A very long baseline interferometer based on electronic phase delay technique

Abstract

A very long baseline interferometer based on electronic phase delay technology comprises a laser, a coupler, a phototube, a power divider, an electronic phase delay device, a frequency mixer, a filter, a phase meter, an ultra-stable clock and a lock arm controller; a radio frequency signal is obtained by down-converting a laser signal, and the radio frequency signal is delayed for tens of seconds to form an unequal arm length interferometer. The interferometer can be used to realize lock arm frequency stabilization and time delay interference technology to reduce laser frequency noise. The application solves the problem of long time transmission loss of a laser interferometer on the ground, simplifies the technical implementation difficulty while retaining phase information by using an electronic phase delay method, and realizes high stability, multifunction and laser frequency noise suppression by electronic integration, which has a wide application prospect in the field of precision measurement.

Description

Technical Field

[0001] This invention relates to the field of space laser interferometry and precision measurement technology, specifically to an inter-satellite laser interferometer for tasks such as gravitational wave detection, and particularly to a very long baseline interferometer based on electronic phase delay technology. Background Technology

[0002] Very Long Baseline Interferometry (VLBI) is a high-precision space measurement and detection technology that plays a crucial role in gravitational wave detection, deep space navigation, and Earth rotation monitoring. Traditional VLBI systems are typically based on optical phase delay technology, using long-distance optical fibers or free-space transmission to delay optical signals and thus simulate the long-baseline interference effect. However, as the baseline length increases, optical delay systems face challenges such as significant signal attenuation, sensitivity to environmental interference, high system complexity, and difficulty in achieving stable delays over long periods.

[0003] In recent years, domestic and international research has proposed interferometer schemes based on electronic phase delay technology, attempting to overcome the limitations of traditional optical delay by down-converting optical signals to radio frequency signals and then performing digital delay processing. For example, patent [Application Publication No.: CN120805319A] proposes a time-delay interferometry technology and a semi-physical experimental verification method for locking arm frequency stabilization. Its focus is on describing the data transmission process of locking arm frequency stabilization and time-delay interferometry. However, this scheme provides a relatively general description of the specific implementation of the delay unit, the clock synchronization mechanism, and the locking arm control strategy, lacking in-depth explanation of the hardware implementation details. Patent [Application Publication No.: CN120370435A] focuses on the processing method of the interference signal and noise modeling, with less attention paid to the physical architecture and control loop design of the system, failing to fully demonstrate the advantages of electronic delay systems in terms of integration and scalability.

[0004] Therefore, existing technologies still have significant shortcomings in achieving long-delay, high-stability, low-noise, and integrable very long baseline interferometers, and there is an urgent need for an innovative solution in terms of hardware implementation, clock synchronization, and control strategies. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing optical delay methods in very long baseline interferometers, such as large signal attenuation, environmental sensitivity, difficulty in achieving long-term stable delay, and high system complexity. This invention proposes a very long baseline interferometer based on electronic phase delay technology, which not only achieves long-delay, low-noise interferometric measurements at the methodological level, but also incorporates in-depth optimization and innovation in implementation details. Specifically: FPGA implementation of the electronic phase delayer: An FPGA circuit integrating an analog-to-digital converter, memory, and digital-to-analog converter is used to achieve real-time high-fidelity acquisition, storage, and reconstruction of RF signals, supporting adjustable delays of up to tens of seconds; High-precision clock synchronization system: All delayers and phase meters share the same ultra-stable clock source, ensuring phase consistency across the entire system; Arm locking controller: Based on a Zynq series FPGA design, it supports multi-channel phase data processing and real-time feedback control, enabling various frequency stabilization modes such as single-arm locking, differential arm locking, and dual-arm locking; High system integration and scalability: Through modular design, it supports various interferometer configurations, facilitating system function expansion and adaptation to different measurement needs. Through the innovation of the above-mentioned specific implementation details, this invention significantly improves the stability, flexibility and engineering practicality of the system, and provides reliable technical support for the application of very long baseline interferometers in the fields of space exploration and precision measurement.

[0006] The technical solution of the present invention is as follows: A very long baseline interferometer based on electronic phase delay technology, characterized in that it includes: Local laser, reference laser; First coupler, second coupler, third coupler; First phototube, second phototube, third phototube; First power divider, second power divider, third power divider, fourth power divider, fifth power divider; First mixer, second mixer, third mixer, fourth mixer; First electronic phase delayer, second electronic phase delayer; First filter, second filter, third filter, fourth filter; phase meter, ultra-stable clock, locking arm controller; First slave laser, second slave laser; The output of the local laser and the output of the reference laser are respectively connected to the two inputs of the first coupler. The output of the first coupler is connected to the input of the first phototube. The output of the first phototube is connected to the input of the first power divider. The first output of the first power divider is connected to the input of the second power divider. The second output of the first power divider is connected to the input of the third power divider. The first output terminal of the second power divider is connected to the first input terminal of the first electronic phase delayer; the first output terminal of the first electronic phase delayer is connected to the RF port of the second mixer; the second output terminal of the second power divider is connected to the LO port of the first mixer. The output terminals of the first laser and the reference laser are respectively connected to the two input terminals of the second coupler. The output terminal of the second coupler is connected to the input terminal of the second phototube. The output terminal of the second phototube is connected to the input terminal of the fourth power divider. The first output terminal of the fourth power divider is connected to the second input terminal of the first electronic phase delay unit. The second output terminal of the first electronic phase delay unit is connected to the RF port of the first mixer. The second output terminal of the fourth power divider is connected to the LO port of the second mixer. The output of the first mixer is connected to the input of the first filter, and the output of the first filter is connected to the first channel of the phase meter; the output of the second mixer is connected to the input of the second filter, and the output of the second filter is connected to the second channel of the phase meter; thus forming a first interferometer; The first output terminal of the third power divider is connected to the first input terminal of the second electronic phase delayer, and the first output terminal of the second electronic phase delayer is connected to the RF port of the fourth mixer; the second output terminal of the third power divider is connected to the LO port of the third mixer. The output of the second slave laser and the output of the reference laser are respectively connected to the two inputs of the third coupler. The output of the third coupler is connected to the input of the third phototube. The output of the third phototube is connected to the input of the fifth power divider. The first output of the fifth power divider is connected to the second input of the second electronic phase delay unit. The second output of the second electronic phase delay unit is connected to the RF port of the third mixer. The second output of the fifth power divider is connected to the LO port of the fourth mixer. The output of the third mixer is connected to the input of the third filter, and the output of the third filter is connected to the third channel of the phase meter; the output of the fourth mixer is connected to the input of the fourth filter, and the output of the fourth filter is connected to the fourth channel of the phase meter; thus forming a second interferometer; The clock output terminal of the ultra-stable clock is connected to the clock input terminal of the first electronic phase delay unit, the clock input terminal of the second electronic phase delay unit, and the clock input terminal of the phase meter, respectively, so that the three share the same clock source. The data output terminal of the phase meter is connected to the data input terminal of the locking arm controller, and the feedback output terminal of the locking arm controller is connected to the control input terminal of the local laser.

[0007] Furthermore, the first electronic phase delayer and the second electronic phase delayer are respectively composed of FPGA circuit boards. The FPGA circuit boards integrate analog-to-digital converters, memory and digital-to-analog converters to acquire radio frequency signals in real time, delay and restore them.

[0008] Furthermore, the locking arm controller is made of a Zynq series FPGA, which integrates an ARM processor and a programmable logic unit. The input terminal of the programmable logic unit serves as the data input terminal, used to receive multi-channel phase data sent by the phase meter and perform parallel processing. The ARM processor runs a PID control algorithm, and its output terminal serves as the feedback output terminal, outputting a feedback signal to the control input terminal of the local laser.

[0009] Furthermore, the locking arm controller is configured to execute at least one of the following locking arm modes: single-arm locking arm mode, differential locking arm mode, and dual-arm locking arm mode; in the single-arm locking arm mode, only the phase data of the first channel or the fourth channel of the phase meter is input to the locking arm controller; in the dual-arm locking arm mode, all the phase data of the first channel and the fourth channel of the phase meter are input to the locking arm controller simultaneously.

[0010] Furthermore, the phase meter is a digital quadrature demodulation phase meter or frequency counter, used to analyze the phase difference of the beat frequency signal of each channel in real time and output it in digital data form.

[0011] Furthermore, the local laser, the first slave laser, and the second slave laser all undergo frequency down-conversion with the same reference laser. That is, the output light of each laser and the reference laser is combined by their respective couplers and then converted into a down-frequency radio frequency signal by their respective phototubes.

[0012] Furthermore, the ultra-stable clock is a low-phase-noise atomic clock or a high-stability crystal oscillator.

[0013] Furthermore, in the locked-arm frequency stabilization mode, the first slave laser and the second slave laser are phase-locked with the local laser through a phase-locked loop circuit, so that the phase difference output by the phase meter reflects the frequency noise of the local laser; in the time-delay interference mode, the first slave laser and the second slave laser can be selectively not phase-locked with the local laser, and the phase difference data output by the phase meter is used for offline post-processing.

[0014] Furthermore, the interferometer also includes one or more additional slave lasers, and correspondingly added additional couplers, additional phototubes, additional power dividers, additional mixers, additional filters, and additional electronic phase delayers. The additional slave lasers and the reference laser are combined by the additional couplers and converted into down-frequency radio frequency (RF) signals by the additional phototubes. The RF signals are split into two paths by the additional power divider. One path is delayed by the additional electronic phase delayer and then connected to the RF port of the additional mixer, and the other path is connected to the LO port of another additional mixer. The RF signals from the local laser link are split into two paths by the additional power divider. One path is connected to the LO port of the additional mixer, and the other path is delayed by the additional electronic phase delayer and then connected to the RF port of another additional mixer. The outputs of each additional mixer are connected to the additional channels of the phase meter after passing through the additional filters, thereby expanding to form three or more interferometers and obtaining six or more mixed signals.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1) This method enables ultra-long time delay simulation: Electronic phase delay technology can achieve a delay time of more than ten seconds, which is much higher than the microsecond or millisecond level of traditional fiber delay lines, thus meeting the requirements of very long baseline interferometers for long baseline simulation.

[0016] 2) The electronic phase delay technology of this invention employs a high-speed analog-to-digital converter and a digital-to-analog converter to acquire and reconstruct signals. Compared to optical delay methods, electronic phase delay technology reduces the coverage of useful signals by noise signals, ensuring the integrity of the interference signal. Through digital storage and signal regeneration, signal loss and noise interference inherent in physical optical fibers are avoided.

[0017] 3) This invention has the advantages of miniaturization and integration, with the electronic phase delayer based on an FPGA. Compared to complex very long baseline interferometers, this invention is easier to miniaturize, reduce costs, and make portable.

[0018] 4) This invention is characterized by its flexibility and scalability. The electronic phase delay technology allows for flexible adjustment of the delay time via software programs and supports Doppler frequency shift simulation, adapting to variations in baseline length. Furthermore, the system supports multi-channel delay, making it easily expandable to more complex multi-arm interferometer models, thus enhancing the versatility and adaptability of laser interferometers. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of an embodiment of a very long baseline interferometer based on electronic phase delay technology according to the present invention; Figure 2 This is a schematic diagram of the electronic phase delayer in this invention; Figure 3 This is a schematic diagram of the locking arm controller in this invention. Detailed Implementation The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. These embodiments are used to illustrate the present invention but are not intended to limit its scope. The specific structural and functional details disclosed herein are only for describing exemplary embodiments of the present invention. However, the present invention can be embodied in many alternative forms and should not be construed as being limited to the embodiments described herein.

[0020] It should be understood that although the terms first, second, etc., may be used herein to describe various units, these units should not be limited by these terms. These terms are only used to distinguish one unit from another. For example, a first unit may be referred to as a second unit, and similarly, a second unit may be referred to as a first unit, without departing from the scope of the exemplary embodiments of the invention.

[0021] Example See Figure 1 This embodiment provides a very long baseline interferometer based on electronic phase delay technology, specifically including the following components: a local laser 1, a reference laser 2, a first coupler group 3, a first phototube 4, a first power divider 5, a second power divider 6, a third power divider 7, a first mixer 8, a first electronic phase delayer 9, a second mixer 10, a first slave laser 11, a second coupler 12, a second phototube 13, a fourth power divider 14, a first filter 15, a second filter 16, a phase meter 17, an ultra-stable clock 18, a third mixer 19, a second electronic phase delayer 20, a fourth mixer 21, a second slave laser 22, a third coupler 23, a third phototube 24, a fifth power divider 25, a third filter 26, a fourth filter 27, and a locking arm controller 28; The output beams of the local laser 1 and the reference laser 2 are combined by the first coupler 3 and then converted by the first phototube 4 to obtain a down-frequency radio frequency (RF) signal. This RF signal contains frequency jitter information of the local laser relative to the reference laser. The RF signal is input to the first power divider 5 and split into two paths: one path is output from the first output terminal 52 of the first power divider 5 to the input terminal 61 of the second power divider 6, and the other path is output from the second output terminal 53 of the first power divider 5 to the input terminal 71 of the third power divider 7.

[0022] The second power divider 6 further splits the incoming radio frequency signal into two paths. One path is output from the first output terminal 62 of the second power divider 6 and connected to the first input port 91 of the first electronic phase delay unit 9. The other path is output from the second output terminal 63 of the second power divider 6 and connected to the LO port 81 of the first mixer 8.

[0023] The internal structure of the first electronic phase delayer 9 is as follows: Figure 2As shown, the circuit is constructed from an FPGA board and integrates an analog-to-digital converter (ADC), a memory (RAM), and a digital-to-analog converter (DAC). After the radio frequency signal is acquired by the ADC, it is written into the memory. Under the control of the ultra-stable clock 18, after a preset delay time (e.g., 10 seconds, 30 seconds, or longer), it is read out by the DAC and reconstructed into an analog radio frequency signal, which is then output from the first output port 92 to the radio frequency (RF) port 101 of the second mixer 10.

[0024] On the other hand, the output light from the first laser 11 and the reference laser 2 is combined by the second coupler 12 and then converted by the second phototube 13 to obtain a down-frequency radio frequency (RF) signal. This RF signal is input to the fourth power divider 14 and split into two paths. One path is output from the first output terminal 142 of the fourth power divider 14 and enters the second input port 93 of the first electronic phase delay unit 9. After the same delay, it is output from the second output terminal 94 to the RF port 82 of the first mixer 8. The other path is output from the second output terminal 143 of the fourth power divider 14 and enters the LO interface 102 of the second mixer 10. The first mixer 8 mixes the two signals from the LO port 81 and the RF port 82. The beat frequency signal output from its output terminal 83 is filtered by the first filter 15 to remove high-frequency signals and then connected to the first channel 171 of the phase meter 17. The second mixer 10 mixes the signals from the RF port 101 and the LO port 102. The beat frequency signal output from its output terminal 103 is filtered out by the second filter 16 to remove high-frequency signals before being connected to the second channel 172 of the phase meter 17. This forms the first interferometer. Similarly, the radio frequency signal from the first power divider 5 to the third power divider 7 is split into two paths: one path is output from the first output terminal 72 of the third power divider 7 and connected to the first input port 201 of the second electronic phase delay unit 20; the other path is output from the second output terminal 73 of the third power divider 7 and connected to the LO port 191 of the third mixer 19.

[0025] The second electronic phase delayer 20 has the same structure as the first electronic phase delayer 9, and both are implemented based on FPGA. After delay, the signal is output from the first output port 202 of the second electronic phase delayer 20 to the RF interface 211 of the fourth mixer 21.

[0026] The output light from the second laser 22 and the reference laser 2 is combined by the third coupler 23, converted by the third phototube 24 to obtain a down-frequency radio frequency signal, which is then input to the input terminal 251 of the fifth power divider 25. The fifth power divider 25 splits the signal into two paths: one path is output from the first output terminal 252 of the fifth power divider 25, enters the second input terminal 203 of the second electronic phase delay unit 20, and after delay, is output from its second output port 204 to the RF port 192 of the third mixer 19. The other path is output from the output terminal 253 of the second electronic phase delay unit 20 and enters the LO interface 212 of the fourth mixer 21; the beat frequency signal output from the output terminal 193 of the third mixer 19 is filtered by the third filter 26 to remove high-frequency signals and then connected to the third channel 173 of the phase meter 17. The beat frequency signal output from the output terminal 213 of the fourth mixer 21 is filtered by the fourth filter 27 to remove high-frequency signals and then connected to the fourth channel 174 of the phase meter 17. At this point, the second interferometer link is complete.

[0027] To achieve system-wide phase consistency and high-precision delay, the first electronic phase delay unit 9, the second electronic phase delay unit 20, and the phase meter 17 all use the same ultra-stable clock 18 as their clock source. This ultra-stable clock 18 is preferably a low-phase-noise atomic clock or a high-stability crystal oscillator, ensuring that all sampling, storage, reconstruction, and phase calculation operations are performed under a strictly synchronized time reference, eliminating additional phase errors introduced by clock asynchrony.

[0028] When the first slave laser 11 and the second slave laser 22 are in a phase-locked state with the local laser 1, this embodiment can achieve arm-locked frequency stabilization. The first electronic phase delay unit 9 and the second electronic phase delay unit 20 delay the radio frequency signal from the local laser link and then mix it with the undelayed slave laser link signal, respectively. The resulting beat frequency signals of the four channels all contain the frequency jitter information of the local laser 1, and because the electronic delay introduces an equivalent long baseline, the frequency jitter is converted into a measurable phase difference.

[0029] Phase meter 1 analyzes the phase difference data from the first channel 171 to the fourth channel 174 in real time and sends this data to the locking arm controller 28 via a parallel data bus (e.g., SPI or LVDS interface). Locking arm controller 28, as shown... Figure 3 As shown, it is implemented using a Zynq series FPGA, which integrates an ARM processor and a programmable logic unit.

[0030] Single-arm locking mode: Using only the data from the first channel 171 or the fourth channel 174, the locking arm controller 28 runs a proportional-integral-derivative (PID) control algorithm to calculate the feedback control signal and output it to the frequency tuning port (such as piezoelectric ceramic or current modulation port) of the local laser 1, thereby compressing the frequency noise of the local laser 1 to below the noise floor of the reference laser 2.

[0031] Dual-arm locking mode: Using data from two channels 171 and 174 simultaneously, the locking arm controller 28 can execute the dual-arm locking algorithm to further suppress noise and improve frequency stabilization.

[0032] In time-delayed interferometry (TDI) mode, the first slave laser 11 and the second slave laser 22 do not require phase-locking with the local laser 1. Phase meter 17 continuously acquires the phase difference data from the four channels and outputs it to the host computer. After storing this data, the host computer performs offline post-processing according to a time-delayed interferometry algorithm (such as a first-order or second-order TDI combination). By constructing different delay combinations, laser frequency noise and clock noise are canceled out, ultimately achieving ultra-high precision interferometric measurement.

[0033] In summary, the very long baseline interferometer based on electronic phase delay technology provided in this embodiment has the following technical advantages: 1) This method enables ultra-long time delay simulation: Electronic phase delay technology can achieve a delay time of more than ten seconds, which is much higher than the microsecond or millisecond level of traditional fiber delay lines, thus meeting the requirements of very long baseline interferometers for long baseline simulation.

[0034] 2) The electronic phase delay technology of this invention employs a high-speed analog-to-digital converter and a digital-to-analog converter to acquire and reconstruct signals. Compared to optical delay methods, electronic phase delay technology reduces the coverage of useful signals by noise signals, ensuring the integrity of the interference signal. Through digital storage and signal regeneration, signal loss and noise interference inherent in physical optical fibers are avoided.

[0035] 3) This invention has the advantages of miniaturization and integration, with the electronic phase delayer based on an FPGA. Compared to complex very long baseline interferometers, this invention is easier to miniaturize, reduce costs, and make portable.

[0036] 4) This invention is characterized by its flexibility and scalability. The electronic phase delay technology allows for flexible adjustment of the delay time via software programs and supports Doppler frequency shift simulation, adapting to variations in baseline length. Furthermore, the system supports multi-channel delay, making it easily expandable to more complex multi-arm interferometer models, thus enhancing the versatility and adaptability of laser interferometers.

[0037] This embodiment provides a very long baseline interferometer based on electronic phase delay technology that has a clear structure, is feasible to implement, and has superior performance. It effectively solves many defects of optical delay schemes in the prior art and has significant industrial application value.

[0038] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the patent. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A very long baseline interferometer based on electronic phase delay technology, characterized in that, include: Local laser (1), reference laser (2); First coupler (3), second coupler (12), third coupler (23); First phototube (4), second phototube (13), third phototube (24); First power divider (5), second power divider (6), third power divider (7), fourth power divider (14), fifth power divider (25); First mixer (8), second mixer (10), third mixer (19), fourth mixer (21); First electronic phase delay unit (9), second electronic phase delay unit (20); First filter (15), second filter (16), third filter (26), fourth filter (27); Phase meter (17), ultra-stable clock (18), lock arm controller (28); First slave laser (11), second slave laser (22); The output of the local laser (1) and the output of the reference laser (2) are respectively connected to the two inputs of the first coupler (3). The output of the first coupler (3) is connected to the input of the first phototube (4). The output of the first phototube (4) is connected to the input (51) of the first power divider (5). The first output (52) of the first power divider (5) is connected to the input (61) of the second power divider (6). The second output (53) of the first power divider (5) is connected to the input (71) of the third power divider (7). The first output terminal (62) of the second power divider (6) is connected to the first input terminal (91) of the first electronic phase delay unit (9); the first output terminal (92) of the first electronic phase delay unit (9) is connected to the RF port (101) of the second mixer (10); the second output terminal (63) of the second power divider (6) is connected to the LO port (81) of the first mixer (8). The output of the first laser (11) and the output of the reference laser (2) are respectively connected to the two inputs of the second coupler (12). The output of the second coupler (12) is connected to the input of the second phototube (13). The output of the second phototube (13) is connected to the input (141) of the fourth power divider (14). The first output (142) of the fourth power divider (14) is connected to the second input (93) of the first electronic phase delay unit (9). The second output (94) of the first electronic phase delay unit (9) is connected to the RF port (82) of the first mixer (8). The second output (143) of the fourth power divider (14) is connected to the LO port (102) of the second mixer (10). The output terminal (83) of the first mixer (8) is connected to the input terminal of the first filter (15), and the output terminal of the first filter (15) is connected to the first channel (171) of the phase meter (17); the output terminal (103) of the second mixer (10) is connected to the input terminal of the second filter (16), and the output terminal of the second filter (16) is connected to the second channel (172) of the phase meter (17); thus forming a first interferometer; The first output terminal (72) of the third power divider (7) is connected to the first input terminal (201) of the second electronic phase delay unit (20), and the first output terminal (202) of the second electronic phase delay unit (20) is connected to the RF port (211) of the fourth mixer (21); the second output terminal (73) of the third power divider (7) is connected to the LO port (191) of the third mixer (19). The output of the second slave laser (22) and the output of the reference laser (2) are respectively connected to the two inputs of the third coupler (23). The output of the third coupler (23) is connected to the input of the third phototube (24). The output of the third phototube (24) is connected to the input (251) of the fifth power divider (25). The first output (252) of the fifth power divider (25) is connected to the second input (203) of the second electronic phase delay unit (20). The second output (204) of the second electronic phase delay unit (20) is connected to the RF port (192) of the third mixer (19). The second output (253) of the fifth power divider (25) is connected to the LO port (212) of the fourth mixer (21). The output terminal (193) of the third mixer (19) is connected to the input terminal of the third filter (26), and the output terminal of the third filter (26) is connected to the third channel (173) of the phase meter (17); the output terminal (213) of the fourth mixer (21) is connected to the input terminal of the fourth filter (27), and the output terminal of the fourth filter (27) is connected to the fourth channel (174) of the phase meter (17); thus forming a second interferometer; The clock output terminal of the ultra-stable clock (18) is connected to the clock input terminal of the first electronic phase delay unit (9), the clock input terminal of the second electronic phase delay unit (20), and the clock input terminal of the phase meter (17), respectively, so that the three share the same clock source. The data output terminal of the phase meter (17) is connected to the data input terminal of the locking arm controller (28), and the feedback output terminal of the locking arm controller (28) is connected to the control input terminal of the local laser (1).

2. A very long baseline interferometer based on electronic phase delay technology according to claim 1, characterized in that, The first electronic phase delayer (9) and the second electronic phase delayer (20) are respectively composed of FPGA circuit boards. The FPGA circuit boards integrate analog-to-digital converters, memory and digital-to-analog converters to collect radio frequency signals in real time, delay and restore them.

3. A very long baseline interferometer based on electronic phase delay technology according to claim 1, characterized in that, The locking arm controller (28) is made of Zynq series FPGA and integrates an ARM processor and a programmable logic unit. The input terminal of the programmable logic unit serves as the data input terminal, which is used to receive multi-channel phase data sent by the phase meter (17) and perform parallel processing. The ARM processor runs a PID control algorithm, and its output terminal serves as the feedback output terminal, outputting a feedback signal to the control input terminal of the local laser (1).

4. A very long baseline interferometer based on electronic phase delay technology according to claim 1, characterized in that, The arm locking controller (28) is configured to execute at least one of the following arm locking modes: single arm locking mode, differential arm locking mode, and dual arm locking mode; in the single arm locking mode, only the phase data of the first channel (171) or the fourth channel (174) of the phase meter (17) is input to the arm locking controller (28); in the dual arm locking mode, all the phase data of the first channel (171) and the fourth channel (174) of the phase meter (17) are input to the arm locking controller (28) simultaneously.

5. A very long baseline interferometer based on electronic phase delay technology according to claim 1 or 4, characterized in that, The phase meter (17) is a digital quadrature demodulation phase meter or frequency counter, used to analyze the phase difference of each channel beat frequency signal in real time and output it in digital data form.

6. A very long baseline interferometer based on electronic phase delay technology according to claim 1 or 4, characterized in that, The local laser (1), the first slave laser (11) and the second slave laser (22) are all frequency down-converted with the same reference laser (2). That is, the output light of each laser and the reference laser are combined by the corresponding coupler and then converted into a down-frequency radio frequency signal by the corresponding phototube.

7. A very long baseline interferometer based on electronic phase delay technology according to claim 1 or 4, characterized in that, The ultra-stable clock (18) is a low-phase-noise atomic clock or a high-stability crystal oscillator.

8. A very long baseline interferometer based on electronic phase delay technology according to claim 1, characterized in that, In the locked-arm frequency stabilization mode, the first slave laser (11) and the second slave laser (22) are phase-locked with the local laser (1) through a phase-locked loop circuit, so that the phase difference output by the phase meter (17) reflects the frequency noise of the local laser (1); in the time delay interference mode, the first slave laser (11) and the second slave laser (22) may not be phase-locked with the local laser (1), and the phase difference data output by the phase meter (17) is used for offline post-processing.

9. A very long baseline interferometer based on electronic phase delay technology according to claim 1, characterized in that, The interferometer further includes one or more additional slave lasers, and corresponding additional couplers, additional phototubes, additional power dividers, additional mixers, additional filters, and additional electronic phase delayers. The additional slave lasers and the reference laser are combined by the additional couplers and converted into down-frequency radio frequency (RF) signals by the additional phototubes. These RF signals are split into two paths by the additional power divider. One path is delayed by the additional electronic phase delayer and then connected to the RF port of the additional mixer, while the other path is connected to the LO port of another additional mixer. The RF signal from the local laser link is split into two paths by the additional power divider. One path is connected to the LO port of the additional mixer, while the other path is delayed by the additional electronic phase delayer and then connected to the RF port of another additional mixer. The outputs of each additional mixer are connected to the additional channels of the phase meter after passing through additional filters, thereby expanding to form three or more interferometers and obtaining six or more mixed signals.

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