A microwave photonic filter with stable and tunable center frequency

Abstract

A microwave photon filter with a stable and tunable center frequency belongs to the field of microwave photons. The microwave photon filter includes an optical amplifier, a first optical isolator, a 1×2 optical coupler, an upload-download microring resonant cavity, a first circulator, a microwave source, an electric power divider, a first phase modulator, an intensity modulator, a slave laser, a second circulator, a second phase modulator, a second optical isolator, and a photodetector. The present invention provides a microwave photon filter with a stable and tunable center frequency. It utilizes the complementary characteristics of optical filtering at the transmission end and the download end of the same resonant ring to lock the center angular frequency difference between the optical carrier and the band-stop optical filter in the MPF, so that the angular frequency difference between the optical carrier and the band-stop optical filter is fixed to 2πNf m , thus obtaining the center frequency Nf m The bandpass MPF eliminates the influence of temperature on the center frequency of the MPF and realizes an MPF ​​with a stable center frequency.

Description

Technical Field

[0001] The invention belongs to the field of microwave photons, and in particular relates to a microwave photon filter with a stable and tunable central frequency. Background Art

[0002] In radio frequency communication systems, the performance of the entire system is closely related to the ability to process microwave signals. Microwave filters are the core components of microwave signal processing. Their primary function is to filter the original transmitted radio frequency signal from complex environmental noise and various stray signals, or to eliminate interference signals caused by phenomena such as optical interference in the communication system, thereby improving the signal-to-noise ratio of the microwave signal and thus significantly enhancing the transmission quality of the microwave signal. Therefore, high-performance microwave filters are extremely important in the entire radio frequency communication system. Their filtering capability directly determines the performance of the next-level radio frequency communication system.

[0003] The entire filtering process of traditional microwave filters is completed in the electrical domain. They have shortcomings such as poor tunability, poor flexibility, too narrow operating frequency band, large transmission loss, poor ability to resist electronic interference, and high price. It is difficult to meet the performance requirements of current communication systems for filters.

[0004] Microwave photonic filters combine traditional microwave technology with modern optics, replacing traditional microwave circuits with optoelectronic composite links. This optical approach significantly improves the shortcomings of traditional microwave filters. Microwave photonic filters offer broad prospects for development due to their flexible tuning, integration, wide tuning range, strong electromagnetic interference resistance, compact size, and light weight.

[0005] However, the center wavelength of optical filters is easily affected by environmental factors such as temperature, and the center frequency stability of microwave photonic filters (MPFs) is poor, severely restricting their practical application in modern electronic information systems. Therefore, addressing this technical bottleneck, research on technologies to eliminate the impact of environmental factors such as temperature on the center frequency of MPFs is of great significance. Summary of the Invention

[0006] The present invention aims to address the problems of the prior art by proposing a microwave photonic filter (MPF) with a stable and tunable center frequency. This MPF addresses the issues of the optical filter's center wavelength being susceptible to temperature and the MPF's poor center frequency stability, improving the center frequency stability of the MPF based on the PM-IM conversion principle. Furthermore, the MPF's frequency tuning range is increased and its frequency tuning step is reduced by leveraging an optical frequency comb and optical injection locking mechanisms.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A microwave photon filter with a stable and tunable center frequency includes a master laser module, an optical frequency comb generation module, and a microwave photon bandpass filter module. The master laser module is composed of an optical amplifier, a first optical isolator, a 1×2 optical coupler, an upload-download microring resonator, and a first circulator. The optical frequency comb generation module is composed of a first phase modulator, an intensity modulator, an electrical power divider, and a microwave source. The microwave photon bandpass filter module is composed of a second circulator, a slave laser, a second phase modulator, a second optical isolator, a photodetector, and an upload-download microring resonator.

[0009] The output port of the optical amplifier is connected to the input port of the first optical isolator, the output port of the first optical isolator is connected to the input port of the 1×2 optical coupler, the output port Port1 of the 1×2 optical coupler is connected to the input port Port1 of the microring resonator, the Drop port Port3 of the microring resonator is connected to the Port2 port of the first circulator, and the Port3 port of the first circulator is connected to the input port of the optical amplifier; the output port Port2 of the 1×2 optical coupler is connected to the input port of the first phase modulator, the output port of the microwave source is connected to the input port of the electric power divider, and the output port Port1 of the electric power divider is connected to the RF input port of the intensity modulator. The output port Port2 of the electric power divider is connected to the RF input port of the first phase modulator, the output port of the first phase modulator is connected to the input port of the intensity modulator; the output port of the intensity modulator is connected to the Port1 port of the second circulator, the Port2 port of the second circulator is connected to the slave laser, the Port3 port of the second circulator is connected to the input port of the second phase modulator, the output port of the second phase modulator is connected to the input port of the second optical isolator, the output port of the second optical isolator is connected to the Port1 port of the first circulator, and the Through port Port4 of the microring resonator is connected to the input port of the photodetector.

[0010] The upload-download type micro-ring resonant cavity may be a high-Q value upload-download optical resonant cavity in the form of a micro-ring, a micro-disk, a micro-sphere, an optical fiber, or the like.

[0011] The microwave photon filter of the present invention includes three modules: a main laser module, an optical frequency comb generation module, and a microwave photon bandpass filter module. The main laser module uses an optical amplifier and an optical bandpass filter to form a positive feedback optical resonant cavity to generate a narrow linewidth laser. The optical bandpass filter is implemented by a sub-bandpass transfer spectrum under a resonant ring. The wavelength of the generated laser is equal to the central angular frequency ω0 of the resonant ring optical bandpass filter. The optical frequency comb generation module uses a microwave source to control the tuning step by adjusting the microwave source radio frequency signal frequency f mAdjust the comb tooth spacing of the optical frequency comb generated after passing through the phase modulator; the main laser module generates a seed light with a frequency of ω0, and the generated frequency is ω0+2πNf m In the microwave photonic bandpass filter module, the optical frequency comb generated by the optical frequency comb generation module is injected into the slave laser through the second circulator. The angular frequency of the optical frequency comb is ω0+2πNf m The comb teeth are close to the oscillation mode of the slave laser, the slave laser works in a steady-state locked state, and the wavelength of the slave laser is locked at ω0+2πNf m The angular frequency of the output of the second circulator port3 is ω0+2πNf m The laser enters the second phase modulator to generate an optical frequency comb, which serves as the optical carrier of the microwave photon bandpass filter module, forming an MPF ​​based on the PM-IM conversion principle.

[0012] The present invention provides a microwave photon filter with a stable and tunable center frequency. The process of improving the frequency stability of the MPF based on photon complementary filtering is as follows:

[0013] The wavelength of the laser generated by the master laser module is equal to the central angular frequency ω0 of the upload-download microring resonator. The seed light with a central angular frequency of ω0 generated by the master laser module is input into the optical frequency comb generation module, and the intensity and phase modulators are modulated by the frequency f m The microwave source is modulated to generate a frequency interval of f m The optical frequency comb generated by the optical frequency comb generation module is injected into the slave laser through the second circulator. The angular frequency of the optical frequency comb is ω0+2πNf m The comb teeth are close to the oscillation mode of the slave laser, the slave laser works in a steady-state locked state, and the wavelength of the slave laser is locked at ω0+2πNf m The angular frequency of the output of the second circulator port3 is ω0+2πNf m The laser enters the second phase modulator to generate an optical frequency comb, which serves as the optical carrier of the microwave photon bandpass filter module. Since the center frequencies of the transmission spectra of the Drop port and the Through port of the microring resonator are the same, both are ω0, the angular frequency of the optical carrier output from the laser is ω0+2πNf m The difference between the comb teeth and the center angular frequency of the band-stop filter (through end of the microring resonator) is fixed to (ω0+2πNf m )-(ω0)=2πNf m , so the frequency of the microwave radio frequency signal generated after the photoelectric detector is fixed at 2πNf m , forming an MPF ​​based on the PM-IM conversion principle, whose central angular frequency is 2πNf m, where N is an integer representing the Nth comb tooth in the generated optical frequency comb.

[0014] Furthermore, injection locking is achieved when the frequency difference between the master and slave lasers meets the following conditions:

[0015]

[0016] Where ω1 is the angular frequency of a comb tooth in the optical frequency comb input at port 1 of the second circulator, ω2 is the frequency when the laser is running freely, and Q e is the quality factor of the master laser, I1 is the frequency interval f m The optical frequency comb is the light intensity of the comb light of a certain frequency, and I2 is the light intensity when the laser is running freely.

[0017] Furthermore, when tuning f m Alternatively, when the slave laser in the microwave photonic bandpass filter module is locked to different comb teeth N of the optical frequency comb, the frequency tuning step adjustment of the microwave photonic bandpass filter can be achieved.

[0018] The present invention provides a microwave photon filter with a stable and tunable center frequency. The filter utilizes the complementary characteristics of the optical filtering of the transmission (through) end and the download (drop) port of the same resonant ring to fix the center angular frequency difference between the optical carrier and the band-stop optical filter in the microwave photon filter, so that the angular frequency difference between the optical carrier and the band-stop optical filter is fixed to 2πNf m Therefore, when the microwave source frequency f in the optical frequency comb generation module is m When the frequency is constant, the center frequency of the microwave photon filter is not affected by temperature and is a fixed value; when the tuning f m Alternatively, when the slave laser in the microwave photonic bandpass filter module is locked to different comb teeth N of the optical frequency comb, the center frequency of the microwave photonic filter can be tuned. Ultimately, a stable and tunable microwave photonic filter is achieved based on complementary photonic filtering and PM-IM conversion.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention provides a microwave photonic filter with stable and tunable center frequency. It utilizes the complementary characteristics of optical filtering at the transmission end and the download end of the same resonant ring to lock the center angular frequency difference between the optical carrier and the band-stop optical filter in the MPF, so that the angular frequency difference between the optical carrier and the band-stop optical filter is fixed to 2πNf. m , thus obtaining the center frequency Nf mThe bandpass MPF eliminates the influence of temperature on the MPF center frequency, achieving an MPF ​​with a stable center frequency. A freely tunable optical frequency comb is used as a master laser to lock a tunable slave laser. Fine tuning the slave laser by tuning the free spectrum of the optical frequency comb allows for small-step tuning of the MPF center frequency. By tuning the slave laser so that it is locked to different teeth of the optical frequency comb, large-step tuning of the MPF center frequency is achieved. In summary, this invention improves the stability of the MPF center frequency while also increasing the frequency tuning range and reducing the frequency tuning step. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the main laser module structure;

[0022] Figure 2 A schematic structural diagram of a microwave photon filter with a stable and tunable center frequency provided by the present invention;

[0023] Figure 3 A schematic diagram of the principle of a microwave photon filter with a stable and tunable center frequency provided by the present invention. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0025] Example

[0026] like Figure 1 The figure shows a schematic structural diagram of a main laser module in a microwave photonic filter with a stable and tunable center frequency according to an embodiment; the module includes an optical amplifier, a first optical isolator, a 1×2 optical coupler, an upload-download microring resonator, and a first circulator. The output port of the optical amplifier is connected to the input port of the first optical isolator, the output port of the first optical isolator is connected to the input port of the 1×2 optical coupler, the output port Port1 of the 1×2 optical coupler is connected to the input port Port1 of the microring resonator, the drop port Port3 of the microring resonator is connected to Port2 of the first circulator, and Port3 of the first circulator is connected to the input port of the optical amplifier.

[0027] like Figure 2The figure shows a schematic diagram of the structure of a microwave photon filter with a stable and tunable center frequency provided by the present invention; it includes an optical amplifier, a first optical isolator, a 1×2 optical coupler, an upload-download microring resonator, a first circulator, a microwave source, an electrical power divider, a first phase modulator, an intensity modulator, a slave laser, a second circulator, a second phase modulator, a second optical isolator, and a photodetector. The output port Port2 of the 1×2 optical coupler is connected to the input port of the first phase modulator, the output port of the microwave source is connected to the input port of the electric power divider, the output port Port1 of the electric power divider is connected to the RF input port of the intensity modulator, the output port Port2 of the electric power divider is connected to the RF input port of the first phase modulator, and the output port of the first phase modulator is connected to the input port of the intensity modulator; the output port of the intensity modulator is connected to the Port1 port of the second circulator, the Port2 port of the second circulator is connected to the slave laser, the Port3 port of the second circulator is connected to the input port of the second phase modulator, the output port of the second phase modulator is connected to the input port of the second optical isolator, and the output port of the second optical isolator is connected to the Port1 port of the first optical circulator. Since the microring is a symmetrical structure, the Through port Port4 of the upload-download type microring resonator is connected to the input port of the photodetector.

[0028] The master laser module consists of an optical amplifier, a first optical isolator, a 1×2 optical coupler, an upload-download microring resonator, and a first circulator. In the master laser module, a positive feedback optical resonator composed of an optical amplifier and a bandpass optical filter generates narrow-linewidth laser light. The optical bandpass filter is implemented by a bandpass transfer spectrum at the drop end of the resonant ring. The first phase modulator, intensity modulator, electrical power splitter, and microwave source form the optical frequency comb generation module. The second circulator, a slave laser, a second phase modulator, a second optical isolator, a photodetector, and an upload-download microring resonator form the microwave photonic bandpass filter module.

[0029] The MPF provided in the embodiment eliminates the influence of temperature on the MPF center frequency and achieves tunability through the following process:

[0030] The optical amplifier generates an optical signal, which has many modes. The optical signal is filtered by the bandpass spectrum characteristics of the drop end of the microring resonator. Figure 1 The main laser module shown in the figure performs cyclic amplification and filtering in the loop, and finally outputs a single-mode seed light after the first optical isolator, whose frequency is ω0, as shown in Figure 3 (a). Set the frequency of the RF signal emitted by the microwave source to f m The seed light with the central angular frequency of ω0 generated by the main laser module is input into the optical frequency comb generation module, and the electro-optical modulator is driven by the frequency of f mThe microwave source is modulated to generate a frequency interval of f m The optical frequency comb, such as Figure 3 (b) The optical frequency comb generated by the optical frequency comb generation module is injected into the slave laser through a circulator. The angular frequency of the optical frequency comb is ω0+2πNf m The comb teeth are close to the oscillation mode of the slave laser, the slave laser works in a steady-state locked state, and the wavelength of the slave laser is locked at ω0+2πNf m , the output of the second circulator port3 is as follows Figure 3 The angular frequency shown in (c) is ω0+2πNf m The laser enters the phase modulator to generate an optical frequency comb, which serves as the optical carrier of the microwave photon bandpass filter module to form an MPF ​​based on the PM-IM conversion principle. The PM-IM conversion is completed by using the band-stop filtering characteristics of the transmission spectrum of the through port of the micro-ring resonator. Figure 3 As shown in (d). Finally, the photodetector is used for beat frequency. Since the center frequencies of the transmission spectra of the drop port and the through port of the microring resonator are the same, both are ω0, the optical carrier angular frequency is ω0+2πNf m The difference between the comb teeth and the center frequency of the band-stop filter is fixed at (ω0+2πNf m )-(ω0)=2πNf m , and the center frequency is Nf m Bandpass MPF.

[0031] Among them, by changing the free spectrum range of the optical frequency comb, the slave laser can be fine-tuned to achieve small-step tuning of the MPF center frequency, and by tuning the slave laser so that the slave laser is locked to different comb teeth of the optical frequency comb, the MPF can be tuned in large steps. m =10GHz, select N=1, then the bandpass MPF with the center frequency of 10GHz is realized; select N=2, then the bandpass MPF with the center frequency of 20GHz is realized; select N=3, then the bandpass MPF with the center frequency of 30GHz is realized; select N=10, then the bandpass MPF with the center frequency of 100GHz is realized. When N=1, select f m =8GHz, then a bandpass MPF with a center frequency of 8GHz is realized; when N=1, select f m =9GHz, then a bandpass MPF with a center frequency of 9GHz is realized. When N=2, select f m =8GHz, then a bandpass MPF with a center frequency of 16GHz is realized; select f m =9GHz, then a bandpass MPF with a center frequency of 18GHz is realized. When N=10, select f m =8GHz, then a bandpass MPF with a center frequency of 80GHz is realized; select fm =9GHz, a bandpass MPF with a center frequency of 90GHz is realized.

Claims

1. A microwave photon filter with a stable and tunable center frequency, characterized in that: The device comprises an optical amplifier, a first optical isolator, a 1×2 optical coupler, an upload-download type microring resonator, a first circulator, a first phase modulator, an intensity modulator, an electric power divider, a microwave source, a second circulator, a slave laser, a second phase modulator, a second optical isolator and a photodetector; The output port of the optical amplifier is connected to the input port of the first optical isolator, the output port of the first optical isolator is connected to the input port of the 1×2 optical coupler, the output port Port1 of the 1×2 optical coupler is connected to the input port Port1 of the microring resonator, the Drop port Port3 of the microring resonator is connected to the Port2 port of the first circulator, and the Port3 port of the first circulator is connected to the input port of the optical amplifier; the output port Port2 of the 1×2 optical coupler is connected to the input port of the first phase modulator, the output port of the microwave source is connected to the input port of the electric power divider, and the output port Port1 of the electric power divider is connected to the RF input port of the intensity modulator. The output port Port2 of the electric power divider is connected to the RF input port of the first phase modulator, the output port of the first phase modulator is connected to the input port of the intensity modulator; the output port of the intensity modulator is connected to the Port1 port of the second circulator, the Port2 port of the second circulator is connected to the slave laser, the Port3 port of the second circulator is connected to the input port of the second phase modulator, the output port of the second phase modulator is connected to the input port of the second optical isolator, the output port of the second optical isolator is connected to the Port1 port of the first circulator, and the Through port Port4 of the microring resonator is connected to the input port of the photodetector.

2. The microwave photon filter with stable and tunable center frequency according to claim 1, characterized in that: The upload-download type micro-ring resonant cavity is an upload-download type optical resonant cavity in the form of a micro-ring, a micro-disk, a micro-sphere or an optical fiber.

3. The microwave photon filter with stable and tunable center frequency according to claim 1, characterized in that: The optical amplifier, the first optical isolator, the 1×2 optical coupler, the upload-download microring resonator and the first circulator constitute a master laser module; the first phase modulator, the intensity modulator, the electric power divider and the microwave source constitute an optical frequency comb generation module; the second circulator, the slave laser, the second phase modulator, the second optical isolator, the upload-download microring resonator and the photodetector constitute a microwave photon bandpass filter module.

4. The microwave photon filter with stable and tunable center frequency according to claim 3, characterized in that: The seed light with a central angular frequency of ω0 generated by the main laser module is input into the optical frequency comb generation module, and the intensity and the first phase modulator are modulated by the frequency f m The microwave source is modulated to generate a frequency interval of f m The optical frequency comb generated by the optical frequency comb generation module is injected into the slave laser through the second circulator, so that the slave laser works in a steady-state locked state, and the wavelength of the slave laser is locked at ω0+2πNf m The angular frequency of the output of the second circulator port3 is ω0+2πNf m The laser enters the second phase modulator to generate an optical frequency comb, which serves as the optical carrier of the microwave photon bandpass filter module; the center frequency of the transmission spectrum of the Drop port and the Through port of the microring resonator is the same, both ω0, and the output after the photodetector beats the frequency (ω0+2πNf m )-(ω0)=2πNf m A microwave radio frequency signal, where N is an integer representing the Nth comb tooth in the generated optical frequency comb.

5. The microwave photon filter with stable and tunable center frequency according to claim 4, characterized in that: When the frequency difference between the master and slave lasers meets the following conditions, the slave laser operates in a steady-state locked state: Where ω1 is the angular frequency of a comb tooth in the optical frequency comb input at port 1 of the second circulator, ω2 is the frequency when the laser is running freely, and Q e is the quality factor of the master laser, I1 is the intensity of the comb light at a certain frequency of the optical frequency comb, and I2 is the intensity of the light when the slave laser is running freely.

6. The microwave photon filter with stable and tunable center frequency according to claim 1, characterized in that: By tuning the frequency f of the microwave source m Alternatively, the slave laser is tuned so that it is locked to different teeth of the optical frequency comb, thereby achieving frequency tuning step adjustment of the microwave photonic filter.

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