Silicon-based integrated Fourier domain mode-locked optoelectronic oscillator chip, system, and compensation method

Abstract

This invention discloses a silicon-based integrated Fourier domain mode-locked optoelectronic oscillator chip, system, and compensation method, relating to the field of optoelectronics technology. This chip integrates high-speed electro-optic modulators, micro-ring filters, high-speed photodetectors, and other optoelectronic devices onto a single silicon-based photonic chip to generate a broadband linear frequency modulated signal, significantly improving the resolution of traditional radar. Integrating and chip-based radar signal generation systems reduces system size, power consumption, and costs. The swept-frequency optical signal generated by the silicon-based integrated Fourier domain mode-locked optoelectronic oscillator chip is input into an unbalanced Mach-Zehnder fiber interferometer to obtain a compensation signal. Based on the resampling theorem, the swept-frequency nonlinearity of the linear frequency modulated signal is compensated in real time. Since only the beat frequency signal needs to be acquired, the sampling rate of the back-end signal processing devices is reduced.

Description

Technical Field

[0001] This invention relates to the field of optoelectronics technology, specifically to silicon-based integrated Fourier domain mode-locked optoelectronic oscillator chips, systems, and compensation methods. Background Technology

[0002] In modern warfare centered on information warfare and electromagnetic spectrum warfare, rapidly acquiring battlefield intelligence and conducting real-time monitoring and reconnaissance of battlefield information are key factors in determining victory. Radar, due to its all-weather, all-day, and long-range detection capabilities, has become a primary means of battlefield environmental awareness. However, the increasing complexity and diversity of the detection environment and targets place higher demands on radar's high-resolution target identification. Since high radar resolution corresponds to a wide-bandwidth transmitted signal, broadband radar signal generation is one of the key research directions and popular research areas.

[0003] Currently, broadband radar signals are mostly generated using Direct Digital Synthesis (DDS). However, due to the nonlinearity of digital circuits and limited storage capacity, DDS technology struggles to achieve high-purity broadband signal synthesis. In contrast, photonics technology inherently possesses characteristics such as high bandwidth, low transmission loss, and resistance to electromagnetic interference, and is hailed as a key enabling technology for overcoming radar bandwidth bottlenecks and "illuminating the future of radar." Among these technologies, Optical Oscillator (OEO) is a novel optical generation technology for microwave signals, capable of achieving broadband, tunable, high-purity microwave signal synthesis. Current research on OEO is focusing on higher frequencies, integration, shock resistance, and overload resistance.

[0004] OEO is a typical microwave photonic resonant system. It utilizes low-loss optical fiber as the energy storage medium to construct a high-quality-factor resonant cavity, ultimately generating a high-purity, wide-range tunable microwave signal. The basic structure of OEO mainly includes a light source, an electro-optic modulator, an optical amplifier, a photodetector, an electrical amplifier, and a bandpass filter. When the gain of the resonant loop is greater than 1, the injected noise in the loop, including the RIN noise of the light source, the thermal noise of the amplifier, and the shot noise of the photodetector, continuously circulates and accumulates within the cavity, eventually forming a stable single-mode oscillation at the center frequency of the bandpass filter.

[0005] In traditional OEO systems, although the frequency of the output microwave signal can be changed by adjusting the center frequency of the bandpass filter, new stable oscillation modes need to be continuously established from noise during frequency tuning. Due to the long mode settling time, traditional OEOs cannot generate broadband linear frequency modulated (LFM) signals. To meet the development requirements of anti-jamming radar, broadband LFM signal synthesis can be achieved using a Fourier domain mode-locked optoelectronic oscillator (SDO). By introducing a frequency-sweeping microwave photonic filter into the OEO loop, a broadband LFM signal can be generated when the sweep period of the filter's center frequency is synchronized with the OEO's loop cavity delay. Each oscillation mode within the filter's sweep range returns to the filter after gain and transmission, at which point the filter's frequency window is precisely tuned to the same frequency position. Therefore, all modes within the filter's sweep range oscillate simultaneously in the Fourier domain SDO, thus overcoming the mode settling time of traditional OEOs and generating broadband LFM signals.

[0006] Currently, existing Fourier-domain mode-locked optoelectronic oscillators (SDOs) are all based on discrete optoelectronic device packaging, resulting in problems such as large size, high cost, high power consumption, and complex structure. In recent years, with the rapid development of photonic integration technology, integration and chip-based architecture have become inevitable trends in the development of Fourier-domain mode-locked optoelectronic oscillators. Currently, silicon-based photonic platforms are among the most promising optoelectronic integration platforms, possessing unique and balanced advantages: silicon-based photonic processes are compatible with existing CMOS platforms, thus offering potential advantages for hybrid optoelectronic monolithic integration. However, chip-based Fourier-domain mode-locked optoelectronic oscillators based on silicon-based integrated optoelectronic devices have not yet been reported. Furthermore, due to the non-ideal sweep frequency response of the microwave photonic filter in the Fourier-domain mode-locked optoelectronic oscillator, the generated broadband linear frequency-modulated signal suffers from poor linearity, leading to the generation of false targets in radar imaging and affecting radar detection accuracy. Therefore, the sweep frequency nonlinearity of Fourier-domain mode-locked optoelectronic oscillators is a problem that urgently needs to be solved. Summary of the Invention

[0007] In view of this, the present invention provides a silicon-based integrated Fourier domain mode-locked optoelectronic oscillator chip, system, and compensation method. It mainly comprises a silicon-based integrated Fourier domain mode-locked optoelectronic oscillator chip and an unbalanced Mach-Zehnder fiber interferometer, which can compensate for the sweep frequency nonlinearity of broadband linear frequency modulated (LFM) signals using a resampling method. The compensated broadband LFM signal can be used in one-dimensional and two-dimensional radar imaging to effectively remove interference from false targets.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: a silicon-based integrated Fourier domain mode-locked optoelectronic oscillator chip, comprising a first grating coupler, a second grating coupler, a third grating coupler, a fourth grating coupler, a fifth grating coupler, a phase modulator, a microdisk resonator, and a first photodetector.

[0009] The output of the first grating coupler is connected to the drop terminal of the microdisk resonator; the output of the second grating coupler is connected to the input terminal of the high-speed phase modulator; the output of the third grating coupler is connected to the add terminal of the microdisk resonator; the output of the high-speed phase modulator is connected to the input terminal of the microdisk resonator; the through terminal of the microdisk resonator is connected to the output of the fourth grating coupler; and the output of the fifth grating coupler is connected to the first photodetector.

[0010] Preferably, the bandwidth of the first photodetector is 20 GHz.

[0011] Another embodiment of the present invention provides a silicon-based integrated Fourier domain mode-locked optoelectronic oscillator chip system, which adds the following peripheral devices to the above-mentioned silicon-based integrated Fourier domain mode-locked optoelectronic oscillator chip: a laser, a delay fiber, a microwave amplifier, a power divider, an unbalanced Mach-Zehnder fiber interferometer, and a second photodetector.

[0012] The output of the laser is connected to the input of the second grating coupler; the input of the delay fiber is connected to the input of the fourth grating coupler; the output of the delay fiber is connected to the input of the fifth grating coupler; the input of the microwave amplifier is connected to the output of the first photodetector; the output of the microwave amplifier is connected to the input of the power divider; the two output ports of the power divider are connected to output a linear frequency modulated signal and to the modulation port of the phase modulator; the input of the unbalanced Mach-Zehnder fiber interferometer is connected to the input of the first grating coupler; the output of the unbalanced Mach-Zehnder fiber interferometer is connected to the input of the second photodetector.

[0013] Preferably, the bandwidth of the second photodetector is on the order of MHz.

[0014] Another embodiment of the present invention provides a compensation method for a silicon-based integrated Fourier domain mode-locked optoelectronic oscillator chip system. Using the aforementioned silicon-based integrated Fourier domain mode-locked optoelectronic oscillator chip system, the following method is employed for real-time compensation of frequency sweep nonlinearity:

[0015] The laser generates a frequency of f c A single-frequency optical signal is coupled to a second grating coupler, and then incident on the optical input port of a phase modulator. This signal is then applied to the RF input of the phase modulator, generating a double-sideband modulated optical signal. The frequencies of the optical carrier and the positive and negative first-order sidebands are f0 and f1, respectively. c f c +f m and f c -f mThe single-sideband modulated optical signal generated by the high-speed phase modulator 6 is incident on the microdisk filter; the resonant wavelength of the pre-microdisk filter can be expressed as...

[0016]

[0017] Where R and n eff These represent the radius and effective refractive index of the pre-disk filter, respectively, where m is a positive integer and λ is a negative integer. m The m-th periodic resonant wavelength. The microdisk filter incorporates metal micro / nano heating electrodes. By utilizing the thermo-optical effect, the resonant wavelength of the pre-microdisk filter is adjusted, thus enabling the first-order sideband f... c +f m Output from the drop end, while the optical carrier and the negative first-order sideband f c and f c -f m The output from the through port completes the conversion from phase modulation to intensity modulation. Subsequently, the optical carrier and the negative first-order sideband f... c and f c -f m It is incident into the time-delay fiber via the fourth grating coupler, and then enters the first photodetector through the fifth grating coupler to complete the photoelectric conversion.

[0018] When the sweep period of the microdisk resonator and the cavity delay of the optoelectronic oscillator are synchronized, i.e., satisfying the following equation...

[0019]

[0020] Where N is a positive integer, T filter T is the scan period of the microdisk resonator 7. c Let n be the cavity delay of the optoelectronic oscillator, n be the effective refractive index of the fiber core, Lc be the cavity length of the optoelectronic oscillator, and c be the speed of light in vacuum. Each oscillation mode within the frequency sweep range returns to the microdisk resonator after gain and transmission. At this time, the center wavelength of the microdisk resonator is tuned to the same frequency position. All modes within the frequency sweep range oscillate simultaneously in the optoelectronic oscillator loop, generating a linear frequency modulated signal.

[0021] The first-order sideband f from the drop output of the microdisk resonator c +f m The signal is incident on an unbalanced Mach-Zehnder fiber interferometer, and then a compensation signal is generated by a second photodetector. Based on the resampling theorem, the nonlinear frequency sweep of the linear frequency sweep signal can be compensated in real time.

[0022] Beneficial effects:

[0023] 1. A silicon-based integrated Fourier domain mode-locked optoelectronic oscillator chip, by integrating high-speed electro-optic modulators, micro-ring filters, high-speed photodetectors, and other optoelectronic devices onto a single silicon-based photonic chip, generates a broadband linear frequency modulated signal, significantly improving the resolution of traditional radar. Integrating and chip-based radar signal generation systems reduces system size, power consumption, and costs.

[0024] 2. A swept-frequency optical signal generated by a silicon-based integrated Fourier domain mode-locked optoelectronic oscillator chip is input into an unbalanced Mach-Zehnder fiber interferometer to obtain a compensation signal. Based on the resampling theorem, the swept-frequency nonlinearity of the linear frequency modulated signal is compensated in real time. Since only the beat frequency signal needs to be acquired, the sampling rate of the back-end signal processing devices is reduced. Attached Figure Description

[0025] Figure 1 A block diagram of the silicon-based integrated Fourier domain mode-locked optoelectronic oscillator chip and its sweep frequency nonlinearity real-time compensation method provided by the present invention.

[0026] Figure 2 This is a diagram of the silicon-based integrated Fourier domain mode-locked optoelectronic oscillator chip in this invention;

[0027] Figure 3 The figures show the radar imaging experimental results before and after frequency sweep nonlinear compensation in this invention. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0029] The technical solution provided by this invention is as follows:

[0030] A silicon-based integrated Fourier domain mode-locked optoelectronic oscillator chip for generating broadband linear frequency modulated (LFM) signals; and an unbalanced Mach-Zehnder fiber interferometer for real-time compensation of the sweep frequency nonlinearity problem of broadband LFM signals.

[0031] In the above scheme, the silicon-based integrated Fourier domain mode-locked optoelectronic oscillator chip includes:

[0032] Five grating couplers are used for optical signal coupling between the optical fiber and the chip.

[0033] A high-speed electro-optic modulator is used to modulate the radio frequency signal to be transmitted into the optical domain. By adjusting the DC bias voltage of the electro-optic modulator and the phase difference between the two radio frequency input signals, a double-sideband modulated signal is generated.

[0034] A pre-amplified micro-ring optical filter is used to suppress first-order sidebands.

[0035] A high-speed photodetector receives the optical signal from a micro-ring optical filter and converts the optical signal into an electrical signal.

[0036] Since silicon-based photonics platforms cannot integrate lasers, off-chip lasers are used as the light source.

[0037] In the above scheme: the unbalanced Mach-Zehnder interferometer includes

[0038] A delay fiber is used to generate a delay in optical signals.

[0039] Two 1×2 optical couplers are used. One 1×2 optical coupler is used to split the optical signal into two paths. One signal goes directly into the other 1×2 optical coupler, and the other signal goes into the other 1×2 optical coupler through a delay fiber.

[0040] like Figure 1 As shown, the laser 9 generates a frequency of f. c A single-frequency optical signal is coupled to the second grating coupler 2, and then incident on the optical input port of the phase modulator 6. Through the RF input applied to the phase modulator 6, a double-sideband modulated optical signal is generated, with the frequencies of the optical carrier and the positive and negative first-order sidebands being f0 and f1, respectively. c f c +f m and f c -f m The single-sideband modulated optical signal generated by the high-speed phase modulator 6 is incident on the microdisk filter 7. The resonant wavelength of the periodic components in the pre-microdisk filter 7 can be expressed as...

[0041]

[0042] Where R and n eff These represent the radius and effective refractive index of the pre-disk filter, respectively, where m is a positive integer and λ is a negative integer. m The m-th periodic resonant wavelength. The microdisk filter incorporates metal micro / nano heating electrodes. By utilizing the thermo-optical effect, the resonant wavelength of the pre-microdisk filter is adjusted, thus enabling the first-order sideband f... c +f m Output from the drop end, while the optical carrier and the negative first-order sideband f c and f c -f m The output from the through port completes the conversion from phase modulation to intensity modulation. Subsequently, the optical carrier and the negative first-order sideband f... c and f c -f m It is incident into the delay fiber 11 via the fourth grating coupler 4, and then enters the photodetector 8 through the fifth grating coupler 5 to complete the photoelectric conversion.

[0043] When the sweep period of the microdisk resonator 7 is synchronized with the ring cavity delay of the optoelectronic oscillator, that is, when the following equation is satisfied...

[0044]

[0045] Where N is a positive integer, T filter T is the scan period of the microdisk resonator 7. c Let n be the cavity delay of the optoelectronic oscillator, n be the effective refractive index of the fiber core, Lc be the cavity length of the optoelectronic oscillator, and c be the speed of light in vacuum. Each oscillation mode within the swept frequency range returns to the microdisk resonator 7 after gain and propagation, at which point the center wavelength of the microdisk resonator 7 is precisely tuned to the same frequency. Therefore, all modes within the swept frequency range oscillate simultaneously in the optoelectronic oscillator loop, thus breaking through the mode settling time of traditional optoelectronic oscillators. This allows for the generation of wide-bandwidth linear frequency-modulated signals.

[0046] To address the issue of frequency sweep nonlinearity, the positive first-order sideband f output from the microdisk resonator 7drop is used. c +f m The signal is incident on the unbalanced Mach-Zehnder fiber interferometer 14, and then passes through the second photodetector 15 to generate a compensation signal. Based on the resampling theorem, the nonlinear frequency sweep of the linear frequency sweep signal can be compensated in real time. Here, the bandwidth of the second photodetector 15 is on the order of MHz.

[0047] In the silicon-based integrated Fourier domain mode-locked optoelectronic oscillator chip provided by this invention, the signal transmission process is as follows: the output terminal of the first grating coupler 1 is connected to the drop terminal of the microdisk resonator 7; the output terminal of the second grating coupler 2 is connected to the input terminal of the high-speed phase modulator 6; the output terminal of the third grating coupler 3 is connected to the add terminal of the microdisk resonator 7; the output terminal of the high-speed phase modulator 6 is connected to the input terminal of the microdisk resonator 7; the through terminal of the microdisk resonator 7 is connected to the output terminal of the fourth grating coupler 4; the output terminal of the fifth grating coupler 5 is connected to the first photodetector 8; the bandwidth of the first photodetector 8 is 20 GHz.

[0048] The output of laser 9 is connected to the input of the second grating coupler 2 in the silicon-based integrated Fourier domain mode-locked opto-oscillator chip 10; the input of delay fiber 11 is connected to the input of the fourth grating coupler 4; the output of delay fiber 11 is connected to the input of the fifth grating coupler 5; the input of microwave amplifier 12 is connected to the output of the first photodetector 8; the output of microwave amplifier 12 is connected to the input of power divider 13; the two output ports of power divider 13 are respectively for outputting a linear frequency modulated signal and connected to the modulation port of high-speed phase modulator 6 in the silicon-based integrated Fourier domain mode-locked opto-oscillator chip 10. The input of unbalanced Mach-Zehnder fiber interferometer 14 is connected to the input of the first grating coupler 1 in the silicon-based integrated Fourier domain mode-locked opto-oscillator chip 10; the output of unbalanced Mach-Zehnder fiber interferometer 14 is connected to the input of low-speed photodetector 15.

[0049] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A compensation method for a silicon-based integrated Fourier domain mode-locked optoelectronic oscillator chip system, characterized in that, The silicon-based integrated Fourier domain mode-locked optoelectronic oscillator chip is used, including a first grating coupler (1), a second grating coupler (2), a third grating coupler (3), a fourth grating coupler (4), a fifth grating coupler (5), a phase modulator (6), a micro disk resonator (7), and a first photodetector (8). The output of the first grating coupler (1) is connected to the drop end of the microdisk resonator (7); the output of the second grating coupler (2) is connected to the input end of the high-speed phase modulator (6); the output of the third grating coupler (3) is connected to the add end of the microdisk resonator (7); the output of the high-speed phase modulator (6) is connected to the input end of the microdisk resonator (7); the through end of the microdisk resonator (7) is connected to the output of the fourth grating coupler (4); and the output of the fifth grating coupler (5) is connected to the first photodetector (8). It also includes the following peripheral devices, including a laser (9), a time-delay fiber (11), a microwave amplifier (12), a power divider (13), an unbalanced Mach-Zehnder fiber interferometer (14), and a second photodetector (15). The output of the laser (9) is connected to the input of the second grating coupler (2); the input of the delay fiber (11) is connected to the input of the fourth grating coupler (4); the output of the delay fiber (11) is connected to the input of the fifth grating coupler (5); the input of the microwave amplifier (12) is connected to the output of the first photodetector (8); the output of the microwave amplifier (12) is connected to the input of the power divider (13); one of the two output ports of the power divider (13) outputs a linear frequency modulated signal, and the other is connected to the modulation port of the phase modulator (6); the input of the unbalanced Mach-Zehnder fiber interferometer (14) is connected to the input of the first grating coupler (1); the output of the unbalanced Mach-Zehnder fiber interferometer (14) is connected to the input of the second photodetector (15). In the silicon-based integrated Fourier domain mode-locked optoelectronic oscillator chip, the signal transmission process is as follows: the output end of the first grating coupler (1) is connected to the drop end of the micro disk resonator (7); the output end of the second grating coupler (2) is connected to the input end of the high-speed phase modulator (6); the output end of the third grating coupler (3) is connected to the add end of the micro disk resonator (7); the output end of the high-speed phase modulator (6) is connected to the input end of the micro disk resonator (7); the through end of the micro disk resonator (7) is connected to the output end of the fourth grating coupler (4); the output end of the fifth grating coupler (5) is connected to the first photodetector (8); the bandwidth of the first photodetector (8) is 20 GHz; the bandwidth of the second photodetector (15) is on the order of MHz. The following method is used for real-time compensation of frequency sweep nonlinearity: The laser (9) generates a frequency of f c The single-frequency optical signal is coupled by the second grating coupler (2) and then incident on the optical input port of the phase modulator (6). By loading the radio frequency input of the phase modulator (6), it generates a double-sideband modulated optical signal. The frequencies of the optical carrier and the positive and negative first-order sidebands are f1 and f2, respectively. c f c +f m and f c -f m The double-sideband modulated optical signal generated by the phase modulator (6) is incident on the microdisk resonator (7); the resonant wavelength of the microdisk resonator (7) is expressed as... （1.1） Where R and n eff Here, λ represents the radius and effective refractive index of the pre-amplifier microdisk resonator, respectively, where m is a positive integer. The m-th periodic resonant wavelength; the microdisk resonator has metal micro / nano heating electrodes, and the resonant wavelength of the pre-microdisk resonator is adjusted by utilizing the thermo-optic effect, so that the positive first-order sideband f c +f m Output from the drop end, while the optical carrier and the negative first-order sideband f c and f c -f m The output from the through port completes the conversion from phase modulation to intensity modulation; subsequently, the optical carrier and the negative first-order sideband f... c and f c -f m It is incident into the delay fiber (11) via the fourth grating coupler (4), and then enters the first photodetector (8) through the fifth grating coupler (5) to complete the photoelectric conversion; When the sweep period of the microdisk resonator (7) is synchronized with the cavity delay of the optoelectronic oscillator, that is, when the following equation is satisfied... （1.2） Where N is a positive integer, T filter T is the scan period of the microdisk resonator (7). c For the ring cavity delay of the photoelectric oscillator, n is the effective refractive index of the fiber core, Lc is the cavity length of the photoelectric oscillator, and c is the speed of light in vacuum; each oscillation mode in the frequency sweep range returns to the micro disk resonator (7) after gain and transmission. At this time, the center wavelength of the micro disk resonator (7) is tuned to the same frequency position. All modes in the frequency sweep range start oscillating in the photoelectric oscillator loop at the same time, generating a linear frequency modulation signal. The positive first-order sideband f output from the drop end of the microdisk resonator (7) c +f m The signal is incident on an unbalanced Mach-Zehnder fiber interferometer (14), and then a compensation signal is generated by a second photodetector (15). Based on the resampling theorem, the nonlinear frequency sweep of the linear frequency sweep signal can be compensated in real time.

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