A distributed passive phase-stabilized transmission method and system

Abstract

The present invention discloses a distributed passive phase-stable transmission method, comprising the following steps: connecting a main station with a plurality of substations to form an optoelectronic oscillation loop, injecting a local oscillator signal into the optoelectronic oscillation loop after electro-optical modulation at the main station, and making the optoelectronic oscillation loop realize injection locking of the local oscillator signal and output a two-frequency signal; detecting the two-frequency signal output by the optoelectronic oscillation loop at the main station and down-converting it with the local oscillator signal, then electro-optically modulating the generated down-converted signal, and making the generated optical down-converted signal transmitted in the optoelectronic oscillation loop in reverse direction; receiving the optical down-converted signal transmitted in reverse direction and the optical two-frequency signal transmitted in the optoelectronic oscillation loop in the substation, performing photoelectric conversion respectively, and then performing up-conversion, so as to obtain the local oscillator signal for phase-stable transmission. The present invention also discloses a distributed passive phase-stable transmission system. The present invention realizes point-to-multipoint distributed optical fiber passive phase-stable transmission through the loop characteristics of the optoelectronic oscillator.

Description

Technical Field

[0001] The present invention relates to a passive phase-stabilized transmission method, and in particular to a distributed passive phase-stabilized transmission method and system, belonging to the technical field of radio frequency phase-stabilized transmission. Background Art

[0002] With the continuous innovation and development of technology, the demand for high-stability frequency sources and synchronization between long-distance signals is increasing day by day. For example, in the fields of radar, navigation and communication, signal synchronization in long-distance transmission can realize the coherent synthesis of detection echo signals, which is of great significance to detection and navigation communication.

[0003] The current RF phase-stable transmission technology mainly transmits frequency through optical fiber, which has the advantages of large bandwidth, low loss, and anti-electromagnetic interference. When the RF signal is transmitted over long distances, the signal will be affected by environmental factors during the transmission process, so the phase of the signal will change during the transmission, and the signal needs to be phase compensated to maintain phase-stable transmission. The current phase-stable transmission technology mainly includes active phase compensation technology and passive phase compensation technology. The active phase compensation technology mainly extracts the phase noise introduced by the link jitter, combines relevant algorithms and controllable devices to add a phase conjugate with the link jitter to the transmitted signal, thereby achieving active phase compensation. The principle of active phase noise compensation is to mix the local signal to be transmitted with the signal after passing through the loop, extract the jitter introduced by the link, and then convert its phase information into control information through the feedback mechanism to control the corresponding compensation module to compensate the corresponding jitter of the link in real time [Jianguo Shen, Guiling Wu, Liang Hu, Weiwen Zou, and Jianping Chen, "Active phase drift cancellation for optic-fiber frequency transfer using aphotonic radio-frequency phase shifter," Opt. Lett. 39, 2346-2349 (2014)]. However, there are some limitations in active compensation technology, such as the accuracy and dynamic range of the compensation module need to be strictly controlled. Due to the shortcomings of active phase compensation technology, a new phase compensation method has received extensive attention and research. The core idea of ​​passive phase compensation technology is to use the detection signal to introduce the phase generated by the link delay jitter, and mix it with the transmitted signal to achieve compensation for the link phase noise. The existing passive phase compensation technologies mainly include f-2f compensation and f-3f compensation.

[0004] f-2f compensation mainly obtains the jitter information of the link by bidirectional transmission of the detection signal in the transmission link, and compensates the signal to be transmitted by mixing. The frequency of the detection signal is half of the signal to be transmitted. The phase compensation method can be achieved by pre-compensation at the transmitter and post-compensation at the far end [Juan Wei, Fangzheng Zhang, Yonggang Zhou, De Ben, and Shilong Pan,"Stable fiber delivery of radio-frequency signal based on passive phase correction," Opt. Lett. 39, 3360-3362 (2014)]. f-3f compensation requires a detection signal with a frequency of one-third of the signal to be transmitted to detect jitter.

[0005] Since the active phase compensation method is limited by the accuracy and control range of the compensation feedback control device, the passive compensation technology has no compensation range limitation, does not require feedback control operation, and has a relatively simple structure. The passive phase compensation method has obvious advantages over the active compensation method. However, since the passive phase compensation method introduces an electrical divider module, and the electrical divider has problems such as co-frequency spurious, some co-frequency signals will interfere with the phase of the transmission signal during mixing, affecting the final phase stability. Therefore, in some actual distributed applications, the existing passive compensation technology is difficult to apply.

[0006] In the transmission of long-distance signals, the phase stability of the signal is particularly important. How to realize a point-to-multipoint distributed phase-stable system is currently a hot topic for researchers. For example, in communications, when transmitting local oscillator signals at different sites, due to the distance limit between sites, optical fiber transmission will be affected by environmental factors. How to synchronize the local oscillator signals of each sub-station with the local oscillator signal of the main site is a very meaningful thing. At present, the distributed phase-stable transmission technology of point-to-multipoint is mainly realized through optical links. The main implementation method is to form an optical link between the main site and the sub-site, access different access user points in the optical link, and realize the phase synchronization between different access user points and the main site through the round trip of the link [Hongwei Li, Guiling Wu, Jiapeng Zhang, Jianguo Shen, and Jianping Chen, "Multi-access fiber-optic radio frequency transfer with passive phase noise compensation," Opt. Lett. 41, 5672-5675 (2016)]. How to realize a non-link-type point-to-multipoint distributed phase-stable transmission system and provide a new distributed phase-stable structure is a hot topic pursued by researchers. Summary of the invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a distributed passive phase-stable transmission method, which utilizes a frequency-divided optoelectronic oscillator loop to replace the electrical frequency divider in the traditional link, and realizes point-to-multipoint distributed optical fiber passive phase-stable transmission through the characteristics of the optoelectronic oscillator loop.

[0008] The present invention specifically adopts the following technical solutions to solve the above technical problems:

[0009] A distributed passive phase-stabilized transmission method comprises the following steps:

[0010] The main station and multiple substations are connected end to end through optical fibers to form an optoelectronic oscillation loop, and the main station electro-optically modulates the local oscillator signal and injects it into the optoelectronic oscillation loop, so that the optoelectronic oscillation loop can achieve injection locking of the local oscillator signal and output a two-frequency division signal;

[0011] The binary frequency signal outputted by the optoelectronic oscillation loop is detected at the master station and down-converted with the local oscillator signal, and then the generated down-converted signal is electro-optically modulated, and the generated optical down-converted signal is transmitted in reverse in the optoelectronic oscillation loop;

[0012] The optical down-conversion signal of the reverse transmission is received in the substation and is converted into an optical signal to obtain a down-conversion signal carrying the phase information of the entire loop and the phase information of the reverse transmission from the main station to the substation; the substation simultaneously receives the optical two-frequency division signal transmitted in the forward direction in the optoelectronic oscillation loop and converts it into an optical signal to obtain a frequency division signal carrying the phase information of the forward transmission from the main station to the substation; the down-conversion signal and the frequency division signal are up-converted, and the phase information of the entire loop and the phase information of the forward and reverse transmission from the main station to the substation are offset each other, that is, a local oscillator signal of stable phase transmission is obtained.

[0013] Preferably, the optoelectronic oscillation loop is made to achieve two-way frequency injection locking of the local oscillator signal by making the electro-optic modulator in the optoelectronic oscillation loop operate in a carrier suppressed double-sideband modulation state.

[0014] Furthermore, optical carriers of different frequencies are used at the master station to perform electro-optical modulation on the local oscillator signal and the down-converted signal respectively.

[0015] Based on the same inventive concept, the following technical solutions can also be obtained:

[0016] A distributed passive phase-stable transmission system comprises: a master station and a plurality of substations connected end to end by optical fibers to form an optoelectronic oscillation loop;

[0017] The master station is used to electro-optically modulate the local oscillator signal and then inject it into the optoelectronic oscillation loop, so that the optoelectronic oscillation loop can achieve injection locking of the local oscillator signal and output a two-frequency signal, detect the two-frequency signal output by the optoelectronic oscillation loop and down-convert it with the local oscillator signal, then electro-optically modulate the generated down-converted signal, and make the generated optical down-converted signal transmitted in the optoelectronic oscillation loop in reverse direction;

[0018] The substation is used to receive the optical down-conversion signal of the reverse transmission and perform photoelectric conversion on it, so as to obtain a down-conversion signal carrying the phase information of the entire loop and the phase information of the reverse transmission from the main station to the substation; the substation simultaneously receives the optical two-frequency division signal transmitted forward in the photoelectric oscillation loop and performs photoelectric conversion on it, so as to obtain a frequency division signal carrying the phase information of the forward transmission from the main station to the substation; the down-conversion signal and the frequency division signal are up-converted, and the phase information of the entire loop and the phase information of the forward and reverse transmission from the main station to the substation cancel each other out, so as to obtain a local oscillator signal of stable phase transmission.

[0019] Preferably, the master station enables the optoelectronic oscillation loop to achieve two-division frequency injection locking of the local oscillator signal by enabling the electro-optic modulator in the optoelectronic oscillation loop to operate in a carrier suppressed double-sideband modulation state.

[0020] Preferably, the master station uses optical carriers of different frequencies to perform electro-optical modulation on the local oscillator signal and the down-conversion signal respectively.

[0021] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0022] The present invention improves the existing link-type distributed passive phase-stable transmission system by introducing an optoelectronic oscillation loop and using a frequency-dividing optoelectronic oscillator to replace the frequency divider in the traditional link solution, thereby avoiding the additional crosstalk introduced by the frequency divider, etc., and using the optoelectronic oscillator to optimize the phase noise of the transmission signal, and realizing a point-to-multipoint loop-type distributed phase-stable transmission through the characteristics of the optoelectronic oscillator; and the injection-locked optoelectronic oscillator optimizes the stability of the system to a certain extent, and enhances the effect of the phase-stable transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the principle of the distributed passive phase-stabilized transmission system of the present invention;

[0024] Figure 2 It is a schematic diagram of a specific implementation structure of the distributed passive phase-stabilized transmission system of the present invention. DETAILED DESCRIPTION

[0025] In view of the shortcomings of the existing point-to-point link-type distributed passive phase-stable transmission system, the solution of the present invention is to introduce an optoelectronic oscillation loop and use a frequency-divided optoelectronic oscillator to replace the use of the divider in the traditional link solution, thereby avoiding the additional crosstalk introduced by the divider, etc., and using the optoelectronic oscillator to optimize the phase noise of the transmission signal, and realize a point-to-multipoint loop-type distributed phase-stable transmission through the characteristics of the optoelectronic oscillator.

[0026] The technical solution proposed by the present invention is as follows:

[0027] A distributed passive phase-stabilized transmission method comprises the following steps:

[0028] The main station and multiple substations are connected end to end through optical fibers to form an optoelectronic oscillation loop, and the main station electro-optically modulates the local oscillator signal and injects it into the optoelectronic oscillation loop, so that the optoelectronic oscillation loop can achieve injection locking of the local oscillator signal and output a two-frequency division signal;

[0029] The binary frequency signal outputted by the optoelectronic oscillation loop is detected at the master station and down-converted with the local oscillator signal, and then the generated down-converted signal is electro-optically modulated, and the generated optical down-converted signal is transmitted in reverse in the optoelectronic oscillation loop;

[0030] The optical down-conversion signal of the reverse transmission is received in the substation and is converted into an optical signal to obtain a down-conversion signal carrying the phase information of the entire loop and the phase information of the reverse transmission from the main station to the substation; the substation simultaneously receives the optical two-frequency division signal transmitted in the forward direction in the optoelectronic oscillation loop and converts it into an optical signal to obtain a frequency division signal carrying the phase information of the forward transmission from the main station to the substation; the down-conversion signal and the frequency division signal are up-converted, and the phase information of the entire loop and the phase information of the forward and reverse transmission from the main station to the substation are offset each other, that is, a local oscillator signal of stable phase transmission is obtained.

[0031] A distributed passive phase-stable transmission system comprises: a master station and a plurality of substations connected end to end by optical fibers to form an optoelectronic oscillation loop;

[0032] The master station is used to electro-optically modulate the local oscillator signal and then inject it into the optoelectronic oscillation loop, so that the optoelectronic oscillation loop can achieve injection locking of the local oscillator signal and output a two-frequency signal, detect the two-frequency signal output by the optoelectronic oscillation loop and down-convert it with the local oscillator signal, then electro-optically modulate the generated down-converted signal, and make the generated optical down-converted signal transmitted in the optoelectronic oscillation loop in reverse direction;

[0033] The substation is used to receive the optical down-conversion signal of the reverse transmission and perform photoelectric conversion on it, so as to obtain a down-conversion signal carrying the phase information of the entire loop and the phase information of the reverse transmission from the main station to the substation; the substation simultaneously receives the optical two-frequency division signal transmitted forward in the photoelectric oscillation loop and performs photoelectric conversion on it, so as to obtain a frequency division signal carrying the phase information of the forward transmission from the main station to the substation; the down-conversion signal and the frequency division signal are up-converted, and the phase information of the entire loop and the phase information of the forward and reverse transmission from the main station to the substation cancel each other out, so as to obtain a local oscillator signal of stable phase transmission.

[0034] In order to facilitate public understanding, the technical solution of the present invention is described in detail below with reference to the accompanying drawings:

[0035] The basic principle of the technical solution of the present invention is as follows Figure 1 As shown, the master station and multiple substations build an optoelectronic oscillation loop through optical fiber. Assume that the microwave local oscillator signal to be transmitted can be expressed as LO: where ω LO , are the initial angular frequency and initial phase of the microwave local oscillator signal respectively, such as Figure 1 As shown, the local oscillator signal is injected into the optoelectronic oscillation loop. When the modulator in the oscillation loop works in carrier suppressed double sideband, by adjusting the phase in the loop, the binary frequency signal of the local oscillator signal can be obtained in the oscillation loop, that is, When the local oscillator signal is injected and locked with the optoelectronic oscillation loop, the oscillating signal frequency is equal to the local oscillator signal frequency, that is, ω oeo =ωLO When the generated two-frequency signal is transmitted through the optoelectronic oscillation loop, it carries the phase information in the loop, that is, The signal is divided by the power divider at the master station and then down-converted with the local oscillator signal to obtain a down-converted two-frequency signal. The down-converted two-frequency signal Modulated onto an optical carrier, it passes through a circulator and enters the optoelectronic oscillation loop in reverse, and is transmitted to a substation in the optoelectronic oscillation loop. After optoelectronic conversion, a half-frequency signal is obtained. The local oscillator signal is transmitted forward to the substation through the photoelectric oscillation loop, and after photoelectric conversion, a half-frequency signal is obtained. Then, by up-converting these two half-frequency signals, the output signal of the substation can be obtained as The stable phase transmission of microwave local oscillator signal can be realized.

[0036] Figure 2 A specific implementation structure of the distributed passive phase-stable optical carrier transmission system of the present invention is shown; Figure 2 As shown, the distributed passive phase-stable transmission system of this embodiment mainly includes a master station, a substation and an optical loop connecting the master station and the substation; wherein the master station includes a laser 1, a laser 2, a modulator 1, a photodetector 1, a modulator 2, a mixer 1 and a mixer 2, an optical circulator, a phase-locked loop module composed of a mixer 1 and a low-pass filter and a voltage-controlled phase shifter, an amplifier 1, an amplifier 2, a bandpass filter 1, and a bandpass filter 6; the substation mainly includes a photodetector 2, a photodetector 3 and a mixer 3, a bandpass filter 2, and a bandpass filter 3; as shown Figure 2 As shown, the local oscillator signal to be transmitted is divided into two paths, one for down-conversion in mixer 2, and the other for electro-optical modulation by modulator 1 to generate a modulated optical signal which is injected into the optoelectronic oscillation loop and locked by a phase-locked loop. When the modulator 1 works at the carrier suppression point, the half frequency signal of the phase-locked signal in the optoelectronic oscillation loop obtains the phase information of the entire loop after passing through the loop once, and then the signal is down-converted with the local oscillator signal, and the obtained down-converted signal is electro-optically modulated by the modulator 2 to generate a modulated optical signal, which is reversely transmitted to the substation in the optoelectronic oscillation loop through the circulator, and the substation receives the reversely transmitted optical down-converted signal and performs photoelectric conversion on it through the photoelectric detector 3 to obtain a down-converted signal carrying the phase information of the entire loop and the reverse transmission phase information from the master station to the substation. The substation simultaneously receives the optical two-frequency signal transmitted forward by the master station and performs photoelectric conversion on it through the photoelectric detector 2 to obtain a frequency-divided signal carrying the forward transmission phase information from the master station to the substation, and the down-converted signal and the frequency-divided signal are up-converted in the substation through the mixer 3, so that the phase information of the entire loop and the forward and reverse transmission phase information from the master station to the substation cancel each other out, and an output signal of stable phase transmission is obtained.

[0037] Since a portion of the optical fiber in the optoelectronic oscillation loop transmits forward and reverse optical signals, in order to avoid backscattering that deteriorates the signal quality, in this embodiment, laser 1 and laser 2 output different optical wavelengths.

[0038] The following is a detailed derivation and analysis of the principle of binary frequency division technology based on the optoelectronic oscillator.

[0039] Assume that the RF signal input to modulator 1, i.e., the signal to be divided, is:

[0040] V in (t) = V0 cos(ω0t+θ0)

[0041] Among them, V0, ω0, and θ0 are the amplitude, frequency, and phase of the microwave signal to be divided, respectively.

[0042] Assume that the oscillation signal in the loop is x in (t), when V in (t) and x in (t) are in the loop together, at this time, the modulator 1 in the loop realizes carrier suppressed double-sideband modulation. Assume that the frequency-divided oscillation signal is:

[0043] x in (t) = V1 cos(ω1t+θ1)

[0044] Among them, V1, ω1, and θ1 are the amplitude, frequency, and phase of the frequency-divided microwave signal, respectively.

[0045] The combined wave of the signal to be divided and the divided signal in the loop should be expressed as:

[0046] V(t)=V in (t)+x in (t)

[0047] =V0cos(ω0t+θ0)+V1cos(ω1t+θ1)

[0048] Therefore, the output optical signal of modulator 1 can be expressed as:

[0049]

[0050] Among them, E in (t) is the input optical signal of modulator 1, V π is the modulated half-wave voltage, V dc is the DC bias voltage. After the delay τ of the photoelectric loop, the output photocurrent signal after the photoelectric conversion of the photodetector 1 is:

[0051]

[0052] in is the responsivity of the photodetector 1, P is the input optical power of the modulator 1, 1-α is the fiber attenuation coefficient, The phase term is introduced for the bias voltage, β0 and β1 are the signal modulation depths. Since modulator 1 works at the minimum point, The above formula can be transformed into:

[0053]

[0054] Among them, J n is the nth-order first-kind Bessel function. After amplification and filtering, the high frequency will be filtered out. After ignoring the DC component, the above formula is simplified to:

[0055]

[0056] G is the gain introduced by amplification. When the system is in a steady state, the intermediate frequency signal in the above formula will be equal to the divided frequency signal, that is: in (t) = i(t), so the two-frequency steady-state condition is:

[0057]

[0058] From the above formula, we can see that The system realizes binary frequency division, and the frequency division needs to meet certain amplitude and phase conditions.

[0059] Next, the technical principle of the system's phase-stable transmission is introduced in detail.

[0060] like Figure 2 As shown, assuming that the microwave local oscillator signal LO output signal is:

[0061]

[0062] where ω LO , are the initial angular frequency and initial phase of the local oscillator signal respectively.

[0063] The local oscillator signal source is injected into the optoelectronic oscillation loop. When the modulator works in carrier suppressed double sideband, the system can produce a two-frequency signal of the injected signal. After the two-frequency signal is transmitted back to the master station through the loop, the signal separated by the power divider is:

[0064]

[0065] Among them, ω oeo , are the initial angular frequency and initial phase of the oscillation signal respectively, and ω oeo =ω LO , the separated signal and the local oscillator microwave signal are down-converted to obtain

[0066]

[0067] The down-converted signal is re-modulated onto an optical carrier by the modulator 2, and is transmitted in reverse to the substation in the oscillation loop through the circulator. After photoelectric conversion and filtering by the photoelectric detector 3 in the substation, the following is obtained:

[0068]

[0069] The forward transmission signal in the photoelectric oscillation loop is obtained after photoelectric conversion and filtering by photoelectric detector 2:

[0070]

[0071] The two signals are up-converted by the mixer to obtain the up-converted signal:

[0072]

[0073] Therefore, the system realizes steady-phase transmission between the master station and the substations. The formulas for the remaining substations are derived in the same way, thus realizing distributed steady-phase transmission from one point to multiple points in the master station.

Claims

1. A distributed passive phase-stabilized transmission method, characterized in that: The following steps are involved: The main station and multiple substations are connected end to end through optical fibers to form an optoelectronic oscillation loop, and the main station electro-optically modulates the local oscillator signal and injects it into the optoelectronic oscillation loop, so that the optoelectronic oscillation loop can achieve injection locking of the local oscillator signal and output a two-frequency division signal; The binary frequency signal outputted by the optoelectronic oscillation loop is detected at the master station and down-converted with the local oscillator signal, and then the generated down-converted signal is electro-optically modulated, and the generated optical down-converted signal is transmitted in reverse in the optoelectronic oscillation loop; The optical down-conversion signal of the reverse transmission is received in the substation and is converted into an optical signal to obtain a down-conversion signal carrying the phase information of the entire loop and the phase information of the reverse transmission from the main station to the substation; the substation simultaneously receives the optical two-frequency division signal transmitted in the forward direction in the optoelectronic oscillation loop and converts it into an optical signal to obtain a frequency division signal carrying the phase information of the forward transmission from the main station to the substation; the down-conversion signal and the frequency division signal are up-converted, and the phase information of the entire loop and the phase information of the forward and reverse transmission from the main station to the substation are offset each other, that is, a local oscillator signal of stable phase transmission is obtained.

2. The distributed passive phase-stabilized transmission method according to claim 1, characterized in that: By making the electro-optic modulator in the optoelectronic oscillation loop work in the carrier suppressed double sideband modulation state, the optoelectronic oscillation loop realizes the two-division frequency injection locking of the local oscillation signal.

3. The distributed passive phase-stabilized transmission method according to claim 1, characterized in that: At the master station, optical carriers of different frequencies are used to perform electro-optical modulation on the local oscillator signal and the down-converted signal respectively.

4. A distributed passive phase-stabilized transmission system, characterized in that: include: A master station and multiple substations are connected end to end through optical fibers to form an optoelectronic oscillation loop; The master station is used to electro-optically modulate the local oscillator signal and then inject it into the optoelectronic oscillation loop, so that the optoelectronic oscillation loop can achieve injection locking of the local oscillator signal and output a two-frequency signal, detect the two-frequency signal output by the optoelectronic oscillation loop and down-convert it with the local oscillator signal, then electro-optically modulate the generated down-converted signal, and make the generated optical down-converted signal transmitted in the optoelectronic oscillation loop in reverse direction; The substation is used to receive the optical down-conversion signal of the reverse transmission and perform photoelectric conversion on it, so as to obtain a down-conversion signal carrying the phase information of the entire loop and the phase information of the reverse transmission from the main station to the substation; the substation simultaneously receives the optical two-frequency division signal transmitted forward in the photoelectric oscillation loop and performs photoelectric conversion on it, so as to obtain a frequency division signal carrying the phase information of the forward transmission from the main station to the substation; the down-conversion signal and the frequency division signal are up-converted, and the phase information of the entire loop and the phase information of the forward and reverse transmission from the main station to the substation cancel each other out, so as to obtain a local oscillator signal of stable phase transmission.

5. The distributed passive phase-stabilized transmission system according to claim 4, characterized in that: The master station enables the electro-optic modulator in the optoelectronic oscillation loop to work in a carrier suppressed double-sideband modulation state, so that the optoelectronic oscillation loop realizes two-division frequency injection locking of the local oscillation signal.

6. The distributed passive phase-stabilized transmission system according to claim 4, characterized in that: The master station uses optical carriers of different frequencies to perform electro-optical modulation on the local oscillator signal and the down-converted signal respectively.

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