Narrow linewidth microwave signal generation method based on all-optical mutual injection semiconductor laser

Abstract

The invention discloses a narrow linewidth microwave signal generation method based on an all-optical mutual injection semiconductor laser. The method comprises the following steps: two distributed feedback lasers carry out mutual injection coupling through a free space; wherein the distributed feedback laser is not provided with an isolator; by adjusting the driving current and temperature of the two distributed feedback lasers, the two distributed feedback lasers generate a frequency difference so as to generate a narrow linewidth microwave signal; the coupling strength and the coupling phase are controlled according to the narrow-linewidth microwave signal, so that the distributed feedback laser works in a P1 state, and the stable narrow-linewidth microwave signal is generated. According to the invention, the signal quality is improved while the system cost is reduced, and the problem that the phase and polarization are not matched in the optical fiber transmission process is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of microwave signals, and in particular relates to a method for generating narrow-linewidth microwave signals based on all-optical mutual injection semiconductor lasers. Background Art

[0002] In recent years, high-frequency millimeter-wave signals have gradually become one of the key technologies in these fields due to their wide application prospects in many fields such as communications, networks, military and medical care. Especially in 5G communications, radar detection, high-precision positioning and imaging technology, millimeter-wave signals have attracted widespread attention because they can provide larger bandwidth and stronger penetration. However, traditional millimeter-wave signal generation methods, such as electrical methods such as gyroscopes, electronic oscillators and crystal oscillators, although they meet the technical requirements to a certain extent, still have significant deficiencies in high frequency, high power output and signal stability. Specifically, the operating frequency of these electrical methods is limited by the bandwidth of electronic devices, and there are also problems of large power loss and poor system stability.

[0003] In order to overcome these limitations, in recent years, the method of using optical technology to assist in the generation of microwave signals has been widely studied and applied. Such technologies include optical heterodyne method, external modulation method and optoelectronic oscillator, etc. These methods can achieve the generation of high-frequency signals through the principles of optical modulation and optoelectronic conversion, and effectively avoid the limitations of traditional electrical methods. For example, the optical heterodyne method generates microwave signals with large frequency differences by mixing two optical signals, which can break through the bandwidth limitations of traditional electronic devices and achieve advantages in frequency and power; optoelectronic oscillators use frequency modulation or external excitation of optical signals to generate high-stability, low-noise microwave signals, which are widely used in fields such as high-precision measurement and high-speed communication.

[0004] Although optoelectronic oscillator technology performs well in generating high-quality microwave signals, its implementation process still inevitably relies on electro-optical modulation and optoelectronic conversion, which are often limited by the performance of electronic devices, thus affecting the stability and reliability of the system. For example, during the electro-optical modulation process, the amplitude, phase, and frequency of the optical signal may be affected by fluctuations in the performance of the modulator, resulting in unstable signal quality. Therefore, although optoelectronic oscillators have significant advantages in low noise and high frequency stability, they are still subject to the problem of limitations of electronic devices.

[0005] In order to effectively solve the above problems, the technology of all-optical generation of microwave signals came into being and became an important way to break through the bottleneck of traditional technology. This technology generates microwave signals by completely relying on optical means, without relying on traditional electronic devices or photoelectric conversion processes, fundamentally avoiding the performance limitations brought by electronic devices. The technology of all-optical generation of microwave signals can not only break through the limitations of high-frequency microwave signal generation, but also provide significant advantages in low power consumption, low noise and high stability. Therefore, as an important innovation in pure electrical or optoelectronic hybrid technology, the technology of all-optical generation of microwave signals provides an effective solution to the performance bottleneck of electronic devices.

[0006] In the technical solution for all-optical microwave signal generation, DFB (distributed feedback) semiconductor lasers are widely used as core light sources. DFB lasers have the characteristics of tunable wavelength, single-mode stable output, high power output and strong anti-interference ability, and are ideal light sources for injection locking and all-optical microwave signal generation. Compared with traditional lasers, DFB lasers can provide more stable output signals, greatly improving the stability and anti-interference ability of microwave signals.

[0007] At present, most common all-optical microwave signal generation methods use a main laser to inject another laser through a unidirectional optical fiber path to achieve signal generation. However, this method has some significant defects. First, the unidirectional optical fiber injection method is prone to cause instability of microwave signals, and its frequency linewidth is large, which cannot meet the requirements of high precision and high stability; secondly, the optical fiber structure is prone to introduce phase and polarization jitter, which in turn causes the phase and polarization mismatch of the laser signal, thereby affecting the quality of the final microwave signal. In addition, this fiber optical path injection solution usually requires the use of complex optical devices such as circulators, resulting in a complex system structure and high cost.

[0008] To solve these problems, researchers have proposed a new mutual injection scheme in recent years, where multiple lasers are mutually injected through a precise optical structure to stably generate all-optical microwave signals. Although this scheme has certain advantages in theory, it still faces challenges in optical phase control in practice, especially in the process of optical fiber transmission, where the phase and polarization mismatch problem has not been effectively solved. Summary of the invention

[0009] The present invention proposes a method for generating narrow linewidth microwave signals based on all-optical mutual injection semiconductor lasers to solve the problems existing in the above-mentioned prior art.

[0010] To achieve the above object, the present invention provides a method for generating a narrow linewidth microwave signal based on an all-optical mutual injection semiconductor laser, comprising the following steps:

[0011] Two distributed feedback lasers are mutually injected and coupled through free space; wherein the distributed feedback lasers are not provided with an isolator;

[0012] By adjusting the driving current and temperature of the two distributed feedback lasers, the two distributed feedback lasers generate a frequency difference, thereby generating a narrow linewidth microwave signal;

[0013] The coupling strength and coupling phase are controlled according to the narrow linewidth microwave signal, so that the distributed feedback laser works in the P1 state, thereby generating a stable narrow linewidth microwave signal.

[0014] Preferably, controlling the coupling strength and the coupling phase according to the narrow linewidth microwave signal comprises:

[0015] The spectral and electrical spectrum data of narrow linewidth microwave signals are collected through a real-time monitoring and analysis system, and the coupling intensity and coupling phase are controlled through the spectral and electrical spectrum data.

[0016] Preferably, the real-time monitoring and analysis system comprises a spectrometer, an electric spectrometer, a frequency meter, a photodetector and an electric amplifier.

[0017] Preferably, controlling the coupling intensity comprises: adjusting the power of the laser through a gradient neutral density filter.

[0018] Preferably, controlling the coupling phase comprises: moving the distributed feedback laser at the nanometer level by means of a micro-nano platform to change the phase of the standing wave injection.

[0019] Preferably, the spectra of the two distributed feedback semiconductor lasers are consistent within a range of 0.18 nm.

[0020] Preferably, the wavelength band of the distributed feedback semiconductor laser is 1550 nm.

[0021] The present invention also proposes a narrow linewidth microwave signal generating device based on all-optical mutual injection semiconductor laser, comprising:

[0022] Two distributed feedback semiconductor lasers with the same wavelength;

[0023] A laser beam splitter, used for splitting the output light of each distributed feedback semiconductor laser into two paths;

[0024] A graded neutral density filter for adjusting the optical power injected into another distributed feedback semiconductor laser, thereby controlling the coupling strength;

[0025] Micro-nano platform, used to move distributed feedback semiconductor lasers at the nanoscale and change the phase of standing wave injection;

[0026] A collimator, used for receiving and collimating the output light of the laser;

[0027] Optical fiber, used to transmit collimated optical signals;

[0028] Photodetectors, which convert light signals into electrical signals;

[0029] An electrical amplifier, used to amplify electrical signals;

[0030] An electrical spectrometer, used to analyze the frequency characteristics of electrical signals;

[0031] A spectrometer, used to analyze the spectral characteristics of optical signals;

[0032] Laser driver platform, used to control the current and temperature of the laser.

[0033] Compared with the prior art, the present invention has the following advantages and technical effects:

[0034] The present invention discloses a method for generating narrow linewidth microwave signals based on all-optical mutual injection semiconductor lasers, comprising the following steps: two distributed feedback lasers are mutually injected and coupled through free space; wherein the distributed feedback lasers are not provided with an isolator; by adjusting the driving current and temperature of the two distributed feedback lasers, the two distributed feedback lasers generate a frequency difference, thereby generating a narrow linewidth microwave signal; according to the narrow linewidth microwave signal, the coupling strength and coupling phase are controlled, so that the distributed feedback laser operates in the P1 state, thereby generating a stable narrow linewidth microwave signal. The present invention improves the signal quality while reducing the system cost, and solves the problem of phase and polarization mismatch during optical fiber transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0036] Figure 1 A schematic diagram of mutual injection of a distributed feedback semiconductor laser according to an embodiment of the present invention;

[0037] Figure 2 A schematic diagram of mutual injection to generate microwave signals according to an embodiment of the present invention;

[0038] Figure 3 is a schematic diagram of a device according to an embodiment of the present invention;

[0039] Figure 4 The probability density diagram of microwave signals generated by different coupling phase matching degrees according to the embodiment of the present invention. DETAILED DESCRIPTION

[0040] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0041] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0042] Embodiment 1

[0043] like Figure 1-2 As shown, this embodiment provides a method for generating a narrow linewidth microwave signal based on an all-optical mutual injection semiconductor laser, comprising the following steps:

[0044] Two distributed feedback lasers are mutually injected and coupled through free space; wherein the distributed feedback lasers are not provided with an isolator;

[0045] By adjusting the driving current and temperature of the two distributed feedback lasers, the two distributed feedback lasers generate a frequency difference, thereby generating a narrow linewidth microwave signal;

[0046] The coupling strength and coupling phase are controlled according to the narrow linewidth microwave signal, so that the distributed feedback laser works in the P1 state, thereby generating a stable narrow linewidth microwave signal.

[0047] Further, controlling the coupling strength and coupling phase according to the narrow linewidth microwave signal includes:

[0048] The spectral and electrical spectrum data of narrow linewidth microwave signals are collected through a real-time monitoring and analysis system, and the coupling intensity and coupling phase are controlled through the spectral and electrical spectrum data.

[0049] Furthermore, the real-time monitoring and analysis system includes a spectrometer, an electric spectrometer, a frequency meter, a photoelectric detector and an electric amplifier.

[0050] Furthermore, controlling the coupling intensity includes: adjusting the power of the laser through a gradient neutral density filter.

[0051] Furthermore, controlling the coupling phase includes: moving the distributed feedback laser at the nanometer level through the micro-nano platform to change the phase of the standing wave injection.

[0052] Furthermore, the spectra of the two distributed feedback semiconductor lasers are consistent within a range of 0.18 nm.

[0053] Furthermore, the wavelength band of the distributed feedback semiconductor laser is 1550 nm.

[0054] The principle of the present invention is as follows:

[0055] Figure 1 The general model of mutual injection of two distributed feedback semiconductor lasers is depicted. In this model, both distributed feedback lasers are not equipped with isolators, and mutual injection coupling can be achieved through optical fiber links, free space or integrated chip optical paths. By controlling the coupling intensity κ, coupling phase ψ and delay τ, the dynamic characteristics of the mutually coupled lasers are studied. A large number of nonlinear dynamic states such as mutual injection locking, P1 state, multi-cycle oscillation, four-wave mixing, and chaotic state of photon-electron and photon-photon interaction can occur from two unrelated main oscillation peaks. The advantage of using a free-space mutual injection coupling system is that the output light phase is stable compared to the optical fiber link laser and will not change due to optical fiber jitter. Compared with the integrated chip, its coupling parameters can be controlled by a single variable.

[0056] In this embodiment, the principle of generating microwave signals by mutual injection is mainly based on P1 oscillation and sideband modulation.

[0057] LD1 injects into LD2, and by controlling the driving current and temperature of the laser and adjusting the appropriate frequency difference, a beat frequency signal will be generated. At this time, the mutually injected laser works in the P1 state, such as Figure 2 As shown in (a). The beat frequency signal modulates the output light of LD2, which is manifested as spectrum shift in the frequency domain. As the sideband order increases, the power gradually decreases. Figure 2 (b). Similarly, the mutual injection structure is completely symmetrical, and the output light of LD1 is also frequency modulated, such as Figure 2 (c). In this case, the oscillation is completely undamped due to the change in the damping factor at the relaxation resonance frequency enhancement caused by the photon-photon resonance effect. There is a gain region around the cavity mode, represented by the black curve. Any external weak optical modulation sideband can get a good power enhancement if it happens to be located in this region. Therefore, the first-order sideband of LD2 that falls in the cavity mode gain region of LD1 will get a power enhancement; the first-order sideband of LD1 that falls in the cavity mode gain region of LD2 will get a power enhancement.

[0058] The specific implementation is as follows:

[0059] Two identical 1550nm distributed feedback semiconductor lasers without isolators produced in the same batch were selected, and the spectra were consistent within the range of 0.18nm to match the parameters. The output light of DFB-LD1 was divided into two paths by the laser beam splitter BS, one of which was injected into DFB-LD2 after attenuation of 3dBm through transmission, and the other was received by the collimator and coupled into the single-mode optical fiber after attenuation of 3dBm through reflection, and then the spectrum, electrical spectrum and other data were collected by the real-time monitoring and analysis system. Similarly, due to the symmetry of the mutual injection structure, the output light of DFB-LD2 was divided into two paths by the laser beam splitter BS, one of which was injected into DFB-LD1 after attenuation of 3dBm through transmission, and the other was received by the collimator and coupled into the single-mode optical fiber after attenuation of 3dBm through reflection, and the data was also observed and collected by the real-time detection and analysis system. The devices and instruments used in the real-time monitoring and analysis system in the experiment are: spectrometer OSA (Anritsu MS9710C) with a resolution of 0.05nm, spectrometer ESA with a bandwidth of 40G (Agilent 8564EC), frequency meter (Keysight 53230A), photodetector PD, and electric amplifier EA. During the experiment, the current and temperature of the laser were controlled by the laser driving platform (Gooch & Housego, EM595) to change the free oscillation frequency and output power of the laser, with an accuracy of +-0.01mA, +-0.01℃. The coupling intensity was adjusted by changing the power of the laser through the neutral density filter NDF. The micro-nano platform (P66.X60S, repeatability: 0.05%) was controlled by the host computer to realize the movement of the laser at the nanometer level, thereby changing the phase of the standing wave injection. Since the distance between DFB-LD1 and DFB-LD2 is much larger than the moving range of the micro-nano platform, the optical path length is 15cm, and it can be considered that the coupling time of the two lasers is 0.5ns.

[0060] The following experiments were conducted:

[0061] By adjusting the adjustment frame where the laser, beam splitter cube and collimator are located, all spatial optical paths are adjusted to the same horizontal plane to achieve good coupling. Since the output light of the DFB laser is linearly polarized, the polarization direction can be consistent by rotating the laser through the adjustment frame. Adjust the current of LD1 to 50.7mA, the temperature to 24.97℃, the output power to 11.20dBm, the current of LD2 to 40.0mA, the temperature to 24℃, the output power to 9.70dBm, rotate the filter to adjust the appropriate coupling intensity, and observe the spectrum and electrical spectrum in the real-time monitoring system. Keep the spectral detuning Δf between the lasers unchanged, and change the coupling phase between the lasers by moving LD2 within the wavelength range of 1550nm.

[0062] The stepping distance of the micro-nano platform controlled by the host computer is 155nm. For the standing wave, the phase changes by π / 5. The frequency values ​​of 20s are collected at different coupling phases in one phase cycle. Since the beat frequency signal is a high-frequency signal, the principle of frequency meter sampling is integration. The gate value of the frequency meter is adjusted to 10ms to make the collected data more accurate. Ten sets of frequency data under different coupling phase conditions are obtained, and the probability density distribution diagrams of the ten sets of data are obtained, as shown in Fig. Figure 4 As shown, within the period, affected by the coupling phase matching, the 3dB linewidth of the beat frequency signal is as small as 3.43MHz, thereby generating a high-frequency microwave signal with a narrow linewidth.

[0063] like Figure 3 As shown, this embodiment also proposes a narrow linewidth microwave signal generating device based on all-optical mutual injection semiconductor laser, comprising:

[0064] Two distributed feedback semiconductor lasers with the same wavelength;

[0065] A laser beam splitter, used for splitting the output light of each distributed feedback semiconductor laser into two paths;

[0066] A graded neutral density filter for adjusting the optical power injected into another distributed feedback semiconductor laser, thereby controlling the coupling strength;

[0067] Micro-nano platform, used to move distributed feedback semiconductor lasers at the nanoscale and change the phase of standing wave injection;

[0068] A collimator, used for receiving and collimating the output light of the laser;

[0069] Optical fiber, used to transmit collimated optical signals;

[0070] Photodetectors, which convert light signals into electrical signals;

[0071] Electrical amplifier, used to amplify electrical signals;

[0072] An electrical spectrometer, used to analyze the frequency characteristics of electrical signals;

[0073] A spectrometer, used to analyze the spectral characteristics of optical signals;

[0074] Laser driver platform, used to control the current and temperature of the laser.

[0075] Figure 3In it, DFB-LD stands for distributed feedback semiconductor laser, Bias stands for bias current, TEC stands for temperature control, BS stands for laser beam splitter, NDF stands for gradient neutral density filter, Micro Nano stands for micro-nano platform, col stands for collimator, optical fiber stands for optical fiber, PD stands for photodetector, AMP stands for electrical amplifier, ESA stands for electrical spectrometer, and OSA stands for spectrometer.

[0076] This device selects two identical 1550nm distributed feedback semiconductor lasers without isolators produced in the same batch, and the spectra are consistent within the range of 0.18nm to match the parameters. The output light of DFB-LD1 is divided into two paths by the laser beam splitter BS. One path is injected into DFB-LD2 after attenuation of 3dBm through transmission, and the other path is attenuated by 3dBm after reflection, and then received by the collimator and coupled into the single-mode optical fiber, and then the spectrum, electrical spectrum and other data are collected by the real-time monitoring and analysis system. Similarly, due to the symmetry of the mutual injection structure, the output light of DFB-LD2 is divided into two paths by the laser beam splitter BS. One path is injected into DFB-LD1 after attenuation of 3dBm through transmission, and the other path is attenuated by 3dBm after reflection, and then received by the collimator and coupled into the single-mode optical fiber. The real-time detection and analysis system also observes and collects the data. The devices and instruments used in the real-time monitoring and analysis system in the experiment are: spectrometer OSA (Anritsu MS9710C) with a resolution of 0.05nm, spectrometer ESA with a bandwidth of 40G (Agilent 8564EC), frequency meter (Keysight 53230A), photodetector PD, and electric amplifier EA. During the experiment, the current and temperature of the laser were controlled by the laser driving platform (Gooch & Housego, EM595) to change the free oscillation frequency and output power of the laser, with an accuracy of +-0.01mA, +-0.01℃. The coupling intensity was adjusted by changing the power of the laser through the neutral density filter NDF. The micro-nano platform (P66.X60S, repeatability: 0.05%) was controlled by the host computer to realize the movement of the laser at the nanometer level, thereby changing the phase of the standing wave injection. Since the distance between DFB-LD1 and DFB-LD2 is much larger than the moving range of the micro-nano platform, the optical path length is 15cm, and it can be considered that the coupling time of the two lasers is 0.5ns.

[0077] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for generating narrow linewidth microwave signals based on all-optical mutual injection semiconductor lasers, characterized in that: The following steps are involved: Two distributed feedback lasers are mutually injected and coupled through free space; Among them, the distributed feedback laser does not have an isolator; By adjusting the driving current and temperature of the two distributed feedback lasers, the two distributed feedback lasers generate a frequency difference, thereby generating a narrow linewidth microwave signal; The coupling strength and coupling phase are controlled according to the narrow linewidth microwave signal, so that the distributed feedback laser works in the P1 state, thereby generating a stable narrow linewidth microwave signal.

2. The method according to claim 1, characterized in that: Controlling the coupling strength and coupling phase based on narrow linewidth microwave signals includes: The spectral and electrical spectrum data of narrow linewidth microwave signals are collected through a real-time monitoring and analysis system, and the coupling intensity and coupling phase are controlled by the spectral and electrical spectrum data.

3. The method according to claim 2, characterized in that The real-time monitoring and analysis system comprises a spectrometer, an electric spectrometer, a frequency meter, a photoelectric detector and an electric amplifier.

4. The method according to claim 1, characterized in that: Controlling the coupling strength involves adjusting the power of the laser through a graded neutral density filter.

5. The method according to claim 1, characterized in that Controlling the coupling phase includes: moving the distributed feedback laser at the nanometer level through a micro-nano platform to change the phase of the standing wave injection.

6. The method according to claim 1, characterized in that The spectra of the two distributed feedback semiconductor lasers are consistent within a range of 0.18 nm.

7. The method according to claim 1, characterized in that The wavelength band of the distributed feedback semiconductor laser is 1550nm.

8. A narrow linewidth microwave signal generating device based on all-optical mutual injection semiconductor laser, characterized in that: include: Two distributed feedback semiconductor lasers with the same wavelength; A laser beam splitter, used for splitting the output light of each distributed feedback semiconductor laser into two paths; A graded neutral density filter for adjusting the optical power injected into another distributed feedback semiconductor laser, thereby controlling the coupling strength; Micro-nano platform, used to move distributed feedback semiconductor lasers at the nanoscale and change the phase of standing wave injection; A collimator, used for receiving and collimating the output light of the laser; Optical fiber, used to transmit collimated optical signals; Photodetectors, which convert light signals into electrical signals; An electrical amplifier, used to amplify electrical signals; An electrical spectrometer, used to analyze the frequency characteristics of electrical signals; A spectrometer, used to analyze the spectral characteristics of optical signals; Laser driver platform, used to control the current and temperature of the laser.

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