous wave laser. It does not carry information itself, just like the carrier wave in radio broadcasting, which is a medium for carrying information Modulation refers to the process of changing one or more characteristics (such as amplitude, frequency, phase) of the carrier with a signal (modulation signal) carrying information in communication. In the present scheme, it can be intensity modulation, that is, changing the intensity of the optical carrier with the modulation signal.

[0053] The modulated optical signal refers to the optical carrier after modulation. Its intensity is no longer constant, but varies with the law of the modulation signal, carrying the information in the modulation signal.

[0054] Specifically, the process of modulating the obtained optical carrier to form a modulated optical signal is completed by a double-drive Mach-Zehnder modulator. It has two input terminals that can receive electrical signals. One of the input terminals receives a mixed coded signal (containing three triangular waves, etc.) from an arbitrary waveform generator, which directly controls the intensity variation of the optical carrier to form the basic modulated optical signal. At the same time, the other input terminal receives the target microwave signal fed back from the electrical coupler, which is used to "lock" the state of the modulator, so that the entire loop generates stable mode-locked pulses. Therefore, the modulation process is actually double-driven.

[0055] S20, adjusting the modulated optical signal to obtain an adjusted modulated optical signal.

[0056] The modulated optical signal is first transmitted through a single-mode long optical fiber. In the optical fiber, the modulated optical signal will experience a dispersion effect, which will cause the pulse to broaden in time. At the same time, the optical fiber also introduces a certain transmission loss, causing the signal power to decrease. Although the nonlinear effect of the single-mode optical fiber is usually weak, it may exist under certain conditions. Therefore, after transmission through the optical fiber, the shape (broadening) and power (decrease) of the modulated optical signal have changed, and the further modulated optical signal enters an erbium-doped fiber amplifier (EDFA). The role of the EDFA is to compensate for the optical power lost during the transmission process in the optical fiber and may further enhance the power of the signal. This is an active power adjustment process to ensure that the signal has sufficient intensity in the subsequent link (such as a photodetector).

[0057] Therefore, "adjusting the modulated optical signal" includes 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 "adjusted modulated optical signal" finally obtained refers to the optical signal after transmission broadening and power recovery (or enhancement). The pulse width, shape, and power level of the adjusted signal are more suitable for entering the next optical-electric conversion link, S30, optoelectronically converting the adjusted modulated optical signal to obtain a first microwave signal.

[0058] The optoelectronic conversion refers to the process of converting the optical signal into an electrical signal using a photodetector. When the optical signal shines on the detector, it will excite electron-hole pairs to form a current or voltage proportional to the light intensity.

[0059] The first microwave signal is an electrical signal obtained by photoelectric conversion. Since the adjusted modulated light signal is periodically changing (especially in the mode-locked state, it contains a series of equally spaced pulses), the rapidly changing light intensity on the photodetector will generate an alternating current / voltage of the corresponding frequency, which is usually in the microwave range (several hundred MHz to several tens of GHz), hence the name first microwave signal. It contains all the time-domain information of the optical signal.

[0060] S40, amplifying the first microwave signal to obtain an amplified first microwave signal.

[0061] Amplification refers to enhancing the strength (power or voltage) of the signal. Since the signal output by the photodetector is usually relatively weak, it needs to be amplified to drive the subsequent circuit.

[0062] S50, filtering the amplified first microwave signal to obtain a target microwave signal.

[0063] Filtering refers to the process of using an electrical bandpass filter to extract the components of a specific frequency range from the signal while suppressing other frequency components.

[0064] The electrical bandpass filter refers to a circuit or device that only allows electrical signals within a specific frequency range to pass through while blocking signals outside that range. The "passband" center frequency is usually set at the desired mode-locked frequency.

[0065] The target microwave signal refers to the microwave signal obtained after filtering, which meets the requirements in terms of frequency and waveform.

[0066] S60, outputting the target microwave signal.

[0067] After the target microwave signal is output from the electrical bandpass filter, it enters the electrical coupler, which has two main functions: 1. Feedback: a portion of the target microwave signal is fed back to one of the drive terminals of the dual-drive Mach-Zehnder modulator (as the mode-locked drive signal) to maintain and stabilize the mode-locked state. 2. Output: another portion of the target microwave signal is output 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, amplified and filtered, and can be used for subsequent communication, radar or other applications.

[0068] The scheme can effectively load information into the optical signal by modulating the obtained optical carrier, realize the basis of high-speed and high-capacity information transmission; adjust the modulated optical signal, improve the signal quality, reduce the noise and distortion, and ensure the stability and accuracy of subsequent conversion and processing; after photoelectric conversion, the optical signal is successfully converted into a microwave signal, realizing seamless connection of optical communication and microwave communication, and expanding the range of signal application; further amplifying the first microwave signal enhances the signal strength, improves the signal-to-noise ratio, and ensures the integrity of the signal in the transmission and processing process; the target microwave signal obtained by filtering to remove redundant frequencies and noise is more pure, meeting the high requirements of the system on signal quality; finally, the high-quality target microwave signal is output, ensuring that the signal can be stably and accurately transmitted to the downstream equipment or system, and improving the performance and reliability of the overall communication system.

[0069] In one possible example, the modulation of the obtained optical carrier to form a modulated optical signal includes: obtaining a hybrid encoding signal and a second microwave signal, the second microwave signal being a microwave signal formed when any waveform generator in the system does not work in an initial state; modulating the optical carrier according to the hybrid encoding signal and the second microwave signal to obtain the modulated optical signal.

[0070] Wherein, the hybrid encoding 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 be amplitude, phase, time position, etc.

[0071] Wherein, the second microwave signal refers to the microwave signal generated when the system is in a specific "initial state". The key feature of this initial state is that the "arbitrary waveform generator does not work", indicating that there is no hybrid encoding signal from the AWG participating in the modulation at this time.

[0072] Wherein, the modulation process is realized by a double-drive Mach-Zehnder modulator. The DD-MZM has two independent drive electrodes. One electrode (or channel) may be driven by a hybrid encoding signal to load complex amplitude or phase information (realize hybrid encoding) on the optical pulse; the other electrode (or channel) is driven by the second microwave signal. The function of this second microwave signal is usually to drive the modulator to work in the mode-locked state, or to adjust the envelope, center frequency, etc. of the pulse to maintain oscillation and mode locking. By applying these two signals to the modulator at the same time, complex encoding and mode locking / pulse shaping can be realized in the optical domain at the same time. The final modulated optical signal is a sequence of optical pulses carrying hybrid encoding information and in a stable mode-locked state.

[0073] It can be seen that in this embodiment, the mixed encoding signal generated by the AWG is used to realize information loading, 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 to perform pulse shaping, so as to realize complex information encoding and stable pulse generation on a single optical pulse sequence.

[0074] In one possible example, the mixed encoding signal contains amplitude modulation and pulse position modulation.

[0075] Among them, amplitude modulation means that the mixed encoding signal changes the size of its level or power. In the optical domain, this usually manifests as a change in the intensity (brightness) of the optical pulse. For example, the pulse can be modulated to high, low or zero intensity to represent different data bits (such as binary 1 and 0).

[0076] Among them, pulse position modulation means that the mixed encoding signal carries information by changing the appearance position of the pulse on the time axis. For example, within a fixed time window, the pulse can appear at different preset positions (such as position 1, position 2, position 3, etc.), and each position represents a different information symbol or data block. PPM is an efficient modulation method, especially in power-limited systems.

[0077] Among them, the period of the mixed encoding signal is the same as the free spectral range of the actively mode-locked optoelectronic oscillator, and each period of the mixed encoding signal contains three triangular wave signals, and the shapes and amplitudes of the triangular wave signals are used for amplitude modulation.

[0078] Among them, the free spectral range (FSR) is a key parameter of an optical ring cavity (formed by optical fiber 3 and other elements), which refers to the frequency interval between two adjacent longitudinal modes (i.e. the frequency of light waves that can stably exist in the cavity), or in other words, the range of optical frequencies that the cavity can accommodate. For a stable mode-locked fiber ring, the FSR determines the repetition frequency of the output pulse sequence.

[0079] Among them, the period of the mixed encoding signal is the same as the free spectral range of the actively mode-locked optoelectronic oscillator, and each period of the mixed encoding signal contains three triangular wave signals, and the shapes and amplitudes of the triangular wave signals are used for amplitude modulation.

[0080] Among them, each period contains three triangular wave signals, which means that in each pulse repetition period, the modulator will be modulated by three different triangular waveforms.

[0081] The period of the hybrid coded signal generated by the arbitrary waveform generator is consistent with the free spectral range of the actively mode-locked optoelectronic oscillator, and each period contains three triangular wave signals; the three triangular wave signals are sequentially recorded as No. 1 triangular wave, No. 2 triangular wave and No. 3 triangular wave according to the order of generation in time domain from first to last; The time width of the No. 1 triangular wave in each period is one fifth, indicating that the second highest bit of the four-bit binary number is 1, and the time width of the No. 1 triangular wave in each period is one tenth, indicating that the second highest bit of the four-bit binary number is 0; The time width of the No. 2 triangular wave in each period is one fifth, indicating that the second lowest bit of the four-bit binary number is 1, and the time width of the No. 2 triangular wave in each period is one tenth, indicating that the second lowest bit of the four-bit binary number is 0; The time width of the No. 3 triangular wave in each period is one fifth, indicating that the lowest bit of the four-bit binary number is 1, and the time width of the No. 3 triangular wave in each period is one tenth, indicating that the lowest bit of the four-bit binary number is 0; The time interval between the peak value of the No. 2 triangular wave and the peak value of the No. 1 triangular wave in each period is three tenths, indicating that the highest bit of the four-bit binary number is 1, and the time interval between the peak value of the No. 2 triangular wave and the peak value of the No. 1 triangular wave in each period is five tenths, indicating that the highest bit of the four-bit binary number is 0; The following gives an example of three triangular wave signals (two period waveforms) corresponding to three different four-bit binary numbers: the example corresponding to the four-bit binary number 0110 is shown as Figure 3 The example corresponding to the four-bit binary number 0111 is shown as Figure 4 The example corresponding to the four-bit binary number 1111 is shown as Figure 5 .

[0082] The pulse signal is used for pulse position modulation (PPM). In pulse position modulation, information is encoded by changing the position of the pulse signal within each period. That is, the time position of the pulse will change according to the change of the input signal. This modulation method has high anti-interference ability, because the information is transmitted through the pulse position rather than the amplitude.

[0083] After the three triangular wave period signals with coded information generated by the arbitrary waveform generator, three pulse signals corresponding to the three triangular waves will be generated in the second loop, and the period is consistent with the free spectral range of the actively mode-locked optoelectronic oscillator. The three pulse signals are sequentially recorded as No. 1 pulse, No. 2 pulse and No. 3 pulse according to the order of generation in time domain from first to last; The time width of the triangular wave in each period is one fifth, which can generate a loop pulse signal with high amplitude, and the time width of the triangular wave in each period is one tenth, which can generate a loop pulse signal with low amplitude, thereby realizing amplitude modulation coding; the time interval between the No. 2 triangular wave and the No. 1 triangular wave can control the time interval between the No. 2 pulse and the No. 1 pulse in the three pulse period signals, thereby realizing pulse position modulation coding.

[0084] Figure 3 As shown in the figure, after the three triangular wave signals corresponding to the four-bit binary number 0110 modulate the optical carrier, the active mode-locked optoelectronic oscillator loop generates three pulse signals corresponding to the binary number 0110, as shown in the figure. Figure 6 Figure 4 As shown in the figure, after the three triangular wave signals corresponding to the four-bit binary number 0111 modulate the optical carrier, the active mode-locked optoelectronic oscillator loop generates three pulse signals corresponding to the binary number 0111, as shown in the figure. Figure 7 Figure 5 As shown in the figure, after the three triangular wave signals corresponding to the four-bit binary number 1111 modulate the optical carrier, the active mode-locked optoelectronic oscillator loop generates three pulse signals corresponding to the binary number 1111, as shown in the figure. Figure 8

[0085] It can be seen that, in the embodiment, the amplitude modulation and pulse position modulation hybrid encoded signal generated by the arbitrary waveform generator enables the active mode-locked optoelectronic oscillator to generate the amplitude modulation and pulse position modulation hybrid encoded signal, thereby realizing the transmission of the four-bit binary number and solving the problem that the existing active mode-locked optoelectronic oscillator cannot generate the hybrid encoded signal. The pulse position modulation encoding transmits information through the position of the pulse on the time axis, rather than the amplitude, frequency or phase, and is therefore not sensitive to amplitude noise such as additive white Gaussian noise. As long as the arrival time of the pulse signal is not completely covered by noise, the receiving end can extract valid information through time synchronization, and therefore has high anti-interference performance. The amplitude modulation encoding can improve the spectral efficiency. The present application uses the two encoding methods in combination, combines the advantages of the two encoding methods, and enables the hybrid encoded signal generated by the active mode-locked optoelectronic oscillator to be applicable to scenarios that require consideration of anti-interference performance, bandwidth efficiency and adaptability to complex environments, and simultaneously transmits information in two dimensions of time and amplitude, thereby improving the data transmission rate.

[0086] It should be noted that, in each of the above embodiments, there is no certain sequence between the above steps, and those skilled in the art can understand from the description of the embodiments of the present application that the above steps can have different execution sequences in different embodiments, that is, they can be executed in parallel, or they can be executed in exchange, and the like.

[0087] ​​​Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by a computer program instructing relevant hardware. The program can be stored in a computer readable storage medium, and when the program is executed, the program can include the processes of the above-mentioned embodiment methods. The storage medium can be a magnetic disc, an optical disc, a read-only memory (ROM), a random access memory (RAM), or the like.

[0088] The above disclosure is merely preferred embodiments of the present application and cannot limit the scope of the present application. Therefore, equivalent changes made according to the claims of the present application are still within the scope of the present application.

Claims

1. A hybrid coding signal generation system based on an active mode-locked optoelectronic oscillator, characterized in that: The invention comprises an active mode-locked optoelectronic oscillator, which is composed of a semiconductor continuous wave laser, a dual-driven 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-driven 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 to 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 electrical bandpass filter is used to filter the amplified first microwave signal to obtain a target microwave signal; The electrical 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 coding signal to modulate the optical carrier.

2. The system according to claim 1, wherein: In an initial state, the arbitrary waveform generator is not working, the semiconductor continuous-wave laser is connected to the first port of the dual-driven Mach-Zehnder modulator, the dual-driven 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-driven Mach-Zehnder modulator, forming a first loop, and the target microwave signal generated by the first loop is the second microwave signal.

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

4. The system according to claim 2, wherein: After the second microwave signal corresponding to the first loop is formed, the arbitrary waveform generator is started, the semiconductor continuous-wave laser is connected to the first port of the dual-driven Mach-Zehnder modulator, the arbitrary waveform generator is connected to the third port of the dual-driven Mach-Zehnder modulator, the dual-driven Mach-Zehnder modulator transmits a signal 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-driven Mach-Zehnder modulator, thereby forming a second loop. The target microwave signal generated by the second loop is a fourth microwave signal.

5. The system according to claim 4, characterized in that 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 dual-drive Mach-Zehnder modulator modulates the mixed coded signal and the second microwave signal onto the second optical carrier to form a second modulated optical signal. The second modulated optical signal is transmitted through the optical fiber and transmitted to the erbium-doped fiber amplifier. 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 subjected to photoelectric conversion by the photodetector to form a second photocurrent to obtain a fifth microwave signal. The radio frequency amplifier is used to amplify the fifth microwave signal to obtain an amplified fifth microwave signal. The electrical bandpass filter is used to filter the amplified fifth microwave signal to obtain the fourth microwave signal; the electrical coupler is used to feed the fourth microwave signal back to the dual-drive Mach-Zehnder modulator and output the microwave pulse.

6. The system according to claim 5, characterized in that The period of the hybrid coding signal is the same as the free spectrum range of the active mode-locked optoelectronic oscillator. Each period of the hybrid coding signal contains three triangular wave signals, and the corresponding shapes and amplitudes of the triangular wave signals are used for amplitude modulation.

7. The system according to claim 6, characterized in that After generating the triangular wave signals, the second loop 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, and the pulse signal is used for pulse position modulation.

8. A method for generating a hybrid coded signal based on an active mode-locked optoelectronic oscillator, implemented based on the system according to any one of claims 1 to 7, characterized in that: include: Modulating the acquired optical carrier to form a modulated optical signal; Adjusting the modulated optical signal to obtain an adjusted modulated optical signal; performing photoelectric conversion on the adjusted modulated optical signal to obtain a first microwave signal; amplifying the first microwave signal to obtain an amplified first microwave signal; filtering the amplified first microwave signal to obtain a target microwave signal; The target microwave signal is output.

9. The method according to claim 8, characterized in that The step of modulating the acquired optical carrier to form a modulated optical signal includes: Acquire a mixed coded signal and a second microwave signal, where the second microwave signal is a microwave signal generated when the arbitrary waveform generator in the system is not operating in an initial state; The optical carrier is modulated according to the mixed coded signal and the second microwave signal to obtain a modulated optical signal.

10. The method according to claim 9, characterized in that The hybrid coded signal includes amplitude modulation and pulse position modulation.

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