A tunable narrow linewidth microwave photonic oscillator based on forward brillouin scattering

Abstract

The application belongs to the technical field of microwave photon and optical communication, and particularly relates to a tunable narrow-line-width microwave photon oscillator based on forward Brillouin scattering, which solves the technical problems of existing microwave photon generation methods, such as complex structure, poor tunability and line width not meeting requirements. In the structure, the erbium-doped fiber amplifier is connected to the first optical fiber coupler through a filter, two output ends of the first optical fiber coupler are respectively connected to the third optical fiber coupler and the second optical fiber coupler, two output ends of the second optical fiber coupler are respectively connected to an optical spectrum analyzer and sequentially connected with a photoelectric detector and a spectrum analyzer, two output ends of the third optical fiber coupler are respectively sequentially connected to the input end c of the fourth optical fiber coupler through the first polarization controller and the first single-mode optical fiber and connected to the input end b of the fourth optical fiber coupler through the second polarization controller and the second single-mode optical fiber, and the fourth optical fiber coupler is connected to the erbium-doped fiber amplifier through the third polarization controller.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of microwave photonics and optical communication, and particularly relates to a tunable narrow linewidth microwave photonics oscillator based on forward Brillouin scattering. BACKGROUND

[0002] With the development of the times, the application field of microwave photonics is more and more extensive, including battlefield communication, electronic information war, broadband communication, precision measurement, etc. These application scenarios require the microwave photonics system to be improved in frequency, bandwidth, dynamic adjustable range and anti-interference ability, so as to improve the performance of the microwave photonics system. This leads to great challenges for microwave photonics technology.

[0003] Among them, the backward Brillouin scattering of the optical fiber is widely used in the field of microwave photonics by researchers due to its low threshold and narrow linewidth, including the generation of microwave photonics signals, microwave photonics signal filters, microwave photonics phase shifters, etc. However, due to the wide gain bandwidth of the backward Brillouin scattering, the linewidth of the generated microwave signal is limited to the order of kHz. Therefore, we focus on studying the forward Brillouin scattering in the optical fiber. By taking advantage of the smaller gain bandwidth of the forward Brillouin scattering compared to the backward Brillouin scattering, a frequency tunable microwave photonics with narrower linewidth is generated.

[0004] In 2017, London Y reported an electro-optomechanical radio frequency oscillator formed by forward Brillouin scattering in a single-mode optical fiber. The phase modulation is converted into intensity modulation by a Sagnac loop and drives the feedback modulation light pump, thereby realizing oscillation. The oscillation frequency is 319MHz, corresponding to the frequency of the forward R 07 mode polarization, and the 3dB linewidth is only 300Hz. In 2016, Peng's group reported a thulium-doped soliton fiber laser. In a very short photonic crystal fiber, a passive mode-locked state is achieved through strong opto-acoustic interaction. The fundamental frequency is 1.446GHz, corresponding to the 52th harmonic of the cavity round-trip frequency. Under such strong opto-acoustic interaction, stable and repeatable gigahertz pulse trains are generated at a wavelength of 1.85um.

[0005] However, in the experimental device of the optoelectronic oscillator based on forward Brillouin scattering, a Sagnac loop is needed to convert phase modulation into intensity modulation, and an electro-optical conversion device is needed to realize electro-optical modulation, and an optoelectronic converter is needed to realize optical-electric conversion. This will affect the performance of the optoelectronic oscillator, and also increase the complexity of the experimental device 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 resonance frequency of the microwave photon is determined by the cavity length of the laser, so that the tunability of the system is almost zero. In summary, the existing microwave photon generation methods have the problems of complex structure, poor tunability and linewidth that does not meet the requirements. SUMMARY

[0006] In order to overcome the technical defects of the existing microwave photon generation method, such as complex structure, poor tunability and line width not meeting the requirements, the application provides a tunable narrow line width microwave photon oscillator based on forward Brillouin scattering.

[0007] The application provides a tunable narrow line width microwave photon oscillator based on forward Brillouin scattering, which comprises an erbium-doped fiber amplifier, a filter, a first fiber coupler, a second fiber coupler, a third fiber coupler, a fourth fiber coupler, an optical spectrum instrument, a photodetector, a frequency spectrum instrument, 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 optical spectrum instrument, 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 the input end of the frequency spectrum instrument; 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 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 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 light splitting ratio of the output end b and the output end c of the first fiber coupler is 90:10; the light splitting ratio of the output end b and the output end c of the second fiber coupler is 50:50; the light splitting ratio of the output end b and the output end c of the third fiber coupler is 50:50; the light splitting ratio of the input end b and the input end c of the fourth fiber coupler is 50:50; and the length of the first single-mode fiber is less than the length of the second single-mode fiber.

[0008] The tunable narrow linewidth microwave photon oscillator provided by the application has energy provided by an erbium-doped fiber amplifier, a 980nm laser in the erbium-doped fiber amplifier excites an erbium-doped fiber, and the erbium-doped fiber oscillates in a ring cavity to form erbium 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. An optical filter can control the resonant wavelength of the laser and adjust the gain of the forward Brillouin. 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. Among them, 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 part are coupled links, and the branch formed by the first polarization controller and the first single-mode fiber and the second polarization controller and the second single-mode fiber is an uncoupled link. The first single-mode fiber and the second single-mode fiber of different lengths form two ring cavities of different lengths.

[0009] The polarization direction of the pump light and the Stokes light in the ring cavity is adjusted by the third polarization controller in the coupled link, which is used 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 resonant frequency of the short cavity and the long cavity respectively, so that the intrinsic resonant frequencies of the long cavity and the short cavity coincide under different forward Brillouin gain modes, and finally the first polarization controller and the second polarization controller are adjusted to realize the tunable effective suppression of the output microwave photon signal sideband, and the tuning of the output signal is realized.

[0010] The pump light in the ring cavity is self-excited in the ring cavity by the erbium-doped fiber amplifier, and the pump light wavelength can be moved in the range of 1520-1570nm by the filter. By narrowing the intrinsic linewidth of the ring resonant cavity, the linewidth of the forward Brillouin gain is narrowed, and a narrow linewidth microwave photon signal output is realized.

[0011] When only the long cavity exists, that is, the coupled link formed by the first polarization controller and the first single-mode fiber is disconnected, at this time the short cavity does not work, the vernier effect cannot be generated in the cavity, the pump light enters the second single-mode fiber after passing through the output end b of the third fiber coupler and the second polarization controller to excite the forward Brillouin acoustic mode signal, the forward Brillouin acoustic mode signal resonates with the resonant frequency in the cavity, and multiple modes of the forward Brillouin appear in the cavity, which correspond to 220MHz (R 05), 270MHz (R 06 ), 318MHz (R 07 ), 365MHz (R 08 ), 414MHz (R 09 ), 460MHz (R 0(10) ), the gain size of the forward Brillouin is determined by the phase difference between the intracavity eigenresonance frequency and the acoustic mode center resonance frequency.

[0012] When the long cavity and the short cavity exist simultaneously, that is, the coupling link formed by the first polarization controller and the first single-mode fiber is connected, at this time the short cavity plays a role, the vernier effect is generated in the cavity, the forward Brillouin excites the forward Brillouin in the longer second single-mode fiber, the only resonant mode in the cavity is selected to resonate with the acoustic mode in the cavity, the forward Brillouin acoustic mode resonance microwave photon oscillation is formed, and circulates in the cavity.

[0013] The free spectral ranges of the two ring cavities are FSR1 and FSR2 respectively, and the double-cavity structure formed by the cooperation of the two ring cavities needs to meet the effective FSR. When the forward Brillouin gain spectrum simultaneously meets the free spectral ranges of the long cavity and the short cavity, the forward Brillouin acoustic mode resonance and the forward Brillouin gain appear.

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

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

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

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

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

[0019] The technical scheme provided by the application has the following technical effects compared with the prior art: the tunable narrow-line-width microwave photon oscillator provided by the application utilizes a full-fiber structure, builds an erbium-doped fiber laser and realizes forward Brillouin microwave photon oscillation, does not need a Sagnac ring and an electrical device, realizes mode selection through a vernier effect by building a double-ring cavity, realizes tuning of the forward Brillouin oscillation mode, and realizes stable tunable narrow-line-width single-longitudinal-mode microwave photon generation; the third polarization controller of the coupling part is adjusted to adjust the polarization direction of the pump light and the Stokes light in the ring cavity, so that the FSBS coupling efficiency is improved, the first polarization controller and the second polarization controller of the uncoupling part are used to control the periodic pulse resonance frequency of the two ring cavities, side modes are effectively suppressed, and the tuning of the output signal is realized. BRIEF DESCRIPTION OF DRAWINGS

[0020] The drawings incorporated into the specification and forming part of the specification, show embodiments consistent with the application, and together with the specification serve to explain the principles of the application.

[0021] In order to more clearly illustrate the technical scheme in the embodiments of the application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows, and obviously, other drawings can also be obtained by those skilled in the art without creative effort on the basis of these drawings.

[0022] Figure 1 A structure schematic diagram of the tunable narrow-line-width microwave photon oscillator based on forward Brillouin scattering in some embodiments of the application;

[0023] Figure 2 A non-single-longitudinal-mode spectrum diagram of the tunable narrow-line-width microwave photon oscillator based on forward Brillouin scattering in some embodiments of the application when the center frequency is 317 MHz;

[0024] Figure 3 A single-longitudinal-mode spectrum diagram of the tunable narrow-line-width microwave photon oscillator based on forward Brillouin scattering in some embodiments of the application when the center frequency is 317 MHz;

[0025] Figure 4 A frequency response diagram of the tunable narrow-line-width microwave photon oscillator based on forward Brillouin scattering in some embodiments of the application when the center frequency is 317 MHz;

[0026] Figure 5 A tuning schematic diagram of the tunable narrow-line-width microwave photon oscillator based on forward Brillouin scattering in some embodiments of the application;

[0027] Figure 6A phase noise schematic diagram of a tunable narrow-linewidth microwave photonic oscillator based on forward Brillouin scattering according to an embodiment of the present application.

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

[0029] In order to more clearly understand the above-mentioned purposes, features and advantages of the present application, the schemes of the present application will be further described below. It should be noted that the embodiments of the present application 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", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance. It should be noted that, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting" should be understood in a broad sense, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be the communication inside two elements. For those skilled in the art, the specific meanings of the above terms can be understood according to the specific circumstances.

[0031] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application, but the present application can also be implemented in other ways different from those described herein; obviously, the examples in the specification are only some of the embodiments of the present application, not all the embodiments.

[0032] The following will be described in detail with reference to the accompanying drawings Figures 1 to 6 The specific embodiments of the present application will be described in detail.

[0033] In one embodiment, as Figure 1As shown, a tunable narrow linewidth microwave photonic 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, an optical spectrum analyzer 4, a photodetector 5, a frequency 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 optical spectrum analyzer 4, the output end c of the second fiber coupler 3B is connected to the input end of the photodetector 5, the output end of the photodetector 5 is connected to the input end of the frequency spectrum analyzer 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 fiber 8A in turn, 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 fiber 8B in turn, the output end a of the fourth fiber coupler 3E is connected to the input end of the third polarization controller 7C, 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 and the output end c of the first fiber coupler 3A is 90:10; the splitting ratio of the output end b and the output end c of the second fiber coupler 3B is 50:50; the splitting ratio of the output end b and the output end c of the third fiber coupler 3D is 50:50; the splitting ratio of the input end b and the input end c of the fourth fiber coupler 3E is 50:50; the length of the first single-mode fiber 8A is less than the length of the second single-mode fiber 8B.

[0034] The tunable narrow linewidth microwave photonic oscillator provided by the application has energy provided by an erbium-doped fiber amplifier 1, a 980nm laser in the erbium-doped fiber amplifier 1 excites an erbium-doped fiber and oscillates in a ring cavity to form 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. An optical filter 2 can control the resonant wavelength of the laser and adjust the gain of the forward Brillouin. Two ring cavities are formed in the tunable narrow linewidth microwave photonic oscillator, one of which is a long cavity and the other is a short cavity. The short cavity is composed of the erbium-doped fiber amplifier 1, the filter 2, the first optical fiber coupler 3A, the third optical fiber coupler 3D, the first polarization controller 7A, the first single-mode optical fiber 8A, the fourth optical fiber coupler 3E and the third polarization controller 7C. The long cavity is composed of the erbium-doped fiber amplifier 1, the filter 2, the first optical fiber coupler 3A, the third optical fiber coupler 3D, the second polarization controller 7B, the second single-mode optical fiber 8B, the fourth optical fiber coupler 3E and the third polarization controller 7C. Among them, in the short cavity and the long cavity, the erbium-doped fiber amplifier 1, the filter 2, the first optical fiber coupler 3A, the third optical fiber coupler 3D, the fourth optical fiber coupler 3E and the third polarization controller 7C are part of the coupling link, and the branches formed by the first polarization controller 7A and the first single-mode optical fiber 8A and the second polarization controller 7B and the second single-mode optical fiber 8B are uncoupled links. The first single-mode optical fiber 8A and the second single-mode optical fiber 8B of different lengths form two ring cavities of different lengths.

[0035] The polarization direction of the pump light and the Stokes light in the ring cavity is adjusted by the third polarization controller 7C in the coupling link, which is used 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 resonant frequency of the short cavity and the long cavity respectively, so that the intrinsic resonant frequencies of the long cavity and the short cavity coincide under different forward Brillouin gain modes, and finally the first polarization controller 7A and the second polarization controller 7B are adjusted to realize the tunable effective suppression of the output microwave photonic signal sideband, and the tuning of the output signal is realized.

[0036] The pump light in the ring cavity is self-excited in the ring cavity by the erbium-doped fiber amplifier 1, and the pump light wavelength can be moved in the range of 1520-1570nm by the filter 2. By narrowing the intrinsic linewidth of the ring resonant cavity, the linewidth of the forward Brillouin gain is narrowed, and the narrow linewidth microwave photonic signal output is realized.

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

[0038] When the long cavity and the short cavity exist at the same time, that is, the coupling link composed of the first polarization controller 7A and the first single-mode optical fiber 8A is connected, at this time the short cavity works, the vernier effect is generated in the cavity, the forward Brillouin excites the forward Brillouin in the longer second single-mode optical fiber 8B, the only resonant mode in the cavity is selected to resonate with the acoustic mode in the cavity, the forward Brillouin acoustic mode resonance microwave photon oscillation is formed, and circulates in the cavity. The short cavity is added to the oscillator to select the mode, so as to improve the side mode suppression ratio and suppress the phase noise. The long cavity is used to generate the forward Brillouin scattering, and the short cavity is used to generate the vernier effect, so as to realize the stable narrow linewidth tunable single longitudinal mode microwave photon generation without the Sagnac ring and the electrical related device.

[0039] The free spectral ranges of the two ring cavities are FSR1 and FSR2 respectively, and the double-cavity structure formed by cooperation of 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] On the basis of the above embodiment, in a preferred embodiment, the wavelength tuning range of the filter 2 is 1450-1650nm, and the bandwidth setting range is 50-950pm. The filter 2 can control the resonant wavelength of the laser and adjust the gain of the forward Brillouin.

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

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

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

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

[0045] The free spectral ranges of the long cavity and the short cavity are FSR1 and FSR2 respectively, and the effective FSR of the double-cavity structure formed by the two ring cavities satisfies the following condition:

[0046] FSR=n1FSR1=n2FSR2 (1)

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

[0048]

[0049] wherein L m represents the ring 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 5000m, and the first single-mode optical fiber in the short cavity is 500m. 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 simultaneously satisfies the free spectral ranges of the main ring cavity and the auxiliary ring cavity, the forward Brillouin acoustic mode resonance occurs and the forward Brillouin gain appears.

[0050] When the pump wave is incident into the medium fiber, the guided acoustic wave Brillouin scattering, also called forward self-phase Brillouin scattering, is generated. The pump wave and the Stokes wave are co-directional in the fiber, and the generated acoustic wave is mainly the transverse acoustic mode, which is a mode transmitted radially along the fiber axis in the cross section of the fiber. Since the pump wave and the Stokes wave are co-directional, the increase of the pump power increases the accumulation of the forward Brillouin scattering, so the Stokes light is enhanced, and then the interference between the pump wave and the forward Stokes wave is also enhanced, which enhances the acoustic wave and the Stokes wave. In the forward stimulated Brillouin scattering, the incident pump wave and the Stokes wave are co-polarized, and the dispersion curves of the two light waves are in the same direction. Moreover, the acoustic wave dispersion curve of the forward Brillouin scattering is close to flat near the zero wave vector, so the frequency of the acoustic mode vibration is approximately a pump light frequency independent cutoff 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 the self-phase matching, high-order Stokes and anti-Stokes light can be easily generated, and the frequency shift is equal to the cutoff frequency.

[0051] Figure 2 and Figure 3 are the frequency spectra corresponding to the case without the short cavity structure and the case with the short cavity structure when the center frequency of the tunable narrow linewidth microwave photonic oscillator is R 07 . Figure 2 and Figure 3 It can be seen that, after the short cavity structure composed of the first single-mode fiber 8A and the first polarization controller 7A is added, it is obviously a single longitudinal mode output.

[0052] Figure 4 is an enlarged view of the single longitudinal mode spectrum of Figure 3 . It can be seen from Figure 4 that the tunable narrow linewidth microwave photonic oscillator can realize narrow linewidth output, and the 3dBb linewidth is about 65Hz.

[0053] It can be seen from Figure 5 that by controlling the second polarization controller 7B, the tuning from R 05 to R 08 can be freely realized.

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

[0055] The above description is merely one specific implementation of the application, and thus the technical solutions recorded in the foregoing embodiments can be modified or some or all of the technical features can be substituted equivalently by those skilled in the art, without departing from the scope of the technical solutions of the embodiments, and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the embodiments, and should be included in the protection scope of the claims.

Claims

1. A tunable narrow linewidth microwave photonic oscillator based on forward Brillouin scattering, characterized in that, The application relates to 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 spectrum analyzer (4), a photodetector (5), a frequency 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 spectrum analyzer (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 input end of the frequency spectrum analyzer (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 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 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 light splitting ratio of the output end b to the output end c of the first fiber coupler (3A) is 90:10; the light splitting ratio of the output end b to the output end c of the second fiber coupler (3B) is 50:50; the light splitting ratio of the output end b to the output end c of the third fiber coupler (3D) is 50:50; the light splitting ratio of the input end b to the input end c of the fourth fiber coupler (3E) is 50:50; and the length of the first single-mode fiber (8A) is smaller than the length of the second single-mode 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 1450-1650nm, and the bandwidth setting range is 50-950pm.

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 spectrum analyzer (4) is 600-1700nm, the wavelength resolution is 0.02-2nm, and the measurement power range is -90-20dBm.

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 50GHz, and the linear response of the optical input power is 10dBm.

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

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

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