Microwave photonic filter with stable and tunable center frequency

Abstract

The invention discloses a microwave photonic filter with stable and tunable center frequency, and belongs to the field of microwave photons. The microwave photonic filter comprises an optical amplifier, a first optical isolator, a 1 * 2 optical coupler, an upload-download type micro-ring 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 photoelectric detector. According to the microwave photonic filter with the stable and tunable center frequency provided by the invention, the optical carrier in the MPF and the center angular frequency difference of the band-stop optical filter are locked by utilizing the complementary characteristic of optical filtering at the transmission end and the downloading end of the same resonant ring, so that the angular frequency difference between the optical carrier and the band-stop optical filter is fixed to be 2pi Nfm; therefore, the band-pass MPF with the center frequency being Nfm is obtained, the influence of the temperature on the center frequency of the MPF is eliminated, and the MPF with the stable center frequency is achieved.

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 the RF communication system, the performance of the whole system is closely related to the processing capability of microwave signals. Therefore, the microwave filter is the core component in microwave signal processing. Its main function is to filter out the original transmitted RF signal from the complex environmental noise and various stray signals or eliminate the interference signal caused by optical interference and other phenomena in the communication system, thereby improving the signal-to-noise ratio of the microwave signal, thereby greatly improving the transmission quality of the microwave signal. Therefore, high-performance microwave filters are extremely important in the whole RF communication system, and their filtering capability directly determines the performance of the next-level RF 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 photon filters combine traditional microwave technology with modern optics, use optoelectronic composite links to replace traditional microwave circuits, and greatly improve the shortcomings of traditional microwave filters through optical means. Microwave photon filters have technical advantages such as flexible tuning, integration, large tuning range, strong anti-electromagnetic interference ability, small size, and light weight, and have broad prospects.

[0005] However, the center wavelength of optical filters is easily affected by environmental factors such as temperature, and the center frequency stability of microwave photon filters (MPFs) is poor, which seriously restricts their practical application in modern electronic information systems. Therefore, in order to address this technical bottleneck, it is of great significance to study the technology to eliminate the influence of environmental factors such as temperature on the center frequency of MPFs. Summary of the invention

[0006] The purpose of the present invention is to propose a microwave photonic filter (MPF) with a stable and tunable center frequency in view of the problems existing in the background technology. The MPF of the present invention can solve the problems that the center wavelength of the optical filter is easily affected by temperature factors and the center frequency stability of the MPF is poor, and improve the center frequency stability of the MPF based on the PM-IM conversion principle; at the same time, based on the optical frequency comb and optical injection locking mechanism, the frequency tuning range of the MPF is improved and its frequency tuning step is reduced.

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

[0008] A microwave photon filter with a stable and tunable center frequency comprises a master laser module, an optical frequency comb generation module and a microwave photon bandpass filter module; wherein the master laser module is composed of an optical amplifier, a first optical isolator, a 1×2 optical coupler, an upload-download type microring resonant cavity and a first circulator, the optical frequency comb generation module is composed of a first phase modulator, an intensity modulator, an electric power divider and a microwave source, and 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 type microring resonant cavity;

[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, 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, 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 type 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 comprises 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, wherein the optical bandpass filter is realized by a sub-bandpass transfer spectrum under a resonant ring, and 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, and adjusts 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 photon 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, and 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 to form 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, and the process of improving the frequency stability of 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 type 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 modulator is modulated by a frequency of 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 at (ω0+2πNf m )-(ω0)=2πNf m , so the frequency of the microwave radio frequency signal generated after the photodetector is fixed at 2πNf m , forming an MPF ​​based on the PM-IM conversion principle, with a central angular frequency of 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 to 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 I2 is the intensity of the comb light of a certain frequency in the optical frequency comb, and I2 is the intensity of the light 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 complementary characteristics of optical filtering at the transmission (through) end and the download (drop) port of the same resonant ring are used 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 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 Or when the slave laser in the microwave photon bandpass filter module is locked to different comb teeth N of the optical frequency comb, the center frequency of the microwave photon filter can be tuned. Finally, a stable and tunable microwave photon filter is realized based on complementary photon 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 photon filter with stable and tunable center frequency. The complementary characteristics of the optical filter at the transmission end and the download end of the same resonant ring are used 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 center frequency of the MPF, and realizes an MPF ​​with a stable center frequency; the optical frequency comb with tunable free frequency range is used as the master laser to lock the tunable slave laser, and the slave laser is finely tuned by tuning the free spectrum range of the optical frequency comb to realize small step tuning of the center frequency of the MPF, and the slave laser is locked by different teeth of the optical frequency comb by tuning the slave laser to realize large step tuning of the center frequency of the MPF. In summary, the present invention improves the frequency tuning range of the MPF and reduces the frequency tuning step while improving the stability of the center frequency of the MPF. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0022] Figure 2 A schematic diagram of the structure 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 central frequency provided by the present invention. DETAILED DESCRIPTION

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

[0025] Example

[0026] like Figure 1 The figure shows a schematic diagram of the structure of the main laser module in a microwave photonic filter with a stable and tunable center frequency in an embodiment; it includes an optical amplifier, a first optical isolator, a 1×2 optical coupler, an upload-download type micro-ring resonant cavity, 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 micro-ring resonant cavity, the Drop port Port3 of the micro-ring resonant cavity 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.

[0027] like Figure 2As shown, it is 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 type 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 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 optical amplifier, the first optical isolator, the 1×2 optical coupler, the upload-download type micro-ring resonant cavity, and the first circulator together constitute the main laser module. In the main laser module, the optical amplifier and the bandpass optical filter constitute a positive feedback optical resonant cavity to generate narrow linewidth laser, wherein the optical bandpass filter is realized by the bandpass transfer spectrum of the resonant ring download end (Drop); the first phase modulator, the intensity modulator, the electric power divider, and the microwave source constitute the optical frequency comb generation module; the second circulator, the slave laser, the second phase modulator, the second optical isolator, the photodetector, and the upload-download type micro-ring resonant cavity constitute the microwave photon bandpass filter module.

[0029] The MPF provided in the embodiment achieves the process of eliminating the influence of temperature on the center frequency of the MPF and being tunable as follows:

[0030] The optical amplifier generates an optical signal, which has many modes. The optical signal is filtered through 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, and its frequency is ω0, as shown in Figure 3 (a). The frequency of the RF signal emitted by the microwave source is set to f m 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 electro-optic modulator is driven by a 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 is used 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 filter characteristics of the transmission spectrum of the Through port of the microring resonator. Figure 3 Finally, the photodetector is used for frequency beating. 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 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 finely tuned to achieve small step tuning of the MPF center frequency, and by tuning the slave laser so that the slave laser is locked by different comb teeth of the optical frequency comb, the MPF can be tuned in large steps. m =10GHz, select N=1, then a bandpass MPF with a center frequency of 10GHz is realized; select N=2, then a bandpass MPF with a center frequency of 20GHz is realized; select N=3, then a bandpass MPF with a center frequency of 30GHz is realized; select N=10, then a bandpass MPF with a 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 achieved. 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 achieved.

Claims

1. A microwave photon filter with a stable and tunable center frequency, characterized in that: It includes an optical amplifier, a first optical isolator, a 1×2 optical coupler, an upload-download type micro-ring 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, 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, 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 type microring resonant cavity 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 type microring resonant cavity 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 a frequency of 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 frequencies of the transmission spectra of the Drop port and the Through port of the microring resonator are the same, both ω0, and the output after the photodetector beats (ω0+2πNf m )-(ω0)=2πNf m A microwave radio frequency signal is generated, 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 to 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 main laser, I1 is the intensity of the comb light of 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 by different teeth of the optical frequency comb, thereby achieving the frequency tuning step adjustment of the microwave photonic filter.

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