阅读说明：本技术 一种基于注入锁定光电振荡器的信号远距离传输稳相系统 (Signal remote transmission phase stabilization system based on injection locking photoelectric oscillator ) 是由 谢正洋 张开羽 郑铮 于 2021-07-14 设计创作，主要内容包括：本发明一种基于注入锁定光电振荡器的信号远距离传输稳相系统,是基于无源补偿原理和注入锁定光电振荡器OEO微波信号产生技术,提出了一种高频率稳定度、低相位噪声的本振微波信号远距离稳相传输实现方案。一方面,相比于使用主动补偿方法的稳相传输技术,该方案能够适用于更高的频段、更大带宽、相位噪声水平更好的微波信号传输。传统的主动补偿方案具有电器件限制频段带宽和引入电热噪声的劣势。另一方面,一般的无源被动补偿方案则有相位噪声水平较高等问题,使得传输到远端的信号短期稳定性受限。本发明能够使微波信号稳相传输得到更为广泛的应用,弥补传统方案在相位噪声上的缺陷。(The invention discloses a signal remote distance transmission phase stabilization system based on an injection locking photoelectric oscillator, which is based on a passive compensation principle and an injection locking photoelectric oscillator OEO microwave signal generation technology and provides a local oscillator microwave signal remote distance phase stabilization transmission implementation scheme with high frequency stability and low phase noise. On one hand, compared with a phase-stable transmission technology using an active compensation method, the scheme can be suitable for microwave signal transmission with higher frequency band, larger bandwidth and better phase noise level. Conventional active compensation schemes have the disadvantages of electrical devices limiting the bandwidth of the frequency band and introducing electrothermal noise. On the other hand, the general passive compensation scheme has the problems of high phase noise level and the like, so that the short-term stability of the signal transmitted to the far end is limited. The invention can make the microwave signal stable phase transmission more widely applied and make up the defects of the traditional scheme on phase noise.)

1. A signal remote transmission phase stabilization system based on an injection locking photoelectric oscillator is characterized in that: the system consists of a local station and a remote station; the local station includes a body portion, an injection locking portion, and a phase conjugation portion of the OEO loop; the remote station includes a mixing filtering section; the optical fiber connected between the local station and the remote station comprises two sections of single-mode optical fibers, and an optical fiber loop is used as a resonant cavity of the photoelectric oscillator; detecting the phase delay change of the long optical fiber ring by the OEO oscillation signal, sending the phase delay change into a mixer, mixing the phase delay change with a signal of a local reference microwave signal after passing through a frequency multiplier, and then selecting the frequency by a band-pass filter to generate a phase conjugate signal; the phase conjugate signal is modulated onto the optical carrier generated by the continuous light source via the electro-optical modulator, enters the circulator, is reversely transmitted back to the remote station, and is mixed with the forward transmission signal, so that the phase fluctuation caused by the optical fiber can be automatically eliminated.

2. An injection locked optoelectronic oscillator based on high frequency stability of a signal long distance transmission phase-stabilized system as claimed in claim 1, wherein: in a signal remote transmission phase stabilization system structure based on an injection locking photoelectric oscillator, a local reference microwave signal and an OEO oscillation signal are coupled and injected into an electro-optical modulator together in an injection locking mode, so that an effect of mode locking is achieved on OEO multimode oscillation, and the OEO multimode oscillation can be stably oscillated in a single mode; meanwhile, in order to further ensure that injection locking is not lost, a voltage control phase shifter VCP is required to be added to a microwave loop part in the OEO oscillator before the microwave loop part enters the electro-optical modulator, the oscillation frequency is adjusted by controlling the VCP, and the tunable OEO is used as a voltage controlled oscillator VCO which is driven by a phase error signal between an OEO oscillation signal and a local reference microwave signal; and a phase-locked loop system consisting of the phase discriminator, the low-pass filter and the VCO helps to lock the local reference signal and the OEO oscillation signal, so that the stability is improved.

3. The passive compensation method for low phase noise of the injection locked optoelectronic oscillator based signal long-distance transmission phase-stabilized system according to claim 1, wherein the passive compensation method comprises the following steps: in a signal remote transmission phase stabilization system structure based on an injection locking photoelectric oscillator, a long optical fiber in an OEO loop is used as a remote transmission means, and the long optical fiber is used as an energy storage cavity with a high quality factor, so that an oscillating signal with low phase noise can be generated, a local signal can be transmitted to a far end, and the short-term stability of the system is improved;

in the optical path part of the OEO, the output light of the laser diode passes through the electro-optical modulator and the optical fiber loop and is detected by the photoelectric detector; the oscillation signal generated by the circuit part is amplified by an amplifier, and is filtered by a band-pass filter and amplified by an electric amplifier; the oscillation signal generated by OEO is represented as

Wherein ω is_oeo＝2πf_oeoIs the frequency of the oscillation of the oscillator,andinitial phase and phase offset introduced by the optical fiber loop respectively; the local reference microwave signal is represented as

Wherein ω is_LOIs the angular frequency of the wave to be transmitted,is the initial phase;

when the local reference signal and the OEO oscillation signal are locked, the frequency of the local reference signal and the frequency of the OEO oscillation signal are equal, and the phase difference is constant; the remote station obtains a portion of the forward transmitted signal through the coupler and is detected by a detector and filtered by a bandpass filter to remove spurious components, represented as

WhereinIs the phase jitter introduced by the single mode fiber;

the system passive compensation uses a two-stage mixing method, and the mixer mixes the frequency-multiplied local reference signal with the oscillation signal to generate a phase conjugate signal represented as

The phase conjugate signal is then transmitted back along the single mode fiber to the far end and is detected by a detector and filtered by a bandpass filter, denoted as

WhereinIs phase jitter introduced by a single mode fiber and is preserved in the case of slow fiber delay variations

The forward and backward signals are then passed through a mixer 223 and a frequency divider 224 to obtain a signal of

As seen from the formula, a signal that cancels the phase jitter and retains the initial phase is finally obtained at the far end.

The technical field is as follows:

the invention provides a signal remote transmission phase stabilization system based on an injection locking photoelectric oscillator, and relates to the field of microwave photonics microwave signal phase stabilization transmission research.

Background art:

nowadays, high-stability local oscillator signal transmission on optical fibers is of great significance to various applications, such as remote clock synchronization and comparison, radio astronomy, distributed coherent aperture radar, and the like. However, the transmission delay of the optical fiber is affected by the ambient temperature disturbance and pressure variation, so that the phase stability of the transmitted local oscillator microwave signal will be significantly reduced at the remote site. As the frequency and stability requirements of users for signal transmission are increasing, the phase noise level and frequency of the conventional transmission structure have not been able to meet the requirements, and thus a transmission scheme based on the phase compensation principle is proposed and used. At present, the phase stabilization transmission of microwave signals is mainly divided into two phase stabilization means based on round-trip delay calibration, namely active compensation and passive compensation. As shown in fig. 1 (a).

In the active compensation structure, a signal at a local end passes through a phase compensation device 101, reaches a far end 103 through transmission of a long optical fiber 102, reversely transmits the received signal at the far end, performs phase detection 104 with the signal at the local end, extracts phase jitter information introduced by a link, and finally performs real-time compensation on the phase compensation device through a compensation algorithm to counteract phase jitter, so as to achieve the purpose of phase-stable transmission. However, the range of active compensation is limited by the bandwidth of the compensating electrical device, and additional noise is introduced into the electrical device, so that the noise level of the whole system is increased and the stability of the system is affected.

On the other hand, the phase-stabilizing transmission method based on the passive compensation technology breaks through the limitation of the bandwidth of the compensation signal and has a simpler structure. The principle of passive compensation is shown in fig. 1 (b).

In the configuration of fig. 1(b), the continuous light source 108 enters the intensity modulator 109 directly for rf signal modulation, and is transmitted to the remote receiver 112 via the long optical fiber 111, and then transmitted back to the local circulator 110. The microwave signal obtained by the beat frequency of the photodetector 107 and the signal of the local oscillator signal after passing through the frequency tripler 105 are input to the mixer 106, so as to obtain a phase conjugate signal. Then, the optical carrier is modulated onto an optical carrier and transmitted to a far end through a long optical fiber, and finally a phase jitter-free signal is obtained through the photoelectric detector 113 and the frequency divider 114. Because a new signal is not needed to be generated, the phase conjugate inversion is carried out to eliminate the far-end phase jitter, thereby improving the compensation range of the system. However, as the transmission distance (the length of the optical fiber) is increased, frequency drift caused by slow change of the optical fiber during transmission may be accumulated and cannot be compensated in time, and phase noise in the local oscillation signal generation process is difficult to suppress and further superimposed on the phase noise spectrum of the far-end signal, so that short-term stability of the system is affected during frequency mixing compensation.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a signal remote transmission phase stabilization system based on an injection locking photoelectric oscillator, which is shown in figure 2.

In the system scheme shown in fig. 2, the system mainly consists of two parts, namely a local station and a remote station, wherein the local station comprises a main body part, an injection locking part and a phase conjugation part of an OEO loop; the remote station includes a mixer filter section. The optical fiber connected between the local and remote stations includes two lengths of single mode optical fiber 216 and 217, the fiber loop also acting as a resonant cavity for the opto-electronic oscillator. The OEO oscillation signal detects the phase delay variation of the long fiber loop and is sent to a mixer 208, mixed with the local reference microwave signal after passing through a frequency multiplier 210, and then frequency-selected through a band-pass filter 209 to generate a phase conjugate signal. The phase conjugate signal is modulated onto the optical carrier generated by the continuous optical source 201 via the electro-optic modulator 202, enters the circulator 203 for transmission back to the remote station, and is mixed with the forward transmission signal, which automatically eliminates fiber-induced phase fluctuations.

According to an aspect of the present invention, there is provided a high frequency stability optoelectronic oscillator, comprising:

in the signal long-distance transmission phase-stabilizing system structure based on the injection locking photoelectric oscillator, a local reference microwave signal and an OEO oscillation signal are coupled and injected into the electro-optical modulator 215 together in an injection locking mode, so that an effect of mode locking is achieved on OEO multimode oscillation, and the OEO multimode oscillation can be stably oscillated in a single mode. Also to further ensure that the injection locking is not lost, the microwave loop part of the OEO oscillator needs to incorporate a voltage controlled phase shifter (VCP)213 before entering the electro-optical modulator to adjust the oscillation frequency by controlling the VCP, while the tunable OEO acts as a Voltage Controlled Oscillator (VCO) driven by the phase error signal between the OEO oscillation signal and the local reference microwave signal. And a phase-locked loop system consisting of the phase detector 211, the low-pass filter 212 and the VCO can help to lock the local reference signal and the OEO oscillation signal, so that the long-term stability of the system is greatly improved.

According to one aspect of the present invention, a passive compensation scheme with low phase noise is provided. It is characterized by comprising:

in the signal remote transmission phase stabilization system structure based on the injection locking photoelectric oscillator, a long optical fiber in an OEO loop is used as a remote transmission means, and the long optical fiber is used as an energy storage cavity with a high quality factor, so that the oscillation signal with low phase noise can be generated, and a local signal can be transmitted to a far end, so that the short-term stability of the system is improved.

In the optical path portion of the OEO, the output light of the laser diode 214 passes through the electro-optic modulator, the fiber loop and is detected by the photodetector 204; the oscillation signal generated by the circuit portion is amplified by an amplifier 205, filtered by a band-pass filter 206 and amplified by an electric amplifier 207. The oscillation signal generated by the OEO can be expressed as

Wherein ω is_oeo＝2πf_oeoIs the frequency of the oscillation of the oscillator,andrespectively the initial phase and the phase offset introduced by the fiber loop. The local reference microwave signal is represented as

Wherein ω is_LOIs the angular frequency of the wave to be transmitted,is the initial phase.

When the local reference signal and the OEO oscillation signal are locked, the frequencies of the two signals are equal, and the phase difference is constant. The remote station takes part of the forward transmitted signal through coupler 218 and is detected by detector 219 and filtered by bandpass filter 221 of spurious components, represented as

WhereinIs the phase jitter introduced by the single mode fiber 217.

The system passive compensation uses a two-stage mixing method, and the mixer 208 mixes the frequency-multiplied local reference signal with the oscillation signal to generate a phase conjugate signal represented as

The phase conjugate signal is then transmitted back along the single mode fiber 216 to the far end and is detected by detector 220 and filtered by bandpass filter 222, shown as

WhereinIs the phase jitter introduced by the single mode fiber 216 and is preserved in the case of slow fiber delay variations

The forward and backward signals are then passed through a mixer 223 and a frequency divider 224 to obtain a signal of

It can be seen from the formula that a signal that cancels the phase jitter and retains the initial phase is finally obtained at the far end.

The invention has the advantages and beneficial effects that:

the invention mainly aims at the defects of active compensation stable phase transmission bandwidth limitation and noise deterioration, passive compensation stable phase transmission phase noise and the like. On the basis of a passive compensation technology, the method for transmitting the microwave signal in the stable phase mode with low phase noise and high stability by utilizing the signal remote transmission phase-stabilizing system based on the injection locking photoelectric oscillator is firstly proposed. The scheme can eliminate phase drift caused by optical fiber transmission, can remove phase noise of a far-end receiving signal, has the advantages of large bandwidth, wide compensation range, low phase noise and the like compared with an active compensation method, and has the advantages of higher stability, lower phase noise and the like compared with a passive compensation method. The microwave signal stable-phase transmission can be widely applied, and the defects of the traditional scheme on phase noise are overcome.

Drawings

Fig. 1(a) is a basic block diagram of an active compensation technique.

Fig. 1(b) is a basic block diagram of the passive compensation technique.

Fig. 2 is a schematic diagram of a long-distance phase-stabilized system for signal transmission based on injection-locked OEO.

FIG. 3 is a block diagram of an example of the present invention.

Figure 4 is a phase noise comparison of free running OEO, passively compensated OEO, and injection locked passively compensated OEO.

Fig. 5 is a phase fluctuation comparison of free-running OEO, passive compensation, and injection-locked passive compensation OEO.

Figure 6 is a comparison of the allen variances of free-running OEO, passive compensation and injection-locked passive compensation OEO.

The numbers in the figures illustrate the following:

phase compensation device 101, optical fiber 102, remote station 103, phase detector 104, frequency triplexer 105, mixer 106, photodetector 107, continuous light source 108, intensity modulator 109, local circulator 110, long optical fiber 111, remote receiver 112, photodetector 113, and frequency divider 114;

a continuous light source 201, an electro-optical modulator 202, a circulator 203, a photodetector 204, an amplifier 205, a band-pass filter 206, a point amplifier 207, a mixer 208, a band-pass filter 209, a frequency multiplier 210, a phase detector 211, a low-pass filter 212, a voltage-controlled phase shifter (VCP)213, a laser 214, an electro-optical modulator 215, single-mode fibers 216, 217, a coupler 218, a detector 219, a detector 220, a band-pass filter 221, a band-pass filter 222, a mixer 223, and a frequency divider 224;

continuous light source 301, modulator 302, circulator 303, photodetector 304, electrical amplifier 305, band pass filter 306, electrical amplifier 307, mixer 308, band pass filter 309, frequency multiplier 310, phase detector 311, PID operator 312, voltage controlled phase shifter 313, continuous light source 314, intensity modulator 315, optical fiber 316, optical fiber 317, optical coupler 318, photodetectors 319, 320, amplifiers 321, 322, band pass filters 323, 324, input mixer 325, frequency divider 326, electrical spectrum analyzer 327, frequency counter 328;

Detailed Description

The invention provides a signal remote transmission phase stabilization system based on an injection locking photoelectric oscillator, which is further described in detail below with reference to the accompanying drawings and specific embodiments.

The invention provides a signal remote transmission phase stabilization system based on an injection locking photoelectric oscillator, the circuit structure of which is shown in figure 3 and comprises:

the invention is based on the consideration that: in a signal remote transmission phase stabilization system based on an injection locking photoelectric oscillator, the phase jitter of an optical fiber loop is detected through an OEO oscillation signal, and the phase jitter is mixed with a local reference microwave signal to obtain a phase conjugate signal. The backward transmission is carried out back to the far end to carry out frequency mixing with the received forward transmission signal, thereby effectively offsetting the phase jitter introduced by the optical fiber, simultaneously using the long optical fiber to improve the quality of the transmitted local signal and reduce the phase noise level of the far-end output signal. The stray component of the OEO loop is suppressed locally by using a phase-locking and injection locking mode, single-mode oscillation is realized, and the long-term stability of the system is further improved.

Example (c):

an exemplary embodiment of the invention is shown in fig. 3. The method is exemplarily applied to the most basic signal remote transmission phase stabilization system structure based on the injection locking photoelectric oscillator, and experimental comparison tests are carried out on the free-running OEO, the passive compensation scheme and the passive compensation scheme based on the injection locking OEO. Specific embodiments of the examples are as follows: the OEO loop body for generating the local oscillation signal is composed of a continuous light source 314, an intensity modulator 315, long optical fibers 316 and 317, a circulator 303, a photoelectric detector 304, an electric amplifier 305 and a band-pass filter 306; the local reference microwave source is divided into three paths, one path of signal enters the mixer 308 together with the OEO loop oscillation signal after being frequency-doubled by the frequency multiplier 310 to be mixed to obtain a phase conjugate signal, the phase conjugate signal passes through the amplifier 309 and then is modulated onto an optical carrier generated by the continuous light source 301 through the modulator 302, and then is reversely transmitted to a far end along the optical fiber 316; one path of signal is injected into a phase detector 311, a PID operation module 312 and a voltage-controlled phase shifter 313 form phase-locked OEO, an OEO oscillation signal is transmitted to a far end along an optical fiber 317 in a forward direction, and enters a mixer 325 after passing through photoelectric detectors 319 and 320, amplifiers 321 and 322 and band-pass filters 323 and 324 respectively together with a backward signal through an optical coupler 318 to obtain a frequency-doubled non-phase-jittered signal; one signal is input to an electric spectrum analyzer 327 and a frequency counter 328 together with the signal of the far end after frequency division by a frequency divider 326, to measure and evaluate the frequency distribution performance.

First, a phase noise spectrum was measured with 327, and the result is shown in fig. 4. It can be seen that the phase noise level of the present invention at 10kHz frequency offset is much lower than that of the conventional passive compensation scheme and free running OEO, and the method has significantly improved short-term frequency stability compared to most microwave phase-stabilized transmission systems.

Next, the microwave transmission system was tested for phase drift on the fiber loop using 328, the results of which are shown in fig. 5. It can be seen that in the measurement time of 10000s, the free running OEO phase drift without using the passive compensation scheme is up to 540ps, while the phase drift of the passive compensation scheme is reduced to within 2.3ps, the invention can well limit the phase drift to within 0.42ps, and the system has lower phase jitter.

The allen square error was used to reflect the long-term stability of the transmission system, and the results are shown in fig. 6. It can be seen that the frequency stability of the passive compensation scheme and injection-locked passive compensation OEO system is improved by two orders of magnitude over the free running OEO system within a measurement time of 10000 s. And in 1s measuring time, the short-term stability of the invention is improved by 2 times compared with passive compensation.

It should be understood that the description of the present invention in the foregoing description and description is intended to be illustrative rather than limiting and that various changes, modifications, and/or alterations to the embodiments described above may be made without departing from the invention as defined by the appended claims.