Frequency agility photoelectric oscillator with ultralow phase noise

Abstract

The invention provides a frequency agility photoelectric oscillator with ultralow phase noise. The frequency agility photoelectric oscillator comprises an optical amplifier, an optical isolator, an optical filter, an optical delay unit, an optical coupler, an electro-optical modulation unit, an optical detector, a radio frequency filtering unit, a phase regulation and control unit, a radio frequency power divider, a dual-channel voltage control unit and the like. The device has the advantages of frequency agility, low phase noise, high stability, compact structure, rapid frequency switching and the like, and can be applied to the fields of radar, communication, quantum precision measurement and the like.

Description

Technical Field

[0001] The present application relates to the field of microwave photon technology, and in particular to a frequency-agile optoelectronic oscillator with ultra-low phase noise, which can be widely used in radar, communication, quantum precision measurement and other fields. Background Art

[0002] With the increasing demand for transmission bandwidth, processing speed and anti-interference ability in modern communication technology, high-performance microwave sources have become an indispensable core component in the fields of radar, communication, quantum precision measurement, etc. Among them, optoelectronic oscillators, as a technical system that uses optoelectronic feedback cavities with high quality factors (Q) to generate high-performance microwave signals, have received considerable attention in the fields of military weapons and civilian products. In particular, with the rapid development of electronic information technology in recent years, many application fields have high requirements not only for the phase noise of microwave frequency sources, but also for the rapid switching of output frequencies. Therefore, frequency-agile optoelectronic oscillators with ultra-low phase noise have received considerable attention in related application fields.

[0003] The optoelectronic oscillator based on the coupled optoelectronic feedback system overcomes the disadvantage of using short optical fibers to achieve ultra-low phase noise due to the Q-value doubling characteristics of its active optical cavity, making it a typical solution for ultra-low phase noise optoelectronic oscillators. Compared with the traditional single-ring cavity system, it has great advantages in the miniaturization of the optoelectronic oscillator structure and phase noise suppression. However, according to the increasing demand for high-performance microwave sources in radar and other fields, the current technical system also has the following difficulties:

[0004] (1) Traditional coupled optoelectronic oscillators can only emit a single frequency microwave signal output. In practical applications, it is difficult to meet the demand for fast switching of different microwave frequencies, and multiple optoelectronic oscillators of different frequencies need to be switched, which greatly limits its widespread use;

[0005] (2) Traditional frequency-agile optoelectronic oscillators use tunable light sources or filters to switch microwave frequencies. However, it is difficult to effectively suppress phase noise during the frequency conversion process under the limited single-loop structure.

[0006] (3) The oscillation frequency interval of the generated microwave signal is related to the length of the delay fiber. The longer the delay fiber, the smaller the frequency interval and the more difficult it is to suppress the spurious signal. This places high demands on the bandwidth and stability of the RF filter.

[0007] Therefore, in order to obtain an optoelectronic oscillator with fast frequency switching, low phase noise, high frequency stability and good integration performance, the present invention proposes an agile frequency optoelectronic oscillator with ultra-low phase noise. Summary of the invention

[0008] In order to solve the problem that a single-frequency output optoelectronic oscillator cannot directly respond to the demand for fast switching of microwave signals of different frequencies in the communication field, a frequency-agile optoelectronic oscillator can be used to quickly replace microwave sources of different frequencies, so as to meet the demand for fast switching of microwave signal output frequencies in the communication field. The present invention provides an agile frequency-agile optoelectronic oscillator with ultra-low phase noise, which has the advantages of frequency agility, low phase noise, high stability, compact structure, and fast frequency switching, and can be applied to radar, communication, quantum precision measurement and other fields.

[0009] Specifically, a frequency-shifting optoelectronic oscillator with ultra-low phase noise is characterized in that it is mainly composed of an optical amplifier for generating optical gain, an optical isolator for unidirectional transmission of optical signals, an optical filtering unit for suppressing optical signal stray signals, an optical delay unit for optical delay and energy storage, an optical coupler for optical signal splitting, an electro-optical modulation unit for optical signal modulation and mode locking, an optical detector for photoelectric conversion, a radio frequency filter for microwave signal stray suppression and mode selection, a radio frequency amplification unit for radio frequency signal amplification, a phase modulation unit for phase control, a power divider for equally dividing the power of microwave signals, a dual-channel voltage control unit for digital voltage control of the radio frequency filter and the phase control unit, a polarization beam splitter for polarization splitting of optical signals, and an optical reflection unit for optical signal reflection.

[0010] Furthermore, the active optical loop includes two structures: a closed-loop optical cavity composed of an optical amplifier, an optical isolator, an optical filtering unit, an optical delay unit, an optical coupler, and an electro-optical modulation unit in sequence; and a closed-loop optical cavity composed of an optical amplifier, an optical isolator, an optical filtering unit, a polarization beam splitter, an optical delay unit, an optical reflection unit, an optical coupler, and an electro-optical modulation unit.

[0011] Furthermore, the optical delay unit includes a variety of high quality factor optical cavities such as a low-loss optical fiber ring, a whispering gallery cavity or a FP resonant cavity.

[0012] Furthermore, the radio frequency filter is a digital voltage-controlled variable frequency filter, including a variable frequency cavity filter or a variable frequency dielectric filter.

[0013] Furthermore, the phase control unit is an electrically controlled phase shifter that controls the phase shift amount through a voltage signal, and the phase shift amount can be accurately controlled through a digital voltage.

[0014] Furthermore, the dual-channel voltage control unit synchronously controls the center frequency of the radio frequency filter and the phase shift amount of the phase control unit by transmitting a digital voltage pair.

[0015] Furthermore, the dual-channel voltage control unit simultaneously generates a pair of corresponding digital voltage pairs, one for adjusting the center frequency of the RF filter, and the other for synchronously adjusting the phase shift of the phase control unit to achieve phase matching during the frequency conversion process.

[0016] Furthermore, the optical amplifier includes an erbium-doped fiber amplifier or a semiconductor optical amplifier.

[0017] Furthermore, the radio frequency amplifier is a cascade gain structure of a low noise amplifier and a low phase noise amplifier.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] (1) In order to solve the problem that traditional single-frequency optoelectronic oscillators are difficult to simultaneously meet the requirements of rapid frequency switching during use, this solution adopts a dual-channel voltage control unit to synchronously control the center frequency of the RF filter and the phase shift of the phase control unit. By transmitting a digital voltage pair, the phase shift is synchronously controlled during the microwave frequency switching process, thus achieving agile frequency output of microwave signals.

[0020] (2) In order to address the problem that it is difficult to achieve ultra-low phase noise suppression in traditional electro-optical modulators, this scheme uses a coupled optoelectronic feedback structure that combines an active optical loop with a radio frequency link to effectively enhance the quality factor (Q) of the resonant cavity, providing support for the ultra-low phase noise suppression of the agile frequency optoelectronic oscillator.

[0021] (3) In order to solve the problem that microwave signal spurious signals are difficult to suppress in traditional systems, this scheme adopts high-Q whispering gallery cavities, FP resonant cavities and other optical delay units with small mode volumes and large frequency intervals. These units not only effectively improve the mode selection and spurious suppression capabilities of microwave signals, but also further enhance the Q value of the resonant cavity, thus providing support for the spurious suppression of the agile frequency optoelectronic oscillator with ultra-low phase noise.

[0022] In general, the present invention proposes an agile frequency optoelectronic oscillator with ultra-low phase noise, which effectively suppresses phase noise by adopting an optical delay unit (such as a low-loss optical fiber ring, a whispering gallery cavity, and an FP resonant cavity) to enhance the quality factor (Q) value of the resonant cavity of the optoelectronic oscillator. The center frequency of the RF filter and the phase shift of the phase control unit in the RF gain link are synchronously controlled by a dual-channel voltage control unit to achieve agile frequency output of microwave signals, and finally achieve agile frequency stable signal output with ultra-low phase noise, so as to achieve the effect of using the same optoelectronic oscillator to quickly respond to different microwave frequencies, thereby reducing the cost of switching between multiple fixed-frequency optoelectronic oscillators. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 It is a structural schematic diagram of a frequency-agile optoelectronic oscillator with ultra-low phase noise according to the present invention;

[0025] Figure 2 The present invention Figure 1 The schematic diagram of the principle of realizing frequency agility by the optoelectronic oscillator of the structure shown;

[0026] Figure 3 It is another structural schematic diagram of another frequency-agile optoelectronic oscillator with ultra-low phase noise of the present invention;

[0027] Figure 4 Schematic diagram of the structure of the optical delay unit in the present invention: (a) optical fiber ring, (b) whispering gallery cavity, (c) FP resonant cavity.

[0028] 1: optical amplifier, 2: optical isolator, 3: optical filter unit, 13: polarization beam splitter, 4: optical delay unit (optical fiber, WGM, FP cavity), 14: optical reflection unit (reflector, grating), 5: optical coupler, 6: electro-optic modulation unit (mode locking unit), 7: optical detector, 8: RF filter (electrically controlled), 9: RF amplification unit, 10: phase control unit (electrically controlled phase shifter), 11: RF power divider, 12: dual-channel voltage control unit; 4.1: input interface, 4.2: optical fiber ring, 4.3: output interface, 4.4: whispering gallery cavity (WGM), 4.5: FP resonant cavity. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. It should be noted that, in the absence of conflict, the various features in the embodiments of the present application can be combined with each other, and the combined embodiments are still within the scope of protection of the present application.

[0030] In the description of the present application, it should be noted that, unless otherwise specified and limited, the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. indicate the orientation or position relationship based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the product of the application is usually placed when in use. They are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0031] In the description of this application, it should also be noted that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" 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 the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0032] The present invention proposes an agile frequency optoelectronic oscillator with ultra-low phase noise, which is mainly composed of an optical amplifier for generating optical gain, an optical isolator for unidirectional transmission of optical signals, an optical filtering unit for suppressing optical signal stray, an optical delay unit for optical delay and energy storage, an optical coupler for optical signal beam splitting, an electro-optical modulation unit for optical signal modulation and mode locking, an optical detector for photoelectric conversion, a radio frequency filter for microwave signal stray suppression and mode selection, a radio frequency amplification unit for radio frequency signal amplification, a phase modulation unit for phase control, a power divider for equally dividing microwave signal power, a dual-channel voltage control unit for digital voltage control of the radio frequency filter and the phase control unit, a polarization beam splitter for polarization beam splitting of optical signals, and an optical reflection unit for optical signal reflection.

[0033] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0034] Example 1

[0035] In one embodiment, according to the functional characteristics of the frequency-agile optoelectronic oscillator, a schematic diagram of the structure of a frequency-agile optoelectronic oscillator with ultra-low phase noise provided by the present invention is shown in the attached figure. Figure 1 As shown, it is mainly divided into three functional areas including active optical loop, RF gain link and digital voltage control unit.

[0036] The active optical loop is mainly composed of an optical amplifier (1), an optical isolator (2), an optical filter unit (3), an optical delay unit (4), an optical coupler (5), an electro-optical modulation unit (6), etc. It is mainly used to generate high-coherence optical signals and is the power source of the optoelectronic oscillator.

[0037] The radio frequency gain link is mainly composed of a light detector (7), a microwave filter (8), a radio frequency amplification unit (9), a phase control unit (10), a radio frequency power divider (11), etc., and is mainly used to convert a high-coherence high-comb signal into a microwave signal.

[0038] The digital control unit is mainly composed of a dual-channel voltage control unit, which mainly performs voltage control on a microwave filter (8) and a phase control unit (10) in a radio frequency gain link through digital voltage control, so as to realize frequency conversion control of the microwave filter (8) and phase control of the phase control unit (10).

[0039] Through the organic combination of three functional components, namely, active optical loop, RF gain link and digital voltage control unit, an agile frequency optoelectronic oscillator with ultra-low phase noise is realized.

[0040] The frequency-changing optoelectronic oscillator of this embodiment can be divided into three parts according to its function, namely, an active optical loop part, a radio frequency gain link part and a digital voltage control part. The active optical loop is a closed optical resonant cavity that can generate an optical signal. In this process, the optical amplifier (1) first generates an initial optical signal and enters the optical delay unit (4) through the optical isolator (2) and the optical filter unit (3). After the energy storage delay of the optical delay unit (4), it is output from the other end to enter the optical coupler (5). The optical signal output from the optical coupler passes through the electro-optical modulation unit (6) and is output from the other end. The other end of the electro-optical modulation unit (6) is connected to the output end of the optical amplifier (1) to form a closed active optical loop. The optical signal undergoes multiple resonances in the active optical loop and forms a signal as shown in the attached figure. Figure 2 (a) The resonant optical mode is distributed in the form of a spacing of Δv, forming an optical signal with a series of spacings of Δv.

[0041] The optical signal is connected to the RF gain link from the other output end of the optical coupler (5). First, the optical signal output from the other output end of the optical coupler (5) enters the optical detector (7). The main function of the optical detector (7) is to realize photoelectric conversion and beat frequency, and generate a series of radio frequency (RF) signals with a frequency interval of Δv. In this process, if only one of the optical frequencies f is considered 1 With another adjacent optical frequency f 0The mixing characteristics between the two signals will generate a sum frequency signal and a difference frequency signal through the beat frequency after the optical signal enters the photodetector (7). However, due to the limitation of the response bandwidth of the optical detector (7), it can only respond to the difference frequency signal shown below:

[0042]

[0043] Among them, P 0 (t) represents the frequency f 0 The optical signal enters the photodetector (7) optical power, P 1 (t) represents the frequency f 1 = ... 0 and f 1 Based on this principle, a series of RF beat mode signals with an interval of Δv will be generated after the beat frequency, as shown in the attached figure. Figure 2 (b) as shown.

[0044] The initial microwave signal formed enters the RF power divider (11) through the RF filter unit (8), the RF amplification unit (9) and the phase control unit (10), and an output end of the RF power divider (11) is connected to the RF input port of the electro-optical modulation unit (6), thereby forming a closed optoelectronic feedback loop. In this process, the electro-optical modulation unit (6) is mainly used for modulation and mode locking of optical signals, and is the core component of the optoelectronic loop to form a locked mode. When a series of RF beat frequency modes do not form a single RF mode after filtering through the RF gain link, and the microwave frequency incident from an output end of the RF power divider (10) into the RF port of the electro-optical modulation unit (6) does not meet the locking condition between the active optical loop, a microwave signal with more stray frequencies will be formed within the filtering bandwidth of the RF filter unit (8), as shown in the attached figure. Figure 2 When the bandwidth of the RF filter unit (8) is smaller than the mode interval it can accommodate, and the active optical loop and the RF gain link meet the mode locking condition by adjusting the phase control unit (10), a frequency-stable microwave signal operation will be achieved within the filtering bandwidth of the RF filter unit (8), as shown in FIG. Figure 2 (d) The microwave signal with a frequency of nΔv is output from another port of the RF power divider (11).

[0045] The radio frequency filter unit (8) is an electrically controlled variable frequency bandpass filter, and its frequency can be changed by controlling the digital voltage of the dual-channel voltage control unit (12). At the same time, the phase control unit is an electrically controlled phase shifter, and its phase range can be changed by controlling the digital voltage of the dual-channel voltage control unit (12). In this process, the center frequency of the radio frequency filter unit (8) is nΔv, where n is a positive integer. When the center frequency of the radio frequency filter unit (8) changes, the other channel of the dual-channel voltage control unit (12) immediately transmits a corresponding digital voltage signal to automatically control the phase control unit (10), so that the photoelectric feedback system forms a stable mode locking state at the frequency conversion frequency. The dual-channel voltage control unit (12) automatically controls the radio frequency filter unit (8) and the phase control unit (10) respectively, so as to realize the agile frequency conversion output of the microwave signal.

[0046] Example 2

[0047] In another embodiment, the frequency-agile optoelectronic oscillator also mainly includes three functional components, namely, a source optical ring cavity, a radio frequency gain link, and a digital voltage control unit. Figure 3 As shown, the active optical loop of this embodiment is composed of an optical amplifier (1), an optical isolator (2), an optical filter unit (3), an optical polarization beam unit (13), an optical delay unit (4), an optical reflection unit (14), an optical coupler (5), and an electro-optical modulation unit (6). The optical signal generated by the optical amplifier (1) is transmitted sequentially through the optical isolator (2) and the optical filter unit (3) and then enters an input end of the polarization beam splitting unit (13). The optical signal entering the polarization beam splitting unit (13) passes through the optical delay unit (4) and the optical reflection unit (14) and then is reflected by the optical reflection unit (14) and then returns to the polarization beam splitting unit (13) along the original path and is output from another port of the polarization beam splitting unit (13), which is connected to the input end of the optical coupler (5). The optical signal output from the polarization beam splitting unit (13) enters the electro-optical modulation unit (6) through the optical coupler (5), and the output end of the electro-optical modulation unit (6) is connected to the input end of the optical amplifier (1), thereby forming a closed active optical loop. The optical signal undergoes multiple gain amplifications in the active optical resonant cavity and eventually forms a steady-state laser signal output.

[0048] The RF link part mainly includes a photodetector (7), a RF filter (8), a RF amplifier (9), a phase control unit (10) and a power divider (11). The function is the same as that in Example 1, which mainly beats, filters, amplifies and feeds back the equally spaced optical signals to the electro-optical modulation unit (6). Through the organic coordination between the active optical loop and the RF link, a closed photoelectric feedback loop is formed to achieve stable microwave signal output. In this process, the generation of the optical mode signal with a frequency interval of Δv, the generation of the RF beat frequency mode, and the generation of the microwave signal are shown in the attached figure. Figure 2 The principle schematic diagram shown is basically the same as the principle of Example 1.

[0049] In addition, as in Example 1, the dual-channel voltage control unit (12) is mainly used to perform digital voltage control on the radio frequency filtering unit (8) and the phase control unit (10). The dual-channel voltage control unit (12) transmits a digital voltage pair to respectively control the center frequency of the radio frequency filtering unit (8) and the phase shift of the phase control unit (10). Through the synchronous voltage control of the dual-channel voltage control unit (12), a microwave signal with agile frequency output is realized.

[0050] In Embodiment 1 and Embodiment 2, the optical delay unit (4) comprises Figure 4 The three structures shown are the fiber ring assembly, the whispering gallery cavity assembly and the FP resonant cavity assembly. Their main function is to store energy and delay the input optical signal to enhance the quality factor (Q) value of the active optical loop. The Q value of the active optical loop is the key to achieve ultra-low phase noise suppression. Figure 4 In the optical delay unit shown, the fiber ring assembly mainly includes an input interface (4.1), a fiber ring (4.2), and an output interface (4.3); the whispering gallery optical cavity assembly mainly includes an input interface (4.1), a whispering gallery optical cavity (4.4), and an output interface (4.3); and the FP resonant cavity mainly includes an input interface (4.1), an FP resonant cavity (4.5), and an output interface (4.3). In the process of Example 1 and Example 2, all optical components in the active optical loop are connected by fusion or spatial optical coupling, and all components in the radio frequency link are connected by micro adapters. The quality factor (Q) value of the resonant cavity is enhanced by the optical delay unit to achieve effective suppression of ultra-low phase noise, and the center frequency of the radio frequency filter and the phase shift of the phase control unit are synchronously controlled by the dual-channel voltage control unit, and finally a frequency-agile microwave signal output with ultra-low phase noise is achieved.

[0051] Although the present invention has been disclosed as above with preferred embodiments, the embodiments are not intended to limit the present invention. Any equivalent changes or modifications made without departing from the spirit and scope of the present invention also fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the content defined by the claims of the present application.

Claims

1. A frequency-agile optoelectronic oscillator with ultra-low phase noise, characterized in that: It is mainly composed of an optical amplifier for generating optical gain, an optical isolator for unidirectional transmission of optical signals, an optical filtering unit for suppressing optical signal stray waves, an optical delay unit for optical delay and energy storage, an optical coupler for optical signal beam splitting, an electro-optical modulation unit for optical signal modulation and mode locking, an optical detector for photoelectric conversion, a radio frequency filter for suppressing microwave signal stray waves and mode selection, a radio frequency amplification unit for radio frequency signal amplification, a phase modulation unit for phase control, a power divider for equally dividing the power of microwave signals, a dual-channel voltage control unit for digital voltage control of the radio frequency filter and the phase control unit, a polarization beam splitter for polarization beam splitting of optical signals, and an optical reflection unit for optical signal reflection.

2. The optoelectronic oscillator according to claim 1, characterized in that: The active optical loop includes two structures: a closed-loop optical cavity composed of an optical amplifier, an optical isolator, an optical filter unit, an optical delay unit, an optical coupler, and an electro-optical modulation unit in sequence; and a closed-loop optical cavity composed of an optical amplifier, an optical isolator, an optical filter unit, a polarization beam splitter, an optical delay unit, an optical reflection unit, an optical coupler, and an electro-optical modulation unit.

3. The optoelectronic oscillator according to claim 1 or 2, characterized in that: The optical delay unit includes a variety of high-quality factor optical cavities such as low-loss optical fiber ring, whispering gallery cavity or FP resonant cavity.

4. The optoelectronic oscillator according to claim 1, characterized in that: The radio frequency filter is a digital voltage-controlled variable frequency filter, including a variable frequency cavity filter or a variable frequency dielectric filter.

5. The optoelectronic oscillator according to claim 1, characterized in that: The phase control unit is an electrically controlled phase shifter that controls the phase shift amount through a voltage signal and can accurately control the phase shift amount through a digital voltage.

6. The optoelectronic oscillator according to claim 1, characterized in that: The dual-channel voltage control unit synchronously controls the center frequency of the radio frequency filter and the phase shift amount of the phase control unit by transmitting a digital voltage pair.

7. The optoelectronic oscillator according to claim 4, 5 or 6, characterized in that: The dual-channel voltage control unit simultaneously generates a pair of corresponding digital voltage pairs, one for adjusting the center frequency of the RF filter, and the other for synchronously adjusting the phase shift of the phase control unit to achieve phase matching during the frequency conversion process.

8. The optoelectronic oscillator according to claim 1, wherein the optical amplifier comprises an erbium-doped fiber amplifier or a semiconductor optical amplifier. 9 . The optoelectronic oscillator according to claim 1 , wherein the radio frequency amplifier is a cascade gain structure of a low noise amplifier and a low phase noise amplifier.

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