CN116155391B - Bandwidth and center frequency adjustable microwave photon filtering system - Google Patents

Abstract

The invention discloses a microwave photon filter system with adjustable bandwidth and center frequency. By taking polarization control optimization measures and optical link length control optimization measures, a method is adopted in which an optical signal initially filtered based on the Brillouin effect is interfered with an optical signal of the same source and wavelength to improve the out-of-band suppression of the microwave photon filter. At the same time, a radio frequency optical carrier signal of another wavelength is introduced through a wavelength division multiplexer for phase control of the system, thereby avoiding the problem of system phase drift without additionally increasing the complexity of the system. By means of loading linear frequency modulation and continuous wave synthesis signals on an intensity modulator, the center frequency and bandwidth of the filter are adjustable, thereby greatly improving the performance of the microwave photon filter system and having good practical value.

Description

A microwave photon filter system with adjustable bandwidth and center frequency

Technical Field

The invention relates to the technical field of microwave photon filtering systems, and in particular to a microwave photon filtering system with adjustable bandwidth and center frequency.

Background technique

Microwave photonic filter (MPF) modulates the microwave signal to be filtered onto an optical carrier, processes it through an optical system composed of various photonic devices, and then obtains the microwave signal of the required frequency through photoelectric detection. Microwave photonic filters are mainly used in microwave photonic links to achieve signal screening and selection optimization, and can eliminate channel interference and suppress noise. With the development of optical devices and optical communications, microwave photonic filters have been more widely used, mainly in the fields of wireless over fiber (ROF) communication systems, ultra-wideband signal generation systems, optoelectronic oscillators, satellite remote sensing, radar, etc. The structural design of microwave photonic filters almost always modulates microwave signals onto optical carriers through modulators, and achieves different frequency responses through different photonic devices. Tunability and reconfigurability are two important characteristics of microwave photonic filters, which have a significant impact on the filtering effect of the filter. Tunable microwave photonic filters refer to devices in the filter, such as light source devices, modulators, delay devices, etc., which change the passband center frequency of the filter or the frequency interval between the two filter passbands/stopbands. According to different implementation principles, it can be divided into: microwave photon filters based on stimulated Brillouin effect, microwave photon filters based on fiber parametric amplification principle and frequency transfer. According to different delay devices, it can be divided into: microwave photon filters based on fiber delay line, fiber ring microwave photon filters, fiber grating microwave photon filters, and microwave photon filters based on dispersion compensation fiber.

In the early days, the passband of microwave photon filters based on fiber delay lines and fiber gratings was multi-tapped, which limited the free spectral range and the passband center frequency was not easy to tune; later, microwave photon filters based on phase modulators and stimulated Brillouin scattering were developed. Microwave photon filters with tunable bandpass functions based on PM and SBS are based on the principle of Brillouin selective sideband amplification to achieve effective PM-AM conversion. When the phase-modulated sideband falls into the SBS gain spectrum, the corresponding sideband is amplified, and vice versa. However, optical filters based on the Brillouin effect often have narrow bandwidths, and the passband bandwidth is limited to the line width of the fiber Brillouin gain spectrum ~30MHz, so only narrowband filtering can be achieved. In the past, microwave photon filters introduced pump lasers and adjusted the wavelength of the pump lasers to adjust the center frequency of the filter, but the system required additional pump lasers, and the wavelength adjustment range of the pump lasers was limited.

Summary of the invention

In order to solve the technical problems existing in the background technology, the present invention proposes a microwave photon filtering system with adjustable bandwidth and center frequency.

The invention provides a microwave photon filter system with adjustable bandwidth and center frequency, comprising: a main laser module, an intensity modulator module, an optical amplifier module, a first optical circulator module, a phase modulator module, an optical isolator module, a wavelength division multiplexing module, a de-wavelength division multiplexing module, a first photodetector module, a second optical circulator module, an optical fiber module, a first optical coupler module and a second optical coupler module;

The optical output end of the main laser module is connected to the input end of the first optical coupler module, and the first output end of the first optical coupler module is connected to the intensity modulator module, the optical amplifier module and the A port of the first optical circulator module in sequence; the second output end of the first optical coupler module is connected to the phase modulator module, the optical isolator module, the optical fiber module and the B port of the first optical circulator module in sequence; the third output end of the first optical coupler module is connected to the first input end of the wavelength division multiplexing module, the common output end of the wavelength division multiplexing module is connected to the A end of the second optical circulator module, and the C end of the second optical circulator module is connected to the common input end of the de-wavelength division multiplexing module;

The C end of the first optical circulator module and the first output end of the de-wavelength division multiplexing module are respectively connected to the input end of the second optical coupler module, and the first photodetector module is connected to the output end of the second optical coupler module;

The intensity modulator module is provided with a central reference signal interface, the phase modulator module is provided with a signal interface to be filtered, and the output end of the first photoelectric detector module is a signal outlet after filtering.

Preferably, it also includes: a directly modulated laser module, an adjustable optical fiber delay module, a mixer module, a 1*2 radio frequency power divider module, a radio frequency phase detector module and a second photodetector module;

The optical output end of the direct-modulated laser module is connected to the second input end of the wavelength division multiplexing module, the 1*2 RF power splitter module has a phase-stable signal interface, the RF input end of the direct-modulated laser module is connected to the O port of the 1*2 RF power splitter module, the Q end of the mixer module is connected to the P port of the 1*2 RF power splitter module, and the R port of the mixer module is connected to the RF output port of the second photodetector module;

The input port of the radio frequency phase detector module is connected to the combining end of the mixer module, and the output of the radio frequency phase detector module is connected to the input control port of the adjustable optical fiber delay module.

Preferably, the wavelength of the directly modulated laser module is different from that of the master laser module.

Preferably, the main laser module is an external cavity semiconductor laser or a DFB laser.

Preferably, the intensity modulator module is a Mach-Zehnder intensity modulator.

Preferably, the optical fiber module is a long-distance single-mode optical fiber or a highly nonlinear optical fiber.

In the present invention, the proposed microwave photon filter system with adjustable bandwidth and center frequency, the light output by the main laser module is divided into three optical paths through the first optical coupler module, the first optical path passes through the intensity modulator module, the optical amplifier module and the A port of the first optical circulator module in sequence; the second optical path passes through the phase modulator module, the optical isolator module, the optical fiber module and the B port of the first optical circulator module in sequence; the third optical path passes through the first input end of the wavelength division multiplexing module, the A end of the second optical circulator module and the common input end of the de-wavelength division multiplexing module in sequence. By taking polarization control optimization measures and optical link length control optimization measures, the method of interfering the optical signal based on the initial filtering of the Brillouin effect with the same source and wavelength optical signal improves the out-of-band suppression of the microwave photon filter; at the same time, the radio frequency optical carrier signal of another wavelength is introduced through the wavelength division multiplexer for the phase control of the system, avoiding the problem of system phase drift, without additionally increasing the complexity of the system, and by loading the linear frequency modulation and continuous wave synthesis signal on the intensity modulator, the filter center frequency and bandwidth adjustable function is realized, so that the performance of the microwave photon filter system is greatly improved, and it has good practical value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of module connections of an implementation of a microwave photon filtering system with adjustable bandwidth and center frequency proposed by the present invention.

FIG. 2 is a schematic diagram of signal flow of an implementation of a microwave photon filtering system with adjustable bandwidth and center frequency proposed by the present invention.

Detailed ways

As shown in Figures 1 and 2, Figure 1 is a module connection diagram of an implementation of a microwave photon filter system with adjustable bandwidth and center frequency proposed by the present invention, and Figure 2 is a signal flow diagram of an implementation of a microwave photon filter system with adjustable bandwidth and center frequency proposed by the present invention.

1 and 2 , a microwave photon filter system with adjustable bandwidth and center frequency proposed by the present invention includes: a main laser module 1, an intensity modulator module 2, an optical amplifier module 3, a first optical circulator module 4, a phase modulator module 5, an optical isolator module 6, a wavelength division multiplexing module 8, a de-wavelength division multiplexing module 10, a first photodetector module 11, a second optical circulator module 15, an optical fiber module 17, a first optical coupler module 18 and a second optical coupler module 19;

The optical output end of the main laser module 1 is connected to the input end of the first optical coupler module 18, and the first output end of the first optical coupler module 18 is connected to the intensity modulator module 2, the optical amplifier module 3 and the A port of the first optical circulator module 4 in sequence; the second output end of the first optical coupler module 18 is connected to the phase modulator module 5, the optical isolator module 6, the optical fiber module 17 and the B port of the first optical circulator module 4 in sequence; the third output end of the first optical coupler module 18 is connected to the first input end of the wavelength division multiplexing module 8, the common output end of the wavelength division multiplexing module 8 is connected to the A end of the second optical circulator module 15, and the C end of the second optical circulator module 15 is connected to the common input end of the de-wavelength division multiplexing module 10;

The C end of the first optical circulator module 4 and the first output end of the de-WDM module 10 are respectively connected to the input end of the second optical coupler module 19, and the first photodetector module 11 is connected to the output end of the second optical coupler module 19;

The intensity modulator module 2 has a central reference signal interface, the phase modulator module 5 has a signal interface to be filtered, and the output end of the first photodetector module 11 is a filter signal outlet.

In the specific working process of the microwave photon filter system of this embodiment, first, the output light of the main laser module 1 is divided into three paths by the first optical coupler module 18. The first path of light passes through the intensity modulator module 2, the optical amplifier module 3 and the A port of the first optical circulator module 4 in sequence, and the second path of light passes through the phase modulator module 5 and the optical isolator module 6 in sequence and enters the optical fiber module 17. The third path of light passes through the first input end of the wavelength division multiplexing module 8, the second optical circulator module 15 and the de-wavelength division multiplexing module 10 in sequence. The C port of the first optical circulator module 4 and the first output end of the de-wavelength division multiplexing module 10 are connected to the two input ends of the optical coupler module 19.

The center reference signal F1 is loaded onto the intensity modulator module 2 through the radio frequency interface, and the center reference signal is a combination of a linear frequency modulation signal and a continuous wave signal. The signal to be filtered F2 is loaded onto the phase modulator module 5 through the radio frequency interface, and the filtered signal F4 is output from the radio frequency interface of the first photodetector module 11. Since the light input from the A port of the optical circulator module 4 will be output from the B port, and the light input from the B port will be output from the C port. Therefore, the A port of the first optical circulator is the input end of the output light of the optical amplifier, and the amplified light enters the optical fiber from the B port of the first optical circulator, generating a Brillouin effect, thereby filtering the F2 signal.

In the specific selection of the laser, the main laser module 1 is an external cavity semiconductor laser or a DFB laser, and the wavelength is selected from the C-band standard ITU wavelength. Similarly, the direct modulation laser module 7 can also adopt the same configuration, and the wavelength of the direct modulation laser module 7 is different from that of the main laser module 1, ensuring that it falls within the channel of the wavelength division multiplexing module 8.

In wavelength adjustment, the operating wavelength of the wavelength division multiplexing module 8 matches the selected laser wavelength and the designed combination.

In the actual selection of each functional module, the intensity modulator module 2 is a Mach-Zehnder intensity modulator. The optical fiber module 17 is a long-distance single-mode optical fiber or a highly nonlinear optical fiber to ensure the generation of the Brillouin effect.

In this embodiment, the proposed microwave photon filter system with adjustable bandwidth and center frequency improves the out-of-band suppression of the microwave photon filter by taking polarization control optimization measures and optical link length control optimization measures, and interfering the optical signal initially filtered based on the Brillouin effect with the optical signal of the same source and wavelength; at the same time, a radio frequency optical carrier signal of another wavelength is introduced through a wavelength division multiplexer for phase control of the system, thereby avoiding the problem of system phase drift without increasing the complexity of the system; and by loading linear frequency modulation and continuous wave synthesis signals on the intensity modulator, the center frequency and bandwidth of the filter are adjustable, so that the performance of the microwave photon filter system is greatly improved, and it has good practical value.

In a specific implementation, in order to stabilize the phase of the modulated signal, the microwave photon filter system of this embodiment further includes: a directly modulated laser module 7, an adjustable optical fiber delay module 9, a mixer module 12, a 1*2 RF power splitter module 13, a RF phase detector module 14 and a second photodetector module 16;

The optical output end of the direct-modulated laser module 7 is connected to the second input end of the wavelength division multiplexing module 8, the 1*2 RF power splitter module 13 has a phase-stable signal interface, the RF input end of the direct-modulated laser module 7 is connected to the O port of the 1*2 RF power splitter module 13, the Q end of the mixer module 12 is connected to the P port of the 1*2 RF power splitter module 13, and the R port of the mixer module 12 is connected to the RF output port of the second photodetector module 16;

The input port of the RF phase detector module 14 is connected to the combining end of the mixer module 12 , and the output of the RF phase detector module 14 is connected to the input control port of the adjustable optical fiber delay module 9 .

In the specific phase stabilization work, the RF signal F3 used for phase stabilization is connected to the input end of the 1*2 RF power divider module 13, and its O port is connected to the RF input port of the direct-modulated laser module 7. The P port of the 1*2 RF power divider module is connected to the Q port of the mixer module 12. The R port of the mixer module 12 is connected to the RF output port of the second photodetector module 16. The input port of the RF phase detector module 14 is connected to the combining end of the mixer module 12. The output of the RF phase detector module 14 is connected to the input control port of the adjustable fiber delay module 9. By adjusting the width of the linear frequency modulation signal loaded on the intensity modulator and the center frequency of the continuous wave signal, and adjusting the length of the adjustable fiber delay module 9 and the state of the polarization controller, the light of the M port and the N port interferes to achieve an ideal filtering effect, and at the same time realizes the functions of adjustable bandwidth and center frequency.

In the phase stabilization process, the phase detection result of the radio frequency phase detector module 14 directly controls the adjustable optical fiber delay module 9, and the maximum delay amount of the adjustable optical fiber delay module 9 is selected according to the system.

The system of the present invention is simple and can realize the adjustable functions of filter center frequency and bandwidth through polarization control, phase-stabilization design, and adjustment of the optically adjustable optical fiber delay module. It is suitable for all-optical processing of microwave signals, optical wireless communication systems, and the like.

The above description is only a preferred specific implementation manner 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 scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims (5)

1. A microwave photon filter system with adjustable bandwidth and center frequency, characterized in that it comprises: a main laser module (1), an intensity modulator module (2), an optical amplifier module (3), a first optical circulator module (4), a phase modulator module (5), an optical isolator module (6), a wavelength division multiplexing module (8), a de-wavelength division multiplexing module (10), a first photodetector module (11), a second optical circulator module (15), an optical fiber module (17), a first optical coupler module (18) and a second optical coupler module (19); The optical output end of the main laser module (1) is connected to the input end of the first optical coupler module (18); the first output end of the first optical coupler module (18) is connected in sequence to the intensity modulator module (2), the optical amplifier module (3) and the A port of the first optical circulator module (4); the second output end of the first optical coupler module (18) is connected in sequence to the phase modulator module (5), the optical isolator module (6), the optical fiber module (17) and the B port of the first optical circulator module (4); the third output end of the first optical coupler module (18) is connected to the first input end of the wavelength division multiplexing module (8); the common output end of the wavelength division multiplexing module (8) is connected to the A end of the second optical circulator module (15); and the C end of the second optical circulator module (15) is connected to the common input end of the de-wavelength division multiplexing module (10); The C end of the first optical circulator module (4) and the first output end of the de-wavelength division multiplexing module (10) are respectively connected to the input end of the second optical coupler module (19), and the first photodetector module (11) is connected to the output end of the second optical coupler module (19); The intensity modulator module (2) has a central reference signal interface, the phase modulator module (5) has a signal interface to be filtered, and the output end of the first photodetector module (11) is a filtered signal outlet; It also includes: a directly modulated laser module (7), an adjustable optical fiber delay module (9), a mixer module (12), a 1*2 radio frequency power divider module (13), a radio frequency phase detector module (14) and a second photoelectric detector module (16); The optical output end of the direct-modulated laser module (7) is connected to the second input end of the wavelength division multiplexing module (8); the 1*2 radio frequency power splitter module (13) has a phase-stable signal interface; the radio frequency input end of the direct-modulated laser module (7) is connected to the O port of the 1*2 radio frequency power splitter module (13); the Q end of the mixer module (12) is connected to the P port of the 1*2 radio frequency power splitter module (13); and the R port of the mixer module (12) is connected to the radio frequency output port of the second photodetector module (16); The input port of the radio frequency phase detector module (14) is connected to the combining end of the mixer module (12), and the output of the radio frequency phase detector module (14) is connected to the input control port of the adjustable optical fiber delay module (9). 2. The microwave photon filter system with adjustable bandwidth and center frequency according to claim 1, characterized in that the wavelength of the directly modulated laser module (7) is different from that of the main laser module (1). 3. The microwave photon filter system with adjustable bandwidth and center frequency according to claim 1, characterized in that the main laser module (1) is an external cavity semiconductor laser or a DFB laser. 4. The microwave photon filter system with adjustable bandwidth and center frequency according to claim 1, characterized in that the intensity modulator module (2) is a Mach-Zehnder intensity modulator. 5. The microwave photon filtering system with adjustable bandwidth and center frequency according to claim 1, characterized in that the optical fiber module (17) is a long-distance single-mode optical fiber or a highly nonlinear optical fiber.