Optical Signal Passive Difference Frequency Detection and Digital Coherent Superposition Device and Method

Abstract

The present invention relates to the field of dual-beam digital coherent superposition, and particularly to an optical signal passive heterodyne detection and digital coherent superposition device and method. The first optical component of the device is arranged on the optical path between the target light source and the input end of the optical switch. The second optical component is arranged on the optical path between the local oscillator light source and the input end of the optical switch. The output end of the optical switch is connected to the input ends of the first mixer and the second mixer. The first balanced detector group is arranged on the optical path from the output end of the first mixer to the input end of the signal acquisition system. The second balanced detector group is arranged on the optical path from the output end of the second mixer to the input end of the signal acquisition system. The output end of the signal acquisition system is connected to the computer system, and the computer system is used for timing processing and outputs the first coherent signal and the second coherent signal obtained through coherent superposition. In this way, the time alignment of the dual beams can be achieved by using a digital method.

Description

Technical Field

[0001] The present invention belongs to the field of dual-beam digital coherent superposition, and particularly relates to an optical signal passive heterodyne detection and digital coherent superposition device and method. Background Art

[0002] When two or more light waves of the same source meet and overlap in three-dimensional space, these light waves will perform vector superposition, and then form a specific interference pattern, that is, interference fringes. The distribution and shape of these interference fringes depend on factors such as the amplitude, frequency, and phase difference of the light waves. For a broadband light source, the light it emits actually contains continuously distributed frequency components, and the initial phases of each frequency component can be considered as independent random distribution functions, which means that the coherence of the broadband light source is poor. Therefore, the coherence length of the broadband light source is usually very short, and obvious coherence enhancement or weakening peaks can only be observed in a very small area where the optical path difference between the two beams is almost zero, that is, the so-called coherence region.

[0003] The phenomenon of dual-beam interference has shown extensive application potential in scientific research and industrial production, such as optical synthetic aperture imaging technology. However, its practical application is limited by problems such as optical path consistency and environmental stability. The optical path difference, as a core parameter in the dual-beam interference phenomenon, plays a decisive role in the formation and distribution of interference fringes. Under ideal conditions, precisely controlled optical path difference can ensure the stability and predictability of interference fringes, thus supporting high-precision measurement and sensing applications. However, in actual operation, any slight change in the optical path may significantly affect the position and shape of the interference fringes, resulting in deviation of the measurement results and decreased reliability. Especially in synthetic aperture imaging, the control requirements for the optical path difference are extremely strict, usually requiring the optical path difference between different apertures to be less than one-twentieth of the wavelength to ensure the clarity and resolution of the final image. In addition, the demand for environmental stability in the dual-beam interference experiment cannot be ignored. Any slight fluctuation in the experimental environment, including slight changes in temperature, slight air flow, or slight differences in air pressure, may have a significant impact on the optical system. These environmental factors may not only cause slight deformation of the optical components, but also change the phase distribution, polarization state, and light intensity distribution of the light beam, thus directly interfering with the superposition effect of the dual beams and reducing the quality of the interference fringes. Summary of the Invention

[0004] In view of this, the present invention aims to provide an optical signal passive heterodyne detection and digital coherent superposition device and method, which reduces the strict requirements for external conditions such as optical path consistency and environmental stability in dual-beam coherent superposition, and greatly reduces the implementation difficulty and cost.

[0005] To achieve the above object, the technical solution of the present invention is realized as follows:

[0006] An optical signal passive difference frequency detection and digital coherent superposition device, comprising a target light source, a local oscillator light source, a first optical component, a second optical component, an optical switch, a first mixer, a second mixer, a first balanced detector group, a second balanced detector group, a signal acquisition system and a computer system;

[0007] The first optical component is arranged on the optical path between the target light source and the input end of the optical switch; the second optical component is arranged on the optical path between the local oscillator light source and the input end of the optical switch;

[0008] The output end of the optical switch is connected to the input ends of the first mixer and the second mixer; the first balanced detector group is arranged on the optical path from the output end of the first mixer to the input end of the signal acquisition system; the second balanced detector group is arranged on the optical path from the output end of the second mixer to the input end of the signal acquisition system; the output end of the signal acquisition system is connected to the computer system, and the computer system is used for timing processing and outputting a first coherent signal and a second coherent signal obtained through coherent superposition.

[0009] Further, the optical switch is used for chopping and modulating the target optical signal from the target light source and the local oscillator optical signal from the local oscillator light source, and outputting a first target signal and a first local oscillator signal obtained after chopping and modulating to the first mixer, and outputting a second target signal and a second local oscillator signal obtained after chopping and modulating to the second mixer;

[0010] The first mixer performs mixing processing on the first target signal and the first local oscillator signal, and outputs four-phase-modulated first difference frequency signals to the first balanced detector group; the second mixer performs mixing processing on the second target signal and the second local oscillator signal, and outputs four-phase-modulated second difference frequency signals to the second balanced detector group;

[0011] The first balanced detector group outputs a first in-phase output signal and a first quadrature output signal to the signal acquisition system, and the second balanced detector group outputs a second in-phase output signal and a second quadrature output signal to the signal acquisition system;

[0012] The computer system is used for timing processing and outputting a first coherent signal obtained through coherent superposition of the first in-phase output signal and the second in-phase output signal, and a second coherent signal obtained through coherent superposition of the first quadrature output signal and the second quadrature output signal.

[0013] Further, it further includes a signal generator, the output end of the signal generator is connected to the input end of the optical switch and the input end of the signal acquisition system, and the signal generator is used for outputting a modulation reference signal to the input end of the optical switch and the input end of the signal acquisition system;

[0014] The signal acquisition system is used to screen the first in-phase output signal, the second in-phase output signal, the first quadrature output signal, and the second quadrature output signal according to the modulation reference signal.

[0015] Further, the computer system includes a signal processing module, and the signal processing module is used for timing processing. The timing processing includes:

[0016] Performing cross-correlation calculation on the first in-phase output signal and the second in-phase output signal to determine the first relative time delay information between the first in-phase output signal and the second in-phase output signal; performing cross-correlation calculation on the first quadrature output signal and the second quadrature output signal to determine the second relative time delay information between the first quadrature output signal and the second quadrature output signal;

[0017] And using the first in-phase output signal as the reference signal, adjusting the time of the second in-phase output signal according to the first relative time delay information; using the first quadrature output signal as the reference signal, adjusting the time of the second quadrature output signal according to the second relative time delay information.

[0018] Further, after adjusting the time of the second in-phase output signal and adjusting the time of the second quadrature output signal, the timing processing further includes:

[0019] Performing sine difference fitting on the first in-phase output signal, the second in-phase output signal, the first quadrature output signal, and the second quadrature output signal;

[0020] Performing cross-correlation calculation on the first in-phase output signal and the second in-phase output signal after sine difference fitting to determine the third relative time delay information between the first in-phase output signal and the second in-phase output signal after sine difference fitting; performing cross-correlation calculation on the first quadrature output signal and the second quadrature output signal after sine difference fitting to determine the fourth relative time delay information between the first quadrature output signal and the second quadrature output signal after sine difference fitting;

[0021] And using the first in-phase output signal after sine difference fitting as the reference signal, adjusting the time of the second in-phase output signal after sine difference fitting according to the third relative time delay information; using the first quadrature output signal after sine difference fitting as the reference signal, adjusting the time of the second quadrature output signal after sine difference fitting according to the fourth relative time delay information.

[0022] Further, the computer system includes a filtering module, and the filtering module is used for filtering the first in-phase output signal, the second in-phase output signal, the first quadrature output signal, and the second quadrature output signal input to the computer system.

[0023] Further, the first optical component includes a collimator and two transmission optical components. The collimator is used to modulate the target optical signal from the target light source. The transmission optical component includes a beam reducing lens and an optical fiber collimator. The beam reducing lens is arranged on the optical path from the collimator to the optical fiber collimator. The beam reducing lens is used to focus the modulated target optical signal on the front focal point of the optical fiber collimator, and transmit the target optical signal to the input end of the optical switch through the optical fiber collimator.

[0024] Further, the second optical component includes an optical fiber coupler and two optical intensity attenuators. The optical fiber coupler is arranged on the optical path from the local oscillator light source to the two optical intensity attenuators. The optical fiber coupler is used to evenly divide the local oscillator optical signal of the local oscillator light source into two sub-local oscillator optical signals, and transmit them to the input end of the optical switch after passing through the two optical intensity attenuators respectively.

[0025] Further, the target light source is a broad-spectrum light source; and / or

[0026] The local oscillator light source is a narrow linewidth laser.

[0027] An optical signal passive heterodyne detection and digital coherent superposition method is applied to the optical signal passive heterodyne detection and digital coherent superposition device as described above. The optical signal passive heterodyne detection and digital coherent superposition method includes:

[0028] Transmit the target optical signal from the target light source to the input end of the optical switch through the first optical component; transmit the local oscillator optical signal from the local oscillator light source to the input end of the optical switch through the second optical component;

[0029] Chop and modulate the target optical signal from the target light source and the local oscillator optical signal from the local oscillator light source through the optical switch, and output the first target signal and the first local oscillator signal obtained after chop modulation to the first mixer, and output the second target signal and the second local oscillator signal obtained after chop modulation to the second mixer;

[0030] Perform mixing processing on the first target signal and the first local oscillator signal through the first mixer, and output four-phase-modulated first difference frequency signals to the first balanced detector group; perform mixing processing on the second target signal and the second local oscillator signal through the second mixer, and output four-phase-modulated second difference frequency signals to the second balanced detector group;

[0031] The first balanced detector group outputs a first in-phase output signal and a first quadrature output signal to the signal acquisition system, and the second balanced detector group outputs a second in-phase output signal and a second quadrature output signal to the signal acquisition system;

[0032] The first in-phase output signal, the second in-phase output signal, the first quadrature output signal, and the second quadrature output signal output from the signal acquisition system enter the computer system, where timing processing is performed, and a first coherent signal obtained by coherently superimposing the first in-phase output signal and the second in-phase output signal and a second coherent signal obtained by coherently superimposing the first quadrature output signal and the second quadrature output signal are output.

[0033] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0034] In the optical signal passive heterodyne detection and digital coherent superposition device according to the embodiment of the present invention, a first mixer and a second mixer are adopted. The first mixer and the second mixer can use the local oscillator signal as the carrier signal to mix the target signal and the local oscillator signal, and efficiently obtain the difference frequency signal between the target signal and the local oscillator signal. This process not only improves the signal-to-noise ratio but also amplifies the target signal, enabling precise acquisition of the target signal, further enhancing the anti-interference ability, and ensuring good performance even in a high-noise environment. At the same time, timing processing can be performed through the computer system, and cross-correlation calculations are respectively performed on the first in-phase output signal and the second in-phase output signal, and the first quadrature output signal and the second quadrature output signal to accurately obtain the relative time delay information. The relative time delay information reflects the propagation time difference caused by the optical path difference on different paths, so that the optical path difference between signals can be processed in the digital domain, enabling coherent superposition of two signals without relying on requirements such as optical path consistency and environmental stability, thereby improving the accuracy and stability of interference measurement, effectively suppressing the interference of environmental noise and noise, and greatly reducing the implementation difficulty and cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0036] Figure 1 is a schematic diagram of the optical signal passive heterodyne detection and digital coherent superposition device according to the embodiment of the present invention;

[0037] Figure 2 is a flowchart of the optical signal passive heterodyne detection and digital coherent superposition method according to the embodiment of the present invention.

[0038] Description of the reference numerals:

[0039] 10. Optical signal passive heterodyne detection and digital coherent superposition device; 11. Target light source; 12. Local oscillator light source; 13. First optical component; 14. Second optical component; 15. Optical switch; 16. First mixer; 17. Second mixer; 18. First balanced detector group; 19. Second balanced detector group; 20. Signal acquisition system; 21. Computer system; 22. Collimator; 23. Transmission optical component; 24. Beam reducing lens; 25. Fiber optic collimator; 26. Signal generator; 27. First balanced detector; 28. Second balanced detector; 29. Fiber optic coupler; 30. Optical intensity attenuator. Detailed implementation manners

[0040] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. Similar elements in different embodiments are labeled with related similar element numbers. In the following embodiments, many details are described to make the present invention better understood. However, those skilled in the art can easily recognize that some of the features can be omitted in different situations, or can be replaced by other elements, materials, or methods. In some cases, some operations related to the present invention are not shown or described in the specification, in order to avoid the core part of the present invention being overwhelmed by excessive description. For those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations according to the description in the specification and the general technical knowledge in the art.

[0041] It should be noted that, without conflict, the embodiments and features in the embodiments of the present invention can be combined with each other to form various embodiments. At the same time, the steps or actions in the method description can also be adjusted in the order that can be obvious to those skilled in the art. Therefore, the various sequences in the specification and drawings are only for clearly describing a certain embodiment, and do not mean that they are the necessary sequences, unless it is stated that a certain sequence must be followed.

[0042] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0043] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "mounted", "connected", "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific circumstances.

[0044] The present invention will be described in detail below with reference to the drawings and in conjunction with embodiments.

[0045] See Figure 1As shown in the figure, the embodiment of the present invention provides an optical signal passive difference frequency detection and digital coherent superposition device 10. The optical signal passive difference frequency detection and digital coherent superposition device 10 includes a target light source 11, a local oscillator light source 12, a first optical component 13, a second optical component 14, an optical switch 15, a first mixer 16, a second mixer 17, a first balanced detector group 18, a second balanced detector group 19, a signal acquisition system 20, and a computer system 21. In one embodiment, the target light source 11 is a broadband light source. The target light source 11 can be the sun, a halogen lamp, a black body, etc. The target light source 11 generates a target optical signal, and the target optical signal can be natural ambient light. Its main feature is that the phase of the target optical signal is a random function of time. In one embodiment, the local oscillator light source 12 is a narrow linewidth laser. The local oscillator light source 12 can be a DFB (Distributed Feedback) narrow linewidth laser. The local oscillator light source 12 generates a local oscillator optical signal, and the local oscillator optical signal can be a DFB laser signal with excellent monochromaticity emitted by the DFB narrow linewidth laser. This DFB laser signal has the characteristics of a narrow linewidth and extremely high frequency stability and phase stability, and can provide a stable and consistent frequency and phase, which is beneficial to subsequent signal modulation and signal processing. Among them, the local oscillator optical signal can be used as a carrier to effectively amplify the target optical signal to improve the detection sensitivity of the target optical signal.

[0046] The first optical component 13 is arranged on the optical path between the target light source 11 and the input end of the optical switch 15, and is used to transmit the target optical signal from the target light source 11 to the input end of the optical switch 15.

[0047] In one embodiment, the first optical component 13 includes a collimator 22 and two transmission optical components 23. The collimator 22 is configured to modulate a target optical signal from a target light source 11. The target optical signal from the target light source 11 can be converted into parallel light. The collimator 22 can ensure that the target optical signal is equivalent to a plane wave during propagation, thereby reducing signal distortion caused by optical wavefront aberration. The collimator 22 includes an internal lens group. By adjusting the internal lens group, the equiphase surface of the target optical signal is perpendicular to the optical axis direction, so as to ensure the parallelism of the target optical signal output from the collimator 22. The two transmission optical components 23 are arranged on the output optical path of the collimator 22. The two transmission optical components 23 are configured to divide the target optical signal modulated by the collimator 22 into two sub-target optical signals, and couple each sub-target optical signal into a single-mode optical fiber by spatial light. The transmission optical component 23 includes a beam reducing lens 24 and an optical fiber collimator 25. The beam reducing lens 24 is arranged on the optical path from the collimator 22 to the optical fiber collimator 25. The beam reducing lens 24 is configured to focus the modulated target optical signal on the front focal point of the optical fiber collimator 25, and transmit the target optical signal to the input end of the optical switch 15 through the optical fiber collimator 25. Among them, the beam reducing lens 24 can also be replaced by a beam splitter or a plurality of coupling lenses with smaller apertures. The optical fiber collimator 25 is an optical fiber collimator 25 with a pigtail. It can couple the target optical signal emitted from the beam reducing lens 24 into a single-mode optical fiber, and transmit the target optical signal to the input end of the optical switch 15 through the single-mode optical fiber.

[0048] The second optical component 14 is arranged on the optical path between the local oscillator light source 12 and the input end of the optical switch 15, and is configured to transmit the local oscillator optical signal from the local oscillator light source 12 to the input end of the optical switch 15.

[0049] In one embodiment, the second optical component 14 includes an optical fiber coupler 29 and two optical intensity attenuators 30. The optical fiber coupler 29 can be a 1×2 polarization-maintaining optical fiber coupler 29 with a coupling ratio of 50:50. The optical fiber coupler 29 is arranged on the optical path from the local oscillator light source 12 to the two optical intensity attenuators 30. The optical fiber coupler 29 is configured to evenly divide the local oscillator optical signal of the local oscillator light source 12 into two sub-local oscillator optical signals, and transmit them to the input end of the optical switch 15 after passing through the two optical intensity attenuators 30 respectively. By adjusting the settings of the two optical intensity attenuators 30, it can be ensured that the intensities of the two sub-local oscillator optical signals are exactly the same, so that the two sub-local oscillator optical signals with the same intensity are transmitted to the input end of the optical switch 15 at the same time.

[0050] The output end of the optical switch 15 is connected to the input ends of the first mixer 16 and the second mixer 17. The optical switch 15 is used to perform chopping modulation on the target optical signal from the target light source 11 and the local oscillator optical signal from the local oscillator light source 12, and output the first target signal and the first local oscillator signal obtained after chopping modulation to the first mixer 16, and output the second target signal and the second local oscillator signal obtained after chopping modulation to the second mixer 17.

[0051] The first mixer 16 performs mixing processing on the first target signal and the first local oscillator signal, and outputs four paths of phase-modulated first difference frequency signals to the first balanced detector group 18. The second mixer 17 performs mixing processing on the second target signal and the second local oscillator signal, and outputs four paths of phase-modulated second difference frequency signals to the second balanced detector group 19. In this embodiment, the first mixer 16 and the second mixer 17 can be 90° mixers. The first mixer 16 can mix the input first target signal and first local oscillator signal according to a specific phase difference, so as to output four paths of phase-modulated first difference frequency signals. The process of the first mixer 16 performing mixing processing is based on the wave nature of light and the principle of vector addition. After the first target signal and the first local oscillator signal are superimposed, four paths of first difference frequency signals containing target optical information are generated. The frequency of the first difference frequency signal is equal to the difference between the frequency of the corresponding part of the target optical signal and the frequency of the local oscillator optical signal. The amplitude of the first difference frequency signal is proportional to the product of the optical intensity of the target optical signal and the optical intensity of the local oscillator optical signal, thereby realizing the amplification and modulation of the target optical signal. Among them, there is a 90° phase delay between the complex amplitudes of the four paths of phase-modulated first difference frequency signals, that is, the phase delays of the four paths of phase-modulated first difference frequency signals relative to the complex amplitude after the superposition of the input first target signal and first local oscillator signal are 0°, 90°, 180°, and 270° respectively. The process of the second mixer 17 performing mixing processing is the same as that of the first mixer 16. It is also based on the wave nature of light and the principle of vector addition, and can realize the amplification and modulation of the target optical signal. Among them, there is a 90° phase delay between the complex amplitudes of the four paths of phase-modulated second difference frequency signals, that is, the phase delays of the four paths of phase-modulated second difference frequency signals relative to the complex amplitude after the superposition of the input second target signal and second local oscillator signal are 0°, 90°, 180°, and 270° respectively.

[0052] The first balanced detector group 18 is arranged on the optical path from the output end of the first mixer 16 to the input end of the signal acquisition system 20. The first balanced detector group 18 outputs a first in-phase output signal and a first quadrature output signal to the signal acquisition system 20. In this embodiment, the first balanced detector group 18 includes two first balanced detectors 27. Signals with phase delays of 0° and 180° in the first difference frequency signal can be input into one first balanced detector 27 for differential processing. Since the difference frequency signal can be regarded as the superposition of multiple sine functions, through the differential processing by the first balanced detector 27, a first in-phase output signal can be obtained. The first in-phase output signal is in phase with the input signal with a phase delay of 0°, and its amplitude is twice that of the input signal with a phase delay of 0°. Similarly, signals with phase delays of 90° and 270° in the first difference frequency signal can be input into the other first balanced detector 27 for differential processing, and a first quadrature output signal can be obtained. The first quadrature output signal is in phase with the input signal with a phase delay of 90°, and its amplitude is twice that of the input signal with a phase delay of 90°.

[0053] The second balanced detector group 19 is arranged on the optical path from the output end of the second mixer 17 to the input end of the signal acquisition system 20. The second balanced detector group 19 outputs a second in-phase output signal and a second quadrature output signal to the signal acquisition system 20. In this embodiment, the second balanced detector group 19 includes two second balanced detectors 28. Signals with phase delays of 0° and 180° in the second difference frequency signal can be input into one second balanced detector 28 for differential processing, and a second in-phase output signal can be obtained. The second in-phase output signal is in phase with the input signal with a phase delay of 0°, and its amplitude is twice that of the input signal with a phase delay of 0°. Signals with phase delays of 90° and 270° in the second difference frequency signal can be input into the other second balanced detector 28 for differential processing, and a second quadrature output signal can be obtained. The second quadrature output signal is in phase with the input signal with a phase delay of 90°, and its amplitude is twice that of the input signal with a phase delay of 90°. In this way, the signal-to-noise ratios of the first difference frequency signal and the second difference frequency signal can be improved by differential means, and the DC components can be filtered out.

[0054] In one embodiment, the optical signal passive heterodyne detection and digital coherent superposition device 10 further includes a signal generator 26. The output end of the signal generator 26 is connected to the input end of the optical switch 15 and the input end of the signal acquisition system 20. The signal generator 26 is used to output a modulation reference signal to the input end of the optical switch 15 and the input end of the signal acquisition system 20. The modulation reference signal can be a modulation square wave signal. Among them, the high level of the modulation square wave signal is the working trigger signal of the optical switch 15. The optical switch 15 can work when the modulation square wave signal is at a high level and can stop working when the modulation square wave signal is at a low level. The signal acquisition system 20 is used to screen the first in-phase output signal, the second in-phase output signal, the first quadrature output signal, and the second quadrature output signal according to the modulation reference signal. The signal acquisition system 20 can determine the time stage corresponding to when the modulation square wave signal is at a high level and screen the signals among the first in-phase output signal, the second in-phase output signal, the first quadrature output signal, and the second quadrature output signal that are in this time stage. During the period when the modulation square wave signal is at a high level, the quality of the signal is higher and the influence of noise is relatively small, thereby ensuring the accuracy and reliability of data processing.

[0055] The output end of the signal acquisition system 20 is connected to the computer system 21. The computer system 21 is used for timing processing and outputs the first coherent signal and the second coherent signal obtained by coherent superposition. Among them, the computer system 21 outputs the first coherent signal obtained by the coherent superposition of the first in-phase output signal and the second in-phase output signal, and the second coherent signal obtained by the coherent superposition of the first quadrature output signal and the second quadrature output signal. The first in-phase output signal and the second in-phase output signal after timing processing can achieve precise alignment in the time domain and be in-phase in time, that is, the optical paths experienced by the two signals after timing processing are the same, meeting the co-phase condition. Thus, the coherent superposition of the amplitudes of the first in-phase output signal and the second in-phase output signal can be performed, that is, it can be considered that the first in-phase output signal and the second in-phase output signal after timing processing are added in amplitude and the sum of squares is taken, so that the light intensity after coherent superposition reaches the maximum value, that is, the maximum value of the double-beam superposition. The same is true for the first quadrature output signal and the second quadrature output signal after timing processing, so that the coherent superposition of the amplitudes of the first quadrature output signal and the second quadrature output signal can be performed. Since the process of coherent superposition is carried out in the computer system 21, that is, in the digital domain, precise calculation and control can be carried out using the computer system 21, which is convenient to operate and can obtain a high-quality coherent superposition result.

[0056] In one embodiment, the computer system 21 includes a filtering module configured to perform filtering processing on a first in-phase output signal, a second in-phase output signal, a first quadrature output signal, and a second quadrature output signal input to the computer system 21. Since the frequency range of light is relatively large and exceeds the operating bandwidth of the balanced detector, the portion exceeding the operating bandwidth of the balanced detector can be regarded as noise signals, which will reduce the signal-to-noise ratio of the signal. Therefore, it is necessary to filter the first in-phase output signal, the second in-phase output signal, the first quadrature output signal, and the second quadrature output signal input to the computer system 21, and only retain the data within the response frequency range of the balanced detector. A suitable characteristic frequency range can be selected according to the response frequency range of the balanced detector, and digital filtering processing is performed on the first in-phase output signal, the second in-phase output signal, the first quadrature output signal, and the second quadrature output signal. After the digital filtering processing, obvious envelope structures exist in the first in-phase output signal, the second in-phase output signal, the first quadrature output signal, and the second quadrature output signal. In this way, the noise components outside the characteristic frequency range can be accurately and effectively filtered out. The noise components include environmental noise, internal system noise, and shot noise, thermal noise, etc. related to the local oscillator optical signal, thereby minimizing the adverse impact of noise on the signal quality and effectively improving the signal-to-noise ratio of the signal. Through digital filtering processing, it can be ensured that the first in-phase output signal, the second in-phase output signal, the first quadrature output signal, and the second quadrature output signal maintain high clarity and high accuracy during subsequent signal processing.

[0057] In one embodiment, the computer system 21 includes a signal processing module for performing timing processing, which includes: performing cross-correlation calculation on the first in-phase output signal and the second in-phase output signal to determine the first relative time delay information between the first in-phase output signal and the second in-phase output signal. Performing cross-correlation calculation on the first quadrature output signal and the second quadrature output signal to determine the second relative time delay information between the first quadrature output signal and the second quadrature output signal. Taking the first in-phase output signal and the second in-phase output signal as an example, performing cross-correlation calculation on the first in-phase output signal and the second in-phase output signal to obtain the cross-correlation degree between the first in-phase output signal and the second in-phase output signal. Among them, the cross-correlation degree represents the similarity degree between two signals at different time delays. The greater the cross-correlation degree, the higher the similarity degree between the two signals. When the cross-correlation degree reaches the maximum, it can be considered that the external environments of the two signals are the same, that is, the optical paths experienced are the same. The corresponding time delay at this time can be considered as the time lag caused by different optical paths of the two signals, that is, the first relative time delay information. And taking the first in-phase output signal as the reference signal, according to the first relative time delay information, performing time adjustment on the second in-phase output signal; taking the first quadrature output signal as the reference signal, according to the second relative time delay information, performing time adjustment on the second quadrature output signal. In this way, the consistency in time between the first in-phase output signal and the second in-phase output signal, and the consistency in time between the first quadrature output signal and the second quadrature output signal are ensured, providing a solid foundation for subsequent signal processing.

[0058] In one embodiment, after performing time adjustment on the second in-phase output signal and performing time adjustment on the second quadrature output signal, the timing processing further includes:

[0059] Performing sine difference fitting on the first in-phase output signal, the second in-phase output signal, the first quadrature output signal, and the second quadrature output signal.

[0060] Performing cross-correlation calculation on the first in-phase output signal and the second in-phase output signal after sine difference fitting to determine the third relative time delay information between the first in-phase output signal and the second in-phase output signal after sine difference fitting. Performing cross-correlation calculation on the first quadrature output signal and the second quadrature output signal after sine difference fitting to determine the fourth relative time delay information between the first quadrature output signal and the second quadrature output signal after sine difference fitting.

[0061] Taking the first in-phase output signal after sine difference fitting as the reference signal, according to the third relative time delay information, the second in-phase output signal after sine difference fitting is adjusted in time. Taking the first quadrature output signal after sine difference fitting as the reference signal, according to the fourth relative time delay information, the second quadrature output signal after sine difference fitting is adjusted in time. In this way, more accurate time delay information can be obtained, thus ensuring the accuracy of subsequent signal processing. The first in-phase output signal, the second in-phase output signal, the first quadrature output signal, and the second quadrature output signal can be registered in time by the computer system 21, so that the optical path can be accurately corrected in the digital domain, thereby ensuring that the first in-phase output signal and the second in-phase output signal can remain in-phase during coherent superposition, and the first quadrature output signal and the second quadrature output signal can remain in-phase during coherent superposition.

[0062] In the optical signal passive heterodyne detection and digital coherent superposition device 10 according to the embodiment of the present invention, the first mixer 16 and the second mixer 17 are adopted. The first mixer 16 and the second mixer 17 can use the local oscillator signal as the carrier signal to mix the target signal and the local oscillator signal, and efficiently obtain the difference frequency signal between the target signal and the local oscillator signal. This process not only improves the signal-to-noise ratio, but also amplifies the target signal, enabling accurate acquisition of the target signal, further enhancing the anti-interference ability, and ensuring good performance in a high-noise environment. At the same time, the computer system 21 can be used for timing processing, and cross-correlation calculations are respectively performed on the first in-phase output signal and the second in-phase output signal, and the first quadrature output signal and the second quadrature output signal to accurately obtain the relative time delay information. The relative time delay information reflects the propagation time difference caused by the optical path difference on different paths, so that the optical path difference between signals can be processed in the digital domain, making it possible to achieve coherent superposition of two signals without relying on requirements such as optical path consistency and environmental stability, thereby improving the accuracy and stability of interference measurement, effectively suppressing the interference of environmental noise and noise, and greatly reducing the implementation difficulty and cost.

[0063] The present invention successfully realizes an efficient, accurate and low-cost digital beam synthesis method by using passive heterodyne detection technology, two detectors and digital signal processing technology. It not only avoids the high-precision requirement of equal optical path, but also effectively suppresses the influence of environmental noise and other interference factors on the target optical signal by using the local oscillator optical signal as the carrier, opening up a new path for the development and application of beam synthesis technology. Moreover, by further utilizing the flexibility and precision of digital signal processing, it is not only applicable to static measurement, but also can maintain high measurement accuracy and robustness in a dynamically changing environment, providing strong support for the application of double-beam interference technology in a wider range of fields.

[0064] See Figure 2 As shown, the embodiment of the present invention provides a method for passive optical signal difference frequency detection and digital coherent superposition, which is applied to the passive optical signal difference frequency detection and digital coherent superposition device as described above. The method for passive optical signal difference frequency detection and digital coherent superposition includes steps S1 to S5.

[0065] Step S1: Transmit the target optical signal from the target light source 11 to the input end of the optical switch 15 through the first optical component 13. Transmit the local oscillator optical signal from the local oscillator light source 12 to the input end of the optical switch 15 through the second optical component 14.

[0066] Step S2: The optical switch 15 performs chopping modulation on the target optical signal from the target light source and the local oscillator optical signal from the local oscillator light source 12, and outputs the first target signal and the first local oscillator signal obtained after chopping modulation to the first mixer 16, and outputs the second target signal and the second local oscillator signal obtained after chopping modulation to the second mixer 17.

[0067] Step S3: The first mixer 16 performs mixing processing on the first target signal and the first local oscillator signal, and outputs four-phase-modulated first difference frequency signals to the first balanced detector group 18. The second mixer 17 performs mixing processing on the second target signal and the second local oscillator signal, and outputs four-phase-modulated second difference frequency signals to the second balanced detector group 19.

[0068] Step S4: The first balanced detector group 18 outputs a first in-phase output signal and a first quadrature output signal to the signal acquisition system 20. The second balanced detector group 19 outputs a second in-phase output signal and a second quadrature output signal to the signal acquisition system 20.

[0069] Step S5: The first in-phase output signal, the second in-phase output signal, the first quadrature output signal, and the second quadrature output signal output from the signal acquisition system 20 enter the computer system 21, and are processed by the computer system 21 for timing, and output a first coherent signal obtained by coherent superposition of the first in-phase output signal and the second in-phase output signal, and a second coherent signal obtained by coherent superposition of the first quadrature output signal and the second quadrature output signal.

[0070] It should be understood that various forms of processes shown above can be used, reordering, adding or deleting steps. For example, the steps recorded in the disclosure of the present invention can be executed in parallel, sequentially, or in a different order, as long as the desired results of the technical solution disclosed in the present invention can be achieved. This is not limited herein.

[0071] The above specific embodiments do not constitute a limitation on the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A device for passive difference frequency detection and digital coherent superposition of optical signals, characterized in that: It includes a target light source, a local oscillator light source, a first optical component, a second optical component, an optical switch, a first mixer, a second mixer, a first balanced detector group, a second balanced detector group, a signal acquisition system and a computer system; The first optical component is arranged on the optical path between the target light source and the input end of the optical switch; the second optical component is arranged on the optical path between the local oscillator light source and the input end of the optical switch; The output end of the optical switch is connected to the input end of the first mixer and the input end of the second mixer. The optical switch is used to chop and modulate the target optical signal from the target light source and the local oscillator optical signal from the local oscillator light source, and output the first target signal and the first local oscillator signal obtained after the chopping modulation to the first mixer, and output the second target signal and the second local oscillator signal obtained after the chopping modulation to the second mixer; the first balanced detector group is arranged on the optical path from the output end of the first mixer to the input end of the signal acquisition system; the second balanced detector group is arranged on the optical path from the output end of the second mixer to the input end of the signal acquisition system, the first balanced detector group outputs a first in-phase output signal and a first orthogonal output signal to the signal acquisition system, and the second balanced detector group outputs a second in-phase output signal and a second orthogonal output signal to the signal acquisition system; the output end of the signal acquisition system is connected to the computer system, and the computer system is used to perform timing processing and output a first coherent signal and a second coherent signal obtained by coherent superposition; The timing processing includes: A cross-correlation calculation is performed on the first in-phase output signal and the second in-phase output signal to determine a first relative time delay information between the first in-phase output signal and the second in-phase output signal; a cross-correlation calculation is performed on the first orthogonal output signal and the second orthogonal output signal to determine a second relative time delay information between the first orthogonal output signal and the second orthogonal output signal.

2. The optical signal passive difference frequency detection and digital coherent superposition device according to claim 1, characterized in that: The first mixer performs mixing processing on the first target signal and the first local oscillator signal, and outputs four phase-modulated first difference frequency signals to the first balanced detector group; the second mixer performs mixing processing on the second target signal and the second local oscillator signal, and outputs four phase-modulated second difference frequency signals to the second balanced detector group; The computer system is used to perform timing processing and output a first coherent signal obtained by coherently adding the first in-phase output signal and the second in-phase output signal, and a second coherent signal obtained by coherently adding the first orthogonal output signal and the second orthogonal output signal.

3. The optical signal passive difference frequency detection and digital coherent superposition device according to claim 2, characterized in that: It also includes a signal generator, the output end of the signal generator is connected to the input end of the optical switch and the input end of the signal acquisition system, and the signal generator is used to output a modulated reference signal to the input end of the optical switch and the input end of the signal acquisition system; The signal acquisition system is used to screen the first in-phase output signal, the second in-phase output signal, the first quadrature output signal, and the second quadrature output signal according to the modulated reference signal.

4. The optical signal passive difference frequency detection and digital coherent superposition device according to claim 2, characterized in that: The computer system includes a signal processing module, and the signal processing module is used to perform the timing processing, and the timing processing also includes: And using the first in-phase output signal as a reference signal, the second in-phase output signal is time-adjusted according to the first relative time delay information; using the first orthogonal output signal as a reference signal, the second orthogonal output signal is time-adjusted according to the second relative time delay information.

5. The optical signal passive difference frequency detection and digital coherent superposition device according to claim 4, characterized in that: After time adjustment is performed on the second in-phase output signal and time adjustment is performed on the second quadrature output signal, the timing processing further includes: Performing sinusoidal difference fitting on the first in-phase output signal, the second in-phase output signal, the first quadrature output signal, and the second quadrature output signal; Performing cross-correlation calculation on the first in-phase output signal and the second in-phase output signal after sine difference fitting, and determining third relative time delay information between the first in-phase output signal and the second in-phase output signal after sine difference fitting; performing cross-correlation calculation on the first orthogonal output signal and the second orthogonal output signal after sine difference fitting, and determining fourth relative time delay information between the first orthogonal output signal and the second orthogonal output signal after sine difference fitting; And using the first in-phase output signal after sinusoidal difference fitting as a reference signal, according to the third relative time delay information, time adjustment is performed on the second in-phase output signal after sinusoidal difference fitting; using the first orthogonal output signal after sinusoidal difference fitting as a reference signal, according to the fourth relative time delay information, time adjustment is performed on the second orthogonal output signal after sinusoidal difference fitting.

6. The optical signal passive difference frequency detection and digital coherent superposition device according to claim 2, characterized in that: The computer system includes a filtering module, and the filtering module is used to filter the first in-phase output signal, the second in-phase output signal, the first quadrature output signal, and the second quadrature output signal input to the computer system.

7. The optical signal passive difference frequency detection and digital coherent superposition device according to claim 1, characterized in that: The first optical component includes a collimator and two transmission optical components. The collimator is used to modulate the target light signal from the target light source. The transmission optical component includes a beam reduction lens and a fiber collimator. The beam reduction lens is arranged on the optical path from the collimator to the fiber collimator. The beam reduction lens is used to focus the modulated target light signal on the front focus of the fiber collimator, and transmit the target light signal to the input end of the optical switch through the fiber collimator.

8. The optical signal passive difference frequency detection and digital coherent superposition device according to claim 1, characterized in that: The second optical component includes a fiber coupler and two light intensity attenuators. The fiber coupler is arranged on the optical path from the local oscillator light source to the two light intensity attenuators. The fiber coupler is used to evenly divide the local oscillator light signal of the local oscillator light source into two beams of sub-local oscillator light signals, and transmit them to the input end of the optical switch after passing through the two light intensity attenuators respectively.

9. The optical signal passive difference frequency detection and digital coherent superposition device according to claim 1, characterized in that: The target light source is a broad-spectrum light source; and / or The local oscillator light source is a narrow linewidth laser.

10. A method for passive difference frequency detection and digital coherent superposition of optical signals, characterized in that: Applied to the optical signal passive difference frequency detection and digital coherent superposition device as described in any one of claims 1 to 9, the optical signal passive difference frequency detection and digital coherent superposition method comprises: The target optical signal from the target light source is transmitted to the input end of the optical switch through the first optical component; the local oscillator optical signal from the local oscillator light source is transmitted to the input end of the optical switch through the second optical component; chopping and modulating the target light signal from the target light source and the local oscillator light signal from the local oscillator light source through the optical switch, and outputting the first target signal and the first local oscillator signal obtained after the chopping and modulation to the first mixer, and outputting the second target signal and the second local oscillator signal obtained after the chopping and modulation to the second mixer; The first target signal and the first local oscillator signal are mixed by the first mixer, and four phase-modulated first difference frequency signals are output to the first balanced detector group; the second target signal and the second local oscillator signal are mixed by the second mixer, and four phase-modulated second difference frequency signals are output to the second balanced detector group; The first balanced detector group outputs a first in-phase output signal and a first quadrature output signal to the signal acquisition system, and the second balanced detector group outputs a second in-phase output signal and a second quadrature output signal to the signal acquisition system; The first in-phase output signal, the second in-phase output signal, the first orthogonal output signal and the second orthogonal output signal output from the signal acquisition system enter a computer system, are time-series-processed by the computer system, and output a first coherent signal obtained by coherently adding the first in-phase output signal and the second in-phase output signal, and a second coherent signal obtained by coherently adding the first orthogonal output signal and the second orthogonal output signal.

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