CN115267974A - Narrow-band tunable microwave photon filter based on Brillouin fiber laser - Google Patents
Narrow-band tunable microwave photon filter based on Brillouin fiber laser Download PDFInfo
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Abstract
The invention relates to the field of microwave photon signal processing, and discloses a narrow-band tunable microwave photon filter based on a Brillouin optical fiber laser, wherein a narrow-linewidth continuous wave optical fiber laser I is sequentially connected with a polarization controller I, a phase modulator and an annular cavity I; the narrow-linewidth continuous wave optical fiber laser II is sequentially connected with a polarization controller II, an erbium-doped optical fiber amplifier and an annular cavity I, and the annular cavity I is connected with a photoelectric detector, a vector network analyzer and a phase modulator. The invention provides a narrow-linewidth double-ring Brillouin laser and microwave photon filtering structure design which are combined, narrow-band filtering is realized by utilizing the characteristic of an effective narrow stimulated Brillouin scattering gain spectrum of the Brillouin optical fiber laser, the technical problem that the conventional microwave photon filter realizes sub-kHz-level single-pass-band filtering is solved, in addition, a dual-wavelength structure is adopted, modulated light and Brillouin pumping light are respectively provided, and the central frequency of a pass band of the filter is tuned by changing the wavelength of the modulated light, so that a narrow-band tunable microwave photon filter is finally realized.
Description
Technical Field
The invention relates to the field of microwave photon signal processing, in particular to a narrow-band tunable microwave photon filter based on a Brillouin fiber laser.
Background
The traditional electronic filter device is limited by the electronic transmission rate, so that the control and the processing of high-frequency broadband signals are difficult to complete; the microwave photon filtering technology for processing optical carrier microwave signals based on various optical effects has been paid attention to by people for many years due to the excellent characteristics of large bandwidth, low loss, electromagnetic interference resistance and the like and the potential of overcoming the limitation of electronic transmission, and becomes a key technology in the next generation of wireless radio frequency system.
Due to the increasing complexity of radio frequency systems, microwave photonic filters are evolving in the forward direction towards high frequencies, high Q-values and tunability. The quality factor Q value is an important index for measuring the selection capability of the filter on the target frequency band, and the higher the Q value is, the stronger the frequency selection capability of the filter is. The key index for determining the Q value is the 3dB bandwidth delta f of the filter passband 3dB From
Can be obtained as Δ f 3dB The smaller the Q value is, the larger the Q value is, and the fine frequency components of the signal to be measured can be filtered out. Therefore, the realization of an ultra-narrow bandwidth microwave photonic filter with a large tuning range has become a leading edge and a hot spot of recent research.
A variety of tunable, narrow bandwidth microwave photonic filters have been proposed. For example, a narrow-band and adjustable microwave photonic filter realized by using a phase modulator and a super-structure fiber Bragg grating has a 3dB bandwidth of 143MHz and a tunable range of 0.4-6.4 GHz; the broadband tunable microwave photonic filter is realized by using four-wave mixing of a distributed feedback semiconductor laser based on optical injection, the 3dB bandwidth and the side mode suppression ratio are respectively 61.2MHz and 25dB, and the frequency tuning range is 27.72GHz. Patent document No. CN105589221B discloses a "tunable dual-passband microwave photonic filter based on stimulated brillouin scattering", which performs closed-loop control on an electro-optical modulator by using a bias feedback control module, outputs a stable dual-sideband modulation signal with narrow-wave suppression, and effectively reduces the gain spectrum width of the stimulated brillouin scattering by using stimulated brillouin scattering in combination with stokes gain and anti-stokes loss in an optical fiber, thereby realizing amplitude response of the dual-passband filter, which can realize a narrow bandwidth of 20.1MHz, can realize tuning in a range of 1.8 GHz-20 GHz, and obtain a stop-band suppression ratio exceeding 35 dB.
The bandwidth of the existing microwave photon filter is mostly concentrated on the magnitude of MHz, the structure for realizing the narrow band and the tuning function is mostly complex, the narrow band and the tuning function are mostly difficult to have the functions of wide frequency tuning range and kHz and even sub-kHz narrow band filtering, and the urgent requirements of the advanced technical fields such as high-resolution microwave photon sensing, high-purity spectrum microwave photon signal generation, high-precision microwave photon radar and the like on the ultra-narrow bandwidth tunable microwave photon filter cannot be met. In order to solve the problems, the invention provides a narrow-band tunable microwave photonic filter based on a Brillouin fiber laser.
Disclosure of Invention
The invention aims to solve the problem that the traditional electronic filter device is difficult to control and process high-frequency broadband signals; the embodiment of the invention provides a narrow-bandwidth tunable microwave photonic filter based on a Brillouin fiber laser, which solves the technical problem that the existing microwave photonic filter is difficult to have the functions of wide frequency tuning range and narrow-band filtering of kHz and even sub-kHz; by combining the narrow-linewidth Brillouin laser with the microwave photonic filter and utilizing the obvious gain spectrum linewidth compression characteristic of the Brillouin laser, the filter passband is narrowed to the sub-kHz magnitude, and the narrow-band tunable microwave photonic filter based on the Brillouin fiber laser has the advantages of being ultra-narrow-band, tunable, simple in structure, high in out-of-band rejection ratio and the like.
The invention is realized by adopting the following technical scheme:
a narrow-band tunable microwave photon filter based on a Brillouin optical fiber laser is characterized in that the output end of a narrow-linewidth continuous wave optical fiber laser I is connected with the input end of a polarization controller I, the output end of the polarization controller I is connected with an a port of a phase modulator, a c port of the phase modulator is connected with an a port of an optical fiber coupler I, and a b port of the optical fiber coupler I is connected with an a port of a single-mode optical fiber I; the output end of the narrow-linewidth continuous wave fiber laser II is connected with the input end of a polarization controller II, the output end of the polarization controller II is connected with the input end of an erbium-doped fiber amplifier, the output end of the erbium-doped fiber amplifier is connected with an a port of an optical circulator, a b port of the optical circulator is connected with a b port of a single-mode fiber I, a c port of the optical circulator is connected with an a port of an optical fiber coupler II, a c port of the optical fiber coupler II is connected with the input end of the single-mode fiber II, the output end of the single-mode fiber II is connected with a port d of the optical fiber coupler II, a b port of the optical fiber coupler II is connected with an a port of an optical fiber coupler III, a b port of the optical fiber coupler III is connected with the input end of the polarization controller III, and a c port of the optical fiber coupler I at the output end of the polarization controller III is connected; and the c port of the optical fiber coupler III is connected with the input end of the photoelectric detector, the output end of the photoelectric detector is connected with the input end of the vector network analyzer, and the output end of the vector network analyzer is connected with the b port of the phase modulator.
In implementation, the narrow-band tunable microwave photonic filter based on the brillouin fiber laser provided by the invention is characterized in that a narrow-line-width continuous wave fiber laser i is a tunable narrow-line-width laser for emitting a light carrier, the output end of the narrow-line-width continuous wave fiber laser i is connected with the input end of a polarization controller i, the output end of the polarization controller i is connected with an a port of a phase modulator, a c port of the phase modulator is connected with an a port of a fiber coupler i, the fiber coupler i has a splitting ratio of 50, a b port of the fiber coupler i is connected with an a port of a single-mode fiber i, and the length of the single-mode fiber i is 100m; the narrow linewidth continuous wave fiber laser II is a tunable narrow linewidth laser for emitting pump light, the output end of the narrow linewidth continuous wave fiber laser II is connected with the input end of a polarization controller II, and the polarization controller IIThe output end of the optical fiber amplifier is connected with the input end of an erbium-doped optical fiber amplifier, the output end of the erbium-doped optical fiber amplifier is connected with an a port of an optical circulator, a b port of the optical circulator is connected with a b port of a single-mode optical fiber I to form a narrow-linewidth Brillouin optical fiber laser, the 3dB bandwidth of the kHz magnitude is obtained, a c port of the optical circulator is connected with an a port of an optical fiber coupler II, the optical fiber coupler II is a fiber splitting ratio of 50; the b port of the optical fiber coupler II is connected with the a port of the optical fiber coupler III, the splitting ratio of the optical fiber coupler III is 90, the a port is an input port, the b port is a 90% output port, the c port is a 10% output port, the b port of the optical fiber coupler III is connected with the input end of the polarization controller III, the c port of the optical fiber coupler I at the output end of the polarization controller III is connected, the optical fiber coupler I, the single-mode optical fiber I, the optical circulator, the optical fiber coupler II, the optical fiber coupler III and the polarization controller III are connected to form a Brillouin laser resonant cavity to form a ring cavity I, the ring cavity I and the ring cavity II are cascaded to form a ring Fabry-Perot resonant cavity to form a vernier effect, different periodic resonances of the two ring cavities are utilized, an edge mode is effectively inhibited, and a required frequency band signal is filtered; and the c port of the optical fiber coupler III is connected with the input end of the photoelectric detector, the output end of the photoelectric detector is connected with the input end of the vector network analyzer, and the output end of the vector network analyzer is connected with the b port of the phase modulator. When in use, the narrow linewidth continuous wave fiber laser I emits a signal with a center frequency f c1 Enters the phase modulator from the a port of the phase modulator through a polarization controller I as a carrier, and generates a frequency f from a vector network analyzer RF The radio frequency signal enters the phase modulator through a port b to perform double-sideband frequency sweeping modulation on a carrier, the modulated signal is output from a port c of the phase modulator, enters the optical fiber coupler I through a port a of the optical fiber coupler I and is output from a port b, and enters a single mode through a port a of the single mode optical fiber IIn the optical fiber I; the center frequency of the emitted signal from the narrow linewidth continuous wave fiber laser II is f c2 The pump light frequency f can be changed by changing the laser wavelength of the narrow-linewidth continuous wave fiber laser II c2 So as to change the center frequency of the stimulated Brillouin scattering gain spectrum and realize the stable tunable function of the microwave photon filter, pumping light enters the erbium-doped fiber amplifier through the polarization controller II to be amplified to exceed the stimulated Brillouin scattering threshold value, then is input from the port a of the optical circulator and output from the port b, then enters from the port b of the single-mode fiber I, the stimulated Brillouin scattering is excited by interaction in the single-mode fiber I, and the upper sideband f of a modulation signal c1 +f RF Amplified by a Brillouin gain spectrum with the center frequency of f c2 -f B Wherein, f B Is a brillouin frequency shift; the modulation signal amplified by the Brillouin gain is output from a port b of the optical circulator and a port c of the optical circulator, is injected into a port a of the optical fiber coupler II, enters a ring cavity II formed by connecting the port c of the optical fiber coupler II, the single-mode optical fiber II and a port d of the optical fiber coupler II from the port c, is output from the port b of the optical fiber coupler after the ring cavity II resonates, and enters a port a of the optical fiber coupler III to reach the optical fiber coupler III with the splitting ratio of 90; the modulation signal is divided into a first laser beam and a second laser beam after passing through an optical fiber coupler III, 90% of the first laser beam is output through a port b of the optical fiber coupler III, then is injected into the optical fiber coupler I from a port c of the optical fiber coupler I in a counterclockwise mode through a polarization controller III to complete primary resonance, and then is subjected to multiple resonance in an annular cavity I formed by connecting the optical fiber coupler I, a single-mode optical fiber I, an optical circulator, an optical fiber coupler II, the optical fiber coupler III and the polarization controller III, and the modulation signal output from the port c of the phase modulator is input into the annular cavity I through the port b of the optical fiber coupler I and interacts with the stimulated Brillouin scattering signal; 10% second laser is input into a photoelectric detector through a c port of the optical fiber coupler III, and a signal subjected to photoelectric conversion by the photoelectric detector is input into a vector network analyzer to measure amplitude frequency response to obtain the proposed signalThe filter characteristics of a narrow-band tunable microwave photonic filter.
Compared with the prior art, the invention has the following beneficial effects: the narrow-linewidth Brillouin laser is combined with the microwave photon filter, the image is observed by utilizing the obvious gain spectrum linewidth compression characteristic of the Brillouin laser, the side mode of the microwave photon filter with the single-ring cavity structure can be obviously inhibited, the side mode inhibition ratio is 25dB, the remarkable breakthrough is achieved on the 3dB bandwidth narrowing, the filter passband is narrowed to the kHz magnitude, the 3dB bandwidth of the sub kHz magnitude is obtained, and the passband bandwidth of the filter is greatly narrowed. The filter passband can be stably tuned by simply changing the wavelength of the pump light, and the design problem of the microwave photonic filter with a large tuning range and an ultra-narrow filter bandwidth is solved. The microwave photon filter can be stably tuned in the frequency range of 0-20 GHz, the out-of-band rejection ratio is about 20dB, and the 3dB bandwidth and the maximum Q value are respectively 114Hz and 1.753 multiplied by 10 8 The tunable filter has extremely high frequency selectivity and a large tunable range, and has great potential in the aspects of realizing filtering bandwidth of kHz and below, high rejection ratio and tunable single-pass band filtering.
Compared with the characteristic that a single ring-shaped resonant cavity is narrow in line width of the stimulated Brillouin scattering gain, the vernier effect formed by the ring-shaped Fabry-Perot resonant cavity formed by cascading the ring-shaped cavities R2 and R1 is utilized, the double-ring-cavity structure can provide a higher line width compression ratio, greatly inhibits side modes, and is beneficial to realization of a microwave photon filter with a higher Q value. Compared to self-induced fiber bragg gratings, circulator-based ring cavities have the advantage that the brillouin pump frequency does not need to be matched to the cavity mode, there is no additional cavity attenuation except for the intrinsic loss of the device, and it is difficult to generate higher order stokes due to the low nonlinear coefficient of single-mode fibers. A narrow-band tunable microwave photonic filter based on a brillouin fiber laser is an effective solution for obtaining a narrow-band tunable microwave filter.
Drawings
Fig. 1 shows a schematic structural view of the present invention.
FIG. 2 is a schematic diagram of a narrow-band tunable microwave photonic filter based on a Brillouin fiber laser provided in an embodiment of the present invention;
wherein a is the output frequency f of the narrow linewidth continuous wave fiber laser I c1 Optical carrier wave of, radio frequency signal f from vector network analyzer RF Performing a spectrogram of the double-sideband modulated signal through a phase modulator;
b is the Brillouin pumping optical frequency f output by the narrow linewidth continuous wave optical fiber laser II c2 The spectrum is emitted into the single-mode fiber I and generated in the stimulated Brillouin process;
c is the upper sideband f of the modulated signal c1 +f RF A spectrogram amplified by a brillouin gain spectrum; the center frequency and bandwidth of the Brillouin gain spectrum are respectively f c2 -f B And Δ f B ；
d is a spectrogram of periodic resonance of the annular cavity I;
and e is a Brillouin gain spectrogram with vernier effect suppression side modes and narrow pressure formed by matching free spectral ranges of the annular cavity I and the annular cavity II.
Fig. 3 shows a vernier effect schematic diagram adopted by the narrow-band tunable microwave photonic filter based on the brillouin fiber laser provided in the embodiment of the present invention.
Fig. 4 shows frequency response diagrams of microwave photonic filters corresponding to different structures of the narrow-band tunable microwave photonic filter based on the brillouin fiber laser provided in the embodiment of the present invention.
Fig. 5 shows a tunable characteristic diagram of the center frequency of the narrow-band tunable microwave photonic filter based on the brillouin fiber laser provided in the embodiment of the present invention, specifically, a diagram of a change of the pump optical wavelength output by the narrow-linewidth continuous wave fiber laser ii in a range from 1550.2320 to 1550.3920 nm.
In the figure: the optical fiber laser comprises a 1A-narrow linewidth continuous wave optical fiber laser I, a 1B-narrow linewidth continuous wave optical fiber laser II, a 2A-polarization controller I, a 2B-polarization controller II, a 2C-polarization controller III, a 3-phase modulator, a 4A-optical fiber coupler I, a 4B-optical fiber coupler II, a 4C-optical fiber coupler III, a 5A-single mode optical fiber I, a 5B-single mode optical fiber II, a 6-erbium-doped optical fiber amplifier, a 7-optical circulator, an 8-photoelectric detector, a 9-vector network analyzer, an R1-annular cavity I and an R2-annular cavity II.
Detailed Description
The following describes an embodiment of the present invention with reference to the drawings.
A narrow-band tunable microwave photon filter based on a Brillouin optical fiber laser is disclosed, as shown in figure 1, a narrow-linewidth continuous wave optical fiber laser I1A is a tunable narrow-linewidth laser for emitting optical carriers, the output end of the narrow-linewidth continuous wave optical fiber laser I1A is connected with the input end of a polarization controller I2A, the output end of the polarization controller I2A is connected with an a port of a phase modulator 3, a c port of the phase modulator 3 is connected with an a port of an optical fiber coupler I4A, the optical fiber coupler I4A has a splitting ratio of 50, a b port of the optical fiber coupler I4A is connected with an a port of a single-mode optical fiber I5A, and the length of the single-mode optical fiber I5A is 100m; the narrow linewidth continuous wave optical fiber laser II 1B is a tunable narrow linewidth laser for transmitting pump light, a single mode optical fiber I5A and a single mode optical fiber II 5B which stimulate Brillouin scattering effect are arranged in the same thermostat to avoid errors caused by temperature drift, the output end of the narrow linewidth continuous wave optical fiber laser II 1B is connected with the input end of a polarization controller II 2B, the output end of the polarization controller II 2B is connected with the input end of an erbium-doped optical fiber amplifier 6, the output end of the erbium-doped optical fiber amplifier 6 is connected with an a port of an optical circulator 7, a B port of the optical circulator 7 is connected with a B port of the single mode optical fiber I5A, the Brillouin optical fiber laser with a narrow line width is formed, a 3dB bandwidth of a kHz magnitude is obtained, a port c of an optical circulator 7 is connected with a port a of an optical fiber coupler II 4B, the optical fiber coupler II 4B is a fiber splitting ratio of 50; the B port of the optical fiber coupler II 4B is connected with the a port of the optical fiber coupler III 4C, the optical fiber coupler III 4C is a fiber splitting ratio of 90.
When in use, the narrow linewidth continuous wave fiber laser I1A emits a signal with a center frequency f c1 Enters the phase modulator 3 from the a port of the phase modulator 3 through the polarization controller I2A as a carrier wave, and generates a frequency f from the vector network analyzer 9 RF The radio frequency signal enters a carrier through a port b of the phase modulator 3 to carry out double-sideband frequency sweeping modulation, the modulated signal is output from a port c of the phase modulator 3, enters the optical fiber coupler I4A through a port a of the optical fiber coupler I4A and is output from a port b, and enters the single-mode optical fiber I5A through a port I5 Aa of the single-mode optical fiber; the center frequency of the light emitted by the narrow linewidth continuous wave fiber laser II 1B is f c2 The pump light frequency f can be changed by changing the laser wavelength of the narrow-linewidth continuous wave fiber laser II 1B c2 Thereby, the purpose of changing the center frequency of the stimulated Brillouin scattering gain spectrum is achieved, the stable tunable function of the microwave photon filter is realized, the pump light is tuned to the optimal polarization state through the polarization controller II 2B, enters the erbium-doped optical fiber amplifier 6 to amplify the power until the power exceeds the stimulated Brillouin scattering threshold value, then is input through the port a of the optical circulator 7 and is output through the port B, and then is transmitted and enters through the port B of the single-mode optical fiber I5A along the opposite direction of the modulated optical signal, and the pump light interacts with the stimulated Brillouin scattering gain spectrum in the single-mode optical fiber I5AStimulated Brillouin scattering is emitted, and the upper sideband f of a modulated signal c1 +f RF Amplified by the Brillouin gain spectrum with the center frequency of f c2 -f B Wherein f is B Is a brillouin frequency shift; the modulation signal amplified by the Brillouin gain is output from a port B of the optical circulator 7 and a port C of the optical circulator, is injected into a port a of the optical fiber coupler II 4B, enters a ring cavity II R2 formed by connecting the port C of the optical fiber coupler II 4B, the single-mode optical fiber II 5B and a port d of the optical fiber coupler II 4B from the port C, is output from a port B of the optical fiber coupler 4B after the ring cavity II R2 resonates, and enters a port a of the optical fiber coupler III 4C to reach the optical fiber coupler III 4C with the splitting ratio of 90; the modulation signal is divided into a first laser beam and a second laser beam after passing through an optical fiber coupler III 4C, 90% of the first laser beam is output through a port B of the optical fiber coupler III 4C, then is injected into the optical fiber coupler I4A counterclockwise through a port C of the optical fiber coupler I4A after passing through a polarization controller III 2C to complete primary resonance, then is subjected to multiple resonance in an annular cavity IR 1 formed by connecting the optical fiber coupler I4A, a single-mode optical fiber I5A, an optical circulator 7, an optical fiber coupler II 4B, the optical fiber coupler III 4C and the polarization controller III 2C, and the modulation signal output from the port C of a phase modulator 3 is input into the annular cavity IR 1 through the port B of the optical fiber coupler I4A to interact with a stimulated Brillouin scattering signal; 10% of second beam laser is input into the photoelectric detector 8 through a port C of the optical fiber coupler III 4C, and a signal subjected to photoelectric conversion by the photoelectric detector 8 is input into the vector network analyzer 9 to measure the amplitude response, so that the filter characteristic of the provided narrow-band tunable microwave photonic filter is obtained.
The adopted working principle is as follows: the Brillouin optical fiber laser is formed by the main resonant cavity to narrow the spectral line width after the interaction of a Brillouin gain spectrum and an optical modulation signal by using the double-annular resonant cavity formed by the main cavity with the cavity length of 100m and the auxiliary cavity with the cavity length of 10m, and the side modes are effectively inhibited by using the vernier effect formed by different periodic resonances of the double-annular cavity, so that the ultra-narrow-band microwave photon filtering based on the Brillouin laser is realized.
As shown in fig. 2: the center frequency of the microwave photonic filter can be expressed as:
f pass ＝f c2 -f B
from the above formula, by tuning the frequency f c2 Changing the center frequency f of the microwave photonic filter pass And tuning the unmodulated signal frequency f c1 The limitation of (2).
As shown in fig. 3: Δ f B Frequency shift f associated with stimulated Brillouin scattering pump light for stimulated Brillouin gain spectral bandwidth B Is defined as:
f B ＝(2ν A /c)ν P
wherein v is A Representing the speed of sound in the medium, c the speed of vacuum light, v P Represents the optical frequency of the pump light; f. of B And about 10.737GHz in the 1550nm wavelength range. Free spectral range FSR of two ring cavities according to vernier effect 1 ，FSR 2 The effective FSR with the double ring cavity structure satisfies the following conditions:
FSR＝n 1 FSR 1 ＝n 2 FSR 2
in the formula, FSR 1 Corresponding ring cavity IR 1 ；FSR 2 Corresponding ring cavity IIR 2 ；n m (m =1,2) is an integer. That is, the effective free spectral range FSR of the double ring cavity structure is FSR 1 And FSR 2 The least common multiple of;
the free spectral ranges of ring cavity ir 1 and ring cavity iir 2 are given by:
in the formula, L m (m =1, 2) is the ring length of ring cavity ir 1 and ring cavity ir 2; the effective refractive index n =1.468, L in this embodiment 1 ＝100m，L 2 =10m; the free spectral ranges of the annular cavity I R1 and the annular cavity II R2 are 1.86MHz and 18.6MHz respectively; the microwave photonic filter has an effective free spectral range of 18.6MHz. When the effective free spectral range exceeds the Brillouin gain bandwidth and the gain is greater than the loss, the laser mode only satisfies the ring cavity IR at the same time1 and ring cavity IIR 2.
As shown in fig. 4: the 3dB bandwidth of the Brillouin gain spectrum is about 9.926MHz, and in this example only ring cavity IR is added 1 The 3dB bandwidth of the microwave photonic filter is narrowed to sub-KHz levels. But in the embodiment cascaded ring cavities IIR 2 Then, a double-ring cavity structure is formed, and the 3dB bandwidth of the microwave photon filter is further reduced to a hundred hertz order; compared with images of a single-ring cavity structure and a double-ring cavity structure, the side mode of the microwave photon filter with the single-ring cavity structure is obviously inhibited, and the side mode inhibition ratio is 19dB, so that the microwave photon filter disclosed by the embodiment makes an obvious breakthrough in the aspect of 3dB bandwidth narrowing, and can reach the sub-kHz magnitude. At 19.98GHz simultaneously, by the formula Q = f/delta f 3dB Calculated Q =1.753 × 10 8 The microwave photonic filter disclosed by the invention has extremely high selectivity and a larger tunable range, and has huge potential in the aspect of realizing tunable single-passband filtering with high suppression ratio of sub-kHz-level bandwidth.
As shown in fig. 5: when the wavelength is changed in the range of 1550.2320 to 1550.3920nm, the passband of the microwave photonic filter is stably tuned to 2-20GHz, and the out-band rejection exceeds 25dB
The relationship between the available wavelength λ and the frequency f is in inverse proportion, wherein f represents the frequency of the stimulated Brillouin scattering pump light, λ represents the wavelength of the stimulated Brillouin scattering pump light, and the light speed c =3 × 10 8 m/s. The minimum tuning precision in the embodiment depends on the minimum tuning precision of the narrow-linewidth continuous wave fiber laser ii 1B, and the tuning range and the tuning precision can be further improved by improving the working bandwidth and the tuning precision of the device.
The 3dB bandwidth delta f of the microwave photonic filter in the embodiment pass The side mode suppression ratio is small in fluctuation in a tuning range; the main reasons for this variation are temperature variations and the annular chamber IR of the embodiment 1 Annular cavity IIR 2 The matching problem between free spectral ranges. By adjusting the control of the polarizationThe third 2C system solves the matching problem between the two ring cavities and maintains parallel polarization between the pump and stokes waves in the optical path.
The scope of the invention is not limited to the above embodiments, and various modifications and changes may be made by those skilled in the art, and any modifications, improvements and equivalents within the spirit and scope of the invention should be included.
Claims (5)
1. A narrow-band tunable microwave photon filter based on a Brillouin fiber laser is characterized in that: the optical fiber coupler comprises a narrow-linewidth continuous wave optical fiber laser I (1A) and a narrow-linewidth continuous wave optical fiber laser II (1B), wherein the output end of the narrow-linewidth continuous wave optical fiber laser I (1A) is connected with the input end of a polarization controller I (2A), the output end of the polarization controller I (2A) is connected with an a port of a phase modulator (3), a c port of the phase modulator (3) is connected with an a port of an optical fiber coupler I (4A), and a B port of the optical fiber coupler I (4A) is connected with an a port of a single-mode optical fiber I (5A); the output end of the narrow linewidth continuous wave fiber laser II (1B) is connected with the input end of a polarization controller II (2B), the output end of the polarization controller II (2B) is connected with the input end of an erbium-doped fiber amplifier (6), the output end of the erbium-doped fiber amplifier (6) is connected with the port a of an optical circulator (7), the port B of the optical circulator (7) is connected with the port B of a single-mode fiber I (5A), the port C of the optical circulator (7) is connected with the port a of a fiber coupler II (4B), the port C of the fiber coupler II (4B) is connected with the input end of a single-mode fiber II (5B), the output end of the single-mode fiber II (5B) is connected with the port d of a fiber coupler II (4B), the port B of the fiber coupler II (4B) is connected with the port a of a fiber coupler (4C), the port B of the fiber coupler II (4C) is connected with the input end of a polarization controller III (2C), and the port B of the port of the fiber coupler III (4C) is connected with the output end of a polarization controller III A; and a port C of the optical fiber coupler III (4C) is connected with an input end of a photoelectric detector (8), an output end of the photoelectric detector (8) is connected with an input end of a vector network analyzer (9), and an output end of the vector network analyzer (9) is connected with a port b of the phase modulator (3).
2. The narrow-band tunable microwave photonic filter based on the Brillouin fiber laser of claim 1, wherein: the optical fiber coupler I (4A), the single-mode optical fiber I (5A), the optical circulator (7), the optical fiber coupler II (4B), the optical fiber coupler III (4C) and the polarization controller III (2C) are connected to form an optical resonant cavity to form an annular cavity I (R1); and the c port of the optical fiber coupler II (4B), the single-mode optical fiber II (5B) and the d port of the optical fiber coupler II (4B) are connected to form an annular cavity II (R2).
3. The narrow-band tunable microwave photonic filter based on the Brillouin fiber laser of claim 1, wherein: the fiber coupler III (4C) is a fiber splitting ratio of 90, a port a is an input port, a port b is a 90% output port, and a port C is a 10% output port; the splitting ratio of the optical fiber coupler I (4A) and the splitting ratio of the optical fiber coupler II (4B) are both 50.
4. The narrow-band tunable microwave photonic filter based on the Brillouin fiber laser in claim 1, wherein: the narrow linewidth continuous wave fiber laser I (1A) is a tunable narrow linewidth laser for emitting optical carriers, and the narrow linewidth continuous wave fiber laser II (1B) is a tunable narrow linewidth laser for emitting pump light.
5. The narrow-band tunable microwave photonic filter based on the Brillouin fiber laser of claim 1, wherein: the length of the single-mode optical fiber I (5A) is 100m, and the length of the single-mode optical fiber II (5B) is 10m.
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