Broadband continuous frequency tuning device of dual-wavelength heterodyne photonics millimeter wave source

Abstract

The invention relates to the technical field of millimeter wave signal generation, in particular to a broadband continuous frequency tuning device of a dual-wavelength heterodyne photonics millimeter wave source, which comprises a dual-wavelength generation module and an optical frequency shift accurate frequency tuning module. The dual-wavelength generation module generates two optical signals with different frequencies and transmits the optical signals to the optical frequency shift accurate frequency tuning module, thereby realizing frequency tuning. In the optical frequency shift accurate frequency tuning module, due to the frequency shift characteristic of an acousto-optic modulator, the frequency of a first optical signal can be shifted according to the frequency of a modulation signal generated by a signal generator to realize frequency tuning, and during frequency tuning, an optical fiber circulator and an optical fiber Bragg grating are combined to realize frequency tuning. High-efficiency utilization of optical signal power is realized, the composition of the system is simplified, and separation of two optical signals is quickly realized. The continuously tuned millimeter wave signal generated by the tuning device has the remarkable advantages of large tuning bandwidth, high tuning precision, simple system structure and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of millimeter-wave signal generation, and particularly to a broadband continuous frequency tuning device for a dual-wavelength heterodyne photonic millimeter-wave source, which can be applied to fields such as millimeter-wave communication, electronic countermeasure, and radar imaging. Background Art

[0002] The millimeter-wave frequency band is a spectrum band that has been widely studied and developed in recent years and plays a key role in fields such as mobile communication and radar imaging. Among them, the millimeter-wave signal source technology is the cornerstone of such applications. The millimeter-wave signal source based on optical heterodyne beat frequency has technical advantages such as high frequency band, multiple frequency bands, and low phase noise. However, the optical signals filtered by the longitudinal modes of the ring resonator are all limited by the free spectral range. The millimeter-wave signals generated by beat frequency have tuning blind spots in the frequency band, and the continuous tuning frequency generated by interferometer scanning has problems such as low accuracy, poor coherence, and narrow working bandwidth, making it difficult to meet the scenarios that require high-quality arbitrary millimeter-wave signal output in practical applications.

[0003] Through a comprehensive search of the prior art, it is found that the existing research results for the technical problems of generating millimeter-wave signals by photonics are as follows:

[0004] For example, the literature ("Photonic millimeter-wave generation beyond the cavity thermal limit", Optica, 2024 11(11): 1583-1587.) reports that two semiconductor lasers are used to lock the frequency on the resonant mode of the resonator through PDH (Pound-Drever-Hall) frequency locking technology, and then the frequency difference between the two resonant modes is obtained through optical heterodyne beat frequency, and then a millimeter-wave signal with a step of 23.6 GHz frequency is obtained. However, this scheme of preselecting the frequency difference using the resonant mode of the resonator is always limited by the free spectral range of the resonator, resulting in tuning blind spots in the millimeter-wave signal source.

[0005] For another example, the literature ("Broadband linearly chirped light source with narrowlinewidth based on external modulation", Optics Letters, 2018.) reported that a dual-parallel Mach-Zehnder interferometer was used for optical frequency offset and optical frequency scanning to generate millimeter-wave signals with a tunable frequency of 200 GHz. This implementation scheme divides 200 GHz into 16 frequency bands, that is, 16×12.5 GHz, and realizes continuous tuning of 200 GHz by inputting the optical frequency scanner through the optical cycle frequency shifter loop. However, the tuning accuracy is limited by the linewidth of the distributed feedback laser, and as the number of cycles increases, the linewidth will gradually deteriorate. The linewidth of the first frequency band is 21.6 kHz, and that of the last frequency band is 39.5 kHz. The increase in linewidth will greatly limit the tuning range and tuning accuracy.

[0006] For another example, the literature ("Microwave Photonics based Millimeter Wave SignalGeneration Technique for 5G Systems", IEEE Transactions on Instrumentation andMeasurement, 2024.) reported that two parallel Mach-Zehnder modulators and a series Mach-Zehnder modulator were used to tune millimeter-wave signals, and a 15 GHz radio frequency signal was used as the modulation signal to generate stepped millimeter-wave signals in the range of 30 - 60 GHz. Most of these implementation schemes still require high-performance filters to filter out stray waves, and the cascading of multiple devices introduces more instabilities and increases the complexity of the system, which has very limited effects in practical applications.

[0007] Generally speaking, the current dual-wavelength heterodyne photonics millimeter-wave source has two limitations: one is that in the high-frequency band, it is mostly a single, stepped-tuning millimeter-wave source, with a large number of tuning frequency blind spots in the frequency band, and the technical solutions for continuously tunable millimeter-wave sources are not yet mature; the other is that the system for generating tunable millimeter-wave sources is complex, and the continuously tunable millimeter-wave signals have problems such as low accuracy, poor coherence, and narrow working bandwidth. Summary of the Invention

[0008] The object of the present invention is to provide a broadband continuous frequency tuning device for a dual-wavelength heterodyne photonics millimeter-wave source, to solve the problems of low tuning accuracy, poor coherence, and narrow working bandwidth existing in the existing continuous frequency tuning device, as well as the problem of frequency tuning blind spots caused by the free spectral range of the optical frequency reference.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] A broadband continuous frequency tuning device for a dual-wavelength heterodyne photonic millimeter-wave source, comprising:

[0011] A tuning controller that controls temperature and stress to regulate the optical filtering frequency range of a fiber Bragg grating;

[0012] A dual-wavelength generation module that generates a first optical signal and a second optical signal, where the wavelengths and frequencies of the first and second optical signals are different, the frequency of the first optical signal is f1, and the frequency of the second optical signal is f2;

[0013] An optical fiber circulator, whose first port receives the first optical signal and the second optical signal output by the dual-wavelength generator and outputs the first optical signal and the second optical signal to the fiber Bragg grating through the second port; the second port also receives the reflected optical signal output by the fiber Bragg grating and outputs the reflected optical signal to the acousto-optic modulator through the third port;

[0014] A fiber Bragg grating that receives the first optical signal and the second optical signal output by the optical fiber circulator; within the optical filtering range controlled by the tuning controller, the first optical signal is separated into a reflected optical signal and reflected, and the second optical signal is separated into a transmitted optical signal and transmitted;

[0015] A first modulation signal generator for generating a single-frequency radio frequency signal with a frequency of δf as a frequency modulation signal;

[0016] An acousto-optic modulator that receives the frequency modulation signal output by the signal generator and the reflected optical signal output by the optical fiber circulator, and performs acousto-optic modulation on the reflected optical signal according to the frequency modulation signal to generate a frequency-shifted optical signal with a frequency of δf;

[0017] An optical fiber coupler that receives the frequency-shifted optical signal output by the acousto-optic modulator and the transmitted optical signal output by the fiber Bragg grating, and combines the transmitted optical signal and the frequency-shifted optical signal;

[0018] A millimeter-wave photodetector that receives the combined optical signal output by the optical fiber coupler and performs beat frequency processing on the transmitted optical signal and the frequency-shifted optical signal in the combined optical signal to generate a millimeter-wave signal output.

[0019] Further, the broadband continuous frequency tuning device for the dual-wavelength heterodyne photonic millimeter-wave source further includes a signal controller for generating a control signal for controlling the frequency and amplitude of the modulation signal according to requirements.

[0020] Further, the millimeter-wave photodetector is a single-carrier photodetector.

[0021] Further, the dual-wavelength generation module includes:

[0022] A single-mode laser, which is used to provide an optical signal for a dual-drive Mach-Zehnder modulator;

[0023] A DC voltage source, which is used to provide the half-wave voltage required for the operation of the dual-drive Mach-Zehnder modulator;

[0024] A second modulation signal generator, which is used to generate a single-frequency radio frequency signal with a frequency of f0 and transmit it to a first radio frequency amplifier and a second radio frequency amplifier respectively;

[0025] A first radio frequency amplifier, which is used to amplify the power of the received single-frequency radio frequency signal with a frequency of f0, and after phase shift through a first phase controller, obtain a first optical modulation signal and output it to the dual-drive Mach-Zehnder modulator;

[0026] A second radio frequency amplifier, which is used to amplify the power of the received single-frequency radio frequency signal with a frequency of f0, and after phase shift through a second phase controller, obtain a second optical modulation signal and output it to the dual-drive Mach-Zehnder modulator;

[0027] A dual-drive Mach-Zehnder modulator, which is used to modulate the optical signal according to the received first optical modulation signal and second optical modulation signal, and generate multiple high-order modulation sidebands and output them to an optical tunable filter;

[0028] An optical tunable filter, which filters multiple high-order modulation sidebands according to requirements to obtain a first optical signal with a frequency of f1 and a second optical signal with a frequency of f2.

[0029] Furthermore, the frequency difference between the first optical signal and the second optical signal is the frequency of the millimeter-wave signal.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] Benefiting from the frequency shift characteristic of the acousto-optic modulator, the present invention can realize frequency tuning by shifting the frequency of the first optical signal according to the magnitude of the modulation signal frequency generated by the signal generator, and the shift amount is related to the frequency of the modulation signal, that is, the accuracy of the tuning frequency depends on the frequency stability of the modulation signal. Therefore, fine continuous frequency tuning operations can be achieved through this characteristic, and the frequency tuning blind area caused by the free spectral range of the optical frequency reference can be covered.

[0032] In the frequency tuning section, by combining an optical fiber circulator and an optical fiber Bragg grating, the efficient utilization of the optical signal power is achieved while simplifying the system configuration. This combination provides a simple separation and propagation method for separating the first optical signal and the second optical signal. In addition, the optical fiber circulator also has good isolation for the previous optical path, which can effectively prevent the backward-propagating optical signal from flowing back to the previous stage and affecting the system stability. Moreover, due to the frequency shift characteristic of the acousto-optic modulator, the optical signal is offset by the frequency of the modulation signal generated by the signal generator according to the magnitude of the modulation signal frequency. The accuracy of the tuning frequency depends on the frequency stability of the modulation signal, enabling fine continuous frequency tuning and covering the frequency tuning blind area caused by the free spectral range of the optical frequency reference. The continuously tuned millimeter-wave signal generated by this system has significant advantages such as a large tuning bandwidth, high tuning accuracy, and a simple system structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is the schematic diagram of the broadband continuous frequency tuning device of the present invention;

[0034] Figure 2 is the structural schematic diagram of the broadband continuous frequency tuning device of the embodiment;

[0035] REFERENCE SIGNS:

[0036] 1 - Dual-wavelength generation module; 11 - Single-mode laser; 12 - Dual-drive Mach-Zehnder modulator; 13 - DC voltage source; 14 - Second modulation signal generator; 15 - RF amplifier; 16 - RF amplifier; 17 - Phase controller; 18 - Phase controller; 19 - Optical tunable filter; 2 - Acousto-optic frequency shift precise frequency tuning module; 21 - Circulator; 22 - Optical fiber Bragg grating; 23 - Tuning controller; 24 - Acousto-optic modulator; 25 - First modulation signal generator; 26 - Coupler; 3 - Millimeter-wave photodetector. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] The technical solution of the present invention will be described in detail below with reference to the drawings.

[0038] As Figure 1 shown, a broadband continuous frequency tuning device for a dual-wavelength heterodyne photonics millimeter-wave source provided in this embodiment includes a dual-wavelength generation module 1, a tuning controller, an optical fiber circulator 21, an optical fiber Bragg grating 22, a signal controller, a first modulation signal generator 24, an acousto-optic modulator 23, an optical fiber coupler 25, and a millimeter-wave photodetector. Among them, the optical fiber circulator 21, the optical fiber Bragg grating 22, the tuning controller 23, the signal controller, the modulation signal generator 24, the acousto-optic modulator 24, the optical fiber coupler 26, and the millimeter-wave photodetector 3 form an acousto-optic frequency shift precise frequency tuning module 2.

[0039] The connection relationships of the components are as Figure 2 shown and are specifically described as follows:

[0040] The dual-wavelength generation module 1 is used to generate a first optical signal and a second optical signal. The wavelengths and frequencies of the first optical signal and the second optical signal are different. The frequency of the first optical signal is f1, and the frequency of the second optical signal is f2. The dual-wavelength generation module 1 includes: a single-mode laser 11, a DC voltage source 13, a dual-drive Mach-Zehnder modulator 12, a second modulation signal generator 14, a first RF amplifier 15, a second RF amplifier 16, a first phase controller 17, a second phase controller 18, and an optical tunable filter 19.

[0041] Among them:

[0042] The single-mode laser is connected to the optical input end of the dual-drive Mach-Zehnder modulator 12 and is used to provide an optical signal for the dual-drive Mach-Zehnder modulator 12. The DC voltage source 13 is used to provide the half-wave voltage required for the operation of the dual-drive Mach-Zehnder modulator 12. The second modulation signal generator 14 is respectively connected to the first RF amplifier 15 and the second RF amplifier 16 and is used to generate a single-frequency RF signal with a frequency of and respectively transmit it to the first RF amplifier 15 and the second RF amplifier 16. The first RF amplifier 15 is connected to the dual-drive Mach-Zehnder modulator 12 via the first phase controller 17 and is used to amplify the power of the received single-frequency RF signal with a frequency of f0 and then perform a phase shift via the first phase controller 17 to obtain a first optical modulation signal and output it to the dual-drive Mach-Zehnder modulator 12. The second RF amplifier 16 is connected to the dual-drive Mach-Zehnder modulator 12 via the second phase controller 18 and is used to amplify the power of the received single-frequency RF signal with a frequency of and then perform a phase shift via the second phase controller to obtain a second optical modulation signal and output it to the dual-drive Mach-Zehnder modulator 12. The output end of the dual-drive Mach-Zehnder modulator 12 is connected to the optical tunable filter 19 and is used to modulate the optical signal according to the received first optical modulation signal and second optical modulation signal to generate multiple high-order modulation sidebands and output them to the optical tunable filter 19. The optical tunable filter 19 filters the multiple high-order modulation sidebands according to the requirements to obtain the first optical signal with a frequency of f1 and the second optical signal with a frequency of f2.

[0043] In the optical frequency shift and precise frequency tuning module 2: The optical fiber circulator 21 is connected to the optical tunable filter 19. Its first port receives the first optical signal with a frequency of f1 and the second optical signal with a frequency of f2 output by the dual-wavelength generator, and outputs the first optical signal with a frequency of f1 and the second optical signal with a frequency of f2 to the fiber Bragg grating 22 through the second port; The second port also receives the reflected optical signal output by the fiber Bragg grating 22, and outputs the reflected optical signal to the acousto-optic modulator 23 through the third port. The fiber Bragg grating 22 exhibits different screening properties for two optical signals with different frequencies. It receives the first optical signal and the second optical signal output from the second port of the optical fiber circulator 21, reflects the first optical signal with a frequency of f1, and transmits the second optical signal with a frequency of f2; within the optical filtering range controlled by the tuning controller 23, the first optical signal with a frequency of f1 is separated into a reflected optical signal and reflected, and the second optical signal with a frequency of f2 is separated into a transmitted optical signal and transmitted. The modulation signal generator 25 is connected to the acousto-optic modulator 24, and is used to generate a single-frequency radio frequency signal with a frequency of δf as the frequency modulation signal. The acousto-optic modulator 24 is connected to the optical fiber coupler 26, and is used to receive the frequency modulation signal output by the modulation signal generator 25 and the reflected optical signal output by the optical fiber circulator 21, and perform acousto-optic modulation on the reflected optical signal according to the frequency modulation signal to generate a frequency-shifted optical signal with a frequency of f1 - δf. The optical fiber coupler 26 is connected to the millimeter-wave photodetector 3, and is used to receive the frequency-shifted optical signal output by the acousto-optic modulator 24 and the transmitted optical signal output by the fiber Bragg grating 22, and combine the transmitted optical signal and the frequency-shifted optical signal; the frequency difference between the transmitted optical signal and the frequency-shifted optical signal is Δf. The working bandwidth of the millimeter-wave photodetector 3 is greater than the frequency Δf. It receives the combined optical signal output by the optical fiber coupler, and performs beat frequency processing on the transmitted optical signal and the frequency-shifted optical signal in the combined optical signal to generate a millimeter-wave signal output, and the frequency of the millimeter-wave signal is Δf.

[0044] Benefiting from the frequency shift characteristic of the acousto-optic modulator 24 in this embodiment, the optical signal is offset by the frequency of the modulation signal input according to the frequency magnitude of the modulation signal generated by the signal generator. The accuracy of the tuned frequency depends on the frequency stability of the modulation signal, and fine continuous frequency tuning can be achieved, and the frequency tuning blind area caused by the free spectral range of the optical frequency reference can be covered. In the frequency tuning part, through the combination of the optical fiber circulator 21 and the fiber Bragg grating 22, the optical signal power is utilized efficiently and the system structure is simplified, providing a simple separation and propagation method for separating dual-wavelength optical signals. At the same time, the optical fiber circulator 21 also takes into account the isolation of the previous optical path, can effectively prevent the optical signal propagating in the reverse direction from returning to the previous stage and affecting the system stability, and the continuously tuned millimeter-wave signal generated by this system has the advantages of large tuning bandwidth, high accuracy, and simple system structure.

Claims

1. A broadband continuous frequency tuning device for a dual-wavelength heterodyne photonic millimeter-wave source, characterized in that: include: A tuning controller that controls temperature and stress to achieve regulation of the optical filtering frequency range of the fiber Bragg grating; A dual-wavelength generating module, which is used to generate a first optical signal and a second optical signal, the first optical signal and the second optical signal have different wavelengths and frequencies, the frequency of the first optical signal is f1, and the frequency of the second optical signal is f2; A fiber circulator, wherein the first port receives the first optical signal and the second optical signal output by the dual-wavelength generator, and outputs the first optical signal and the second optical signal to the fiber Bragg grating through the second port; the second port also receives the reflected optical signal output by the fiber Bragg grating, and outputs the reflected optical signal to the acousto-optic modulator through the third port; A fiber Bragg grating receives a first optical signal and a second optical signal output by a fiber circulator; within the optical filtering range controlled by a tuning controller, separates the first optical signal into a reflected optical signal and reflects the reflected optical signal, and separates the second optical signal into a transmitted optical signal and transmits the transmitted optical signal; A first modulation signal generator, used to generate a single-frequency radio frequency signal with a frequency of δf as a frequency modulation signal; an acousto-optic modulator, which receives the frequency modulation signal output by the signal generator and the reflected light signal output by the optical fiber circulator, and performs acousto-optic modulation on the reflected light signal according to the frequency modulation signal to generate a frequency-shifted light signal with a frequency of δf; A fiber coupler receives the frequency-shifted optical signal output by the acousto-optic modulator and the transmitted optical signal output by the fiber Bragg grating, and combines the transmitted optical signal and the frequency-shifted optical signal; The millimeter wave photoelectric detector receives the combined light beam output by the optical fiber coupler, and performs beat frequency processing on the transmitted light signal and the frequency-shifted light signal in the combined light beam to generate a millimeter wave signal output.

2. The broadband continuous frequency tuning device according to claim 1, characterized in that: The broadband continuous frequency tuning device of the dual-wavelength heterodyne photonics millimeter wave source also includes a signal controller, which is used to generate a control signal for controlling the frequency and amplitude of the modulation signal according to requirements.

3. The broadband continuous frequency tuning device according to claim 1, characterized in that: The millimeter wave photoelectric detector is a single-row carrier type photoelectric detector.

4. The broadband continuous frequency tuning device according to claim 1, characterized in that: The dual-wavelength generation module comprises: A single-mode laser for providing an optical signal for a dual-drive Mach-Zehnder modulator; A DC voltage source, which is used to provide a half-wave voltage required for the dual-drive Mach-Zehnder modulator to work; A second modulation signal generator, which is used to generate a single-frequency radio frequency signal with a frequency of f0, and transmit the signal to the first radio frequency amplifier and the second radio frequency amplifier respectively; A first radio frequency amplifier is used to amplify the power of a received single-frequency radio frequency signal with a frequency of f0, and after phase shifting by a first phase controller, obtain a first optical modulation signal to output to a dual-drive Mach-Zehnder modulator; A second radio frequency amplifier is used to amplify the power of the received single-frequency radio frequency signal with a frequency of f0, and after phase shifting by a second phase controller, obtain a second optical modulation signal to output to the dual-drive Mach-Zehnder modulator; A dual-drive Mach-Zehnder modulator, used to modulate the optical signal according to the received first optical modulation signal and the second optical modulation signal, and generate a plurality of high-order modulation sidebands to output to the optical tunable filter; The optical tunable filter filters multiple high-order modulation sidebands according to requirements to obtain a first optical signal with a frequency of f1 and a second optical signal with a frequency of f2.

5. The broadband continuous frequency tuning device according to claim 1, characterized in that: The frequency difference between the first optical signal and the second optical signal is the frequency of the millimeter wave signal.

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