A single-mode opto-oscillator based on low-frequency drift of all-optical microwave phase conjugation

Abstract

This invention discloses a low-frequency drift single-mode opto-oscillator based on all-optical microwave phase conjugation. It utilizes the all-optical microwave phase conjugation passive compensation principle and nonlinear dual-ring vernier effect mode selection technology to propose an opto-oscillator with low frequency drift, low phase noise, and high side-mode rejection ratio. On one hand, compared to opto-oscillators using linear symmetric dual-ring vernier effect mode selection, this opto-oscillator scheme achieves both a higher side-mode rejection ratio and higher amplitude stability for the output mode. On the other hand, the use of all-optical microwave phase conjugation passive compensation technology ensures frequency stability while avoiding the constraint of external RF sources on near-carrier phase noise in injection-locked technology, thus overcoming dependence on low-phase-noise external sources. The opto-oscillator of this invention can achieve stable frequency output while maintaining single-mode oscillation, overcoming the shortcomings of traditional schemes in mode selection and mode frequency stability.

Description

Technical fields:

[0001] This invention proposes a single-mode optoelectronic oscillator with stable frequency output based on all-optical phase conjugate passive compensation, which relates to the research field of high-quality radio frequency signal generation. Background technology:

[0002] Microwave sources are a key component in many disciplines, such as radar, communications, sensing, testing, and measurement. They hold promise for providing high-frequency carriers for radar and wireless communications, high-speed clocks for wired communications, and local oscillators for test instruments. In particular, the long-term frequency stability and short-term phase noise of microwave sources are two critical metrics in applications. Photonic-based optoelectronic oscillators can overcome the phase noise limitations of purely electronic oscillators at high frequencies and are a good candidate for generating high-spectral-purity microwave or millimeter-wave signals. By using long optical fibers in the oscillation circuit, optoelectronic oscillators exhibit excellent short-term phase noise performance. However, due to the temperature dependence of the effective refractive index of the fiber, the dominant mode frequency of the optoelectronic oscillator drifts with changes in ambient temperature. Furthermore, the long fiber narrows the free spectrum range, making the suppression of side-mode spurious signals near the dominant mode difficult, as extremely narrow high-quality factor filters are challenging to fabricate at high frequencies.

[0003] In recent years, phase-stable transmission of microwave signals based on the principle of phase compensation has been proposed and widely discussed. It is mainly divided into two types: active compensation and passive compensation. Active compensation schemes compensate for signal phase shifts in real time through phase detection and compensation algorithms, correcting and canceling phase jitter. However, its compensation bandwidth and frequency band are severely limited by the compensation components, and it introduces additional noise, reducing the system's frequency stability. Passive compensation schemes, on the other hand, use mixers and frequency multipliers to conjugate and invert the phase shift of the received signal, thus transmitting it back to the remote end to cancel phase jitter. This overcomes the bandwidth limitations of the components and has a simple structure. However, because phase conjugation requires a large number of nonlinear devices, it introduces problems such as local oscillator leakage and harmonic spurious signals, which are superimposed on the phase noise spectrum at the remote end, further deteriorating frequency stability. The drift compensation of the output frequency of an optoelectronic oscillator is similar to the phase compensation in the phase-stable transmission of microwave signals, including active compensation and passive compensation. Similarly, the active compensation scheme uses a phase-locked loop to detect and then compensate, but it is limited by the bandwidth and frequency band of the compensation components. The passive compensation scheme injects an external stable radio frequency source into the compensation loop to lock the optoelectronic oscillator to the injected radio frequency source, thereby achieving a low-frequency drift output. However, this scheme is limited by the phase noise of the externally injected source.

[0004] In addition, single-mode oscillation of optoelectronic oscillators has been extensively studied. Mode selection methods mainly include injection locking, multi-cavity vernier effect and parity-time symmetry. Among them, multi-cavity vernier effect has been extensively studied because it has good stability and overcomes the dependence on external radio frequency sources. Among them, nonlinear dual-loop has the best performance because it not only has a higher side-mode rejection ratio, but also more stable power of output cavity mode. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and propose a low-frequency drift single-mode optoelectronic oscillator based on all-optical microwave phase conjugation, such as... Figure 1 As shown.

[0006] exist Figure 1 The system scheme shown is based on an all-optical microwave phase-conjugated optoelectronic oscillator, which includes an all-optical microwave phase-conjugated part and a frequency-doubling optoelectronic oscillator part; wherein,

[0007] The all-optical microwave phase conjugate section consists of a second optical circulator 105, a second electro-optic modulator 106, a first optical filter 112, a second photodetector 113, and a second electrical bandpass filter 114.

[0008] In addition to the basic first continuous laser 101, first electro-optic modulator 102, first single-mode fiber 104, first photodetector 108, first electrical amplifier 109, and first electrical bandpass filter 110, the frequency doubling optoelectronic oscillator also includes a first optical circulator 103, a first optical coupler 107, and a frequency divider 111.

[0009] The optical carrier generated by the first continuous laser 101 is modulated into an optical two-tone signal by the first electro-optic modulator 102 to detect the phase delay change of the long optical fiber. After passing through the first optical circulator 103 and the first single-mode fiber 104, it undergoes all-optical microwave phase conjugation in the second electro-optic modulator 106. The phase conjugated signal is transmitted in reverse through the second optical circulator 105, the first single-mode fiber 104, and the first optical circulator 103 to the first optical coupler 107, where it is split into two optical two-tone signals. One of the two-tone signals is photoelectrically converted into a second harmonic signal by the first photodetector 108, the first electrical amplifier 109, and the first electrical bandpass filter 110. This signal is then split into two paths: one path returns to the radio frequency drive port of the second electro-optic modulator 106 to form the first loop of the photoelectric oscillator; the other path is converted into a fundamental frequency signal by the frequency divider 111 and returns to the radio frequency port of the first electro-optic modulator 102 to form the second loop of the photoelectric oscillator. The second optical dual-tone signal split from the first optical coupler 107 passes through the first optical filter 112, and then undergoes photoelectric conversion in the second photodetector 113 and the second electrical bandpass filter 114, thereby eliminating the time delay drift caused by the optical fiber. This frequency-doubled opto-oscillator contains a nonlinear double-loop structure, enabling effective single-mode oscillation output. Furthermore, the all-optical microwave phase conjugate component added to the frequency-doubled opto-oscillator effectively eliminates the time delay drift of the optical fiber, improving the frequency stability of the output.

[0010] This invention also provides a scheme for realizing single-mode oscillation of an optoelectronic oscillator through a nonlinear double-ring structure, characterized by comprising:

[0011] Two cascaded electro-optic modulators, 102 and 106, form a nonlinear coupled double loop, both operating at the carrier suppression point. The loop optical signal is generated by a first continuous laser 101, passes sequentially through a first electro-optic modulator 102, a first optical circulator 103, a first single-mode fiber 104, a second optical circulator 105, and a second electro-optic modulator 106, then propagates in the reverse direction through the second optical circulator 105, the first single-mode fiber 104, the first optical circulator 103, and the first optical coupler 107, before passing sequentially through a first photodetector 108, a first electrical amplifier 109, and a first electrical bandpass filter 110. The signal is then split into two paths: one path passes through a first frequency divider 111 and is fed into the first electro-optic modulator 102 to form the first loop; the other path is fed into the second electro-optic modulator 106 to form the second loop. That is, the output of the second loop modulates the signal in the first loop, changing its spectral structure. When it is transmitted in reverse in the first single-mode fiber 104, the phase shift is eliminated, resulting in a significant reduction in the equivalent loop length of the signal in the first loop. The delay is determined only by the electrical loop and can be regarded as a short loop.

[0012] Therefore, according to the vernier effect, the mode interval of this photoelectric oscillator is determined by the shorter loop. τ2 represents the time delay of the signal passing through the circuit consisting of the first photodetector 108, the first electrical amplifier 109, and the first electrical bandpass filter 110. On the other hand, the phase noise of the oscillator is determined by the long loop, resulting in a large mode spacing and low phase noise. After mode selection by the bandpass filter, effective single-mode oscillation can be achieved.

[0013] According to one aspect of the present invention, a photoelectric oscillator scheme capable of outputting a low-frequency drift electrical signal is provided. Its features include:

[0014] Step 1: Generate an optical dual-tone signal to detect delay jitter in the optical fiber of the photoelectric oscillator:

[0015] When the photoelectric oscillator achieves nonlinear dual-ring single-mode oscillation, assuming the angular frequency of this single-mode oscillation is w r The radio frequency signal injected into the first electro-optic modulator 102 can be expressed as:

[0016]

[0017] in The phase of the radio frequency signal is t, where t is the time variable. The first continuous laser 101 generates an angular frequency of ω. c The optical carrier is suppressed and modulated by small-signal carrier in the first electro-optic modulator 102, and the resulting double-sideband signal E1 can be expressed as:

[0018]

[0019] Where i is the imaginary unit. After the signal is transmitted through the first optical circulator 103 in the first single-mode optical fiber 104, the resulting forward transmission signal E2 is:

[0020]

[0021] in τ1 and τ2 are the phase shift and time jitter introduced by the first single-mode fiber 104.

[0022] Step two: Generate a phase conjugate signal and propagate it in reverse in the optical fiber of the opto-oscillator:

[0023] The injected signal of the second electro-optic modulator 106 is divided by the first frequency divider 111 to obtain signal V1. Therefore, the radio frequency signal V2 injected into the second electro-optic modulator 106 can be expressed as:

[0024]

[0025] Forward transmission signal E2 is fed into the second electro-optic modulator 106 through the second optical circulator 105 for carrier-suppressed double-sideband modulation, resulting in signal E3:

[0026]

[0027] The phase conjugate signal is transmitted in reverse through the first optical circulator 103, the first single-mode fiber 104, and the first optical coupler 107 to eliminate phase shift. The obtained backward transmission signal E4 is:

[0028]

[0029] Step 3: Filter out third-order stray sidebands to obtain a low-frequency drifted electrical signal output:

[0030] The signal is split into two paths by the first optical coupler 107. One path passes through the first optical filter 112 to remove the positive and negative third-order sidebands, and is then converted into an electrical signal by the second photodetector 113 and filtered out for spurious signals by the second electrical bandpass filter 114. The resulting second harmonic signal is:

[0031]

[0032] It can be seen that there is no phase shift caused by fiber delay jitter in V3. This means that an optoelectronic oscillator capable of outputting low-frequency drift electrical signals has been realized.

[0033] The advantages and beneficial effects of this invention are as follows:

[0034] This invention primarily addresses the issues of output RF frequency drift and spurious side-mode suppression in optoelectronic oscillators caused by changes in ambient temperature. It introduces all-optical phase conjugation passive compensation technology into the structural design of optoelectronic oscillators for the first time. By employing all-optical microwave phase conjugation, it eliminates RF phase drift caused by fiber delay jitter while avoiding frequency stability degradation due to local oscillator leakage and harmonic spurs. Simultaneously, it utilizes an equivalent nonlinear dual-ring resonant cavity mode selection method in a single ring, ensuring high-quality single-mode oscillation while stabilizing the amplitude of the output RF signal. This has significant practical implications for the future miniaturization and integration of optoelectronic oscillators. Attached Figure Description

[0035] Figure 1 This is a diagram of a low-frequency drift, low-spurious opto-oscillator based on all-optical phase conjugation.

[0036] Figure 2 This is an example block diagram of the present invention.

[0037] Figure 3(a) is a spectrum of the photoelectric oscillator before single-mode oscillation, measured in an example of the present invention.

[0038] Figure 3(b) is a spectrum of the photoelectric oscillator after single-mode oscillation measured in an example of the present invention.

[0039] Figure 4This is a graph showing the frequency measurement results of the photoelectric oscillator before and after frequency drift compensation, obtained from an example of the present invention.

[0040] Figure 5(a) is a diagram showing the phase noise measurement results of the photoelectric oscillator before frequency drift compensation, obtained in an example of the present invention.

[0041] Figure 5(b) is a graph showing the phase noise measurement results of the photoelectric oscillator after frequency drift compensation, obtained from an example of the present invention.

[0042] The labels in the diagram are explained as follows:

[0043] A first continuous laser 101, a first electro-optic modulator 102, a first optical circulator 103, a first single-mode fiber 104, a second optical circulator 105, a second electro-optic modulator 106, a first optical coupler 107, a first photodetector 108, a first electrical amplifier 109, a first electrical bandpass filter 110, a first frequency divider 111, and a first optical filter 112.

[0044] Second photodetector 113, second electrical bandpass filter 114;

[0045] The system includes a second continuous laser 201, a first polarization controller 202, a third electro-optic modulator 203, a third optical circulator 204, a second single-mode fiber 205, a fourth optical circulator 206, an optical amplifier 207, a second polarization controller 208, a fourth electro-optic modulator 209, a second optical coupler 210, a third photodetector 211, a second electrical amplifier 212, a third electrical bandpass filter 213, an electrical coupler 214, a second frequency divider 215, a second optical filter 216, a fourth photodetector 217, a fourth electrical bandpass filter 218, a phase noise analyzer 219, and a frequency counter 220. Detailed Implementation

[0046] This invention proposes a low-frequency drift, low-spurious single-mode optoelectronic oscillator based on all-optical microwave phase conjugation, which is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0047] This invention proposes a circuit principle for a low-frequency drift, low-spurious single-mode optoelectronic oscillator based on all-optical phase conjugation, as follows: Figure 1 As shown, the photoelectric oscillator includes:

[0048] The optical carrier generated by the first continuous laser 101 is modulated into an optical two-tone signal by the first electro-optic modulator 102 to detect the phase delay change of the long optical fiber. After passing through the first optical circulator 103 and the first single-mode fiber 104, it undergoes all-optical microwave phase conjugation in the second electro-optic modulator 106. The phase conjugated signal is transmitted in reverse through the second optical circulator 105, the first single-mode fiber 104, and the first optical circulator 103 to the first optical coupler 107, where it is split into two optical two-tone signals. One of the two-tone signals is photoelectrically converted into a second harmonic signal by the first photodetector 108, the first electrical amplifier 109, and the first electrical bandpass filter 110. This signal is then split into two paths: one path returns to the radio frequency drive port of the second electro-optic modulator 106 to form the first loop of the photoelectric oscillator; the other path is converted into a fundamental frequency signal by the frequency divider 111 and returns to the radio frequency port of the first electro-optic modulator 102 to form the second loop of the photoelectric oscillator. The second optical dual-tone signal split from the first optical coupler 107 passes through the first optical filter 112, and then undergoes photoelectric conversion in the second photodetector 113 and the second electrical bandpass filter 114, thereby eliminating the time delay drift caused by the optical fiber. This frequency-doubled optoelectronic oscillator contains a nonlinear double-loop structure, enabling effective single-mode oscillation output. Furthermore, the all-optical microwave phase conjugation component added to the frequency-doubled optoelectronic oscillator effectively eliminates the time delay drift of the optical fiber, improving the frequency stability of the output. This invention is based on the consideration that, in a long-fiber-based frequency-doubled optoelectronic oscillator, by introducing a passive compensation system based on all-optical phase conjugation and a nonlinear double-loop structure into the fiber loop, the multi-mode competition and dominant mode drift of the optoelectronic oscillator output signal are effectively overcome. This achieves low spurious emissions, low frequency drift, and low phase noise output from the optoelectronic oscillator.

[0049] Example:

[0050] like Figure 2The exemplary embodiment of the present invention is shown below. A specific implementation of the example is as follows: The all-optical microwave phase conjugation section comprises a fourth optical circulator 206, an optical amplifier 207, a second polarization controller 208, a fourth electro-optic modulator 209, a second optical filter 216, a fourth photodetector 217, and a fourth electrical bandpass filter 218. The frequency-doubling optoelectronic oscillator section, in addition to the commonly included second continuous laser 201, first polarization controller 202, third electro-optic modulator 203, second single-mode fiber 205, third photodetector 211, second electrical amplifier 212, and third electrical bandpass filter 213, also includes a third optical circulator 204, a second optical coupler 210, an electrical coupler 214, and a second frequency divider 215. In this frequency-doubled optoelectronic oscillator, the second single-mode fiber 205 is reverse-multiplexed under the action of the fourth optical circulator 206. The signal is transmitted twice in both forward and reverse directions in the fiber ring before being detected by the third photodetector 211. The resulting frequency-doubled electrical signal is amplified and filtered, and then split into two paths by the electrical coupler 214. One path serves as the RF electrical signal input terminal of the fourth electro-optic modulator 209, and the other path, after passing through the second frequency divider 215, serves as the RF electrical signal input terminal of the third electro-optic modulator 203. These two paths constitute a nonlinear double-loop structure, which can achieve effective single-mode oscillation output. The frequency of the single-mode oscillation signal selected by the third electrical bandpass filter 213 according to formula (1) is 4.9 GHz. In addition, the addition of an all-optical microwave phase conjugate part to this frequency-doubled optoelectronic oscillator can effectively eliminate the time delay drift of the optical fiber and improve the frequency stability of the output. The third electro-optic modulator 203 of the opto-oscillator operates at the carrier suppression point, thus obtaining the double-sideband signal (2). After passing through the third optical circulator 204 and the second single-mode fiber 205, it carries phase jitter information to obtain the signal (3). Then, it passes through the fourth optical circulator 206 and enters the optical amplifier 207 for amplification. The second polarization controller 208 eliminates polarization loss. Then, it is injected into the fourth electro-optic modulator 209 and carrier-suppressed modulated by the signal (4) with a frequency of 9.8 GHz to obtain the phase conjugate signal (5). Then, it passes through the fourth optical circulator 206, the second single-mode fiber 205, the third optical circulator 204, and the second optical coupler 210 for reverse transmission to obtain the signal (6). Finally, the third-order sideband is filtered out by the second optical filter 216, and the signal is converted by the fourth photodetector 217 and the fourth bandpass filter 218 to obtain the low-frequency drift 9.8 GHz opto-oscillator signal (7) and output.

[0051] All components used in this invention can be implemented using conventional products. The effectiveness of the low-frequency drift, low-spurious optoelectronic oscillator proposed in this invention is verified through the following examples. In this embodiment, the third electro-optic modulator 203 uses an intensity modulator of model FTM7962, and the fourth electro-optic modulator 209 uses a dual-parallel modulator of model FTM7961EX; a 1km long second single-mode optical fiber 205 is used as the resonant cavity; and a third photodetector 211 and a fourth photodetector 217 of model (MPRV1331A) are used. A second electrical amplifier 212 of model JiTai (LNA0015) is used, and a Teraxion (PS-TNL) second continuous laser 201 is used to generate continuous laser light.

[0052] To measure the frequency-doubled RF signal output by the electric bandpass filter 218 in this example and to observe the difference between this frequency-doubled RF signal and the output signal of the optoelectronic oscillator before single-mode oscillation (i.e., the frequency-doubled RF signal output by the fourth electric bandpass filter 218 after removing the connection between the electric coupler 214 and the RF drive of the fourth electro-optic modulator 209), a conventional phase noise analyzer 219 (containing an electric spectrometer) was set at the output of the fourth electric bandpass filter 218 to measure the spectrum. The measurement results are shown in Figure 3(a) and Figure 3(b). It can be seen that this example can achieve 68dB of side-mode suppression.

[0053] Secondly, the frequency measurement results of the frequency-diminished RF electrical signal V3 with frequency drift compensation and the frequency-diminished RF electrical signal without frequency drift compensation (i.e., the electrical signal output after the third electrical bandpass filter 213) were compared within 600 seconds using a conventional frequency counter (53230A) 220. Figure 4 As shown, the frequency shift of the frequency-doubled radio frequency signal without frequency drift compensation can reach 1.5 ppm, while the frequency drift of the frequency-doubled radio frequency signal with frequency drift compensation is within 0.04 ppm. It can be seen that the photoelectric oscillator of this invention has excellent frequency stability output performance.

[0054] Finally, the phase noise of the frequency-doubled RF signal V3 output in this example was measured using a conventional phase noise analyzer 219. The phase noise of the frequency-doubled RF signal V3 measured in this example was compared with the phase noise measurement results of the frequency-doubled RF signal without frequency drift compensation (i.e., the signal output after the third electrical bandpass filter 213). As can be seen from Figures 5(a) and 5(b), the phase noise at a frequency offset of 10kHz is -110dBc / Hz before and after compensation. Therefore, the phase noise performance of this invention has not deteriorated compared to before frequency drift compensation, that is, it improves long-term stability without deteriorating short-term stability.

[0055] It should be understood that the description of the invention in the foregoing description and explanation is illustrative and not limiting, and various changes, modifications and / or alterations can be made to the above embodiments without departing from the invention as defined in the appended claims.

Claims

1. A single-mode optoelectronic oscillator with low-frequency drift based on all-optical microwave phase conjugation, characterized in that: It includes an all-optical microwave phase conjugation section and a frequency-doubled photoelectric oscillator section; among which, The all-optical microwave phase conjugate section consists of a second optical circulator, a second electro-optic modulator, a first optical filter, a second photodetector, and a second electrical bandpass filter. In addition to the first continuous laser, the first electro-optic modulator, the first single-mode fiber, the first photodetector, the first electrical amplifier, and the first electrical bandpass filter, the frequency doubling optoelectronic oscillator also includes a first optical circulator, a first optical coupler, and a frequency divider. In this process, the optical carrier generated by the first continuous laser enters the first electro-optic modulator and is modulated into an optical two-tone signal to detect the phase delay change of the long optical fiber. After passing through the first optical circulator and the first single-mode optical fiber, it undergoes all-optical microwave phase conjugation in the second electro-optic modulator. The phase conjugate signal is transmitted in reverse through the second optical circulator, the first single-mode fiber, and the first optical circulator to the first optical coupler, where it is split into two optical dual-tone signals. One of the dual-tone signals is photoelectrically converted into a second harmonic signal by the first photodetector, the first electrical amplifier, and the first electrical bandpass filter. This signal is then split into two paths: one path returns to the RF drive port of the second electro-optic modulator to form the first loop of the opto-oscillator; the other path is converted into a fundamental frequency signal by a frequency divider and returns to the RF port of the first electro-optic modulator to form the second loop of the opto-oscillator. The second optical dual-tone signal split from the first optical coupler passes through the first optical filter and then undergoes photoelectric conversion in the second photodetector and the second electrical bandpass filter to eliminate the time delay drift caused by the optical fiber. The frequency doubling photoelectric oscillator has a nonlinear double-loop structure, which realizes effective single-mode oscillation output.

2. A single-mode oscillation method for an optoelectronic oscillator based on a nonlinear double-ring structure, characterized in that: Two cascaded electro-optic modulators, the first and the second, form a nonlinear coupled double loop, both operating at the carrier suppression point. The loop optical signal is generated by a first continuous laser, passes sequentially through the first electro-optic modulator, the first optical circulator, the first single-mode fiber, the second optical circulator, and the second electro-optic modulator, and then propagates in the reverse direction through the second optical circulator, the first single-mode fiber, the first optical circulator, and the first optical coupler. After passing through the first photodetector, the first electrical amplifier, and the first electrical bandpass filter, it is split into two electrical signals. One signal passes through the first frequency divider and is fed into the first electro-optic modulator to form the first loop; the other signal is fed into the second electro-optic modulator to form the second loop. That is, the output of the second loop modulates the signal in the first loop, changing its spectral structure. When propagating in the reverse direction in the first single-mode fiber, the phase shift is eliminated, resulting in a reduction in the equivalent loop length of the signal in the first loop. The delay is determined only by the electrical loop and is considered a short loop.

3. The single-mode oscillation of the photoelectric oscillator according to claim 2, characterized in that, include: The mode interval of this photoelectric oscillator is determined by a shorter loop. ,in The time delay is the time delay of the signal passing through the circuit consisting of the first photodetector, the first electrical amplifier, and the first electrical bandpass filter.

4. A method for outputting a low-frequency drift electrical signal based on a single-mode optoelectronic oscillator; characterized in that, The steps are as follows: Step 1, generate an optical dual-tone signal to detect the delay jitter in the optical fiber of the photoelectric oscillator; Step 2, generate a phase conjugate signal and transmit it in reverse in the optical fiber of the photoelectric oscillator; Step 3, filter out the third-order stray sidebands to obtain a low-frequency drift electrical signal output. In step one, after the photoelectric oscillator achieves nonlinear dual-ring single-mode oscillation, the angular frequency of the single-mode oscillation is set to be... The radio frequency signal injected into the first electro-optic modulator is represented as: (1) in, It is the phase of the radio frequency signal. It is a time variable; the first continuous laser generates an angular frequency of... The optical carrier is subjected to small-signal carrier suppression modulation in the first electro-optic modulator, resulting in a double-sideband signal. Represented as: (2) in, The imaginary unit is used; the forward transmission signal obtained after the signal is transmitted through the first optical circulator in the first single-mode fiber is... for: (3) in, and It is the phase shift and time jitter introduced by the first single-mode fiber; In step two, the injection signal from the second electro-optic modulator is divided by the first frequency divider to obtain the signal. Therefore, the radio frequency signal injected into the second electro-optic modulator Represented as: (4) Forward transmission signal The signal is obtained by carrier-suppressed double-sideband modulation via a second optical circulator connected to a second electro-optic modulator. for: (5) The phase conjugate signal is transmitted in reverse through the first optical circulator, the first single-mode fiber, and the first optical coupler to eliminate phase shift. The obtained backward transmission signal for: (6)； In step three, the signal is split into two paths by the first optical coupler. One path passes through the first optical filter to remove the positive and negative third-order sidebands, and is then converted into an electrical signal by the second photodetector and filtered for spurious signals by the second electrical bandpass filter. The resulting second harmonic signal is: (7) There is no phase shift caused by fiber delay jitter. This means that an optoelectronic oscillator capable of outputting low-frequency drift electrical signals has been realized.

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