Dual-channel microwave photon down-conversion system

Abstract

The invention discloses a dual-channel microwave photon down-conversion system. The system comprises an optical frequency comb generation module for generating an optical frequency comb based on an optical injection and modulation technology, a radio frequency signal loading module for providing a dual-channel microwave signal, and a frequency conversion module for performing frequency beating and filtering on the microwave signal by using the generated optical frequency comb. The distance between the optical frequency combs is changed by changing the injection coefficients of the master laser and the slave laser in the optical frequency combs, carrier suppression double-sideband modulation is carried out by using the Mach-Zehnder modulator as an intensity modulator in the radio frequency signal loading module, and two high-frequency microwave signals are down-converted to intermediate frequency at the same time.

Description

Technical Field

[0001] The 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 large bandwidth are the direction of application and development of wireless communication systems in the future. How to perform frequency conversion processing on the high-frequency microwave signals generated by the wireless transmission and receiving system is a key technology. Compared with the traditional electrical frequency conversion method, the microwave photonic frequency conversion method has the advantages of ultra-wideband, high isolation and strong anti-electromagnetic interference ability, and has gradually developed into a key technology for obtaining frequency conversion signals. Based on the down-conversion technology of microwave photons, the high-frequency microwave signal is loaded onto the optical frequency through the electro-optical modulator, the microwave signal is processed in the optical domain, and finally converted into a medium and low frequency microwave signal suitable for processing, which effectively solves the limitation of the device for the difficulty of 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 microwave photon down-conversion link realized by cascading phase modulators (PM), and the experiment successfully achieved the down-conversion conversion of 10 GHz microwave signals to 100 MHz signals. However, the cascade method will cause problems such as large losses. Amplifiers are required in the link, and optical filters are used to filter out stray optical sidebands, which increases the complexity of the system. In 2017, Peking University proposed a microwave photon down-conversion method based on the parallel structure of Mach-Zehnder Modulator (MZM) and Phase Modulator (PM). This scheme only requires a DC bias voltage to complete signal modulation, but two parallel discrete modulators are used in the parallel structure, which requires additional external optical fiber for connection. The upper and lower optical paths are unstable due to environmental interference, and unstable coherence phenomena are prone to occur during coupling, resulting in large transmission losses and unstable system performance. Recently, the Shanghai Satellite Engineering Research Institute used DP-DPMZM to achieve carrier suppressed single sideband modulation to complete frequency conversion. Experiments show that the scheme has high signal isolation and good spectrum purity, but the scheme can only achieve frequency conversion of one channel and cannot be expanded to a multi-channel frequency conversion scheme.

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

[0005] The purpose of the present application is to solve 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 purpose, the present application provides a dual-channel microwave photon down-conversion system, which includes an optical frequency comb generation module, the optical frequency comb generation module includes a first laser source to provide light injection, a first radio frequency source, a first MZM and a distributed feedback semiconductor laser, in the non-modulation mode of the first MZM, the first laser source, the first radio frequency source and the distributed feedback semiconductor laser are used to generate a seed optical frequency comb, and in the modulation mode of the first MZM, the comb tooth spacing of the seed optical frequency comb is changed at a first modulation frequency δf=Δf / 2, where Δf is the comb tooth spacing; a radio frequency signal loading module includes 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 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, the first RF source, the first MZM, an optical circulator, the distributed feedback semiconductor laser, and a spectrometer formed by the output end of the tunable laser 1 through a 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 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 make the distributed feedback semiconductor laser in 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 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 through a combiner and then connects to the RF input port of the second MZM, the third interface of the optical circulator passes through the 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 electric filter output port 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] The present application utilizes the nonlinear effect of light injection into a semiconductor laser to generate an optical frequency comb, changes the spacing of the optical frequency comb by changing the injection coefficients of a master laser and a slave laser, and combines the carrier suppressed double sideband modulation method of MZM to achieve simultaneous down-conversion of two high frequency signals to an intermediate frequency.

[0013] The beneficial effects of the present application are as follows: on the one hand, the embodiments of the present application generate an optical frequency comb based on the single-cycle oscillation state of the optically injected distributed feedback semiconductor laser, and the spacing of the optical frequency comb can be flexibly tuned by changing the injection intensity of the tunable laser, thereby widening the frequency range of the intermediate frequency signal. On the other hand, the modulated optical signal carrying microwave signal information is coupled to the optical frequency comb through the optical heterodyne method to achieve down-conversion of ultra-wideband microwave signals. 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 is a 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 clearly, further detailed descriptions are given below in conjunction with the accompanying drawings and embodiments.

[0019] In general, the dual-channel microwave photon down-conversion system proposed in this application is further described in detail below to make the purpose, technical solution and effect of the present invention clearer and more specific. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used 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 can be implemented in many alternative forms and should not be interpreted as being limited to only 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 are not limited to the first unit.

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

[0023] The terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments. Unless the context clearly indicates otherwise, the singular forms "one", "one" and "item" used herein are also intended to include plural numbers. It should also be understood that the terms "include" and / or "comprise" used herein specify the existence of stated features, integers, steps, operations, units and / or components, without excluding the existence 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, depending on the functions / actions involved, two figures shown in succession may actually be performed substantially simultaneously or may sometimes be performed in the reverse order.

[0025] The structure of a dual-channel microwave photon down-conversion system proposed in an 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 electric filter 11, a spectrometer 12 and a spectrometer 13. The output end of the tunable laser 1 is divided into two paths through a first optical splitter 14, wherein 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, and after the third interface 43 of the optical circulator, it is divided into two paths through 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, that is, the upper branch to form a second laser source, the second laser source is connected to the input port 81 of the second MZM8, the output port 82 of the second MZM8 is connected to the input port 91 of the EDFA9, the second RF source 6 outputs two microwave signals and is connected to the RF input port 83 of the second MZM8 after passing through the combiner 7, the other path of the third interface 43 of the optical circulator after passing through the second optical splitter 15 and the output port 92 of the EDFA9 is 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 electric filter 11, and the output port of the electric filter 11 is connected to the spectrum analyzer 12.

[0027] The optical frequency comb 200 generated based on the light injection and modulation technology is included in the above-mentioned dual-channel microwave photon down-conversion system, which is composed of a master laser, that is, a first laser source provided by a tunable laser 1, a first radio frequency source 2, a first MZM3, an optical circulator 4, a slave laser, that is, a DFB laser 5, and a spectrometer 13, wherein the first laser source is connected to the input port 31 of the first MZM3, the output port 32 of the first MZM3 is connected to the first interface 41 of the optical circulator 4, the radio frequency input port 23 of the first MZM3 is connected to the first radio frequency source 2, the second interface 42 of the optical circulator 4 is connected to the DFB laser 5, and after the third interface 43 of the optical circulator, it is divided into two paths through a second optical splitter, 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 interface 41 of the optical circulator 4 and then entering the output optical signal through the second interface 42 of the optical circulator 4 is f s DFB laser 5, let f d =f m -f s , where f d is the detuned frequency of the tunable laser 1 and the DFB laser 5. Due to the light injection of the tunable laser 1, a series of nonlinear effects occur in the cavity of the DFB laser 5, and the injection intensity of the tunable laser 1 is adjusted to make it in a single-cycle oscillation state. From the third output 43 of the optical circulator 4, the spectrum at this time is observed on the spectrometer 13 in the form of an optical frequency comb with a small number of comb teeth. The present invention uses this optical frequency comb as a seed optical frequency comb, and its comb tooth spacing is Δf.

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

[0030] Based on the above-mentioned use of light injection DFB laser 5 to generate the seed optical frequency comb, in the second state of the first MZM 3, it is configured to tune the optical signal f output 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] The upper branch is subjected to carrier suppressed double-sideband modulation through the second MZM8, wherein the second RF source 6 is configured to generate two different output modulation signals, represented by f1 and f2 respectively, and connected to the second MZM8 after passing through the combiner 7, and then combined with the lower branch light through the optical combiner 16 after optical amplification by the EDFA 9, and then connected to the input port of the photodetector 10. In the heterodyne 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 required intermediate frequency signals, so 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 IF signals.

[0032] The output wavelength range of the tunable laser 1 is 1549.312nm~1549.622nm; the modulation signal range of the first RF source 2 is 12.5GHz; the bandwidth of the first MZM3 and the second MZM8 are both 40GHz; the output wavelength range of the DFB laser 5 is 1548.264nm~1551.488nm; the modulation signal range of the output of the second RF source 6 is 11GHz and 26GHz; the working wavelength range of the EDFA 9 is 1530nm~1565nm, and the signal gain is 40dB; the bandwidth of the photodetector 10 is 18GHz; the bandwidth of the electric 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 realization of 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 branches by the first optical splitter 14, and the lower branch is modulated by the first MZM3, in which the first RF source 2 provides a modulation signal of 12.5GHz. 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, and an optical frequency comb with a frequency interval of 12.5GHz can be observed, 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 modulation signals. After being optically amplified 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 is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solution and inventive concept of the present invention within the technical scope of the present invention, which should be included in the protection scope 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 for providing light injection, a first radio frequency source, a first MZM and a distributed feedback semiconductor laser, generating a seed optical frequency comb by using the first laser source, the first radio frequency source and the distributed feedback semiconductor laser in a non-modulation mode of the first MZM, and changing the comb tooth spacing of the seed optical frequency comb at a first modulation frequency δf=Δf / 2 in a modulation mode of the first MZM, wherein Δf is the comb tooth spacing; The radio frequency signal loading module includes a second 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 f1 and f2, 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, comprising a photodetector for beating the optical signal of the optical frequency comb with the amplified modulated microwave signal; and an electric filter, wherein the electric filter is configured to filter out the intermediate frequency signals f corresponding to the two microwave signals in the electric signal obtained by the beat frequency. IF1 ,f IF2 ,in 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 MZM3 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 after the third interface of the optical circulator, it is divided into two paths through the optical splitter, 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 of 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 in a single-cycle oscillation state.

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

5. The dual-channel microwave photon down-conversion system according to claim 1, 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 down-conversion method based on optical heterodyne method 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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