A sweeping microwave photonic signal generation device and method
By utilizing gain fiber to form standing waves and dynamic gratings in a microwave photonic signal generation device, stable single-frequency laser output and wavelength self-sweeping laser output were achieved. This solved the problems of low coherence and narrow sweep frequency range of microwave signals in the prior art, and realized microwave photonic signal output with high coherence, wide tuning/sweep frequency range and low phase noise.
Patent Information
- Application Number
- CN202310153149.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-02-22
- Publication Date
- 2026-01-30
- Estimated Expiration
- 2043-02-22
AI Technical Summary
Existing technologies using dual-wavelength lasers to generate microwave signals suffer from low coherence and a narrow sweep range, making it difficult to simultaneously achieve high coherence, a wide tuning/sweep range, and low phase noise.
A swept-frequency microwave photonic signal generation device, consisting of a pump source, wavelength division multiplexer, fiber optic circulator, and polarization beam splitter, achieves stable single-frequency laser output and wavelength self-sweeping laser output by forming a standing wave structure and dynamic grating through gain fiber, and generates swept-frequency microwave signals by using dual-cavity beat frequency.
It achieves microwave photonic signal output with high coherence, wide tuning/sweep range and low phase noise. The device has a simple structure and is easy to operate.
Smart Images
Figure CN116093721B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of microwave technology, and specifically relates to a sweeping microwave photonic signal generation device. Background Technology
[0002] Microwave signals have immense application value in detection, medicine, biology, and communications. Microwave signals generated using optical methods offer significant advantages in high frequency, wide bandwidth, and low phase noise, and the devices can be easily integrated into fiber optic links, thus attracting considerable attention. Currently, many technologies are dedicated to generating microwave photonic signals, such as dual-wavelength beat frequency generation, microwave photonic frequency doubling, photoelectric oscillators, and optical frequency combs. Dual-wavelength beat frequency generation has garnered widespread attention due to its simple structure, wide frequency range, and high operability; however, limitations in the linewidth and bandwidth of the light source affect the coherence and sweep range of the generated tunable microwave signal. Therefore, in the field of microwave photonics, simultaneously ensuring high signal coherence, wide tuning / sweep range, low phase noise, and a simple and easy-to-operate overall device structure is a very challenging problem. Summary of the Invention
[0003] In order to overcome the shortcomings of the prior art, the present invention aims to provide a swept-frequency microwave photonic signal generation device and method, so as to solve the problems of low coherence and narrow swept-frequency range in the generation of microwave photonic signals by dual-wavelength lasers in the prior art.
[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0005] A swept-frequency microwave photonic signal generation device includes a pump source. The output of the pump source is connected to the blue end of a wavelength division multiplexer (WDM). The common end of the WDM is connected to one end of a gain fiber 3. The other end of the gain fiber 3 is connected to the incident end of a polarization beamsplitter. The two output ends of the polarization beamsplitter are respectively connected to port 1 of fiber circulator 1 and port 1 of fiber circulator 2. Port 2 of fiber circulator 1 is connected to reflector 1 through gain fiber 1. Port 2 of fiber circulator 2 is connected to reflector 2 through gain fiber 2. Ports 3 of fiber circulator 1 and 3 of fiber circulator 2 are respectively connected to the two input ends of an output coupler. The output end of the output coupler is connected to the red end of the WDM, forming two ring resonant cavities. The length of gain fiber 1 is greater than the length of gain fiber 2.
[0006] In one embodiment, the resonant cavity of the ring containing the fiber optic circulator is called resonant cavity one, and the resonant cavity of the ring containing the fiber optic circulator two is called resonant cavity two. The resonant cavity one stably outputs a single-frequency laser, and the resonant cavity two outputs a wavelength-scanning single-frequency fiber laser. The two output lasers beat at the output coupler to generate a swept-frequency microwave photon signal output.
[0007] In one embodiment, the first gain fiber, the second gain fiber, and the third gain fiber serve as saturable absorbers. The light wave is reflected by the first or the second reflection end to form a standing wave structure in the first or the second gain fiber, and a dynamic grating is formed to achieve laser frequency self-scanning single-frequency operation. The bandwidth of the first or the second reflection end determines the wavelength range of the frequency self-scanning.
[0008] In one embodiment, the first gain fiber, the second gain fiber, and the third gain fiber are doped fibers.
[0009] In one embodiment, the doped fiber is a ytterbium-doped fiber capable of generating excitation light near 1 μm, an erbium-doped fiber capable of generating excitation light near 1.6 μm, or a thulium-doped fiber capable of generating excitation light near 1.9 μm.
[0010] In one embodiment, the operating wavelengths of the pump source, wavelength division multiplexer, fiber circulator one, fiber circulator two, polarization beam splitter, and output coupler are consistent with the excitation wavelengths of each gain fiber.
[0011] In one embodiment, the pump, wavelength division multiplexer, fiber circulator one, fiber circulator two, polarization beam splitter, output coupler, and each gain fiber are all connected to each other using single-mode fiber connections.
[0012] In one embodiment, the first and second reflecting ends are fiber Bragg fibers, fiber Sagnac total reflection mirrors, or fiber circulators.
[0013] In one embodiment, a polarization controller is provided between port 2 of the first fiber optic circulator and the first gain fiber, and a polarization controller is provided between port 2 of the second fiber optic circulator and the second gain fiber. The polarization controllers one and two utilize birefringence to control the standing wave interference state and loss within their respective cavities.
[0014] The present invention also provides a method for generating a swept-frequency microwave photonic signal, which is implemented based on the swept-frequency microwave photonic signal generating device described in 1, and the steps are as follows:
[0015] The pump source outputs a pump laser, which is introduced into the gain fiber 3 via a wavelength division multiplexer. The gain fiber 3 absorbs the pump light and generates corresponding broadband stimulated emission light through energy level transitions. After passing through a polarization beam splitter, two polarized beams are output. One beam enters resonant cavity 1, passes through port 1 of fiber circulator 1 to port 2, passes through gain fiber 1, is reflected by reflection end 1, and then passes through gain fiber 1 again to ports 2 and 3 of fiber circulator 1 to reach the output coupler. The other beam enters resonant cavity 2, passes through port 1 of fiber circulator 2 to port 2, passes through gain fiber 2, is reflected by reflection end 2, and then passes through gain fiber 2 again to ports 2 and 3 of fiber circulator 2 to reach the output coupler. The output coupler couples the two polarized beams and outputs a portion of the light according to the coupling ratio. The remaining light will pass through the wavelength division multiplexer back into gain fiber 3 for amplification and optical circulation will be performed again.
[0016] In one embodiment, a polarization controller one is provided between port 2 of the first fiber optic circulator and the first gain fiber, and a polarization controller two is provided between port 2 of the second fiber optic circulator and the second gain fiber.
[0017] In resonant cavity one, polarization controller one is controlled to form a stable ultra-narrowband dynamic induced grating in gain fiber one. The center wavelength of the grating is consistent with the wavelength of the light operating in the cavity, generating a stable single-wavelength single-frequency laser. In resonant cavity two, polarization controller two is controlled to generate a dynamic induced grating in gain fiber two whose reflection spectrum has a wavelength detuning from the operating laser. This grating forces resonant cavity two to generate a stable wavelength self-sweeping laser. The stable single-wavelength single-frequency laser and the stable wavelength self-sweeping laser beat in a coupler to generate a swept-frequency output microwave signal.
[0018] Compared with existing technologies, this invention proposes a wide-range tunable microwave photonic signal generation method based on the dual-wavelength beat frequency method, which has advantages such as good stability and simple operation and analysis. As for the device system itself, it can achieve frequency sweep output of microwave signals, while the output laser has high monochromaticity. The optical path is simple, the size is small, and the cost is low. Attached Figure Description
[0019] Figure 1 This is a schematic diagram of the structure of the present invention. Detailed Implementation
[0020] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings and examples.
[0021] like Figure 1As shown, this invention provides a swept-frequency microwave photonic signal generation device, mainly comprising a pump source 1, a wavelength division multiplexer 2, three gain fiber segments (gain fiber one 31, gain fiber two 32, and gain fiber three 33), a polarization beam splitter 4, two fiber circulators (fiber circulator one 51 and fiber circulator two 52), two reflecting ends (reflector one 71 and reflector two 72), and an output coupler 8. Additionally, when necessary, it also includes two polarization controllers (polarization controller one 61 and polarization controller two 62).
[0022] In this configuration, the output of pump source 1 is connected to the blue end of wavelength division multiplexer 2, the common end of wavelength division multiplexer 2 is connected to one end of gain fiber 33, the other end of gain fiber 33 is connected to the incident end of polarization beam splitter 4, one output end of polarization beam splitter 4 is connected to port 1 of fiber optic circulator 51, port 2 of fiber optic circulator 51 is connected to reflection end 71 through gain fiber 31, port 3 is connected to one input end of output coupler 8, and the output end of output coupler 8 is connected to the red end of wavelength division multiplexer 2, thus forming a ring resonant cavity 1, i.e., Cavity1 in the figure.
[0023] On the other hand, the other output end of the polarization beam splitter 4 is connected to port 1 of the fiber optic circulator 2 52. Port 2 of the fiber optic circulator 2 52 is connected to the reflection end 2 72 through the gain fiber 2 32. Port 3 is connected to the other input end of the output coupler 8. The output end of the output coupler 8 is connected to the red end of the wavelength division multiplexer 2, thereby forming a ring resonant cavity 2, namely Cavity2 in the figure.
[0024] Cavity1 and Cavity2 share a pump source 1, wavelength division multiplexer 2, gain fiber 33, polarization beam splitter 4, and output coupler 8. Fiber circulator 1 51 and fiber circulator 2 52 change the direction of light wave propagation and provide high optical isolation to prevent the reverse propagation of light waves.
[0025] In this invention, gain fiber 1 31, gain fiber 2 32, and gain fiber 33 serve as saturable absorbers. Light waves enter port 2 from port 1 of fiber optic circulator 51 and pass through gain fiber 1 31. Reflected by reflector 71, a standing wave structure is formed in gain fiber 1 31, creating a dynamic grating to achieve self-scanning single-frequency operation of the laser. The wavelength range of this self-scanning is determined by the bandwidth of reflector 71. Similarly, light waves, reflected by reflector 72, form a standing wave structure in gain fiber 2 32, creating a dynamic grating to achieve self-scanning single-frequency operation of the laser. The wavelength range of this self-scanning is determined by the bandwidth of reflector 72.
[0026] In this invention, Cavity1 and Cavity2 form a dual laser resonator with an all-fiber structure. The two resonators have the same fiber structure, differing only in the length of the saturable absorber. For ease of description, this invention sets the length of gain fiber 31 to be greater than the length of gain fiber 32. That is, Cavity1 uses a longer fiber saturable absorber, which, together with polarization controller 61 and reflection end 71, ensures stable single-frequency laser output. Cavity2 uses a shorter saturable absorber, which, together with polarization controller 62 and reflection end 72, ensures stable, broadband wavelength-scanning single-frequency laser output. The two output laser beams beat at the output coupler 8 to generate a swept-frequency microwave photonic signal output.
[0027] In this invention, the two output laser beams possess high monochromaticity and low phase noise. Since two freely rotating laser beams of different frequencies can generate microwave signals through coupling, one highly coherent single-frequency laser beam maintains a stable frequency, while the other highly coherent single-frequency laser beam undergoes a broadband (nm-level) frequency sweep operation with equal wavelength intervals. By polarizing and splitting the same beam using a polarization beam splitter 4, the two laser beams can generate low phase noise when combined and output through the coupler 8. Therefore, this invention can generate microwave photonic signals with high coherence, a wide tuning / sweep range, and low phase noise.
[0028] Cavity1 achieves stable single-mode laser output by using a longer fiber saturable absorber in conjunction with a polarization controller. Cavity2, using a shorter fiber saturable absorber, generates periodic, spontaneous, and stable wavelength self-scanning under the influence of self-scanning and filtering effects. Therefore, the microwave signal is generated by combining the narrow-linewidth single-frequency lasers of Cavity1 and Cavity2 in coupler 8. As the wavelength-scanning single-frequency laser of Cavity2 outputs, the microwave signal will vary according to the difference in laser frequencies between the two cavities, resulting in a time-varying microwave signal.
[0029] For example, in this invention, gain fiber one 31, gain fiber two 32, and gain fiber three 33 are selected as doped fibers. The optional doping structures are ytterbium-doped fiber capable of generating excitation light near 1 μm, erbium-doped fiber capable of generating excitation light near 1.6 μm, or thulium-doped fiber capable of generating excitation light near 1.9 μm. Regardless of the selection, gain fiber one 31, gain fiber two 32, and gain fiber three 33 should be selected as doped fibers of the same type capable of generating excitation light in the same wavelength band.
[0030] For example, in this invention, the operating wavelengths of pump source 1, wavelength division multiplexer 2, fiber optic circulator 1 51, fiber optic circulator 2 52, polarization beam splitter 4, and output coupler 8 are consistent with the excitation wavelengths of each gain fiber. Of course, other wavelengths and doped fibers with other doping media can also be used, as long as the function of the doped fiber in this invention can be achieved, they are within the scope of protection of this invention.
[0031] For example, in this invention, the pump source 1, wavelength division multiplexer 2, fiber optic circulator 1 51, fiber optic circulator 2 52, polarization beam splitter 4, output coupler 8, and each gain fiber are all connected to each other using single-mode fiber connections.
[0032] For example, in this invention, the first reflecting end 71 and the second reflecting end 72 are narrowband reflecting ends, such as optical fiber Bragg fiber, optical fiber Sagnac total reflection mirror or optical fiber circulator, etc. The first reflecting end 71 and the second reflecting end 72 can be different.
[0033] According to the apparatus of the present invention, the method for generating swept-frequency microwave photonic signals is as follows:
[0034] Pump source 1 outputs pump laser light, which is introduced into gain fiber 33 by wavelength division multiplexer 2. Gain fiber 33 absorbs the pump light and generates corresponding broadband stimulated emission light through energy level transitions. After passing through polarization beam splitter 4, two polarized beams are output. One beam enters resonant cavity 1, passes through port 1 of fiber circulator 51 to port 2, passes through gain fiber 31, is reflected by reflection end 71, and then passes through gain fiber 31 again to enter ports 2 and 3 of fiber circulator 51 to reach output coupler 8. The other beam enters resonant cavity 2, passes through port 1 of fiber circulator 52 to port 2, passes through gain fiber 32, is reflected by reflection end 72, and then passes through gain fiber 32 again to enter ports 2 and 3 of fiber circulator 52 to reach output coupler 8. Output coupler 8 couples the two polarized beams and outputs a portion of the light according to the coupling ratio. The remaining light will pass through wavelength division multiplexer 2 and re-enter gain fiber 33 for amplification, and then perform optical circulation again.
[0035] This invention provides dual-cavity gain through a pump laser and doped fiber. Stable single-wavelength, single-frequency laser output and stable wavelength-sweeping single-frequency laser output are achieved using saturable absorbers of different fiber lengths in the dual cavities. This results in two narrow-linewidth laser outputs: one with a stable wavelength and the other undergoing a frequency sweep over time. The two narrow-linewidth lasers beat to generate a microwave signal, the change of which constitutes the frequency sweep output. The self-sweeping wavelength switches at equal intervals according to the cavity settings, simultaneously beating with the stable single-wavelength, single-frequency laser generated in the first resonant cavity to achieve frequency sweeping of the beat-frequency microwave signal. The microwave signal sweep range and sweep speed are consistent with the wavelength-sweeping laser parameters (related to the sweep range and sweep speed of the self-sweeping laser) and can be controlled by the pump laser power.
[0036] In the above method, after multiple cycles, the light in the two resonant cavities absorbs light in gain fiber 1 (31) and gain fiber 2 (32), creating periodically arranged "spatial holes" along the fiber and causing a slight change in refractive index. Further, when setting polarization controller 1 (61) and polarization controller 2 (62), in resonant cavity 1, polarization controller 1 (61) is controlled to form a stable ultra-narrowband dynamic induced grating in gain fiber 1 (31). The center wavelength of this grating is consistent with the wavelength of the light operating within the cavity, generating a stable single-wavelength single-frequency laser. In resonant cavity 2, polarization controller 2 (62) is controlled to generate a dynamic induced grating in gain fiber 2 (32) whose reflection spectrum has a wavelength detuning from the operating laser. This grating forces resonant cavity 2 to generate a stable wavelength self-sweeping laser. The stable single-wavelength single-frequency laser and the stable wavelength self-sweeping laser beat in coupler 8 to generate a swept-frequency output microwave signal.
Claims
1. A swept microwave photonic signal generation apparatus, characterized by, It comprises a pump source (1), the output of the pump source (1) is connected to the blue end of a wavelength division multiplexer (2), the common end of the wavelength division multiplexer (2) is connected to one end of a gain fiber three (33), the other end of the gain fiber three (33) is connected to the incident end of a polarization beam splitter (4), the two emission ends of the polarization beam splitter (4) are respectively connected to the 1 port of a fiber circulator one (51) and the 1 port of a fiber circulator two (52), the 2 port of the fiber circulator one (51) is connected to a reflection end one (71) through a gain fiber one (31), the 2 port of the fiber circulator two (52) is connected to a reflection end two (72) through a gain fiber two (32), the 3 port of the fiber circulator one (51) and the 3 port of the fiber circulator two (52) are respectively connected to the two input ends of an output coupler (8), the output end of the output coupler (8) is connected to the red end of the wavelength division multiplexer (2), forming two annular resonant cavities, wherein the length of the gain fiber one (31) is greater than the length of the gain fiber two (32), the annular resonant cavity in which the fiber circulator one (51) is located is a resonant cavity one, and the annular resonant cavity in which the fiber circulator two (52) is located is a resonant cavity two. The resonant cavity one stably outputs single-frequency laser, and the resonant cavity two outputs wavelength self-sweeping single-frequency fiber laser, and the two output lasers are frequency-mixed in the output coupler (8) to generate a swept-frequency microwave photon signal output.
2. The swept microwave photonic signal generation apparatus of claim 1, wherein, The gain fiber one (31), the gain fiber two (32) and the gain fiber three (33) act as saturable absorbers, and under the reflection of the reflection end one (71) or the reflection end two (72), standing wave structures are formed in the gain fiber one (31) or the gain fiber two (32), and dynamic gratings are formed to realize laser frequency self-sweeping single-frequency operation, and the bandwidth of the reflection end one (71) or the reflection end two (72) determines the wavelength range of the frequency self-sweeping.
3. The swept microwave photonic signal generation apparatus of claim 2, wherein, The gain fiber one (31), the gain fiber two (32) and the gain fiber three (33) are doped optical fibers.
4. The swept microwave photonic signal generation apparatus of claim 3, wherein, The doped optical fiber is a ytterbium-doped optical fiber capable of generating excitation light near 1 μm, an erbium-doped optical fiber capable of generating excitation light near 1.6 μm, or a thulium-doped optical fiber capable of generating excitation light near 1.9 μm.
5. The swept microwave photonic signal generation apparatus of claim 1, wherein, The operating wavelengths of the pump source (1), the wavelength division multiplexer (2), the fiber circulator one (51), the fiber circulator two (52), the polarization beam splitter (4) and the output coupler (8) are consistent with the excitation wavelengths of the gain fibers.
6. The swept microwave photonic signal generation apparatus of claim 1 or 5, wherein, The connections between the pump source (1), the wavelength division multiplexer (2), the fiber circulator one (51), the fiber circulator two (52), the polarization beam splitter (4), the output coupler (8) and the gain fibers are all single-mode fiber connections.
7. The swept microwave photonic signal generation apparatus of claim 1, wherein, A polarization controller one (61) is arranged between the 2 port of the fiber circulator one (51) and the gain fiber one (31), and a polarization controller two (62) is arranged between the 2 port of the fiber circulator two (52) and the gain fiber two (32), and the polarization controller one (61) and the polarization controller two (62) control the standing wave interference state and loss in the respective cavities by using the birefringence effect. 8.A method for generating a swept-frequency microwave photonic signal, implemented based on the swept-frequency microwave photonic signal generation device of claim 1, characterized in that, The steps are as follows: The pump source (1) outputs pump laser, which is introduced into the gain fiber three (33) by the wavelength division multiplexer (2). The gain fiber three (33) absorbs the pump light to generate corresponding broadband stimulated radiation light through energy level transition. The two beams of polarized light are output respectively through the polarization beam splitter (4); one of the beams enters the resonant cavity one, enters the 2 port of the fiber loop one (51) through the 1 port, passes through the gain fiber one (31), is reflected by the reflection end one (71), and then enters the 2 port and the 3 port of the fiber loop one (51) through the gain fiber one (31) again to reach the output coupler (8); the other beam enters the resonant cavity two, enters the 2 port of the fiber loop two (52) through the 1 port, passes through the gain fiber two (32), is reflected by the reflection end two (72), and then enters the 2 port and the 3 port of the fiber loop two (52) through the gain fiber two (32) again to reach the output coupler (8); the output coupler (8) couples the two beams of polarized light and outputs a part of light according to the coupling ratio, and the remaining light will re-enter the gain fiber three (33) through the wavelength division multiplexer (2) for amplification and perform light circulation again.
9. The method of claim 8, wherein the frequency-swept microwave photonic signal is generated by a frequency-swept microwave photonic signal generator. A polarization controller one (61) is arranged between the 2 port of the fiber loop one (51) and the gain fiber one (31), and a polarization controller two (62) is arranged between the 2 port of the fiber loop two (52) and the gain fiber two (32); In the resonant cavity one, the polarization controller one (61) is controlled to form a stable ultra-narrow band dynamic induced grating in the gain fiber one (31), the center wavelength of the grating is consistent with the wavelength of the light in the cavity, and stable single-wavelength single-frequency laser is generated; in the resonant cavity two, the polarization controller two (62) is controlled to generate a dynamic induced grating in the gain fiber two (32), the reflection spectrum of the grating has a wavelength mismatch with the operating laser, and the grating forces the resonant cavity two to generate stable wavelength self-sweeping laser; the stable single-wavelength single-frequency laser and the stable wavelength self-sweeping laser beat in the output coupler (8) to generate a swept output microwave signal.