Integrated parallel transmission method and device for photoelectric time-frequency signals

Abstract

The invention discloses an integrated parallel transmission method and device for a photoelectric time-frequency signal, and the method comprises the steps: generating a broadband spread spectrum modulation intermediate-frequency carrier signal through a time-frequency modem, and carrying out the phase modulation through an up-converter and an electro-optical modulator, and obtaining an A-station ultra-stable laser and a B-station laser; a photoelectric detector obtains a downlink microwave modulation signal through coherent detection, and the downlink microwave modulation signal passes through a down converter and a time-frequency modem to obtain frequency deviation of a station A and a station B; the A station and the B station generate optical heterodyne signals respectively, optical phase locking control is completed through an acousto-optic modulator, and the frequency of the laser of the B station is adjusted through feedback, so that the laser of the B station is locked to the ultra-stable laser of the A station. According to the integrated parallel transmission method for the photoelectric time-frequency signals, three kinds of time-frequency signals are transmitted in parallel through a single optical carrier in a frequency division multiplexing mode of a time-frequency signal frequency spectrum layer, dispersion of multiple transmission channels is avoided, and therefore the time domain coherence characteristic between the time-frequency signals is better guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of laser time-frequency signal transmission, and relates to an integrated parallel transmission method and device for optoelectronic time-frequency signals. Background Art

[0002] To achieve the remote transmission of multiple time-frequency signals, the carrier frequency division multiplexing method was previously used to load different time-frequency signals on different microwave or optical carriers and then transmit them to the required user terminals through a combined transmission method. However, the carrier frequency division multiplexing method cannot overcome the dispersion problem of different carriers in the transmission channel, resulting in inherent channel delays in the transmission and demodulation channels of different time-frequency signals, and there is also channel delay drift, causing an uncontrollable coherence degradation in the phase relationship between time-frequency transmission signals. Summary of the Invention

[0003] The present invention proposes an integrated parallel transmission method and device for optoelectronic time-frequency signals to solve the problem that the traditional laser time-frequency signal transmission method cannot overcome the dispersion of different carriers in the transmission channel.

[0004] The present invention provides the following technical solutions:

[0005] In a first aspect, the present specification provides an integrated parallel transmission method for optoelectronic time-frequency signals, including:

[0006] A time-frequency modem generates a broadband spread-spectrum modulated intermediate-frequency carrier signal, which is converted into an uplink microwave modulation signal through an upconverter and phase-modulated using an electro-optic modulator to obtain an ultra-stable laser at Station A and a laser at Station B;

[0007] An optoelectronic detector obtains a downlink microwave modulation signal through coherent detection, which is converted into a broadband spread-spectrum modulated intermediate-frequency carrier signal through a downconverter, and a Doppler frequency measurement value at the local reference frequency is measured using a time-frequency modem to obtain the frequency deviation between Stations A and B;

[0008] The optoelectronic detector at Station A generates an optical heterodyne signal between the ultra-stable laser at Station A and the laser at Station B, and an optical phase-locked control is completed using an acousto-optic modulator to lock the ultra-stable laser at Station A to the laser at Station B;

[0009] The optoelectronic detector at Station B generates an optical heterodyne signal between the laser at Station B and the ultra-stable laser at Station A, and the frequency of the laser at Station B is adjusted through feedback to lock the laser at Station B to the ultra-stable laser at Station A.

[0010] In a second aspect, the present invention provides an integrated parallel transmission device for optoelectronic time-frequency signals, including:

[0011] Two-station laser generation module, used to control the time-frequency modem to generate a broadband spread-spectrum modulated intermediate-frequency carrier signal, which is converted into an uplink microwave modulation signal through an upconverter, and phase modulation is performed using an electro-optic modulator to obtain the ultra-stable laser at Station A and the laser at Station B;

[0012] Two-station frequency difference determination module, used to control the photodetector to obtain the downlink microwave modulation signal through coherent detection, which is converted into a broadband spread-spectrum modulated intermediate-frequency carrier signal through a downconverter, and the Doppler frequency measurement value at the local reference frequency is measured using the time-frequency modem to obtain the frequency deviation between Station A and Station B;

[0013] First laser locking module, used to control the photodetector at Station A to generate an optical heterodyne signal between the ultra-stable laser at Station A and the laser at Station B, and complete optical phase-locked control using an acousto-optic modulator to lock the ultra-stable laser at Station A to the laser at Station B;

[0014] Second laser locking module, used to control the photodetector at Station B to generate an optical heterodyne signal between the laser at Station B and the ultra-stable laser at Station A, and adjust the frequency of the laser at Station B through feedback to lock the laser at Station B to the ultra-stable laser at Station A.

[0015] The integrated parallel transmission method and device for optoelectronic time-frequency signals provided by the embodiments of the present invention use the frequency-division multiplexing method at the time-frequency signal spectrum level to enable three time-frequency signals to be transmitted in parallel through a single optical carrier, avoiding the dispersion of multiple transmission channels, thereby better ensuring the time-domain coherence characteristics between time-frequency signals. Description of the Drawings

[0016] Figure 1 It is a schematic diagram of the overall scheme design of the integrated parallel transmission of optoelectronic time-frequency signals in the embodiments of the present invention;

[0017] Figure 2 It is a schematic diagram of the coherent laser frequency synchronization scheme design in the embodiments of the present invention;

[0018] Figure 3 It is a schematic diagram of the two-way comparison timing in the embodiments of the present invention;

[0019] Figure 4 In the embodiments of the present invention Figure 1 Schematic diagram of the spectrum at positions ①-④;

[0020] Figure 5 It is a schematic diagram of the output spectrum of the photodetector in the embodiments of the present invention.

[0021] Other features and advantages of the present invention will be set forth in the following description, and in part will be obvious from the description, or may be learned by practice of the present invention. The objectives and other advantages of the present invention may be realized and attained by the structure particularly pointed out in the written description, claims, as well as the drawings. Detailed Description of the Invention

[0022] To make the objectives, technical solutions and advantages of this specification clearer, the technical solutions of this specification will be clearly and completely described below in conjunction with the specific embodiments of this specification and the corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this specification, rather than all the embodiments. Based on the embodiments in this specification, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of this specification.

[0023] As described herein, the term "comprising" and its various variants can be understood as open-ended terms, meaning "including but not limited to", and the term "one embodiment" can be understood as "at least one embodiment".

[0024] The inventors found that the traditional laser time-frequency signal transmission method has the problem of being unable to overcome the dispersion of different carriers in the transmission channel. In view of this, in the embodiments of the present invention, through the frequency division multiplexing method at the time-frequency signal spectrum level, three time-frequency signals are transmitted in parallel through a single optical carrier to avoid the dispersion of multiple transmission channels.

[0025] Embodiment 1

[0026] As Figure 1 shown, the embodiments of the present invention provide an integrated parallel transmission method for optoelectronic time-frequency signals. This method is executed by a processor and includes the following steps:

[0027] Step 1: The time-frequency modem generates a broadband spread-spectrum modulated intermediate-frequency carrier signal, which is converted into an uplink microwave modulation signal through an upconverter, and phase modulation is performed using an electro-optic modulator to obtain the ultra-stable laser at Station A and the laser at Station B.

[0028] In specific implementation, the time-frequency modem of Station A generates the first wideband spread-spectrum modulated intermediate-frequency carrier signal of Station A. The first wideband spread-spectrum modulated intermediate-frequency carrier signal of Station A includes the wideband pseudo-code modulation signal of Station A and the one-way measurement data of Station A. Record the transmission time under the local clock reference of Station A. The first wideband spread-spectrum modulated intermediate-frequency carrier signal of Station A passes through the up-converter of Station A and is converted into the uplink microwave modulation signal of Station A. The electro-optic modulator of Station A performs phase modulation on the uplink microwave modulation signal of Station A to obtain the ultra-stable laser of Station A. The time-frequency modem of Station B generates the first wideband spread-spectrum modulated intermediate-frequency carrier signal of Station B. The first wideband spread-spectrum modulated intermediate-frequency carrier signal of Station B passes through the up-converter of Station B and is converted into the uplink microwave modulation signal of Station B. The electro-optic modulator of Station B performs phase modulation on the uplink microwave modulation signal of Station B to obtain the laser of Station B.

[0029] Step 2: The photodetector obtains the downlink microwave modulation signal through coherent detection, passes through the down-converter, and is converted into the wideband spread-spectrum modulated intermediate-frequency carrier signal. The time-frequency modem is used to measure the Doppler frequency measurement value under the local reference frequency at the local end to obtain the frequency deviation between Stations A and B.

[0030] In specific implementation, the photodetector of Station A obtains the downlink microwave modulation signal of Station A through coherent detection. The downlink microwave modulation signal of Station A passes through the down-converter of Station A and is converted into the second wideband spread-spectrum modulated intermediate-frequency carrier signal of Station A. The time-frequency modem of Station A strips the wideband pseudo-code modulation signal of Station A and the one-way measurement data of Station A from the second wideband spread-spectrum modulated intermediate-frequency carrier signal of Station A to obtain the stripped wideband spread-spectrum modulation signal of Station A. According to the stripped wideband spread-spectrum modulation signal of Station A, determine the self-transmitted and self-received signal reception time of Station A and the inter-site transmission signal reception time of Station A. The time-frequency modem of Station A measures the Doppler frequency measurement value under the local reference frequency at the local end according to the second wideband spread-spectrum modulated intermediate-frequency carrier signal of Station A to obtain the carrier frequency measurement value of Station A;

[0031] The B Station photoelectric detector obtains the B Station downlink microwave modulation signal through coherent detection. The B Station downlink microwave modulation signal passes through the B Station downconverter and is converted into the B Station second broadband spread-spectrum modulated intermediate-frequency carrier signal. The B Station time-frequency modem strips the B Station broadband pseudo-code modulation signal and the B Station one-way measurement data from the B Station second broadband spread-spectrum modulated intermediate-frequency carrier signal, obtaining the stripped B Station broadband spread-spectrum modulated signal. Based on the stripped B Station broadband spread-spectrum modulated signal, the B Station self-transmission and self-reception signal reception time and the B Station inter-site transmission signal reception time are determined. Based on the A Station self-transmission and self-reception signal reception time, the A Station inter-site transmission signal reception time, the B Station self-transmission and self-reception signal reception time, and the B Station inter-site transmission signal reception time, the time difference between the A and B Stations is obtained. The B Station time-frequency modem measures the Doppler frequency measurement value at the local reference frequency based on the B Station second broadband spread-spectrum modulated intermediate-frequency carrier signal, obtaining the B Station carrier frequency measurement value;

[0032] Based on the A Station carrier frequency measurement value and the B Station carrier frequency measurement value, the frequency deviation between the A and B Stations is obtained.

[0033] Specifically, the time difference between the A and B Stations is calculated according to the following formula:

[0034]

[0035] where ΔT is the time difference between the A and B Stations, T A1 is the A Station self-transmission and self-reception signal reception time, T A2 is the A Station inter-site transmission signal reception time, T B1 is the B Station self-transmission and self-reception signal reception time, T B2 is the B Station inter-site transmission signal reception time, τ TXA is the A Station internal transmission delay, τ TXB is the B Station internal transmission delay, (τ TXA -τ TXB ) is the signal uplink differential link term.

[0036] Specifically, the A Station carrier frequency measurement value is calculated according to the following formula:

[0037]

[0038] where f AB is the A Station carrier frequency measurement value, f IF is the intermediate-frequency carrier frequency of the transmitted signal, f0 is the reference frequency, df is the frequency difference between the A and B Stations, f LOA is the nominal frequency conversion frequency of the A Station up / downconverter, f LOB is the nominal frequency conversion frequency of the B Station up / downconverter, and Δf is the frequency noise introduced by the optical fiber transmission link.

[0039] Specifically, the carrier frequency measurement value of Station B is calculated according to the following formula:

[0040]

[0041] where f BA is the carrier frequency measurement value of Station B, f IF is the intermediate frequency carrier frequency of the transmitted signal, f0 is the reference frequency, df is the frequency difference between Stations A and B, f LOA is the nominal frequency conversion frequency of the up / down converter at Station A, f LOB is the nominal frequency conversion frequency of the up / down converter at Station B, and Δf is the frequency noise introduced by the optical fiber transmission link.

[0042] Specifically, the frequency deviation between Stations A and B is calculated according to the following formula:

[0043]

[0044] where df clk is the frequency deviation between Stations A and B, f AB is the carrier frequency value received at Station B, f BA is the carrier frequency value received at Station A, f LOA is the nominal frequency conversion frequency of the up / down converter at Station A, f LOB is the nominal frequency conversion frequency of the up / down converter at Station B, f IF is the intermediate frequency carrier frequency of the transmitted signal, and f0 is the reference frequency.

[0045] Step 3: The optoelectronic detector at Station A generates an optical heterodyne signal between the ultra-stable laser at Station A and the laser at Station B, and uses an acousto-optic modulator to complete optical phase-locked control to lock the ultra-stable laser at Station A to the laser at Station B.

[0046] In specific implementation, the ultra-stable laser at Station A is divided into a first laser beam and a second laser beam through a 2×2 fiber coupler;

[0047] The first laser beam is introduced into the optoelectronic detector signal at Station A through a 2×1 fiber coupler to obtain a first laser heterodyne signal;

[0048] The first laser heterodyne signal passes through a phase-locked control loop to obtain an acousto-optic modulation signal;

[0049] The second laser beam is introduced into the acousto-optic modulation signal for acousto-optic modulation and frequency pre-compensation to obtain a pre-compensated laser. After being transmitted through an optical fiber link or a free space link, the ultra-stable laser at Station A with superimposed frequency noise is obtained, and the ultra-stable laser at Station A with superimposed frequency noise is transmitted to Station B.

[0050] Step 4: The optoelectronic detector at Station B generates an optical heterodyne signal between the laser at Station B and the ultra-stable laser at Station A, and adjusts the frequency of the laser at Station B through feedback to lock the laser at Station B to the ultra-stable laser at Station A.

[0051] Specifically, when implemented, the optoelectronic detector at Station B generates the laser at Station B, and the laser at Station B is divided into a third laser beam and a fourth laser beam by a 2×2 fiber coupler;

[0052] The third laser beam is introduced into the signal of the optoelectronic detector at Station B through a 2×1 fiber coupler to obtain a second laser heterodyne signal;

[0053] The fourth laser beam is transmitted through an optical fiber link or a free-space link to obtain the laser at Station B with superimposed frequency noise, and the laser at Station B with superimposed frequency noise is transmitted to Station A;

[0054] The second laser heterodyne signal passes through a phase-locked control loop to perform feedback adjustment on the frequency of the laser at Station B, and locks the output center frequency of the laser at Station B to the frequency of the ultra-stable laser at Station A; and

[0055] The signal of the optoelectronic detector at Station B is the ultra-stable laser at Station A with superimposed frequency noise;

[0056] The signal of the optoelectronic detector at Station A is the signal obtained after the laser at Station B with superimposed frequency noise is subjected to acousto-optic modulation.

[0057] Embodiment 2

[0058] The embodiment of the present invention also provides an integrated parallel transmission method for optoelectronic time-frequency signals. This method is executed by a processor and uses a two-way transmission measurement method to achieve the integrated parallel transmission of coherent optical frequencies, microwave frequencies, and time signals between stations. The design of this method and device is as Figure 1 shown, and can be divided into three parts, namely coherent laser frequency synchronization, microwave frequency signal comparison, and time signal comparison, including the following steps:

[0059] Step 1: Coherent laser frequency synchronization as a whole uses two-way loop frequency interlocking.

[0060] Specifically, when implemented, the optoelectronic detector in Station A generates an optical heterodyne signal (f beat1 ) between the ultra-stable laser in Station A and the incoming laser in Station B, and then uses an acousto-optic modulator to complete optical phase-locked control to lock the ultra-stable laser in Station A to the incoming laser in Station B. The optoelectronic detector in Station B generates an optical heterodyne signal (f beat2 ) between the laser in Station B and the incoming ultra-stable laser in Station A, and then adjusts the frequency of the laser in Station B through feedback to lock the laser in Station B to the incoming ultra-stable laser in Station A. Using the above two phase-locked control loops, the lasers in Stations A and B are mutually locked.

[0061] From the overall scheme design Figure 1 , a coherent laser frequency synchronization scheme for Stations A and B can be abstracted, as Figure 2 shown. In Station A, the ultra-stable laser frequency is ν. The output laser is divided into two beams by a 2×2 fiber coupler. Among them, one beam is introduced into the signal of the photodetector through a 2×1 fiber coupler for heterodyne detection of the laser in Station A; the other beam is introduced into acousto-optic modulation and frequency pre-compensation is completed. The nominal frequency shift frequency of the acousto-optic modulation is f AOM . After compensation, the laser frequency is After transmission through the fiber optic link or free space link, the pre-compensated laser is superimposed with the frequency noise introduced by the fiber optic link, and the frequency becomes Among them, is the change in the laser frequency introduced by the fiber optic link noise, is the change in the pre-compensation frequency of the phase-locked control. After this laser signal is transmitted to Station B, it is combined with the laser in Station B through a 2×2 fiber coupler and a 2×1 fiber coupler to generate a heterodyne signal f beat2 . By using a phase-locked control loop, the center frequency of the laser output in Station B can be locked to ν, but affected by the reference laser incident on Station B, the laser in Station B contains a frequency perturbation term That is, the real-time output frequency of the laser in Station B is

[0062] The laser in Station B returns to Station A along the fiber optic link. Assuming that the frequency noise introduced by the fiber optic link is equal during the forward and reverse transmission of the laser in the fiber optic link, the frequency of the laser in Station B entering Station A is Subsequently, after passing through the acousto-optic modulator, the frequency of the incident laser in Station B becomes After this signal is combined with the coherent laser in Station A, the generated heterodyne frequency f beat1 . By using a phase-locked control loop, the perturbation frequency between the two beams of lasers can be detected and suppressed That is, through feedback control, make The frequency synchronization of the coherent lasers in Stations A and B in the system can be achieved.

[0063] Step 2: The microwave frequency signal comparison adopts two-way comparison.

[0064] Specifically, during the uplink transmission part of the signals in Stations A and B, the time-frequency modem generates broadband spread-spectrum modulated intermediate-frequency carrier signals (f IF1 , f IF2 ). Subsequently, through the upconverter, it is converted into microwave modulation signals (f RF1 + f IF1 , f RF2 + f IF2)。The electro-optic modulator completes the phase modulation of the coherent laser signal by the microwave modulation signal. Subsequently, the laser signal is introduced into the photodetector and the optical fiber or free-space link through a 2×2 optical fiber coupler and a 2×1 optical fiber coupler respectively. Among them, the signal introduced into the photodetector is used to complete the spontaneous self-receiving Doppler frequency measurement subsequently, and the signal introduced into the optical fiber or free-space link is used to complete the Doppler frequency measurement between stations subsequently. In the downlink receiving part of the signals at stations A and B, the coherent detection method is adopted, and the photodetector obtains the microwave modulation signal. This signal is then down-converted by the down-conversion module to recover the wideband spread-spectrum modulated intermediate-frequency carrier signal (f IF1 ', f IF2 '). The time-frequency modem measures the Doppler frequency measurement value at the local reference frequency using the wideband modulated intermediate-frequency signal carrier.

[0065] The clock frequencies of stations A and B are respectively denoted as

[0066] f clockA = f0 (1)

[0067] f clockB = f0 + df (2)

[0068] where df is the frequency difference between stations A and B. Taking the example of station A transmitting and station B receiving, the intermediate-frequency carrier frequency of the transmitted signal at station A is denoted as f IF . Assuming that the frequency noise introduced by the optical fiber transmission link is denoted as Δf, the received frequency at station B is

[0069] f AB = f IF + Δf (3)

[0070] However, the result of formula (3) is referenced to the reference frequency f0, which does not conform to the actual application scenario. In practice, the frequency measurement value at station A is referenced to f clockA , while the frequency measurement value at station B is referenced to f clockB . Since the frequency measurement value conversion relationship for the same frequency signal under different reference frequency references is

[0071]

[0072] where f n is the frequency measurement value under the reference frequency n, f m is the frequency measurement value under the reference frequency m, f ref n is the reference frequency n, and f ref m is the reference frequency m. The carrier frequency value received at station B in formula (3) is corrected to

[0073]

[0074] Similarly, the carrier frequency value received by Site A is

[0075]

[0076] By combining Formulas (5) and (6), the frequency deviation df between Stations A and B is obtained. In the invention, it is necessary to convert the intermediate-frequency carrier of the broadband spread-spectrum modulation signal to the microwave frequency band to obtain a higher microwave frequency comparison accuracy. After adding the frequency conversion process, the measured carrier frequency values of Stations A and B listed in Formulas (5) and (6) are respectively adjusted to

[0077]

[0078] where f LOA and f LOB are the nominal frequency conversion frequencies of the up-converter and down-converter at Stations A and B respectively. In this configuration, the frequency deviation df between Stations A and B clk The solution result is

[0079]

[0080] where df clk is the frequency deviation between Stations A and B, f AB is the carrier frequency value received by Site B, f BA is the carrier frequency value received by Site A, f IF is the intermediate-frequency carrier frequency of the transmitted signal, and f0 is the reference frequency.

[0081] Step 3: The time signal comparison adopts two-way comparison.

[0082] Specifically, in the uplink transmission part of the signals at Stations A and B, the time-frequency modem generates a broadband spread-spectrum modulation signal and records the transmission time T A0 、T B0This signal contains a broadband pseudo-code modulated signal and local end one-way measurement data. The broadband pseudo-code modulated signal is then passed through an up-conversion module, and an electro-optic modulator performs phase modulation on the coherent laser signal, enabling the coherent laser to carry the local broadband pseudo-code modulated signal and one-way measurement data. Subsequently, the laser signal is introduced into a photodetector and a fiber or free-space link through a 2×2 fiber coupler and a 2×1 fiber coupler respectively. Among them, the signal introduced into the photodetector is used to complete the measurement of the spontaneous self-receiving time delay subsequently, and the signal introduced into the fiber or free-space link is used to complete the measurement of the time delay between stations subsequently. In the signal downlink reception part of stations A and B, a coherent detection method is adopted, and the photodetector obtains a broadband spread-spectrum modulated signal. This signal is then input into a time-frequency modem through a down-conversion module. The time-frequency modem strips the broadband pseudo-code modulated signal and one-way measurement data respectively, and further determines the reception time (T A1 、T B1 ) of the spontaneous self-receiving signal and the reception time (T A2 、T B2 ) of the signal transmitted between stations using the broadband pseudo-code modulated signal.

[0083] To obtain the in-station time delay of stations A and B, it is necessary to obtain the in-station times T A1 、T B1 、T A2 and T B2 of the spontaneous self-receiving and mutual transmission and reception signals respectively. Taking the signal transmission times T A0 、T B0 as the "door opening" actions in the internal time counter; T A1 、T B1 、T A2 and T B2 are indicated by the corresponding moments of the maximum correlation of the modulated and demodulated signals, indicating the "door closing" actions in the internal time counter.

[0084] As Figure 3 shown, the time difference between station A and station B is denoted as ΔT. The signal transmission times of stations A and B are T A1 、T B1 respectively, that is

[0085] ΔT = T B0 - T A0 (10)

[0086] Under the respective time scales of stations A and B, at times T A1 and T B1 respectively, stations A and B receive the above signals respectively, and at subsequent times T A2 and T B2 respectively, stations A and B receive the above signals sent by the other station. Combining Figure 1 , the spontaneous self-receiving time delay measurement of stations A and B is

[0087] T A1 -T A0 = τ TXA + τ RXA (11)

[0088] T B1 -T B0 = τ TXB + τ RXB (12)

[0089] where τ TXA and τ TXB are the transmission time delays within stations A and B respectively, and τ RXA and τ RXB are the reception time delays within stations A and B respectively. The time delay measurement of mutual transmission and reception between stations A and B is

[0090] T A2 -T A0 = (T A2 -T B0 ) + ΔT = τ TXB + τ BA + τ RXA + ΔT (13)

[0091] T B2 -T B0 = (T B2 -T A0 ) - ΔT = τ TXA + τ AB + τ RXB - ΔT (14)

[0092] Assume that the two-way transmission time delay of the optical fiber link is equal, i.e.,

[0093] τ AB = τ BA (15)

[0094] Combining formulas (11) to (15), the time difference between stations A and B is

[0095]

[0096] where the third term in formula (16) is the signal uplink differential link term, which can be eliminated by calibration. Therefore, by exchanging the measurement results T A1 , T B1 , T A2 and T B2 , stations A and B can independently obtain the time difference between the two stations respectively.

[0097] It should be noted that when measuring the time difference between stations A and B using formula (16), since T is measured in parallelA1 and T B1 , it is possible to simultaneously monitor the device delays in stations A and B in parallel, so as to understand the changes in the operating status of the in-station devices.

[0098] In a specific embodiment, the time-frequency signal composite modulation at the transmitting end includes: the time-frequency signal composite modulation refers to the process of completing the superposition of time signals, microwave frequency signals, and coherent laser signals. The specific implementation method is that the broadband spread-spectrum modulation signal carries the time signal; the broadband spread-spectrum modulation signal is shifted to the microwave frequency band through the up-conversion module, so as to superimpose the microwave frequency modulation signal; subsequently, this composite signal is superimposed on the coherent laser signal through the electro-optic modulator. The modulated coherent laser signal realizes the overall spectral shift by the acousto-optic modulator and the optical heterodyne frequency phase-locked loop in the system. Figure 1 The spectra at positions ①-④ in Figure 4 are shown as

[0099] In a specific embodiment, the time-frequency signal hierarchical stripping at the receiving end includes: the time-frequency signal hierarchical stripping is realized by frequency division and code division methods respectively. Using the coherent detection method, the electrical spectrum obtained by the photodetector in the system is as shown in Figure 5 . The coherent laser heterodyne signal between the two stations is close to the DC end and can be extracted by low-pass filtering. Modulated by the microwave frequency signal, the broadband spread-spectrum modulation signal is shifted to the high-frequency end. From the spectrum shown in Figure 4 , the broadband spread-spectrum modulation signals of the two stations' self-transmission and self-reception and mutual transmission and mutual reception are at the same frequency point. However, the modulation pseudo-code patterns in the self-transmission and self-reception and mutual transmission and mutual reception signals are different, and the code division method can be used to strip and extract them respectively. Due to the mirror symmetry characteristic of the modulation signal components, the modulation signal components in the higher frequency band can be ignored.

[0100] Through the frequency division multiplexing method at the time-frequency signal spectrum level in the above embodiments, the three time-frequency signals are transmitted in parallel through a single optical carrier, avoiding the dispersion of multiple transmission channels, thus better ensuring the time-domain coherence characteristics between the time-frequency signals, and solving the problem that the traditional laser time-frequency signal transmission method cannot overcome the dispersion of different carriers in the transmission channel.

[0101] Embodiment 3

[0102] Based on the same technical concept, the embodiment of the present invention also provides an integrated parallel transmission device for optoelectronic time-frequency signals. Since the principle of solving problems by the above device is similar to that of the integrated parallel transmission method of optoelectronic time-frequency signals, therefore, the implementation of the above device can refer to the implementation of the method, and the repeated parts will not be elaborated.

[0103] The embodiment of the present invention provides an integrated parallel transmission device for optoelectronic time-frequency signals, including:

[0104] A two-station laser generation module, which is used to control a time-frequency modem to generate a broadband spread-spectrum modulated intermediate-frequency carrier signal. After passing through an up-converter, it is converted into an uplink microwave modulation signal. An electro-optic modulator is used for phase modulation to obtain an ultra-stable laser at Station A and a laser at Station B;

[0105] A two-station frequency difference determination module, which is used to control a photodetector to obtain a downlink microwave modulation signal through coherent detection. After passing through a down-converter, it is converted into a broadband spread-spectrum modulated intermediate-frequency carrier signal. A time-frequency modem is used to measure the Doppler frequency measurement value at the local reference frequency to obtain the frequency deviation between Station A and Station B;

[0106] A first laser locking module, which is used to control a photodetector at Station A to generate an optical heterodyne signal between the ultra-stable laser at Station A and the laser at Station B, and use an acousto-optic modulator to complete optical phase-locking control to lock the ultra-stable laser at Station A to the laser at Station B;

[0107] A second laser locking module, which is used to control a photodetector at Station B to generate an optical heterodyne signal between the laser at Station B and the ultra-stable laser at Station A, and adjust the frequency of the laser at Station B through feedback to lock the laser at Station B to the ultra-stable laser at Station A.

[0108] In summary, through the frequency-division multiplexing method at the time-frequency signal spectrum level, the embodiments of the present invention enable three time-frequency signals to pass through a single optical carrier in parallel, avoiding the inherent channel delay and channel delay drift of different time-frequency signal transmission and demodulation channels, preventing the uncontrollable coherence degradation of the phase relationship between time-frequency transmission signals, and better ensuring the time-domain coherence characteristics between time-frequency signals.

[0109] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concepts. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0110] Those skilled in the art know that in addition to implementing the systems, subsystems, modules, and units provided by the present invention in the form of pure computer-readable program codes, the method steps can be logically programmed to enable the systems, subsystems, modules, and units provided by the present invention to be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, etc. to achieve the same functions. Therefore, the systems, subsystems, modules, and units provided by the present invention can be regarded as both the structures within hardware components and the software modules for implementing the methods.

[0111] Obviously, those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims

1. An integrated parallel transmission method for optoelectronic time-frequency signals, characterized in that, Including: The time-frequency modem generates a broadband spread-spectrum modulated intermediate-frequency carrier signal, which is converted into an uplink microwave modulated signal through an upconverter, and phase modulation is performed using an electro-optic modulator to obtain the ultra-stable laser at Station A and the laser at Station B; The photodetector obtains the downlink microwave modulated signal through coherent detection, which is converted into a broadband spread-spectrum modulated intermediate-frequency carrier signal through a downconverter. The time-frequency modem measures the Doppler frequency measurement value at the local reference frequency to obtain the frequency deviation between Stations A and B; The photodetector at Station A generates an optical heterodyne signal between the ultra-stable laser at Station A and the laser at Station B, and uses an acousto-optic modulator to complete optical phase-locked control to lock the ultra-stable laser at Station A to the laser at Station B; The photodetector at Station B generates an optical heterodyne signal between the laser at Station B and the ultra-stable laser at Station A, and adjusts the frequency of the laser at Station B through feedback to lock the laser at Station B to the ultra-stable laser at Station A.

2. The method according to claim 1, wherein The time-frequency modem generates a broadband spread-spectrum modulated intermediate-frequency carrier signal, which is converted into an uplink microwave modulated signal through an upconverter, and phase modulation is performed using an electro-optic modulator to obtain the ultra-stable laser at Station A and the laser at Station B, specifically including: The time-frequency modem at Station A generates the first broadband spread-spectrum modulated intermediate-frequency carrier signal at Station A. The first broadband spread-spectrum modulated intermediate-frequency carrier signal at Station A includes the broadband pseudo-code modulation signal at Station A and the one-way measurement data at Station A. The transmission time under the local clock reference at Station A is recorded. The first broadband spread-spectrum modulated intermediate-frequency carrier signal at Station A is converted into the uplink microwave modulated signal at Station A through the upconverter at Station A. The electro-optic modulator at Station A performs phase modulation on the uplink microwave modulated signal at Station A to obtain the ultra-stable laser at Station A; The time-frequency modem at Station B generates the first broadband spread-spectrum modulated intermediate-frequency carrier signal at Station B. The first broadband spread-spectrum modulated intermediate-frequency carrier signal at Station B is converted into the uplink microwave modulated signal at Station B through the upconverter at Station B. The electro-optic modulator at Station B performs phase modulation on the uplink microwave modulated signal at Station B to obtain the laser at Station B.

3. The method according to claim 1, wherein The photodetector obtains the downlink microwave modulated signal through coherent detection, which is converted into a broadband spread-spectrum modulated intermediate-frequency carrier signal through a downconverter. The time-frequency modem measures the Doppler frequency measurement value at the local reference frequency to obtain the frequency deviation between Stations A and B, specifically including: The photodetector at Station A obtains the downlink microwave modulated signal at Station A through coherent detection. The downlink microwave modulated signal at Station A is converted into the second broadband spread-spectrum modulated intermediate-frequency carrier signal at Station A through the downconverter at Station A. The time-frequency modem at Station A strips the broadband pseudo-code modulation signal at Station A and the one-way measurement data at Station A from the second broadband spread-spectrum modulated intermediate-frequency carrier signal at Station A to obtain the stripped broadband spread-spectrum modulated signal at Station A. According to the stripped broadband spread-spectrum modulated signal at Station A, the self-transmission signal reception time at Station A and the inter-site transmission signal reception time at Station A are determined. The time-frequency modem at Station A measures the Doppler frequency measurement value at the local reference frequency according to the second broadband spread-spectrum modulated intermediate-frequency carrier signal at Station A to obtain the carrier frequency measurement value at Station A; The B station photodetector obtains the B station downlink microwave modulation signal through coherent detection. The B station downlink microwave modulation signal passes through the B station downconverter and is converted into the B station second broadband spread-spectrum modulated intermediate-frequency carrier signal. The B station time-frequency modem strips the B station broadband pseudo-code modulation signal and the B station one-way measurement data from the B station second broadband spread-spectrum modulated intermediate-frequency carrier signal to obtain the stripped B station broadband spread-spectrum modulated signal. According to the stripped B station broadband spread-spectrum modulated signal, the B station self-transmission and self-reception signal reception time and the B station inter-site transmission signal reception time are determined. According to the A station self-transmission and self-reception signal reception time, the A station inter-site transmission signal reception time, the B station self-transmission and self-reception signal reception time, and the B station inter-site transmission signal reception time, the time difference between stations A and B is obtained. The B station time-frequency modem measures the Doppler frequency measurement value at the local reference frequency according to the B station second broadband spread-spectrum modulated intermediate-frequency carrier signal to obtain the B station carrier frequency measurement value; According to the A station carrier frequency measurement value and the B station carrier frequency measurement value, the frequency deviation between stations A and B is obtained.

4. The method according to claim 3, wherein Calculate the time difference between stations A and B according to the following formula: Among them, ΔT is the time difference between Station A and Station B, T A1 is the reception time of the self-transmitted and self-received signal at Station A, T A2 is the reception time of the inter-station transmission signal at Station A, T B1 is the reception time of the self-transmitted and self-received signal at Station B, T B2 is the reception time of the inter-station transmission signal at Station B, τ TXA is the transmission delay within Station A, τ TXB is the transmission delay within Station B, (τ TXA - τ TXB ) is the uplink differential link term of the signal.

5. The method according to claim 3, characterized in that, Calculate the A station carrier frequency measurement value according to the following formula: Among them, f AB is the measured value of the carrier frequency of Station A, f IF is the intermediate frequency carrier frequency of the transmitted signal, f0 is the reference frequency, df is the frequency difference between Stations A and B, f LOA is the nominal frequency conversion frequency of the up / down converter of Station A, f LOB is the nominal frequency conversion frequency of the up / down converter of Station B, and Δf is the frequency noise introduced by the optical fiber transmission link.

6. The method according to claim 3, characterized in that, Calculate the B station carrier frequency measurement value according to the following formula: Among them, f BA is the measured value of the B station carrier frequency, f IF is the intermediate frequency carrier frequency of the transmitted signal, f0 is the reference frequency, df is the frequency difference between stations A and B, f LOA is the nominal frequency conversion frequency of the up / down converter at station A, f LOB is the nominal frequency conversion frequency of the up / down converter at station B, and Δf is the frequency noise introduced by the optical fiber transmission link.

7. The method according to claim 3, wherein Calculate the frequency deviation between stations A and B according to the following formula: Among them, df clk is the frequency deviation between stations A and B, f AB is the carrier frequency value received by station B, f BA is the carrier frequency value received by station A, f LOA is the nominal frequency conversion frequency of the up / down converter at station A, f LOB is the nominal frequency conversion frequency of the up / down converter at station B, f IF is the intermediate frequency carrier frequency of the transmitted signal, and f0 is the reference frequency.

8. The method according to claim 1, characterized in that The A station photodetector generates an optical heterodyne signal between the A station ultra-stable laser and the B station laser, and uses an acousto-optic modulator to complete optical phase-locking control to lock the A station ultra-stable laser to the B station laser, specifically including: The A station ultra-stable laser is divided into a first laser beam and a second laser beam by a 2×2 fiber coupler; The first laser beam introduces the A station photodetector signal through a 2×1 fiber coupler to obtain a first laser heterodyne signal; The first laser heterodyne signal passes through a phase-locked control loop to obtain an acousto-optic modulation signal; The second laser beam introduces the acousto-optic modulation signal for acousto-optic modulation and frequency pre-compensation to obtain a pre-compensated laser. After the pre-compensated laser is transmitted through an optical fiber link or a free space link, the A station ultra-stable laser with superimposed frequency noise is obtained, and the A station ultra-stable laser with superimposed frequency noise is transmitted to the B station.

9. The method according to claim 1, wherein The B station photodetector generates an optical heterodyne signal between the B station laser and the A station ultra-stable laser, and locks the B station laser to the A station ultra-stable laser by feedback-adjusting the frequency of the B station laser, specifically including: The B station photodetector generates a B station laser, and the B station laser is divided into a third laser beam and a fourth laser beam by a 2×2 fiber coupler; The third laser beam introduces the B station photodetector signal through a 2×1 fiber coupler to obtain a second laser heterodyne signal; The fourth laser beam is transmitted through an optical fiber link or a free space link to obtain the B station laser with superimposed frequency noise, and the B station laser with superimposed frequency noise is transmitted to the A station; The second laser heterodyne signal passes through a phase-locked control loop to feedback-adjust the frequency of the B station laser, and lock the output center frequency of the B station laser to the frequency of the A station ultra-stable laser; and The signal of the optoelectronic detector at Station B is the ultra-stable laser at Station A after superimposing frequency noise; The signal of the optoelectronic detector at Station A is the signal obtained by acousto-optically modulating the laser at Station B after superimposing frequency noise.

10. An apparatus for implementing the integrated parallel transmission method of the optoelectronic time-frequency signal according to any one of claims 1-9, characterized in that, It includes: Two-station laser generation modules, which are used to control the time-frequency modem to generate a broadband spread-spectrum modulated intermediate-frequency carrier signal, which is converted into an uplink microwave modulation signal through an upconverter, and phase modulation is performed using an electro-optic modulator to obtain the ultra-stable laser at Station A and the laser at Station B; Two-station frequency difference determination module, which is used to control the optoelectronic detector to obtain a downlink microwave modulation signal through coherent detection, convert it into a broadband spread-spectrum modulated intermediate-frequency carrier signal through a downconverter, and use the time-frequency modem to measure the Doppler frequency measurement value at the local reference frequency to obtain the frequency deviation between Stations A and B; The first laser locking module is used to control the optoelectronic detector at Station A to generate an optical heterodyne signal between the ultra-stable laser at Station A and the laser at Station B, and use the acousto-optic modulator to complete optical phase-locking control to lock the ultra-stable laser at Station A to the laser at Station B; The second laser locking module is used to control the optoelectronic detector at Station B to generate an optical heterodyne signal between the laser at Station B and the ultra-stable laser at Station A, and adjust the frequency of the laser at Station B through feedback to lock the laser at Station B to the ultra-stable laser at Station A.

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