Microwave frequency shifting method and device based on optical injection locking

Abstract

The present invention discloses a microwave frequency shifting method based on optical injection locking. A continuous single-frequency optical carrier is divided into three channels; the first channel of continuous single-frequency optical carrier is subjected to carrier suppression single-sideband modulation with the microwave signal to be frequency-shifted to obtain signal light; the second channel of continuous single-frequency optical carrier is used as the injection optical signal, injected into the slave laser and makes the slave laser work in the injection locking mode of a single-cycle oscillation state, the phase and power of the third channel of continuous single-frequency optical carrier are adjusted so that it is equal to the injection locking optical signal output from the slave laser but opposite in phase, and then the two signals are coupled into one channel to obtain a local oscillator optical signal containing only the red-shifted resonant component of the slave laser; finally, the local oscillator optical signal is beat with the signal light to obtain a frequency-shifted microwave signal. The present invention also discloses a microwave frequency shifting device based on optical injection locking. Compared with the prior art, the present invention can tune the frequency shift amount over a large range and improve the spurious suppression effect.

Description

Technical Field

[0001] The invention relates to a microwave frequency shifting method, belonging to the technical field of microwave photons. Background Art

[0002] A microwave frequency shifter is a device that can change the frequency of an input microwave signal. It is widely used in electronic countermeasures, Doppler velocity measurement, radar equipment testing, communication channelized reception and other systems. The traditional microwave signal frequency shifting method mainly uses microwave I / Q mixers to achieve single-sideband modulation. However, due to the influence of electronic I / Q mixers, there are common problems such as narrow working bandwidth and I / Q amplitude and phase imbalance, which gradually cannot meet the urgent needs of radar, electronic countermeasures and other systems for large instantaneous bandwidth, wide frequency band coverage and low spurious distortion capabilities.

[0003] Microwave photonics is an emerging interdisciplinary subject that combines microwave technology and photonics technology. It mainly studies the interaction between microwaves and light. Microwave photonics can overcome the advantages of traditional microwave technology in terms of processing speed and transmission bandwidth. Compared with traditional electronic systems, microwave photonic systems have the advantages of wide operating frequency band, large transmission bandwidth, small transmission loss, and strong anti-electromagnetic interference ability, which can achieve high-quality generation, transmission and processing of microwave signals. This allows microwave photonic systems to still have a flat response when facing large-bandwidth signals. In addition, optoelectronic devices are small in size and light in weight and can be used in various scenarios. Microwave signal frequency shifting technology based on microwave photonics is expected to overcome the electronic bottleneck problem faced by analog electronic systems and provide a more effective solution for ultra-wideband microwave signal frequency shifting.

[0004] The microwave signal frequency shifting methods based on microwave photons reported so far mainly include: acousto-optic frequency shifting (AOFS), sawtooth phase modulation (SPM), and microwave photon I / Q modulation.

[0005] The above three microwave photon frequency shifting methods benefit from the large bandwidth characteristics of photon technology and have a wide operating frequency range and instantaneous bandwidth. The frequency shifting method based on AOFS can realize accurate microwave signal frequency shifting, and the spectrum after frequency shifting is pure, the spurious suppression ratio is high, and the stability is good. However, AOFS has high requirements on the driving signal power, and because the center frequency of AOFS is fixed, the frequency shift amount has poor tunability. The frequency shifting method based on SPM can realize microwave signal frequency shifting of any frequency and different directions by changing the amplitude, frequency, and duty cycle of the sawtooth wave. It has high tunability and low system cost. However, the sideband spurious suppression ratio after frequency shifting is greatly affected by the quality of the sawtooth wave signal, and the frequency shift amount is limited by the digital-to-analog converter. The microwave photon frequency shifting method based on I / Q modulation has a large frequency shifting range and good tuning characteristics, but the spurious suppression ratio is more sensitive to the amplitude and phase imbalance of the I / Q signal, and the modulation efficiency of the Mach-Zehnder modulator is relatively low, resulting in low frequency shifting efficiency. In addition, in order to improve the spurious suppression ratio, the modulator is required to have a higher extinction ratio and the I / Q signal to have a higher amplitude and phase balance.

[0006] Since the above solutions have problems such as poor structural tunability, limited frequency shift, low spurious suppression ratio, and high requirements for optoelectronics, there is an urgent need for a simple and easy-to-implement solution that can not only achieve frequency shift of optical microwave signals, but also tune the frequency shift over a large range and improve the spurious suppression effect. Summary of the invention

[0007] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a microwave frequency shifting method based on optical injection locking, which can tune the frequency shifting amount over a large range and improve the spurious suppression effect.

[0008] The present invention specifically adopts the following technical solutions to solve the above technical problems:

[0009] The microwave frequency shifting method based on optical injection locking is as follows: a continuous single-frequency optical carrier is divided into three paths; a first path of continuous single-frequency optical carrier is subjected to carrier suppressed single-sideband modulation with a microwave signal to be frequency-shifted to obtain a signal light; a second path of continuous single-frequency optical carrier is used as an injection optical signal, injected into a slave laser and causes the slave laser to operate in an injection locking mode of a single-cycle oscillation state; the phase and power of the third path of continuous single-frequency optical carrier are adjusted so that the phase and power are equal to the injection-locked optical signal output from the slave laser but opposite in phase; and the two signals are then coupled into one path to obtain a local oscillator optical signal containing only the red-shifted resonance component of the slave laser; finally, the local oscillator optical signal is made to beat with the signal light to obtain a frequency-shifted microwave signal with a frequency of |f0-f1-f2|, wherein f0 is the frequency of the continuous single-frequency optical carrier, f1 is the frequency of the microwave signal to be frequency-shifted, and f2 is the red-shifted resonance component of the slave laser.

[0010] Furthermore, the frequency shift amount is adjusted by adjusting the light injection intensity.

[0011] Based on the same inventive concept, the following technical solutions can also be obtained:

[0012] A microwave frequency shifting device based on optical injection locking, comprising:

[0013] An optical splitter module is used to split a continuous single-frequency optical carrier into three paths;

[0014] A modulation module, used for performing carrier suppressed single sideband modulation on the first continuous single-frequency optical carrier with the microwave signal to be frequency-shifted to obtain signal light;

[0015] A local oscillator optical construction module is used to use the second continuous single-frequency optical carrier as an injection optical signal, inject it into the slave laser and make the slave laser work in an injection locking mode of a single-cycle oscillation state, adjust the phase and power of the third continuous single-frequency optical carrier so that it is equal to the injection locking optical signal output by the slave laser but opposite in phase, and then couple the two signals into one to obtain a local oscillator optical signal containing only the red-shifted resonance component of the slave laser;

[0016] The photoelectric detection module is used to make the local oscillator light signal beat with the signal light to obtain a frequency-shifted microwave signal with a frequency of |f0-f1-f2|, wherein f0 is the frequency of the continuous single-frequency optical carrier, f1 is the frequency of the microwave signal to be frequency-shifted, and f2 is the red-shifted resonant component from the laser.

[0017] Furthermore, the frequency shift amount is adjusted by adjusting the light injection intensity.

[0018] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0019] The present invention modulates the microwave signal into the optical domain to obtain the signal light, and uses the optical injection locking technology and the phase cancellation technology to construct the frequency-adjustable local oscillator light. After the signal light and the local oscillator light beat each other, the frequency-shifted microwave signal is output, and the frequency shift amount is adjusted over a large range by adjusting the optical injection intensity. The present invention uses the optical injection locking technology to achieve the frequency shift of the microwave signal, which can effectively solve the problems of poor tunability, limited frequency shift amount, low spurious suppression ratio, and excessively high photoelectric requirements in the current microwave frequency shift technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of the structural principle of a specific embodiment of the microwave frequency shifting device of the present invention;

[0021] Figure 2 A specific structural diagram for realizing carrier suppressed single sideband modulation;

[0022] Figure 3Schematic diagram of the generation and adjustment principle of local oscillator optical signal. DETAILED DESCRIPTION

[0023] In view of the shortcomings of the existing technology, the solution of the present invention is to modulate the microwave signal into the optical domain to obtain signal light, and use optical injection locking technology and phase cancellation technology to construct a frequency-adjustable local oscillator light. After the signal light and the local oscillator light beat each other, a frequency-shifted microwave signal is output, and the frequency shift amount can be adjusted over a large range by adjusting the light injection intensity.

[0024] The technical solution proposed by the present invention is as follows:

[0025] The microwave frequency shifting method based on optical injection locking is as follows: a continuous single-frequency optical carrier is divided into three paths; a first path of continuous single-frequency optical carrier is subjected to carrier suppressed single-sideband modulation with a microwave signal to be frequency-shifted to obtain a signal light; a second path of continuous single-frequency optical carrier is used as an injection optical signal, injected into a slave laser and causes the slave laser to operate in an injection locking mode of a single-cycle oscillation state; the phase and power of the third path of continuous single-frequency optical carrier are adjusted so that the phase and power are equal to the injection-locked optical signal output from the slave laser but opposite in phase; and the two signals are then coupled into one path to obtain a local oscillator optical signal containing only the red-shifted resonance component of the slave laser; finally, the local oscillator optical signal is made to beat with the signal light to obtain a frequency-shifted microwave signal with a frequency of |f0-f1-f2|, wherein f0 is the frequency of the continuous single-frequency optical carrier, f1 is the frequency of the microwave signal to be frequency-shifted, and f2 is the red-shifted resonance component of the slave laser.

[0026] A microwave frequency shifting device based on optical injection locking, comprising:

[0027] An optical splitter module is used to split a continuous single-frequency optical carrier into three paths;

[0028] A modulation module, used for performing carrier suppressed single sideband modulation on the first continuous single-frequency optical carrier with the microwave signal to be frequency-shifted to obtain signal light;

[0029] A local oscillator optical construction module is used to use the second continuous single-frequency optical carrier as an injection optical signal, inject it into the slave laser and make the slave laser work in an injection locking mode of a single-cycle oscillation state, adjust the phase and power of the third continuous single-frequency optical carrier so that it is equal to the injection locking optical signal output by the slave laser but opposite in phase, and then couple the two signals into one to obtain a local oscillator optical signal containing only the red-shifted resonance component of the slave laser;

[0030] The photoelectric detection module is used to make the local oscillator light signal beat with the signal light to obtain a frequency-shifted microwave signal with a frequency of |f0-f1-f2|, wherein f0 is the frequency of the continuous single-frequency optical carrier, f1 is the frequency of the microwave signal to be frequency-shifted, and f2 is the red-shifted resonant component from the laser.

[0031] In order to facilitate public understanding, the technical solution of the present invention is described in detail below through a specific embodiment and in conjunction with the accompanying drawings:

[0032] The microwave frequency shifting device in this embodiment is as follows Figure 1 As shown, it includes a master laser, a slave laser, a beam splitter, a modulation module, an attenuator 1, an attenuator 2, a phase shifter, a polarization controller, a circulator, an optical coupler and a photodetector.

[0033] The working process and principle of the device are as follows:

[0034] 1) If Figure 1 As shown, the continuous single-frequency optical carrier output by the laser is divided into three paths by a beam splitter, and the frequency of each continuous single-frequency optical carrier is f0;

[0035] 2) Taking a single-tone signal as an example (it can actually be a linear frequency modulation signal or a phase coded signal of a radar system, or an amplitude modulation signal, a phase modulation signal or a vector modulation signal of a communication system, etc.), the frequency of the microwave signal is f1, and the modulated carrier suppressed single sideband signal obtained after passing through the modulation module is the signal light, and the frequency is f0-f1;

[0036] 3) One of the continuous single-frequency optical carriers enters port 1 of the circulator after passing through attenuator 1 and polarization controller, port 2 of the circulator is connected to the slave laser, and the output signal of port 3 of the circulator enters the optical coupler;

[0037] 4) Another continuous single-frequency optical carrier enters the optical coupler after passing through the phase shifter and attenuator 2. The two signals are coupled into one signal. The output signal of the coupler is the optical local oscillator signal obtained after the frequency shift of the laser spectrum. The frequency of the optical local oscillator signal is f2.

[0038] 5) The local oscillator light and the signal light enter the two input ends of the photodetector, complete the beat frequency in the photodetector, and the final output signal frequency is |f0-f1-f2|, realizing the frequency shift of the microwave signal.

[0039] The modulation module in this embodiment realizes carrier suppressed single sideband modulation through a 90-degree bridge and a dual parallel Mach-Zehnder modulator, and can also be realized through other existing or future technologies such as a modulator connected to an optical filter; Figure 2 The figure shows the structure of the dual parallel Mach-Zehnder modulator, which consists of two sub-MZMs: MZM1 and MZM2 and one main MZM: MZM3. The two sub-MZMs are respectively embedded in the upper arm and lower arm of the main MZM. In addition, the main modulator MZM3 only has a DC bias voltage input port. By controlling the DC bias voltage of MZM3, the phase of the optical signal output by MZM2 can be adjusted. The microwave signal is input to the RF port of the dual parallel Mach-Zehnder modulator after passing through a 90-degree bridge. The bias voltages of the three MZMs are adjusted to:

[0040]

[0041] At this time, carrier suppressed single sideband modulation can be achieved, the positive first-order sideband and the carrier are suppressed, and the output of the modulation module is the modulated negative first-order sideband.

[0042] Combine the following Figure 1 , Figure 3 The structure and adjustment method of the local oscillator are explained:

[0043] like Figure 1 As shown, one of the continuous single-frequency optical carriers output by the optical beam splitter passes through attenuator 1 and a polarization controller and then is injected into the slave laser through a circulator. The output optical signal of the slave laser is output after passing through the circulator. The polarization controller in the system is used to match the polarization direction of the incident optical signal and the slave laser to obtain the maximum injection power. Figure 3 As shown, the frequency of the light wave output from the laser is f s , power is P s , the frequency of the injected light is f0, the power is P0, and the injection intensity ξ=P0 / P s , the detuning frequency is f i =f0-f s , the injected light is injected into the slave laser through the circulator, the phase of the slave laser is locked, and the intracavity oscillation is locked at the frequency f0-f2. Moreover, under the light injection condition, the intracavity gain required by the slave laser will decrease, and the refractive index of the intracavity gain medium will increase, resulting in an increase in the equivalent cavity length of the slave laser, so the cavity resonance frequency increases from f s Redshifted to f2. By adjusting the injected light intensity and the optical frequency detuning amount, various nonlinear dynamic states of the slave laser can be excited, including steady-state locking, single-cycle oscillation, period-doubling oscillation and chaotic oscillation states. Among them, single-cycle oscillation occupies most of the state space, so the single-cycle oscillation frequency of the light-injected semiconductor laser can be tuned in a wide range. Among the four dynamic states of light injection locking, the present invention utilizes the single-cycle oscillation state to achieve the frequency shift of the slave laser optical signal. In the single-cycle oscillation state, there is a dynamic competition between the laser oscillation excited by the light injection and the red-shifted cavity resonance caused by the light injection in the slave laser, changing the dynamic characteristics of the semiconductor laser. Under appropriate injection intensity and detuning frequency, a uniform optical double-sideband signal is generated due to the Hopf bifurcation, and the sideband spacing f m =f0-f2, this frequency is called the single-cycle oscillation frequency. When the detuning frequency is constant, as the light injection intensity increases, the frequency of the red-shifted resonant component light gradually decreases and moves away from the injected light frequency, so the frequency of the local oscillator light signal can be adjusted by adjusting the injected light intensity.

[0044] Another continuous single-frequency optical carrier output by the beam splitter is coupled with the injection-locked optical signal output from the laser in the optical coupler through the phase shifter and attenuator 2. By adjusting the parameters of the phase shifter and attenuator 2, the two coupled optical signals are made equal in magnitude and opposite in phase, thereby achieving spectral cancellation. The signal output from the coupler has only the red-shifted resonant component, thereby obtaining a local oscillator signal. By adjusting the intensity of the light injection, the red-shifted frequency of the spectrum from the laser can be changed, thereby obtaining local oscillator lights of different frequencies.

[0045] Finally, the local oscillator light and the signal light beat in the photodetector, and finally a frequency-shifted microwave signal with a frequency of |f0-f1-f2| is obtained. The frequency shift amount of the microwave signal can be adjusted by attenuator 1.

Claims

1. A microwave frequency shifting method based on optical injection locking, characterized in that: The continuous single-frequency optical carrier is divided into three paths; the first path of continuous single-frequency optical carrier is subjected to carrier suppressed single-sideband modulation by using the microwave signal to be frequency-shifted to obtain signal light; the second path of continuous single-frequency optical carrier is used as the injection optical signal, injected into the slave laser and makes the slave laser work in the injection locking mode of the single-cycle oscillation state, the phase and power of the third path of continuous single-frequency optical carrier are adjusted so that the phase and power of the third path of continuous single-frequency optical carrier are equal to the injection locking optical signal output by the slave laser and the phase is opposite, and then the two signals are coupled into one path to obtain a local oscillation optical signal containing only the red-shifted resonance component of the slave laser, and the frequency shift amount is adjusted by adjusting the light injection intensity; finally, the local oscillation optical signal is made to beat with the signal light to obtain a frequency-shifted microwave signal with a frequency of |f0-f1-f2|, wherein f0 is the frequency of the continuous single-frequency optical carrier, f1 is the frequency of the microwave signal to be frequency-shifted, and f2 is the red-shifted resonance component of the slave laser.

2. A microwave frequency shifting device based on optical injection locking, characterized in that: include: An optical splitter module is used to split a continuous single-frequency optical carrier into three paths; A modulation module, used for performing carrier suppressed single sideband modulation on the first continuous single-frequency optical carrier with the microwave signal to be frequency-shifted to obtain signal light; A local oscillator optical construction module is used to use the second continuous single-frequency optical carrier as an injection optical signal, inject it into the slave laser and make the slave laser work in an injection locking mode of a single-cycle oscillation state, adjust the phase and power of the third continuous single-frequency optical carrier so that it is equal to the injection locking optical signal output by the slave laser but opposite in phase, and then couple the two signals into one to obtain a local oscillator optical signal containing only the red-shifted resonance component of the slave laser, and adjust the frequency shift by adjusting the light injection intensity; The photoelectric detection module is used to make the local oscillator light signal beat with the signal light to obtain a frequency-shifted microwave signal with a frequency of |f0-f1-f2|, wherein f0 is the frequency of the continuous single-frequency optical carrier, f1 is the frequency of the microwave signal to be frequency-shifted, and f2 is the red-shifted resonant component from the laser.

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