System, device and method for suppressing phase noise of oscillator

Abstract

The invention discloses a system, a device and a method for suppressing phase noise of an oscillator. The system comprises the oscillator, and a self-injection locking loop and a self-phase locking loop which are used for suppressing the phase noise of the oscillator. The laser and the Mach-Zehnder modulator which are sequentially connected in sequence are connected with at least two optical fiber delay lines with different lengths, the two optical fiber delay lines are respectively connected with the photoelectric detector, optical signals are converted into electric signals, the electric signals enter the input end of the electric bridge, constructive interference and destructive interference are carried out in the electric bridge, and the optical signals are output. The bridge output end correspondingly generates a first interference signal and a second interference signal; the first interference signal is output and fed back to the oscillator for self-injection locking; the second interference signal and part of the first interference signal are subjected to frequency mixing 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 jointly suppress the phase noise of the oscillator.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave signal phase noise suppression, and in particular relates to a system, device and method for suppressing oscillator phase noise. Background Art

[0002] Oscillators play an irreplaceable role in electronic systems, often called the "heart" of electronic systems. They are the prerequisite and guarantee for their stable operation. Modern communications, radar, sensors, navigation, remote sensing, precision measurement, electronic warfare, and deep space exploration are placing increasing demands on the performance of high-frequency oscillators. Quartz oscillators generate high-frequency signals through multiple frequency multiplication, but their phase noise deteriorates significantly with increasing frequency multiplication. Surface acoustic wave oscillators generate signals with frequencies up to the GHz range, but with low Q factors and high phase noise. Sapphire oscillators, a type of dielectric oscillator, can generate high-frequency signals with ultra-low phase noise, but they only have high Q factors at specific frequencies and require operation at ultra-low temperatures, making them expensive to manufacture and use. Therefore, phase noise suppression is crucial for high-performance high-frequency oscillators.

[0003] Currently, methods for suppressing RF source phase noise are mainly divided into two categories: the first category, such as external injection locking (EIL), phase-locked loop (PLL), or a combination of EIL and PLL (EIL-PLL), are used to lock to a high-performance external reference source. These technologies require that the phase noise of the external reference is significantly lower than the phase noise of the RF source, thereby increasing the cost and complexity of the noise reduction system; the second category is self-injection locking (SIL), self-phase locked loop (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 technologies 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 usually includes a laser diode (LD), a Mach-Zehnder modulator (MZM), a single-mode fiber (SMF), a photodetector (PD) and a low-noise amplifier (LNA). If the MZM is not used, the LD can also be modulated directly; Figure 17As shown in Figure (b) in [1], 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 first modulates the light emitted by the LD through the MZM to produce a modulated optical signal, which is then transmitted through the optical fiber and converted back into an RF signal by the PD. Finally, it is amplified by the LNA and then 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 [2]. Figure 17 Figure (c) shows another method for reducing VCO phase noise using a self-phase-locked (SPL) loop supported by PhDL. Unlike systems using SIL supported by PhDL, systems deploying SPL first measure the VCO phase noise by mixing the signal directly from the VCO with its delayed replica. The measured phase fluctuation represents 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, which combines an external RF source (EIL) with a phase-locked loop (PLL), can also be used to suppress VCO phase noise. Experiments and computational simulations show that this EIL-PLL exhibits lower near-carrier phase noise and a wider injection-locking range than either the EIL or PLL alone. The EIL-PLL can suppress the oscillator's phase noise and extend the locking range. To eliminate the need for an external reference RF source in an EIL-PLL system, it is feasible to combine self-injection locking with a self-phase-locked loop (SIL-SPLL) to suppress VCO phase noise, as shown in Figure 2. Figure 17 Figure (d) in Figure 1 shows the structure of a PhDL-supported SIL-SPLL system, in which a portion of the VCO signal is delayed by the PhDL and fed directly back to the VCO as the SIL signal, while the other portion forms an SPLL with the undelayed signal directly from the VCO. Unfortunately, the SIL-SPLL also inherits the noise limitations of the PhDL, namely the RPN of the LNA and the RIN from the light source and fiber. Summary of the Invention

[0005] The present application provides a system, device and method for suppressing the phase noise of an oscillator, which suppresses the phase noise of the oscillator by combining a self-injection locked loop with a self-phase locked loop.

[0006] Other purposes and advantages of the present invention can be further understood from the technical features disclosed in the present invention.

[0007] To achieve one, part, or all of the above objectives or other objectives, the present invention provides a system, device, and method for suppressing oscillator phase noise.

[0008] A system for suppressing oscillator phase noise, comprising:

[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 locked loop includes a laser, a Mach-Zehnder modulator, and at least two optical fiber delay lines of different lengths connected in sequence. The two optical fiber delay lines are respectively connected to a photodetector. The photodetector converts 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 and then enter the input end of the bridge. Constructive microwave interference is performed in the bridge. A first output end of the bridge generates a first interference signal. The first interference signal is processed by a low-noise amplifier and then output to the oscillator to perform self-injection locking.

[0011] The self-phase locked loop includes a laser, a Mach-Zehnder modulator, and at least two optical fiber delay lines of different lengths connected in sequence. The two optical fiber delay lines are respectively connected to a photodetector. The photodetector converts 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 and enter the input end of the bridge. Constructive interference and destructive interference are performed in the bridge. The first output end of the bridge generates a first interference signal, and the second output end of the bridge generates a second interference signal. The second interference signal is processed by a low-noise amplifier, mixed with a portion of the first interference signal through a mixer, and output to a filter. After being processed by the filter, the signal is output to the oscillator to perform self-phase locking.

[0012] The self-injection locked loop is combined with the self-phase locked loop to jointly suppress the phase noise of the oscillator.

[0013] The photodetectors connected to the two optical fiber delay lines are respectively connected to a phase shifter and an attenuator, and the phase shifter and the attenuator are connected to the input end 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 the 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 are controlled to have the same amplitude by adjusting the attenuator, so that the two electrical signals constructively interfere with each other in the bridge, and a first interference signal is generated at the first output end of the bridge;

[0015] 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, so that the two electrical signals undergo destructive interference in the bridge, and a second interference signal is generated at the second output end 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 to perform self-injection locking.

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

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

[0019] A phase shifter is connected between the low noise amplifier and the mixer to perform phase adjustment on the second interference signal 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 by an optoelectronic oscillator, and the phase noise of the optoelectronic oscillator is suppressed by combining the self-injection locked loop with the self-phase locked loop;

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

[0024] The optoelectronic oscillator includes a Mach-Zehnder modulator, a microring, a photodetector, a first radio frequency coupler, a phase shifter, a low noise amplifier, and a second radio frequency coupler connected in sequence, wherein 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 processed by the self-injection locking loop is directly injected into the other input end of the first radio frequency coupler through a coaxial cable to achieve self-injection locking;

[0026] The second radio frequency coupler divides the radio frequency 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 micro-ring, and the parallel plate capacitor electrode receives a feedback signal 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 is integrated with a first parallel plate capacitor electrode and a second parallel plate capacitor electrode that are independent of each other. The continuous light wave generated by the laser enters the microring. The first parallel plate capacitor electrode and the second parallel plate capacitor electrode on the microring receive the feedback signal from the self-phase locked loop and the radio frequency signal output by the second radio frequency coupler, respectively.

[0031] The second radio frequency coupler divides the radio frequency signal into two parts, one part enters the parallel plate capacitor electrode on the micro ring, and the other part is output through another output port.

[0032] The optoelectronic oscillator includes a phase modulator, a microring, a photodetector, a first radio frequency coupler, a low noise amplifier, and a second radio frequency coupler connected in sequence, wherein 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 micro-ring, and the parallel plate capacitor electrode receives a feedback signal from the self-phase locked loop;

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

[0035] The first interference signal processed by the self-injection locking loop is directly injected into the other input end of the first radio frequency coupler through a coaxial cable to achieve self-injection locking;

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

[0037] The optoelectronic oscillator comprises:

[0038] A Mach-Zehnder modulator and a microring are integrated on the same photonic chip, and an external laser is connected to the Mach-Zehnder modulator to output an optical signal to the Mach-Zehnder modulator;

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

[0040] The other end of the semiconductor optical amplifier is connected to an optical isolator to isolate the reflected light signal 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 optical fiber ring of the chip through the microring. After long-delay transmission through the optical fiber ring, the optical signal is injected into the semiconductor optical amplifier through the microring. The photodetector converts the optical signal of the semiconductor optical amplifier into an electrical signal and injects it into the microring, forming a closed loop.

[0043] A system for suppressing oscillator phase noise, comprising:

[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 locked loop includes: the optoelectronic oscillator inputs an optical signal into two optical fiber delay lines of different lengths, which are respectively connected to photodetectors; 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 and then enter the input end of the bridge, undergo constructive interference in the bridge, and generate a first interference signal corresponding to the first output end of the bridge; the first interference signal is re-injected into the optoelectronic oscillator to perform self-injection locking;

[0046] The self-phase locked loop includes: the optoelectronic oscillator inputs an optical signal into 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 enter the input end of the bridge, undergo constructive interference and destructive interference in the bridge; the first output end of the bridge correspondingly generates a first interference signal, and the second output end correspondingly generates a second interference signal; the second interference signal is processed by a low-noise amplifier, mixed with a portion of the first interference signal through a mixer, and output to a filter; after being processed by the filter, the second interference signal is injected into the optoelectronic oscillator again to perform self-phase locking.

[0047] The optoelectronic oscillator comprises:

[0048] The Mach-Zehnder modulator integrated on the same photonic chip is sequentially connected to a fiber coupler, a time delay device, a photodetector, a low-noise amplifier, a bandpass filter, a radio frequency coupler, and a 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 laser and optical isolator external to the photonic chip, it forms the optoelectronic oscillator.

[0049] A device for suppressing oscillator phase noise, comprising:

[0050] The microring, fiber Bragg grating, photodetector, voltage-controlled phase shifter and low-noise amplifier form a closed loop and are integrated on the same photonic chip, and together with the laser external to the photonic chip, form an optoelectronic 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, and then injects the electrical signal into the microring after being processed by the voltage-controlled phase shifter and the low-noise amplifier;

[0052] A self-injection locked loop and a self-phase locked loop are combined to suppress the phase noise of the optoelectronic oscillator;

[0053] The self-injection locked loop comprises:

[0054] The fiber Bragg grating reflects the optical signal of the microring and outputs it to two optical fiber delay lines of different lengths. The two optical fiber delay lines are respectively connected to photodetectors. The photodetectors convert 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 and enter the input end of the bridge. Constructive interference and destructive interference are performed in the bridge. The first output end of the bridge generates a first interference signal, and the second output end of the bridge generates a second interference signal. The first interference signal is processed by a low-noise amplifier and then injected into the microring to perform self-injection locking.

[0055] The self-phase locked loop comprises:

[0056] The fiber Bragg grating reflects the optical signal of the microring and outputs it to two optical fiber delay lines of different lengths. The two optical fiber delay lines are respectively connected to photodetectors. The photodetectors convert 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 enter the input end of the bridge. Constructive interference and destructive interference are performed in the bridge. The first output end of the bridge generates a first interference signal, and the second output end of the bridge generates a second interference signal. The second interference signal is processed by a low-noise amplifier and a phase shifter, and is mixed with the signal processed by the voltage-controlled phase shifter through a mixer. The signal processed by the mixer is output to the voltage-controlled phase shifter again for self-phase locking.

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

[0058] The reflective semiconductor optical amplifier 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, and then injects the electrical signal into the microring and the self-phase locked loop after being processed by the voltage-controlled phase shifter and the bandpass filter;

[0059] The self-injection locked loop is combined with the self-phase locked loop to jointly suppress the phase noise of the optoelectronic 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 end of the photonic chip;

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

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

[0063] The Mach-Zehnder modulator integrated on the same photonic chip is sequentially connected to a microring, 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; and together with the reflective semiconductor optical amplifier external to the photonic chip, it forms an optoelectronic oscillator.

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

[0065] A self-injection locked loop and a self-phase locked loop are combined to suppress the phase noise of the optoelectronic oscillator;

[0066] The self-injection locked loop includes: the Mach-Zehnder modulator outputs a signal to two optical fiber delay lines of different lengths, the two optical fiber delay lines are respectively connected to a photodetector, the photodetector converts 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, enter the input end of the bridge, undergo constructive interference in the bridge, and generate a first interference signal at the first output end of the bridge, the first interference signal is processed by a low-noise amplifier and then injected into the coupler to perform self-injection locking;

[0067] The self-phase locked loop includes: the Mach-Zehnder modulator outputs a signal to two optical fiber delay lines of different lengths, the two optical fiber delay lines 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, enter the input end of the bridge, undergo constructive interference and destructive interference in the bridge, the first output end of the bridge correspondingly generates a first interference signal, and the second output end of the bridge correspondingly generates a second interference signal; the second interference signal is processed by a low-noise amplifier, mixed with the signal output by the coupler through a mixer, and output to a filter, and then processed by the filter and output to the voltage-controlled phase shifter for self-phase locking.

[0068] Mach-Zehnder modulators, microrings, fiber Bragg gratings, and photodetectors 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, a portion of the optical signal output by the Mach-Zehnder modulator is injected into the microring, and the other portion is output to the two optical fiber delay lines of different lengths;

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

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

[0072] A method for suppressing oscillator phase noise, comprising:

[0073] A self-injection locked loop and a self-phase locked loop are combined to suppress the phase noise of the oscillator;

[0074] A Mach-Zehnder modulator is connected to a laser and an oscillator. The Mach-Zehnder modulator outputs two optical signals, which respectively enter two optical fiber delay lines of different lengths for transmission. A photodetector connected to the optical fiber delay line converts the optical signal into an electrical signal. The two electrical signals undergo constructive and destructive interference in an electrical bridge. A first output end of the electrical bridge generates a first interference signal, and a second output end of the electrical bridge generates a second interference signal.

[0075] The first interference signal is processed by a low noise amplifier and then injected into the oscillator to perform self-injection locking;

[0076] The second interference signal is processed by a low noise amplifier and mixed with a part of the first interference signal through a mixer, and then injected into the oscillator after being processed by a filter to perform self-phase locking.

[0077] Compared with the prior art, the beneficial effects of the present invention mainly include:

[0078] The optical signal output by the Mach-Zehnder modulator of the present application is transmitted through two optical fiber delay lines of different lengths and then converted into an electrical signal by a photodetector. The optical signal then enters the input end of the bridge, undergoes constructive interference and destructive interference in the bridge, and the output end of the bridge generates a first interference signal and a second interference signal accordingly; the first interference signal is output and 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 and fed back to the oscillator for self-phase locking; the self-injection locking loop and the self-phase locking loop are combined to jointly suppress the phase noise of the oscillator.

[0079] In order to make the above and other objects, features and advantages of the present invention more clearly understood, preferred embodiments are given below with reference to the accompanying drawings for detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] In order to more clearly illustrate the technical solutions in the specific embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0081] Figure 1 A schematic diagram of the system structure for suppressing oscillator phase noise provided in Example 1 of the present application.

[0082] Figure 2 A schematic diagram of the system structure for suppressing oscillator phase noise provided in Example 2 of the present application.

[0083] Figure 3 A schematic diagram of the system structure for suppressing oscillator phase noise provided in Example 3 of the present application.

[0084] Figure 4 Schematic diagram of the structure of the optoelectronic oscillator provided in Example 3 of this application Figure 1 .

[0085] Figure 5 Schematic diagram of the structure of the optoelectronic oscillator provided in Example 3 of this application Figure 2 .

[0086] Figure 6 Schematic diagram of the structure of the optoelectronic oscillator provided in Example 3 of this application Figure 3 .

[0087] Figure 7 Schematic diagram of the structure of the optoelectronic oscillator provided in Example 3 of this application Figure 4 .

[0088] Figure 8 Schematic diagram of the structure of the optoelectronic oscillator provided in Example 3 of this application Figure 5 .

[0089] Figure 9 Schematic diagram of the structure of the optoelectronic oscillator provided in Example 3 of this application Figure 6 .

[0090] Figure 10 Schematic diagram of a device for suppressing oscillator phase noise provided in Example 5 of the present application.

[0091] Figure 11 Schematic diagram of a device for suppressing oscillator phase noise provided in Example 6 of the present application.

[0092] Figure 12 Schematic diagram of the optoelectronic oscillator structure provided in Example 6 of the present application.

[0093] Figure 13Schematic diagram of a device for suppressing oscillator phase noise provided in Example 7 of the present application.

[0094] Figure 14 This is a schematic diagram of the optoelectronic oscillator structure provided in Example 7 of the present application.

[0095] Figure 15 Experimental results provided for Example 8 of this application Figure 1 .

[0096] Figure 16 Experimental results provided for Example 8 of this application Figure 2 .

[0097] Figure 17 Schematic diagram of a device for suppressing phase noise of a radio frequency source provided as background technology of this application.

[0098] Figure 18 A schematic diagram of the system structure for suppressing oscillator phase noise provided in Example 4 of the present application.

[0099] Figure 19 Schematic diagram of the optoelectronic oscillator structure provided in Example 4 of the present application. DETAILED DESCRIPTION

[0100] The foregoing and other technical aspects, features, and functions of the present invention are clearly presented in the following detailed description of a preferred embodiment with reference to the accompanying drawings. Directional terms such as up, down, left, right, front, and back, used in the following embodiments, are intended solely to refer to the directions in the accompanying drawings. Therefore, the directional terms used are for illustrative purposes only and are not intended to limit the present invention.

[0101] The present application provides a system, device and method for suppressing the phase noise of an oscillator, which suppresses the phase noise of the oscillator by combining a self-injection locked loop with a self-phase locked loop.

[0102] The following detailed description of the various embodiments of the present application is provided in conjunction with the accompanying drawings. However, those skilled in the art will appreciate that many technical details are provided in the various embodiments of the present application to facilitate a better understanding of the present application. However, even without these technical details and the various variations and modifications based on the following embodiments, the technical solutions claimed in the present application can still be implemented.

[0103] Theoretical analysis and experimental verification of self-injection locking (SIL) systems implemented using coaxial cable delay lines have established an inverse relationship between the oscillator phase noise and the delay line length. However, due to the high loss of coaxial cables, it is not practical 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 due to its low loss, low cost, and compact size.

[0104] Carrier suppression interferometry (CSI) was initially deployed to measure the close-to-carrier phase noise of two-port microwave devices. In a CSI system, carrier suppression allows the measured phase noise to be significantly amplified without causing saturation, thereby enhancing the sensitivity of the phase noise measurement. In addition, CSI converts the measured phase noise into amplitude noise, effectively eliminating the limitation of the LNA's RPN on the measurement sensitivity. The PhDL-supported CSI self-phase locking (CSI-SPL) scheme, which suppresses the phase noise of the optoelectronic oscillator (OEO), has demonstrated a 20dB phase noise suppression at a 10Hz offset from a 10GHz carrier. The theory of measuring ultra-low phase noise using the PhDL-supported CSI system has been established and experimentally verified, which shows that the PhDL-supported CSI can effectively prevent the phase noise contribution of the LNA in the PhDL and the RIN from limiting the measurement sensitivity of the 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 the PhDL, while the carrier suppression interferometry method can effectively suppress the contribution of the residual phase noise of the low-noise amplifier, the relative intensity noise of the laser, and the scattering noise in the optical fiber to the noise floor of the self-phase locking system.

[0105] Example 1

[0106] like Figure 1 A system for suppressing oscillator phase noise is shown, comprising:

[0107] An oscillator, and a self-injection locked loop and a self-phase locked loop for suppressing oscillator phase noise;

[0108] A self-injection locked loop includes a laser, a Mach-Zehnder modulator, and at least two optical fiber delay lines of different lengths connected in sequence. The two optical fiber delay lines are respectively connected to a photodetector. The photodetector converts 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 and then enter the input end of an electric bridge. Constructive microwave interference is performed in the electric bridge. A first interference signal is generated corresponding to the first output end of the bridge. The first interference signal is processed by a low-noise amplifier and then output to an oscillator to perform self-injection locking.

[0109] A self-phase-locked loop includes a laser, a Mach-Zehnder modulator, and at least two optical fiber delay lines of different lengths connected in sequence. The two optical fiber delay lines are respectively connected to a photodetector. The photodetector converts 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 and then enter the input end of an electric bridge. Constructive and destructive interference occur within the electric bridge. A first interference signal is generated at a first output end of the electric bridge, and a second interference signal is generated at a second output end of the electric bridge. The second interference signal is processed by a low-noise amplifier, mixed with a portion of the first interference signal through a mixer, and output to a filter. The second interference signal is processed by the filter and then output to an oscillator to perform self-phase locking.

[0110] The self-injection locked loop is combined with the self-phase locked loop to suppress the phase noise of the oscillator.

[0111] Specifically, if Figure 1 As shown, the photodetectors connected to the two optical fiber delay lines are connected to the phase shifter and the attenuator respectively, and the phase shifter and the attenuator are connected to the input end 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 the attenuator.

[0112] By adjusting the phase shifter to control the phase difference between the two electrical signals output by the photodetector to be 0 degrees or 360 degrees, and by adjusting the attenuator to control the two electrical signals to have the same amplitude, the two electrical signals constructively interfere in the bridge, and a first interference signal is generated at the first output end of the bridge. The signal at the "bright end" of the bridge is called the first interference signal;

[0113] By adjusting the phase shifter to control the phase difference between the two electrical signals output by the photodetector to be 180 degrees, and by adjusting the attenuator to control the two electrical signals 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 end of the bridge. The "dark end" signal of the bridge is called the first interference signal.

[0114] 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 to perform self-injection locking.

[0115] The radio frequency coupler is connected to the mixer, and the other part of the first interference signal is input into the mixer to be mixed with the second interference signal in the mixer.

[0116] The second interference signal is processed by a low noise amplifier, mixed with another part of the first interference signal through a mixer, and then processed by a filter and output to an oscillator for self-phase locking;

[0117] A phase shifter is connected between the low noise amplifier and the mixer to adjust the phase of the second interference signal processed by the low noise amplifier.

[0118] Specifically, if Figure 1 As shown, the continuous light output by the semiconductor laser (DFB) enters a dual-output Mach-Zehnder intensity modulator (MZM). The RF signal output by the oscillator (OSC) is loaded onto the optical signal through the MZM. The MZM outputs two optical signals. One optical signal passes through a relatively long single-mode fiber (SMF1) and enters the photodetector PD1, where it is converted into a microwave signal. The other optical signal passes through a relatively short single-mode fiber (SMF2) and enters the photodetector PD2, where PD2 converts the optical signal into an electrical signal. The signal output by PD1 passes through a manual phase shifter (MPS1) or an electric phase shifter and the electrical signal output from PD1, and then passes through a manual attenuator (VA). The signals then interfere in a 3dB bridge. By adjusting MPS1 and VA, the two signals output by the 3dB bridge produce constructive interference to generate a first interference signal (the "bright" end). By adjusting MPS1 and VA, the two signals output by the 3dB bridge produce destructive interference to generate a second interference signal (the "dark" end).

[0119] The signal after the 3dB bridge can be divided into two parts. The first part is a dual-loop self-injection locking system based on PhDL. The "bright" end signal passes through a low-noise amplifier (LNA) and is split into two parts by a radio frequency coupler (RFC). One part is directly injected into the VCO via a coaxial cable to form a self-injection locking system based on a two-photon delay line (short delay line and long delay line). This system suppresses the oscillator's phase noise over a large frequency offset range. The second part is a CSI self-phase locking system based on PhDL. The "dark" end signal is a carrier-suppressed signal, which mainly comes from the oscillator's phase noise. After passing through a relatively high-gain low-noise amplifier and MPS2, this signal enters the RF end of a double-balanced mixer (DBM) and mixes with another signal from the RF coupler (RFC). By adjusting MPS2, the phase difference between the two signals entering the DBM is close to 0 degrees or 180 degrees, thereby generating a low-frequency voltage signal related to the oscillator's phase noise. This voltage signal passes through a low-pass filter (LPF) and is applied to the oscillator's frequency adjustment terminal or phase locking terminal to further suppress the oscillator's phase noise.

[0120] Because the carrier is suppressed, the "dark" end signal can be amplified many times by the low-noise amplifier (LNA), preventing saturation of the LNA and significantly improving CSI test sensitivity. Because the carrier suppression interferometer is insensitive to amplitude noise, it is also insensitive to the laser's RIN and scattering noise within the fiber. The small carrier signal remaining in the "dark" end signal effectively avoids the LNA's residual phase noise, while also allowing the LNA to boost the measured noise well above 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 LNA's residual phase noise can be ignored. Typically, the LNA's amplitude noise is much smaller than its phase noise, so it does not affect the test sensitivity of the PhDL-CSI system.

[0121] Example 2

[0122] like Figure 2 As shown, a radio frequency coupler is connected between the oscillator and the Mach-Zehnder modulator;

[0123] The RF signal output by the oscillator is divided into two parts by the RF coupler, one part enters the Mach-Zehnder modulator, and the other part enters the bridge after being processed by the attenuator.

[0124] like Figure 2 As shown, relatively short fiber delay lines are replaced with coaxial cables.

[0125] Example 3

[0126] like Figure 3 As shown, the oscillator is replaced by an optoelectronic oscillator, and the phase noise of the optoelectronic oscillator is suppressed by combining a self-injection locked loop with a self-phase locked loop; and the optoelectronic oscillator and the Mach-Zehnder modulator are integrated on the same photonic chip.

[0127] Specifically, if Figure 4 As shown, the optoelectronic oscillator includes a Mach-Zehnder modulator, a microring, a photodetector, a first RF coupler, a phase shifter, a low-noise amplifier, and a second RF coupler connected in sequence. The second RF coupler feeds back the output signal to the Mach-Zehnder modulator to form a closed loop.

[0128] The first interference signal processed by the self-injection locking loop is directly injected into the other input end of the first radio frequency coupler through the coaxial cable to achieve self-injection locking;

[0129] The second radio frequency coupler divides the radio frequency signal into two parts, one part enters the Mach-Zehnder modulator, and the other part is output through another output port.

[0130] Specifically, the integrated optoelectronic oscillator (IOO) consists of an MZM, a microring (MRR), a photodetector (PD), an RF coupler 1, an electrodynamic 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 acts as a resonant cavity with a relatively high Q value in the structure. The other port of the RF coupler 1 is self-injection locked, and the other port of the RF coupler 2 is used to generate the microwave signal output. The electrodynamic phase shifter is used to fine-tune the frequency of the OEO or receive feedback signals from the carrier suppression interferometer system to reduce the phase noise of the OEO.

[0131] As a preferred embodiment of the present invention, 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 a feedback signal from a self-phase locked loop.

[0132] Specifically, a parallel plate capacitor electrode is made on the MRR. By applying a voltage signal to the electrode, the FSR of the MRR is changed. This can be used to adjust the frequency of the integrated OEO. It can also receive feedback signals from the carrier suppression interferometer system to reduce the phase noise of the OEO. In this system, applying different bias voltages to the MRR can achieve OEO frequency adjustment.

[0133] As a preferred embodiment of the present invention, Figure 6 As shown, 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;

[0134] In this embodiment, a first parallel plate capacitor electrode and a second parallel plate capacitor electrode are integrated on the microring, which are independent of each other. The continuous light wave generated by the laser enters the microring, and the first parallel plate capacitor electrode and the second parallel plate capacitor electrode on the microring receive the feedback signal from the self-phase locked loop and the radio frequency signal output by the second radio frequency coupler respectively.

[0135] The second radio frequency coupler divides the radio frequency signal into two parts, one part enters the parallel plate capacitor electrode on the micro ring, and the other part is output through another output port.

[0136] Specifically, two independent parallel plate capacitor electrodes are made on the MRR. One of them receives the feedback signal from the carrier suppression interferometer system to reduce the phase noise of the OEO, and the other is used as an intensity modulator, receiving the signal from RFC1 to form a closed loop of the OEO. In addition, applying different bias voltages to the MRR in this system can also achieve OEO frequency adjustment.

[0137] As a preferred embodiment of the present invention, Figure 7 As shown, the integrated optoelectronic oscillator in this embodiment includes a phase modulator, a microring, a photodetector, a first RF coupler, a low-noise amplifier, and a second RF coupler connected in sequence. The second RF coupler feeds back the output signal to the phase modulator to form a closed loop.

[0138] A parallel plate capacitor electrode is integrated on the micro-ring, and the parallel plate capacitor electrode receives the feedback signal from the self-phase locked loop;

[0139] The continuous light wave generated by the laser enters the phase modulator;

[0140] The first interference signal processed by the self-injection locking loop is directly injected into the other input end of the first radio frequency coupler through the coaxial cable to achieve self-injection locking;

[0141] The second radio frequency coupler divides the radio frequency signal into two parts, one part enters the phase modulator, and the other part is output through another output port.

[0142] Specifically, in addition to achieving a small-range adjustment of the OEO frequency by applying a bias voltage to the MRR, the OEO frequency can also be adjusted over a large range by changing the wavelength of the light input to the PM.

[0143] As a preferred embodiment of the present invention, Figure 8 As shown, the optoelectronic oscillator in this embodiment includes:

[0144] 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 an optical signal to the Mach-Zehnder modulator.

[0145] The photodetector is connected to the semiconductor optical amplifier and the Mach-Zehnder modulator. The photodetector converts the optical signal of the semiconductor optical amplifier into an electrical signal and then injects it into the Mach-Zehnder modulator. The optical signal output by the Mach-Zehnder modulator enters the optical fiber ring, is transmitted through the optical fiber ring with a long delay, and then is injected into the optical isolator through the micro ring, forming a closed loop.

[0146] The other end of the semiconductor optical amplifier is connected to an optical isolator to isolate the reflected light signal from the photodetector and the semiconductor optical amplifier.

[0147] Specifically, if Figure 8 As shown in the figure, 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 mode selection of the OEO, the semiconductor optical amplifier (SOA) is used to compensate for the loss of the loop, the photodetector converts the optical signal into an electrical signal, and the optical isolator (ISO) is used to isolate the reflected light signals from the photodetector (PD) and SOA. The electrical signal output by the PD is injected into the MZM to form an OEO closed loop. The optical signal output from the MZM enters the optical fiber ring, is transmitted after a long delay, and is injected into the OEO loop through the MRR to form a self-injection locked OEO.

[0148] As a preferred embodiment of the present invention, Figure 9 As shown, the optoelectronic oscillator in this embodiment includes a microring, a semiconductor optical amplifier, and a photodetector integrated on the same photonic chip, and the photodetector is connected to the semiconductor optical amplifier;

[0149] The external laser injects the optical signal into the chip's external optical fiber ring through the microring. After long-delay transmission through the optical fiber ring, the optical signal is injected into the semiconductor optical amplifier through the microring. The photodetector converts the optical signal of the semiconductor optical amplifier into an electrical signal and injects it into the microring, forming a closed loop.

[0150] Specifically, the electrical signal is directly converted into photoelectricity through the MRR modulator. In this structure, the MRR serves as an optical resonant cavity and is also used to select the OEO oscillation mode. In addition, the MRR, SOA, and PD are integrated on the same chip, and the DFB light source and fiber ring are external.

[0151] Example 4

[0152] like Figure 18 A system for suppressing oscillator phase noise is shown, comprising:

[0153] Optoelectronic oscillator, and self-injection locked loop and self-phase locked loop for suppressing phase noise of the optoelectronic oscillator;

[0154] A self-injection locked loop includes an optoelectronic oscillator inputting an optical signal into two optical fiber delay lines of different lengths, each of which is 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 and then enter the input end of an electric bridge. Constructive interference occurs within the electric bridge, and a first interference signal is generated correspondingly at the first output end of the electric bridge. The first interference signal is then injected into the optoelectronic oscillator again to perform self-injection locking.

[0155] The self-phase locked loop includes: an optoelectronic oscillator inputs an optical signal into 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 enter the input end of an electric bridge, undergo constructive interference and destructive interference in the electric bridge; the first output end of the electric bridge generates a first interference signal, and the second output end generates a second interference signal; the second interference signal is processed by a low-noise amplifier, mixed with a part of the first interference signal through a mixer, and output to a filter; after being processed by the filter, it is injected into the optoelectronic oscillator again to perform self-phase locking.

[0156] Specifically, if Figure 19 As shown, the optoelectronic oscillator in this embodiment includes:

[0157] The Mach-Zehnder modulator integrated on the same photonic chip is connected in sequence to a fiber coupler, a delay device, a photodetector, a low-noise amplifier, a bandpass filter, a radio frequency coupler and a 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 laser and optical isolator outside the photonic chip, it forms an optoelectronic oscillator.

[0158] Example 5

[0159] like Figure 10 As shown, a device for suppressing oscillator phase noise includes:

[0160] The microring, fiber Bragg grating, photodetector, voltage-controlled phase shifter and low-noise amplifier form a closed loop and are integrated on the same photonic chip. Together with the laser outside the photonic chip, they form an optoelectronic oscillator.

[0161] The laser injects the optical signal into the microring, the fiber Bragg grating connects the microring and the photodetector, and 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 and then injected into the microring.

[0162] The self-injection locked loop and the self-phase locked loop are combined to suppress the phase noise of the optoelectronic oscillator;

[0163] Self-injection locked loop, including:

[0164] After the fiber Bragg grating reflects the optical signal of the microring, it is output to two optical fiber delay lines of different lengths. The two optical fiber delay lines are respectively connected to photodetectors. The photodetectors convert the two optical signals transmitted by the two optical fiber delay lines into two electrical signals. The two electrical signals are modulated by phase shifters and attenuators respectively and then enter the input end of the bridge. Constructive interference and destructive interference are carried out in the bridge. The first output end of the bridge generates a first interference signal, and the second output end of the bridge generates a second interference signal. The first interference signal is processed by a low-noise amplifier and then injected into the microring to perform self-injection locking.

[0165] Self-phase locked loop, including:

[0166] After the fiber Bragg grating reflects the optical signal of the microring, it is output to two optical fiber delay lines of different lengths. The two optical fiber delay lines are respectively connected to photodetectors. The photodetectors convert the two optical signals transmitted by the two optical fiber delay lines into two electrical signals. The two electrical signals are modulated by phase shifters and attenuators and then enter the input end of the bridge. Constructive interference and destructive interference are carried out in the bridge. The first output end of the bridge generates a first interference signal, and the second output end of the bridge 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 through a mixer. The signal processed by the mixer is output to the voltage-controlled phase shifter again for self-phase locking.

[0167] The microring is a dual-drive microring, with a micro 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 the side modes generated by the OEO to improve the side mode suppression ratio. In addition, CSI and self-injection phase locking can also be used to further reduce its phase noise.

[0168] Example 6

[0169] like Figure 11 As shown, a reflective semiconductor optical amplifier injects an optical signal into the microring, a fiber Bragg grating connects the microring and the photodetector, and the photodetector converts the optical signal into an electrical signal, which is then processed by a voltage-controlled phase shifter and a bandpass filter and then injected into the microring and the self-phase-locked loop.

[0170] Specifically, the "bright" end output signal 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 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 VPS after passing through the LPF to further suppress the phase noise of the COEO.

[0171] The self-injection locked loop is combined with the self-phase locked loop to suppress the phase noise of the optoelectronic oscillator.

[0172] As a preferred embodiment of the present invention, Figure 12 As shown, the reflective semiconductor optical amplifier in this embodiment injects part of the optical signal into the micro-ring and outputs the other part to the output end of the photonic chip;

[0173] A fiber Bragg grating connects the microring and the photodetector. The fiber Bragg grating reflects the light signal, part of which is injected into the microring, and the other part is injected into two optical fiber delay lines of different lengths and transmitted to the self-injection locked loop and the self-phase locked loop.

[0174] The photodetector detects the light signal reflected by the fiber Bragg grating.

[0175] Specifically, part of the optical signal output by the 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 the FBG enters the dual-drive MRR, and the other part enters the dual-loop self-injection system and carrier suppression system. The PD is used to detect the transmitted optical signal from the FBG.

[0176] Example 7

[0177] like Figure 13 As shown, the Mach-Zehnder modulator integrated on the same photonic chip is sequentially connected to a microring, 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; and together with the reflective semiconductor optical amplifier outside the photonic chip, it forms an optoelectronic oscillator.

[0178] A reflective semiconductor optical amplifier injects the optical signal into the Mach-Zehnder modulator;

[0179] The self-injection locked loop and the self-phase locked loop are combined to suppress the phase noise of the optoelectronic oscillator;

[0180] A self-injection locked loop includes: a Mach-Zehnder modulator outputs a signal to two optical fiber delay lines of different lengths, the two optical fiber delay lines are respectively connected to a photodetector, the photodetector converts 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, enter the input end of an electric bridge, undergo constructive interference in the electric bridge, and generate a first interference signal at a first output end of the electric bridge, the first interference signal is processed by a low-noise amplifier, and then injected into a coupler to perform self-injection locking;

[0181] The self-phase locking loop includes: a Mach-Zehnder modulator outputs a signal to two optical fiber delay lines of different lengths, the two optical fiber delay lines 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, enter the input end of the bridge, perform constructive interference and destructive interference in the bridge, the first output end of the bridge generates a first interference signal, and the second output end of the bridge generates a second interference signal; the second interference signal is processed by a low-noise amplifier, mixed with the signal output by the coupler through a mixer, and output to a filter, and then output to a voltage-controlled phase shifter after being processed by the filter to perform self-phase locking.

[0182] Specifically, the "bright" end output signal is amplified by a low-noise amplifier and then injected into the COEO through the MZM to form dual PhDL self-injection to suppress the phase noise of the COEO. The CSI suppression system detects the phase noise of the COEO and passes it through the LPF and VPS to further suppress the phase noise of the COEO.

[0183] As a preferred embodiment of the present invention, Figure 14 As shown, the Mach-Zehnder modulator, microring, fiber Bragg grating, and photodetector in this embodiment are connected in sequence and integrated on the same photonic chip;

[0184] An external reflective semiconductor optical amplifier injects the optical signal into the Mach-Zehnder modulator. Part of the optical signal output by the Mach-Zehnder modulator is injected into the microring, and the other part is output to two optical fiber delay lines of different lengths.

[0185] The fiber Bragg grating reflects the light signal and injects it into the microring, forming a mode-locked laser;

[0186] The photodetector detects the light signal reflected by the fiber Bragg grating.

[0187] Specifically, the optical signal output by the RSOA enters the MZM modulator, part of the optical signal output by the MZM enters the MRR, and the other part is output from one end of the chip; the reflected optical signal of the FBG enters the MRR to form a mode-locked laser, and the PD is used to detect the transmitted optical signal from the FBG.

[0188] Example 8

[0189] A method for suppressing oscillator phase noise, comprising:

[0190] The self-injection locked loop is combined with the self-phase locked loop to suppress the phase noise of the oscillator;

[0191] A Mach-Zehnder modulator is connected to a laser and an oscillator. The Mach-Zehnder modulator outputs two optical signals, which are transmitted into two optical fiber delay lines of different lengths. A photodetector connected to the optical fiber delay line converts the optical signal into an electrical signal. The two electrical signals undergo constructive and destructive interference in the bridge. The first output end of the bridge generates a first interference signal, and the second output end of the bridge generates a second interference signal.

[0192] The first interference signal is processed by a low-noise amplifier and then injected into the oscillator for self-injection locking;

[0193] The second interference signal is processed by a low noise amplifier and mixed with a part of the first interference signal through a mixer, and then injected into the oscillator after being processed by a filter to perform self-phase locking.

[0194] 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 suppressed by 46dB compared with free oscillation, and the phase noise is -144dBc / Hz at a frequency offset of 10kHz, which is suppressed by 39dB compared with free oscillation.

[0195] like Figure 16 As shown in the figure, after using the above-mentioned phase noise suppression system, the spectrum of the 10GHz signal decreases significantly compared to the free oscillation near the carrier, and its side mode suppression 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 the self-injection system alone has a higher side mode suppression ratio than that of the two methods at the same time, but its spectrum near the carrier is higher.

[0196] The present application provides a system, device and method for suppressing the phase noise of an oscillator, which suppresses the phase noise of the oscillator by combining a self-injection locked loop with a self-phase locked loop.

[0197] In order to facilitate the description of the present invention, some common English nouns or letters are used for illustrative reference only and are not intended to be restrictive or specific. The scope of protection of the present invention should not be limited by their possible Chinese translations or specific letters.

[0198] It should also be noted that, in this article, relational terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any 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 locked loop includes a laser, a Mach-Zehnder modulator, and at least two optical fiber delay lines of different lengths connected in sequence. The two optical fiber delay lines are respectively connected to a photodetector. The photodetector converts 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 and then enter the input end of the bridge. Constructive microwave interference is performed in the bridge. A first output end of the bridge generates a first interference signal. The first interference signal is processed by a low-noise amplifier and then output to the oscillator to perform self-injection locking. The self-phase locked loop includes a laser, a Mach-Zehnder modulator, and at least two optical fiber delay lines of different lengths connected in sequence. The two optical fiber delay lines are respectively connected to a photodetector. The photodetector converts 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 and then enter the input end of the bridge. Constructive interference and destructive interference occur within the bridge. The first output end of the bridge generates a first interference signal, and the second output end of the bridge generates a second interference signal. The second interference signal is processed by a low noise amplifier and mixed with a part of the first interference signal through a mixer and output to a filter, and then processed by the filter and output to the oscillator for self-phase locking; The self-injection locked loop is combined with the self-phase locked loop to jointly suppress the phase noise of the oscillator.

2. The system for suppressing oscillator phase noise according to claim 1, wherein: The photodetectors connected to the two optical fiber delay lines are respectively connected to a phase shifter and an attenuator, and the phase shifter and the attenuator are connected to the input end 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 the attenuator.

3. The system for suppressing oscillator phase noise according to claim 2, wherein: 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 are controlled to have the same amplitude by adjusting the attenuator, so that the two electrical signals constructively interfere with each other in the bridge, and a first interference signal is generated at the first output end of the bridge; By adjusting the phase shifter to control the phase difference between the two electrical signals output by the photodetector to be 180 degrees, and by adjusting the attenuator to control the two electrical signals to have the same amplitude, the two electrical signals perform destructive interference in the bridge, and a second interference signal is generated correspondingly at the second output end of the bridge.

4. The system for suppressing oscillator phase noise according to claim 1, wherein: 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 to perform self-injection locking. The radio frequency coupler is connected to the mixer, and inputs another part of the first interference signal into the mixer to be mixed with the second interference signal in the mixer.

5. The 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 mixed with another part of the first interference signal through a mixer, and then processed by a filter and output to the oscillator for self-phase locking; A phase shifter is connected between the low noise amplifier and the mixer to perform phase adjustment on the second interference signal processed by the low noise amplifier.

6. The 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. The system for suppressing oscillator phase noise according to claim 1, wherein: The oscillator is replaced by an optoelectronic oscillator, and the phase noise of the optoelectronic oscillator is suppressed by combining the self-injection locked loop with the self-phase locked loop; The optoelectronic oscillator and the Mach-Zehnder modulator are integrated on the same photonic chip.

8. The 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 phase shifter, a low noise amplifier, and a second radio frequency coupler connected in sequence, wherein the second radio frequency coupler feeds back the output signal to the Mach-Zehnder modulator to form a closed loop; The first interference signal processed by the self-injection locking loop is directly injected into the other input end of the first radio frequency coupler through a coaxial cable to achieve self-injection locking; The second radio frequency coupler divides the radio frequency signal into two parts, one part enters the Mach-Zehnder modulator, and the other part is output through another output port.

9. The 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 micro-ring, and the parallel plate capacitor electrode receives a feedback signal from the self-phase locked loop.

10. The 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 is integrated with a first parallel plate capacitor electrode and a second parallel plate capacitor electrode that are independent of each other. The continuous light wave generated by the laser enters the microring. The first parallel plate capacitor electrode and the second parallel plate capacitor electrode on the microring receive the feedback signal from the self-phase locked loop and the radio frequency signal output by the second radio frequency coupler, respectively. The second radio frequency coupler divides the radio frequency signal into two parts, one part enters the parallel plate capacitor electrode on the micro ring, and the other part is output through another output port.

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

12. The system for suppressing oscillator phase noise according to claim 7, characterized in that: The optoelectronic oscillator comprises: A Mach-Zehnder modulator and a microring are integrated on the same photonic chip, and an external laser is connected to the Mach-Zehnder modulator to output an optical signal to the Mach-Zehnder modulator; A photodetector is connected to the semiconductor optical amplifier and the Mach-Zehnder modulator, and the photodetector converts the optical signal of the semiconductor optical amplifier into an electrical signal and then injects the electrical signal into the Mach-Zehnder modulator; The optical signal output by the Mach-Zehnder modulator enters the optical fiber ring, is transmitted through the optical fiber ring with a long delay, and 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 the reflected light signal from the photodetector and the semiconductor optical amplifier.

13. The 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 optical fiber ring of the chip through the microring. After long-delay transmission through the optical fiber ring, the optical signal is injected into the semiconductor optical amplifier through the microring. The photodetector converts the optical signal of the semiconductor optical amplifier into an electrical signal and injects it into the microring, forming a closed loop.

14. The 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 locked loop includes: the optoelectronic oscillator inputs an optical signal into two optical fiber delay lines of different lengths, which are respectively connected to photodetectors; 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 and then enter the input end of the bridge, undergo constructive interference in the bridge, and generate a first interference signal corresponding to the first output end of the bridge; the first interference signal is re-injected into the optoelectronic oscillator to perform self-injection locking; The self-phase locked loop includes: the optoelectronic oscillator inputs an optical signal into 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 enter the input end of the bridge, undergo constructive interference and destructive interference in the bridge; the first output end of the bridge correspondingly generates a first interference signal, and the second output end correspondingly generates a second interference signal; the second interference signal is processed by a low-noise amplifier, mixed with a portion of the first interference signal through a mixer, and output to a filter; after being processed by the filter, the second interference signal is injected into the optoelectronic oscillator again to perform self-phase locking.

15. The system for suppressing oscillator phase noise according to claim 14, characterized in that: The optoelectronic oscillator comprises: The Mach-Zehnder modulator integrated on the same photonic chip is sequentially connected to a fiber coupler, a time delay device, a photodetector, a low-noise amplifier, a bandpass filter, a radio frequency coupler, and a voltage-controlled phase shifter, wherein 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 the photoelectric oscillator.

16. A device for suppressing oscillator phase noise, characterized in that: include: The microring, fiber Bragg grating, photodetector, voltage-controlled phase shifter and low-noise amplifier form a closed loop and are integrated on the same photonic chip, and together with the laser external to the photonic chip, form an optoelectronic 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, and then injects the electrical signal into the microring after being processed by the voltage-controlled phase shifter and the low-noise amplifier; A self-injection locked loop and a self-phase locked loop are combined to suppress the phase noise of the optoelectronic oscillator; The self-injection locked loop comprises: The fiber Bragg grating reflects the optical signal of the microring and outputs it to two optical fiber delay lines of different lengths. The two optical fiber delay lines are respectively connected to photodetectors. The photodetectors convert 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 and enter the input end of the bridge. Constructive interference and destructive interference are performed in the bridge. The first output end of the bridge generates a first interference signal, and the second output end of the bridge generates a second interference signal. The first interference signal is processed by a low-noise amplifier and then injected into the microring to perform self-injection locking. The self-phase locked loop comprises: The fiber Bragg grating reflects the optical signal of the microring and outputs it to two optical fiber delay lines of different lengths. The two optical fiber delay lines are respectively connected to photodetectors. The photodetectors convert 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 enter the input end of the bridge. Constructive interference and destructive interference are performed in the bridge. The first output end of the bridge generates a first interference signal, and the second output end of the bridge generates a second interference signal. The second interference signal is processed by a low-noise amplifier and a phase shifter, and is mixed with the signal processed by the voltage-controlled phase shifter through a mixer. The signal processed by the mixer is output to the voltage-controlled phase shifter again for self-phase locking. The microring is a dual-drive microring, and a micro photodetector for monitoring optical signals is integrated on the photonic chip.

17. The device for suppressing oscillator phase noise according to claim 16, characterized in that: The reflective semiconductor optical amplifier 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, and then injects the electrical signal into the microring and the self-phase locked loop after being processed by the voltage-controlled phase shifter and the bandpass filter; The self-injection locked loop is combined with the self-phase locked loop to jointly suppress the phase noise of the optoelectronic oscillator.

18. The device 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 end of the photonic chip; The fiber Bragg grating is connected to the microring and the photodetector. The fiber Bragg grating reflects the light signal, a part of the reflected light signal is injected into the microring, and the other part is injected into the two optical fiber delay lines of different lengths, and transmitted to the self-injection locked loop and the self-phase locked loop; The photodetector detects the optical signal reflected by the fiber Bragg grating.

19. The device 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 microring, 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; and together with the reflective semiconductor optical amplifier external to the photonic chip, it forms an optoelectronic oscillator. The reflective semiconductor optical amplifier injects the optical signal into the Mach-Zehnder modulator; A self-injection locked loop and a self-phase locked loop are combined to suppress the phase noise of the optoelectronic oscillator; The self-injection locked loop includes: the Mach-Zehnder modulator outputs a signal to two optical fiber delay lines of different lengths, the two optical fiber delay lines are respectively connected to a photodetector, the photodetector converts 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, enter the input end of the bridge, undergo constructive interference in the bridge, and generate a first interference signal at the first output end of the bridge, the first interference signal is processed by a low-noise amplifier and then injected into the coupler to perform self-injection locking; The self-phase locked loop includes: the Mach-Zehnder modulator outputs a signal to two optical fiber delay lines of different lengths, the two optical fiber delay lines 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, enter the input end of the bridge, undergo constructive interference and destructive interference in the bridge, the first output end of the bridge correspondingly generates a first interference signal, and the second output end of the bridge correspondingly generates a second interference signal; the second interference signal is processed by a low-noise amplifier, mixed with the signal output by the coupler through a mixer, and output to a filter, and then processed by the filter and output to the voltage-controlled phase shifter for self-phase locking.

20. The device for suppressing oscillator phase noise according to claim 19, characterized in that: Mach-Zehnder modulators, microrings, fiber Bragg gratings, and photodetectors 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, a portion of the optical signal output by the Mach-Zehnder modulator is injected into the microring, and the other portion is output to the two optical fiber delay lines of different lengths; The fiber Bragg grating reflects the light signal and injects it into the microring to form a mode-locked laser; The photoelectric detector detects the light signal reflected by the fiber Bragg grating.

21. A method for suppressing oscillator phase noise, characterized in that: include: A self-injection locked loop and a self-phase locked loop are combined to suppress the phase noise of the oscillator; A Mach-Zehnder modulator is connected to a laser and an oscillator. The Mach-Zehnder modulator outputs two optical signals, which respectively enter two optical fiber delay lines of different lengths for transmission. A photodetector connected to the optical fiber delay line converts the optical signal into an electrical signal. The two electrical signals undergo constructive and destructive interference in an electrical bridge. A first output end of the electrical bridge generates a first interference signal, and a second output end of the electrical bridge generates a second interference signal. The first interference signal is processed by a low noise amplifier and then injected into the oscillator to perform self-injection locking; The second interference signal is processed by a low noise amplifier and mixed with a part of the first interference signal through a mixer, and then injected into the oscillator after being processed by a filter to perform self-phase locking.

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