Microwave photon filter and method for controlling the same

Abstract

The application discloses a microwave photon filter and a control method thereof, and belongs to the field of optical fiber communication. The filter comprises an optical ring cavity, a tunable laser source, an electro-optic intensity modulator, a photoelectric detector and an electric vector network analyzer. The first input end of the electro-optic intensity modulator is connected with the output end of the tunable laser source, the second input port of the electro-optic intensity modulator is connected with the output end of the electric vector network analyzer, and the output end of the electro-optic intensity modulator is connected with the input end of an optical circulator in the optical ring cavity. The output end of the optical circulator in the optical ring cavity is connected with the input end of the photoelectric detector, and the output end of the photoelectric detector is connected with the input end of the electric vector network analyzer. The application can overcome the problem that the device parameters cannot be adjusted after the structure of the microwave photon filter is determined.

Description

Technical Field

[0001] This application relates to the field of optical fiber communication technology, and in particular to a microwave photonic filter and its control method. Background Technology

[0002] With the development of broadband wireless communication, radar, and fiber optic communication technologies, higher requirements have been placed on the flexibility and reconfigurability of microwave signal spectral filtering and analysis. Microwave photonic filters utilize optical devices to achieve frequency domain processing of microwave signals, offering advantages such as large bandwidth and strong resistance to electromagnetic interference, and have become an important technical solution for broadband microwave signal processing.

[0003] Existing microwave photonic filters mostly achieve periodic filtering based on fiber optic ring cavities or micro-ring resonant structures. Their center filtering frequency and free spectral range are typically determined by the optical path length of the device, while the 3 dB bandwidth of a single passband is mainly determined by the coupling coefficient and device loss. Once the device structure is determined, these parameters are usually difficult to adjust independently, especially the 3 dB bandwidth and center filtering frequency, which are often fixed, limiting the flexible use of the filter in different application scenarios.

[0004] Therefore, there is an urgent need for a technical solution that can flexibly adjust the center filtering frequency and 3dB bandwidth of microwave photonic filters without changing the physical structure of the device, so as to meet the application requirements of broadband and reconfigurable microwave signal processing. Summary of the Invention

[0005] This application provides a microwave photonic filter and its control method, which can overcome the problem that the device parameters cannot be adjusted after the structure of the microwave photonic filter is determined.

[0006] To achieve the above objectives, according to a first aspect of this application, an optical annular cavity is provided, comprising an optical circulator and a coupler; wherein the optical circulator includes a coupling end of the optical circulator, and the coupler includes a first input end of the coupler; the coupling end of the optical circulator is connected to the first input end of the coupler.

[0007] To achieve the above objectives, according to a second aspect of this application, a microwave photonic filter is also provided, the filter comprising an optical ring cavity, a tunable laser source, an electro-optic intensity modulator, a photodetector, and an electric vector network analyzer; the optical ring cavity includes an input terminal and an output terminal of an optical circulator; a first input terminal of the electro-optic intensity modulator is connected to the output terminal of the tunable laser source, a second input terminal of the electro-optic intensity modulator is connected to the output terminal of the electric vector network analyzer, and the output terminal of the electro-optic intensity modulator is connected to the input terminal of the optical circulator in the optical ring cavity; the output terminal of the optical circulator in the optical ring cavity is connected to the input terminal of the photodetector, and the output terminal of the photodetector is connected to the input terminal of the electric vector network analyzer.

[0008] To achieve the above objectives, according to a third aspect of this application, a control method for a microwave photonic filter is also provided, the control method being applied to the microwave photonic filter described in the second aspect; the method includes the following steps: S1. Obtain an optical carrier from a tunable laser source and transmit the optical carrier to an electro-optic intensity modulator. The single-frequency cosine microwave signal generated by the electro-optic intensity modulator is modulated onto the optical carrier to obtain a modulated optical signal. S2. The modulated optical signal is transmitted to the optical ring cavity and subjected to spectrum-selective filtering to obtain the filtered optical signal; S3. The filtered optical signal is transmitted to the photodetector and converted into an electrical signal.

[0009] In this application, the optical cavity in the microwave photonic filter is redesigned. The optical cavity includes an optical circulator and a coupler. The optical signal enters from the optical circulator, is transmitted through the coupling end of the optical circulator to the coupler for optical coupling, and then outputs the modulated optical signal through the coupling end of the optical circulator. This allows the optical signal to form a specific propagation path and feedback relationship in the optical cavity, thereby achieving effective control of the filtering response characteristics. This enables the center filtering frequency and 3dB bandwidth of the microwave photonic filter to be continuously adjustable simultaneously, making the tuning method more flexible. When adjusting the center wavelength of the optical carrier output from the laser, the overall time delay of the optical cavity is changed, thereby changing the center filtering frequency and 3dB bandwidth of the microwave photonic filter, achieving the purpose of tunability. Since the adjustment of the filtering characteristics is achieved by changing the optical carrier wavelength, there is no need to mechanically adjust the optical cavity structure or introduce complex temperature control or thermal tuning devices, thus effectively simplifying the system structure and reducing the system implementation complexity. Attached Figure Description

[0010] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0011] Figure 1 This is a schematic diagram of an optical annular cavity structure provided according to an embodiment of this application; Figure 2 This is a 3dB bandwidth tunable microwave photonic filter provided according to an embodiment of this application; Figure 3 This is a flowchart of a control method for a microwave photonic filter according to an embodiment of this application; Figure 4This is a schematic diagram representing the transfer curve of a microwave photonic filter with 100 microwaves according to an embodiment of this application. Figure 5 This is a schematic diagram representing the transfer curve of a microwave photonic filter with 1000 microwaves according to an embodiment of this application. Figure 6 This is a schematic diagram representing the transfer curve of a microwave photonic filter with 3000 microwaves according to an embodiment of this application. Figure 7 This is an enlarged schematic diagram representing the transfer curve of a microwave photonic filter with 3000 microwave units according to an embodiment of this application. Figure 8 This is a comparison chart of filtering effects when the latency is 0.5ns, according to an embodiment of this application. Figure 9 This is a comparison chart of filtering effects when the latency is 0.8ns, according to an embodiment of this application. Figure 10 This is a comparison chart of filtering effects when the latency is 1.5ns, according to an embodiment of this application. Figure 11 This is a comparison chart of the filtering effect when the delay is 2ns according to the embodiments of this application.

[0012] Label Explanation: 1. Optical circulator; 101. Input terminal of optical circulator; 102. Coupler of optical circulator; 103. Output terminal of optical circulator; 2. Coupler; 201. First input terminal of coupler; 202. Second input terminal of coupler; 203. First output terminal of coupler; 204. Second output terminal of coupler; 301. First optical element; 302. Second optical element; 4. Tunable laser source; 5. Electro-optic intensity modulator; 6. Photodetector; 7. Electric vector network analyzer. Detailed Implementation

[0013] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0014] This embodiment provides an optical annular cavity, including an optical circulator 1 and a coupler 2; wherein, the optical circulator 1 includes a coupling end 102 of the optical circulator, and the coupler 2 includes a first input end 201 of the coupler; the coupling end 102 of the optical circulator is connected to the first input end 201 of the coupler.

[0015] Furthermore, the coupler 2 also includes a second input terminal 202 of the coupler, which is connected to the first optical element 301; the first optical element 301 is a reflective linear chirped Bragg fiber grating or a reflector.

[0016] Furthermore, the coupler 2 also includes a first output terminal 203 of the coupler, which is connected to a second optical element 302, the second optical element 302 being a reflective linear chirped Bragg fiber grating.

[0017] Optionally, the coupler 2 further includes a second output terminal 204 of the coupler, which is not connected to any optical device.

[0018] Furthermore, the reflection delay of the second optical element 302 is positively correlated with the center wavelength of the optical carrier; that is, the larger the center wavelength of the optical carrier, the higher the reflection delay of the grating.

[0019] in, The reflection delay of the grating, The center wavelength of the optical carrier; When the first optical element 301 and the second optical element 302 are identical reflective linear chirped Bragg fiber gratings, the overall time delay of the optical ring cavity is as follows:

[0020] in, This refers to the total time for the optical signal to propagate in the coupler fiber section; in this embodiment, the center filtering frequency and 3dB bandwidth of the photonic filter are related to the overall time delay of the optical ring cavity. Regarding the overall time delay of the optical ring cavity when adjusting the center wavelength of the optical carrier output from the laser. As changes occur, the center filtering frequency and 3dB bandwidth of the microwave photonic filter change accordingly, thereby achieving tunability.

[0021] This embodiment also provides a microwave photonic filter, which includes an optical cavity, a tunable laser source 4, an electro-optic intensity modulator 5, a photodetector 6, and an electric vector network analyzer 7. The optical cavity includes an input terminal 101 and an output terminal 103 of an optical circulator. The first input terminal 501 of the electro-optic intensity modulator is connected to the output terminal of the tunable laser source 4, the second input port 502 of the electro-optic intensity modulator is connected to the output terminal of the electric vector network analyzer 7, and the output terminal 503 of the electro-optic intensity modulator is connected to the input terminal 101 of the optical circulator in the optical cavity. The output terminal 103 of the optical circulator in the optical cavity is connected to the input terminal of the photodetector 6, and the output terminal of the photodetector 6 is connected to the input terminal of the electric vector network analyzer 7.

[0022] Furthermore, the tunable laser source 4 is used to generate several optical carriers of different wavelengths; the optical ring cavity generates several center filtering frequencies and 3dB bandwidths under several optical carriers of different wavelengths for spectrum-selective filtering; the electric vector network analyzer 7 is used to generate single-frequency cosine microwave signals; the electro-optic intensity modulator 5 modulates the single-frequency cosine microwave signals onto the optical carriers; and the photodetector 6 is used for photoelectric detection and photoelectric conversion, converting optical signals into electrical signals.

[0023] This embodiment also provides a control method for a microwave photonic filter, which is applied to a microwave photonic filter; the method includes the following steps: S1. Obtain an optical carrier from the tunable laser source 4 and transmit the optical carrier to the electro-optic intensity modulator 5. The single-frequency cosine microwave signal generated by the electro-optic intensity modulator 5 is modulated onto the optical carrier to obtain the modulated optical signal. S2. The modulated optical signal is transmitted to the optical ring cavity and subjected to spectrum-selective filtering to obtain the filtered optical signal; S3. The filtered optical signal is transmitted to the photodetector 6 and converted into an electrical signal.

[0024] Optionally, S1 further includes the following steps: Based on the electric vector network analyzer 7, a single-frequency cosine microwave signal is generated using the following formula. :

[0025] in, The frequency of the single-frequency cosine microwave signal. The amplitude of the single-frequency cosine microwave signal. It is a time vector; in this embodiment, it can be taken as a time vector during normalization. ; Set the center frequency of the optical carrier to The single-frequency cosine microwave signal is modulated onto the optical carrier by the electro-optic intensity modulator 5 to obtain the modulated optical signal. :

[0026] in, Let be the impulse function.

[0027] Optionally, step S2 further includes the following steps: In the current cycle, the modulated optical signal enters from the input terminal 101 of the optical circulator, is transmitted to the first input terminal 201 of the coupler via the coupling terminal 102 of the optical circulator, and after optical coupling, reaches the first output terminal 203 and the second output terminal 204 of the coupler. The modulated optical signal arriving at the second output terminal 204 of the coupler is discarded. The modulated optical signal arriving at the first output terminal 203 of the coupler is reflected by the second optical element 302. After optical coupling, the modulated optical signal arrives at the first input terminal 201 and the second input terminal 202 of the coupler. The modulated optical signal arriving at the first input terminal 201 of the coupler is used as the output optical signal and transmitted through the coupling terminal 102 of the optical circulator to the output terminal 103 of the optical circulator, and then sent to the photodetector 6; the modulated optical signal arriving at the second input terminal 202 of the coupler is reflected by the first optical element 301 and together with the modulated optical signal of the next cycle received in the first input terminal 201 of the coupler, it serves as the input signal of the coupler 2 for the next cycle. The modulated optical signal is subjected to spectral selective filtering to obtain the filtered optical signal. :

[0028] in, Let be the frequency domain transfer function of the optical ring cavity.

[0029] Optionally, step S3 further includes the following steps: Filtered optical signal Photoelectric conversion is performed to obtain an electrical signal. :

[0030] The electrical signal The spectral envelope is directly used as the frequency domain transfer function of the microwave photonic filter; The difference between the maximum and minimum frequencies of the microwave signal is not less than the free spectral range (FSR) of the optical ring cavity.

[0031] in, This is the time delay of light traveling one revolution in the optical cavity; The electrical signal is transmitted to the electric vector network analyzer 7. By analyzing the center frequency and intensity changes of the input and output signals, the frequency transmission characteristics of the optical ring cavity are characterized.

[0032] In this embodiment, the center wavelength of the laser output carrier is adjusted so that the overall time delay of the optical ring cavity is... ns, then the free spectral range of the optical ring cavity GHz. To obtain a complete transmission curve, the microwave frequency generated by the electric vector network analyzer 7 was set from 0.5 GHz to 1.5 GHz, while the microwave frequency interval was adjusted, and the number of microwaves was set to 100, 1000, and 3000 respectively. The transmission envelope curve was obtained from... Figures 4 to 6 As shown, consistent with the previous analysis, the smaller the microwave frequency interval and the greater the number of microwaves, the more precise and smooth the envelope of the transmission curve, and the more accurate the result. Furthermore, regardless of the number of microwaves, the frequency point corresponding to the maximum intensity of the transmission curve is... The GHz position indicates that the center filtering frequency of the microwave photonic filter is... GHz. Figure 7 for Figure 6 The local magnification shows that a 3dB decrease in the maximum intensity corresponds to a frequency range of 34MHz, meaning the 3dB bandwidth of the microwave photonic filter is [missing value]. MHz. The intensity of the transmission envelope curves has been normalized.

[0033] To demonstrate the tunability of the 3dB bandwidth of the microwave photonic filter, the center wavelength of the output carrier of the tunable laser source 4 was adjusted so that the time delay of the optical ring cavity was 0.5ns, 0.8ns, 1.5ns and 2ns respectively. The microwave frequency was reasonably set in the electric vector network analyzer 7, and a sufficiently small microwave frequency interval was set so that the output transmission envelope curve appeared as smooth as possible. Figures 8 to 11 Corresponding to the transmission envelope curves for the aforementioned delays, the center filtering frequencies are 2GHz, 1.25GHz, 0.67GHz, and 0.5GHz (marked in green), and the 3dB bandwidths are 68MHz, 42MHz, 23MHz, and 17MHz (marked in red), respectively. It is clear that the center filtering frequency and 3dB bandwidth of the microwave photonic filter are related to the delay of the optical cavity: the greater the delay of the optical cavity, the higher the center filtering frequency of the microwave photonic filter. The smaller the value, the more the center filter position changes, even with the same 3dB bandwidth. The smaller.

[0034] One of the above technical solutions has the following advantages or beneficial effects: 1. The optical cavity structure in the microwave photonic filter was redesigned. The optical cavity includes an optical circulator and a coupler. The optical signal is input through the optical circulator 1 and transmitted to the coupler 2 for optical coupling via the coupling end 102 of the optical circulator. After coupling, the optical signal is output through the coupling end 102 of the optical circulator, thus obtaining a modulated optical signal. Through the above structural design, the optical signal forms a specific propagation path and feedback relationship in the optical cavity, thereby achieving effective control of the filtering response characteristics. This allows the center filtering frequency and 3 dB bandwidth of the microwave photonic filter to be continuously adjustable simultaneously, making the tuning method more flexible.

[0035] 2. By adjusting the center wavelength of the optical carrier output from the tunable laser source 4, the propagation conditions of the optical signal in the optical cavity can be changed, altering the overall time delay of the optical cavity. This, in turn, changes the center filtering frequency and 3dB bandwidth of the microwave photonic filter, achieving tunable control of the filtering characteristics. Since the filtering characteristics are adjusted by changing the optical carrier wavelength, there is no need for mechanical adjustment of the optical cavity structure or the introduction of complex temperature control or thermal tuning devices, thus effectively simplifying the system structure and reducing the system implementation complexity.

[0036] 3. By modulating the filter response using the time delay variation of the optical ring cavity, the center filter frequency and 3dB bandwidth can be adjusted synergistically. This not only increases the freedom of filter parameter tuning but also allows for flexible configuration according to different application requirements. Furthermore, this tuning method primarily relies on light source parameter control, resulting in fast response speed and high adjustment precision. This improves system stability and reliability, and enhances the applicability of microwave photonic filters in wideband signal processing, reconfigurable RF systems, and other applications.

[0037] 4. It is suitable for applications such as broadband microwave signal filtering and spectrum analysis, and has high engineering application value.

[0038] In the embodiments provided in this application, it should be understood that the disclosed methods and apparatus can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative. For instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces, or indirect coupling or communication connection between devices or units, and may be electrical, mechanical, or other forms.

[0039] Furthermore, the functional units in the embodiments of this application can be integrated into one processing unit, or each unit can be physically comprised separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or in the form of hardware plus software functional units.

[0040] The above description is the preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principles described in this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. An optical annular cavity, characterized in that, It includes an optical circulator (1) and a coupler (2); wherein the optical circulator (1) includes a coupling end (102) of the optical circulator, and the coupler (2) includes a first input end (201) of the coupler; the coupling end (102) of the optical circulator is connected to the first input end (201) of the coupler.

2. The optical annular cavity according to claim 1, characterized in that, The coupler (2) further includes a second input terminal (202) of the coupler, which is connected to a first optical element (301); the first optical element (301) is a reflective linear chirped Bragg fiber grating or a reflector.

3. The optical annular cavity according to claim 2, characterized in that, The coupler (2) also includes a first output terminal (203) of the coupler, which is connected to a second optical element (302), and the second optical element (302) is a reflective linear chirped Bragg fiber grating.

4. The optical annular cavity according to claim 3, characterized in that, The reflection delay of the second optical element (302) is positively correlated with the center wavelength of the optical carrier: in, The reflection delay of the grating, The center wavelength of the optical carrier; When the first optical element (301) and the second optical element (302) are identical reflective linear chirped Bragg fiber gratings, the overall time delay of the optical ring cavity is as follows: in, This represents the total time it takes for the optical signal to travel through the fiber optic portion of the coupler.

5. A microwave photonic filter, characterized in that, The filter includes an optical cavity, a tunable laser source (4), an electro-optic intensity modulator (5), a photodetector (6), and an electric vector network analyzer (7); the optical cavity includes an input terminal (101) and an output terminal (103) of an optical circulator; the first input terminal (501) of the electro-optic intensity modulator is connected to the output terminal of the tunable laser source (4), the second input port (502) of the electro-optic intensity modulator is connected to the output terminal of the electric vector network analyzer (7), the output terminal (503) of the electro-optic intensity modulator is connected to the input terminal (101) of the optical circulator in the optical cavity, the output terminal (103) of the optical circulator in the optical cavity is connected to the input terminal of the photodetector (6), and the output terminal of the photodetector (6) is connected to the input terminal of the electric vector network analyzer (7).

6. A control method for a microwave photonic filter, wherein the control method is applied to the microwave photonic filter of claim 5; characterized in that, The method includes the following steps: S1. Obtain an optical carrier from a tunable laser source (4) and transmit the optical carrier to an electro-optic intensity modulator (5). The single-frequency cosine microwave signal generated by the electro-optic intensity modulator (5) is modulated onto the optical carrier to obtain a modulated optical signal. S2. The modulated optical signal is transmitted to the optical ring cavity and subjected to spectrum-selective filtering to obtain the filtered optical signal; S3. The filtered optical signal is transmitted to the photodetector (6) and photoelectric conversion is performed to obtain an electrical signal.

7. The control method for the microwave photonic filter according to claim 6, characterized in that, S1 further includes the following steps: Based on the electric vector network analyzer (7), a single-frequency cosine microwave signal is generated by the following formula. : in, The frequency of the single-frequency cosine microwave signal. The amplitude of the single-frequency cosine microwave signal. It is a time vector; Set the center frequency of the optical carrier to The single-frequency cosine microwave signal is modulated onto the optical carrier by an electro-optic intensity modulator (5) to obtain the modulated optical signal. : in, Let be the impulse function.

8. The control method for the microwave photonic filter according to claim 7, characterized in that, S2 also includes the following steps: In the current cycle, the modulated optical signal enters from the input terminal (101) of the optical circulator, is transmitted to the first input terminal (201) of the coupler via the coupling terminal (102) of the optical circulator, and after optical coupling, reaches the first output terminal (203) and the second output terminal (204) of the coupler. The modulated optical signal reaching the second output terminal (204) of the coupler is discarded. The modulated optical signal reaching the first output terminal (203) of the coupler is reflected by the second optical element (302). After optical coupling, the modulated optical signal reaches the first input terminal (201) and the second input terminal (202) of the coupler. The modulated optical signal arriving at the first input terminal (201) of the coupler is used as the output optical signal and transmitted to the output terminal (103) of the optical circulator via the coupling terminal (102) of the optical circulator, and sent to the photodetector (6); the modulated optical signal arriving at the second input terminal (202) of the coupler is reflected by the first optical element (301) and together with the modulated optical signal of the next cycle received in the first input terminal (201) of the coupler, it serves as the input signal of the coupler (2) for the next cycle.

9. The control method for the microwave photonic filter according to claim 8, characterized in that, S2 also includes the following steps: The modulated optical signal is subjected to spectral selective filtering to obtain the filtered optical signal. : in, Let be the frequency domain transfer function of the optical ring cavity.

10. The control method for the microwave photonic filter according to claim 9, characterized in that, S3 also includes the following steps: Filtered optical signal Photoelectric conversion is performed to obtain an electrical signal. : The electrical signal The spectral envelope is directly used as the frequency domain transfer function of the microwave photonic filter; The difference between the maximum and minimum frequencies of the microwave signal is not less than the free spectral range (FSR) of the optical ring cavity. in, This is the time delay of light traveling one revolution in the optical cavity; The electrical signal is transmitted to the electric vector network analyzer (7), and the frequency transmission characteristics of the optical ring cavity are characterized by analyzing the center frequency and intensity changes of the input and output signals.

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