Tunable narrow-linewidth microwave photonic oscillator based on forward Brillouin scattering

Abstract

The invention belongs to the technical field of microwave photons and optical communication, particularly relates to a tunable narrow-linewidth microwave photonic oscillator based on forward Brillouin scattering, and solves the technical problems that an existing microwave photon generation method is complex in structure and poor in tunability, and linewidth cannot meet requirements. The erbium-doped optical fiber amplifier is connected to a first optical fiber coupler through a filter, two output ends of the first optical fiber coupler are respectively connected to a third optical fiber coupler and a second optical fiber coupler, and two output ends of the second optical fiber coupler are respectively connected to a spectrograph and are sequentially connected with a photoelectric detector and a spectrum analyzer; two output ends of the third optical fiber coupler are respectively connected to an input end c of a fourth optical fiber coupler through a first polarization controller and a first single-mode optical fiber and connected to an input end b of the fourth optical fiber coupler through a second polarization controller and a second single-mode optical fiber in sequence; and the fourth optical fiber coupler is connected to an erbium-doped optical fiber amplifier through a third polarization controller.

Description

Technical Field

[0001] The invention relates to the technical field of microwave photons and optical communications, and in particular to a tunable narrow-linewidth microwave photon oscillator based on forward Brillouin scattering. Background Art

[0002] With the development of the times, microwave photonics are being applied in more and more fields, including battlefield communications, electronic information warfare, broadband communications, precision measurement, etc. These application scenarios require microwave photonic systems to improve in frequency, bandwidth, dynamic adjustable range and anti-interference ability, thereby improving the performance of microwave photonic systems. This has led to great challenges for microwave photonic technology.

[0003] Among them, the backward Brillouin scattering of optical fiber is widely used by researchers in the field of microwave photons due to its low threshold and narrow linewidth, including the generation of microwave photon signals, microwave photon signal filters, microwave photon phase shifters, etc. However, due to the wider gain bandwidth of backward Brillouin scattering, the linewidth of the generated microwave signal is limited to the kHz level. Therefore, we focus on the study of forward Brillouin scattering in optical fiber. Taking advantage of the fact that the gain bandwidth of forward Brillouin scattering is smaller than that of backward Brillouin scattering, frequency-tunable microwave photons with narrower linewidth are generated.

[0004] In 2017, London Y reported an electro-optical mechanical RF oscillator formed by forward Brillouin scattering in a single-mode fiber. The phase modulation was converted into intensity modulation through a Sagnac loop and the feedback modulated optical pump was driven to achieve oscillation. The oscillation frequency was 319 MHz, corresponding to the forward R 07 The frequency of the first-order polarization mode is only 300Hz when the line width drops by 3dB. In 2016, Peng Meng's research group reported a thulium-doped soliton fiber laser that achieved passive mode locking through strong photoacoustic interaction in an extremely short photonic crystal fiber. The fundamental frequency was 1.446GHz, corresponding to the 52nd harmonic of the cavity round-trip frequency. Such strong photoacoustic interaction ensured the generation of stable and repeatable gigahertz pulse trains at a wavelength of 1.85um.

[0005] However, in the experimental device of the optoelectronic oscillator based on forward Brillouin scattering, a Sagnac ring is required to convert phase modulation to intensity modulation, and an electro-optical conversion device is also required to realize electro-optical modulation, and an optoelectronic converter is required to perform optoelectronic conversion. This will affect the performance of the optoelectronic oscillator and increase the complexity of the experimental device construction and the experimental cost. The microwave photon generation method based on the passive mode-locked laser needs to maintain the stability of the mode-locked state, and the resonant frequency of the microwave photon is determined by the cavity length of the laser, making the tunability of the system almost zero. In summary, the existing microwave photon generation methods have the problems of complex structure, poor tunability and line width that cannot meet the requirements. Summary of the invention

[0006] In order to overcome the technical defects of the existing microwave photon generation methods, such as complex structure, poor tunability and line width that cannot meet the requirements, the present invention provides a tunable narrow linewidth microwave photon oscillator based on forward Brillouin scattering.

[0007] The present invention provides a tunable narrow-linewidth microwave photon oscillator based on forward Brillouin scattering, comprising an erbium-doped fiber amplifier, a filter, a first fiber coupler, a second fiber coupler, a third fiber coupler, a fourth fiber coupler, a spectrometer, a photodetector, a spectrometer, a first polarization controller, a second polarization controller, a third polarization controller, a first single-mode fiber and a second single-mode fiber; the output end of the erbium-doped fiber amplifier is connected to the input end of the filter, the output end of the filter is connected to the input end a of the first fiber coupler, the output end b of the first fiber coupler is connected to the input end a of the third fiber coupler, the output end c of the first fiber coupler is connected to the input end a of the second fiber coupler, the output end b of the second fiber coupler is connected to the input end of the spectrometer, the output end c of the second fiber coupler is connected to the input end of the photodetector, and the output end of the photodetector is connected to to the input end of the spectrometer; the output end b of the third fiber coupler is connected to the input end c of the fourth fiber coupler through the first polarization controller and the first single-mode optical fiber in sequence, the output end c of the third fiber coupler is connected to the input end b of the fourth fiber coupler through the second polarization controller and the second single-mode optical fiber in sequence, the output end a of the fourth fiber coupler is connected to the input end of the third polarization controller, and the output end of the third polarization controller is connected to the input end of the erbium-doped fiber amplifier; the splitting ratio of the output end b of the first fiber coupler to its output end c is 90:10; the splitting ratio of the output end b of the second fiber coupler to its output end c is 50:50; the splitting ratio of the output end b of the third fiber coupler to its output end c is 50:50; the splitting ratio of the input end b of the fourth fiber coupler to its input end c is 50:50; the length of the first single-mode optical fiber is less than the length of the second single-mode optical fiber.

[0008] In the tunable narrow linewidth microwave photon oscillator described in the present invention, energy is provided by an erbium-doped fiber amplifier, and a 980nm laser in the erbium-doped fiber amplifier excites the erbium-doped fiber and oscillates in a ring cavity to form an erbium-doped laser; the minimum output power of the erbium-doped fiber amplifier is 15dBm, and the maximum output power of the erbium-doped fiber amplifier is 25dBm. The optical filter can control the resonant wavelength of the laser and adjust the forward Brillouin gain. Two ring cavities are formed in the tunable narrow linewidth microwave photon oscillator, one of which is a long cavity and the other is a short cavity. The short cavity is composed of an erbium-doped fiber amplifier, a filter, a first fiber coupler, a third fiber coupler, a first polarization controller, a first single-mode fiber, a fourth fiber coupler and a third polarization controller. The long cavity is composed of an erbium-doped fiber amplifier, a filter, a first fiber coupler, a third fiber coupler, a second polarization controller, a second single-mode fiber, a fourth fiber coupler and a third polarization controller. In the short cavity and the long cavity, the erbium-doped fiber amplifier, the filter, the first fiber coupler, the third fiber coupler, the fourth fiber coupler and the third polarization controller are coupled links, and the branches formed by the first polarization controller and the first single-mode fiber and the second polarization controller and the second single-mode fiber are uncoupled links. Two ring cavities of different lengths are formed by the first single-mode fiber and the second single-mode fiber of different lengths.

[0009] The third polarization controller in the coupling link is used to adjust the polarization directions of the pump light and the Stokes light in the ring cavity, so as to adjust the polarization between the Stokes light and the pump light to be the same and maintain the maximum FSBS gain; at the same time, the first polarization controller and the second polarization controller in the uncoupled link are used to control the periodic pulse resonance frequencies of the short cavity and the long cavity respectively, so as to achieve the coincidence of the intrinsic resonance frequencies of the long cavity and the short cavity in different forward Brillouin gain modes; finally, the first polarization controller and the second polarization controller are coordinated and adjusted with each other, so as to achieve the tunable suppression of the side mode of the output microwave photon signal and the tuning of the output signal.

[0010] The pump light in the ring cavity is obtained by self-excitation of the erbium-doped fiber amplifier in the ring cavity, and the pump light wavelength can be moved within the range of 1520-1570nm through a filter. By reducing the intrinsic linewidth of the ring resonator, the linewidth of the forward Brillouin gain is reduced, and the narrow linewidth microwave photon signal output is achieved.

[0011] When only the long cavity exists, that is, the coupling link formed by the first polarization controller and the first single-mode optical fiber is disconnected, the short cavity does not work, and the vernier effect cannot be generated in the cavity. The pump light passes through the output end b of the third optical fiber coupler and the second polarization controller and then enters the second single-mode optical fiber to excite the forward Brillouin acoustic mode signal. The forward Brillouin acoustic mode signal resonates with the resonant frequency in the cavity, and multiple forward Brillouin modes appear in the cavity, corresponding to 220MHz (R 05)、270MHz(R 06 )、318MHz(R 07 )、365MHz(R 08 )、414MHz(R 09 )、460MHz(R 0(10) ), the forward Brillouin gain is determined by the phase difference between the cavity's intrinsic resonant frequency and the acoustic mode's center resonant frequency.

[0012] When the long cavity and the short cavity exist at the same time, that is, when the coupling link formed by the first polarization controller and the first single-mode optical fiber is connected, the short cavity comes into play and a vernier effect is generated in the cavity. The forward Brillouin will excite the forward Brillouin in the longer second single-mode optical fiber, select the only resonant mode in the cavity to resonate with the acoustic mode in the cavity, and form a forward Brillouin acoustic mode resonant microwave photon oscillation, which circulates in the cavity.

[0013] The free spectral ranges of the two ring cavities are FSR1 and FSR2 respectively, and the dual cavity structure formed by the two ring cavities needs to meet the effective FSR. When the forward Brillouin gain spectrum meets the free spectral ranges of the long cavity and the short cavity at the same time, the forward Brillouin acoustic mode resonates and the forward Brillouin gain appears.

[0014] Preferably, the wavelength tuning range of the filter is 1450-1650 nm, and the bandwidth setting range is 50-950 pm. The filter can control the resonant wavelength of the laser and adjust the forward Brillouin gain.

[0015] Preferably, the wavelength range of the spectrometer is 600 to 1700 nm, the wavelength resolution is 0.02 to 2 nm, and the measurement power range is -90 to 20 dBm.

[0016] Preferably, the bandwidth of the photodetector is 50 GHz, and the linear response of the optical input power is 10 dBm.

[0017] Preferably, the frequency test range of the spectrum analyzer is 10 Hz to 30 GHz, and the frequency resolution is 0.1 Hz.

[0018] Preferably, the length of the first single-mode optical fiber is 500 m, and the length of the second single-mode optical fiber is 5000 m. Then the free spectral range of the short cavity is 40 kHz, and the free spectral range of the long cavity is 400 kHz.

[0019] Compared with the prior art, the technical solution provided by the present invention has the following technical effects: the tunable narrow-linewidth microwave photon oscillator described in the present invention utilizes an all-fiber structure to construct an erbium-doped fiber laser and realize forward Brillouin microwave photon oscillation, does not require a Sagnac ring and electrical related devices, constructs a dual ring cavity to realize mode selection through a vernier effect, and can realize the tuning of the forward Brillouin oscillation mode, thereby realizing stable tunable narrow-linewidth single longitudinal mode microwave photon generation; the present invention adjusts the polarization direction of the pump light and the Stokes light in the ring cavity by adjusting the third polarization controller of the coupling part, thereby improving the FSBS coupling efficiency, and simultaneously utilizes the first polarization controller and the second polarization controller of the uncoupled part to control the periodic pulse resonance frequency of the two ring cavities, effectively suppresses the side mode, and realizes the tuning of the output signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 It is a schematic structural diagram of a tunable narrow-linewidth microwave photonic oscillator based on forward Brillouin scattering according to an embodiment of the present invention;

[0023] Figure 2 This is a non-single longitudinal mode spectrum diagram of a tunable narrow linewidth microwave photonic oscillator based on forward Brillouin scattering at a center frequency of 317 MHz in an embodiment of the present invention;

[0024] Figure 3 A single longitudinal mode spectrum diagram of a tunable narrow linewidth microwave photonic oscillator based on forward Brillouin scattering at a center frequency of 317 MHz described in an embodiment of the present invention;

[0025] Figure 4 A frequency response diagram of a tunable narrow-linewidth microwave photonic oscillator based on forward Brillouin scattering at a center frequency of 317 MHz described in an embodiment of the present invention;

[0026] Figure 5 A schematic diagram of the tunability of a tunable narrow-linewidth microwave photonic oscillator based on forward Brillouin scattering described in an embodiment of the present invention;

[0027] Figure 6The figure is a schematic diagram of the phase noise of a tunable narrow-linewidth microwave photonic oscillator based on forward Brillouin scattering described in an embodiment of the present invention.

[0028] In the figure: 1, optical fiber amplifier; 2, filter; 3A, first optical fiber coupler; 3B, second optical fiber coupler; 3D, third optical fiber coupler; 3E, fourth optical fiber coupler; 4, spectrometer; 5, photodetector; 6, spectrometer; 7A, first polarization controller; 7B, second polarization controller; 7C, third polarization controller; 8A, first single-mode optical fiber; 8B, second single-mode optical fiber. DETAILED DESCRIPTION

[0029] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0030] In the description, it should be noted that the terms "first" and "second" are only used for descriptive purposes and should not be understood as indicating or implying relative importance. It should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be internal communication between two components. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0031] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all of the embodiments.

[0032] The following is combined with Figures 1 to 6 The specific embodiments of the present invention are described in detail.

[0033] In one embodiment, Figure 1As shown, a tunable narrow-linewidth microwave photon oscillator based on forward Brillouin scattering is disclosed, comprising an erbium-doped fiber amplifier 1, a filter 2, a first fiber coupler 3A, a second fiber coupler 3B, a third fiber coupler 3D, a fourth fiber coupler 3E, a spectrometer 4, a photodetector 5, a spectrometer 6, a first polarization controller 7A, a second polarization controller 7B, a third polarization controller 7C, a first single-mode fiber 8A and a second single-mode fiber 8B; the output end of the erbium-doped fiber amplifier 1 is connected to the input end of the filter 2, the output end of the filter 2 is connected to the input end a of the first fiber coupler 3A, the output end b of the first fiber coupler 3A is connected to the input end a of the third fiber coupler 3D, the output end c of the first fiber coupler 3A is connected to the input end a of the second fiber coupler 3B, the output end b of the second fiber coupler 3B is connected to the input end of the spectrometer 4, the output end c of the second fiber coupler 3B is connected to the input end of the photodetector 5, and the output of the photodetector 5 The end is connected to the input end of the spectrometer 6; the output end b of the third fiber coupler 3D is connected to the input end c of the fourth fiber coupler 3E through the first polarization controller 7A and the first single-mode optical fiber 8A in sequence, the output end c of the third fiber coupler 3D is connected to the input end b of the fourth fiber coupler 3E through the second polarization controller 7B and the second single-mode optical fiber 8B in sequence, the output end a of the fourth fiber coupler 3E is connected to the input end of the third polarization controller 7C, and the output end of the third polarization controller 7C is connected to the input end of the erbium-doped fiber amplifier 1; the splitting ratio of the output end b of the first fiber coupler 3A to its output end c is 90:10; the splitting ratio of the output end b of the second fiber coupler 3B to its output end c is 50:50; the splitting ratio of the output end b of the third fiber coupler 3D to its output end c is 50:50; the splitting ratio of the input end b of the fourth fiber coupler 3E to its input end c is 50:50; the length of the first single-mode optical fiber 8A is less than the length of the second single-mode optical fiber 8B.

[0034] In the tunable narrow linewidth microwave photon oscillator described in the present invention, energy is provided by an erbium-doped fiber amplifier 1, and the 980nm laser in the erbium-doped fiber amplifier 1 excites the erbium-doped fiber and oscillates in the ring cavity to form an erbium-doped laser; the minimum output power of the erbium-doped fiber amplifier 1 is 15dBm, and the maximum output power of the erbium-doped fiber amplifier 1 is 25dBm. The optical filter 2 can control the resonant wavelength of the laser and adjust the forward Brillouin gain. Two ring cavities are formed in the tunable narrow linewidth microwave photon oscillator, one of which is a long cavity and the other is a short cavity. The short cavity is composed of an erbium-doped fiber amplifier 1, a filter 2, a first fiber coupler 3A, a third fiber coupler 3D, a first polarization controller 7A, a first single-mode fiber 8A, a fourth fiber coupler 3E and a third polarization controller 7C. The long cavity is composed of an erbium-doped fiber amplifier 1, a filter 2, a first fiber coupler 3A, a third fiber coupler 3D, a second polarization controller 7B, a second single-mode fiber 8B, a fourth fiber coupler 3E and a third polarization controller 7C. In the short cavity and the long cavity, the erbium-doped fiber amplifier 1, the filter 2, the first fiber coupler 3A, the third fiber coupler 3D, the fourth fiber coupler 3E and the third polarization controller 7C are coupled links, and the branch formed by the first polarization controller 7A and the first single-mode fiber 8A and the second polarization controller 7B and the second single-mode fiber 8B is an uncoupled link. Two ring cavities of different lengths are formed by the first single-mode fiber 8A and the second single-mode fiber 8B of different lengths.

[0035] The third polarization controller 7C in the coupling link is used to adjust the polarization directions of the pump light and the Stokes light in the ring cavity, so as to adjust the polarization between the Stokes light and the pump light to be the same and maintain the maximum FSBS gain; at the same time, the first polarization controller 7A and the second polarization controller 7B in the uncoupled link are used to control the periodic pulse resonance frequencies of the short cavity and the long cavity respectively, so as to achieve the coincidence of the intrinsic resonance frequencies of the long cavity and the short cavity in different forward Brillouin gain modes; finally, the first polarization controller 7A and the second polarization controller 7B are coordinated and adjusted with each other to achieve the tunable suppression of the side mode of the output microwave photon signal and the tuning of the output signal.

[0036] The pump light in the ring cavity is obtained by self-excitation of the erbium-doped fiber amplifier 1 in the ring cavity, and the wavelength of the pump light can be moved within the range of 1520-1570nm through the filter 2. By reducing the intrinsic linewidth of the ring resonator, the linewidth of the forward Brillouin gain is reduced, and the narrow linewidth microwave photon signal output is achieved.

[0037] When only the long cavity exists, that is, the coupling link formed by the first polarization controller 7A and the first single-mode optical fiber 8A is disconnected, the short cavity does not work, and the vernier effect cannot be generated in the cavity. The pump light passes through the output end b of the third optical fiber coupler 3D and the second polarization controller 7B and then enters the second single-mode optical fiber 8B to excite the forward Brillouin acoustic mode signal. The forward Brillouin acoustic mode signal resonates with the resonant frequency in the cavity, and multiple forward Brillouin modes appear in the cavity, corresponding to 220 MHz (R 05 )、270MHz(R 06 )、318MHz(R 07 )、365MHz(R 08 )、414MHz(R 09 )、460MHz(R 0(10) ), the forward Brillouin gain is determined by the phase difference between the cavity's intrinsic resonant frequency and the acoustic mode's center resonant frequency.

[0038] When the long cavity and the short cavity exist at the same time, that is, when the coupling link formed by the first polarization controller 7A and the first single-mode optical fiber 8A is connected, the short cavity plays a role at this time, and a vernier effect is generated in the cavity. The forward Brillouin will excite the forward Brillouin in the longer second single-mode optical fiber 8B, and select the only resonant mode in the cavity to resonate with the acoustic mode in the cavity, forming a forward Brillouin acoustic mode resonant microwave photon oscillation, and circulate in the cavity. The present invention adds a short cavity to the oscillator for mode selection to improve the side mode suppression ratio and suppress phase noise. The long cavity is used to generate forward Brillouin scattering, and the short cavity is used to generate a vernier effect, so as to achieve stable narrow linewidth tunable single longitudinal mode microwave photon generation without the need for a Sagnac ring and electrical related devices.

[0039] The free spectral ranges of the two ring cavities are FSR1 and FSR2 respectively, and the dual cavity structure formed by the two ring cavities needs to meet the effective FSR. When the forward Brillouin gain spectrum meets the free spectral ranges of the long cavity and the short cavity at the same time, the forward Brillouin acoustic mode resonates and the forward Brillouin gain appears.

[0040] Based on the above embodiments, in a preferred embodiment, the wavelength tuning range of the filter 2 is 1450-1650 nm, and the bandwidth setting range is 50-950 pm. The filter 2 can control the resonant wavelength of the laser and adjust the forward Brillouin gain.

[0041] On the basis of the above embodiments, in a preferred embodiment, the wavelength range of the spectrometer 4 is 600 to 1700 nm, the wavelength resolution is 0.02 to 2 nm, and the measurement power range is -90 to 20 dBm.

[0042] On the basis of the above embodiments, in a preferred embodiment, the bandwidth of the photodetector 5 is 50 GHz, and the linear response of the optical input power is 10 dBm.

[0043] On the basis of the above embodiments, in a preferred embodiment, the frequency test range of the spectrum analyzer 6 is 10 Hz to 30 GHz, and the frequency resolution is 0.1 Hz.

[0044] Based on the above embodiment, in a preferred embodiment, the length of the first single-mode optical fiber 8A is 500 m, and the length of the second single-mode optical fiber 8B is 5000 m. Then the free spectral range of the short cavity is 40 kHz, and the free spectral range of the long cavity is 400 kHz.

[0045] The free spectral ranges of the long cavity and the short cavity are FSR1 and FSR2 respectively. The effective FSR of the dual-cavity structure formed by the two ring cavities meets the following conditions:

[0046] FSR=n1FSR1=n2FSR2(1)

[0047] Among them, FSR1 corresponds to the long cavity, FSR2 corresponds to the short cavity, and n m (m=1, 2) is an integer, and the free spectral range of the two ring cavities is expressed by the following formula:

[0048]

[0049] Where L m represents the length of the ring cavity; m = 1 or 2, m represents the serial number of the ring cavity; n = 1.468 is the effective refractive index of the optical fiber; the second single-mode optical fiber in the long cavity is 5000 meters, and the first single-mode optical fiber in the short cavity is 500 meters. Therefore, the free spectral ranges of the two ring cavities are 40kHz and 400kHz respectively. According to formula (1), when the forward Brillouin gain spectrum satisfies the free spectral ranges of the main ring cavity and the secondary ring cavity at the same time, the forward Brillouin acoustic mode resonates and the forward Brillouin gain appears.

[0050] When the pump wave is incident into the dielectric fiber, it will generate guided acoustic wave Brillouin scattering, also known as forward spontaneous Brillouin scattering. The pump light and Stokes light are transmitted in the same direction in the fiber, and the generated acoustic wave is mainly a transverse acoustic mode, which is a mode that is transmitted radially along the fiber axis in the fiber cross section. Since the pump wave and the Stokes wave remain in the same direction, the increase in pump power increases the accumulation of forward Brillouin scattering, so the Stokes light is enhanced. Subsequently, as in the backward Brillouin scattering mode, the interference between the pump wave and the forward Stokes light wave is also enhanced, enhancing the acoustic wave and the Stokes light wave. In the forward stimulated Brillouin scattering, the incident pump light and Stokes light are kept in the same polarization, and the dispersion curves of the two light waves are in the same direction. And the acoustic wave dispersion curve of the forward Brillouin scattering is close to flat near the zero wave vector, so the vibration frequency of the acoustic mode is approximately a cutoff frequency that is independent of the pump light frequency, and the frequency value is related to the fiber diameter and the internal structure of the fiber. Therefore, when the pump wave and the Stokes wave satisfy self-phase matching, it is easy to generate high-order Stokes and anti-Stokes light, and the frequency shift is equal to the cutoff frequency.

[0051] Figure 2 and Figure 3 The center frequency of the tunable narrow linewidth microwave photonic oscillator is 317 MHz (R 07 mode), the spectrum without and with the short cavity structure is compared. Figure 2 and Figure 3 It can be seen that after adding the short cavity structure composed of the first single-mode optical fiber 8A and the first polarization controller 7A, it obviously becomes a single longitudinal mode output.

[0052] Figure 4 yes Figure 3 The single longitudinal mode spectrum enlargement diagram is shown by Figure 4 It is known that the tunable narrow-linewidth microwave photonic oscillator described in the present invention can achieve narrow-linewidth output, and its 3dBb linewidth is around 65Hz.

[0053] pass Figure 5 It can be seen that by controlling the second polarization controller 7B, it is possible to freely realize the change from R 05 to R 08 of tuning.

[0054] pass Figure 6 It can be seen that the dual-cavity structure after adding the first single-mode optical fiber 8A has higher phase noise and excellent edge suppression capability.

[0055] The above is only a specific implementation of the present invention, which enables those skilled in the art to understand or implement the present invention. Although detailed descriptions are given with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments, and they should all be covered by the protection scope of the claims.

Claims

1. A tunable narrow-linewidth microwave photon oscillator based on forward Brillouin scattering, characterized in that: The invention comprises an erbium-doped fiber amplifier (1), a filter (2), a first fiber coupler (3A), a second fiber coupler (3B), a third fiber coupler (3D), a fourth fiber coupler (3E), a spectrometer (4), a photodetector (5), a spectrum analyzer (6), a first polarization controller (7A), a second polarization controller (7B), a third polarization controller (7C), a first single-mode fiber (8A) and a second single-mode fiber (8B); the output end of the erbium-doped fiber amplifier (1) is connected to the input end of the filter (2), the output end of the filter (2) is connected to the input end a of the first fiber coupler (3A), the output end b of the first fiber coupler (3A) is connected to the input end a of the third fiber coupler (3D), the output end c of the first fiber coupler (3A) is connected to the input end a of the second fiber coupler (3B), the output end b of the second fiber coupler (3B) is connected to the input end of the spectrometer (4), the output end c of the second fiber coupler (3B) is connected to the input end of the photodetector (5), and the output end of the photodetector (5) is connected to the spectrum analyzer ( The output end b of the third optical fiber coupler (3D) is connected to the input end c of the fourth optical fiber coupler (3E) through the first polarization controller (7A) and the first single-mode optical fiber (8A) in sequence, the output end c of the third optical fiber coupler (3D) is connected to the input end b of the fourth optical fiber coupler (3E) through the second polarization controller (7B) and the second single-mode optical fiber (8B) in sequence, the output end a of the fourth optical fiber coupler (3E) is connected to the input end of the third polarization controller (7C), and the output end a of the third polarization controller (7C) is connected to the input end of the fourth optical fiber coupler (3E). The end is connected to the input end of the erbium-doped fiber amplifier (1); the splitting ratio of the output end b of the first fiber coupler (3A) and its output end c is 90:10; the splitting ratio of the output end b of the second fiber coupler (3B) and its output end c is 50:50; the splitting ratio of the output end b of the third fiber coupler (3D) and its output end c is 50:50; the splitting ratio of the input end b of the fourth fiber coupler (3E) and its input end c is 50:50; the length of the first single-mode optical fiber (8A) is less than the length of the second single-mode optical fiber (8B).

2. The tunable narrow-linewidth microwave photonic oscillator based on forward Brillouin scattering according to claim 1, characterized in that: The wavelength tuning range of the filter (2) is 1450-1650 nm, and the bandwidth setting range is 50-950 pm.

3. The tunable narrow linewidth microwave photonic oscillator based on forward Brillouin scattering according to claim 1, characterized in that: The wavelength range of the spectrometer (4) is 600-1700 nm, the wavelength resolution is 0.02-2 nm, and the measurement power range is -90-20 dBm.

4. The tunable narrow linewidth microwave photonic oscillator based on forward Brillouin scattering according to claim 1, characterized in that: The bandwidth of the photodetector (5) is 50 GHz, and the linear response of the optical input power is 10 dBm.

5. The tunable narrow linewidth microwave photonic oscillator based on forward Brillouin scattering according to claim 1, characterized in that: The frequency test range of the spectrum analyzer (6) is 10 Hz to 30 GHz, and its frequency resolution is 0.1 Hz.

6. A tunable narrow linewidth microwave photonic oscillator based on forward Brillouin scattering according to any one of claims 1 to 5, characterized in that: The length of the first single-mode optical fiber (8A) is 500 m, and the length of the second single-mode optical fiber (8B) is 5000 m.

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