A system and apparatus for suppressing oscillator phase noise

Abstract

A system and device for suppressing oscillator phase noise, comprising: an oscillator, and a self-injection locking loop and a self-phase locking loop for suppressing oscillator phase noise. A laser, a Mach-Zehnder modulator, at least two optical fiber delay lines of different lengths connected in sequence, two optical fiber delay lines connected to photodetectors, converting optical signals into electrical signals and entering the input end of a bridge, carrying out constructive interference and destructive interference in the bridge, and the output end of the bridge corresponding to generating a first interference signal and a second interference signal; the first interference signal output is fed back to the oscillator for self-injection locking; the second interference signal is mixed with part of the first interference signal and then output is fed back to the oscillator for self-phase locking; the self-injection locking loop and the self-phase locking loop of the application are combined to jointly suppress the phase noise of the oscillator.

Description

Technical Field

[0001] This application belongs to the field of microwave signal phase noise suppression technology, and particularly relates to a system and device for suppressing oscillator phase noise. Background Technology

[0002] Oscillators play an irreplaceable role in electronic systems, often referred to as the "heart" of these systems. They are a prerequisite and guarantee for the stable operation of electronic systems. Modern fields such as communication, radar, sensors, navigation, remote sensing, precision measurement, electronic warfare, and deep space exploration are constantly demanding higher performance from high-frequency oscillators. Quartz oscillators generate high-frequency signals through multiple frequency harmonics, but the phase noise deteriorates significantly with increasing harmonic number. Surface acoustic wave oscillators generate signals with frequencies up to the GHz level, but have low Q values ​​and high phase noise. Sapphire oscillators, a type of dielectric oscillator, can generate ultra-low phase noise high-frequency signals, but they only have a high Q value at a specific frequency and require ultra-low temperatures to operate, resulting in high manufacturing and usage costs. Therefore, phase noise suppression for high-performance high-frequency oscillators is extremely important.

[0003] Currently, methods for suppressing phase noise of radio frequency (RF) sources are mainly divided into two categories: The first category includes externally injected locking (EIL), phase-locked loops (PLL), or combinations of EIL and PLL (EIL-PLL), which lock onto a high-performance external reference source. These techniques require the phase noise of the external reference to be significantly lower than that of the RF source, thereby increasing the cost and complexity of the noise reduction system. The second category includes self-injected locking (SIL), self-phase-locked loops (SPLL), or a combination of self-injection and self-phase locking (SIL-SPLL) to suppress the phase noise of the RF source. Compared with the first category, these techniques avoid the need for an external reference signal, reducing the complexity and cost of the noise reduction system.

[0004] like Figure 17 Figure (a) shows a PhDL, which typically includes a laser diode (LD), a Mach-Zehnder modulator (MZM), a single-mode fiber (SMF), a photodetector (PD), and a low-noise amplifier (LNA). Alternatively, the LD can be directly modulated without using an MZM; for example... Figure 17As shown in Figure (b), PhDL can be used in SIL systems to provide the required long delay to reduce the phase noise of the voltage-controlled oscillator (VCO). The RF signal generated by the VCO is first modulated by the light emitted by the MZM modulated LD to generate a modulated optical signal, which is then transmitted through the optical fiber, converted back to an RF signal by the PD, and finally amplified by the LNA before being re-injected into the VCO. This process increases the effective Q factor of the oscillator, reduces frequency fluctuations, and achieves phase noise suppression proportional to the delay length. However, the amount of phase noise suppression in a PhDL-assisted SIL system is ultimately limited by the residual phase noise in the PhDL. This noise originates from the residual phase noise (RPN) of the LNA and the relative intensity noise (RIN) caused by Rayleigh scattering in the laser and optical fiber. It is also limited by the injection power and locking bandwidth of the oscillator; as shown in Figure (b). Figure 17 Figure (c) illustrates another method for reducing VCO phase noise using a PhDL-supported Self-Phase-Locked (SPL) loop. Unlike PhDL-supported SIL systems, SPL-deployed systems first measure VCO phase noise by mixing a signal directly from the VCO with its delayed copy. The measured phase fluctuations represent the VCO phase noise, which is then filtered by a low-pass filter (LPF) and amplified by a voltage amplifier before being fed back to the VCO to suppress its phase noise. Injection locking combining an external RF source (EIL) and a phase-locked loop (PLL) can also be used to suppress VCO phase noise. Experimental and computational simulations show that this EIL-PLL exhibits lower near-carrier phase noise and a wider injection locking range than either EIL or PLL alone. The EIL-PLL can suppress oscillator phase noise and extend the locking range. To eliminate the need for an external reference RF source in an EIL-PLL system, combining self-injection locking with a self-phase-locked loop (SIL-SPLL) to suppress VCO phase noise is feasible, as shown below. Figure 17 Figure (d) shows the structure of a PhDL-supported SIL-SPLL system, where a portion of the VCO signal is delayed by PhDL and directly fed back to the VCO as a SIL signal, while another portion forms an SPLL with the undelayed signal directly from the VCO. Unfortunately, SIL-SPLL also inherits the noise limitations of PhDL, namely the RPN of the LNA and the RIN originating from the light source and fiber. Utility Model Content

[0005] This application provides a system and apparatus for suppressing oscillator phase noise, which suppresses the oscillator phase noise by combining a self-injection lock-in loop and a self-phase lock-in loop.

[0006] Other objectives and advantages of this application can be further understood from the technical features disclosed herein.

[0007] To achieve one or more of the above objectives or other objectives, this application provides a system and apparatus for suppressing oscillator phase noise.

[0008] A system for suppressing oscillator phase noise includes:

[0009] An oscillator, and a self-injection locked loop and a self-phase locked loop for suppressing phase noise of the oscillator;

[0010] The self-injection locking loop includes a laser, a Mach-Zehnder modulator, and at least two fiber delay lines of different lengths connected in sequence. The two fiber delay lines are respectively connected to a photodetector. The photodetector converts the two optical signals transmitted by the two fiber delay lines into two electrical signals. The two electrical signals are modulated by a phase shifter and an attenuator, respectively, and then enter the input of a bridge circuit. Constructive microwave interference is performed in the bridge circuit. The first output of the bridge circuit generates a first interference signal. The first interference signal is processed by a low-noise amplifier and then output to the oscillator for self-injection locking.

[0011] The self-phase-locked loop includes a laser, a Mach-Zehnder modulator, and at least two fiber delay lines of different lengths connected in sequence. The two fiber delay lines are respectively connected to a photodetector. The photodetector converts the two optical signals transmitted through the two fiber delay lines into two electrical signals. These two electrical signals are modulated by a phase shifter and an attenuator, respectively, and then enter the input of the bridge circuit. Constructive and destructive interference occur within the bridge. The first output of the bridge generates a first interference signal, and the second output generates a second interference signal. The second interference signal is processed by a low-noise amplifier and then mixed with a portion of the first interference signal by a mixer before being output to a filter. After processing by the filter, the output is sent to the oscillator for self-phase locking.

[0012] The self-injection locking loop and the self-phase locking loop work together to suppress the phase noise of the oscillator.

[0013] The photodetectors, which are connected to the two fiber delay lines respectively, are connected to a phase shifter and an attenuator. The phase shifter and attenuator are connected to the input of the bridge. The interference of the two electrical signals output by the photodetectors in the bridge is controlled by adjusting the phase shifter and attenuator.

[0014] The phase difference between the two electrical signals output by the photodetector is controlled to be 0 degrees or 360 degrees by adjusting the phase shifter, and the two electrical signals have the same amplitude by adjusting the attenuator. The two electrical signals undergo constructive interference in the bridge, and a first interference signal is generated at the first output terminal of the bridge.

[0015] By adjusting the phase shifter, the phase difference between the two electrical signals output by the photodetector is controlled to be 180 degrees. By adjusting the attenuator, the two electrical signals are controlled to have the same amplitude. The two electrical signals undergo destructive interference in the bridge, and a second interference signal is generated at the second output terminal of the bridge.

[0016] The first interference signal is processed by a low-noise amplifier and then enters a radio frequency coupler. The radio frequency coupler divides the first interference signal into two parts. One part of the first interference signal is directly injected into the oscillator through a coaxial cable for self-injection locking.

[0017] The radio frequency coupler is connected to the mixer, and inputs another part of the first interference signal to the mixer, where it is mixed with the second interference signal within the mixer.

[0018] The second interference signal is processed by a low-noise amplifier and then mixed with another part of the first interference signal by a mixer. After being processed by a filter, the signal is output to the oscillator for self-phase locking.

[0019] A phase shifter is connected between the low-noise amplifier and the mixer to adjust the phase of the second interference signal after it has been processed by the low-noise amplifier.

[0020] A radio frequency coupler is connected between the oscillator and the Mach-Zehnder modulator;

[0021] The radio frequency signal output by the oscillator is divided into two parts by the radio frequency coupler. One part enters the Mach-Zehnder modulator, and the other part enters the bridge after being processed by the attenuator.

[0022] The oscillator is replaced with a photoelectric oscillator, and the phase noise of the photoelectric oscillator is suppressed by combining the self-injection locking loop with the self-phase locking loop.

[0023] The photoelectric oscillator and the Mach-Zehnder modulator are integrated on the same photonic chip.

[0024] The optoelectronic oscillator includes a Mach-Zehnder modulator, a micro-ring, a photodetector, a first radio frequency coupler, a phase shifter, a low-noise amplifier, and a second radio frequency coupler connected in sequence. The second radio frequency coupler feeds back the output signal to the Mach-Zehnder modulator to form a closed loop.

[0025] The first interference signal, after being processed by the self-injection locking loop, is directly injected into the other input terminal of the first RF coupler via a coaxial cable to achieve self-injection locking.

[0026] The second RF coupler splits the RF signal into two parts: one part enters the Mach-Zehnder modulator, and the other part is output through another output port.

[0027] The optoelectronic oscillator includes a Mach-Zehnder modulator, a microring, a photodetector, a first radio frequency coupler, a low-noise amplifier, and a second radio frequency coupler connected in sequence.

[0028] A parallel plate capacitor electrode is integrated on the microring, and the parallel plate capacitor electrode receives feedback signals from the self-phase-locked loop.

[0029] The optoelectronic oscillator includes a micro-ring, a photodetector, a first radio frequency coupler, a low-noise amplifier, and a second radio frequency coupler connected in sequence.

[0030] The microring integrates independent first parallel plate capacitor electrodes and second parallel plate capacitor electrodes. The continuous light wave generated by the laser enters the microring. The first parallel plate capacitor electrodes and the second parallel plate capacitor electrodes on the microring respectively receive feedback signals from the self-phase locked loop and radio frequency signals output by the second radio frequency coupler.

[0031] The second RF coupler splits the RF signal into two parts: one part enters the parallel plate capacitor electrode on the microring, and the other part is output through another output port.

[0032] The optoelectronic oscillator includes a phase modulator, a micro-ring, a photodetector, a first radio frequency coupler, a low-noise amplifier, and a second radio frequency coupler connected in sequence. The second radio frequency coupler feeds back the output signal to the phase modulator to form a closed loop.

[0033] A parallel plate capacitor electrode is integrated on the microring, and the parallel plate capacitor electrode receives feedback signals from the self-phase locked loop;

[0034] The continuous light wave generated by the laser enters the phase modulator;

[0035] The first interference signal, after being processed by the self-injection locking loop, is directly injected into the other input terminal of the first RF coupler via a coaxial cable to achieve self-injection locking.

[0036] The second RF coupler splits the RF signal into two parts: one part enters the phase modulator, and the other part is output through another output port.

[0037] The photoelectric oscillator includes,

[0038] A Mach-Zehnder modulator and a microring are integrated on the same photonic chip. An external laser is connected to the Mach-Zehnder modulator to output optical signals to the Mach-Zehnder modulator.

[0039] A photodetector is connected to a semiconductor optical amplifier and the Mach-Zehnder modulator. The photodetector converts the optical signal from the semiconductor optical amplifier into an electrical signal and injects it into the Mach-Zehnder modulator. The optical signal output from the Mach-Zehnder modulator enters an optical fiber loop, is transmitted with a long delay through the optical fiber loop, and is then injected into the optical isolator through the micro-ring to form a closed loop.

[0040] The other end of the semiconductor optical amplifier is connected to an optical isolator to isolate reflected light signals from the photodetector and the semiconductor optical amplifier.

[0041] The optoelectronic oscillator includes a micro-ring, a semiconductor optical amplifier, and a photodetector integrated on the same photonic chip, wherein the photodetector is connected to the semiconductor optical amplifier.

[0042] An external laser injects an optical signal into an external fiber optic ring of the chip through the micro-ring. After long-delay transmission through the fiber optic ring, the signal is injected into the semiconductor optical amplifier through the micro-ring. The photodetector converts the optical signal from the semiconductor optical amplifier into an electrical signal and injects it into the micro-ring, forming a closed loop.

[0043] A system for suppressing oscillator phase noise includes:

[0044] An optoelectronic oscillator, and a self-injection locked loop and a self-phase locked loop for suppressing phase noise of the optoelectronic oscillator;

[0045] The self-injection locking loop includes: the photoelectric oscillator inputs an optical signal to two optical fiber delay lines of different lengths, which are respectively connected to a photodetector; the photodetector converts the two optical signals transmitted by the two optical fiber delay lines into two electrical signals; the two electrical signals are modulated by a phase shifter and an attenuator, respectively, and then enter the input end of a bridge circuit, where constructive interference occurs within the bridge circuit, and a first interference signal is generated at the first output end of the bridge circuit; the first interference signal is then injected back into the photoelectric oscillator for self-injection locking.

[0046] The self-phase-locked loop includes: the photoelectric oscillator inputs an optical signal to two fiber delay lines of different lengths, which are respectively connected to a photodetector; the photodetector converts the two optical signals transmitted by the two fiber delay lines into two electrical signals; the two electrical signals are modulated by a phase shifter and an attenuator, respectively, and then enter the input terminal of the bridge circuit; constructive interference and destructive interference occur within the bridge circuit; a first interference signal is generated at the first output terminal of the bridge circuit, and a second interference signal is generated at the second output terminal; the second interference signal is processed by a low-noise amplifier and then mixed with a portion of the first interference signal by a mixer and output to a filter; after processing by the filter, the signal is injected back into the photoelectric oscillator for self-phase locking.

[0047] The photoelectric oscillator includes,

[0048] The Mach-Zehnder modulator integrated on the same photonic chip is sequentially connected to an optical fiber coupler, a delay unit, a photodetector, a low-noise amplifier, a bandpass filter, an RF coupler, and a voltage-controlled phase shifter. The voltage-controlled phase shifter is connected to the Mach-Zehnder modulator to form a closed loop. Together with the laser and optical isolator external to the photonic chip, they form the optoelectronic oscillator.

[0049] An apparatus for suppressing oscillator phase noise, comprising:

[0050] The micro-ring, fiber Bragg grating, photodetector, voltage-controlled phase shifter, and low-noise amplifier form a closed loop integrated on the same photonic chip, which together with the external laser of the photonic chip form a photoelectric oscillator;

[0051] The laser injects an optical signal into the microring. The fiber Bragg grating connects the microring and the photodetector. The photodetector converts the optical signal into an electrical signal, which is then processed by the voltage-controlled phase shifter and the low-noise amplifier before being injected into the microring.

[0052] The combination of self-injection locking loop and self-phase locking loop jointly suppresses the phase noise of the photoelectric oscillator;

[0053] The self-injection locking loop includes:

[0054] The fiber Bragg grating reflects the optical signal from the microring and outputs it to two fiber delay lines of different lengths. The two fiber delay lines are connected to photodetectors, which convert the two optical signals transmitted by the two fiber delay lines into two electrical signals. The two electrical signals are modulated by a phase shifter and an attenuator, respectively, and then enter the input of a bridge circuit. Constructive and destructive interferences occur within the bridge circuit. The first output of the bridge circuit generates a first interference signal, and the second output of the bridge circuit generates a second interference signal. The first interference signal is processed by a low-noise amplifier and then injected into the microring for self-injection locking.

[0055] The self-phase-locked loop includes:

[0056] The fiber Bragg grating reflects the optical signal from the micro-ring and outputs it to two fiber delay lines of different lengths. Each fiber delay line is connected to a photodetector. The photodetector converts the two optical signals transmitted through the two fiber delay lines into two electrical signals. These two electrical signals are modulated by a phase shifter and an attenuator, respectively, and then enter the input of the bridge circuit. Constructive and destructive interference occur within the bridge. The first output of the bridge generates a first interference signal, and the second output generates a second interference signal. The second interference signal is processed by a low-noise amplifier and a phase shifter, and then mixed with the signal processed by the voltage-controlled phase shifter via a mixer. The signal processed by the mixer is then output back to the voltage-controlled phase shifter for self-phase locking.

[0057] The microring is a dual-drive microring, and the photonic chip integrates a miniature photodetector for monitoring optical signals.

[0058] A reflective semiconductor optical amplifier injects an optical signal into a microring. The fiber Bragg grating connects the microring and the photodetector. The photodetector converts the optical signal into an electrical signal, which is then processed by the voltage-controlled phase shifter and the bandpass filter before being injected into the microring and the self-phase-locked loop.

[0059] The combination of self-injection locking loop and self-phase locking loop jointly suppresses the phase noise of the photoelectric oscillator.

[0060] The reflective semiconductor optical amplifier injects part of the optical signal into the micro-ring, and outputs the other part to the output terminal of the photonic chip;

[0061] The fiber Bragg grating connects the microring and the photodetector. The fiber Bragg grating reflects the optical signal. Part of the reflected optical signal is injected into the microring, and the other part is injected into the two fiber delay lines of different lengths, and then transmitted to the self-injection locked loop and the self-phase locked loop.

[0062] The photodetector detects the light signal reflected by the fiber Bragg grating.

[0063] The Mach-Zehnder modulator integrated on the same photonic chip is sequentially connected to a micro-ring, a fiber Bragg grating, a photodetector, a low-noise amplifier, a bandpass filter, a coupler, and a voltage-controlled phase shifter. The voltage-controlled phase shifter is connected to the Mach-Zehnder modulator to form a closed loop. Together with the external reflective semiconductor optical amplifier on the photonic chip, they form a photoelectric oscillator.

[0064] The reflective semiconductor optical amplifier injects the optical signal into the Mach-Zehnder modulator;

[0065] The combination of self-injection locking loop and self-phase locking loop jointly suppresses the phase noise of the photoelectric oscillator;

[0066] The self-injection locking loop includes: the Mach-Zehnder modulator outputs a signal to two fiber delay lines of different lengths, the two fiber delay lines are respectively connected to a photodetector, the photodetector converts the two optical signals transmitted by the two fiber delay lines into two electrical signals, the two electrical signals are modulated by a phase shifter and an attenuator respectively and then enter the input end of a bridge circuit, where constructive interference occurs within the bridge circuit, and a first interference signal is generated at the first output end of the bridge circuit. The first interference signal is processed by a low-noise amplifier and then injected into the coupler for self-injection locking.

[0067] The self-phase-locked loop includes: the Mach-Zehnder modulator outputs a signal to two fiber delay lines of different lengths, the two fiber delay lines are respectively connected to a photodetector, the photodetector converts the two optical signals transmitted by the two fiber delay lines into two electrical signals, the two electrical signals are modulated by a phase shifter and an attenuator respectively and then enter the input of the bridge, where constructive interference and destructive interference are performed. The first output of the bridge generates a first interference signal, and the second output of the bridge generates a second interference signal. The second interference signal is processed by a low-noise amplifier and then mixed with the signal output by the coupler through a mixer and output to a filter. After being processed by the filter, it is output to the voltage-controlled phase shifter for self-phase locking.

[0068] Mach-Zehnder modulator, micro-ring, fiber Bragg grating, and photodetector are connected in sequence and integrated on the same photonic chip;

[0069] An external reflective semiconductor optical amplifier injects an optical signal into a Mach-Zehnder modulator. Part of the optical signal output from the Mach-Zehnder modulator is injected into the micro-ring, and the other part is output to the two optical fiber delay lines of different lengths.

[0070] The fiber Bragg grating reflects the optical signal and injects it into the microring to form a mode-locked laser.

[0071] The photodetector detects the light signal reflected by the fiber Bragg grating.

[0072] Compared with the prior art, the beneficial effects of this application mainly include:

[0073] The optical signal output from the Mach-Zehnder modulator of this application is transmitted through two optical fiber delay lines of different lengths and then converted into an electrical signal by a photodetector. The signal then enters the input of a bridge circuit, where constructive and destructive interference occur. Correspondingly, a first interference signal and a second interference signal are generated at the output of the bridge. The first interference signal is output and fed back to the oscillator for self-injection locking. The second interference signal is mixed with a portion of the first interference signal and then output and fed back to the oscillator for self-phase locking. The self-injection locking loop and the self-phase locking loop are combined to suppress the phase noise of the oscillator.

[0074] To make the above and other objects, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0075] To more clearly illustrate the technical solutions in the specific embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0076] Figure 1 This is a schematic diagram of a system structure for suppressing oscillator phase noise provided in Embodiment 1 of this application.

[0077] Figure 2 This is a schematic diagram of a system structure for suppressing oscillator phase noise provided in Embodiment 2 of this application.

[0078] Figure 3 This is a schematic diagram of a system structure for suppressing oscillator phase noise provided in Embodiment 3 of this application.

[0079] Figure 4 Schematic diagram of the optoelectronic oscillator structure provided in Embodiment 3 of this application Figure 1 .

[0080] Figure 5 Schematic diagram of the optoelectronic oscillator structure provided in Embodiment 3 of this application Figure 2 .

[0081] Figure 6 Schematic diagram of the optoelectronic oscillator structure provided in Embodiment 3 of this application Figure 3 .

[0082] Figure 7 Schematic diagram of the optoelectronic oscillator structure provided in Embodiment 3 of this application Figure 4 .

[0083] Figure 8 Schematic diagram of the optoelectronic oscillator structure provided in Embodiment 3 of this application Figure 5 .

[0084] Figure 9 Schematic diagram of the optoelectronic oscillator structure provided in Embodiment 3 of this application Figure 6 .

[0085] Figure 10 This is a schematic diagram of a device for suppressing oscillator phase noise provided in Embodiment 5 of this application.

[0086] Figure 11 This is a schematic diagram of a device for suppressing oscillator phase noise provided in Embodiment 6 of this application.

[0087] Figure 12 This is a schematic diagram of the optoelectronic oscillator structure provided in Embodiment 6 of this application.

[0088] Figure 13 This is a schematic diagram of a device for suppressing oscillator phase noise provided in Embodiment 7 of this application.

[0089] Figure 14 This is a schematic diagram of the optoelectronic oscillator structure provided in Embodiment 7 of this application.

[0090] Figure 15 Experimental results provided for Example 7 of this application Figure 1 .

[0091] Figure 16 Experimental results provided for Example 7 of this application Figure 2 .

[0092] Figure 17 A schematic diagram of a device for suppressing radio frequency source phase noise provided in the background art of this application.

[0093] Figure 18 This is a schematic diagram of a system structure for suppressing oscillator phase noise provided in Embodiment 4 of this application.

[0094] Figure 19 This is a schematic diagram of the optoelectronic oscillator structure provided in Embodiment 4 of this application. Detailed Implementation

[0095] The foregoing and other technical contents, features, and effects of this application will be clearly presented in the following detailed description of a preferred embodiment with reference to the accompanying drawings. The directional terms mentioned in the following embodiments, such as up, down, left, right, front, or back, are merely for reference to the accompanying drawings. Therefore, the directional terms used are for illustrative purposes and not for limiting the scope of this application.

[0096] This application provides a system and apparatus for suppressing oscillator phase noise, which suppresses the oscillator phase noise by combining a self-injection lock-in loop and a self-phase lock-in loop.

[0097] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0098] After theoretical analysis and experimental verification, a self-injected locking (SIL) system implemented via a coaxial cable delay line established an inverse relationship between oscillator phase noise and delay line length. However, due to the high loss of coaxial cables, it is practically impossible to achieve low phase noise using long delay lines. In contrast, PhDL, which uses optical fiber for signal transmission, has been shown to provide better performance for SIL, thanks to its advantages of low loss, low cost, and compact size.

[0099] Carrier-suppressed interferometry (CSI) was initially deployed to measure the near-carrier phase noise of two-port microwave equipment. In a CSI system, carrier suppression allows for significant amplification of the phase noise under test without causing saturation, thereby enhancing the sensitivity of the phase noise measurement. Furthermore, CSI converts the phase noise under test into amplitude noise, effectively eliminating the limitation of LNA RPN on measurement sensitivity. The PhDL-supported CSI self-phase-locked (CSI-SPL) scheme for suppressing the phase noise of the optoelectronic oscillator (OEO) demonstrates a 20 dB phase noise suppression at a 10 Hz offset from a 10 GHz carrier. The theory of measuring ultra-low phase noise using a PhDL-supported CSI system has been established and experimentally verified. This shows that PhDL-supported CSI can effectively prevent the phase noise contribution of the LNA in PhDL and limit the measurement sensitivity of the RIN-limited system. This ensures that the PhDL-supported CSI-SPL scheme can be applied to any VCO, effectively suppressing its phase noise to a level far below the limit imposed by PhDL. Meanwhile, carrier suppression interferometry can effectively suppress the contribution of residual phase noise of the low-noise amplifier, relative intensity noise of the laser, and scattering noise in the fiber to the noise floor of the self-phase-locked system. Example 1

[0100] like Figure 1 As shown, a system for suppressing oscillator phase noise includes:

[0101] Oscillator, and self-injection locked loop and self-phase locked loop for suppressing oscillator phase noise;

[0102] The self-injection locking loop includes a laser, a Mach-Zehnder modulator, and at least two fiber delay lines of different lengths connected in sequence. The two fiber delay lines are respectively connected to a photodetector. The photodetector converts the two optical signals transmitted by the two fiber delay lines into two electrical signals. The two electrical signals are modulated by a phase shifter and an attenuator, respectively, and then enter the input of a bridge circuit. Constructive microwave interference is performed in the bridge circuit. The first output of the bridge circuit generates a first interference signal. The first interference signal is processed by a low-noise amplifier and then output to an oscillator for self-injection locking.

[0103] A self-phase-locked loop includes a laser, a Mach-Zehnder modulator, and at least two fiber delay lines of different lengths connected in sequence. The two fiber delay lines are each connected to a photodetector. The photodetector converts the two optical signals transmitted through the two fiber delay lines into two electrical signals. These two electrical signals are modulated by a phase shifter and an attenuator, respectively, and then enter the input of a bridge circuit. Constructive and destructive interference occur within the bridge. The first output of the bridge generates a first interference signal, and the second output generates a second interference signal. The second interference signal is processed by a low-noise amplifier and then mixed with a portion of the first interference signal by a mixer before being output to a filter. After further processing by the filter, the output is sent to an oscillator for self-phase locking.

[0104] The combination of self-injection locking loop and self-phase locking loop jointly suppresses the phase noise of the oscillator.

[0105] Specifically, such as Figure 1 As shown, the photodetectors connected to the two fiber delay lines are respectively connected to a phase shifter and an attenuator. The phase shifter and attenuator are connected to the input of the bridge. The interference of the two electrical signals output by the photodetectors in the bridge is controlled by adjusting the phase shifter and attenuator.

[0106] The phase difference between the two electrical signals output by the photodetector is controlled to be 0 degrees or 360 degrees by adjusting the phase shifter. The two electrical signals have the same amplitude by adjusting the attenuator. The two electrical signals perform constructive interference in the bridge and generate the first interference signal at the first output end of the bridge. The signal at the "bright end" of the bridge is called the first interference signal.

[0107] The phase difference between the two electrical signals output by the photodetector is controlled to be 180 degrees by adjusting the phase shifter, and the two electrical signals have the same amplitude by adjusting the attenuator. The two electrical signals undergo destructive interference in the bridge, and a second interference signal is generated at the second output terminal of the bridge. The signal at the "dark end" of the bridge is called the first interference signal.

[0108] After being processed by a low-noise amplifier, the first interference signal enters the radio frequency coupler. The radio frequency coupler divides the first interference signal into two parts. One part of the first interference signal is directly injected into the oscillator through a coaxial cable for self-injection locking.

[0109] The radio frequency coupler is connected to the mixer, and another part of the first interference signal is input to the mixer, where it is mixed with the second interference signal.

[0110] The second interference signal is processed by a low-noise amplifier and then mixed with another part of the first interference signal by a mixer. After being processed by a filter, the signal is output to an oscillator for self-phase locking.

[0111] A phase shifter is connected between the low-noise amplifier and the mixer to adjust the phase of the second interference signal after it has been processed by the low-noise amplifier.

[0112] Specifically, such as Figure 1 As shown, the continuous light output from the semiconductor laser (DFB) enters a dual-output Mach-Zehnder intensity modulator (MZM). The RF signal output from the oscillator (OSC) is loaded onto the optical signal through the MZM. The MZM outputs two optical signals. One signal passes through a relatively long single-mode fiber (SMF1) and enters photodetector PD1, where it is converted into a microwave signal. The other signal passes through a relatively short single-mode fiber (SMF2) and enters photodetector PD2, where it is converted into an electrical signal. The signal output from PD1 passes through a manual phase shifter (MPS1) or an electric phase shifter and interferes with the electrical signal output from PD1 after passing through a manual attenuator (VA) in a 3dB bridge. By adjusting MPS1 and VA, the two signals output from the 3dB bridge produce constructive interference, generating the first interference signal ("Bright" end). By adjusting MPS1 and VA, the two signals output from the 3dB bridge produce destructive interference, generating the second interference signal ("Dark" end).

[0113] The signal after the 3dB bridge can be divided into two parts: The first part is a PhDL-based dual-loop self-injection locking system: the "bright" end signal is divided into two parts by the radio frequency coupler (RFC) after passing through a low-noise amplifier (LNA). One part is directly injected into the VCO through a coaxial cable to form a self-injection locking system based on two photon delay lines (short delay line and long delay line). This system suppresses the phase noise of the oscillator over a large frequency offset range. The second part is a PhDL-based CSI self-phase locking system: the "dark" end signal is a carrier rejection signal, which mainly comes from the phase noise of the oscillator. This signal passes through a low-noise amplifier with a relatively large gain and MPS2 and then enters the RF end of the dual balanced mixer (DBM) to be mixed with another signal from the output of the radio frequency coupler (RFC). By adjusting MPS2, the phase difference between the signals entering the two ends of the DBM is made close to 0 degrees or 180 degrees, thereby obtaining a low-frequency voltage signal related to the phase noise of the oscillator. This voltage signal is then applied to the frequency adjustment end or phase locking end of the oscillator after passing through a low-pass filter (LPF) to further suppress the phase noise of the oscillator.

[0114] Because the carrier is suppressed, the "dark" end signal can be amplified many times by the low-noise amplifier without causing saturation, thus greatly improving the test sensitivity of the CSI. Since the carrier suppression interferometer is insensitive to amplitude noise, it is also insensitive to the laser's RIN and the scattering noise within the fiber. The small residual carrier signal at the "dark" end effectively avoids residual phase noise in the low-noise amplifier, while simultaneously amplifying the measured noise to a level far exceeding the mixer's noise floor. By adjusting the phase shifter to make the DBM sensitive to amplitude noise (phase noise has been converted to amplitude noise), the residual phase noise of the low-noise amplifier can be ignored. Typically, the amplitude noise of the low-noise amplifier is much smaller than its phase noise; therefore, the amplitude noise of the low-noise amplifier does not affect the test sensitivity of the PhDL-CSI system.

[0115] Example 2

[0116] like Figure 2 As shown, an RF coupler is connected between the oscillator and the Mach-Zehnder modulator;

[0117] The RF signal output from the oscillator is split into two parts by the RF coupler. One part enters the Mach-Zehnder modulator, and the other part enters the bridge circuit after being processed by the attenuator.

[0118] like Figure 2 As shown, the relatively short fiber optic delay line is replaced by a coaxial cable.

[0119] Example 3

[0120] like Figure 3As shown, the oscillator is replaced with an opto-oscillator, and the phase noise of the opto-oscillator is suppressed by combining a self-injection locking loop and a self-phase locking loop; and the opto-oscillator and the Mach-Zehnder modulator are integrated on the same photonic chip.

[0121] Specifically, such as Figure 4 As shown, the optoelectronic oscillator includes a Mach-Zehnder modulator, a micro-ring, a photodetector, a first radio frequency coupler, a phase shifter, a low-noise amplifier, and a second radio frequency coupler connected in sequence. The second radio frequency coupler feeds back the output signal to the Mach-Zehnder modulator to form a closed loop.

[0122] The first interference signal, after being processed by the self-injection locking loop, is directly injected into the other input terminal of the first RF coupler via a coaxial cable to achieve self-injection locking.

[0123] The second RF coupler splits the RF signal into two parts: one part enters the Mach-Zehnder modulator, and the other part is output through another output port.

[0124] Specifically, the integrated optoelectronic oscillator consists of an MZM, a microring (MRR), a photodetector (PD), an RF coupler 1, an electric phase shifter, a low-noise amplifier, and an RF coupler 2. These devices are connected in sequence to form an OEO closed loop. The MRR and PD form a microwave photonic filter to select the mode of the integrated OEO. The mode spacing (FSR) of the MRR determines the oscillation frequency. In addition, the MRR also acts as a resonant cavity with a relatively high Q value in this structure. The other port of the RF coupler 1 is self-injected and locked. The other port of the RF coupler 2 is used to generate a microwave signal output. The electric phase shifter is used to fine-tune the frequency of the OEO or to receive feedback signals from the carrier suppression interference system to reduce the phase noise of the OEO.

[0125] As a preferred embodiment of this application, such as Figure 5 As shown, the optoelectronic oscillator includes a Mach-Zehnder modulator, a microring, a photodetector, a first radio frequency coupler, a low-noise amplifier, and a second radio frequency coupler connected in sequence; a parallel plate capacitor electrode is integrated on the microring, and the parallel plate capacitor electrode receives feedback signals from the self-phase-locked loop.

[0126] Specifically, a parallel plate capacitor electrode is made on the MRR. By applying a voltage signal to this electrode, the FSR of the MRR is changed. This can be used to adjust the frequency of the integrated OEO, and can also receive feedback signals from the carrier suppression interference system to reduce the phase noise of the OEO. In this system, applying different bias voltages to the MRR can achieve the adjustment of the OEO frequency.

[0127] As a preferred embodiment of this application, such as Figure 6 As shown, the opto-oscillator includes a micro-ring, a photodetector, a first radio frequency coupler, a low-noise amplifier, and a second radio frequency coupler connected in sequence.

[0128] In this embodiment, the microring is integrated with independent first parallel plate capacitor electrodes and second parallel plate capacitor electrodes. The continuous light wave generated by the laser enters the microring, and the first parallel plate capacitor electrodes and the second parallel plate capacitor electrodes on the microring respectively receive the feedback signal from the self-phase locked loop and the radio frequency signal output by the second radio frequency coupler.

[0129] The second RF coupler splits the RF signal into two parts: one part enters the parallel plate capacitor electrode on the microring, and the other part is output through another output port.

[0130] Specifically, two independent parallel plate capacitor electrodes are made on the MRR. One receives the feedback signal from the carrier suppression interference system to reduce the phase noise of the OEO, and the other is used as an intensity modulator to receive the signal from RFC1 to form a closed loop of the OEO. In addition, the OEO frequency can also be adjusted by applying different bias voltages to the MRR in this system.

[0131] As a preferred embodiment of this application, such as Figure 7 As shown, the integrated optoelectronic oscillator in this embodiment includes a phase modulator, a micro-ring, a photodetector, a first radio frequency coupler, a low-noise amplifier, and a second radio frequency coupler connected in sequence. The second radio frequency coupler feeds back the output signal to the phase modulator to form a closed loop.

[0132] A parallel plate capacitor electrode is integrated on the microring, and the parallel plate capacitor electrode receives feedback signals from the self-phase locked loop.

[0133] The continuous light wave generated by the laser enters the phase modulator;

[0134] The first interference signal, after being processed by the self-injection locking loop, is directly injected into the other input terminal of the first RF coupler via a coaxial cable to achieve self-injection locking.

[0135] The second RF coupler splits the RF signal into two parts: one part enters the phase modulator, and the other part is output through another output port.

[0136] Specifically, in addition to applying a bias voltage to the MRR to achieve a small range of adjustment of the OEO frequency, the OEO frequency can also be adjusted over a large range by changing the wavelength of the light input to the PM.

[0137] As a preferred embodiment of this application, such as Figure 8 As shown, the photoelectric oscillator in this embodiment includes,

[0138] The Mach-Zehnder modulator and microring are integrated on the same photonic chip, and an external laser is connected to the Mach-Zehnder modulator to output optical signals to the Mach-Zehnder modulator.

[0139] The photodetector is connected to the semiconductor optical amplifier and the Mach-Zehnder modulator. The photodetector converts the optical signal from the semiconductor optical amplifier into an electrical signal and then injects it into the Mach-Zehnder modulator. The optical signal output from the Mach-Zehnder modulator enters the fiber optic loop, is transmitted with a long delay through the fiber optic loop, and is then injected into the optical isolator through the micro-ring to form a closed loop.

[0140] The other end of the semiconductor optical amplifier is connected to an optical isolator to isolate reflected light signals from the photodetector and the semiconductor optical amplifier.

[0141] Specifically, such as Figure 8 As shown, the MZM and MRR are integrated on the same photonic chip. An external DFB laser is used to provide the light source, the MRR is used for OEO mode selection, the semiconductor optical amplifier (SOA) is used to compensate for loop loss, the photodetector converts the optical signal into an electrical signal, and the optical isolator (ISO) is used to isolate the reflected optical signal from the photodetector (PD) and SOA. The electrical signal output from the PD is injected into the MZM to form an OEO closed loop. The optical signal output from the MZM enters the fiber loop, is transmitted with a long delay, and is then injected into the OEO loop through the MRR to form a self-injected locked OEO.

[0142] As a preferred embodiment of this application, such as Figure 9 As shown, the photoelectric oscillator in this embodiment includes a micro-ring, a semiconductor optical amplifier, and a photodetector integrated on the same photonic chip, with the photodetector connected to the semiconductor optical amplifier.

[0143] An external laser injects an optical signal into an external fiber optic ring of the chip through a micro-ring. After long-delay transmission through the fiber optic ring, the signal is injected into a semiconductor optical amplifier through the micro-ring. A photodetector converts the optical signal from the semiconductor optical amplifier into an electrical signal and injects it into the micro-ring, forming a closed loop.

[0144] Specifically, the electrical signal is directly converted into photoelectric signal through the MRR modulator. In this structure, the MRR serves as an optical resonant cavity and is also used for selecting the OEO oscillation mode. In addition, the MRR, SOA, and PD are integrated on the same chip, while the DFB light source and fiber optic ring are external.

[0145] Example 4

[0146] like Figure 18 As shown, a system for suppressing oscillator phase noise includes:

[0147] Optoelectronic oscillator, and self-injection locked loop and self-phase locked loop for suppressing phase noise of optoelectronic oscillator;

[0148] The self-injection locking loop includes: an opto-oscillator inputs an optical signal to two optical fiber delay lines of different lengths, which are respectively connected to a photodetector; the photodetector converts the two optical signals transmitted by the two optical fiber delay lines into two electrical signals; the two electrical signals are modulated by a phase shifter and an attenuator, respectively, and then enter the input end of a bridge circuit, where constructive interference occurs within the bridge circuit, and a first interference signal is generated at the first output end of the bridge circuit; the first interference signal is then injected back into the opto-oscillator for self-injection locking.

[0149] The self-phase-locked loop includes: an optical oscillator inputs an optical signal to two fiber delay lines of different lengths, which are respectively connected to a photodetector; the photodetector converts the two optical signals transmitted by the two fiber delay lines into two electrical signals; the two electrical signals are modulated by a phase shifter and an attenuator, respectively, and then enter the input of a bridge circuit; constructive interference and destructive interference occur within the bridge circuit; a first interference signal is generated at the first output of the bridge circuit, and a second interference signal is generated at the second output; the second interference signal is processed by a low-noise amplifier and then mixed with a portion of the first interference signal by a mixer and output to a filter; after processing by the filter, the signal is injected back into the optical oscillator for self-phase locking.

[0150] Specifically, such as Figure 19 As shown, the photoelectric oscillator in this embodiment includes,

[0151] The Mach-Zehnder modulator integrated on the same photonic chip is sequentially connected to an optical fiber coupler, a delay unit, a photodetector, a low-noise amplifier, a bandpass filter, an RF coupler, and a voltage-controlled phase shifter. The voltage-controlled phase shifter is connected to the Mach-Zehnder modulator to form a closed loop; together with the laser and optical isolator external to the photonic chip, it forms an optoelectronic oscillator.

[0152] Example 5

[0153] like Figure 10 As shown, a device for suppressing oscillator phase noise includes:

[0154] The micro-ring, fiber Bragg grating, photodetector, voltage-controlled phase shifter, and low-noise amplifier form a closed loop integrated on the same photonic chip, which together with the external laser of the photonic chip form an optoelectronic oscillator.

[0155] The laser injects the optical signal into the micro-ring. The fiber Bragg grating connects the micro-ring and the photodetector. The photodetector converts the optical signal into an electrical signal, which is then processed by a voltage-controlled phase shifter and a low-noise amplifier before being injected into the micro-ring.

[0156] The combination of self-injection locking loop and self-phase locking loop jointly suppresses the phase noise of the photoelectric oscillator;

[0157] Self-injection locking loop includes:

[0158] The optical signal reflected by the fiber Bragg grating microring is output to two fiber delay lines of different lengths. The two fiber delay lines are connected to photodetectors. The photodetectors convert the two optical signals transmitted by the two fiber delay lines into two electrical signals. The two electrical signals are modulated by a phase shifter and an attenuator, respectively, and then enter the input of a bridge circuit. Constructive interference and destructive interference are performed in the bridge circuit. The first output of the bridge circuit generates a first interference signal, and the second output of the bridge circuit generates a second interference signal. The first interference signal is processed by a low-noise amplifier and then injected into the microring for self-injection locking.

[0159] Self-phase-locked loop, including:

[0160] The optical signal from the fiber Bragg grating reflection microring is output to two fiber delay lines of different lengths. Each delay line is connected to a photodetector, which converts the two optical signals transmitted through the delay lines into two electrical signals. These electrical signals are modulated by a phase shifter and an attenuator, respectively, and then input to a bridge circuit. Constructive and destructive interference occur within the bridge, generating a first interference signal at the first output and a second interference signal at the second output. The second interference signal is then processed by a low-noise amplifier and a phase shifter, and mixed with the signal processed by a voltage-controlled phase shifter via a mixer. The mixed signal is then output back to the voltage-controlled phase shifter for self-phase locking.

[0161] The microring is a dual-drive microring, with a miniature photodetector integrated on the photonic chip for monitoring optical signals; the MPD is used to monitor the optical signal output by the OEO, and the FBG further filters out the side modes generated by the OEO to improve the side mode suppression ratio. In addition, CSI and self-injection phase lock can also be used to further reduce its phase noise.

[0162] Example 6

[0163] like Figure 11 As shown, the reflective semiconductor optical amplifier injects the optical signal into the micro-ring, the fiber Bragg grating connects the micro-ring and the photodetector, the photodetector converts the optical signal into an electrical signal, which is then processed by the voltage-controlled phase shifter and the bandpass filter before being injected into the micro-ring and the self-phase-locked loop.

[0164] Specifically, the output signal of the "bright" end is amplified by a low-noise amplifier and then injected into the COEO through one of the RF input ports of the dual-drive MRR to form a dual PhDL self-injection to suppress its phase noise. The CSI suppression system detects the phase noise of the COEO and injects it into the COEO through the LPF and VPS to further suppress the phase noise of the COEO.

[0165] The combination of self-injection locking loop and self-phase locking loop jointly suppresses the phase noise of the photoelectric oscillator.

[0166] As a preferred embodiment of this application, such as Figure 12 As shown, in this embodiment, the reflective semiconductor optical amplifier injects part of the optical signal into the micro-ring, and outputs the other part to the output end of the photonic chip;

[0167] The fiber Bragg grating connects the micro-ring and the photodetector. The fiber Bragg grating reflects the optical signal. Part of the reflected optical signal is injected into the micro-ring, and the other part is injected into two fiber delay lines of different lengths, which are then transmitted to the self-injection locked loop and the self-phase locked loop.

[0168] A photodetector detects the light signal reflected by a fiber Bragg grating.

[0169] Specifically, part of the optical signal output by RSOA enters the dual-drive MRR modulator, and the other part is output from one end of the chip. Part of the reflected optical signal from FBG enters the dual-drive MRR, and the other part enters the dual-ring self-injection system and carrier suppression system. PD is used to detect the transmitted optical signal from FBG.

[0170] Example 7

[0171] like Figure 13 As shown, the Mach-Zehnder modulator integrated on the same photonic chip is sequentially connected to the micro-ring, fiber Bragg grating, photodetector, low-noise amplifier, bandpass filter, coupler, and voltage-controlled phase shifter. The voltage-controlled phase shifter is connected to the Mach-Zehnder modulator to form a closed loop; and together with the external reflective semiconductor optical amplifier of the photonic chip, they form a photoelectric oscillator.

[0172] A reflective semiconductor optical amplifier injects an optical signal into a Mach-Zehnder modulator;

[0173] The combination of self-injection locking loop and self-phase locking loop jointly suppresses the phase noise of the photoelectric oscillator;

[0174] The self-injection locking loop includes: a Mach-Zehnder modulator outputs a signal to two fiber delay lines of different lengths, the two fiber delay lines are respectively connected to a photodetector, the photodetector converts the two optical signals transmitted by the two fiber delay lines into two electrical signals, the two electrical signals are modulated by a phase shifter and an attenuator respectively and then enter the input end of a bridge circuit, where constructive interference is performed in the bridge circuit, and a first interference signal is generated at the first output end of the bridge circuit. The first interference signal is processed by a low-noise amplifier and then injected into a coupler for self-injection locking.

[0175] The self-phase-locked loop includes: a Mach-Zehnder modulator outputs a signal to two fiber delay lines of different lengths, the two fiber delay lines are respectively connected to photodetectors, the photodetectors convert the two optical signals transmitted by the two fiber delay lines into two electrical signals, the two electrical signals are modulated by a phase shifter and an attenuator respectively and then enter the input of a bridge circuit, where constructive interference and destructive interference are performed within the bridge circuit, the first output of the bridge circuit generates a first interference signal, and the second output of the bridge circuit generates a second interference signal; the second interference signal is processed by a low-noise amplifier and then mixed with the signal output from the coupler by a mixer and output to a filter, and after being processed by the filter, it is output to a voltage-controlled phase shifter for self-phase locking.

[0176] Specifically, the output signal of the "bright" end is amplified by a low-noise amplifier and then injected into the COEO through the MZM to form a dual PhDL self-injection to suppress the phase noise of the COEO. The CSI suppression system detects the phase noise of the COEO and then passes it through the LPF and VPS to further suppress the phase noise of the COEO.

[0177] As a preferred embodiment of this application, such as Figure 14 As shown, in this embodiment, the Mach-Zehnder modulator, micro-ring, fiber Bragg grating, and photodetector are connected in sequence and integrated on the same photonic chip.

[0178] An external reflective semiconductor optical amplifier injects the optical signal into a Mach-Zehnder modulator. Part of the optical signal output from the Mach-Zehnder modulator is injected into the micro-ring, and the other part is output to two optical fiber delay lines of different lengths.

[0179] A fiber Bragg grating reflects the optical signal and injects it into a microring to form a mode-locked laser;

[0180] A photodetector detects the light signal reflected by a fiber Bragg grating.

[0181] Specifically, the optical signal output from RSOA enters the MZM modulator, part of the optical signal output from MZM enters the MRR, and the other part is output from one end of the chip; the reflected optical signal from FBG enters the MRR to form a mode-locked laser, and PD is used to detect the transmitted optical signal from FBG.

[0182] like Figure 15 As shown, after using the above-mentioned phase noise suppression system, the phase noise of the 10GHz signal is -123dBc / Hz at a frequency offset of 1kHz, which is 46dB lower than that of free oscillation, and -144dBc / Hz at a frequency offset of 10kHz, which is 39dB lower than that of free oscillation.

[0183] like Figure 16 As shown, after using the above phase noise suppression system, the spectrum of the 10GHz signal near the carrier is significantly reduced compared to free oscillation, and its side-mode rejection ratio can reach 110dB. This value is mainly related to the length of the optical fiber used. At the same time, the spectrum diagram also shows that the spectrum of using the self-injection system alone has a higher side-mode rejection ratio than using both methods at the same time, but its spectrum near the carrier is higher.

[0184] This application provides a system and apparatus for suppressing oscillator phase noise, which suppresses the oscillator phase noise by combining a self-injection lock-in loop and a self-phase lock-in loop.

[0185] The common English terms or letters used in this application for clarity are merely illustrative references and not restrictive interpretations or specific uses. They should not be used to limit the scope of protection of this application based on their possible Chinese translations or specific letters.

[0186] It should also be noted that in this article, relational terms such as “first” and “second” are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

Claims

1. A system for suppressing oscillator phase noise, characterized in that, include: An oscillator, and a self-injection locked loop and a self-phase locked loop for suppressing phase noise of the oscillator; The self-injection locking loop includes a laser, a Mach-Zehnder modulator, and at least two fiber delay lines of different lengths connected in sequence. The two fiber delay lines are respectively connected to a photodetector. The photodetector converts the two optical signals transmitted by the two fiber delay lines into two electrical signals. The two electrical signals are modulated by a phase shifter and an attenuator, respectively, and then enter the input of a bridge circuit. Constructive microwave interference is performed in the bridge circuit. The first output of the bridge circuit generates a first interference signal. The first interference signal is processed by a low-noise amplifier and then output to the oscillator for self-injection locking. The self-phase-locked loop includes a laser, a Mach-Zehnder modulator, and at least two fiber delay lines of different lengths connected in sequence. The two fiber delay lines are respectively connected to a photodetector. The photodetector converts the two optical signals transmitted by the two fiber delay lines into two electrical signals. The two electrical signals are modulated by a phase shifter and an attenuator, respectively, and then enter the input of the bridge. Constructive interference and destructive interference are performed in the bridge. The first output of the bridge generates a first interference signal, and the second output of the bridge generates a second interference signal. The second interference signal is processed by a low-noise amplifier and then mixed with a portion of the first interference signal by a mixer before being output to a filter. After being processed by the filter, the output is sent to the oscillator for self-phase locking. The self-injection locking loop and the self-phase locking loop work together to suppress the phase noise of the oscillator.

2. The system for suppressing oscillator phase noise according to claim 1, characterized in that, The photodetectors, which are connected to the two fiber delay lines respectively, are connected to a phase shifter and an attenuator. The phase shifter and attenuator are connected to the input of the bridge. The interference of the two electrical signals output by the photodetectors in the bridge is controlled by adjusting the phase shifter and attenuator.

3. The system for suppressing oscillator phase noise according to claim 2, characterized in that, The phase difference between the two electrical signals output by the photodetector is controlled to be 0 degrees or 360 degrees by adjusting the phase shifter, and the two electrical signals have the same amplitude by adjusting the attenuator. The two electrical signals undergo constructive interference in the bridge, and a first interference signal is generated at the first output terminal of the bridge. The phase difference between the two electrical signals output by the photodetector is controlled to be 180 degrees by adjusting the phase shifter, and the two electrical signals are controlled to have the same amplitude by adjusting the attenuator. The two electrical signals undergo destructive interference in the bridge, and a second interference signal is generated at the second output terminal of the bridge.

4. The system for suppressing oscillator phase noise according to claim 1, characterized in that, The first interference signal is processed by a low-noise amplifier and then enters a radio frequency coupler. The radio frequency coupler divides the first interference signal into two parts. One part of the first interference signal is directly injected into the oscillator through a coaxial cable for self-injection locking. The radio frequency coupler is connected to the mixer, and inputs another part of the first interference signal to the mixer, where it is mixed with the second interference signal within the mixer.

5. A system for suppressing oscillator phase noise according to claim 4, characterized in that, The second interference signal is processed by a low-noise amplifier and then mixed with another part of the first interference signal by a mixer. After being processed by a filter, the signal is output to the oscillator for self-phase locking. A phase shifter is connected between the low-noise amplifier and the mixer to adjust the phase of the second interference signal after it has been processed by the low-noise amplifier.

6. A system for suppressing oscillator phase noise according to claim 1, characterized in that, A radio frequency coupler is connected between the oscillator and the Mach-Zehnder modulator; The radio frequency signal output by the oscillator is divided into two parts by the radio frequency coupler. One part enters the Mach-Zehnder modulator, and the other part enters the bridge after being processed by the attenuator.

7. A system for suppressing oscillator phase noise according to claim 1, characterized in that, The oscillator is replaced with a photoelectric oscillator, and the phase noise of the photoelectric oscillator is suppressed by combining the self-injection locking loop with the self-phase locking loop. The photoelectric oscillator and the Mach-Zehnder modulator are integrated on the same photonic chip.

8. A system for suppressing oscillator phase noise according to claim 7, characterized in that, The optoelectronic oscillator includes a Mach-Zehnder modulator, a micro-ring, a photodetector, a first radio frequency coupler, a phase shifter, a low-noise amplifier, and a second radio frequency coupler connected in sequence. The second radio frequency coupler feeds back the output signal to the Mach-Zehnder modulator to form a closed loop. The first interference signal, after being processed by the self-injection locking loop, is directly injected into the other input terminal of the first RF coupler via a coaxial cable to achieve self-injection locking. The second RF coupler splits the RF signal into two parts: one part enters the Mach-Zehnder modulator, and the other part is output through another output port.

9. A system for suppressing oscillator phase noise according to claim 7, characterized in that, The optoelectronic oscillator includes a Mach-Zehnder modulator, a microring, a photodetector, a first radio frequency coupler, a low-noise amplifier, and a second radio frequency coupler connected in sequence. A parallel plate capacitor electrode is integrated on the microring, and the parallel plate capacitor electrode receives feedback signals from the self-phase-locked loop.

10. A system for suppressing oscillator phase noise according to claim 7, characterized in that, The optoelectronic oscillator includes a micro-ring, a photodetector, a first radio frequency coupler, a low-noise amplifier, and a second radio frequency coupler connected in sequence. The microring integrates independent first parallel plate capacitor electrodes and second parallel plate capacitor electrodes. The continuous light wave generated by the laser enters the microring. The first parallel plate capacitor electrodes and the second parallel plate capacitor electrodes on the microring respectively receive feedback signals from the self-phase locked loop and radio frequency signals output by the second radio frequency coupler. The second RF coupler splits the RF signal into two parts: one part enters the parallel plate capacitor electrode on the microring, and the other part is output through another output port.

11. A system for suppressing oscillator phase noise according to claim 7, characterized in that, The optoelectronic oscillator includes a phase modulator, a micro-ring, a photodetector, a first radio frequency coupler, a low-noise amplifier, and a second radio frequency coupler connected in sequence. The second radio frequency coupler feeds back the output signal to the phase modulator to form a closed loop. A parallel plate capacitor electrode is integrated on the microring, and the parallel plate capacitor electrode receives feedback signals from the self-phase locked loop; The continuous light wave generated by the laser enters the phase modulator; The first interference signal, after being processed by the self-injection locking loop, is directly injected into the other input terminal of the first RF coupler via a coaxial cable to achieve self-injection locking. The second RF coupler splits the RF signal into two parts: one part enters the phase modulator, and the other part is output through another output port.

12. A system for suppressing oscillator phase noise according to claim 7, characterized in that, The photoelectric oscillator includes, A Mach-Zehnder modulator and a microring are integrated on the same photonic chip. An external laser is connected to the Mach-Zehnder modulator to output optical signals to the Mach-Zehnder modulator. A photodetector is connected to a semiconductor optical amplifier and the Mach-Zehnder modulator. The photodetector converts the optical signal from the semiconductor optical amplifier into an electrical signal and then injects it into the Mach-Zehnder modulator. The optical signal output from the Mach-Zehnder modulator enters the optical fiber ring, and after long-delay transmission through the optical fiber ring, it is injected into the optical isolator through the micro-ring to form a closed loop. The other end of the semiconductor optical amplifier is connected to an optical isolator to isolate reflected light signals from the photodetector and the semiconductor optical amplifier.

13. A system for suppressing oscillator phase noise according to claim 7, characterized in that, The optoelectronic oscillator includes a micro-ring, a semiconductor optical amplifier, and a photodetector integrated on the same photonic chip, wherein the photodetector is connected to the semiconductor optical amplifier. An external laser injects an optical signal into an external fiber optic ring of the chip through the micro-ring. After long-delay transmission through the fiber optic ring, the signal is injected into the semiconductor optical amplifier through the micro-ring. The photodetector converts the optical signal from the semiconductor optical amplifier into an electrical signal and injects it into the micro-ring, forming a closed loop.

14. A system for suppressing oscillator phase noise according to claim 1, characterized in that, include: An optoelectronic oscillator, and a self-injection locked loop and a self-phase locked loop for suppressing phase noise of the optoelectronic oscillator; The self-injection locking loop includes: the photoelectric oscillator inputs an optical signal to two optical fiber delay lines of different lengths, which are respectively connected to a photodetector; the photodetector converts the two optical signals transmitted by the two optical fiber delay lines into two electrical signals; the two electrical signals are modulated by a phase shifter and an attenuator, respectively, and then enter the input end of a bridge circuit, where constructive interference occurs within the bridge circuit, and a first interference signal is generated at the first output end of the bridge circuit; the first interference signal is then injected back into the photoelectric oscillator for self-injection locking. The self-phase-locked loop includes: the photoelectric oscillator inputs an optical signal to two fiber delay lines of different lengths, which are respectively connected to a photodetector; the photodetector converts the two optical signals transmitted by the two fiber delay lines into two electrical signals; the two electrical signals are modulated by a phase shifter and an attenuator, respectively, and then enter the input terminal of the bridge circuit; constructive interference and destructive interference occur within the bridge circuit; a first interference signal is generated at the first output terminal of the bridge circuit, and a second interference signal is generated at the second output terminal; the second interference signal is processed by a low-noise amplifier and then mixed with a portion of the first interference signal by a mixer and output to a filter; after processing by the filter, the signal is injected back into the photoelectric oscillator for self-phase locking.

15. A system for suppressing oscillator phase noise according to claim 14, characterized in that, The photoelectric oscillator includes, The Mach-Zehnder modulator integrated on the same photonic chip is sequentially connected to an optical fiber coupler, a delay unit, a photodetector, a low-noise amplifier, a bandpass filter, an RF coupler, and a voltage-controlled phase shifter. The voltage-controlled phase shifter is connected to the Mach-Zehnder modulator to form a closed loop. Together with the external laser and optical isolator of the photonic chip, they form the optoelectronic oscillator.

16. A device for suppressing oscillator phase noise, characterized in that, include: The micro-ring, fiber Bragg grating, photodetector, voltage-controlled phase shifter, and low-noise amplifier form a closed loop integrated on the same photonic chip, which together with the external laser of the photonic chip form a photoelectric oscillator; The laser injects an optical signal into the microring. The fiber Bragg grating connects the microring and the photodetector. The photodetector converts the optical signal into an electrical signal, which is then processed by the voltage-controlled phase shifter and the low-noise amplifier before being injected into the microring. The combination of self-injection locking loop and self-phase locking loop jointly suppresses the phase noise of the photoelectric oscillator; The self-injection locking loop includes: The fiber Bragg grating reflects the optical signal from the microring and outputs it to two fiber delay lines of different lengths. The two fiber delay lines are connected to photodetectors, which convert the two optical signals transmitted by the two fiber delay lines into two electrical signals. The two electrical signals are modulated by a phase shifter and an attenuator, respectively, and then enter the input of a bridge circuit. Constructive and destructive interferences occur within the bridge circuit. The first output of the bridge circuit generates a first interference signal, and the second output of the bridge circuit generates a second interference signal. The first interference signal is processed by a low-noise amplifier and then injected into the microring for self-injection locking. The self-phase-locked loop includes: The fiber Bragg grating reflects the optical signal from the micro-ring and outputs it to two fiber delay lines of different lengths. Each fiber delay line is connected to a photodetector. The photodetector converts the two optical signals transmitted through the two fiber delay lines into two electrical signals. These two electrical signals are modulated by a phase shifter and an attenuator, respectively, and then enter the input of the bridge circuit. Constructive and destructive interference occur within the bridge. The first output of the bridge generates a first interference signal, and the second output generates a second interference signal. The second interference signal is processed by a low-noise amplifier and a phase shifter, and then mixed with the signal processed by the voltage-controlled phase shifter via a mixer. The signal processed by the mixer is then output back to the voltage-controlled phase shifter for self-phase locking. The microring is a dual-drive microring, and the photonic chip integrates a miniature photodetector for monitoring optical signals.

17. The apparatus for suppressing oscillator phase noise according to claim 16, characterized in that, A reflective semiconductor optical amplifier injects an optical signal into a microring. The fiber Bragg grating connects the microring and the photodetector. The photodetector converts the optical signal into an electrical signal, which is then processed by the voltage-controlled phase shifter and the bandpass filter before being injected into the microring and the self-phase-locked loop. The combination of self-injection locking loop and self-phase locking loop jointly suppresses the phase noise of the photoelectric oscillator.

18. The apparatus for suppressing oscillator phase noise according to claim 17, characterized in that, The reflective semiconductor optical amplifier injects part of the optical signal into the micro-ring, and outputs the other part to the output terminal of the photonic chip; The fiber Bragg grating connects the microring and the photodetector. The fiber Bragg grating reflects the optical signal. Part of the reflected optical signal is injected into the microring, and the other part is injected into the two fiber delay lines of different lengths, and then transmitted to the self-injection locked loop and the self-phase locked loop. The photodetector detects the light signal reflected by the fiber Bragg grating.

19. The apparatus for suppressing oscillator phase noise according to claim 16, characterized in that, The Mach-Zehnder modulator integrated on the same photonic chip is sequentially connected to a micro-ring, a fiber Bragg grating, a photodetector, a low-noise amplifier, a bandpass filter, a coupler, and a voltage-controlled phase shifter. The voltage-controlled phase shifter is connected to the Mach-Zehnder modulator to form a closed loop. Together with the external reflective semiconductor optical amplifier on the photonic chip, they form a photoelectric oscillator. The reflective semiconductor optical amplifier injects the optical signal into the Mach-Zehnder modulator; The combination of self-injection locking loop and self-phase locking loop jointly suppresses the phase noise of the photoelectric oscillator; The self-injection locking loop includes: the Mach-Zehnder modulator outputs a signal to two fiber delay lines of different lengths, the two fiber delay lines are respectively connected to a photodetector, the photodetector converts the two optical signals transmitted by the two fiber delay lines into two electrical signals, the two electrical signals are modulated by a phase shifter and an attenuator respectively and then enter the input end of a bridge circuit, where constructive interference occurs within the bridge circuit, and a first interference signal is generated at the first output end of the bridge circuit. The first interference signal is processed by a low-noise amplifier and then injected into the coupler for self-injection locking. The self-phase-locked loop includes: the Mach-Zehnder modulator outputs a signal to two fiber delay lines of different lengths, the two fiber delay lines are respectively connected to a photodetector, the photodetector converts the two optical signals transmitted by the two fiber delay lines into two electrical signals, the two electrical signals are modulated by a phase shifter and an attenuator respectively and then enter the input of the bridge, where constructive interference and destructive interference are performed. The first output of the bridge generates a first interference signal, and the second output of the bridge generates a second interference signal. The second interference signal is processed by a low-noise amplifier and then mixed with the signal output by the coupler through a mixer and output to a filter. After being processed by the filter, it is output to the voltage-controlled phase shifter for self-phase locking.

20. The apparatus for suppressing oscillator phase noise according to claim 19, characterized in that, Mach-Zehnder modulator, micro-ring, fiber Bragg grating, and photodetector are connected in sequence and integrated on the same photonic chip; An external reflective semiconductor optical amplifier injects an optical signal into a Mach-Zehnder modulator. Part of the optical signal output from the Mach-Zehnder modulator is injected into the micro-ring, and the other part is output to the two optical fiber delay lines of different lengths. The fiber Bragg grating reflects the optical signal and injects it into the microring to form a mode-locked laser. The photodetector detects the light signal reflected by the fiber Bragg grating.

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