A light domain assisted signal-to-noise ratio improvement system and method

Abstract

The present invention discloses a light-domain-assisted signal-to-noise ratio enhancement system and method, which belongs to the field of microwave photon and radar technology. The system includes a first optical signal, a slave laser, and an optical fiber, wherein the first optical signal is used as an input signal and injected into the slave laser through the optical fiber; the slave laser is used to receive the first optical signal and output a second optical signal after nonlinear photon resonance amplification, wherein the slave laser operates in an optical injection locking state, wherein the optical injection locking state means that the difference between the wavelength of the free oscillation of the slave laser and the wavelength of the first optical signal satisfies a preset range, and the output optical power of the slave laser and the optical power of the first optical signal are in a weak injection proportional relationship. The present invention realizes differential amplification of signals and noise with a streamlined architecture, suppresses noise while amplifying signals, and improves the noise performance of microwave links from a new dimension.

Description

Technical Field

[0001] The present invention belongs to the field of microwave photon and radar technology, and specifically relates to a light-domain assisted signal-to-noise ratio improvement system and method. Background Art

[0002] The noise factor is an important core indicator of radar receivers. It represents the deterioration of the signal after passing through the microwave link. It directly determines the quality of the radar receiving system's output signal and directly affects the efficiency and accuracy of the radar's back-end information acquisition. High signal-to-noise ratio and low sensitivity are important indicators and core demands of modern electronic receivers. For radar and electronic reconnaissance, it represents a longer reconnaissance distance, a higher intercept probability, and a lower false alarm rate and false alarm rate. For communications, remote sensing and navigation, it represents better communication quality and higher position accuracy.

[0003] Traditional microwave devices introduce additional noise during the amplification / attenuation of received signals due to their own factors such as device thermal noise, which deteriorates the signal-to-noise ratio of the signal passing through the microwave device, increasing the noise coefficient of the microwave link. The more cascaded devices in the microwave link and the more complex the system, the more serious the deterioration phenomenon. Therefore, improving the signal-to-noise ratio of the system link and reducing its noise coefficient are the inevitable problems and bottlenecks that all types of receivers face in order to maximize their performance.

[0004] Existing radar receiving systems mostly use front-end phased array reception and back-end pulse coherent accumulation or pulse compression to amplify weak echo signals to a state with a certain signal-to-noise ratio, and improve the signal-to-noise ratio of the received signal until the detection threshold is met. Phased array reception uses spatial multi-channel reception, where each signal is coherent and the noise is incoherent. When multiple signals are combined, the signal-to-noise ratio is improved compared to the input signal; pulse coherent accumulation is to coherently accumulate multiple pulses at different times in the time domain, where the signal between each pulse is coherent and the noise is incoherent, and long-term accumulation improves the signal-to-noise ratio of the pulse signal; the pulse compression method is to match the broadband signal from the frequency domain, use a pulse compression signal consistent with the broadband signal, and the noise is incoherent with it, thereby improving the signal detection signal-to-noise ratio. Among these methods, only the phased array reception method is a hardware method to improve the signal-to-noise ratio, but it requires multi-channel synchronous reception, which increases the complexity of the system. Summary of the invention

[0005] To solve the above technical problems, the present invention provides a light-domain-assisted signal-to-noise ratio improvement system and method, which explores from the light-domain dimension, differentially amplifies signals and noises, improves the signal-to-noise ratio of the receiving signal system, suppresses noise while amplifying the signal, and realizes the improvement of the signal-to-noise ratio of the input signal in the hardware circuit before software processing.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A light domain assisted signal-to-noise ratio improvement system, the system comprises a first optical signal, from a laser, an optical fiber, wherein:

[0008] The first optical signal is used as an input signal and injected into the slave laser through an optical fiber;

[0009] The slave laser is used to receive a first optical signal and output a second optical signal after nonlinear photon resonance amplification, wherein the slave laser operates in an optical injection locking state, wherein the optical injection locking state is that the difference between the wavelength of the free oscillation of the slave laser and the wavelength of the first optical signal satisfies a preset range, and the output optical power of the slave laser and the optical power of the first optical signal are in a weak injection proportional relationship.

[0010] In another aspect, the present invention provides a method for improving signal-to-noise ratio using light domain assistance, comprising:

[0011] Step 1, injecting a first optical signal into a slave laser through a polarization-maintaining optical fiber;

[0012] Step 2, the slave laser receives a first optical signal, and outputs a second optical signal after nonlinear photon resonance amplification, wherein the slave laser operates in an optical injection locking state, wherein the optical injection locking state means that the difference between the wavelength of the free oscillation of the slave laser and the wavelength of the first optical signal satisfies a preset range, and the output optical power of the slave laser and the optical power of the first optical signal are in a weak injection proportional relationship.

[0013] In a third aspect, the present invention provides an electronic device, comprising: one or more processors; a memory for storing one or more programs; wherein, when the one or more programs are executed by the one or more processors, the one or more processors implement the aforementioned light-domain-assisted signal-to-noise ratio improvement method.

[0014] In a fourth aspect, the present invention provides a computer-readable storage medium having executable instructions stored thereon, which, when executed by a processor, enables the processor to implement the aforementioned light-domain-assisted signal-to-noise ratio enhancement method.

[0015] The beneficial effects of the present invention are:

[0016] The present invention improves the signal-to-noise ratio from the perspective of the optical domain. It utilizes photon resonance amplification and optical injection locking technology, and does not require simultaneous measurement of multiple signals. It can improve the signal-to-noise ratio of a single microwave / optical signal. It achieves differentiated amplification of signals and noise with a streamlined architecture, amplifies signals while suppressing noise, and improves the noise performance of microwave links from a new dimension.

[0017] The present invention can not only improve the signal-to-noise ratio of the input electrical signal, and realize near-zero or even negative noise amplification in combination with a low-noise amplifier, but also realize negative noise coefficient amplification of the optical signal, thereby greatly improving and helping the sensitivity of the microwave photonic system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a block diagram of an optical domain-assisted microwave link signal-to-noise ratio improvement system of the present invention;

[0019] Figure 2 Verify link schematic for signal-to-noise ratio improvement;

[0020] Figure 3 This is a comparison chart of the signal-to-noise ratio improvement under different input microwave signal signal-to-noise ratio conditions;

[0021] Figure 4 This is a comparison chart of the improvement of signal-to-noise ratio under different input useful microwave signal power and noise power;

[0022] Figure 5 This is the locking state diagram under weak injection based on classical laser parameters. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0024] In order to improve the signal-to-noise ratio of the receiving signal system and suppress noise while amplifying the signal, the present invention proposes an optical domain-assisted microwave link signal-to-noise ratio improvement system to differentially amplify the signal and noise. The system includes: a first optical signal, from a laser, an optical fiber, such as Figure 1 shown.

[0025] The first optical signal, as an input signal, is injected into the slave laser through an optical fiber. The first optical signal may be light modulated by a first microwave signal, and the first microwave signal may be modulated on an optical signal through an electro-optical modulator to form the first optical signal. The first microwave signal may be a single-tone signal, a multi-tone signal, a broadband signal, etc., and the signal type is not limited; the optical signal may also be an optical signal containing information about the product under test.

[0026] The optical fiber is used to transmit an optical signal to each microwave photonic device. The optical fiber needs to be a polarization-maintaining optical fiber to ensure the polarization state of the first optical signal from the laser.

[0027] The slave laser receives the first optical signal and outputs the second optical signal after nonlinear photon resonance amplification. When the difference between the wavelength of the free oscillation of the slave laser and the wavelength of the first optical signal meets the preset range (i.e., they are the same or similar), the output optical power of the slave laser and the optical power of the first optical signal are in a certain proportional relationship (i.e., the ratio of the output optical power of the slave laser to the optical power of the first optical signal reaches Figure 5 When the slave laser is locked with the first optical signal, the first optical signal will force the slave laser to operate strictly at the injection frequency, and the wavelength of the second optical signal output by the slave laser is strictly consistent with the first optical signal; in the case of weak injection, the output power is constant and has nothing to do with the injection power; the higher the injection power, the greater the difference in the free oscillation wavelength allowed between the first optical signal and the slave laser.

[0028] The second optical signal, as an output signal, has a higher signal-to-noise ratio than the first optical signal after the present invention. When the first optical signal carries the first microwave signal, the second optical signal carries the second microwave signal, and the signal-to-noise ratio of the second microwave signal is higher than that of the first microwave signal.

[0029] For more information about optical injection locking, refer to Figure 5 , showing the locking state diagram under weak injection based on classical laser parameters. Optical injection locking mainly uses weak external injected photons to compete for carriers inside the active resonant cavity under weak injection conditions, so that it can obtain gain. Similarly, since the noise in the broadband signal band does not have a stable frequency component, it cannot trigger a stable locked resonance, and it is difficult to obtain sufficient gain. Based on this phenomenon, the suppression of in-band noise is achieved. In fact, starting from the improved steady-state solution of the rate equation, it can be found that whether the injection power is weaker or stronger than the injected laser, it does not affect the occurrence of the locked resonance phenomenon. Through the numerical simulation of the steady-state solution, the relationship between the output power and the injection power after the laser optical injection locking, as well as the relationship between the locking bandwidth and the injection power ratio can be obtained; when the overall injection power ratio is low, it can be found that the range of steady-state locking in interval A is symmetrical with the free oscillation wavelength of the laser as the center. This is also the main working range of the photon resonant amplification of the present invention. In particular, when the injected light is a broadband signal, a suitable frequency detuning must be set to ensure that resonant amplification can occur stably within the entire signal bandwidth. Compared with other narrow intervals that require precise control, the stable A interval has sufficient working bandwidth and can meet the higher optical gain supply. It should be pointed out that Figure 2-Figure 3 The analysis results are obtained from FP resonant cavity lasers. Due to the differences in parameter settings and the physical and chemical characteristics of the lasers themselves, the semiconductor lasers mainly used in the present invention have the same overall trend characteristics, but the specific injection power ratios are quite different.

[0030] In interval B, the steady-state locking range is divided into two asymmetric parts. It can be found that under the same injection power ratio, the negative detuning with the external injection light frequency less than the slave laser frequency and the positive detuning with the opposite show completely different characteristics. Due to the existence of relaxation oscillation of the slave laser itself, the steady-state locking range of the positive detuning range gradually disappears with the increase of the injection power ratio. Then the typical asymmetric distribution of the steady-state locking range appears in interval C. Due to the existence of the cavity mode redshift phenomenon (linewidth gain factor α), it can be seen that with the continuous increase of the injection power ratio, the steady-state locking range of the negative detuning is also constantly shifting. With the continuous increase of the injection power ratio, when it comes to interval D, the locking appears bistable. When the external injection light enters the steady-state locking interval from different directions, the specific boundary range will change accordingly, which is unfavorable in the sensing measurement application based on microwave photonic links. For frequency periodic reciprocating signals such as frequency modulated continuous waves, the slave laser will not be able to maintain steady-state locking under critical conditions.

[0031] Based on the resonant amplification characteristics of optical injection locking, high gain of broadband weak signals can be achieved. Figure 5 Both the A and B regions shown can achieve the light injection locking state of the present invention. Preferably, the optimal frequency detuning range is the A interval. At this time, the locking state is stable and easy to control, and can provide an optical gain of nearly 30 dB in a weak injection state. As the injection power ratio continues to increase, the steady-state locking range expands rapidly, and the steady-state interval of positive detuning will reappear. When the injection power ratio is reversed, the external injection light will reversely power the injected laser, which can improve the line width of the laser and its relaxation oscillation characteristics.

[0032] On the other hand, the optical domain assisted signal-to-noise ratio improvement method proposed in the present invention comprises the following steps:

[0033] Step 1, injecting a first optical signal into a slave laser through a polarization-maintaining optical fiber;

[0034] Step 2, the slave laser receives the first optical signal, and outputs the second optical signal after nonlinear photon resonance amplification, wherein the difference between the free oscillation wavelength of the slave laser and the wavelength of the first optical signal satisfies a preset range (i.e., the same or similar), the output optical power of the slave laser and the optical power of the first optical signal are in a weak injection proportional relationship, and the slave laser operates in an optical injection locked state.

[0035] Specifically, Figure 2As shown, the master laser generates an original optical signal, and the first optical fiber coupler OC1 divides the optical signal into two branches, an upper branch and an lower branch. The lower branch is connected to an input end of the second optical fiber coupler OC2 through an optical fiber. The upper branch optical signal passes through an optoelectronic modulator to modulate the first microwave signal D1 (including the useful microwave signal S1 and the noise signal N1 of the same frequency and bandwidth) on the original optical signal to form a first optical signal. After passing through an optical filter, one of the sidebands is retained and then injected into the slave laser through an optical circulator. The second optical signal generated by the slave laser passes through the circulator to the other input end of the second optical fiber coupler OC2, and after being combined with the original optical signal of the lower branch, enters the photoelectric detector and is converted into a second microwave signal D2.

[0036] Optical injection locking is essentially forced resonance in the optical domain. It is a phenomenon in which externally injected photons interact with photons in an active resonant cavity to achieve frequency and phase synchronization, thereby enabling the regeneration of signals of a specific frequency and achieving selective amplification. In the case of weak injection, weaker externally injected photons compete with carriers inside the active resonant cavity, thereby gaining gain. Since the useful microwave signal S1 has a stable frequency and phase, a stable locked gain can be obtained, while the noise signal N1 does not have a stable frequency component and cannot trigger a stable locked resonance, making it difficult to obtain sufficient gain. Based on this phenomenon, in-band noise suppression is achieved.

[0037] Distributed Feedback (DFB) lasers are often used as slave lasers. The multi-quantum well structure of DFB lasers ensures that only transverse electromagnetic waves (TE mode) can obtain obvious optical injection locking effects, so polarization state control is required before injection. The free oscillation wavelength of the slave laser is close to that of the master laser. When the output optical powers of the two are in a certain ratio, the slave laser works in the optical injection locking state and performs optical resonance amplification on the input optical signal. At this time, the wavelength of the optical signal output by the slave laser is exactly the same as the wavelength of the input optical signal. The useful microwave signal S1 injected into the first optical signal has a stable time-frequency characteristic, which produces resonance in the cavity, triggering optical injection locking, thereby obtaining a higher optical gain. However, the phase of the in-band noise N1 is random and cannot produce stable resonance, so it cannot be locked and amplified.

[0038] Therefore, the useful microwave signal S1 obtains an optical gain stronger than the in-band noise N1. Figure 2 After the microwave photon link is processed, the signal-to-noise ratio of the output second microwave signal D2 is improved compared with the signal-to-noise ratio of the input first microwave signal D1, achieving the benefit of improving the signal-to-noise ratio of the microwave link. Figure 3It is the improvement of signal-to-noise ratio for different input microwave signal signal-to-noise ratios. The horizontal axis is the input microwave signal signal-to-noise ratio, and the vertical axis is the improvement of the output microwave signal signal-to-noise ratio compared with the input microwave signal signal-to-noise ratio. The useful microwave signal is a 6-8GHz broadband linear frequency modulation signal, and the noise signal frequency range is 6-8GHz. It can be seen that under most input signal-to-noise ratio conditions, the method proposed in the present invention achieves an improvement in the signal-to-noise ratio, with a maximum improvement of about 1.5dB. Compared with the existing microwave devices that deteriorate the signal-to-noise ratio, the invention improves the signal-to-noise ratio, which is of great significance to improving system performance.

[0039] Figure 3 The reason why the signal-to-noise ratio does not improve in the case of medium and low input signal-to-noise ratio is that the system does not work in the light injection locking state and cannot resonantly amplify the signal. The competition between the signal in the laser cavity and the in-band noise for carriers becomes more intense, which is directly reflected in the power distribution between the resonant amplification obtained by the signal and the dielectric gain obtained by the noise. The signal-to-noise ratio does not improve in the case of high input signal-to-noise ratio because the shot noise of the photodetector causes the system performance to begin to decline.

[0040] Figure 4 The figure shows the improvement of microwave link signal-to-noise ratio under different input conditions of useful microwave signal and noise power. The horizontal axis is the input noise power, and the vertical axis is the input useful microwave signal power. The direction of the solid arrow indicates the direction of total power increase, and the dotted arrow indicates the direction of signal-to-noise ratio increase. The lighter the color in the figure, the better the signal-to-noise ratio improvement effect. Figure 4 It can be seen that under the same signal-to-noise ratio, that is, in the same solid line direction, the signal power gradually increases in this direction, and the signal-to-noise ratio improvement effect gradually increases, and finally reaches a certain bottleneck and does not change, which means that the present invention needs to ensure that the laser works in the light injection locking state under a certain input power condition to have a positive benefit. Under the same input power condition, that is, in the same dotted line direction, the signal-to-noise ratio gradually increases in this direction, and the signal-to-noise ratio improvement effect has experienced a change from low to high and then to low, which is different from Figure 3 The results are consistent, indicating that the benefits of the method of the present invention need to be under a certain input signal-to-noise ratio. Too low or too high input signal-to-noise ratio will inhibit the signal-to-noise ratio improvement benefits of the present invention.

[0041] In a third aspect, the present invention provides an electronic device, comprising: one or more processors; a memory for storing one or more programs; wherein, when the one or more programs are executed by the one or more processors, the one or more processors implement the aforementioned light-domain-assisted signal-to-noise ratio improvement method.

[0042] In a fourth aspect, the present invention provides a computer-readable storage medium having executable instructions stored thereon, which, when executed by a processor, enables the processor to implement the aforementioned light-domain-assisted signal-to-noise ratio enhancement method.

[0043] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A light domain assisted signal-to-noise ratio improvement system, characterized in that: The system includes a first optical signal, a slave laser, an optical fiber, a master laser, an electro-optical modulator, an optical filter, a circulator, a first optical fiber coupler, and a second optical fiber coupler, wherein: The first optical signal is used as an input signal and injected into the slave laser through an optical fiber; The slave laser is used to receive a first optical signal, and output a second optical signal after nonlinear photon resonance amplification, wherein the slave laser operates in an optical injection locking state, wherein the optical injection locking state is that the difference between the wavelength of the free oscillation of the slave laser and the wavelength of the first optical signal satisfies a preset range, and the output optical power of the slave laser and the optical power of the first optical signal are in a weak injection proportional relationship; When entering the optical injection locking state, the slave laser is locked with the first optical signal, the first optical signal forces the slave laser to operate at the injection frequency, and the wavelength of the output second optical signal is consistent with the first optical signal; The master laser is used to generate an original optical signal. The first optical fiber coupler divides the original optical signal into two upper and lower branches. The original optical signal of the lower branch is connected to an input end of the second optical fiber coupler through an optical fiber. The original optical signal of the upper branch is modulated by a first microwave signal on the original optical signal through an optoelectronic modulator to form a first optical signal. After passing through an optical filter, one of the sidebands is retained and then injected into the slave laser through an optical circulator. The second optical signal generated by the slave laser passes through the circulator to the other input end of the second optical fiber coupler, and after being combined with the original optical signal of the lower branch, enters the photoelectric detector and is converted into a second microwave signal. The first microwave signal contains a useful microwave signal and a noise signal of the same frequency and bandwidth. The signal-to-noise ratio of the second microwave signal is better than that of the first microwave signal.

2. The light domain assisted signal-to-noise ratio improvement system according to claim 1, characterized in that: In the optical injection locking state, the higher the injection power, the greater the difference in the allowed free oscillation wavelength between the first optical signal and the slave laser.

3. The light-domain-assisted signal-to-noise ratio improvement system according to claim 1, characterized in that: The first optical signal is an optical signal modulated by the first microwave signal or a laser signal containing information of the product under test, and the first microwave signal is any one of a single-tone signal, a multi-tone signal, and a broadband signal.

4. The light domain-assisted signal-to-noise ratio improvement system according to claim 1, characterized in that: The optical fiber is a polarization-maintaining optical fiber.

5. A light domain assisted signal-to-noise ratio improvement method, applied to the system according to any one of claims 1 to 4, characterized in that: include: Step 1, injecting a first optical signal into a slave laser through a polarization-maintaining optical fiber; Step 2, the slave laser receives a first optical signal, and outputs a second optical signal after nonlinear photon resonance amplification, wherein the slave laser operates in an optical injection locking state, wherein the optical injection locking state means that the difference between the wavelength of the free oscillation of the slave laser and the wavelength of the first optical signal satisfies a preset range, and the output optical power of the slave laser and the optical power of the first optical signal are in a weak injection proportional relationship.

6. An electronic device, characterized in that: include: one or more processors; A memory for storing one or more programs; Wherein, when one or more programs are executed by the one or more processors, the one or more processors implement the light domain-assisted signal-to-noise ratio improvement method of claim 5.

7. A computer-readable storage medium, characterized in that: Executable instructions are stored thereon, and when the instructions are executed by the processor, the processor can implement the light domain-assisted signal-to-noise ratio improvement method described in claim 5.

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