A dual-channel microwave photon down-conversion system

Abstract

This application discloses a dual-channel microwave photonic down-conversion system. The system includes an optical frequency comb generation module that generates an optical frequency comb based on optical injection and modulation techniques, an RF signal loading module that provides dual-channel microwave signals, and a frequency conversion module that uses the generated optical frequency comb to beat and filter the microwave signals. By varying the injection coefficients of the master and slave lasers in the optical frequency comb to change the spacing of the optical frequency comb, combined with carrier-suppressed double-sideband modulation using a Mach-Zehnder modulator as an intensity modulator in the RF signal loading module, the system simultaneously down-converts two high-frequency microwave signals to an intermediate frequency.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave photons, and in particular relates to a microwave photon down-conversion system. Background Art

[0002] High carrier frequency and wide bandwidth are the future directions for the application and development of wireless communication systems. Frequency conversion of the high-frequency microwave signals generated by wireless transmission and reception systems is a key technology. Compared with traditional electrical frequency conversion methods, microwave photonic frequency conversion offers advantages such as ultra-wideband, high isolation, and strong resistance to electromagnetic interference, and has gradually become a key technology for generating frequency-converted signals. Microwave photonic down-conversion technology uses an electro-optical modulator to load high-frequency microwave signals onto optical frequencies, processes the microwave signals in the optical domain, and finally converts them into suitable low- and medium-frequency microwave signals, effectively overcoming the device's difficulty in processing high-frequency signals.

[0003] So far, researchers have proposed a variety of microwave photon down-conversion methods, such as the microwave photon down-conversion system based on stimulated Brillouin scattering effect proposed by Li Qiang et al.; another example is the realization of a microwave photon down-conversion link through a cascaded phase modulator (PM), which successfully achieved the down-conversion conversion of 10 GHz microwave signals to 100 MHz signals. However, the cascaded approach can lead to high losses and other issues. Amplifiers are required in the link, and optical filters are used to filter out stray optical sidebands, increasing system complexity. In 2017, Peking University proposed a microwave photon down-conversion method based on a parallel structure of a Mach-Zehnder modulator (MZM) and a phase modulator (PM). This scheme requires only a DC bias voltage to complete signal modulation. However, the parallel structure uses two parallel discrete modulators, requiring an external optical fiber for connection. The optical path difference between the upper and lower optical paths can be unstable due to environmental interference, leading to unstable coherence during coupling, resulting in high transmission losses and unstable system performance. Recently, the Shanghai Satellite Engineering Research Institute used DP-DPMZM to implement carrier-suppressed single-sideband modulation for frequency conversion. Experiments have shown that this scheme has high signal isolation and good spectral purity, but it can only achieve frequency conversion for a single channel and cannot be expanded to a multi-channel frequency conversion solution.

[0004] In the design of microwave photonic frequency conversion systems, parallel multi-channel frequency conversion functions are usually required, but multi-channels often require more electro-optical devices, making the system structure complex and costly. Summary of the Invention

[0005] The purpose of this application is to address the deficiencies of the above-mentioned prior art and to propose an improved microwave photon down-conversion system.

[0006] In order to achieve the above-mentioned object, the present application provides a dual-channel microwave photon down-conversion system, which includes an optical frequency comb generation module, wherein the optical frequency comb generation module includes a first laser source for providing light injection, a first radio frequency source, a first MZM and a distributed feedback semiconductor laser, wherein the first laser source, the first radio frequency source and the distributed feedback semiconductor laser are used to generate a seed optical frequency comb in a non-modulation mode of the first MZM, and the comb tooth spacing of the seed optical frequency comb is changed at a first modulation frequency δf=Δf / 2 in a modulation mode of the first MZM, where Δf is the comb tooth spacing; and a radio frequency signal loading module including a second A laser source, a second radio frequency source, and a second MZM, wherein the second laser source provides a carrier, and the second radio frequency source provides two microwave signals with frequencies f_1 and f_2, respectively. The two microwave signals are combined and then subjected to carrier suppressed double-sideband modulation in the second MZM, and then optically amplified by an erbium-doped fiber amplifier to obtain an amplified modulated microwave signal; and a frequency conversion module, including a photodetector for beating the optical signal of the optical frequency comb with the amplified modulated microwave signal; and an electrical filter, wherein the electrical filter is configured to filter out the intermediate frequency signals f_1 and f_2, respectively, corresponding to the two microwave signals, from the electrical signal obtained by the beating. IF1 ,f IF2 , where f IF1 ,f IF2 ∈[0,δf / 2].

[0007] In some embodiments, the optical frequency comb generation module includes the first laser source formed by the output end of the tunable laser 1 through the first optical splitter, the first RF source, the first MZM, an optical circulator, the distributed feedback semiconductor laser, and a spectrometer, wherein the first laser source is connected to the input port of the first MZM, the output port of the first MZM is connected to the first interface of the optical circulator, the RF input port of the first MZM is connected to the first RF source, the second interface of the optical circulator is connected to the distributed feedback semiconductor laser, and the optical splitter is used to divide the optical circulator into two paths after the third interface of the optical circulator, one of which is connected to the spectrometer.

[0008] In some embodiments, the light injection of the first laser source causes a series of nonlinear effects to occur in the cavity of the distributed feedback semiconductor laser, and the injection intensity of the first laser source is adjusted to put the distributed feedback semiconductor laser into a single-cycle oscillation state.

[0009] In some embodiments, the RF signal loading module includes a second laser source formed by the output end of a tunable laser passing through a first optical splitter, the second laser source is connected to the input port of a second MZM, the output port of the second MZM is connected to the input port of the erbium-doped fiber amplifier, the second RF source outputs the two microwave signals, which are connected to the RF input port of the second MZM after passing through a combiner, and the third interface of the optical circulator passes through a second optical splitter and then is combined with the output of the erbium-doped fiber amplifier into one signal through an optical combiner.

[0010] In some embodiments, the photodetector input port of the frequency conversion module is connected to the output of the optical combiner, the photodetector output port is connected to the input port of the electric filter, and the output port of the electric filter is connected to the spectrum analyzer.

[0011] In some embodiments, the first path after the third interface of the optical circulator and after the second optical splitter is beat with the microwave output signal of the output port of the erbium-doped fiber amplifier to achieve microwave photon down conversion.

[0012] This application utilizes the nonlinear effect of light injection into a semiconductor laser to generate an optical frequency comb. By changing the injection coefficients of the master laser and the slave laser, the spacing of the optical frequency comb is changed. Combined with the carrier-suppressed double-sideband modulation method of the MZM, two high-frequency signals are simultaneously down-converted to an intermediate frequency.

[0013] The beneficial effects of this application are as follows: On the one hand, the embodiments of this application generate an optical frequency comb based on the single-cycle oscillation state of optically injected distributed feedback semiconductor lasers. By varying the injection intensity of a tunable laser, the spacing of the optical frequency comb can be flexibly tuned, thereby broadening the frequency range of the intermediate frequency signal. On the other hand, by coupling a modulated optical signal carrying microwave signal information with the optical frequency comb through optical heterodyning, down-conversion of ultra-wideband microwave signals is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the structure of a dual-channel microwave photon down-conversion system according to an embodiment of the present application.

[0015] Figure 2 Spectrum diagram of an optical frequency comb according to an embodiment of the present application.

[0016] Figure 3 Spectrum diagram of 1 GHz and 1.5 GHz intermediate frequency signals according to an embodiment of the present application.

[0017] The reference numerals in the figure are as follows: tunable laser 1; first RF source 2; first Mach-Zehnder modulator (first MZM) 3; optical circulator 4; distributed feedback semiconductor laser (DFB laser) 5; second RF source 6; combiner 7; second Mach-Zehnder modulator (second MZM) 8; erbium-doped fiber amplifier (EDFA) 9; photodetector 10; electrical filter 11; spectrometer 12; spectrometer 13. DETAILED DESCRIPTION

[0018] In order to make the technical problems solved by the present invention, the technical solutions adopted and the technical effects achieved more clear, further detailed description is given below with reference to the accompanying drawings and embodiments.

[0019] In general, the dual-channel microwave photon down-conversion system proposed in this application is described in further detail below to make the objectives, technical solutions, and effects of the present invention more clear and explicit. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0020] The specific structural and functional details disclosed herein are merely representative and are for the purpose of describing exemplary embodiments of the present application. However, the present application may be implemented in many alternative forms and should not be construed as being limited to the embodiments set forth herein.

[0021] It should be understood that although the terms "first," "second," etc. may be used herein to describe various units, these units should not be limited by these terms. These terms are used only to distinguish one unit from another. For example, a first unit may be referred to as a second unit, and similarly, a second unit may be referred to as a first unit without departing from the scope of the exemplary embodiments. The terms "and / or" used herein refer to units that are not limited to a first unit.

[0022] "Or" includes any and all combinations of one or more of the associated listed items.

[0023] The terms used herein are intended only to describe specific embodiments and are not intended to limit exemplary embodiments. Unless the context clearly indicates otherwise, the singular forms "a", "an", "an item" used herein are also intended to include the plural. It should also be understood that the terms "comprise" and / or "include" used herein specify the presence of stated features, integers, steps, operations, units and / or components, and do not preclude the presence or addition of one or more other features, integers, steps, operations, units, components and / or combinations thereof.

[0024] It should also be noted that, in some alternative implementations, the functions / actions mentioned may occur in a different order than that indicated in the accompanying drawings. For example, two figures shown in succession may actually be performed substantially simultaneously or may sometimes be performed in the reverse order, depending on the functions / actions involved.

[0025] The structure of the dual-channel microwave photon down-conversion system proposed in one embodiment of the present invention is as follows: Figure 1 As shown, it includes a tunable laser 1, a first RF source 2, a first MZM 3, an optical circulator 4, a DFB laser 5, a second RF source 6, a combiner 7, a second MZM 8, an EDFA 9, a photodetector 10, an electrical filter 11, a spectrum analyzer 12, and a spectrometer 13. The output end of the tunable laser 1 is split into two paths via a first optical splitter 14. The first path, i.e., the lower branch, forms a first laser source. The first laser source is connected to the input port 31 of the first MZM 3. The output port 32 of the MZM 3 is connected to the first interface 4-1 of the optical circulator. The RF input port 33 of the first MZM 3 is connected to the first RF source 2. The second interface 42 of the optical circulator is connected to the DFB laser 5. After the third interface 43 of the optical circulator, the tunable laser 1 is split into two paths via a second optical splitter 15, one of which is connected to the spectrometer 13.

[0026] The output end of the tunable laser 1 passes through the second path after the optical splitter, i.e., the upper branch, to form a second laser source. The second laser source is connected to the input port 81 of the second MZM 8, and the output port 82 of the second MZM 8 is connected to the input port 91 of the EDFA 9. The second RF source 6 outputs two microwave signals, which are connected to the RF input port 83 of the second MZM 8 after passing through the combiner 7. The other path of the optical circulator third interface 43 after passing through the second optical splitter 15 and the output port 92 of the EDFA 9 are combined into one path through the optical combiner 16 and connected to the input port of the photodetector 10. The output port of the photodetector 10 is connected to the input port of the electrical filter 11, and the output port of the electrical filter 11 is connected to the spectrum analyzer 12.

[0027] The optical frequency comb 200 generated based on optical injection and modulation technology is included in the above-mentioned dual-channel microwave photonic down-conversion system, which consists of a master laser, i.e., a first laser source provided by a tunable laser 1, a first RF source 2, a first MZM 3, an optical circulator 4, a slave laser, i.e., a DFB laser 5, and a spectrometer 13. The first laser source is connected to the input port 31 of the first MZM 3, the output port 32 of the first MZM 3 is connected to the first interface 41 of the optical circulator 4, the RF input port 23 of the first MZM 3 is connected to the first RF source 2, the second interface 42 of the optical circulator 4 is connected to the DFB laser 5, and the optical frequency comb is divided into two paths by a second optical splitter after the third interface 43 of the optical circulator, one of which is connected to the spectrometer 13.

[0028] In the step of generating the seed optical frequency comb, the optical signal f output by the tunable laser 1 is m The optical signal f is divided into two paths by the optical splitter. In the lower branch, the first MZM3 is configured not to process the optical signal f in its first state. m Modulation is performed, and the optical signal f m Therefore, the optical signal entering the 41 interface of the optical circulator 4 and then passing through the second interface 42 of the optical circulator 4 is output as f s DFB laser 5, let f d =f m -f s , where f d is the detuned frequency between tunable laser 1 and DFB laser 5. Due to the light injection from tunable laser 1, a series of nonlinear effects occur within the cavity of DFB laser 5, adjusting the injection intensity of tunable laser 1 to cause it to oscillate in a single cycle. The spectrum at this point, observed on spectrometer 13 from third output 43 of optical circulator 4, appears as an optical frequency comb with a small number of teeth. This optical frequency comb is used as a seed optical frequency comb in the present invention, and its teeth are spaced a certain distance apart.

[0029] Under external light injection, the cavity mode frequency of DFB laser 5, that is, the frequency of single-cycle oscillation in the cavity, will be red-shifted. The red-shift frequency is Δf-f d By changing the injection intensity of the tunable laser 1, the magnitude of the red-shifted frequency can be changed, so the spacing of the seed optical frequency comb can be flexibly tuned.

[0030] On the basis of generating the seed optical frequency comb by light injection into the DFB laser 5, in the second state of the first MZM 3, it is configured to tune the optical signal f outputted by the tunable laser 1. m By performing external modulation and setting the modulation signal frequency δf=Δf / 2, the modulated light output by the first MZM3 is injected into the DFB laser 5. At this time, the output optical frequency comb generates new comb teeth between the comb teeth of the original seed optical frequency comb. The number of comb teeth at this time is twice the number of comb teeth of the seed optical frequency comb before modulation, and the comb tooth spacing is 1 / 2 of the original.

[0031] In the upper branch, carrier suppressed double-sideband modulation is performed by the second MZM 8, where the second RF source 6 is configured to generate two different output modulated signals, represented by f1 and f2 respectively. After passing through the combiner 7, they are connected to the second MZM 8, and then after optical amplification by the EDFA 9, they are combined with the lower branch light through the optical combiner 16 and then connected to the input port of the photodetector 10. In the heterodyning process, f1 and f2 have beats with almost every comb line of the optical frequency comb (OFC), but only the beats between the comb lines closest to them are the desired intermediate frequency signals. Therefore, the frequency range of the intermediate frequency signal is The output port of the photodetector 10 is connected to the input port of the electric filter 11, and only the required frequency band signal is retained. At this time, f can be observed on the spectrum analyzer. IF1 ,f IF2 Two intermediate frequency signals.

[0032] The output wavelength range of the tunable laser 1 is 1549.312nm to 1549.622nm; the modulation signal range output by the first RF source 2 is 12.5GHz; the bandwidth of the first MZM 3 and the second MZM 8 are both 40GHz; the output wavelength range of the DFB laser 5 is 1548.264nm to 1551.488nm; the modulation signal range output by the second RF source 6 is 11GHz and 26GHz; the operating wavelength range of the EDFA 9 is 1530nm to 1565nm, and the signal gain is 40dB; the bandwidth of the photodetector 10 is 18GHz; and the bandwidth of the electrical filter 11 is 40GHz.

[0033] The working process of the dual-channel microwave photon down-conversion system is as follows: After the system is connected, turn on the switch of each device to put each device into working state. Take the dual-channel microwave photon down-conversion of 1GHz and 1.5GHz as an example: the optical signal with a wavelength of 1551.138nm output by the tunable laser 1 is divided into two paths by the first optical splitter 14, and the lower branch is modulated by the first MZM3, wherein the first RF source 2 provides a 12.5GHz modulated signal. Then, the modulated optical signal is injected into the DFB laser 5 with an output wavelength of 1551.184nm through the second interface 42 of the optical circulator 4, and the third interface 43 of the optical circulator 4 is connected to the second optical splitter 15. One of the two outputs of the second optical splitter 15 is connected to the spectrometer 13 to observe the optical frequency comb with a frequency interval of 12.5GHz, as shown in FIG. Figure 2 As shown. The upper branch is modulated by the second MZM8, where the second RF source 6 provides 11GHz and 26GHz modulated signals. After optical amplification by EDFA9, it is combined with the lower branch light through the optical combiner 16. The combined light is input to the photodetector 10 and then passes through the electrical filter 11, leaving only the 0-2GHz intermediate frequency signal. Finally, the 1GHz and 1.5GHz intermediate frequency signals can be observed on the spectrum analyzer, as shown. Figure 3 shown.

[0034] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art who, within the technical scope of the present invention, makes equivalent substitutions or modifications based on the technical solution and inventive concept of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A dual-channel microwave photon down-conversion system, characterized in that: include An optical frequency comb generation module, the optical frequency comb generation module comprising a first laser source providing light injection, a first radio frequency source, a first MZM and a distributed feedback semiconductor laser; the optical frequency comb generation module is configured to make the optical signal output by the first laser source in the non-modulation mode of the first MZM The input and output optical signals are The distributed feedback semiconductor laser, the first laser source and the distributed feedback semiconductor laser detuning frequency satisfy , so that the light injection intensity of the first laser source is adjusted to be in a single-cycle oscillation state, thereby generating a seed light frequency comb; and in the modulation mode of the first MZM with a first modulation frequency Changing the tooth spacing of the seed optical frequency comb, wherein is the comb tooth spacing of the seed optical frequency comb; The RF signal loading module includes a second laser source, a second RF source, and a second MZM. The second laser source provides a carrier, and the second RF source provides a frequency of and The two microwave signals are combined, and then carrier suppressed double-sideband modulated in the second MZM is performed, and then optically amplified by an erbium-doped fiber amplifier to obtain an amplified modulated microwave signal; as well as a frequency conversion module, comprising a photodetector for performing beat frequency conversion between the optical signal of the optical frequency comb and the amplified modulated microwave signal; as well as The electric filter is configured to filter out the intermediate frequency signals corresponding to the two microwave signals in the electric signal obtained by the beat frequency. ,in ; The first laser source and the second laser source output optical signals with the same frequency.

2. The dual-channel microwave photon down-conversion system according to claim 1, characterized in that: The optical frequency comb generation module includes the first laser source, the first radio frequency source, the first MZM, an optical circulator, a distributed feedback semiconductor laser, and a spectrometer, which are formed by the output end of the tunable laser 1 through the first optical splitter, wherein the first laser source is connected to the input port of the first MZM, the output port of the first MZM is connected to the first interface of the optical circulator, the radio frequency input port (33) of the first MZM is connected to the first radio frequency source, the second interface of the optical circulator is connected to the distributed feedback semiconductor laser (5), and the optical splitter is used to divide the optical circulator into two paths after the third interface, one of which is connected to the spectrometer.

3. The dual-channel microwave photon down-conversion system according to claim 2, characterized in that: The light injection from the first laser source causes a series of nonlinear effects to occur in the cavity of the distributed feedback semiconductor laser. The injection intensity of the first laser source is adjusted to put the distributed feedback semiconductor laser into a single-cycle oscillation state.

4. The dual-channel microwave photon down-conversion system according to claim 1, characterized in that: The radio frequency signal loading module comprises a second laser source formed by the output end of the tunable laser (1) passing through a first optical splitter, the second laser source is connected to the input port of the second MZM, the output port of the second MZM is connected to the input port of the erbium-doped fiber amplifier, the second radio frequency source outputs the two microwave signals which are connected to the radio frequency input port of the second MZM after passing through a combiner, the third interface of the optical circulator passes through the second optical splitter and then is combined with the output of the output port of the erbium-doped fiber amplifier into one signal through the optical combiner.

5. The dual-channel microwave photon down-conversion system according to claim 4, characterized in that: The photoelectric detector input port of the frequency conversion module is connected to the output of the optical combiner, the photoelectric detector output port is connected to the input port of the electric filter, and the electric filter output port is connected to the spectrum analyzer.

6. The dual-channel microwave photon down-conversion system according to claim 1, characterized in that: The first path after the third interface of the optical circulator and after the second optical splitter is beat with the microwave output signal of the output port of the erbium-doped fiber amplifier to achieve microwave photon down conversion.

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